The Spacer Cations Interplay for Efficient and Stable Layered 2D Perovskite Solar Cells

Abstract Organic spacer cations in layered 2D (A 1 ) 2 (A 2 ) n −1 B n X 3 n +1 (where A 1 is an organic cation acting as a spacer between the perovskite layers, A 2 is a monovalent cation, e.g., Cs + ,CH 3 NH 3 + , CH(NH 2 ) 2 + ) perovskite materials improve the long‐term stability of the resulting solar cells, but hamper their power conversion efficiency due to poor carrier generation/transportation. Rational guidelines are thus required to enable the design of organic spacer cations. Herein, mixed A 1 cations are employed in layered 2D perovskites to investigate the interplay between alkylamine cations and unsaturated alkylamine cations. It is revealed that alkylamine spacer cations are able to facilitate precursor assembly, which results in the orientated growth of perovskite crystals. Unsaturated alkylamine cations further lead to reduced exciton binding energy, which improves carrier pathway in the 2D perovskites. By mixing both cations, substantially improved open circuit voltage is observed in the resultant photovoltaic cells with the efficiency of 15.46%, one of the highest one based on (A 1 ) 2 (A 2 ) 3 Pb 4 I 13 layered 2D perovskites. The generality of the design principle is further extended to other cation combinations.