Method for improving the ohmic contact behaviour of a metal electrode structure of a silicon wafer solar cell

Abstract

The invention relates to a method for improving the ohmic contact behaviour between a semiconductor wafer surface of a silicon wafer solar cell and a metal electrode structure which is applied to the semiconductor wafer surface and has a plurality of mutually separated metallic contact fingers. The object of the invention is therefore to propose a method for improving the ohmic contact behaviour of the metal electrode structure of a silicon solar cell, which method can be used for improving the ohmic contact behaviour on only one side of the silicon solar cell and is therefore also suitable for tandem solar cells. This object is achieved in that: the silicon wafer solar cell is first provided with the mutually separated contact fingers of the metal electrode structure; at least one first section of a first contact finger of the plurality of metallic contact fingers is contacted with a first contacting device electrically connected to one pole of a voltage source; at least one first section of a second contact finger of the plurality of metallic contact fingers is contacted with a second contacting device electrically connected to the other pole of the voltage source; by generating a voltage by means of the voltage source, a current flow is produced between the first contact finger and the second contact finger along a portion of the semiconductor surface lying between the first and second contact fingers; and this current flow, with respect to the area of the first contact finger, exhibits a current density of 0.1 A / cm² to 50,000 A / cm², preferably 0.5 A / cm² to 40,000 A / cm², more preferably 1 A / cm² to 30,000 A / cm², even more preferably 5 A / cm² to 25,000 A / cm², and is applied for a duration of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

Description

[0001] Method for improving the ohmic contact behavior of a metal electrode structure of a silicon wafer solar cell

[0002] The invention relates to a method for improving the ohmic contact behavior between a semiconductor wafer surface of a silicon wafer solar cell and a metal electrode structure attached to the semiconductor wafer surface with several separated metallic contact fingers.

[0003] A method for improving the ohmic contact behavior of a metal electrode structure of a silicon wafer solar cell is known from the prior art, specifically from DE 102018 001 057 A1. In this method, the metal electrode structure and a counter electrode of the silicon wafer solar cell are electrically biased against their forward direction. The electrically biased silicon wafer solar cell is then scanned section by section on its solar-active area with a point light source. This induces a current flow in the illuminated area, thereby improving the ohmic contact behavior between the metal electrode structure and the semiconductor wafer surface of the silicon wafer solar cell.

[0004] Silicon wafer solar cells with a metal electrode structure, comprising several separated metallic contact fingers, are known from WO 2014 / 124675 A1 and US 2011 / 0126878 A1. When the metallic contact fingers of the metal electrode structure are deposited onto a semiconductor wafer surface of the silicon wafer solar cell, no metallic common contacts are created to connect the contact fingers to one another. Only when several of these solar cells are electrically interconnected are the contact fingers connected to each other, for example, via metallic wires or metal ribbons. The method known from DE 102018 001 057 A1 for improving the ohmic contact behavior of the contact grid can also be applied to these solar cells before interconnection.

[0005] To further increase the efficiency of solar cells, so-called tandem solar cells are increasingly being developed. These tandem solar cells combine different semiconductor materials in a monolithically stacked arrangement. The increase in efficiency is primarily due to the fact that the different semiconductor materials in the layer stack are optimized for different wavelength ranges of absorbed light, thus increasing the overall light yield of these tandem solar cells. Typically, a tandem solar cell is created by combining the layer structure of a silicon wafer solar cell with the layer structure of a solar cell made of a different semiconductor material. For example, a tandem solar cell is formed by depositing the layer structure of a 111-V solar cell (e.g., perovskite) onto the layer structure of a silicon wafer solar cell.The voltage generated when the tandem solar cell is illuminated is dissipated via a contact structure located on the silicon wafer solar cell side and a contact structure located on the side of the I1I-V solar cell. The contact structure on the silicon wafer solar cell side is typically created by printed metallic contacts. The contact on the side with the II-IV solar cell is typically made via a transparent, electrically conductive oxide (TCO), such as indium tin oxide (ITO) or aluminum-doped zinc oxide (ZnO:Al).

[0006] If the method known from DE 10 2018 001 057 A1 is used for such tandem solar cells, the high currents flowing within the tandem solar cell could cause thermal damage to the II IV solar cell.

[0007] The task is therefore to propose a method for improving the ohmic contact behavior of the metal electrode structure of a silicon solar cell, which can be used to improve the ohmic contact behavior on only one side of the silicon solar cell and is therefore also suitable for tandem solar cells.

[0008] According to the invention, this problem is solved by a method with the features of claim 1. Advantageous embodiments are specified in dependent claims 2 to 13.

[0009] For the purposes of the invention, the multiple, separated metallic contact fingers are to be understood as such that these contact fingers are not electrically connected to each other within the metal electrode structure. Although the contact fingers may be electrically connected to each other via the semiconductor material of the silicon solar cell, there is no electrical connection between the contact fingers within the metal electrode structure.

[0010] According to the invention, a current flow is generated between a first contact finger and a second contact finger separated from this first contact finger within the metal electrode structure by means of a voltage source along a section of the semiconductor surface located between the first and second contact fingers, wherein the current flow has a current density of 0.1 A / cm² relative to the area of ​​the first contact finger. 2 up to 50,000 A / cm 2 preferably 0.5 A / cm2 up to 40,000 A / cm 2 , preferably 1 A / cm 2 up to 30,000 A / cm 2 , even more preferably 5 A / cm 2 up to 25,000 A / cm 2 , and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms. This enables an improvement in the ohmic contact behavior of the metal electrode structure of the silicon solar cell on only one side. The voltage supplied by the voltage source is applied only to the metal electrode structure, so that the resulting current flows only along this metal electrode structure and a semiconductor surface located below the metal electrode structure. An electrode structure at the opposite pole to the metal electrode structure remains unaffected, since, unlike in the prior art method, no current flows along this electrode structure at the opposite pole to the metal electrode structure.

[0011] The area of ​​the first contact finger to which the current density refers is the area covered by the first contact finger on the semiconductor wafer surface.

