Stability Of Quantum Dots Research Articles

Highly Efficient, Bright, and Stable Colloidal Quantum Dot Short‐Wave Infrared Light‐Emitting Diodes

AbstractUnbalanced charge injection is deleterious for the performance of colloidal quantum dot (CQD) light‐emitting diodes (LEDs) as it deteriorates the quantum efficiency, brightness, and operational lifetime. CQD LEDs emitting in the infrared have previously achieved high quantum efficiencies but only when driven to emit in the low‐radiance regime. At higher radiance levels, required for practical applications, the efficiency decreased dramatically in view of the notorious efficiency droop. Here, a novel methodology is reported to regulate charge supply in multinary bandgap CQD composites that facilitates improved charge balance. The current approach is based on engineering the energetic potential landscape at the supra‐nanocrystalline level that has allowed to report short‐wave infrared PbS CQD LEDs with record‐high external quantum efficiency in excess of 8%, most importantly, at a radiance level of ≈5 W sr−1 m2, an order of magnitude higher than prior reports. Furthermore, the balanced charge injection and Auger recombination reduction has led to unprecedentedly high operational stability with radiance half‐life of 26 068 h at a radiance of 1 W sr−1 m−2.

Convenient synthesis of high-quality, all-inorganic lead halide perovskite nanocrystals for high purity monochrome QLED

ABSTRACT In recent years, perovskite quantum dots (QDs) have become a new class of semiconductor materials due to their high monodispersity and adjustable emission spectra. However, there are few studies on perovskite QDs ligands, and there are some problems such as poor stability and low photoluminescence quantum yield (PLQY). Here, we prepared CsPbBr3 QDs with excellent optical properties and crystallinity by using caesium stearate as the precursor. Besides, we systematically studied the effects of different chain length organic amines on the yield, optical properties and stability of CsPbBr3 QDs. The experimental results show that the long-chain organic amin oleylamine and dodecylamine (DOAm) have better encapsulation properties, and the synthesised QDs have better crystallinity and stability. CsPbBr3 QDs with PLQY of 90%were obtained by using oleic acid (OA)/DOAm as a ligand at 140°C. Moreover, a high purity monochrome quantum dot light-emitting diode was prepared.

Internally-externally defects-tailored MAPbI3 perovskites with highly enhanced air stability and quantum yield

Methyl-ammonium lead iodide (MAPbI3) perovskite quantum dots (QDs) have emerged as a promising material for photoelectronic, however, they usually suffer intrinsically from the environmental instability and low photoluminescence quantum yield (PLQY), which will seriously impede their commercial applications. Here, we report an internal-external combination strategy by lowering the dose of good solvent and reducing the chain length of amine ligand to simultaneously enhance the air stability and PLQY of MAPbI3 QDs. The low-dose solvent can effectively reduce internal iodine vacancies defects and external residual solvent molecules, meanwhile, the faster and denser assembly of nimble short-chain (SC) ligand on the MAPbI3 QDs surface can helpfully enhance the external surface passivation. As a result, compared to MAPbI3 QDs synthesized by traditional ligand-assisted reprecipitation (LARP) method, the air stability and PLQY of which are improved by more than four orders of magnitude (from a few minutes to dozens of days) and nearly two times (from 42% to 80%) prepared by our strategy. Besides, this strategy can widely tune the color of MAPbX3 (X = Cl, Br, I) QDs from 388 to 735 nm through regulating components. This internal-external combination strategy can provide some beneficial enlightenment for preparing long-term air-stable hybrid perovskite QDs with high PLQY, which drastically driving their commercial applications.

Zn-doping enhances the photoluminescence and stability of PbS quantum dots for in vivo high-resolution imaging in the NIR-II window

Lead sulfide (PbS) quantum dots (QDs) are important near infrared (NIR) luminescent materials with tunable and strong emission covering a broad NIR region. However, their optical properties are quite sensitive to air, water, and high temperature due to the surface oxidation, thus limiting their applications in optoelectronic devices and biological imaging. Herein, a cation-doping strategy is presented to make a series of high-quality Zn-doped PbS QDs with strong emission covering whole second near-infrared window (NIR-II, 1,000-1,700 nm). First-principle calculations confirmed that Zn dopants formed dopant states and decreased the recombination energy gap of host PbS. Notably, the Zn dopants significantly improved the quantum yield, photoluminescence lifetime and thermal stability of PbS QDs. Moreover, the PEGylated Zn-doped PbS QDs emitting in the NIR-llb window (1,500-1,700 nm) realized the noninvasive imaging of cerebral vascular of mouse with high resolution, being able to distinguish blood capillary. This material not only provides a new tool for deep tissue fluorescence imaging, but is also promising for the development of other NIR related devices.

