Glass powder, conductive silver paste and its preparation methods, front electrode and N-type silicon solar cell

Abstract

This invention discloses a glass powder, a conductive silver paste, a method for preparing the same, a front electrode, and an N-type silicon solar cell. The glass powder, with a total molar percentage of 100%, comprises the following components: a first oxide (0.1%–50.0%), a second oxide (30.0%–80.0%), a third oxide (0.1%–15.0%), and a fourth oxide (10.0%–50.0%). The first oxide includes one or more oxides of Si, Ti, Zr, and Ge; the second oxide includes oxides of B, or a combination of oxides of B with one or more oxides of Al, Ga, Fe, La, and Y; the third oxide includes oxides of W, or a combination of oxides of W with one or more oxides of Se, Nb, Te, and P; and the fourth oxide includes one or more oxides of Pb and Bi, or a combination of one or more oxides of Pb and Bi with one or more oxides of Ba, Zn, Mg, and Ca. This invention enables N-type silicon solar cells to have high photoelectric conversion efficiency.

Description

Technical Field

[0001] This invention relates to the field of silicon solar cell technology, and in particular to a glass powder, a conductive silver paste and its preparation method, a front electrode and an N-type silicon solar cell. Background Technology

[0002] Significant progress has been made in silicon solar cell power generation technology, with cell types gradually shifting from the early P-type to the current mainstream N-type, such as N-type TOPCon cells, ABC cells, and HPBC cells. Currently, N-type TOPCon cells using LECO (laser-enhanced contact optimization) sintering technology are gradually becoming the market mainstream. Consequently, the matching electronic silver paste has also undergone multiple iterations, achieving phased improvements in photoelectric conversion efficiency. However, there is still a significant gap between the efficiency and the theoretical efficiency limit of N-type TOPCon cells, indicating considerable room for further efficiency improvement. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a glass powder, a conductive silver paste and its preparation method, a front electrode and an N-type silicon solar cell, in order to overcome the shortcomings of the above-mentioned background technology. The conductive silver paste can be well matched with the laser sintered N-type silicon solar cell, enabling it to have high photoelectric conversion efficiency.

[0004] This invention provides a glass powder suitable for the front electrode of an N-type silicon solar cell. Based on the total molar percentage of oxides in the glass powder (100%), the glass powder comprises the following components:

[0005] First oxide 0.1%~50.0%;

[0006] Second oxide 30.0%~80.0%;

[0007] Tertiary oxide 0.1%~15.0%;

[0008] Quaternary oxides: 10.0%~50.0%;

[0009] in,

[0010] The first oxide includes one or more oxides of Si, Ti, Zr, and Ge;

[0011] The second oxide includes an oxide of B, or an oxide of B combined with one or more oxides of Al, Ga, Fe, La, and Y.

[0012] The third oxide includes oxides of W, or a combination of oxides of W and oxides of Se, Nb, Te, and P.

[0013] The fourth oxide includes one or more of Pb oxides and Bi oxides, or a combination of one or more of Pb oxides and Bi oxides with one or more of Ba, Zn, Mg, and Ca oxides.

[0014] Furthermore, the glass powder also includes a fifth oxide, which includes one or more oxides of Li, Na, K, and Ag, and the molar percentage of the fifth oxide does not exceed 5% of the total molar content of all components of the glass powder.

[0015] Furthermore, the glass powder has a particle size distribution range of 0.1~6.0μm and a D50 distribution range of 0.6~1.8μm.

[0016] The present invention also provides a conductive silver paste suitable for the front electrode of an N-type silicon solar cell, wherein the conductive silver paste comprises, based on 100% of its total weight:

[0017] Silver powder content: 85.0%~90.0%;

[0018] The glass powder content is 1.0% to 3.5% as described above;

[0019] Organic carriers: 7.0%–12.0%;

[0020] Inorganic additives: 0.0%~0.5%.

[0021] Furthermore, the silver powder is spherical or near-spherical, with a particle size distribution range of 0.2~3.0μm and a D50 distribution range of 0.5~1.0μm.

