WO2015076157A1

WO2015076157A1 - Method for producing conductive composition

Info

Publication number: WO2015076157A1
Application number: PCT/JP2014/079872
Authority: WO
Inventors: 高橋　洋祐
Original assignee: 株式会社ノリタケカンパニーリミテド
Priority date: 2013-11-20
Filing date: 2014-11-11
Publication date: 2015-05-28
Also published as: JP6114389B2; JPWO2015076157A1; TW201526027A

Abstract

[Problem] To provide a method for producing a conductive composition which enables good electrical bonding when an electrode of a solar cell is formed. [Solution] A method for producing a conductive composition for forming an electrode of a solar cell, which comprises: a step for preparing a silver powder, a tellurium-containing composition and a tellurium valence adjustment material; and a step for producing a conductive composition by adjusting the blending ratio of the silver powder, the tellurium-containing composition and the tellurium valence adjustment material so that the average valence of tellurium (Te) contained in the interface between a substrate of a solar cell and the conductive composition is from 4.3 to 5.1 (inclusive) if the conductive composition is applied over the substrate and fired thereon.

Description

Method for producing conductive composition

The present invention relates to a method for producing a conductive composition for forming an electrode of a solar cell, a conductive composition obtained by such a production method, and a solar cell.
This application claims priority based on Japanese Patent Application No. 2013-240014 filed on Nov. 20, 2013, the entire contents of which are incorporated herein by reference.

As a typical example of a solar cell that converts solar light energy into electric power, a solar cell that uses crystalline silicon (single crystal or polycrystal) as a semiconductor substrate, a so-called crystalline silicon solar cell is known. As such a crystalline silicon solar cell, for example, a single-sided light receiving type solar cell (single cell) 110 as shown in FIG. 2 is known.
This solar cell 110 includes an n-Si layer 116 formed by pn junction formation on the light-receiving surface (upper surface in FIG. 2) side of a p-type silicon substrate (Si wafer: p-Si layer made of p-type crystalline silicon) 111. And an antireflection film 114 made of titanium oxide, silicon dioxide, or silicon nitride, and a surface electrode (light-receiving surface electrode) 112 made of silver (Ag). On the other hand, on the back surface (bottom surface in FIG. 2) side of the p-type silicon substrate (p-Si layer) 111, a back-side external connection electrode 122 made of silver (Ag) as well as the light-receiving surface electrode 112 and a so-called back-surface electric field. An aluminum electrode 120 having a (BSF; Back Surface Field) effect and a p ⁺ layer (BSF layer) 124 formed by diffusing aluminum into the p-Si layer 111 are provided. Here, as prior arts related to the conductive composition used for forming the light-receiving surface electrode 112, for example, Patent Documents 1 to 7 and the like can be cited.

Japanese Patent Application Publication No. 2001-303400 Japanese Patent Application Publication No. 2006-302890 Japanese Patent Application Publication No. 2011-96747 Japanese Patent No. 4754655 International Publication No. 2012/020694 International Publication No. 2012/141187 International Publication No. 2012/144335

By the way, the light receiving surface electrode of the silicon-based solar cell typically includes a linear bus bar electrode (connecting electrode) and a plurality of fine linear grid electrodes (collecting electrodes) connected to the bus bar. It is comprised by. Since these light receiving surface electrodes are formed on the light receiving surface of the solar cell, shadow loss (light blocking loss) can be generated. For this reason, thinning (fine line) of light receiving surface electrodes, especially the grid electrodes with a large number, is performed in order to increase the light receiving area per unit area of the cell and improve the output per unit cell area, that is, the photoelectric conversion efficiency. It is required to plan. For example, the width of the grid electrode, which was about 130 μm in a conventional solar cell, is required to be 110 μm or less. However, for example, if the width of the grid electrode is reduced, the ohmic contact between the light-receiving surface electrode and the n layer deteriorates and the contact resistance increases and the current density decreases, so that the conversion efficiency can be simply increased. There was a problem that I could not.

The present invention has been made in the background of the circumstances as described above, and the object of the present invention is to provide a conductive composition capable of realizing good electrical bonding when forming an electrode of a solar cell. An object is to provide a manufacturing method. Also, excellent electrical properties (eg, open-circuit voltage, fill factor and energy conversion efficiency) provided with a conductive composition formed using such a conductive composition, and an electrode formed with this conductive composition. It is another object to provide a solar cell comprising:

As for the conductive composition for forming the electrode of the solar cell, for example, as disclosed in Patent Documents 3 to 7, the tellurium is contained in the conductive composition in the form of a compound such as an oxide, or It is known that the ohmic contact and the like can be improved by containing it as a glass constituent component. However, since the solar cell may differ depending on the product form, for example, the configuration of the substrate itself or the required characteristics may be slightly different. For this reason, the detailed composition of each constituent material in the conductive composition is determined. The fact was that the guidelines were lacking.
Under such circumstances, as a result of intensive studies by the inventor, the same tellurium source (for example, a tellurium-containing glass composition, tellurium oxide, etc.) is used for a conductive composition containing tellurium. It was found that the valence of tellurium (that is, the electronic state of Te atom) in the electrode after formation can be changed even when the conductive composition is prepared. And it was discovered that the valence of tellurium affects the solar cell characteristics, particularly the ohmic contact between the substrate and the electrode, regardless of the form of the tellurium source, and the present invention has been completed.

That is, the present invention provides a method for producing a conductive composition for forming an electrode of a solar cell. This manufacturing method is characterized by including the following steps (1) and (2).
(1) To prepare silver powder, a tellurium-containing composition, and a tellurium valence adjusting material.
(2) When the conductive composition is applied to the substrate of the solar cell and fired, the average valence of tellurium (Te) contained in the interface between the substrate and the conductive composition is 4.3 or more and 5 Adjusting the blending of the silver powder, the tellurium-containing composition and the tellurium valence adjusting material so as to be 1 or less, to prepare a conductive composition.

