Wafer-based solar cell, and method for manufacturing such a wafer-based solar cell

Abstract

The invention relates to a wafer-based solar cell comprising a semiconductor wafer that is made of a semiconductor material consisting of silicon and that has a semiconductor wafer surface, at least one p-doped region, and at least one n-doped region, wherein the p-doped region and / or the n-doped region is electrically contacted, via opening regions and current contact regions located therein, with a metal electrode structure attached to the semiconductor wafer surface, and the metal electrode structure covers an electrode cover area on the semiconductor wafer surface, and wherein the semiconductor wafer surface of the wafer-based solar cell has a passivation layer arranged between the semiconductor material and the metal electrode structure, and wherein this passivation layer consists at least in part of an aluminium oxide and / or the metal electrode structure is formed from a metallic material containing, at least in part, aluminium, and wherein the current contact regions pass through the passivation layer and wherein, at the current contact regions, a metal-silicon mixture is formed in a first mixing region in the transition region between the metal electrode structure, the passivation layer, and the semiconductor material. The aim of the invention is to provide a wafer-based solar cell, wherein the wafer-based solar cell has a reduced electrical contact resistance in order to increase the efficiency of the wafer-based solar cell. This aim is achieved by forming, in the current contact regions (5), a second mixing region in the semiconductor material at an end of the first mixing region (9) facing the semiconductor material, and embedding aluminium atoms in the semiconductor material within this second mixing region (10).

Description

[0001] Wafer solar cell and method for producing such a wafer solar cell

[0002] The present invention relates to a wafer solar cell. A wafer solar cell in the sense of the present invention is understood to be a solar cell produced from a silicon semiconductor wafer, and this semiconductor wafer forms the structural framework of the solar cell. The semiconductor wafer formed from semiconductor material (silicon) has a semiconductor wafer surface and at least one p-doped region and at least one n-doped region, wherein the p-doped region and / or the n-doped region are each electrically contacted with a metal electrode structure applied to the semiconductor wafer surface via current contact regions, and each metal electrode structure covers an electrode covering area on the semiconductor wafer surface. The metal electrode structure is important for discharging charge carriers from the wafer solar cell in the form of an electric current flow. The p-doping of the silicon can be carried out with boron, gallium, or aluminum.

[0003] It is known that wafer solar cells can have at least one dielectric passivation layer arranged between the metal electrode structure and the semiconductor wafer surface. The passivation layer is typically composed of materials selected from the group consisting of: AlOx (aluminum oxide), SiNx (silicon nitride), SiOxNy (silicon oxynitride), SiOx (silicon oxide), and / or poly-Si (polycrystalline silicon). This passivation layer typically has a thickness in the range of 50 nm to 200 nm. Optionally, additional layers—for example, an anti-reflection layer—can be provided on this passivation layer.

[0004] P-type wafer solar cells and n-type wafer solar cells are known. In p-type wafer solar cells, the semiconductor wafer has a positively charged silicon base, the upper surface of which is negatively charged due to doping with an impurity. The negatively charged upper surface forms the emitter of the p-type wafer solar cell. In n-type wafer solar cells, the semiconductor wafer has a negatively charged silicon base, the upper surface of which is positively charged due to doping with an impurity. The positively charged upper surface forms the emitter of the n-type wafer solar cell.

[0005] To form the metal electrode structure of a wafer solar cell with a passivation layer, metal pastes are printed onto the semiconductor wafer surface using a screen printing process, for example. In a subsequent annealing step, these metal pastes are etched or burned into the passivation layer, at least in part. This at least partial burning creates openings in the passivation layer. In at least some of these openings, current contact areas are also formed, which completely penetrate the passivation layer. The current contact areas primarily form the current paths for the charge carriers generated in the semiconductor wafer to reach the metal electrode structure. The current contact areas are therefore crucial for the electrical contact resistance between the metal electrode structure and the doped semiconductor wafer surfaces of the wafer solar cell.This contact resistance should be as low as possible.

[0006] It is known from the prior art that low contact resistances to the metal electrode structure on boron or gallium p-doped emitters can only be achieved if the metal pastes used to create the metal electrode structure contain at least a small amount of aluminum. In contrast, the use of aluminum-free metal pastes (e.g., aluminum-free silver paste) usually results in poor electrical contact between the semiconductor material and the metal electrode structure. On the other hand, the aluminum particles used in metal pastes are usually relatively large, which in turn limits the minimum finger width for screen printing and also narrows the process window for firing these metal pastes.

[0007] The object of the invention is to provide a wafer solar cell, wherein the wafer solar cell has a reduced electrical contact resistance with reduced impairment of the semiconductor material in order to increase the efficiency of the wafer solar cell.

[0008] This object is achieved in wafer solar cells having a p-doped region of the semiconductor material with aluminum. A second mixed region is formed in the semiconductor material in the current contact regions at an end of the first mixed region facing the semiconductor material. Aluminum atoms are embedded in the semiconductor material in this second mixed region, and the concentration of aluminum atoms in the second mixed region is greater than the concentration of aluminum atoms in the semiconductor material outside the first and second mixed regions. Thus, an intermediate layer (second mixed region) is provided at the transition between the first mixed region and the semiconductor material, in which the semiconductor material is doped with aluminum atoms in a higher concentration.

[0009] This leads to a significant reduction in the contact resistance between the metal electrode structure and the doped semiconductor wafer surfaces of the wafer solar cell. The reduction in contact resistance can be seen in the fact that the semiconductor material formed from silicon is locally more highly doped with the embedded aluminum atoms in the second mixed region.

[0010] Furthermore, in wafer solar cells having a boron or gallium p-doped region of the semiconductor material, the object is achieved by forming a second mixing region in the semiconductor material in the current contact regions at an end of the first mixing region facing the semiconductor material, and by embedding aluminum atoms in this second mixing region in the semiconductor material. Thus, an intermediate layer (second mixing region) is provided at the transition between the first mixing region and the semiconductor material, in which the semiconductor material is doped with aluminum atoms.

[0011] This leads to a significant reduction in the contact resistance between the metal electrode structure and the doped semiconductor wafer surfaces of the wafer solar cell. The reduction in contact resistance can be attributed to the fact that, on the one hand, the semiconductor material formed from silicon in the second mixed region is locally doped with the embedded aluminum atoms.

[0012] If aluminum atoms are already embedded in the boron or gallium p-doped region of the semiconductor material from the outset in the sense of an impurity of the starting material, the invention is to be understood in such a way that here too a concentration of the aluminum atoms in the second mixed region is greater than a concentration of the aluminum atoms in the semiconductor material outside the first and second mixed region.

[0013] Regarding the second mixing regions, it is clarified again that these are only provided locally at the current contact areas. The individual, local second mixing regions below the metal electrode structure are separated from one another. The second mixing regions together do not form a coherent layer below the metal electrode structure.

[0014] In one embodiment, the passivation layer is formed at least partially from an aluminum oxide and / or the metal electrode structure is formed from a metallic material containing at least partially aluminum.

[0015] According to the invention, the second mixing regions are created by locally heating the opening regions and / or current contact regions. During the local heating of the opening regions and / or current contact regions, temperatures in the range of 600°C to 1,500°C are reached, particularly in the aluminum oxide layer and in a zone of the semiconductor material adjacent to the aluminum oxide layer. Heating in this temperature range should last for a period of time in the range of 10 ns to 1 s. The local heating can be achieved, for example, by means of LECO (Laser Enhanced Contact Optimization) treatment or by means of local radiation-assisted direct heating.In LECO treatment, the wafer solar cell is electrically contacted at both polarities, a reverse voltage is applied, and a light source or point light source, such as a laser beam, is guided over the surface of the wafer solar cell. The resulting local current flows result in local heating of the wafer solar cell. In local radiation-assisted direct heating, the relevant area of ​​the wafer solar cell is locally irradiated, for example, using laser radiation. The laser energy is coupled directly into the wafer solar cell as thermal energy, thus leading to direct, local heating.

[0016] In an advantageous embodiment, the second mixing regions have a lateral extent in a plane parallel to the passivation layer in the range from 100 nm to 1,000 nm, preferably in the range from 200 nm to 800 nm, particularly preferably in the range from 400 nm to 700 nm.

