Carrier Dynamics in Alloyed Chalcogenide Quantum Dots and Their Light‐Emitting Devices

Li, Zhaohan; Wei, Jing; Wang, Fangfang; Tang, Yanan; Li, Anming; Guo, Yating; Pan, Heng; Brovelli, Sergio; Shen, Huaibin; Li, Hongbo

doi:10.1002/aenm.202101693

Cited by 34 publications

(43 citation statements)

References 179 publications

(225 reference statements)

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“…3a , the curves were fitted well with a double exponential function. In the light of Fermi golden rule, the PL lifetime was in reverse proportion with the overlap of electron and hole functions 43 . As a result, the fast decay process was considered as band-edge emission because of the large overlap of electrons and holes whereas the slow decay process was considered as trap emission 41 , 44 .…”

Section: Resultsmentioning

confidence: 99%

Highly efficient green InP-based quantum dot light-emitting diodes regulated by inner alloyed shell component

Cao

Shan³

et al. 2022

Light Sci Appl

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InP-based quantum dot light-emitting diodes (QLEDs), as less toxic than Cd-free and Pb-free optoelectronic devices, have become the most promising benign alternatives for the next generation lighting and display. However, the development of green-emitting InP-based QLEDs still remains a great challenge to the environmental preparation of InP quantum dots (QDs) and superior device performance. Herein, we reported the highly efficient green-emitting InP-based QLEDs regulated by the inner alloyed shell components. Based on the environmental phosphorus tris(dimethylamino)phosphine ((DMA)3P), we obtained highly efficient InP-based QDs with the narrowest full width at half maximum (~35 nm) and highest quantum yield (~97%) by inserting the gradient inner shell layer ZnSexS1−x without further post-treatment. More importantly, we concretely discussed the effect and physical mechanism of ZnSexS1–x layer on the performance of QDs and QLEDs through the characterization of structure, luminescence, femtosecond transient absorption, and ultraviolet photoelectron spectroscopy. We demonstrated that the insert inner alloyed shell ZnSexS1−x provided bifunctionality, which diminished the interface defects upon balancing the lattice mismatch and tailored the energy levels of InP-based QDs which could promote the balanced carrier injection. The resulting QLEDs applying the InP/ZnSe0.7S0.3/ZnS QDs as an emitter layer exhibited a maximum external quantum efficiency of 15.2% with the electroluminescence peak of 532 nm, which was almost the highest record of InP-based pure green-emitting QLEDs. These results demonstrated the applicability and processability of inner shell component engineering in the preparation of high-quality InP-based QLEDs.

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Section: Resultsmentioning

confidence: 99%

Highly efficient green InP-based quantum dot light-emitting diodes regulated by inner alloyed shell component

Cao

Shan³

et al. 2022

Light Sci Appl

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“…[ 35 ] Therefore, the Cd element mainly distributes inside the inner cores or intermediate shells of QDs in most cases. [ 21 ] Meanwhile, the Zn 2p, Se 3d, S (or Se) 3p and Cd 3d peaks exhibit strong intensities in the XPS spectra, which reveals that Cd, Zn, S and Se are the main elements in these QDs (Figure S5 , Supporting Information). [ 36 ]…”

Section: Resultsmentioning

confidence: 99%

“…[24][25][26] Also, it could be used as an intermediate shell to gradually change the chemical composition of QDs from the inner cores (or shells) to the outside shells, affording these QDs with less lattice mismatch and hence less interface defects. [21,32] Therefore, CdZnS could be used as the outermost shell material to get the red emitting CdZnSe/ZnSe/ZnS/CdZnS (R3) and afford R3 with an excellent nanocrystal quality. [33] In addition, the other red QDs also exhibit a fine core/shell structure and good nanocrystal quality.…”

Section: Morphology and Structure Studies Of Red Qdsmentioning

confidence: 99%

“…[15][16][17] To achieve much more balanced recombination, the general approaches would be to slow down the electron transport and decrease the energy barrier for hole injection at the interface of HTLs/EMLs. [6,[18][19][20][21][22] For example, Peng and co-workers reported an efficient red QLED by inserting an insulating interlayer PMMA (poly(methyl methacrylate)) between the QD EML and the ZnO ETL in 2014. [6] The use of PMMA is to significantly slow down the electron transport and avoid the excitons inside the QD EML from being quenched by ZnO.…”

Section: Introductionmentioning

confidence: 99%

“…It is noted that most of the efficient QLEDs are achieved by using a typical type‐II QD structure, in which the bandgaps of the materials used in QDs are gradually increased from inner cores to outside shells. [ 21 ] It creates a significant barrier for charge injection, especially for holes, although the use of shells with broad bandgaps is to achieve high PLQYs of QDs. [ 19 ] Herein, we develop a new strategy in which CdZnS is used as an outermost shell material to achieve an unconventional type‐II QD structure, which is characterized by the initially increased but then decreased bandgaps from the inside cores to the outside shells (Figure 1b ).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Cadmium‐Doped Zinc Sulfide Shell as a Hole Injection Springboard for Red, Green, and Blue Quantum Dot Light‐Emitting Diodes

