Orientation Regulation of Photoactive Layer in Tin‐Based Perovskite Solar Cells with Allylammonium Cations

Abstract

The low power conversion efficiency (PCE) of tin‐based perovskite solar cells is mainly caused by severe Sn 2+ oxidation and trap state formation. Herein, the reduction of Sn 4+ content and trap density is realized through the formation of quasi‐2D tin‐based perovskite by incorporating allylammonium (ALA) cations into formamidinium tin iodide (FASnI 3 ). The composition modification substantially enhances the crystallinity and morphology of the perovskite films, leading to a preferred crystal orientation that facilitates charge carrier transport. After optimization, a high maximum PCE of 9.48% is achieved in a planar p‐i‐n photovoltaic device based on (ALA) 2 (FA) n −1 Sn n X 3 n +1 (< n > = 25). In the meantime, the device also shows improved stability compared with the FASnI 3 ‐based one.