Recent development of phenanthroimidazole-based fluorophores for blue organic light-emitting diodes (OLEDs): an overview

Tagare, Jairam; Vaidyanathan, Sivakumar

doi:10.1039/c8tc03689f

Cited by 235 publications

(145 citation statements)

References 230 publications

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“…To overcome this problem, the phosphorescent emitters are usually doped into suitable host materials at low concentration. Consequently, it is critical to build up high performance host materials for PhOLEDs …”

Section: Introductionmentioning

confidence: 99%

“…Consequently, it is critical to build up high performance host materials for PhOLEDs. [10,11] Desired host materials are expected to be equipped with good carrier transport properties that can balance the charge exchange and thus increase the possibility for electron and hole recombination within the emitting layer (EML). [12] In addition, efficient host molecules should also have a high triplet exited state energy (E T ) to achieve efficient energy transfer from the host to the doped emitter [13] as well as appropriate HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels to match the energy levels of the hole and electron transport layers to reduce the driving voltages of devices.…”

Section: Introductionmentioning

confidence: 99%

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Versatile Host Materials for Highly‐Efficient Green, Red Phosphorescent and White Organic Light‐Emitting Diodes

et al. 2019

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To build up efficient host materials, two novel organic small molecules ICz‐PPI and 2ICz‐PPI were designed and synthesized, in which phenanthro[9,10‐d]imidazole (PI) is proposed as a potential luminophore with high stability, while the indolo[3,2,1‐jk]carbazole (ICz) has a high triplet energy and excellent thermal stability. Both exhibited weak intramolecular charge transfer, high decomposition temperature (Td) and high quantum yield. ICz‐PPI and 2ICz‐PPI can act as the emitting layer in non‐doped organic light‐emitting diodes (OLEDs), which achieved an external quantum efficiency (EQE) of 2.47 and 1.94 % with CIE coordinates of (0.153, 0.121) and (0.161, 0.102), respectively. In addition, the high triplet energy allows them to be used as hosts for phosphorescent OLEDs (PhOLEDs). Accordingly, high performance for green (62.5 cd A−1, 70.9 lm W−1, 17.8 %) and red (25.7 cd A−1, 26.9 lm W−1, 19.4 %) had been achieved from the ICz‐PPI‐based PhOLED. Particularly, the ICz‐PPI‐based red PhOLED showed surprisingly low roll‐off and maintained an EQE of 14.9 % at 10 000 cd m−2. Furthermore, an ICz‐PPI‐based white OLED (WOLED) exhibited warm white light (CIEx,y=(0.427, 0.468)) and high efficiencies with a CEmax of 31.8cd A−1, PEmax of 37.0lm W−1 and EQEmax of 14.4 %.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Versatile Host Materials for Highly‐Efficient Green, Red Phosphorescent and White Organic Light‐Emitting Diodes

et al. 2019

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“…Literature reports other examples of PI as donor group [ 101 ] showing that PI can both donate (as in 94 ) or receive (as in 93 ) electrons, see a recent review on phenanthroimidazole‐based fluorophores. [ 102 ] Thus, 94 possesses a deeper HOMO (−5.46 eV) than 89 (−5.28 eV). The solid‐state PL spectra of 89 – 96 are centered between 433 and 457 nm, close to the values recorded for the parent compounds with a biphenyl central π‐system ( 85 – 88 ).…”

Section: Donor–π–acceptor (D–π–a) Designmentioning

confidence: 99%

Blue Single‐Layer Organic Light‐Emitting Diodes Using Fluorescent Materials: A Molecular Design View Point

