Focusing on Ambient-Processed Active Layers for Organic Solar Cells with High Humidity Tolerance

Organic solar cells (OSCs) have attracted significant attention as next-generation photovoltaics due to their unique advantages such as mechanical flexibility, lightweight, and solution processability. While state-of-the-art power conversion efficiencies (PCEs) exceeding 20% are achieved in inert atmospheres, ambient processing remains a critical challenge for scalable production. Particularly detrimental is moisture penetration into the active layer, which induces a cascade of deleterious effects including trap state formation, charge carrier mobility imbalance, enhanced non-radiative recombination, and disruption of crystalline ordering, ultimately leading to severe device performance losses. Addressing these challenges necessitates strategic molecular engineering to enhance intrinsic moisture resistance by incorporating functional side chains into donor and acceptor materials and using small-molecule additives that suppress water condensation, stabilize morphology, and maintain efficient charge transport. This review systematically summarizes recent progress in the field of humidity-tolerant ambient-processed OSCs. Donor:acceptor systems are categorized according to the reported processing humidity levels, including unspecified conditions, low humidity (RH < 40%), moderate humidity (RH = 40-70%), and high humidity (RH > 70%). Encouragingly, even under 90% RH, some systems achieve the PCEs over 18%, demonstrating significant progress toward air-processed OSCs with high humidity tolerance. These advancements highlight the great promise of molecular engineering strategies to enable the scalable fabrication of high-performance OSCs under ambient conditions with enhanced humidity tolerance.