Quantum Dot-Functionalized Extracellular Matrices for In Situ Monitoring of Cardiomyocyte Activity

Quantum dots (QDs) have been hypothesized as potential probes for the optical monitoring of electrogenic cell activity given their high optical absorption cross sections compared to organic fluorophores, high brightness, and low photobleaching. Despite the theoretical predictions, less than a handful of papers reported QD-based imaging of cell activity responses because of the critical membrane localization requirements for membrane voltage sensing. Moreover, to the best of our knowledge, two-photon imaging of cellular activity-dependent QD photoluminescence was never demonstrated. The high spatial and temporal resolutions and higher penetration depths, inherent to nonlinear light–tissue interactions, are particularly interesting for biological imaging. In this work, we functionalized fibrous collagen matrices with semiconductor QDs and thereby created artificial extracellular matrices that can optically report cardiomyocyte contractile activity based on QD two-photon fluorescence. We have applied these optically addressable nanofiber matrices to monitor the contractile activity of primary cardiomyocytes, and, for validation, we compared the optical responses with the simultaneously recorded patch-clamp data. Given the long-term stability of QD fluorescence, near-infrared excitation, and high spatiotemporal resolution achievable through multiphoton imaging, this approach can be used for continuous monitoring of cellular functions in cardiac tissue constructs.

Electrogenerated Chemiluminescence and Spectroelectrochemistry Characteristics of Blue Photoluminescence Perovskite Quantum Dots.

Lead-based perovskite MAPbX3 (MA = CH3NH3, X = Cl and Br) has shown great potential benefits to advance modern optoelectronics and clean energy harvesting devices. Poor structural stability is one of the major challenges of MAPbX3 perovskite materials to overcome to achieve desired device performance. Here, we present the electrochemical stability study of CH3NH3PbCl1.08Br1.92 quantum dots (QDs) by electrogenerated chemiluminescence (ECL) and photoluminescence (PL) spectroelectrochemistry methods. Electrochemical anodization of pristine MAPbX3 QD film results in the disproportionate loss of methylammonium and halide ions (X = Cl and Br). ECL efficiency and stability of perovskite QDs in the presence of coreactant tripropyl amine (TPrA) can be greatly improved after being incorporated into a polystyrene (PS) matrix. Mass spectrum and X-ray photoelectron spectroscopy (XPS) measurements were used to provide chemical composition variation details of QDs, which are responsible for the ECL and PL characteristics (e.g., wavelength redshift) of perovskite QDs in an electrochemical cell.

Micro-light-emitting diodes with quantum dots in display technology

Micro-light-emitting diodes (μ-LEDs) are regarded as the cornerstone of next-generation display technology to meet the personalised demands of advanced applications, such as mobile phones, wearable watches, virtual/augmented reality, micro-projectors and ultrahigh-definition TVs. However, as the LED chip size shrinks to below 20 μm, conventional phosphor colour conversion cannot present sufficient luminance and yield to support high-resolution displays due to the low absorption cross-section. The emergence of quantum dot (QD) materials is expected to fill this gap due to their remarkable photoluminescence, narrow bandwidth emission, colour tuneability, high quantum yield and nanoscale size, providing a powerful full-colour solution for μ-LED displays. Here, we comprehensively review the latest progress concerning the implementation of μ-LEDs and QDs in display technology, including μ-LED design and fabrication, large-scale μ-LED transfer and QD full-colour strategy. Outlooks on QD stability, patterning and deposition and challenges of μ-LED displays are also provided. Finally, we discuss the advanced applications of QD-based μ-LED displays, showing the bright future of this technology.

Quantum Dots in an InSb Two-Dimensional Electron Gas

Indium antimonide (InSb) two-dimensional electron gases (2DEGs) have a unique combination of material properties: high electron mobility, strong spin-orbit interaction, large Land\'{e} g-factor, and small effective mass. This makes them an attractive platform to explore a variety of mesoscopic phenomena ranging from spintronics to topological superconductivity. However, there exist limited studies of quantum confined systems in these 2DEGs, often attributed to charge instabilities and gate drifts. We overcome this by removing the $\delta$-doping layer from the heterostructure, and induce carriers electrostatically. This allows us to perform the first detailed study of stable gate-defined quantum dots in InSb 2DEGs. We demonstrate two distinct strategies for carrier confinement and study the charge stability of the dots. The small effective mass results in a relatively large single particle spacing, allowing for the observation of an even-odd variation in the addition energy. By tracking the Coulomb oscillations in a parallel magnetic field we determine the ground state spin configuration and show that the large g-factor ($\sim$30) results in a singlet-triplet transition at magnetic fields as low as 0.3 T.

