Light - Indium Tin Oxide Interaction I need to understand the mechanisms behind the light - indium thin oxide interaction for an ITO deposited solar cell. Does it act like a metal or semiconductor? Does it generate electron-hole pairs when photons are absorbed?
However, I realized that most of the online resources are focused on production and brief characterization of ITO. So, can you recommend me some resources which explain the optical and electrical properties of ITO (or more generally transparent conductive oxides) in detail?
 A: ITO is a "degenerately doped" semiconductor.  Essentially it's a poor metal, has the Fermi level in the conduction band.  Is black colored in sintering targets.  It functions as the elctrode in a solar cell by allowing 90%+ of the light to get through, while giving good conducivity for collecting current.  (The units of interest are called Seimens per square.)
It's really not that much different (in thin film form) than an extremely thin layer of conventional metal, which can have 50%+ transparency in very thin layers.  It has a pretty flat temperature-resistivity plot.  Less drop-off than normal for a metal, with temp.  But nothing like the temperature-activated conductivity of a conventional (not degenerate) semiconductor.  Note that this is not a special feature of ITO.  Si can also be degenerately doped.  However, the base (undoped) material is preferable with ITO because that band gap is ~4ev (i.e. passes visible light).  However, there certainly is still a small percentage of light that is absorbed by the material.  It's far from the transmission of a glass or quartz (and that's even with very thin layer as opposed to bulk).
Some helpful links:
https://en.wikipedia.org/wiki/Degenerate_semiconductor
https://en.wikipedia.org/wiki/Transparent_conducting_film
