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R. Kopecek – What is behind c-Si material?

What is behind c-Si material?

2R. 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

1

2

3

4


quartz and MG-Si

1


Firma Elkem, Norwegen

quartz: different quality and price


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


purification

2


chemical purification


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


Siemens-method (poly-Si)



Poly-Si manufacturer and their expansion plans


(Estimation of HEMLOCK, 2007)


Poly-Si capacity in 2005 (30.000t)



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


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 ?



Chem. Reinigung: Vapour to Liquid Abscheidung

(Tokuyama)



Metall. Reinigung: Direct route (SINTEF, ECN)

metallurgical purification


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%



Metall. Reinigung: Elkem´s route



Metall. Reinigung: Dow Corning´s route

?

→ Efficiency for large area (12.5x12.5 cm2) industrial solar cells: >16%

→ High efficiency solar cells (2x2 cm2): ???%



crystallisation

3


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, ...


Einkristallin Multikristallin

crystallisation of mono and mc-ingots


ingot diameter

Casting: 200 kg (1997)580x580x260 mm3

CZ: 200 kg ?Ø 300 mm

FZ: Ø 200 mm ?


FZ-technique


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


Cz-technique


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Anfang . . . . . Ende

Ziehdauer: bis 30 hQuartztiegel-Auflösung: 7 µm/h


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


hoch-p(Bor)-dotiertes Si

Keine Seed-Kristall!

directional solidification technique


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


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


properties of parameters

Minoritäten-Lebensdauer

Spez.WiderstandVersetzungsdichte


crucible materials

Flüssiges Silizium reagiert mitpraktisch allen denkbarenTiegelmaterialien.

Kandidaten:• Quartzglas (SiO2)• Graphit• Beschichtung mit Si3N4

Wiederverwendbarkeit?


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Grenzfläche fest-flüssig:

Cs = Cl * k0

k0 : Segregations-koeffizient

B: k0 = 0.8O: k0 = 1.25


impurities thresholdGrenzwerte für die Degradation durch Verunreinigungen


impurities threshold


„Bösartige“ Verunreini-gungen (Übergangs-metalle) haben einen kleinen Segregations-koeffizienten!

impurity segregation


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)


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 [%]


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]


ingots from compensated materialSimple example: Na=1ppma, various Nd content Rc=(Na+Nd)/(Na-Nd)


20 40 60 80 1000

2

4

6

8

10

1ppma B 0.0ppma P Rc=1

resi

stiv

ity [Ω

cm]


ingots from compensated materialNa=1ppma, Nd=0ppma Rc=(Na+Nd)/(Na-Nd)


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]


ingots from compensated materialNa=1ppma, Nd=0.5ppma Rc=(Na+Nd)/(Na-Nd)


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]




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]




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


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


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%


properties of CM compared to Rc=1

• minority carrier lifetime

• majority carrier mobility

• light induced degradation




0 20 40 60 80 1001

10

100Cz compensated

resistivity lifetime before gettering

ρ [Ω

cm],

τ [µ

s]





0 20 40 60 80 1001

10

100Cz compensated

resistivity lifetime before gettering lifetime AFTER gettering

ρ [Ω

cm],

τ [µ

s]




• minority carrier lifetime• contamination free material for evaluation necessary

• lifetime increasing with increasing compensation






0 20 40 60 80 1001

10

100Cz compensated

resistivity mobility before gettering mobility AFTER gettering

ρ [Ω

cm],

µ hall [

Vs/

cm2 ]





0 20 40 60 80 100100

150

200

250

300

Cz compensated mobility before gettering mobility AFTER gettering

µ hall [

Vs/

cm2 ]




• 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




• 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


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]


Rc=2

Rc=25


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)


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)


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


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)


sheets and ribbonsString Ribbon (1980)

EFG (1972)

RGS (1989)

DC (2008)


sawing and slicing


industrial process – sawing


Max. Drahtgeschwindigkeit: 15 m/s Drahtdurchmesser: 0,14 mm, Länge: 800 km

Industrielle Maschine

industrial process - slicing


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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