Quantum Dot Light-emitting Diodes Research Articles

Hybrid Design of Light‐Emitting Diodes in Tandem Structures

AbstractOrganic light‐emitting diodes in tandem structures (TOLEDs) have long been an effective strategy to realize multifold increased electroluminescence (EL) efficiency relative to the single‐unit OLEDs, making TOLEDs promising candidates for lighting and display applications. Benefitted from the development of organic emitters, hybrid tandem OLEDs (HTOLEDs) composing two or more types of OLED emitters (phosphorescence, fluorescence, and thermally‐activated delayed fluorescence (TADF)) are developed. The different energy conversion processes of these emitters can facilitate manipulated exciton distribution inside the device, leading to enhanced device performance. On the other hand, different emission technologies can also be integrated to form another kind of hybrid tandem light‐emitting diodes (HTLED) thanks to the compatibility of OLEDs with quantum dot LEDs (QLEDs) and perovskite LEDs (PeLEDs). In this review, the performance of different types of HTOLEDs and HTLEDs is comprehensively reviewed particularly focusing on the exciton regulations and manipulation of emission spectra in the sub‐units, aiming to provide guidelines for the EL performance optimization of HTOLEDs.

Application of quantum dot light-emitting diode harvest by quantum dot solar cells

Recent progress in photovoltaic (PV) cell usage has been hindered due to a shortage of suitable materials that emit adequate wavelengths of light energy and convert it to electricity. Quantum dot light-emitting diodes (QLEDs) and quantum dot solar cells (QDSCs) have been identified as promising artificial light sources and PV cell types to nicely fit into this solution, not only complying with that but also being controllable, flexible, portable, and lightweight. The purpose of this study is to provide a review of the application of how QLEDs can be collected for QDSCs. First, we introduce QLEDs as artificial light sources, briefly outline their mechanics and benefits, and compare them to other light sources for QDSC harvesting. Then, we summarize the mechanisms that occur when a QDSC absorbs a photon from a QLED, as well as how these energy flow pathways influence artificial light energy harvest. Finally, we explore the optoelectronic properties of lead sulphide (PbS) and lead selenide (PbSe) as appropriate quantum dots (QDs) materials for current applications in QDSC and QLED technologies. We anticipate that the literature will be comprehensive and relevant to the scientific community interested in creating artificial light energy harvesting and thus researching the most recent alternative method of getting healthy energy.

Highly enhanced Quantum dot light-emitting diode performance by controlling energy resonance in inorganic insertion layers

Quantum-dot light-emitting diodes (QLED) have become a research trend in the field of new displays due to their low cost, wide color gamut, narrow bandwidth, and characteristics that enable production through the solution-gel method. However, the electrical performance of QLED is consistently constrained by energy losses and imbalanced charge carrier injection. This motivates our focus on exciton recombination and energy losses within the quantum-dot layer to enhance the electrical efficiency of QLED. In this work, we introduce a method using a CdZnS quantum dot (B-QD) interlayer to modulate energy transfer and charge carrier transport in QLED devices employing CdSe quantum dot (G-QD) as the emissive layer. By strategically incorporating a B-QD layer between the G-QD and HTL/ETL, we facilitate energy transfer due to the overlap between the excitation wavelength of B-QD and the absorption wavelength of G-QDs. This leads to enhanced energy injection in QLED devices, resulting in a high current efficiency of 39.54 Cd/A and a peak brightness of 522,272 cd/m2 for efficient QLED. The corresponding external quantum efficiency (EQE) is greatly improved from 5.62 % to 9.4 %. Our work provides a straightforward and effective approach to modulate exciton recombination and energy injection and further can be applicable to other photo-electronics devices.

Solution‐Processed Tandem Quantum‐Dot Light‐Emitting Diodes with Dual Charge Generation Interfaces: Achieving Over Threefold Efficiency Enhancement

AbstractDespite the commercialization of thermally evaporated tandem organic light‐emitting diodes (OLEDs), challenges remain for solution‐processed tandem quantum‐dot light‐emitting diodes (QLEDs), including low efficiency and solvent‐induced damage to functional layers. Therefore, there is an urgent need for the optimization of the interconnecting layer (ICL) design in order to fabricate high‐performance solution‐processed tandem QLEDs. Here, by introducing a phosphomolybdic acid (PMA) layer between poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and poly(9‐vinylcarbazole) (PVK), an novel ICL, PVK/PMA/PEDOT:PSS/ZnO is proposed, with dual charge generation interfaces (CGIs): PVK/PMA and PEDOT:PSS/ZnO. The PMA interlayer serves not only smoothing the morphology of PEDOT:PSS to improve charge transport, but also forming a PVK/PMA CGI to enhance charge generation. Based on the excellent electrical and optical properties of the dual‐CGI ICL, the solution‐processed inverted tandem red QLEDs achieve an increased external quantum efficiency (EQE) of over three times compared to single‐junction devices. This provides a novel approach for the high‐efficiency solution‐processed tandem QLEDs, paving the way for the practical application of QLEDs.

