CA1077161A - Photo-voltaic power generating means and methods - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to systems and methods for generating electrical power from light radiation, and specifically from solar radiation. Among the most impor-tant existing devices for converting solar energy into electricity are devices comprising photoelectric material which is substantially monocrystalline and must be grown from crystalline solution, with a high failure rate. De-vices and fabrication techniques utilizing polycrystalline semiconductive materials have generally proven inadequate due to high production costs. Also, the failure rate in fabricating such devices is relatively high because of penetration by impurities. There has been a recent attempt to form photo-voltaic power generating means with a com-pound semiconductor materials having a cadmium sulfide layer. However, the results were poor since the oadmium sulfide was sometimes porous giving rise to shorted junc-tions. The present invention provides an economical and reliable semiconductor photo-voltaic cell and a method for making It. The semiconductor in the present invention is electrolytically formed at a cathode in an electrolytic solution by causing discharge or decomposition of ions or molecules of a non-metallic component with deposition of the non-metallic component on the cathode and simultane-ously providing ions of a metal component which discharge and combine with the non-metallic component at the cathode thereby forming the semiconductor compound film material thereon. By stoichiometrically adjusting the amounts of the components, or otherwise by introducing dopants into the desired amounts, an N-type layer can be formed and thereafter a P-type layer can be formed with a junction therebetween.

Description

`- 10771~
The invention relates to systems and methods for generating electrical power from light radiation, and speci-fically from solar radiation.
The increasingly aggravated inadequacy of fossil fuels for energy generation of all types has led to many efforts to tap alternative energy sources. A particularly attractive alternative source is light radiation, and par-ticularly solar rad-lation, which comprlses enormous amounts of easily accessible energy and is largely untapped.
Among the most important ex~sting devices for converting solar energy into electricity are devices of the type de-veloped in the space effort. These devices comprise net-works of s~aller area thin monocrystalline layers connected in serles. These devices have relatively high efficlency in terms of power generation in relation to weight. This criterion, however, is substantially inapplicable to the problem of power generation for normal commercial and consumer purposes, in which the criterlon of usefulness is related to economic factors, such as power generation per unit cost. Under this criterion of efficiency, units which are useful in the space effort are impractical.
These units are comprised of photoelectric material which is substantially monocrystalline and must be grown from crystalline solutlon, wlth a high fa~lure rate. These constraints limit such units to small dimensions and re-quire many such units to provide even a minimal power source.
Devices and fabrication techniques utilizlng polycrystalline semiconductive materials have generally proYen inadequate due to high production costs. Among the contributing factors to these high costs is the requirement of use of structural materials of high heat resistance due to the high temperature utilized with ~/5 7~

1~77~

these fabrication techniques. Moreover, such devices generally utilize metallic internal conductors, thus fur-ther increasing costs. Also, the failure rate in fabri-cating such devices is relatively high because of penetra-tion by impurities, in the course of fabrication. Further, control of the deposition of semiconductive material in such process presents substantial problems.
There has been a recent attempt to form photo-voltaic power generating means with a compound semi-conductor material having an N-type region and a P-type region and in which the N-type and P-type regions were doped. In this case, the first semiconductor section, constituting an N-type section, was formed by a vapor phase deposition of a metal, such as cadmium with the addition of sulfur to provide a cadmium sulfide layer.
The second, or P-type, semiconductor section was formed by dipping the material into a hot aqueous solution of CuCl which caused formation of CuxS. However, the results were poor since the cadmium sulfide was sometimes porous giving rise to shorted junctions. In addition, a large amount of unused cadmium was required in the deposition, thereby creating a substantially expensive photo-voltaic power generating means, oftentimes of low efficiency.
U.S. Patent No. 3,573,177 issued March, 1971 to William McNeill describes a prior art technique by which polycrystalline cadmium, zinc, or cadmium-zinc sulfide or selenide is formed by electrochemical deposition on a Cd or Zn or Cd, Zn anode and where sulfur or selenium is provided from a solution containing $= or Se= ions and which polycrystal-line material is usable as a semiconductor material. Theconcept of forming thin films of semiconductor materials by electrochemical techni~ues is relatively new and due, in part, to the teachings in the aforesaid McNeill patent.

In accordance with the McNeill patent, electrochemical discharge o~ ions, such as those ylelded by sulfides or selenides dissolved -in an eleckrolyte, occur with respect to cadmium or zinc actlng as an anocle in an electrolytic cell. This electrochemical discharge converts the zinc or cadmium, or the alloys of these metals, to the corres-ponding sulfldes or sul~oselenides.
The McNeill patent has advanced the art of pro~
ducing semiconductive materials by electrochemical tech-niques and presents many advantages, including the abilityto apply ~ilms of semiconductor materials to irregularly shaped substrates which were not thoroughly cleaned.
Nevertheless, the McNeill patent su~fers ~rom many limi-tations in that the end product is not necessarily capa-ble o~ functloning as a P-N semiconductor ~unction mater-ial necessary in the operation of a photo-voltaic cell or simllar diode. McNeill is essentially concerned with the manufacture o~ non-~unction semiconductor ~ilms, such as those found in the electro-luminescent panels, electro-sonic transducers and photosensitive conductors.
The essence of the McNeill patent lies primarily with anodic plating, with discharge of S= and Se ions.
However, it is not known that the McNeill process can be applied to e.g. discharge of Te= ions which is more ideal in the case of photo-voltaic cells. Yet it is such a discharge, forming CdTe and a ZnTe that is of prime importance for the manu~acture o~ solar cells since cad-mlum telluride has a dlrect band-gap uniquely optimized for sunlight at 1.5eV.
There has also been a proposed prior art tech-nique ~or electrochemically precipitating metals at a cathode for producing a selenium recti~ier. This tech-nique is reported in an article entitled, "Electrochemische 1~771~1 ~bscheidung von Metallseleniden", by H. ~on Gobrecht, H.D.
L-less and A. Tausend, in Ber. ~eutsche Bunsengesellschaft 6F (1973), page 930. Thls article does not describe the production of photo-voltaic power generating cells. In accordance with this prlor art technique, deposition of the less noble component and the more noble component must be very care~ully controlled due to the difference in standard precipitation potentials. The more noble component had to be added in carefully controlled small dose9 in order to operate with this technique.
Therefore, there has been, and is, a well recog-nized, but unfulfilled need for photo-voltaic power generating means having relatively high power generating capability per dollar of cost to produce and having a form suitable for commercial and consumer use, and for a method of producing such means.
It is, therefore, the primary ob~ect of the pres-ent invention to provide a photo-voltaic power generating means in the form of a power generating cell which is cons~ructed of semiconductor material having an N-type region and a P-type region.
It is another obJect of the present invention to provide a photo-voltaic power generating means of the type stated which operates with a relatively high degree of efficiency and which can also be made at a relativel~
low cost, compared to convenbional and proposed photo-voltaic power generating means.
It is a further object of the present invention to provide a photo-voltaic power generating means which can be produced in the form of a relatively flat sheet for disposltion upon a surface which is located to receive solar radiation.

