Synthesis and optical characterization of nanocrystalline fluorine-doped tin oxide films: conductive window layer for optoelectronic applications

The spray pyrolysis as a simple and cost-effective thin film deposition technique was used to obtain transparent conductive oxides (TCOs) thin films of SnO₂ and F-doped SnO₂ on soda-lime glass substrates at 500 °C. The surface morphology and average crystallite size of the deposited TCOs thin films were investigated by the field emission scanning electron microscope and X-ray diffraction technique. The crystalline grains of the as deposited films preferentially oriented along (101) plane according to the tetragonal crystal structure of SnO₂. The tetragonal phase of SnO₂ for the deposited films has been confirmed from the fundamental peaks of Raman spectrum. The optical constants like optical band gap, refractive index, and absorption coefficient for SnO₂ and F-doped SnO₂ films have been evaluated on the basis of Swanepoel model depending on the transmission spectra for the deposited films. All TCOs films under study have direct optical band gap its value increased slightly with the F doping level. The figure of merit of the thin films under study was calculated to check the availability of the films as TCOs in thin film solar cell applications. The charge carrier concentration and Hall mobility of the thin films under investigation also have been determined from the Hall measurements. The effect of γ-irradiation with distinct doses on the transmittance, optical band gap, and crystal structure also has been studied for the deposited films.