高效率共轭聚合物主体绿光磷光发光二极管

因电致发光效率高和器件制备工艺简单,聚合物为主体的绿色磷光电致发光成为一个研究热点.共轭聚合物的三线态能级一般低于绿色磷光材料的三线态能级,易对磷光的发光引起猝灭导致低的发光效率,所以较少被用作绿色磷光材料的主体.通过增加聚乙烯基咔唑（PVK）作为空穴传输层,获得了高发光效率的共轭聚合物聚芴（PFO）作主体绿色磷光发射,甚至高于相同条件下以PVK为主体的绿色磷光发射.究其原因,PVK的电子阻挡作用使发光中心靠近PVK与PFO的界面,界面处PVK因为其高的三线态能级增强了绿色磷光的发光.当三-（2-苯基吡啶）-Ir（Ir（ppy）₃）掺杂浓度为2％时得到了最高的亮度效率24.8 cd/A,此时的电流密度为4.65 mA/cm²,功率效率为11 lm/W,最高亮度达到35054 cd/m²,色坐标是（0.39,0.56）. 关键词： 共轭聚合物 磷光 绿光发光     

Enhanced Green Electrophosphorescence from Oxadiazole-Functionalized Iridium Complex-Doped Devices Using Poly（9,9-Dioctylfluorene） Instead of Poly（N-Vinylcarbazole） as a Host Matrix

Optoelectronic properties of the oxadiazole-functionalized iridium complex-doped polymer light-emitting devices （PLEDs） are demonstrated with two different polymeric host matrices at the dopant concentrations 1-8%. The devices using a blend of poly（9,9-dioctylttuorene）（PFO） and 2-（4-biphenyl）-5-（4-tert-butylphenyl）-1,3,4-oxadiazole （PBD） as a host matrix exhibited a maximum luminance efficiency of 11.3 cd/A at 17. 6 mA/cm^2. In contrast, the devices using a blend of poly（N-vinylcarbazole） （PVK） and PBD as a host matrix reveal only a peak luminance efficiency of 6.Scd/A at 4.1 mA/cm^2. The significantly enhanced electrophosphorescent emissions are observed in the devices with the PFO-PBD blend as a host matrix. This indicates that choice of polymers in the host matrices is crucial to achieve highly efficient phosphorescent dye-doped PLEDs.     

High performance polymer light-emitting diodes doped with a novel phosphorescent iridium complex

High performance polymer light-emitting diodes (PLEDs) based on a phosphor of noble metal complex bis(1,2-dipheny1-1H-benzoimidazole) iridium (acetylacetonate) [(pbi)₂Ir(acac)] doped in poly(N-vinylcarbazole) (PVK) host with various concentration were demonstrated. The photoluminescence (PL) and electroluminescence (EL) spectra of the PLEDs exhibited an emission intensity decrease of PVK and a gradually enhanced feature of (pbi)₂Ir(acac) with increased doping concentration. The device with a 5 wt% (pbi)₂Ir(acac) doped PVK system showed a high power efficiency of 3.84 lm/W and a luminance of 26,006 cd/m². The results indicated that both energy transfer and charge trapping have a significant influence on the performance of PLEDs. The devices have a broadened EL spectrum of full-width at half-maximum (FWHM) more than 100 nm, which can be realized for WOLEDs.     

Optimization of polymeric host composition for polymer-based electrophosphorescent devices

We have demonstrated an optimized polymeric host material comprising a blend of poly(9-vinylcarbazole) (PVK) and a fluorescent polymer for a highly efficient electrophosphorescence system. Although the chemical compatibility between the blue-emitting-fluorescent polymer and iridium complex, tris[2-phenylpyridine]iridium(III) (Ir-(ppy)₃), is very poor, efficient energy transfers from the blended host to the Ir complex was observed when a small amount of blue-emitting-fluorescent polymer was added to the PVK matrix. The device showed a maximum external quantum efficiency at 5 wt% blue-emitting-fluorescent polymer and 8 wt% Ir complex doping concentrations.     

Enhancement of efficiency of multilayer polymer light-emitting diodes by inserting blocking layers

In this study, the electroluminescence efficiency of the blue-green polymer light-emitting diodes (PLEDs) is enhanced by the insertion of blocking layers. PLEDs are multilayered structures prepared with spin-coating and thermal evaporation. Blue host is doped with green guest to form a single emission layer. Poly(9-vinylcarbazole) (PVK) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) are used as materials for the blocking layers. The optimal thicknesses of the PVK and BCP layers are 10 and 0.2 nm, respectively. PVK plays an important role of blocking holes and electrons, and BCP not only confines holes in the emission layer but also enhances the injection of electrons from Alq₃ to the emission layer. The efficiency of a PLED with a dual-blocking layer is 2.37 times higher than that of a PLED without a blocking layer prepared because of the improved carrier balance and the enhanced carrier recombination.     