[0012] The term "silicon wafer solar cell" also encompasses corresponding semi-finished products. The structure of such a semi-finished product includes at least the semiconductor surface with the metal electrode structure. The electrode structure at the opposite pole may still be missing for the formation of the finished silicon wafer solar cell. Nevertheless, such a semi-finished product can be processed using the method according to the invention.

[0013] To induce the voltage from the voltage source into the metal electrode structure, at least a first section of the first contact finger is contacted with a first contacting device electrically connected to one pole of the voltage source. At least a first section of a second contact finger of the multiple metallic contact fingers is contacted with a second contacting device electrically connected to the other pole of the voltage source.

[0014] The first and second contacting devices can be designed in various ways. Firstly, the first and second contacting devices can each have at least one contact pin or contact bar, which is placed on the respective contact finger. Likewise, the first and second contacting devices can each have several contact pins or contact bars, which are placed on multiple sections of the first and second contact fingers.

[0015] In addition to contact pins, the first and second contacting devices can each also have contact rollers. The contact rollers can be positioned on the respective contact fingers such that their axes of rotation are essentially parallel to a longitudinal axis of the contact fingers. When the silicon wafer solar cell is moved relative to the first and second contacting devices, the contact rollers then roll over the metal electrode structure and are moved from contact finger to contact finger. In an alternative embodiment, the axes of rotation of the contact rollers are aligned essentially perpendicular to a longitudinal axis of the contact fingers. When the silicon wafer solar cell is moved relative to the first and second contacting devices, the contact rollers then roll over the metal electrode structure and are moved along the contact fingers.

[0016] In an advantageous embodiment of the method, after the voltage is applied, the voltage source is reversed and, by generating a reverse voltage through the voltage source, a reverse current flow is generated between the first contact finger and the second contact finger along the section of the semiconductor surface located between the first and second contact fingers, and this current flow, relative to the area of ​​the first contact finger, has a current density of 0.1 A / cm² to 50,000 A / cm², preferably 0.5 A / cm² to 40,000 A / cm², more preferably 1 A / cm² to 30,000 A / cm², and even more preferably 5 A / cm² to 25,000 A / cm², and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, and more preferably 100 ns to 500 ms.

[0017] The polarity of the voltage can be reversed by swapping the first and second contact points. Alternatively, the poles within the voltage source itself can be reversed using an electronic switching device. Furthermore, the polarity can also be reversed by applying a suitable alternating voltage.

[0018] Reversing the polarity can further improve contact formation at the contact fingers. Depending on the current flow direction at the interfaces between the semiconductor wafer surface and the contact fingers, the height of the potential barrier, and thus the magnitude of the power drop at the contact finger, can be influenced.

[0019] Furthermore, this problem is solved according to the invention by a method with the features of claim 14. Advantageous embodiments are specified in dependent claims 15 to 16.

[0020] First, the silicon wafer solar cell with the metal electrode structure is provided, and at least a first section of a first contact finger of the multiple metallic contact fingers is contacted with a first contacting device electrically connected to one pole of a voltage source. At least a first section of the semiconductor wafer surface is directly contacted with a second contacting device electrically connected to the other pole of the voltage source. By generating a voltage through the voltage source, a current flow is generated between the first contact finger and the semiconductor wafer surface, wherein this current flow, based on the area of ​​the first contact finger, exhibits a current density of 0.1 A / cm² to 50,000 A / cm², preferably 0.5 A / cm² to 40,000 A / cm², more preferably 1 A / cm² to 30,000 A / cm², and even more preferably 5 A / cm² to 25 A / cm².000 A / cm2, and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

[0021] To process another section of the first contact finger, the first contacting device is removed from the first section of the first contact finger and placed on a second section of the first contact finger.

[0022] To process a second contact finger, the first contacting device is removed from the first or second section of the first contact finger and placed onto at least one first section of this second contact finger. By generating a voltage from the voltage source, a current flow is created between the second contact finger and the semiconductor wafer surface. This current flow, based on the area of ​​the second contact finger, has a current density of 0.1 A / cm² to 50,000 A / cm², preferably 0.5 A / cm² to 40,000 A / cm², more preferably 1 A / cm² to 30,000 A / cm², and even more preferably 5 A / cm² to 25,000 A / cm², and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, and more preferably 100 ns to 500 ms.

[0023] Exemplary embodiments of the invention are explained below with reference to the drawings. The drawings show:

[0024] Fig. 1 shows a simplified spatial representation of a silicon wafer solar cell known from the prior art.

[0025] Fig. 2 shows the silicon wafer solar cell according to Fig. 1 with a first contacting device and a second contacting device.

[0026] Fig. 3 shows the silicon wafer solar cell according to Fig. 1 with a modified positioning of the first and second contacting device compared to Fig. 2.

[0027] Fig. 4 shows the silicon wafer solar cell according to Fig. 1 with first and second contacting devices having contact rollers. Fig. 5 shows the silicon wafer solar cell according to Fig. 1 with first and second contacting devices having contact rollers in a modified orientation.

[0028] Fig. 6 shows the silicon wafer solar cell according to Fig. 1 with first and second contacting devices having several contact pins.

[0029] Fig. 7 shows the silicon wafer solar cell according to Fig. 1 with first and second contacting devices having several contact pins and an arrangement of these contact pins that is alternative to Fig. 6.

[0030] Fig. 8 shows the silicon wafer solar cell according to Fig. 1 with a modified version of the contacting device compared to Fig. 6.

[0031] Fig. 9 shows the silicon wafer solar cell according to Fig. 1 with a modified embodiment of the contacting device compared to Fig. 3.

[0032] Fig. 10 shows the silicon wafer solar cell according to Fig. 1 with a modified embodiment of the contacting device compared to Fig. 9.

[0033] Fig. 11 shows the silicon wafer solar cell according to Fig. 1 with a further embodiment of the contacting device for carrying out a further embodiment of the method according to the invention.

