Editorial

3 pages, 187 KiB

Open AccessEditorial

Editorial for the Special Issue on Quantum Dots Frontiers

by Wei Chen and Junjie Hao

Micromachines 2023, 14(5), 1026; https://0-doi-org.brum.beds.ac.uk/10.3390/mi14051026 - 10 May 2023

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Thanks to state-of-the-art chemical and device engineering in past decades, we have witnessed more and more novel applications based on semiconductor nanocrystals: quantum dots (QDs) [...] Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

Research

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8 pages, 2452 KiB

Open AccessArticle

Performance Enhancement of Perovskite Quantum Dot Light-Emitting Diodes via Management of Hole Injection

by Weigao Wang, Yiyang Li, Yu Duan, Mingxia Qiu, Hua An and Zhengchun Peng

Micromachines 2023, 14(1), 11; https://0-doi-org.brum.beds.ac.uk/10.3390/mi14010011 - 21 Dec 2022

Cited by 3 | Viewed by 1466

Abstract

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is widely used in optoelectronic devices due to its excellent hole current conductivity and suitable work function. However, imbalanced carrier injection in the PEDOT:PSS layer impedes obtaining high-performance perovskite light-emitting diodes (PeLEDs). In this work, a novel poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,40-(N-(p-butylphenyl))diphenylamine)] (TFB) [...] Read more.

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is widely used in optoelectronic devices due to its excellent hole current conductivity and suitable work function. However, imbalanced carrier injection in the PEDOT:PSS layer impedes obtaining high-performance perovskite light-emitting diodes (PeLEDs). In this work, a novel poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,40-(N-(p-butylphenyl))diphenylamine)] (TFB) is applied as the hole transport layers (HTLs) to facilitate the hole injection with cascade-like energy alignment between PEDOT:PSS and methylammonium lead tribromide (MAPbBr₃) film. Our results indicate that the introduced TFB layer did not affect the surface morphology or lead to any additional surface defects of the perovskite film. Consequently, the optimal PeLEDs with TFB HTLs show a maximum current efficiency and external quantum efficiency (EQE) of 21.26 cd A⁻¹ and 6.68%, respectively. Such EQE is 2.5 times higher than that of the control devices without TFB layers. This work provides a facile and robust route to optimize the device structure and improve the performance of PeLEDs. Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

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9 pages, 1520 KiB

Open AccessArticle

Development of a Highly Specific Fluoroimmunoassay for the Detection of Doxycycline Residues in Water Environmental and Animal Tissue Samples

by Tao Le, Rongli Xu, Lulan Yang and Yong Xie

Micromachines 2022, 13(11), 1864; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13111864 - 30 Oct 2022

Cited by 4 | Viewed by 1242

Abstract

Doxycycline (DOX) and its metabolite residues in food and the environment pose a serious threat to human health and the ecological environment. In this work, a novel method, termed competitive fluoroimmunoassays (cFIA), based on monoclonal antibody (mAb) bio-conjugated CdSe/ZnS core–shell quantum dots (QDs), [...] Read more.

Doxycycline (DOX) and its metabolite residues in food and the environment pose a serious threat to human health and the ecological environment. In this work, a novel method, termed competitive fluoroimmunoassays (cFIA), based on monoclonal antibody (mAb) bio-conjugated CdSe/ZnS core–shell quantum dots (QDs), was developed for sensitive and rapid bioanalyses of DOX in natural water and commercial meats. After the optimization of the experimental conditions, 1 μg mL⁻¹ of coating antigen and 0.5 μg mL⁻¹ of QD-labeled mAb were used for the establishment of the cFIA. With this assay, the 50% inhibition concentration was found to be 0.35 ng mL⁻¹ of DOX in phosphate-buffered saline samples, and the limit of detection was 0.039 ng mL⁻¹ with minor cross-reactivity to other tetracycline members. The recoveries from natural water and commercial meats spiked with DOX concentrations of 10–600 ng mL⁻¹ were 81.3–109.8%, and standard deviation were all below 12%. Levels measured with the QD-cFIA for thirty authentic samples were confirmed by high-performance liquid chromatography with good correlations. These results indicate that QD-cFIA is sultable for the rapid and quantitative detection of DOX residue in environmental and food samples. Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

