Glass frit and solar cell electrode paste composition comprising same

Abstract

The present invention relates to a glass frit and a paste composition for a solar cell electrode, wherein the paste composition includes the glass frit. The glass frit according to one embodiment of the present invention is a PbO-SiO2-B2O3 glass frit used in a paste for a solar cell electrode, and further contains boron powder. According to the present invention, the amount of Pb precipitation following firing is reduced by the boron powder added to the glass frit, and thus the contact characteristics with a wafer may be enhanced through the suppression of over-etching and improved firing fluidity. Accordingly, the series resistance (Rs) decreases, and thus the efficiency of the solar cell may be improved.

Description

Glass frit and paste composition for solar cell electrode containing the same

[0001] The present invention relates to a glass frit and a paste composition for a solar cell electrode comprising the same, and more particularly, to a glass frit for a paste for an N-type solar cell electrode and a paste composition for a solar cell electrode comprising the same.

[0002] Recently, with the predicted depletion of existing natural energy resources like oil and coal, coupled with environmental concerns surrounding thermal power generation and safety concerns surrounding nuclear power, interest in alternative renewable energy sources like solar energy, solar thermal energy, and wind power has grown. Among these, solar power generation, due to its ability to utilize the inexhaustible solar energy resource and environmental friendliness, is receiving significant research and development, and is being installed and operated in numerous locations.

[0003] A solar power generation device for solar power generation includes a number of solar cell modules (panels), and a solar cell module is composed of a plurality of solar cells.

[0004] Solar cells are semiconductor devices that convert sunlight energy into electrical energy. Depending on the raw material, they are broadly classified into silicon solar cells and compound semiconductor solar cells, with silicon solar cells being the most widely used.

[0005] Silicon solar cells are constructed by forming a p-n junction on a silicon wafer, with front and back electrodes formed on the front and back of the silicon wafer, respectively, to allow internal electrons to flow outward. When light is irradiated on these solar cells, the photoelectric effect generates free electrons within the silicon wafer. These electrons then migrate through the p-n junction and flow to an external circuit through electrodes formed on the surface of the silicon wafer, generating current. Furthermore, an anti-reflection film is formed on the surface of the silicon wafer to reduce reflection loss of irradiated sunlight, thereby improving the efficiency of converting sunlight into electrical energy.

[0006] The electrode of a solar cell is formed by applying a conductive paste to one surface of a silicon wafer. The conductive paste (hereinafter, “solar cell electrode paste”) composition includes a conductive powder, glass frit, and an organic vehicle. After applying the solar cell electrode paste and firing it, the glass frit decomposes and removes a predetermined portion of the antireflection film and attaches to the silicon wafer, thereby conducting the two.

[0007] Conventional P-type solar cells have a problem where the N layer becomes damaged after etching the antireflection film as the thickness of the N layer at the PN junction becomes thinner (shallow emitter). To address this issue, TeO2, a low-temperature firing component, is being introduced. This prevents excessive etching by PbO, thereby preventing deterioration of cell characteristics and the occurrence of shunts.

[0008] However, in the case of N-type solar cells, the TeO2 component may react with Al, resulting in poor contact characteristics due to secondary phases such as oxide films. A technology is known to improve contact characteristics using Ag-Al metal adhesives for N-type solar cells, but this can result in a loss of open circuit voltage (Voc).

[0009] The present invention is intended to solve the problems of the above-described prior art, and its purpose is to provide a paste for a solar cell electrode capable of preventing open-circuit voltage loss while improving contact characteristics in an N-type solar cell, and a glass frit provided therein.

[0010] In addition, the present invention aims to provide a solar cell electrode paste and a glass frit provided therein that can improve the contact characteristics of the solar cell electrode and enhance the conversion efficiency.

[0011] A glass frit according to one embodiment of the present invention is a glass frit used in a paste for a solar cell electrode, and is of the PbO-SiO2-B2O3 system and further includes boron powder.

