BODIPY-modified terpolymer donors for efficient fullerene- and nonfullerene-polymer solar cells

Developing efficient polymer donor materials to well-match with acceptors affords continuous contributions to the eminent progress of polymer solar cells (PSCs). Herein, a new series of terpolymer donors is developed by embedding electron-deficient boron dipyrromethene (BODIPY) as the third monomer into the backbone of the benchmark copolymer PTB7-Th. Terpolymers afford less-rigid planarity, ascensive light-harvest ability, down-shifted HOMO levels and modified aggregation properties. Compared with copolymer PTB7-Th, synchronously improved photovoltaic performance is realized by employing terpolymers as electron donors both for fullerene and nonfullerene acceptors, with the average power conversion efficiency (PCE) enhanced from 8.78% to 9.52% for PC71BM- and from 8.79% to 10.05% for IEICO-4F-based devices, respectively. Interestingly, it is found that in terpolymer:fullerene blends, favorable light-harvesting contributes to boosted PCE. Additionally, for PSCs based on nonfullerene acceptors, improved photovoltaic performance is mainly ascribed to the modified morphology by a terpolymer approach. Our results not only confirm the advantages of BODIPY units in constructing efficient terpolymers, but also illuminate the unique virtues of the terpolymer strategy in synergistical optimization of the photovoltaic parameters to contribute to both efficient fullerene- and nonfullerene-PSCs.