POLYMER: FULLERENE SOLAR CELL

by

FAIZZWAN BIN FAZIL

(101180216)

A report submitted in partial fulfillment of the requirements for the

degree of Bachelor of Engineering (PHOTONIC Engineering)

SCHOOL OF MICROELECTRONIC ENGINEERING

UNIVERSITI MALAYSIA PERLIS

May 2013

ii

UNIVERSITI MALAYSIA PERLIS (UniMAP)

SCHOOL OF MICROELECTRONIC ENGINEERING

DECLARATION OF REPORT

Author’s full name : FAIZZWAN BIN FAZIL

Date of birth : 10 July 1988

Title : Polymer: Fullerene Solar Cells

…………………………………………………………………….............................

…………………………………………………………………….............................

Academic Session : 2013/2013

I hereby declare that the report becomes the property of Universiti Malaysia Perlis (UniMAP) and to be placed at the

library of UniMAP. This report is classified as:

CONFIDENTIAL (Contains confidential information under the Official Secret Act 1972)*

RESTRICTED (Contains restricted information as specified by the organization where research was done)*

OPEN ACCESS I agree that my report is to be made immediately available as hard

copy or on-line open access (full text)

I, the author, give permission to the UniMAP to reproduce this report in whole or in part for the purpose of research or

academic exchange only (except during a period of _____ years, if so requested above).

Certified by:

_________________________ _________________________________

SIGNATURE SIGNATURE OF SUPERVISOR

___________________________ _________________________________

(880710-26-5213) MUKHZEER MOHAMAD SHAHIMIN

Date :_________________ Date : _________________

*NOTES: If the report is CONFIDENTIAL or RESTRICTED, please attach with the letter from the organization with period and reasons for confidentially or restriction.

iii

UNIVERSITI MALAYSIA PERLIS (UniMAP)

SCHOOL OF MICROELECTRONIC ENGINEERING

DECLARATION SHEET

I, FAIZZWAN BIN FAZIL, declare that the report entitled POLYMER: FULLERENE

SOLAR CELLS and the work presented in the report are both my own, and have been

generated by me as the result of my own original research. I confirm that:

Signature :

Name : FAIZZWAN BIN FAZIL

Date :

This report titled POLYMER: FULLERENE SOLAR CELLS was prepared and submitted

by FAIZZWAN BIN FAZIL (Matrix Number: 101180216) and has been found satisfactory

in terms of scope, quality and presentation as partial fulfillment of the requirement for the

Bachelor of Engineering (Photonic Engineering) in Universiti Malaysia Perlis (UniMAP).

Checked and Approved by

……………………….

(MUKHZEER MOHAMAD SHAHIMIN)

Supervisor

School of Microelectronic Engineering

Universiti Malaysia Perlis

(Date: ..................................)

iv

Acknowledgement

First of all, I would love to express my appreciation and grateful to Allah S.W.T

for giving me such a good health since the beginning of this project till finish, ability to

learn the knowledge and sufficient time to complete my Final Year Project.

I would also like to express a lot of thanks to my supervisor Dr. Mukhzeer

Mohamad Shahimin and all technicians at Failure Analysis Laboratory especially Mr.

Bahari and Dr. Praba, my colleagues Ms. Bariah, Ms. Suriati and Mr. Ang Keng Chuan,

and all staff and lecturers of School of Microelectronic Engineering (SoME) UniMAP for

their great support and valuable criticism that really gave me a lot of knowledge, skills and

experienced. I really appreciate their brilliant suggestions, guidance and encouragement for

me.

I wish to acknowledge and thank the various people who were involved directly or

indirectly during completing my Final Year Project. To all my friends that were kindly

gave me full co-operation during my Final Year Project.

Last but not least, I am deeply grateful to all my family members for supporting

me from the beginning till now. I also like to thank to all UniMAP’s lecturers especially

from School of Microelectronic Engineering for giving me a great opportunity to complete

my Final Year Project. I had observed and gain great knowledge, experience and skills,

also i gained new experience.

v

UNIVERSITI MALAYSIA PERLIS (UniMAP)

PUSAT PENGAJIAN KEJURUTERAAN MIKROELEKTRONIK

ABSTRAK

TAJUK (SEL SOLAR POLIMER: FULERIN)

oleh Faizzwan Bin Fazil

Kajian tesis ini berkenaan dengan prinsip kerja polimer: fulerin sel solar. Ia

termasuklah setiap fungsi mekanisme, hubungan ketebalan lapisan aktif terhadap

kecekapan pengubahan kuasa, penentuan kadar terbaik penyediaan setiap larutan, proses

fabrikasi yang sesuai, langkah pengujian setiap sel solar, catatan keputusan

pengujian,analisa keputusan, pengenalpastian penyebab perlemahan dan penyiasatan

berkenaan langkah-langkah yang paling bersesuaian untuk memperbaiki pencapaian sel

solar yang dibuat. Langkah- langkah yang digunakan untuk fabrikasi sel solar ini adalah

penyalutan pusingan dan kelajuan pusingan dijadiakan variasi kepada 1000rpm, 2000rpm,

3000rpm dan 4000rpm. Kadar larutan lapisan aktif ditentukan dengan nilai 1mg “poly [2-

methoxy-5-(2 -ethyl-hexyloxy)-1,4-phenylene vinylene]” (MEH PPV), 4mg “[6,6]-Phenyl-

C61-butyric acid methyl ester” (PC60BM) dan 1mL klorofom. Kad kerja yang

mengandungi setiap langkah- langkah dan maklumat mengenai peralatan, bahan dan

parameter perlu disediakan untuk memastikan eksperimen dapat dilaksanakan tanpa

masalah. “Atomic Force Microscopy” digunakan untuk mendapatkan kekasaran

permukaan lapisan aktif yang telah disalutkan pada sel solar dan mendapatkan ketebalan

lapisan aktif setiap sel solar yang dihasilkan daripada penggunaan kelajuan pusingan yang

berbeza, “UV- Vis Spectroscopy” digunakan untuk menganalisa kadar penyerapan bagi

setiap sel solar berdasarkan panjang gelombang dari spektrum “Ultra Violet” hinggalah ke

spektrum “Near Infra Red”, dan “Semiconductor Parametric Analyzer” digunakan untuk

pengujian lengkungan I- V dan mencatatkan nilai arus maksimum (Imax), voltan

maksimum (Vmax), voltan litar terbuka (Voc) dan arus litar terpintas (Isc) bagi tujuan

pengiraan factor pengisian (FF) dan kecekapan pengubahan kuasa (PCE). Keputusan akhir

ujikaji membuktikan aplikasi karbon sebagai terminal berlawanan berjaya

menambahkaikan pungutan elektron-elektron.

vi

UNIVERSITI MALAYSIA PERLIS (UniMAP)

SCHOOL OF MICROELECTRONIC ENGINEERING

ABSTRACT

POLYMER: FULLERINE SOLAR CELLS

by Faizzwan Bin Fazil

This study is about the about the polymer: fullerene (MEH PPV: PC60BM) solar

cells working principle including each mechanism, relation between thickness of the

active layer with the efficiency of power conversion, finest tune optimization, fabrication

process, devices inspection, results obtained, results analysis, error identification, and

investigation of the device enhancement method. The method used in fabricating the

devices is spin coating and the spin speed is varied to 1000rpm, 2000rpm, 3000rpm and

4000rpm. The tuning of the active layer solvent is fixed to 1mg of MEH PPV, 4mg of

PC60BM and 1mL of chloroform. The runcard which is consisted of every steps in

fabricating the devices is constructed in order to guide experimental process. Atomic Force

Microscopy (AFM) is used to inspect the surface roughness and the thickness of each

device, UV- Vis Spectroscopy is used to analyse the absorbance of each device from the

ultra violet (UV) spectrum till the near infra red (NIR) spectrum and the Semiconductor

Parametric Analyzer is used to inspect the I-V curve and record the maximum current

(Imax), maximum voltage (Vmax), open circuit voltage (Voc) and Isc for FF and PCE

evaluation purpose. The final result of experiment conducted proved the application of

carbon as a counter electrode enhances the electrons collection.

vii

Table of Contents

DECLARATION OF REPORT .................................................................... ii

DECLARATION SHEET ............................................................................ iii

Acknowledgement ....................................................................................... iv

ABSTRAK v

ABSTRACT vi

Table of Contents .................................................................................... vii

List of Tables x

List of Figures ............................................................................................ xi

List of Abbreviations ................................................................................. xiii

Chapter 1 Introduction ............................................................................. 1

1.1 Aims and motivation ................................................................................................................. 2

1.2 Objective of the experimental ................................................................................................... 3

1.3 Project Challenges .................................................................................................................... 3

1.4 Introduction of Inorganic Solar Cells ........................................................................................ 4

1.5 Introduction of Organic Solar Cells ..........................................................................................6

1.5.1 Introduction of Single Layer Cells..............................................................................6

1.5.2 Introduction of Bilayer Cells ......................................................................................8

1.5.3 Introduction of Bulk Heterojunction Cells ............................................................... 9

1.6 The Idea of Structuring the device ........................................................................................... 11

Chapter 2 Literature review .................................................................... 13

2.1 Introduction .............................................................................................................................. 13

2.2 Comparison of Nanostructured Material Processing using Different Chemical Techniques .. 14

2.2.1 The mainTechnique Used: Spin Coating ...................................................................17

2.3 Tuning Optimization ............................................................................................................... 20

2.3.1 MEH PPV: PCBM .................................................................................................... 20

viii

Figure ‎2.9 chemical structure of the reviewed MEH PPV: PCBM [38] .................................................21

Table ‎2.2 characteristic of MEH PPV: PCBM, P3HT: PCBM and PCDTBT: PCBM [35] ...................21

Figure ‎2.10 refractive indices of the reviewed P3HT: PCBM [18] ...................................................... 24

Figure ‎2.11 chemical structure of the reviewed P3HT: PCBM [33] .................................................... 24

Table ‎2.4 the parameters of P3HT: PCBM fabrication with the results reviewed ................................ 25

2.4 Safety Requirements ............................................................................................................... 28

2.5 Conclusion .............................................................................................................................. 29

Chapter 3 Methodology .......................................................................... 30

3.1 Introduction ............................................................................................................................. 30

3.2 Preparation of the Solvents based on the finest tuning ........................................................... 32

3.2.1 MEH PPV:PCBM ..................................................................................................... 32

3.3 Full Fabrication Process .......................................................................................................... 32

3.4 Conclusion .............................................................................................................................. 36

Chapter 4 Results and discussion ............................................................. 37

4.1 Introduction ............................................................................................................................. 37

4.1.1 Characterisation ........................................................................................................ 38

Table ‎4.1 Devices Characterisation ....................................................................................................... 38

4.1.2 Experimental results of UV-Visible λ evaluated based on the spin speeds: ............. 39

4.2 Conclusion .............................................................................................................................. 41

4.3 Experimental results I-V Curve evaluated based on the spin speeds: ..................................... 41

Figure ‎4.3 Typical I-V Curve for Solar Cells [50] ................................................................................ 42

Figure ‎4.4 I-V Curve obtained by each device ...................................................................................... 42

Table ‎4.2 The results obtained via SPA inspection (Plight is fixed) ..................................................... 43

Figure ‎4.5 I-V Curve obtained by a 1000RPM with carbon................................................................. 44

Table ‎4.3 The results obtained via SPA inspection (Plight is fixed) with carbon applied device ......... 45

4.4 Conclusion .............................................................................................................................. 45

Chapter 5 Business plan.......................................................................... 46

5.1 Introduction ............................................................................................................................ 46

5.2 Market analysis including effect on society and environment ............................................... 46

5.3 Business structure ................................................................................................................... 47

5.4 Costing ................................................................................................................................... 48

5.4.1 Capital cost .............................................................................................................. 48

5.4.2 Operational cost ........................................................................................................ 50

5.4.3 Material cost ............................................................................................................. 50

ix

5.5 Conclusion ...............................................................................................................................51

Chapter 6 Conclusion and future work .................................................... 52

6.1 Conclusion .............................................................................................................................. 52

6.2 Future work ............................................................................................................................. 54

List of publications ...................................................................................... 56

References 57

x

List of Tables

Table ‎2.1 Comparison of the method used in nanostructured material processing [14] .............. 16

Table ‎2.2 characteristic of MEH PPV: PCBM, P3HT: PCBM and PCDTBT: PCBM ...................... 21

Table ‎2.3 the parameters of MEH PPV: PCBM fabrication with the results reviewed ..................... 23

Table ‎2.5 the parameters of P3HT: PCBM fabrication with the results reviewed ............................ 25

Table ‎2.7 the parameters of PCDTBT: PCBM fabrication with the results reviewed .............. 27

Table ‎3.1 Predicted number of devices that required to be fabricated .............................................. 30

