Synergistic Defect Passivation and Phase Separation Suppression for Efficient Wide‐Bandgap Perovskite and Tandem Photovoltaics

Wide‐bandgap perovskite solar cells (WBG PSCs) have attracted significant attention as the top cell in tandem perovskite solar cells. However, the complexity of the composition leads to challenges such as defect formation and phase separation during the crystallization process, which impose significant constraints on the power conversion efficiency (PCE) and stability of the devices. Herein, we introduce a multifunctional additive, 1‐benzenesulfonyl‐piperazine (BP), which, through its multiple functional groups, suppresses the formation of defects and phase separation from multiple angles. Moreover, the strong interaction between the BP molecules and perovskite effectively retards the crystallization kinetics, resulting in improving film quality and promoting energy level matching. Therefore, this strategy has effectively facilitated the development of highly efficient WBG PSCs, reducing losses and enhancing stability. The champion device demonstrated a PCE of 21.18%, with a of 1.39 V, and the champion all‐perovskite tandem solar cell achieved a PCE of 29.31%. Notably, the WBG PSCs exhibited a retention of 85% of their initial efficiency following 1200 h of continuous operation.