US2244264A - Photoelectric cell - Google Patents

Description

June 3, 1941. sgrrz JR 2,244,264

PHOTOELECTRIC CELL Filed Sept. 27, 1937 Patented June 3, 1941 rno'roELEo'rmc cELL Louis J. Seitz, Jr., Elizabeth, N. J., assignor to Weston Electrical Instrument Corporation, Newark, N. L, a corporation of New Jersey Application September 27, 1937, Serial No. 166,026

' Claims.

This invention relates to photoelectric cells and more particularly to cells of the dry disk or barrier layer type.

This type of cell includes a layer of light-sensitive material between a back electrode and a light-transmitting outer or contact electrode. No difficulty is experienced in establishing a good electrical connection between the back electrode and an external circuit but prior arrangements for providing a terminal connection to the outer electrode have not been entirely satisfactory. The'current output of the cell to an external circuit will not remain constant during use when the terminal is held against a portion of the outer electrode (hereinafter termed the cell contact area) under a relatively light pressure.-

It was found, however, that an increase in contact pressure resulted or might result in several disturbing effects. Pressure between the terminal and the cell contact area tended to cause a decrease in the internal resistance of the cell, thus altering the cell characteristics. The full effect of this resistance change was not always immediately evident, and it would frequently occur that the cell characteristics would alter after the cell had been calibrated. A release of the contact pressure usually caused the internal resistance and dependent cell characteristics to alter again in a direction towards and possibly to that of the original calibration.

A difliculty additional to that of the delayed change or drift in the cell characteristics was that the terminal had a tendency to dig into or through the cell contact area under the required contact pressure, thus shortening the electrical path through the cell as well as permanently isolating or destroying sections of the cell. This resulted in a decrease in the cell output as the damaged areas did not supply to the external circuit that part of the generated current that they had-originally contributed. g Variations in the size and shape of resilient contact fingers on the terminal did not eliminate l these difllculties, and the soldering or welding of the terminals to the 'cell contact area did not result in stable cell output during normal use.

An object of the present invention is to provide a barrier layer type photoelectric cell having a terminal construction that eliminates the above stated difiiculties and disadvantages. An object is to provide a cell of the type stated in which the terminal construction provides a contact pressure adequate for stable output without producing a delayed change or drift of the cell characteristics. A further object of the invention is to provide a barrier layer type of cell including a soft metal bedding or pad between the terminal and the cell contact area. More specifically, an object is to provide a barrier layer photoelectric cell of the selenium type in which a bedding or pad of cadmium is arranged between the cell contact area and a terminal that engagesihe soft metal with a substantial contact pressure.

These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. 1 is a greatly enlarged and somewhat schematic perspective view, with parts in section, illustrating an embodiment of the invention;

Fig. 2 is a fragmentary enlarged sectionalview of a cell assembly embodying the invention; and Fig. 3 is a front elevation, on a smaller scale, of the cell assembly of Fig. 2.

In Fig. 1 of the drawing, the barrier layer type I tion and/or to the minutely irregular surface of the layer 2. The lower terminal connection may be formed by an annulus I of copper, phosphor bronze or the like, which is held against the back electrode I when the cell is assembled in a 2 case or other mounting.

It has been the practice to form the other terminal as an annulus 5 of phosphor bronze or other-resilient metal having a lug 6 for connection to a terminal pin and a; plurality of resilient contact fingers 1 for engaging the outer electrode layer 3. An insulating ring 8 was usually arranged between the cell and the annulus 5, the

thickness of the insulation being such that the contact fingers ,l were pressed upon the electrode 3 when the cell and terminals were mounted in a case.

In accordance with the present invention, ,bedding or pads 9 of a soft'metal, such as cadmium or a low melting point bismuth-lead-tin alloy are arranged between the resilient contact fin gers 1 and the electrode 3. The bedding metal flows or is deformed under the applied pressure to conform to the irregularities in/ the upper surface of the electrode 3, and thus establishes a uniform or approximately uniform pressure over the cell contact area.

istlc of the soldered terminal connections that were unsatisfactory. The soft metal appears to function as an electrical expansion joint which precludes substantial, change in the pressure upon the cell contact area with changes in temperature, extent and conditions of use, and other variables. i

The location of the cadmium layer between the outer electrode and the phosphor bronze terminal minimizes the possibility of damage to outer electrode by electrolytic action in the event that moisture collects on-these contact areas. llhis protective action is due to the fact that cadmium lies between the outer electrode metal and phosphor bronze in the electromotive series.

