JP5375414B2 - Solar cell and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell of high performance capable of maintaining low contact resistance even with thinner electrodes. <P>SOLUTION: The solar cell includes a first conductive type silicon substrate 1, a diffusion layer 2 of the conductive type opposite to the first one which is formed on a light receiving surface side of the silicon substrate 1, a light receiving surface electrode 7 which is electrically connected to the diffusion layer 2, a diffusion layer 3 of the conductive type identical to the first one formed on the rear surface side of the first conductive type silicon substrate 1, and a rear surface electrode 7 which is electrically connected to the diffusion layer 3. A dielectric film 4 is so formed not to contact to the diffusion layer 2 of the conductive type opposite to the first one arranged directly under the light receiving surface side electrode. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a solar cell that directly converts light energy into electric energy and a method for manufacturing the solar cell.

  A solar cell is a semiconductor element that converts light energy into electric power, and includes a pn junction type, a pin type, a Schottky type, and the pn junction type is widely used. Further, when solar cells are classified based on their substrate materials, they are broadly classified into three types: silicon crystal solar cells, amorphous (amorphous) silicon solar cells, and compound semiconductor solar cells. Silicon crystal solar cells are further classified into single crystal solar cells and polycrystalline solar cells. Since a silicon crystal substrate for a solar cell can be manufactured relatively easily, its production scale is currently the largest and is expected to become more widespread in the future (for example, Patent Document 1: JP-A-8-073297). Publication).

The output characteristics of a solar cell are generally evaluated by measuring an output current voltage curve using a solar simulator. The product of the output current I _max and the output voltage V _max on this curve, the point at which I _max × V _max is maximum is called the maximum output P _max , and this P _max is the total light energy (S × (I: S is the element area, I is the intensity of the irradiated light))
η = {P _max / (S × I)} × 100 (%)
Is defined as the conversion efficiency η of the solar cell.

In order to increase the conversion efficiency η, the short-circuit current Isc (output current value when V = 0 in the current-voltage curve) or Voc (output voltage value when I = 0 in the current-voltage curve) is increased. It is important to make the output current voltage curve as close to a square as possible. The squareness of the output current voltage curve is generally
FF = P _max / (Isc × Voc)
It means that the output current voltage curve approaches an ideal square and the conversion efficiency η increases as the value of the FF is closer to 1.

  One of the main factors that determine FF is various series resistance components. Among the series resistance components, one of the main components is due to the contact resistance at the interface between the metal electrode and the semiconductor substrate surface. In particular, the light receiving surface electrode usually has a thick bus bar electrode 7 formed at an appropriate interval for reducing internal resistance, as shown in FIG. A thin finger electrode 5 branched from the bus bar electrode 7 into a comb shape at a predetermined interval is configured. As the finger electrode becomes thinner, the contact area of the semiconductor interface is limited, and the relative influence ratio on the contact resistance of the interface tends to increase.

  In order for solar cells to become more widespread in the future, higher conversion efficiency is required. As means for increasing the conversion efficiency, for example, there is a reduction in shadowing loss due to thinning of the light receiving surface electrode. Therefore, in the silicon crystal solar cells which are currently mainstream, after silver (Ag) paste is directly screen-printed on the dielectric film as the light-receiving surface electrode, the metal component in the Ag paste is obtained under appropriate firing conditions. A method is used in which a dielectric film is penetrated (fire through) to reach a silicon substrate. However, when the light receiving surface electrode is thinned, the metal component in the Ag paste decreases when a dielectric film is interposed between the silicon substrate and the finger electrode as in the method of forming the light receiving surface electrode as described above. Therefore, there is a problem that fire-through is insufficient, the contact property between the finger electrode and the silicon substrate is deteriorated, and the contact resistance is increased.

