42 results on '"F. Galeotti"'
Search Results
2. Investigation into aggregation types in a benzodithiophene–isoindigo copolymer.
- Author
-
Asmare, Eninges, Hone, Fekadu Gashaw, Mammo, Wendimagegn, Krüger, Tjaart P. J., and Tegegne, Newayemedhin A.
- Subjects
TIME-dependent density functional theory ,CHARGE-transfer transitions ,ELECTRONIC equipment ,LIGHT emitting diodes ,CONJUGATED polymers ,SOLAR cells ,POLYMERS - Abstract
The type of aggregation in conjugated polymers determines their use in electronic devices. H-type aggregates are most suitable for solar cell applications, while J-type aggregates are recommended for light-emitting diodes. In this work, we used three methods to determine the type of aggregates in a benzodithiophene–isoindigo-based (PBDTI-DT) copolymer, namely, Huang–Rhys factor evolution with temperature, Franck–Condon analysis, and relative quantum yield (QY) calculation. All three methods indicate that both aggregation types are present, and the QY calculation clearly indicates that H-aggregates are more dominant. Time-dependent density functional theory was used to identify the two absorption bands of PBDTI-DT as local π − π* and intramolecular charge-transfer transitions. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
Catalog
3. Synthetic Strategy for the Development of Conjugated Polyelectrolytes as Cathode Interfacial Layers: Toward Sustainable Organic Devices.
- Author
-
Pasini, Mariacecilia, Galeotti, Francesco, Mróz, Wojciech, Squeo, Benedetta Maria, Luzzati, Silvia, Botta, Chiara, Scavia, Guido, and Giovanella, Umberto
- Subjects
OPTOELECTRONIC devices ,LIGHT emitting diodes ,CATHODES ,ELECTRONIC equipment ,SOLAR cells ,PHOSPHONATES - Abstract
The use of conjugated polyelectrolytes (CPEs) as interfacial layers (ILs) to increase the efficiency of organic light‐emitting diodes (OLEDs), organic solar cells (OSCs), and organic transistors is a well‐established strategy. Here, the rational process is reported that led to develop the bifunctional poly[(2,7‐(9,9'‐bis(6'‐diethoxylphosphorylhexyl)‐fluorene)‐alt‐(2,7‐(9,9′‐bis(6″‐trimethylammonium bromide)hexyl)‐fluorene)] (PF‐NBr‐EP). PF‐NBr‐EP is successfully incorporated as a cathode IL (CIL) in diverse electronic and optoelectronic devices. The properties of two fluorene‐based CPEs containing, respectively, phosphonate (EP) and ammonium (NBr) moieties used as building blocks for the synthesis of the PF‐NBr‐EP copolymer and their mixtures are investigated to evaluate the combined effect of the two moieties and therefore to gain insight into the behavior of PF‐NBr‐EP chemical structure in the devices. Additionally, the performance of OLEDs and OSCs is analyzed based on established active layers, incorporating all these neat and mixed CILs. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
4. Cascade Chirality Transfer Through Diastereomeric Interaction Enables Efficient Circularly Polarized Electroluminescence.
- Author
-
Chen, Zhanxiang, Huang, Manli, Zhong, Cheng, Cao, Xiaosong, Xie, Guohua, Gong, Shaolong, and Yang, Chuluo
- Subjects
ELECTROLUMINESCENCE ,FLUORESCENCE resonance energy transfer ,CHIRALITY ,ORGANIC light emitting diodes ,LIGHT emitting diodes ,DISRUPTIVE innovations ,QUANTUM efficiency - Abstract
Organic light‐emitting diodes (OLEDs) with circularly polarized emission can bring a breakthrough innovation in display technologies. However, it remains challenging due to the difficulty in obtaining high efficiency and large dissymmetry factor simultaneously. Herein, it is demonstrated that robust circularly polarized (CP) electroluminescence can be induced by cascade chirality transfer within the emitting layer. Through spectroscopic data and theoretical analysis, the initiation of this chirality transfer process is assigned to diastereomeric interaction. Utilizing this interaction and excellent Förster resonance energy transfer ability to the well‐known racemic emitter, CP‐OLEDs with an electroluminescence dissymmetry factor (|gEL|) up to 3.2 × 10−3 and high external quantum efficiency (EQE) of 32% are successfully fabricated. These devices also show ultra‐low efficiency roll‐off at high brightness, with EQE ≥ 20% at 128 000 cd m−2. This study paves the way for the future development of CP‐OLEDs through synergistic materials and device engineering. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
5. Efficient Circularly Polarized Electroluminescence from Achiral Luminescent Materials**.
- Author
-
Xu, Letian, Liu, Hao, Peng, Xiaoluo, Shen, Pingchuan, Tang, Ben Zhong, and Zhao, Zujin
- Subjects
DELAYED fluorescence ,ELECTROLUMINESCENCE ,LIGHT emitting diodes ,PHOSPHORESCENCE ,QUANTUM efficiency - Abstract
Circularly polarized electroluminescence (CP‐EL) is generally produced in organic light‐emitting diodes (OLEDs) based on special CP luminescent (CPL) materials, while common achiral luminescent materials are rarely considered to be capable of direct producing CP‐EL. Herein, near ultraviolet CPL materials with high photoluminescence quantum yields and good CPL dissymmetry factors are developed, which can induce blue to red CPL for various achiral luminescent materials. Strong near ultraviolet CP‐EL with the best external quantum efficiencies (ηexts) of 9.0 % and small efficiency roll‐offs are achieved by using them as emitters for CP‐OLEDs. By adopting them as hosts or sensitizers, commercially available yellow‐orange achiral phosphorescence, thermally activated delayed fluorescence (TADF) and multi‐resonance (MR) TADF materials can generate intense CP‐EL, with high dissymmetry factors and outstanding ηexts (30.8 %), demonstrating a simple and universal avenue towards efficient CP‐EL. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
6. Exploring the Electroluminescent Applications of Imidazole Derivatives.
- Author
-
Lin, Yan‐Ding, Tsai, Wei‐Wen, and Lu, Chin‐Wei
- Subjects
IMIDAZOLES ,DELAYED fluorescence ,LIGHT emitting diodes ,ELECTRIC batteries ,MOLECULAR structure ,FLEXIBLE structures - Abstract
Recently, the fields of organic light‐emitting diodes (OLEDs) and light‐emitting electrochemical cells (LECs) have improved tremendously with regard to tunable emission, efficiency, brightness, and thermal stability. Imidazole derivatives are excellent deep blue‐green light‐emitting layers in the OLED or LEC devices. This Review summarizes the major breakthroughs of various electroluminescence (EL) layers with imidazole‐containing organic or organometallic derivatives, the molecular design principles, and their light‐emitting performances as effective EL materials. The highly tunable chemical structures and flexible molecular design strategies of imidazole‐based compounds are advantages that provide great opportunities for researchers. They can provide a good basis for the design and development of new EL materials with narrower emission and higher efficiency. Moreover, imidazole compounds have demonstrated breakthrough performances in thermally activated delayed fluorescence (TADF) properties where triplet excitons are utilized to inhibit anti‐intersystem quenching, showing great promise in breaking the theoretical external quantum efficiencies (EQE) limits in traditional fluorescent devices. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
7. Highly Emissive Chiral Mn(II) Bromide Hybrids for UV‐Pumped Circularly Polarized LEDs and Scintillator Image Applications.
- Author
-
Davydova, Maria P., Meng, Lingqiang, Rakhmanova, Mariana I., Bagryanskaya, Irina Yu., Sulyaeva, Veronica S., Meng, Hong, and Artem'ev, Alexander V.
