Efficiency of Energy Conversion in Thermoelectric Nanojunctions

TL;DR

This study uses first-principles methods to analyze how the thermoelectric figure of merit $ZT$ varies with temperature and length in nanojunctions, revealing opposite length dependencies for metallic and insulating chains and factors to enhance efficiency.

Contribution

It provides a detailed quantitative analysis of $ZT$ dependence on temperature and length in nanojunctions, introducing a characteristic temperature $T_0$ and contrasting behaviors in metallic versus insulating chains.

Findings

$ZT$ scales as $T^2$ when $T \

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Abstract

Using first-principles approaches, this study investigated the efficiency of energy conversion in nanojunctions, described by the thermoelectric figure of merit $ZT$. We obtained the qualitative and quantitative descriptions for the dependence of $ZT$ on temperatures and lengths. A characteristic temperature: $T_{0}= \sqrt{\beta/\gamma(l)}$ was observed. When $T\ll T_{0}$, $ZT\propto T^{2}$. When $T\gg T_{0}$, $ZT$ tends to a saturation value. The dependence of $ZT$ on the wire length for the metallic atomic chains is opposite to that for the insulating molecules: for aluminum atomic (conducting) wires, the saturation value of $ZT$ increases as the length increases; while for alkanethiol (insulating) chains, the saturation value of $ZT$ decreases as the length increases. $ZT$ can also be enhanced by choosing low-elasticity bridging materials or creating poor thermal contacts in nanojunctions. The results of this study may be of interest to research attempting to increase the efficiency of energy conversion in nano thermoelectric devices.