JP2015062251A - Solar cell and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and highly efficient solar cell having an electrode that has good electric contact with a silicon substrate and suppresses wiring resistance.SOLUTION: A method for manufacturing a solar cell is provided, including steps of: applying an electrode paste for forming a first electrode comprising conductive particles and glass frit on an emitter layer of a first major surface of a crystalline silicon substrate; forming a passivation film thereon; further applying an electrode paste for forming a second electrode comprising conductive particles and glass frit on the passivation film to partially overlap the first electrode; subjecting the substrate to an electrode firing heat treatment so as to form first and second electrodes, as well as to form a passivation film penetration layer that electrically conducts between the first and second electrodes by inducing a fire-through process in the passivation layer by the electrode pastes in the overlapped part of the first electrode and the second electrode, while leaving the passivation film without penetration by the electrode paste just below the electrode paste of the second electrode in a region where the second electrode does not overlap the first electrode.

Description

  The present invention relates to an inexpensive and highly efficient solar cell and a manufacturing method thereof.

FIG. 1B shows the appearance of a general mass-produced solar cell using a single crystal or polycrystalline silicon substrate.
On the light-receiving surface side of the p-type silicon substrate 101 to which a dopant such as B or Ga is added, a dopant such as P or Sb imparting n-type conductivity is diffused to form an emitter layer 102.
A passivation film 103 is formed on the emitter layer 102. The passivation film 103 also functions as an antireflection film. As the passivation film 103, a SiNx film formed by chemical vapor deposition (CVD) or the like is widely used. An important function of the passivation film is termination of the silicon surface. The silicon atoms inside the crystal are in a stable state due to covalent bonding between adjacent atoms. However, an unstable energy level called a dangling bond or a dangling bond appears due to the absence of adjacent atoms to be bonded on the surface which is the terminal of the atomic arrangement. Since dangling bonds are electrically active, they capture and extinguish charges generated in the silicon, thereby deteriorating the characteristics of the solar cell. Therefore, the solar cell is subjected to some surface termination treatment or treatment to form an electric field so that photogenerated carriers are not captured by dangling bonds. The SiNx film formed by CVD is widely used because its optical characteristics are suitable for silicon solar cells, the film itself has a positive fixed charge, and has a dangling bond termination effect. This is because it contains a large amount of hydrogen and has a high passivation effect.

  A large number of extraction electrodes 104 with a width of several hundreds to several tens of μm are formed on the passivation film 103 to extract photogenerated charges from the silicon substrate 101 to the outside, and the charges collected by the extraction electrodes 104 are formed. Several collecting electrodes 105 having a width of several millimeters are formed as electrodes for concentrating and connecting solar cells.

For these electrodes, an electrode paste in which metal fine particles such as Ag, glass frit, and an organic binder are mixed is used from the viewpoint of cost. For example, the electrodes are printed and dried using a screen plate having the pattern shown in FIG. After that, the electrode firing heat treatment is performed at about several hundred to 850 ° C. to form the passivation film penetrating layer 108 immediately below the electrode, and the substrate 101 and the electrode 104 are electrically connected (so-called fire-through method). Is widely used.
In the present invention, the passivation film penetrating layer refers to a layer in which an electrically conductive portion and a portion where the passivation film remains are mixed.

On the non-light-receiving surface side, a back electrode 107 having a polarity opposite to that of the light-receiving surface side electrode is used, and a metal paste in which metal fine particles such as Al and Ag are mixed with an organic binder is used. After being printed and dried using a method such as the above, it is formed by an electrode firing heat treatment at about several hundred to 850 ° C.
In addition, a dopant such as Al, B, or Ga that imparts the same p-type conductivity as that of the substrate is provided between the silicon substrate 101 and the back electrode 107 in order to more efficiently extract the charge generated on the back side to the outside. The electric field layer 106 is included by high-concentration electrode heat treatment.

  Here, the external appearance of the general mass-produced solar cell before the electrode firing heat treatment is shown in FIG. Prior to the electrode firing heat treatment, the passivation film penetrating layer 108 is not formed immediately below the light receiving surface side extraction electrode 104, and the electric field layer 106 is not formed immediately below the back surface electrode 107.

The electrode paste used in the conventional method contains a glass frit at a relatively high rate in order to penetrate the passivation film directly under the electrode by electrode baking heat treatment and bring the electrode into contact with the silicon substrate. For this reason, good electrical contact between the electrode and the silicon substrate can be obtained, but the content ratio of the metal particles responsible for the conduction of electric charges taken out from the silicon substrate has to be lowered, resulting in a decrease in the output of the solar cell. There was a problem of letting it go. (Problems with single-layer electrodes)
In response to this problem, the inventors previously overlapped an electrode for penetrating the passivation film and contacting the silicon substrate with a low resistance electrode for carrying electric conduction, and has a high aspect ratio. In addition, a method for forming a multilayer electrode in which defects such as disconnection hardly occur has been proposed (International Publication No. 2008/026415 Pamphlet: Patent Document 1).

