Polycrystalline silicon solar cells on metallurgical silicon substrates

The use of a polycrystalline silicon p-n junction structure deposited on low-cost substrates is a promising approach for the fabrication of low-cost solar cells. Metallurgical-grade silicon, with a purity of about 98% and a cost of about $1/kg, was cast into plates in a boron nitride container and used as substrates for the deposition of solar cell structures. The substrates were polycrystalline with millimeter size crystallites. Solar cells of the configurations n>⁺-silicon/p-silicon/metallurgical silicon and n⁺-silicon/p⁺-silicon/metallurgical silicon were prepared by the thermal decomposition of silane and the thermal reduction of trichlorosilane containing appropriate dopants. The AMO efficiencies of n⁺-silicon/p-silicon/metallurgical silicon solar cells were up to 2.8% (with no anti-reflection coatings) and were limited by the grain boundaries in the p-layer. The grain boundary effects were reduced by increasing the dopant concentration in the p-layer, and AMO efficiencies of about 3.5% were obtained from n⁺-silicon/p⁺-silicon/metallurgi silicon solar cells.