MXPA99008281A - Semiconductor element, especially a solar cell, and method for the production thereof - Google Patents

Abstract

A semiconductor element (50) which is especially designed as a solar cell, comprising at least one semiconductor base material (40) with a monocrystalline or polycrystalline structure. The seminconductor base material (40) is at least partially made of pyrite with a chemical composition of FeS2 which is purified in order to obtain a specific degree of purity. The semiconductor base material (40) is composed to a highly advantageous extent of at least one pyrite layer (51), at least one boron layer (51) and at least one layer of phosphorus (53). An optimum embodiment is provided when the inventive semiconductor element is used as a solar cell.

Description

"SEMICONDUCTOR COMPONENT, IN PARTICULAR A SOLAR CELL, WHICH HAS AT LEAST ONE BASE MATERIAL, SEMICONDUCTOR AND METHOD TO PRODUCE SUCH COMPONENT" The invention relates to a semiconductor component, in particular a solar cell, with at least one semiconductor base material consisting of a mono or polycrystalline structure, which consists at least in part of -L pyrite with the chemical composition FeS2 and that is cleaned with the purpose of achieving a defined degree of purity. A number of semiconductor components or generic semiconductor photocomponents are already recognized, which, given an efficiency level of approximately 15%, are used commercially on the basis of of the photo inner effect of radiation energy of the sun or light. Thin crystals of silicon or gallium iron arsenide with areas of conductivity p and n are predominantly used as semiconductor materials. Also recognized are thin multi-layer solar cells, the case of which the semiconductor layers are positioned on a base by means of a metallization or the like to produce thicknesses in the micrometer range (1 to 5 μm). Materials such as cadmium sulfide, cadmium telluride, copper sulfide or the like are used for the semiconductor layers. These semiconductor components can only achieve an efficiency of 5% - 8%. However, they have a useful power-to-weight ratio and are essentially more cost-effective to produce than silicon-iron crystals. According to Patent Specification EP-A 0 173 642, a generic solar cell is a layer of photoactive pyrite with the chemical formula FeS2- -, which has a concentration of undesirable impurities of < 1020 porcm3 and impurities of manganese (Mn) or arsenic (As) and / or cobalt (Co) or Chlorine (Cl). In practice, it would seem that a solar cell with this composition could not achieve the required level of efficiency. In contrast, the object of this invention is to create a semiconductor component, in particular a solar cell, on the basis of the aforementioned type, which can be used to achieve a higher efficiency than known solar or light radiation. Moreover, the production costs with respect to this semiconductor component will be low enough for this type of solar cell to be suitable for mass production. A further object of this invention is to use semiconductor material that can be easily removed in a manner that does not affect the environment. The invention can reach the object in that the semiconductor base material, which consists of at least part of pyrite with the chemical composition FeS2, is combined or mixed with at least boron and phosphorus respectively. With a very advantageous type, the semiconductor base material is produced from at least one pyrite layer together with the boron and phosphor elements. Used in this way, an optimum and highly efficient composition is achieved, especially for solar cells. According to the invention, these semiconductor components can be used to produce solar cells that have an efficiency greater than any other known solar cell. Pyrite used as a semiconductor material has the advantage of being a natural material, which can also be synthetically produced. Production costs can be maintained at a level such that, given the increase in the level of efficiency, profitable use can be obtained. Typical examples of the invention and additional advantages thereof are explained below with the help of the diagram. This sample: Fig. 1 a schematic cross-section through a semiconductor component according to the invention, shown on an enlarged scale.

Fig. 2 a schematic view of the energy division of the Fe-condition in the deformed octahedral and octahedral ligation fields of pyrite. Fig. 3 a schematic cross-section through a semiconductor component according to the invention with a hetero-link, shown on an enlarged scale, and Fig. 4 a schematic view of the energy bands with a hetero-link of a semiconductor component in accordance with the invention Figure 1 is a schematic of a semiconductor component 10 according to the invention, which is formed in particular as a solar cell. In the example example shown, this semiconductor component 10 has a multilayer structure and can, for example, together with a number of adjacent cells, be inserted into a metal shell in the form of a panel, which is not shown in FIG. detail. The solar cell preferably has as a cover a plate of a transparent material, for example a glass layer 1 1 or the like, which provides the cell with a general protection against the effects of mechanical forces, such as impacts, etc., against the humidity and / or adverse weather conditions. A laminar layer 12, for example resin, together with an insulator 14 arranged in the lower part, for example a ceramic plate, surround the solar cell, so that the inner part of the solar cell is closed and therefore both impermeable to moisture, water or similar. According to the invention, the semiconductor base material 20 consists of iron pyrite or pyrite, which possesses the chemical composition FeS2. The semiconductive base material 20 is combined or blended with at least boron or phosphorus, according to which, in the example shown, the semiconductor base material consists of a layer 20 of FeS2 The semiconductor component 10 formed as a status cell solid consists of a layer of semiconductor base material 20 produced from pyrite, a phosphorus layer 21 and a boron layer 22. This phosphor layer 21 and this boron layer 22 are applied to the corresponding surface of the pyrite layer 20, such that there is a bond in the sense of an impurity between the semiconducting base material and the phosphorus (P) with respect to the boron. (B) Preferably, these phosphorus 21 and boron layers 22 are applied in very thin layers of several micrometers through a process described below.

