JP2013106006A - Electrode structure, solar cell and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode structure excellent in adhesion to a transparent electrode layer and having less contact resistance; and provide a solar cell and the like equipped with the electrode structure.SOLUTION: An electrode structure 6 comprises: a first conductive layer 6a provided on a transparent electrode layer 5 in a patterned manner and having conductive particles and a high molecular compound; and a second conductive layer 6b provided on the first conductive layer 6a and having conductive particles but not having a high molecular compound serving as a binder. It is preferable that the second conductive layer 6b contains at least two types of conductive particle groups having particle-size distributions different from each other, and that a content rate of the conductive particle group is more than 99.0 mass%. When a hardening agent hardened at a temperature not less than 120°C and less than 180°C is used as the high molecular compound, the electrode structure can be used favorably as a collecting electrode of a solar cell having a chalcopyrite compound semiconductor layer.

Description

  The present invention relates to an electrode structure, a solar cell, and a manufacturing method thereof, and more particularly, to an electrode structure having excellent adhesion to a transparent electrode layer and a small contact resistance, a solar cell including the electrode structure, and a manufacturing method thereof.

A solar cell (hereinafter referred to as a CIGS solar cell) having a CIGS (Cu (In, Ga) Se ₂ ) -based chalcopyrite compound semiconductor layer having a high conversion efficiency as a light absorption layer has been studied in various fields. ing. In this CIGS solar cell, a comb-like collector electrode is formed on a transparent electrode layer. The current collecting electrode generally forms a vacuum deposited film obtained by vacuum depositing a material such as Al or Ni. However, the thickness of the vacuum-deposited film is limited to a few microns, and when the collector electrode becomes longer due to the increase in the area of the solar cell, the resistance of the collector electrode increases and the fill factor (FF) is increased. There is a problem that decreases.

  In order to solve such a problem, a current collecting electrode made of a conductive paste is being considered instead of a vacuum deposited film. For example, in Patent Document 1, a conductive paste containing a conductive filler made of Ag and a thermosetting resin is screen-printed on an ITO (indium tin oxide) film as a collecting electrode applicable to a solar cell having a HIT structure. Then, it has been proposed to heat cure at 200 ° C. to form a current collecting electrode. In this technique, a thin-film Ag layer is provided between the ITO film and a collecting electrode made of a conductive paste, thereby reducing contact resistance between them and improving moisture resistance.

  Also in Patent Document 2, as a collecting electrode applicable to an amorphous silicon solar cell, a single crystal solar cell, and a thin film polycrystalline solar cell, a conductive filler and a binder resin selected from various conductive powders are used. It has been proposed that a conductive paste containing a curing agent is printed on an ITO electrode and then thermally cured at 180 ° C. to form a current collecting electrode. In this technique, the current collecting electrode made of a conductive paste has a two-layer structure (first electrode and second electrode) to reduce contact resistance with the ITO film and improve interlayer adhesion.

  Also in Patent Document 3, a conductive paste containing a granular conductive filler, a flaky conductive filler, and a curable binder resin is applied to the surface of a transparent electrode layer showing an uneven texture structure and cured at 200 ° C. Thus, a technique for forming a collector electrode has been proposed. In this technique, the content of the granular conductive filler with respect to the entire conductive filler made of Ag is set to 40% or more to reduce the contact resistance between the collector electrode and the transparent electrode layer.

JP 2005-268239 A JP-A-6-318724 JP 2002-76398 A

  The present inventor screen-printed a conductive paste containing a conductive filler and a binder resin as described in the above prior art document in the course of studying the collector electrode structure of a CIGS solar cell, and then 180 When the current collecting electrode was formed by curing under the baking and curing conditions at ° C., the conversion efficiency of the CIGS solar cell was lowered unlike the result of the silicon solar cell described in the prior art document. The cause of the reduction in conversion efficiency was the influence of heat applied to the CIGS solar cell during baking and curing of the conductive paste. In order to confirm the effect of heat, a CIGS solar cell using an Al vacuum-deposited film as a collecting electrode was produced, and when the temperature of 180 ° C. or higher was applied to the solar cell, the conversion efficiency decreased However, since the conversion efficiency did not decrease when a temperature of 150 ° C. or lower was applied, it was confirmed that the decrease in the conversion efficiency had an effect on the characteristics of the CIGS compound semiconductor layer. did.

  On the other hand, when the current collecting electrode is formed of Ag paste containing a binder resin instead of the above-described Al vacuum deposition film, the current collecting electrode cured under baking and curing conditions of 150 ° C. or less has a too high resistivity and can be used. There wasn't. The reason was that the temperature of 150 ° C. given as the baking and curing conditions was insufficient, and the baking was not performed sufficiently. In addition, when the current collecting electrode was formed from an Ag paste containing no binder resin, the adhesion to the transparent electrode layer was extremely poor and the contact resistance was increased, making it unsuitable for the current collecting electrode.

  The present invention has been made in order to solve the above-mentioned problems, and the object thereof is an electrode structure having excellent adhesion to the transparent electrode layer and a small contact resistance, and a solar cell having the electrode structure, and It is in providing the manufacturing method of the solar cell.

  The inventor forms a first conductive layer on a transparent electrode layer with a conductive paste containing conductive particles and a binder resin that is cured at 120 ° C. or higher and lower than 180 ° C., and a conductive paste that does not contain a binder resin thereon. When the second conductive layer was formed, the first conductive layer was responsible for good adhesion to the transparent electrode layer, and the second conductive layer was found to be responsible for the conductivity as the current collecting electrode. It has been found that the semiconductor layer is not thermally damaged. Furthermore, the inventors have found that such an electrode structure is effective as an electrode structure beyond the use of a collecting electrode for solar cells, and completed the present invention.

  In order to solve the above problems, an electrode structure according to the present invention is provided on a transparent electrode layer in a pattern, a first conductive layer having conductive particles and a polymer compound, and a first conductive layer provided on the first conductive layer. And a second conductive layer having conductive particles without having a polymer compound as a binder.

  According to this invention, the first conductive layer having conductive particles and a polymer compound is provided on the transparent electrode layer, and the first conductive layer is conductive without having a polymer compound as a binder. Since the second conductive layer having particles is provided, the first conductive layer having good adhesion to the transparent electrode layer bears good adhesion with the transparent electrode layer, and the first conductive layer is on the first conductive layer. The second conductive layer having good conductivity bears the conductivity as an electrode. As a result, the electrode structure composed of the first conductive layer and the second conductive layer can reduce the contact resistance with respect to the transparent electrode layer and can exhibit better conductivity.

  In the electrode structure according to the present invention, the first conductive layer has the polymer compound as a binder and the conductive particles are bonded to each other, and the second conductive layer is directly bonded to the conductive particles. doing.

  According to this invention, in the first conductive layer, the high molecular compound serves as a binder and the conductive particles are bonded to each other, and in the second conductive layer, the high molecular compound as a binder is not included, and the conductive particles are Since it is directly bonded, as described above, the first conductive layer having good adhesion to the transparent electrode layer bears good adhesion between the transparent electrode layer and the conductivity on the first conductive layer. A good second conductive layer bears good conductivity as an electrode.

  In the electrode structure according to the present invention, the second conductive layer includes at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups is greater than 99.0% by mass. Is preferred.

  According to the present invention, since the second conductive layer includes at least two types of conductive particles having different particle size distributions, the conductive particles having a small particle size can be obtained without including a binder component that is a polymer compound. It is possible to enter between the conductive particles having a large diameter to bond the particles to each other and to improve the electrical coupling. Moreover, since the content rate of a conductive particle group is more than 99.0 mass% in a 2nd conductive layer, a 2nd conductive layer does not contain the high molecular compound as a binder substantially. As a result, high conductivity can be exhibited.

  In the electrode structure according to the present invention, the polymer compound is a curing agent that cures at 120 ° C. or more and less than 180 ° C., and is preferably used as a collector electrode of a solar cell having a chalcopyrite compound semiconductor layer.

