脉冲激光沉积及硒化法制备Cu(In,Ga)Se2薄膜研究

采用脉冲激光沉积和硒化后热处理的方法在石英衬底上制备Cu(In,Ga)Se2（简写为CIGS）薄膜，研究脉冲激光沉积（PLD）技术在制备CIGS薄膜太阳能电池材料上的应用，分析了不同预制层沉积顺序及厚度对CIGS薄膜组织结构、表面形貌、成分以及光学性能的影响。实验结果表明：(1)利用PLD技术及后硒化处理的工艺，制得的CIGS太阳能电池吸收层具有纯相和高结晶度等特性；(2)CuGa/In金属预制层的叠层顺序和叠层数、硒化退火温度对薄膜的结晶质量、晶粒尺寸、成分都具有重要的影响，其中叠层顺序影响最为明显；(3)样品均表现出对可见光区具有透射率低和吸收系数高的光学特性。本工作为制备性能优良的CIGS太阳能电池吸收层，提供了一个新颖的工艺手段。     

Effects of Deflection on the Sio2 Barrier Layer and Mo Back Electrode of Cu（In,Ga）Se2 Thin-Film Solar Cells on Stainless Steel Substrates

This paper studies the effects of deflection on the SiO2 barrier layer and molybdenum(Mo)back electrode of Cu(In,Ga)Se2 thin-film solar cells,prepared via magnetron sputtering on type SUS431 stainless steel substrates.The surface micro-cracks and sheet resistance of thin films had been observed and measured for in-situ bend tests.Experimental results show that increasing the thickness of the SiOx barrier has a better property to prevent cracks induced by bending stress.The sheet resistance of a Mo film increases alongside the bending of the curvature radius.The maximum allowed value of the curvature radius of the SiOx barrier layer,molybdenum electrodes,and the thin film CIGS absorbing layer should be 16 mm,20 mm,and 26 mm,respectively.Therefore,the maximum curvature radius limit should be 26 mm or less for CIGS thin-film solar cells prepared via sputtering on type SUS431 stainless steel substrates.     

铜铟镓硒薄膜太阳能电池的研究进展及发展前景

介绍了薄膜太阳能电池结构、性能特点以及目前在研究和生产过程中铜铟镓硒电池的制备方法;阐述了国内外在铜铟镓硒薄膜太阳能电池方面研究开发现状。最后探讨了铜铟镓硒太阳能电池存在的问题及今后研究方向。     

In-situ crack propagation observation in fully lamellar Ti-49%Al alloy

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3D monitoring of delamination growth in a wind turbine blade composite using optical coherence tomography

In this paper, delamination and delamination growth in a glass fiber composite used for the spar webs in wind turbine blades is investigated by optical coherence tomography (OCT). The cross-sectional and volumetric images clearly showed the microstructure and the crack within the specimen. After applying an optimized signal processing algorithm, 3D crack growth measured using OCT were demonstrated for the first time to the best of our knowledge. The crack structures inside the composite material at different stages during the delamination growth were revealed.     

全层状TiAl基合金断裂机理原位观察

通过对裂纹与晶内片层和晶界的交互作用的原位观察,研究了全层状组织TiAl基合金的断裂机制。结果表明：裂纹萌发和扩展方式不仅依赖于片层与拉伸轴的相对取向,还受晶界取向的制约。当片层与拉伸轴成较大角度时,沿片层裂纹扩展是通过主裂纹与沿片层微裂纹的连接及剪切的过程;而当拉伸轴近乎平行片层时,跨片层裂纹依靠对界面分离和跨片层微裂纹这两种形式的微裂纹的连接进行扩展的,纵向交叉晶界有利于断裂韧性的提高,而横向晶界则不利于材料断裂韧性。     

Effect of Grain Boundaries on the Performance of Thin-Film-Based Polycrystalline Silicon Solar Cells: A Numerical Modeling

