Xue-Mei Ou

Management of Singlet and Triplet Excitons in a Single Emission Layer: A Simple Approach for a High‐Efficiency Fluorescence/Phosphorescence Hybrid White Organic Light‐Emitting Device

A high-efficiency single-emission-layer (EML) hybrid white organic light emitting device is fabricated based on an ideal sky-blue fluorophor, DADBT, using a novel doping concentration regulation strategy, which effectively separates and respectively utilizes the singlet and triplet excitons in the single-EML. The white device shows excellent electroluminescence performance with maximum total efficiencies of 26.6%, 53.5 cd A(-1) and 67.2 lm W(-1) .

Prediction and Design of Efficient Exciplex Emitters for High‐Efficiency, Thermally Activated Delayed‐Fluorescence Organic Light‐Emitting Diodes

High-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes based on exciplex emitters are demonstrated. The best device, based on a TAPC:DPTPCz emitter, shows a high external quantum efficiency of 15.4%. Strategies for predicting and designing efficient exciplex emitters are also provided. This approach allow prediction and design of efficient exciplex emitters for achieving high-efficiency organic light-emitting diodes, for future use in displays and lighting applications.

Highly efficient non-doped deep-blue organic light-emitting diodes based on anthracene derivatives

Three deep-blue-emitting anthracene derivatives, 2-tert-butyl-9,10-bis(9,9-dimethylfluorenyl) anthracene (TBMFA), 2-tert-butyl-9,10-bis[4-(2-naphthyl)phenyl] anthracene (TBDNPA), and 2-tert-butyl-9,10-bis[4-(9,9-dimethylfluorenyl)phenyl] anthracene (TBMFPA), with naphthalene or 9,9-dimethylfluorene side units, have been designed, synthesized, and characterized. The anthracene derivatives show strong deep-blue emission both in solution and in thin films. The three derivatives also have high glass-transition temperatures (Tg ≥ 133 °C) due to the presence of sterically congested terminal groups. Organic light-emitting diodes (OLEDs) prepared using these anthracene derivatives as non-doped emitters exhibit bright and saturated deep-blue emissions. OLEDs based on TBDNPA give the best performance with a low turn-on voltage (3.0 V with a brightness of 1 cd m−2), and a high efficiency (5.17% external quantum efficiency at 8.4 mA cm−2). These results are among the best ever reported for saturated deep-blue OLEDs with a CIE coordinate of y < 0.10.

One‐Step Self‐Assembly, Alignment, and Patterning of Organic Semiconductor Nanowires by Controlled Evaporation of Confined Microfluids

