Research

Jump to: Review

8 pages, 2360 KiB

Open AccessArticle

Structural and Optical Properties of NiO/ZnS Core–Shell Nanostructures for Efficient Quantum Dot Light-Emitting Diodes

by Jungho Kim and Jiwan Kim

Materials 2023, 16(14), 5106; https://doi.org/10.3390/ma16145106 - 20 Jul 2023

Viewed by 986

Colloidal quantum dots (QDs) have emerged as promising candidates for optoelectronic devices. In particular, quantum dot light-emitting devices (QLEDs) utilizing QDs as the emission layer offer advantages in terms of simplified fabrication processes. However, the use of poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) as a hole injection layer [...] Read more.

Colloidal quantum dots (QDs) have emerged as promising candidates for optoelectronic devices. In particular, quantum dot light-emitting devices (QLEDs) utilizing QDs as the emission layer offer advantages in terms of simplified fabrication processes. However, the use of poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) as a hole injection layer (HIL) in QLEDs presents limitations due to its acidic and hygroscopic nature. In this study, NiO/ZnS core–shell nanostructures as an alternative HIL were studied. The ZnS shell on NiO nanoparticles effectively suppresses the exciton quenching process and regulates charge transfer in QLEDs. The fabricated QLEDs with NiO/ZnS HIL demonstrate high luminance and current efficiency, highlighting the potential of NiO/ZnS as an inorganic material for highly stable all-inorganic QLEDs. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Figure 1

13 pages, 2969 KiB

Open AccessEditor’s ChoiceArticle

Highly Efficient ITO-Free Quantum-Dot Light Emitting Diodes via Solution-Processed PEDOT:PSS Semitransparent Electrode

by Jin Hyun Ma, Min Gye Kim, Jun Hyung Jeong, Min Ho Park, Hyoun Ji Ha, Seong Jae Kang and Seong Jun Kang

Materials 2023, 16(11), 4053; https://doi.org/10.3390/ma16114053 - 29 May 2023

Cited by 1 | Viewed by 1510

Abstract

We present a study on the potential use of sulfuric acid-treated poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a viable alternative to indium tin oxide (ITO) electrodes in quantum dot light-emitting diodes (QLEDs). ITO, despite its high conductivity and transparency, is known for its disadvantages of [...] Read more.

We present a study on the potential use of sulfuric acid-treated poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a viable alternative to indium tin oxide (ITO) electrodes in quantum dot light-emitting diodes (QLEDs). ITO, despite its high conductivity and transparency, is known for its disadvantages of being brittle, fragile, and expensive. Furthermore, due to the high hole injection barrier of quantum dots, the need for electrodes with a higher work function is becoming more significant. In this report, we present solution-processed, sulfuric acid-treated PEDOT:PSS electrodes for highly efficient QLEDs. The high work function of the PEDOT:PSS electrodes improved the performance of the QLEDs by facilitating hole injection. We demonstrated the recrystallization and conductivity enhancement of PEDOT:PSS upon sulfuric acid treatment using X-ray photoelectron spectroscopy and Hall measurement. Ultraviolet photoelectron spectroscopy (UPS) analysis of QLEDs showed that sulfuric acid-treated PEDOT:PSS exhibited a higher work function than ITO. The maximum current efficiency and external quantum efficiency based on the PEDOT:PSS electrode QLEDs were measured as 46.53 cd/A and 11.01%, which were three times greater than ITO electrode QLEDs. These findings suggest that PEDOT:PSS can serve as a promising replacement for ITO electrodes in the development of ITO-free QLED devices. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Figure 1

12 pages, 53403 KiB

Open AccessArticle

Anisotropic Etching of InGaN Thin Films with Photoelectrochemical Etching to Form Quantum Dots

by Xiongliang Wei, Syed Ahmed Al Muyeed, Haotian Xue and Jonathan J. Wierer, Jr.

Materials 2023, 16(5), 1890; https://doi.org/10.3390/ma16051890 - 24 Feb 2023

Viewed by 1000

Abstract

Traditional methods for synthesizing InGaN quantum dots (QDs), such as the Stranski-Krastanov growth, often result in QD ensembles with low density and non-uniform size distribution. To overcome these challenges, forming QDs using photoelectrochemical (PEC) etching with coherent light has been developed. Anisotropic etching [...] Read more.

