Utilizing Thiazole and Thioalkyl Side Chains in DPP-based Donor-Acceptor Copolymers for Organic Electronics

Organic semiconducting polymers are a popular topic of research for their use in electronics, such as organic field effect transistors (OFETs) and solar cells. Relative to inorganic semiconductors, organic semiconductors have the advantage of higher affordability, improved sustainability, and easier large-scale fabrication. Current research is aimed at developing new donor-acceptor (D-A) polymers with increased stability, charge carrier mobilities, and effective π-π interactions, while limiting the size of bandgaps to optimize the number of excited electrons that can be collected. Previously, we have shown that replacing thiophene with thiazole in diketopyrrolopyrrole (DPP)-based polymers resulted in decreased electron density along the polymer backbone, lowering the HOMO and LUMO levels. This resulted in an increased charge carrier mobility, leading to the design of new DPP-based D-A polymers. To decrease strain and increase stability, the benzodithiophene (BDT) moiety is copolymerized with the DPP unit to form several BDT-DPP donor-acceptor polymers. Specifically, the focus is on substitution of flanking DPP groups to improve planarity across the polymer backbone, which leads to higher effective conjugation and charge carrier mobilities. Furthermore, the incorporation of thioalkyl side chains on the BDT unit could further stabilize the band gap. Initial results show high stability with ionization potentials (Ip) and electron affinities (EA) at approximately 5.91eV and 3.87eV. Intriguingly, these polymers were designed to function as donor materials in solar cells, yet they have demonstrated varying degrees of ambipolarity. With this new development, solar cells will be constructed to ascertain how successfully they function as donors and acceptors.
National Science Foundation (U.S.) - NSF DMR 1809495
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