Enhanced Coupling of Light from Organic Electroluminescent Device Using Diffusive Particle Dispersed High Refractive Index Resin Substrate

To improve light extraction from organic electroluminescent (EL) devices, we introduced a diffusive substrate with 25 μm thickness consisting of high refractive index resin and scattering particles. It is expected that the diffusive substrate with high refractive index matrix converts the waveguided emission into external emission from both glass substrate and indium-tin-oxide/organic layer. We used the ray tracing method to optimize the scattering effect and to verify the coupling out effect of the diffusive high refractive index substrate. With the use of the ray tracing calculation, an increase in the external emission up to a factor of 2.7 was expected compared to use of a common glass substrate. Experimentally, the coupling out effect of the diffusive high refractive index substrate strongly depended on the thickness of electron transporting layer (ETL) due to the well-known interference effect. The current efficiency increased by a factor of 1.3 for an organic EL device with a 60-nm-thick ETL and by a factor of 6.8 for one with a 120-nm-thick ETL.     

Design and optimization of thin film polarizer at the wavelength of 1540 nm using differential evolution algorithm

In this paper, a thin film polarizer at the wavelength of 1540 nm in infrared region was designed and optimized using differential evolution method. It is shown how the algorithm’s parameters can change the output result to obtain the best consequence of optimization. This polarizer consists of a few pairs of high and low refractive index dielectric materials, titanium dioxide and silicon dioxide, respectively, with \(BK_{7}\) glass substrate and the angle of incident light was supposed 56° that is the Brewster angle for \(BK_{7}\) glass. Our final optimized polarizer has 91.20 and 0.336% transmittance for P and S polarization, respectively, and a 271 ratio of \(\frac{{T_{P} }}{{T_{S} }}\) which has high significance for this polarizer. It consists of eight pairs of layers with low and high refractive index materials and 3369.1 nm physical thickness which is used to separate S and P polarized light for Q-switching process.     

利用泄漏波导测量低折射率薄膜的折射率和厚度

根据泄漏波导原理对K_9玻璃基板上的冰晶石薄膜进行折射率测量,达到的精度为1×10~(-4),与真实波导的情况相似。文中讨论了利用添加高折射率薄层减小待测薄膜的最小厚度的可能性。文中还利用光电方法观察反射光中暗条纹的方法判别波导的激发,并测出了冰晶石薄膜在4500到6500范围内的折射率。     

A novel proposal for enhancement of light extraction efficiency in WOLEDs based on optimized photonic crystal structures

In this paper we propose a framework to enhance light extraction efficiency in white organic light emitting diodes (WOLED) using photonic crystal (PhC) structures sandwiched between indium tin oxide (ITO, n_ITO = 1.8+0.01i) and glass (n_glass = 1.51) substrate, according to the high refractive index contrast of these two layers almost 50% of the generated light inside WOLED gets trapped in the mentioned interface. The main purpose of this article is to suggest a method to intentionally optimize PhC structures to reduce total internal reflections (TIR) happening at ITO/glass interface. Here three different patterns are considered including rectangular, hexagonal and circular lattices. Using Finite Difference Time Domain (FDTD) method and the presented framework for choosing structural parameters the portion of 50% trapped light in ITO was reduced to 20% which is a large enhancement in extraction efficiency of WOLED. Also far-field results before and after adding PhCs are investigated.     

Light extraction efficiency enhancement in organic light emitting diodes based on optimized multilayer structures

The main focus of this study is to improve the light extraction efficiency, as well as directionality of organic light emitting diodes (OLEDs) using multi-layer structures between Indium tin Oxide (ITO) and glass layers in a typical OLED. In conventional OLEDs, only about half of the light generated in the emission zone can reach to the glass substrate due to refractive index mismatch in ITO (n = 1.8?i0.01)/glass (n = 1.51) interface. The main attempt is to reduce the share of total internal reflection (TIR) and hence, the effect of different structures such as Thue-Morse and Fibonacci have been investigated and optimized with suitable layer thickness and materials based on Transfer Matrix Method (TMM). The most effective Multi-layer structures have been added to conventional OLED and have been analyzed the extraction efficiency using Finite Difference Time Domain (FDTD) method. Results show large enhancement of extraction efficiency (about 40%) in ITO/glass interface. Using this idea and applying micro-lenses array to glass substrate at the same time, one can get even higher extraction efficiency in OLED. The interesting aspect of this project is its easy fabrication process in order to commercialize the product with highest extraction efficiency and low fabrication cost.     

