Speaker Name: Beate Röder

Work for: Humboldt-University

2018 PPIC 光伏聚合物国际大会演讲题目：

Prospects of 2D-luminescence spectroscopy for aging investigations of the embedding EVA polymer in PV modules

For a reliable lifetime prediction of photovoltaic (PV) modules, the investigation of degradation processes of materials in the product is a fundamental prerequisite. Especially for nondestructive characterization of the encapsulating material, suitable characterization methods are needed.

Luminescence has recently been introduced as a non-destructive method to follow the degradation of the most common encapsulation material, ethylene-vinyl acetate copolymer (EVA). In aged PV modules inhomogeneous luminescence patterns were found, which are specific for different aging factors such as accelerated thermal aging, UV aging or outdoor weathering

Moreover the quality of the cross-linking of the EVA is of great interest for the industry, as this greatly affects the service life of PV modules. At present no suitable methods exist, which allow an in situ inspection. Here we present a promising method that allows non-destructive examination of the degree of crosslinking and its homogeneity in the PV module by luminescence measurements. The luminescence of EVA after UV excitation is presented here as a non-destructive method to determine the degree of crosslinking. The luminescence intensity increases with the degree of crosslinking. Moreover, evaluating the time-dependent luminescence signal for defined spectral region it becomes possible to determine the degree of cross linkage and differentiate spatial efficiency of crosslinking. The results substantiate that a spatial inhomogeneity of crosslinking properties is a manifestation of aging effects, which is attributed to diffusion limited oxidation (DLO) conditions in the EVA between cell and front glass. The characterization of the EVA luminescence behavior taken over the module surface appears as a valuable tool to assess DLO effects.

The results imply that photoluminescence can be used to follow material degradation and detect inhomogeneous material aging due to diffusion-limited oxidation. Prospective applications for aging investigations of complex products arise as this method improves upon drawing a connection between accelerated aging and outdoor weathering.

      要对光伏组件进行可靠的寿命预测，基本前提是研究组件用材料的降解过程。特别是对于封装材料的无损表征，需要一种合适的表征方法。近年来，冷光被引入作为一种非破坏性的方法来跟踪最常见的封装材料EVA的降解行为。在经过老化的光伏组件中所发现的不均匀冷光发光分布，可以反映出不同老化因素如加速热老化、紫外老化或户外老化。

       此外，行业也非常感兴趣EVA的交联度，因为交联度极大地影响了组件的使用寿命。之前一直没有特别合适的方法允许现场检测EVA交联度。在这里，我们提出了一种有前景的方法，允许非破坏性地检测组件中EVA交联度，并通过发光测量来检测组件EVA交联度的均匀性。在紫外激发的作用下，测量EVA的发光可以不破坏组件就确定交联度。EVA的发光强度随交联程度的增加而增加。此外，通过在限定的光谱区域内评估时间依赖性的发光信号，可以确定交联度并区分交联的空间效率。结果证实，交联性能的空间不均匀性是不同老化行为的反映，根本原因是由于EVA、电池和玻璃间的扩散限制氧化（Diffusionlimited oxidation, 简称DLO）。通过表征组件表面的EVA发光行为来评估DLO效应看来非常有价值。

       结果表明，光致发光可以用于研究材料降解，检测由于扩散限制的氧化引起的非均匀材料老化。由于这种方法可以大大改善建立加速老化和户外老化之间的相关性，预期可广泛用于复杂产品老化研究。

Speaker Introduction:

Dr. Beate Röder,  Professor of Humboldt-Universität zu Berlin, MNF, Department of Physics. Beate graduated from Gorki-University (Ukrain) and 2 Medical Institute Moscow, got her Dr. degree in Institute of Physic at Humboldt University in 1982.  In Humboldt University, she got the Humboldt-Forschungspreis scientific awards in 1986 and E.T.S. Walton Award Professor in 2009. Beate mainly focused on photobiophysics and photodynamic activity.