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Keating LP, Lee H, Rogers SP, Huang C, Shim M. Charging and Charged Species in Quantum Dot Light-Emitting Diodes. NANO LETTERS 2022; 22:9500-9506. [PMID: 36459088 DOI: 10.1021/acs.nanolett.2c03564] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Despite recent rapid advances in improving quantum dot light-emitting diodes, many fundamental aspects of the device operating mechanism remain unresolved. Through transient electroluminescence and time-resolved photoluminescence measurements, the effects of offset voltage on charging and charge transport are examined. First, capacitive charging occurs with a time constant of ∼500 ns, followed by electron transport through quantum dots with a mobility of ∼10-5 cm2 V-1 s-1. Hole injection then initiates an electroluminescence rise that is independent of offset voltage. The photoluminescence lifetime is also unaffected by the offset voltage, indicating no injection of charges into the quantum dots or on their surfaces prior to the voltage pulse. A slower equilibration to steady-state electroluminescence is dependent on the offset voltage, indicative of another charging process. Elemental mapping shows that ZnO deposition from solution can lead to the diffusion of charged species into the quantum dot layer, which may cause the slower process.
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Affiliation(s)
- Logan P Keating
- Department of Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois61801, United States
| | - Hyunho Lee
- Department of Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois61801, United States
| | - Steven P Rogers
- Department of Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois61801, United States
| | - Conan Huang
- Department of Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois61801, United States
| | - Moonsub Shim
- Department of Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois61801, United States
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2
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Baek GW, Kim YJ, Lee M, Kwon Y, Chun B, Park G, Seo H, Yang H, Kwak J. Progress in the Development of Active-Matrix Quantum-Dot Light-Emitting Diodes Driven by Non-Si Thin-Film Transistors. MATERIALS (BASEL, SWITZERLAND) 2022; 15:ma15238511. [PMID: 36500003 PMCID: PMC9736594 DOI: 10.3390/ma15238511] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 11/18/2022] [Accepted: 11/27/2022] [Indexed: 05/28/2023]
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 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.
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Affiliation(s)
- Geun Woo Baek
- Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea
| | - Yeon Jun Kim
- Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea
| | - Minhyung Lee
- Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea
| | - Yeunwoo Kwon
- Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea
| | - Beomsoo Chun
- Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea
| | - Ganghyun Park
- Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea
| | - Hansol Seo
- Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea
| | - Heesun Yang
- Department of Materials Science and Engineering, Hongik University, Seoul 04066, Republic of Korea
| | - Jeonghun Kwak
- Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea
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Abstract
Anisotropic heterostructures of colloidal nanocrystals embed size-, shape-, and composition-dependent electronic structure within variable three-dimensional morphology, enabling intricate design of solution-processable materials with high performance and programmable functionality. The key to designing and synthesizing such complex materials lies in understanding the fundamental thermodynamic and kinetic factors that govern nanocrystal growth. In this review, nanorod heterostructures, the simplest of anisotropic nanocrystal heterostructures, are discussed with respect to their growth mechanisms. The effects of crystal structure, surface faceting/energies, lattice strain, ligand sterics, precursor reactivity, and reaction temperature on the growth of nanorod heterostructures through heteroepitaxy and cation exchange reactions are explored with currently known examples. Understanding the role of various thermodynamic and kinetic parameters enables the controlled synthesis of complex nanorod heterostructures that can exhibit unique tailored properties. Selected application prospects arising from such capabilities are then discussed.
