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

Cu22Sn10S32 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 Cu22Sn10S32 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 Cu21.4In0.6Sn10S32 and Cu21.6Zn0.4Sn10S32 at 723 K, respectively.