[0034] Fig. 1 shows a simplified three-dimensional representation of a silicon wafer solar cell 1 known from the prior art. This silicon wafer solar cell 1 has a semiconductor wafer surface 2 and a region 3 with at least one pn junction. A metal electrode structure 4 with several metallic contact fingers 5a, 5b, 5c, 5d separated from one another within the metal electrode structure 4 is deposited on the semiconductor wafer surface 2. This metal electrode structure 4 forms an electrical pole for tapping the voltage generated when the silicon wafer solar cell 1 is illuminated. The counter pole 6 is located on the opposite side of the region 3. This counter pole can be deposited over the entire surface, as shown, or can also consist of metallic contact fingers.

[0035] Fig. 2 shows the silicon wafer solar cell 1 according to Fig. 1 with a first contacting device 7 and a second contacting device 8. A voltage source 9 is also shown, wherein the first contacting device 7 is connected to one pole of this voltage source 9 and the second contacting device 8 is connected to the other pole of this voltage source 9.

[0036] To carry out the inventive method for improving the ohmic contact behavior between the semiconductor wafer surface 2 of the silicon wafer solar cell 1 and the metal electrode structure 4 applied to the semiconductor wafer surface 2, the silicon wafer solar cell 1 with the metal electrode structure 4 is first provided. Subsequently, at least a first section of the first contact finger 5a is contacted with the first contacting device 7, which is electrically connected to one pole of a voltage source, and at least a first section of the second contact finger is contacted with the second contacting device 8, which is electrically connected to the other pole of the voltage source. By generating a voltage through the voltage source 9, a current flow is then generated between the first contact finger 5a and the second contact finger 5b along a section of the semiconductor surface 2 located between the first contact finger 5a and the second contact finger 5b.This current flow has a current density of 0.1 A / cm² with respect to the area of ​​the first contact finger 5a. 2 up to 50,000 A / cm 2 preferably 0.5 A / cm 2 up to 40,000 A / cm 2 , preferably 1 A / cm 2 up to 30,000 A / cm 2 , even more preferably 5 A / cm 2 up to 25,000 A / cm 2 , and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

[0037] In a further embodiment of the method, after the voltage is applied, the voltage source is reversed and, by generating a reverse voltage through the voltage source, a reverse current flow is generated between the first contact finger 5a and the second contact finger 5b along the section of the semiconductor surface 2 located between the first and second contact fingers 5a, 5b, and this current flow, with respect to the area of ​​the first contact finger 5a, has a current density of 0.1 A / cm² to 50,000 A / cm², preferably 0.5 A / cm² to 40,000 A / cm², more preferably 1 A / cm² to 30,000 A / cm², and even more preferably 5 A / cm² to 25,000 A / cm², and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

[0038] In the illustrated embodiment, the first contacting device 7 and the second contacting device 8 each have a contact pin 7a and 8a respectively designed as contact means.

[0039] In the embodiment shown in Fig. 2, the adjacent contact fingers 5a, 5b are machined. To machine the further contact fingers 5c, 5d of the metal electrode structure 4, after machining the first and second contact fingers 5a, 5b, the contact pins 7a, 8a of the first and second contacting device 7, 8 are placed onto the further adjacent contact fingers 5c, 5d of the metal electrode structure 4 and the voltage is applied to them to generate the current flow. Typically, the metal electrode structures of silicon wafer solar cells 1 have more than four contact fingers 5a, 5b, 5c, 5d. To machine the entire metal electrode structure 4, all adjacent contact fingers 5a, 5b, 5c, 5d are contacted successively and the voltage is applied to them to generate the current flow. In the illustrated embodiment, four contact fingers 5a, 5b, 5c, 5d are shown in the metal electrode structure 4.However, the metal electrode structure 4 of a conventional silicon wafer solar cell 1 contains significantly more than four contact fingers, whereby the method according to the invention is then carried out according to the number of contact fingers of the metal electrode structure 4.

[0040] In further versions of the procedure, the polarity of the voltage can also be reversed at the other contact fingers.

[0041] However, it is not mandatory that the voltage be applied to adjacent contact fingers 5a, 5b, 5c, 5d. For example, the voltage can also be applied to non-adjacent contact fingers 5a, 5b, 5c, 5d. Fig. 3 shows an embodiment in which the two contact fingers 5a and 5c are contacted with the contact pins 7a, 8a of the first and second contacting devices 7, 8, and the contact finger 5b in between remains uncontacted.

[0042] The contact pins 7a, 8a can be configured such that the voltage is applied to the respective contact fingers 5a, 5b, 5c, 5d at a single point. For reliable contact, it can be advantageous for the contact pins 7a, 8a to have flat surfaces on their sides that rest on the contact fingers 5a, 5b, 5c, 5d. Furthermore, it can also be advantageous if these surfaces extend along the entire length of the contact fingers 5a, 5b, 5c, 5d, thus ensuring a homogeneous application of the voltage to the contact fingers 5a, 5b, 5c, 5d. Otherwise, for example, if the voltage is applied to the center of the contact fingers 5a, 5b, 5c, 5d, the current flowing through them could cause a voltage drop along the contact fingers, leading to a reduction in the effective voltage at the finger ends and consequently a reduction in the effective current flow at these finger ends.

[0043] In the embodiment shown in Fig. 4, the first contacting device 7 and the second contacting device 8 each have electrically conductive contact rollers 7b and 8b, respectively. For the implementation of the method according to the invention, contact pins 7a, 8a are not placed on the contact fingers 5a, 5b, 5c, 5d, but rather these contact rollers 7b, 8b. Analogous to the illustration in Fig. 3, the first contacting device 7 is connected to the contact finger 5a via the contact roller 7b. The second contacting device 8 is placed on the contact finger 5c via the contact roller 8b. In this state, the voltage from the voltage source is applied via the contact fingers 5a and 5c, so that the current flows with the current density and duration mentioned above between the contact fingers 5a and 5c through the intervening section of the semiconductor surface 2.The current flow, particularly through thermal effects, improves the contact behavior both between the contact finger 5a and the semiconductor surface 2 and between the contact finger 5c and the semiconductor surface 2.

