多重激子效应及其在先进太阳电池中的应用(上)

以多重激子产生的碰撞电离过程为其物理机制,结合Fermi在1950年建立的统计模型理论,建立了一个能够解释较大尺度范围内的纳米半导体颗粒中多重激子产生效应的统计模型。PbSe量子点中多重激子效应的计算结果不仅证实了该模型的正确性,并能初步解决该领域现存的争议。此外,改进了计算太阳电池效率的细致平衡模型,详细探讨了多重激子产生对于纳米结构的先进太阳电池效率的增强作用。     

激子和载流子输运研究：I.有机肖特基型固态太阳电池

提出了有机肖特基型固态太阳电池的理论模型，假设只有势垒区的激子和产生于中性区且扩散到势垒区的激子才能被内建场离解成自由载流子，而被电极收集。该模型综合考察了内建场对激子产生、输运和离解及自由载流子分离和由电极收集的影响，并解释了场依赖的收集率以及电池的光导作用光谱与份菁薄膜的吸收光谱同相的原因。研究了表面复合速度对自由载流子收集率的影响。据此，认为强的取向内建场、超薄膜化和分子排列取向化是提高有机     

新发明——光电功率转换器

目前,把光能直接变为电能主要是利用光伏器件。这种器件又有多种形式,其理论效率20%左右,而实际效率仅约10%。各种植物的绿叶或藻类细胞含有某种结构,能把光子能转换为包含碳、氢、氧和少量其他元素(如镁)的化学能。这种过程就是光合作用,这也是光化转换的一种方式。其他一些利用光电化学能直接产生电能的方法,其效率为6%到7%,理论效率也只有20%。美国的Alvin M.Marks发明了一种和普通光电池根本不同的光电功率转换器。它利用微型偶极天线阵和微型整流器,将光子能直接变为直流电能,可将转换效率提高到75%。     

水热法制备TiO2纳米晶胶体及其在DSSC电池中的应用

采用钛酸异丙酯作前驱体，利用水热法制备了TiO2纳米溶胶溶液。以此制备了染料敏化太阳能电池的光阳极并组装电池。对产物采用激光粒度仪（HPPS）、X射线衍射（XRD）、扫描电镜（SEM）等进行表征。XRD显示了TiO2纳米颗粒为纯锐钛矿结构，SEM观察薄膜电极呈多孔结构。表征电池的光电化学性能，所制备的TiO2纳米晶薄膜的光电转换效率达到3．03％。     

光化学在环境保护中的应用

所谓光化学反应，就是只有在光的作用下才能进行的化学反应。该反应中分子吸收光能被激发到高能态，然后电子激发态分子进行化学反应。光化学反应的活化能来源于光子的能量。在太阳能利用中，光电转换以及光化学转换一直是光化学研究十分活跃的领域。８０年代初，开始研究光化学应用于环境保护，其中光化学降解治理污染尤受重视，包括无催化剂和有催化剂的光化学降解。前者多采用臭氧和过氧化氢等作为氧化剂，在紫外光的照射下使污染物氧化分解；后者又称光催化降解，一般可分为均相、多相两种类型。均相光催化降解主要以Ｆｅ２＋或Ｆｅ３＋…     

激子和载流子输运的研究：Ⅱ.有机p—n异质结固态太阳电池

在实验工作的基础上，提出双层ｐ－ｎ异质结有机太阳电池中激子和载流子输运的理论模型。假设只有扩散到结区的激子和该区产生的激子，才对形成光电流有贡献。这些激子被有机／有机界面的内建场离解成自由载流子。而后，电子在北红（ｎ型有机半导体）层传导，空穴在酞菁（ｐ型有机半导体）层传导。据此，讨论了双层异质结电池的填充因子和光电转换效率均比单层肖特基型电池获得改善的机制。结合实验分析，认为在北红／酞菁异质结电池中北红（Ｍｅ－ＰＴＣ）层和酞菁（ＣｌＡｌＰｃ）层之间存在Ｆｏｒｓｔｅｒ能量转移。     

