JP6068559B2 - Solar cell and its electrode - Google Patents

Description

  The present invention relates generally to solar cell technology, and more particularly to solar cells and their electrodes.

  A solar cell can convert light irradiation into electricity by its semiconductor material. The structure of the solar cell includes a photoelectric conversion layer, and the photoelectric conversion layer is manufactured by a PN junction formed of a P-type semiconductor material and an N-type semiconductor material. When sunlight is irradiated onto the photoelectric conversion layer, the band of light corresponding to the semiconductor material is absorbed by the photoelectric conversion layer, and the light energy is converted into electricity in the form of electron-hole pairs to achieve photoelectric conversion. , Supplied to a metal wire bonded to the P-type semiconductor material layer and the N-type semiconductor material layer.

  A solar cell is a semiconductor device that can convert light energy into electricity by the photovoltaic effect. Basically, semiconductor diodes can be used to convert light energy into electrical energy. Solar cells generate electricity based on two factors: a photoconductive effect and an internal electric field. Therefore, the selection of the solar cell material needs to take into account its photoconductive effect and how it generates its internal electric field.

  The performance of a solar cell is mainly determined by the conversion efficiency between light and electricity. Factors affecting conversion efficiency are: sunlight intensity and temperature; material resistance and substrate quality and defect density; pn junction concentration and depth; surface reflectivity to light; metal electrode line width, line height and Includes contact resistance. Therefore, in order to manufacture a solar cell having high conversion efficiency, it is necessary to strictly control the above influential factors.

  Conversion efficiency and manufacturing cost are key considerations for today's solar cell manufacturing. Of the solar cell products on the market today, solar cells made of silicon have the largest market share. When classified by crystal structure, they can be divided into single crystal silicon solar cells, polycrystalline silicon solar cells and amorphous silicon solar cells. From a conversion efficiency standpoint, single crystal silicon solar cells are the most efficient with a conversion efficiency of approximately 24%, while polycrystalline silicon is approximately 19% and amorphous silicon is approximately 11%. is there. By using another compound semiconductor such as III-V compound semiconductor GaAs as the photoelectric conversion substrate, the conversion efficiency can be increased to 26% or more.

  Working with innovative mechanisms to increase energy conversion efficiency and reducing silicon wafer thickness is another major focus in the development of solar cell technology. In terms of wafer thickness issues, existing technologies use laser irradiating contact (LFC) methods to reduce battery thickness to less than 37 μm and raise efficiency levels to 20%. The steps involved are, roughly described, an evaporation process is introduced to produce an aluminum layer, a passivation layer thereby forming on the back side of the solar cell, and a laser beam penetrating the aluminum layer to form a conductive contact. Used to do. The previous problem of losing electrical energy can be solved by LFC technology and further used to form holes in the passivation layer (located on the back side of the silicon substrate) to hold the aluminum electrode Traditionally expensive lithographic and etching techniques are no longer required.

  In addition, current can flow to the external load side by the two metal electrode terminals of the semiconductor substrate, so that the current generated by the solar cell flows out as available electrical energy. Naturally, the metal electrode blocks the light receiving surface (ie, the positive surface) of the substrate and interferes with the absorption of sunlight, so the area of the metal electrode on the positive surface of the solar cell increases the light receiving area of the solar cell. For as small as possible. Thus, metal electrodes are generally manufactured on the positive / backside of solar cells as a mesh electrode structure by using screen printing techniques. In the manufacture of electrodes, a conductive metal paste (such as a silver paste) is printed on an impurity-doped silicon substrate by use of a screen printing technique according to a designed diagram. The organic solvent in the conductive metal paste volatilizes under available sintering conditions, so that the metal particles interact with the silicon surface to form a silicon alloy as a good ohmic contact, thereby making the solar cell Positive and back metal electrodes. However, electrode fingerlines that are too thin can easily cause breaks or increase resistivity and decrease the conversion efficiency of solar cells. Therefore, the technical focus is on how to achieve thinning without reducing the overall output efficiency of the battery. In general, the thickness of the metal electrode is about 10 to 25 microns (μm), and the width of the positive metal line (finger line) is approximately 120 to 200 microns. It has the advantages of automation, high throughput and low cost by using such technology to manufacture solar cell electrodes. In previous studies, the conductive paste composition may not easily pass through the screen printing mesh or form large lumps that damage the screen printing plate.