Table ‎4.1 Devices Characterisation ................................................................................................... 38

Table ‎4.2 The results obtained via SPA inspection (Plight is fixed) ................................................. 43

Table ‎4.3 The results obtained via SPA inspection (Plight is fixed) with carbon applied device ..... 45

Table ‎5.1 the minimum estimated price list of capital assets ....................................................... 50

Table ‎5.2 the price list of operational cost yearly ......................................................................... 50

Table ‎5.3 the price list of the materials used with available quantity ................................................. 51

xi

List of Figures

Figure ‎1.1 Phenomenon of EHP generation [51] ............................................................................ 4

Figure ‎1.2 Phenomenon of EHP diffusion [51] ............................................................................... 5

Figure ‎1.3 Phenomenon of EHP separation [51] ............................................................................ 5

Figure ‎1.4 Structure of Single layer cells [50] ................................................................................. 6

Figure ‎1.5 Phenomenon of EHP dissociation by Single Layer Cells [37] ..................................... 7

Figure ‎1.6 Structure of Bilayer cells [50]......................................................................................... 8

Figure ‎1.7 Phenomenon of EHP dissociation by Bilayer Cells [37]............................................... 9

Figure ‎1.8 Structure of Bulk Heterojunction Cells [50] ................................................................ 10

Figure ‎1.9 Phenomenon of EHP dissociation by Bulk Heterojunction Cells [37] ....................... 10

Figure ‎1.10 Structure of Bulk Heterojunction Polymer: Fullerene Solar Cells ........................... 11

Figure ‎2.1 alkylthiol modified nanoparticles onto bare Au [20] .................................................. 14

Figure ‎2.2 alkythiol modified surface under pure Au [20] ........................................................... 14

Figure ‎2.3 hydrolysis and condensation of a liquid precursor to a solid [20].............................. 16

Figure ‎2.4 Solution dispersion onto the substrate (ω = 0) [20] ..................................................... 17

Figure ‎2.5 Acceleration to its nominal rotation speed (dω/dt > 0) [20] ....................................... 17

Figure ‎2.6 Thinning of a liquid layer during rotation at a constant nominal speed dominating

by viscous force (dω/dt = 0) [20] ........................................................................................... 17

Figure ‎2.7 Hardening of the coating dominating by the solvent evaporation (dω/dt = 0) [20] .. 18

Figure ‎2.8 refractive indices of the reviewed MEH PPV: PCBM [19] ........................................ 20

Figure ‎2.9 chemical structure of the reviewed MEH PPV: PCBM [38] ............................................. 21

Figure ‎2.10 refractive indices of the reviewed P3HT: PCBM [18] .................................................. 24

Figure ‎2.11 chemical structure of the reviewed P3HT: PCBM [33] ................................................ 24

Figure ‎2.12 chemical structure of the reviewed PCDTBT: PCBM [32] .................................... 26

Figure ‎3.1 Device fabrication steps ................................................................................................. 31

Figure ‎3.2 .......................................................................................................................................... 32

Figure ‎3.3 .......................................................................................................................................... 33

Figure ‎3.4 .......................................................................................................................................... 33

Figure ‎3.5 .......................................................................................................................................... 34

Figure ‎3.6 .......................................................................................................................................... 34

Figure ‎3.7 ......................................................................................................................................... 34

Figure ‎4.1 Electromagnetic Spectrum ........................................................................................... 39

Figure ‎4.2 UV-Vis Lambda Graph ................................................................................................ 40

Figure ‎4.3 Typical I-V Curve for Solar Cells [50] ............................................................................ 42

Figure ‎4.4 I-V Curve obtained by each device .................................................................................. 42

Figure ‎4.5 I-V Curve obtained by a 1000RPM with carbon.............................................................. 44

Figure ‎6.1 New structure of polymer: fullerene solar cells .......................................................... 53

Figure ‎6.2 ......................................................................................................................................... 54

Figure ‎6.3 ......................................................................................................................................... 54

Figure ‎6.4 ......................................................................................................................................... 54

xii

xiii

List of Abbreviations

AFM Atomic Force Microscopy

A Absorbance

Al Aluminum

Au Gold

C Carbon

CF Chloroform

CB Chlorobenzene

CdTe Cadmium Telluride

CIGS Copper

Ca Calium

BOE Buffered Oxide Etch

DCB Dichlorobenzene

EHP Electron Hole Pair

Eg Energy Gap

Ef Fermi Energy Level

eV Electron Volt

FF Fill Factor

G Gram

HOMO Highest Occupied Molecular Orbital

ITO Indium Tin Oxide

Kg Kilogram

L Litre

LUMO Lowest Unoccupied Molecular Orbital

uL Micro litre

mL Millilitre

Mg Magnesium

N Refractive Index

NA Not applicable

NIR Near Infra Red

MEH PPV poly[2-methoxy-5-(2�-ethyl-hexyloxy)-1,4-phenylene vinylene]

PC60BM [6,6]-Phenyl-C61-butyric acid methyl ester

PC70BM [6,6]-Phenyl-C71-butyric acid methyl ester

PEDOT: PSS poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)

PCDTBT Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-

(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]

P3HT poly(3-hexylthiophene-2,5-diyl)

Rpm Rotation Per Minute

SCL Space Charge Layer

Si Silicon

SPA Semiconductor Parametric Analyzer

TiOx Titanium Suboxide

xiv

TiO2 Titanium Oxide

UV Ultra Violet

Vis Visible

1

Chapter 1 Introduction

Nowadays, a lot of development had been made in order to obtain high reliability,

green energy source with a reasonable capital cost. By replacing the non-renewable

electrical generating source such as fuel, charcoal and nuclear energy, photovoltaic device

also known as solar cell has been introduced which is operating to generate and dissociate

EHP by havesting photon shined by the sun. Generally, they are two types of solar cell

which are inorganic and organic solar cell.

In 1954, the 1st crystalline silicon solar cell was developed by Chapin, Fuller and

Pearson.[46] The highest efficiencies up to 25% was achieved by monocrystalline silicon

solar cell. However, the capital cost of production is very high. Another alternative is taken

which is producing a thin film solar cell from the material of inorganic such as CdTe

(Cadmium Telluride) or CIGS (Copper Indium Gallium Selenide) with the higest

efficiency obtained is around 16.7% to 19.%.[47] But these thin film solar cells are heavy

regarding to the usage of glass as protective layer; 1.2 m x 0.6 m modules weight 12.0

kg.[48]

The basic principal of a typical silicon solar cell is the absorption of photon also

considered as EHP (electron hole pair) or exciton into the the device and the EHP is

moving towards the SCL (space charge layer) also known as depletion region from both

side, the P side which side is excess with positively charge, holes and the N side which is

excess with negatively charge, electrons. Due to a huge potential different between P side

and N side, electric field is occurred. In depletion region, the EHP is dissociated where

electron is separated to the conduction band at the same time moving to the cathode, and

hole is moving towards anode and energy in form of electron volt (eV) is produced.

For the organic solar cell is totally different compared to inorganic solar cell. This

solar cell was developed specially to reduce the capital cost of production, at the same time

the avaibility of the material is very high. There’s a lot of investigation of this solar cell

have been made in order to increase the low efficiency obtained till the development made

by Solarmer Energy which was achieving 8.13% efficiency in 2010.[49] The efforts of

researching the method of increasing the efficiency never stopped. The experimental using

polymer:fullerene as active layer, the morphology of the active layer whether fabricated in

form of single layer, bilayer or bulk hetero junction, the materials used as active layer with

2

the suitable dilution, and the suitable and low cost fabrication method being used have

been made.

1.1 Aims and motivation

In order to produce a reliable and efficient organic solar cell, they are several

elements that need to be considered properly. By referring to the basic principle of organic

solar cell such as the absorption of photon, exciton (electron-hole pair) diffusion, exciton

(electron-hole pair) dissociation,and the electron and hole mobility towards electrodes; the

elements that need to be put as main priority are determined.

Photon absorbed in Polymer: fullerene active layer will excite electrons to a state

above band gap and forming exciton. Columbic attraction forces are tightly binding the

hole and electron in this state (0.3-1eV). To collect as much as possible the exciton, the

light trapping system might be needed to be mounted on the top of glass surface so the

incident photon reflected on the top surface can be reduced which mean the absorption of

the photon is increased.

Before vanishing, the polymer in range of 10nm can be diffused through by the

exciton. Bulk heterojunction active layer is introduced where the distance between

polymer (electron donor) and fullerene (electron acceptor) can be minized. The donor and

the acceptor material are everywhere in the layer so the interfaces also are at everywhere.

So, the EHP is easily diffused to the interface between donor and acceptor. In order to

obtain free charge carriers before vanishing, It requires the energy of electric field which

must be greater than exciton binding energy, in other words, must be greater than 0.4eV to

break that exciton binding. Thus, electron and hole will be dissociated apart.

After dissociation occurred, the free charges obtained need to be mobilized to the

electrode. This step is important to trap the entire dissociated free charge carrier. The

material used will determine the efficiency of hole harvesting at anode, electron harvesting

at cathode. That’s why TiOx is used as hole blocker from collected by cathode and

PEDOT: PSS is used because it is good at conducting hole so it will allow hole to move to

anode easily.

All of this additional elements will be investigated their performance in the

experiments. The structure and the materials might be changed if it couldn’t perform well

in the results. The volume of solvents and another ingredients also will play major role in

the experiment due to the limited material and equipment.

3

1.2 Objective of the experimental

There are several purposes of conducting these experimental. The spin speeds of

spin coating deposition for active layer (polymer: fullerene layer) need to be varied to

1000RPM, 2000RPM, 3000RPM and 4000RPM. The purpose is to relate the the relation

between the thicknesses obtained using the Atomic Force Microscopy (AFM) after the

application of those various spin speed with the absorbance which is obtained by using the

UV- Vis Spectroscopy and the PCE obtained using the SPA which provide several reading

for PCE evaluation purpose. Among those spin speed, which device fabricated providing

the best performance is the milestone of this experimental purpose.

Besides investigating the effect of varied spin speeds on depositing the active layer,

another parameter of the material also has to be reviewed and fixed for the poly(3,4-

ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT: PSS) solvent deposition, the

temperature with annealing duration, and the weight ratio of polymer: fullerene with

suitable dilution. Eventhough this study is out from the experimental conduct but a robust,

proper tuning is required to minimize the undesired result.

Another additional component that will be introduced in this experiment is the usage

of Titanium Oxide (TiO2) as the holes blocker and the usage of Indium Tin Oxide (ITO)

coated glass as cathode by replacing the Aluminum (Al). The outcome of this application

will be observed whether it can bring the improvement or not. If it fails to improve the

perfoemance, proper solution is required to overcome the failure. But the application of the

ITO as a replacement for the Al is a must due to fabricate the simple and affordable device.

1.3 Project Challenges

Eventhough polymer: fullerene solar cell is easier to be fabricated and require lower

cost compared to inorganic solar cell, the material itself is highly sensitive to H20 and O2.

The samples might degrade either during fabrication process or inspection process where

the samples are exposed to the mentioned causes.

The deposited PEDOT: PSS might be dissolved with the H2O left on the ITO

surface if the cleaned ITO coated glass is not dried thoroughly. When the deposited

PEDOT: PSS dissolved with the water, the holes transportation potential of its will be

degraded and will affect the performance of power conversion to be weakened.

The application of the ITO as a substituent for Al also might result a poor result due

to its electron mobility is not as good as Al’s. The experiment of studying this process

4

might be worthwhile due to the fresh idea of innovation new fabrication method

eventhough the becoming results will be not good as using the Al.

The insufficient material of PCBM is the biggest challenge in this experiment. The

amount of PCBM purchased is just 1g for a bottle. The price is about RM900 and the

shipping of the item takes a lot of time. Due to the highest efficiency obtained by 1: 4

weight ratio of polymer: fullerene, so it requires greater amount of fullerene which is 4

times more than polymer for fabricating those devices.

1.4 Introduction of Inorganic Solar Cells

The inorganic solar celss are involving the P-N junction in their operation. Basically

the silicon is used as the substrate. Light is applied on the silicon solar cell, EHP is

generated at both side p and n domain. This phenomenon can be observed in figure 1.1.

Figure 1.1 Phenomenon of EHP generation [51]

The electrons diffuse across the p-n junction to a lower energy level. The holes

diffuse in the opposite direction. New electron pairs (EHP) continue to be formed during

the light striking onto the solar cell. This phenomenon can be observed in the figured 1.2.

Generation

Generation

energy emitter junction base

5

Figure 1.2 Phenomenon of EHP diffusion [51]

As electrons continuously diffusing, a negative charge builds up the emitter. A

corresponding positive charge builds up in base. The p-n junction has separated the

electrons from the holes and transformed the generation current between the bands into an

electric current across the p-n junction. This phenomenon can be observed in the figure

1.3.

