Glass frit and paste composition for solar cell electrode comprising same

Abstract

The present invention relates to a glass frit and a paste composition for a solar cell electrode comprising the same. A glass frit according to one embodiment of the present invention is a glass frit for use in a paste for solar cell electrodes, the glass frit being a PbO-SiO2-B2O3 system, and further containing a boron powder. According to the present invention, by adding the boron powder to the glass frit, the amount of Pb precipitation after sintering is reduced, and thus the contact characteristics with a wafer can be improved by suppressing over-etching and improving sintering fluidity. As a result, the series resistance (Rs) value is reduced, and the efficiency of the solar cell can be improved.

Description

TECHNICAL FIELD

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

[0002] In recent years, as traditional natural energy resources such as oil or coal are predicted to be depleted, and environmental problems of thermal power generation and safety problems of nuclear power generation are raised, attention to renewable energy such as sunlight, solar heat, and wind power, which can replace these energy resources, is increasing. Among them, solar power generation can apply infinite solar energy resources and is environmentally friendly, and thus, a great deal of research and development is being conducted, and is being installed and used in many sites.

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

[0004] A solar cell is a semiconductor element that converts light energy of the sun into electric energy, and is broadly classified into a silicon solar cell and a compound semiconductor solar cell according to a raw material substance, and the silicon solar cell is mostly used.

[0005] A silicon solar cell is formed by forming a P-N junction on a silicon wafer and forming a front electrode and a back electrode on the front surface and the back surface of the wafer, respectively, in order to allow internal electrons to flow to the outside. If light is irradiated to such a solar cell, free electrons are generated in the silicon wafer by a photoelectric effect, the electrons move due to the P-N junction, and flow to an external circuit through an electrode formed on the surface of the silicon wafer, thereby generating electric current. Also, an anti-reflection film is formed on the surface of the silicon wafer to reduce reflection loss of sunlight, thereby improving efficiency of conversion of sunlight into electric energy.

[0006] An electrode of a solar cell is formed by applying a conductive paste to one side of a silicon wafer. A conductive paste (hereinafter, referred to as a solar cell electrode paste) composition includes a conductive powder, a glass frit, and an organic vehicle, and in a process of sintering after the solar cell electrode paste is applied, the glass frit is decomposed and removes a predetermined portion of the anti-reflection film, and is attached to the silicon wafer, thereby achieving conduction of both.

[0007] According to the conventional technology, in the case of a P-type solar cell, there is a problem that, as the thickness of the N layer on the P-N junction is gradually thinned (shallow emitter), the N layer is damaged after etching of the anti-reflection film. In order to improve this problem, a TeO2 component is introduced into a low-temperature sintering component. Thereby, over-etching caused by PbO can be prevented to prevent degradation of cell characteristics and occurrence of shunt short circuit.

[0008] However, in the case of an N-type solar cell, the TeO2 component reacts with Al, and there is a possibility that the contact characteristics are deteriorated due to a secondary phase such as an oxide film. In the case of an N-type solar cell, a technique of using an Ag-Al metal adhesive material to improve the contact characteristics is known, but in this case, there is a possibility that a loss of open-circuit voltage (Voc) occurs. SUMMARY

[0009] TECHNICAL PROBLEM TO BE SOLVED BY THE INVENTION

[0010] The present application is to solve the above-described conventional technology problems, and aims to provide a paste for solar cell electrodes capable of improving contact characteristics in an N-type solar cell and preventing a loss of open-circuit voltage, and a glass frit included therein.

[0011] Further, the present application aims to provide a paste for solar cell electrodes capable of improving contact characteristics of solar cell electrodes and improving conversion efficiency, and a glass frit included therein.

[0012] MEANS FOR SOLVING THE TECHNICAL PROBLEM

[0013] The glass frit according to an embodiment of the present application is a glass frit for a paste for solar cell electrodes, and is a PbO-SiO2-B2O3 system and further includes a boron powder.

[0014] The glass frit according to an embodiment of the present application can include 66 to 85 wt% of PbO, 5 to 15 wt% of B2O3, and 4 to 10 wt% of SiO2.

[0015] The glass frit according to an embodiment of the present application can include a boron powder at a content of 1.5 wt% to 3 wt%.

[0016] According to an embodiment of the present application, the boron powder can be configured to have a particle size of 1 μm to 3 μm.

[0017] The glass frit according to an embodiment of the present application can further include one or more of ZnO, Al2O3, BaO, Li2O, and Na2O.

