KR20120086389A - Conductive pastes for electrodes of solar cell and methods of manufacturing solar cells using the conductive pastes - Google Patents

Abstract

PURPOSE: A conductive paste is provided to comprise metal particle and organic metal compounds as conductive components, and to reduce contact resistance between metal and semiconductor, thereby capable of improving efficiency of a solar cell. CONSTITUTION: A conductive paste comprises a conductive material comprising organo-metallic compound in which a metal component and an organic component are combined, a glass frit, a binder, and a solvent. The organic component is an aromatic group or an aliphatic hydrocarbon compound comprising at least one selected from a group consisting of a carboxy group, a mercapto group, an amino group, an ester group, an ether group, a butyl group, and a sulfurous acid group. The organic metal compound comprises an organo-silver compound in which the metal component is silver(Ag). The conductive material additionally comprises a silver powder.

Description

CONDUCTIVE PASTES FOR ELECTRODES OF SOLAR CELL AND METHODS OF MANUFACTURING SOLAR CELLS USING THE CONDUCTIVE PASTES}

The present invention relates to a conductive paste for forming a solar cell electrode and a manufacturing method of a solar cell using the same, and more particularly, a conductive paste for forming a solar cell electrode capable of forming a conductive film on the solar cell, and a manufacturing method of a solar cell using the same. It is about.

Recently, high oil prices have been sustained due to the crisis of oil resource exhaustion and resource nationalism, and international GHG regulations are being strengthened by the Kyoto Protocol's entry into the climate change convention to prevent global warming. As a result, energy and environmental issues are of great interest to the world at the same time, and research on clean energy-related technologies such as solar power is being conducted. Photovoltaic is not only an infinite energy source, but also an environmentally friendly A-support, and the solar cell market is growing rapidly in recent years.

Solar cells may be generally classified into silicon solar cells, compound semiconductor solar cells, etc. according to materials and manufacturing techniques, and may be classified into substrate type solar cells and thin film type solar cells according to the types of materials. Among the various solar cells, substrate type crystalline silicon solar cells are widely used for photovoltaic generation.

A solar cell is a semiconductor device that converts solar energy directly into electrical energy and has a junction form of a p-type semiconductor and an n-type semiconductor. When sunlight is incident on the solar cell, the valence band electrons of the p-type semiconductor are excited into the conduction band by the incident solar energy to generate an electron-hole pair inside the p-type semiconductor. The electrons in the electron-hole pairs thus generated are transferred to the n-type semiconductor by an electric field existing between the p-n junctions to supply current to the outside.

In order to manufacture such a solar cell, a conductive film having various functions must be formed. Recently, screen printing is used as a method for forming a conductive film. In order to form a conductive film of a solar cell by a screen printing method, a conductive paste is required. At present, researches on a conductive paste capable of producing a high efficiency solar cell have been actively conducted.

The present invention provides a conductive paste for forming a solar cell electrode capable of producing a high efficiency solar cell by reducing the series resistance.

The present invention also provides a method of manufacturing a solar cell using a conductive paste for forming a solar electrode.

In order to achieve the above object of the present invention, the conductive paste for forming a solar cell electrode according to the embodiments of the present invention is a conductive material, a glass frit, including an organic metal compound (Organo-Metallic Compound) combined with a metal component and an organic component And an organic binder and a solvent. The organic component may be an aromatic or aliphatic hydrocarbon compound having at least one of a carboxyl group, a mercapto group, an amino group, an ester group, an ether group, a butyl group and a sulfite group.

In an embodiment of the present invention, the organometallic compound may include an organo-silver compound in which the metal component is silver (Ag), and the conductive material may further include a silver powder. In one example, the silver powder may have a spherical shape having an average size of 0.4 to 2.0㎛.

The conductive paste for forming a solar cell electrode according to embodiments of the present invention may further include zinc oxide powder having a specific surface area of 30 m ² / g or more. In addition, the glass frit is SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ system, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -MgO-based, SiO ₂ -Al ₂ O ₃ -PbO- B ₂ O ₃ -ZrO _{2 system, SiO 2 -Al 2 O 3 -PbO} -B 2 O 3 -ZnO _{-based, SiO 2 -Al 2 O 3 -PbO} -B 2 O 3 -MgO-ZrO 2 type, SiO ₂ -Al may be _{2 O 3 -PbO-B 2 O} 3 -ZrO 2 -ZnO -based, and _{SiO 2 -Al 2 O 3 -PbO-} B 2 O 3 -MgO-ZrO 2 -ZnO system of one of the composite powder. For example, the composite powder may have an average particle diameter of 1.5 to 3.5㎛.

In another embodiment of the present invention, the organometallic compound may include an organo-silver compound in which the metal component is silver (Ag), and the conductive material may further include a silver powder. For example, the silver powder may have a flake shape having an average size of 0.9 μm to 1.9 μm. Furthermore, the conductive material may further include spherical aluminum powder having an average size of 3.5 to 5.5 μm.

