Universal host materials for red, green and blue high-efficiency single-layer phosphorescent organic light-emitting diodes

Lucas, Fabien; Quinton, Cassandre; Fall, Sadiara; Heiser, T.; Tondelier, Denis; Geffroy, Bernard; Leclerc, Nicolas; Rault‐Berthelot, Joëlle; Poriel, Cyril

doi:10.1039/d0tc04650g

Cited by 44 publications

(105 citation statements)

References 86 publications

(95 reference statements)

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“…However, despite the logical implications for triplet energies and how these determine host/guest compatibility, it is not commonplace to report neat film phosphorescence of new OLED host materials. Instead, low temperature solution measurements currently dominate the literature in reports of this kind [69, 76–87] . A recent study by Forrest and Thompson [73] has demonstrated that such solution measurements do not give appropriate triplet energies for the design of OLEDs, while the results here show that phosphorescence in dilute polymer films is also not suitable in this regard.…”

Section: Resultsmentioning

confidence: 72%

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

Wright

Danos

Montanaro

et al. 2021

Chemistry A European J

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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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Section: Resultsmentioning

confidence: 72%

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

Wright

Danos

Montanaro

et al. 2021

Chemistry A European J

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“…The most popular blue phosphor used in the field of PhOLEDs is the bis[2‐(4,6‐difluorophenyl)pyridinato‐C 2 ,N](picolinato)iridium(III) commonly abbreviated FIrpic. [ 31 ] However, FIrpic displays an E T of 2.67 eV (measured in 2‐methyl‐tetrahydofuran (2‐MeTHF) at room temperature (RT), [ 32 ] other values exist depending on the experimental conditions, see ref. [ 32 ] ) and is considered as a sky blue or greenish‐blue emitter (λ max = 465 and 497 nm in 2‐MeTHF).…”

Section: Part I Single‐layer Pholedsmentioning

confidence: 99%

“…[ 31 ] However, FIrpic displays an E T of 2.67 eV (measured in 2‐methyl‐tetrahydofuran (2‐MeTHF) at room temperature (RT), [ 32 ] other values exist depending on the experimental conditions, see ref. [ 32 ] ) and is considered as a sky blue or greenish‐blue emitter (λ max = 465 and 497 nm in 2‐MeTHF). Its HOMO/LUMO energy levels obtained from electrochemical studies in CH 2 Cl 2 + Bu 4 NPF 6 0.2 m are of ‐5.55/‐2.52 eV.…”

Section: Part I Single‐layer Pholedsmentioning

confidence: 99%

“…Its HOMO/LUMO energy levels obtained from electrochemical studies in CH 2 Cl 2 + Bu 4 NPF 6 0.2 m are of ‐5.55/‐2.52 eV. [ 32 ] In addition, when incorporated in an OLED, this phosphor suffers from an instability, which has hindered the development of blue‐emitting PhOLEDs. [ 33,34 ]…”

Section: Part I Single‐layer Pholedsmentioning

confidence: 99%

“…Bis(2,4‐difluorophenylpyridinato)‐tetrakis(1‐pyrazolyl)borate iridium(III), FIr6, [ 35 ] displays a higher E T (2.72 eV measured in 2‐MeTHF at RT, [ 32 ] other values exist depending of the experimental conditions, see ref. [ 32 ] ) and an extended HOMO (‐5.66 eV)/LUMO (‐2.32 eV) gap (3.34 eV vs 3.03 eV for FIrpic). Compared to FIrpic, its phosphorescence is blue‐shifted ((λ max = 456 and 486 nm in 2‐MeTHF [ 32 ] ).…”

Section: Part I Single‐layer Pholedsmentioning

confidence: 99%

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Designing Host Materials for the Emissive Layer of Single‐Layer Phosphorescent Organic Light‐Emitting Diodes: Toward Simplified Organic Devices

