Efficient Quantum Dot Research Articles

Progress on perovskite quantum dots and light-emitting diodes

Abstract. Perovskite quantum dots have become a popular material for the development of new high-efficiency light-emitting diodes (LED) because of their high photoluminescence quantum yield, adjustable luminescence spectrum, narrow spectral width, high defect tolerance and unique quantum limit effect. We review the recent progress based on LED of different types of perovskite quantum dots. First, the properties, existing problems and applications of fully inorganic perovskite quantum dots are introduced. Subsequently, both organic and inorganic perovskites and their applications are discussed, and several methods to improve the LED efficiency of perovskite quantum dots are explored. Finally, this paper analyzes the current challenges of LED of perovskite quantum dots, such as instability and toxicity, and its application prospect in the field of high-efficiency display and lighting is discussed. That is, the EQE of LED based on perovskite quantum dots has increased to more than 20% in four years, and the service life has been extended to tens of hours. This review provides useful insights for the development of more efficient and safer perovskite quantum dot luminescence devices.

Full-angle light out-coupling enhancement of quantum dot light-emitting diodes by Mie-scattering micro-lens arrays

High efficiency, high brightness, and long-life quantum dot light-emitting diodes (QLEDs) are crucial for realizing integrated display and lighting applications. However, about 80% of the light is confined inside the device with substrate mode, waveguide mode, and plasma mode, which greatly weakens the brightness, efficiency and lifetime of the device. Here, a quasi-periodic concave template with large area was fabricated through the spontaneous condensation of droplets on the substrate surface. Based on the quasi-periodic template, SiO2 micro-lens arrays (SiO2-MLAs) Mie scattering composite structure was fabricated by imprinting on a SiO2-nanosphere thin film, which significantly improved light out-coupling at full angles with optimized quasi-Lambertian luminescence characteristics. In comparison to the planar QLED with state-of-the-art, the external quantum efficiency (EQE) demonstrated a qualitative improvement (>20%). Accordingly, the EQE, luminance (L), T50 lifetime (reduce to half brightness) of the green QLEDs with SiO2-MLAs structure have been optimized by 22%, 28%, 31%, and up to 24.21%, 381962.6 cd/m2, 111335 h, respectively. This strategy provides valuable insights into mass-producing and utilizing SiO2-MLA Mie scattering composite structures to boost QLED performance in high-efficiency display and lighting applications.

Construction of 0-dimensional silver quantum dot/MoSe2@MXene/3-dimensional porous copper foam composite electrodes with heterogeneous interfaces for synergistic electrocatalytic degradation of antibiotics

This study proposes a novel and efficient Ag quantum dots (QDs)/MoSe2@two-dimensional transition metal carbide/nitride (MXene)/copper foam (CF) composite electrode to address the challenge of electrocatalytic degradation of antibiotics in water. The electrode formed a unique electron donor–acceptor system by loading Ag QDs and heterostructured nanosheets on CF, significantly facilitating charge transfer and segregation at the interface. The catalytically active sites at the edges and defective locations of MoSe2 in conjunction with the two-dimensional MXene structure, which formed an efficient electron transfer channel, promoted the electron transfer from the interior to the surface and accelerated the hydrogen adsorption and reduction reactions. Moreover, the charge redistribution at the interface of Ag QDs and MoSe2@MXene formed interfacial dipoles, increasing the active sites on the catalyst surface and promoting the generation of cathodic atomic hydrogen (H*). Under optimal conditions, the degradation rate of tigecycline (TGC) reached as high as 90.1 % ± 2.4 % within 60 min. The anode-generated OH and HClO, along with the cathode-generated H, further promoted the degradation of TGC through co-catalysis. The degradation pathways were analyzed using density-functional theory (DFT) calculations and liquid chromatography-mass spectrometry (LC-MS) techniques. Moreover, toxicity analysis of the degradation products was carried out to ensure the safety of the treated wastewater discharge. A reflux continuous effluent reactor was also designed to achieve high degradation efficiency and low energy consumption after stable operation, laying the foundation for industrial applications. This technology provides new ideas for the design of green, efficient, stable, and low-consumption electrocatalytic reactors and contributes to a sustainable future environment.

