Morphology and properties of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV): N,N′-bis(1-ethylpropyl)-3,4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) based solar cells

The influence of two components blend ratio, solution concentration and thermal annealing on the morphology of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV): N,N′-bis(1-ethylpropyl)-3,4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) blend films spin-cast from chloroform solutions has been studied using atomic force microscopy (AFM). The AFM images show that the dimension of the phase separation increases with the EP-PTC content and total solution concentration. When the annealing temperature increases from 90 to 150 °C, the EP-PTC crystal-like clusters grow rapidly. Solar cells based on MEH-PPV:EP-PTC blend films with different weight ratios were fabricated. The device with 1:3 weight ratio has a higher power conversion efficiency (PCE) of 0.072% compared with the devices with 1:1, 1:2 and 1:4 ratio, which increases by about 14 times over that of the device with 1:1 ratio that has a PCE of 0.005%. It is indicated that the optimum performance of the photovoltaic device is strongly related to the finer phase separation between MEH-PPV and EP-PTC on a submicron scale which enables an efficient dissociation of photogenerated excitons, and the pure EP-PTC phase can build up a percolating network with pathways large enough to enhance electron transport.     

Exciplex emission in the blend of two blue luminescent materials

Organic light-emitting diodes (OLEDs) based on the blend of two blue luminescent materials N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-diphenyl-4,4′-diamine (NPB) and 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) were fabricated. The electroluminescence (EL) spectra of this device showed a new emission that is different from their intrinsic exciton emission. Compared with the photoluminescence (PL) spectra of single layer NPB and PBD, respectively, there was an apparent red shift in that of their blend. Thus the exciplex formation in the blend can be concluded due to the similar emission in both PL and EL spectra. The exciplex formation process and the effect of applied voltage were analyzed by Gaussian fitting.     

PBD分子对聚合物发光二极管特性的影响

研究了由聚合物发光材料poly(2-methoxy,5-(2-ethy lhexyloxy)-1,4-phenyleneviny lene)(MEH-PPV)掺杂2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(PBD)制成的发光层厚度为80,170nm的高分子发光器件(PLEDs)。研究了PBD不同掺杂浓度时器件的电流密度-电压(J-V)和亮度-效率-电压(L-E-V)特性,发现PBD除传输电子外,还阻挡空穴的注入和传输。研究发现,PBD的最优掺杂浓度为20%,掺入PBD后MEH-PPV的EL光谱红移且发生窄化,当PBD掺杂浓度为40%时MEH-PPV的EL光谱窄化最明显,EL光谱半峰全宽从100nm减小到44nm。     

Photophysical characterizations of 2-(4-biphenylyl)-5 phenyl-1,3,4-oxadiazole in restricted geometry

Langmuir and Langmuir-Blodgett (LB) films of non-amphiphilic 2-(4-Biphenylyl)-5-phenyl-1,3,4-oxadiazole (abbreviated as PBD) mixed with stearic acid (SA) as well as with the inert polymer matrix poly(methyl methacrylate) (PMMA) have been studied. Surface pressure versus area per molecule (π-A) isotherm studies suggest that PBD molecules very likely stand vertically on the air-water interface and this arrangement allows the PBD molecules to form stacks and remain sandwiched between SA/PMMA molecules. At lower surface pressure, phase separation between PBD and matrix molecules occurs due to repulsive interaction. However, at higher surface pressure, PBD molecules form aggregates. The UV-vis absorption and steady-state fluorescence spectroscopic studies of the mixed LB films of PBD reveal the nature of the aggregates. H-type aggregate predominates in the mixed LB films, whereas I-type aggregate predominates in the PBD-PMMA spin-coated films. The degree of deformation produced in the electronic levels are largely affected by the film thickness and the surface pressure of lifting.     

