14th Project Integration Meeting Handout PIM... · with you to the PIM!! fi ll fl u ... Low-Cost...

5101-140

Department of Energy

Low-Cost Solar Array Project

14th Project Integration Meeting

Handout

California Institute of Technology December 5 and 6, 1979

Jet Propu lsion Laboratory California Institute of Technology

Pasadena, California

Prepared by the Jc t Propulsio n Laboratory, California Institute of Technology, for the Department of Energy through an agreement with the Natio nal

Aero nautics and Space Adm inis tration .

The JPL Low-Co~t Solar Array Project is sponsored by the Departmen t of Energy (DOE) and for ms part of the Solar Pho tovoltaic Conversion Progra m to initiate a major effo rt toward the development o f Iow-co~t solar arrays.

This report was prepared as an account of work sponsored by the United States Government. Neither the Un ited States nor the United States Departmen t of Energy, nor any of their e mployees, nor any of the ir contrac tors, subcontractors, or the ir employee~. makes any warranty, ex press or implied , o r assumes any legal liabili ty or responsibility for the accuracy, complete ness or useful ness of a ny information, apparatus, product o r pr0<.:es~ disclosed, or represents that its use wou ld not infringe private ly o wned ri ghts.

REMINDER :

Please bring this Handout

with you to the PIM!!

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5101-140

Department of Energy

Low-Cost Solar Array Project

14th Project Integration Meeting

Handout

California Institute of Technology December 5 and 6, 1979

Jet Propulsion Laboratory California Institute of Technology

Pasadena, California

-

I TECHNOLOGY DEVELOPMENT

AREA

K.M. KOLIWAD, MGR

SILICON

Ila-MATERIAL TASK

R. LUTWACK, MGR

LARGE AREA Si SHEET TASK -

J .K. LIU, MGR

ENCAPSULATION TASK -

C. COULB!:RT, MGR

ADVANCED PHOTOVOL T AICS - TASK R.J. STIRN, MGR

* ACTING

~ ~

LOW-COST SOLAR ARRAY PROJECT

PROJECT MANAGER W. T, CALLAGHAN

DEPUTY MANAGER R.R. McDONALD

SECY: M.J. PHILLIPS P.R. & D

A.M. PEARSON, MGR'* FINANCIAL

B.S. LENCK, MGR PROCUREMENT

P .S. -RYKEN QUALITY ASSURANCE

K.J. ANHALT

I I I PRODUCTION ANALYSIS AND ENGINEERING OPERATIONS

PROCESS AND EQUIP. INTEGRATION AREA AREA AREA AREA

D .B. BICKLER, MGR P.K. HENRY, MGR R.G. ROSS, MGR L. N. DUMAS, MGR

~ PROCESS AUTOMATION - PROJECT 1i- ARRAY ENGINEERING LARGE SCALE INTEGRATION PRODUCTION

~

- NEWLY DEVELOPED - ADVANCED ARRAY TASK ~ARRAY TECHNOLOGY PROCESSES COSTS REQUIREMENTS L.D. RUNKLE

- TECHNOLOGY TRANSFER - ECONOMICS/

- ARRAY - FAILURE DEVELOPMENT

INDUSTRIALIZATION ANALYSIS AND - ASSESSMENT OF

- ENVIRONMENTAL REPORTING EMERGING TECHNOLOGY - ARRAY LIFE CYCLE TESTING R&D ANALYSIS

- ENVIR/FIELD ..... NEAR-TERM COST - ENVIRONMENTAL TESTS REDUCTION

ASSESSMENT - PERFORMANCE

MEAS URE MEN TS

- MODULE INTERFACE AND CONTROL

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CONTENTS

MEETING OBJECTIVES------------------------------------ 1

AGENDAS----------------------------------------------- 3

STATUS OF TECHNOLOGY TRANSFER------------------------- 9

COMMERCIAL SOLAR CELL MODULE MANUFACTURERS------------ 13

TECHNICAL SUMMARIES

Silicon Material-------------------------------- 15

Large-Area Silicon Sheet------------------------ 23

Encapsulation----------------------------------- 41

Production Process and Equipment---------------- 49

Engineering------------------------------------- 69

Operations-------------------------------------- 73

Large-Scale Productiori -------------------------- 75

LSA PROJECT ACTIVE CONTRACTS-------------------------- 85

LSA PROJECT PUBLISHED DOCUMENTS----------------------- 91

MAPS: Pasadena Area; Caltech Meeting Locations----- Inside Back

Cover

For Your Information

Check-in: Please check in at the registration desk in the Ramo Auditorium lobby before the start of the meeting on Wedneday morning.

Telephone Messages: Incoming calls will be received at JPL on (213) 577-9520. Constant coverage of this phone will be provided and messages transmitted.

Badges: We will appreciate your returning your badges at the end of the meeting.

Next PIM: The 15th LSA Project Integration Meeting is planned for early April, 1980.

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MEETING OBJECTIVES

The LSA Project is convening its fourteenth Project Integration Meeting (PIM). We will be meeting on December 5 and 6, 1979 at the Caltech Campus in Pasadena, California, with registration beginning at 7:30 a.m. December 5 in the lobby of Ramo Auditorium. Attendance is by invitation only •

The objectives of the fourteenth Pil-1 are to assess the general technology development status of the Project; gain knowledge about the newest module designs and module design technology; to discuss LSA Project technical activities that influence or are influenced by other technical tasks and/or areas; to exchange and discuss technical information at the working level; and to provide an overview of LSA Project technical status and plans.

The theme of this PIM is "Module Design" and is intended to be an overview of photovoltaic module design knowledge based upon LSA experience of the past five years. The theme will be highlighted by 1) Display of Block IV prototype modules, other company's commercially available modules, experimental encapsulation modules, and other hardware; 2) Presentations by manufacturers regarding their Block IV module designs and design rationale; 3) Sunnnaries of lessons learned that influence module design; 4) A 4-1/4 hour module design session, Thursday morning; and 5) A number of parallel sessions immediately after lunch on Thursday. Module manufacturer representatives will be available for discussions and questions at two designated module display times; 10:00 to 11:00 Wednesday morning and 1:30 to 3:00 Thursday afternoon. The agenda for the 4-1/4 hour module design session, Thursday morning, is only tentative. A final agenda, which will be available at the PIM, will reflect coIIllllents and suggestions solicited from the PIM attendees. Also the parallel sessions Thursday at 1:30 p.m. may be modified.

The LSA Project Integration Meetings are conducted to enable the exchange of data and information required to assess recent progress; to identify, implement, and evaluate integration activities; to gain perspective of trends and new developments; and to guide the Project's near- and long-term planning and adjustment of priorities. Consequently, final conclusions are not necessarily reached during one PIM. Often, subjects brought up for discussion during one meeting will be continued in subsequent PIM sessions •

1

AGENDA NOTE: PP&E will have a Contractor Technical Summary Session on Tuesday December 4, 8 :30 a.m. at

145 No. Altadena Dr . , Pasadena . The meeting will be located in the PP&E Laboratory in Buil ding 512.

WEDNESDAY - December 5

7:30

8:30 -8:40 -9:00 -9: 20 -9:50 -

10 :00

11:00 -12:00 -12:10

Registration

Welcome/LSA Announcements

DOE & PV Lead Center Announcements

FPUP Status

Silicon Material Summary

Introduction of Module Manufacturers

Viewing of Modules* and Coffee

Lessons Learned that Affect Module Design

Discussion

Lunch

Technology Sessions (Simultaneous)

Silicon Material

Large Area S1e t

l

Ramo Auditorium Lobby

w. Callaghan

L. Magid/R. Forney

Ramo Auditorium A. Lawson

K. Koliwad/R. Ferber

D. Runkle

Dabney Pat io

R. Ross /L . Dumas Ramo Auditorium

w. Callaghan

151 Crellin R. Lutwack'

155 Arms J . Liu

60 min.

10 min.

20 min .

20 min .

30 min.

10 min .

60 min.

60 min.

10 min .

2 hours

z hours

Block IV Module Designs and ) Design Rat ionale - Presentat- io-ns _

1 -

3: 00 - 4:00

3:45 -Baxter Lecture Hall

by Module~~rs ---------------

Coffee available

Technology Sessions (Simul taneous)

Silicon Mater1 al

Large Area Sheet

t.ncapsulati on

PP&E - Copper Metallization

t.,Engineering/Operations/PA&l

Outside Ramo Auditorium Lobby

151 Crellin

155 Ar ms

130 Church

365 So . Mudd

Baxt e r Lecture 11all

D. Runkle

R. Lutwack

J . Liu

c. Coul bert

D. Bickler

J . Arnett

*Block IV prototype modules , other commercially availab l e modules , and advanced encapsulation concept modules .

NOTE: A social hour will be held Wednesday, Dec . 5 at the Pasadena Holiday Inn, Piazza Room , 303 Cordova St , star t i ng at 5 : 30 g.m.

THURSDAY - December 6

8:00

9 : 30-11 :00

1:30

Technol ogy Sess~ons (Simultaneous)

Si licon Material

Large Area Sheet

o ule esign (see detailed agen a

Coffee available

Pa r all e 1 Sessions

Automat ed Module Assembly Studies

Module/cell Life Prediction and Modeling (includes EVA studi es)

Test and Applications Experiments Status - Lead Center PROA 38 - Sandia Experience - MIT/LeRC

Modul es on Displ ay

Coffee

24 Beckman Lab R. Lutwack

155 Arms J . Liu

axter ecture !la 1 R. Ross


147 Noyes D. Bickler

24 Beckman Lab c. Coulbert

Baxte r Lecture Hall L. Dumas

Dabney Patio


2-1/4 hr7)

2 hours

2 hours

2 ;iours

2 hours

2 hours

4 hours

4 hours

4-1/4 hrs .

1- 1/2 hrs .

1- 1/2 hrs .

1- 1/2 hrs.

3 : 00

3 :1~

3 :45

Product Reliability and Liabili t y

l A. \.Jeinstein, 30 min . Carnegie Mellon Univ .

Summaries Ramo Auditorium

LSA

DOE/Lead Cen t er

5: 00 End of Meeting

3

• Introduction

TENTATIVE MODULE DESIGN SESSION THURSDAY MORNING

Chairman - Ron Ross

Approximate time - ~ hours 15 min.

• Objective/Agenda

• Overall Module/Array Optimization

•

•

• Interdependency and cost importance of module design features (efficiency, circuit design, thermal design, structural design, etc.)

Module Electrical Design

• Finished cell characteristics ~nd variances • Cell shape, size, and arrangement in module • Interconnect design and cell attachment • Dealing with cell mismatch • Building a fault tolerant circuit • Implications of hot-spot heating • Selection of module voltage/current levels

Module Terminations

• • Choices and costs Attachment to modules of terminations

factors versus cost

• Module Design·for a Safe System

• • Electrical insulation and grounding Fire safety

• Discussion

• Coffee

• Module Thermal Performance

• • Design practices for a cool module Roof mounting implicaticns

• Module Structural Design

•

• Module/Array structural interface • Wind loading and handling requirements • Designing for hail impact • Glass sizing

Encapsulation Material Selection and Processing

• Module construction alternatives • • •

Encapsulation material candidates PVB VS EVA VS other materials EVA performance capabilities

• Design for Low-Cost Fabrication and Processing

• QA and Process Control

• Environmental Requirements

•

•

• • • Humidity, thermal cycling, UV, etc • Special environments: salt, fog Soiling

Specific Application Requirements

• Installation • Maintenance

• • •

Design for extreme environments Validity of existing qual tests and potential changes for special uses Test and field experience

Summary of 1986 Preliminary Module Specification

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SILICON MATERIAL

WEDNESDAY - 1:15 - 5:15 p.m.

Technology Session

R. Lutwack, Chairman

1:15 1:45

2:15 2:45

Process Analysis Chemical Vapor Deposition

Process Silane/Silicon Process Hydrogenation of Silicon

tretrachloride

Coffee 3:15

3:45

4: 15

Gaseous Melt Replenishment System

In-house Silicon Program

THURSDAY - 8:00 a.m. - 12 noon

Technology Session

R. Lutwack, Chairman

)8:00 Fine Reduction of Silicon Tetrachloride

8:30 Arc Heater Process

9:00 Sodi.ton Reduction of Silicon Tetrafluoride

9:30 Laboratory Studies

10:00 Coffee

10:30 Definition of Purity Requirements

11:00 Effects of Impurities on Solar Cell Performance

11:30 Effects of Impurities on Solar Cell Performance

5

151 Crellin

Lamar University Hemlock Semiconductor

Corp. Union Carbide Corp. Massachusetts Institute

of Technology

Energy Materials Corp.

JPL

24 Beckman Lab

Battelle Columbus Labs.

Westinghouse Electric Corp.

SRI International

AeroChem Research Labs.

Westinghouse R&D Center

C.T. Sah Associates

Solarex Corp.

LARGE-AREA SHEET

WEDNESDAY - 1:15 - 5:45 p.m.

Technology Session*

A. Morrison, Chairman

1:15 HEM and Fast 1:45 Enhanced I.D. Slicing 2:10 I.D. Slicing 2:35 Advanced Cz 3:00 Low Cost Cz

3:20 Coffee

3:45 Advanced Cz 4:10 soc 4:35 EFG 5:00 WEB 5:15 Discussion

THURSDAY - 8:00 - 10:30 a.m.

Technology Session*

F. Uno, Chairman

8:00 8:25 8:50 9:15 9:40

10:05

Vacuum Die Casting Cell Fabrication Cell Fabrication Characterization of Silicon Oxygen Partial Pressure Discussion

155 Arms

Crystal Systems, Inc. Siltec STC Hamco Hamco

Siltec Honeywell Mobil Tyco Westinghouse JPL

155 Arms

Arco Solar Applied Solar Energy Spectra Lab Cornell University of Missouri JPL

*15-min. presentations; 5-min. discussion after each presentation.

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ENGINEERING/OPERATIONS/PA&!

WEDNESDAY - 3:45 - 5:30 p.m.

Technology Session

J. Arnett, Chairman

3:45 4:05 4:25 4:45 5:10

!PEG Status Electrical Termination Study Glass Superstrate Sizing Array Structure Prototype Engineering Potpourri

7

Baxter Lecture Hall

R. Aster/JPL Motorola D. Moore/JPL A. Wilson/JPL R. Ross/JPL

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STATUS OF TECHNOLOGY TRANSFER

The Production Processes and Equipment Area is concerned with the transfer of technologies developed by the LSA Project for manufacturers of solar modules. The status of this transfer activity is reported periodically to provide an overview of processes available from JPL, and to promote experimentation, modification, and application. Inquiries and requests for process specifications should be directed the LSA Project PP&E Area at (213) 577-9225.

PROCESS

TEXTURE ETCH

LASER ANNEAL

PROXIMITY TEXTURING

TEXTURE ETCH

ANTI-REFLECT! VE COATING

SPRAY A-R

SPRAY A-R

WAX-MASKING

CVD Si3N4

PLASMA DAMAGE ETCH

DIP A-R

PLASMA METAL PATTERN DEFINITION

ION IMPLANTATION

WAFER SUR FACE PREP.

PLASMA CVD

SURFACE PREPARATION

CONTRACTOR

SENSOR TECH.

LOCKHEED

TEXAS INST.

LOCKHEED

SENSOR TECH.

LOCKHEED

RCA

MOTOROLA

MOTOROLA

MOTOROLA

WESTINGHOUSE

MOTOROLA

MOTOROLA

SENSOR TECH.

SENSOR TECH.

STATUS SURVEYED BY

AVAILABLE LOCKHEED

AVAILABLE

UNDER DEV.

UNDER EVAL GENERAL ELECTRIC UNIV. OF PA.

UNDER DEV.

UNDER EVAL SPECTROLAB

UNDER EVAL SPECTROLAB SENSOR TECH. UNIV. OF PA.

UNDER EVAL WESTING HOUSE UNIV. OF PA.

AVAILABLE

UNDER EVAL SPECTROLAB OCLI WESTINGHOUSE UNIV. OF PA.

UNDER EVAL GENERAL ELECTRIC

UNDER EVAL OCLI

UNDER EVAL OCLI UNIV. OF PA.

UNDER EVAL UNIV. OF PA.

AVAILABLE

45 PROCESSES LISTED 22 BEING EVALUATED BY INDUSTRY 10 CONFIRMED BY INDUSTRY

9

COMMENTS

CONFIRMED RECOMMEND MOD.

ECONOMIC ONLY

ECONOMIC ONLY

ECONOMIC ONLY

CONFIRMED ECONOMIC ONLY

ECONOMIC ONLY

ECONOMIC ONLY

to

STATUS OF TECHNOLOGY TRANSFER (Continued)

JUNCTION FORMATION

PROCESS CONTRACTOR STATUS SURVEYED BY COMMENTS

PRINT & FIRE BSF SPECTROLAB UNDER EVAL WESTINGHOUSE CONFIRMED RCA GENERAL ELECTRIC

ION IMPLANTATION SPIRE EVALUATED RCA CONFIRMED FURNACE ANNEAL UNDER EVAL GENERAL ELECTRIC

UNIV. OF PA. ECONOMIC ONLY MOTOROLA CONFIRMED

LASER ANNEALING LOCKHEED AVAi lABLE

. CVD p+ WESTINGHOUSE AVAllABLE

ION IMPLANT LOCKHEED UNDER EVAL GENERAL ELECTRIC

LASER SCRIBING SENSOR TECH. EVALUATED MOBIL TYCO CONFIRMED SPECTROLAB CONFIRMED UNIV. OF PA. ECONOMIC ONLY

PLASMA EDGE ETCH MBA UNDER DEV.

