柔性有机电致发光器件制备及光电性能研究

制作了结构为ITO／PVK：TPD／Alq3／Al、分别以PET为衬底的柔性的和以玻璃为衬底的普通的有机电致发光二极管（OLED）,对两种器件的电流密度-电压曲线、光电流-电压曲线及量子效率-电流密度曲线进行了测量与分析。结果表明,它们的光电特性非常接近,但柔性OLEDs（FOLEDs）的开启电压略高;在20V电压驱动下,FOLEDs的亮度达到1000cd／m^2,量子效率为0．27％。对器件进行了抗弯折性能的测试。     

Organic light-emitting devices based on new rare earth complex Tb（p-CIBA）3phen

A new rare earth complex Tb（p-CIBA）3phen was synthesized and introduced into organic tight emitting devices （OLEDs） as emitting material. The Tb（p-CIBA）3phen was doped into PVK to improve the filmforming and hole-transporting property. Two kinds of devices were fabricated. The device structure is as the following. Single-layer device： ITO/PVK： Tb （p-CIBA） 3 phen /LiF/Al; double-layer device： ITO/PVK： Tb（p-CIBA）3phen/AIQ/LiF/AI. The performances of both devices were investigated carefully. We found that the emission of PVK was completely restrained,and only the green emission was observed from the electroluminescence. The full width at half maximum （FWHM） was less than 10 nm. The highest EL brighthess of the single-layer device is 25.4 cd/cm^2 at a fixed bias of 18 V,and the highest EL brightness of the double-layer device reaches 234.8 cd/cm^2 at a voltage of 20 V.     

Influence of reaction temperature on the formation process of ZnO quantum dots and the optical properties

ZnO quantum dots (QDs)with the sizes of 3.0-5.6 nm are synthesized by solution-phase method at different temperatures. We find that temperature has great influence on the size of ZnO QDs. The growth process is the most sensitive to temperature, and the process is well explained by Lifshitz-Slyozov-Wagner (LSW) model. By photoluminescence (PL) spectra of the quantum dots at different temperatures and reactive time, we come to a conclusion that ultraviolet emission is mainly due to surface defects, and the or...     

High power output quasi-continuous-wave nanosecond optical parametric generator based on periodically poled lithium niobate

We report on a high power output quasi-continuous-wave nanosecond optical parametric generator （OPG） of congruent periodically poled lithium niobate （PPLN） pumped by a 1 064 nm acousto-optically Q-switched Nd-YVO4 laser （duration. 70 ns,repetition rate：45 kHz,spatial beam quality M2〈 1,3）. The OPG consists of a 38.7 mm long PPLN crystal with a domain period of 28.93 μm. With 5.43 W of average pump power the maximum average output power is 991 mW at 1 517.1 nm signal wave of the PPLN OPG.     

White organic light-emitting diodes based on emission from DPVBi-doped 4,48-bis (2,28-diphenylvinyl)-1, 18-biphenyl

Organiclight-emitting diodes (OLEDs) have beenin-vestigated for many years on account of their highlumi-nance,low driven voltages ,wide visual range,flexiblesubstratesinflat-panel ,full color displays and backlightapplications .For high brightness and eff…     

Influence of connecting units’ thicknesses on tandem organic devices’ performances

The present work investigates the influence of the Alq₃:Mg and MoO₃ thicknesses in the connecting unit on the performance of tandem organic light-emitting devices (OLEDs). By systematically varying the Alq₃:Mg and MoO₃ thicknesses, we obtained a higher current efficiency of 37.3 cd/A for a device with 30 nm Alq₃:Mg and 3 nm MoO₃ layer as connecting units. The optimal device performance is enhanced by at least 14%, compared with those of devices we fabricated in this paper. It suggests that appropriate Alq₃:Mg and MoO₃ thicknesses can enhance the charge generating ability for connecting units. On the other hand, it was found that the charge transporting layer would decrease strongly because of much thicker or thinner MoO₃ thicknesses. The results demonstrate that it is an effective method to improve the performance of OLEDs by using a optimal thickness for Alq₃:Mg and MoO₃ layers.     