[0018] According to an embodiment of the present application, the ratio of Pb / PbO after sintering can be 0.3 to 0.6.

[0019] The paste composition for a solar cell electrode according to an embodiment of the present application includes an electrically conductive powder, a glass frit, and an organic vehicle. The glass frit is a PbO-SiO2-B2O3 system, and further includes a boron powder.

[0020] Effects of the Invention

[0021] According to the present application, by the boron powder added to the glass frit, the amount of Pb precipitated after sintering is reduced, and c, thereby the over-etching of the anti-reflection film can be suppressed to prevent the loss of open-circuit voltage (Voc) caused by the increase in line width, etc.

[0022] Further, according to the present application, by improving the sintering fluidity of the glass frit to improve the contact characteristics with the wafer, the series resistance (Rs) value is reduced, and thereby the efficiency of the solar cell can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 FIG. 1 is a cross-sectional view schematically showing the structure of a solar cell according to an embodiment of the present application.

[0024] Figure 2 FIG. 2 is a diagram schematically showing the etching process of a SiN x layer based on the paste composition for a solar cell electrode.

[0025] Figure 3 FIG. 3 is a diagram schematically showing the sintering process of the paste composition for a solar cell electrode.

[0026] Figure 4 FIG. 4 is a diagram schematically showing the state at the time of cooling of the paste composition for a solar cell electrode.

[0027] Figure 5 FIG. 5 is an electron microscope photograph showing the wafer erosion of a glass frit according to the prior art and a glass frit according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] Unless defined differently, all the technical and scientific terms used in the present specification have the same meanings as those generally understood by those skilled in the art to which the present application pertains. All the terms used in the present specification are selected as general terms in order to more clearly explain the present application, and are not intended to limit the scope of the present application. The terms "comprise", "comprising", "have", "having", "include", "including", etc. used in the present specification are used to designate the presence of the features, numbers, steps, actions, elements, parts, or the like described in the specification, and are not intended to preclude the presence or addition of one or more other features, numbers, steps, actions, elements, parts, or the like.

[0029] The preferred embodiments of the present application will be described in detail below with reference to the attached drawings. In order to clarify the present application, the description of parts irrelevant to the present application is omitted.

[0030] Structure of a solar cell

[0031] Figure 1 is a cross-sectional view schematically showing the structure of a solar cell based on an embodiment of the present application.

[0032] Reference Figure 1 The solar cell (100) includes a silicon wafer (110), a front surface electrode (130) and a back surface electrode (140) formed on the front surface and the back surface of the silicon wafer (110), respectively. Further, the solar cell (100) includes an anti-reflection film (120) formed between the silicon wafer (110) and the front surface electrode (130) and between the silicon wafer (110) and the back surface electrode (140).

[0033] The silicon wafer (110) includes an N-type semiconductor (111) and a P-type semiconductor (113). In the N-type semiconductor (111), a Group V element such as P, As, Sb, or the like as an N-type impurity can be doped in silicon, and in the P-type semiconductor (113), a Group III element such as B, Ga, In, or the like as a P-type impurity can be doped in silicon. A P-N junction is formed between the N-type semiconductor (111) and the P-type semiconductor (113), and if light is incident on the P-N junction, free electrons generated by the photoelectric effect move to the N-type semiconductor (111), so that a photovoltaic voltage can be generated.

[0034] The anti-reflection film (120) is formed on the P-type semiconductor (113) of the silicon wafer (110), and reduces the reflectance of light incident on the front surface of the silicon wafer (110), can function as an insulating layer, and can perform the function of passivating defects present on the surface or inside of the silicon wafer (110). If the reflectance of incident light is reduced due to the anti-reflection film (120), the amount of light reaching the P-N junction increases, and as a result, 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) can be formed of any one of a silicon nitride film, a silicon oxide film, a silicon oxynitride film, or a multilayer film in which two or more films are stacked, for example, and in addition, can be formed of a film having a publicly known composition.

[0035] The front electrode (130) of the solar cell (100) is formed on the front surface of the silicon wafer (110), as shown in the figure, and can be formed in a state of penetrating the anti-reflection film (120) and being connected 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) by sintering to allow the paste composition to penetrate into the anti-reflection film (120), thereby being connected to the P-type semiconductor (113) of the silicon wafer (110).

