A benzothiadiazole-based oligothiophene for vacuum-deposited organic photovoltaic cells

We introduced a benzothiadiazole unit into a small molecule conjugated system and determined the electronic features and organic photovoltaic cell (OPV) characteristics of the resulting material, 4,7-bis(5′-hexyl-2,2′-bithiophene-5-yl)benzothiadiazole (DH5TB). DH5TB showed remarkably red-shifted UV–vis absorption and photoluminescence (PL) emission spectra compared with α,α′-dihexyl-quinquethiophene (DH5T). The low energy band gap of 1.95 eV and good film morphology of DH5TB resulted in good OPV performance. We investigated the DH5TB:C60 blend ratio dependence on OPV performance and further improved the efficiency by introducing a C60 interlayer on top of the DH5TB:C60 layer. In the present work, the best photovoltaic cells had a JSC of 4.75 mA/cm2, a VOC of 0.53 V, and a fill factor (FF) of 0.38, giving a power conversion efficiency of 0.97% under AM 1.5 (100 m/cm2) without thermal annealing.