High‐Efficiency and Stable Quantum Dot Light‐Emitting Diodes Enabled by a Solution‐Processed Metal‐Doped Nickel Oxide Hole Injection Interfacial Layer

Abstract

Stabilization is one critical issue that needs to be improved for future application of colloidal quantum dot (QD)‐based light‐emitting diodes (QLEDs). This study reports highly efficient and stable QLEDs based on solution‐processsed, metal‐doped nickel oxide films as hole injection layer (HIL). Several kinds of metal dopants (Li, Mg, and Cu) are introduced to improve the hole injection capability of NiO films. The resulting device with Cu:NiO HIL exhibits superior performance compared to the state‐of‐the‐art poly(3,4‐ethylenedioxythiophene):poly(styrene‐sulfonate) (PEDOT:PSS)‐based QLEDs, with a maximum current efficiency and external quantum efficiency of 45.7 cd A−1 and 10.5%, respectively. These are the highest values reported so far for QLEDs with PEDOT:PSS‐free normal structure. Meanwhile, the resulting QLED shows a half‐life time of 87 h at an initial luminance of 5000 cd m−2, almost fourfold longer than that of the PEDOT:PSS‐based device.

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

“…In addition, the HTLs also function as electron blocking layer, and therefore, they should have low LUMO levels to block the excess electrons overflowing from the QDs. Among the reported HTLs, PVK and TFB are the two most widely used HTLs in blue QLEDs due to their strengths of solution‐processable property, deep HOMO level, and high hole mobility …”

“…Recently, colloidal quantum dot (QD) light‐emitting diodes (QLEDs) have been extensively investigated thanks to their unique optical and electrical properties such as high color saturation, tunable emission color, favorable stability, and ease of solution processability. These superiorities make QLEDs promising candidates for new generation display technology . With the rapid development of QD materials and device structures, the performances of red and green devices have been substantially improved; for example, the external quantum efficiencies (EQE) of red and green QLEDs have reached 20.5% and 21% and they have been lately improved from 23.1% to 27.6% by using tandem structures, which are very close to those of organic LEDs (OLEDs) .…”

“…These superiorities make QLEDs promising candidates for new generation display technology. [1][2][3][4][5][6][7][8] With the rapid development of QD materials and device structures, the performances of red and green devices have been substantially improved; for example, the external quantum efficiencies (EQE) of red and green QLEDs have reached 20.5% 1 and 21% 9 and they have been lately improved from 23.1% to 27.6% by using tandem structures, 10 which are very close to those of organic LEDs (OLEDs). 11,12 And blue QLEDs with EQE of 19.8% 13 and 21.4% 10 have also been reported very recently.…”

“…16 To solve these problems, the hole injection should be effectively enhanced by using HTLs with deep-lying HOMO levels and high hole mobility. Among all reported HTLs, poly(9-vinylcarbazole) (PVK) 4,14,[17][18][19] and poly[9,9dioctylfluorene-co-N-(4-(3-methylpropyl))diphenylamine] (TFB) 8,14,20 are the two most widely used materials due to their advantages of deep-lying HOMO levels and high hole mobility, respectively. In this work, we systematically investigate various HTLs and their influence on the performance of blue QLEDs.…”

“…Among the reported HTLs, PVK and TFB are the two most widely used HTLs in blue QLEDs due to their strengths of solution-processable property, deep HOMO level, and high hole mobility. 4,8,14,[17][18][19][20] Figure 2 indicates the effect of different HTLs on the performance of blue QLEDs. With regard to the current density-voltage (J-V) characteristics, devices with TFB exhibit significantly larger current density; for example, at a driving voltage of 6 V, the TFB-devices exhibit a current density of 318.7 mA/cm 2 , which is about threefold higher than 76.4 mA/cm 2 of the PVK-devices.…”