JP2014187256A - Conductive paste, method for manufacturing solar battery cell, and solar battery cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste for a solar cell electrode which can achieve good contact resistance between a baked electrode and a semiconductor substrate, and which can suppress the increase in the contact resistance and the occurrence of peeling of the electrode even after prolonged exposure to high temperature and high humidity, or even under the influence of moisture of rain water or the like.SOLUTION: A conductive paste comprises: conductive powder including main component powder of Ag and auxiliary component powder of Al; a binder resin; and solvent. In the conductive powder, the content of the auxiliary component powder is 0.4-4 wt.%; and the main component powder includes atomization powder having an average primary particle diameter of 0.5-10 μm. The atomization powder preferably accounts for 50 wt.% or more in the main component powder. The conductive paste is used to fabricate a light-receiving surface electrode 8 of a solar battery cell 1.

Description

  The present invention relates to a conductive paste, a method for manufacturing a solar battery cell, and a solar battery cell, and more specifically, a conductive paste suitable for forming an electrode of a solar battery cell, and a solar battery manufactured using this conductive paste. The present invention relates to a battery cell manufacturing method and a solar battery cell manufactured using the manufacturing method.

  A solar power generation system converts solar energy into electric energy, and is actively researched and developed as a clean and renewable energy source.

  A solar battery cell which is a basic component of a photovoltaic power generation system realizes a pn junction by forming an n-type semiconductor layer or a p-type semiconductor layer on the surface of a p-type semiconductor substrate or an n-type semiconductor substrate, and the n-type semiconductor Alternatively, a light-receiving surface electrode having a predetermined pattern is formed on the main surface of the p-type semiconductor layer. Further, an antireflection film is formed on the semiconductor layer excluding the light receiving surface electrode, and the reflection loss of incident sunlight is suppressed by the antireflection film, thereby converting the conversion efficiency of sunlight into electric energy. Has improved.

  This light-receiving surface electrode is usually formed as follows using a conductive paste. That is, the conductive paste contains a conductive powder, a binder resin, an organic solvent, etc., and the conductive paste is applied to the surface of the antireflection film formed on the p-type or n-type semiconductor layer, A conductive film having a predetermined pattern is formed. In the firing process, fire through (fired penetration) is performed to decompose and remove the antireflection film under the conductive film, whereby the conductive film is sintered to form a light receiving surface electrode, and the light receiving surface electrode and the semiconductor layer Are joined, and both are made conductive.

  And as this kind of conductive paste, for example, as shown in Patent Document 1, Ag powder having a blending ratio in the range of 85 to 98.5 wt%, in the range of 0.5 to 10 wt%, and Al powder having an average particle size in the range of 5 to 20 μm and any one of lead borosilicate glass frit, bismuth borosilicate glass frit, or zinc borosilicate glass frit, and 1 to 10 wt. % Kneaded glass frit in the range of% and organic vehicle is known.

  In this patent document 1, it is going to obtain a favorable ohmic contact between a p-type semiconductor substrate and an electrode by forming an electrode using the said electrically conductive paste.

Japanese Patent No. 3625081 (Claim 1, paragraph number [0027] etc.)

  By the way, in this type of solar power generation system, from the viewpoint of reliability and durability, a predetermined number of solar cells are sealed with a sealing material to form a solar cell module, and such solar cell modules are connected in series or / And used in parallel.

  And as a sealing material, from viewpoints of workability, permeability, etc., ethylene-vinyl acetate copolymer (Ethylene-vinyl acetate copolymer; hereinafter referred to as “EVA”) represented by the chemical formula (1) is widely used. It is used.

As apparent from the chemical formula (1), EVA contains an acetic acid group (OCOCH ₃ ). Therefore, when this EVA comes into contact with moisture such as rainwater or moisture, it undergoes a hydrolysis reaction to produce acetic acid.

  On the other hand, Patent Document 1 describes that an electrode is formed using a p-type semiconductor substrate, but the conductive paste described in Patent Document 1 contains Al acting as an acceptor impurity, Therefore, it is considered that the present invention can be applied when a p-type semiconductor layer is formed on an n-type semiconductor substrate.

  However, when an electrode is formed on an n-type semiconductor substrate using the conductive paste described in Patent Document 1, when an aqueous acetic acid solution is generated by the hydrolysis reaction of EVA, the aqueous acetic acid solution penetrates into the electrode, For this reason, Al or Ag, which is a conductive component, particularly Al having inferior corrosion resistance is corroded, and as a result, the contact resistance Rc between the electrode and the n-type semiconductor substrate may be increased, or the electrode and the n-type semiconductor substrate may be separated. There is a risk of lowering reliability.

  FIG. 6 is a schematic diagram showing a state in which an aqueous acetic acid solution has entered the electrode.

  In FIG. 6, a p-type semiconductor layer 102 is formed on the surface of an n-type semiconductor substrate 101 containing Si as a main component, and Al particles 104 are interposed between Ag particles 103.

  Then, in the electrode 105 after firing, an Ag—Al alloy phase 106 is formed along the interface between the Ag particles 103 grown by necking during firing and the Al particles 104 melted during firing. That is, since Ag and Al have a eutectic point at a temperature equal to or lower than the firing temperature (600 to 700 ° C.), Ag is an eutectic alloy along the interface between the Ag particles 103 and the Al particles 104 during firing. It is considered that the Al alloy phase 106 is formed.

