Nonetheless, the high n-type TE performance of Bi-doped Y 2 Te 3 cannot be ignored. Although our defect calculations do not directly explain the high electron concentrations of Bi-doped samples assuming a simple site substitution doping mechanism (see Section 2.3), Bi doping appears to be a feasible route to realizing high zT in Y 2 Te 3 . We recommend that future studies focus on optimizing electron concentration via halogen doping and clarify the anomalous Bi doping.