Feb. 6, 1940. ` Q_ W, HEWLETT 2,189,580 METHOD OF MAKING A PHOTOELECTRIC CELL Filed May 29, 1937 Inventor : Clarence VV. Hewlett, is Attorney Patented Feb. 6, 1940 , 2,189,580 UNITED’ STATES PATENT OFFICE _, g aisance METHOD 0F MAKING A PHUTOELECTRIC Clarence W. Hewlett, Schenectady, N. Y., assigner to General Electric Company, a corporation of New York Application May 29, 1937, Serial No. 145,539 4 Claims. (CLES-8.9) The present invention relates to light-sensitive posited .on the selenium. The first, which is devices, more particularly to photoelectric cells, designated by reference character 4, is preferably which generate a measurable electromotive force of cadmium, and the uppermost metal layer 6 is when subjected to light of practical intensities. a relatively non-oxidizable metal preferably 5 In my application Serial No. 716,677, filed platinum. A contact ring 6 of any suitable metal March 21, 1934, I have disclosed and claimed a such as cadmium is applied in any convenient photo-voltaic cell which consists of a metal plate manner either to the selenium layer 3 before the or base member coated first with selenium and sputtered layers have­ been deposited, or to the then with cadmium and a relatively non-oxidiz platinum 5 after both metal layers have been de l0 able metal such as platinum in order. The cad posited. In case the ring is applied to the se 10 mium and platinum layers are preferably laid lenium layer, the sputtered layers are deposited down by‘sputtering and are so t-hin as to be semi not only over the selenium layer but also over ` transparent to light. When light shines on Wthe the cadmium ring. The contact ring and the ` double metal layer, an electromotive force is gen manner of forming the same constitute one of 15 erated between this layer and the selenium, and the features of the present invention and will l5 the current produced may be conducted away be described presently. The groove 2 is prefer from the cell by conductors secured in any suit ably positioned directly under the ring 5 and is able manner to this sexnitransparent metal layer slightly wider than the ring as is explained in my and to the base member.' This current is of suiil copending application Serial No. 145,538, entitled 20 cient intensity to be measured by a microammeter “Photoelectric cells.” The purpose of this groove which may be calibrated in foot candles to indi as pointed out in the said application is to pro cate the intensity of the light impinging on the vide an excess of selenium and thereby increase metal. The present invention concerns devices the resistance of the path of the current which of this character, and the objects are to increase iiows from the sputtered layer back to those por the sensitiveness of photo-voltaic cells and to lm tions of the selenium from which it started under 25 prove their manufacture. Another object is to the iniiuence of the light. The selenium con 25 Aprovide a practical method of making a rigid tained in the groove ­also serves to prevent a contact between one of the current-carrying con striking-through of the selenium layer when the ductors and the thin metal layer. In accordance contact ring is deposited in the manner described with these objects, the sensitiveness of the cell hereinafter. Y ' ` ' 3 is increased by controlling the vapor content of In the manufacture of these-cells, the first step 30 the gaseous chamber in which the sputtering is to provide the metal plate I with the annular takes place. In order to provide the rigid con groove or channel referred to hereinbefore. The tact between the conductor and the thin metal side of the plate which is grooved is then rough 35 layer, a metal ring of vsubstantial thickness is in ened by sandblast in order to provide a good tegrally. joined, for example, by spraying, to the >gripping surface for the selenium which is to be 35 selenium surface and the sputtered ñlm overlays deposited. The plate is then heated and wetted the ring and the selenium surface. Then the with selenium, the latter being thoroughly rubbed conductor is pressed in any suitable manner into the surface. The selenium may be scraped A against this ring. The objects andthe manner off the plate or disk, leaving the channel full and in which they are attained will be more clearly only a thin layer of selenium on the surface. 