A New Small-Molecule Donor Containing Non-Fused Ring Pi-Bridge Enables Efficient Organic Solar Cells With High Open Circuit Voltage And Low Acceptor Content

To achieve high open-circuit voltage (V-oc) and low acceptor content, the molecular design of a small-molecule donor with low energy loss (E-loss) is very important for solution-processable organic solar cells (OSCs). Herein, we designed and synthesized a new coplanar A-D-A structured organic small-molecule semiconductor with non-fused ring structure pi-bridge, namely B2TPR, and applied it as donor material in OSCs. Owing to the strong electron-withdrawing effect of the end group and the coplanar pi-bridge, B2TPR exhibits a low-lying highest occupied molecular orbital and strong crystallinity. Furthermore, benefiting from the coplanar molecular skeleton, the high hole mobility, balanced charge transport and reduced recombination were achieved, leading to a high fill factor (FF). The OSCs based on B2TPR : PC71BM blend film (w/w=1 : 0.35) demonstrates a moderate power conversion efficiency (PCE) of 7.10 % with a remarkable V-oc of 0.98 V and FF of 64 %, corresponding to a low fullerene content of 25.9 % and a low E-loss of 0.70 eV. These results demonstrate the great potential of small-molecule with structure of B2TPR for future low-cost organic photovoltaic applications.