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© Fraunhofer ISE TOPCon – Poly-Si based Passivating Contacts Jochen Rentsch, Frank Feldmann, Martin Hermle, Ralf Preu, Stefan W. Glunz Fraunhofer Institute for Solar Energy Systems ISE PV CellTech Penang, March 12th, 2019 www.ise.fraunhofer.de © Fraunhofer ISE 2 Introduction  Silicon is still the working horse of Photovoltaic  Conversion efficiency is the key to further bring down the levelized costs of electricity and to survive competition.  Learning curve for efficiency improvement at 0.6abs/year  Passivating contacts represent promising concept for next generation solar cells after PERC [1] [1] https//www.pv-magazine.com/2018/12/31/14-pv-trends-for-2019/ [2] M. Hermle, ETIP PV, PV Manufacturing in Europe, 2017, Brussels [2] © Fraunhofer ISE 3 Introduction Poly-Si as Passivating Contact is already an old story SIPOS Hetero- contact[1] Voc 720mV Polysilicon Emitters for IBC cells[2] Low J0 and c [1]Yablonovich, Applied Physics Letters 1985 [2] Gan and Swanson, IEEE PVSC 1990 [3] F. Feldmann et al., EU-PVSEC 2013 Tunnel Oxide Passivating Contact TOPCon by Fraunhofer ISE [4] Solar cell with Voc 703 mV and  23.7 1985 1990 2013 © Fraunhofer ISE 4 TOPCon Process[1]  Tunnel oxide HNO3, UV/O3[2], O3[2], TO  Interface passivation  PECVD deposition single-sided doped a-SiCx layer  Carrier-selectivity The TOPCon Approach Process n-base SiOx P-doped Si layer [1] F. Feldmann et al., SolMat 2014 [2] A. Moldovan et al., SolMat 2015 © Fraunhofer ISE 5 TOPCon Process[1]  Tunnel oxide HNO3, UV/O3, O3, TO  Interface passivation  PECVD deposition single-sided doped a-SiCx layer  Carrier-selectivity  Furnace Anneal  partial crystallization  dopant diffusion  Hydrogenation RPHP  Defect passivation The TOPCon Approach Process SiOx P-doped Si layer n-base [1] F. Feldmann et al., SolMat 2014 © Fraunhofer ISE 6  Record lifetimes on both p-type 0.095 s and n-type 0.225 s FZ Si TOPCon Tunnel Oxide Passivated Contact Surface Passivation with Hydrogenation Graph from Niewelt et al., SolMat accepted © Fraunhofer ISE 7  Improved TOPCon process  Excellent surface passivation with iVoc 740 mV demonstrated  Low contact resistivity c 10 mΩcm²  Efficient passivating and carrier-selective contact TOPCon Tunnel Oxide Passivated Contact Electrical properties 0.1 1 10 700 710 720 730 740 900 °C 950 °C 900 °C Tunn el ox ide HNO 3 O 3 TO Implied V oc [mV] Contact resistivity [m  cm 2 ] 800 °C SiOx P-doped Si layer n-base © Fraunhofer ISE 8 2013 2014 2015 2016 2017 2018 2019 21 22 23 24 25 26 27 Hybrid Top/Rea r Efficiency [ ] Year Both Side Contacted Record Cells with TOPCon p boron-diffused Full-area rear contact TOPCon c-Sinp Hybrid ■ Lab scale cells on n-type Fz-Si © Fraunhofer ISE 9 Material Area Contact Voc Jsc FF η techn. [mV] [mA/cm2] [] [] n-type Mono 4 cm² da PLEvap. 724 42.9 83.1 25.8*,1 n-type Multi 4 cm² ap PLEvap. 674 41.1 80.5 22.3*,2 n-type Mono 100 cm² ap PLEvap. 