Organic semiconductors, which have unique electronic and optical properties that differ from those of their inorganic counterparts, have attracted intense attention for potential applications in optoelectronic devices such as organic lightemitting diodes (OLEDs), 2] organic field-effect transistors (OFETs), organic solar cells (OSCs), and gas sensors. 11] Numerous reports have indicated that organic semiconductor molecules predominantly aggregate and selfassemble into one-dimensional (1D) nanowires or nanorods along the direction of p–p stacking or other directional intermolecular interactions. Owing to excellent performance in carrier transport, such one-dimensional nanostructures may serve as attractive building blocks in future organic electronic applications. However, to fabricate practical devices on a large scale, a major challenge is to design a method to deposit and align a large number of such nanowires in a desired position. In most cases, nanostructures selfassembled directly from solution tend to be distributed in a macroscopically random fashion on the substrate. Disordered alignment of organic semiconductors may significantly increase the overall cost due to material consumption and also result in poor performance of electronic devices. Therefore, a facile deposition and patterning method for organic semiconductor molecules is highly desirable. To date, several strategies for alignment of 1D nanowires have been investigated, including the Langmuir–Blodgett technique, electric or magnetic field assisted alignment, dip coating, electrostatic alignment, and so on. However, these methods usually require an external facility and are limited in producing large-area ordered patterns. In recent years, evaporation-induced self-assembly (EISA) has been reported to prepare well-ordered 2D patterns. The EISA method depends on the simple fact that a drop of colloidal solution always leaves a ringlike deposit at the perimeter. During the evaporation process, the loss of solvent mainly occurs at the contact line, and an outward capillary flow carries the solvent and dispersed solute from the interior to the contact line. Therefore, the key parameter to achieve well-ordered 2D patterns is an efficient method to control the contact line. Recently, Lin et al. reported a simple method for controlling droplet evaporation in a confined geometry, which leaves behind well-organized gradient concentric ring patterns. With a spherical lens on the substrate, the contact line is well controlled and hence gradient concentric rings are obtained. However, the asprepared patterns are usually amorphous and no specific nanostructures are formed because of the hard-to-crystallize materials used in evaporation process, such as polymer and inorganic quantum dots (QDs). On the other hand, organic semiconductor molecules can easily self-assemble into 1D nanostructures by evaporation. 44] We have developed a facile method to prepare aligned organic nanowires on a solid substrate or liquid/liquid interface based on the EISA method. 45] With the aid of solvent evaporation, selfassembly of molecules and alignment of as-obtained nanostructures can be combined to produce a large-area ordered pattern of organic nanowires or films. However, the method wastes a lot of solvent, and the contact line is not easy to control. We have now integrated the EISA method with the concentric ring patterns of Lin et al. , so that simultaneous self-assembly, alignment, and patterning of organic semiconductor nanowires can be achieved in one step. Here we demonstrate such a facile approach to fabricate large-scale concentric arrays of nanowires by solvent evaporation in a confined geometry. N,N’-Dimethylquinacridone (DMQA) was selected as a nonvolatile solute in this experiment. It is an industrially important red organic dye with intense fluorescence, which is widely used in photovoltaic and other organic electroluminescent devices. It was synthesized according to the reported procedure and was purified twice by vacuum sublimation. Concentric ring patterns of DMQA nanowires were prepared from chloroform solutions of DMQA with concentrations of 0.2, 0.1, and 0.05 mmolL . The confined [*] Z. L. Wang, R. R. Bao, X. M. Ou, Prof. J. C. Chang, Prof. X. H. Zhang Nano-organic Photoelectronic Laboratory and Key Laboratory of Photochemical Conversion and Optoelectronic Materials Technical Institute of Physics and Chemistry Chinese Academy of Sciences, Beijing (China) E-mail: xhzhang@mail.ipc.ac.cn

Novel Carbazol-Pyridine-Carbonitrile Derivative as Excellent Blue Thermally Activated Delayed Fluorescence Emitter for Highly Efficient Organic Light-Emitting Devices

A novel blue thermally activated delayed fluorescence (TADF) emitter, CPC (2,6-di(9H-carbazol-9-yl)-4-phenylpyridine-3,5-dicarbonitrile), was designed and synthesized. By directly linking carbazole (to serve as electron-donor) and pyridine-3,5-dicarbonitrile (to serve as electron-acceptor), and distributing cyanogroups and carbazole groups at the para-position of pyridine core, CPC successfully achieves an extremely small singlet-triplet splitting and fairish photoluminescence quantum yield, thus can act as the highly efficient blue TADF emitter. The optimized organic light-emitting diode (OLED) based on 13 wt % CPC doped in mCP (1,3-bis(9H-carbazol-9-yl)benzene) host exhibits maximum current efficiency, power efficiency, and external quantum efficiency of 47.7 cd A(-1), 42.8 lm W(-1), and 21.2%, respectively, which are the best results in reported blue TADF-based devices up to date and even comparable with the best reported blue phosphorescent OLEDs.

Iodine‐Doped‐Poly(3,4‐Ethylenedioxythiophene)‐Modified Si Nanowire 1D Core‐Shell Arrays as an Efficient Photocatalyst for Solar Hydrogen Generation

A new 1D core-shell strategy is demonstrated for a hydrogen-generation photo-electrochemical cell (PEC). This Si/iodine-doped poly(3,4-ethylenedioxythiophene) (PEDOT) 1D nanocable array shows an encouraging solar-to-chemical energy-conversion efficiency. Coating with iodine-doped PEDOT can effectively enhance the photocatalytic efficiency and stability of SiNW arrays. The PEC model proposed shows a potentially promising structure for H(2) production using solar energy.

