Advances in Quantum-Dot-Based Displays

Modelling-assisted geometrical optimization of colloidal quantum color convertor based pixels fabricated by dielectrophoretic directed assembly

HYPOTHESIS

Building competitive color conversion pixels for microdisplays made of semiconductor nanocrystals requires reaching a deposition thickness high enough to absorb all the blue light from the backlight unit. In the case of dielectrophoretic directed assembly of such nanocrystals, modeling and simulations may help understand what the intrinsic limitations of the process are, and may be used to propose new assembly routes.

EXPERIMENTS

A theoretical model of dielectrophoretic interactions between polarizable nano-spheres and an electrostatically patterned substrate has been developed. Monte Carlo simulations have been run using this model to rationalize the effects of parameters driving the dielectrophoretic directed assembly and to find optimal deposition conditions for reaching a maximal thickness of nanocrystal pixels. Experiments with CdSe quantum plates and with alumina spheres embedding quantum plates (micro-pearls) have been carried out and compared to the model.

FINDINGS

Modeling and simulations reveal that the directed assembly of semiconductor nanocrystals is limited essentially by the small object size, which sets the maximum dielectrophoretic force they can undergo. They indicate that using larger objects should allow reaching unprecedented assembly heights, but will induce lateral extension of the assembly. This trade-off has been illustrated with diagrams in the parameter space and confirmed experimentally with micro-pearls.

Potassium Iodide Doping for Vacancy Substitution and Dangling Bond Repair in InP Core-Shell Quantum Dots

This work highlights the novel approach of incorporating potassium iodide (KI) doping during the synthesis of In0.53P0.47 core quantum dots (QDs) to significantly reduce the concentration of vacancies (i.e., In vacancies; VIn-) within the bulk of the core QD and inhibit the formation of InPOx at the core QD-Zn0.6Se0.4 shell interfaces. The photoluminescence quantum yield (PLQY) of ~97% and full width at half maximum (FWHM) of ~40 nm were achieved for In0.53P0.47/Zn0.6Se0.4/Zn0.6Se0.1S0.3/Zn0.5S0.5 core/multi-shell QDs emitting red light, which is essential for a quantum-dot organic light-emitting diode (QD-OLED) without red, green, and blue crosstalk. KI doping eliminated VIn- in the core QD bulk by forming K+-VIn- substitutes and effectively inhibited the formation of InPO4(H2O)2 at the core QD-Zn0.6Se0.4 shell interface through the passivation of phosphorus (P)-dangling bonds by P-I bonds. The elimination of vacancies in the core QD bulk was evidenced by the decreased relative intensity of non-radiative unpaired electrons, measured by electron spin resonance (ESR). Additionally, the inhibition of InPO4(H2O)2 formation at the core QD and shell interface was confirmed by the absence of the {210} X-ray diffraction (XRD) peak intensity for the core/multi-shell QDs. By finely tuning the doping concentration, the optimal level was achieved, ensuring maximum K-VIn- substitution, minimal K+ and I- interstitials, and maximum P-dangling bond passivation. This resulted in the smallest core QD diameter distribution and maximized optical properties. Consequently, the maximum PLQY (~97%) and minimum FWHM (~40 nm) were observed at 3% KI doping. Furthermore, the color gamut of a QD-OLED display using R-, G-, and B-QD functional color filters (i.e., ~131.1%@NTSC and ~98.2@Rec.2020) provided a nearly perfect color representation, where red-light-emitting KI-doped QDs were applied.

Advancements in Micro-LED Performance through Nanomaterials and Nanostructures: A Review

Micro-light-emitting diodes (μLEDs), with their advantages of high response speed, long lifespan, high brightness, and reliability, are widely regarded as the core of next-generation display technology. However, due to issues such as high manufacturing costs and low external quantum efficiency (EQE), μLEDs have not yet been truly commercialized. Additionally, the color conversion efficiency (CCE) of quantum dot (QD)-μLEDs is also a major obstacle to its practical application in the display industry. In this review, we systematically summarize the recent applications of nanomaterials and nanostructures in μLEDs and discuss the practical effects of these methods on enhancing the luminous efficiency of μLEDs and the color conversion efficiency of QD-μLEDs. Finally, the challenges and future prospects for the commercialization of μLEDs are proposed.

