JP2010251645A - Solar cell, and conductive paste for forming electrode of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive paste for forming a front electrode and a back electrode of a crystal-system silicon solar cell providing high adhesion strength between a solar cell substrate of the crystal-system silicon solar cell, and a metal ribbon for interconnect. <P>SOLUTION: This conductive paste for forming an electrode of this solar cell contains conductive particles each containing silver, and vanadium oxide particles. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a conductive paste for forming an electrode of a solar cell, in particular, a conductive paste for forming a front or back electrode of a crystalline silicon solar cell using crystalline silicon such as single crystal silicon or polycrystalline silicon as a substrate, and the electrode The present invention relates to a solar cell manufacturing method using a forming conductive paste and a solar cell manufactured by the manufacturing method.

  In recent years, the production amount of a crystalline silicon solar cell using a crystalline silicon obtained by processing single crystal silicon or polycrystalline silicon into a flat plate shape as a substrate has greatly increased. These solar cells have electrodes for taking out the generated electric power.

  As an example, a schematic cross-sectional view of a crystalline silicon solar cell is shown in FIG. In a crystalline silicon solar cell, an n-type diffusion layer (n-type silicon layer) 3 is generally formed on the surface of the p-type crystalline silicon substrate 4 on the light incident side. An antireflection film 2 is formed on the n-type diffusion layer 3. Furthermore, the pattern of the light incident side electrode 1 (surface electrode) is printed on the antireflection film 2 using a conductive paste by screen printing or the like, and the light incident side electrode 1 is formed by drying and baking the conductive paste. It is formed. At the time of firing, the conductive paste fires through the antireflection film 2 so that the light incident side electrode 1 can be formed in contact with the n-type diffusion layer 3. Note that the term “fire through” means that the antireflection film, which is an insulating film, is etched with glass frit or the like contained in a conductive paste, and the light incident side electrode 1 and the n-type diffusion layer 3 are made conductive. Since light does not need to enter from the back side of the p-type silicon substrate 4, the back electrode 5 is generally formed on almost the entire surface. A pn junction is formed at the interface between the p-type silicon substrate 4 and the n-type diffusion layer 3. Light such as sunlight passes through the antireflection film 2 and the n-type diffusion layer 3 and enters the p-type silicon substrate 4, and is absorbed in this process to generate electron-hole pairs. In these electron-hole pairs, electrons are separated into the light incident side electrode 1 and holes are separated into the back electrode 5 by an electric field generated by a pn junction. Electrons and holes are taken out as currents through these electrodes.

  In a crystalline silicon solar cell, the influence of an electrode on solar cell characteristics such as conversion efficiency is large, and in particular, the influence of a light incident side electrode is very large. The light incident side electrode has a sufficiently low contact resistance at the interface with the n-type diffusion layer and needs to be in ohmic contact. In addition, the electrical resistance of the electrode itself needs to be sufficiently low, and therefore, it is also important that the resistance (conductor resistance) of the electrode material itself is low. Further, in order to improve productivity and prolong the service life, it is further important that the metal ribbon for interconnects soldered to the electrode material has high adhesive strength.

  A conductive paste containing conductive particles, a glass frit, an organic binder, a solvent and other additives is used for forming electrodes of conventional solar cells, particularly crystalline silicon solar cells. As the conductive particles, silver particles are mainly used. As an example of using such a conductive paste, Patent Document 1 includes at least one selected from the group consisting of silver powder, an organic vehicle, glass frit, boron powder, an inorganic boron compound, and an organic boron compound. A method for manufacturing a solar cell is disclosed in which an electrode is formed on a p-type conductive layer using a conductive paste containing.

  In Patent Document 2, a) conductive silver powder, b) a Zn-containing additive, and c) one or more glass frits that are lead-free are dispersed in d) an organic medium. A thick film conductive composition is disclosed. In Patent Document 1, this thick film conductive composition includes (a) a metal selected from Zn, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu, and Cr; b) Metal oxide of one or more metals selected from Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu, and Cr, and (c) the metal of (b) by firing It is described that it further comprises an additional metal / metal oxide additive selected from any compound capable of producing an oxide and (d) mixtures thereof.