Figure 1.3 Phenomenon of EHP separation [51]

Generation

Generation

energy emitter junction base

Generation

Generation

energy emitter junction base

6

1.5 Introduction of Organic Solar Cells

Organic solar cells are totally different compared to inorganic semiconductor

solar cells in terms of structure. But for the working principal, both are approximately the

same. The difference is the inorganic solar cells are using the P-N junction with the

valance and concuction band while the organic solar cells are using Donor –Acceptor with

the HOMO (Highest Occupied Molecular Orbital) and the LUMO (Lowest Unoccupied

Molecular Orbital). Organic solar cell also provide one biggest advantage which is it can

be fabricate on the flexible substrate. It can be intergrated onto clothing, bagpack and very

versatile. The capital cost also is reasonable compare to the inorganic solar cell.

Organic solar cells were founded built with a single active layer, followed by

bilayer active layer, and recently, bulk heterojunction active layer.

1.5.1 Introduction of Single Layer Cells

Well known as the simplest organic solar cells invented, a layer of conjugated

material between two metallic conductors are sandwiched the organic layer in the

fabrication of this device, shown in the figure 1.4. The electrode can be made using ITO

(indium tin oxide) and a low work function whether Al, Mg, or Ca electrode. The

characteristic determination of solar cell also based on the selection of the electrodes. In

analysing the device behaviour, work function can be considered as the key parameter. The

electric field in dissociating the excitons is created by the difference in the work functions

of electrodes.

Figure 1.4 Structure of Single layer cells [50]

Al, Mg,Ca

polymer

ITO

7

Figure 1.5 Phenomenon of EHP dissociation by Single Layer Cells [37]

By referring to the figure 1.5, electrons are excited to LUMO level and leaves hole

in HOMO level when the polymer (electron donor) is absorbing light. An electric field is

setup by the difference of work function between the electrodes.

8

1.5.2 Introduction of Bilayer Cells

Two different organic layers for example polymer and fullerene; are deposited

between two conductive electrodes like shown as the figure 1.6. Sometimes, this solar cells

are called as planar-donor acceptor-heterojunction solar cells. The exciton dissociation spot

located at the interface between electron donor layer and electron donor acceptor. The

differences of these materials are having ionization difference and electron affinities,

determined as a good reason why they are selected to be sandwiched as active layer. It will

causing electrostatic forces to appear at the interface. Donor which is excess with electron

carrier and acceptor which is excess with hole carrier will tribute to the production of

electric field. This phenomenon may separate up the excitons better than the single layer

cells do.

Figure 1.6 Structure of Bilayer cells [50]

Referring to the figure 1.7, electrons in donor material will be excited from

HOMO level to LUMO level and forming excitons once illuminated by photons. The

excitons can transfer to the LUMO of the acceptor and will be dissociated at the interface

if an acceptor molecule in state of being close to this exciton. When the ionization

potential of excited state for donor (ID*) satisfies the (1.1) equation, the transfer will occur.

* 0D A CI A U ( 1.1 )

ID* = potential of excited state for donor

AA = Acceptor material electron affinity

UC = Effective columbic interaction

Al, Mg,Ca

polymer

fullerene

ITO

9

Figure 1.7 Phenomenon of EHP dissociation by Bilayer Cells [37]

The biggest obstacle in this device in achieving higher efficiency in dissociation

stage is the length of exciton diffusion in these material is too short and can’t reach the

interface where the dissociation occur. To overcome this problem, bulk heterojunction has

been introduced.

1.5.3 Introduction of Bulk Heterojunction Cells

The donor and acceptor material are blended together as an active layer for this

device. This morphology will enrich the generated excitons to reach the interface of donor-

acceptor if the length of the blend is same as the diffusion length of excitons. The

efficiency of electron hole pairs (EHP) might be improved.

The excitons in the bulk which are created by the absorption of photon, are

everywhere. To observe the dissociation of exciton, we considered the exciton placed close

to the interface between Donor and Acceptor.

In the figure below the absorbed exciton reaching the interface of Donor-Acceptor

and the electron is separated from the exciton due to the binding energy broken by the

electric field occurred in the interface, excited to the LUMO of Donor. The electron

transported from LUMO of Donor to the LUMO of Acceptor then diffused and captured

by the cathode.

The hole which remains will be transported towards anode and captured.

10

Figure 1.8 Structure of Bulk Heterojunction Cells [50]

Figure 1.9 Phenomenon of EHP dissociation by Bulk Heterojunction Cells [37]

ITO

Al, MG, Ca

11

1.6 The Idea of Structuring the device

Figure 1.10 Structure of Bulk Heterojunction Polymer: Fullerene Solar Cells

ITO coated glass is the best choice for the substrate due to its high electrical

properties and transparency. It is composed by 90% Indium Oxide (In2O3) and 10% Tin

Oxide (SnO2). ITO acts as both electrodes in this device. For optical properties, it is

providing high refractive index which is N = 2.35046 for ITO layer which mean it could

trap incoming light besides being the electrode. Referring to the Figure 1.4a, 2 pieces of

ITO glass are used to sandwich the PEDOT: PSS, active layer and TiOx. This is because

Al has been replaced with the ITO as the anode of this device.

PEDOT: PSS is chosen due to the roughness of ITO it can has good contact with

polymer in spin coating process so PEDOT:PSS is used to overcome this problem by

smoothing the ITO surface plus it has good hole collecting (efficient electron blocking).

Moreover, good transparency also be part of its benefit to allow light to travel into.

MEH PPV: PCBM is investigated and compared to the previous polymer:

fullerene used which are P3HT: PCBM and MEH PPV: PCBM. The entire active layer will

be varied to two types of fullerene (electron acceptor) which are PC70BM and PC60BM.

Both fullerenes have their own advantage in contributing to the enhancement of polymer in

solar cells. For PC60BM, electrons transportation is more efficient and spatial distribution

of PC60BM clusters are larger than that of PC70BM clusters. But, in the wavelength regions

from 350 to 500 nm, PC70BM exhibits better absorption behavior. To achieve the most

efficient exciton dissociation, Bulk Hetero Junction polymer:fullerene had been decided

due to its advantage of being able to affect most of generated exciton to reach the interface

of donor and acceptor by equating the length of the blend with the excitons diffusion

length. CdTe also will be added in the active layer and the devices will be varied in four

conditions which are MEH PPV: PC70BM, MEH PPV: PC70BM: CdTe, MEH PPV:

PC60BM and MEH PPV: PC60BM:CdTe. CdTe is being investigated to determine whether

12

it can provide a nano-scale interpenetrating network of electron donor and electron

acceptor.

TiOx (Titanium Suboxide) is used as an optical spacer to gain greater light

absorption (it has high refractive index) by breaking the symmetry and blocking hole

(electron collecting). It is also can reduce “dead layer”. It is placed between Al and active

layer to comprise phase separated blend.

13

Chapter 2 Literature review

2.1 Introduction

In order to fabricate the device with obtaining reasonable result, it requires the

appropriate techniques of fabrication and tools handling, robust knowledge of the

characterization of the materials used to find the finest tune of solvent involved and the

condition of the workplace.

In choosing the appropriate techniques, there’s several condition need to be

considered such as adhesion, thermal stability, mechanical properties, thickness precision,

level of ordering and industrial compatibility.

The architecture of polymer:fullerene morphology also plays major role in order to

harvest as much as possible excitons, to trap them inside, to maximize the the exciton

diffusion length or minimize the distance of interface between electron donor and electron

acceptor, to increase electron and hole towards electrode, and the morphology of active

layer whether bilayer form, heterojunction or bulk heterojunction. Last but not least, it

requires to use the finest tune of solvent to create a device.

Besides putting the results as main priority, the safety tips also need to be followed

to avoid any undesired incident happen. This is important especially dealing with

hazardous material.

14

2.2 Comparison of Nanostructured Material Processing using

Different Chemical Techniques

There are multiple ways of depositing a colloid nanoparticles onto the solid

substrate..It can be categorised into 5 techniques which are Electro-deposition, Chemical

Self-Assembly, Electrostatic, Langmuir-Blodgett and Spin Coating.

Chemical Self-Assembly method provides remarkable result with the simplest

method deposition method which is introduced by Netzer and Sagiv. This method

involving absorbed objects’ strong covalent bonding (such as monomer or polymer

molecules) upon the substrate by special functional groups. For example, the groups of the

compounds that have a strong affinity to gold are thiol (SH) or amine (NH2). This can be

observed at the Figure 2.1 and Figure2.2.

Figure 2.1 alkylthiol modified nanoparticles onto bare Au [20]

Figure 2.2 alkythiol modified surface under pure Au [20]

15

Electrodeposition is one of the earliest methods for depositing inorganic coating on

the solid surface. It has two types of electrodepositions which are the combination of the

formation for stabilized colloids particle with their electrodeposition and electrodeposition

of preformed colloid nanoparticles. Somekind of surfactant should be added to the

electrolyte solution in order to form nanostructured material. Nanocrystals are coated and

prevented from further aggregation by the surfactants which act as stabilizing agent. The

role of the substrate is very important factor of adhesive percentage in elctrodeposition.

The growth of monodispersed nanoclusters can be stimulated due to highly ordered

substrate surfaces. A variety of materials including metals, semiconductors, ceramics and

polymers could be deposited using this method.[20]

The sol-gel process can be described as the hydrolysis and condensation of a liquid

precursor to a solid. Usually, the beginning precursors can be either organic species such

as metal oxide or inorganic salt. The whole process can be characterized by several

important steps by referring to the figure 2.3. The steps are formation of of stable solution

of precursors (the sol); further reaction of the sol with a bridged rigid, porous network (the

gel) enclosing a continuous liquid phase by gelation; drying vial the removal of liquids

from the gel network; and densification and decomposition of the gels at high temperature.

The nature of the specific reactions involved in hydrolysis and condensation differ

substantially between various types of precursors.Finding a suitable precursor and solvent

is the key to the synthesis of monodispersed semiconductor NPs by means of sol-gel

process.[41]

16

Figure 2.3 hydrolysis and condensation of a liquid precursor to a solid [20]

The table 2.1 is showing comparison of the method used in nanostructured

material processing.

Table 2.1 Comparison of the method used in nanostructured material processing [14]

17

2.2.1 The mainTechnique Used: Spin Coating

This method is about depositing polymer layers onto flat solid surfaces,

particularly for photoresist and another dopant in microelectronic fabrication. Polymer

layer adhesion can be occurred by spreading polymer solution onto the substrate which is

fixed held on chuck, rotated at a speed in order of thousands of revolutions per minute.

Under the influence of the central force, the polymer solution spreads evenly over the large

area and dries out due to solvent evaporation during the rotation. After additional baking at

elevated temperatures, a polymer layer is finally formed on the substrate surface.

The stage processes of spin coating is shown in the figure 2.4, 2.5, 2.6 and 2.7.

Figure 2.4 Solution dispersion onto the substrate (ω = 0) [20]

Figure 2.5 Acceleration to its nominal rotation speed (dω/dt > 0) [20]

Figure 2.6 Thinning of a liquid layer during rotation at a constant nominal speed dominating

by viscous force (dω/dt = 0) [20]

18

Figure 2.7 Hardening of the coating dominating by the solvent evaporation (dω/dt = 0) [20]

The hydrodynamic theoretical model was developed for the two last stage (viscous

and evaporation). In the viscose domination stage, the equilibrium between centrifugal and

viscous forces take place according to a following equation: [20]

2

2

2

Vr

Z

( 2.1 )

Z = vertical direction

r =radial direction

η = fluid viscocity

= fluid density

= fluid velocity

c = fluid concentration

= rotation frequency (2πf)

By considering the substrate is well uniformed, the substrate thickness (h) is

invariant on the radius. The solution of (1) with the flow of continuity condition

2 32

3

dh h

dt

( 2.2 )

h = film thickness

and the appropriate boundary condition yields a following expression for the film thickness

21/2

0 0

4[1 ( ) ]

3h h h t

( 2.3 )

19

h0 = initial thickness at (t = 0) which is at the beginning of stage 3 of a stable rotation. The

evaporation of solvent from the spun fluid wasn’t considered at the above situation, so that

both the fluid density and viscosity remain constant. So, the dependencies of h ~ ω-1

and h

~ t-1/2

are characteristic for stage 3 of the spin coating.

