Redox Cascade‐Driven Structural Degradation Under Reverse Bias in All‐Perovskite Tandem Solar Cells

Abstract

ABSTRACT Reverse bias, originating from current mismatch or shading, has emerged as a hidden yet fatal instability in all‐perovskite tandem solar cells. Here we reveal that sustained reverse bias triggers a redox‐coupled lattice collapse within the narrow‐bandgap subcells. Under electrical stress, hole injection oxidizes iodide ions into neutral iodine species, which subsequently oxidize tin cations and drive field‐directed ion migration. This redox cascade propagates vertically through the lattice, coupling ionic transport with structural reconstruction and interfacial corrosion, ultimately leading to irreversible performance loss. These findings expose all‐perovskite tandems as chemomechanical systems in which electrical stress is converted into internal electrochemical damage. To suppress this feedback loop, we introduce a “multideck‐fence” interfacial design that integrates a nanometric oxide diffusion barrier with a chemically stable dual‐metal electrode. This strategy halts the redox‐driven degradation, yielding a power conversion efficiency of 29.03% and more than 30‐fold enhancement in reverse‐bias endurance. Our results redefine reverse bias as a chemomechanically driven failure mode and establish a mechanistic framework for bias‐resilient perovskite architectures.