Rong-Huei Yi

Publication date: 15 August 2022

Source: Chemical Engineering Journal, Volume 442, Part 1

Author(s): Zhen Zhang, Yu-e Shi, Yibo Liu, Yifei Xing, Ding Yi, Zhenguang Wang, Dongpeng Yan

Publication date: 1 August 2022

Source: Chemical Engineering Journal, Volume 441

Author(s): Xinxin Ban, Tao Zhou, Kaizhi Zhang, Qingpeng Cao, Fengjie Ge, Dongen Zhang, Peng Zhu, Zunzheng Liu, Zimin Li, Wei Jiang

Publication date: May 2022

Source: Dyes and Pigments, Volume 201

Author(s): Kaibo Hu, Guangchang Lian, Yuling Wang, Tingyu Shao, Meng Zhou, Ying Liu, Guofan Jin

Publication date: June 2022

Source: Dyes and Pigments, Volume 202

Author(s): Puttavva Meti, Fahad Mateen, Do Yeon Hwang, Ye-Eun Lee, Sung-Kyu Hong, Young-Dae Gong

Publication date: June 2022

Source: Dyes and Pigments, Volume 202

Author(s): Ying-Chen Duan, Ying Gao, Xiao-Xia You, Yong Wu, Yun Geng, Yue-Gang Fu, Zhong-Min Su

Publication date: June 2022

Source: Dyes and Pigments, Volume 202

Author(s): Jia-Wei Liu, Han-Chen Zhou, Zi-Kun Wang, Xiong Tang, Hua-Yu Wu, Shi Wang, Wen-Yong Lai, Yong-Hua Li

Optimized tandem device of the multi-resonance type blue emitter achieves high external quantum efficiency over 25% and extremely long device lifetime of over 500 h at 1000 cd m⁻² and 30000 h at 100 cd m⁻² up to 95% of initial luminance.

Abstract

In this study, a multiple resonance (MR) type blue emitter is synthesized, characterized, and evaluated for highly efficient and stable blue fluorescent organic light-emitting diodes (OLEDs). The MR blue fluorescent emitter has a di-tert-butyl benzene substituent in the MR core structure to minimize quenching mechanisms by intermolecular interaction. The emitter shows a high photoluminescence quantum yield and small full width at half maximum of 22 nm, which realize high external quantum efficiency (EQE) of 11.4% in the single unit OLED and device lifetime up to 95% of the initial luminance (LT₉₅) of 208 h at 1000 cd m⁻² and over 10 000 h at 100 cd m⁻². The optimized tandem device of the new blue emitter achieves high EQE over 25% and extremely long LT₉₅ of over 500 h at 1000 cd m⁻² and 30 000 h at 100 cd m⁻². The lifetime of this work is one of the best data of blue OLED lifetime reported in the literature.

Three vibrational emission peaks of the first excited triplet state T ₁ are identified in triplet–triplet annihilation (TTA) molecules at room temperature. Compared with its high-energy counterpart, the low-energy vibrational T ₁ is more likely to localize and acts as an energy-loss state; thus, this state makes only slight contributions to the TTA-based upconversion process.

Abstract

Triplet–triplet annihilation (TTA) is a feasible approach for utilizing electrically generated triplet excitons in organic light-emitting diodes. However, low TTA efficiency is often observed in solids. Owing to the optically inaccessible nature of triplets, the main loss routes of the TTA process remain unknown. In this work, three vibrational emission peaks of the first excited triplet state (T ₁) are identified in the sensitized room-temperature phosphorescence of TTA molecules. These peaks provide strong evidence of the loss channels of TTA. It is found that the monomolecular recombination of T ₁ represents an energy-loss channel that combines the transient photoluminescence of both upconversion fluorescence and phosphorescence. Moreover, the study demonstrates that low-energy vibrational T ₁ acts as an energy-loss channel with only slight contributions to TTA. This work presents constructive insights into the improvement of TTA efficiency in solid films.

