FR2878374A1 - Solar cell with a heterojunction and buried metallization, made with a crystalline semiconductor substrate and an amorphous semiconductor layer with different types of conductivity - Google Patents

Abstract

A solar cell (100) incorporates, on at least one of the surfaces (2) of a crystalline semiconductor substrate (1) with a first type of conductivity, at least one layer (4) of amorphous semiconductor doped with a second type of conductivity opposite to the first type of conductivity. It includes some collection fingers (5.1 to 5.n) and at least one collection bus (6), electrically connecting the collection fingers, metallised on the amorphous semiconductor layer and at least one transparent conducting oxide layer (7) covering the amorphous semiconductor layer and the assembly of collection fingers, but not the totality of the collection bus. Independent claims are also included for : (A) a module of solar cells incorporating several of these solar cells connected in series and/or parallel; (B) the production of the solar cell.

Description

2878374 1

  SOLAR CELL WITH HETEROGRAPHY AND BOTTOM METALLIZATION

DESCRIPTION TECHNICAL FIELD

  The present invention relates to a solar cell with heterojunction and buried metallization, and the method for its manufacture. The method is particularly suitable for producing this type of silicon solar cell.

  STATE OF THE PRIOR ART The principle of amorphous / crystalline heterojunction is already known. Solar cells incorporating this principle have already been patented.

  The principle of this type of cell is to use a crystalline semiconductor substrate doped with a first type of conductivity. On one of its faces, an amorphous semiconductor layer doped with a second type of conductivity, opposite to the first type of conductivity, then comes into contact. A PN junction called heterojunction is then obtained because the two semiconductors used, although of the same atomic composition, do not have the same band gap since they do not have the same crystallographic arrangement. It then suffices to make a transparent electrode on one face of the junction and, on another face, opposite to the previous face, to make an ohmic contact electrode to obtain a heterojunction solar cell.

  US-A-5,066,340 discloses a heterojunction solar cell. This comprises a heterojunction formed by a crystalline silicon substrate of a first conductivity type and an amorphous silicon layer of a second conductivity type, opposite to the first conductivity type, produced on one of the faces of the crystalline substrate. This cell also integrates, between the crystalline substrate and the amorphous silicon layer, an intrinsic microcrystalline silicon layer.

  US-A-5,213,628 also discloses a heterojunction solar cell. As in US-A-5,066,340, this cell comprises a heterojunction formed by a crystalline silicon substrate of a first conductivity type and an amorphous silicon layer of a second conductivity type, opposite to the first type of conductivity, performed on one side of the crystalline substrate. This cell integrates, between the crystalline substrate and the amorphous silicon layer, an intrinsic amorphous silicon layer.

  US-A-6 091 019 discloses a heterojunction solar cell. On one side of a crystalline silicon substrate of a first conductivity type, several successive depositions are made so as to form a stack of several layers: first an intrinsic amorphous silicon layer, then an amorphous silicon layer doped with a second type of conductivity opposite to the first conductivity type, then a conductive transparent oxide layer, for example tin oxide and indium (known under the trade name ITO for Indium Tin Oxide) ), and finally the metallization of silver collecting fingers. On another face, opposite to the previous face, of the crystalline silicon substrate, the deposits are identical except for the second layer which is amorphous silicon doped with the first type of conductivity. Collection buses are then deposited on the metallizations made on both sides of the solar cell.

  In this type of cell, the metallizations can be made by screen printing. They must then be annealed. In order not to damage the amorphous silicon layers, the metallizations must be annealed at low temperature, that is to say at a temperature below about 400 C. This condition involves the use of specific so-called low-temperature screen printing pastes , for example based on polymer / silver. The major disadvantage of these so-called low-temperature screen printing pastes is that they have a resistivity ten times greater than so-called high-temperature screen printing pastes used in particular in the manufacture of homojunction solar cells. This high resistivity increases the series resistance of heterojunction cells, resulting in a decrease in the form factor. The form factor is the ratio of the product of the maximum output voltage to the maximum output current and the product of the open circuit voltage to the current of the short-circuit current. This decrease in the form factor causes a decrease in the efficiency of the solar cells.

