Abstract
To date, thermoelectric materials research stays focused on optimizing the material’s band edge details and disfavors low mobility. Here, we shifts the paradigm from the band edge to the mobility edge, exploring high thermoelectricity near the border of band conduction and hopping. Through co-alloying iodine and sulfur, we modularize the plain crystal structure of liquid-like thermoelectric material Cu2Te with mosaic nanodomains and the highly size mismatched S/Te sublattice that chemically quenches the Cu sublattice and drives the electronic states from itinerant to localized. A state-of-the-art figure of merit of 1.4 is obtained at 850 K for Cu2(S0.4I0.1Te0.5); and remarkably, it is achieved near the Mott-Ioffe-Regel limit unlike mainstream thermoelectric materials that are band conductors. Broadly, pairing structural modularization with the high performance near the Mott-Ioffe-Regel limit paves an important new path towards the rational design of high-performance thermoelectric materials. Thermoelectric (TE) material-based energy conversion technology has attracted increasing global attention in virtue of the technical merits such as no moving parts, no greenhouse emission, noiseless, friendliness for miniaturization, and reliability.1–4 Based on the Seebeck and Peltier effects, thermoelectricity enables a direct energy conversion between temperature difference and electricity.5, 6 The performance of a TE material is primarily gauged by the material’s figure of merit, zT = S2T/ρκ, where S is the Seebeck coefficient, T is the absolute temperature, ρ is the electrical resistivity, and κ is the total thermal conductivity (consisting of the lattice thermal conductivity κL and the electronic thermal conductivity κE).