In this case, the glass frit is SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -based, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -MgO-based, SiO ₂ -Al ₂ O ₃ -B ₂ O _3- ZrO ₂ based, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -ZnO based, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -MgO-ZrO ₂ based, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -ZrO ₂ -ZnO-based, and may be a _{SiO 2 -Al 2 O 3 -B 2} O 3 -MgO-ZrO 2 -ZnO system of one of the lead-free composite powder.

In the method of manufacturing a solar cell according to embodiments of the present invention, first, an anti-reflection film is formed on the light receiving surface of a semiconductor substrate having a p-n junction therein. Subsequently, the front electrode is printed by applying a first conductive paste including a metal particle including silver particles, an organic silver compound combined with silver and an organic component, a glass frit, an organic binder, and a solvent on the anti-reflection film by a screen printing method. . Thereafter, a rear electrode is formed on the rear surface of the semiconductor substrate facing the light receiving surface. Then, the semiconductor substrate on which the front electrode and the back electrode are formed is fired to manufacture a solar cell.

In order to form the back electrode, screen printing a second conductive paste including a metal particle including silver particles or aluminum particles, an organic silver compound combined with silver and an organic component, a lead-free glass frit, an organic binder, and a solvent on an upper portion of the rear surface. A method of forming a first back electrode pattern by applying a method, and including a metal particle including lead-free aluminum particles, a lead-free glass frit, an organic binder, and a solvent on an upper portion of the back surface to overlap the first back electrode pattern by a predetermined width. The conductive paste may be applied by screen printing to form a second back electrode pattern.

According to the conductive paste for forming a solar cell electrode and a method of manufacturing a solar cell using the same, since the conductive component includes not only metal particles but also organometallic compounds, the contact resistance between the metal and the semiconductor can be reduced, and as a result, The efficiency can be improved.

1 is a photograph showing a state of printing a conductive paste prepared according to the embodiments and comparative examples of the present invention.
2 is a graph illustrating a heat treatment process according to an embodiment of the present invention.

Hereinafter, a conductive paste for forming a solar cell electrode and a method of manufacturing a solar cell using the same according to embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals are used for like elements in describing each drawing. In the accompanying drawings, the dimensions of the structures are enlarged to illustrate the present invention in order to clarify the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to refer to the existence of a feature, number, step, operation, component, part, or combination thereof described on the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Conductive paste

The conductive paste according to the embodiments of the present invention includes conductive particles, an organometallic compound, a glass frit, an organic binder, and a solvent. In addition, the conductive paste according to the embodiments of the present invention may further include an additive. Hereinafter, the components of the conductive paste according to the embodiments of the present invention will be described in detail.

(A) electroconductive particle

The conductive paste contains conductive particles. Electroconductive particle imparts electrical conductivity to the electrically conductive film formed of an electrically conductive paste.

The conductive particles may include metal particles. The metal particles may include metal particles such as silver (Ag), gold (Au), palladium (Pd), platinum (Pt), copper (Cu), aluminum (Al), or alloy particles including the metal components. have. In addition, as the metal or alloy particles, only particles of a single component may be used, or two or more kinds of metal or alloy particles may be mixed and used, or metal or alloy particles having a core shell structure may be used.

The metal particles may have a spherical shape, a flake shape, a plate shape, a fiber shape, or an irregular shape. In addition, the metal particles may be used by mixing metal particles of at least two or more of a spherical shape, a flake shape, a plate shape, a fiber shape, a rod shape, and an irregular shape. have. In order for the conductive film formed by the conductive paste to have a low resistance and to reduce the cost for forming the conductive film, the shape of the metal particles is preferably spherical or flake shaped.

The size of the metal particles is preferably selected in consideration of the sintering behavior and printability of the metal particles. As the size of the metal particles increases, the sintering temperature increases and the sintering speed tends to be slow. In addition, when the conductive paste is applied by the method of screen printing, the size of the metal particles needs to be selected to be suitable for screen printing. Considering the above, the metal particles may have a size of about 0.1 to 15 μm. When the size of the metal particles is less than 0.1 μm, there is a problem of causing a mismatch in the sintering rate in relation to the conductive paste that is applied to the rear surface of the solar cell and mainly contains aluminum as the conductive powder, and the size of the metal particles is 15 μm. If exceeded, the sintering of the conductive paste does not proceed sufficiently, thereby lowering the electrical conductivity and reducing the strength of the conductive film formed by the conductive paste.

The metal particles are preferably mixed at about 40 to 90% by weight based on the total weight of the conductive paste. When the content of the metal particles is less than 40% by weight based on the total weight of the conductive paste, there is a problem that the electrical conductivity of the conductive film formed by the conductive paste is too low, and when it exceeds 90% by weight, the printability of the conductive paste is lowered. There is a problem that the dispersion degree is poor.

