Antimony telluride (Sb2Te3) and bismuth telluride (Bi2Te3)-containing alloys can be used for various applications, including in solar cells, thermoelectric (TE) devices, and phase-change devices. TE energy converters that make use of such alloys have attracted attention as they exhibit numerous interesting features such as solid-state operation, zero-emissions, vast scalability, low maintenance, and along operating lifetime. The efficiency of TE materials is directly related to a dimensionless figure of merit, ZT, which is defined as ZT=S2σT/k, where S is the Seebeck coefficient of the material in question, σ its electrical conductivity, k its thermal conductivity, and T the absolute temperature.
Owing to the superior thermoelectric characteristics of such materials at temperatures close to room temperature, a number of techniques for fabricating high quality thermoelectric thin films, such as metal organic chemical vapor deposition (MOCVD), physical vapor deposition (PVD), and molecular beam epitaxy (MBE) have been well established. The incorporation of heterogeneous nanostructures within these materials can enable one to manipulate their electrical and thermal conductivities independently. This can result in increases in the ZT value.
In this study, we investigated the effect of a surfactant on the electrodeposition of Sb2Te3 and Bi2Te3 films, and on their morphologies and structural, mechanical, electrical, and thermoelectric properties. On the addition of the cationic surfactant cetylt rimethyl ammonium bromide (CTAB), theelectrodeposited Sb2Te3 and Bi2Te3 films showed improvements in their morphologies and densities. Annealing played an important role in controlling the various phases and crystallinities of the films, factors that are critical to the TE performance of the films.
Sb2Te3 thin films with Te nanodots were potentiostatically electrodeposited at room temperature using the surfactant CTAB with annealing process. The presence of the surfactant decreased the deposition rate of Sb owing to its adsorption onto Te ions and reduced the size of the crystallites, resulting in the formation of a highly dense amorphous structure. Annealing the films significantly decreased the in their electrical resistances due to the reduction of the structural defects.
Observations of their microstructures confirmed that the Sb2Te3 films that contained Te nanodots 10?20 nm in size and had a dispersion fraction of 11.4 vol% could be obtained after annealing at 200°C. In addition, the power factor of the films increased from 105.0 to 716.0 μW/m·K2 after being annealed at 200°C. the morphology of the Sb2Te3 films deposited using CTAB was much better than that of the AC-plated films. This increase in the power factor suggested that it might be possible to increase the ZT values of Sb2Te3 bulk materials by embedding Tenanodots within them. In addition, the increase in the mechanical properties of the electrodeposited films because of the Te nanodots should help in device manufacturing, particularly of devices based on thin films.
(중간생략)
The maximum power factor of 336.2 μW/m?K2 was obtained from the Bi-rich Bi2Te3 film deposited using the solution of 7.5mM Bi(NO3)3. However, both the post-annealing process and mediation of CTAB don''t improve the thermoelectric properties due to the inter dependence of the Seebeck coefficient and the electrical conductivity.