The solvent evaporation, which is extremely important part of forming a solid spun

film, can be taken into account by adding the evaporation rate (e) in the continuity

condition:

2 32( )

3

dh he

dt

( 2.4 )

Condensing and hardening of the spun fluid during evaporating the solvent are

causing both parameters in (2.4) which are and η to become time dependent. At the 4th

stage of spin coating, fully controlled by solvent evaporation because the exact solution of

(2.4) is difficult and requires numerical calculation. Thus, respective critical values of o,

ηo, and co are introduced:

2

00

0

2(1 )

3c e

( 2.5 )

The evaporation becomes dominating from this point onwards, and from (2.4) can

exclude viscous term. The formula below is giving the expetected final thickness of a spun

film solution :

1/2 1/3 2/3 1/3

0 0

0

(1 ) ( )ofh c c e

( 2.6 )

hf value will approximately same with -2/3

the evaporation rate is constant

during 4th stage which may take place for highly volatile such as hexane, benzene, toluene

and particularly chloform. [20]

20

2.3 Tuning Optimization

There are several parameter need to be varied and fixed properly in order to obtain

well-functioning morphology of Polymer: Fullerene Solar Cell such as the weight ratio of

active layer, types of the dilution used for the active layer weight over volume, annealing

temperature and its duration, the weight ratio of active layer to nano-scale interpenetrating

network material such as CdTe or CdSe, types of dilution used for nano-scale

interpenetrating network material weight over volume, and the varied spin speed used in

depositing all of the materials on the ITO glass substrate. Thus, a fully properly review had

been made in order to make variffication of those amount of tuning.

2.3.1 MEH PPV: PCBM

MEH PPV is one of conductive polymers that developed in the earliest of the

invented organic solar cell. Its role in active layer as electron donor which means the

majority charge carrier is electrons. The refractive indices obtained when it diluted

together with PCBM in Chloroform are quite a number. When the electric field is applied

on the material, the refractive indices are changed as well. It can be concluded that the

active layer will be obtained is a type of birefringence material. The figure 2.8 is showing

the obtained result based on the reviewed literature.

Figure 2.8 refractive indices of the reviewed MEH PPV: PCBM [19]

Another characteristic of MEH PPV: PCBM compared to P3HT: PCBM and

PCDTBT: PCBM is shown in the table 2.2 and the chemical structure of MEH PPV:PCBM

can be observed in figure 2.9.

21

Figure 2.9 chemical structure of the reviewed MEH PPV: PCBM [38]

Characteristic

MEH PPV:PCBM

P3HT: PCBM

PCDTBT:

PCBM

mn (m2/Vs) (electron

mobility)

5.66x10-8

8.78x10-8

1.41x10-8

mp (m2/Vs) (hole

mobility)

1.83x10-9

3.47x10-8

7.66x10-9

Lx (nm) (exciton

diffusion length)

11.4

5.6 12.4

fx (%) (exciton

collection efficiency)

94

80 95

Nc=Nv (m_3)

(effective density of

states of the

conduction/the valence

band)

2x1026

2.5x1026

1x1025

Eg (eV) (energy gap)

1.37

1.1 1.2

Table 2.2 characteristic of MEH PPV: PCBM, P3HT: PCBM and PCDTBT: PCBM [35]

Regarding to the table 2.2, the MEH PPV: PCBM is providing the the longest

exciton diffusion length and the greatest energy gap among those three active layer

materials. The exciton collection efficiency of the MEH PPV: PCBM also can compete

with the PCDTBT: PCBM’s.

The advantage of having a longer diffusion length is the potential of the exciton to

reach the interface (SCL) between Donor and Acceptor where the dissociation of the EHP

occurs also increased. When the number of EHP dissociation is increased, the amount of

eV also increased thus the PCE percentage can be improved.

The greater Eg of the MEH PPV: PCBM make it able to absorb wider wavelength.

Based on calculation using the provided value, it has been proved the previous statement.

22

hcEg

( 2.7 )

34 8(6.63 10 )(3 10 )1.37

251.986 10

1.37

251.986

1.37e

= 905nm

The wider absorbance of electromagnetic spectrum enhances the percentage of

exciton collection efficiency whether it is illuminated indoor or outdoor; at the same time

enriching the potential of the EHP dissociation to occur at the Donar- Acceptor interface.

Annealing

Process

MEH

PPV:PCBM

MEH

PPV:PCBM:CdTe

Spin Speed/

Thickness

Efficiency Dilution

Ratio

DCB:CF

Reference

NA 1:0 NA 2500rpm

100nm

For Al:6.7

For

Au:0.15

1:0

(10mg/ml)

[1]

NA

NA NA 3000rpm

150nm

2.25 NA [2]

NA

NA NA NA EQE:

60%

65%

70%

0:1

1:0

1:1

[3]

100oC

(5

minutes

each)

1:2

1:3

1:4

1:5

NA NA

1.9%

1.7%

1:0

(7mg/ml)

1:0=1.9%

0:1=1.7%

[4]

120oC

(30

minutes

SiO2

substrate)

1:4 NA 1500rpm

60s

[5]

23

120oC

(10

minutes

each)

1:4 NA 2000rpm 0.58% NA [6]

NA

2.25x105

g/mol:5mg/ml

NA 2000rpm=20s

0.5%

0.9%

0.8%

(5-

6.5mg/ml)

1:0

0:1

1:1

[7]

NA

1:4 700rpm=40s 1.2% 1:0

(8mg/ml)

[8]

NA

NA 1:0:3

(10mg MEH PPV

in 1 ml CB)

NA PCE:

0.052%

1:1

(1ml:1ml)

[9]

NA

1:4 NA NA 2.9% 1:0 [10]

90oC

(45

minutes)

1:2 NA 1000rpm

60s

PCE:

0.87%

0.55%

0.24%

0.54%

0.29%

0.17%

0:2

0:3

0:4

3:0

4:0

5:0

[11]

Table 2.3 the parameters of MEH PPV: PCBM fabrication with the results reviewed

As a result based on the efficiency recorded in the table 2.3, the best efficiency

achieved by the MEH PPV: PCBM with weigth ratio of 1:4 and DCB:CF dilution ratio is

1:0 and other information are not given in the literature. To construct the the finest tune

based on the information obtained, the majority of ratio/material used, the suitability and

avaiblity of the material have to be considered. The weight ratio of MEH PPV: PCBM:

CdTe has been determined as 1:4:3 and dissolved using chloroform which means 1mg of

MEH PPV, 4mg of PCBM and 3mg of CdTe are diluted together in 1ml of chloroform.

The weight ratio of MEH PPV: PCBM is obtained by referring to [10] which is using 1:4

and resulting 2.9% PCE. The weight ratio of CdTe is obtained by referring to the [9] but

the result is quite poor because of the active layer used is just MEH PPV without PCBM,

so the usage of CdTe might be reconsidered. This weight ratio is going to be used in the

experimental and is fixed. 20ul for each drop on a single ITO glass substrate. The

temperature is determined as 90oC for 5 minutes for each annealing process. Most of the

temperatures shown in the table are quite high and the heating durations are quite long too.

Thus, to avoid from dissipating the conductivity characteristic of each material, 90oC

temperature and 5 minutes annealing duration for each annealing process has been chosen.

24

The spin speeds that will be used in the experimental are varied as 1000rpm,

2000rpm, 3000rpm, and 4000rpm for 60seconds for every device whether with CdTe or

without CdTe, using PC60BM or PC70BM.

2.3.2 P3HT: PCBM

After the development of the MEH PPV: PCBM solar cell, P3HT:PCBM as the

active layer has been investigated. Its role in active layer as electron donor which means

the majority charge carrier is electrons and PCBM as electron acceptor. The refractive

indices obtained when it diluted together with PCBM in Chloroform are quite a number.It

can be concluded that the active layer is a type of birefringence material. The figure 2.3.2a

is showing the obtained result based on the reviewed literature. The wavelength shows the

range of visible light and the consistent refractive index could be estimated as n= 2.

Figure 2.10 refractive indices of the reviewed P3HT: PCBM [18]

Another characteristic of P3HT: PCBM is shown in the table 2.2 and the chemical

structure of P3HT:PCBM can be observed in figure 2.11.

Figure 2.11 chemical structure of the reviewed P3HT: PCBM [33]

25

Annealing

Process

P3HT:PCBM P3HT:PCBM:CdTe Spin

Speed/

Thickness

Efficiency Dilution

Ratio

DCB:CF

Refere

nce

110

oC

10min

1:1

20mg/ml 1:1

31mg/ml 800rpm

45s NA

(gain

investigation)

1:0 [12]

120oC

30min

1:0.8 NA

1550rpm

180s

2.60%

1.31%

3.22%

2.18%

1:0

50mg/ml

60mg/ml

70mg/ml

80mg/ml

[13]

130 oC

1:0.6 NA 700rpm

4.49% 1:0 [14]

40 oC

55 oC

80 oC

(60min)

1:1

20mg/ml

NA 1000rpm

60s

0.1%

0.6%

3.5%-5%

1:0

DCB

1:0

CB

[15]

150 oC

10min

1:1

20mg/ml

NA 1500rpm

45s

0.23 ±0.03 %

to

2.9 ±0.2 %

1:0

CB

[16]

120 oC to

150 oC

30min

1:1

10mg/ml

NA 1000rpm 1.2% to 3% 0:1 [17]

NA

(simulation)

1:1 NA

(simulation)

NA

(simulation)

5.5% NA

(simulatio

n)

[18]

110 oC to

180 oC

0.5:1 to 2:1 NA 500 and

above

4% NA

(o-

dichlorobe

nzene,

chlorobenz

ene,

toluene, o-

xylene)

[21]

80 oC

10min

1:0.6 NA 900rpm

5s

3.54% 3:1

(DCB:CB)

1ml

[23]

Table 2.4 the parameters of P3HT: PCBM fabrication with the results reviewed

As a result based on efficiency recorded in the table 2.5, the suitability and the

avaiblity of the material, the ideal weight ratio of P3HT: PCBM: CdTe has been

determined as 1:1:1 and dissolved using chloroform which means 1mg of P3HT, 1mg of

PCBM and 1mg of CdTe are diluted together in 1ml of chloroform eventhough the results

obtained by reviewing shows the usage of CB provided higher PCE, but due to the

avaibality of the dilution, only CF is provided. The weight ratio of P3HT: PCBM is

obtained by referring to [12], [15], [16], [17] and [18] which is using 1:1 and resulting the

PCE between 0.1% to 5%. The weight ratio of CdTe is obtained by referring to [12] but the

PCE wasn’t provided. But the usage of CdTe still need be reconsidered to reach the

milestone.

26

The ideal annealing temperature obtained is between 80oC to 120

oC for 10 to 30

minutes for each annealing process. Most of the temperature shown in the table are quite

high and the heating durations are quite long too. Thus, to avoid from dissipating the

conductivity characteristic of each material, 90oC temperature and 5 minutes annealing

duration for each annealing process has been fixed.

2.3.3 PCDTBT: PCBM

The most recent electron donor polymeric material, PCDTBT, is currently being

deeply investigated in order to obtain the most efficient of polymer: fullerene solar cells.

Not only the performance, the morphology, architecture and lifetime of this device also

arebeing investigated. So, this material is still fresh and some information couldn’t be

obtained from rewiewing technical jurnals such as the usage of CdTe together with

PCDTBT:PCBM as active layer and the neither the refractive index. But, some important

characteristics are obtained as shown in the table 2.3.3a and the the chemical sctructure of

PCDTBT:PCBM and the characteristic of PCDTBT: PCBM can be observed in figure 2.12

and table 2.2.

Figure 2.12 chemical structure of the reviewed PCDTBT: PCBM [32]

Annealing

Process

PCDTBT:PCBM PCDTBT:PCBM:

CdTe

Spin

Speed/

Thickness

Efficiency Dilution

Ratio

DCB:CF

Refere

nce

NA

1:4 NA

1000rpm

120s 6.79% 1:0

(CB) [22]

80oC

10min

1:4 NA

900rpm

5s

5.77% 3:1

(DCB:CB)

1ml

[23]

140 oC

10min

1:4 NA NA

(vacuum

evaporation)

4.24% 0:1

(CF)

4mg/ml

[24]

80oC 1:4 NA 5000rpm 4.9% 0:1 [25]

27

30min

20mg/ml (C:F)

4mg/ml

120 oC

60min

1:4

1:2

NA

NA

C60

5.2%

4.25%

C70

6.1

%

5.7

%

1:0

(CB)

[26]

140 oC

15min

65 oC

15min

1:4

25mg/ml

1:4

35mg/ml

NA 1500rpm

45s

700rpm

45s

NA

(lifetime

investigation)

1:0

(DCB)

7mg/ml

50%

Ethanol

[27]

60 oC

1:4 NA NA

(80nm)

5±0.15% 1:0

(DCB)

7mg/ml

[28]

140 oC

15min

1:2

1:3

1:4

NA NA

100nm

DCB

5.6

6.0

6.0

CF

5.7

5.6

5.0

1/1

1/1

1/1

[29]

70 oC

60min

1:4 NA 700rpm

25s

40nm

4.63±0.15% 1:0 [30]

Fresh

80

100

120

1:2 NA 1000rpm

(80nm-

100nm)

5.27%

5.12%

3.71%

2.83%

0:1

(CF)

[31]

Table 2.5 the parameters of PCDTBT: PCBM fabrication with the results reviewed

As a result based on efficiency recorded in the table 2.7, the ideal weight ratio of

PCDTBT: PCBM: CdTe has been determined as 1:4:3 and can be dissolved using

chloroform which means 1mg of PCDTBT, 4mg of PCBM and 3mg of CdTe are diluted

together in 1ml of chloroform. Chloroform is used due to reliability of its performance

shown by [25] [31] that solvent. The weight ratio of PCDTBT: PCBM is obtained by

referring to the majority of reviewed articles which are [22], [23], [24], [25], [26], [27],

[28], [29] and [30] using 1:4 and resulting is about 4.24% to 6.79% PCE. The weight

ratio of CdTe is obtained by referring to the CdTe applied in MEH PPV: PCBM which got

similarity of polymer: fullerene weight ratio (1:4) nevertheless it is new idea in order to

enhance the PCE of PCDTBT: PCBM based solar cells.