The dependence of the ideality factor on the charge density of a conjugated polymer (MEH-PPV) doped with some laser dyes

Blends made of poly[2-methyl-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) conducting polymer and cresyl violet 670 (CV) and coumarin 460 (C₄₆₀) have been utilized for preparation of organic Schottky diodes. The I–V characteristics of these diodes are then determined and interpreted in terms of thermoionic emission (TIE) conduction process. Upon blending MEH-PPV with CV and C₄₆₀ dyes, the conduction is seen to completely be through TIE conduction. The turn on voltage for MEH-PPV diode is found to be 2.0 V and decreases with CV blending in contrast to the blend of MEH-PPV-C₄₆₀. The Schottky parameters are determined where the potential barrier is found to be around 0.75 V which is consistent with reported values. The charge densities of the respective blends are calculated and found to reduce by in MEH-PPV-C₄₆₀ blends while it has been enhanced in the CV samples by an order of magnitude compared that of MEH-PPV. The correlation between the ideality factor with the dielectric constant and the charge density is inspected. It is found that the ratio between the charge density of the polymeric blend and the charge density of the Al-electrode is crucial for obtaining low ideality factor.     

Femtosecond laser micromachining in the conjugated polymer MEH-PPV

Femtosecond-laser micromachining of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] films is investigated using 130 fs pulses at 800 nm from a laser oscillator operating at 76 MHz repetition rate. We investigate the effect of pulse energy and translation speed on the depth and morphology of the micromachined regions. We quantified the MEH-PPV photobleaching induced by the fs-laser, and the conditions in which the emission of MEH-PPV is preserved after the micromaching.     

制膜工艺对聚合物太阳电池性能影响的研究

用渡越时间法（TOF）分别测试了采用旋涂和滴涂方法制备的poly［2-methoxy-5-（2′-ethylhexyloxy）-1,4- phenylenevinylene］（MEH-PPV）薄膜的空穴迁移率,用原子力显微镜对这两种方法制备的薄膜表面形貌进行了研究.结果表明使用滴涂法有利于聚合物形成有序薄膜结构,能有效提高空穴迁移率.用滴涂法制备的基于MEH-PPV：phenyl C61- butyric acid methyl ester（PCBM）共混薄膜的太阳电池,对比用旋涂法制备的太阳电池,其能量 关键词： 太阳电池 聚合物 迁移率     

Valence band and core level X-ray photoelectron spectroscopy of lead sulfide nanoparticle-polymer composites

Valence band and core level X-ray photoelectron spectroscopy (XPS) were used to probe lead sulfide (PbS) nanoparticle-polymer nanocomposites. Composite materials were prepared by trapping commercially available monodisperse 3 and 10 nm PbS nanoparticles in two polymers, the non-conducting polymer, polystyrene, and the conjugated polymer, poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene (referred to below as MEH-PPV). The nanocomposites prepared from commercial nanoparticles underwent oxidation, mainly to form lead sulfate. However, the narrow size distributions of the commercial nanoparticles allowed observation of distinct changes in the valence band from the 3 to 10 nm nanoparticles. Nanocomposites of 2-5 and 4-7 nm PbS nanoparticles were synthesized by growing the particles in poly(vinyl alcohol) (referred to below as PVA) and MEH-PPV, respectively. These composites both indicated the formation of lead sulfide nanoparticles. Furthermore, the XP spectra for the PVA/PbS composite displayed bonding between the PbS nanoparticles and the polymer while MEH-PPV showed no PbS-polymer bonding. The nanoparticles synthesized in MEH-PPV did not undergo oxidation. The particle size distributions of the synthesized nanoparticles were too broad to display size-dependent changes in the valence band.     

Charge carrier injection and transport in polymer blend films

The steady current-voltage characteristics of single layer organic devices based on MEH-PPV and N,N′-diphenyl-N,N′-bis(4′-[N,N-bis(naphth-1-yl)-amino]-biphenyl-4-yl)-benzidine (TPTE) blend with different TPTE concentrations was investigated. The thickness dependence of the current-voltage relationship clearly demonstrates that the current at low voltage and at high voltage are all space charge limited. The current density-electric field characteristic proves the blend polymer LEDs to operate in the tunneling-controlled model. The effective hole mobility is directly determined by space charge limited current at high voltage and increases with increasing TPTE content in the blend. The EL efficiency shows concentration dependence, which is attributed to the change of the transport of holes in the blend film.     

