Facile Synthesis of Cu2ZnSnS4 Photovoltaic Absorber Thin Films via Sulfurization of Cu2SnS3/ZnS Layers

Abstract

Copper zinc tin sulfide (Cu2ZnSnS4) has been receiving a lot of attention in recent years as a new, alternative absorber for the production of cheap thin film solar cells owing to the high natural abundance of all the constituents, its tunable direct-band-gap energy, and its large optical absorption coefficient. In addition, to overcome the problem of expensive vacuum-based methods, solution-based approaches are being developed for Cu2ZnSnS4 deposition. In this study, Cu2ZnSnS4 thin films were grown on soda lime glass substrates via the sulfurization of solution grown Cu2SnS3/ZnS stacked sulfide layers. A new facile route to overcome the difficulty of depositing Cu2ZnSnS4 thin film with a desired stoichiometric composition in a single cation solution has been presented. The influences of deposition cycles of layers on the morphological, compositional, structural, and optical properties of the samples were investigated. It was observed from scanning electron microscopy (SEM) images that the films were continuous and composed of homogenously distributed large grains. Possible chemical formulations of the best samples were predicted to be Cu1.99Zn1.25Sn1.00S3.76 and Cu1.97Zn1.03Sn1.29S3.71 via energy-dispersive X-ray spectroscopy (EDXS) results. The X-ray diffraction (XRD) patterns of the samples matched very well with the reference values. The Raman-scattering analysis of the films proved the phase purity of the CZTS samples. The optical absorption coefficient of the films was found to be about 104 cm−1 based on absorbance spectroscopy. The optical band gaps of the films were estimated to be between 1.36 and 1.50 eV. From these we are able to conclude that CZTS thin films can be effectively obtained via the vacuum-atmosphere sulfurization of Cu2SnS3/ZnS stacked sulfide layers.