Cooperative Dipole Engineering Unlocks 92.8% Shockley–Queisser Voltage Limit in Wide-Bandgap Perovskites for Tandem Photovoltaics

Wide-bandgap (WBG) perovskite solar cells (PSCs, Eg ≃ 1.67 eV) still suffer from pronounced open-circuit-voltage (VOC) deficits. Here, we report a synergistic surface-passivation strategy that coassembles a dipolar quaternary-ammonium salt, acetylcholine chloride (ACCl), with an electron-rich long-chain alkylammonium halide, n-octylammonium iodide (OAI). A mixed ACCl:OAI treatment reconstructs the perovskite surface, lowers surface-trap density, and aligns the valence band with the hole-transport layer. Consequently, the champion WBG PSC delivers VOC = 1.29 V, JSC = 20.0 mA cm–2, FF = 82.8%, and PCE = 21.27%, corresponding to 92.8% of the Shockley–Queisser voltage limit. When integrated as the top absorber in a monolithic n-i-p perovskite/p-type Si tandem, the passivated WBG cell contributed to a PCE of 26.8% with a VOC of 1.91 V. These results reveal that cooperative defect passivation and energy-level engineering are both essential to unlock the full voltage potential of WBG perovskites.