Synthesis and characterization of thermochromic Ag2HgI4 thin films

Silver mercury iodide thin films (Ag2HgI4) were successively deposited onto pre-cleaned glass substrates at room temperature by chemical bath deposition at different deposition times producing films of different thicknesses. The elemental composition of the as-deposited films measured by energy dispersive X-ray analysis shows the formation of stoichiometric Ag2HgI4 thin films. X-ray diffraction patterns reveal that Ag2HgI4 films are single phase of a polycrystalline structure, and have a dominant diffraction along [111] direction. The structure of the films was further investigated by transmission electron microscope verifying the polycrystalline nature of samples and nearly matching with X-ray diffraction data. The FESEM images reveal dense and well-defined grains. The optical properties of as-deposited films have been calculated from the recorded transmission and reflection data in the spectral range 400-2500nm. The analysis of the optical absorption coefficient indicates the presence of direct and indirect optical transition whose values decrease with the increase of thickness, while the values Urbach energy follow is a reverse behavior. The study of optic parameters of 558nm thick film heated at 330K was also investigated. The electrical conductivity was measured by four-probe experiment in the range from 300 to 500K. The activation energy was found to nearly equal half of the direct band gap indicating the intrinsic conduction of studied films is dominant.