Preparation of indium tin oxide thin films and investigation of hydrogen post-treatment effect

The development of optoelectronic devices including solar cells, liquid crystal displays, touchscreen panels and electrochromics has required a broad application of transparent conductive oxides (TCOs) as an essential component. TCOs come into prominence due to their outstanding properties such as 80% and more transmittance in the visible region of the solar spectrum and sheet resistance lower than 300 Ω/sq. Among TCOs, tin doped indium oxide (ITO) films are the most extensively preferred thin films owing to their high transmittance (~90 %) at 550 nm and low sheet resistance between 20-100 Ω/sq. Using vacuum based techniques such as magnetron sputtering can be very efficient to obtain low sheet resistance, however, this causes a dramatic increase in the production cost. Since ITO is the most extensively used transparent conductive electrode and it will have a huge market share in the near future; it is very obvious that the optical and electrical properties of the ITO films should be enhanced by means of simple and cost-effective preparation techniques. The aim of this thesis was the preparation of ITO thin films by scalable and low cost solution based methods with improved optical and electrical properties. For this purpose, thin films prepared by spin coating technique were subjected to post-treatment process to decrease sheet resistance and increase surface smoothness without causing any change in optical transmittance and crystalline structure. Effect of different parameters such as In:Sn ratio, concentration, temperature, number of deposition and post-treatment with hydrogen to sheet resistance, transparency, surface characteristics and crystalline structure were investigated. The properties of thin films were characterized by four probe measurement set-up, UV-visible spectroscopy (UV-Vis), scanning electron microscopy (SEM) and X-ray diffractometer (XRD). It has been found that 7 times deposition of 0.5 M solution including In:Sn with the ratio of 90:10 was the optimum process condition when the films were annealed at 500-600°C in air. For all samples, transmittance were measured in between 80 and 92 % at 550 nm and minimum sheet resistance was measured as 350 Ω/sq after post-treatment. Post-treatment provided a growth in crystalline size, distinct grain boundaries, and homogeneous particle distribution without influencing cubic crystalline structure due to XRD and SEM results. Subjecting the ITO films to 10 % H2 containing Ar medium at 300 °C for 3 hours was found as the most efficient process condition for post-treatment and as a result of that, approximately 70% efficiency was achieved on the reduction of sheet resistance without affecting the transmittance of the thin films.