Enhancing Halogen Phase Synchronous Crystallization Enables High‐Performance Wide‐Bandgap Perovskite Photovoltaics

Wide-bandgap (WBG) perovskite solar cells (PSCs) have promising applications in tandem cells, offering a viable pathway to surpass the theoretical efficiency limits of single-junction photovoltaic devices. However, WBG perovskite with increasing bromide content suffers from inhomogeneous phase distribution and bulk defects, owing to the mismatched crystallization kinetics between halogen phases. Herein, we propose a synchronous halogen crystallization strategy utilizing a multifunctional additive, 4,4',4″-tricarboxyl triphenylamine (TTA), to modulate the bromine/iodine phase competitive crystallization. TTA preferentially coordinates with bromine-rich components and reduces its rapid crystallization, while simultaneously accelerating the crystallization of the iodine-rich phase, resulting in their synchronous crystallization. This approach also improves composition uniformity and film quality, which effectively suppresses non-radiative recombination and enhances phase stability under light irradiation and voltage bias. As a result, the TTA-modified device achieves a remarkable power conversion efficiency (PCE) of 20.55% with an open-circuit voltage (V_OC) of 1.339 V. Moreover, the unencapsulated device retains 90% of its initial efficiency after 1050 h of storage in the ambient environment and exhibits an extended T₉₀ lifetime of 750 h under ISOS-L-1 conditions. This work offers a new perspective for addressing inhomogeneous crystallization in mixed-halide perovskite and facilitates their integrated into tandem photovoltaics.