Traditional methods for synthesizing InGaN quantum dots (QDs), such as the Stranski-Krastanov growth, often result in QD ensembles with low density and non-uniform size distribution. To overcome these challenges, forming QDs using photoelectrochemical (PEC) etching with coherent light has been developed. Anisotropic etching of InGaN thin films is demonstrated here with PEC etching. InGaN films are etched in dilute H₂SO₄ and exposed to a pulsed 445 nm laser with a 100 mW/cm² average power density. Two potentials (0.4 V or 0.9 V) measured with respect to an AgCl|Ag reference electrode are applied during PEC etching, resulting in different QDs. Atomic force microscope images show that while the QD density and sizes are similar for both applied potentials, the heights are more uniform and match the initial InGaN thickness at the lower applied potential. Schrodinger-Poisson simulations show that polarization-induced fields in the thin InGaN layer prevent positively charged carriers (holes) from arriving at the c-plane surface. These fields are mitigated in the less polar planes resulting in high etch selectivity for the different planes. The higher applied potential overcomes the polarization fields and breaks the anisotropic etching. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Figure 1

10 pages, 7651 KiB

Open AccessCommunication

All-Solution-Processed Quantum Dot Light-Emitting Diode Using Phosphomolybdic Acid as Hole Injection Layer

by Jeong Ha Hwang, Eunyong Seo, Sangwook Park, Kyungjae Lee, Dong Hyun Kim, Seok Hyoung Lee, Yong Woo Kwon, Jeongkyun Roh, Jaehoon Lim and Donggu Lee

Materials 2023, 16(4), 1371; https://doi.org/10.3390/ma16041371 - 06 Feb 2023

Cited by 3 | Viewed by 1899

Abstract

In this study, we investigate phosphomolybdic acid (PMA), which allows solution processing of quantum dot light-emitting diodes. With its low cost, easy solution processes, and excellent physical and optical properties, PMA is a potential candidate as the hole injection layer (HIL) in optoelectronic [...] Read more.

In this study, we investigate phosphomolybdic acid (PMA), which allows solution processing of quantum dot light-emitting diodes. With its low cost, easy solution processes, and excellent physical and optical properties, PMA is a potential candidate as the hole injection layer (HIL) in optoelectronic devices. We evaluate the physical and electrical properties of PMA using various solvents. The surface morphology of the PMA film was improved using a solvent with appropriate boiling points, surface tension, and viscosity to form a smooth, pinhole-free film. The energy level was regulated according to the solvent, and PMA with the appropriate electronic structure provided balanced charge carrier transport in quantum dot electroluminescent (QD-EL) devices with enhanced efficiency. A device using PMA dissolved in cyclohexanone was demonstrated to exhibit improved efficiency compared to a device using PEDOT:PSS, which is a conventional solution HIL. However, the stability of PMA was slightly poorer than PEDOT:PSS; there needs to be further investigation. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Figure 1

15 pages, 2739 KiB

Open AccessEditor’s ChoiceArticle

Enhancing the Performance of Quantum Dot Light-Emitting Diodes Using Solution-Processable Highly Conductive Spinel Structure CuCo₂O₄ Hole Injection Layer

by Min Ho Park, Min Gye Kim, Jin Hyun Ma, Jun Hyung Jeong, Hyoun Ji Ha, Wonsik Kim, Soohyung Park and Seong Jun Kang

Materials 2023, 16(3), 972; https://doi.org/10.3390/ma16030972 - 20 Jan 2023

Viewed by 1700

Abstract

Charge imbalance in quantum-dot light-emitting diodes (QLEDs) causes emission degradation. Therefore, many studies focused on improving hole injection into the QLEDs-emitting layer owing to lower hole conductivity compared to electron conductivity. Herein, CuCo₂O₄ has a relatively higher hole conductivity than [...] Read more.

Charge imbalance in quantum-dot light-emitting diodes (QLEDs) causes emission degradation. Therefore, many studies focused on improving hole injection into the QLEDs-emitting layer owing to lower hole conductivity compared to electron conductivity. Herein, CuCo₂O₄ has a relatively higher hole conductivity than other binary oxides and can induce an improved charge balance. As the annealing temperature decreases, the valence band maximum (VBM) of CuCo₂O₄ shifts away from the Fermi energy level (E_F), resulting in an enhanced hole injection through better energy level alignment with hole transport layer. The maximum luminance and current efficiency of the CuCo₂O₄ hole injection layer (HIL) of the QLED were measured as 93,607 cd/m² and 11.14 cd/A, respectively, resulting in a 656% improvement in luminous performance of QLEDs compared to conventional metal oxide HIL-based QLEDs. These results demonstrate that the electrical properties of CuCo₂O₄ can be improved by adjusting the annealing temperature, suggesting that solution-processed spinel can be applied in various optoelectronic devices. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Graphical abstract