[0044] In the illustrated embodiment, a rotational axis 10 of the contact roller 7b is aligned parallel to a longitudinal axis 11 of the contact finger 5a. A rotational axis 12 of the contact roller 8b is aligned parallel to a longitudinal axis 13 of the contact finger 5c.

[0045] To further improve the contact behavior of contact fingers 5b and 5d, contact roller 7b can be moved first to contact finger 5b and then contact roller 8b to contact finger 5d while voltage remains applied to contact rollers 7b and 8b. Alternatively, both contact rollers can be moved simultaneously so that contact roller 7b and contact roller 8b move to contact finger 5b and contact finger 5d, respectively, at the same time. Similarly, with contact rollers 7b and 8b stationary, the silicon wafer solar cell can be displaced relative to contact rollers 7b and 8b in the direction of the arrow shown in Fig. 4. A displacement by the distance between contact fingers 5a and 5b will then cause contact roller 7b to rest on contact finger 5b and contact roller 8b on contact finger 5d.The voltage applied to the contact rollers 7b, 8b then induces the current flow with the aforementioned current density and duration between the contact fingers 5b and 5d along the section of the semiconductor surface 2 located between the contact fingers 5b and 5c, which leads to an improvement in the contact behavior both between the contact finger 5b and the semiconductor surface 2 and between the contact finger 5d and the semiconductor surface 2. In all cases, however, when the voltage is applied, the silicon wafer solar cell 1 and the first and second contacting devices 7, 8 are displaced relative to each other in a direction perpendicular to the longitudinal axis 11 of the first contact finger 5a.

[0046] The invention is not limited to the embodiment shown. Firstly, the contact rollers 7b, 8b can also rest on adjacent contact fingers 5a, 5b, 5c, 5d. Secondly, more than one uncontacted contact finger 5a, 5b, 5c, 5d can be present between the contact fingers 5a, 5b, 5c, 5d on which the contact rollers 7b, 8b rest.

[0047] It is advantageous if the axis of rotation 10 of the contact roller 7b of the first contacting device 7 and the axis of rotation 12 of the contact roller 8b of the second contacting device 8 have a distance from each other that corresponds to a single or multiple of the distance between adjacent equidistant contact fingers 5a, 5b, 5c, 5d of the metal electrode structure 4 – in the embodiment shown in Fig. 4, therefore, twice the distance between the contact fingers 5a and 5b. Advantageously, the length of the contact rollers 7b, 8b along their axes of rotation 10, 12 corresponds essentially to the length of the contact fingers 5a, 5b, 5c, 5d, so that a homogeneous application of the voltage to the contact fingers 5a, 5b, 5c, 5d is achieved. However, the invention is not limited to this.

[0048] Furthermore, for rapid processing of the silicon wafer solar cell, especially in the case of a metal electrode structure 4 with a very large number of contact fingers 5a, 5b, 5c, 5d, it can be advantageous to provide several contact rollers 7b, 8b arranged next to each other, so that more than two contact fingers 5a, 5b, 5c, 5d can be processed simultaneously in one processing step.

[0049] Fig. 5 shows a further embodiment of the method according to the invention. The first contacting device 7 and the second contacting device 8 each have at least one electrically conductive contact roller 7c and 8c, respectively. The at least one contact roller 7c of the first contacting device 7 is placed on a first section of the contact finger 5a, wherein an axis of rotation 14 of this contact roller 7c is oriented substantially perpendicular to the longitudinal axis 11 of the contact finger 5a. The at least one contact roller 8c of the second contacting device 8 is placed on a first section of the contact finger 5b, wherein the axis of rotation 14 of this contact roller 8c is oriented substantially perpendicular to a longitudinal axis 15 of the contact finger 5b.In this state, the voltage from the voltage source is applied across the contact fingers 5a and 5b, causing the current to flow with the aforementioned current density and duration between contact fingers 5a and 5b through the intervening section of the semiconductor surface 2. This current flow, particularly through thermal effects, improves the contact behavior both between contact finger 5a and the semiconductor surface 2 and between contact finger 5b and the semiconductor surface 2.

[0050] To achieve optimal improvement of the ohmic contact behavior both between contact finger 5a and the semiconductor surface 2 and between contact finger 5b and the semiconductor surface 2 along contact fingers 5a, 5b, the silicon wafer solar cell 1 and the contact rollers 7c, 8c are displaced relative to each other in a direction parallel to the first contact finger 5a when voltage is applied. For this purpose, the contact rollers 7c, 8c can be displaced relative to the silicon wafer solar cell 1, or the silicon wafer solar cell 1 can be displaced relative to the contact rollers 7c, 8c (along the direction of the arrow shown in Fig. 6) (or a combination of both).During the relocation, the contact roller 7c is guided along the contact finger 5a and the contact roller 8c along the contact finger 5b, thus moving the contact roller 7c from a first section of the first contact finger to a second section of the first contact finger 5a and the contact roller 8c from a first section of the second contact finger 5b to a second section of the second contact finger 5b.

[0051] Advantageously, the contact rollers 7c, 8c are moved along the entire length of the contact fingers 5a and 5b.

[0052] In order to process contact fingers 5c, 5d after processing contact fingers 5a, 5b, the contact rollers 7c and 8c can then be placed on contact fingers 5c, 5d and guided along contact fingers 5c, 5d with voltage applied, in accordance with the previous procedure.

[0053] To minimize the processing time for the metal electrode structure 4 of the silicon wafer solar cell 1, additional contact rollers 7d and 8d can be provided alongside contact rollers 7c and 8c. Contact roller 7d is part of the first contacting device 7 and is placed on contact finger 5c. Contact roller 8d is part of the second contacting device 8 and is placed on contact finger 5d.

