Thin-Silicon, Low-Cost Solar Photovoltaic Modules Using Kerfless Epitaxial Silicon Lift-off Technology

Transcription

1 Happy Diwali Indian Festival of Lights! Thin-Silicon, Low-Cost Solar Photovoltaic s Using Kerfless Epitaxial Silicon Lift-off Technology Mehrdad M. Moslehi Solexel, Inc. Stanford University 14 November 2012 [ 1 ]

2 Agenda Our Company and Value Proposition Crystalline Silicon PV Technology and Market Why Thin Crystalline Silicon for Solar Cells Our Disruptive Technology and Progress Summary [ 2 ]

3 Solexel: High-Efficiency, Low-Cost, Thin-Silicon PV Incorporated and funded (Series A) in 2007 AWARDS TIER MILPITAS, 1 INVESTORS & LICENSES CA Fully operational pilot production fab and test lab 170+ inventions: issued, pending, licensed $17M in DOE and NSF awards Malaysia incentive package for volume manufacturing $113M Series A (2007) and B (2008) equity raises Closing Series C funding ($60M) to demonstrate high-volume manufacturability A: B: C: [ 3 ]

4 Solexel Eliminates Performance vs Cost Trade-Off 12 Price: $1.35/Watt 12 Price: $0.78/Watt High Efficiency (20-22%) Low Cost High Energy Yield Pliable & Lightweight (Low Balance of Systems) Proven Crystalline Silicon High Efficiency All-Black Aesthetics CZ Crystalline Silicon % efficiency 12 Cost: $1.25/Watt Much Less Silicon Usage 12 Cost: $0.72/Watt Low Cost Less Material Usage Scalable: Low Capex Less Energy Usage 12.7% efficiency Scalable: Low Capex Much Less Energy Usage All-Black Aesthetics IP Protected Technology Platform [ 4 ]

5 TCS TCS Traditional Silicon PV Process Is Complex and Costly Trichlorosilane Gas Polysilicon Processing Ingot Growth Wafer Slicing Cell Processing Processing Balance of System $0.00 $0.20 $0.40 $0.60 $0.80 $1.00 $1.20 $1.40 $1.60 Industry Cost, 2012 Poly Ingot Wafer Cell Balance of System $1.57/W Industry Cost, Floor Poly Ingot Wafer Cell Balance of System $1.25/W Note: Balance of System includes mounting structure, inverter, cabling, labor, land/roof cost, permitting [ 5 ]

6 Solexel Eliminates the Most Costly Steps While Delivering Superior Performance TCS TCS Trichlorosilane Gas Thin Polysilicon Silicon Processing Growth Ingot Growth Wafer Slicing Cell Processing Proven Crystalline-Silicon Processing Decoupled from Silicon Supply Chain Balance of System 10x Less Silicon 2-3x Less Capex 2x Less Energy Usage Superior Efficiency & Yield $0.42/W Cost $0.45/W in System Cost $0.00 $0.20 $0.40 $0.60 $0.80 $1.00 $1.20 $1.40 $1.60 Industry Cost, 2012 Poly Ingot Wafer Cell Balance of System $1.57/W Industry Cost, Floor Poly Ingot Wafer Cell Balance of System $1.25/W Solexel Cost Thin Silicon Cell Balance of System $0.80/W Note: Balance of System includes mounting structure, inverter, cabling, labor, land/roof cost, permitting [ 6 ]

7 Agenda Our Company and Value Proposition Crystalline Silicon PV Technology and Market Why Thin Crystalline Silicon for Solar Cells Our Disruptive Technology and Progress Summary [ 7 ]

8 Global PV Demand (GW) Global PV Demand 60 Europe Actuals Forecast 50 Asia Pacific & Australia America 40 China Middle East & Africa 30 Rest of World Source: Global Market Outlook, May 2012, European Photovoltaic Industry Association (EPIA); projections are average of EPIA s Moderate and Policy-Driven scenarios [ 8 ]