Restricted-Enhanced Electrochemiluminescence biosensor of low excitation potential carbon quantum dots driven by magnetic Metal-Organic frameworks for sensitive immunoassay of neuron specific enolase

Electrochemiluminescence (ECL) of highly efficient and non-toxic carbon quantum dots (CQDs) plays an important role in immunoassays. However, the high absolute value of the excitation potential and poor controllability make precise detection of low levels difficult. In this work, novel CQDs with low excitation potential were reported to be used for the ultra-sensitive immunoassay of neuron-specific enolase (NSE). It is noteworthy that the narrow bandgap CQDs exhibit a trigger potential of −0.5 V and show excellent applicability of ECL signal at an excitation potential of −0.8 V. This property eliminates side reactions and electrode passivation and significantly improves ECL efficiency. Based on this, the magnetic zeolite-imidazole framework (MZIF) nanoreactor with co-reaction acceleration was employed as a carrier for the in-situ encapsulation of CQDs. The constrained-enhanced ECL sensor platform demonstrated the ability to achieve stable and controllable signal output. A sandwich-type biosensor was constructed by introducing copper sulfide (Cu7S4) as a dual-mechanism quencher, with NSE serving as the target analyte. Moreover, the electrochemical detection method based on the differential pulse voltammetry (DPV) properties of Cu7S4, was successfully validated against ECL. The sensors constructed on magnetic electrodes exhibited a bimodal signal output of ECL and DPV, encompassing a wide detection range (0.001 ng/mL − 500 ng/mL) and low detection limit (0.18 pg/mL for ECL and 0.15 pg/mL for DPV). This design offers a novel approach to understanding the efficient emission of carbon dots and provides a solution for the sensitive detection of biomarkers in clinical research.

Manipulating exciton confinement for stable and efficient flexible quantum dot light-emitting diodes

Flexible quantum dot light-emitting diodes (QLEDs) show great promise for the next generation of flexible, wearable, and artificial intelligence display applications. However, the performance of flexible QLEDs still lags behind that of rigid substrate devices, hindering their commercialization for display applications. Here we report the superior performance of flexible QLEDs based on efficient red ZnCdSe/ZnS/ZnSe QDs (A-QDs) with anti-type-I nanostructures. We reveal that using ZnS as an intermediate shell can effectively confine the exciton wavefunction to the inner core, reducing the surface sensitivity of the QDs and maintaining its excellent emission properties. These flexible QLEDs exhibit a peak external quantum efficiency of 23.0% and a long lifetime of 63,050 h, respectively. The anti-type-I nanostructure of A-QDs in the device simultaneously suppresses defect-induced nonradiative recombination and balances carrier injection, achieving the most excellent performance of flexible QLEDs ever reported. This study provides new insights into achieving superior performance in flexible QD-based electroluminescent devices.

Stable and efficient all-inorganic quantum dot light-emitting diodes based on a double-layer electron transport layer

Abstract The most advanced quantum light-emitting diodes (QLEDs) have achieved almost unity external quantum efficiency (EQE) due to organic materials for high transport efficiency, but organic materials are less stable and can lead to irreversible degradation of the devices. The use of stable inorganic hole-transporting layers (HTLs), such as NiOx, becomes a promising alternative. ZnO is a common electron-transporting material in QLEDs, which possesses high mobility and tunable conductivity properties, but ZnO-based QLEDs devices undergo loss of efficiency due to exciton bursting, poor shelf stability, and pronounced positive aging effects. SnO2, as a common electron-transporting material, has better stability than ZnO. In this work, the SnO2/ZnO dual electron transport layer strategy is adopted, which can reduce the non-radiative burst and aging behavior, and at the same time, the electron transport is regulated by adjusting the film thickness. Inorganic QLEDs with high external quantum efficiency (9.5%) as well as high operational stability have been fully realized. This strategy provides effective ideas for future high-performance display devices.

