Universal Electroluminescence at Voltages below the Energy Gap in Organic Light‐Emitting Diodes

The Cz-DEPVI device showed high efficiencies of L: 13955 cd m−2, ηex: 4.90%, ηc: 6.0 cd A−1, ηp: 5.4 lm W−1 and CIE coordinates of (0.15, 0.06) at 2.8 V.

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Enhanced performance of organic light-emitting diodes by inserting wide-energy-gap interlayer between hole-transport layer and light-emitting layer

Thin Solid Films ◽

10.1016/j.tsf.2009.07.016 ◽

2009 ◽

Vol 518 (2) ◽

pp. 545-547 ◽

Cited By ~ 3

Author(s):

Yusuke Honda ◽

Toshinori Matsushima ◽

Hideyuki Murata

Keyword(s):

Light Emitting Diodes ◽

Energy Gap ◽

Hole Transport ◽

Organic Light Emitting Diodes ◽

Transport Layer ◽

Hole Transport Layer ◽

Light Emitting ◽

Organic Light ◽

Wide Energy

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High-Efficiency Hyperfluorescence White Light-Emitting Diodes Based on High-Concentration-Doped TADF Sensitizer Matrixes via Spatial and Energy Gap Effects

Chemical Science ◽

10.1039/d1sc05753g ◽

2021 ◽

Author(s):

Hui Xu ◽

Chunbo Duan ◽

Ying Xin ◽

Zicheng Wang ◽

Jing Zhang ◽

...

Keyword(s):

High Efficiency ◽

Light Emitting Diodes ◽

Energy Gap ◽

State Of The Art ◽

Organic Light Emitting Diodes ◽

High Concentration ◽

Light Emitting ◽

Organic Light ◽

White Light Emitting Diodes ◽

Gap Effects

Despite the success of monochromic hyperfluorescence (HF) organic light-emitting diodes (OLED), high-efficiency HF white OLEDs (WOLED) are still a big challenge. Herein, we demonstrate a HF WOLED with the state-of-the-art...

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Delayed Fluorescence from Inverted Singlet and Triplet Excited States for Efficient Organic Light-Emitting Diodes

10.21203/rs.3.rs-478258/v1 ◽

2021 ◽

Author(s):

Daigo Miyajima ◽

Naoya Aizawa ◽

Yong-Jin Pu ◽

Atsuko Nihonyanagi ◽

Ryotaro Ibuka ◽

...

Keyword(s):

Excited States ◽

Light Emitting Diodes ◽

Energy Gap ◽

Delayed Fluorescence ◽

Organic Light Emitting Diodes ◽

Positive Energy ◽

Light Emitting ◽

Organic Light ◽

Spin Singlet ◽

Triplet Excited States

Abstract Hund’s multiplicity rule states that for a given electronic configuration, a higher spin state has a lower energy. Rephrasing this rule for molecular excited states predicts a positive energy gap between spin-singlet and spin-triplet excited states, which has been consistent with numerous experimental observations over almost a century. Here, we report a fluorescent molecule that disobeys Hund’s rule, possessing a negative singlet–triplet energy gap of –11 meV. The energy inversion of the singlet and triplet excited states results in delayed fluorescence with short time constants of 0.2 μs, which anomalously decrease with decreasing temperature due to the emissive singlet character of the lowest-energy excited state. Organic light-emitting diodes using this molecule exhibited a fast transient electroluminescence decay with a peak external quantum efficiency of 17%, demonstrating potential implications for optoelectronic devices, including displays, lighting, and lasers.

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Fluorinated Poly(N-vinylcarbazole) Host for Triplet Energy Confinement on Phosphorescent Emitter in Organic Light-emitting Diodes

MRS Proceedings ◽

10.1557/proc-1197-d02-08 ◽

2009 ◽

Vol 1197 ◽

Author(s):

Yukitami Mizuno ◽

Isao Takasu ◽

Shuichi Uchikoga ◽

Shintaro Enomoto ◽

Tomoaki Sawabe ◽

...

Keyword(s):

Light Emitting Diodes ◽

Energy Gap ◽

Organic Light Emitting Diodes ◽

Lumo Energy ◽

Light Emitting ◽

Energy Gaps ◽

Organic Light ◽

Host Materials ◽

Homo Lumo ◽

Polymer Host

AbstractFluorinated carbazoles as host materials have been investigated for highly efficient organic light emitting diodes (OLEDs). By molecular orbital calculations, we found that fluorinations at position 2, 4, 5 and 7 of carbazole ring were effective for widening HOMO-LUMO energy gap. The energy gaps of our synthesized 2,7-difluorocarbazole (F2-Cz) and 2,4,5,7-tetrafluorocarbazole (F4-Cz), were estimated to be 3.71 eV and 3.87 eV by the absorption spectra, respectively. These energy gaps were higher than that of the non-substituted carbazole (Cz, 3.59 eV). We synthesized poly(N-vinyl-2,7-difluorocarbazole) (F2-PVK) and poly(N-vinyl-2,4,5,7-tetrafluorocarbazole) (F4-PVK) as solution processable polymer host materials. However, the F4-PVK was found to be an unsolved polymer. The F2-PVK could be compared with non substituted poly(N-vinylcarbazole) (PVK) in OLEDs. The emission layer (EML) contained iridium(III) bis [(4,6-di-fluorophenyl)-pyridinato-N,C2′] picolinate (FIrpic) as a blue phosphorescent dopant, and iridium(III) bis [2-(9,9-dihexylfluorenyl)-1-pyridine] acetylacetonate as a yellow dopant. The white OLED with the F2-PVK showed 1.4 times higher luminous current efficiency (24 cd/A) than the PVK (17 cd/A). These data show that the excitation energy is confined on dopants by using fluorinated polymer host material with higher T1 corresponding to wider HOMO-LUMO energy gap.

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Fabrication and Characterization of Organic Light-Emitting Diodes Containing Small Molecules Blends as Emissive Layer

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.795.106 ◽

2013 ◽

Vol 795 ◽

pp. 106-109 ◽

Cited By ~ 2

Author(s):

Mohd Arif Mohd Sarjidan ◽

Siti Hajar Basri ◽

W.H. Abd Majid

Keyword(s):

Small Molecules ◽

Light Emitting Diodes ◽

Energy Gap ◽

High Energy ◽

Organic Light Emitting Diodes ◽

Optical Energy Gap ◽

Guest Molecules ◽

Light Emitting ◽

Organic Light

Organic light-emitting diodes (OLEDs) were fabricated containing guest molecule of Tris (8-hydroxyquinoline) aluminum (Alq3) blend with host molecules of N,N-diphenyl-N,N-bis (3-methylphenyl)-1,1-biphenyl-4,4-diamine (TPD) and 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) small molecules. Optical, photoluminescence (PL) and electroluminescence (EL) properties were investigated with respect to blend systems. The obtained optical energy gap and PL intensity in the blend systems increased due to the transfer of high energy from the host to guest molecules. Luminance and current efficiency were enhanced for blended OLEDs as compared to that of pure Alq3, related to high exiton recombination in guest caused by high injection and accumulation of charge carrier.

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