Influence of rear-side passivation on solar cell performance of bosco solar cells

The recently introduced BOSCO (""Both Sides Collecting and Contacted"") solar cell exhibits emitter regions on front and rear side, which are interconnected by diffused vias. This allows double-sided collection of carriers in the base and bifacial operation while supporting standard module interconnection technology. Since the BOSCO cell's rear side exhibits p-doped as well as highly n+-doped surfaces the dielectric used as rear-side passivation needs to be suitable to passivate both polarities. This work compares the passivation of the BOSCO cell's rear side by a PECVD aluminium oxide (AlOx) and a thermally grown silicon oxide (SiO2). A difference in efficiency of up to = 0.5 %abs occurs between BOSCO cells with AlOx and SiO2 passivation, with the AlOx passivated solar cells achieving better cell performance. The difference in efficiency is dominated by a loss in fill factor of up to FF = 1.6 %abs for cells with SiO2 passivation compared to AlOx passivated cells. An investigation of the suns-Voc characteristics shows that this loss is mainly caused by increased recombination at lower injection, which strongly affects the pseudo fill factor. This work shows that the choice of rear-side passivation is essential to optimize the performance of BOSCO solar cells.