Current Status of Silicon Materials Research for Photovoltaic Applications

The desire for high solar cell efficiencies has been a strong factor in determining the course of recent silicon crystal growth research efforts for photovoltaics. This review, therefore, focuses on single-crystal, dislocation-free ingot growth methods (Czochralski growth, float zoning, and cold crucible growth) and on sheet growth technologies, generally multicrystalline, that have achievedmoderately high (>13.5%) laboratory-scale efficiencies. These include dendritic web growth, growth from capillary dies, edge-supported pulling, ribbon-against-drop growth, and a recent technique termed crucible-free horizontal growth. Silicon ribbon crystals provide a favorable geometry and require no wafering, but they contain defects that limit solar cell performance. Growth processes, theircurrent status, and cell efficiencies are discussed. Silicon material process steps before and after crystal growth are described, and the advantages of silicon are presented.