  According to this invention, the polymer compound is a curing agent that cures at 120 ° C. or more and less than 180 ° C., and is used as a collecting electrode of a solar cell having a chalcopyrite compound semiconductor layer, without deteriorating the semiconductor characteristics. Good adhesion and contact resistance can be achieved.

  In order to solve the above problems, an electrode structure according to the present invention is provided on a transparent electrode layer in a pattern, a first conductive layer having conductive particles and a polymer compound, and a first conductive layer provided on the first conductive layer. And a second conductive layer having conductive particles, and the second conductive layer includes at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups is 99.0. It is characterized by exceeding mass%.

  According to this invention, since the second conductive layer includes at least two kinds of conductive particle groups having different particle size distributions, the conductive particles having a small particle size enter between the conductive particles having a large particle size, and the particles are separated from each other. The electrical coupling can be improved while being coupled. Moreover, since the content rate of a conductive particle group is more than 99.0 mass% in a 2nd conductive layer, a 2nd conductive layer does not contain the high molecular compound as a binder substantially. As a result, high conductivity can be exhibited.

  A solar cell according to the present invention for solving the above problems is a solar cell in which at least a back electrode layer, a chalcopyrite compound semiconductor layer, a buffer layer, a transparent electrode layer, and a collecting electrode are provided in that order on a substrate. A first conductive layer, wherein the current collecting electrode is provided in a pattern on the transparent electrode layer and has conductive particles and a polymer compound that cures at 120 ° C. or higher and lower than 180 ° C., and the first conductive layer And a second conductive layer having conductive particles without having a polymer compound as a binder.

  According to the present invention, the current collecting electrode that does not need to be formed at a high firing temperature of 180 ° C. or higher is applied as the current collecting electrode of the solar cell using the chalcopyrite compound semiconductor layer as the light absorption layer. Thermal damage to the semiconductor layer can be suppressed. As a result, the fill factor can be increased and a solar cell with high conversion efficiency can be obtained.

  In the solar cell according to the present invention, the second conductive layer includes at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups is more than 99.0% by mass. preferable.

  According to this invention, since the second conductive layer includes at least two kinds of conductive particle groups having different particle size distributions, the conductive particles having a small particle size can be obtained without including a polymer compound as a binder. The conductive particles having a large diameter can enter each other to bond the particles to each other and to improve the electrical coupling. Moreover, since the 2nd conductive layer does not contain the high molecular compound as a binder substantially, it can show high electroconductivity.

  A solar cell according to the present invention for solving the above problems is a solar cell in which at least a back electrode layer, a chalcopyrite compound semiconductor layer, a buffer layer, a transparent electrode layer, and a collecting electrode are provided in that order on a substrate. A first conductive layer, wherein the current collecting electrode is provided in a pattern on the transparent electrode layer and has conductive particles and a polymer compound that cures at 120 ° C. or higher and lower than 180 ° C., and the first conductive layer A second conductive layer having conductive particles provided thereon, the second conductive layer including at least two types of conductive particle groups having different particle size distributions, and a content ratio of the conductive particle groups Is over 99.0% by mass.

  According to this invention, since the second conductive layer includes at least two kinds of conductive particle groups having different particle size distributions, the conductive particles having a small particle size enter between the conductive particles having a large particle size, and the particles are separated from each other. The electrical coupling can be improved while being coupled. Moreover, since the 2nd conductive layer does not contain the high molecular compound as a binder substantially, it can show high electroconductivity.

  In the method for producing a solar cell according to the present invention for solving the above problems, at least a back electrode layer, a chalcopyrite compound semiconductor layer, a buffer layer, a transparent electrode layer, and a collecting electrode are provided in this order on a substrate. In the method for manufacturing a solar cell, the step of forming the current collecting electrode is performed using a conductive paste containing conductive particles and a polymer compound that cures at a temperature of 120 ° C. or higher and lower than 180 ° C. on the transparent electrode layer. Forming a first conductive layer in a pattern, and forming a second conductive layer in a pattern by providing a conductive paste having conductive particles without a polymer compound as a binder on the first conductive layer And a process.

  According to the present invention, since the current collecting electrode is formed in the first conductive layer forming step and the second conductive layer forming step described above, the transparent electrode layer has good conductivity and high adhesion. A collecting electrode can be provided.

  In the method for manufacturing a solar cell according to the present invention, in the step of forming the first conductive layer, the polymer compound contained in the conductive paste joins the conductive particles, and in the step of forming the second conductive layer, The conductive particles contained in the conductive paste include at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups is more than 99.0% by mass, and the 120 ° C. or higher and 180 ° C. The conductive particles are preferably bonded to each other at a temperature below.

  According to the present invention, both the first conductive layer and the second conductive layer can be formed at a temperature of 120 ° C. or higher and lower than 180 ° C. that does not cause thermal damage to the chalcopyrite compound semiconductor layer. As a result, the electromotive force photoelectrically converted by the calcopalite compound semiconductor layer without heat damage can be collected by the collecting electrode provided on the transparent electrode layer with good conductivity and high adhesion.

  According to the electrode structure of the present invention, the first conductive layer having good adhesion to the transparent electrode layer bears good adhesion with the transparent electrode layer, and the conductivity on the first conductive layer is good. The second conductive layer has conductivity as an electrode. As a result, the electrode structure composed of the first conductive layer and the second conductive layer can reduce the contact resistance with respect to the transparent electrode layer and can exhibit better conductivity.

  According to the solar cell of the present invention, the current collecting electrode that does not need to be formed at a high baking temperature of 180 ° C. or higher is applied as the current collecting electrode of the solar cell having the chalcopyrite compound semiconductor layer as the light absorbing layer. The thermal damage to the chalcopyrite compound semiconductor layer can be suppressed. As a result, the fill factor can be increased and a solar cell with high conversion efficiency can be obtained.

  According to the method for manufacturing a solar cell according to the present invention, the current collecting electrode is formed in the first conductive layer forming step and the second conductive layer forming step. The collector electrode can be provided with conductivity and high adhesion. Further, both the first conductive layer and the second conductive layer can be formed at a temperature of 120 ° C. or higher and lower than 180 ° C. that does not cause thermal damage to the chalcopyrite compound semiconductor layer. As a result, the electromotive force photoelectrically converted by the calcopalite compound semiconductor layer without heat damage can be collected by the collecting electrode provided on the transparent electrode layer with good conductivity and high adhesion. In addition, since a high firing temperature is not applied, the warpage of the solar cell can be reduced, and there is an effect of suppressing delamination due to stress.

It is a schematic cross section which shows an example of the solar cell provided with the electrode structure which concerns on this invention. It is a schematic cross section which shows another example of the solar cell provided with the electrode structure which concerns on this invention. It is explanatory drawing which shows an example of the manufacturing process of the solar cell which concerns on this invention. FIG. 4 is a perspective view of FIG. 3 is a cross-sectional observation photograph of a collecting electrode of Sample 2 obtained in Experimental Example 1. 4 is a graph showing i-V measurement results of the solar cell obtained in Experimental Example 1. It is a graph which shows the influence which drying temperature obtained in Experimental example 4 has on sheet resistance.

  Hereinafter, an electrode structure, a solar cell, and a manufacturing method thereof according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the form of the drawings and the following description as long as the technical features are included.

[Electrode structure]
The electrode structure 6 according to the present invention is provided with an electrode pattern structure having good adhesion to the transparent electrode layer 5 and good conductivity on the transparent electrode layer 5, for example, FIGS. 1 to 3. As shown in FIG. 2, the first conductive layer 6a is provided in a pattern on the transparent electrode layer 5, and the second conductive layer 6b is provided on the first conductive layer 6a. The first conductive layer 6a is a conductive layer having conductive particles and a polymer compound, and the second conductive layer 6b is a conductive layer having conductive particles without having a polymer compound as a binder. There is a special feature. Alternatively, the second conductive layer 6b includes at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups is more than 99.0% by mass. Whether the polymer compound is acting as a binder is determined by observing the cross section of the layer with a transmission electron microscope (TEM), and whether the polymer compound is present between the conductive particles. It can be judged by how. Further, whether or not the conductive particles are directly bonded can also be determined by observing the cross section of the layer with a transmission electron microscope (TEM).

