1
|
Rajeev K, Vipin CK, Sajeev AK, Shukla A, McGregor SKM, Lo SC, Namdas EB, Narayanan Unni KN. Blue emitting exciplex for yellow and white organic light-emitting diodes. FRONTIERS OF OPTOELECTRONICS 2023; 16:46. [PMID: 38095740 PMCID: PMC10721783 DOI: 10.1007/s12200-023-00101-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Accepted: 10/29/2023] [Indexed: 12/17/2023]
Abstract
White organic light-emitting diodes (WOLEDs) have several desirable features, but their commercialization is hindered by the poor stability of blue light emitters and high production costs due to complicated device structures. Herein, we investigate a standard blue emitting hole transporting material (HTM) N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) and its exciplex emission upon combining with a suitable electron transporting material (ETM), 3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ). Blue and yellow OLEDs with simple device structures are developed by using a blend layer, NPB:TAZ, as a blue emitter as well as a host for yellow phosphorescent dopant iridium (III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2')acetylacetonate (PO-01). Strategic device design then exploits the ambipolar charge transport properties of tetracene as a spacer layer to connect these blue and yellow emitting units. The tetracene-linked device demonstrates more promising results compared to those using a conventional charge generation layer (CGL). Judicious choice of the spacer prevents exciton diffusion from the blue emitter unit, yet facilitates charge carrier transport to the yellow emitter unit to enable additional exciplex formation. This complementary behavior of the spacer improves the blue emission properties concomitantly yielding reasonable yellow emission. The overall white light emission properties are enhanced, achieving CIE coordinates (0.36, 0.39) and color temperature (4643 K) similar to daylight. Employing intermolecular exciplex emission in OLEDs simplifies the device architecture via its dual functionality as a host and as an emitter.
Collapse
Affiliation(s)
- Kavya Rajeev
- Centre for Sustainable Energy Technologies, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram, 695 019, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | - C K Vipin
- Centre for Sustainable Energy Technologies, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram, 695 019, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | - Anjali K Sajeev
- Centre for Sustainable Energy Technologies, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram, 695 019, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | - Atul Shukla
- Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, QLD, 4072, Australia
- School of Mathematics and Physics, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Sarah K M McGregor
- Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, QLD, 4072, Australia
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Shih-Chun Lo
- Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, QLD, 4072, Australia
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Ebinazar B Namdas
- Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, QLD, 4072, Australia
- School of Mathematics and Physics, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - K N Narayanan Unni
- Centre for Sustainable Energy Technologies, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram, 695 019, India.
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India.
| |
Collapse
|
2
|
Joo E, Hur JW, Ko JY, Kim TG, Hwang JY, Smith KE, Lee H, Cho SW. Effects of HAT-CN Layer Thickness on Molecular Orientation and Energy-Level Alignment with ZnPc. Molecules 2023; 28:molecules28093821. [PMID: 37175231 PMCID: PMC10179936 DOI: 10.3390/molecules28093821] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Revised: 04/27/2023] [Accepted: 04/28/2023] [Indexed: 05/15/2023] Open
Abstract
Efficient energy-level alignment is crucial for achieving high performance in organic electronic devices. Because the electronic structure of an organic semiconductor is significantly influenced by its molecular orientation, comprehensively understanding the molecular orientation and electronic structure of the organic layer is essential. In this study, we investigated the interface between a 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) hole injection layer and a zinc-phthalocyanine (ZnPc) p-type organic semiconductor. To determine the energy-level alignment and molecular orientation, we conducted in situ ultraviolet and X-ray photoelectron spectroscopies, as well as angle-resolved X-ray absorption spectroscopy. We found that the HAT-CN molecules were oriented relatively face-on (40°) in the thin (5 nm) layer, whereas they were oriented relatively edge-on (62°) in the thick (100 nm) layer. By contrast, ZnPc orientation was not significantly altered by the underlying HAT-CN orientation. The highest occupied molecular orbital (HOMO) level of ZnPc was closer to the Fermi level on the 100 nm thick HAT-CN layer than on the 5 nm thick HAT-CN layer because of the higher work function. Consequently, a considerably low energy gap between the lowest unoccupied molecular orbital level of HAT-CN and the HOMO level of ZnPc was formed in the 100 nm thick HAT-CN case. This may improve the hole injection ability of the anode system, which can be utilized in various electronic devices.