  Patent Document 3 describes a printable, homogeneous, particle-free etching medium having non-Newtonian fluidity for etching an inorganic glassy or crystalline surface. Patent Document 3 describes that this etching medium is an etching medium for the surface of glass containing an element selected from the group consisting of manganese and vanadium. Patent Document 3 describes that the etching medium can be used for an etching process of a silicon oxide and silicon nitride-based glass layer such as a solar cell.

Patent Document 4 discloses a solar cell including a contact made from a mixture, and the mixture is a. A solid portion; b. An organic moiety, c. The solid portion is i. From about 85 to about 99 weight percent of a conductive metal component, ii. A solar cell is described, comprising about 1 to about 15% by weight of a glass component, wherein the glass component does not contain lead. Further, the glass component (Paste Glass) is described that includes V ₂ O _5.

JP 2006-93433 A JP 2006-332032 A Special table 2003-531807 gazette Special table 2008-543080 gazette

  In crystalline silicon solar cells, electrical connection between the crystalline silicon solar cells is performed by soldering an interconnect metal ribbon to an electrode formed in the solar cells. Therefore, in order to eliminate the initial defects of crystalline silicon solar cells and maintain the solar cell characteristics at a stable height over a long period of time, it is necessary that the adhesive strength of the interconnect metal ribbon to the solar cell substrate is high. is there.

  Accordingly, the present invention provides a solar cell having high adhesion strength between a solar cell substrate of a crystalline silicon solar cell and a metal ribbon for interconnect soldered to the solar cell substrate via a front electrode and a back electrode of the solar cell. The object is to obtain a battery. In addition, the present invention provides a conductive paste for forming an electrode for a crystalline silicon solar cell, which can obtain a high adhesive strength between the solar cell substrate of the crystalline silicon solar cell and a metal ribbon for interconnect. For the purpose.

  The present invention is a conductive paste for forming an electrode of a solar cell, comprising conductive particles containing silver and vanadium oxide particles.

The preferable aspect of the electroconductive paste for electrode formation of this invention is shown below. In the present invention, these embodiments can be appropriately combined.
(1) The vanadium oxide particles are included in an amount of 0.01 to 0.3 parts by weight with respect to 100 parts by weight of the conductive paste.
(2) Further containing manganese oxide particles.
(3) Manganese oxide particles are included in an amount of 0.01 to 0.5 parts by weight with respect to 100 parts by weight of the conductive paste.
(4) The solar cell is a single crystal silicon solar cell or a polycrystalline silicon solar cell.

  Moreover, this invention is a manufacturing method of the solar cell including the process of forming an electrode on a solar cell substrate, and the step of forming an electrode comprises the above-mentioned electrode-forming conductive paste as a surface electrode of a solar cell substrate. A solar cell comprising: a step of printing to form a soldering pad on the back electrode and / or the surface electrode and / or the back electrode; and a step of drying and baking the electrode-forming conductive paste. It is a manufacturing method.

  Moreover, this invention is a solar cell manufactured with the above-mentioned manufacturing method.

  According to the present invention, there is provided a solar cell having high adhesive strength between a solar cell substrate of a crystalline silicon solar cell and a metal ribbon for interconnect soldered to the solar cell substrate via a front electrode and a back electrode of the solar cell. Obtainable. In addition, according to the present invention, a conductive paste for forming an electrode of a crystalline silicon solar cell, which can obtain a high adhesive strength between the solar cell substrate of the crystalline silicon solar cell and the metal ribbon for interconnect, is obtained. be able to.

It is a cross-sectional schematic diagram of the surface electrode vicinity just before baking of the electroconductive paste for electrode formation of a crystalline silicon solar cell.

