Fabrication of Nanostructured Thermoelectric Bismuth Telluride Thick Films by Electrochemical Deposition

Abstract

Bismuth telluride (Bi 2 Te 3 )-based solid solutions are state-of-the-art thermoelectric (TE) materials for cooling applications at room temperature with a high figure of merit ZT. Nanostructured TE bismuth telluride thick films have been fabricated by electrodeposition from a solution containing bismuth nitrate and tellurium dioxide in 1 M nitric acid onto gold-sputtered aluminum substrates. A conventional threeelectrode cell was used with a platinum sheet as the counter electrode and a saturated calomel electrode (SCE) as the reference electrode. Ethylene glycol (EG) was added to the electrolyte in order to increase the thickness of the deposited films, and its effect on the structure, morphology, and compositional stoichiometry of the deposited film was investigated. SEM and XRD were used for structural and compositional characterization. Bismuth telluride films with thicknesses of ca. 350 µm, a stoichiometric composition of Bi 2 Te 3 , and a hexagonal crystal structure were obtained. A microprobe technique was used to measure the lateral Seebeck coefficient in several samples. The free-standing films were shown to be of high homogeneity, where the abundance distribution of the Seebeck coefficient showed a half width of less than 1 µV K -1 and a high electrical conductivity of around 450 S cm -1 at room temperature.

A novel route to nanostructured bismuth telluride films by electrodeposition

“…Preliminary thermoelectric measurements conducted on stoichiometric nanostructured Bi 2 Te 3 films prepared from phytantriol with thicknesses of 2-6 µm yielded a Seebeck coefficient of -88 µV K -1 . This value is high when compared against literature values of electrodeposited bismuth telluride films with thicknesses in the region of several hundreds of micrometers [19,21,22] which were on average around -60 µV K -1 .…”

Optimizations of Pulsed Plated p and n‐type Bi2Te3‐Based Ternary Compounds by Annealing in Different Ambient Atmospheres

“…Due to their advantage to exhibit peak performance at room temperature, the materials of main interest are Bi 2 Te 3 -based nanostructures (nanowires, superlattices, etc) [1][2][3][4][5] as well as fi lms. [6][7][8] Most references report that electrodeposited Bi 2 Te 3 is always n-doped, although the type of doping can theoretically also be of p-type, which has been reported exclusively by Glatz et al [ 9 ] In order to make the deposited materials applicable for energy harvesting of waste heat, a second, p-doped material is necessary for implementation into a thermoelectric generator. [ 10 ] The corresponding p-doped material, Sb 2 Te 3 , crystallizes in spacegroup (R3m) with Sb atoms replacing the Bi lattice sites.…”

Electrochemical deposition of bismuth telluride thick layers onto nickel

“…These include low cost, high controllability over size, thickness, crystallinity [4], scalability, roomtemperature fabrication, and fast deposition rate which are suitable for producing thick films that can be incorporated into practical TE devices. To harvest thermal energy more effectively, thick Bi 2 Te 3 films are required as thick layers for practical TE devices (≥300 µm) [5][6][7]. However, to obtain uniformly thick Bi 2 Te 3 films by electrodeposition still represents a significant challenge due to a number of factors: the Bi 2 Te 3 film tends to crack due to the built-up of internal stress as the thickness increases; constant stoichiometry over the entire thickness is compromised due to the change in the precursors' concentration in the electrolyte bath as deposition progresses; and the surface tends to be rougher as the thickness increases.…”