Effect of Branching position of alkyl side chain on charge-transport characteristics of diketopyrrolopyrrole- and dichlorodithienylethene-based organic field-effect transistors

Abstract Herein, two donor-acceptor (D-A) conjugated copolymers, 2DPP-ClTVT and 7DPP-ClTVT, were designed and synthesized using 2,5-bis(2-decyltetradecyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (2DPP) and 2,5-bis(7-decylnonadecyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (7DPP) as acceptors for use in organic field-effect transistors (OFETs). Both copolymers exhibited ambipolar transport characteristics owing to the introduction of (E)-1,2-bis(3-chlorothiophen-2-yl)ethene (ClTVT) as a relatively weak donor unit. However, the different branching positions of the alkyl side chains caused significant changes in the morphology and charge carrier mobilities between 2DPP-ClTVT and 7DPP-ClTVT in OFET devices. In our cases, 2DPP-ClTVT with a branching position closer to the backbone produced a smoother film surface and a denser lamellar structure, which account for its better ambipolar transport characteristics.