  As used herein, “crystalline silicon” includes single crystal or polycrystalline silicon. The “crystalline silicon substrate” refers to a material obtained by forming crystalline silicon into a shape suitable for element formation, such as a flat plate shape, for the formation of an electric element or an electronic element. Any method may be used for producing crystalline silicon. For example, the Czochralski method can be used for single crystal silicon, and the casting method can be used for polycrystalline silicon. In addition, other manufacturing methods such as a polycrystalline silicon ribbon produced by a ribbon pulling method, a polycrystalline silicon formed on a different substrate such as glass, and the like can also be used as the crystalline silicon substrate. The “crystalline silicon solar cell” refers to a solar cell manufactured using a crystalline silicon substrate. In addition, as an index representing solar cell characteristics, a curve factor (fill factor, hereinafter also referred to as “FF”, which is referred to as “FF value”) obtained from measurement of current-voltage characteristics under light irradiation is used. Use.

  The present invention provides a solar cell having a high adhesive strength between a solar cell substrate of a crystalline silicon solar cell and a metal ribbon for interconnect soldered to the solar cell substrate via a front electrode and a back electrode of the solar cell. The purpose is to obtain. As a result of the diligent efforts of the inventors of the present invention, the adhesive paste of the metal ribbon for interconnects to the solar cell substrate (hereinafter referred to as “ribbon adhesive strength”) is obtained because the conductive paste for electrode formation of solar cells contains vanadium oxide particles. ") Is also increased, and the present invention has been achieved. Note that it is necessary to add the vanadium oxide particles as particles different from the glass frit in order to obtain high ribbon adhesive strength. Hereinafter, the conductive paste for electrode formation of the present invention will be described in detail.

The conductive paste for forming an electrode of the present invention is a conductive paste containing silver as a main component for forming an electrode for an n-type silicon layer of a crystalline silicon solar cell. The conductive paste for electrode formation of the present invention is characterized by containing vanadium oxide particles. As vanadium oxide, any valence can be used, but vanadium pentoxide (V ₂ O ₅ ) is preferably used because it is stable in the atmosphere. The electrode-forming conductive paste of the present invention may further contain a glass frit, an organic binder, a solvent and other additives as required.

  In the conductive paste for electrode formation of the present invention, the amount of vanadium oxide particles added is preferably 0.01 to 0.3 parts by weight with respect to 100 parts by weight of the conductive paste, and 0.02 to 0.3. More preferably, the amount is 0.02 to 0.2 parts by weight. When the addition amount of vanadium oxide particles is less than 0.01 parts by weight with respect to 100 parts by weight of the conductive paste, it is difficult to obtain sufficient ribbon adhesive strength. Moreover, when the addition amount of vanadium oxide particles exceeds 0.3 parts by weight with respect to 100 parts by weight of the conductive paste, the characteristics (FF) of the solar cell tend to deteriorate.

The electrode-forming conductive paste of the present invention preferably further contains manganese oxide particles. This is because when a conductive paste further containing manganese oxide particles is used, high ribbon adhesive strength stability over a long period of time can be obtained. Manganese oxide having any valence can be used, but it is preferable to use manganese dioxide (MnO ₂ ) from the viewpoint of ensuring high ribbon adhesive strength stability over a long period of time.

  In the conductive paste for electrode formation of the present invention, in order to obtain high ribbon adhesive strength even when exposed to a harsh environment for a long time, the amount of manganese oxide particles added is 0 with respect to 100 parts by weight of the conductive paste. The amount is preferably 0.01 to 0.5 parts by weight, more preferably 0.015 to 0.2 parts by weight, and still more preferably 0.02 to 0.1 parts by weight.

  The main component of the conductive particles contained in the electrode-forming conductive paste of the present invention is silver. The conductive paste for electrode formation of the present invention can contain other metals other than silver as long as the performance of the solar cell electrode is not impaired. However, from the viewpoint of obtaining low electrical resistance and high reliability, the conductive particles are preferably made of silver.

