Effect of thickness on the structural, optical and electrical properties of thermally evaporated PbI2 thin films

This work describes the physical properties of lead iodide (PbI2) thin films with different thicknesses that were deposited on ultrasonically cleaned glass substrates using a thermal evaporation technique at 5×10-6 torr. The initial material was purified by the zone refining technique under an atmosphere of argon gas. XRD analysis of the material demonstrates that the thin films were preferably oriented along the (001) direction. The size of the crystallites was calculated from the Scherer relation and found to be in the range of ∼5–10 nm, with higher values being observed for increasing film thicknesses. The optical energy band gaps were evaluated and determined to belong to direct transitions. Because the band gap increased with decreasing film thickness, a systematic blue shift was observed. The surface morphologies of PbI2 films exhibited a clear increase in grain size with increasing film thickness. The photoluminescence and dc conductivity of the thin films are also discussed.