Ultrathin Metal films for Transparent Electrodes of Flexible Optoelectronic Devices

The need for the development of transparent conductive electrodes (TCEs) supported on flexible polymer substrates has explosively increased in response to flexible polymer-based photovoltaic and display technologies; these TCEs replace conventional indium tin oxide (ITO) that exhibits poor performance on heat-sensitive polymers. An efficient, flexible TCE is required to exhibit high electrical conductance and high optical transmittance, as well as excellent mechanical flexibility and long-term stability, simultaneously. Recent advances in technologies utilizing an ultrathin noble-metal film in a dielectric/metal/dielectric structure, or its derivatives, have attracted attention as promising alternatives that can satisfy the requirements of flexible TCEs. This review will survey the background knowledge and recent updates of synthetic strategies and design rules toward highly efficient, flexible TCEs based on ultrathin metal films, with a special focus on the principal features and available methodologies involved in the fabrication of highly transparent, conductive, ultrathin noble-metal films. This survey will also cover the practical applications of TCEs to flexible organic solar cells and light-emitting diodes.