  The metallizations can also be carried out by other processes such as evaporation or spraying. However, even if these methods make it possible to avoid the use of so-called low-temperature screen printing pastes, the metallizations thus produced have a high contact resistance. This high contact resistance also increases the series resistance of cells with heterojunction, and thus results in a decrease in the efficiency of the solar cells.

  In addition, whatever the method used, the adhesion of metallizations to semiconductor materials is not always satisfactory. This poor adhesion then poses problems when interconnecting solar cells by welding on the collection buses.

  PRESENTATION OF THE INVENTION The object of the present invention is to propose a heterojunction solar cell which does not have the drawbacks mentioned above, that is to say having a lower series resistance than that of known heterojunction cells, and having metallizations having good adhesion with the semiconductor materials.

  To achieve these objects, the present invention proposes a solar cell comprising, on at least one of the faces of a crystalline semiconductor substrate of a first conductivity type, at least one doped amorphous semiconductor layer of a second type. conductivity sensor, opposite to the first conductivity type, and having collection fingers and at least one collection bus, electrically connecting the collection fingers to each other, metallized on the amorphous semiconductor layer, and at least one layer of Conductive transparent oxide which covers the amorphous semiconductor layer and the collection finger set, but not the entire collection bus.

  Thus, instead of producing a heterojunction solar cell whose collection fingers are metallized on the conductive transparent oxide layer, a heterojunction solar cell is produced whose collection fingers and the collection bus are directly metallized on the layer. amorphous semiconductor, and whose conductive transparent oxide layer covers all collection fingers and the amorphous semiconductor layer, but not the entire collection bus. This new cell makes it possible to significantly improve the contact resistance between the metallizations and the amorphous semiconductor material. This therefore causes a decrease in the series resistance of the cell, and therefore an increase in the form factor, which ultimately results in an increase in efficiency. This cell also makes it possible to improve the adhesion of the metallizations to the semiconductor material.

  The collection fingers and / or the collection bus can be made with so-called low-temperature screen printing paste, by evaporation or by spraying.

  The collection fingers and / or the collection bus are preferably made from aluminum or a noble metal.

  The collecting fingers may be arranged substantially parallel to one another.

  The collection fingers may also be regularly spaced relative to each other. This arrangement makes it possible to obtain a homogeneous collection of the current.

  The collection bus preferably extends over the collection fingers, substantially perpendicular to them.

  It can be envisaged that the solar cell comprises, between the semiconductor substrate and the amorphous semiconductor layer, an intermediate layer of semiconductor. This semiconductor layer may be made of intrinsically amorphous or polymorphic semiconductor or gradually doped with the second type of conductivity. This intermediate layer has a gap band gap intermediate that of the semiconductor substrate and that of the amorphous semiconductor layer. It ensures a good interface state between the semiconductor substrate and the amorphous semiconductor layer.

  In this case, the intermediate layer of semiconductor is preferably made of silicon, for example thin layer.

  It is preferable that the semiconductor substrate is of monocrystalline silicon or polycrystalline silicon, depending on the type of device desired.

  The doped amorphous semiconductor layer of the second conductivity type is preferably silicon.

  In addition, the doped amorphous semiconductor layer of the second conductivity type may be in a thin layer.

  It is conceivable that the conductive transparent oxide layer is tin oxide and indium oxide.

  Several solar cells can be grouped together to form a module, these cells being connected in series and / or parallel.

  The present invention also relates to a method for producing a solar cell comprising the following steps: a) depositing, on at least one face of a crystalline semiconductor substrate of a first conductivity type, at least one layer of doped amorphous semiconductor of a second conductivity type, opposite to the first conductivity type, b) metallization of a set of collecting fingers on the amorphous semiconductor layer, c) metallization of at least one collection bus on the amorphous semiconductor layer, electrically connecting the collecting fingers to each other; d) producing at least one conductive transparent oxide layer on the amorphous semiconductor layer, also covering all of the collecting fingers; and the collection bus, e) etching in the transparent conductive oxide layer of at least one window exposing at least a portion of the collection bus.