[0036] The back electrode (140) is formed on the back surface of the silicon wafer (110), i.e., the surface opposite to the surface on which the front electrode (130) is formed, and functions to collect electrons generated by the photoelectric effect and moving toward the N-type semiconductor (111) and move them to the outside, thereby allowing current to flow. The back electrode (140) can also be formed in a state of penetrating the anti-reflection film (120') and being connected 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') by sintering to allow the paste composition to penetrate into the anti-reflection film (120'), thereby being connected to the N-type semiconductor (111) of the silicon wafer (110).

[0037] On the other hand, according to an embodiment of the present application, the electrode paste composition for a solar cell, by using a glass frit of a specific composition, can achieve the effects inherent to the present application described above, and hereinafter, the electrode paste composition for a solar cell and the glass frit used therefor will be described in detail.

[0038] Paste composition for solar cell electrode

[0039] The electrode paste for a solar cell according to an embodiment of the present application includes a conductive powder, a glass frit, and an organic vehicle.

[0040] The conductive powder of the electrode paste composition for a solar cell is used to impart electrical properties to the paste composition, and according to the present embodiment, silver (Ag) powder can be used as the conductive powder. The silver powder can be included in an amount of 80 to 90 wt% based on the entire paste composition. The silver powder can have a particle size in the range of nanometers to micrometers, and silver powders having two or more different sizes can be used in combination.

[0041] The glass frit of the slurry composition for solar cell electrode performs a function of making the slurry contact with the silicon wafer (110) by etching the anti-reflection film (120) formed of SiNx in the sintering process of the slurry for solar cell electrode, and the glass frit according to the present embodiment is formed of a PbO-SiO2-B2O3 system. According to the present embodiment, the glass frit can be contained in an amount of 0.5 to 5% by weight, based on the entire slurry composition.

[0042] Figure 2 is a diagram schematically showing an etching process of the anti-reflection film (SiN x ) based on the slurry composition for solar cell electrode. The etching of the anti-reflection film proceeds according to the following reaction at a temperature of 500 to 650°C.

[0043] [Chemical Formula 1]

[0044]

[0045] [Chemical Formula 2]

[0046]

[0047] Figure 3 is a diagram schematically showing a sintering process of the slurry composition for solar cell electrode. According to the above-described etching process, the glass frit in the slurry for solar cell electrode contacts with the silicon wafer, and the following reaction proceeds when sintering is performed at a temperature of 600 to 820°C.

[0048] [Chemical Formula 3]

[0049]

[0050] [Chemical Formula 4]

[0051] 2Ag2O + Si → SiO2 + 4Ag

[0052] [Chemical Formula 5]

[0053] 2PbO + Si → 2Pb + SiO2

[0054] [Chemical Formula 6]

[0055]

[0056] [Chemical Formula 7]

[0057] Ag2O + Pb → 2Ag + PbO

[0058] The reaction of Chemical Formula 3 to 7 continuously occurs in sintering. As Chemical Formula 4 and Chemical Formula 5, a part of the upper portion of the silicon wafer (Si) is dissolved by Ag2O and PbO in the paste for solar cell electrode, and SiO2 is formed as the silicon is oxidized, and as a result, adhesion is generated between the paste for solar cell electrode and the silicon wafer. At this time, the amount of Ag precipitates formed greatly depends on oxygen (O2). Therefore, sufficient oxygen is required at a temperature of 650°C or more.

[0059] Figure 4 is a diagram briefly showing a state at the time of cooling of the paste composition for solar cell electrode. Referring to Figure 4 When Ag of the paste for electrode is cooled while being in contact with the silicon wafer (Si), Ag precipitates in a nanocrystalline form are generated on the silicon wafer (Si). The glass frit enables Ag to be easily decomposed from Ag2O so that more Ag is allowed to react, thereby enabling Ag to be densely sintered.

[0060] As described above, the glass frit of the paste composition for solar cell electrode according to an embodiment of the present application is formed of a PbO-SiO2-B2O3 system.

[0061] PbO is used to improve the etching performance of the anti-reflection film based on the paste composition for solar cell electrode, and can be contained in an amount of 66 to 85% by weight based on the glass frit. PbO enables the etching of the anti-reflection film and the sintering penetration process to be easily performed through the anti-reflection film, and penetrates into the anti-reflection film so that the electrode can be connected to the silicon wafer.