多层有机薄膜太阳电池的结构优化

针对由CuPc/PTCDA/C60组成的3层有机薄膜太阳电池结构,基于光学干涉效应以及激子扩散理论,研究光波在多层薄膜中的传输特性,深入分析限制有机光伏效率的光吸收和激子扩散两个主要过程。利用Matlab软件从理论上对该结构中各层有机薄膜的厚度进行优化,从而可提高电池的外量子效率和光生电流密度,得到CuPc(4 nm)/PTCDA(23 nm)/C60(67 nm)的最佳膜厚组合,使得外量子效率达到34.67%,光生电流密度为0.1417 A/m2,稳态激子浓度分布显著增加,而未经优化的电池结构的外量子效率为9.7%,光生电流密度为0.1291 A/m2。     

光电化学电池（PEC）分解水制氢技术

本文较全面地阐述了光电化学电池分解水制氢的各种结构及其工作原理,对各种结构的优势、存在的问题以及能量转换效率等进行了较详细的分析,并介绍了目前的最新成果和研究动向。     

新产品

能捕获超过90%光能量的新型纳米天线据美国物理学家组织网5月17日(北京时间)报道,美国密苏里大学工程人员开发出一种柔性太阳能薄片,能捕获超过90%的光能量,并计划在5年内制造出可用于消费领域的样机。相关设计与制造过程在《太阳能工程》杂志上有详细介绍。该设备是一种纳米天线电磁收集器(nanoantenna     

澳研制出太阳能高效接收涂层

澳大利亚的研究人员研制出一种高效的太阳能接收涂层。它可将 98%的照射来的阳光转换志热能。它涂地太阳能热收集器的表面。他们还把这种涂层装入太阳能发电机 ,它利用热能把水煮沸并用蒸气驱动一台汽轮机从而发电。这个系统对照射其上的太阳光的转换率是 2 0 % ,这使之可与普通电厂相竞争 ,或者比普通电厂成本更低。研究者称 ,该涂层高效、选择性表面 (ＨＥＳＳ)由数层金属、陶瓷合金以及绝缘材料构成。这种夹层结构使层体能有效地吸收阳光中的高能辐射。同时 ,层体限制了低能红外辐射的再辐射。这意味着新涂层的热量散失仅为现有热表面散…     

Efficient one-dimensional Pt-based nanostructures for methanol oxidation reaction: An overview

The direct methanol fuel cells (DMFCs) have motivated researchers to conduct multifaceted investigations by the virtues of inexpensive raw material and high energy density. Tuning the morphology and composition of Pt-based catalysts with one-dimensional (1D) nanostructures has been proved to be determinant to design high-performance electrocatalysts towards methanol oxidation reaction (MOR) for DMFCs. Over the past decade, significant progress has been achieved in improving the MOR activity of Pt-based catalysts. Herein, this review briefly presents several typical 1D Pt-based nanostructures, including nanowires, nanorods, nanochains, and nanotubes, for their applications in the MOR process. Some classic instances are listed and detailed to assist readers in better recognizing the superiorities of 1D Pt-based nanostructures. This review firstly focuses on the mechanism of action and evaluation parameters of Pt-based catalysts in MOR, then the strategies employed to synthesize 1D Pt-based nanostructures are briefly summarized. The importance of rationally designing 1D Pt-based catalysts for performance enhancement is emphasized by the MOR application of various 1D nanostructures. Finally, the conclusion and outlook for future research directions in this field were proposed to motivate future challenges.     

Status and research development of Si NWs/PEDOT∶PSS hybrid solar cells

硅基太阳电池作为当前主流的光伏器件,进一步降低成本并提升效率仍是人们努力的方向.基于此,一方面,可以从太阳电池材料入手,用硅纳米线阵列代替平板硅,硅纳米线阵列具有优异的光学和电学性能,可大幅减少光反射,增加光的吸收和利用,有望提高光伏器件的效率,并可降低硅原料消耗,降低材料成本;另一方面,将硅微纳结构与有机材料进行复合,充分利用两种材料的优势,制备杂化太阳电池,以达到增强稳定性,提高效率和降低成本的目的.本文概括了Si纳米线阵列SiNWs/PEDOT∶PSS杂化太阳电池的发展现状和存在的问题,并针对相应问题的解决思路和发展方向进行了讨论.     

