Double-type-I charge-injection heterostructure for quantum-dot light-emitting diodes

Wang, Lixi; Tang, Cindy G.; Tan, Zhao-Siu; Phua, Hao-Yu; Chen, Jing; Lei, Wei; Png, Rui‐Qi; Chua, Lay‐Lay; Ho, Peter K. H.

doi:10.1039/d1mh00859e

Cited by 10 publications

(7 citation statements)

References 61 publications

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“…This conclusion is somewhat counterintuitive since it is generally assumed that QDs with wider band gaps will have deeper valence bands which would make hole injection into them more difficult. This observation is however consistent with some recent reports. , Such observation suggests that using QDs with wider band gaps relative to those in the QDs-EMLs as ILs in QLEDs may indeed facilitate hole injection into these QDs-EMLs.…”

Section: Results and Discussionsupporting

confidence: 93%

“…This observation is however consistent with some recent reports. 39,40 Such observation suggests that using QDs with wider band gaps relative to those in the QDs-EMLs as ILs in QLEDs may indeed facilitate hole injection into these QDs-EMLs. Therefore, to investigate this effect further, HODs with R-QDs layers that further contain B-QDs or G-QDs-ILs on either side of the R-QDs layers (i.e.…”

Section: ■ Results and Discussionmentioning

confidence: 97%

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Inverted Solution-Processed Quantum Dot Light-Emitting Devices with Wide Band Gap Quantum Dot Interlayers

Azadinia

Davidson‐Hall

Chung

et al. 2023

ACS Appl. Mater. Interfaces

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Despite its benefits for facilitating device fabrication, utilization of a polymeric hole transport layer (HTL) in inverted quantum dots (QDs) light-emitting devices (IQLEDs) often leads to poor device performance. In this work, we find that the poor performance arises primarily from electron leakage, inefficient charge injection, and significant exciton quenching at the HTL interface in the inverted architecture and not due to solvent damage effects as is widely believed. We also find that using a layer of wider band gap QDs as an interlayer (IL) in between the HTL and the main QDs' emission material layer (EML) can facilitate hole injection, suppress electron leakage, and reduce exciton quenching, effectively mitigating the poor interface effects and resulting in high electroluminescence performance. Using an IL in IQLEDs with a solution-processed poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) (TFB), HTL improves the efficiency by 2.85× (from 3 to 8.56%) and prolongs the lifetime by 9.4× (from 1266 to 11,950 h at 100 cd/m 2 ), which, to the best of our knowledge, is the longest lifetime for an R-IQLED with a solution-coated HTL. Measurements on single-carrier devices reveal that while electron injection becomes easier as the band gap of the QDs decreases, hole injection surprisingly becomes more difficult, indicating that EMLs of QLEDs are more electron-rich in the case of red devices and more hole-rich in the case of blue devices. Ultraviolet photoelectron spectroscopy measurements verify that blue QDs have a shallower valence band energy than their red counterparts, corroborating these conclusions. The findings in this work, therefore, provide not only a simple approach for achieving high performance in IQLEDs with solution-coated HTLs but also novel insights into charge injection and its dependence on QDs' band gap as well as into different HTL interface properties of the inverted versus upright architecture.

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Section: Results and Discussionsupporting

confidence: 93%

Section: ■ Results and Discussionmentioning

confidence: 97%

Inverted Solution-Processed Quantum Dot Light-Emitting Devices with Wide Band Gap Quantum Dot Interlayers

Azadinia

Davidson‐Hall

Chung

et al. 2023

ACS Appl. Mater. Interfaces

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“…These n-doped polymers have been successfully applied in conventional OLED structures with electron injection from the top electrode. Recently, bottom electron-injecting blue inverted multilayer quantum-dot LEDs have been demonstrated with such n-doped polymers, in which charge confinement is achieved with additional blocking layers 21 . However, it is still unclear if these n-doped polymers can also be successfully applied in inverted OLEDs in the single-layer architecture without charge-transport or confinement layers.…”