DCM掺杂PVK体系的超快光谱

利用稳态荧光光谱和时间分辨超快光谱研究了DCM掺杂PVK(聚乙烯咔唑)体系的发光特性和能量转移。根据DCM的吸收光谱与PVK的荧光光谱,用Frster理论估算出DCM:PVK掺杂体系能量转移的临界半径及其效率。在DCM:PVK掺杂薄膜中,随着掺杂浓度的升高,DCM的发射强度增强,PVK的发射强度减弱,两者相对强度之比与估算结果一致。还利用时间分辨超快光谱研究了DCM:PVK掺杂薄膜体系的能量转移动力学过程,观察到DCM:PVK掺杂薄膜的荧光寿命随着掺杂浓度的升高逐渐变短。结果表明,在DCM:PVK掺杂薄膜中,存在从PVK到DCM较为有效的Frster能量转移。     

Solution-processed white organic light-emitting diodes with mixed-host structures

Efficient white light-emitting diodes (WOLEDs) were fabricated with a solution-processed single emission layer composed of a molecular and polymeric material mixed-host (MH). The main host used was a blue-emitting molecular material of 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) and the assisting host used was a hole-transport-type polymer of poly(9-vinylcarbazole) (PVK). By co-doping 4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl and 5,6,11,12-tetraphenylnaphacene into the MH, the performances of the fabricated devices made with different mixing ratio of host materials were investigated, and were to depend on the mixing ratios. Under the optimal PVK:DPVBi ratio (3:7), we achieved a maximum luminance of 14 110 cd/m² and a maximum current efficiency of 9.5 cd/A. These improvements were attributed to the MH structure, which effectively improved the thermal stability of spin-coated film and enhanced the hole-injection/transporting properties of WOLEDs.     

掺咔唑取代卟啉铂的高效聚合物红色磷光发射

以笼形多面体硅氧烷(POSS)封端的聚烷基芴PFO(poss)为主体，掺杂电子传输的NFDA3二唑衍生物PDB，以新型磷光化合物6CPt作为客体得到了高效红光聚合物发光二极管，不仅获得高效率发光(最大外量子效率达到568%)，而且发现PBD在器件中除了起到电子传输的作用之外，还能有效促进激发态能量由PFO(poss)向6CPt进行转移. 关键词： 聚合物磷光器件 卟啉铂络合物 电子传输材料     

Efficient polymer white-light-emitting diodes with a single-emission layer of fluorescent polymer blend

Efficient polymer white-light-emitting diodes (WPLEDs) have been fabricated with a single layer of fluorescent polymer blend. The device structure consists of ITO/PEDOT/PVK/emissive layer/Ba/Al. The emissive layer is a blend of poly(9,9-dioctylfluorene) (PFO), phenyl-substituted PPV derivative (P-PPV) and a copolymer of 9,9-dioctylfluorene and 4,7-di(4-hexylthien-2-yl)-2,1,3-benzothiadiazole (PFO-DHTBT), which, respectively, emits blue, green and red light. The emission of pure and efficient white light was implemented by tuning the blend weight ratio of PFO: P-PPV: PFO-DHTBT to 96:4:0.4. The maximum current efficiency and luminance are, respectively, 7.6 cd/A at 6.7 V and 11930 cd/m² at 11.2 V. The CIE coordinates of white-light emission were stable with the drive voltages.     

Luminescence properties of poly(9,9-dioctylfluorene)/polyvinylcarbazole blends: Role of composition on the emission colour stability and electroluminescence efficiency

Light-emitting diodes (LEDs), based on blue-emitting polyfluorenes are usually prone to the appearance of a contaminant green emission (centered around 520 nm), leading to an apparent whitish light emission. We find that, for LEDs based on poly(9,9-dioctylfluorene), PFO, the blending with the hole transporting polyvinylcarbazole, PVK, can suppress such green emission. LEDs based on a PFO/PVK blend with a 1:2 weight ratio and with aluminum cathodes show a quite stable blue emission. This result reveals the important role played by the interchain interactions on the observed contaminant green emission. In addition, we observe that in Al-based devices blending causes a decrease in EL efficiency while in Mg-based devices we obtained higher efficiencies with the blend PFO:3PVK when compared with neat PFO-based devices.     

