Efficient and stable Ruddlesden-Popper layered tin-based perovskite solar cells enabled by ionic liquid-bulky spacers

The crucial component, bulky spacers, in two-dimensional Ruddlesden-Popper (2DRP) layered tin (Sn) perovskites are highly limited by halide ammonium salts, leading to the insufficient control of complex crystallization process due to the limited interaction between bulky spacers and 2DRP perovskite frameworks. Here, we report an ionic liquid-bulky spacer, butylammounium acetate (BAAcO), for constructing efficient and stable 2DRP Sn-based perovskite solar cells (PSCs). In contrast to the traditional halide ammonium bulky spacer, butylammounium iodide (BAI), the AcO − -functional group in BAAcO has a strong interaction with formamidine ions (FA + ) and Sn 2+ . The inter-component interaction allows the formation of controllable intermediates for the favorable growth of smooth, dense, and highly oriented perovskite films. A PSC with power conversion efficiency of 10.36% (7.16% for BAI) is achieved, which is the highest report, along with improved stability with ∼90% retained after ∼600 h storage in N 2 atmosphere without any encapsulation.