Experimental and Ab Initio Investigation of the Physical Properties of PbS Thin Films Prepared by Chemical Bath Deposition (CBD)

In this work, high-quality PbS thin films were prepared by the chemical bath deposition (CBD) method for different molarities of sulfur precursors (1 M to 1.4 M) in a basic solution. The composition, morphology, and structural and optical properties of the PbS thin films were studied by means of scanning electron microscopy (SEM–EDS), X-ray diffraction (XRD), and UV–visible spectrophotometry (UV–Vis). The spectra obtained by XRD show that the PbS thin films crystallize in a NaCl structure with the grating parameter ( a = 5.9202 Å) and the (002) plane is a preferential orientation of the films. The optical band gap decreases from 1.5 to 1.23 eV as the grain size of the PbS thin films increases from 15 to 37 nm. The decrease in the band gap is due to quantum confinement effects promoted by the small Bohr radius of this material (18 nm). Our experimental results have been validated by theoretical calculations in the framework of the functional density theory (FDT) using the full potential linearized augmented plane wave (FP-LAPW) as implemented in the WIEN2K code. The value of the optical band gap found in PbS nanoparticles is suitable for solar cell applications.