Carbon quantum dot-modified TiO2/SrTiO3 heterojunction for boosting photocatalytic CO2 reduction

An efficient carbon quantum dot (CQD)-modified TiO2/SrTiO3 heterojunction was constructed for photocatalytic CO2 reduction in this paper. Photogenerated electrons of SrTiO3 transferred to TiO2 via the transfer channel of CQDs for electron-hole recombination, while the photogenerated electrons migrated from TiO2 to CQDs to participate in the photocatalytic CO2 reduction reaction. Meanwhile, the up-conversion of CQDs enhanced the light harvesting ability of the catalyst and the CQDs enriched the active reaction sites. Due to the above advantages, the CO and CH4 produce rate over 0.1-CTS reached 54.9 and 35.9 μmol g−1 h−1, respectively, which was dramatically increased compared with pure TiO2 and pure SrTiO3. This work proposes a feasible strategy for integrating CQDs with TiO2 and SrTiO3 for the optimistic cooperative effect to obtain an effective catalyst for photocatalytic CO2 reduction.

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

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

InGaN blue resonant cavity micro-LED with RGY quantum dot layer for broad gamut, efficient displays

The technology of RGBY micro resonant cavity light emitting diodes (micro-RCLEDs) based on quantum dots (QDs) is considered one of the most promising approaches for full-color displays. In this work, we propose a novel structure combining a high color conversion efficiency (CCE) QD photoresist (QDPR) color conversion layer (CCL) with blue light micro RCLEDs, incorporating an ultra-thin yellow color filter. The additional TiO2 particles inside the QDPR CCL can scatter light and disperse QDs, thus reducing the self-aggregation phenomenon and enhancing the eventual illumination uniformity. Considering the blue light leakage, the influences of adding different color filters are investigated by illumination design software. Finally, the introduction of low-temperature atomic layer deposition (ALD) passivation protection technology at the top of the CCL can enhance the device's reliability. The introduction of RGBY four-color subpixels provides a viable path for developing low-energy consumption, high uniformity, and efficient color conversion displays.

A 4.7‐inch 650 PPI AMQLED display prepared by direct photolithography

AbstractIn this work, a highly efficient photosensitive quantum dot (QD) system was designed. The optimized photosensitive QD system had high photoluminescence quantum yield and colloidal stability. By direct photolithography, RGB pixel arrays with a single sub‐pixel size of 39 μm × 5 μm were successfully prepared. Further, the full‐color QLED device was realized. There were no residual QD emission peaks from neighboring sub‐pixels observed in the electroluminescence spectra. Experience on the full‐color QLED device guided the successful preparation of a 4.7‐inch 650 PPI active matrix QLED prototype. The active matrix QLED prototype could display clear and complete pictures. The color gamut reached 85% of the BT2020 standard. This is the first active matrix QLED prototype prepared with a record‐high resolution by direct photolithography, which promoted the development of QLED display technology.

Facile synthesis of highly stable and efficient MAPbI3 perovskite quantum dots: Spectroscopic characterization and defect analysis

The hybrid methylammonium-based perovskite quantum dots (PQDs) have attracted tremendous attraction for display devices due to their low cost, high luminescence, and color purity. The large-scale production of PQDs is constrained due to the use of toxic and hazardous solvents such as dimethylformamide (DMF) in the synthesis process. Here, a novel approach to prepare PQDs using an environment-friendly solvent, gamma-valerolactone (GVL), is proposed. The synthesized PQDs were found to be uniform with less defect states as compared to the conventionally used DMF solvents, confirmed by different characterizing techniques. The stability of GVL-based PQDs was also found to be improved and proved the efficiency of the present method. Photoluminescence quantum yield (PLQY) of 98 % and single tetragonal CH3NH3PbI3 phase of GVL-derived sample retained over 15 days while the decomposition and degradation were observed in the DMF-derived sample within a short duration. A protocol for the preparation of CH3NH3PbI3 PQDs with less intrinsic defects and uniform optoelectronic properties is presented and paves the way for further modifications and applications.

Programmable multiphoton quantum interference in a single spatial mode.

The interference of nonclassical states of light enables quantum-enhanced applications reaching from metrology to computation. Most commonly, the polarization or spatial location of single photons are used as addressable degrees of freedom for turning these applications into praxis. However, the scale-up for the processing of a large number of photons of these architectures is very resource-demanding due to the rapidly increasing number of components, such as optical elements, photon sources, and detectors. Here, we demonstrate a resource-efficient architecture for multiphoton processing based on time-bin encoding in a single spatial mode. We use an efficient quantum dot single-photon source and a fast programmable time-bin interferometer to observe the interference of up to eight photons in 16 modes, all recorded only with one detector, thus considerably reducing the physical overhead previously needed for achieving equivalent tasks. Our results can form the basis for a future universal photonics quantum processor operating in a single spatial mode.

