Recent Progress of Benzodifuran-Based Polymer Donors for High-Performance Organic Photovoltaics.

At present, a variety of benzo[1,2-b:4,5-b']dithiophene (BDT)-based polymer donors are designed and synthesized, which have made great progress toward achieving high power conversion efficiencies (PCEs) of polymer solar cells (PSCs). Despite many advantages of benzo[1,2-b:4,5-b']difuran (BDF) compared with BDT unit, the overall performance of BDF polymer-based PSCs lags far behind that of the counterpart BDT-based polymers. Recently, great advances have been achieved in BDF polymer-based PSCs with the highest PCEs over 16%, suggesting that BDF-based polymers have the significant potential to catch up or even surpass the performance of BDT-based polymers. In this review, the recent advances of BDF polymers in PSCs are first summarized and then the design strategies and the chemical structure-performance relationships of BDF polymers are discussed. Finally, perspectives on the future development of BDF polymers for high-efficiency PSCs are provided.