N+ & p+ SENSOR TECH. UNDER DEV. POLYMERS

SPIN-ON DOPANTS TEXAS INST. AVAILABLE

POCL3 DIFFUSION RCA AVAi lABLE

POLYMER DIFFUSED SPECTROLAB AVAi lABLE WAFER

SPRAY-ON DOPANTS SENSOR TECH. AVAllABLE

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STATUS OF TECHNOLOGY TRANSFER (Continued)

METALLIZATION

PROCESS CONTRACTOR STATUS SURVEYED BY COMMENTS

ELECTRO LESS Pd/Ni MOTOROLA UNDER EVAL WESTINGHOUSE CONFIRMED (MOD) OCLI CONFIRMED SENSOR TECH. SOLAREX SOLAR POWER SOLOMAT UNIV. OF PA. ECONOMIC ONLY

THICK Fl LM RCA UNDER EVAL GENERAL ELECTRIC LOCKHEED UNDER EVAL GENERAL ELECTRIC

UNIV. OF PA. ECONOMIC ONLY

WRAP AROUND SPECTROLAB SUSPENDED NOT COST-EFFECTIVE

ALUMINUM BACK ARCO SOLAR UNDER EVAL WESTINGHOUSE CONFIRMED CONTACTS UNIV. OF PA. ECONOMIC ONLY

PLATE COPPER OCLI UNDER DEV.

ELECTROLESS Ni SOLAREX UNDER EVAL MOTOROLA UNIV. OF PA. ECONOMIC ONLY

ALUMINUM P+ ARCO UNDER EVAL GENERAL ELECTRIC WESTINGHOUSE SOLAR POWER UNIV. OF PA. ECONOMIC ONLY

SILVER PRINTING SPECTROLAB UNDER EVAL UNIV. OF PA. ECONOMIC ONLY PASTE

ELECTROLESS Ni SENSOR TECH. UNDER EVAL UNIV. OF PA. ECONOMIC ONLY

PRINT & FIRE SPECTROLAB UNDER EVAL UNIV. OF PA. ECONOMIC ONLY FRONT CONTACT

REMOVE OXIDE & CLEAN ALUM BACK

SPECTROLAB UNDER EVAL UNIV. OF PA.

PROCESS

EDGE MOLD I NG

DOUBLE GLASS

MODULE ASSEMBLY

CONTRACTOR I

MBA

RCA

STATUS

MASS SOLDERING RCA

UNDER DEV.

AVAILABLE

AVAILABLE

SUSPENDED GAP WELD RCA

FLAME SPRAY ON GLASS

HOLE IN CELL

APPLYING INTERCONNECTS

SOLAREX UNDER DEV.

SENSOR TECH. AVAi LABLE

SPECTROLAB AVAi LABLE

11

SURVEYED BY

ECONOMIC ONLY

COMMENTS

NOT COST-EFFECT! VE

Octoher 1979

COMMERC IAL SOLAR CELL MODULE MANUFACTURERS (Flat, Non-Concentrator)

DOE/JPL does not endorse the products of these manufacturers nor of any manufacturer.

TO THE BEST OF OUR KNOWLEDGE, THTS IS A LIST OF THOSE ORGANIZATIONS THAT ARE NOW MANUFACTURING PHOTOVOLTAIC MODULES FOR SALE TO THE PUBLIC. ADDITIONAL ORGANIZATIONS ARE DEVELOPING SOLAR CELLS AND MODULES FOR SALE IN THE FUTURE.

APPLIED SOLAR ENERGY CORPORATION 15251 East Don Julian Road City of Industry, CA 91746 Attn: · Wayne C. Stevenson

Sales Manager (213) %8-6581

ARCO SOLAR, INC. 20554 Plunnner Street Chatsworth, CA 91311 Attn: Jack Cotter

Sales Manager (213) QQ8-2482

MOTOROLA, INC. Solar Energy Department Phoenix, AZ 95008 Attn: Eoh Hannnond

Marketing Manager ( 60?) 244-5459

PHOTOWA'TT INTERNATIONAL, INC. 21012 Lassen Street Chatsworth, CA 9131 1 Attn: Sanieev Chitre, Vice Pres.

Director, Marketi ng (21.1) 88?.-4100

SES INCORPORATED Tral ee Indu st rial Park Newark, DE 19711 Attn: Greg Love

Manager of Industrial Sales (302) 731-0990

SILICON SENSORS, INr,. Highway 18 Fast Dodgeville, WT 53,33 Attn: Robert Bachne r

PreRid ent, Marketing Mgr. ( 608) 93S-?707

S01AR POWER CORPORATION 20 Cabot Road Woburn, MA 01801 Attn: Bill Brusseau

Marketing Manager (617) 935-4600

SOLAREX CORPORATION 1335 Piccard Drive Rockville, MD 20850 Attn: Ted Blumenstock

Director of Marketing ( 301) 948-0202

SOLEC INTERNATIONAL, INC. 12533 Chadron Avenue Hawthorne, CA 90210 Attn: Robert W. Craford

Vice President, Marketing (213) 970-00/65

SOI.ENERGY CORPORATION 23 North Avenue Wakefield, MA 0]880 Attn: Robert W. Willis

President, Marketing Manager (617) 246-1815

SOLLOS, INC. 2231 S. Carmelina Los Angeles, CA 90064 Attn: Dr. Milo Macha

President, Marketing Manager (213) 820-5181

TTDET..AND STGNAL CORPORATION 4310 Directors Road P. 0. Box 52430 Houston, TX 77052 Attn: Carl Kotila

Environmental Energy Manager (711) 681-6101

13

TECHNICAL SUMMARIES

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Contract Title:

Contract No.:

SILICON MATERIAL TASK

Energy Materials Corporation

Harvard, Masschusetts

GASEOUS MELT REPLENISHMENT SYSTEM

955269

The objective of this program is to develop a system which incorporates both silicon formation and melt replenishment in the same equipment. The processes and equipment are scaled such that a modest investment can make available to the Czochralski crystal grower a low cost source of silicon.

The chemical reactions, H2 reduction of SiHCl3, are those in commercial use for poly formation. The major innovation is in reactor design which allows a high productivity of silicon. Calculations based on epitaxial deposition rates indicate that a reasonable sized system can produce material rapidly enough to keep pace with either 10 cm or 12 cm diameter Czochralski crystal growth operating in a semi-continuous mode.

Polycrystalline silicon will be deposited on the inside walls of a resistively heated, multi-walled fused silica reaction chamber by Hz reduction of SiHC1 3 . After sufficient silicon has been produced, the reactor is flushed with argon and the silicon melted out of the reactor into a Czochralski crystal growth crucible. The reactor is then returned to the deposition stage. The reaction chamber and a heated delivery tube to the crystal growth system are separated by a "U" tube which acts as a valve by adjusting the temperature above or below the melting point of silicon contained in the U-bend.

The first phase of the program comprises development of a prototype system capable of a production rate of 0.5 kg/hr. During the past three months we have continued design and procurement of the prototype system and components. Construction of the gas handling and reactor system and associated systems is nearly complete. We expect to begin testing and initial runs of the prototype within the month.

ApproZ?t' Signature 15

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Date

SILICON MATERIALS TASK

HEMLOCK SEMICONDUCTOR CORPORATION HEMLOCK, MICHIGAN 48626

Contract Title: Development of a Polysilicon Process Based on Chemical Vapor Deposition

Contract No. : 955533

The objective of this program is to demonstrate the feasibility of a chlorosilane vapor deposition process for the production of low cost solar cell grade polysilicon.

Chemical vapor deposition (CVD) of high purity polycrystalline silicon from a chlorosilane forms the basis of the entire semiconductor-grade polysilicon industry. Based on the substantial data base available, weaknesses in the current CVD technology have been identified and work initiated in October of 1979 to bring about significant cost reduction in polysilicon production. A program plan consisting of four technical task areas was prepared. Areas of investigation include:

o Dichlorosilane Reactor Feasibility

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Intermediate Dichlorosilane Reactor Development

Dichlorosilane Process/Product Evaluation, and

Preliminary EPSDU Design/Integration

During this reporing period (October - November) an experimental reactor was identified and modification of feed system completed to permit use of dichlorosilane. Baseline trichlorosilane and dichlorosilane runs have been initiated.

Alternative designs were completed for the redistribution of trichlorosilane to dichlorosilane and subsequent distillation. Specification of analytical instrumentation for this unit is complete and site selection has been initiated.

Approval Signature James R. McCormick

16

October 30, 1979

Date

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Contract Tit I e :

Contract No. :


LAMAR UNIVERSITY

Beaumont, Texas 77710

PROCESS FEASIBILITY STUDY IN SUPPORT OF SILICON

MATERIAL TASK I

954343

During this reporting period, major activities were devoted to process system properties, chemical engineering and economic analyses.

For process system properties, analyses were continued for chemical materials important in the production of silicon. Primary efforts were expended for physical, transport and thermodynamic property data for silicon. Progress and status including ~reliminary data collection and analysis results are reported for the primary activities of data collection (80%), data analysis (70%), estimation (60%), and correlation (50%).

For economic analyses, cost, sensitivity and profitability analysis results are presented for the BCL Process - Case A (two reactors, six electrolytic cells).· The results are based on the preliminary process design of a plant to produce 1000 Mr/yr of silicon. The cost analysis results indicate a total product cost of 12.08 $/kg (1980 dollars) including raw materials, labor, utilities and other items composing pro-. duct cost. For sensitivity analysis, the order of cost parameter influence on product costs is given by plant investment (most)., raw materials (intermediate), utilities (intermediate) and labor (least). The profitability results disclose a sales price of 14 $/kg (1980 dollars) of silicon at a 7.5% DCF rate of return on investment after taxes.

These economic results for case A indicate good potential of the BCL process for meeting the goal of 14 $/kg (1980 dollars) for silicon.

Major chemical engineering activities were initiated on the preliminary process design for Case B (one deposition, two electrolytic cells) of the BCL process.

Date

17

Contract Title:

Contract No. :


MASSACHUSETTS INSTITUTE OF TECHNOLOGY Cambridge, Massachusetts

Investigation of the Hydrogenation of SiC14

955382 (subcontract under NASA Contract NAS7-100, Task Order No. RD-152)

A research and development program has been initiated in April of this year to study the hydrogenation of silicon tetrachloride to trichlorosilane,

3 SiC14 + 2H2 +Sit. 4 SiHC13

A laboratory scale stainless steel reactor has been constructed and installed to study this reaction at pressures up to 500 psig and at temperatures up to 600°C. After a thorough safety review, the reactor was started up for hydrogenation experiments in mid September.

Initial experiments on equilibrium constant measurements showed that the hydrogenation of SiC14 in a bed of Si metal reached equilibrium slowly. Since the fluidized-bed reactor design is not suitable for very long residence time studies, a sealed, static bed reactor has been designed for these equilibrium measurements. A series of experiments was carried out to collect reaction kinetic data at reactor pressure of 500 psig and at various reaction temperatures (450°, 500° and 550°C). As expected, the higher reactor pressure at 500 psig gave higher SiHC~conversion per pass. For example, at 500 psig, at 180 seconds res1aence time and a H

2:sic14 ratio of 2.8, the hydrogenation

of Sic14 at 450°C, 500°C and 550°C gave 30%, 37% and 40% SiHC13 conversion respectively. The rate of reaction increases rapidly as a function of increasing reactor temperature. More experiments are in progress to collect equilibrium and kinetic data as functions of pressure, temperature and H2/SiC14 ratio.

18


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Silicon Material Task

SRI INTERNATIONAL

MENLO PARK, CA 94025

Contract Title: NOVEL DUPLEX VAPOR-ELECTROCHEMICAL METHOD FOR PRODUCING SILICON

Contract No. : 9 544 71

The reaction of SiF4 and Na to form NaF and Si has been routinely performed in our 13 cm diameter pyrex reactor. Batches of 4-5 kg of mixed reaction product containing about 0.5 kg Si have been produced with complete reaction of Na. Solid Na feed has been used in the form of chips. The mixed product (Si, NaF} has been used in melt separation tests. An 18-cm diameter Inconel reactor capable of producing 10-kg batches of reaction products (containing about 1 kg silicon) has been put into operation. Sodium reaction was complete even when reactants were added at a fast rate equivalent to 0.45 kg silicon/hr.

Batches of reaction products (Si, NaF) up to 6 kg have been melt separated into a Si layer covered by a NaF layer. A continuous feed system has been developed to add the granular mixture of Si and NaF into a graphite crucible maintained at 1450 ± 20°c. The lateral feeder was reloaded during melt operation.

Impurity levels of most elements in the melt separated Si are in the parts per billion range. Elements in the range 1 to 10 ppm are B, Fe, Cr and Ni; Na is present at several hundred ppm.

Studies of combined SiF4-Na reaction and melt separation in the same reactor have been initiated. When the reactor-melter is initially at 600°c to aoo0 c, a reaction products sponge is formed in the graphite crucible. Initial temperatures above 1200°c produce excessive volatilization of products.

Approval Signature

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October 31, 1979

Date

Contract Title:

Contract No. :


UNION CARBIDE CORPORATION

Tonawanda, New York 14150

Silane-to-Silicon EPSDU

954334

Design and engineering work on the EPSDU, sized for 100 MT/YR throughput, is progressing towards detailed definition of facility requirements. A preliminary process and instrumentation diagram has been developed which establishes process control loops, equipment-process piping requirements, and interfaces with data collection/ quality assurance sub-systems. Bid specifications have been issued and initial vendor offerings have been received for most major pieces of process and auxiliary equipment. Unique process equipment items requiring in-house design have been identified and functional specifications have been developed. Operability considerations are being integrated into the engineering design including equipment accessibility, personnel safety protection, and environmental constraints. A test PDU was constructed to provide design and operating data on the waste burner sub-system.

Fabrication of free-space reactor Pnu·components was completed and assembly is progressing for a targeted November, 1979 start-up. Melter sub-contract proposal requests were issued to six potential sub-contractors. Four vendors have responded with proposals to develop a cost-effective melter/consolidation system. These proposals are presently being technically evaluated. A small fixed-bed reactor has been assembled to study critical silane concentration and deposition rate data in support of the fluid-bed development work. Initial experiments at 1% and 10% silane-in-hydrogen have identified temperature-powder formation relationships. Fluid-bed capacitive heating tests continue with acceptable bed sintering at high temperatures and design optimization for preferential withdrawal of large particles.

A preliminary analytical plan has been developed for the EPSDU operation. On-line chromatography will be utilized for bulk composition data to evaluate process performance. Selected tests for silane and silicon quality have been identified including "Siemens" type and epitaxy reactors for converting silane to equivalent quality silicon prior to electrical characterization.

10/29/79

Approval~ Date

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SILICON MATERIALS TASK

Westinghouse R&D Center/Dow Corning Corp.

Pittsburgh, PA

Contract Title: INVESTIGATION OF THE EFFECTS OF IMPURITIES AND

PROCESSING ON SILICON SOLAR CELLS

Contract No.: 954331

The overall objective of this program is to define the effects of impurities, various thermochemical processes, and any impurity-p1:0cess interactions on the performance of terrestrial silicon solar cells. The results of the study form a basis for silicon producers, wafer manufacturers and cell fabricators to develop appropriate cost-benefit relationships for the use of less pure, less costly Solar Grade silicon. The Phase III technical effort is now 95% completed.

Recently we have completed measurements of the segregation coefficients of Ag, Sn and Pd (three common solar cell contact materials). Spark source mass spectroscopy was used to determine C8 , the silicon crystal impurity content, while atomic absorption was used to obtain c1 , the impurity concentration in the liquid from which the crystal grew. The effective segregation coefficients~ keff = C8 /Ci, determined this way were kAg = 1.7xlo-S, ksn = 2.3x10- and kpd = Sx10-S.

HCi and POCt3 gettering of low resistivity (0.2 ncm) silicon doped with Mo or Ti enhances cell performance, a result similar to data earlier obtained for high resistivity material. However, cells made on the gettered low resistivity material exhibit considerable performance variation which tends to negate any benefits due the gettering itself. This behavior, especially evident when Mo-doped material is treated in POCt3, is due to excessive junction currents in the devices. We ascribe the result to precipitate formation near the high field region of the cell during the high temperature treatment.

We have verified by deep level spectroscopy that Ti concentration gradients, or profiles, are formed in Ti-doped silicon wafers during 1100°C gettering treatments. At this temperature the Ti depleted region extends from the surface to over 2 mils deep in the wafer; at 850°C, the cell fabrication temperature, the profile extended only about 12µm. In contrast, Mo-doped wafers exhibit abrupt profiles; after 1100° treatment the Mo concentration returns to the bulk value within 6µm of the surface. This probably explains the small response of cell performance to gettering in Mo-doped silicon.

We found no systematic variation in cell performance attributable to non-uniform impurity distributions in 3 inch diameter CZ ingots doped with Fe or Cu or in 3 to 4 cm wide silicon webs doped with Ti or V. From DLTS data we have estimated the segregation coefficients for Ti and V during the growth of single crystal ribbons by the dendritic web process: kri ~ 4xlo-6 and kv ~ 6.4x10-6. These estimates are in fair agreement with values calculated from a theoretical model of the web process.

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LARGE AREA SILICON SHEET TASK

Applied Solar Energy Corporation (Formerly OCLI)

City of Industry, California

Contract Title: Silicon Solar Cell Process Development, Fabrication and Analysis


The objective of this program is to investigate, develop and utilize technologies appropriate and necessary for improving the efficiency of solar cells made from various unconventional silicon sheets. In this period, work has progressed in processing solar cells from EFG (RH) multiribbon, dendritic webs and cast silicon by HEM.

Solar cells were fabricated using a standard process, typical of those used currently in the silicon solar cell industry, and also by a back surface field (BSF) process if applicable. Other process modifications, such as a shallow junction formation, fine front grid line formation, application of better AR coating, and gettering experiments, were also carried out. Performance was evaluated from the illumination characteristics under.AMO conditons and comparison was made with AMl characteristics for a given measurement conditions. In addition, back-up measurements were made from minority carrier diffusion length, spectral response, dark I-V characteristics and small light spot scanning. Generally good agreement was found between these back-up measurements and the cell performance.

Discussion is given of the problems related to the back surface field (BSF) process, specifically increased junction shunting. Ion microprobe/SIMS analysis, lateral and depth profile, of the shunted solar cell will be included.

Jd. ~ /I It /71 Date ApprovSign

23

Contract Title:

Contract No. :

SILICON SHEET TASK

ARCO Solar, Inc. Chatsworth, California

Vacuum Die Casting of Silicon Sheet for Photovoltaic Applications

955325

The objective of this program is to develop a vacuum die casting process for producing silicon sheet suitable for photovoltaic cells and to develop production techniques for optimization of polycrystalline silicon solar cell output.

