High thermoelectric performance of Cu3SbSe4 nanocrystals with Cu2-xSe in situ inclusions synthesized by a microwave-assisted solvothermal method.

(Ag,Sn) co-doped Cu3SbSe4 nanocrystals are obtained via a facile microwave-assisted solvothermal method, and their thermoelectric properties are investigated in the temperature range from 300 K to 623 K. Sn-doping on Sb sites dramatically increases the carrier concentration and thus the electrical conductivity, promoting the thermoelectric power factor. Further alloying with Ag on Cu sites strongly suppresses the lattice thermal conductivity close to the glass limit. Aside from point defect scattering, such reduction in lattice thermal conductivity largely relies on the formation of Cu2-xSe nanoinclusions, which serve as additional scattering centers for phonons. Overall, the sample with the nominal composition of Cu2.8Ag0.2Sb0.95Sn0.05Se4 reaches a minimum lattice thermal conductivity of 0.27 W m-1 K-1 and a maximum zT of 1.18 at 623 K, which is the best result for the Cu3SbSe4-based materials in the same temperature region. Our results demonstrate that the microwave-assisted synthesis method is capable of fabricating Cu based ternary compounds with high thermoelectric performance.