Optimization of the electron transport in quantum dot light-emitting diodes by codoping ZnO with gallium (Ga) and magnesium (Mg)

Kim, Hong Hee; Kumi, David O.; Kim, Ki Woong; Park, Donghee; Yi, Yeonjin; Cho, So-Hye; Park, Cheolmin; Ntwaeaborwa, O.M.; Choi, Won‐Kook

doi:10.1039/c9ra06976c

Cited by 24 publications

(29 citation statements)

References 28 publications

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“…12,13 Among various dopants, the Mg ion has an ion radius (0.57 Å) comparable to that of the Zn ion (0.60 Å), and the incorporation of Mg ions into ZnO NPs would result in substitutional doping. 14 Indeed, QLEDs using ZnO NPs doped with the Mg ion as the ETL have achieved remarkable success and have reached efficiencies as high as 20.19% 15 and lifetimes of more than 1 720 000 h. 16 Despite the advantages of Zn 1−x Mg x O NPs as the ETL and the achieved efficiency of QLEDs equivalent to that of organic LEDs (OLEDs), 17−20 many challenges still remain in both scientific research and commercial applications. 21 One of the key issues is to control the reproducibility and size uniformity of In this work, we explored a new method to synthesize Zn 1−x Mg x O NPs using the Corning advanced-flow reactor (AFR).…”

Section: ■ Introductionmentioning

confidence: 99%

Finely Controlled Synthesis of Zn_1–xMg_xO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs

Yang

Meng

et al. 2022

ACS Appl. Electron. Mater.

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In this work, we report the finely controlled synthesis of Zn 1−x Mg x O nanoparticles (NPs) by a Corning advanced-flow reactor (AFR), which produced a uniform size distribution with 75% NPs in the range 3−4 nm with good reproducibility. The Zn 1−x Mg x O NPs have been applied as an electron transport layer (ETL) in red quantum light-emitting diodes (QLEDs). Different from the traditional method of one-pot synthesis which needs several hours to finish a synthetic cycle, the synthesis by AFR is much faster due to the fast heat and mass transport in the reaction chamber, and a typical synthetic cycle in the AFR needs only a few minutes. Optical properties of the NPs indicate that the Mg ion that substitutes the Zn ion in the ZnO matrix is almost linear with the doping concentration in the solution, which is consistent with the first-principles calculations. The Zn 1−x Mg x O NPs synthesized with the AFR were subsequently used as the ETL in fabricating red QLEDs, and the resultant performance exceeded that of the device based on the traditional one-pot synthesized NPs. For example, the external quantum efficiency, current efficiency, and power efficiency improved by 25.1%, 21.6%, and 26.9%, respectively. Moreover, better luminescence uniformity was observed in the QLED using the ZnMgO NPs synthesized with the AFR. The device reached an optimal performance when x is 15% in Zn 1−x Mg x O. The finely controlled synthesis of stable Zn 1−x Mg x O NPs has the potential in industry application to solve the critical issues of ETLs that impede progress in the mass production of QLEDs.

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Section: ■ Introductionmentioning

confidence: 99%

Finely Controlled Synthesis of Zn_1–xMg_xO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs

Yang

Meng

et al. 2022

ACS Appl. Electron. Mater.

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“…ZnO ETL-based QLEDs rapidly reached high performance with an external quantum efficiency (EQE) of 20% and lifetimes (>10 5 h at 100 cd/m 2 ) comparable to those of state-of-the-art OLEDs [7]. Besides ZnO QDs, a co-doped type of Zn (Ga, Mg)O QDs [8,9], as well as hybrid types of ZnO@TiO 2 [10], core-shell QDs were adopted as ETL to improve the performance of CdSe/CdS-based QLEDs. The hybrid type of ZnO@SnO 2 [4] was also used to improve the efficiency of inorganic perovskite solar cells.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Luminance of CdSe/ZnS Quantum Dots Light-Emitting Diodes Using ZnO-Oleic Acid/ZnO Quantum Dots Double Electron Transport Layer

