Fabrication of APCVD PSG Emitter-Based Industrial PERC Solar Cells Reaching >21.0% Conversion Efficiencies
Atmospheric pressure chemical vapour deposition (APCVD) of phosphosilicate glass (PSG) layer allows a separation of glass deposition and phosphorous diffusion step. This permits the application of the selective laser-doping process either before or after the thermal diffusion, which increases the freedom of tailoring the doping profiles of both lowly and highly doped regions of selective emitter structures. We fabricate industrial p-type PERC solar cells featuring APCVD PSG-based selective emitters and study the effect of laser-doping process on current-voltage characteristics. Mean conversion efficiency mean = 21.1% and an absolute gain mean = 0.2% to the homogeneous emitters is achieved for solar cells after applying the laser-doping process either before or after the thermal drive-in. The most promising selective emitter group is the one featuring the laser process before the thermal diffusion step, where a carrier concentration profile with depth d = 0.9 mm as well as a low specific contact resistivity (C,mean ≈ 3 mO cm2) are achieved. The major electrical loss of this group is related to the spectral response, where a higher front-reflection and an increased recombination at the illuminated fraction of the highly doped region need to be minimized in order to further push the efficiency level to > 21.5%.