[0012] According to one embodiment of the present invention, the glass frit may include 66 to 85 wt% of PbO, 5 to 15 wt% of B2O3, and 4 to 10 wt% of SiO2.

[0013] The glass frit according to one embodiment of the present invention may contain 1.5 wt% to 3 wt% of boron powder.

[0014] According to one embodiment of the present invention, the boron powder may be configured to have a particle size of 1 μm to 3 μm.

[0015] The glass frit according to one embodiment of the present invention may further include one or more of ZnO, Al2O3, BaO, Li2O, and Na2O.

[0016] According to one embodiment of the present invention, the ratio of Pb / PbO after firing may be 0.3 to 0.6.

[0017] A paste composition for a solar cell electrode according to one embodiment of the present invention comprises a conductive powder, a glass frit, and an organic vehicle. Here, the glass frit is of the PbO-SiO2-B2O3 system and further comprises boron powder.

[0018] According to the present invention, the amount of Pb precipitation after firing is reduced by the boron powder added to the glass frit, thereby suppressing excessive etching of the antireflection film, thereby preventing open circuit voltage (Voc) loss due to an increase in line width, etc.

[0019] Furthermore, according to the present invention, the efficiency of a solar cell can be improved by reducing the series resistance (Rs) value due to improved contact characteristics with a wafer resulting from improved plastic fluidity of the glass frit.

[0020] FIG. 1 is a cross-sectional view schematically showing the structure of a solar cell according to one embodiment of the present invention.

[0021] Figure 2 shows SiN by a paste composition for solar cell electrodes. x This is a drawing that briefly shows the etching process of the layers.

[0022] Figure 3 is a drawing briefly showing the sintering process of a paste composition for a solar cell electrode.

[0023] Figure 4 is a drawing briefly showing the state of a paste composition for a solar cell electrode during cooling.

[0024] FIG. 5 is an electron microscope photograph showing wafer erosion of a glass frit according to a prior art and a glass frit according to an embodiment of the present invention.

[0025] All technical and scientific terms used herein, unless otherwise defined, have the meaning commonly understood by one of ordinary skill in the art to which the present invention pertains, and all terms used herein have been selected for the purpose of more clearly describing the present invention and have not been selected to limit the scope of the present invention. Expressions such as "comprising," "having," and the like used herein should be understood as open-ended terms that imply the possibility of including other embodiments, unless otherwise stated in the phrase or sentence in which the expression is included.

[0026] Hereinafter, with reference to the attached drawings, preferred embodiments of the present invention will be described in detail to a degree that those skilled in the art can easily implement the invention. For the sake of clarity, descriptions of parts unrelated to the present invention will be omitted.

[0027] Structure of a solar cell

[0028] FIG. 1 is a cross-sectional view schematically showing the structure of a solar cell according to one embodiment of the present invention.

[0029] Referring to FIG. 1, a solar cell (100) includes a silicon wafer (110), and a front electrode (130) and a back electrode (140) formed on the front and back surfaces of the silicon wafer (110), respectively. In addition, the solar cell (100) further includes an anti-reflection film (120) formed between the silicon wafer (110) and the front electrode (130), and between the silicon wafer (110) and the back electrode (140).

[0030] A silicon wafer (110) includes an N-type semiconductor (111) and a P-type semiconductor (113). The N-type semiconductor (111) may be silicon doped with a group 5 element such as P, As, or Sb as an N-type impurity, and the P-type semiconductor (113) may be silicon doped with a group 3 element such as B, Ga, or In as a P-type impurity. A PN junction is formed between the N-type semiconductor (111) and the P-type semiconductor (113), and when light is incident on the PN junction, free electrons generated by the photoelectric effect move to the N-type semiconductor (111), thereby generating photovoltaic power.

