Highly efficient and stable blue quantum-dot light-emitting diodes based on polyfluorenes with carbazole pendent groups as hole-transporting materials

Gao, Peili; Wang, Jianbo; Wang, Lunhui; Wang, Dan; Peng, Wen Yu; Zou, Shu-Hua; Mo, Yueqi; Zhang, Yong

doi:10.1016/j.orgel.2021.106138

Cited by 14 publications

(9 citation statements)

References 46 publications

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“…Figure a shows the solution-processed QLEDs in a structure of glass/ITO/PEDOT:PSS (40 nm)/ x wt % DPPE:PVK (40 nm)/blue CdSe/CdS/ZnS QDs (30 nm)/ZnO (40 nm)/Al (100 nm), along with the chemical structure of PVK and DPPE. Additionally, Figure b provides the energy diagrams of the materials used to construct the blue QLEDs. − Compared to the HOMO energy level of PVK defined as 5.70 eV, the HOMO energy level of DPPE and 4 wt % DPPE:PVK can be calculated as 5.63 and 5.80 eV, respectively, using ultraviolet photoelectron spectroscopy (UPS) (Figure S1). − In addition, the lowest unoccupied molecular orbital (LUMO) energy level can be determined and calculated by UV–visible microscopy (Figure S2) as 2.00 eV in DPPE and 2.17 eV in 4 wt % DPPE:PVK .…”

Section: Resultsmentioning

confidence: 99%

Enhanced Performance and High Resistance to Efficiency Degradation of Blue Quantum-Dot Light-Emitting Diodes Using the Lewis Base Blended Hole-Transporting Layers

Liu,

Yan,

Shu

et al. 2023

ACS Appl. Mater. Interfaces

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The distinctive characteristics of blue quantum dots (QDs) such as their deep valence band and large bandgap give rise to an elevated hole injection barrier between the hole transport layers (HTLs) and the QD active layer. This results in an imbalance of carrier transport and injection across the device, leading to a degrading performance in QD light-emitting diodes (QLEDs). In this paper, high-efficiency and low-efficiency degradation blue CdSe/ CdS/ZnS QLEDs were fabricated by using the Lewis base, 1,2bis(diphenylphosphino)ethane (DPPE), blended with poly(9-vinylcarbazole) (PVK) (DPPE:PVK) as HTLs. The device performance of blue QLEDs can be finely adjusted by manipulating the blending ratio between DPPE and PVK. When 4 wt % DPPE was blended with PVK (4 wt % DPPE:PVK) as the HTL, the device achieved its optimal performance. Compared to the device with neat PVK as the HTL, the turn-on voltage of blue QLEDs with the 4 wt % DPPE:PVK HTL is reduced from 3.21 to 2.9 V. The maximum current efficiency (CE) and external quantum efficiency (EQE) of blue QLEDs increase from 2.92 cd A −1 and 5.89% in neat PVK to 5.75 cd A −1 and 11.75% for the 4 wt % DPPE:PVK HTL. Furthermore, the QLEDs incorporating DPPE:PVK HTLs exhibited exceptional resistance to efficiency degradation (EQE = 8.83%@L = 12,000 cd m −2 for 4 wt % DPPE:PVK as the HTL and EQE = 2.80%@L = 12,000 cd m −2 for neat PVK as the HTL). A more in-depth analysis reveals that enhanced device performance results from the chelating and bridging effect of the bidentate ligand Lewis base DPPE. These effects strengthen the binding of free metal ions in the blue QDs, reduce the charge barriers, enhance the contact between the HTLs and the QD active layer, and ultimately improve hole injection.

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Section: Resultsmentioning

confidence: 99%

Enhanced Performance and High Resistance to Efficiency Degradation of Blue Quantum-Dot Light-Emitting Diodes Using the Lewis Base Blended Hole-Transporting Layers

Liu,

Yan,

Shu

et al. 2023

ACS Appl. Mater. Interfaces

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“…The target QLED was endowed with a markedly increase of EQE from 7.9% (PVK based) to 12.61% (PFCz based). [6] Tang et al selected 4,4′,4′′-tris(carbazol-9-yl)triphenylamine (TCTA) with deep HOMO energy level as the dopant in TFB to ameliorate the original large energy offset between TFB and blue QDs (1.04 eV). The peak luminance and EQE of the QLEDs reached 34 874 cd m −2 and 10.7% as profited from the reduction of hole injection barrier.…”