In one embodiment of the present invention, the metal particles may include silver (Ag) particles. In one example, the silver particles may have a spherical shape, and may have an average particle diameter of about 0.4 to 1.2 μm. As another example, the silver particles have a flake shape and may have an average size of about 0.9 to 1.9 μm. The solar cell may include a front electrode formed on the front surface of the substrate to which sunlight is incident and a rear electrode formed on the rear surface of the substrate opposite to the front surface. The back electrode may be formed by a conductive paste mainly containing aluminum as a conductive component. The first back electrode pattern to be formed and the conductive powder may include a second back electrode pattern formed mainly by a conductive paste which may mainly include silver and additionally include aluminum. The conductive paste according to the present embodiment may be used to form the second back electrode pattern among the front electrode of the solar cell or the back electrode of the solar cell. For example, when the conductive paste according to the present embodiment is used to form the front electrode of the solar cell, spherical silver particles may be used, and used to form the second rear electrode pattern of the rear electrodes of the solar cell. In the case of flake silver particles can be used.

In another embodiment of the present invention, the metal particles may include silver (Ag) particles and aluminum (Al) particles. For example, the silver particles may have a flake shape and have an average size of about 0.9 to 1.9 μm, and the aluminum particles may have a spherical shape and an average particle diameter of about 3.5 to 5.5 μm. The conductive paste according to the present embodiment may be used to form the second back electrode pattern of the back electrodes of the solar cell.

In order to improve electrical conductivity and reduce manufacturing costs, the conductive particles may further include a carbonaceous material such as graphite, carbon black, graphene, carbon nanotube, or a conductive polymer material.

In addition, the conductive particles may further include powders such as metal oxides and metal carbides in order to improve electrical conductivity and reduce manufacturing costs. For example, the conductive particles may further include silver oxide powder.

(B) Organo-Metallic Compound

The conductive paste may further include an organometallic compound in order to improve electrical conductivity, reduce manufacturing cost, and improve efficiency of the solar cell. An organometallic compound is a substance formed by chemically bonding a metal component and an organic component, and refers to a substance in which the metal component and the organic component are decomposed with each other at a temperature lower than the melting temperature of the metal, and the metal component is metallized. . For example, in the organometallic compound, the metal component may be chemically bonded to the hetero atom P, S, O or N of the organic component. Specifically, in the organometallic compound, the metal component is a carboxyl group (R-COOH), a carbonyl group (R-CO-R '), a mercapto group (R-SH), an amino group (R-NH ₂ ), an ester group ( R-COO-R '), ether group (RO-R'), may be coupled to a butyl group or the like (R-C4H9) or sulfurous acid group (R-SO _3).

The metal component of the organometallic compound may include Ag, Au, Pd, Pt, Cu, and the like. For example, the organometallic compound may be an organosilver compound having a metal component of silver (Ag). Specifically, the organic silver compound is, for example, silver-formate, silver-oxalate, silver-citrate, silver-butylate, silver pro Cyanate, silver-malonate, silver-acetate, silver-succinate, silver-maleate, silver-trimate trimesinate), silver-terephthalate, silver-bensoate, and the like. In addition, the organic silver compound is, for example, silver-formate, silver-oxalate, silver-citrate, silver-butylate, silver propionate (siver-propionate), silver-malonate, silver-acetate, silver-succinate, silver-maleate, silver-trimesinate It may include a material formed by reacting at least one or more of silver-terephthalate, silver-bensoate, and the like with an amine.

For example, in the case of an organic silver compound in which an organic component having a carboxyl group is bonded to a silver component, the organic component may have a structure as shown in Structural Formula 1 below. In the following structural formula 1, R represents an aromatic hydrocarbon compound or an aliphatic hydrocarbon compound having 0 to 16 carbon atoms.

<Structure 1>

The conductive paste may contain two or more kinds of organometallic compounds having different decomposition temperatures from each other.

In one embodiment of the present invention, the conductive paste may include two or more organometallic compounds having the same metal component but different organic components. Specifically, the conductive paste may include an organometallic compound having a relatively low decomposition temperature and an organometallic compound having a relatively high decomposition temperature. For example, the conductive paste has a decomposition temperature and at least one organic silver compound of silver-formate, silver-oxalate, and silver-citrate having a decomposition temperature of less than about 200 ° C. Silver-butylate, silver-propionate, silver-malonate, silver-acetate, silver-succinate The organic silver compound may include at least one of silver-maleate, silver-trimesinate, silver-terephthalate, and silver-bensoate.

The structural formula and decomposition temperature of the organic silver compound having a relatively low decomposition temperature among the organic silver compounds described above are as follows.