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Affiliation(s)
- Gryphon A Drake
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 United States
| | - Logan P Keating
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 United States
| | - Moonsub Shim
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 United States
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Kim GH, Lee J, Lee JY, Han J, Choi Y, Kang CJ, Kim KB, Lee W, Lim J, Cho SY. High-Resolution Colloidal Quantum Dot Film Photolithography via Atomic Layer Deposition of ZnO. ACS APPLIED MATERIALS & INTERFACES 2021; 13:43075-43084. [PMID: 34463100 DOI: 10.1021/acsami.1c11898] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
High-resolution patterning of quantum dot (QD) films is one of the preconditions for the practical use of QD-based emissive display platforms. Recently, inkjet printing and transfer printing have been actively developed; however, high-resolution patterning is still limited owing to nozzle-clogging issues and coffee ring effects during the inkjet printing and kinetic parameters such as pickup and peeling speed during the transfer process. Consequently, employing direct optical lithography would be highly beneficial owing to its well-established process in the semiconductor industry; however, exposing the photoresist (PR) on top of the QD film deteriorates the QD film underneath. This is because a majority of the solvents for PR easily dissolve the pre-existing QD films. In this study, we present a conventional optical lithography process to obtain solvent resistance by reacting the QD film surface with diethylzinc (DEZ) precursors using atomic layer deposition. It was confirmed that, by reacting the QD surface with DEZ and coating PR directly on top of the QD film, a typical photolithography process can be performed to generate a red/green/blue pixel of 3000 ppi or more. QD electroluminescence devices were fabricated with all primary colors of QDs; moreover, compared to reference QD-LED devices, the patterned QD-LED devices exhibited enhanced brightness and efficiency.
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Affiliation(s)
| | | | | | | | | | | | - Ki-Bum Kim
- Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Korea
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Shen Q, Hao Y, Ma L, Wang X. Comparative Study of Red/Green/Blue Quantum-Dot Light-Emitting Diodes by Time-Resolved Transient Electroluminescence. J Phys Chem Lett 2021; 12:7019-7025. [PMID: 34286994 DOI: 10.1021/acs.jpclett.1c01560] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
To understand the electronic processes in quantum-dot light-emitting diodes (QLEDs), a comparative study was performed by time-resolved transient electroluminescence (TREL). We fabricated red, green, and blue (R-, G-, and B-) QLEDs with poly(9,9-dioctylfluorene-co-N-(4-sec-butylphenyl)diphenylamine) as the hole-transporting layer with conventional structures. The external quantum efficiency (EQE) and current efficiency were 19.2% and 22.7 cd A-1 for R-QLEDs, 21.1% and 93.3 cd A-1 for G-QLEDs, and 10.6% and 10.4 cd A-1 for B-QLEDs, respectively. The TREL results for B-QLEDs were remarkably different from those for R- and G-QLEDs because of the insufficient electron injection crossing the type II heterojunction between the emission layer and the electron-transporting layer. We further applied poly(N-vinylcarbazole) as the hole-transporting layer and obtained much better performance for B-QLEDs, with EQE and current efficiency of 15.9% and 15.4 cd A-1, respectively. Concomitant with the increase in EQE are an increase in the turn-on voltage from 2.3 to 3.7 V and a transient electroluminescence spike after voltage turn-off.
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Affiliation(s)
- Qibin Shen
- Department of Physics and State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
| | - Yanlei Hao
- Center for Chemistry of High-Performance and Novel Materials, State Key Laboratory of Silicon Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Luying Ma
- Center for Chemistry of High-Performance and Novel Materials, State Key Laboratory of Silicon Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Xiaoyu Wang
- Department of Physics and State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
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6
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Rhee S, Chang JH, Hahm D, Jeong BG, Kim J, Lee H, Lim J, Hwang E, Kwak J, Bae WK. Tailoring the Electronic Landscape of Quantum Dot Light-Emitting Diodes for High Brightness and Stable Operation. ACS NANO 2020; 14:17496-17504. [PMID: 33252236 DOI: 10.1021/acsnano.0c07890] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The charge injection imbalance into the quantum dot (QD) emissive layer of QD-based light-emitting diodes (QD-LEDs) is an unresolved issue that is detrimental to the efficiency and operation stability of devices. Herein, an integrated approach to harmonize the charge injection rates for bright and stable QD-LEDs is proposed. Specifically, the electronic characteristics of the hole transport layer (HTL) is delicately designed in order to facilitate the hole injection from the HTL into QDs and confine the electron overflow toward the HTL. The well-defined exciton recombination zone by the engineered QDs and HTL results in high performance with a peak luminance exceeding 410 000 cd/m2, suppressed efficiency roll-off characteristics (ΔEQE < 5% between 200 and 200 000 cd/m2), and prolonged operational stability. The electric and optoelectronic analyses reveal the charge carrier injection mechanism at the interface between the HTL and QDs and provides the design principle of QD heterostructures and charge transport layers for high-performance QD-LEDs.
