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

Abstract

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'-hexy1-2,2'-bithiophene-5-yl)benzothiadiazole (DH5TB). DH5TB showed remarkably red-shifted UV-vis absorption and photoluminescence (PL) emission spectra compared with alpha,alpha'-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:C-60 blend ratio dependence on OPV performance and further improved the efficiency by introducing a C-60 interlayer on top of the DH5TB:C-60 layer. In the present work, the best photovoltaic cells had a J(sc) of 4.75 mA/cm(2), a V-OC 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/cm(2)) without thermal annealing. (C) 2010 Elsevier B.V. All rights reserved.