WO2020111906A1 - Conductive paste for solar cell electrode, and solar cell manufactured using same - Google Patents

Abstract

The present invention provides a solar cell electrode manufactured by applying a conductive paste comprising a metal powder, a glass frit, a metal oxide, an organic binder and a solvent, and then drying and firing same, wherein the upper shape of an electrode formed using the conductive paste is controlled by adjusting the components and amount of the organic binder.

Description

Conductive paste for solar cell electrodes and solar cell manufactured using the same

The present invention relates to a conductive paste used for forming an electrode of a solar cell and a solar cell manufactured using the conductive paste.

A solar cell is a semiconductor device that converts solar energy into electrical energy, and generally has a p-n junction type, and its basic structure is the same as that of a diode. The solar cell device is generally constructed using a p-type silicon semiconductor substrate having a thickness of 180 to 250 μm. On the light-receiving surface side of the silicon semiconductor substrate, an n-type impurity layer having a thickness of 0.3 to 0.6 µm, an antireflection film and a front electrode are formed thereon. In addition, a back electrode is formed on the back side of the p-type silicon semiconductor substrate. The front electrode is coated with a conductive paste containing silver-based conductive particles (silver powder), glass frit, organic vehicle, and additives on an anti-reflection film, and then fired to form an electrode. The back electrode is formed by applying an aluminum paste composition composed of aluminum powder, glass frit, organic vehicle, and additives by screen printing, drying, and baking at a temperature of 660° C. (melting point of aluminum) or higher. During the firing, aluminum diffuses into the p-type silicon semiconductor substrate, whereby an Al-Si alloy layer is formed between the back electrode and the p-type silicon semiconductor substrate, and at the same time, a p+ layer is formed as an impurity layer by diffusion of aluminum atoms. do. The presence of the p+ layer prevents recombination of electrons and obtains a back surface field (BSF) effect that improves the collection efficiency of product carriers. A rear silver electrode may be further positioned under the rear aluminum electrode.

The direction of technology development related to the front electrode to increase the efficiency of the existing solar cell was to realize a high aspect ratio in which the line width spread rate is reduced while realizing a fine line width as shown in FIG. 1. However, in the case of having a high aspect ratio, the light receiving amount increases, but there is a limit.

An object of the present invention is to provide a conductive paste capable of controlling the shape of the upper portion of the front electrode and a solar cell manufactured using the same, in order to maximize the amount of light received by the front electrode.

However, the objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

The present invention is an electrode for a solar cell prepared by applying a conductive paste containing a metal powder, glass frit, metal oxide, organic binder and solvent, followed by drying and firing, and controlling the component and content of the organic binder to control the conductive paste. Provided is an electrode for a solar cell whose upper shape of the formed electrode is controlled.

In addition, the electrode for the solar cell is characterized in that the ratio of the upper line width to the lower line width is 20 to 30%.

In addition, the conductive paste is characterized in that it comprises at least one selected from the group consisting of cellulose-based resin, acrylic-based resin, polyvinyl-based resin and phenol resin as an organic binder.

In addition, the organic binder is characterized in that included 0.3wt% to 0.5wt% based on the total weight of the conductive paste.

In addition, the conductive paste is characterized in that it contains two or more cellulose ether compounds having different molecular weights.

In addition, the cellulose ether compounds having different molecular weights have a low molecular weight of 50,000 to 100,000 g/mol, and the cellulose ether compounds having different molecular weights of 200,000 to 350,000 g/mol and the total content of the total amount of the conductive paste. Based on 0.3wt% to 0.5wt%, it characterized in that it contains more compounds having a high molecular weight than a compound having a low molecular weight.

In addition, the conductive paste is characterized in that the ratio (T.I) of the viscosity of 10 rpm to 100 rpm measured at 25°C using a Brookfield DV-3T, spindle 14 is 5.0 to 6.0.

In addition, the electrode for the solar cell is characterized in that the reflectivity measured using a KONICA MINOLTA Chroma meter CR-400 is 13 to 16, and the PL value measured using a BT imaging R2 device is 30,000 to 45,000.

