Structural Tailoring the Phenylenediamine Isomers to Obtain 2D Dion–Jacobson Tin Perovskite Solar Cells with Record Efficiency.

2D Dion–Jacobson (DJ) tin halide perovskite shows impressive stability by introducing diamine organic spacer. However, due to the dielectric confinement and uncontrollable crystallization process, 2D DJ perovskite usually exhibits large exciton binding energy and poor film quality, resulting in unfavorable charge dissociation, carrier transport and device performance. Here, the ortho‐, meta‐, and para‐isomers of phenylenediamine (PDA) are designed for 2D DJ tin halide perovskites. Theoretical simulation and experimental characterizations demonstrate that compared with p‐PDA and m‐PDA, o‐PDA shows larger dipole moment, which further reduces the exciton binding energy for the 2D perovskites. Besides, there is a strong hydrogen bond interaction between o‐PDA cation and inorganic octahedron, which not only improves the structural stability, but also induces larger aggregates in the precursor to form dense and uniform high‐quality films, and strengthens the antioxidant barrier. More interestingly, femtosecond transient absorption further proves that o‐PDA organic spacers can reduce unfavorable small n‐phases, resulting in sufficient and effective charge transfer between different n‐value. As a result, the 2D DJ (o‐PDA)FA3Sn4I13 solar cells achieve a record power conversion efficiency of 7.18%. The study furnishes an effective method to optimize the carrier transport and device performance by tailoring the chemical structure of organic spacers. [ABSTRACT FROM AUTHOR]