Section: Introductionmentioning

confidence: 99%

Constructing Effective Hole Transport Channels in Cross‐Linked Hole Transport Layer by Stacking Discotic Molecules for High Performance Deep Blue QLEDs

Zhang

et al. 2022

Advanced Science

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The inadequate hole injection limits the efficiency and lifetime of the blue quantum dot light‐emitting diodes (QLEDs), which severely hampers their commercial applications. Here a new discotic molecule of 3,6,10,11‐tetrakis(pentyloxy)triphenylene‐2,7‐diyl bis(2,2‐dimethylpropanoate) (T5DP‐2,7) is introduced, in which the hole transport channels with superior hole mobility (2.6 × 10 –2 cm 2 V –1 s –1 ) is formed by stacking. The composite hole transport material (HTM) is prepared by blending T5DP‐2,7 with the cross‐linked 4,4′‐ bis(3‐vinyl‐9H‐carbazol‐9‐yl)‐1,1′biphenyl (CBP‐V) which shows the deep highest occupied molecular orbital energy level. The increased hole mobility of the target composite HTM from 10 –4 to 10 –3 cm 2 V –1 s –1 as well as the stepwise energy levels facilitates the hole transport, which would be beneficial for more balanced carrier injection. This composite hole transport layer (HTL) has improved the deep‐blue‐emission performances of Commission International de I'Eclairage of (0.14, 0.04), luminance of 44080 cd m −2 , and external quantum efficiency of 18.59%. Furthermore, when L 0 is 100 cd m −2 , the device lifetime T 50 is extended from 139 to 502 h. The state‐of‐the‐art performance shows the successful promotion of the high‐efficiency for deep blue QLEDs, and indicates that the optimizing HTL by discotic molecule stacking can serve as an excellent alternative for the development of HTL in the future.

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“…The typical QLED structure is indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/hole transport layer (HTL)/QD/electron transport layer (ETL)/cathode, 16 where polymers 17,18 and metal oxides 6,7,19–21 have been utilized as HTLs and ETLs by spin-coating, respectively. Among them, poly( N -vinylcarbazole) (PVK), widely used as a HTL of QLEDs due to its deep highest occupied molecular orbit (HOMO) energy level, has a low hole mobility of 2.5 × 10 −6 cm 2 V −1 s −1 , which is much lower than the electron mobility of metal oxides, such as ZnO (∼10 −3 cm 2 V −1 S −1 ).…”

Section: Introductionmentioning

confidence: 99%

“…Among them, poly( N -vinylcarbazole) (PVK), widely used as a HTL of QLEDs due to its deep highest occupied molecular orbit (HOMO) energy level, has a low hole mobility of 2.5 × 10 −6 cm 2 V −1 s −1 , which is much lower than the electron mobility of metal oxides, such as ZnO (∼10 −3 cm 2 V −1 S −1 ). 18–21 On the other hand, holes are more difficult to inject into the QD emissive layer than electrons because most QDs have a lower valence band than the HOMO energy level of the HTL. 22 As a result, electrons easily accumulate at the interface of the HTL and the QD active layer, thus making the QDs charged and electrons leak into the HTL without recombination, which can greatly deteriorate the device performance of QLEDs.…”

Section: Introductionmentioning

confidence: 99%

Highly efficient blue quantum-dot light-emitting diodes based on a mixed composite of a carbazole donor and a triazine acceptor as the hole transport layer

Wang

Huang

Liu

et al. 2022

Phys. Chem. Chem. Phys.

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Highly efficient and stable blue quantum-dot light-emitting diodes based on polyfluorenes with carbazole pendent groups as hole-transporting materials

Cited by 14 publications

References 46 publications

Enhanced Performance and High Resistance to Efficiency Degradation of Blue Quantum-Dot Light-Emitting Diodes Using the Lewis Base Blended Hole-Transporting Layers

Enhanced Performance and High Resistance to Efficiency Degradation of Blue Quantum-Dot Light-Emitting Diodes Using the Lewis Base Blended Hole-Transporting Layers

Constructing Effective Hole Transport Channels in Cross‐Linked Hole Transport Layer by Stacking Discotic Molecules for High Performance Deep Blue QLEDs

Highly efficient blue quantum-dot light-emitting diodes based on a mixed composite of a carbazole donor and a triazine acceptor as the hole transport layer

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