Crystallization of μc-Si on plastic substrate by using a pulsed double-frequency YAG laser

Thin film transistors （TFTs） of microcrystalline silicon （μc-Si） can provide higher mobility and stability than that of a-Si and better uniformity than that of poly-Si TFTs, and it would be more suitable to be applied to larger-area AMOLEDs. By using 2coYAG laser ann. ealing, crystalline μc-Si thin film on plastic substrate has been investigated and the proper laser energy needed for crystallization has been indicated. It has been found that the dehydrogenation process at 300-450℃ for a few of hours could be omitted by decreasing the H content in the crystallization precursor, which is suitable for laser crystallization on plastic substrates. The crystalline volume fraction （Xc） and the grain size of the resulted μc-Si could be adjusted by controlling the laser energy. By this method, the μc-Si on plastic substrate with Xc and grain size is respectively 85% （at the maximum） and 50 nm.     

High performance blue organic light-emitting devices fabricated by using the doped AIq3 in NPB hole transmistion layers

We have designed a new structure blue emission device with doped Alq3 of 3% in hole transmission layers of NPB. The CIE coordination of the devices is （0.17,0.19）. The maximum electroluminescence efficiency is 4.1 cd/A at 11 V, the brightness is 118.8 cd/m^2 at 7 V, and the maximum brightness is 10770 cd/m^2 at 13 V.     

P-μc-Si1-xGex ：H thin film by VHF-PECVD

In this paper, a series of boron doped microcrystalline hydrogenated silicon-germanium （p-μc-Si1-xGex：H） was deposited by very high frequency plasma-enhanced chemical vapor deposition （VHF-PECVD） from SiH4 and GeF4 mixtures. The effect of GeF4 concentration on films＇ composition, structure and electrical properties was studied. The results show that with the increase of GeF4 concentration, the Ge fraction x increases. The dark conductivity and crystalline volume fraction increase first, and then decrease. When the GC is 4%, p-μc-Si1-xGex：H material with high conductivity, low activation energy （σ= 1.68 S/cm, E8=0.047 eV）, high crystalline volume fraction （60%） and with an average transmission coefficient over the long wave region reaching 0.9 at the thickness of 72 nm was achieved. The experimental results were discussed in detail.     

Tuning of the electrical characteristics of organic bistable devices by varying the deposition rate of Alq3 thin film

Organic bistable devices with an Al/Alq₃/n-type Si structure are investigated at different deposition rates of Alq₃ thin film. We can obtain current–voltage characteristics of these devices similar to those of metal/organic semiconductor/metal structures that are widely used for organic bistable devices. The bistable effect of the Al/Alq₃/n-type Si structure is primarily caused by the interface defects at the Al/Alq₃ junction. Moreover, the electrical properties of these devices can be modified and controlled by utilizing the appropriate deposition rates of the Alq₃ thin film by thermal deposition. XPS, AFM, and GIXRD measurements are performed to characterize the properties of Alq₃ thin film and Alq₃/Al interface. This type of devices involves an extremely simple fabrication process and offers great potential in future advanced organic electronics.     

Color switching behaviors of organic bistable light-emitting devices fabricated utilizing an aluminum-nanoparticle-embedded tris(8-hydroxyquinoline)aluminum layer and double emitting layers

Organic bistable light-emitting devices (OBLEDs) with an aluminum (Al)-nanoparticle-embedded tris(8-hydroxyquinoline)aluminum (Alq₃) layer and double emitting layers (EMLs) were fabricated to investigate their color switching behaviors. Scanning electron microscopy images showed that Al nanoparticles were formed on the Alq₃ layer. The Al nanoparticles in the Alq₃ layer improved the storage margin of the organic bistable devices (OBDs), and the double EMLs changed the emission color of the organic light-emitting devices (OLEDs) according to the variations of the ON and the OFF states of the OBDs. The variations of the ON and the OFF states of the OBDs could be clearly distinguished by the color switching of the OLED. The luminances of the OBLEDs with double EMLs in the ON and the OFF states were 641.80 and 22.25 cd/m², respectively, and their CIE coordinates at 20 V were (0.42, 0.46) and (0.51, 0.47), respectively, which corresponded to the ON and the OFF states of the OBLEDs.     

Applying Hopfield neural network to QoS routing in communication network

The main goal of routing solutions is to satisfy the requirements of the Quality of Service （QoS） for every admitted connection as well as to achieve a global efficiency in resource utilization. In this paper proposes a solution based on Hopfield neural network （HNN） to deal with one of representative routing problems in uni-cast routing, i. e. the multi-constrained（MC） routing problem. Computer simulation shows that we can obtain the optimal path very rapidly with our new Lyapunov energy functions.     

