Influence of cell edges on the performance of silicon heterojunction solar cells

Abstract

Full size silicon heterojunction solar cells reach conversion efficiencies above 25%. However, photoluminescence pictures of such cells (full or cut) reveal a significant recombination activity at the cell edges. Therefore, mitigating recombination at the edges can in principle represent an interesting path to unlock higher cell efficiencies. This challenge is all the more important for cells with a high perimeter/area ratio, as achieved through the cutting of full size cells. For such technologies, the edges resulting from cutting are cleaved while the remaining edges typically feature a gap where TCO is missing to avoid front to back short-circuit. In this paper, we specify the physical mechanisms involved in the edge-induced performance losses for SHJ cells. In light of these results, we provide guidelines for the mitigation of such losses at the full-size and cut cells scale for M6 to M12 sizes such as the reduction of the TCO-free region and the c-Si bulk resistivity. Having a closer look at cut cells, we calculate the cell performance as a function of its size (from half-to sixth-cell), the size of its mother cell (from M6 to M12) and the passivation quality of the cut-edges. Our results emphasize on the interest to develop suitable repassivation schemes for cut cells to improve or even surpass the efficiency of the mother cell.