Efficient white polymer light-emitting diodes based on a phosphorescent iridium complex and a fluorescent silole and carbazole copolymer

White polymer light-emitting diodes (WPLEDs) were fabricated with blue phosphorescent iridium bis(2-(4,6-difluorophenyl)-pyridinato-N,C²′) picolinate (FIrpic) and red fluorescent silole and carbazole copolymer PCz-MPTST within a poly(N-vinylcarbazole) (PVK): 1,3-bis[(4-tert-butylphenyl)-1,3,4- oxadiazolyl] phenylene (OXD-7) host matrix. Efficient white emission consisting two emission peaks was achieved with luminous efficiency of 9.2 cd/A and CIE coordinates of (0.37, 0.40). By means of transient photoluminescence response, energy transfer among the blending components was investigated and discussed.     

Numerical simulation of single layer polymer light-emitting diodes

A numerical model for the electrical properties for polymeric light-emitting diodes (PLEDs) is presented which accounts for drift- and diffusion transport, recombination and re-emission processes. The current–voltage characteristics of single layer polymer light-emitting diodes are found to be dominated by the space-charge limited bulk hole-conductivity. The device efficiency is found to increase with bias as electron current is strongly reduced by injection barrier. The operating voltage increases with increased thickness of polymer layer. The understanding of these characteristics will facilitate the further optimization of the performance of polymer LEDs.     

Enhanced luminance of MEH-PPV based PLEDs using single walled carbon nanotube composite as an electron transporting layer

An efficient electron transporting layer (ETL) based on single walled carbon nanotube (SWCNT) composites has been developed for poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) based orange polymer light emitting diodes (PLEDs) and its effect on the performance of PLEDs has been examined. It is observed that with increase in SWCNT concentration, in ETL, the luminance and luminous efficiency of the PLEDs increase (about 5 times increase in luminance is observed at 5% w/w SWCNT concentration). The SWCNTs present in the MEH-PPV ETL boost the mobility of electrons injected from the cathode towards the emissive layer by establishing highly conducting percolation paths. This balances the concentration of holes and electrons in the emissive layer, which leads to enhanced emission from the PLEDs.     

Influence of dipole moments on light-emitting features of cardo-type 1H-pyrazolo[3,4-b]quinolines

Several 1H-pyrazolo[3,4-b]quinoline derivatives were synthesized from 9,9′-di(p-aminophenyl)fluorene as possible dye chromophore for the organic light-emitting diodes. All the compounds exhibit strong fluorescence in solution and in solid state as well. The maximally achieved brightness was 65 Cd/m² and spectral range of electroluminescence (EL) covers the wavelength ranges from 420 up to 470 nm. The prepared compounds were used as dye luminophores in poly(N-vinylcarbazole) (PVK) matrix for single-layer EL light-emitting device. Principal goal of the work consists in an establishment of a possibility to operate by their light-emitting features (spectral positions of emitting lines, efficiency of electroluminescence, brightness, etc.) by appropriate changes of state dipole moments of the particular chromophore determined by semi-empirical quantum chemical calculations. The principal physical mechanism of such effects is explained within dipole-dipole interactions between the dye chromophores and PVK polymer chains.     

Effects of UV-ozone treatment on the electronic structures of F8BT and PFO polymeric thin films

The property changes of polymeric films upon degradation are important to develop strategies to prolong the device lifetimes. In this regard, we investigated the effects of ultraviolet-ozone (UVO) treatment on the electronic structures of poly (9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) films. We found that as the UVO treatment time increased, the intensities of the UV–vis and photoluminescence spectra of both F8BT and PFO films exponentially decayed owing to the destruction of the conjugated system of the films. As per the X-ray photoelectron spectra, both the F8BT and PFO films showed significant oxidation and p-doping effects upon UVO treatment. In addition, UVO treatment caused the etching of the polymeric films, and their thickness gradually decreased; the etching rate with UVO treatment was faster for PFO than for F8BT. These results indicate that the functionalization of polymers with UVO treatment requires the careful consideration of the resulting changes in their electronic structure.     

碳纳米管受限空间对共轭高分子聚(9,9-二辛基芴-2,7-二基)链段运动行为的影响

在纳米受限空间中,高分子往往会表现出与本体状态不同的性质,如异常的链段运动特性及晶相间转变行为等,这些性质对于研究和开发新型高分子材料具有重要的意义,因此针对受限环境下高分子的物理化学特性研究也一直是高分子界关注的焦点.本文通过化学气相沉积法制备垂直取向排列的多壁碳纳米管阵列,借助溶剂润湿–收缩法获得规整的高密度阵列结构,其取向排列的碳纳米管间隙形成了准一维的纳米受限空间,尺寸在5—50 nm尺度下可调.进一步将共轭高分子聚(9,9-二辛基芴-2,7-二基)(PFO)填充到碳管间隙的纳米空间中,制备PFO与取向多壁碳纳米管阵列复合膜.结果发现在碳纳米管形成的纳米受限空间中,PFO的链段热运动行为与本征态PFO薄膜相比受到了明显的抑制,不同晶型间转变速度大大减缓,提高了构象的热稳定性,同时取向排列的碳纳米管对PFO分子链取向排列分布具有明显的诱导作用,有利于获得高性能的PFO晶体.这种高密度取向排列的碳纳米管阵列结构未来可以用于制备优良发光性能及高稳定性的PFO光电器件.     

