Improvement of Seebeck coefficient in as-grown Bi2Te3-ySey electrodeposited films by the addition of additives and bath optimization

Bi_2.0Te_2.7Se_0.3 is the most widely used thermoelectric n-type leg for large-scale cooling applications. However, as-grown electrodeposited Bi₂Te_3-ySe_y films typically have a Seebeck coefficient around a third of the bulk value, which sometimes can be improved with thermal annealings. In this work, we report as-grown Bi₂Te_3-ySe_y films having a Seebeck coefficient of approximately half the value of bulk without additional thermal treatments. All samples reported were deposited in baths containing no additives, sodium lignosulfonate (SLS), or both SLS plus ethylenediaminetetraacetic acid (EDTA) with a concentration of 1 M HNO₃ (pH of 0 ± 0.1) and 0.6 M HNO₃ (pH of 0.3 ± 0.1). For each scenario, the deposition was carried out at two different temperatures (0 °C and 5 °C). Seebeck values of −120 μV K⁻¹ have been measured for as-grown films with an optimum morphology and stoichiometry (Bi₂Te_2.7Se_0.3), which is ∼50% of the value obtained for this composition in bulk and the highest among as-grown electrochemically deposited films reported to date. These results are an incentive to revisit and further explore the chemistry behind the electrodeposition of bismuth telluride selenide films to improve the performance of electrodeposited thermoelectric films.