713 41.4 83.1 24.5*,3 n-type Mono 100 cm² ap LCONi/Cu Plat. 697 41.4 81.2 23.4* Both Side Contacted Record Cells with TOPCon [3] F.Feldmann et al., Evaluation of TOPCon technology on large area solar cells EUPVSEC, Amsterdam, 2017 Cu-Plating [1] A. Richter et al., Tunnel oxide passivating electron contacts as full‐area rear emitter of high‐efficiency p‐type silicon solar cells, Prog Photovolt Res Appl. 2018;26579–586 [2] J. Benick et al., High-Efficiency n-Type HP mc Silicon Solar Cells, IEEE JPV, Vol. 7, No. 5, 2017 *confirmed by Fraunhofer ISE CalLab PL Contacts defined by Photolithography © Fraunhofer ISE 10 Both Side Contacted Record Cells with TOPCon Material Area Contact Voc Jsc FF η techn. [mV] [mA/cm2] [] [] n-type Mono 4 cm² da PLEvap. 724 42.9 83.1 25.8*,1 n-type Multi 4 cm² ap PLEvap. 674 41.1 80.5 22.3*,2 n-type Mono 100 cm² ap PLEvap. 713 41.4 83.1 24.5*,3 n-type Mono 100 cm² ap LCONi/Cu Plat. 697 41.4 81.2 23.4*,4 [4] B.Steinhauser et al., Large Area TOPCon Technology Achieving 23.4 Efficiency IEEE PVSC, Hawaii, 2018 [3] F.Feldmann et al., Evaluation of TOPCon technology on large area solar cells EUPVSEC, Amsterdam, 2017 [1] A. Richter et al., Tunnel oxide passivating electron contacts as full‐area rear emitter of high‐efficiency p‐type silicon solar cells, Prog Photovolt Res Appl. 2018;26579–586 [2] J. Benick et al., High-Efficiency n-Type HP mc Silicon Solar Cells, IEEE JPV, Vol. 7, No. 5, 2017 *confirmed by Fraunhofer ISE CalLab © Fraunhofer ISE 11 Both Side Contacted Record Cells with TOPCon p boron-diffused Full-area rear contact TOPCon c-Sinp Hybrid ■ Lab scale cells on n-type Fz-Si ■ First industrial adoptions on large area n-type Cz-Si 2013 2014 2015 2016 2017 2018 2019 21 22 23 24 25 26 27 Hybrid Top/Rea r Efficiency [ ] Year [1] http//ir.jinkosolar.com/news-releases/news-release-details/ jinkosolar-large-area-n-type-topcon-monocrystalline-silicon [2] Presentation Duttagupta et.al., CSPV14 Xian, China 2018 [3] Presentation Zhifeng Liu, et.al. Jolywood, EU-PVSEC 2018 [1] [2][3] © Fraunhofer ISE 12 Challenges for Industrial Implementation of TOPCon ■ How to upgrade from existing PERC lines Material  Change from p- to n-type silicon material PERC TOPCon c-Sip c-Sin © Fraunhofer ISE 13 Challenges for Industrial Implementation of TOPCon ■ How to upgrade from existing PERC lines Material  Change from p- to n-type silicon material Front side  Replace POCl3 with BBr3 diffusion, shift AlOx/SiNx passivation Diffusion LP-BBr3 SDE texture Chemical edge isolation Diffusion LP-POCl3 SDE texture Chemical edge isolation Laser Selective Emitter Laser Selective Emitter c-Sipn Al2O3 front PECVD SiNx front c-Sinp n-emitter SiNx AlOx SiNxp-emitter PECVD SiNx front © Fraunhofer ISE 14 Challenges for Industrial Implementation of TOPCon ■ How to upgrade from existing PERC lines Material  Change from p- to n-type silicon material Front side  Replace POCl3 with BBr3 diffusion, shift AlOx/SiNx passivation Rear side  Implement TOPCon layer formation replacing LCO Diffusion LP-BBr3 TOPCon Oxidation SDE texture Chemical edge isolation TOPCon PECVD TOPCon High-T anneal Al2O3 front PECVD SiNx front PECVD SiNx rear Diffusion LP-POCl3 SDE texture Chemical edge isolation Al2O3 rear PECVD SiNx rear Laser Contact Opening Laser Selective Emitter Laser Selective Emitter PECVD SiNx front c-Sipn c-Sinp SiNxpc-Six TOLCO © Fraunhofer ISE 15 Challenges for Industrial Implementation of TOPCon ■ How to upgrade from existing PERC lines Material  Change from p- to n-type silicon material Front side  Replace POCl3 with BBr3 diffusion, shift AlOx/SiNx passivation Rear side  Implement TOPCon layer formation replacing LCO  Adapt metallization grid Diffusion