  Furthermore, the back electrode structure includes a silver electrode part (finger line electrode part) and an aluminum electrode part (back surface electric field part) with respect to the silicon substrate (that is, the non-light-receiving surface) of the solar cell. In general industrial practice, as shown in FIG. 1, the silver electrode 11 pattern is printed on the back side of the silicon substrate 10 by use of a screen printing method, and then the aluminum electrode 12 pattern is formed on the silver electrode 11. The Solar cell modules cannot be electrically connected to each other by direct soldering due to the low soldering ability of aluminum. Therefore, the solder ribbon 20 is generally soldered to the silver electrode 11 region on the back surface of the solar cell so that the solar cell modules are electrically integrated with each other. In the structure of FIG. 1, the silver electrode-silicon substrate interface 30 and the aluminum electrode-Si substrate interface 50 form a eutectic layer during the sintering process, thereby being firmly bonded. However, it is difficult to form a eutectic structure between silver and aluminum, and the interface 40 between the silver electrode and the aluminum electrode tends to peel off, causing a crack between the silver electrode and the aluminum electrode. Reduces the overall performance of the solar cell. Therefore, after the solar cell module is manufactured, in addition to the conversion efficiency of the test, the adhesion test of the solder ribbon 20 and the peel test between the silver electrode-aluminum electrode interface 40 are performed to confirm the soundness of the back surface structure of the module. You may go to

  As described above, in addition to the formation of the PN junction semiconductor substrate, the main part for manufacturing the solar cell is a conductive composition. Known techniques for conductive compositions are made with metal powders (especially silver), glass frit, organic vehicles, and additives, where the composition, content, and ratio of process parameters are the performance of the final electrode product. To affect. Taking the back side of the metal electrode as an example, in addition to the adhesive strength of the solder ribbon and the degree of delamination at the interface between the silver electrode and the aluminum electrode, the quality of the conductive silver composition and the aluminum composition depends on the conversion efficiency of the solar cell. It directly affects η, open circuit voltage Voc, short circuit current (Isc), fill factor, series resistance Rs, and shunt resistance Rsh (shunt resistance), and determines the effective range of the sintering temperature T and the bond strength. Therefore, the method of developing the conductive composition that improves the solar cell performance described above is given priority in industrial development.

  Silver aluminum paste generally includes a mixture of silver powder and aluminum powder. However, it is difficult to form a eutectic structure between silver and aluminum, resulting in poor adhesion between the silver-aluminum conductive paste and easy delamination between the silver and glass frit . If all the conductive particles are used with silver material, the cost increases. The present invention is therefore to provide a method for producing a conductive composition which is better than the prior art to overcome these drawbacks.

  The electrode of the solar cell according to the first aspect of the present invention includes a conductive functional mixture, glass and an additive. The conductive functional mixture is composed of metal and metal oxide, the metal oxide is as a filler material, the metal is as a body for enhancing the bond strength between Ag-Ag and between Ag-glass. , Metal oxide, glass and additives are mixed into the organic vehicle, the metal comprises silver, the sum of the metal oxide and metal weight percent is 52-60%, the metal oxide is aluminum oxide, Contains cupric oxide, zinc oxide, zirconium oxide, silicon oxide or any combination thereof.