It is an additional object of the present 77~ti1 invention to provide a low-temperature method of producing photo-voltaic power generating means and which eliminates the high temperature operation which was heretofore employed to produce such power generating means having semiconductor materials.
It is also an object of the present invention to provide a method of cathodically depositing semiconductor forming material at the cathode of an electrolytic cell.
It is yet another object of the present invention to provide a photo-voltaic power generating means which is created by cathodically depositing semiconductor forming material at the cathode of an electrolytic cell to produce a semiconductor compound which is photoreactive.
It is another salient object of the present invention to provide a method of producing photo-voltaic power generating means of the type stated which is highly efficient and substantially eliminates material waste.
In accordance with one broad aspect, the invention relates to a method of preparing a photo-voltaic power generating cell comprising the step of depositing electro-chemically on an electrode a coating of at least one semi-conductor compound from an electrolytic bath including the components of said semiconductor compound, said compound being capable of forming a semiconductor junction, being transmissive to light radiation and being capable of forming electron-hole pairs upon being irradiated with photons, said components being formed of at least one of the metal elements of Class IIB
and non-metal elements of Class VIA of the Periodic Table of Elements.
With the above and other objects in view, our invention resides in the novel features of form, construction, arrangement, .

77~61 and combination of parts presently described and pointed out in the claims.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings in which:
FIGURE 1 is a somewhat simplified perspective view of a photo-voltaic power generating means in accordance with the present invention;
FIGURE 2 is a somewhat schematic side-elevational view of a power cell in the power generating means of Figure l;
FIGURE 3 is a side-elevational view, somewhat similar to Figure 2, and showing a slightly modified form ~ -5a-1~771~i1 of photo-voltaic power cell;
FIGURE ~ is a perspective view, partially broken away and shown in sectlon, and showing a preferred power cell construction in accordance with the present invention;
FI~URE 5 is a schematic electrical circuit view showing an equivalent electrical network for a solar energy operated cell in accordance with the present in-vention;
FIGURE 6 is a schematic side-elevational view showing one method for forming a pboto-voltaic power cell ln accordance with the present invention;
FIGURE 7 is a schematic side-elevational view, 8 omewhat similar to Figure 6, and showing another modified form of creating a photo-voltaic power cell in accordance wit, the present invention;
FIGURE 8 is a schematic side-elevational vlew, somewhat similar to Figure 6, and showing another method for forming a photo-voltaic power cell in accordance with the present invention;
FIGURE 9 is a somewhat schematic side-elevational vlew, somewhat simllar to Figure 6, and showlng still another modified form of method for creating a photo-voltaic power cell in accordance with the present inven-tion;
FIGURE 10 is a schematic side-elevational view, somewhat slmilar to Figure 9, and showing yet another modified form of method for creating a photo-voltaic power cell utilizing a plurality of anodes in accordance with the present invention;
FIGURE 11 is a schematic side-elevational view, somewhat similar to Figure 10, and showing another modified method of the present invention which also utilizes a pair of anodes;

-` ~077~ti1 FIGURE 12 is a schema~lc side-elevational view, somewhat simllar to Figure 11, and showing an additional modifled form of the present invention for creating a photo-voltaic power cell in accordance with the present invention;
FIGURE 13 is a schematic diagrammatic view show-ing the steps ut-llized in the method of the present inven-tion.
Re~errlng now in more detail and by reference characters to the drawingsJ 20 designates a photo-voltaic power generating means, as depicted in Figure 1, in a form suitable for commercial and consumer use and con-figured as a sheet or panel 22. This panel 22 is si~ed to be disposed upon a surface 24 as shown as the roof of a dwelling. In the depicted application, the photo-voltaic power source 20 generates power as a consequence of having solar radiation incident thereupon. The inven-tion may~ of course, be utilized in a wide range of other applicationsJ including heavy stationary installations, vehicles, and laboratory uses, with other light sources and in other configurations.
The power generating means 20 comprises as a ma~or integral component thereof, a photo-voltaic power generating cell 26, (Figure 2) which is formed of semi-conductor material. In this respect, the sheet or panel 22 may be comprised of a plurality of series-connected cells, such as the cells 26. The cell 26 in its simplest form includes an N-type region 28 and a P-type region 30, which are separated by a ~unction 32, in a manner to be hereinafter described in more detail. While the present invention is erfective with a hetero-~unction, it is also possible to produce the N-type region 2~ and the P-type region 30 with homo-junction therebetween.

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10771~;1 The term "photo-voltaic" as used herein refers to a compound semiconductor which is capable of generating electrlcal power when the compound semiconductor is sub-Jected to the incidence of solar radiation or similar forms of light radiation. The semiconductor in its simplest form is often referred to as a "cell". In ~any cases the term "cell" is also used to encompass not only the compound semiconductorl but the substrate and ter-minals or electrodes as well. In each case the cell will have two region~, e.g., an N-type region and a P-type region, e~tablishing a junction therebetween.
The N-type region 28 ls formed of an N-type material which may comprlse any of a number of well-known compositions which exhibit N-type semiconductor proper-ties. The P-type region 30 is formed of a P-type material formed of any well known composition which exhibits P-type properties. In a preferred aspect of the invention, the cation is preferably cadmium or zinc and the anion is sulfur, selenium or tellurium.
Figure 3 illustrates a modified form of photo-voltaic power generating cell 34 which comprises a sub-strate 36 formed of a relatively inert electrically non-conductive material which is preferably transparent to llght radiation. The substrate 36 may be formed of a relatlvely low-cost material, such as any of a number of plastics, and particularly that plastic sold under the trademark "Mylar" and the material sold under the trade name "Kapton" of relatively low heat resistance and of low cost. However, any of a number of other substrate materials may also be used in accordance with the present invention, and include any fiber-reinforced plastic sub-strates, such as for examp~e, epoxy resin impregnated fiberglas substrates, or the like. In essence, the ~771~1 substrate should be one which is relatively inert with respect to electrical conductivity and may be without sub-stantial heat resistAnce.
Bonded to one flat surface of the substrate 36 is an electrlcally conductive metal electrode 38 which may be composed of a relatlvely inert electrically con-ductive metal, such as stainless steel, nickel or the like. In thls case, it can be observed that the electrode 38 comprises a thin layer o~ sheet, although the electrode 10 38 may take other forms and may have other positions in -accordance wlth the present invention. The electrode 38 may also be secured to the substrate 36 by any of a variety of ~nown techniques, such as metal vapor deposi- -tion, electrolytic deposition, or the like. Otherwise, the electrode 38 may be prefabricated as a strip and bonded to the substrate 36 by means of conventional ad-heslves, etc.
Secured to the exposed flat surface of the electrode 38 is a photo-electric power cell 40 which ls substantially similar in construction to the power cell 26. In this case, the photo-voltaic cell 40 ls comprised of a compound semiconductor material. This cell 40 is provided with an N-type section region 44, similar to the N-type section 28, and a P-type section 46, similar to the P-type section 30, with a ~unction 48 therebetween.
An electrlcally conductive cover sheet 50 is secured to the outer eurface of the section 30.
The N-type region 44 and the P-type region 46 are ~imilarly ~ormed in the same manner as the N~type region 28 and the P-type region 30 were formed in the cell 26. Moreover, in this case, the N-type region 44 and the P-type region 46 may also have a homo-junction 48 therebetween, as in the case where the N-type and khe .