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Affiliation(s)
- Seunghyun Rhee
- SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 16419, Korea
| | - Jun Hyuk Chang
- SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 16419, Korea
| | - Donghyo Hahm
- SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 16419, Korea
| | - Byeong Guk Jeong
- SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 16419, Korea
| | - Jaeyoul Kim
- Department of Electrical Engineering and Computer Science, Inter-University Semiconductor Research Center (ISRC), Seoul National University, Seoul 08826, Korea
| | - Hyunkoo Lee
- Department of Electronics Engineering, Sookmyung Women's University, Seoul 04310, Korea
| | - Jaehoon Lim
- Department of Energy Science, Center for Artificial Atoms, Sungkyunkwan University, Suwon 16419, Korea
| | - Euyheon Hwang
- SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 16419, Korea
| | - Jeonghun Kwak
- Department of Electrical Engineering and Computer Science, Inter-University Semiconductor Research Center (ISRC), Seoul National University, Seoul 08826, Korea
| | - Wan Ki Bae
- SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 16419, Korea
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7
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Rhee S, Chang JH, Hahm D, Kim K, Jeong BG, Lee HJ, Lim J, Char K, Lee C, Bae WK. "Positive Incentive" Approach To Enhance the Operational Stability of Quantum Dot-Based Light-Emitting Diodes. ACS APPLIED MATERIALS & INTERFACES 2019; 11:40252-40259. [PMID: 31590488 DOI: 10.1021/acsami.9b13217] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Balanced charge injection promises high efficiency of quantum dot-based light-emitting diodes (QD-LEDs). The most widely used approach to realize charge injection balance impedes the injection rate of the dominant charge carrier with energetic barriers. However, these approaches often accompany unwanted outcomes (e.g., the increase in operation voltage) that sacrifice the operational stability of devices. Herein, a "positive incentive" approach is proposed to enhance the efficiency and the operational stability of QD-LEDs. Specifically, the supply of hole, an inferior carrier than its counterpart, is facilitated by adopting a thin fullerene (C60) interlayer at the interface between the hole injection layer (MoOX) and hole transport layer (4,4'-bis(9-carbazolyl)-1,1'-biphenyl). The C60 interlayer boosts the hole current by eliminating the universal energy barrier, lowers the operation voltage of QD-LEDs, and enhances the charge balance in the QD emissive layer within the working device. Consequently, QD-LEDs benefitting from the adoption of the C60 interlayer exhibit significantly enhanced device efficiency and operation stability. Grounded on the quantitative assessment of the charge injection imbalance within the QD emissive layer, the impact of electrical parameters of QD-LEDs on their optoelectronic performance and operational stability is also discussed.
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Affiliation(s)
| | | | | | | | - Byeong Guk Jeong
- SKKU Advanced Institute of Nanotechnology , Sungkyunkwan University , Suwon 16419 , Korea
| | | | - Jaehoon Lim
- Department of Chemical Engineering , Ajou University , Suwon 16499 , Korea
| | | | | | - Wan Ki Bae
- SKKU Advanced Institute of Nanotechnology , Sungkyunkwan University , Suwon 16419 , Korea
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8
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Moon H, Lee C, Lee W, Kim J, Chae H. Stability of Quantum Dots, Quantum Dot Films, and Quantum Dot Light-Emitting Diodes for Display Applications. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1804294. [PMID: 30650209 DOI: 10.1002/adma.201804294] [Citation(s) in RCA: 178] [Impact Index Per Article: 35.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2018] [Revised: 10/10/2018] [Indexed: 05/06/2023]
Abstract
Quantum dots (QDs) are being highlighted in display applications for their excellent optical properties, including tunable bandgaps, narrow emission bandwidth, and high efficiency. However, issues with their stability must be overcome to achieve the next level of development. QDs are utilized in display applications for their photoluminescence (PL) and electroluminescence. The PL characteristics of QDs are applied to display or lighting applications in the form of color-conversion QD films, and the electroluminescence of QDs is utilized in quantum dot light-emitting diodes (QLEDs). Studies on the stability of QDs and QD devices in display applications are reviewed herein. QDs can be degraded by oxygen, water, thermal heating, and UV exposure. Various approaches have been developed to protect QDs from degradation by controlling the composition of their shells and ligands. Phosphorescent QDs have been protected by bulky ligands, physical incorporation in polymer matrices, and covalent bonding with polymer matrices. The stability of electroluminescent QLEDs can be enhanced by using inorganic charge transport layers and by improving charge balance. As understanding of the degradation mechanisms of QDs increases and more stable QDs and display devices are developed, QDs are expected to play critical roles in advanced display applications.
