Improvement of photovoltaic properties of benzo[1,2-b:4,5-b′]difuran-conjugated polymer by side-chain modification

The development of polymer solar cells (PSCs) for the donor materials based on benzo[1,2-b:4,5-b′]dithiophene (BDT) has significantly boosted the power conversion efficiency (PCE). However, the PCE of polymer donor materials for benzo[1,2-b:4,5-b′]difuran (BDF)-based lags far behind that of their BDT analogs. To further explore efficient copolymers based on BDF units, a two-dimensional (2D) side-chain strategy was proposed to investigate the atom-changing effects on the copolymer donors for the properties of electron and optical. In this study, we designed and synthesized three new BDF-based copolymer donor materials, named PBDF-C, PBDF-O, and PBDF-S. Owing to the balanced charge transport and favorable phase separation of PBDF-S:Y6, a high PCE of 13.4%, a short-circuit current (J_sc) of 25.48 mA cm⁻², an open-circuit voltage (V_oc) of 0.721 V, and a fill factor (FF) of 72.6% was obtained. This research demonstrates that the BDF building block has great potential for constructing conjugated copolymer donors for high-performance PSCs and that 2D side-chain modification is a facile approach for designing high-performance BDF-based copolymer materials.