  1-3 is an example in which the electrode structure 6 according to the present invention is applied as a collector electrode of a solar cell, but the electrode structure 6 according to the present invention is limited to application to a collector electrode of a solar cell. In addition, the present invention can be applied to current collecting electrodes other than solar cells. Moreover, you may apply not only to a collector electrode but to the other wiring electrode provided on the transparent electrode layer 5. FIG. In addition, when applied as a collecting electrode of a solar cell, it can be applied to various types of solar cells. For example, a single crystal silicon solar cell, a polycrystalline silicon solar cell, a thin film silicon solar cell, a HIT solar cell, a CIGS solar cell, CdTe The present invention is applicable to solar cells, multi-junction solar cells, dye-sensitized solar cells, organic thin-film solar cells, and the like. In particular, the treatment at a relatively low temperature (less than 180 ° C., preferably 150 ° C. or less) is preferably applied to a solar cell of a type that is desirable in terms of improved characteristics and stability, for example, a CIGS solar cell.

  Hereinafter, each component of the electrode structure 6 will be described. In addition, in the following, although the case where it applies to a CIGS type | system | group solar cell is demonstrated as an example, this invention is not limited only to a CIGS type | system | group solar cell.

(Transparent electrode layer)
The transparent electrode layer 5 is a base material on which a laminate of the first conductive layer 6a and the second conductive layer 6b constituting the electrode structure 6 according to the present invention is provided. The transparent electrode layer 5 is also called a so-called transparent conductive film, and is a transparent conductive metal oxide film. Examples include ITO (indium tin oxide), IZO (indium zinc oxide), ZnO doped with group III elements such as Al (Al-doped ZnO, B-doped ZnO, etc.), SnO ₂ doped with Sb or F, and the like. it can. In the CIGS solar cell, the transparent electrode layer 5 is formed on the buffer layer 4 described later by a sputtering method or a CVD method. Although the thickness is not specifically limited, Usually, it is 0.1-1 micrometer.

(First conductive layer)
The first conductive layer 6a is provided in a pattern on the transparent electrode layer 5, and constitutes the electrode structure 6 together with the second conductive layer 6b. The first conductive layer 6a has conductive particles (hereinafter referred to as “conductive particles A”) and a polymer compound, and the polymer compound serves as a binder to bond the conductive particles together. The first conductive layer 6a is provided on the transparent electrode layer 5 with good adhesion.

  The conductive particles A may be one kind of particle group having a single particle size distribution, two or more kinds of particle groups having the same particle size distribution, or two or more particles. One type of particle group having a diameter distribution may be used, or two or more types of particle groups having two or more particle size distributions may be used. In the first conductive layer 6a, one kind of particle group having a single particle size distribution is usually used. For example, a particle group having a particle size distribution with an average particle size in the range of 0.1 μm to 2 μm can be used. The “single particle size distribution” means a certain distribution (for example, normal distribution) of conductive particle groups having a certain average particle diameter, and the “particle group” means such a certain particle size distribution. It is the electroconductive particle A which has. Moreover, the average particle diameter of the conductive particles A is measured and calculated from, for example, an image taken with a scanning microscope.

  Examples of the conductive particles A include any one or more metal particles selected from gold or an alloy thereof, silver or an alloy thereof, and copper or an alloy thereof. Since these metal particles exhibit good conductivity, they are preferable as a constituent material of the first conductive layer 6a. The conductive particles A may be metal particles other than these, for example, palladium or an alloy thereof, platinum or an alloy thereof, aluminum or an alloy thereof, nickel or an alloy thereof.

  The polymer compound is not particularly limited as long as it can join the conductive particles. Usually, the binder resin contained in a general electrically conductive paste can be mentioned. Examples of such a polymer compound include a thermosetting resin and an ultraviolet curable resin. When the electrode structure 6 according to the present invention is used as, for example, a collector electrode of a solar cell, it is preferable to use a thermosetting resin that cures in a temperature range that does not reduce the conversion efficiency of the solar cell, and in particular, a CIGS solar cell. In this case, it is preferable to use a thermosetting resin that cures at a relatively low temperature (less than 180 ° C., preferably 150 ° C. or less). Specifically, an epoxy resin or the like can be used. Such a polymer compound usually acts so as to remain on the first conductive layer 6a after the conductive paste is applied and baked, and to bond the conductive particles A, and further adheres the transparent electrode layer 5 and the electrode structure 6 to each other. Also works.

  The first conductive layer 6a is usually formed by selectively applying a conductive paste pattern. Compared to the conventional method using a vapor deposition method or a sputtering method (when the mask substrate is used, it is also formed on the mask substrate), the material cost and the process cost (man-hour) are compared. It is much more advantageous.

  The conductive paste for forming the first conductive layer 6a is a paste-like fluid containing conductive particles A, a polymer compound, and a solvent. The solvent is a medium for making the conductive particles A into a paste, and acts to disperse the conductive particles A. Examples of the solvent include terpenes such as α-terpineol; alcohols such as isopropyl alcohol; glycols such as butyl carbitol and butyl carbitol acetate and esters thereof; hydrocarbons such as toluene and cyclohexanone; ketones such as methyl ethyl ketone; be able to. This solvent may contain a dispersant for dispersing the conductive particles A without aggregating them. Examples of the dispersant include a surfactant. Further, other additives may be included as long as they do not depart from the spirit of the present invention.

  The formed first conductive layer 6a has high adhesion to the transparent electrode layer 5 below it, and also has high adhesion to the second conductive layer 6b above it, so that the electrode structure 6 adheres to the transparent electrode layer 5 It preferably functions as a layer that plays a role of enhancing the property.

  The thickness of the first conductive layer 6a is usually in the range of 1 μm or more and 100 μm or less, and in the range of 10 μm or more and 50 μm or less from the viewpoint of resistance value and pattern accuracy. The first conductive layer 6a within this range has good adhesion to the transparent electrode layer 5, and excellent adhesion to the second conductive layer 6b formed thereon. As a result, the adhesion of the electrode structure 6 can be improved, and the contact resistance with the transparent electrode layer 5 can be reduced. If the thickness of the 1st conductive layer 6a is less than 1 micrometer, it may be too thin and adhesiveness with the transparent electrode layer 5 may be inadequate. On the other hand, if the thickness of the first conductive layer 6a exceeds 100 μm, it is too thick, resulting in an increase in cost and pattern printing to a line width of 100 μm or less from the relationship between the film thickness and the line width (aspect ratio). It becomes difficult. In the screen printing method, the ratio between the film thickness and the line width is 1: 1 at the maximum.

(Second conductive layer)
The second conductive layer 6b is provided on the first conductive layer 6a and constitutes the electrode structure 6 together with the first conductive layer 6a. The second conductive layer 6b does not have a polymer compound as a binder and has conductive particles (hereinafter referred to as “conductive particles B”). Here, “without a polymer compound as a binder” means both a case where no polymer compound acting as a binder is contained and a case where a polymer compound is not substantially contained, and will be described in detail later. Alternatively, the second conductive layer 6b includes at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups is greater than 99.0% by mass.

