Improve the quality of HC(NH2)2PbIxBr3-x through iodine vacancy filling for stable mixed perovskite solar cells

Formamidinium-based (FA-based) with broader light absorption spectra have been attracted enormous attention. However, the FAI-PbI2-DMSO intermediate anisotropic fibers can easily produce yellow delta-FAPbI(3) and uncontrolled excess PbI2, which significantly increased the defect and reducing the reproducibility of devices. Furthermore, the iodine defect in polycrystalline films would enlarge the perovskite tolerance factor and trigger ion migration. This ion migration within perovskite layer leads to device degradation and impedes large scale commercial applications. Herein, we develop a vacancy filling (VF) method to repair iodine vacancy as well as yield pure black phase FA perovskite. Upon post treatment with FABr, the point defects on surface and the notorious delta-FAPbI(3) caused by lager tolerance are removed though vancancy fulling. The champion of obtained FAPbI(x)Br(3-x) device presents the power conversion efficiency (PCE) up to 18.2% and could remain > 85% of the original PCE after 20 days in the dark at room temperature (10-25 degrees C) and humidity of 10-40%. Therefore, this VF technique provides an interesting entry for obtaining high pure black perovskite phase.