How to make PERC suitable for perovskite–silicon tandem solar cells: A simulation study

Low-cost and high-efficiency tandem solar cells are promising candidates for a future industrial mass production. Nowadays, the passivated emitter and rear cell (PERC) technology makes up the major market share; therefore, it is an attractive option to use the PERC technology as bottom cell concept for a perovskite–silicon tandem device. Long-term optimization of the PERC technology led to highly efficient, low-cost, and mature devices. For PERC-like bottom cells, mainly an adapted front-side design is needed: Design constrains of a PERC single junction are relaxed to some extent, because such an updated PERC bottom cell only needs to absorb long wavelength photons, transports about half the current and, in a monolithic tandem, lateral transport, and the use of firing-through local silver contacts is not a mandatory prerequisite. Consequently, to make PERC suitable for tandem application, a systematic reevaluation of the current PERC technology is performed here considering five different front-side concepts. We investigate locally contacted and full-area transparent conducting oxide (TCO)-based interconnection concepts for PERC, as well as the full-area tunnel oxide passivating contact (TOPCon). Our simulation work elaborates on the advantages and physical constrains of each concept and gives guidelines for the optimization of the phosphorus diffused emitter and front interconnection layers. We conclude that both full-area and locally contacted front-side concepts are promising candidates for achieving tandem cell efficiencies of about 30%.