Defect Tolerance of Mixed B-Site Organic-Inorganic Halide Perovskites

Further improvements in the photovoltaic performance of B-site alloyed organic-inorganic halide perovskites (OIHPs) will rely on accurate modeling of defect properties and passivation strategies. Herein, we report that B-site alloying results in defect behaviors distinct from those of pure OIHPs, a finding obtained by uniting first-principles calculations with experimental measurements. We identify from computational studies a defect-tolerant region spanning a Sn content of 30-70% in mixed Pb-Sn perovskites and experimentally observe notably longer carrier lifetimes in 50% Sn mixed perovskite films than at other Sn contents. We discuss a strategy of applying defect-tolerant 50% Pb-Sn perovskites in ideal-bandgap (1.3-1.4 eV) active layer materials which conventionally rely on 25-30% Sn compositions. The composition (FA(0.75)Cs(0.25)Pb(0.5)Sn(0.5)(I0.9Br0.1)(3)) achieves increased carrier lifetimes of >1 mu s. This work reveals a general trend in defect tolerance for B-site alloying: a higher valence band maximum (lower conduction band minimum), along with strengthened ionic bonding, can potentially contribute to improved photovoltaic performance.