Reducing Emission Linewidth of Pure-Blue ZnSeTe Quantum Dots through Shell Engineering toward High Color Purity Light-Emitting Diodes

Hot Carrier Cooling and Multiphoton Absorption of Quasi-Type II ZnSeTe-Based Quantum Dots

Ternary ZnSeTe quantum dots (QDs) are regarded as the most promising Cd-free blue emitters, while their fundamental optical properties such as hot carrier (HC) cooling process and multiphoton absorption (MPA) remain unclear, which will hinder their potential application. In this work, we compare the HC cooling processes of ZnSeTe/ZnSeS and ZnSeTe/ZnSeS/ZnS QDs and find that the HC cooling times of ZnSeTe/ZnSeS/ZnS QDs are insensitive to excitation intensity as a result of the suppressed hot-phonon bottleneck and Auger effect. Importantly, we have determined the two- to five-photon absorption cross sections of two kinds of QDs, highlighting the advantages of ZnS shells in enhancing MPA cross sections of ZnSeTe-based QDs. These insightful findings shed light on the underlying optical properties of ZnSeTe-based QDs and emphasize the critical role of the shell in engineering their HC cooling and MPA performance.

X-Type Ligands Effect on the Operational Stability of Heavy-Metal-Free Quantum Dot Light-Emitting Diodes

ZnSeTe quantum dots (QDs) offer an efficient avenue for realizing heavy-metal-free light-emitting diodes (LEDs) that meet the Rec.2100 blue standard. Synthetic core-shell engineering has enabled big advances in the external quantum efficiency (EQE) of ZnSeTe QD-LEDs. However, the mechanisms behind the degradation of the operational stability of ZnSeTe QD-LEDs remain relatively unexplored. In this study, we explore the impact of ligand density and composition on both material and device stability. We developed a solid-film ligand exchange utilizing an inorganic X-type ligand (zinc chloride), revealing that the substitution of inorganic ligands for organic counterparts significantly influences the stability of both materials and devices.

Recent Progress of Quantum Dots Light-Emitting Diodes: Materials, Device Structures, and Display Applications

Colloidal quantum dots (QDs), as a class of 0D semiconductor materials, have generated widespread interest due to their adjustable band gap, exceptional color purity, near-unity quantum yield, and solution-processability. With decades of dedicated research, the potential applications of quantum dots have garnered significant recognition in both the academic and industrial communities. Furthermore, the related quantum dot light-emitting diodes (QLEDs) stand out as one of the most promising contenders for the next-generation display technologies. Although QD-based color conversion films are applied to improve the color gamut of existing display technologies, the broader application of QLED devices remains in its nascent stages, facing many challenges on the path to commercialization. This review encapsulates the historical discovery and subsequent research advancements in QD materials and their synthesis methods. Additionally, the working mechanisms and architectural design of QLED prototype devices are discussed. Furthermore, the review surveys the latest advancements of QLED devices within the display industry. The narrative concludes with an examination of the challenges and perspectives of QLED technology in the foreseeable future.

ZnSeTe quantum dots modified with zinc chloride toward bright trap-state emission

ZnSeTe quantum dots (QDs) attract growing interest owing to their low threats to health and the environment. They are widely applied as emitters in displays and lighting devices. Previous findings have indicated that inorganic halides are excellent candidates for surface ligands on QDs. By incorporating inorganic halides during the synthesis process, the photoluminescence (PL) intensity and quantum yield (QY) of QDs can be significantly enhanced. However, the alteration of surface states in QDs induced by zinc halide modification and the mechanism of formation of trap-state radiative recombination processes have been less discussed. Herein, we proposed a synthesis strategy for ZnSeTe/ZnSe/ZnSeS/ZnS core/shell/shell/shell QDs modified with ZnCl2, and by comparing the morphology and elemental composition of QDs with different amounts of ZnCl2 added, we revealed the regulatory mechanism of nanocrystal growth in the presence of ZnCl2. QDs with modification of ZnCl2 exhibited broad yellow fluorescence, distinct from the intrinsic blue emission. Through spectroscopic and surface ligand analyses, we attributed this yellow emission to the intermediate state energy levels caused by the defects on the surface. Finally, we used the QDs with broad linewidth emission to fabricate a simple white-light-emitting diode (WLED). This work provided new insights into the role of inorganic ligands and the use of a single emitting material in solid-state lighting devices.

