GB178300A - An improved process for the manufacture of photo-electric cells - Google Patents

Abstract

178,300. Case, T. W. March 23, 1921. Vacuum tubes. - A method of producing an electronemitting cathode, such as the lightsensitive cathode of a photo-electric cell consists in depositing a layer of material on an element which forms part of the cathode, by means of a discharge, for which the element forms the anode, while another electrode, such as an incandescent filament, comprising the material to be deposited, forms the cathode. A filament is coated with the oxide of a metal, such as an alkaline earth metal, or superposed coatings of different oxides may be used. The corresponding nitrates may be deposited on the filament and reduced to oxides by heating the filament. Sodium and potassium may also be used in the coating. The coated filament 1 and a metal electrode 2 are mounted in a bulb which is exhausted of air and baked. The metal electrode is heated to redness to drive off remaining gases, by means of a discharge between the filament, heated by a battery 3, and the electrode 2 acting as an anode, for instance by connecting the electrode and the filament with the secondary of a transformer 4. The temperature of the electrode 2 is then reduced by regulating the potential, and the filament temperature is adjusted so that the discharge causes metal or metals to be emitted from the oxide coating and to be deposited as a layer on the electrode 2. The tube is connected with a pump so as to maintain the vacuum. The deposition process is stopped at intervals and the photoelectric qualities of the tube are tested. The electrode 2 forms the cathode in the completed cell, and the filament is used as an unheated electrode. An inert gas such as argon or helium mav be admitted to the tube to increase the conductivity.