The effect of electric field strength on electroplex emission at the interface of NPB/PBD organic light-emitting diodes

Organic light-emitting diode (OLED) based on two kinds of blue emission materials N,N′-bis(1-naphthyl)-N,N′-diphenyl-l,l′-diphenyl-4,4′-diamine (NPB) and 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) was fabricated. There is only one emission peak in photoluminescence (PL) spectrum which originates from NPB exciton emission. And the electroluminescence (EL) emission peaks have an apparent red-shift with the increase of driving voltage. The red-shift emission from exciplex emission could be ruled out. Thus, by the method of Gaussian fitting it should be ascribed to the overlap of exciton emission and electroplex emission which occurs at the interface between NPB and PBD. The formation of the electroplex emission under high electric field is analyzed.     

Stability of polymer thin-film transistors based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene)

Polymer thin-film transistors (PTFTs) based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) semiconductor are fabricated by spin-coating process and characterized. In the experiments, solution preparation, deposition and device measurements are all performed in air for large-area applications. Hysteresis effect and gate-bias stress effect are observed for the devices at room temperature. The saturation current decreases and the threshold voltage shifts toward the negative direction upon gate-bias stress, but carrier mobility hardly changes. By using quasi-static C-V analysis for MOS capacitor structure, it can be deduced that the origin of threshold-voltage shift upon negative gate-bias stress is predominantly associated with hole trapping within the SiO₂ gate dielectric near the SiO₂/MEH-PPV interface due to hot-carrier emission.     

高分子发光二极管载流子注入过程研究

采用交流阻抗谱，电容-电压，电容-频率等实验方法，研究了共轭高分子MEH-PPV(poly［2-methoxy，5-(2-ethylhexoxy)-1，4-phenylene vinylene］)发光二极管的载流子注入过程.对于结构为ITO/PEDOT/MEH-PPV/Ba/Al的发光器件，实验结果表明，电极界面是欧姆接触的，载流子的注入是非平衡的，器件薄膜中存在陷阱容易俘获注入电荷，形成空间电荷区，陷阱密度约为3.75×10¹⁶cm^-3. 关键词： 高分子发光二极管 交流阻抗谱 cole-cole图 载流子注入     

Study of solvent-conjugated polymer interactions by polarized spectroscopy: MEH-PPV and Poly(9,9′-dioctylfluorene-2,7-diyl)

Absorption, emission, and anisotropy measurements were performed on poly-[2-methoxy-5(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly-(9,9′-dioctylfluorene-2,7-diyl) (PF) solutions of various solvents, and in thin films deposited from them. The good correlation of MEH-PPV absorption and emission energy with Hildebrandt's dispersive parameter indicate that dispersive forces regulate the effective extent of the luminophore. The excitation and the emission spectra of α and β chains can be distinguished in PF solutions using the steady-state anisotropy. PF films show greater memory effect from the solutions from which they were spun than MEH-PPV. Anisotropy of MEH-PPV is very low, both in solutions and in films reflecting efficient energy migration. Anisotropy of PF in solutions and films demonstrates great differences in energy transfer efficiency within the α and β phases, while there is no energy transfer between these chain conformations.     

Broadband optical limiting performance of polymer-wrapped carbon nanotubes in the orange-NIR region

Soluble multi-walled carbon nanotubes (MWNTs) have been obtained by noncovalent modification with poly [2-methoxy,5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV). For the composite MWNT/MEH-PPV, there is π-π interaction between the MEH-PPV and MWNTs in addition to the wrapping of the polymer. The nonlinear optical transmittance was measured using a nanosecond optical parametric oscillator pumped with a Nd:YAG system. Excellent optical limiting performance of the composite MWNT/MEH-PPV was observed both in the visible region of 590-680 nm and at the wavelength of 1064 nm. By means of time-correlated single-photon counting fluorescence measurement, an explanation based on the nonlinear absorption of MWNT dominated by the intermolecular energy transfer was proposed.     

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.     