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8 pages, 1820 KiB

Open AccessArticle

Zinc Carboxylate Surface Passivation for Enhanced Optical Properties of In(Zn)P Colloidal Quantum Dots

by Doheon Yoo, Eunyoung Bak, Hae Mee Ju, Yoo Min Shin and Min-Jae Choi

Micromachines 2022, 13(10), 1775; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13101775 - 19 Oct 2022

Cited by 1 | Viewed by 1585

Abstract

Indium phosphide (InP) colloidal quantum dots (CQDs) have generated great interest as next-generation light-emitting materials owing to their narrow emission spectra and environment-friendly components. The minimized surface defects is essential to achieve narrow full-width at half-maximum (FWHM) and high photoluminescence quantum yield (PLQY). [...] Read more.

Indium phosphide (InP) colloidal quantum dots (CQDs) have generated great interest as next-generation light-emitting materials owing to their narrow emission spectra and environment-friendly components. The minimized surface defects is essential to achieve narrow full-width at half-maximum (FWHM) and high photoluminescence quantum yield (PLQY). However, InP CQDs are readily oxidized in ambient condition, which results in formation of oxidation defect states on the surface of InP CQDs. Herein, we introduce a strategy to successfully passivate the surface defects of InP core by zinc complexes. The zinc carboxylates passivation reduces FWHM of InP CQDs from 130 nm to 70 nm and increases PLQY from 1% to 14% without shelling. Furthermore, the photoluminescence (PL) peak has shifted from 670 nm to 510 nm with an increase of zinc carboxylates passivation, which suggests that excessive zinc carboxylates functions as a size-regulating reagent in the synthesis. Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

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11 pages, 1796 KiB

Open AccessArticle

Fabrication of Highly Efficient Perovskite Nanocrystal Light-Emitting Diodes via Inkjet Printing

by Taikang Ye, Siqi Jia, Zhaojin Wang, Rui Cai, Hongcheng Yang, Fangqing Zhao, Yangzhi Tan, Xiaowei Sun, Dan Wu and Kai Wang

Micromachines 2022, 13(7), 983; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13070983 - 22 Jun 2022

Cited by 5 | Viewed by 2578

Abstract

As an effective manufacturing technology, inkjet printing is very suitable for the fabrication of perovskite light-emitting diodes in next-generation displays. However, the unsatisfied efficiency of perovskite light-emitting diode created with the use of inkjet printing impedes its development for future application. Here, we [...] Read more.

As an effective manufacturing technology, inkjet printing is very suitable for the fabrication of perovskite light-emitting diodes in next-generation displays. However, the unsatisfied efficiency of perovskite light-emitting diode created with the use of inkjet printing impedes its development for future application. Here, we report highly efficient PeLEDs using inkjet printing, with an external quantum efficiency of 7.9%, a current efficiency of 32.0 cd/A, and the highest luminance of 2465 cd/m²; these values are among the highest values for the current efficiency of inkjet-printed PeLED in the literature. The outstanding performance of our device is due to the coffee-ring-free and uniform perovskite nanocrystal layer on the PVK layer, resulting from vacuum post-treatment and using a suitable ink. Moreover, the surface roughness and thickness of the perovskite layer are effectively controlled by adjusting the spacing of printing dots. This study makes an insightful exploration of the use of inkjet printing in PeLED fabrication, which is one of the most promising ways for future industrial production of PeLEDs. Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

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7 pages, 15178 KiB

Open AccessArticle

Red and Green Quantum Dot Color Filter for Full-Color Micro-LED Arrays

by Bingxin Zhao, Qingqian Wang, Depeng Li, Hongcheng Yang, Xue Bai, Shang Li, Pai Liu and Xiaowei Sun

Micromachines 2022, 13(4), 595; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13040595 - 10 Apr 2022

Cited by 10 | Viewed by 2531

Abstract

This work demonstrated color-conversion layers of red and green quantum dots color filter for full-color display arrays. Ligands exchange using (3-glycidyloxypropyl) trimethoxysilane with epoxy functional groups to treat QDs in the liquid phase was performed for photolithography use. The combination of ligands of [...] Read more.

