All-inorganic Quantum Dot Light-emitting Diodes Research Articles

Improvement of the Stability of Quantum-Dot Light Emitting Diodes Using Inorganic HfOx Hole Transport Layer.

One of the major challenges in QLED research is improving the stability of the devices. In this study, we fabricated all inorganic quantum-dot light emitting diodes (QLEDs) using hafnium oxide (HfOx) as the hole transport layer (HTL), a material commonly used for insulator. Oxygen vacancies in HfOx create defect states below the Fermi level, providing a pathway for hole injection. The concentration of these oxygen vacancies can be controlled by the annealing temperature. We optimized the all-inorganic QLEDs with HfOx as the HTL by changing the annealing temperature. The optimized QLEDs with HfOx as the HTL showed a maximum luminance and current efficiency of 66,258 cd/m2 and 9.7 cd/A, respectively. The fabricated all-inorganic QLEDs exhibited remarkable stability, particularly when compared to devices using organic materials for the HTL. Under extended storage in ambient conditions, the all-inorganic device demonstrated a significantly enhanced operating lifetime (T50) of 5.5 h, which is 11 times longer than that of QLEDs using an organic HTL. These results indicate that the all-inorganic QLEDs structure, with ITO/MoO3/HfOx/QDs/ZnMgO/Al, exhibits superior stability compared to organic-inorganic hybrid QLEDs.

Stable and efficient all-inorganic quantum dot light-emitting diodes based on a double-layer electron transport layer

Abstract The most advanced quantum light-emitting diodes (QLEDs) have achieved almost unity external quantum efficiency (EQE) due to organic materials for high transport efficiency, but organic materials are less stable and can lead to irreversible degradation of the devices. The use of stable inorganic hole-transporting layers (HTLs), such as NiOx, becomes a promising alternative. ZnO is a common electron-transporting material in QLEDs, which possesses high mobility and tunable conductivity properties, but ZnO-based QLEDs devices undergo loss of efficiency due to exciton bursting, poor shelf stability, and pronounced positive aging effects. SnO2, as a common electron-transporting material, has better stability than ZnO. In this work, the SnO2/ZnO dual electron transport layer strategy is adopted, which can reduce the non-radiative burst and aging behavior, and at the same time, the electron transport is regulated by adjusting the film thickness. Inorganic QLEDs with high external quantum efficiency (9.5%) as well as high operational stability have been fully realized. This strategy provides effective ideas for future high-performance display devices.

Impact of Alternating-Current Operation on All-Inorganic Quantum Dot Light-Emitting Diodes.

In colloidal quantum dot light-emitting diodes (QD-LEDs), replacing organic hole transport layers (HTLs) with their inorganic counterparts is expected to yield distinct advantages due to their inherent material robustness. However, despite the promising characteristics of all-inorganic QD-LEDs, some challenges persist in achieving stable operation; for example, the electron overflow toward the inorganic HTL and charge accumulation within working devices return a temporal inconsistency in device characteristics. To address these challenges, we propose an operational approach that employs an alternating-current (AC) in all-inorganic QD-LEDs. We carry out comprehensive studies on the optoelectrical characteristics of all-inorganic QD-LEDs under direct-current (DC) or AC operation and demonstrate that AC operation can facilitate efficient charge carrier recombination within the QD emissive layer, leading to improved device efficiency and temporally invariant optoelectronic characteristics. Leveraging the intrinsic material robustness of inorganic charge transport layers (CTLs), our current study suggests a promising pathway toward enhancing the performance and stability of QD-LEDs, particularly for futuristic display applications.

All-inorganic quantum dot light-emitting diodes realizing a synergistically regulated carrier mobility dynamic equilibrium mechanism

All-inorganic quantum dot light-emitting diodes realizing a synergistically regulated carrier mobility dynamic equilibrium mechanism

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

High performance and super stable all-inorganic full-color quantum dot light-emitting diodes (QLEDs) are constructed by adopting solution-processed Mg-doped NiOx (Mg-NiOx ) nanoparticles as hole transport layer (HTL) and Al-doped ZnO (AZO) as electron transport layer (ETL). Mg-NiOx nanoparticles possess the advantages of low-temperature solution processability, intrinsic stability, and controllable electronic properties. UV-ozone (UVO) treatment is applied to the Mg-NiOx 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 38444cd m-2 and 5.09% for R-QLEDs, 177825cd m-2 and 10.1% for G-QLEDs, and 3103cd 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 NiOx and AZO nanoparticles would facilitate the design and development of highly efficient and super stable QLEDs.

