EFFECT OF pH ON OPTICAL PROPERTIES OF NANOSTRUCTURED Cu-DOPED ZnS THIN FILMS FOR PHOTOVOLTAIC APPLICATIONS

Using the simple Chemical Bath Deposition (CBD) method, Cu-doped thin films of zinc sulfide (ZnS) were deposited on glass substrates in a concentration range of 0.05-0.1% Cu. These films were made to be used as a buffer or window layer in solar cells. Different deposition conditions were investigated to find the optimal growth conditions; after that, the conditions were deployed to deposit the required films. XRD graphs confirmed a hexagonal structure, and SEM images indicated that the incorporation of Cu stabilises small grain growth in the films. The appearance of the sample surface was dense, with an ordered granular shape, and free of any cracks. The optical and surface properties of the prepared films have been analysed using state-of-the-art instruments. The effect of pH on such properties has also been investigated. The transmittances of the films were about 20–85%, and the incident wavelength range was 300–1100 nm. The transmission line shows a sharply increasing tendency. After that, it increases slowly and goes to a stable state above 400 nm. A film of pH 10.0 showed a high transmission coefficient (85%). Also, the absorbance of the ZnS thin films rapidly decreases up to 360 nm. After that, it decreases slowly and becomes stable above 400 nm. The band gap is in the range of 3.58–3.62 eV, which indicates that it absorbed the UV portion of the electromagnetic wave and could be used as the UV filter.