Organosilver compounds Decomposition Temperature (℃) constitutional formula Silver Form Eight
(silver-formate) 117

Silver oxalate
(silver-oxalate) 172

Silver Citrate
(silver-citrate) 185

The structural formula and decomposition temperature of the organic silver compound having a relatively high decomposition temperature among the organic silver compounds described above are as follows.

Organosilver compounds Decomposition Temperature (℃) constitutional formula Silver butyrate
(silver-butylate) 228

Silver Propionate
(siver-propionate) 230

Silver malonate
(silver-malonate) 263

Silver acetate
(siver-acetate) 282

Silver Succinate
(silver-succinate) 290

Silver Maliate
(silver-maleate) 300

Silver trimeshinate
(silver-trimesinate) 380

Silver terephthalate
(silver-terephthalate) 420

Silver benzoate
(silver-bensoate) 430

In another embodiment of the present invention, the conductive paste may include two or more types of organometallic compounds having the same organic component but different metal components.

In still another embodiment of the present invention, the conductive paste may include two or more kinds of organometallic compounds having different organic components as well as metal components.

(C) Glass Frit

The conductive paste includes glass frits. The glass frit assists the sintering of the metal particles and improves the adhesion of the conductive film to the substrate during firing. The glass frit may include at least one or more of SiO ₂ , Al ₂ O ₃ , PbO and B ₂ O ₃ , MgO, ZrO ₂ , ZnO, TiO ₂ , Bi ₂ O _3, and the like.

In one embodiment of the present invention, the glass frit is SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ system, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -MgO system, SiO _2- Al ₂ O ₃ -PbO-B ₂ O ₃ -ZrO ₂ based, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -ZnO based, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -MgO -ZrO ₂ system, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -ZrO ₂ -ZnO system, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -MgO-ZrO ₂ -ZnO system Can be used. Glass frits of such components can be used, for example, in conductive pastes for forming front electrodes of solar cells.

In another embodiment of the present invention, the glass frit is SiO ₂ -Al ₂ O ₃ -B ₂ O _{3 type} , SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -MgO type, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -ZrO ₂ system, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -ZnO system, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -MgO-ZrO ₂ system, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -ZrO ₂ -ZnO system, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -MgO-ZrO ₂ -ZnO system and the like can be used. The glass frit of such a component can be used, for example, in a conductive paste for forming a second back electrode pattern of the back electrodes of a solar cell.

Glass frit is added in the form of composite particles of the above components. The shape of the glass frit particles is not particularly limited, and may be spherical, acicular or irregular. The size of the glass frit particles is also not particularly limited, but the average particle diameter is preferably about 0.1 to 5 μm. In particular, it is more preferable that the average particle diameter of a glass frit is 1.5-3.5 micrometers.

The glass frit preferably has a softening point of about 350 to 600 ° C. If the softening point is less than 350 ° C., there is a problem that the sintering proceeds excessively, and if the softening point exceeds 600 ° C., sufficient melt flow is not obtained during firing and sufficient adhesive strength cannot be obtained, and liquid phase sintering of the metal may be promoted. There is no problem. "Softening point" in this application is a value measured by the Fiber Elongation Method of ASTM C338-57.

Glass frit may be contained in 2 to 10% by weight based on the total weight of the conductive face. If the content of the glass frit is less than 2% by weight, there is a problem that the adhesive strength of the conductive film formed by the conductive paste is insufficient, and when the content of the glass frit is more than 10% by weight, the glass frit is performed in a later step by glass floating or the like. There is a problem that causes soldering problems.

(D) Organic Binder

The conductive paste may include an organic binder. The organic binder affects the viscosity of the conductive paste and allows the conductive film formed by the conductive paste to adhere to the substrate before firing. Examples of the organic binder include acrylic resins, epoxy resins, phenolic resins, alkyd resins, cellulose derivatives, polyvinyl chloride resins, polypropylene resins, terpene resins, rosin resins, aliphatic resins, acrylic ester resins and xylenes. Resin-based resin, xumaron indene-based resin, styrene resin, dicyclopentadiene-based resin, polybutene-based resin, urea-based resin, melamine-based resin, vinyl acetate-based resin, polyisobutyl-based resin and the like can be used. The materials may be used alone or as a mixture of two or more kinds as the organic binder.

The organic binder may be contained in about 0.1 to 30% by weight based on the total weight of the conductive paste. If the content of the organic binder is less than 0.1% by weight, there is a problem in that sufficient adhesive strength cannot be secured. If the content of the organic binder is more than 30% by weight, the problem of lowering printability by raising the viscosity of the conductive paste is increased. have.

(E) Solvent

The conductive paste contains a solvent. The solvent influences the printability of the conductive paste by adjusting the viscosity of the conductive face.

The solvent is not particularly limited as long as it can dissolve the organic binder. Such solvents include hexane, toluene, cyclohexanone, ethyl cellosolve, butyl cellosolve, butyl cellosolve acetate, butyl carbitol, butyl carbitol acetate, diethylene glycol diethyl ether, diacetone alcohol, terpine Ol, benzyl alcohol and the like can be used. These substances may be used alone or as a solvent by mixing two or more kinds.

