Optical properties of textured sheets. An efficient matrix-based modelling approach
A large variety of optical systems incorporate multiple textured surfaces for reflectance reduction, light redirection or absorptance enhancement. One example for such a system is a textured silicon wafer solar cell. We introduce the OPTOS (Optical Properties of Textured Optical Sheets) formalism for the modelling of light propagation and absorption in optically thick sheets with two arbitrary surface textures at the front and rear side, and demonstrate applications. In contrast to many optical simulation techniques, which are tailored to specific surface morphologies, the OPTOS formalism is a matrix-based method that allows including textures that are described by different optical modelling techniques (e.g. ray optical or wave optical) within one simulation tool. It offers the computationally efficient simulation of light redistribution and non-coherent propagation inside thick sheets. After calculating redistribution matrices for each individual surface texture with the most appropriate technique, optical properties of the complete textured sheet, like e. g. angle dependent reflectance, transmittance or depth resolved absorptance, can be determined via iterative matrix multiplications (for propagation and redistribution) with low computational effort. In this work, we focus on textured wafer-based silicon solar cells as application examples for the OPTOS formalism. The simulation enables us to investigate and optimize combinations of front and rear textures on solar cells in order to increase the photocurrent generation. A solar cell with inverted pyramid front side and a diffractive grating at the rear is found to show similar light trapping properties as one with Lambertian scattering at the rear.