High performance thermoelectrics from low-cost and abundant CuS/CuI composites

Materials with simultaneously excellent electrical conductivity (σ) and high Seebeck coefficient (S) are important for thermoelectric applications. However, obtaining such materials is a difficult task as σ and S vary inversely with respect to each other. Here, a new fabrication process has been demonstrated that produces composite materials with desired properties. Electrically highly conducting copper sulphide (CuS) particles are encapsulated within a compound with a high Seebeck coefficient, i.e. copper iodide (CuI), to form core-shell type composites. The presented results show that the concept of producing such composites allows the optimisation of both σ and S to provide enhanced thermoelectric performance (measured by the figure of merit, zT) when compared to the individual starting materials. Quantum mechanical calculations are performed to elaborate on the Schottky barrier formed at the interface between copper iodide and copper sulphide and elucidate aspects of the improved transport mechanism. Furthermore, an optimized compositional ratio between the respective composite parts is identified, which at the same time exhibits a high power factor and reduced thermal conductivity. As a result, an improved zT value of 0.46 at room temperature has been observed, demonstrating that these simple, abundant, and non-toxic CuS/CuI composites are attractive candidates for thermoelectrics.