Curing the fundamental issue of impurity phases in two-step solution-processed CsPbBr3 perovskite films

Inorganic lead halide perovskite CsPbBr 3 offers attractive photophysical properties and phase stability for high-performance optoelectronic devices. However, CsPbBr 3 films produced by the classic solution-based two-step method are always accompanied with impurity phases of CsPb 2 Br 5 and Cs 4 PbBr 6 , which represents a major efficiency-limiting factor for future advances of CsPbBr 3 -based devices. The challenge lies in the complexity of the Cs-Pb-Br phase system, requiring both spatially and temporally precise control of the precursor stoichiometry during solution-phase growth of CsPbBr 3 films. By adopting 2-methoxyethanol as the solution conversion medium instead of commonly applied methanol, the reaction between CsBr and PbBr 2 can be finely controlled to yield single phase CsPbBr 3 films within a few minutes; extending the solution-conversion step to 24 h does not alter the phase purity of resulting CsPbBr 3 films. The present work paves the way to regulate the crystal growth behaviors of two-step solution-processed CsPbBr 3 films by simple solvent engineering.