JP2013120807A - Paste composition for solar cell electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paste composition for a solar cell electrode, with which the control of an entry amount of an electrode material can be easily performed even when an electrode is formed by a fire-through method in a solar cell having a shallow emitter structure with a thin n layer, and a solar cell high in FF value, low in leakage current and high in efficiency can be obtained.SOLUTION: A light-receiving surface electrode is configured of a thick silver film that contains 1-10 pts.wt. of lead glass relative to 100 pts.wt. of silver, the lead glass having a composition that contains 6-62 (mol%) of PbO, 1-18 (mol%) of BO, 8-49 (mol%) of SiO, 0-30 (mol%) of AlO, 1-30 (mol%) of LiO, 1-30 (mol%) of TiO, 0-30 (mol%) of ZnO, 0-1.0 (mol%) of ZrO, and 0-6 (mol%) of PO, respectively. Accordingly, an eroded amount is controlled in a range of about 80-90 (nm), so that, even though a line width is narrowed to about 100 (μm), good ohmic contact is obtained, and a photoelectric conversion efficiency of a solar cell is enhanced.

Description

  The present invention relates to a conductive paste composition suitable for a solar cell electrode formed by a fire-through method.

For example, a general silicon-based solar cell includes an antireflection film and a light-receiving surface electrode through an n layer formed by doping a donor element such as phosphorus on the upper surface of a silicon substrate that is a p-type polycrystalline semiconductor. , And has a structure in which a back surface electrode (hereinafter simply referred to as “electrode” when not distinguished from each other) is provided via a p ⁺ layer on the lower surface, and power generated at the pn junction of the semiconductor by light reception is applied to the electrode. It comes to take out through. The antireflection film is for reducing the surface reflectance and increasing the light receiving efficiency while maintaining a sufficient visible light transmittance, and is made of a thin film such as silicon nitride, titanium dioxide, or silicon dioxide.

  Since the above-described antireflection film has a high electric resistance value, it prevents an electric power generated at the pn junction of the semiconductor from being efficiently extracted. Therefore, the light-receiving surface electrode of the solar cell is formed by a method called fire-through, for example. In this electrode formation method, for example, after the antireflection film is provided on the entire surface of the n layer, a conductive paste, that is, a paste-like electrode material is formed in an appropriate shape on the antireflection film by using, for example, a screen printing method. Apply and bake. As a result, the electrode material is heated and melted, and at the same time, the antireflection film in contact with the electrode material is melted, and the light receiving surface electrode and the semiconductor are brought into contact with each other. The conductive paste is mainly composed of, for example, silver powder, glass frit (a piece of flaky or powdered glass that is crushed as necessary after melting and quenching the glass raw material), an organic vehicle, and an organic solvent. Since the glass component in the conductive paste breaks the antireflection film in the baking process, an ohmic contact is formed by the conductive component in the conductive paste and the n layer (for example, Patent Document 1). See). In this conductive paste, conductivity is obtained by blending various trace components made of a metal or a compound such as phosphorus, vanadium, bismuth, and tungsten. According to the above electrode forming method, the process is simplified as compared with the case where the antireflection film is partially removed and an electrode is formed on the removed portion, and there is a problem of misalignment between the removed portion and the electrode forming position. There is an advantage that does not occur.

  In the formation of the light-receiving surface electrode of such a solar cell, various proposals have been made for the purpose of improving the fire-through property and improving the ohmic contact, and thus increasing the fill factor (FF value) and energy conversion efficiency. Has been made. For example, by adding a Group 5 element such as phosphorus, vanadium, bismuth or the like to the conductive paste, there is a material that promotes the redox action on the antireflection film of glass and silver and improves the fire-through property (for example, (See Patent Document 1). In addition, by adding chloride, bromide, or fluoride to the conductive paste, these additives help the glass and silver break the antireflection film, thereby improving ohmic contact (for example, patents). See reference 2.) Examples of the fluoride include lithium fluoride, nickel fluoride, and aluminum fluoride. It is also shown that a Group 5 element is added in addition to the above additives. The glass is, for example, borosilicate glass.

Further, a thick film conductive composition in which silver powder, a zinc-containing additive, and a glass frit having a softening point in a range of 300 to 600 (° C.) are dispersed in an organic solvent has been proposed (for example, a patent See reference 3.) This thick film conductive composition is for forming a light-receiving surface electrode of a solar cell, and conductivity and solder adhesion are improved by adding zinc. Further, as the glass frit, the SiO ₂ 21~29 (wt%), the _{Al 2 O 3 0.1~8 (wt%} ), a PbO 50~62 (wt%), B 2 O 3 7-10 ( wt%), ZnO and _{0~4 (wt%), Li 2} O and 0~0.1 (wt%), it has been shown that the TiO ₂ may be used 2 to 7 (wt%) containing lead glass.

Further, the SiO ₂ 1~10 (wt%), a _{B 2 O 3 5~15 (wt%} ), the _{Al 2 O 3 1~15 (wt%} ), a PbO 68~89 (wt%), CuO SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -PbO-based low melting point glass containing 0 to 10 wt%, TiO ₂ 0 to 10 wt%, and having a softening point of 350 to 500 (° C.) A conductive paste for a light-receiving surface electrode of a polycrystalline Si solar cell that can obtain a stable ohmic contact by using is shown (for example, see Patent Document 4).

In addition, an electrode material containing Ag powder, organic vehicle, glass frit, and at least one of Ti, Bi, Co, Zn, Zr, Fe, and Cr on an antireflection film made of Si ₃ N ₄ or SiO ₂ or the like. There is one that attempts to obtain stable ohmic contact and solder bonding strength by baking (see, for example, Patent Document 5). Ti, Bi and the like are preferably 0.05 to 5 parts by weight with respect to 100 parts by weight of Ag. The reason why the above effect is obtained is not shown, but if Ti, Bi, etc. are contained, they dissolve in the glass during the firing process of the electrode material, and then the electrode material acts on the antireflection film. Therefore, the reaction with the antireflection film is stabilized as compared with the case where Bi or the like is not contained.

Japanese Patent Laid-Open No. 62-049676 JP 11-213754 A JP 2006-302890 A JP 2009-098771 A JP 2001-313400 A

  By the way, in the solar cell described above, the impurity concentration of the n layer located on the light receiving surface side is lowered or the n layer is made thin (that is, the doping depth of the donor element is made shallow) to increase the sheet resistance of the n layer. Attempts have been made to create a shallow emitter. As a result, the surface recombination rate can be reduced, and thus the voltage and the current that can be extracted can be improved, so that the solar cell can be highly efficient. When a shallow emitter is formed in this way, the short wavelength side particularly near 400 (nm) also contributes to power generation, which is considered an ideal solution in terms of improving the efficiency of solar cells. In the shallow emitter, the thickness of the n layer on the light receiving surface side is 70 to 100 (nm), which is even thinner than the conventional silicon solar cell 100 to 200 (nm). Of these, the portion that could not be effectively used by changing to heat before reaching the pn junction is reduced, so that the short-circuit current Isc is increased, which in turn increases the power generation efficiency.

  However, when the n layer is thin like the shallow emitter, that is, the pn junction is shallow, the antireflection film is sufficiently broken by fire-through in the above-described firing process for forming the light receiving surface electrode, and the pn junction is formed. It is very difficult to control the penetration depth so that the electrode material does not penetrate. Therefore, there is a problem that the FF value tends to decrease as the leakage current Id increases and extends. Also, when firing the substrate, the pn junction is more easily damaged under conditions where the amount of heat is strong, such as when the maximum holding temperature is high or when the time required from the start of temperature increase to the end of temperature decrease is long, which is more than the theoretical value. Characteristics are likely to deteriorate. Therefore, the temperature range in which good characteristics can be obtained, that is, the firing margin is narrowed.

  The present invention has been made in the background of the above circumstances, and its purpose is to control the amount of electrode material intrusion even when an electrode is formed by a fire-through method in a solar cell having a thin n-layer shallow emitter structure. An object of the present invention is to provide a solar cell electrode paste composition that is easy, has a high FF value, has a small leakage current, and can provide a highly efficient solar cell.

