Large area polycrystalline silicon solar cells on unidirectionally solidified acid-treated metallurgical grade silicon

Large-area polycrystalline silicon solar cells were prepared by the chemical vapor deposition (CVD) of a p⁺-n junction using the hydrogen reduction of trichlorosilane. The substrate was prepared by melting and then unidirectionally solidifying fine-grain metallurgical-grade silicon on a graphite plate. The starting silicon was purified by continuous heating with aqua regia under reflux conditions, and the gettered by heating at 1050°C with P₂O₅ prior to recrystallization. The front contact to the cell was formed by the vacuum deposition of a Ti/Ag film through a metal mask. The graphite was the back contact. An antireflection coating of SnO₂ was deposited by CVD. The cells were characterized by measuring the cell efficiency, short-circuit current spectral response, and minority carrier diffusion length. Heat treatment at 900°C in hydrogen further improved the cell response