TWI506650B - Silver paste and use thereof in production of photovoltaic device - Google Patents

Description

Silver paste and its use for the manufacture of photovoltaic elements

The present invention relates to a silver paste and its use for the manufacture of a photovoltaic device, and in particular, for the manufacture of a front electrode for a photovoltaic element, facilitates formation of tunneling conductivity (tunneling conductivity) ) The microstructure of the silver paste.

Photovoltaic devices have been widely used because they convert energy that is easily obtained from a light source (eg, sunlight) into electricity to manipulate electronic devices such as computers, computers, heaters, and the like. use. The most common photovoltaic component is a germanium based solar cell.

A ruthenium-based solar cell refers to a solar cell fabricated using a crystalline ruthenium substrate obtained from a single crystal twin rod or a polycrystalline tantalum ingot. In the prior art for forming an electrode on a ruthenium-based solar cell, after the metal paste is coated on the front surface and the back surface of the ruthenium-based solar cell by a process such as screen printing, it is necessary to perform two sintering processes to form a good one. Ohmic contact metal electrode. A typical bismuth-based solar cell is coated with a conductive silver paste on its front surface and a conductive aluminum paste and a conductive silver paste (or conductive silver-aluminum paste) on its back surface.

Co-firing technology has been applied to the electrode of the bismuth-based solar cell, and the co-firing technology only needs to perform a sintering process, that is, a front electrode having good ohmic contact and a bus bar for soldering are simultaneously formed. A bus bar, a back electrode formed of aluminum, and a back bus bar electrode for soldering. The front electrode includes a grid electrode having a thin line width and a front bus bar electrode having a thick line width and used for soldering. Partial diffusion of aluminum to cerium-based solar cells In the back surface, a back surface filed (BSF) is formed. The back surface electric field reflects minority carriers and increases the collection of most carriers to be transmitted to the back electrode formed of silver or silver aluminum, thereby improving the overall efficiency of the germanium-based solar cell.

Please refer to FIG. 1, which is a partial cross-sectional view of a conventional germanium-based solar cell 1. 1 shows only the tantalum wafer 10 and the front electrode 12 which is coated on the front surface 102 of the tantalum wafer 10 by silver paste and sintered. After the sintering process, a layer of interface glass layer 14 is formed between the germanium wafer 10 and the front side electrode 12. Clearly, the interface glass layer 14 reduces the conductivity of the carrier transport to the front electrode 12. The conventional ruthenium-based solar cell 1 utilizes a composition that changes the composition of the silver paste, and the front electrode 12 from which the silver paste is sintered includes a bulk electrode 122 (or a sintered silver electrode) and grows between the interface between the interface glass layer 14 and the tantalum wafer 10. Ag crystallites 126 and/or nano-Ag colloids 124 grown in the interface glass layer 14. The tunneling conductivity between the front electrode 12 and the germanium wafer 10 can be improved by the silver microcrystals 126 and/or the nanosilver particles 124.

However, no silver paste has been found to effectively promote the formation of microstructures that facilitate tunneling conductivity.

Therefore, the technical problem to be solved by the present invention is to provide a silver paste and use thereof for manufacturing a photovoltaic element, and the silver paste of the present invention can be used to manufacture a microelectrode for facilitating tunneling conductivity when used for manufacturing a front electrode of a photovoltaic element. Structure formation.

A silver paste according to a preferred embodiment of the present invention comprises an organic vehicle, a glass frit, and a material particle containing silver. The silver-containing material powder may be a silver powder, an organometallic silver compound powder or a silver oxide powder. In particular, the silver paste of the present invention further comprises a silver microcrystalline precipitation promoter of about 0.01 to 0.6 weight percent. Therefore, when the silver paste of the present invention is used for manufacturing the front electrode of the photovoltaic element, there is a lot of silver microcrystallization at the interface between the interface glass layer and the germanium wafer. A large number of nano silver particles are also precipitated in the interface glass layer to enhance the overall efficiency of the photovoltaic element fabricated using the silver paste of the present invention.

In one embodiment, the silver microcrystallization precipitation promoter may be Te or Bi ₂ Te ₃ .

In one embodiment, the organic carrier accounts for about 1 to 10 by weight of the silver paste of the present invention, and the glass powder accounts for about 1 to 5 by weight of the silver paste of the present invention. The silver microcrystalline precipitation promoter accounts for the present invention. The silver paste has a weight percentage of about 0.01 to 0.6, and the remainder of the silver-containing material powder as a percentage by weight of the silver paste of the present invention.

In one embodiment, the glass powder may be PbO-SiO glass powder, PbO-B ₂ O ₃ glass powder or PbO-SiO ₂ -B ₂ O ₃ glass powder.

