Optical Modeling of the Rear Surface Roughness of Passivated Silicon Solar Cells

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Solar cells featuring a dielectrically coated rear side combine excellent electrical passivation, yielding high open circuit voltages, with high light trapping capabilities, yielding high short circuit currents. The roughness of the rear side is a crucial parameter for the optical properties of these devices. We therefore analyze the influence of the rear surface roughness on the charge carrier generation and the spectral reflection of the devices using predictive, three dimensional modeling of the rear surface based on the transfer-matrix formalism. After the verification of this so-called tilted-mirrors-model, we compare it to the widely used Phong model. When fitting the spectral reflectance of the Phong model using its two empirical parameters to the spectral reflectance obtained with the predictive model, we calculate 0.2 - 0.4mA/cm2 lower photogenerated current densities. We further use the predictive model to demonstrate the optical impact of variations of the thickness of the passivation layers.