  The particle shape and particle size of the conductive particles are not particularly limited. As the particle shape, for example, a spherical shape or a flake shape can be used. The particle size refers to the size of the longest length part of one particle. The particle size of the conductive particles is preferably 0.05 to 20 μm and more preferably 0.1 to 5 μm from the viewpoint of workability.

  In general, since the size of the fine particles has a constant distribution, it is not necessary that all the particles have the above-mentioned particle size, and the particle size (D50) of the total value of 50% of all the particles is within the above-mentioned range of the particle size. It is preferable that Moreover, the average value of particle size (average particle size) may be in the above range. The same applies to particles other than the conductive particles described in this specification.

  The glass frit contained in the electrode-forming conductive paste of the present invention may be a glass frit containing Pb or a Pb-free glass frit. In the conductive paste for electrode formation of the present invention, high strength can be obtained by adding vanadium oxide particles or vanadium oxide particles and manganese oxide particles as particles different from glass frit regardless of the type of glass frit. Can do.

The glass frit containing Pb that can be included in the conductive paste for electrode formation of the present invention includes PbO—SiO ₂ —B ₂ O ₃ system, Bi ₂ O ₃ —PbO—SiO ₂ —B ₂ O ₃ system, and the like. It can be illustrated.

Further, as a glass frit that can be included in the electrode forming conductive paste of the present invention, a Pb-free glass frit (for example, Bi ₂ O ₃ —B ₂ O ₃ —SiO ₂ —CeO ₂ —LiO ₂ —NaO ₂ system) is used. And SiO ₂ —B ₂ O ₃ —Li ₂ O-based) can be used, but is not limited thereto. 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. The particle size refers to the size of the longest length part of one particle. The addition amount of the glass frit to the electrode-forming conductive paste of the present invention is usually 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight with respect to 100 parts by weight of the conductive particles.

  The conductive paste for electrode formation of the present invention can contain ZnO. The amount of ZnO added to the electrode-forming conductive paste of the present invention is usually 0.1 to 20 parts by weight, preferably 5 to 10 parts by weight, based on 100 parts by weight of the conductive particles. By containing ZnO, the conductive paste for electrode formation of the present invention can ensure the stability of the ribbon adhesive strength.

  The conductive paste for electrode formation of the present invention can contain an organic binder and a solvent. The organic binder and the solvent play a role of adjusting the viscosity of the conductive paste and are not particularly limited. It is also possible to use an organic binder dissolved in a solvent.

  As the organic binder, cellulose resins (for example, ethyl cellulose, nitrocellulose and the like) and (meth) acrylic resins (for example, polymethyl acrylate and polymethyl methacrylate) can be used. The addition amount of the organic binder is usually 0.5 to 30 parts by weight, preferably 1 to 5 parts by weight with respect to 100 parts by weight of the conductive particles.

  Examples of the solvent include alcohols (for example, terpineol, α-terpineol, β-terpineol, etc.), esters (for example, hydroxy group-containing esters, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, butyl Carbitol acetate, etc.) can be used. The addition amount of the solvent is usually 0.5 to 30 parts by weight, preferably 10 to 25 parts by weight with respect to 100 parts by weight of the conductive particles.

  Furthermore, a plasticizer, an antifoaming agent, a dispersing agent, a leveling agent, a stabilizer, an adhesion promoter, and the like can be added to the conductive paste for electrode formation of the present invention as necessary. Among these, as the plasticizer, phthalic acid esters, glycolic acid esters, phosphoric acid esters, sebacic acid esters, adipic acid esters, citrate esters, and the like can be used.

  Next, the manufacturing method of the electroconductive paste for electrode formation of this invention is demonstrated. In the conductive paste for electrode formation of the present invention, conductive particles and vanadium oxide particles are added to the organic binder and the solvent, preferably manganese oxide particles are further added, and glass frit is further added as necessary. , Mixed and dispersed.

  Mixing can be performed with a planetary mixer, for example. Further, the dispersion can be performed by a three-roll mill. Mixing and dispersion are not limited to these methods, and various known methods can be used.