Colloidal quantum dot materials for next-generation near-infrared optoelectronics

Colloidal quantum dots (CQDs) are a promising class of materials for next-generation optoelectronic devices, such as displays, LEDs, lasers, photodetectors, and solar cells. CQDs can be obtained at low cost and in large quantities using wet chemistry. CQDs have also been produced using various materials, such as CdSe, InP, perovskites, PbS, PbSe, and InAs. Some of these CQD materials absorb and emit photons in the visible region, making them excellent candidates for displays and LEDs, while others interact with low-energy photons in the near-infrared (NIR) region and are intensively utilized in NIR lasers, NIR photodetectors, and solar cells. In this review, we have focused on NIR CQD materials and reviewed the development of CQD materials for solar cells, NIR lasers, and NIR photodetectors since the first set of reports on CQD materials in these particular applications.

A single molecule diode based on gold electrodes and benzene molecule: conductivity and coupling analysis

CONTEXT

In this paper, we simulate a single-molecule diode to calculate the effective coupling and investigate the conductivity, as well as the effect of the electric field on these two parameters. First, we obtain the molecule states and energies at 0 V. The next step is to calculate the electrode/molecule coupling using the obtained electrode and molecule Hamiltonian. The electrode/molecule coupling depends on distance. By increasing the distance from 5 to 5.5 angstroms, the coupling decreases from 0.004 to 0.0002 eV. After calculating the electrode/molecule coupling, which is the most significant parameter in electron transfer, the results can be used to obtain the current-voltage and conductivity curves of the device. Simulation results demonstrate that externally applied electric field to the benzene molecule (isolated molecule) can cause a reduction in the effective coupling between the Au electrode and benzene, leading to decreased current and conductivity. Additionally, the applied electric field narrows the gap between the HOMO and LUMO energy levels.

METHODS

We conducted this computational work using Gaussian 09 software and a MATLAB code, both of which are based on the density functional theory (DFT) approach and the self-consistent field (SCF) method. For DFT calculations, we employed the three-parameter Beck hybrid exchange functional (B3), hybridized with the nonlocal correlation functional developed by Lee, Yang, and Parr (LYP). All optimizations were performed with triple-zeta polarized (TZP) split-valence 6-311G basis sets. The final step involved calculating the electrode/molecule coupling using the Huckel method and integrating the site-to-state transformation with Huckel parameters and the Fermi golden rule. After this calculation, we obtained the current-voltage and conductivity curves using MATLAB software.

Technological Breakthroughs in Chip Fabrication, Transfer, and Color Conversion for High-Performance Micro-LED Displays

The implementation of high-efficiency and high-resolution displays has been the focus of considerable research interest. Recently, micro light-emitting diodes (micro-LEDs), which are inorganic light-emitting diodes of size <100 µm2 , have emerged as a promising display technology owing to their superior features and advantages over other displays like liquid crystal displays and organic light-emitting diodes. Although many companies have introduced micro-LED displays since 2012, obstacles to mass production still exist. Three major challenges, i.e., low quantum efficiency, time-consuming transfer, and complex color conversion, have been overcome with technological breakthroughs to realize cost-effective micro-LED displays. In the review, methods for improving the degraded quantum efficiency of GaN-based micro-LEDs induced by the size effect are examined, including wet chemical treatment, passivation layer adoption, LED structure design, and growing LEDs in self-passivated structures. Novel transfer technologies, including pick-up transfer and self-assembly methods, for developing large-area micro-LED displays with high yield and reliability are discussed in depth. Quantum dots as color conversion materials for high color purity, and deposition methods such as electrohydrodynamic jet printing or contact printing on micro-LEDs are also addressed. This review presents current status and critical challenges of micro-LED technology and promising technical breakthroughs for commercialization of high-performance displays.

