Narrowband Pure Near-Infrared (NIR) Ir(III) Complexes for Solution-Processed Organic Light-Emitting Diode (OLED) with External Quantum Efficiency Over 16 %

Highly efficient near-infrared (NIR) emitters have significant applications in medical and optoelectronic fields, but the development stays a great challenge due to the energy gap law. Here, we report two NIR phosphorescent Ir(III) complexes which display emission peaks around 730 nm with a narrow full width at half maximum of only 43 nm. Therefore, pure NIR luminescence can be obtained without having a very long emission wavelength, thus alleviating the restriction of the energy gap law, and obtaining impressively high photoluminescence quantum yield up to 0.70. More importantly, the pure NIR organic light-emitting diode (OLED) fabricated by the solution-processed mothed shows outstanding device performance with the highest external quantum efficiency of 16.43 %, which sets a new record for solution-processed NIR-OLEDs based on different emitters. This work sheds light on the development of Ir(III) complexes with narrowband emissions as highly efficient pure NIR-emitters.     

Construction of a Hexameric Zn(II)‐metallomacrocycle and its Photo‐ and Electroluminescence Properties: [Zn6(O‐hexyl‐3,5‐bis(2,2′:6′,2″‐terpyridine)phenol)6(BF4)12]

Summary: An O‐hexyl‐3,5‐bis(terpyridine)phenol ligand has been synthesized and transformed into a hexagonal Zn(II)‐metallomacrocycle by a facile self‐assembly procedure capitalizing on terpyridine‐Zn(II)‐terpyridine connectivity. The structural composition was confirmed by NMR and mass spectral techniques; photo‐ and electroluminescence properties were also investigated. The OLED device shows green electroluminescent emission at 515 nm with a maximum luminance of 39 cd · m⁻² and maximum efficiency of 0.16 cd · A⁻¹.

Structure and electroluminescent properties of the metallomacrocycle investigated.     

Zig-Zag Type Molecular Design Strategy of N-Type Hosts for Sky-Blue Thermally-Activated Delayed Fluorescence Organic Light-Emitting Diodes

N-type hosts for long lifetime in sky-blue thermally-activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) were investigated by synthesizing four hosts with zig-zag-type backbone structure for high triplet energy. The four hosts had two CN units at different positions of the zig-zag-type backbone structure and two dibenzofuran units through either the 2 or 4-position of dibenzofuran. The position of the CN unit was controlled at the meta and para-positions in the zig-zag-type backbone to study the relationship between material parameters and lifetime of the TADF OLEDs. It was revealed that the meta-orientation of the CN units in the backbone was advantageous to extend device lifetime of the sky-blue TADF OLEDs.     

Theoretical investigations on electronic structures and photophysical properties of novel bridged triphenylamine derivatives

It has been proved that triphenylamine (TPA) derivatives can be excellent candidates for hole‐transporting materials in organic light‐emitting diodes (OLEDs). To improve on the thermal and morphological stability, a fully diarymethylene‐bridged TPA derivative (FATPA) which has been proven to enhance electroluminescent (EL) efficiency was synthesized. On the basis of FATPA, two series of novel bridged TPA derivatives have been designed by using diarylmethylene (Series A) or dimethyfluorene (Series B) as the linkage between the ortho‐positions of the phenyl rings in this work (see Fig. 1 ). To reveal the relationships between electronic structures and photophysical properties of these novel functional materials, an in‐depth theoretical investigation was elaborated via quantum chemical calculations using the density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods. In addition, the feasibility of using these bridged TPA derivatives as host in the device of ITO/MoO₃/NPB/mCP/host:Ir(ppy)₃/TAZ/LiF/Al was also evaluated, which including the discussion to their energy levels match with adjacent layers and energy transfer from host to guest. These calculated results show that photophysical properties can be easily tuned by the introduction of various substituent groups into the bridged TPA derivatives, such as the highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), the energies difference between the HOMOs and LUMOs (Δ_H‐L), the lowest singlet (E_S) and triplet (E_T) excitation energies, ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ) and the absorption and emission spectra, indicating that these bridged TPA derivatives have great potential applications for OLEDs. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Red‐Emitting Dendritic Iridium(III) Complexes for Solution Processable Phosphorescent Organic Light‐Emitting Diodes

Functionalization of a red phosphorescent iridium(III) complex core surrounded by rigid polyphenylene dendrons with a hole‐transporting triphenylamine surface allows to prevent the intermolecular aggregation‐induced emission quenching, improves charge recombination, and therefore enhances photo‐ and electroluminescence efficiencies of dendrimer in solid state. These multifunctional shape‐persistent dendrimers provide a new pathway to design highly efficient solution processable materials for phosphorescent organic light‐emitting diodes (PhOLEDs).     

