Making a display just like printing a newspaper? The use of liquid metal EGaIn electrode has made that dream possible
Quantum dot light-emitting diode (QLED) is a promising candidate for the next generation display due to its advantages of high color saturation, tunable emission color and inherent high stability. Compared with organic light-emitting diode (OLED), QLED can be fabricated through solution-processed which makes the fabrication both low cost and compatible with printing technology. However, the back electrode, usually based on Al, Ag or Cu metal thin films, still need to be deposited by costly vacuum evaporation. To lower the fabrication cost and achieve full printing procession, the back electrode should also be deposited by solution/printing methods. The traditional solution-processable conductive materials such as Ag paste, metal nanowires, graphene and/or carbon nanotubes are usually dissolved in organic solvents, and during the coating processes, the underneath functional layers could be dissolved and damaged by these solvents, further leading to the instability even failure of the devices.
Therefore, to avoid the damage and improve the stability, it is necessary to develop a solvent-free printable electrode material. Researchers in Southern University of Science and Technology have recently proposed a method to apply liquid gallium alloys as a printable electrode for QLED. The study had been published on the Nanoscale. Eutectic gallium indium (EGaIn, 75 wt% Ga, 25 wt% In) have a low melting point <15.7 °C, and thus it is in liquid state at room temperature. It can be easily deposited and patterned by printing methods. In addition, the liquid metal alloy does not contain organic solvents and thus does not need high-temperature thermal-annealing treatment. Plus the high electrical conductivity and appropriate work function, it is a promising printable electrode material for QLED.
During the fabrication process, the functional layers are spin-coated on the pre-patterned ITO substrate, while the EGaIn cathode is printed onto the cover glass (Fig. 1). Finally, the functional layer-coated-substrate and the EGaIn-coated-cover glass are assembled together and sealed by UV epoxy. Because EGaIn is in liquid state and is soft in nature, a good electrical contact between the functional layers and the EGaIn can be obtained. With printed EGaIn cathodes, vacuum-free-processed QLEDs exhibit high external quantum efficiency (EQE) of 11.51%, 12.85% and 5.03% for R-, G- and B-devices, respectively, which are about 2-, 1.5- and 1.1-fold higher than those of the devices with thermally evaporated Al cathodes. The improved performance is attributable to the reduction of electron injection by the native oxide of EGaIn, which serves as an electron-blocking layer for the devices and improves the balance of carrier injection.
The results demonstrate EGaIn-based solvent-free liquid metals are promising printable electrodes for realizing efficient, low-cost and vacuum-free-processed QLEDs. The elimination of vacuum and high-temperature processes significantly reduces the production cost and paves the way for industrial roll-to-roll manufacturing of large area displays.
Siting Wang, Shuming Chen
Department of Electrical and Electronic Engineering,
Southern University of Science and Technology, Shenzhen, P. R. China
Efficient vacuum-free-processed quantum dot light-emitting diodes with printable liquid metal cathodes.
Peng H, Jiang Y, Chen S
Nanoscale. 2016 Oct 20
|Stanford team brings quantum computing closer to… Quantum computing could outsmart current computing for complex problem solving, but only if scientists figure out how to make it practical. A Stanford team is investigating new materials that could…|
|Microbial assisted electrochemical desalination: a… Wastewater discharged from industries can lead to adverse ecological effects. Commonly used conventional technologies for wastewater treatment are efficient in removing organic matter and nutrients (N and P) but less…|
|Transparent coatings and see-through materials from heating Many modern technologies are based on materials that are deposited on special underlying materials. Optical coatings can prevent tarnishing, give anti-reflection benefits, and in some cases filter out harmful UV…|
|Lighting up a flashlight without batteries What people often do is the usage of batteries to light a lamp or a flashlight for illumination. Herein, researchers from Institute of Intelligent Machines (IIM), Chinese Academy of Sciences…|
|Modeling pattern deposition subject to contact angle… In this paper we propose a theoretical model for the pattern deposition of a non-volatile solute mass off an evaporating sessile drop of a dilute solution. The dynamics of the…|
|Computational study of optical and electronic… The computational methods for studying the various properties of nanomaterials like Graphene, have become extremely popular these days. Thanks to the ever increasing processor speeds. These methods include Density functional theory…|