  Moreover, the electrode of the solar cell which concerns on the 2nd aspect of this invention contains a conductive functional mixture, a conductive coating part, glass, and an additive. The conductive functional mixture is composed of metal and metal oxide, the metal oxide is as a filler material, the metal is as a body for enhancing the bond strength between Ag-Ag and between Ag-glass. The conductive coating simply covers part of the surface of the filler material, and the metal oxide, glass and additives are mixed into the organic vehicle, and the metal oxide comprises aluminum oxide, second oxide. Including copper, zinc oxide, zirconium oxide, silicon oxide or any combination thereof, the metal includes silver and the weight percentage of the metal oxide is 0.5-3.8%.

  Furthermore, the solar cell according to the third aspect of the present invention is a solar cell comprising a back electrode, a PN semiconductor layer formed on the back electrode, and a positive electrode formed on the PN semiconductor layer. The back electrode or the positive electrode is composed of a conductive functional mixture, glass and an additive, the conductive functional mixture is composed of a metal and a metal oxide, the metal oxide is as a filling material, and the metal is Ag− As a body for enhancing the bond strength between Ag and between Ag and glass, the metal oxide, glass and additives are mixed into the organic vehicle, the metal comprises silver, the metal oxide and the metal The weight percentage ratio is 2/50 to 4/50, and the metal oxide is aluminum oxide, cupric oxide, zinc oxide, zirconium oxide, silicon oxide or any combination thereof Including.

  According to the present invention, the conductivity can be enhanced and the impedance can be lowered.

  The elements, features and advantages of the present invention can be understood by reference to the detailed description of the preferred embodiment as outlined in the specification and the attached drawings.

It is sectional drawing of the silicon substrate of a solar cell. It is sectional drawing of the structure of a silicon wafer solar cell. It is a manufacture flowchart of the electroconductive composition used for the solar cell of this invention. It is a test graph of adhesion. It is a microscopic structure of alumina particles observed by using a scanning electron microscope (SEM). It is a microscopic structure of alumina particles observed by using a scanning electron microscope (SEM). It is the microscopic structure of Al / alumina particles observed with the use of SEM. It is the microscopic structure of Al / alumina particles observed with the use of SEM. It is the microscopic structure of Al / alumina particles observed with the use of SEM. It is a microscopic structure of alumina particles observed by using SEM. It is a microscopic structure of alumina particles observed by using SEM. It is a microscopic structure of alumina particles observed by using SEM. It is a figure explaining the adhesion | attachment by the face-up and face-down in a sintering process. It is a figure explaining the adhesion | attachment by the face-up and face-down in a sintering process. It is a figure explaining the adhesion | attachment by the face-up and face-down in a sintering process. It is a figure explaining the adhesion | attachment by the face-up and face-down in a sintering process. It is a figure explaining the adhesion | attachment by the face-up and face-down in a sintering process. It is a figure explaining the adhesion | attachment by the face-up and face-down in a sintering process.

  Several preferred embodiments of the present invention will now be described in more detail. However, it should be recognized that the preferred embodiments of the present invention are provided by way of illustration and not limitation. Furthermore, the present invention may be implemented in a wide variety of other embodiments in addition to those explicitly described, and the scope of the present invention is not expressly limited except as specified in the appended claims.

  References in the specification to “one embodiment” or “one embodiment” refer to specific features, structures, or characteristics described in connection with the preferred embodiments, which are at least one of the present invention. It is included in the embodiment. Thus, the various appearances “in one embodiment” or “in one embodiment” do not necessarily refer to the same embodiment. Furthermore, the particular features, structures or characteristics of the invention may be suitably combined in one or more preferred embodiments.

  As shown in FIG. 2, this shows a cross-sectional view of the structure of a silicon wafer solar cell. The structure of the silicon wafer solar cell is only one embodiment of the present invention, but is not intended to limit the present invention of the structure of the silicon wafer solar cell and its method. As shown in FIG. 2, the silicon wafer solar cell 100 includes a first electrode 101, a second electrode 103, and a PN semiconductor layer 102, the two electrodes being conductive, at least one of which is It is transparent. The PN semiconductor layer 102 is configured on the first surface of the first electrode 101.