This work demonstrated color-conversion layers of red and green quantum dots color filter for full-color display arrays. Ligands exchange using (3-glycidyloxypropyl) trimethoxysilane with epoxy functional groups to treat QDs in the liquid phase was performed for photolithography use. The combination of ligands of QDs with photo-initiator played a protective role on QDs. Moreover, the pixel size of green QDCF can be reduced to 50 μm, and a high optical density (OD) of 1.2 is realized. Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

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7 pages, 2164 KiB

Open AccessArticle

Temperature-Dependent Optical Properties of Perovskite Quantum Dots with Mixed-A-Cations

by Lei Hu, Weiren Zhao, Weijia Duan, Guojie Chen, Bingfeng Fan and Xiaoli Zhang

Micromachines 2022, 13(3), 457; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13030457 - 17 Mar 2022

Cited by 6 | Viewed by 2343

Abstract

In this work, metal halide perovskite quantum dots (QDs) with Formamidinium (FA) and Cs mixed cations were fabricated using a solution-processed method at room temperature. By controlling Cs doping ratios in a precursor, the optical properties of mixed-cation perovskite QDs were systematically studied. [...] Read more.

In this work, metal halide perovskite quantum dots (QDs) with Formamidinium (FA) and Cs mixed cations were fabricated using a solution-processed method at room temperature. By controlling Cs doping ratios in a precursor, the optical properties of mixed-cation perovskite QDs were systematically studied. With the increase in Cs ion doping, the photoluminescence (PL) spectra of perovskite QDs were blueshifted, which was mainly due to the smaller radius of Cs ions than those of FA. Temperature-dependent PL spectra were conducted on mixed-cation perovskite QDs. As the temperature gradually increased from 4 K to 300 K, PL peaks were blue shifted, and full-width at half maximum (FWHM) was widened, which was directly related to lattice thermal expansion and the carrier-photon coupling effect under temperature variation. At the same time, excess Cs ion doping had a prominent influence on optical properties at low temperatures, which was mainly due to the introduction of detrimental defects in perovskite crystals. Therefore, it is particularly important to control doping concentration in the preparation of high-quality perovskite QDs and efficient photoelectric devices. Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

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9 pages, 2435 KiB

Open AccessArticle

Study of the Electron-Phonon Coupling in PbS/MnTe Quantum Dots Based on Temperature-Dependent Photoluminescence

by Nur Diyana Halim, Muhammad Safwan Zaini, Zainal Abidin Talib, Josephine Ying Chyi Liew and Mazliana Ahmad Kamarudin

Micromachines 2022, 13(3), 443; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13030443 - 15 Mar 2022

Cited by 4 | Viewed by 2398

Abstract

The temperature dependence of photoluminescence (PL) emission is a valuable tool for investigating carrier localization, recombination, and carrier–phonon interactions. Herein, electron–phonon couplings in lead sulfide (PbS) quantum dots (QDs) and lead sulfide/manganese tellurite (PbS/MnTe) QDs is reported. The effect of temperature on the [...] Read more.

The temperature dependence of photoluminescence (PL) emission is a valuable tool for investigating carrier localization, recombination, and carrier–phonon interactions. Herein, electron–phonon couplings in lead sulfide (PbS) quantum dots (QDs) and lead sulfide/manganese tellurite (PbS/MnTe) QDs is reported. The effect of temperature on the PL emission of PbS and PbS/MnTe was explored within a temperature range of 10 to 300 K. When temperature increased, PL emission was blue-shifted due to the confinement effect. The gradual broadening of the full width at half maximum (FWHM) with increasing temperature indicates electron–phonon interactions. An analysis based on the Boson model revealed that the values of the exciton acoustic phonon coupling coefficient, σ, and temperature-dependent linewidth, γ, for PbS/MnTe were larger than those for PbS, indicating stronger exciton longitudinal-optical–phonon coupling in the compound structure. Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

