Detailed Analysis of Random Pyramid Surfaces With Ray Tracing and Image Processing

For the optimization of alkaline texturing in industrial monocrystalline silicon solar cells, it is of paramount importance to understand the correlation between surface reflectance and surface morphology. In this study, the reflectance is related to the surface geometry using image processing and ray tracing. Surfaces with a variation of random pyramid texturing were scanned with laser scanning microscopy. The resulting height maps were either directly used as input for the ray tracing or used as a template for a synthetic height map. A procedure was developed to extract an effective pyramid base angle from the images. It takes on values from 47.9° to 54.3°, which are below the {111} pyramid base angle of 54.74°. The reflectance decreases linearly with the effective base angle and the pyramid height. Ray tracing of as-measured and reconstructed height maps with ideal pyramid base angle shows that both are a poor representation of the pyramid landscape. The best fit between measured and simulated reflectance is obtained when the effective base angle is used to reconstruct the surface. The surface with lowest reflectance is characterized by pyramids with high base angle and large size.

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