According to the production method of the present invention, the composition of each constituent material constituting the conductive composition is adjusted so that tellurium contained in the conductive composition can exist in an optimal electronic state (electronic configuration) in the electrode after formation. Is done. For example, in an electrode obtained by firing a conductive composition under general firing conditions, tellurium is oxidized to a state close to hexavalent (typically in the range of 5.2 to 5.5). However, in the present invention, the valence of tellurium in the electrode after firing on the substrate or the like to be used is maintained in a more reduced state as described above by adjusting the composition of each constituent material. I have control. Specifically, the blend of the tellurium-containing composition and the tellurium valence adjusting material in the conductive composition is mainly prepared, and the average of tellurium (Te) while satisfying the charge neutrality condition as the whole conductive composition. A blend having a valence within the above range is realized. Although the detailed mechanism is not clear, the presence of such tellurium in the electronic state in the vicinity of the interface between the substrate and the electrode can favorably improve the electrical bonding state between the electrode and the substrate. This makes it possible for these tellurium atoms to exist in an electronic state that can effectively contribute to the realization of a low-resistance ohmic contact in the electrode, regardless of the form and amount of tellurium in the conductive composition. The

In the present specification, the means for measuring the valence of tellurium is not particularly limited. For example, as a suitable method for measuring the valence of tellurium, the X-ray absorption fine structure (XAFS) analysis method or the X-ray photoelectron spectroscopy (XPS) method is used. Is mentioned.
For XAFS, more specifically, the X-ray Absorption Near Edge Structure (XANES) analysis method is used to excite the inner electrons of tellurium atoms to unoccupied and quasi-continuous levels. From the X-ray absorption spectrum based on energy, the chemical state (electronic state) of the tellurium atom can be grasped. In this specification, the valence of tellurium is the average valence calculated from the shift amount of the peak near 4350 eV of the XANES spectrum measured by the transmission method using the XAFS analyzer in the beam line BL14B2 of SPring-8 as described later. Is adopted. The absorbed energy used for calculating the average valence is not limited to the one near 4350 eV, and for example, absorbed energy at the Te-K end, L end, etc. can be used.

As for XPS, information on the elemental composition and chemical state of the surface can be obtained by observing the kinetic energy of photoelectrons emitted by irradiating the sample surface under ultra-high vacuum with X-rays. Specifically, by analyzing the energy spectrum of photoelectrons, the tellurium atoms present on the material surface are identified, and information on the valence and bonding state is obtained from the chemical shift of the tellurium peak based on narrow scan analysis. Can do. The valence of tellurium is, for example, in an XPS spectrum obtained using an XPS analyzer (manufactured by ULVAC-PHI Co., Ltd., PHI5000) and using, for example, an Al—Kα ray (hv = 1486.6 eV excitation) as a radiation source. The results obtained by calculating the average valence of tellurium from the relationship between the valence of tellurium and the shift amount of the binding energy using the Te-3d _5/2 peak near the binding energy of 576 eV as an index are adopted. be able to. Note that the peak used for calculating the average valence is not limited to Te-3d _5/2 , and may be another peak such as Te-3d _3/2 (586 eV).

In a preferred embodiment of the method for producing a conductive composition disclosed herein, the tellurium-containing composition is a tellurium compound powder containing tellurium (Te) as a constituent element.
Such a configuration is preferable because the method for blending tellurium and the blending ratio can be easily adjusted.

In a preferred embodiment of the method for producing a conductive composition disclosed herein, the tellurium-containing composition is a glass composition containing tellurium (Te) as a constituent element.
According to such a configuration, tellurium can reach the substrate satisfactorily together with the glass component at the time of fire-through, and can contribute to the realization of a low-resistance ohmic contact. In addition, an electrode having high adhesive strength can be formed by using a conductive composition having a glass composition containing tellurium.

In a preferred embodiment of the method for producing a conductive composition disclosed herein, the glass composition is a mixture of a basic glass component not containing tellurium and a tellurium-containing glass component containing tellurium. .
According to this configuration, the valence of tellurium after firing can be controlled more easily, and a conductive composition having a high effect of improving ohmic contact can be more easily produced.

In a preferred embodiment of the method for producing a conductive composition disclosed herein, the tellurium valence adjusting material is at least one selected from the group consisting of Ti, V, Mn, Fe, Co, Ni, Cu and Zn. It is characterized by being a metal or metal compound containing a seed metal element.
In the electrode after firing, the metal element has a characteristic that the electronic state is likely to vary depending on the environment. According to such a configuration, the valence of tellurium contained in the tellurium-containing composition can be more suitably controlled. Further, by including these metals or metal compounds, it is possible to improve the adhesion strength of the formed electrode and reduce the contact resistance.

In another aspect, the present invention provides a conductive composition produced by any one of the production methods described above. According to this, the compounded tellurium component can exist in a state that can sufficiently contribute to the formation of a good (low resistance) ohmic contact in the electrode after firing, and an electrode having excellent adhesion can be formed. A conductive composition is provided. Such a conductive composition is adjusted so that tellurium can exist in an optimal electronic state (electronic configuration) depending on the substrate used, so that it is open when used to form solar cell electrodes. A solar cell excellent in electrical characteristics such as voltage, fill factor and energy conversion efficiency can be realized. From this aspect, the present invention also provides a solar cell having excellent electrical characteristics and reliability by including an electrode formed using this conductive composition.

FIG. 1 is a cross-sectional view schematically showing an example of the structure of a solar cell configured using the conductive composition of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of the structure of a solar cell configured using a conventional conductive composition.

Hereinafter, preferred embodiments of the present invention will be described. In addition, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, a method of applying a conductive composition to a substrate, a baking method, a configuration of a solar cell, etc.) It can be grasped as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The method for producing a conductive composition disclosed herein is intended for production of a conductive composition for forming an Ag electrode used for forming a silver (Ag) electrode in a solar cell. As described above, the production method includes (1) preparing silver powder that is a constituent material of the conductive composition, a tellurium-containing composition, and a tellurium valence adjusting material, and (2) the conductive composition. So that the average valence of tellurium (Te) contained in the interface between the substrate and the conductive composition when it is applied to the substrate of the solar cell and baked is 4.3 or more and 5.1 or less. Adjusting the compounding of the silver powder, the tellurium-containing composition and the tellurium valence adjusting material to prepare a conductive composition.

[Silver powder]
The silver powder contained as the main solid content in the conductive composition disclosed herein is an aggregate of particles mainly composed of silver (Ag), and is typically an aggregate of particles composed of Ag alone. . However, even if such silver powder contains a small amount of impurities other than Ag and Ag-based alloys, it can be included in the “silver powder” as long as it is an aggregate of Ag-based particles as a whole. The silver powder may be produced by a conventionally known production method and does not require special production means.
The shape of the particles constituting such silver powder is not particularly limited. Although it is typically spherical, it is not limited to a so-called true spherical shape. Other than spherical shapes, for example, flake shapes and irregular shapes can be mentioned. Such silver powder may be composed of particles having such various shapes. When such silver powder is composed of particles having a small average particle size (typically several μm size), it is preferable that 70% by mass or more of the particles (primary particles) have a spherical shape or a similar shape. . For example, a silver powder in which 70% by mass or more of the particles constituting the silver powder has an aspect ratio (that is, the ratio of the major axis to the minor axis) of 1 to 1.5 is preferable.