- Subjects
X-ray imaging ,LIGHT emitting diodes ,IONIC structure ,METAL halides ,X-ray detection ,SCINTILLATORS - Abstract
Organic–inorganic hybrid metal halides are a promising platform for the design of materials for circularly polarized luminescence (CPL) and X‐ray detection applications. Meanwhile, despite the recent progress in this hot field, hybrid metal halides, simultaneously endowed with efficient CPL and high photoluminescence quantum yield (PLQY), are still limited to a few examples. Herein, the efficient, stable, and low‐cost CPL‐active Mn(II) hybrids are developed via blending of luminogenic [MnBr4]2− anions with N/OH‐bond free R/S‐[MBA‐Me3]+ cations in a single ionic structure. The synthesized R/S‐[MBA‐Me3]MnBr4 hybrids display brightly green Mn2+‐centered circularly polarized phosphorescence with near‐unity PLQY and a high glum factor of 0.0045. Single crystals of R/S‐[MBA‐Me3]MnBr4 are used to fabricate UV‐pumped circularly polarized light‐emitting diodes (LEDs) displaying a high optical selectivity upon exposure to right‐handed and left‐handed circular polarization conditions. Moreover, the titled compounds are found to emit strong X‐ray radioluminescence with excellent linear response to X‐ray dose rate that is used for X‐ray imaging demonstration. These findings reveal a great potential of R/S‐[MBA‐Me3]MnBr4 as low‐cost materials for CPL‐LEDs, scintillators, and X‐ray imaging applications. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
8. Organic Light‐Emitting Diodes Based on Silandiol‐Bay‐Bridged Perylene Bisimides.
- Author
-
Brust, Felix, Nagler, Oliver, Shoyama, Kazutaka, Stolte, Matthias, and Würthner, Frank
- Subjects
LIGHT emitting diodes ,PERYLENE ,BISIMIDES ,ORGANIC light emitting diodes ,OPTOELECTRONIC devices ,QUANTUM efficiency ,FLUOROPHORES - Abstract
Perylene bisimides (PBIs) are among the best fluorophores but have to be enwrapped for optoelectronic applications by large and heavy substituents to prevent their ππ‐stacking, which is known to accelerate non‐radiative decay processes in the solid state. Here, light‐weight di‐tert‐butylsilyl groups are introduced to bridge 1,12‐dihydroxy and 1,6,7,12‐tetrahydroxy PBIs to afford sublimable dyes for vacuum‐processed optoelectronic devices. For both new compounds, this substitution provides a twisted and shielded perylene π‐core whose, via OSiObridges, rigid structure affords well‐resolved absorption and emission spectra with strong fluorescence in solution, as well as in the solid state. The usefulness of these dyes for vacuum‐processed optoelectronic devices is demonstrated in organic light‐emitting diodes (OLEDs) that show monomer‐like emission spectra and high maximum external quantum efficiency (EQEmax) values of up to 3.1% for the doubly silicon‐bridged PBI. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
9. Atomically flat semiconductor nanoplatelets for light-emitting applications.
- Author
-
Bai, Bing, Zhang, Chengxi, Dou, Yongjiang, Kong, Lingmei, Wang, Lin, Wang, Sheng, Li, Jun, Zhou, Yi, Liu, Long, Liu, Baiquan, Zhang, Xiaoyu, Hadar, Ido, Bekenstein, Yehonadav, Wang, Aixiang, Yin, Zongyou, Turyanska, Lyudmila, Feldmann, Jochen, Yang, Xuyong, and Jia, Guohua more...
- Subjects
QUANTUM wells ,LIQUID crystal displays ,NANOPARTICLES ,LIGHT emitting diodes ,ELECTRONIC spectra ,SEMICONDUCTORS ,OPTICAL properties ,HEAVY elements - Abstract
The last decade has witnessed extensive breakthroughs and significant progress in atomically flat two-dimensional (2D) semiconductor nanoplatelets (NPLs) in terms of synthesis, growth mechanisms, optical and electronic properties and practical applications. Such NPLs have electronic structures similar to those of quantum wells in which excitons are predominantly confined along the vertical direction, while electrons are free to move in the lateral directions, resulting in unique optical properties, such as extremely narrow emission line width, short photoluminescence (PL) lifetime, high gain coefficient, and giant oscillator strength transition (GOST). These unique optical properties make NPLs favorable for high color purity light-emitting applications, in particular in light-emitting diodes (LEDs), backlights for liquid crystal displays (LCDs) and lasers. This review article first introduces the intrinsic characteristics of 2D semiconductor NPLs with atomic flatness. Subsequently, the approaches and mechanisms for the controlled synthesis of atomically flat NPLs are summarized followed by an insight on recent progress in the mediation of core/shell, core/crown and core/crown@shell structures by selective epitaxial growth of passivation layers on different planes of NPLs. Moreover, an overview of the unique optical properties and the associated light-emitting applications is elaborated. Despite great progress in this research field, there are some issues relating to heavy metal elements such as Cd
2+ in NPLs, and the ambiguous gain mechanisms of NPLs and others are the main obstacles that prevent NPLs from widespread applications. Therefore, a perspective is included at the end of this review article, in which the current challenges in this stimulating research field are discussed and possible solutions to tackle these challenges are proposed. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
10. Helical Stacking Assembly of Orderly Silicon Nanowire Multilayers for Ultrastrong Dissymmetrical Amplification of Circularly Polarized Light.
- Author
-
Dong, Tai‐Ge, Wu, Zheng‐Guang, Li, Fang‐Ling, Wang, Jun‐Zhuan, Zheng, You‐Xuan, and Yu, Lin‐Wei
- Subjects
SILICON nanowires ,QUANTUM computing ,LIGHT emitting diodes ,MULTILAYERS ,SPATIAL arrangement ,ELECTROLUMINESCENCE ,CHOLESTERIC liquid crystals - Abstract
Circularly polarized organic light‐emitting diodes (CP‐OLEDs) are ideal candidates to explore novel applications such as 3D displays, optical storage, and quantum computing. However, the low dissymmetry (g) factor of most chiral organic materials remains as a major challenge for practical applications. In this work, a helical stacking assembly of orderly silicon nanowires (hs‐SiNWs) into a flexible multilayer 3D superstructure is demonstrated to accomplish a strong chiroptical activity. These orderly SiNWs are batch‐fabricated via a low temperature in‐plane solid–liquid–solid growth mechanism, with precisely‐controlled spatial arrangement and mean diameter and length of Dnw = 126 ± 24 nm and Lnw > 100 µm, respectively. To construct such helically‐stacked superstructure, the SiNW arrays are transferred and stacked upon transparent glass or flexible polymer substrates, with incremental rotational angle for each layer, which can strongly augment the circularly polarized electroluminescence (CPEL) from conventional CP‐OLEDs. Strikingly, the dissymmetry factor increases with more stacking layer up to g = ±0.17, which is more than 40 times of magnitude higher than that of the original CPEL, among the highest ones reported for CP‐OLEDs. These results indicate a promising helical‐stacking avenue to boost the chiroptical performance of various CP‐OLEDs for scalable and flexible chiroptical applications. [ABSTRACT FROM AUTHOR] more...
- Published
- 2022
- Full Text
- View/download PDF
11. Improved Efficiency of Light‐Emitting Diodes by Plasmonic Nanopatterning of the Charge‐Transfer Layer.
- Author
-
Lin, Lyuye, Krahne, Roman, and Proietti Zaccaria, Remo
- Subjects
NANOPATTERNING ,PLASMONICS ,QUANTUM efficiency ,OPTICAL properties ,REFRACTIVE index ,CHARGE transfer ,LIGHT emitting diodes - Abstract
Light‐emitting diodes (LEDs) are presently not exploited at their full potential due to a multiple range of detrimental effects, such as generation of local modes, either surface plasmon‐like or optical modes, ohmic losses, or total internal reflection caused by refractive index mismatch. Herein, the authors focus on LEDs with layered architectures by investigating the effects of interface nanopatterning occurring in the electron‐transport layer on their overall performance. In particular, the integration of photonic nanostructures is investigated, while leaving the optical properties of the emitting material unchanged. The numerical results show that specifically designed nanopatterning can strongly contribute to the enhancement of the Purcell factor, outcoupling efficiency and thereby increase the external quantum efficiency by a factor of 2 with respect to the unpatterned structures. This demonstrates that, as in other light‐emission technologies, morphological patterning is a valid strategy to improve the performance of LEDs. [ABSTRACT FROM AUTHOR] more...
- Published
- 2022
- Full Text
- View/download PDF
12. High Quantum Yield Blue InP/ZnS/ZnS Quantum Dots Based on Bromine Passivation for Efficient Blue Light‐Emitting Diodes.
