Plasma spraying process for preparing polycrystalline solar cells

Abstract

Polycrystalline silicon films useful in preparing solar cells primarily for terrestrial application are prepared by a plasma spraying process. A doped silicon powder is injected into a high temperature ionized gas (plasma) to become molten and to be sprayed onto a low-cost substrate. Upon cooling, a dense polycrystalline silicon film is obtained. A p-n junction is formed on the sprayed film by spray deposition, diffusion or ion implantation. A sprayed junction is produced by plasma spraying a thin layer of silicon of opposite polarity or type over the initially deposited doped film. In forming a diffused junction, dopant is applied over the surface of the initial plasma-sprayed film usually from the vapor phase and heat is used to cause the dopant to diffuse into the film to form a shallow layer of opposite polarity to that in the original film. A junction is also formed by implanting dopant ions in the surface of the originally deposited film by the use of electrical fields. When used in conjunction with ohmic contacts and electrical conductors, the p-n junctions produced using plasma-sprayed polycrystalline silicon films are formed into solar cells which are useful for directly converting sunlight into electricity by means of the photovoltaic effect.