A review of TiO2 nanostructured catalysts for sustainable H2 generation

Hydrogen is an attractive alternative to fossil fuels that addresses several environmental and energy shortage issues. Nano-sized TiO₂-based photocatalysts with unique structural and functional properties are the most extensively studied photocatalytic nanomaterials for hydrogen production and pollutant degradation. However, titania is hampered by a wide band gap, low utilization of solar light and a rapid recombination of electron/hole pairs. These issues limit its photocatalytic performance. In this review, we present the latest developments in the fabrication of different higher dimensional TiO₂ nanostructured materials that aim to address these inherent limitations to an otherwise very promising material. Specifically, we will look into critical engineering strategies to enlarge the active surface area, enhance visible light absorption and suppress the recombination of electrons/holes that benefit their photo/photoelectric-catalytic water splitting activity. Finally, the current challenges and perspectives for TiO₂ nanostructures are also discussed. Continuous efforts are necessary to endow TiO₂-based materials with novel advanced functionality and commercialization potential in the coming years.     

Truncated chlorophyll antenna size of the photosystems—a practical method to improve microalgal productivity and hydrogen production in mass culture

Unicellular microalgae hold the promise of commercial exploitation in mass culture for hydrogen and biomass production. In any microalgal production system, the achievable photosynthetic productivity and light utilization efficiency of the algae are the single most important factors in the determination of cost. Microalgal mass cultures growing under full sunlight have a low per chlorophyll (Chl) productivity since, at high photon flux densities, the rate of photon absorption by the Chl antenna far exceeds the rate at which photons can be utilized for photosynthesis. Excess photons are dissipated as fluorescence or heat. Up to 80% of absorbed photons could thus be wasted, reducing light conversion efficiencies and cellular productivity to fairly low levels. This shortcoming could possibly be alleviated by the development of microalgal strains with a limited number of Chl molecules in the light-harvesting antenna of their photosystems, i.e., strains that have a truncated Chl antenna size. It is expected that individually, such microalgae will not be able to saturate rates of photosynthesis and, thus, will not be subject to wasteful dissipation of excitation energy. In turn, the productivity of the mass culture will be improved. The method of choice to reach the objective of a “truncated light-harvesting Chl antenna” size (tla) employed DNA insertional and chemical mutagenesis of the unicellular green algae Chlamydomonas reinhardtii and Dunaliella salina, followed by a rigorous screening protocol to identify mutants with a smaller light-harvesting Chl antenna size. Molecular and genetic analyses of isolated tla strains were performed. Biochemical and physiological analyses in terms of photosynthetic productivity and light conversion efficiencies are presented. The results show that a truncated Chl antenna size of PSII is more important than that of PSI in terms of the photosynthetic productivity of a mass culture. A list of genes that confer a “truncated light-harvesting Chl antenna” size to green algae is being compiled for future application in algal hydrogen and biomass production.     

Modifying the solar spectrum to enhance silicon solar cell efficiency—An overview of available materials

There are three ways in which the cell efficiency of silicon solar cells may be improved by better exploitation of the solar spectrum: down-conversion (cutting one high energy photon into two low energy photons), photoluminescence (shifting photons into wavelength regions better accepted by the solar cell) and up-conversion (combining low energy photons to one high energy photon). In this paper, we present the state of the art of these three methods and discuss the suitability of materials available today for application to silicon solar cells.     

Photo-stimulated hydrogen desorption from magnesium nanoparticles

Hydrogen remains an attractive energy carrier because it is abundant, environmentally friendly and has the highest gravimetric energy density of any known substance. Despite this high gravimetric energy density, hydrogen suffers from a low volumetric energy density as a room-temperature gas. To maximize volumetric energy density, storing hydrogen as a magnesium hydride is an efficient and economically viable route, owing to the low weight and high earth abundance of magnesium. A long-lasting obstacle for using magnesium is the high temperature required to release hydrogen once absorbed by magnesium. Although nanoscale magnesium is known to have a favorable effect on the hydrogen desorption temperature, it is not sufficient. In this work, hydrogen absorption and release was investigated by measuring optical changes, which correspond to certain hydrogen concentrations in magnesium nanoparticles. Remarkably, hydrogen desorption from the magnesium nanoparticle assembled thin films at room temperature could be achieved by illumination. This photo-stimulated hydrogen desorption introduces an effective and simple method to enable reversible hydrogen storage in magnesium. The sensitivity of the optical method here used is demonstrated by the fact that even hydrogen absorption from ambient air at 1 ppm has been measured. This work demonstrates that hydrogen can be efficiently stored and released from magnesium nanoparticles using only photons.     