Simultaneous Enhancement of the Luminescence Intensity and Stability of Deep-Red CsPbI3 Perovskite Quantum Dots Achieved by a Doping Strategy

The phase instability of CsPbI3 perovskite quantum dots (PQDs) restricts their practical applications due to the easy conversion from the luminescent cubic phase to the non-luminescent orthorhombic phase. The elemental doping route has been regarded as one of the most effective strategies to achieve high-quality PQDs-based phosphors. Herein, a stoichiometric amount of nickel chloride (NiCl2) has been effectively doped into the CsPbI3 lattice. The incorporation of Ni2+ ions has little effect on the crystal phase, structure, and morphology of the CsPbI3 PQDs but greatly influences their luminescence properties. The Ni2+ doping not only improves the luminescence performance but also greatly enhances the stability against temperature, storage time, and polar solvent. The formation process and luminescence and stability improvement mechanisms have been discussed. Moreover, the influence of a series of other metal chlorides (KCl, NaCl, MgCl2, ZnCl2, SnCl2, and CaCl2) on the luminescence performance of CsPbI3 PQDs has been systematically investigated, revealing that the luminescence intensity increases by introducing CaCl2, SnCl2, or ZnCl2 but decreases after doping MgCl2, NaCl, or KCl into the CsPbI3 lattice. The as-proposed doping strategy may have a significant impact on tackling the intrinsic instability of all-inorganic CsPbX3 PQDs, shedding light on their future applications in light-emitting diode (LED) devices and solid-state lighting.

Facet Engineering for Amplified Spontaneous Emission in Metal Halide Perovskite Nanocrystals

Auger recombination and thermalization time are detrimental in reducing the gain threshold of optically pumped semiconductor nanocrystal (NC) lasers for future on-chip nanophotonic devices. Here, we report the design strategy of facet engineering to reduce the gain threshold of amplified spontaneous emission by manyfold in NCs of the same concentration and edge length. We achieved this hallmark result by controlling the Auger recombination rates dominated by processes involving NC volume and thermalization time to the emitting states by optimizing the number of facets from 6 (cube) to 12 (rhombic dodecahedron) and 26 (rhombicuboctahedrons) in CsPbBr₃ NCs. For instance, we demonstrate a 2-fold reduction in Auger recombination rates and thermalization time with increased number of facets. The gain threshold can be further reduced ∼50% by decreasing the sample temperature to 4 K. Our systematic studies offer a new method to reduce the gain threshold that ultimately forms the basis of nanolasers.

Surface defects and particle size determine transport of CdSe quantum dots out of plastics and into the environment

Polymers incorporating quantum dots (QDs) have attracted interest as components of next-generation consumer products, but there is uncertainty about how these potentially hazardous materials may impact human health and the environment. We investigated how the transport (migration) of QDs out of polymers and into the environment is linked to their size and surface characteristics. Cadmium selenide (CdSe) QDs with diameters ranging from 2.15 to 4.63 nm were incorporated into low-density polyethylene (LDPE). Photoluminescence was used as an indicator of QD surface defect density. Normalized migration of QDs into 3% acetic acid over 15 days ranged from 13.1 ± 0.6-452.5 ± 31.9 ng per cm² of polymer surface area. Migrated QD mass was negatively correlated to QD diameter and was also higher when QDs had photoluminescence consistent with larger surface defect densities. The results imply that migration is driven by oxidative degradation of QDs originating at surface defect sites and transport of oxidation products along concentration gradients. A semi-empirical framework was developed to model the migration data. The model supports this mechanism and suggests that QD surface reactivity also drives the relationship between QD size and migration, with specific surface area playing a less important role.

