Minority Carrier Diffusion Length in Si Ribbon Solar Cells

Minority carrier diffusion length Lp in Si ribbon solar cells was investigated using a scanning electron microscope. It was found that Lp was lowered at irregular crystal boundaries. The low Lp region around an irregular boundary was only 10∼20 µm in width, and occupied less than 5 percent of the total solar cell area in most cases. The value of Lp in regions without crystal boundaries scattered appreciably. Average Lp value had no dependence on carrier density whose range was 1016∼1017 cm-3, which means that photocurrent is almost independent of carrier density. As a result, it is expected that ribbon crystals with higher carrier densities are preferable as base material for solar cells to obtain higher efficiency.