Lightweight diamond-like structure (DLS) materials are
excellent
candidates for thermoelectric (TE) applications due to their low costs,
eco-friendly nature, and property stability. The main obstacles restricting
the energy-conversion performance by the lightweight DLS materials
are high lattice thermal conductivity and relatively low carrier mobility.
By investigating the anion substitution effect on the structural,
microstructural, electronic, and thermal properties of Cu2CoSnS4–xSex, we show that the simultaneous enhancement of the crystal
symmetry and bonding inhomogeneity engineering are effective approaches
to enhance the TE performance in lightweight DLS materials. Particularly,
the increase ofxin Cu2CoSnS4–xSexmakes the DLS structure
with the ideal tetrahedral bond angles of 109.5° favorable, leading
to better crystal symmetry and higher carrier mobility in samples
with higher selenium content. In turn, the phonon transport in the
investigated DLS materials is strongly disturbed due to the bonding
inhomogeneity between anions and three sorts of cations inducing large
lattice anharmonicity. The increase of Se content in Cu2CoSnS4–xSexonly intensified this effect resulting in a lower lattice
component of the thermal conductivity (κL) for Se-rich
samples. As a result of the enhanced power factorS2ρ–1and the low κL, the dimensionless thermoelectric figure of meritZTachieves a high value of 0.75 for Cu2CoSnSe4DLS material. This work demonstrates that crystal symmetry and bonding
inhomogeneity play an important role in the transport properties of
DLS materials and provide a path for the development of new perspective
materials for TE energy conversion.