Use of benzothiadiazole–triphenylamine amorphous polymer for reproducible performance of polymer–fullerene bulk-heterojunction solar cells

An amorphous polymer, poly(BTD-TPA), which consists of benzothiadiazole and triarylamine units, can be successfully utilized to fabricate bulk heterojunction (BHJ) organic photovoltaics (OPVs), and the OPV performance can be demonstrated to be independent of the casting solvent or thermal annealing temperature. The OPV based on poly(BTD-TPA):PC70BM (1:4) that was fabricated using chloroform (boiling point of 61 °C) and annealed at 60 °C for 10 min exhibited a power conversion efficiency (PCE) of 2.81% under simulated solar irradiation through an air mass of 1.5 at 100 mW cm−2. On the other hand, the OPV fabricated using o-dichlorobenzene (boiling point of 181 °C) and annealed at 110 °C for 10 min exhibited a PCE of 2.65%. Almost the same PCEs and incident photon to current conversion efficiencies (IPCEs) were obtained in both OPVs. The use of an amorphous film of poly(BTD-TPA) in the fabrication of OPVs offers great advantages over the use of a polycrystalline film of regioregular poly(3-hexylthiophene) (P3HT) in terms of high reproducibility of the OPV performance.

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► BHJ OPVs based on an amorphous polymer, poly(BTD-TPA), were fabricated.
► OPV performance was independent of the casting solvent and the thermal annealing temperature.
► OPVs exhibited a PCE of 2.81%.
► Use of poly(BTD-TPA) offers advantages in terms of high reproducibility of the OPV performance.