- Author
-
Zhang, Wenda, Tan, Yangzhi, Duan, Xijian, Zhao, Fangqing, Liu, Haochen, Chen, Wei, Liu, Pai, Liu, Xiaogang, Wang, Kai, Zhang, Zhikuan, and Sun, Xiao Wei
- Subjects
LIGHT emitting diodes ,PASSIVATION ,QUANTUM dots ,BROMINE ,QUANTUM efficiency ,ZINC sulfide ,BINDING energy - Abstract
Red and green InP quantum dots (QDs) already have been demonstrated with excellent luminescence performance closing the gap with CdSe‐based QDs. However, the performance of blue InP QDs still lags behind that of red and green QDs. For blue InP QDs synthesized by aminophosphine and zinc iodide, the inherent I– possesses weak passivation ability. By introducing Br– with a smaller ion radius and larger binding energy, the quantum yield of blue InP QDs is increased from 54% to 93%, which is the highest value reported so far. Meanwhile, the long‐chain 1‐dodecanethiol is replaced by the short‐chain 1‐octanethiol through ligand exchange to increase the carrier injection efficiency. The blue quantum dot light‐emitting diodes (QLEDs) made of these QDs showed an external quantum efficiency of 2.6%, which is notably the highest blue InP QLED reported so far. [ABSTRACT FROM AUTHOR] more...
- Published
- 2022
- Full Text
- View/download PDF
13. Highly Efficient Sensitized Chiral Hybridized Local and Charge‐Transfer Emitter Circularly Polarized Electroluminescence.
- Author
-
Kong, Fan‐Cheng, Yang, Sheng‐Yi, Liao, Xiang‐Ji, Feng, Zi‐Qi, Shen, Wan‐Shan, Jiang, Zuo‐Quan, Zhou, Dong‐Ying, Zheng, You‐Xuan, and Liao, Liang‐Sheng
- Subjects
DELAYED fluorescence ,ELECTROLUMINESCENCE ,LIGHT emitting diodes ,QUANTUM efficiency ,CHARGE transfer - Abstract
This work describes the first hot exciton fluorescent material based on benzo[c][1,2,5]thiadiazole and chiral binaphthol enabling circularly polarized luminescence (CPL) through a chiral perturbation strategy. The new molecular architecture displays CPL, hybridized local and charge transfer (HLCT) properties concurrently. Utilizing it as the emitter, circularly polarized organic light‐emitting diodes (CP‐OLEDs) achieve an external quantum efficiency (EQE) of 7.2% with a good exciton utilization (36%) and a moderate circularly polarized electroluminescence (CPEL) dissymmetry factor (gEL, 2.1 × 10−3). In addition, the CP‐HLCT molecule is sensitized by a thermally activated delayed fluorescence material, significantly ameliorating the efficiency of HLCT fluorescent CP‐OLEDs. Excellent performances of twofold maximum EQE (EQEmax) of 15.3% and 82% exciton utilization are obtained in the sensitized device, regarding an extremely low‐efficiency roll‐off of 2.6% at 1000 cd m−2 as well as CPEL with a gEL value of 2.0 × 10−3. [ABSTRACT FROM AUTHOR] more...
- Published
- 2022
- Full Text
- View/download PDF
14. Disordered Nano‐Hemisphere Molybdenum Trioxide for Enhanced Light Out‐Coupling in Organic Light‐Emitting Diodes.
- Author
-
Ren, ZhanPeng, Cheng, Jiang, Liao, XiaoQing, Song, Zhihao, Xu, Da, Li, Lu, and Yu, Junsheng
- Subjects
LIGHT emitting diodes ,SEMICONDUCTOR technology ,QUANTUM efficiency ,MOLYBDENUM ,TRIOXIDES ,ORGANIC light emitting diodes - Abstract
A 2D‐array scattering layer composed of disordered, wavelength‐sized molybdenum trioxide (MoO3) nano‐hemispheres that are introduced into existing organic light‐emitting diodes (OLEDs) can maximize light out‐coupling. This MoO3 nano‐hemisphere scattering layer (M‐NSL) obtained by in situ annealing‐spraying is investigated in depth based on considerations of larger refractive index, higher transparency, and internal light scattering. With the simulation of finite‐difference time‐domain, M‐NSL can effectively reduce the optical loss among the structural layers caused by the mismatch of refractive indexes is observed and induce strong diffuse transmission, which reduces the total internal reflection in the substrate, thus improving light out‐coupling. The power efficiency and external quantum efficiency of the device with M‐NSL demonstrated performance metrics of 139.5 lm W−1 power efficiency and 47.5% external quantum efficiency at 1000 cd m−2, which increased by 82.4% and 64.5%, respectively, compared with the control device without M‐NSL. Potentially, the scheme will be easy to implement and incorporate into existing semiconductor device technologies, and it can be used separately or in conjunction with other methods to mitigate the critical angle loss in OLEDs. [ABSTRACT FROM AUTHOR] more...
- Published
- 2022
- Full Text
- View/download PDF
15. TADF‐Sensitized Fluorescent Enantiomers: A New Strategy for High‐Efficiency Circularly Polarized Electroluminescence**.
- Author
-
Li, Meng and Chen, Chuan‐Feng
- Subjects
DELAYED fluorescence ,LIGHT emitting diodes ,ELECTROLUMINESCENCE - Abstract
A promising strategy of thermally activated delayed fluorescence (TADF) sensitized circularly polarized luminescence (CPL) has been proposed for improving the electroluminescence efficiencies of circularly polarized fluorescent emitters. Compared with chiral TADF emitters which suffer from the dilemma of small ΔEST accompanied by small kr, the TADF‐sensitized CPL (TSCP) strategy using TADF molecules as sensitizers and CP‐FL molecules as emitters might be the most promising method to construct high‐performance circularly polarized organic light‐emitting diodes (CP‐OLEDs). Consequently, by taking advantage of the theoretically 100 % exciton utilization of TADF sensitizers, especially, by designing CP‐FL emitters with high PLQY, narrow FWHM and large glum values, TSCP‐type CP‐OLEDs with excellent overall performances can be realized. [ABSTRACT FROM AUTHOR] more...
- Published
- 2022
- Full Text
- View/download PDF
16. Efficient Perovskite Nanocrystal‐Based Optoelectronic Devices.
- Author
-
Han, Myeonggeun and Noh, Yong-Young
- Subjects
PEROVSKITE ,LIGHT emitting diodes ,BINDING energy ,OPTOELECTRONIC devices ,EXCITON theory ,OPTOELECTRONICS ,NANOCRYSTALS - Abstract
Halide perovskites are expected to be widely used in light‐emitting diodes (LEDs) due to their excellent optoelectronic properties, such as high luminous efficiency, controllability of luminescence wavelength, and wide color gamut. However, because the exciton binding energy of 3D halide perovskite films is relatively low (≈150 meV), various techniques have been applied to increase the exciton binding energy and thereby improve the performance of devices. Among them, 0D halide perovskite nanocrystals (NCs) are widely used because the low‐dimensional perovskite effectively confines the excitons in NCs. In particular, perovskite NCs facilitate color tuning with quantum confinement by controlling the size. Herein, it is aimed to provide an overview of various approaches for synthesizing perovskite NCs and post‐treatment methods to achieve high‐efficiency LEDs. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
17. Blue Axially Chiral Biphenyl Based Thermally Activated Delayed Fluorescence Materials for Efficient Circularly Polarized OLEDs.
