Cationic concentration and pH effect on the structural, morphological and optical band gap of chemically synthesized lead sulfide thin films

Abstract

Lead sulfide (PbS) thin films were deposited by chemical bath deposition method from two baths to study the effects of bath pH and lead ion concentration. The X-ray diffraction analyses revealed that all the films synthesized from the two baths were polycrystalline in nature. The XRD results also verified that the crystalline size decreased from 40 nm to 25 nm while lead ion concentration increased from 0.1 M to 0.3 M. Moreover, the XRD analyses confirmed that the highest strain was found from bath-A at a pH of 10.5. The elemental analyses were performed by EDX and it was confirmed that a better stoichiometric ratio was found for higher pH value. The optical absorption study revealed that the optical band gap of the PbS thin films found from bath-B decreased from 1.15 eV to 0.81 eV while the lead ion concentration decreased from 0.3 M to 0.1 M. Whereas, a higher optical band gap of 1.57 eV was found for pH = 10.5 from bath-A. Photoluminescence study revealed that the PbS thin film exhibited a broadband emission spectra from 410 nm to 625 nm with well defined twin peaks around 451 nm and 465 nm in the visible region. The PL emission spectra confirmed that emission intensity decreased gradually as the lead ion concentration decreased from 0.3 M to 0.1 M. Keywords: Lead sulfide, Chemical bath deposition, pH, Microstrain, Thin film