Decorating highly efficient VN quantum dots onto N-doped hollow carbon nanospheres enables effective inhibition of the shuttle effect and acceleration of LiPSs conversion in lithium–sulfur batteries

Decorating highly efficient VN quantum dots onto N-doped hollow carbon nanospheres enables effective inhibition of the shuttle effect and acceleration of LiPSs conversion in lithium–sulfur batteries

High efficiency quantum dot light-emitting diodes with femtosecond laser post-treatment

Quantum dot light-emitting diodes (QLEDs), as an emerging display technology, have garnered widespread attention due to their excellent color rendering, high efficiency, and long lifespan. However, the inherent differences in the properties of charge transport layer materials inevitably lead to charge injection imbalances and low device performance. Herein, we developed a simple technique by using femtosecond laser scanning over the QLED devices. The results indicate that scanning with a femtosecond laser improves the conductivity of the hole transport layer and increases the external quantum efficiency of the QLED devices. Our work provides an effective route for realizing high performance QLED devices with efficient post-treatment.

Unlocking Invisible Defects of ZnSe Alloy Shells in Giant Quantum Dots with Near Unity Quantum Yield

AbstractPhotoluminescence quantum yield (PL QY) of colloidal quantum dots (QDs) can be improved by growing a shell, but it is rather limited if the shell thickness exceeds a threshold. Lattice mismatch between the core and shell is known to determine this critical shell thickness, securing QDs from defect formation through strain release. However, it cannot explain the recently reported high efficiency QDs with giant shells. Based on CdSe/ZnSe thick shell QDs, this study aims to identify the culprit limiting PL QY. In the shell growth process, the gradual reduction in PL QY is accompanied by a low‐energy tail emission, but the additional compressive strain by the outmost shell eliminates such abnormalities. It is revealed that the zinc vacancy in the shell provides shallow hole trap states. The computational study successfully explains the hole‐accepting zinc vacancy states above the CdSe 1Shh state, raised by compressive strain along radial direction. Additional hydrostatic compressive strain lifts the 1Shh state for this strained heterostructure to minimize the energetic gap with the zinc vacancy states. The finding suggests that critical shell thickness can be limited by atomic vacancy incorporated during shell growth, not by formation of misfit dislocation caused by strain release.

Efficient Quantum Dot Infrared Photovoltaic with Enhanced Charge Extraction via Applying Gradient Electron Transport Layers

AbstractPbS quantum dot (QD) infrared (IR) solar cells that can absorb low‐energy photons are promising photovoltaic devices to improve utilization of sunlight energy by broadening absorption range of the sunlight spectrum to short‐wave infrared region. For PbS QD photovoltaics, depleted heterojunction established between photoactive layer and ZnO electron transport layer (ETL) is critical to determine the performance of devices. However, undesired defects in ZnO films and mismatched energy levels have limited the improvement of device properties. Herein, a novel and simple gradient ZnO ETL is developed for achieving high‐performance QD IR solar cells by depositing a Cs‐doped ZnO thin layer on the pristine ZnO film. The resulting gradient ETL exhibits significantly suppressive trap states and a much smoother surface, efficiently reducing the trap‐assisted nonradiative recombination at the interfaces. Meanwhile, realigned energy levels of the gradient ZnO ETL facilitate the transport and extraction of photogenerated carriers. As a result, the champion device shows a high IR open circuit voltage (VOC) of 0.446 V and IR power conversion efficiency (PCE) of 1.27% under 1100 nm filtered illumination. The VOC and PCE are 0.507 V and 11.04% under AM1.5 illumination, respectively. These results demonstrate a promising strategy for exploiting high‐performance infrared optoelectronic devices.

Reduced Surface Trap States of PbS Quantum Dots by Acetonitrile Treatment for Efficient SnO2-Based PbS Quantum Dot Solar Cells.