  The conductive particles B may be one kind of particle group having a single particle size distribution, two or more kinds of particle groups having the same particle size distribution, or two or more particles. One type of particle group having a diameter distribution may be used, or two or more types of particle groups having two or more particle size distributions may be used. In the second conductive layer 6b, one type or two or more types of particles having two or more particle size distributions are preferably used. For example, one particle group is a nanoparticle group (hereinafter, referred to as “conductive particle B1”) having a particle size distribution of 100 μm or less and a certain particle size distribution, and the other particle group is more than the conductive particle B1. Is a group of particles having a larger particle size (hereinafter referred to as “conductive particles B2”). The conductive particle B2 means a particle having a particle size larger than that of the conductive particle B1, and includes a plurality of metal particle groups (B2, B2 ′, B2 ″,...) Having different average particle sizes. As in the case of the first conductive layer 6a, the “single particle size distribution” means a certain distribution (for example, a normal distribution) of conductive particle groups having a certain average particle size. The “particle group” refers to the conductive particles B having such a constant particle size distribution. In addition, the average particle diameter of the conductive particles B is calculated by measuring from, for example, an image taken with a scanning microscope.

  As the electroconductive particle B, any 1 type, or 2 or more types of metal particles chosen from gold or its alloy, silver or its alloy, and copper or its alloy can be mentioned. Since these metal particles exhibit good conductivity, they are preferable as a constituent material of the first conductive layer 6b. In addition, metal particles other than these may be sufficient, for example, the metal particle which consists of palladium or its alloy, platinum or its alloy, aluminum or its alloy, nickel or its alloy may be sufficient.

  The difference between the constituent materials of the conductive particles B1 and the conductive particles B2 is not particularly limited. If the same metal type is used, the second conductive layer 6b is constituted by a single metal type, and there is an advantage that there is no complication such as composition management, and further, resistance increases when different metal types are blended. There is an advantage that the problem of fear can be avoided. On the other hand, if different metal species are used, the function of one metal species and the effect of the other metal species can be separated to provide functional characteristics. Usually, it is preferable to form the conductive particles B1 and the conductive particles B2 with the same kind of metal.

  Further, if the second conductive layer 6b is made of the same kind of material as that of the conductive particles A constituting the first conductive layer 6a, the mutual bond can be improved, so that the adhesion is improved and the contact resistance is increased. It is more preferable from the viewpoint of reduction.

  The conductive particles B1 are a group of metal nanoparticles having a particle size of 100 nm or less, and the average particle size of the particle group is in the range of 5 to 50 nm. The conductive particles B1 act so as to enhance the contact between the particles by filling the spaces between the conductive particles B2 having a larger average particle diameter than the conductive particles B1. Further, the surface of the first conductive layer 6a composed of the conductive particles A and the polymer compound is also in close contact with each other so as to improve the contact between the second conductive layer 6b and the first conductive layer 6a. Works. In addition, what is called a nanoparticle with a particle size of 100 nm or less can use a commercially available thing. The conductive particles B1 may be a mixture of a plurality of fine particle groups (B1, B1 ′, B1 ″,...) Having different average particle diameters as long as the particle diameter is 100 nm or less. For example, the particle diameter is measured and calculated from an image taken with a scanning electron microscope.

  The conductive particles B2 are a group of metal particles having an average particle size larger than that of the conductive particles B1. Specifically, those having an average particle diameter in the range of 0.1 to 2 μm can be used. When the average particle size of the conductive particles B2 is less than 0.1 μm, the material cost increases, and the paste viscosity tends to be too low to make it difficult to perform pattern printing by screen printing. On the other hand, if the average particle diameter exceeds 2 μm, voids may appear in the second conductive layer 6b, and the electrical resistance tends to increase or the film strength tends to be weak. The conductive particle B2 may be a mixture of a plurality of particle groups (B2, B2 ', ...) having different average particle diameters.

  The second conductive layer 6b is formed by selectively applying a conductive paste. Compared to the conventional method using a vapor deposition method or a sputtering method (when the mask substrate is used, it is also formed on the mask substrate), the material cost and the process cost (man-hour) are compared. It is much more advantageous.

  The conductive paste is a paste-like fluid containing, for example, conductive particles B having at least conductive particles B1 and conductive particles B2 and a solvent. The solvent is a medium for making the conductive particles B into a paste, and acts to disperse the conductive particles B. Examples of the solvent include terpenes such as α-terpineol; alcohols such as isopropyl alcohol; glycols such as butyl carbitol and butyl carbitol acetate and esters thereof; hydrocarbons such as toluene and cyclohexanone; ketones such as methyl ethyl ketone; be able to. This solvent may contain a dispersant for dispersing the conductive particles B (the conductive particles B1 and the conductive particles B2) without aggregating them. Examples of the dispersant include a surfactant. Further, other additives may be included as long as they do not depart from the spirit of the present invention.

  The conductive paste does not substantially contain a polymer compound as a binder. The polymer compound as a binder is a compound that acts as a binder contained in a general conductive paste, and refers to a resin component such as a thermosetting resin or an ultraviolet curable resin. Such a polymer compound usually acts to bond the conductive particles B by remaining in the conductive layer after applying and baking the conductive paste. However, firing of a conductive paste containing a polymer compound as a binder usually requires a temperature of 180 ° C. or higher to 200 ° C. or higher, and if it cannot be fired at such a temperature, the electrical resistance of the conductive layer obtained is The contact resistance between the first conductive layer 6a and the lower first conductive layer 6a is not increased, and the electrode structure 6 becomes unsuitable.

  In the present invention, the conductive paste is substantially free of a polymer compound as a binder, and instead contains the metal particles (conductive particles B1 and conductive particles B2). Even in the case where the temperature cannot be raised to higher than or equal to 200 ° C. or higher, the second conductive layer 6b made of metal particles can be formed. In particular, the presence of the conductive particles B1 that fill the gaps between the conductive particles B2 and bond the conductive particles B2, can provide the second conductive layer 6b having good electrical resistance, and the lower first conductive layer. The contact resistance with 6a can be reduced and the adhesion can be improved.

  The polymer compound as a binder is a resin component responsible for a binder function for bonding particles, and the term “substantially does not contain” the polymer compound means that the meaning of the present invention is not included at all. When it is included in the range that does not inhibit, it means both. Here, “does not impede the gist of the present invention” means that the second conductive layer 6b has good electrical resistance and good contact even when the polymer compound is detected from the second conductive layer 6b. It shows resistance and good adhesion. As will be described in an experimental example to be described later, the second conductive layer 6b obtained by drying or baking after applying the conductive paste has a polymer compound in the second conductive layer 6b of 0.1% by mass or less. Although it was a favorable characteristic, the characteristic fell at 1 mass% or more. As a result, the polymer compound contained in at least the second conductive layer 6b is preferably less than 1% by mass, more preferably 0.3% by mass or less, and particularly preferably 0.1% by mass or less. preferable. In other words, the content of the conductive particle component contained in the second conductive layer 6b is preferably more than 99.0% by mass, more preferably 99.7% by mass or more, and 99.9% by mass or more. It is particularly preferred that In the present invention, such a range means “substantially free of a polymer compound as a binder”.

  The conductive paste for forming the second conductive layer 6b does not contain a polymer compound as a binder, but may contain any polymer compound that does not act as a binder. However, actually, even if the polymer compound does not act as a binder, the formed second conductive layer 6b is contained within a range showing good electrical resistance, good contact resistance, and good adhesion. For example, when a conductive polymer compound is included, a certain amount of content will be allowed. However, as described above, it is substantially the same as the “substantially free” range. Degree.

  The second conductive layer 6b contains substantially no polymer compound because the content of the conductive particle components (conductive particles B1 and conductive particles B2) is more than 99.0% by mass. And since the 2nd conductive layer 6b contains the electroconductive particle B1 of the said particle size, even if it does not contain the high molecular compound as a binder, the electroconductive particle B1 whose particle size is smaller than the electroconductive particle B2 is the electroconductivity. The conductive particles B2 having a particle size larger than that of the conductive particles B1 to serve as a binder for the conductive particles B2, thereby improving the bonding between the conductive particles B2 and improving the electrical coupling. it can.

  The formation of the second conductive layer 6b includes substantially no high molecular compound as a binder, and a conductive paste containing the conductive particles B including the conductive particles B1 and the conductive particles B2 is used as the first conductive layer 6a. Apply on top. The application on the first conductive layer 6a can be performed by pattern printing means such as screen printing of the conductive paste. Such selective application is advantageous in terms of cost because it saves expensive materials.