Electroluminescent materials toward near ultraviolet region.

Near ultraviolet (NUV) light-emitting materials and devices are significant due to unique applications in anti-counterfeit, manufacturing industries, and hygienic treatments. However, the development of high-efficiency NUV electroluminescent devices encounters great challenges and is far behind their RGB emitter counterparts. Besides the photoluminescence quantum yields (PLQYs) of NUV materials being higher than 40%, charge injection and lopsided carrier transport also determine the device performance, leading to great efforts in optimizing the frontier molecular orbitals to fit the adjacent function layer. In the exploration of NUV materials, organic molecules are one of the primary candidates, given their preparative facility and structural variability. Recently, all-inorganic quantum-dot light-emitting diodes (QLEDs) of Cd-based, ZnSe, graphene and inorganic perovskite emitters and organic-inorganic hybrid lead halide perovskite nanocrystals (NCs) were demonstrated for achieving NUV electroluminescence. Owing to the great efforts devoted to NUV material engineering and device configuration, NUV materials and devices have achieved great advances over the last two decades. In this review, we retrospect the development of NUV materials and devices covering all promising systems, which may inspire the enthusiasm of researchers to explore the huge potential in the NUV region.

Improved Efficiency of All-Inorganic Quantum-Dot Light-Emitting Diodes via Interface Engineering

As the charge transport layer of quantum dot (QD) light-emitting diodes (QLEDs), metal oxides are expected to be more stable compared with organic materials. However, the efficiency of metal oxide-based all-inorganic QLEDs is still far behind that of organic–inorganic hybrid ones. The main reason is the strong interaction between metal oxide and QDs leading to the emission quenching of QDs. Here, we demonstrated nickel oxide (NiOx)-based all-inorganic QLEDs with a maximum current efficiency of 20.4 cd A−1 and external quantum efficiency (EQE) of 5.5%, which is among the most efficient all-inorganic QLEDs. The high efficiency is mainly attributed to the aluminum oxide (Al2O3) deposited at the NiOx/QDs interface to suppress the strong quenching effect of NiOx on the QD emission, together with the molybdenum oxide (MoOx) that reduced the leakage current and facilitated hole injection, more than 300% enhancement was achieved compared with the pristine NiOx-based QLEDs. Our study confirmed the effect of decorating the NiOx/QDs interface on the performance enhancement of the all-inorganic QLEDs.

Performance Enhancement of All-Inorganic Quantum Dot Light-Emitting Diodes via Surface Modification of Nickel Oxide Nanoparticles Hole Transport Layer

All-inorganic quantum dot light-emitting diodes (QLEDs) show promise for advanced lighting and display due to their superior advantage in stability. However, all-inorganic QLEDs suffer from low efficiency because of the exciton quenching and inefficient hole transport from the inorganic hole transport layer (HTL) to QDs. Herein, we demonstrate an efficient all-inorganic QLED with NiO nanoparticles (NPs) HTL modified by 11-mercaptoundecanoic acid (MUA). The MUA can passivate the defects of NiO and suppress the exciton quenching. Moreover, the declined valence band level of modified NiO could facilitate the hole transport, promoting the charge balance. In addition, the surface engineering improves the quality of the NiO film, leading to the decrease of current leakage. As a result, the maximum current efficiency and external quantum efficiency (EQE) of our QLEDs achieve 5.50 cd/A and 1.28%, respectively, exhibiting an enhancement of 4.5- and 1.72-fold, respectively. Meanwhile, the stability of the device is...

All-Inorganic Quantum-Dot Light-Emitting Diodes with Reduced Exciton Quenching by a MgO Decorated Inorganic Hole Transport Layer.

Here, wide-bandgap magnesium oxide (MgO) is employed as a decorator for the nickel oxide (NiO x) hole transport layer (HTL), by means of a bulk dopant as well as a surface modifier. QLEDs with Ni0.88Mg0.12O x serving as the HTL achieve an ∼19.5% efficiency improvement compared to devices using pristine NiO x. Further inserting an ultrathin MgO layer between the Ni0.88Mg0.12O x and QDs to separate the accumulated charges from excitons goes on boosting the peak efficiency by another ∼35%. Finally, a maximum brightness over 40 000 cd/m2 at 10 V is obtained, which is the highest among the reported values.

Influence of Shell Thickness on the Performance of NiO-Based All-Inorganic Quantum Dot Light-Emitting Diodes.

