US2538588A - Photocell - Google Patents

Description

Jan. 16, 1951 s. PAKSWER ET AL PHOTOCELL Filed June 23, 1948 INVENTOR. R s E. FA K5 w E R Patented Jan. 16, 1951 UNITED STATES PATENT OFFICE PHOTOCELL Serge Pakswer and John J. Benes, Jr., Geneva, 111., assignors to Continental Electric Company, Geneva, 111., a corporation of Delaware Application June 23, 1948, Serial N 0. 34,604

1'7 Claims. -1

This invention relates to improvements in photo-cells and methods of making the same, and particularly to photo-cells having the oath-- ode on the wall of the envelope.

One object of this invention is to provide an improved photo-cell, especially of the character having a silver or other metal-on-glass cathode.

A further object of this invention is to provide a photo-cell that has a silver or other metal-onglass cathode and metal terminal seal with the cathode in direct contact with the terminal seal.

Another object of this invention is to provide a new and improved photo-cell of the cathodeon-glass wall type that has a good geometry, low dark current and high out-put.

A further object of this invention is to provide an improved connection between a cathode on the wall of a photo-cell and a metal terminal seal.

A still further object of this invention is to provide a method of making a photo-cell which has a silver or other metal-omglass cathode and a metal terminal seal which is simple and inexpensive to make and is particularly adapted for mass production.

One embodiment of this invention is illustrated in the accompanying drawings, in which:

Fig. 1 is a perspective view of a photo-electriccell embodying this invention;

Fig. 2 is a partial sectional view therethrough,

taken on the line 22 in Fig. 1;

Fig. 3 is a partial perspective sectional view taken on the line 3--3 in Fig. 2, showing how the cathode, is extended continuously over both the envelope and the terminal seal;

Fig. 4 is an enlarged section view of a part of the photo-cell shown in Fig. 2, illustrating the relationship of the glass envelope, terminal cap and cathode; and

Fig. 5 is an enlarged section view of the glass envelope and cathode.

Referring now to the drawings, numeral 5 designates a tubular envelope shown as of glass or having a transparent window, and having both ends thereof sealed with metal terminal seal caps 6 and '1. respectively. These terminal caps 6 and I should be of a metal which lends itself adequately to make a good metal-to-glass seal, of which there are a number of such metals well known and in use at the present time. The caps preferably are stamped to the size and shape desired before they are sealed to the envelope. The terminal seal cap 6 has afiixed thereto, in any suitable manner, an anode 8 which is shown and illustrated here as a single wire preferably of nickel extending axially of the center of the tubular envelope 5 and extending throughout the major portion of the active length of the envelope.

Both of the caps 6 and I are bonded to the glass 2 envelope 5 by a method which will be discussed more in detail later.

Carried upon the anode 8 is a pill 9 which contains a sensitizing material such as caesium or the like. The pill 9, as shown, is located adjacent the terminal seal cap 6 so as to be well out of the way of any light rays striking the tube.

The metal terminal seal cap I is provided with an aperture 10, a tip-off seal H, and a tip-off seal cap I2. The cap I2 is spring-snapped into a dimple I2 in the cap l2 to protect the tip-off seal ll.

Coated upon the inner wall of the envelope 5 is a cathode generally designated at l3. This cathode 13, as shown more clearly in Figs. 3 to 5, preferably consists of an under layer I 4 painted of silver or other metal, a plurality of layers l5 of deposited silver or other metal and a layer of sensitizing material I6 such as caesium or the like in the other named and on the inner wall of the envelope, as shown in Fig. 5. It has been deemed expedient for the sake of clarity to illustrate these layers greatly enlarged in the sectional view of Fig. 5, because, as is obvious, the layers are molecular.

Preferably, the initial layer Id of silver or other metal is first painted onto the inner wall of the envelope 5 and it has been found desirable to utilize a good grade of conductive silver paint for this purpose. The painted silver layer It extends continuously without interruption or break over the desired portions of the envelope and metal terminal seal 1, as best shown in Fig. 3, but should only extend circumferentially of the tube to the extent desired for the finished cathode.

