有机电致发光

详细介绍了有机电致发光的原理、结构和制备方法，分析了用于有机电致发光的各种材料的性能以及蓝色有机ＥＬ，最后提出了存在的问题及展望。     

Far-infrared electroluminescence characteristics of an InGaP/InGaAs/Ge triple-junction solar cell under forward DC bias

The far-infrared electroluminescence characteristics of an InGaP/InGaAs/Ge solar cell are investigated under forward DC bias at room temperature in dark conditions. An electroluminescence viewgraph shows the clear device structures, and the electroluminescence intensity is shown to increases exponentially with bias voltage and linearly with bias current. The results can be interpreted using an equivalent circuit of a single ideal diode model for triple-junction solar cells. The good fit between the measured and calculated data proves the above conclusions. This work is of guiding significance for current solar cell testing and research.     

Electroluminescence of ZnSe enhanced by improved layered optimization structure

The electroluminescence thin-film device with layered optimization structure based on ZnSe emitting layer was deposited by electron-beam evaporation. Electroluminescence of ZnSe film, which has not appeared in device with traditional double insulator structure, was observed. According to this phenomenon, SiO₂ ultra-thin layer was inserted into the middle of ZnSe layer and the device with this kind of improved layered optimization structure was prepared. Its electroluminescence intensity is higher than that of the device with traditional layered optimization structure. The dependence of electroluminescence on applied voltage and frequency was studied in detail. The luminescence mechanism and the contribution of SiO₂ ultra-thin layer to the electroluminescence intensity of the device were discussed. This phenomenon can provide a way to obtain bright blue inorganic electroluminescence.     

有机电致发光薄膜的电流输运机理的分析

用TPD作空穴传输层、8－羟基喹啉锌作发光层,制备了有机薄膜器件,测量了其电致发光特性。分析了该器件的电流输运机理,认为该有机薄膜器件在电致发光时流过器件的电流受热电子注入效应、空间电荷限制效应、隧穿效及器件电阻效应的影响。     

热处理对白色有机电致发光器件发光性能的影响

为获得优质的有机电致发光器件．它的发射光谱是一个关键的因素。传统的方法是采用红、绿、蓝色多层叠合产生白光,但难以控制各基色的峰值强度。制备了利用混合型聚合物作为白色发光层的单层结构有机电致发光器件((OLED),其制备过程比多层结构器件简单得多。一种热处理方法(180℃,1h)用来控制此类白光OLED中各主要电致发光光谱峰值强度间的比例。经过热处理后,这种白光器件的电致发光光谱很接近于Nichia公司的无机白色发光二极管产品的电致发光光谱。由此可推测器件的色坐标接近于白色等能点,而且其阈值电压比热处理前降低了1V。     

980nm垂直腔型面发射和接收器件及列阵的研制

采用相同生长结构的MOCVD外延片,研究制备适用于单片集成的垂直腔面发射与接收器件及列阵,发射及接收波长相同,由谐振腔模式决定.采用双氧化电流限制结构,优化串联电阻,提高电光转换效率,制备980nm波段发光器件及1×16列阵芯片,发射谱线半宽≤4.8nm,注入电流为50mA时,发射功率为0.7mW.对列阵芯片用探针进行在线检测,器件均有良好的发光特性.接收器件光电响应具有良好的波长和空间选择特性,谐振接收波长可利用不同角度光入射实现简单易行的调节.通过腐蚀器件顶部DBR的方法调节入射镜反射率,可以分别实现具有单片集成结构的谐振增强型发射和接收器件的优化设计.     

980nm垂直腔型面发射和接收器件及列阵的研制

采用相同生长结构的MOCVD外延片,研究制备适用于单片集成的垂直腔面发射与接收器件及列阵,发射及接收波长相同,由谐振腔模式决定.采用双氧化电流限制结构,优化串联电阻,提高电光转换效率,制备980nm波段发光器件及1×16列阵芯片,发射谱线半宽≤4.8nm,注入电流为50mA时,发射功率为0.7mW.对列阵芯片用探针进行在线检测,器件均有良好的发光特性.接收器件光电响应具有良好的波长和空间选择特性,谐振接收波长可利用不同角度光入射实现简单易行的调节.通过腐蚀器件顶部DBR的方法调节入射镜反射率,可以分别实现具有单片集成结构的谐振增强型发射和接收器件的优化设计.     

Reprint of: GaN nanowires on diamond

The current research of GaN nanowires on diamond substrates is reviewed and extended by recent results. Both the self-assembled and the selective area growth mechanisms using plasma-assisted molecular beam epitaxy are summarized. Structural and optical properties of as-grown nanowires as well as doping-related issues are discussed and compared to nanowires on silicon substrate. The electronic characteristics of p-diamond/n-GaN nanowire heterojunctions are addressed theoretically by band structure simulations and experimentally by transport measurements. Finally, electroluminescence of a fabricated prototype nanoLED device is demonstrated.     

