Elimination of Light-Induced Degradation by Black Silicon-Toni P. Pasanen

14th China SoG Silicon and PV Power Conference Elimination of Light-Induced Degradation by Black Silicon Toni P. Pasanena, Chiara Modanesea, Ville Vhnissia, Hannu S. Lainea, Franziska Wolnyb, Alexander Oehlkeb, Christian Kustererb, Ismo T. S. Heikkinena,c, Matthias Wagnerb, Hele Savina aAalto University, Department of Electronics and Nanoengineering, Espoo, Finland bSolarWorld Industries GmbH, Bonn, Germany cBeneq Oy, Espoo, Finland 8-10 November 2018, Xi’an, China Black silicon provides several benefits Negligible reflectance  Improved Isc  No need for AR-coating Diamond wire sawing of mc-Si possible1  Material savings Enhanced impurity gettering2 Applicable to industrial production3 Long-term stability important 1F. Toor et al. Nanoscale 2016;815448. 2T.P. Pasanen et al. Sci Rep. 2018;91991. 3T.P. Pasanen et al. 35th EU PVSEC, 2018. 0 5 10 15 20 25 30 35 40 45 300 500 700 900 1100 Re flec tan ce Wavelength nm b-Si AlOx Acidic-texture SiNx 10.11.2018 T.P. Pasanen et al. 2 Industrial black mc-Si PERC 10.11.2018 T.P. Pasanen et al. 3 p-type mc-Si CVD AlOx CVD SiNx ALD AlOx CVD SiNx n p-type mc-Si Degradation one week under 0.5 sun illumination at 75 ˚C Black Si Acidic texture n LID imaging by PL 10.11.2018 4 initial – degraded / initial PL counts [a.u.] T.P. Pasanen et al. no degradation large degradation  Black Si shows no degradation Saw damage removed, no texture ΔPL map Internal quantum efficiency Degradation one week under 0.5 sun illumination at 75 ˚C 10.11.2018 T.P. Pasanen et al. 5 Clear degradation in the bulk or at rear 0.70 0.75 0.80 0.85 0.90 0.95 1.00 850 900 950 1000 1050 Int ernal qu an tum effic ien cy IQE Wavelength nm Int ernal qu an tum effic ien cy IQE IQE 10.11.2018 T.P. Pasanen et al. 6  Black Si shows no degradation 0.985 0.99 0.995 1 1.005 0 50 100 150 Nor maliz ed V oc Degradation time h Nor maliz ed V oc 0.95 0.96 0.97 0.98 0.99 1.00 1.01 1.02 0 50 100 150 Normal ized ef fic ien cy Degradation time h Normal ized ef fic ien cy Cell efficiency 10.11.2018 7 T.P. Pasanen et al. Similar trend in Voc Physical background in enhanced impurity gettering 10.11.2018 T.P. Pasanen et al. 8 n n P P P P Larger surface area → higher P concentration 1-3  Enhanced impurity gettering4 70 μs 700 μs 1J. Oh et al. Nat Nanotech. 2012;7743-748. 2B. Kafle et al. Sol Energy Mater Sol Cells 2016;15294-102. 3T. Pasanen et al. Energy Procedia 2017;124307-312. 4T.P. Pasanen et al. Sci Rep. 2018;91991. After gettering b-Si 47 Ω/□ polished 74 Ω/□ 0.95 0.96 0.97 0.98 0.99 1.00 1.01 1.02 0 50 100 150 Norm ali zed ef fic ien cy Degradation time h Effect of hydrogen 10.11.2018 9 acidic texture, SiNx T.P. Pasanen et al. b-Si, AlOx b-Si, SiNx Hydrogen related Black Si related Conclusions Significantly reduced LID in b-Si cells Efficiency of b-Si cells remains stable, while acidic-textured equivalents degrade by nearly 4 rel. Excellent optical properties of b-Si allow to replace hydrogen-rich SiNx with ALD AlOx.  Promotes elimination of LID Benefits of b-Si not limited to the excellent optical properties Accepted for publication in Progress in Photovoltaics Research and Applications DOI10.1002/pip.3088 10.11.2018 10 T.P. Pasanen et al. Acknowledgements 10.11.2018 11 T.P. Pasanen et al. Thank you for your attention Toni P. Pasanen Aalto University Department of Electronics and Nanoengineering toni.pasanenaalto.fi Effect of wafer thickness Acidic textured cell 165 m SDR edge 155 m b-Si center area 140 m  Magnitude of LID scales with surface area rather than wafer thickness. 10.11.2018 T.P. Pasanen et al. 13 Black Si cells Initial thickness 180 m - SDR 2 x 10 m - b-Si etching 15 m - rear side etching 5 m Final thickness 140 m Acidic-textured cells Initial thickness 180 m - acidic texturing 2 x 5 m - rear side etching 5 m Final thickness 165 m