SE451353B - PHOTO-SENSITIVE, AMORFT MULTI CELLS - Google Patents

Description

451 353 PN transitions are required.

These crystal culture processes yield such relatively small crystals that solar cells require the composition of many single crystals to cover the desired area for only a single solar cell panel. The amount of energy required to produce a solar cell in this process, the limitation caused by the size limitations of silicon crystal, and the necessity of cutting and assembling such a crystalline material have all resulted in an impossible economic obstacle to large-scale use of crystalline semiconductor crystals. cells for energy conversion. Crystalline silicon also has an indirect optical edge, which results in poor light absorption in the material. Due to the poor light absorption, crystalline solar cells must be at least 50 μm thick to absorb the incident sunlight. Even if the single crystal material is replaced by polycrystalline silicon with cheaper manufacturing processes, the indirect optical edge still remains, so the material thickness is not reduced. The polycrystalline material also includes the addition of grain boundaries and other problematic defects.

A further disadvantage of the crystalline material for solar applications is that the band gap of crystalline silicon of approximately 1, l is itself below the optimal band gap of approximately 1.5 eV. Although admixture of germanium is possible, it narrows the band gap, further reducing the sunlight conversion efficiency.

In summary, crystalline silicon devices have fixed parameters, which are not variable in the desired manner, require large amounts of material, can only be produced with relatively small areas and are expensive and time-consuming to produce. Amorphous silicon-based devices can eliminate these disadvantages of crystalline silicon. Amorphous silicon has an optical absorption edge with properties similar to those of a direct gap semiconductor, and only a material thickness of 1 μm or less is necessary for absorbing the same amount of sunlight as crystalline silicon with a thickness of 50 um. Furthermore, amorphous silicon can be produced faster, easier and with larger areas than crystalline silicon can. "Consequently, considerable effort has been made to develop processes for easily depositing amorphous semiconductor alloys or films, each of which may, if desired, comprise relatively large areas, limited only by the size of the deposition equipment, and which could be easily doped to form P-type and N-type materials, then the production of PN transducers, which are equivalent to those produced by their crystalline counterparts. For many years this work was largely unsuccessful. Amorphous silicon or germanium films (group IV) are normally four-fold coordinated and were found to have microscopic cavities and "dangling" bonds as well as other defects, which give a high density of local states in their energy gap. The presence of high density of local conditions in the energy gap of amorphous silicon semiconductor films results in low-grade photoconductivity and short life for charge carriers, making these films unsuitable for photosensitive applications. In addition, these films cannot be successfully doped or otherwise modified to shift Fermi levels close to the conduction or valence bands, making them unsuitable for fabricating PN junctions for solar cell and current regulator applications.

In an attempt to minimize the above-mentioned problems associated with amorphous silicon and germanium, W.B. Spear and P.G. Le Comber at the Carnegie Laboratory of Physics, University of Dundee, Dundee, Scotland, some work on "Substitutional Doping of Amorphous Silicon", as reported in an article published in Solid State Communications, Vol. 17, page ll93- -ll96, 1975, in order to reduce the local conditions 451 353 4 in the energy gap in amorphous silicon or germanium in order to make them more closely mimic self-conducting, crystalline silicon or germanium and to substitute in a substitute way the amorphous materials with suitable, classical doping means, such as in the doping of crystalline materials, to make them pertinent and P- or N-type conductive.

The reduction of the local conditions was accomplished by glow discharge deposition of amorphous silicon films, passing a silane gas (SiH 4) through a reaction tube, where the gas was decomposed by a radio frequency glow discharge and deposited on a substrate at a substrate temperature of about 500-600 ° K (227 ° C). 327 ° C).

The material so deposited on the substrate was a self-conducting amorphous material, consisting of silicon and hydrogen.

To produce a doped amorphous material, a phosphorus gas (PH3) for N-type conductivity or a diborane gas (BZHS) for P-type conductivity was mixed in advance with the silane gas and passed through the glow discharge reaction tube under the same operating conditions.

The gas concentration of the dopants used was between about 5x10 6 and 10-2 parts by volume. The material thus deposited probably contained substituting phosphorus or table tops and was shown to be an interfering conductor and an N- or P-type conductor.

Although these researchers did not know it, it is now known from the work of others that the hydrogen in the silane at an optimum temperature combines with many of the "dangling" bonds in the silicon during the glow discharge deposition to significantly reduce the density of local conditions in the energy gap. purpose of bringing the electronic properties of the amorphous material closer to the properties of the corresponding crystalline material.

D.I. Jones, W.E. Spear, P.G. Le Comber, S. Li and R. Martins also worked on the production of a-Ge: H from GeH4 using similar deposition techniques. The material obtained testified to a high density of local conditions in the energy gap of the material. Although the material could be doped, the efficiency was significantly reduced relative to that which could be achieved with a-Si: H. In this work, reported in Philsophical Magazine B, Vol. 39, page 147 (1979), the authors conclude that due to the high density of gap states, the material obtained is ".... a less attractive material than a-Si for doping experiments and possible applications". .

In working with a similar method for glow discharge fabricated amorphous silicon solar cells utilizing the silane, D.E. Carlson to use germanium in the cells to narrow the optical gap to the optimal solar cell value of about 1.5 eV in his best, manufactured solar cell material, which has a band gap of 1.65 - 1.70 eV. (DE Carlson, Journal of Non Crystalline Solids, Vol. 35 and 36 (1980), pp. 707-717, presented at the 8th International Conference on Amorphous and Liquid Semi-Conductors, Cambridge, Mass., 27-31 August 1979) . Carlson has further stated, however, that the addition of germanium from germangas was not successful, as it causes significant reductions in all the photovoltaic parameters of the solar cells. Carlson stated that the deterioration of the photovoltaic properties suggests that defects in the energy gap are created (D.E. Carlson, Tech. Dig. 1977 IEDM, Washington, D.C., p. 214).

The idea of using several cells to increase the efficiency of the photovoltaic device was discussed at least as early as 1955 by E.D. Jackson, U.S. Patent 2,949,498. The multicellular structures discussed utilized PN transitions having crystal in the deposited films. semiconductor devices, but the amplification ideas are similar to C regardless of whether amorphous or crystalline devices are used.

The idea is essentially to use ballasts with different bandgaps to more efficiently collect different parts of the solar spectrum and raise Voc. The stacked cell 451 353 \ 6 has two or more cells, the light being passed serially through each cell and a large bandgap material being followed by a smaller bandgap material for absorbing the light passed through the first cell or the first. the layer. Many articles on crystalline stacked cells have been reported after Jackson, and more recently several articles have been published which deal with materials a-Si: H utilized in stacked cells. Marfaing proposed the use of silane-deposited amorphous Si-Ge alloys in stacked cells but did not report that it was possible to do so (Y. Marfaing, Proc.

Znd European Communities Photovoltaic Solar Energy Conf., Berlin, West Germany, pp. 287, 1979).

Hamakawa et al reported the possibility of using a-Si: H in a configuration, which is to be defined here as a multiple cell of cascade type. The cascade cell is hereinafter referred to as a multiple cell without separation or isolation layers between each of the cells. Each of the cells was made of a-Si: H- material with the same bandgap in a PIN transition configuration. Attempts to adjust the short-circuit current (Jsc) were made by increasing the thickness of the cells in the serial light path. As expected, the total Voc of the device increased and was proportional to the number of cells.

