Unraveling the hole injection mechanism of organic/quantum-dot heterointerfaces

Shen, Qi; Sun, Xiaojuan; Chen, Xingtong; Li, Rui; Li, Xinrui; Chen, Song

doi:10.1016/j.device.2023.100061

Cited by 4 publications

(8 citation statements)

References 42 publications

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“…Compared with Figure 1b, one substantial difference is the bending of energy levels at interfaces, which can be ascribed to the electron transfer from the HTL's distributed HOMO states to the electrode during the process of establishing thermal equilibrium. 20 As discussed in the following, this electrostatic phenomenon strongly affects the hole injection barrier.…”

Section: Resultsmentioning

confidence: 98%

“…30 A more recent study that also considers the DOS in HTL suggests an even smaller Δ 2 ′ value because the holes located around the HOMO max of the organic layer contribute to most of the injection current. 20 We used the modified Miller−Abrahams expression to calculate the hopping rate across the HTL/QD interface (see Note S2 for calculation theories). 20 Figures 5a−c showcase the calculated current distributions, J(E), for the three HTL/QD combinations.…”

Section: Resultsmentioning

confidence: 99%

“…20 We used the modified Miller−Abrahams expression to calculate the hopping rate across the HTL/QD interface (see Note S2 for calculation theories). 20 Figures 5a−c showcase the calculated current distributions, J(E), for the three HTL/QD combinations. It is obvious that regardless of the changes in HTL material or carrier density (represented by quasi-Fermi level), the vast majority of injected holes jump from the HOMO max of HTL to QDs.…”

Section: Resultsmentioning

confidence: 99%

“…This has been attributed to the distributed and localized density of states (DOS) in disordered semiconductors. 19,20 In this study, we have explored how the energy levels of the electrodes and HTL materials impact the degradation of blue QLEDs. We studied the voltage change within the emission layer through electroabsorption and monitored QDs' photoluminescence (PL) decay using EL-PL measurements.…”

Section: Introductionmentioning

confidence: 99%

“…Recent studies using the Miller–Abrahams hopping theory pointed out that the HTL/QD hole injection barriers are substantially different from those predicted from the energy levels of isolated materials. This has been attributed to the distributed and localized density of states (DOS) in disordered semiconductors. , …”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Hole-Injection-Barrier Effect on the Degradation of Blue Quantum-Dot Light-Emitting Diodes

Sun,

Chen,

et al. 2024

ACS Nano

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Inefficient hole injection presents a major challenge in achieving stable and commercially viable solution-processed blue electroluminescent devices. Here, we conduct an in-depth study on quantum-dot light-emitting diodes (QLEDs) to understand how the energy levels of common electrodes and hole-transporting layers (HTL) affect device degradation. Our experimental findings reveal a design rule that may seem nonintuitive: combining an electrode and HTL with matched energy levels is most effective in preventing voltage rise and irreversible luminance decay, even though it causes a significant energy offset between the HTL and emissive quantum dots. Using an iterative electrostatic model, we discover that the positive outcomes, including a T 95 lifetime of 109 h (luminance = 1000 nits, CIE-y = 0.087), are due to the enhanced p-type doping in the HTL rather than the assumed reduction in barrier heights. Furthermore, our modified hole injection dynamics theory, which considers distributed density-of-states, shows that the increased HTL/quantum-dot energy offset is not a primary concern because the effective barrier height is significantly lower than conventionally assumed. Following this design rule, we expect device stability to be enhanced considerably.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Hole-Injection-Barrier Effect on the Degradation of Blue Quantum-Dot Light-Emitting Diodes

Sun,

Chen,

et al. 2024

ACS Nano

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Improved Charge Injection Balance in Quantum Dot Light-Emitting Diodes through Interface Texture

Sun,

Chen,

Sun

et al. 2024

J. Phys. Chem. Lett.

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The existing methods to improve the charge balance of quantum dot light-emitting diodes (QLEDs) rely on energy-level matching, but these approaches have been limited by material availability and Fermi-level pinning.Here, we propose a solution that does not require changes to the materials' electronic properties. By using nanoimprinting technology to texture the interface between the hole-transporting layer (HTL) and colloidal quantum dot (CQD) layer, we can increase the HTL−CQD contact area. This significantly enhances the hole injection rate while keeping the electron injection rate essentially unchanged. Compared with the conventional planar structure, QLEDs with textured HTL exhibit lower luminance threshold voltage, significantly higher external quantum efficiency at low bias voltages, improved operational stability, and a similar Lambertian factor. Comprehensive measurements confirm that the HTL−CQD interface texture allows more efficient hole injection into CQDs to occur under lower bias, resulting in less CQD charging and more efficient exciton recombination.

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Diagnosing the Charge Dynamic Behaviors in Quantum-Dot Light-Emitting Diodes by Temperature-Dependent Measurements

Bai,

Liu,

Chi

et al. 2024

J. Phys. Chem. Lett.

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Distinguishing and understanding the nonradiative recombination of charges are crucial for optimizing quantum-dot light-emitting diodes (QLEDs). Auger recombination (AR), a well-known nonradiative process, is widely recognized to occur in QLEDs. However, it has not yet been directly observed in a real working QLED. Here, the AR effect is verified in the QLED at temperatures of <150 K. At low temperatures, the QLED exhibits a unique S-shaped external quantum efficiency (EQE) evolution as the driving current density increases. Experimental and modeling results indicate that this S-shaped EQE results from the asynchronous changes in the behavior of injection of electrons and holes into the quantum-dot emission layer. At low driving voltages, both electron and hole currents are limited by the Fowler−Nordheim (F−N) tunneling behavior. The relatively low barrier for electrons leads to overwhelming electron injection and seriously imbalanced charges in the quantum dots, triggering the AR process. As the voltage increases, the electron current within the emission layer is no longer governed by F−N tunneling but limited by space charges. Then, charge injection becomes balanced, and the EQE increases. These results offer valuable insights into the charge injection and recombination processes within QLEDs, as well as implications for device design.

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Unraveling the hole injection mechanism of organic/quantum-dot heterointerfaces

Cited by 4 publications

References 42 publications

Hole-Injection-Barrier Effect on the Degradation of Blue Quantum-Dot Light-Emitting Diodes

Hole-Injection-Barrier Effect on the Degradation of Blue Quantum-Dot Light-Emitting Diodes

Improved Charge Injection Balance in Quantum Dot Light-Emitting Diodes through Interface Texture

Diagnosing the Charge Dynamic Behaviors in Quantum-Dot Light-Emitting Diodes by Temperature-Dependent Measurements

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