[0054] Advantageously, the contact rollers 7c, 7d, 8c, 8d are connected to each other via an electrically insulating roller element 17. This facilitates the uniform displacement of the contact rollers 7c, 7d, 8c, 8d along the contact fingers 5a, 5b, 5c, 5d. Fig. 5 shows such an embodiment. When a voltage is applied, a current flow with the above-mentioned current density and duration is induced between the contact fingers 5a and 5b along the section of the semiconductor wafer surface 2 located between the contact fingers 5a and 5b, as well as between the contact fingers 5b and 5c along the section of the semiconductor wafer surface 2 located between the contact fingers 5b and 5c, and between the contact fingers 5c and 5d along the section of the semiconductor wafer surface 2 located between the contact fingers 5c and 5d.

[0055] Advantageously, the distances between adjacent contact rollers 7c, 8c, 7d, 8d correspond to the distances between the contact fingers 5a, 5b, 5c, 5d assigned to these contact rollers.

[0056] Fig. 6 shows a further embodiment of the contacting for carrying out the method according to the invention. The first and the second contacting devices 7, 8 each have a second electrically conductive contact element, which is configured as a contact pin 7e, 8e. The second contact pin 7e of the first contacting device 7 is placed on a second section of the contact finger 5c adjacent to the first section of the contact finger 5c. The second contact pin 8e of the second contacting device 8 is placed on a second section of the second contact finger 5d adjacent to the first section of the contact finger 5d. Then, the voltage from the voltage source 9 is applied via an electrical changeover circuit, initially with the contact pins 7e, 8e de-energized, between the contact pin 7a of the first contacting device 7 and the contact pin 8a of the second contacting device 8.The voltage from the voltage source 9 is then applied via the electrical changeover circuit between contact pin 7e of the first contacting device 7 and contact pin 8e of the second contacting device 8, while contact pins 7a and 8a are de-energized. This applies the current flow with the aforementioned current density and duration, first in the first section of contact fingers 5c and 5d, and then in the second section of contact fingers 5c and 5d, thereby improving the contact behavior between contact fingers 5c and 5d and the semiconductor wafer surface 2, particularly along the first and second sections of contact fingers 5c and 5d.To process further sections of the contact fingers of the 5c, 5d, further contact means of the first contacting device 7 designed as contact pins 7f, 7g, 7h and further contact means of the second contacting device 8 designed as contact pins 8f, 8g, 8h may be provided.

[0057] To process contact fingers 5c and 5d, contact pins 7a and 8a are first energized with the voltage from voltage source 9, resulting in a current flow with the aforementioned current density and duration. The remaining contact pins 7e, 7f, 7g, 7h, 8e, 8f, 8g, and 8h remain de-energized. Subsequently, via an electrical changeover circuit, contact pins 7e and 8e are energized with the voltage from the voltage source, leaving contact pins 7a, 8a, 7g, 7h, 8e, 8f, 8g, and 8h de-energized. In this way, all adjacent contact pins 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h are gradually subjected to the voltage of the voltage source and the contact fingers 5c, 5d are completely processed over their entire length.

[0058] To process the remaining contact fingers 5a and 5b, the contact pins 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h can now be placed onto contact fingers 5a and 5b, with contact pins 7a, 7e, 7f, 7g, 7h then making contact with contact finger 5a and contact pins 8a, 8e, 8f, 8g, 8h making contact with contact finger 5b. Subsequently, the contact pins of 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h are actuated in the manner described for contact fingers 5c and 5d. As an alternative to relocating the contact pins 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h from the contact fingers 5c, 5d to the contact fingers 5a, 5b, the first contacting device 7 and the second contacting device 8 can also have further contact pins 7i - 7m and 8i - 8m.Advantageously, these additional 7i - 7m, 8i - 8m are connected to the contact pins 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h to form a unit, so that the contact pins 7i - 7m, 8i - 8m, 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h can be placed simultaneously on the contact fingers 5a, 5b, 5c, 5d. The connection of the contact pins 7i-7m, 8i-8m, 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h can, for example, be effected via an electrically insulating plate element 16 to which the contact pins 7i-7m, 8i-8m, 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h are attached. Such an embodiment is shown in Fig. 6, without the invention being limited thereto.

[0059] In the illustration in Fig. 6, only the electrical conductors between the voltage source 9 and the contact pins 7h and 8h are shown. The other conductors to the contact pins 7i-7m, 8i-8m, 7a, 8a, 7e, 7f, 7g, 8e, 8f, 8g have not been shown for clarity. However, the other contact pins 7i-7m, 8i-8m, 7a, 8a, 7e, 7f, 7g, 8e, 8f, 8g can be connected to the voltage source via the (also not shown) changeover switch, as described above. Contact pins with the same hatching are each assigned to the same contacting device 7, 8.

[0060] In another alternative embodiment, the contact pins 7i-7m, 8i-8m, 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h are arranged according to Fig. 7. Here, a kind of checkerboard pattern is formed by the arrangement of the contact pins. Starting from the contact fingers 5c and 5d, contact pin 7a of the first contacting device 7 is placed on a first section of contact finger 5c, and contact pin 8a of the second contacting device 8 is placed on a first section of contact finger 5d. Contact pin 7e of the first contacting device 7 is placed on a second section of contact finger 5d adjacent to the first section of contact finger 5d, and contact pin 8e of the second contacting device 8 is placed on a second section of contact finger 5c adjacent to the first section of contact finger 5c.The contact pin 7f of the first contacting device 7 is placed on a third section of the contact finger 5c adjacent to the second section of the contact finger 5c, and the contact pin 8f of the second contacting device 8 is placed on a third section of the contact finger 5c adjacent to the second section of the contact finger 5c. The contact pins 7g, 7h, 8g, 8h are placed in a corresponding manner, resulting in the alternating pattern shown in Fig. 7. The contact pins 7i-7m and 8i-8m are also distributed on the contact fingers 5a and 5b according to the same scheme. Thus, contact pins of the first contacting device and contact pins of the second contacting device are arranged alternately along the contact fingers.Furthermore, along a direction perpendicular to the alignment of the contact fingers, adjacent contact fingers are alternately occupied with contact pins of the first contacting device and contact pins of the second contacting device.

