Influence of annealing temperature on the properties of non-stoichiometric Cu1.66Zn1.25GeSe4 thin films

This study focuses the annealing temperature influence on the fabrication of Cu1.66Zn1.25GeSe4 film. We have deposited of Cu1.66Zn1.25GeSe4 film as an absorber layer for the solar cell application using thermal evaporation technique. Various properties of the Cu1.66Zn1.25GeSe4 thin film were studied by characterization tools such as X-ray diffraction (XRD), Raman scattering, Field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Hall measurement set up. It is found that the annealing temperature have significant influence on the Cu1.66Zn1.25GeSe4 phase formation and only films annealed ≥ 773 K formed an impurity free single phase. Raman spectra shows that the as-prepared film have GeSe2 impurity phases and annealing at higher temperature (≥ 773 K) and selenization changes the alloy to impurity free crystalline phase. In the optical studies, the band gap of Cu1.66Zn1.25GeSe4 thin film selenized at 823 K is calculated to be 1.55 eV, which is very close to the optimum value for solar cell applications. The carrier concentration, resistance, conductivity and mobility of selenized thin film are 5.24 × 1015 cm−3, 2217.01 Ω/□, p-tye and 5.53 cm2V−1s−1 respectively. We also have confirmed the junction formation in Mo substrate/Cu1.66Zn1.25GeSe4/CdS device geometry. The study show an improvement in the Cu1.66Zn1.25GeSe4 properties are possible by controlled annealing and this material can be a promising candidate for thin film solar cells.