- Author
-
Tu, Zhen‐Long, Lu, Jun‐Jian, Luo, Xu‐Feng, Hu, Jia‐Jun, Li, Si, Wang, Yi, Zheng, You‐Xuan, Zuo, Jing‐Lin, and Pan, Yi
- Subjects
DELAYED fluorescence ,CARBAZOLE ,LIGHT emitting diodes ,SPIN-orbit interactions ,DIPHENYL ,ORGANIC light emitting diodes ,MOLECULAR structure - Abstract
This work presents two axial chiral biphenyl based blue thermally activated delayed fluorescence materials (M‐BPCZ4 and P‐BPCZ4) with four carbazole (CZ) donors and two cyano (CN) acceptors. The rigid CZ‐CN based molecular structures with multiple chromophores result in small gaps among charge transfer states (CTs), and the spin−orbit coupling between CT and locally excited states pushes the reverse intersystem crossing (RISC) process. Besides, this chiral luminescence center strategy with the close distance between chiral units and chiral luminescence region contributes to satisfying circularly polarized luminescence properties with dissymmetry factor |gPL| of 5.0 × 10−3 for (R/S)‐M‐BPCZ4 and 4.7 × 10−3 for (R/S)‐P‐BPCZ4 enantiomers, respectively. Furthermore, the positions of other two CZ units have great effects on the racemization temperatures and circularly polarized electroluminescence properties of the enantiomers. The chiral dyes doped circularly polarized organic light‐emitting diodes compatibly display good performances with external quantum efficiency of 18.3% with slight efficiency roll‐off and high electroluminescence |gEL| of 5.5 × 10−3. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
18. Chiral Thermally Activated Delayed Fluorescence Materials Based on R/S‐N2,N2′‐Diphenyl‐[1,1′‐binaphthalene]‐2,2′‐diamine Donor with Narrow Emission Spectra for Highly Efficient Circularly Polarized Electroluminescence
- Author
-
Yan, Zhi‐Ping, Liu, Ting‐Ting, Wu, Ruixia, Liang, Xiao, Li, Zhi‐Qiang, Zhou, Liang, Zheng, You‐Xuan, and Zuo, Jing‐Lin
- Subjects
DELAYED fluorescence ,ELECTROLUMINESCENCE ,MOLECULAR spectra ,QUANTUM efficiency ,LIGHT emitting diodes ,PHOTOLUMINESCENCE - Abstract
In this study, two pairs of chiral thermally activated delayed fluorescence (TADF) materials enabling circularly polarized luminescence (CPL) named R/S‐p‐BAMCN (rod‐shape) and R/S‐o‐BAMCN (helix‐shape) are prepared based on a new pair of chiral donor (D*), R/S‐N2,N2′‐diphenyl‐[1,1′‐binaphthalene]‐2,2′‐diamine (R/S‐BAM), and two cyano (CN) acceptors. Due to the rigid molecular structure and special intramolecular arrangement, the chiral TADF materials show high photoluminescence quantum efficiency (up to 0.86) with narrow full‐width at half‐maximum (38 nm in cyclohexane, 51 nm in toluene) and photoluminescence dissymmetry factor (|gPL|) up to 5.3 × 10−3. Particularly, the circularly polarized OLEDs (CP‐OLEDs) with rod‐shaped R/S‐p‐BAMCN as the emitter show high device performances with the maximum external quantum efficiency nearing 28%. Meanwhile, the semi‐transparent CP‐OLEDs based on helix‐shaped R/S‐o‐BAMCN exhibit obvious circularly polarized electroluminescence (CPEL) properties with the electroluminescence |gEL| factors around 4.6 × 10−3. The strategy of rigid D*‐A‐D* structure with special arrangement of chiral donor provides a direct way to obtain efficient CP‐TADF materials with narrow emission spectra and promising CPL properties for better CPEL performance. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
19. Slot‐Die Coating of All Organic/Polymer Layers for Large‐Area Flexible OLEDs: Improved Device Performance with Interlayer Modification.
- Author
-
C, Amruth, Dubey, Deepak K., Pahlevani, Majid, and Welch, Gregory C.
- Subjects
ORGANIC light emitting diodes ,ORGANIC coatings ,LIGHT emitting diodes ,PHENYL ethers ,SURFACE coatings - Abstract
Organic light‐emitting diodes (OLEDs) fabricated on flexible transparent substrates have found application in displays, lighting, and signage. Optimization of the fabrication procedures is critical for commercialization to maximize performance and reduce costs. Utilization of the slot‐die coating technique, a solution‐processing roll‐to‐roll method, has emerged as a viable method to manufacture flexible OLED devices. Here, the fabrication of flexible OLEDs via the slot‐die coating technique under ambient condition is reported. The OLEDs have a simple architecture of polyethylene terephthalate (PET)/indium–tin oxide (ITO)/hole injection layer (HIL)/emissive layer (EML)/electron injection layer (EIL)/Ag, where poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is used as the HIL, Super Yellow (SY, poly(1,4‐phenylenevinylene) copolymer) is used as the EML, and poly((9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)) (PFN) is used as the EIL. The optimization of the PFN layer using slot‐die coating technique is focused by varying solvent, solvent additives, substrate temperature, and coating speeds. The OLEDs that have PFN layers processed with the known solvent additives, 1,8‐diiodooctane (DIO) or diphenyl ether (DPE), show a performance increase compared to OLEDs based on PFN layers processed with no solvent additives. Finally, large‐area multicolor OLEDs are constructed with organic/polymer layers being slot‐die coated in sequence, of which all display homogeneous luminance under bending/folding conditions, highlighting the potential of this simple device structure and processing method. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
20. Semitransparent Circularly Polarized Phosphorescent Organic Light‐Emitting Diodes with External Quantum Efficiency over 30% and Dissymmetry Factor Close to 10−2.
- Author
-
Lu, Guangzhao, Wu, Zheng‐Guang, Wu, Ruixia, Cao, Xiaosong, Zhou, Liang, Zheng, You‐Xuan, and Yang, Chuluo
- Subjects
PHOSPHORESCENCE ,LIGHT emitting diodes ,QUANTUM efficiency ,ORGANIC light emitting diodes ,ELECTROLUMINESCENCE ,IRIDIUM ,MAGNITUDE (Mathematics) - Abstract
To concurrently realize large electroluminescence dissymmetry factor and high device efficiency remains a formidable challenge in the development of circularly polarized organic light‐emitting diode (CP‐OLED). In this work, by introducing a famous chiral resource of R‐camphor, two green chiral iridium(III) isomers of Λ/Δ‐Ir‐(R‐camphor) containing dual stereogenic centers at iridium and ancillary ligand, are efficiently synthesized. Benefiting from their high phosphorescence quantum yields (≈93%) and obvious circularly polarized photoluminescence property with dissymmetry factors (|gPL|) in the 10−3 order of magnitude, the circularly polarized phosphorescent organic light‐emitting diodes using these chiral emitters show excellent performances with the maximum external quantum efficiency (EQEmax) of 30.6%, low efficiency roll‐off, and intense circularly polarized electroluminescence signal with dissymmetry factor (gEL) in the 10−4 order of magnitude. By the novel device engineering with semitransparent cathode, the resulting gEL values are significantly boosted by one order of magnitude, up to 7.70 × 10−3, which is the highest among the CP‐OLEDs with chiral iridium complexes. Noteworthy, the semitransparent devices deliver a record‐high EQEmax of 18.8% among the semitransparent OLEDs. The combination of novel chiral Ir(III) complexes and the semitransparent devices sheds light on the development of high performance CP‐OLEDs with simultaneously high efficiency and large dissymmetry factor. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
21. Hybrid MoS2/PEDOT:PSS transporting layers for interface engineering of nanoplatelet-based light-emitting diodes.
- Author
-
Sorrentino, Roberto, Worsely, Robyn, Lagonegro, Paola, Martella, Christian, Alieva, Adriana, Scavia, Guido, Galeotti, Francesco, Pasini, Mariacecilia, Dubertret, Benoit, Brovelli, Sergio, Molle, Alessandro, Casiraghi, Cinzia, and Giovanella, Umberto more...