Ultranarrow Deep-Blue Luminescence of Perovskite Nanocrystals by A-Site Cation Control

Metal-halide perovskite nanocrystals (NCs) are one of the most promising emitters for the application of display and nanolight sources. The full width at half-maximum (FWHM) of photoluminescence (PL) emission is essential for color purity, which however remains a difficulty to further reduce the FWHM of the perovskite NCs at room temperature. Here, we show the quasi-sphere perovskite NCs with narrow PL emission at a deep-blue wavelength of ∼430 nm; its PL FWHM reaches ∼11 nm at room temperature, owing to the monodispersion in size distribution as well as the symmetric quasi-sphere morphology of NCs releasing the fine structure splitting-induced inhomogeneous broadening. Through regulating A cations with respect to the ratio of FA (or MA)-to-Cs and Cs-to-Pb, the PL emission of the NCs could be tuned from ∼505 to ∼430 nm combined with varied morphologies from large cube to small quasi-sphere. Such spectroscopic and morphological discrepancies are supposed to be attributed to the different crystalline kinetics that is strongly dependent on the synthetic condition. To be specific, in the case of increasing FA (or MA)-to-Cs, the growth rate of CsPbBr3 and FAPbBr3 (or MAPbBr3) perovskites is determined by the reactivity of transient species, while in the case of decreasing the Cs-to-Pb ratio, the growth rate of perovskites is slowed down by the serious reduction of Cs+ in the precursor. This study provides an effective strategy to adjust the emission across from green to deep-blue color and promotes the perovskite NCs with a narrow FWHM, and tunable PL emission facilitates in application of optoelectronic devices.

Blue ZnSeTe quantum dot light-emitting diodes with low efficiency roll-off enabled by an in situ hybridization of ZnMgO nanoparticles and amino alcohol molecules

ZnSeTe quantum dots (QDs) have been employed as promising emitters for blue QD-based light-emitting diodes (QLEDs) due to their unique optoelectronic properties and environmental friendliness. However, such QLEDs usually suffer from serious efficiency roll-off primarily stemming from exciton loss at the interface of the QD layer and the ZnMgO (ZMO) electron transport layer (ETL), which remarkably hinders their application in flat-panel displays. Herein, we propose an in situ hybridization strategy that involves the pre-introduction of amino alcohols into the reaction solution. This strategy effectively suppresses the nucleophilic condensation process by facilitating the coordination of ammonium and hydroxyl groups with metal cations (M2+, i.e. Zn2+ and Mg2+). It slows down the growth rate of ZMO nanoparticles (NPs) while simultaneously facilitating M-O coordination, resulting in the synthesis of small-sized and low-defect ZMO NPs. Notably, this in situ hybridization approach not only alleviates emission quenching at the QDs/ETL interface but also elevates the energy level of the ETL for enhancing carrier injection. We further investigated the impact of amino alcohols with varying carbon-chain lengths on the performance of ZMO NPs and the corresponding LED devices. The optimal blue ZnSeTe QLED demonstrates an impressive EQE of 8.6% with only an ∼11% drop when the current density is increased to 200 mA cm-2, and the device operating lifetime extends to over 1300 h. Conversely, the device utilizing traditionally post-treated ZMO NPs as the ETL exhibits 45% efficiency roll-off and device lifetime of merely 190 h.