[0031] The anti-reflection film (120) is formed on the P-type semiconductor (113) of the silicon wafer (110), and reduces the reflectivity of light incident on the front surface of the silicon wafer (110), functions as an insulating layer, and can also play a role in deactivating defects existing on the surface or inside of the silicon wafer (110). When the reflectivity of light incident on the anti-reflection film (120) is reduced, the amount of light reaching the PN junction increases, and accordingly, the short-circuit current of the solar cell (100) increases, so that the conversion efficiency of the solar cell (100) can be improved. The anti-reflection film (120) may be formed of, for example, one of a silicon nitride film, a silicon oxide film, and a silicon oxynitride film, or may be formed of a multilayer film in which two or more films are laminated, and may also be formed of a film having a known composition.

[0032] The front electrode (130) of the solar cell (100) is formed on the front surface of the silicon wafer (110), and as illustrated, can be formed in a form that penetrates the anti-reflection film (120) and connects to the P-type semiconductor (113) of the silicon wafer (110). Specifically, the front electrode (130) can be formed by applying an electrode paste on the anti-reflection film (120) and then etching the anti-reflection film (120) through firing to allow the paste composition to penetrate into the anti-reflection film (120), thereby connecting to the P-type semiconductor (113) of the silicon wafer (110).

[0033] A back electrode (140) is formed on the back of the silicon wafer (110), that is, the opposite side to the side where the front electrode (130) is formed. The back electrode (140) collects electrons that are generated by the photoelectric effect and move to the N-type semiconductor (111) and moves them to the outside to cause current to flow. The back electrode (140) can also be formed in a form that penetrates the anti-reflection film (120') and connects to the N-type semiconductor (111) of the silicon wafer (110). Specifically, the back electrode (140) can be formed by applying an electrode paste on the anti-reflection film (120') and then etching the anti-reflection film (120') through firing to allow the paste composition to penetrate into the anti-reflection film (120'), thereby connecting to the N-type semiconductor (111) of the silicon wafer (110).

[0034] Meanwhile, according to one embodiment of the present invention, a paste composition for an electrode of a solar cell can achieve the above-described effects of the present invention by using a glass frit of a specific composition. Hereinafter, the paste composition for an electrode of a solar cell and the glass frit used therein will be described in detail.

[0035] Paste composition for solar cell electrodes

[0036] A paste for a solar cell electrode according to one embodiment of the present invention includes a conductive powder, glass frit, and an organic vehicle.

[0037] The conductive powder of the paste composition for solar cell electrodes is intended to impart electrical properties to the paste composition, and according to the present embodiment, silver (Ag) powder may be used as the conductive powder. The silver powder may be included in an amount of 80 to 90 wt% based on the entire paste composition. The silver powder may have a particle size of nano-size to micro-size, and it is also possible to use a mixture of two or more silver powders having different sizes.

[0038] The glass frit of the paste composition for solar cell electrodes serves to bring the paste and the silicon wafer (110) into contact by etching the anti-reflection film (120) made of SiNx during the firing process of the paste for solar cell electrodes, and the glass frit according to the present embodiment is made of a PbO-SiO2-B2O3 system. According to the present embodiment, the glass frit may be included in an amount of 0.5 to 5 wt% based on the entire paste composition.

[0039] Figure 2 is an antireflection film (SiN) using a paste composition for solar cell electrodes. x ) is a schematic diagram illustrating the etching process. The etching of the anti-reflection film is performed according to the following reaction at a temperature of 500 to 650°C.

[0040]

[0041]

[0042] Figure 3 is a schematic diagram illustrating the firing process of a paste composition for solar cell electrodes. According to the etching process described above, the glass frit within the paste for solar cell electrodes comes into contact with a silicon wafer, and when firing is performed at a temperature of 600°C to 820°C, the following reaction occurs.

