First-principles study of the thermoelectric properties of Cu2S

The mineral chalcocite, or copper sulphide (Cu$_2$S), is of interest as a thermoelectric material due to its abundance and non-toxic nature. Yet, the study of Cu$_2$S is complicated by the disordered phases (hexagonal and face-centered cubic) that it exists in at high temperatures. Here, we discuss our random structure search leading to the most stable structures. Based on these results, we report the thermoelectric properties of hole doped Cu$_2$S using first-principles calculations and Boltzmann transport theory. We show that a high Seebeck coefficient of over 200 $\mu$V/K is achievable with hole doping levels up to $10^{20}$ cm$^{3}$ above 500 K.