The vacuum die casting process requires a die which is not wetted by molten silicon and does not react with it. A variety of potential die materials were evaluated during this period and a number of castings attempted. Experiments with boron nitride showed no wetting but the exposed silicon was heavily doped p-type. Low density graphite was destroyed by the melt. Although high density graphite survived molten silicon, it was wetted through formation of silicon carbide. Silicon nitride showed minimal reactivity with silicon. However, some sticking did occur for hot pressed and reaction-bonded Si3N4 - - less for CVD material. Coatings of boron nitride and of sodium silicatesodium flouride on graphite were successful in that the coating wetted the graphite and the silicon did NOT wet the coating.

A number of successful casting experiments were carried out in boron nitride dies. A 1/4 inch diameter rod was cast in a one-piece mold and a small disc was cast in a mold which could be mechanically disassembled. First attempts to cast a sheet in a split mold failed when the die lost vacuum and the silicon ran out before solidifying. A subsequent attempt using a split mold in a coated graphite die box produced some sheet.

A standard process has been developed for polycrystalline solar cells using Wacker Silso material. The cells show excellent curve fill factors with good efficiency but some current output reduction due to lowered long wavelength response. Laser scanning and EBIC examination indicate only minor degradation in collected current at the boundaries which is consistent with the good visible-light response of the cells as a whole.

Charles F. Day

Approval Signature

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November 2, 1979

Date


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CORNELL UNIVERSITY Department of Materials Science & Engineering

Ithaca, NY 14853

Contract Title: Characterization of Structural, Electrical and Chemical Properties of Silicon Sheet Material


EFG and RTR ribbons were investigated with TEM, EBIC and SIMS. Results to date are:

a) TEM. The majority of the linear defects in EFG material are coherent twin boundaries. Occasionally, incoherent twin boundaries on (112) planes are also observed. An analysis using common reflections shows that in this case the two crystals are shifted fractions of interatomic distances parallel and perpendicular to the boundary plane. High angle grain boundaries are rare. High resolution lattice images show that an (optically) single coherent twin boundary consists of bundles of coherent microtwins. Terminating microtwins frequently omit dislocation networks. Lattice dislocations entering coherent twin boundaries dissociate into DSC dislocations with b - a/6 (112). In EFG, no impurity precipitates were found. RTR, on the other side, shows heavy metal precipitates, the chemical nature of which is being analyzed.

b) EBIC. EBIC studies show that twin boundaries contain both electrically active and inactive sections. What governs the electrical activity could not be clarified to date. Interactions with lattice dislocations, termination of microtwin parts and/or decoration with impurities are under investigation. EBIC images of ribbons which were Sirtl or Secco etched prior to the deposition of the Schottky diode show conclusively that not all dislocations intersecting the surface are revealed by etch pits. In order to evaluate the effectiveness of boundary passivation, a method was developed to deposit, remove and re-deposit Schottky diodes without influencing the EBIC image. Only a fraction of the boundaries show reduced electrical activity after passivation with atomic hydrogen.

c) SIMS. Mobil-Tyco EFG ribbons were analyzed with a CEMECA 300 ion microprobe for the influence of the die design on the spatial distribution of dopant and impurities. In undoped ribbons, Mo, Al and B were below the detection limit (-1.1016). In doped ribbons, SIMS indicated a B content of -2.1017/ccm. Yield enhancement due to the presence of unidentified impurities is being investigated.

~proval Signature Dieter Ast

25

11-2-79

Date


CRYSTAL SYSTEMS, INC.

SALEM, MA 01970

Contract Title: SILICON INGOT CASTING--HEAT EXCHANGER METHOD/MULTI-WIRE

SLICING--FIXED ABRASIVE SLICING TECHNIQUE (PHASE III)

Contract No.: 9 543 7 3

This contract is for casting silicon ingots by the Heat Exchanger Method (HEM) and slicing by multi-wire Fixed Abrasive Slicing Technique (FAST).

Significant advancements have been made in the area of crystal casting since the last PIM. It has been demonstrated that nearly single crystal ingots can be cast with a single HEM solidification of upgraded metallurgical grade silicon. The impurities were rejected to the last material to freeze--near the wall of the crucible. The resistivity of the silicon after directional solidification by HEM was 0.1 - 0.2 n-cm. Macroscopic impurities, presumably SiC, did not break down the solid-liquid interface and, in some cases, caused only localised twin formation. With this silicon, the material cost could be reduced below the cost goal and the projected silicon short-fall would be avoided.

Square ingots 22 cm x 22 cm x 18 cm high weighing 16.3 kg have been solidified out of high purity melt stock. The ingots were almost entirely single crystalline.

In the area of silicon slicing using FAST approach, high throughput of the slicer and extended life of the wires have been demonstrated. Cutting rates of about 40% more than the projected estimates used in the economic analysis to meet 1986 goals have been achieved. This has been accomplished through the combination of higher surface speeds of the slicer and improvement in the wire. A life of two slices per wire has been demonstrated for impregnated wires and three slices per wire with electroplated wires.

Emphasis in the area of blade development has been on impregnation using CS! technology of putting diamonds only in the cutting edge. A systematic study of impregnation variables improved the quality of impregnated blades and.cutting performance.

26

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Contract No. :

LARGE AREA SHEET GROWTH

Energy Materials Corporation

Harvard, Massachusetts

LOW ANGLE SILICON SHEET GROWTH

955378

This program's objective is to demonstrate the feasibility of a novel approach to horizontal crystal growth. Low Angle Silicon Sheet Growth has the potential of combining the material quality and high volume solidification rates of casting and Czochralski growth with the direct shaping characteristics of ribbon growth. This technique will also allow very high pull rates without generating the stresses which appear.to limit ribbon growth. In horizontal crystal growth the ribbon is pulled horizontally or at a small positive angle from the melt surface. The key feature is that the direction of the ribbon pull is essentially perpendicular to the direction of the bulk crystal growth. The freezing interface is oriented so that the crystal grows slowly into the melt and loses heat of fusion through the thin ribbon above it, radiating from the large solid surface. The leading edge of the interface must grow at an equal, but opposite, velocity .to the pulling velocity. This thin edge is then the continuously forming seed for the bulk crystal growth.

The basic premise of our approach to control of the growth rates at the leading edge, the lateral edges, and in -the thickness direction (into the melt) is that thermal impedances in the crucible can function to provide the required temperature distribution which will lead to inherent growth stability. A small positive angle of growth from the melt surface, to provide a slightly raised meniscus under the solidifying crystal, and a relatively shallow melt to preclude convection currents are also important aspects of this approach .

Progress to date indicates that the process works. Initial experiments demonstrated the utility of a scraper mechanism to stabilize a meniscus under the growing ribbon. Difficulties were encountered with wetting of the quartz elements by the melt and spurious nucleation of freezing by the scraper and crucible walls. Provision of a water-cooled cold shoe with He to improve heat transfer has resulted in growth in three different runs. Ribbon lengths up to 19 cm were obtained, widths varied from 0.6 to 2.5 cm, while thickness v~ried from 0.06 to 0.25 cm. Growth Tates were typically 20 cm/min. One ribbon was grown at speeds from 40 to 68 cm/min. Growths were terminated by the melt level dropping so that the ribbon would freeze to the plateau. No melt level control was available in these experiments.

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27

Contract Title:

Contract No. :

Large Area Silicon Sheet Growth

Hamco Division of Kayex Corporation

Rochester, New York 14624

Continuous Czochralski Ingot Growth

954888

The objective of this program is to develop equipment and process for the growth of up to 100 kg of silicon ingot from one crucible by periodic melt replenishment.

To date, 100 kg runs have been accomplished under this contract on five occasions. Three of the five runs have been reported at previous PIM meetings. They are Run #30, 47, and 49.

The two runs completed in this reporting period are summarized below:

Total silicon melted ({155-14" cruc.; 112-12" cruc.)

Total ingot pulled Total run time Pulled yield Single crystal Throughput Recharge material

No. 55

106 .1 kg 106.6 kg

79 hrs 94.8%

75.1 kg (74.6%) 1.27 kg/hr

100% lump

No. 2*

104.5 kg 100.3 kg

108 hrs 96%

63.9 kg(63.7%) 0.93 kg/hr

100% ltunp

*Run 112 was performed on the new JPL contract #955270 crystal grower at the request of the JPL technical monitor. It was only the second run attempted on this machine and, although mechanical problems on the machine reduced the throughput rate, a total of 100.3 kg of ingot was produced.

The yield of single crystal grown during Run #55 decreased significantly after a small water leak developed in a weld area. '!he run was continued and the yield obtained on the balance of ingots pulled was reduced to 18%. Prior to the development of the water leak, the yield of silicon ingots grown was 92.5%.

The results of the solar cells fabricated from Run #49 have been verbally communicated to us. Efficiencies range from 11% to 13.5% AMl.

Impurity analysis results have been received for selective samples from Run #30, 47, and 49. We are using these results to determine the effects of contamination from different sources on crystal growth and crystal structure loss. Samples from Run #55 and #2* have been sub-mittK.lil:J:2 analysis. Jcf '3">, 'fi

Approval Signature Date

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Rochester, NY 14624

Contract Title: Low Cost Czochralski Crystal Growing Technology


The purpose of this program is to demonstrate the growth of up to 150 kilograms of 6" diameter single crystal silicon from one crucible utilizing the Czochralski method.

Utilization of new equipment designs will allow alternate cycles of crystal growth and hot melt replenishment without contamination.

The contract is divided into the following sections: 1. Accelerated melt back program (a) rods and (b) chunk material 2. Accelerated growth rate 3. Microprocessor controls.

Delivery of both the R.F. generator and the contractor-owned CG2000 crystal grower have been received and the installation is cQmplete. The interface of the R.F. supply and feed-thru system is underway and scheduled for completion during November.

Design of the cold crucible system for melting polycrystalline chunk material is underway and is scheduled for release to the subcontractor during November.

Programming of software is scheduled for completion during the first week of November. Drawings for interfacing of the micro-

. processor to the crystal puller are complete. Actual inte'rfacing should take approximately ten days.

All production hardware and polycrystalline silicon rods have been received.

To date, two runs have been made on the puller. The puller was operated in the standard resistance heated mode. Run #1 achieved a total of 28.4" zero D. 4" diameter material. A growth rate of up to 4. 9" per hour was achieved.

Run #2 was undertaken at the request of the JPL technical monitor as part of contract #954888. A total weight of 100.3 kg was pulled from a total charged weight of 104.5 kg. This represents a pulled yield of 96%. The approximate good quality crystal yield was 63.7%.

(Jtf .J t) l ·, 1 Approval Signature Dote

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Contract Tit I e :

Contract No. :

LARGE AREA SILICON SHEET

HONEYWELL TECHNOLOGY CENTER

BLOOMINGTON, MN 55420

Silicon-On-Ceramic Process

954356

The experimental dip-coater has produced 200 µm thick layers at a growth rate of 0.2 cm/sec. Cooling shoes were employed near the liquid-solid interface to provide both convective and radiative cooling. Helium gas was used and the gas flow rate on the back side of the substrate was about four times the rate on the front side. An afterheater was employed to prevent fracture of the coated substrate during cooling. At a growth speed of 0.2 cm/sec, the 200 µm thick layers show good evidence of unidirectional solidification. At the present time, the cooling jets are being redesigned to provide more uniform cooling, so that the resulting silicon layers will be more uniform in thickness.

The SCIM process has produced photodiodes with total-area conversion efficiencies of 5% (AMl,AR). The best diode has a Jsc of 23 mA/cm2 (activearea) indicating good material quality. The photodiode performance was limited primarily by series resistance. The SCIM material was grown at 0.06 cm/sec. As was noted in the last PIM, continuous coating of SOC material was demonstrated after two improvements were made in the SCIM coater. First, the transverse temperature gradients were improved by modification in the heater design. Second, growth stability was improved by inclining the substrate at an angle during growth. The crystallographic texture and diffusion lengths of SCIM coated material appears to be similar to those observed in dip-coated material.

The best SOC cell so far has a conversion efficiency of 10% (AMl,AR) for an area of 4.1 cm2 • This cell was fabricated from dip-coated SOC material grown at 0.06 cw/sec. Recently, a large number of cells have been fabricated to determine the optimum bL-.se doping concentration and the optimum diffusion conditions. The optimum concentration appears to be about 3 x 1016/cm3, although any value in the range from 5 x 1015 to 5 x l016/cm3 is acc~ptable since efficiency is not a strong function of the base doping concentration. The optimum diffusion conditions appear to be 850° for 30 min, although additional experiments will be required to verify these values. The optimum concentration and the optimum diffusion conditions should produce only a small increase in the average conversion efficiency of SOC cells.

The light-beam-induced-current (LBIC) technique has been used to compare diffusion lengths (L) before and after solar cell processing. We find a significant increasenin L due to processing in spite of the fact that a specific gettering step Bas not included in the processing.

Approval Signature

30

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Large Area Silicon Sheet Task

Materials Research, Inc.

Salt Lake City, Utah 84110

Contract Tit I e : Quantitative Analysis of Defects in Silicon


During the reporting period, the Quantimet 720 Image Analyzer (QTM 720) was upgraded to enhance its capability for the automated defect analysis of silicon sheet samples . .Also, during this period sixty silicon samples were analyzed using the upgraded QTM 720 System .

The previous QTM 720 System made use of a Hewlett-Packard Model 9810 Programmable Calculator interfaced to the system by means of a special QTM module, the Field Data Interface. The data was printed on a conventional teletype. In the present configuration, the H-P 9810 Calculator has been replaced by a PDP-11 /03 Computer and the teletype replaced with a Digital Equipment Corporation Deckwriter III high speed printer. A dual floppy disk drive has also been added to the QTM 720 System. These new additions have substantially improved the data acquisition and analysis capability of the QTM, as well as increasing the speed with which the silicon samples may be analyzed.

A computer program was written for the PDP 11 /03 computer to provide for software control of many of the QTM functions and automated analysis of silicon samples.

After chemical polishing and etching, sixty silicon sheet samples were analyzed for twin boundaries & dislocation pits on the upgraded QTM 720 System. Thirtytwo of these samples were manufactured by Motorola, twentyseven by Mobil-Tyco, and one by Tylan. The twin boundary and dislocation pit densities for these samples are listed as computer printouts in the technical reports: MRI-272, -273, and -274. Grainboundary length measurements were made on these samples by optical microscopy technique. These data and a preliminary analysis of data are also included in the aforementioned reports. All samples have been returned to JPL for solar-cell fabrication. Conversion efficiencies will measured on these samples and attempt will be made to correlate efficie:pcies with defect densities in these samples.

Approval Signature

31

October 29, 1979 Date

LARGE AREA SHEET

MOBIL TYCO SOLAR ENERGY CORPORATION

Waltham, Mass 02154

Contract Title: LARGE AREA SILICON SHEET BY EFG


In the past four month period, work was continued in particular on 10 cm wide ribbon. At present, single cartridge 10 cm wide growth is conducted in Machines 3A and 17.

Machine 3A, the multiple furnace, operates with continuous melt replenishment but at present in the single cartridge mode. So far, it has produced, in the first few months of running, about 67 meters of 10 cm wide ribbon at about 3.5 cm/minute average growth speed. Only recently, however, has it been possible to produce silicon carbidefree ribbon. So far, strictly clean conditions have not been observed, and the diffusion lengths have been consequently low. To improve this situation will be the thrust of the program through the remainder of the year, while also two other cartridges will be introduced in this furnace to accomplish three ribbon multiple growth.

Machine 17 came on stream growing 10 cm wide ribbon last month. It is not melt replenished, but is capable of growing 3.5 meter lengths of 10 cm wide ribbon. Soar, this machine has demonstrated growth at 4 cm/minute with no stress and minimal buckling. It will also be run under clean conditions from now through the end of the year.

In Machine 1, work has continued on the effects of the furnace atmosphere on the ribbon quality. This area of effort is at present somewhat complicated by the fact that different growth conditions yield material that responds in different ways to solar cell processing parameters.

Fritz V. Wald 11/5/79


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Contract No. :


RCA SOLIC STATE DIVISION AND RCA LABORATORIES SOMERVILLE, N.J. AND PRINCETON, N.J.

DEVELOPMENT OF MEGASONIC CLEANING FOR SILICON WAFERS

955342

The purpose of the program is to scale up, automate, and improve the existing RCA-invented megasonic cleaning system to increase its throughput from about 600 wafers/hour to about 2500 wafers/hour in preparation for the large-scale production of flat-plate silicon solar-cell arrays. The program was begun on March 15, 1979.

During this period the megasonic cleaning system was integrated and debugged. The system consists of the megasonic cleaning sink, a rinse station, an air dryer, and an inspection station equipped with a lasser scanner for the detection of light-scattering centers on a wafer. The recirculation-filtration system is operating satisfactorily. The preliminary data on wafer cleaning and rinsing indicate that the design criteria of cleaning ability, ease of operation, and wafety have been largely met. Chemicals usage appears to be even better than forecast.

While the present rate of cleaning by use of 3/16-in. spaced carriers does not meet the design objective, it can be increased by better platen design, closer spacing of wafers in the carriers, and faster belt speeds. It remains to be determined whether extra power or another pair of transducers is required to increase the rate to 2500/hour.

The drying rate with the·present equipment is likely to be on the order of 1500 wafers/hour. If that is so, the recommendation will be to increase the active dryer length proportionally to the rate requirement.

Wafers that had been contaminated with 0.3 microns diameter alumina from aqueous as well as from 1-1-1 trichlorethane-wax suspensions were successfully cleaned as judged by the wafer scanner counts.

It is recommended to continue the program as planned but to delay the move to mountaintop until after delivery of the belt drive and sufficient time to ensure that it functions properly.

11/2/79 Approval Signature Date

33


SILICON TECHNOLOGY CORPORATION

OAKLAND, N.J.

Contract Title: Slicing of Silicon Ingots Using Inside Diameter Saws


This program is directed toward the development of I.D. wafering techniques to reduce the total kerf and slice thickness and to reduce add-on slicing costs for silicon wafers to be used for solar cells.

