Fully Unlocking Additive's Effects for High‐Performance Perovskite Photovoltaics by Incorporating During Crystallization

Mitigating structural and chemical defects in perovskite films is pivotal for advancing photovoltaic performance, yet achieving inclusive inhibition of defects and residual strain remains a formidable challenge. Conventional additive engineering, where modifiers are introduced before or after crystallization, often leads to suboptimal spatial distribution and limited functional efficacy. Here, we demonstrate that incorporating additives during crystallization (DC) unlocks their multifunctional roles beyond mere passivation. We reveal that the DC strategy enables precise additive accumulation at grain boundaries, which simultaneously modulates crystallization kinetics, promotes preferential orientation, and facilitates strain relaxation. This stands in stark contrast to the ineffective distribution and functional constraints observed with conventional methods. By integrating DC additive incorporation with optimized nucleation temperature, we achieved strain-free, defect-tolerant perovskite films. These films yield a champion power conversion efficiency of 26.32% in solar cells and retain 92% of their initial performance after 1 200 h of operational stability testing. Our work establishes a spatiotemporal additive-engineering paradigm that fully leverages additive multifunctionality, providing a generalizable route toward high-performance and durable perovskite optoelectronics.