Prominent Short-Circuit Currents of Fluorinated Quinoxaline-Based Copolymer Solar Cells with a Power Conversion Efficiency of 8.0%

A tailor-made medium-band gap fluorinated quinoxaline-based conjugated polymer of PBDT-TFQ was designed and synthesized as a donor material for bulk-heterojunction (BHJ) solar cells. This polymer is possessed of an intrachain donor–acceptor architecture and exhibits a broad and strong absorption spectrum across the entire UV–vis region. The introduction of F atoms with high electron affinity to the quinoxaline moiety is effective in further lowering both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of PBDT-TFQ to attain higher open-circuit voltage (V_oc). With an optimized blend ratio of PBDT-TFQ:PC₇₁BM (1:1, w/w), a high power conversion efficiency (PCE) of 8.0% was obtained, with a V_oc of 0.76 V, a short-circuit current density (J_sc) of 18.2 mA cm^–2, and a fill factor (FF) of 58.1% under AM 1.5G irradiation. The resulting copolymer reveals an outstanding J_sc value, arising from the higher hole mobility of PBDT-TFQ, together with the better continuous percolation pathways within the polymer blend for efficient exciton dissociation and charge transport.