**6. Challenges and future prospect**

A variety of IO/IO based nanostructured materials ranging from nanodots to nanorods, nanoneedles, nanowires or nanoplates have been obtained for various applications that are already discussed in this chapter. In case of IO based materials particularly for TCO application, the efforts have already been focused on the enhancement of electrical conductivity by adopting suitable material fabrication techniques and tuning the chemical composition with doping level of impurities. Apart from the electrical and optical properties, some other properties such as thermal stability, chemical and mechanical durability, deposition temperature, toxicity and cost of the TCO materials have also to be taken into consideration for a specific application. These properties are influenced by diverse factors, some of which being controlled by the preparation method. The main challenges for the extreme improvements of TCO as well as optoelectronics performances rely on three major areas. Firstly, it is important to understand the mechanism of structure-properties relationships and carrier mobility of TCO materials for achieving low resistivity and high transparency over extended wavelength region. Secondly, it is very much important to develop the deposition methods of IO based materials as TCO on varieties of substrates especially on temperature sensitive substrates for more efficient use of these materials and reduce the overall manufacturing costs. Moreover, it is required to perform the manufacturing and recycling techniques that would be compliant with environmental protocols. Last but not the least, fabrication/deposition of nanostructured IO based materials with reproducible properties would definitely represent a long-term opportunity in TCO industry. It is expected that the development of multicomponent IO based nanomaterials would be highly beneficial to use in various applications starting from photovoltaics to lighting, TCO, electronic devices, smart windows, gas sensors and so on.
