Miscibility Control by Tuning Electrostatic Interactions in Bulk Heterojunction for Efficient Organic Solar Cells

The morphology of the bulk heterojunction plays a vital role in determining the efficiencies of the organic photovoltaic (OPV) cells. Although the device efficiencies have been greatly improved, the practice guidelines in morphology control are still lacking. In this work, impressive performance of 17.7% was achieved by modulating the electrostatic interaction and, thus, the miscibility between the newly designed polymer donors (P5T, P5T-2F) and a nonfullerene acceptor (NFA) named eC9. Three model compounds (8T, 8T2F, and TT-2Cl) are prepared to deeply study the miscibility of the donors and acceptors in the active layers. Our findings demonstrate that the decreased molecular interaction and miscibility in P5T-2F:eC9 combinations is more favorable for obtaining suitable phase separation morphology. This work proposes specific molecular design strategy to optimize the donor:acceptor (D:A) bulk morphology, which is crucial for further boosting the efficiency of the OPV cells.

Automated summary

The morphology of the bulk heterojunction is crucial for the efficiency of OPV cells, and modulating electrostatic interaction plays a key role in improving efficiency. Compatibility between the donor and acceptor in the active layer is important for phase separation morphology, and a specific molecular design strategy is proposed to optimize the D:A bulk morphology.