Achieving high photovoltaics conversion efficiencies in perovskite-silicon multi-junction solar cells requires a precisely tailored distribution of the solar spectrum between subcells. It calls for simultaneous optimization of front-side incoupling, forward and backwards scattering at the cell interfaces, reducing parasitic absorption losses, and at the same time optimizing the angular redistribution of scattered light to enhance light trapping. This requires a multi-scale approach in determining the optimum combination of layers and textures combining ray optical and wave optical methods.

In this work, we investigate light coupling and trapping in silicon–perovskite tandem solar cells with a focus on light trapping in the silicon subcell. We study different nano- and micro-texture types and their impact on reflection, transmission, light trapping and parasitic absorption losses in full tandem stacks. Using an angular scattering matrix formalism, we compute redistribution matrices of textured interfaces, allowing us to quantify the redirection and distribution of light in each of the absorber layers.

We analyze multiple scattering interactions between the front and rear interfaces in silicon and silicon-perovskite model systems featuring a random pyramidal front texture and a nanostructured metallo-dielectric rear diffraction grating that was recently used to achieve a record 36.1% efficiency for Si-based solar cells using a Si/III-V triple-junction geometry.^1,2 We then optimize the design of the rear diffractive grating, taking into account the angular redistribution of light refracted from the front interface into polar angles 23.3° and 64.8°. The detailed understanding of scattering channels arising from transmission and reflection at the front interface enables the identification of key design constraints for the optimization of the rear back-reflector, including minimization of plasmonic scattering losses and front-interface outcoupling. We establish a step-by-step optimization strategy based on controlling diffraction orders, angular selectivity and parasitic absorption at the rear interface. This combined understanding of front- and rear-interface scattering enables targeted design of rear nanostructures for increased optical path length in the silicon subcell and improved light management in silicon-perovskite and other multi-junction solar cells.