Optimization of quaternary compound kesterite Cu2ZnSnS4 (CZTS) optical band gap using dip-coating for photovoltaic absorbers

This study focuses on the synthesis of Cu₂ZnSnS₄ (CZTS) thin films, a promising material for photovoltaic absorbers, using the sol-gel method combined with dip-coating technique, and optimized through a Taguchi design of experiments. Six factors were investigated (annealing temperature and time, dip-coating speed, solvent type, copper concentration, sulfur-to-metal ratio), each at three levels, according to a L27 orthogonal array. Analysis of the results, based on the signal-to-noise (S/N) ratio and analysis of variance (ANOVA), highlighted the predominant influence of annealing time, followed by annealing temperature and dip-coating speed, on the optical band gap energy (Eg). The optimal configuration (A3B3C1D1E3F1) yielded a band gap of 1.5 eV, which is ideal for thin-film solar cell applications. Structural (XRD, Raman), morphological (SEM), optical (UV-Vis, Tauc), electrical (four-point probe), and chemical (EDS) characterizations confirmed the formation of a pure CZTS phase, free from secondary phases, with good crystallinity, high absorption (α > 10⁴ cm⁻¹), and suitable conductivity (σ ≈ 13.61 S/cm). These results demonstrate the relevance of the adopted approach for the fabrication of high-performance CZTS thin films, compatible with the requirements of photovoltaic devices. By this method, the optical band gap was adjusted to the optimal 1.5 eV, ensuring better light absorption.