Efficient vacuum-free-processed quantum dot light-emitting diodes with printable liquid metal cathodes

Abstract

Colloidal quantum dot light-emitting diodes (QLEDs) are recognized as promising candidates for next generation displays. QLEDs can be fabricated by low-cost solution processing except for the metal electrodes, which, in general, are deposited by costly vacuum evaporation. To be fully compatible with the low-cost solution process, we herein demonstrate vacuum-free and solvent-free fabrication of electrodes using a printable liquid metal. With eutectic gallium-indium (EGaIn) based liquid metal cathodes, vacuum-free-processed QLEDs are demonstrated with superior external quantum efficiencies of 11.51%, 12.85% and 5.03% for red, green and blue 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 thus improves the balance of carrier injection. Also, the T half-lifetime of the vacuum-free-processed QLEDs is about 2-fold longer than that of the devices with Al cathodes. Our results demonstrate that 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.

80‐1: Invited Paper: Developing AMQLED Technology for Display Applications

“…IJP, nano-imprinting, gravure printing etc.) [3], while possibly utilizing only inorganic materials, making it potentially less expensive and more durable with longer operational lifetime compared to AMOLED. When considering AMQLED display architecture, there is a very important area, with a lot of research effort is being focused onit is a quantum dot light emitting diode (QLED) architecture.…”

“…The only expensive part of the process, thus is deposition of the top electrodes that still has to be formed using either vacuum evaporation or magnetron sputtering. There are methods being currently developed that would allow top electrodes to be printed as well [3], but they are still some time away from being viable for mass production. However, even with current state of technology it is entirely possible to fabricate inexpensive AMQLED displays of various sizes.…”

73‐4: Tandem Red Quantum‐Dot Light‐Emitting Diodes with External Quantum Efficiency over 34 %

“…2) balance of charge injection. The surface of EGaIn is covered with a thin native oxide which helps to reduce the injection of electrons and thereby improve the balance of charge injection [18]. The performances of the bottom, the top and the tandem devices are summarized in Table 1.…”

All solution‐processed white quantum‐dot light‐emitting diodes with three‐unit tandem structure

“…Light-emitting diodes (LEDs) based on colloidal quantum dots (QDs) are recognized as one of the potential candidates for next-generation displays because of their intrinsic properties such as tunable emission color, high color purity, good photostability and simple fabrication process. [1][2][3][4][5][6][7] With the development of the QD materials and the device structures, the performances of the QLEDs have been rapidly and significantly improved. 8,9 For example, red, green and blue QLEDs with external quantum efficiencies (EQE) of 20.5, 10 21 11 and 12.2%, 2 respectively, have been demonstrated recently.…”