In order to achieve such an object, the gist of the present invention is a paste composition for a solar cell electrode containing a conductive powder, a glass frit, and a vehicle, wherein the glass frit is 6 in terms of oxide. and PbO of ~62 (mol%), and B ₂ O ₃ of 1~18 (mol%), and SiO ₂ of 8~49 (mol%), and Li ₂ O of 1~30 (mol%), 1 30 and TiO ₂ of (mol%), 0~6 and a P ₂ O ₅ in (mol%), and Pb / (Si + Ti) ( mol ratio) be made of glass which is in the range of 0.2 to 2.4 It is in.

In this way, a solar cell electrode paste composition, the glass frit constituting the this, PbO of 6~62 (mol%), 1~18 ( mol%) of B ₂ O _3, 8~49 ( mol%) SiO ₂ , 1 to 30 (mol%) Li ₂ O, 1 to 30 (mol%) TiO ₂ and Pb / (Si + Ti) (mol ratio) in the range of 0.2 to 2.4 Furthermore, although it is not essential, it is made of glass containing P ₂ O ₅ in a range of 0 to 6.0 (mol%) as a preferable component, so that even when the pn junction portion is shallow, the electrode material can be easily penetrated. Can be controlled. Therefore, when the paste composition of the present invention is used for forming the light-receiving surface electrode, a solar cell module having a small leak current Id, a high fill factor FF value, a large current value, and a high photoelectric conversion rate can be produced.

  In the glass frit composition, PbO is a component that lowers the softening point of the glass and is a component that enables low-temperature firing, and PbO is 6 (mol%) or more in order to obtain good fire-through properties. And it is necessary to be 62 (mol%) or less. If the amount of PbO is less than 6 (mol%), the softening point becomes too high, making it difficult to vitrify and erosion of the antireflection film, and as a result, good ohmic contact cannot be obtained. On the other hand, if it exceeds 62 (mol%), the softening point becomes too low and the erosion becomes so strong that the pn junction is broken, and the FF value becomes small. The amount of PbO is more preferably 60 (mol%) or less. That is, the range of 6 to 60 (mol%) is more preferable. Further, 38 (mol%) or more is more preferable, and 59 (mol%) or less is more preferable. That is, the range of 38 to 59 (mol%) is particularly preferable.

B ₂ O ₃ is a glass-forming oxide (that is, a component that forms a glass skeleton), and is a component for lowering the softening point of glass. To obtain good fire-through properties, B ₂ O ₃ Is required to be 1 (mol%) or more and 18 (mol%) or less. If the amount of B ₂ O ₃ is less than 1 (mol%), the softening point becomes too high, so that it is difficult for the antireflection film to erode. As a result, good ohmic contact cannot be obtained, and the moisture resistance also decreases. In particular, in the present invention, since Li is contained in the glass, it is extremely difficult to melt unless 1 (mol%) or more of B ₂ O ₃ is contained. On the other hand, if it exceeds 18 (mol%), the softening point becomes too low and the erosion becomes so strong that the pn junction is broken. In any case, the open circuit voltage Voc tends to decrease. The amount of B ₂ O ₃ is more preferably 3 (mol%) or more, and further preferably 12 (mol%) or less. That is, the range of 3 to 12 (mol%) is more preferable. Further, it is more preferably 8 (mol%) or less. That is, the range of 3 to 8 (mol%) is particularly preferable.

In addition, SiO ₂ is a glass-forming oxide, a component for increasing the chemical resistance of the glass, SiO ₂ is 8 (mol%) or more and 49 (mol%) to obtain good fire-through properties ) It must be: If the amount of SiO ₂ is less than 8 (mol%), the chemical resistance is insufficient and glass formation becomes difficult.On the other hand, if it exceeds 49 (mol%), the softening point becomes too high and vitrification becomes difficult, resulting in an antireflection film. It becomes difficult to erode, and thus good ohmic contact cannot be obtained. The amount of SiO ₂ is more preferably 32 (mol%) or less.

Further, Li ₂ O is a component to lower the softening point of the glass, in order to obtain good fire-through property, Li ₂ O is 1.0 (mol%) and not more than 30 (mol%) must be less that It is. When Li ₂ O is less than 1.0 (mol%), the softening point becomes too high and the erosion property to the antireflection film becomes insufficient. On the other hand, if it exceeds 30 (mol%), the alkali is eluted and the erosion becomes too strong, so that the electrical characteristics are deteriorated. Incidentally, Li is generally an impurity for semiconductors because it promotes diffusion, and Li tends to deteriorate the characteristics, so it is desirable to avoid it in semiconductor applications. In particular, when Li is contained when the amount of Pb is large, the erodibility tends to be too strong and control tends to be difficult. However, in solar cell applications such as those described above, no deterioration in properties was observed even when glass containing Li was used, but the proper amount was included on the contrary, thereby improving the fire-through property and enhancing the properties. Li is a donor element, which can lower the contact resistance Rc, and has an advantage that the firing margin is further widened by the donor compensation effect. In addition, it was recognized that the composition range of the glass capable of obtaining good fire-through properties was increased by adopting a composition containing Li. However, even in solar cell applications, if included excessively, the erodibility becomes too strong, and the electrical characteristics tend to deteriorate. The amount of Li ₂ O is more preferably 12 (mol%) or less.

In addition, TiO ₂ has the effect of increasing the FF value by reducing the contact resistance Rc and thus reducing the series resistance Rs, and is included in the range of 1.0 (mol%) to 30 (mol%). It is necessary to be If the amount of Ti is less than 1.0 (mol%), Rc and Rs cannot be sufficiently lowered, and the FF value becomes low. On the other hand, when Ti exceeds 30 (mol%), the softening point increases, and therefore it becomes difficult to produce frit in a normal firing furnace having a firing temperature of 1250 (° C.) or less.

In addition, PbO, SiO ₂ , and TiO ₂ are not only in the above ranges, respectively, and Pb / (Si + Ti) (mol ratio) needs to be 0.2 or more and 2.4 or less. If the Pb / (Si + Ti) mol ratio is less than 0.2, that is, if (Si + Ti) is excessive with respect to Pb, it will be difficult to melt, so the fire-through property will decrease, the Rc between the light-receiving surface electrode and n layer will increase, and eventually the FF value Decreases. In order to make it easy to melt, it is conceivable to increase Li and Zn, but these lower the FF value further. On the other hand, when the Pb / (Si + Ti) mol ratio exceeds 2.4, the influence of Pb increases, so the erosion becomes so strong that the pn junction is destroyed, and Id is significantly increased, so the FF value decreases. As a result, sufficient output characteristics cannot be obtained. In short, as mentioned above, Ti raises the glass softening point, so it affects the amount of erosion during fire-through in the same way as Si, so when increasing the amount of Ti, Pb / (Si + Ti) mol It is necessary to control the amount of erosion by simultaneously adjusting the Pb amount and the Si amount so that the ratio is within the above range. Pb / (Si + Ti) is more preferably 2.0 or less. Further, 1.0 or more is more preferable, and 1.9 or less is more preferable. That is, 1.0 to 1.9 is particularly preferable.

  Incidentally, it has been proposed to obtain a good ohmic contact by containing Ti in the glass frit constituting the conductive paste, thereby suppressing the decrease in the FF value (see Patent Documents 4 and 5, etc.). See). If Ti is contained, silicide is formed at the time of firing, so that it is considered that Rc between the n-type silicon layer and the silver electrode can be reduced as described above. Such ohmic contact improvements are essential for high sheet resistance shallow emitters, but Ti has the effect of increasing the penetration depth of the electrode material, making it more difficult to control the penetration depth. . On the other hand, according to the present invention, by setting Pb / (Si + Ti) to an appropriate range as described above, there is an advantage that Rc is lowered and penetration depth control is facilitated.

  In forming a shallow emitter, the n layer has a high sheet resistance as described above. However, when the donor element concentration near the surface is lowered, the barrier barrier between Ag and Si is increased, resulting in an ohmic contact. It is difficult to ensure contact. On the other hand, when the n layer is made thin, it becomes difficult to control the penetration depth, and Rc between the n layer and the Ag electrode increases. In any case, the FF value was reduced, but according to the present invention, these problems can be solved by appropriately controlling the Ti amount and the Pb / (Si + Ti) amount as described above. It is.

Further, P ₂ O ₅ is a donor element for the n layer, and is an optional component that is optionally included because it facilitates securing an ohmic contact of the light-receiving surface electrode. P ₂ O ₅ needs to be 6.0 (mol%) or less. If it exceeds 6.0 (mol%), the glass becomes difficult to melt and a dead layer (layer with a high recombination rate) is formed.

In general, in order to ensure ohmic contact, it is desirable to dissolve the donor element in a high concentration. On the other hand, in the high sheet resistance cell constituting the shallow emitter, the thickness of the antireflection film made of, for example, Si ₃ N _{4 is set} to about 80 (nm), and the amount of erosion by the electrode is in the range of 80 to 90 (nm). That is, it is desirable to control with an accuracy of 10 (nm). However, such control is extremely difficult and must be controlled to be slightly over-eroded. Therefore, the decrease in output due to excessive erosion is suppressed by supplementing the eroded n layer with a donor element. In order to ensure ohmic contact under such conditions, it is desirable that the concentration of the donor element be 10 ¹⁹ (pieces / cm ³ ) or more, preferably 10 ²⁰ (pieces / cm ³ ) or more. Elements other than glass components that can obtain such a high concentration are limited to As, P, and Sb. Of these, As is highly toxic and is not preferred for glass production operated in an open system, but Sb is an element that can be used in place of P.

  In addition, although it is difficult to specify in which form each of the above components is contained in the glass, these ratios are all values converted to oxides.

  In addition, the glass constituting the conductive paste of the present invention may contain other various glass components and additives as long as the properties are not impaired. For example, Al, Zn, Zr, Na, Ca, Mg, K, Ba, Sr, etc. may be contained. These may be included in a total range of 30 (mol%) or less, for example. Among these, Al and Zn are contained in appropriate amounts, thereby improving the parallel resistance Rsh, and thus improving Voc and Isc. Since both Al and Zn are acceptors, they obstruct donor compensation that is essential in a shallow emitter. On the other hand, since Li and P have a donor compensation effect as described above, when Al or Zn is contained, it is desirable to contain a considerable amount of Li or P.

  In addition, as described above, the conductive paste composition of the present invention can easily obtain good ohmic contact. Therefore, for example, the present invention is suitably applied to a high sheet resistance substrate having a sheet resistance value of about 80 to 120 (Ω / □). However, the present invention can be applied to a substrate having a sheet resistance value lower than this, and similarly applicable to a solar cell having a conventional structure that is not a shallow emitter. In addition, since the glass component in the paste can be reduced as compared with the conventional one, the resistance value of the silver grid electrode can be lowered, so that there is an advantage that thinning is easy.

Here, preferably, the glass and PbO having 6 to 60 in terms of oxides (mol%), and B ₂ O ₃ of 3 to 12 (mol%), and SiO ₂ of 8 to 32 (mol%) 1-30 includes a Li ₂ O of (mol%), and TiO ₂ of 1 to 30 (mol%), and P ₂ O ₅ of 0 to 4 (mol%), and Pb / (Si + Ti) ( mol The ratio is preferably in the range of 0.2 to 2.0.

Also, preferably, the glass and PbO of 38 to 59 in terms of oxides (mol%), and B ₂ O ₃ of 3 to 8 (mol%), and SiO ₂ of 8 to 32 (mol%), 1-12 and Li ₂ O of (mol%), and TiO ₂ of 3~30 (mol%), 0~2 and a P ₂ O ₅ in (mol%), and Pb / (Si + Ti) ( mol ratio ) Is preferably in the range of 1.0 to 1.9.

  The glass frit has an average particle size (D50) in the range of 0.3 to 3.0 (μm). If the average particle size of the glass frit is too small, melting will be too early when the electrode is fired, resulting in a decrease in electrical characteristics, but if it is 0.3 (μm) or more, moderate melting properties can be obtained, so that the electrical characteristics are further enhanced. . In addition, since agglomeration is unlikely to occur, better dispersibility can be obtained during paste preparation. Also, the dispersibility of the entire powder is lowered when the average particle size of the glass frit is significantly larger than the average particle size of the conductive powder, but better dispersibility can be obtained when it is 3.0 (μm) or less. Moreover, a further melting property of the glass can be obtained. Therefore, in order to obtain a better ohmic contact, the average particle diameter is preferable.

  The average particle size of the glass frit is a value obtained by the air permeation method. The air permeation method is a method for measuring the specific surface area of a powder from the permeability of a fluid (for example, air) to a powder layer. The basis of this measurement method is the Kozeny-Carmann equation, which shows the relationship between the wetted surface area of all particles making up the powder layer and the flow velocity and pressure drop of the fluid passing therethrough. The specific surface area of the sample is obtained by measuring the flow velocity and pressure drop with respect to the powder layer filled under the conditions determined by the above. In this method, the gap between the filled powder particles is regarded as pores, and the wetted surface area of the particles that resists the flow of air is determined. Usually, the value is smaller than the specific surface area determined by the gas adsorption method. Show. An average particle diameter assuming powder particles can be calculated from the obtained specific surface area and particle density.

  Preferably, the conductive powder is a silver powder having an average particle diameter (D50) in the range of 0.3 to 3.0 (μm). Although copper powder, nickel powder, etc. can be used as the conductive powder, silver powder is most preferable in order to obtain high conductivity. Further, if the average particle size of the silver powder is 3.0 (μm) or less, better dispersibility can be obtained, and thus higher conductivity can be obtained. Moreover, if it is 0.3 (μm) or more, aggregation is suppressed and better dispersibility can be obtained. Since silver powder of less than 0.3 (μm) is extremely expensive, 0.3 (μm) or more is preferable from the viewpoint of manufacturing cost. Further, if the average particle diameter of both the conductive powder and the glass frit is 3.0 (μm) or less, there is an advantage that clogging hardly occurs even when the electrode is printed by a fine line pattern.

  The silver powder is not particularly limited, and enjoys the basic effect of the present invention that thinning can be achieved while maintaining conductivity even when a powder of any shape such as a spherical shape or a scale shape is used. Can do. However, when the spherical powder is used, the printability is excellent and the filling rate of the silver powder in the coating film is increased, so that, together with the use of highly conductive silver, other shapes such as scales are used. Compared with the case where the silver powder of this is used, the electrical conductivity of the electrode produced | generated from the coating film becomes high. Therefore, it is particularly preferable because the line width can be further reduced while ensuring the necessary conductivity.

  Also preferably, the solar cell electrode paste composition has a viscosity at 25 (° C.)-20 (rpm) in the range of 150 to 250 (Pa · s), a viscosity ratio (ie, 10 (rpm)). Viscosity / viscosity at 100 (rpm)) is 3-8. By using a paste having such a viscosity characteristic, the viscosity is suitably reduced during squeezing and transmitted through the screen mesh. After the transmission, the viscosity returns to a high viscosity and the expansion of the printing width is suppressed. Thus, a fine line pattern can be easily obtained while maintaining the printability such that clogging does not easily occur and clogging does not occur. The viscosity of the paste composition is more preferably in the range of 180 to 230 (Pa · s), and the viscosity ratio is more preferably in the range of 3.2 to 6.5. In addition, a viscosity ratio of 4 to 6 is desirable for thinning a design line width of 100 (μm) or less.

  Note that increasing the film thickness so that the cross-sectional area can be maintained even if the line width is reduced includes, for example, increasing the emulsion thickness of the printing plate, increasing the tension, and reducing the line diameter. It is also possible to widen the aperture. However, when the emulsion thickness is increased, the separation of the plate is deteriorated, so that the stability of the printed pattern shape cannot be obtained. In addition, when the tension is increased or the wire diameter is reduced, the screen mesh is easily stretched, so that it is difficult to maintain the dimensional and shape accuracy and the durability of the printing plate making is lowered. In addition, since it is provided with a large width, a bus bar that is unnecessary to increase the film thickness is also increased, resulting in a problem of waste of material.