The first electrode 101 (known as a working electrode or a semiconductor electrode) contains some material having electrical conductivity. For example, the first electrode 101 may be formed of glass, PET, PEN plastic, or a conductive polymer coated thereon with indium tin oxide (ITO) or fluorine tin oxide (FTO). The second electrode 103 (known as the back electrode) also includes some material having electrical conductivity. The second electrode 103 is coated with a conductive substrate, titanium oxide, zinc oxide, Ga ₂ O ₃ , Al ₂ O ₃ , tin-based oxide, and a composition thereof that can be formed by selecting from ITO or FTO. Metal sheet. In one embodiment, the material of the first electrode 101 and the second electrode 103 may be any combination of transparent and opaque materials.

  It should be noted that the conductive composition of the present invention can be applied to the front or back side of any kind of silicon wafer solar cell. In other words, the disclosed conductive composition can be applied to a positive electrode or a back electrode.

  In any case, regarding the example of the back electrode, the present invention discloses a conductive composition that can be applied as a material of the back electrode, and a manufacturing method. The conductive composition comprises a conductive functional phase mixture made of metal and metal oxide, where the metal oxide is used as a filler and the metal functions as a body that enhances adhesion; Is a divalent to tetravalent metal. The covering portion may cover substantially at least a part of the surface of the filler, and the covering portion contains at least a metal or an alloy in order to improve conductivity. The melting point of the metal oxide is higher than the sintering temperature. The weight percent of filler is 3 to 5. When the conductive particles of the metal oxide covering the coating part are subjected to a heat treatment process, the surface of the coating part flows to fill the gaps between the metal oxides and enhance the bond strength between the conductive compositions. Thus, the conductivity can be enhanced and the impedance can be lowered. Further, the material cost of the filler and the covering portion can be reduced from that of the main body, and a low-cost material that replaces the high-cost core can be achieved, and the adhesion and conductivity can be increased.

  In the accompanying drawings and embodiments, a method for producing the conductive composition of the present invention is described.

  As shown in FIG. 3, it shows a manufacturing flow chart of the conductive composition used in the solar cell of the present invention. First, in step 110, filler, silver particles, glass melt (glass frit) and additives coated thereon with a conductive material are added to the organic vehicle. The shape of the particles includes flakes, spheres, cylinders, clumps, or other unspecified shapes with available dimensions. The particle size range is about 0.1 to 10 microns (μm). The organic vehicle can be selected from hydroxypropyl cellulose (HPC), polyethylene glycol (PEG), polyethylene oxide (PEO), polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP) or other polymer resins. The organic vehicle can be used to improve the dispersibility of the filler and silver particles and further improve adhesion to the substrate.

  Next, in step 111, to mix the predispersed solution with the organic vehicle, for example, using a premixing mixer (about 5 to 10 minutes) or a homogenizer using ultrasonic vibration with vigorous stirring. The agent, silver particles, glass melt block (glass frit) and additives are mixed with the organic vehicle. Finally, in step 112, a three-roll mill is used to grind the dispersion to prepare a silver paste, i.e. form a conductive composition.

  The formation of alumina is shown in FIGS. 5 and 6, which show the microscopic structure of the alumina (powder) particles observed by using a scanning electron microscope (SEM). 7, 8 and 9 show the microscopic structure of Al / alumina particles observed with the use of SEM. 10, 11 and 12 show the microscopic structure of the alumina particles observed with the use of SEM.

  FIG. 7 shows the microscopic structure of silver / alumina powder particles in different spectra.