Sulfides mediate the migration of nanoparticle mass out of nanocomposite plastics and into aqueous environments

We show that inorganic sulfides strongly influence transfer (migration) of nanoparticle mass out of polymer nanocomposites (PNCs) and into aqueous environments. We first manufactured two families of PNCs: one incorporating silver nanoparticles (AgNPs) and one incorporating CdSe quantum dots (QDs). Then, we assessed migration out of these PNCs and into aqueous media containing Na₂S at concentrations ranging from 0 to 10^-4 M. Results show that Na₂S strongly suppressed migration of Ag from AgNP-based PNCs: the migration into water spiked with 10^-6 M Na₂S was 79% less than migration into water without Na₂S, and no migration was detected (LOD ≈ 0.01 ng/cm²) in water spiked with Na₂S at 10^-5 M or 10^-4 M. With CdSe QD-based PNCs, Na₂S suppressed Cd migration but enhanced Se migration, resulting in only a small net effect on the total QD migration but a large shift of the leachate composition (from favoring Cd by an average of 5.8 to 1 in pure water to favoring Se 9.4 to 1 when Na₂S was present at 10^-4 M). These results show that common inorganic substances like sulfides may play a strong role in determining the environmental fate of polymer-dispersed nanoparticles and imply that migration tests conducted in purified water may not always accurately reflect migration into real environments.

Quantum Dot-Based White Organic Light-Emitting Diodes Excited by a Blue OLED

In this study, white organic light-emitting diodes (OLEDs) consisting of red quantum dots (RQD) and green quantum dots (GQD) were investigated. These are the most exciting new lighting technologies that have grown rapidly in recent years. The white OLED development processes used consisted of the following methods: (a) fabrication of a blue single-emitting layer OLED, (b) nanoimprinting into QD photoresists, and (c) green and red QD photoresists as color conversion layers (CCL) excited by blue OLEDs. To fabricate the blue OLED, the HATCN/TAPC pair was selected for the hole injection/transport layer on ITO and TPBi for the electron transport layer. For blue-emitting material, we used a novel polycyclic framework of thermally activated delayed fluorescence (TADF) material, ν-DABNA, which does not utilize any heavy metals and has a sharp and narrow (FWHM 28 nm) electroluminescence spectrum. The device structure was ITO/HATCN (20 nm)/TAPC (30 nm)/MADN: ν-DABNA (40 nm)/TPBi (30 nm)/LiF (0.8 nm)/Al (150 nm) with an emitting area of 1 cm × 1 cm. The current density, luminance, and efficiency of blue OLEDs at 8 V are 87.68 mA/cm2, 963.9 cd/m2, and 1.10 cd/A, respectively. Next, the bottom emission side of the blue OLED was attached to nanoimprinted RQD and GQD photoresists, which were excited by the blue OLED in order to generate an orange and a green color, respectively, and combined with blue light to achieve a nearly white light. In this study, two different excitation architectures were tested: BOLED→GQD→RQD and BOLED→RQD→GQD. The EL spectra showed that the BOLED→GQD→RQD architecture had stronger green emissions than BOLED→RQD→GQD because the blue OLED excited the GQD PR first then RQD PR. Due to the energy gap architectures in BOLED-GQD-RQD, the green QD absorbed part of the blue light emitted from the BOLED, and the remaining blue light penetrated the GQD to reach the RQD. These excited spectra were very close to the white light, which resulted in three peaks emitting at 460, 530, and 620 nm. The original blue CIE coordinates were (0.15, 0.07). After the excitation combination, the CIE coordinates were (0.42, 0.33), which was close to the white light position.

