Material quality requirements for efficient epitaxial film silicon solar cells

The performance of 2-mu m-thick crystal silicon (c-Si) solar cells grown epitaxially on heavily doped wafer substrates is quantitatively linked to absorber dislocation density. We find that such thin devices have a high tolerance to bulk impurities compared to wafer-based cells. The minority carrier diffusion length is about half the dislocation spacing and must be roughly three times the absorber thickness for efficient carrier extraction. Together, modeling and experimental results provide design guidelines for film c-Si photovoltaic cells.