Quantum dot solar concentrators

The luminescent properties of core-shell quantum dots are being exploited in an unconventional solar concentrator, which promises to reduce the cost of photovoltaic electricity. Luminescent solar collectors have advantages over geometric concentrators in that tracking is unnecessary and both direct and diffuse radiation can be collected. However, development has been limited by the performance of luminescent dyes. We present experimental and theoretical results with a novel concentrator in which the dyes are replaced by quantum dots. We have developed a self-consistent thermodynamic model for planar concentrators and find that this three-dimensional flux model shows excellent agreement with experiment.     

Carbon Nanoparticles as Versatile Auxiliary Components of Perovskite-Based Optoelectronic Devices

Metal halide perovskite-based optoelectronics has experienced an unprecedented development in the last decade, while further improvements of efficiency, stability, and economic gains of such devices require novel engineering concepts. The use of carbon nanoparticles as versatile auxiliary components of perovskite-based optoelectronic devices is one strategy that offers several advantages in this respect. In this review, first, a brief introduction is offered on metal halide perovskites and on the major performance characteristics of related optoelectronic devices. Then, the versatility and merits of different kinds of carbon nanoparticles, such as graphene quantum dots and carbon dots, are discussed. The tunability of their electronic properties is focused upon, their interactions with perovskite components are analyzed, and different strategies of their implementation in optoelectronic devices are introduced, which include solar cells, light-emitting diodes, luminescent solar concentrators, and photodetectors. It is shown how carbon nanoparticles influence charge carriers extraction and transport, promote perovskite crystallization, allow for efficient passivation, block ion migration, suppress hysteresis, enhance their environmental stability, and thus improve the performance of perovskite-based optoelectronic devices.     

Phase matching limitations of high efficiency second harmonic generation

-A discussion of second harmonic generation with imperfect phase matching in the high conversion limit is presented. Phase modulation of the fundamental pulse, dispersion, central frequency wavevector mismatch, and fundamental depletion are included. The results show that even small amounts of phase modulation or central frequency wavevector mismatch can limit harmonic generation and must be considered at high conversion efficiency. Both spatial and temporal phase matching parameters are more restrictive at high conversion efficiency because of the narrowing of the central phase matching peak. If the harmonic conversion process is overdriven, severe distortion of the harmonic and transmitted fundamental pulses can result. Cascade harmonic generation of neodymium laser radiation to 266 nm is presented as an example.     

Fundamental Tradeoff between Emission Intensity and Efficiency in Light‐Emitting Electrochemical Cells

The characteristic doping process in polymer light‐emitting electrochemical cells (LECs) causes a tradeoff between luminescence intensity and efficiency. Experiments and numerical modeling on thin film polymer LECs show that, on the one hand, carrier injection and transport benefit from electrochemical doping, leading to increased electron‐hole recombination. On the other hand, the radiative recombination efficiency is reduced by exciton quenching by polarons involved in the doping. Consequently, the quasi‐steady‐state luminescent efficiency decreases with increasing ion concentration. The transient of the luminescent efficiency shows a characteristic roll‐off while the current continuously increases, attributed to ongoing electrochemical doping and the associated exciton quenching. Both effects can be modeled by exciton polaron‐quenching via diffusion‐assisted Förster resonance energy transfer. These results indicate that the tradeoff between efficiency and intensity is fundamental, suggesting that the application realm of future LECs should be sought in high‐brightness, low‐production cost devices, rather than in high‐efficiency devices.     

三代半导体功率器件的特点与应用分析

以S i双极型功率晶体管为代表的第一代半导体功率器件和以GaAs场效应晶体管为代表的第二代半导体功率器件为雷达发射机的大规模固态化和可靠性提高做出了贡献。近年来以S iC场效应功率晶体管和GaN高电子迁移率功率晶体管为代表的第三代半导体--宽禁带半导体功率器件具有击穿电压高、功率密度高、输出功率高、工作效率高、工作频率高、瞬时带宽宽、适合在高温环境下工作和抗辐射能力强等优点。人们寄希望于宽禁带半导体功率器件来解决第一代、第二代功率器件的输出功率低、效率低和工作频率有局限性以至于无法满足现代雷达、电子对抗和通信等电子装备需求等方面的问题。文中简要介绍了半导体功率器件的发展背景、发展过程、分类、特点、应用、主要性能参数和几种常用的半导体功率器件;重点叙述了宽禁带半导体功率器件的特点、优势、研究进展和工程应用;对宽禁带半导体功率器件在新一代雷达中的应用前景和要求进行了探讨。     