In this way, the required function of this semiconductor component 10 formed as a solar cell is derived from which, together with the solar radiation, an electric current is produced, which is conveniently captured by the conductive materials 13 and 15, which are disposed above and below the semiconductor layers by a recognized method, wherein the conductive material is protected by the insulator 14. These conductive materials are connected to a consumer unit or the like by means of cables, for the which a diagram is not provided. Figure 1 shows a solar cell with a simple structure according to the invention. Clearly, both the conductive materials and the semiconductor layer can be provided in various configurations and in various amounts. This type of semiconductor component can be used as various types of solar cells, both for very small cells, such as calculators, or for solar cells to heat large houses and plants, in which case they are used in particular to convert solar energy in electric power. Pyrite and iron pyrite in the form of natural rock are the most widespread sulfides on Earth, and exist for example in Spain as a hydrothermal area of ores. The individual crystals of pyrite are bronze or mortar, with a high degree of hardness, approximately 6 to 6.5 on the Mohs hardness scale. Pyrite has a coefficient of thermal expansion at 90 to 300 K. of 4.5x 10"6 K" 'and 300 to 500 K of 8.4x 10"6' 1. Pyrite with a chemical composition of FeS2 has an elemental cell of 12 atoms and a unit cell length of approximately 5.4185 Armstrong units.

The typical basic form of pyrite crystal is a hexahedron, a cubic shape, a pentagonal dodecagon or an octahedron. An additional advantage of this semiconductor component is that pyrite is highly compatible with the environment. In terms of the efficiency of this solar cell 10 as described in the invention, According to the general rules of quantum mechanics, only those photons whose energy is at least equivalent to the width of the forbidden zone and no greater than the equivalent to the energy differential between the lower end of the valence band and the upper end of the driving band. The number of charge carriers resulting depends not only on the energy and the number of photons radiated per unit area, but also on the absorption coefficient α of the semiconductor. Compared with traditional semiconducting materials, pyrite has a very high absorption coefficient, which, at the end of the band with an absorption coefficient of >; 105 cm " ', presents a value of d < 1 μm. By creating the semiconductor 19 according to the invention, an optimum use of these pyrite properties is made. - According to Figure 2, the energy division of Fe-d conditions can be seen in the octahedral Oh and octahedral deformed ligation field Dld of the pyrite. An interval in the band is created in the semiconductor material by dividing the Fe conditions-d under busy conditions t2g and idle e, in which said interval in the band can reach 0.7 eV or more. The valence band has a width of 0.8 eV or more, and the basic group is separated by a range of also 0.8 eV. Conditions above the conduction band are based on Fe 4s and 4p conditions. In the area of orbital molecular theory, the energy intervals in the case of pyrite are produced by dividing 3d conditions of iron under energetically lower conditions of occupied t2g and unoccupied eg. The division is caused by the octahedral ligation field of sulfur, which is easily deformed and leads to a later, and in this significant case, division in the energy level. Figure 3, on the other hand, shows in schematic form a section of a semiconductor component 50 according to the invention, which is formed by at least one upper layer of pyrite 51, 1a which forms the semiconductive base material 40, and consisting of a boron layer 52 and a phosphor layer 53. The pyrite 51 is disposed at the top, which initially accepts the effects of solar radiation or the like. However, according to the invention, with this layer arrangement, a compound is formed with the adjacent pyrite 51 base material, or phosphorus 53 and boron 52 are integrated into the basic pyrite material. The conductive elements can be arranged in such a way that they are in contact with the layers 51, 52, 53, for which no details are provided. In contrast to the semiconductive base material 40 produced by layers, as shown in Figure 3, one or more layers of boron and / or one or more layers of phosphorus may be disposed laterally in the objective of pyrite produced, for example, as a single crystal.

