JP2010123999A - Paste material for solar battery and method for manufacturing solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery in which energy conversion efficiency is improved. <P>SOLUTION: A paste material for the solar battery is a paste material used when a p<SP>+</SP>-layer 4, a counter electrode 3 or a photodetective surface electrode 5 are formed on one surface side of a silicon (Si) substrate 1. The paste material for the solar battery contains aluminum (Al) and powder of Al-Si alloy in which the weight ratio of silicon (Si) to aluminum (Al) is 5% or more and 50% or less as the main component, and also contains organic solvent as the remaining component. When the p<SP>+</SP>-layer 4, the counter electrode 3 or the photodetective surface electrode 5 is formed on the surface of the silicon (Si) substrate 1 according to one method for manufacturing the solar battery, the paste material including the powder of Al-Si alloy is applied and then the substrate is dried and annealed to form the p<SP>+</SP>-layer 4, the counter electrode 3 or the photo detective surface electrode 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a technique for forming an electrode or p ⁺ layer of a silicon (Si) solar cell, specifically, a Si solar cell having a pn junction.

Si solar cell, usually a ^{p +} layer provided on one main surface (front surface) side of the p-type Si substrate in ^{the n +} layer and the other main surface (back surface) ^side, the n + / p / ^{p +} junction on the formation, placing a light-transmitting light-receiving surface electrode on the n ⁺ layer, a structure in which the counter electrode on the p ⁺ layer.

The light-receiving surface electrode on the n ⁺ layer is formed by applying silver (Ag) paste in a comb-like shape by printing, then drying, and then annealing, and facing the p ⁺ layer. For example, an aluminum paste consisting of 70% by weight of Al powder, 1% by weight of glass frit, 3% by weight of organic binder and 26% by weight of organic solvent is applied to the electrode, and then dried and then annealed. It is formed.

  In recent years, as an improved type of the above-mentioned aluminum paste, from Al powder, 0.5 to 50 parts by weight of Si with respect to 100 parts by weight of Al powder, an organic solvent, and an organic binder added as necessary According to this, after the annealing of the aluminum paste, the phenomenon that the Si substrate warps due to the difference in the thermal expansion coefficient between the Al layer and the Si substrate is reduced, and the cassette storage and the next process are performed. In the manufacturing process in (1), it is assumed that the handling error of the automatic transfer machine or the like, or the occurrence of cracks or chipping of the elements and the decrease in the manufacturing yield are reduced. (Patent Document 1)

JP 2001-313402 A

However, the difference in thermal expansion coefficient between the Al layer and the Si substrate (Al; 23.25 × 10 ⁻⁶ deg ⁻¹ , Si; 2.5 × 10 ⁻⁶ deg ⁻¹ ) is about one digit as described above. It ’s a big difference. That is, simply using a paste in which Al powder and Si powder are mixed, in practice, in order to eliminate warping of the Si substrate, it is necessary to set the mixing ratio of Si powder to Al powder in the aluminum paste to be considerably high. It is. And if the compounding ratio of Si powder becomes high, after annealing of the applied paste, conversely, the conductivity of the electrode material will be reduced, and the characteristics of the solar cell will be deteriorated. Specifically, in order to eliminate warpage of the Si substrate, it is predicted that the blending ratio of the Si powder needs to be about 10 wt% to 50 wt%. In addition, in the Example in patent document 1 mentioned previously, the specific data in case the compounding ratio of Si powder is less than 10 weight% is not disclosed. If not only the mixing ratio of Si but also the mixing method is not optimized, Si will be unevenly distributed in the electrode layer, and the conversion efficiency will not be improved.

  An object of the present invention is to realize a remarkable performance improvement of a Si solar cell by substantially lowering the mixing ratio of Si contained in the electrode layer and forming an electrode in which Si is uniformly dispersed. is there.