The ideal annealing temperature is determined as 90oC for 5 minutes for each

annealing process. Most of the temperatures shown in the table are quite high and the

heating durations are quite long too. Thus, to avoid from dissipating the conductivity

characteristic of each material, 90oC temperature and 5 minutes annealing duration for

each annealing has been chosen as ideal temperature and duration.

28

2.4 Safety Requirements

In order to avoid any unpleasant incident from happening in the laboratory, proper

ethics and protocol need to be followed. They are Safety First, Acid Safety and Solvents

Safety.

Safety First is more describing about the ethics and behaviour of the personnel

(people who use the laboratory) themselves. They must wear long pants, no shorts or

skirts, wear fully closed toe shoes and avoid wearing contact lens in clean room. They

must label every container used with this information; chemical, time and date, and their

name. Before entering the laboratory (or cleanroom), they should clean up after

themselves.Food or drink are forbidden in the lab. They also must know the exact position

or location of emergency shower, eye wash and calcium cream. Report any chemical spills

to technician or supervisor. If any accident happen, call the emergency number as soon as

possible.

Usually they will be exposed to the usage of acids in the etching process. Most of

the acids are corrosive, flammable and might be a minority type of them could be mutative.

A very proper way of handling must be taken. Always wear safety glasses and chemical

resistant gloves. Always Add Acid to water (AAA). Pour acids in slowly. Unwanted

reactions may occur if mixed incorrectly. Don’t inhale any fumes in the lab. Always use

chemicals under a fume hood.After mixing acid solutions make sure they are cooled to

room temperature before capping. This is to avoid pressure build up in the bottle. Make

sure acid bottles are always capped. Acids and solvents have to be disposed of in their

respective disposal bottle. If any acid is spilled on their person, rise thoroughly with large

quantities of water. Report the occurrence to the lab instructor immediately. When using

HF always use plastic. Don’t use any glass. The glass will be etched then unusable.[42]

In solvents preparation, this Solvent Safety is extremely important for the

personnel to follow. Most importantly in solvents handling, do not mix acids and solvents

together because by mixing them will cause highly explosive solutions or other unwanted

reaction. After done using the solvents, do not pour them down the sink. The Lab

instructor (technician) will show you the proper way to dispose of them. They go into the

solvent waste bottle if there is not a specific bottle for it. Always use solvents in a fume

hood. Most of the solvents fumes have some sort of toxic property. Don’t get solvents on

the skin. Most are readily absorbed through the skin and some are carcinogenic.

Photoresist contains these solvents so handle photoresist with the utmost care. In general

solvents are flammable, so be very careful around ignition sources. Do not allow solvent

fumes to come near an ignition source. Always wash gloves after handling solvents, so that

29

if the gloves come in contact with acids there in not chemical reaction. Don’t use the same

gloves for handling solvents and acids. The stains left on the glove might react too. For

more information about the safety in dilution process, referring to the material safety data

sheet (MSDS) is a must.[42]

2.5 Conclusion

Based on the comparison of all appropriate technique that can be used to deposit the

solvents on the substrate, it can be concluded that electro-deposition is the best technique

can be used. But the avaibality of the equipment also need to be considered. Thus, spin

coating is used due to the avaibality, lower cost and easier to be used. Eventhough the

theoretical calculation formula is covered in this chapter, but it’s not the purpose of

proving the thickness obtained by the experiment compared to the thickness evaluated

using a calculation. The characteristic of MEH PPV: PCBM, P3HT: PCBM and PCDTBT:

PCBM are recorded, compared and MEH PPV: PCBM is chose to be used as the active

layer in the experiment.

The main purpose of studying those 3 types of active layer is to investigate what

process involved, the parameter and finest tune, and the best PCE obtained. When the

required information is obtained, the variation and parameter can be set, the proper method

of producing the device can be arranged. It could save cost too regarding to the prevention

of buying inappropriate materials.

Besides that, by reviewing several articles regarding to the Safety Requirement in

the laboratory, a proper way of handling tools, suit required and hazardous of the material

can be determined. Thus, any accident at laboratory could be avoided.

30

Chapter 3 Methodology

3.1 Introduction

In order to fabricate the polymer:fullerene solar cells, the main method of processing

the layer has to be determined and the characteristic of the materials themselves need to be

recognized well so the proper methods could be arranged well. A lot of litereature has been

reviewed in order to obtain the methods and the material finest tunings with their power

conversion efficiencies obtained.

This fabrication is involving material preparation such as active layer dilutions

(solvent preparations), spin coating, cleaning, annealing, etching, results observation and

efficiencies calculation.

After obtaining all the required information, the table of conditions varied for the

solar cell is constructed to determine the amount of samples need to be fabricated.

Table 3.1 Predicted number of devices that required to be fabricated

Referring to the Table 3.1 a, it can be concluded that the amount of the samples need

to be fabricated are 16 samples. The varied conditions are the types of fullerene used

(whether using PC60BM or PC70BM) the additive of CdTe or without CdTe, and the spin

speeds of spin coating. The flow of fabrication process can be observed in Figure 3.1.

Polymer: Fullerene Solar Cells

MEH PPV

PC60BM PC70BM

No CdTe CdTe No CdTe CdTe

1000rpm 1000rpm 1000rpm 1000rpm

2000rpm 2000rpm 2000rpm 2000rpm

3000rpm 3000rpm 3000rpm 3000rpm

4000rpm 4000rpm 4000rpm 4000rpm

31

Figure 3.1 Device fabrication steps

PEDOT: PSS deposition

Substrate annealing

TiO2 Paste

ITO coated glass sandwiching

Start

Preparation of the Solvents based on the finest tuning

ITO etch

ITO coated glass cleaning and drying

Clean?

Yes

No

PEDOT: PSS etch

MEH PPV: PCBM deposition

Substrate annealing

MEH PPV: PCBM etch

Substrate annealing

UV-Vis Absorbance and I-V characteristic inspection

End

32

3.2 Preparation of the Solvents based on the finest tuning

3.2.1 MEH PPV:PCBM

The weight ratio of MEH PPV: PCBM: CdTe has been determined as 1:4:3 and

dissolved using chloroform which means 1mg of MEH PPV, 4mg of PCBM and 3mg of

CdTe are diluted together in 1ml of chloroform. This weight ratio is going to be used in the

experimental and is fixed. 20ul each drop. The PEDOT: PSS is already in the form of

chemical so it doesn’t require a dilution process.

The TiO2 is in form of powder so it requires to be diluted. 9ml of acid acetic nitric

is required to dissolve 6 gram of TiO2. The process need to be done little by little which

means 1ml is dropped into beaker filled with 6g of TiO2 at the same time the mixture is

grinded slowly but heavily pressed. This process is continuously done till the 9ml of acid

acetic nitric is finished. After that, the complete mixture need to be anneal on the hot plate

with 300oC for 10min to20min (until the colour is changed to brown and back to white).

3.3 Full Fabrication Process

First of all, a piece of ITO coated glass is cut to 100 samples with 2cm x 2cm unit

area. Then all the samples are cleaned using acetone or deconex which mean they are

dipped in a beaker filled with that solutions. After 20 to 30 minutes, all the glass substrates

are rinsed using DI water and dried using an air pump.

3/4 of the ITO layer which means 1.5cmx1.5cm unit area need to be etched. The

mixture of acid nitric and HCL with ratio 1:3 can be used for this process. The part to be

etched is dipped into a beaker filled with either one of those solution for 5min to 10min.

As the substrate is dipped, bubble will appear on the etched ITO surface and this

phenomenon stops when the ITO is totally etched. Then the glass substrate is cleaned using

DI water and dried using an air pump. This process is done for all the hundred substrate.

The figure 3.2 shows the cross section of the substrate.

Bottom glass Top glass

Figure 3.2

Glass

ITO

33

The PEDOT:PSS is coated on the substrate using a Spin Coater with speed of

2500rpm and 20ul a drop. Before that, the 1/8 which is approximately 0.25cm of ITO layer

which is located from the right edge of the bottom glass is covered or pasted using a

sellotape. The covered area is approximately 0.5cmx0.5cm. After depositing, the sellotape

is removed. After finishing that process for all the required sample, all the deposited

substrates are baked with 90oC for 5min. These steps are applied to all required

substrates.The figure 3.3 shows the cross section of the substrate.

Figure 3.3

The active layer solvent prepared will be deposited at the varied spin speeds which

are 1000rpm, 2000rpm, 3000rpm and 4000rpm. But before that, the area covered with the

sellotape again get covered. A drop of active layer solvent which is 20ul is dropped on the

substrate. Once it finishes, the sellotape is removed and annealed on the hot plate with

90oC for 5min. The figure 3.4 shows the cross section of the substrate.

Figure 3.4

0.25cm from the left edge of the active layer required to be etched but not fully

etched. Whole surface is covered with the sellotape except those etched area. Cotton bud is

dipped into Piranha or RCA1 solvent to etch that part.make sure the process (pressure

applied by hand) is applied is very lightly to ensure not whole of the part to be etched. The

expected cross section can be observed in the figure 3.5.

Glass

ITO

PEDOT:PSS

Glass

ITO

PEDOT:PSS

Polymer: Fullerene Blend

34

Figure 3.5

The TiO2 is applied on the etched area using a cotton bud and rod. Then, annealed

with 90oC for 5min. Before annealing process, the sellotape applied need to be removed.

The result is shown in the figure 3.6.

Figure 3.6

As the finishing of the fabrication process, the top glass is sandwiching the bottom

glass by using the epoxy as a paste like shown in the figure 3.7.

Figure 3.7

Glass

ITO

PEDOT:PSS

Polymer: Fullerene Blend

Glass

ITO

PEDOT:PSS

TiO2 Polymer: Fullerene

Blend

Glass

ITO

PEDOT:PSS

TiO2

Polymer: Fullerene Blend

35

After finishing fabricating all the devices, they are required to be inspected using

SPA where the sample is placed on the micro probe station to observe electrical

characteristic (I-V curve) of the samples. The probe (needles look alike) A and B are

define as anode and cathode and used do obtaine a reading from the cathode and anode of

the sample. The Keithley Interactive Test Environment is used with the setting of

Photovoltaic Measurement and appropriate range of eV and current value. An external

light source is applied on the sample as incoming Plight which is standardized at

1000mW/cm2. Five points of each electrode are inspected to obtain the best reading among

them. This equipment providing the reading of the Isc, Voc, Pmax, Imax and FF for

recording purpose. The I-V curve also automatically plotted.

For the characterisation purpose, the AFM is used to obtain the thickness and

surface roughness of each device. Four pieces of 4cm x 4cm ITO coated need to be etched

using the Acid Acetic Nitric. Once the subsrates were etched, all the substrates are

deposited with the prepared active layer solvent using 1000RPM, 2000RPM, 3000RPM

and 4000RPM. The prepared samples then inspected using AFM. Firstly, launch the SPM

Cockpit™ or InkCAD software then open a configuration file (contact or close-contact) in

SPM Cockpit or select type of the probe to be used in InkCAD. Retract the tip and raise the

AFM scanner to provide safe clearance between the probe tip and the sample puck. Load a

sample on the sample puck. Install a probe on the AFM scanner and align the detector.

For close contact mode only, set the resonance frequency for the installed cantilever.

Locate features for imaging and bring the probe into contact with the sample. the sample is

scanned. Perform the image processing and analysis routines and finally, retract the probe

from the sample.[44]

Last inspection that is required to be conducted is UV-Vis versus the absorbance.

The Lamda UV/Vis Spectrometer is used. In order to inspect the samples, Lamda UV/Vis

Spectrometer needs to be calibrated properly, appropriately to the samples inspection

purpose. The wavelength should be calibrated from 250nm to 800nm where the absorbance

could be observed within this range. Use the Peak/Spectrum function to annotate each

peak, then print the entire spectrum and the wavelength report to determine the

exact wavelength maxima. After done calibrating the wavelength, the photometric

also required the calibration. Basic potassium chromate is recommended as a

photometric standard by the National Bureau of Standards. Use the fixed

wavelength then specify the wavelength. Read and record the absorbance obtained

by each sample for analysis purpose.

