Stability Of Quantum Dots Research Articles

Solution-Processed NiO as a Hole Injection Layer for Stable Quantum Dot Light-Emitting Diodes

In this work, we fabricated quantum dot light-emitting diodes using solution-processed NiO as the hole injection layer to replace the commonly used poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonate) (PEDOT:PSS) layer. We successfully prepared NiO films by spin coating the NiO precursor, then annealing them, and then treating them with UV-ozone under optimized conditions. The best device with the NiO film shows higher current efficiency (25.1 cd/A) than that with the PEDOT:PSS layer (22.3 cd/A). Moreover, the long-term stability of the devices with NiO which is annealed at 500 °C is improved substantially. These results suggest that the NiO layer can be a good alternative for developing stable devices.

In-situ guanidinium bromide passivation treatment of CsPbBr3 perovskite quantum dots exhibiting high photoluminescence and environmental stability

All-inorganic CsPbX3 perovskite quantum dots (QDs) are of great interest in the new-generation optoelectronic applications. However, the inferior long-term stability of CsPbX3 QDs has severely hindered their real applications. In this paper, we have developed a simple and efficient in-situ guanidinium bromide (GABr) passivation approach to synthesize CsPbBr3 QDs by introducing appropriate amount of GABr into the precursor solution using the traditional hot injection method. The in-situ GABr passivation treatment is demonstrated to effectively improve the crystallinity and regulate the grain size of CsPbBr3 QDs without changing the crystal structure. More importantly, the in-situ GABr passivation treatment strategy can induce the passivation of surface defects and formation of the stable bromine-rich surface with tri-ligand mode. Consequently, the in-situ GABr passivated CsPbBr3 QDs display remarkably improved optical properties and environmental stability. Additionally, the in-situ GABr passivated CsPbBr3 QDs have been successfully employed in photodetectors and white light-emitting diodes (WLEDs), showing great practical application prospects. Our work may afford a new guideline to prepare CsPbBr3 QDs with high photoluminescence and environmental Stability.

Design of Chemically Stable Organic Perovskite Quantum Dots for Micropatterned Light-Emitting Diodes through Kinetic Control of a Cross-Linkable Ligand System.

Perovskite quantum dot (QD) light-emitting diodes (PeLEDs) are ideal for next-generation display applications because of their excellent color purity, high efficiency, and cost-effective fabrication. However, developing a technology for high-resolution multicolor patterning of perovskite QDs remains challenging, owing to the chemical instability of these materials. To overcome these issues, in this work, the generation of surface defects is prevented by controlling the ligand-binding kinetics using a stable ligand system (Stable LS). The crystalline reconstruction of perovskite QDs after addition of the Stable LS results in an ≈18% increase in their photoluminescence quantum yield in solution and it also improves the ambient stability of the perovskite QD solution. Moreover, the perovskite QDs with Stable LS can undergo cross-linking under UV irradiation. The tightly bridged perovskite QDs effectively prevent moisture-assisted ligand dissociation in film state due to the increased hydrophobicity and restricted movement of the cross-linked surface ligands. Thus, the cross-linked perovskite QD film shows improved chemical/environmental stability without substantial deterioration in optoelectrical properties. As a result, a white electroluminescent device with high resolution (≈1 μm) is successfully fabricated by inkjet printing using green and red perovskite QDs.

Novel CsPbX3@mica composites with excellent optical properties for high efficiency and wide color gamut white light-emitting diode

All inorganic CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) have been widely reported. However, the poor stability of CsPbX3 QDs limits their application in the field of optoelectronics. In this work, CsPbX3 QDs were prepared by the hot injection strategy. We compounded CsPbX3 QDs with mica to improve stability. A series of novel CsPbX3@mica composites with high thermal stability and light radiation stability were successfully fabricated and the narrow full width at half maximum (FWHM) of blue, green and red emissions are ~17 nm, ~21 nm and ~37 nm, respectively. What's more, the photoluminescence quantum yield (PLQY) of CsPbBr3@mica composite is 38.5%. Notably, the white light-emitting diodes (wLED) device can be manufactured by coupling the red-emitting CsPbBr1I2@mica composite material and commercial phosphor YAG: Ce3+ with the InGaN chip to produce bright natural white light. Meanwhile, CsPbX3@mica composites can be used as color conversion materials to construct a LED device, which exhibits a wide color gamut covering up 115.7% of National Television System Committee (NTSC). This present work provided novel CsPbX3@mica composites and could bring the potential inspiration in backlit display and lighting applications.

