Collaborative Research: Thermoelectric transport and carrier dynamics in three-dimensional chalcogenide nanowire networks

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Nontechnical description: Heat is abundant in the environment, and thus solid-state thermal energy harvesting holds great promises as an alternative power source for wearable electronics and sensors. However, conventional bulk semiconductors are mostly heavy and nonflexible, therefore not readily suitable for these applications. This project explores new material concepts and novel material synthesis techniques based on nanotechnology to create lightweight, flexible, and scalable material systems for efficient thermal energy harvesting. The objective of this project is to understand the fundamental thermal and electrical transport processes in nanowire network-based composites and advance the knowledge of how these underlying physical processes affect the thermal-to-electric energy conversion properties. The project actively promotes education and training of next-generation scientists and engineers, particularly from underrepresented groups, in the interdisciplinary fields that are technologically important and critical for sustained economic vitality of the nation. As direct outcomes of the research activities, online simulation tools are developed for use in courses, as well as for broader audiences.Technical description: This project investigates the fundamental thermoelectric transport physics in three-dimensional chalcogenide nanowire networks. Various thermoelectric chalcogenide nanowires are solution-synthesized and uniformly dispersed in thick flexible matrices such as polydimethylsiloxane to create stable three-dimensional nanowire networks. These nanowire networks provide efficient thermoelectric transport paths for charge carriers in the resulting composite. The impact of carrier tunneling at the junctions between nanowires on the macroscopic thermoelectric properties is extensively studied in this project. The matrices offer stable and uniform dispersion of nanowires, along with their own advantages such as lightweight, low cost, mechanical flexibility, and solution-processability, all in all, making the composites suitable for the development of large-scale flexible thermoelectric materials. In this project, nanowire interfaces are additionally modified with surface-bound organic molecules or particulate conjugated polymers to study their impacts on the transport properties. Heterostructure barrier particles grown at the two ends of the nanowires during the nanowire synthesis are systematically investigated for further enhancement of thermoelectric properties via carrier energy filtering and minority carrier blocking effects. A generalized transport theory including the junction tunneling effects is developed through the project to understand the underlying physics over a broad range of transport regimes, and provide insights for further material advancement.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.