Charge balance control of quantum dot light emitting diodes with atomic layer deposited aluminum oxide interlayers

Jin, Hoseok; Moon, Hyungseok; Lee, Woosuk; Hwangbo, Hyeok; Yong, Sang Heon; Chung, Ho Kyoon; Chae, Heeyeop

doi:10.1039/c9ra00145j

Cited by 33 publications

(15 citation statements)

References 38 publications

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“…depends on the efficiency of radiative recombination of excitons inside the QD active layer and proper balancing of the incoming electron and hole fluxes. This balancing can be achieved by using appropriate materials which have energy levels matching those of QDs, or by modulation of the electron and hole mobilities inside the device using charge carrier blocking layers 5,9,52,53 . In this study, we investigated a series of QLEDs with ETLs based on doped ZnO NPs with the structure ITO/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS)/ poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (poly-TPD)/poly(9-vinlycarbazole) (PVK)/QDs/ (Li,Mg,Al,Ga)ZnO NPs/Al.…”

Section: Performance Of Qleds With Doped and Undoped Zno Etls The Inmentioning

confidence: 99%

Al-, Ga-, Mg-, or Li-doped zinc oxide nanoparticles as electron transport layers for quantum dot light-emitting diodes

Alexandrov

Zvaigzne

Lypenko

et al. 2020

Sci Rep

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layers, which limited the injection of charge carriers, particularly electrons, into the emissive QD layer. Thus, replacement of the organic charge transport layers with inorganic materials seemed to be the solution. As it was reported 12 , the use of zinc tin oxide for an n-type charge transport layer and nickel oxide for a p-type one led to a higher current density in QLEDs, reaching 4 A/cm 2. However, because of the considerable energy barrier between NiO and QDs, the device suffered from an insufficient hole injection rate and, hence, had an EQE lower than 0.1%. Then, engineering of hybrid devices with an inorganic ETL and an organic HTL became the main direction of QLED evolution, which continues to the present day 4,13,14. Although early studies reported the use of various inorganic oxides and chalcogenides as electron-transport materials 15 , ZnO has been proved to be the most favorable ETL material due to its high transparency, low work function, and high electron mobility 4,5. Formation of ZnO ETLs for QLEDs could be done using different deposition techniques, such as the sol-gel method 16,17 , spray pyrolysis 18,19 , sputtering 20 , etc. Nevertheless, colloidal ZnO NPs have become the most widely used material for QLED ETL due to their optimal electronic structure, simple synthesis, and the possibility of using them as a wet-process-compatible conductive ink 13,21-24. However, in the QLED structure, electron transfer from the QDs to ZnO induced by the energy difference between the conduction band minima (CBM) of these materials often leads to exciton dissociation and significant reduction of the EL efficiency. This mechanism is known as the cause of QD luminescence quenching in various QD-based systems 25-27. In this regard, the possibility to control the CBM energy level of a ZnO-based ETL by doping can be a promising way to optimize the electronic structure and performance of the device. One of the first dopants that was used for this purpose was magnesium (Mg) 8,28,29. Zhang et al. demonstrated a peak EQE of 18.2% and 18.1% for red and green QLEDs employing ZnMgO ETLs, respectively 30. Here, a single-layer ETL consisting of Zn 0.9 Mg 0.1 O NPs, which efficiently suppressed interfacial quenching of QD luminescence, has been used. However, because it was found that the charge transfer rate and QD blinking in the multilayer structures are mostly related to the Fermi levels of metal oxide 31,32 , group-III elements, such as aluminum (Al) 33-35 and gallium (Ga) 7 , became widely used as n-type dopants 36 for fabrication of ZnO ETLs. For instance, the use of ZnO doped with Al (AZO) as the ETL material in solution-processed QLEDs led to a 1.8-fold enhancement of device performance compared with ZnO-based QLEDs 35. The reason for this was effective suppression of spontaneous electron transfer at the interface of QDs and ETL, which was attributed to a decreased work function (WF) and the proper CBM alignment of the electron-transport layer and QDs, both induced by the presence of Al dopants inside the ZnO mat...