Enhancing stability and luminescence quantum yield of CsPbBr3 quantum dots by embedded in borosilicate glass

Halide perovskite quantum dots have attracted considerable research interest as excellent candidate for photonic and optoelectronic applications due to their unique optoelectronic properties. Stability is prerequisite and therefore is of critical importance. Here we demonstrate highly stable luminescent CsPbBr3 quantum dots (QDs) can be achieved in different glass matrices via the high temperature melting process and melt-quench method. The microstructure of CsPbBr3 QDs glass as well as their optical properties are systematically characterized by microscopic techniques and time-resolved spectroscopic techniques. We conclude the surface passivation is the key aspect for the high stability and high luminescence by embedding the quantum dots in the glass matrix. This study provides technical method to form highly stable luminescent solid devices and detailed physical understanding which is critical for the practical applications.

Fabrication and optical properties of high-quality blue-emitting CsPbBr3 QDs-PMMA films

Abstract The blue-emitting CsPbBr3 quantum dots (QDs) have currently received widespread attention due to high photoluminescence quantum yields (PLQYs), but their instability mainly caused by self-aggregation or environmental erosion (i.e. moisture and oxygen) should be solved to gain more progress in further application. This paper presented a feasible approach to high-quality blue-emitting CsPbBr3 QDs-polymethylmethacrylate (PMMA) films, in which PMMA provided a solid framework to protect CsPbBr3 QDs by the chelation between C O and Pb2+ ions, thus resulting in the stability of CsPbBr3 QDs. The CsPbBr3 QDs-PMMA films exhibited remarkable properties including water resistance, flexibility, deep-blue emission (465 nm), and comparatively high PLQY (45%). The blue LED fabricated by the films displayed a CIE coordinate (0.14, 0.10), which was corresponding to the standard blue CIE coordinate (0.14, 0.08) according to National Television System Committee (NTSC).

Perovskite Light‐Emitting Diodes: Perovskite Quantum Dots with Ultralow Trap Density by Acid Etching‐Driven Ligand Exchange for High Luminance and Stable Pure‐Blue Light‐Emitting Diodes (Adv. Mater. 15/2021)

In article number 2006722, Jianjun Tian and co-workers report pure-blue perovskite light-emitting diodes (LEDs) based on ultralow-trap-density and extremely stable small-sized CsPbBr3 quantum dots, which is achieved by a novel acid-etching-driven ligand exchange. The LEDs exhibit electroluminescence at 470 nm wavelength with external quantum efficiency of 4.7%, remarkable high luminance (3850 cd m−2), and long-term operational stability T50 of 12 h.

Highly stable CsPbBr3 quantum dots by silica-coating and ligand modification for white light-emitting diodes and visible light communication

Owing to their superior optical and electronic properties, all inorganic metal halide CsPbX3 (X = Cl, Br, and I) perovskite quantum dots (QDs) are regarded as excellent candidates for various optoelectronic applications. However, the instability of such materials greatly hampers their practical applications. In this work, silica-coated didodecyldimethylammonium bromide (DDAB) capped CsPbBr3 QDs are prepared via a facile method at room temperature. The as-prepared DDAB-CsPbBr3/SiO2 QDs composites demonstrate an effectively improved photoluminescence quantum yield (PLQY) and stability against ethanol and heat. Moreover, the green DDAB-CsPbBr3/SiO2 QDs composites and red InAgZnS QDs are applied as color-converting layers on a blue LED chip for warm white light-emitting diodes (WLEDs). Such WLEDs exhibit an excellent luminescent performance with a color rendering index (CRI) of 88, a color coordinate of (0.41, 0.38), a correlated color temperature (CCT) of 3209 K, and a high power efficiency of 63.4 lm W−1. Besides, such WLEDs are used for visible light communication (VLC), exhibiting a typical low-pass frequency response, with a corresponding −3 dB bandwidth of about 1.5 MHz. By applying orthogonal frequency division multiplexing (OFDM) with a bit loading, a maximum achievable rate of the VLC system reaches 5.9 Mbps, which is almost four times of their measured −3 dB bandwidth. These results demonstrate the potential of prepared DDAB-CsPbBr3/SiO2 QDs composites not only in high-performance WLEDs, but also as an excitation light source to achieve VLC.

