Thermoelectric Performance of n-type Bi2S3-alloyed Bi2Te2.7Se0.3

The effect of isovalent sulphur substitution on the thermoelectric properties of n-type Bi2Te2.7Se0.3 alloy has been studied systematically. At low sulphur concentrations, where the samples are single phase, changes in defect chemistry and density of states impacted significantly on electrical resistivity and thermopower, improving thermopower while reducing thermal conductivity due to increased phonon scattering at defects. This reduction in thermal conductivity was particularly noticeable in samples containing Bi2S3-based secondary phase. The thermopower of these samples improved greatly due to the formation of an impurity band at the interface of two phases, resulting in increased electron donation and reduced electrical resistivity. Isovalent sulphur substitution enhanced thermopower and reduced thermal conductivity for both single and multiphase samples.