  In this case, the thermal expansion coefficient of Ag is 19.1 ppm / K, whereas the thermal expansion coefficient of Al is 23.5 ppm / K. Since Al has a larger thermal expansion coefficient than Ag, the electrode after firing is used. A residual stress is partially generated in 105.

  In this state, when EVA comes into contact with moisture to cause a hydrolysis reaction and the acetic acid aqueous solution 106 is generated, the generated acetic acid aqueous solution 107 erodes the inside of the electrode 105. As a result, a gap 108 is generated inside the electrode 105, and a driving force is generated to relieve the residual stress from the gap 108 as a starting point. When such recontraction of the electrode 105 occurs, a gap 108 or the like is generated, and the contact area between the electrode 105 and the n-type semiconductor substrate 101 is reduced, leading to an increase in the contact resistance Rc, and the conductivity is deteriorated. This may lead to a decrease in energy conversion efficiency. Furthermore, when the above-described re-shrinkage occurs, electrode peeling occurs in which the electrode 105 peels from the n-type semiconductor substrate 101, and there is a concern that reliability may be reduced.

  The present invention has been made in view of such circumstances, and the contact resistance between the electrode after firing and the semiconductor substrate is good, and it is left for a long time under high temperature and high humidity, or the influence of moisture such as rain water. Even if it receives, it can suppress that the contact resistance increases, and can suppress the occurrence of electrode peeling, and a method for manufacturing a solar battery cell using this conductive paste, and this manufacturing method. It aims at providing the photovoltaic cell produced using.

  The present inventor found that a conductive paste using conductive powder containing Ag as a main component powder and Al as a subcomponent powder was left under a high temperature and high humidity for a long time or was affected by moisture such as rain water. As a result of diligent research, the contact resistance between the electrode and the semiconductor substrate is increased by including atomized powder having an average primary particle size of 0.5 to 10 μm as the main component powder. The knowledge that it can suppress and generation | occurrence | production of electrode peeling can be suppressed was acquired.

  And it turned out that the contact resistance Rc after baking becomes favorable by making content of the said subcomponent powder in the said electroconductive powder into 0.4 to 4 weight%.

  The present invention has been made on the basis of such knowledge, and the conductive paste according to the present invention is a conductive paste for forming an electrode of a solar cell, and is composed of Ag as a main component powder and Al as a secondary powder. The conductive powder contained as a component powder, a binder resin, and a solvent, the content of the subcomponent powder in the conductive powder is 0.4 to 4% by weight, and the main component powder Is characterized by containing atomized powder having an average primary particle size of 0.5 to 10 μm.

  Here, the primary particles are particles generated by the growth of a single crystal nucleus, and the average particle size is arbitrarily extracted by visually observing with a scanning electron microscope (hereinafter referred to as “SEM”). The average value of the diameter calculated | required by converting into a circle about the predetermined | prescribed number of primary particles.

  In the conductive paste of the present invention, the atomized powder content in the main component powder is preferably 50% by weight or more.

  Thereby, generation | occurrence | production of electrode peeling can be suppressed much more effectively.

  In addition, as a result of further earnest research by the present inventors, even when Ca or Mg is contained in the atomized powder within a predetermined range, or at least one of Zn oxide and Zr oxide is contained, more It was found that a good contact resistance increase suppression effect and an electrode peeling occurrence suppression effect are possible.

  That is, in the conductive paste of the present invention, the atomized powder preferably contains Ca and Mg in a total range of 0.005 to 0.030% by weight.

  Moreover, it is preferable that the electrically conductive paste of this invention contains at least any one of Zn oxide and Zr oxide.

  Also by this, generation | occurrence | production of electrode peeling can be suppressed much more effectively.

  Further, in the method for manufacturing a solar cell according to the present invention, an antireflection film is formed on at least one main surface of a semiconductor substrate, and the conductive paste according to any one of the above is applied to the surface of the antireflection film. A solar battery cell is manufactured by performing a baking process, disassembling and removing the antireflection film, and bonding the semiconductor substrate and an electrode which is a sintered body of the conductive paste.

  Further, in the solar cell according to the present invention, an antireflection film and an electrode penetrating the antireflection film are formed on at least one main surface of a semiconductor substrate, and the electrode is the conductive paste according to any one of the above Is characterized by being sintered.

  According to the conductive paste of the present invention, the conductive paste containing Ag as a main component powder and Al as a subcomponent powder, a binder resin, and a solvent, the subcomponent powder in the conductive powder. The content is 0.4 to 4% by weight, and the main component powder contains atomized powder having an average primary particle size of 0.5 to 10 μm. Therefore, a eutectic of Ag and Al. Since alloying and sinterability can be relaxed, the occurrence of residual stress can be suppressed, and thereby the contact resistance Rc after firing can be improved.

  And since the generation | occurrence | production of a residual stress can be suppressed as mentioned above, even if it receives to the influence of a water | moisture content, a recontraction behavior can be suppressed. Therefore, it is possible to suppress an increase in the contact resistance Rc even when left for a long time under high temperature and high humidity or to be affected by rainwater, etc., and to suppress the electrode peeling, which is suitable for forming an electrode of a solar battery cell. A conductive paste can be realized.

