TW201731982A - Paste composition for forming solar cell electrode - Google Patents

Abstract

Disclosed is a conductive paste composition, which has an excellent continuous printability and is used for forming a front electrode of a solar cell by screen printing. The conductive paste composition comprises a conductive metal powder, a glass frit, a binder, a thixotropic agent, and an organic solvent, and has a viscosity expressed by mathematical formula 1 below and a loss angle expressed by mathematical formulas 2 and 3 below. [Mathematical formula 1] 15 Pa·s ≤ [eta]100 ≤ 35 Pa·s; [Mathematical formula 2] 5 DEG ≤ Loss angle ≤ 20 DEG when strain is 0.01%; and [Mathematical formula 3] 70 DEG ≤ Loss angle ≤ 85 DEG when strain is 300%, wherein [eta]100 represents the viscosity value at a shear rate of 100 s-1, and the loss angle is measured by the oscillatory strain step test (1 Hz) in which the strain is continuously repeated between 0.01% and 300%.

Description

Paste composition for forming solar cell electrodes

The present invention provides a paste composition for forming a solar cell electrode, and more particularly, to provide a conductive paste composition having excellent continuous printability and forming a front electrode of a solar cell by screen printing.

A solar cell is a device that obtains electric power by generating a photovoltaic effect by generating electric light when incident light is incident on a semiconductor substrate, and generally has a front surface of a semiconductor substrate formed of p-type germanium or the like. (front, surface irradiated with sunlight) A negative electrode is formed, and a positive electrode is formed on the back surface. The solar cell electrode is screen-printed on a substrate to form a paste composition for forming an electrode, and the paste composition for forming an electrode is composed of a conductive powder and a glass frit (frit). ), an organic solvent and a conductive organic medium of a cellulose resin binder.

In order to improve the efficiency of a solar cell, a conductive paste composition which can form an electrode having a fine line width and which has excellent continuous printing properties is required. In the beginning of 2000, a front electrode having a line width of about 100 μm was used, but recently, a fine line width mask having a pattern hole of 40 μm or less, for example, 36 μm to 40 μm, was used to form a front electrode having a line width of 50 μm to 60 μm. Pattern (wiring pattern). However, when the electrode pattern is printed by using a usual conductive paste composition and a fine line width mask, there is a problem of printability such as disconnection of the electrode (circuit) pattern or clogging of the mask mesh, or The effect of lowering the performance of the solar cell or lowering the production yield due to the aspect ratio (height/width ratio) of the electrode pattern formed is low.

Technical problem solved

Accordingly, it is an object of the present invention to provide a paste composition for forming a solar cell electrode which has excellent continuous printability when a conductive paste is screen printed on a semiconductor substrate using a photomask having a fine line width pattern. .

Another object of the present invention is to provide a paste composition for forming a solar cell electrode capable of suppressing wire breakage and clogging of a mask to form a high-precision printed wiring.

Technical means

In order to achieve the above object, the present invention provides a paste composition for forming a solar cell electrode, wherein the paste composition for forming a solar cell electrode comprises a conductive metal powder, a glass frit, a binder, a shaker, and an organic solvent. And has a viscosity expressed by the following Mathematical Formula 1 and a Loss angle represented by Mathematical Formula 2 and Mathematical Formula 3 : Mathematical Formula 1:15 Pa.s ≦ ₁₀₀ ≦35 Pa.s; Mathematical Formula 2: When When the strain rate (Strain) is 0.01%, the 5° ≦ Loss angle ≦ 20°; Mathematical formula 3: When the deformation rate is 300%, the 70° ≦ loss angle ≦ 85°.

Where η ₁₀₀ represents a viscosity value in a shear rate of 100 s ^-1 , and the loss angle is determined by continuously repeating an Oscillatory Strain Step test (1 Hz) of a deformation rate of 0.01% and a deformation rate of 300%. of.

Preferably, the paste composition for forming a solar cell electrode of the present invention has a strain (SMC, Strain at Modulus Cross-point) value represented by the following Mathematical Formula 4: Mathematical Formula 4:25 The strain at the intersection of the % ≦ modulus is ≦ 75%.

Wherein, the strain value at the intersection of the modulus represents the storage modulus and the loss mode when the corresponding strain rate (Strain) is such that the storage modulus (Loss Modulus) and the loss modulus (Loss Modulus) are patterned. The value of the deformation rate in the Modulus Cross-point.

Further, the present invention provides a paste composition for forming a solar cell electrode, the above paste composition for forming a solar cell electrode comprising: (1) 80% by weight to 94% by weight of silver (Ag) powder as conductivity Metal powder; (2) 1% by weight to 5% by weight of glass frit; (3) 0.1% by weight to 2.0% by weight of ester or ether binder; (4) 0.6% by weight to 1.0% by weight of amide wax a rocking agent; (5) 0.1 to 3 weight percent of a rocking aid; and (6) 3 to 8 weight percent of a solvent selected from carbitol solvents (glycol ethers), ester solvents, and The solvent of its mixture. Further, the present invention provides a solar cell electrode in which a paste composition for forming a solar cell electrode is screen-printed on a semiconductor substrate and fired.

Effect of the invention

The paste composition for forming a solar cell electrode of the present invention can have excellent continuous printing property and suppress electrode breakage when screen-printing a conductive paste on a semiconductor substrate by using a mask having a fine line width pattern. The wire and the mask net are clogged, so that high-precision printed wiring can be formed.