77~
P-type regions are formed of substantially the same material. Otherwlse, these two regions may be formed of different materials and have a hetero~unction 4~ there-between. Finally, an electrically conductive connector 52 is connected to the metal electrode 3~ and an elec-trically conductlve connector 54 is connected to the sheet 50. This cell 34 operates in substantially the same manner as the cell 26 and will generate a current flow through a load connected across the connectors or terminals 52 and 51~ when solar radiation is incident upon the cell 34.
The cell 26 or the cell 34 may be ¢ompletely enveloped within and contained by a container, or similar form of contalner means, or so-called envelope (not shown), which is formed of a material transparent to light radia-tion. The container means may be formed of any of a number of known materials capable of passing solar radia-tion and including all forms of light radiation as, for example/ plastic material including polyethylene sheets.
Polybutyral sheets and other forms of plastics, as well as other electrically non-conductive like transparent materials, may also be used in the formation of the con-tainer.
The cell 40, as well as the previously described cells, may be formed of cadmium sulfide or cadmium sel-enide, and preferably of cadmium telluride. In the depicted embodiment, the cell 40 is in the form of a thin layer, although in other applications the cell 40 and the N-type and P-type regions 44 and 46 may be configured in any appropriate manner. ~s described in detail below, the thickness of the cell 40 is readily controllable through the method of fabrication of the photo-voltaic power generating means in accordance with the invention, 1~7716~
thereby affordlng substantial economy. In any evenk, the cell 40, as well as the other layers of the cell 40, as described below, may be of the order of 1-20 microns in thlckness, although the cells will prererably range in thickness between about 0.1 to 40 microns.
The top surface of the container means for the cells 26 or 34 and cover sheet 50 would be transmissive of light and comprises an element of a light path 56 as schematically illustrated in Figure 3 of the drawings.
An additional or alternative light path (not shown) may be provided through the lower surface of the cover in which the substrate 36 and electrode 38 may comprlse grid structures to permit access of light and will be very thln to minimlze internal electrical reslstance.
In accordance wlth the above, it may be observed that the photo-voltaic power generating means of the present invention may be dlsposed in contact with llght receiving surfaces, such as roofs of structures, in the form of continuous panels which may be fltted to the size.
These features, among other previously descrlbed and hereinafter described in more detail, constitute a sub-stantial advantage of the invention in terms of ease of use and economy.
As indicated previously, the cover means over the photo-voltaic cell would be transmlssive of llght and comprise~ an element of the path 56 glvlng access to the cell 40, that is through the P-type semlconductor region 46. In this case, the P-type semlconductor reglon 46 is the region which is exposed to light radiatlon, although it should be observed that the N-type region 44 could also be the outermost region exposed to light radiatlon through the path 56.

The leads ~2 and 54 connect the cell 40, and 10771~1 hence the power ~ neratin~ means, to an external load (not shown). This load may comprise, for example, the main power source of a vehicle or of electrical systems within a vehicle. In operation, light traversing the light path 56 strikes the photo-cell 40 and causes a movement of electrons from the semiconductor material of the P-type region ~6 across the ~unction 1~8 to the N-type region 44, under well-known phenomena of photo interaction with semiconductive materials. Consequently, a migration of electrons to the plus termlnal 52 occurs and a current appears in the leads and ln the load.
In the embodiment of the cell illustrated in Figure 3, where the light path is designated 56, at least the electrode 50 must be transparent. In this case, the electrode 38 and the substrate 36 would not have to be transparent. However, -ln accordance with the present invention, the cell could have a transparent electrode 38 and a transparent substrate 36, formed of a conductive glass or transparent plastic substrate, as described in more detail hereinafter. In this construction, the cell would respond to a light path designated as 56' in Figure 3 of the drawings. However, it should be recognized that all components of the cell 34 could be transparent.
Where the cell 34 is constructed so that it responds to the light path 56, the narrow band gap mater-ial will be incidental to the electrodes 38 and the wide band gap material will be incidental to the electrode 50.
When the cell 34 is constructed so that it responds to the light path 56'~ the wide band gap material will be incidental to the electrode 38 and the narrow band gap material will be incidental to the electrode 50. In essence, the wide band gap material will always face the source of light. In the present invention, a CdS layer 1077~ti1 has a wider band gap than the CdSe layer, which in turn, has a wider band gap than a CdTe layer.
In accordance with the invention, the electrode 50 need not be ~ormed of a metal~ but could be formed of a conductive transparent o~ide as hereinafter described.
Again, the electrode 38 could be formed of a conductive transparent oxide. In addition the substrate 36 could be conducting and constitute an electrode, thereby elimin-atlng the necessity of the electrode 38.
One of the preferred embodiments of a photo-voltalc power cell construction in accordance with the present invention, is more fully illustrated in Figure 4 of the drawings. In this case, the preferred embodiment of the power cell is designated by reference numeral 57 and lncludes a substrate 58 which is electrically non-conductive, such as a glass substrate. This substrate 58 i8 preferably relatively thick with about a thickness of one-eighth inch. A metallic electrode 60 is disposed on one flat surface of the substrate 58 and this electrode 60, in the form of a grid, is comprised of a plurality o~
parallel spaced apart transversely extending strips 62 and a plurality of parallel transversely spaced apart longitudinal extending strips 64. In the preferred as-pect of the invention, the strips 62 and the strips 64 are ~ocated in an essentially perpendicular relationship.
A conductive coating 66 is applied to the sur-face of the substrate 58 in which the metal grid 60 is applied and this substrate 58 is preferably an electric-ally conductive coating comprised of stannous oxide doped with antimony, or indium oxide doped with tin. The - electrically conductive coating essentially completely covers the entire inner surface of the substrate 58 except for the portions of the grid in contact therewith 1~7~
and completely covers the metal gr-ld 60 and is in electri-cal contact therewith while the grid 60 is on the inner surface of the substrate 58.
This last substrate 58 may be formed of any transparent substrate material as, for example, polymethyl-methacrylate, or the like. In addition, the substrate 58 could actually form part Or a basic cell buildlng block in the ~orm of a glass roof or wall tile. In any event, it is important that the substrate is surficiently trans-parent to admit the passage of light, when the cell isoriented for passage o~ light through the substrate.
The coating 66 which also faces the source of solar energy ~s coated upon the substrate 58, preferably by vapor coating, in the form of a uniform thin film of electrically conductive material which is preferably antimony-doped tin oxide, or indium oxide doped with tin.
In accordance wlth the present invention, it has been found that it is not necessary to use a metal as an elec-trode and that a relatively thick transparent substrate can serve as the electrode when made electrically conduc-tive through application of a conductive oxide. The con-ductive oxide is an N-type material and therefore the conductive oxide must be in contact with the N-region or otherwise another ~unction would be established.
The grid 60, often referred to as a "bridge I~J iS
on the surface of the substrate 58 and located between the substrate 58 and the tin oxide coating 66 in order to lower the ohmic resistance. In this way, the grid 60 becomes a first electrode which has a resistivity well below one 3 ohm per square inch. A terminal 68 extending fromone portion of the grid 60 serves as a first terminal for making electrical connection to the cell. A flat bus bar (not shown) may ~so extend around the periphery of the 10'~7~

