Tuning Frontier Orbital Energetics of Azaisoindigo-Based Polymeric Semiconductors to Enhance the Charge-Transport Properties

Abstract

To establish a structure–property relationship between polymer backbone structures and field-effect transistor performance has emerged as a new topic in organic electronics. The tunability and diversity of organic semiconductors provide the feasibility of controlling the electrical properties. Herein the characterization of thienothiophene-, dithiophenylethene-, biselenophene-, and diselenophenylethene-containing azaisoindigo copolymers is presented. As suggested by both theoretical calculations and experimental results, backbone electronic structure and linearity, density of side chains, aggregation, and thin film microstructure are involved in the differences in optical and electrical properties of these polymers. As the conjugation lengthens, n-type behaviors of the polymer semiconductors are suppressed, leading to a variation from nearly balanced ambipolar behaviors to predominant p-type characteristics. The effect of heteroatom substitution is also investigated. Notably, high hole and electron mobilities of 1.14 and 1.54 cm2 V−1 s−1 extracted from approximately ideal I–V curves are achieved with the top-gate/bottom-contact configuration transistors, demonstrating the potential of 7,7′-diazaisoindigo-based semiconducting polymers for applications in organic electronics.