  After applying the conductive paste, the temperature environment is set to remove the solvent contained in the conductive paste. Such a temperature environment varies depending on the configuration of the conductive particles B and the type of solvent, but is usually in the range of 120 ° C. or more and 200 or less. As shown in an experimental example to be described later, for example, in the case of the electrode structure 6 of a CIGS solar cell, when a temperature of 180 ° C. or higher is applied during the formation of the second conductive layer 6b, the chalcopyrite compound semiconductor layer is heated. Since the conversion efficiency may decrease due to damage, the treatment is performed at a temperature of less than 180 ° C., preferably 150 ° C. or less.

  The thickness of the second conductive layer 6b is usually in the range of 1 μm or more and 100 μm or less, and in the range of 10 μm or more and 50 μm or less from the viewpoint of the resistance value and pattern accuracy as the electrode structure 6. If the thickness of the second conductive layer 6b is less than 1 μm, it is too thin and the resistance value becomes high, which is not suitable for the electrode structure 6. On the other hand, if the thickness of the second conductive layer 6b exceeds 100 μm, not only is the thickness too high, the cost increases, but also the line width is patterned to 100 μm or less due to the relationship between the film thickness and the line width (aspect ratio). It becomes difficult to print. In the screen printing method, the ratio between the film thickness and the line width is 1: 1 at the maximum.

As described above, the electrode structure 6 according to the present invention includes the second conductive layer 6b having a low electric resistance, and includes the first conductive layer 6a between the second conductive layer 6b and the transparent electrode layer 5. Therefore, it is possible to reduce the contact resistance in a mode in which the adhesion of the second conductive layer 6b is enhanced. In addition, as shown in an experimental example to be described later, a result that the resistivity of the collecting electrode is 10 ⁻⁵ Ωcm or less is also obtained.

[Solar cell and manufacturing method thereof]
As shown in FIGS. 1 and 2, the solar cell 10 according to the present invention includes at least the electrode structure 6 and the chalcopyrite compound semiconductor layer 5 according to the present invention described above. In the example of FIG. 1, at least the back electrode layer 2, the chalcopyrite compound semiconductor layer 3, the buffer layer 4, the transparent electrode layer 5, and the collecting electrode 6 (same as the above “electrode structure 6”) on the substrate 1. .) Is the solar cell 10 stacked in that order. Then, the current collecting electrode 6 is provided on the transparent electrode layer 5 in a pattern, and includes a first conductive layer 6a having conductive particles A and a polymer compound that cures at 120 ° C. or higher and lower than 180 ° C., and the first conductive layer 6a. And a second conductive layer 6b having conductive particles B without having a polymer compound as a binder provided on the layer 6a. The example of FIG. 2 is a solar cell (reference numeral 10 ′) in which a doped layer 7 is provided between the back electrode layer 2 and the chalcopyrite compound semiconductor layer 3 in the solar cell 10 of FIG.

  In the method for manufacturing such solar cells 10 and 10 ′, at least a back electrode layer 2, a chalcopyrite compound semiconductor layer 3, a buffer layer 4, a transparent electrode layer 5, and a collecting electrode 6 are provided in this order on a substrate 1. In the method, the first conductive layer is formed by using the conductive paste containing the conductive particles A and the polymer compound that cures at a temperature of 120 ° C. or higher and lower than 180 ° C. on the transparent electrode layer 5. Forming a second conductive layer 6b in a pattern by providing a conductive paste having conductive particles B without a polymer compound as a binder on the first conductive layer 6a. And a step of performing.

  Hereinafter, the structure of the solar cell shown in FIG.1 and FIG.2 is demonstrated in order of the manufacturing process of the solar cell 20 shown in FIG.

(Formation and division of back electrode layer)
First, as shown in FIG. 3A, a strip-shaped back electrode layer 2 is formed on a substrate 1. This step includes a step of preparing the substrate 1, a step of forming the back electrode layer 2 on the prepared substrate 1, and a step of processing the back electrode layer 2 into a strip shape.

  As the substrate 1, a glass substrate is preferably used. The glass substrate may be a soda lime glass substrate or an alkali-free glass substrate, and is not particularly limited. Any glass substrate is preferably used because it has both insulating properties and heat resistance compared to a metal substrate or a resin substrate.

  The back electrode layer 2 is provided on the prepared substrate 1. As the back electrode layer 2, a metal layer made of molybdenum or the like, or a transparent conductive layer made of ITO (indium tin oxide) or the like can be preferably applied. The back electrode layer 2 can be formed by a vacuum deposition method, a sputtering method, a CVD method, or the like, and the thickness is usually about 0.1 to 1 μm.

  The strip-shaped back electrode layer 2 can be formed by removing a part of the deposited back electrode layer 2 in a stripe shape and dividing the back electrode layer 2 into a plurality of strips. As such a dividing means, it is preferable to use a laser scribing method.

(Formation of compound semiconductor layer and buffer layer)
Next, as shown in FIG. 3B, a chalcopyrite compound semiconductor layer 3 is formed on the plurality of divided back electrode layers 2 (including portions removed in a stripe shape) so as to cover the whole. Thereafter, the buffer layer 4 is formed on the chalcopyrite compound semiconductor layer 3. The chalcopyrite compound semiconductor layer 3 is formed on the back electrode layer 2 (in the case where the doped layer 7 is provided, see FIG. 2). The chalcopyrite compound semiconductor layer 3 is a so-called light absorption layer, and is a layer made of a semiconductor containing a group Ib element, a group IIIb element, and a group VIb element. Specifically, a chalcopyrite compound semiconductor layer 3 containing Cu, one or both of In and Ga, and one or both of Se and S can be preferably exemplified. As an example, CuInSe ₂ , CuIn (Se, S) ₂ , Cu (In, Ga) Se ₂ , or Cu (In, Ga) (Se, S) ₂ can be exemplified.

Various methods can be applied as a method for forming the chalcopyrite compound semiconductor layer 3. For example, in the case of Cu (In, Ga) Se ₂ , the substrate temperature is set to, for example, about 300 ° C., and Se, In, Ga is deposited by, for example, ¹⁰ -4 ^{to 10} -5 coevaporation while controlling the pressure range of about Pa, followed by raising the substrate temperature, for example, about 600 ° C., Se and Cu, for example, ¹⁰ -4 ^{to 10 -5} It is possible to deposit In, Ga and Se under the same pressure control while depositing while controlling in the pressure range of about Pa and further maintaining the substrate temperature at about 600 ° C., for example. Thus, the chalcopyrite compound semiconductor layer 3 made of Cu (In, Ga) Se ₂ can be formed. The chalcopyrite compound semiconductor layer 3 can be formed by sputtering in addition to the above co-evaporation method while controlling Cu, In, and Ga to a pressure range of about 10 ⁻³ to 10 ⁻⁵ Pa, for example. After the deposition, a method of converting the metal layer into selenide by setting the substrate temperature to, for example, about 600 ° C. in an atmosphere containing Se is also possible. The thickness of the chalcopyrite compound semiconductor layer 3 is usually 1 to 2 μm.

  The buffer layer 4 is a semiconductor layer provided on the chalcopyrite compound semiconductor layer 3 in order to form a pn junction. Examples of the buffer layer 4 include a layer made of a compound containing CdS or Zn. Examples of the compound containing Zn include Zn (O, S) and ZnMgO. The buffer layer 4 can be formed by a solution growth (CBD) method, a sputtering method or a CVD method, and its thickness is not particularly limited, but is usually about 0.01 to 0.1 μm.

  Further, a second semiconductor layer may be further stacked as a part of the buffer layer 4. As such a second semiconductor layer, a layer made of ZnO or a layer made of a material containing ZnO can be given. This layer can also be formed by sputtering or CVD, and its thickness is not particularly limited, but is usually about 0.01 to 1 μm.