10 pages, 2689 KiB

Open AccessArticle

Improving the Performance of Solution−Processed Quantum Dot Light−Emitting Diodes via a HfO_x Interfacial Layer

by Jun Hyung Jeong, Min Gye Kim, Jin Hyun Ma, Min Ho Park, Hyoun Ji Ha, Seong Jae Kang, Min-Jae Maeng, Young Duck Kim, Yongsup Park and Seong Jun Kang

Materials 2022, 15(24), 8977; https://doi.org/10.3390/ma15248977 - 15 Dec 2022

Viewed by 1380

Abstract

One of the major obstacles in the way of high−performance quantum dot light−emitting diodes (QLEDs) is the charge imbalance arising from more efficient electron injection into the emission layer than the hole injection. In previous studies, a balanced charge injection was often achieved [...] Read more.

One of the major obstacles in the way of high−performance quantum dot light−emitting diodes (QLEDs) is the charge imbalance arising from more efficient electron injection into the emission layer than the hole injection. In previous studies, a balanced charge injection was often achieved by lowering the electron injection efficiency; however, high performance next−generation QLEDs require the hole injection efficiency to be enhanced to the level of electron injection efficiency. Here, we introduce a solution−processed HfO_x layer for the enhanced hole injection efficiency. A large amount of oxygen vacancies in the HfO_x films creates gap states that lower the hole injection barrier between the anode and the emission layer, resulting in enhanced light−emitting characteristics. The insertion of the HfO_x layer increased the luminance of the device to 166,600 cd/m², and the current efficiency and external quantum efficiency to 16.6 cd/A and 3.68%, respectively, compared with the values of 63,673 cd/m², 7.37 cd/A, and 1.64% for the device without HfO_x layer. The enhanced light−emitting characteristics of the device were elucidated by X−ray photoelectron, ultra−violet photoelectron, and UV−visible spectroscopy. Our results suggest that the insertion of the HfO_x layer is a useful method for improving the light−emitting properties of QLEDs. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Graphical abstract

11 pages, 3555 KiB

Open AccessArticle

Effective Blue Light-Absorbing AuAg Nanoparticles in InP Quantum Dots-Based Color Conversion

by Hyo-Jin Yeo, Suk-Young Yoon, Dae-Yeon Jo, Hyun-Min Kim, Jeonghun Kwak, Sung-Phil Kim, Myung-Joon Kim and Heesun Yang

Materials 2022, 15(23), 8455; https://doi.org/10.3390/ma15238455 - 27 Nov 2022

Cited by 1 | Viewed by 1742

Abstract

In typical color-by-blue mode-based quantum dot (QD) display devices, only part of the blue excitation light is absorbed by QD emitters, thus it is accompanied by the leakage of blue light through the devices. To address this issue, we offer, for the first [...] Read more.

In typical color-by-blue mode-based quantum dot (QD) display devices, only part of the blue excitation light is absorbed by QD emitters, thus it is accompanied by the leakage of blue light through the devices. To address this issue, we offer, for the first time, the applicability of AuAg alloy nanoparticles (NPs) as effective blue light absorbers in InP QD-based color-by-blue platforms. For this, high-quality fluorescent green and red InP QDs with a double shell scheme of ZnSe/ZnS were synthesized and embedded in a transparent polymer film. Separately, a series of Au/Ag ratio-varied AuAg NPs with tunable plasmonic absorption peaks were synthesized. Among them, AuAg NPs possessing the most appropriate absorption peak with respect to spectral overlap with blue emission are chosen for the subsequent preparation of AuAg NP polymeric films with varied NP concentrations. A stack of AuAg NP polymeric film on top of InP QD film is then placed remotely on a blue light-emitting diode, successfully resulting in systematically progressive suppression of blue light leakage with increasing AuAg NP concentration. Furthermore, the beneficial function of the AuAg NP polymeric overlayer in mitigating undesirable QD excitation upon exposure to ambient lights was further examined. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Figure 1

11 pages, 2713 KiB

Open AccessArticle

A Label-Free Fluorescent Sensor Based on Si,N-Codoped Carbon Quantum Dots with Enhanced Sensitivity for the Determination of Cr(VI)

by Jinyu Zhang, Cai Jing and Binsong Wang

Materials 2022, 15(5), 1733; https://doi.org/10.3390/ma15051733 - 25 Feb 2022

Cited by 6 | Viewed by 1647

Abstract

A signal shut-off probe of Si, N-codoped carbon quantum dots (Si, N-CQDs) was exploited to detect Cr(VI) by fluorescence quenching without the aid of any biomolecules or labeling materials. The sensing system prepared the precursor of diacetone acrylamide and the silane coupling agent [...] Read more.

