Direct Molecule Substitution Enabled Rapid Transformation of Wet PbBr₂(DMF) Precursor Films to CsPbBr₃ Perovskite

Owing to the solubility limitation of the bromide ion, a two-step dipping method was mostly used to prepare CsPbBr3 films. However, the commonly used well-crystallized PbBr2 precursor film is too compact for the diffusion of CsBr solution. Inconvenient conversion resulted in CsPbBr3 films with poor phase purity. Additionally, long immersion time in solution made films suffer from destructive decomposition. Herein, a wet PbBr2(DMF) precursor film was proposed to rapidly form the CsPbBr3 film. A direct molecule substitution between the DMF (N,N-dimethylformamide) ligand and CsBr promotes the conversion, which was experimentally proved by Fourier transform infrared spectroscopy. Phase purity, surface coverage, and crystallinity of final CsPbBr3 films were improved. The best-performance planar carbon-based CsPbBr3 perovskite solar cell (PSC) obtained with a wet PbBr2(DMF) film showed a power conversion efficiency (PCE) of 5.25%. Compared with the optimized PSC assembled using CsPbBr3 obtained with a well-crystallized PbBr2 film, which has a PCE of 2.64%, the PCE was boosted by ∼100%.