Quantum dot-integrated GaN light-emitting diodes with resolution beyond the retinal limit

Near-eye display technology is a rapidly growing field owing to the recent emergence of augmented and mixed reality. Ultrafast response time, high resolution, high luminance, and a dynamic range for outdoor use are all important for non-pixelated, pupil-forming optics. The current mainstream technologies using liquid crystals and organic materials cannot satisfy all these conditions. Thus, finely patterned light-emissive solid-state devices with integrated circuits are often proposed to meet these requirements. In this study, we integrated several advanced technologies to design a prototype microscale light-emitting diode (LED) arrays using quantum dot (QD)-based color conversion. Wafer-scale epilayer transfer and the bond-before-pattern technique were used to directly integrate 5-µm-scale GaN LED arrays on a foreign silicon substrate. Notably, the lithography-level alignment with the bottom wafer opens up the possibility for ultrafast operation with circuit integration. Spectrally pure color conversion and solvent-free QD patterning were also achieved using an elastomeric topographical mask. Self-assembled monolayers were applied to selectively alter the surface wettability for a completely dry process. The final emissive-type LED array integrating QD, GaN, and silicon technology resulted in a 1270 PPI resolution that is far beyond the retinal limit.

Augmented reality technologies typically rely on near-eye displays, which requires displays with very high resolutions. Here, Bae et al demonstrate a quantum-dot integrated GaN light emitting diode arrays with a pixels per inch resolution of 1270, well beyond the retinal limit.

Spectral-temporal luminescence properties of Colloidal CdSe/ZnS Quantum Dots in relevant polymer matrices for integration in low turn-on voltage AC-driven LEDs

This work employs spectral and spectral-temporal Photoluminescence (PL) spectroscopy techniques to study the radiative mechanisms in colloidal CdSe/ZnS Quantum Dot (QD) thin films without and with 1% PMMA polymer matrix embedding (QD_PMMA). The observed bimodal transient-spectral PL distributions reveal bandgap transitions and radiative recombinations after interdot electron transfer. The PMMA polymer embedding protects the QDs during the plasma-sputtering of inorganic layers electroluminescent (EL) devices, with minimal impact on the charge transfer properties. Further, a novel TiO₂-based, all-electron bandgap, AC-driven QLED architecture is fabricated, yielding a surprisingly low turn-on voltage, with PL-identical and narrow-band EL emission. The symmetric TiO₂ bilayer architecture is a promising test platform for alternative optical active materials.

High-Uniform and High-Efficient Color Conversion Nanoporous GaN-Based Micro-LED Display with Embedded Quantum Dots

Quantum dot (QD)-based RGB micro-LED technology is seen as one of the most promising approaches towards full color micro-LED displays. In this work, we present a novel nanoporous GaN (NP-GaN) structure that can scatter light and host QDs, as well as a new type of micro-LED array based on an NP-GaN embedded with QDs. Compared to typical QD films, this structure can significantly enhance the light absorption and stability of QDs. As a result, the green and red QDs exhibited light conversion efficiencies of 90.3% and 96.1% respectively, leading to improvements to the luminous uniformity of the green and red subpixels by 90.7% and 91.2% respectively. This study provides a viable pathway to develop high-uniform and high-efficient color conversion micro-LED displays.

Photoluminescent Carbon Quantum Dots: Synthetic Approaches and Photophysical Properties

A number of synthetic methodologies and applications of carbon quantum dots (CQDs) have been reported since they were first discovered nearly two decades ago. Unlike metal-based or semiconductor-based (e. g., metal chalcogenides) quantum dots (MSQDs), CQDs have the unique feature of being prepared through a variety of synthetic protocols, which are typically understood from considerations of reaction models and photoluminescence mechanisms. Consequently, this brief review article describes quantum dots, in general, and CQDs, in particular, from various viewpoints: (i) their definition, (ii) their photophysical properties, and (iii) the superiority of CQDs over MSQDs. Where possible, comparisons are made between CQDs and MSQDs. First, however, the review begins with a general brief description of quantum dots (QDs) as nanomaterials (sizes≤10 nm), followed by a short description of MSQDs and CQDs. Described subsequently are the various top-down and bottom-up approaches to synthesize CQDs followed by their distinctive photophysical properties (emission spectra; quantum yields, Φs).