Degradation of HTL layers during device operation in PhOLEDs

Different analytical tools and methodologies are currently employed to determine degradation products of organic blue light emitting devices in order to identify the failure mechanisms which determine the lifetime of these devices. This article provides a deeper understanding of degradation mechanisms of organic light emitting diodes (OLEDs) during device operation. Degradation products of blue emitting devices containing 8% of the phosphorescent emitter iridium(III)bis(4,6-difluorophenyl)-pyridinato-N,C^2′ picolinate (FIrpic) in a matrix containing bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminium (BAlq) as electron transport layer (ETL), 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA) and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine (α-NPD) were investigated using laser desorption ionization (LDI) coupled with a time of flight mass spectrometry (TOF/MS). Especially chemical degradation pathways of the hole transport materials TCTA and α-NPD were investigated. The comparison of experimental data of unstressed and stressed device revealed that new reaction products are formed during the device operation. The linkage of TCTA fragments to the α-NPD core in an interfacial reaction as well as a dimerization of TCTA itself was observed. Ten new reaction products could be characterized via LDI-TOF-MS. Some of these compounds might possess a negative influence on the drop of efficiency and lifetime of blue light emitting devices based on FIrpic.     

Concentration quenching effect of organic light‐emitting devices using DCM1‐doped tetraphenylgermole

We examine the concentration quenching of a 4‐(dicyanomethylene)2‐methyl‐6‐(p‐dimethylaminostyryl)‐4H‐pyran (DCM1)‐doped 1,1‐bis(2‐phenylethynyl)‐2,3,4,5‐tetraphenylgermole (HPAG)‐based light‐emitting diode. Originally, HPAG emits in the ~500‐nm (green) region, which can be converted to a red‐emission material by using DCM1 doping. As the DCM1 concentration increased from 1 to 10 wt%, the electroluminescence peak positions are red‐shifted from 604 to 644 nm, respectively. Increasing doping density not only shows the red‐shift but also shows decreasing luminance efficiency. Förster energy transfer between the HPAG host material and the DCM1 guest material is responsible for the strong red‐emission behavior. The calculated Förster radius (4.0 nm) for excellent Förster energy transfer characteristics with increasing doping concentration of DCM1 is consistent with experimental results. The maximum luminance efficiency was 6.64 cd/A at 11.0 mA/cm². The HPAG germole compound shows excellent red‐emission host–guest system properties for red organic light‐emitting device applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Silsesquioxane-based nanocomposite dendrimers with photo-luminescent and charge transport properties

The synthesis and characterization of octavinylsilsesquioxane (OVS)-based nanocomposite dendrimers with luminescent and charge transport properties are reported. The nanocomposite dendrimers were prepared in high yield using mild Heck chemistry of mono-haloaromatic compounds with the peripheral vinylsilane groups of OVS. Attachment of 2-naphthalene, 2-(9,9-dimethyl)fluorene, and 2-(4-phenyl)-5-(1-naphthyl)-1,3,4-oxadiazole resulted in materials with blue-violet emission (360-380 nm) and photo-luminescent quantum efficiencies (PLQEs) from 1 to 26%. Blue-green emission was observed for attachment of 1-pyrene, 9-anthracene, and N1-(4-phenyl)-N1,N4,N4-triphenylbenzene-1,4-diamine with PLQEs ranging from 23 to 50%. Despite the planar characteristics of the organic dendrons, the nanocomposite dendrimers are completely amorphous and have high glass transition temperatures (Tg) ranging from 115 to 186 degrees C with decomposition temperatures (Td) exceeding 450 degrees C. Matrix-assisted laser desorption ionization-time of flight shows that unlike traditional Heck chemistry, haloaromatic compounds are adding twice across the vinylsilane groups. Finally, organic light emitting diodes using the aromatic amine-based dendrimer as hole injection layers show 55% improvement in device efficiency over traditional materials (5.16 vs. 3.24 cd A(-1)) with brightness levels exceeding 40,000 cd m(-2).     

有机发光器件中空穴注入对负电容的影响

对不同结构的有机发光器件(OLED)进行了电容-电压(C-V)特性测量,研究了不同空穴注入结构对OLED负电容的影响。结果表明,负电容的产生与OLED内部电场的分布有着密切的关系,负电容开始出现的频率与电压的平方根呈指数关系。与超薄的单层空穴注入层相比,掺杂的空穴注入层不仅能降低器件的驱动电压,而且其载流子传输特性和出现负电容时的初始电压对频率有着更强的依赖性。     

基于新型连接层的有机叠层电致发光器件

制备了一种基于新的电荷生成层m-MTDATA∶MoO3的叠层有机电致发光器件。叠层器件与单发光层器件相比,发光亮度和电流效率均有成倍的提高。叠层器件的最大电流效率达到了30.06 cd/A,最大亮度为83 210 cd/m2,分别约为普通器件的2倍。除此之外,叠层器件在整个电流密度范围内的电流效率都很稳定。结果表明:m-MTDATA∶MoO3可以作为高效率的叠层有机电致发光器件的电荷生成层。