Designed Polar Cosolvent‐Prepared Zinc Oxide Film for Efficient and Stable Inverted Organic Solar Cells

Abstract Here, a simple method of applying dimethylformamide (DMF) as cosolvent in the sol‐gel technology is used to improve the quality of ZnO bulk films. First‐principles calculations show that with the addition of polar solvent DMF, the adsorption energy (E ads ) between the solvent and Zn(OH)₂ increases from −1.42 to −1.74 eV, which can stabilize the existence of Zn(OH)₂, thereby promoting the ZnO synthesis. Besides, the elimination of amine residues in the DMF‐ZnO film significantly suppress the photocatalytic activity induced by amine‐induced coordination or redox reactions. Inverted organic solar cells (OSCs) based on PM6:Y6 and PM6:BTP‐eC9 achieves impressive power conversion efficiencies (PCE) of 17.58 and 18.14%, respectively. Furthermore, benefiting from the reduced defects of bulk ZnO, pseudo‐bilayer bulk heterojunction (PBHJ) devices based on the optimized ZnO film exhibited superior stability, the PM6:Y6 devices based on DMF‐ZnO ETLs can maintain 90.28% of their initial PCE after 1000 h of thermal aging at 85 °C, and 80.98% of their initial PCE after 168 h of UV aging. This simple solvent optimization strategy can significantly improve the charge transport of ZnO bulk films, making it a reliable strategy for the preparation of electron transport layers in OSCs.