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Affiliation(s)
- Hyungsuk Moon
- School of Chemical Engineering, Sungkyunkwan University (SKKU), Seoburo 2066, Jangan-gu, Suwon, Gyeonggi-do, 16419, Republic of Korea
| | - Changmin Lee
- School of Chemical Engineering, Sungkyunkwan University (SKKU), Seoburo 2066, Jangan-gu, Suwon, Gyeonggi-do, 16419, Republic of Korea
| | - Woosuk Lee
- School of Chemical Engineering, Sungkyunkwan University (SKKU), Seoburo 2066, Jangan-gu, Suwon, Gyeonggi-do, 16419, Republic of Korea
| | - Jungwoo Kim
- School of Chemical Engineering, Sungkyunkwan University (SKKU), Seoburo 2066, Jangan-gu, Suwon, Gyeonggi-do, 16419, Republic of Korea
| | - Heeyeop Chae
- School of Chemical Engineering, Sungkyunkwan University (SKKU), Seoburo 2066, Jangan-gu, Suwon, Gyeonggi-do, 16419, Republic of Korea
- SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University (SKKU), Seoburo 2066, Jangan-gu, Suwon, Gyeonggi-do, 16419, Republic of Korea
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9
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Lee S, Flanagan JC, Kim J, Yun AJ, Lee B, Shim M, Park B. Efficient Type-II Heterojunction Nanorod Sensitized Solar Cells Realized by Controlled Synthesis of Core/Patchy-Shell Structure and CdS Cosensitization. ACS APPLIED MATERIALS & INTERFACES 2019; 11:19104-19114. [PMID: 31066260 DOI: 10.1021/acsami.9b02873] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Here, we report the successful application of core/patchy-shell CdSe/CdSe xTe1- x type-II heterojunction nanorods (HNRs) to realize efficient sensitized solar cells. The core/patchy-shell structure designed to have a large type-II heterointerface without completely shielding the CdSe core significantly improves photovoltaic performance compared to other HNRs with minimal or full-coverage shells. In addition, cosensitization with CdS grown by successive ionic layer adsorption and reaction further improves the power conversion efficiency. One-diode model analysis reveals that the HNRs having exposed CdSe cores and suitably grown CdS result in significant reduction of series resistance. Investigation of the intercorrelation between diode quality parameters, diode saturation current density ( J0) and recombination order (β = (ideality factor)-1) reveals that HNRs with open CdSe cores exhibit reduced recombination. These results confirm that the superior performance of core/patchy-shell HNRs results from their fine-tuned structure: photocurrent is increased by the large type-II heterointerface and recombination is effectively suppressed due to the open CdSe core enabling facile electron extraction. An optimized power conversion efficiency of 5.47% (5.89% with modified electrode configuration) is reported, which is unmatched among photovoltaics utilizing anisotropic colloidal heterostructures as light-harvesting materials.