After the layer of painted silver [4 has been applied to the tube, several additional layers [5 of silver are then deposited over the layer M of painted conductive silver. This coating process may be accomplished in any one of several ways, but preferably should be done as will be described later. A sensitizing material, such as caesium I6, is then deposited on the last silverdeposited layer and may be deposited in any one of several well known ways, but it has been found quite satisfactory and convenient to deposit this light-sensitive material in the manner described below. v

As will be seen from the foregoing description, a satisfactory and highly efficient photo-cell having a cathode with an electrical connection to the terminal seal cap 1, is thus produced.

Turning now to the particular details of the method of constructing the photo-electric-cell embodied in this invention, first, the terminal cap I is sealed to the glass cylinder 0r tubular envelope 5 by heating, as with a high frequency current. After sealing the cap I to the envelope 5. a small amount of conductive silver I4 is pointed over the envelope 5 and the adjacent portion of the terminal can 1.

Next, this entire assembly is baked in -air to 500 C. and is removed at room temperature. This step fuses the painted strip ll of silver to the wall of the envelope 8 and to the metal of the terminal cap I, thus making an electrical contact between the cathode II on the envelope 5 and the terminal cap 1. This baking operation, fusing the conducting silver to the envelope '5 and terminal cap I, thoroughly anneals the seal and cleans the envelope of all organic material that may hinder deposition of the silver cathode.

The next step in the method of forming the photo-cell embodied in this invention is to deposit several layers I! of silver on the inner wall of the envelope 5 over the painted silver layer I 4. From two to four layers of this deposited silver may be applied. Any suitable method of depositing the silver, as well as any suitable composition of silver solution may be used, without deviating from the spirit of this invention. However, it has been found that the following method 7 and material works quite satisfactory:

C. One part:

(1) 20 grams silver nitrate C. P. (AgNOa). (2) 10 grams sodium hydroxide C. P. (NaOH). (3) 300 ml. distilled water (H).

(4) Ammonium hydroxide (NHQOH) (sufllcient to dissolve precipitate).

It has been found that when the above composition is used, the silver deposits evenly in .about fifteen minutes when the solution is maintained at C. It is here pointed out that while it is desirable to extend the cathode ll only partially down the envelope S as is shown in Fig. 1, that the above noted processes will cover a much greater portion of the envelope. It is only necessary in carrying out my method of making a photo-electric-cell, that a sufilcient area of the envelope 5 be covered so as to give the minimum desired size to the finished cathode.

The deposited silver is next washed with distilled water and dried at 100 C. for several minutes. The next step is to remove all undesired portions of the painted and silver deposits. This may be accomplished in any of several obvious ways, such as by physically scraping ofl the deposited silver or by dissolving the undesired portion of the silver layers, and it has been found in actual practice that it is more satisfactory to dissolve these layers than to remove them mechanically.

To remove the excess portion of silver deposit from the envelope 5, a solution of the following has been found quite satisfactory:

51 ml. 3% hydrogen peroxide (H202).

10 ml. conc. ammonium hydroxide C. P.

(NHioH).

87 ml. distilled water (H2O).

This solution is first poured into a suitable container, the depth of the solution coinciding with the amount of silver to be removed from the glass envelope, Next, the open end of the glass envelope 5 is placed in the solution and allowed to remain until the silver deposits I4 and II are removed.

Next, the anode, which preferably should be of nickel, is welded or otherwise electrically connected to the terminal cap 6, and the pill I containing the sensitizing material. such as caesium or the like, is spot welded to the anode I. As has been pointed out above, this pill 0 should be sufllciently low in the envelope 5 or sufliciently close to the terminal seal 6 so as not to obstruct any light rays to the cathode II. The terminal seal cap 8 is then sealed to the envelope I in any suitable manner as by high frequency current or the like. This seal is then annealed in a soft flame to remove all strains.

