Unconventional Perovskite-to-perovskite Tandem Cell Designed by Stacking with Large-gap Phosphonium-based Analogs

We present a material design strategy for stacking large-gap unconventional derivatives on the prevailing hybrid organic-inorganic perovskites, (MA, FA)(Sn, Pb)I as a perovskite-to-perovskite tandem cell. To this end, we employ an unconventional structurally well-matched hybrid organic-inorganic perovskite derivative MPSnBr with large-sized weakly hybridized A-site methylphosphonium (MP) cations to construct a heterojunction with its structural analogs (MA, FA)(Sn, Pb)I to simulate the two subcells of the tandem cell. Compared with the popular ammonium-based perovskites, density-functional theory computation suggests that MPSnBr possesses a wider bandgap and lower conduction band minimum (CBM) level induced by the weak-hybrid MP cations, which can be a more suitable wide-range light absorber than its traditional ammonium counterparts. We show that such a heterostructure exhibits a desirable positive ”spike-like” BO, resulting in higher V and more effective suppression of undesirable carrier recombination. Hence, MPSnBr as a structural well-matched absorber, can potentially serve as the wide-range subcell in perovskite tandem cell devices.