[0022] Furthermore, the inorganic additive includes one or more of aluminum powder, silicon powder, lead oxide powder, tungsten trioxide powder, titanium dioxide powder, and zinc oxide powder, with a particle size distribution range of 0.1~3.5μm and a D50 distribution range of 0.2~1.2μm.

[0023] Furthermore, the organic carrier comprises organic solvent, organic resin, and additives, and the content of each component is as follows, based on the total weight of the organic carrier as 100%:

[0024] Organic solvents: 60.0%~85.0%;

[0025] Organic resin 5.0%~30.0%;

[0026] Additives 2.0%~15.0%.

[0027] The present invention also provides a method for preparing the conductive silver paste as described above, comprising the following steps:

[0028] Preparation of glass powder: Weigh and mix the raw materials for glass powder according to the set ratio, then melt, cool and dry them, and finally grind them to obtain glass powder;

[0029] Preparation of organic carrier: Weigh the raw materials of organic carrier according to the set ratio, heat and stir to mix, disperse evenly by high-speed centrifugation, and then filter to obtain organic carrier;

[0030] Preparation of conductive silver paste: Silver powder, prepared glass powder, and inorganic additives are added to the prepared organic carrier according to the mass ratio, mixed and stirred evenly, and then ground, adjusted, and filtered to obtain conductive silver paste.

[0031] The present invention also provides a front electrode, which is made by printing conductive silver paste suitable for the front electrode of N-type silicon solar cells onto a silicon wafer as described above, and then sintering it using LECO technology.

[0032] The present invention also provides an N-type silicon solar cell, comprising the front electrode as described above.

[0033] The beneficial effects of this invention are as follows: The first oxide constructs a stable network framework, ensuring the physicochemical stability of the glass powder; the second oxide, as a network former and flux, is responsible for providing and regulating the basic fluidity of the glass phase; the fourth oxide, as a network exogenous body, is used to regulate reactivity; and the third oxide, as a reaction regulator, can buffer and stabilize reaction kinetics, precisely controlling and slowing down the corrosion rate and depth of the glass on the polycrystalline silicon layer. By adjusting the proportions of each component, especially optimizing the ratio of the first and second oxides and the content of the third oxide, the wetting and transport capacity of the glass powder to silver particles is enhanced while maintaining the necessary stability of the glass network. This allows for precise control of the quantity and activity of the glass phase transported to the silver-silicon interface during high-temperature processes, promoting the uniform formation of the silver-silicon alloy at the interface. The LECO technology treats the early pre-sintering process, resulting in a low-content, inert glass phase that protects the passivation layer.

[0034] In the LECO technology stage, the glass phase is selectively activated, guiding the formation of a uniform, dense, and thickness-controllable interface contact layer. This process ensures that while completely removing the insulating film on the battery surface and forming a low-resistance ohmic contact, the ultra-thin polycrystalline silicon passivation layer and PN junction of the TOPCon battery are protected to the maximum extent, thereby significantly reducing open-circuit voltage loss.

[0035] In the LECO technology stage, the inorganic additives added in this invention act as interfacial performance fine-tuning agents. Through synergistic effects with glass powder and silver powder, they promote the silver-silicon contact process, achieving excellent alloying contacts and precisely modulating the thermodynamic and kinetic processes of local reactions. Simultaneously, they promote the formation of a uniform and stable interfacial microstructure. This synergistic effect allows for precise control of the entire metallization process, ensuring efficient formation of ohmic contacts while suppressing the risk of damage to the PN junction and passivation layer, thereby generating synergistic gains in improving open-circuit voltage and fill factor.

[0036] In summary, this invention achieves comprehensive control over the location, extent, rate of interfacial reactions, and the metallization microstructure through precise design of the glass powder composition. When matched with the LECO process, it provides TOPCon cells with an electrode solution that combines high open-circuit voltage, low contact resistance, high fill factor, and excellent reliability, thereby comprehensively improving the photoelectric conversion efficiency of the cells. Detailed Implementation

[0037] The term "range" disclosed herein takes the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive and composable; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0038] In this invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions. In this invention, unless otherwise specified, all steps mentioned herein can be performed sequentially or randomly, but sequential performance is preferred.