Enhancement and stability of luminescence in thin-film light-emitting devices based on heterostructure of ladder-type poly (p-phenylene)

The microcavity thin-film light-emitting devices were fabricated, which use two organic material layers, ladder-type poly(p-phenylene) (LPPP) and (8-hydroxyquimalin) aluminum (Alq₃), sandwiched between two injecting electrodes. With the ribbon-type macromolecule structure, the LPPP exhibits higher thermal and chemical stability than its linear analog. The broad photoluminescence (PL) and electroluminescence (EL) emission means LPPP can be tuned over the full visible region. LPPP was the emitting layer and the cavity transporter. Alq₃ was the electron transporter. The investigation on EL and PL properties of the devices indicated that the microcavity effect has been achieved by adjusting the thickness of organic light-emitting layers. The experimental results showed that directional emission and net emission were efficiently enhanced. The heavily born-doped diamond electrode in place of the metal electrode aluminum can also greatly improve the stability of the devices.     

Origin of improvement in device performance via the modification role of cesium hydroxide doped tris(8-hydroxyquinoline) aluminum interfacial layer on ITO cathode in inverted bottom-emission organic light-emitting diodes

It has been found that cesium hydroxide (CsOH) doped tris(8-hydroxyquinoline) aluminum (Alq₃) as an interfacial modification layer on indium-tin-oxide (ITO) is an effective cathode structure in inverted bottom-emission organic light-emitting diodes (IBOLEDs). The efficiency and high temperature stability of IBOLEDs with CsOH:Alq₃ interfacial layer are greatly improved with respect to the IBOLEDs with the case of Cs₂CO₃:Alq₃. Herein, we have studied the origin of the improvement in efficiency and high temperature stability via the modification role of CsOH:Alq₃ interfacial layer on ITO cathode in IBOLEDs by various characterization methods, including atomic force microscopy (AFM), ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS) and capacitance versus voltage (C–V). The results clearly demonstrate that the CsOH:Alq₃ interfacial modification layer on ITO cathode not only enhances the stability of the cathode interface and electron-transporting layer above it, which are in favor of the improvement in device stability, but also reduces the electron injection barrier and increases the carrier density for current conduction, leading to higher efficiency.     

Increase of current density and luminance in organic light-emitting diode with reverse bias driving

When applying the voltage pulses (6 V) to the organic light-emitting diode based on tris(8-hydroxyquinolinato) aluminium (Alq₃) as the electron transporting layer, current density and luminance increased by 16% and 20%, respectively, by providing the reverse bias (−16 V) during the off-period. By using displacement current measurement, we can deduce that such an enhancement resulted from the interfacial positive charges trapped at the Alq₃/cathode interface, with the relaxation time ∼0.4 ms. By doping the organic material as the carrier trapping sites at Alq₃/cathode interface, such current density and luminance increase can be further enhanced. 25% and 36% increase in current density and luminance was demonstrated with such driving technique, respectively.     

Nonvolatile memory and opto-electrical characteristics of organic memory devices with zinc oxide nanoparticles embedded in the tris(8-hydroxyquinolinato)aluminum light-emitting layer

The nonvolatile organic memory devices based on the tris(8-hydroxyquinolinato)aluminum (Alq₃) emitting layer embedded with zinc oxide nanoparticles (ZnO-NPs) are reported. The devices have a typical tri-layer structure consisting of the Alq₃/ZnO-NPs/Alq₃ layers interposed between indium tin oxide (ITO) and aluminum (Al) electrodes. An external bias is used to program the ON and OFF states of the device that are separated by a four-orders-of-magnitude difference in conductivity. No significant degradation of the device is observed in either the ON or OFF state after continuous stress (∼10⁵ s) and multicycle (∼10³ cycles) testings. These nanoparticles behave as the charge trapping units, which enable the nonvolatile electrical bistability when biased to a sufficiently high voltage. Impedance spectroscopy, capacitance–voltage (C–V) and current–voltage (I–V) analysis are used to verify the possible physical mechanism of the switching operation. Moreover, it is found that the location of the ZnO-NPs could affect the memory and opto-electrical characteristics of the devices, such as the ON/OFF ratio, threshold voltage and turn-on voltage, which can be attributed to the influence of the ZnO-NPs and diffused Al atoms in the bulk of the Alq₃ layer.     

