Improving the electronic and optical properties of chalcogenide Cu2ZnSnS4 compound with transition metal dopants: A first-principles investigation

Abstract

The influences of transition metal dopants including Ag, Au, and Pd at various atomic sites of Cu2ZnSnS4 compound are investigated by employing density functional theory. To find the most favorable doping sites, the formation energies are calculated revealing that the Sn site of Cu2ZnSnS4 compound has the lowest formation energy in contrast to Zn, Cu and S sites. In addition, the effect of Pd dopant at Sn site is more prominent than Ag and Au. Indeed, after introducing Pd dopant, the band gap of the compound is reduced and leads to higher electron conductivity and minority carrier lifetime, enabling the compound to be used in high efficiency and low loss energy harvesting solar cells. The first principles method based on first-order perturbation theory is employed for the calculation of optical properties. The Cu2ZnSnS4 compound shows a high dielectric constant of 9.23 at zero energy in the presence of Pd dopant, greater than 6.93 eV in pristine form. The good conductivity and high absorption coefficient, ⍺>104 cm−1 as well as a tunable wavelength from violet in the visible region to near infrared spectrum are also favorable for photovoltaic applications.