The terminology used in the specification is used for the purpose of illustrating the exemplary embodiments and is not intended to limit the invention. As long as there is no explicit meaning in the context, the singular representation includes the plural. It is to be understood that the terms "comprises" or "comprises" or "an" or "an" Or the existence or additional possibility of digits, steps, structural elements or combinations thereof. The invention may be susceptible to various modifications and various embodiments. The specific embodiments are illustrated herein and described in detail. It is to be understood, however, that the invention is not intended to be limited

According to the present invention, in order to prepare a paste composition for forming a solar cell electrode excellent in continuous printing property, it is necessary to adjust rheological properties such as viscosity (Viscosity, η), modulus of elasticity (Modulus), and loss angle (Loss angle) as Rheological indicators of the paste composition. In the present invention, the rheological properties (viscosity, modulus of elasticity, and viscosity of the paste composition) were measured at 25 ° C using a rheometer (product of TA instrument, product name: Discovery Hybrid Rheometer-2). The loss angle, etc.), and the Plate SST 25mm Sandblast spindle (accessory of TA instrument company) was used to reduce the occurrence of slip when the measurement was performed, and was also used in the platform for placing the paste to be measured. 1000-grit Sandpaper. When the viscosity is measured, the spindle clearance is set to 100 μm, and in addition, when the rheology such as Modulus and Loss angle is measured, the spindle clearance is set to 200 μm.

The paste composition for forming a solar cell electrode of the present invention contains a conductive metal powder, a glass frit, a binder, a shaker, and an organic solvent, and has a viscosity represented by the following Math.

Mathematical formula 1:15Pa.s≦η ₁₀₀ ≦35Pa.s.

Where η ₁₀₀ represents the viscosity value in the shear rate (Shear rate) 100 s ^-1 .

The paste composition of the present invention has a viscosity (η ₁₀₀ ) of from 15 Pa.s to 35 Pa.s, specifically from 20 Pa.s to 35 Pa.s, in a shear rate of 100 s ^-1 to suit a screen-printed pattern. form. The viscosity (η ₁₀₀ ) is usually such that when the paste composition is printed, the paste is subjected to a shear rate at the time of transfer through the screen reticle, and is measured at a shear rate of 100 s ^-1 . Under such conditions, if the viscosity is too low, the aspect ratio of the printed pattern can be lowered or a pattern of a form that is distorted in an unbalanced manner can be formed. If the viscosity is too high, a mask mesh can occur. The blockage, the broken line of the pattern, etc. are not good.

Further, the paste composition for forming a solar cell electrode of the present invention has a loss angle represented by the following Mathematical Formula 2 and Mathematical Formula 3.

Math Figure 2: When the strain rate (Strain) is 0.01%, 5° ≦ Loss angle ≦ 20°.

Math Figure 3: When the strain rate (Strain) is 300%, 70° ≦ Loss angle ≦ 85°.

The Loss angle was measured by continuously repeating the oscillation strain step test (1 Hz) of deformation ratio (Strain) of 0.01% and 300%. The loss ratio of the paste composition of the present invention in the deformation ratio of 0.01% is specifically 7 to 18, and the loss angle in the deformation rate of 300% is specifically 72 to 83. Loss tangent can be expressed as the ratio of Loss Modulus (G") / Storage Modulus (G'), and 0 if it is completely elastic, if it is completely sticky Sex, which is infinity, δ corresponding to the angle of loss tangent (tan δ) means a loss angle (ie, tan δ = G" / G', 0 ° ≦ δ ≦ 90 °). Therefore, the smaller the loss angle, the more solid-like, the larger the loss angle, and the more liquid-like. The paste composition of the present invention has the loss angles represented by the above formulas 2 and 3, and when both conditions are satisfied, when the deformation rate at the time of printing is high, it is easy to discharge due to stickiness. If the sheet separation is caused after printing, a uniform pattern form can be formed due to excellent elastic recovery speed. When the strain rate (Strain) in the oscillating strain step test (1 Hz) is 0.01%, if the loss angle is larger than 20°, it is difficult to embody a fine pattern due to a low elastic recovery speed after printing, and a loss angle of less than 5°. Although it is theoretically possible to exhibit excellent elastic recovery characteristics, it can actually be regarded as a value that is difficult to achieve using a paste. When the strain rate (Strain) is 300%, if the loss angle is more than 85°, although it is theoretically possible to exhibit excellent discharge characteristics at the time of printing, it is actually a value that is difficult to realize by using a paste. When the loss angle is less than 70°, it can be considered as a paste having poor discharge characteristics at the time of printing, and it is possible to cause various printing defects such as poor illuminance and disconnection.

Also, preferably, the paste composition for forming a solar cell electrode of the present invention has a strain value at a modulus intersection point represented by the following Math.

Mathematical formula 4: strain at the intersection of 25% ≦ modulus is 75%.

The strain value at the intersection of the modulus represents the storage modulus and loss when the storage modulus (Loss Modulus) and the loss modulus (Loss Modulus) are plotted against the strain rate (Strain). The value of the strain rate in the Modulus Cross-point where the modulus crosses (reverses). The strain value at the modulus intersection of the paste composition of the present invention is more specifically from 30% to 60%. The strain at the intersection of the modulus means that when printing is performed, if a certain degree of shear deformation occurs, the internal structure of the paste is deformed, causing the storage modulus and loss modulus to be reversed. Time point. In the case of an ideal paste, since it has a solid characteristic when it is not deformed (the storage modulus is high before the strain at the intersection of the modulus), when it is deformed, it has the characteristic of the liquid (in the modulus After the strain at the intersection, the loss modulus is high), and therefore, under the same printing procedure conditions (when subjected to prescribed deformation), the printability is greatly affected by the value of the strain at the intersection of the modulo. If the strain value at the intersection of the modulus is too large (greater than 75%), the flowability is reduced when the printing process is performed, so that the frequency of occurrence of disconnection of the electrode is increased, and there is a problem in continuous printability. On the contrary, if the strain value at the intersection of the modulus is too small (less than 30%), even if the deformation rate of the paste is low, the fluidity of the paste composition is increased, and therefore, the line width of the printed pattern can be increased. problem.

The paste composition for forming a solar cell electrode of the present invention may comprise a conductive metal powder, a glass frit, a binder, a rocking agent and an organic solvent, and may adjust an organic solvent, a type and molecular weight of the binder, and a shaker. The viscosity (η), the strain value at the intersection of the modulus, and the loss angle are adjusted in the same manner as in Mathematical Formula 1 to Mathematical Formula 4, as in Mathematical Formula 1 to Mathematical Formula 4. Specifically, the paste composition for forming a solar cell electrode according to an embodiment of the present invention comprises: (1) 80% by weight to 94% by weight of silver (Ag, Silver) powder as a conductive metal powder; (2) 1% by weight to 5% by weight of glass frit; (3) 0.1% by weight to 2.0% by weight of ester or ether binder; (4) 0.6% by weight to 1.0% by weight of guanamine wax shaker; 0.5 to 3 weight percent of the shaking aid; (6) 3 to 8 weight percent of a solvent selected from the group consisting of carbitol solvents (glycol ethers), ester solvents, and mixtures thereof. Hereinafter, each component which can be used in the paste composition of the present invention will be specifically described.

The silver (Ag) powder used in the paste composition of the present invention can be used as a component for imparting conductivity to an electrode formed by the paste composition, and silver powder which is usually used for formation of a solar cell electrode can be used without limitation. Or particles. The silver powder is present in an amount of from 80% by weight to 94% by weight, based on the total paste composition, specifically from 85% by weight to 92% by weight. When the content of the silver powder is too small, it is difficult to ensure the conductivity as the front electrode, and if the content of the silver powder is too large, the uniformity of the paste composition can be lowered or the viscosity can be lowered to lower the printability. The silver powder may be used regardless of its shape, but for example, spherical particles, plate-shaped particles or a mixture thereof may be used, and more specifically, spherical particles may be used. When spherical particles are used, it is advantageous in that the fine line width at the time of printing is exhibited because of excellent dispersibility. The number average particle diameter of the silver powder particles may be from about 0.1 μm to 5 μm, specifically, from about 1 μm to 2.5 μm. When the particles of the silver powder are too small, the size of the voids between the particles becomes small, and when the sintering is performed, the formation of an ohmic contact of the glass frit can be hindered, and if the particle size is too large, the inside of the paste is lowered. The dispersibility and the printability of the paste are lowered, so that it is difficult to reflect the fine line width.

The glass frit serves to form an ohmic contact of the semiconductor substrate and the electrode during sintering after the paste for forming the electrode is applied. The glass frit is present in an amount of from 1% by weight to 5% by weight, specifically from 1.5% by weight to 4% by weight, based on the total paste composition. When the content of the glass frit is too small, the formation of an ohmic contact between the electrode and the semiconductor substrate may be insufficient, and the contact resistance may increase. If the content of the glass frit is too large, there is a concern that the linear resistance in the electrode excessively increases. .

The ester-based or ether-based adhesive used in the paste composition of the present invention functions to impart viscoelasticity to the paste composition and maintain the pattern in the form of a pattern. As the ester binder or the ether binder, an ester or ether binder which is generally used in a solar cell electrode composition can be used without limitation. For example, a polyester binder or a polyester polyol can be used for bonding. Agent, polyether binder, polyether polyol binder and mixtures thereof. The weight average molecular weight (Mw) of the binder may be from 50,000 to 70,000. Since the weight average molecular weight of the binder can have a large influence on the viscosity of the composition, a binder having a different molecular weight can be used in combination in order to more accurately match the target viscosity. If the weight average molecular weight of the binder is too small or too large, there is a fear that a viscosity suitable for screen printing (15 Pa.s to 35 Pa.s in a shear rate of 100 s ^-1 ) cannot be obtained. The binder is present in an amount of from 0.1% by weight to 2% by weight, specifically from 0.2% by weight to 1% by weight, based on the total paste composition. If the content of the binder is too small, there is a fear that the minimum strength and rheology due to the use of the binder cannot be ensured, and if the content of the binder is too large, there is a concern that the conductivity of the electrode formed by the paste composition is lowered. .

An amide wax thixotropic agent is used as an additive for forming a network of a network structure in the interior of a paste composition to impart rocking and rheological properties (rheological properties), and can be used without limitation. A typical guanamine wax shake agent sold on the market. Since the content of the shaker has a large influence on the rheological properties of the paste, it is necessary to perform accurate adjustment according to the printing method and the characteristics of the printing machine. The content of the guanamine wax shaker is from 0.6 weight percent to 1.0 weight percent relative to the total paste composition. When the content of the oscillating agent is too small, the aspect ratio of the pattern at the time of paste printing becomes small. If the content of the oscillating agent is too large, there is a problem of clogging of the mask net and disconnection of the pattern. Worry.