In a recent report on increasing the cell efficiency of several transitions exhibiting (stacked) solar cells of amorphous silicon (a-Si: H), deposited from the silane in the above-mentioned manner, it was reported that "[g] ermanium has been found to be a harmful contamination in a-Si: H, which lowers its Jsc exponentially with increasing Ge .... "From their work as well as Carlsons, Marfaings and Hamakawas, they concluded that alloys of amorphous silicon, germanium and hydrogen" have been shown to have poor photovoltaic properties "and thus new photovoltaic film cell materials must be found which have spectral response at about 1 μm for efficient stacked cell combinations l5 4s1" 3ss 7 (JJ Hanak, B. Faughnan, V. Korsun and JP, Pellicane, presented at the 14th IEEE Photo- voltaic Specialists Conference ", San Diego, California, January 7-10, 1980).

The inclusion of hydrogen in the above process not only has limitations due to the solid ratio of hydrogen to silicon in the silane, but also different Si: H ions with a-Si: H ".binding configurations also introduce, which is of paramount importance New anti-binding conditions, which can have harmful consequences in these materials, Perhaps most importantly, hydrogen cannot compensate or remove defective conditions caused by the introduction of germanium into the alloy. There are therefore fundamental limitations in reducing the density of local conditions in these materials, which are particularly harmful in terms of effective P- as well as N-doping.The resulting state density in silane-deposited materials leads to a narrow depletion width, which in turn limits the efficiencies of solar cells and other devices, whose work N is dependent on the operating motion of free charge carriers.

The method of producing these materials by using only silicon and hydrogen also results in a high density of surface conditions, which affect all the above-mentioned parameters. Although previous attempts to reduce the band gap of the material were successful in reducing the gap, they have at the same time added condition to the gap.

The increase in condition in the bandgap results in a reduction or total loss of photoconductivity and is thus a decrease in productivity in the production of photosensitive devices.

After the glow discharge deposition of silane gas silicon gas was developed, work was performed on sputtering deposition of amorphous silicon films in the atmosphere of a mixture of argon (required by the sputtering deposition process) and molecular hydrogen to determine the results of this molecular hydrogen on the amorphous properties of the amorphous hydrogen. silicon films. This 451 353 '8 research suggested that hydrogen acted as a compensatory agent, which was bound in such a way that it reduced the local conditions in the energy gap. However, the degree to which the local state of the energy gap was reduced in the sputtering deposition process was "much less than that obtained by the silane deposition process described above. The P and N dopant gases described above were also introduced in the sputtering process to produce P and N-doped materials.

These materials had a lower doping efficiency than the materials generated in the glow discharge process.

Neither process produced effective P-doped materials with sufficiently high acceptor concentrations for the production of commercial PN or PIN junction devices. The N-doping efficiency was below the desired acceptable commercial levels and the P-doping was particularly undesirable, as it reduced the bandgap width and increased the number of local conditions in the bandgap.

The earlier deposition of amorphous silicon, which has been modified with hydrogen from the silane gas in an attempt to make it more closely mimic crystalline silicon and which has been doped in a manner similar to that for crystallization of crystalline silicon, has properties which in all significant respects are worse than those of doped crystalline silicon. Insufficient doping efficiencies and conductivity were thus achieved especially in the P-type material, and the photovoltaic properties of these silicon films left much to be desired.

Significantly improved amorphous silicon alloys with significantly reduced concentrations of local states in the energy gap of the alloys as well as high quality electronic properties have been produced by glow discharge, as fully described in U.S. Pat. No. 4,226,898, and by vapor phase deposition, as fully described in U.S. Pat. .

As disclosed in these patents, fluorine is introduced into the amorphous silicon semiconductor to substantially reduce the density of local conditions therein.

Activated fluorine diffuses particularly easily into and binds to the amorphous silicon in the matrix backbone, substantially to reduce the density of local fault conditions therein, since the small size of the fluorine atoms allows them to be easily introduced into the amorphous backbone.

The fluorine binds to the dangling bonds of the silicon and forms what is believed to be a partially ionic stable bond with flexible bonding angles, which results in a more stable and more effective compensation or change than that formed by hydrogen and other compensating or changing agents. Fluorine is considered to be a more effective, compensating or altering substance than hydrogen, when used alone or in combination with hydrogen, due to its unparalleled small size, high reactivity, chemical bond specificity and highest electronegativity. Fluorine is thus qualitatively different from other halogens and is thus considered a superhalogen.

As an example, compensation can be achieved with fluorine alone or in combination with hydrogen with the addition of the substance or substances in very small amounts (eg fractions of 1 atom%). However, the amounts of fluorine and hydrogen that are most desirable to use are much larger than these small percentages, so that a silicon-hydrogen-fluorine alloy is formed. These alloying amounts of fluorine and hydrogen can, for example, be in the range of 1 - 5% or greater.

It is probable that the new alloy thus formed has a lower density of defective states in the energy gap than is achieved by merely neutralizing dangling bonds and similar defective states. This greater amount of fluorine is believed to particularly significantly participate in a new structural configuration of an amorphous silicon-containing material and facilitates the addition of other alloying materials, such as germanium. In addition to its other properties mentioned above, it is likely that fluorine organizes the local structure in the silicon 451 353 f containing the alloy by inductive and ionic effects. It is probable that fluorine also has an effect on hydrogen bonding by having a beneficial effect in reducing the density of defective conditions, to which hydrogen contributes at the same time as it acts as a state density-reducing substance. The ionic role that fluorine plays in such an alloy is believed to be a significant factor expressed in relation to the nearest neighbor.

The non-optimal spectral response of the prior art amorphous photosensitive silicon devices is overcome in accordance with the present invention by arranging bandgap-adjusted, amorphous, photosensitive alloy cells for adjusting the device's bandgap to the optimum usage characteristics for particular applications of essential applications. conditions in the gap. The high-quality electronic properties of the material are thus not significantly affected by the formation of the new, bandgap-adjusted multicellular devices.

The amorphous alloys include at least one state density reducing agent, fluorine. The compensating or changing substance, fluorine, and / or other substances may be added during the sale or thereafter.

The adjusting substance (s) can be activated and can be added during vapor deposition, sputtering or glow discharge processes. The bandgap can be adjusted as needed for a particular application by introducing the required amount of one or more adjusting substances into the deposited alloy cells, at least in their photocurrent generation area for at least some of the cells of the device.

The band gap of the cells is adjusted without a significant increase in the number of states in the band gap of the alloy due to the presence of fluorine in the alloy. The previously silane-deposited films are typically deposited on substrates heated to 250-350 ° C to maximize the incorporation and compensation of silicon with hydrogen in the films.

The previous attempts to add germanium to this film failed because the hydrogen-germanium compound is too weak to be stable in the required temperature for deposition on the substrate.

The presence of fluorine in the alloy of the invention provides a silicon alloy which differs physically, chemically and electrochemically from other silicon alloys in that fluorine not only covalently binds but also positively affects the structural alignment of the material. This allows adjusters, such as germanium, tin, carbon or nitrogen, to be effectively added to the alloy, as fluorine forms stronger and more stable bonds than hydrogen does. Fluorine compensates or changes silicon as well as germanium and due to the silicon without the other band-adjusting substance (s) in the alloy more efficiently than hydrogen due to the stronger, more thermally stable bonds and more flexible bond configurations due to the ionic nature of the fluorine bond . The use of fluorine provides the alloy or film described in U.S. Patent No. 4,217,374, in which the state density of the band gap is much lower than that provided by a combination of silicon and hydrogen, such as from silane. Because the band-adjusting substance or substances are tailored to the cells without the addition of significant harmful conditions due to the action of fluorine, the new cell alloy retains high-quality electronic properties and photoconductivity when the adjustable substance (s) are added to adapt the device's wavelength characteristics. application. Hydrogen further improves the fluorine-compensated or altered alloy and can be added during deposition together with fluorine or after deposition, as is the case with fluorine and other altering substances. The inclusion of hydrogen after deposition is advantageous, as it is desired to utilize the higher substrate temperatures for deposition allowed by fluorine.

