Molecular Design of Self-Doping Cathode Interlayer for Efficient and Humidity-Resistant Organic Photovoltaic Cells

The power conversion efficiency (PCE) of organic photovoltaic (OPV) cells has surpassed 20%. However, their stability remains a critical issue that requires further improvement, particularly due to severe performance degradation under humid conditions. To tackle this challenge, a series of cathode interlayer materials─NDIP-M, NDIP3F-M, and NDIP4F-M─were rationally designed and synthesized through side-chain engineering combined with fluorination strategies. These materials exhibit enhanced hydrophobicity and maintain good solubility in alcohol-based solvents. Among them, NDIP3F-M showed optimized energy level alignment and reduced trap activation energy, leading to an improved fill factor and a PCE of 20.1%. Notably, due to the excellent humidity resistance of NDIP3F-M, an unencapsulated OPV cell based on NDIP3F-M retained 50% of its initial PCE after 400 h of exposure to air at 85% relative humidity, which is significantly higher than that of OPV cells employing commonly used cathode interlayer materials.