Nearly non-roll-off high efficiency fluorescent yellow organic light-emitting diodes

Jou, Jwo‐Huei; Wang, Yishan; Lin, Chia‐Hua; Shen, Shengchun; Chen, Pin-Chu; Tang, Maochun; Wei, Yi; Tsai, Fang-Yuan; Chen, Chien‐Tien

doi:10.1039/c1jm12530c

Cited by 29 publications

(10 citation statements)

References 33 publications

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“…The efficacy roll‐off may be attributed to numerous factors, including concentration quenching,53, 54 exciton quenching,54, 55 imbalance carrier injection,56 and ineffective carrier confinement 57. To improve this, employing much diluted emitter,58 using multiple emission layers with step‐wise energy‐levels to extend exciton generation zone or enabling excitons to generate on both host and guest,59 improving the injection of minor carrier to balance the carriers,60 and incorporating effective electron and/or hole confinement layers21, 61 have been found to be effective. These approaches may be adopted to further improve the efficacy of the present devices.…”

Section: Resultsmentioning

confidence: 99%

Candle Light‐Style Organic Light‐Emitting Diodes

Jou

Hsieh

Tseng

et al. 2012

Adv Funct Materials

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119

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In response to the call for a physiologically-friendly light at night that shows low color temperature, a candle light-style organic light emitting diode (OLED) is developed with a color temperature as low as 1900 K, a color rendering index (CRI) as high as 93, and an effi cacy at least two times that of incandescent bulbs. In addition, the device has a 80% resemblance in luminance spectrum to that of a candle. Most importantly, the sensationally warm candle light-style emission is driven by electricity in lieu of the energywasting and greenhouse gas emitting hydrocarbon-burning candles invented 5000 years ago. This candle light-style OLED may serve as a safe measure for illumination at night. Moreover, it has a high color rendering index with a decent effi ciency.

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Section: Resultsmentioning

confidence: 99%

Candle Light‐Style Organic Light‐Emitting Diodes

Jou

Hsieh

Tseng

et al. 2012

Adv Funct Materials

Self Cite

119

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“…The reason behind this may be attributed to (i) balanced charge carrier transport in the radiative recombination zone and (ii) the paired host and guest energy levels in the emissive layer, allowing excitons to generate mostly on the guest at low voltage, but with increasing exciton generation on the host as the voltage increases, enabling possibilities of utilizing all of the recombination sites generated in an emissive layer. 68 The designed device structure favors the formation of the majority of excitons on the dopant at low bias because the barrier for the hole to enter the host is comparatively higher. The generated low-energy excitons could not trigger the high energy emission of the dopant molecules, hence poor device performance.…”

Section: Resultsmentioning

confidence: 99%

Functional Pyrene–Pyridine-Integrated Hole-Transporting Materials for Solution-Processed OLEDs with Reduced Efficiency Roll-Off

et al. 2021

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A series of new functional pyridine-appended pyrene derivatives, viz., 2,6-diphenyl-4-(pyren-1-yl)pyridine ( Py-03 ), 2,6-bis(4-methoxyphenyl)-4-(pyren-1-yl)pyridine ( Py-MeO ), 4-(pyren-1-yl)-2,6-di- p -tolylpyridine ( Py-Me ), and 2,6-bis(4-bromophenyl)-4-(pyren-1-yl)pyridine ( Py-Br ) were designed, developed, and studied as the hole-transporting materials (HTMs) for organic light-emitting diode (OLED) application. The crystal structures of two molecules revealed to have a large dihedral angle between the pyrene and pyridine units, indicating poor π-electronic communication between them due to ineffective orbital overlap across the pyrene–pyridine systems as the two p-orbitals of pivotal atoms are twisted at 66.80° and 68.75° angles to each other in Py-03 and Py-Me , respectively. The influence of variedly functionalized pyridine units on the electro-optical properties and device performance of the present integrated system for OLED application was investigated. All of the materials have suitable HOMO values (5.6 eV) for hole injection by closely matching the HOMOs of indium tin oxide (ITO) and the light-emitting layer. All of the synthesized molecules have suitable triplet energies, glass transition temperatures, and melting temperatures, which are highly desirable for good HTMs. The pyrene–pyridine-based devices demonstrated stable performance with low-efficiency roll-off. The device with Py-Br as HTM showed a maximum luminance of 17300 cd/m 2 with a maximum current efficiency of 22.4 cd/A and an EQE of 9% at 3500 cd/m 2 with 7% roll-off from 1000 to 10 000 cd/m 2 . Also, the devices with Py-Me and Py-03 showed performance roll-up while moving from 1000 to 10 000 cd/m 2 .

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“…To reach more energy-saving and hence have a long lasting device lifetime, devising OLEDs with a higher power efficiency is always demanded before reaching their theoretical efficiency limits. To achieve a higher device efficiency, three different merits must be met at the same time, which are materials with superb electroluminescent characters [6][7][8], device architectures with further improved efficiency by more effective energy-level pairings between layers, [9][10][11] and light extraction structures with higher out-coupling efficiency [12][13][14]. Unquestionably, phosphorescent materials that can harvest 100% internal quantum efficiency (IQE) would be the first priority as emissive layers, especially for obtaining intensive emission in the light-blue, green or red region with a sound lifespan.…”

Section: Introductionmentioning

confidence: 99%