Although the principles of the present invention apply to each of the above-mentioned deposition processes, a vapor and a plasma-activated vapor deposition environment are described herein for illustrative purposes. The glow discharge system disclosed in U.S. Patent No. 4,226,898 has other process variables which can be advantageously utilized in conjunction with the principles of the present invention.

Accordingly, a first object of the present invention is to provide an improved, photosensitive, amorphous multicellular device having at least two cells, each comprising an alloy comprising silicon and at least one state density reducing agent, which is fluorine, the device being characterized in that each cell alloy a bandgap adjusting substance is included without significantly increasing the state of the gap, each such cell alloy having a bandgap, which is adjusted for a particular photosensitivity wavelength * function, distinct from any other cell alloy.

A second object of the present invention is to provide an improved, photosensitive multicellular device comprising at least two superimposed cells of different materials, at least one cell comprising an amorphous semiconductor multilayer alloy having an active photosensitive region having a bandgap! and which may be struck by radiation to provide charge carriers, the alloy comprising at least one state density reducing substance which is fluorine, the device being characterized in that the alloy further comprises a bandgap adjusting substance at least in the photosensitive region to enhance its radiation absorption without significantly increase the states 1 in the gaps, and the band gap of the alloy is adjusted for a special photosensitivity wavelength function, which differs from the other cell. The preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings. Fig. 1 is a schematic view of more or less conventional vacuum deposition equipment, to which substances have been added for carrying out the addition of fluorine (and hydrogen) by the addition of molecular fluorine or fluorine containing fluorine compounds, such as SiF 4, and hydrogen inlets as well as generating units for activated fluorine and hydrogen, which units decompose the molecular fluorine and hydrogen in the evacuated space of the vapor deposition equipment to convert the molecular fluorine and hydrogen to activated fluorine and hydrogen and conducting one or both to the substrate during the deposition of an amorphous alloy containing silicon . Fig. 2 illustrates vacuum deposition equipment similar to that shown in Fig. 1, together with activated fluorine (and hydrogen) generating means, which means comprise a source of ultraviolet light which irradiates the substrate during the process of depositing the amorphous alloy. this light source replacing the generator units for the activated fluorine and hydrogen shown in Fig. 1 as well as the means for generating the adjusting substance. Fig. 3 illustrates the vacuum deposition equipment in Fig. 1, to which additional means have been added for doping the deposition alloy with a material which provides N- or P-conductivity. Fig. 4 illustrates an application where the deposition of amorphous alloy and the addition of the activated fluorine and hydrogen can be carried out as separate steps and in separate casings. Fig. 5 illustrates an exemplary apparatus for diffusing activated hydrogen into a previously deposited amorphous alloy.

Fig. 8 is a fragmentary cross-sectional view of multi-cell devices with stacked cells according to the present invention, which means comprises a plurality of Schottky barrier solar cells, each having an amorphous photosensitive semiconductor alloy according to the present invention. Fig. 9 is a fragmentary cross-sectional view of a toothed or cascade type multicellular device comprising a plurality of Schottky barrier solar cells, each comprising an amorphous semiconductor alloy of the present invention. Fig. 10 is a fragmentary cross-sectional view of a multi-cell device with stacked cells, which means comprises a plurality of PIN solar cells, each comprising an amorphous semiconductor alloy according to the present invention.

Fig. 11 is a fragmentary cross-sectional view of a tandem or cascade type multicellular device, including a plurality of PIN solar cells, each comprising an amorphous semiconductor alloy according to the present invention. Fig. 12 is a schematic view of a plasma-activated vapor deposition system for depositing the amorphous alloys together with the adjusting substance or substances according to the invention, which are incorporated in the alloys. Pig 13 is a solar spectrum radiation diagram illustrating the normal sunlight wavelengths available for various photosensitive applications.

Fig. 1, to which reference is now made in particular, shows an equipment 10 for deposition from the vapor phase, which equipment may be conventional vapor deposition equipment, to which are added means described below for injecting activated compensating or changing material. As illustrated, this equipment includes a glass bell 12 or similar housing enclosing an evacuated space 14 in which is located one or more crucibles, such as a crucible 16, which contains the amorphous film-producing semiconductor blank or blanks. to be deposited on a substrate 18. In the described form of the invention, the crucible 16 initially contains silicon to form an amorphous alloy containing silicon on the substrate 18, which may be, for example, a metal, a crystalline or polycrystalline semiconductor or other material. on which it is desired to form the alloy cells of the present invention. An electron beam source 20 is provided adjacent the crucible 16, which schematically damaged electron beam source usually includes a filament and beam deflection means (not shown) which direct an electron beam toward the silicon in the crucible 16 to vaporize it.

A high voltage direct current source 22 supplies a suitably high voltage, for example 10 000 V DC, the positive connection of the source being connected via a control unit 24 and a conductor 26 to the crucible 16. The negative connection of the current source is connected via the control unit 24 and a conductor 28 to the filament of the electron beam source 20.

The control unit 24 comprises relays or the like for interrupting the connection between the current source 22 and the conductors 26 and 28, when the film thickness of an alloy deposition sensing unit 30 in the evacuated space 14 reaches a given value, which is set by actuation of a manual control means 32 on a control panel 34 of the control unit 24. The alloy sensing unit comprises a cable 36 extending to the control unit 24, which comprises well known means for responding to both the thickness of the alloy deposited on the alloy sensing unit 30 and the rate of alloy deposition. A manual control means 38 on the control panel 34 may be provided to determine the desired rate of deposition of the alloy controlled by the value of the current supplied to the filaments of the electron beam source via a conductor 40 in a well known manner.

The substrate 18 is supported on a substrate holder 42, on which a heater 44 is mounted. A cable 46 supplies drive current to the heater 44, which controls the temperature of the substrate holder 42 and the substrate 18 in accordance with a temperature setting determined by a manual control means 48 on the control panel 34 of the control unit 24.

The clock 12 is shown as extending upwardly from a support base 50, from which the various cables and other connections to the components within the clock 12 may extend. The support base 50 is mounted on a housing 52, which is connected to a line 54, which is connected to a vacuum pump 56. The vacuum pump 56, which can operate continuously, evacuates the space 14 inside the clock 12. The desired the pressure in the clock is set by means of a control knob 58 on the control panel 34.

In this form of the invention, this setting controls the pressure level at which the flow of activated fluorine (and hydrogen) is regulated into the 12 o'clock clock. If the control knob is set to a clock pressure of 10-4 torr, then the flow of fluorine (and hydrogen) will into the clock 12 to be such that this pressure is maintained in the clock as the vacuum pump 56 continues to operate.

Sources 60 and 62 for molecular fluorine and hydrogen are shown connected via lines 64 and 66, respectively, to the control unit 24. A pressure sensor 68 at clock 12 is connected by means of a cable 70 to the control unit 24. Flow valves 72 and 74 are controlled by the control unit 24 for maintaining the set pressure in the watch. Lines 76 and 78 extend from the control unit 24 and pass through the support base 50 into the evacuated space 14 of the bell 12. Lines 76 and 78 are connected to the units 80 and 82 for generating activated fluorine and hydrogen, which units convert the molecular fluorine respectively. hydrogen to activated fluorine and hydrogen, which may be atomic and / or ionized forms of these gases.