In one embodiment, the organic vehicle comprises about 10 wt.% solid cellulose polymer, about 0-20 wt.% of 2,2,4-trimethyl-1,3-penta The diol monoisobutyrate and the remainder of the organic vehicle are terpineol (Terpineol).

A method of fabricating a photovoltaic element in a preferred embodiment of the invention begins with the preparation of a semiconductor structure combination. The semiconductor structure combination includes at least one p-n junction and has a positive surface. Next, the method of the present invention selectively coats and dries the silver paste disclosed in the present invention on the front surface to form a plurality of parallel first conductive strips on the front surface. Next, the method of the present invention selectively coats and dries the metal paste on the front surface to form at least one second conductive strip perpendicular to the plurality of first conductive strips on the front surface. Finally, the method of the present invention sinters a plurality of first conductive strips and at least one second conductive strip to form a front surface electrode on a front surface.

In one embodiment, an interface glass layer is formed between the front electrode and the front surface. The front electrode includes a bulk electrode formed on the interface glass layer, a plurality of silver microcrystals between the interface glass layer and the front surface, and a plurality of nano silver particles in the interface glass layer.

In a specific embodiment, the semiconductor structures are combined and comprise an anti-reflective layer. The reflective layer provides a positive surface for the combination of semiconductor structures.

In a specific embodiment, the semiconductor structure combination further includes a passivation layer. The passivation layer provides a positive surface for the combination of semiconductor structures.

In one embodiment, the metal paste is the silver paste disclosed herein.

Compared with the prior art, when the silver paste according to the present invention is used to manufacture the front electrode of the photovoltaic element, a large amount of silver microcrystals are precipitated at the interface between the interface glass layer and the germanium wafer, and there is also no in the interface glass layer. The precipitation of the nano-silver particles allows the overall performance of the photovoltaic element manufactured by using the silver paste of the present invention to be significantly improved.

The advantages and spirit of the present invention will be further understood from the following detailed description of the invention.

1‧‧‧Photovoltaic components

10‧‧‧矽 wafer

102‧‧‧ front surface

12‧‧‧Front electrode

122‧‧‧Block electrode

124‧‧‧Nano silver particles

126‧‧‧Silver microcrystallization

14‧‧‧Interface glass layer

2‧‧‧Photovoltaic components

20‧‧‧Semiconductor structure combination

201‧‧‧ Crystalline substrate

202‧‧‧ front surface

204‧‧‧Back surface

206‧‧‧p-n junction

208‧‧‧passivation layer

22‧‧‧Front electrode

222‧‧‧ grid electrode

221‧‧‧First Conductive Strip

224‧‧‧ Positive bus bar electrode

223‧‧‧Second strip

226‧‧‧Block electrode

227‧‧‧Nano silver particles

228‧‧‧Silver microcrystals

229‧‧‧Interface glass layer

24‧‧‧Back electrode

242‧‧‧ Conductive layer

26a, 26b‧‧‧ backside bus electrodes

262, 264‧‧‧ third conductive strip

28‧‧‧Anti-reflective layer

1 is a partial cross-sectional view of a conventional germanium based solar cell.

Figure 2 is a top plan view of a photovoltaic element fabricated in accordance with the method of the present invention.

Figure 3 is a bottom plan view of a photovoltaic element fabricated in accordance with the method of the present invention.

4A through 4D are schematic views of a method of fabricating a photovoltaic element as shown in cross-sectional view along line A-A of Fig. 2, in accordance with a preferred embodiment of the present invention.

4E is a partial enlarged view of the interface between the front electrode and the passivation layer in FIG. 4D.

Fig. 5 is a SEM photograph showing the unsintered front electrode of the control group, the battery A, and the battery B.

Fig. 6 is a SEM photograph of the front electrode of the control group, the battery A, and the battery B after sintering at 630 °C.

Fig. 7 is a SEM photograph of the front electrode of the control group, Battery A, and Battery B after sintering at 810 °C.

A silver paste according to a preferred embodiment of the present invention comprises an organic vehicle, a glass powder, and a powder of a silver-containing material. The silver-containing material powder may be a silver powder, an organometallic silver compound powder or a silver oxide powder. In particular, the silver paste of the present invention further comprises a silver microcrystalline precipitation promoter of about 0.01 to 0.6 weight percent. Therefore, when the silver paste of the present invention is used to manufacture the front electrode of the photovoltaic element, a large amount of silver microcrystals are precipitated at the interface between the interface glass layer and the germanium wafer, and a plurality of nano silver are also present in the interface glass layer. The particles are precipitated to enhance the overall effectiveness of the photovoltaic element fabricated using the silver paste of the present invention.

In one embodiment, the silver microcrystallization precipitation promoter may be Te or Bi ₂ Te ₃ .

