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扫描电子显微镜

Scanning Electron Microscope

 
 
 
 
 

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扫描电镜应用之:薄膜太阳能电池(CIGS Solar Cell)能谱EDS分析  

2011-08-08 21:31:13|  分类: 默认分类 |  标签: |举报 |字号 订阅

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Pat Camus, Ph.D., Thermo Fisher Scientific, Madison, WI, USA
翻译: 驰奔

Abstract摘要
The Thermo Scientific NORAN System 7 energy dispersive spectrometry (EDS) system was used to investigate the elemental structure of a thin-film CIGS solar cell. The sample was investigated in both the planar and cross-sectional views.
使用热电科技NORAN系统第7代X射线能谱仪(EDS)研究CIGS薄膜太阳能电池的化学元素组成结构。通过表面和剖面对样品进行研究。

Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell - 驰奔 - --COXEM有限公司 中国代表处--
                                                                           Thermo Scientific NORAN System 7(NS7--EDS)

 Introduction介绍
         CIGS solar cells are based on copper indium gallium diselenide [Cu(In,Ga)Se2] thin films. These solar cells have demonstrated excellent efficiencies and are potential replacements for silicon based solar cells, which are more expensive to produce and are substantially thicker.
        CIGS太阳能电池是基于铜、铟、镓、硒 [Cu(In,Ga)Se2]薄膜。这种太阳能电池已经展现了优秀的效率,有替代制造成本更高尺寸更厚的硅基太阳能电池的潜能,
        CIGS solar cells are formed by layering thin films on a substrate (historically glass, but currently polymers) as shown on Figure 1. The molybdenum layer and the zinc oxide layer form the electrical contacts. The CIGS film acts as the sunlight absorber layer, with a thin CdS layer forming the p-n junction. The most common manufacturing methods evaporate or sputter copper, indium, and gallium simultaneously or sequentially onto the substrate. Vaporized selenium is reacted with the film to establish the final film composition.
        CIGS太阳能电池通过在基体上(过去是玻璃,但当前为聚合物)成多层薄膜加工而成,如图1。钼层和氧化锌层形成电接触电极。CIGS膜层作为阳光吸收层,一薄层硫化镉形成P-N节。最通常的制造方法是同时或者按照顺序在基体上蒸发或溅射 铜、铟、镓。被蒸发上的硒和膜层反应从而确定最终的合成膜层。
        The major challenge in producing these thin layer solar cells is to control film composition. Reproducibility of required layer structure in commercial volumes has proven to be problematic and this is critical as the electrical properties of the cell depend on the exact composition of the layers. EDS analyses can be used to determine the spatial distribution of the elements through the device.
        在制造薄膜太阳能电池过程中的主要挑战是控制膜层的成分。商品化所需要的膜层结构重复再现性,结果是不确定的,这和依靠膜层精确成分的电池的电学性质同样重要。EDS分析能够适用于确定整个装置的化学元素空间分布。

Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell - 驰奔 - --COXEM有限公司 中国代表处--

Figure 1: Scanning electron micrograph of a Cu(In,Ga)Se2 solar cell   (cross-section) and its mode of operation1
图1:Cu(In,Ga)Se2 薄膜太阳能电池(剖面)的扫描电镜图和它的操作模式-光伏效应。

Experimental实验
         A commercially available CIGS solar cell was disassembled to extract a portion of a single cell. It was analyzed in both the planar and cross-sectional views. The cross-section view was prepared in an epoxy mount and polished.
        市场上可以买到的CIGS太阳能电池,分解后提取单一元件的一部分。观察分析表面和断面,断面观察采用环氧树脂镶样和抛光。
         Examination took place using a Tungsten-filament SEM. Planar-view analyses were performed initially at 20 kV to determine the elemental constituents. Subsequent analyses of the cross section were performed at 5 kV to reduce the interaction volume. When it was discovered that a substantial portion of the substrate was polymer, care was taken to keep the induced charge to low levels. Even at these levels, a small amount of charging was present and drift compensation was required for mapping.
         使用钨灯丝扫描电镜进行检测。表面分析初步使用20KV加速电压来确定元素成分。随后的剖面分析使用5kv加速电压以减小作用区。当发现基体的主要材料大部分是聚合物,需要注意保持较低的荷电水平。即使在这样的水平,少量的荷电出现,漂移补偿作为面分布分析还是需要的。
         NORAN System 7 was used to collect X-rays from a NanoTrace SiLi detector. Both Point and Shoot spectral mode and Spectral Imaging mapping mode were used to characterize elemental constituents of the sample.
         NS7能谱仪使用纳米痕迹的液氮制冷锂漂移硅探测器收集X-ray。包括多点分析模式、谱图像、面分布都用于表征样品的元素组成。

Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell - 驰奔 - --COXEM有限公司 中国代表处--

 

 

Results结果
Planar View二维表面观察
During disassembly, some of the CIGS material delaminated from the substrate (Figure 2a). This provided a unique opportunity to measure (1) the top layers of the sample,
(2) the underlying metallic substrate, and (3) the metallic surface electrical contact material. Figure 2b is a Point and Shoot spectral analysis of these regions.
在拆解电池过程中,一些CIGS材料从基体上剥落(图2a)。这给了测量难得的机会。(1),样品顶层,(2),下层的金属基体 (3),金属表面电接触材料。图2b:选定区域的多点谱分析

 
Figure 2a: Planar view of delaminated CIGS material 图2a:剥落的CIGS材料的表面二维观察。

Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell - 驰奔 - --COXEM有限公司 中国代表处--

 图2b:CIGS材料的最上层表面EDS能谱分析。自动多点分析。point&shoot
Table 1: Quantitative Elemental Composition Analysis of the Top Surface of CIGS Material
表一:CIGS材料最上层表面的的元素成分定量分析结果

Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell - 驰奔 - --COXEM有限公司 中国代表处--

       Locations 1 and 2 on the film are the same material consisting of a majority of In and Se with a small amount of Cu and a small amount of Ga. Only small amounts of Zn, O, Cd and S are measured due to the thin nature of these layers.
      薄膜上的位置1和2,具有相同的材料组成,主要成分是铟和硒和少量的铜和镓。由于氧化锌和硫化镉的薄层特性,只有少部分的Zn,O,Cd和S被测出
       Location 3 on the metallic contact layer seems to be Ag paint.
       金属接触层上的位置3好像是银漆
       Location 4 where the film is removed shows the base Mo substrate that the layers are grown on.
       膜层去除的位置4 显示膜层生长的钼基体

Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell - 驰奔 - --COXEM有限公司 中国代表处--

                               Figure 3: Electron image and net count elemental maps of CIGS cross-section at low magnification
                               图3:CIGS剖面包含所有计数的X-ray元素面分布,扫描电镜图像在低加速电压下5kv,

