Large grain silicon films on metallurgical silicon substrates for photovoltaic applications

Abstract

Metallurgical silicon at a cost of about $ 1/kg is an economical substrate for the deposition of silicon films for photovoltaic applications. To prepare the substrate, pulverized metallurgical silicon, purified by acid-extraction and phosphorus pentoxide treatment, was recrystallized on graphite by unidirectional solidification and zone-melting. The structural and crystallographic properties of metallurgical silicon substrates prepared at different rates of solidification were investigated. Silicon films of controlled electrical resistivity were deposited on metallurgical silicon substrates by the thermal reduction of trichlorosilane containing appropriate dopants. The concentration and distribution of metallic impurities, Hall mobilities, potential barriers and minority carrier diffusion length profile in these films were investigated. Solar cells of 9 cm 2 area were prepared from silicon films of 25–30 μm thickness containing a p-n junction. By using a drift field in the surface region and a back surface field at the silicon film/substrate interface, AM1 efficiencies of up to 9.75% have been obtained.