- Subjects
LIGHT emitting diodes ,MOLYBDENUM disulfide ,CONDUCTING polymers ,MANUFACTURING processes ,CONJUGATED polymers ,NANOSTRUCTURED materials - Abstract
Colloidal semiconductor nanoplatelets (NPLs) are a subgroup of quantum confined materials that have recently emerged as promising active materials for solution processed light-emitting diodes (LEDs) thanks to their peculiar structural and electronic properties as well as their reduced dimensionality. Nowadays, the conventional structure for NPL-based LEDs makes use of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a hole transporting layer (HTL). This is a well-known conjugated conductive polymer because it leads to high LED efficiency, though it has limited stability in air due to its intrinsic acidity and hygroscopicity. Here, we develop a nanocomposite aqueous ink, obtained by blending commercial PEDOT:PSS with water-based, stable and highly concentrated molybdenum disulfide (MoS
2 ) nanosheets, obtained via liquid phase exfoliation (LPE), which is suitable as a HTL for solution processed NPL-based LEDs. We demonstrate that the MoS2 additive effectively works as a performance booster in unpackaged devices, thereby prolonging the lifetime up to 1000 hours under ambient conditions. Moreover, the addition of MoS2 induces a modification of the anode interface properties, including a change in the work function and a significant enhancement of the permittivity of the HTL. [ABSTRACT FROM AUTHOR] more...- Published
- 2021
- Full Text
- View/download PDF
22. High‐Performance Ultrapure Green CdSe/CdS Core/Crown Nanoplatelet Light‐Emitting Diodes by Suppressing Nonradiative Energy Transfer.
- Author
-
Wen, Zuoliang, Liu, Pai, Ma, Jingrui, Jia, Siqi, Xiao, Xiangtian, Ding, Shihao, Tang, Haodong, Yang, Hongcheng, Zhang, Chaojian, Qu, Xiangwei, Xu, Bing, Wang, Kai, Teo, Kie Leong, and Sun, Xiao Wei
- Subjects
LIGHT emitting diodes ,ENERGY transfer ,FIELD emission ,QUANTUM efficiency ,NANOPARTICLES ,NANOCRYSTALS ,LOW voltage systems - Abstract
Colloidal nanoplatelets (NPLs) are an emerging semiconductor nanocrystal in the display community due to their ultranarrow emission linewidth. Herein, an ultrapure green emitting nanocrystal light‐emitting diode (LED) based on four‐monolayer CdSe/CdS core/crown NPLs is developed. By applying the nonstacked nanoplates, the nonradiative energy transfer in the NPLs film is successfully suppressed. The nonstacked NPL‐LEDs with pure green emission of 521.5 nm exhibit a low turn‐on voltage of 2.1 V, a maximum luminance of 22 400 cd m−2, a peak external quantum efficiency (EQE) of 2.16%, which is a sixfold enhancement comparing to the stacked NPL‐LED (EQE = 0.34%). This work demonstrates the potential of core/crown NPLs for ultrawide color gamut displays. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
23. Designs and Applications of Circularly Polarized Thermally Activated Delayed Fluorescence Molecules.
- Author
-
Frédéric, Lucas, Desmarchelier, Alaric, Favereau, Ludovic, and Pieters, Grégory
- Subjects
DELAYED fluorescence ,LIGHT emitting diodes ,ORGANIC light emitting diodes - Abstract
The design of fluorophores merging circularly polarized luminescence and thermally activated delayed fluorescence properties has recently emerged as a promising direction for the development of efficient CP‐Organic Light‐Emitting Diodes (CP‐OLEDs). This progress report gives an overview of the molecular designs explored to obtain CP‐TADF properties, of their performances as chiral emitters in CP‐OLEDs, and discusses future challenges for this burgeoning field of research. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
24. Efficient Circularly Polarized Electroluminescence from Chiral Thermally Activated Delayed Fluorescence Emitters Featuring Symmetrical and Rigid Coplanar Acceptors.
- Author
-
Xie, Feng‐Ming, Zhou, Jing‐Xiong, Zeng, Xin‐Yi, An, Zhi‐Dong, Li, Yan‐Qing, Han, Dong‐Xue, Duan, Peng‐Fei, Wu, Zheng‐Guang, Zheng, You‐Xuan, and Tang, Jian‐Xin
- Subjects
DELAYED fluorescence ,ELECTROLUMINESCENCE ,LIGHT emitting diodes ,ASYMMETRIC synthesis ,QUANTUM efficiency ,LUMINESCENCE - Abstract
Circularly polarized organic light‐emitting diodes (CP‐OLEDs) that enable circularly polarized luminescence (CPL) are promising for 3D display and photonic applications. However, the device efficiency and CPL character of CP‐OLEDs still lag behind the practical requirements. Here, two pairs of axially chiral emitting enantiomers, flexible (R/S)‐ODQPXZ and rigid (R/S)‐ODPPXZ, are reported by fusing (R/S)‐octahydro‐binaphthol chiral source, diphenyl quinoxaline (DQ)/dibenzo[a,c]phenazine (DP) acceptors and phenoxazine (PXZ) donors. The symmetrical chiral‐acceptor‐donor configuration endows them thermally activated delayed fluorescence (TADF) properties with small singlet–triplet energy gaps of 0.16 and 0.07 eV, high photoluminescence quantum yields of 92% and 89% in doped films, and obvious mirror‐image CPL characteristics, respectively. The CP‐OLEDs based on these TADF enantiomers not only show a maximum external quantum efficiency of 28.3% with yellow emission for (R/S)‐ODQPXZ and 20.3% with orange‐red emission for (R/S)‐ODPPXZ, but also display the CPL with dissymmetry factors (gEL) of 6.0 × 10−4 and 2.4 × 10−3, respectively. The high efficiency and obvious CPL of (R)‐ODPPXZ arise from a synergetic interplay of the TADF skeleton and the rigid coplanar acceptor for efficient chiral induction and suppressed intramolecular rotational quenching. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
25. Chiral Spiro‐Axis Induced Blue Thermally Activated Delayed Fluorescence Material for Efficient Circularly Polarized OLEDs with Low Efficiency Roll‐Off.
- Author
-
Zhang, Yi‐Pin, Liang, Xiao, Luo, Xu‐Feng, Song, Shi‐Quan, Li, Si, Wang, Yi, Mao, Zhi‐Ping, Xu, Wen‐Ye, Zheng, You‐Xuan, Zuo, Jing‐Lin, and Pan, Yi
- Subjects
DELAYED fluorescence ,ORGANIC light emitting diodes ,SPACE charge ,ELECTROLUMINESCENCE ,QUANTUM efficiency ,LIGHT emitting diodes - Abstract
A spiro‐axis skeleton not only introduces circularly polarized luminescence (CPL) into thermally activated delayed fluorescence (TADF) molecules but also enhances the intramolecular through space charge transfer (TSCT) process. Spiral distributed phenoxazine and 2‐(trifluoromethyl)‐9H‐thioxanthen‐9‐one‐10,10‐dioxide act as donor and acceptor units, respectively. The resulting TADF enantiomers, (rac)‐OSFSO, display emission maxima at 470 nm, small singlet‐triplet energy gap (ΔEST) of 0.022 eV and high photoluminescence quantum yield (PLQY) of 81.2 % in co‐doped film. The circularly polarized OLEDs (CP‐OLEDs) based on (R)‐OSFSO and (S)‐OSFSO display obvious circularly polarized electroluminescence (CPEL) signals with dissymmetry factor up to 3.0×10−3 and maximum external quantum efficiency (EQEmax) of 20.0 %. Moreover, the devices show remarkably low efficiency roll‐off with an EQE of 19.3 % at 1000 cd m−2 (roll‐off ca. 3.5 %), which are among the top results of CP‐OLEDs. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
26. Strong‐Induced CPL Emission Promoted from Achiral Conjugated Polymer‐Containing Emissive Nematic Liquid Crystals (P‐N*‐LCs).
- Author
-
Chen, Yihan, Xu, Zhaoran, Hu, Wenrui, Li, Xiaojing, Cheng, Yixiang, and Quan, Yiwu
- Subjects
CONJUGATED polymers ,LIQUID crystals ,POLYMER liquid crystals ,LIGHT emitting diodes ,NEMATIC liquid crystals ,SEMICONDUCTOR diodes ,THREE-dimensional printing - Abstract
With the rapid development on 3D printing technology, more and more works have been devoted to 3D display. 3D display will really come true by using circularly polarized luminescence (CPL)‐active materials with both high quantum yield and dissymmetry factor (gem) in organic light‐emitting diode or liquid crystals (LCs). But so far most of these CPL materials cannot meet the real application requirement because of the low gem values in the range of 10−5–10−2. In this paper, ternary chiral emissive LCs (P‐N*‐LCs) is designed by doping chiral binaphthyl‐based enantiomers as chiral dopant (Guest 1) and achiral conjugated polymer as induced CPL emitter (Guest 2) into nematic liquid crystal (N‐LCs) Host 5CB. Both Guest 1 and Guest 2 show excellent compatibility with Host 5CB. The obtained ternary P‐N*‐LCs can emit strong‐induced CPL signal with gem up to 1.12 and ФFL up to 66.1%. This work first develops a new strategy for the smart design of excellent CPL materials from versatile achiral conjugation fluorescence polymers. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
27. A Single‐Step Hot Embossing Process for Integration of Microlens Arrays in Biodegradable Substrates for Improved Light Extraction of Light‐Emitting Devices.
