Lead Sulphide (PbS) is an important binary semiconductor from IV–VI group with a narrow band gap of 0.41 eV. It has a large exciton Bohr radius of 18nm which results in strong quantum confinement for electrons and holes even for large particles. PbS nanoparticles are promising in optical and photonic device applications such as solar cells, gas sensors and other optoelectronic devices and also IR detectors . When the size and shape of PbS are transferred from bulk material to nanoparticles, the optical band gap shifts from 0.41 eV to the values up to 5.2 eV which is suitable to build optical sensors with adjustable properties

In this work, PbS thin films were deposited on glass substrates by chemical bath deposition method. We observe that the film thickness was doubled by repeating the chemical reaction. The effect of varying film thickness on structure and optical properties was studied. XRD reveals that all of the films were polycrystalline with (200) preferred crystal orientation. Increasing the film thickness enhances the crystallinity as well as reduces the dislocation density and strain of the films. Optical measurements show that as the thickness of the PbS film increases, the band gap of the films decreases from 1.47eV to 0.77eV and shifts from visible region to IR region. One of the prepared samples was used as an IR detector in the range of (800 nm to 1800 nm) it shows good agreement with the commercial PbS detector .