  To solve this problem, for example, screen-printing an etching paste on the dielectric film directly under the light-receiving surface electrode, and heating the printed etching paste to etch the printed portion of the etching paste before forming the light-receiving surface electrode. There is a method of removing a dielectric film corresponding to an electrode formation position (Patent Document 2: Japanese Translation of PCT International Publication No. 2003-531807). However, this method has a problem that the printing shape of the etching paste changes depending on the printing amount of the etching paste, the heating temperature, and the like, and etching with a precise pattern is difficult. There is also a method of removing the dielectric film directly under the light-receiving surface electrode by a method using a photomask, but in this case, the use of a photomask requires an increase in man-hours and a highly accurate apparatus, resulting in a manufacturing cost. However, there is a problem that efficient manufacturing becomes difficult.

  Further, in the method of forming the dielectric film after simply forming the light-receiving surface electrode, a dielectric film is formed on the bus bar electrode, which causes a problem in solderability when assembling the module.

JP-A-8-073297 Special table 2003-531807 gazette

  The present invention has been made in view of the above circumstances, and it is possible to improve the output characteristics by reducing the contact resistance with the silicon substrate interface without reducing the contact performance even for the thinning of the finger electrode. An object of the present invention is to provide a solar cell that can be manufactured and a method for manufacturing the solar cell.

  As a result of intensive studies to achieve the above object, the present inventors have found that at least finger electrodes are formed and then a dielectric film is formed, and then a bus bar electrode is formed. The present invention has found a structure in which a dielectric film is not formed only directly under the finger electrode formation without any steps, and as a result, has found a method for manufacturing an excellent solar cell in which contact resistance with a silicon substrate does not increase even when the finger electrode is thinned. It came to make.

Therefore, this invention provides the following solar cell and its manufacturing method.
Claim 1:
Light reception comprising a first conductive type silicon substrate, a conductive type diffusion layer opposite to the first conductive type formed on the light receiving surface side of the silicon substrate, and finger electrodes and bus bar electrodes electrically connected to the diffusion layer A solar cell comprising a surface electrode, a diffusion layer of the same conductivity type as the first conductivity type formed on the back surface side of the first conductivity type silicon substrate, and a back electrode electrically connected to the diffusion layer. The finger electrode is directly formed on the conductive type diffusion layer opposite to the first conductive type, and a silicon oxide film, a silicon nitride film, a titanium oxide film, an aluminum oxide film, a tin oxide film, a zinc oxide film, and magnesium fluoride. A dielectric film comprising a film or a combination of these films is formed to cover the finger electrode and a conductive type diffusion layer opposite to the first conductive type in a region excluding the finger electrode; Serial dielectric is formed on the film, and a solar cell of the dielectric film by firing through, characterized in that formed by connecting to the finger electrode.
Claim 2:
On the back side of the silicon substrate, the back electrode is directly formed on a diffusion layer of the same conductivity type as the first conductivity type on the back side of the silicon substrate, and the dielectric film excludes the back electrode and the back electrode A diffusion layer of the same conductivity type as that of the first conductivity type in the region is formed, and a backside bus bar electrode is formed on the dielectric film, and connected to the backside electrode through a fire-through of the dielectric film The solar cell according to claim 1, wherein the solar cell is formed.
Claim 3:
The solar cell according to claim 1, wherein the dielectric film is made of a silicon nitride film.
Claim 4:
Light reception comprising a first conductive type silicon substrate, a conductive type diffusion layer opposite to the first conductive type formed on the light receiving surface side of the silicon substrate, and finger electrodes and bus bar electrodes electrically connected to the diffusion layer Manufacturing a solar cell comprising a surface electrode, a diffusion layer of the same conductivity type as the first conductivity type formed on the back surface side of the first conductivity type silicon substrate, and a back electrode electrically connected to the diffusion layer A method wherein a conductive type diffusion layer opposite to the first conductive type is formed on the light receiving surface side of the silicon substrate, the finger electrode is directly formed on the diffusion layer, and the finger electrode and the region excluding the finger electrode are formed Covering the diffusion layer opposite to the first conductivity type of silicon oxide film, silicon nitride film, titanium oxide film, aluminum oxide film, tin oxide film, zinc oxide film, magnesium fluoride film, or these films After forming the dielectric film consisting of combined, the dielectric film is fire-through the bus bar electrode is formed by manufacturing method of a solar cell, characterized in that connected to the finger electrode over the dielectric film.
Claim 5:
On the back side of the silicon substrate, a back electrode is directly formed on the diffusion layer of the same conductivity type as the first conductivity type, and the same conductivity type as the first conductivity type in the region excluding the back electrode and the back electrode. The dielectric film is formed so as to cover a diffusion layer, and then the dielectric film is fired through from above the dielectric film to form a back busbar electrode and connected to the back electrode. 4. The method for producing a solar cell according to 4.
Claim 6:
The finger electrode and the back electrode are formed by firing at the same time, and the bus bar electrode and the back bus bar electrode are fired at the same time to form the dielectric films on the light receiving surface and the back surface by fire-through, respectively. Item 6. A method for producing a solar cell according to Item 5.
Claim 7:
The method for manufacturing a solar cell according to claim 4, wherein the dielectric film is formed by a plasma CVD method.

