Bulk minority carrier diffusion length and photogenerated carrier profile in silicon photovoltaic cells

Abstract

The bulk minority carrier diffusion length of single-crystal and polycrystalline ribbon silicon photocells was measured with monochromatic light of various wavelengths and flux densities. We noted that the diffusion length shows a gradual reduction as the illumination wavelength becomes shorter in both types of cells. In addition, the light enhancement phenomenon of the diffusion length in the ribbon cells diminished when shorter wavelength lights were used. In the single-crystal cells, however, no enhancement effect was observed for any wavelength. The interpretation of these results is based on the examination of the photogenerated minority carrier profile as a function of diffusion length and wavelength in the bulk region of the cell. We correlate the measured diffusion length with the depth in which a positive minority carrier concentration gradient exists.