Optimal band structure for thermoelectrics with realistic scattering and bands

Junsoo Park,Anubhav Jain,Yi Xia,Vidvuds Ozoliņš

doi:10.1038/s41524-021-00512-w

Abstract

Understanding how to optimize electronic band structures for thermoelectrics is a topic of long-standing interest in the community. Prior models have been limited to simplified bands and/or scattering models. In this study, we apply more rigorous scattering treatments to more realistic model band structures—upward-parabolic bands that inflect to an inverted-parabolic behavior—including cases of multiple bands. In contrast to common descriptors (e.g., quality factor and complexity factor), the degree to which multiple pockets improve thermoelectric performance is bounded by interband scattering and the relative shapes of the bands. We establish that extremely anisotropic “flat-and-dispersive” bands, although best-performing in theory, may not represent a promising design strategy in practice. Critically, we determine optimum bandwidth, dependent on temperature and lattice thermal conductivity, from perfect transport cutoffs that can in theory significantly boost zT beyond the values attainable through intrinsic band structures alone. Our analysis should be widely useful as the thermoelectric research community eyes zT > 3.

Highlights

Thermoelectricity enables clean electricity generation and fluidfree cooling
The Seebeck coefficient predicted at a fixed EF is provided in Supplementary Discussion, which pinpoints how and why our model predictions deviate from the single parabolic band (SPB) model
A light band is definitely preferred: the power factor (PF) and zT both decrease with increase in m, as numerous studies agree upon[27,28,29]

Summary

Introduction

Thermoelectricity enables clean electricity generation and fluidfree cooling. The ultimate goal of basic thermoelectric materials research is to design or discover materials with high figure of merit zT, commonly expressed as: zT 1⁄4 α2σ κe þ κlat T: (1)Here, the thermoelectric power factor (PF) is the product of Ohmic charge conductivity (σ) and the Seebeck coefficient (α) squared. The ultimate goal of basic thermoelectric materials research is to design or discover materials with high figure of merit zT, commonly expressed as: zT 1⁄4 α2σ κe þ κlat T: (1). The total thermal conductivity κ is the sum of electronic thermal conductivity (κe) and lattice thermal conductivity (κlat). A lattice property, is relatively independent, though it too exhibits some positive correlation with σ through structural symmetry. These interrelations make it difficult to determine the effect of various design strategies to optimize zT

Methods

Results

Conclusion