Synergistic Effect of Pseudo-Halide Thiocyanate Anion and Cesium Cation on Realizing High-Performance Pinhole-Free MA-Based Wide-Band Gap Perovskites

The performance of wide-band gap perovskite solar cells has a profound impact on the multijunction tandem device efficiency. However, once bromide (Br–) has been adopted to substitute the iodide (I–) in the MAPbI3 framework, it becomes very challenging to achieve uniform and high crystalline perovskite films. Here, a synergistic effect of pseudo-halide anion thiocyanate (SCN–) and inorganic cation cesium (Cs+) on the crystallization and film formation of MA-based wide-band gap perovskite is reported. It is found that the intrinsic ability of SCN– for increasing the perovskite crystal size can make the crystallization process more tolerable to the different affinity of the initial inhomogeneous small particles. However, the introduction of SCN– usually comes along with undesired large PbI2 aggregates. By further incorporating Cs+ in the precursor solution to improve the solubility of the halide/pseudo-halide coordination to Pb2+, the formation of the aggregated PbI2 particles is successfully inhibited. As a result, uniform pinhole-free MA0.9Cs0.1PbI2Br(SCN)0.08 perovskites with a wide band gap of 1.77 eV can be achieved. The corresponding photovoltaic device exhibits a record-high fill-factor over 80% and a promising power conversion efficiency of 16.3%.