Effects of tin valence on microstructure, optical, and electrical properties of ITO thin films prepared by sol–gel method

This study aimed to understand the microstructural, optical, and electrical properties of tin-doped indium oxide (ITO) prepared with tetravalent and divalent tin salts. The influence of tin valence on the electrical, optical, structural, and morphological properties of the films were characterized by the mean of four-point probe, thermogravimetric analysis, differential thermal analysis (DTA), UV–Vis spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscope. XRD results revealed formation of cubic bixbyite structure of In₂O₃ with a small shift in major peak position toward lower angles with addition of Sn²⁺ and Sn⁴⁺. TG–DTA showed that the optimum heat treatment temperatures for thin films prepared with divalent and tetravalent tin salts are 500 and 450 °C, respectively. FESEM showed that with decreasing tin valence, grain size was gradually increased. The surface coverage for both thin films is similar, without any remarkable cracks. By increasing the tin valence from II to IV, high transparency (88.5 % in the visible region) and low conductivity (10 kΩ/sq.) can be obtained after calcination in air at 450 °C, which can be considered acceptable for electrostatic and antistatic applications of ITO thin films. The Haacke figures of merit at λ = 550 nm are comprised of between 2.94 × 10⁻⁵ Ω⁻¹ and 1.83 × 10⁻⁵ Ω⁻¹ for ITO prepared from tetravalent and divalent tin salt, respectively.