In addition, when forming an Ag electrode on one surface (typically a light-receiving surface, but may be the back surface) of a substrate (for example, a Si substrate) constituting a solar cell, a desired dimension (line width, The coating amount and the coating form of the conductive composition can be taken into consideration so that the film thickness and the like can be realized. Here, the silver powder suitable for forming the light-receiving surface electrode of the solar cell is not particularly limited, but those having an average particle diameter of 20 μm or less of the particles constituting the powder are suitable. The thickness is preferably 0.01 μm or more and 10 μm or less, more preferably 0.3 μm or more and 5 μm or less, for example, 2 μm ± 1 μm. Here, the average particle diameter means a particle diameter at a cumulative volume of 50% in a particle size distribution measured by a laser diffraction / scattering method, that is, D50 (median diameter).
For example, it is also possible to use a silver (mixed) powder in which a plurality of silver powders (typically two types) having different average particle diameters are mixed and the average particle diameter of the mixed powder is within the above range. it can. By using silver powder having an average particle diameter as described above, a dense Ag electrode suitable as a light-receiving surface electrode can be formed.

The content of the silver powder in the conductive composition disclosed herein is not particularly limited, but when the total amount of the conductive composition (solid content) is 100% by mass, 50% by mass to 99% thereof. It is preferable to adjust the content so that the silver powder is not more than mass%, more preferably not less than 65 mass% and not more than 98 mass%, for example, not less than 75 mass% and not more than 95 mass%. When the silver powder content rate in the manufactured electroconductive composition exists in the said range, Ag electrode (film | membrane) with high electroconductivity and the further improved compactness can be formed.

[Tellurium-containing composition]
As the tellurium-containing composition, any powdered material containing tellurium (Te) as a constituent element can be used without particular limitation. For example, specifically, it may be a tellurium (Te) simple substance, an organic compound containing tellurium as a constituent element, a compound powder such as an inorganic compound, a powdery glass composition, or the like. These may be a mixture or composite of any two or more types exemplified below.
[Tellurium-containing organic or inorganic substances]
Examples of organic compounds include various tellurols, tellurides, telluroxides, tellurons and derivatives thereof. Tellurium-containing inorganic compounds include tellurium and other metal compounds, oxides, oxoacids, hydroxides, halides, sulfates, phosphates, nitrates, carbonates, acetates, metal complexes (coordination compounds) And the like. As these inorganic or organic tellurium-containing compositions, typically, tellurium oxide such as tetratellurafulvalene (TTeF), TeO ₂ , Te ₂ O ₃ , Te ₂ O ₅ , TeO ₃ , Te (OH), etc. Telluric acid salt represented by ₆ , such as telluric acid, potassium metatellate, sodium metatellurate, zinc telluride, aluminum telluride, cobalt telluride, tin telluride, tungsten telluride, titanium telluride, copper telluride, tellurium Examples thereof include metal telluride compounds such as lead iodide, bismuth telluride, manganese telluride, and molybdenum telluride. In these tellurium-containing compositions, tellurium can have values such as 0, 3, 4, 5, and 6. The tellurium-containing composition used here is preferably a compound in which tellurium is pentavalent or hexavalent, and examples thereof include Te ₂ O ₅ , TeO ₃ , and Te (OH) ₆ .

[Tellurium-containing glass component]
In addition, as the tellurium-containing glass component, various glass compositions containing tellurium as a glass constituent component, and tellurium compound-supported glass compositions in which a tellurium compound is supported on the surface of a glass composition substantially free of tellurium Etc. can be considered. That is, in the tellurium-containing glass component, the tellurium component is not present as a component that is separated from the glass composition, but is present as a component that constitutes the glass composition itself or without being liberated from the glass composition. ing. Such a tellurium-containing glass component can be a component that effectively acts to form an Ag electrode as a light-receiving surface electrode of a solar cell from above the antireflection film by a fire-through method. It can also be an inorganic additive that improves the adhesion strength of the formed electrode to the substrate.

By using a glass composition containing tellurium as a glass constituent component, the softening temperature of the glass composition can be lowered, and a conductive composition with higher adhesion can be realized. The composition of the glass composition containing tellurium as a glass component is not particularly limited. For example, a glass composition having the following composition (oxide conversion composition; the entire glass frit is 100 mol%) is used. Can be preferably used.

The structure (oxide conversion composition) of such tellurium-containing glass composition will be described in detail below.
TeO ₂ can be a component (glass network former) constituting a glass skeleton together with other elements, and has a function of lowering the softening point of glass. Moreover, the effect which suppresses the excessive corrosion of the board | substrate at the time of a fire through is exhibited by being contained in the electroconductive composition for electrode formation of a solar cell. Such TeO ₂ can be contained, for example, in a ratio of about 70 mol% or less in the glass composition (in the glass composition not containing tellurium described later, it can be 0 mol%). Since TeO ₂ is relatively expensive, if the amount is too large, the cost increases, which is not preferable. TeO ₂ is preferably in a proportion of about 5 to 65 mol%, more preferably 10 to 50 mol%.

SiO ₂ is a component constituting a glass skeleton (glass network former), and can be contained in the glass composition at a ratio of about 0 to 70 mol%, for example. As the amount of SiO ₂ increases, the solubility of the glass decreases and the softening point increases. For example, if SiO ₂ exceeds 70 mol%, the fire-through characteristic is deteriorated, which is not preferable. When a glass network former in place of SiO ₂ is contained in the glass composition, the content of SiO ₂ may be 0 mol% (that is, SiO ₂ is not substantially contained). When SiO ₂ is contained, it is preferable that SiO ₂ is in a proportion of about 5 to 65 mol%, more preferably 10 to 50 mol%, from the viewpoint of the chemical stability, durability and handling properties of the glass structure. It is desirable that

B ₂ O ₃ has a function of suppressing the thermal expansion of the glass composition and lowering the viscosity and the melting temperature, and can be contained in the glass composition at a ratio of about 0 to 40 mol%. When there is too much B ₂ O ₃ , crystal precipitation is likely to occur during melting and cooling when adjusting the glass composition, which is not preferable. Since B ₂ O ₃ can cause a decrease in long-term durability (particularly long-term high-temperature durability), the content of B ₂ O ₃ is 0 mol% (that is, B ₂ O ₃ is not substantially contained). It may be. B ₂ O ₃ is preferably in a ratio of about 1 to 30 mol%, more preferably about 5 to 25 mol%.

Bi ₂ O ₃ is an optional additive component that adjusts the thermal expansion coefficient. Moreover, physical stability can also be improved because a glass bonding material is comprised by a multi-component system. The ratio of Bi ₂ O ₃ in the glass composition is preferably about 1 to 30 mol%, and more preferably about 5 to 25 mol%.

PbO is an optional additive component and can be contained, for example, in a ratio of about 0 to 65 mol% for the purpose of lowering the softening point of the glass. The content of PbO may be 0 mol% (that is, B ₂ O ₃ is not substantially included) in consideration of the influence on human health and the environment. In the blend containing PbO, the proportion of PbO is preferably about 10 to 50 mol%, and more preferably about 30 to 40 mol%.

