Effect of cationic precursor pH on optical and transport properties of SILAR deposited nano crystalline PbS thin films

The lead sulfide (PbS) thin films were deposited on glass substrate using successive ionic layer adsorption and reaction (SILAR) method at different pH of the cationic precursor, keeping the pH of the anionic precursor invariant. In this work, we establish that the pH of the cationic precursor and in turn the size of the crystallites affects the optical and electrical properties of PbS thin films. The characterization of the film was carried out using X-ray diffraction, scanning electron microscopy, optical and electrical measurement techniques. The presence of nanocrystallites was revealed by optical absorption and structural measurements. The PbS thin films obtained under optimal deposition conditions were found to be polycrystalline with face centered cubic structure. The lattice parameter, grain size, micro strain, average internal stress and dislocation density in the film were calculated and correlated with pH of the solution. The values of average crystallite size were found to be in the range 16–23 nm. Optical studies revealed the existence of direct and indirect band gap values in the range 0.99–1.84 eV and 0.60–0.92 eV, respectively. The room temperature resistivity of the synthesized PbS films was in the range of 1.2 × 107 to 3.5 × 107 Ω cm.

► We have prepared and characterized PbS thin films in acidic, neutral and basic media of the cationic precursor merely by varying the concentration complexing agent.
► We have correlated the transport properties to the structural, morphological and optical aspects of the film.
► Increase in pH leads to improvement in crystalline nature of the PbS thin films.
► Enhancement of reflectance in the IR region offers the possibility to use the films in advanced photovoltaic applications.
► pH variation gives rise to strong quantum confinement effects which shift the band gap from the mid-IR bulk values to higher energies.