Highly crystalline CsPbI 2 Br films for efficient perovskite solar cells via compositional engineering.

All-inorganic CsPbI 2 Br shows high thermal stability for promising application in perovskite solar cells (PSCs). The performance of PSCs is significantly affected by their morphology and crystallinity induced by compositional ratio, solvent/anti-solvent engineering and post thermal annealing. In this study, the compositional ratio effect of two precursors, PbI 2 and CsBr, on the power conversion efficiency (PCE) of a device with ITO/SnO 2 /CsPbI 2 Br/Spiro-MeOTAD/Au structure was investigated. With the assistance of anti-solvent chlorobenzene, perovskite with a PbI 2  : CsBr ratio of 1.05 : 1 showed a high quality thin film with higher crystallinity and larger grain size. In addition, the molar ratio of precursors PbI 2 and CsBr improved the PCE of the PSCs, and the PSCs fabricated using the perovskite with an optimal ratio of PbI 2 and CsBr exhibited a PCE of 13.34%.