  According to the present invention, a dielectric film is not formed on a silicon substrate immediately below the formation of a light-receiving surface electrode, and a high-performance solar cell that can maintain a low contact resistance even when the electrode is thinned can be provided. In particular, when forming a finger electrode and a bus bar electrode, by forming a dielectric film after the finger electrode is formed, the finger electrode can be formed without a dielectric film between the silicon substrate and the finger electrode. The finger electrode can be thinned without deteriorating the contact property with the substrate. Further, since the fire-through is easy between the finger electrode and the bus bar electrode even through the dielectric film, the bus bar electrode is formed after the dielectric film is formed, so that the solderability on the bus bar electrode is also good. A solar cell can be manufactured.

It is a schematic sectional drawing which shows an example of the solar cell of this invention. It is a schematic plan view explaining the example of light-receiving surface electrode formation of a solar cell. (A)-(G) is a schematic sectional drawing which demonstrates the process sequentially about an example of the manufacturing method of the solar cell of this invention. (A)-(F) is a schematic sectional drawing which demonstrates the process sequentially about an example of the manufacturing method of the solar cell of a comparative example.

The solar cell of the present invention includes a first conductive type silicon substrate, a conductive type diffusion layer opposite to the first conductive type formed on the light receiving surface side of the silicon substrate, and a light receiving surface electrode electrically connected thereto. A diffusion layer of the same conductivity type as the first conductivity type formed on the back surface side of the first conductivity type silicon substrate, and a back electrode electrically connected to the diffusion layer, The conductive type diffusion layer opposite to the first conductive type directly below the surface side electrode is not in contact with the dielectric film.
In this case, the light-receiving surface electrode is preferably composed of finger electrodes and bus bar electrodes. 1-3 show an example of such a solar cell.
1 is a schematic cross-sectional view of a solar cell according to one embodiment of the present invention, FIG. 2 is a plan view seen from the light receiving surface side of FIG. 1, and FIG. 3 is one embodiment of the present invention. It is a schematic sectional drawing explaining the manufacturing method of the solar cell which concerns on.

  This solar cell includes a silicon substrate 1, a p-type diffusion layer 2 formed on the light-receiving surface side of the silicon substrate 1, finger electrodes 5 and bus bar electrodes 7 electrically connected to the p-type diffusion layer 2, A solar cell including an n-type diffusion layer 3 formed on the back surface side of the silicon substrate 1 and a back electrode 6 electrically connected to the n-type diffusion layer 3, After forming the n-type diffusion layer on the back surface side of the silicon substrate, the p-type diffusion layer is formed on the light receiving surface side of the silicon substrate, and then the back electrode 6 and the finger electrode 5 are formed. Thereafter, the dielectric film 4 is formed on the silicon substrate surface by plasma CVD, and then the bus bar electrodes 7 are formed on the back surface and the light receiving surface side.

  Hereinafter, the manufacturing method of the solar cell of this invention is demonstrated in detail.

