Orientation Regulation of Tin‐Based Reduced‐Dimensional Perovskites for Highly Efficient and Stable Photovoltaics

Tin‐based perovskites have exhibited high potential for efficient photovoltaics application due to their outstanding optoelectrical properties. However, the extremely undesired instabilities significantly hinders their development and further commercialization process. A novel tin‐based reduced‐dimensional (quasi‐2D) perovskites is reported here by using 5‐ammoniumvaleric acid (5‐AVA⁺) as the organic spacer. It is demonstrated that by introducing appropriate amount of ammonium chloride (NH₄Cl) as additive, highly vertically oriented tin‐based quasi‐2D perovskite films are obtained, which is proved through the grazing incidence wide‐angle X‐ray scattering characterization. In particular, this approach is confirmed to be a universal method to deliver highly vertically oriented tin‐based quasi‐2D perovskites with various spacers. The highly ordered vertically oriented perovskite films significantly improve the charge collection efficiency between two electrodes. With the optimized NH₄Cl concentration, the solar cells employing quasi‐2D perovskite, AVA₂FA_n?1Sn_nI_3n+1 (<n> = 5), as light absorbers deliver a power conversion efficiency up to 8.71%. The work paves the way for further employing highly vertically oriented tin‐based quasi‐2D perovskite films for highly efficient and stable photovoltaics.