Synthesis and investigation of thermoelectric properties of Cu-doped bismuth sulfide (Bi2S3) nanostructures: an experimental approach

In this study, we have prepared Bi2S3 nanostructures as it has good thermoelectric characteristics, and to enhance the thermoelectric effects, we doped the pure Bi2S3 nanostructures with two different concentrations of copper (Cu). These nanostructures were synthesized at 450 °C. X-ray diffraction (XRD) confirmed the successful synthesis of all samples with an orthorhombic crystal structure. The average crystallite size of Bi2S3 was 26 nm, and after doping of Cu of two different concentrations, reduced crystallite sizes, i.e., 21 nm and 16 nm, were recorded. UV–visible spectroscopy showed that the band gap of Bi2S3 nanostructures increased after doping it with Cu. The electrical conductivity measured by the LCR meter showed an increasing trend with increasing doping concentration. DC conductivity was increased, and resistivity is observed to be decreased after doping of Cu in Bi2S3 nanostructures. This might be due to the contribution of charge carriers from Cu. Enhanced Seebeck coefficients measured in the temperature range of 303–366 K were recorded after every doping concentration. In the end, the power factor was calculated for all three materials, and a surprising increase in power factor was recorded for Bi1.85Cu0.15S3 as compared to Bi2S3 and Bi1.95Cu0.05S3 nanostructures. Power factors were recorded as (sim) 0.15 (mathrm{mu W}/{mathrm{mK}}²), (sim) 0.58 (mathrm{mu W}/{mathrm{mK}}²), and (sim) 1.50 (mathrm{mu W}/{mathrm{mK}}²) for Bi2S3, Bi1.95Cu0.05S3, and Bi1.85Cu0.15S3 nanostructures, respectively. These all-recorded data prove the suitability of Cu-doped Bi2S3 nanostructures for the conversion of heat into electricity, i.e., for thermoelectric devices.