The solvent may be contained in an amount of 1 to 40% by weight based on the total weight of the conductive paste for the printability of the conductive paste.

(F) Additives

The conductive paste may further include zinc oxide powder to improve printability and reduce contact resistance between the metal component and the semiconductor component of the substrate. Specifically, zinc oxide powder improves the aspect ratio of the printed conductive film. In addition, the zinc oxide powder serves to guide the metal component of the conductive paste to the substrate during firing. The zinc oxide powder may have a specific surface area of about 10 m ² / g or more. Preferably the zinc oxide may have a specific surface area of at least about 30 m ² / g.

The conductive paste may further include a dispersant such as stearic acid, palmitic acid, myristic acid, oleic acid, lauric acid, etc. in order to improve the dispersibility of the conductive particles. In addition, the conductive paste may further include additives such as an antifoaming agent and a viscosity modifier.

Hereinafter, specific examples of the present invention and comparative examples related thereto will be described. The following examples are merely examples of the present invention and are not intended to limit the concept of the present invention. Accordingly, the examples and comparative examples disclosed below should not be construed as limiting the scope of the invention.

First, embodiments of a conductive paste that can be used to form a front electrode of a solar cell and related examples thereof will be described.

&Lt; Example 1 >

Spherical silver (Ag) powder with an average particle size of 0.6 to 1.2 μm, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -MgO-based glass frit, zinc oxide powder with a specific surface area of about 30 m ² / g, and 88w% of mixed powder composed of organosilver compound powder, 12w% of a binder solution obtained by dissolving ethyl cellulose resin and rosin in butyl carbitol acetate and tepineol mixed solvent were premixed using a planetary mixer. Kneading with a roll kneader to prepare a conductive paste composition having a viscosity of 224000 to 374000 cPs. In the conductive paste, glass frit was mixed with 3 wt%. The said viscosity was measured using the viscometer (The Brookfield HBDV-II + Pro type | mold viscosity meter, spindle # 14, rpm 10) at the temperature of 25 degreeC.

<Example 2>

A conductive paste was prepared in the same composition and in the same manner as in Example 1 except that 2 wt% of glass frit was added and the viscosity was 197000 cPs.

&Lt; Comparative Example 1 &

Conductive paste in the same composition and in the same manner as in Example 1 except that a spherical silver (Ag) powder having an average particle size of 1.1 mu m was added, an organic silver compound powder was not added, and the viscosity was 210000 cPs. Was prepared.

Comparative Example 2

Except for the addition of spherical silver (Ag) powder with an average particle size of 1.1 μm and no addition of organic silver compound powder, the specific surface area of zinc oxide is 6 m ² / g and the viscosity is 201000 cPs The conductive paste was prepared in the same composition and in the same manner as in Example 1.

Performance evaluation

Conversion efficiency
(Eff,%) Series resistance
(Rs, mΩ) Filling rate
(FF,%) Printability Example 1 16.62 9.1 73.71 Good Example 2 16.25 9.3 72.69 Good Comparative Example 1 15.17 14.5 67.35 Good Comparative Example 2 16.15 14.5 70.43 Bad

The conductive pastes prepared in Examples 1, 2, Comparative Example 1 and Comparative Example 2 were screen printed on a front surface of a p-type silicon wafer having a thickness of 180 μm, a width of 127 mm, and a length of 127 mm using a 325 mesh stainless steel wire mask. ) To form a conductive film having a line width of 100 μm, dried, and then baked at a temperature of 600 ° C. or higher (maximum temperature 785 ° C.) for 5 seconds to form a solar cell front electrode. After completing the solar cell including the front electrode formed as described above, the conversion efficiency (Eff), series resistance (Rs) and charge rate (FF) were measured using a Wacom cell efficiency meter, and the results are shown in Table 3. It was.

In addition, the printability of the front electrode was observed through an electron microscope, the results are shown in Table 3, and the photographs are shown in FIG.

Referring to Table 3, forming the conductive film with the conductive pastes of Examples 1 and 2 to which the organic silver compound was added is more effective than forming the conductive film with the conductive pastes of Comparative Examples 1 and 2 without the organic silver compound added. It was excellent in all aspects such as conversion efficiency, series resistance and charge rate. In particular, in terms of series resistance, the conductive pastes of Examples 1 and 2 were significantly superior to those of Comparative Examples 1 and 2, respectively. From these results, it was found that the organic silver compound reduces the contact resistance between the conductive component of the conductive paste and the semiconductor of the substrate.