  In the method for forming a multilayer electrode, the lower electrode in contact with the silicon substrate contains at least silver and glass frit, and the upper electrode disposed thereon has a high total silver content (75 wt% to 95 wt%). And a conductive paste having an average content of silver particles having an average particle size of 4 μm or more and 8 μm or less with respect to the total content of silver is higher than the content in the lower electrode.

An example of the appearance of a solar cell in which the multilayer electrode forming method is applied to the general solar cell is shown in FIGS. FIG. 2A shows the appearance before the electrode firing heat treatment, and FIG. 2B shows the appearance after the electrode firing heat treatment.
The manufacturing method is the same as that of the general solar battery until the formation of the passivation film, and the first electrode 204 is formed on the passivation film as a lower electrode in this example, and the upper electrode is formed thereon. As a result, the second electrode 205 is formed. Thereafter, a passivation film penetrating layer 208 is formed immediately below the first electrode 204 and an electric field layer 206 is formed directly below the back electrode 207 by electrode firing heat treatment.

The problem with the multilayer electrode forming method is that, in order to form an electrode with low wiring resistance, it is necessary to form the second electrode on the first electrode by overlapping at least once, preferably a plurality of times. The number will increase. (Problems of the multilayer electrode formation method)
In the multilayer electrode forming method, in order to form an electrode with a low wiring resistance by keeping the number of electrode forming steps to a minimum, that is, each time the first electrode and the second electrode are once, the first electrode and the second electrode It is necessary to minimize the glass frit content contained and increase the silver particle content as much as possible.

On the other hand, it is known that the glass frit contained in the electrode paste has the following characteristics.
-It reacts with the passivation film by the electrode baking heat treatment, and decomposes and penetrates the passivation film, so that metal particles contained in the electrode paste are in electrical contact with the substrate. (So-called fire-through function)
-The glass frit remaining without reacting with the passivation film by the electrode firing heat treatment increases the adhesion strength between the substrate and the electrode. (So-called adhesive function)
In order to fully develop the function of these glass frit, if the amount of glass frit contained in the electrode paste is excessively increased, the fire-through function and the adhesive function are increased, but the wiring resistance of the electrode is increased, and the passivation film is also increased. The amount of glass flakes that remain without reacting with the solder increases, and a glass film is formed on the interface between the substrate and the electrode or on the surface of the electrode to increase contact resistance or solder when connecting wiring from the electrode to the outside. There are problems such as worsening wettability. (Problems caused by excessive glass frit)

  On the contrary, if the glass frit contained in the electrode paste is reduced too much, the wiring resistance of the electrode is lowered, but the fire-through function is deteriorated by a short-time electrode firing heat treatment, and the contact resistance between the substrate and the electrode is increased, In addition, the adhesive function also deteriorates, and there are problems such as a decrease in the adhesive strength of the electrode. (Problems when the glass frit is reduced too much)

  On the other hand, when the electrode firing heat treatment is heated to a high temperature or for a long time, the bulk lifetime of the substrate is deteriorated, the passivation property due to the passivation film is lowered, and the open circuit voltage and the short circuit current are lowered. There is. (Problems when the electrode firing heat treatment is heated or prolonged)

  Actually, in order to prevent these problems as much as possible, the type and amount of glass frit contained in the electrode paste and the electrode firing heat treatment conditions are adjusted to keep the wiring resistance and contact resistance low, and the substrate. In addition, the adhesive strength between the electrode and the electrode is kept above a certain level, and the decrease in the open circuit voltage and the short circuit current is suppressed.

For this reason, usually, the electrode paste contains more glass frit than is necessary for penetrating the passivation film, and the glass frit that reacts with the passivation film by the electrode baking heat treatment is actually included in the electrode. Of the glass frit to be produced, only a part in the vicinity of the passivation film is present.
In order to efficiently react the passivation film and the glass frit contained in the electrode paste, it is necessary to increase the contact area between the electrode and the passivation film.

International Publication No. 2008/026415 Pamphlet

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an inexpensive and highly efficient solar cell having an electrode with good electrical contact with a silicon substrate and suppressed wiring resistance.

  In order to solve the above problems, the present inventors have conducted extensive research on a method for forming an electrode of a solar cell. As a result, the first electrode containing conductive particles and glass frit is directly formed on the emitter layer, and the first electrode is formed thereon. A passivation film is formed, and further, a second electrode containing conductive particles and glass frit is formed thereon so as to partially or entirely overlap with the first electrode, and thus the first electrode and the second electrode are formed. Are formed through a passivation film, and the first and second electrodes are electrically connected to each other by a through-hole, using the passivation film between the first and second electrodes as a passivation film penetrating layer. Is effective in providing an inexpensive and highly efficient solar cell having an electrode with good resistance and reduced wiring resistance, and is included in the electrode paste compared to the conventional method Furthermore it becomes possible to reduce the glass frit amount that, the wiring resistance can be suppressed. In addition, the present inventors have found that the process can be realized by a combination of a conventional passivation film forming method and a screen printing method, and is extremely effective for cost reduction, and has led to the present invention.

  Therefore, the present invention applies a first electrode forming electrode paste containing conductive particles and glass frit on the emitter layer of at least the first main surface of the crystalline silicon substrate, forms a passivation film thereon, and A second electrode forming electrode paste containing conductive particles and glass frit is applied on the passivation film so as to partially overlap the first electrode, and then the first and second electrodes are formed by electrode baking heat treatment, The electrode paste where the first electrode and the second electrode overlap each other passes through the passivation film between them to form a passivation film through layer that conducts between the first and second electrodes, and The part of electrode paste that does not overlap with the first electrode of the two electrodes penetrates the passivation film directly below To provide a method of manufacturing a solar cell characterized by leaving the passivation film without.

Further, in the present invention, after applying a first electrode forming electrode paste containing conductive particles and glass frit on the emitter layer of at least the first main surface of the crystalline silicon substrate, and forming a passivation film thereon, A first electrode is formed by an electrode baking heat treatment, and the electrode paste is fired through the passivation film corresponding to the first electrode formation position, and then conductive so as to partially overlap the first electrode on the passivation film. The second electrode forming electrode paste containing the conductive particles and the glass frit is applied, and then the second electrode is formed by electrode baking heat treatment, and the second electrode forming electrode paste corresponds to the second electrode forming position. The first and second electrodes are overlapped with the first electrode by fire-through the membrane. A method of manufacturing a solar cell, comprising: forming a passivation film penetrating layer that conducts between electrodes; and leaving the passivation film without penetrating the passivation film immediately below the first electrode in a portion that does not overlap with the first electrode I will provide a.
In these solar cell manufacturing methods, the first electrode is applied in a pattern of only an extraction electrode, and the second electrode is a pattern of an extraction electrode and a collector electrode. The pattern of the extraction electrode is the first electrode. It is preferable to apply so as to overlap with each other, and a plurality of substantially parallel dotted lines are applied as the first electrode, and a plurality of substantially parallel linear patterns are applied as the extraction electrodes of the second electrode. However, it is preferable to leave the passivation film immediately below which is a single layer without overlapping the first electrode in the extraction electrode of the second electrode.

Furthermore, a solar cell manufactured by the method for manufacturing a solar cell, the first electrode layer formed directly on the emitter layer on at least the first main surface of the crystalline silicon substrate, and covering the first electrode layer A passivation film formed on the emitter layer, and a second electrode layer formed so as to partially overlap the first electrode layer via the passivation film, and between the first and second electrode layers The overlapping portion of the passivation film is formed as a passivation film penetrating layer that conducts between the first and second electrode layers by fire-through of the first and second electrode layers, and overlaps the first electrode of the second electrode. Provided is a solar cell characterized in that the passivation film is provided directly under a portion that does not fit into a single layer.
In this case, it is preferable that the first electrode is composed only of an extraction electrode, the second electrode is composed of an extraction electrode and a collecting electrode, and the extraction electrodes of the first electrode and the second electrode overlap each other, and the silicon On the first main surface of the substrate, the first electrode comprises a plurality of substantially parallel dotted lines, the second electrode extraction electrode comprises a substantially parallel plurality of linear patterns, In the two-electrode extraction electrode, the passivation film is preferably provided immediately below the first electrode without overlapping with the first electrode.
Moreover, it is preferable that the electrode which consists of a combination of a said 1st electrode and a said 2nd electrode is formed in the light-receiving surface side of a solar cell. The passivation film can be formed of any one of silicon oxide, silicon nitride, silicon carbide, aluminum oxide, amorphous silicon, microcrystalline silicon, and titanium oxide, or a combination thereof.