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11 pages, 2941 KiB

Open AccessArticle

An Investigation on CCT and Ra Optimization for Trichromatic White LEDs Using a Dual-Weight-Coefficient-Based Algorithm

by Hua Xiao, Yan Li, Binghui Li and Guancheng Wang

Micromachines 2022, 13(2), 276; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13020276 - 09 Feb 2022

Cited by 4 | Viewed by 1565

Abstract

Spectral optimization is applied as an effective tool in designing solid-state lighting devices. Optimization speed, however, has been seldomly discussed in previous reports as regards designing an algorithm for white light-emitting diodes (WLEDs). In this study, we propose a method for trichromatic WLEDs [...] Read more.

Spectral optimization is applied as an effective tool in designing solid-state lighting devices. Optimization speed, however, has been seldomly discussed in previous reports as regards designing an algorithm for white light-emitting diodes (WLEDs). In this study, we propose a method for trichromatic WLEDs to obtain the optimal Ra under target correlated color temperatures (CCTs). Blue-, yellow-, and red-color monochromatic spectra, produced by the GaN LED chip, YAG:Ce³⁺ phosphors, and CdSe/ZnSe quantum dots, respectively, are adopted to synthesize white light. To improve the effectiveness of our method, the concept of dual weight coefficients is proposed, to maintain a numerical gap between the proposed floating CCT and the target CCT. This gap can effectively guarantee that Ra and CCT ultimately move toward the targeting value simultaneously. Mechanisms of interaction between CCT, Ra, and dual-weight coefficients are investigated and discussed in detail. Particularly, a fitting curve is drawn to reveal the linear relationship between weight coefficients and target CCTs. This finding effectively maintains the accuracy and accelerates the optimization process in comparison with other methods with global searching ability. As an example, we only use 29 iterations to achieve the highest Ra of 96.1 under the target CCT of 4000 K. It is hoped that this study facilitates technology development in illumination-related areas such as residential intelligent lighting and smart planting LED systems. Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

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7 pages, 2342 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Flexible CdSe/ZnS Quantum-Dot Light-Emitting Diodes with Higher Efficiency than Rigid Devices

by Mijin Kim, Dongjin Kim, Ohun Kwon and Honyeon Lee

Micromachines 2022, 13(2), 269; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13020269 - 07 Feb 2022

Cited by 16 | Viewed by 3014

Abstract

Fabrication of high-performance, flexible quantum-dot light-emitting diodes (QLEDs) requires the reliable manufacture of a flexible transparent electrode to replace the conventional brittle indium tin oxide (ITO) transparent electrode, along with flexible substrate planarization. We deposited a transparent oxide/metal/oxide (OMO) electrode on a polymer [...] Read more.

Fabrication of high-performance, flexible quantum-dot light-emitting diodes (QLEDs) requires the reliable manufacture of a flexible transparent electrode to replace the conventional brittle indium tin oxide (ITO) transparent electrode, along with flexible substrate planarization. We deposited a transparent oxide/metal/oxide (OMO) electrode on a polymer planarization layer and co-optimized both layers. The visible transmittance of the OMO electrode on a polyethylene terephthalate substrate increased markedly. Good electron supply and injection into an electron-transporting layer were achieved using WO_X/Ag/ WO_X and MoOx/Ag/MoO_X OMO electrodes. High-performance flexible QLEDs were fabricated from these electrodes; a QLED with a MoO_X/Ag/ MoO_X cathode and an SU-8 planarization layer had a current efficiency of 30.3 cd/A and luminance more than 7 × 10⁴ cd/m². The current efficiency was significantly higher than that of a rigid QLED with an ITO cathode and was higher than current efficiency values obtained from previously reported QLEDs that utilized the same quantum-dot and electron-transporting layer materials as our study. Full article

(This article belongs to the Special Issue Quantum Dot Frontiers)

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