Recent Progress in Functional Dye-Doped Liquid Crystal Devices

As a typical representative of dopants, organic functional dyes have demonstrated their significant roles in novel smart liquid crystal (LC) devices, and dye-doped LCs have also been a source of inspiration for scientists to design and fabricate stimuli-gated materials or devices for envisioned applications in a wide range of areas. In this review, the focus on dichroic dyes, fluorescent dyes, and photothermal dyes, and the recent progress of the LC devices employing these dyes as dopants are overviewed. The review highlights the developments of the novel LC devices doped with these dyes. The structures, designs, and applications of these devices are outlined. The underlying principles of dichroic dyes, fluorescent dyes, and photothermal dyes which are utilized as functional dopants in LC devices are first introduced. Subsequently, the novel developments of functional dye-doped LC devices in the application fields of smart windows, attenuators for augmented reality (AR) systems, color-changeable textiles, dichroic color filters, dual-mode circular polarizers, chirality detectors, optical limiters, switchable luminescent solar concentrators, multiple information encryption, anti-counterfeiting, photo-addressed transparent displays, circularly polarized luminescence, tunable lasers, and light-driven soft actuators are discussed. Finally, the challenge and the strategies for the future improvement of dye-doped LC devices are also discussed.     

Manufacturing cost of active-matrix liquid-crystal displays as afunction of plant capacity

This work models the cost of 10-in class active-matrix liquid-crystal display (AM-LCD) manufacturing as a function of plant capacity for both first generation plants in 1993 and second generation plants in 1995. In order to model manufacturing costs as a function of plant capacity, this work distinguishes between capacity-dependent and capacity-independent costs. Among the costs included in our model are the costs of capital equipment, materials and labor. Decreases in materials and components costs and improvements in process yield are shown to be the primary factors driving reductions in manufacturing cost per display for large-scale plants. The minimum efficient scale is found to be roughly 57000 displays per month for a first generation plant and roughly 150000 displays per month for a second generation plant     

Using combinatorial designs to construct partial concentrators

Partial concentrators have been shown to be useful in the construction of various types of interconnecting networks. It is shown how a large class of combinatorial designs, which are well studied in the literature, can be used to construct partial concentrators and thus provide a direct link between the fields of combinatorial designs and switching networks. A construction efficiency factor called the cost ratio is introduced, and some lower bounds on the capacity of partial concentrators having certain characteristics are established. It is shown how to use various combinatorial designs to construct partial concentrators having these same characteristics and corresponding capacities     

Evidence for the Band‐Edge Exciton of CuInS2 Nanocrystals Enables Record Efficient Large‐Area Luminescent Solar Concentrators

Ternary I‐III‐VI₂ nanocrystals (NCs), such as CuInS₂, are receiving attention as heavy‐metals‐free materials for solar cells, luminescent solar concentrators (LSCs), LEDs, and bio‐imaging. The origin of the optical properties of CuInS₂ NCs are however not fully understood. A recent theoretical model suggests that their characteristic Stokes‐shifted and long‐lived luminescence arises from the structure of the valence band (VB) and predicts distinctive optical behaviours in defect‐free NCs: the quadratic dependence of the radiative decay rate and the Stokes shift on the NC radius. If confirmed, this would have crucial implications for LSCs as the solar spectral coverage ensured by low‐bandgap NCs would be accompanied by increased re‐absorption losses. Here, by studying stoichiometric CuInS₂ NCs, it is revealed for the first time the spectroscopic signatures predicted for the free band‐edge exciton, thus supporting the VB‐structure model. At very low temperatures, the NCs also show dark‐state emission likely originating from enhanced electron‐hole spin interaction. The impact of the observed optical behaviours on LSCs is evaluated by Monte Carlo ray‐tracing simulations. Based on the emerging device design guidelines, optical‐grade large‐area (30×30 cm²) LSCs with optical power efficiency (OPE) as high as 6.8% are fabricated, corresponding to the highest value reported to date for large‐area devices.     

Joint partial computation offloading and resource allocation inMEC-enable networks

The sudden surge of various applications poses great challenges to the computation capability of mobile devices. To address this issue, computation offloading to multi-access edge computing(MEC) was proposed as a promising paradigm. This paper studies partial computation offloading scenario by considering time delay and energy consumption, where the task can be splitted into several blocks and computed both in local devices and MEC, respectively. Since the formulated problem is a nonconvex probl...     