  Preferably, the solar cell electrode paste composition includes the conductive powder in a proportion of 74 to 90 parts by weight and the vehicle in a proportion of 3 to 20 parts by weight. In this way, a paste composition can be obtained that can easily form an electrode having good printability, thin line width, and high conductivity.

  Preferably, the conductive paste composition contains the glass frit in a range of 1 to 10 parts by weight with respect to 100 parts by weight of the conductive powder. If it is contained in an amount of 1 part by weight or more, sufficient erosion property (fire-through property) can be obtained, so that a better ohmic contact can be obtained. Further, if it is kept at 10 parts by weight or less, it is difficult to form an insulating layer, and sufficient conductivity can be obtained. The amount of glass based on 100 parts by weight of the conductive powder is more preferably 1 to 8 parts by weight, and still more preferably 1 to 7 parts by weight.

  In addition, since the conductive paste composition of the present invention can suitably control the diffusion of silver when forming an electrode by fire-through as described above, it can be suitably used for a light-receiving surface electrode. Examples of the constituent material of the antireflection film provided on the light receiving surface include various materials such as titanium oxide, silicon dioxide, and silicon nitride. The paste of the present invention can be applied to any case, but is particularly suitable when the antireflection film is formed of a silicon nitride thin film.

Further, the glass frit can be synthesized from various raw materials that can be vitrified within the composition range, and examples thereof include oxides, hydroxides, carbonates, nitrates, etc. Silicon dioxide SiO ₂ can be used, boric acid B ₂ O ₃ can be used as the B source, and red lead Pb ₃ O ₄ can be used as the Pb source. Titanium oxide TiO ₂ as the Ti source, lithium carbonate Li ₂ CO ₃ as the Li source, ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ as the P source, and aluminum oxide Al ₂ O as the Al source ₃ may be used respectively.

It is a schematic diagram which shows the cross-section of the solar cell module provided with the solar cell with which the paste composition for electrodes of one Example of this invention was applied for formation of a light-receiving surface electrode. It is a figure which shows an example of the light-receiving surface electrode pattern of the solar cell of FIG. (a), (b) is the top view and side view for demonstrating the electrode pattern for contact resistance measurement. It is a figure which shows the relationship between the line space | interval and resistance value which were obtained by the measuring method of FIG. It is a figure explaining the measurement principle of contact resistance.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios, shapes, and the like of the respective parts are not necessarily drawn accurately.

  FIG. 1 is a diagram schematically showing a cross-sectional structure of a solar cell module 12 including a silicon-based solar cell 10 to which a conductive composition according to an embodiment of the present invention is applied. In FIG. 1, the solar cell module 12 includes the solar cell 10, a sealing material 14 for sealing the solar cell 10, a surface glass 16 provided on the sealing material 14 on the light receiving surface side, and a solar cell from the back surface side. 10 and a protective film (that is, a back sheet) 18 provided to protect the sealing material 14. The sealing material 14 is made of, for example, EVA, and is appropriately blended with a crosslinking agent, an ultraviolet absorber, an adhesion protective agent and the like so as to have sufficient weather resistance. The protective film 18 is made of, for example, fluorine resin, polyethylene terephthalate (PET) resin, or a laminate of a plurality of resin films made of PET, EVA, etc., and has high weather resistance, water vapor barrier properties, etc. I have.

The solar cell 10 includes, for example, a silicon substrate 20 which is a p-type polycrystalline semiconductor, an n layer 22 and a p ⁺ layer 24 respectively formed on the upper and lower surfaces thereof, and a reflection formed on the n layer 22. A prevention film 26 and a light receiving surface electrode 28, and a back electrode 30 formed on the p ⁺ layer 24 are provided. The thickness dimension of the silicon substrate 20 is, for example, about 100 to 200 (μm).

The n layer 22 and the p ⁺ layer 24 are provided by forming layers having a high impurity concentration on the upper and lower surfaces of the silicon substrate 20, and the thickness dimension of the high concentration layer is, for example, 70 n. ˜100 (nm), and the p ⁺ layer 24 is about 500 (nm), for example. The n layer 22 is about 100 to 200 (nm) in a general silicon-based solar cell, but is thinner than that in this embodiment, and has a structure called a shallow emitter. The impurity contained in the n layer 22 is an n-type dopant such as phosphorus (P), and the impurity contained in the p ⁺ layer 24 is a p-type dopant such as aluminum (Al) or boron (B). .

The antireflection film 26 is a thin film made of, for example, silicon nitride Si ₃ N ₄ , and is provided with an optical thickness of, for example, about 1/4 of the visible light wavelength, for example, about 80 (nm). It is configured to have an extremely low reflectance of 10 (%) or less, for example, 2 (%).

  The light receiving surface electrode 28 is made of, for example, a thick film conductor having a uniform thickness. As shown in FIG. 2, the light receiving surface electrode 28 is a comb having a large number of thin line portions substantially on the entire surface of the light receiving surface 32. Are provided in a planar shape.

The above thick film conductor is made of thick film silver containing, for example, 6.0 parts by weight of glass in a range of 1 to 10 parts by weight of glass with respect to 100 parts by weight of Ag. within the 6-62 of (mol%), for example 39.0 (mol%), the range of the _{B 2 O 3 1~18 (mol%} ), for example, 8.0 (mol%), the SiO ₂ 8~49 (mol in the range of%), for example 31.0 (mol%), in the range of Al ₂ O ₃ of 0 to 30 (mol%), for example, 3.0 (mol%), the Li ₂ O in the range of 1 to 30 (mol%) , for example, 12.0 (mol%), a TiO ₂ in the range of 1 to 30 (mol%), for example, 3.0 (mol%), in the range of ZnO 0 to 30 of (mol%), for example, 3.0 (mol%), ZrO within ₂ 0-1.0 of (mol%), for example, 0 (mol%), the P ₂ O ₅ in the range of 0~6 (mol%), lead glass containing each at a rate of for example 1.0 (mol%) is there. In the lead glass, PbO, SiO ₂ , and TiO ₂ are included so that the Pb / (Si + Ti) molar ratio is in the range of 0.2 to 2.4, for example, 1.10.

  In addition, the thickness dimension of the conductor layer is, for example, in the range of 20-30 (μm), for example, about 25 (μm), and the width dimension of each thin wire portion is, for example, in the range of 80-130 (μm), for example, It is about 100 (μm) and has sufficiently high conductivity.

The back electrode 30 is formed by applying a full-surface electrode 34 formed by applying a thick film material containing aluminum as a conductor component on the p ⁺ layer 24 over substantially the entire surface, and a strip-like application on the full-surface electrode 34. The band-shaped electrode 36 made of thick silver is formed. The strip electrode 36 is provided in order to make it possible to solder a solder ribbon 38 or a conductive wire to the back electrode 30. A solder ribbon 38 is welded to the light receiving surface electrode 28 in the same manner as the back surface side.

Solar cell 10 of the embodiment, the range of the PbO 6~62 (mol%) as the light-receiving surface electrode 28 described above, the range of the _{B 2 O 3 1~18 (mol%} ), the SiO ₂ 8-49 within the range of _{(mol%), Al 2 O} 3 within the range of 0~30 (mol%), in the range of Li ₂ O and 1~30 (mol%), a TiO ₂ 1 to 30 (mol in the range of%), the proportion of the range within the range of the ZnO 0 to 30 (mol%), in the range of ZrO ₂ and _{0~1.0 (mol%), P 2} O 5 to Less than six (mol%) Is composed of thick film silver containing 1 to 10 parts by weight of lead glass having a composition of 1 to 10 parts by weight with respect to 100 parts by weight of silver. Since the depth is controlled to a depth that is about 10 (nm) larger than the thickness dimension of 26, the line width is reduced to about 100 (μm), but between the n layer 22 Good ohmic contact is obtained and contact resistance is low.

  In addition, since the light receiving surface electrode 28 of the present embodiment has high conductivity since the glass amount is as small as about 1 to 10 parts by weight as described above, the film thickness and the line width can be any. Although the line resistance is low, the photoelectric conversion efficiency of the solar cell 10 is enhanced in combination with the low contact resistance.

  The light receiving surface electrode 28 as described above is formed, for example, by a well-known fire-through method using an electrode paste composed of conductive powder, glass frit, vehicle, and solvent. An example of the manufacturing method of the solar cell 10 including the formation of the light receiving surface electrode will be described below.

First, the glass frit is produced. Titanium oxide TiO ₂ as Ti source, lithium carbonate Li ₂ CO ₃ as Li source, aluminum oxide Al ₂ O ₃ as Al source, ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ as P source, Si source Prepare silicon dioxide SiO ₂ , boric acid B ₂ O ₃ as a B source, and lead Pb ₃ O ₄ as a Pb source, and weigh and prepare them to have an appropriate composition within the above-mentioned range. This is put into a crucible, melted at a temperature in the range of 900 to 1250 (° C.) according to the composition for about 30 minutes to 1 hour, and rapidly cooled to be vitrified. This glass is pulverized using an appropriate pulverizing apparatus such as a planetary mill or a ball mill. The average particle size (D50) after pulverization is, for example, about 0.3 to 3.0 (μm). In addition, the average particle diameter of the said glass powder is computed using the air permeation method mentioned above.

  On the other hand, as the conductor powder, for example, a commercially available spherical silver powder having an average particle diameter (D50) in the range of 0.3 to 3.0 (μm) is prepared. By using such silver powder having a sufficiently small average particle diameter, the filling rate of the silver powder in the coating film can be increased and the electrical conductivity of the conductor can be increased. The vehicle is prepared by dissolving an organic binder in an organic solvent. For example, butyl carbitol acetate is used as the organic solvent, and ethyl cellulose is used as the organic binder. The ratio of ethyl cellulose in the vehicle is, for example, about 15 (wt%). A solvent added separately from the vehicle is, for example, butyl carbitol acetate. That is, although it is not limited to this, the same solvent as that used for the vehicle may be used. This solvent is added for the purpose of adjusting the viscosity of the paste.

  Prepare the above paste materials, for example, conductor powder in the range of 77-88 (wt%), glass frit in the range of 1-10 (wt%), vehicle in the range of 8-14 (wt%) Among these, the solvent is weighed at a ratio in the range of 2 to 5 (wt%), mixed using a stirrer or the like, and then subjected to a dispersion treatment using, for example, a three roll mill. Thereby, the electrode paste is obtained. The viscosity of the paste was adjusted to be in the range of 180 to 230 (Pa · s) under the conditions of 20 (rpm) and 25 (° C.).

While preparing the electrode paste as described above, the n layer 22 and the p ⁺ layer are diffused or implanted into an appropriate silicon substrate by a well-known method such as a thermal diffusion method or ion plantation. By forming 24, the silicon substrate 20 is produced. Next, a silicon nitride thin film is formed thereon by an appropriate method such as PE-CVD (plasma CVD), and the antireflection film 26 is provided.

  Next, the electrode paste is screen-printed on the antireflection film 26 with the pattern shown in FIG. This is dried at, for example, 150 (° C.), and further subjected to a baking treatment at a temperature in the range of 700 to 800 (° C.) in a near infrared furnace. As a result, the glass component in the electrode paste melts the antireflection film 26 in the firing process, and the electrode paste breaks the antireflection film 26. Therefore, the conductor component in the electrode paste, that is, silver and the n layer 22 Electrical connection is obtained, and an ohmic contact between the silicon substrate 20 and the light-receiving surface electrode 28 is obtained as shown in FIG. The light receiving surface electrode 28 is formed in this way.

  The back electrode 30 may be formed after the above process, but may be formed by firing at the same time as the light receiving surface electrode 28. When the back electrode 30 is formed, the full surface electrode 34 made of a thick aluminum film is formed on the entire back surface of the silicon substrate 20 by, for example, applying an aluminum paste by screen printing or the like and performing a baking process. Further, the strip electrode 36 is formed by applying the electrode paste on the surface of the entire surface electrode 34 in a strip shape by screen printing or the like and performing a baking treatment. Thereby, the back electrode 30 which consists of the full surface electrode 34 which covers the whole back surface, and the strip | belt-shaped electrode 36 provided in strip shape on a part of the surface is formed, and the said solar cell 10 is obtained. In the above process, when manufacturing by simultaneous firing, a printing process is performed before firing the light-receiving surface electrode 28.

Next, the result of having manufactured and evaluated the solar cell 10 according to said manufacturing process by changing glass composition variously is demonstrated. About the solar cell characteristic, the output was measured using the commercially available solar simulator, and the fill factor FF value and the leakage current Id were obtained. Rc is the contact resistance between the n layer 22 and the light-receiving surface electrode (Ag electrode) 28, and was determined using the Transfer Length Method (TLM) method as follows. That is, first, in the same manner as the formation of the light-receiving surface electrode 28 in the manufacturing process, a plurality of strip-shaped ohmic electrodes are formed on the n layer by fire-through so as to be mutually parallel and mutually different. The formed electrode pattern is shown in FIGS. Next, the electrical resistance between the formed electrode pairs is measured using a four-terminal method. When the measured electrical resistance is written on the coordinates with the electrode interval taken on the horizontal axis (x-axis) and the measured electrical resistance value taken on the vertical axis (y-axis), the approximation obtained from the points shown in FIG. The y-intercept of a typical primary line is 2Rc. FIG. 5 illustrates this measurement principle. When the measured resistance value is Rtotal, the sheet resistance between the electrode pairs is Rsheet, and the electrode interval is d, the following relational expression is established. The y-intercept is 2Rc.
Rtotal = 2Rc + Rsheet · d
Note that the slope of the graph is Rsheet. The x-intercept is referred to as a transition length Lt, which is defined as a region that affects electrical contact under the electrode. Further, the specific contact resistance ρc can be calculated from the above Rc, Lt, and the length of the ohmic electrode.

The evaluation results are shown in Table 1 together with the glass composition. In Table 1, the numbers in the No. column marked with Δ are comparative examples outside the scope of the present invention, and the others are examples within the scope of the present invention. That is, Nos. 5, 7, 14, 18 to 20, 25, 28, 33, 35, 39, 42, 46, 48, and 49 are comparative examples, and others are examples. Among these examples, those marked with a circle in the No. column (Nos. 8, 11, 12, 21, 23, 24, 29, 32) are optimal within the scope of the present invention as described later. The composition is particularly preferable (Nos. 12, 21, 24, 29, 32). The FF value is a determination as to whether or not a good ohmic contact is obtained. In general, a solar cell can be used if the FF value is 70 or more. In the examples, those having an FF value greater than 75 were considered acceptable. The leak current Id is a criterion for determining whether or not an electrode has entered the pn junction, and is preferably lower, but can be used if it is -10 (V) or less than 1.0 (A). , 0.2 (A) or less was evaluated as ◎, 0.5 (A) or less as ◯, 1.0 (A) or less as Δ, and over 1.0 (A) as ×. In addition, the specific contact resistance ρc is one of the factors for lowering the FF value, and although a lower one is preferable, a high FF value is not necessarily obtained even if ρc is low, but it is one of various FF value lowering factors. It has been published for the purpose of evaluating the glass composition in a state in which is excluded, and confirming the effect of Ti addition.

  Each sample was prepared using spherical Ag powder having an average particle size of 1.6 (μm) and glass frit having an average particle size of 1.5 (μm). The mixing ratio is based on Ag powder 83 (wt%), glass frit 4 (wt%), vehicle 8 (wt%), solvent 5 (wt%), and 25 (° C) − The amount of vehicle and the amount of solvent were adjusted so that the viscosity at 20 (rpm) would be 180 to 230 (Pa · s). The printing plate making for forming the light-receiving surface electrode 28 was made by providing a 20 (μm) thick emulsion on a SUS325 screen mesh having a wire diameter of 23 (μm). The printing conditions were set so that the width of the grid line was 100 (μm). The sheet resistance of the n layer of the substrate is 90 ± 10 (Ω / □).