The activated fluorine and hydrogen generating units 80 and 82 may be heated tungsten wires which raise the molecular gases to their decomposition temperatures, or a plasma generating unit which is well known in the art for producing a plasma of decomposed gases. Activated fluorine and hydrogen in ionized forms, formed by plasma, can also be accelerated and injected into the depositing alloy by applying an electric field between the substrate and the activating source. In either case, the activated fluorine and hydrogen generating units 80 and 82 are preferably located in the immediate vicinity of the substrate 18, so that the relatively short-lived activated fluorine and hydrogen emitted from the units are immediately injected. in the vicinity of the substrate 18, where the alloy is deposited.

As previously stated, at least fluorine will be included in the alloy and hydrogen will also preferably be included. The activated fluorine (and hydrogen) as well as other compensating or altering substances can also be produced from compounds containing the substances, instead of from a source of molecular gas.

For the production of useful amorphous alloys which have the desired properties for use in photosensitive multicellular devices, such as photoreceptors, solar cells, PN junction current regulators, etc., as previously stated, the compensating or altering agents, materials or substances provide a very low density. of local states in the energy gap without changing the basic self-conducting property of the film. This result is achieved with relatively small amounts of activated fluorine and hydrogen, so that the pressure in the evacuated bell space 14 can still be a relatively low pressure (such as 10-4 torr). The gas pressure in the generator can be higher than the pressure in the clock by adjusting the size of the generator outlet.

The temperature of the substrate 18 is adjusted to obtain the maximum reduction in the density of local conditions in the energy gap for the amorphous alloy in question. The surface temperature of the substrate will generally be such as to ensure high mobility of the depositing materials, and preferably a temperature below the crystallization temperature of the depositing alloy.

The surface of the substrate can be irradiated with radiant energy to further increase the mobility of the depositing alloy material, for example by mounting a source of ultraviolet light (not shown) in the clock space 14. Instead of the generator units 80 and 82 for activated fluorine and hydrogen in Fig. 1, these units may alternatively be replaced by a source 84 of ultraviolet light, shown in Fig. 2, which source directs ultraviolet energy towards the substrate 18. This ultraviolet light will decompose the molecular fluorine (and hydrogen) both separately from and at the substrate 18 to form activated fluorine (and hydrogen), which diffuses into the depositing amorphous alloy, which is condensed on the substrate 18. The ultraviolet light also improves the surface mobility of the depositing alloy material.

In Figs. 1 and 2, the bandgap adjusting blanks can be added in gaseous form in an identical manner to the fluorine and hydrogen by replacing the hydrogen generator 82 or by adding one or more generators 86 and 88 (Fig. 2) for activated adjusting blank. Each of these generators 86 and 88 will typically be dedicated to one of the adjusting agents, such as germanium, tin, carbon or nitrogen. Generator 86 could, for example, supply germanium as in the form of germane gas (GeH4).

Reference is now made to Fig. 3, which illustrates additions to the equipment shown in Fig. 1 for supplying other agents or substances to the depositing alloy. For example, an N-type conductive dopant, such as phosphorus or arsenic, may be added from the beginning to make the moderately self-conducting N-type alloy a more substantial N-type alloy, and then a P-dopant may be added. such as aluminum, gallium or indium, are added to form a good PN junction inside the alloy. A crucible 90 is shown for receiving a dopant such as arsenic, which is vaporized by being bombarded with an electron beam from an electron beam source 92, such as the previously described radiation source 20. The rate at which the dopant evaporates to the atmosphere at 12 o'clock and which is determined by the intensity of the electron beam generated by the electron beam source 92, is set by means of a manual control means 94 on the control panel 34, which means controls the current supplied to the filament forming part in this beam source to provide the set evaporation rate. The rate of evaporation is measured by means of a thickness sensing unit 96, on which the dopant material is deposited and which generates a signal on a cable 98 extending between the unit 96 and the control unit 24, which signal indicates the rate at which the dopant material is deposited on the unit 96.

After the desired thickness of amorphous alloy with the desired degree of N-conductivity has been deposited, the evaporation of silicon and of the N-type conductivity dopant is completed and the crucible 90 (or another crucible not shown) is provided with a described P-type conductivity dopant, after which the deposition process of the amorphous alloy and the dopant continue as before to increase the thickness of the amorphous alloy by an area in the P-type conductivity alloy.

The band-adjusting substance or substances can also be added by a process similar to that described for the dopant, by using another crucible, similar to crucible 90.

In the case where the amorphous alloys comprise two or more substances, which are solid at room temperature, it is usually desirable to individually evaporate each substance, placed in a separate crucible, and to control the rate of deposition of each substance on in any suitable manner, for example by means of setting control means on the control panel 34, which in conjunction with the deposition rate and the deposition thickness sensing units control the thickness and composition of the deposition alloy.

Although activated fluorine (and hydrogen) are believed to be the most advantageous compensating agents for use in compensating for amorphous cell alloys comprising silicon, in accordance with the further aspects of the invention, other compensating or altering agents may be provided. ... i-l -... im ._ _ a ... ..._. m. _ _ ...___ .........___._._ ..._ ....__.__...__....._._..._. 451 353 be used. For example, carbon and oxygen can be useful in reducing the density of local conditions in the energy gap, as these substances are used in small amounts to change the self-conducting property of the cell alloy. § Although, as previously stated, it is preferred that compensating and other agents be incorporated into the amorphous alloy as it is deposited, the process of depositing amorphous alloy and the process of injecting the compensating and other agents into the semiconductor alloy may be performed in a environment, which is completely separate from the deposition of the amorphous alloy. This can give an advantage in certain applications, since the conditions for injecting such agents are then completely independent of the conditions for the alloy deposition. If the vapor deposition process produces a porous cell alloy, as previously explained, the porosity of the alloy can in some cases be more easily reduced by completely different environmental conditions than those present in the vapor deposition process. For this purpose, reference is now made to Figures 4 and 5, which illustrate the amorphous deposition process, the process for diffusion of the compensating or altering agent being carried out as separate steps in completely different environments. Fig. 5 illustrates an apparatus for performing the compensation diffusion process afterwards.

As shown, a low pressure container body 100 is provided, which has a low pressure chamber 102 with an opening 104 at its upper part. This opening 104 is closed by means of a cover 106 with threads 108, which engages around a corresponding threaded portion on the outer part of the container body 100. A sealing O-ring 110 is inserted between the cover 106 and the upper surface of the container body. A sample holding electrode 111 is mounted on an insulating bottom wall 144 in the chamber 100. A substrate 166, on which an amorphous semiconductor cell alloy 118 has already been deposited, is placed on the electrode 111. The upper surface of the substrate 451 353 211 116 contains the amorphous cell alloy 118, which is to be altered or compensated in the manner now to be described.

At a distance above the substrate 116 is an electrode 120. The electrodes 112 and 120 are connected by means of cables 122 and 124 to a direct current or radio frequency supply source 126, which applies a voltage between the electrodes 112 and 120 to provide an activated plasma of the compensating or changing the gas or gases, such as fluorine, hydrogen and the like, which are fed into the chamber 102. For simplicity, Fig. 5 illustrates only the introduction of molecular hydrogen into the chamber 102 by means of an inlet line 128 passing through the housing 106 and extends from a molecular hydrogen storage container 130. Other compensating or changing gases (such as fluorine and the like) may also be similarly fed into the chamber 102. The pipeline 128 is shown connected to a valve 132 near the container 130. A flow rate indicating gauge 134 is shown connected to the inlet line 128 beyond the valve 132. .

