Optimization of Anti-Reflection Coatings for Bifacial Solar Cells with Upconversion Layers

Upconversion is an optical process in which two or more low-energy photons are converted to one high-energy photon. Placing layers capable of performing this process at the rear face of a standard bifacial solar cell allows for utilization of sub-bandgap photons that would be otherwise lost. Optimization of antireflection coatings for devices using upconversion is particularly important as it needs to take into account the normally neglected sub-bandgap part of the spectrum. In this paper we study the optimization of antireflection coatings for bifacial silicon solar cells for upconversion applications. A 3-layer stack of MgF2/Si3N4/TiO2 shows the lowest weighted reflectance with 88.6% transmission at 1520 nm as compared to 78% transmission for 1-layer ARC. Minimizing reflection losses results in greater number of photons reaching the upconverter layer resulting in a potential enhancement of 28% in the short-circuit current due to upconversion.