SILIZIUM-PHOTOVOLTAIK STATUS UND NEUE ENTWICKLUNGEN

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1 SILIZIUM-PHOTOVOLTAIK STATUS UND NEUE ENTWICKLUNGEN Stefan Glunz Fraunhofer Institute for Solar Energy Systems ISE Seminarreihe Erneuerbare Energien 27. Juni 2018, Hochschule Karlsruhe Fraunhofer ISE PV Module Production Development by Technology It is still silicon Production 2016 (GWp) Thin film 4.9 Multi-Si 57.5 Mono-Si 20.2 Fraunhofer ISE 2 Data: from 2000 to 2010: Navigant; from 2011: IHS (Mono-/Multi- proportion from cell production). Graph: PSE 2017 Stefan Glunz, Fraunhofer ISE

2 PAST 3 PAST The Bell labs 1954 Gerald Pearson, Darryl Chapin, and Calvin Fuller testing their silicon solar cell. 4 Stefan Glunz, Fraunhofer ISE

3 PAST The Beginning Strong increase of efficiency in the 1950s n-type silicon dominates as base material Efficiency [%] % G.L- Pearson, American J. Phys. 25, p.591 (1957) 5 5 mono-si (p-type) mono-si (n-type) PAST The First Application Space 1957 Sputnik (USSR) 1958 Explorer 1 (USA) Sputnik Vanguard First solar-powered satellite Vanguard 1 6 Stefan Glunz, Fraunhofer ISE

4 PAST From Space to Earth Switch to p-type silicon due to higher radiation stability for space applications Reduction of recombination losses Model for current industrial cell generation 7 Efficiency [%] Blakers et al., Appl. Phys. Lett. 55, 1363 (1989) Small area 29.4% 5 mono-si (p-type) mono-si (n-type) PRESENT Average Price for PV Rooftop Systems in Germany System costs strongly area-related Further increase of cell efficiency BOS incl. Inverter Modules Fraunhofer ISE Percentage of the Total Cost Data: BSW-Solar. Graph: PSE Stefan Glunz, Fraunhofer ISE

5 PRESENT Large-area Record Cells on n-type Silicon Interdigitated back contact back junction solar cells Excellent contact passivation (a-si/c-si heterojunction, passivated contacts) Sanyo 1 (da=143.7 cm 2 ) 25.6% (V oc = 740 mv) SunPower 2 (ta=153.5 cm 2 ) 25.2% 3 (V oc = 737 mv) 2016: Kaneka (da=180.4 cm 2 ) 26.6% 3 (V oc = 744 mv) 26.7% 9 Panasonic/Sanyo 1 Masuko et al., IEEE PVSC (2014) SunPower: 2 Smith et al., IEEE PVSC (2014) 3 Yoshikawa et al., Nature Energy (2017) PRESENT Record Cells on Crystalline Silicon Large-area (Sunpower, Sanyo/Panasonic, Kaneka) Sophisticated cell architecture Excellent material quality needed Efficiency [%] Small area 29.4% Large area 5 mono-si (p-type) mono-si (n-type) Stefan Glunz, Fraunhofer ISE

6 THE Working Horse Screen-printed Al-BSF solar cell on p-type silicon Still the main technology of the PV technology (70 to 80% of the market) Efficiencies up to 19% (multi-si) or 20% (mono-si) Incremental improvements (better pastes, surface passivation) It is hard to beat the main stream! n-contact ARC n-emitter pn- Junction p-base Al-BSF p-contact Process Saw Damage Removal Texture + Cleaning Diffusion PSG Removal and Isolation ARC Screenprinting Firing 11 The Next Industrial Cell Generation Partial Rear Contact Cells (PRC or PERC) The successor of Al-BSF cells: Partial Rear Contact (PRC) cells also known as PERC (25 years after its invention!) - + Passivation layer - + Reduced contact area 12 Improved electrical (= less recombination) and optical (=higher internal reflection) Stefan Glunz, Fraunhofer ISE