Poriel

Rault‐Berthelot

2021

Adv Funct Materials

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Thanks to the tremendous effort over the last 20 years, phosphorescent organic light‐emitting diodes (PhOLEDs) represent a prevalent technology. In this technology, all the high‐efficiency PhOLEDs are multi‐layer devices constituting, in addition to the emissive layer (EML), of a stack of functional organic layers. These layers play a crucial role in the device performance as they improve the injection, transport, and recombination of charges within the EML. Single‐layer PhOLEDs (SL‐PhOLEDs) represent ideal OLEDs, consisting only of the electrodes and the EML. However, reaching high‐performance SL‐PhOLED is far from easy, as removing the functional layers of an OLED stack dramatically decreases the performance. To achieve high SL‐PhOLED efficiency, the efficient injection, transport, and recombination of charges should be insured by the EML, and particularly, by the host material. In the present exhaustive review, the different molecular design strategies are analyzed, which have been used to construct high‐efficiency hosts for SL‐PhOLED. The impact of the electronic properties (triplet energy, HOMO/LUMO energy, mobility etc.) on the device characteristics (threshold voltage, electroluminescent spectrum, external quantum efficiency, etc.) are discussed. This allows to draw a structure/properties/device performance relationship map of interest for the future design of functional materials for SL‐PhOLEDs.

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Diarylfluorene‐Based Organic Semiconductor Materials toward Optoelectronic Applications

Han

Bai

Lin

et al. 2021

Adv Funct Materials

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reorganizing these two types of π orbitals, thus endowing the active films with significantly different optoelectronic property. In order to design high-performance and stable conjugated molecules, some basic principles should be followed, such as electronic structure, conformation and topology, steric hindrance, as well as supramolecular interaction, which also called four fundamental nodes proposed by Huang group. [8] Particularly, steric hindrance design is an effective strategy to enhance device performance and stability via adjusting the spatial arrangement of active molecular bricks, the morphology of films, and the fine optoelectronic properties. [9,10] The sterically hindered groups are capable to rotate the dihedral angles of the adjacent monomer units, which can inhibit interchain interactions and further reduce aggregation. In addition, the rigid bulks are favorable for improving the morphological and emission spectral stability of light-emitting conjugated polymers in solid state. Besides, beyond the intrinsic electronic structures, molecular conformation and topology is a crucial for precisely tuning the physical process, controlling film morphology, device performance, and stability.Similar to the industrial manufacturing, modular production of conjugated materials enable them to present a precise electron-structure tunability, controllable structural modification, and low-cost large-scale preparation, similar to Lego building block. In the last decades, amounts of building blocks, such as fluorene, carbazole (Cz), thiophene (Th), and benzothiadiazole, have been employed to design various conjugated molecules for specific applications. [11][12][13][14][15] Among these synthons, fluorene-based bulks have been widely reported to construct high performance organic semiconductors for efficient optoelectronic devices, owing to their easy chemical modification, stable thermodynamic property, high fluorescence quantum yield, and appropriate charge transport capability. [16][17][18][19] Nevertheless, the conventional fluorene units suffer from poor color purity and luminous stability due to significantly interchain aggregation and photo-/electro-oxidation of the alkyl pendant groups at C9 position, which restricted their actual development. [20] The appearance of diarylfluorene structure provides a broader space for the design and preparation of blue emitters with higher purity and efficiency. In 1905, the simplest diarylfluorene (9,9′-diphenylfluorene) was synthesized by Ullmann and Wurstemberger for the first time. [21] As a most promise and popular alternative, diarylfluorene is a non-planar architecture

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Universal host materials for red, green and blue high-efficiency single-layer phosphorescent organic light-emitting diodes

Abstract: Simplifying the structure of Organic Light-Emitting Diodes (OLEDs) has been for the last twenty years the purpose of many studies. However, despite these efforts, only a few materials provide high...

Cited by 44 publications

References 86 publications

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

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

Designing Host Materials for the Emissive Layer of Single‐Layer Phosphorescent Organic Light‐Emitting Diodes: Toward Simplified Organic Devices

Diarylfluorene‐Based Organic Semiconductor Materials toward Optoelectronic Applications

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