The semiconductor base material 20 and / or 40 for these solar cells 10, 50, according to the invention, can be produced by several methods. The pyrite in the composition of FeS2 can be obtained either as a natural material or can be synthetically produced from iron and sulfur. When using natural crystals of pyrite as a semiconductor base material, this pyrite, which has a net charge transport concentration of approximately O 0 '^ cm ", must be treated by a recognized multi-zone cleaning process, in such a way as to achieve a Also, the composite or impure materials, phosphorus and boron respectively, must also reach a purity of 99.9%, in order to produce cells of the highest quality according to the invention. methods for the artificial production or synthesis of semiconductor pyrite base material, according to which the base material is also treated by a multi-zone cleaning process, in order to reach the maximum degree of purity of the chemical compound. suitable for gas phase transport (CVT), for which the temperature gradient for the production of the iron-sulfur compound must be be between 250 ° and 1200 ° C. If pyrite is used as a natural base material, the temperature on the coldest side can vary between 250 ° and 850 ° C. As a means of transport to feed the sulfur to iron, bromide (Br2FeBr3) or other material can be used. Crystal synthesis can occur, for example, in a sodium poly-sulfate solution. Pyrite can be synthesized from the basic elements clean, fuel and sulfur, both at temperature gradients between 250 ° and 1200 ° C, and also at a gradient of 200 ° to 1400 ° C. The CVT method offers improved reproducibility during production and in this way absolutely pure crystals can be obtained. To obtain large pieces of pyrite from a single crystal, the production method using a solution fused with tellurium, BrCl2, Na, S2 or similar materials is used. There is another production variant for pyrite in the sprayed RF. This occurs in a spray unit, in which a pyrite lens is sprayed with an argon-sulfur plasma. The flow of argon is generally between 0.1 and 300 ml / min, and the sulfur is obtained by the vaporization of elemental sulfur. During separation, the working pressure is maintained at 0.01 mbar or higher, or even lower. The DC Potential Self-Bias used is placed at 0 to 400 volts. The temperature of the substance is selected in the range of 801 to 950 ° C. With this process, a poly-crystalline structure can be produced in principle. To produce the semiconductor components according to the invention as a thin layer, an incongruent material system can be used. The reactive spray produced from a pyrite lens, the MOCVD methods and the spray pyrolysis are appropriate. On the other hand, the method of thermal evaporation assisted by a transport system that carries small amounts of a powder compound to the source of hot evaporation, ensures that the material, depending on the high temperature, vaporizes almost completely. This type of vaporization offers the benefit that influence can be exerted both on the stoichiometry as well as on a potential impurity, since for example, the impurity can be added directly to the powder compound. If iron filings are sulphurised, both in purely thermal form and with the help of plasma, it is possible to start with pure base materials. The thickness of the active layer has a great influence on the efficiency of the solar cell. To estimate the efficiency and the required parameters of the cell, appropriate border areas can be specified.

To mix or combine the semiconductor base material with phosphorus and boron respectively, it is preferred to use the latter in a massive percentage of 10"6 to 20% of the base material, this depends on the required characteristics of the finished semiconductor product. According to the invention it can also be produced as the so-called tandem cell, in this case, an impure layer of pyrite and an additional layer p and n of another semiconductor crystal, such as silicon, gallium arsenide or other available material, can create an effect With this type of semiconductor component, maximum spectrum use can be achieved, provided that these various base semiconductor materials can cover the energy interval between 1.0 and 1.8 eV, according to Figure 4, and within the framework of In this invention, heterolinks can be used between several semiconductor components, as explained in detail in the previous paragraph with respect to the type variant shown in Figure 3. However, the condition is that the reticulation constants and the coefficients of thermal expansion of both materials do not vary greatly. As an example, according to the invention, a semiconductor-p 3 1 of pyrite can be combined with a n-conductor semiconductor 32 of a different material. This hetero-bond causes discontinuities in the band, which is used in an innovative way to influence the load carrier. With the two semiconductor materials 3 1 and 32 separated, the band intervals Eg, the work function Ó ^ and the affinity to the é electrons are different. Epitaxial growth methods are recognized, developed especially for the production of heterolinks, which are also used in relation to the semiconductor base material used in this invention. Both molecular epitaxial flow (MBE) and gaseous epitaxy (MOCVD) exist in the form of gaseous depositions of metal-organic compounds. In the case of the thin solar cell with a hetero link, phosphorus and boron are integrated or mixed preferably by an ion implantation, within the surface of the pyrite semiconductor base material, which occurs with the help of particle accelerators. In this way, after ionization, the mixed atoms increase their energy level to very high levels and are injected into the base of the material, where, after a characteristic penetration depth, they are arrested and remain. With this implementation process, the cross-linking of the semiconductor crystal suffers considerable damage and must be regenerated by means of a thermal treatment. In this way, the implanted impurities diffuse and integrate simultaneously with the grid. Accordingly, composite profiles are formed starting from ion implementations and diffusion of impurities. The process of molecular epitaxial flow (MBE) is a special method of vapor deposition. The material is vaporized in hot cylindrical tubes with a small opening in the front. The size of this opening and the vapor pressure created in the boiler by the heat determine the transport material for the target. An ultra high vacuum, controlled by a mass analyzer and a cooled protection plate create very clean crystal deposits. The structure of these crystal deposits can be controlled quasi-on-line by means of the so-called RHEED reading (Reflected Diffraction of * Electrons with High Energy) and the thickness of the layers is created precisely by means of a regulation of the temperature and a fast sealing to a layer of atoms. In the case of a multi-layer structure, the semiconductor component can have up to one hundred layers. It would then be feasible for the semiconductor component shown in Figure 3 to be created from more than three different layers, in this way, several layers of pyrite could be used and if appropriate, several layers of boron could be used and / or phosphorus. The semiconductor component used as pyrite - as explained above - can be created - within the scope of the invention - not only as a single-layer or multi-layer solid-state solar cell, but also as a thin solar cell, such like a solar cell MIS, a photo-chemical cell or similar.