(1) Silicon substrate The silicon substrate 1 may be n-type or p-type, but an n-type substrate is used in one embodiment of the present invention. This silicon single crystal substrate may be produced by any of the Czochralski (CZ) method and the float zone (FZ) method. The specific resistance of the silicon substrate 1 is preferably 0.1 to 20 Ω · cm, and more preferably 0.5 to 2.0 Ω · cm from the viewpoint of producing a high-performance solar cell. As the silicon substrate, a phosphorus-doped n-type single crystal silicon substrate is preferable. The phosphorus-doped dopant concentration is preferably 1 × 10 ¹⁵ cm ^{−3 to} 5 × 10 ¹⁶ cm ⁻³ [FIG. 3A].

(2) Damage etching / texture formation For example, the silicon substrate 1 is immersed in an aqueous sodium hydroxide solution, and the damaged layer is removed by etching. For removing damage from the substrate, a strong alkaline aqueous solution such as potassium hydroxide may be used, and a similar purpose can be achieved with an acid aqueous solution such as hydrofluoric acid. A random texture is formed on the substrate 1 subjected to damage etching. In general, a solar cell preferably has an uneven shape on the surface. The reason is that in order to reduce the reflectance in the visible light region, it is necessary to cause the light receiving surface to perform reflection at least twice as much as possible. The size of each mountain is preferably about 1 to 20 μm. Typical surface uneven structures include V-grooves and U-grooves. These can be formed using a grinding machine. In order to create a random uneven structure, wet etching can be performed by dipping in an aqueous solution obtained by adding isopropyl alcohol to sodium hydroxide, or acid etching, reactive ion etching, or the like can be used. In the drawing, the texture structure formed on both sides is fine and therefore omitted.

(3) Formation of n-type diffusion layer The n-type diffusion layer 3 is formed on the back surface by applying a coating agent containing a dopant to the back surface of the silicon substrate 1 and then performing heat treatment [FIG. 3 (B)]. After the heat treatment, the glass component attached to the silicon substrate 1 is washed by glass etching or the like. The dopant is preferably phosphorus. The surface dopant concentration of the n-type diffusion layer 3 is preferably 1 × 10 ¹⁸ cm ^{−3 to} 5 × 10 ²⁰ cm ^{−3, and} more preferably 5 × 10 ¹⁸ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ .

(4) Formation of p-type diffusion layer A similar process is performed on the light-receiving surface to form the p-type diffusion layer 2 on the entire light-receiving surface [FIG. 3C]. A p-type diffusion layer 2 is formed by applying a coating agent containing a dopant to the light receiving surface and performing a heat treatment. The dopant is preferably boron, and the surface dopant concentration of the p-type diffusion layer 2 is preferably 1 × 10 ¹⁸ cm ^{−3 to} 5 × 10 ²⁰ cm ^{−3 and} more preferably 5 × 10 ¹⁸ cm ⁻³ to 1 × 10. ²⁰ cm ⁻³ is more preferable.

(5) Pn junction isolation Pn junction isolation is performed using a plasma etcher. In this process, the sample is stacked so that plasma and radicals do not enter the light-receiving surface and the back surface, and the end surface is cut by several microns in that state. After bonding and separation, glass components, silicon powder, and the like attached to the substrate are washed by glass etching or the like.

(6) Finger electrode formation Using a screen printing device or the like, a paste containing silver, for example, is printed on the p-type diffusion layer and the n-type diffusion layer using a screen printing device on the light-receiving surface side and the back surface side. Apply in a pattern and dry. Finally, firing is performed at 500 to 900 ° C. for 1 to 30 minutes in a firing furnace to form the finger electrode 5 and the back electrode 6 that are electrically connected to the p-type diffusion layer and the n-type diffusion layer [FIG. D)].

