Effect of dopants and nanostructuring on the thermoelectric properties of ZnO materials

Son D N Luu, Tuan Anh Duong and Thang Bach Phan

Abstract

Zinc oxides have attracted attention in high-temperature waste heat recovery due to their high melting points. This review aims to provide a comprehensive summary of the effects of dopant on thermoelectric properties of ZnO based bulk, thin films, nanowire as well as the effects of nanostructuring on ZnO based materials. In general, the thermoelectric performance can be enhanced by a single doping. Among single dopant elements, Al dopant seems to be effective dopant resulting in better thermoelectric properties. However, the solubility limit of the dopant in single doping limits the improvement of thermoelectric performance. Efforts in dual doping to improve the thermoelectric properties of ZnO materials have been conducted. As a result, the drastic improvement of the thermoelectric performance from Al-Ga dually doped ZnO bulk and Ga-In dually doped ZnO thin films shows strong evidence of this approach. In addition to doping effects, the thermoelectric performance can also be enhanced through structural effects such as mismatches between the film and substrate, morphology, thermal treatments or introducing nano-precipitated materials. In addition, the low-dimensional structure such as nanowire structure is promising for improving the thermoelectric properties of materials because of their strong quantum confinement effect. This leads to the increase of the Seebeck coefficient according to the Mott's relationship without lowering the electrical conductivity