  Moreover, according to the method for manufacturing a solar cell of the present invention, an antireflection film is formed on at least one main surface of a semiconductor substrate, and the conductive paste according to any one of the above is applied to the surface of the antireflection film. After that, a baking treatment is performed, and the antireflection film is decomposed and removed to adhere the semiconductor substrate and the electrode which is a sintered body of the conductive paste. Since the powder is contained, the contact resistance Rc after firing can be improved, and the increase in the contact resistance Rc can be suppressed even if left for a long time under high temperature and high humidity or affected by rainwater. Furthermore, since the occurrence of electrode peeling can be suppressed, it is possible to obtain a solar cell having good reliability and capable of suppressing a decrease in energy conversion efficiency as much as possible.

  Moreover, according to the solar cell of the present invention, an antireflection film and an electrode penetrating the antireflection film are formed on one main surface of the semiconductor substrate, and the electrode is the conductive paste according to any one of the above As described above, the contact resistance Rc after firing can be improved, and the contact resistance Rc can be increased even when left for a long time under high temperature and high humidity, or when it is affected by rainwater. Since it is possible to suppress the occurrence of electrode peeling, it is possible to obtain a highly reliable solar battery cell in which a decrease in energy conversion efficiency is suppressed.

It is a perspective view showing typically one embodiment of a solar cell module in which a photovoltaic cell concerning the present invention was built. It is principal part sectional drawing which shows one Embodiment of the photovoltaic cell manufactured using the electrically conductive paste which concerns on this invention. FIG. 3 is an enlarged plan view schematically showing a light receiving surface electrode side of the solar battery cell of FIG. 2. It is the enlarged bottom view which showed the back electrode side typically. It is the top view which showed typically the electrode pattern produced in the Example. It is a schematic diagram for demonstrating the conventional subject.

  Next, an embodiment of the present invention will be described in detail.

  FIG. 1 is a perspective view showing an embodiment of a solar battery module in which a solar battery cell according to the present invention is incorporated.

  In this solar cell module, sealing materials 2a and 2b made of EVA are arranged on both surfaces of the solar battery cell 1, and a tempered glass 3 such as a hot white plate tempered glass is arranged on the surface of one sealing material 2a. The back surface protection sheet 4 is arranged on the back surface of the sealing material 2b. As this back surface protection sheet 4, for example, a resin sheet formed of polyvinyl fluoride or the like and having a metal such as Al sandwiched therebetween is preferably used.

  FIG. 2 is a cross-sectional view of an essential part showing one embodiment of the solar battery cell.

  In this solar cell 1, a p-type semiconductor layer 6 is formed on the upper surface of an n-type semiconductor substrate 5 containing Si as a main component, and an antireflection film 7 and a light-receiving surface electrode 8 are formed on the main surface of the p-type semiconductor layer 6. The back electrode 9 is formed on the other main surface of the n-type semiconductor substrate 5 while being formed.

  Further, in FIG. 2, the surface of the n-type semiconductor substrate 5 is described in a flat shape. However, in order to effectively confine sunlight in the n-type semiconductor substrate 5, the surface has a micro uneven structure. Is formed.

The antireflection film 7 is formed of an insulating material such as silicon nitride (SiN _x ), suppresses the reflection of light to the light receiving surface indicated by the arrow A, and allows the sunlight to be rapidly applied to the p-type semiconductor layer 6. Lead efficiently. The material constituting the antireflection film 7 is not limited to the above-described silicon nitride, and other insulating materials such as silicon oxide and titanium oxide may be used, and two or more kinds of insulating materials may be used. May be used in combination. In addition, as long as it is crystalline Si, either single crystal Si or polycrystalline Si may be used.

  The light receiving surface electrode 8 is formed on the p-type semiconductor layer 6 through the antireflection film 7. The light-receiving surface electrode 8 is formed by applying a conductive paste of the present invention, which will be described later, onto the antireflection film 7 by using screen printing or the like to produce a conductive film and baking it. That is, in the firing process of forming the light-receiving surface electrode 8, the p-type semiconductor layer 6 is formed by the diffusion of Al (acceptor impurity), and the antireflection film 7 under the conductive film is decomposed and removed and fired through, As a result, the light-receiving surface electrode 8 is formed on the p-type semiconductor layer 6 so as to penetrate the antireflection film 7.

  Specifically, as shown in FIG. 3, the light-receiving surface electrode 8 includes a large number of finger electrodes 10a, 10b,... 10n arranged in a comb-teeth shape and intersecting with the finger electrodes 10a, 10b,. Bus bar electrode 11 is provided, and finger electrodes 10a, 10b,... 10n and bus bar electrode 11 are electrically connected. Then, an antireflection film 7 is formed in the remaining region excluding the portion where the light receiving surface electrode 8 is provided. Thus, the electric power generated in the n-type semiconductor substrate 5 is collected by the finger electrodes 10a, 10b,... 10n and taken out to the outside by the bus bar electrode 11.

  Specifically, as shown in FIG. 4, the back electrode 9 is formed on the back surface of the n-type semiconductor substrate 5 and made of Al or the like, and on the back surface of the current collector electrode 12. It is comprised with the extraction electrode 13 which consists of Ag etc. which were electrically connected with the current collection electrode 12. FIG. Then, the electric power generated in the n-type semiconductor substrate 5 is collected by the collecting electrode 12 and is taken out by the extracting electrode 13.

  Next, the conductive paste of the present invention for forming the light receiving surface electrode 8 will be described in detail.

  The conductive paste of the present invention contains a conductive powder containing Ag as a main component powder and Al as a subcomponent powder, a binder resin, and an organic solvent (solvent). And the content of the subcomponent powder in the conductive powder is 0.4 to 4% by weight, and the main component powder is an atomized powder having an average primary particle size of 0.5 to 10 μm. Contains.

