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R. Kopecek – What is behind c-Si material?
What is behind c-Si material?
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R. Kopecek – What is behind c-Si material?
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From quartz to MGFrom quartz to MGFrom quartz to MGFrom quartz to MG----SiSiSiSi Quartz: sources and purity
MG-Si production process
Purification processesPurification processesPurification processesPurification processes Chemical purification
- Siemens process
- Fluidized bed reactor
- Alternative processes
Metallurgical purification
- Different processes for compensated material
CrystallisationCrystallisationCrystallisationCrystallisation Mono c-Si crystallisation
Multi c-Si crystallisation
Compensated material and cells
Ribbons and sheets
Cutting
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quartz and MG-Si
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Firma Elkem, Norwegen
quartz: different quality and price
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Firma Elkem, Norwegen
Elkem produziert
ca. 49% des Welt-
Siliziumaufkommens
200 000 t pro Jahr
für
- Aluminium-Industrie
- Chemie (Silikone)
- Halbleiter-Industrie
PV benötigte in 2008
ca. 50 000 t pro Jahr
SiO2 + C = Si + C02mit Hilfe von
Elektrizität
Reinheit: 98%
MG-Si
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purification
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chemical purification
9R. Kopecek – What is behind c-Si material?
Erforderliche Reinheit:
für Elektronik-Industrie:
98 % -> 10-13 %
für Photovoltaik
98 % -> 10-9 %
klassisches Verfahren:
- Destillation von SiHCl3- Abscheidung von
Silizium aus der
Gasphase (Abb. links)
chemical purification
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Chemical purification
R. Kopecek – What is behind c-Si material?
Siemens-method (poly-Si)
chemical purification
R. Kopecek – What is behind c-Si material?
Poly-Si manufacturer and their expansion plans
chemical purification
(Estimation of HEMLOCK, 2007)
R. Kopecek – What is behind c-Si material?
Poly-Si capacity in 2005 (30.000t)
chemical purification
R. Kopecek – What is behind c-Si material?
alternative purification methods
MG-Si
CHEMICAL PURIFICATION METALLURGICAL PURIFICATION
Siemens rod
Hemlock…
Fluidized bed
MEMC, Wacker, REC…
Vapor to liquid depos.
Tokuyama
Direct route
FESIL+Sunergy
“Elkem´s route”
Elkem
“Dow´s route”
“6Nsilicon route”
“Timinco route”
o use of silane or TCS
o deposition with CVD (1350-1600°C)
o Very pure Si (10N)
o Use of very pure quarts and carbon black
o purification of the MG-Si melt
o Pure Si (6N)
EU: CC SP1 EU: CC SP1 EU: FoXy
ISC bilateral
ISC bilateralISC bilateral
ISC bilateral
ISC bilateral
?
Chemical and metallurgical purification
ISC bilateral
R. Kopecek – What is behind c-Si material?
Chem. Reinigung: Fluidized bed method (MEMC, Wacker, REC)
MEMC: 3200 t in 2005 poly-Si (7000 t/a Kapazität von 2010)
Wacker: ca. 100-200 t in 2005 SoG-Si ? (500 t/a von Mitte 2006)
STATUS:
REC: ca. 6000 t/a von 2008 SoG-Si ?
chemical purification
R. Kopecek – What is behind c-Si material?
Chem. Reinigung: Vapour to Liquid Abscheidung
(Tokuyama)
chemical purification
R. Kopecek – What is behind c-Si material?
Chem. Reinigung: Vapour to Liquid Abscheidung
(Tokuyama)
chemical purification
R. Kopecek – What is behind c-Si material?
Chem. Reinigung: Vapour to Liquid Abscheidung
(Tokuyama)
chemical purification
R. Kopecek – What is behind c-Si material?
Chem. Reinigung: Vapour to Liquid Abscheidung
(Tokuyama)
chemical purification
R. Kopecek – What is behind c-Si material?
Metall. Reinigung: Direct route (SINTEF, ECN)
metallurgical purification
R. Kopecek – What is behind c-Si material?
Metall. Reinigung: Direct route (SINTEF, ECN)
metallurgical purification
R. Kopecek – What is behind c-Si material?
Metall. Reinigung: Elkem´s route
→ Efficiency for large area (12.5x12.5 cm2) industrial solar cells: >16%
→ High efficiency solar cells (2x2 cm2): 18.1%
metallurgical purification
R. Kopecek – What is behind c-Si material?
Metall. Reinigung: Elkem´s route
metallurgical purification
R. Kopecek – What is behind c-Si material?
Metall. Reinigung: Elkem´s route
metallurgical purification
R. Kopecek – What is behind c-Si material?
Metall. Reinigung: Dow Corning´s route
?