terminal portions of the grid 60 to serve as one o~ the two terminals for providing the electrical connection to the cell.
The photo-voltaic cell 57 will also include the cell structure of the type illustrated in Figure 2 of the drawings~ In this case, the cell structure includes an N-type section 70, equivalent to the N-type section 44 in Figure 3, and a P-type section 72, equivalent to the P-type section 46 in Figure 3 of the drawings, with a lQ ~unction 74 therebetween. The N-type section 70 may be comprised of, e.g. cadmium selenide or cadmium telluride, whereas the P-type section may be formed of the same material wlth a homo-junction or a different material with a heterojunction. A relatively thin metallic film 76 is applied to the outer surface of the P-type section 72 in the manner as illustrated in Figure 4. This outer metallic film 76 constitutes the rear electrode assembly, and is provided with an electrically conductlve lead wire 78.
It can be observed that the construction of the c ell of Figure 4 enables light to pass through the sub-strate 58, thereby eliminating the need of a third metal substrate. Moreover, it can be observed that the grid 60 is also electrically conductive and in conductive relation-ship to the N-type region 20 through the conductive trans-parent oxide film 66. The outer metallic film may have a reflective surface facing the substrate 50 SQ as to cause reflection of the light which entered the cell and thereby : cause greater energy conversion efficiency.
A relatively high efficiency value for a poly-crystalline photo-voltaic cell can be achieved by a com-bination of factors including the use of a thin layer of cadmium telluride facilitating maximum bransport o~ photons .

--` 1077161 to the junction region. The use of a thin film of modi-fied metal, as for example, vapor deposited nickel, performs as an anti~reflection coating on the surface of the glass facing the sun rays. The dlsclosed structure is quite effective ln that it reduced ohmic losses in the two elec-trodes and the semiconductor material.
This form of cell structure is highly advan-tageous over previous prior art cell structures of the single crystal type in that the cell structures described hereln include substantial economies which become possible through the deposition of thin layers of one or more costly active materials on an inexpensive glass or transparent plastic substrate. In accordance with this latter embodi-ment of the invention, this embodiment provides the ability to make a large integrated area cell without the necessary recourse to intraconnecting a multiplicity of small or independent units in a connected arrangement. More0~er, this cell structure includes the possibility of the employ-ment of printed circuit type conductors to connect a plur-ality of indlvidual cells on a tile or similar substratein series or series-parallel arrangement.
Figure 5 illustrates, in schematic form, a pre-ferred electrical configuration of at least one or more cells connected in accordance with the present invention.
It has been well established that absorption of photons having wave lengths shorter than the optical band-gap creates electronic-hole pairs in a crystal lattice of the semiconductor material. A built-in field provided by the P-N ~unction, e.g. the P-N ~unction 32 or the junction ~8, or otherwise, a Schottky batrier, separates the electrons and the holes generating a photovoltage which biases the ~unction in a forward direction. Thus, in this way, a solar cell of the type proposed by the present invention '' : : :' , 107~71ti1 can be represented hy the equivalent circuit in Flgure 5 o~ the drawings.
More fully considerlng Figure 5, it can be ob-served that each of the cells are designated by reference numeral 80 which functions as a current generator per unit area. These cells have a diode 82 connected in parallel therewith in the manner illustrated in Figure 5 of the drawings. The diodes 82 are of unit area with respect to the current generators, such as the photo-voltaic cells 80.
In this respect, it can be observed that while the cells 80 are connected across the diodes 82 ln parallel relation-ship, the opposed terminals of the diodes 82 are connected to a positive line 84 and a ground line 86. Resistors 88 and 90 represent th~ sheet resistance of the electrodes and of the ad~acent electrically neutral portions of the semi-conductors bordering the built-in field region. Resistors g2 and 94 are representative of the contact resistances per unit area of the neutral regions with these electrodes and the reslstance per unit area of these neutral regions.
Each cell has similar resistive functions and diode func-tions in the manner as illustrated in Figure 5 of the drawings.
For optimal conversion efficiency, the resis-tances 88 and 90, as well as resistances 92 and 94, the latter of which constitute parasitic resistances, should be made as small as possible. The selection of the semi-- conductor material for optimizing similar energy conversion thus involves maximizing the effective full type conver-sion into electron-pairs for solar radiation. In other words, this efficiency is created by maximizing the current generator, e.g., the solar cells 80 and maximizing the forward resistance of the various diodes 82. The maxi-mization is required with respect to the solar cells 80 1077~L6~
and the diodes 82 and t~lese requirements are interrelated resultlng in a compromise on the band-gap of the semlcon-ductor material which is chosen with decreasing band-gap as more radiation is absorbed. However, the internal resistance of the barrier decreases, leading to optimal band-gaps for cadmlum telluride of approximately 1.5eV for solar radiation conversion at the earth's surface on a cloudy day.
The technique for making the photo-voltaic power cells in accordance with the present invention is more fully illustrated in Figures 6-12 of the drawings with a schematic flow diagram thereof illustrated in Figure 13 of the drawings. In essence, the present invention provldes for the controllable electrochemical production of Junc-tions of cadmium and zinc-type compound semiconductors used as photo-voltaic cells. In accordance with the invention, a semiconductor compound material is formed at the cathode where both the more noble components and the less noble components are discharged.
Referring now to Figure 6, 100 designates a con-tainer, such as a beaker, formed of a relatively inert material. Located within the container 100 is a cathode 102 which is slmilarly formed of a relatively inert mater-ial, nickel as shown. However, any other form of metal electrode which is inert to the reaction, such as steel or glass or plastic provided with a conductive oxide coat-ing, for example, may be used. Also located w~thin th~
container 100 is an anode 104 which may also be inert, or otherwise the anode may be formed of cadmium or zinc or selenium or tellurium, as hereinafter described. As illustrated, the anode 104 is formed of an inert platinum material. Both of the electrodes 102 and 104 are disposed within an electDolyte 106, as hereinafter described, and ~077~

both the anode and the cathode are e:Lectrically connected through a source of electrical current 108.
This particular arrangement of Figure 6 repre-sents a simplified system which illustrates the formation of a coating at the cathode 102. ~y way of example, it is possible to electrochemically deposit sulfur on the nickel aathode 102 to form a sulfur coatlng, designated as S in Figure 6, through the use of an electrolyte such as S02 in H20. In this way, the reaction which proceeds is represented by:
4e~ ~ 4H+ + H2S03 = 3H20 + S-This reaction demonstrates that sulfur is reduced during deposition at the cathode. Similarly, the H2S03 is oxi-dized to H2S0~ at the anode. In this case, deposition would occur pre~erably at about 10C to about 20C, with about three to six volts applied across the anode and cathode, along with a current density of 0.1 amp. per square centimeter. An optimal depositio~ of the sulfur occurs from a 1 mg 1~1 solution of S02 in water.
In the event that it was desired to form cadmium sulfide, as opposed to a mere sulfur layer at the cathode, the electrolyte could be changed from S02 in water to S02 -~ 3CdS04.4H20. In the ionic dissociation of the cadmium sulfate in water, positively charged cadmium ions are formed. ~hese cadmium ions are attracted to and dis-charged at the cathode on which sulfur is also being deposited simultaneously. Thus, the cadmium and the sulfur will combine as they are simultaneously discharged at the cathode to form a layer of cadmium sulfide on the cathode.
In this way, it is possible to form a film of cadmium sulfide with any desired stoichiometry, as established through the concentrations of the solutes used in the electrolyte.