Heterovalent Substitution in Mixed Halide Perovskite Quantum Dots for Improved and Stable Photovoltaic Performance

One of the strategies to improve the device performance of metal-halide perovskite solar cells is to alter the electronic and optical properties of the perovskite lattice by metal ion doping. In this work, aliovalent doping of silver at the lead site of CsPbBr1.5I1.5 quantum dots (QDs) shows striking prospects in improving the photovoltaic (PV) device performance. Lattice doping could be achieved only up to ∼3.5 atom % Ag+ with respect to Pb2+ which has significant impact on the electronic and optical properties of the QDs. The band gap could be reduced from 2.15 eV for pristine QDs to 2.12 eV with 3.5 atom % Ag-doping, beyond which midband gap states are created along with the formation of a secondary AgI phase with higher Ag+ substitution. Density functional theory (DFT) shows enhanced optical absorption coefficient and p-type character of the Ag-doped QDs. With the QDs having 3.5 atom % Ag, a significant ∼20% enhancement in photoconversion efficiency (PCE) is observed up to 9.67 ± 0.12% due to the reduction of surface and intrinsic defects, decrease in nonradiative recombination leading to an increase in carrier lifetime, and increase in charge transfer. Although in general all-inorganic perovskite (AIPSK) QDs are attractive because of their higher crystallinity, better optical property, and easy solution processability, the solution stability of AIPSK QDs is not the same as that in PV devices. After 3.5 atom % Ag-doping, our PV devices show extremely promising ambient stability for 575 h (24 days) with less than 5% drop in PCE in comparison to 12% drop for pristine QD devices.

Performance of Spherical Quantum Well Down Converters in Solid State Lighting.

We report the color conversion performance of amber and red emitting quantum dots (QDs) on InGaN solid-state lighting (SSL) light emitting diode (LED) packages. Spherical quantum well (SQW) architectures (CdS/CdSe1-xSx/CdS) were prepared using a library of thio- and selenourea synthesis reagents and high throughput synthesis robotics. CdS/CdSe1-xSx QDs with narrow luminescence bands were coated with thick CdS shells (thickness = 1.6-7.5 nm) to achieve photoluminescence quantum yields (PLQY) up to 88% at amber and red emission wavelengths (λmax = 600-642 nm, FWHM < 45 nm). The photoluminescence from SQWs encapsulated in silicone and deposited on LED packages was monitored under accelerated aging conditions (oven temperature = 85 °C, relative humidity = 5-85%, blue optical power density = 3-45 W/cm2) by monitoring the red photon output over several hundred hours of continuous operation. The growth of a ZnS shell on the SQW surface increases the stability under long-term operation but also reduces the PLQY, especially of SQWs with thick CdS shells. The results illustrate that the outer ZnS shell layer is key to optimizing the PLQY and the long-term stability of QDs during operation on SSL packages.

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

High performance and super stable all-inorganic full-color quantum dot light-emitting diodes (QLEDs) are constructed by adopting solution-processed Mg-doped NiOx (Mg-NiOx ) nanoparticles as hole transport layer (HTL) and Al-doped ZnO (AZO) as electron transport layer (ETL). Mg-NiOx nanoparticles possess the advantages of low-temperature solution processability, intrinsic stability, and controllable electronic properties. UV-ozone (UVO) treatment is applied to the Mg-NiOx film to modulate its surface composition. By carefully controlling the UVO treating time, favorable energy levels can be achieved to minimize the energy barrier for hole injection. At the cathode side, Al-doping can reduce the conductivity of ZnO ETL and decrease the interface charge transfer, effectively, thus leading to more balanced charge injection and consequent high luminance and efficiency. The maximum luminance and EQE can reach as high as 38444cd m-2 and 5.09% for R-QLEDs, 177825cd m-2 and 10.1% for G-QLEDs, and 3103cd m-2 and 2.19% for B-QLEDs. The luminance values are the highest ever reported for all-inorganic QLEDs. Furthermore, the all-inorganic devices show much better resistance to water and oxygen existing in air. The results show that the ion-doped NiOx and AZO nanoparticles would facilitate the design and development of highly efficient and super stable QLEDs.

Highly Stable Perovskite Quantum Dots Modified by Europium Complex for Dual-Responsive Optical Encoding.

Inorganic perovskite quantum dots (QDs) have attracted great scientific attention in the field of luminescent materials, but the application has been limited by the inferior stability that results from highly dynamic capping ligands. In this work, we use a rare-earth complex to modify perovskite QDs with ligand exchange to realize perovskite functionalization; meanwhile, the stability of perovskite QDs is greatly improved. Density functional theory calculation results show that the adsorption energy of the europium complex to QDs is higher than that with traditional ligands, which provides a thermodynamic basis for stability improvement. Furthermore, the modified QDs exhibit attractive dual-response property, including temperature and pH response ascribed to QDs and europium complexes, respectively. The superior property can be applied to multi-stimuli-responsive optical encoding, which is further capable of enhancing the security of encrypted information. This study not only affords a strategy for the synthesis of highly stable perovskites but also provides a method for the functionalization of perovskites.

