Highly Efficient and Fully Solution-Processed Inverted Light-Emitting Diodes with Charge Control Interlayers

Abstract

In this work, we developed a charge control sandwich structure around QD layers for the inverted QLEDs, the performance of which is shown to exceed that of the conventional QLEDs in terms of the external quantum efficiency (EQE) and the current efficiency (CE). The QD light-emitting layer (EML) is sandwiched with two ultrathin interfacial layers: one is a poly(9-vinlycarbazole) (PVK) layer to prevent excess electrons, and the other is a polyethylenimine ethoxylated (PEIE) layer to reduce the hole injection barrier. The sandwich structure resolves the imbalance between injected holes and electrons and brings the level of balanced charge carriers to a maximum. We demonstrated the highly improved performance of 89.8 cd/A of current efficiency, 22.4% of external quantum efficiency, and 72 814 cd m of maximum brightness with the solution-processed inverted QLED. This sandwich structure (PVK/QD/PEIE), as a framework, can be applied to various QLED devices for enhancing performance.

Stability of Quantum Dots, Quantum Dot Films, and Quantum Dot Light‐Emitting Diodes for Display Applications

“…The introduction of an insulating interfacial layer between the ETL and the QDs is known to be effective in controlling charge balance. Materials such as poly(methyl methacrylate) (PMMA), polyethylenimine, aluminium oxide (Al 2 O 3 ), PVK, and tert‐butyldimethylsilyl chloride‐modified poly( p ‐phenylene benzobisoxazole) have been applied as interfacial layers to control electron injection . The introduction of a nanometer‐thin PMMA layer between the ZnO and QD layers to delay electron injection greatly improved the lifetime of the resulting QLED from 5000 to 100 000 h at a brightness of 100 cd m −2 .…”

“…Among these, QDs have recently been commercialized in display applications in the form of QD films for liquid crystal display (LCD) panels, and they will soon be applied in color conversion matrices in micro light‐emitting diodes (µ‐LED) and self‐emitting layers in quantum dot light‐emitting diodes (QLEDs), due to their narrow‐emission spectra, wide color gamut, and high quantum yield . QLEDs have recently demonstrated luminance and external quantum efficiency (EQE) values comparable to those of organic light‐emitting diodes (OLEDs) . Despite these merits, QDs still have issues with toxicity, efficiency, and instability.…”

Efficiency Enhancement of All‐Solution‐Processed Inverted‐Structure Green Quantum Dot Light‐Emitting Diodes Via Partial Ligand Exchange with Thiophenol Derivatives Having Negative Dipole Moment

“…The VBM levels of QDs were measured via UPS using a Sigma Probe (Thermo VG Scientific). The TEM measurement of QDs and measurement of QLEDs followed same methods as previous reports …”

“…Inverted‐structure QLEDs are advantageous because they are suitable for integrated circuits of n‐type metal oxide transistors having low processing costs . The performance of all‐solution‐processed inverted QLEDs has been improved by introducing various interface and charge transport (CT) layers …”

P‐113: Ligand‐Dependent Stabilities and Optical Properties of InP / GaP / ZnS Quantum Dots

“…Colloidal Quantum dots (QDs) are incredibly attractive in display applications due to their outstanding optical properties such as tunable band-gaps, narrow emission bandwidth, and high efficiency. [1,2] QDs are commercialized recently in back light unit (BLU) of liquid crystal display (LCD) panels as color conversion film. In addition, quantum dots are being intensively studied as color conversion layer to emitting pure red, green color by using micro LED or blue organic light emitting diode (OLED) light source, or an active layer of quantum dot light emitting diode (QLED).…”