**5. Applications of indium oxide based nanomaterials**

Because of high optical transmittance and excellent electrical conductivity, indium oxide/IO based nanomaterials have variety of applications especially for fabrication of optoelectronic and microelectronics devices [2, 16, 17]. These are discussed in the next sub-sections.

#### **5.1 Transparent conducting oxide**

Generally, transparent conducting oxides (TCOs) are the materials that possess two major properties of (a) high electrical conductivity and (b) excellent optical transparency. Indium oxide is an important MOS material that mainly uses as TCO [62]. The properties of In2O3 are improved by doping or coupling of other semiconductors with wide BEGs. Improved electrical and optical properties of In2O3 based nanomaterials can promote to fabricate a variety of potential modern devices such as touch screen displays, low emissivity windows, solar cells, and gas sensors [2, 62]. Till date, ITO is the most successful TCO in terms of optoelectronic properties used commercially. It is found that ITO demonstrates a very high electrical conductivity and carrier concentrations without losing visible light transparency [62, 63].

#### *5.1.1 Transparent conductive electrode*

Transparent conductive electrodes made with TCOs are hugely used in flat panel displays, touch panels, lamps and thin film solar cells [62, 63]. Among the various TCOs, IO and ITO are highly used to fabricate transparent conductive coatings. It is noted that various properties of TCO thin films can be tuned by selecting suitable dopant with its optimized concentration. Thus, impurity doped ZnO, In2O3,

and SnO2 thin films are the best materials for practical utilization as transparent conducting electrodes [62, 63]. Also, different indium oxide based materials have already been explored to fabricate transparent conductive electrode [62–64].

## *5.1.2 Antireflection coating*

Antireflection coating (ARC) is an optical coating which reduces undesirable reflections from substrate surfaces and increases transmittance [65, 66]. It is extensively used in industrial applications such as solar cells and photovoltaics, electronic device displays, and also general purposes, like spectacle and photographic lenses [65–67]. In this regard, IO based nanomaterials especially ITO has gained a special attention and ARC can be applied on this TCO thin films for the applications [66, 67].
