Vinylene-Bridged Alkoxyfluorobenzothiadiazole (FOBTzE)-Based Semiconducting Polymers for Enhanced Performance in Non-Fullerene Organic Photovoltaic Cells

Abstract

To mitigate the strong aggregation and limited solubility observed in the previously reported vinylene-bridged alkoxyfluorobenzothiadiazole (FOBTzE)-based polymer, PFOE4T, we designed and synthesized PBFOE-1. This novel semiconducting polymer, based on the FOBTzE framework, incorporates an alkylthienyl-substituted benzodithiophene (BDT) as the donor unit. PBFOE-1 demonstrated broad and intense absorption between 300 and 700 nm with a relatively wide bandgap of 1.7 eV. Additionally, PBFOE-1 features a low HOMO energy level (−5.43 eV) compared to PFOE4T (−5.23 eV), likely due to the incorporation of weakly electron-donating BDT into the polymer backbone. While the PFOE4T/Y12-based solar cell yielded a modest power conversion efficiency (PCE) of 4.37%, characterized by a short-circuit current density (J _sc) of 13.5 mA cm⁻², an open-circuit voltage (V _oc) of 0.69 V, and a fill factor (FF) of 0.47, the PBFOE-1/Y12 cell exhibited a substantially higher PCE of 10.96%. This improvement is reflected in the enhanced J _sc (23.23 mA cm⁻²), V _oc (0.84 V), and FF (0.56). The superior performance of PBFOE-1 is primarily attributed to its improved solubility and aggregation behavior, promoting a more ordered face-on orientation and optimal blend morphology.