硅太阳电池材料的研究进展

目前各种太阳电池材料中，硅是最主要的材料。文章简要介绍单晶硅、多晶硅、带状硅、非晶硅以及多晶硅薄膜材料的研究状况，并对有关问题和太阳电池材料的发展趋势进行了讨论。     

Quantitative evaluation of hydrogen embrittlement susceptibility in various steels for energy use using an in-situ small punch test

Recently, as hydrogen has been increasingly applied in the field of new energy, it has become necessary to evaluate the mechanical characteristics of hydrogen embrittlement (HE) when materials are used to reduce costs as well as ensure safety in hydrogen facilities. However, to obtain a large amount of data in a short period of time and ensure reliability when selecting materials used in hydrogen energy applications, a simple test method for screening the HE susceptibility of materials under high-pressure hydrogen environments should be established and applied. In this study, the HE behaviors of three structural steels to be used in the hydrogen energy field were examined at room temperature and low temperatures under high-pressure hydrogen environments using the newly established in-situ small punch test method. The effects of test temperature and punch velocity on the HE susceptibility of each steel were quantitatively evaluated using the characterizing factor, known as the relative reduction of thickness.     

Development of lanthanum strontium cobalt ferrite perovskite electrodes of solid oxide fuel cells – A review

There is an enormous driving force in solid oxide fuel cells (SOFCs) to reduce the operating temperatures from high temperatures (800–1000 °C) to intermediate and low temperatures (400–800 °C) in order to increase the durability, improve thermal compatibility and thermal cycle capability, and reduce the fabrication and materials costs. One of the grand challenges is the development of cathode materials for intermediate and low temperature SOFCs with high activity and stability for the O₂ reduction reaction (ORR), high structural stability as well as high tolerance toward contaminants like chromium, sulfur and boron. Lanthanum strontium cobalt ferrite (LSCF) perovskite is the most popular and representative mixed ionic and electronic conducting (MIEC) electrode material for SOFCs. LSCF-based materials are characterized by high MIEC properties, good structural stability and high electrochemical activity for ORR, and have played a unique role in the development of SOFCs technologies. However, there appears no comprehensive review on the development and understanding of this most important MIEC electrode material in SOFCs despite its unique position in SOFCs. The objective of this article is to provide a critical and comprehensive review in the structure and defect chemistry, the electrical and ionic conductivity, and relationship between the performance, intrinsic and extrinsic factors of LSCF-based electrode materials in SOFCs. The challenges, strategies and prospect of LSCF-based electrodes for intermediate and low temperature SOFCs are discussed. Finally, the development of LSCF-based electrodes for metal-supported SOFCs and solid oxide electrolysis cells (SOECs) is also briefly reviewed.     

Hydrogen retention and affecting factors in rolled tungsten: Thermal desorption spectra and molecular dynamics simulations

Hydrogen isotope retention of tungsten in nuclear fusion reactors is one of the hot research issues all along. In this paper, tungsten samples in different rolled surfaces were polished by mechanical processing, subsequently subjected to D₂⁺ irradiation and thermal desorption. To better understand the experimental observations, this study also performed molecular dynamics (MD) simulation and investigated the effects of temperature, grain number, grain boundary density, and crystal orientation on hydrogen retention. It is found that the grain number and grain boundary density of rolled tungsten increase successively in RD/TD, RD/ND, and TD/ND surfaces. The RD/ND surface exhibits the best hydrogen radiation resistance, whereas the TD/ND surface is unsatisfactory. MD simulations further indicate that hydrogen retention is more obvious with the increase of grain density in tungsten, and hydrogen atoms are more easily enriched at the grain boundaries. With the increase in temperature, the retention of hydrogen atoms in monocrystalline/polycrystalline tungsten decreases significantly. The average implantation depth of H atoms is deepest along the <111> and <112> crystalline directions, which reveals that hydrogen retention is dependent on the crystal orientations. The good agreement between the experimental data and simulation results reveals that grain boundaries play an important role in hydrogen retention.     

Enhancing safety of hydrogen containment components through materials testing under in-service conditions

The capabilities in the Hydrogen Effects on Materials Laboratory (HEML) at Sandia National Laboratories and the related materials testing activities that support standards development and technology deployment are reviewed. The specialized systems in the HEML allow testing of structural materials under in-service conditions, such as hydrogen gas pressures up to 138 MPa, temperatures from ambient to 203 K, and cyclic mechanical loading. Examples of materials testing under hydrogen gas exposure featured in the HEML include stainless steels for fuel cell vehicle balance of plant components and CrMo steels for stationary seamless pressure vessels.     