Publication date: 15 July 2022

Source: Chemical Engineering Journal, Volume 440

Author(s): Shengbing Xiao, Ying Gao, Runze Wang, Haichao Liu, Weijun Li, Changjiang Zhou, Shanfeng Xue, Shi-Tong Zhang, Bing Yang, Yuguang Ma

Bromo-triarylborane o -BrTAB exhibits dual phosphorescence at room temperature; a short-lived higher energy emission originates from single molecules (T₁ ^M) whereas the long-lived component at lower energy results from an aggregate (T₁ ^A). Under 365 nm UV light irradiation, crystalline o -BrTAB emits bright pale blue light (fluorescence). After turning off the light, a persistent yellow afterglow remains for 2 s.

Abstract

Designing highly efficient purely organic phosphors at room temperature remains a challenge because of fast non-radiative processes and slow intersystem crossing (ISC) rates. The majority of them emit only single component phosphorescence. Herein, we have prepared 3 isomers (o, m, p-bromophenyl)-bis(2,6-dimethylphenyl)boranes. Among the 3 isomers ( o -, m - and p -BrTAB) synthesized, the ortho-one is the only one which shows dual phosphorescence, with a short lifetime of 0.8 ms and a long lifetime of 234 ms in the crystalline state at room temperature. Based on theoretical calculations and crystal structure analysis of o -BrTAB, the short lifetime component is ascribed to the T₁ ^M state of the monomer which emits the higher energy phosphorescence. The long-lived, lower energy phosphorescence emission is attributed to the T₁ ^A state of an aggregate, with multiple intermolecular interactions existing in crystalline o -BrTAB inhibiting nonradiative decay and stabilizing the triplet states efficiently.

A new kind of small organic NIR-II fluorophore molecule (ZS-1010) was developed as a NIR-II fluorescent probe for trimethylamine (TMA) detection based on intermolecular charge transfer. This is the first example of TMA fluorescent probe in the NIR-II window showing deep penetration, fast response speed, high selectivity and pH stability.

Abstract

A new kind of small organic NIR-II fluorophore molecule (ZS-1010) based on intermolecular charge transfer was developed as a NIR-II fluorescent probe for trimethylamine (TMA) detection, which is important for the diagnosis of cardiovascular disease, chronic kidney disease and diabetes. ZS-1010 has a strong push–pull electron system composed of electron donor unit and electron acceptor unit, exhibiting strong absorption and emission in the NIR-II region. When mixed with TMA which possesses strong electron-donating characteristics, the push–pull system of ZS-1010 will be affected along with the dipole moment change, leading to the quenching of fluorescence. This is the first example of TMA fluorescent probe in the NIR-II window showing deep penetration, fast response speed, high selectivity and pH stability.

A rational design principle is proposed to achieve an advanced nanowire nano-architecture from an ultra-deep-blue emissive conjugated molecule (FCz-C8-Am) via the synergistic effect of the hydrogen bonding - and pendant π–π stacking interactions. This nano-architecture presents a stable ultra-deep-blue emission with an efficiency of >75% and a CIE value of (0.16, 0.06), associated with a single-molecular excitonic behavior.

Abstract

Organic conjugated molecules with a rigid rod-like π-backbone structure automatically and easily self-assemble into an anisotropic nanostructure. However, supersecondary structures obtained from the hierarchical secondary self-assembly of nanostructures have rarely been reported for non-amphiphilic conjugated molecules. Here, a nanowire architecture as a supersecondary structure from an ultra-deep-blue fluorene-based conjugated molecule (FCz-C8-Am) to improve the emission efficiency and stability is reported. In significant contrast to the four reference molecules, the FCz-C8-Am molecules grow into soft nanowires and further self-assemble into a series of nanowire architectures in the gelation process. This is associated with the synergistic effect of the hydrogen bonds among the amide units, pendant π–π stacking interactions between pendant Cz units, and appropriate soft steric interaction among side-chains, which are the three design requirements for preparing these nanowire architectures. Interestingly, this supersecondary architecture of FCz-C8-Am has a stable ultra-deep-blue emission, with an efficiency of ≈77% and a Commission Internationale de L'Eclairage (CIE) value of (0.16, 0.06) in the solid state. These findings provide a profound understanding of the relationship between the inherent molecular structure, supramolecular interaction, and supersecondary nano-architecture, offering useful information for the development of new functional optoelectronic materials.