Section: Introductionmentioning

confidence: 99%

Inverted device architecture for high efficiency single-layer organic light-emitting diodes with imbalanced charge transport

Tan,

Dou,

Chua

et al. 2024

Nat Commun

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Many wide-gap organic semiconductors exhibit imbalanced electron and hole transport, therefore efficient organic light-emitting diodes require a multilayer architecture of electron- and hole-transport materials to confine charge recombination to the emissive layer. Here, we show that even for emitters with imbalanced charge transport, it is possible to obtain highly efficient single-layer organic light emitting diodes (OLEDs), without the need for additional charge-transport and blocking layers. For hole-dominated emitters, an inverted single-layer device architecture with ohmic bottom-electron and top-hole contacts moves the emission zone away from the metal top electrode, thereby more than doubling the optical outcoupling efficiency. Finally, a blue-emitting inverted single-layer OLED based on thermally activated delayed fluorescence is achieved, exhibiting a high external quantum efficiency of 19% with little roll-off at high brightness, demonstrating that balanced charge transport is not a prerequisite for highly efficient single-layer OLEDs.

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“…[ 3c,10 ] Type‐I band alignment based vdWs heterostructures are used for numerous photoelectronic devices such as light‐emitting diodes, because type‐I band alignment provides the best efficiency and illumination intensity in optoelectronic devices. [ 11 ] Type‐II band alignment offers tremendous photoelectronic properties such as rapid carrier charge excitation at the surface of vdWs heterostructure, bandgap tuning, and much more that have potential applications for developing photovoltaic and photoconduction‐based optoelectronic devices. [ 12 ] Type‐III band alignment based vdWs heterostructures are usually employed for designing the tunneling field effect transistors, tunnel diodes Esaki diodes, etc.…”

Section: Introductionmentioning

confidence: 99%

Progress and Insight of Van der Waals Heterostructures Containing Interlayer Transition for Near Infrared Photodetectors

Ahmad

Peng

Khan

et al. 2023

Adv Funct Materials

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Van der Waals (vdWs) heterostructures enable bandgap engineering of different 2D materials to realize the interlayer transition via type‐II band alignment leading to broaden spectrum that is beyond the cut‐off wavelength of individual 2D materials. Interlayer transition has a significant effect on the optoelectronic performance of vdWs heterostructure devices, and strong interlayer transition in 2D vdWs heterojunction is always demandable for sufficient charge transfer and rapid speed response. Herein, a state‐of‐the‐art review is presented on recent progress on interlayer transition in vdWs heterostructures for near‐infrared (NIR) photodetectors. First, the general synthesis techniques for vdWs heterostructures, band alignments in the vdWs heterostructures are provided. Then, the mechanism of interlayer transition in vdWs heterostructure and recent progress on interlayer transition in vdWs heterostructures for NIR photodetectors are summarized. Afterward, some worthy applications of NIR photodetectors are reviewed in related areas of this topic. At the last, an outlook, challenges, and future research directions of vdWs heterostructures for photodetectors at broaden response spectrum are presented.

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Double-type-I charge-injection heterostructure for quantum-dot light-emitting diodes

Abstract: Enforcing balanced electron–hole injection into the emitter layer of quantum-dot light-emitting diodes through a double-type-I heterostructure using polymer semiconductors maximizes the quantum efficiency over a wide current density range.

Cited by 10 publications

References 61 publications

Inverted Solution-Processed Quantum Dot Light-Emitting Devices with Wide Band Gap Quantum Dot Interlayers

Inverted Solution-Processed Quantum Dot Light-Emitting Devices with Wide Band Gap Quantum Dot Interlayers

Inverted device architecture for high efficiency single-layer organic light-emitting diodes with imbalanced charge transport

Progress and Insight of Van der Waals Heterostructures Containing Interlayer Transition for Near Infrared Photodetectors

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