With the multilayer electrode structure of the present invention, since the passivation film is sandwiched between the first electrode layer and the second electrode layer, the glass frit contained in the respective electrode pastes of the first electrode and the second electrode is Thus, fire-through occurs efficiently, and the first electrode and the second electrode are electrically connected through the passivation film penetrating layer. Further, since the first electrode is formed directly on the emitter layer, the contact resistance can be further reduced as compared with the conventional method.
For this reason, it becomes possible to further reduce the amount of glass frit contained in the electrode paste as compared with the conventional method, and the wiring resistance can be suppressed.
Further, the process can be realized by a combination of a conventional passivation film forming method and a screen printing method, which is extremely effective for cost reduction.

It is a perspective view of the solar cell which has the conventional single layer electrode structure, (A) is before an electrode baking heat processing, (B) is a figure after an electrode baking heat processing. It is a perspective view of the solar cell which has the conventional multilayer electrode structure, (A) is before an electrode baking heat processing, (B) is a figure after an electrode baking heat processing. It is a perspective view of the solar cell which has the multilayer electrode structure which concerns on one Example of this invention, (A) is before an electrode baking heat processing, (B) is a figure after an electrode baking heat processing. It is a perspective view of the solar cell which has the multilayer electrode structure which concerns on the other Example of this invention, (A) is before electrode baking heat processing, (B) is a figure after electrode baking heat processing. (A)-(D) are each a top view which shows the example of the printing plate making used for electrode formation. It is a perspective view of the solar cell which has a multilayer electrode structure which shows another Example of this invention, (A) is before an electrode baking heat processing, (B) is a figure after an electrode baking heat processing. It is a perspective view of the solar cell which has the multilayer electrode structure which shows another Example of this invention, (A) is before an electrode baking heat processing, (B) is a figure after an electrode baking heat processing. It is a graph which shows the relative value of the contact resistance and wiring resistance in an Example (condition 3) and a comparative example (condition 1, condition 2).

  As described above, the solar cell according to the present invention includes the first electrode layer directly formed on the emitter layer on at least the first main surface of the crystalline silicon substrate, and the first electrode layer covering the first electrode layer on the emitter layer. A passivation film formed, and a second electrode layer formed at least partially overlapping the first electrode layer via the passivation film, the passivation film between the first and second electrode layers being a first The first and second electrode layers are formed as a passivation film penetrating layer that conducts between the first and second electrode layers by fire-through of the first and second electrode layers.

Examples of the present invention will be described below with reference to FIGS. 3 to 7, but the solar cell of the present invention is not limited to the illustrated examples.
FIG. 3 shows an embodiment of a solar cell according to the present invention.
The solar cell according to the present invention is a solar cell having a passivation film 303 and an electrode on at least one surface of a crystalline silicon substrate 301, and has at least a first electrode 304 layer in contact with the silicon substrate 301, and the first electrode 304 layer. The passivation film penetrating layer 308 is provided on the passivation film penetrating layer 308, and the second electrode 305 layer having the same composition as or different from the first electrode 304 layer is formed on the passivation film penetrating layer 308.
In addition, 302 is an emitter layer, 308 is a passivation film penetration layer, 306 is an electric field layer, and 307 is a back electrode.

An example of a method for manufacturing the solar cell of the present invention will be described below. However, the present invention is not limited to the solar cell manufactured by this method.
Slicing damage on the surface of an as-cut single crystal {100} p-type silicon substrate doped with a high purity silicon group III element such as B or Ga and having a resistivity of 0.1 to 5 Ω · cm, concentration of 5 to 60% by mass Etching is performed using a high concentration alkali such as sodium hydroxide or potassium hydroxide, or a mixed acid of hydrofluoric acid and nitric acid. The single crystal silicon substrate may be manufactured by either the CZ method or the FZ method.

  Subsequently, minute unevenness called texture is formed on the substrate surface. Texture is an effective way to reduce solar cell reflectivity. The texture is 10 to 10 in an alkaline solution (concentration 1 to 10% by mass, temperature 60 to 100 ° C.) such as heated sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium hydrogen carbonate, tetramethylammonium hydroxide. It is easily produced by dipping for about 30 minutes. In many cases, a predetermined amount of 2-propanol is dissolved in the solution to control the reaction.

After texture formation, washing is performed in an acidic aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid or the like, or a mixture thereof. From the viewpoint of cost and characteristics, washing in hydrochloric acid is preferred. In order to improve the cleanliness, 0.5 to 5 mass% hydrogen peroxide solution may be mixed in the hydrochloric acid solution and heated to 60 to 90 ° C. for washing.
On this substrate, an emitter layer is formed by vapor phase diffusion using phosphorus oxychloride. The P concentration and depth of the emitter layer are determined by the balance between the resistance to the current flowing through the emitter layer and the effect of surface passivation. In general, the sheet resistance of the emitter layer measured by the four-probe method is preferably about 30 to 100Ω / □.

