AVS PAG Meeting UNIFORM GROWTH OF LARGE AREA a-Si / c-Si TANDEM JUNCTION SOLAR CELLS BY CAPACITIVE COUPLED PECVD

Yi Zheng, Alan Tso, Fan Yang, Rongping Wang, Tom Tanaka, Ned Hammond, Lin Zhang, Zheng Yuan and Brian Shieh

Thin Film Solar Products Division, Applied Materials, Santa Clara, CA 95054

Display & SunFab Solar Applied Materials External Types of Solar Cells

. Crystalline – Monocrystalline, Multicrystalline, Ribbon, etc.

. Thin Films – Amorphous and

– (CdTe) – Copper Indium Selenide (CIS, CIGS)

. Concentration – Silicon, multi-junction III-V,

. Emerging Technologies – Organic materials, Nanostructures, etc.

Crystalline Si and Thin Films dominate market today 2

Display & SunFab Solar Applied Materials External NREL Cell Efficiency Map

Thin Film Efficiencies Rapidly Advancing 3

Display & SunFab Solar Applied Materials External PV Module Price Reduction

$100 Historical Prices

1982 1980 $18.73/Wp 1985 $12.01/Wp 1995 c-Si $6.88/Wp $10 2003 2007e $3.53/Wp $3.98/Wp

Thin Film $1.00/W 2007e @ ~300 GWp Module Price (2006 $/Wp) Module Price (2006 $1.00/W @ <20 GWp $1 1 10 100 1,000 10,000 100,000 1,000,000 Source: Adapted from NREL; Cumulative Production (MWp) Historical data from Navigant Consulting

Module price decreases 20% for every 2x production increase

4

Display & SunFab Solar Applied Materials External Thin-film Advantages and Disadvantages

Advantages Disadvantages . CIS . CIS – Highest thin-film efficiencies – Mftg yield and volume

– Good cell stability – Indium price / availability – Good product appearance – Field durability

. CdTe . CdTe – High deposition rate – Mftg and product restrictions (Cd)

– Proven large-volume mftg – High-temperature process – Current low cost leader – Absorber thickness ; Te availability

. Si . Si – Well-known Si-based PV science – Single-junction efficiency

– Multi-junctions for high efficiency – Deposition rate – Large-area, large-volume mftg – Multi-junction mftg control

5

Display & SunFab Solar Applied Materials External Leading Thin Film PV Technologies

TF Si CdTe CIGS

Ag/Al Back Metal ZnO:Al ZnO:Al Back Material i-ZnO CdS

µc-Si

doped Si CdTe CIGS a-Si

CdS

SnO2:F, ZnO:Al SnO2:F Mo Barrier Barrier Barrier

Low Iron Glass Soda Lime Glass Soda Lime Glass Superstrate Superstrate Substrate

6

Display & SunFab Solar Applied Materials External Thin Film Technology Comparison

CIGS CdTe TJ a-Si/uc-Si Module Size (m2) ≤ 0.72 m2 ≤ 0.72 m2 1.43m2, 2.86m2, 5.72m2 Stabilized Module 8-12% 10% 8% Efficiency Today Stabilized Module Efficiency Roadmap 15% 12% 10% to 2010 Best Laboratory Cell 19.5% 17% 13.5% Efficiency Temperature -0.36 % / °C -0.25 % / °C - 0.2 % / °C Coefficient, Power Raw Materials for PV 3 – 5 GW annual 3 – 5 GW annual (limited Indium increases (limited Telluride Unlimited Si supply cost) increases cost) Volume Production Material, uniformity, t-put, Ramp Readiness equipment maturity, In volume production In volume production etc. Module Reliability Limited field data impacts Limited but growing field a-Si >20 years financiability data Production Cost / Wp No volume production <$1.00 /Wp <$1.00 /Wp in 2010 cost data Applications Solar Farms, Rooftop, Solar Farms, Rooftop, Rooftop, BIPV BIPV BIPV

