High‐Resolution Pixelated Light Emitting Diodes Based on Electrohydrodynamic Printing and Coffee‐Ring‐Free Quantum Dot Film

Abstract

Inkjet printing for preparing quantum dot light emitting diodes (QLEDs) has become increasingly attractive due to its large‐area, low‐cost fabrication features. However, the rather low resolution and coarse morphology induced by the printing and uneven evaporation of droplet restrict its further development. Herein, electrohydrodynamic (EHD) printing and mixed solvent method are employed to fabricate high‐resolution pixelated QLEDs. By optimizing the mixed solvent ratio to weaken capillary flow, coffee‐ring‐free quantum dot (QD) films can be obtained. With the help of EHD printing process optimization and pixel defining layers introduction, high‐resolution pixelated QLED with 306 pixels per in. is achieved, which can meet the requirements of manufacturing mobile phones. Finally, an inverted pixelated QLED with a low turn‐on voltage of 3 V and a maximum luminance of 8533 cd m−2 is fabricated, demonstrating that the presented strategy has huge potential in high‐resolution and high‐quality QD display manufacturing.

Micro‐Light‐Emitting Diodes Based on InGaN Materials with Quantum Dots

“…achieve high resolutions down to 1 µm and is compatible with a wide viscosity range of inks, is the main QD-deposition technology in the Micro-LED display industry. [77] In 2019, VueReal announced that their Micro-LED microdisplays had achieved a brightness of 100 000 nits and a density of over 30 000 PPI through a printing process. In addition, Samsung launched a manufacturing line equipped with IJP facilities for QD colorconversion TVs (QD-OLED TVs) in 2019, with plans to enter the consumer market in 2021.…”

“…EHD printers can produce narrow linewidths or small droplets in the range of 1-10 µm. [77,[79][80][81] When QD printing on Micro-LEDs, the critical factor is to form a uniform QD layer, which is closely related to highly efficient color-conversion. In many cases, the QDs in a QD ink droplet become concentrated at the droplet edge as it dries, resulting in the so-called coffee ring effect (CRE).…”

“…Furthermore, EHD printing with QDs in the optimized solvent mixture enables the printing of CRE-free QD films and the production of highresolution pixelated QD-LEDs with 306 PPI. [77] In 2015, the application of QD printing for full-color Micro-LED displays with color-conversion technology was first introduced by using aerosol jet printing by the Kuo group, as shown in Figure 2. [75] To remove residual UV or blue excitation light, a distributed Bragg reflector (DBR) was placed on top of the QD film.…”

Effects of ZnMgO Electron Transport Layer on the Performance of InP-Based Inverted Quantum Dot Light-Emitting Diodes

“…In the past decade, quantum dot (QD) has been considered a promising next-generation light-emitting material due to its outstanding photo-electrical properties [ 1 , 2 , 3 ] and great solution-processing ability [ 4 , 5 ]. Among well-documented QD materials, cadmium (Cd)-based QDs have tremendous potential in commercial application of displays [ 6 , 7 , 8 ] because of their high external quantum efficiency (EQE) [ 9 ] and excellent luminescence performance [ 10 ].…”

“…Among these layers, the ETL plays an important role in electron injection efficiency, exciton dissociation, and hole blocking [ 22 , 23 , 24 ]. A well-known and widely applied ETL material is zinc oxide (ZnO), which has good stability and high electron mobility [ 5 , 24 , 25 ]. However, many challenges still exist for ZnO application in InP QLED, such as surface defects, work function mismatching, and so forth, which may cause the quenching of excitons and interface barriers.…”