Enhanced Seebeck Coefficients of Thermoelectric Bi2Te3 Nanowires as a Result of an Optimized Annealing Process

Abstract

Although an annealing approach for bulk or thick Bi–Te material had been done for the enhancement of thermoelectric efficiency, this is the first time to report an annealing process for a Bi–Te nanostructure with a high aspect ratio. As is well-known, the Seebeck coefficient, one of the thermoelectric efficiency factors, is strongly influenced by the chemical composition of the material. However, tellurium element tends to be easily evaporated in the high-temperature range (more than 400 °C) due to its low melting point and high evaporation pressure. Furthermore, it is more serious in such a nanostructure with a high aspect ratio. In this article, we suggested the way to prevent the evaporation of tellurium element in the high annealing temperature range (300–623 °C) and investigated why the Seebeck coefficients for annealed Bi–Te nanowires were enhanced. Seebeck coefficients for Bi–Te nanowires were improved 3 times higher than those for the as-prepared ones at the optimized annealing process due to increased crystal defect concentrations, especially for edge dislocations. Consequently, this annealing process can be applied for nanostructured TE devices for the enhancement of thermopower (S).