[0043]

[0044]

[0045]

[0046]

[0047]

[0048] The reactions of Chemical Formulas 3 to 7 occur continuously during firing. As shown in Chemical Formulas 4 and 5, a portion of the upper portion of the silicon wafer (Si) is dissolved by Ag2O and PbO in the solar cell electrode paste, and SiO2 is formed through oxidation of Si, thereby creating adhesion between the solar cell electrode paste and the silicon wafer. At this time, the amount of Ag precipitate formed is highly dependent on oxygen (O2). Therefore, sufficient oxygen is required at temperatures above 650°C.

[0049] Figure 4 is a schematic diagram illustrating the cooling state of a paste composition for a solar cell electrode. Referring to Figure 4, when Ag in the electrode paste comes into contact with a silicon wafer (Si) and is cooled, nanocrystal-shaped Ag precipitates are formed on the silicon wafer (Si). The glass frit facilitates the decomposition of Ag from Ag2O, allowing more Ag to react and densely sinter the Ag.

[0050] As described above, the glass frit of the paste composition for a solar cell electrode according to one embodiment of the present invention is composed of a PbO-SiO2-B2O3 system.

[0051] PbO is intended to increase the etching performance of the antireflection film by the paste composition for solar cell electrodes, and may be included in an amount of 66 to 85 wt% based on the glass frit. PbO facilitates the etching and sintering process of the antireflection film and penetrates the antireflection film, thereby allowing the electrode to connect with the silicon wafer.

[0052] SiO2 is a component that controls crystallization during glass melting, and can be included in an amount of 4 to 10 wt% based on the glass frit. If SiO2 is contained in an amount less than 4 wt%, it is difficult to expect a crystallization control effect, and if it is contained in an amount exceeding 10 wt%, it can impair contact characteristics due to an increase in the glass transition point and an increase in the firing temperature. In addition, SiO2 can have the effect of preventing excessive etching by reducing the fluidity of the glass.

[0053] B2O3 is a composition added to improve the conversion efficiency of solar cells, and may be included in an amount of 5 to 15 wt% based on glass frit.

[0054] In addition, the glass frit according to one embodiment of the present invention may further include one or more of ZnO, Al2O3, BaO, Li2O, and Na2O, and these metal oxides may be included in an amount of 1 to 7 wt% based on the glass frit.

[0055] As described above, a configuration using Ag-Al metal adhesives to improve contact characteristics in N-type solar cells is known. However, according to the prior art, when the PbO content is high, such as around 70%, excessive electrode penetration (fire-through) may occur during the firing of the paste for the front electrode of the solar cell, which may result in a loss of open circuit voltage (Voc). To prevent this, if the PbO content is reduced, the problem of insufficient contact characteristics between the electrode and the wafer may arise.

[0056] To solve these problems, the glass frit according to the present embodiment further includes boron powder in addition to PbO-SiO2-B2O3.

[0057] According to one embodiment of the present invention, boron powder serves to reduce Pb precipitation during the firing of a solar cell electrode paste. As Pb precipitation is reduced, the frequency of occurrence and growth of Pb-Al alloy can be suppressed, thereby exhibiting thin etching characteristics.

[0058] According to one embodiment of the present invention, the glass frit may contain 1.5 wt% to 3 wt% of boron powder. In one embodiment, the boron powder may be configured to have a particle size of 1 μm to 3 μm.

[0059] In one embodiment of the present invention, in order to evaluate the Pb precipitation property, Pb / PbO (Pb) was analyzed by XPS after firing of the electrode paste composition. 2+ ) values ​​are measured. According to one embodiment of the present invention, the glass frit may have a Pb / PbO value of 0.3 to 0.6 when the electrode paste is fired. If the Pb / PbO value exceeds 0.6, the contact characteristics between the paste and the wafer may be good, but damage to the wafer due to excessive etching may occur, resulting in a loss of open circuit voltage (Voc). Conversely, if the Pb / PbO value is less than 0.3, the contact characteristics with the silicon wafer may be insufficient, resulting in a high series resistance (Rs), which may lower power efficiency.

