First-Principles Informed Analysis of Thermoelectric Materials for Applications
thesisposted on 06.12.2019 by Evan L Witkoske
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
Thermoelectric (TE) devices are useful in niche applications that require reliability and durability, including energy harvesters for sensors, cooling electronics, and power generation at high temperatures. Assessing, optimizing, and implementing materials into practical TE devices and systems have been difficult theoretical and engineering problems. The goal of this research is to develop a first-principles informed approach to analyze thermoelectric materials for potential practical applications.
TE materials and devices are traditionally quantified using a material figure of merit (FOM), zT, and device FOM, ZT. Using full numerical descriptions of band structures and solutions to the Boltzmann transport equation (BTE) in the relaxation time approximation (RTA), we examine how band convergence may or may not increase zT depending on the relative strength of intra- and inter-band scattering. We compute zT vs. a generalized TE quality factor (b-factor) and examine a dozen complex TE materials showing none exceeds the performance of a simple, parabolic energy band. In fact, a plot of zT vs. b-factor appears to be universal. We test this conclusion based on RTA solutions to the BTE using a simple treatment of scattering against more rigorous first-principles approaches.
In addition, we theoretically assess a low-cost TE oxide (2H-CuAlO2), which has durability at high temperatures and is earth abundant, making it attractive for applications. Finally, with an eye towards minimizing the $cost/kW-hr of thermoelectric energy generation, we discuss our approach to a few specific high temperature environments and discuss their viability as practical system level applications.