SVC 2009 PV Summit Conference Page 1

Thin Films and Thin Wafers: Thin Films and Thin Wafers: Challenges and Challenges and

Opportunities with BIPV Opportunities with BIPV

PV SummitJune 3rd 2009

Andy Skumanich, Ph.D.SolarVision Consulting

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Outline

Opportunities and challenges

• Market potential for BIPV– Flexible PV modules

• Challenges– Potential for cost reduction and aesthetic integration

• Thin film trajectory: CE and cost– Various types including CIGS

• Ultra-thin wafer trajectory: thickness, CE, and cost– PV processing sequence– Handling considerations

• Conclusions

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Market Opportunities

• General PV forecast: 6-9 GW in 2010

• Demand for glass: 2010 – 1Billion m2 WW– Take 1/10% as BIPV, 10% CE1GW of PV glass

• Roof-tops residential: coverage by PV– 7 million new houses in typical year– If 1/10% have BIPV roof, 10%CE1GW of rooftop PV for residential

• BIPV could potentially be a major market driver

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BIPV Market Requirements

• Aesthetics, cost• Customizability• Product availability• Product features: Flexibility, Shape, etc.

• Market opportunity for flexible TF, and c-Si foils

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Challenges

• Thin Film: – Improved efficiency– Flexible substrate extends applications – maintain CE– Viability of materials without exchange

• Wafer based c-Si:– Foils which are flexible and robust– Improved efficiency for ultra-thin wafers – recover CE– Processing of wafers-to-cells

• Common– Customizability in design– Product range

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Turn-key Landscape: TF & c-Si

a-Si and Tandem

CIGS CdTe c-Si

• Oerlikon (11)• AMAT (14)• Ulvac (3)• Other misc

• Centrotherm • (Roth & Rau) Full chain:• Centrotherm• Schmid

Multiple sub-lines

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Thin Film CE gains

• CIGS starting to show promise– Turnkey line from Centrotherm

• a-Si needs to achieve >10% capability• CdTe needs to confirm reliability

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Centrotherm CIGS Turn-key

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Value of thin wafers for c-Si PV

• Potential benefits– Improved theoretical conversion efficiency– Potentially improved flexibility below 100um

S. Schoenfelder EuroSim, 2006

??Post-

degradation

CZ P-type (w/ B-O)

!!

Strength vs ThicknessC.E. vs Thickness (R&D data)

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11

Cell Efficiency vs. Thickness

10

12

14

16

18

20

22

24

350 300 250 200 150 100

SunPowerSolar Cell

ConventionalSolar Cell

ConversionEfficiency %

Cell Thickness (microns)

Cost reduction

Solar cell thickness reduction is a key cost reduction path. SunPower solar cell efficiency improves as wafer thickness decreases versus conventional solar cells

which become less efficient on thinner wafers.

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12

Wafer Thickness Roadmap

0

50

100

150

200

250

300

350

2002 2004 2006 2008 2010 2012

Waf

er T

hic

knes

s (u

m)

150120

(Source: NREL Silicon Strategy, Dick Swanson – SunPower, SVC)

Multi -crystalline

Mono -crystalline

SunPowermono c-Si, (125mm)

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Cell Efficiency Roadmap

13

0

5

10

15

20

25

2002 2004 2006 2008 2010 2012

Cell Efficiency History and NREL PlanConversion Efficiency

Multi -crystalline

Mono -crystalline

SunPowermono c-Si,

CE

(%)

(Source: NREL Silicon Strategy, Dick Swanson – SunPower, SVC)

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Ultra-thin wafer processing

• Aggressive activities world wide

– EU: Fraunhofer Institute– Japan: NEDO– USA: various including commercial companies

• Key developments: e.g. back surface treatment– Example is GIT – Dr. Ajeet Rohatgi

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14

15

16

17

18

19

20

21

0 100 200 300 400 500Solar Cell Thickness (um)

Eff

icie

ncy

(%)

lifetime=100us, BSRV=50cm/s, BSR=97%

lifetime=100us, BSRV=400cm/s, BSR=65%

lifetime=25us, BSRV=50cm/s, BSR=97%

lifetime=25us, BSRV=400cm/s, BSR=65%

Current Status

Our Goal

GIT modeling for sub 100um wafers

• Bulk lifetime, thickness, BSRV and BSR targets for achieving 19-20% efficiency cells with screen printed front contacts

GIT Dr. Ajeet

Rohatgi

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Roadmap to 20%-efficient c-Si solar cells with screen printed contacts

17.0%

18.2%

19.3%

20.1% 20.0%

10%

12%

14%

16%

18%

20%

22%

Current SolarCell

Improved Text,AR & SP

(Ref=1.04%FF=79.1%M.C.=5.0)

BSR (97%)BSRV

(100cm/s)

High Sheet Res.Emitter (R=100

ohm/sq)

Reduce CellThickness (100

µm)

Eff

icie

ncy

GIT Dr. Ajeet

Rohatgi

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New Process Vs Full Al BSF IQE & RetroRefl

0

10

20

30

40

50

60

70

80

90

100

300 400 500 600 700 800 900 1000 1100 1200Wavelength (nm)

IQE

(%)

0

10

20

30

40

50

60

70

80

90

100

Ref

lect

ance

(%)

New Process

Full Al BSF

New Process

Full Al BSF

Voc(mV) 652 639

Jsc(mA/cm2) 39.4 37.9

FF(%) 78.1 78.9

Eff (%) 20.1 19.1

GIT Dr. Ajeet

Rohatgi

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IV-curve for the best Screen Printed New Process cell

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700Voc (mV)

Isc

(A) ? : 20.1 %

VOC : 652 m VJSC : 39.4 mA/cm2FF : 78.1 %

Dielectric passivated rear LBSF raised the efficiency from 19.1 to 20.1%

GIT Dr. Ajeet

Rohatgi

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Handling issues

• Breakage– Of course the major concern for module manufacturers

• Warped wafers cause issues– Ultra thin may have benefits and drawbacks

• Start-stop needs to be abrupt for high tpt– Wafers act like “wings” during motion

• Multiple challenges for handling

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Alternative Companies for Handling

• Equipment: Automation Technology Inc:– Bernoulli grippers– But still not developed

• Researchers at the Texas Manufacturing Assistance Center (University of Texas, Arlington)

– prototype air system able to both acquire wafers from a stack and move them along a track with no moving components

– contrasts with Bernoulli grippers which only acquire wafers and must use manipulators and robotic elements to move wafers

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Summary

• Decreasing thickness still moving forward– Market leaders driving to wafers 150um and then below– New improvements for thin films (CIGS specifically)

• Market forces will be pushing prices down– Foreseeable future: more pressure on cost reduction– Companies with tech advantages will survive

• Thin Film are steadily developing improved CE with CIGS leading in CE, (not in market)– Multiple challenges: higher CE >10% at low cost production

• Thin, and ultra-thin wafers now are driving processing– Mulitple challenges: maintain CE below 100um, breakage

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Conclusions

• Industry needs to drive metrics and dimensions– BOS may be substantially lower for frame and labor– May be closer to “grid parity” with lower BOS

• Increased focus on BIPV is also required

• Also, product portfolio needs to be expanded– Flexible, multi-dimensional, etc.

• Current development capabilities can open up the BIPV market in increase the demand for TF and ultra-thin c-Si

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TF BIPV

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SolarVision Consulting

Contact: Dr. Andy SkumanichAndySkumanich@gmail.comwww.solarvisionconsulting.com