色散效应对GaAs太阳电池双层减反射膜的影响

考虑双层减反射膜材料的折射率色散效应,采用光学干涉矩阵法计算了SiO2/ZnSe和SiO2/ZnS两种GaAs太阳电池双层减反射膜的反射率与波长的函数曲线,以及加权平均反射率随着顶层减反射膜SiO2厚度变化的函数曲线,并与未考虑色散效应的情况进行了对比.计算结果表明,色散效应对双层减反射膜的反射率有较大的影响,特别是对300～500nm波长范围的影响更大,且对不同材料的减反射膜的影响也是不同的.与未考虑色散效应的情况相比,考虑色散效应后,SiO2/ZnSe双层减反射膜的最小加权平均反射率从1.14%增加到1.55%,而SiO2/ZnS双层减反射膜的最小加权平均反射率却从1.49%减小到1.46%.     

Ag颗粒表面等离子体增强GaAs太阳电池双层减反射膜的设计与模拟

Surface plasmon enhanced antireflection coatings for GaAs solar cells have been designed theoretically.The reflectance of double-layer antireflection coatings（ARCs） with different suspensions of Ag particles is calcu-lated as a function of the wavelength according to the optical interference matrix and the Mie theory.The mean dielectric concept was adopted in the simulations.A significant reduction of reflectance in the spectral region from 300 to 400 nm was found to be beneficial for the design of ARCs.A new SiO2/Ag-ZnS double-layer coating with better antireflection ability can be achieved if the particle volume fraction in ZnS is 1%-2%.     

AlGaN /GaN分布布拉格反射镜的MOCVD生长

文中利用MOCVD方法,采用高质量GaN作为缓冲层,在（0001）取向的蓝宝石衬底上实现了不同组分的AlxGa1-xN/GaN分布布拉格反射镜（DBR）的制备.通过XRD、SEM、AFM、反射谱等测量分析手段,研究了AlxGa1-xN/GaN DBR的结构质量、厚度和表面形貌.     

Porous silicon multilayer stacks for optical biosensing applications

Porous silicon (PS) multilayer stacks were developed for their use as interference filters in the visible range. The optical behavior of these structures was previously simulated by the use of a computational program, from which the optical constants and thickness of the individual PS layers were determined. The possibility of using these structures as biosensors has been explored, based on the significant changes in the reflectance spectra before and after exposing the PS multilayer to proteins (antibodies). In particular, it is shown that there is a notably reduction of reflectance from PS structures when this material is exposed to polyclonal mouse antibodies. Thus, the experimental results open the possibility of developing biosensors based on the variation of the shape and/or position of the optical or photoluminescent spectrum from PS.     

(Al,Ga)Sb long-wavelength distributed Bragg reflectors

The authors have grown long-wavelength distributed Bragg reflectors (DBRs), using alternating layers of the semiconductors AlSb and (Al,Ga)Sb, and measured their properties. The large refractive index ratio available with these materials allows for high-reflectivity mirrors with relative few mirror pairs. A simple 10-period AlSb/GaSb DBR had a maximum reflectivity of over 98% at a wavelength of 1.92 μm, and a 12-period Al_0.2Ga_0.8Sb/AlSb DBR exhibited reflectance greater than 99% at 1.38 μm. These structures are easily grown by molecular beam epitaxy (MBE) and are suitable for use in surface-normal photonic devices operating at long wavelengths     

Wide Dynamic Range in Tunable Electrochromic Bragg Stacks from Doped Semiconductor Nanocrystals

Electrochromic properties can be enhanced by constructing photonic architectures, in which the reflectance contributes to optical modulation along with the intrinsic dynamic absorptivity of the material. However, optimization of reflectance is challenging without a rational design approach. Here, electrochemically tunable Bragg reflectors are demonstrated that are tuned to be highly transparent in the “off” state, achieving synergistic dynamic optical modulation of absorption and reflection in the visible and near‐infrared range. These Bragg stacks are composed of alternating doped semiconductor nanocrystal (NC) layers of 5 nm sized oxygen vacancy‐doped WO_3?x and 15 nm sized 0.4 at% Sn:In₂O₃ NCs. Combining judicious NC selection and processing optimization with guidance from optical simulations, optimized Bragg stacks are implemented for electrochromic window applications. NCs with high absorption coefficients are essential for strong transmission modulation, though this characteristic limits the dynamic range of the Bragg reflectance. Optimal reflectance modulation including a highly transparent “off” state is confirmed with in situ reflectance and transmittance measurement. More broadly, ligand‐stripped NCs can enable fabrication of complex device architectures on low‐cost flexible substrates. These results guide the design rules for accessing different types of doped semiconductor NC‐based tunable Bragg stacks, an exemplary photonic structure, over a broad wavelength range.     