[0039] This invention provides an N-type silicon solar cell, which typically includes a silicon substrate, a PN junction, an anti-reflection coating, a front electrode, and a back electrode, sequentially stacked or integrated. The front electrode is prepared by applying conductive silver paste to the surface of a silicon wafer that has undergone surface passivation and anti-reflection coating deposition via screen printing or spraying, followed by sintering using LECO technology.

[0040] This invention provides a conductive silver paste suitable for the front electrode of an N-type silicon solar cell. Based on 100% of the total weight of the conductive silver paste, it comprises: 85.0%–90.0% silver powder; 1.0%–3.5% glass powder; 7.0%–12.0% organic carrier; and 0.0%–0.5% inorganic additives. The silver powder is spherical or near-spherical, with a particle size distribution ranging from 0.2 to 3.0 μm and a D50 distribution ranging from 0.5 to 1.0 μm. The inorganic additives include one or more of aluminum powder, silicon powder, lead oxide powder, tungsten trioxide powder, titanium dioxide powder, and zinc oxide powder, with a particle size distribution ranging from 0.1 to 3.5 μm and a D50 distribution ranging from 0.2 to 1.2 μm. Based on 100% of the total weight of the organic carrier, the organic carrier comprises 60.0%–85.0% organic solvent; 5.0%–30.0% organic resin; and 2.0%–15.0% additives. The organic solvent is selected from a mixture of at least two of the following: dodecyl alcohol ester, diethylene glycol butyl ether acetate, diethylene glycol butyl ether phthalate, diethylene glycol butyl ether, and pentaerythritol triacrylate; the organic resin is selected from one or more of SEPS resin, polyvinyl butyral resin, acrylic resin, and hydroxyethyl cellulose; and the additive is selected from one or more of silicone oil, palmitic acid, polyamide wax, and hydrogenated castor oil.

[0041] Based on the total molar percentage of oxides in the glass powder being 100%, the glass powder suitable for the above-mentioned conductive silver paste provided in this embodiment includes 0.1%~50.0% of a first oxide; 30.0%~80.0% of a second oxide; 0.1%~15.0% of a third oxide; and 10.0%~50.0% of a fourth oxide. The first oxide includes one or more oxides of Si, Ti, Zr, and Ge; the second oxide includes oxides of B, or a combination of oxides of B and one or more oxides of Al, Ga, Fe, La, and Y.

[0042] The third oxide includes oxides of W, or a combination of oxides of W with one or more of the oxides of Se, Nb, Te, and P; the fourth oxide includes one or more of the oxides of Pb and Bi, or a combination of one or more of the oxides of Pb and Bi with one or more of the oxides of Ba, Zn, Mg, and Ca. The glass powder also includes a fifth oxide, which includes one or more oxides of Li, Na, K, and Ag, and the molar percentage of the fifth oxide does not exceed 5% of the total molar content of all components of the glass powder. The particle size distribution of the glass powder ranges from 0.1 to 6.0 μm, and the D50 distribution ranges from 0.6 to 1.8 μm.

[0043] Specifically, the Si element in the first oxide can be partially or completely replaced by Ti, Zr, and Ge elements; the B element in the second oxide can be partially replaced by Al, Ga, Fe, La, and Y elements; the W element in the third oxide can be partially replaced by Se, Nb, Te, and P elements; and the Pb element in the fourth oxide can be partially or completely replaced by Bi element and partially replaced by Ba, Zn, Mg, and Ca elements. For example, the glass powder can be a Si-BWO-Pb structure type glass powder or a Si-BWO-Bi structure type glass powder, and so on. In this conductive silver paste, the glass powder is a single-component glass powder or a composition of multiple glass powders with different component structures. For example, the glass powder can be a mixture of Si-BWO-Pb structure type glass powder and Si-BWO-Bi structure type lead-free glass powder, or a single Si-BWO-Pb structure type glass powder, or a single Si-BWO-Bi structure type glass powder. Oxides of the corresponding elements or substances that can decompose to obtain oxides of the element can be directly added to the glass powder. For example, CaO or CaCO3 can be added. During the glass powder melting process, CaCO3 decomposes to obtain CaO.