(Split)
Next, as shown in FIG. 3C, the chalcopyrite compound semiconductor layer 3 and the buffer layer 4 are divided into a plurality of strips. The striped removal position at this time is preferably a position adjacent to the removal position performed in FIG. 3A from the viewpoint of avoiding a useless area. As a method of dividing the chalcopyrite compound semiconductor layer 3 and the buffer layer 4 into a plurality of strips, it is preferable to use a mechanical scribing method using a metal needle, unlike the method performed in FIG.

(Formation and division of transparent electrode layer)
Next, as shown in FIG. 3D, a transparent electrode layer 5 is formed on the buffer layer 4 divided into a plurality of parts (including a portion removed in a stripe shape) so as to cover the whole, and then The chalcopyrite compound semiconductor layer 3, the buffer layer 4, and the transparent electrode layer 5 are divided into a plurality of strips. Since the transparent electrode layer 5 is as described in detail in the section of “Electrode Structure 6”, the description thereof is omitted. The striped removal position performed in the division processing is preferably a position adjacent to the removal position performed in FIG. 3C from the viewpoint of avoiding a useless area. As a method of dividing the chalcopyrite compound semiconductor layer 3, the buffer layer 4, and the transparent electrode layer 5 into a plurality of strips, a mechanical scribing method using a metal needle is used as in the method performed in FIG. By such division processing, the respective solar battery cells 9, 9, 9 are connected in series by the back electrode layer 2 and the transparent electrode layer 5.

(Formation of current collecting electrode)
Finally, as shown in FIGS. 3E and 4, the collector electrode 6 (also referred to as a grid electrode) is formed on the transparent electrode layer 5 for the purpose of reducing the resistance value and facilitating current flow. Same as electrode structure 6 "). The collecting electrode 6 is a line extending in a direction perpendicular to the processing line 8 in the scribing process, and a plurality of the collecting electrodes 6 are formed with a line width of 0.1 to 0.5 mm and an interval of 1 to 20 mm. The configuration of the collecting electrode 6 (the first conductive layer 6a and the second conductive layer 6b) is the same as described in the column of the electrode structure 6, and the description thereof is omitted. Thus, an integrated solar cell 20 in which the solar cells 9 are connected in series can be manufactured.

(Other)
The solar cell according to the present invention may be provided with the doped layer 7 shown in FIG. The doped layer 7 is a layer provided for doping the chalcopyrite compound semiconductor layer 3 with a group Ia element. The group Ia element is an element such as Li, Na, and K. When these elements diffuse and are doped into the chalcopyrite compound semiconductor layer 3, the conversion efficiency after the solar cell 10 is configured increases. Examples of the doped layer 7 include an oxide layer of Na such as soda lime glass and a compound layer such as NaF and Na ₂ S, and can be formed by a vapor deposition method, a sputtering method, or a CVD method. . The thickness of this dope layer is usually about 0.005 to 0.2 μm.

  When a soda lime glass base material is used as the base material 1, Na in the soda lime glass base material diffuses and is contained in the chalcopyrite compound semiconductor layer 3, so the dope layer 7 is not provided. Also good. On the other hand, in order to prevent indefinite amount of Na from diffusing from the soda lime glass base material into the chalcopyrite compound semiconductor layer 3, a blocking layer for blocking the diffusion of Na is provided between the soda lime glass base material and the chalcopyrite compound semiconductor layer 3. You may provide in arbitrary positions between. The blocking layer may be provided between the soda lime glass substrate and the back electrode layer 2 or between the back electrode layer 2 and the chalcopyrite compound semiconductor layer 3. Examples of the barrier layer include oxides or nitrides such as aluminum, silicon, titanium, and zirconium, or layers made of metals such as titanium, zirconium, tantalum, tungsten, and hafnium. It can be formed by a CVD method. When the blocking layer is provided between the back electrode layer 2 and the chalcopyrite compound semiconductor layer 3, the blocking layer is preferably a layer made of metal in order to ensure conductivity. The thickness of this blocking layer is usually about 0.05 to 1 μm.

  As described above, according to the solar cell of the present invention, the solar cell using the chalcopyrite compound semiconductor layer 3 as the light absorption layer as the collector electrode 6 that does not need to be formed at a high firing temperature of 180 ° C. or higher. Therefore, thermal damage to the chalcopyrite compound semiconductor layer 3 can be suppressed. In addition, since the resistance of the collecting electrode 6 can be reduced and the contact resistance with the transparent electrode layer 5 can be reduced, the fill factor can be increased and a solar cell with high conversion efficiency can be obtained. Can do.

  Moreover, according to the manufacturing method of the solar cell which concerns on this invention, in the solar cell which used the chalcopyrite compound semiconductor layer 3 as the light absorption layer, formation of the current collection electrode 6 is formed in the formation process of the above-mentioned 1st conductive layer 6a. And the formation process of the second conductive layer 6b, the current collecting electrode 6 can be provided on the transparent electrode layer 5 with good conductivity and high adhesion. In addition, both the first conductive layer 6a and the second conductive layer 6b can be formed at a temperature of 120 ° C. or higher and lower than 180 ° C. that does not cause thermal damage to the chalcopyrite compound semiconductor layer 3. As a result, the electromotive force photoelectrically converted by the calcopalite compound semiconductor layer 3 without heat damage can be collected by the collecting electrode 6 provided on the transparent electrode layer 5 with good conductivity and high adhesion. In addition, since a high firing temperature is not applied, the warpage of the solar cell can be reduced, and there is an effect of suppressing delamination due to stress.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples. The following experimental example is an example, and the present invention is not limited to the following experimental example.

[Experimental Example 1]
This Experimental Example 1 is an experimental example in which the structural form of the electrode structure 6 provided on the transparent electrode layer 5 was examined. A 10 cm square soda lime glass substrate was prepared as the base material 1, the glass substrate was washed and dried, and then a Mo layer was formed as the back electrode layer 2 by a DC sputtering method. The thickness of the Mo layer may be 0.1 to 1 μm, but here it is 0.8 μm. Subsequently, a copper, indium, gallium and selenium (CIGS) based semiconductor layer 3 which is a p-type semiconductor was formed on the back electrode layer 2 by a co-evaporation method (commonly referred to as a three-stage method). The thickness of the CIGS semiconductor layer 3 may be 1 to 2 μm, but is 2 μm here. Subsequently, a CdS layer, which is an n-type semiconductor, was formed as a buffer layer 4 on the CIGS semiconductor layer 3 by a solution growth method (CBD method). The solution used for the solution growth method is an aqueous solution containing cadmium sulfate, thiourea, and ammonia. The substrate is immersed while this solution is stirred and held at a solution temperature of 70 ° C. for 15 minutes. The film was formed with a thickness of 80 nm. Subsequently, a zinc oxide film was formed as the transparent electrode layer 5 by an RF sputtering method. The zinc oxide film was formed by laminating i-ZnO, which is an intrinsic insulator (no dopant), and ZnO: Al doped with Al. The film thickness of i-ZnO is suitably 0.2 μm or less, and is 0.1 μm here. The film thickness of ZnO: Al may be 0.3-1 μm, but here it is 0.3 μm.

  Subsequently, the collector electrode 6 was produced on the transparent electrode layer 5 in the following two forms of Samples 1 and 2. <Sample 1>: A collector electrode in which an Al film having a thickness of 1 μm is deposited on the transparent electrode layer 5 through a metal mask, <Sample 2>: the first conductive layer 6a is formed on the transparent electrode layer 5, and The collector electrode 6 in which the second conductive layer 6b is formed on the first conductive layer 6a is used. Among these, in the sample 2, the first conductive layer 6a and the second conductive layer 6b are coated with the first conductive paste and the second conductive paste having the following composition by the screen printing method, respectively, and 30 in an oven at 120 ° C. It was formed by sequentially drying and baking for a minute. Although the thickness of the first conductive layer 6a and the second conductive layer 6b is 10 μm, it can be changed to 1 to 100 μm (preferably 20 to 80 μm) by selecting the thickness of the screen plate.