Mechanical modeling of flexible OLED devices

General expressions are deduced for the stresses developed in the individual thin layers of a multi-layer structure as a result of bending to a specified radius. These are appropriate for analysing flexible organic light emitting diode (FOLED) devices on flexible substrates. Residual stress (caused internally by temperature change and differential thermal expansion) after material deposition and return to ambient temperatures is not considered. The reduced elastic modulus of the typical small molecule OLED materials: N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPD) and tris-(8-hydroxyquinoline)aluminum (Alq₃) are measured as thin-films using nano-indentation techniques. A conventional device: polyethylene terephthalate (PET)/Buffer layer (BL)/ITO/OLED/Al is considered from a modeling standpoint, as a preliminary to actual fabrication and subsequent comparative testing of OLED performance on rigid and flexible supports.     

Improved property in organic light-emitting diode utilizing two Al/Alq3 layers

We reported on the fabrication of organic light-emitting devices (OLEDs) utilizing the two Al/Alq₃ layers and two electrodes. This novel green device with structure of Al(110 nm)/tris(8-hydroxyquinoline) aluminum (Alq₃)(65 nm)/Al(110 nm)/Alq₃(50 nm)/N,N′-dipheny1-N, N′-bis-(3-methy1phyeny1)-1, 1′-bipheny1-4, 4′-diamine (TPD)(60 nm)/ITO(60 nm)/Glass. TPD were used as holes transporting layer (HTL), and Alq₃ was used as electron transporting layer (ETL), at the same time, Alq₃ was also used as emitting layer (EL), Al and ITO were used as cathode and anode, respectively. The results showed that the device containing the two Al/Alq₃ layers and two electrodes had a higher brightness and electroluminescent efficiency than the device without this layer. At current density of 14 mA/cm², the brightness of the device with the two Al/Alq₃ layers reach 3693 cd/m², which is higher than the 2537 cd/m² of the Al/Alq₃/TPD:Alq₃/ITO/Glass device and the 1504.0 cd/m² of the Al/Alq₃/TPD/ITO/Glass. Turn-on voltage of the device with two Al/Alq₃ layers was 7 V, which is lower than the others.     

CdS薄层对有机电致发光器件性能的影响

将光电材料硫化镉(CdS)薄层插入到结构为ITO/NPB/Rubrene/NPB/DPVBi/Alq3/LiF/Al的白光有机发光器件(OLED)的Alq3和LiF之间,研究了CdS对OLED性能的影响。结果表明,0.1nm厚的CdS插入Alq3和LiF之间的器件性能最好。器件电压从7 V变化到14 V时,色度均在白光的中心区域;当电压为7V时,器件的最大电流效率为9.09cd/A;当电压为14V时,器件的最大亮度为16 370cd/m2。不加CdS时,当电压为8V时,器件的最大效率为5.16cd/A;当电压为14V时,最大亮度为6 669cd/m2。加CdS的器件比不加CdS的器件最大效率提高了1.76倍,最大亮度提高了2.42倍。     

Comparison of two cohost systems for doped red organic light-emitting devices in an effort to improve the efficiency and the lifetime

Blue-emitting 2-methyl-9,10-di(2-napthyl)anthracene (MADN) and yellow-emitting 5,6,11,12-tetraphenylnaphthacene (rubrene) were used as cohost materials together with tris(8-hydroxyquinolinato)aluminum (Alq₃) to form emission layers doped with the red dopant molecule 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB). DCJTB-doped red organic light-emitting diodes based on both cohost systems showed remarkable improvements in terms of efficiency compared to DCJTB-doped Alq₃ single-host devices. With 2% DCJTB doping, the respective efficiencies of Alq₃ single-host, Alq₃ (60%)/rubrene (40%)-, and Alq₃ (20%)/MADN (80%)-cohost devices were 1.79, 4.44 and 5.42 cd/A at 20 mA/cm². Unlike Alq₃/rubrene-cohost devices, which experienced substantial current-induced quenching, Alq₃/MADN-cohost devices showed only a slight efficiency change at high current densities. At the luminance of 7680 cd/m², which was the benchmark for a practical passive-matrix OLED array with 64 scan-lines, an aperture ratio of 50%, and a polarizer transmittance of 50%, the power efficiency of the 2% DCJTB Alq₃/MADN-cohost device was 4.1 and 1.5 times better than that of Alq₃ single-host and Alq₃/rubrene-cohost devices, respectively. Moreover, the half-decay lifetime of the Alq₃/MADN-cohost device, measured as 14,000 h at an initial luminance of 1000 cd/m², was 4.4 and 1.9 times longer than the respective half-decay lifetimes of Alq₃ single-host and Alq₃/rubrene-cohost devices.