无硒气氛退火下掺入Sb2S3提高CIGS薄膜晶粒尺寸的研究

将一薄层Sb_2S_3置于Cu(InGa)Se_2(CIGS)薄膜与Mo薄膜之间,于不含硒源的惰性气氛中退火,发现随Sb_2S_3厚度的增加,CIGS薄膜的晶粒尺寸显著增大,薄膜的择优生长面由(112)晶面向(220/204)晶面转变。为阐明晶粒的生长机理,研究退火温度对Sb_2S_3掺杂的CIGS薄膜的晶粒尺寸和物相的影响规律,发现薄膜在450～500℃之间晶粒尺寸增大显著。在实验结果的基础上提出一种气相促进晶粒生长的模型和液相促进晶粒生长的模型。     

In2Se3薄膜生长及结晶择优取向的影响因素研究

(In,Ga)2Se3薄膜的生长结晶性的好坏直接影响着在其基础上化合生长的Cu(In,Ga)Se2(CIGS)薄膜以及CIGS太阳电池器件的性能.实验就多源共蒸发制备In2Se3预制层工艺中3个主要条件,即衬底材质、Se源温度、衬底温度进行研究.分析讨论上述3种因素对In2Se3薄膜的结晶生长和择优取向生长的影响.发现:在Mo/苏打石灰玻璃(Mo/SLG)衬底上生长,Se源温度在270℃以上或衬底温度为380～400℃的较高温度时,制备的In2Se3预制层是单一晶相的In2Se3,其x射线衍射峰是以(110)和(300)峰为择优取向.反之,生长在苏打石灰玻璃(SLG)衬底上,Se源温度为230℃以下或衬底温度为较低温度300℃时,In2Se3预制层结晶质量较差,其X射线衍射峰则多以In2Se3(006)衍射峰为择优取向.     

效率为12.1%的Cu(In,Ga)Se2薄膜太阳电池

利用共蒸发的三步法制备了较高质量的四元化合物Cu(In，Ga)Se2(CIGS)薄膜，并采用Mo／CIGS／CdS／ZnO结构为基础做出转换效率超过10％的薄膜太阳电池，其最高转换效率达到12．1％(测试条件为：AM1．5，Global 1000W／m^2)。通过与国际最高水平的CIGS太阳电池各参数的比较，分析了我们所制备的CIGS太阳电池在工艺和物理方面存在的问题。     

H_2Se气态硒化后退火温度对CIGS薄膜中Ga再分布的影响

采用H_2Se气体在400℃下对溅射的Cu-In-Ga金属预制层进行硒化处理制备CIGS薄膜,然后采用原位退火的方法改善Ga元素在CIGS薄膜内的纵向分布和薄膜内的晶粒尺寸,研究退火温度对CIGS薄膜表面Ga元素含量和结晶性的影响。CIGS薄膜中Ga元素的分布决定薄膜的禁带宽度和太阳电池的开路电压,通过优化退火温度,CIGS太阳电池的转换效率相对增益达到20%,最终达到14.39%的转换效率和590 mV的开路电压。     

硒蒸气硒化法制备CIGS薄膜的影响因子(Ⅰ)氩气流量对CIGS薄膜结构和形貌的影响

采用中频交流磁控溅射方法,在Mo层上沉积了CulEnGa(cIc)预制膜.以Ar为载气,采用固态硒化法制备获得了Cu(In1-xGax)Se2(CIGS)吸收层薄膜,考察了Ar流量对CIGS薄膜结构和形貌的影响.采用SEM和EDS观察和分析了薄膜的表面形貌和成份,采用XRD表征了薄膜的组织结构.结果表明,在不同Ar流量下制备的CIGS薄膜均具有单一的黄铜矿相结构,薄膜具有(112)面的择优取向.随着Ar流量的增大,CIGS薄膜晶粒直径增大.当Ar流量为0.20m3/h时,薄膜的孔隙最少.当Ar流量达到0.40m3/h时,薄膜晶粒出现明显的柱状生长.当Ar流量为0.10、0.20和0.30 m3/h时,所制得的CIGS薄膜的Cu、In、Ga原子含量比,处于弱p型的理想范围.     