The position of triplet exciton is key to enhancing operational stability of organic light-emitting diode device. With judicious selection of the functional group within the acceptor moiety, the locus of triplet exciton can be repositioned away from the weak carbon–nitrogen bond, entailing higher dissociation barrier in the excited state and leading to a 2.3-fold increase in device lifetime.

Abstract

Thermally activated delayed fluorescence (TADF) has emerged as a promising and pragmatic light-generation method for producing efficient organic light-emitting diodes (OLEDs). However, the low operational stability associated with blue-light TADF emitters is a major drawback and the excited-state molecular degradation process remains poorly understood. Archetypal TADF emitters are comprised of cycloamine donor and aromatic acceptor moieties, with the corresponding C–N bond considered as the weakest link in the molecular structure. Understanding mechanism of the C–N dissociation in the excited state is, thus, crucial to the engineering of more stable OLEDs. Here, by using a carbazole donor and a triazine acceptor with various functional groups, it is shown that the position of the triplet exciton is the key to enhancing operational stability and, therefore, device lifetime. Interestingly, repositioning the triplet exciton away from the C–N bond causes the dissociation pathway to diverge from a smooth transition state to a more abrupt conical intersection with a higher energy barrier. We realize a 2.3-fold increase in device lifetime without compromising traditional design factors, such as the singlet–triplet energy gap, with judicious introduction of functional groups to the acceptor.

A comprehensive optimization strategy, including 2-phenylethylammonium ligand (PEA⁺)-passivated FAPbI₃ quantum dots (QDs), synergistic coverage effects between the QDs and hole-transporting layers, and effective electron-transporting layers for constructing a feasible device structure leads to a high-efficiency near-infrared (NIR) QD-based light-emitting diode (QLED) centered at 772 nm and exhibiting a maximum external quantum efficiency up to 15.4%, the highest external quantum efficiency recorded for perovskite-based NIR QLEDs.

Abstract

In recent years, the performance of perovskite quantum dots (QDs) and QD-based light-emitting diodes (QLEDs) has improved greatly, with electroluminescence (EL) efficiency of green and red emission exceeding 20%. However, the development of perovskite near-infrared (NIR) QLEDs has reached stagnation, where the reported maximum EL efficiency is still below 6%, limiting their further applications. In this work, new NIR-emissive FAPbI₃ QDs are developed by post-treating long alkyl-encapsulated QDs with 2-phenylethylammonium iodide (PEAI). The incorporation of PEAI reduces the QD surface defects for giving a high photoluminescence quantum yield up to 61.6%. The n-octane solution of PEAI-passivated FAPbI₃ QDs is spin coated on top of the PEDOT:PSS-treated ITO electrode modified with a thermally crosslinked hole-transporting layer to give a full-coverage, smooth, and dense QD film. Incorporating with an effective electron-transporting material, CN-T2T, which has deep lowest unoccupied molecular orbital and good electron mobility, the optimal device with EL λ_max at 772 nm achieves an external quantum efficiency up to 15.4% at a current density of 0.54 mA cm⁻² (2.6 V), which is the highest efficiency ever reported for perovskite-based NIR QLEDs. This study provides a facile strategy to prepare high-quality perovskite QD films suitable for highly efficient NIR QLED applications.

