Influence of annealing on chemically grown PbS thin films and its DFT study

We report here, lead sulfide (PbS) NC thin films were synthesized by low-temperature one-pot chemical synthesis technique and effect of air annealing on it. The thickness of the film ∼247 nm. The as-synthesized films were annealed at 150 °C for 2 hr. X-ray diffraction (XRD) patterns of the thin films showed a stable cubic phase, changes in peak intensity after annealing. The average crystallite size was found ∼23 nm. Field emission scanning electron microscopy (FE-SEM) micrographs showed their randomly oriented nanocrystals over the entire surface of the glass substrate. The optical measurements confirmed that PbS thin films have a direct band gap that increases by annealing treatment, this obtained blue shift in band gap as compared to bulk due to the quantum confinement effect of nanocrystals. Raman spectrum confirms the formation of the crystalline structure of PbS NC's. Photoabsorbing properties of the as-synthesized and annealed PbS NC's thin films were studied by I-V measurement. Finally, the electronic structure of PbS NC was calculated by first principle investigation within the density functional theory.