折返点匹配的宽带二倍频实验研究

在二次谐波转换中,基频光和倍频光的群速失配是限制转换带宽的主要因素。利用折返点匹配的宽带谐波转换技术能同时实现基频光和倍频光的相位匹配和群速匹配,理论计算表明在折返点匹配的情况下,倍频转换带宽将显著增加。分别利用厚度10 mm,氘含量12%的KD*P晶体和厚度12 mm的KDP晶体对中心波长为1053 nm,谱宽为31 nm,能量为620μJ的基频光进行折返点匹配二倍频和传统二倍频的对比实验,前者取得了22 nm的转换带宽,远大于后者7 nm的转换带宽。实验结果证实了理论计算的正确性,显示了折返点匹配宽带谐波转换技术的优越性。相应地,前者转换效率为25%,大于后者20%的转换效率,导致倍频转换效率较低的主要因素是入射基频光的光束质量和光谱质量较差。     

Electrical performance evaluation of low‐concentrating non‐imaging photovoltaic concentrator

Second generation prototype photovoltaic facades of reduced costs incorporating devices with optically concentrating elements (PRIDE) incorporate 6 mm wide ‘Saturn’ solar cells at the absorber of the dielectric concentrator. The concentrators were made using injection moulding technique with potential to manufacture in large‐scale applications. Four different concentrator panels have been experimentally verified at outdoors to identify the non‐identical current–voltage (I–V) curves. The I–V curve, fill factor and solar to electrical conversion efficiency of four PRIDE concentrator modules have been evaluated from the 24 manufactured in the ‘IDEOCONTE’ project. The maximum solar to electrical conversion efficiency and the fill factor of the PRIDE concentrator were 9·1 and 70%, respectively. The mismatch loss of the ‘unit concentrators’ has been identified that occurred due to the lack of bonding between the concentrator unit and the solar cell and the rear glass. The average power concentration ratio of PRIDE concentrators manufactured by the improved method was 2·10 compared to a similar non‐concentrating panel and the optical efficiency of the PRIDE system was 83%. Copyright © 2008 John Wiley & Sons, Ltd.     

新型半导体功率器件在现代雷达中的应用研究(Ⅰ)

目前第一代半导体功率器件的制造技术和应用技术已趋于成熟,S波段及以下波段功率器件的输出功率、工作效率和可靠性指标都已达到相当高的水平。近年来第二代半导体功率器件的制造技术和应用技术发展迅速,S波段、C波段和X波段的器件已经形成了一定的系列化商品。但是面对现代雷达等新一代电子装备的需求,半导体功率器件在高功率、高效率和高频率等方面与真空管器件相比仍逊色许多,Si和GaAs功率器件的输出功率工作频率短期内不大可能有大的提高,而第三代半导体功率器件——宽禁带半导体器件固有的宽禁带、高击穿场强和良好的热稳定性等特性,决定了其可以输出更高功率、工作在更高频率、具有更高效率,并可更好地满足现代雷达的要求。     

Effect of ultrasonic treatment on photoelectric and luminescent properties of ZnSe crystals

The results of the effect of ultrasonic treatment of ZnSe crystals on the structure of the energy spectrum of electronic states of centers with deep levels forming photoelectric and luminescent properties of this compound are presented. It is for the first time proved experimentally that the climb of edge dislocations under the effect of ultrasound leads to regrouping and generation of defects forming deep levels, which manifest themselves in phenomena of photosensitivity and radiative recombination.     

Third generation photovoltaics: Ultra‐high conversion efficiency at low cost

Since the early days of terrestrial photovoltaics, a common perception has been that ‘first generation’ silicon wafer‐based solar cells eventually would be replaced by a ‘second generation’ of lower cost thin‐film technology, probably also involving a different semiconductor. Historically, cadmium sulphide, amorphous silicon, copper indium diselenide, cadmium telluride and now thin‐film polycrystalline silicon have been regarded as key thin‐film candidates. Any mature solar cell technology seems likely to evolve to the stage where costs are dominated by those of the constituent materials, be they silicon wafers or glass sheet. It is argued, therefore, that photovoltaics is likely to evolve, in its most mature form, to a ‘third generation’ of high‐efficiency thin‐film technology. By high efficiency, what is meant is energy conversion values double or triple the 15–20% range presently targeted, closer to the thermodynamic limit of 93%. Tandem cells are the best known of such high‐efficiency approaches, where efficiency can be increased merely by adding more cells of different bandgap to a cell stack, at the expense of increased complexity and spectral sensitivity. However, a range of other more ‘paralleled’ approaches offer similar efficiency to an infinite stack of tandem cells. These options are reviewed together with possible approaches for practical implementation, likely to become more feasible with the evolution of materials technology over the next two decades. Copyright © 2001 John Wiley & Sons, Ltd.     