The rocking aid acts to improve the rheological properties of the paste composition along with the rocking agent to increase the aspect ratio of the electrode pattern formed by the paste composition. Specific examples of the rocking aid include, for example, a sulphonane compound such as a resin (Rosin), a rosin ester, a polyoxyalkylene or a cyclooxy compound, and two Silica powder, Aliphatic amine, carboxylic acid amide, combinations thereof, and the like. The content of the shake aid is from 0.1% by weight to 3% by weight, specifically from 0.5% by weight to 2% by weight, relative to the total paste composition. If the content of the shaking aid is too small, the aspect ratio of the electrode pattern can be made small or the durability of the electrode pattern can be lowered. If the content of the shaking aid is too large, the action of the binder and the rocking agent is hindered, and the vibration is caused. The characteristics are declining.

The solvent used in the composition of the present invention is a solvent which imparts fluidity and improves printability by using a binder and a rocking agent which dissolve the paste composition, and contains a solvent selected from the boiling point for application to a printing process. It is at least one solvent of a carbitol solvent (glycol ether), an ester solvent, and a mixture thereof at 170 ° C or higher. Usually, the solvent of the glycol ether is a carbitol solvent, and as an example of the carbitol solvent, carbitol, carbitol acetate, butyl carbitol, diethylene glycol butyl ether acetate can be exemplified. Ester, Diethylene glycol dibutyl ether, diethyl carbitol, dimethyl carbitol, ethylene glycol methyl ethyl ether, and the like. Examples of the ester solvent include EEP (ethyl ethoxypropionate), isooctyl acetate, DBE (dibasic ester), Texanol, alcohol ester dodecaisobutyrate, and pine oil. Alcohol, etc. Two or more solvents may be used in combination depending on the characteristics required for the paste. In order to replenish the solubility of the binder and the shaker having different solubility with respect to a single solvent, if a solvent having excellent solubility in dissolution of the binder and a solvent having excellent solubility in dissolution of the shaker are used in combination, Further, it is possible to supplement the insufficient characteristics of each solvent with respect to the miscibility of the entire paste composition, and it is also possible to contribute to the deformation which easily causes the internal structure of the paste. The solvent is present in an amount of from 3 to 8 weight percent, specifically from 5 to 7 weight percent, relative to the total paste composition. Further, the content of the Diethylene glycol dibutyl ether solvent is preferably from 0.1% by weight to 2% by weight based on the total paste composition. When the content of the solvent is too small, the viscosity of the composition is increased, and the printing property is lowered due to the fact that the drying speed of the solvent is increased. When the content of the solvent is too large, the viscosity of the paste composition is excessively lowered. Reduce the concern about printability.

The paste composition for forming a solar cell electrode of the present invention may further contain a usual additive such as a dispersant or a stabilizer, as needed. The dispersing agent makes the dispersion state of the paste composition uniform to maintain the rocking property and maintain the viscosity higher in the energy storage to improve the storage stability of the paste composition. As the dispersing agent, a dispersing agent which is generally used for a solar cell electrode paste composition can be used without particular limitation, and specifically, an ionic or nonionic surfactant, a guanamine compound or the like can be used, for example, A dispersant selected from the group consisting of an Aliphatic ammonium salt, an Aliphatic carboxylic acid salt, and a mixture thereof is used. In the case of using a salt-formed agglomerated dispersant, ions having a functional group can form a network of meshes with nano-sized inorganic particles in a solvent, and form a gel structure with expansion to prevent sedimentation. Ensure rheological stability and improve energy storage stability. Specific examples of the dispersing agent include polyhydroxy carboxylic acid esters, polyhydroxy carboxylic acid amides, polyamine amides, and unsaturated polyamine oxime. Unsaturated polyamine amides salt, Aliphatic carboxylic acid hydroxylalkylamine salt, long chain fatty acid derivative amine salt, long chain fatty acid alkylamine (long chain fatty acid alkylamine) Long chain fatty acid alkyl amine salt), modified polyester amine salt, high molecular weight carboxylic acid amide amine salt, modified phosphate amine salt (Modified phosphate) Ester amine salt), Carboxylic acid alkylol alkylammonium salt, Alkylammonium salt of a polycarboxylic acid, polycarboxylic acid polycarboxylate (Polycarboxylic acid) Acid salt of polyamine amides), pentanoic acid-5-(dimethylamino)-2-methyl-5-oxo-methyl ester and lithium chloride (Pentanoic ac Id 5-(dimethylamino)-2-methyl-5-oxo-methyl ester and Lithium chloride), N-(tallow alkyl)-1,3-propanediamine oleate (N-(Tallow alkyl)-1 , 3-propanediamine oleates), polysiloxane unsaturated carboxylic acid salt, and the like. The dispersant is usually used in an amount of from 0.01% by weight to 2% by weight based on the total of the paste composition. When the amount of the dispersant used is too small, there is a concern that the dispersibility or the storage stability of the paste composition is lowered. When the amount of the dispersant used is too large, there is a rheological property (viscosity, modulus of elasticity, Worries about loss angles, etc.)