The objectives of this program are:

1) To develop low kerf blades (8.5 to 9.5 mil kerf)

2) To use crystal rotation, programmed feed rates, automated wafer recovery and monitoring devices to achieve the goals of this program

All equipment modification and design have been completed, and 10 cm ingots have been sliced using crystal rotation and automated recovery to transport and automatically load sliced wafers into a cassette.

Kerf thickness during slicing has been reduced to 9 mils.

Slicing speeds of up to 1 inch per minute during rotation have been achieved with minimal edge chipping. (Edge chipping had been a concern for rotational slicing).

Presently under development are studies to increase wafer productivity by the use of a highly accurate electromechanical programmed feed rate system which has been installed on the saw being used for this program.

Peter Aharonyan ,l· ,'i-71 Approval Signature Dote

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Contract No. :


Siltec Corporation Menlo Park, California

CONTINUOUS LIQUID FEED CZOCHRALSKI GROWTH

DOE/JPL-954886

This project is directed toward the design and development of equipment and processes to demonstrate continuous growth of crystals, by use of the Czochralski method, suitable for producing monocrystalline silicon for use in solar cells. "Continuous" is defined as the growth of at least 150 kg of monocrystalline silicon ingots, 150 mm in diameter, obtained from one growth container. Our approach in meeting this goal is to develop a furnace with continuous liquid replenishment of the growth crucible. This would be accomplished through use of a meltdown system with a continuous solid silicon feeder and a melt transfer system, with associated automatic feedback controls. In order to establish process parameters for conventional CZ growth of 150 mm ingots, 15 runs with 12-kg charges were performed, and solidification rates of 2.7 to 3.5 kg/hr were achieved. Of the total material grown, 96% was monocrystalline. This series of runs has provided a control group for future runs with continuous melt replenishment. Significant progress has been made in the development of a new melt transfer system. Basic material problems relating to the high temperature environment were solved. The cost of the new transfer mechanism is lowered substantially through multiple use of major system components. Manufacturing of parts and installation of the polyrod feed mechanism for continuous recharging of the meltdown chamber was completed, together with the feedback control system which uses the melt level sensor of the growth crucible as input. The design for a continuous particle feeder into the meltdown chamber has been completed, and the fabrication of this system is currently in progress. Several short melt replenishment runs with 5 to 8 kg of continuous melt transfer were performed in an effort to develop feedback control systems for solid rod and particle feeding as well as to establish the permissable pressure region in which melt transfer can be assured. Growth demonstration runs with the new transfer system were delayed for several weeks due to manufacturing problems of some of the system components. A preliminary economic analysis for the CLF system for both polyrod feeding and particle recharging to the meltdown chamber was performed.

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Contract Tit I e :

Contract No. :


Siltec Corporation Menlo Park, California

ENHANCED I.D. SLICING TECHNOLOGY

DOE/JPL-955282

The purpose of this program is to develop and demonstrate enhanced I.D. slicing technology that will significantly increase the number of useable slices per inch of ingot over industry practice. This method requires a reduction of both blade and slice thickness and will be achieved through a combination of three key slicing technology elements: ingot rotation with minimum exposed blade area, dynamic cutting edge control and the use of prefabricated insert blades. Demonstration runs of ingot cutting with ingot rotation and minimum exposed blade area were performed. Slices with a diameter of 100 mm, 250 µm thick, with kerfs of 200 um were produced. Applied cutting feed rates were in the range of 12 to 13 mm/min. The test runs were performed with 12-in blades and 76 um core thicknesses. Blade deflection during cutting was detennined to be between 64 um and 76 um using noncontact sensing devices. The tests showed clearly that control of the cutting edge position is required for blades with cores< 90 um to assure minimum blade deflection as well as cutting stability at a reasonable cutting feed rate. A characterization of the slices from the test series was perfonned, analyzing such data as taper, bow, thickness variation and depth of saw damage.

The major effort is presently directed towards the achievement of the blade cutting edge control through a feedback control system. Fundamental parameters needed for the design of the cutting edge positioning device were identified and numerically determined. The design of the position controller was completed. Blade development efforts to reduce kerf to 152 um through introduction of a prefabricated insert are continuing. An alternative blade construction requiring special etching techniques was developed which will produce a kerf of 152 um. The blades are presently manufactured and will shortly undergo testing.

I Date

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Spectrolab, Inc.

Sylmar, CA 91342

Contract Title: Silicon Solar Cell Process Development, Fabrication

and Analysis


The objective of this contract is the fabrication of solar cells from the various unconventional silicon materials by a baseline process, to fabricate solar cells from these same materials by methods intended to obtain improved conversion efficiency by known techniques, to fabricate solar cells by low cost methods to measure the solar cells and provide an analysis of the results.

At this PIM we report on optimization processing of HEM material, and low cost processing methods as applied to EFG {RH) and Web material. These low cost methods include screen printed contacts, screen printed back surface field sources and spin-on diffusion sources.

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Contract Title:

Contract No. :


University of Missouri - Rolla

Rolla, Missouri

Determination of Effect of Varying Partial Pressures of Reactant Gases, Primarily Oxygen and Nitrogen, in a Furnace Atmosphere Where Molten Silicon is in Contact With Die and Container Material. 955415

Construction of a new portable thoria - 7 wt% yttria polycrystalline ceramic solid electrolyte cell designed to be used in measuring the oxygen partial pressure above silicon melts at the sheet and ribbon production facilities of other Task II contractors has been completed. The operating temperature of the cell is 1000°c. A reference gas having an oxygen partial pressure in the range 10-8 atmospheres to 10-30 atmospheres at 1000°c may be used depending on the value of the oxygen partial pressure to be measured and the desired accuracy. The cell is capable of measuring oxygen partial pressures in the range of 1 atmosphere to <lo-22 atmospheres at 1700°K. Calibration procedures and initial results at other Task II contractor laboratories will be described.

Experiments to determine the relationship between the atmospheric environment over the sessile drop tests (oxygen partial pressure, buffer system, and background gas composition) and the devitrification of

'vitreous silica substrates in our sessile drop furnace have been completed. Initial results obtained under a previous Eagle-Picher subcontract indicated that devitrification of vitreous silica substrates at oxygen partial pressures of the order of 10-19 atmospheres precluded obtaining meaningful contact angle data.

The controlled atmosphere furnace used in these experiments is not capable of rapid heating and cooling cycles like those used by other investigators. Experiments have now been conducted at oxygen partial pressures ranging from 10-19 atmospheres to 0.2 atmospheres. In all cases, devitrification precluded meaningful contact angle measurements. However, a trend of a greater degree of devitrification at lower oxygen partial pressures was indicated. The slow heating and cooling rates inherent in the furnace were not insignificant factors in this result.

Silicon sessile drop measurements on CVD silicon carbide and sibeon substrates will be made when supplied by JPL.

38

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Westinghouse Research and Development Center

Pittsburgh, PA 15235

Contract Title: SILICON WEB PROCESS DEVELOPMRNT

Contract No. : DOE/JPL 954654

In the period since the last Project Integration Meeting work emphasis. has concentrated on increased rates of area throughput and on simultaneous melt replenishment and web growth.

The highest area throughput rate thus far demonstrated, 27.lcm2/minute, is

important as it relates to the economic analysis of the silicon dendritic web growth process. The projected cost for web growth at this rate for prolonged periods is well below the JPL 1986 goal, if the polysilicon price is assumed to be $25/Kg or less.

The accuracy of the web growth model has been verified by way of thermal measurements coupled with determinations of web thickness and growth velocity. The model simulation of the behavior predicted for a given susceptor and lid configuration was in excellent agreement with experimental data. The model will be used in future work to guide the design of components for increased web throughput rates.

To maintain high area throughput rates for prolonged periods simultaneous melt replenishment must be provided. Development in this direction is progressing well. Five hours of continuously melt-replenished growth, more than double that previously attained, was demonstrated. The quality of web grown with melt replenishment has been shown to be high, producing solar cells of equal or higher conversion efficiency as compared to cells fabricated from web grown without melt replenishment.

Further development of the melt replenishment system is progressing in several ways. A melt level sensor, using a laser beam reflected from the melt surface onto a position detector has been designed, fabricated and installed in the ~E web growth system with melt replenishment. Operation will be initiated in the near future. In another development, dynamic thermal trimming has been added in the form of heat shielding which can be adjusted during web growth. This feature pennits thermal adjustment of the melt and growth system to suit growth requirements ranging from the condition for the start of growth to the condition for the maximum rate of growth. In association with this development, an infrared detector has been installed temporarily to serve as a diagnostic tool for evaluating and characterizing the effect of the thermal trimmer.


39


In-House Program

Establishment of the in-house solar cell fabrication and testing laboratories for direct support of contractor activities has progressed with two additional laboratories now functional.

1. Photovoltaic Materials and Device Testing Laboratory:

A materials preparation facility consisting of dicing saw and lapping and polishing machines is in use.

The operational testing facilities consist of:

a. Scanning electron microscooe, type ISl-60A with 411 stage and electron beam induced current (EBIC) measurement set-up.

b. A comouter controlled automated system for measurement of the minority carrier diffusion length by the surface ohotovolta9e (SPV) technique and measurement of the solar cell spectral response. The set-up is capable of scanning along x and y axis. It can also be adapted for laser scan using a helium-neon laser with a focused beam diameter of lOµm.

c. A computer controlled automated system for the measurement of light and dark I-V characteristics of solar cells using bench model Oriel Solar Simulator (AM0 and AMl).

d. Spreading resistance set-up, 1-R Spectroohotometer, four point probe set-up, microscopes, etc.

2. Solar Cell Prototype Fabrication Laboratory:

This fabrication laboratory is now functional with diffusion and sintering furnaces, metal and antireflection coating evaporation and sputtering unit, wet chemistry facilities for wafer cleaning and etching and the photolithograohic facilities. Preliminary solar cell fabrication runs have been done with baseline processing.

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ENCAPSULATION

Case Weste·:rn Reserve University

Cleveland, Ohio

Contract Title: Systems Studies of Basic Aging and Diffusion


The objective of this study is to establish the kinetics and mechanism of thermal and photo-oxidative degradation of candidate encapsulation materials for the LSA Project. That information is to be used to develop accelerated testing and life performance prediction methods and to guide the continuing selection of optimum performance encapsulation material systems. The study is being carried out in cooperation with related studies at JPL.

The present work is a.iJ?led towaxd establishing the modes of degradation of p~ly(n-butylacrylate) (PNBA), poly(n-butylmethacrylate), and their copolymers. It has been found that for PNBAa

1. The polymer mass increases slightly during the first JOO hours of photo-irradiation in a filtered QUV Accelerated Weathering Tester.

2. The degradation rate is temperature dependent.

J. There is rapid growth of an absorbance band at 27 5 nm during the first 20 hours of UV exposure at 4o0 c, but little growth thereafter,

It is postulated that PNBA contains trace ketone groups which are sensitive to JOO nm radiation. This ketone may be converted to a degradation product which is relatively more stable.

Continuing studies include the determination ofa

1. Chemical changes during the early stages of degradation.

2. The dependence of degradation mechanism on light intensity.

J. The quantum efficiency of the reactions •

The results are being used to establish the validity of predictions of long exposure performance based on short term testing and to evaluate the feasibility of using these polymeric materials as encapsulants,


41

ENCAPSULATION TASK

Dow Corning Corporation

Midland, Michigan

Contract Title: DEVELOPMENT OF SILICONE ENCAPSULATION SYSTEMS FOR TERRESTRIAL SOLAR ARRAYS


August 1979 through November 1979

The objective of this program is to develop cost effective encapsulation systems for photovoltaic modules using silicone based materials. ·

Most of the effort during this period was oriented toward the preparation and evaluation of silicone-acrylic cover materials containing UV absorbers. An acrylate functional silicone intermediate w~s copolymerized with mixtures of methylmethacrylate and butyl acrylate. The ratio of 20% silicone, 40% methylmethacrylate, 40% butyl acrylate gave a clear hard surfaced film. The physical properties of this formulation were improved by minimizing the amount of mercaptan chain regulator. Lowering the chain regulator increases the molecular weight of the polymer which improves the physical properties, however, below some minimum level of chain regulator the solution of polymer gels.

Permasorb MA, a cormnercially available acrylate functional UV absorber was incorporated into the above polymer in two ways: by c6reacting it with the acrylate monomers during polymerization and by physically blending it with a solution of the copolymer. The Permasorb MA which was physically blended with the polymer was more easily and rapidly extracted from cured films than the Permasorb MA which was chemically incorporated in the polymer.

Samples of cellulose acetate which degrade rapidly when exposed to UV radiation are protected by a coating of this polymer. In one example, a sheet of cellulose acetate protected with a coating 1 mil thick containing 1% Permasorb MA exposed for over 500 hours in an Atlas Weatherometer has not visibly changed. An unprotected sample of cellulose acetate becomes visibly crazed within 48 hours of exposure.

If such a film is suitable as a cover material for UV sensitive pottants its cost would be~5¢/ft 2 (1980 dollars).

Approval Signature

42

October 25, 1979

Date

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MOTOROLA INC., SEMICONDUCTOR GROUP

PHOENIX, ARIZONA

Contract Title: ANTIREFLECTION COATINGS ON LARGE AREA GLASS SHEETS


Summary of Progress from August 1 to November 1.

Samples of antireflective films on glass are being prepared by withdrawing glass sheets from sodium silicate solutions. At present, samples are being prepared at different withdrawal speeds, in combination with silicate solutions of different concentrations. Transmission measurements will be performed on the samples at a later date and correlated with the speed and solution concentrations used in producing each sample in an effort to devise a way of predicting the optical performance of films solely on the basis of withdrawal speed and silicate concentration.

Abrasion testing has been performed on samples of the silicate films and indicates that the film should be durable enough to withstand the severe natural abrasion to which solar panels are exposed. The films tested were much stronger in this respect than any other antireflective coatings tested, and may .be as strong as a bare glass surface.

The random unevenenss of film produced in earlier experiments has been greatly reduced by the use of a dust-free nitrogen atmosphere surrounding the filming facility. Attention has.now turned to study of the film irregularities near the edges of the glass surface. Although such "edge effects" are not detrimental to performance in solar panels, where the edges of the coverglass are used for bonding and sealing, it is possible that an understanding of edge effects will permit further improvement of the film formed on the central glass area.


43

ENCAPSULATION TASK


PHOENIX, ARIZONA

Contract Title: ANTIREFLECTIVE COATINGS APPLIED BY ACID LEACHING



In excess of 300 4 inch square samples of acid etched antireflection coated glass have been produced and are now being tested for optical performance, and chemical and physical durability.

Out of the 30o+ samples produced, ten have been measured to have 99.8% transmission of normally incident light at a wavelength of 0.45 µM, far above the 92.5% transmission typical of unfilmed glass.

Abrasion tests have been performed on three batches of acid etched filmed glass. The data indicates that the samples with the best optical performance were least resistant to abrasion, presumably because of the greater porosity of highly effective films.

Samples of filmed glass are currently being exposed to concentrated atmospheric pollutants and staining agents as part of a chemical durability test program. In addition, a detailed study of optical performance as affected by etch composition is under way.

1t/f,/79 Approval Signature Date

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ENCAPSULATION TASK

ROCKWELL INTERNATIONAL SCIENCE CENTER

THOUSAND OAKS, CA 91360

Contract Title: Study Program for Encapsulation Materials Interface for Low Cost Silicon Solar Array (LSA}


The major objectives of this program a re to conduct a phys i ca 1 / chemical study of surface and interface degradation in solar cell encapsulant systems induced by moisture, temperature and UV radiation. Current efforts are now concentrated upon development and validation of an atmospheric corrosion model and test plan for low cost solar arrays (LSA}.

An atmospheric corrosion model has been developed for (LSA} which treats the separate and combined effect of moisture, temperature and UV radiations. This model treats the probabilistic conditions for moisture condensation and evaporation during climatic variations at the Mead, Nebraska test site as an important input to material responses and moisture related interfacial corrosion processes. Original assumptions that corrosion initiates in microscopic defects and is rate-controlled by diffusion processes are retained and shown to correlate with incipient corrosion failure processes in Solarex test modules aged at Mead, Nebraska test site.

Designs are completed for a Mead climatology simulator which will be implemented in laboratory corrosion studies. This Mead climatology simulator is designed to generate four naturally occurrin~ extremes on the solar array which are: solar radiation= 1000 watts/m, maximum temperature= 307K, and cyclic variations from front to back surface of maximum temperature change= ±39K and maximum moisture supersaturation (maximum dow point temperature minus minimum temperature}= 37K. This Mead climatology simulator will be first utilized in corrosion model verification studies and later to examine the potential of acceleration and early detection of corrosion degradation. These studies will include nondestructive evaluation of solar cell response by photovoltaic current voltage (1-V) response, AC impedance scanning, and chemical analysis of interface corrosion processes by Auger spectroscopy and profiling through the interface.

M.21. Jt?9 Approval Signature Dote

45

Contract Title:

Contract No:

ENCAPSULATION TASK

Spire Corporation

Bedford, MA

Integral Glass Encapsulation for Solar Arrays

954521

(August - November 1979)

This program is aimed at the development of electrostatic bonding (ESB) as an advanced encapsulation technique for terrestrial solar arrays. The electrostatic bonding process is used to join cells directly to the front cover glass without use of adhesives or other organic materials. A variety of backings can be applied to this bonded assembly.

As of August 1979 glass for larger sized ESB modules had been received. A square cell, providing high packing density while utilizing an optimum amount of a three inch wafer had been designed. Alignment fixturing which provides reproducible registration of multiple cell configurations had been designed.

During the present period all equipment, materials and parts necessary for the fabrication of integral glass front modules have been obtained and made operational. Process development required for scaling up the module size has been completed. An initial run of modules has been bonded and backings consisting of ethylene vinyl acetate (EVA) and an aluminum foil/Mylar laminate have been applied. Four of these ESB assemblies are mounted on a standard JPL minimodule frame.

Studies of multiple cell front bonding and the bonding of all glass module backs were carried out during the present period. It can now be said that both module front bonding and module back bonding are routine processes. Process yields now exceed 90 percent.

