Discovery of a New Intermediate Enables One-Step Deposition of High-Quality Perovskite Films via Solvent Engineering

Bromide-based organo-metal halide perovskites have shown great potential for use in tandem solar cells (SCs), light-emitting diodes (LEDs), and photodetectors. Herein, a new protocol using a one-step deposition method for producing formamidinium lead bromide (FAPbBr(3)) perovskites is reported, which features a solvent-engineered intermediate phase to achieve superior films. For the first time, a FABr-PbBr2-DMSO intermediate is identified and single crystals of the same intermediate compound are synthesized. A systematic investigation of phase evolution in the film formation process reveals that DMSO enables crystallization of the FABr-PbBr2-DMSO intermediate and thus modulates the crystallization process of FAPbBr(3) perovskite, achieving uniform, smooth films with Volmer-Weber morphology. To prevent hole leakage arising from the larger bandgap of FAPbBr(3) than FAPbI(3), an additional layer of Mg-doped ZnO nanoparticles is added. As a result, inverted SCs using these solvent engineered films achieve power conversion efficiencies (PCEs) of up to 9.06%, the highest reported efficiency for inverted FAPbBr(3) perovskite devices.