The tube is then processed on the pump through the tubulation l I in a conventional inanner. This involves baking the tube to degas glass, drying silver, liberating the sensitizing material and baking until the maximum output is reached. The tubulation II is then tipped off and the protector I2 is placed over the tip-oi! ll.

Another method of depositing the layers of silver I and II to form the cathode It may be done as follows: A conductive silver paint I I is first painted on the inner wall of th glass cylinder and the terminal seal 1 so as to make a contact between the cathode II and the terminal seal 1 in the same manner as described before. 5

Likewise as described before, the silver is painted on the envelope in the form which the finished cathode I3 is to take. As above, the size of the v cathode is not limited, and the shape, the location and other geometric physical characteristics of this cathode may all be varied for various types of photo-cells without departing from the spirit of this invention. Next, the baking operation is performed as described above, simultaneously fusing the silver, annealing the seal and cleaning the tube. Then a heavy, rough layer of silver is deposited over the painted conductive silver by means of silverplating. The silverplating solution is of the sodium silver cyanide type and is deposited in any well known conventional manner.

It is to be understood that various changes in the structure and methods of making the photocell may be made without deviating from the spirit of this invention, such as using any form or shape or character of tubular envelope desired; using any type of metalin the terminal caps 6 and l insofar as the metal lends itself readily to a metal-glass seal. While the process described in detail above specifying layers of silver on the envelope and the terminal cap is preferred, it is to be understood that metals other than silver likewise may be used without departing from the spirit of this invention. Also, that methods of tubulation, depositing th silver or other metal, methods of depositing the lightsensitive material, and that various light-sensitive materials other than caesium, also may be used, without departing from the spirit of this invention.

We claim:

A photo-sensitive cell comprising an envelope having an aperture therein, an anode, a terminal seal cap of electrically conductive material closing the aperture in said envelope 'and sealed thereto, anda light-sensitive cathode coating extending continuously over a portion of said envelope and said terminal seal.

2. A photo-sensitive cell comprising an envelope having an aperture therein, an anode, a

metal terminal seal closing the aperture in said envelope and sealed thereto and a light-sensitive cathode layer extending continuously over a portion of said envelope and said terminal seal.

3. A photo-sensitive cell comprising an envelope having an aperture therein, a metal terminal seal closing the aperture in said envelope and forming an integral wall thereof, and a lightsensitive cathode on the wall of said envelope, comprising a metallic layer coated on the envelope and extending continuously over the envelope and the metal terminal seal and forming a connector for the cathode.

4. A photo-sensitive cell comprising a glass envelope having an aperture therein, a metal terminal seal cap closin the aperture in said envelope, and a light-sensitive cathode on the wall of said envelope comprising a silver layer coated on the envelope extending continuously over the envelope and the metal terminal cap and forming a connector for the cathode.

5. A photo-sensitive cell comprising an envelope having an aperture therein, an anode, a metal terminal seal cap closing the aperture in said envelope and forming an integral wall thereof, and a cathode extending over at least a portion of said envelope and said terminal cap, said cathode comprisin a layer of silver having a light-sensitive surface thereon.

6. A photo-sensitive cell comprising an envelope having an aperture therein, an anode, a metal terminal seal cap closing the aperture in said envelope and forming an integral wall thereof, and a cathode extending over at least a portion of said envelope and said terminal cap, said cathode comprising a layer of silver having a layer of caesium deposited on a portion thereof.

'7. A photo-sensitive cell comprising a tubular envelope, an anode, a metal terminal cap closing one end of said envelope, and a cathode extending continuously over at least a portion of the inner surface of said envelope and said terminal cap, said cathode comprising a metal deposited coating and a layer of light-sensitive material on the surface of the coating.

8. The method of making a photo-sensitive cell having a cathode within an envelope having an aperture therein and a metal terminal cap covering said aperture and closing and sealing said aperture, comprising sealing the terminal cap to the envelope, at least partially coating the inside surface of both the envelope and the terminal cap with a continuous layer of conductive metal having a light-sensitive surface.