Development of preformed contacts consisting of wire screens trapped between the module front glass and bare wafers has continued. Individual 5x5 cm cells with 1-V curve factors of 74 percent have been demonstrated, and four cell modules with curve factors of 65 percent have been produced.

During the upcoming quarter 40 integral front ESB modules will be prepared. Conventional backings will be applied to the ESB assembly at Spire.

2. #vv-esc,. ~ tf "1 ') Date

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Task III - Encapsulation

Springborn Laboratories, Inc.

Enfield, Connecticut

Contract Title: Investigation of Test Methods, Material Proper

ties and Processes for Solar Cell Encapsulants

Contract No.: LSA 954527

This program involves the evaluation of materials and processes for the encapsulation of Solar cells. Material selections are based on the 1986 cost objective of $2.70/"f!l- (1975 dollars), ($3.78/"f!l- - 1980 dollars).

During this quarter experimental evaluations of module fabrication were continued with the use of ethylene/vinyl acetate (EVA) pottant. Other pottants were also brought under investigation for module production. Baseline properties were determined for the initial formulations of ethylene-propylene-diene rubber (EPDM), aliphatic polyurethane, polyvinyl chloride plastisol, and a low cost silicone rubber. The last three pottants are liquids intended for casting, as an alternative to vacuum bag lamination. The baseline properties being studied included selection of primers for bonding to cells and substrates/superstrates, salt spray corrosion resistance, thermal stability and mechanical properties. All pottants of interest are also under exposure to natural weathering conditions and RS/4 sunlamp. Modules have been constructed using these pottants and are undergoing thermal/humidity cycle testing.

Low cost outer covers for substrate designed modules have been investigated further. Attempts to saponify and ion-exchange acrylic films to improve surface characteristics have not yet been successful. A new UV absorbing silicone acrylic film appears very promising and modules prepared with this coating are being tested for durability. The use of abrasion resistant coatings has not been successful to date due to the weathering and degradation of the commercial treatments attempted so far •

Insulation resistance has been determined on module of glass-EVA-aluminum foil construction. High voltage breakdown appears to be uniformly in the range of 5.6 kilovolts, indicating that EVA should provide adequate insulation for series connected modules.

10/29/79


47

Encapsulation Task

In-House Program Life Prediction Modeling

Quantitative relationships that relate environmental stresses such as solar ultraviolet, wind, temperature extremes, and moisture to the rate of degradation of module performance and structural integrity are objectives of the Encapsulation Task in-house efforts. These activities are integrated with contractual activities to develop an over-all module life prediction methodology.

Photodegradation rates and mechanisms and ultraviolet absorption characteristics of polymeric encapsulants are being measured as a function of polymer composition and test exposure conditions. Data are being obtained for silicones, EVA, and P-nBA. Additional materials will be characterized during the coming year.

Encapsulation material degradation data for low-cost advanced encapsulant systems is being gathered using various test hardware such as mini-modules (12" x 16"), one and two-cell modules and individual material samples. Exposure facilities include JPL laboratory reactors and selected field test sites such as Point Vicente, JPL, and Goldstone.

A thermomechanical computer model of a photovoltaic module has been formulated and is being refined and used to study failure modes associated with temperature and moisture expansion stresses within the module encapsulation system. The Mead, Nebraska array hardware has been used in this initial analytical study.

A long term accelerated module life test is being implemented to evaluate the validity of a life testing plan developed by Battelle. A closely controlled and monitored module degradation rate experiment with accelerated temperature cycling, high humidity and applied current flow will be conducted with ten prototype modules simultaneously over a four to six month test period.

Date

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PRODUCTION PROCESS AND EQUIPMENT



Contract Title: Developm~nt of High Efficiency (14%) Solar Cell Array Module


The objectives of this program are (1) to design and develop 3" diameter, P/N solar cells with conversion efficiency of 16.5% or better at AMl and 28°C, (2) to design and fabricate tooling necessary to produce the cells and the modules, and (3) to design, fabricate and deliver six modules with a minimum output of 90 watts at AMl and 28°C and with the design goal of 14% overall efficiency. The modules design has been firmly established as previously reported. All components for the modules are in house.

During this quarter, effort has been concentrated on the development of high efficiency, large area (45.5 cm 2

),

P/N solar cells. A number of experimental runs have been performed varying the time-temperture parameters for the formation of PN junction and back surface field. The best efficiency achieved to date for a 3" diameter cell is 15.6% at AMl and 28°C. Recent experiments indicated that the efficiency of cells with textured surface is 1% higher than that of polished surface, both coated with multilayer AR coating. All future cells will have textured surface. The main difficulty in fabrication of high efficiency, P/N cells appears to be the inconsistency of starting N-type silicon ingots. Work on cell development is continuing.

The following tooling required for the fabrication of the solar cells and the modules has been completed and checked out: (1) AR tooling which utilizes high power magnets to shield the center contact from coating material which impairs solderability of the cell, (2) a back contact soldering machine which solders 120 cells into a seriesparallel connected cell assembly, (3) vacuum pick up, and (4) test fixtures.


49


Applied Solar Energy Corporation (Formerly OCLI) City of Industry, California

Contract Title: Developm~nt of Low Cost Contacts to Silicon Solar Cells


The goal of this contract is to test the technical feasibility and effective cost of a copper plating system for the production of low cost contacts in the manufacture of solar cells for high volume production.

The paper analysis of copper diffusion through different metallic barrier has been completed. Nickel was indicated as the best platable candidate metal to provide a barrier to the copper diffusion.

A heat treatment study of evaporated Cr-Ag, Pd-Ag, Cr-Cu, and Pd-Cu systems has been completed. Possible degradation of functioning cells after various heat treatments was studied.

A screenable plating mask has been found, and used with a newly developed contact pattern for the screens. Solar cells (using 2~" cells) utilizing the new contact pattern with the old plating procedure have been successfully made. The cells have shown good I-V characteristics and good contact adhesion.

c;)~j 'f'd~ Approval Signature Date

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Contract Title:

Contract No. :


ARCO Solar, Inc.

Chatsworth, California

Automated Solar Panel Assembly Line

955278

The objectives of this program are to design, develop and demonstrate an automated solar cell module production line. Included in this program are (1) a module design compatible with automation methods, (2) a machine capable of soldering interconnects at a rate of 12 cells/minute, and (3) a lamination system capable of producing 12 laminates per hour.

The solar cell/interconnect configuration incorporates full redundance utilizing multiple small solder connections. Ribbon and solder connection locations are identical on both the front and back surfaces of the solar cell.

The soldering machine incorporates auto-cassette unloading and wafer alignment, ribbon feed and deployment, simultaneous soldering of front and backside interconnects, in-line removal of soldering flux, and attachment of a plastic strip to the back of each solar cell string for. handling.

The lamination system is a two chamber vessel separated by a rubber diaphragm. High speed vacuum throughput, infrared heating and thinner lamination capability are key features of this equipment.

During the third quarter of this program breadboard models of RF roller soldering, wafer alignment and ribbon feed and deployment were successfully demonstrated. Detail drawings commenced for the fabrication of hardware for these remaining elements of the soldering machine.

The prototype production lamination chamber was used to laminate over 300 modules with 97% process yield. A lamination system consisting of 8 chambers has been fabricated and delivered.

~val Signature

51

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Contract Title:

Contract No. :

PRODUCTION PROCESS AND EQUIPMENT AREA

BERND ROSS ASSOCIATES San.Diego, CA 92109

Development of Economical Improved Thick Film Solar Cell Contact

955164

The objective of this investigation is the development of fritless inks through the substitution of low melting point metal powders in conjunction with an oxide scavenging agent. The resultant screenable metal paste should be firable in a non oxidizing atmosphere to allow use of economical base metal systems.

The quartz tube furnace and gas handling system have been installed and operated.

Nickel and copper system pastes were prepared using lead and tin powders as the liquid phase sintering media. Pastes were screened using the linear array of contacts reported previously. Pastes were fired in hydrogen, nitrogen and forming gas (N2 + 10% Hz). None of the nickel pastes gave adherent and coherent contacts. No sintering action was observed in the nickel inks under SEM micrography. Nickeltin inks fired in hydrogen at higher temperatures (650°, 700°C) appeared to have a smaller particle size than the starting material. This was ascribed to the formation of intermetallics such as Ni3 Sn, Ni3 sn2 and Ni3 Sn4.

Copper-lead and copper-tin inks fired in hydrogen showed sintering action but lacked adhesion. An experiment was performed to determine if hydrogen interfered with the fluxing action of silver fluoride, or if it tended to lift the structure during the sintering phase. It was found that silver fluoride fluxing was inhibited by the presence of hydrogen. A two step firing process using nitrogen atmospheres during fluxing, and hydrogen during the sintering phase proved feasible. Resultant contacts were adherent, scratch resistant and solderable.

A glassy phase of material associated with silver fluoride decomposition was observed. This material was identified and mapped by SEM X-ray fluorescence techniques at JPL. The material was attributed to a major contamination of the silver fluoride with sodium fluoride by the supplier.

Approval Signature

52

October 30 2 1979

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Rochester, NY 14624

Contract Title: Low Cost Czochralski Crystal Growing Technology


The purpose of this program is to demonstrate the growth of up to 150 kilograms of 6" diameter single crystal silicon from one crucible utilizing the Czochralski method.

Utilization of new equipment designs will allow alternate cycles of crystal growth and hot melt replenishment without contamination.

The contract is divided into the following sections: 1. Accelerated melt back program (a) rods and (b) chunk material 2. Accelerated growth rate 3. Microprocessor controls.

Delivery of both the R.F. generator and the contractor-owned CG2000 crystal grower have been received and the installation is complete. The interface of the R.F. supply and feed-thru system is underway and scheduled for completion during November.

Design of the cold crucible system for melting polycrystalline chunk material is underway and is scheduled for release to the subcontractor during November.

Programming of software is scheduled for completion during the first week of November. Drawings for interfacing of the micro-

. processor to the crystal puller are complete. Actual interfacing should take approximately ten days.

All production hardware and polycrystalline silicon rods have been received.

To date, two runs have been made on the puller. 'Ille puller was operated in the standard resistance heated mode. Run #1 achieved a total of 28. 4" zero D. 4" diameter material. A growth rate of up to 4. 9" per hour was achieved.

Run #2 was undertaken at the request of the JPL technical monitor as part of contract #954888. A total weight of 100.3 kg was pulled from a total charged weight of 104.5 kg. This represents a pulled yield of 96%. The approximate good quality crystal yield was 63.7%.

(<J{{ J", 1'i Approval Signature Date

53


KULICKE AND SOFFA INDUSTRIES, INC.

HORSHAM, PA., 19044

Contract Title: Automated Solar Module Assembly Line


The machine which Kulicke and Soffa is to deliver under this contract is a cell stringing and string applique machine which will be flexible in design, capable of handling a variety of cells and assembling strings of cells which can then be placed in a matrix up to 2' X 4' in series or parallel arrangement. The target machine cycle is to be 5 seconds per cell. This machine will be primarily adapted to 3 inch diameter round cells with one or two tabs between cells. The design of the machine will be flexible so that it can be modified to handle other cell sizes.

While induction heating has certain desirable aspects as a bond technique for solar cell interconnects, it was determined that the further development required to utilize the induction heating technology would not fit within the constraints of the contract schedule. Therefore, it has been decided to proceed with pulsed heat as the prime candidate for the bond technique. ·

During this reporting period, an order was placed for a supply of commercially available 3 inch diameter solar cells to be used in testing the machine. Work proceeded and hardware was built on the theta orient station, bond station and vacuum pick-up assembly and lance system. The bond station has been equipped with greater capacity electrodes and power supply to accommodate the heat requirements of the station. Tests were conducted on the vacuum pick-up and lance assembly to simulate picking up fifteen (15) 3 inch diameter solar cells which represent a 4 foot string. The vacuum lance system was also tested with only two adjacent cells, which represent the minimum string to be handled to verify that there is ample vacuum to pick up any partial string.

The solar cell will be inverted as it is transferred from the walking beam system of the first half of the machine to the string conveyor of the second half of the machine. This is being done to minimize contact on the sun (collector) side of the cell, allow bonding from the 2nd interconnect from the top side, and facilitate making string interconnections in the module array.

Max Bycer 1 November 1979

54

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San Ramon, CA 94583

Contract Title: Automated Cell Placement and Interconnection Using an Industrial Robot


The scope of work under this contract involves analysis, assessment and development of techniques for automating the placement and interconnection of solar cell. The diversity of solar cell shapes, sizes and metallization patterns requires a versatile interconnection system, unless or until an optimum, industry-wide standard emerges. Progrannnable automation provides this versatility in an off-the-shelf form.

We are using a Unimate 2000B industrial robot which gives us the versatility and reliability of a well proven design. Our method incorporates a robot and effector which combines an induction heating coil and a compliant vacuum pick up. Prototype vacuum pick ups have been used on the robot with nearly zero breakage rate. Encapsulated induction coils, identical to the final design, have been used to solder strings of cells using the same sequence of operations as the proposed system. Our scheme of robot operation requies that it interface with a "smart" preparation station. This station must accept standard H" bar cassettes of randomly oriented cells, unload the cells, rotate them to the orientation the robot is expecting, apply the proper amount of solder paste in the correct places, measure and cut lengths of interconnect lead, place a stress-relief crimp in the correct place in the lead and do it all with a cycle time less than or equal to that of the robot. The robot then picks up this fully-prepared cell, begins heating it while "in transit," and places the hot cell on top of the exposed, solder-coated leads from the previous cell completing the connection. A small micro computer is being used to synchronize all of this activity. The preparation station has been built and successfully interfaced with the robot. The micro computer has been used to control events with sub-millisecond spacing. All of the various systems are currently undergoing integration for final testing.

Jack Hagerty October 31, 1979


55

Contract Title:

Contract No. :

PROGUCTION PROCESS AND EQUIPMENT

MB Associates San Ramon, CA 94583

Use of Glass Reinforced Concrete (GRC) as a Substrate for Photovoltaic Modules

955281

This program is in its final stages. A GRC substrate solar array panel design has been completed, 15 full scale panels fabricated and 12 delivered to JPL for testing. Two full size (4 ft. x 8 ft.) panels will be completed covered with cells and delivered to JPL. Mini modules on GRC substrates were completed and delivered to JPL for testing. The thermocycle tests developed wrinkling in the laminations around the cells. This was believed caused by the aluminum moisture barrier backing in the lamination. The aluminum will be eliminated in the full size modules (1 ft. x 4 ft. laminations on 4 ft. x 8 ft. panels).

Some concern has been expressed about the possibility of current leakage to ground. Preliminary hipot tests using a dry untreated GRC substrate on which the cells were encapsulated directly using EVA, cotton scrim cloth, cells, EVA and Tedlar cover film were well within requirements. The leakage measured was 5 microamps at 3000 VDC. However, after the test module was soaked in H20 for 12 hours, the leakage was 500 microamps at 1,500 VDC. Further tests will be conducted using GRC which has been water proofed with SEALCRETE and various laminations including additional EVA, Glass Scrim cloth and Tedlar backings.

Preliminary cost calculations indicate that the MBA designed photovoltaic solar array panels fabricated from GRC could be installed at a cost below the project cost goals. This design is amenable to mass production, (resists weathering) composed of readily available inexpensive materials, rigid and four point suspended on simple mountings which facilitate installation.

Jim Eirls

Approval Signature

56

October 31, 1979

Date

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PHOENIX, ARIZONA

PHASE 2 OF THE AUTOMATED ARRAY ASSEMBLY TASK OF THE LOW-COST SILICON SOLAR-ARRAY PROJECT

954847

Summary of Progress for Period of August 1979 through October, 1979.

This portion of the contract is concerned with specification of process control parameters and limits which will allow progress toward automation of the process sequence. The main objective of this contract is sufficient process control limit definition to permit advanced equipment prototypes to be designed for incorporation into an advanced pilot line facility.

Motorola is developing a process sequence which is capable of utilizing both sliced ingot wafers or directly grown sheet. The sequence incorporates texture etching, ion implantation, LPCVD silicon nitride (for an antireflection coating, surface passivation, and as a plating mask), mechanically masked plasma patterning of the nitride, and plated metallization.

During this period, a plated metallization process which utilizes palladium, nickel, and copper has been shown to be viable. For this process, only the immersion palladium process is utilized, eliminating the more expensive electroless palladium step. Further, heat treatments at 300°C and 400°c have shown nickel to be a suitable barrier to copper, preventing copper diffusion into silicon.

Also during this period, simultaneous plasma patterning of both sides of a silicon nitride coated solar cell has been demonstrated. In this process, the cell is sandwiched between two masks. Line-width replication from the mask to the cell is excellent, limited now by the mask manufacturing process, not by the plasma etching process.

M. G. Coleman 11-1-79 Approval Signature Date

57

Contract Tit I e :

Contract No. :



PHOENIX, ARIZONA

THE DEVELOPMENT OF A METHOD OF PRODUCING ETCH RESISTANT WAX PATTERNS ON SOLAR CELLS

955324


A manually operated printing device has been constructed and used for the experimental printing of wax on silicon wafers. The device is equiped with vacuum chucks for holding both printing plates and wafers.

Attempts to print using melted wax presented more problems than originally anticipated. The problem of maintaining the waxes in a molten state during printing was the most serious problem, with freezing of the wax during plate-to-wafer contact occuring frequently. In addition, the formation of wax filaments during plate and wafer separation, the poor wax viscosity control at elevated temperature, and the damage of printing plates by high heat suggested the use of some other wax printing system.

These problems have led to the investigation of wax solvent systems for printing instead of molten wax. It has been found that two of our current waxes, glycol phthalate and Apiezon, form solutions in methylene chloride. Multiwax 195M does not form solutions but, rather, fine suspensions in such solvents as mineral spirits. Both solutions and suspensions permit wax to be printed at room temperature, without any possibility of freezing the plate and wafer together. Additionally, they permit simple adjustment of viscosity by means of varying the wax-solvent ratio, and display less of a tendency to bead up on certain printing plate materials.

