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(2 DRP) 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 2 DRP perovskite frameworks. Here, we report an ionic liquid-bulky spacer, butylammounium acetate(BAAc O), for constructing efficient and stable 2 DRP Sn-based perovskite solar cells(PSCs). In contrast to the traditional halide ammonium bulky spacer, butylammounium iodide(BAI), the Ac O--functional group in BAAc O has a strong interaction with formamidine ions(FA+) and Sn2+. 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 N2 atmosphere without any encapsulation.