Lightpath concentrators for all-optical networks

In some deployments of all-optical networks, it is necessary to concentrate the lightpaths from some fibers to fewer fibers. An N/spl times/M lightpath concentrator is an optical component for this purpose, and it concentrates the lightpaths from N incoming fibers to M outgoing fibers. In this paper, three designs of N/spl times/M lightpath concentrators are proposed. The first design is a generalization of optical crossconnects, and it requires M/spl times/M optical switches. The second design incorporates the concept of partial concentration so that it requires only m/spl times/m optical switches (where m相似文献   

Search strategy switching: A cost model and an analysis of backtracking

Test generation algorithms contain search strategies which are used to control decision making when the algorithm encounters a choice of signal value, or what action to perform next. Our study of traditional search strategies used in automatic test pattern generation has led us to the observation that no single strategy is superior for all faults in a circuit and all circuits. Further experimentation led to the conclusion that a combination of search strategies provides better fault coverage and/or faster ATPG for a given backtrack limit. Instead of using just one strategy up to the backtrack limit, a primary strategy is used for the first half of the backtrack limit, then a secondary strategy is used for the second half of the backtrack limit. This article presents a qualitative ATPG cost model based on the number of test generation events, uses this model to explain why search strategy switching is faster, and shows experimental evidence to verify both the cost model and search strategy switching theory. The experiments were performed with the ISCAS circuits and our implementation of the FAN algorithm.     

Defect‐Minimized PEDOT:PSS/Planar‐Si Solar Cell with Very High Efficiency

Hybrid solar cells made of a p‐type conducting polymer, poly(3,4‐ethyl thiophene):polystyrenesulfonate (PEDOT:PSS), on Si have gained considerable interest in the fabrication of cost‐effective high‐efficiency devices. However, most of the high power conversion efficiency (PCE) performances have been obtained from solar cells fabricated on surface‐structured Si substrates. High‐performance planar single‐junction solar cells have considerable advantages in terms of processing and cost, because they do not require the complex surface texturing processes. The interface of single‐junction solar cells can critically influence the performance. Here, we demonstrate the effect of adding different surfactants in a co‐solvent‐optimized PEDOT:PSS polymer, which, in addition to acting as a p‐layer and as an anti‐reflective coating, also enhances the device performance of a hybrid planar‐Si solar cell. Using time‐of‐flight secondary ion mass spectrometry, we conduct three‐dimensional chemical imaging of the interface, which enables us to characterize the micropore defects found to limit the PCE. Upon minimizing these micropore defects with the addition of optimized amounts of fluorosurfactant and co‐solvent, we achieve a PEDOT:PSS/planar‐Si cell with a record high PCE of 13.3% for the first time. Our present approach of micropore defect reduction can also be used to improve the performance of other organic electronic devices based on PEDOT:PSS.     

Defect engineering in implantation technology of silicon light-emitting structures with dislocation-related luminescence

Results obtained in development of physical foundations of ion implantation technology for fabrication of silicon light-emitting structures (LESs) based on dislocation-related luminescence and intended for operation at wavelengths close to ∼1.6 μm are summarized. The development of the concept of defect engineering in the technology of semiconductor devices makes it possible to determine the fundamental aspects of the process of defect formation; reveal specific features of the emission spectra related to changes in the implantation conditions of Er, Dy, Ho, O, and Si ions and the subsequent annealing; and design light-emitting structures with a desirable spectrum of luminescent centers and extended structural defects. The technological conditions in which only a single type of extended structural defect (Frank loops, perfect prismatic loops, or pure edge dislocations) is introduced into the light-emitting layer are found, which enables analysis of the correlation between the concentration of extended defects of a certain type and the intensity of lines of the dislocation-related luminescence. The key role of intrinsic point lattice defects in the origination and transformation of extended structural defects and luminescent centers responsible for the dislocation-related luminescence is revealed. It is found that the efficiency of luminescence excitation from the so-called D1 centers, which are of particular interest for practical applications, varies by more than two orders of magnitude between structures fabricated using different technological procedures. High-efficiency silicon light-emitting diodes with room-temperature dislocation-related luminescence have been fabricated.     

A Highly Integrated Power Management IC for Advanced Mobile Applications

Wireless communication now has the speed and power to converge seamlessly with other consumer and business electronics. However, battery technology has not kept pace with advancement in circuit technology. As a result, design of power management is becoming a more complex problem for this new generation of wireless devices with converged voice, data, and multimedia. In this paper, a highly integrated power management IC (PMIC) is presented which enables mobile devices that are more cost effective, thinner and more compact with better power efficiency. The overall architecture and system level design considerations are described. The design details of two key building blocks - low-dropout linear regulator (LDO) and switch-mode DC-DC converter - are also discussed, including a novel frequency compensation method for LDO.