Approval Signature

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PHOENIX, ARIZONA

THE ESTABLISHMENT OF A PRODUCTION-READY MANUFACTURING PROCESS UITLIZING THIN SILICON SUBSTRATES FOR.SOLAR CELLS

955328

Summary of Progress for period of August 1979 to November 1979.

This program calls for investigation, development, and characterization of methods to establish a production-ready manufacturing process which utilizes thin silicon substrates for solar cells. These thin substrates are prepared by sawing directly to thicknesses of 8 mils and 5 mils.

Initial cost evaluations have been performed which compare the slicing process for standard thickness (13 mils) wafers against 8 mils and 5 mils • Format A sheets have been prepared and an !PEG analysis was completed.

Processing changes have been effected to accommodate the thinnest substrates and improve processing yields. Several test lots are in process to verify these changes. Both an all-diffusion and an allimplantation process sequence are being studied. One of these sequences will be recommended as the final production process.

Wafers with varying degrees of surface damage removal will be processed with the recommended process to determine the required amount of surface etching after sawing.


59


PHOTOWATT INTERNATIONAL, INC. (SENSOR TECHNOLOGY, INC.) CHATSWORTH, CALIFORNIA 91311

Contract Tit I e : PHASE 2 ARRAY AUTOMATED ASSEMBLY TASK


An ongoing investigation of several spray-on process applications were performed this quarter. High resistivity (10 "'20 ohm-cm) silicon material yielded a more effective spray-on aluminum back surface field than lower resistivity (3"' 8 ohm-cm) silicon material. The highest open circuit voltage obtained to date with spray-on aluminum back surface field solar cell structures was 0.605 volts, with 10 "'20 ohm-cm silicon material. Spray-on equipment parameter adjustments are being made in order to obtain a spray-on A.R. coating thickness which results in minimal reflection losses.

Initial effort in the area of microwave heating for solar cell fabrication was directed this quarter toward the design and development of appropriate microwave heating equipment. Conventional microwave ovens were· found to be unsuitable for solar cell heating applications. In view of this situation, two novel microwave heating configurations were conceptually designed on the basis of theoretical considerations. The construction of these two microwave heating configurations is currently underway.

C> Ap{..oval Signature

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Contract Tit I e : DEVELOPMENT OF LOW-COST POLYSILICON SOLAR CELLS


The production of low-cost, large area, high efficiency polysilicon solar cells is the overall goal of this program. The major tasks which comprise this project include; (1) development of a low-cost polysilicon solar cell process sequence which achieves ten percent (10%) efficient large area polysilicon solar cells in batch quantities, (2) development of a front surface grid pattern optimized.with respect to crystal grain size, (3) investigation of a polysilicon wafer surface macrostructure or texturizing process suitable for large scale production, (4) study of junction formation techniques, (5) investigation of antireflective coatings suitable for polysilicon solar cells, and. (6) exploration of other processes, as necessary, to obtain high efficiency or low-cost polysilicon solar cells.

Solar cell fabrication sequences for Wacker polysilicon wafers, Crystal Systems polysilicon wafers, and Exotic Materials polysilicon wafers were investigated this quarter. Efficiencies achieved to date for the respective large area polysilicon wafer materials are 10.5 percent, 8.7 percent, and 7.2 percent. The three types of polysilicon materials were characterized by an average crystal grain size, distribution of grain sizes, and degree of single crystallinity. A grid pattern study was made. The effect of isotropic surface etching, texturizing, gettering, diffusion, spray-on dopants, and A.R. coatings were also investigated.

61

Nov J, J 919 Date

PRODUCTION PROCESS & EQUIPMENT DEVELOPMENT (TASK 4)

RCA Laboratories Princeton, New Jersey 08540

Contract Title: AUTOMATED ARRAY ASSEMBLY, PHASE II

Contract No.: DOE/ JPL-954868

21 July - 26 October 1979

During this period, work has continued on studies of three manufacturing sequences for solar cells based on ion-implanted junctions, furnace annealing, screen printed contacts, and spray-on AR coatings. The starting material has been primarily "solar-grade," N- and P-type 3" diameter wafers; in addition, a small quantity of dendritic web has been evaluated with selected processes. A total of 1500 solar cells has been fabricated and evaluated.

As a result of this work, two problems areas have been identified relating to materials and process compatibility.

First, screen printed thick film inks do not contact ion implanted junctions as well as diffused junctions. Previously we had demonstrated screen printed contacts and determined suitable ink formulations and firing techniques on diffused junction solar cells. We now find that when identical techniques are used with ion implanted junctions that contact resistance problems typically occur on the ion implanted cells. In most cases, the performance of diffused junction solar cells is good immediately after the screen printed.inks are fired. In contrast, the AMl characteristics of ion implanted solar cells are quite poor immediately after firing. They require a HF acid treatment and typically are not as good as diffused junction cells. In addition, we have also noted degradation of the contact characteristics after spray AR coating.

Second, we have found that the previously determined optimum ion implantation/ anneal process must be modified to accommodate the starting silicon material.

In cell interconnection and panel assembly, a solder reflow process has been demonstrated in which the cells are individually tabbed then placed in an array which is soldered by means of a bank of infrared lamps which traverse the array. With the present system, this latter process is accomplished at a rate of one linear ft. of array/min.

R. V. D'Aiello

Approval Signature

62

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SOL/LOS Incorporated Los Angeles, California.

Contract Title: A new method of metallization for silicon solar cells


July 1979 through September 1979.

The third quarter of the project was concerned with the environmental tests of solar cells metallized with the Mo-Sn ink, lhe test consisted of one week exposure in a waterbath maintained at the constant temperature of 45°c, followed by ten thermoshock cycles between 100°c (boiling water) and -45-~ ( a mixture of dry ice and acetone). T,wo groups of cells, one with peak firing temperature of 550°c and the other group metallized at peak temperature of 700°c, followed by 15 minutes annealing at 450°c, were subjected to the test. The cells metallized at 550°c showed degradation of the V-I characteristics after the humidity cycle. The cells metallized at 700°c with the post annealing period did not show any such degradation. It was further established that the degraded cells recovered to the original V-I characteristics af:.er 15 minutes annealing at 450°c in a forming gas atmosphere. The cells subjected to the tests were 2cm x 2cm P/N structure. Metallization of N/P cells is scheduled for corapr~.rison with Ti-Ag contacts.

Approval Signature

63

1,0/19/1979 Date


Spectrolab, Inc.

Sylmar, CA

Contract Title: Array Automated Assembly Task Solar Cell and Module Process Sequence


The objective of this effort is to develop, optimize and demonstrate the feasibility of a process sequence for low cost fabrication of solar cells and solar cell modules.

The infrared furnace for firing printed contacts has been received and installed. Evaluation of the furnace for firing silver front contacts has been completed with completely satisfactory results being obtained.

An evaluation of silicon material having varying resistivity and minority carrier lifetimes has been made. Significantly inferior results are obtained with low lifetime material. These results suggest a specification of minimum diffusion length or some equivalent will be required.

Investigation of oxide and silicon removal by plasma etching has been intitated. Preliminary results indicate that plasma etching with sulfur hexaflouride (SF6) gives a somewhat slower rate but more uniform surface than does Freon 14 (CF4) with 8% oxygen. The surface produced by Freon 14 becomes intensely pitted as the etching proceeds. Preliminary results indicate that the surface produced by etching in sulfur hexaflouride is a suitable standard surface condition for use with the PX-10 spray-on diffusion process.

Evaluation of the improvement of cell performance by plasma etching the front surface has shown that the improvement occurs across the spectral range. Part of the improvement obtained with Freon 14 can be definitely attributed to antireflective or microtexturing effects, but half or more remains unaccounted for. Further experiments to determine the effect of etching with sulfur hexaflouride are under way.

10/29/79

Date

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Contract No.:


Spect rolab, Inc.

Sylmar, CA

High Resolution, Low Cost Solar Cell Contact Development

955298

The objective of this effort is to demonstrate the fe~ibility of forming solar cell collector grid contacts by the MIDFILM\!9 process. This is a proprietary process developed by the Ferro Corporation, a subcontractor for the program.

The MIDFILM process attains a line resolution characteristic comparable to photoresist methods with a process related to screen printing. The surface to be processed is first coated with a thin layer of photoresist material. Upon exposure to ultraviolet light through a suitable mask, the resist in the non-pattern areas remains tacky. The conductor material is applied in the form of a dry mixture of metal and frit particles which adhere to the tacky pattern area. The assemblage is then fired to ash the photo-polymer and sinter the fritted conductor powder.

During.the past period a number of silver powders have been formulated and evaluated. It was shown that a "spherical" powder produces cells with a lower series resistance than a flake powder. Spherical type silver powder with a suitable frit has demonstrated the feasibility of producing solar cells with an efficiency on the order of 15%, AMI. At present, yield of the higher efficiency cells is low due to inconsistent sintering of the powder. This results in a high series resistance. Environmental evaluation of the cells has been initiated and may show a slight humidity sensitivity.

10/29/79 Dote

65


University of Pennsylvania

Philadelphia PA

Contract Title: Analysis and Evaluation of Processes and Equipment

Contract No.: JPL-954 796

During the last several months, the effort was concentrated on collecting data for the process options for metallization (contact formation) and antireflection coating. Most of the data available in contract reports and in the literature have been extracted and organized. Particularly for metallization, the options form a sizable submatrix, with many combinations possible. What has made progress on the comparative analyses difficult, however, are attributes particularly pronounced at the metallization processes: 1. the processes contain a considerable amount of "artiness", with many process details not documented or even purposely held proprietary; and 2. data on solar cell performance in relation to the metallization processes used, are frequently not given, or are overshadowed by other process variables not directly connected with metallization. Personal contacts have been, and will continue to be used to obtain additional information, as far as it is available.

From the data collected so far, 10 primary process sequences have been identified which are presently used on production lines or which have beeri more extensively explored. In fact, the old electroless nickel plating process, in several variations, is or has recently been used on at least five production or pilot lines, the Ti-Pd-Ag vapor deposition on at least 3 lines, and Ag-paste screen printing on at least four lines, while numerous experimental processes, particularly with base metals, are currently being investigated at numerous places.

The key task on this project for the immediate future is to arrange the large amount of collected data into an order which permits comparative evaluation, and to derive from it a cost-effectiveness analysis.

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10/31/79

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Contract No. :


Westinghouse Electric Corporation

Pittsburgh, PA 15235

PHASE 2 OF THE AUTOMATED ARRAY ASSEMBLY TASK

954873

Open circuit voltages in the range of O. 565 - O. 595 hav·e been achieved from aluminum back surface fields using+both sputtered and silk screened Ai. Since the metallurgical p region obtained in this work (surface concentration, profile and depth) conforms to the present theoretical understanding, the V may be depressed due to limitations in the front junction. Several giperiments have shown that some form of protection for the front surface is desirable. The most effective methods (and also+cost effective) is to leave the phosphorous doped glass (from then diffusion) on the sun side of the cell during BSF formation. Cells fabricated in this way had parameters which were significantly better, but the V was still below 0.600V.

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A total of more than 300 cells, each 1.6 x 7.0 cm have been fabricated from dendritic web silicon using the selected process sequence. The average efficiency of the cells was 12 to 13% with OCD lifetime from 3 - 10 µsec. These cells had At BSF with the excess At left on the back for contact purposes. This excess At caused significant bowing in the long direction of the cell, and the cells were brittle. If the excess Ai was removed, the cells became flat but remained brittle.

The parameters of force, power, and time required to obtain high strength, low resistance bonds for ultrasonic welding of intercon-· nections have been determined. Good bonds have been achieved using Ai, Cu and Ni straps to Ag, Cu and Ai contact metals. A problem developed with thin(< 130 µm) cells having aluminum back surface fields. These cells often cracked during the bonding process. Due to this yield problem, soldering was substituted for ultrasonic bonding as an interconnection technique •

Four demonstration modules Wzre fabricated using these cells. Each module had an area of 830 cm and contained 72 cells .

A new grid mask has been designed and tested which has a 4% area coverage as compared to the normal mask, with 9% coverage, but equivalent series and shunt resistances. Cells having grid patterns defined by this new mask show an increase in I and efficiency corresponding to this area coverage difference~c

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Approvpl Signature Date

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ENGINEERING AREA

Bechtel National, Inc.

San Francisco, CA

Contract Tit I e : MODULE/ARRAY INTERFACE STUDY


The objectives of this study are to: (1) evaluate the technical and economic feasibility of a curved glass-superstrate module configuration and (2) develop voltage isolation requirements for module encapsulation systems.

Installed costs have been estimated for four array configurations utilizing curved glass-superstrate modules.· A preliminary review of the cost data indicates that the curved glass module configuration can result in support structure and panel framing savings of about $7.00/m2 of module area (1975 dollars) ($9.80/m2 1980 dollars). However, results of a glass industry survey indicate that cost premiums for bending the glass may be in the range of $14.00 to 23.00/m2 (1975 dollars) ($19.60 to 32.23/m2 1980 dollars) for a production rate of 4.6 x 105 m2/ year (5 x 106 ft2/year). Several glass suppliers indicated that higher production rates could result in.lower fabrication costs, however all declined to predict how·much.

In the area of electrical insulation, existing industry design practices and test procedures have been reviewed, and published electrical properties of candidate encapsulating material have been catalogued. Available data mostly relates to insulation in ac fields and reflects work done in the.cable industry. In general the dielectric strength of insulating materials is degraded during service by both electric field effects (e.g., corona) and environmental conditions (e.g., moisture and ultra violet radiation). Encapsulation systems must therefore be designed to provide acceptable dielectric strength throughout the life of the module. Proposed module designs appear acceptable for systems operated below 1000 volts, however, it is likely that both accelerated aging and real time testing will be required to verify the voltage endurance of individual module designs •

Drafting of the final report is essentially completed with the exception of documentation of the finite-element computer analysis of the curved glass module design.

,· /_. ,, Approval Signature Date

69

ENGINEERING AREA

Clemson University

Clemson, SC 29631

Contract Title: INVESTIGATION OF RELIABILITY ATTRIBUTES AND ACCELERATED STRESS FACTORS ON TERRESTRIAL SOLAR CELLS


The objective of this study is to develop test methods for evaluation of solar cells, perform investigations of factors involved in the reliability of terrestrial solar cells and develop specifications for the accelerated stress testing of solar cells. The overall program approach involves determining the reliability characteristics of currently available commercial cells by accelerated stress testing. This seccond year's effort also entials studying methods of second-quadrant characterization, and some preliminary experimental work on second-quadrant effects.

A cell reliability test facility was established and jigs have been designed and constructed for electrical measurement and stress testing of a total of seven cell types to date. The capability for reproducible measurements of Isc, V0 c, Im, Vm, FF, Rs, Rsh has been demonstrated, although that capability is reduced considerably for non-planar cells which have been encountered in the study. Stress test equipment is in place and operational for temperature-voltage (T-V) stress, temperaturehumidity-bias under pressure (T-H-B) stress, pulsed power-temperature stress, temperature-voltage-humidity (S5°C-85RH and 121°c/15 Psig steam), and thermal cycle/thermal shock.

The study has shown that different cell types show differing amounts of maximum output power (Pm) degradation when subjected to various stress conditions. The three cell types, identified by letter, in this year's effort are an EFG cell (F), a textured Czochralski cell (G), and a polycrystalline, ion implanted cell (H). Preliminary results show little Pm degradation for F cells subjected to 7s 0c and 135°c bias-temperature (B-T) stress. G cells show moderate degradation when subjected to these same stress conditions. Both types show moderate degradation at 150°c B-T stress. On the other hand, G cells are showing little degredation when subjected to bias-temperature-humidity whereas F cells appear to be degrading moderately. H cells have only recently begun stress testing and preliminary results are not available. Interestingly enough it appears that temperature-humidity testing may be as severe a stress under some circumstances as bias-temperature-humidity testing. This rather unexpected result is being closely examined.

Second quadrant measurements taken at constant temperature under pulsed conditions indicate large differences both between cell types and within cell types with values ranging from 30 volts to 120 volts. When measurements are made !n free air without the benefit of a heat sink and under equilibrium conditions, breakdown occurs in the vicinity of 15 volts in all cases.

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ENGINEERING AREA

DSET LABORATORIES, INC •

PHOENIX, ARIZONA

SUNLIGHT AGING TESTS OF SOLAR CELL MODULES

BQ-713131

The accelerated aging of mini-modules was continued using DSET's Super-Maq® Fresnel-concentrating accelerated weathering machine. Through October 30, 1979, the two Block II modules have been subjected to 1,821,770 langleys of radiation, and the six Block III modules have been subjected to 403,910 langleys of radiation. The Block II modules have been exposed to an equivalent of 10 years of outdoor weathering in an "average" southwestern environment.

Weekly visual inspections, monthly 35nun slide photos, and monthly I-V measurements were used in monitoring the physical and electrical characteristics of the modules.

A new 5000 cfm blower assembly was installed on the Super-Maq® in order to maintain the modules at or near NOCT during exposure. Initial data indicated that a significant drop in module temperature was achieved with the new blower assembly. We now have the option of adding evaporative cooling or refrigeration to the SuperMaq@, should additional cooling capacity be required next June (1980).

The JPL algorithms that were progranuned into DSET's Data General Nova 3D computer facility have been quality controlled and are now operable. I-V curves and supporting data will be normalized to standard conditions of 28°C and 100 mw/cm2 commencing with the November measurements.

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November 1, 1979

Date

ENGINEERING AREA


PHOENIX, ARIZONA

Contract Tit I e : PHOTOVOLTAIC MODULE ELECTRICAL TERMINATION REQUIREMENTS STUDY


The objective of the Photovoltaic Module Electrical Termination Requirements Study was to develop information which would facilitate the selection of electrical termination hardware for terrestrial solar cell modules and arrays_. The study is drawing upon the large variety of existing outdoor electrical termination hardware.

Accomplishments include: 1. Termination hardware requirements, including environmental,

system interface and design requirements. 2. A catalog of existing termination hardware and their attributes. 3. A summary of the attribute cost dependencies, cost driver

sensitivities, and life cycle costs. 4. Candidate electrical termination hardware for solar cell modules

and arrays. 5. Areas for cost and design improvement.