In addition, the present invention provides a solar cell comprising a front electrode on the upper substrate and a rear electrode on the lower substrate, wherein the front electrode includes the electrode for the solar cell.

In the present invention, by controlling the composition of the organic binder and the content of the silver powder contained in the conductive paste for the solar cell electrode, to control the upper shape of the electrode manufactured by using it to minimize the reflection of light and increase the amount of light received by the solar cell Power generation efficiency can be maximized.

1 shows a front electrode manufacturing shape required in the related art.

Figure 2 shows a conventional front electrode shape.

3 shows the shape of the front electrode according to the present invention.

Before describing the present invention in detail below, it is understood that the terms used herein are only for describing specific embodiments and are not intended to limit the scope of the present invention, which is limited only by the scope of the appended claims. shall. All technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art unless otherwise stated.

Throughout this specification and claims, unless otherwise stated, the terms comprise, comprises, comprising means referring to an article, step or group of articles, and steps, and any other article It is not meant to exclude a step or group of things or a group of steps.

On the other hand, various embodiments of the present invention can be combined with any other embodiments, unless otherwise indicated. Any feature indicated as particularly preferred or advantageous may be combined with any other feature or features indicated as preferred or advantageous. Hereinafter, embodiments and effects according to the present invention will be described with reference to the accompanying drawings.

The conventional front electrode was developed in the direction of improving the electrical conductivity by increasing the aspect ratio and minimizing the line resistance value through a trapezoidal shape, as shown in FIG. 2, but in the case of such a trapezoidal electrode shape, the reflectance of light is large. There is a problem in that the amount of light received decreases.

The conductive paste according to an embodiment of the present invention is a paste suitable for use in forming a solar cell electrode, and the upper shape of the electrode manufactured by using it is controlled in a round form as shown in FIG. 3 to increase the discharge amount and the line height. Conductivity improvement is possible. When measuring the upper line width of the manufactured electrode, when the upper line width is widened, the reflectivity increases and the PL characteristic decreases, resulting in a short circuit current, and when the upper line width is narrow, the discharge amount decreases and the series resistance (Rs) increases. Since there is a problem, an appropriate ratio of the upper line width to the lower line width exists, and the conductive paste according to the present invention controls the ratio of the upper line width to the lower line width to 20 to 30%. In addition, the present invention can further improve the electrical conductivity characteristics by preventing the drop in charge rate that may occur in the case of a round shape by increasing the thickness (line height) of the electrode (increasing the aspect ratio).

The conductive paste composition according to the present invention may include metal powder, glass frit, metal oxide, organic vehicle, and the like. In addition, various additives may be included.

As the metal powder, Ag, Au, Cu, Pt, Pb, Sn, Ni, Al, W, Mo, Ru powder, etc. may be used. For the front electrode, silver powder is mainly used, and for the back electrode, aluminum powder is mainly used. Is used. Hereinafter, for convenience, the metal powder will be described using silver powder as an example. The following description may be equally applied to other metal powders.

The content of the metal powder is 70 to 95 wt% based on the total weight (wt) of the conductive paste composition, more preferably 85 to 95 wt%, considering the electrode thickness formed during printing and the line resistance of the electrode. By increasing the content of the metal powder within the content range, it is possible to increase the electrode thickness (line height) to improve the electrical conductivity properties.

The silver powder is preferably a pure silver powder, and in addition, a silver-coated composite powder having at least a surface of a silver layer, an alloy containing silver as a main component, or the like can be used. Further, other metal powders may be mixed and used. Examples include aluminum, gold, palladium, copper, and nickel.

The average particle diameter of the silver powder may be 0.05 to 3 µm, and 0.5 to 2.5 µm is preferable when considering ease of pasting and density during firing, and the shape may be at least one of spherical, needle, plate and amorphous. have. The silver powder may be used by mixing two or more kinds of powders having different average particle diameters, particle size distributions, and shapes.

The glass frit comprises at least one composition prepared from the group consisting of Bi ₂ O ₃ , ZnO, B ₂ O ₃ , SiO ₂ , PbO, TeO ₂ , Al ₂ O ₃ , CuO, MgO, BaO, SnO and TiO ₂ Includes. The combination of the organic content of each component prevents an increase in the electrode line width and can improve contact resistance at high surface resistance and can improve short-circuit current characteristics.

The average particle size of the glass frit is not limited, but may have a particle size within the range of 0.05 to 4 μm, and may be used by mixing multi-particulate particles having different average particle sizes. Preferably, at least one glass frit having an average particle diameter of 0.1 µm or more and 3 µm or less is preferable. Through this, the reactivity at the time of firing becomes excellent, and particularly, the damage of the n layer can be minimized at a high temperature, the adhesion is improved, and the open voltage (Voc) can be improved. In addition, it is possible to reduce the increase in line width of the electrode during firing.

The transition temperature of the glass frit may be 200°C to 500°C, preferably 250°C to 450°C, and when the range is satisfied, an effect of desired physical properties can be more efficiently achieved.

The content of the glass frit is 0.1 to 15 wt% based on the total weight of the conductive paste composition, and further preferably 0.5 to 4 wt%.

The metal oxide is tungsten (W), antimony (Sb), nickel (Ni), copper (Cu), magnesium (Mg), calcium (Ca), ruthenium (Ru), molybdenum (Mo) and bismuth (Bi) It comprises an oxide of any one or more metals selected from the group consisting of. The average particle diameter may be 0.01 to 5 μm, and considering the effect, 0.02 to 2 μm is preferable.

When the metal oxide contains at least one of the oxides of the metal, it is preferable that the oxide of the antimony (Sb) is preferably included. When the oxide of antimony is included, the content of the metal oxide is preferably 0.1 wt% to 0.5 wt% based on the total weight of the conductive paste, and more preferably 0.2 wt% to 0.4 wt%.

The metal oxide is preferably tungsten (W), antimony (Sb), nickel (Ni), copper (Cu), magnesium (Mg), calcium (Ca), ruthenium (Ru), molybdenum (Mo) and bismuth It is preferable to include any two or more first metal oxides and second metal oxides selected from the group consisting of (Bi).

When the metal oxide includes two or more types of oxides of the metal, preferably, the oxide of tungsten (W) as the first metal oxide and the oxide of antimony (Sb) as the second metal oxide must be included. good. In this case, the weight ratio of the first metal oxide to the second metal oxide is preferably 1:1 to 5. In addition, when the oxide of tungsten and the oxide of antimony are included, the content of the first metal oxide is 0.1wt% to 0.3wt% based on the total weight of the conductive paste, and the content of the second metal oxide is 0.1wt% to 0.5wt %, more preferably, the content of the first metal oxide is 0.1wt% to 0.3wt%, and the content of the second metal oxide preferably includes 0.2wt% to 0.4wt%.

The organic vehicle includes an organic binder and a solvent. The organic vehicle may be 3 to 25 wt% based on the total weight of the conductive paste composition, and preferably 5 to 15 wt%.

The organic vehicle requires properties to maintain a uniform mixture of metal powder and glass frit, for example, when the conductive paste is applied to the substrate by screen printing, the conductive paste is homogenized and the printed pattern is blurred. And properties that suppress flow and further improve the dischargeability and plate separation properties of the conductive paste from the screen plate.

The organic binder included in the organic vehicle includes any one or more selected from the group consisting of cellulose-based resins, acrylic-based resins, polyvinyl-based resins, and phenolic resins.

The cellulose-based resin includes a cellulose ester-based compound and a cellulose ether compound. Examples of the cellulose ester-based compound include cellulose acetate and cellulose acetate butylate, and examples of the cellulose ether compound include ethyl cellulose, methyl cellulose, and hydroxy flow. Examples include pill cellulose, hydroxy ethyl cellulose, hydroxy propyl methyl cellulose, and hydroxy ethyl methyl cellulose.