基于折射率变化的一种新型盐度测量原理研究

研制了一种用于测量海水盐度的新装置。基于表面等离子共振技术,根据盐溶液折射率与盐度的关系原理,实现对盐度测量。结构中使用一只K9玻璃制成的棱镜为衬底,在棱镜的一边淀积一层厚度为55nm的Ag膜,在Ag膜上设置待测盐溶液样品池和参考池。在白光的激励下,在Ag膜中发生表面等离子共振现象。盐溶液的折射率不仅与盐的质量分数有关,且与温度有关,而样品池和装有蒸馏水的参考池具有相同温度,用两者共振波长差的变化来反映盐度,克服了温度对测量结果的影响,理论分析和实验结果验证了设计的可行性。     

Effects of substrate treatment on the electroluminescence performance of flexible OLEDs

Electroluminescence (EL) performance of flexible organic light-emitting device (FOLED) has been found to be highly dependent upon the morphology of the surface of the indium thin oxide (ITO)/plastic substrate as well as the patterning and processing conditions of the substrate. We will present evidence showing that luminance efficiency of FOLED can be greatly improved by pretreatment. Surface analysis of the ITO/PET by means of atomic force microscope (AFM) and optical microscope will be compared with that of the ITO/glass and the influence of flexible OLEDs substrate treatment by various methods on EL performance will also be discussed.     

K+-Na+二次离子交换制作玻璃波导

通过数值计算模拟了K⁺Na⁺二次扩散玻璃波导的折射率轮廓,阐述了利用K⁺Na⁺二次离子交换的方法,在BK7玻璃上制作波导的过程,分析了极化率不同的扩散离子对的选择对波导有效折射率变化的影响,以及扩散平衡时体积变化对表面折射率的影响,描述了扩散引起的波导内部诱导应力变化设计了测试波导损耗以及波导表面折射率改变的实验装置,对尺寸10mm×10mm×1.5mm和10mm×5mm×1.5mm两组BK7玻璃基片上的玻璃波导进行了测试,测试结果与理论吻合较好.     

Ultrathin nickel oxide film as a hole buffer layer to enhance the optoelectronic performance of a polymer light-emitting diode

In order to promote a polymer LED (PLED), we fabricated and introduced an ultrathin nickel oxide (NiO) buffer layer (<10 nm) between the indium tin oxide (ITO) anode and the poly (3, 4-ethylenedioxythiophene) hole injection layer in the PLED. The NiO buffer layer was easily formed on the ITO anode by electron-beam deposition of a nickel (Ni) metal source and an oxygen plasma treatment process. As a result, the PLED device with the NiO buffer layer on its ITO anode had the same turn-on voltage as conventional PLED devices without the NiO buffer layer, and the luminance of the PLED device with the NiO buffer layer was doubled, compared with the conventional PLED devices without the NiO buffer layer. Improvement of the optoelectronic performance of the PLED can be attributed to the increase of the current driven into the diode, resulting from the NiO buffer layer, which can enhance the hole injection and balance the injection of the two types of carriers (holes and electrons). Thus it is an excellent choice to introduce the NiO buffer layer onto the ITO anode of the PLED devices in order to enhance the optoelectronic performance of PLED devices.     

Formation of Au nano-patterns on various substrates using simplified nano-transfer printing method

For future device applications, fabrication of the metal nano-patterns on various substrates, such as Si wafer, non-planar glass lens and flexible plastic films become important. Among various nano-patterning technologies, nano-transfer print method is one of the simplest techniques to fabricate metal nano-patterns. In nano-transfer printing process, thin Au layer is deposited on flexible PDMS mold, containing surface protrusion patterns, and the Au layer is transferred from PDMS mold to various substrates due to the difference of bonding strength of Au layer to PDMS mold and to the substrate. For effective transfer of Au layer, self-assembled monolayer, which has strong bonding to Au, is deposited on the substrate as a glue layer.In this study, complicated SAM layer coating process was replaced to simple UV/ozone treatment, which can activates the surface and form the -OH radicals. Using simple UV/ozone treatments on both Au and substrate, Au nano-pattern can be successfully transferred to as large as 6 in. diameter Si wafer, without SAM coating process. High fidelity transfer of Au nano-patterns to non-planar glass lens and flexible PET film was also demonstrated.     

可弯曲式有机电玫发光器件的出光率

基于几何光学模型及其原理,推导出在不同弯曲情况下可弯曲式有机电致发光器件的出光率表达式,分析了器件出光率受基板曲率、厚度及有机层折射率的影响,并与平整有机电致发光器件的出光情况作了比较.结果表明:当器件向外弯曲时,出光率随着基板曲率与基板厚度的增大而增大,随着有机层折射率的增大而减小;当器件向内弯曲时,出光率随着基板曲率与基板厚度的增大而减小,随着有机层折射率的增大而减小.对于平整器件,其出光率随有机层折射率的增大而减小.     