The stabilizer in the additive functions to reduce the reactivity of the composition component by adjusting the pH of the paste composition, thereby constantly maintaining the viscosity of the paste. For example, when the paste composition other than the stabilizer is alkaline, an acid compound excellent in compatibility and miscibility with the composition can be added as a stabilizer in order to lower the pH of the composition. As such an acid compound stabilizer, an aliphatic carboxylic acid (Aliphatic carboxylic acid), an aliphatic amine (Aliphatic amine), a mixture thereof, or the like can be used, and specific examples thereof include oleic acid and linoleic acid. (Linoleic acid), Malonic acid, Glycolic acid, Unsaturated polycarboxylic acid, Polysiloxane copolymer, Acid polyester polyamine (Acidic) Polyester polyamide), acid polyether (Acidic polyether) and the like. On the other hand, when the paste composition other than the stabilizer is acidic, a mercapto compound which is excellent in compatibility and miscibility with the composition can be added as a stabilizer in order to increase the pH of the composition. As such a mercapto compound stabilizer, an aminopropyldiethanolamine or a 2-[(1-methylpropyl)amino]ethanol can be exemplified. Sec-butylamine, diethylamine, Diethylaminopropylamine, Diisopropylpropylamine, Dimethylaminopropylaminopropylamine, Ethyldiisopropylamine ), Ethylmethylamine, 3-Isopropoxy propylamine, Monoethylamine, Monoisopropyl amine, 3-methoxypropylamine (3- Methoxypropylamine), Triethylamine, Tributylamine, Trioctylamine, Tetramethylpropylenediamine, 2-Amino-2-ethyl-1,3-propanediol (2) -Amino-2-Ethyl-1,3-Propane-Diol), 2-amino-2-methyl-1-propanol (2-Amino-2-Methyl-1-Propanol), and the like. The stabilizer is used in an amount of usually from 0% by weight to 2% by weight, based on the total paste composition, for example, from 0.001% by weight to 2% by weight. Stabilizers may not be included depending on the procedural conditions and other constituents. However, if the content of the stabilizer becomes too large, there is a fear that the rheological properties (viscosity, elastic modulus, loss angle, and the like) suitable for printing are deviated.

Examples of the antioxidant include a phenol (Phenol) compound, an aromatic amine (Amine) compound, and the like, and these are roughly classified into a main antioxidant and an ultraviolet (UV) stabilizer. Further, an antioxidant which decomposes the generated peroxide group into a stable form of radicals is classified as a secondary antioxidant. Hindered Phenolics, one of the most commonly used compounds among the major antioxidants, can be distinguished as simple phenolics, bisphenolics, polyphenols ( Polyphenolics), thiobisphenolics. The most representative of the hindered phenol compounds is dibutyl hydroxy toluene (BHT), which is an antioxidant of polyolefin, Styrenics, vinyls and elastomers. . Although butylhydroxytoluene is a very effective chain terminator, it has a high volatility weakness. If a long aliphatic group is used in place of the methyl group at the para position of the butylhydroxytoluene, although the volatility is reduced, the reactivity of the OH group is reduced relative to the same weight ( Reactive). Compared to the former, bisphenolic compounds and polyphenolic compounds have low volatility and relatively low equivalent weight based on high molecular weight. In general, phenolic compounds are nonstaining and nondiscoloring, but if oxidation is achieved, multiple compounds are converted into a highly chromophoric structure. A high molecular weight (HWM, High Molecular Weight) phenol compound is used in combination with butylhydroxytoluene for optimum processability. As a well-known polyphenolic antioxidant, it has 8-Hydroxyquinoline, 8-Hydroxyquinoline sulfate, and 8-hydroxyquinoline-5-sulfonic acid (8-Hydroxyquinoline- 5-sulfonic acid), tetrakis (methylene-3.5-di-t-butyl-4-hydroxyl hydrocinnamate) methane Wait. Although Thiobisphenols do not have a good effect as terminators of peroxy radicals, they can also be used when the processing temperature exceeds 100 °C. The role of oxide decomposers. Secondary amines function as hydrogen donation similarly to phenolic compounds, and they also function as peroxide decomposers under high temperature conditions. Therefore, the amine groups belonging to the main antioxidants are more effective than the phenol compounds due to the action of their chain terminators and peroxide decomposers, but they are colored in color due to their discoloring characteristics. The use of areas of importance or in the field of appearance of products is limited. Amines are most commonly used in polyolefins containing carbon black.

The auxiliary antioxidant comprises a plurality of trivalent phosphorous compounds and divalent sulfur-containing compounds, and is known as Organophosphites, Thioester, Thioamine ( Thioamide), Thiamine. Auxiliary antioxidants are associated with preventive stabilizers and, therefore, they are used to prevent the diffusion of alkoxy groups and alkoxy&hydrox radicals based on the decomposition of hydroperoxides. Phosphites change the hydroperoxide to ethanol, changing itself to phosphate (Phosphates). An important drawback of Phosphite is sensitivity to Hydrolysis. Several hydrolysiss reduce sensitivity when combined with multiple additives. Hydrolysis of Phosphite eventually forms Phos-phorous acid, which causes corrosion of the processing equipment. When a phosphite stabilizer (Phosphite Stabilizer) is used together with a hindered phenolic compound (Hindered Phenolics), an ascending effect can be expected. In some cases, stability against ultraviolet exposure (Ultraviolet Exposure) is also increased. Aliphatic esters of Thiodipropionic acid are very effective peroxide decomposers in applications where they are exposed to heat for extended periods of time. In the case of using a thioester (Thioesters) together with a main antioxidant, it exhibits an excellent rising effect. The antioxidant is used in an amount of usually from 0% by weight to 2% by weight, based on the total paste composition, for example, from 0.001% by weight to 2% by weight, and can be optionally used. Depending on the program conditions and other ingredients, antioxidants may not be included. However, if the content of the antioxidant is too large, there is a fear that the rheological properties (viscosity, elastic modulus, loss angle, and the like) suitable for printing are deviated.