:1077~
Figure 7 -1llustrates a system similar to Figure 6, except t~lat in t~lls case the cathode which is employed will constitute the metal upon which a coating is desired to be formed. It can be observed that the cathode 102 is *ormed o~ cadmium and wlth the aforementioned reaction, sulfur can be catho~lcally deposited as along with cad-mium a film upon the cadmium cathode to obtain, for example, cadmium sulflde.
Figure 8 illustrates another embodiment of the method of making a cadmium sulfide compound film on an inert cathode, which in this case, is shown as glass having a conductive oxide coating thereon. Again, the anode is also formed of an inert material, such as platinum. In order to produce the cathodic coating of cadmium sulfide, the sulfur is introduced into a solution of the electro-lyte in the form of S02 in H20, and the cadmium is intro-duced in the form of 3CdS04.4H20, dissolved in this solu-tion as previously described. It should also be observed that cadmium telluride and cadmium selenide, etc,, zinc sulfide, zinc selenide and zinc telluride could be formed in the same way. Thus, in order to form a cadmium tel-luride coating on the cathode 102, the electrolyte would constitute tellurous acid as the source of tellurium and cadmium sulfate as the source of cadmium. In this way, the positively charged cadmium ions which are thus formed would be discharged at the cathod. In like manner, the tellurium would be deposited at the cathode and simultan-eously react with the cadmium to form the cadmium telluride film.
It can be observed that it would be necessary to plate out the cadmium and the tellurium, or the other com-ponents used, in the desired stoichiometric amounts. How-ever, the standard voltage required for plating out the 1o7~

