Enhanced carrier mobility and thermoelectric performance in Cu2FeSnSe4 diamond-like compound via manipulating the intrinsic lattice defects

Diamond-like compounds represent a large family of new high-performance thermoelectric (TE) materials that have been extensively studied since 2009. However, their carrier mobilities are usually low because of the severe intrinsic lattice defects. In this study, we show a successful example of optimizing the carrier mobility of quaternary Cu2FeSnSe4 diamond-like compound by manipulating the intrinsic lattice defects. A series of Cu-rich Cu2+δFe1-δSnSe4 (δ = 0, 0.025, 0.05, 0.075, and 0.1) samples have been prepared in experiment. The rich Cu atoms effectively suppress the formation of negatively charged Cu vacancy defects, which are the main intrinsic lattice defects in Cu2FeSnSe4 according to the defect formation energy calculation. The reduction of Cu vacancy defects significantly weakens the ionized impurity scattering to the carriers, leading to the substantially increased carrier mobility and optimized electrical transport properties in these Cu-rich Cu2+δFe1-δSnSe4 samples. Consequently, the dimensionless figure of merit of Cu2.1Fe0.9SnSe4 at 800 K is enhanced by 53% as compared with that of the stoichiometric Cu2FeSnSe4. This study also sheds light on the optimization of TE performance in other materials with similar severe intrinsic lattice defects.