Micropillar Cavity Design for 1.55-μm Quantum-Dot Single-Photon Sources

The 1.55-μm quantum-dot (QD) micropillar cavities are strongly required as single photon sources (SPSs) for silica-fiber-based quantum information processing. Theoretical analysis shows that the adiabatic distributed Bragg reflector (DBR) structure may greatly improve the quality of a micropillar cavity. An InGaAsP/InP micropillar cavity is originally difficult, but it becomes more likely usable with inserted tapered (thickness decreased towards the center) distributed DBRs. Simulation turns out that, incorporating adiabatically tapered DBRs, a Si/SiO₂-InP hybrid micropillar cavity, which enables weakly coupling InAs/InP quantum dots (QDs), can even well satisfy strong coupling at a smaller diameter. Certainly, not only the tapered structure, other adiabatic designs, e.g., both DBR layers getting thicker and one thicker one thinner, also improve the quality, reduce the diameter, and degrade the fabrication difficulty of Si/SiO₂-InP hybrid micropillar cavities. Furthermore, the problem of the thin epitaxial semiconductor layer can also be greatly resolved by inserting adiabatic InGaAsP/InP DBRs. With tapered DBRs, the InGaAsP/InP-air-aperture micro-pillar cavity serves as an efficient, coherent, and monolithically producible 1.55-μm single-photon source (SPS). The adiabatic design is thus an effective way to obtain prospective candidates for 1.55-μm QD SPSs.     

Simultaneous Improvement of Charge Generation and Extraction in Colloidal Quantum Dot Photovoltaics Through Optical Management

Inverted structure heterojunction colloidal quantum dot (CQD) photovoltaic devices with an improved performance are developed using single‐step coated CQD active layers with a thickness of ≈60 nm. This improved performance is achieved by managing the device architecture to simultaneously enhance charge generation and extraction by raising optical absorption within the depletion region. The devices are composed of an ITO/PEDOT:PSS/PbS‐CQD/ZnO/Al structure, in which the p–n heterojunction is placed at the rear (i.e., opposite to the side of illumination) of the devices (denoted as R‐Cell). Sufficient optical generation is achieved at very low CQD layer thicknesses of 45–60 nm because of the constructive interference caused by the insertion of ZnO between the CQD and the Al electrode. The power conversion efficiency (PCE) of R‐Cells containing a thin CQD layers (≈60 nm) is much higher (≈6%) than that of conventional devices containing CQD layers with a thickness of ≈300 nm (PCE ≈4.5%). This optical management strategy provides a general guide to obtain the optimal trade‐off between generation and extraction in planar p–n junction solar cells. In terms of device engineering, all the layers in our R‐Cells are fabricated using single coating, which can lead to compatibility with high‐throughput processes.     

Quantum Dot–Carbon Nanotube Hybrid Phototransistor with an Enhanced Optical Stark Effect

Enhanced carrier–carrier interactions in hybrid nanostructures exhibit exceptional electronic and optoelectronic properties. Carbon nanotubes demonstrate excellent switching behavior with high on/off ratio and high mobility but do not show photoresponse in the visible range, whereas quantum dots (QDs) shows excellent optical response in various optical ranges which can be tuned with diameter. Here, a simple and effective way to develop hybrid phototransistors with extraordinary optoelectronic properties is presented by decorating semiconducting QDs on the surface of a single‐walled carbon nanotube (SWCNT). This hybrid structure demonstrates clear negative photoresponse and optical switching behavior, which could be further tuned by applying external gate bias in the future. A clear type conversion of SWCNT transistor from p‐type to n‐type caused by a charge transfer from attached QDs to CNT is demonstrated. Moreover, this hybrid structure also demonstrates an enhancement in ‘optical Stark effect’ without applying any external electric field. Charged SWCNT surface plays a key role behind the enhancement of optical Stark effect in QDs. The carrier dynamics of the QD and CNT heterostructures system highlights the potential application opportunity of the quantum dot systems, which can be adaptable to the current technologies.     

