Design and Efficiency Enhancement of Heterojunctions Formed by CZTS and S-Based Buffer Layers for Photovoltaic Applications

The quaternary material consisting of copper, zinc, tin and sulfur has long attracted the attention of the scientific world in the development of thin layers for photovoltaic applications. In this work, we proposed to make the junction between the absorbent layer consisting of copper-zinc-tin-sulfur Cu₂ZnSnS₄ (CZTS) and different buffer layers such as zinc sulfide ZnS, tin disulfide SnS₂, and cadmium sulfide CdS for comparison purposes, in using the simple and low-cost technique of spray pyrolysis at 380 °C for all stages. All the films obtained were characterized by X-ray diffraction (XRD), and UV–visible spectroscopy and the morphology and topography of the layers were assessed under the scanning electron microscope (SEM) and EDXA. Characterization results showed the formation of CZTS thin films whose kesterite structure was improved by annealing at 450 °C under sulfur atmosphere. The grain size also improved from 6.7 to 7.9 nm after annealing. Subsequently, a simulation study by SCAPS-1D is made to assess the efficiency of the photovoltaic cell thus produced. It exhibited the highest power conversion efficiency (PCE) for the cell using SnS₂ as a buffer layer, i.e., 20.25%, compared to 16.14% for the cell using CdS. This confirmed the possibility of favoring SnS₂ in the design of CZTS-based solar cells, suggested in the literature, as a replacement for CdS, and this by the simple technique of spray pyrolysis.