  As a result of earnest research to achieve the above object, the inventors have an adverse effect on the energy conversion efficiency as a solar cell not only when the proportion of Si powder is too large but also when the proportion is too low. I found out. In other words, if the proportion of Si in the Al powder used as the base material is too low, Si atoms diffuse from the Si substrate side to the back metal electrode side during electrode formation, and therefore in the interface region with the back electrode on the Si substrate side. It became clear that many defects were generated, which would lead to deterioration in conversion efficiency. Furthermore, the inventors have studied not only the blending ratio of Si powder but also means for mixing Al and Si. As a result, the inventors simply formed the electrode by mixing Al powder and Si powder with a binder. However, it is better to prepare an alloy of Al and Si first, and to form an electrode using a paste material mixed with a powder formed by pulverizing the alloy and a binder, so that Si is uniformly contained in the Al base material. As a result, it was found that the electrode can be formed, and as a result contributes to the conversion efficiency, and the present invention has been completed.

That is, in the solar cell according to the present invention, an n ⁺ layer is provided on one surface of the p-type silicon (Si) layer between the light-receiving surface electrode and the counter electrode, and the other of the silicon (Si) layer is provided. The electrode has a structure in which a p ⁺ layer is provided on the surface, and the electrode disposed on the surface of the p ⁺ layer includes a granular sintered body of an Al—Si alloy. Here, it is preferable in terms of energy conversion efficiency that the p ⁺ layer is in contact with the granular sintered body via an Al—Si alloy layer. This is because the p ⁺ layer is in contact with the granular sintered body of the Al—Si alloy through the Al—Si alloy layer, which is advantageous in that Si on the surface of the p ⁺ layer hardly diffuses into the electrode. Here, the term “granular” refers to not only the case where the grains are divided into one piece but also present in the alloy, as well as the case where a plurality of grains are combined or agglomerated in the alloy. Shall be included.

The paste material for solar cell according to the present invention is a paste material used when forming a p ⁺ layer or an electrode on one surface side of a silicon (Si) substrate, and silicon (Si) with respect to aluminum (Al) as a main component. The Al—Si alloy powder having a weight ratio of 5% to 50% is included. By using the powder of this material, the melting point of the entire paste material is lowered, and as a result, the uniformity of the Al—Si alloy can be improved. The weight ratio of silicon (Si) to aluminum (Al) in the final paste material is preferably 1% or more and 10% or less. If it is less than 1%, it is far below the solid solution limit value of silicon (Si) with respect to aluminum (Al), and in particular, from the Si substrate side with respect to the p ⁺ layer and the electrode layer during the annealing process in the manufacturing process of the solar cell. The diffusion of Si atoms is promoted, and the energy conversion efficiency of the solar cell is deteriorated. On the other hand, if it exceeds 10%, the resistance of the electrode becomes high, so that the solar cell characteristics, particularly the fill factor (FF), is deteriorated, and the energy conversion efficiency of the solar cell is lowered. In order to reduce these adverse effects, the weight ratio of silicon (Si) to aluminum (Al) in the final paste material is preferably 1.5% or more and 3% or less. Moreover, since it is easy to adjust the viscosity of the paste material, it is preferable that the remaining components contain glass frit, an organic binder, an organic solvent, and the like. Further, the paste material preferably contains 50% by weight or more of Al—Si alloy powder. This is because if it is less than 50% by weight, the bonding between the powders becomes insufficient, and the electric resistance of the final molded product increases.

In the method of manufacturing a solar cell according to the present invention, in the step of forming a p ⁺ layer or an electrode on the surface of a silicon (Si) substrate, an Al—Si alloy powder-containing paste material is applied, dried, and then annealed. And forming the p ⁺ layer or electrode. The Al—Si alloy preferably has a weight ratio of silicon (Si) to aluminum (Al) of 1% to 10%. This suppresses Si diffusion from the surface of the p ⁺ layer of Si to the back metal electrode with a small Si content, eliminates the occurrence of defects on the surface of the p ⁺ layer, and further improves the energy conversion efficiency of the solar cell as the final product Because it can.