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Section: Performance Of Qleds With Doped and Undoped Zno Etls The Inmentioning

confidence: 99%

Al-, Ga-, Mg-, or Li-doped zinc oxide nanoparticles as electron transport layers for quantum dot light-emitting diodes

Alexandrov

Zvaigzne

Lypenko

et al. 2020

Sci Rep

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show abstract

“…At the end, prospects of ALD applications on QDs based devices are discussed from the aspects of ALD materials, process parameters, in-situ characterization and device simulations. 86,88 CdSe/ZnS 61,66,77,87 ZnCdSSe/ZnS 68 CdSe@ZnS/ZnS 63 CdSe/CdS/ZnS 69,71 PbS 56,67,72,78,81,[83][84][85]89 PbSe 55,57,74,79,80 APbX3 60,65,70,75 Sphere 65 Film 57,58,66,69,70,73,74,77 FET 55,62,76,[78][79][80]83,86,88 Solar cell 56,82,84,85 Photodetector 67,…”

Section: (Iii) and (Iv)mentioning

confidence: 99%

“…Chae et al achieved charge balance control by employing 1.0 nm thick Al 2 O 3 interlayer as an electron blocking layer to reduce leakage current, suppress the excitons quench-ing and prolong the operation lifetime ( Fig. 6(b)) 63 . The improvement of device performance via the Al 2 O 3 interlayer was attributed to the reduction of electron injection and Auger recombination 68,71 .…”

Section: Interface Engineeringmentioning

confidence: 99%

Atomic layer deposition for quantum dots based devices

Zhou

Liu

Wen

et al. 2020

Opto-Electronic Advances

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Quantum dots (QDs) are promising candidates for the next-generation optical and electronic devices due to the outstanding photoluminance efficiency, tunable bandgap and facile solution synthesis. Nevertheless, the limited optoelectronic performance and poor lifetime of QDs devices hinder their further applications. As a gas-phase surface treatment method, atomic layer deposition (ALD) has shown the potential in QDs surface modification and device construction owing to the atomic-level control and excellent uniformity/conformality. In this perspective, the attempts to utilize ALD techniques in QDs modification to improve the photoluminance efficiency, stability, carrier mobility, as well as interfacial carrier utilization are introduced. ALD proves to be successful in the photoluminance quantum yield (PLQY) enhancement due to the elimination of QDs surface dangling bonds and defects. The QDs stability and devices lifetime are improved greatly through the introduction of ALD barrier layers. Furthermore, the carrier transport is ameliorated efficiently by infilling interstitial spaces during ALD process. Attributed to the ultra-thin and dense coating on the interface, the improvement on optoelectronic performance is achieved. Finally, the challenges of ALD applications in QDs at present and several prospects including ALD process optimization, in-situ characterization and computational simulations are proposed.

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“…Another approach is to insert an EBL between the ETL and the QD layer to restrict the flow of electrons. In the framework of this approach, Al 2 O 3 [14] and poly(methyl methacrylate) (PMMA) [15] have been demonstrated to be effective materials for the EBL. However, a thin film of poly (methyl methacrylate) (PMMA) is more often used as an EBL [15,16], because the positions of its energy levels provide a high potential barrier for electron injection into the emitting layer for most types of QDs.…”

Section: Introductionmentioning

confidence: 99%

Optimizing the PMMA Electron-Blocking Layer of Quantum Dot Light-Emitting Diodes

et al. 2021

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Quantum dots (QDs) are promising candidates for producing bright, color-pure, cost-efficient, and long-lasting QD-based light-emitting diodes (QDLEDs). However, one of the significant problems in achieving high efficiency of QDLEDs is the imbalance between the rates of charge-carrier injection into the emissive QD layer and their transport through the device components. Here we investigated the effect of the parameters of the deposition of a poly (methyl methacrylate) (PMMA) electron-blocking layer (EBL), such as PMMA solution concentration, on the characteristics of EBL-enhanced QDLEDs. A series of devices was fabricated with the PMMA layer formed from acetone solutions with concentrations ranging from 0.05 to 1.2 mg/mL. The addition of the PMMA layer allowed for an increase of the maximum luminance of QDLED by a factor of four compared to the control device without EBL, that is, to 18,671 cd/m2, with the current efficiency increased by an order of magnitude and the turn-on voltage decreased by ~1 V. At the same time, we have demonstrated that each particular QDLED characteristic has a maximum at a specific PMMA layer thickness; therefore, variation of the EBL deposition conditions could serve as an additional parameter space when other QDLED optimization approaches are being developed or implied in future solid-state lighting and display devices.

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Charge balance control of quantum dot light emitting diodes with atomic layer deposited aluminum oxide interlayers

Abstract: We developed a 1.0 nm thick aluminum oxide (Al2O3) interlayer as an electron blocking layer to reduce leakage current and suppress exciton quenching induced by charge imbalance in inverted quantum dot light emitting diodes (QLEDs).

Cited by 33 publications

References 38 publications

Al-, Ga-, Mg-, or Li-doped zinc oxide nanoparticles as electron transport layers for quantum dot light-emitting diodes

Al-, Ga-, Mg-, or Li-doped zinc oxide nanoparticles as electron transport layers for quantum dot light-emitting diodes

Atomic layer deposition for quantum dots based devices

Optimizing the PMMA Electron-Blocking Layer of Quantum Dot Light-Emitting Diodes

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