The Thermoelectric Properties of Bismuth Telluride

Abstract

Bismuth telluride is the working material for most Peltier cooling devices and thermoelectric generators. This is because Bi 2 Te 3 (or more precisely its alloys with Sb 2 Te 3 for p‐type and Bi 2 Se 3 for n‐type material) has the highest thermoelectric figure of merit, zT, of any material around room temperature. Since thermoelectric technology will be greatly enhanced by improving Bi 2 Te 3 or finding a superior material, this review aims to identify and quantify the key material properties that make Bi 2 Te 3 such a good thermoelectric. The large zT can be traced to the high band degeneracy, low effective mass, high carrier mobility, and relatively low lattice thermal conductivity, which all contribute to its remarkably high thermoelectric quality factor. Using literature data augmented with newer results, these material parameters are quantified, giving clear insight into the tailoring of the electronic band structure of Bi 2 Te 3 by alloying, or reducing thermal conductivity by nanostructuring. For example, this analysis clearly shows that the minority carrier excitation across the small bandgap significantly limits the thermoelectric performance of Bi 2 Te 3, even at room temperature, showing that larger bandgap alloys are needed for higher temperature operation. Such effective material parameters can also be used for benchmarking future improvements in Bi 2 Te 3 or new replacement materials.