AbstractWide‐bandgap perovskites have attracted considerable attention due to their adjustable bandgap properties, making them ideal candidates for top subcells in tandem solar cells (TSCs). However, wide‐bandgap (WBG) perovskites often face challenges such as inhomogeneous crystallization and severe non‐radiative recombination loss, leading to high open‐circuit voltage (V_OC) deficits and poor stability. To address these issues, we introduce a multifunctional phenylethylammonium acetate (PEAAc) additive that enhances uniform halide phase distribution and reduces defect density in perovskite films by regulating the mixed‐halide crystallization rate. This approach successfully developed efficient WBG perovskite solar cells (PSCs) with reduced V_OC loss and enhanced stability. By applying this universal strategy to the FAMACsPb(I_1‐xBr_x)₃ system with a range of bandgaps of 1.72, 1.79, 1.85, and 1.92 eV, we attained power conversion efficiencies (PCE) of 21.3%, 19.5%, 18.1%, and 16.2%, respectively. These results represent some of the highest PCEs reported for the corresponding bandgaps. Furthermore, integrating the WBG perovskite with low‐bandgap organic photovoltaics, we achieved an impressive PCE of over 24% for two‐terminal perovskite/organic TSCs, with a record V_OC of ∼ 2.2 V. This work establishes a foundation for addressing phase separation and inhomogeneous crystallization in Br‐rich perovskite components, paving the way for the development of high‐performance WBG PSCs and TSCs.This article is protected by copyright. All rights reserved