Effects of Alkyl Chain Length on Crystal Growth and Oxidation Process of Two-Dimensional Tin Halide Perovskites

Two-dimensional (2D) Sn-based lead-free perovskites have attracted extensive attention because of their nontoxicity and wide light absorption. It has been proven that the introduced organic spacer cations in the perovskite crystal prevent Sn2+ from oxidation to Sn4+. However, the effects of the alkyl chain length of these cations on the perovskite properties are unclear. Here, we investigate the impacts of chain length on crystal orientation and phase distribution of 2D Sn-based perovskite films by employing different alkylamines spacer cations (butylamine, octylamine, and dodecylamine). With the increase of alkyl chain length, the phase distribution of 2D Sn-based perovskite crystals become disordered and less oriented. Therefore, benefiting from application of a short alkyl chain in the organic spacer cation (e.g., BA), we manage to retard the oxidation process of Sn2+ for better device performance. Our work provides systematic understanding of configuration and size of organic spacer cations, which will further contribute to highly stable and efficient lead-free perovskite solar cells.