The structural features of TiO2 thin films formed by pyrosol methods

Abstract

Photovoltaic cells employing an extremely thin absorber layer can be fabricated as p-i-n devices with TiO2 as the transparent, n-type component. We have examined in detail the structural features of such TiO2 films fabricated via an aerosol pyrolysis method. A precursor solution, produced by dissolving Ti powder in hydrogen peroxide and ammonium hydroxide, was diluted in water and atomized using a 2.4-MHz ultrasonic nebulizer. The resultant aerosol was transported with a carrier gas to heated, ITO-coated glass substrates. The effects on the film structures of different fabrication conditions were investigated. Samples were structurally characterized by X-ray powder diffraction and electron microscopy. Average properties were determined using synchrotron X-rays and a detailed mapping of structural features was provided by a laboratory diffraction system. The crystalline films were shown to consist of mostly anatase and to be compact. On average, the TiO2 crystallites possessed significant microstrain that remained constant with increasing precursor concentration. Mapping across the aerosol “footprint” showed that the thickest and most crystalline films were formed from the greatest precursor concentration at 350 °C. Furthermore, it was also shown that the film crystallinity was significantly lower in a “penumbra” region, where a greater degree of preferred orientation was demonstrated.