The influence of Ge substitution and H2S annealing on Cu2ZnSnS4 thin films

Cu2Zn(Sn1-xGex)S4 thin films (where x = 0, 0.25, 0.50, 0.75, and 1) were deposited by spin coating technique and annealed under 30 and 40 ccm H2S:Ar (1:9) flows to understand the influence of Ge atom content ratio and H2S flow rate during the annealing of thin films on morphological, structural and optical properties of Cu2Zn(Sn1-x Gex)S4 thin films. It was seen that the Ge content has a strong influence on the structural and optical properties of the films. The crystal size of the films decreased sharply for Cu2Zn(Sn0.75Ge0.25)S4 thin film and started to increase slowly owing to the formation of high dislocation density and strain in the structures. The Raman spectra show the formation of kesterite thin films and blue Raman shift with Ge substitution to the content. The films obtained under 40 ccm H2S:Ar (1:9) flows have weak secondary peaks associated with ZnS formation. The UV–Vis data showed the increase of optical bandgap from 1.52 to 2.05 eV with a rise in Ge ratio in the structures.