Structural, morphological and optical properties of the vacuum-free processed CZTS thin film absorbers

In this work, we have investigated the influence of different zinc precursors and different Cu/(Zn+Sn) stoichiometries (1.4, 1.19 and 0.92) on the structural, morphological, optical and electrical properties of the solution derivable Cu2ZnSnS4 (CZTS) thin-films by using dip coating technique. X-ray diffraction (XRD) results pointed out that the CZTS thin films crystallized in the kesterite structures with (112) preferred orientation. It was founded that the peak intensity of zinc acetate based CZTS thin films was twice as severe as zinc nitrate based. It was also observed that changing Cu/(Zn+Sn) stoichiometry resulted in a highly improved crystallinity of the thin films. Scanning electron microscopic micrographs exhibited a remarkable improvement in size and morphology depended on using zinc precursor and Cu/(Zn+Sn) stoichiometry. Optical analyses showed that the absorption intensity was higher in zinc acetate based CZTS thin film than that of the zinc nitrate based CZTS film. Among all the CZTS films the highest absorption was observed for the Cu/(Zn+Sn) stoichiometry of 1.4. UV–vis spectra analyses showed a direct band gap varying from 1.64 to 1.9 eV, which upon on the used zinc precursor and Cu/(Zn+Sn) stoichiometry. The computed optical constants showed a high dependence on the zinc precursors and different Cu/(Zn+Sn) stoichiometries. Hall measurements confirmed p-type conductivity and the electrical properties of the films were considerably changed with respect to the zinc precursors and Cu/(Zn+Sn) stoichiometries. According to the observed results the zinc acetate based CZTS thin films with Cu/(Zn+Sn) stoichiometry of 0.92 has promising potential for thin film solar cell applications.