In the mounted cell assembly of Figs. 2 and 3, the case is formed by the outer cap I and a base ll having a projecting annular shoulder 12 upon which the cell C is supported. A washer i3 is arranged between the shoulder i2 and the bottom terminal 5. The soft metal bedding comprises an annulus 5' whose outer edge overlies the insulating ring 8 and whose inner edge lies between the closely spaced narrow contact fingers I of the phosphor bronze terminal ring 5 and the surface of the electrode 3. The cover glass ing over portions of said outer electrode, a layer of soft metal between" each resilient contact 7 electrical connections to spaced areas of said outer electrode, pads of soft metal between said fingers and said areas, and means maintaining said fingers in resilient engagement with said pads of soft material..

5. The invention as claimed in claim 4, wherein said pads consist of cadmium.

6. In a photoelectric cell assembly, the combination with a barrier layer type cell having a layer of light sensitive material between a back electrode and an outer light-transmitting electrode, said outer electrode having peripheral portions thereof providing the cell contact area for connection to an external circuit, of a terminal engaging the back electrode, a layer of soft metal at the periphery of the outer electrode, a second terminal having spring contact fingers projecting into engagement with the soft metal layer, and a casing enclosing said cell and H rests upon the terminal ring 5' and the as-.

sembly is clamped in place by pressure applied to the cover glass by the lip of the cap ll) through a washer I5 when the case sections are threaded into each other. Terminal pins [6 project from the wall of the casing cap [0 and are connected by leads, not shown, to the terminal rings 4, 5', respectively.

I have found that a cadmium ring 9 appr-oximately 0.004 inch thick serves adequately to maintain the pressure relationships that are essential for stability of cell output. A bedding layer of cadmium will not alloy with selenium at the temperatures usually encountered, and therefore no secondary action is introduced to afiect the cell output.

It is to be'understood that the invention is: not limited to the particular constructions herein described and that there is considerable latitude in the design and construction of photoelectric cells conforming to this invention.

I claim:

1. In a photoelectric cell assembly, a barrier 7 layer type cell having a back electrode and an" outer electrode, and means for establishing a. circuit connectionto portions of the outerelectrode at the periphery thereof; said means including a layer of. soft metal overlying said portions of the outer electrode, and a terminal having resilient contact fingers engaging said soft metal layer with a pressure sufficient to deform the same.

2. In a. photoelectric cell assembly, a barrier layer type cell having an outer electrode, a terminal extending around the periphery of said cell and having resilient contact fingers extendterminals, said casing including -means to retain said terminals in relative positions which establish a substantial pressure of said contact fingers upon said soft metal layer.

7. In a photoelectric cell assembly, the combination with a barrier layer type cell having a layer of light sensitive material between a back electrode and an outer light-transmitting electrode, said outer electrode having peripheral por-' tions thereof providing the cell contact area for connection to an external circuit, of a terminal engaging the back electrode, a layer of soft metal at the periphery of the outer electrode, a second terminal having spring contact fingers projecting into engagement with the soft metal layer, a base supporting said cell and terminals,

. and acap adjustable with respect to said base to press said terminals towards each other to establish a substantial pressure of said contact fingers upon said soft metal layer, said base and cap comprising a casing enclosing said cell and terminals.

' 8. In a photoelectric cell assembly, a cell comprising a layer of crystalline selenium between a back electrode and an outer electrode, a terminal contacting the back electrode, a ring of insulating material overlying the periphery of the outer electrode, a ring of cadmium overlying-said insulating ring and an adjacent portion of the outer electrode, and a terminal having an outer annulus portion overlying the outer portion of the cadmium ring and resilient contact fingers in resilient engagement with the portion of said cadmium ring that overlies the outer electrode.

9. A photoelectric cell assembly as claimed in claim 8, in combination with a casing enclosing said cell and comprising means to force said second terminal towards said cell, thereby to press said contact fingers upon said cadmium layer.

10. In a photoelectric cell assembly, the combination with a barrier layer type cell including a layer of crystalline material between a back electrode and an outer translucent electrode, a terminal having resilient contact fingers, and means adjustable to press said resilient contact fingers towards said outer electrode, or means to prevent variation of the cell characteristics with incidental variations in a relatively heavy contact 5 outer electrode.

pressure established at said contact flngersby a given adjustment of said first means, said variation-preventing means comprising a thin sheet of soft metal between said contact fingers and said LOUIS J. SEITZ, JR.

CERTIFICATE OF CORRECTI ON Patent No. 2,?J4lh26h. June 5, 1911.1.

LOUIS J. SEITZ, JR.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows! Page 2, second'column, line 20, claim ii, for the word "material" rend --metal-; and that the said -Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.'

Signed and sealed this 8th day of July, A. D. 19in.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

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