Nitrogen‐Doped Carbon Networks for High Energy Density Supercapacitors Derived from Polyaniline Coated Bacterial Cellulose

Bacterial cellulose (BC) is used as both template and precursor for the synthesis of nitrogen‐doped carbon networks through the carbonization of polyaniline (PANI) coated BC. The as‐obtained carbon networks can act not only as support for obtaining high capacitance electrode materials such as activated carbon (AC) and carbon/MnO₂ hybrid material, but also as conductive networks to integrate active electrode materials. As a result, the as‐assembled AC//carbon‐MnO₂ asymmetric supercapacitor exhibits a considerably high energy density of 63 Wh kg^?1 in 1.0 m Na₂SO₄ aqueous solution, higher than most reported AC//MnO₂ asymmetric supercapacitors. More importantly, this asymmetric supercapacitor also exhibits an excellent cycling performance with 92% specific capacitance retention after 5000 cycles. Those results offer a low‐cost, eco‐friendly design of electrode materials for high‐performance supercapacitors.     

Planar light-emitting microcavities based on hydrogenated amorphous silicon carbide

The plasma-enhanced chemical vapor deposition (PECVD) method is used to fabricate planar Fabry-Perot microcavities (MCs) with an active region emitting light at the boundary between the visible and infrared (IR) spectral ranges. The MCs comprise an α-Si_{1 ? x} C _x :H active layer with an increased carbon content and distributed Bragg reflectors (DBRs) constituted by alternating nonemitting α-Si_{1 ? x} C _x :H/α-SiO₂ layers. The active layer and the DBRs are grown in a single technological cycle. Owing to the high optical contrast and low absorption of the layers constituting the DBRs, a high Q factor of the microcavities (Q = 316) and high emission directivity from the MCs for three pairs of layers in the DBRs are achieved. The intensity of the room-temperature photoluminescence exceeds by two orders of magnitude the emission intensity of an identical α-Si_{1 ? x} C _x :H layer without DBRs. Comparison of the experimental transmittance spectra and those calculated by the transfer-matrix method with consideration for dispersion of the real and imaginary parts of the refractive index of α-Si_{1 ? x} C _x :H is used to estimate the degree of systematic deviation of the layer thicknesses in the DBRs and to determine the upper limit of the absorption coefficient in α-Si_{1 ? x} C _x :H layers.     

Towards high‐efficiency multi‐junction solar cells with biologically inspired nanosurfaces

Multi‐junction solar cells offer extremely high power conversion efficiency with minimal semiconductor material usage, and hence are promising for large‐scale electricity generation. However, suppressing optical reflection in the UV regime is particularly challenging due to the lack of adequate dielectric materials. In this work, bio‐inspired antireflective structures are demonstrated on a monolithically grown Ga_0.5In_0.5P/In_0.01Ga_0.99As/Ge triple‐junction solar cell, which overcome the limited optical response of reference devices. The fabricated device also exhibits omni‐directional enhancement of photocurrent and power conversion efficiency, offering a viable solution to concentrated illumination with large angles of incidence. A comprehensive design scheme is further developed to tailor the reflectance spectrum for maximum photocurrent output of tandem cells. Copyright © 2012 John Wiley & Sons, Ltd.     

Microcavity polymer electroluminescent devices with solution-processed dielectric distributed Bragg reflectors utilizing inorganic copper (I) thiocyanate and insulating polymers

The concept of using printed inorganic/organic hybrid distributed Bragg reflectors (DBRs) utilizing inorganic semiconductor and insulating polymers in microcavity polymer electroluminescent devices is introduced to provide an approach to achieve the spectral narrowing and the strong forward directionality. The large refractive index contrast of approximately 0.5 (0.44) between inorganic copper(I) thiocyanate, CuSCN, and insulating polymer of poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE) (cellulose acetate, CA) results in the fabrication of solution-processed inorganic-organic hybrid dielectric DBRs with high reflectivity (>90%) from nanostructures consisting of only four (five) bilayers. For DBRs composed of CuSCN/CA alternative dielectric layers, all-solution processed microcavity polymer light-emitting diode based on highly conductive poly(ethylenedioxythiophene):poly(styrenesulfonate) anode except for Ag cathode exhibits the narrowing of EL spectrum with a full width at half maximum of approximately 25 nm and the maximum luminance of above 10,000 cd/m². From the viewpoint of dielectric DBRs based on ferroelectric polymer P(VDF-TrFE) with both low refractivity and high permittivity, we demonstrate a microcavity AC voltage-driven polymer electroluminescent device (μcACEL) which exhibits the spectral narrowing and the strong forward directionality. This work is anticipated to be useful for the development of solution-processed μcACEL with unique device architecture.     