Evaluation of efficiency and degradation of mono- and polycrystalline PV modules under outdoor conditions

This paper presents the experimental results carried out over a period of years of several photovoltaic modules of two basic types, e.g. monocrystalline and polycrystalline, obtained from various sources. These panels were exposed outdoors under the climatic conditions of Bahrain. Our observations show that two of the “first generation” monocrystalline panels completely failed and severe corrosion developed. The rest of the panels show a degradation in efficiency, however polycrystalline modules show a greater drop in output.     

Profile of impurities in polycrystalline silicon samples purified in an electron beam melting furnace

The photovoltaic properties of the polycrystalline silicon depend mainly on the crystalline structure (grain size and presence of defects) and of the purity of the material. The production of monocrystalline silicon for high-efficiency solar cells requires an extremely complex and expensive process. Therefore, the production of photovoltaic energy for terrestrial use, on a large scale, demands an alternative and low-cost method, especially in terms of purification of the starting material. The use of metallurgical grade silicon and the purifying of the same, through melting in electron beam furnace under a 10⁻³ Pa vacuum, is a method, which is able to provide high-purity material (99.999% Si). In this research, the results of the chemical analysis of polycrystalline silicon purified in an electron beam melting furnace, specially in terms of distribution of impurity due to their position in the sample related to the direction of solidification, are presented.     

Preparation of Li-Mg-N-H hydrogen storage materials for an auxiliary power unit

Solid hydrogen storage materials as H₂ supply for PEM fuel cells have been attempted over the past decades because of their high efficiencies in H₂ storage. However, most investigations were focused on the stage of tank design for the storage materials. The Li-Mg-N-H hydrogen storage system was for the first time integrated into a HT-PEM fuel cell stack for a prototype auxiliary power unit, the maximum working temperature being 200 °C. With a designed output of 1 kW, a few kilograms of storage materials are needed. By using commercially available raw materials, an up-scaled preparation of the storage material was performed using laboratory facilities. Preparation conditions were established with the aid of FTIR, TG-DSC and x-ray diffraction to ensure the desired quality of materials. Prior to power the fuel cell stack, the storage materials need to go through an exothermic metathesis, and severe temperature overshooting is expected, which may cause deterioration in material performance and safety issue. Operation conditions were tested and the temperature overshooting could be effectively prevented under adequate conditions.     

Progress in new semiconductor materials classes for solar photoelectrolysis

For several decades, the main body of research in photoelectrochemical (PEC) hydrogen production has centered on a small number of semiconductor materials classes, including stable but inefficient metal‐oxides, as well as some more efficient materials such as III–V compounds which suffer from high cost and poor stability. While demonstrating some limited success in meeting the rigorous PEC demands in terms of bandgap, optical absorption, band‐edge alignment, surface energetics, surface kinetics, stability, manufacturability and cost, none of the ‘traditional’ PEC semiconductors are adequate for application in water‐splitting devices with high performance (greater than 15% solar‐to‐hydrogen conversion) and long durability (greater than 200 h life). As a result, it is widely held that new semiconductor classes and configurations need to be identified and developed specifically for practical implementation of solar water‐splitting. Examples include ternary and quaternary metal‐oxide compounds, as well as non‐oxide semiconductor materials, such as silicon‐carbide and the copper‐chalcopyrites. This paper describes recent progress at the University of Hawaii to develop improved semiconductor absorbers and interfaces for solar photoelectrolysis based on polycrystalline tungsten trioxide and polycrystalline copper‐gallium‐diselenide. Specific advantages and disadvantages of both materials classes in terms of meeting long‐term PEC hydrogen production goals are detailed. Copyright © 2010 John Wiley & Sons, Ltd.     

铸造单晶硅性能和应用分析

以G6型多晶硅定向凝固铸锭炉生长的铸造单晶硅为研究对象,对其性能特点及应用进行分析.铸造单晶硅中含有位错、亚晶粒、多晶晶粒、间隙态元素和硬质点等缺陷.在铸造单晶硅制备过程中,因长晶界面不平及杂质存在的原因,硅锭生长时存在较大的应力,致使硅原子排列出现错排,从而导致位错、亚晶粒和多晶晶粒的产生,其中多晶晶粒的晶向主要有(...     