Highly sensitive, reproducible, and stable SERS sensors based on well-controlled silver nanoparticle-decorated silicon nanowire building blocks

Surface-enhanced Raman scattering (SERS), as a powerful analytical tool, has attracted great interest in the development of chemical and biological sensors because of its ultrahigh sensitivity and amenability to molecular fingerprinting. However, practical applications with current SERS sensors based on colloidal metal nanoparticles (NPs) or a rough metal film remain great challenges, due to the poor stability and low reproducibility. Here, we report a facile strategy to prepare highly sensitive SERS sensors with excellent reproducibility and stability based on uniform and well-controlled silver NP-decorated silicon nanowire (AgNP@SiNW) building blocks. In this strategy, uniform, size- and interparticle distance-controlled AgNPs are deposited on SiNWs, yielding abundant hot spots. A single AgNP@SiNW exhibits ultrahigh sensitivity with an enhancement factor of 4.12 × 109, spot-to-spot and wire-to-wire reproducibility, and good stability in an aqueous environment. Furthermore, sensors fabricated with this AgNP@SiNW building block have diverse applications that are demonstrated with a single NW for microscopic detection of a low concentration of carbaryl (0.01 mg mL−1) residues on a cucumber surface with 1 s acquisition time and an assembled thin film sensor for label-free, real-time detection of E. coli in drinking water. This combination of prominent SERS performances, highly efficient detection, and accessibility in multiple sample matrices indicates that our facile SERS sensor fabrication strategy has the potential to increase the applicability of the SERS technique in the real world.

Multifunctional terpyridine/diphenylamine derivatives as highly efficient blue fluorescent emitters and red phosphorescent hosts

Three terpyridine (TPY)/diphenylamine (DPA) derivatives, with DPA functioning as the electron donor and TPY as the electron acceptor, were designed and synthesized. By switching the position of the nitrogen atom in the substituted pyridine of TPY acceptors, we can adjust the electron-drawing strength of the TPY group, and hence, further modify the fluorescence, lowest unoccupied molecular orbital energy levels, carrier transporting properties of three compounds, but barely influence triplet energy levels. Three compounds satisfy the requirements of multifunctional blue fluorophores and are successfully used as highly efficient blue fluorescent emitters and red phosphorescent hosts in organic light-emitting devices (OLEDs). Non-doped blue fluorescent OLEDs that use TPY22DPA, TPY33DPA, and TPY44DPA as emitters exhibit maximum external quantum efficiencies (EQEs) of 4.9%, 3.8%, and 2.7%, respectively. Meanwhile, red phosphorescent OLEDs that use TPY22DPA, TPY33DPA, and TPY44DPA as host materials exhibit maximum EQEs of 19.1%, 20.9%, and 17.2%, respectively. These results are among the best reported multifunctional blue fluorophore efficiencies.

A high-efficiency hybrid white organic light-emitting diode enabled by a new blue fluorophor

A new efficient blue fluorophor 4-(4-diphenylaminophenyl)diphenylsulfone (SOTPA), with high triplet energy and balanced charge-transporting properties, has been designed and synthesized, and showed impressive performance both as blue emitter and as a host for phosphors. A green phosphorescent device containing SOTPA as host showed a maximum external quantum efficiency (EQE) as high as 19.2%, suggesting almost complete triplet harvesting from the blue fluorophor by the green phosphor. Single-emitting layer (EML) F–P hybrid white organic light-emitting devices (WOLEDs) based on SOTPA also gave outstanding electroluminescence performance, with a low turn-on voltage of 2.7 V and maximum EQE and power efficiency (PE) of 15.4% and 40.2 lm W−1, respectively. Even at a practical brightness of 1000 cd m−2 the PE still remained as high as 24.1 lm W−1. This excellent performance represents the highest efficiency yet reported among single-EML F–P hybrid WOLEDs.

Efficient visible light photocatalyst fabricated by depositing plasmonic Ag nanoparticles on conductive polymer-protected Si nanowire arrays for photoelectrochemical hydrogen generation.

Photoelectrochemical (PEC) water splitting to produce H2 is a renewable method for addressing the worldwide energy consumption increasing and fossil fuels storage shrinking. In order to achieve sustainable PEC H2 production, the semiconductor electrodes should have good photo-absorption ability, proper band positions, and chemical stability in aqueous condition. Different from the large-band-gap semiconductors such as TiO2, which can work efficiently under UV light, Si is an narrow-band-gap semiconductor that can efficiently absorb visible light; however, Si is indirect semiconductor and susceptible to photocorrosion in aqueous solution. In this paper, we demonstrate a new strategy of first protecting and then activating to develop a stable visible light photoanode for photoelectrochemical hydrogen production. This AgNPs/PEDOT/SiNW arrays show an encouraging solar-to-chemical energy conversion efficiency of 2.86 % and a pronounced incident photo-to-current conversion efficiency (IPCE) across the whole visible region. Our strategy proposed here contributes to further improvement of corrosion protection and solar energy harvesting for narrow-band-gap semiconductors that employed in visible light photoelectrochemical and photoelectric conversion applications.