Experimental and theoretical investigation of 2D nanoplatelet-based conversion layers for color LED microdisplays

In the field of augmented reality, there is a need for very bright color microdisplays to meet the user specifications. Today, one of the most promising technology to manufacture such displays involves a blue micro-LED technology and quantum dots-based color conversion layers. Despite recent progress, the external power conversion efficiencies (EPCE) of these layers remain under ∼25%, below the needs (>40%) to reach a white luminance of 100,000 cd/m². In this work, we have synthesized CdSe_xS_1-x nanoplatelet-based conversion layers for red and green conversion, and measured their absorption properties and EPCE performances with respect to layer thickness. On this basis, a model was developed that reliably predicts the layer EPCE while using only few input data, namely the layer absorption coefficients and the photoluminescence quantum yield (PLQY) of color photoresist. It brings a new insight into the conversion process at play at a micro-LED level and provides a simple method for extensive optimization of conversion materials. Finally, this study highlights the outstanding red conversion efficiency of photoresist layers made of core-double shell CdSe_xS_1-x nanoplatelets with 31% EPCE (45% external PLQY) for 8 µm-thick conversion layer.

Emerging Nanopixel Light-Emitting Displays: Significance, Challenges, and Prospects

The requirement for increased resolution has created the concept of displays with nanoscale pixels; that is, each subpixel consists of multiple or even a single nanolight source, which is considered the ultimate light source for light field, near-eye, and implantable displays. However, related research is still at an early stage, and further insights into this future display concept should be provided. In this Perspective, we provide our proposed term for this future display, namely, nanopixel light-emitting display (NLED). We present an overview of nanolight-emitting diodes, which are considered the core component of NLEDs. Then, a roadmap to realize NLEDs from the view of material design is provided. Finally, we introduce our proposed operation mode (nonelectrical contact and noncarrier injection mode) for NLEDs and recommend possible nanopixel-level drive approaches. We hope that this Perspective will be helpful in designing innovative display technologies.

Perovskite Light-Emitting Devices with Doped Hole Transporting Layer

Perovskite quantum dots (PQDs) have drawn global attention in recent years and have been used in a range of semiconductor devices, especially for light-emitting diodes (LEDs). However, because of the nature of low-conductive ligands of PQDs and surface and bulk defects in the devices, charge injection and transport should be carefully managed in order to maximize the electroluminescent performances. In this study, we employed three p-dopants, i.e., 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), 1,3,4,5,7,8-hexafluoro-11,11,12,12-tetracyanonaphtho-2,6-quinodimethane (F6-TCNNQ), and 11,11,12,12-tetracyanonaphtho-2,6-quinodimethane (TCNH14), respectively doped into the commonly used hole transporting layer (HTL) poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA). Compared with the devices with the neat PTAA, those with the doped PTAA as the HTLs achieved the improved electroluminescent performances. In particular, the device with the strong oxidant F4-TCNQ exhibited an improvement factor of 27% in the peak external quantum efficiency compared with the control device with the neat PTAA. The capacitance and transient electroluminescent measurements were carried out to identify the imperceptible interactions in the doped HTL and at the interface between the HTL and PQDs.

Low-Temperature Molten Salts Synthesis: CsPbBr3 Nanocrystals with High Photoluminescence Emission Buried in Mesoporous SiO2

Using mesoporous SiO₂ to encapsulate CsPbBr₃ nanocrystals is one of the best strategies to exploit such materials in devices. However, the CsPbBr₃/SiO₂ composites produced so far do not exhibit strong photoluminescence emission and, simultaneously, high stability against heat and water. We demonstrate a molten-salts-based approach delivering CsPbBr₃/mesoporous-SiO₂ composites with high PLQY (89 ± 10%) and high stability against heat, water, and aqua regia. The molten salts enable the formation of perovskite nanocrystals and other inorganic salts (KNO₃-NaNO₃-KBr) inside silica and the sealing of SiO₂ pores at temperatures as low as 350 °C, representing an important technological advancement (analogous sealing was observed only above 700 °C in previous reports). Our CsPbBr₃/mesoporous-SiO₂ composites are attractive for different applications: as a proof-of-concept, we prepared a white-light emitting diode exhibiting a correlated color temperature of 7692K. Our composites are also stable after immersion in saline water at high temperatures (a typical underground environment of oil wells), therefore holding promise as oil tracers.