Advances in display technology: augmented reality, virtual reality, quantum dot-based light-emitting diodes, and organic light-emitting diodes

Virtual reality, augmented reality, quantum dot light-emitting diodes, and organic light-emitting diodes have progressed over the last two years. Key achievements in these displays are discussed in terms of device performance.

Research Progress of Heavy-Metal-Free Quantum Dot Light-Emitting Diodes.

At present, heavy-metal-free quantum dot light-emitting diodes (QLEDs) have shown great potential as a research hotspot in the field of optoelectronic devices. This article reviews the research on heavy-metal-free quantum dot (QD) materials and light-emitting diode (LED) devices. In the first section, we discussed the hazards of heavy-metal-containing quantum dots (QDs), such as environmental pollution and human health risks. Next, the main representatives of heavy-metal-free QDs were introduced, such as InP, ZnE (E=S, Se and Te), CuInS2, Ag2S, and so on. In the next section, we discussed the synthesis methods of heavy-metal-free QDs, including the hot injection (HI) method, the heat up (HU) method, the cation exchange (CE) method, the successful ionic layer adsorption and reaction (SILAR) method, and so on. Finally, important progress in the development of heavy-metal-free QLEDs was summarized in three aspects (QD emitter layer, hole transport layer, and electron transport layer).

Low-Temperature Cross-Linked Hole Transport Layer for High-Performance Blue Quantum-Dot Light-Emitting Diodes.

Quantum-dot light-emitting diodes (QLEDs), a kind of promising optoelectronic device, demonstrate potential superiority in next-generation display technology. Thermal cross-linked hole transport materials (HTMs) have been employed in solution-processed QLEDs due to their excellent thermal stability and solvent resistance, whereas the unbalanced charge injection and high cross-linking temperature of cross-linked HTMs can inhibit the efficiency of QLEDs and limit their application. Herein, a low-temperature cross-linked HTM of 4,4'-bis(3-(((4-vinylbenzyl)oxy)methyl)-9H-carbazol-9-yl)-1,1'-biphenyl (DV-CBP) with a flexible styrene side chain is introduced, which reduces the cross-linking temperature to 150 °C and enhances the hole mobility up to 1.01 × 10-3 cm2 V-1 s-1. More importantly, the maximum external quantum efficiency of 21.35% is successfully obtained on the basis of the DV-CBP as a cross-linked hole transport layer (HTL) for blue QLEDs. The low-temperature cross-linked high-mobility HTL using flexible side chains could be an excellent alternative for future HTL development.

Heterointerface Effects on Carrier Dynamics in Colloidal Quantum Dots and Their Application to Light-Emitting Diodes.

Colloidal quantum dots (QDs) are promising candidates for next-generation display technology because of their unique optical properties and have already appeared in the market as a high-end product. On the basis of their extraordinary properties, QD emissions with a given chemical composition can be tailored in a wide spectral window due to quantum size effects, which constitutes a key advantage of QDs in the display field. Specifically, investigations of structure-dependent and composition-dependent characterizations outside the quantum confinement effect have become an important part of practical applications. Therefore, from the perspective of designing nanostructures with well-defined heterointerfaces, strong quantum confinement effects with effective carrier confinement are desirable. Our results show that the photoluminescence (PL) intensity of CdSe/CdZnS core-shell QDs was enhanced 5.7 times compared with that of the CdSe core QDs. Supplementary analytical techniques involving transmission electron microscopy revealed the heterointerface configuration and composition distribution of the core and shell materials. The effects of the heterointerface on carrier dynamics in core-shell QDs were revealed by monitoring wavelength-dependent time-resolved PL. To further develop the QD light-emitting diodes (QD-LEDs), we produced an all-solution processed inverted QD-LEDs using CdSe/CdZnS core-shell QDs as the emitter. The electroluminescence spectrum of deep-red emissive QD-LEDs with CIE chromaticity coordinates of (0.68, 0.32) exhibited a peak at 638 nm.

