Advanced, Thin, Polycrystalline Silicon-Film(TM) Solar Cells on Low-Cost Substrates

Thin, polycrystalline silicon solar cells have the potential for the realization of a 15%, low-cost photovoltaic product. As a photovoltaic material, polycrystalline material is abundant, benign, and electrically stable. The thin-film polycrystalline silicon solar cell design achieves high efficiency by incorporating techniques to enhance optical absorption, ensure electrical confinement, andminimize bulk recombination currents. AstroPower's approach to a thin-film polycrystalline silicon solar cell technology is based on the Silicon-Film (TM) process, a continuous sheet manufacturing process for the growth of thin films of polycrystalline silicon on low-cost substrates. A new barrier layer and substrate have been developed for advanced solar cell designs. External gettering withphosphorus has been employed to effect significant improvements leading to effective minority carrier diffusion lengths greater than 250 micrometers in the active silicon layer. Light trapping has been observed in 60-micrometer thick films of silicon grown on the new barrier-coated substrate. An efficiency of 12.2% in a 0.659 cm2 solar cell has been achieved with the advanced structure.