The Investigation of Al-BSF Passivation Quality

Abstract

The screen-printed Al-back surface field (Al-BSF) is widely used to passivate the back surface of silicon solar cells. In order to increase the cost-effectiveness of solar cells, there is a strong trend to further reduce the wafer thickness down to at least 200µm. So the back surface recombination velocity (Sb) begins to strong influence solar cells performance when the minority carrier diffusion length approaches or exceeds device thickness. Al-BSF which can decrease Sb becomes much more important. Previously, most researchers utilized solar cell internal quantum efficiency (IQE) to analysis the quality of Al-BSF. But this method is could not characterize Al-BSF directly because of other factors. In this paper, the back-surface fields is formed using screen-printed Al layer on Cz P-type silicon directly followed sintering in belt furnace and we measure the minority carrier lifetime after firing. Through theoretical calculation of the surface recombination velocity, it helps us to analysis Al-BSF passivation quality directly and effectively.