Thin films of (AgxCu1−x)2ZnSn(S,Se)4 (x = 0.05–0.20) prepared by spray pyrolysis

The recent investigation of kesterite type quaternary compounds showed that one of the main detrimental problems, which limits the efficiency of the solar cells based on these materials, is related to the high defect concentrations, mainly Cu-Zn disorder. To overcome this problem partial replacement of Cu or Zn cations in the classical Cu₂ZnSn(S,Se)₄ compounds was proposed. One of the promising cations was found to be Ag, which partially replaces Cu and the solid solution of (Ag_xCu_1-x)₂ZnSn(S,Se)₄ (ACZTSSe) is formed. In the present study, ACZTSSe thin films with different Ag concentrations were deposited by the spray pyrolysis method, with subsequent annealing in S + Se atmosphere. From the analysis of the chemical composition of the thin films a good correlation of measured silver concentration with initial concentration (dissolved in the main solution for deposition) for the samples with up to 15 % Ag were found. These results were also confirmed by the structural studies and analysis of the Raman scattering spectra. On the other hand, thin film with higher Ag concentration (20 %) has shown strong compositional inhomogeneity and presence of secondary phases was detected. Analysis of the modulated surface photo-voltage yielded the optical transition at ~ 1.5 eV, correlated with the band gap energy, and a transition at lower energy. From the temperature dependence of resistivity investigation no significant change in the resistivity for the samples with low silver concentration and strong increase for the samples with 20 % of Ag were found.