Effect of film thickness on the structural, optical and electrical properties of SnO2: F thin films prepared by spray ultrasonic for solar cells applications

Abstract

In this work, undoped tin dioxide (SnO2) and fluorine doped tin dioxide (SnO2: F) thin films were deposited on 480°C heated glass using spray ultrasonic technique. SnCl2 and NH4F were used as sources of SnO2 and fluorine doping respectively. Effects of films thickness on the optical, structural and opto-electrical properties of undoped and 6wt.% fluorine doped SnO2 (FTO) thin films were investigated. Optical transmittance spectra of the films showed high transparency of about 76–84% in visible region. The optical gap, for SnO2 and 6wt.% F doped SnO2 thin films, were found to be in 3.77–3.93eV range. X-ray diffraction (XRD) patterns showed that both SnO2 and SnO2: F films were polycrystalline with cassiterite tetragonal crystal structure. The preferential orientation for undoped SnO2 was along (211) plane whereas F doped SnO2 preferential orientations were along (200) planes. The calculated grain sizes were in 25.63–33.53nm average. Figure of merit for FTO thin films revealed maximum value about 9.04×10−3 (Ω−1) at λ=800nm. The high conducting and transparent elaborated FTO thin films are promising to be used as window layer in solar cells.