- Author
-
Jürgensen, Nils, Fritz, Benjamin, Mertens, Adrian, Tisserant, Jean‐Nicolas, Kolle, Mathias, Gomard, Guillaume, and Hernandez‐Sosa, Gerardo
- Subjects
ELECTRIC batteries ,BIODEGRADABLE materials ,LIGHT sources ,BIOPOLYMERS ,RAY tracing ,POLYDIMETHYLSILOXANE ,LIGHT emitting diodes ,BIODEGRADABLE plastics - Abstract
Integration of light management solutions relying on biodegradable materials in organic light‐emitting devices could assist the development of sustainable light sources or conformable and wearable display technology. Using industrially relevant processing techniques, it is shown that microlens arrays can be seamlessly integrated into flexible and biodegradable cellulose diacetate substrates to facilitate extraction of the trapped substrate modes in light‐emitting electrochemical cells. The substrates are patterned for light extraction and optimized for scalable printing processes in a single step by thermally embossing microlenses with polydimethylsiloxane molds on one substrate surface and simultaneous flattening of the other. Furthermore, by implementing the biopolymer substrate with microlens arrays, the total volume fraction of biodegradable materials in the microlense equipped device is 99.94%. The embossed microstructures on the biopolymer substrates are investigated by means of scanning electron microscopy and the angular light extraction profile of the devices is measured and compared to ray tracing simulations. Light‐emitting electrochemical cells with integrated microlens array substrates achieve an efficiency enhancement factor of 1.45, exceeding conventional organic light‐emitting diodes on glass substrates with laminated microlens arrays (enhancement factor of 1.23). [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
28. Solution‐Processed White Circularly Polarized Organic Light‐Emitting Diodes Based on Chiral Binaphthyl Emitters.
- Author
-
Zhang, Yu, Li, Jie, Quan, Yiwu, Ye, Shanghui, and Cheng, Yixiang
- Subjects
ORGANIC light emitting diodes ,LIGHT emitting diodes ,ELECTROLUMINESCENCE ,LOW voltage systems ,CHIRALITY - Abstract
By combining the blue and orange CPL or functionalized bis‐benzoxanethones emitters (S‐/R‐BN‐tCz and S‐/R‐BN‐PXZ), warm white CP‐OLEDs were fabricated using solution‐processed single emitting layer strategy. The successful realization of white CP‐EL benefited from the same stable binaphthyl chirality and similar rigid structure of the two emissive CPL emitters. The devices exhibited the low turn‐on voltage of ≈4.3 V, maximum luminance of ≈10200 cd m−2 and maximum current efficiency of ≈2.0 cd A−1. Most significantly, the devices with CIE coordinates of (0.32, 0.45) displayed intense CP‐EL signals in the spectral range of 450 to 650 nm, and showed stable gEL values of ≈10−3 as the luminance increased from 100 to 6000 cd m−2. To the best of our knowledge, this work provides for the first time a simple and feasible strategy to fabricate solution‐processed white CP‐OLEDs based on the co‐doping of the CPL emitters. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
- Full Text
- View/download PDF
29. Maximizing Chiral Perturbation on Thermally Activated Delayed Fluorescence Emitters and Elaboration of the First Top‐Emission Circularly Polarized OLED.
- Author
-
Frédéric, Lucas, Desmarchelier, Alaric, Plais, Romain, Lavnevich, Leonid, Muller, Gilles, Villafuerte, Cassie, Clavier, Gilles, Quesnel, Etienne, Racine, Benoit, Meunier‐Della‐Gatta, Sylvia, Dognon, Jean‐Pierre, Thuéry, Pierre, Crassous, Jeanne, Favereau, Ludovic, and Pieters, Grégory more...
- Subjects
DELAYED fluorescence ,LIGHT emitting diodes - Abstract
Molecular designs merging circularly polarized luminescence (CPL) and thermally activated delayed fluorescence (CP‐TADF) using the concept of chiral perturbation appeared recently as a cornerstone for the development of efficient CP‐organic light emitting diodes (CP‐OLED). Such devices could strongly increase the energy efficiency and performances of conventional OLED displays, in which 50% of the emitted light is often lost due to the use of antiglare filters. In this context, herein, ten couples of enantiomers derived from novel chiral emitter designs are reported, exhibiting CPL, TADF, and aggregation induced enhancement emission properties (AIEE). Representing the first structure properties relationship investigation for CP‐TADF materials, this thorough experimental and theoretical work brings crucial findings on the key structural and electronic parameters (isomerism, nature of the carbazole substituents) governing the synergy between CPL and TADF properties. To conclude this study, the first top emission CP‐OLED is elaborated as a new approach of generating CP light in comparison with classical bottom‐emission CP‐OLED architecture. Indeed, the top‐emission configuration represents the only relevant device architecture for future microdisplay applications. Thereby, in addition to offer molecular guidelines to combine efficiently TADF and CPL properties, this study opens new avenues toward practical applications for CP‐OLEDs. [ABSTRACT FROM AUTHOR] more...
- Published
- 2020
- Full Text
- View/download PDF
30. Chiral Platinum‐Based Metallomesogens with Highly Efficient Circularly Polarized Electroluminescence in Solution‐Processed Organic Light‐Emitting Diodes.
- Author
-
Qian, Gaowei, Yang, Xuefeng, Wang, Xiangbing, Herod, Jordan D., Bruce, Duncan W., Wang, Shengyue, Zhu, Weiguo, Duan, Pengfei, and Wang, Yafei
- Subjects
LIGHT emitting diodes ,PHOSPHORESCENCE ,ELECTROLUMINESCENCE ,MESOGENIC groups ,SMALL-angle X-ray scattering ,MICROSCOPY ,METALLOMESOGENS ,DELAYED fluorescence - Abstract
Circularly polarized luminescence (CPL) is of interest due to its wide potential application in semiconductors. To balance the emission efficiency and luminescence dissymmetry factor (gPL) of a CPL emitter, in this context, two chiral, phosphorescent and liquid‐crystalline cyclometalated platinum complexes, abbreviated R‐Pt and S‐Pt, are prepared. The complexes, which show an intense green emission at 504 nm both in solution and in the solid state, contain a simple, ortho‐metalated 2‐phenylpyridine unit functionalized with a chiral 2‐octanol chain, with liquid crystallinity being induced by modifying the β‐diketonato ligand with mesogenic groups. Interestingly, both the chiral smectic (SmA*) and nematic (N*) phases are found by a combination of polarized optical microscopy, differential scanning calorimetry, and small‐angle X‐ray scattering. By annealing, distinct CPL emission is achieved in the solid state with a gPL around 0.02. Employing the chiral platinum complexes as the dopant, solution‐processable organic light‐emitting diodes present an external quantum efficiency of 11.3% and strong, circularly polarized electroluminescence with an extremely high luminescence dissymmetry value (gEL) of 0.06 after annealing at 100 °C. This work opens an avenue for designing CPL‐active emitters with high emission efficiency and high dissymmetry factor. [ABSTRACT FROM AUTHOR] more...
