Efficiency enhancement of organic solar cells enabled by interface engineering of sol-gel zinc oxide with an oxadiazole-based material

Organic solar cells (OSCs) have acquired much attentions owing to their advantages in terms of solution-processability, low-cost, lightweight and compatibility for large-scale roll-to-roll processing. Aside from materials design, studies on interface engineering are also crucial to enhance photovoltaic performance for the realization of high-performing OSCs. In this study, interface engineering on sol-gel zinc oxide (ZnO) electron-transporting layer (ETL) was conducted by introducing additional oxadiazole-based electron-transporting materials, PBD between ZnO ETL and photoactive layer. The significance of incorporating PBD on ZnO was demonstrated by investigating the change in optical, electrical and morphological properties of pristine ZnO ETL. Herein, the utilization of PBD could enhance ZnO film's conductivity, which was favorable for better charge transport ability. As compared to ZnO ETL, ZnO/PBD ETL had lower work function to facilitate more efficient electron extraction from the photoactive layer. Moreover, PBD could smoothen the ZnO film's morphology and improve hydrophobicity of the surface to provide uniform and intimate interfacial contact between ETL and the photoactive layer. As a result, through this hybrid bilayer strategy, inverted OSCs based on PBDB-T:IT-M photoactive layer system exhibited ~7% enhancement in the power conversion efficiency from 10.8% (ZnO-based device) to 11.6% (optimized ZnO/PBD-based device).