The effect of shell thickness on the performance of all-inorganic quantum dot light-emitting diodes (QLEDs) is explored by employing a series of green quantum dots (QDs) (Zn xCd1- xSe/ZnS core/shell QDs with different ZnS shell thicknesses) as the emitters. ZnO nanoparticles and sol-gel NiO are employed as the electron and hole transport materials, respectively. Time-resolved and steady-state photoluminescence results indicate that positive charging processes might occur for the QDs deposited on NiO, which results in emission quenching of QDs and poor device performance. The thick shell outside the core in QDs not only largely suppresses the QD emission quenching but also effectively preserves the excitons in QDs from dissociation of electron-hole pairs when they are subjected to an electric field. The peak efficiency of 4.2 cd/A and maximum luminance of 4205 cd/m2 are achieved for the device based on QDs with the thickest shells (∼4.2 nm). We anticipate that these results will spur progress toward the design and realization of efficient all-inorganic QLEDs as a platform for the QD-based full-colored displays.

High-efficiency all-inorganic full-colour quantum dot light-emitting diodes

All-inorganic quantum dot light-emitting diodes (QLEDs) with excellent device stability have attracted significant attention for solid state lighting and flat panel display applications. However, the performance for the present all-inorganic QLEDs is far inferior to that of the well-developed QLEDs with organic charge transport layers. Our all-inorganic full-colour QLEDs show the maximum brightness and efficiency values of 21,600 cd/m2 and 6.52%, respectively, which are record-breaking among the existing all-inorganic QLEDs. The outstanding performance is achieved by an efficient design of device architecture with solution-processed charge transport layers (CTLs). Meanwhile, the ultrathin double-sided insulating layers are inserted between the quantum dot emissive layer and their adjacent oxide electron transport layers to better balance charge injection in the device and reduce the quenching effects for inorganic CTLs on QD emission. This study is the first account for high-performance, all-inorganic QLEDs insightfully offering detailed investigations into the performance promotion for inorganic electroluminescent devices.

Ultrasonic Spray Processed, Highly Efficient All-Inorganic Quantum-Dot Light-Emitting Diodes

All-inorganic and low-cost quantum-dot light-emitting diodes (QLEDs) are always desired considering the easy processing and outstanding physical and chemical stability of inorganic oxides. Herein, efficient all-inorganic QLEDs are demonstrated by using NiO and ZnO as the charge transport layers fabricated via ultrasonic spray processes. Excellent device performance is achieved thanks to the introduction of an Al2O3 interlayer between quantum dots (QDs) and an amorphous NiO layer. Transient photoluminescence and electricity measurements indicate that the Al2O3 layer can suppress the exciton quenching induced by the NiO layer and reduce the electron leakage from QDs to NiO. In consequence, relative to that of a device without an Al2O3 layer, the efficiency of an Al2O3-containing device is enhanced by a factor of 539%, increasing from 3.8 cd/A to 20.5 cd/A, and it exhibits color-saturated green emission (peak at 530 nm) and high luminescence (>20 000 cd/m2). These are the best performances for all-inorganic QLEDs reported to date. Meanwhile, it is demonstrated that ultrasonic spray is a feasible and cost-effective technology to construct efficient all-inorganic QLEDs. We anticipate that these results will spur the progress toward realization of high performance and mass production of all-inorganic QLEDs as a platform for QD-based full-color displays.

All-inorganic quantum-dot light-emitting diodes based on perovskite emitters with low turn-on voltage and high humidity stability

We present the all-inorganic QLEDs, including inorganic perovskite emitters (CsPbBr3) and inorganic charge transport layers (CTLs), with emphasis on the significantly improved device stability and low turn-on voltage.

All-inorganic quantum-dot light-emitting-diodes with vertical nickel oxide nanosheets as hole transport layer

All-inorganic quantum dot light emitting diodes (QLEDs) have gained great attention as a result of their high stability under oxygen-rich, humid and high current working conditions. In this work, we have fabricated an all-inorganic QLED device (FTO/NiO/QDs/AZO/Ag) with sandwich-structure, wherein the inorganic metal oxides thin films of NiO and AZO were employed as hole and electron transport layers, respectively. The porous NiO layer with vertical lamellar nanosheets interconnected microstructure have been directly synthesized on the substrate of conductive FTO glass and increased the wettability of CdSe@ZnS QDs, which result in an enhancement of current transport performance of the QLED.

NiO-Based All-Inorganic Quantum-Dot Light-Emitting Diodes by Sol–Gel Method

NiO-Based All-Inorganic Quantum-Dot Light-Emitting Diodes by Sol–Gel Method