ION-IMPLANTED POLY-SI / C-SI JUNCTIONS AS A BACK-SURFACE FIELD IN BACK-JUNCTION BACK-CONTACTED SOLAR CELLS

摘要

We present back-junction back-contacted n-type silicon solar cells with a carrier selective back-surface field fabricated by ion-implanted n~+ polycrystalline (poly-) Si. In terms of the two-diodes model, we find an enhanced J_(02)-like recombination compared to reference solar cells fabricated with a conventionally doped back-surface field in monocrystalline (c-) Si. By comparing the J_(02)-values of solar cells with different geometries we find that the J_(02)-values are correlated with the index of the back-surface field. Thus, we conclude that this recombination component is caused by the p~+n~+ junction between the poly-Si and the BBr_3 diffused c-Si emitter, which probably exhibits a lot of defects in the poly-Si side of the space charge region. Due to the high J_(02)-like recombination, the best efficiency measured on a cell with poly-Si back-surface field of 21.7% does not exceed the best efficiency of 23.35 % measured on a reference with a c-Si back-surface field. Approaches to suppress the recombination at the p~+n~+ junction between emitter and BSF in poly-Si BJBC cells are proposed.