6. Thin films based on transparent conductive oxides

Several metal oxides are transparent in the visible range of the solar spectrum (T _L ≈ 85% or even 90%). Deposited in thin layers a few hundred nanometers thick, they have been known and used for over fifty years. They have the property of being particularly stable, hard and adherent to many substrates. This property is due to their electronic structure: electrons are distributed in the valence band, a set of linked energy levels. If they are given sufficient energy, they can pass into the conduction band, a set of higher-energy levels, and take part in electrical conduction: they are free electrons in the sense of the Drude model. For these oxides, there is an energy domain, called the band gap, which electrons cannot occupy.

The bandgap width of transparent oxides is the minimum energy that must be imparted to an electron...