Highly Reproducible Sn‐Based Hybrid Perovskite Solar Cells with 9% Efficiency

The low power conversion efficiency (PCE) of tin‐based hybrid perovskite solar cells (HPSCs) is mainly attributed to the high background carrier density due to a high density of intrinsic defects such as Sn vacancies and oxidized species (Sn4+) that characterize Sn‐based HPSCs. Herein, this study reports on the successful reduction of the background carrier density by more than one order of magnitude by depositing near‐single‐crystalline formamidinium tin iodide (FASnI3) films with the orthorhombic a‐axis in the out‐of‐plane direction. Using these highly crystalline films, obtained by mixing a very small amount (0.08 m) of layered (2D) Sn perovskite with 0.92 m (3D) FASnI3, for the first time a PCE as high as 9.0% in a planar p–i–n device structure is achieved. These devices display negligible hysteresis and light soaking, as they benefit from very low trap‐assisted recombination, low shunt losses, and more efficient charge collection. This represents a 50% improvement in PCE compared to the best reference cell based on a pure FASnI3 film using SnF2 as a reducing agent. Moreover, the 2D/3D‐based HPSCs show considerable improved stability due to the enhanced robustness of the perovskite film compared to the reference cell. An all‐tin‐based perovskite solar cell with a record power conversion efficiency of 9% is reported for the first time. The outstanding performance is attributed to the fact that the addition of a trace amount of 2D tin perovskite initiates the homogenous growth of highly crystalline and oriented FASnI3 grains at low temperature.