Electronic and Excitonic Processes in Quantum Dot Light-Emitting Diodes

Yu, Pengchao; Yuan, Qilin; Zhao, Jialong; Zhang, Hanzhuang; Ji, Wenyu

doi:10.1021/acs.jpclett.2c00604

Cited by 30 publications

(36 citation statements)

References 43 publications

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“…Transient behaviors of QLEDs have been investigated using a transient electroluminescence (TREL) analysis which is useful to observe complicated processes in QLED operation regarding charge dynamics, exciton formation, and annihilation. [24][25][26][27][28][29][30][31][32][33] For instance, Su et al used the TREL analysis to investigate the charge balance and charge injection efficiency in QLEDs, and then they improved device performance based on their analysis results. [28] Similar works were done to understand charge carrier injection and distribution in QLEDs by analyzing the rising and falling edges of the TREL curves.…”

Section: Doi: 101002/smll202202290mentioning

confidence: 99%

Transient Dynamics of Charges and Excitons in Quantum Dot Light‐Emitting Diodes

Kim

Hahm

Bae

et al. 2022

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Wide interest in quantum dot (QD) light‐emitting diodes (QLEDs) for potential application to display devices and light sources has led to their rapid advancement in device performance. Despite such progress, detailed operation mechanisms of QLEDs, which are necessary for the fundamental understanding and further improvements, have been still uncertain because of the intricate interaction between charges and excitons in electrical operation. In this work, the transient electroluminescence (TREL) signals of dichromatic QLEDs which are purposely designed to consist of two different color‐emitting QD layers are analyzed. As a result, not only can the charge injection and exciton recombination processes be visualized but the electron mobility of the QD layer can also be estimated. Furthermore, the effects of Förster resonant energy transfer between two QDs and exciton quenching near the QD layer are quantitatively measured in QLED operation. The authors believe that their results based on TREL analyses will contribute to the understanding and development of high‐performance QLEDs.

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Section: Doi: 101002/smll202202290mentioning

confidence: 99%

Transient Dynamics of Charges and Excitons in Quantum Dot Light‐Emitting Diodes

Kim

Hahm

Bae

et al. 2022

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“…34 On the other hand, Yu et al reported a larger EL overshoot with TiO 2 compared to ZnO as ETL. 43 They attributed the larger overshoot to less efficient electron injection with TiO 2 which can lead to larger hole population in the QD film, allowing Auger recombination via positive trions to be more feasible and therefore more nonradiative overall. If the application of negative offset voltage introduces holes into the QD film and causes the overshoot, an initial reduction in EL can be expected.…”

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confidence: 99%

“…Figure c shows the EL rise region for different V D , where both t d and t r decrease with increasing V D . Rigorous modeling of TrEL requires consideration of many complicating factors and progress is being made by modifying the Langevin model employed in OLEDs, , but many of the necessary parameters are not known and simulations become difficult with increasing number of QD layers. , For a simple and intuitive understanding of V D dependence of t d , we consider the following. Assuming a linear potential drop across the device, t d can be estimated from the drift velocity equation ( v⃗ = μ E⃗ ): − t normald = d 2 μ · V normalD where d is the distance carriers traverse and μ is the carrier mobility.…”

mentioning

confidence: 99%

“…In the case of ETL composition affecting EL overshoot near the rise region, Kim et al have attributed this effect to the buildup of electrons at the ETL/QD EML interface . On the other hand, Yu et al reported a larger EL overshoot with TiO 2 compared to ZnO as ETL . They attributed the larger overshoot to less efficient electron injection with TiO 2 which can lead to larger hole population in the QD film, allowing Auger recombination via positive trions to be more feasible and therefore more nonradiative overall.…”

mentioning

confidence: 99%

“…Notably, a varying EL spike upon voltage pulse turnoff has been reported with amine-capped QDs, 59 and a varying degree of overshoot near the EL rise region has been observed with different ETL materials. 34,43 The EL spike near the fall region has been attributed to charge trapping on the surface of the QDs by amine ligands. These charges on the QD surface accumulate during the driving voltage pulse and are released upon removal of the voltage, leading to additional carriers for radiative recombination.…”

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confidence: 99%

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Charging and Charged Species in Quantum Dot Light-Emitting Diodes

et al. 2022

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Despite recent rapid advances in improving quantum dot light-emitting diodes, many fundamental aspects of the device operating mechanism remain unresolved. Through transient electroluminescence and time-resolved photoluminescence measurements, the effects of offset voltage on charging and charge transport are examined. First, capacitive charging occurs with a time constant of ∼500 ns, followed by electron transport through quantum dots with a mobility of ∼10–5 cm2 V–1 s–1. Hole injection then initiates an electroluminescence rise that is independent of offset voltage. The photoluminescence lifetime is also unaffected by the offset voltage, indicating no injection of charges into the quantum dots or on their surfaces prior to the voltage pulse. A slower equilibration to steady-state electroluminescence is dependent on the offset voltage, indicative of another charging process. Elemental mapping shows that ZnO deposition from solution can lead to the diffusion of charged species into the quantum dot layer, which may cause the slower process.

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Ultralow Roll‐Off Quantum Dot Light‐Emitting Diodes Using Engineered Carrier Injection Layer

Liao,

Mallem,

Prodanov

et al. 2023

Advanced Materials

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Quantum dot light‐emitting diodes (QLED) have attracted extensive attention due to their high color purity, solution‐processability, and high brightness. Due to extensive efforts, the external quantum efficiency (EQE) of QLED has approached the theoretical limit. However, because of the efficiency roll‐off, the high EQE can only be achieved at relatively low luminance, hindering their application in high‐brightness devices such as near‐to‐eye displays and lighting applications. Here, we report an ultralow roll‐off QLEDs that is achieved by simultaneously blocking electron leakage and enhancing the hole injection, thereby shifting the recombination zone back to the emitting quantum dots (QDs) layer. These devices maintain EQE over 20.6% up to 1000 mA·cm−2 current density, dropping only by ∼5% from the peak EQE of 21.6%, which is the highest value ever reported for the bottom‐emitting red QLEDs. Furthermore, the maximum luminance of the optimal device reached 320,000 cd·m−2, 2.7 times higher than the control device (Lmax: 128,000 cd·m−2). We also demonstrated a passive matrix QLED display panel with high brightness based on the optimized device structure. The proposed approach advances the potential of QLEDs to operate efficiently in high‐brightness scenarios.This article is protected by copyright. All rights reserved

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Electronic and Excitonic Processes in Quantum Dot Light-Emitting Diodes

Cited by 30 publications

References 43 publications

Transient Dynamics of Charges and Excitons in Quantum Dot Light‐Emitting Diodes

Transient Dynamics of Charges and Excitons in Quantum Dot Light‐Emitting Diodes

Charging and Charged Species in Quantum Dot Light-Emitting Diodes

Ultralow Roll‐Off Quantum Dot Light‐Emitting Diodes Using Engineered Carrier Injection Layer

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