[0062] SiO2 is a component for controlling crystallization at the time of glass melting, and can be contained in an amount of 4 to 10% by weight based on the glass frit. When SiO2 is contained in an amount of less than 4% by weight, the crystallization control effect cannot be expected, and when SiO2 is contained in an amount of more than 10% by weight, it can be possible that the contact characteristics are hindered due to the increase in the glass transition temperature and the increase in the sintering temperature. In addition, SiO2 can also have an effect of reducing the flowability of the glass to prevent excessive etching.

[0063] B2O3 is a component added to improve the conversion efficiency of the solar cell, and can be contained in an amount of 5 to 15% by weight based on the glass frit.

[0064] In addition, the glass frit according to an embodiment of the present application can further contain one or more of ZnO, Al2O3, BaO, Li2O, and Na2O, and can contain these metal oxides in an amount of 1 to 7% by weight based on the glass frit.

[0065] As described above, in the case of an N-type solar cell, a configuration using an Ag-Al metal adhesive material to improve contact properties is known. However, according to the conventional technology, since the PbO content is as large as about 70%, an excessive electrode fire through phenomenon occurs when a paste for a front electrode of a solar cell is sintered, which can cause a loss of open circuit voltage (Voc). When a smaller PbO content is used to prevent this phenomenon, a problem of insufficient contact properties between the electrode and the wafer can occur.

[0066] To solve this problem, the glass frit according to the present embodiment contains boron powder in addition to PbO-SiO2-B2O3.

[0067] According to an embodiment of the present application, the boron powder functions to reduce Pb precipitation when a paste for a solar cell electrode is sintered. As the Pb precipitation is reduced, the frequency and growth of Pb-Al alloy can be suppressed, and as a result, a shallow etching property can be exhibited.

[0068] The glass frit according to an embodiment of the present application can contain 1.5 to 3 wt% of boron powder. In an embodiment, the boron powder can be configured to have a particle size of 1 to 3 μm.

[0069] In an embodiment of the present application, to evaluate Pb precipitation, the Pb / PbO (Pb 2+ ) value is measured by XPS analysis after sintering of the electrode paste composition. The Pb / PbO value of the glass frit according to an embodiment of the present application can be 0.3 to 0.6 when the paste for an electrode is sintered. When the Pb / PbO value exceeds 0.6, a good contact property between the paste and the wafer is exhibited, but a loss of open circuit voltage (Voc) can occur due to damage to the wafer caused by excessive etching. Conversely, when the Pb / PbO value is less than 0.3, the contact property with the silicon wafer is insufficient, the series resistance (Rs) is high, and the power efficiency can decrease.

[0070] Figure 5 FIGS. 1 and 2 are electron microscope photographs showing wafer etching of a glass frit according to the conventional technology and a glass frit according to an embodiment of the present application. In the case of the glass frit according to the conventional technology, it can be confirmed that the etching depth of the wafer is deep and the etching amount is large due to the generation of Pb-Al alloy at a temperature of 660°C or higher caused by a large amount of Pb precipitation (see (a) of FIG. 1). Conversely, in the case of the glass frit according to the embodiment of the present application, it can be confirmed that the generation and growth of Pb-Al alloy are suppressed due to the reduction of the amount of Pb precipitation, and as a result, the etching depth of the wafer is shallow and the etching amount is small (see (b) of FIG. 2). Figure 5 Figure 5 ​​

[0071] The organic vehicle of the paste composition for solar cell electrode is used to impart a viscosity suitable for printing of the paste composition, and can include the balance other than the electrically conductive powder and the glass frit in the paste composition as a whole. The organic vehicle can generally include a binder resin and a solvent. For example, as the binder resin, an acrylate or cellulose resin, ethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, a mixture of ethyl cellulose and a phenol aldehyde resin, an alkyd resin, a phenol aldehyde resin, an acrylate resin, a xylene resin, a polybutene resin, a polyester resin, a urea resin, a melamine resin, a vinyl acetate resin, a poly methacrylate of wood rosin or alcohol, or the like can be used, and as the solvent, at least one of hexane, toluene, ethyl cellosolve, cyclohexanone, butyl cellosolve, 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, methyl ethyl ketone, benzyl alcohol, γ-butyrolactone, or ethyl lactate, or the like can be used.

[0072] Further, in order to improve flow properties, process properties, and the like, the paste composition for solar cell electrode can also include a general additive. The additive can use one or more of a dispersant, a plasticizer, a viscosity stabilizer, an antioxidant, and the like.

[0073] Experimental example

[0074] Hereinafter, the effects of the present application will be specifically described based on experimental results obtained by measuring conversion efficiency and the like based on the composition of the glass frit used in the paste composition for solar cell electrode.