[0060] FIG. 5 is an electron microscope photograph showing wafer erosion of a glass frit according to a prior art and a glass frit according to an embodiment of the present invention. In the case of the glass frit according to the prior art, since the amount of Pb precipitation is large, a Pb-Al alloy is generated at a temperature of 660°C or higher, and it can be confirmed that the erosion depth of the wafer due to this is deep and the amount of erosion is large (see (a) of FIG. 5). On the other hand, in the case of the glass frit according to an embodiment of the present invention, since the generation and growth of the Pb-Al alloy are suppressed due to a decrease in the amount of Pb precipitation, the erosion depth of the wafer is shallow and the amount of erosion is also small (see (b) of FIG. 5).

[0061] The organic vehicle of the paste composition for solar cell electrodes is intended to provide a viscosity suitable for printing of the paste composition, and may be included in the remaining amount of the entire paste, excluding the conductive powder and glass frit. Typically, the organic vehicle may include a binder resin and a solvent. For example, as a binder resin, acrylate or cellulose resin, ethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, a mixture of ethyl cellulose and phenol resin, alkyd resin, phenol resin, acrylic ester resin, xylene resin, polybutene resin, polyester resin, urea resin, melamine resin, vinyl acetate resin, wood rosin, or polymethacrylate of alcohol can be used, and as a solvent, hexane, toluene, ethyl cellosolve, cyclohexanone, butyl cenrosolve, butyl carbitol (diethylene glycol monobutyl ether), dibutyl carbitol (diethylene glycol dibutyl ether), butyl carbitol acetate (diethylene glycol monobutyl ether acetate), propylene glycol monomethyl ether, hexylene glycol, terpineol, It can be used by including at least one of methyl ethyl ketone, benzyl alcohol, gamma butyrolactone, or ethyl lactate.

[0062] In addition, the paste composition for solar cell electrodes may further include conventional additives to improve flow characteristics, process characteristics, etc. The additives may include one or more dispersants, plasticizers, viscosity stabilizers, and antioxidants.

[0063] Experimental example

[0064] Below, the effects of the present invention are specifically described based on the experimental results measuring conversion efficiency, etc. according to the components of glass frit used in a paste composition for solar cell electrodes.

[0065] Table 1 shows the composition of the glass frit of the paste composition according to each example and comparative example in forming a solar cell electrode. In this experimental example, the paste composition includes about 89 wt% of Ag powder, about 3 wt% of glass frit, and the remainder of an organic vehicle. After firing the glass frit according to each example and comparative example, the Pb / PbO bonding state was distinguished using an XPS analyzer.

[0066] Glass frit composition ratio (weight%) Boron powder addition (weight%) PbOB2O3 SiO2 ZnO Al2O3 BaOLi2O+Na2O Example 1 7858522-3 Example 2 66.3 14772.7-32 Example 3 75135322-2 Example 4 7710452-22 Example 5 80510221-3 Example 6 736873-31.5 Example 7 8248321-3 Comparative Example 1 736873-3-Comparative Example 2 8284321--Comparative Example 3 8284321-0.5 Comparative Example 4 8284321-5

[0067] Table 2 shows the results of measuring the glass transition point of the glass frit of each example and comparative example and the conversion efficiency in a solar cell formed with a paste composition for a solar cell electrode containing the glass frit.

