US2320185A - Photoelectric cell - Google Patents

Description

May 25, 1943. A. H. LAMB 2,320,185v

- 'PHOTOELECTRIG CELL Filed April 3, `1942 Patented May 25, 194.3

PHOTOELECTRIC CELL Anthony H. Lamb, Roselle Park, N. J.. assigner to Weston Electrical Instrument Corporation, Newark, N. J., a corporation of New Jersey Application April 3, 1942-, Serial No. 437,602

(Cl. 13G- 89) 24 Claims.

This invention relates to photoelectric cells and particularly to photoelectric cells -of the barrier layer or current-generating type.

The prior practice in the manufacture of both copper oxide and selenium photocells hasbeen' to form the barrier layer between the photosensitive material and the outer electrode as a plane surface. The present invention contemplates a deliberate deformation of the barrierlayer to increase the total effective area of the photocell, thereby to increase the current output, to control the relative sensitivity of the cell to light y rays approaching from different directions and/or .surfaces at which the electric current is gener- Aated by the incident radiations.

An object is` -to provide photocells with either symmetrically or non-symmetrically ridged or corrugated surfaces to increasethe photocell sensitivity to radiations approaching along an axis normal to the general plane of the photocell or from a direction inclined to that axis. An object is to provide a photocell having a non-planar active surface, and more particularly a photocell including a light sensitive selenium layer upon the plane .surface of aback electrode, the selenium v layer vbeing of increased thickness at the portions thereof that are to receive a sprayed-on l metallic current collector. A further object is to provide a photoelectric cell of the selenium type in which the .selenium layer has a` non-planar outer surface including ridge portions that are not covered by the applied outer electrode, the

Fig. 2 is af/section throughv the same 'on the.

plane indicated by the line 2-2 of Fig.. 1'. the thickness of each component layer being exaggerated and not to scale for clarity of illustration; Fig. 3 is a similar section through another embodiment of the invention;

Fig'. 4 is a plan view of another 'embodiment of the invention; and

Fig.,5'is a transverse section throughthe sam on the plane of line 5-5 of Fig. 4.

The invention will be described in detail with reference to selenium type photocells that comprise a back electrode of iron or an ironL alloy, a'

relatively thin layer of selenium on the back electrode, and an outer, translucent electrode layer of metal or metals that may be applied by a sputtering process. As noted above, the drawings are'not to scale as it is "not possible to illustrate the actualrelative thicknesses of the three essential layers in a transverse section of small size.

In Figs. 1 and 2, the reference numeral I identifies the back electrode that may be stamped from a thin iron or `iron alloy plate in the usual manner. The layer 2 ofselenium has a plane lower surface in contact with the plane unbroken surface of the back electrode I but the selenium layer 2 differs from prior practice in that its outer surface is not planar but is ribbed or corrugated to increase the totalv surface area presented towards'theincident radiations. As illustrated, the base-electrode l is circular in outline, and the outer surface of the major portion of the selenium layer is circumferentially grooved or, as viewed in transverse section along a diametrical plane, is of undulating or substantially sine wave form. The peripheral edge portion 3' of the selenium is relatively thick, for reasons that will be explained later, and a number of radial grooves or ribs 4 extend from the thick edge portion 3 to the small central area 5 that is depressed, as shown, or alternatively is elevated above the medial plane of the circumferentially grooved portion of the selenium. This central area 5 may be embossed or indented with an identifying symbol 6 that may be a type identification or the manufacturers trade-mark.

An annulus l of a soft metal or alloy is preferably sprayed upon the thickened rim portion 3 of the selenium layer before the translucent outer electrode layer 8 is applied byI sputtering or in any other desired manner. The electrode layer is of molecular or approximately molecular thickness.v

The initial steps in the manufacture of photocells embodying the invention may conform to present practice. The selenium may beplaced on the base electrode l in powder or pill form, and the assembly heated to the melting point of the selenium to effect a flow of the selenium over the surface of the base electrode. The thickness of the selenium layer at this stage may be of the order of a few thousandths of an inch. A die of desired irregular or non-planarsurface configuration is then pressed upon the selenium.

layer and the assembly is heated to a tempera-.

ture somewhat below the melting point of the selenium to form the cell unit under heat and pressure. The unit is light sensitized at the completion of the forming operation, and the. current collector ring 'i and electrode layer 8 are then applied.