The final report is anticipated to be available in November, 1979.

Significant conclusions as a result of this study include: 1. Life-cycle costing was determined to be unnecessary since

existing termination MTBF's were found to exceed the 20 year expected system life.

2. Code interpretation by individual inspectors is likely to vary due to the lack of guidelines.

3. Candidate termination hardware include the plug/receptacletype, crimp-type, and terminal block-type.

-:i.~.rn~°'"~. F~. Mosna Jr. 11/1/79

Date Approval Signature

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OPERATIONS AREA

JPL

Pasadena, Cal.

As of the end of October, 207 kW (96%) of the Block III module deliveries have been completed. Photowatt is using 100 nnn wafers for their remaining production due to shortages of the 50 mm wafers previously used.

Preliminary design reviews have been conducted for all Block IV design and qualification contracts.

Test reports for the "flat panel experiments" (PRDA-38) module environmental tests have been completed and forwarded to Sandia for distribution. The test report for Block III module qualification testing has been published (5101-134).

Block III exploratory environmental testing is 80% complet~; only salt fog exposure remains to be done. This test series is similar to that performed on Block II modules (see 5101-98), but several of the test environments are somewhat more rigorous. The humidity-freezing test has induced considerable physical degradation and some module failures. This test includes two +90 to -40°C temperature cycles, two humidity cycles, and a three hour -40°C freeze. The results of the exploratory tests will be compared with field experience for possible incorporation in future qualification test specifications •

The on-site module evaluations at the various field test sites have been completed. Further details will be given in the annual field test report.

TIME IN SITE BLOCK FIELD QUANTITY FAILURES

LOCAL (JPL) I 3 yrs 247 37

LOCAL (JPL) II 2-1/2 yrs 149 5

LOCAL (JPL) III 1 yr 45 0

REMOTE (LeRC) II 1-2 yrs 188 2

629 44

11/02/79 Date

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In-House Program

OPERATIONS AREA

JPL

Pasadena, Cal.

The main problem/failure analysis for the period centered on a number of cell failures at the Mount Laguna installation associated with back biasing and overheating. A report on this investigation will be presented at this Integration Meeting.

11/02/79 Dote

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Contract Title: Third Generation Design Solar Cell Module


The objective of this program is to design, fabricate, acceptance test, and evaluate ten (10) pre-production modules complying with the requirements of JPL Document No. 5101-16, Revision A, entitled, "Block IV Solar Cell Module Design and Test Specification for Intermediate Load Center Applications", dated 1 November 1978. The total power output of the ten (10) modules shall be in excess of 900 watts at AMl.5, NOCT, and VNO• In addition, ASEC is to prepare a standardized price estimate using SAMICS for 10, 100 and 1000 kilowatts of solar modules.

To satisfy the requirement of VNo of 15 VDC or a fraction or multiple of 15 VDC at NOCT, the module had to be redesigned. The dimensions of the redesigned module are 27.38" x 47.24". Each module will have 136 3.05" diameter solar cells, connected thirty-four (34) in series and four in parallel. To enhance the reliability of the module, four cells in every sixth row from each end of the series strings will be connected in parallel on the P-side. The reasons for the increase in cell size from 3" to 3.05" diameter is to improve the packing factor which is 76.8%. The concept of the mechanical assembly remains unchanged.

The first module was built to determine the electrical output of the module and to verify dimensions of all components. The efficiency of the 136 solar cells varies from 15.4% to 16% at AMl.5 and 28°C. The module measured at JPL pulsed xenon solar simulator was found to be 80 watts at 48°C. The module measured in sunlight at ASEC was 92 watts at 48°C. The discrepancy in measurements is being investigated. Mechanically, all components fit well.

Approval Signature

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Contract Title:

Contract No.:

LARGE-SCALE PRODUCTION

ARCO Solar, Inc.

Chatsworth, California

Design, Fabrication, Test, Qualification and Price Analysis of "Third Generation" Design Solar Modules

955402

The objectives of this program are to design, fabricate, test and perform price analysis of intermediate load preproduction solar cell modules and residential load preproduction solar cell modules.

Both modules will use ARCO Solar's standard 100mm diameter wafer. The intermediate load module will be designed to be compatible for fabrication with the production equipment currently being developed under another JPL program. This will assure that the proposed work will have the direct effect of reducing the price of intermediate load modules before the end of 1979.

For the intermediate load center module, ARCO Solar will use 35 solar cells in series which will produce about 34 watts of power at a NOTC of 48°c. The cells will be encapsulated in a tempered glass, PVC and Tedlar combination.

The residential module measures 2 feet by 4 feet, has 55 cells wired in parallel mounted on a steel substrate. The substrate is part of a standard batten and seam roof which is commonly used in certain style buildings. The cells are encapsulated in a Korad polymer which provides environmental protection. AMP, Inc. has designed a connector especially for this application which is weatherproof and simply snaps leads together.

ARCO Solar will fabricate about 1000 watts of both the intermediate and residential load modules. These panels will be delivered for test evaluation over the next several months.

16 -ZZ-1'} Date /

76


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Contract Title:

Contract No. :


General Electric Company-Space Division Phil adel phi a, PA

Design, Fabrication, Test, Qualification and Price Analysis of "Third-Generation" Design Solar Cell Modules

955401

The objective of this program is the development and price analysis of a shingle-type module which meets the requirements for a residential application as defined in JPL Document 5101-83. The design of this module has been completed and was presented to JPL at a Preliminary Design Review which was held on August 24, 1979. This module uses nineteen series-connected 100 mm diameter cells in a hexagon-shaped shingle module configuration which has 0.1955 m2 of exposed glass area when installed. The calculated module output under Standard Operating Conditions, which results in an NOCT of 640C, is 17.14 watts.

The fabrication and qualification testing activities are currently underway. This includes the assembly of two simulated roof test articles, one of which will be subjected to a series of qualification environmental exposures including thermal cycling, humidity cycling and wind loading.

A SAMICS/SAMIS pricing analysis will be performed for quantities of 10,100 and 1000 kW of solar cell modules.

" ~ sk1~J )'. Approval Signature}

77



PHOENIX, ARIZONA

Contract Title: DESIGN' FABRICATION, TEST, QUALIFICATION AND PRICE ANALYSIS OF "THIRD GENERATION" DESIGN SOLAR CELL MODULES.


Summary of Progress for Period of August, 1979 through October, 1979.

The objective of this contract is to design and test an advanced solar module that meets or exceeds JPL 5101-16 requirements. Motorola's objective is also to design in a significant degree of tolerance to normal production related defects such as cells containing terminated cracks. Efforts during this quarter have centered about finalizing the engineering, manufacturing and quality document packages, and production of twenty-eight modules. Initial production modules have been fabricated and are under test.

78


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LARGE - SCALE PRODUCTION


Contract Title: DESIGN, FABRICATION, TEST, QUALIFICATION AND

PRICE ANALYSIS OF THIRD GENERATION SOLAR MODULE


The object of this program is the design, fabrication, test, qualification, and cost analysis of "Third Generation" design solar cell modules for intermediateload application.

At this time, minor design changes and corrections of the Engineering and Manufacturing Documentation and Inspection System plan have been completed and approved by JPL. The initial batch of solar cells was processed, and a preliminary test of the lamination procedure was initiated.

The preproduction module fabrication and qualification tests will start during November, 1979.

App~ Signature

79

Nov l, J 929 Date


SES, Incorporated

Newark, DE

Contract Tit le : Exchange of Information

Contract No.: LK-694034

SES, Incorporated is preparing for production of photovoltaic modules based on the use of cadmium sulfide/copper sulfide as the active materials.

Performance Characteristics of Marketed Product

Module: 8-1/8" x 8-1/8" with 24 rectangular cadmium sulfide cells in series.

Rated at 170 ma at 14.0* volts (battery charging) 160 ma at 16.0* volts (peak power)

(Measured at AMl, 100 mw/cm2, 250C)

*Operating characteristic voltage for 2 modules in series with isolation diode and series connection losses.

Module features a true hermetic seal, the edges of the tempered glass superstrate are metalized, allowing a solder seal to be made to the metal pan enclosing the cells.

Panels: Panels consist of 2, 4, or 8 modules wired in series/ parallel for 6 or 12 volt operation.

A shunt type, thermal compensated voltage regulator with an isolation diode is built into each panel.

Panel frames are constructed from extruded aluminum.

Module efficiency is 3% at maximum power point including series diode and series connection losses.

Fill factors are approximately 67%.

Individual cell size is 6.6 cm, yielding a current density of 10.1 ma/cm2.

10/30/79


80


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Solarex Corporation

Rockville, Maryland

Contract Ti tie : Design, Fabrication, Test, Qualification and Price Analysis of "Third Generation" Design Solar Cell Modules


Solarex is building 36 modules, 18 for intermediate load center applications and 18 for residential applications. Features include:

Semicrystalline silicon as the basic cell material.

72 9.5 CM x 9.5 CM cells arranged in a high density pattern.

Cells which are made by a low cost manufacturing process which is amenable to high volume rates.

Cell-interconnect design which allows all solder interconnections to be made from the back.

Outside envelope dimensions of 63.5 CM x 120 CM.

3/16 11 tempered Sunadex Superstrate, Ethylene Vinyl Acetate (EVA) Pottant, White Tedlar moisture barrier.

Modules fabricated by a vacuum-pressure, heat application lamination procedure.

The Preliminary Design Review has been completed at JPL. Production and environmental test will begin in December.

Jack R. Anderson Approval Signature

81

November 6, 1979 Date


Solar Power Corporation

Woburn, Massachusetts

Contract Title: Design, Fabrication, Test, Qualification and Price Analysis of "Third Generation" Design Solar Modules


The objectives of this program are to design, fabricate, test, qualify, and perform a price analysis on modules intended for use in the 20-500 kW range.

Task I - Design and Analysis

Final module design is complete. Several modifications were made as a result of the Preliminary Design Review held on August 20, 1979.

Task II - Fabrication

All fixturing and equipment for fabrication is complete. All component parts have been procured and/or fabricated for prototype manufacture.

Task III - Data

SAMIS analysis is in process.

David A. Dilts, Project Manager

Approval Signature

82

November 6, 1979

Date


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LARGE~CALEPRODUCTION

Spire Corporation

Bedford, MA

Contract Title: Design, Fabrication, Test, Qualification and Price Analysis of Third Generation Design Solar Cell Modules

Contract No: 955405

This contract, started on 25 May 1979, is aimed at the design of a high efficiency panel capable of delivering 50 watts at standard operating conditions. Cell efficiency goal is 15 percent. Twenty modules, designed for Intermediate Load Center Applications, will be delivered to JPL. The module will contain 152 ion implanted rectangular cells in a closely packed configuration. The cells will be encapsulated with EVA between Sunadex glass and a laminated backing of Mylar and aluminum foil. A two piece stainless steel frame will contain the encapsulated structure.

As of August 1979, the module design had been completed and the Preliminary Design review had been held at JPL. Minor design changes, resulting from the design review, have been completed.

Development of the encapsulation equipment and processes has been completed. At this time the fabrication procedures are being proven. Concurrently prototype modules are being fabricated. Production of deliverable modules will begin in November.

83

14th PROJECT INTEGRATION MEETING

SUMMARIES RECEIVED TOO LATE TO BE INCLUDED IN THE PUBLICATION OF THE HANDOUT.

TASK 1 - SILICON MATERIAL TASK

AeroChem Research Laboratories

Princeton, NJ

Contract Title: Development of Processes for the Production of Solar Grade

Silicon from Halides and Alkali Metals

Contract No.: 955 491

The objective of this program is to develop processes involving hightemperature reactions of silicon halides and alkali metals for the production of solar grade silicon. The near term objectives of the program are to examine, on a laboratory scale, the overall rate of reaction of silicon tetrachloride and sodium vapor, and to determine the nature of the products formed.

This program commenced on 30 October 1979. The first few weeks of the program have been used to acquire and assemble components for a reactor system for conducting the experiments. Initial tests in which the completeness of reaction as a function of reactor volume, reactant flow rates and pressure will start shortly. Also, pro-visions for using a jet impaction technique for collecting Si(t) droplets formed by the reaction will be included in these experiments so that the important property of Si(t) droplet size (which strongly affects Si/NaCl separation efficiency) as a function of operating parameters may be determined.

Approval Signature

12 November 1979

Date

Contract Title:

Contract No. :


BATTELLE'S COLUMBUS LABORATORIES

Columbus, Ohio 43201

EVALUATION OF SELECTED CHEMICAL PROCESSES FOR PRODUCTION OF LOW-COST SILICON

954339

Battelle's Columbus Laboratories (.BCL) is studying the zinc vapor reduction of silicon tetrachloride in a fluidized bed of seed particles as a promising route to the preparation of low-cost high-purity silicon granules.

Since the 13th PIM in August, the effort at BCL has been concentrated on the construction of a Process Development Unit (PDU) consisting of four critical components of the design adopted for a 50 MT Si/year Experimental Process System Development Unit (EPSDU). The PDU is to be operated in a batch mode (8-hour) to check out the design and operation of the fluidized bed reactor, the ZnCl2/Zn by-product condenser, the zinc vaporizer, and the electrolytic cell used for electrolysis of the ZnC12•

Owing to suppliers' errors in the fabrication of components, requiring correction, and to an overall slippage in promised delivery dates, construction of the PDU has been set back approximately 1.5 months. It is now estimated that the system will have been assembled and checked out "dry," and will be ready for the introduction of reactant materials about the middle of November.

It is now planned to operate the PDU with SiCl4 and silicon seed of high purity so that the course of impurities in the system can be traced and the purity capability maximized.

Independent check-out of the zinc vaporizer operation has led to design changes in the liquid-zinc feed system to improve operability.

s/M. Browning/J. Blocher

Approval Signature November 12, 1979

Date

Contract Title:

Contract No.:

SILICON MATERIAL

Solarex Corporation 1335 Piccard Drive

Rockville, MD 20850

Analysis of the Effects of Impurities in Silicon

955307

The purpose of this program is to conduct a solar cell fabrication and analysis program to determine the effects on the resultant solar cell efficiency of impurities intentionally incorporated into silicon. The program will employ "flight-quality" technologies and quality assurance to assure that variations in cell performance are due to the impurities incorporated in the silicon.

At the end of this quarter, twenty (20) experimental lots have bee~ processed and tested. The cells from control silicon including verification, monitor and control cells have exhibited average AMO cell efficiencies of nearly 13% at 25°c (in excess of 15% AMl at 25°c). No cross contamination of control or monitor cells has been observed.

Cells with various doping materials and doping levels have been fabricated. The test cells appear to be clustered in two distinct resistivity ranges, namely around 0.2 0-cm and between 3.0 and 4.0 n-cm. The lower resistivity cells in general exhibit higher voltages and lower currents than the control cells (1.0 to 3.0 0-cm). The higher resistivity cells exhibit lower voltages. The current is much more susceptible to change by impurity incorporation than the voltage although several lots have shown severe degradation of both current and voltage.

The various test lots will be identified by type and level of impurity doping and the cell performance presented as well as a discussion of the mechanisms responsible for the degradation of cell performance.

John H. Wohlgemu Program Manager

Contract Title:

Contract No. :

Silicon Materials

Westinghouse Power Circuit Breaker Division Trafford, PA

Development Of A Process For High Capacity Arc Heater Production Of Silicon For Solar Arrays

954589

The objective of this program is to develop a high capacity, low-cost process for production of solar grade silicon, based on the hightemperature sodium reduction of silicon tetrachloride.

The Na, SiCl4, Reactor, Cooling Water, Gas, Effluent, Electrical, Control & Instrumentation and Data Logging subsystems have been checked and are ready to operate as an experimental verification unit. A number of tests have been conducted with the arc heater/ reactor system operating on hydrogen and argon gas. When these tests are completed, the reactor will be operated on Na & SiCl4 at an equivalent flow of 100 lbm/hr of silicon.

In addition, safety and operation procedure manuals have been prepared and a safety training program for operational personnel has been conducted.

10/31/79 Date

Contract Tit I e :

Contract No. :

PRODUCTION PROCESSES AND EQUIPMENT

RCA Corporation-Solid State Division-Somerville, N.J. 08876

RCA Laboratories-Princeton, New Jersey 08540

Development of Megasonic Cleaning for Silicon Wafers

955342

The purpose of the program is to scale up, automate, and improve the existing RCA-invented Megasonic Cleaning System to increase its throughput from about 600 wafers/hour to about 2500 wafers/hour in preparation for the large-scale production of flat-plate silicon solar-cell arrays. The program was begun on March 15, 1979.

During this period the Megasonic Cleaning System was integrated and debugged. The system consists of the Megasonic Cleaning sink, a rinse station, an air dryer, and an inspection station equipped with a lasser scanner for the detection of light-scattering centers on a wafer. The recirculation-filtration system is operating satisfactorily. The preliminary data on wafer cleaning and rinsing indicate that the design criteria of cleaning ability, ease of operation, and safety have been largely met. Chemicals usage appears to be even better than forecast.

While the present rate of cleaning by use of 3/16-in.-spaced carriers .. · does not meet the design objective, it can be increased by better platen design, closer spacing of wafers in the carriers, and faster belt speeds. It remains to be determined whether extra power or another pair of transducers is required to increase the rate to 2500/hour.

The drying rate with the present equipment is likely to be on the order of 1500 wafers/hour. If that is so, the recommendation will be to increase the active dryer length proportionally to the rate requirement.

Wafers that had been contaminated with 0.3 microns diameter alumina from aqueous as well as from 1-1-1 trichlorethane-wax suspensions were successfully cleaned as judged by the wafer scanner counts.

It is recommended to continue the program as planned but to delay the move to Mountaintop until after delivery of the belt drive and sufficient time to ensure that it functions properly.



Solarex Corporation

Rockville, Maryland

Contract Title: Phase 2 of the Array Automated Assembly Task for the Low Cost Silicon Solar Array Project

Contract No: 954854

This program is a study of electroless nickel metallization of solar cells. The work includes five experimental tasks, the first four of which are studies of some physical processes which are important in understanding and in assessing the utility of electroless nickel plating of contacts to solar cells, while the fifth is a direct comparison of one process in which nickel is plated directly on the solar cell with another process in which the electroless nicke1 plating is preceded by several steps of palladium plating and sintering.

