Synthesis and properties of a novel narrow band gap oligomeric diketopyrrolopyrrole-based organic semiconductor

A trimer of diketopyrrolopyrole (DPP), Tri-BTDPP, was synthesized and characterized. Tri-BTDPP has a HOMO level of -5.34 eV, a low band gap of 1.33 eV, and a hole mobility of similar to 10(-3) cm(2) V-1 s(-1) in organic field effect transistors (OFETs). Organic photovoltaic (OPV) devices using the donor/acceptor blends of Tri-BTDPP and PC71BM exhibited low power conversion efficiencies (PCE) of up to 0.72%, even though the desirable optical and electronic characteristics of this compound as a donor semiconductor for achieving high performance for OPV. Through an intensive study of the active layer using AFM, XRD, and DSC, it was found that Tri-BTDPP and PC71BM were unable to intermix and formed oversized Tri-BTDPP phases, resulting in poor charge separation. Some guidance on how to improve the OPV performance of Tri-DPP compounds is provided. (C) 2016 Elsevier Ltd. All rights reserved.