Cross-sectional View剖面观察分析
Low Magnification低倍
A Spectral Imaging mapping analysis was performed at low magnification on the cross-section sample to understand all of the layers that constitute the material. The thickness of all of the layers was approximately 1/3 mm. Interestingly, a majority of the layers consisted of C, indicating a large
polymer content in the layers. In addition to the polymer layers, Aluminum and Iron layers were also observed,Figure 3.
样品剖面在低倍进行谱图像面分布分析,理解所有层的材料组成。所有层的厚度大约1/3mm。有趣的是,多数层中含有C,表明多数的聚合物包含在这些层中。除了聚合物层,铝和铁层也被观察到。如图3
High Magnification高倍率
Further investigation concentrated on the outmost surface of the Iron layer at higher magnification. Elemental maps indicated layers of Cu, Ga, Se, Mo and In. Quantitative maps, Figure 4, removed the background X-ray intensity of the maps and formed maps with a much higher contrast than observed in the gross count maps. Thermo Scientific COMPASS software phase analysis was able to locate the individual layers in the structure at the micro scale, Figure 5. COMPASS maps reveal a Mo layer against the Fe substrate, followed by 2 Cu-Ga-Se layers. The first Cu-Ga-Se layer
had very low X-ray counts and the second layer was higher in In content. The low X-ray count layer seemed to be recessed in physical appearance indicating preferential polishing of this particular layer of the sample may have occurred. Because of the thin nature and common environment, this preferential polishing indicates a different hardness and could derive from a different composition than the following layer. The thickness of the Mo layer was just under 1 μm while the Cu-Ga-Se layers were just under 3 μm and 1.5 μm respectively. No CdS or ZnO phases were observed, probably due to their thin nature and the larger X-ray generation volume.
在高倍率下,进一步对最外面的铁层进行研究。元素面分布表明Cu, Ga, Se, Mo and In 层。定量面分布,图4,移除了在面分布图像的背底x射线强度后,比总体计数的面分布具有更高的对比度。热电科技(Thermo)的COMPASS软件相分析能够在微小尺度定位显微组织中的单个层,图5,COMPASS面分布揭示了相对铁基体的Mo层,然后是Cu-Ga-Se 层。第一层Cu-Ga-Se 的计数很低,第二层包含铟的Cu-Ga-Se-In计数要高的多。低X-ray计数层像是在形貌上凹陷,这个样品特殊层表明的优先抛光可能发生。因为薄层性质和环境相同,所以这个优先抛光部分表明,源于和下层不同的成分不同,具有不同硬度。Mo层厚度小于1μm,而Cu-Ga-Se层分别小于3μm和1.5μm。没有发现Cds或者ZnO相,可能由于层太薄,过大的X-ray生成作用区。

Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell - 驰奔 - --COXEM有限公司 中国代表处--

Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell - 驰奔 - --COXEM有限公司 中国代表处--

 Figure 4: Quantitative element maps of CIGS cross-section at high magnification
图4:CIGS剖面在高倍率下的定量元素面分布

扫描电镜应用之:薄膜太阳能电池(CIGS Solar Cell)能谱EDS分析 - 驰奔 - --COXEM有限公司 中国代表处--
扫描电镜应用之:薄膜太阳能电池(CIGS Solar Cell)能谱EDS分析 - 驰奔 - --COXEM有限公司 中国代表处--
扫描电镜应用之:薄膜太阳能电池(CIGS Solar Cell)能谱EDS分析 - 驰奔 - --COXEM有限公司 中国代表处--
扫描电镜应用之:薄膜太阳能电池(CIGS Solar Cell)能谱EDS分析 - 驰奔 - --COXEM有限公司 中国代表处--
扫描电镜应用之:薄膜太阳能电池(CIGS Solar Cell)能谱EDS分析 - 驰奔 - --COXEM有限公司 中国代表处--
扫描电镜应用之:薄膜太阳能电池(CIGS Solar Cell)能谱EDS分析 - 驰奔 - --COXEM有限公司 中国代表处--
                                    Figure 5: Compass phase maps of CIGS cross-section at high magnification
                                    图5:CIGS 剖面在高倍率下的 Compass相分布


Summary概括
Energy Dispersive X-ray spectroscopy provides compositional information about the structure of CIGS solar cells. If a majority of the sample is polymer, low beam energy and beam current, and drift compensation are required to obtain meaningful results. The spatial resolution of the results
depends upon the incident electron beam energy and the beam diameter. Ultra-thin layers may not be observed in bulk samples.
X射线能谱仪提供有关CIGS太阳能电池的结构成分信息。如果样品大部分是聚合物,需要降低电子束能量和探针电流,需要漂移补偿获得有意义的结果。结果的空间分辨率有赖于入射电子束能量和束斑直径。在大块样品中,在面分布图中可能观察不到超薄膜层
Conclusion结论
The NORAN System 7 enables the analysis of complex samples such as a CIGS solar cell under low accelerating voltages and beam currents in the scanning electron microscope.
NS7使得分析复合样品成为可能。例如在扫描电镜低加速电压和低探针电流下的CIGS太阳能电池。
Reference
1. D. Abou-Ras et al. Elemental distribution profiles across Cu(In,Ga)Se2
solar-cell absorbers acquired by various techniques. Proceedings of EMC
2008, volume 1, p. 741.
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