- Published
- 2020
- Full Text
- View/download PDF
31. Realization of Microlens Array on Flat Encapsulant Layer for Enhancing Light Efficiency of COB-LEDs.
- Author
-
Yu, Xingjian, Xiang, Linyi, Zhou, Shuling, Pei, Naiqi, and Luo, Xiaobing
- Abstract
The conventional chip-on-board light-emitting diodes (COB-LEDs) with flat encapsulant layer present low light efficiency due to the total internal reflection (TIR) happens at the encapsulant-air interface. In this study, microlens array was realized on the flat encapsulant layer of COB-LEDs to diminish the TIR at the encapsulant-air interface. The microlens array was fabricated by selectively exposing the UV glue film in UV-light through a pre-designed photomask. Micro-pillars form after the UV-light exposure and microlens array forms spontaneously due to the wetting process of uncured UV glue on the micro-pillars. The geometry of the microlens array was experimentally optimized, and the light efficiency enhancement of COB-LEDs by the microlens array was analyzed. The results show that optimal geometry of microlens array with curvature of ~41° and base diameter of $\sim 87~\mu \text{m}$ can be realized by adjusting the UV-light exposure time as >40 s and UV glue film thickness as $> 80~\mu \text{m}$. Compared to the traditional flat encapsulant layer, the microlens array with optimal geometry increases the light efficiency of blue and ~5000 K white COB-LEDs by 50.9% and 9.31%. [ABSTRACT FROM AUTHOR] more...
- Published
- 2020
- Full Text
- View/download PDF
32. A Simple Method to Realize Millilens Array on Encapsulant Layer for Enhancing Light Efficiency of COB-LEDs.
- Author
-
Yu, Xingjian, Xiang, Linyi, Pei, Naiqi, Zhou, Shuling, and Luo, Xiaobing
- Subjects
LIGHT emitting diodes ,REFRACTION (Optics) ,BLUE light - Abstract
The chip-on-board light-emitting diodes (COB-LEDs) present low light efficiency due to the total internal reflection (TIR) at the flat encapsulant–air interface. In this study, a simple method based on complementary printing was proposed to realize the millilens array on the flat encapsulant layer to diminish the TIR effect, and thereby improve the light efficiency of the COB-LEDs. Experiments and optical simulation based on the Monte Carlo ray-tracing method were conducted to investigate the effect of the lens curvature θ, lens radius R, and lens spacing D on the light efficiency of the COB-LEDs. The results show that the light efficiency of the COB-LEDs increases with R and decreases with D, and COB-LEDs with hemispherical lens arrays (θ = 90°) have the highest light efficiency when R and D are fixed. Compared with the conventional COB-LEDs with a flat encapsulant, closely arranged hemispherical lens arrays with an R of 0.5, 1, and 1.5 mm enhance the light efficiency of the blue COB-LEDs by 87.56%, 90.62%, and 95.73% and enhance the light efficiency of ~6000-K white COB-LEDs by 17.24%, 18.86%, and 20.33%, respectively. [ABSTRACT FROM AUTHOR] more...
- Published
- 2020
- Full Text
- View/download PDF
33. Achieving Highly Efficient and Stable Quantum Dot Light-Emitting Diodes With Interface Modification.
- Author
-
Tian, Fengqing, Zhu, Yangbin, Xu, Zhongwei, Li, Baoyu, Zheng, Xiaojing, Ni, Ziquan, Hu, Hailong, Chen, Ying, Zhuang, Jinyong, Wu, Longjia, Fu, Dong, Yan, Xiaolin, and Li, Fushan
- Subjects
LIGHT emitting diodes ,ATOMIC layer deposition ,PHOSPHORESCENCE ,QUANTUM efficiency ,QUANTUM dots ,OXYGEN in water ,PHOSPHORS - Abstract
In conventional quantum dot light-emitting diodes (QLEDs), the organic charge transport materials are susceptible to erosion by water and oxygen, which would reduce the efficiency and lifetime of the devices. Herein, we modified the surface of the organic hole transport layer with an ultra-thin Al2O3 layer, which is deposited by using atomic layer deposition technique, to obtain the highly efficient and stable QLEDs. It is indicated that the ultra-thin Al2O3 interlayer plays a significant role in decreasing leakage current, suppressing exciton quenching and passivating the defects. The device with Al2O3 interface modification exhibits the maximum external quantum efficiency (EQE) of 20.8%, current efficiency (CE) of 21.6 cd A−1, and lifetime of 482000 h. In comparison with the control device, the EQE, CE and lifetime are improved by 31%, 32%, and 330%, respectively. The results indicate that the strategy of Al2O3 interface modification could provide an effective way for realizing highly efficiency QLED with long lifetime. [ABSTRACT FROM AUTHOR] more...
- Published
- 2020
- Full Text
- View/download PDF
34. Axially Chiral Biphenyl Compound‐Based Thermally Activated Delayed Fluorescent Materials for High‐Performance Circularly Polarized Organic Light‐Emitting Diodes.
- Author
-
Tu, Zhen‐Long, Yan, Zhi‐Ping, Liang, Xiao, Chen, Lei, Wu, Zheng‐Guang, Wang, Yi, Zheng, You‐Xuan, Zuo, Jing‐Lin, and Pan, Yi
- Subjects
LIGHT emitting diodes ,FRONTIER orbitals ,DIPHENYL ,DELAYED fluorescence ,QUANTUM efficiency - Abstract
To boost intrinsic circularly polarized luminescence (CPL) properties of chiral emitters, an axially chiral biphenyl unit is inlaid in thermally activated delayed fluorescent (TADF) skeleton, urging the participation of chiral source in frontier molecular orbital distributions. A pair of enantiomers, (R)‐BPPOACZ and (S)‐BPPOACZ, containing the cyano as electron‐withdrawing moieties and carbazole and phenoxazine as electron‐donating units are synthesized and separated. The circularly polarized TADF enantiomers exhibit both high photoluminescence quantum yield of 86.10% and excellent CPL activities with maximum dissymmetry factor |gPL| values of almost 10−2 in solution and 1.8 × 10−2 in doped film, which are among the best values of previously reported small chiral organic materials. Moreover, the circularly polarized organic light‐emitting diodes based on the TADF enantiomers achieve the maximum external quantum efficiency of 16.6% with extremely low efficiency roll‐off. Obvious circularly polarized electroluminescence signals with |gEL| values of 4 × 10−3 are also recorded. [ABSTRACT FROM AUTHOR] more...
- Published
- 2020
- Full Text
- View/download PDF
35. Doping-free circularly polarized electroluminescence of AIE-active chiral binaphthyl-based polymers.
- Author
-
Yang, Lan, Zhang, Yu, Zhang, Xueyan, Li, Nengquan, Quan, Yiwu, and Cheng, Yixiang
- Subjects
ELECTROLUMINESCENCE ,ENANTIOMERS analysis ,CHIRALITY ,CIRCULAR polarization ,LIGHT emitting diodes ,DOPING agents (Chemistry) - Abstract
AIE-active chiral polymer enantiomers (S-/R-P) can emit green circularly polarized electroluminescence (CP-EL) with g
EL up to 0.024 without alignment layers and chiral dopants, which represents the first example of CP-OLEDs based on AIE-active main-chain chiral polymers. [ABSTRACT FROM AUTHOR] more...- Published
- 2018
- Full Text
- View/download PDF
36. White LED light production using dibromoperylene derivatives in down conversion of energy.
- Author
-
Aksoy, Erkan, Demi̇r, Nuriye, and Varlikli, Canan
- Subjects
LED lighting ,PERYLENE derivatives ,ESTERS ,PHOSPHORS ,CHEMICAL synthesis ,ENERGY conversion ,LIGHT emitting diodes ,EQUIPMENT & supplies - Abstract
Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) more...
- Published
- 2018
- Full Text
- View/download PDF
37. Recent Advances in Polymer Organic Light-Emitting Diodes (PLED) Using Non-conjugated Polymers as the Emitting Layer and Contrasting Them with Conjugated Counterparts.
- Author
-
Wong, Michael
- Subjects
POLYMERS ,ORGANIC light emitting diodes ,LIGHT emitting diodes ,ELECTRONICS ,ORGANIC semiconductors - Abstract
Polymer organic light-emitting diodes (PLED) are one of the most studied subjects in flexible electronics thanks to their economical wet fabrication procedure for enhanced price advantage of the product device. In order to optimize PLED efficiency, correlating the polymer structure with the device performance is essential. An important question for the researchers in this field is whether the polymer backbone is conjugated or not as it affects the device performance. In this review, recent advances in non-conjugated polymers employed as the emitting layer in PLED devices are first discussed, followed by their contrast with the conjugated counterparts in terms of polymer synthesis, sample quality, physical properties and device performances. Such comparison between conjugated and non-conjugated polymers for PLED applications is rarely attempted, and; hence, this review shall provide a useful insight of emitting polymers employed in PLEDs. Graphical Abstract: [ABSTRACT FROM AUTHOR] more...
