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Diesing S, Zhang L, Zysman-Colman E, Samuel IDW. A figure of merit for efficiency roll-off in TADF-based organic LEDs. Nature 2024; 627:747-753. [PMID: 38538942 PMCID: PMC10972759 DOI: 10.1038/s41586-024-07149-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 02/01/2024] [Indexed: 04/01/2024]
Abstract
Organic light-emitting diodes (OLEDs) are a revolutionary light-emitting display technology that has been successfully commercialized in mobile phones and televisions1,2. The injected charges form both singlet and triplet excitons, and for high efficiency it is important to enable triplets as well as singlets to emit light. At present, materials that harvest triplets by thermally activated delayed fluorescence (TADF) are a very active field of research as an alternative to phosphorescent emitters that usually use heavy metal atoms3,4. Although excellent progress has been made, in most TADF OLEDs there is a severe decrease of efficiency as the drive current is increased, known as efficiency roll-off. So far, much of the literature suggests that efficiency roll-off should be reduced by minimizing the energy difference between singlet and triplet excited states (ΔEST) to maximize the rate of conversion of triplets to singlets by means of reverse intersystem crossing (kRISC)5-20. We analyse the efficiency roll-off in a wide range of TADF OLEDs and find that neither of these parameters fully accounts for the reported efficiency roll-off. By considering the dynamic equilibrium between singlets and triplets in TADF materials, we propose a figure of merit for materials design to reduce efficiency roll-off and discuss its correlation with reported data of TADF OLEDs. Our new figure of merit will guide the design and development of TADF materials that can reduce efficiency roll-off. It will help improve the efficiency of TADF OLEDs at realistic display operating conditions and expand the use of TADF materials to applications that require high brightness, such as lighting, augmented reality and lasing.
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Affiliation(s)
- S Diesing
- Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
- Organic Semiconductor Centre, EaStCHEM, School of Chemistry, St Andrews, UK
| | - L Zhang
- Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
- Organic Semiconductor Centre, EaStCHEM, School of Chemistry, St Andrews, UK
| | - E Zysman-Colman
- Organic Semiconductor Centre, EaStCHEM, School of Chemistry, St Andrews, UK.
| | - I D W Samuel
- Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK.
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Siddiqui I, Kumar S, Tsai YF, Gautam P, Shahnawaz, Kesavan K, Lin JT, Khai L, Chou KH, Choudhury A, Grigalevicius S, Jou JH. Status and Challenges of Blue OLEDs: A Review. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:2521. [PMID: 37764550 PMCID: PMC10536903 DOI: 10.3390/nano13182521] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Revised: 09/04/2023] [Accepted: 09/05/2023] [Indexed: 09/29/2023]
Abstract
Organic light-emitting diodes (OLEDs) have outperformed conventional display technologies in smartphones, smartwatches, tablets, and televisions while gradually growing to cover a sizable fraction of the solid-state lighting industry. Blue emission is a crucial chromatic component for realizing high-quality red, green, blue, and yellow (RGBY) and RGB white display technologies and solid-state lighting sources. For consumer products with desirable lifetimes and efficiency, deep blue emissions with much higher power efficiency and operation time are necessary prerequisites. This article reviews over 700 papers covering various factors, namely, the crucial role of blue emission for full-color displays and solid-state lighting, the performance status of blue OLEDs, and the systematic development of fluorescent, phosphorescent, and thermally activated delayed fluorescence blue emitters. In addition, various challenges concerning deep blue efficiency, lifetime, and approaches to realizing deeper blue emission and higher efficacy for blue OLED devices are also described.
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Affiliation(s)
- Iram Siddiqui
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Sudhir Kumar
- Institute for Chemical and Bioengineering, ETH Zürich, 8093 Zürich, Switzerland
| | - Yi-Fang Tsai
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Prakalp Gautam
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Shahnawaz
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Kiran Kesavan
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Jin-Ting Lin
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Luke Khai
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Kuo-Hsien Chou
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Abhijeet Choudhury
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Saulius Grigalevicius
- Department of Polymer Chemistry and Technology, Kaunas University of Technology, LT-50254 Kaunas, Lithuania
| | - Jwo-Huei Jou
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
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Recent Advances on Furan-Based Visible Light Photoinitiators of Polymerization. Catalysts 2023. [DOI: 10.3390/catal13030493] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/04/2023] Open
Abstract
Photopolymerization is an active research field enabling to polymerize in greener conditions than that performed with traditional thermal polymerization. At present, a great deal of effort is devoted to developing visible light photoinitiating systems. Indeed, the traditional UV photoinitiating systems are currently the focus of numerous safety concerns so alternatives to UV light are being actively researched. However, visible light photons are less energetic than UV photons so the reactivity of the photoinitiating systems should be improved to address this issue. In this field, furane constitutes an interesting candidate for the design of photocatalysts of polymerization due to its low cost and its easy chemical modification. In this review, an overview concerning the design of furane-based photoinitiators is provided. Comparisons with reference systems are also established to demonstrate evidence of the interest of these photoinitiators in innovative structures.
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Wright IA, Danos A, Montanaro S, Batsanov AS, Monkman AP, Bryce MR. Conformational Dependence of Triplet Energies in Rotationally Hindered N- and S-Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials. Chemistry 2021; 27:6545-6556. [PMID: 33560550 PMCID: PMC8251716 DOI: 10.1002/chem.202100036] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 02/08/2021] [Indexed: 12/22/2022]
Abstract
A series of four heterocyclic dimers has been synthesized, with twisted geometries imposed across the central linking bond by ortho-alkoxy chains. These include two isomeric bicarbazoles, a bis(dibenzothiophene-S,S-dioxide) and a bis(thioxanthene-S,S-dioxide). Spectroscopic and electrochemical methods, supported by density functional theory, have given detailed insights into how para- vs. meta- vs. broken conjugation, and electron-rich vs. electron-poor heterocycles impact the HOMO-LUMO gap and singlet and triplet energies. Crucially for applications as OLED hosts, the triplet energy (ET ) of these molecules was found to vary significantly between dilute polymer films and neat films, related to conformational demands of the molecules in the solid state. One of the bicarbazole species shows a variation in ET of 0.24 eV in the different media-sufficiently large to "make-or-break" an OLED device-with similar discrepancies found between neat films and frozen solution measurements of other previously reported OLED hosts. From consolidated optical and optoelectronic investigations of different host/dopant combinations, we identify that only the lower ET values measured in neat films give a reliable indicator of host/guest compatibility. This work also provides new molecular design rules for obtaining very high ET materials and controlling their HOMO and LUMO energies.
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Affiliation(s)
- Iain A. Wright
- Department of ChemistryDurham UniversitySouth RoadDurhamDH1 3LEUK
- Department of ChemistryLoughborough UniversityLoughboroughLeicestershireLE11 3TUUK
| | - Andrew Danos
- Department of PhysicsDurham UniversitySouth RoadDurhamDH1 3LEUK
| | - Stephanie Montanaro
- Department of ChemistryLoughborough UniversityLoughboroughLeicestershireLE11 3TUUK
| | | | | | - Martin R. Bryce
- Department of ChemistryDurham UniversitySouth RoadDurhamDH1 3LEUK
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