One task comprises a group of four environmental stress tests on solar cells havi~g electroless nickel metallization. Two of these tests, a 1,000 hour test at 150°C, and a 1,000 hour bias - temperature - humidity test, are underway, while oells have been fabricated for thermal cycle and thermal shock.tests as well as for a control group. Electrical measurements and peel strength tests will be used to assess any effects of the environmental stresses on cell contact integrity.

A second task comprises a determination of nickel penetration into silicon as a result of heating or sintering procedures which might be used in solar cell manufacture. Specimens have been plated, sintered, mounted and angle lapped for microprobe analysis.

A third task which has been started involves electrol~ss nickel plating on silicon which has an oxide film up to 200 .A thick. The oxide film is thought to pose a problem with respect to reproducibility of electroless nickel plate contacts. The fourth task, which has not yet been initiated, is a determination of the effect of plating time on the properties of the P/N junction in solar cells.

The program is in its early stages and no data is yet available.

11-7-79 Date

Contract Title:

Contract No. :

ENGINEERING Development of Photovoltaic

and Module Safety Requirements

Underwriters Laboratories Inc.

Melville, N. Y.

Investigation of Photovoltaic Array and Module

Safety Requirements

955392

Work is underway concerning methods of affording protection against shock hazards associated with direct personal contact with live parts. One method being considered, the use of ground fault detection devices, requires low (relative to detection level sensitivity) standing leakage currents. Whether or not such low leakage currents can be achieved in potentially moist environments of array installation is in question.

Other sources of potential shock hazards, particularly breakdown of insulation due to excessive stressing, are being considered. System grounding, or "virtual grounding" to effect voltage stabilization is being studied.

Work also underway involves consideration of the hazards of tissue burns as might be created by personal contact with hot backfed cells, and hazards of material flaming, as might also evolve from the high temperature cells. The feasibility of guards or spacings is being considered and questioned.


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LSA PROJECT ACTIVE CONTRACTS

-----·-------------------------------Contractor

AeroChem, Res Labs Princeton, NJ

Aerospace Corp Los Angeles, CA

Battelle Labs Columbus, OH

Dow Corning Corp Hemlock, MI

Energy Materials Harvard, MA

Hemlock Semiconductor Corp Hemlock, MI

Lamar University Beaumont, TX

Lawrence Livermore Labs Livermore, CA

MIT Cambridge, MA

Sah, C.T. Associates Urbana, IL

Solarex Corp Rockville, MD

SRI International Menlo Park, CA

Union Carbide Corp Sisterville, WV

Westinghouse Electric Corp Trafford, PA

Westinghouse Research Pittsburgh, PA


Contract Number Description

Silicon Material

954777

955201

954339

954559

qs5269

955533

954343

8626

955382

954685

955307

954471

954334

954589

954331

954589

85

Si halide-alkali metal flames process

Comp measurements - analytical photon

Semiconductor grade Si processes

Solar cell grade Si process, arc furnace

Gaseous melt replenishment

Solar cell grade Si process -arc furnace

Technology and economic analysis

Neutron activation

Hydrogenation of SiCl4

Effects of impurities

Effects of impurities

Solar cell grade Si process

Semiconductor grade Si process - silane/silicon

High capacity arc heater process

Solar cell grade Si definition

High capacity arc heater production

Contractor Contract

Number Description

Large-Area Sheet

ARCO Solar, Inc Chatsworth, CA

Cornell University Ithaca, NY

955325

954852

Crystal Systems, Inc 954373 Salem, MA

Energy Materials Corp 955378 Harvard, MA

Charles Evans & Assoc LK694028 San Mateo, CA

Honeywell Corp 954356 Bloomington, NM

Kayex Corp 954888 Rochester, NY

Kayex Corp 955270 Rochester, NY

Materials Research 954977 Salt Lake City, UT

Mobil-Tyco Solar Energy 954355 Waltham, MA

Optical Coating Lab 955089 City of Industry, CA

Silicon Technology Corp 955131 Oakland, NJ

Siltec Corp 954886 Menlo Park, CA

Siltec Corp 955282 Menlo Park, CA

Spectrolab, Inc 955055 Sylmar, CA

UCLA 954902 Los Angeles, CA

86

Vacuum die casting

Characterization - Si properties

Cast ingot and slicing

Low-angle Si sheet

Tech for impurity and surface analysis

Silicon on ceramic (SOC)

Advanced Cz coating

Cz growth

Analysis of defects in silicon

Ribbon growth - EFG

Si cell process development

Ingot slicing

Advanced Cz

Ingot slicing

Si solar cell fabrication, development and analysis

Si cell fabrication tech


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Contractor Contract

Number Description

Large-Area Sheet (Continued)

Univ of Missouri Columbia, MO


Case Western University Cleveland, OH

Dow Corning Midland, MI

Illinois Tool Works, Inc Elgin, IL

MBAssociates San Ramon, CA

Motorola, Inc Phoenix, AZ

Motorola Phoenix, AZ

Rockwell Science Center Thousand Oaks, CA

Spectrolab, Inc Sylmar, CA

Spire Corp Bedford, MA

Springborn Labs, Inc Enfield, CT

Univ of Massachusetts Amherst, MA

955415

954654

Partial pressures of reactant gases

Dendritic web process

Encapsulation

954738

954995

955506

955281

955339

955387

954739

955567 -

954521

954527

955531

87

System studies of basic aging and diffusion

Encapsulation systems

Application of ion plating to environmentally resistant solar cells

Glass reinforced concrete

A/R coating

A/R coating

Materials interface problem study

Design, analysis, and test verification of advanced encapsulation systems

Electrostatic bonding process

Test methods and materials properties evaluation

Development of synthesis procedures for polymeric uv stabilizers and absorbers

Contractor Con.tract

Number Description

Production Process and Equipment

ARCO Solar, Inc Chatsworth, CA

Bernd Ross Associates San Diego, CA

Kulick & Soffa Inc Morsham, PA

MBAssociates San Ramon, CA




Optical Coating Lab City of Industry, CA




RCA Princeton, NJ

RCA Princeton, NJ

Sensor Technology Chatsworth, CA


Sol/Los, Inc Los Angeles, CA

955278

955164

955287

954882

954847

955324

955328

955118

955217

955244

955423

954868

955342

954865

955265

955318

88

Automated solar panel assembly

Thick film solar cell contact

Automated solar module assembly

PH II, process development


Etch-resistant wax patterns

Thin substrate

Ion implanter invest

High-efficiency solar module

Low-cost contacts

Laboratory services


Megasonic cleaning

PH II, production process

Polysilicon solar cell

Metallization


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~~-C_o_n_t_r_a_c_t_o_r~--~~----~~N_u_m_b_e_r~~--~~~~~ Description

Production Process and Equipment (Continued)







TBA Los Angeles, CA

Univ of Pennsylvania Philadelphia, PA


Bechtel National Columbus, OH

Boeing Co Seattle, WA

Burt Hill Assoc Butler, PA

Clemson University Clemson, SC

DSET Laboratories, Inc Phoenix, AZ


Underwriters Lab Melville, NY

954822

954854

955077

954853

955298

954786

955519

954796

954873

High-density panels


Wafer thickness evaluation


High resolution contract development

Ion implanter

Development of technical manuals and mathematical models

Automated array


Engineering

954698

954833

955149

954929

681934

955367

955392

89

Curved glass module and module electrical isolation study

Wind loading study on module/ array structures

Residential pv module requirements study

Solar cell reliability test

Accelerated sunlight testing of modules

Study of termination design requirements

Solar array and module safety requirements

Contractor

ARCO Solar Chatsworth, CA

General Electric Philadelphia, PA


Optical Coating Labs City of Industry, CA




Solar Power Corp Woburn, MA




Contract Number Description

Large Scale Production

955402 Block IV

955401 Block IV

955406 Block IV

955409 Block IV

BF672593 40 kW - Block III

BF681926 5 kW - Block III

955410 Block IV

955403 Block IV

955404 Block IV

BF681928 5 kW

955405 Block IV

90


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LSA PROJECT PUBLISHED DOCUMENTS*

Document No.

5040-29

Author

DOANE, J. W. June, 1976

5101-7 PROJECT OFFICE ERDA/JPL-1012-76/6 October, 8, 1976

5101-10 PROJECT OFFICE ERDA/JPL-1012-77/1

5101-12 ZOUTENDYK, J. October 28, 1976

5101-13 GONZALEZ, C. C. February 14, 1977

5101-14 EDELSON, E. January 26, 1977

The Cost of Energy From Utility-owned Solar Electric Systems

LSA First Quarterly Report - April to June 1976

LSA Second Quarterly Report - July to September 1976

Progress in Silicon for Terrestrial Photovoltaic Crystal Technology'Solar Energy Conversion

Availability of Ultraviolet Radiation Data (for Encapsulation System Design)

Preliminary Analysis of Industrial Growth and the Factors that Affect Growth Rate

5101-15 CHAMBERLAIN, R. G. SAMICS (Solar Array Manufacturing Industry Costing September 1977 Standards) Workbook

5101-16 LSA ENGR. AREA Rev. A November 1, 1978 DOE/JPL-1012-78/10

5101-19

5101-20

5101-21 Rev .. B

5101-24 ERDA/ JPL-10.12-77 / 2

5101-31

5101-32 OOE/JPL-1012-77/3

MOORE, D. February 28, 1977

CANTU, A. H. February 28, 1977

BISHOP/ANHALT November 3, 1978

PROJECT OFFICE

STULTZ/WEN July 29, 1977

PROJECT OFFICE

Block IV Solar Cell Module Design and Test Specification for Intermediate Load Center Applications

Cyclic Pressure-Load Developmental Testing of Solar Panels

Test Program on Low-Cost Connector For Solar Array Modules

Acceptance/Rejection Criteria for JPL/LSA Modules

Project Quarterly Report-3 for the Period October 1976 to December 1976

Thermal Performance Testing and Analysis of Photovoltaic Modules in Natural Sunlight

Quarterly Report-4 for the Period January 1977 to March 1977

5101-33 CHAMBERLAIN/ASTER Interim Price Estimation Guidelines: A Precursor and September 10, 1977 an Adjunct to SAMIS III, Version One

5101-36 SHOKLER, M. User Handbook for Block II Silicon Solar Cell Modules October 15, 1977

5101-39 JAFFE, f. LSA Field Test Activity System Description

5101-40

5101-43

August 3, 1977

COULBERT, C. D. June 8, 1977

GRIPPI, R. A. October 7, 1977

Development & Validation of A Life-Prediction Methodology for LSA Encapsulated Modules

Module Efficiency Definitions, Characteristics and Ex~mples

* Documents with DOE/JPL numbers are available from: Technical Information Center P.O. Box 62 Oak Ridge, TN 37830 Phone: (615) 576-1304

91

Document No.

5101-44 Rev. A DOE/JPL-1012-22

5101-45

Author

CHAMBERLAIN/ASTER March 1, 1979

GONZALEZ, C. C. December 6, 1977

5101-46 PROJECT OFFICE DOE/JPL-1012-77/4 June 1977

5101-51 PRATURI/LUTWACK/ Hsu July 17, 1977

5101-53 O'DONNELL/LEIPOLD/ DOE/JPL-1012-77/6 HAGAN

March l, 1978

5101-54 Vol. I SMITH, J. L. DOE/JPL-1012-78/1 April 1978

5101-54 Vol. II SMITH, J. L. DOE/JPL-1012-78/1 April 1978

5101-55 PROJECT OFFICE DOE/JPL-1012-78/2

5101-56 TURNER, G. B. DOE/JPL-1012-78/3 March l, 1978

5101-57 CHEN, C. P. DOE/JPL-1012-78/7 February 22, 1978

5101-58 ESTEY, R. S. March 15, 1978

5101-59 CHAMBERLAIN, R. G. February 1, 1978

5101-60 METCLF, M. S. March 24, 1978

5101-61 CUDDIHY, E. April 13, 1978

5101-62 MOORE/WILSON DOE/JPL-1012-78/6

5101-65 LSA ENGR. AREA DOE/JPL-1012/78/7A March 24, 1978

5101-68

5101-69

ASTER, R. W. May 12, 1978

DAUD/KOLIWAD June 15, 1978

Title

SAMICS Input Data Preparation

Environmental Hail Model for Assessing Risk to Solar Collectors

Project Quarterly Report-5 for the Period April 1977 to June 1977

Chemical Vapor Deposition of Silicon from Silane Pyrolysis

Compatability Studies of Various Refractory Materials in Contact with Molten Silicon

Historical Evidence of Importance to the Industrialization of Flat-Plate Silicon Photovoltaic Systems: Executive Summary

Historical Evidence of Importance to the Industrialization of Flat-Plate Silicon Photovoltaic Systems

Project Quarterly Report-6 for the Period July 1977 to September 1977

Structure of Deformed Silicon and Implications for Low-Cost Solar Cells

Multi-Wire Slurry Wafering Demonstrations

Measurement of Solar and Simulator Ultraviolet Spectral Irradiance

SAMICS Usage No. 1

SAMIS Computer Program User's Guide - Release l

Encapsulation Material Trends Reliability 1986 Cost Goals

Photovoltaic Solar Panel Resist - Simulated Hail

Photovoltaic Module Design, Qualification and Testing Specification

Price Allocation Guidelines

Effect of Grain Boundary in Silicon Sheet on Minority Carrier Diffusion Length and Solar Cell Efficiency

5101-70 CHAMBERLAIN/FIRNETT SAMIS III Design Document (Solar Array March 24, 1978 Manufacturing Industry Simulation)

Release 1

92

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Document No.

5101-71

5101-72

5101-73 DOE/JPL-1012-78/8

5101-75

5101-76 DOE/JPL-1012-78/9

5101-77

5101-79

Author

CHAMBERLAIN, R. G. March 24, 1978

MAXWELL, H. June 15, 1978

VON ROOS, O. May 31, 1978

SMITH, J. L. May 30, 1978

STULTZ, J. W. July 31, 1918

GUPTA, A. August 10, 1978

GUPTA, A. August 18, 1978

5101-81 PROJECT OFFICE DOE/JPL-1012-78/13 November 15, 1978

5101-82 DOE/JPL-1012-79/6

5101-83 DOE/JPL-1012-78/14

5101-84 DOE/JPL-1012-78/11

5101-85 DOE/JPL-1012-78/12

5101-88 JPL Publ. 79-14

5101-93 DOE/JPL-1012-79/5

5101-94 DOE/JPL-1012-78/17

5101-98 DOE/JPL-1012-79/1

5101-99

5101-100

SMOKLER, M. I. November 15, 1979

LSA ENGR. AREA November 1, 1978

HOFFMAN/MILLER October 15, 1978

JAFFE, P. September 15, 1978

PROJECT OFFICE

CHAMERLAIN, R. G. January 15, 1979

ASTER, R • December 1, 1978

GRIFFITH, J. S. January 1, 1979

PROJECT OFFICE

PROJECT OFFICE

Title

SAMIS III Computer Program Source Code

Encapsulant Candidate Materials for 1982 Cost Goals

Determination of Bulk Diffusion Lengths for Angle-Lapped Semiconductor Material via the Scanning Electron Microscope - A Theoretical Analysis

The Penetration of the International Market by Domestically Produced Photovoltaic Power Systems: A Survey of Recent Estimates

Thermal and Other Tests of Photovoltaic Modules Performed in Natural Sunlight

Photodegradation of Polymeric Encapsulants of Solar Cell Modules

Effect of Photodegradation on Chemical Structure and Surface Characteristics of Silicon Pottants Used in Solar Cell Modules

Project QQarterly Report-7 for the Period October 1977 to December 1977

User Handbook for Block Ill Silicon Solar Cell Modules

Block IV Solar Cell Module Design and Test Specification for Residential Applications

Bias-Humidity Testing of Solar Modules

LSA Field Test Annual Report August 1977 to August 1978

Project Quarterly Report-8 for the Period of January - March 1978

A Normative Price for a Manufactured Product: The SAMICS Methodology Volume I: Executive Summary/Volume II: Analysis

Economic Analysis of a Candidate 50¢/Wpk Flat-Plate Photovoltaic Manufactur-ing Technology

Environmental Testing of Block II Solar Cell Modules

Project Quarterly Report-9 for the Period April - June 1978

Project Quarterly Report-10 for the Period July - September 1978

93

Doc\Dilent No.

5101-102

5101-103 DOE/JPL-1012-79/8A

5101-104 DOE/JPL-1012-79/1

5101-105 DOE/ JPL-lQ.12-20

5101-106 DOE/JPL-1012-21

5101-107 DOE/ JPL-1012-18

5101-108 DOE/JPL-1012-19

5101-112 DOE/JPL 1012-27

5101-134 JPL Publ. 79-96

5101-135 JPL Publ. 79-92

Author

SLONSKI, M. L. February 15, 1979

REPAR, J. · January 1, 1979

GRIFFITH, J. S.: January 1, 1979

PRATURI, A. K. April 15, 1979

PRATURI, A. K. April 1, 1979

RHEIN, R. A. April 15, 1979

RHEIN, R. A. April 15, 1979

PROJECT OFFICE

GRIFFITH, J. S. September 1, 1979

LAUE/GUPTA

Title

Energy Systems Economic Analysis (ESEA) Methodology & User's Guide

Experience with Silicones in Photovoltaic Modules

Environmental Testing of Block II Solar Cell Modules

Modeling of Silicon Particle Growth; a Progress Report

On the Modeling of Silane Pyrolysis in a Continuous Flow Reactor

Purification of Silicon by the Silicon Fluoride Transport Process - A Thermochemical Study

Silicon Preparation and Purity from the Reaction of Sodium with Silicon Tetrafluoride and Silicon Tetrachloride - A Thermochemical Study

Progress Report 12 for the Period January to April 1979

Environmental Testing of Block III Solar Cell Modules - Part 1: Qualification Testing of Standard Production Modules

Reactor for Simulation and Acceleration of Solar Ultraviolet Damage

94


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BECKMAN AUDITORIUM

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