硒蒸气硒化法制备CIGS薄膜的影响因子(Ⅱ)预制膜对CIGS薄膜结构和形貌的影响

采用中频交流磁控溅射方法,在Mo层上沉积了多层和双层CuInGa(CIG)预制膜,采用固态硒化法制备获得了Cu(In1-xGax)Se2(CIGS)吸收层薄膜,考察了预制膜对CIGS薄膜结构和形貌的影响.采用SEM和EDS观察和分析了薄膜的表面形貌和成分,采用XRD表征了薄膜的组织结构.结果表明,CIG多层预制膜由Cu11 In9、CuIn和In相组成,CIG双层预制膜由Cu11 In9、CuIn、In和CuGa相组成.通过硒化CIG双层和多层预制膜,所获得的CIGS薄膜均为黄铜矿相结构,薄膜具有(112)面的择优取向.当硒化时间为17min时,通过硒化CIG双层预制膜所获得的CIGS薄膜出现了上层致密,下层疏松的结构,延长硒化时间为25min,CIGS薄膜变得致密.     

H2Se气体硒化中温度对CIGS吸收层特性的影响

采用H_2Se气体对铜-铟-镓金属预制层进行硒化制备铜铟镓硒(CIGS)光吸收层,研究硒化过程中温度对CIGS结晶质量及光学特性的影响。400~500℃单一温度硒化制作的CIGS薄膜的表面平整性较差,存在颗粒状聚集物。在硒化前引入200℃低温预处理过程,可提高CIGS薄膜表面的平整性和致密性。在400℃硒化后导入500℃高温热处理过程可提高CIGS的结晶质量并改善Ga元素掺入的均匀性。光学特性测量显示,优化硒化温度可降低CIGS薄膜的缺陷态,从而提高Ga元素在薄膜中的掺入效果,CIGS薄膜的光学带隙可达1.14 e V。利用CIGS薄膜制备的太阳电池光电转换效率达13.1%,开压为519 m V,有效面积为0.38 cm~2。     

柔性不锈钢衬底CIGS薄膜太阳电池

以轻质柔性不锈钢材料为衬底,利用三步共蒸发法制备较高质量的四元化合物Cu(In,Ga)Se_2薄膜,CIGS层在Mo导电层上具有很强的附着力。利用XRD和XRF分别分析了所制备薄膜的晶相和组分。以ZnO:Al/i-ZnO/ CdS/CIGS/Mo/Stainless steel结构为基础得到最高转换效率为9.39%的柔性太阳电池。最后讨论了衬底粗糙度、有害杂质的扩散和不含有Na元素等不利因素对于电池性能的影响。     

CIGS-BIPV示范建筑的日发电性能分析

以惠州市潼湖科技创新小镇的铜铟镓硒建筑光伏一体化(CIGS-BIPV)示范项目为例,对该示范项目中示范建筑不同朝向立面上的铜铟镓硒(CIGS)薄膜光伏组件在夏季、冬季典型日的发电量特点和变化规律进行分析,结果显示：1)初夏的5月12日,安装在东南侧、西南侧、东北侧的CIGS薄膜光伏组件的日发电量大体相当,西南侧安装的CIGS薄膜光伏组件与东南侧、东北侧安装的CIGS薄膜光伏组件的日发电量曲线大致呈镜像关系。2)初冬的11月22日,安装在东南侧、西南侧的CIGS薄膜光伏组件的日发电量大体相当,均是安装在东北侧的CIGS薄膜光伏组件的约3倍。3)安装在东南侧、西南侧的CIGS薄膜光伏组件在11月22日的高效率发电时长高于其在5月12日的,发电量更大;安装在东北侧的CIGS薄膜光伏组件在5月12日的发电量是在11月22日的2.5倍。该研究结果可为采用薄膜光伏组件的BIPV项目和低纬度沿海地区的光电建筑应用提供借鉴。     

Mo背电极对CIGS吸收层成分与结构的影响

采用直流磁控溅射法,通过调整溅射气压制备双层和三层Mo背电极层,并在其上制备(In,Ga)_2Se_3(IGS)和Cu(In,Ga)Se_2(CIGS)。采用X射线荧光光谱(XRF)和X射线光电子能谱(XPS)测量成分;用扫描电子显微镜(SEM)观察IGS和CIGS的表面和断面形貌;用X射线衍射(XRD)研究背电极层对IGS和CIGS结晶取向的影响。结果表明,背电极的不同可影响CIGS表面Na的分布;三层Mo背电极层上制备的CIGS吸收层具有112择优,晶粒较大,贯通性更优;三层Mo背电极层上制备的CIGS电池的效率为14.1%,其中较双层J_(sc)和FF分别有9.4%和15.5%的提升。     

