Studies the effects of bath pH and lead molar concentrations on the structural, optical and electrical properties of lead sulphide thin films prepared by chemical route
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Lead sulphide (PbS) nanocrystalline thin films were prepared by chemical bath deposition route from two different chemical baths. The first bath (bath-A) was synthesized by varying the volume of ammonia to study the effect of bath pH, while the second bath (bath-B) was complexed by potassium hydroxide and the effect of lead molar concentrations were investigated. The X-ray diffraction analyses confirmed that all deposited thin films from the two baths had face centered cubic crystal structure. The XRD results also verified that the crystalline size increased from 25 to 40 nm when lead molar concentration decreased to 0.1 M. The HRTEM images showed that the grains are grown along different planes which confirmed a typical polycrystalline nature of the deposited PbS thin films from both chemical baths. The elemental analyses were carried out by EDX and confirmed the formation of PbS compound. The optical absorption study showed that the lowest optical band gap of 0.81 eV was estimated from bath-B at 0.1 M lead concentration, whereas, a highest band gap of 1.57 eV was found from bath-A. The transmittance study verified that the transmittance was increased with the wavelength and the maximum transmittance was measured around 24.51% for pH 10.5. The photoluminescence study revealed that the PbS thin film exhibited a broadband emission spectra from 410 to 625 nm regardless of bath pH and lead concentration. The dc-two point probe measurement verified that the electrical properties of the PbS thin films were considerably changed by bath pH and lead molar concentrations. The room temperature resistivity of the thin films found in the order of 104 Ω cm.
The authors are thankfully for Prof. H. C Swart and Prof R. Kroon from Bloemfontein campus to support us for the characterization techniques.
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