Solar cells/photovoltaic, a renewable energy source, is appraised to be the most effective alternative to the conventional electrical energy generator. A cost-effective alternative of crystalline wafer-based solar cell is thin-film polycrystalline-based solar cell. This paper reports the numerical analysis of dependency of the solar cell parameters (i.e., efficiency, fill factor, open-circuit voltage and short-circuit current density) on grain size for thin-film-based polycrystalline silicon (Si) solar cells. A minority carrier lifetime model is proposed to do a correlation between the grains, grain boundaries and lifetime for thin-film-based polycrystalline Si solar cells in MATLAB environment. As observed, the increment in the grain size diameter results in increase in minority carrier lifetime in polycrystalline Si thin film. A non-equivalent series resistance double-diode model is used to find the dark as well as light (AM1.5) current–voltage (I-V) characteristics for thin-film-based polycrystalline Si solar cells. To optimize the effectiveness of the proposed model, a successive approximation method is used and the corresponding fitting parameters are obtained. The model is validated with the experimentally obtained results reported elsewhere. The experimentally reported solar cell parameters can be found using the proposed model described here.     

联氨浓度对化学水浴沉积ZnS薄膜性能的影响

利用化学水浴法(CBD)在硫酸锌、氨水、联氨、硫脲的沉积体系下制备CIGS太阳能电池的ZnS缓冲层薄膜,研究了联氨浓度对缓冲层ZnS薄膜的生长过程、晶体结构及物理性能的影响。结果表明,联氨浓度能够显著影响ZnS薄膜的生长速度,联氨浓度越高,薄膜厚度越大,薄膜的致密性也随之提高;联氨浓度对薄膜的结晶性影响较小,CBD法制备的ZnS薄膜均为非晶薄膜;制备的ZnS薄膜有较高的透过率,禁带宽度为3.85 eV左右,能够使更多短波、高能量光子透过缓冲层到达CIGS吸收层,从而提高电池性能。     

Grain boundary engineering based on fractal analysis for control of segregation-induced intergranular brittle fracture in polycrystalline nickel

The effect of grain boundary microstructure on the fracture resistance of sulfur-doped polycrystalline nickel was investigated using specimens with different grain boundary microstructures to reveal the usefulness of grain boundary engineering for control of segregation-induced intergranular brittle fracture of polycrystalline materials. The sulfur-doped polycrystalline nickel specimen with more homogeneous fine-grained structure and a higher fraction of low-Σ coincidence site lattice (CSL) boundaries shows higher fracture resistance than the specimen with coarse-grained structure and a lower fraction of low-Σ CSL boundaries. It was found that high-energy random boundaries play a key role as the preferential crack path in fracture processes. The resistance to sulfur segregation-induced intergranular brittle fracture was evaluated by analyzing the fractal dimension of random boundary connectivity in the polycrystalline nickel specimens studied. The fractal dimension of random boundary connectivity decreases with increasing fraction of low-Σ CSL boundaries, resulting in the generation of a higher fracture resistance by restricting more frequent branching and deflection of propagating crack path along random boundaries from the main crack.     

Carrier transportation in polycrystalline CuInSe_2 thin films with Cu-deficient grain boundaries

The interface energies and electronic structures of(112) grain boundaries of Cu In Se2 thin films were investigated by first-principle calculations.It is found that the grain boundary with a Cu vacancy has low interface energy and exists widely in the films.The Cu deficiency may cause the charge imbalance and result in an upward band bending at the grain boundary.It also weakens the repulsion between Cu-3d orbital and Se-4p orbital and leads to the downward shift of valence band maximum.The two mechanisms,namely the band bending from the charge imbalance and the depression of the valence band maximum, have effects on the(112) grain boundaries with different defects.The change of band structure forms a potential barrier to prevent electrons or holes from approaching the grain boundary and reduces their recombination.This might be used to explain the effects of the grain boundary on carrier transportation and why polycrystalline Cu(In,Ga)Se2thin film solar cells have better performance than single-crystal cells.     

High-cycle fatigue performance of solution-treated metastable-β titanium alloys

The effect of grain boundary misorientation on the high-cycle fatigue performance of solution-treated, metastable-β titanium alloys was investigated. Initial damage during cyclic deformation was associated with the formation of coarse, planar slip bands, these often propagating through several grains without obstruction or redirection when intersecting with a grain boundary. This “continuous” slip through several grains was associated with the presence of a significant number of “low-angle” grain boundaries. Fatigue crack initiation was associated with crack initiation at intersecting planar slip bands at the free surface. The increase in operative slip length occasioned by the presence of low-angle grain boundaries lead to enhanced crack initiation and reduced lifetime. Fatigue crack propagation was characterized by step-like features formed through the interaction of the propagating crack and the coarse slip bands present in the plastic zone ahead of the crack tip. The direction of local fatigue crack propagation was also minimally affected when crossing low-angle grain boundaries.     