7 The Next Industrial Cell Generation Switching from Al-BSF to PRC (PERC) Al-alloyed back surface field (Al-BSF) solar cells have dominated the industry for decades Partial rear contact cells (PRC) like PERC/PERL are introduced in production = 19% - 20% = 20% % Mandelkorn and Lamneck, J. Appl. Phys. 44, 4785 (1973) Blakers et al., Appl. Phys. Lett. 55, 1363 (1989) 13 The Next Industrial Cell Generation Industrial process for PERC cells Two additional process steps Dielectric passivation Local contact opening (LCO) SDE/Texture POCl diffusion Edge Isolation PSG etching Al 2 SiN O 3 / ARC SiN RS Laser SP Ag Opening FS SP Al/Ag RS Drying & Firing 14 Stefan Glunz, Fraunhofer ISE

8 The Next Industrial Cell Generation Partial Rear Contact Cells (PRC or PERC) The successor of Al-BSF cells: Partial Rear Contact (PRC) cells also known as PERC (25 years after its invention!) Record cell results: p-type mono-si: 22.1% (Trina) 22.0% (Solar World) > 23% (Jolywood) p-type multi-si 21.25% (Trina) 22% (Jinko Solar) 15 P. Verlinden, WCPEC, Kyoto, 2014 PERC Modules Bifacial p-type PERL Solar Cells Starting point: PERC-process Fingers on front and back side Bifacial power conversion Dullweber et al. PiP 2015 SolarWorld BiSun technology 16 Stefan Glunz, Fraunhofer ISE

9 Module Technology No More Busbars Cell has only fingers and no busbars Interconnection with solder-coated wires Lower reflection losses Improved aesthetics Meyer&Burger Smart Wire LG Neon module 17 Bridging the Gap State-of-the-Art Silicon Solar Cell: Cost Analysis???? Allowed costs for same levelized costs of electricity (LCOE) as a function of cell efficiency normalised cost of cell production [%] p-type mc Al-BSF n-type Cz World Record cell efficiency [%] 18 M. Hermle et. al., 29 th EUPVSC Stefan Glunz, Fraunhofer ISE

10 Bridging the Gap State-of-the-Art Silicon Solar Cell: Cost Analysis Allowed costs for same levelized costs of electricity (LCOE) as a function of cell efficiency Bridging the gap: - Higher efficiency - Reasonable complexity normalised cost of cell production [%] p-type mc Al-BSF n-type Cz World Record cell efficiency [%] 19 PRESENT PERC Restrictions p + n ++ n-base J 0,met > J 0,pass PERC cells have high efficiency potential But: Strongly two-dimensional cell structure (contact distance = 5 cell thickness) Trade-off in cell design: V oc vs. FF Influence of base resistivity Additional patterning step required local contact 20 Stefan Glunz, Fraunhofer ISE

11 Bridging the Gap n-type PRC Restrictions n ++ p + n-base p + n-base J 0,met > J 0,pass J 0,met = J 0,pass local contact passivating contact 21 Bridging the Gap Hybrid TOPCon Cell n-type hybrid cell with boron emitter at the front and a passivated rear side offers 1. transparent front side 2. less influence of base resistivity 3. no patterning of the rear side p + n-base J 0,met = J 0,pass passivating contact 22 Stefan Glunz, Fraunhofer ISE

12 TOPCon (Tunnel Oxide Passivated Contact) Combining a-si Hetero and poly-si/tunnel Oxide Approach E C E F Higher band gap Very good selectivity Better thermal stability Tunnel oxide E C E F n-si Base E V Tunnel oxide E V Amorphous n-si Base Polycrystalline Si(n)-Layer Si(n)-Layer E C E F n-si Base E V Amorphous/Polycryst. Si (n)-layer 23 F. Feldmann et al., SOLMAT 120 (2014) TOPCon (Tunnel Oxide Passivated Contact) Combining a-si Hetero and poly-si/tunnel Oxide Approach a-/nc-si 24 Stefan Glunz, Fraunhofer ISE

