Quantum Dot LEDs: Over 30% External Quantum Efficiency Light‐Emitting Diodes by Engineering Quantum Dot‐Assisted Energy Level Match for Hole Transport Layer (Adv. Funct. Mater. 33/2019)

Song, Jiaojiao; Ouyang, Wei; Shen, Huaibin; Lin, Qingli; Li, Zhaohan; Wang, Lei; Zhang, Xintong; Li, Lin Song

doi:10.1002/adfm.201970226

Cited by 48 publications

(74 citation statements)

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“…When considering the additional light extraction caused by light interference, over 29% out‐coupling efficiency in QLEDs is reasonable. [ 44,45 ] To examine the repeatability, the EQE of 16 QLEDs from different fabrication batches were measured. As shown in Figure 4f, these devices exhibit a mean EQE of 20.63% with a low standard deviation of 0.6, indicating excellent device reproducibility.…”

Section: Resultsmentioning

confidence: 99%

Suppressing Förster Resonance Energy Transfer in Close‐Packed Quantum‐Dot Thin Film: Toward Efficient Quantum‐Dot Light‐Emitting Diodes with External Quantum Efficiency over 21.6%

Zhang

Chen

2020

Advanced Optical Materials

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the presence of Förster resonance energy transfer (FRET) among the close-packed QDs, [19][20][21][22][23][24] which thus limits the efficiency of QD LEDs (QLEDs). FRET is a nonradiative energy transfer process, in which the energy is down-transferred from a fluorescent donor to an acceptor via the dipoledipole coupling if the distance between donor and acceptor is smaller than the transfer radius (typically <10 nm). [24][25][26] In close-packed QD solids, interdot FRET can be very efficient due to the small distance between proximal dots. [25][26][27] Via interdot FRET, excitons therefore can migrate from small dots to nearby large dots, consequently leading to the redshift of the emission spectra. [24,[26][27][28] Along with the redshifted emission, the PL intensity is remarkably decreased, which is caused by the finite probability of nonradiative deactivation whenever an exciton transfers to a new dot with defects. [28] The defective dots function as effective quenching sites that can rapidly quench the excitons of surrounding QDs, leading to the reduction of QY of QD ensembles. Therefore, to improve the PL QY of QD solids, the interdot FRET should be suppressed. Since the FRET rate is very sensitive to the distance between donor and acceptor, [25][26][27]29] we can increase the interdot distance to reduce the FRET rate. This could be realized by tailoring the structure of QDs. For example, by designing giant QDs with thick shell, the devices exhibited an improved performance due to the suppression of interdot FRET. [22,[30][31][32] Alternatively, by embedding the QDs in a polymer matrix, the QDs can be separated spatially, which increases the interdot distance and thereby decreases the interdot FRET. [33][34][35][36][37] However, by physically blending the QDs with polymer, it is difficult to uniformly disperse the QDs within polymer matrix due to phase separation. [33] Recently, by chemically capping the surface of QDs with copolymer, a more homogeneous distribution of QDs is achieved. [34,36] Although increasing the shell thickness or embedding the QDs into a polymer matrix can lead to the suppression of FRET, [22,[30][31][32][33][34] the charge injection and transport are adversely affected by the thick shell or polymer matrix. Therefore, it remains challenging to obtain a device with nearunity internal quantum efficiency (IQE) though QDs with high PL QY of over 90% are routinely reported. Colloidal II-VI quantum dots (QDs) exhibit near-unity photoluminescence (PL) quantum yield (QY) when they are dissolved in dilute solution. However, when they are assembled into thin film, the PL QY is decreased significantly due to the presence of nonradiative Förster resonance energy transfer (FRET) among the close-packed QDs. In this work, the FRET is suppressed by developing a binary-QD light emission layer (EML), where blue-QDs are introduced as spacers to spatially separate the red-QDs. Due to the separation of red-QDs, the FRET among red-QDs is effectively suppressed and thus the emission properties of red-QDs are ...

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Section: Resultsmentioning

confidence: 99%

Suppressing Förster Resonance Energy Transfer in Close‐Packed Quantum‐Dot Thin Film: Toward Efficient Quantum‐Dot Light‐Emitting Diodes with External Quantum Efficiency over 21.6%

Zhang

Chen

2020

Advanced Optical Materials

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“…[ 6,12,13 ] While, most of the pure blue LEDs reported so far, are based on semiconductor quantum dots (QDs). [ 13–22 ] These pure blue light‐emitting diodes involved the traditional QDs (QLEDs) containing heavy metal elements, such as gallium nitride, gallium arsenide, and cadmium sulfide, which are harmful to mankind and the daily environment. [ 23,24 ] It is a great challenge to develop the cost‐effective, environmental‐friendly, low toxic, and highly efficient luminescent materials, as well as, their pure blue LEDs.…”

Section: Introductionmentioning

confidence: 99%

Ultra‐Bright and Stable Pure Blue Light‐Emitting Diode from O, N Co‐Doped Carbon Dots

Wang

et al. 2021

Laser & Photonics Reviews

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The pure blue light‐emitting diodes (LEDs) play a key role in the application of solid display and illumination. Most of pure blue LEDs reported so far, are based on semiconductor quantum dots and metal complex, involving heavy metal elements. Here, the fabrication of O, N co‐doped carbon dots (CDs) by a hydrothermal method from perylene‐3,4,9,10‐tetracarboxylic dianhydride and 2,3‐diaminophenazine is shown. These CDs show strong photoluminescence (PL) emission peaked at 447 nm (in ethanol) with absolute PL quantum yields of 88.9%. They are then doped into poly(vinyl carbazole) to form the active emission layer in the pure blue CDs LEDs. The electroluminescence emission of these CDs LEDs is centered at 452 nm with Commission Internationale d'Eclairage (CIE) coordinates of (0.14, 0.10). Moreover, the pure blue CDs LEDs show a high external quantum efficiency of 2.114%, high brightness of 648 cd m–2, long half‐lifetime (T50) of 200 h, and a favorable current efficiency of 2.2 cd A−1. This work opens a new way to develop cost‐effective, environmental‐friendly, and high‐efficient metal‐free pure blue LEDs.

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“…QDs are usually terminated with long chain ligands such as oleic acid (OA) or oleylamine which hinder CT . This problem can be solved by replacing the long chain ligands with short chain ligands . The functionalized ligands can strengthen the molecular bonds between QDs, improving the QD passivation and stability, and allowing direct chemical bonding to polymer matrices .…”

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

Advanced Optical Materials

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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.

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Quantum Dot LEDs: Over 30% External Quantum Efficiency Light‐Emitting Diodes by Engineering Quantum Dot‐Assisted Energy Level Match for Hole Transport Layer (Adv. Funct. Mater. 33/2019)

Cited by 48 publications

References 0 publications

Suppressing Förster Resonance Energy Transfer in Close‐Packed Quantum‐Dot Thin Film: Toward Efficient Quantum‐Dot Light‐Emitting Diodes with External Quantum Efficiency over 21.6%

Suppressing Förster Resonance Energy Transfer in Close‐Packed Quantum‐Dot Thin Film: Toward Efficient Quantum‐Dot Light‐Emitting Diodes with External Quantum Efficiency over 21.6%

Ultra‐Bright and Stable Pure Blue Light‐Emitting Diode from O, N Co‐Doped Carbon Dots

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

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