Nanobulk Thermoelectric Materials Fabricated from Chemically Synthesized Cu₃Zn_{1- x} Al _x SnS_{5- y} Nanocrystals

Direct energy conversion of heat into electricity using thermoelectric materials is an attractive solution to help address global energy issues. Developing novel materials composed of earth-abundant and nontoxic elements will aid progress toward the goal of sustainable thermoelectric materials. In this study, we chemically synthesized Cu-Zn-Sn-S nanocrystals and fabricated a Cu₃ZnSnS_5-y thermoelectric material using nanocrystals as building blocks. The figure-of-merit (ZT) value of the Cu₃ZnSnS_5-y material was found to be 0.39 at 658 K. We substituted Zn with Al in the Cu₃ZnSnS_5-y system to form Cu₃Zn_1-x Al _x SnS_5-y (x = 0.25, 0.5, 0.75, and 1) to lower the lattice thermal conductivity of the resulting materials. Complete substitution of Al for Zn substantially decreased the lattice thermal conductivity and dramatically increased the electrical conductivity of the material. However, the ZT value could not be significantly enhanced, which could be primarily attributed to the high carrier thermal conductivity. These results highlight the production of Cu₃Zn_1-x Al _x SnS_5-y thermoelectric materials and unveil the scope for improvement of ZT values by altering transport properties.