Surface Passivation of Crystalline Silicon Solar Cells Past, Present and Future

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/336135721 Surface Passivation of Crystalline Silicon Solar Cells: Past, Present and Future Presentation · April 2019 CITATIONS0 READS792 3 authors, including: Some of the authors of this publication are also working on these related projects: Determination of the Uncertainty of the Absorption Coefficient of Crystalline Silicon View project NanoPERC View project Jan Schmidt Institute for Solar Energy Research (ISFH) 320 PUBLICATIONS 12,797 CITATIONS SEE PROFILE Robby Peibst Institute for Solar Energy Research (ISFH) 143 PUBLICATIONS 2,383 CITATIONS SEE PROFILE All content following this page was uploaded by Jan Schmidt on 30 September 2019. The user has requested enhancement of the downloaded file. SiliconPV 2019 Leuven, Belgium, 10 th April 2019 Surface passivation of crystalline silicon solar cells: Past, present and future J. Schmidt, 1,2 R. Peibst 1,3 and R. Brendel 1,2 1 Institute for Solar Energy Research Hamelin (ISFH), Germany 2 Institute of Solid-State Physics, Leibniz University Hannover, Germany 3 Institute of Electronic Materials and Devices, Leibniz University Hannover, Germany https://commons.wikimedia.org/ Wolfgang Pauli, 1900-1958 (Nobel Prize in Physics, 1945) God made the bulk; the surface was invented by the devil. –Wolfgang Pauli The Si/SiO 2 interface is the sine qua non of the semiconductor industry, and what most distinguishes silicon from all other material alternatives. SiO 2 as a key enabler in microelectronics and photovoltaics Michael Riordan, “From Bell labs to silicon Valley: A saga of semiconductor technology transfer, 1955-61”, The Electrochemical Society Interface (2007), p. 36-41. Stefan Glunz, Frank Feldmann, “SiO 2 surface passivation layers –a key technology for silicon solar cells”, Sol. En. Mat. Sol. Cells 185, 260 (2018). Jean Hoerni, “Planar Silicon Transistors and Diodes,” Fairchild Semiconductor Corp. Report No. TP-14, 1961 (Stanford University Archives) Surface passivation of silicon solar cells by dielectric layers Fundamental mechanisms of surface passivation it D Silicon C E V E f Q + + + C E V E ‘Chemical passivation’ ‘Population control’ • Saturation of interface states (e.g. by hydrogen) • Reduction of interface state density D it • Reduction of one carrier type at interface • Realized via -fixed charge density Q f -doping of a surface-near region Dopant-diffused solar cells n + c-Si (p-type) Ag dielectric front passivation dielectric rear passivation - + C D A B p + Al front pass i vation c-Si n + along line A-B ‐ + re ar passiva tion electron s elective hole s elec tive silicon wafer E n ergy Position ‐ + • Unmetallized surfaces: Dielectric- layer passivation • Metallized surfaces: Passivation via doping alonglineC-D n + -diffused c-Si surfaces SiO 2 A. Cuevas et al., J. Appl. Phys. 80, 3370 (1996). • Minimize overall J 0 by -high doping under metal contacts -low doping for surfaces passivated by dielectric layer • Pragmatic approach: homogeneously doped emitter of intermediate sheet resistance “Selective emitter” SiN x passivation of n + -diffused surfaces J. Schmidt et al., Semicond. Sci. Technol. 