Examples of the acrylic resin include polyacrylamide, polymethacrylate, polymethyl methacrylate, and polyethyl methacrylate.

Examples of the vinyl-based resin include polyvinyl butyral, polyvinyl acetate, and polyvinyl alcohol.

The organic binders may be selected and used at least one. Preferably, a cellulose ether compound is preferably used, and more preferably, two or more cellulose ether compounds having different molecular weights are mixed and used.

Cellulose ether compounds having different molecular weights are preferably used by mixing a compound having a low molecular weight of 50,000 to 100,000 g/mol and a compound having a high molecular weight of 200,000 to 350,000 g/mol.

The organic binder contains 0.3wt% to 0.5wt% based on the total weight of the conductive paste, and even when using a mixture of cellulose ether compounds having different molecular weights, the summed content does not exceed the above range, and the high molecular weight It is best to mix more compounds with compounds with lower molecular weight.

Solvents used for dilution of the composition include alcohols such as ethanol, isopropanol, terpineol and glycols such as ethylene glycol, acetates such as ethyl acetate, butyl carbitol acetate, ethyl carbitol acetate, methyl cellosolve, and butyl Ethers such as cellosolve, hydrocarbon-based organic solvents such as hexane, heptane, and parapan oil, and aromatic hydrocarbon-based organic solvents such as benzene, toluene, and xylene may be used.

As an additive, a dispersant, a thickener, a thixotropic agent, a leveling agent, etc. may be used, and the dispersant may include BYK-110, 111, 108, 180, etc., and the thickener may be BYK-410. 411. 420, etc., and thixotropic agents include BYK-203, 204,205, and leveling agents such as BYK-308, 378, 3440, but are not limited thereto.

In the present invention, by controlling the composition and content of the aforementioned organic binder, the content of the metal powder, etc., it is possible to provide an effect of improving the power generation efficiency of the solar cell according to control of the upper shape of the electrode, reduction of reflectance through the electrode, and increase of the received light amount.

It will be described in more detail through the following examples.

Example Preparation of conductive paste

(1) Example 1

As the silver powder, particles of LS-Nikko Copper (D50) = 2.0 µm / Tap Density = 4.8 g/cm 3 were used, and 89.0 wt% of the total paste composition was added. The glass frit is a Pb type having a Tg of 280? and 3.0 wt% of the total paste composition is added. As a resin, 0.4 wt% of STD-10 (molecular weight 80,000 g/mol) from DOW was added, and as a solvent, 1.5 wt% of DBE (Dibasic ester manufacturer Dimethyl adipate, dimethyl glutrate, dimrthyl succinate) from DBE, Eastman's buthyl carbitol acetate 3.5 wt%, 0.5 wt% of THIXATROL MAX from ELEMENTS to impart thixotropic properties as an additive, and 1.0 wt% of ED-152 from KUSUMOTO as a dispersant were added.

(2) Example 2

In Example 1, the resin DOW company STD-10 (molecular weight 80,000 g / mol) was carried out in the same manner, except that 0.3 wt% was added.

(3) Example 3

In Example 1, the resin DOW company STD-10 (molecular weight 80,000 g / mol) was carried out in the same manner except that 0.5 wt% was added.

(4) Example 4

In Example 1, the same was carried out except that STE-200 (molecular weight ~~~~g/mol) was used instead of STOW-10 (molecular weight 80,000g/mol) as DOW.

(5) Example 5

In Example 4, the resin DOW Co., Ltd. STD-200 (molecular weight 280,000 g/mol) was carried out in the same manner, except that 0.3 wt% was added.

(6) Example 6

In Example 4, the resin DOW Co., Ltd. STD-200 (molecular weight 280,000 g/mol) was carried out in the same manner, except that 0.5 wt% was added.

(7) Example 7

In Example 1, DOW company STD-10 (molecular weight 80,000g/mol) 0.1wt%, DOW company STD-200 (molecular weight 280,000g/mol) was carried out in the same manner, except that 0.3 wt% was mixed. .

