Remarkable thermoelectric property enhancement in Cu₂SnS₃-CuCo₂S₄nanocompositesvia3D modulation doping

P-type ternary sulfide Cu₂SnS₃and CuCo₂S₄with merits of low toxicity, natural abundance and intrinsically low lattice thermal conductivity are considered as promising eco-friendly thermoelectric materials. Here, we report a remarkable thermoelectric property enhancement in a Cu₂SnS₃-based nanocomposite material with the incorporation of 5 mol% CuCo₂S₄. Like the traditional modulation doping approach, in such a two-phase nanocomposite, charge carriers are mainly derived from the CuCo₂S₄(metal-like) phase and transferred to the Cu₂SnS₃(semiconductor) phase enabled by an appropriate band alignment. Results reveal that such a hetero-structure can simultaneously improve the unsatisfactory carrier concentration of both the phases to a moderate level and also maintain the high carrier mobility of pristine Cu₂SnS₃, contributing to an increased power factor of ∼10 μW cm⁻¹K⁻²at 773 K. Meanwhile, the homogeneous distribution of the nanoscale minor phase can effectively impede phonon transport and results in a suppressed lattice thermal conductivity of ∼0.5 W m⁻¹K⁻¹at 773 K. Ultimately, a highZT∼ 0.83 has been achieved at 773 K which is comparable with that of the best Cu₂SnS₃-based material obtained by cobalt doping.