  The method may comprise, between step b) and step c), a step of performing a cold sintering of all the collecting fingers, by pressing these collecting fingers.

  For this method of realization, the pressing of the collection fingers can be achieved with a hydraulic or pneumatic press.

  The pressing is preferably carried out at a temperature between about room temperature and 400 C. The temperature of 400 C is approximately the maximum temperature because at a higher temperature, there would be a deterioration of the semiconductor device.

  It is also preferable that the pressing is carried out at a pressure level of between approximately 106 Pa and 5x108 Pa, making it possible to perform cold sintering of the collection fingers.

  The etching can be performed by laser or by deposition of screen printing paste.

  It can be envisaged that the metallization of the collecting fingers and / or the metallization of the collection bus are carried out with so-called low-temperature screen-printing paste, by evaporation or else by spraying.

  It is preferable that the collection fingers and / or the collection bus are made of aluminum or a noble metal.

BRIEF DESCRIPTION OF THE DRAWINGS

  The present invention will be better understood on reading the description of exemplary embodiments given purely by way of indication and in no way limiting, with reference to the appended drawings in which: FIG. 1 represents a perspective view of an example of a solar cell with heterojunction buried metallization, object of the present invention, - Figure 2 shows a sectional view of a heterojunction solar cell buried metallization, object of the present invention, realized according to another embodiment than that of Figure 1, - Figures 3A to 3D show sectional views, along a sectional plane perpendicular to that of Figure 2, of the steps of producing a buried metallization heterojunction solar cell, object of the present invention, according to the embodiment of FIG. 1; FIG. 4 represents a view from above of a module formed of several solar cells, linked together, also object of the present invention.

  Identical, similar or equivalent parts of the various figures described below bear the same numerical references so as to facilitate the passage from one figure to another.

  The different parts shown in the figures are not necessarily in a uniform scale, to make the figures more readable.

  DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS Referring to Figure 1 which shows in perspective a solar cell 100, object of the present invention. It is represented a solar cell 100 comprising on at least one of the faces 2 of a crystalline semiconductor substrate 1 of a first conductivity type, at least one doped amorphous semiconductor layer 4 of a second conductivity type. , opposite the first type of conductivity. On this layer of amorphous semiconductor 4 is a set of collecting fingers 5.1 to 5.n. At least one collection bus 6, for example located on the collection fingers 5.1 to 5. n, electrically connects these collecting fingers 5.1 to 5.n. The set of collection fingers 5.1 to 5.n and the collection bus 6 are metallized on the amorphous semiconductor layer 4. A conductive transparent oxide layer 7 covers the amorphous semiconductor layer 4 and the set of collection fingers 5.1 to 5.n, but not the collection bus 6.

  This solar cell 100 comprises the semiconductor substrate 1. This semiconductor substrate 1 may be, for example, of monocrystalline or polycrystalline silicon, of a first type of conductivity, for example N. It is not necessary to use a silicon of excellent quality because, due to the absence of strong thermal stresses during the cell production process, the silicon will not see the life of its charge carriers altered. The thickness of the semiconductor substrate 1 may be for example between about 10 micrometers and a few hundred micrometers.

  The semiconductor substrate 1 comprises on the face 2 the doped amorphous semiconductor layer 4 of the second type of conductivity, that is to say P. This layer of amorphous semiconductor 4 extends over the entire surface of the 2 side of the semiconductor substrate 1. The amorphous semiconductor layer 4 may be silicon, for example thin layer. The thickness of this layer 4 is then a few nanometers, for example about 7.5 nanometers.

  The collection fingers 5.1 to 5.n are metallized on the amorphous semiconductor layer 4. In the example of Figure 1, these collecting fingers 5.1 to 5.n are made with so-called low-temperature screen printing paste. It can also be envisaged that they are made by spraying or by evaporation. They have for example a width of about 100 micrometers and a metallization height of about 10 micrometers. They each have a substantially identical metallization height and are regularly spaced apart by a distance of about 2 millimeters. This arrangement makes it possible to obtain a homogeneous collection of the current. The number of collecting fingers 5.1 to 5.n thus depends on the dimensions of the solar cell 100. This number must be sufficient for the series resistance presented by the solar cell 100 is not too high. The collection fingers 5.1 to 5.n are arranged parallel to each other, and are based on aluminum or a noble metal, such as silver.