Long-time stable colloidal Zn–Ag–In–S quantum dots with tunable midgap-involved emission

Quaternary Zn–Ag–In–S (ZAIS) quantum dots (QDs) with efficient, tunable, and stable photoluminescence (PL) emission were prepared via a simple, effective, and low-cost reflux method. The structural analysis revealed the dominance of the quantum confinement effect. The calculated PL emission quantum yield was enhanced from 8.2% to 28.7% with experimental parameters indicating their marked influence on the PL emission properties of the final product. Particularly, it was found that by varying the precursors' feeding ratio, tunable emission from green to red was achieved. A set of direct and indirect pieces of evidence such as the broad-band emission spectrum (FWHM &amp;gt; 100 nm), large Stokes shift more than 120 nm, and predominantly a biexponentially long-lived decay profile with an average lifetime of about 366 ns were observed, showing the contribution of midgap localized energy levels in the recombination process. These data were obtained independently on the experimental condition used, which confirmed that this is mostly an intrinsic electronic property of quaternary In-based QDs. Finally, to ensure the stability of QDs in terms of colloidal and optical emission, their emission ability was evaluated after 26 months of storage. Colloidal QDs were still luminescent with strong yellowish-orange color with emission efficiency of ∼20.3% after 26 months. The combination of synthesis simplicity, compositional non-toxicity, PL emission superiority (strong, tunable, stable, and long lifetime emission), and colloidal stabilities confirms that the present ZAIS QDs are promising candidates for a wide range of applications in biomedicine, anticounterfeiting, and optoelectronics.

Dual-encapsulation for highly stable all-inorganic perovskite quantum dots for long-term storage and reuse in white light-emitting diodes

Although perovskite quantum dots (PQDs) have fascinating optical performances and wide uses in light-emitting diodes (LEDs), laser and photodetectors etc., their commercialization and practical applications are seriously hampered by the poor stability against moisture or water, heat, photo-oxidation and ion exchange. Herein, we report a dually encapsulating strategy of PQDs in fluorinated silica (FSiO2) and porous polydimethylsiloxane (PPDMS) foam. Owning to the superhydrophobic and thermal insulation layers, the dually-encapsulated CsPbBr3 QDs are very stable in the moisture, heat, and irradiation environment and can be long-term stored in air environment for at least 3 months without losing their optical properties. Moreover, the FSiO2-coated CsPbBr3 QDs can be easily released out from PPDMS foam and applied in white LEDs to display pure white emission with ideal CIE (Commission Internationale de L’Eclairage 1931) chromaticity coordinate of (0.33, 0.33). This novel dual-encapsulation strategy through combination of solid airtight shells and thermally insulated porous materials provides a new idea and solution to improve the stability of perovskite quantum dots.

Synthesis and size modulation of MoS2 quantum dots by pulsed laser ablation in liquid for viable hydrogen generation

In the present work, MoS2 quantum dots (QDs) were synthesized by chemical-free, single step photo-exfoliation of a solid MoS2 target using pulsed laser ablation in distilled water. MoS2 quantum dots (QDs) with average sizes of ∼4, 2.9, and 6.1 nm were synthesized by ablating an MoS2 target for ablation durations of 5, 10, and 20 min at a fixed laser energy of 40 mJ. Furthermore, quantum dots with average sizes of ∼2.9, 3.6, and 4.0 nm were also synthesized at laser energies of 10, 20, and 40 mJ, respectively, for a fixed ablation duration of 5 min. The quantum dots resulted in luminescence in the visible region. The as-synthesized colloidal solution of MoS2 quantum dots in distilled water showed excitation wavelength-dependent luminescence shifted to longer wavelength by varying excitation wavelength from 290 to 390 nm exhibiting the effect of wide size distribution. Energy dispersive x-ray spectroscopy, selected area electron diffraction pattern, and zeta potential analysis demonstrated the formation of stoichiometric, highly crystalline, and stable MoS2 quantum dots. Raman spectra of the samples showed two sharp and intense Raman active modes A1g and E2g1 of the MoS2 crystal, indicating crystalline MoS2 quantum dot formation. As an electrocatalytic activity, MoS2 quantum dots exhibited a high rate of hydrogen generation with a minimum Tafel slope of ∼57 mV/dec. High surface area with a large number of active edges makes MoS2 QDs an active catalyst for hydrogen production.