[0044] In this embodiment, the first oxide constructs a stable network framework, ensuring the physicochemical stability of the glass powder; the second oxide, as a network former and flux, is responsible for providing and regulating the basic fluidity of the glass phase; the fourth oxide, as a network exogenous body, is used to regulate reactivity; and the third oxide, as a reaction regulator, can buffer and stabilize reaction kinetics, precisely controlling and slowing down the corrosion rate and depth of the glass on the polycrystalline silicon layer. By adjusting the proportions of each component, especially optimizing the ratio of the first and second oxides and the content of the third oxide, the wetting and transport capacity of the glass powder to silver particles is enhanced while maintaining the necessary stability of the glass network. This allows for precise control of the quantity and activity of the glass phase transported to the silver-silicon interface during high-temperature processes, promoting the uniform formation of the silver-silicon alloy at the interface. This makes it particularly suitable for, and excellent at, achieving the printing and sintering of high-performance fine grid lines when used to prepare front electrodes. Specifically, this conductive silver paste can maximize the protection of the underlying ultrathin passivation layer while forming low-resistance ohmic contacts, thereby meeting the stringent requirements of fine grid lines for high conductivity, high reliability, and low contact damage.

[0045] For example, using the Si-BWO-Pb system, SiO2 (the first oxide) constructs a stable network framework, ensuring the physicochemical stability of the glass powder; B2O3 (the second oxide) acts as a network former and flux, responsible for providing and regulating the basic fluidity of the glass phase; PbO or Bi2O3 (the fourth oxide) acts as a network exogenous body, used to regulate reaction activity; and WO3 (the third oxide) acts as a reaction regulator, which can buffer and stabilize reaction kinetics, precisely regulate and slow down the corrosion rate and depth of the glass on the polycrystalline silicon layer.

[0046] Furthermore, in the early pre-sintering process of LECO technology, the low-content glass phase remains inert, protecting the passivation layer. During the LECO technology stage, the glass phase is selectively activated, guiding the formation of a uniform, dense, and controllable thickness interface contact layer. This process ensures that while completely removing the insulating film on the battery surface and forming a low-resistance ohmic contact, the ultra-thin polycrystalline silicon passivation layer and PN junction of the TOPCon battery are protected to the maximum extent, thereby significantly reducing open-circuit voltage loss.

[0047] In the LECO technology stage, the small amount of inorganic additives added in this invention acts as interfacial performance fine-tuning agents. Through synergistic effects with glass powder and silver powder, they promote the silver-silicon contact process, achieving excellent alloying contacts and precisely modulating the thermodynamic and kinetic processes of local reactions. Simultaneously, they promote the formation of a uniform and stable interfacial microstructure. This synergistic effect allows for precise control of the entire metallization process, ensuring efficient formation of ohmic contacts while suppressing the risk of damage to the PN junction and passivation layer, thereby generating synergistic gains in improving open-circuit voltage and fill factor.

[0048] The present invention also provides a method for preparing the conductive silver paste as described above, comprising the following steps:

[0049] Preparation of glass powder: The raw materials for glass powder are weighed and mixed according to the set ratio, then melted, cooled, and dried, and then ground to obtain glass powder. Specifically, the raw materials for glass powder that are mixed evenly are put into a crucible and placed in a high-temperature furnace, and melted at a high temperature of 900~1250℃. After the raw materials are completely melted and decomposed into a uniform glass liquid, they are taken out and rapidly cooled. Then the cooled glass is dried. Finally, the dried glass particles or glass fragments are crushed and inspected multiple times to obtain the required glass powder.

[0050] Preparation of organic carrier: Weigh the raw materials (organic solvent, organic resin, additives) of organic carrier according to the set ratio, heat and stir to mix, disperse evenly by high-speed centrifugation, and then filter to obtain organic carrier.

[0051] Preparation of conductive silver paste: Silver powder, prepared glass powder, and inorganic additives are added to the prepared organic carrier according to the mass ratio, mixed and stirred evenly, and then milled (three-roll mill), adjusted for viscosity, and filtered to obtain conductive silver paste.

