Combination of Carrier Concentration Regulation and High Band Degeneracy for Enhanced Thermoelectric Performance of Cu₃SbSe₄

The effect of Al-, Ga-, and In-doping on the thermoelectric (TE) properties of Cu₃SbSe₄ has been comparatively studied on the basis of theoretical prediction and experimental validation. It is found that tiny Al/Ga/In substitution leads to a great enhancement of electrical conductivity with high carrier concentration and also large Seebeck coefficient due to the preserved high band degeneracy and thereby a remarkably high power factor. Ultimately, coupled with the depressed lattice thermal conductivity, all three elements (Al/Ga/In) substituted samples have obtained a highly improved thermoelectric performance with respect to undoped Cu₃SbSe₄. Compared to the samples at the same Al/In doping level, the slightly Ga-doped sample presents better TE performance over the wide temperature range, and the Cu₃Sb_0.995Ga_0.005Se₄ sample presents a record high ZT value of 0.9 among single-doped Cu₃SbSe₄ at 623 K, which is about 80% higher than that of pristine Cu₃SbSe₄. This work offers an alternative approach to boost the TE properties of Cu₃SbSe₄ by selecting efficient dopant to weaken the coupling between electrical conductivity and Seebeck coefficient.