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

Inorganic lead halide perovskite CsPbBr3 offers attractive photophysical properties and phase stability for high-performance optoelectronic devices. However, CsPbBr3 films produced by the classic solution-based two-step method are always accompanied with impurity phases of CsPb2Br5 and Cs4PbBr6, which represents a major efficiency-limiting factor for future advances of CsPbBr3-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 CsPbBr3 films. By adopting 2-methoxyethanol as the solution conversion medium instead of commonly applied methanol, the reaction between CsBr and PbBr2 can be finely controlled to yield single phase CsPbBr3 films within a few minutes; extending the solution-conversion step to 24 h does not alter the phase purity of resulting CsPbBr3 films. The present work paves the way to regulate the crystal growth behaviors of two-step solution-processed CsPbBr3 films by simple solvent engineering.