Diketopyrrolopyrrole (DPP)-based terpolymers-P(DPP-TPyT) and P(DPP-T3MTT)-bearing bithiophene donating groups and weak accepting units such as pyridine (Py) or methyl thiophene-3-carboxylate (3MT), in the polymer backbone, were successfully synthesized. Although the two polymers had similar physical and electrochemical properties, grazing incidence X-ray diffraction patterns of P(DPP-TPyT) and P(DPP-T3MTT) showed mixed and edge-on orientations, respectively, in thermally annealed films. Accordingly, the P(DPP-T3MTT) showed twice the hole mobility of P(DPP-TPyT) in a thin-film transistor, and a blended film of P(DPP-T3MTT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) showed better power conversion efficiency in a polymer solar cell. (C) 2015 Wiley Periodicals, Inc.