Suitable means are provided for heating the interior of the chamber 102 so that the temperature of the substrate is suitably raised to a temperature below but close to the crystallization temperature of the cell alloy. Heating wire windings 136 are shown in the bottom wall 114 of the chamber 102, to which windings a cable (not shown) is connected, which cable passes through the walls of the container body 100 to a power source for heating the bottom wall.

The high temperature together with a gas plasma, which contains one or more compensating substances and is developed between the electrodes 112 and 120, causes a reduction of the local conditions in the bandgap of the cell alloy. The compensation or change of the amorphous alloy 118 can be enhanced by irradiating the amorphous alloy 118 with radiant energy from a source 138 of ultraviolet light, which source is shown outside the container body 100 and directs ultraviolet light between the electrodes 112 and 120. through a quartz window 140 mounted in the side wall of the container body 100.

The low pressure or vacuum in the chamber 102 may be developed by a vacuum pump (not shown) such as the pump 56 in Fig. 1. The pressure of the chamber 102 may be of the order of 0.3-2 dry with a substrate temperature of the order of 200-450 ° C. The activated fluorine (and water) as well as other compensating or altering substances can also be prepared from compounds containing the substances, instead of from a source of molecular gas, as previously mentioned.

Fig. 6 illustrates a photovoltaic multicellular device 141 with stacked cells, which device has three electrically separate, individual photovoltaic cells 143, 145 and 147. These individual cells may be physically separated, each cell being made on its own special substrate, or they may be physically cohesive and separated by a deposited, electrically insulating layer.

For example, the three cells have decreasing bandgaps, which are preferably selected to equalize or respond to the current generated by each of the cells. The cells are connected by external terminals 149 and 151, which may include load matching circuits or may be insulated between each cell. The cells 143 may, for example, be made of an α-Si: F: H-1 alloy with a gap of approximately 1.9 eV. The cell 145 may be made with a small amount of a band-adjusting substance, such as germanium, with a gap of 1.5 eV.

The third cell 147 may be made with a larger amount of one or more band adjusting substances and has a band gap of 1.2 eV.

The photon energies absorbed by each cell are indicated by wavy lines 153, 155 and 157. Lines 153, 155 and 157 represent photon energies above 1.9 ev, 1.5 eV and 1.2 eV, respectively. If desired, the cells can also have graded bandgaps. By substantially adjusting the currents generated from each cell, the entire no-load voltage Voc of the device is improved without a significant reduction of the short-circuit current Jsc.

A multi-cell device 159 of the tandem or cascade type is illustrated in Fig. 7. This device can be manufactured with the cells according to Fig. 6, the currents from each of the cells being adapted to each other. The adapted current having cells 143 ', 145' and 147 'absorbs the same photon energies, represented by 153, 155 and 157. The cells have no external connections between them but instead use transitions 161 and 163 as the electrical connections between the cells. Although the radiation energy discussed above is typically from the solar spectrum, other multicellular applications utilizing other light sources can also be achieved by the invention. Although the cell substrates of cells 143 and 145 must be substantially transparent to the photon energy of interest, further, the substrates of cells 147 and 147 'are not so limited. The external connections of cells 141 and 159 are not shown.

Different types of cells of amorphous alloys can be utilized in the multicellular devices of the present invention.

As an example, cell 143 may have an increased bandgap, as revealed. As another example, the cell 145 may be substantially self-conducting or have a bandgap adjustment. Cell 147 may have a bandgap alignment and each of the cells may be graded.

Fig. 8 shows a multicellular device 142 with stacked cells in fragmentary cross-section, the device comprising a plurality of Schottky barrier solar cells. The solar cell device 142 comprises three Schottky barrier solar cells 142a, 142b and 142c. As shown in the figure, the device 142 may comprise additional cells, if desired.

The solar cell 142a comprises a substrate or an electrode 144 of a material having good electrical conductivity properties and the ability to make ohmic or barrier-free contact with an amorphous alloy 146a, which has been compensated or altered to achieve low density. of local states in the energy gap and has a band gap, which is optimized by the processes according to the present invention. The substrate 144 may comprise a semi-transparent metal or a low performance metal, such as aluminum, tantalum, stainless steel or other material adapted to the amorphous alloy 1446a deposited thereon, which alloy preferably comprises silicon compensated or altered on the method of the previously described alloys, so that it has a low density of local conditions in the energy gap. Most preferred is that the alloy has an area 148a closest to the electrode 144, which area forms a strongly doped N + type conductivity interface and with low resistance between the electrode and an undoped area 150a with relatively high dark resistance, which area is a self-conducting area with low conductivity of N-type.

As seen in Fig. 8, the upper surface of the amorphous alloy 145a connects to a metal area 1252a, the interface between this metal area and the amorphous alloy. l46a forms a Schottky barrier l54a. The metal area l52a is transparent or semi-transparent to solar radiation, has good electrical conductivity and has a high working function (eg 4.5 eV or larger, for example generated of gold, platinum, palladium, etc.) relative to that of the amorphous alloy 146a. The metal area l52a may be a single layer of a metal or may consist of several layers. The amorphous alloy 146a may have a thickness of about 0.5 .mu.m and the metal region 1252a may have a thickness of about 100 Å to be semi-transparent to solar radiation.

On the surface of the metal area l52a, a grid electrode l56a made of a metal with good electrical conductivity is deposited. The grid may comprise orthogonally related lines of conductive material, which occupy only a small proportion of the area of the metal area, while the rest of the area shall be exposed to solar energy. The grid l56a l5 451 353 can, for example, occupy only about 5-10% of the entire area of the metal area l52a. The grid electrode l56a uniformly collects current from the metal area l52a to ensure a good, low series resistance for the device.

An insulating layer l58a is applied over the grid electrode l56a to insulate the cell l42a from the adjacent cell l42b. The insulating layer 175a may be, for example, SiO 2 or Si 3 N 4.

The cell 142b and each of the other intermediate cells between the lower cell 142a and the upper cell 142c comprises a grid electrode 160b deposited on the layer of the adjacent cell, such as the insulating layer 158a of the cell 142a. The grid 16d is preferably identical to the grid 166a and aligned therewith to exclude unnecessary shading. above the grid 163 a transparent or semi-transparent metal area l62b is deposited. The metal area l62b preferably has good electrical conductivity and high work function, as does the area lS2a. over the metal area 162b, another amorphous alloy 146b is deposited, which preferably comprises silicon and is compensated or altered in the manner of the previously described alloys. The alloy 146b comprises an area 148b closest to the metal 162b, which forms a strongly doped interface with N + type conductivity and low resistance between the metal 162b and an undoped area 150b with relatively high dark resistance, which area is self-conducting but has low N-type conductivity. . The alloy 146b is preferably bandgap adjusted in a manner previously described, so that the bandgap of the alloy 146b is larger than the bandgap of the alloy 146a.

Like the cell 142a, the cell 142b comprises a transparent or semi-transparent metallic region 152, which forms a Schottky barrier at 154b, and a grid electrode 156b over the region 152b. above the grid electrode l56b, another insulating layer l58b is deposited to insulate the cell l42b from the cell l42c. l5 451 353 26 The upper cell l42c is substantially identical to the intermediate cell l42b except that it does not comprise any insulating layer but instead has an anti-reflective layer l63 deposited over the grid electrode l56c. The amorphous alloy 146c, which includes the N + region 144c and the self-conducting region 150c with weak N-type conductivity and high dark resistance, is also band gap adjusted to have a band gap larger than the band gap 1446 of the alloy.