The solar cell electrode paste composition of the present invention can be utilized, and the front electrodes of solar cells and solar cells can be prepared by the methods generally used in the art to which the present invention pertains. Fig. 1 is a view showing the structure of a solar cell and an electrode which can be prepared by using the solar cell electrode paste composition of the present invention. As shown in Fig. 1, a solar cell to which the composition of the present invention can be applied includes a p-type germanium substrate 10 including an n-type semiconductor portion 12 on a front surface of the p-type germanium substrate 10, and a front electrode 20 formed on an n-type The semiconductor portion 12 and the back surface electrode 30 are formed on the p-type germanium substrate 10. The anti-reflection film 14 can be formed on the upper surface of the n-type semiconductor portion 12 excluding the front surface electrode 20. When the solar cell electrode paste composition of the present invention is screen printed on the n-type semiconductor portion 12 and fired, an electrode of the solar cell can be formed. Specifically, the front electrode 20 of the solar cell can be formed.

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples. The following examples are intended to illustrate the invention, and the scope of the invention is not limited to the examples.

Examples 1 to 3, Comparative Example 1 to Comparative Example 4: Preparation of a paste composition for forming a solar cell electrode

According to the components and contents (% by weight) shown in Table 1 below, the ester binder is mixed with the carbitol solvent A, the carbitol solvent B and the ester ethanol solvent to form an organic vehicle, and the organic solvent is formed. The carrier was charged with a amide wax and a rocking aid, and stirred by a high speed mixer. The dispersing agent and the glass frit were placed in the organic carrier which was stirred, and the mixture was stirred with a stirrer, and then silver powder was added thereto, and the mixture was stirred again, and then dispersed by a three-roller to prepare a paste composition.

In Table 1 below, the ester binder is Cellulose Acetate Butyrate having a weight average molecular weight of 50,000 to 70,000, and the carbitol solvent A is Diethylene glycol monobutyl ether acetate. The carbitol solvent B is Diethylene glycol dibutyl ether, and the ester ethanol solvent is TEXANOL (2,2,4-trimethyl-1,3-pentanediol isobutyrate). Further, a decylamine wax was used as a rocking agent, a rosin ester compound was used as a rocking aid, and an alkyldiamine dioleate was used as a dispersing agent.

Table 1

Experimental Example 1-1: Determination of rheological properties (strain values at the intersection of the modulus)

With respect to the compositions of Examples 1 to 3 and Comparative Examples 1 to 4, the strain rate (Strain sweep) was changed from 0.01% to 1000%, and the storage modulus of the composition was measured (Storage) Modulus, G') and Loss Modulus (G") are shown in Table 2 below for representative storage modulus (G'), loss modulus (G"), and modulus intersection. The strain value.

Table 2

As can be seen from the above Table 2, the strain at the intersection of the modulus of the composition of the examples (Strain at Modulus Cross-point, %) was 25% to 75%.

Experimental Example 1-2: Determination of rheological properties (loss angle and viscosity)

With respect to the compositions of Examples 1 to 3 and Comparative Examples 1 to 4, the loss ratio (Loss Angle) and the viscosity (η, shear rate 100 s ^{-1 in} deformation ratio (Strain) 0.01% and 300% were measured. The viscosity in the middle) is presented in Table 3 below.

table 3

As apparent from the above Table 3, the loss angle of the composition of the examples was 10 to 20 in the deformation ratio of 0.01%, 70 to 75 in the deformation rate of 300%, and the viscosity in the shear rate of 100 s ^-1 ( η) is from 20 Pa.s to 29 Pa.s.

Experimental Example 1-3: Evaluation of Printing Characteristics of Paste Composition

The front electrode of the solar cell was printed using the paste compositions of Examples 1 to 3 and Comparative Examples 1 to 4. A high surface resistance battery (Cell) having a sheet resistance of 90 Ω/□ was used as a tantalum wafer for printing electrodes. The paste for the back surface silver electrode was printed on the back surface of the ruthenium substrate, and dried to form a back surface silver electrode, and screen-printed so that the back surface aluminum electrode paste and a part of the back surface Ag electrode were overlapped. dry. The drying temperature of each paste was 170 °C. At this time, the printing reticle used a 360 mesh reticle having a total thickness of 47 μm, and the pattern formed a front electrode using a finger line having a width of 40 μm and a bus bar pattern having a width of 1.5 mm. The line width and thickness of the front electrode of the formed solar cell were measured by a VK analyzer of Keyence, and a louver (Lupe) was used to evaluate the clogging failure and disposal of the mask net used for screen printing ( Scraper) Poor character (degree of poor printing), so that the degree of defect is classified into 0 to 10 standards. The clogging when there is no mesh at all is classified as 0, and when the clogging of the mesh occurs more than 10 points, it is classified as 10 standards. In the case of waste characteristics, when printing is performed in the same procedure, a uniform coating is applied when a paste is applied to the reticle by a squeegee, and no abnormality is classified as 0, and uniformity cannot be formed because The coating was not carried out by the same procedure, and the speed or pressure of the squeegee was changed to 10 standards, and then presented in Table 4 below.

Experimental Example 1-4: Fabrication and Performance Evaluation of Solar Cells

The printed matter of the above Experimental Example 1-3 was dried at 170 ° C, and then fired at 960 ° C to prepare a solar cell, and the performance was evaluated. The solar cell's electrical characteristics (I-V curve) were measured using a solar simulator and are presented together in Table 4 below. In Table 4 below, Isc [A] is a short-circuit current, which is a short-circuit current that causes a short circuit of a solar cell electrode terminal to flow, and Voc [V] is an open-circuit voltage and is an open solar energy. The open circuit voltage measured by the battery electrode terminal, Rs [mΩ], is a resistor that acts in series between the upper electrode and the lower electrode of the solar cell. FF[%] is used as a fill factor, which is the ratio of the maximum output voltage and the maximum output current multiplied by the product of the open circuit voltage and the short circuit current. The efficiency [%] is defined as the unit area. The ratio of incident light energy to the output of a solar cell.