A signal shut-off probe of Si, N-codoped carbon quantum dots (Si, N-CQDs) was exploited to detect Cr(VI) by fluorescence quenching without the aid of any biomolecules or labeling materials. The sensing system prepared the precursor of diacetone acrylamide and the silane coupling agent 3-aminopropyltriethoxysilane (KH-550) by a simple hydrothermal method, and the quantum yield is as high as 75% Si, N-CQDs. The fluorescence stability and microstructure of the Si, N-CQDs were studied. The Si, N-CQDs has a high sensitivity for detecting Cr(VI) with the linear range of 0–200 μM and the detection limit of 0.995 μM. The quenching mechanism of Si, N-CQDs is attributed to FRET. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Graphical abstract

Review

Jump to: Research

23 pages, 11165 KiB

Open AccessReview

Cadmium-Based Quantum Dots Alloyed Structures: Synthesis, Properties, and Applications

by Fadia Ebrahim, Omar Al-Hartomy and S. Wageh

Materials 2023, 16(17), 5877; https://doi.org/10.3390/ma16175877 - 28 Aug 2023

Viewed by 1244

Abstract

Cadmium-based alloyed quantum dots are one of the most popular metal chalcogenides in both the industrial and research fields owing to their extraordinary optical and electronic properties that can be manipulated by varying the compositional ratio in addition to size control. This report [...] Read more.

Cadmium-based alloyed quantum dots are one of the most popular metal chalcogenides in both the industrial and research fields owing to their extraordinary optical and electronic properties that can be manipulated by varying the compositional ratio in addition to size control. This report aims to cover the main information concerning the synthesis techniques, properties, and applications of Cd-based alloyed quantum dots. It provides a comprehensive overview of the most common synthesis methods for these QDs, which include hot injection, co-precipitation, successive ionic layer adsorption and reaction, hydrothermal, and microwave-assisted synthesis methods. This detailed literature highlights the optical and structural properties of both ternary and quaternary quantum dots. Also, this review provides the high-potential applications of various alloyed quantum dots. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Graphical abstract

18 pages, 2746 KiB

Open AccessReview

Progress in the Development of Active-Matrix Quantum-Dot Light-Emitting Diodes Driven by Non-Si Thin-Film Transistors

by Geun Woo Baek, Yeon Jun Kim, Minhyung Lee, Yeunwoo Kwon, Beomsoo Chun, Ganghyun Park, Hansol Seo, Heesun Yang and Jeonghun Kwak

Materials 2022, 15(23), 8511; https://doi.org/10.3390/ma15238511 - 29 Nov 2022

Cited by 2 | Viewed by 2280

Abstract

This paper aims to discuss the key accomplishments and further prospects of active-matrix (AM) quantum-dot (QD) light-emitting diodes (QLEDs) display. We present an overview and state-of-the-art of QLEDs as a frontplane and non-Si-based thin-film transistors (TFTs) as a backplane to meet the requirements [...] Read more.

This paper aims to discuss the key accomplishments and further prospects of active-matrix (AM) quantum-dot (QD) light-emitting diodes (QLEDs) display. We present an overview and state-of-the-art of QLEDs as a frontplane and non-Si-based thin-film transistors (TFTs) as a backplane to meet the requirements for the next-generation displays, such as flexibility, transparency, low power consumption, fast response, high efficiency, and operational reliability. After a brief introduction, we first review the research on non-Si-based TFTs using metal oxides, transition metal dichalcogenides, and semiconducting carbon nanotubes as the driving unit of display devices. Next, QLED technologies are analyzed in terms of the device structure, device engineering, and QD patterning technique to realize high-performance, full-color AM-QLEDs. Lastly, recent research on the monolithic integration of TFT–QLED is examined, which proposes a new perspective on the integrated device. We anticipate that this review will help the readership understand the fundamentals, current state, and issues on TFTs and QLEDs for future AM-QLED displays. Full article

(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Quantum Dots for Optoelectronic Devices

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (10 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI