Optimized Metal-Free Back Reflectors for High-Efficiency Open Rear c-Si Solar Cells

The photovoltaic (PV) industry has recently become more oriented toward n-type c-Si solar cells. Among the different n-type solar cell architectures, bifacial cells are quickly emerging. The open-rear configuration of a bifacial device results in high transmittance (T) losses at long wavelengths (>1000 nm). This limitation is usually overcome at the module level either by using a bifacial encapsulation or by placing a reflective foil on the rear side. In this paper, we have investigated the application of a distributed Bragg reflector (DBR) and TiO2-based white paint (WP) as alternative metal-free back-reflector options applied to the textured open-rear of bifacial n-Pasha cells. Because of the high T losses at long wavelengths of the DBR applied on textured surface, its design and fabrication is studied in detail. The dielectric (DBR and WP) and optimized Ag back-reflectors, which are used as a reference, are applied to bifacial n-Pasha cells, and their performance is evaluated. In particular, we demonstrate T below 20% at 1200 nm by optimizing the DBR thickness for textured surfaces. In addition, the optimized DBR and WP show performance comparable with a state-of-the-art Ag back-reflector. The highest increase of the conversion efficiency is measured for the WP back-reflector: +0.34% absolute compared with n-Pasha measured with no-additional back-reflector.