Atomistic simulation of ∑3 (111) grain boundary fracture in tungsten containing various impurities

The effect of various impurities and micro-alloying additions (B, N, C, O, Al, Si, S and P) on the intrinsic resistance of the ∑3 (111) grain boundary in tungsten has been investigated using the molecular dynamics simulation. The atomic interactions have been accounted for through the use of Finnis-Sinclair interatomic potentials. The fracture resistance of the grain boundary has been characterized by computing, in each case, the ideal work of grain boundary separation, the mode I stress intensity factor and the Eshelby's F₁ conservation integral at the onset of crack propagation. The results obtained suggest that pure tungsten is relatively resistant to grain boundary decohesion and that this resistance is further enhanced by the presence of B, C and N. Elements such as O, Al and Si however, have a relatively minor effect on the cohesion strength of the ∑3 (111) grain boundary. In sharp contrast, S and P greatly reduce this strength making tungsten quite brittle. These findings have been correlated with the effect of the impurity atoms on material evolution at the crack tip.     

The role of mechanical twinning on microcrack nucleation and crack propagation in a near-γ TiAl alloy

The role of mechanical twinning on microcrack nucleation and crack propagation in a near-γ TiAl alloy was investigated in 4-point bend specimens using selected area channeling patterns and electron channeling contrast imaging to obtain the true crystal orientation image crystal defects. Two types of bend specimens were used, a conventional specimen that was deformed to a surface strain of about 1.4%, but not fractured, and a bi-layer notched specimen with an aluminum backing that prevented catastrophic fracture so that crack arrest features could be examined. Most grains showed activity of 1–4 twinning systems, and their activity correlated closely with the Schmid factor. Grain boundary microcracks were most frequently found where twins interacted with the grain boundary, and crystallographic analysis indicated that the twinning shear caused these cracks to open. In the crack growth specimen, extensive twinning and dislocation activity occurred in the grain with the arrested crack tip, but with continued straining, these same twins caused grain boundary microcracks to form and link-up to form full intergranular cracks, resulting in renucleation of the primary failure crack.     

Effect of substrate thickness on oxide scale spallation for solid oxide fuel cells

In this paper, the effect of the ferritic interconnect thickness on the delamination/spallation of the oxide scale was investigated experimentally and numerically. At the operating environment of solid oxide fuel cells (SOFCs), a combination of growth stress with thermal stresses may lead to scale delamination/buckling and eventual spallation during SOFC stack cooling, even leading to serious degradation of cell performance. The experimental and numerical results show that the interfacial shear stresses increase with the growth of the oxide scale and also with the thickness of the ferritic substrate, i.e., the thick ferritic substrate can easily lead to scale delamination and spallation.     

超声强化2D12铝合金疲劳断裂过程的微观分析

采用超声强化工艺对2D12铝合金进行表面处理,借助金相显微镜和扫描电镜,并结合原位跟踪测量裂纹长度的方法,对强化后的疲劳断裂行为进行了研究。结果表明,超声强化后2D12铝合金表面晶粒得到细化,疲劳源主要产生于试样表面,仅个别向内部转移,强化后疲劳寿命提升了约8倍。其原因一方面是强化过程在试样表面引入了残余压应力,由于裂纹扩展过程倾向于连接裂纹扩展路径上的缺陷,所以残余压应力的存在效降低了裂纹在两缺陷间的扩展速率;另一方面晶粒细化导致晶界密度增加,加强了对裂纹扩展的阻碍,从而有益于提高裂纹扩展寿命。     

晶粒尺寸对纳晶双峰材料断裂韧性的影响

为了描述由纳晶基体和粗晶颗粒组成的纳晶双峰材料的断裂韧性,通过建立一个粘聚力模型来研究纳晶双峰材料的临界应力强度因子K_(IC)(表征材料断裂韧性)。考虑到纳晶双峰材料的一个典型情况:裂纹位于2个纳晶颗粒的交界面处,裂纹尖端与粗晶粒的晶界相交,假设粘聚区的尺寸等于纳晶颗粒的尺寸d。裂纹的钝化和扩展过程受位错和粘聚力的共同影响,刃型位错是从粘聚力裂纹的尖端发射,该过程对裂纹产生屏蔽效应。模型计算结果显示:当粗晶颗粒尺寸D确定时,K_(IC)随着纳晶材料晶粒尺寸d的增大而增大;当纳晶材料晶粒尺寸d确定时,K_(IC)随着粗晶材料晶粒尺寸D的增大而增大;相对于纳晶颗粒的尺寸,断裂韧性对粗晶晶粒的尺寸更加敏感。     