LP-BBr3 TOPCon Oxidation SDE texture Chemical edge isolation TOPCon PECVD TOPCon High-T anneal Al2O3 front PECVD SiNx front SP front and back PECVD SiNx rear FFO Diffusion LP-POCl3 SDE texture Chemical edge isolation SP front and back FFO Laser Contact Opening Laser Selective Emitter Laser Selective Emitter c-Sinpc-Sipn Ag-GridAl finger Ag Pads Al2O3 rear PECVD SiNx rear PECVD SiNx front © Fraunhofer ISE 16 Research for Industrial Implementation PV-TEC pilot manufacturing platform Over 2000 m² for Highest efficiency solar cell processing Cutting edge automated pilot equipment from leading manufacturers, including © Fraunhofer ISE 17 Poly-Si deposition Batch PECVD – Thin n-TOPCon films  Excellent homogeneity over the boat  Textured wafers, 15 nm thin pc-Si film - 1 S D 1 S D 50 M a x M in 725 730 735 740 745 i V OC Performance over Boat i V OC [mV] Me an ± 1 SD Data 15 61 56 mm ², text ur ed 1  cm n- ty pe 15 0 µm thickn ess © Fraunhofer ISE 18 Poly-Si deposition Inline PECVD  Comparison of two PECVD sources for n-TOPCon film deposition  Both provide excellent passivation  So far, only MW allows for deposition of thick films without blistering 100 nm which are essential for fire-through metallization 0 10 20 30 40 50 680 700 720 740 plana r t ex tured Impli ed V oc mV Nom inal thickness [nm] 0 20 40 60 80 100 120 140 680 700 720 740 plana r t ex tured Implied V oc [mV] Nomina l thickn ess [nm ] MW source RF source © Fraunhofer ISE 19 Benefits and Challenges for Industrial Implementation Challenges  Fire-through metallization1-3  Very thick pc-Si needed for current generation of pastes  Low Rsheet but high parasitic absorption for front/rear illumination  Further paste development essential [1] R. Naber et al., EU PVSEC, 2016 [2] S. Mack et al., Phys. Status Solidi RLL, 2017 [3] H. E. Ciftpinar et al., Energy Proc., 2017 © Fraunhofer ISE 20 Screen printed based metallization Contacting poly-Si  Suitable J0,met and 𝜌𝑐 for adapted Ag paste found  Process window 830°C compatible also with front side BBr3 emitter, J0,met 600 fA/cm², 𝜌𝑐 3 mΩcm² n-base SiOx P-doped Si layer SiNx Sample test structure Ag contact © Fraunhofer ISE 21 Analysis of processing cost with Bottom-Up TCO approach Diffusion LP-BBr3 TOPCon Oxidation SDE texture Chemical edge isolation TOPCon PECVD TOPCon High-T anneal Al2O3 front PECVD SiNx front SP front and back PECVD SiNx rear FFO Diffusion LP-POCl3 SDE texture Chemical edge isolation SP front and back FFO Laser Contact Opening Laser Selective Emitter Laser Selective Emitter c-Sinc-Sip Al2O3 rear PECVD SiNx rear PECVD SiNx front PERC TOPCon n-type wafer 2.7 €ct/cell © Fraunhofer ISE 22 Analysis of processing cost with Bottom-Up TCO approach Diffusion LP-BBr3 TOPCon Oxidation SDE texture Chemical edge isolation TOPCon PECVD TOPCon High-T anneal Al2O3 front PECVD SiNx front SP front and back PECVD SiNx rear FFO Diffusion LP-POCl3 SDE texture Chemical edge isolation SP front and back FFO Laser Contact Opening Laser Selective Emitter Laser Selective Emitter c-Sinc-Sip Al2O3 rear PECVD SiNx rear PECVD SiNx front PERC TOPCon BBr3 diffusion 0.3 €ct/cell © Fraunhofer ISE 23 Analysis of processing cost with Bottom-Up TCO approach Diffusion LP-BBr3 TOPCon Oxidation SDE texture Chemical edge isolation TOPCon PECVD TOPCon High-T anneal Al2O3 front PECVD SiNx