Investigations on the Photon-Recycling Properties of Different Back-sheets

29th European Photovoltaic Solar Energy Conference and Exhibition; 3115-3118
In a state-of-the-art photovoltaic module the solar cell area accounts for about 85 to 90% of the total module area. The rest of the module area is dominated by the back-sheet. Light impinging onto the back-sheets is mostly reflected and a part of the reflected light is re-directed onto the solar cells. This photon recycling effect is well known, but the efficiency of this process is not well understood until now. In this paper we present the results of a study on the photon-recycling efficiency of different ISOVOLTAIC back-sheets and investigate the reasons for their varying optical performances. A series of mono-cell-modules with different back-sheets was manufactured and carefully investigated under Standard Test Conditions and by applying the Laser Beam Induced Current method. In addition, the scattering properties of the back-sheets were measured which are the basis for the modelling of the photon recycling efficiency. The experimental as well as the modelling results show good agreement. In particular it is shown the photon recycling efficiency within a module significantly depends on the type of back-sheet used. The average photon recycling efficiency of a typical module boarder region is found to range from about 19 to 23%, depending on the type of back-sheet used.