13 TOPCon (Tunnel Oxide Passivating Contact) A New Rear Contact Si Thin Film Boron emitter n-base Tunnel oxide Highly doped silicon thin film Metal F. Feldmann et al.,solmat (2014) 25 High-Efficiency Solar Cells Cells with Top/Rear Contacts Material Area V oc J sc FF η [cm 2 ] [mv] [ma/cm 2 ] [%] [%] UNSW/ PERL 1 p-type 400 μm 4 (da) Kaneka/ HJT 2 n-type 200 μm 152 (ap) Zhao et al., Progr. Photovolt. (1999) 2 Adachi et al., Appl. Phys. Lett. (2015) 26 Stefan Glunz, Fraunhofer ISE

14 High-Efficiency Solar Cells Cells with Top/Rear Contacts Material Area V oc J sc FF η [cm 2 ] [mv] [ma/cm 2 ] [%] [%] UNSW/ PERL p-type mono-si 4 (da) Kaneka/ HJT n-type mono-si 152(ap) ISE / TOPCon 1 n-type mono-si 4 (da) *ISE CalLab Measurement p ++ n-base 27 TOPCon: J 0,rear º 3-5 fa/cm² High-Efficiency Solar Cells Cells with Top/Rear Contacts Material Area V oc J sc FF η [cm 2 ] [mv] [ma/cm 2 ] [%] [%] UNSW/ PERL p-type mono-si 4 (da) Kaneka/ HJT n-type mono-si 152(ap) ISE / TOPCon 1 n-type mono-si 4 (da) * FELA [mw/cm 2 ] *ISE CalLab Measurement Front Recomb p ++ n-base TOPCon: J 0,rear º 3-5 fa/cm² Bulk Recomb Resistive Losses; 0.05 External R s and R p 0.49 Rear Recomb Stefan Glunz, Fraunhofer ISE

15 High-Efficiency Solar Cells Cells with Top/Rear Contacts Material Area V oc J sc FF η [cm 2 ] [mv] [ma/cm 2 ] [%] [%] UNSW/ PERL p-type mono-si 4 (da) Kaneka/ HJT n-type mono-si 152(ap) ISE / TOPCon 1 n-type mono-si 4 (da) *ISE CalLab Measurement p ++ n-base 29 TOPCon: J 0,rear º 3-5 fa/cm² High-Efficiency Solar Cells Cells with Top/Rear Contacts Material Area V oc J sc FF η [cm 2 ] [mv] [ma/cm 2 ] [%] [%] UNSW/ PERL p-type mono-si 4 (da) Kaneka/ HJT n-type mono-si 152(ap) ISE / TOPCon 1 n-type mono-si 4 (da) * *ISE CalLab Measurement p ++ n-base 30 TOPCon: J 0,rear º 3-5 fa/cm² 1 Richter et al., SOLMAT (2017) Stefan Glunz, Fraunhofer ISE

16 High-Efficiency Solar Cells Cells with Top/Rear Contacts Material Area V oc J sc FF η [cm 2 ] [mv] [ma/cm 2 ] [%] [%] UNSW/ PERL p-type mono-si 4 (da) Kaneka/ HJT n-type mono-si 152(ap) ISE / TOPCon ISE/ TOPCon 1 n-type mono-si n-type multi-si 4(da) * 22.3* *ISE CalLab Measurement 31 1 Benick et al., IEEE JPV (2017) Record Efficiencies 32 October 2017 Stefan Glunz, Fraunhofer ISE

17 Record Efficiencies Mono-Si heterojunction Mono-Si homojunction Perovskite (not stabilized) CIGS Multi-Si CdTe 33 October 2017 What is the limit? Detailed Balance Shockley und Queisser, 1961 Detailed balance between sun and solar cell Assumption: Solar cell emits photons via radiative recombination E k Radiative recombination in a direct semiconductor W. Shockley & H. Queisser 34 Stefan Glunz, Fraunhofer ISE