Crystallographic and Photophysical Analysis on Facet-Controlled Defect-Free Blue-Emitting Quantum Dots

The burgeoning demand for commercializing self-luminescing quantum dot (QD) light-emitting diodes (LEDs) has stimulated extensive research into environmentally friendly and efficient QD materials. Hydrofluoric acid (HF) additive improves photoluminescence (PL) properties of blue-emitting ZnSeTe QDs, ultimately reaching a remarkable quantum yield (QY) of 97% with an ultranarrow peak width of 14 nm after sufficient HF addition. The improvement in optical properties of the QDs is accompanied by a morphology change of the particles, forming cubic-shaped defect-free ZnSeTe QDs characterized by a zinc blende (ZB) crystal structure. This treatment improves the QD-emitting properties by facilitating facet-specific growth, selectively exposing stabilized (100) facets, and reducing the lattice disorders. The facet-specific growth process gives rise to defect-free monodispersed cubic dots that exhibit remarkably narrow and homogeneous PL spectra. Meticulous time-resolved spectroscopic studies allow an understanding of the correlation between ZnSeTe QDs' particle shape and performance following HF addition. These investigations shed light on the intricacies of the growth mechanism and the factors influencing the PL efficiency of the resulting QDs. The findings significantly contribute to understanding the role of HF treatment in tailoring the optical properties of ZnSeTe QDs, thereby bringing it closer to the realization of highly efficient and bright QD-LEDs for various practical applications.

Ultrastable Photodetectors Based on Blue CsPbBr3 Perovskite Nanoplatelets via a Surface Engineering Strategy

Recently, photodetectors based on perovskite nanoplatelets (NPLs) have attracted considerable attention in the visible spectral region owing to their large absorption cross-section, high exciton binding energy, excellent charge transfer properties, and appropriate flexibility. However, their stability and performance are still challenging for perovskite NPL photodetectors. Here, a surface engineering strategy to enhance the optical stability of blue-light CsPbBr3 NPLs by acetylenedicarboxylic acid (ATDA) treatment has been developed. ATDA has strong binding capacity and a short chain length, which can effectively passivate defects and significantly improve the photoluminescence quantum efficiency, stability, and carrier mobility of NPLs. As a result, ATDA-treated CsPbBr3 NPLs exhibit improved optical properties in both solutions and films. The NPL solution maintains high PL performance even after being heated at 80 °C for 2 h, and the NPL film remains nondegradable after 4 h of exposure to ultraviolet irradiation. Especially, photodetectors based on the treated CsPbBr3 NPL films demonstrate exceptional performance, especially when the detectivity approaches up to 9.36 × 1012 Jones, which can be comparable to the best CsPbBr3 NPL photodetectors ever reported. More importantly, the assembled devices demonstrated high stability (stored in an air environment for more than 30 days), significantly exceeding that of untreated NPLs.

Blue-Emissive ZnSeTe Quantum Dots and Their Electroluminescent Devices

Over the last two decades, quantum-dot light-emitting diodes (QLEDs), also known as quantum dot (QD) electroluminescent devices, have gained prominence in next-generation display technologies, positioning them as potential alternatives to organic light-emitting diodes. Nonetheless, challenges persist in enhancing key device performances such as efficiency and lifetime, while those of blue QLEDs lag behind compared with green and red counterparts. In this Perspective, we discuss key factors affecting the photoluminescence characteristics of environmentally benign blue-emissive ternary ZnSeTe QDs, including composition, core/shell heterostructure, and surface ligand. Notably, we highlight the recent progress in breakthrough strategies to enhance blue QLED performance, examining the effects of the ZnSeTe QD attribute and device architecture on device performance. This Perspective offers insights into integrated aspects of QD material and device structure in overcoming challenges toward a high-performance blue ZnSeTe QLED.

Repercussions of the Inner Shell Layer on the Performance of Cd-Free Quantum Dots and Their Light-Emitting Diodes

Indium phosphide (InP) and zinc selenium tellurium (ZnSeTe) quantum dots (QDs) as less toxic alternatives have received substantial attention. The structure of QDs generally consists of a QD core, inner shell layer, and outer shell layer. We reckon that the inner shell layer, especially its components and thickness, have a significant influence on the optical and electronic performances of QDs. In this Perspective, we compare optical properties of these QDs with different inner shells and summarize how typical inner shell components and thickness influence their optical properties. The impact of the inner shell on the performance of QD light-emitting diodes (QLEDs) has also been discussed. The appropriate components and thickness of the inner shell both contribute to alleviate valence or lattice mismatch, thereby enhancing the performance of QDs. We expect that this Perspective could heighten awareness of the significance and impact of the inner shell layer in QDs and facilitate further development of QDs and QLEDs.