36

3.4 Conclusion

The spin coating has been used in depositing nanostructured material on the top of

surface.The spin speeds have to be varied to four speeds which are 1000rpm, 2000rpm,

3000rpm and 4000rpm in order to investigate the ideal thickness of active layer in

obtaining the best Power Conversion Efficiency (PCE). Typically, the best PCE obtained

by 65-100nm. The advantage of using this method is it is simple, easily used, and cheaper.

Another processes involved in this chapter is solvents preparation (dilution),

annealing, cleaning and etching process. Dilution is required in order to dissolve the

materials which are in form of powder like MEH PPV and PCBM (fullerene). After

completing this solvent preparation, material deposition (spin coating) can be proceed.

Cleaning process is required to avoid any contamination on the substrate’s surface.

Annealing process which is involving the usage of hot plate is required in order to ensure

the dopant is really bond with the subsrates; moreover it could improve the performance of

solar cells.

37

Chapter 4 Results and discussion

4.1 Introduction

After preparing all the samples, they are severals methods to do in inspecting the

device characteristic and performance. Basically this inspection purpose is about gathering

the behaviour information of each device.

Typically the informations obtained are the power max (Pmax), current max (Imax),

voltage max (Vmax), open circuit voltage (Voc), short circuit current (Isc) and fill factor

(FF). Pin or Plight is the illumination light applied on each device where the power is fixed

to 1000mW. Using this obtained information, the power conversion efficiency can be

evaluated by replacing the values in the formula below : [35]

(Im max)

( )

ax VFF

Isc Voc

( 4.1 )

( )FF Voc Isc

Pin

( 4.2 )

In the experiments conducted, there are several results obtained which are varied

based on the spin speeds, the usage and non-usage of carbon as counter electrode,and the

usage and non usage of CdTe as nano-scale interpenetrating network. The characterization

and the results of each device is recorded.

The instruments used in this section are Atomic Force Microscopy (AFM) which

is used to characterize the surface roughness and the thickness of coated active layer, UV-

Visible Spectroscopy which is used to analyse the absorbance and transmittance of the

polymer: fullerene layer, and Semiconductor Parametric Analyzer (SPA) which is used to

inspect the I-V curved and evaluation of power conversion efficiency (PCE) also

simbolized as η.

38

4.1.1 Characterisation

The characterisation is obtained via setting up the variation of the spin speed.

There are four spin speeds varied which is 1000rpm, 2000rpm, 3000rpm and 4000rpm.

This is to investigate how do the thickness and the morphology of the active layer affecting

the efficiency of the device.

Spin

Speeds

Thickness of

MEHPPV:PCBM

1:4

Surface Roughness

1000 RPM 40nm

2000 RPM 30nm

3000 RPM 20nm

4000 RPM 10nm

Table 4.1 Devices Characterisation

39

Table 4.1 shows that the differences of the thicknesses and the surface roughnesses

are obtained by using different spin speeds. For the lowest spin speed, coarsest surface was

obtained with the thickness is 40nm followed by 2000rpm with 30nm, 3000rpm with 20nm

and 4000rpm with 10nm and smoothest surface. The purpose of this characterization is to

relate the thickness obtained to the performance of each device.

4.1.2 Experimental results of UV-Visible λ evaluated based on the

spin speeds:

This experiment was conducted to observe the relation of the thickness of the

active layer with the absorption to the fixed value of the wavelength which is from 250nm

to 800nm. 250nm to 375nm is under UV spectrum, 375nm to 745nm is under Visible (Vis)

spectrum, and 745nm to 800nm is under Near Infra-Red (NIR) spectrum. This is shown in

the figure 4.1.

Figure 4.1 Electromagnetic Spectrum

40

Figure 4.2 UV-Vis Lambda Graph

The graph shows the trend of absorption versus lamda. At the 300nm, the

maximum peak of the absorbance is obtained at absorbance (A) =2.35. By referring to the

electromagnetic spectrum, which can be concluded the maximum A could be obtained at

the boundary between UV region and visible region. From A=2.5, the value drastically

drop to A=1and this trend occur for all samples. This phenomenon occurs within near

visible region between 300nm to 330nm approximately and the median of A for all spin

speed is A=1.5.

Starting from 330nm to 530nm, the absorbance of all the devices are once again

dropping (in form of a concave curve) but this time every sample indicates different

median of A. For the 4000rpm sample, it shows the median of A=0.4 at 380nm, followed

by 3000rpm shows A=0.35, 2000rpm shows A=0.25, and 1000rpm shows A=0.23. The λ

=380nm is under visible region. The 4000rpm sample shows the greatest absorbance and

the 1000rpm sample shows the lowest absorbance while entering the visible region. From

530nm to 570nm which is the median of wavelength is 550nm, the trend of the graph is

dropping (in form of a convex curve) and the median of each absorbance starting from

4000rpm A=0.3, 3000rpm A=0.27, 2000rpm A=0.25 and 1000rpm A=0.22. By referring to

the electromagnetic spectrum, it could be concluded that the obtained readings in the

middle of the visible spectrum which is around 550nm to 560nm where the absorbances

show the changing. From 570nm to 800nm, the absorbances of all the samples are slightly

41

decrease. The median of the wavelength is 685nm and the absorbances observed are

A=0.25 for 4000rpm, A=0.22 for 3000rpm, A=0.18 for 2000rpm, and A=0.1 for 1000rpm.

By referring to the electromagnetic spectrum, the absorbances observered at this median of

wavelength occur at NIR region.

4.2 Conclusion

Based on overall results obtained, the trend of graph shows all the absorbance

achieve maximum peak in UV region, dramatically drop at near visible, the 4000rpm

device shows the highest absorbance at all trends of graph. This phenomenon is related to

the thickness obtained. At 4000rpm spin speed, it should adhere the thinnest active layer

solvent. It will allow most of the UV, Vis and NIR to be absorbed by the layer. Followed

by the 3000rpm, 2000rpm and 1000rpm. For the 1000rpm device, it shows the lowest

absorbance compare to all samples due to the thickest active layer obtained. Even it has the

weakest absorbance but it allows the light to be trapped the most due to the highest

thickness and surface roughness obtained.

4.3 Experimental results I-V Curve evaluated based on the

spin speeds:

This experiment was conducted to observe the relation between the thickness of

the active layer with the current and voltage. The recorded readings are the open circuit

voltage (Voc), short circuit current (Isc), maximum current (Imax), maximum voltage

(Vmax). After obtaining all the information, the information is plugged into the formula to

evaluate the Fill Factor (FF) and the power conversion efficiency (PCE). All solar cells

reliability is determined by the PCE obtained. The Voc, Isc, Imax and Vmax could be

obtained from the I-V curve graph. The typical I-V curve graph is shown in the figure 4.3.

C) Efficiency Measurement

FF = Fill factor Isc = Short circuit current Voc = Open Circuit Voltage Plight = Incident light power

42

Figure 4.3 Typical I-V Curve for Solar Cells [50]

To locate the Voc and Isc, it requires the plotted graph (cross-point) to touch on

the 0 of x-axis and 0 of y-axis. When the graph cross at the 0 of x-axis which is Voltage

axis, the Isc value could be obtained. When the graph cross at the 0 of y-axis which is

current axis, the Voc value could be obtained. The experimental of spin speed investigation

results was shown in the figure 4.4 and the values required are recorded in table 4.2.

Figure 4.4 I-V Curve obtained by each device

43

Table 4.2 The results obtained via SPA inspection (Plight is fixed)

By comparing the obtained results with the ideal organic solar cells I-V curve

reviewed previously, obviously the huge error could be observed. The Voc supposedly

occur at the positive voltage region of the graph and the Isc supposedly occur at the

negative current region of the graph. The value of FF also supposedly obtained as a

positive value because the FF indicates the ratio of the maximum power from the solar

cells to the product of Voc and Isc.[45]

The best power conversion efficiency is obtained by 1000rpm device (PCE

percentage = 1.2484488 x 10-5

) with the thickest active layer eventhough the I-V curve

obtained indicates the graph of degraded devices. The degradation could occur during

illumination and in the dark and the main cause of degradation involving organic

(polymer) as the active layer is the exposure of the active layer material towards the

oxygen and water (H2O).[43] Others sample show worse performance especially the

4000rpm sample. Due to the thinnest active layer produced, the process of exciton

production can’t be maximized and the dissociation process is attenuated by the reduced of

Donor- Acceptor interface number.

This exposure could occur during fabrication process where the active layer

solvent preparation isn’t made in the proper glove box where the oxygen is sucked up out

of the box and dried the atmosphere for whole fabrication duration from solvent

preparation to the deposition of the solvent on the ITO glass substrate. The importance of

ensuring the ITO substrate after cleaning process is also to prevent the deposited

PEDOT:PSS layer to dissolve with water on the substrate (PEDOT:PSS can’t dissolve

with Chloroform and Dichlorobenzene).[43]

Another trial of experimental is done to replace the usage of the TiO2 to capture

electrons and blocking holes due to the problem of pasting the TiO2 on the active layer.

The TiO2 dry in such a short period and crusty. When the paste is dried, it’s hard to adhere

Spin Speed (RPM)

Voc (V) Isc (A/cm2) FF Plight

(mW) PCE (%)

1000 (40nm)

-32.0000E-3 80.1478E-9 -48.6776E+0 1000 1.2484488 x 10-5

2000 (30nm)

-10.0000E-3 48.9684E-9 -251.0371E+0

1000 1.2293 x 10-5

3000 (20nm)

-48.0000E-3 135.4012E-9

-14.6055E+0 1000 1.075441 x 10-5

4000 (10nm)

-26.0000E-3

19.4816E-12

-121.8237E+0

1000 6.17063 x10 -11

44

with the substrate. As a solution, the application of carbon as a counter electrode to capture

electrons is introduced.

The experimental only conducted using a 1000rpm due to the ideal thickness

obtained and no more PCBM left. The figure 4.5 below shows the I-V curve obtained with

the evaluation recorded in the table 4.3.

Figure 4.5 I-V Curve obtained by a 1000RPM with carbon

There is a huge different PCE obtained from 1000rpm device without carbon as a

counter electrode compared to with carbon as counter electrode device. The counter

electrode serves to transfer electrons from external circuit to polymer and fullerene in the

active layer. The enhanced PCE is about 550 times after applying carbon on the ITO

surface of cathode side. It means the mobility of the electrons have been enhanced. The

potential of electrons to be captured by cathode also are being improved as well.

45

Table 4.3 The results obtained via SPA inspection (Plight is fixed) with carbon applied device

4.4 Conclusion

The main objective to investigate the new morphology of active layer by adding

CdTe together with MEH PPV: PCBM can’t be achieved due to insufficient of the PCBM

material. The experiment on using Dichlorobenzene also cannot be conducted due to this

issue. But in the end of the experimental, some new innovation has been reached where the

carbon is introduced as counter electrode and establishes better mobility for electrons to

diffuse to the cathode.

Spin Speed (RPM)

Voc (V) Isc (A/cm2) FF Plight

(mW) PCE (%)

1000 (40nm)

-32.0000E-3 80.1478E-9 -48.6776E+0 1000 1.2484488 x

10-5

2000 (30nm)

-10.0000E-3 48.9684E-9 -251.0371E+0

1000 1.2293 x 10-5

3000 (20nm)

-48.0000E-3 135.4012E-9

-14.6055E+0 1000 1.075441 x

10-5

4000 (10nm)

-26.0000E-3

19.4816E-12

-121.8237E+0

1000 6.17063 x10 -11

1000 (40nm) Carbon

2.2000E-3

180.1765E-6

173.0310E+0

1000 6.8588 x10-3

46

Chapter 5 Business plan

5.1 Introduction

Due to the appropriate climate in our country which is summer for the whole year, it

turns to be a huge advantage to use a green, renewable energy harvesting method. It will

become good replacement the Gas usage to generate electricity. Regarding of a lot

development and approaching in order to increase the efficiency with lower cost material,

the price is decreased. This is a positive opportunity to trigger a huge development in

producing solar cell including organic solar cell which costs the cheapest among the

photovoltaic devices.

The latest news is Panasonic Malaysia Sdn Bhd is launching new solar

manufacturing base in Kulim Hitech Kedah, predicted to start operation this December

2012. Panasonic ready to spend RM1.82 billion to develop this facility which can produce

approximately 300MW a year.

5.2 Market analysis including effect on society and

environment

Nowadays, peoples realize the importance of having a green, environmental

unharmful energy sources. The global warming are the biggest issues and always being

discuss among peoples. The technology and the lifestyles are enhanced from days to days.