front SP front and back PECVD SiNx rear FFO Diffusion LP-POCl3 SDE texture Chemical edge isolation SP front and back FFO Laser Contact Opening Laser Selective Emitter Laser Selective Emitter c-Sinc-Sip Al2O3 rear PECVD SiNx rear PECVD SiNx front PERC TOPCon TOPCon layer 5.4 €ct/cell Passivation © Fraunhofer ISE 24 Analysis of processing cost with Bottom-Up TCO approach Diffusion LP-BBr3 TOPCon Oxidation SDE texture Chemical edge isolation TOPCon PECVD TOPCon High-T anneal Al2O3 front PECVD SiNx front SP front and back PECVD SiNx rear FFO Diffusion LP-POCl3 SDE texture Chemical edge isolation SP front and back FFO Laser Contact Opening Laser Selective Emitter Laser Selective Emitter c-Sinc-Sip Al2O3 rear PECVD SiNx rear PECVD SiNx front PERC TOPCon alt. metallization scheme 3.3 €ct/cell add. cost TOPcon 12.4 €ct/cell Passivation © Fraunhofer ISE 25 Cost reduction potentials Short term solutions expected – TOPCon ■ n-type wafer Reduction of cost difference to p-type from currently 10 to 5 due to  Higher ingot yield due to narrower resistivity distribution optimisation of continous Cz pulling technology up to 2 €ct/wafer © Fraunhofer ISE 26 Cost reduction potentials Short term solutions expected – TOPCon ■ n-type wafer Reduction of cost difference to p-type from currently 10 to 5 ■ Reducing process and automation complexity by using inline capable process technologies, e.g.  Integration of oxide formation within edge isolation tool  APCVD or PVD technology for poly-Si deposition  Annealing within Inline high temperature furnaces up to 1-2 €ct/wafer © Fraunhofer ISE 27 Cost reduction potentials Short term solutions expected – TOPCon ■ n-type wafer Reduction of cost difference to p-type from currently 10 to 5 ■ Reducing process and automation complexity by using inline capable process technologies, e.g. ■ Reduction of poly-Si thickness from currently 120 down to 30 nm with optimized screen printing pastes up to 1 €ct/wafer © Fraunhofer ISE 28 Cost reduction potentials Short term solutions expected – TOPCon ■ n-type wafer Reduction of cost difference to p-type from currently 10 to 5 ■ Reducing process and automation complexity by using inline capable process technologies, e.g. ■ Reduction of poly-Si thickness from currently 120 down to 30 nm with optimized screen printing pastes ■ Alternative metallization schemes like NiCu plating instead of screen printed Ag up to 1.3 €ct/wafer © Fraunhofer ISE 29 Analysing TCO along the PV value chain Expected benefit of TOPCon approach  All-in module cost comparison for 60cell Glass-glass modules  PERC benchmark  TOPCon current status  TOPCon incl. short term cost reduction potential Current status TOPCon process TOPCon PERC benchmark Targeted efficiency range PERC TOPCon Modul type Glass-glass, EVA, 5 BB interconnection CTM - 3.2 Cz PERC TOPCon TOPCon © Fraunhofer ISE 30 Analysing TCO along the PV value chain Expected benefit of TOPCon approach *1st year degradation 3 2 years degradation 0.5 p.a.  Bifaciality advantage of TOPCon can over- compensate higher cost  Current status affords 0.6 abs. efficiency gain to PERC Targeted efficiency range PERC benchmark Irradiation 1700 kWh/m²a Cz PERC TOPCon TOPCon PERC TOPCon Bifaciality 75 90 Albedo 10 System life* 25 years WACC nom. 5
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