Efficient green light-emitting diodes based on alloy quantum dots with an organic/inorganic hybrid surface passivation

As we know, the ligands on the surface of core/shell structured quantum dots (QDs) play an important role. They not only bind with metal ions to passivate surface defects but also have a great influence on colloidal stability. All-organic or all-inorganic ligands afford QDs with some disadvantages such as low conductivity, poor dispersibility and undesirable stability. By combining with the advantages of organic and inorganic ligands, herein, we achieve an organic/inorganic hybrid surface passivation through exchanging partial oleic acid ligands with chlorine ions (Cl−), affording QD with a core/shell structure of CdZnSe/ZnSe/ZnS/OACl. It exhibits an excellent nanostructure with a mean size of around 11.6 nm. According to X-ray photoelectron spectroscopy (XPS) spectra, around 30% oleid acid ligands are removed by Cl−, resulting in the hybrid surface passivation. The CdZnSe/ZnSe/ZnS/OACl QD exhibit an efficient green emission at the wavelength of around 535 nm with a quantum yield of over 90%. The QD light-emitting diode (QLED) based on CdZnSe/ZnSe/ZnS/OACl exhibits a peak EQE of 15.6% and a brightness of over 1.1 × 105 cd m−2 at 6 V, corresponding to an efficient green emitting device. Therefore, we believe that the hybrid surface passivation could provid a reliable avenue to efficient QD materials.

Bright, Flexible, and Waterproof Top-Emitting InP Quantum Dot Light-Emitting Diodes on Al Foil

Bright, Flexible, and Waterproof Top-Emitting InP Quantum Dot Light-Emitting Diodes on Al Foil

The influence of solvent refractive index on the photoluminescence decay of thick-shell gradient-alloyed colloidal quantum dots investigated in a wide range of delay times.

Colloidal semiconductor quantum dots have many potential optical applications, including quantum dot light-emitting diodes, single-photon sources, or biological luminescent markers. The optical properties of colloidal quantum dots can be affected by their dielectric environment. This study investigated the photoluminescence (PL) decay of thick-shell gradient-alloyed colloidal semiconductor quantum dots as a function of solvent refractive index. These measurements were conducted in a wide range of delay times to account for both the initial spontaneous decay of excitons and the delayed emission of excitons that has the form of a power law. It is shown that whereas the initial spontaneous PL decay is very sensitive to the refractive index of the solvent, the power-law delayed emission of excitons is not. Our results seem to exclude the possibility of carrier self-trapping in the considered solvents and suggest the existence of trap states inside the quantum dots. Finally, our data show that the average exciton lifetime significantly decreases as a function of the solvent refractive index. The change in exciton lifetime is qualitatively modeled and discussed.

Recent Developments in Quantum Dot Patterning Technology for Quantum Dot Display

Colloidal quantum dot (QDs) have emerged as a crucial building block for LEDs due to their size-tunable emission wavelength, narrow spectral line width, and high quantum efficiency. Tremendous efforts have been dedicated to improving the performance of quantum dot light-emitting diodes (QLEDs) in the past decade, primarily focusing on optimization of device architectures and synthetic procedures for high quality QDs. However, despite these efforts, the commercialization of QLEDs has yet to be realized due to the absence of suitable large-scale patterning technologies for high-resolution devices., This review will focus on the development trends associated with transfer printing, photolithography, and inkjet printing, and aims to provide a brief overview of the fabricated QLED devices. The advancement of various quantum dot patterning methods will lead to the development of not only QLED devices but also solar cells, quantum communication, and quantum computers.

Enhancing the performance of CdSe/ZnS quantum-dot light-emitting diodes by utilizing hole injection layers fabricated with a solution-processed mixture of vanadium oxide and molybdenum oxide

We developed a high-performance CdSe/ZnS quantum-dot light-emitting diode (QLED) incorporating a hole injection layer (HIL) composed of a solution-processed vanadium oxide (VO) and molybdenum oxide (MoO) mixture. The QLED with a VO:MoO ratio of 1:1 in the HIL demonstrated a current efficiency of 62.0 cd/A, representing a 60% improvement over the QLED utilizing poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the HIL. Besides improved performance, the substitution of the highly reactive PEDOT: PSS with chemically stable metal oxides in HIL fabrication is anticipated to enhance device reliability. The highest occupied molecular orbital level of the VO:MoO ratio of 1:1 HIL was higher than that of HILs with other mixing ratios. Additionally, the VO:MoO ratio of 1:1 HIL exhibited higher oxidation number states compared to HILs with other mixing ratios. These characteristics contributed to the superior performance of the QLED with the VO:MoO ratio of 1:1 HIL. Our approach, which employs chemically stable metal oxides as HIL materials for high-performance QLEDs, can advance future QLED technology.