  According to any invention of the present invention, the solar cell produced using the paste material containing the Al-Si alloy powder is more Si than the case where the paste material obtained by simply mixing the Al powder and the Si powder is used. It is possible to minimize the diffusion from the substrate to the Al base material that is an electrode, and as a result, it is possible to effectively suppress the occurrence of defects in the outermost surface layer of the Si substrate and to increase the conversion efficiency. It was observed. Of course, the energy conversion efficiency of the solar cell can be further increased compared to the case where Si is not contained.

Cross-sectional structure diagram of Si solar cell of Example Electromotive force (current-voltage) characteristic diagram of the Si solar cell of the example (A) is a graph showing the relationship between annealing temperature and conversion efficiency (circle), and the relationship between annealing temperature and curve factor (triangle), (b) is the annealing temperature and open circuit voltage (circle). ) And the relationship between the annealing temperature and the short-circuit current density (triangles).

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional structure diagram of a Si solar cell in an example of the present invention. In order to form this Si solar cell, first, a (100) plane p-type silicon substrate 1 having a specific resistance of about 10 Ωcm is used, and a phosphorous (P) -containing coat layer is formed on the surface side and heat treatment at 900 ° C. N ⁺ layer 2 was formed. Next, on the back surface of the substrate 1, an aluminum alloy paste (hereinafter referred to as an Al-Si alloy paste) in which aluminum (Al) alone and a powder of a silicon-containing aluminum alloy (hereinafter referred to as an Al-Si alloy) are used as main components. Was applied by screen printing, followed by drying at 150 ° C. for 10 minutes, followed by annealing at 700 ° C. for 1 minute to form the counter electrode 3. At this time, the p ⁺ layer 4 is formed on the back surface of the substrate 1 by diffusion introduction of Al in the Al—Si alloy paste. Next, a silver (Ag) paste is applied onto the n ⁺ layer 2 in a comb-like shape by screen printing, and then dried at 150 ° C. for 10 minutes, and further annealed at 550 ° C. for 1 to 10 minutes. The light-receiving surface electrode 5 was formed by heat treatment. The counter electrode 3 manufactured through the above steps contained a granular sintered body in which the weight ratio of Si to Al was not less than the solid solution limit value, that is, 1.60% and not more than 50%. The weight ratio of Si to Al contained in the entire counter electrode was 1% or more and 10% or less.

  Here, the Al-Si alloy paste uses a powder prepared by pulverizing an Al-Si alloy having a weight ratio of 5% to 50% with respect to Al. It is preferable in terms of making it easier. The weight ratio of silicon (Si) to aluminum (Al) in the final paste material is preferably 1% or more and 10% or less. This is because diffusion from the Si substrate to the electrode layer using Al as a base material can be effectively suppressed. As for the weight ratio in the final paste material, the use of an Al—Si alloy paste having a weight ratio of 1.5% or more and 3% or less, which is close to the maximum of the solid solution, can further exert the above effect. preferable. In particular, the lower limit of the weight ratio is most preferably 1.59 which is the solid solution limit value. In the case of an Al-Si alloy formed using a paste material whose weight ratio in the final paste material is adjusted in advance, since Si is the maximum solid solution and uniformly distributed in Al, the Si distribution in Al is uniform. It is. Therefore, in the heat treatment process of the paste material (for example, annealing for electrode formation), the amount of Si dissolved in Al is negligibly small.

  For comparison, an Si solar cell using an aluminum paste material containing only Al powder and containing no Si as a main component was also manufactured.

  FIG. 2 is an electromotive force (current-voltage) characteristic diagram of a Si solar cell manufactured based on the steps of the above embodiment. However, some processes are changed. Specifically, the characteristic curve (a) is obtained by forming the counter electrode with only Al powder without containing Si in the paste, and the characteristic curve (c) is obtained by mixing 2% by weight of Al—Si alloy powder in the paste. This is a case in which the counter electrode is formed using a thin film. The characteristic curve (b) is obtained when a treatment at 600 ° C. is performed for 4 minutes when forming the counter electrode with a paste mixed with 2 wt% Si-containing Al—Si alloy powder.

