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Morphological characterization and microstructural study of Cu2ZnSnSe4 thin films with compositional variation

In second generation thin film solar cell, Cu2ZnSnSe4 (CZTSe) is used as an absorber layer due to some remarkable properties like non-toxicity and earth abundancy. In this paper we have presented the preparation of Cu2ZnSnSe4 thin films in five different elemental ratios employing the RF-DC sputtering and E-beam deposition technique. In order to study the effects of elemental compositional variation on structural and morphological properties, thin films were characterized using SEM-EDX, XRD and AFM technique. Elemental compositional variation is studied using EDX technique. Numerical analysis of the surface parameters affected by compositional variations are presented against the data processed by AFM images. Watershed based segmentation algorithm is employed to present a quantitative grain size distribution. Variation in growth exponent (β) and roughness critical exponent (α) due to compositional variation in CZTSe thin films is studied using height-height correlation function. Auto correlation length varied from 3.65 nm to 4.44 nm while Rku is found greater than three for all thin films. A critical analysis of fractal dimension and auto correlation length with surface parameters like amplitude parameters, spacing parameters and hybrid parameters is also presented. Optoelectronic properties are studied with respect to compositional variation. Sample with lowest Cu/(Zn+Sn) ratio showed the lowest value of band gap of 0.909 eV . EDX results confirmed that the atomic ratio of Cu-Zn-Sn-Se in thin films of all CZTSe samples remained controlled. Films showed tetragonal kesterite crystal structure with the space group of I −4 2 m with preferential orientation along the (105) plane.