[0052] The conductive silver paste described above is printed onto a silicon wafer by screen printing or spraying, and then sintered using LECO technology to obtain a front electrode containing the conductive silver paste.

[0053] The following description is based on specific embodiments.

[0054] Preparation of glass powder: First, weigh the raw materials for preparing glass powder according to the set ratio, then mix the various raw materials evenly, and place them in a crucible in a high-temperature furnace for high-temperature melting at 900~1250℃. After the raw materials are completely melted and decomposed into a homogeneous glass liquid, remove it and rapidly cool the high-temperature glass liquid. Then, dry the cooled glass. Finally, the dried glass particles or glass fragments are repeatedly crushed and inspected to obtain the required glass powder, which is numbered C01-C06. The specific molar composition ratios of the glass powders numbered C01-C06 are shown in Table 1.

[0055] Preparation of organic carriers: Organic solvent, organic resin, and additives were weighed according to the set ratio, and stirred and mixed evenly under water bath heating to 60-100℃. Then, the mixture was centrifuged and dispersed at 1000-3000 rpm, filtered, and stirred and mixed again at room temperature to obtain the organic carriers, which were sequentially numbered L01-L06. The specific weight composition ratios of the organic carriers numbered L01-L06 are shown in Table 2.

[0056] Preparation of conductive silver paste: First, weigh the corresponding mass of organic carrier according to the preset ratio, and weigh the corresponding mass of silver powder, glass powder, and inorganic additives respectively; mix the weighed materials with the organic carrier, stir evenly, then grind and adjust the viscosity through a three-roll mill, and finally filter to obtain conductive silver paste, which is numbered Q01-Q15. The specific weight percentages of conductive silver paste numbered Q01-Q15 are shown in Table 3.

[0057] Table 1. Mole percentage of each component in glass powder (mol%)

[0058]

[0059] Table 2. Weight composition (wt%) of each component in the organic carrier

[0060]

[0061] Table 3. Weight composition of silver paste in the examples (wt%)

[0062]

[0063] The silver pastes Q01-Q15 prepared in the above embodiments were printed onto N-type TOPCon cells under the same printing conditions, sintered using LECO technology, and the electrical performance of the sintered cells was tested.

[0064] To visually compare the effects of this invention, 995PFB silver paste specifically for N-type TOPCon batteries, widely used by Shanghai Silver Paste Technology Co., Ltd., was selected as a comparative example. It was printed onto N-type TOPCon batteries under the same printing conditions. The printed comparative battery cells were divided into two groups: one group was sintered using LECO technology, marked as 995PFB-T1; the other group was sintered using a traditional sintering method, marked as 995PFB-T2. The electrical performance of the comparative examples was tested under the same conditions, and all electrical performance test data are recorded in Table 4.

[0065] Table 4 Test data of the silver paste of the present invention and the comparative silver paste

[0066]

[0067] As shown in Table 4:

[0068] Compared with the commercially available product 995PFB, in embodiments Q01-Q15 of this invention, the photoelectric conversion efficiency of the 995PFB battery after sintering using LECO technology (labeled as 995PFB-T1) and the conventional sintering method (labeled as 995PFB-T2) did not increase due to the improvement of the sintering process, but instead decreased slightly. This indicates that the traditional silver paste is difficult to adapt to LECO technology to improve the photoelectric conversion efficiency of N-type TOPCon batteries.

[0069] Compared to the traditionally sintered 995PFB-T2, the silver paste of this invention significantly improves both open-circuit voltage and photoelectric conversion efficiency, with an efficiency increase of 0.06% to 0.20%. Furthermore, the silver paste of this invention exhibits excellent corrosion resistance in acetic acid corrosion tests, with an acetic acid degradation rate of only 5.12% to 10.45%, far lower than the control sample. This indicates that the electrodes formed by the paste of this invention possess excellent long-term environmental reliability, effectively resisting the corrosion of acidic substances caused by the aging of encapsulation materials in humid and hot environments, and maintaining the integrity of the electrode structure and low contact resistance over a long period. This characteristic is of great significance for ensuring that photovoltaic modules meet a long-term power warranty of more than 25 years, reducing system power generation degradation, and enhancing the investment value of end-users.