7 *Sources: NREL, Deutsche Bank, USGS, Photon International Display & SunFab Solar Applied Materials External Thin Film Si PV Cell - Single Juction & Tandem Junction

a-Si a-Si/µc-Si a-Si:H/µc-Si:H Single Junction Tandem Junction advantages Low-cost Glass Substrate Glass Substrate Better temperature Transparent Conductor Transparent Conductor stability p thin a-Si p Better diffuse light i i Amorphous Silicon ~2 µm Amorphous Silicon n ~2-3 µm efficiency µc-Si p n TCO Paths to higher CE Back Contact Al i Microcrystalline back Silicon contact

n TCO Back Contact Ag ) E+19 -1 5 a-Si:H/µc-Si:H a-Si:H junction

c-Si:H junction micron

100 -1 s challenges

4 -2 80 Large area film 3 uniformity 60 High equipment cost 2 40 Low dep rate 20 1 Low CE AM 1.5 global spectrum 0 Relative External Quantum Efficiency, % 0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Numberof Sunlight Photons(m Wavelength, microns 8

Display & SunFab Solar Applied Materials External AppliedApplied’’ss ToolTool BoxBox

Silicon Systems

Advancing Technology Innovating Productivity

Display Business Fab Solutions Driving Fab Productivity Delivering New Technology and Scale

Energy & Thin Film Crystalline Environmental Solutions

Changing the Energy Equation Baccini*

9

Display & SunFab Solar Applied Materials External Our demonstrated capability in large area TFT-LCD tools 6 up 52.0” Wide panels

AKT PECVD Size Evolution 6 up 6 up 46.0” Wide panels 37.0” Wide panels 6 up 19.0” ~ 24.0” 6 up 4 up 6 up 15.0” ~ 17.0” 10.4” 12.1”

Gen 2 Gen 3 / 3.5 Gen 4 Gen 5 Gen 5 Gen 5.5 Gen 6 Gen 7 / 7.5 Gen 8 1st Release 2/ '93~ 4/ '95~ 1/ '00~ 8/ '01~ 6/ '02~ 8/ '04~ 5/ '03~ 7/ '04~ 2006

System Layout

ACLS ACLS ACLS ACLS ACLS

3500 / 4300 / 4300A Model 1600 5500/5500A 10K 15K / 15KA 20K 25K / 25KA 40K / 40KA 50K 550x650 Substrate 370x470 680x880 1000x1200 1100x1250 1300x1500 1500x1800 1870x2200 2160x2400 class 600x720 2160x2460 Size (mm) 400x500 730x920 1200x1300 1500x1850 1950x2250 620x750 Substrate 2,000 cm2 4,650 cm2 6,716 cm2 12,000 cm2 15,600 cm2 19,500 cm2 27,750 cm2 41,140 cm2 53,136 cm2 Area (1.00) (2.33 from 1600) (1.44 from 4300) (1.79 from 5500) (1.30 from 10K) (1.25 from 15 K) (1.78 from 15 K) (1.52 from 25 K) (1.21 from 40 KA) Panel size 10.4 12.1 15 ~ 17 19 ~ 23 21 ~ 2432W 37W 46W 52W Inch Panel/sub 46 6 6 66 6 6 6

Application Note PC ------> Monitor ------> TV

10

Display & SunFab Solar Applied Materials External SunFab Value Proposition – 12 Lines Worldwide

. Module Right Sizing Advantage & Flexibility – Flexible panel size (¼, ½, and Full Size) serves multiple markets: residential rooftop, commercial rooftop, BIPV, and utility scale – SunFab full size panel (5.7m2), world’s largest, delivers the highest power out per panel 560Wp . Leading Technology – High Efficiency Tandem Junctions, Better Energy Harvest due to lower temperature coefficients – High-speed, high-yield processing of thin glass substrates (2.2x2.6m) . Fastest to Scale – World class equipment serves as foundation for Factory performance – <6 months from factory ready to Volume Production

Full Size SunFab Panel Cost 560 Wp

Watts ¼Size

Applied SunFab Gen 8.5 PECVD

11

Display & SunFab Solar Applied Materials External PECVD chamber structure

. Process gases:

–SiH4 , H2 RF power supply – Dopants (C3H 9B for p- and PH for n-doping) 3 Gas feed Observation – Single gas feed through at the Diffuser Slit valve center of the chamber lid window . Diffuser: – Distribute gas flow – RF electrode – Proprietary hallow cathode design Glass substrate . Enhanced gas dissociation To pump Susceptor . Uniformly dissociated reactant gases . Susceptor – Multiple heating and cooling zones . Ensure temperature uniformity – RF ground . Slit valve for substrate loading / unloading

