Study on electrical conductivity of transparent SnO 2 :Al thin films

SnO2 (SnO2:Al) based transparent conducting thin films doped with Al were prepared by sol–gel from SnCl2·2H2O precursor, with Al(NO3)3·9H2O as Al doping source and anhydrous ethanol as solvent. The influence of aluminum doping amount, annealing temperature and coating time on the electrical conductive properties of the SnO2:Al thin films was investigated. The phase composition, microstructure, sheet resistance and visible light transmittance of the SnO2:Al thin films were analyzed and characterized by X-ray diffraction, scanning electron microscopy, four-point probe and UV–Vis spectrophotometry. The results showed that when Al doping amount increased, sheet resistance increased firstly and then decreased when Al/Sn is less than 14 mol%, and sheet resistance increased lastly over 14 mol% Al-doping. Sheet resistance decreased firstly and then increased when annealing temperature and coating time respectively increased. When Al doping amount was lower than 8 mol%, SnO2:Al thin films behaved as an n-type material and SnO2:Al thin films behaved as a p-type material when Al doping amount was over 8 mol%. When Al doping amount was 14 mol%, annealing temperature of 450 °C, and 10 layer coating, the sheet resistance of SnO2:Al thin films was 18.4 kΩ/□ and the visible light transmittance was above 85%.