  As a result, the contact resistance Rc between the light-receiving surface electrode 8 and the p-type semiconductor layer 6 after firing can be improved. Further, even when left for a long time under high temperature and high humidity or under the influence of rain water, the increase in the contact resistance Rc can be suppressed, and the electrode peeling of the light receiving surface electrode 8 from the p-type semiconductor layer 6 can be suppressed. Desired continuity can be ensured and reliability can be improved.

  That is, wet reduction methods and atomization methods are known as methods for producing this type of conductive powder.

  Among these, the wet reduction method produces a slurry containing a metal oxide by adding an alkali to an aqueous solution containing a metal salt such as an Ag salt, and a reducing agent is added to the slurry to reduce and precipitate the metal powder. This is a method for producing a powder, and a fine powder of 4 μm or less can be easily produced. Conventionally, wet powder produced by this wet reduction method has been widely used in solar cell electrodes that require thin layers.

  On the other hand, in the atomization method, high-pressure water or the like is sprayed onto a powder material such as Ag which has been heat-treated to form a droplet, and droplets are formed and solidified while dropping the powder material, thereby producing a powder. The powder produced by the atomization method is atomized powder, and a powder having a large crystallite diameter can be generated. That is, since the atomized powder has a large crystallite size, the reactivity is low, the reactivity with Al in the molten subcomponent powder is reduced, and eutectic alloying is suppressed. Moreover, since the average particle diameter of the primary particles is larger than that of the wet powder and the sinterability becomes slow, it is possible to suppress excessive shrinkage, thereby suppressing the occurrence of residual stress.

  As described above, the atomized powder is considered to be able to suppress the occurrence of residual stress. Therefore, a good ohmic contact can be obtained between the light-receiving surface electrode 8 and the n-type semiconductor substrate 5 after firing, and the contact resistance Rc. Can be made good. Furthermore, since the residual stress is small, it is possible to suppress the generation of a gap inside the light receiving surface electrode 8 even if the acetic acid aqueous solution enters the light receiving surface electrode 8 due to being left for a long time under high temperature and high humidity or rain water. can do. As a result, re-shrinkage starting from the gap hardly occurs, and increase in the contact resistance Rc and electrode peeling can be suppressed.

  In order to obtain such an effect, the atomized powder needs to have an average primary particle size of at least 0.5 μm or more. If the average particle size of the primary particles is less than 0.5 μm, the average particle size is too small, and if left for a long time under high temperature and high humidity or affected by rain water, the contact resistance Rc increases and electrode peeling occurs. This may lead to a decrease in reliability.

  On the other hand, when the average particle diameter of the primary particles exceeds 10 μm, the uniform arrangement of the atomized powder in the electrode is lowered, and the effect of suppressing shrinkage is reduced. Also in this case, when left for a long time under high temperature and high humidity or affected by rainwater, the contact resistance Rc increases, and electrode peeling tends to occur, which may lead to a decrease in reliability.

  Therefore, the average particle size of the primary particles of the atomized powder needs to be 0.5 to 10 μm.

  In addition, content of the atomized powder in a main component powder is not specifically limited. That is, the whole amount may not be formed with atomized powder, and may be a mixed powder of atomized powder and wet reduced powder. However, in order to effectively suppress the increase in contact resistance Rc and the occurrence of electrode peeling, the content of atomized powder in the main component powder is preferably 50% by weight or more, more preferably 80% by weight or more. .

  Moreover, in this Embodiment, content in the electroconductive powder of subcomponent powder shall be 0.4 to 4.0 weight%.

  That is, the sub-component powder contains Al powder, but this Al powder acts as an acceptor impurity during firing, and forms the p-type semiconductor layer 6 on the surface of the n-type semiconductor substrate 5. Then, such a p-type semiconductor layer 6 is formed to form a good ohmic contact with the light-receiving surface electrode 8, and a good contact resistance Rc can be obtained.

  However, if the content of the sub-component powder is less than 0.4% by weight in the conductive powder, the ohmic contact property is impaired and it is difficult to obtain a desired good contact resistance Rc.

  On the other hand, if the content of the sub-component powder in the conductive powder exceeds 4.0% by weight, the content of the sub-component powder becomes excessive, and if the sub-component powder is left for a long time under high temperature and high humidity or affected by rainwater. The corrosion of Al, which is inferior in corrosion resistance, progresses, increasing the contact resistance Rc and increasing the probability of electrode peeling, leading to a decrease in reliability.

  Therefore, in the present embodiment, as described above, the content of the subcomponent powder in the conductive powder is set to 0.4 to 4.0% by weight.

  In addition, the shape of Al contained in subcomponent powder is not specifically limited, For example, spherical shape, flat shape, an irregular shape, or these mixed powders can be used.

  Further, although the average particle diameter of Al is not particularly limited, from the viewpoint of obtaining a desired ohmic contact between the light-receiving surface electrode 8 and the n-type semiconductor substrate 5 by forming a desired p-type semiconductor layer 6. Is preferably 0.2 to 5.0 μm.

  Moreover, it is also preferable that the conductive powder of the present embodiment contains a trace amount of an additive such as alkaline earth metal typified by Ca or Mg in the main component powder. In particular, when the content of Ca and Mg in the atomized powder is 0.005 to 0.030 wt% in total (total content), compared to the case where the total content of Ca and Mg is outside the above range, contact It is possible to exhibit the effect of suppressing the increase in resistance Rc and the effect of suppressing the occurrence of electrode peeling.