9 Cumulative Installed PV Capacity (GW) Cumulative Global Installed PV Capacity PV has a multi-tw installed capacity market size potential, possibly at least 10 TW! Europe Asia Pacific & Australia America Actuals Forecast China 200 Middle East & Africa Rest of World 150 Thin Film Installations 100 ~100 GW 50 0 Source: Global Market Outlook, May 2012, European Photovoltaic Industry Association (EPIA); projections are average of EPIA s Moderate and Policy-Driven scenarios Note: historical thin film installations are based on First Solar production plus a cushion for other manufacturers [ 9 ]

10 Wafer Price ($/wafer) Poly Price ($/kg) PV Pricing: Polysilicon, Multi- Wafer, Mono- Wafer $12 $11 $10 $9 Multi-Crystalline Silicon Wafer ($/wafer) Mono-Crystalline Silicon Wafer ($/wafer) Polysilicon ($/kg) $360 $330 $300 $270 $8 $7 $6 $5 Poly cost (2012 vs 2008): ~20x Wafer cost (2012 vs 2008): ~10x Spot Prices 10/31/12 Polysilicon: $16.58/kg 156 mm mc-si Wafer: $ mm mono Wafer: $1.12 c-si s: $0.67/W $240 $210 $180 $150 $4 $120 $3 $90 $2 $60 $1 $30 $0 $ Source: PVInsights [ 10 ]

11 Cost or Price in $/Watt PV and BOS Costs $3.50 $3.00 c-si Lower Cost Than Thin Film $2.50 $2.00 $1.50 $1.00 BOS $1.73 BOS $1.85 BOS $1.58 BOS $1.73 BOS $1.55 BOS $1.36 BOS $1.53 BOS $1.27 BOS $1.51 BOS $1.20 BOS $1.50 BOS $1.12 BOS $1.48 BOS $1.05 $0.50 $0.00 $0.77 $1.20 $0.74 $1.13 $0.73 $0.70 $0.66 $0.68 $0.61 $0.66 $0.57 $0.64 $ $0.62 Thin Film c-silicon Thin Film c-silicon Thin Film c-silicon Thin Film c-silicon Thin Film c-silicon Thin Film c-silicon Thin Film c-silicon Source: historical module data from First Solar and Trina Solar; module projections based on expected improvements; BOS projections from Photon Consulting [ 11 ]

12 Solar Radiation Spectrum and Portion Utilized by Si Maximum Fraction Available For Quantum-Cutting: 149 W/m 2 E < 1.11 ev for Si Excess Energy Thermalized No Contribution to IQE, J sc Power Available to be Utilized by Silicon [ 12 ]

13 Key Measures for c-si Solar Cells and s Solar Cell Short Circuit Current: I sc (A) Open-Circuit Voltage: V oc (V) Description Max possible current (when V=0) Max possible voltage (when I=0) Max. Power Point (MPP) Current: I mp (A) Current at which max power is produced Max. Power Point (MPP) Voltage: V mp (V) Voltage at which max power is produced Maximum Power (P max ) The maximum generated power (V mp.i mp ) Fill Factor (%) Measure of IV squareness: FF=(V mp.i mp )/(V oc.i sc ) Conversion Efficiency (%) = V oc.j sc.ff Temperature Coefficient (%/C) Normal Operating Cell Temp.-NOCT (C) Internal Quantum Efficiency: IQE (%) External Quantum Efficiency: EQE (%) Energy Yield (kwh/kwp) % of solar power converted to electric power Power change with temperature change Temp. of open-circuit cells in an open backside mounted module (800 W/m 2, 20 C, 1 m/s wind) Fraction of absorbed photons converted to I sc Fraction of incident photons converted to I sc kwh energy produced per kwp installed [ 13 ]

14 Si (1.11 ev) GaAs (1.43 ev) Ge (0.67 ev) Short Circuit Current Density vs Bandgap In an ideal cell (IQE = 100%), each photon with energy E g produces one electron-hole pair so J sc increases with smaller E g Silicon solar cell has a maximum possible J sc = 46 ma/cm 2 (at AM1.5) But V oc and FF Increase with Larger E g! [ 14 ]