Highly luminescent and stable CH3NH3PbBr3 quantum dots with 91.7% photoluminescence quantum yield: Role of guanidinium bromide dopants

Abstract Although perovskite quantum dots (PQDs) have received considerable attention, defects in PQDs can significantly degrade the properties and device performance. In this study, we report on an effective strategy for synthesizing highly luminescent CH3NH3PbBr3 quantum dots (QDs) by a simple doping. To remove such defects, guanidinium bromide (GuBr) was doped into the CH3NH3PbBr3 QDs synthesized by the ligand-assisted reprecipitation technique. From XRD and TEM studies, the doping of GuBr into the QD lattices was verified. In addition, the surfaces of PQDs with and without GuBr dopants were analyzed by XPS to trace the metallic Pb acting as a major recombination center. The GuBr doping resulted in the size uniformity of QDs and effectively eliminated defects and metallic Pb, which enhanced the photoluminescence quantum yield (PLQY) through the inhibition of the non-radiative recombination pathway. Furthermore, the recombination dynamics in the QDs were examined by using time-resolved photoluminescence and fluorescence lifetime imaging to verify the role of GuBr dopants. By optimizing the amount of GuBr doping, the CH3NH3PbBr3 QDs with strong green emission achieved a maximum PLQY of 91.7%.

Shell properties play an important role in the stability of green quantum dots

A comprehensive study reveals the structural requirements for achieving bright and stable green light-emitting quantum dots that exhibit suppressed blinking or photobleaching.

N,N′,N′-trisubstituted thiourea as a novel sulfur source for the synthesis of Mn-doped ZnS QDs

Abstract Doping of semiconductor quantum dots (QDs) by transition metals (such as Mn, Cu, Ni, etc.) is a great technique to impact the optical and structural properties of the host materials. The introduction of a small amount of impurity into the host semiconductor matrix leads to the shift of PL emission due to the change in the recombination process. The new emission pathways created by dopant influence the photoluminescence intensity, Stokes shift, lifetime and stability of QDs. Mn-doped ZnS QDs (1–15 mol. %) have been synthesized by the effective low-cost and nontoxic hot-injection method. N-phenylmorpholine-4-carbothioamide has been successfully applied as a novel source of sulfur in the synthesis of Mn-doped ZnS QDs. X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and infrared (IR) spectroscopy were used for the characterization of morphology and structure of synthesized Mn-doped ZnS QDs. Our materials exhibit strong photoluminescence yellow-orange emission with a photoluminescence quantum yield (PL QY) of 41%. All Mn-doped ZnS QDs have a face-centered cubic structure with a mean crystalline size of 3.8–5.1 nm. Additionally, this synthetic approach enables the synthesis of Mn-doped ZnS QDs with tunable band gaps between ∼3.5 eV and 3.60 eV.

Highly Stable All‐Inorganic Perovskite Quantum Dots Using a ZnX2‐Trioctylphosphine‐Oxide: Application for High‐Performance Full‐Color Light‐Emitting Diode

AbstractPerovskite is a very promising material that is being extensively studied at the bulk and nanosize scales because it has outstanding optical properties, including high quantum efficiency and narrow emission spectra. However, perovskite has stability issues related to heat, air, and light. To overcome these, highly stable perovskite quantum dots (PeQDs) are developed using excess Zn precursor and trioctylphosphine‐oxide (TOPO). In particular, it is clarified that Zn and TOPO are combined and these complexes are attached to the surface of the PeQDs through 31P NMR. They not only have high quantum efficiency and sharp full width at half maximum values (15–30 nm) but also have improved long‐term stability at high temperature. Additionally, XPS measurements are conducted for a detailed surface analysis of PeQDs, finding that the TOPO‐Zn complex effectively decrease PbO bonding in the lattice. Perovskite full‐color electroluminescence (EL) devices are fabricated using PeQDs and 9,9‐bis[4‐[(4‐ethenylphenyl)methoxy]phenyl]‐N2,N7‐di‐1‐naphthalenyl‐N2,N7‐diphenyl‐9H‐fluorene‐2,7‐diamine (VB‐FNPD) as a new cross‐linkable hole transporting material. The VB‐FNPD has a high‐hole carrier mobility compared to the PVK as conventional hole‐transporting layer. As a result of EL performance, they have high EQE (%) and current efficiency (Cd A−1) of (7.12%, 9.93 Cd A−1) for red, (6.06%, 32.5 Cd A−1) for green, and (0.56%, 0.88 Cd A−1) for blue‐emitting devices, respectively.