(7) Dielectric Film Formation Subsequently, a silicon nitride film as the dielectric film 4 is deposited on the n-type diffusion layer 3 and the p-type diffusion layer 2 using a CVD apparatus [FIG. 3 (E)]. This film thickness is preferably 70 to 100 nm. Other antireflection films include silicon oxide films, titanium dioxide films, zinc oxide films, tin oxide films, aluminum oxide films, magnesium fluoride films, and combinations of these films, which can be substituted. In addition to the above, the formation method includes a remote plasma CVD method, a coating method, a vacuum deposition method, and the like. From an economical viewpoint, it is preferable to form the silicon nitride film or the like by the plasma CVD method.

(8) Bus bar electrode formation Similar to the finger electrode and back surface electrode formation, a screen printing device or the like is used, and, for example, a paste containing silver is applied to the light receiving surface side and the back surface side on the dielectric film formed using the screen printing device. Print and dry [FIG. 3 (F)]. Subsequently, firing is performed at 500 to 900 ° C. for 1 to 30 minutes in a firing furnace to form a bus bar electrode 7 connected to the finger electrode [FIG. 3 (G)]. FIG. 3F shows a state before firing, and FIG. 3G shows a state after firing.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Example 1]
The solar cell shown in FIG. 1 was manufactured according to the manufacturing method flowchart shown in FIG.
Crystal plane orientation (100), 15.65 cm square 200 μm thickness, as-slice specific resistance 2 Ω · cm (dopant concentration 7.2 × 10 ¹⁵ cm ⁻³ ) Phosphorus-doped n-type single crystal silicon substrate is immersed in an aqueous sodium hydroxide solution The damaged layer was removed by etching, and texture formation was performed by soaking in an aqueous solution obtained by adding isopropyl alcohol to an aqueous potassium hydroxide solution and performing alkali etching. After applying the coating agent containing a phosphorus dopant to the back surface of the obtained silicon substrate 1, heat treatment was performed at 900 ° C. for 1 hour to form the n-type diffusion layer 3 on the back surface. After the heat treatment, the glass component attached to the substrate was removed by high concentration hydrofluoric acid solution and then washed.
Subsequently, a coating agent containing a boron dopant was applied to the light receiving surface, followed by heat treatment at 1000 ° C. for 1 hour to form the p-type diffusion layer 2 over the entire light receiving surface.

Next, pn junction isolation was performed using a plasma etcher. In order to prevent plasma and radicals from entering the light-receiving surface and back surface, the end face was cut several microns with the target stacked. The glass component attached to the substrate was removed with a high-concentration hydrofluoric acid solution and then washed.
Next, silver paste was electrode-printed on the light-receiving surface side and the back surface side, respectively, dried, and then fired at 800 ° C. for 20 minutes to form the finger electrode 5 and the back electrode 6.
Subsequently, a silicon nitride film 4 as a dielectric film was laminated on the light receiving surface side p-type diffusion layer and the back surface n-type diffusion layer using a direct plasma CVD apparatus. This film thickness was 70 nm.
Finally, a silver paste was electrode-printed on each of the light-receiving surface side and the back surface side, dried, and then fired at 800 ° C. for 20 minutes to form bus bar electrodes 7.

[Comparative Example 1]
As shown in FIG. 4, the light-receiving surface electrode and the back surface electrode were formed by the same method as in Example 1 except that the formation was performed after the silicon nitride film was formed.
That is, when compared with the embodiment of FIG. 3, the process up to FIG. 4C is the same as that up to FIG. 3C, but after forming the p-type diffusion layer, as shown in FIG. Then, a silicon nitride film 4 is formed on the light-receiving surface side p-type diffusion layer 2 and the back surface n-type diffusion layer 3 by a direct plasma CVD apparatus, and then, as shown in FIG. 6 is fired through and connected to each of the diffusion layers 2 and 3, and a bus bar electrode is further formed. 4E and 4F show that the finger electrode 5 and the back electrode 6 are not connected to the diffusion layers 2 and 3, but are fired through by firing, and are actually not as complete as the examples. Although not, it is connected to the diffusion layers 2 and 3.

  The production flowchart of Example 1 is shown in Table 1, and the production flowchart of Comparative Example 1 is shown in Table 2.

