Targeted Functional Group‐Modulated Benzoic Additive for High‐Performance 2‐Terminal Perovskite/Silicon Tandems

High‐quality wide‐bandgap (WBG) perovskite films are indispensable for advancing high‐performance perovskite/silicon tandem solar cells. However, WBG perovskite films typically suffer from substantial defect density and severe halide segregation‐two critical bottlenecks that drastically limit device efficiency and long‐term stability. To address these challenges, this work develops a targeted molecular design strategy for a carboxylic acid‐based additive, featuring the strategic integration of guanidinium cation (Gua + ) into the benzoic acid (BZH) molecular backbone. This rational modification precisely modulates the electrostatic potential distribution, enhances the molecular dipole moment, and reduces the acid dissociation constant (pKa). Consequently, the optimized additive enables the fabrication of WBG perovskite films with markedly reduced defect density, uniform halide distribution, and superior morphological quality. The resultant WBG perovskite single‐junction cell exhibits enhanced open‐circuit voltage ( V oc) and fill factor (FF), achieving a champion power conversion efficiency (PCE) of over 22.9% alongside outstanding device stability. Ultimately, the integrated perovskite/silicon tandem solar cell attains a PCE surpassing 31%, highlighting the enormous potential of this additive design strategy for enabling high‐performance, stable tandem photovoltaics.