Optimized optical/electrical/mechanical properties of ultrathin metal films for flexible transparent conductor applications: review [Invited]

Abstract

Transparent conductors are essential for high-performance optoelectronic devices. Recently, ultrathin metal films have received great attention as emerging transparent conductors to replace status quo indium tin oxide (ITO) due to their excellent optoelectrical properties with mechanical flexibility. Understanding an ultrathin metal film's optoelectrical properties with respect to thickness scaling is the prerequisite for the design of high-performance metal film-based transparent conductors. This review paper aims to focus on the evolution of ultrathin metal film’s optical properties as thickness scales. Such evolution of optical properties will be associated with electrical properties by exploring various resistivity scattering models aiming to better understand a film’s intrinsic physical property at an extremely thin scale and provide a guideline for enhancing the film’s intrinsic optoelectrical properties for transparent conductor application. Next, optical design considerations to enhance transparency at visible and near-infrared range are discussed including recent reinforcement learning methods as a potential strategy for transparent conductor design. Then, mechanical flexibility of various ITO-replacement electrodes is discussed as well as the mechanism for the metal film-based transparent conductor's excellent endurance against mechanical stress. Lastly, some of the unique benefits of using a metal film transparent conductor for optoelectronic device application are discussed.