Household alternating current electricity plug-and-play quantum-dot light-emitting diodes

As an intrinsically direct current device, quantum-dot LED cannot be directly driven by household alternating current electricity. Thus, a driver circuit is required, which increases the complexity and cost. Here, by using a transparent and conductive indium-zinc-oxide as an intermediate electrode, we develop a tandem quantum-dot LED that can be operated at both negative and positive alternating current cycles with an external quantum efficiency of 20.09% and 21.15%, respectively. Furthermore, by connecting multiple tandem devices in series, the panel can be directly driven by household alternating current electricity without the need for complicated back-end circuits. Under 220 V/50 Hz driving, the red plug-and-play panel demonstrates a power efficiency of 15.70 lm W−1 and a tunable brightness of up to 25,834 cd m−2. The developed plug-and-play quantum-dot LED panel could enable the production of cost-effective, compact, efficient, and stable solid-state light sources that can be directly powered by household alternating current electricity.

High-brightness green InP-based QLEDs enabled by in-situ passivating core surface with zinc myristate

The performance of red InP and blue ZnTeSe-based quantum dots (QDs) and corresponding QD light emitting diodes (QLEDs) has already been improved significantly, whose external quantum efficiencies (EQEs) and luminances have exceeded 20% and 80 000 cd m−2, respectively. However, the inferior performance of the green InP-based device hinders the commercialization of full-color Cd-free QLED technology. The ease of oxidation of the highly reactive InP cores leads to high non-radiative recombination and poor photoluminescence quantum yield (PL QY) of the InP-based core/shell QDs, limiting the performance of the relevant QLEDs. Here, we proposed a fluoride-free synthesis strategy to in-situ passivate the InP cores, in which zinc myristate reacted with phosphine dangling bonds to form Zn–P protective layer and protect InP cores from the water and oxygen in the environment. The resultant InP/ZnSe/ZnS core/shell QDs demonstrated a high PL QY of 91%. The corresponding green-emitting electroluminescence devices exhibited a maximum EQE of 12.74%, along with a luminance of over 175 000 cd m−2 and a long T50@100 cd m−2 lifetime of over 20 000 h.

Photothermal Synergic Cross-Linking Hole Transport Layer for Highly Efficient RGB QLEDs.

Developing an insoluble cross-linkable hole transport layer (HTL) plays an important role for solution-processed quantum dots light-emitting diodes (QLEDs) to fabricate a multilayer device with separated quantum dots layers and HTLs. In this work, a facile photothermal synergic cross-linking strategy is simultaneous annealing and UV irradiation to form the high-quality cross-linked film as the HTL without any photoinitiator, which efficiently reduces the cross-linking temperature to the low temperature of 130 °C and enhances the hole mobility of the 3-vinyl-9-{4-[4-(3-vinylcarbazol-9-yl)phenyl]phenyl}carbazole (CBP-V) thin films. The obtained high-quality cross-linked CBP-V films exhibited smooth morphology, excellent solvent resistance, and high mobility. Moreover, the high-performance red, green, and blue (RGB) QLEDs are successfully fabricated by using the photothermal synergic cross-linked HTLs, which achieved the maximum external quantum efficiency of 25.69, 24.42, and 16.51%, respectively. This work presents a strategy of using the photothermal synergic cross-linked HTLs for fabrication of high-performance QLEDs and advancing their related device applications.

Charge Carrier Regulation for Efficient Blue Quantum-Dot Light-Emitting Diodes Via a High-Mobility Coplanar Cyclopentane[b]thiopyran Derivative.

