Inkjet‐Printed High‐Efficiency Multilayer QLEDs Based on a Novel Crosslinkable Small‐Molecule Hole Transport Material

Abstract

Quantum dots light‐emitting diodes (QLEDs) have attracted much interest owing to their compatibility with low‐cost inkjet printing technology and potential for use in large‐area full‐color pixelated display. However, it is challenging to fabricate high efficiency inkjet‐printed QLEDs because of the coffee ring effects and inferior resistance to solvents from the underlying polymer film during the inkjet printing process. In this study, a novel crosslinkable hole transport material, 4,4′‐bis(3‐vinyl‐9H‐carbazol‐9‐yl)‐1,1′‐biphenyl (CBP‐V) which is small‐molecule based, is synthesized and investigated for inkjet printing of QLEDs. The resulting CBP‐V film after thermal curing exhibits excellent solvent resistance properties without any initiators. An added advantage is that the crosslinked CBP‐V film has a sufficiently low highest occupied molecular orbital energy level (≈−6.2 eV), high film compactness, and high hole mobility, which can thus promote the hole injection into quantum dots (QDs) and improve the charge carrier balance within the QD emitting layers. A red QLED is successfully fabricated by inkjet printing a CBP‐V and QDs bilayer. Maximum external quantum efficiency of 11.6% is achieved, which is 92% of a reference spin‐coated QLED (12.6%). This is the first report of such high‐efficiency inkjet‐printed multilayer QLEDs and demonstrates a unique and effective approach to inkjet printing fabrication of high‐performance QLEDs.

Interfaces and pattern resolution of inkjet-printed organic light-emitting diodes with a novel hole transport layer

“…The non-uniformity of the inkjet-printed device with the CB single solvent (Figure 4(a)) could have reduced the cd/A efficiency and the brightness, as shown in Figure 5(c). The insertion of the organic soluble HTL between PEDOT:PSS and the solution-processed emitting layer and the cross-linking of the HTL materials were found to be effective in drastically improving the chemical and interfacial stability of solution-processed multilayers, both for OLED and Quantum Dot LEDs [19][20][21]. The properties of solution-processable small molecular thin films that can be transformed into an insoluble layer by an amine-alcohol condensation reaction have been previously reported, and the detailed procedure has been illustrated elsewhere [20,21].…”

Robust Nanofiber Films Prepared by Electro‐Microfluidic Spinning for Flexible Highly Stable Quantum‐Dot Displays

“…Quantum dots based liquid crystal displays (QD‐based LCDs) are a promising candidate for the next‐generation of displays owing to their superiorities in wide color gamut, pure color emission, high brightness, and long lifetime. [ 1–6 ] For conventional LCD, the color gamut of is only ca. 70% of the National Television System Committee (NTSC) standard even using the best phosphor materials as the fluorescence converter.…”

High‐Resolution Inkjet Printing of Quantum Dot Light‐Emitting Microdiode Arrays

“…Inkjet printing is a widely available, comparatively straightforward technique that is material‐effective and can form individual pixels and is very flexible in the design of the printed device . Jiang et al printed a full‐color QLED display with a pixel density of 120 pixels per inch (ppi) using a commercial piezo print head and reported a maximum brightness of 400 cd m −2 .…”