Poriel

Rault‐Berthelot

2020

Adv Funct Materials

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technology is mastered, it suffers from a real complexity, a high cost, and is time-consuming. Simplifying the multilayer structure with the so-called single-layer OLEDs (SL-OLEDs), the simplest device only made of the electrodes and the EML has hence rapidly appeared as a promising and appealing solution in this technology (Scheme 2, left).However, removing the functional organic layers of an OLED stack often leads to a dramatic decrease of the performance and reaching high efficiency blue SL-OLEDs has required intense researches and especially in term of materials design. Indeed, if one removes all the organic layers surrounding the EML, the efficient injection, transport, and recombination of charges within the device, should be insured by the EML itself and therefore the fluorophore. However, this appears to be a real obstacle to cross for blue emitting materials. Indeed, blue fluorophores usually possess a high HOMO and a low LUMO energy rendering the injection of charges in such materials very difficult. This has been one of the main issue to address in this field. Common properties required for high-performance blue emitting materials can be summarized as follows: 1) blue light emission between 380 and 500 nm with maximum wavelength around 450 nm; 2) a narrow full width at half maximum less than 60 nm; which produces low Commission Internationale de l'Eclairage (CIE) y-coordinate of less than 0.10 for TVs and cell phones; 3) thermal and morphological stability for stable device operation and a long device lifetime; 4) balance charge transport between electrons and holes flow and 5) adequate HOMO/LUMO energy levels for charge recombination and injection.Gathering all these properties in a single molecule is far from being an easy task and requires very precise designs. Indeed, as soon as one tries to adjust the HOMO/ LUMO energy levels of an organic semiconductor (OSC) with the Fermi levels of OLED electrodes, its gap is contracted and the emission wavelength is bathochromically shifted. This design strategy can hence lead to a material in which the charges can be more easily injected (the gap is contracted) but with an emission wavelength no more in the blue region. Trying to find the best compromise between adequate HOMO/LUMO energy and a blue emission has been the main challenge to address in the molecular design of efficient fluorophores for blue SL-OLEDs. This particularity has strongly restrained the development of such materials. However, for the last 30 years, research groups have developed many different molecular design strategies, which have led in some cases to high performance blue SL-OLEDs. Reaching high performance SL-OLEDs by molecular engineering of the fluorophore and Cyril Poriel is

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“…Although many different approaches to the development of functional materials and devices are designed for improving the performance of blue OLED devices, until now, the efficiency and stability of blue OLEDs still have few concerns . Due to their poor photophysical properties, efficient deep‐blue materials are developed gradually until the emergence of thermally activated delayed fluorescence materials . A wide variety of blue luminescent organic materials with excellent photophysical properties has been developed by using reasonable molecular design concepts and general synthetic routes .…”

Section: Introductionmentioning

confidence: 99%

Microcavity‐Enhanced Blue Organic Light‐Emitting Diode for High‐Quality Monochromatic Light Source with Nonquarterwave Structural Design

Lin

Liu

2020

Advanced Optical Materials

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Despite their rapid development, organic light‐emitting diodes (OLEDs) are limited to display and lighting applications, and exploiting the application and development of OLEDs has become one of the critical issues. In this study, a new type of distributed Bragg reflector (DBR) with low absorption spacer as a bottom mirror is developed through nonquarterwave structural design. Different factors affecting the electroluminescence (EL) properties of microcavity OLEDs (MOLEDs) are investigated by using the optical microcavities with different structures to regulate the EL properties of 4,4′‐bis[(N‐carbazole)styryl] biphenyl (BSB‐Cz). The optimized MOLEDs with quarterwave DBRs exhibited a maximum external quantum efficiency of 8.86 ± 0.06%, demonstrating an enhancement of 79% compared to a reference device. Under the premise of almost not changing the electrical injection of the functional layer materials in the cavity, the spectral full‐width at half maximum of MOLEDs with a nonquarterwave structural design is as narrow as 2 ± 0.05 nm. These improvements are not only suitable for small organic molecules or polymeric materials, but also for novel nanoluminescent materials, such as quantum dots, perovskites, etc. Overall, the current study suggests the general applicability of this novel concept to obtain high‐quality monochromatic light, irrespective of the type of materials used.

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Recent development of phenanthroimidazole-based fluorophores for blue organic light-emitting diodes (OLEDs): an overview

Abstract: Full color displays (white OLEDs) require all the primary colors: blue, green, and red. In recent decades, numerous phenanthroimidazole-based emitting materials have been developed for efficient blue OLEDs.

Cited by 235 publications

References 230 publications

Versatile Host Materials for Highly‐Efficient Green, Red Phosphorescent and White Organic Light‐Emitting Diodes

Versatile Host Materials for Highly‐Efficient Green, Red Phosphorescent and White Organic Light‐Emitting Diodes

Blue Single‐Layer Organic Light‐Emitting Diodes Using Fluorescent Materials: A Molecular Design View Point

Microcavity‐Enhanced Blue Organic Light‐Emitting Diode for High‐Quality Monochromatic Light Source with Nonquarterwave Structural Design

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