High-brightness white light-emitting organic electroluminescent devices using poly(N-vinylcarbazole) as a hole-transporter

A white light-emitting organic electroluminescent (EL) device with multilayer thin-film structure, which shows high-brightness and high-efficiency, is demonstrated. The device structure of glass substrate/indium–tin oxide/poly(N-vinylcarbazole) (PVK)/1,1,4,4-tetraphenyl-1,3-butadiene/8-(quinolinolate)-aluminum (Alq) doped with 5,6,11,12-tetraphenylnaphthacene/Alq/Mg/Al was employed. The turn-on voltage is as low as 2.5 V. The white light emission covers a wide range of the visible region, and the Commission Internationale de 1' Eclairage coordinates of the emitted light are (0.319, 0.332) at 10 V. Bright white light, over 20 000 cd/m², was successfully obtained at about 18 V, and the maximum efficiency reaches to 1.24 lm/W at 9 V. The reasons of obtaining high level EL properties of our device have been discussed.     

基于液晶/聚合物光栅的高转化效率有机半导体激光器

采用有机半导体发光材料聚[2-甲氧基-5-(2-乙基己氧基)-1,4-苯乙炔]作为增益介质,低官能度光敏单体制备的液晶/聚合物光栅作为外部反馈谐振腔,制备出参数可独立控制的分离式结构的有机半导体激光器.液晶/聚合物光栅中液晶分子的取向影响光栅折射率调制量,从而影响光栅的反馈能力,最终影响激光器出射激光的性能.通过研究发现决定液晶分子取向的主要有两种与光栅周期有关的作用力,利用这一原理制备不同周期的光栅,光栅周期小于450 nm时,相分离出的液晶分子取向由光栅矢量方向变为光栅沟槽方向,此时光栅的折射率调制量增加,光反馈能力增强.采用周期为395 nm的液晶/聚合物光栅制备二级布拉格散射的有机半导体激光器,相较于大周期光栅(593 nm)制备的激光器,激光阈值由0.70μJ/pulse降低至0.18μJ/pulse,转化效率由2.5%提高到6.4%,且出射激光垂直于基板表面发射,有利于后续的处理及应用.     

Low-temperature and solution-processable inorganic hole injection layer for flexible quantum-dot light-emitting diodes

A low-temperature solution-processable inorganic vanadium oxide (V₂O₅) hole injection layer (HIL) was synthesized for flexible quantum-dot light-emitting diodes (QLEDs). Efficient hole injection characteristics were observed in the hole-only devices; furthermore, the process temperature of V₂O₅ was as low as 30 °C. We investigated the source of the efficient hole injection behavior using ultraviolet and x-ray photoelectron spectroscopy. The density of gap states was found to increase in accordance with process temperature reduction. Therefore, QLEDs with low-temperature solution-processable V₂O₅ HILs were fabricated on a glass substrate, which showed excellent characteristics. The maximum luminance and luminous efficiency of the device were 56,717 Cd/m² and 4.03 Cd/A, respectively. Due to the low-temperature process of the V₂O₅ HIL, it was also possible to fabricate QLEDs on a flexible plastic substrate without mechanical or thermal deformation of the substrate. Our results suggest that the low-temperature V₂O₅ inorganic HIL is a feasible alternative to organic HILs for flexible QLEDs.     

基于时间控厚离子束溅射技术的宽带减反膜制备

 为了制备满足设计要求的宽角度、宽波段减反膜,利用离子束溅射沉积技术,在时间-功率控厚的模式下,对膜层沉积速率进行了精确修正。在实验中,利用时间-功率控厚的离子束溅射沉积技术,选择HfO₂和SiO₂作为高低折射率组合,在超抛ZF6玻璃基底上制备了宽角度、宽带减反膜,通过对实验后的透过率光谱曲线的数值反演计算,获得膜层厚度修正系数,初步得到了沉积速率随沉积时间变化的规律。利用修正后的沉积参数制备设计的膜系,在0°~30°入射角度下,600~1 200 nm波段的平均透过率达到99%以上。     

Flexible NiO nanocrystal-based resistive memory device fabricated by low-temperature solution-process

In this study, a nickel oxide (NiO) nanocrystal (NC) based flexible resistive memory device is demonstrated at temperature as low as 180 °C by ligand exchange process. The fabricated device for flexible application with structure Ni/NiO/Ni on PI substrate exhibits excellent switching characteristics with low set/reset voltages and stable resistance values in both ON and OFF states for over 100 switching cycles of memory operation. Also, this flexible memory device shows stable resistive switching properties under compressive stress with bending radius to 10 mm and consecutive bending cycles. The ReRAM fabricated by a low-temperature solution-process shows potential for next generation flexible electronics.     