Remote sensing and the optical properties of the narrow cylindrical leaves of juncus roemerianus

To develop a more complete foundation for remote sensing of the marsh grass Juncus roemerianus, we measured the optical properties of its cylindrical leaves at sites of different canopy height, biomass composition and amount, and connectivity to ocean flushing. To measure the leaf optical properties, we adapted a technique used for conifer needles. After establishing the reliability and limits of the adapted technique to the wider J.roemerianus leaves, mean transmittance and reflectance spectra were compared to associated leaf diameters from two dates in 1999 and 2002 and at each site. Transmittance was inversely related to leaf diameter. Mean transmittance and reflectance generated from reoccupation of many field sites in 2002 indicated little or no difference in transmittance between years, a slight reflectance difference in the visible (<2%) and a slightly higher reflectance difference in the near infrared (NIR) (<4%). Site comparison indicated limited ability to separate leaf transmittance but not reflectance by marsh type (e.g., low, medium, high) or biomass. Excluding one outlier, we found leaf transmittances could be adequately represented as 1% /spl plusmn/ 0.2% in the visible and 9% /spl plusmn/ 1% in the NIR and leaf reflectances represented from 14% to 16% in the visible and 71% to 75% in the NIR (the reflectance ranges represent 1999 and 2002 means). Reflectance and transmittance spectra associated with the dead J. roemerianus leaves displayed a spectrally flat increase from the visible to the NIR wavelengths. In total, we documented the atypical optical properties of the cylindrical J. roemerianus leaves and showed that to a first approximation, single means could represent leaf transmittance and visible leaf reflectance across all marsh zones and, after accounting for sample standardization, possibly the NIR reflectance as well.     

采用光学干涉方法实现高对比度聚合物发光二极管

为了得到高对比度的聚合物发光二极管（PLED）．设计并制作了消光干涉结构位于有机层之外的新型聚合物二极管。消光干涉层的结构为：CrOx／Cr／1TO／Cr。在玻璃衬底和ITO阳极之间溅射的光学干涉层可以部分消去背景光的反射。这种方法不需要考虑光学干涉层和OLED或PLED材料之间功函数匹配．以及在溅射过程中对有机层的损伤等问题。制作的器件的对比度为14．7：1．这比没有采用光学干涉结构的器件的对比度要高得多。结果说明新型的光学干涉结构确实起到了提高器件对比度的效果，对器件参数的进一步优化有望达到一个实用化目标。     

Molecular packing correlated fluorescence in TIPS-pentacene films

The molecular packing and optical properties of exposed and buried layers (i.e. the layers at the top surface and near the substrate, respectively) were systematically studied in 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) films coated by spin-coated (SC) and droplet-pinned-crystallization (DPC) methods. Buried layers in both films exhibit intense photoluminescence (PL) resembling the behaviors of the molecules in dilute solution ascribing to weak π-π stacking, while the exposed layers show extremely weak PL due to strong crystallinity. Polarized excitation PL spectra demonstrate that molecular orientation of the buried layers is quasi-ordered in the film coated by DPC method and completely disordered in the film coated by SC method. Besides, the strong crystallinity of the exposed TIPS-pentacene is verified by grazing incident wide-angle X-ray scattering measurement. The distinct differences in optical and structural properties between the exposed and buried layers indicate that TIPS-pentacene films are inhomogeneous in vertical direction due to interfacial effect, which affects the performance of photodiode fabricated with both films. The understanding of the molecular packing correlated fluorescence in TIPS-pentacene films is vital for optimizing the film structure to achieve high performance organic electronic devices.     

