GB343930A - Improvements in or relating to photo-electric cells - Google Patents

Abstract

343,930. Photo-electric cells. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN, 13A, Emmasingel, Eindhoven, Holland, Nov. 25, 1929, No. 36072. Convention date, May 16. [Class 39 (i).] In a photo-electric cathode in which a layer of photo-electric substance such as caesium is supported on an intermediate layer consisting of or containing a compound which is a better absorbent of the photo-electric substance than is the support and which may be an oxide or halide such as calcium fluoride, particles of an electrically conducting substance, such as tungsten, the photo-electric substance itself, or a mixture of these, are distributed throughout the intermediate layer so as to reduce the resistance. A layer of photo-electric substance may be applied to the intermediate layer and the layers heated after the cell has been sealed off, so that the photo-electric substance diffuses throughout the intermediate layer ; or the intermediate layer and conducting particles may be volatilized from an electrode and deposited on a support.. Preferably a ring-shaped electrode 6 is coated with a mixture containing a difficultly volatilizable metal such as tungsten, and a compound of a readily volatilizable metal with another ingredient capable of forming with tungsten &c. a readily volatilizable compound. For example a mixture of tungsten and calcium fluoride is heated by passing a current through the electrode 6. Tungsten fluoride and calcium are deposited on the envelope and react to form the starting materials, tungsten and calcium fluoride mixed in a finely-divided state. Or a mixture of iron or zirconium with sodium chloride or potassium chloride may be used. A substance such as silica may be added to the mixture to facilitate the reaction : in this case tungsten oxide and calcium are deposited in the envelope and react to form tungsten and calcium oxide, sodium fluoride being removed by a pump. Alkali metal forming the photo-electric material may be introduced by evaporation from a side tube at 9, for example as described in Specification 323,718, [Class 39 (i), Electric lamps, Arc &c.]. After sealing, the cell is heated to 200‹ C. to cause alkali metal to penetrate throughout the intermediate layer. Otherwise a mixture of caesium chromate, zirconium and sodium fluoride is heated to volatilize caesium, zirconium flouride and sodium, the last two substances reacting to form zirconium and sodium fluoride in a finely-divided state with which caesium is mixed.