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Affiliation(s)
- Sangheon Lee
- WCU Hybrid Materials Program, Department of Materials Science and Engineering, Research Institute of Advanced Materials , Seoul National University , Seoul 08226 , Korea
| | - Joseph C Flanagan
- Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Jaewook Kim
- WCU Hybrid Materials Program, Department of Materials Science and Engineering, Research Institute of Advanced Materials , Seoul National University , Seoul 08226 , Korea
| | - Alan Jiwan Yun
- WCU Hybrid Materials Program, Department of Materials Science and Engineering, Research Institute of Advanced Materials , Seoul National University , Seoul 08226 , Korea
| | - Byungho Lee
- WCU Hybrid Materials Program, Department of Materials Science and Engineering, Research Institute of Advanced Materials , Seoul National University , Seoul 08226 , Korea
| | - Moonsub Shim
- Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Byungwoo Park
- WCU Hybrid Materials Program, Department of Materials Science and Engineering, Research Institute of Advanced Materials , Seoul National University , Seoul 08226 , Korea
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Bai X, Purcell-Milton F, Gun'ko YK. Optical Properties, Synthesis, and Potential Applications of Cu-Based Ternary or Quaternary Anisotropic Quantum Dots, Polytypic Nanocrystals, and Core/Shell Heterostructures. NANOMATERIALS 2019; 9:nano9010085. [PMID: 30634642 PMCID: PMC6359286 DOI: 10.3390/nano9010085] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Revised: 12/28/2018] [Accepted: 12/31/2018] [Indexed: 12/29/2022]
Abstract
This review summaries the optical properties, recent progress in synthesis, and a range of applications of luminescent Cu-based ternary or quaternary quantum dots (QDs). We first present the unique optical properties of the Cu-based multicomponent QDs, regarding their emission mechanism, high photoluminescent quantum yields (PLQYs), size-dependent bandgap, composition-dependent bandgap, broad emission range, large Stokes’ shift, and long photoluminescent (PL) lifetimes. Huge progress has taken place in this area over the past years, via detailed experimenting and modelling, giving a much more complete understanding of these nanomaterials and enabling the means to control and therefore take full advantage of their important properties. We then fully explore the techniques to prepare the various types of Cu-based ternary or quaternary QDs (including anisotropic nanocrystals (NCs), polytypic NCs, and spherical, nanorod and tetrapod core/shell heterostructures) are introduced in subsequent sections. To date, various strategies have been employed to understand and control the QDs distinct and new morphologies, with the recent development of Cu-based nanorod and tetrapod structure synthesis highlighted. Next, we summarize a series of applications of these luminescent Cu-based anisotropic and core/shell heterostructures, covering luminescent solar concentrators (LSCs), bioimaging and light emitting diodes (LEDs). Finally, we provide perspectives on the overall current status, challenges, and future directions in this field. The confluence of advances in the synthesis, properties, and applications of these Cu-based QDs presents an important opportunity to a wide-range of fields and this piece gives the reader the knowledge to grasp these exciting developments.
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Affiliation(s)
- Xue Bai
- School of Chemistry and CRANN Institute, Trinity College Dublin, Dublin 2, Dublin, Ireland.
| | - Finn Purcell-Milton
- School of Chemistry and CRANN Institute, Trinity College Dublin, Dublin 2, Dublin, Ireland.
| | - Yuri K Gun'ko
- School of Chemistry and CRANN Institute, Trinity College Dublin, Dublin 2, Dublin, Ireland.
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11
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Chang JH, Park P, Jung H, Jeong BG, Hahm D, Nagamine G, Ko J, Cho J, Padilha LA, Lee DC, Lee C, Char K, Bae WK. Unraveling the Origin of Operational Instability of Quantum Dot Based Light-Emitting Diodes. ACS NANO 2018; 12:10231-10239. [PMID: 30347988 DOI: 10.1021/acsnano.8b03386] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We investigate the operational instability of quantum dot (QD)-based light-emitting diodes (QLEDs). Spectroscopic analysis on the QD emissive layer within devices in chorus with the optoelectronic and electrical characteristics of devices discloses that the device efficiency of QLEDs under operation is indeed deteriorated by two main mechanisms. The first is the luminance efficiency drop of the QD emissive layer in the running devices owing to the accumulation of excess electrons in the QDs, which escalates the possibility of nonradiative Auger recombination processes in the QDs. The other is the electron leakage toward hole transport layers (HTLs) that accompanies irreversible physical damage to the HTL by creating nonradiative recombination centers. These processes are distinguishable in terms of the time scale and the reversibility, but both stem from a single origin, the discrepancy between electron versus hole injection rates into QDs. Based on experimental and calculation results, we propose mechanistic models for the operation of QLEDs in individual quantum dot levels and their degradation during operation and offer rational guidelines that promise the realization of high-performance QLEDs with proven operational stability.
