Optimization of sol–gel spin-coated Cu2ZnSnS4 (CZTS) thin-film control parameters by RSM method to enhance the solar cell performance

This present study aims to investigate a specific optimum deposition condition for the synthesis of Cu2ZnSnS4 (CZTS) thin films by a sol–gel spin-coating method. Spin speed (X1), spin time (X2), annealing temperature (X3) and annealing time (X4) are considered as the major control parameters (independent variables). Response surface methodology technique is implemented for the first time to optimize multiple responses (dependent variable) for sol–gel spin-coated CZTS thin films. Band gap and power conversion efficiency (PCE) are considered as the responses. All the independent variables are varied at three different levels. The Box–Behnken design (BBD) array is opted for the optimization, as it gives optimized results for more than three parameters in less number of experiments. Four control variables and three levels involve 81 experiments to find out optimum deposition condition, whereas BBD can achieve more specific optimum condition in only 29 experiments. Furthermore, mathematical models for band gap and PCE are established as the function of control parameters. Additionally, the influence of the control parameters on both responses is investigated by ANOVA results of models. By the optimization of models, a specific optimum deposition condition X1 = 2104 rpm, X2 = 38 s, X3 = 527 °C and X4 = 68 min is achieved. 1.51 eV band gap and 3.53% PCE are predicted for the optimum condition. Moreover, a validation experiment is carried out at nearest integer value: X1 = 2100 rpm, X2 = 38 s, X3 = 530 °C and X4 = 68 min. 1.50 eV band gap and 3.55% PCE are achieved as the results, which is in good agreement with predicted results. The optimum condition leads to 17.55% of enhancement in PCE than PCE achieved without optimization.