Non-destructive monitoring of ethylene vinyl acetate crosslinking
in PV-modules by luminescence spectroscopy
Jan Caspar Schlothauer
Received: 22 June 2017 / Accepted: 27 November 2017
Springer Science+Business Media B.V., part of Springer Nature 2017
This work reports on the prospects of using luminescence spectroscopy as a non-destructive method for the characterization of
ethylene vinyl acetate copolymer (EVA) crosslinking in photovoltaic (PV) modules. Luminescence has the potential to be easily
applied in-line for monitoring purposes, e.g. during manufacturing. We investigate the correlation of luminescence, Raman
spectroscopy and differential scanning calorimetry with the EVA crosslinking. We show that all these methods, including the lumi-
nescence method, show a good correlation with the hold time during the lamination process. Furthermore, time-dependent lumines-
cence measurements are introduced. These make use of the fact that the luminescence decreases upon the ultraviolet irradiation during
the measurement. In contrast to steady-state luminescence, this facilitates measurements that are inherently less dependent on possible
interfering signal artifacts, as these may occur in industrial PV modules due to other components of the PV module.
Ethylene vinyl acetate
The use of photovoltaics (PV) as a renewable source of elec-
trical energy has dramatically increased during the last years.
In addition to a low price, a long service life is a prerequisite
for the economic success of PV modules. Manufacturers of
PV modules therefore guarantee a lifetime of about 20–
30 years, within which the power output of the PV module
is allowed a maximum loss in output power of 20%.
To achieve these long lifetimes, a detailed monitoring and
quality control of the production process is necessary. A key
step in module manufacturing is the lamination of all compo-
nents of a PV module - usually consisting of front glass, a
front-layer of the encapsulation material, the cells, a back-
layer of the encapsulation material and a back sheet (or glass).
For the most common encapsulation material, ethylene-vinyl-
acetate copolymer (EVA), the crosslinking quality (degree of
crosslinking and homogeneity across the module) is of vital
importance for the lifetime of a PV module [1–4].
Therefore, the determination of the degree of crosslinking
during or immediately after the production process is essential
for the industry. Currently several destructive methods coexist
for determination of the degree of crosslinking of EVA [1,
5–7]. Standard practice is the determination using
SOXLETH extraction according to ASTM D2765–11 .
For this a sample is dissolved in a solvent and the insoluble
fraction (Gel content) is weighted against the soluble fraction.
A disadvantage is the long duration of the extraction process
and the demanding experimental precision. Other methods for
characterization, such as differential scanning calorimetry
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s10965-017-1409-y) contains supplementary
material, which is available to authorized users.
* Beate Röder
Jan Caspar Schlothauer
Humboldt-Universität zu Berlin, Unter den Linden 6,
10099 Berlin, Germany
CTR Carinthian Tech Research AG, Europastraße 4/1,
9524 Villach, Austria
PCCL Polymer Competence Center Leoben, Roseggerstraße 12,
8700 Leoben, Austria
Journal of Polymer Research (2017) 24:233