Insight into the Dependence of Photovoltaic Performance on Interfacial Energy Alignment in Solar Cells with Mobile Ions

Abstract

A key aspect in the optimization of perovskite (PVK) solar cells is the mitigation of interface losses, which are determined by energy band offsets and recombination. Counterintuitively, recent experimental evidence on inorganic PVK solar cells shows that increasing band offsets may improve open-circuit voltage at efficiency levels over 20%. In order to improve the knowledge of the impact of interfaces, the authors model solar cells consisting of an intrinsic absorber material containing mobile ions, sandwiched between two wide-gap charge transport layers. The results show that minimizing band offsets decreases interface losses in various scenarios, but cannot be adopted as a universal optimization rule. For instance, even in the absence of interface recombination, unequal majority carrier band offsets avoid high injection conditions. Moreover, assuming a fixed band offset at one interface, the band offset at the opposite interface should be reduced if it shows the highest interface recombination, or increased if it shows the lowest recombination. Remarkably, it is found that solar cells with mobile ions hold the potential to outperform of ion-free counterparts, depending on the extent to which the interplay between band offsets and Debye layers result in the establishment of a majority carrier concentration in the intrinsic absorber.