Thermoelectric properties including thermal conductivity of electrodeposited bismuth selenide thin films fabricated using different acid solutions

Abstract

Using electrodeposition to prepare thermoelectric thin films enables the fabrication of energy-harvesting devices with low manufacturing cost. However, it is difficult to compute the thermal conductivity of these electrodeposited thin films owing to their large surface roughness. In this work, we prepared electrodeposited bismuth selenide (Bi2Se3) thin films using hydrochloric acid (HCl) and nitric acid (HNO3) solutions and measured the thermal conductivity using the 3ω method. The Bi2Se3 thin films prepared using the HCl solution consisted of round grains with relatively large pores that reached the substrate appearing between the grains. In contrast, the Bi2Se3 thin films prepared using the HNO3 solution were composed of flake-like grains with the appearance of relatively small and shallow pores. As a result, the thermal conductivity could only be measured for the Bi2Se3 thin films synthesized utilizing HNO3 solution; however, the measured thermal conductivity was about 0.14 W/(m⋅K). The low value of thermal conductivity was attributed to their amorphous structure. To improve the electrical properties of Bi2Se3 thin films, the electrodeposited samples were subjected to a thermal annealing treatment. An improvement in the electrical properties of the thin films was noticed with an annealing temperature of 300 °C; however, the thermal conductivity also increased to 0.76 W/(m⋅K). Therefore, the dimensionless quantity which represents the performance of the Bi2Se3 thin film, ZT, was determined to be 0.08–0.09. Therefore, the effectiveness of the proposed method for preparing electrodeposited thin films while estimating the thermal conductivity and ZT was successfully demonstrated.