Synthetic Approach for Enhancing Semiconductor Properties of Water-Borne DPP-Copolymer

Abstract

We introduce a synthetic approach to enhance coalescence phenomenon during solidification of water-borne colloids so that thin, even, and continuous film morphology of polymer semiconductors can be realized. From the theoretical study of complex colloids, we show that small-sized and uniform colloid particles are essential to minimize depletion contact energy between colloid particles and thus to enhance coalescence. Therefore, the newly synthesized polymer semiconductor in this study is designed with the aim of better molecular affinity with surfactants, so that phase transfer of polymer semiconductors from organic phase to water phase can proceed more efficiently during mini-emulsion synthesis. This is achieved by substituting a Si atom to the branching C atom of the alkyl solubilizing group of a conventional donor-acceptor polymer semiconductor. Such a chemical modification increases the volumetric portion of hydrophobic alkyl chains and thus enables higher solubility as well as higher hydrophobicity, all of which are closely related with enhancing molecular affinity between polymer semiconductor and surfactant, as proved by surface energy, dynamic light scattering, transmission electron microscopy, and scanning electron microscopy analyses. As a result, it is shown that the performance of organic field-effect transistors fabricated from water-borne colloids can be improved to a level similar to the case of organic solvents, 0.91 cm2 V-1 s-1. More importantly, we also show the reproducibility of transistor performance is greatly improved due to the uniform and small water-borne colloidal particles. © 2018 American Chemical Society.