Recent Strategies for Mitigating Degradation Mechanisms in Organic Solar Cells

Organic solar cells (OSCs) are attractive photovoltaic technologies due to their mechanical flexibility, low weight, and compatibility with low-cost solution processing. Power conversion efficiencies above 20% have recently been achieved, largely through the development of non-fullerene acceptors and improved control of bulk-heterojunction morphology. However, insufficient operational lifetime continues to limit commercialization. Performance losses arise from interconnected photoinduced, thermal, morphological, interfacial, environmental, and mechanical processes that are accelerated under realistic operating conditions involving light, heat, oxygen, and moisture. This review examines the principal mechanisms responsible for these changes, with particular attention to photo-oxidation, thermally driven morphological evolution, and interfacial chemical reactions. Stability trends in donor:fullerene, donor:non-fullerene, and all-polymer systems are compared to establish relationships between material composition, microstructure, and device durability. Recent mitigation strategies are then assessed, including molecular design of more stable materials, processing routes that suppress unfavorable morphological evolution, interface and device engineering, and advanced encapsulation. The review is organized around a mechanism-to-mitigation framework that connects molecular, morphological, and interfacial degradation processes with their photovoltaic consequences and the corresponding stabilization strategies across fullerene, non-fullerene, and all-polymer systems. Recent advances demonstrate that appropriately stabilized NFA-based systems can retain ≥85–90% of their initial efficiency for hundreds to thousands of hours under thermal stress, while optimized interfaces have enabled operational lifetimes exceeding several thousand hours under accelerated aging. Remaining challenges include standardized stability protocols, reliable lifetime prediction, and scalable architectures that retain performance under prolonged operation. Such a combined materials-morphology-interface perspective provides a framework for translating high OSC efficiencies into longer and more predictable device lifetimes.