Novel high-performance photovoltaic D–A conjugated polymers bearing 1,2-squaraine moieties as electron-deficient units

Two D–A type conjugated polymers bearing 3,4-dithiophenyl-1,2-squaraine as acceptor segment, thiophene and benzo[1,2-b;4,5-b′]dithiophene (BDT) as donor moieties, namely, PTTST and PBDTTST, are synthesized by Stille coupling reaction. Compared with their reference polymer PBDTTT without 1,2-squaraine unit, both PTTST and PBDTTST possess more extended absorption in the vis–NIR region of 600–800 nm and lowered HOMO energy levels of 0.1–0.2 eV. Bulk-heterojunction PSC with PBDTTST as p-type material shows high performance with the best PCE value of 1.26% (Voc=0.87 V, Jsc=3.81 mA/cm2, FF=0.38) under irradiation of 100 mW/cm2, while that of PBDTTT-based PSC is 0.36%. Therefore, 1,2-squaraine is a promising electron-acceptor component for construction of high performance photovoltaic D–A type conjugated photovoltaic polymers.

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► Two novel D–A type conjugated polymers (PTTST and PBDTTST) bearing 1,2-squaraine moieties as electron-deficient units.
► These polymers possess a very deep HOMO levels (−5.4–5.5 eV) and a relative low band gaps around 1.60 eV.
► PBDTTST exhibits the best performance (PCE=1.26%) of polysquaraine system studied to date.
► 1,2-squaraines are good candidates as electron acceptor segment for polymer solar cells.