Understanding Thermal Transport Properties in Electrically Conductive Polymers

Electrically conductive polymers have revolutionized modern devices, enabling advancements in plastic solar cells, electronics, and thermoelectric devices. The performance of these devices is linked to how heat is dissipated through conduction or how heat is trapped through insulation. This project aims to investigate how thermal transport properties in electrically conductive polymers are affected by charge carriers and polymer backbone structures. By enhancing our fundamental understanding of thermal transport in polymers, this project will provide valuable new knowledge and new practical strategies to design high-efficiency polymer-based devices. By providing research opportunities to underrepresented minority communities and promoting the diversity of the renewable energy field, this project will also educate K-12 and undergraduate students with hands-on renewable thermal energy harvesting projects, creating the next generation of engineers and scientists in energy technologies. Understanding thermal transport physics in polymers has been a long-standing challenge. Existing theories and simulations do not quantitatively describe thermal conductivity enhancement (or reduction) in polymers. The overarching goal of this project is to elucidate how charge carriers (polarons and bipolarons) and structural parameters (short-range positional orders, orientational orders, and chain conformations) quantitively affect thermal conductivities along (and across) chain directions, which are the missing pieces in providing a microscopic picture of heat conduction in electrically conductive polymers. This project will study temperature-dependent thermal conductivities, heat capacities, electrical conductivities, and Seebeck coefficients through state-of-the-art techniques including a transient frequency-domain thermoreflectance. To tune the thermal conductivities predictively, thiophene-based conjugated polymers with precisely controlled doping levels, tuned charge carrier densities, and tailored chain structures will be designed and synthesized by electrochemical doping engineering. This project will not only create insights into thermal transport processes in electrically conductive polymers, but also provide transformative opportunities to develop novel electronic devices based on the interaction of microscopic energy carriers. As a model polymer, poly(3-alkylthiophene) conjugated polymer that is widely used for organic electronics, including field-effect transistors and solar cells, with controllable thermal conductivity will offer unique opportunities for improved efficiency. The broader technical impacts of this work include new strategies for better thermal management applications such as organic light-emitting diodes (OLEDs) without overheating issues. The education plan will promote diversity and inclusion of all groups in engineering workforce, including women and individuals from underrepresented racial and ethnic groups. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.