An anti-reflective layer 163 may be applied over the grid electrode l56c and the areas of the metal area lS2c between the grid electrode areas. The anti-reflective layer 163 has a solar radiation receiving surface 164, against which solar radiation is incident. For example, the anti-reflection layer 163 may have a thickness of the same order of magnitude as the wavelength of the point of maximum energy in the solar radiation spectrum, divided by 4 times the refractive index of the anti-reflection layer 163. If the metal region IS2c consists of platinum with a thickness of 100 Å, a suitable anti-reflective layer 163 would consist of zirconia having a thickness of about 500 Å and a refractive index of 2.1.

The band-adjusting substance or substances are supplied to at least the photocurrent generating area 150a, 150b and 150c.

The Schottky barrier l54a, l54b and 1540 formed at the interface between the areas lSOa and l52a, l50b and l52b and l52b and lS2c respectively the grid electrode l56a, l56b and l56c. All grids are preferably aligned to exclude unnecessary shading. An oxide layer (not shown) having a thickness of the order of 30O may also be added between each of the layers 150a, 150b and 150c and 152a, 1252b and 152 to provide a stacked MIS (metal insulator-semiconductor) solar cell. Fig. 9 shows in fragmentary cross-sectional view a tandem or cascade type multicellular device 166, which device also comprises a plurality of Schottky barrier solar cells.

The solar cell 166 comprises three Schottky barrier solar cells 16a, 16b and 16c. As indicated in the figure, the device 166 may include additional cells, if desired.

The solar cell 166a comprises a substrate or electrode 167 of a material having good electrical conductivity and the ability to form an ohmic or barrier-free contact with an amorphous alloy 16a, which is compensated or altered to provide a layer of dense of leaky conditions in the energy gap, which is optimized by the processes of the present invention. The substrate 167 may comprise a transparent or semi-transparent metal or a low working number metal, stainless steel or adapted to the amorphous alloy, such as aluminum, other material, which is the ring 168a, which is deposited thereon and preferably includes silicon or germanium, compensated or altered in the manner of the previously described alloys, so that it has a low density of local conditions in the energy gap. Most preferably, the alloy has an area l69a closest to the electrode 167, which area forms a strongly doped N + type conductivity interface and with low resistance between the electrode and an undoped area l70a with relatively high dark resistance, which area is self-conducting but weakly conductive of N-type.

As seen in Fig. 9, the upper surface of the amorphous alloy 168a connects to a metal area 17a, an interface between this metal area and the amorphous alloy 168a forming a Schottky barrier 172a. The metal region l7la is transparent or semi-transparent to solar radiation, has electrical conductivity and has a high working function (eg 4.5 ev or larger, for example generated of gold, platinum, palladium, etc.) relative to that of the amorphous alloy l68a. The metal area 10 l5 451 353 28 l7la may be a single layer of a metal or may consist of several layers. The amorphous alloy l68a may have a thickness of about 0.5 - 1 μm and the metal region l1la may have a thickness of about 100 Å to be semi-transparent to solar radiation. The cell 166b and all other intermediate cells between the lower cell 1666a and the upper cell 1666c comprise an amorphous alloy 168b, which preferably comprises silicon and is compensated or altered in the manner of the previously described alloys. The alloy l68b comprises an area l69b closest to the metal l7la, which forms a strongly doped interface with N + type conductivity and with low resistance between the metal l1la and an undoped area l70b with relatively high dark resistance, which area is a self-conducting but low conductivity of N-type exhibiting range.

The alloy 168b is preferably, at least in the area 17b, bandgap adjusted in a manner previously described, so that the bandgap of the alloy 168b is higher than the bandgap of the alloy 168a. Like cell l66a, cell l66b comprises a transparent or semi-transparent metal region l7lb, which forms a Schottky barrier at l72b.

The upper cell 166c is substantially identical to the intermediate cell 166b except that it further comprises a grid electrode 173 and an anti-reflection layer 174, which is deposited over the grid electrode 173. The amorphous alloy 168c, comprising the N + region 169c and the weakly N-conducting , self-conducting and high dark resistance having the region l70c, is bandgap adjusted, at least in the region l70c to have a bandgap which is larger than the bandgap of the alloy l68b.

The grid electrode 173 on the surface of the metal area 152 is made of a metal with good electrical conductivity.

The grid may comprise orthogonally related lines of conductive material, which occupy only a small proportion of the area of the metal area, while the rest of the area is to be exposed to solar energy. The grid 173 can, for example, occupy only about 5-10% of the entire area of the metal area 177c. The grid electrode 173 uniformly collects current from the metal area 171 to ensure a good, low series resistance from the device.

The anti-reflection layer 174 may be applied over the grid electrode 173 and the areas of the metal region 171c between the grid electrode regions. The anti-reflection layer 174 has one. solar radiation receiving surface 175, against which solar radiation is incident. For example, the anti-reflection layer 174 may have a thickness of the order of magnitude of the wavelength of the point of maximum energy in the solar radiation spectrum, divided by four times the refractive index of the anti-reflection layer 174. If the metal region 17c consists of platinum with a thickness of 100 Å, a suitable anti-reflective layer 174 consists of zirconia with a thickness of approximately 500 A and a refractive index of 2.1.

The band-adjusting substance or substances are supplied to the photocurrent beach areas 17a, 170b and 170c. The Schottky barriers l72a, l72b and l72c, respectively, formed at the interface between regions 170a and 17a, 17b and 17b, and 170c and 17c, respectively, allow photons from solar radiation to provide charge carriers in the alloys l68a, l68b, l68b and l68c. is collected as current by the grid electrode 173. A non-ViSa oxide layer with a thickness of the order of 30 A can be added between the layers 17a and 17a, 17b and 17b and 17c and 17c, respectively, to provide a MIS (metal insulator-semiconductor) solar cell of tandem or cascade type.

As used herein, the terms compensating agents or materials and modifying agents, substances or materials are those materials included in the amorphous cell alloy for altering or altering its structure, such as, for example, activated fluorine (and hydrogen), including the amorphous alloy containing silicon. to form an amorphous alloy having a composition of 451 353 1. » - «...._.........-. silicon-fluorine hydrogen, with a desired band gap and a low density of local conditions in the energy gap. The activated fluorine (and hydrogen) is bound to the silicon in the alloy and reduces the density of local conditions therein.

Due to the small size of the fluorine and hydrogen atoms, they can both be easily introduced into the amorphous alloy without significant dislocation of the silicon atoms and their relationship in the amorphous alloy. This is especially true due to the extreme electronegativity, specificity, small size and reactivity of fluorine, all of which properties help to influence and organize the local order of the alloys.

In creating this new alloy, fluorine's strong inductive forces and its ability to have an organizing effect on the local system are important. Fluorine's ability to bind both silicon and hydrogen results in the formation of new and superior alloys with a minimum of local defective conditions in the energy gap. Consequently, fluorine and hydrogen are introduced into the energy gap without significant formation of other local conditions in order to form the new alloys.

In addition to the stacked and tandem or cascaded Schottky barrier solar cells or MIS multi-solar cells shown in Figures 8 and 9, there are solar cell constructions which utilize pin transitions in the body of the amorphous alloy forming part thereof. in accordance with successive deposition, compensation or change and doping steps, as previously described. These other forms of solar cells are generally illustrated in Figures 10 and 11.

In Fig. 10, to which reference will now be made, a multicellular device 180 with several stacked cells, including a plurality of pin solar cells 11a, 18b and 18lc, is illustrated.

