New pi-extended diketopyrrolopyrrole-based conjugated molecules for solution-processed solar cells: Influence of effective conjugation length on power conversion efficiency

Abstract

New organic semiconducting molecules containing diketopyrrolopyrrole and thiophene units were designed to investigate the influence of effective conjugation length on the performance of organic photovoltaics made with [6,6]-phenyl-C61-butyric acid methyl ester. New D-A-D-A-D type molecules (where; D = donor, A = acceptor) such as ter- and quarter-thiophene bridged diketopyrrolopyrrole dimers were synthesized with different numbers of conjugative units. The field-effect mobilities of these molecules were determined by fabricating thin film transistors. The new molecules displayed moderately high mobility between 3.6 x 10(-2) and 1.1 x 10(-2) cm(2) V-1 s(-1) without a thermal annealing process for TT(BTDPP)2 and QT(BTDPP)(2). The TT(BTDPP)(2) molecule possesses a longer effective conjugation length (c.f. QT(BTDPP)2) and shows a high carrier mobility. When employing the ter- and quarter-thiophene bridged diketopyrrolopyrrole dimers as donor molecule in combination with [6,6]-phenyl-C61-butyric acid methyl ester [TT(BTDPP)2:PC61BM = 1:0.8 w/w], the photovoltaic cell provides the highest power conversion efficiency of 3.76%. (C) 2014 Elsevier Ltd. All rights reserved.