Room temperature synthesis of Sn2+ doped highly luminescent CsPbBr3 quantum dots for high CRI white light-emitting diodes.

With a high photoluminescence quantum yield (PLQY) being able to exceed 90% for those prepared by the hot injection method, CsPbBr3 quantum dots (QDs) have attracted intensive attention for white light-emitting diodes (WLEDs). However, the whole process is carried out in a 3-neck flask via air isolation and at a relatively high temperature. In addition, CsPbBr3 QDs suffer from poor stability under ambient atmosphere. In this work, an effective strategy through doping of Sn2+ ions at room-temperature is proposed to improve the emission efficiency and stability of CsPbBr3 QDs. Compared with pure CsPbBr3 QDs, a higher PLQY and a better stability are obtained. The detailed physical mechanism for this performance enhancement is discussed and described. An optimum result is found at an Sn2+ doping amount of 20%, which shows a high PLQY of 82.77%. WLEDs based on these 20% Sn2+ doped CsPbBr3 QDs are also studied, exhibiting a high color rendering index of 89 and a correlated color temperature (CCT) of 3954. The method proposed here provides an effective strategy to enhance the fluorescence and stability of CsPbBr3 QDs, which might have promising potential in the lighting fields.

Stable lead-halide perovskite quantum dots as efficient visible light photocatalysts for organic transformations.

Lead halide perovskite (LHP) based colloidal quantum dots (CQDs) have tremendous potential for photocatalysis due to their exceptional optical properties. However, their applicability in catalysis is restricted due to poor chemical stability and low recyclability. We report halide-passivated, monodisperse CsPbBr3CQDs as a stable and efficient visible-light photocatalyst for organic transformations. We demonstrate oxidative aromatization of a wide range of heterocyclic substrates including examples which are poor hydrogen transfer (HAT) reagents. Two to five-fold higher rate kinetics were observed for reactions catalyzed by CsPbBr3CQDs in comparison with bulk-type CsPbBr3 (PNCs) or conventionally synthesized CsPbBr3CQDs and other metal organic dyes (rhodamine 6G and [Ru(bpy)3]2+). Furthermore, these CQDs exhibit improved air-tolerance and photostability and in turn show a higher turnover number (TON) of 200, compared to conventionally prepared CQDs (TON = 166) and state-of-the-art bulk-type perovskite-based catalyst (TON = 177). Our study paves the way for the practical applicability of energy-level tunable, size-controlled LHP CQDs as efficient photocatalysts in organic synthesis.

Nanomolar level detection of metal ions by improving the monodispersity and stability of nitrogen-doped graphene quantum dots

Highly fluorescent and stable nitrogen-doped graphene quantum dots used as nanosensor for the selective and sensitive detection of Fe3+ ions at nanomolar range based on the dynamic quenching.

Highly luminescent and stable quasi-2D perovskite quantum dots by introducing large organic cations.

Herein, ultra-stable quasi-two-dimensional perovskite quantum dots (quasi-2D PQDs) are synthesized by introducing the butylamine cation (BA+) into the methylamine lead bromide perovskite (MAPbBr3). By reducing the dimensionality of the perovskite structure, the quasi-2D perovskite (BA)2(MA)x−1PbxBr3x+1 presents higher luminescence efficiency and better environmental stability than traditional 3D perovskites, which is mainly because the dimensionality-reduced perovskite has higher exciton binding energy and formation energy. Under an optimal MA : BA ratio of 1 : 1, the quasi-2D perovskite exhibits about four times higher luminescence efficiency (PLQY = 49.44%) than pristine MAPbBr3; meanwhile it emits stable luminescence in an environment with 80% humidity for 50 days. Most importantly, carbon quantum dot (CQD) doping has also been applied in this work, which effectively passivates the defects of (BA)2(MA)x−1PbxBr3x+1via H-bond interaction, further improving the stability of the perovskite in water. Inspired by the superior performances of the proposed quasi-2D nanomaterial, a novel colorimetric method based on halide ion exchange has been developed for H2O2 detection, which also demonstrates that PQDs show significant potential in the field of environmental monitoring.

Tailoring the lateral size of two-dimensional silicon nanomaterials to produce highly stable and efficient deep-blue emissive silicene-like quantum dots

A highly stable and efficient deep-blue emissive silicon nanomaterial is demonstrated, opening the door towards the silicon-material for blue-emitting applications.