Large organic cation incorporation induces vertical orientation growth of Sn-based perovskites for high efficiency solar cells

The potential toxic issue of lead content is still a problem for prohibiting the commercialization of lead halide perovskite solar cells (PSCs). As an element of group 14 metals, tin (Sn) is the most likely substitute for lead element in perovskites. However, Sn-based PSCs still suffer from the low power conversion efficiency (PCE) because Sn²⁺ in tin-based perovskites is easily oxidized into Sn⁴⁺ once exposed to air. To fabricate stable and efficient Sn-based PSCs, herein we incorporate large ethylammonium (EA⁺) cation into CH₃NH₃SnI₃ (MASnI₃) abided by the Goldschmidt tolerance factor to fabricate vertically oriented 2D/3D mixed perovskite films. The vertically oriented structure provides a direct pathway for electron and hole transport. As a result, the PCE is highly improved to 9.24% and the corresponding PSC still retains 95% of the initial efficiency after being kept for 30 days without encapsulation in the glovebox. Therefore, our results suggest a promising strategy to develop highly efficient and stable Sn-based PSCs.