Impact of the Rear Surface Roughness on Industrial-Type PERC Solar Cells

Abstract

Screen-Printed PERC solar cells are a promising candidate for next-generation industrial-type solar cells. Industrial PERC cell process flows typically involve wet chemical polishing of the rear side in order to reduce the surface roughness and to improve the conversion efficiency. In this paper, we show that Al2O3/SiNx passivation stacks achieve an excellent surface recombination velocity below 10 cm/s even for small polishing removal of 5 μm corresponding to rough surfaces. In contrast, SiOx/SiNy passivation stacks exhibit a strong increase of the surface recombination velocity up to 30 cm/s for rough surfaces. Accordingly, we find that the efficiency of PERC solar cells with Al2O3/SiNx rear passivation is almost independent of the polishing etch depth with best efficiencies up to 19.7% for 7.5 μm polishing removal whereas the efficiency of SiOx/SiNy rear passivated PERC cells strongly decreases for rougher surfaces.