Analysis of electrically conductive adhesives in shingled solar modules by X-ray imaging techniques

The failure mechanisms of electrically conductive adhesives (ECAs) in solar modules are difficult to study since the ECA layer is not easily accessible within the module package. In this work, we present two complementary imaging modalities—X-ray radiography and X-ray microcomputed tomography (XCT)—that reveal important morphological features of the ECA within a shingled module. X-ray radiography uses single X-ray projections to provide fast and non-destructive imaging of the shingled interconnection, illuminating the alignment of the ECA relative to the busbars, the size and shape of the ECA, and the presence of voids within it. Through X-ray radiography, we observed, for example, that the average void coverage area of ECA segments reduced from 36.7 % to 4.4 % when an ECA was cured for 60 s prior to module lamination. XCT is a three-dimensional imaging technique that can identify regions in which the ECA makes electrical contact to busbars on cells and regions in which the ECA has cracked, among other features. XCT can also be used to image the individual metal particles within ECA, from which the metal volume fraction of an ECA was found here to be 70.4 %. This is a quantity that is not often reported by ECA manufacturers but is important to ensure isotropic conduction. As X-ray projections can be performed non-destructively on full modules, the technique may be used to pinpoint ECA failures in accelerated degradation testing. XCT is complementary and is suited to forensic analysis of failing modules.

太阳能组件中导电胶（ECA）的失效机制难以研究，因为在组件封装内ECA层不易触及。在这项工作中，我们提出了两种互补的成像方式——X射线照相术和X射线微计算机断层扫描（XCT）——它们揭示了叠瓦式组件内ECA的重要形态特征。X射线照相术利用单次X射线投影，对叠瓦式互连进行快速且无损的成像，显示ECA相对于汇流条的排列、ECA的大小和形状以及其中是否存在空隙。例如，通过X射线照相术我们观察到，在组件层压之前将ECA固化60秒时，ECA部分的平均空隙覆盖面积从36.7%降至4.4%。XCT是一种三维成像技术，它能够识别ECA与电池上的汇流条形成电接触的区域以及ECA开裂的区域等其他特征。XCT还可用于对ECA内的单个金属颗粒进行成像，由此发现此处ECA的金属体积分数为70.4%。这是一个ECA制造商通常不报告但对确保各向同性传导很重要的量。由于可以对完整的组件无损地进行X射线投影，该技术可用于在加速老化测试中查明ECA的失效情况。XCT是互补的，适用于对失效组件进行法医分析。