  Next, a method for manufacturing a crystalline silicon solar cell using the electrode forming conductive paste of the present invention will be described with reference to FIG.

  FIG. 1 is a schematic cross-sectional view immediately before firing of a conductive paste near the surface electrode 1. The crystalline silicon solar cell shown in FIG. 1 has a surface electrode 1, an antireflection film 2, an n-type diffusion layer (n-type silicon layer) 3, a p-type silicon substrate 4, and a back electrode 5 formed on the light incident side. .

  In the method for producing a solar cell of the present invention, the above-mentioned conductive paste for electrode formation of the present invention is applied to the surface electrode, the back electrode and / or the soldering pad on the surface electrode and / or the back electrode of the substrate for solar cell. Printing to form the part.

  The electrode-forming conductive paste of the present invention can be used when either the front electrode 1 or the back electrode 5 is formed. That is, the electrode forming conductive paste of the present invention can be used for forming electrodes on both the n-type silicon surface and the p-type silicon surface. When the electrode-forming conductive paste of the present invention is used to form the surface electrode 1 of a single-crystal silicon or polycrystalline silicon solar cell substrate, it is printed directly on the n-type silicon layer of the silicon substrate. It is also possible to print on the antireflection film 2 on the n-type diffusion layer (n-type silicon layer) 3. When the conductive paste for electrode formation of the present invention is printed on the antireflection film 2, the conductive paste fires through the antireflection film 2 during the subsequent firing, and the surface is formed on the n-type diffusion layer 3. Electrode 1 is formed.

  The conductive paste for electrode formation of the present invention can also be used when forming a soldering pad portion on at least one electrode on the front electrode 1 and the back electrode 5 of the solar cell substrate. . Therefore, the conductive paste for electrode formation of the present invention is at least one of the front surface electrode 1, the back surface electrode 5, the soldering pad portion on the front surface electrode 1, and the soldering pad portion on the back surface electrode 5 of the solar cell substrate. Can be used to form one.

  Note that, from the viewpoint of obtaining high photoelectric conversion efficiency, it is preferable that the surface of the crystalline silicon substrate on the light incident side has a pyramidal texture structure.

  In order to manufacture the structure shown in FIG. 1, the electrode-forming conductive paste of the present invention is formed on a crystalline silicon substrate having an n-type diffusion layer 3 on the surface by a method such as screen printing or n-type. An electrode pattern is printed on the antireflection film 2 formed on the diffusion layer 3.

  Further, in the case of forming a soldering pad portion, the electrode forming conductive paste of the present invention so that a predetermined pad pattern is formed on the front electrode 1 or / and the back electrode 5 on the solar cell substrate. To print.

  The method for producing a solar cell of the present invention includes the steps of drying and baking the electrode-forming conductive paste printed as described above. That is, first, the printed electrode pattern is dried for several minutes (for example, 5 minutes) at a temperature of about 100 to 150 ° C. Similarly, the electrode forming conductive paste of the present invention or other conductive paste (for example, a conductive paste containing aluminum as a main component) is printed on almost the entire surface of the back surface and dried, whereby FIG. The structure shown in FIG.

  Thereafter, the structure shown in FIG. 1 is baked in the atmosphere using a furnace such as a tubular furnace at a temperature of about 500 to 850 ° C. for 0.5 to 3 minutes, and the surface electrode 1 and the back surface on the light incident side The electrode 5 is formed. When the electrode forming conductive paste of the present invention is printed on the antireflection film 2, the high temperature paste material fires through the antireflection film 2 during firing. The mold diffusion layer 3 can be electrically connected. The firing conditions are not limited to the above, and can be selected as appropriate.

  Electrodes are formed using the conductive paste for electrode formation of the present invention in all back electrode type (so-called back contact structure) and solar cells in which the light incident side electrode is connected to the back surface through a through hole provided in the substrate. can do.