CFD simulations of filling and emptying of hydrogen tanks

During the filling of hydrogen tanks high temperatures can be generated inside the vessel because of the gas compression while during the emptying low temperatures can be reached because of the gas expansion. The design temperature range goes from ?40 °C to 85 °C. Temperatures outside that range could affect the mechanical properties of the tank materials. CFD analyses of the filling and emptying processes have been performed in the HyTransfer project. To assess the accuracy of the CFD model the simulation results have been compared with new experimental data for different filling and emptying strategies. The comparison between experiments and simulations is shown for the temperatures of the gas inside the tank, for the temperatures at the interface between the liner and the composite material, and for the temperatures on the external surface of the vessel.     

Photocatalytic water oxidation at bismuth vanadate thin film electrodes grown by direct liquid injection chemical vapor deposition method

Photoelectrochemical cells (PECs) are devices that can harvest and convert solar energy to produce consumable fuel, e.g. by splitting water into oxygen and hydrogen. Photocatalytic semiconductor materials play a major role in PECs, and their overall efficiency is usually limited by short carrier diffusion length because of structural defects, poor light absorptivity, and sluggish kinetics of photoelectrochemical reactions at the semiconductor electrode. Synthesis of high quality defect-free semiconductor materials using high temperature deposition techniques generally yield films with good adhesion to substrates while improving charge carrier transport and hence the overall efficiency of a PEC. A direct liquid injection chemical vapor deposition (DLI-CVD) technique has been utilized to synthesize monoclinic clinobisvanite phase bismuth vanadate (BiVO₄) films for photocatalytic water oxidation. The technique yields dense high quality epitaxial and polycrystalline BiVO₄ films on Yttria stabilized zirconia (YSZ) and Fluorine doped tin oxide (FTO) substrates, respectively, at growth temperature in the range of 500–550 °C. The photoelectrochemical characteristics of the films grown on FTO have been studied and a photocurrent value of 2.1 mA/cm² at 1.23 V vs Normal hydrogen electrode (NHE) (0.5 V vs. Ag/AgCl), with onset potential values as low as 0.23 V vs. NHE (?0.5 V vs. Ag/AgCl), are obtained despite the low porosity of the films. The PEC performance is further improved by synthesizing BiVO₄ directly on top of a tungsten oxide interlayer and modifying its surface with FeOOH co-catalyst.     

Material behavior of rubber sealing for proton exchange membrane fuel cells

Reliable sealing is necessary for the stable operation of proton exchange membrane fuel cell (PEMFC). In practical application, various materials have been tried in PEMFC sealing. However, the mechanical properties of these sealing materials, which play a key role in the sealing stability, have not been fully understood in PEMFC environment, especially after long-term operation. In this paper, according to the operating environment of PEMFC, sealing material experiments are carried out to explore the differences in mechanical behaviors of sealing materials, including silicone rubber (SR), fluororubber (FR), nitrile rubber (NBR) and ethylene-propylene-diene-terpolymer rubber (EPDM) and the variation of mechanical properties of these sealing materials is predicted as time goes on. The results indicate that compression rate has a great influence on sealing contact stress. SR and EPDM, with the variation of 0.15 MPa and 0.45 MPa in stress, show the best and worst mechanical stability at different compression rates, respectively. In terms of temperature, it is found that SR can adapt to different operating temperature of PEMFC and only 18% variation is found from 20 °C to 100 °C. Finally, based on Time-Temperature Superposition (TTS), high temperature experiments are conducted to predict long-term relaxation stress under PEMFC working condition. The analysis results are beneficial for choosing suitable sealing material, and it can also be applied to predict sealing ability in PEMFC.     

Temperature effect in cavitation risk assessments of polymers for hydrogen systems

Hydrogen storage at high pressure is currently attained by the use of different materials, such as elastomers in sealing joints, thermoplastics and thermosetting polymers in high-pressure containers, and metallic tube connections. Hydrogen containers type IV use a thermoplastic polymer for hydrogen tightness and composite materials for mechanical resistance, usually made with thermosetting resins and carbon or glass fibre. International standards impose a wide range of operative temperatures for such containers, from −40 °C to 85 °C.Once saturated with hydrogen at high pressure, a fast depressurisation process can create stress in the polymeric materials, causing its degradation by the formation of cavities. In a previous work, we were able to make a generalization of cavitation risk by the use of non-dimensional parameters, based on a simplified mechanical failure model. We observed that for the model, material's hydrogen diffusivity and yield strength are of upmost importance. In present work, we analyse the effect of temperature on these two properties, as they have an inverse evolution with temperature. Results confirm the pertinence of considering temperature in the whole application range of technology under analyse.     