  At least one collection bus 6 is metallized on the amorphous semiconductor layer 4. Again, the number of collection buses 6 depends on the dimensions of the solar cell 100. The number of collection buses 6 must be adapted according to the width of the solar cell 100. In FIG. 1, a single collection bus 6 is metallized on the amorphous semiconductor layer 4. In the example of FIG. 1, this collection bus 6 is made of paste so-called low-temperature screen printing. It can also be envisaged that it is carried out by spraying or by evaporation. It extends over the collection fingers 5. 1 to 5.n, substantially perpendicular to them, and electrically connecting them. The collection bus 6 has a width greater than that of the collection fingers 5.1 to 5.n. It is about 2 millimeters. Its metallization height is about 100 micrometers. The collection bus 6 is based on aluminum or a noble metal, such as silver.

  The transparent conductive oxide layer 7, for example tin oxide and indium oxide, is stacked on the amorphous silicon layer 4. This transparent conductive oxide layer 7 also covers the collecting fingers 5.1 to 5. .not. This transparent conductive oxide layer 7 has a thickness of about 85 nanometers. The collection bus 6 is not entirely covered by the transparent conductive oxide layer 7 because a window 8 is etched at the level of the collection bus 6, through the transparent conductive oxide layer 7, making it possible to put exposed at least part of the collection bus 6. In Figure 1, the bus is stripped in full. The collection bus 6 thus forms an electrode of the solar cell 100.

  The solar cell 100 comprises, for example, on another face 10 of the semiconductor substrate 1, opposite the face 2, a metal layer 9. This metal layer 9, for example based on aluminum or noble metal such as silver, is the second electrode of the solar cell 100. The solar cell 100 may comprise on the other side 10 a different structure of the metal layer 9. For example, the solar cell 100 may comprise on the other side 10 the same elements as those on the face 2, except the doped amorphous semiconductor layer which would be N-doped. In another embodiment, the solar cell 100 may comprise, between the face 2 of the semiconductor substrate 1 and the amorphous semiconductor layer 4, an intermediate layer of semiconductor 3, as can be seen in FIG. 2. FIG. 2 is a view along a section plane perpendicular to the collection fingers 5.1 to 5.n . The semiconductor intermediate layer 3 has a bandgap width intermediate that of the semiconductor substrate 1 and that of the amorphous semiconductor layer 4. It makes it possible to ensure a good interface state between the semiconductor substrate. 1 and the amorphous semiconductor layer 4. This ultimately leads to an improvement in the efficiency of the solar cell. This semiconductor layer 3 can be made in intrinsic amorphous or polymorphic semiconductor, as described in US Pat. No. 5,213,628, or gradually doped with the second type of conductivity, or else in intrinsic microcrystalline semiconductor, as described in US-A-5,066,340. The thickness of this semiconductor layer 3 is substantially identical to that of the amorphous semiconductor layer 4, that is to say a few nanometers, for example, about 7.5 nanometers.

  We will now be interested in a method of producing a solar cell 100 also object of the present invention.

  As can be seen in FIG. 3A, one starts from a semiconductor substrate 1 of a first conductivity type, for example N. On a face 2 of the semiconductor substrate 1, the deposition of a semiconductor layer is carried out. amorphous conductor 4 doped with a second conductivity type, opposite to the first conductivity type, that is to say P. This amorphous semiconductor layer 4 extends over the entire surface of the face 2 of the semiconductor substrate. Conductor 1. The deposition of this layer of amorphous semiconductor 4 may for example be carried out by a plasma-enhanced chemical vapor deposition technique (known by the British name PECVD for Plasma Enhanced Chemical Vapor Deposition).

