Diketopyrrolopyrrole-based small molecules with simple structure for high VOC organic photovoltaics

A series of simple structured small molecules based on diketopyrrolopyrrole (DPP) are synthesized and their photovoltaic properties are investigated in terms of the type of electron donating unit. By introducing a donor unit with different electron-donating power such as thiophene (T) and phenylene (Ph), into A-D-A type small molecule, the frontier orbital energy levels of small molecules can effectively be tuned. The small molecule with a weak donor unit of Ph, Ph(TDPP)(2) exhibits a power conversion efficiency of 4.01% with a remarkably high open circuit voltage of 0.93 V when it is blended with [6,6]-phenyl-C-71-butyric acid methyl ester as an active layer material in bulk heterojunction solar cells. (C) 2012 Elsevier B V. All rights reserved.