The semiconductor component according to the invention is used to its best advantage as a solar cell, since as such, it achieves an extraordinarily high degree of efficiency. Clearly, this semiconductor component can be used for other purposes, such as diode, transistor, tristor, or the like. In theory a semiconductor component according to the invention could also work, if a pyrite layer and a compound thereof are produced on the basis of boron (B) or phosphorus (P).

Claims (5)

1. CLAIMS 1 .- A semiconductor component, in particular a solar cell, having at least one semiconductor base material consisting of a mono or polycrystalline structure, which consists at least in part of pyrite with the chemical composition FeS2 and which is cleaned for the purpose of achieving a defined degree of purity, characterized in that the semiconducting base material comprising at least in part pyrite with the chemical composition FeS2, is combined or mixed with boron and / or phosphorus.
2. 2. A semiconductor component according to claim 1, characterized in that the FeS2 semiconductor base material is combined or mixed with boron and phosphorus.
3. 3. A semiconductor component according to claim 1, characterized in that the semiconductor base material consists of at least one pyrite layer, at least one boron layer, and at least one phosphor layer.
4. 4. A semiconductor component according to claim 1, characterized in that, with a multilayer semiconducting base material, it has at least one layer p or n of pyrite and at least one layer n or p of a different semiconductor. 5. A semiconductor component according to any of the preceding Claims characterized in that the concentration of each of the elements integrated to the base material has a mass percentage of between 10"8 and 20. __ '6.- A semiconductor component of according to any of the preceding claims characterized in that the semiconductor component is formed as a single layer or multi-layer cell, such as a thin solar cell, a solar cell MIS, a photochemical cell or the like 7.- A semiconductor component according to any of the preceding Claims characterized in that the pyrite has a coefficient of thermal expansion at 90 to 300 K of 4.5x 10"6 K" 1 and 300 to 500 K of 8.4x10"ft _ '. 8. A semiconductor component according to any of the preceding Claims characterized in that the pyrite with a FeS2 chemical composition has an elementary cell of 12 atoms and a unit cell length of approximately 5.4185 Armstrongs, in which the basic form of the crystal of pyrite is cubic, dodecagonal, pentagonal or octahedral hexahedron. 9. A semiconductor component according to any of the above claims characterized in that the semiconductor base material is pyrite, treated by a multi-zone purification process and preferably has a purity of 99.9999%. 10. A semiconductor component according to any of the preceding Claims characterized in that in the case of a multi-layer structure, the semiconductor component has up to one hundred layers. 1. A method for producing a semiconductor component, in particular a solar cell according to one of the preceding Claims, characterized in that the semiconducting base material used is both a naturally occurring pyrite and a synthesized iron pyrite. and sulfur, with the chemical composition of FeS2, which is combined or mixed with boron and / or phosphorus respectively. 12. A method according to claim 1, characterized in that the pyrite and / or the iron and sulfur base material, when the pyrite is produced synthetically, are treated by a multi-zone purification process in order to achieve a high purity level of 99.9999% ». 13. A method according to claim 1, characterized in that the pyrite is produced by a hydrothermal process and a wet chemical process (CVT). 14. A method according to claim 1, characterized in that the pyrite is produced by a process which melts tellurium, NaS2 or FeCl2.
5. 5. A method according to claim 11, characterized in that the pyrite is produced and / or mixed by the gas phase transport method. 16. A method according to claim 15, characterized in that Br2 is used as a transport medium in gas phase transport. 17. A method according to claim 1 1, characterized in that the pyrite is produced by the sulphuration of plasma, a thermal sulphidation, a MOCVD process, reactive pulverization, spray pyrolysis, or by a different process. 8. A method according to claim 11, characterized in that boron and phosphorus are combined or mixed respectively with pyrite by an epitaxial growth method. 19. A method according to claim 1, characterized in that the boron and / or phosphorus are combined or mixed respectively with the pyrite base material by an ion implantation method. 20. - A method according to claim 1, characterized in that boron and / or phosphorus possess a degree of purity of 99.999%) before being combined with pyrite.