MEH-PPV与TiO2共混体系太阳电池性能分析

以MEH-PPV(poly(2-methoxy-5-(2′-ethylhexoxy)-1,4-phenylene vinylene)为电子给体材料(Donor,D), TiO₂纳米线为电子受体材料(Acceptor,A),制成了共混体系太阳电池. 从D/A材料共混体系的紫外可见吸收光谱(UV-vis)、光荧光谱(PL)、器件的电荷传输的光导J-V图等方面,分析了MEH-PPV∶TiO₂体系器件性能变化的原因. 得出了当在纯MEH-PP 关键词： 太阳电池 聚合物 性能     

Influence of tetrabutylammonium hexafluorophosphate (TBAPF6) doping level on the performance of organic light emitting diodes based on PVK:PBD blend films

The effect of doping level of tetrabutylammonium hexafluorophosphate (TBAPF₆) on the performance of single-layer organic light emitting diodes (OLEDs) with ITO/PVK:PBD:TBAPF₆/Al structure were investigated where indium tin oxide (ITO) was used as anode, poly(9-vinylcarbazole) (PVK) as hole-transporting polymeric host, 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as electron-transporting molecule and aluminium (Al) as cathode. It was found that the doped devices underwent a unique transition at the first voltage scan as indicated by drastically increasing of current at certain applied voltage. After the transition, the threshold voltage for current injection as well as the turn-on voltage decreased significantly as compared to the undoped device. The current injection threshold voltage and turn-on voltage decreased with the increase of TBAPF₆ doping level. More importantly, a relatively low current injection threshold voltage of 3 V has been achieved by doping a significant amount of TBAPF₆ (weight ratio greater than five) in the single-layer OLED based on PVK:PBD blend films with high work function Al metal as cathode. The significant improvement was attributed to the reduction of both electron and hole injection energy barriers caused by accumulation of ionic species at the interface.     

Electrical and optical characterization of (PEO+PVAc) polyblend films

Solid polymer blend films based on polyethylene oxide and polyvinyl acetate (PVAc) were prepared in various concentrations by solution cast technique. The features of complexation of the blend films were studied by X-ray diffraction. The electrical conductivity of films was found to increase with increasing PVAc concentration. The conductivity–temperature plots were found to follow Arrhenius nature and showed a decrease in activation energy with increasing PVAc concentration. Optical properties like absorption edge and direct and indirect band gaps were estimated for pure and blend films from their optical absorption spectra. It was found that the energy gap and band edge values shifted to lower energies on blending with PVAc.     

Effect of TiO2 Nanotubes on Polymer-Fullerene Bulk Heterojunction Solar Cells

We investigate the photovoltaic properties of hybrid organ/c solar cell based on the blend of poly[2-methoxy-5-（2- ethylhexoxy-l,4-phenylenevinylene） （MEH-PPV）, C60 and titanium dioxide （TiO2） nanotubes. In comparison of the composite devices with different TiO2：[MEH-PPV ＋C60] weight ratios of lw$.% （D1-1）, 2wt.% （D1-2）, 3wt.% （D1-3）, 5wt.% （D1-4）, 10wt.% （D1-5） and 20wt.% （D1-6）, it is found that the device Dl-a exhibits the best performance. The conversion efficiency is improved by a factor of 3 compared with the MEH-PPV：C60 device.     

溶剂效应对聚苯撑乙烯掺杂苝二酰亚胺太阳电池性能的影响

研究了不同溶剂对2-甲氧基-5-(2-乙基己氧基)-1，4-对苯撑乙烯(MEH-PPV): N,N′-二(1-乙基丙基)-3，4，9，10-苝四羧酸二亚酰胺(EP-PTC)复合膜的形貌及其对以MEH-PPV: EP-PTC复合膜为活性层的太阳电池性能的影响.结果表明：非芳香性溶剂不利于MEH-PPV与EP-PTC的相容，MEH-PPV与EP-PTC两相间形成微米尺寸(0.5—5 μm)的相分离，因而以MEH-PPV: EP-PTC复合膜为活性层的太阳电池中的电荷分离效率较低，进而电池的能量转换效率较低.而 关键词： 太阳电池 相分离 能量转换效率