Optimisation of chemical solution deposition of indium tin oxide thin films

• Spin coating of indium tin oxide using an aqueous solution was optimised.
• The conductivity was enhanced by thermal annealing in reducing atmosphere.
• The conductivity of is comparable to the conductivity of sputtered films.
• A relaxation process in the reduced thin film was observed after exposure in air.

An environmentally friendly aqueous sol–gel process has been optimised to deposit indium tin oxide (ITO) thin films, aiming to improve the film properties and reduce the deposition costs. It was demonstrated how parameters such as cation concentration and viscosity could be applied to modify the physical properties of the sol and thereby reduce the need for multiple coatings to yield films with sufficient conductivity. The conductivity of the thin films was enhanced by adjusting the heat treatment temperature and atmosphere. Both increasing the heat treatment temperature of the films from 530 to 800 °C and annealing in reducing atmosphere significantly improved the electrical conductivity, and conductivities close to the state of the art sputtered ITO films were obtained. A pronounced decreased conductivity was observed after exposing the thin films to air and the thermal reduction and ageing of the film was studied by in situ conductivity measurements.