9. The method of making a photo-sensitive cell having a cathode within an envelope and a metal terminal cap, comprising sealing the terminal cap to the envelope, at least partially coating both the envelope and the terminal cap with a continuous layer of silver, depositing an additional layer of silver over said first-mentioned layer of silver, baking said cell to fuse the silver layers to th envelope and the terminal cap, and rendering the surface of the fused silver layers light-sensitive to form a cathode.

10. The method of making a photo-sensitive cell having a cathode within a tubular envelope and a metal terminal cap sealed to one end of said envelope, comprising sealing the terminal cap to the envelope, painting a coating of conductive silver continuously'on a portion of the envelope and the terminal cap, depositing a layer of silver on the .painted layer of silver, fusing said silver layers to the envelope and the terminal cap, evacuating the envelope, and depositing a light-sensitive material on the silver layers to form a cathode.

11. The method of making a photo-sensitive cell having a cathode within a tubular glass envelope and a metal terminal cap, comprising sealing said terminal cap to one end of the envelope, coating a portion of the inside surface of the envelope and terminal cap with a conductive silver layer extending continuously over a portion of the envelope and the terminal cap, subsequently removing a portion of the silver coating from the end of the tubular envelope opposite the terminal cap, and depositing a light-sensitive material on the silver coating to form a cathode.

12. The method of making a photo-sensitive cell having a silver-onv-glass cathode within a tubular glass envelope and a metal terminal cap, comprising sealing the terminal cap to the end of said envelope, coating a portion of said envelope and terminal cap with a layer of conductive silver paint extending continuously over a portion of the envelope and the terminal cap, depositing additional layers of silver on the painted conductive layer, subsequently removing a portion of the silver layers from the end of the glass envelope opposite the terminal seal, and depositing a light-sensitive material on the silver coatings to form a cathode.

13. The method of making a photo-sensitive cell having a cathode within an envelope having an aperture therein and a metal terminal cap, comprising sealing the terminal cap to the envelope over the aperture, at least partially coating the inside of both the envelope and the terminal cap with a continuous layer of conductive metal, and depositing a light-sensitive substance on the layer of conductive metal to form a cathode.

14. The method of making a photo-sensitive cell having a cathode within an evelope and a metal terminal cap, comprising sealing the ter* minal cap to the envelope, coating portions of both the envelope and the terminal cap with a continuous strip layer of metal paint, depositing an additional layer of metal over said first-mentioned layer, baking said cell to fuse the metal layers to the envelope and the terminal cap, and depositing a layer of light-sensitive substance on the fused metal layers to form a cathode.

15. A photo-sensitive cell comprising a tubular envelope, an anode, a metal terminal cap closing one end of said envelope, and a cathode extending continuously over a portion of the inner surface of said envelope and said terminal cap, said cathode comprising a layer of metal paint, a layer of deposited metal coating on said paint, and a layer of light-sensitive material on the surface of the layer of metal paint.

16. A photo-sensitive cell comprising a tubular envelope, ananode, a metal terminal cap closing one end of said envelope and sealed thereto, and a cathode extending continuously over a portion of the inner surface of said envelopeand said terminal cap, said cathode comprising a layer of silver paint, a layer of deposited silver coating on said paint, and a layer of light-sensitive material on said layers.

15'. A photo-sensitive cell comprising a tubular envelope, an anode, a metal terminal cap closing one end of said envelope and sealed thereto, and a cathode extending continuously over a portion of the inner surface of said envelope and said terminal cap, said cathode comprising a layer of silver paint and a layer of deposited silver coating on said paint, said layers of silver being use: 1

i 1 8 fused to the wall or the envelope and flu terml- UNITED STATES PAI'ENTS 1 ml cap.

I Number Name Date f ium 1,917,854 Rentschler July 11, mas 2,161,859 Geflcken et a1 June 13, 1939 1 REFERENCES CITED 3 2. 2 Bickley my 5, 1942 The following references are of record in the 14013 1m me of am patent:

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