cadmium and tellurium would be different. For example, a more negatlve voltage would be needed for the less noble component as, for example, cadmium, than for the more noble component, as for example, tellurium or selenium. While there ls somewhat of a compensating effect with respect to the deposition voltages when a semiconductor component is formedJ it is usua]ly desirable to decrease the concen-tration of the more noble component. Thus, in the case Or producing cadmium telluride, the amount of tellurium 1~ in solution would be decreased with respect to the amount of cadmium.
In order to form a cadmium telluride or similar photo-voltaic device, as illustrated in Figures 2, 3 or 4, a first layer of cadmium telluride would be plated on the nickel anode 104, in the manner as previously described.
The film thus formed on the cathode would be produced as an N-region or a P-region, depending upon the ratio of the cadmium and tellurium. After forming the first cadmium telluride layer on the cathode, as for example the glass with oxide coating cathode in Figure 8, a second electrolyte 9 imilarly including the same compositions to produce the source of cadmium ions and the tellurium ions would also be used. However, the concentration ratio of the cadmium and tellurium in the second solution would be different from that of the first solution in order to form the other of the P-type region or N-type region. Thus, for example, if a first film of cadmium telluride were placed onto the nickel cathode 102 with, e.g., 50.01% cadmium~ this film would constitute the N-type layer 28. When the second film of cadmium telluride from the second electro}yte is placed on the first film, this second film could have a lower concentratlon of cadmium as, for example, 49.99%.
In this case, the second film would function as, and -10771~;1 constitute, the P-kype layer 30~ Thus, it can be observed that by merely controlling the stoichiometry of the metal component, e.g., cadmium, and the nonmetal component, e.g.
tellurlum, or otherwise the ions of any other metal and nonmetal components used in accordance with the present invention, it is possible to produce elther an N-type layer or a P-type layer. In accordance with this exampleJ it can be observed that the two films thus formed on the n ickel cathode 102 will form a homojunction 32 therebetween.
It should be observed in accordance with the present invention that it is possible to produce the N-type region and the P-type region from different materials with a hetero~unction therebetween. In this case, e.g., cadmium selenide would be formed as a first film on the anode 102, which is glass with a conductive oxide coating as shown. Thereafter, the electrolyte would be changed to plate out, e.g. cadmium telluride. The cadmium tel-luride would then be plated onto the first layer of cadmium selenide. In this way, the concentrations of the cadmium with respect to the tellurium and the selenium would be stoichiometrically ad~usted so as to create both an N-type region and a P-type region. Thus~ the cadmlum selenide layer could operate as either a P-type region or an N-type region, but more preferably an N-type region, and the same holds true of the cadmium telluride layer which would preferably be a P-type layer.
Figure 9 illustrates another alternative technique for producing a cathodically formed film in accordance with the present lnvention. In this case, the cathode is also inert as, for example, the glass with the conductive oxide coating as shown. The anode, ln this case, would be formed of the metal component as, for example, a solid cadmium or zinc sheet, or otherwise a cadmium or zinc-..
~' - . ' ' ' -10771~;1 plated æheet. The electrolyte would be comprised of those materials which provided the nonmetal component of the com-pound. Thus, in the case of sulfur, the electrolyte would comprlse a solution of S02 in water. In this way, cadmium sulfide would be formed at the cathode. Again, tellurous acid could be used as the electrolyte and, in which case, cadmium telluride would be formed on the nickel cathode.
With cadmium sulfide, it has been found that the cadmium sulfide can be formed on the cathode with a layer 10 of a thickness of about 5 mlcrons for preferred results.
These layers are obtained from a 5~ solution of S02 at about 45C. f With the embodiment of Figure 9, as well as some of the other embodiments herein, it is also possible to utilize cadmium and similar metal anodes containing dopents.
Thus, indium as a donor dopant could be combined with the cadmium as a cadmium-indium alloy to be used as the anode. In this way, the electro-chemical process of the invention has the advantage of forming a cadmium sulfide 20 film which contains indium in solid solution. By choosing the proper concentration of the cadmium-indium alloy, the indium concentration in the cadmium sulfide, or otherwise cadmium telluride, etc., can be regulated.
Thus, it can be observed that thoee systems illustrated in Figures 6, 7, 8 and 9 are all effective in forming the desired photo-voltaic film material on the cathode. Moreover, in each of these systems, by changing the electrolyte it is possible to form a second film in the same manner as previously described. Thus, if the 30 two films are formed of the same material with one being of the N-type and the other being of the P-type, they will form a homojunction therebetween, and with different materials they will form a hetero~unction therebetween.
As also previously describedl the N-type region and the P-type region can be formed merel-y by adjustlng the stoichiometry of the components used. However, it is also possible to use any of several dopants in the two regions. Thus, one of the regions could be doped with indium, aluminum or gallium, etc., as donors, or with p hosphorus, arsenic or antimony, etc., as acceptors.
The present inventlon is primarily effective for use in produclng cathodically formed films with cadmium and zinc ions and sulfur, tellurium and selenium ions. In addition, mixed crystals of the types Cd(S,Se), Cd(S,Te), Cd(Se,Te), Cd,Z~(Te), Cd,Hg(Te) and Cd,Mg(Te), etc., can be produced. Thus, any combination of mixed crystals formed of ions of cadmlum, mercury, magnesium, zinc and any form o~ mixed crystals, as, for example, those formed of ions of sulfur, selenium and tellurium may be produced by the present invention. These substances may be pure or doped with those donors or acceptDrs as previously described or any other form of effective and acceptable donor or accep-tor.
As indicated above, electrolytic deposition on a conducting cathode permits ions from both the metal and nonmetal components in the electrolyte to be simultaneously discharged at the cathode and formed a semiconductor com-pound material on the cathode. As also indicated, S02 may be used as the electrolyte in order to form a sulfide layer, as prevlously described. Cadm~um sulfate is also used in combination wlth the S02 in order to form the cadmium sulfide layer. When ~orming the various cadmium salt films as semiconductor compounds, various acids, such as ~2SeO3, H2S03 or H2TeO3 may be used, or otherwise the alkaline salts o~ these acids may be used with an 10771ti1 inert anode. In add-ltion, solutlons in acid of S02, SeO2 or TeO2 may be utilized with an inert anode. The compositlon of the deposited film is controlled through the composition of the electrolyte as described. Alter-natively, it is possible to use as an electrolyte a solu-tion o* S02, SeO2 or TeO2 in water with an anode of Cd (Cd,Zn), (Cd,Hg) or (Cd,Mg), etc.
The ions formed by the metal components, e.g., cadmium and zinc, and the ions formed by the nonmetal components, e.g., sulfur, selenium and tellurium, in solu-tion cannot necessarily be characterized as single cations and anions. Generally, the cadmium and zinc in solution will form single cations since they are generally posi-tively charged, e.g., Cd and Zn++. In many cases the nonmetal components provide ions, e.g., S and Se .
Tellurium, for example, can adopt several valence states as Te . However, TeO3= complex ions can be formed. More-over, Te~4 ions could be formed with TeO2 in hydrofluoric - acid. In this case, TeF4 would form which dissociates to produce Te~4 in solution.
The electrochemical principles which might be ; applicable to explain the plating of both the metal and nonmetal components as a semiconductor compound on the cathode are not fully understood. Nevertheless, it has been established that these components do plate out at the cathode to form a semiconductor compound. With re-spect to the ions of the metal components, these ions would normally be attracted to and discharged at the cathode. The reasons for the discharge of the ions of the nonmetal components is more complex.
The nonmetal components present ions in solution in the presence of hydrogen. Thus, for example, the non-metal components are introduced in an acid form, in most cases presenting~ an available source of hy~rogen. It has been theorized that the hydrogen in proximity to the cathode alds in the reduction of the nonmetal ions in proximity to the cathode. Thus, for example, TeO3= -~ 6H+
provides Te which are available at and become discharged at the cathode. Nevertheless, whlle the exact principles may not be fully understood, it has been established that the cathodic formation of the semiconductor compound material does occur.
The method for producing the photo-voltaic power cells of the present invention can also be effectively operated with a plurality of anodes, as illustrated in the arrangements of Figures 10 and 11. In this case, the method would also utilize a container 110, such as a beaker, equivalent to the container 100. Moreover, in the arrange-ment illustrated in Figure 10, a relatively inert cathode 112 as, for example, a cathode formed of glass with a conductive oxide coating, as shown, would also be utilized, along with a neutral anode 114 formed of an inert material as, for example, platinum as shown. In addition, a second anode 116 formed of cadmium would be utilized. The two anodes 114 and 116 are connected to the cathode 112 through a source of electrical current 118. Potentiometers 120 and 122 are respectively connected to the anodes 114 and 116 and to the source 118, in the configuration as illustrated in Figure 10. Also, the cathode 112, along with the anodes 114 and 116, are slso disposed in a suitable elec-trolyte 124, as those electrolytes heretofore described and as hereinafter described.
The anode 116 which is formed of cadmium may otherwise be a cadmium-plated anode. In like manner, the anode 116 could be formed of an alloy of cadmium with a desired dopant. Tellurium ions would be provided in , 1~77161 solut-lon as, for example, hy a tellurous acid composltion.
By carefully controlling the current flow to the respectlve anodes 11l~ and 116, it is possible to introduce cadmlum into solution fr~m the anode 116. In this way, the tellur-ium ions contained in the tellurous acid will be discharged at the cathode 112, and in like manner the cadmium entered into solution from the anode 116 will also be discharged at the cathode 112. In order to form cadmium sulfide or cadmium selenide, H2S03 would be used to form the cad-mium sulfide and H2SeO3 would be used to form the cadmiumselenide.
Again, a first layer could be formed on the cathode 112 or other inert cathode, and which would either constitute an N-type or P-type region according to the amount of cadmium introduced from the anode 116 into solu-tlon. The amount of cadmium introduced via the cadmium anode can be controlled by adJustment of the two potenti-ometers 120 and 122. Thereafter, a second layer could be formed on the first-mentioned layer in order to form either a P-type region or an N-type region which is oppo-site to the first deposited layer. In all cases where two anodes are employed in the arrangement as illustrated in Figure 10, or otherwise the arrangement illustrated in Figure 11 as hereinafter described, the ratio of the metal ion to the nonmetal ion or molecule in the compound which is deposited is determined by the currents flowing through the respective anodes to the single cathode. Moreover, it can also be observed that it is equally easy to provide semiconductor films with a homojunction as well as a hetero~unction. By merely changing the electrolyte to form the second layer, it will be possible to form the heterojunction materlals.

Figure 11 illustrates an arrangement whereby a , ., ~o ~7~6~ :
nonmetal anode 126 is used in place of the cadmium anode 116. Moreover, the electrolyte 124 would be replaced by an electrolyte 128 containlng cadmium ions in solution.
As indicated, the cadmium could be introduced in the solu-tion as, ~or example, from a solution of cadmium salts.
In accordance with this arrangement, it is possible t~
carefully control the amount of tellurium introduced into solution through adjustment of the respective potentio-meters 120 and 122.
The tellurium anode of Figure 11 could also be formed as an alloy with, e.g., antimony, phosphorus or arsenic, etc., to provide a dopant. In either case, the use of the two anodes provides a means to continually supply the mlnority component in order to slowly replenish the same in solution. ~eplenishing of the minority com-ponent, generally the more noble component, is usually required when there is a large ratio between the concen-trations of the ma~ority and minority components in the electrolyte. In the case where two anodes are not employed, and where a large ratio does exist, the minority component could be slowly add~d on a continued basis, as by dripping the same into the electrolyte, based on the ratio of de-pletion of the minority component.
In any of these embodiments illustrated in Figures 10 and 11 it is possible to provide the P-type region and N-type region by stoichiometrically adjusting the amount of cadmium with respect to the nonmetals, such as tellur-ium, selenium, sulfur, etc. Otherwise, it is posslble to introduce dopants into the solutions. In the more pre-ferred form, the dopant could actually be contained withinthe material formed in one o~ the anodes as an alloy there-of, as, for example, cadmlum-indium alloys as an anode.

