Quantification of Abrasion-induced ARC Transmission Losses from Reflection Spectroscopy
Klemens K. Ilse1,2,3, Charlotte Pfau1,2, Paul-T. Miclea1,2, Stephan Krause1,2,3, Christian Hagendorf1,2
1Fraunhofer Center for Silicon Photovoltaics CSP, Halle (Saale), Germany
/2Fraunhofer Institute for Microstructure of Materials and Systems IMWS, Halle (Saale), Germany
/3Anhalt University of Applied Sciences, Köthen (Anhalt), Germany

Front side anti-reflective coatings (ARC) provide a significant contribution to performance and energy yield in PV modules, solar thermal housings and green house applications. However, ARC degradation and abrasion may lead to long term losses in optical performance. In order to quantify these losses and benchmark various ARC before and after abrasion testing, it is mandatory to perform optical spectroscopy measurements which allow an assessment of the ARC front side independent of glass substrate absorption and internal reflections from the backside. Here, we present a methodology for the quantitative measurement of front side ARC performance and its impact on optical transmittance from a simple reflection spectroscopy measurement at large glass panes. An absorber structure is applied to suppress the internal backside reflections and scattering within the glass substrate at a broad band width. Results on reflection spectroscopy are presented at full size standard ARC coated solar glasses with and without internal reflection suppression, which represent the application scenarios in PV modules and green houses, respectively. Absorption and scattering characteristics of the glass substrate are separately determined. The optical transmittance of the front side ARC is calculated based on a simplified approach based on the law of energy conservation, which is validated through optical modeling and comparison to experimental data. Finally, the simplified method for a quantitative optical front side ARC assessment is applied in successive and gradual ARC abrasion experiments.