Potassium tetrafluoroborate-induced defect tolerance enables efficient wide-bandgap perovskite solar cells

Wide-bandgap (WBG) perovskites play a crucial role for top cells in tandem solar cells (TSCs), which provides a promising avenue to boost the performance of widely used commercial solar cells. However, such WBG perovskite solar cells (PSCs) show poor performance compared to that of similar to 1.6 eV bandgap PSCs due to high defects density and photo-instability, resulting in relatively large open-circuit voltage loss (V-loss). Herein, we introduce alkali pseudo-halide KBF4 into the perovskite precursor solution for preparing less defect WBG perovskite film. It is showed that the interstitial occupancy of K+ in the perovskite lattice and the suppression of recombination by BF4, thereby inhibiting the ion migration and reducing the trap density. As a result, the champion WBG PSC (Energy gap (E-g), E-g = 1.74 eV) delivers a high open-circuit voltage (V-OC) of 1.21 V and a power conversion efficiency (PCE) of 17.49%. This work provides new insight into the defect tolerance upon metal pseudo-halides doping in the WBG perovskite. (C) 2021 Published by Elsevier Inc.