[0017] An advantageous embodiment provides that the second mixing regions have a lateral extent perpendicular to a plane parallel to the passivation layer in the range from 25 nm to 250 nm, preferably in the range from 50 nm to 200 nm, particularly preferably in the range from 75 nm to 150 nm.

[0018] It is proposed that the aluminum atoms are incorporated in the second mixing region at a concentration in the range of 0.1 wt% to 2.0 wt%, preferably in the range of 0.3 wt% to 1.8 wt%, more preferably in the range of 0.5 wt% to 1.5 wt% (unit wt% is weight percent to indicate a mass fraction of a mixture of substances).

[0019] It is further proposed that the first mixing areas in the plane of the passivation layer each have an area in the range of 0.05 pm 2 until 1:00 pm 2 , preferably in the range of 0.1 pm 2 until 0.8 pm 2 , particularly preferably in the range of 0.2 pm 2 until 0.5 pm 2 , have.

[0020] In an advantageous embodiment, the first mixing regions in the plane of the passivation layer each have a lateral extent in the range from 100 nm to 1,000 nm, preferably in the range from 200 nm to 800 nm, particularly preferably in the range from 400 nm to 700 nm.

[0021] A further advantageous embodiment provides that 500 to 45,000 first mixing areas per mm 2 , preferably 2,000 to 15,000 first mixing areas per mm 2 , particularly preferably 3,000 to 6,000 first mixing areas per mm 2 , are provided.

[0022] Furthermore, a method for producing the wafer solar cell according to the invention is proposed. This method provides that the wafer solar cell is first prepared with the semiconductor material, the passivation layer, and the formed metal electrode structure. Subsequently, in a tempering step, the current contact regions are locally heated to a temperature in the range of 600°C to 1,500°C for a time in the range of 10 ns to 1 s.

[0023] It is proposed that the temperature be in the range of 900 °C to 1,500 °C, preferably in the range of 1,100 °C to 1,500 °C, more preferably in the range of 1,250 °C to 1,500 °C.

[0024] Particularly when using aluminum-free metal pastes, local heating can dissolve a portion of the aluminum from a passivation layer formed from Al2O3 and also react with an aluminum-free metal paste. The aluminum is also available, at least temporarily, for a possible reduction in the melting temperature of an alloy formed from this aluminum and the aluminum-free metal paste.

[0025] In an advantageous embodiment, the local heating is carried out by means of a LECO treatment or by means of a local radiation-assisted direct heating.

[0026] In a LECO treatment, the wafer solar cell is electrically contacted at both polarities, a reverse voltage is applied, and a light source or point light source, such as a laser beam, is guided over the surface of the wafer solar cell, so that the resulting local current flows result in local heating of the wafer solar cell. In local radiation-assisted direct heating, the relevant area of ​​the wafer solar cell is locally irradiated, for example, using laser radiation. The laser energy of the laser radiation is coupled directly into the wafer solar cell as thermal energy, thus leading to direct, local heating. An exemplary embodiment of the invention is explained below with reference to the drawings.

[0027] Fig. 1 is a cross-sectional view of a wafer solar cell according to the invention

[0028] Fig. 2 a detailed view of section A of the cross-sectional view according to Fig. 1

[0029] Fig. 3 a detailed view of section B of the cross-sectional view according to Fig. 1

[0030] Fig. 1 shows a schematic cross-sectional view of an n-type wafer solar cell according to the invention. The wafer solar cell has a silicon semiconductor wafer 1 with a semiconductor wafer surface comprising a front side and a back side. In the front side, a p-doped region 3 with boron, gallium, or aluminum is formed, while in the back side, an n-doped region 2 is formed. A passivation layer 6 is applied to each of the n-doped region 2 and the p-doped region 3. The passivation layer 6 applied to the p-doped region 3 is additionally covered with an anti-reflective layer 7. However, the anti-reflective layer 7 is optional and not mandatory. The passivation layer 6 has at least one layer formed from an aluminum oxide (for example, Al2O3). That is,The passivation layer 6 can consist entirely of a layer formed of aluminum oxide or, in addition to a layer formed of aluminum oxide, can have additional layers. These additional layers can be formed, for example, from SiNx (silicon nitride), SiOxNy (silicon oxynitride), SiOx (silicon oxide), and / or poly-Si (polycrystalline silicon).

[0031] A metal electrode structure 4 in the form of finger electrodes is arranged on the passivation layer 6 applied to the n-doped region 2 and on the anti-reflective layer 7. The metal electrode structure 4 covers an electrode covering surface when viewed from the front or back. The metal electrode structures 4 on the anti-reflective layer are electrically connected to the p-doped region 3 via current contact regions 5 (Fig. 2), which are located within opening regions 8 (Fig. 2) of the passivation layer 6 and anti-reflective layer 7. Likewise, the metal electrode structures 4 on the passivation layer 6 are electrically connected to the n-doped region 2 via current contact regions 5, which are located within opening regions 8 of the passivation layer 6 applied to the n-doped region 2.In the illustrated embodiment, the metal electrode structure 4 is formed from a metallic material that at least partially contains aluminum, or from an aluminum-free metallic material. For example, the metallic material can consist of silver, or the metallic material can consist of silver mixed with aluminum. Fig. 2 shows a detailed view of section A of the cross-sectional view according to Fig. 1. In this detailed view, a conductor track of the metal electrode structure 4 as well as sections of the passivation layer 6, the anti-reflective layer 7, and the p-doped region 3 of the semiconductor material made of silicon are visible. Furthermore, an opening region 8 with a current contact region 5 arranged therein can be seen. In the opening region 8, the material of the metal electrode structure 4 has partially penetrated into the anti-reflective layer 7.In the current contact region 5, the material of the metal electrode structure 4 has penetrated through the passivation layer 6 and the anti-reflection layer 7 into the p-doped region 3 of the semiconductor material.

[0032] At the current contact region 5, a metal-silicon mixture is formed in a first mixing region 9 at the transition between the metal electrode structure 4, the passivation layer 6, and the semiconductor material. Furthermore, a second mixing region 10 is formed in the semiconductor material in the current contact region 5 at an end of the first mixing region 9 facing the semiconductor material. If the p-doped region of the semiconductor material is doped with boron or gallium, aluminum atoms are now embedded in the p-doped region of the semiconductor material in the second mixing region 10. If the p-doped region of the semiconductor material was already doped with aluminum during construction of the wafer solar cell, the concentration of aluminum atoms in the second mixing region 10 is now greater than the concentration of aluminum atoms in the semiconductor material outside the first and second mixing regions 9, 10.

[0033] Fig. 3 shows a detailed view of section B of the cross-sectional view according to Fig. 1. In this detailed view, a conductor track of the metal electrode structure 4 as well as sections of the passivation layer 6 and the n-doped region 2 of the silicon semiconductor material are visible. Furthermore, an opening region 8 with a current contact region 5 arranged therein can be seen. In the opening region 8, the material of the metal electrode structure 4 has partially penetrated into the passivation layer 6. In the current contact region 5, the material of the metal electrode structure 4 has penetrated through the passivation layer 6 into the n-doped region 2 of the semiconductor material.

[0034] At the current contact region 5, a metal-silicon mixture is formed in a first mixing region 9 at the transition between the metal electrode structure 4, the passivation layer 6, and the semiconductor material. Furthermore, a second mixing region 10 is formed in the semiconductor material in the current contact region 5 at an end of the first mixing region 9 facing the semiconductor material. In this second mixing region 10, aluminum atoms are embedded in the n-doped region of the semiconductor material.

[0035] Both in the metal electrode structure 4 on the p-doped side of the semiconductor material and in the metal electrode structure 4 on the n-doped side of the semiconductor material, a plurality of opening regions 8 and current contact regions 5 arranged therein are provided.

[0036] The second mixing regions 10 have a lateral extent in a plane parallel to the passivation layer in the range of 100 nm to 1,000 nm, preferably in the range of 200 nm to 800 nm, particularly preferably in the range of 400 nm to 700 nm. Perpendicular to a plane parallel to the passivation layer, the second mixing regions 10 have a lateral extent in the range of 25 nm to 250 nm, preferably in the range of 50 nm to 200 nm, particularly preferably in the range of 75 nm to 150 nm.

