Patent GB-381606-A (GB)
Title: Improvements in or relating to photo-electric cells
IPC: H01J40/06
Filed: 1931-07-10
Abstract: 381,606. Photo-electric cells. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Stilwell, G. R. ; 1023, West 5th Street, Plainfield, New Jersey, and Prescott, C. H. ; 552, Riverside Drive, New York, both in U.S.A.) July 10, 1931, No. 19904. Convention date, Aug. 11, 1930. [Class 39 (i).] The light-sensitive electrode of a photoelectric cell is conditioned to receive the photo-electric material by first oxidizing its surface, then reducing the oxidized surface to roughen it, repeating the oxidation and reduction if necessary, and finally oxidizing the surface to receive the photo-electric layer. Both the oxidation and reduction are preferably effected by means of an electric discharge, the discharge being rendered effective for the reduction by causing a heating of the electrode. The final oxidation is effected by discharging a predetermined quantity of electricity to produce an amount of oxide proportional to the amount of light-sensitive material to be deposited. The photo-electric cell shown in Fig. 1 comprises a bulb 1 enclosing an anode 2, a silver cathode 3, and a conductive loop 4 of low resistance connected in series with a capsule or pill 5 containing a mixture of caesium chromate, chromic oxide, and aluminium. The bulb 1 is provided with a press or stem 7 carrying supports 10 for the cathode 3 and rods carrying a saddle 11 for supporting the loop 4 and capsule 5. An apparatus for use in the production of four cells is shown in Fig. 2, and comprises a frame 15 carrying an electric oven 20 adapted to be raised into a position surrounding the bulbs 1. The bulbs are connected by a tube 17 to a pumping system by means of which they may be exhausted or supplied with oxygen from an apparatus 26 or with argon or other inert gas from an apparatus 27. Current is supplied to the bulbs from the apparatus shown in Fig. 3, which comprises a direct current supply circuit 31, a potentiometer 32, a switch 33 for connecting the supply either to a condenser system 34 and through kevs 35 to the electrodes 2, 3 of the bulbs 1, or direct through the keys to the electrodes. The electric oven 20 carries a heating apparatus, Fig. 4, comprising a hollow base member 36, divided into compartments by baffles 37. The lower compartment is connected to a compressed air supply and encloses a heating unit 40, while the upper compartment communicates with four chimneys 44 which are adapted to be raised into a position surrounding the bulbs. In operation, the bulbs are connected through the tube 17 to the pumping apparatus, and heated to a high temperature to drive off occluded gases. Oxygen is now admitted to the bulbs from the apparatus 26 and, with the switch 33 in its right-hand position, the keys 35 are actuated intermittently to cause a large current discharge between the electrodes, whereby the surface of the cathode 3 is ionically bombarded and caused to enter into combination with the oxygen. The oxide layer is now reduced on each cathode by holding down the corresponding key 35 whereby the oxidized surface is continuously bombarded. The treatment may be repeated, if necessary, to produce a surface roughened to the desired degree. The bulbs are now evacuated, refilled with oxygen at a low pressure, the switch 33 is thrown to its left-hand position and each key 35 is intermittently closed a predetermined number of times, whereby the condenser system 34 is alternately charged and discharged through the corresponding bulb 1. The oxygen is then pumped out, and the caesium-containing capsule 5 is flashed by applying high frequency current to a coil 14 surrounding the conductor 4 and capsule. The chemical reaction between the ingredients of the capsule liberates the caesium at a high temperature, but the hot vapour is prevented from coming into contact with the press 7 and the elements carried thereby by means of a shield 6, which directs the vapour on to the wall of the bulb 1 where it is deposited. The oven 20 is then raised into position, and the bulbs are heated to vaporize the caesium and cause the latter to deposit on the relatively cool cathode. Argon is now introduced into the cell from the apparatus 27 until the desired pressure is obtained and the cell is sealed off. Other metals, such as nickel or copper, may be used instead of silver for the cathode, and any of the alkali metals, e.g. rubidium, potassium or sodium, may be substituted for caesium as the light-sensitive material. The method of depositing the caesium on the cathode forms the subject-matter of Specification 381,608.