Alkaline earth metal component (MO: specifically, at least one of MgO, CaO, ZnO, SrO and BaO) is not necessarily a necessary component, but as a network modifier oxide (network modifier) It is a component that contributes to control of the thermal stability of the glass composition. When these are included, for example, any one or more of them can be included in a total ratio of about 1 to 25 mol%, and the total ratio is more preferably about 1 to 10 mol%.

An alkali metal component (RO: specifically, at least one of Li ₂ O, Na ₂ O, and K ₂ O) is also a component that increases the meltability of the glass composition, although it is not necessarily a necessary component. Any one or more can be included. These components can be included in a ratio of about 1 to 15 mol% in total, for example, and more preferably about 1 to 7 mol%.

As a glass composition contained in the conductive composition disclosed herein, it may be composed only of typical glass components as described above, or as long as the effect of the present invention is not significantly impaired, Arbitrary components other than the above may be included. Examples of such additional components include oxides such as Al ₂ O ₃ , TiO ₂ , ZrO ₂ , WO ₃ , V ₂ O ₅ , Nb ₂ O ₅ , FeO, CuO, SnO ₂ , P ₂ O. ₅ , La ₂ O ₃ , CeO _{2 and the} like. Moreover, the additive (a well-known clarifying agent, coloring agent, etc.) generally used conventionally for this kind of glass bonding material as needed can also be included. The ratio of these additional components and various additives is preferably less than about 5 mol% (typically less than 4 mol%, for example, less than 1 mol%) of the entire glass composition. In addition, it is needless to say that inevitable impurities other than those shown in the above composition, which are derived from raw materials and manufacturing processes, are allowed.
On the other hand, although not necessarily limited to this, in a suitable one aspect | mode, it can be set as the mixing | blending which does not contain an arsenic (As) component substantially in addition to the said lead (Pb) component. Arsenic components and lead components are not preferable from the viewpoints of environmental performance, workability, and safety because they can adversely affect the human body and the environment.

As the tellurium-containing glass composition as described above, more specifically, for example, the following glass L, glass M, and glass N are shown as preferred examples.
[Glass L]
SiO ₂ : 9 mol% or more and 53 mol% or less B ₂ O ₃ : 1 mol% or more and 7 mol% or less PbO: 10 mol% or more and 57 mol% or less TeO ₂ : 10 mol% or more and 70 mol% or less [Glass M]
SiO ₂ : 9 mol% or more and 65 mol% or less B ₂ O ₃ : 1 mol% or more and 18 mol% or less PbO: 9 mol% or more and 65 mol% or less Li ₂ O: 0.6 mol% or more and 18 mol% or less TeO ₂ : 10 mol% or more and 70 mol% or less

[Glass N]
Bi ₂ O ₃ : 10 mol% or more and 29 mol% or less B ₂ O ₃ : 10 mol% or more and 33 mol% or less SiO ₂ : 0 mol% or more and 20 mol% or less ZnO: 10 mol% or more and 30 mol% or less TeO ₂ : 10 mol% or more and 60 mol% or less Li ₂ Total of O, Na ₂ O and K ₂ O: 8 mol% or more and 21 mol% or less When the conductive composition of the present invention uses any one of the above glass L, glass M and glass N, the electrical characteristics of the solar cell Can be improved particularly preferably. That is, as a glass composition that exhibits a fire-through effect, for example, any of glass L and glass M, which are lead-containing glasses, and glass N, which is lead-free glass, is suitable for forming a light-receiving surface electrode of a solar cell. Can be performed.

On the other hand, in the tellurium compound-supported glass composition, the tellurium compound is inseparably integrated with the glass composition as a carrier, but is mainly included as a crystalline phase, not as a component constituting the glass. Yes. For example, specifically, one or a plurality of tellurium compound particles may be bonded to one flaky or powdery glass frit and supported on the glass frit. A plurality of glass frit carrying tellurium compound particles may be further bonded. Here, the relative sizes of the glass frit and the tellurium compound particles are not particularly limited, and either of them may be larger or the same size. It is sufficient that the relative positional relationship between the two is maintained.

Paying attention to the structure of the tellurium compound-supported glass composition, the tellurium compound-supported glass composition has a glass composition (glass phase) and a crystalline tellurium compound phase (crystal phase) integrated via an interface. It has a structure. Here, the glass phase is mainly composed of glass that does not substantially contain tellurium (Te). That is, the glass phase may contain Te, but may be contained as a secondary component, not as a component that forms the main glass skeleton. The tellurium compound phase is crystalline with the tellurium compound as a main component (for example, it is intended that 50% by mass or more is occupied by the tellurium compound), and the glass phase clearly has a crystal structure. Can be distinguished. The glass phase may be composed of one type of glass phase, or a plurality of types of glass phases may be present. Further, the tellurium compound phase may be composed of one kind of tellurium compound phase, or a plurality of kinds of tellurium compound phases may be present. For example, a plurality of tellurium compound phases having different compositions may be integrated into one glass phase, or a plurality of glass phases having different compositions and a plurality of tellurium compound phases having different compositions may be integrated. good.

Since these glass phase and tellurium compound phase may diffuse each other at the bonding interface, for example, they may contain each other in the vicinity of the interface. In other words, the components may be unevenly distributed in the vicinity of the interface. Typically, for example, the glass phase may contain Te near the interface with the tellurium compound phase. However, Te may not be included in the vicinity of the center of the glass phase. Depending on the size of the glass phase, a form containing Te in the vicinity of the center is also conceivable, but in such a case, it can be understood that Te does not exist as a main glass network former (ie, glass skeleton). In addition, the tellurium compound phase may include a constituent component of the glass phase in the vicinity of the interface with the glass phase. In this case, the constituent component of the glass phase is locally contained as one constituent component of the tellurium compound.
That is, in the tellurium-supported glass frit, the glass phase and the tellurium compound phase are bonded via the interface, and the components of each other can diffuse near the interface, but one phase is not completely taken into the other phase, In essence, it exists as a separate and distinct phase.

In such a tellurium-supported glass composition, the shape of the glass composition supporting the tellurium compound (which may be a glass phase; the same shall apply hereinafter) is not particularly limited, and is typically obtained by pulverizing glass or the like. The glass may be in the form of flakes or powder. The composition is not particularly limited, and can be the same as the glass frit or the like conventionally used for this type of conductive composition.
Examples of such glass frit include, for example, lead-based, zinc-based, borosilicate-based, alkaline-based glass, glass containing barium oxide, bismuth oxide, or a combination of two or more of these. Is done. The composition of the glass frit can be considered according to the configuration of the tellurium-containing glass composition (other than TeO ₂ ). More specifically, for example, a glass composition having a representative composition as shown below (an oxide conversion composition; the entire glass frit is 100 mol%) is given as a preferred example.