Liu

Guo

et al. 2022

Advanced Science

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A new strategy is developed in which cadmium‐doped zinc sulfide (CdZnS) is used as the outermost shell to synthesize red, green, and blue (RGB) quantum dots (QDs) with the core/shell structures of CdZnSe/ZnSe/ZnS/CdZnS, CdZnSe/ZnSe/ZnSeS/CdZnS, and CdZnSe/ZnSeS/ZnS/CdZnS, respectively. Firstly, the inner ZnS and ZnSe shells confine the excitons inside the cores of QDs and provide a better lattice matching with respect to the outermost shell, which ensures high photoluminescence quantum yields of QDs. Secondly, the CdZnS shell affords its QDs with shallow valence bands (VBs). Therefore, the CdZnS shell could be used as a springboard, which decreases the energy barrier for hole injection from polymers to QDs to be below 1.0 eV. It makes the holes to be easily injected into the QD EMLs and enables a balanced recombination of charge carriers in quantum dot light‐emitting diodes (QLEDs). Thirdly, the RGB QLEDs made by these new QDs exhibit peak external quantum efficiencies (EQEs) of 20.2%, 19.2%, and 8.4%, respectively. In addition, the QLEDs exhibit unexpected luminance values at low applied voltages and therefore high power efficiencies. From these results, it is evident that CdZnS could act as an excellent shell and hole injection springboard to afford high performance QLEDs.

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High‐Performance Blue Quantum‐Dot Light‐Emitting Diodes by Alleviating Electron Trapping

Wang

Hua

Lin

et al. 2022

Advanced Optical Materials

Self Cite

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of high-quality QDs, QLEDs have gained huge progress and the performance is comparable with that of state-of-the-art organic light-emitting diodes. Especially, the red and green QLEDs have delivered the external quantum efficiency (EQE) over 20% and operating lifetime up to a few millions of hours. [13,14] Currently, blue QLEDs become the short slab for the QLED-based display technology.The introduction of wide bandgap shells (such as ZnS), which help to confine the charges/excitons to the cores and to passivate various defects, pave the way to high photoluminescence (PL) quantum yields (QYs), and stability for blue QDs. [3,[15][16][17] However, the other side of the coin is that the wide bandgap shells increase the holeinjection barrier inevitably, which is particularly pronounced in blue QLEDs due to the inherently lower valance band (VB) of blue QDs. Therefore, how to improve hole injection or charge balance becomes a core research area for further development of QLEDs. Efficient blue QLEDs with EQE over 16% were achieved by introducing poly(methyl methacrylate) (PMMA) or tert-butyldimethylsilyl chloride-modified poly(p-phenylene benzobisoxazole) (TBS-PBO) to impede the electron injection and improve the charge-injection/transfer balance. [18,19] CNPr-TFB hole transporting polymer has been developed by Wu and co-workers, which exhibits a superior hole conductivity and much more stabilized highest-occupied molecular orbital (HOMO) in comparison with TFB. Therefore, much more holes are delivered into the QD emissive layers when it was used as hole-transport layer (HTL). [20] Currently, Se used throughout ZnCdSe/ZnSe QDs and/or cadmium-doped zinc sulfide (CdZnS) as the outermost shell was proposed, which reduced the hole-injection barrier and enhanced hole injection. Then, the resulted blue QLED achieved outstanding luminance up to 62 600 cd m −2 . However, the EQE of this blue QLED was only 8.5% and/or 8.4%. [14,21] Even though these are optimizing strategies, the performance of blue QLEDs still lags behind that of red and green ones. The fundamental and essential issues in the devices need to be uncovered and resolved. To achieve efficient blue QLEDs, HTLs with low HOMO energy levels are commonly employed to achieve balanced charge injection. To date, poly-N-vinylcarbazole (PVK) is the most popular HTL for the blue QLEDs. [15,19,22] Currently, blue quantum-dot light-emitting diodes (QLEDs) remain the bottleneck limiting the development of QLED-based applications. To achieve high-performance blue QLEDs, poly-N-vinylcarbazole (PVK) is usually employed as the hole-transport layer (HTL) to reduce the hole injection barrier. However, fabrication of efficient blue QLEDs with PVK HTL remains challenging and empirical/accidental. Here, it is demonstrated that PVK layer can trap electrons and hence resulting in low device efficiency. This is why the performance of blue QLEDs is highly dependent on the PVK batch received from the manufacturers. As an interlayer, ZnSe/ZnS quantum dots (QDs) are inserted between PVK and bl...

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Carrier Dynamics in Alloyed Chalcogenide Quantum Dots and Their Light‐Emitting Devices

Cited by 34 publications

References 179 publications

Highly efficient green InP-based quantum dot light-emitting diodes regulated by inner alloyed shell component

Highly efficient green InP-based quantum dot light-emitting diodes regulated by inner alloyed shell component

Cadmium‐Doped Zinc Sulfide Shell as a Hole Injection Springboard for Red, Green, and Blue Quantum Dot Light‐Emitting Diodes

High‐Performance Blue Quantum‐Dot Light‐Emitting Diodes by Alleviating Electron Trapping

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