Perovskite solar cells (PSCs) consisting of interfacial two- and three-dimensional heterostructures that incorporate ammonium ligand intercalation have enabled rapid progress toward the goal of uniting performance with stability. However, as the field continues to seek ever-higher durability, additional tools that avoid progressive ligand intercalation are needed to minimize degradation at high temperatures. We used ammonium ligands that are nonreactive with the bulk of perovskites and investigated a library that varies ligand molecular structure systematically. We found that fluorinated aniliniums offer interfacial passivation and simultaneously minimize reactivity with perovskites. Using this approach, we report a certified quasi–steady-state power-conversion efficiency of 24.09% for inverted-structure PSCs. In an encapsulated device operating at 85°C and 50% relative humidity, we document a 1560-hour
T
85
at maximum power point under 1-sun illumination.
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 (I 0.9 Br 0.1 ) 3 ) achieves increased carrier lifetimes of >1 μs. 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.
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