Collapse
Affiliation(s)
- Eunah Joo
- Department of Physics and Engineering Physics, Yonsei University, 1 Yonseidae-gil, Wonju-si 26493, Republic of Korea
| | - Jin Woo Hur
- Department of Physics and Engineering Physics, Yonsei University, 1 Yonseidae-gil, Wonju-si 26493, Republic of Korea
| | - Joon Young Ko
- Department of Physics and Engineering Physics, Yonsei University, 1 Yonseidae-gil, Wonju-si 26493, Republic of Korea
| | - Tae Gyun Kim
- Department of Physics and Engineering Physics, Yonsei University, 1 Yonseidae-gil, Wonju-si 26493, Republic of Korea
| | - Jung Yeon Hwang
- Department of Physics and Engineering Physics, Yonsei University, 1 Yonseidae-gil, Wonju-si 26493, Republic of Korea
| | - Kevin E Smith
- Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, MA 02215, USA
| | - Hyunbok Lee
- Department of Physics and Institute of Quantum Convergence Technology, Kangwon National University, 1 Gangwondaehak-gil, Chuncheon-si 24341, Republic of Korea
| | - Sang Wan Cho
- Department of Physics and Engineering Physics, Yonsei University, 1 Yonseidae-gil, Wonju-si 26493, Republic of Korea
| |
Collapse
|
3
|
de la Rie J, Enache M, Wang Q, Lu W, Kivala M, Stöhr M. Self-Assembly of a Triphenylene-Based Electron Donor Molecule on Graphene: Structural and Electronic Properties. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2022; 126:9855-9861. [PMID: 35747511 PMCID: PMC9207905 DOI: 10.1021/acs.jpcc.1c10266] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Revised: 05/16/2022] [Indexed: 06/15/2023]
Abstract
In this study, we report on the self-assembly of the organic electron donor 2,3,6,7,10,11-hexamethoxytriphenylene (HAT) on graphene grown epitaxially on Ir(111). Using scanning tunneling microscopy and low-energy electron diffraction, we find that a monolayer of HAT assembles in a commensurate close-packed hexagonal network on graphene/Ir(111). X-ray and ultraviolet photoelectron spectroscopy measurements indicate that no charge transfer between the HAT molecules and the graphene/Ir(111) substrate takes place, while the work function decreases slightly. This demonstrates that the HAT/graphene interface is weakly interacting. The fact that the molecules nonetheless form a commensurate network deviates from what is established for adsorption of organic molecules on metallic substrates where commensurate overlayers are mainly observed for strongly interacting systems.
Collapse
Affiliation(s)
- Joris de la Rie
- Zernike
Institute for Advanced Materials, University
of Groningen, Nijenborgh
4, Groningen 9747 AG, The Netherlands
| | - Mihaela Enache
- Zernike
Institute for Advanced Materials, University
of Groningen, Nijenborgh
4, Groningen 9747 AG, The Netherlands
| | - Qiankun Wang
- Zernike
Institute for Advanced Materials, University
of Groningen, Nijenborgh
4, Groningen 9747 AG, The Netherlands
| | - Wenbo Lu
- Zernike
Institute for Advanced Materials, University
of Groningen, Nijenborgh
4, Groningen 9747 AG, The Netherlands
| | - Milan Kivala
- Institute
of Organic Chemistry, University of Heidelberg, Im Neuenheimer Feld 270, Heidelberg 69120, Germany
- Centre
for Advanced Materials, University of Heidelberg, Im Neuenheimer Feld 225, Heidelberg 69120, Germany
| | - Meike Stöhr
- Zernike
Institute for Advanced Materials, University
of Groningen, Nijenborgh
4, Groningen 9747 AG, The Netherlands
| |
Collapse
|
4
|
Zhang T, Rai D, Holmes RJ. Device-Based Probe of Triplet Exciton Diffusion in Singlet Fission Materials. J Phys Chem Lett 2021; 12:966-972. [PMID: 33464089 DOI: 10.1021/acs.jpclett.0c02825] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Probing triplet transport in singlet fission materials can be challenging due to the presence of multiple diffusing species. We present a device-based method to measure the intrinsic triplet diffusion length (LD) in organic semiconductor thin films exhibiting singlet fission. Triplet states are optically injected into the singlet fission material of interest via energy transfer from an adjacent thin film characterized by strong spin-orbit coupling. Injected triplets migrate through the full thickness of the material before undergoing dissociation at a donor-acceptor interface. By modeling the ratio of injector and acceptor photocurrent as a function of layer thickness, the triplet LD is extracted separate from processes of unknown efficiency including singlet fission and diffusion. In considering three archetypical fission systems, a wide range is found for the triplet LD, ranging from 3.3 ± 0.4 nm for 5,12-bis((triisopropylsilyl)ethynyl)tetracene to 17.1 ± 1.3 nm for pentacene and 32.1 ± 2.6 nm for tetracene.