Real-time measurement of desorption temperature and kinetics of magnesium hydride powder sample based on optical reflection

We demonstrate the proof-of-principle that interaction between visible light and a magnesium hydride sample in reflective mode can be used to determine the desorption temperature and kinetics of magnesium hydride in powder form. The demonstrated optical technique requires only milligrams of sample and can potentially be used to measure the de/absorption temperature and kinetics of magnesium nanostructures, which are often fabricated via the physical vapor deposition method inside an optically transparent quartz tube. This would help to eliminate the common problem of oxidation associated with removal and transport of the freshly fabricated nanostructures into an inert protective environment. This optical technique could be applied to any hydrogen-storage material in the form of powder which shows a significant difference in its optical absorption between the hydride and the non-hydride phase.     

0D, 1D and 2D nanomaterials for visible photoelectrochemical water splitting. A Review

Global energy problems of the 21st century have led to the search for alternative energy sources, among which is hydrogen produced via photoelectrochemical solar water splitting. Photo-electrochemical water splitting using semiconductor nanostructured materials is a progressive method for producing hydrogen. The unique electronic, mechanical, surface and optical properties of nanomaterials make it possible to create photocatalysts with complex structures of energy zones, allowing the use of a wide range of sunlight and exerting a positive effect on absorption and scattering of sunlight. This review contains a detailed analysis of current studies aimed at improving the efficiency of photocatalytic systems by using 0D, 1D and 2D nanostructures. Special attention is paid to the mechanisms of photocatalytic water splitting to produce hydrogen with the help of various nanostructures.     

Synthesis of potential nanostructures based on strontium hexaferrite for electrochemical hydrogen storage

Today, the reduction of fossil fuel resources and the increase of their destructive environmental effects are important challenges. One strategy to this problem is application of new sources of energy supply. Hydrogen can play an important role in future energy supplies due to its unique properties such as clean combustion and high energy content relative to mass. In addition, hydrogen is considered as a green energy because it can be produced from renewable sources and is not polluting. The most important issue in hydrogen as a fuel is its storage. Hydrogen must be stored reversibly in a completely safe manner as well as with high storage efficiencies. One of the best ways to store hydrogen is using of new nanostructured adsorbents. In this study, first strontium hexaferrite (SrFe₁₂O₁₉) nanostructures are synthesized by sol-gel auto-combustion method. Then, the samples structure is studied using various techniques. Furthermore, the nanostructures are used as hydrogen storage materials. Using electrochemical techniques, the hydrogen storage properties of the materials are investigated in alkaline media. The obtained electrochemical results show that the maximum hydrogen storage capacity of SrFe₁₂O₁₉ nanostructures is about 3100 mAh/g.     

The role of the optical properties of solids in solar direct absorption process

Solid particles are considered to be good candidates for absorbing solar energy in an endothermic reaction, due to both their ability to absorb solar radiation directly (as opposed to heat transfer mechanism) and their high ratio of absorbed radiation to mass. Only a limited number of studies have been devoted so far to convert solar energy to chemical energy by means of direct absorption. The major advantages of this concept are the inherent high efficiency of the light absorption, and the short time required to reach the desired reaction temperature.In the work described, an attempt to evaluate the effect of the optical properties of the particles and their temperature dependence, upon the solar driven chemical reaction was carried through. The particles investigated were oil shale particles. Their optical properties were measured in the optical lab at the DLR, Stuttgart, whereas the solar gasification experiments of the oil shale, were conducted in the central receiver of the Weizmann Institute.The results show that temperature profiles for the gasification experiments of oil shales can be predicted with good accuracy by assuming isotropic scatter and a particle albedo of 0.5. This is due to the relatively limited role of direct absorption in low expanding fluidized beds. Calculations of a set-up however, where direct absorption is dominant, show resulting temperature profiles to be sensitive to optical properties. Temperature differences arising from calculations based on assumed optical properties compared to those based on measured optical properties are as high as 300°C.