- Published
- 2017
- Full Text
- View/download PDF
38. Deep-blue light-emitting polyfluorenes containing spiro[fluorene-9,9′-thioxanthene- S,S-dioxide] isomers.
- Author
-
Peng, Feng, Xu, Jin, Zhang, Yuhao, He, Ruifeng, Yang, Wei, and Cao, Yong
- Subjects
LIGHT emitting diodes ,THIOXANTHENES ,FLUORENE compounds ,ISOMERS ,REDSHIFT - Abstract
ABSTRACT Blue light-emitting polyfluorenes, PPF-FSOs and PPF-SOFs were synthesized via introducing spiro[fluorene-9,9′-thioxanthene- S,S-dioxide] isomers (2,7-diyl and 2′,7′-diyl) (FSO/SOF) into the poly[9,9-bis(4-(2-ethylhexyloxy) phenyl)fluorene-2,7-diyl] (PPF) backbone, respectively. With the increasing contents of FSO and SOF moieties, the absorption and PL spectra of PPF-FSOs show slight red shift, while that of PPF-SOFs exhibit blue shift, respectively. The HOMO and LUMO levels reduce gradually with increasing SOF unit in PPF-SOFs. The polymers emit blue light peaked around 430-445 nm and show an excellent spectral stability with the variation in current densities. The distinctly narrowing EL spectra were observed with the incorporation of isomers in the polymers. The full width at half maximum reduced by 15 nm for PPF-SOFs, resulting in a blue shift with the CIE coordinates from (0.16, 0.11) to (0.16, 0.08). With a device configuration of ITO/PEDOT:PSS/EML/CsF/Al, a maximum luminance efficiency (LE
max ) of 2.00 cd A−1 , a maximum external quantum efficiency (EQEmax ) of 3.76% with the CIE coordinates of (0.16, 0.08) for PPF-SOF15 and a LEmax of 1.68 cd A−1 , a EQEmax of 2.38% with CIE (0.16, 0.12) for PPF-FSO10 were obtained, respectively. The result reveals that spiro[fluorene-9,9′-thioxanthene- S,S-dioxide] isomers are promising blocks for deep-blue light-emitting polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2332-2341 [ABSTRACT FROM AUTHOR] more...- Published
- 2017
- Full Text
- View/download PDF
39. Inverted Tandem Architecture of Quantum-dot Light Emitting Diodes with Solution Processed Charge Generation Layers.
- Author
-
Kim, Hyo-Min, Lee, Jieun, Hwang, Eunsa, Kim, Jeonggi, and Jang, Jin
- Subjects
QUANTUM dots ,LIGHT emitting diodes - Abstract
An inverted tandem quantum-dot light-emitting diode (QLEDs) is demonstrated using solution processed charge generation layers (CGLs) for the first time. The tandem QLEDs with the CGL, consisting of green QDs (G-QDs) for bottom and red QDs (R-QDs) for top cells, exhibited yellow emission with current efficiency of 15.9 cd/A at 1,000 cd/m
2 . [ABSTRACT FROM AUTHOR] more...- Published
- 2016
- Full Text
- View/download PDF
40. Lanthanide-Based Multifunctional Materials : From OLEDs to SIMs
- Author
-
Pablo Martin-Ramos, Manuela Ramos-Silva, Pablo Martin-Ramos, and Manuela Ramos-Silva
- Subjects
- Secondary ion mass spectrometry, Rare earth metals, Light emitting diodes
- Abstract
Lanthanide-Based Multifunctional Materials: From OLEDs to SIMs serves as a comprehensive and state-of the art review on these promising compounds, delivering a panorama of their extensive and rapidly growing applications. After an introductory chapter on the theoretical description of the optical and magnetic behaviour of lanthanides and on the prediction of their properties by ab-initio methods, four chapters are devoted to lanthanide-based OLEDs, including the latest trends in visible emitters, the emerging field of near infrared emitters and the first achievements attained in the field of chiral OLEDs. The use of lanthanide complexes as molecular magnets spreads over another two chapters, which explain the evolution of 4f-elements-based SIMs and the most recent advances in heterometallic 3d–4f SMMs. Other very active research areas are covered in the remaining five chapters, dedicated to lanthanide-doped germanate and tellurite glasses, luminescent materials for up-conversion, luminescent thermosensors, multimodal imaging and therapeutic agents, and chemosensors. The book is aimed at academic and industrial researchers, undergraduates and postgraduates alike, and is of particular interest for the Materials Science, Applied Physics and Applied Chemistry communities. - Includes the latest progress on lanthanide-based materials and their applications (in OLEDs, SIMs, doped matrices, up-conversion, thermosensors, theragnostics and chemosensors) - Presents basic and applied aspects of the Physics and Chemistry of lanthanide compounds, as well as future lines of action - Covers successful examples of devices and proofs-of-concept and provides guidelines for the rational design of new materials more...
- Published
- 2018
41. OLED Displays and Lighting
- Author
-
Mitsuhiro Koden and Mitsuhiro Koden
- Subjects
- Light emitting diodes, Organic semiconductors
- Abstract
Explains the fundamentals and practical applications of flat and flexible OLEDs for displays and lighting Organic light-emitting diodes (OLEDs) have emerged as the leading technology for the new display and lighting market. OLEDs are solid-state devices composed of thin films of organic molecules that create light with the application of electricity. OLEDs can provide brighter, crisper displays on electronic devices and use less power than conventional light-emitting diodes (LEDs) or liquid crystal displays (LCDs) used today. This book covers both the fundamentals and practical applications of flat and flexible OLEDs. Key features: Covers all of the aspects necessary to the design and manufacturing of OLED displays and lighting. Explains the fundamental basic technologies and also related technologies which might contribute to the next innovation in the industry. Provides several indications for future innovation in the OLED industry. Includes coverage of OLED vacuum deposition type and solution type materials. The book is essential reading for early career engineers developing OLED devices and OLED related technologies in industrial companies, such as OLED device fabrication companies. more...
- Published
- 2016
42. Organic Light-Emitting Materials and Devices
- Author
-
Zhigang Rick Li and Zhigang Rick Li
- Subjects
- Polymers--Electric properties, Light emitting diodes, Electroluminescent devices--Materials
- Abstract
Organic Light-Emitting Materials and Devices provides a single source of information covering all aspects of OLEDs, including the systematic investigation of organic light-emitting materials, device physics and engineering, and manufacturing and performance measurement techniques. This Second Edition is a compilation of the advances made in recent years and of the challenges facing the future development of OLED technology.Featuring chapters authored by internationally recognized academic and industrial experts, this authoritative text: Introduces the history, fundamental physics, and potential applications of OLEDs Reviews the synthesis, properties, and device performance of electroluminescent materials used in OLEDs Reflects the current state of molecular design, exemplifying more than 600 light-emitting polymers and highlighting the most efficient materials and devices Explores small molecules-based OLEDs, detailing hole- and electron-injection and electron-transport materials, electron- and hole-blocking materials, sensitizers, and fluorescent and phosphorescent light-emitting materials Describes solution-processable phosphorescent polymer LEDs, energy transfer processes, polarized OLEDs, anode materials, and vapor deposition manufacturing techniques employed in OLED fabrication Discusses flexible display, the backplane circuit technology for organic light-emitting displays, and the latest microstructural characterization and performance measurement techniques Contains abundant diagrams, device configurations, and molecular structures clearly illutrating the presented ideas Organic Light-Emitting Materials and Devices, Second Edition offers a comprehensive overview of the OLED field and can serve as a primary reference for those needing additional information in any particular subarea of organic electroluminescence. This book should attract the attention of materials scientists, synthetic chemists, solid-state physicists, and electronic device engineers, as well as industrial managers and patent lawyers engaged in OLED-related business areas. more...
- Published
- 2015
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.