[0037] In the second mixing region 10, the aluminum atoms are incorporated at a concentration in the range of 0.1 wt% to 2.0 wt%, preferably in the range of 0.3 wt% to 1.8 wt%, more preferably in the range of 0.5 wt% to 1.5 wt%.

[0038] The first mixing regions 9 each have an area in the range of 0.05 pm in the plane of the passivation layer 6 2 until 1:00 pm 2 , preferably in the range of 0.1 pm 2until 0.8 pm 2 , particularly preferably in the range of 0.2 pm 2 until 0.5 pm 2 , perpendicular to the plane of the passivation layer 6, the first mixing regions 9 each have a lateral extent in the range from 100 nm to 1,000 nm, preferably in the range from 200 nm to 800 nm, particularly preferably in the range from 400 nm to 700 nm.

[0039] Over the electrode covering area there are 500 to 45,000 first mixing areas 9 per mm 2 , preferably 2,000 to 15,000 first mixing areas 9 per mm 2 , particularly preferably 3,000 to 6,000 first mixing areas 9 per mm 2 , is provided.

[0040] The invention is not limited to the illustrated embodiment. For example, the wafer solar cell can also be a p-type wafer solar cell, where the p-doped and n-doped regions are reversed compared to the n-type wafer solar cell. Furthermore, in both a p-type wafer solar cell and an n-type wafer solar cell, the passivation layer 6 formed from aluminum oxide can be provided only on the n-doped side or only on the p-doped side. Deviating from the previously described embodiments, the passivation layer 6 can also not be formed from aluminum oxide. For example, the passivation layer 6 can be formed from SiNx (silicon nitride), SiOxNy (silicon oxynitride), SiOx (silicon oxide), and / or poly-Si (polycrystalline silicon).

[0041] To produce the wafer solar cell according to the invention, the wafer solar cell is first prepared with the semiconductor material, the passivation layer 6, and the formed metal electrode structure 4. Subsequently, in a tempering step, the current contact regions 5 are locally heated to a temperature in the range of 600°C to 1,500°C for a time in the range of 10 ns to 1 s. In further embodiments, the temperature is in the range of 900°C to 1,500°C, preferably in the range of 1,100°C to 1,500°C, more preferably in the range of 1,250°C to 1,500°C. The local heating is carried out by means of a LECO treatment or by means of local radiation-assisted direct heating.

[0042] The aluminum atoms embedded in the semiconductor material in the second mixing region 10 can, for example, originate from the passivation layer 6 formed at least partially from an aluminum oxide and / or from the metal electrode structure 4 formed from a metallic material containing at least partially aluminum, without the invention being restricted thereto, however.

[0043] List of reference symbols

[0044] 1 semiconductor wafer

[0045] 2 p-doped region

[0046] 3 n-doped region

[0047] 4 Metal electrode structure

[0048] 5 Power contact area

[0049] 6 Passivation layer

[0050] 7 Anti-reflective coating

[0051] 8 opening areas

[0052] 9 first mixing area

[0053] 10 second mixing area

Claims

Patent claims 1. Wafer solar cell with a semiconductor wafer (1) made of silicon semiconductor material, having a semiconductor wafer surface and at least one boron or gallium p-doped region (2) and at least one n-doped region (3), wherein the p-doped region (2) and / or the n-doped region (3) is electrically contacted with a metal electrode structure (4) applied to the semiconductor wafer surface via opening regions (8) and current contact regions (5) located therein, and the metal electrode structure (4) covers an electrode covering area on the semiconductor wafer surface, and wherein the semiconductor wafer surface of the wafer solar cell has a passivation layer (6) arranged between the semiconductor material and the metal electrode structure (4), and wherein the current contact regions (5) are guided through the passivation layer (6), and wherein at the current contact regions (5) in the transition between the metal electrode structure,a metal-silicon mixture is formed between the passivation layer (6) and the semiconductor material in a first mixing region (9), characterized in that a second mixing region is formed in the semiconductor material in the current contact regions (5) at an end of the first mixing region (9) facing the semiconductor material, and aluminum atoms are embedded in the semiconductor material in this second mixing region (10).