Table 4

As is apparent from the above Table 4, when the strain value (%) at the intersection of the modulus is large or the loss angle at the deformation rate of 300% is small, the continuous printing characteristics exhibited are poor (Comparative Example 3, Comparative Example 4). In this case, the elasticity of the paste composition is greater than the viscosity. Therefore, when printing is performed, if it is subjected to a predetermined deformation, it is difficult to reverse the elasticity due to the strong solid like property, resulting in a paste. The discharge becomes difficult, the line width becomes thin, and the thickness becomes large, but the printing failure due to breakage or the like is greatly increased, and the continuous printability becomes very poor. On the contrary, the strain value (%) at the intersection of the modulus is 0% to 30%, that is, in the case of small (Comparative Examples 1, 2), substantially, the elasticity of the paste composition is low and the viscosity is strong, so that When the deformation is small, the absolute value of the viscoelasticity becomes small, and therefore, the viscosity is lowered. This means that the internal structure of the paste is easily deformed in the case where small deformation occurs, so that the viscosity is easily reversed, and, although it is advantageous for continuous printing, it is not suitable because of the large line width and low thickness. Further, it exhibits an effect on Isc according to the size of the line width, an effect on Rs and FF depending on the printing defect, and a case where the content of the indoleamine wax as a rocking agent is 0.6% to 1.0%. Underneath, a higher efficiency value can be obtained.

Examples 4 to 6 and Comparative Examples 5 to 7: Preparation of a paste composition for forming a solar cell electrode

Two or more kinds of pastes may be used in combination depending on the characteristics of the paste required. A solvent having excellent solubility in dissolving the binder and a solvent having excellent solubility in dissolving the rocking agent may be mixed to improve the miscibility of the entire composition, and may contribute to easy formation of the paste. The role of deformation of the internal structure. Diethylglycol monoacetate acetate, a carbitol solvent having excellent solubility in the dissolution of a binder, according to the composition and content (% by weight) TEXANOL (2,2,4-trimethyl-1,3-pentanediol isobutyrate) and dibutyl carbitol (carbitol solvent B, Diethylene glycol) have excellent solubility in rocking agents. The composition of the dibutyl ether was changed, and a paste composition was prepared in the same manner as in Example 1. In the order of Comparative Example 4 to Comparative Example 5, Examples 4 to 6 and Comparative Example 7, butyl carbitol acetate (carbitol solvent A) and dibutyl carbitol (carbitol) were used. The composition of the solvent B) was changed and evaluated.

table 5

Experimental Example 2-1: Determination of rheological properties (strain values at the intersection of the modulus)

With respect to the compositions of Examples 4 to 6 and Comparative Examples 5 to 7, the strain ratio Strain sweep was 0.01% to 1000%, and the storage modulus of the composition was measured (Storage) Modulus, G') and Loss Modulus (G") are presented in Figure 1, and representative storage modulus (G'), loss modulus (G) are shown in Table 6 below. ") and the strain value at the intersection of the modulus.

Table 6

As can be seen from the above Table 6, the strain at the intersection of the modulus of the composition of the examples (Strain at Modulus Cross-point, %) was 25% to 75%.

Experimental Example 2-2: Determination of rheological properties (loss angle and viscosity)

With respect to the compositions of Examples 4 to 6 and Comparative Examples 5 to 7, the loss ratio (Strain) 0.01% and the loss angle (Loss Angle) and viscosity (η, shear rate 100 s ^{-1 in} 300%) were measured. Viscosity in) and is presented in Table 7 below.

Table 7

As apparent from the above Table 7, the loss angle of the composition of the examples was 10 to 15 in the deformation ratio of 0.01%, 70 to 75 in the deformation rate of 300%, and the viscosity in the shear rate of 100 s ^-1 . (η) is 23 Pa.s to 28 Pa.s.

Experimental Example 2-3: Evaluation of Printing Characteristics of Paste Composition

Using the paste compositions of Examples 4 to 6 and Comparative Examples 5 to 7, the front electrode of the solar cell was formed in the same manner as in Experimental Example 1-3, and the solar cell was used by a magnifying glass (Lupe). The line width and thickness of the front electrode, the clogging failure of the screen-printed mask net, the scraper characteristics, and the poor degree of scrap characteristics are classified as 0 to 10 standards. The clogging when there is no mesh at all is classified as 0, and when the clogging of the mesh occurs more than 10 points, it is classified as 10 standards. In the case of squeegee characteristics and discarding characteristics, when printing is performed in the same procedure, printing will be obtained in a balanced manner, and if no abnormality is classified as 0, uneven coating and squeezing will be formed, and The case of changing the speed or pressure of the squeegee or squeezing is classified as 10 standards, which are then presented in Table 8 below.

Experimental Example 2-4: Fabrication and Performance Evaluation of Solar Cells

Using the paste compositions of Examples 4 to 6 and Comparative Examples 5 to 7, a solar cell was produced in the same manner as in Experimental Example 1-4, and the solar cell was measured by a solar simulator. The IV curve is presented in Table 8 below.

Table 8

As is apparent from the above Table 8, when the content of the carbitol solvent B is from 0.5% by weight to 2% by weight (Examples 4 to 6), the strain at the intersection of the modulus is sharply lowered, and the loss angle is increased from As a result, it can be judged that it is possible to have a large influence on the improvement of continuous printability, and when low deformation is applied, it can be maintained without lowering the elasticity value, and continuous printing can be maintained while performing continuous printing. quality. It can be judged that the carbitol solvent B which is relatively non-polar acts as a printing property improving assistant which softens the mesh structure mesh in the paste. Also, in this case, a rocking aid can be added to further improve the elastic and elastic recovery rate.