[Glass L ']
SiO ₂ : 9 mol% or more and 53 mol% or less B ₂ O ₃ : 1 mol% or more and 7 mol% or less PbO: 46 mol% or more and 57 mol% or less [Glass M ′]
SiO _2: 20 mol% or more 65 mol% or less B ₂ O _3: more than 1 mol% 18 mol% or less PbO: 20 mol% or more 65 mol% or less Li ₂ O: 0.6mol% or more 18 mol% or less

[Glass N ']
Bi ₂ O ₃ : 10 mol% or more and 29 mol% or less B ₂ O ₃ : 20 mol% or more and 33 mol% or less SiO ₂ : 0 mol% or more and 20 mol% or less ZnO: 15 mol% or more and 30 mol% or less Li ₂ O, Na ₂ O and K ₂ O Total: 8 mol% or more and 21 mol% or less

The above composition is representative, and various kinds of materials are used for the purpose of obtaining good adhesion to the substrate, electrode film formability, erosion to the reaction antireflection film, and good ohmic contact. It goes without saying that the components may be adjusted and further glass modifying components (alkali metal elements, alkaline earth metal elements and other various glass forming components) may be added.

Moreover, there is no restriction | limiting in particular also about the tellurium compound carry | supported by the said glass composition, For example, the various tellurium compounds illustrated above can be considered. The ratio of the tellurium compound supported on the glass frit is not particularly limited. For example, when the tellurium compound is converted to tellurium oxide (TeO ₂ ) with respect to 100 parts by mass of the glass frit, as an approximate guideline. It is preferably carried at a ratio of 20 parts by mass to 60 parts by mass, more preferably about 30 parts by mass to 50 parts by mass.

According to the tellurium-supported glass composition having the above structure, the tellurium compound is present in a suitable state in the conductive composition without being too uniform without being too uniform with the glass composition, without being too close without being too close. It is thought that. This preferred positional relationship is continuously maintained from the preparation of the conductive composition to the time when the glass component is melted by firing as well as during the application and drying of the conductive composition. The According to the conductive composition containing such a tellurium-supported glass composition, it is possible to form an electrode capable of realizing high energy conversion efficiency with low resistance compared to a silver paste containing a tellurium compound as a single paste constituent. it can. Moreover, according to the electroconductive composition containing this tellurium carrying | support glass composition, an electrode with high adhesive strength can be formed compared with the electroconductive composition containing the glass frit which contains tellurium as a network former. That is, an electrode having high adhesive strength (for example, solder strength) and low contact resistance can be formed.

[Basic glass components]
The tellurium-containing glass disclosed herein does not necessarily have to be various glass compositions and / or tellurium-supported glass compositions containing tellurium as a glass constituent, as described above. For example, various glass compositions and / or tellurium-supported glass compositions containing tellurium as glass constituent components may be used as basic glass components that do not contain the tellurium component conventionally used in this type of conductive composition (containing non-tellurium). It may be used by mixing with glass. There is no particular limitation on the composition of such a basic glass components, for example, it can be considered according to the arrangement of the tellurium-containing glass composition (other than TeO _2). More specifically, a glass having any composition of the above glass L ′, glass M ′ and glass N ′ can be mentioned as a suitable example. In this case, the ratio between the tellurium-containing glass and the basic glass component can be appropriately determined in consideration of the total amount of the glass components in the conductive composition and the tellurium content of the tellurium-containing glass.
A preferable ratio of the whole glass component in the conductive composition (solid content) is not limited to this, but is approximately 0.5% by mass or more and 5% by mass or less, preferably 0.5% by mass or more and 3% by mass. The mass% or less, more preferably 1 mass% or more and 3 mass% or less is appropriate.

In addition, although the tellurium-containing composition content depends on the form of the tellurium-containing composition to be used, it cannot be generally stated, but the conductive composition is applied to the substrate of the solar cell and fired. The blending ratio of the silver powder and the tellurium valence adjusting material is determined so that the average valence of tellurium (Te) contained in the interface with the conductive composition is 4.3 or more and 5.1 or less. For example, when the tellurium-containing glass described in the examples described later is used as the tellurium-containing composition, as an approximate guide, when the entire conductive composition (solid content) is 100% by mass, the tellurium-containing composition It is preferable to adjust appropriately in the range of 0.5 mass% to 50 mass%, more preferably 1 mass% to 35 mass%, for example, 5 mass% to 25 mass%.

[Tellurium valence adjusting material]
As the tellurium valence adjusting material, a powder made of a compound containing an element whose oxidation number is relatively easy to change can be preferably used. For example, a transition metal, a typical metal and a metal containing a rare earth element or a compound thereof that can be an ion having a valence of +3 or more can be considered. More preferably, it may be a metal of an element belonging to Group 3A to Group 3B of the periodic table or a compound thereof, typically a transition metal element belonging to Group 3A to Group 2B of the periodic table, particularly Preferably, scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel, which are first transition elements (3d transition elements) The powder of the metal which consists of (Ni), copper (Cu), and zinc (Zn) or its compound can be considered. More preferably, it is a powder of a metal composed of Fe, Co, Ni, Ti or its oxide, and more limited may be Ni or NiO. Any one of these powders may be included alone, or two or more thereof may be included.
The average particle diameter of the particles constituting these powders is suitably 1 nm or more and 200 nm or less, preferably 5 nm or more and 200 nm or less, more preferably 15 nm or more and 200 nm or less.

As for the content of the tellurium valence adjusting material, the average valence of tellurium (Te) contained in the interface between the substrate and the conductive composition when the conductive composition is applied to the substrate of the solar cell and baked is 4. It is determined as a blending ratio of the silver powder and the tellurium-containing composition so as to be 3 or more and 5.1 or less. The average number of tellurium can be controlled effectively by adjusting the content of the tellurium valence adjusting material. The content of the tellurium valence adjusting material is not strictly limited, but as an approximate guide, the tellurium valence adjusting material occupies when the entire conductive composition (solid content) is 100% by mass. The ratio can be about 0.5% by mass or less. Preferably they are 0.001 mass% or more and 0.3 mass% or less, More preferably, they are 0.001 mass% or more and 0.2 mass% or less.

[Organic medium]
The conductive composition formulated as described above may be provided in the form of a solid powder (typically in the form of a mixture) containing silver powder, a tellurium-containing composition, and a tellurium valence adjusting agent, For example, it may be provided in a state dispersed in an organic medium. That is, the conductive composition can contain an organic medium as a component other than the above-described solid content. Any organic medium may be used as long as it can disperse the above-described solid content, particularly silver powder, and any of those used in conventional pastes of this type can be used without particular limitation. Typically, an organic vehicle in which an organic binder is dispersed in a solvent can be considered. For example, as a solvent constituting the organic medium, one or a combination of high-boiling organic solvents such as ethylene glycol and diethylene glycol derivatives (glycol ether solvents), toluene, xylene, butyl carbitol (BC), and terpineol are used. can do. Moreover, as an organic binder, various resin components can be included. Any resin component may be used as long as it can provide a conductive composition with good viscosity and film-forming ability (adhesiveness to a substrate), and those used in conventional pastes of this type can be used without any particular limitation. can do. Examples thereof include those mainly composed of acrylic resin, epoxy resin, phenol resin, alkyd resin, cellulosic polymer, polyvinyl alcohol, rosin resin and the like. Among these, cellulosic polymers such as ethyl cellulose are particularly preferable.

The proportion of the organic medium in the entire conductive composition (solid content + organic medium) is suitably 5% by mass to 60% by mass, preferably 7% by mass to 50% by mass, and more preferably Is 10 mass% or more and 40 mass% or less. Further, the organic binder contained in the vehicle is preferably contained in a proportion of about 1% by mass to 10% by mass, more preferably about 1% by mass to 7% by mass of the entire conductive composition. By adopting such a configuration, it is easy to form (apply) a coating film having a uniform thickness on the substrate as an electrode (film), it is easy to handle, and it takes a long time to dry before firing the electrode film. It is preferable because it can be suitably dried without any problems.

In addition, the conductive composition in a form in which a solid content is dispersed in an organic medium (which may be in a state of so-called paste, ink, etc.) can be suitably adjusted by, for example, the following method.
That is, the silver powder prepared above, a tellurium-containing composition, and a tellurium valence adjusting material are dispersed in an organic medium. The dispersion of the solid content in the organic medium is typically performed by using, for example, a three-roll mill or other kneader to add silver powder having a predetermined blending ratio, a tellurium-containing composition, and a tellurium valence adjusting material. Mix and agitate with vehicle. In mixing the above materials, all the materials may be mixed at the same time or may be added in two or more times. For example, silver powder and tellurium-containing composition (excluding tellurium-supported glass) may be mixed in advance, and then tellurium-supported glass and tellurium valence adjusting material may be added. Furthermore, a part of the materials may be mixed in the form of a dispersion liquid previously dispersed in a medium such as an aqueous solvent or alcohol. Thereby, the electroconductive composition of the form with which solid content was disperse | distributed to the organic medium can be prepared suitably.

[Preparation of tellurium-supported glass]
In the tellurium-containing composition, the tellurium-supported glass can be prepared, for example, by mixing a predetermined glass powder and a tellurium compound and firing the mixture. The firing is preferably carried out in a temperature range of (Tm−35) ° C. to (Tm + 20) ° C. typically in an oxidizing atmosphere (eg, air atmosphere) when the melting point of the glass powder is Tm ° C. When the firing temperature exceeds (Tm + 20) ° C., melting of the glass powder proceeds, and the tellurium compound is taken into (dissolved) in the glass phase, which is not preferable. The firing temperature is more preferably (Tm + 15) ° C. or less, and further preferably Tm ° C. or less (that is, the melting point of the glass powder or less). Further, if the firing temperature is lower than (Tm-35) ° C., the possibility that the tellurium compound cannot be reliably supported increases, which is not preferable. The firing temperature is preferably (Tm-30) ° C. or higher, more preferably (Tm-20) ° C. or higher. Thereby, the tellurium carrying | support glass disclosed here can be prepared.

Note that the tellurium-supported glass as a fired product obtained after firing may be sintered as a whole to form large aggregates. In such a case, such agglomerate is crushed and sieved as necessary so that a particle size suitable for the preparation of the conductive composition (for example, about 0.01 μm to 10 μm) is used. Anyway. By sintering, the glass powder and the tellurium compound are combined to form a neck. Although this bond is stronger than adhesion by adsorption or the like, the glass powder and the tellurium compound are sintered in a mixed state without being compacted. Can be easily reduced to a desired particle size by light crushing (for example, manual crushing or light mixing using a mortar, pestle, etc.) without using a simple device.

[Production of electrodes]
The conductive composition obtained as described above can be handled in the same manner as, for example, a silver paste that has been conventionally used for forming an Ag electrode as a light-receiving surface electrode on a substrate. That is, a conventionally known method can be employed without any particular limitation for the formation of the electrode from the conductive composition disclosed herein.

As a method for forming the light receiving surface electrode 12, for example, an antireflection film 14 is formed on almost the entire surface of the silicon substrate 11, and a silver paste is applied to a portion where the light receiving surface electrode 12 is formed on the antireflection film 14. A so-called fire-through method may be used in which the anti-reflection film 14 under the silver paste is melted by direct coating and baking to make electrical contact between the silver paste and the silicon substrate 11.
For example, when the silver electrode (light-receiving surface electrode 12) in the solar cell 10 shown in FIG. 1 is formed by the fire-through method, the n ⁺ layer 16 and the antireflection film 14 are formed on the light-receiving surface of the substrate as in the conventional case. After the formation, the conductive composition of the present invention is supplied (applied) on the antireflection film 14 so as to have a desired film thickness (for example, about 20 μm) and a desired coating film pattern. The conductive composition can be typically supplied by a screen printing method, a dispenser coating method, a dip coating method, or the like. As the substrate, a silicon (Si) substrate 11 is suitable, and typically a Si wafer. The thickness of the substrate 11 includes a desired solar cell size, film thicknesses of the Ag electrode 12, the back electrode 20, the antireflection film 14 and the like formed on the substrate 11, and the strength (for example, destruction) of the substrate 11. (Strength) and the like can be set. The thickness of the substrate 11 is, for example, generally 100 μm or more and 300 μm or less, preferably 150 μm or more and 250 μm or less, and may be 160 μm or more and 200 μm, for example. The conductive composition can also be used for the substrate 11 having a shallow emitter structure in which the n ⁺ layer 16 is thin and the dopant concentration is low.

The conductive composition disclosed herein can be constituted, for example, by mainly dispersing silver powder and a glass component as a tellurium-containing composition in an organic medium. In such a conductive composition, an ohmic contact between the silver component in the composition and the n-Si layer 16 is realized by the glass component in the composition breaking the antireflection film 14 in the firing process. is there. According to such a method, the number of steps can be reduced as compared with an electrode formation method that involves partial removal of the antireflection film 14, and a deviation occurs between the removal portion of the antireflection film 14 and the formation position of the light receiving surface electrode 12. There is no worry. Therefore, such a fire-through method can be preferably used for forming the light receiving surface electrode 12.
In the case where the fire-through method is not employed, for example, the following method can be employed. That is, first, the n ⁺ layer 16 and the antireflection film 14 are formed on the light receiving surface by CVD or the like over almost the entire surface of the silicon substrate 11. Thereafter, the formation portion of the light-receiving surface electrode 12 in the antireflection film 14 is peeled (removed) with a desired electrode pattern using hydrofluoric acid (HF) or the like. And supplying a conductive composition with the desired film thickness to this peeling part is mentioned.
Next, the conductive composition coating (coating film) supplied to the substrate 11 is dried at an appropriate temperature (eg, room temperature or higher, typically about 100 ° C.). After drying, the dried coating film is baked by heating in an appropriate baking furnace (for example, a high-speed baking furnace) under appropriate heating conditions (for example, 600 ° C. to 900 ° C., preferably 700 ° C. to 800 ° C.) for a predetermined time. I do. Thereby, the coated material is baked on the substrate 11 to form a silver electrode 12 as shown in FIG.

