The Environmentally-Friendly Natural Polymer Works as Universally Interfacial Modifier for Fullerene and Non-Fullerene Polymer Solar Cells
The green fabrication is an attractive technique in organic electronics, including green materials and green solvents. Especially, the application of green materials is becoming an emerging issue for polymer solar cells (PSCs). In this study, an enviromentally-friendly natural polymer derivative of hydroxypropyl cellulose (HPC) is utilized successfully as efficient cathode interfacial modifier in PSCs. The HPC shows an universal property as interfacial modifier both in fullerene and non-fullerene PSCs. Through introducing the HPC as the cathode interfacial layer (CIL), the photovoltaic performance is improved more dramatically than the devices without HPC CILs. Compared to bare cathode, the PSCs with HPC as CIL has obtained the higher open circuit voltages (VOCs) and fill factors (FFs), resulting from the HPC forming a better, denser, and more uniform high-quality film on the active layer as demonstrated by atomic force microscopy (AFM), and water contact angle (WCA) measurements. In addition, the existence of polar hydroxypropyl groups in HPC could contact well between active layer and metal cathodes to decrease the work functions of cathodes efficiently, leading to the lower geminate recombination and higher charge mobility than those without CIL both in fullerene and non-fullerene systems. These findings indicate that the natural polymer HPC is a promising candidate as CIL both for highly efficient fullerene and non-fullerene PSCs.