EQUILIBRIUM MOLECULAR DYNAMICS STUDY OF PHONON THERMAL TRANSPORT IN NANOMATERIALS

In this work, the thermal conductivity of nanofilms, nanowires, and nanoparticles are studied using molecular dynamics simulation. It is found that their thermal conductivity depends significantly on the characteristic size until it reaches a large value. Comparison with results of the lattice Boltzmann method reflects strong effects of surface structure, especially when the film thickness is comparable to the mean free path of phonons. Study of the phonon thermal transport in nanowires and nanoparticles reveals much stronger boundary-scattering effect on thermal transport than in nanofilms, which is attributed to the more confined phonon movements in these two- and one-dimensional nanomaterials.     

Experimental study on thermal characteristics of suspended platinum nanofilm sensors

In this paper, the thermal characteristics of suspended platinum (Pt) nanofilm sensors have been investigated experimentally. The Pt nanofilm sensors with the thickness of 28–40 nm, the width of 260–601 nm, and the length of 5.3–5.7 μm were fabricated by electron beam lithography, electron beam physical vapor deposition and isotropic/anisotropic etching processes. Based on the one-dimensional heat conduction model, the in-plane thermal conductivity of the nanofilm sensors was obtained from the linear relation of the volume-averaged temperature increase and the heating rate measured in vacuum. Furthermore, natural convection heat transfer coefficients of air around the suspended nanofilm sensors at the pressures ranging from 1 × 10⁻² Pa to 1 atm were also investigated. The experimental results show that the in-plane thermal conductivities of the nanofilm sensors are much lower than those of the bulk values, the natural convection heat transfer coefficients are, however, very high at the atmospheric pressure.     

Influence of the Au interlayer on the contact resistance and morphology of CdTe films deposited on molybdenum substrate

Development of a proper electrical contact between CdTe and the metallic substrate is one of the hurdles in the fabrication of flexible solar cells on metal foils. From the point of view of matching thermal expansion coefficient; Molybdenum (Mo) is favored as the substrate material. However, the large difference in work, function of CdTe and Mo necessitates a no-rectifying interlayer. In this work we are presenting some preliminary results of our efforts on developing a pseudo-ohmic layer between CdTe and Mo substrate. A thin interlayer of Au seems to reduce the contact resistance. The dependence of the film morphology on the substrate material as well as the substrate temperature is discussed.     

Thermal Stresses in Thin Auxetic Plates

This article investigates the effect of auxeticity on the thermal stresses of isotropic plates. The thermal stress is non-dimensionalized against the coefficient of thermal expansion, the change in temperature and at least one of the moduli so as to express the dimensionless thermal stresses solely in terms of Poisson's ratio of the plate material. Results show that increasing auxeticity leads to mild and significant drop in the thermal stresses under the conditions of constant Young's modulus and constant shear modulus, respectively. However, increasing auxeticity causes increase in the thermal stress under the condition of constant bulk modulus. It is also shown that increasing auxeticity under the condition of constant product of all the three moduli reduces the thermal stress if Poisson's ratio falls within a wide range of ?1 and 0.303. These results suggest that, under most circumstances, the replacement of conventional plate materials with auxetic solids is useful for reducing thermal stresses therein. The use of auxetic materials, therefore, provides an additional choice for the reduction of thermal stresses in plates other than selecting materials of lower modulus and low coefficient of thermal expansion.     

EFFECTS OF TEMPERATURE-DEPENDENT PHYSICAL PROPERTIES ON THE RESPONSE OF THERMALLY POSTBUCKLED PLATES

It is known that the values of physical properties, such as the moduli of elasticity and thermal expansion coefficients, cannot be assumed constant over a wide range of high-temperature applications. We therefore examine how the linear temperature variations of physical properties would affect the static and dynamic responses of thermally postbuckled plates. It is found for a clamped aluminum plate that the postbuckled maximum displacement, static x-strain, and root-mean-squared (RMS) x-strain are increased by the same order-of-magnitude percent jump in the thermal expansion coefficient. On the other hand, the critical buckling temperature, x-stress, and RMS x-stress are all decreased by the same order-of-magnitude percent drop in Young's modulus. These observations have also been collaborated with the available composite plate computations. Therefore, this provides an overall estimate on temperature dependency based on the linear temperature variations of physical properties over the operating temperature range.     

