Transparent Conductive Oxide (TCO) Films Prepared By Sol-gel Approach

SnO₂ and ZnO based transparent conductive oxide thin films doped with suitable dopants have excellent optical and electrical properties, and are widely applied as transparent and conductive oxide electrodes in various electrical and optical devices including liquid crystal display, solar cell and so on. In this paper, influence of dopant style and dopant concentration of Sb³⁺, F-, Al³⁺ on electirical and optical properties of SnO₂ and ZnO films were investigated.SnO₂ films doped with Sb³⁺, F- were prepared by sol-gel method from SnC₂O₄. Chelation of SnC₂O₄ in carboxylic acid-base system and effect of doping on sheet resistance were discussed. Effect of pH on chelation of SnC₂O₄ in carboxylic acid-base system and factors affecting the surface topography, electronic, optical properties such as sol concentration, Sb³⁺, F- doping concentration, film thickness and temperature were elucidated. ZnO:Al:F films doped with AlF3 were prepared by sol-gel method from Zincacetate. Factors affecting the surface topography, electronic, optical properties such as AlF3 doping concentration, film thickness, temperature and atmosphere were discussed. IR, Raman, XRD, FESEM, XPS, FETEM, UV-VIS and Four-Point probe method were used to characterize sol forming, chemical components, microstructure, optical and electrical properties of SnO₂ and ZnO based thin films. It was proposed that two processes are required for dissolving of SnC₂O₄:destruction of SnC₂O₄ and activation of carboxylic acid chelation ability. F element is stabilized by chelation between Trifluoroacetic acid (TFA) and Sn²⁺. Electronic property of ZnO film doped by AlF3 is improved based on increasing of current carrier concentration and migration.The experimental results showed that carboxylic acid acts as chelation agent, and base performs double function of destruction of SnC₂O₄ and activation of carboxylic acid chelation ability. The dissolution of SnC₂O₄ is effected by pH and the prime range is 6.4⁷.0. SnO₂ films prepared by this process are composed of nano particles with diameter below 10nm. The lowest sheet resistance of SnO₂:Sb is 30Ω/â–¡with 6at%Sb doping and 750nm film thickness after annealed at 450°C⁵00°C, and transmittance is >80%. Formation of Sb₂O₄ at high Sb doping worsen electronic property. The lowest sheet resistance of SnO₂:F is 130Ω/â–¡with 30at%Sb doping and 1000nm film thickness after annealed at 450°C, and transmittance is >80%. F element is stabilized by chelation between TFA and Sn²⁺, which make F volatilize mildly and reduce the stress in the films. The sheet resistance of 1at% AlF3 doped ZnO film from 0.6M sol concentration annealed in air atmosphere was high and decreased sharply to 25Ω/â–¡by heat treatment in H2 above 300°C. Homogenous, dense thin films were obtained and grain growth strongly preferred orientation of c-axis perpendicular to the substrate surface.