[Production of solar cells]
Note that materials and processes for manufacturing a solar cell other than forming an electrode (typically, a light-receiving surface electrode) using the conductive composition manufactured by the manufacturing method of the present invention are the same as in the past. It may be. And a solar cell (typically crystalline silicon solar cell) provided with the electrode formed with the said conductive composition can be manufactured, without requiring a special process etc. A typical example of the structure of such a crystalline silicon solar cell is the structure shown in FIG.
As a process other than the formation of the light receiving surface electrode, formation of the aluminum electrode 20 as the back surface electrode 20 can be mentioned. The procedure for forming the aluminum electrode 20 is as follows. For example, first, as described above, the conductive composition for forming the light-receiving surface electrode 12 is printed on the light-receiving surface, and the conductive composition for forming the back-side external connection electrode 22 is also formed on the back surface (disclosed here). A conductive composition prepared by a manufacturing method may be printed on a desired area and dried. Thereafter, the aluminum electrode paste material is printed and dried so as to overlap a part of the printing region of the conductive composition for the backside external connection electrode, and all the coating films are fired. Usually, the aluminum electrode 20 is baked and a P ⁺ layer (BSF layer) 24 is also formed. That is, the aluminum electrode 20 to be the back electrode 20 is formed on the p-type silicon substrate 11 by firing, and the aluminum atoms are diffused into the substrate 11 to form the p ⁺ layer 24 containing aluminum as an impurity. The Rukoto. In this way, the solar battery (cell) 10 can be manufactured.

As described above, the conductive composition disclosed herein is controlled so that the average valence of tellurium contained in the interface between the substrate and the electrode after firing is 4.3 or more and 5.1 or less. . The tellurium in the electronic state is present at the interface between the substrate and the electrode, so that the contact between the substrate and the electrode becomes good, and the power generated in the substrate 11 of the solar cell 10 is lost via the electrode. Can be taken out to the outside in a low state. Thereby, it becomes possible to produce a solar cell with high energy conversion efficiency. Moreover, since this electrically conductive composition essentially contains a tellurium component, it is possible to produce a solar cell with high adhesive strength and high durability and reliability. Therefore, according to such a conductive composition, a solar cell having excellent solar cell characteristics (for example, FF of 0.78 or more and power generation efficiency of 16.5% or more) can be provided.

Note that the performance of the solar cell 10 formed by the fire-through method, such as energy conversion efficiency, largely depends on the quality of the ohmic contact formed as described above. That is, high energy conversion efficiency can be achieved by reducing the contact resistance between the formed light receiving surface electrode 12 and the silicon substrate 11. As described above, the conductive composition disclosed herein can improve ohmic contact, and thus contributes favorably to the realization of the solar cell 10 with enhanced fill factor (FF) and energy conversion efficiency. Can do.

Further, in a general configuration of a conventional solar cell, short-wavelength light has low transmissivity, so that it reaches the pn junction and does not contribute to power generation, but is absorbed by the n-Si layer and changed to heat. (Heat loss). In a preferred embodiment of the solar cell 10 disclosed herein, the thickness of the n-Si layer 16 (for the purpose of increasing the photoelectric conversion efficiency by delivering light having a shorter wavelength to the pn junction portion with as high an intensity as possible. The depth may be reduced to reduce heat loss. The thickness of the n-Si layer 16 can be, for example, about 300 nm to 500 nm as in the conventional case. However, for example, the thickness can be reduced to 300 nm or less, more preferably about 250 nm or less.

In general, when the thickness of the n-Si layer is reduced in this way, the n-Si layer itself increases in resistance and increases in sheet resistance, and it is necessary to lower the dopant concentration in order to suppress surface recombination. For this reason, it is difficult to obtain a good ohmic contact between the light-receiving surface electrode and the n-Si layer, and there is a concern that the problem of increased contact resistance may occur. In addition, when the above-described fire-through method is applied to the formation of the light-receiving surface electrode, the electrode paste not only reaches the n-Si layer, but also erodes to the vicinity of the pn junction interface beyond the n-Si layer. Strict conditions were required, and there was a risk of adverse effects on the fill factor (FF) and energy conversion efficiency of solar cells. However, by forming the light-receiving surface electrode using the conductive composition disclosed herein, the ohmic contact can be reliably improved as described above. Therefore, for example, even when the thickness of the n-Si layer 16 is reduced to 250 nm or less or the firing conditions are adjusted so as not to erode the pn junction, an increase in contact resistance can be suppressed and a good junction can be realized. Is possible.

Hereinafter, examples related to the present invention will be described, but the present invention is not intended to be limited to those shown in the following examples.

Conductive compositions 1 to 10 including silver powder (average particle size 1.6 μm), Ni powder (average particle size 0.15 μm) and the glass composition shown below were prepared. These conductive compositions are dispersed in an organic vehicle composed of a binder (ethylcellulose) and an organic solvent (terpineol), and the viscosity is 160 to 180 Pa · s (20 rpm, 25 ° C.) by adding the organic solvent. Adjusted. A three-roll mill was used for preparing the paste. The composition of the paste-like conductive composition thus obtained was as follows: silver powder: 77 to 88% by mass, Ni powder: 0.01 to 0.2% by mass, glass composition: 1 to 10% by mass, The organic vehicle was 4 to 14% by mass and the organic solvent was 2 to 8% by mass.

In addition, as said glass composition, the tellurium amount which occupies the basic glass frit which does not contain tellurium, and the tellurium containing glass frit containing tellurium in an electroconductive composition is shown in "Te addition amount" of the following Table 1 It mixed and used so that it might become a value. As the basic glass frit, a glass having an average particle diameter of 1.1 μm and having the following composition A or composition B was used. Further, as the tellurium-containing glass frit, a glass having the following composition was used.