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Affiliation(s)
- Jun Hyuk Chang
- School of Chemical and Biological Engineering , Seoul National University , Seoul 08826 , Korea
| | - Philip Park
- Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095 , United States
| | - Heeyoung Jung
- School of Electrical and Computer Engineering, Inter-University Semiconductor Research Center , Seoul National University , Seoul 08826 , Korea
| | - Byeong Guk Jeong
- Department of Chemical and Biomolecular Engineering, KAIST Institute for the NanoCentury , Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 34141 , Korea
| | - Donghyo Hahm
- School of Chemical and Biological Engineering , Seoul National University , Seoul 08826 , Korea
| | - Gabriel Nagamine
- Instituto de Fisica "Gleb Wataghin" , Universidade Estadual de Campinas , UNICAMP, P.O. Box 6165, 13083-859 Campinas , São Paulo , Brazil
| | - Jongkuk Ko
- Department of Chemical and Biological Engineering , Korea University , Seoul 02841 , Korea
| | - Jinhan Cho
- Department of Chemical and Biological Engineering , Korea University , Seoul 02841 , Korea
| | - Lazaro A Padilha
- Instituto de Fisica "Gleb Wataghin" , Universidade Estadual de Campinas , UNICAMP, P.O. Box 6165, 13083-859 Campinas , São Paulo , Brazil
| | - Doh C Lee
- Department of Chemical and Biomolecular Engineering, KAIST Institute for the NanoCentury , Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 34141 , Korea
| | - Changhee Lee
- School of Electrical and Computer Engineering, Inter-University Semiconductor Research Center , Seoul National University , Seoul 08826 , Korea
| | - Kookheon Char
- School of Chemical and Biological Engineering , Seoul National University , Seoul 08826 , Korea
| | - Wan Ki Bae
- SKKU Advanced Institute of Nanotechnology (SAINT) , Sungkyunkwan University , Suwon-si , Gyeonggi-do 16419 , Korea
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12
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Kim HM, Cho S, Kim J, Shin H, Jang J. Li and Mg Co-Doped Zinc Oxide Electron Transporting Layer for Highly Efficient Quantum Dot Light-Emitting Diodes. ACS APPLIED MATERIALS & INTERFACES 2018; 10:24028-24036. [PMID: 29952540 DOI: 10.1021/acsami.8b04721] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Zinc-oxide (ZnO) is widely used as an n-type electron transporting layer (ETL) for quantum dot (QD) light-emitting diode (QLED) because various metal doping can be possible and ZnO nanoparticle can be processed at low temperatures. We report here a Li- and Mg-doped ZnO, MLZO, which is used for ETL of highly efficient and long lifetime QLEDs. Co-doping, Mg and Li, in ZnO increases its band gap and electrical resistivity and thus can enhance charge balance in emission layer (EML). It is found also that the O-H concentration at the oxide surface decreases and exciton decay time of QDs on the metal oxide increases by co-doping in ZnO. The inverted green QLEDs with MLZO ETL exhibits the maximum current efficiency (CEmax) of 69.1 cd/A, power efficiency (PEmax) of 73.8 lm/W, and external quantum efficiency (EQEmax) of 18.4%. This is at least two times higher compared with the efficiencies of the QLEDs with Mg-doped ZnO ETL. The optimum Li and Mg concentrations are found to be 10% each. The deep-red, red, light-blue, and deep-blue QLEDs with MLZO ETLs exhibit the CEmax of 6.0, 22.3, 1.9, and 0.5 cd/A, respectively. The MLZO introduced here can be widely used as ETL of highly efficient QLEDs.
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Affiliation(s)
- Hyo-Min Kim
- Advanced Display Research Center (ADRC), Department of Information Display , Kyung Hee University , Dongdaemoon-ku, Seoul 130-701 , Korea
| | - Sinyoung Cho
- Advanced Display Research Center (ADRC), Department of Information Display , Kyung Hee University , Dongdaemoon-ku, Seoul 130-701 , Korea
| | - Jeonggi Kim
- Advanced Display Research Center (ADRC), Department of Information Display , Kyung Hee University , Dongdaemoon-ku, Seoul 130-701 , Korea
| | - Hyeonjeong Shin
- Advanced Display Research Center (ADRC), Department of Information Display , Kyung Hee University , Dongdaemoon-ku, Seoul 130-701 , Korea
| | - Jin Jang
- Advanced Display Research Center (ADRC), Department of Information Display , Kyung Hee University , Dongdaemoon-ku, Seoul 130-701 , Korea
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