15 Efficiency Limit of Single Junction Solar Cells: The Shockley-Queisser Efficiency Limit for a SJ Solar Cell (1 Sun) Maximum Efficiency (%) Ge (0.67 ev) Si (1.11 ev) GaAs (1.43 ev) Multi-junction solar cells can have higher efficiency values than shown here ~33% Si and GaAs have near-optimal bandgap energies for SJ solar cells! Higher J sc Higher V oc and Fill Factor Semiconductor Bandgap (ev) [ 15 ]

16 Solar Cell Loss Mechanisms Optical losses: Optical losses are accounted for by the External & Internal Quantum Efficiency (EQE & IQE) and primarily impact J sc Recombination losses (surface and bulk): Recombination losses are accounted for by the Internal Quantum Efficiency (IQE), J sc, V oc, and Fill Factor Resistive (electrical ohmic) losses: Resistive losses are mainly accounted for by the Fill Factor, but also affect the IQE and V oc [ 16 ]

17 Crystalline Silicon Solar Cell Efficiency Limit: The loss waterfall going from thermodynamic limit to future practical cells Theoretical limit efficiency of SJ crystalline silicon solar cell at AM1.5 ~29% What s practical limit efficiency for SJ crystalline cell? Possibly ~26% - 27% range SQ: ~33% Source: Dick Swanson ~29% Theoretical Limit for SJ c-si Practical Limit ~26-27%? 24.1% (2012) [ 17 ]

18 Impact of R S and R SH on Fill Factor (FF) Ideally, FF would only depend on V oc Normalized v oc = V oc /(kt/q) FF = [v oc - ln(v oc +0.72)]/(v oc + 1) FF degrades with higher R S and lower R SH Higher R S results in loss of voltage and P max Lower R SH results in loss of current and P max I L I 0 V MPP MPP Small R SH Also Degrades Low-Light Performance! [ 18 ]

19 Mainstream Crystalline Silicon Solar Cells and s Front-contact, front-junction solar cells, mostly 156 mm x 156 mm format Pseudo-square cells using CZ p-si, or full-square cells using cast mc or qm p-si Alkaline (mono Si) or acidic (mc-si) surface texture Homogeneous or selective n+ phosphorus emitter with PECVD SiNx passivation Screen printed / fired blanket Al BSF for rear passivation and contact Screen printed / fired Ag paste front-side emitter metallization Cells efficiencies of ~15% to ~19% and module efficiencies of ~13% to ~17% Saw Damage Removal Alkaline or Acidic Texturing Phosphorus Diffusion (n+ Emitter) Edge Isolation (Laser Scribe) PECVD SiNx Passivation & ARC Screen Print Ag and Al Pastes Metallization Firing Photo Source: Newport Corp./Spectra-Physics [ 19 ]

20 Efficiency Commercial-Scale Efficiency 22.0% 20.0% 18.0% 16.0% 14.0% 14.2% 13.9% Mono-Crystalline Multi-Crystalline Thin Film (CdTe) 15.6% 14.9% 14.6% 15.1% 14.8% 14.4% SunPower: 21.2% SunPower 20.1% Solexel: 20% 15.9% 15.6% 12.5% 16.9% 16.1% 13.3% (forecast) 17.6% 16.5% 14.0% 18.3% 17.0% 14.5% Solexel: 22% (forecast) 18.6% 17.3% 14.8% 12.0% 10.7% 11.0% 11.3% 11.7% 10.0% Source: based on estimates and projections by Greentech Media, June 2012 [ 20 ]

21 Major Technology Trends in Crystalline Silicon Solar PV Key Transitions and Trends Homogeneous Emitter to Selective Emitter Driving Force and Impact Improved Blue IQE & Cell Efficiency Rear Al BSF to Dielectric Rear Passivation, Local Contacts Improved Red IQE & Cell Efficiency Rear Al BSF to ALD Al 2 O 3 Dielectric Rear F.A. Passivation p-si to n-si, n+ Emitter to p+ Emitter, PECVD SiN x to Al 2 O 3 /SiN x Frontside Emitter Passivation Front-Contact to Back-Contact Cells (MWT-PERC) Front-Contact to Back-Contact/Back-Junction IBC Cells Homo-junction Emitter to Hetero-junction Emitter (HIT) Screen Printed Silver to Plated Copper CZ Silicon to Seeded Cast (Quasi) Mono Silicon Improved Red IQE and Cell Efficiency Enhanced Effective Carrier Lifetime Increased Cell Efficiency, no LID Reduced Optical Reflection Losses Increased QE and Cell Efficiency Lowest Optical Reflection Losses Highest QE and Cell Efficiency Enhanced V oc and Cell Efficiency Reduce Cell Metallization Cost Reduce Starting Wafer Cost [ 21 ]