[0068] Number of Pb / PbOAl spikes (100㎛) 2)Al spike depth Open circuit voltage (Voc) (mV) Rs (mΩ) Conversion efficiency (%) Example 10.60 10~17 Medium 7 12.8 1.20 24.3 Example 20.3 15~10 Shallow 7 13.8 1.35 24.0 Example 3 0.3 8 8~15 Shallow 7 13.0 1.21 24.5 Example 4 0.5 6 10~17 Medium 7 12.5 1.17 24.3 Example 5 0.4 5 8~16 Medium 7 11.6 1.132 3.9 Example 60.367~14 Shallow 7 13.31.23 24.2 Example 7 0.399~16 Medium 7 12.21.15 24.1 Comparative Example 10.85 15~26 Deep 7 09.81.07 23.4 Comparative Example 21.027~40 Deep 7 07.50.96 22.5 Comparative Example 30.80 18~32 Deep 7 08.61.04 23.1 Comparative Example 4 05 or less - 7 12.21.5 3 22.9

[0069] Referring to Table 1 and Table 2, first of all, in the case of not including boron powder or containing a small amount of boron powder (Comparative Examples 1 to 3), Pb / PbO (Pb 2+ ) is confirmed to be high at 0.8 or higher. On the other hand, in the case where boron powder is included according to an embodiment of the present invention (Examples 1 to 7), the Pb / PbO value is confirmed to be 0.3 to 0.6. In addition, referring to Tables 1 and 2, in the case where the glass frit does not include boron powder or includes a small amount of boron powder (Comparative Examples 1 to 3), it can be confirmed that the number of Al spikes is large compared to the embodiments of the present invention, and the depth of the Al spikes is deep. In addition, it can be confirmed that the open circuit voltage (Voc) is low and the conversion efficiency is also low.

[0070] In addition, when the glass frit contains 5 wt% or more of boron powder (Comparative Example 4), the number of Al spikes is small, but the series resistance (Rs) value is high compared to the examples of the present invention, and accordingly, it can be confirmed that the conversion efficiency is also low.

[0071] In comparison, in Examples 1 to 7, the depth of the Al spike is not deep and the resistance is not high, so it can be confirmed that the conversion efficiency is excellent.

[0072] In this way, the glass frit used in the solar cell electrode paste according to one embodiment of the present invention suppresses excessive etching by reducing the amount of Pb precipitation by adding 1.5 wt% to 3 wt% of boron powder to the glass frit of the PbO-SiO2-B2O3 system, and improves the sintering fluidity, thereby improving the contact characteristics with the wafer, increasing the open circuit voltage (Voc), and obtaining excellent conversion efficiency characteristics.

[0073] While preferred embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical concept or essential features thereof. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0074] [Explanation of symbols]

[0075] 100: Solar cells

[0076] 110: Silicon wafer

[0077] 111: N-type semiconductor

[0078] 113: P-type semiconductor

[0079] 120, 120': Anti-reflection coating

[0080] 130: Front electrode

[0081] 140: Rear electrode

[0082] 150: Rear field layer

[0083] According to the present invention, the amount of Pb precipitation after firing is reduced by the boron powder added to the glass frit, thereby suppressing excessive etching of the antireflection film, thereby preventing open circuit voltage (Voc) loss due to an increase in line width, etc.

[0084] Furthermore, according to the present invention, the efficiency of a solar cell can be improved by reducing the series resistance (Rs) value due to improved contact characteristics with a wafer resulting from improved plastic fluidity of the glass frit.

Claims

1. As a glass frit used in paste for solar cell electrodes, It is a PbO-SiO2-B2O3 system, Containing more boron powder Glass frit.

2. In paragraph 1, 66 to 85 wt% PbO, 5 to 15 wt% B2O3, 4 to 10 wt% SiO2, Including Glass frit.

3. In paragraph 1, The above boron powder is 1.5 to 3 wt% Glass frit.

4. In paragraph 1, The above boron powder has a particle size of 1 to 3 μm. Glass frit.

5. In paragraph 1, Further comprising one or more of ZnO, Al2O3, BaO, Li2O and Na2O Glass frit.

6. In paragraph 1, After firing, the ratio of Pb / PbO is 0.3 to 0.6, Glass frit.

7. Challenging powder, Glass frit and organic vehicle Including, The above glass frit is of the PbO-SiO2-B2O3 system and further contains boron powder. Paste composition for solar cell electrode.

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