The optical transparency and electrical conductivity in these materials depend on the nature, number, and atomic arrangements of metal cations in crystalline or amorphous oxide structures, surface morphology, and the presence of intrinsic
or intentionally introduced defects. The physics behind TCO materials as to why they possess both high conductivity and high transparency is important in attempting to improve our understanding of them and develop new TCO materials. Minami et al. [8] reviewed the status of and prospects for further
development of polycrystalline or amorphous TCO thin films for transparent electrode applications, circa 2005. A recent review of TCO materials by Exarhos and Zhou [9] discusses processing approaches, presents a microscopic description of electronic conductivity in transparent metal oxide systems, and offers guidelines for the design and subsequent development of new materials. The current article briefly reviews reported results on the development and properties of TCOs in the realm of thin film transparent electrode applications for LEDs and solar cells, since these newly developed TCOs can alleviate the undesirable compromise between the need to increase the light absorbing/emitting area
and the need for low series resistance. They also address the expected shortage of In