Coordination Engineering Enables Efficient 1.77 eV Wide‐Bandgap Perovskites for All‐Perovskite Tandem Solar Cells

Wide‐bandgap (WBG) perovskites are essential components for all‐perovskite tandem solar cells, yet they often suffer from substantial open‐circuit voltage ( V _OC ) deficits and uncontrolled crystallization kinetics. Herein, we employ a coordination engineering strategy with a multifunctional additive, 4‐(Trifluoromethyl) benzene‐1‐sulfonyl chloride (BSCF ₃ ), to optimize 1.77 eV WBG perovskite films. Detailed spectroscopic characterizations reveal that the –SO ₂ Cl group acts as a Lewis base to coordinate with Pb ²⁺ ions and the strongly electronegative –CF ₃ group forms hydrogen bonds with formamidinium (FA ⁺ ) cations. These synergistic effects regulate the subsequent nucleation and crystallization kinetics. Driven by this controlled growth process, the resulting films exhibit enlarged grain sizes and suppressed residual PbI ₂ phases. This enhanced structural integrity, in turn, minimizes the trap‐state density and significantly mitigates nonradiative recombination at the grain boundaries. As a result, the inverted 1.77 eV WBG perovskite solar cells achieve a champion power conversion efficiency (PCE) of 19.81% with a high V _OC of 1.32 V. Furthermore, the optimized monolithic all‐perovskite tandem cells deliver a remarkable PCE of 27.26%. Under continuous 1‐sun illumination in a nitrogen atmosphere, both the single‐junction and tandem devices retain approximately 80% of their initial efficiencies after 1000 and 300 h aging, respectively.