In Table 1, Al ₂ O ₃ , Li ₂ O, TiO ₂ , ZnO, ZrO ₂ , and P ₂ O ₅ were added to PbO—B ₂ O ₃ —SiO ₂ constituting the basic skeleton as an example. 9 component system of PbO-B ₂ O ₃ —SiO ₂ —Al ₂ O ₃ —Li ₂ O—TiO ₂ —ZnO—ZrO ₂ —P ₂ O ₅ and 4 component system lacking some of these elements An 8-component glass is shown. In the present invention, five elements of Pb, B, Si, Li, and Ti are essential components, and the examples are composed of these five components, or in addition to these, include one to four of the other four components. Having a composition.

Nos. 1 to 4 confirm the upper limit of the Li amount. Pb 9.0-17.0 (mol%), B 12.0 (mol%), Si 15.0 (mol%), Al 6.0 (mol%), Li 25.0-30.0 (mol%), Ti 15.0 (mol%) ), Zn is 7.0 to 13.0 (mol%), Zr and P are 0 (mol%), and Pb / (Si + Ti) is within the range of 0.3 to 0.6. was gotten. No. 4 was confirmed by changing the amount of Li less than No. 1 to 3 near the upper limit. In addition, Id tends to increase as Pb increases, that is, Pb / (Si + Ti) increases, but when comparing No. 3 and 4, Id can be suppressed to 0.5 (A) or less in No. 4. Therefore, it is considered that this tendency is alleviated by reducing Li and increasing Zn. Moreover, ρc was a sufficiently low value of 0.008 to 0.010 (Ω · cm ² ). According to these evaluation results, Li can be contained in a range of 30.0 (mol%) or less, although there is a balance with the amount of other elements, particularly Pb.

  No. 5 was confirmed with the composition of five essential components in combination with No. 10 and confirmed the upper limit of Si content. Pb was 29.5-46.0 (mol%), B was 1.0-14.6 (mol%), Si was 49.0 ~ 51.2 (mol%), Al is 0 (mol%), Li is 3.0 to 3.7 (mol%), Ti is 1.0 (mol%), Zn, Zr and P are 0 (mol%), Pb / (Si + In the composition where Ti) is in the range of 0.6 to 0.9, as shown in No. 10, sufficient characteristics were obtained in which Si was 49.0 (mol%), FF value was 76, and Id was 1.0 (A) or less. As shown in No. 5, when Si was 51.2 (mol%), the FF value was significantly reduced to 36, and Id was also increased to more than 1.0 (A). According to this evaluation result, the upper limit of Si is considered to be 49.0 (mol%). That is, even if the Ti amount is appropriate, if the Si amount is excessive, the FF value becomes low. In addition, although it is a 7-component system including Al and P, No. 49 also has a composition exceeding the upper limit of the Si amount, and the FF value was as low as 44.

  No. 7 confirmed the upper limit of Li amount together with No. 1 to 3, Pb 29.0 (mol%), B 4.0 (mol%), Si 20.0 (mol%), Al is In the composition of 0 (mol%), Li 35.0 (mol%), Ti 12.0 (mol%), Zn, Zr and P 0 (mol%), Pb / (Si + Ti) 0.9, the FF value is The result was insufficient. Ti has the effect of lowering ρc and increasing the FF value. However, when Li as the donor element is excessive, the FF value is lowered even if ρc is lowered, and the Ti addition effect can be fully enjoyed. Can not. This is presumably because Li diffuses excessively in the n layer, and recombination of electrons is promoted. From this result and the results of Nos. 1 to 3, the upper limit of the Li amount is 30.0 (mol%).

  No.14 was confirmed the upper limit of P amount together with No.31, Pb 38.6-45.0 (mol%), B 6.0-7.9 (mol%), Si 24.0-28.5 (mol%) Al is 0.5 to 6.0 (mol%), Li is 12.0 (mol%), Ti is 1.0 to 3.0 (mol%), Zn is 0 (mol%), Zr is 0 to 0.5 (mol%), and P is 6.0. -9.0 (mol%), Pb / (Si + Ti) in the range of 1.2-1.8, as shown in No. 31, P amount is 6.0 (mol%), FF value is 76, Id is 0.5 (A) The following sufficient characteristics were obtained. However, as shown in No. 14, when the P content was 9.0 (mol%), the FF value remained at 68, resulting in an insufficient result. It is considered that when the amount of P is excessive, recombination of electrons is promoted as in the case where Li is excessive. According to these results, the upper limit of the amount of P is 6.0 (mol%).

  No.16 is the essential 5 component system together with No.18 and confirmed the upper limit of B amount. Pb is 37.0 to 38.0 (mol%), B is 18.0 to 21.0 (mol%), Si is 15.0 to 17.0 (mol%), Al 0 (mol%), Li 12.0 (mol%), Ti 15.0 (mol%), Zn, Zr, and P 0 (mol%), Pb / (Si + Ti) In the composition within the range of 1.2, as shown in No. 16, sufficient characteristics were obtained in which the B amount was 18.0 (mol%), the FF value was 76, and Id was 0.5 (A) or less. As shown in FIG. 18, when the B content was 21.0 (mol%), the FF value remained at 74, which was insufficient. According to these results, the upper limit of the amount of B is 18.0 (mol%). Note that No. 13 was confirmed by confirming the change by reducing the B amount in the vicinity of the upper limit than No. 16, and a similar result was obtained.

  No.17 is a combination of No.10, No.25, and 28 that confirms the lower limit of Ti amount. As shown in No.10 and 17 in various compositions of 5 to 9 components, It was confirmed that when the Ti amount was 1.0 (mol%), an FF value of 76 or more and an Id of 1.0 (A) or less were obtained. On the other hand, in No. 25 and 28 which lack Ti, FF value stayed at 72-74. According to these results, the lower limit of the Ti amount is 1.0 (mol%).

  No. 19 is a five-component system in which the lower limit of Si content and the upper limit of Ti content were confirmed together with No. 24. As shown in No. 24, Pb was 48.0-50.0 (mol%), B was 6.0 (mol%), Si 5.0-8.0 (mol%), Al 0 (mol%), Li 6.0 (mol%), Ti 30.0-35.0 (mol%), Zn, Zr, and P 0 (mol%), Pb / (Si + Ti) in the range of 1.2 to 1.3, Si amount 8.0 (mol%), Ti amount 30.0 (mol%), FF value 78, Id 0.2 ( A) The following extremely high characteristics were obtained, but as shown in No. 19, when the Si content was 5.0 (mol%) and the Ti content was 35.0 (mol%), the glass raw material melted during the production of the glass frit. It was impossible to evaluate. According to these results, the lower limit of Si content is 8.0 (mol%), and the upper limit of Ti content is 30.0 (mol%).

  No. 20 is a five-component system in which the lower limit of B content has been confirmed together with No. 10 and No. 22, Pb is 46.0-54.0 (mol%), B is 0-1.0 (mol%), Si is 23.0 ~ 49.0 (mol%), Al is 0 (mol%), Li is 3.0 to 12.0 (mol%), Ti is 1.0 to 15.0 (mol%), Zn, Zr, and P are 0 (mol%), Pb / In the composition where (Si + Ti) is in the range of 0.9 to 1.3, as shown in No. 10 and 22, the amount of B is 1.0 (mol%), the FF value is 76 to 77, and Id is 1.0 (A) or less. Although high characteristics were obtained, as shown in No. 20, the FF value remained at 71 when the B amount was 0 (mol%). According to these results, the lower limit of the amount of B is 1.0 (mol%).

  No.32 was confirmed the lower limit of Li amount together with No.39, Pb is 51.0-58.5 (mol%), B is 4.0-0.0 (mol%), Si is 25.0-28.0 (mol%) Al is 0 to 3.0 (mol%), Li is 0 to 1.0 (mol%), Ti is 3.0 to 10.0 (mol%), Zn is 0 to 4.0 (mol%), Zr is 0 to 0.5 (mol%) , P in the range of 0 to 2.0 (mol%) and Pb / (Si + Ti) in the range of 1.5 to 1.9, as shown in No. 32, the Li amount is 1.0 (mol%) and the FF value is 78. , Id obtained an extremely high characteristic of 0.2 (A) or less, but as shown in No. 39, when the Li amount was 0 (mol%), the FF value remained at 74, and Id was over 1.0 (A). became. According to these results, the lower limit of the Li amount is 1.0 (mol%).