Chemically resistant and thermally stable quantum dots prepared by shell encapsulation with cross-linkable block copolymer ligands

Endowing quantum dots (QDs) with robustness and durability have been one of the most important issues in this field, since the major limitations of QDs in practical applications are their thermal and oxidative instabilities. In this work, we propose a facile and effective passivation method to enhance the photochemical stability of QDs using polymeric double shell structures from thiol-terminated poly(methyl methacrylate-b-glycidyl methacrylate) (P(MMA-b-GMA)-SH) block copolymer ligands. To generate a densely cross-linked network, the cross-linking reaction of GMA epoxides in the PGMA block was conducted using a Lewis acid catalyst under an ambient environment to avoid affecting the photophysical properties of the pristine QDs. This provides QDs encapsulated with robust double layers consisting of highly transparent PMMA outer-shell and oxidation-protective cross-linked inner shell. Consequently, the resulting QDs exhibited exceptional tolerance to heat and oxidants when dispersed in organic solvents or QD-nanocomposite films, as demonstrated under various harsh conditions with respect to temperature and oxidant species. The present approach not only provides simple yet effective chemical means to enhance the thermochemical stability of QDs, but also offers a promising platform for the hybridization of QDs with polymeric materials for developing robust light-emitting or light-harvesting devices.

Core/Shell Quantum Dots Solar Cells

AbstractSemiconductor nanocrystals, the so‐called quantum dots (QDs), exhibit versatile optical and electrical properties. However, QDs possess high density of surface defects/traps due to the high surface‐to‐volume ratio, which act as nonradiative carrier recombination centers within the QDs, thereby deteriorating the overall solar cell performance. The surface passivation of QDs through the growth of an outer shell of different materials/compositions called “core/shell QDs” has proven to be an effective approach to reduce the surface defects and confinement potential, which can enable the broadening of the absorption spectrum, accelerate the carrier transfer, and reduce exciton recombination loss. Here, the recent research developments in the tailoring of the structure of core/shell QDs to tune exciton dynamics so as to improve solar cell performance are summarized. The role of band alignment of core and shell materials, core size, shell thickness/compositions, and interface engineering of core/thick shell called “giant” QDs on electron–hole spatial separation, carrier transport, and confinement potential, before and after grafting on the carrier scavengers (semiconductor/electrolyte), is described. Then, the solar cell performance based on core/shell QDs is introduced. Finally, an outlook for the rational design of core/shell QDs is provided, which can further promote the development of high‐efficiency and stable QD sensitized solar cells.

Facile Preparation of Stable Solid-State Carbon Quantum Dots with Multi-Peak Emission.

Aggregation-caused quenching (ACQ) effect, known as the main cause to restrain solid-state luminescence of carbon quantum dots (CQDs), hinders further application of CQDs in white light-emitting diodes (WLED). Here, a complex of CQDs and phthalimide crystals (CQDs/PC) was prepared through a one-step solvothermal method. CQDs/PC prevented CQDs from touching directly by embedding the CQDs in phthalimide crystal matrix in situ, which effectively reduced the ACQ effect. Furthermore, CQDs/PC exhibited multi-peak fluorescence spectra that span the green, yellow and orange spectral regions. Finally, a WLED fabricated based on CQDs/PC achieved a color-rendering index of 82 and a correlated color temperature of 5430 K. This work provides a quick and effective strategy to apply CQDs to WLED.

ZnCl2 Enabled Synthesis of Highly Crystalline and Emissive Carbon Dots with Exceptional Capability to Generate O2⋅–

Summary Highly crystalline and emissive carbon dots (CDs) are firstly synthesized via an ionothermal method in organic solvents. In contrast to well-established approaches, ZnCl2 is utilized as the pyrolysis-promoting agent to prepare emissive CDs with tunable wavelengths, directly by carbonization from different O and N precursors under a mild reaction condition at 210°C. More than 50% synthetic yield and 39% photoluminescent quantum yield (blue CD) are obtained. XAFS measurements, in conjunction with TEM, HAADF-STEM, UPS, and ESR analyses, allow us to obtain energy diagram configuration and confirm the luminescent nature of these hard-core structured CDs. Importantly, the resulting CDs exhibit excellent capability to photogenerate superoxide radical anion (O2⋅–), which can be exemplified by both photodynamic therapy and photooxidative cyclization synthesis of tetrahydroquinolines. Representative pharmaceutical mifepristone can be derivatized in 90% yield within 10 min of irradiation of the CDs in an elegant flow reactor.