→ Efficiency for large area (12.5x12.5 cm2) industrial solar cells: >16%
→ High efficiency solar cells (2x2 cm2): ???%
metallurgical purification
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crystallisation
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different techniques
Crystallization from the melt:(crystal growth, solidification, freezing)
1. Ingot-Method:• mono c-Si: CZ (1950), FZ (1952)• mc-Si: Casting (1959,1970),
Directional solidification (DS) (1976)
2. Sheet, film, ribbon – Methods(min.14!):• z.B. Dendritic Web (1963), EFG (1972), RGS (1989?), DC
(2008)
other methods: CVD, LPE, ...
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Einkristallin Multikristallin
crystallisation of mono and mc-ingots
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ingot diameter
Casting: 200 kg (1997)580x580x260 mm3
CZ: 200 kg ?Ø 300 mm
FZ: Ø 200 mm ?
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FZ-technique
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FZ-ingot properties
• Diameter till 200 mm • Ziehgeschwindigkeit 2-5 mm/min (2-10 kg/h)
+ Beste Materialqualität, τ > 1 ms(Kristallfehler, O- und C-Gehalt, sonstige Fremdatome)
+ Keine Tiegelproblematik+ Konstante Dotierkonzentration
- Aufwendig, schwierig, teuer
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Cz-technique
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Anfang . . . . . Ende
Ziehdauer: bis 30 hQuartztiegel-Auflösung: 7 µm/h
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Cz-ingot properties
• Standard für Halbleiter – Industrie• Quarz – Tiegel• Durchmesser bis 300 mm,
Ziehgeschwindigkeit 1-2 mm/min (2-10 kg/h)
+ Gute Materialqualität (wenig Kristallfehler), τ ≈ 300µs+ Etwas günstiger als FZ
- Hoher O-Gehalt (Quartz-Tiegel, [O] > 1018cm-3)- Tiegelverschleiß- Mehr Verunreinigungen als FZ-Si
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hoch-p(Bor)-dotiertes Si
Keine Seed-Kristall!
directional solidification technique
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several directional sol. techniquesTiegel:• Ein Tiegel (directional solidification)• Zwei Tiegel (casting):crucible+mold• „Ohne Tiegel“: cold crucible
Wärmeabfuhr / Kristallisationsfront:• Bridgman/Stockbarger• Regelbare Heizzonen• Heat Exchanger (HEM)• Polix
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directional solidification properties
• Ingot: 100-400 kg, 3x3 - 5x5 Säulen, Höhe 20-40 cm• Abschneiden: Boden&Rand: 15 mm Oben: 20-50 mm• Ingot-Ausbeute: 85% (gesamt nach Sägen: 40%, ähnlich
wie Cz)
• Wachstumsrate: 0.1-1 mm/min (3-30 kg/h) (Cz:2-10 kg/h)• Kristallisationszeit: 5-30 h• Gesamte Zykluszeit: - 60 h
• Energieverbrauch: 8 kWh/kg (Cz:20-40 kWh/kg)
• [O]≈1017cm-3 (Cz: [O]>1018cm-3)• relativ einfache Technik und Bedienung
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properties of parameters
Minoritäten-Lebensdauer
Spez.WiderstandVersetzungsdichte
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crucible materials
Flüssiges Silizium reagiert mitpraktisch allen denkbarenTiegelmaterialien.
Kandidaten:• Quartzglas (SiO2)• Graphit• Beschichtung mit Si3N4
Wiederverwendbarkeit?
40R. Kopecek – What is behind c-Si material?
content
Grenzfläche fest-flüssig:
Cs = Cl * k0
k0 : Segregations-koeffizient
B: k0 = 0.8O: k0 = 1.25
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impurities thresholdGrenzwerte für die Degradation durch Verunreinigungen
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impurities threshold
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„Bösartige“ Verunreini-gungen (Übergangs-metalle) haben einen kleinen Segregations-koeffizienten!
impurity segregation
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today's mc-Si manufacturers
Directional Solidification
Casting
Cold crucible (EMC)
•Photowatt Polix•Crystal Systems HEM
•Bayer SOPLIN (Baysix)•Wacker SILSO•Solarex SEMIX•Kyocera•Daido Hoxan
•Sumitomo SITIX, (Photowatt)
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Bridgman/Stockbarger - Verfahren
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• Ein Tiegel (Quartzglas), viele Gußformen (beschichtet)
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Sumitomo SITIX, EPM-Madylam&Photowatt (Forschung)
R. Kopecek – What is behind c-Si material?
compensated material
• motivation• Si from metallurgical purification techniques is available
• P content in such Si materials is not negligible any more
• question: effect of compensation on Si material and solar cells?
