Q: Why FTO substrate is more frequently used than ITO?

A1: Usually FTO is used in place of ITO as a TCO when a post annealing process in air is needed for the thin film you are depositing on top of it (e.g. in dye-sensitized solar cells or perovskite-based solar cells where you need a TiO2 layer on top of the TCO which should be thermal treated). ITO electrical properties can be degraded in presence of oxygen at relatively high temperature (i.e. around 500 °C), while FTO is much more stable in such conditions.

A2: Fluorine-doped tin oxide (FTO) coated glass is electrically conductive and ideal for use in a wide range of devices, including applications such as opto-electronics, touch screen displays, thin film photovoltaics, energy-saving windows, RFI/EMI shielding and other electro-optical and insulating applications. Fluorine doped tin oxide has been recognized as a very promising material because it is relatively stable under atmospheric conditions, chemically inert, mechanically hard, high-temperature resistant, has a high tolerance to physical abrasion and is less expensive than indium tin oxide.