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)I₃ as a perovskite-to-perovskite tandem cell. To this end, we employ an unconventional structurally well-matched hybrid organic–inorganic perovskite derivative MPSnBr₃ with large-sized weakly hybridized A-site methylphosphonium (MP) cations to construct a heterojunction with its structural analogs (MA, FA)(Sn, Pb)I₃ to simulate the two subcells of the tandem cell. Compared with the popular ammonium-based perovskites, density-functional theory computation suggests that MPSnBr₃ possesses a wider bandgap and lower conduction band minimum 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’ band offset, resulting in higher V_oc and more effective suppression of undesirable carrier recombination. Hence, MPSnBr₃ as a structural well-matched absorber can potentially serve as the wide-range subcell in perovskite tandem cell devices. © 2024 Elsevier Ltd.