40 understood when reference is made to'the follow The plate is then chilled. This thin wetting layer ing specification and the accompanying drawing of selenium is then recrystallized by heating the in which Fig. l is an elevational, view of a sputter plate. The plate with the grooved side up is then 45 ing chamber for depositing metal layers on the placed in a heated heavy metal ñxture 8, shown selenium; Fig. 2 is' a sectional view of a cell in in Fig. 2, which has a countersunk or depressed 45 the process of making and the fixture for holding portion of a size snugly to receive the plate. This the same; Fig. 3 shows another step in the proc ,countersunk portion is of a depth greater than ess; Fig.` ‘i shows an improved method of apply . the thickness of the plate i by an amount repre 50 ing a contactring to the cell; and Fig. 5 is a senting the thickness of the selenium layer which sectional view of the completed cell, ready for is to be deposited on the plate. Selenium, in 50 mounting. paste, form, is spread on the disk l and the excess Referring to Fig. 5, numeral I designates a ñat is scraped od by a tool 9 which bridges the metal plate of any configuration, for example, countersunk portion of the ñxture t and leaves a 55 circular, and made preferably of iron or nickel. layer of selenium of the proper thickness depend 55 One side of the plate, the upper as shown, is pro ing upon the depth of the recess in the fixture. vided with an annular groove 2 and on top of the After a smooth surface has been obtained on the plate, filling this groove, is a layer of selenium 3. selenium by drawing the scraper in several di As is pointed out in the said application referred rections'across the upper surface of the fixture 8, ’ 60 to hereinbefore, there are two metal layers de the selenium coated plate l is then removed from 60 2 2,189,580 the fixture and the element is chilled. The next ' carries a rotatable drum I8 and a stationary rod step in the process is to obtain a smooth, glassy member I9. A flat metal plate 20 is secured to appearing, compact layer of selenium of uniform the upper end of the rod I9. 'I'he purpose of this thickness on the plate, and this is conveniently plate will be explained presently. 'I'he drum accomplished by a hot press treatment. member I8 carries a pair of oppositely extending A suitable fixture for this treatment is shown shafts 2|, 22, one of which (element 2I) termi in Fig. 3 and consists of a metal plate P contain nates in a counterweight 23. The other shaft 22 ing heating elements (not shown) let into holes carries a magnetic member 24 of arcuate form, ~ H, and a die I 0 containing a recess of a depth and at a position intermediate the ends of the corresponding to the ñnished thickness of the rod, also carries an upright shaft 25. A carrier 10 selenium coated plate. Before placing the se fixture 26 provided with a central recess 21 is lenium plate on the press, the apparatus is heat secured to the upper end of the rod 25. This ed to a temperature of about 140° C., and the recess has a diametral size and thickness suf selenium coated plate I is then placed, selenium iicient to accommodate the selenium coated disk side down, against the plate P. The die I0 is I. In addition to the upright I1, the base I6 is 15 then placed on top of the selenium coated plate, also provided with a glass upright 28 which ter and pressure applied in any suitable manner, minates at the top in a pair of forked arms 26. for example by means of a clamp. At the tem The arms 29 contain a pair of conductors 3D, 3|, perature mentioned, the selenium softens and one of which is secured to a mesh member 32 flows, the excess being exuded around the edges composed of platinum, and the other carries a of the plate as indicated at B. Although as stat disk 33 of cadmium which lies directly above the ed hereinbefore, the selenium at ñrst softens carrier 26. and flows, in a few minutes it begins to harden, The arrangement is such that by means of a and after 10 to 30 minutes the pressure may be magnet 34, which is adapted to be moved around relieved and the plate removed from fixture. the bell jar, the armature 24 is caused to move The selenium layer is now hard, smooth, and of within the chamber and this movement serves uniform thickness, and the excess exuded sele to rotate the carrier 26 from a position directly nium may be removed from the edges. The sele under the disk 33, as shown in Fig.` 1, to .a po nium coated plate I which has thus been treated sition directly under the mesh member 32.