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.

High-Performance Transparent Ultrabroadband Electromagnetic Radiation Shielding from Microwave toward Terahertz

“…Then, with the bending cycles increasing to 4000 times, the EMI SE of TE waves shows a slight decline to ∼20 dB, while it drops to ∼7 dB for TM waves. Thanks to the ductile metal interlayer and the crack-resistant dielectric/metal/dielectric configuration of the USP, it inherits great flexibility from the ultrathin Ag layer and good endurance against mechanical stress in bending tests. , …”

“…Thanks to the ductile metal interlayer and the crack-resistant dielectric/metal/ dielectric configuration of the USP, it inherits great flexibility from the ultrathin Ag layer and good endurance against mechanical stress in bending tests. 57,58 The decrease in EMI shielding capability can be correlated with crack formation and propagation in the films observed by microscopic images. As shown in Figure S6 in the Supporting Information, cracks on the films at the same viewing area tend to be denser and deeper with the increase of the bending cycles, and it results in the sharp decrease of the electrical conductivity, causing the EMI shielding failure.…”

Extreme Dewetting Resistance and Improved Visible Transmission of Ag Layers Using Sub-Nanometer Ti Capping Layers

“…Silver films of thickness 10 nm or less are widely used in many applications such as thin film photovoltaics, , flexible electronics, transparent conductors, antireflective coatings, transparent heaters, resistive temperature sensors, plasmonic devices, radiation detectors, optical and photonic devices, chemical sensing, and low emissivity (low-E) coatings . Low-E windows are commonly used to prevent heat loss or build up in buildings, and are a requirement under recent energy near zero building regulations .…”

Multispectral Holographic Intensity and Phase Imaging of Semitransparent Ultrathin Films

“…Despite being only a few nanometers thick, the films can exhibit strong interactions with light, leading to a wide range of optical and optoelectronic applications. These include optical coatings, color filters, − infrared absorbers, transparent conductors − for displays or solar cells, meta-materials, − meta-surfaces, , and plasmonics, − to name a few. An ongoing trend in photonics is the transition from thin to ultrathin films and atomically thin materials .…”