The electrical contact resistance between the silicon and the electrode is related to the carrier concentration of the silicon surface, i.e., the dopant concentration and the electrode material, and when making electrical contact with silicon in a general printed Ag electrode, the dopant concentration on the silicon surface is at least 1 × 10 ¹⁹ cm ⁻³ or more is required, and preferably 5 × 10 ¹⁹ cm ⁻³ or more is required.

In general silicon solar cells, it is necessary to form a pn junction only on the light receiving surface, and in order to achieve this, diffusion is performed in a state where two substrates are overlapped, or a diffusion layer on one side is made of an alkaline aqueous solution or the like. It is necessary to devise such that the pn junction cannot be formed on the back surface by etching. After diffusion, the glass formed on the surface is removed with hydrofluoric acid or the like. Thereafter, a general semiconductor silicon substrate may be cleaned using a hydrochloric acid / hydrogen peroxide mixed solution or an ammonia / hydrogen peroxide mixed solution.
Next, a first electrode is formed on the emitter layer. For the first electrode, for example, a conductive paste such as an Ag paste in which conductive particles such as Ag powder and glass frit are mixed with an organic binder is used, and the first electrode is formed by a screen printing method or the like.

The glass frit includes a Pb glass frit (for example, PbO—B ₂ O ₃ —SiO ₂ system) and a Pb free glass frit (for example, Bi ₂ O ₃ —B ₂ O ₃ —SiO ₂ —CeO ₂ —LiO _2). it can be used -NaO ₂ system, etc.), but is not limited to them. The shape of the glass frit is not particularly limited, and for example, a spherical shape or an indefinite shape can be used. The particle size is not particularly limited, but from the viewpoint of workability, the average particle size (average particle size) is preferably in the range of 0.01 to 10 μm, and more preferably in the range of 0.05 to 1 μm.

  As the organic binder, a cellulose resin (for example, ethyl cellulose, nitrocellulose and the like) and a (meth) acrylic resin (for example, polymethyl acrylate and polymethyl methacrylate) can be used, but the organic binder is not limited thereto. The addition amount of the organic binder is usually 1 to 10 parts by mass, preferably 1 to 4 parts by mass with respect to 100 parts by mass of the conductive particles.

Next, an antireflection / passivation film for the light receiving surface is formed. A chemical vapor deposition apparatus is used for film formation, and a SiNx film or the like is formed to a thickness of about 80 to 120 nm, preferably about 100 nm. As the reaction gas, monosilane (SiH ₄ ) and ammonia (NH ₃ ) are often mixed and used, but nitrogen can be used instead of NH ₃ , and the film formation species can be diluted with H ₂ gas. And adjusting the process pressure and diluting the reaction gas to achieve the desired refractive index. Note that the passivation film is not limited to SiNx, but instead of chemical vapor deposition, silicon oxide, silicon carbide, aluminum oxide, amorphous silicon, microcrystalline silicon, titanium oxide, etc. can be used by methods such as heat treatment and atomic layer deposition. You may use for.

Next, a second electrode is formed by screen printing or the like so as to overlap the first electrode from the passivation film formed on the first electrode.
The second electrode may have high conductivity in order to suppress a wiring resistance loss when the electric charge extracted from the silicon substrate to the first electrode flows to the current collecting electrode. Such an electrode may be the same as the electrode paste for forming the first electrode, but in order to obtain higher conductivity, for example, an electrode paste such as an Ag paste with a higher proportion of Ag particles than the first electrode. Can be obtained by using Further, the resistivity of the second electrode at this time is preferably as low as possible, but it is desirably 5 μΩ · cm or less, preferably 3 μΩ · cm or less at the highest.

  Thereafter, the first electrode and the second electrode are made conductive. This is because the SiNx film sandwiched between the first electrode and the second electrode reacts with the glass frit contained in the electrode paste by the electrode baking heat treatment, decomposes, and Ag. According to a so-called fire-through method, in which conductive particles such as powder penetrate a passivation film such as a SiNx film and electrically contact the first electrode and the second electrode. The fire-through technique itself is generally widely used as a method for manufacturing a crystalline silicon solar cell.

  The electrode firing procedure of the first electrode and the second electrode includes printing and drying the first electrode, forming a passivation film, printing and drying the second electrode, followed by firing the second electrode and firing the second electrode. The first electrode and the second electrode may be baked separately so as to be fired. However, the first electrode is printed and dried, a passivation film is formed, the second electrode is printed and dried, and the first electrode is fired. And the second electrode may be fired at the same time by a single electrode firing heat treatment. From the viewpoint of cost, the method of performing both of them simultaneously by the latter one electrode baking heat treatment is desirable.

