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 Sn2+ oxidation and trap state formation. Herein, the reduction of Sn4+ 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)SnnX3n+1(<n> = 25). In the meantime, the device also shows improved stability compared with the FASnI(3)-based one.