The influence of the hole transport layers on the performance of blue and color tunable quantum dot light‐emitting diodes

Abstract

The performance of the blue quantum dot light‐emitting diodes (QLEDs) is largely affected by the hole transport layers (HTLs). As a consequence of the deep valance band level of blue quantum dots (QDs), hole injection is relatively difficult in blue QLEDs. To favor the hole injection, HTLs with high hole mobility and deep‐lying highest occupied molecular orbital level are desired. In this work, various HTLs and their influence on the performance of blue QLEDs are demonstrated. Devices with poly(N‐vinylcarbazole) (PVK) HTL exhibit the highest external quantum efficiency while devices with poly[9,9‐dioctylfluorene‐co‐N‐(4‐(3‐methylpropyl))‐diphenylamine] (TFB) exhibit the lowest driving voltage. By combining the advantages of PVK and TFB, the blue QLEDs with TFB/PVK bilayered HTL simultaneously exhibit a low driving voltage of 2.6 V and a high external quantum efficiency of 5.9%. Moreover, the exciplex emission at the interface of HTL/QDs is also observed, and the emission intensity can be tuned by modulating the hole injection. By utilizing PVK doped with 25% poly(3‐hexylthiophene) (P3HT) as HTL, exciplex emission is significantly enhanced at low driving voltage while QD emission is dominant at high driving voltage. By combining the exciplex emission and the QD emission, the emission color can be effectively tuned from red to blue as the driving voltage changing from 2 to 10 V.

Effect of Air Exposure of ZnMgO Nanoparticle Electron Transport Layer on Efficiency of Quantum-Dot Light-Emitting Diodes

“…However, the external quantum efficiency (EQE) of Cd-based QLEDs is vulnerable to offset between the highest occupied molecular orbital (HOMO) level of TFB and QDs hole level which is particularly high for ZnS-coated QDs . As a result, device performance is very sensitive to the electron accumulation in the QDs layer that leads to a drop of radiative recombination efficiency as a result of Auger processes . Accumulated electrons tend also to leak into the adjacent TFB layer and cause electrochemical reactions deteriorating hole transport in TFB which is essential for device stability …”

“…22 As a result, device performance is very sensitive to the electron accumulation in the QDs layer that leads to a drop of radiative recombination efficiency as a result of Auger processes. 23 Accumulated electrons tend also to leak into the adjacent TFB layer and cause electrochemical reactions deteriorating hole transport in TFB which is essential for device stability. 24 For this reason, it is important to provide a strategy either to minimize the hole injection barrier or to reduce electron injection.…”

Synthesis of UV/blue light-emitting aluminum hydroxide with oxygen vacancy and their application to electrically driven light-emitting diodes

“…, interfacial recombination between organic and inorganic layer due to high injection barrier) that is originated from the recombination transition at the interface between trap states in the emissive layer and BCBP of HTL. 34–37 The J–V–L graph and the luminance pixel photo of the device with Sample-B emissive layer shown in Fig. 5(b) exhibit the turn-on voltage as around 8.2 V and have luminance up to 133.49 cd m −2 .…”

Significant Enhancement in Quantum Dot Light-Emitting Device Stability via a Cascading Hole Transport Layer

“…Using this approach, we have obtained a LT50 of 864,000 h (for a L 0 of 100 cd m –2 ) for red QDLEDs using a conventional core/shell QD emitter while also increasing the EQE to 11.1% compared to a device utilizing CBP alone as the HTL. Although there have been several reports of bilayer stepwise HTLs that demonstrate improvements in QDLED performance, ,,,− we have found that a three-layer CHTL utilizing CBP, tris­(4-carbazoyl-9-ylphenyl)­amine (TCTA), and N , N ′-bis­(naphthalen-1-yl)- N , N ′-bis­(phenyl)­benzidine (NPB) allows for fine control over hole accumulation and electron–hole recombination in QDLEDs. To the best of our knowledge, this represents the longest LT50 for QDLEDs utilizing conventional core/shell QDs, suggesting that further stability enhancements may be possible if graded core/shell QDs are used in this QDLED architecture.…”