[0061] As already described in relation to Fig. 6, the contact pins located on adjacent contact fingers are now successively energized by the voltage from the voltage source via the changeover switch (also not shown), so that the current flow with the aforementioned current density and duration is gradually generated along the entire length of the contact fingers 5a, 5b, 5c, 5d. In Fig. 7, contact pins belonging to the same contacting device 7, 8 also have the same hatching.

[0062] Fig. 8 shows a comparable embodiment of the contacting device to Fig. 6. However, unlike Fig. 6, here the contact pins 7i - 7m, 8i - 8m, 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h, each assigned to a contact finger 5a, 5b, 5c, 5d, are connected to each other on the plate element 16 via conductive traces.

[0063] In an embodiment not shown, the contact pins 7i - 7m, 8i - 8m, 7a, 8a, 7e, 7f, 7g, 7h, 8e, 8f, 8g, 8h, each assigned to a contact finger 5a, 5b, 5c, 5d, are combined to form a contact bar.

[0064] Fig. 9 shows an embodiment of the contacting device comparable to Fig. 3. However, unlike Fig. 3, the contact elements of the first contacting device 7 and the second contacting device 8 are not designed as contact pins, but as contact bars 7n, 8n. The contact bar 7n contacts a section of the contact finger 5a. The contact bar 8n contacts a section of the contact finger 5c.

[0065] Fig. 10 shows a comparable embodiment of the contacting device to that shown in Fig. 9. Compared to the embodiment shown in Fig. 9, the contact bars 7n, 8n are longer, so that they almost completely cover the respective contact fingers 5a, 5c.

[0066] Fig. 11 shows a further embodiment of the inventive method for improving the ohmic contact behavior between a semiconductor wafer surface of a silicon wafer solar cell 1 and a metal electrode structure 4 mounted on the semiconductor wafer surface 2, the metal electrode structure 4 having several metallic contact fingers 5a, 5b, 5c, 5d separated from one another within it. First, the silicon wafer solar cell 1 with the metal electrode structure 4 is provided. At least a first section of a first contact finger 5a of the several metallic contact fingers 5a, 5b, 5c, 5d is contacted by a first contacting device 7 electrically connected to one pole of a voltage source 9. At least a first section of the semiconductor wafer surface 2 is directly contacted by a second contacting device 8, which is electrically connected to the other pole of the voltage source 9, via a contact means 8o.By generating a voltage through the voltage source 9, a current flow is then generated between the first contact finger and the semiconductor wafer surface 2, wherein this current flow, based on the area of ​​the first contact finger 5a, has a current density of 0.1 A / cm2 to 50,000 A / cm2, preferably 0.5 A / cm2 to 40,000 A / cm2, more preferably 1 A / cm2 to 30,000 A / cm2, and even more preferably 5 A / cm2 to 25,000 A / cm2, and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

[0067] To treat another section of the contact finger 5a, at least a second section of the first contact finger 5a is then contacted with the first contacting device 7 and the current flow is generated.

[0068] To treat the further contact finger 5c, at least a first section of the further contact finger 5c is contacted with the first contacting device 7 and a current flow is generated between the further contact finger 5c and the semiconductor wafer surface 2 by generating a voltage through the voltage source, wherein this current flow has a current density of 0.1 A / cm2 to 50,000 A / cm2, preferably 0.5 A / cm2 to 40,000 A / cm2, more preferably 1 A / cm2 to 30,000 A / cm2, and even more preferably 5 A / cm2 to 25,000 A / cm2, based on the area of ​​the further contact finger 5c, and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

[0069] In further embodiments of the method, the polarity of the voltage can also be reversed in the setups shown in Figures 3 to 11, analogous to the procedure with the arrangement shown in Figure 2. Reference numeral list

[0070] Silicon wafer solar cell

[0071] Semiconductor wafer surface

[0072] Area with pn transition

[0073] Metal electrode structure a - 5d Contact fingers of the metal electrode structure 4 Counter pole first contacting device second contacting device a Contact pin of the first contacting device 7a Contact pin of the second contacting device 8b Contact roller of the first contacting device 7c, 7d Contact rollers of the first contacting device 7e - 7m Contact pin of the first contacting device 7n Contact bar of the first contacting device 7b Contact roller of the first contacting device 8c, 8d Contact rollers of the first contacting device 8e - 8m Contact pin of the second contacting device 8n Contact bar of the second contacting device 8o Contact means of the second contacting device 8

[0074] Voltage source 0 Axis of rotation of the contact roller 7b 1 Longitudinal axis of the contact finger 5a 2 Axis of rotation of the contact roller 8b 3 Longitudinal axis of the contact finger 5b 4 Axis of rotation of the contact rollers 7c, 7d, 8c, 8d 5 Longitudinal axis of the contact finger 5b 6 Electrically insulating plate element 7 Electrically insulating roller element 8 Conductor tracks

Claims

Patent claims 1. A method for improving the ohmic contact behavior between a semiconductor wafer surface (2) of a silicon wafer solar cell (1) and a metal electrode structure (4) mounted on the semiconductor wafer surface (2) with several metallic contact fingers (5a - 5d) separated from one another within the metal electrode structure (4), characterized in that the silicon wafer solar cell (1) with the metal electrode structure (4) is first provided and that at least a first section of a first contact finger (5a - 5d) of the several metallic contact fingers (5a - 5d) is contacted with a first contacting device (7) electrically connected to one pole of a voltage source (9) and that at least a first section of a second contact finger of the several metallic contact fingers (5a - 5d) is contacted with a second contacting device (8) electrically connected to the other pole of the voltage source (9) and that with theGeneration of a voltage by the voltage source (9) generates a current flow between the first contact finger (5a - 5d) and the second contact finger (5a - 5d) along a section of the semiconductor surface located between the first and second contact fingers (5a - 5d) and that this current flow, with respect to the area of ​​the first contact finger (5a - 5d), results in a current density of 0.1 A / cm² 2 up to 50,000 A / cm 2 preferably 0.5 A / cm 2 up to 40,000 A / cm 2 , preferably 1 A / cm 2 up to 30,000 A / cm 2 , even more preferably 5 A / cm 2 up to 25,000 A / cm 2 , exhibits and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

