Transparent conducting oxides (TCO): TCO have wide band gap between 3 and 4 eV and would not be expected to have significant intrinsic conductivity. They can be extrinsically doped with cation from one group higher in periodic table (Al in ZnO). Intrinsic O2 vacancies are believed to contribute to carrier concentration. In extrinsically doped TCO׳s not all the impurities are ionized i.e. extrinsically active. They often depend on fabrication condition. TCO layer act as ARC due to change of refractive indices of interface. A metallic layer is deposited onto the TCO interlayer which acts as back contact surface. This back contact surface improves the refractive indices [96].