First Principle Investigation on Electronic Properties of Cationic and Anionic CO-Alloyed Cu2ZnSnS4 Kesterite Material

Abstract

The primary goal of kesterite alloying is to allow for fine tweaking of the material's characteristics for advanced device engineering. Additionally, it is seen as a viable solution to inherent kesterite absorber difficulties such as the Cu/Zn disorder or Sn multivalency. The most interesting alloying elements for kesterite are Ag replacing Cu, Cd replacing Zn, and Ge replacing Sn for cationic substitution, as well as Se replacing S for anionic substitution. This research work investigates the effect of alloying CZTS with Silver (Ag) (Cation) and Selenium (Se) (Anion) theoretically using Density Functional Theory (DFT). The compounds were found to exhibit indirect bandgap characteristics, with conduction band minima (CBM) and valence band maxima (VBM) located between the N and gamma points of the Brillouin zone for pure kesterite Cu2ZnSnS4 and between the N and A points for alloyed Ag2ZnSnSe4 respectively. The bandgap of around 1.22 eV and 0.78 eV were recorded for the pure and alloyed kesterite materials. From the obtained results, a shrink in bandgap was observed due to the presence of heavy anion (Se) and cation (Ag) alloying at the same time. It was also found that the contribution of different atomic orbitals to the formation of the valence and conduction bands is approximately identical for pure and alloyed materials.