12

Display & SunFab Solar Applied Materials External Big Challenge - 5.7m2 Substrate µc-Si Film

amorphous phase at corners

Crystalline fraction along diagonal

80

70

60

50 fc (%) fc 40

30

20 0 500 1000 1500 2000 2500 Distance (mm)

a-Si due to lower power density

Amorphous Microcrystalline Result is lower cell Jsc & FF

13

Display & SunFab Solar Applied Materials External Structure of µc-Si:H

Porous Compact Cracks/columns in TEM Cracks/columns in TEM High spin density Low spin density

Bad solar cells Good solar cells

Decreasing crystalline volume fraction concentration, power, frequency, temperature, ...

several stationary 100 nm columnar growth

incubation ~30-50 nm zone substrate

crystallites amorphous voids regions 14 Display & SunFab Solar Applied Materials External Parameters that Affect Film Uniformity

Gas Flow Diffuser

Spacing

Susceptor

. Plasma Uniformity . Gas Flow Distribution To pump

. Pumping Mechanism

15

Display & SunFab Solar Applied Materials External Plasma Uniformity - Proprietary Electrode Design

3000 Gate Insulator quality SiNx film 2500 500 2000 1500 Gen 8 400 1000 ) 500 Gen 7 Depo. Rate (A/min) Rate Depo. 0 300 0 500 1000 1500 2000 Gen 6 Distance (mm) 200

Thickness (nm Gen 5

Before standing wave correction 100 Uniformity: < +/- 10% 0 -1250 -750 -250 250 750 1250 Distance from Edge (mm)

Diffuser Profile Change

Susceptor

16

Display & SunFab Solar Applied Materials External Chamber Flow Simulation

. Chamber pumping flow simulation indicated non-uniform flow distribution

17

Display & SunFab Solar Applied Materials External Full Size 5.7m2 uc-Si Film

µc-Si layer with LCD Hardware Crystalline Fraction (fc) 70 • a-Si deposition in the 60 corners due to lower power density 50 • Result is lower cell Voc & (%)

c 40

f FF

30

20 0 500 1000 1500 2000 2500 Distance (mm)

µc-Si layer with New Hardware TJ Cell Efficiency & Jsc 12

) CE • New Hardware improved 2 10 uniformity and crystalline 8 fraction Jsc (mA/cm • Results in better

sc 6

, J homogeneity and higher 4 efficiency

2 CE (%)

0 0 500 1000 1500 2000 2500

18

Display & SunFab Solar Applied Materials External Two Remaining Issues:

Thickness Across Panel Crystalline Fraction Across Panel 80 500 450 75

400 70 350 300 65 250 60 200 Fc (%) Fc Dep Rate (A/min) Dep Rate 150 55 100 TL to BR 50 50 BL to TR 0 45 0 400 800 1200 1600 2000 2400 X (mm) 40 0 400 800 1200 1600 2000 2400 • Asymetry of uc-Si Crystalline X (mm) Fraction Uniformity 5.7 m2 • Corner low dep rate 2200 mm

19 2600 mm Display & SunFab Solar Applied Materials External

Balance the Plasma – Unbalance the Feed

1000 500 0 -500 -1000 -1000

72 RF power

100 supply -500 Observation Slit valve

window

0

150

500

200

213 1000 Mean = 128.3, NU = 49.3% = NU 128.3, = Mean

(a) (b)

RF field intensity w/ RF field intensity w/ 20 original RF feed displaced RF feed Display & SunFab Solar Applied Materials External RF Fee Location Effects on mc-I Thickness and Fc Uniformity BKM RF Feed RF Feed Rev1 RF Feed Rev2 500 500 500

450 450 450

400 400 400

350 350 350

300 300 300

250 250 250

200 Unif: 17.8% 200 DR (A/min) 200 Dep Rate (A/min) Dep Rate (A/min) 150 150 Unif: 7% 150 Unif: 5%

100 100 100

50 50 50

0 0 0 0 400 800 1200 1600 2000 2400 0 400 800 1200 1600 2000 2400 0 400 800 1200 1600 2000 2400 X (mm) X (mm) X (mm)

80 80 80

75 75 75

70 70 70

65 65 65

60 60 60 Fc (%) Fc (%) Fc Fc (%) Fc 55 55 55 TL to BR TL to BR TL to BR 50 BL to TR 50 BL to TR 50 BL to TR 45 45 45 40 40 40 0 400 800 1200 1600 2000 2400 0 400 800 1200 1600 2000 2400 0 400 800 1200 1600 2000 2400 X (mm) X (mm) X (mm)

Rev2 RF Feed improved thickness and fc uniformity 21

Display & SunFab Solar Applied Materials External Local RF Density Enhancement – Grounding Approach: modify grounding configuration to modulate the electrical field at corners.

