Defect passivation and carrier management via a multifunctional additive for efficient and stable wide-bandgap perovskite solar cells with high fill factor

Wide-bandgap (WBG) Methylammonium (MA)-free based perovskite solar cells (PSCs) have attracted widespread research interests due to their broad applicability in multijunction tandem. Nevertheless, the efficiency of WBG PSCs is restricted by unfulfilled potential in fill factor and large deficits in open-circuit voltage. The imbalanced carrier mobility not only plays a critical role in bulk non-radiative recombination loss but also hinders efficient charge collection for mixed I/Br WBG perovskites. Herein, we introduced additive named 2,8-Diiododibenzothiophene to overcome above issues. Inverted devices with enhanced photostability and a record fill factor of 85.7% are demonstrated. Moreover, combining the semitransparent WBG PSCs with 1.25 eV-bandgap perovskite bottom cells, we realized 4-terminal tandem devices and a champion PCE of 28% is achieved. The multifunctional additive strategy demonstrated here, will open new avenues for improving WBG PSCs' performance.