It will be apparent that the area of the irregu-.

lar surface of the photocell is substantially larger than the area of a photocell of the same dimensions and of the conventional at surface type, and-that the current output for a given illumination is thereby increased. The shape and dimensionsnf the surface irregularities may be varied as desired in accordance with the desired photocell characteristics. 'I'he thickness of the selenium layer 2 may be, for example, about 0.001 inch at the thinner sections and about 0.020 inch at the ribbed or thicker sections. v

The fiat radial grooves or ribs 4 provide channels of low electrical resistance from the interior portion of the photocell to the outer edge portion to which a terminal connection is to be made. The translucent electrode layeris of relatively high resistance and the current developed at the center of the photocell would be forced to travel up and down the undulating electrode layer 8 to reach the cell periphery if the shorte length channels were omitted.

yThe grooves of the irregular photocell surface may be nlled with a transparent lacquer or resin 9 that reinforces the cell structure and increases the total current output by a reflection of the radiations from one surface or slope of the photocell ridges to another.

The additional thickness of the selenium layer 3 at the cell periphery reduces the possibility of a short-cireuiting of the cell by a penetration of the sprayed current collector l through the selenium layer, and increases the internal resistance of the cell. y

The dimensions and shape of the non-planar elements of the selenium layer may be Varied in accordance with lthe desired characteristics of the cell. .As shown in Fig. 3, the outer surface of the selenium layer 2a may comprise sets of plane surfaces of different widths that are angularly arranged and non-symmetrical with respect to a plane normal to the mean surface of they selenium surface. A photocell with a saw-toothed surface of this type will have a maximumv response to those rays, as indicated by the arrows a, that are substantially normal to the larger area elements of the non-planar surface. TheY directional sensitivity of the photocell may be controlled by an' appropriate design of the non-symmetrical ridges and grooves of the selenium layer. This form of the invention is well adapted for use in illumination controlling systems in which lights are to be turned on when the `solar illumination falls below some selected value. The photocell may be arranged vertically in a protective housing and have the northern sky sensitivity that was previously obtained by tilting the photocell.,

Furthermore, the\nonplanar selenium latter:V

may be shaped to provide a self-contained. iiie for'limiting the acceptance angle of the photocell. In the embodiment shown in Figs. 4 and 5, the selenium layer 2b is die pressed during the forming operation to provide upstanding ridges l2 of generally hexagonal contour, as viewed in plan, but with gaps I4 in the ridges or hexagonal compartment walls. The translucent electrode' layer 8a is not applied to the sides and tops of the ridges but overlies the bottom of each hexagonal well and is continuous through the gaps I4 to form-low resistance connections between the electrode layers within the hexagonal compartments and the electrode layer that extends over the current collector ring 1. The dimensions of the ridges I2 may be suchas t'o provide the desired acceptance angle limitation or to cooperate with superposed optical or mechanical baiiie members, not shown, of small thickness, to establish the desired acceptance angle of the photocell.

Photocells or photocell assemblies have been proposed in which selenium layers 4of uniform thickness were applied to a back electrode or electrodes of non-planar form but it is broadly new. so far as now known, to impart a non-planar surface conguration to the outer surface of the thin layer of selenium or other, photosensitive' material on-aat plate back electrode. Itis therefore to be understood that the invention is not limited to the particular embodiments herein shown and described, and that various changes that may occur to those skilled in the art fall within the scope of my invention as set forth in the following claims.

i. A current generating photocell of the type comprising a back electrode, a llayer of photosensitive material on said back electrode, and a translucent electrode overlying the photosensitive material laye'r, characterized b y the fact that the outer surface of the photosensitive material layer is non-planar.

2. A current generating photocell as recited invclaim 1, wherein the non-planar outer surface of the photosensitive material layer is undulating as viewed iii-transverse section. L

3. A current generating photocell as recited in claim 1, wherein the non-planar outer surface of the photosensitive material layer is undulating and .of approximately sine wave form as viewed in transverse section.

4. A current generating photocell as recited in claim 1, wherein the non-planar outer surface of the photosensitivematerial layer is constituted by lnarrow angularly arranged plane surface elements. Y

5. A current generating photocell as recited in claim '1, wherein the non-planar outer Surface of the photosensitive material layer is constituted by narrow angularly arranged plane surface elements, the adjacent surface elements being arranged non-symmetrically with respect to a plane normal to the mean plane of the irregular surface of the photosensitive material layer.

