Theoretical studies on structural, electronic and optical properties of kesterite and stannite Cu<inf>2</inf>ZnGe(S/Se)<inf>4</inf> solar cell absorbers

Structural, electronic and optical properties of Cu2ZnGe(S/Se)4 semiconductor materials in their kesterite and stannite phase have been investigated using density functional theory (DFT) approach using full potential linearized augmented plane wave (FP-LAPW) method. Modified Becke-Johnson (mBJ) exchange correlation is used for computing physical properties. These kesterite and stannite Cu2ZnGeS4 and Cu2ZnGeSe4 are direct band semiconductors with band gap values ∼1.15 eV and 1.0 eV for Cu2ZnGeS4 and 0.64 eV and 0.24 eV for Cu2ZnGeSe4, respectively at Γ point. A scissor correction of 1 eV raised these band gap values equal to the experiment values. Optical properties are investigated in terms of refractive index, extinction coefficient, reflectivity, optical conductivity, and optical absorption using dielectric constant.