The future applications of organic solar cells (OSCs) necessitate a thorough consideration of their ambient stability and processability, particularly for large area air-processed engineering, but water-induced degradation of active layer critically restricts its development. To surmount this hurdle, a water-obstructing guest (WOG) strategy is proposed to attenuate the interaction of the active layer with water molecules, reduce defects in blend films, and enhance the devices stability under high relative humidity (RH) conditions by introducing a siloxane-containing polymer D18-SiO. In addition to suppressing trap density, the WOG with hydrophobic and low surface free energy characteristics, forms a capping layer that blocks moisture penetration while preserving ideal nano-micromorphology with high crystallinity and tight packing properties. Power conversion efficiencies (PCE) of >
19% is reported for spin coating OSCs fabricated across an RH range of 20 to 90%, and PCE of >
17% blade coating OSCs at 90% RH. The D18-SiO, serves as a protective barrier to enhance the device stability, and the corresponding unencapsulated OSCs retained 80.7% of its initial performance in air (≈ 40% RH) after 600-h maximum power point tracking under continuous light illumination, showcasing great potential in designing WOG strategy for large-scale production of air-processed OSCs.