6. In a photoelectri'c cell, a plane surfaced back electrode, a layer of photosensitive material upon the plane surface of said back electrode, and an outer electrode layer. upon the photosensitive material layer, theboundary surface between said photosensitive'material layer and said outer electrode layer being non-planan.

1. In -a photoelectric cell, the-invention as recited in claim 6 wherein the non-planar outer l 2,320,185 lsurface. of said photosensitive material lay-er is impressed with ribs and grooves.

8. In a photoelectric cell, the invention as recited in claim 6 wherein the non-planar outer surface of said photosensitive material layer isimpressed with ribs and grooves having surfaces non-symmetrical with respect to a plane normal to the mean plane of the irregular surface of the photosensitive material layer.

"9. In a photoelectric cell, a back electrode. a layer of photosensitive material on said back electrode, the outer surface of said layer being ribbed and having plane-surfaced strips extendnon-planar layer of photosensitive material on y said base electrode. said non-planar surface being defined .by upstanding ridges forming the walls defining a`series of compartments 'with gaps inthe ridges, and a translucent electrode layer extending over the bottoms of the compartments and through the gaps of said ridges.

the sides and tops of the ridges being free from said electrode layer to form bailies for determining the acceptance angle of the cell..

18. In a photoelectric cell, a back electrode, a

.layer-.of photosensitive material on said electrode and having a ribbed outer surface, a translucent ing across the ribs, and a translucent electrode Ilayer extending over said photosensitive material layer.

10. In a photoelectric cell. a back electrode.

electrode, said layer having an identifyingdesign impressed thereon, and a translucent outer electrode layer extending over said photosensitive material layer.

ll. In a photoelectric cell, the invention as recited in claim v10.`wherein said design is im-l pressedA upon a portion of the outer surface of maining portion of said surface is non-planar.

12. In a photoelectric cell,`the invention as recited in,claim 10, wherein said design is impressed upon a portion of the outer surface'of I a layer of photosensitive material on said back.

-said photosensitive material layer, and the re-' said photosensitive material layer, and the remaining portion of said surface is ribbed.

13. In a photoelectric cell, a back'electrode 'with a .plane unbroken upper surface,'a layer of selenium on said surface and thickened at the periphery thereof, a current collector sprayed upon said thickened periphery of the selenium layer, and a translucent electrode layer overelectrode layer over-said photosensitive material layer, and transparent material nlling theY grooves of the photocell.

i9. In the manufactureof aphotoelectric cell of the type including a layer of photosensitive ,material between a back electrode and an outer translucent electrode, the method of increasing the photocell output at a given illumination which comprises shaping the boundary between said photosensitive material and said layer as a non-planar surface.

20. The process of making a photoelectric cel that comprises applying a layer of selenium to a at back electrode, die shaping the selenium layertoimpart to the outer surface thereof a non-planar configuration, and applying a trans- `lucent electrode layer to the irregular outer sur-v face ofthe selenium layer. u

21. Ihe process of making a photoelectric cell that comprises applying a layer of selenium to a flat back electrode, die shaping the selenium layer to forma thickened portion at the periphery thereof, and applying, an outer translucent electrode layer over the selenium layer.

22. The process of making a photoelectric cell that comprises applyinga layer of selenium to a flat back electrode, die shaping the selenium v layer to form a thickened portion atV tle petion with a depressed central portion anda v ribbedportion extending from the depressed central portion to the thickened periphery.

16. In a photoelectric cell, the .invention as of the selenium layer is of irregular configuration with a depressed central portion and a ribbed portion extending from the depressed central'portion to the thickened periphery, said central portion being impressed with'an idenl tifylns' symbol.

l'l. In a photoelectric cell, a base electrode. a

i claimed-m claim is wherein the outer sui-:cee`

riphery thereof. spraying metal upon the thickened outer portion of the selenium layer, and applylnga translucent electrode layer over the selenium and the sprayed-on metal.

23. In the manufacture of a photoelectric cel1,

fthe process which comprises forming on a back electrode a layer of light sensitive material` with upstanding ridges defining compartments and applying an-outer electrode layer ofthecompartments.' l

24. In the manufacture of a photoelectric cell. the process which comprises forming on a back to thebottms electrode a layer of light sensitive material with upstanding discontinuous-.ridges denning compartments communicating through the-gaps in the ridges. and applying an outer electrode layer to the vbottoms of thecompartments and the gaps -in said ridges.

' 5\ .xN'rnoNY H. mus.

translucent

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