Plane Pinning Kinetics Enable Crystallographic Organization in Wide‐Bandgap Perovskites for Efficient and Stable All‐Perovskite Tandems

ABSTRACT Wide‐bandgap (WBG) mixed‐halide perovskites are pivotal front absorbers for monolithic tandem solar cells but remain limited by large V OC deficits and photoinduced phase segregation arising from defect accumulation, residual strain, and ion migration. Here, we reveal crystallographic organization as an overarching lever that synchronizes charge‐transport anisotropy, strain relaxation, and mixed‐halide stability, and we introduce a kinetic plane‐competition rule in which preferred texture emerges from selective suppression of undesired planes. An organic chloride additive bearing sulfinyl (S═O) and ammonium (─NH 3 + ) groups is designed as a crystallographic shaping agent. Theory and experiments show preferential adsorption on kinetically active lateral planes, effectively pinning their advancement and redirecting crystallization toward vertical growth, producing films with aligned transport channels and reduced structural disorder. This ordered architecture promotes balanced electron–hole extraction and thereby mitigates light‐driven halide redistribution. The optimized WBG devices achieve a champion power conversion efficiency (PCE) of 20.26% with substantially reduced voltage loss, while monolithic all‐perovskite tandems reach a PCE of 28.24%. The WBG device retains >85% of its initial efficiency after 1500 h of maximum power point tracking (MPPT) without encapsulation, and encapsulated devices maintain 90% after 1648 h under damp heat (85°C/85% RH).