  The content of Ca and Mg in the atomized powder can be appropriately controlled by adjusting the production conditions of the atomization method.

  Further, even when a trace amount of Zn oxide or Zr oxide is added to the conductive paste, even if it is left for a long time under high temperature and high humidity, or is affected by moisture such as rain water, the contact resistance Rc is even better. Can be secured, and the occurrence of electrode peeling can be suppressed, which is more preferable.

  Furthermore, in order to improve the adhesion between the light-receiving surface electrode 8 and the p-type semiconductor layer 6, it is also preferable to contain glass frit in the conductive paste.

  In the case where glass frit is contained in the conductive paste, the type is not particularly limited, but various borosilicates such as borosilicate glass, lead borosilicate glass, bismuth borosilicate glass, zinc borosilicate glass, etc. System glass can be used with preference. Moreover, when it contains glass frit, the content is preferably 1 to 10% by weight.

  The content of the conductive powder in the conductive paste is not particularly limited, but is usually preferably 70 to 90% by weight, and particularly preferably 75 to 85% by weight.

  An organic vehicle is formed with a binder resin and an organic solvent. Here, the ratio of the binder resin to the organic solvent is adjusted to be, for example, 1 to 3: 7 to 9 by volume ratio. The binder resin is not particularly limited, and for example, ethyl cellulose resin, nitrocellulose resin, acrylic resin, alkyd resin, or a combination thereof can be used. Also, the organic solvent is not particularly limited, and α-terpineol, xylene, toluene, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, etc. alone or in combination thereof Can be used.

  And this electrically conductive paste can be easily manufactured with the following method.

  That is, the main component powder and the secondary powder containing atomized powder having an average primary particle size of 0.5 to 10 μm so that the content of the secondary powder in the conductive powder is 0.4 to 4% by weight. The component powders are weighed, and further, the organic vehicle and, if necessary, various additives are weighed and mixed so as to have a predetermined mixing ratio, and dispersed and kneaded using a three-roll mill or the like. The conductive paste can be easily manufactured.

  Thus, this conductive paste contains conductive powder containing Ag as a main component powder and Al as a subcomponent powder, a binder resin, and a solvent, and contains the subcomponent powder in the conductive powder. The amount is 0.4 to 4% by weight, and the main component powder contains atomized powder having an average primary particle size of 0.5 to 10 μm. Therefore, a eutectic alloy of Ag and Al. Therefore, the occurrence of residual stress can be suppressed, and thus the contact resistance Rc after firing can be improved.

  Furthermore, since the generation of the residual stress can be suppressed, the re-shrinkage behavior can be suppressed even under the influence of moisture. Therefore, it is possible to suppress an increase in the contact resistance Rc even when left for a long time under high temperature and high humidity or to be affected by rainwater, etc., and to suppress the electrode peeling, which is suitable for forming an electrode of a solar battery cell. A conductive paste can be realized.

  And this photovoltaic cell can be manufactured with the following method.

First, an n-type semiconductor substrate 5 containing Si as a main component is prepared. Then, using a thin film forming method such as plasma enhanced chemical vapor deposition (PECVD), an antireflection film having a thickness of 70 to 80 nm made of an insulating material such as silicon nitride (SiN _x ) on the n-type semiconductor substrate 5. 7 is formed.

  Next, an Al paste containing Al powder having an average particle diameter of 5 μm is prepared, and further an Ag paste containing Ag powder having an average particle diameter of 1.5 μm is prepared. And this Al paste is apply | coated to the whole back surface of the said n-type semiconductor substrate 5, Furthermore, Ag paste is screen-printed and dried, and the electrically conductive film for back electrodes is formed.

  Next, the conductive paste is applied to the surface of the antireflection film 7 and dried to form a light receiving surface electrode conductive film.

  Thereafter, a baking treatment is performed at a firing temperature of 600 to 700 ° C. using a belt-type firing furnace conveyed in 1 to 3 minutes from the entrance to the exit. As a result, Al in the conductive paste diffuses as an acceptor impurity on the surface of the n-type semiconductor substrate 5 to form the p-type semiconductor layer 6, and the antireflection film 7 is decomposed and removed. Through the fire-through, the p-type semiconductor layer 6 and the light-receiving surface electrode 8 which is a sintered body of the conductive paste are joined, whereby a solar battery cell is manufactured.

  As described above, according to the method for manufacturing a solar cell and the solar cell, the antireflection film 7 is formed on one main surface of the n-type semiconductor substrate 5, and the conductive paste is applied to the surface of the antireflection film 7. After coating, firing treatment is performed, the antireflection film 7 is decomposed and removed, and the p-type semiconductor layer 6 on the n-type semiconductor substrate 5 and the light-receiving surface electrode 8 which is a sintered body of conductive paste are joined. Since the atomized powder having a predetermined particle size is contained in the main component powder, the contact resistance Rc after firing can be improved, and it can be left for a long time under high temperature and high humidity. Even if it is affected by moisture, the increase in contact resistance Rc can be suppressed, and furthermore, the occurrence of electrode peeling can be suppressed, so that it is possible to obtain a highly reliable solar cell that can suppress the reduction in energy conversion efficiency as much as possible. it can.