All the technology also requires energy source.

The globalization is involving the whole world and all the countries won’t be left

behind. If the hydro power plant and gas power plant are built in huge number, many trees,

jungle and hills need to be cut down due the space required in building those power plants.

The trees are contributing the most in air circulation and stabilize the atmosphere. If the

trees are cutdown, the atmosphere wont be stabil no more yet causing to the global

warming.

47

Worse, this phenomenon could lead to the big flood when the trees are gone and the

hills are shrinked, there are no more rain fall filtering. The rains will directly fall to the soil

without being scattered by any filter and the soil cant manage to absorb all the water inside

at the very same time. This phenomenon will cause a big flood.

Thus, the invention and application of solar cells is reasonable for society especially

the organic solar cells. Inside the earth is rich with polymer materials and yet not all of are

investigated. The transparency of the polymer solar cells make it suitable to be installed as

a window of the house and vehicle. The flexibility of the plastic substrates make it

appropriate to be mounted on the clothes and even the umbrella. So a lot of space can be

saved. This advantages make it suitable to earn profit as much as possible in the marketing.

But, due to it’s low power conversion efficiency and short lifetime (easily degrade when

exposed to the water), a lot of effort to investigate and proper solutions are required to

ensure the marketing profit can be achieved.

The previous solar cells was introduced before the organic solar cells which is the

inorganic solar cells like silicon solar cells is providing splendid in power conversion

efficiency, the strong reliability against the outdoor weather, and longer lifetime. The

material used as a main substrate which is the sand is easily obtained everywhere and

easily processed too. But the capital cost for whole process is bigger compared to the

organic solar cells. It requires more equipment, solvents, dopants, longer fabrication

duration, and the processes are even more complex. The substrates also have heavier

weight and solid form; make it appropriate to be mounted on the roof or on the stand only.

5.3 Business structure

In order to become a good entrepreneur, several characteristic of successful

entrepreneur needs to be practiced. One of them are the entrepreneur should has passion

for the business; means the business require full commitment and full desire. The

entrenpreneur also need to focus on customer’s needs and demand. This is important to

avoid producing some wasting products and too risky to obtain customers. The business

won’t succeed if the product can’t brings benefit. In experiments of innovating the

product’s stage, failure is first step to success for tenacity entrepreneurs. Tenacity is

important because it show a potential customer the commitment of the entrepreneur about

his or her new products and services. To enhance or repair the error of the product, a

proper execution intelligence is required. It is important in order to analyse the opportunity

or troubleshooting to overcome the error thus enhancing the product performance.

48

Innovation is also important element in entrepreneurship, which can be defined by

a combination of the vision to create a good idea and the perseverance and dedication to

remain with the concept through implementation. They are four types of innovations which

are invention, extension, duplication, and synthesis. The invention innovation means the

product is totally new product, new service and using new processing method. The

extension innovation means the new use or different application of an already existing

product, service, or process. The duplication innovation means the creative replication of

an existing concept. The synthesis innovation means the combination of existing concepts

and factors into a new formulation or use.

To sustain the development of this polymer: fullerene solar cells, it requires bigger

material cost due to higher cost for the active layer conductive polymer powder like P3HT

and PCDTBT. The cooperation from outsiders or public also might needed to contribute a

share in developing and experimenting the new outcome of a new device.

5.4 Costing

The total estimated cost for this project consisted by several group of costing. They

are capital cost, operational cost, and material cost.

5.4.1 Capital cost

The capital cost is the cost estimated for starting the whole project such as the cost

for building the laborotary, protocol dress like bunny suit, glove, mask, safety shoes, and

the handling tools such as a tweeser, beaker and the equipments.

The proper laboratory will cost about RM200 to RM400 million including all the

facility like air circulation system (for ensuring the cleanliness and the best temperature of

the laboratory for proceeding any fabrication process), piping, 3 phase electrical wiring

installation with proper busbar and distribution board, and the suitable furniture like tables,

chairs and lockers.

To start fabricating the device, proper dresses are required due to the safety of the

personnel and the cleanliness of the device. The proper dress is including the coat or bunny

suit, mask, safety shoes, the latex glove or the thick glove (for handling high temperature

or high corrosive chemical), and of course, proper hand tools are also required to handle

the substrates or samples and chemicals like tweeser, beaker and etc. The estimated cost

for all of this items are approximately RM20k or below.

49

The invention of this sandwiching-polymer solar cells also can reduce the capital

cost because this device didn’t require the deposition of Aluminum as cathode. The

estimated of reduced cost is approximately RM200k (the price of the Modu-Lab Physical

Vapour Deposition). The main equipments for fabricating this device are Spin Coater

which is cost about RM18k, Hot Plate’s cost is about RM10k, and the air pump’s cost is

about RM5k. The characterization and inspection equipments also are required in order to

inspect the performance of the polymer solar cells. The required equipments are

Semiconductor Parametric Analyzer (SPA) which is cost about RM30 to 50k, Atomic

Force Microscopy (AFM) which is cost about RM70k to RM350 million, and Lamda

UV/Vis Spectrometer which is cost about RM26k to 30k. The evaluation of the total

capital cost which is divided into two types; the eternal property (long lasting properties)

and temporary property (short period lasting properties) can be observed in the table 5.1.

The purpose of dividing the properties into eternal property and temporary property is to

ease the process of budgeting for maintenance and restocking the property. Eternal

property is considered as a long lasting property and the gap for maintenance scheduling is

quite far. Compared to the temporary property which is easily worn out and running out of

stock.

Assets Type of Asset Price

Laboratory + air circulation

system + piping + 3 phase

electrical wiring with busbar

Eternal property RM200 000 000

Laboratory Tables Eternal property RM5000

Laboratory Chairs Eternal property RM2000

Wardrobe Eternal property RM500

Lockers Eternal property RM1500

Computers Eternal property RM20 000

Bunny Suits/ Laboratory

Coats

Temporary property RM4000

Latex Gloves Temporary property RM300

High Temperature Resistant

Gloves

Temporary property RM150

Safety Shoes Temporary property RM1200

Hair Cover Temporary property RM100

Handling Tools Eternal property RM3000

Spin Coater Eternal property RM18 000

Hot Plate Eternal property RM10 000

Air Pump Eternal property RM5000

50

Table 5.1 the minimum estimated price list of capital assets

5.4.2 Operational cost

To operate the equipments, it requires a big load of electricity like 415V 3 phase

supply. The deionized water also required in cleaning process. The cost for both operation

are approximately RM5k monthly. The equipments maintenance also is considered under

this operational cost which is estimated around RM10k a year.

Operation Period Cost

Electrical Supply Once a month RM3500

Deionized water supply Once a month RM1500

Equipment Services/

Maintenance

Once a year RM10 000

Total cost estimated yearly RM70000

Table 5.2 the price list of operational cost yearly

5.4.3 Material cost

The material cost is including the chemicals, solvents, and powder material cost

such as Hidrochloric, Acid Acetic Nitric, Acetone, Chloroform, epoxy,PEDOT: PSS,

Dichlorobenzene, MEH-PPV, TiO2, and CdTe. The price and the quantity of each material

can be observed in the table 5.3.

Semiconductor Parametric

Analyzer

Eternal property RM30 000

Force Atomic Microscopy Eternal property RM70 000

Lamda UV-Vis

Spectrometer

Eternal property RM26 000

Total assets cost for the lowest budget RM200 196 750

51

Table 5.3 the price list of the materials used with available quantity

5.5 Conclusion

From the market analysis, it can be concluded that this polymer: fullerene might

have a great potential to challenge the others solar cells like silicon solar cells which cost

more expensive and reach the limit of enhancement. The total estimated capital cost is

RM200, 179 000. For the operational cost to run a laboratory yearly, it is estimated aroun

RM70k. The material cost that can produce around 150 to 200 samples is estimated around

RM12, 791.50.

The approach of this polymer: fullerene solar cells are using the extension

innovation which provides some major changes in the structure and active layer

morphology.

Material Quantity Price

MEH-PPV (polymer) 1g RM2250

PC60BM (fullerene) 1g RM894

PC70BM (fullerene) 1g RM2694

CdTe 5g RM434

TiO2 50g RM593

PEDOT: PSS 100mL RM894

Chloroform 500mL RM122.50

Dichlorobenzene 6L RM3002

Acetone 205L RM57

Epoxy Resin 100mg RM638

Hidrochloric 2.5L RM368

Acid Acetic Nitric 19L RM805

ITO glass 1piece = (1m x1m) RM40

Total material cost for a minimum amount order RM12791.50

52

Chapter 6 Conclusion and future

work

6.1 Conclusion

In the first chapter, the history and the development of inorganic and organic solar

cells are studied to get the image and basic working principle of solar cells. The purpose of

investigation is to understand the mechanism of each process in order to convert photon

(sun light) to charge carrier (electrons holes pair) and dissociated to the external circuit or

load. The target was achieved and chapter 2 was proceeded to get some idea on structuring

the device.

A lot of literatures were reviewed in order to find the finest tune of solvents in term

of weight ratio, the appropriate dilutions, the morphology of the active layer, the ideal

temperature for annealing processes with time duration, the ideal of spin speed for

depositing the PEDOT: PSS layer with time duration, the suitable solutions for cleaning

purpose, the deposition methods, laboratory protocols and Material Safety Data Sheet

(MSDS). Not only MEH PPV: PCBM solar cells is reviewed, but the P3HT: PCBM and

PCDTBT: PCBM solar cells as well. This is because the reviewed information can be used

for any further future work. Once all the parameter is studied, the methodology of

fabricating the device can be engineered and run card can be prepared.

After obtaining the information on the device itself and the image of the device

structure, the main process is decided by using spin coating to deposit the solvents on the

substrate. The spin speeds are varied to four spin speed which are 1000rpm, 2000rpm,

3000rpm, and 4000rpm in order to investigate the ideal spin speed need to be used to get

the ideal thickness of the active layer. The spin speed for depositing the PEDOT:PSS layer

is fixed to 2500rpm for all devices due to its ideal spin speed investigated by reviewing the

jurnal. The temperature for annealing purpose is set to 90°C for 5. The required etching

solvent also is identified.

After done fabricating the devices of 1000rpm, 2000rpm, 3000rpm, and 4000rpm,

those devices were inspected using UV/Vis Spectroscopy, Atomic Force Microscopy and

Semiconductor Parametric Analyzer to analyse UV/ Visible spectrum with the absorbance,

the surface roughness with the thickness of each active layer, and to analyse and evaluate

53

the efficiency of each device. The best results is obtained by the 1000rpm device but every

device showed the degraded I-V curve. So another litereature review was done in order to

find the problem theoretically. The application of TiO2 also is not helping at all infact, it

won’t adhere to the substrate by using dr blade deposition method. Practically, every

device was degraded due to exposed to the free air during fabrication process and maybe

the substrates were’nt dried properly after the cleaning process. Thus, to find another

material to replace the usage of the TiO2, the carbon was introduced and resulting a huge

enhancement of power conversion efficiency. The figure 6.1 shows a new structure after

modification being made. Carbon can be applied on the ITO by burning with the candle.

cathode

anode

Figure 6.1 New structure of polymer: fullerene solar cells

Glass

ITO

PEDOT:PSS

Carbon

Polymer: Fullerene Blend

54

6.2 Future work

In the future, a lot of fabrication methods need to be improved. To ensure the

fabrication process is made without involving degradation to occur; the cleaning process,

the solvents preparation, the depositions process and the annealing process are required to

be processed in the glove box where the oxygen is pumped out of the box. Wait until the

top and bottom substrates are adhered together (the epoxy dried). Then take out the device

out of the glove box for inspection purpose.

Based on the results varied by the spin speed, it can be concluded that the thicker

the active layer, the better performance is obtained. So, for the next active layer deposition

process, no need to use the spin coating method. Infact, try to deposit the active layer

directly on the PEDOT: PSS layer and anneal it on the hot plate at 90°C for 5 minutes

(until the solvent dry and adhere to the substrate). The figure6.2a, 6.2b and 6.2c will

project the whole process mentioned.

Figure 6.2

Figure 6.3

Figure 6.4

Instead of applying new method of fabrication, the new structure and material used

to contruct the device also need to be considered. For example, the usage of carbon as

counter electrode need to be maintained.

CdTe also can be used in the active layer by mixing it together with polymer and

fullerene. It will provide a nanoscale interpenetrating networks where it can capture the

electrons and holes before recombination occur and distribute to the anode and cathode.

MEH PPV also can be replaced with P3HT and PCDTBT. These two polymers were

covered in the chapter two to obtain some informative information. Moreover, these two

materials are harder to degrade, compared to the MEH PPV which is easier degrading once

exposed to the oxygen or water.

