SiO2 nanosphere textured back reflectors for enhanced light trapping in amorphous and nanocrystalline silicon solar cells
Boesch, Ryan (2009) SiO2 nanosphere textured back reflectors for enhanced light trapping in amorphous and nanocrystalline silicon solar cells. Masters thesis, Iowa State University.
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Silica microspheres were investigated as a back surface texturing agent for hydrogenated amorphous (a-Si:H) and nanocrystalline (nc-Si:H) silicon solar cells. Absorption of long wavelength photons (>600nm) is minimal for a-Si:H and nc-Si:H thin films which limits the efficiency of thin-film solar cells. Textured back reflectors are often used to increase the efficiency of these solar cells by diffusely reflecting light and trapping it in the absorbing layer. In this research, stainless steel substrates were spin coated with silica spheres to add texture. After a post-anneal, silver was deposited on the substrates. Two sphere diameters (250nm and 500nm) were investigated for their impact on diffuse reflection versus wavelength. It was found that the peak in diffuse reflection could be controlled by varying the sphere diameter. The thickness of the silver layer was determined by maximizing the total reflection, and diminishing returns were found for a silver layer greater than 300nm. External quantum efficiency measurements were used to characterize carrier collection versus wavelength. An increase in carrier collection at long wavelengths (>600nm) was observed for both a-Si:H and nc-Si:H solar cells on the silica sphere textured substrates. The thin a-Si:H solar cells often shorted out during testing which limits the industrial application of this back reflector. Shorting was not found to be a problem with the nc-Si:H devices.
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