Decoding Light‐Soaking Pre‐Stabilization for Real‐World Performance Benchmarking in Large‐Area Perovskite Modules

ABSTRACT The light–soaking effect in perovskite solar cells (PSCs), while widely observed, presents a complex interplay between performance enhancement and operational instability, the physical origin of which remains insufficiently understood. Herein, based on high–efficiency, large–area modules (21 cm 2 ) with certified 23.09% efficiency and 96.29% geometric fill factor, we decouple the underlying mechanisms by combining multi–modal in–situ characterizations with a self–consistent drift–diffusion model that explicitly accounts for coupled ion–electron dynamics. We reveal that light–soaking activation is primarily driven by the cooperative migration of anion (I − ) and cation (Cs + ) ions, which selectively accumulate at the respective charge–transporting interfaces. This interfacial ion redistribution fundamentally reconstructs the energy band alignment, enhancing the built–in potential and optimizing charge extraction while passivating interfacial defects. Crucially, we demonstrate that molecular engineering of the hole–transport layer (e.g., employing a phosphonic acid–based self–assembled monolayer) is pivotal for regulating this process, enabling superior ion immobilization and stabilization compared to conventional poly[bis(4‑phenyl)(2,4,6‑trimethylphenyl)amine (PTAA). Based on the state‐of‐the‐art modules, we establish that the activation/deactivation kinetics are intensely dependent on external stimuli (light intensity, spectrum, and temperature), providing a definitive link between operational conditions and device metastability. Our work elucidates the microscopic physico–chemical picture of light–induced performance evolution in PSCs and establishes interface–ion interaction as a central design rule for achieving highly efficient and operationally stable photovoltaics.