(8) Example 8

In Example 1, DOW company STD-10 (molecular weight 80,000 g/mol) 0.2 wt%, DOW company STD-200 (molecular weight 280,000 g/mol) was used in the same manner except that 0.2 wt% was mixed. .

(9) Example 9

In Example 1, except that the DOW company STD-10 (molecular weight 80,000g/mol) 0.3wt%, DOW company STD-200 (molecular weight 280,000g/mol) 0.1 wt% mixed and was carried out in the same manner. .

(10) Example 10

In Example 9, it was carried out in the same manner, except that the content of the silver powder was increased to 89.3 wt%.

(11) Example 11

In Example 9, it was carried out in the same manner, except that the content of the silver powder was increased to 89.6 wt%.

Manufacturing Example Production of Solar Cell

In manufacturing a substrate for a solar cell, a 156 mm x 156 mm single crystal silicon wafer was used. Doping phosphorus (P) through a diffusion process using POCl ₃ at 900° C. in a tube furnace to form a 100-500 nm thick emitter layer having a sheet resistance of 90 μs/sq, and An anti-reflection film was formed on the emitter layer by PECVD using a silicon nitride film with a thickness of 80 nm. The back electrode was screen printed using D company. Subsequently, a drying process was performed using a BTU drying furnace at 300°C for 30 seconds, followed by sintering in a 900°C firing furnace for 60 seconds to prepare a substrate for a solar cell. The drying process was dried at 300° C. for 30 seconds using BTU equipment, and firing was sintered at 900° C. for 60 seconds using Despatch to form a 30 μm thick back electrode.

Characteristic test

(1) Viscosity measurement

The viscosity of the conductive pastes prepared according to Examples 1 to 11 was measured at 25°C using a No. 14 spindle with a Brookfield DV-3T device and is shown in Table 1 below.

Viscosity (1rpm)_kcps Viscosity (10rpm)_kcps Viscosity (100rpm)_kcps T.I (1rpm/10rpm) T.I (10rpm/100rpm) Example 1 380 330 60 1.15 5.50 Example 2 360 340 65 1.06 5.23 Example 3 430 325 55 1.32 5.91 Example 4 460 350 65 1.31 5.38 Example 5 430 355 70 1.21 5.07 Example 6 530 340 60 1.56 5.67 Example 7 460 345 68 1.33 5.07 Example 8 430 340 65 1.26 5.23 Example 9 410 340 61 1.21 5.57 Example 10 390 350 64 1.11 5.47 Example 11 370 360 66 1.03 5.45

(2) Measurement of electrode shape Using the conductive paste prepared according to Examples 1 to 11, a pattern was printed on the front surface of the wafer by a screen printing technique, and the screen printing was performed using a Baccini printing machine, and the mask was 360-16 mesh. The electrode was printed using a 15 μm emulsion film opening 33 μm mask. At this time, the discharge amount of the conductive paste and the line height of the pattern, and the line widths of the upper and lower portions are shown in Table 2 below.

Discharge amount (g) Line height (㎛) Upper line width (㎛) Lower line width (㎛) Upper/lower line width ratio Example 1 0.084 15.2 10 45 22.2 Example 2 0.087 16.1 13 44 29.5 Example 3 0.081 14.6 7 47 14.9 Example 4 0.082 12.9 16 43 37.2 Example 5 0.085 13.5 18 42 42.9 Example 6 0.079 12.8 15 44 34.1 Example 7 0.083 14.1 14 42 33.3 Example 8 0.084 14.5 13 42 31.0 Example 9 0.085 15.1 11 43 25.6 Example 10 0.086 15.3 11 42 26.2 Example 11 0.087 15.5 10 42 23.8

(3) Measurement of reflectivity, PL characteristics and IV characteristics The reflectivity of the electrodes formed using the conductive pastes prepared according to Examples 1 to 11 was measured using a KONICA MINOLTA Chroma meter CR-400, and the PL intensity was BT imaging. It was measured using R2 equipment, and IV characteristics were measured using HALM Electronix equipment. The results are shown in Table 3 below.