  Thus, a laminated structure of the solar cell having the form shown in FIG. 1 was produced. In Experimental Example 1, in order to evaluate the basic performance of the solar cell, the basic laminated structure shown in FIG. 1 was used instead of the embodiment shown in FIG.

(Conductive paste)
The first conductive paste used for forming the first conductive layer 6a is a conductive paste (trade name: ECM-100 AF4500, manufactured by Taiyo Ink Manufacturing Co., Ltd.) containing Ag particles and a polymer compound. The polymer compound in the first conductive paste is a thermoplastic resin, and the content thereof is 5 to 10% by mass. The Ag particles contained in the first conductive paste are a group of particles having a single particle size distribution and an average particle size of 1 to 2 μm, and the content thereof is 80% by mass. The balance is a solvent (diethylene glycol monoethyl ether acetate). On the other hand, the second conductive paste used for forming the second conductive layer 6b is a conductive paste containing Ag nanoparticles (manufactured by Mitsuboshi Belting Co., Ltd., trade name: MDot-SLP / H). The Ag nanoparticles contained in the second conductive paste have a group of particles having an average particle size of 10 to 30 nm (here, conductive particles B1 having an average particle size of about 20 nm) and an average particle size of about 1 μm particle group (conductive particles B2) is mixed. Conductive particle B1: Conductive particle B2 is 1: 2 to 2: 1 (mass ratio) (here, about 1: 1). The content of Ag nanoparticles in the second conductive paste is 90 to 95% by mass, the remainder is a solvent (α-terpineol), and does not contain a polymer compound as a binder.

(Evaluation)
The cross section of the current collecting electrode 6 of the obtained sample 2 was observed at an acceleration voltage of 3.0 kV using an electron microscope (manufactured by Hitachi High-Technologies Corporation, model number: SU8000). The results are shown in FIG. It was confirmed that both the first conductive layer 6a and the second conductive layer 6b were formed with a thickness of about 10 μm.

  In the obtained solar cell, the tape peeling test of the current collecting electrode 6 of the formed sample 1 and sample 2 was performed. For tape peeling, a tape having a width of 8 mm (manufactured by Nichiban Co., Ltd., trade name: CT24) is attached to each collector electrode, one end of the tape is folded back 180 ° and pulled up at a speed of about 300 mm / second to collect the collector electrode 6 The presence or absence of peeling was confirmed. As a result, peeling of the collecting electrode 6 of Sample 1 and Sample 2 was not observed.

The i-V characteristic of the obtained solar cell was evaluated. The i-V characteristic was measured by dividing the test cell into a plurality of test cells (0.5 cm ² ) by a mechanical scribe method, and measuring the test cell with a solar simulator (AM1.5). The results are shown in Table 1 and FIG. As shown in Table 1 and FIG. 6, in the comparison between the current collecting electrode (Al vapor deposition film) of sample 1 and the current collecting electrode of sample 2 (first conductive layer 6a + second conductive layer 6b), in particular, the fill factor FF Increased from 76.4% to 78.1%, resulting in an increase in conversion efficiency. The fill factor FF (Fill Factor) is a parameter representing the good current-voltage characteristic curve (i-V curve) as a solar cell, and is represented by [maximum output / (open circuit voltage × short circuit current)]. . When this value is large, the internal loss of the solar cell is small and the performance is excellent.

In Sample 2, the contact resistance between the first conductive layer 6a and the second conductive layer 6b was evaluated by a direct current four-terminal method, and a good result of 1 mΩ · cm ² or less was obtained.

[Experiment 2]
In Sample 2 of Experimental Example 1, only the second conductive layer 6b was formed directly on the transparent electrode layer 5 with the second conductive paste without forming the first conductive layer 6a. Other than that was carried out similarly to the sample 2 of Experimental example 1, and produced the solar cell which concerns on Experimental example 2. FIG. However, in this solar cell, the second conductive layer 6b was easily peeled off simply by applying air blow to the second conductive layer 6b.

[Experiment 3]
In Experimental Example 3, the influence of the change in the content of the polymer compound in the second conductive paste forming the second conductive layer 6b on the sheet resistance of the second conductive layer 6b was examined. A 3 cm square soda lime glass substrate was washed and dried, and a conductive paste having the following composition was printed on the glass substrate with a 2.8 cm square solid pattern by screen printing. The screen plate had a line number of 325 and an emulsion thickness of 20 μm. After printing, it was dried in a clean oven set at 120 ° C. for 30 minutes to form only the second conductive layer 6b on the glass substrate.

(Conductive paste)
The conductive paste is a predetermined amount (0.1% by mass, 0.3% by mass, 1.0% by mass) in a conductive paste containing Ag nanoparticles (trade name: MDot-SLP / H, manufactured by Mitsuboshi Belting Co., Ltd.). Epoxy resin (Japan Epoxy Resin Co., Ltd., trade name: Grade 826) and a curing agent (Japan Epoxy Resin Co., Ltd., trade name: Dicyandiamide, Grade DICY 7) are added. In addition, the hardening | curing agent mixed 5 mass parts with respect to 100 mass parts of epoxy resins. Ag nanoparticles include a group of fine particles having an average particle diameter of 10 to 30 nm (here, conductive particles B1 having an average particle diameter of about 20 nm) and particles having an average particle diameter of about 1 μm (conductive particles B2). )). Conductive particle B1: Conductive particle B2 is 1: 2 to 2: 1 (mass ratio) (here, about 1: 1). The content of Ag particles in the conductive paste is 90 to 95% by mass, the contents of the epoxy resin and the curing agent are as described above, and the balance is the solvent (α-terpineol). The conductive paste containing Ag nanoparticles and the epoxy resin were kneaded by stirring with a self-revolving stirrer for 1 minute.

(Evaluation)
The sheet resistance of the printed conductive layer was measured by Loresta-EP, and the results are shown in Table 2. Compared with the conductive layer formed with the conductive paste used in Sample 2 of Experimental Example 1 to which no epoxy resin was added, the conductive layer formed with the conductive paste to which 1% by mass of epoxy resin was added had a resistance value of 4 times or more. It was unsuitable as a current collecting electrode. On the other hand, a conductive layer formed of a conductive paste to which 0.3% by mass of epoxy resin is added can suppress an increase in resistance value to about 60% (about 50% in specific resistance), and 0.1% by mass of epoxy resin. The conductive layer formed of the added conductive paste could suppress an increase in resistance value to about 10% (about 10% in specific resistance), and there was no problem. Therefore, it can be judged that the content of the epoxy resin blended in the second conductive paste is less than 1% by mass, preferably 0.3% by mass or less, particularly preferably 0.1% by mass or less.

[Experimental Example 4]
In Experimental Example 4, the influence of the drying temperature of the conductive paste on the resistance of the conductive layer was examined. A 3 cm square soda lime glass substrate was washed and dried, and a conductive paste having the following composition was printed on the glass substrate with a 2.8 cm square solid pattern by screen printing. The screen plate had a line number of 325 and an emulsion thickness of 20 μm. After printing, a conductive layer was formed by drying for 30 minutes in a clean oven set to 100 ° C., 120 ° C., and 150 ° C., respectively.

(Conductive paste)
The conductive paste is a conductive paste containing Ag nanoparticles (manufactured by Mitsuboshi Belting Co., Ltd., trade name: MDot-SLP / H). The Ag particles contained in the conductive paste are a group of fine particles having an average particle size in the range of 10 to 30 nm (here, conductive particles B1 having an average particle size of about 20 nm are used) and particles having an average particle size of about 1 μm ( It is a mixture of conductive particles B2). Conductive particle B1: Conductive particle B2 is 1: 2 to 2: 1 (mass ratio) (here, about 1: 1). The content of Ag nanoparticles in the conductive paste is 90 to 95% by mass, the balance is a solvent (α-terpineol), and no binder resin is contained.

