Efficient Organic Semiconductors Containing Fluorine-Substituted Benzothiadiazole for Solution-Processed Small Molecule Organic Solar Cells

The synthesis and photovoltaic characteristics of new organic semiconductors, [bisDMFA-Th]-BT-HxTh(3) (1), [bisDMFA-Th]-MonoF-BT-HxTh(3) (2), and [bisDMFA-Th]-DiF-BT-HxTh(3) (3), are reported. These semiconductors have an unsymmetrical donor A-acceptor-donor B (D-A-A-D-B) framework composed of a benzothiadiazole (BT; fluorinated or unfluorinated) acceptor between two different donors bisDMFA and terthiophene. We have demonstrated that these compounds are suitable for use in p-type organic semiconductors for high efficiency solution-processed small molecule organic solar cells (SMOSCs), for which we achieved a remarkable power conversion efficiency of 4.24% with a maximum V-oc of 0.89 V. The fluorine substitution on BT decreased its HOMO level and increased hole mobilities of [bisDMFA-Th]-BT-HxTh(3) derivatives, leading to an increased V-oc in the SMOSCs and improved hole carrier transport properties of the material. In addition, we determined that the insertion of a TiOx functional layer into a bulk heterojunction (BHJ) solar cell significantly reduced the interfacial resistance between the photoactive film and metal electrode, resulting in an increased photocurrent with facile electron transfer between these two layers.