Soft Breakdown Behavior of Interdigitated-back-contact Silicon Solar Cells

The soft reverse IV characteristic of interdigitated-back-contact (IBC) silicon solar cells consisting of contiguous p+ and n+ regions on the rear side (Figure 1) was investigated in this study. Our IBC cell concept, which is a 6-inch IBC cell with a diffused phosphorous BSF and a boron front floating emitter, features a relatively low breakdown voltage of about - 3.7 V. We measured a negative temperature coefficient at reverse bias in the dark. The low breakdown voltage and the negative temperature coefficient both support the hypothesis that the high reverse current is caused by the tunneling effect [1]. We demonstrated that by changing the doping profiles, the breakdown voltage of the IBC cells can be modified. Our simulations show that the reverse bias current is mainly caused by the band-to-band tunneling across the borders of the p+ and n+ regions, and that the breakdown voltage changes with doping profiles. Furthermore, a qualitative agreement is found between the experimental and simulated reverse currents. In principle, the same theory may apply for studying the early breakdown behavior of MWT, EWT or any other cells that feature p+n+ junctions.