Optical modeling of the internal back reflectance of various c-Si dielectric stacks featuring AlOx, SiNx, TiO2 and SiO2

One promising path to a reduced cost of crystalline silicon (c-Si) photovoltaics (PV) is to increase silicon usage efficiency by using thinner wafers. Many challenges arise when transitioning to thin wafer cells, including increased surface recombination at the rear side of the cell, increased wafer bowing, and a reduction in optical absorption due to a decreased optical path length within the silicon. Rear side passivation provides great promise in addressing these challenges. This paper addresses rear side dielectric configurations that can optimize back surface reflectance, in addition to providing excellent surface passivation. Optical modeling of various stack configurations is examined to explore the back surface reflectance at the Si-dielectric interface for different film combinations and thicknesses as a function of wavelength and internal angle of incidence. Specifically, configurations using aluminum oxide (AlO_x), silicon nitride (SiN_x), titanium dioxide (TiO₂), and silicon dioxide (SiO₂) were investigated with a focus on designing stack configurations that will also allow for high quality passivation and are compatible with a high-volume manufacturing environment.