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Quantum Dots for Optoelectronic Devices
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Quantum Dots for Optoelectronic Devices

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Quantum Materials".

Deadline for manuscript submissions: closed (20 June 2023) | Viewed by 22978

Special Issue Editors

Prof. Dr. Heesun Yang

E-Mail Website
Guest Editor
Department of Materials Science and Engineering, Hongik University, Seoul 04066, Korea
Interests: quantum dots; materials chemistry; photoluminescence; electroluminescence; light-emitting diodes
Special Issues, Collections and Topics in MDPI journals
Dr. Jeonghun Kwak

E-Mail Website
Guest Editor
Department of Electrical and Computer Engineering, Seoul National University, Seoul 08826, Republic of Korea
Interests: quantum dots; light-emitting diodes; organic thin-film transistors; organic thermoelectrics; organic photovoltaics

Special Issue Information

Dear Colleagues,

Semiconductor quantum dots (QDs) have been receiving immense attention due to their intriguing beneficial attributes—particularly in electronic and optical aspects. Thus, they are considered a promising class of active nanomaterials for next-generation optoelectronic devices. Enabled by the great advances in the synthesis of QDs and their in-depth electro- and photo-physical understanding, they are very near the level of commercialization.

This Special Issue is aimed at offering recent informative QD-associated resources to readers by including a broad range of subjects from QD materials chemistry, characterization and processing to optoelectronic device fabrication. Special focus will cover not only the synthesis of colloidal QDs with diverse compositions including not only the group II-VI, III-V, I-III-VI, IV-VI, halide perovskite, and carbon species; heterostructural/morphological engineering; surface functionalization and electro/photophysical findings, but also their various optoelectronic applications (e.g., color-conversion-/electroluminescence-based light-emitting diodes, energy-harvesting-luminescent solar concentrators, photovoltaics and photo-detecting/sensing devices).

We believe that this collection will provide an opportunity to circulate innovative ideas and useful experimental outcomes on these scientifically and technologically important topics, and will contribute to the dissemination of expertise for young and leading researchers in the fields related to QDs.

Prof. Dr. Heesun Yang
Prof. Dr. Jeonghun Kwak
Guest Editors

Manuscript Submission Information

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Keywords

  • quantum dots
  • materials chemistry
  • light-emitting diodes
  • luminescent solar concentrators
  • photovoltaics
  • photo-detecting/sensing

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Published Papers (10 papers)

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Research

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8 pages, 2360 KiB  
Article
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 1475
Abstract
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)
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13 pages, 2969 KiB  
Article
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 4 | Viewed by 2245
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)
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12 pages, 53403 KiB  
Article
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 1451
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)
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10 pages, 7651 KiB  
Communication
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 - 6 Feb 2023
Cited by 4 | Viewed by 2558
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)
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15 pages, 2739 KiB  
Article
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 2192
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 (EF), 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)
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10 pages, 2689 KiB  
Article
Improving the Performance of Solution−Processed Quantum Dot Light−Emitting Diodes via a HfOx 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
Cited by 1 | Viewed by 1824
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 HfOx layer for the enhanced hole injection efficiency. A large amount of oxygen vacancies in the HfOx 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 HfOx 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 HfOx 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 HfOx 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)
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Graphical abstract

11 pages, 3555 KiB  
Article
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 2476
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)
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11 pages, 2713 KiB  
Article
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 9 | Viewed by 1995
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)
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Review

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23 pages, 11165 KiB  
Review
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
Cited by 2 | Viewed by 2485
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)
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18 pages, 2746 KiB  
Review
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 5 | Viewed by 3064
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)
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