The solution-phase ligand-exchange strategy offers a simple pathway to prepare PbS quantum dots (QDs) and their corresponding solar cells. However, the production of high-quality PbS QDs with reduced surface trap state density for efficient PbS QD solar cells (QDSCs) still faces challenges. As the hydroxyl group (-OH) has been demonstrated to be the primary source of the surface trap states on PbS QDs in the general oleic acid method, here, we present an effective and facile strategy for reducing the surface -OH content of PbS QDs by using acetonitrile (ACN) as precipitant to wash the surface of QDs, which significantly decreases the trap state density and enables the preparation of superior PbS QDs. The resulting solar cell with an ITO/SnO2/n-PbS/p-PbS/Au structure obtained an improved photoelectric conversion efficiency (PCE) from 8.53 to 10.49% with an enhanced air storage stability, realizing a high PCE for SnO2-based PbS QDSCs.

Optimizing Surface Passivation of n‐Type Quantum Dots for Efficient PbS Quantum Dot Solar Cells

The n‐type quantum dot (QD) active layer is the core component of lead sulfide QD solar cells (PbS QDSCs). In the state‐of‐the‐art PbS QDSCs, the active layer is commonly obtained through liquid‐phase ligand exchange (LPLE). Due to the intricate chemical state of the ligand exchange solution providing halide ligand, therefore, the PbS‐OAQD solutions is used at concentrations of 20, 30, and 40 mg mL−1 for LPLE, aiming to investigate the reasons for different surface states post‐exchange and their impact on device performance. The results indicate that when the concentration of the PbS‐OA QD solution is 30 mg mL−1, the exchanged QDs exhibit complete removal of surface OA, a higher content of short‐chain ligand PbX2 (X = I, Br), Consequently, devices fabricated using PbS‐PbX2 QD obtained through the exchange of 30 mg mL−1 PbS‐OA QD solution achieve a higher power conversion efficiency (PCE) of 12.53%. This study presents a simple and effective strategy to enhance the performance of PbS QDSCs.

Inorganic-Organic Dual-Ligand-Regulated Photocatalysis of CdS@ZnxCd1-xS@ZnS Quantum Dots for Lignin Valorization.

In a dual-functional lignin valorization system, a harmonious oxidation and reduction rate is a prerequisite for high photocatalytic performance. Herein, an efficient and facile ligand manipulating strategy to balance the redox reaction process is exploited via decorating the surface of the CdS@ZnxCd1-xS@ZnS gradient-alloyed quantum dots with both inorganic ligands of hexafluorophosphate (PF6-) and organic ligands of mercaptopropionic acid (MPA). Inorganic ion ligands in this system provide a promotion for intermediator reduction reactions. By optimizing the ligand composition on the quantum dot surface, we achieve precise control over the extent of oxidation and reduction, enabling selective modification of reaction products; that is, the conversion rate of 2-phenoxy-1-phenylethanol reached 99%. Surface engineering by regulating the ligand type demonstrates that PF6- and thiocyanate (SCN-) inorganic ion ligands contribute significantly toward electron transfer, while MPA ligands have beneficial effects on the hole-transfer procedure, which is predominantly dependent on their steric hindrance, electrostatic action, and passivation effect. The present study offers insights into the development of efficient quantum dot photocatalysts for dual-functional biomass valorization through ligand design.

Near‐Unity Quantum Yield ZnSeTe Quantum Dots Enabled by Controlling Shell Growth for Efficient Deep‐Blue Light‐Emitting Diodes

AbstractCore–shell structural ZnSeTe/ZnSe/ZnS quantum dots (QDs) have attracted great attention for advanced illumination and displays because of their environmentally friendly composition, but still suffering from poor photoluminescence (PL) and electroluminescence (EL) performance due to severe non‐radiative charge recombination. Herein, a stepwise injection shell growth process to manipulate the monomer concentration and ensure adequate growth interval is devised, which enables the controllable uniform epitaxial growth of ZnSe and ZnS shells on the ZnSeTe core, thus relieving the lattice distortion and defects to greatly suppress the non‐radiative charge recombination. The ZnSeTe/ZnSe/ZnS QDs presented deep‐blue emission at 448 nm with narrow full width at half maximum (FWHM, 23 nm), and near‐unity PL quantum yield (PLQY, ≈100%) The light‐emitting diodes (LEDs) based on the QDs exhibited a high external quantum efficiency (EQE) of 10.9%, a maximum brightness of 10240 cd cm−2, and a high current efficiency of 7.9 cd A−1, demonstrating a good performance for deep blue QDs LEDs (QLEDs) This shell growth strategy will be an effective approach to achieving efficient QDs and QLEDs.