  The example of the solar cell using the p-type silicon substrate has been described above. However, even in the case of the crystalline silicon solar cell using the n-type silicon substrate, the impurity forming the diffusion layer is changed from n-type impurities such as phosphorus to boron or the like. A solar cell using the electrode-forming conductive paste of the present invention is manufactured by the same process except that the p-type impurity is changed to form a p-type diffusion layer instead of the n-type diffusion layer. Can do.

  When the conductive paste for electrode formation of the present invention is used, the adhesive strength of the interconnect metal ribbon to the solar cell substrate is increased, and thus a long-life solar cell having excellent solar cell characteristics can be obtained.

  Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.

<Material and preparation ratio of conductive paste>
The composition of the conductive paste used in the experimental example is as follows.
-Conductive particles: Ag (100 parts by weight)
Spherical, BET value 1.0-1.2 m ² / g.
Organic binder: ethyl cellulose (3 parts by weight).
Solvent: ester alcohol (13 parts by weight).
Glass frit: Pb-based glass frit (PbO—B ₂ O ₃ —SiO ₂ ) (2 parts by weight), (BET value 4.0 to 5.0 m ² / g).
Additive: ZnO (9 parts by weight) (BET value 9 to 11 m ² / g).
· _V 2 _O 5: (BET value 1.0~1.2m ² / g).
As the manganese oxide, particulate V ₂ O ₅ was used. The amount of vanadium oxide particles added to the conductive paste was varied depending on the experimental conditions as described later.
・ MnO ₂ :
As the manganese oxide, particulate MnO ₂ was used. The amount of MnO ₂ particles added to the conductive paste was added in an amount described later depending on the experimental conditions.

Next, the conductive paste was prepared by mixing the materials of the above-mentioned predetermined preparation ratio with a planetary mixer, further dispersing with a three-roll mill, and forming a paste.
<Prototype solar cell substrate>

  Evaluation of the conductive paste for electrode formation of this invention was performed by making a prototype of a solar cell using the adjusted conductive paste and measuring its characteristics. The solar cell prototype method is as follows.

  The substrate used was a B (boron) -doped P-type Si polycrystalline substrate (substrate thickness 200 μm).

  First, a silicon oxide layer having a thickness of about 20 μm was formed on the substrate by dry oxidation, and then etched with a mixed solution of hydrogen fluoride, pure water and ammonium fluoride to remove damage on the substrate surface. Further, heavy metal cleaning was performed with an aqueous solution containing hydrochloric acid and hydrogen peroxide.

  Next, a texture (uneven shape) was formed on the substrate surface by wet etching. Specifically, a pyramidal texture structure was formed on one side (surface on the light incident side) by a wet etching method (sodium hydroxide aqueous solution). Thereafter, it was washed with an aqueous solution containing hydrochloric acid and hydrogen peroxide.

Next, phosphorus oxychloride (POCl ₃ ) is used on the surface having the texture structure of the substrate, and phosphorus is diffused by a diffusion method at a temperature of 950 ° C. for 30 minutes, and the n-type diffusion layer has a depth of about 0.5 μm. An n-type diffusion layer was formed. The sheet resistance of the n-type diffusion layer was 50Ω / □.

Next, a silicon nitride thin film having a thickness of about 60 nm was formed on the surface of the substrate on which the n-type diffusion layer was formed, using a silane gas and an ammonia gas by a plasma CVD method. Specifically, a silicon nitride thin film (antireflection film) having a film thickness of about 60 nm was formed by plasma CVD method by glow discharge decomposition of a mixed gas of 1 Torr (133 Pa) of NH ₃ / SiH ₄ = 0.5.

  The solar cell substrate thus obtained was cut into a 15 mm × 15 mm square and used.

  The conductive paste for the light incident side (surface) electrode was printed by a screen printing method. On the above-mentioned antireflection film of the substrate, printing was performed with a pattern comprising a 2 mm square bus electrode part and a 100 μm wide finger electrode part so that the film thickness was about 20 μm, and then dried at 150 ° C. for about 1 minute.

