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

► Three new TDPP-based small molecules, (TDPP)2, T(TDPP)2, and Ph(TDPP)2, were synthesized. ► HOMO energy levels of small molecules were controlled by electron-donating unit. ► Ph(TDPP)2 showed the highest VOC due to the weakest electron-donating unit, phenylene. ► The blend of Ph(TDPP)2/PC71BM achieved a promising PCE of 4.01% with a high VOC of 0.93 V.