For example, as shown in FIG. 3, the extraction electrode and the collection electrode may have a laminated structure of the first electrode and the second electrode. For example, as shown in FIG. 4, the extraction electrode may be the first electrode. And the second electrode, and the collecting electrode may have a single layer structure including only the second electrode.
In these electrode structures, for example, in screen printing of electrode paste, the first electrode is a pattern of only the extraction electrode as shown in FIG. 5A or 5B, or the extraction electrode as shown in FIG. The second electrode can be printed with a pattern of only the collector electrode as shown in FIG. 5 (D) or FIG. 5 (C). is there.

  The method for forming the electrodes is not limited to screen printing, and may be ink jet, dispenser, plate printing, aerosol deposition, or the like.

In the case of a structure in which a single-layer electrode composed of only the second electrode is partially provided, the second electrode is in contact with the emitter layer 402 through the passivation layer 403 by fire-through, for example, as shown in FIG. Alternatively, the passivation layer 603 may not be penetrated as shown in FIG.
When a passivation film is left immediately below the single-layer electrode composed of only the second electrode, recombination of carriers on the silicon surface is suppressed by this portion, and solar cell characteristics can be improved. The passivation film penetrability of the electrode paste is adjusted by the glass frit addition amount. Accordingly, in this case, an electrode paste with a relatively small amount of glass frit added is used to form the second electrode.

The back electrode is formed by screen printing a paste in which Al powder is mixed with an organic binder. After printing, the back electrode and the electric field layer are formed by baking at a temperature of 600 to 900 ° C. for 5 to 30 minutes.
The electric field layer can be formed, for example, by vapor phase diffusion of boron bromide. In this case, from the viewpoint of suppressing the wiring resistance, it is preferable to use an Ag paste for forming the back electrode.
The back electrode and the light-receiving surface electrode can be fired at once. The order of forming the electrodes on each surface may be changed.

<When applied to the back side>
The electrode comprised by the combination of the 1st electrode and 2nd electrode by this invention can also be applied to the non-light-receiving surface of a solar cell.
FIG. 7 shows an example in which the electrode of the present invention is applied to both the light receiving surface and the non-light receiving surface.
With such a structure of the non-light-receiving surface, the non-light-receiving surface can be covered with the electric field layer 706 and the passivation film 703, and the collection efficiency of photogenerated carriers can be increased. Note that in the case where a passivation film having a sufficiently high passivation effect is obtained, the electric field layer 706 is not necessarily formed.

  The shapes and configurations of the first electrode 704b on the non-light-receiving surface and the second electrode 705b on the non-light-receiving surface can be the same as those of the light-receiving surface electrodes in FIGS. That is, on the non-light-receiving surface, the extraction electrode may have a laminated structure of the first electrode and the second electrode, and the collecting electrode may have a single-layer structure having only the second electrode, or the extraction electrode and the collecting electrode may each be the first electrode. In addition, a single-layer structure of the second electrode may be used, or both the extraction electrode and the collecting electrode may be a stacked structure of the first electrode and the second electrode.

  A reflection material is preferably provided on the non-light-receiving surface (not shown) in order to capture again the light transmitted through the substrate. As the reflective material, Al or Ag formed by vacuum deposition or the like may be used, but a sufficient effect can be obtained only by using a white back sheet or the like for the solar cell module without performing additional processing. . On the other hand, it is possible to generate power by making scattered light incident from the back side without using a reflective material, and it is also possible to generate power by arranging solar cells so that the non-light receiving surface is on the light receiving surface side. Is possible.

<< N-type substrate >>
As mentioned above, although the embodiment about the solar cell of this invention was mentioned taking the case where a P-type silicon substrate was used as an example, this invention can also be applied to the solar cell using an N-type silicon substrate.
In this case, referring to FIG. 7 as an example, the silicon substrate 701 and the electric field layer 706 are N-type, and the emitter layer 702 is P-type.

  Here, as the silicon substrate 701, n-type crystalline silicon having a resistivity of 0.1 to 5 Ω · cm by doping high purity silicon with a group V element such as P or Sb is generally used. Further, the emitter layer 702 can be formed by doping B by a vapor phase diffusion method using, for example, boron bromide, and the electric field layer 706 can be formed by a vapor phase diffusion method using phosphorus oxychloride.