• ingots from compensated material• definition of compensation constant
Rc=(Na+Nd)/(Na-Nd)
• depending on Na level and compensation
constant various resistivity profiles
• simple calculation with Scheil Equation
20 40 60 80 1000
2
4
6
8
10 1ppma B / 0ppma P / Rc=1 1ppma B / 0.5ppma P / Rc=3 1ppma B / 1ppma P / Rc=inf. 1ppma B / 2ppma P / Rc=-3
resi
stiv
ity [Ω
cm]
solidified fraction [%]
R. Kopecek – What is behind c-Si material?
20 40 60 80 1000
2
4
6
8
10 1ppma B 2.0ppma P Rc=-3 1ppma B 1.0ppma P Rc=inf. 1ppma B 0.5ppma P Rc=3 1ppma B 0.0ppma P Rc=1
resi
stiv
ity [Ω
cm]
solidified fraction [%]
ingots from compensated materialSimple example: Na=1ppma, various Nd content Rc=(Na+Nd)/(Na-Nd)
R. Kopecek – What is behind c-Si material?
20 40 60 80 1000
2
4
6
8
10
1ppma B 0.0ppma P Rc=1
resi
stiv
ity [Ω
cm]
solidified fraction [%]
ingots from compensated materialNa=1ppma, Nd=0ppma Rc=(Na+Nd)/(Na-Nd)
R. Kopecek – What is behind c-Si material?
20 40 60 80 1000
2
4
6
8
10
1ppma B 0.5ppma P Rc=3 1ppma B 0.0ppma P Rc=1
resi
stiv
ity [Ω
cm]
solidified fraction [%]
ingots from compensated materialNa=1ppma, Nd=0.5ppma Rc=(Na+Nd)/(Na-Nd)
R. Kopecek – What is behind c-Si material?
20 40 60 80 1000
2
4
6
8
10
1ppma B 1.0ppma P Rc=inf. 1ppma B 0.5ppma P Rc=3 1ppma B 0.0ppma P Rc=1
resi
stiv
ity [Ω
cm]
solidified fraction [%]
ingots from compensated materialNa=1ppma, Nd=1.0ppma Rc=(Na+Nd)/(Na-Nd)
R. Kopecek – What is behind c-Si material?
20 40 60 80 1000
2
4
6
8
10 1ppma B 2.0ppma P Rc=-3 1ppma B 1.0ppma P Rc=inf. 1ppma B 0.5ppma P Rc=3 1ppma B 0.0ppma P Rc=1
resi
stiv
ity [Ω
cm]
solidified fraction [%]
ingots from compensated materialNa=1ppma, Nd=2.0ppma Rc=(Na+Nd)/(Na-Nd)
R. Kopecek – What is behind c-Si material?
ingots from mc-Si and Cz-Si
0 20 40 60 80 1000,1
1
10 Cz compensated mc compensated mc reference
spec
ific
resi
stiv
ity [Ω
cm]
fraction solidified after caps removal [%]
• mc-Si ingots• reference: 0.80 Ωcm
• compensated: 0.65 Ωcm
• Cz-Si ingot• compensated: 2-10 Ωcm
• compensation coefficient Rc: 2-25
R. Kopecek – What is behind c-Si material?
solar cells from compensated ingots
• cell process• no surface texture!