16, 164 (2001). • High-temperature SiO 2 provides excellent passivation, but difficult to transfer to industrial cell production • Low-temperature PECVD-SiN x provides only slightly higher J 0 • SiO 2 /SiN x provide combination of excellent J 0 and is industrial feasible SiN x industrial standard today Sheet resistance [/sq] 0 100 200 300 400 500 R e com b i n at i o n cur r e nt p ar am et er J 0 [fA / c m 2 ] 1 10 100 phosphorus-diffused n + -Si SiN x SiO 2 /SiN x alnealed SiO 2 Positive- and negative-charge dielectrics on undiffused p-Si surfaces • Parasitic shunting for positively charged dielectric layer (e.g. SiN x ) on p-Si • No parasitic shunting occurs for negatively charged dielectric layer • Al 2 O 3 provides very high negative charge density Q f in combination with low D it S. Dauwe, J. Schmidt, A. Metz, and R. Hezel, Proc. 29th IEEE PVSC (2002), p. 162 Al 2 O 3 optimal dielectric for p-Si rear passivation J. Schmidt, A. Merkle, R. Brendel, B. Hoex, M. van de Sanden, W. Kessels, Prog. Photovolt. 16, 461 (2008). B. Hoex, J. Schmidt, P. Pohl, M. van de Sanden, W. Kessels, J. Appl. Phys. 104, 044903 (2008). Firing-stable Al 2 O 3 /SiN x stacks • Thin Al 2 O 3 single-layers degrade during firing • Al 2 O 3 /SiN x stacks provide S eff 28% for all combinations with poly-Si for both polarities Combinations of selective layers max [%] Se&h Electron-selective contacts P-diffused n + a-Si:H(i) /a-Si:H(n) th-SiO x / poly-Si(n + ) PECVD th-SiO x / poly-Si(n + ) LPCVD chem-SiO x / poly-Si(n + ) LPCVD SiO x /TiO y MgO x H o l e - s e l ec t i v e c o n ta c t s Al-p + 24.5 (PERC) 11.7 26.8 12.8 26.9 12.8 27.1 12.9 27.1 13.0 26.3 12.5 24.9 11.9 a-Si:H(i/p) 24.7 11.8 27.5 (HIT) 13.2 27.7 13.3 27.9 13.5 28.0 13.5 26.8 12.8 25.1 12.0 SiO x / poly-Si(p + ) 24.9 11.9 28.1 13.6 28.3 13.8 28.7 14.2 28.7 14.2 27.3 13.1 25.4 12.1 SiO x /Si:C (p + ) 24.9 11.9 28.0 13.5 28.2 13.7 28.5 14.0 28.6 14.1 27.2 13.0 25.3 12.1 a-Si:H(i)/MoO x 24.4 11.7 26.5 12.6 26.6 12.7 26.8 12.8 26.8 12.8 26.0 12.4 24.7 11.8 MoO x 24.1 11.6 25.9 12.3 26.0 12.4 26.1 12.4 26.1 12.4 25.5 12.2 24.4 11.7 PEDOT:PSS 24.1 11.6 26.0 12.4 26.1 12.4 26.2 12.5 26.2 12.5 25.6 12.2 24.5 11.7 Data fromvariousgroups, referencesin: J. Schmidt, R. Peibst, andR. Brendel, Sol. En. Mat. Sol. Cells 187, 39 (2018). • Combinations of a-Si/c-Si and poly-Si contacts give higher selectivitiesthan HIT max [%] Se&h Electron-selective contacts P-diffused n + a-Si:H(i) /a-Si:H(n) th-SiO x / poly-Si(n + ) PECVD th-SiO x / poly-Si(n + ) LPCVD chem-SiO x / poly-Si(n + ) LPCVD SiO x /TiO y MgO x H o l e - s e l ec t i v e c o n ta c t s Al-p + 24.5 (PERC) 11.7 26.8 12.8 26.9 12.8 27.1 12.9 27.1 13.0 26.3 12.5 24.9 11.9 a-Si:H(i/p) 24.7 11.8 27.5 (HIT) 13.2 27.7 13.3 27.9 13.5 28.0 13.5 26.8 12.8 25.1 12.0 SiO x / poly-Si(p + ) 24.9 11.9 28.1 13.6 28.3 13.8 28.7 14.2 28.7 14.2 27.3 13.1 25.4 12.1 SiO x /Si:C (p + ) 24.9 11.9 28.0 13.5 28.2 13.7 28.5 14.0 28.6 14.1 27.2 13.0 25.3 12.1 a-Si:H(i)/MoO x 24.4 11.7 26.5 12.6 26.6 12.7 26.8 12.8 26.8 12.8 26.0 12.4 24.7 11.8 MoO x 24.1 11.6 25.9 12.3 26.0 12.4 26.1 12.4 26.1 12.4 25.5 12.2 24.4 11.7 PEDOT:PSS 24.1 11.6 26.0 12.4 26.1 12.4 26.2 12.5 26.2 12.5 25.6 12.2 24.5 11.7 Combinations of selective layers Data fromvariousgroups, referencesin: J. Schmidt, R. Peibst, andR. Brendel, Sol. En. Mat. Sol. Cells 187, 39 (2018). • Several unexplored combinations show high potential -poly-Si(n + ) & Al-p + -poly-Si(p + ) & TiO 2 ,… Summary • Past and presence: passivation of non-contacted areas of c-Si surfaces passivation by dielectric layers such as SiO 2 , SiN x , and Al 2 O 3 • Future: carrier-selective layers providing excellent passivation of contacted and non-contacted areas on c-Si solar cells • Carrier-selective layers must -suppress minority-carrier recombination -allow for an effective majority-carrier transport • Highest selectivitiesfor both-polarity poly-Si on oxide layers • Several unexplored combinations show high selectivies -poly-Si(n + ) & Al-p + -poly-Si(p + ) & TiO 2 ,… • Transfer into industrial cell concepts will be the next major challenge Maximize selectivity S 10 View publication statsView publication stats