The fullerene PC60BM also can be replaced using PC70BM due to its characteristic

which has better absorption. The experimental with using different dilution also could be

90°C

55

conducted to observe each potential of dilution to contribute to the performance of each

device.

The dichlorobenzene (DCB), tolune, and chloroform can be used to dissolve each

polymer: fullererne material. The dilution can be used as a stand alone dilution or mix. For

a mixed dilution, it can be 1: 1 weight ratio of DCB and CF.

56

List of publications

Papers: -

Exhibition: Final Year Project Expo (FYPEX) held by School Of

Microelectronic (SoME) UniMAP on 13 March 2013 (Winning a

Bronze Medal)

Conferences attended: -

57

References

1. K.Inpor, S.Rabaenko, P. Boonchan, C. Junin, C. Euvananont, S. Sahasithiwat, P.

Limthongkul, C. Sae-Kung, P. Sichanugrist and C. Thanachayanont, “Bulk

Heterojunction MEH-PPV:TiO2 Porous Structured Solar Cell” 12120 Pathumthani

Thailand.

2. Quynh Nhu Nguyen Truong, Nguyen Tam Nguyen Truong, Chinho Park and Jae

Hak Jung. “Study of MEH-PPV:PCBM active layer morphology and its

application for hybrid solar cells performance”, 712-749 Gyeongsan, Republic of

Korea, March 2011.

3. S. Alem, T. Chu, C. Tse, Salem Wakim, J. Lu, R. Movileanu, Y.Tao, F. Belanger,

D. Desilets, S. Beaupre, M. Leclerc, S. Rodman, D. Waller, R. Gaudiana. “Effect

of mixed solvents on PCDTBT:PC70BM based solar cells”, MA 01852, USA,

2011.

4. Salima Alem, Remi de Bettignies, and Jean-Michel Nunzi. “Efficient polymer-

based interpenetrated network photovoltaic cells”, 49045 Angers, France, March

2004.

5. DavidDuche , PhilippeTorchio, Ludovic Escoubas, Florent Monestier, Jean-

Jacques Simon, Franc-ois Flory, Ge´ rardMathian. “Improving light absorption in

organic solar cells by plasmonic contribution”, 13451 Marseille Cedex 20, France.

February 2009.

6. Liu Xiao-Dong, Zhao Su-Ling, Xu Zheng, Zhang Fu-Jun, Zhang Tian-Hui, Gong

Wei, Yan Guang, Kong Chao, Wang Yong-Sheng, and Xu Xu-Rong.

“Performance improvement of MEH-PPV:PCBM solar cells using bathocuproine

and bathophenanthroline as the buffer layers”, Beijing 100044, China. January

2011.

7. Lili Xue, LeijingLiu, QiangGao, ShanpengWen, JiatingHe, WenjingTian. “Planar-

diffused photovoltaic device based on the MEH-PPV/PCBM system prepared by

solution process”, Changchun 130012, PR China. December2008.

8. Elizabeth Alice Thomsen. “Characterisation Of Materials For Organic

Photovoltaics”, University of St. Andrews. 2008.

9. Sandeep Kumar and Thomas Nann. “First solar cells based on CdTe

nanoparticle/MEH-PPV composites”,Freiburg D-79104, Germany. April 2004.

58

10. Sheila G. Bailey Glem, Jerry D. Harris, Aloysius E Hepp Glem. “Thin-Film

Organic-Based Solar Cells for Space Power”, Cleveland, Ohio. August 2002.

11. Riski Titian Ginting, Chi Chin Yap, Muhammad Yahaya and Muhamad Mat

Salleh. “MEH-PPV: PCBM Solution Concentration Dependence of Inverted Type

Organic Solar Cells Based on Eosin-Y-coated ZnO Nanorod Arrays”, Selangor,

Malaysia.

12. Hsiang-Yu Chen, Michael K. F. Lo, Guanwen Yang, Harold G. Monbouquette,

and Yang Yang, “Nanoparticle-assisted High Photoconductive Gain in Composites

of Polymer and Fullerene”, Macmillan Publishers Limited, 2008.

13. O. Ourida et al. / SATRESET, Vol. 1, No. 3, pp. 90-92, September 2011

14. Transactions On Electrical And Electronic Materials Vol. 13, No. 2, pp. 98-101,

April 25, 2012

15. Gang Li, Vishal Shrotriya, Yan Yao, Jinsong Huang and Yang Yang;

“Manipulating regioregular poly(3-hexylthiophene) : [6,6]-phenyl-C61-butyric

acid methyl ester blends—route towards high efficiency polymer solar cells”,

Journal of Materials Chemistry, 11th June 2007.

16. Jenna deBoisblanc, Synthesis and Characterization of P3HT:PCBM Organic Solar

Cells, Senior Thesis, May 2010.

17. Giovanni Fanchini, Steve Miller and Manish Chhowalla, In situ

photoluminescence and Raman study of nanoscale morphological changes in

organic photovoltaics during solvent vapor annealing.

18. Young Min Nam, June Huh and Won Ho Jo; Optimization of thickness and

morphology of active layer for high performance of bulk-heterojunction organic

solar cells, Solar Energy Materials & Solar Cells 94 1118–1124, 2010

19. Kaloian Koynov, Ayi Bahtiar, Taek Ahn, and Christoph Bubeck; “Molecular

weight dependence of birefringence of thin films of the

conjugated polymer poly.2-methoxy-5-.28-ethyl-hexyloxy.-1,

4-phenylenevinylene”, Applied Physics Letters Volume 84, Number 19, 10 MAY

2004.

20. Nabok, Alexei “Organic and Inorganic nanostructures” Artech House MEMS

series, 2005.

21. Sigma-Aldrich, “Poly (3-hexylthiophene-2,5-diyl)”, Product Information.

22. Zhicai He , Chengmei Zhong , Xun Huang , Wai-Yeung Wong , Hongbin Wu ,

59

Liwei Chen , Shijian Su , and Yong Cao, “Simultaneous Enhancement of Open-

Circuit Voltage, Short-Circuit Current Density, and Fill Factor in Polymer Solar

Cells”, Adv. Mater. 23, 4636–4643, 2011.

23. Dong Hwan Wang, Do Youb Kim, Kyeong Woo Choi, Jung Hwa Seo, Sang Hyuk

Im, Jong Hyeok Park,O Ok Park, and Alan J. Heeger, “Enhancement of Donor–

Acceptor Polymer Bulk Heterojunction Solar Cell Power Conversion Efficiencies

by Addition of Au Nanoparticles”, Angew. Chem. Int. Ed. , 50, 5519 –5523, 2011.

24. Bo Wu, Than Zaw Oo, Xianglin Li, Xinfeng Liu, Xiangyang Wu, Edwin Kok Lee

Yeow, Hong Jin Fan, Nripan Mathews and Tze Chien Sum, “Efficiency

Enhancement in Bulk-Heterojunction Solar Cells Integrated with Large-Area Ag

Nanotriangle Arrays”, The Journal of Physical Chemistry C, 2012.

25. http://www.ossila.com/datasheets/Ossila_PCDTBT_data_sheet_v2.pdf

26. Ta-Ya Chu, Salima Alem, Pierre G. Verly, Salem Wakim and Jianping Lu,

“Highly efficient polycarbazole-based Organic Photovoltaic Devices”, Appl. Phys.

Lett. 95, 063304,2009.

27. Craig H. Peters, I. T. Sachs-Quintana, William R. Mateker, Thomas Heumueller,

Jonathan Rivnay, Rodigo Noriega, Zach M. Beiley, Eric T. Hoke, Alberto Salleo,

and Michael D. McGehee, “ The Mechanism of Burn-in Loss in a High Efficiency

Polymer Solar Cell”, Adv. Mater. 24, 663–668, 2012.

28. Craig H. Peters, I. T. Sachs-Quintana, John P. Kastrop, Serge Beaupre, Mario

Leclec, and Michael D. McGehee, “High Efficiency Polymer Solar Cell with Long

Operating Lifetimes”, Adv. Mater,1,491-494, 2011.

29. S. Alem, Ta-Ya Chu, Shing C. Tse, S. Wakim, Jianping Lu, R. Movileanu, Ye

Tao, F. Belanger, D. Desilets, S. Beaupre, M. Leclrec and Sheila Rodman, “Effect

of mixed solvents on PCDTBT:PC70BM based solar cells”, Organic Electronics

12, 1788-1793, 2011.

30. Abd.Rashid b. Mohd Yusoff, “Inverted Organic Solar Cells with TiOx cathode and

Graphene Oxide anode buffer layers” Solar Energy Materials & Solar Cells 109

63–69, 2013.

31. Yang Shao-Peng, Kong Wei-Guang, Liu Bo-Ya, Zheng Wen-Yao, Li Bao-Min,

Liu Xian-Hao and Fu Guang-Sheng, “Highly Efficient PCDTBT:PC71 BM Based

Photovoltaic Devices without Thermal Annealing Treatment”, CHIN. PHYS.

LETT. Vol. 28, No. 12 128401, 2011.

32. Shizuyasu Ochiai, Masaki Uchiyama, and Santhakumar Kannappan “Evaluation of

the Performance of an Organic Thin Film Solar Cell Prepared Using the Active

Layer of Poly[[9-(1-octylnonyl)-9H-carbazole-2.7-diyl]-2.5-thiophenediyl-2.1.3-

60

benzothiadiazole-4.7-Diyl-2.5-thiophenediyl]/[6,6]-Phenyl C71 Butyric Acid

Methyl Ester Composite Thin Film” Department of Electrical Eng., Aichi Institute

of Technology, 1247 Yakusa, Toyota 470-0392, Japan October 31, 2011.

33. Organic Solar Cell, Universita Degli Studi Di Padova.

34. “Recent Organic Solar Cell Technology & Market Forecast” (2010~2015) 2nd

Edition Solar&Energy Co., Ltd. April. 2011.

35. Marcos Soldera, Kurt Taretto, and Thomas Kirchartz “Comparison of device

models for organic solar cells: Band-to-band vs. tail states recombination”

Departamento de Electrotecnia, Universidad Nacional del Comahue, Buenos Aires

1400, 8300 Neuque´n, Argentina, Department of Physics, ImperialCollege

London, South Kensington SW7 2AZ, UK 4 May 2011.

36. Kangmin Wu “Advanced Materials and Fabrication Methods for Organic Solar

Cells” Thesis, Mc Master University ,11 January 2010.

37. Laxman Anishetty ,“Schottky behavior of organic solar cells with different

cathode deposition methods” thesis, Master of Science Degree in Electrical

Engineering.

38. Yen-Ju Cheng, Sheng-Hsiung Yang, and Chain-Shu Hsu ,“Synthesis of

Conjugated Polymers for Organic Solar Cell Applications”,Department of Applied

Chemistry, National Chiao Tung University, 1001 Ta Hsueh Road, Hsin-Chu

30049, Taiwan May 7, 2009.

39. “Photolitography”, Fabrication Fundamental EMT261 SoME, UniMAP 2010

40. Kang-Shyang Liao, Soniya D. Yambem , Amrita Haldar , Nigel J. Alley and

Seamus A. Curran, “Designs and Architectures for the Next Generation of Organic

Solar Cells”, Institute for NanoEnergy, Department of Physics, University of

Houston, Houston, TX 77004, USA ,School of Physical Sciences, Dublin City

University, Glasnevin, Dublin 9, Ireland March, 2010.

41. Zhen Guo and Li Tan, “Fundamentals and Applications of Nanomaterials”, Artech

House, 2009.

42. Dr. Todd J. Kaiser, “Introduction, Safety and Protocol”, EE580 Solar Cell Basics

for Teachers; Montana State University: Solar Cells.

43. Frederik C. Krebs, Kion Norrman, J. Mikkel, "Stability/ degradation of Polymer

Solar Cells", National Laboratory for Sustainable Energy, Technical University of

Denmark, ScienceDirect, 2008.

44. http://www.stevens.edu/lmsi/Files/How_to_use_AFM_simple_instruction.pdf

45. http://pveducation.org/pvcdrom/solar-cell-operation/fill-factor

61

46. Brian R. Saunders, “Hybrid polymer/nanoparticle solar cells: Preparation,

principles and challenges”, Journal of Colloid and Interface Science 369,

Manchester 2012.

47. http://www.slideshare.net/khanmtk/study-of-charge-transport-mechanism-in-

organic-and-organicinorganic-hybrid-systems-with-application-to-organic-solar-

cells.

48. Ricardo K. M. Bouwer, "Fullerene bisadducts for organic photovoltaics" Stratingh

Institute for Chemistry and Zernike Institute for Advanced Materials, University of

Groningen, The Netherlands, 2012.

49. http://www.osa-direct.com/osad-news/323.html

50. Klaus Petritsch, " Organic Solar Cell Architectures", Cambridge and Graz, July

2000.

51. http://www.southampton.ac.uk