Thin‐Metal‐Film‐Based Transparent Conductors: Material Preparation, Optical Design, and Device Applications

Abstract

Transparent conductors are essential elements in an array of optoelectronic devices. The most commonly used transparent conductor – indium tin oxide (ITO) suffers from issues including poor mechanical flexibility, rising cost, and the need for annealing to achieve high conductivity. Consequently, there has been intensive research effort in developing ITO‐free transparent conductors over the recent years. This article gives a comprehensive review on the development of an important ITO‐free transparent conductor, that is based on thin metal films. It starts with the background knowledge of material selection for thin‐metal‐film‐based transparent conductors and then surveys various techniques to fabricate high‐quality thin metal films. Then, it introduces the spectroscopic ellipsometry method for characterizing thin metal films with high accuracy, and discusses the optical design procedure for optimizing transmittance through thin‐metal‐film‐based conductors. The review also summarizes diverse applications of thin‐metal‐film‐based transparent conductors, ranging from solar cells and organic light emitting diodes, to optical spectrum filters, low‐emissivity windows, and transparent electromagnetic interference coatings.

Tackling light trapping in organic light-emitting diodes by complete elimination of waveguide modes

“…Ge, Cu, and Al seed layers were compared on the basis of film roughness, binding strength energy, electrical resistivity, transmittance ( T ) of Ag films on these layers, and film stability, where the best performance was observed with a 5-Å Cu seed layer (see section S3). The readers can refer to a recent review article on thin metal film–based transparent conductors ( 44 ).…”

23‐4: Ultrathin Foldable Organic Light‐Emitting Diodes with High Efficiency

“…Our previous works showed that the ultrathin Ag alloy is highly flexible and can even enhance outcoupling efficiency of OLEDs by suppressing waveguide mode formation (4,5). Ag alloy with two adjacent dielectric layers, called dielectric-metal-dielectric (DMD) electrode, is more widely used in many applications since DMD forms ultrasmooth surface and is compatible with the conventional OLED structure and fabrication processes (6)(7)(8).…”

Regulating Ag Wettability via Modulating Surface Stoichiometry of ZnO Substrates for Flexible Electronics

“…The rapid advances in flexible and wearable optoelectronic devices, such as light‐emitting diodes, photovoltaic cells, electrochromic devices, and transparent heating devices, necessitate the development of high‐performance transparent conductive electrodes (TCEs). [ 1–9 ] The critical requirements for TCEs are high visible transparency, electrical conductivity (typically represented as sheet resistance), and sufficient flexibility. Currently, the most commonly used material for TCEs is indium tin oxide (ITO) which when prepared at elevated temperatures above 473 K can achieve a sheet resistance close to 10 Ωsq –1 and an average optical transmittance of 80–90% over the visible spectral range.…”

“…[ 3 ] Therefore, a primary approach toward fabricating high‐performance OMO electrodes has been to achieve 2D‐like metallic growth at the minimum film thickness. [ 2,3 ] To this end, a variety of wetting inducers have been proposed, including trace amounts of gas additives incorporated during Ag layer deposition, [ 9,21 ] co‐sputtering metallic impurities during Ag layer deposition, [ 17 ] and introducing high‐surface‐energy seed layers [ 22 ] and polymer surfactants [ 16 ] prior to Ag deposition. While some of these approaches have achieved considerable success, the TCE performance, commonly quantified by the Haacke figure of merit (FOM = T 10 / R s ), [ 23 ] is still inferior to that of high‐quality ITO electrodes.…”