Highly Efficient and Super Stable Full‐Color Quantum Dots Light‐Emitting Diodes with Solution‐Processed All‐Inorganic Charge Transport Layers

Abstract

Colloidal quantum dots (QDs) have attracted great attention due to their high quantum efficiency, full color tunability, narrow emission bandwidth, high chemical stability, and High performance and super stable all-inorganic full-color quantum dot lightemitting diodes (QLEDs) are constructed by adopting solution-processed Mgdoped NiO x (Mg-NiO x) nanoparticles as hole transport layer (HTL) and Al-doped ZnO (AZO) as electron transport layer (ETL). Mg-NiO x nanoparticles possess the advantages of low-temperature solution processability, intrinsic stability, and controllable electronic properties. UV-ozone (UVO) treatment is applied to the Mg-NiO x film to modulate its surface composition. By carefully controlling the UVO treating time, favorable energy levels can be achieved to minimize the energy barrier for hole injection. At the cathode side, Al-doping can reduce the conductivity of ZnO ETL and decrease the interface charge transfer, effectively, thus leading to more balanced charge injection and consequent high luminance and efficiency. The maximum luminance and EQE can reach as high as 38 444 cd m −2 and 5.09% for R-QLEDs, 177 825 cd m −2 and 10.1% for G-QLEDs, and 3103 cd m −2 and 2.19% for B-QLEDs. The luminance values are the highest ever reported for all-inorganic QLEDs. Furthermore, the all-inorganic devices show much better resistance to water and oxygen existing in air. The results show that the ion-doped NiO x and AZO nanoparticles would facilitate the design and development of highly efficient and super stable QLEDs.

Steering Interface Dipoles for Bright and Efficient All-Inorganic Quantum Dot Based Light-Emitting Diodes

“…We construct all-inorganic QD-LEDs in a multilayered architecture of ITO//NiO (HTL)//QDs (EML)//ZnMgO (ETL)//Al (Figure ), wherein holes and electrons drift into QDs via a NiO HTL and a ZnMgO ETL, respectively. ,, In particular, in order to change the potential profile across the device, molecular dipole layers are synergistically incorporated (Figure a,b); PF-BT on NiO HTL and DMA-BT ligands on QDs, respectively. In the case of the device without the adoption of molecular dipoles (referred to as the reference device), the hole injection from the NiO HTL into QDs is hindered substantially by a large energy offset between valence band edge energy levels of the NiO HTL and the QD EML ( E offset = 0.7 eV), while the conduction band edge energy level (E CBE ) of the ZnMgO ETL matches well with the lowest quantized state for the conduction band of the QD EML ( E offset = −0.2 eV), allowing for nearly barrier-free injection of electrons into QDs (Supplementary Figure 1).…”

“…Colloidal quantum dot (QD) based light-emitting diodes (QD-LEDs) feature a wide color gamut, characteristic wavelength tunability across the visible to near-infrared range, and lightweight and flexible form factors, providing great opportunities as next-generation light sources. − In the past decade, the efficiency and stability of QD-LEDs have surged by leaps and bounds to meet the requirements for display commercialization. − The envelope has been pushed beyond indoor or low-power displays, as recent advancement in QD-LEDs promises to expand their applications toward outdoor and optical projection-type displays (e.g., augmented reality, virtual reality, or head-up display).…”

“…Although organic HTLs have shown excellent performance in QD-LEDs, their intrinsic instability under joule heat and/or high current density ,, restricts practical light-emitting applications that demand high brightness, such as signages, projection-type displays, or outdoor displays. As an alternative, the use of thermally robust inorganic HTLs have been suggested for the operational stability of QD-LEDs, ,,− especially under high current injection. The device performance with inorganic HTLs, however, is lagging behind compared to conventional QD-LEDs employing hybrid CTLs.…”

“…e ., the peak EQE = 5.5%) . The biggest hurdle in the way of achieving high-performance all-inorganic QD-LEDs comes from the limited materials choice for the transparent inorganic HTL, such as NiO ,,, and W­(PO 4 ) 2 , , which makes it difficult to control the potential profile across the device. Specifically, the significant energy barrier against the holes from the NiO HTL to QDs ( ca .…”

Flexible PDMS/Al2O3 Nanolaminates for the Encapsulation of Blue OLEDs

“…Flexible displays such as organic light-emitting diodes (OLEDs) and quantum dot light-emitting diodes have emerged as the potential candidates for the next-generation displays due to the advantages of light weight, low fabrication cost, low power consumption, and good portability. [1][2][3][4][5] Nevertheless, the emitting materials are easy to be eroded by the oxygen and moisture in the ambient, resulting in the severe degradation of the device performance. Particularly, the blue LEDs would be more of the encapsulation structures, [21,28,29] in which the inorganic layers play the role of the barriers, and the organic layers serve as the defect-decoupling and stress-release layers.…”