不同镍含量奥氏体基低密度热轧钢的组织与力学性能

研究了3种Fe-18Mn-10Al-1C-(0, 3, 5)Ni-0.08V-0.03Nb(wt%)奥氏体基低密度双相钢在热轧后的组织和力学性能。结果表明,热轧后,试验钢的组织由拉长的奥氏体、条带状B2相及沿再结晶奥氏体晶粒晶界处的块状B2颗粒组成。此外,在奥氏体晶粒和B2颗粒中分别形成了纳米级κ-碳化物和DO₃相。5Ni钢屈服强度高达1352 MPa,这主要是由于奥氏体晶界存在大量纳米级别的B2颗粒以及VC相产生析出强化效果。随着Ni含量的增加,钢的强度与硬度均增加,5Ni钢屈服强度比0Ni钢高116 MPa,归因于5Ni钢中更多的B2相含量(16.9%)。但含Ni钢在强度增加的同时,极大损失了塑性,导致钢的伸长率极低,分析其原因为条带状B2相主要分布在奥氏体晶界处,试样在变形过程中裂纹更易沿晶界断裂,断口有分层现象。     

A crystallographic mechanism for fatigue crack propagation through grain boundaries

A crystallographic model is proposed which takes into account both crack-plane twist and tilt effects on crack retardation at grain boundaries. The twist and tilt angles of the crack-plane deflection at a grain boundary are the key factors that control the path and growth rate of a short crack. Because of crack-plane twist, the area between the traces on the grain-boundary plane of the crack planes across the boundary has to be fractured in order for the crack to propagate through the boundary. This presents significant resistance to crack growth. As the area to be fractured increases with the extent of crack growth beneath the surface of observation, the grain boundary could still resist crack growth after the crack tip has passed the grain boundary on the surface, until the crack propagates through the whole boundary below the surface. A grain boundary with a large twist component could cause a short crack to arrest or branch. Studies of short fatigue crack growth in an Al–Li 8090 alloy plate provide evidence that supports the model.     

磁控溅射制备ZnO缓冲层薄膜的微观结构和光学性能

研究了衬底温度、溅射气压对磁控溅射沉积ZnO缓冲层薄膜的微观结构、表面形貌和光学性能的影响。结果表明,衬底温度、溅射气压对ZnO缓冲层薄膜表面形貌、晶粒尺寸、禁带宽度和光学透过率等有较大影响。综合分析得出最佳的制备ZnO缓冲层薄膜的工艺为250℃、0.6 Pa。在此工艺下制备的ZnO缓冲层薄膜具有很好的ZnO(002)面c轴择优取向,结构致密、尺寸均匀,禁带宽度为3.24 eV,可见光平均透过率为86.93%,符合作CIGS太阳能电池缓冲层的要求。     

A NEW CONCEPT TOWARD INDUSTRIALIZATION OF Cu-Ⅲ-Ⅳ2 THIN FILM SOLAR CELLS AND SOME PRELIMINARY EXPERIMENT RESULTS

A new concept of full vacuum manufacturing for Cu-Ⅲ-Ⅳ2 thin-film solar cells has been discussed Cu-Ⅲ-Ⅳ2 thin-film solar cells manufactured using full in-line reactive sputtering will result in lower cost than that of the conventional method with CdS layer fabricated with chemical bath deposition (CBS) method. Using reactive sputtering process with organometallic gases, the compositions and electronic properties of Cu-Ⅲ-Ⅳ2 thin-film can be fine-tuned and precisely controlled, n-type Cu-Ⅲ-Ⅳ2 film and ZnS suffer layer can also be deposited using the in-line sputtering instead of using the CdS layer. The environmental pollution problems arising from using CdS can be eliminated and the ultimate goal of full in-line process development can then be realized. Some preliminary experimental results on a modal solar cell fabricated by the new technique in the new concept have been presented.