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

ABSTRACT 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 T 90 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.