Eco-Compatible and Highly Efficient Organic Solar Cells with Aggregation-Controlled Terpolymer Strategy

Owing to the development of highly efficient donor and non-fullerene small-molecule acceptor materials, the power conversion efficiency (PCE) of organic solar cells (OSCs) has reached 17%−19%. However, most of the best-efficiency OSC devices still use a toxic halogen solvent in their device fabrication process, which dilute its potential for scale-up production. In this study, we report a terpolymer strategy to develop eco-friendly process-available donor polymers by controlling the aggregation behavior. By introducing ethyl thiophene-3-carboxylate (ET) into the molecular structure of D18, the consequential solubility is improved significantly enough for dissolution in eco-compatible solvents, while preserving the appropriate aggregation. As a result, the newly developed terpolymers (PDs) can be processed with an eco-compatible solvent o-xylene, and the OSC of PD with 10 mol% of ET and Y6-BO exhibits an outstanding PCE of 15.5%, without any treatments such as additive addition, solvent vapor annealing, or thermal annealing. This excellent OSC performance is attributed to the superior charge carrier mobility, suppressed trap-assisted recombination, and substantial semi-crystalline behavior of o-xylene processed the PBET10:Y6-BO blend films. In addition, our o-xylene-based device shows a very good result of maintaining 90% compared to the initial PCE for 300h at 100 ℃ environment.