GaN nanowires on diamond

The current research of GaN nanowires on diamond substrates is reviewed and extended by recent results. Both the self-assembled and the selective area growth mechanisms using plasma-assisted molecular beam epitaxy are summarized. Structural and optical properties of as-grown nanowires as well as doping-related issues are discussed and compared to nanowires on silicon substrate. The electronic characteristics of p-diamond/n-GaN nanowire heterojunctions are addressed theoretically by band structure simulations and experimentally by transport measurements. Finally, electroluminescence of a fabricated prototype nanoLED device is demonstrated.     

Low-frequency noise measurement and analysis in organic light-emitting diodes

Low-frequency noise characteristics of organic light-emitting diodes are investigated. Two noise components were found in experimental low-frequency noise records, namely: 1) 1/f Gaussian noise from device bulk materials and 2) an excessive frequency-related part of noise related to device interfaces or defects and traps. 1/f noise is said to be related to carrier mobility. Degradation, especially photo-oxidation of the electroluminescence polymer, is a possible reason that affects carrier mobility. The excessive part of noise is believed to be related to the carrier numbers and could come from the interface deterioration, defects and traps generation and furnish. The excessive part of noise increases much faster during device stress. This shows that the degradation related interface defects and traps is much faster.     

Studies of high DC current induced degradation in III-V nitridebased heterojunctions

We report experiments on high dc current stressing in commercial III-V nitride based heterojunction light-emitting diodes. Stressing currents ranging from 100 mA to 200 mA were used. Degradations in the device properties were investigated through detailed studies of the current-voltage (I-V) characteristics, electroluminescence, deep-level transient Fourier spectroscopy and flicker noise. Our experimental data demonstrated significant distortions in the I-V characteristics subsequent to electrical stressing. The room temperature electroluminescence of the devices exhibited a 25% decrement in the peak emission intensity. Concentration of the deep-levels was examined by deep-level transient Fourier spectroscopy, which indicated an increase in the density of deep-traps from 2.7×10¹³ cm^-3 to 4.2×10¹³ cm^-3 at E₁=E _C-1.1 eV. The result is consistent with our study of 1/f noise, which exhibited up to three orders of magnitude increase in the voltage noise power spectra. These traps are typically located at energy levels beyond the range that can be characterized by conventional techniques including DLTS. The two experiments, therefore, provide a more complete picture of trap generation due to high dc current stressing     

ZnO:Al/n-ZnO/p-GaN异质结电致发光特性研究

利用ZnO和GaN材料制备了ZnO:Al/n-ZnO/p-GaN透明电极异质结发光二极管。通过SEM、TEM和荧光光谱对ZnO纳米棒进行了结构表征和发光特性表征。通过半导体特性分析系统和光谱测试技术对ZnO:Al/n-ZnO/p-GaN异质结进行了电致发光性能测试和机理分析。结果表明该器件能产生有效的蓝紫色电致发光,其发光分别来自于n型ZnO、p型GaN以及界面辐射;并且采用ZnO:Al作为透明电极可以提高该器件的出光效率。该异质结可应用于高效率短波发光器件。     

有机薄膜电致发光的回顾和展望

综述了有机薄膜电致发光（ＯＴＦＥＬ）的发展过程，总结了ＯＴＦＥＬ的四种器件结构和工作原理，介绍了器件的制备并了选择有机发光材料的基本原则，文末展望了ＯＴＦＥＬ的应用前景。     

Modification of Exciton Lifetime by the Metal Cathode in Phosphorescent OLEDs,and Implications on Device Efficiency and Efficiency Roll‐off Behavior

Time resolved photoluminescence and electroluminescence measurements are used to study changes in the emission characteristics of materials typically used in phosphorescent organic light emitting devices (PhOLEDs). Studies on archetypical PhOLEDs with phosphorescent material, fac‐tris(2‐phenylpyridine) iridium (Ir(ppy)₃), show that the lifetime of triplet exciton is modified when in close proximity to a metal layer. Interactions with a metal layer ～30–100 nm away, as is typically the case in PhOLEDs, result in an increase in the spontaneous emission decay rate of triplet excitons, and causes the exciton lifetime to become shorter as the distance between the phosphorescent material and the metal becomes smaller. The phenomenon, possibly the result of the confined radiation field by the metal, affects device efficiency and efficiency roll‐off behavior. The results shed the light on phenomena affecting the efficiency behavior of PhOLEDs, and provide new insights for device design that can help enhance efficiency performance.     