A solar thermal MgO-powder receiver with working temperatures of more than 1600°C: Model investigation by using a laser as an irradiation source

The efficiency of solar thermal power plants increases rapidly with increasing working temperatures. The problem has to be solved by the improvement of the materials and via the construction variation of the continuously heat-exposed structural members. Especially the receiver obtains the whole irradiation reflected from the heliostat field. Resistance to high temperatures, to high-temperature corrosion and oxidation, to thermal shock and thermal fatigue load due to changing working temperatures has to be fulfilled by the receiver materials.Usually, black or coloured materials are preferred because of their higher absorption. In this work, the working temperatures of a gas-heat exchanging receiver reached more than 1600°C because of the employment of a white reflecting material instead of a black absorbing material. The receiver was constructed as a gas-heat conducting exchanger. An irradiation reflecting MgO-powder with argon was used as the heat transport medium. Thermal shock and thermal fatigue conditions could at least be restricted by dynamic controlling.     

Crystalline and thin-film silicon solar cells: state of the art and future potential

Bulk crystalline silicon solar cells have been the workhorse of the photovoltaic industry over the past decades. Recent major investments in new manufacturing facilities for monocrystalline and multicrystalline wafer-based cells, as well as for closely related silicon ribbon and sheet approaches, ensure this role will continue well into the future. Such investments suggest that the silicon wafer-based approach has successfully withstood the challenge mounted by thin-film chalcogenide-based cells, in the form of polycrystalline films of CdTe and CuInSe₂, as well as that mounted by thin-film cells based on amorphous silicon and its alloys with germanium. The encumbent now faces a fresh challenge by a new wave of thin-film technologies developed in the 1990s, more closely related to the bulk approach and with some advantages over the earlier contenders. One new approach is based on a stack of two silicon thin-film cells, one cell using amorphous silicon and the other mixed-phase microcrystalline silicon. The second uses silicon thin-films in polycrystalline form deposited onto glass, even more directly capturing the strengths of the wafer-based approach.     

The effect of hydrogen on the electronic,mechanical and phonon properties of LaMgNi4 and its hydrides for hydrogen storage applications

Density functional theory calculations are used herein to explore the effect of hydrogen on the electronic, mechanical and phonon properties of LaMgNi₄ and its hydrides. The polycrystalline elastic moduli, Poisson's ratios and Debye temperatures are calculated based on the single-crystal elastic constants and Voigt-Reuss-Hill approximations. It is also found that all these materials are metallic behavior, ductile and anisotropic in nature. The mechanical anisotropy is discussed via several anisotropy indices and three-dimensional (3D) surface constructions. The effect of high temperature on the free energy, entropy, and heat capacity are also studied by using the quasi-harmonic Debye model. LaMgNi₄ and its hydrides are found to be energetically, mechanically and dynamically stable. Also, they are thermodynamically stable and the order of phase stability is LaMgNi₄H₇ > LaMgNi₄H₄ > LaMgNi₄H > LaMgNi₄. In addition, the highest gravimetric hydrogen storage capacity is found to be 1.74 wt% for LaMgNi4H₇.     

Comparative studies of EFG poly-Si grown by different procedures

The impurity content in EFG polycrystalline silicon materials grown by different procedures from graphite and quartz crucible has been extensively studied using Fourier transform IR technique. It is shown that the oxygen content in the material is much more dependent on the growth atmosphere at meniscus than on the type of crucible. In all samples the carbon content remains supersaturated up to very high temperatures of annealing, not affected by the oxygen presence.     

Minimum Compliance Optimization of a Thermoelastic Lattice Structure with Size-Coupled Effects

The minimum compliance design of thermoelastic structures forced by mechanical and thermal loads simultaneously composed of periodic lattice materials is studied in this paper. The Extended Multi scale Finite Element Method (EMsFEM) is utilized to connect the macro structural and material microstructural scales. In the optimization, sectional areas of the microcomponents are set as design variables under volume constraints. In numerical examples, we discuss the influence of the geometrical dimensions of the material microstructure, the amount of base material and the different ratios of thermal load over the mechanical load on the optimization results.     

Experimental studies of the monocrystal and polycrystal characteristics of silicon photovoltaic modules under environmental conditions of Tashkent

Studies of monocrystalline and polycrystalline silicon photovoltaic modules under environmental conditions of Tashkent were carried out. A decrease in the power of mono-PVM and poly-PVM was revealed, which in the summer period was 30 and 28% respectively. It was shown that, under otherwise equal conditions, the average temperature T _t of the poly-PVM appeared to be 2°C lower than T _t of the mono-PVM. In this case, both PVM types had average efficiency values of ~13.3%. It was found that the productivity factor of the studied poly-PVM and mono-PVM under environmental conditions of Tashkent was 0.75 and 0.77, respectively.