Defect passivation and crystallization modulation in methylammonium-free wide-bandgap perovskites for all-perovskite tandem solar cells

Wide-bandgap (WBG; >1.65 electron volts) perovskites based on iodine-bromine (I-Br) mixed halides are critical components of perovskite-based tandem solar cells (TSCs). However, the uncontrolled crystallization dynamics of Br-rich species lead to reduced grain sizes and high defect densities in WBG perovskite films. Herein, a multifunctional additive 3,4,5-trifluorobenzamide (TFBZ) was introduced to enhance the crystallinity and passivate defects of the methylammonium (MA)–free WBG perovskite films. The TFBZ demonstrates superior passivation capability compared to benzamide, effectively mitigating both iodine vacancies and undercoordinated Pb 2+ defects via fluorine-enhanced interactions. In addition, the fluorine substituents in TFBZ could form N–H···F hydrogen bonds with formamidinium iodide to retard the crystallization rate of the perovskite. This proposed method is effective in defect passivation and crystal growth modulation for both 1.67– and 1.79–electron volt MA-free WBG perovskites, enabling the fabrication of MA-free all-perovskite TSCs with an encouraging power conversion efficiency of 29.01% (certified at 28.52%).