  Next, the conductive paste for the back electrode was printed by a screen printing method. A conductive paste mainly composed of aluminum particles, glass frit, ethyl cellulose, and a solvent was printed at 12 mm square on the back surface of the substrate and dried at 150 ° C. for 1 minute. The film thickness of the conductive paste for the back electrode after drying was about 20 μm.

  Predetermined in the atmosphere using a near-infrared firing furnace (manufactured by NGK Japan's high-speed firing test furnace for solar cells) using a halogen lamp as a heating source on the substrate printed with the conductive paste on the front and back surfaces as described above It baked by the conditions of. The firing conditions were such that the peak temperature was constant at 760 ° C. or the peak temperature was changed in the range of 720 ° C., 760 ° C., and 800 ° C., and both sides were simultaneously fired in air in-out 2 minutes in the firing furnace. A solar cell was prototyped as described above.

<Measurement of solar cell characteristics>
The measurement of the electrical characteristics (FF) of the solar battery cell was performed as follows. That is, the current-voltage characteristics of the prototype solar cell were measured under irradiation of solar simulator light (AM1.5, energy density 100 mW / cm ² ), and the fill factor (FF) was calculated from the measurement results. In addition, 10 samples were produced and the measured value was calculated as an average value of 10 samples.

<Measurement of adhesive strength>
A sample for measuring the adhesive strength of the soldered metal ribbon was prepared and measured as follows. First, the same 15 mm square solar cell substrate with an antireflection film as that for measuring solar cell characteristics was used as the substrate. A soldering pad having a width of 3 mm and a length of 12 cm was printed on a substantially central portion of the substrate surface using a predetermined conductive paste, dried and fired. Next, a copper ribbon (width 1.5 mm × total thickness 0.16 mm, eutectic solder [tin: lead = 64: 36 weight ratio] with a film thickness of about 40 μm) as a metal ribbon for interconnects, Soldering was performed on a soldering pad at a temperature of 250 ° C. for 3 seconds using a flux. Thereafter, the ring-shaped portion provided at one end of the ribbon is pulled in the direction of 90 degrees with respect to the substrate surface by a digital tensile gauge (manufactured by A & D Co., Ltd., digital force gauge AD-4932-50N), and the fracture strength of adhesion is measured. Thus, the adhesive strength was measured. In addition, 10 samples were produced and the measured value was calculated as an average value of 10 samples.

<Experiment 1>
As shown in Table 1, the conductive paste in which the amount of vanadium oxide added to the conductive paste was changed from 0 to 0.5 parts by weight with respect to 100 parts by weight of the conductive particles was used for forming the surface electrode of the solar cell. A solar cell was prototyped. In addition, all the peak temperatures of baking at the time of solar cell preparation were 760 degreeC. Table 1 shows the measurement results of the solar cell characteristics (value of the fill factor FF) and soldering strength of the obtained solar cell.

  As is apparent from Table 1, when the amount of vanadium oxide added is 0.01 parts by weight or more, it has become clear that good adhesive strength of the metal ribbon can be obtained. Moreover, when the addition amount of vanadium oxide increased and it exceeded 0.3 weight part, it became clear that a solar cell characteristic (FF) will fall. Therefore, in the conductive paste in which the amount of vanadium oxide added is in the range of 0.01 to 0.3 parts by weight with respect to 100 parts by weight of the conductive particles, the adhesive strength of the metal ribbon is good and the favorable value of 0.75 or more. It has become clear that the solar cell characteristics (FF) can be obtained together.