Flexible Near‐Infrared Plastic Phototransistors with Conjugated Polymer Gate‐Sensing Layers

Flexible near‐infrared (NIR) light‐sensing detectors are strongly required in the fast‐growing flexible electronics era, because they can serve as a vision system like eyes in various innovative applications including humanoid robots. Recently, keen interest has been paid to organic phototransistors due to their unique signal amplification and active matrix driving features over organic photodiodes. However, conventional NIR‐sensing organic phototransistors suffer from the limited use of organic materials because the channel layers play a dual role in both charge transport and sensing so that organic semiconducting materials with reasonably high charge mobility can be applied only. Here, it is demonstrated that a conjugated polymer, poly[{2,5‐bis‐(2‐ethylhexyl)‐3,6‐bis‐(thien‐2‐yl)‐pyrrolo[3,4‐c]pyrrole‐1,4‐diyl}‐co‐{2,2′‐(2,1,3‐benzothiadiazole)]‐5,5′‐diyl}] (PEHTPPD‐BT), which exhibits no transistor performance as a channel layer, can stably detect a NIR light (up to 1000 nm) as a gate‐sensing layer (GSL) when it is placed between gate‐insulating layers and gate electrodes. The flexible array (10 × 10) detectors with the PEHTPPD‐BT GSLs could effectively sense NIR light without visible light interference by applying visible light cut films.     

聚合物含量对锆钛酸铅多层膜光学特性的影响

利用溶胶-凝胶法,由添加高分子聚合物聚乙烯吡咯烷酮(PVP)的化学溶液制备了锆钛酸铅(Pb Zr0.4Ti0.6O3,PZT)多层膜,研究了溶液中聚合物PVP的含量对多层膜光学性能的影响.测试表明,PZT多层膜呈现出由致密层和多孔层交替排布的层状结构,在可见光区具有单一的高反射率带,且反射带中心波长在一定范围内随着溶液中PVP浓度的升高向长波方向移动.在PVP的相对摩尔比为x=1.0时,多层膜反射性能达到最优,室温绝对反射率高达89%,反射带宽为44 nm.     

An Integrated Multifunctional Nanoplatform for Deep‐Tissue Dual‐Mode Imaging

The combination of biocompatible superparamagnetic and photoluminescent nanoparticles (NPs) is intensively studied as highly promising multifunctional (magnetic confinement and targeting, imaging, etc.) tools in biomedical applications. However, most of these hybrid NPs exhibit low signal contrast and shallow tissue penetration for optical imaging due to tissue‐induced optical extinction and autofluorescence, since in many cases, their photoluminescent components emit in the visible spectral range. Yet, the search for multifunctional NPs suitable for high photoluminescence signal‐to‐noise ratio, deep‐tissue imaging is still ongoing. Herein, a biocompatible core/shell/shell sandwich structured Fe₃O₄@SiO₂@NaYF₄:Nd³⁺ nanoplatform possessing excellent superparamagnetic and near‐infrared (excitation) to near‐infrared (emission), i.e., NIR‐to‐NIR photoluminescence properties is developed. They can be rapidly magnetically confined, allowing the NIR photoluminescence signal to be detected through a tissue as thick as 13 mm, accompanied by high T₂ relaxivity in magnetic resonance imaging. The fact that both the excitation and emission wavelengths of these NPs are in the optically transparent biological windows, along with excellent photostability, fast magnetic response, significant T₂‐contrast enhancement, and negligible cytotoxicity, makes them extremely promising for use in high‐resolution, deep‐tissue dual‐mode (optical and magnetic resonance) in vivo imaging and magnetic‐driven applications.     

Lateral Phase Separation Gradients in Spin‐Coated Thin Films of High‐Performance Polymer:Fullerene Photovoltaic Blends

In this study, it is demonstrated that a finer nanostructure produced under a rapid rate of solvent removal significantly improves charge separation in a high‐performance polymer:fullerene bulk‐heterojunction blend. During spin‐coating, variations in solvent evaporation rate give rise to lateral phase separation gradients with the degree of coarseness decreasing away from the center of rotation. As a result, across spin‐coated thin films the photocurrent at the first interference maximum varies as much as 25%, which is much larger than any optical effect. This is investigated by combining information on the surface morphology of the active layer imaged by atomic force microscopy, the 3D nanostructure imaged by electron tomography, film formation during the spin coating process imaged by optical interference and photocurrent generation distribution in devices imaged by a scanning light pulse technique. The observation that the nanostructure of organic photovoltaic blends can strongly vary across spin‐coated thin films will aid the design of solvent mixtures suitable for high molecular‐weight polymers and of coating techniques amenable to large area processing.