Thickness delta map Thickness delta map (Experiment) (Simulation) Delta: Ground Strap Rev4 - BKM (SF BKM5) 73.1 - 45.1 43 - 45.1 - 43 40.9 - 43 - 40.9 38.8 - 40.9 - 38.8 36.7 - 38.8 - 36.7 34.6 - 36.7 - 34.6 32.5 - 34.6 - 32.5 30.4 - 32.5 - 30.4 28.3 - 30.4 - 28.3 26.2 - 28.3 - 26.2 24.1 - 26.2 - 24.1 22 - 24.1 - 22 19.9 - 22 - 19.9 17.8 - 19.9 - 17.8 15.7 - 17.8 - 15.7 13.6 - 15.7 - 13.6 11.5 - 13.6 - 11.5 9.4 - 11.5 - 9.4 7.3 - 9.4 - 7.3 5.2 - 7.3 - 5.2 3.1 - 5.2 - 3.1 1 - 3.1 - 1 -1.1 - 1 - -1.1 -3.2 - -1.1 - -3.2 -5.3 - -3.2 - -5.3 -7.4 - -5.3 - -7.4 -9.5 - -7.4 - -9.5 -11.6 - -9.5 - -11.6 -13.7 - -11.6 - -13.7 -15.8 - -13.7 - -15.8 -17.9 - -15.8 - -17.9 -20 - -17.9 - -20 g

Corner thickness increase Corner RF straps removed

Good correlation between simulation and experiment

22

Display & SunFab Solar Applied Materials External Uniform Large-Area uc-Si Film

Uniform uc-Si coating Unif: 5% (1s, 400pts)

23

Display & SunFab Solar Applied Materials External a-Si:H single layer uniformity change

800

. With original RF feed 700 Original RF feed Modified RF feed – Average thickness 390 nm 600

– Standard deviation of thickness, 500 400 t = 20 nm 300 – Non-uniformity = 4.3%

a-Si thickness (nm) thickness a-Si 200

100 Slit valve max  tt min window (NU) uniformity-non (NU)  0 max  tt min 0 500 1000 1500 2000 2500 Distance (mm) . After modifying the RF feed location – Average thickness unchanged

– t = 21nm – Non-uniformity was 3.2% . Insignificant change in thickness

profile and uniformity Slit valve

24

Display & SunFab Solar Applied Materials External performance uniformity

. Uniformity of Jsc 14 – Improved from 7.9% to 2.9% 12 10 ) 2 . Uniformity of Voc 8 – Improved from 4.8% to 3.3% 6 Legend RF feed NU (%)

Jsc (mA/cm Original Original 7.9 4 . Uniformity of FF RF Rev 1Modified 2.9 2 window Slit valve – Improved from 5.8% to 4.1% 0 0 500 1000 1500 2000 2500 Distance (mm) 1.6 100 90 1.5 80 1.4 70 1.3 1.2 ) 60 50 1.1 Legend RF feed NU (%) FF (%FF Legend RF feed NU (%) 40 (V) Voc 1 Original Original 30 Original 5.8 0.9 Original 4.8 20 RF Rev 1Modified 4.1 0.8 RF Rev 1Modified 3.3

10 Slit valve

window 0.7 window Slit valve 0 0.6 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 Distance (mm) Distance (mm)

25

Display & SunFab Solar Applied Materials External Development of High Dep Rate uc-Si Processes

Conventional Approach [1]

High H2 dilution ratio, R~100R~100 High total flow Medium RF power (0.5~0.7W/cm2) Results Good cell efficiency Compromising Approach Medium deposition rate COMPROMISING Low H dilution ratio, R~30 Large area 2 [1] B. Rech, etetc.,c., SolarSolar EnerEnergy MaterialsMaterials & SolarSolar cells 6666 Medium total flow (2001)(2001) 267-273. High RF power Results Pure Silane Approach [2] Good cell efficiency Zero H2 dilution ratio, R=0 Very low total flow High deposition rate Small RF power Large area Results Good cell efficiency Medium deposition rate Small area [2] M. N. Donker, etc., J. Mater. Res., Vol. 22. No. 7, Jul 2007.