Reflectivity (L*) PL count Isc(A) Rs(Ω) Example 1 15 32500 10.02 0.00098 Example 2 16 30500 9.98 0.00095 Example 3 14 34300 9.99 0.00101 Example 4 17 28700 10 0.00107 Example 5 18 26500 9.98 0.00103 Example 6 17 28400 10.01 0.00111 Example 7 17.5 27000 10 0.00103 Example 8 16 30050 10.01 0.00101 Example 9 15.5 32300 10.02 0.00096 Example 10 15.5 31800 10.03 0.00095 Example 11 15 33000 10.035 0.00098

Examples 1 to 9 evaluate the results of using or mixing resin molecular weights (STD10 (low molecular weight)/ STD200 (high molecular weight)) alone for electrode shape control purposes. As can be seen from the above results, when the polymer alone is applied, it can be confirmed that Isc decreases due to an increase in reflectivity and a decrease in PL count (intensity) as the line width of the upper electrode increases. In addition, it can be seen that when the resin content of the small molecule or the polymer increases, the upper line width decreases but the discharge amount decreases and the Rs (series resistance) increases. Examples 10 to 11 were evaluated in Example 9, which showed the best results in view of the discharge amount, printability, and efficiency as a result of evaluation.In order to increase the FF, when the electrode shape is a round shape instead of a trapezoid shape, there is an improvement in Isc, but the electrical conductivity is poor. Since there may be FF drop, the electrode thickness is increased to further improve the electrical conductivity. Example 10 shows the best results.

Features, structures, effects, and the like exemplified in each of the above-described embodiments may be combined or modified with respect to other embodiments by a person having ordinary knowledge in the field to which the embodiments belong. Therefore, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

Claims (10)

It is an electrode for solar cells manufactured by drying and firing after applying a conductive paste containing metal powder, glass frit, metal oxide, organic binder and solvent, An electrode for a solar cell in which an upper shape of an electrode formed by using the conductive paste is controlled by adjusting a component and content of the organic binder. According to claim 1, The electrode for the solar cell is a solar cell electrode, characterized in that the ratio of the upper line width to the lower line width of 20 to 30%. According to claim 1, The conductive paste is an electrode for a solar cell, characterized in that it comprises at least one selected from the group consisting of cellulose-based resin, acrylic-based resin, polyvinyl-based resin and phenol resin as an organic binder. According to claim 3, The organic binder is an electrode for a solar cell, characterized in that contained 0.3wt% to 0.5wt% based on the total weight of the conductive paste. According to claim 3, The conductive paste is a solar cell electrode, characterized in that it comprises two or more cellulose ether compounds having different molecular weights. The method of claim 5, The cellulose ether compound having a different molecular weight includes a compound having a low molecular weight of 50,000 to 100,000 g/mol, and a compound having a high molecular weight of 200,000 to 350,000 g/mol. The method of claim 6, The cellulose ether compounds having different molecular weights have a combined content of 0.3 wt% to 0.5 wt% based on the total weight of the conductive paste, An electrode for a solar cell comprising a compound having a high molecular weight more than a compound having a low molecular weight. According to claim 1, The conductive paste is Brookfield DV-3T, the electrode for a solar cell, characterized in that the ratio (T.I) of the viscosity of 10rpm to 100rpm viscosity measured at 25 ℃ using a spindle 14 is 5.0 to 6.0. According to claim 1, The electrode for the solar cell is a solar cell electrode characterized in that the reflectivity measured using a KONICA MINOLTA Chroma meter CR-400 is 13 to 16, and the PL value measured using a BT imaging R2 device is 30,000 to 45,000. In the solar cell having a front electrode on the upper substrate, and a rear electrode on the lower substrate, The front electrode, the solar cell comprising the electrode for a solar cell of claim 1.

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