Theoretical study of defects Cu3SbSe4: Search for optimum dopants for enhancing thermoelectric properties

• We present the first systematic study of defects in Cu3SbSe4.
• Possible n-type and p-type dopants are suggested for Cu and Sb site.
• Transition-metal substitutions on Sb potentially improve thermoelectric properties.
• Transition-metal substitutions on Se strongly distort local crystal geometry.
• p-type behavior of as synthesized Cu3SbSe4 is most likely due to Cu.

Cu3SbSe4 is a promising thermoelectric material due to high thermopower (>400μV/K) at 300 K and higher. Although it has a simple crystal structure derived from zinc blende structure, previous work has shown that the physics of band gap formation is quite subtle due to the importance of active lone pair (5s2s2) of Sb and the non-local exchange interaction between these and Se 5p electrons. Since for any application of semiconductors understanding the properties of defects is essential, we discuss the results of a systematic study of several point defects in Cu3SbSe4 including vacancies and substitutions for each of the components. First principles calculations using density functional theory show that among variety of possible dopants, p-type doping can be done by substituting Sb with group IV elements including Sn, Ge, Pb and Ti and n-type doping can be done by replacing Cu by Mg, Zn. Doping at the Se site appears to be rather difficult. Electronic structure calculations also suggest that the p-type behavior seen in nominally pure Cu3SbSe4 is most likely due to Cu vacancy rather than Se vacancy.