Collapse
Affiliation(s)
- Tao Zhang
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Deepesh Rai
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Russell J Holmes
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| |
Collapse
|
5
|
Shin HG, Kang D, Jeong Y, Kim K, Cho Y, Park J, Hong S, Yi Y, Im S. High-Performance van der Waals Junction Field-Effect Transistors Utilizing Organic Molecule/Transition Metal Dichalcogenide Interface. ACS NANO 2020; 14:15646-15653. [PMID: 33136370 DOI: 10.1021/acsnano.0c06509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Two-dimensional (2D) transition metal dichalcogenide (TMD) hetero PN junctions with a van der Waals (vdW) interface have received much attention, because PN diodes are basically important to control the vertical current across the junction. Interestingly, the same vdW PN junction structure can be utilized for junction field-effect transistors (JFETs) where in-plane current is controlled along the junction. However, 2D vdW JFETs seem rarely reported, despite their own advantages to achieve when good vdW junction is secured. Here, we present high-performance p-MoTe2 JFETs using almost perfect vdW organic Alq3/p-MoTe2 junctions and demonstrate organic NPB/n-MoS2 JFETs. The p- and n-channel JFETs stably show high mobilities of 60-80 and ∼800 cm2/V s, respectively, along with a high ON/OFF current ratio (>1 × 105) and minimal gate leakage at 5 V even after a few months. Such performances are attributed to a quality vdW junction at organic layer/TMD interfaces.
Collapse
Affiliation(s)
- Hyung Gon Shin
- van der Waals Materials Research Center, Department of Physics, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Donghee Kang
- van der Waals Materials Research Center, Department of Physics, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Yeonsu Jeong
- van der Waals Materials Research Center, Department of Physics, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Kitae Kim
- van der Waals Materials Research Center, Department of Physics, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Yongjae Cho
- van der Waals Materials Research Center, Department of Physics, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Jeehong Park
- van der Waals Materials Research Center, Department of Physics, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Sungjae Hong
- van der Waals Materials Research Center, Department of Physics, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Yeonjin Yi
- van der Waals Materials Research Center, Department of Physics, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Seongil Im
- van der Waals Materials Research Center, Department of Physics, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| |
Collapse
|
6
|
Zhang D, Huang T, Duan L. Emerging Self-Emissive Technologies for Flexible Displays. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e1902391. [PMID: 31595613 DOI: 10.1002/adma.201902391] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2019] [Revised: 07/01/2019] [Indexed: 06/10/2023]
Abstract
Featuring a combination of ultrathin and lightweight properties, excellent mechanical flexibility, low power-consumption, and widely tunable saturated emission, flexible displays have opened up a new possibility for optoelectronics. The demands for flexible displays are growing on a continual basis due not only to their successful commercialization but, more importantly, their endless possibilities for wearable integrated systems. Up to now, self-emissive technologies for displays, flexible active-matrix organic light-emitting diodes (flex-AMOLED), flexible quantum dot light-emitting diodes (flex-QLEDs), and flexible perovskite light-emitting diodes (flex-PeLEDs) have been widely reported, but despite the significant progress made in these technologies, enormous obstacles and challenges remain for the vision of truly wearable applications, in particular with flex-QLEDs and flex-PeLEDs. Here, a review of the recent progress of all three self-emissive technologies for flexible displays is conducted, including the emissive active materials, device structures and approaches to manufacturing, the flexible substrates, and conductive electrodes, as well as the encapsulation techniques. The fast-paced improvement made to the efficiency of flexible devices in recent years is also summarized. The review concludes by making suggestions on the future development in this area, and is expected to help researchers in gaining a comprehensive understanding about the newly emerging technologies for flexible displays.
Collapse
Affiliation(s)
- Dongdong Zhang
- Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, 100084, China
| | - Tianyu Huang
- Center for Flexible Electronics Technology, Tsinghua University, Beijing, 100084, P. R. China
| | - Lian Duan
- Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, 100084, China
- Center for Flexible Electronics Technology, Tsinghua University, Beijing, 100084, P. R. China
| |
Collapse
|
7
|
Cho Y, Park JH, Kim M, Jeong Y, Yu S, Lim JY, Yi Y, Im S. Impact of Organic Molecule-Induced Charge Transfer on Operating Voltage Control of Both n-MoS 2 and p-MoTe 2 Transistors. NANO LETTERS 2019; 19:2456-2463. [PMID: 30855970 DOI: 10.1021/acs.nanolett.9b00019] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Since transition metal dichalcogenide (TMD) semiconductors are found as two-dimensional van der Waals materials with a discrete energy bandgap, many TMD based field effect transistors (FETs) are reported as prototype devices. However, overall reports indicate that threshold voltage ( Vth) of those FETs are located far away from 0 V whether the channel is p- or n-type. This definitely causes high switching voltage and unintended OFF-state leakage current. Here, a facile way to simultaneously modulate the Vth of both p- and n-channel FETs with TMDs is reported. The deposition of various organic small molecules on the channel results in charge transfer between the organic molecule and TMD channels. Especially, HAT-CN molecule is found to ideally work for both p- and n-channels, shifting their Vth toward 0 V concurrently. As a proof of concept, a complementary metal oxide semiconductor (CMOS) inverter with p-MoTe2 and n-MoS2 channels shows superior voltage gain and minimal power consumption after HAT-CN deposition, compared to its initial performance. When the same TMD FETs of the CMOS structure are integrated into an OLED pixel circuit for ambipolar switching, the circuit with HAT-CN film demonstrates complete ON/OFF switching of OLED pixel, which was not switched off without HAT-CN.
