Preparation Of FTO Transparent Conductive Films By Improved Sol-gel Method

Transparent conductive oxide(TCO) thin film is indispensable in flat panel displays, solar cells and transparent optoelectronic devices due to its low resistivity and good optical transmittance. Among the TCO films, the fluorine-doped tin oxide(FTO) film has virtues of relatively low cost, good thermal stability and high chemical stability, good optical transparency and electrical conductivity. There are many methods for the preparation of FTO films. Based on the conventional sol-gel method, we have developed the process for the preparation of sol and film forming technology, prepared good photoelectric properties FTO films.In order to reduce the influence of anion impurities on photoelectric properties of FTO films and remove anion impurities in the films, sol is prepared by redissolving the dry gel. This method can effectively remove Cl- ions in the sol, and thus reduce the scattering effect on the carrier and improve conductivity and transmittance of the films. To reduce the influence of cations in the glass substrate, which may permeate into film in the process of preparation of FTO film, the glass substrate is coated with a layer of Si O2 film before the preparation of FTO film. This can effectively prevent the Na+, Ca+ and other ions doping into FTO films. In addition, compared with annealing in air, conductivity of the film is significantly improved by annealing in nitrogen.Dependence of solvent, F-doped concentration, the amount of H2 O, Sn O2 concentration, PH value and stabilizer on the properties of FTO film were studied in detail. Ethanol and acetic acid need to be separated as solvent, PH value regulator and stabilizer. The uniform, clear transparent and fast-maturing sol with obvious Tyndall effect was obtained with 20% F-doping concentration, 0.4 mol/L Sn O2, 3 of PH, 5 ml of H2 O. In this condition, The FTO film with high transparency and low resistivity prepared by sol-gel has even and smooth surface.The influence of spin-coating layers, annealing temperature and atmosphere on the photoelectric properties of FTO films was also discussed. By scanning cross section of the film with SEM, we get that a layer thickness of film is about 75 nm. The lowest resistivity of 8.45×10-3 ?·cm and the average optical transmittance of 75% was obtained with 20% F-doping concentration and 600 nm thickness of film. With the increase of annealing temperature, the electrical conductivity and transparency of the films increase gradually. The films with good photoelectric properties are obtained while the annealing temperature is 500℃. After annealing for 1 h under the protection of nitrogen, the conductivity of films is 4 times higher than samples annealing in air. The annealing atmosphere has a bit influence on the transparency.