[Examples and Comparative Examples]
In order to confirm the effectiveness of the present invention, the power generation performance of a solar cell having a general multilayer electrode structure and a solar cell having a multilayer electrode structure of the present invention was compared.
After removing the damaged layer with hot concentrated potassium hydroxide aqueous solution on 90 boron-doped {100} p-type as-cut silicon substrates having a substrate thickness of 250 μm, 125 mm square and specific resistance of 1 Ω · cm, potassium hydroxide / 2-p Texture formation was performed by dipping in an aqueous solution of oral propanol, followed by washing in a hydrochloric acid / hydrogen peroxide mixed solution.
Next, heat treatment was performed in a phosphorus oxychloride atmosphere at 870 ° C. with the back surfaces overlapped, and the light receiving surface was doped with phosphorus at a high concentration to form a pn junction having a sheet resistance of 50Ω / □. Thereafter, the diffusion layer on the non-light-receiving surface was etched away with hydrofluoric acid, the phosphor glass was removed with hydrofluoric acid, washed with an ammonia / hydrogen peroxide mixed solution, rinsed and dried.

Here, the substrate was divided into 30 groups each of three sets of condition 1, condition 2, and condition 3, and processed as follows.
In the following, different Ag pastes were used as the light-receiving surface electrode for each condition, but printing was performed using a plate making in which the extraction electrode and the collecting electrode as shown in FIG. 5D were patterned on the same screen. In addition, the printing conditions of the electrode paste were determined in advance, and printing conditions such as printing pressure and squeegee angle were controlled so that the same line width and cross-sectional area were obtained after firing for each condition.

Condition 1 is one of comparative examples according to the prior art, and a 90 nm-thickness SiNx film was formed on the entire surface of the light-receiving surface as a passivation film on the substrate after the cleaning using a plasma CVD apparatus.
Next, a paste A (a relatively high glass frit content) of a general fire-through paste as a first electrode was screen-printed and dried.
Next, a high-conductivity Ag paste B (having a relatively small glass frit content) was screen-printed as a second electrode so as to completely overlap the first electrode.
Thereafter, baking at 780 ° C., which is an optimized condition, was performed in an air atmosphere.

Condition 2 is another comparative example according to the prior art. A SiNx film having a thickness of 90 nm was formed as a passivation film on the entire surface of the sample on the light receiving surface as a passivation film using the plasma CVD apparatus.
Subsequently, a fire-through paste C having a glass frit content lower than that of the paste A was screen printed and dried as a first electrode.
Next, a high-conductivity Ag paste B (having a relatively small glass frit content) was screen-printed as a second electrode so as to completely overlap the first electrode.
Thereafter, baking at 780 ° C., which is an optimized condition, was performed in an air atmosphere.

Condition 3 is an application example of the present invention, and a fire-through paste C having a glass frit content less than that of the paste A as a first electrode was screen-printed and dried on the cleaned substrate. Next, as a passivation film, a 90 nm-thickness SiNx film was formed on the entire surface of the light-receiving surface using a plasma CVD apparatus.
Next, a high-conductivity Ag paste B (having a relatively small glass frit content) was screen-printed as a second electrode so as to completely overlap the first electrode.
Thereafter, baking at 780 ° C., which is an optimized condition, was performed in an air atmosphere.

  Next, an Al paste was applied to the entire surface of the sample on the back surface of all the solar cells, and thereafter, baking at 770 ° C., which is an optimized condition, was performed in an air atmosphere. In order to confirm the shape of the light-receiving surface electrode for the solar cells under the above conditions 1, 2 and 3, 5 samples were extracted from each condition, and the extraction electrode line widths and cross-sectional areas at 9 locations in the sample surface were measured with a laser microscope. It was measured by.

  The structure of the emitter layer under each condition before the electrode firing heat treatment, the electrode paste types of the first electrode and the second electrode, and the average values of the measured values of the electrode line width and cross-sectional area are shown in Table 1 below. As a result, it was confirmed that an equivalent electrode shape was obtained under all conditions.

Next, the characteristics of all the solar cells were measured with a current-voltage measuring device using artificial sunlight having an air mass of 1.5.
The average value of the solar cell characteristics under each condition is shown in Table 2 below.

From the comparison between Condition 1 and Condition 2, in the conventional multilayer electrode structure, when the glass frit content was reduced from the electrode paste of the first electrode, the fill factor increased.
From the comparison of Condition 2 and Condition 3, in the multilayer electrode structure of the present invention of Condition 3, the highest curve factor was obtained and high solar cell characteristics were obtained despite using the same electrode paste as in Condition 2.

Next, 15 pieces were extracted from each condition, and the contact resistance and wiring resistance between the silicon substrate and the electrode were measured. Contact resistance quantification was performed by a ladder method, and wiring resistance quantification was obtained from a current voltage value when a probe was placed at both ends of an electrode in a sample obtained by partially cutting out an extraction electrode portion from a solar cell.
FIG. 8 shows the relative value of each resistance with respect to each condition.

  From the result of Condition 2, in the conventional multilayer electrode structure, when the glass frit content was reduced from the electrode paste of the first electrode, the contact resistance increased and the wiring resistance decreased. In Table 2, it can be said that Condition 2 has a low fill factor due to an increase in contact resistance.