<Experiment 2>
Next, in order to obtain the relationship between the influence of the addition of vanadium oxide to the conductive paste on the adhesive strength of the metal ribbon and the firing peak temperature, the firing peak temperature was changed to 720 ° C., 760 ° C. and 800 ° C. A battery was prototyped. The amount of vanadium oxide added was constant 0.04 parts by weight with respect to 100 parts by weight of the conductive particles. In Table 2, the measurement result of the solar cell characteristic (FF) of the obtained solar cell and the adhesive strength of a metal ribbon is shown. In addition, the adhesive strength described in Table 2 indicates the relative adhesive strength normalized by setting the adhesive strength of Experiment No. 2-1a (the conductive paste of “no vanadium oxide added” at 720 ° C.) to 1.00. Yes. For example, in Table 2, it is shown that the adhesive strength of the metal ribbon of the solar cell obtained by Experiment 2-1b was 1.90 times the ribbon adhesive strength of Experiment 2-1a.

  From the results shown in Table 2, when the baking conditions were baked at 720 ° C. to 800 ° C., the conductive paste added with 0.04 part by weight of vanadium oxide was compared with the solar cell using the conductive paste without adding vanadium oxide. The solar cell used was found to have good solar cell properties and metal ribbon adhesion strength.

<Experiments 3-5>
In order to accelerate the long-term stability of the adhesive strength, solar cell characteristics (FF) and adhesion of metal ribbons after a solar cell using the following three types of conductive paste was exposed to a temperature of 150 ° C. for a predetermined time. The strength was measured. The relative adhesive strengths listed in Tables 3 to 5 are adhesive strengths normalized with the adhesive strength at an elapsed time of 0 minutes being 1.00.

・ Experiments 3-1 to 5
For both V ₂ O ₅ and MnO ₂ , an additive-free conductive paste was used. Table 3 shows the results.

・ Experiments 4-1-5
V ₂ O ₅ was added, but MnO ₂ was an additive-free conductive paste. The amount of V ₂ O ₅ added was 0.04 parts by weight with respect to 100 parts by weight of the conductive particles. Table 4 shows the results.

・ Experiments 5-1 to 5
A conductive paste to which both V ₂ O ₅ and MnO ₂ were added was used. The amount of V ₂ O ₅ added was 0.04 parts by weight with respect to 100 parts by weight of the conductive particles. The amount of MnO ₂ added was 0.04 parts by weight with respect to 100 parts by weight of the conductive particles. Table 5 shows the results.

As is apparent from the results of Tables 3 and 4, by using a conductive paste to which V ₂ O ₅ is added, a high adhesive strength of the metal ribbon is obtained even after being exposed to a temperature of 150 ° C. for a long time. It became clear that it was possible. Further, as is clear from the results of Tables 3 to ₅ , by using a conductive paste in which MnO ₂ is added in addition to V ₂ O ₅ , the metal ribbon of a higher metal ribbon even after being exposed to a temperature of 150 ° C. for a long time. It became clear that adhesive strength could be obtained.

1 Light incident side electrode (surface electrode)
2 Antireflection film 3 N-type diffusion layer (n-type silicon layer)
4 p-type silicon substrate 5 Back electrode

Claims (7)

  A conductive paste for forming an electrode of a solar cell, comprising conductive particles containing silver and vanadium oxide particles.   The electroconductive paste for electrode formation of Claim 1 which contains 0.01-0.3 weight part of vanadium oxide particles with respect to 100 weight part of conductive paste.   The conductive paste for electrode formation according to claim 1 or 2, further comprising manganese oxide particles.   The conductive paste for electrode formation of Claim 3 which contains 0.01-0.5 weight part of manganese oxide particles with respect to 100 weight part of conductive paste.   The conductive paste for electrode formation according to any one of claims 1 to 4, wherein the solar cell is a single crystal silicon solar cell or a polycrystalline silicon solar cell. A method for manufacturing a solar cell including a step of forming an electrode on a solar cell substrate, wherein the step of forming an electrode comprises:
The conductive paste for electrode formation according to any one of claims 1 to 5 is used to form a front surface electrode, a back surface electrode and / or a front surface electrode and / or a soldering pad portion on the back surface electrode of a solar cell substrate. A process of printing to
The process of drying and baking the electroconductive paste for electrode formation, The manufacturing method of a solar cell.   The solar cell manufactured with the manufacturing method of Claim 6.

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