Optimization of Carrier Concentration in Cu₂₂Sn₁₀S₃₂ through In- and Zn-Doping for Enhanced Thermoelectric Performance

Cu 22 Sn 10 S 32 is a recently discovered material in the Cu–Sn–S system, which contains a relatively high intrinsic carrier concentration. In this work, Zn- and In-doped Cu 22 Sn 10 S 32 compounds were prepared by ball milling combined with spark plasma sintering. It is found that the incorporation of In and Zn at the Cu site leads to a decrease of electrical conductivity, which is primarily due to the reduction in hole carrier concentration. The In doping shows a much stronger effect on the reduction of electrical conductivity. By combining positron annihilation measurements, it is speculated that the intrinsic hole carriers originate from Cu Sn antisites. The substitution of In and Zn for the Cu sites may contribute donor carriers or cause suppression of the Cu Sn antisite formation, thus leading to a reduction in hole carrier concentration. The significant decrease in electrical conductivity leads to a reduction in electronic thermal conductivity. On the other hand, due to the difference in the molar mass and ionic radius, the lattice thermal conductivity of the In-doped sample is also significantly reduced, resulting in a total thermal conductivity as low as 0.85 W m –1 K –1 at 723 K. Maximum zT values of 0.45 and 0.36 are reached in Cu 21.4 In 0.6 Sn 10 S 32 and Cu 21.6 Zn 0.4 Sn 10 S 32 at 723 K, respectively.