2. Wafer solar cell with a semiconductor wafer (1) made of silicon semiconductor material, having a semiconductor wafer surface and at least one p-doped region (2) with aluminum and at least one n-doped region (3), wherein the p-doped region (2) and / or the n-doped region (3) is electrically contacted with a metal electrode structure (4) applied to the semiconductor wafer surface via opening regions (8) and current contact regions (5) located therein, and the metal electrode structure (4) covers an electrode covering area on the semiconductor wafer surface, and wherein the semiconductor wafer surface of the wafer solar cell has a passivation layer (6) arranged between the semiconductor material and the metal electrode structure (4), and wherein the current contact regions (5) are guided through the passivation layer (6), and wherein at the current contact regions (5) in the transition between the metal electrode structure,a metal-silicon mixture is formed between the passivation layer (6) and the semiconductor material in a first mixing region (9), characterized in that in the current contact regions (5) at an end of the first mixing region (9) facing the semiconductor material, a second, A mixing region is formed in the semiconductor material and aluminum atoms are embedded in this second mixing region (10) and a concentration of the aluminum atoms in the second mixing region is greater than a concentration of the aluminum atoms in the semiconductor material outside the first and second mixing regions (9, 10).

3. Wafer solar cell according to one of the preceding claims, characterized in that the passivation layer (6) is formed at least partially from an aluminum oxide and / or the metal electrode structure (4) is formed from a metallic material containing at least partially aluminum.

4. Wafer solar cell according to one of the preceding claims, characterized in that aluminum atoms are incorporated in the second mixing region with a concentration in the range of 0.1 wt% to 2.0 wt%, preferably in the range of 0.3 wt% to 1.8 wt%, more preferably in the range of 0.5 wt% to 1.5 wt%.

5. Wafer solar cell according to claim 1, characterized in that the second mixing regions (10) have a lateral extent in a plane parallel to the passivation layer in the range from 100 nm to 1,000 nm, preferably in the range from 200 nm to 800 nm, particularly preferably in the range from 400 nm to 700 nm.

6. Wafer solar cell according to one of the preceding claims, characterized in that the second mixing regions (10) have a lateral extent perpendicular to a plane parallel to the passivation layer in the range from 25 nm to 250 nm, preferably in the range from 50 nm to 200 nm, particularly preferably in the range from 75 nm to 150 nm.

7. Wafer solar cell according to one of the preceding claims, characterized in that the first mixing regions (9) in the plane of the passivation layer each have an area in the range of 0.05 pm 2 until 1:00 pm 2 , preferably in the range of 0.1 pm 2 until 0.8 pm 2 , particularly preferably in the range of 0.2 pm 2 until 0.5 pm 2 , have.

8. Wafer solar cell according to one of the preceding claims, characterized in that the first mixing regions (9) perpendicular to the plane of the passivation layer each have a lateral extent in the range of 100 nm to 1,000 nm, preferably in the range of 200 nm to 800 nm, particularly preferably in the range of 400 nm to 700 nm.

9. Wafer solar cell according to one of the preceding claims, characterized in that over the electrode covering surface 500 to 45,000 first mixing regions (9) per mm 2, preferably 2,000 to 15,000 first mixing areas (9) per mm 2 , particularly preferably 3,000 to 6,000 first mixing areas (9) per mm 2 , are provided.

10. A method for producing a wafer solar cell according to one of the preceding claims, characterized in that first the wafer solar cell with the semiconductor material, the passivation layer (6) and the formed metal electrode structure (4) is provided and then in a tempering step the current contact regions (5) are heated locally for a time in the range of 10 ns to 1 s to a temperature in the range of 600 °C to 1,500 °C.

11. The method according to claim 10, characterized in that the temperature is in the range from 900 °C to 1,500 °C, preferably in the range from 1,100 °C to 1,500 °C, more preferably in the range from 1,250 °C to 1,500 °C.

12. Method according to one of claims 10 or 11, characterized in that the local heating is carried out by means of a LECO treatment or by means of a local radiation-assisted direct heating.

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