Tuning the Ambipolar Character of Copolymers with Substituents: A Density Functional Theory Study.

Ambipolar copolymers play a vital role in reducing the cost and simplifying the fabrication of ambipolar organic field-effect transistors (OFETs). However, the development of them lags behind that of p-type and n-type copolymers. Herein, we aim to obtain ambipolar copolymers by introducing appropriate substituents into DPP-TVT [diketopyrrolopyrrole-(E)-1,2-di(2-thienyl)ethane]. We study the effects of substituents (-NH2, -OCH3, -F, -CF3, and -CN) on backbone planarity, electronic structures, and charge carrier mobility by density functional simulations. Electronic structure analyses show that the CN-substituted DPP-TVT lies in the trap-free energy window and has the narrowest band gap, suggesting promising ambipolar character. This was further confirmed by the results of its charge carrier mobility along both intra- and interchain directions. Besides the -CN group, the -NH2 group also proved to be effective in turning DPP-TVT into the ambipolar copolymer. Our study provides insights into modulating the performances of OFETs by introducing appropriate substituents into the copolymers to achieve ambipolar character.