Zinc sulphide thin films having nanometre grain size for photovoltaic applications

Zinc sulphide (ZnS) thin films with nanoscale grains of about 8-113 nm were deposited on glass substrates by chemical bath deposition technique using aqueous solution of zinc acetate [ Zn (CH3COO)(2)] and Thiourea. The structure, surface morphology and optical characteristics of the deposited films were investigated for photovoltaic device applications. The crystallinity of the thin films was characterised by X-ray diffraction and they all appeared to be polycrystalline. Scanning electron microscopy (SEM) studies gives the average grain size to be small (8-130 nm) with an uneven surface feature. Fourier transform infrared spectroscopy (FTIR) and UV-VIS measurements showed that the films had more than 65% transmittance in the wavelength larger than 350 nm. The fundamental absorption edge shifted to a shorter wavelength, which corresponds to an increase in the energy band gap ranging from 3.59 to 3.72 eV. The physical conditions were kept identical while growing all the samples. It was found that ZnS films are suitable for use as the buffer layer of CIS solar cells, and it is a viable alternative for replacing CdS in the photovoltaic cell structure.