**3.3 Transparent thin metal films**

Mostly, bulk metallic films having tens to hundreds of nanometers thicknesses are utilized as back-electrodes (opaque-cathodes). But, ultra-thin metal films with only few nanometers thicknesses can also be utilized as front-electrodes (transparent-anodes). Since, these metal layers are thinner in comparison with the light visible wavelength, and thus are optically transparent to human-eye. The thickness and uniformity of the metal films determine the optoelectronic performance of these TEs for the desired soft electronic applications. Several metals having different work-functions, including silver, nickel, gold, and platinum are effectively employed as transparent electrodes in soft electronic devices. [100] However, the vacuum-free fabrication of these ultra-thin transparent metallic films over large area is difficult, and thus substantial advancements in the fabrication methods are required to efficiently mass-produce these thin metal films.
