The effect of solvents and the thickness on structural, optical and electrical properties of ITO thin films prepared by a sol–gel spin-coating process

In this study, tin-doped indium oxide (ITO) thin films were produced by the sol–gel spin-coating technique with an inexpensive salt of indium (In(NO3)3- H2O) and SnCl4 as indium and tin precursors (the molar ratio of In:Sn was 9:1), respectively. Then the prepared thin films were annealed in the temperature of 550 C under argon atmosphere (the pressure of 10 torr). Polyvinylalcohol (PVA) was used as stabilizers in the synthesis of ITO sol. The prepared ITO thin films were characterized by EDX, XRD, FT-IR, UV–Vis spectroscopy and SEM images. The XRD patterns of the thin films indicated the main peak of the (2 2 2) plane corresponded to indium oxide with high degree of crystallinity. The FT-IR spectroscopy confirmed that indium tin oxide has been prepared by appearance of a peak at 470 cm-1 that can be assigned to the vibrations of In–O bonds. The optical direct band gap of ITO thin films was calculated about 3.98–4.17 eV by optical transmittance measurements. The grain size of ITO nanoparticles was obtained at about 25–50 nm by SEM images. The electrical characterization was done by the four-point probe method to determine the sheet resistance and resistivity. The effects of coating number on ITO thin films properties were investigated. The low resistivity (sheet resistance of 2.5 kX/cm2) and highly transparent films were obtained that can be applied as covers on heater windows. Appearance of a peak at 470 cm-1 can be assigned to the vibrations of In–O bonds and are characteristic of cubic In2O3.