With respect to the use of the three or more

-2~-.

1077~
electrodes, it should be understood that plating could occur on one of the electrodes, whlch may not constitute a cathode per se. By properly adjusting the components in the electrolyte and by adjusting the potentlal applied to the electrodes, it ls actually possible to perform anodic deposition and cathodic depositlon at the same time.
Figure 12 illustrates an arrangement with three electrodes wlth one of the electrodes 129 being formed of a sulfur-containing mater~al and the other of the electrodes 130 being formed of a cadmium-containing material. A third electrode 132 is also provided and is preferably of an inert material. Again, by mere adjustment of two poten-tiometers, e.g., the two potentiometers 120 and 122, it is possible to care~ully regulate the amount of cadmium and sulfur ions which are introduced into solution and which are discharged at the electrode 132 in order to form a cadmium sulfide film, as illustrated.
While cadmium sulfide has been described herein as an example, any of the other metal and nonmetal com-ponents could be used. Moreover, in this embodiment, theelectrodes cannot be defined as cathodes and anodes in the classical sense. By way of example, the electrode 129 could have, e.g., a negative 2-volt potential, the elec-trode 132 could have, e.g., a positive 2-volt potential, and the electrode 130 could have, e.g., a positive 4-volt potentlal. In this way, cadmium from the electrode 130 would be discharged and plate out on the electrode 132 through a cathodic process and sulfur from the electrode 129 would be discharged and plate out on the electrode 132 through an anodic process.
As used herein, the terms "inert" or "relatively inert", as, ~or example, with an "inert anode" or "inert cathode", refer to a material which is inert with respect 107~16~
to the reactants being employed. Thus, in the case of an inert cathode, such as a nickel cathode, the cathode would be inert and nonreactive with respect to the electrolyte or any of the ions introduced therein in order to for~ the semiconductor film on the cathode.
The present invention is highly effective in obtaining relatively thin films by use of the electro-chemical technlques described herein. In this instance, films with a thickness ranging from about 0.1 micron to about 40 microns and larger can be obtained as described above. Thus, the use of the term "thin" or "relatively thin" with respect to the film thickness will be based on film thicknesses within the range of about 0.1 micron to about 40 microns, or perhaps greater.
While the present invention is effective with those materials described above, and which can be made in accordance with the processes of the present invention, one of the most effective materials thus found for use in the production of the photo-voltaic cells is that formed of cadmium telluride. It has been found that photo-voltaic cells based on P-N homojunctions have an expected energy conversion efficiency that is a function of the band-gap of the material used with the optimum band-gap occurring near approximately 1.5eV. Moreover, it has been found that cadmium telluride provides a band-gap in this range.
In addltion, the cadmium telluride provides a reasonably high efficiency and also a lower cost with respect to other materials which might be employed. Cadmium telluride is also stable in air, is nontoxic and can withstand temperature variations of several hundred degrees above and below ambient temperatures without decomposing. More-over, cadmium telluride is preferred inasmuch as it is neither deliquescent nor hygroscopic, and furthermore is ~.o77~
not subJect to d.isproportionation uncler conditions of expected terrestrial operation.
Figure 13 illustrates the st;eps employed in the method of producing 'he photo-voltaic power cells in accordance with the present invention. These steps were actually delineated in connection with the previous de-scription. However, referring to Figure 13, lt can be observed that a metal cathode is introduced into the electrolyte and an anode is introduced into the electro-lyte. The meth~ includes the formation of molecules orions of the nonmetallic component in the electrolyte and the formation of ions of the metallic component in the e lectrolyte. As indicated previously, these ions could be introduced into solution in several different ways, and the ions of both components would be discharged at the cathode during the application of the electric field.
Both ions and molecul~s can migrate to the cathode, and upon application of the electric field they are discharged and form a coatlng ln the form of a compound semiconductor, as previously described. As indicated above, the coating would be firsk formed with a f~rst region such as an N-type region or a P-type region. The coating would then be provided with a second region which is the opposite of the first region.
Finally, in the making of the photo-voltaic power cells, conductive terminals could be applied to both the N-region and the P-region. Otherwise, these terminals could be applied to layers in contact with the N-region and the P-region in connection with the embodiments illus-trated in Figures 3 and ~ of the drawings.
One of the unique results which can be obtainedin accordance with the present invention is that either a homo~unction or a heteroJunction can be established between the P~t-~pe regiorl and che N-t~Tpe region. In this way, problems of material waste and impurities are sub-stantially reduced, and almost completely eliminated.
Furthermore, all of the heretofore required stringent control procedures used in the formation of photo-voltaic cells and similar semiconductor materials can be com-pletely obv-lated.
Another one of the unique aspects of the present invent-lon is that the reactions heretofore described may be carried out or close to room temperature. Moreover, and as lndicated, the processes described herein result in very little, if any, waste material. In addition, the processes can be carried out with very little concentra-tions of the required ions.
It should be understood that each of the photo-voltaic power generating means described above do not operate on the basis of a galvanic cell and, hence, do not require the need of an electrolyte in their operation.
Moreover, in order to obtain a greater efficiency of electron travel across the surface of the cell, it is possible to use a conductive coating, such as a trans-parent electrolyte coating or any other form of trans-parent electrolytic gel, for transference of the gener-ated electrons to the electrical contact as, for example, in connection with the embodiment illustrated in Figure 4.
The configuration and method of fabrication of the photo-voltaic power generating means in accordance with the present invention lend themselves to continuous processes of production of substantial lengths and areas 30 of such power generating means. In many applications, ~ -power generating means may be wound upon a roller or other storage means and simply laid out as a sheet or surface covering areas exposed to light, such as roofs -- ~077~
and walls e~posed to solar radiation.
Thus, there has been illustrated and described novel photo-voltaic power generat-lng means and methods of use and methods of fabricaking such power generating means with a relatively high degree of efficiency and which fulfill all of the ob'ects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the power generating means and methods described herein will become apparent to those skilled in the art after consldering this specification and the accompanying drawings. All such changes, modi-flcations, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the following claims.

, . ~: .

Claims (36)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of preparing a photo-voltaic power generat-ing cell comprising the step of depositing electrochemically on an electrode a coating of at least one semiconductor compound from an electrolytic bath including the components of said semi-conductor compound, said compound being capable of forming a semiconductor junction, being transmissive to light radiation and being capable of forming electron-hole pairs upon being irradiated with photons, said components being formed of at least one of the metal elements of Class IIB and non-metal elements of Class VIA
of the Periodic Table of Elements.

2. The method as claimed in Claim 1, wherein said electrode is a metal and said junction is between said metal electrode and said semiconductor compound.

3. The method as claimed in Claim 1, wherein said electrode is a substrate having a conductive coating of a semi-conductor material of a first conductivity type, said semicon-ductor compound being of the opposite conductivity type and said junction is between said conductive coating and said semiconduc-tor compound.