  No. 33 is a combination of No. 34, 38, 47, 48 and confirmed the upper limit of the amount of Pb, Pb 60.0-64.0 (mol%), B 1.0-4.0 (mol%), Si 15.0 -30.0 (mol%), Al 0-1.0 (mol%), Li 0-6.0 (mol%), Ti 1.0-15.0 (mol%), Zn 0-4.0 (mol%), Zr 0 -1.0 (mol%), P is 0 to 2.0 (mol%), and Pb / (Si + Ti) is in the range of 1.9 to 2.4. High characteristics with an FF value of 76-77 and Id of 1.0 (A) or less were obtained at 62.0 (mol%), but as shown in Nos. 33 and 48, FF values were higher than 63.0 (mol%). The value stayed below 73. That is, even if the Ti amount is appropriate, if the Pb amount is excessive, the FF value becomes low. According to these results, the upper limit of the amount of Pb is 62.0 (mol%).

  No. 34 was confirmed with the upper limit of Pb / (Si + Ti) together with No. 35, Pb 60.0-62.0 (mol%), B 4.0-6.0 (mol%), Si 22.0- 25.0 (mol%), Al 0.5-1.0 (mol%), Li 1.0 (mol%), Ti 1.0 (mol%), Zn 4.0-7.0 (mol%), Zr 0-0.5 (mol%) ), P is 2.0 (mol%) and Pb / (Si + Ti) is in the range of 2.4 to 2.6, as shown in No. 34, Pb / (Si + Ti) is 2.4 and FF value is 77. , High characteristics with Id of 1.0 (A) or less were obtained, but as shown in No. 35, the FF value remained at 73 when Pb / (Si + Ti) was 2.6. According to these results, the upper limit of Pb / (Si + Ti) is 2.4. Note that No. 37 was confirmed to be smaller than No. 34 in the vicinity of the upper limit of Pb (Si + Ti), and the leakage current Id was smaller than No. 34, so Pb / (Si + It may be preferable to keep Ti) below 2.0.

  No. 41 was confirmed with the lower limit of Pb amount and Pb / (Si + Ti) in combination with No. 42 and No. 46, Pb 3.0-6.0 (mol%), B 12.0 (mol%), Si Is 15.0 (mol%), Al is 6.0 (mol%), Li is 30.0 (mol%), Ti is 15.0 (mol%), Zn is 16.0 to 19.0 (mol%), Zr, P is 0 (mol%) In the composition where Pb / (Si + Ti) is in the range of 0.1 to 0.2, as shown in No. 41, the amount of Pb is 6.0 (mol%), Pb / (Si + Ti) is 0.2, and the FF value is 77. However, when the Pb content is 3.0 (mol%), the FF value remains at 73 (No. 42), and even when the Pb content is 6.0 (mol%), Pb / ( When Si + Ti was 0.1, the FF value remained at 34 (No. 46). That is, even if the amount of Ti is appropriate, if the Pb / (Si + Ti) is too small, the FF value becomes low. According to these results, the lower limit of the amount of Pb is 6.0 (mol%), and the lower limit of Pb / (Si + Ti) is 0.2.

  In addition, when the above evaluation results are viewed for each component system, No.5, 7, 9, 10, 15, 16, 18-20, 22-24, 29, 30, 33 are only 5 essential elements. System (however, No. 20 lacks B), Pb is 29.0-63.0 (mol%), B is 0-21.0 (mol%), Si is 5.0-51.2 (mol%), Al is 0 (mol%) ), Li is 3.0 to 35.0 (mol%), Ti is 1.0 to 35.0 (mol%), Zn, Zr, and P is in the range of 0 (mol%), Pb is 35.0 to 55.0 (mol%), B is 1.0-18.0 (mol%), Si is 8.0-49.0 (mol%), Li is 3.0-24.0 (mol%), Ti is 1.0-30.0 (mol%), Pb (Si + Ti) is 0.9-1.7 In the range, an FF value of 76 to 78 and an Id of 1.0 (A) or less were obtained.

  Looking at the above evaluation results for individual constituent elements, high characteristics were obtained with an FF value of 77 and an Id of 0.2 (A) or less if Pb was included at 35.0 (mol%) (No. 9). In addition, 55.0 (mol%) obtained an extremely high characteristic with an FF value of 78 and Id of 0.2 (A) or less (No. 29), but 63.0 (mol%) had an insufficient FF value of 73. (No.33). If B is included in 1.0 (mol%), high characteristics with an FF value of 77 and an Id of 0.2 (A) or less can be obtained (No. 22), but without this, the FF value remains at 71 and insufficient. The result is (No. 20). In addition, 18.0 (mol%) provides sufficient characteristics with an FF value of 76 and Id of 0.5 (A) or less (No. 16), but 21.0 (mol%) has an insufficient FF value of 74. (No.18). If Si (8.0% mol%) is included, extremely high characteristics can be obtained with an FF value of 78 and Id of 0.2 (A) or less (No. 24), but 5.0 (mol%) melts the electrode material. As a result, the characteristic evaluation is impossible (No. 19). In addition, if 49.0 (mol%), the FF value is 76 and Id is 1.0 (A) or less, sufficient characteristics can be obtained (No. 10), but 51.2 (mol%) reduces the FF value to 36. It exceeded 1.0 (A) and the result was insufficient (No. 5). Li has a sufficient FF value of 76 and Id of 1.0 (A) or less even at 3.0 (mol%) (No. 10), but 35.0 (mol%) has an insufficient FF value of 73. (No.7). At 24.0 (mol%), excellent characteristics are obtained with an FF value of 77 and an Id of 0.2 (A) or less (No. 9). Ti has sufficient characteristics with an FF value of 76 and Id of 1.0 (A) or less even at 1.0 (mol%) (No. 10), but at 35.0 (mol%), the electrode material melts and the characteristics are evaluated. Became impossible (No. 19). At 30.0 (mol%), extremely high characteristics were obtained with an FF value of 78 and an Id of 0.2 (A) or less (No. 24).

  In the above evaluation range, the B amount is in the range of 1.0 to 18.0 (mol%), the Si amount is in the range of 8.0 to 49.0 (mol%), and the Ti amount is in the range of 30.0 (mol%) or less. It is essential that the Pb content be less than 63.0 (mol%) and the Li content be less than 35.0 (mol%).

  Nos. 8, 11, 36, 39, and 48 are 6-component systems containing Zn or P (however, Nos. 39 and 48 lack Li), Pb is 38.0 to 64.0 (mol%), and B is 3.0 to 10.0 (mol%), Si 25.0 to 31.3 (mol%), Al 0 (mol%), Li 0 to 12.0 (mol%), Ti 1.0 to 10.0 (mol%), Zn 0 to In the composition in the range of 15.0 (mol%), Zr 0 (mol%), P 0-1.0 (mol%), Pb 38.0-40.7 (mol%), B 6.0-8.0 (mol%), FF value of 77-78 in the range of Si 29.0-31.3 (mol%), Li 6.0-12.0 (mol%), Ti 1.0-8.0 (mol%), Pb (Si + Ti) 1.0-1.3 And Id below 0.5 (A) was obtained. In this evaluation result, in the composition containing no Li, the FF value stays below 74 and Id exceeds 1.0 (A) (No. 39, 48), and in particular, when Pb becomes an excessive composition of 64.0 (mol%). The FF value stays at 65. Li is indispensable in the range of this evaluation, and a high FF value cannot be obtained without it. Zn is an arbitrary element, but 15.0 (mol%) may be contained (No. 36).