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Spectrum 4

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Spectrum 5

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Spectrum 1

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Spectrum 2

  The conductive composition of the present invention is prepared by adding a metal oxide as a filler. The surface of the filler is preferably a coating of a conductive layer such as metals, alloys and combinations thereof. Examples of the material for the filler include alumina (aluminum oxide), zirconium oxide, silicon oxide, zinc oxide, cupric oxide, and combinations thereof. The filler is made by surface modification, the surface of which is coated with a silver or copper metal layer to achieve the purpose of improving adhesion, thereby increasing the peel strength between the silver-silver interface and the silver-glass interface. Increase the interlaminar peel strength; and thereby achieve the objective of reducing the cost of the metal oxide filler. In one embodiment, the conductive composition of the present invention can be used on the front or back surface of a solar cell.

  The formed conductive composition can be formed by a screen printing method to form a conductive film, and the specifications of the screen plate are, for example, stainless steel having a thickness of 250 mesh, a diameter of 35 microns (μm), and an emulsion thickness of 5 microns. Steel screen woven fabric; printed figure 153 mm * 4.4 mm * 2 line. The silver paste is used by screen printing, printed on the back surface of the silicon substrate, and dried at a temperature of 200 to 300 ° C. for 0.5 to 1 minute. Then, using an infrared sintering furnace, it is sintered at a peak temperature such as 700 to 900 ° C. by a moving chain belt.

  Next, in soldering the solder ribbon according to the measurement program, the cutting machine cuts the solder ribbon at about 25 centimeters (cm), applies solder flux to the solder ribbon, and removes the oxide layer. The specifications of the solder ribbon are as follows.

  Based on the infrared soldering machine, the test element (solar cell) is placed on the machine's platform set at 140 ° C, then the solder ribbon is placed on the solar cell bus bar, followed by the set time and temperature Solder. The soldering conditions are as follows.

Further, in the adhesion test, the solar cell is fixed to the platform of the bonding machine, and one end of the solder ribbon is fixed with a jig. The solder ribbon is pulled at a 180 degree angle with a speed of 120 mm / s and measured to obtain an adhesion value. The results can refer to FIG.
<Embodiment 1>

In embodiment 1, the Ag / alumina and alumina content has an effect on adhesion; the addition of alumina powder does not disperse easily, it is not easy to bond with silver and it will lead to cracks in the sintering process Indicates. The face-up and face-down adhesion in the sintering process refers to FIGS. 13 and 14, respectively.
<Embodiment 2>

In embodiment 2, the Ag / alumina content affects adhesion; the addition of appropriate Ag / alumina indicates that stable high adhesion is obtained at different sintering temperatures. The adhesion at the face-up and face-down in the sintering process refers to FIGS. 15 and 16, respectively.
<Embodiment 3>

  In embodiment 3, the Ag / alumina content affects adhesion; it is shown that the silver content decreases and print volume decreases, but a weak silver layer cannot be a strong structural support. Ag / alumina can be added to enhance the bond strength between Ag and Ag and between Ag and glass. The adhesion at the face-up and face-down in the sintering process refers to FIGS. 17 and 18, respectively.

From the above, in the present invention, a filler, for example, Ag / alumina (zirconium oxide, silicon oxide, zinc oxide) is appropriately added to the conductive composition to enhance adhesion and separate the original silver layer. As a result, the conductive composition has excellent electrical conductivity and low resistivity.
<Embodiment 4>

  In this embodiment, alumina is added to a conductive composition that is silver as the body. From embodiment 4, the control group contains only silver (Ag), the control group does not add alumina, and the face-up and face-down adhesions are 1.73 and 1.51, respectively. According to the results of experiments and observations of the present invention, adhesion can be improved by adding a small amount of alumina. The weight percentage of alumina is about 0.5-5, and the weight percentage of alumina is preferably about 2-4. It should be noted that the above table shows that the adhesion of the experimental groups (K, L, M, N) is greater than the control group. Therefore, similarly, as shown in Embodiment 4, when the silver content is reduced and the printing volume is reduced, a weak silver layer cannot be a strong structural support. Ag / alumina can be added to enhance the bond strength between Ag and Ag and between Ag and glass. In addition, alumina may also be added to create a similar effect, which can fill voids caused by reduced silver content (more fragile silver layer structure). The present invention provides a conductive composition comprising a mixture having a conductive function made of a metal and a metal oxide, wherein the metal oxide is as a filler and the metal is as a body to enhance adhesion. Yes, the metal contains silver and the weight percentage of alumina is about 0.5-5. The metal oxide includes aluminum oxide (alumina), zirconium oxide (zirconia), silicon oxide (silica), zinc oxide, cupric oxide, and combinations thereof, and the metal oxide includes a divalent to tetravalent metal.