Further, referring to Figure 1 and Table 3, a specific surface area of the zinc oxide having a specific surface area of 6m ² / g powder compared to Example 1, Example 2 and Comparative Example 1 containing the zinc oxide powder is 30m ² / g Comparing Comparative Example 2, the line spread during printing was more severe than other examples, and the printability was evaluated to be not so good. From these results, it was found that the specific surface area of the zinc oxide powder affects the printability of the conductive paste.

Next, embodiments of a conductive paste that can be used to form a second back electrode pattern among back electrodes of a solar cell and comparative examples thereof will be described.

<Example 3>

Butyl carbitol acetate was prepared by mixing 72.2 wt% of flake-shaped silver powder having an average particle size of 0.9 μm, lead-free SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ based glass frit, and an organic silver compound powder. 17.8 wt% of the binder solution dissolved in the terpineol mixed solvent was premixed using a planetary mixer and kneaded with a three-roll kneader to prepare a conductive paste composition having a viscosity of 81000 cPs. The said viscosity was measured using the viscometer (The Brookfield HBDV-II + Pro type | mold viscosity meter, spindle # 14, rpm 10) at the temperature of 25 degreeC.

<Example 4>

A conductive paste was prepared in the same composition and in the same manner as in Example 3 except that 2 wt% of a spherical aluminum powder having an average particle size of 4 to 5 µm was added as the conductive component and the viscosity was 91000 cPs.

&Lt; Comparative Example 3 &

A conductive paste was prepared in the same composition and in the same manner as in Example 3 except that no organosilver compound powder was added and the viscosity was 104000 cPs.

Performance evaluation

Conversion efficiency
(Eff,%) Series resistance
(Rs, mΩ) Filling rate
(FF,%) Example 3 16.66 8.1 75.47 Example 4 16.43 7.9 75.02 Comparative Example 3 16.51 9.2 75.44

The conductive pastes prepared in Examples 3, 4 and Comparative Example 3 were printed on the back surface of a p-type silicon wafer having a thickness of 180 μm, a width of 127 mm, and a length of 127 mm by screen printing (using a 325 mesh stainless steel wire mask). After the conductive film was formed and dried, it was baked at a temperature of 600 ° C. or higher (maximum temperature 785 ° C.) for 5 seconds to form a second rear electrode pattern of the rear electrodes of the solar cell. After completing the solar cell including the second back electrode pattern formed as described above, the conversion efficiency (Eff), series resistance (Rs) and charge rate (FF) were measured using a Wacom cell efficiency meter. 4 is shown.

Referring to Table 4, forming the conductive film with the conductive pastes of Examples 3 and 4 to which the organic silver compound was added reduced the series resistance than forming the conductive film with the conductive paste of Comparative Example 3 without the organic silver compound added. Appeared to. From these results, it was found that the organic silver compound reduces the contact resistance between the conductive component of the conductive paste and the semiconductor of the substrate.

Manufacturing method of solar cell

Silicon solar cells according to embodiments of the present invention are manufactured through a substrate preparation step, an emitter forming step, an anti-reflection film forming step, an electrode printing step and a heat treatment step. Hereinafter, each step for forming the silicon solar cell according to the embodiments of the present invention will be described in detail.

(A) substrate preparation step

As the substrate material, single crystal, polycrystalline or amorphous silicon wafer may be used. Although both p-type and n-type wafers can be used as the substrate, the use of a p-type wafer in the present invention will be described as an example. When a p-type wafer is used as a substrate, not only electron mobility is faster than holes but also impurities are easily diffused to form a p-n junction on the front surface.

Once the silicon substrate is prepared, the substrate surface is textured to reduce the surface reflectance of the incident light. In general, a silicon substrate that is not surface-organized with respect to incident light reflects about 30%, while a silicon substrate that is surface-organized reflects only about 10%.

Surface organization of a silicon substrate means forming a specific structure capable of reducing light reflectance on the surface of a silicon substrate on which light is incident. For example, the surface of the silicon substrate may be organized by forming a plurality of continuous and regular pyramidal structures on the surface of the silicon substrate to which light is incident. Such surface organization of the substrate can be formed through directional etching. For example, the surface of the substrate can be organized by using a basic alkaline solution such as KOH or NaOH or by using gases such as Cl ₂ / CF ₄ / O ₂ , SF ₆ / O ₂ , CHF ₃ / SF ₆ / O _2, and the like. have. Alternatively, the surface of the substrate may be organized by forming grooves using a laser or mechanically removing a portion of the surface using a plurality of diamond blades and then removing the surface defect with a chemical solution.

(B) emitter forming step

The p-n junction is formed on the substrate by doping impurities corresponding to Group 3 or Group 5 of the periodic table on the incident surface of the silicon substrate. For example, when a p-type silicon wafer is used as a substrate, a pn junction is formed by doping impurities corresponding to group 3 of the periodic table, and when a n-type silicon wafer is used as a substrate, The corresponding impurities are doped to form a pn junction. When forming the p-n junction, it is desirable not only to precisely control the concentration distribution of impurities but also to precisely control the implantation depth of the impurities.