• wafers from both mc-Si ingots
processed in one run
• adapted emitter diffusion
• effective bulk hydrogenation
from direct PECVD SiNx layer
• mechanical edge isolation
R. Kopecek – What is behind c-Si material?
0 20 40 60 80 10010
11
12
13
14
15
16
17
Cz compensated mc compensated mc referenceso
lar
cell
effic
ienc
y [%
]
fraction solidified after removal of caps [%]
solar cells from compensated ingots
• mc-Si cells• reference: ∅14.7%
• compensated: ∅ 15.1%
high efficiency cells can be processed with compensated material
(best cell with texture: Cz-Si 17.1%, mc-Si 16.2% )
• Cz-Si cells• compensated: ∅ 16.1%
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1
• minority carrier lifetime
• majority carrier mobility
• light induced degradation
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1
• minority carrier lifetime
0 20 40 60 80 1001
10
100Cz compensated
resistivity lifetime before gettering
ρ [Ω
cm],
τ [µ
s]
fraction solidified after caps removal [%]
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1
• minority carrier lifetime
0 20 40 60 80 1001
10
100Cz compensated
resistivity lifetime before gettering lifetime AFTER gettering
ρ [Ω
cm],
τ [µ
s]
fraction solidified after caps removal [%]
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1
• minority carrier lifetime• contamination free material for evaluation necessary
• lifetime increasing with increasing compensation
• majority carrier mobility
• light induced degradation
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1
• majority carrier mobility
0 20 40 60 80 1001
10
100Cz compensated
resistivity mobility before gettering mobility AFTER gettering
ρ [Ω
cm],
µ hall [
Vs/
cm2 ]
fraction solidified after caps removal [%]
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1
• majority carrier mobility
0 20 40 60 80 100100
150
200
250
300
Cz compensated mobility before gettering mobility AFTER gettering
µ hall [
Vs/
cm2 ]
fraction solidified after caps removal [%]
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1
• minority carrier lifetime• contamination free material for evaluation necessary
• lifetime increasing with increasing compensation
• majority carrier mobility • mobility does not change with gettering
• decreasing mobility with increasing compensation
• light induced degradation
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1
• degradation• 500W halogen lamps
• ca. 40 cm from cell
• illumination at 1 sun and heating
to about 50°C
• measurement• 3 cells for each ingot position
• measurement with sun-simulator
• measurement with sunsVoc
• light induced degradation: set-up
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1 • light induced degradation: Oi-concentration
0 20 40 60 80 1000
5
10
15
20
25
Cz compensated resistivity O
i concentration
ρ [Ω
cm],
Oi c
once
ntra
tion
[ppm
a]
fraction solidified after caps removal [%]
Rc=2
Rc=25
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1 • light induced degradation: carrier-concent.
0 20 40 60 80 100
2,0x1015
4,0x1015
6,0x1015
8,0x1015
1,0x1016
1,2x1016
1,4x1016
acceptors (boron) donors (phosphorus) N
eff= N
a-N
d
carr
ier
conc
entr
atio
n [1
/cm
3 ]
fraction solidified after caps removal
(1Ωcm)
(1.6Ωcm)
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1 • light induced degradation: results
0 10 20-25
-20
-15
-10
-5
0
(∆Voc
=8 mV)
high boron contenthigh compensation
(∆Voc
=20mV)
low boron contentlow compensation
T=50°C
∆
Voc
[mV
]
time [h]
solidified fraction 10 (first solidified) 70 80 90 100 (last solidified)
R. Kopecek – What is behind c-Si material?
properties of CM compared to Rc=1 • light induced degradation: PL spectra
1,0 1,1 1,2
0,00
0,01
0,02
0,03
0,04
0,05
0,06
low compensation
In
tens
ity (
a.u.
)
energy [eV]
high compensationT= 15K
R. Kopecek – What is behind c-Si material?
summary• with compensated material high efficiency solar cells can
be processed• lifetime increases, mobility decreases with increased
compensation level
• LID seems not to be dependent on the total B-content in the compensated Cz-Si material
• P and B may form B-P pairs suppressing the formation of B-O complexes
• Our observation was confirmed by Daniel McDonald at the EUPVSEC conference in Hambug 2009 (plenary talk)
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sheets and ribbonsString Ribbon (1980)
EFG (1972)
RGS (1989)
DC (2008)
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sawing and slicing
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industrial process – sawing
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Max. Drahtgeschwindigkeit: 15 m/s Drahtdurchmesser: 0,14 mm, Länge: 800 km
Industrielle Maschine
industrial process - slicing
74R. Kopecek – What is behind c-Si material?
material requirement for given power
How much Si is needed for 1W power?
- one 156x156mm2 mc-Si cell has a power of about 4 W
- one 156x156mm2 mc-Si wafer (180µm) weights about 12g
>>>> 3g wafer material are needed for 1W
however if the Si loss during sawing is considered (ca. 50%)
>>>> 6g of 6g of 6g of 6g of SiSiSiSi block is needed for 1Wblock is needed for 1Wblock is needed for 1Wblock is needed for 1W
>>>> 6t are needed for 1MW
>>>> ca. 50.000t are required for 8GW ca. 50.000t are required for 8GW ca. 50.000t are required for 8GW ca. 50.000t are required for 8GW
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