Modeling of a reacting nanofilm on a composite substrate

This article provides a detailed computational analysis of the reaction of dense nanofilms and the heat transfer characteristics on a composite substrate. Although traditional energetic compounds based on organic materials have similar energy per unit weight, non-organic material in nanofilm configuration offers much higher energy density and higher flame speed. The reaction of a multilayer thin film of aluminum and copper oxide has been studied by varying the substrate material and thicknesses. The numerical analysis of the thermal transport of the reacting film deposited on the substrate combined a hybrid approach in which a traditional two-dimensional black box theory was used in conjunction with the sandwich model to estimate the appropriate heat flux on the substrate accounting for the heat loss to the surroundings. A procedure to estimate this heat flux using stoichiometric calculations is provided. This work highlights two important findings. One is that there is very little difference in the temperature profiles between a single substrate of silica and a composite substrate of silicon-silica. Secondly, with increase in substrate thickness, the quenching effect is progressively diminished at a given speed. These findings show that the composite substrate is effective and that the average speed and quenching of flames depend on the thickness of the silica substrate, and can be controlled by a careful choice of the substrate configuration.     

MOLECULAR DYNAMICS SIMULATION OF THERMAL CONDUCTIVITY OF NANOSCALE THIN SILICON FILMS

Molecular dynamics simulations are performed to explore the thermal conductivity in the cross-plane direction of single-crystal thin silicon films. The silicon crystal has diamond structure, and the Stillinger-Weber potential is adopted. The inhomogeneous nonequilibrium molecular dynamics (NEMD) scheme is applied to model heat conduction in thin films. At average temperature T = 500 K, which is lower than the Debye temperature Θ_D = 645 K, the results show that in a film thickness range of about 2–32 nm, the calculated thermal conductivity decreases almost linearly as the film thickness is reduced, exhibiting a remarkable reduction as compared with the bulk experimental data. The phonon mean free path is estimated and the size effect on thermal conductivity is attributed to the reduction of phonon mean free path according to the kinetic theory.     

Propagation of thermoelastic waves in unsaturated porothermoelastic media

Abstract

In the present work, the characteristics of bulk wave propagation in an unsaturated porothermoelastic medium are studied taking into consideration of the thermal effect. The wave equations of thermoelastic waves of the problem are established by the mass balance equations, generalized Darcy law, momentum balance equations and generalized non-Fourier heat conduction law of the three-phase medium composed of solid, liquid and gas in unsaturated soils. The dispersion equations of bulk waves in unsaturated porothermoelastic media are derived using the potential functions. Compressional, thermal and shear waves with various speeds are analyzed numerically. It can be found that the thermal expansion coefficient has great influence on the wave speeds of P1 wave and thermal wave. The thermal conductivity only affects the speed of the thermal wave. A rise in the internal temperature of the unsaturated porothermoelastic medium can cause an increase of the wave speeds of compressional, thermal and shear waves.     

STRUCTURAL AND MICROSTRUCTURAL EFFECTS ON THE THERMAL CONDUCTIVITY OF ZIRCONIA THIN FILMS

Thermal properties of thin films are involved in a large number of applications such as electronic and electrooptical devices, or thermal barrier coating. It is known that the structure and the microstructure of thin solid films have a strong influence on the thermal conductivity, which may be considerably lower than for bulk materials. The aim of this study is to highlight the role of structure and microstructure on the thermal conductivity of ZrO 2 thin films (stabilized with Y 2 O 3 or not). Investigations have focused on the influence of film thickness, substrate roughness, and crystallites size on the thermal properties of dielectric thin film samples. For this purpose, a new photothermal method has been developed to measure the thermal conductivity of such films on various kind of substrates with an accuracy better than 10%. It has been observed that a decrease in the dielectric thickness leads to a drastic drop of the apparent thermal conductivity, k a , whatever the ZrO 2 phase is. k a is affected by an additional thermal resistance, R fs , especially between ZrO 2 and alumina substrate. This resistance R fs varies linearly with the substrate roughness. Finally, the influence of crystallite size and grain boundaries on k a have been shown.     

On the size of hot spots in the dry sliding of metals

This paper investigates the influence of the interfacial temperature rise, in the dry sliding of metals, on the size of hot spots. An area expansion coefficient that corrects for such thermally induced changes is introduced. It is shown that the discrepancy between theoretical and experimental estimates of the area ratio, reported by some authors, may be avoided by taking into consideration the effects of temperature elevation on the properties of the sliding pair: namely, material softening and thermal expansion.