Boosting Photovoltaic Performance for Lead Halide Perovskites Solar Cells with BF4− Anion Substitutions

Composition engineering is a particularly simple and effective approach especially using mixed cations and halide anions to optimize the morphology, crystallinity, and light absorption of perovskite films. However, there are very few reports on the use of anion substitutions to develop uniform and highly crystalline perovskite films with large grain size and reduced defects. Here, the first report of employing tetrafluoroborate (BF₄^?) anion substitutions to improve the properties of (FA = formamidinium, MA = methylammonium (FAPbI₃)_0.83(MAPbBr₃)_0.17) perovskite films is demonstrated. The BF₄^? can be successfully incorporated into a mixed‐ion perovskite crystal frame, leading to lattice relaxation and a longer photoluminescence lifetime, higher recombination resistance, and 1–2 orders magnitude lower trap density in prepared perovskite films and derived solar cells. These advantages benefit the performance of perovskite solar cells (PVSCs), resulting in an improved power conversion efficiency (PCE) of 20.16% from 17.55% due to enhanced open‐circuit voltage (V_OC) and fill factor. This is the highest PCE for BF₄^? anion substituted lead halide PVSCs reported to date. This work provides insight for further exploration of anion substitutions in perovskites to enhance the performance of PVSCs and other optoelectronic devices.     

Improving Defect‐Based Quantum Emitters in Silicon Carbide via Inorganic Passivation

Defect‐based color centers in wide‐bandgap crystalline solids are actively being explored for quantum information science, sensing, and imaging. Unfortunately, the luminescent properties of these emitters are frequently degraded by blinking and photobleaching that arise from poorly passivated host crystal surfaces. Here, a new method for stabilizing the photoluminescence and charge state of color centers based on epitaxial growth of an inorganic passivation layer is presented. Specifically, carbon antisite‐vacancy pairs (CAV centers) in 4H‐SiC, which serve as single‐photon emitters at visible wavelengths, are used as a model system to demonstrate the power of this inorganic passivation scheme. Analysis of CAV centers with scanning confocal microscopy indicates a dramatic improvement in photostability and an enhancement in emission after growth of an epitaxial AlN passivation layer. Permanent, spatially selective control of the defect charge state can also be achieved by exploiting the mismatch in spontaneous polarization at the AlN/SiC interface. These results demonstrate that epitaxial inorganic passivation of defect‐based quantum emitters provides a new method for enhancing photostability, emission, and charge state stability of these color centers.     

Causes and Solutions of Recombination in Perovskite Solar Cells

Organic–inorganic hybrid perovskite materials are receiving increasing attention and becoming star materials on account of their unique and intriguing optical and electrical properties, such as high molar extinction coefficient, wide absorption spectrum, low excitonic binding energy, ambipolar carrier transport property, long carrier diffusion length, and high defects tolerance. Although a high power conversion efficiency (PCE) of up to 22.7% is certified for perovskite solar cells (PSCs), it is still far from the theoretical Shockley–Queisser limit efficiency (30.5%). Obviously, trap‐assisted nonradiative (also called Shockley–Read–Hall, SRH) recombination in perovskite films and interface recombination should be mainly responsible for the above efficiency distance. Here, recent research advancements in suppressing bulk SRH recombination and interface recombination are systematically investigated. For reducing SRH recombination in the films, engineering perovskite composition, additives, dimensionality, grain orientation, nonstoichiometric approach, precursor solution, and post‐treatment are explored. The focus herein is on the recombination at perovskite/electron‐transporting material and perovskite/hole‐transporting material interfaces in normal or inverted PSCs. Strategies for suppressing bulk and interface recombination are described. Additionally, the effect of trap‐assisted nonradiative recombination on hysteresis and stability of PSCs is discussed. Finally, possible solutions and reasonable prospects for suppressing recombination losses are presented.     

