In case of ITO thin film the transparency is going down and reflectivity is picking up from 1000 nm. So how does the conductivity properties of ITO are influenced in this region. Can anybody give me the clarification?
Electrical conductivity of conductive materials (metals, heavily doped semiconductors, etc) are independent of illumination. Anyhow, at NIR wavelengths ITO is opaque due to free carrier absorption, i.e. electronics in lower levels of conduction band gets excited to higher levels in the conduction band. However, these electrons are always 'free' so this shouldn't affect its electrical conductivity by much.
If you want to increase near IR transparency and maintain electrical conductivity, you have to increase the electron mobility and reduce the electron concentration by the same factor. Dopants such as Mo and Ti have been better than Sn in this respect.