有机/聚合物异质结电致发光器件的光电性能

器件结构是影响有机发光器件(OLED)性能的重要因素之一.采用8-hydroxyquinoline-aluminum(AlQ)作为发光层(EML)和电子传输层(ETL),polyvinylcarbazole (PVK)作为空穴传输层(HTL),制备了具有有机小分子/聚合物异质结结构的OLED器件,通过其电压-电流-发光亮度(V-J-B)特性测试,研究了HTL的引入及其膜厚对器件性能的影响.实验结果表明,HTL的引入有效地改善了OLED的光电性能,同时HTL膜厚对器件性能具有显著影响,当HTL膜厚为20 nm时,所制备的OLED器件具有最小的驱动电压和启亮电压、最大的发光亮度和发光效率.

Abstract：

The device construction plays an important role in improving the optoelectronic performance of organic electroluminescence devices (OLEDs). Heterojunction OLEDs with a configuration of glass/ITO/PVK/AlQ/Mg/Al were fabricated by using 8-hydroxyquinoline-aluminum (AlQ) as the emission layer (EML) and electron transport layer (ETL) and polyvinylcarbazole (PVK) as the hole transport layer (HTL). The effect of the HTL thickness on the performance of OLEDs was investigated with respect to the driving voltage, turn-on voltage, electroluminescence brightness and efficiency of the devices. Experimental results demonstrate that the optical and electrical properies of OLEDs are closely related to the HTL thickness. The device fabricated with the HTL thickness of 20 nm possesses the best photoelectric properties such as the minimum driving voltage and turn-on voltage, and the maximum electroluminescence brightness and efficiency.     

Electrooptical Analysis of Effects Induced by Floating Metallic Interlayers in Organic LEDs

The aim of this paper is to investigate the electrical and optical property modifications that can be related to the presence of a nanometric metallic layer at the interface between two organic emissive materials in a stacked structure. For purposes of comparison, reference devices have also been analyzed to emphasize the increase of electrical switching and hysteresis behaviors in current–voltage plots and spectral variations in electroluminescence. In this paper, we have tried to summarize the electrical effects of the floating nanometric thin metallic layer by extracting a small number of parameters which can represent the current state of the device.      

Electroluminescence in forward-biased zinc selenide Schottky diodes

Schottky diodes consisting of a metal contact on n-type ZnSe emit light when biased in the forward direction if there is a layer of insulating or semi-insulating material between the metal and the semiconductor. The electroluminescence spectrum is characteristic of luminescent centres in the ZnSe. There is a threshold voltage for electroluminescence which corresponds to the difference between the metal Fermi level and the top of the valence band of the semiconductor. For gold on ZnSe the threshold voltage is 1·3 V. Characteristics of the device differ from those of similar MIS systems because the oxide used here has appreciable conductivity.     

Preparation of CdSe nanocrystals in organic system and electroluminescence characteristics of the devices

Semiconductor nanocrystals have attracted wideinter-estsinthe last fewyears because they have high lumi-nescence efficiency and size-tunable band gap character-istics .The semiconductor nanocrystals could be func-tionalized using various surfactants to ma…     

Anthracene derivatives as efficient emitting hosts for blue organic light-emitting diodes utilizing triplet–triplet annihilation

The molecular design strategies for the host materials suitable for highly efficient, blue fluorescent organic light-emitting diodes (OLEDs) are demonstrated. The device characteristics of blue fluorescent OLEDs are compared with different host materials. Some devices exhibit a highly efficient blue electroluminescence with a high external quantum efficiency of more than 7%. The correlation between OLED efficiency and triplet–triplet annihilation is characterized by measuring the up-conversion of triplet excited states into singlet ones. The host materials require an anthracene unit and a bulky molecular structure to prevent the overlap of anthracene units between adjacent molecules in the film.     

Optoelectrical characteristics of organic light-emitting devices fabricated with different cathodes

Organic light-emitting devices (OLEDs) with various cathode structures were prepared on indium tin oxide (ITO) substrates by vacuum sublimation technique, and the effects of the device cathodes on the electroluminescence (EL) characteristics of OLEDs were studied in terms of the luminance, efficiency, driving voltage and threshold voltage. The results demonstrate that the optical and electrical performance of OLEDs depend on the properties of the devices' cathodes and the characteristics of the cathode–organic interface and the organic–organic interface. The optoelectrical performance of a device with composite cathodes is better than that of the devices with metal alloy and pure metal cathodes. The improvement in the device performance can be attributed to a more efficient electron injection at the cathode–organic interface, a better balanced hole and electron recombination in the light-emitting layer and fewer accumulated charges near the organic–organic interface.