The lower cell 111a has a substrate 182, which may be transparent or semi-transparent or formed of stainless steel or aluminum. The substrate 182 has the desired width and length and preferably a thickness of at least 76.2 μm. Above the substrate 182, an N + layer 183 with low light absorption and high conductivity is deposited. over the N + layer 183 is deposited a layer 184 of self-conducting alloy with an adjusted bandgap, high light absorption, low dark conductivity and high photoconductivity, comprising sufficient amounts of the adjusting substance or substances for optimizing the bandgap. over the self-conducting layer 184 a P + - layer 185 is deposited, which has low light absorption and high electrical conductivity. Above the P + layer-185, a TCO layer 186 (transparent, conductive oxide = TCO) is deposited, which may be, for example, indium tin oxide (ITO), cadmium stannate (Cd2SnO4) or doped tin oxide (SnO2).

An electrode grid 187 is added to the TCO layer 186, which grid may have the shape of the grids previously described.

The cell l8la must be isolated from the adjacent cell l8lb. For that purpose, an insulating layer 188 is applied over the grid 187, which layer 188 may be formed, for example, of S102 or -Si3N4.

The cell 188b and all other intermediate cells, which may be added in the manner indicated in the figure, comprise a body 89 of amorphous alloy, comprising a new layer 190, an individual layer 191 and a P layer 192. Each of these layers has preferential properties. show the same electrical and photoconductive properties as the corresponding layers in cell l8la. However, the self-conducting layer 191 is bandgap adjusted to exhibit a bandgap that is larger than the bandgap of the self-conducting layer 184.

To facilitate current collection, a transparent or semi-transparent contact oxide 193 and a grid electrode 184 are arranged between the N + layer 190 and the insulating layer 188. The layer 193 may, for example, be formed of tin oxide. Similarly, a TCO layer 195 and a grid electrode 196 are disposed adjacent the P + layer 192. The intermediate cell 18b is isolated from the upper cell 451c of a layer of insulating material 197, such as, for example, SiO 2 or Si 3 N 4.

The upper cell 188c is substantially identical to the intermediate cell 181b. It also includes a grid electrode 198, a transparent or semi-transparent contact oxide 199, an N + region 200, a self-conducting region 201, a Pïomraae zoz, a Teo layer 203 and a grating electrode 204. In addition, an anti-reflection layer 205 arranged over the grid electrode 204, and the self-conducting area is preferably bandgap-adjusted in the manner previously described to have a bandgap which is larger than the bandgap of the self-conducting layer 19118b.

To ensure maximum cell efficiency in the cell, all grids should be aligned with each other to exclude unnecessary shading. It is also clear that a NIP multicellular device can be obtained by reversing the order of the N + and P + layers or regions.

In Fig. 11, to which reference will now be made, a multi-cell device 206 of the tandem or cascade type is illustrated, which device comprises a plurality of PIN solar cells 207a, 207b and 207c. The lower cell 207a has a substrate 208, which may be transparent or semi-transparent or formed of stainless steel or aluminum. Each of the cells 207a, 207b and 207c comprises a body 209a, 209b, and 209c, respectively, of an amorphous alloy containing at least silicon. Each of the alloy bodies comprises an N + region or layer 2110a, 210b and 21c, a self-conducting region or layer 21l, 21lb and 21lc and a P + region or layer 212a, 212b and 212c, respectively. The cell 207b is an intermediate cell and, as indicated in the figure, additional intermediate cells may be included in the device, if desired. A NIP multicellular device can also be obtained by reversing the order of the N + and P + layers or areas. For each of the cells 207a, 207b and 207c in Fig. 11, the P + layers are such alloy layers with low light absorption and high electrical conductivity. The self-conducting alloy layers have an adjusted wavelength threshold for high light absorption, low dark conductivity and high photoconductivity, including sufficient amounts of the adjusting substance or substances to optimize the bandgap for cell operation. The self-conducting layers are preferably so bandgap adjusted that cell 207a has the lowest bandgap, cell 207c has the highest bandgap, and cell 207b has a bandgap in between. The lower alloy layers consist of an N + - layer with low light conductivity. The thickness of the N + doped layers is preferably in the range of about 50-500 Å.

The thickness of the amorphous adjusting substance, which contains self-conducting alloy layers, is preferably between about 3000 Å and 30,000 Å. The thickness of the P + layers is also preferably about 50-500 A. Due to the shorter diffusion length of the hole, the P + layers will generally be as thin as possible and of the order of so-iso A. the outermost layer (here the f-layer 212c) will further be kept as thin as possible to avoid light absorption in that contact layer, and will generally not include the bandgap or gaps the adjusting substances.

After the deposition of the various semiconductor alloy layers in the desired order for the cells 209a, 209b and 209c, a further deposition step is performed, preferably in a separate deposition environment. A deposition environment is suitably utilized, since it is a matter of a rapid deposition process. In this step, a TCO step 213 (transparent, conductive oxide) is added, which may be, for example, indium tin oxide (ITO), cadmium stannate (Cd 2 SnO 4) or doped tin oxide (SnO 2). The TCO layer will be added after the post-compensation of fluorine (and hydrogen), if the alloys were not deposited with one or more of the desired compensating or altering elements therein.

If desired, an electrode grid 214 can be added to the device. For a device with a sufficiently small area, the TCO layer 213 is generally sufficiently conductive, so that the grid 214 is not necessary for good efficiency of the device. If the device has a sufficiently large area or if the conductivity of the TCO layer 213 is insufficient, the grid 214 can be placed on the layer 213 to short-circuit the charge carrier path and increase the conductivity of the device.

The band gaps for each of the cells forming the devices in Figures 8, 9, 10 and 11 may also be graded in their self-conducting or actively photosensitive range.

Such a grading can be achieved, as fully described in our patent application (Case 537) filed concurrently herewith.

In Fig. 12, to which reference will now be made, an embodiment of a plasma-activated vapor deposition chamber 226 is illustrated, in which the semiconductor and the band-adjusting blank (s) of the invention can be deposited.

A control unit 228 is used to control the deposition parameters, such as pressure, flow rates, etc., in a manner similar to that previously described in connection with the unit 24 (Fig. 1). The pressure would be maintained at about 10-3 torr or less.

One or more reaction gas pipelines, such as lines 230 and 232, may be used to supply such gases as silicon tetrafluoride (SiF4) and hydrogen (H2) to a plasma region 234. The plasma region 234 is established between a coil 236 fed by a direct current source (not illustrated). , and an anode 238. The plasma activates the supplied gas (s) for supplying activated fluorine (and hydrogen) for deposition on a substrate 240. The substrate 240 can be heated to the desired deposition temperature by means of heating means, as previously described. The band-adjusting substance (s) and silicon may be supplied from two or more evaporation crucibles, such as crucibles 242 and 244. The crucible 242 may, for example, contain germanium and the crucible 244 silicon. The substances in the crucibles 242 and 244 can be evaporated by means of an electron beam or other heating means and activated by the plasma.

If it is desired to layer the band-adjusting substance or substances in the photo-generating area of the film being deposited, a shutter 246 may be used. The shutter could rotate the layer of separate tape adjusters from two or more of the crucibles or could be used to control the deposition of the tape adjuster from the crucible 242 (or others) to create layers in the film or to vary the amount of tape adjuster deposited in the film. . The band-adjusting substance or substances can thus be applied discreetly in layers, mainly constantly or in varying amounts.