The present invention is not limited to the above embodiment. For example, the conductive paste only needs to contain at least Ag in the main component powder and Al in the subcomponent powder, and may contain a silicide containing Fe, W, Ti, Ta, Mo, or the like. In this case, the content of these silicides is preferably 10 parts by weight or less with respect to 100 parts by weight of Ag, and among these silicides, FeSi ₂ is particularly preferable from the viewpoint of ensuring good fire-through properties.

  In addition, it is also preferable to add one or a combination of plasticizers such as di-2-ethylhexyl phthalate and dibutyl phthalate to the conductive paste as necessary. It is also preferable to add a rheology modifier such as a fatty acid amide or a fatty acid, and a thixotropic agent, a thickener, a dispersant, etc. may be added.

Furthermore, it is also preferable to include an appropriate amount (for example, 1.0% by weight or less) of a metal soap that is a metal salt of a long-chain fatty acid in the conductive paste, and to include such a metal soap in the conductive paste. As a result, it is possible to improve the fire-through property, and it is possible to obtain a better ohmic contact. Among these metal soaps, higher fatty acid zinc represented by Zn (OCOC _n H _{2n + 1} ) ₂ (n = 11 to 27) is particularly preferable.

  Moreover, in the said embodiment, although the electrically conductive paste is used for a light-receiving surface electrode, you may use it for a back surface electrode.

  In the above embodiment, the n-type semiconductor substrate 5 is used for explanation. However, the present invention can be similarly applied to a p-type semiconductor substrate.

  Furthermore, in the above-described embodiment, the single-sided light-receiving solar cell has been described. However, the present invention can also be applied to a double-sided light-receiving solar cell provided with the above-described antireflection film and light-receiving surface electrode. .

  Next, examples of the present invention will be specifically described.

(Preparation of conductive paste)
[Sample Nos. 1-15]
Prepare atomized Ag powder with an average primary particle size of 0.3-13.0 μm as the main component powder, spherical Al powder with an average particle size of 5 μm as the secondary component powder, and borosilicate glass as the glass frit did.

  The average particle size of the atomized Ag powder was determined by visually observing the atomized Ag powder with an SEM, measuring the circularly converted particle size of 50 arbitrarily extracted particles, and setting the average value.

  Next, an organic vehicle was produced. That is, the organic cellulose was prepared by mixing the ethyl cellulose resin and texanol so that the binder resin was 10% by weight of ethyl cellulose resin and the organic solvent was 90% by weight of texanol.

  Then, the atomized Ag powder and the Al powder are weighed so that the content of the Al powder in the conductive powder is 0.2 to 6.0% by weight, and the total amount of the conductive powder is 87.2% by weight. The acid glass was weighed to 3% by weight, mixed with an organic vehicle with a planetary mixer, and then kneaded with a three-roll mill, thereby preparing conductive pastes of sample numbers 1 to 15.

[Sample No. 16]
A spherical Ag powder having an average particle diameter of 1.0 μm (hereinafter referred to as “wet Ag powder”) produced by a wet reduction method is used as the main component powder, and the content of the Al powder in the conductive powder is 2. Except for 0% by weight. Sample No. 16 was prepared by the same method and procedure as Sample Nos. 1-15.

(Sample evaluation)
As shown in FIG. 5, predetermined electrode patterns 53a to 53e were formed on the antireflection film 52, and the contact resistance Rc was determined by a TLM (Transmission Line Model) method.

  That is, an antireflection film 52 having a thickness of 0.1 μm is formed on the entire surface of a single crystal n-type silicon substrate 51 having a width X of 156 mm, a length Y of 156 mm, and a thickness T of 0.2 mm by plasma enhanced chemical vapor deposition (PECVD). ).

Here, SiN _X was used as a material type of the antireflection film 52.

  Next, screen printing was performed using each of the conductive pastes of Sample Nos. 1 to 16, and a 20 μm-thick conductive film having a predetermined pattern was produced. Next, each sample was placed in an oven set at a temperature of 150 ° C. to dry the conductive film.

  Then, using a belt-type near-infrared furnace (Despatch, CDF7210), adjusting the transport speed so that the sample is transported between the inlet and the outlet in about 1 minute, and at a firing maximum temperature of 700 ° C. in an air atmosphere. Baking was performed, and evaluation samples of sample numbers 1 to 15 on which the electrodes 53a to 53e were formed were produced. In this firing, Al is diffused as an acceptor impurity on the surface of the n-type silicon substrate 51 to form a p-type semiconductor layer.

  Here, when the distances L1 to L4 of the electrodes 53a to 53e were measured, the distance L1 between the electrode 53a and the electrode 53b was 200 μm, the distance L2 between the electrode 53b and the electrode 53c was 400 μm, and the electrode 53c and the electrode The distance L3 between the electrodes 53d was 600 μm, and the distance L4 between the electrodes 53d and 53e was 800 μm. The electrode length Z was 6 mm.

  Subsequently, contact resistance Rc was calculated | required about each sample of the sample numbers 1-16 using the TLM method.

This TLM method is widely known as a method for evaluating the contact resistance of a thin film sample, and uses the transmission line theory to calculate the contact resistance Rc by regarding the electrode and the underlying semiconductor substrate as equivalent to a so-called transmission line circuit. . That is, Formula (1) is established among the length Z of the electrodes 53a to 53e, the sheet resistance R _SH of the p-type semiconductor layer, the interelectrode distance L, and the interelectrode resistance R.

