Polymer-Modified ZnO Nanoparticles as Electron Transport Layer for Polymer-Based Solar Cells

The optimization of interfacial layer plays a critical role in the ultimate use of polymer-based solar cells (PSCs). By introducing an insulating polymer, polystyrene (PS), into the ZnO nanoparticles (NPs) with large particle size, an electron transport layer (ETL) with a thickness of more than 130 nm is produced. The doping of PS not only improves the film quality of ZnO NPs to generate a denser, smoother, and more uniform ETL, but also increases the contact properties between the hydrophilic ZnO and hydrophobic active layer. In comparison to control devices, the power conversion efficiencies (PCEs), short circuit current densities, and fill factors of PSCs with the PS-modified ETL for a typical fullerene system PTB7-Th:PC71BM and, also, a nonfullerene system PBDB-T:ITIC are increased, with PCEs from 8.49% to 9.54% and 10.03% to 11.05%, respectively. The reproducibility, mechanical endurance, and ambient stability of the PSCs with the PS-modified ZnO NP ETL are significantly improved. The combination of the insulating polymer and ZnO NPs provides a simple, low-cost way to realize the commercialization of high performance, flexible PSCs.