Ni-Doping Effects on the Optical, Structural, Morphological, and Compositional Behavior of Sol-Gel Synthesized CuS Thin Films for Enhanced Optoelectronic Performance

Abstract: Nickel-doped copper sulfide (Ni:CuS) thin films with varying thicknesses and morphologies were successfully synthesized on microscopic glass substrates via a sol-gel dip-coating method to investigate their potential for device applications. The primary precursors included copper (II) tetraoxosulphate (VI), sodium disulphide, and nickel (II) chloride hexahydrate as sources of Cu²⁺, S²⁻, and Ni²⁺ ions, respectively, with ethylene glycol serving as a stabilizing agent. The Ni:CuS thin films underwent optical, structural, morphological, and compositional characterizations using UV-Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). Optical analysis revealed that the Ni:CuS films exhibited high absorbance values in the UV and NIR regions, while their refractive index increased significantly in the VIS-NIR regions. The bandgap energy decreased with increasing Ni concentration, with values of 2.66 eV, 2.50 eV, 2.41 eV, and 2.33 eV for films doped with 0.04 M, 0.06 M, 0.08 M, and 0.10 M Ni ions, respectively. XRD results confirmed the crystalline nature of the films with a hexagonal structure, while crystallite sizes for films doped with 0.02 M, 0.06 M, and 0.10 M Ni ions were determined as 19.45 nm, 19.54 nm, and 19.92 nm, respectively. EDS analysis confirmed the presence of Cu, Ni, and S, alongside trace elements. The properties demonstrated by these Ni:CuS thin films suggest their suitability for various optoelectronic applications, including optical coatings, photothermal applications, photosensors, and window layers for solar cell/photovoltaic devices.

Keywords: Nickel, Copper-Sulphide, Chalcogenides, Bandgap, Opto-electronics, Sol-gel, Dip-coating.