18 What is the limit? Maximum Efficiency as a Function of Bandgap Max. Efficiency ~ 33% High thermalisation for low bandgaps High transmission for high bandgaps Silicon and GaAs are close to the optimum But: Record values of GaAs are closer to the limit. Is III/V-R&D better than silicon-r&d? Efficiency Thermalisation Transmission GaAs 0.25 c-si 0.20 mc-si CIGS InP CdTe GaSb a-si AlGaAs 0.05 Ge Shockley-Queisser Record Efficiencies E G [ev] 35 What is the Limit? Other Recombination Channels Assumption: Ideal solar cell: only radiative recombination (Shockley and Queisser, J. Appl. Phys. 1961) E Phonon k But silicon is an indirect semiconductor radiative recombination has a low probability Radiative recombination in an indirect semiconductor 36 Stefan Glunz, Fraunhofer ISE

19 What is the limit? Auger-Recombination In silicon solar cells Auger-recombination is the limiting intrinsic loss mechanism E k BZB Pierre Auger Auger recombination in an indirect semiconductor 37 What is the limit? Taking Auger Recombination into Account Shockley, Queisser (1961) = 33% (AM1.5) Theoretical efficiency limit for silicon (taking actual Auger model 1 into account) = 29.4% 2 1 Richter, Glunz et al., Phys. Rev. B 86 (2013) 2 Richter, Hermle, Glunz, IEEE J. Photovolt. (2013) 38 Stefan Glunz, Fraunhofer ISE

20 What is the Limit? Taking Auger Recombination into Account Shockley, Queisser (1961) = 33% (AM1.5) Theoretical efficiency limit for silicon (incl. Auger) = 29.4% 1 Best silicon solar cells = 25.6% 2 Corresponds to 87% of theoretical efficiency limit (GaAs = 87% ) Efficiency GaAs 0.25 c-si 0.20 mc-si CIGS InP CdTe GaSb a-si AlGaAs 0.05 Ge Shockley-Queisser Record Efficiencies E G [ev] 1 Richter, Hermle, Glunz, IEEE J. Photovolt. (2013) 2 Masuko et al., IEEE-PVSC (2014) 39 FUTURE Beyond the Shockley-Queisser-Limit Shockley, Queisser (1961): Efficiency limit of solar cell made of one material = 33% Theoretical efficiency for silicon (Auger limit) = 29.4% 1 Light management Up-conversion Beam splitting Tandem cells with silicon as bottom cell Perovskite top cell Silicon quantum dots III/V top cell 40! Efficiency Thermalisation c-si mc-si CIGS InP GaAs CdTe Transmission 0.10 GaSb a-si AlGaAs 0.05 Ge Shockley-Queisser Record Efficiencies E G [ev] 1 Richter, Hermle, Glunz et al., IEEE J. Photovolt Stefan Glunz, Fraunhofer ISE

21 Beyond the Limit Magic Antireflection Coatings (AAA-Coating ) Silicon Solar Cells with AAA-Coating (amazingly active antireflection coating) AAA- Coating Si (1.12 ev) GaInP (1.88 ev) GaAs (1.42 ev) Si (E g = 1.12 ev) Si (1.12 ev) 41 Beyond the Limit Silicon Solar Cell Theoretical limit for E g,si : 33% (29.4% considering Auger recombination) Word record for silicon solar cells: 26.7% Intensity [W m -2 nm -1 ] Thermalization loss Usable power Bandgap Transmission loss Wavelength [nm] 42 Stefan Glunz, Fraunhofer ISE

22 Beyond the Limit Multijunction Solar Cells Tandem cells with Si bottom cell III/V on Si Silicon quantum dots Perovskites Silicon Solar Cell 2.0 Intensity [W m -2 nm -1 ] AM Cell 2. Cell 3. Cell (Si) Wavelength [nm] 43 Beyond the Limit III-V on Silicon Tandem Solar Cells 44 Stefan Glunz, Fraunhofer ISE

