Zinc variation in CZTS thin films for enhanced solar cell efficiency using SCAPS

This study aims to optimize the zinc (Zn) molarity in eco-friendly and cost-effective copper zinc tin sulfide (CZTS) thin films deposited on glass substrates using a spin-coating approach without sulfurization. A sol–gel method was employed to prepare CZTS films with varying zinc salt molarities from 0.5 to 2.5 M. The effects of zinc molarity on the structural, optical, and electrical properties of the films were thoroughly investigated. Structural analysis of the five samples indicated that higher zinc molarity resulted in more pronounced and sharper diffraction peaks in the kesterite crystal structure. In addition, the film composition varied along zinc molarity, with higher levels leading to the formation of a zinc sulfide secondary phase. The optical bandgap energy ranged slightly from 1.46 to 1.58 eV, and the films exhibited p-type conductivity. Numerical measurements carried out to determine the behavior of the PN Junction of CZTS, as well as the performances of each layer of the (CZTS(k2)/ZnS/S:ZnO) structure using the SCAPS-1D structure, achieving an efficiency of 11.13% by optimizing the solar cell interfaces. The simulation results corroborated the experimental findings, indicating that the sample with 1 M zinc molarity (K2) is a promising candidate for the absorber layer in solar cells.