Abstract
The optimized structural parameters, electronic structure, and thermoelectric coefficients of the chalcopyrite alloys Cu
1–
x
Na
x
TlSe
2
, with
x
= 0.00, 0.25, and 0.50 were studied through density functional theory calculations. The Wu–Cohen generalized gradient and the Tran–Blaha modified Becke–Johnson approximations have been employed to describe the exchange–correlation potential. Energy band structure analysis reveals that CuTlSe
2
is a semi-metal, while Cu
0.25
Na
0.75
TlSe
2
and Cu
0.50
Na
0.50
TlSe
2
alloys are semiconductors with gaps of approximately 0.17 eV and 0.35 eV, respectively. The total and partial densities of states were calculated and discussed. Examining the charge density, we point out the formation of the Na–Se ionic bond when Cu is replaced by the Na atom, which is responsible for the metal–semiconductor transition in the Cu
1–
x
Na
x
TlSe
2
alloys. Moreover, variations of the Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivity, power factor, and figure of merit of the Cu
1–
x
Na
x
TlSe
2
alloys with temperature and chemical potential were explored. The obtained results show that the value of the figure of merit increases when doping CuTlSe
2
with sodium to reach 0.46 and 0.87 for
p
-type Cu
0.75
Na
0.25
TlSe
2
and
n
-type Cu
0.50
Na
0.50
TlSe
2
, respectively.