[0070] In summary, this invention, through the design of a matching glass system and inorganic additives, fully aligns with the sintering characteristics of the LECO process, thereby developing a silver paste specifically for N-type TOPCon cells suitable for this novel sintering technology. The silver paste of this invention, combined with the LECO sintering process, can improve the photoelectric conversion efficiency of N-type TOPCon cells by 0.06% to 0.20% compared to traditional silver pastes, while simultaneously providing crucial material assurance for the long-term reliable operation of photovoltaic modules.

[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A glass powder suitable for the front electrode of an N-type silicon solar cell, characterized in that, Based on the total molar percentage of oxides of each component in the glass powder being 100%, the glass powder comprises the following components: First oxide 0.1%~50.0%; Second oxide 30.0%~80.0%; Tertiary oxide 0.1%~15.0%; Quaternary oxides: 10.0%~50.0%; in, The first oxide includes one or more oxides of Si, Ti, Zr, and Ge; The second oxide includes an oxide of B, or an oxide of B combined with one or more oxides of Al, Ga, Fe, La, and Y. The third oxide includes oxides of W, or a combination of oxides of W and oxides of Se, Nb, Te, and P. The fourth oxide includes one or more of Pb oxides and Bi oxides, or a combination of one or more of Pb oxides and Bi oxides with one or more of Ba, Zn, Mg, and Ca oxides. The glass powder also includes a fifth oxide, which includes one or more oxides of Li, Na, K, and Ag, and the molar percentage of the fifth oxide does not exceed 5% of the total molar content of all components of the glass powder.

2. The glass powder as described in claim 1, characterized in that, The glass powder has a particle size distribution range of 0.1~6.0μm and a D50 distribution range of 0.6~1.8μm.

3. A conductive silver paste suitable for the front electrode of an N-type silicon solar cell, characterized in that, Based on the total weight of the conductive silver paste being 100%, the conductive silver paste comprises: Silver powder content: 85.0%~90.0%; The glass powder as described in any one of claims 1-2, ranging from 1.0% to 3.5%; Organic carriers: 7.0%–12.0%; Inorganic additives: 0.0%~0.5%.

4. The conductive silver paste as described in claim 3, characterized in that, The silver powder is spherical or near-spherical, with a particle size distribution range of 0.2~3.0μm and a D50 distribution range of 0.5~1.0μm.

5. The conductive silver paste as described in claim 3, characterized in that, The inorganic additives include one or more of aluminum powder, silicon powder, lead oxide powder, tungsten trioxide powder, titanium dioxide powder, and zinc oxide powder, with a particle size distribution range of 0.1~3.5μm and a D50 distribution range of 0.2~1.2μm.

6. The conductive silver paste as described in claim 3, characterized in that, The organic carrier comprises organic solvent, organic resin, and additives. Based on the total weight of the organic carrier (100%), the content of each component is as follows: Organic solvents: 60.0%~85.0%; Organic resin 5.0%~30.0%; Additives 2.0%~15.0%.

7. A method for preparing conductive silver paste according to any one of claims 3-6, characterized in that, Includes the following steps: Preparation of glass powder: Weigh and mix the raw materials for glass powder according to the set ratio, then melt, cool and dry them, and finally grind them to obtain glass powder; Preparation of organic carrier: Weigh the raw materials of organic carrier according to the set ratio, heat and stir to mix, disperse evenly by high-speed centrifugation, and then filter to obtain organic carrier; Preparation of conductive silver paste: Silver powder, prepared glass powder, and inorganic additives are added to the prepared organic carrier according to the mass ratio, mixed and stirred evenly, and then ground, adjusted, and filtered to obtain conductive silver paste.

8. A front electrode, characterized in that, The front electrode is prepared by printing conductive silver paste, as described in any one of claims 3-6, onto a silicon wafer and then sintering it using LECO technology.

9. An N-type silicon solar cell, characterized in that, Includes the front electrode as described in claim 8.

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