Bromide Incorporation Enhances Vertical Orientation of Triple Organic Cation Tin‐Halide Perovskites for High‐Performance Lead‐Free Solar Cells

Tin-halide perovskite solar cells (THPSCs) are attractive in the photovoltaic field as promising candidates to address the issue of potential lead toxicity and approach the theoretical efficiency limit in lead-halide perovskite photovoltaics. Nevertheless, THPSCs suffer from fast crystallization, low defect tolerance, mismatched energy levels, as well as severe oxidation from Sn2+ to Sn4+, leading to the low performance of devices. Herein, bromide is incorporated in the PEA(0.15)EA(0.15)FA(0.70)SnI(1-X)Br(X) perovskite precursor, which produces 2D/3D hybrid cations tin-halide perovskite films with highly vertical oriented crystallization, favorable band-level alignment, and suppressed tin oxidation. This leads to the decrease of trap density and charge recombination losses and the enhancement of charge carrier extraction in THPSCs. Consequently, the power conversion efficiency of the optimal THPSC (X = 0.30) surges to 10.12% in contrast to 7.13% of the control device (X = 0.00), along with a nearly eliminated current-voltage hysteresis. Furthermore, bromine-incorporated THPSCs exhibit outstanding light soaking and humidity stability. These results are also in good agreement with the density functional theory calculations. This compositional engineering with Br could become a promising approach for improving the efficiency and stability of THPSCs.