22 Efficiency Capability of Crystalline Silicon Technologies 12.0% STC Efficiency Solexel 14.0% 16.0% 18.0% 20.0% 22.0% 24.0% Thin-Film s (~8% to ~14%) First Solar: 12.7% (CdTe, Q4 2012) TSMC: 13.0% % (CIGS, 2013) GE: 14.0% (CdTe, 2013) Yingli Panda (Bifacial) Cell Efficiency = 19.0% Efficiency = 16.5% SunPower Maxeon Gen-III Cell Efficiency = 23.6% Champion Cell: 24.1% Efficiency = 21.2% World-Record Commercial c-si Efficiency 1 sun) MWT-PERC: Passivated Emitter & Rear Contacts Cell Efficiency ~16% to 19% Efficiency ~13% to 17% Panasonic (Sanyo) HIT Cell Efficiency = 21.6% Efficiency = 19.0% PERL: Passivated Emitter and Rear Locally Diffused (UNSW): 24.4% lab cell 14.0% 16.0% 18.0% 20.0% 22.0% 24.0% 26.0% STC Cell Efficiency [ 22 ]

23 Agenda Our Company and Value Proposition Crystalline Silicon PV Technology and Market Why Thin Crystalline Silicon for Solar Cells Our Disruptive Technology and Progress Summary [ 23 ]

24 V oc Limit Increases With Reducing Cell Thickness! Auger recombination imposes the limits on V oc and efficiency of Si solar cells The V oc limit increases from 750 mv for W Si = 300 µm to 800 mv for W Si =20 µm Higher V oc limits for larger L eff /W Si ratios! Thinner silicon for higher efficiency! ~790 mv Limit ~40 µm Si Source: Martin Green, UNSW (Limits on the Open-Circuit Voltage and Efficiency of Silicon Solar Cells Imposed by Intrinsic Auger Processes) [ 24 ]

25 Bulk Lifetime and Surface Recombination Velocity Bulk recombination lifetime: 1/ b = 1/ radiative + 1/ Auger + 1/ defects Si lifetime is dominated by defects (SRH) and band-to-band Auger recombination In Auger recombination, the minority carrier (hole) recombines with an electron, transmitting its energy to a 3 rd charge (an electron in the CB or a hole in the VB) Auger recombination is dominant at N d > 1x10 17 cm -3 doping in good-quality Si Effective lifetime ( eff ) depends on b, S eff, and silicon absorber thickness (W Si ) For small S eff (S eff <D h /4W): 1/ eff 1/ b +2S eff /W Si (highly desirable with thin Si) For large S eff : 1/ eff 1/ b + (/W Si ) 2. D h (undesirable: eff 0.14 µs for W Si =40 µm) Solexel s high-efficiency, thin-silicon solar cell design rules require L eff = D h. eff to be a large multiple of W si for highest V oc ( 700 mv) and J sc ( 40 ma/cm 2 ) L eff 15.W si For 40 µm Si L eff 600 µm For D h 12 cm 2 /s eff 300 µs High-efficiency thin Si demands highest-quality surface passivation: S eff 5 cm/s [ 25 ]

