Profound optical analysis for novel amorphous Cu2FeSnS4 thin films as an absorber layer for thin film solar cells

In this study, quaternary kesterite Cu2FeSnS4 (CFTS4) has been selected due to its interesting optical and electrical characteristics. The CFTS4 films were prepared by exploiting the chemical bath deposition process at room temperature. The films were prepared at different deposition periods (1, 3, 5 and 7 h). The EDAX technique was helped in evaluating the compositional element ratio which near to 2:1:1:4. The morphology and structure of CFTS4 films have been examined by utilizing X-ray diffraction, and field emission scanning electron microscope techniques. XRD charts revealed the absence of sharp peaks and approved the amorphous nature of films under investigations. The transmittance and reflectance data were employed to compute the linear and nonlinear optical constants of the as-deposited CFTS4 films. The energy gap calculations for the CFTS4 films grown on glass substrate displayed a direct energy gap and by increasing the deposition time, a reduction in energy gap values from 1.41 to 1.19 eV was obtained. The deep analysis of linear/nonlinear optical properties as a function of deposition time has revealed many characteristics of the investigated films. Moreover, the nonlinear parameters (refractive index n(2), nonlinear absorption coefficient beta(c) and the third-order nonlinear optical susceptibility chi((3))) of the CFTS4 films were boosted with rising up the film thickness and their high values imply the possibility of utilizing these films in various optoelectronic applications.