  A set of collection fingers 5.1 to 5.n is then metallized on the amorphous semiconductor layer 4. In FIG. 3B, only one collection finger 5.i is shown. The metallization of all the collection fingers 5.1 to 5.n is for example made with so-called low-temperature screen printing paste. It can also be envisaged that they are made by spraying or by evaporation. The collection fingers 5.1 to 5.n are based on aluminum or a noble metal such as silver.

  The collection fingers 5.1 to 5.n can then be cold sintered by pressing these collection fingers 5. 1 to 5.n. The pressing is carried out at a temperature of between about room temperature and 400 ° C., at a pressure of between about 10 6 Pa and 5 × 10 6 Pa, making it possible to cold sinter the collection fingers 5.1 to 5.n. The temperature of 400 C is approximately the maximum temperature because beyond that, there would be a deterioration of the semiconductor device. The pressing can be done by a hydraulic or pneumatic press.

  The collection bus 6 is then metallized with so-called low-temperature screen-printing paste, by spraying or else by evaporation, on the amorphous semiconductor layer 4, also partially covering the collecting fingers 5.1 to 5.n. It is based on aluminum or a noble metal such as silver.

  As can be seen in FIG. 3C, a conductive transparent oxide layer 7, for example tin oxide and indium oxide, is stacked on the amorphous semiconductor layer 4. This oxide layer transparent conductor 7 covers the entire surface of the amorphous semiconductor layer 4, the set of collection fingers 5.1 to 5.n and the collection bus 6. The conductive transparent oxide layer 7 is made, for example, by sputtering.

  The window 8 is then etched at the collection bus 6 through the transparent conductive oxide layer 7, as can be seen in FIG. 3D. This window 8 makes it possible to expose at least part of the collection bus 6 in order to be able to interconnect the solar cell 100 with other elements. This etching is carried out, for example, by laser, or by depositing a stripping screen printing paste.

  Finally, an ohmic contact electrode is formed on another face 10 of the semiconductor substrate 1, opposite to the face 2. This electrode may for example be a metal layer 9, for example based on aluminum or noble metal as for example money, as shown in Figure 2.

  As illustrated in FIG. 4, a plurality of solar cells 101 to 109, in accordance with the invention, can be produced at the same time on the semiconductor substrate 1. The unit cells can then be connected together by their metallization zones 6 and 9 to obtain a module 200 of solar cells. In our example illustrated in FIG. 4, the cells 101 to 103 are connected in series, as are the cells 104 to 106 and the cells 107 to 109. The three groups of series-connected cells thus formed are then connected in parallel to each other. an electrode 13 of the module 200. The electrode 13 is one of the two connection electrodes of the module 200.

  Although several embodiments of the present invention have been described in detail, it will be understood that various changes and modifications can be made without departing from the scope of the invention. In the examples described, the first type of conductivity is the type N and the second type P. It is of course possible that it is the opposite, the person skilled in the art having no problem to choose appropriate materials leading to these conductivities.

Claims (26)