26 Kerfless Thin Crystalline Silicon for Solar Cells Why Thin (Sub-50 µm EPI) Crystalline Silicon? Reduced silicon consumption and cost through kerfless CVD Epi-Si High-quality, high-mcl, low-[o], low[b], in-situ-doped thin epitaxial silicon Larger open-circuit voltage (V oc ) capability with excellent passivation Highly favored by the back-contact/back-junction (IBC) architecture Higher efficiency and lower temperature coefficient of power Cooler Normal Operating Cell Temperature (NOCT) Enhanced module energy yield (kwh/kwp) Flexible lightweight modules Thin-Silicon Challenges Kerfless Formation of Thin Silicon Handling and Processing Yield Loss Epitaxial Seed and Release Layers Economic Epitaxial Silicon Deposition Surface Passivation (very low SRVs) Solexel Approach and Solutions Epitaxial Silicon Lift-Off Process Template and Backplane Supports High-Productivity Porous Silicon Tool SUPREME-288 Epitaxial Tool Advanced field-assisted dielectric passivation [ 26 ]

27 Agenda Our Company and Value Proposition Crystalline Silicon PV Technology and Market Why Thin Crystalline Silicon for Solar Cells Our Disruptive Technology and Progress Summary [ 27 ]

28 Disruptive Technology and Production Process Proven in Semi, Mapped and Scaled to Solar PV Reusable Template Porous Silicon Thin Silicon Growth Cell Processing Flex Backplane TFSS Release Template Re-use Flex Smart Cell High-Performance Smart Reusable Template Foundation for Thin Cell Processing; Reusable >100x Releasable Thin Mono-Crystalline-Silicon 10x to 15x Less Si Usage vs. Traditional Back Contact/Back-Junction Cell Design 3%+ Points Higher Efficiency vs. Traditional Planar Flex Backplane Strength & Support for Cell; Smart Cells for Enhanced Energy Yield Full-Square 156 x 156 mm 2 Cell Boosts Power, All-Black Aesthetics [ 28 ]

29 High-Volume Batch Porous Silicon Tool World s first high-productivity batch porous Si tool for solar PV Solar-scale high productivity: 640 WPH (25 MW per Tool) Very low chemical consumption and very low cost Excellent porosity and thickness control over template areas Enables fast, high-yield mechanical release [ 29 ]

30 High-Volume Batch Epitaxy: SUPREME-288 Solar Ultra-Productivity REactor for Mono-silicon Epitaxy 288-wafer (12x24) batch size, highly modular architecture (12 chambers) World s highest productivity epi tool at 440 WPH (~18 MW per Tool) Good within-wafer and wafer-towafer uniformity & repeatability Very high deposition rate High TCS utilization Very high quality on porous silicon: 300 µs for n-doped epi on por-si Fast in-situ clean with HCl Porous Silicon Doped Epi Reusable Template [ 30 ]

31 World Record 156 mm x 156 mm Full-Square Cell Efficiency Using 43 µm Epitaxial Silicon Cell Absorber NREL-Certified Full-Area Cell Efficiency = 20.13% 156 x 156 mm 2 full-square cell (242.6 cm 2 ) 43 µm epitaxial Si cell, FSRV < 10 cm/s Voc = mv Jsc = ma/cm 2 FF = 77.41% Cell Max Power = 4.88 Wp; I sc = 9.25 A [ 31 ]

32 NREL Best Research-Cell Efficiencies: Solexel holds the Thin-Film Crystal Record Efficiency 20.1% (243 cm 2 ) [ 32 ]

33 World Record 156 mm x 156 mm Full-Square Cell Efficiency Also Providing Excellent Low-Light Cell Performance Solexel-Measured Full-Area Cell Efficiency = 20.62% 20% 1-sun Efficiency 156 x 156 mm 2 full-square cell (243.0 cm 2 ) 43 µm epitaxial silicon cell absorber Voc = mv Jsc = ma/cm 2 FF = 78.88% Cell Max Power = 5.01 Wp; I sc = 9.30 A 96.5% of the STC Efficiency for 390 W/m 2 Irradiation (AM 1.5, 25C) 19.3% 0.39 SUN for Cells With Mean STC =20.0% [ 33 ]

