Optical Analysis of Perovskite/Silicon Tandem Solar Cells: Effect of Rear Side Grating and TOPCon Tunnel Junction

Abstract

In the focus of the presented work is the analysis of a rear side reflection grating in context of a perovskite/silicon tandem solar cell. The typical configuration of a perovskite/Si tandem device requires a hole transport layer at the rear side of the silicon solar cell (p-i-n bottom cell structure). As such a poly-Si passivating contact like TOPCon is an attractive candidate. Until now, research faces the challenge to deposit p-TOPCon layers with good surface passivation properties on textured surfaces. A planar surface would avoid this issue and due to its smaller surface area intrinsically allowing for a better passivation. The optical disadvantage of the planar rear side can be eliminated by an appropriate optical grating at the rear side which enables ideal light trapping. In this work a new approach is developed to describe the optical properties of a diffraction grating as structured rear side reflector in a silicon bottom cell. The light distribution and the parasitic absorption per grating interaction are fitted to reflectance and absorptance measurements of a III-V on silicon triple-junction device with a rear grating structure. Compared to previous models, this new approach makes it possible to reliably quantify the different loss mechanisms in the spectral region above 1000 nm. An application of the simulation model to a perovskite/silicon tandem device shows the potential of the system with rear side grating. In addition, an integration of a TOPCon tunnel junction is evaluated and a process chain for the integration of a structured rear side reflector into the tandem system is discussed.