As a method of doping an impurity into a silicon substrate, there are a method of implanting an impurity during silicon crystal growth and a method of implanting an impurity through the substrate surface after silicon crystal growth. The method of doping impurities through the substrate surface may include exposing the substrate surface to a gas or solid containing impurities in a high temperature state, a method of maintaining a high temperature state after forming a layer containing impurities on the substrate surface. There is a method of doping impurity ions into the substrate by placing the wafer in a vacuum and accelerating impurity ions onto the substrate surface.

(C) antireflection film forming step

After performing a surface organization process on the surface of the substrate on which light is incident, an antireflection film is formed on the surface of the surface structured substrate. The anti-reflection film may reduce the amount of reflected light by increasing the amount of light introduced into the wafer by causing the light reflected from the anti-reflection film surface and the light reflected from the silicon substrate surface to cancel each other. In addition, the anti-reflection film may improve selectivity with respect to light in a specific wavelength region through the cancellation interference as described above. The antireflection film is formed of a material having a predetermined refractive index, and the thickness of the antireflection film needs to be optimized to cause the above-mentioned destructive interference based on the refractive index of the antireflection film and the refractive index of the silicon wafer. In one example, the anti-reflection film may be formed of silicon nitride (SiNx).

The anti-reflection film may be formed in a single layer structure, but may be formed in a laminated structure in which a plurality of layers having different refractive indices are stacked.

(D) electrode printing step

(1) front electrode printing step

After the front electrode is designed to print the front electrode, the conductive paste for the front electrode is applied by screen printing according to the design.

When the area of the front electrode increases, the amount of light incident on the substrate decreases. When the area of the front electrode decreases, the resistance of the front electrode itself increases. Therefore, the optimal front electrode is designed in consideration of these matters. . In detail, the front electrode includes a plurality of first front electrode patterns extending in a first direction and arranged in a second direction perpendicular to the first direction, and a first electrode extending in a second direction and electrically connected to the plurality of first front electrode patterns. It is designed to have two front electrode patterns. In order to increase the efficiency of the solar cell, the width and the spacing of the first front electrode pattern and the width and the spacing of the second front electrode pattern should be designed to the optimum values. For example, the front electrode may have a width and a spacing interval of the electrode patterns to be about 2% to 10% of the total area of the front surface of the substrate.

After the front electrode is designed, the conductive paste for the front electrode is applied to the upper surface of the antireflection film by screen printing according to the design. The conductive paste for the front electrode may include metal particles, an organometallic compound, a glass frit, an organic binder, and a solvent. As the conductive paste for the front electrode, the conductive paste according to the embodiment of the present invention described above may be used. Therefore, the detailed description is abbreviate | omitted about the structure of the electrically conductive paste for front electrodes.

(2) back electrode printing step

The back electrode of the solar cell is formed on the back of the substrate opposite to the front surface on which the front electrode is formed. The back electrode of the solar cell may include a first back electrode pattern and a second back electrode pattern electrically connected thereto.

The first back electrode pattern of the back electrodes is formed using a conductive paste mainly containing aluminum as the conductive powder. The conductive paste for forming the first back electrode pattern may include aluminum particles, a lead-free glass frit containing no lead component, an organic binder, and a solvent.

The second back electrode pattern of the back electrodes may be formed by a conductive paste including metal particles, organometallic compounds, glass frits, organic binders, and solvents including silver particles or aluminum particles. As the conductive paste for forming the second rear electrode pattern among the rear electrodes, the conductive paste according to the embodiment of the present invention described above may be used. Therefore, the detailed description of the structure of the conductive paste for the second back electrode pattern is omitted.

In one embodiment of the present invention, after printing the first back electrode conductive paste containing aluminum and silver as a conductive component by screen printing to form a second back electrode pattern having a predetermined width, the second back electrode The back electrode may be printed by printing the conductive paste for the first back electrode pattern by the screen printing method so as to overlap the edge portion of the second back electrode pattern by a predetermined width with the pattern therebetween to form the first back electrode pattern. .

Unlike this, in another embodiment of the present invention, the conductive paste for the first back electrode pattern is printed by screen printing to form a first back electrode pattern including two or more portions spaced at a predetermined interval, and then the first The back electrode is formed by printing a second back electrode pattern by printing a conductive paste for the second back electrode pattern by screen printing so that both edge portions overlap each other with the first back electrode pattern by a predetermined width. You can also print.

(E) heat treatment step

After printing the front and back electrodes, the substrate is heat treated to have a predetermined temperature profile over time. As one example, the substrate may be heat treated to a profile as shown in FIG. In Figure 2 is heated for 4 to 5 seconds at a temperature of about 600 ℃ or more, the maximum temperature is shown to be about 784.4 ℃, this is only an embodiment of the present invention, in consideration of the composition of the conductive paste, Figure 2 The graph shown in FIG. Can be changed as appropriate.

