Self-doped SnO₂:F synthesis by aerosol-spray deposition technique and their application in relative humidity sensor devices

Fluorine-doped tin-oxide (SnO₂:F) thin films were prepared by aerosol-spray deposition technique on soda lime glass substrate by one-step deposition process. Tin (II) fluoride (SnF₂) was used as source of tin (Sn) and doping element fluorine (F), to synthesis a self-doped transparent conducting electrode. The doping concentration of the thin films was controlled by varying deposition temperature and the molar concentration of the SnF₂ solution. Electrical resistivity of the samples was measured by Van Der Pauw method and the mobility was calculated by Hall measurement technique. SnO₂:F thin films grown under optimum condition showed 1.2 × 10⁻⁴ Ω-cm resistivity and 6.5 × 10²⁰/cm³ carrier concentration. Surface-free energy of the deposited thin films was calculated from the measurement of contact angle for three different probe liquids using the Wendt theory. Sample grown at optimum condition showed the lowest surface-free energy of 63.55 mJ/m² with dominating polar component. Reduced graphene oxide was used to produce a resistive humidity-sensing device to study the effectiveness of FTO thin film as back electrode. Maximum of 18.27% responsivity was observed for the relative humidity of 90% along with the sensitivity of 1.16 Ω/% RH.