2. Method according to claim 1, characterized in that the voltage of the voltage source (9) is subsequently reversed and, by generating a reverse voltage through the voltage source (9), a reverse current flow is generated between the first contact finger (5a - 5d) and the second contact finger (5a - 5d) along the section of the semiconductor surface located between the first and second contact fingers (5a - 5d), and this current flow, with respect to the area of ​​the first contact finger (5a - 5d), results in a current density of 0.1 A / cm². 2 up to 50,000 A / cm 2 preferably 0.5 A / cm 2 up to 40,000 A / cm 2 , preferably 1 A / cm 2 up to 30,000 A / cm 2 , even more preferably 5 A / cm 2 up to 25,000 A / cm 2 , exhibits and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

3. Method according to one of the preceding claims, characterized in that the first and the second contacting device (7, 8) each have at least one first electrically conductive contact means and that the first contact means of the first contacting device (7) is placed on the first section of the first contact finger (5a - 5d) and that the first contact means of the second contacting device (8) is placed on the first section of the second contact finger (5a - 5d).

4. Method according to claim 2, characterized in that the first and the second contacting device (7, 8) each have a second electrically conductive contact means, and that the second contact means of the first contacting device (7) is placed on a second section of the first contact finger (5a - 5d) adjacent to the first section of the first contact finger (5a - 5d), and that the second contact means of the second contacting device (8) is placed on a second section of the second contact finger (5a - 5d) adjacent to the first section of the second contact finger (5a - 5d), and that the voltage of the voltage source (9) is initially applied via an electrical changeover switch between the first contact means of the first contacting device (7) and the first contact means of the second contacting device (8) when the second contact means are de-energized, and subsequently the voltage of the voltage source (9) is applied via the electrical changeover switchA changeover switch is applied between the second contact of the first contacting device (7) and the second contact of the second contacting device (8) when the first contact is de-energized.

5. Method according to claim 2, characterized in that the first and the second contacting device (7, 8) each have a second electrical contact means and that the second contact means of the second contacting device (8) is placed on a second section of the first contact finger (5a - 5d) adjacent to the first section of the first contact finger (5a - 5d) and that the second contact means of the first contacting device (7) is placed on a second section of the second contact finger (5a - 5d) adjacent to the first section of the second contact finger (5a - 5d) and that the voltage of the voltage source (9) is initially applied via an electrical changeover circuit between the first contact means of the first contacting device (7) and the first contact means of the second contacting device (8) when the second contact means are de-energized and subsequently the voltage of the voltage source (9) is applied via the electrical changeover circuit when a voltage-free first contact means is applied between the second contact means of the first contacting device (7) and the second contact means of the second contacting device (8).

6. Method according to claim 5, characterized in that the first contacting device (7) and the second contacting device (8) have, in addition to the first and second contact means, further contact means, and these further contact means are placed on further contact fingers (5a - 5d), and that along these contact fingers (5a - 5d) a contact means of the further contact means of the first contacting device (7) and a contact means of the further contact means of the second contacting device (8) are arranged alternately, and that along a direction perpendicular to the orientation of the contact fingers (5a - 5d), adjacent contact fingers (5a - 5d) are arranged alternately a contact means of the first contacting device (7) and a contact means of the second contacting device (8) on the contact fingers (5a - 5d), and that the voltage is successively applied to the contact fingers (5a - 5d) by means of the electrical switching circuit between oneis applied to a contact means of the first contacting device (7) arranged on a contact finger (5a - 5d) and to a contact means of the second contacting device (8) arranged on an adjacent contact finger (5a - 5d).

7. Method according to one of claims 2 to 6, characterized in that the contact means are designed as contact pins (7a, 8a, 7e - 7m, 8e - 8m) or contact bars (7n, 8n).

8. Method according to claim 1, characterized in that the first and the second contacting device (7, 8) each have at least one electrically conductive contact roller (7c, 8c, 7d, 8d) and that the at least one contact roller (7c, 7d) of the first contacting device (7) is placed on the first section of the first contact finger (5a - 5d), wherein an axis of rotation (14) of this contact roller (7c, 7d) is oriented substantially perpendicular to a longitudinal axis (11) of the first contact finger (5a - 5d), and that the at least one contact roller (8c, 8d) of the second contacting device (8) is placed on the first section of the second contact finger (5a - 5d), wherein an axis of rotation (14) of this contact roller (8c, 8d) is oriented substantially perpendicular to a longitudinal axis (13) of the second contact finger (5a - 5d), and that when the voltage is applied the Silicon wafer solar cell (1) is displaced in a direction parallel to the first contact finger (5a - 5d) relative to the first and second contacting device (7, 8), whereby the at least one contact roller (7c, 7d) of the first contacting device (7) is moved from the first section of the first contact finger (5a - 5d) to a second section of the first contact finger (5a - 5d) and the at least one contact roller (8c, 8d) of the second contacting device (8) is moved from the first section of the second contact finger (5a - 5d) to a second section of the second contact finger (5a - 5d).

9. Method according to claim 8, characterized in that, for a uniform displacement of the at least one contact roller (7c, 7d) of the first contacting device (7) and the at least one contact roller (8c, 8d) of the second contacting device (8), both contact rollers (7c, 8c, 7d, 8d) are connected to each other via an electrically insulating roller element (17).

10. Method according to claim s, characterized in that the first contacting device (7) and the second contacting device (8) each have further contact rollers (7c, 8c, 7d, 8d) and these further contact rollers (7c, 8c, 7d, 8d) are assigned to further contact fingers (5a - 5d) and that one contact finger (5a - 5d) of adjacent contact fingers (5a - 5d) is contacted with a contact roller (7c, 7d) of the first contacting device (7) and the other contact finger (5a - 5d) of adjacent contact fingers (5a - 5d) is contacted with a contact roller (8c, 8d) of the second contacting device (8).