4. The method as claimed in Claim 3, wherein said conductive coating is transmissive to light radiation.

5. The method as claimed in Claim 3, wherein said conductive coating is n-type and said semiconductor compound is p-type.

6. The method as claimed in Claim 3, wherein said conductive coating is p-type and said semiconductor compound is n-type.

7. The method as claimed in Claim 1, further including depositing the semiconductor compound material so that it forms a first layer of a first conductivity type and subsequently deposit-ing a second layer of the opposite conductivity type, said junc-tion being between said layers.

8. The method as claimed in Claim 7, wherein said first layer is n-type and said second layer is p-type.

9. The method as claimed in Claim 7, wherein said first layer is p-type and said second layer is n-type.

10. The method as claimed in Claim 1, wherein at least a portion of the metal and non-metal components are provided from materials dissolved in said electrolytic bath.

11. The method as claimed in Claim 1, wherein at least a portion of the metal and non-metal components is provided from an additional electrode immersed in said electrolytic bath.

12. The method as claimed in Claim 1, further including the step of forming the semiconductor compound of a selected conductivity type by depositing an increased concentration of the corresponding metal element or non-metal element, depending on the selected conductivity type.

13. The method as claimed in Claim 1, further including forming the semiconductor compound material of a selected conduc-tivity type by codepositing with it a doping impurity of the donor or acceptor type corresponding to the selected conductivity type.

14. The method as claimed in Claim 1, further including forming the semiconductor compound having a selected conductivity type by depositing an increased concentration of the correspond-ing metal element or non-metal element and codepositing with it a corresponding doping impurity of the donor or acceptor type, depending on the selected conductivity type.

15. The method as claimed in Claim 1 for forming a photo-voltaic cell on an electrically conductive semiconductive substrate of a first conductivity type, wherein said depositing step includes: immersing the substrate into an electrolytic bath including a highly acid solution of cadmium sulfate; providing an anode having at least a surface layer of tellurium; applying a voltage between the anode and the substrate forming a cathode, the voltage being negative between the cathode and a standard reference electrode; and continuing the plating process until a first thin polycrystalline cadmium telluride layer of said first conductivity type is deposited.

16. The method as claimed in Claim 15, wherein the substrate is of the n-type and consists of indium tin oxide, and wherein the first conductivity type is the n-type.

17. The method as claimed in Claim 16, wherein the electrolytic bath includes an n-type donor impurity for codepo-sition with the n-type cadmium telluride.

18. The method as claimed in Claim 17, wherein the n-type donor impurity consists of indium sulfate.

19. The method as claimed in Claim 16, wherein the substrate is of the p-type and consists of antimony doped tin oxide, and wherein the first conductivity type is the p-type.

20. The method as claimed in Claim 19, wherein the electrolytic bath includes a p-type acceptor impurity for code-position with the p-type cadmium telluride.

21. The method as claimed in Claim 15, further includ-ing the following additional steps: providing an additional electrolyte including cadmium sulfate and an active impurity of the opposite conductivity type; immersing the substrate and the first cadmium telluride layer in the additional electrolyte; and applying a negative voltage with respect to a standard reference electrode between the cathode and anode, the applied voltage being different from that utilized for depositing the first cadmium telluride layer, thereby to deposit a second thin poly-crystalline cadmium telluride layer of the opposite conductivity type, whereby an n-p junction is formed between the first and second cadmium telluride layers to provide a homojunction device.

22. The method as claimed in Claim 21, wherein the substrate is of the n-type and consists of indium tin oxide and wherein the first conductivity type is the n-type, and wherein the additional electrolyte includes a p-type acceptor impurity and wherein the second cadmium telluride layer is of the p-type.

23. The method as claimed in Claim 22, wherein the plating voltage for the first cadmium telluride layer between the cathode and the standard reference electrode is more negative than that applied between the cathode and the standard reference electrode for the second cadmium telluride layer, whereby more tellurium and less cadmium is deposited for the second layer than for the first layer.

24. The method as claimed in Claim 22, wherein the p-type acceptor impurity consists of arsenide pentoxide.

25. The method as claimed in Claim 16, further includ-ing the steps of: removing the n-type cadmium telluride layer from the influence of the electric voltage whereby a thin p-type layer is formed; subjecting the thus formed p-type layer to the influence of a p-type acceptor in the electrolytic bath without applying a voltage thereto; and electroplating a thin tellurium layer onto said p-type layer from an electrolyte including sodium sulfate without any doping impurities by applying a negative voltage for a time sufficient to create a tellurium layer having a predetermined thickness at a very acid pH.

26. The method as claimed in Claim 25, wherein the p-type acceptor for the formation of the p-type layer consists of arsenide pentoxide.

27. The method as claimed in Claim 1 for manufacturing a Schottky barrier photo-voltaic device, wherein said depositing step includes: immersing a metal substrate into an electrolytic bath including cadmium sulfate and serving as a cathode; pro-viding an anode in the bath having at least an outer coating of tellurium; maintaining the electrolytic bath at an acid pH; and applying a voltage between the cathode and the anode, a negative voltage being measured between the cathode and a standard refer-ence electrode, the voltage being so selected with respect to the pH that the deposited cadmium telluride consists of a predeter-mined ratio of cadmium to tellurium to deposit a predetermined conductivity type layer, the deposition being continued until a thin polycrystalline cadmium telluride layer of predetermined thickness is deposited.

28. The method as claimed in Claim 27, wherein the cadmium telluride layer is of the n-type and is obtained by depositing more cadium than tellurium.

29. The method as claimed in Claim 28, wherein an n-type donor impurity is introduced into the electrolytic bath for codeposition with the cadmium telluride.

30. The method as claimed in Claim 29, wherein the n-type donor impurity consists of indium sulfate.

31. The method as claimed in Claim 27, wherein the deposited cadmium telluride layer is of the p-type and consists of less cadmium than tellurium.

32. The method as claimed in Claim 31, wherein a p-type acceptor impurity is introduced into the electrolytic bath for codeposition with the p-type cadmium telluride.

33. The method as claimed in Claim 32, wherein the p-type acceptor impurity consists of arsenide pentoxide.

34. The method as claimed in Claim 1 for depositing a photo-voltaic cell on an electrically conductive n-type semi-conductive substrate consisting of indium tin oxide, wherein said depositing step includes: immersing the substrate into an electro-lytic bath including a highly acid solution of cadmium sulfate;
providing an anode having at least a surface layer of tellurium;
applying a plating voltage between the anode and the substrate forming the cathode, the voltage being negative between the cathode and a standard reference electrode; and continuing the plating process until a thin polycrystalline cadmium telluride layer of p-type conductivity is deposited, and further including the steps of: immersing the p-type cadmium telluride layer into an electrolytic bath including a highly acid solution of cadmium sulfate and sodium sulfate; and electro-plating a thin tellurium layer of the p-type onto said p-type cadmium telluride layer for a predetermined period of time to create a tellurium layer of predetermined thickness.

35. The method as claimed in Claim 34, wherein a p-type acceptor impurity is added to the electrolytic bath for plating the p-type cadmium telluride layer.

36. The method as claimed in Claim 34, wherein the p-type acceptor impurity consists of arsenide pentoxide.