Temperature-Dependent and Aggregation-Breaking Strategy for Benzodifuran-Constructed Organic Solar Cells

Great efforts have been devoted to semiconductive polymers based on the benzo[1,2-b:4,5-b']dithiophene (BDT) unit, and great progress has been achieved in organic solar cells, whereas the analogue core benzo[1,2-b:4,5-b']difuran (BDF) has the similar extended planar structure, and the electronic structure gets less development in the photovoltaic system. Herein, a novel BDF core-based copolymer PBDFTz-SBP is synthesized, which decorates with two 2D extended biphenyl side chains and shows a relatively small polymer segments distortion and strong intermolecular pi-pi interaction in relation to the BDT-based polymer. Using this polymer, an aggregation-breaking strategy to suppress the trend of self-aggregation of polymers' segment is proposed, which obtains an appropriate phase separation and forms favorable bicontinuous interpenetrating networks for charge transport. It is found that PBDFTz-SBP:ITIC achieves an excellent power-conversion efficiency (PCE) of 12.42% with an open-circuit voltage (V-OC) of 0.89 V, a short-circuit current density (J(SC)) of 18.56 mA cm(-2), and a high fill factor (FF) of 75.19% when the spin-coating solution is 120 degrees C, which is higher than that of PBDTTz-SBP:ITIC-based devices even under optimized conditions. This proposed strategy may be a good choice for the BDF unit to construct the donor (D)-acceptor (A) type polymers and surpass the counterpart BDT-based photovoltaic materials and obtain a state-of-the-art PCEs.