A holistic approach to optical characterizations of vacuum deposited Cu2ZnSnS4 thin film coatings for solar absorbing layers

Highlights: • A good absorber layer of Cu₂ZnSnS₄ thin film coatings was produced using spin-coating method. • Thickness of the Cu₂ZnSnS₄ thin film coatings was decreased with increasing rpm. • A body-centered tetragonal lattice structure with Kesterite Cu₂ZnSnS₄ phase was observed. • An average optical band-gap of 1.5 eV was confirmed for Cu₂ZnSnS₄ thin film coatings. • The dielectric constant of the coatings was declined with increasing coatings' thickness. -- Abstract: This article aimed at making a good absorber layer of Cu₂ZnSnS₄ thin film coatings deposited onto glass substrates via spin coating technique with different rotational speeds. Three sets of Cu₂ZnSnS₄ thin film coatings were prepared at rotations of 3000, 3500, and 4000/min. The thickness of the thin film coatings was measured using a surface profilometer, and the coating thickness shows good rpm dependence i.e., the thickness of the coatings decreased with increasing rpm. The thicknesses of the coatings were in the nanometer (nm) range for all samples. The structural, morphological, and optical properties of the as coated thin films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and ultraviolet–visible (UV–Vis) absorption spectroscopy. The XRD pattern confirmed the body-centered tetragonal lattice structure with Kesterite Cu₂ZnSnS₄ phase having good crystallinity. The average crystallite size increases while lattice strain, dislocation density, and crystallite number are decreased with increasing thicknesses of the Cu₂ZnSnS₄ coatings. SEM micrographs represent the homogeneous, agglomerated surface without any cracks and pores. The average optical band-gap of the coatings was found to be 1.5 eV. Dielectric parameters such as refractive index, high-frequency dielectric constant, and static dielectric constant were declined with increasing thickness of Cu₂ZnSnS₄ thin film coatings. These characteristics would allow the Cu₂ZnSnS₄ thin film coatings to be suitable for an absorber layer used in photovoltaic devices.