Passivating the Defects and Modulating the Surface Energy of ZnO Cathode Interlayer for Efficient Nonfullerene Organic Solar Cells

Charge transport is a meaningful process in nonfullerene organic solar cells (NOSCs). However, owing to the inherent defects of its metal oxide, the classic ZnO electron transport layer will severely hinder charge transport, and its high surface energy can cause a mismatch contact with the low surface energy active layer. Therefore, polyethylenimine ethoxylated (PEIE) is treated with quaternization and esterification to obtain polyethylenimine ethoxylated‐phenyl acetyl chloride (PEIE‐PAC). ZnO:PEIE‐PAC (ZnO‐P) with fewer defects and lower surface energy film is prepared by blending PEIE‐PAC with the precursor solution of ZnO. Compared with ZnO‐based control device with a power conversion efficiency (PCE) of 15.30%, the PCE of ZnO‐P‐based device is increased to 16.47% in PM6:Y6 system due to the optimization of oxygen defects and surface roughness. Meanwhile, owing to the decrease of surface energy in ZnO‐P, the contact between ZnO‐P and hydrophobic nonfullerene acceptors is closer, and it can isolate water and oxygen in the external environment, thus enhancing the stability in air of NOSCs. The ZnO‐P‐based PM6:Y6 device maintains long‐term storage stability in both N 2 and ambient temperature, and after 1000 h aging, the PCE of ZnO‐P‐based device is still more than 85% of the initial PCE.