[0075] Table 1 shows the composition of the glass frit of the paste composition based on each of the examples and comparative examples when forming a solar cell electrode. In this experimental example, the paste composition includes about 89 wt% of Ag powder, about 3 wt% of a glass frit, and the balance of an organic vehicle. After sintering of the glass frit based on each of the examples and comparative examples, the Pb / PbO bonding state was distinguished by an XPS analysis device.

[0076] [Table 1]

[0077]

[0078] Table 2 shows the results of measuring the glass transition temperature of the glass frit of each of the examples and comparative examples and the conversion efficiency in a solar cell formed from the paste composition for solar cell electrode including the same.

[0079] [Table 2]

[0080]

[0081] Referring to Tables 1 and 2, first, when boron powder is not contained or contained in small amounts (Comparative Examples 1 to 3), it is confirmed that the Pb / PbO (Pb 2+ ) is high to 0.8 or more. In contrast, when boron powder is contained according to the embodiments of the present application (Embodiments 1 to 7), it is confirmed that the Pb / PbO value is 0.3 to 0.6. Also, referring to Tables 1 and 2, when the glass frit does not contain or contain boron powder in small amounts (Comparative Examples 1 to 3), it can be confirmed that the number of Al spikes is large compared to the embodiments of the present application, and at the same time, the depth of the Al spikes is deep. Also, it can be confirmed that the open circuit voltage (Voc) is low, and the conversion efficiency is also low.

[0082] Also, when the glass frit contains 5% by weight or more of boron powder (Comparative Example 4), it can be confirmed that the number of Al spikes is small, but the series resistance (Rs) value is high compared to the embodiments of the present application, and as a result, the conversion efficiency is also low.

[0083] In this regard, in Embodiments 1 to 7, it can be confirmed that the depth of the Al spikes is not deep, and the resistance is also not high, and thus the conversion efficiency is excellent.

[0084] As such, the glass frit for a solar cell electrode paste based on an embodiment of the present application, by adding 1.5 to 3% by weight of boron powder to a PbO-SiO2-B2O3-based glass frit, suppresses excessive etching and improves sintering fluidity based on the reduction of Pb precipitation, improves the contact characteristics with the wafer, the open circuit voltage (Voc) is increased, and thus excellent conversion efficiency characteristics can be obtained.

[0085] The above-described preferred embodiments of the present application have been described with reference to the accompanying drawings, but it will be understood by those skilled in the art that the present application can be implemented in other specific forms without changing the technical idea or essential characteristics thereof. Therefore, the above-described embodiments should be understood as illustrative in all aspects, not as limiting.

[0086] [Explanation of Symbols]

[0087] 100: solar cell

[0088] 110: silicon wafer

[0089] 111: N-type semiconductor

[0090] 113: P-type semiconductor

[0091] 120, 120': anti-reflection film

[0092] 130: front electrode

[0093] 140: back electrode

[0094] 150: back electric field layer

[0095] Industrial applicability

[0096] According to the present application, by adding the boron powder to the glass frit, the amount of Pb precipitated after sintering is reduced, and the over-etching of the anti-reflection film can be suppressed to prevent the open-circuit voltage (Voc) loss caused by the increase in line width, etc.

[0097] Further, according to the present application, by improving the sintering fluidity of the glass frit to improve the contact characteristics with the wafer, the series resistance (Rs) value is reduced, and thus the efficiency of the solar cell can be improved.

Claims

1. A glass frit for use in a paste for solar cell electrodes, wherein, The glass frit is of the PbO-SiO2-B2O3 system. It also contains boron powder.

2. The glass frit according to claim 1, comprising: 66 to 85% by weight of PbO; 5 to 15% by weight of B2O3; and 4 to 10% by weight of SiO2.

3. The glass frit according to claim 1, wherein, The boron powder is 1.5 to 3% by weight.

4. The glass frit according to claim 1, wherein, The boron powder has a particle size of 1 to 3 μm.

5. The glass frit according to claim 1, further comprising one or more of ZnO, Al2O3, BaO, Li2O and Na2O.

6. The glass frit according to claim 1, wherein, The Pb / PbO ratio after sintering is 0.3 to 0.

6.

7. A paste composition for solar cell electrodes, comprising: Conductive powder; glass frit; and Organic carrier, The glass frit is of the PbO-SiO2-B2O3 system and also contains boron powder.

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