Efficiency optimization of green phosphorescent organic light-emitting device

Using a narrow band gap host of bis[2-(2-hydroxyphenyl)-pyridine]beryllium (Bepp₂) and green phosphorescent Ir(ppy)₃ [fac-tris(2-phenylpyridine) iridium III] guest concentration as low as 2%, high efficiency phosphorescent organic light-emitting diode (PHOLED) is realized. Current and power efficiencies of 62.5 cd/A (max.), 51.0 lm/W (max.), and external quantum efficiency (max.) of 19.8% are reported in this green PHOLED. A low current efficiency roll-off value of 10% over the brightness of 10,000 cd/m² is noticed in this Bepp₂ single host device. Such a high efficiency is obtained by the optimization of the doping concentration with the knowledge of the hole trapping and the emission zone situations in this host-guest system. It is suggested that the reported device performance is suitable for applications in high brightness displays and lighting.     

Full wafer scale nanoimprint lithography for GaN-based light-emitting diodes

A UV-imprinting process for a full wafer was developed to enhance the light extraction of GaN-based green light-emitting diodes (LEDs). A polyvinyl chloride flexible stamp was used in the imprinting process to compensate for the poor flatness of the LED wafer. Two-dimensional photonic crystal patterns with pitches ranging from 600 to 900 nm were formed on the p-GaN top cladding layer of a 2 inch diameter wafer using nanoimprint and reactive ion etching processes. As a result, the optical output power of the patterned LED device was increased by up to 44% at a driving current of 20 mA by suppressing the total internal reflection and enhancing the irregular scattering of photons at the patterned p-GaN surface.     

Synthesis and properties of solution-processible oligomers for the use of organic light-emitting diodes (OLEDs)

Two oligomers with X-shaped repeating units bearing anthracene and fluorene units were synthesized in a facile procedure, and exhibited high photoluminescence efficiencies, thermal stabilities and good solubility. Their ease of processing enabled spin coating with an electron-transporting bitriazine layer to afford organic light-emitting diodes which displayed a light blue emission with the maximum luminance of 3650 cd/m² and the current efficiency of 0.69 cd/A at an operation voltage of 10 V.     

The relationship between the host structure and optimum doping concentration in red phosphorescent organic light-emitting diodes

The effect of the host structure on the optimum doping concentration in red phosphorescent organic light-emitting diodes (PHOLEDs) was investigated. A mixed host of the phosphine oxide derivative (SPPO21) and 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA) was used as the host in the red PHOLED and the device performances were studied according to the doping concentration. The device performance of the red PHOLED was optimized at a doping concentration of 2% in the SPPO21 rich red PHOLED, while the device performance was optimized at a doping concentration of 6% in the device with 50% TCTA content. It was found that the optimum doping concentration was determined by the energy transfer and charge trapping.     

Enhancement of microcrystalline n-i-p solar cell performance via use of pre-covering layers and H2 treatment

We study the effects of a-Si:H and μc-Si:H covering layers and an H₂ treatment on the characteristics of μc-Si:H thin film solar cells deposited in open single chamber very high frequency plasma enhanced chemical vapor deposition systems. Secondary ion mass spectrometry is used to evaluate the phosphor concentration in the μc-Si:H material. Compared to use of an a-Si:H covering layer, use of a μc-Si:H covering layer reduces dopant contamination by a relative 50%, and improves efficiency by a relative 6%, and use of an H₂ treatment reduces dopant contamination by a relative 64%, and improves efficiency by a relative 17%.     

Spin transfer torque and tunneling magnetoresistance dependences on finite bias voltages and insulator barrier energy

We investigate the dependence of perpendicular and parallel spin transfer torque (STT) and tunneling magnetoresistance (TMR) on the insulator barrier energy of the magnetic tunnel junction (MTJ). We employed the single orbit tight binding model combined with the Keldysh non-equilibrium Green's function method in order to calculate the perpendicular and parallel STT and the TMR in the MTJ with finite bias voltages. The dependences of the STT and TMR on the insulator barrier energy are calculated for semi-infinite half metallic ferromagnetic electrodes. We find a perfect linear relation between the parallel STT and the tunneling current for a wide range of insulator barrier energy. Furthermore, the TMR also depends on the insulator barrier energy, contradicting Julliere's simple model.     