23 Beyond the Limit Silicon-based Multijunction Cells Top cells with high bandgap to utilize blue and visible light c-si bottom cells for IR light Deposition by direct epitaxial growth or wafer bonding GaInP (1.88 ev) GaAs (1.42 ev) Si (1.12 ev) 45 Beyond the Limit Silicon-based Multijunction Cells III-V Substrate GaInP pn-junction GaAs pn-junction Si bottom cell III-V substrate lift-off and recycling Bonding to new substrate 46 Stefan Glunz, Fraunhofer ISE

24 Beyond the Limit Silicon-based Multijunction Cells 5-10 μm GaInP pn-junction GaAs pn-junction Si bottom cell Processing of solar cell contacts and ARC 47 Beyond the Limit 2-terminal GaInP/AlGaAs//Si GaInP- cell HRTEM-image of Si/GaAs interface 4 nm thick amorphous layer GaAs- cell GaAs Silicon- cell or wafer 1 µm 10 nm Silicon 48 High Resolution TEM Image, Bright Field, Zone Axis Si, Universität Kiel, Group Prof. Dr. Jäger, 2011 Stefan Glunz, Fraunhofer ISE

25 Beyond the Limit 2-terminal GaInP/AlGaAs//Si Very good current matching: Each cell around 12 ma/cm 2 Efficient utilization of spectrum Intensity [W m -2 nm -1 ] AM1.5g GaInP GaAs Si Total GaInP (1.88 ev) GaAs (1.42 ev) Wavelength [nm] Si (1.12 ev) 49 Beyond the Limit 2-terminal GaInP/AlGaAs//Si AM1.5g Efficient utilization of spectrum Very good current matching Efficiency = 30.2 > 29.4% 50 R. Cariou et al., Fraunhofer ISE IEEE Journal of Photovoltaics 2017 R. Cariou et al., Fraunhofer ISE Nature Energy 2018 Stefan Glunz, Fraunhofer ISE

26 Wafer-Bonded 2-Terminal GaInP/AlGaAs//Si Tandem TOPCon with Nanostructured Diffraction Grating V oc [V] Gen 3 J sc [ma/cm 2 ] FF [%] η [%] p + poly-si 1 µm Ag Resist 51 R. Cariou, Nature Energy (2018) doi: /s Beyond the Limit III-V on Silicon Tandem Solar Cells 1.9 μm of III-V material on Si sufficient to realize = 33.3% solar cell by wafer bonding = 19.7% efficiency reached for GaInP/GaAs/Si triple-junction by direct growth Both values included in PIP Efficiency tables Stefan Glunz, Fraunhofer ISE

27 Beyond the Limit 2-terminal GaInP/AlGaAs//Si > 1-Sun AM1.5g Efficient utilization of spectrum Very good current matching Efficiency = 33.3 > 29.4% Beyond the Auger limit for crystalline silicon solar cells 53 R. Cariou et al., Fraunhofer ISE Nature Energy 2018 Conclusion Photovoltaics is a significant player in the energy market. Prices are already very low. Conversion efficiency is the key to further bring down the levelized costs of electricity and to survive competition. 54 Stefan Glunz, Fraunhofer ISE

28 Conclusion Photovoltaics is a significant player in the energy market. Prices are already very low. Conversion efficiency is the key to further bring down the levelized costs of electricity and to survive competition. New cell structures with high industrial potential. 55 Conclusion Photovoltaics is a significant player in the energy market. Prices are already very low. Conversion efficiency is the key to further bring down the levelized costs of electricity and to survive competition. New cell structures with high industrial potential. New fascinating concepts for an old technology: Crystalline silicon solar cells 2.0 GaInP (1.88 ev) GaAs (1.42 ev) Si (1.12 ev) 56 Stefan Glunz, Fraunhofer ISE

29 Conclusion Photovoltaics is a significant player in the energy market. Prices are already very low. Conversion efficiency is the key to further bring down the levelized costs of electricity and to survive competition. New cell structures with high industrial potential. New fascinating concepts for an old technology: Crystalline silicon solar cells 2.0 GaInP (1.88 ev) GaAs (1.42 ev) Si (1.12 ev) 57 Stefan Glunz, Fraunhofer ISE