  From the comparison of the characteristic curves (a) and (c) of FIG. 2, the one in which the counter electrode is formed of an aluminum alloy paste having 2 wt% Si-containing Al—Si alloy powder in the paste has a high current density and The output characteristics were excellent, and the conversion efficiency was 13.4% also according to this example, which was an increase of 10% or more as an increase rate from 12.0% when Si was not included. This is because even in the treatment at about 700 ° C., the silicon is uniformly diffused into Al. As a result, it has been clarified that the use of a paste material mixed with powder of Al—Si alloy has a so-called defect suppressing action that prevents defects on the backside silicon substrate. In addition, when the counter electrode is formed with less than 1% by weight of Al—Si alloy powder, the result is almost the same as (a) in FIG. 2, and the effect of using the Al—Si alloy powder can be confirmed as significant. There wasn't. As can be seen from the characteristic curve (b), it was found that when the annealing treatment is excessive, the oxidation of Al progresses and the output characteristic fill factor (FF) is significantly reduced.

  FIG. 3 shows the dependence of the annealing temperature on the characteristics of the conversion efficiency (η), fill factor (FF), open circuit voltage (Voc), and short circuit current density (Jsc) for the solar cell of this example. Indicated by From these characteristics, it can also be seen that the annealing conditions can be adjusted so that higher conversion efficiency can be obtained by using Al—Si alloy powder in which Si is mixed in Al. Specifically, as the annealing conditions, it was appropriate to perform the treatment at 650 ° C. or more and 750 ° C. or less when the treatment time was 1 minute.

As described above, the present invention has been described in detail with reference to the Si solar cell of the embodiment and the manufacturing method thereof. However, the present invention is not limited to the single crystal Si solar cell but also to a polycrystalline Si solar cell having the same configuration. Applicable. Further, in this embodiment, as shown in FIG. 1, the light receiving surface electrode is arranged on the surface of the n ⁺ layer and the counter electrode is arranged on the surface of the p ⁺ layer. Even if it is arranged on the surface of the p ⁺ layer and the counter electrode is arranged on the surface of the n ⁺ layer, the substantial effect of the present invention occurs.

  The present invention is applied to various semiconductor devices that use the Al-Si alloy powder-containing paste of the present technology for an electrode structure of a Si semiconductor device, including the use for single crystal and polycrystalline Si solar cells. This can contribute to improving the characteristics.

1 p-type silicon substrate 2 n ⁺ layer 3 counter electrode 4 p ⁺ layer 5 light-receiving surface electrode

Claims (10)

In a paste material used when forming a p ⁺ layer or an electrode on one surface side of a silicon (Si) substrate,
As a main component, including aluminum (Al) and Al—Si alloy powder in which the weight ratio of silicon (Si) to aluminum (Al) is 5% or more and 50% or less,
A solar cell paste material containing an organic solvent as a remaining component. The solar cell paste material according to claim 1, wherein a weight ratio of silicon (Si) to aluminum (Al) is 1% or more and 10% or less. The solar cell paste material according to claim 1, wherein a weight ratio of silicon (Si) to aluminum (Al) is 1.5% or more and 3% or less. The solar cell paste material according to claim 1, wherein the residual component includes an organic binder. The paste material for a solar cell according to claim 1, comprising 50% by weight or more of the Al—Si alloy powder. In the step of forming the p ⁺ layer or electrode on a silicon (Si) surface of the substrate,
A method of manufacturing a solar cell, comprising: applying a powder-containing paste material of an Al—Si alloy, drying, and then annealing to form the p ⁺ layer or electrode. The method for manufacturing a solar cell according to claim 6, wherein the Al—Si alloy powder has a weight ratio of silicon (Si) to aluminum (Al) of 5% or more and 50% or less. The method for manufacturing a solar cell according to claim 6, wherein the paste material has a weight ratio of silicon (Si) to aluminum (Al) of 1% to 10%. The method for manufacturing a solar cell according to claim 6, wherein the paste material has a weight ratio of silicon (Si) to aluminum (Al) of 1.5% to 3%. The method for manufacturing a solar cell according to claim 6, wherein the paste material contains 50 wt% or more of the powder of the Al—Si alloy.

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