When the substrate is heat-treated with a profile as shown in FIG. 2, the volatile solvents of the front electrode paste and the back electrode paste are evaporated at a temperature of about 100 to 200 ° C., and the front electrode at a temperature of about 200 to 400 ° C. At least a part of the organic binder of the paste and the back electrode paste is burned, and the metal component and the organic component of the organometallic compound included in the front electrode paste are decomposed with each other, and at least a part of the decomposed organic component is burned. And the glass frit of the front electrode paste and the back electrode paste is softened at the temperature of about 400-600 degreeC. Subsequently, in the case of the front electrode paste at a temperature of about 600 to 800 ° C., some of the decomposed metal ions and metal ions dissolved from the metal particles move through the antireflection film to the substrate, and sintered adhesion between the metal particles is prevented. In the case of the back electrode paste, an aluminum component diffuses into the substrate to form a back electric field, and sintering adhesion occurs between the metal particles included in the back electrode paste. Subsequently, when the substrate is rapidly cooled, a bond is generated between the silicon of the substrate and the metal components of the conductive paste for the front electrode and the conductive paste for the back electrode.

In the present invention, since the front electrode paste contains an organometallic compound, the metal ion component that can be bonded to the silicon atoms of the substrate is increased. As a result, the contact resistance between the metal of the front electrode and the semiconductor of the substrate is increased. Can be reduced. That is, the solar cell manufactured according to the embodiment of the present invention will have improved efficiency.

While the foregoing has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

Claims (12)

Conductive materials including organo-metallic compounds in which metal and organic components are combined;
Glass frit;
Organic binders; And
Electroconductive paste for solar cell electrode formation containing a solvent. The conductive material of claim 1, wherein the organic component is an aromatic or aliphatic hydrocarbon compound having at least one of a carboxyl group, a mercapto group, an amino group, an ester group, an ether group, a butyl group, and a sulfite group. Paste. The method of claim 2, wherein the organometallic compound comprises an organo-silver compound of which the metal component is silver (Ag),
The conductive material further comprises a silver powder conductive paste for forming a solar cell electrode. The conductive paste of claim 3, wherein the silver powder has a spherical shape having an average size of 0.4 to 2.0 μm. The conductive paste for forming a solar cell electrode according to claim 4, further comprising a zinc oxide powder having a specific surface area of 30 m ² / g or more. The glass frit of claim 4, wherein the glass frit is SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ based, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -MgO based, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -ZrO ₂ based, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -ZnO based, SiO ₂ -Al ₂ O ₃ -PbO-B ₂ O ₃ -MgO-ZrO _{2 based, SiO 2 -Al 2 O 3 -PbO} -B 2 O 3 -ZrO 2 -ZnO -based, and _{SiO 2 -Al 2 O 3 -PbO-} B 2 O 3 -MgO-ZrO 2 -ZnO system of one of the composite powder The electrically conductive paste for solar cell electrode formation characterized by the above-mentioned. The conductive paste of claim 6, wherein the composite powder has an average particle diameter of 1.5 to 3.5 μm. The conductive paste of claim 3, wherein the silver powder has a flake shape having an average size of 0.9 μm to 1.9 μm. The conductive paste of claim 8, wherein the conductive material further comprises spherical aluminum powder having an average size of 3.5 to 5.5 μm. The glass frit according to claim 8 or 9, wherein the glass frit is SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ system, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -MgO system, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -ZrO ₂ system, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -ZnO system, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -MgO-ZrO ₂ system, SiO ₂ -Al Forming a solar cell electrode, characterized in that the lead-free composite powder of one of ₂ O ₃ -B ₂ O ₃ -ZrO ₂ -ZnO and SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -MgO-ZrO ₂ -ZnO Conductive paste. Forming an anti-reflection film on the light receiving surface of the semiconductor substrate having a pn junction therein;
Printing a front electrode on the anti-reflection film by coating a first conductive paste including metal particles including silver particles, an organic silver compound combined with silver and an organic component, a glass frit, an organic binder, and a solvent by screen printing;
Forming a rear electrode on a rear surface of the semiconductor substrate facing the light receiving surface; And
Firing a semiconductor substrate on which the front electrode and the back electrode are formed. The method of claim 11, wherein forming the back electrode comprises:
The first rear electrode is coated with a second conductive paste including a metal particle including silver particles or aluminum particles, an organic silver compound in which silver and an organic component are combined, a lead-free glass frit, an organic binder, and a solvent by using a screen printing method. Forming a pattern; And
The second back electrode is coated with a second conductive paste including a metal particle including aluminum particles, a lead-free glass frit, an organic binder, and a solvent by screen printing to overlap the first back electrode pattern by a predetermined width. A method of manufacturing a solar cell comprising the step of forming a pattern.

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