Enhanced transparent-conducting fluorine-doped tin oxide films formed by Aerosol-Assisted Chemical Vapour Deposition

Abstract

We report a systematic study into the importance of carrier solvent on the Aerosol-Assisted Chemical Vapour Deposition (AACVD) of fluorine-doped tin oxide (FTO) films. In particular, the resultant effects on both the optical transparency and electrical conductivity properties are reported with optimised films showing figures-of merit significantly beyond commercial products. Depositions were carried out at substrate temperatures of 500, 550 and 600 °C using either N2 or air as the carrier gas. The carrier solvent was found to have a marked effect on film quality and performance characteristics. Hall Effect results indicate that use of propan-2-ol as carrier solvent and air as carrier gas gave the best performing n-type FTO thin films overall that exhibited high optical transparency (>80% at 550 nm) and resistivity values of 4 × 10−4 Ω cm, with charge carrier density and carrier mobility values of 4 × 1020 cm−3 and 39 cm2 V−1 s−1 respectively, in addition to haze values of 10–15%. Such parameters are ideal for thin film solar cell applications and have significantly higher figures of merit compared to current commercial materials. Success of this method of deposition is attributed, in part, to a halide transfer reaction in which part fluorine substitution of the tin precursor occurs in the solvent resulting in a direct tin–fluorine bond. The work shows the key role carrier solvents play in AACVD in directing the system chemistry.