R = (L / Z) × R _SH + 2Rc (1)
As is clear from Equation (1), the interelectrode resistance R and the interelectrode distance L have a linear relationship. Therefore, each resistance R in the interelectrode distance Ln (n = 1 to 4) is measured, and 2Rc is obtained by extrapolating L to 0, and the contact resistance Rc can be calculated from this 2Rc.

Therefore, in this example, each resistance R at the interelectrode distance Ln was measured using a micro-ohmmeter, and the contact resistance Rc was calculated for each of the sample numbers 1 to 16. Note that the sheet resistance R _SH of the p-type semiconductor layer can be calculated from the slope when the horizontal axis is L and the vertical axis is R for the straight line derived from the above formula (1). Here, it was 70 Ω / cm.

  Next, 20 samples of sample numbers 1 to 16 were immersed in a 1% by volume acetic acid aqueous solution for 24 hours, after which each sample was taken out from the acetic acid aqueous solution, and the contact resistance Rc after immersion was the same method and procedure as described above. Measured with

  Moreover, about 20 samples of sample numbers 1-16, it visually observed after immersion, it was confirmed whether electrode peeling had generate | occur | produced, and the incidence rate was calculated | required.

  Table 1 shows the average particle size (μm) of the atomized Ag powder in each sample Nos. 1 to 15, the content (% by weight) of Al powder in the conductive powder, the contact resistance Rc (Ω) before and after immersion, and The rate of occurrence of electrode peeling (%) is shown. In Table 1, the contact resistance Rc represents an average value of 20 samples.

  Sample No. 16 used wet Ag powder as the main component powder and did not use atomized Ag powder. Therefore, although the contact resistance Rc was as low as 3.59Ω before immersion, electrode peeling occurred in all.

  Sample Nos. 1 and 7 have a good electrode peeling rate of 5% or less, but the content of Al powder in the conductive powder is too low at 0.2% by weight. It was found that sufficient ohmic contact with the electrodes 53a to 53e could not be obtained, and the contact resistance Rc was 24 to 27Ω before immersion in the acetic acid aqueous solution and about 30Ω after immersion, which was inferior to the contact resistance.

  Sample Nos. 2 and 3 are atomized Ag powder having an average particle diameter of 0.3 μm, so that the effect of using the atomized Ag powder cannot be fully exhibited, and the contact resistance Rc is 3.70Ω before immersion. 4.58Ω, good after immersion, increased to 14.7Ω and 13.44Ω, and the rate of electrode peeling was 75% and 80%, resulting in increased contact resistance and reduced reliability.

  Sample No. 12 has an excessive content of Al powder in the conductive powder of 6.0% by weight. Therefore, even when an atomized Ag powder having an average grain size of 3.5 μm is used, the contact resistance after firing Rc (before immersion) increased to 13.19Ω, increased to 26.8Ω after immersion, and the rate of electrode peeling was also 35%, leading to a decrease in reliability.

  In Sample No. 15, since the average particle size of the atomized Ag powder was too large, 13.0 μm, it was confirmed that electrode peeling occurred in all the samples.

  On the other hand, sample numbers 4-6, 8-11, 13, and 14 have an average particle size of the atomized Ag powder of 0.5 to 10 μm, and the content of the Al powder in the conductive powder of 0.4 to 4. Since it is within 0% by weight and within the scope of the present invention, the contact resistance Rc is as good as 2.47 to 8.09Ω before immersion, and 4.37 to 9.46Ω even after immersion, and an increase in contact resistance can be suppressed. Further, it was found that the occurrence rate of electrode peeling can be suppressed to 15% or less, and good reliability can be obtained.

  In particular, Sample Nos. 5, 6, 8 to 11 and 13 having an average particle size of atomized Ag powder of 1.5 to 5.0 μm can suppress the occurrence rate of electrode peeling to 5% or less, and have better reliability. It was found that can be secured.

  Furthermore, it was found that Sample Nos. 6 and 8 to 11 in which the average particle size of the atomized Ag powder was 2.5 to 3.5 μm had no sample where electrode peeling occurred, and further high reliability could be secured. .

  An atomized Ag powder having an average primary particle diameter of 3.5 μm, a wet Ag powder having an average particle diameter of 1.0 μm, and an Al powder having an average particle diameter of 5 μm were prepared, and borosilicate glass was prepared as a glass frit.

  Then, the atomized Ag powder, the wet Ag powder, and the Al powder are weighed so that the atomized Ag powder and the wet Ag powder as the main component powder in the conductive powder and the Al powder as the subcomponent powder are as shown in Table 2. Further, the conductive powder is weighed so that the total amount is 87.2% by weight and the borosilicate glass is 3% by weight, mixed with an organic vehicle by a planetary mixer, and then kneaded by a three-roll mill. Conductive pastes with numbers 21 to 27 were prepared.

  The same organic vehicle as used in [Example 1] was used.

  Subsequently, the contact resistance Rc before and after immersion and the rate of electrode peeling were measured for 20 samples of sample numbers 21 to 27 in the same manner and procedure as in [Example 1].

  Table 2 shows the content of the conductive powder, the contact resistance Rc (Ω) before and after immersion, and the rate of occurrence of electrode peeling (%) in each of the 20 samples of sample numbers 21 to 27. In Table 2, the contact resistance Rc indicates the average value of 20 samples as in Table 1.