et al. 2022

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The widely used ZnO quantum dots (QDs) as an electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) have one drawback. That the balancing of electrons and holes has not been effectively exploited due to the low hole blocking potential difference between the valence band (VB) (6.38 eV) of ZnO ETL and (6.3 eV) of CdSe/ZnS QDs. In this study, ZnO QDs chemically reacted with capping ligands of oleic acid (OA) to decrease the work function of 3.15 eV for ZnO QDs to 2.72~3.08 eV for the ZnO-OA QDs due to the charge transfer from ZnO to OA ligands and improve the efficiency for hole blocking as the VB was increased up to 7.22~7.23 eV. Compared to the QLEDs with a single ZnO QDs ETL, the ZnO-OA/ZnO QDs double ETLs optimize the energy level alignment between ZnO QDs and CdSe/ZnS QDs but also make the surface roughness of ZnO QDs smoother. The optimized glass/ITO/PEDOT:PSS/PVK//CdSe/ZnS//ZnO-OA/ZnO/Ag QLEDs enhances the maximum luminance by 5~9% and current efficiency by 16~35% over the QLEDs with a single ZnO QDs ETL, which can be explained in terms of trap-charge limited current (TCLC) and the Fowler-Nordheim (F-N) tunneling conduction mechanism.

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“…The interlayer suppresses the spontaneous transfer of charge between the QDs and NPs, and its thickness can be tuned to adjust the electron flow and optimize the charge balance. The second idea is to dope the NPs with, for example, Mg, , Ga, , or Al . This widens the band gap of the NPs and lowers the work function, preventing PL quenching.…”

Section: Introductionmentioning

confidence: 99%

ZnO Nanoparticles for Quantum-Dot-Based Light-Emitting Diodes

Moyen

Kim

et al. 2020

ACS Appl. Nano Mater.

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Zinc oxide (ZnO) nanoparticles (NPs) are widely used as electron-transport layers in quantum dots (QDs) light-emitting diodes (QLEDs). In this work, we show that the size of the NPs can be tuned with the sol–gel synthesis temperature while keeping a constant mass yield. As the NP size decreases, the surface defect density reduces and the band gap broadens. In return, it prevents exciton quenching at the ZnO NPs/emitting QDs (core–shell CdSe@ZnS) interface. Moreover, as the conductivity of the ZnO NP films decreases, the electron–hole balance in QLEDs improves. When the synthesis temperature decreases from 60 to 0 °C, the diameter of the NPs shrinks from 5.4 to 2.8 nm. The optical band gap broadens from 3.44 to 3.66 eV and the energy of the minimum of the conduction band increases from −3.81 to −3.64 eV below the Fermi level. Consequently, the radiative decay rate of a CdSe@ZnS QDs layer coated on ZnO NP films increases from 11.62 to 13.75 ns. The smaller NPs exhibit a faceted surface with a lower density of defects. Under UV illumination, the intensity of the band to band emission from the ZnO NPs increases while the emission from defects decreases as the NPs diameter becomes smaller. The conductivity of the ZnO film decreases by more than 1 order of magnitude, and the current efficiency of QLEDs increases from 35.8 to 50.8 cd/A.

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Optimization of the electron transport in quantum dot light-emitting diodes by codoping ZnO with gallium (Ga) and magnesium (Mg)

Abstract: Optimized QD-LEDs are fabricated using Ga–Mg-codoped ZnO NPs as ETL, which reached the LEmax and PEmax at 15.4 cd A−1 and 10.3 lm W−1.

Cited by 24 publications

References 28 publications

Finely Controlled Synthesis of Zn_1–xMg_xO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs

Finely Controlled Synthesis of Zn_1–xMg_xO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs

Enhanced Luminance of CdSe/ZnS Quantum Dots Light-Emitting Diodes Using ZnO-Oleic Acid/ZnO Quantum Dots Double Electron Transport Layer

ZnO Nanoparticles for Quantum-Dot-Based Light-Emitting Diodes

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Optimization of the electron transport in quantum dot light-emitting diodes by codoping ZnO with gallium (Ga) and magnesium (Mg)

Abstract: Optimized QD-LEDs are fabricated using Ga–Mg-codoped ZnO NPs as ETL, which reached the LEmax and PEmax at 15.4 cd A−1 and 10.3 lm W−1.

Cited by 24 publications

References 28 publications

Finely Controlled Synthesis of Zn1–xMgxO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs

Finely Controlled Synthesis of Zn1–xMgxO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs

Enhanced Luminance of CdSe/ZnS Quantum Dots Light-Emitting Diodes Using ZnO-Oleic Acid/ZnO Quantum Dots Double Electron Transport Layer

ZnO Nanoparticles for Quantum-Dot-Based Light-Emitting Diodes

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Product

Resources

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Finely Controlled Synthesis of Zn_1–xMg_xO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs

Finely Controlled Synthesis of Zn_1–xMg_xO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs