Patent Application
20160322526
The invention relates to a photovoltaic cell which has a semiconductor substrate having a front face and a rear face, wherein at least one front face contact is arranged on the front face and at least one rear face contact is arranged on the rear face. The invention further relates to a photovoltaic module including a plurality of photovoltaic cells, to a method for producing a photovoltaic cell and to a building or a façade element having such a photovoltaic module.
It is known from the art to produce photovoltaic cells from semiconductor material. The photovoltaic cell consists substantially of a flat p-n-diode which is provided with front and rear face contacts. The front face contacts usually cover only a subarea of the semiconductor material, as a result of which sunlight can penetrate the semiconductor material. The electron-hole pairs which are formed when light is absorbed drift to the front face or rear face and can be tapped as electric voltage via the front face contacts and the rear face contacts. Such photovoltaic cells can be used e.g. for the electric energy supply of a building.
In particular when used in transparent solar modules, these known photovoltaic cells have the drawback that Moire effects can occur on the surface of the photovoltaic cells and can confuse a person looking at a building façade equipped therewith. Finally, the known photovoltaic cells and modules produced therefrom offer limited esthetic design options.
Proceeding from this prior art, an object of the invention to provide a photovoltaic cell which offers more diverse design options and is pleasant to look at.
According to the invention, the object is solved by a photovoltaic cell according to claim 1, a photovoltaic module according to claim 12, a building according to claim 16 and a method for producing a photovoltaic cell according to claim 17.
It is proposed according to the invention to compose the photovoltaic cell from a plurality of flat semiconductor substrates, each having a front face and a rear face. By contrast, photovoltaic cells known to date always use a single semiconductor substrate having a front face and an opposite rear face.
At least one pn junction is formed parallel to the front face and/or rear face by doping the semiconductor substrate, and it is at this junction where sunlight which impinges thereon is absorbed. The resulting electron-hole pairs drift to the front face or rear face respectively and can be tapped as electric voltage or electric current via the appropriate contacts.
According to the invention, it has now been found that an individual photovoltaic cell does not necessarily have to be formed from a single flat semiconductor substrate. The photovoltaic cell according to the invention is rather made from a plurality of semiconductor substrates, each of which forms a subarea of the photovoltaic cell. The individual subareas or sub-cells of the photovoltaic cell are electrically connected to one another in parallel. As a result, the electric current formed by the respective subareas adds up whereas the electric voltage remains constant.
Each individual semiconductor substrate from a plurality of flat semiconductor substrates carries a front face contact on the front face thereof and a rear face contact on the rear face thereof. In each case, the front face contact only occupies a subarea of the semiconductor substrate, as a result of which other subareas remain uncovered to allow the penetration of sunlight. In some embodiments of the invention, a plurality of the front face contacts can be available which can be formed e.g. as thin contact fingers or contact lines. Therefore, the resulting electric current can be tapped more effectively since the drift lengths of the minority charge carriers in the semiconductor substrate for reaching the front face contact are smaller.
The rear face contact can also only cover a subarea of the rear face of the semiconductor substrate and can also be formed as thin contact fingers or contact lines. In other embodiments of the invention, the rear face contact can also be applied over the entire area so as to yield a complete or almost complete metallization of the rear faces of the semiconductor substrates.
In some embodiments of the invention, the semiconductor substrate can have at least one bore by means of which the front face contacts can be connected in an electrically conductive way to connecting elements on the rear face. As a result, it is possible to minimize shadowing of the front face by the power rails.
In some embodiments of the invention, the front face contacts and the rear face contact can be applied in generally known manner by screen printing, aerosol printing or pad printing or by the deposition of thin metal layers in vacuo. In some embodiments of the invention, the contacts can be reinforced by electroplating to improve the current load capacity. The material of the front and rear face contacts is usually selected on the basis of the material of the semiconductor substrate and the doping thereof in such a way that ohmic contacts result. In some embodiments of the invention, the contacts can contain or consist of silver, gold or copper.
The semiconductor substrate as such can contain a direct semiconductor material or an indirect semiconductor material. In some embodiments of the invention, the semiconductor substrate can consist of silicon or contain silicon. In addition, the semiconductor substrate can contain dopants to render possible a predeterminable electric conductivity. Furthermore, the semiconductor substrate can contain conventional contaminations. In some embodiments of the invention, the semiconductor substrate can be crystalline. In some embodiments of the invention, the semiconductor substrate can be amorphous. In some embodiments of the invention, the semiconductor substrate can have a thickness of about 50 μm to about 1000 μm or a thickness of about 100 μm to about 500 μm.
In some embodiments of the invention, the photovoltaic cell can have a plurality of power rails, the longitudinal extensions of which run along a first spatial direction and which enclose together with a longitudinal extension of the front face contacts an angle of about 20° to about 90° or an angle of about 45° to about 90° or an angle of about 80° to about 90°. The stated angular ranges here merely refer to the magnitudes, and therefore the angle between the longitudinal extension of the front face contacts and the longitudinal extension of the power rails can be marked off in a positive or negative direction.
Due to this geometry, the plurality of power rails takes care that the current of different subareas of the photovoltaic cell distributes along the longitudinal extension of the power rails. The front face contacts extending approximately orthogonal thereto distribute the current in a direction orthogonal to the longitudinal extension of the power rails, and therefore all front face contacts of all semiconductor substrates are connected to one another via the power rails and the front face contacts of adjacent semiconductor substrates. In an equal way, the rear face contacts of all semiconductor substrates are electrically connected to one another. Therefore, compensating currents can flow along the longitudinal extension of the power rails and via the rear face contacts also in a direction orthogonal thereto. This serves to achieve in an easy way the parallel connection of the subareas of the photovoltaic cell according to the invention.
The photovoltaic cells according to the invention can be joined in a generally known manner to give a photovoltaic module. Therefore, the photovoltaic cells according to the invention should not be mistaken for a known photovoltaic module which also contains a plurality of photovoltaic cells but where each cell only has a single semiconductor substrate.
In some embodiments of the invention, each power rail is connected in an electrically conductive fashion to each other power rail of the corresponding side via at least one front face contact or at least one rear face contact. An electrically conductive connection shall here be understood to mean a direct current coupling between the power rails for the purposes of the present invention.
In some embodiments of the invention, each power rail with the exception of the peripheral power rails can be connected to at least two front face contacts or at least two rear face contacts of different semiconductor substrates. This is equivalent to a geometry where different semiconductor substrates or subareas of the photovoltaic cell overlap in a direction orthogonal to the longitudinal extension of the power rails.
In some embodiments of the invention, at least two semiconductor substrates from the plurality of flat semiconductor substrates of a photovoltaic cell can have a different shape and/or size. The effect of this feature is that irregular, non-periodic structures can be realized which virtually prevent moire effects from occurring.
In some embodiments of the invention, the first power rails and the second power rails can be arranged approximately parallel to one another, the first and second power rails being offset relative to one another in a direction orthogonal to the longitudinal extension of the power rails. This serves to prevent the first and second power rails from causing a short circuit in subareas where no semiconductor substrate is located.
In some embodiments of the invention, the plurality of flat semiconductor substrates can consist of an equal material. In some embodiments of the invention, the plurality of flat semiconductor substrates can consist of the same material. If the individual semiconductor substrates consist of an equal material, they produce an equal electric voltage when irradiated with light, such that a parallel connection of the subareas of the photovoltaic cells is possible without large output currents flowing between the individual semiconductor substrates. Furthermore, the cell voltage is defined by the selection of the semiconductor material. Nevertheless, it is possible to use semiconductor materials from different production charges or offcuts from semiconductor production, which have to be discarded thus far. As a result, the crystalline semiconductor material, which is produced in an energy-intensive way, can be utilized more efficiently.
In some embodiments of the invention, the semiconductor substrates can be provided with coatings having different colors to extend the design options of the photovoltaic cell. Such a coating can contain or consist of silicon nitride of varying thickness, as a result of which the coating acts as an interference filter and gives an intense color effect without influencing the cell voltage.
In other embodiments of the invention, the semiconductor substrates can consist of the same material by cutting all semiconductor substrates out of a single wafer. The cutting can be done e.g. by laser cutting or machining.
In some embodiments of the invention, a photovoltaic cell can contain segments which are not connected electrically to the power rails and/or which are made from an insulating material and have at least one front face contact and/or at least one rear face contact which is electrically connected to at least two power rails. The additional use of segments which are not electrically connected to the power rails, can serve to fill subareas of the photovoltaic cell with material which gives an optical impression which is approximately equal to that of the semiconductor substrate. As a result, the esthetic appearance of the photovoltaic cell can be adapted to different requirements. Segments made from an insulating material and having a front face contact and/or a rear face contact, can be inserted in sites where no photovoltaically active semiconductor substrate is provided which requires a current flow between different power rails to make possible the desired parallel connection of the individual semiconductor substrates.
In some embodiments of the invention, the plurality of flat semiconductor substrates of each photovoltaic cell can have an equal surface area. It is thus ensured that different photovoltaic cells supply an equal electric current in spite of different appearance and different total area. Here, the total area is considered to be the sum of the areas of the semiconductor substrates and the intermediate spaces. This makes possible a low-loss series connection of different photovoltaic cells within a photovoltaic module. In other embodiments of the invention, cells made from different materials can be interconnected to one another and all supply the same current. For this purpose, the respective active surface of the cells can be adapted in such a way that materials having a small current yield have larger surface areas than materials with higher current yield.
In some embodiments of the invention, the power rails can be embedded in an embedding film. This serves to considerably facilitate the handling regarding the assembly or production of the photovoltaic cells according to the invention when photovoltaic modules are produced. In some embodiments of the invention, the embedding film can have an adhesive layer and/or can be sealed with the semiconductor substrates to produce the photovoltaic cell according to the invention.
The invention shall be explained in more detail below by means of drawings without limiting the general inventive concept, wherein:
A possible production method of the photovoltaic cell according to the present invention is explained by means of
In the first method step, a plurality 3 of second power rails 30 is provided, as shown in
As is shown in
In order to avoid a short circuit between the first power rails 40 and the second power rails 30, it is possible to arrange the first and second power rails offset to one another. As a result, the second power rails are arranged in the gaps between two first power rails and the first power rails are arranged in the gaps between two second power rails.
In order to make possible an efficient parallel connection of the individual semiconductor substrates within a photovoltaic cell, said semiconductor substrates can be made from an equal or the same material, as a result of which an equal cell voltage is achieved with constant illumination. In order to obtain an efficient series connection of the photovoltaic cells within the photovoltaic module, the active surface area of all semiconductor substrates processed within a photovoltaic cell can be identical, as a result of which each photovoltaic cell can supply an equal electric current when the light intensity is equal. If there are differences as regards the ability to supply current, segments 16 can be arranged in some photovoltaic cells, said segments consisting of an insulator and, like photovoltaic cells, being provided with front and rear face contacts. These segments 16 can be used to render possible a flow of the current between power rails. However, since the segments 16 per se do not supply any electric energy, the use of these segments 16 can serve to finely adapt the current supplied by the photovoltaic cell 1. In an equal way, it is also possible to insert segments 15, which consist of an insulating material when a current flow beyond the boundaries of the power rails is already ensured by the semiconductor substrates of the photovoltaic cell.
As shown in
Each semiconductor substrate 10a, 10b and 10c has a plurality of front face contacts which adopt the shape of elongate contact fingers. The front face contacts can be arranged up to close to the edge of the semiconductor substrates 10a, 10b and 10c.
However, the edge itself can remain uncovered to avoid a short circuit between front and rear face contacts.
The rear face contact can be made in an equal way as the front face contact or comprise a metallization over the entire surface area. The front and rear face contacts can be applied in generally known manner to each individual semiconductor substrate 10a, 10b and 10c, e.g. by depositing and subsequently structuring a metal layer, by a printing method or by deposition without external current or deposition using electroplating.
The round semiconductor substrates 10a, 10b and 10c can be made from a larger substrate by a cutting method, e.g. by laser cutting. In other embodiments, round starting materials or wafers can be used directly without further cutting being required.
If the outer contour of the semiconductor substrates 10, which is defined by the cutting guide, is slightly larger than the contour of the recesses 107, it can be ensured that an edge is left around the front face contacts 21 and can reliably prevent a short circuit between front face contact and rear face contact.
The middle part of
A rear face contact 22 is disposed on the rear face 102. In the illustrated embodiment, the rear face contact 22 is formed by a metallization over the entire area. However, the rear face contact 22 can also have a structuring as described by means of the front face contact 21.
The rear face contact 22 is in contact with second power rails 30. The second power rails 30 are embedded in an embedding film 31. Here, only a part of the cross-section of the power rails 30 is received in the embedding film 31, as a result of which a metallic surface area of the power rail 30 is exposed in the direction of the rear face contact 22.
In addition, the embedding film 31 can be provided with an adhesive layer to both contact the power rails 30 with the rear face contact 22 and render possible a mechanically robust combination between the power rails and the semiconductor substrates 10 by applying and pressing on the embedding film 31.
In an equal way, first power rails 40 are received in an embedding film 41. The first power rails 40 are placed on the first face 101 of the semiconductor substrate 1, as a result of which these rails contact the front face contacts 21. At least the embedding film 41 can be transparent or translucent, such that sunlight impinges on the first face 101 of the semiconductor substrates 10 when the photovoltaic cell is operated.
Each photovoltaic cell 1a and 1b is composed of a plurality of semiconductor substrates 10, which are interconnected in parallel to one another via first power rails 40 and second power rails 30, whereas the first cell 1a and the second cell 1b form an electric series connection.
As shown in
The varying gross area of the photovoltaic cells 1a and 1b renders possible different design options on a façade. For example, the illusion of a leaking or melting photovoltaic module 5 can be obtained on the edges thereof. Photovoltaic modules which are known to date and have identical photovoltaic cells always have geometrically defined, usually straight edges. Furthermore, the photovoltaic cell 1b can be used with a larger gross area in the region of light bands or window openings to thus render possible the access of light into the building or the unobstructed inhabitants' view from the building. In other surface areas of the façade, the photovoltaic cell 1a renders possible a larger energy output per area element on account of the denser coverage thereof with semiconductor substrates 10.
The embedding films 41 and 31 can be welded together to avoid the penetration of moisture. The solder connections between the front face contacts and the rear face contacts of the photovoltaic cells 1 and the power rails 30 and 40 can simultaneously be made during welding.
A rear face cover 52 borders on the embedding film 31. In some embodiments of the invention, the rear face cover can be transparent or translucent so as to create an unobstructed view through the photovoltaic module between the semiconductor substrates 10. Alternatively, the rear face cover 52 can have a colored design, which either stresses the geometric pattern of the semiconductor substrates 10 or hides the presence of the semiconductor substrates 10 from the viewer so as to create a homogeneous color impression of the photovoltaic module 5.
In some embodiments of the invention, the decorative element 55 can be designed to be readily exchangeable, e.g. as a self-adhesive film or by Velcro fasteners. Due to this, it is possible to adapt the appearance of the photovoltaic module 5 to changing requirements.
The photovoltaic cells 1a and 1b can be arranged in a striped pattern in the photovoltaic module 5. This leads to an angle-dependent absorption of sunlight and an also angle-dependent view through a window provided with the photovoltaic module 5. For example, the view can only be slightly impaired in an almost horizontal viewing direction whereas sunlight, which impinges on the photovoltaic module 5 from a higher position is absorbed in both planes since light which is incident through the intermediate spaces between the photovoltaic cells 1a, is absorbed by the photovoltaic cells 1b and is used for the electric energy production. In some embodiments, the photovoltaic cells 1a can be connected to a first inverter and the photovoltaic cells 1b can be connected to a second inverter.
In order to avoid, or at least reduce, shadowing of the front face 101 by power rails, a bore 211 is located below the front face contact 21, said bore being filled or being conductively coated with a conductive material so as to connect the front face contact 21 to a contact element 210 on the rear face 102 of the semiconductor substrate 10. The contact element 210 can be connected to the power rail 40, as a result of which the two power rails 30 and 40 are arranged on the rear face 102 of the semiconductor substrate 10 and on the photovoltaic cell 1, respectively.
The first photovoltaic cell has three semiconductor substrates 10a, 10b and 10c, each having an approximately round basic form. The contact elements 210 and the rear face contacts 22 are arranged in such a way that the contact elements 210 are contacted by the first power rail 40 and the rear face contacts 22 are contacted by the second power rail 30. This leads to an electric parallel connection of the three semiconductor substrates 10a, 10b and 10c in the photovoltaic cell 1a.
The second photovoltaic cell 1b has a single semiconductor substrate 10d. In other embodiments of the invention, the number of semiconductor substrates can be larger or smaller in the respective cells. However, each photovoltaic cell advantageously has approximately an equal area of semiconductor substrates, as a result of which the voltage and current supplied by the photovoltaic cell are approximately equal. Of course, the respective form of the semiconductor substrates 10 can be different, as already described above.
As is shown in
The invention is, of course, not limited to the embodiments shown in the drawings. The above description should not be regarded as limiting but as explanatory. Features from different, above specified embodiments of the invention can be combined into further embodiments. The below claims should be comprehended in such a way that a stated feature is available in at least one embodiment of the invention. This does not rule out the presence of further features. If the claims and the above description define “first” and “second” features, this designation serves to distinguish between two features of the same kind without determining an order.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 226 943.9 | Dec 2013 | DE | national |
| 10 2014 200 956.1 | Jan 2014 | DE | national |
This application is a 371 nationalization of PCT/EP2014/078317, entitled “PHOTOVOLTAISCHE ZELLE, PHOTOVOLTAIKMODUL SOWIE DESSEN HERSTELLUNG UND VERWENDUNG,” having an international filing date of Dec. 17, 2014, the entire contents of which are hereby incorporated by reference, which in turn claims priority under 35 USC §119 to German patent application DE 10 2014 200 956.1 filed on Jan. 21, 2014, entitled “Photovoltaische Zelle, Photovoltaikmodul sowie dessen Herstellung and Verwendung,” the entire contents of which are hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/078317 | 12/17/2014 | WO | 00 |