Present trends in the encapsulation of anticancer drugs

Different nanomedicine devices that were developed during the recent years can be suitable candidates for their application in the treatment of various deadly diseases such as cancer. From all the explored devices, the nanoencapsulation of several anticancer medicines is a very promising approach to overcome some drawbacks of traditional medicines: administered dose of the drugs, drug toxicity, low solubility of drugs, uncontrolled drug delivery, resistance offered by the physiological barriers in the body to drugs, among others. In this chapter, the most important and recent progress in the encapsulation of anticancer medicines is examined: methods of preparation of distinct nanoparticles (inorganic nanoparticles, dendrimers, biopolymeric nanoparticles, polymeric micelles, liposomes, polymersomes, carbon nanotubes, quantum dots, and hybrid nanoparticles), drug loading and drug release mechanisms. Furthermore, the possible applications in cancer prevention, diagnosis, and cancer therapy of some of these nanoparticles have been highlighted.

Investigation on reliability of red micro-light emitting diodes with atomic layer deposition passivation layers

In this study, AlGaInP red light emitting diodes with sizes ranging from 5 to 50 micrometers were fabricated and characterized. The atomic layer deposition technology is applied to coat a layer of silicon dioxide for passivation and protection. The top emission area is covered by ITO layer to maximize the optical output. From the optical measurement, the linewidth and emission peaks shift very little among different current levels (from 30 to 150 A/cm²). High current level lifetests are performed and a 15 µm ALD device can last 27 hours of continuous operation at 100 A/cm² before their diode junction failed. A much shorter lifetime of 5.32 hours was obtained when the driving current is raised to 400 A/cm². When the same condition was applied to 15 µm PECVD devices, 25 hours and 4.33 hours are registered for 100 A/cm² and 400 A/cm² tests, respectively. The cross-sectional SEM reveals the voids, defects, and dark lines developed during the aging tests, and most of them are caused by top contact failure. The surface layers of ITO and SiO₂ were melted and the dark lines which were originated from the top surface propagated through the device and led to the eventual failure of the diode. The optical intensity degradation slopes of different sizes of devices indicate a large device can last longer in this accelerated aging test. The efficiencies of the devices are also evaluated by the ABC model and the fitted bimolecular coefficient ranges from 1.35 to 3.40×10^-10 cm³/s.

Synthesis of Blue-Emissive InP/GaP/ZnS Quantum Dots via Controlling the Reaction Kinetics of Shell Growth and Length of Capping Ligands

The development of blue-emissive InP quantum dots (QDs) still lags behind that of the red and green QDs because of the difficulty in controlling the reactivity of the small InP core. In this study, the reaction kinetics of the ZnS shell was controlled by varying the length of the hydrocarbon chain in alkanethiols for the synthesis of the small InP core. The reactive alkanethiol with a short hydrocarbon chain forms the ZnS shell rapidly and prevents the growth of the InP core, thus reducing the emission wavelength. In addition, the length of the hydrocarbon chain in the fatty acid was varied to reduce the nucleation kinetics of the core. The fatty acid with a long hydrocarbon chain exhibited a long emission wavelength as a result of the rapid nucleation and growth, due to the insufficient In–P–Zn complex by the steric effect. Blue-emissive InP/GaP/ZnS QDs were synthesized with hexanethiol and lauryl acid, exhibiting a photoluminescence (PL) peak of 485 nm with a full width at half-maximum of 52 nm and a photoluminescence quantum yield of 45%. The all-solution processed quantum dot light-emitting diodes were fabricated by employing the aforementioned blue-emissive QDs as an emitting layer, and the resulting device exhibited a peak luminance of 1045 cd/m², a current efficiency of 3.6 cd/A, and an external quantum efficiency of 1.0%.