Ultra-slim flexible glass for roll-to-roll electronic device fabrication

As displays and electronics evolve to become lighter, thinner, and more flexible, the choice of substrate continues to be critical to their overall optimization. The substrate directly affects improvements in the designs, materials, fabrication processes, and performance of advanced electronics. With their inherent benefits such as surface quality, optical transmission, hermeticity, and thermal and dimensional stability, glass substrates enable high-quality and long-life devices. As substrate thicknesses are reduced below 200 μm, ultra-slim flexible glass continues to provide these inherent benefits to high-performance flexible electronics such as displays, touch sensors, photovoltaics, and lighting. In addition, the reduction in glass thickness also allows for new device designs and high-throughput, continuous manufacturing enabled by R2R processes. This paper provides an overview of ultra-slim flexible glass substrates and how they enable flexible electronic device optimization. Specific focus is put on flexible glass’ mechanical reliability. For this, a combination of substrate design and process optimizations has been demonstrated that enables R2R device fabrication on flexible glass. Demonstrations of R2R flexible glass processes such as vacuum deposition, photolithography, laser patterning, screen printing, slot die coating, and lamination have been made. Compatibility with these key process steps has resulted in the first demonstration of a fully functional flexible glass device fabricated completely using R2R processes.     

Enhancement of light extraction efficiency of organic light emitting diodes using nanostructured indium tin oxide

Improved outcoupling efficiency of organic light emitting diodes (OLEDs) is demonstrated by incorporating a nanostructured indium tin oxide (NSITO) film between a conducting anode and a glass substrate. NSITO film was fabricated using rf-sputtering at oblique angle (85°). Significant reduction in refractive index and improved transmission of NSITO film was observed. OLEDs were then fabricated onto NSITO film to extract the ITO-glass waveguided modes. Extraction efficiency was enhanced by 80% without introducing any detrimental effects to operating voltage, current density, and angular invariance of emission spectra of OLEDs.     

Structural changes in BK7 glass upon exposure to femtosecond laser pulses

A general picture of refractive index change mechanisms in glass modified by a femtosecond laser has proven elusive. In this paper, Raman microscopy was used in conjunction with refractive near‐field profilometry to analyse the structure of borosilicate glass (Schott BK7) modified by a femtosecond laser and determine the mechanism of the observed refractive index change. For a pulse repetition rate of 1 kHz, it was determined that the refractive index change was due to an elevated population of non‐bridging oxygen atoms, resulting in more ionic bonds forming within the glass network and increasing the molar refractivity of the glass. For a pulse repetition rate of 5.1 MHz, the dominant mechanism of refractive index change was densification and rarefaction of the glass network. Different refractive index change mechanisms were attributed to different thermal conditions imparted to the glass under different pulse repetition rates. Implications for device fabrication are also discussed. These findings constitute an important step toward a complete overview of femtosecond‐laser‐induced refractive index change in glass. Copyright © 2010 John Wiley & Sons, Ltd.     

层压工艺对埋入光纤传输性能影响分析

针对层压工艺下,埋入挠性光电基板的光纤,其应力、位移的变化,会影响光路的耦合效率,改变光纤有效折射率,导致传输性能发生变化的问题,采用有限元分析软件,对光纤埋入不同槽型的挠性光电基板进行了力学、传热和电磁场耦合分析.分析结果表明:光纤埋入梯形槽挠性基板的应力最大,达到68.336 7MPa.埋入梯形槽的光纤位移量最大,其值为1.430 4μm.随着槽宽增加,光纤最大等效应力从52.667MPa增加至71.907 MPa;随着槽间距增加,光纤最大应力从51.589 MPa增加至53.567MPa;随着槽深增加,光纤最大应力从52.667MPa减小至47.793 8 MPa,然后增加到67.349 6MPa.随着温度和压力的增加,单模光纤在X方向的有效折射率从1.446 249 977增加至1.446 259 084;Y方向的有效折射率从1.446 326 398增加至1.446 393 041.光纤有效折射率差会随着温度的增加而增大,随着压力的增加而减小.光纤有效折射率增加,限制光的能力增加,能够有效地减小光纤弯曲损耗.本文分析结果对挠性光电基板光纤埋入结构设计和层压工艺具有一定的参考价值和指导意义.