Application of Taguchi method to optimize the sol–gel dip-coating process of the semiconductor Cu2ZnSnS4 with good optical properties

Abstract

This paper presents the optimal configuration of parameters for the elaborated Cu2ZnSnS4 (CZTS) absorber layer, using the sol–gel method associated with dip-coating technique on ordinary glass substrates. Taguchi design of experiments with L27 (38) orthogonal array, a signal-to-noise (S/N) ratio, and an analysis of variance (ANOVA) were used to determine the best optical properties for photovoltaic applications (optical bandgap energy) of CZTS thin films. Eight factors named annealing temperature, Cu/(Zn+Sn) ratio, Zn/Sn ratio, S/metal ratio, number of pre-annealing and dip coating, dip-coating cycle, annealing time, and dip-coating speed were chosen. To conduct the tests, we apply Taguchi method; three levels were fixed for each factor. The most important factors of the deposition approach on the optical properties of the fixed as-synthesized CZTS films were determined. The analysis of the obtained results indicated that the important parameters are the Zn/Sn ratio and annealing temperature in air by employing Taguchi approach. A validation test is also carried out to check whether the found optimal combinations of the parameter are correct. CZTS thin-film synthesis with optimal conditions has been characterized, using an X-ray diffractometer (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), UV–visible spectrophotometer, and four-point probe method. XRD data show a kesterite structure with a preferential orientation along the (112) plan; UV–visible spectrophotometer indicated that the bandgap energy of the CZTS thin film is 1.51 eV and a cross section showed the suitable film thickness in the order of ~1.80 µm.