Alleviating the toxicity of quantum dots to Phanerochaete chrysosporium by sodium hydrosulfide and cysteine.

Quantum dots (QDs) have caused large challenges in clinical tests and biomedical applications due to their potential toxicity from nanosize effects and heavy metal components. In this study, the physiological responses of Phanerochaete chrysosporium (P. chrysosporium) to CdSe/ZnS QDs with either an inorganic sulfide NaHS or an organic sulfide cysteine as antidote have been investigated. Scanning electron microscope analysis showed that the hyphal structure and morphology of P. chrysosporium have obviously changed after exposure to 100nM of COOH CdSe/ZnS 505, NH2 CdSe/ZnS 505, NH2 CdSe/ZnS 565, or NH2 CdSe/ZnS 625. Fourier transform infrared spectroscopy analysis indicated that the existence of hydroxyl, amino, and carboxyl groups on cell surface could possibly conduct the stabilization of QDs in an aqueous medium. However, after NaHS or cysteine treatment, the cell viability of P. chrysosporium exposed to CdSe/ZnS QDs increased as compared to control group, since NaHS and cysteine have assisted P. chrysosporium to alleviate oxidative damage by regulating lipid peroxidation and superoxide production. Meanwhile, NaHS and cysteine have also stimulated P. chrysosporium to produce more antioxidant enzymes (superoxide dismutase and catalase), which played significant roles in the defense system. In addition, NaHS and cysteine were used by P. chrysosporium as sulfide sources to promote the glutathione biosynthesis to relieve CdSe/ZnS QDs-induced oxidative stress. This work revealed that sulfide sources (NaHS and cysteine) exerted a strong positive effect in P. chrysosporium against the toxicity induced by CdSe/ZnS QDs.

Perspective: Toward highly stable electroluminescent quantum dot light-emitting devices in the visible range

With significant improvements in external quantum efficiency (EQE) and stability for red, green, and blue devices over the past decade, the future of electroluminescent quantum dot light-emitting devices (QDLEDs) is bright. State-of-the-art QDLEDs have achieved >30% EQE and a >2 000 000 h electroluminescence half-life for an initial luminance of 100 cd m−2, rivaling those of organic light-emitting devices. To date, most of the improvements in QDLED performance have been primarily achieved via advancements in QD synthesis and design that aim at reducing Auger recombination and improving the balance between electron and hole concentrations in the emissive QD layer. However, recent work is starting to reveal the critical role that other device layers, as well as interlayer interfaces, play in limiting QDLED stability. Degradation within the organic hole transport layer (HTL) and near the QD/HTL interface has recently been found to lead to the formation of nonradiative recombination centers that quench excitons in the emissive QD layer and contribute to QDLED failure over time. Looking forward, minimizing degradation in the charge transport layers will likely be crucial for the realization of highly stable QDLEDs and this perspective provides potential avenues to achieve these enhancements. In particular, tailoring the QD energy levels via material selection or interfacial dipoles may reduce charge carrier accumulation in the transport layers and replacing the organic HTL with an inorganic alternative may be an effective approach to circumvent the inherent susceptibility of organic semiconductors to exciton-induced degradation.

Phase Transfer and DNA Functionalization of Quantum Dots Using an Easy-to-Prepare, Low-Cost Zwitterionic Polymer.

Small, stable, and bright quantum dots (QDs) are of interest in many biosensing and biomedical imaging applications, but current methodologies for obtaining these characteristics can be highly specialized or expensive. We describe a straightforward, low-cost protocol for functionalizing poly(isobutylene-alt-maleic anhydride) (PIMA) with moieties that anchor to the QD surface (histamine), impart hydrophilicity [(2-aminoethyl)trimethylammonium chloride (Me3N+-NH2)], and provide a platform for biofunctionalization via click chemistry (dibenzocyclooctyne (DBCO)). Guidelines to successfully use this polymer for QD ligand exchange are presented, and an example of biofunctionalization with DNA is shown. Stable QD-DNA conjugates are obtained with high yield and without requiring additional purification steps.

Retraction: A facile cation exchange-based aqueous synthesis of highly stable and biocompatible Ag2S quantum dots emitting in the second near-infrared biological window.

Retraction of 'A facile cation exchange-based aqueous synthesis of highly stable and biocompatible Ag2S quantum dots emitting in the second near-infrared biological window' by Rijun Gui et al., Dalton Trans., 2014, 43, 16690-16697, DOI: 10.1039/C4DT00699B.