Publication date: May 2022

Source: Dyes and Pigments, Volume 201

Author(s): Manman Tan, Yingzhong Li, Weihan Guo, Yalan Chen, Mingda Wang, Yigang Wang, Baozhu Chi, Hua Wang, Guomin Xia, Hongming Wang

Publication date: May 2022

Source: Dyes and Pigments, Volume 201

Author(s): Milan Klikar, Dimitris Georgiou, Ioannis Polyzos, Mihalis Fakis, Zdeňka Růžičková, Oldřich Pytela, Filip Bureš

Publication date: May 2022

Source: Dyes and Pigments, Volume 201

Author(s): Nejc Petek, Bibi Erjavec, Dejan Slapšak, Aljaž Gaber, Uroš Grošelj, Franc Požgan, Sebastijan Ričko, Bogdan Štefane, Marina Klemenčič, Jurij Svete

Incorporation of fluorene-bridge in donor–acceptor (D–A) molecules is proven to demonstrates double functions: high photoluminescent quantum yield and balanced carrier mobilities due to decent stacking patterns. Remarkably, the non-doped OLED of the fluorene-bridged D–A materials demonstrate excellent electroluminescent performances with high efficiency, low driving voltage, low rolling-off with boosted and balanced carrier mobility.

Abstract

One of the most important issues of the organic light-emitting diode (OLED) is the highly efficient blue-emissive material, which demands both excellent photoluminescent quantum yield (PLQY) and balanced carrier mobilities. Herein, a series of blue-emissive donor–π–acceptor (D–π–A) materials with fluorene π-bridge and their D–A analogues are synthesized and discovered with a theoretical combined experimental method. Based on the excellent electron mobility of the oxadiazole (OXZ) acceptor, it is further proven that the insertion of the fluorene π-bridge can not only contribute to the formation of hybrid local and charge-transfer excited state with high PLQY, but also give rise to the hole mobilities by enhanced intermolecular face-to-face stacking. As a result, the non-doped OLED of TPACFOXZ exhibits a high maximum external quantum efficiency approaching 10% with boosted and balanced hole and electron mobilities of 5.60 × 10⁻⁵ and 6.60 × 10⁻⁵ cm² V⁻¹ s⁻¹, respectively, which are among the best results of the non-doped blue fluorescent OLEDs.

Publication date: 15 June 2022

Source: Chemical Engineering Journal, Volume 438

Author(s): Wei Yang, Weimin Ning, Hsin Jungchi, Tengxiao Liu, Xiaojun Yin, Changqing Ye, Shaolong Gong, Chuluo Yang

A comprehensive optimization strategy, including 2-phenylethylammonium ligand (PEA⁺)-passivated FAPbI₃ quantum dots (QDs), synergistic coverage effects between the QDs and hole-transporting layers, and effective electron-transporting layers for constructing a feasible device structure leads to a high-efficiency near-infrared (NIR) QD-based light-emitting diode (QLED) centered at 772 nm and exhibiting a maximum external quantum efficiency up to 15.4%, the highest external quantum efficiency recorded for perovskite-based NIR QLEDs.

Abstract

In recent years, the performance of perovskite quantum dots (QDs) and QD-based light-emitting diodes (QLEDs) has improved greatly, with electroluminescence (EL) efficiency of green and red emission exceeding 20%. However, the development of perovskite near-infrared (NIR) QLEDs has reached stagnation, where the reported maximum EL efficiency is still below 6%, limiting their further applications. In this work, new NIR-emissive FAPbI₃ QDs are developed by post-treating long alkyl-encapsulated QDs with 2-phenylethylammonium iodide (PEAI). The incorporation of PEAI reduces the QD surface defects for giving a high photoluminescence quantum yield up to 61.6%. The n-octane solution of PEAI-passivated FAPbI₃ QDs is spin coated on top of the PEDOT:PSS-treated ITO electrode modified with a thermally crosslinked hole-transporting layer to give a full-coverage, smooth, and dense QD film. Incorporating with an effective electron-transporting material, CN-T2T, which has deep lowest unoccupied molecular orbital and good electron mobility, the optimal device with EL λ_max at 772 nm achieves an external quantum efficiency up to 15.4% at a current density of 0.54 mA cm⁻² (2.6 V), which is the highest efficiency ever reported for perovskite-based NIR QLEDs. This study provides a facile strategy to prepare high-quality perovskite QD films suitable for highly efficient NIR QLED applications.