Synthesis, structure and electroluminescent properties of Schiff-base boron complex with anilido-imine ligand

The Schiff-base ligand boron complex, LBF₂ [L=ortho-C₆H₄(NC₆H₃Me₂-2,6)(CH=NC₆H₃Me₂-2,6)], is synthesized and characterized. The crystal structural study reveals that central boron atom is four coordinate and adopts a distorted tetrahedral geometry in LBF₂. The photo/electroluminescent properties of the boron complex have been studied. The electroluminescent devices were fabricated by doping LBF₂ in polymer blends host of poly(vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD) using simple solution spin-coating technique. The single-layer polymer organic light emitter devices exhibited blue-green emission with maximum current efficiency of 1.6 cd/A and maximum luminance of 840 cd/m².     

修饰阴极界面提高聚合物白光二极管发光效率

利用聚合物的不同溶解性,研究用旋涂方法制备双层高分子白光二极管(WPLED),采用器件结构为：ITO/PEDOT(50nm)/PVK:PFO-BT: PFO-DBT(40nm)/PFO(40nm)/Ba(4nm) /Al(120nm),当相对比例为PVK: PFO-BT:PFO-DBT=1∶4%：3%时,得到标准白光,最大电流效率为2.4 cd/A,最大亮度为3215 cd/m²,色坐标为(0.33,0.34).用水溶性的聚电介质层修饰阴极界面,器件效率可以进一步提高到5.28 cd 关键词： 聚合物发光二极管 白光 双发光层结构     

Synthesis and characterization of a solution processible deep blue light-emitting molecule composed of fluorene and pyrene units

A solution processible deep blue light-emitting molecule composed of pyrene and dialkylfluorene units, 1,6-bis(9,9′-dioctylfluorene-2-yl)pyrene (BDOFP) was synthesized and characterized. The synthesized compound was soluble in common organic solvents and the solution gave a smooth thin film after spin coating. The compound was characterized by using thermogravimetric analysis (TGA), differential calorimetry (DSC), UV–visible spectroscopy, fluorescence spectroscopy and cyclic voltammetry. The maximum UV–visible absorption and PL emission of BDOFP thin film were more red-shifted than those of BDOFP solution due to strong intermolecular interaction between flat segments. To improve color purity and film stability BDOFP was doped to a well-known charge-transporting polymer, poly(N-vinylcarbazole) (PVK). BDOFP thin film showed it maximum PL at 457 nm but the thin films of BDOFP doped PVK films showed it at 443 nm. Organic light-emitting diodes were fabricated with the simple structure of ITO/PEDOT:PSS/emitter/BmPyPB/LiF/Al configuration. BDOFP or three kinds of BDOFP:PVK blends with different ratios (10:90, 30:70, 50:50 by weight) were used as the emissive layers and [1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene] (BmPyPB) as the electron-transporting layer. All of light-emitting devices showed their electroluminescence in blue region of spectrum, especially EL using BDOFP: PVK (1:9) showed a deep-blue light emission with CIE coordinates of (0.14, 0.07). Maximum brightness, external quantum efficiency and current efficiency of the device were 500 cd/m², 0.7% and 0.44 cd/A, respectively.     

The effect of driving voltage on the electroluminescent property of a blend of poly(9-vinylcarbazole) and 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole

The impact of driving voltage on the electroluminescence (EL) from organic light emitting diode with ITO/PVK:PBD:TBAPF₆(10:10:1)/Al structure was analyzed by the method of Gaussian fitting. Indium tin oxide (ITO) was used as anode, poly(9-vinylcarbazole) (PVK) as polymeric host, 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as electron-transporting molecule, tetrabutylammonium hexafluorophosphate (TBAPF₆) as organic salt and aluminium (Al) as cathode. A broad EL has been observed and it could be attributed to the overlap of emission from four different excited state complexes, including PVK:PBD exciplex, PVK:PBD electroplex, PBD electromer and PVK electromer. The EL spectra shifted to longer wavelength with the increase of driving voltage. The ratio of PVK electromer to PVK:PBD exciplex emission intensity first declined slightly and then increased remarkably, while the relative intensity of combination of PVK:PBD electroplex and PBD electromer emission remained unchanged when the voltage was increased.