34 Quantum Efficiency/ Reflectivity % World Record 156 mm x 156 mm Full-Square Cell Efficiency: Quantum Efficiency, Efficiency Distribution for 43 µm Epi-Si UV Visible ( nm) nm IR ( 750 nm) EQE Reflectance IQE Solexel-Measured Full-Area Champion Cell Efficiency = 20.62% Continuous Improvement in Cell Efficiency Distribution Wavelength (nm) Excellent Blue (and Visible) Response Excellent Red (and IR) Response 43 µm Epitaxial Silicon Cell Absorber! Cell Efficiency 20% 0.5% (Full-Square 243 cm 2 Area) 43 µm Epi-Lift Off Si Cell [ 34 ]

35 Normal Operating Cell Temperature (NOCT): Solexel s Operate ~5C to 7C Cooler! NOCT measurements performed on 60-cell modules, data over a 2-week period s mounted outdoors, monitored for irradiance, wind speed and direction Thermocouple mounted on module backside or directly to the cell inside Measured NOCT~ C, cooler than traditional c-si modules (47-49C) 1002: NOCT=39.10C TC on Backside 1003: NOCT=41.75C TC on Cell in Irradiance (mw/cm 2 ) Irradiance (mw/cm 2 ) [ 35 ]

36 Design and Reliability Design and Materials Both standard rigid modules and flexible lightweight modules Back-contact module assembly/testing with standard tools, leverage OEM scale Smart s with embedded shade management for enhanced energy yield Developing specialty BIPV rooftop shingles with Owens Corning Reliability Testing Results to Date Extremely reliable backplane-laminated ultrathin epitaxial silicon cells Excellent module reliability No issues identified in Thermal Cycle (>5x), Damp Heat (>3x), Humidity Freeze (~4x), and Highly Accelerated Tests (1x); Solexel module units passed IEC requirements, exhibit long-term robustness All tested module units passed the relevant IEC requirements; No PID NOCT 5-7C is cooler! ~0.50% extra effective absolute efficiency advantage No roadblocks towards full Solexel PV module certification [ 36 ]

37 Go-To-Market Strategy: Partnering with Top-Tier Customers Production Disruptive technology demonstrated on pilot engineering line in California Proving high-volume manufacturability of the HVM toolset in California Will ramp copy-exact HVM lines in Malaysia, will sell PV modules by 2014 Roadmap: module =22%, cost $0.42/W, capex $0.65/W, LCOE $0.06/kWh Customers s appeal to key segments: residential, commercial, utility-scale, BIPV Top-tier strategic customers (leading global developers and distributors) Customers help get Solexel to market: testing, bankability, marketing Production volume fully subscribed by strategic customers Developing BIPV rooftop shingles with Owens Corning (DOE SunShot award) [ 37 ]

38 Agenda Our Company and Value Proposition Crystalline Silicon PV Technology and Market Why Thin Crystalline Silicon for Solar Cells Our Disruptive Technology and Progress Summary [ 38 ]

39 Take Aways Efficiency, Energy Yield, Cost (module, installed system, LCOE) Crystalline silicon PV will retain its market dominance: Higher efficiency at lowest manufacturing cost Proven material and field reliability track record Well-established manufacturing infrastructure Sustainable and non-toxic, meets TW-scale volume Highest-performance SJ c-si PV based on either heterojunction emitter (HIT) or IBC cell designs Kerfless Thin-Silicon Epi enables low cost and high performance through cell design and process innovations Excellent synergy between Kerfless Thin-Silicon Epi and IBC cell [ 39 ]

40 Thin Silicon Total Solution for High Performance, Low Cost Scalable and Extendible Modular Technology Platform Much Less Si: 43 µm Epi Cells Full-Square 156 x 156 mm 2 Inexpensive Input: TCS+H 2 High Lifetimes (>300µs) Capex Reduced Epi & Por-Si HVM Tools THIN EPI SILICON TEMPLATE REUSE Achieved 50+ Template Reuse; Excellent Release Yield Amortize Over 100+ Reuses No Degradation w/ Reuse Recycle Inputs Thin Epi Silicon 20.6% Champion Efficiency 20% 0.5% Passed Reliability Tests Path to 22% Efficiency All-Black Aesthetics; No LID CELL DESIGN BACK- PLANE Smart Cells Always Support Si NOCT: Energy Yield Planar, Flexible, Inexpensive High Cell Yield No Breakage [ 40 ]