Boosting the thermoelectric performance of zinc blende-like CuSnSe through phase structure and band structure regulations

As a variant of the zinc blende structure, p-type semiconducting Cu 2 SnSe 3 exhibits a high potential in the field of thermoelectric energy conversion, due to the low lattice thermal conductivity and large abundance of the constituent elements. Till now, the bottleneck of achieving a comparable thermoelectric performance in Cu 2 SnSe 3 with state-of-the-art thermoelectric material systems is its unsatisfactory electrical power factor. In this work, we realized a simultaneous increment of charge carrier concentration and mobility through In/Sb co-doping at the Sn site; detailed X-ray diffraction (XRD), Rietveld refinement, and density functional theory (DFT) band structure calculations revealed a gradual phase structure (and an associated band structure) transition from a low-symmetry monoclinic phase to a high-symmetry cubic one, which was further verified by Cs-corrected scanning transmission electron microscopy (Cs-corrected STEM) characterization. Eventually, we achieved a peak figure of merit, ZT max ∼0.90 at 773 K and an average ZT avg ∼0.36 (323-773 K) for the composition of Cu 2 (Sn 0.85 In 0.05 Sb 0.05 Ti 0.05 )Se 3 , representing the state of the art for all Cu 2 SnSe 3 -based thermoelectric materials reported thus far. Phase transition from the (cation) ordered δ-phase to the disordered cubic phase upon In/Sb co-doping leading to a significantly enhanced thermoelectric performance in zinc blende-like Cu 2 SnSe 3 .