The current-voltage characteristics of the solar cells obtained in Examples and Comparative Examples were measured in a 25 ° C. atmosphere under a solar simulator (light intensity: 1 kW / m ² , spectrum: AM1.5 global). The results are shown in Table 3. In addition, the number in a table | surface is an average value of ten cells made as an experiment in an Example and a comparative example.

  As described above, the solar cell according to the example resulted in an improved fill factor compared to the comparative example due to the effect of increased contact between the light-receiving surface finger electrode and the silicon substrate interface.

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 P-type diffusion layer 3 N-type diffusion layer 4 Dielectric film 5 Light-receiving surface electrode (finger electrode)
6 Back electrode 7 Bus bar electrode

Claims (7)

Light reception comprising a first conductive type silicon substrate, a conductive type diffusion layer opposite to the first conductive type formed on the light receiving surface side of the silicon substrate, and finger electrodes and bus bar electrodes electrically connected to the diffusion layer A solar cell comprising a surface electrode, a diffusion layer of the same conductivity type as the first conductivity type formed on the back surface side of the first conductivity type silicon substrate, and a back electrode electrically connected to the diffusion layer. The finger electrode is directly formed on the conductive type diffusion layer opposite to the first conductive type, and a silicon oxide film, a silicon nitride film, a titanium oxide film, an aluminum oxide film, a tin oxide film, a zinc oxide film, and magnesium fluoride. A dielectric film comprising a film or a combination of these films is formed to cover the finger electrode and a conductive type diffusion layer opposite to the first conductive type in a region excluding the finger electrode; Serial dielectric is formed on the film, and a solar cell of the dielectric film by firing through, characterized in that formed by connecting to the finger electrode. On the back side of the silicon substrate, the back electrode is directly formed on a diffusion layer of the same conductivity type as the first conductivity type on the back side of the silicon substrate, and the dielectric film excludes the back electrode and the back electrode A diffusion layer of the same conductivity type as that of the first conductivity type in the region is formed, and a backside bus bar electrode is formed on the dielectric film, and connected to the backside electrode through a fire-through of the dielectric film The solar cell according to claim 1, wherein the solar cell is formed. The solar cell according to claim 1, wherein the dielectric film is made of a silicon nitride film. Light reception comprising a first conductive type silicon substrate, a conductive type diffusion layer opposite to the first conductive type formed on the light receiving surface side of the silicon substrate, and finger electrodes and bus bar electrodes electrically connected to the diffusion layer Manufacturing a solar cell comprising a surface electrode, a diffusion layer of the same conductivity type as the first conductivity type formed on the back surface side of the first conductivity type silicon substrate, and a back electrode electrically connected to the diffusion layer A method wherein a conductive type diffusion layer opposite to the first conductive type is formed on the light receiving surface side of the silicon substrate, the finger electrode is directly formed on the diffusion layer, and the finger electrode and the region excluding the finger electrode are formed Covering the diffusion layer opposite to the first conductivity type of silicon oxide film, silicon nitride film, titanium oxide film, aluminum oxide film, tin oxide film, zinc oxide film, magnesium fluoride film, or these films After forming the dielectric film consisting of combined, the dielectric film is fire-through the bus bar electrode is formed by manufacturing method of a solar cell, characterized in that connected to the finger electrode over the dielectric film. On the back side of the silicon substrate, a back electrode is directly formed on the diffusion layer of the same conductivity type as the first conductivity type, and the same conductivity type as the first conductivity type in the region excluding the back electrode and the back electrode. The dielectric film is formed so as to cover a diffusion layer, and then the dielectric film is fired through from above the dielectric film to form a back busbar electrode and connected to the back electrode. 4. The method for producing a solar cell according to 4. The finger electrode and the back electrode are formed by firing at the same time, and the bus bar electrode and the back bus bar electrode are fired at the same time to form the dielectric films on the light receiving surface and the back surface by fire-through, respectively. Item 6. A method for producing a solar cell according to Item 5.   The method for manufacturing a solar cell according to claim 4, wherein the dielectric film is formed by a plasma CVD method.

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