Modulation doping of p-type Cu12Sb4S13 toward improving thermoelectric performance

Abstract

The commercial viability of thermoelectric (TE) devices relies heavily on two factors: cost reduction and efficiency enhancement. In this study, we first produce p-type Cu12Sb4S16–x (x = 0, 3, 4) using a low-temperature bottom-up approach and demonstrate Cu12Sb4S13 to show the best TE performance among the three tested compositions. Subsequently, the TE energy conversion efficiency of Cu12Sb4S13 is further enhanced by optimizing its electronic band structure through the incorporation of small amounts of tellurium. At an optimal Te content of 5 mol%, more than a twofold increase in the TE figure of merit (zT) is obtained. To gain insight into the mechanism of improvement on the transport properties of the material, we compare the interphase transport mechanism by incorporating nanodomains of different metals (Ag and Cu) into the Cu12Sb4S13 matrix. The improved electrical conductivity obtained with Cu12Sb4S13-Te nanocomposites is attributed to a charge flooding of the Cu12Sb4S13 surface. In contrast, excessive downward band-bending at the interphases of Ag/Cu metal-semiconductor drastically reduces the electrical conductivity. Besides, a weighted mobility (μw) analysis shows a dominant thermal activation of carriers in Cu12Sb4S13-Te nanocomposites. In this material, a strong decrease in lattice thermal conductivity is also found, which is associated with a phonon-carrier scattering mechanism. Our work shows the importance of proper band-engineering in TE nanocomposites to decouple electrical and thermal transport to enhance TE performance, and the efficacy of μw for electrical and thermal transport analysis.