Photovoltaic cells

Abstract

A method of making low cost photovoltaic cells on a large scale basis by means of a continuous process of coating sheet glass while the sheet glass moves in and has its under surface immersed in a tank of molten material, comprising forming the film of CdS microcrystals on the glass sheet, which has previously been coated with transparent SnO.sub.x to a thickness of about 0.3 to 0.6 microns. A water solution of a cadmium salt, a sulphur compound, and an aluminum containing soluble compound is intermittenty sprayed on said glass while its exposed surface is maintained at a constant temperature in the range 500.degree. F to 1100.degree. F and while irradiating the surface with intense ultraviolet light so as to form a film of CdS microcrystals. This CdS film has Al impregnated within the stratum of the film adjacent to the SnO.sub.x, but only optionally has Al impregnated in the stratum of the CdS film adjacent to the exposed surface of the CdS film. After the spray process is completed, the temperature of the sheet of glass is brought to the range 450.degree. C to 550.degree. C, 525.degree. being optium. After heating, the glass is cooled to approximately room temperature and the exposed surface of the CdS is converted to Cu.sub.x S, the x of Cu.sub.x S being as close to 2 as possible, by dipping the coated glass in a solution comprising: a solvent, which may be water; a weak acid, such as tartaric acid, citric acid, or lactic acid; a copper containing compound; and, optionally, a quantity of H.sub.2 Ce(SO.sub.4).sub.4 and NaCl, or some other chloride; or by electroplating to form a film of Cu.sub.x S; or, by a combination of dipping and electroplating. The Cu.sub.x S forming process proceeds by ion exchange, i.e., S from CdS combines with Cu to form Cu.sub.x S. Cu is then applied over the Cu.sub.x S, and the cell is cured at a temperature in the range 400.degree. F to 500.degree. F.