Visible quantum dot light-emitting diodes with simultaneous high brightness and efficiency

Thiophenol derivatives having a negative dipole moment such as thiophenol (TP), 4‐methylthiophenol (4‐MTP), and 4‐(dimethylamino)thiophenol (4‐DMATP) are incorporated into quantum dots (QDs) and the efficiency of all‐solution‐processed inverted‐structure quantum dot light‐emitting diodes (QLEDs) is enhanced. The negative dipole moments of TP, 4‐MTP, and 4‐DMATP are attributed to the enhancement of the efficiency of the QLEDs. The valence band maximum (VBM) of the QDs is upshifted, and the energy gap between the VBM and the highest molecular orbital level of the hole transport layer is reduced to −0.16 from 0.46 eV by the negative dipole moment of thiophenol derivatives. The electron and hole transport of the QDs are accelerated, and charge balance is achieved at 5 V with a reduction of 1.25 V by the thiophenol derivatives. The QLEDs with 4‐DMATP exhibit a maximum luminance of 106 400 cd m−2, a maximum current efficiency of 98.2 cd A−1, and an external quantum efficiency (EQE) of 24.8%. The EQE of 24.8% is the highest value reported thus far for all‐solution‐processed inverted‐structure single‐device QLEDs, to the best of knowledge. Improvement by factors of 2.99, 1.57, and 1.54 are achieved in the maximum luminescence, maximum current efficiency, and EQE respectively, compared with a QLED with OA ligands.

Section: Key Characteristics Of the All‐solution‐processed Inverted‐smentioning

confidence: 99%

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

Moon

Chae

2019

“…Micro‐LED displays bring the stability and brightness of inorganic semiconductors to higher‐resolution displays, but the necessity of handling microscale semiconductor components implies fabrication challenges and limits flexibility in display design. An alternative route is the printing of quantum dot light‐emitting diodes (QLEDs) from particle dispersion: quantum dots (QDs) that individually emit light are deposited in suitable stacks in order to create displays . The QDs are composed of inorganic semiconductors and thus potentially more stable and brighter than organic semiconductors.…”

Section: Introductionmentioning

confidence: 99%

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

Yang

Zhang

Kang

et al. 2019

189

122

The direct printing of microscale quantum dot light‐emitting diodes (QLEDs) is a cost‐effective alternative to the placement of pre‐formed LEDs. The quality of printed QLEDs currently is limited by nonuniformities in droplet formation, wetting, and drying during inkjet printing. Here, optimal ink formulation which can suppress nonuniformities at the pixel and array levels is demonstrated. A solvent mixture is used to tune the ejected droplet size, ensure wetting, and provoke Marangoni flows that prevent coffee stain rings. Arrays of green QLED devices are printed at a resolution of 500 pixels in.−1 with a maximum luminance of ≈3000 cd m−2 and a peak current efficiency of 2.8 cd A−1. The resulting array quality is sufficient to print displays at state‐of‐the‐art resolutions.

“…Since the first demonstration of QD‐based light‐emitting diodes (QLEDs) in 1994, device performance has been steadily improved to meet the requirements for low brightness displays (indoor displays). The luminance, external quantum efficiency (EQE), and even operation lifetime of QLEDs is now comparable to that of state‐of‐the‐art organic LEDs (OLEDs) . However, the short operation lifetime under high brightness still limits the application of QLEDs in outdoor displays and lighting.…”

Section: Introductionmentioning

confidence: 99%

Quantum‐Dot Light‐Emitting Diodes for Outdoor Displays with High Stability at High Brightness

Lin

Song

et al. 2019

Self Cite

105

Quantum dot light‐emitting diodes (QLEDs) are considered to be the candidate light sources with the most potential for applications in displays. Recent advances in luminance, external quantum efficiency (EQE), and even the operation lifetime of QLEDs have already satisfied the requirements for low‐light‐level displays. However, the short operation lifetime under high brightness limits the application of QLEDs for outdoor displays and lightings. Here, demonstrated are green QLEDs with a T95 operation lifetime reaching up to 2500 h at high brightness (1000 cd m−2) with a high peak EQE of 23.9%, current efficiency of 100.5 cd A−1, and low efficiency roll‐off at high current. Both the EQE and lifetime of the QLEDs are superior to those reported to date for all solution‐processed green QLEDs. These major advances are qualitatively attributed to the use of a shell‐tailoring strategy for producing compositional graded CdZnSe/ZnSe/ZnSeS/ZnS quantum dots with a high photoluminescence quantum yield, suppressed nonradiative Förster resonant energy transfer and Auger recombination, and favorable valence band alignment for enhanced hole injection. Collectively, this work represents a huge step forward in eventually realizing QLEDs for high‐brightness display and lighting applications.