  Nos. 6, 31, 44, and 49 are 7-component systems containing Al and P. Pb is 27.0 to 46.0 (mol%), B is 4.0 to 10.6 (mol%), Si is 24.0 to 53.2 (mol) %), Al 2.5 to 6.0 (mol%), Li 3.7 to 12.0 (mol%), Ti 1.0 to 10.0 (mol%), Zn and Zr 0 (mol%), P 1.0 to 6.0 (mol) %) In the range of Pb 38.0-46.0 (mol%), B 4.0-6.0 (mol%), Si 24.0-32.0 (mol%), Al 3.0-6.0 (mol%), Li Is 12.0 (mol%), Ti is 1.0 to 10.0 (mol%), P is 1.0 to 6.0 (mol%), Pb (Si + Ti) is in the range of 0.9 to 1.8, FF value of 76 to 77 and 0.5 ( A) The following Id was obtained. In this evaluation result, the FF value stayed at 44 with an excessive composition of Si of 53.2 (mol%) (No. 49). When Si is excessive, the FF value is significantly reduced. P is an arbitrary element, but it may be contained in an amount of 6.0 (mol%) (No. 31).

  Nos. 1 to 4, 13, and 41 to 43 are 7-component systems containing Al and Zn. Pb is 3.0 to 37.3 (mol%), B is 3.0 to 15.0 (mol%), Si is 15.0 to 29.7. (mol%), Al 1.0-6.0 (mol%), Li 6.0-30.0 (mol%), Ti 1.0-15.0 (mol%), Zn 6.0-30.0 (mol%), Zr and P 0 In the composition in the range of (mol%), Pb is 6.0-37.3 (mol%), B is 3.0-15.0 (mol%), Si is 15.0-29.7 (mol%), Al is 1.0-6.0 (mol%) , Li is 6.0 to 30.0 (mol%), Ti is 1.0 to 15.0 (mol%), Zn is 6.0 to 30.0 (mol%), Pb (Si + Ti) is in the range of 0.2 to 1.3, FF value 77 and Id 1.0 (A) or less was obtained. In this evaluation result, the FF value stayed at 73 (No. 42) when Pb was too small (3.0% by mol) and Pb / (Si + Ti) was too small (0.1). Zn is an arbitrary element, but 30.0 (mol%) may be contained (No. 43).

  Nos. 12, 21, 35 and 40 are 8-component systems containing Al, Zn and P. Pb is 39.0 to 60.0 (mol%), B is 3.0 to 8.0 (mol%), Si is 22.0 to 31.0 (mol%), Al 0.5-3.0 (mol%), Li 1.0-12.0 (mol%), Ti 1.0-6.0 (mol%), Zn 2.0-7.0 (mol%), Zr 0 (mol %), P is in the range of 1.0 to 2.0 (mol%), Pb is 39.0 to 54.0 (mol%), B is 3.0 to 8.0 (mol%), Si is 30.1 to 31.0 (mol%), Al Is 0.5 to 3.0 (mol%), Li is 1.0 to 12.0 (mol%), Ti is 3.0 to 6.0 (mol%), Zn is 2.0 to 5.0 (mol%), P is 1.0 to 2.0 (mol%), Pb When (Si + Ti) was in the range of 1.1 to 1.5, FF values of 77 to 78 and Id 0.5 (A) or less were obtained. In this evaluation result, the FF value stayed at 73 (No. 35) in the case of an excessive composition of Pb / (Si + Ti) of 2.6.

  In addition, No.14, 25, 26, 28, 32, 37, 45 is an 8-component system containing Al, Zr, P, Pb 38.6-58.5 (mol%), B 4.0-7.9 (mol%) Si: 25.5-38.0 (mol%), Al: 0.5-12.0 (mol%), Li: 1.0-12.0 (mol%), Ti: 0-3.0 (mol%), Zn: 0 (mol%), Zr Is 0.5 (mol%), P is in the range of 2.0 to 9.0 (mol%), Pb is 50.0 to 58.5 (mol%), B is 4.0 to 6.0 (mol%), Si is 25.5 to 32.0 (mol) %), Al 0.5-12.0 (mol%), Li 1.0-6.0 (mol%), Ti 1.0-3.0 (mol%), Zr 0.5 (mol%), P 2.0 (mol%), Pb When (Si + Ti) was in the range of 1.4 to 2.0, FF values of 77 to 78 and Id 0.5 (A) or less were obtained. In this evaluation result, in the composition lacking Ti, the FF value stayed at 72 to 74 (No. 25, 28), and P was 9.0 (mol%) and the FF value stayed at 68 in the excessive composition (No. 14). . Al is an arbitrary element, but 12.0 (mol%) may be contained (No. 37).

  No. 17, 27, 34, 38, 46 and 47 are 9 component systems, Pb is 6.0 to 62.0 (mol%), B is 3.0 to 10.0 (mol%), Si is 25.0 to 38.0 (mol%) ), Al 0.5-12.0 (mol%), Li 1.0-12.0 (mol%), Ti 1.0-4.0 (mol%), Zn 1.0-16.0 (mol%), Zr 0.5-1.0 (mol%) ), P is in the range of 1.0 to 2.0 (mol%), Pb is 43.0 to 62.0 (mol%), B is 3.0 to 8.0 (mol%), Si is 25.0 to 30.0 (mol%), Al is 0.5-1.0 (mol%), Li 1.0-12.0 (mol%), Ti 1.0-3.0 (mol%), Zr 0.5-1.0 (mol%), P 1.0-2.0 (mol%), Pb ( In the range of Si + Ti) from 1.5 to 2.4, FF values of 76 to 77 and Id 1.0 (A) or less were obtained. In this evaluation result, the FF value stayed at 43 in the case of an excessively small composition of Pb (Si + Ti) of 0.1 (No. 46). That is, even if each component is within a preferable range, a high FF value cannot be obtained if Pb (Si + Ti) is too small or too large.

In the above examples, Nos. 8, 11, 12, 21, 23, 24, 29, and 32 are preferable because the FF value is as high as 78, and Nos. 12, 21, 24, 29, and 32 are The FF value is particularly high because it is as high as 78 and the Id is as small as 0.2 (A) or less. Among these, Nos. 12 and 21 are most preferable because ρc is as low as 0.012 (Ω · cm ² ).

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect, A various change can be added in the range which does not deviate from the main point.

10: solar cell, 12: solar cell module, 14: sealing material, 16: surface glass, 18: protective film, 20: silicon substrate, 22: n layer, 24: p ⁺ layer, 26: antireflection film, 28 : Light receiving surface electrode, 30: Back electrode, 32: Light receiving surface, 34: Full surface electrode, 36: Strip electrode, 38: Solder ribbon

Claims (3)

A solar cell electrode paste composition comprising a conductive powder, a glass frit, and a vehicle,
Wherein the PbO glass frit in terms of oxide 6~62 (mol%), and B ₂ O ₃ of 1~18 (mol%), and SiO ₂ of 8~49 (mol%), 1~30 ( mol %) Li ₂ O, 1 to 30 (mol%) TiO ₂ , and 0 to 6 (mol%) P ₂ O ₅ , and Pb / (Si + Ti) (mol ratio) is 0.2 to 2.4. A paste composition for a solar cell electrode, comprising a glass within the range of. The glass and PbO of 6 to 60 (mol%) in terms of oxide, and B ₂ O ₃ of 3 to 12 (mol%), and SiO ₂ of 8~32 (mol%), 1~30 ( mol% ) Li ₂ O, 1 to 30 (mol%) TiO ₂ , and 0 to 4 (mol%) P ₂ O ₅ , and Pb / (Si + Ti) (mol ratio) is 0.2 to 2.0 The paste composition for solar cell electrodes of Claim 1 which exists in the range. The glass and PbO of 38 to 59 in terms of oxides (mol%), and B ₂ O ₃ of 3~8 (mol%), and SiO ₂ of 8~32 (mol%), 1~12 ( mol% ) Li ₂ O, 3 to 30 (mol%) TiO ₂ , and 0 to 2 (mol%) P ₂ O ₅ , and Pb / (Si + Ti) (mol ratio) is 1.0 to 1.9 The paste composition for solar cell electrodes of Claim 1 which exists in the range.

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