Significant Lifetime Enhancement in QLEDs by Reducing Interfacial Charge Accumulation via Fluorine Incorporation in the ZnO Electron Transport Layer

Chung, Dong Seob; Davidson‐Hall, Tyler; Cotella, Giovanni; Lyu, Quan; Chun, Peter; Aziz, Hany

doi:10.1007/s40820-022-00970-x

Cited by 26 publications

(16 citation statements)

References 73 publications

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“…According to decision tree results, the b 1 values of stable QLED devices are less than 1.55, suggesting a large shunt current resistance ( R shunt ) for stable devices. This conclusion is consistent with the recent reported large R shunt in stable blue and red QLED devices. , In addition, the shunt current of blue QLEDs is higher than those of their red and green counterparts with superlong lifetimes . According to decision tree results, the δ j 2 values of stable QLED devices are more than 0.07.…”

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confidence: 90%

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Machine Learning Assisted Stability Analysis of Blue Quantum Dot Light-Emitting Diodes

Chen

Lin

et al. 2023

Nano Lett.

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The operational stability of the blue quantum dot light-emitting diode (QLED) has been one of the most important obstacles to initialize its industrialization. In this work, we demonstrate a machine learning assisted methodology to illustrate the operational stability of blue QLEDs by analyzing the measurements of over 200 samples (824 QLED devices) including current density–voltage–luminance (J-V-L), impedance spectra (IS), and operational lifetime (T95@1000 cd/m2). The methodology is able to predict the operational lifetime of the QLED with a Pearson correlation coefficient of 0.70 with a convolutional neural network (CNN) model. By applying a classification decision tree analysis of 26 extracted features of J-V-L and IS curves, we illustrate the key features in determining the operational stability. Furthermore, we simulated the device operation using an equivalent circuit model to discuss the device degradation related operational mechanisms.

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confidence: 90%

“…This conclusion is consistent with the recent reported large R shunt in stable blue and red QLED devices. 7,42 In addition, the shunt current of blue QLEDs is higher than those of their red and green counterparts with superlong lifetimes. 43 According to decision tree results, the δj 2 values of stable QLED devices are more than 0.07.…”

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confidence: 99%

Machine Learning Assisted Stability Analysis of Blue Quantum Dot Light-Emitting Diodes

Chen

Lin

et al. 2023

Nano Lett.

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“…22−24 Since in the inverted architecture the ETL is deposited first, annealing it can be easily done without exposing the other layers, which are generally less robust to thermal stress. Though the IQLEDs with a vacuum-deposited HTL can generally have efficiencies and lifetimes comparable to those of their upright counterparts, 25 using solution-coated materials such as polymers as the HTL in the inverted structure remains a major challenge. The ability to use a solution-coated material simplifies the device fabrication process and lowers the fabrication cost.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Though the IQLEDs with a vacuum-deposited HTL can generally have efficiencies and lifetimes comparable to those of their upright counterparts, using solution-coated materials such as polymers as the HTL in the inverted structure remains a major challenge. The ability to use a solution-coated material simplifies the device fabrication process and lowers the fabrication cost.…”

Section: Introductionmentioning

confidence: 99%

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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“…[1][2][3][4][5][6][7][8][9][10][11][12] Progress in QDs synthesis and device architecture engineering to date has led to significant progress in improving the external quantum efficiency (EQE) of QLEDs. [7,[13][14][15][16][17][18] In terms of their electroluminescence (EL) stability, T 50 lifetimes, defined as the time elapsed under electrical bias before the EL intensity of the QLEDs decreases to 50% of the initial value of 100 cd m −2 exceeding 2 300 000 h [14,[19][20] have been demonstrated in red-and greenemitting QLEDs. The EL stability of blue QLEDs however still remains far below that of their red and green counterparts and technology requirements, [16,[21][22][23][24] and continues to be an obstacle for QLEDs commercialization.…”

Section: Introductionmentioning

confidence: 99%

Changes in Hole and Electron Injection under Electrical Stress and the Rapid Electroluminescence Loss in Blue Quantum‐Dot Light‐Emitting Devices

Ghorbani,

Chen,

Chun

et al. 2023

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Blue quantum dot light‐emitting devices (QLEDs) suffer from fast electroluminescence (EL) loss when under electrical bias. Here, it is identified that the fast EL loss in blue QLEDs is not due to a deterioration in the photoluminescence quantum yield of the quantum dots (QDs), contrary to what is commonly believed, but rather arises primarily from changes in charge injection overtime under the bias that leads to a deterioration in charge balance. Measurements on hole‐only and electron‐only devices show that hole injection into blue QDs increases over time whereas electron injection decreases. Results also show that the changes are associated with changes in hole and electron trap densities. The results are further verified using QLEDs with blue and red QDs combinations, capacitance versus voltage, and versus time characteristics of the blue QLEDs. The changes in charge injection are also observed to be partially reversible, and therefore using pulsed current instead of constant current bias for driving the blue QLEDs leads to an almost 2.5× longer lifetime at the same initial luminance. This work systematically investigates the origin of blue QLEDs EL loss and provides insights for designing improved blue QDs paving the way for QLEDs technology commercialization.

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Significant Lifetime Enhancement in QLEDs by Reducing Interfacial Charge Accumulation via Fluorine Incorporation in the ZnO Electron Transport Layer

Cited by 26 publications

References 73 publications

Machine Learning Assisted Stability Analysis of Blue Quantum Dot Light-Emitting Diodes

Machine Learning Assisted Stability Analysis of Blue Quantum Dot Light-Emitting Diodes

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

Changes in Hole and Electron Injection under Electrical Stress and the Rapid Electroluminescence Loss in Blue Quantum‐Dot Light‐Emitting Devices

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