The performance of blue quantum dot light-emitting diodes (QLEDs) is limited by unbalanced charge injection, resulting from insufficient holes caused by low mobility or significant energy barriers. Here, we introduce an angular-shaped heteroarene based on cyclopentane[b]thiopyran (C8-SS) to modify the hole transport layer poly-N-vinylcarbazole (PVK), in blue QLEDs. C8-SS exhibits high hole mobility and conductivity due to the π···π and S···π interactions. Introducing C8-SS to PVK significantly enhanced hole mobility, increasing it by 2 orders of magnitude from 2.44 × 10-6 to 1.73 × 10-4 cm2 V-1 s-1. Benefiting from high mobility and conductivity, PVK:C8-SS-based QLEDs exhibit a low turn-on voltage (Von) of 3.2 V. More importantly, the optimized QLEDs achieve a high peak power efficiency (PE) of 7.13 lm/W, which is 2.65 times that of the control QLEDs. The as-proposed interface engineering provides a novel and effective strategy for achieving high-performance blue QLEDs in low-energy consumption lighting applications.

Near Infrared Light-Emitting Diodes Based on Colloidal InAs/ZnSe Core/Thick-Shell Quantum Dots.

Heavy-metal-free III-V colloidal quantum dots (QDs) exhibit promising attributes for application in optoelectronics. Among them, InAs QDs are demonstrating excellent optical performance with respect to absorption and emission in the near-infrared spectral domain. Recently, InAs QDs attained a substantial improvement in photoluminescence quantum yield, achieving 70% at a wavelength of 900 nm through the strategic overgrowth of a thick ZnSe shell atop the InAs core. In the present study, light-emitting diodes (LEDs) based on this type of InAs/ZnSe QDs are fabricated, reaching an external quantum efficiency (EQE) of 13.3%, a turn-on voltage of 1.5V, and a maximum radiance of 12 Wsr-1m-2. Importantly, the LEDs exhibit an extensive emission dynamic range, characterized by a nearly linear correlation between emission intensity and current density, which can be attributed to the efficient passivation provided by the thick ZnSe shell. The obtained results are comparable to state-of-the-art PbS QD LEDs. Furthermore, it should be stressed not only that the fabricated LEDs are fully RoHS-compliant but also that the emitting InAs QDs are prepared via a synthetic route based on a non-pyrophoric, cheap, and commercially available as precursor, namely tris(dimethylamino)-arsine.

Nickel Oxide Hole Injection Layers for Balanced Charge Injection in Quantum Dot Light-Emitting Diodes.

Quantum dot (QD) light-emitting diodes (QLEDs) are promising for next-generation displays, but suffer from carrier imbalance arising from lower hole injection compared to electron injection. A defect engineering strategy is reported to tackle transport limitations in nickel oxide-based inorganic hole-injection layers (HILs) and find that hole injection is able to enhance in high-performance InP QLEDs using the newly designed material. Through optoelectronic simulations, how the electronic properties of NiOx affect hole injection efficiency into an InP QD layer, finding that efficient hole injection depends on lowering the hole injection barrier and enhancing the acceptor density of NiOx is explored. Li doping and oxygen enriching are identified as effective strategies to control intrinsic and extrinsic defects in NiOx, thereby increasing acceptor density, as evidenced by density functional theory calculations and experimental validation. With fine-tuned inorganic HIL, InP QLEDs exhibit a luminance of 45200cdm-2 and an external quantum efficiency of 19.9%, surpassing previous inorganic HIL-based QLEDs. This study provides a path to designing inorganic materials for more efficient and sustainable lighting and display technologies.

DFT insights into the pressure-induced ultraviolet to visible band gap engineering of TlMgF3 cubic halide perovskites for optoelectronic applications

The current study utilizes first-principle calculation in order to investigate the geometrical, electrical, mechanical, and optical characteristics of TlMgF3 cubic halide perovskites under the effect of hydrostatic pressure. The interatomic distance is significantly reduced, causing a substantial decrease in the unit cell volume and lattice constant of TlMgF3 perovskite. The electronic energy band gap undergoes a transition from the UV to the visible region in response to the hydrostatic pressure, thereby allowing electron transport from the valence band to the conduction band. This causes some interesting observations in the electronic and optical characteristics of many optoelectronic devices. Additionally, at approximately 500 GPa pressure, the direct band gap is tuned from 4.275 eV to 1.66 eV, making the material suitable for use in solar cell applications. Deep optical analysis has recommended the utilization of TlMgF3 in numerous other applications, including microelectronics, QLED (quantum dot light-emitting diode), OLED (organic light-emitting diode), solar heat reduction materials, and surgical instruments. When external hydrostatic pressure is applied, the mechanical properties of the material are also substantially altered, resulting in increased flexibility and anisotropy.