When the content of the carbitol solvent B was 2% by weight or more (Comparative Example 7), the characteristics were abruptly decreased. This can judge the occurrence of agglomeration in the internal structure of the paste due to the repulsive force between the ester-type cellulose binder having polar characteristics. The carbitol solvent B exhibits a loss of loss modulus (Loss Modulus) when the high deformation is applied to more than 2% by weight of the composition, and the storage modulus is increased to exhibit printing. The characteristic that the characteristics are drastically reduced. In general, when the strain at the intersection of the modulus becomes low, the viscosity becomes lower as the elastic value becomes lower as the solvent content increases or the deformation rate in the mold stop state becomes lower, so the viscosity is also lowered. The line width of the printed electrode is substantially increased, and the thickness is reduced. However, in the present invention, it is possible to change the composition by mixing two or more kinds of solvents without increasing the content of the solvent, thereby maintaining the initial elastic value, and reducing the strain at the intersection of the modulus to increase the loss angle, thereby improving the loss. Continuous printability.

In Comparative Example 4 and Comparative Example 5, the result was that the strain value at the intersection of the modulus was high and the loss angle value was low, and the degree of printing failure was high. In Comparative Example 7, the viscosity was lower than that of the comparative example. The viscosity of 4 is also a result of a sharp drop in continuous printability due to the high SMC and low loss angle. On the other hand, in the fourth to sixth embodiments, since the loss angle value is large, the fluidity is made high, and continuous printing and other printability are improved.

10‧‧‧p type 矽 substrate 12‧‧‧n type semiconductor part 14‧‧‧anti-reflection film 20‧‧‧ front electrode 30‧‧‧ back electrode

Fig. 1 is a view showing the structure of a solar cell and an electrode which can be prepared by using the solar cell electrode paste composition of the present invention.

10‧‧‧p type copper substrate

12‧‧‧n-type semiconductor division

14‧‧‧Anti-reflective film

20‧‧‧Front electrode

30‧‧‧Back electrode

Claims (10)

A conductive paste composition comprising a conductive metal powder, a glass frit, a binder, a rocking agent, and an organic solvent, and having a viscosity represented by the following Mathematical Formula 1 and represented by Mathematical Formula 2 and Mathematical Formula 3 below Loss angle, mathematical formula 1:15Pa.s≦η ₁₀₀ ≦35Pa.s; Mathematical formula 2: When the deformation rate is 0.01%, the 5°≦ loss angle ≦20°; and Mathematical formula 3: When the deformation rate is 300% At 70°, the loss angle is °85°, where η ₁₀₀ represents the viscosity value in the shear rate of 100 s ⁻¹ , and the loss angle is an oscillating strain step test by continuously repeating the deformation rate of 0.01% and the deformation rate of 300%. (1 Hz) to determine. The conductive paste composition according to claim 1, wherein the conductive paste composition has a strain value at a modulus intersection point represented by the following Mathematical Formula 4, Mathematical Formula 4: 25% ≦ The strain at the intersection of the modulus is ≦75%. The strain value at the intersection of the modulus indicates that when the storage modulus and the loss modulus are patterned relative to the deformation rate, the storage modulus and the loss modulus are The value of the deformation rate in the intersection. The conductive paste composition according to claim 2, wherein the viscosity (η ₁₀₀ ) in the shear rate of 100 s ^-1 is from 20 Pa·s to 35 Pa·s, and the strain value at the intersection of the modulus is obtained. 30% to 60%, the loss angle in the deformation rate of 0.01% is 7% to 18%, and the loss angle in the deformation rate of 300% is 72% to 83%. The paste composition for forming a solar cell electrode according to claim 1, wherein the binder is an ester binder or an ether binder having a weight average molecular weight (Mw) of 50,000 to 70,000. The paste composition for forming a solar cell electrode according to claim 1, wherein the organic solvent comprises at least one solvent selected from the group consisting of a carbitol solvent, an ester solvent, and a mixture thereof. The paste composition for forming a solar cell electrode according to claim 5, wherein the organic solvent comprises 0.1% by weight to 2% by weight of dibutyl carbitol relative to the total paste composition. Solvent. A paste composition for forming a solar cell electrode, comprising: (1) 80% by weight to 94% by weight of silver powder as a conductive metal powder; (2) 1% by weight to 5% by weight of glass frit; 3) 0.1% by weight to 2.0% by weight of the ester or ether type binder; (4) 0.6% by weight to 1.0% by weight of the guanamine wax shaker; (5) 0.1% by weight to 3% by weight of the shake aid And (6) 3 to 8 weight percent of a solvent selected from the group consisting of carbitol solvents, ester solvents, and mixtures thereof. The paste composition for forming a solar cell electrode according to claim 7, wherein the rocking aid comprises a resin selected from the group consisting of a resin, a rosin ester, a polysiloxane, a cyclodecane, and a cerium oxide powder. At least one component of the group consisting of an aliphatic amine, a carboxylic acid guanamine, and a combination thereof. The paste composition for forming a solar cell electrode according to claim 7, further comprising 0.01 to 2 weight percent of an aliphatic ammonium salt, an aliphatic carboxylate, and a mixture thereof. A dispersant and from 0.001% by weight to 2% by weight of a stabilizer selected from the group consisting of aliphatic carboxylic acids, aliphatic amines, and mixtures thereof. A solar cell electrode, wherein a paste composition for forming a solar cell electrode according to any one of claims 1 to 9 is screen-printed on a semiconductor substrate and fired. form.