Characteristic evaluation on spray-deposited WFTO thin films as a function of W doping ratio

Abstract

In this work, F and F + W simultaneously doped SnO2 highly transparent conducting thin films were deposited on glass substrates at (500 ± 5) °C temperature by the spray pyrolysis method. Microstructural, morphological, electrical and optical properties of FTO films were investigated as a function of tungsten (W) doping, in the range from 0 to 5 at%. X-ray diffraction patterns show that the films exhibit a tetragonal cassiterite structure and (200) preferential orientation of FTO film, and the relative strength of these peaks changes with altering the W doping ratio. The preferred growth of (211) changed to (200) plane with 2 at% W doping level and 3 at% W-doped film had (200) orientation and with further doping, this changed to (110) orientation. The scanning electron microscopy and atomic force microscopy images of the films indicate that the films are made up of dense small particles of a pyramidal shape and have a smooth surface. It was observed that the surface morphology of the films did not change much when the W element was inserted to the FTO structure. It was found that the sheet resistance values of the films varied with W doping ratio, and 2 at% W-doped FTO thin film exhibited the lowest values of sheet resistance (1.12 Ω). Also, the highest figure of merit, infrared reflectivity and optical band gap values were calculated for 2 at% W-doped FTO film as 50.9 × 10−2 Ω−1, 98.82 % and 4.13 eV, respectively. These results make the films an effective candidate for usage in many optoelectronic applications and photo-thermal conversion of solar energy.