A bipolar diketopyrrolopyrrole molecule end capped with thiophene-2,3-dicarboxylate used as both electron donor and acceptor for organic solar cells

It is a primary strategy to manipulate the energy levels of organic semiconductor molecules for getting better performances in organic photovoltaic devices. In this paper, we designed and synthesized a diketopyrrolopyrrole (DPP)-based small molecule, 3,6-bis(5-[(diethyl thiophene-2,3-dicarboxylate)-2-yl]thiophene-2-yl)- 2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione (DPP(C2T)(2)), by introducing ester groups to both alpha and beta-position of the end-capped thiophene ring. Due to the electron withdrawing effect of ester groups, the resulting molecule exhibits low-lying the highest occupied molecular orbital (HOMO) energy level of -5.37 eV and the lowest unoccupied molecular orbital (LUMO) energy level of -3.78 eV. Therefore, DPP(C2T)(2) can be used as either electron donor or acceptor for solution processed organic solar cells and shows a power conversion efficiency (PCE) of 1.66% when blended with [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) and 1.08% with poly(3-hexylthiophene) (P3HT). The crystallinity, carrier mobilities and film morphology are systematically investigated and discussed, in order to study the influence of extra ester group on the properties of the resulting molecule. (C) 2016 Elsevier B.V. All rights reserved.