Study Of The Preparation And Properties On FTO Transparent Conductive Thin Films

Fluorine doped tin oxide?FTO?thin films is a n-type semiconductor material with a wide band gap.Due to the low cost,high hardness,low electrical resistivity,high optical transmittance,and good electrochemical stability,the FTO thin films have been widely used in many areas such as solar cells,gas sensors,flat-panel displays and low-emission films,especially in the deep processing of architectural glass which has been a research focus in the field of energy conservation and environmental protection materials.However,there are still some key technical problems in terms of research and application,such as the uneven surface of FTO thin films,easy cracking on coating as well as doping mechanism.In this paper,based on a simple and easy preparation process,the optimization of coating process,the effects of the concentration of dopant on the properties of FTO films,the effect of fluorine sources on the properties of FTO films,and the doping mechanism were carried out and some significant results were obtained.The high performance FTO thin film was prepared by a novel sol-gel method and the the optimum coating process were studied.On the basis of the previous research,the coating and sintering processes in the process of traditional calcination were combined in the simple evaporation method.The effects of different atomic ratios of F/Sn on the structure,morphology and photoelectric properties of FTO films were investigated.In addition,the effects of different fluorine sources on the properties of FTO thin films were analyzed,and the doping mechanism of different F sources was discussed.The performance parameters of the samples were characterized by XRD,SEM,TEM,TG-DTA and FT-IR.The results are as follows:1.The FTO thin films were prepared by sol-gel-evaporation method with SnCl₄·5H₂O as a tin source,and SnF₂ as a fluorine source.The reaction temperature,reaction time,substrate temperature and coating times were discussed.The results showed that the FTO films of surface resistance of 14.7 ??¨-1 could be obtained when the reaction temperature of the sol was 50 ?,the reaction time was 5 h,the evaporation temperature was 600 ?,and the coating number of was 1 time.2.The effects of different atomic ratios F/Sn?0-22%?on the properties of FTO thin films were studied,and perfermance index of FTO thin films were analyzed.The results showed that the incorporation of F replaced the part of O,formed a SnO₂-x Fx crystal structure,and affected the electrical properties of FTO films.The SnO₂-x Fx crystals were polycrystalline with tetragonal rutile phase?JCPDS card no.41-1445?and had a preferential orientation along the?110?direction.The surface morphology of SnO₂-xFx crystals were the shape of pyramid with an average grain size of 20 nm.The spacing between the lattice fringes was about 0.33 nm,corresponding to the diffraction pattern of the?110?crystal plane.The fractal dimension of the three-dimensional structure of SEM gray images reflected the roughness of the surface of FTO films.With the increase of fractal dimension,the surface of films became rougher and the surface resistance increased.When F/Sn was 14%,the average transmittance was 79.2%,and surface resistance was14.7 ??¨-1.And the quality of FTO thin films with the highest performance index value and infrared reflectivity??TC = 66.1×10-4 ?-1,RIR=86.07%?is the best.3.The FTO films were deposited onto glass substrates by the sol-gel-evaporation method with HF,CF₃ COOH or SnF₂ as a fluorine source,respectively.The effects of different fluorine sources on the structure,surface morphology and photoelectric properties of SnO₂ films were investigated.After all investigations,they were concluded that all the particles of the FTO films presented a tetragonal rutile phase.The surface morphologies of the FTO films corresponded to irregular polygonal shape,rod-shaped and pyramid-shaped for fluorine sources CF₃ COOH,HF and SnF₂.The performance index values of FTO thin films with HF,CF₃ COOH and SnF₂ as a fluorine source were 10.2×10-4 ?-1,49.2×10-4 ?-1and 66.1×10-4 ?-1,respectively.IR reflectivity of FTO films for HF,CF₃ COOH and SnF₂ as a fluorine source were 49.1%,83.1% and 86.07%,respectively.For the optimized sample,the values of sheet resistance and infrared reflectivity were 14.7 ??¨-1 and 86.1%,respectively.These results showed that the photoelectric performance and the thermodynamic performance of FTO film with SnF₂ as a fluorine source was the best.4.The mechanism of three different fluorine sources on the properties of FTO thin films was mainly related to the bonding form between F ion and the growing SnO₂ grains.SnF₂ itself was a tin fluorine compound as a fluorine source as well as a tin source,and the F element was doped directly.HF had a strong corrosive effect on SnO₂ grains,which was easier to be bonded with SnO₂ grains than CF₃ COOH to form tin fluorine compound or bond,and it belonged to indirect doping.