Synergistic Effect of Pseudo-Halide Thiocyanate Anion and Cesium Cation on Realizing High-Performance Pin-Hole Free MA-Based Wide-Bandgap Perovskites

The performance of wide-bandgap perovskite solar cells has a profound impact on the multi-junction 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-bandgap 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, which improves the solubility of the halide/pseudo-halide coordination to Pb2+, and therefore suppresses the formation of the aggregated PbI2 particles. A...