Xinyu Li, Yuanyuan Liu, Yu-Ang Liu, D. C. Li, Yilin Zuo, Shantao Zhang, Yuchen Li, Rongyao Lv, Yuan Li, Guoqing Tong, Tao Chen, Zhengguo Xiao, Xiao Cheng Zeng, Junfa Zhu, Shuang Chen, Zhimin Fang, Guan-Wu Wang, Zonglong Zhu, Shangfeng Yang
Mixed-halide wide-bandgap (WBG) perovskites suffer from defect-induced open-circuit voltage ( V OC ) loss and photoinduced phase segregation. Herein, we introduce rubidium formate (RbFa) as a single dopant to mitigate both challenges through synergistic ion engineering. The Rb + cation enters the lattice to induce contraction, while the formate anion (Fa – ) modulates crystallization kinetics and passivates halide vacancies. This cooperative interaction maximizes residual compressive strain, thermodynamically raising the ion-migration barrier, while vacancy passivation kinetically blocks migration pathways. Consequently, we achieve a high V OC of 1.371 V and enhanced photostability for 1.86 eV WBG perovskite solar cells (PSCs). Monolithic perovskite–organic tandem solar cells deliver an efficiency of 26.03% with a record certified V OC of 2.189 V and retain over 90% of their initial efficiency after 1000 h under continuous 1-sun illumination.