(Evaluation)
The sheet resistance of the printed conductive layer was measured by Loresta-EP, and the results are shown in Table 3 and FIG. When the drying temperature was 100 ° C., the resistance value did not decrease even after 40 minutes. On the other hand, when the drying temperature was 120 ° C., the resistance value settled to a low value in 20 minutes, and at 150 ° C., the resistance value settled to a low value in 10 minutes. Further, the sheet resistance value after 30 minutes is 4.8 mΩ / □ at 120 ° C. and 3.9 mΩ / □ at 150 ° C. When converted into resistivity, it is 9.6 μΩcm at 120 ° C. and 7.50 at 150 ° C. It was 8 μΩcm.

  In addition, when the sheet resistance value of the collector electrode of the Al vapor deposition film (thickness: 1 μm) was measured as in Sample 1 of Experimental Example 1, the value was 20 mΩ / □. The sheet resistance value of the obtained Ag paste layer could be reduced to 1/4 to 1/5 thereof.

[Experimental Example 5]
In Experimental Example 5, heat treatment was performed after the collector electrode was formed, and the influence of the applied temperature on the chalcopyrite compound semiconductor layer was examined. Since this experiment examines the influence of the temperature of the chalcopyrite compound semiconductor layer, a solar cell of Sample 1 (Al vapor deposition film, thickness 1 μm) of Experimental Example 1 was used for the experiment.

(Evaluation)
The obtained solar cell was cut into a plurality of test cells (0.5 cm ² ) by a mechanical scribing method to produce test cells, and the characteristics before and after heating were measured with a solar simulator (AM1.5). Heating was performed for 30 minutes in a clean oven heated to 120 ° C., 150 ° C., 180 ° C., and 200 ° C., respectively. The results are shown in Table 4. As shown in Table 4, as the heating temperature increased, the open circuit voltage decreased greatly and the conversion efficiency decreased. Particularly at 180 ° C. or higher, the conversion efficiency was less than 15%. This result indicates that application of a high temperature should be avoided for the chalcopyrite compound semiconductor layer.

[Experimental Example 6]
In Experimental Example 6, heat treatment was performed before the transparent electrode layer 5 and the collecting electrode 6 were formed, and the influence of the applied temperature on the chalcopyrite compound semiconductor layer 3 was examined. In the experiment, the solar cell of Sample 1 (Al deposited film, thickness 1 μm) of Experimental Example 1 was used as in Experimental Example 5 above.

(Evaluation)
About two samples before forming the transparent electrode layer 5 and the current collection electrode 6, it heat-processed by putting in the clean oven heated at 200 degreeC for 30 minutes. As a comparison, a sample not subjected to heat treatment (two samples) was also prepared. A transparent electrode layer and an Al vapor deposition film were formed on these samples in the same manner as in Sample 1 of Experimental Example 1 to produce solar cells.

The obtained solar cell was cut into a plurality of test cells (0.5 cm ² ) by a mechanical scribing method to produce test cells, and the characteristics of presence or absence of heating were measured with a solar simulator (AM1.5). The results are shown in Table 5. Even when heated after forming the CdS-n type buffer layer (before forming the transparent electrode), the open circuit voltage was lowered and the conversion efficiency was lowered as in the case of heating after the completion of the test cell.

[Experimental Example 7]
In Experimental Example 7, the effect of heat treatment on the characteristics of the solar cell when the material of the transparent electrode layer 5 was replaced with ITO was examined. In Experimental Example 6, i-ZnO (thickness 0.1 μm) was formed as the transparent electrode layer 5 by RF sputtering, and ITO (thickness 0.5 μm) was formed by DC sputtering. Same as Example 6.

(Evaluation)
About two samples which changed the material of the transparent electrode layer 5, it put into the clean oven heated at 200 degreeC for 30 minutes, and heat-processed. The obtained solar cell was cut into a plurality of test cells (0.5 cm ² ) by a mechanical scribing method to produce test cells, and the characteristics of presence or absence of heating were measured with a solar simulator (AM1.5). The results are shown in Table 6. Even if the transparent electrode layer was changed from ZnO: Al to ITO, the performance of the test cell was the same, but after heating at 200 ° C. for 30 minutes, the fill factor was particularly lowered and the conversion efficiency was greatly reduced. From the results of Experimental Examples 6 and 7, it was found that the rate of change before and after heating was larger in ITO than in ZnO: Al.

DESCRIPTION OF SYMBOLS 1 Base material 2 Back electrode 3 P-type light absorption layer (chalcopyrite compound semiconductor layer)
4 n-type buffer layer 5 transparent electrode layer 6 electrode structure (collecting electrode)
6a First conductive layer 6b Second conductive layer 7 Doped layer 8 Processing line 9 Unit cell 10, 20 Solar cell (solar cell sheet)

Claims (10)

  A first conductive layer provided in a pattern on the transparent electrode layer and having conductive particles and a polymer compound, and a conductive particle provided on the first conductive layer without a polymer compound as a binder An electrode structure comprising: a second conductive layer comprising:   2. The first conductive layer according to claim 1, wherein the conductive particles are bonded to each other using the polymer compound as a binder, and the conductive particles are directly bonded to each other in the second conductive layer. The electrode structure described.   3. The second conductive layer according to claim 1, wherein the second conductive layer includes at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups is more than 99.0% by mass. Electrode structure.   The electrode according to any one of claims 1 to 3, wherein the polymer compound is a curing agent that cures at 120 ° C or more and less than 180 ° C, and is used as a collector electrode of a solar cell having a chalcopyrite compound semiconductor layer. Construction.   A first conductive layer provided in a pattern on the transparent electrode layer and having conductive particles and a polymer compound, and a second conductive layer provided on the first conductive layer and having conductive particles, The second conductive layer includes at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups is more than 99.0% by mass. A solar cell in which at least a back electrode layer, a chalcopyrite compound semiconductor layer, a buffer layer, a transparent electrode layer and a collecting electrode are provided in that order on a substrate,
The collector electrode is provided in a pattern on the transparent electrode layer, and includes a first conductive layer having conductive particles and a polymer compound that cures at 120 ° C. or higher and lower than 180 ° C., and the first conductive layer is provided on the first conductive layer. And a second conductive layer having conductive particles without having a polymer compound as a binder.   The solar cell according to claim 6, wherein the second conductive layer includes at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups exceeds 99.0% by mass. A solar cell in which at least a back electrode layer, a chalcopyrite compound semiconductor layer, a buffer layer, a transparent electrode layer and a collecting electrode are provided in that order on a substrate,
The collector electrode is provided in a pattern on the transparent electrode layer, and includes a first conductive layer having conductive particles and a polymer compound that cures at 120 ° C. or higher and lower than 180 ° C., and the first conductive layer is provided on the first conductive layer. And a second conductive layer having conductive particles, the second conductive layer including at least two types of conductive particle groups having different particle size distributions, and the content of the conductive particle groups being 99.99. The solar cell characterized by being more than 0 mass%. On a substrate, at least a back electrode layer, a chalcopyrite compound semiconductor layer, a buffer layer, a transparent electrode layer, and a method for producing a solar cell in which a collecting electrode is provided in that order,
In the step of forming the current collecting electrode, the first conductive layer is formed in a pattern on the transparent electrode layer using a conductive paste containing conductive particles and a polymer compound that cures at a temperature of 120 ° C. or higher and lower than 180 ° C. And a step of forming a second conductive layer in a pattern by providing a conductive paste having conductive particles without having a polymer compound as a binder on the first conductive layer. A method for manufacturing a solar cell. In the step of forming the first conductive layer, the polymer compound contained in the conductive paste joins the conductive particles,
In the step of forming the second conductive layer, the conductive particles contained in the conductive paste include at least two kinds of conductive particle groups having different particle size distributions, and the content of the conductive particle groups is 99.0% by mass. The method for manufacturing a solar cell according to claim 9, wherein the conductive particles are joined at a temperature of 120 ° C. or higher and lower than 180 ° C.