Collapse
Affiliation(s)
- Yongjae Cho
- Van der Waals Materials Research Center, Department of Physics and Applied Physics , Yonsei University , 50 Yonsei-ro , Seodaemun-gu , Seoul 03722 , Korea
| | - Ji Hoon Park
- Van der Waals Materials Research Center, Department of Physics and Applied Physics , Yonsei University , 50 Yonsei-ro , Seodaemun-gu , Seoul 03722 , Korea
| | - Minju Kim
- Van der Waals Materials Research Center, Department of Physics and Applied Physics , Yonsei University , 50 Yonsei-ro , Seodaemun-gu , Seoul 03722 , Korea
| | - Yeonsu Jeong
- Van der Waals Materials Research Center, Department of Physics and Applied Physics , Yonsei University , 50 Yonsei-ro , Seodaemun-gu , Seoul 03722 , Korea
| | - Sanghyuck Yu
- Van der Waals Materials Research Center, Department of Physics and Applied Physics , Yonsei University , 50 Yonsei-ro , Seodaemun-gu , Seoul 03722 , Korea
| | - June Yeong Lim
- Van der Waals Materials Research Center, Department of Physics and Applied Physics , Yonsei University , 50 Yonsei-ro , Seodaemun-gu , Seoul 03722 , Korea
| | - Yeonjin Yi
- Van der Waals Materials Research Center, Department of Physics and Applied Physics , Yonsei University , 50 Yonsei-ro , Seodaemun-gu , Seoul 03722 , Korea
| | - Seongil Im
- Van der Waals Materials Research Center, Department of Physics and Applied Physics , Yonsei University , 50 Yonsei-ro , Seodaemun-gu , Seoul 03722 , Korea
| |
Collapse
|
8
|
Park SG, Lee WJ, Song MJ, Shin J, Kim TW. Effects of the Thickness of N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine on the Electro-Optical Characteristics of Organic Light-Emitting Diodes. MATERIALS (BASEL, SWITZERLAND) 2019; 12:ma12060966. [PMID: 30909501 PMCID: PMC6471192 DOI: 10.3390/ma12060966] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 03/14/2019] [Accepted: 03/21/2019] [Indexed: 06/09/2023]
Abstract
We examined the electro-optical characteristics of organic light emitting diodes according to the N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine (TPD) thicknesses. The thicknesses of TPD were varied from 5 nm to 50 nm. The current density of the device with a TPD thickness of 5 nm was 8.94 times higher than that with a thickness of 50 nm at a driving voltage of 10 V. According to the conduction⁻current characteristics of conductors, the current densities improved with a decreasing TPD thickness. Different from the current density⁻voltage characteristics, the current efficiency⁻current density characteristics showed an improved efficiency with a 50 nm TPD thickness. The current efficiencies of a device with a 5 nm TPD thickness at a driving voltage of 10 V was 0.148 and at a 50 nm TPD thickness 0.993 cd/A, which was 6.7 times higher than the 5 nm TPD thickness. These results indicated that hole transport in Organic Light-Emitting Diode (OLED) devices were more efficient with thin 5 nm TPD than with thick 50 nm TPD, while electron transport was more efficient with thick 50 nm TPD, which caused conflicting results in the current efficiency-current density and current density-voltage characteristics according to TPD thicknesses.
Collapse
Affiliation(s)
- Sang-Geon Park
- Division of Smart Electrical and Electronic, Silla University, 140 Baegyang-daero 700beon-gil, Sasang-gu, Busan 46958, Korea.
| | - Won Jae Lee
- Electrical and Computer Engineering, Stony Brook University, 100 Nicolls Rd, Stony Brook, NY 11794, USA.
| | - Min Jong Song
- Department of Radiation Technology, Gwangju Health College, 73 Bungmun-daero 419 beongil, Gwangsangu, Gwangju 13557, Korea.
| | - Johngeon Shin
- Department of Materials Science and Engineering, Silla University, Busan 46958, Korea.
| | - Tae Wan Kim
- Department of Information Display Engineering, Hongik University, Seoul 04066, Korea.
| |
Collapse
|