11. Method according to claim 10, characterized in that, for a uniform displacement of the contact rollers (7c, 7d) of the first contacting device (7) and the contact rollers (8c, 8d) of the second contacting device (8), these contact rollers (7c, 8c, 7d, 8d) are connected to each other via an electrically insulating roller element (17).

12. Method according to claim 9 or 11, characterized in that the distances between adjacent contact rollers (7c, 8c, 7d, 8d) correspond to the distances between the contact fingers (5a - 5d) assigned to these contact rollers (7c, 8c, 7d, 8d).

13. Method according to claim 1, characterized in that the first and the second Contact device (7, 8) each having at least one electrically conductive contact roller (7b, 8b) and that the at least one contact roller (7b) of the first contacting device (7) is placed on the first section of the first contact finger (5a - 5d), wherein an axis of rotation (10) of this contact roller (7b) is oriented substantially parallel to a longitudinal axis (11) of the first contact finger (5a - 5d), and that the at least one contact roller (8b) of the second contacting device (8) is placed on the first section of the second contact finger (5a - 5d), wherein an axis of rotation (12) of this contact roller (8b) is oriented substantially parallel to a longitudinal axis (13) of the second contact finger (5a - 5d), and that when the voltage is applied, the silicon wafer solar cell (1) is oriented in a direction perpendicular to the longitudinal axis (11) of the first contact finger (5a - 5d) towards the first and second contacting devices (7,8) is displaced and in doing so, at least one contact roller (7b) of the first contacting device (7) is moved from the first contact finger (5a - 5d) to another contact finger (5a - 5d) of the several metallic contact fingers (5a - 5d) and at least one contact roller (8b) of the second contacting device (8) is moved from the second contact finger (5a - 5d) to another contact finger (5a - 5d) of the several metallic contact fingers (5a - 5d).

14. Method according to claim 13, characterized in that the axis of rotation (10) of the contact roller (7b) of the first contacting device (7) and the axis of rotation (12) of the contact roller (8b) of the second contacting device (8) have a distance from each other which corresponds to a single or multiple of the distance between adjacent equidistant contact fingers (5a - 5d) of the metal electrode structure (4) and that the contact rollers (7b, 8b) of the first and second contacting devices (7, 8) are displaced uniformly when moved relative to the silicon wafer solar cell (1).

15. Method for improving the ohmic contact behavior between a semiconductor wafer surface (2) of a silicon wafer solar cell (1) and a metal electrode structure (4) attached to the semiconductor wafer surface (2) with several metallic contact fingers (5a - 5d) separated from one another within the metal electrode structure (4), characterized in that the silicon wafer solar cell (1) with the metal electrode structure (4) is first provided and that at least a first section of a first contact finger (5a - 5d) of the several metallic contact fingers (5a - 5d) is electrically connected to a first contacting device (7) connected to a pole of a voltage source (9). is contacted and that at least a first section of the semiconductor wafer surface (2) is directly contacted with a second contacting device (8) electrically connected to the other pole of the voltage source (9) and that, with the generation of a voltage by the voltage source (9), a current flow is generated between the first contact finger (5a - 5d) and the semiconductor wafer surface (2) and that this current flow, with respect to the area of ​​the first contact finger (5a - 5d), has a current density of 0.1 A / cm² 2 up to 50,000 A / cm 2 preferably 0.5 A / cm 2 up to 40,000 A / cm 2 , preferably 1 A / cm 2 up to 30,000 A / cm 2 , even more preferably 5 A / cm 2 up to 25,000 A / cm 2 , exhibits and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

16. Method according to claim 15, characterized in that the voltage of the voltage source (9) is subsequently reversed and, by generating a reverse voltage through the voltage source (9), a reverse current flow is generated between the first contact finger (5a - 5d) and the second contact finger (5a - 5d) along the section of the semiconductor surface located between the first and second contact fingers (5a - 5d), and this current flow, with respect to the area of ​​the first contact finger (5a - 5d), results in a current density of 0.1 A / cm². 2 up to 50,000 A / cm 2 preferably 0.5 A / cm 2 up to 40,000 A / cm 2 , preferably 1 A / cm 2 up to 30,000 A / cm 2 , even more preferably 5 A / cm 2 up to 25,000 A / cm 2 , exhibits and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

17. Method according to claim 15, characterized in that subsequently at least a second section of the first contact finger (5a - 5d) is contacted with the first contacting device (7) and that by generating a voltage through the voltage source (9) a current flow is generated between the first contact finger (5a - 5d) and the semiconductor wafer surface (2) and that this current flow, with respect to the area of ​​the first contact finger (5a - 5d), results in a current density of 0.1 A / cm² 2 up to 50,000 A / cm 2 preferably 0.5 A / cm 2 up to 40,000 A / cm 2 , preferably 1 A / cm 2 up to 30,000 A / cm 2 , even more preferably 5 A / cm 2 up to 25,000 A / cm 2 , exhibits and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

18. Method according to claim 15 or 16, characterized in that subsequently at least a first section of a second contact finger (5a - 5d) of the several metallic contact finger (5a - 5d) is contacted with the first contacting device (7) and that by generating a voltage through the voltage source (9) a current flow is generated between the second contact finger (5a - 5d) and the semiconductor wafer surface (2) and that this current flow, based on the area of ​​the second contact finger (5a - 5d), results in a current density of 0.1 A / cm² 2 up to 50,000 A / cm 2 preferably 0.5 A / cm 2 up to 40,000 A / cm 2 , preferably 1 A / cm 2 up to 30,000 A / cm 2 , even more preferably 5 A / cm 2 up to 25,000 A / cm 2 , exhibits and acts for a time of 10 ns to 3 s, preferably 10 ns to 1 s, more preferably 100 ns to 500 ms.

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