Pig 13 illustrates the available sunlight spectrum. Air mass O is the available sunlight without atmosphere and with the sun at its zenith. Air mass l corresponds to the same situation after filtration through the earth's atmosphere. Crystalline silicon has an indirect band gap of approximately 1.1 - 1.2 eV, which corresponds to the wavelength of approximately 1.0 μm. This is equated with loss, ie not generation of useful photons, for essentially all light wavelengths above 1.0 μm. As used herein, the band gap or optical energy E is defined as the extrapolated intersection of a curve (uñw) l / 2, where u is the absorption coefficient and fi w (or e) is the photon energy. For light with a wavelength above the threshold defined by the band gap, the photon energies are not sufficient to generate a photocurrent carrier pair and thus do not supply any current to a particular device.

Each of the semiconductor alloy layers of the devices can be deposited by glow charging on the base electrode substrate by means of a conventional glow discharge chamber, which is described in the aforementioned U.S. Pat. No. 10,451,353,364,226,898. The alloy layers can also be deposited in a continuous process. In these cases, the glow-charging system is evacuated, for example, at the beginning to about dry to clear out or eliminate pollutants in the atmosphere from the deposition system. The alloying material is then preferably fed into the deposition chamber in the form of a gaseous compound, most advantageously such as silicon tetrafluoride (SiF4), hydrogen (H2) and, for example, german (GeH4). The glow discharge plasma is preferably obtained from the gas mixture, the deposition system of U.S. Pat. No. 4,226,898 is preferably operated at a pressure in the range of about 0.3 - 1.5 torr, preferably 0.6 - 1.0 torr, such as about 0 , 6 torr.

The semiconductor material is deposited from a self-maintained plasma on the substrate, which is heated, preferably by infrared means, to the desired deposition temperature for each alloy layer. The doped layers of the devices are deposited at different temperatures in the range from 200 ° C to about 100 ° C depending on the shape of the material used. The upper limit of the substrate temperature depends in part on the type of metal substrate used.

For aluminum, the upper temperature should not be above about 600 ° C and for stainless steel it could be above about 10 ° C. Prior to the production of an initially hydrogen-compensated amorphous alloy, as for the formation of the self-conducting layer in NIP or PIN devices, the substrate temperature should be less than about 400 ° C and preferably about 300 ° C.

The doping concentrations are varied to provide the conductivity of the desired P, P +, N or N + type, as the alloy layers are deposited for each device. For N- or P-doped layers, the material is doped with 5 - 100 ppm of the doping material, as it is deposited. For N + or P + doped layers, the material is doped with from 100 ppm to over 1% of the dopant material, as it is deposited. The N-dopant material may be conventional dopants, deposited at the various substrate temperatures, preferably in the range from 100 ppm to over 5000 ppm for the P + material.

The glow discharge deposition process may include an alternating signal generated plasma into which the material is introduced. The plasma is preferably maintained between a cathode and a substrate node with an AC signal of from about 1 kHz to 13.6 MHz.

Although the multicellular devices of the invention can utilize a variety of amorphous alloy layers, it is preferred that they utilize cells with fluorine and hydrogen compensated, glow discharge deposited alloys. In this case, a mixture of silicon tetrafluoride and hydrogen is deposited as an amorphous, compensated alloy material at or below about 400 ° C for an N-type layer. The band-adjusted, self-conducting amorphous alloy layer and the P + layer can be deposited on the electrode layer at a higher substrate temperature above about 450 ° C, which will give a material which is fluorine compensated.

As an example, a mixture of the gases GeH4 + Ar + SiF4 + H2 with relative percentages of GeH4 and SiF4 in the range 0.001 - 1% produces photosensitive alloys with the adjusted band gaps without loss of the desired electronic properties. The mixture has a ratio of SiF4 relative to H2 of 4: 1 - 10: 1. The amount of the adjusting substance or substances in the resulting alloy is much larger than the percentages in the gas and can be considerably above 20% depending on the application. Argon is useful as a diluent but not necessary.

Furthermore, although the bandgap adjusting blank or blanks are added to at least the photosensitive area of the cells, the blank or blanks may also be useful in the other alloy layers of the devices. As previously mentioned, the alloy layers other than the self-conducting alloy layer may be layers other than amorphous layers, such as polycrystalline layers (by the term "amorphous" is meant an alloy or a material which is arranged at a long distance). , although it may be arranged at short or intermediate distances or even contain certain crystalline inclusions).

Claims (13)

A photosensitive, amorphous multicellular device having at least two cells, at least one of which comprises an amorphous, multilayer alloy having an active photosensitivity region, which comprises a bandgap and which may be struck by radiation to produce a charge carrier, the alloy comprising at least one state density reducing substance 1 at least one layer, which substance is fluorine, characterized in that at least one layer of the cell alloy (146a, 146b, 166c, 168b, 168b, 168b, 168b) 184, 189, 191, 209a, 209b, 209c, 2lla, 2llb, Zllc) has a bandgap adjusting substance included therein without significantly increasing the state of the gap, the cell alloy layer being bandgap-adjusted for a particular photosensitivity wavelength function, which is separate from the other cell. 2. A device according to claim 1, characterized in that the cell alloy comprises silicon. A device according to claim 1 or 2, characterized in that the adjusting substance is germanium, tin, carbon or nitrogen. 4. A device according to any one of claims 1 to 3, characterized in that each cell alloy has an active photosensitive region and that the adjusting substance is included at least in said region (146a, 146b, 146c, 168a, 168b, 168c), 184, 191, 201, 2lla, 2llb, 2llc). Device according to one of Claims 1 to 4, characterized in that at least one cell (142a, 142b, 142c, 143, 143 ', 145, 145', 147, 144 ', 154a, 154b, 1540, 166a, l66b, l66c, l1la, l8lb, lllc, 207a, 207b, 207c) further comprises a second state density reducing substance, which is hydrogen. - | - »ann-away 10 15 20 25 30 35 451 355 40 Device according to one of Claims 1 to 5, characterized in that at least one cell (142a, 142b, 142c, 143, 143 ', 145, 145', 147, 147 ', 154a, 154b, 154c, 166a) 166b, l66c, l8la, 181b, 181c, 207a, 207b, 207c) setting. is deposited by glow discharge discharge Device according to one of Claims 1 to 6, characterized in that at least one cell (144a, 142b, 142c, 143, 143 ', 145, 145', 147, 147 ', 154a, 1554b, 1554, 166a) l66b, l66c, l1la, 18lb, 18lc, 207a, 207b, 207c) comprises said adjusting substance in substantially discrete layers. Device according to one of Claims 1 to 7, characterized in that at least one cell (142a, 142b, 142c, 143, 143 ', 145, 145', 147, 147 ', 154a, 1554, 1454, 166a) l66b, l66c, l1la, l8lb, lllc, 207a, 207b, 207c) comprises the adjusting substance in varying amounts. Device according to any one of claims 4 to 8, characterized in that the band gap for the photosensitive area (146a, 146b, 146c, 168a, 168b, 168c, 184, 191, 201, 211b, 211b, 211c) is smaller than 1.6 eV. 10. lO. A device according to any one of claims 1 - 9, characterized in that the adjusting substance is germanium. 11. ll. A device according to any one of claims 1 to 10, characterized in that the alloy forms part of a Schottky barrier solar cell (l42a, l42b, l42c, l54a, l54b, l54c, 166a, l66b, l66c). Device according to one of Claims 1 to 11, characterized in that the alloy forms part of a MIS (solar cell) (142a). Device according to one of Claims 1 to 12, characterized in that the alloy forms part of a PIN device (180, 206).