Tailoring the Electronic Landscape of Quantum Dot Light-Emitting Diodes for High Brightness and Stable Operation

Abstract

The charge injection imbalance into the quantum dot (QD) emissive layer of QD-based light-emitting diodes (QD-LEDs) is an unresolved issue that is detrimental to the efficiency and operation stability of devices. Herein, an integrated approach to harmonize the charge injection rates for bright and stable QD-LEDs is proposed. Specifically, the electronic characteristics of the hole transport layer (HTL) is delicately designed in order to facilitate the hole injection from the HTL into QDs and confine the electron overflow toward the HTL. The well-defined exciton recombination zone by the engineered QDs and HTL results in high performance with a peak luminance exceeding 410 000 cd/m 2 , suppressed efficiency roll-off characteristics (ΔEQE < 5% between 200 and 200 000 cd/m 2 ), and prolonged operational stability. The electric and optoelectronic analyses reveal the charge carrier injection mechanism at the interface between the HTL and QDs and provides the design principle of QD heterostructures and charge transport layers for high-performance QD-LEDs.

Polarized Electroluminescence Emission in High‐Performance Quantum Rod Light‐Emitting Diodes via the Langmuir‐Blodgett Technique

“…Spatial confinement of an electron and hole in a nanometer‐sized core and shell with a smaller dimension than its Bohr radius leads to distinct features of QDs due to the so‐called quantum confinement effect, such as size‐tunable emission wavelength, [ 1–4 ] narrow emission bandwidth, [ 5,6 ] and near‐unity photoluminescence (PL) quantum yield. [ 7–9 ] These properties are particularly tantalizing for display applications, as evidenced by the recent adoption of QD‐based color enhancement films in the display industry and active research regarding the next frontier: self‐emissive QD light‐emitting diodes (QD‐LEDs). [ 10–13 ] QD‐LEDs are electroluminescence devices in which luminescent QDs are electrically pumped by sandwiched organic/inorganic charge transport layers (CTLs).…”

“…As a result of intensive studies, both the efficiency and stability of QD‐LEDs have greatly improved within a couple of decades, reaching the commercialization standards in the display industry. [ 7–9 ] In addition, recent demonstrations of ultra‐high luminescence in QD‐LEDs and optical cavity‐integrated QD‐LEDs exhibit an expanding territory of QD‐LED device application beyond indoor and mobile displays. [ 14,15 ]…”

“…[ 17,25 ] This is much greater than the typical out‐coupling efficiency of randomly oriented QD‐based LEDs, η out < 25%. [ 8 ] Furthermore, this feature is beneficial for the practical use of QR‐LEDs in the display industry, as one can eliminate a front polarizing film by directly using linearly polarized light from QRs, which reduces manufacturing cost and time.…”

Effects of UV Irradiation and Storage on the Performance of Inverted Red Quantum-Dot Light-Emitting Diodes

“…Quantum-dot light-emitting diodes (QLEDs) are promising large-area electroluminescent devices used for display and solid-state lighting applications, due to their high efficiency, tunable color, high color purity, and simple yet cost-effective solution processibility [ 1 , 2 , 3 ]. In the past few years, the performance of QLEDs has been significantly improved via thorough study of the core/shell structure of QDs [ 4 , 5 ], the surface ligands of QDs [ 6 , 7 ], and device structure engineering [ 8 , 9 ]. The QLEDs with high efficiency and long operational lifetime mainly adopt a multilayer hybrid structure with an organic hole injection/transport layer and an inorganic electron injection/transport layer (ZnO or ZnMgO).…”

“…At present, the peak external quantum efficiency (EQE) of red, green, and blue QLEDs reach 30.9% [ 10 ], 23.9% [ 11 ], and 19.8% [ 12 ], respectively. Meanwhile, the extrapolated T 50 operational lifetime (time taken for the luminance to drop to 50% of the initial luminance of 100 cd/m 2 ) of red and green QLEDs has exceeded 1 million hours [ 5 , 9 , 10 , 13 ].…”