<Basic glass frit: Composition A>
_{_{_{Bi 2 O 3: 20mol%,}}} B 2 O 3: 29mol%, SiO 2: 4mol%, ZnO: 30mol%, Li 2 O: 17mol%
<Basic glass frit: Composition B>
_{_{_{PbO: 29mol%, B 2 O}}} 3: 12mol%, SiO 2: 47mol%, Li 2 O: 12mol%
<Glass frit containing tellurium>
_{_{_{Te 2 O: 30mol%, PbO}}} : 29mol%, B 2 O 3: 5mol%, SiO 2: 36mol%

[Preparation of solar cells for evaluation]
Using the paste-like conductive compositions 1 to 10 obtained above as the light-receiving surface electrode forming paste, solar cells for evaluation were produced according to the following procedure.
That is, first, a commercially available p-type single crystal silicon substrate (plate thickness 180 μm) for a solar cell having a size of 156 mm square was prepared, and its surface was acid-etched using a mixed acid obtained by mixing hydrofluoric acid and nitric acid. . Next, a phosphorus-containing solution is applied to the light receiving surface of the silicon substrate on which the fine uneven structure is formed by the etching process, and heat treatment is performed, so that the thickness of the light receiving surface of the silicon substrate is about 0.5 μm. A -Si layer (n ⁺ layer) was formed (see FIG. 1). On this n-Si layer, an antireflection film (silicon nitride film) having a thickness of about 80 nm was formed by plasma CVD (PECVD).
Thereafter, using the prepared conductive composition, a coating film (thickness of 10 μm or more and 30 μm or less) to be a light receiving surface electrode (Ag electrode) was formed on the antireflection film by screen printing. Similarly, a coating film to be a back electrode (Ag electrode) was formed in a pattern. These coating films were dried at 85 ° C. and subjected to the next step.

Next, a predetermined aluminum paste for back electrode is screen printed so as to overlap a part of the Ag electrode pattern on the back side of the silicon substrate (SUS screen mesh, # 325, wire diameter 23 μm, emulsion thickness 20 μm, the same applies hereinafter). Was printed (coated). The printing conditions were set so that the firing width of the grid line was 100 μm. Next, this silicon substrate was baked at a temperature of about 700 ° C. or higher and 800 ° C. or lower in an air atmosphere using a near infrared high-speed baking furnace. Thereby, the solar cell for evaluation provided with the Ag electrode (light-receiving surface electrode) was obtained. Hereinafter, solar cells produced using the conductive compositions 1 to 10 will be referred to as samples 1 to 10, respectively.

[Curve factor (FF) and energy conversion efficiency (Eff)]
Using a solar simulator (Beger, PSS10), the IV characteristics of the solar cells of Samples 1 to 10 were measured. From the obtained IV curves, the open circuit voltage (Voc) and the fill factor (fill factor: FF) and power generation efficiency (η) were obtained. Voc, FF and power generation efficiency were calculated based on the “crystalline solar cell output measurement method” defined in JIS C-8913, and the results are shown in Table 1. This calculated value is an average value of 100 data obtained by the solar simulator.

[Evaluation of valence of tellurium]
For the solar cells of Samples 1 to 10 after the IV characteristics were measured, the electrode on the surface of the silicon substrate was peeled off, and the interface (substrate surface) between the exposed electrode and the substrate was subjected to XAFS analysis. The valence was examined. The analysis conditions were as follows.
Analyzer: SPring-8 Industrial Use II, BL14B2
Monochromator: SPring-8 standard double crystal spectrometer Spectral crystal: Si (111)
Measurement energy range: 4320 eV to 4400 eV
Measurement method: Transmission method In the XANES spectrum, the absorption edge shifts to the higher energy side as the valence number of tellurium increases. In the analysis of the valence of tellurium, TeO ₂ and TeO ₃ are used as tetravalent and hexavalent standard samples, respectively, and from the amount of shift of the absorbed energy in the vicinity of 4350 eV in the XANES spectrum of the standard sample, it is included in the measurement sample. The average valence of tellurium was calculated. The measurement results of the average valence of tellurium are shown in Table 1.

[Evaluation]
The valence of tellurium at the electrode-substrate interface obtained by firing the conductive compositions of Samples 1 to 10 was approximately the same as expected from experience. As shown in Table 1, between the ratio of tellurium contained in the conductive composition and the valence of tellurium at the electrode-substrate interface after firing, the valence of tellurium increases as the Te addition amount increases. There is a tendency to decrease. However, as can be seen from Samples 1, 2 and 5, etc., this relationship does not necessarily hold, and the tellurium valence changes depending on the composition of the glass composition and the tellurium valence adjusting agent. I understand that

And when the valence of tellurium was 4.3 or more and 5.1 or less, it was shown that all of Voc, FF, and power generation efficiency show a good value with good balance. The fill factor (FF) is basically an index that is a measure of the quality of a solar cell, and a typical FF value falls within a range of 0.7 to 0.8. In the latter half region where the FF value is 0.7, the performance as a solar cell is greatly improved by increasing the FF value even by 0.01%. From the results in Table 1, it was confirmed that there was a large difference in the FF values obtained depending on the valence of tellurium in the conductive composition. That is, when the valence of tellurium is 4.3 or more and 5.1 or less, the FF value is 0.78 units, which is much higher than the other cases.
The same tendency is also observed for Voc and power generation efficiency. When the tellurium valence is 4.3 or more and 5.1 or less, all the characteristics are well balanced and can be said to be remarkably improved. .

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

10 Solar cell 11 Substrate 12 Light-receiving surface electrode (Ag electrode)
14 Anti-reflective coating 16 n-Si layer (n ⁺ layer)
20 Back electrode (aluminum electrode)
22 Back side external connection electrode 24 p ⁺ layer

Claims

A method for producing a conductive composition for forming an electrode of a solar cell, comprising:
Preparing a silver powder, a tellurium-containing composition, and a tellurium valence adjusting material;
When the conductive composition is applied to the substrate of the solar cell and fired, the average valence of tellurium (Te) contained in the interface between the substrate and the conductive composition is 4.3 or more and 5.1 or less. Adjusting the composition of the silver powder, the tellurium-containing composition and the tellurium valence adjusting material to prepare a conductive composition,
Manufacturing method.
The production method according to claim 1, wherein the tellurium-containing composition is a tellurium compound powder containing tellurium (Te) as a constituent element.
The manufacturing method according to claim 1 or 2, wherein the tellurium-containing composition is a glass composition containing tellurium (Te) as a constituent element.
The manufacturing method according to claim 3, wherein the glass composition is a mixture of a basic glass component containing no tellurium and a tellurium-containing glass component containing tellurium.
The tellurium valence adjusting material is a metal or metal compound containing at least one metal element selected from the group consisting of Ti, V, Mn, Fe, Co, Ni, Cu and Zn. The manufacturing method of any one of these.
A conductive composition produced by the production method according to any one of claims 1 to 5.
A solar cell comprising an electrode formed using the conductive composition according to claim 6.