  From the results of Condition 3, it can be seen that in the multilayer electrode structure of the present invention, both the contact resistance and the wiring resistance are lower than those in Condition 1 even though the same electrode paste as in Condition 2 is used. Therefore, in Table 2, it can be said that Condition 3 has the highest fill factor as a result of suppression of contact resistance and wiring resistance.

101, 201, 301, 401, 601, 701 ... Silicon substrates 102, 202, 302, 402, 602, 702 ... Emitter layers 103, 203, 303, 403, 603, 703 ... Passivation film 104 .. Extraction electrodes 204, 304, 404, 604, 704a, 704b ... first electrode 105 ... collecting electrodes 205, 305, 405, 605, 705a, 705b ... second electrodes 106, 206, 306 , 406, 606, 706 ... electric field layers 107, 207, 307, 407, 607 ... backside electrodes 108, 208, 308, 408, 608, 708 ... passivated through layer 501 ... extraction electrode printing Pattern 502 ... Collecting electrode printing pattern

Claims (9)

  A first electrode forming electrode paste containing conductive particles and glass frit is applied on at least the first main surface emitter layer of the crystalline silicon substrate, a passivation film is formed thereon, and further a first film is formed on the passivation film. A second electrode forming electrode paste containing conductive particles and glass frit is applied so as to partially overlap the electrode, and then the first and second electrodes are formed by electrode firing heat treatment. The electrode paste of the overlapping part of the two electrodes fires through the passivation film between them to form a passivation film through layer that conducts between the first and second electrodes, and the first electrode of the second electrode The electrode paste is not overlapped with the electrode paste without penetrating the passivation film directly below it. Method of manufacturing a solar cell characterized by leaving a passivation film.   A first electrode forming electrode paste containing conductive particles and glass frit is applied on at least the first main surface emitter layer of the crystalline silicon substrate, a passivation film is formed on the first electrode forming electrode paste, and then a first electrode heat treatment is performed. In addition to forming an electrode, the electrode paste is fired through the passivation film corresponding to the first electrode formation position, and then conductive particles and glass frit are partially overlapped with the first electrode on the passivation film. The second electrode forming electrode paste is applied, then the second electrode is formed by electrode firing heat treatment, and the second electrode forming electrode paste fires through the passivation film corresponding to the second electrode forming position. To conduct between the first and second electrodes in a portion overlapping the first electrode. And forming a passivation film through layer, method of manufacturing a solar cell characterized by leaving the passivation film, a passivation film without penetrating below it in the portion not overlapping the first electrode.   The first electrode is applied in a pattern of only an extraction electrode, and the second electrode is a pattern of an extraction electrode and a collecting electrode, and the extraction electrode pattern is applied so as to overlap the first electrode. The manufacturing method of the solar cell of Claim 1 or 2.   A plurality of substantially parallel dotted lines are applied as the first electrodes, and a plurality of substantially parallel linear patterns are applied as the second electrode extraction electrodes. 4. The method for manufacturing a solar cell according to claim 3, wherein the passivation film immediately below which is a single layer without overlapping with one electrode is left.   A solar cell manufactured by the method for manufacturing a solar cell according to any one of claims 1 to 4, wherein the first electrode layer is formed directly on the emitter layer on at least the first main surface of the crystalline silicon substrate; A passivation film formed on the emitter layer so as to cover the first electrode layer, and a second electrode layer formed so as to partially overlap the first electrode layer through the passivation film, The overlapping portion of the passivation film between the first and second electrode layers is formed as a passivation film through layer that conducts between the first and second electrode layers by fire-through of the first and second electrode layers. A solar cell comprising the passivation film immediately below a portion that is a single layer without overlapping with the first electrode of two electrodes.   The said 1st electrode consists only of an extraction electrode, the said 2nd electrode consists of an extraction electrode and a current collection electrode, and the extraction electrode of the 1st electrode and the 2nd electrode has overlapped. Solar cells.   On the first main surface of the silicon substrate, the first electrode is composed of a plurality of substantially parallel dotted lines, and the second electrode extraction electrode is composed of a plurality of substantially parallel linear patterns, The solar cell according to claim 6, wherein the passivation film has the passivation film directly below the first electrode without overlapping with the first electrode.   The solar cell according to claim 5, wherein an electrode formed by a combination of the first electrode and the second electrode is formed on a light receiving surface side of the solar cell.   The solar cell according to claim 5, wherein the passivation film is made of any one of silicon oxide, silicon nitride, silicon carbide, aluminum oxide, amorphous silicon, microcrystalline silicon, and titanium oxide, or a combination thereof.