国内大型超算中心系统及应用发展态势比较分析

超级计算机系统的计算能力与高性能计算的应用水平作为国内外超级计算发展的重要标杆,已日愈受到高度关注和重视,本文主要从超级计算机系统建设和高性能计算应用两方面,对国内几个具有代表性的大型超算中心的发展态势进行比较分析,探讨促进我国大型超算中心可持续发展的相关问题与建议。     

Feasibility study of a solar-assisted heating/cooling system for an aquatic centre in hot and humid climates

This paper reports on a feasibility study of a solar-powered heating/cooling system for a swimming pool/space combination in a tropical environment. The system utilizes an absorption chiller and a cooling tower to meet the facilities and locker room load. The heating is accomplished by employing hot water generated by heat exchange with the solar collector working fluid. Two thermal storage tanks were employed for the collector and domestic use. The absorption chiller utilizes hot water to regenerate the LiBr solution. The proposed system enables the swimming season to be extended from sixteen weeks to fifty-two weeks. Simulation results indicate that a combination of a double glazed collector area of 600–4800 m² and a storage tank volume of 11·36 m³ results in a 25–37% reduction in the consumption of natural gas. Economic analysis is performed based on the life-cycle-cost method and takes into account the effects of discount rate, fuel price and fuel inflation rate. Different scenarios for which the solar-assisted system is economical are presented and analysed. © 1997 John Wiley & Sons, Ltd.     

B2C电子商务中配送中心选址优化的模型与算法

在考虑商品供应成本因素的基础上,结合B2C电子商务企业物流配送网络的特点,建立了混合0-1整数规划的配送中心选址优化模型．该模型是一种特殊形式的选址-分配模型,具有NP难性质．为求解上述模型,开发了嵌入表上作业法的遗传算法．实例研究表明,该算法能高效求得模型的优化解,是求解物流配送中心选址这类复杂优化问题的一个较好方法．     

Laser cooling of solids containing local centers with electric dipole allowed transitions: a feasibility study

Various insulating materials containing local centers with electric dipole allowed transitions were studied under excitation in the long-wavelength tail of the absorption spectrum (“laser cooling regime”). Though no actual cooling was detected, spectra with a strong anti-Stokes component were observed which demonstrate the possibility to employ electron–phonon bands of electric dipole allowed transitions for optical refrigeration. The mechanisms responsible for the absence of observable optical refrigeration are discussed.     

A novel energy-driven computing paradigm for e-health scenarios

A first-rate e-Health system saves lives, provides better patient care, allows complex but useful epidemiologic analysis and saves money. However, there may also be concerns about the costs and complexities associated with e-health implementation, and the need to solve issues about the energy footprint of the high-demanding computing facilities. This paper proposes a novel and evolved computing paradigm that: (i) provides the required computing and sensing resources; (ii) allows the population-wide diffusion; (iii) exploits the storage, communication and computing services provided by the Cloud; (iv) tackles the energy-optimization issue as a first-class requirement, taking it into account during the whole development cycle. The novel computing concept and the multi-layer top-down energy-optimization methodology obtain promising results in a realistic scenario for cardiovascular tracking and analysis, making the Home Assisted Living a reality.     

Optimal capacity management and planning in services delivery centers

This paper considers human server systems of queues that arise within the information technology services industry. We develop a two-phase stochastic optimization solution approach to effectively and efficiently address the capacity management and planning processes of information technology services delivery centers. A large collection of numerical experiments of real-world human server system environments investigates various issues of both theoretical and practical interest, quantifying the significant benefits of our approach as well as evaluating the financial-performance trade-offs often encountered in practice.     

Key based data analytics across data centers considering bi-level resource provision in cloud computing

Due to the distribution characteristic of the data source, such as astronomy and sales, or the legal prohibition, it is not always practical to store the world-wide data in only one data center (DC). Hadoop is a commonly accepted framework for big data analytics. But it can only deal with data within one DC. The distribution of data necessitates the study of Hadoop across DCs. In this situation, though, we can place mappers in the local DCs, where to place reducers is a great challenge, since each reducer needs to process almost all map output across all involved DCs. In this paper, a novel architecture and a key based scheme are proposed which can respect the locality principle of traditional Hadoop as much as possible while realizing deployment of reducers with lower costs. Considering both the DC level and the server level resource provision, bi-level programming is used to formalize the problem and it is solved by a tailored two level group genetic algorithm (TLGGA). The final results, which may be dispersed in several DCs, can be aggregated to a designative DC or the DC with the minimum transfer and storage cost. Extensive simulations demonstrate the effectiveness of TLGGA. It can outperform both the baseline and the state-of-the-art mechanisms by 49% and 40%, respectively.