Application of GaN-based ultraviolet-C light emitting diodes--UV LEDs--for water disinfection

GaN-based ultraviolet-C (UV-C) light emitting diodes (LEDs) are of great interest for water disinfection. They offer significant advantages compared to conventional mercury lamps due to their compact form factor, low power requirements, high efficiency, non-toxicity, and overall robustness. However, despite the significant progress in the performance of semiconductor based UV LEDs that has been achieved in recent years, these devices still suffer from low emission power and relatively short lifetimes. Even the best UV LEDs exhibit external quantum efficiencies of only 1-2%.The objective of this study was to investigate the suitability of GaN-based UV LEDs for water disinfection. The investigation included the evaluation of the performance characteristics of UV LEDs at different operating conditions as well as the design of a UV LED module in view of the requirements for water treatment applications. Bioanalytical testing was conducted using Bacillus subtilis spores as test organism and UV LED modules with emission wavelengths of 269 nm and 282 nm.The results demonstrate the functionality of the developed UV LED disinfection modules. GaN-based UV LEDs effectively inactivated B. subtilis spores during static and flow-through tests applying varying water qualities. The 269 nm LEDs reached a higher level of inactivation than the 282 nm LEDs for the same applied fluence. The lower inactivation achieved by the 282 nm LEDs was compensated by their higher photon flux. First flow-through tests indicate a linear correlation between inactivation and fluence, demonstrating a well designed flow-through reactor. With improved light output and reduced costs, GaN-based UV LEDs can provide a promising alternative for decentralised and mobile water disinfection systems.     

Degradation of antibiotics in water by non-thermal plasma treatment

The decomposition of three β-lactam antibiotics (amoxicillin, oxacillin and ampicillin) in aqueous solution was investigated using a dielectric barrier discharge (DBD) in coaxial configuration. Solutions of concentration 100 mg/L were made to flow as a film over the surface of the inner electrode of the plasma reactor, so the discharge was generated at the gas-liquid interface. The electrical discharge was operated in pulsed regime, at room temperature and atmospheric pressure, in oxygen. Amoxicillin was degraded after 10 min plasma treatment, while the other two antibiotics required about 30 min for decomposition. The evolution of the degradation process was continuously followed using liquid chromatography-mass spectrometry (LC-MS), total organic carbon (TOC) and chemical oxygen demand (COD) analyses.     

泥炭生物反应墙构建及修复地下水中石油烃

为有效修复地下水中溶解态石油烃污染物,在研究填充介质配比基础上,分别利用低温石油烃降解菌-泥炭-粗砂和泥炭-粗砂构建了泥炭生物反应墙和泥炭反应墙,考察了反应墙对地下水中BTEX、PAHs的修复效果.结果表明,泥炭与粗砂最适体积比为20:80,此时墙体渗透系数为1.17×10-4m/s,有效空隙率为7.5%;泥炭反应墙对...     

双排刚性桩屏障对平面SH波的隔离性状研究

基于Twersky的理论,引入圆柱体对声波和电磁波的多重散射解析解,对用排桩隔离环境振动的问题,提出了一种新的求解任意排列、任意直径刚性桩对平面SH波多重散射的理论方法,解决了传统的假设单重散射的计算方法中不考虑桩列作为整体屏障从而忽略桩间相互干涉关系的不足.随后,在数值计算分析中讨论了散射重数,排间距,桩间距等因素对双排刚性桩隔振效果的影响,对实际工程中利用排桩进行振动污染治理和屏障隔振的设计提出了有意义的结论.