  The foregoing description is a preferred embodiment of the present invention. As will be appreciated by those skilled in the art, the foregoing preferred embodiments of the invention are illustrative of the invention and are not intended to limit the invention. The present invention is intended to encompass various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which is most likely to encompass all such modifications and similar structures. A broad interpretation must be given.

Claims (12)

Comprising a conductive functional mixture, glass and additives, wherein the conductive functional mixture is composed of a metal and aluminum oxide, the aluminum oxide as a filler material, the metal between Ag-Ag, and Ag- As a body to enhance the bond strength between the glasses,
The aluminum oxide, the glass and the additive are mixed in an organic vehicle;
The metal comprises silver, and the sum of the weight percent of the aluminum oxide and the metal is 52-60;
The weight percentage of said aluminum oxide is 0.5-5, The electrode of the solar cell characterized by the above-mentioned.   The shape of the particle | grains of the said aluminum oxide is an electrode of the solar cell of Claim 1 which is flakes, columnar shape, or block shape.   The solar cell electrode according to claim 1 or 2, wherein the aluminum oxide has a weight percentage of 2 to 4.   The electrode of the solar cell according to any one of claims 1 to 3, wherein the melting point of the aluminum oxide is higher than a sintering temperature. The conductive functional mixture includes a conductive functional mixture, a conductive coating, glass, and an additive. The conductive functional mixture is composed of a metal and aluminum oxide, the aluminum oxide is as a filling material, and the metal is Ag-Ag. And as a body for enhancing the bond strength between Ag and glass,
The conductive covering simply covers a part of the surface of the filling material,
The aluminum oxide , the glass and the additive are mixed in an organic vehicle;
Before Symbol metal comprises silver, the total sum of the weight percent of aluminum oxide and the metal is 52 to 60,
The solar cell electrode, wherein the aluminum oxide has a weight percentage of 0.5 to 3.8. The electrode of the solar cell according to claim 5, wherein a shape of the aluminum oxide particles is flakes, columns, or lumps. The solar cell electrode according to claim 5 or 6, wherein the melting point of the aluminum oxide is higher than a sintering temperature.   The electrode of the solar cell of any one of Claims 5-7 whose weight percentage of the said aluminum oxide is 2-3. In a solar cell comprising a back electrode, a PN semiconductor layer formed on the back electrode, and a positive electrode formed on the PN semiconductor layer,
The back electrode or the positive electrode of the solar cell is composed of a conductive functional mixture, glass and an additive, the conductive functional mixture is composed of metal and aluminum oxide , and the aluminum oxide is used as a filling material. The metal is as a body for enhancing the bond strength between Ag-Ag and between Ag-glass;
The aluminum oxide , the glass and the additive are mixed in an organic vehicle;
Wherein the metal comprises silver, said a total sum of the weight percent of aluminum oxide and the metal 52-60, the ratio of the weight percent of the aluminum oxide and the metal, wherein the Ru 2 / 50-4 / 50 der A solar cell.   The solar cell according to claim 9, further comprising a conductive coating portion, wherein the conductive coating portion simply covers a part of the surface of the filling material. The solar cell according to claim 9 or 10, wherein a melting point of the aluminum oxide is higher than a sintering temperature.   The solar cell of claim 9, wherein the aluminum oxide has a weight percentage of 2-4.

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