  As is clear from sample numbers 21 to 27, even when the main component powder is a mixed powder of atomized Ag powder and wet Ag powder, the contact resistance Rc after immersion can be suppressed to about 10Ω, and electrode peeling occurs. It was found that the rate could be suppressed to 15% or less, and good reliability could be obtained.

  In particular, Sample Nos. 23 to 27 in which the content of the atomized Ag powder in the main component powder is 50% by weight or more can suppress the contact resistance Rc to 7.5Ω or less even after immersion, and the rate of electrode peeling is 5%. It can be suppressed to the following, and therefore, it was found that even if left for a long time under high temperature and high humidity or under the influence of rain water, it is possible to suppress damage to the ohmic contact as much as possible and to obtain high reliability.

  Eight types of atomized Ag powder (average particle size: 3.5 μm) containing Ca and / or Mg were prepared. Then, when this atomized Ag powder was dissolved in an acid and subjected to elemental analysis by ICP (inductively coupled plasma) emission analysis, 0.001 to 0.047% by weight of Ca and Mg was included in the atomized Ag powder in total. I found out.

  Subsequently, the conductive paste of sample numbers 31-38 was produced by the same method and procedure as [Example 1], and the contact resistance Rc before and after immersion and the rate of electrode peeling were measured.

  Table 3 shows the total content (% by weight) of Ca and Mg in 20 atomized Ag powders of sample numbers 31 to 38, contact resistance Rc (Ω) before and after immersion, and the rate of occurrence of electrode peeling (% ). In the table, the contact resistance Rc represents an average value of 20 samples.

  As apparent from Sample Nos. 31 to 38, even when Ca and Mg are contained in the atomized Ag powder, the contact resistance Rc after immersion can be suppressed to 11Ω or less, and the occurrence rate of electrode peeling is also 15%. It was found that the following can be suppressed and good reliability can be obtained.

  In particular, sample numbers 33 to 37 having a total content of Ca and Mg in the atomized Ag powder of 0.005 to 0.030 wt% can suppress the contact resistance Rc to 7.1Ω or less even after immersion. The occurrence rate of peeling can be suppressed to 5% or less, and even if left for a long time under high temperature and high humidity or affected by rainwater, it is possible to suppress damage to the ohmic contact as much as possible and to obtain high reliability. It was.

Atomized Ag powder having an average primary particle size of 3.5 μm, wet Ag powder having an average particle size of 1.0 μm, Al powder having an average particle size of 5.0 μm, ZrO ₂ powder having an average particle size of 0.5 μm, A ZnO powder having an average particle size of 0.2 μm was prepared.

Then, the same as [Example 1] except that the atomized Ag powder, wet Ag powder, Al powder, ZrO ₂ , and ZnO were weighed so that the content of each component in the conductive paste was as shown in Table 4. By the method and procedure, the conductive paste of sample numbers 41-44 was produced, and contact resistance Rc before and behind immersion and the incidence rate of electrode peeling were measured.

  Table 4 shows the specification of the conductive paste, the contact resistance R (Ω) before and after immersion, and the rate of occurrence of electrode peeling (%) in each sample of sample numbers 41 to 44. In the table, the contact resistance Rc represents an average value of 20 samples.

As is clear from Table 4, sample numbers 41 and 42 contain ZrO ₂ or ZnO in the conductive paste, but use wet Ag powder and do not use atomized Ag powder. Electrode peeling occurred.

On the other hand, since sample numbers 43 to 44 use atomized Ag powder for Ag powder and contain an appropriate amount of ZrO ₂ or ZnO, the contact resistance Rc after immersion is as small as 2.59 to 3.01Ω, It was found that no electrode peeling occurred.

That is, it was found that the reliability can be further improved by adding an appropriate amount of ZrO ₂ or ZnO in addition to the atomized Ag powder.

  The contact resistance after firing is low, and even if left for a long time under high temperature and high humidity, or affected by rainwater, the increase in contact resistance between the electrode and the semiconductor substrate can be suppressed, and electrode peeling can be prevented. A solar cell that can be suppressed, has high energy conversion efficiency, and high reliability is realized.

5 Semiconductor substrate 7 Antireflection film 8 Light receiving surface electrode (electrode)

Claims (6)

A conductive paste for forming a solar cell electrode,
A conductive powder containing Ag as a main component powder and Al as a subcomponent powder, a binder resin, and a solvent;
The content of the subcomponent powder in the conductive powder is 0.4 to 4% by weight,
And the said main component powder contains the atomized powder whose average particle diameter of a primary particle is 0.5-10 micrometers, The electrically conductive paste characterized by the above-mentioned.   2. The conductive paste according to claim 1, wherein a content of the atomized powder in the main component powder is 50% by weight or more.   The conductive paste according to claim 1 or 2, wherein the atomized powder contains Ca and Mg in a total range of 0.005 to 0.030 wt%.   The conductive paste according to any one of claims 1 to 3, comprising at least one of Zn oxide and Zr oxide.   An antireflection film is formed on at least one main surface of the semiconductor substrate, and after applying the conductive paste according to any one of claims 1 to 4 to the surface of the antireflection film, a baking treatment is performed, A method for manufacturing a solar battery cell, wherein a solar battery cell is manufactured by disassembling and removing an antireflection film and bonding the semiconductor substrate and an electrode that is a sintered body of the conductive paste. An antireflection film and an electrode penetrating the antireflection film are formed on at least one main surface of the semiconductor substrate,
A solar battery cell, wherein the electrode is formed by sintering the conductive paste according to any one of claims 1 to 4.

Images