26

Display & SunFab Solar Applied Materials External Film properties at high deposition rate

. Raman, . XRD

.) (220) / (111) = 2.1 .u

. Stress a (

y it (1 s ( 220 . Conductivity n 11) e t ) In

20 25 30 35 40 45 50 2 Theta (degree)

Experimental data a-Si Grain boundary .)

.u c-Si a Total ( y it s n

e Fc = 55.6% t In TEM shows clear column structure, which agrees with XRD and Raman 380 430 480 530 580 measurement. Raman shift (cm-1)

27

Display & SunFab Solar Applied Materials External IV and QE performance comparison

12 100 Ref 90

) 10 2 HD 80

m Reftop c / 70 A 8 HDtop m (

Refbot Initial IV performance ) 60 y t % i

6 Parameters HD Reference ( 50 HDbot ns

CE (%) 10.7 10.7 QE 40 de

nt 4 Jsc (mA/cm2) 11.2 10.8 e 30 r r

u Voc (V) 1.336 1.379 20 C 2 FF (%) 71.5 71.7 10 0 0 00.250.50.7511.251.5 300 500 700 900 1100 Wavelength (nm) Voltage (V)

 The high deposition rate one (HD with  Same top cell QE response for all the DR=660A/min)DR=660A/min) have initial IV performance cells. No obvious damage/change to comparable to its reference with top cell under high deposition rate for DR=400A/min.DR=400A/min.  All the data shown is taken 6 months after bottom cell I layers. cell fabrication, high deposition rate ones  High deposition rate bottom cells have show stable performance same as QE response comparable to its reference. reference.  LID (two sun lightlight iinntensity, 300 hours, 50˚C) performance is the same for high deposition rate and its reference. (Data not showing here.) 28 Display & SunFab Solar Applied Materials External SunFab:SunFab: UnlockingUnlocking CostCost ReductionReduction

SunFab Solar Projected Output . 60 MWp (TJ) per year . 0.75 km2 of panels per year

. 5.7m2 panels – largest in the world

. >20,000 homes (3kWp each)

. $1/Watt Production Cost 2010

0.72 km2 Forbidden City Beijing China

29

Display & SunFab Solar Applied Materials External 30

Display & SunFab Solar Applied Materials External 31

Display & SunFab Solar Applied Materials External North Germany Southern America Europe Europe China Japan Middle East India

Brazil Australia S. Africa

1 year of world 1min of > energy consumption

32

Display & SunFab Solar Applied Materials External 33

Display & SunFab Solar Applied Materials External Cell to Cell Connection

P3 Scribe P2 Scribe Back Reflector (Back TCO and P1 Scribe Metal)

a-Si p-i-n Front TCO Scribe Front Glass Loss Area Active Area

34

Display & SunFab Solar Applied Materials External End Scribe

Bus Bar (–) P2 Scribe

P1 Scribe

35

Display & SunFab Solar Applied Materials External Light trapping

Back Metal Back TCO n-Type a-Si Intrinsic a-Si p-Type a-Si Front TCO

Front Glass Incoming Light

36

Display & SunFab Solar Applied Materials External c-Si:H layer uniformity change

. No significant thickness change . . Fc: crystalline fraction Measured – Calculated from film Raman

absorption spectrum Ic – Raman condition: Ia Raman absorption intensity , a.u , intensity absorption Raman . Laser wavelength = 532 nm . Temperature = -49 C 600 550 500 450 400 350 300 250 Raman shift (cm-1) – fc is defined as:* 80 I 100 70 fc  c   100  60 Ic  exp1.0  Ia 50   250  40 fc (%) . With modified RF feed 30 Legend RF feed NUfc (%) – fc non-uniformity significantly 20 Series1 Original 8.5 10 Series3 Modified 3.0 Slit valve

improved from 8.5% to 3.0% window 0 0 500 1000 1500 2000 2500 Distance (mm)

37 * R. E. I. Schropp and M. Zeman, Amorphous and microcrystalline silicon solar cells, Kluwer Academic Publishers, 1998 Display & SunFab Solar Applied Materials External