  1. Solar cell (100), comprising, on at least one of the faces (2) of a crystalline semiconductor substrate (1) of a first conductivity type, at least one amorphous semiconductor layer (4) doped with a second conductivity type, opposite to the first conductivity type, characterized in that it comprises collecting fingers (5.1 to 5.n) and at least one collecting bus (6), electrically connecting said fingers of collection (5.1 to 5.n) between them, metallized on the amorphous semiconductor layer (4), and at least one conductive transparent oxide layer (7) which covers the amorphous semiconductor layer (4) and all collection fingers (5.1 to 5.n), but not the entire collection bus (6).   2. solar cell (100) according to claim 1, characterized in that the collecting fingers (5.1 to 5.n) and / or the collection bus (6) are made with so-called low temperature screen printing paste.   3. Solar cell (100) according to claim 1, characterized in that the collecting fingers (5.1 to 5.n) and / or the collection bus (6) are made by evaporation or spraying.   4. Solar cell (100) according to one of the preceding claims, characterized in that the collecting fingers (5.1 to 5.n) and / or the collecting bus (6) are made from aluminum or of a noble metal.   5. Solar cell (100) according to any one of the preceding claims, characterized in that the collecting fingers (5.1 to 5.n) are arranged substantially parallel to each other.   6. solar cell (100) according to any one of the preceding claims, characterized in that the collecting fingers (5.1 to 5.n) are regularly spaced relative to each other.   7. Solar cell (100) according to any one of the preceding claims, characterized in that the collection bus (6) extends over the collecting fingers (5.1 to 5.n), substantially perpendicular to said collecting fingers ( 5.1 to 20 5.n).   8. solar cell (100) according to any one of the preceding claims, characterized in that it comprises between the semiconductor substrate (1) and the amorphous semiconductor layer (4), an intermediate layer of semiconductor ( 3).   9. Solar cell (100) according to claim 8, characterized in that the intermediate semiconductor layer (3) is in amorphous semiconductor or intrinsic polymorphic. 15   10. Solar cell (100) according to claim 8, characterized in that the intermediate semiconductor layer (3) is gradually doped amorphous semi-conductor of the second conductivity type.   11. Solar cell (100) according to any one of claims 8 to 10, characterized in that the intermediate layer of semiconductor (3) is silicon.   12. Solar cell (100) according to any one of claims 8 to 11, characterized in that the intermediate layer of semiconductor (3) is in thin layer.   13. Solar cell (100) according to any one of the preceding claims, characterized in that the semiconductor substrate (1) is monocrystalline silicon or polycrystalline silicon.   14. solar cell (100) according to any one of the preceding claims, characterized in that the amorphous semiconductor layer (4) doped second conductivity type is silicon.   15. Solar cell (100) according to any one of the preceding claims, characterized in that the amorphous semiconductor layer (4) doped second conductivity type is thin layer.   16. Solar cell (100) according to any one of the preceding claims, characterized in that the conductive transparent oxide layer (7) is tin oxide and indium.   17. Module (200) of solar cells, characterized in that it comprises several solar cells (101 to 109) according to one of the preceding claims, connected in series and / or parallel.   18. A method of producing a solar cell (100) comprising the following steps: a) deposition, on at least one face (2) of a crystalline semiconductor substrate (1) of a first conductivity type, from minus one amorphous semiconductor layer (4) doped with a second conductivity type, opposite said first conductivity type, b) metallizing a set of collection fingers (5.1 to 5.n) on the semiconductor layer amorphous (4), c) metallizing at least one collection bus (6) on the amorphous semiconductor layer (4), electrically connecting said collecting fingers (5.1 to 5.n) with each other, d) producing at least one conductive transparent oxide layer (7) on the amorphous semiconductor layer (4), also covering all of the collection fingers (5.1 to 5.n) and the collection bus (6), e) etching in the conductive transparent oxide layer (7) of at least one window (8) exposing at least a portion of the collection bus (6).   19. The method of claim 18, characterized in that it comprises, between step b) and step c), a step of performing a cold sintering of all collection fingers (5.1 to 5.n), by pressing said collecting fingers (5.1 to 5.n).   20. The method of claim 19, characterized in that the pressing of the collecting fingers (5.1 to 5.n) is performed with a hydraulic or pneumatic press.   21. Method according to one of claims 19 or 20, characterized in that the pressing is carried out at a temperature between about room temperature and 400 C.   22. A method according to any one of claims 19 to 21, characterized in that the pressing is carried out at a pressure level between about 106 Pa and 5x108 Pa.   23. Method according to any one of claims 18 to 22, characterized in that the etching is an etching performed by laser or deposition screen printing paste.   24. A method according to any one of claims 18 to 23, characterized in that the metallization of the collection fingers (5.1 to 5.n) and / or the metallization of the collection bus (6) are carried out with pulp of so-called low temperature screen printing.   25. Method according to any one of claims 18 to 23, characterized in that the metallization of the collecting fingers (5.1 to 5.n) and / or the metallization of the collection bus (6) are carried out by evaporation or spraying.   26. Method according to any one of claims 18 to 25, characterized in that the collecting fingers (5.1 to 5.n) and / or the collection bus (6) are made of aluminum or a noble metal.