In one embodiment, the organic carrier accounts for about 1 to 10 by weight of the silver paste of the present invention, and the glass powder accounts for about 1 to 5 by weight of the silver paste of the present invention. The silver microcrystalline precipitation promoter accounts for the present invention. The silver paste has a weight percentage of about 0.01 to 0.6, and the remainder of the silver-containing material powder as a percentage by weight of the silver paste of the present invention.

In one embodiment, the glass powder may be PbO-SiO glass powder, PbO-B ₂ O ₃ glass powder or PbO-SiO ₂ -B ₂ O ₃ glass powder.

In one embodiment, the organic vehicle comprises about 10 wt.% solid cellulosic polymer, about 0-20 wt.% of 2,2,4-trimethyl-1,3-pentanediol monoisobutylene. The acid ester and the rest of the terpineol which is the weight percent of the organic vehicle.

Please refer to FIG. 2, FIG. 3 and FIG. 4A to FIG. 4D. FIG. 2 is based on A top view of a photovoltaic element 2 (e.g., a germanium based solar cell) fabricated by the method of the present invention. Figure 3 is a bottom plan view of a photovoltaic element 2 made in accordance with the method of the present invention. 4A through 4D are cross-sectional views showing a preferred embodiment of the method of the present invention for fabricating the photovoltaic element 2 of the cross-sectional view taken along line A-A of Fig. 2.

As shown in Figures 2 and 3, the photovoltaic element 2 fabricated in accordance with the method of the present invention comprises a semiconductor structure combination 20, a front side electrode 22, a back side electrode 24, and at least one back side bus bar electrode (26a, 26b). The semiconductor structure assembly 20 has a front surface 202 and a back surface 204.

Front electrode 22 is formed on front surface 202 of semiconductor structure assembly 20. As shown in FIG. 2, the front electrode 22 includes a grid 222 having a thin line width and at least one front bus bar electrode 224 having a thick line width. At least one front bus bar electrode 224 is arranged in the Y direction of FIG. 2 and is used for soldering when the photovoltaic elements 2 are connected in series. Typically photovoltaic elements 2 (eg, germanium based solar cells) will have two or three front bus bar electrodes 224.

At least one back bus bar electrode (26a, 26b) is formed on the back surface 204 of the semiconductor structure assembly 20 and is used for soldering the photovoltaic elements 1 in series. In the case shown in FIG. 3, the two parallel back side bus electrodes (26a, 26b) are arranged symmetrically and arranged in the Y direction in FIG.

The back electrode 24 is formed on the back surface 204 of the semiconductor structure assembly 20 and covers a region on the back surface 204 that forms at least one of the back bus bar electrodes (26a, 26b).

As shown in FIG. 4A, the method of the present invention, first, produces a semiconductor structure combination 20. The semiconductor structure assembly 20 includes at least one p-n junction 206 and has a front surface 202 and a back surface 204. The photovoltaic element 2 produced in accordance with the method of the present invention, during use, has a front surface 202 facing upwards that will face the sun. In order to reduce the reflectance of incident sunlight, as shown in FIG. 4A, the front surface 202 is roughened to a rough surface.

Next, as shown in FIG. 4B, the method of the present invention is selectively coated. The silver paste disclosed in the present invention is clothed and dried on the front surface 202 of the semiconductor structure assembly 20 to form a plurality of parallel first conductive strips 221 on the front surface 202. Next, the method of the present invention again selectively coats and dries the first metal paste on the front surface 202 to form at least one second conductive strip 223 that is perpendicular to the plurality of first conductive strips 221 .

Also shown in FIG. 4B, the method of the present invention is applied to the back surface 204 of the semiconductor structure assembly 20 to coat and dry the second metal paste to form a conductive layer 242.

In a specific embodiment, the second metal paste may be a powder mixture formed of aluminum, silver, copper, gold, platinum, palladium, aluminum alloy, silver alloy, copper alloy, gold alloy, platinum alloy, palladium alloy or a mixture thereof. A conductive paste, or other commercially available conductive metal paste. In practice, the second metal paste is preferably a conductive paste in which aluminum powder is mixed.

Also shown in FIG. 4B, the method of the present invention is applied to the back surface 204 of the semiconductor structure assembly 20 to selectively coat and dry the third metal paste to form at least one parallel third conductive strip (262, 264). On the back surface 204.

In one embodiment, the third metal paste may be a mixture of powders of aluminum, silver, copper, gold, platinum, palladium, aluminum alloy, silver alloy, copper alloy, gold alloy, platinum alloy, palladium alloy or a mixture thereof. Conductive paste, or other commercially available conductive metal paste. In practice, the third metal paste is preferably a conductive paste in which silver powder and aluminum powder are mixed.

Finally, as shown in FIG. 4C, the method of the present invention sinters a plurality of first conductive strips 221 and at least one second conductive strip 223 to form front surface 22 on front surface 202. That is, the front surface electrode 22 is composed of a mesh electrode 222 sintered by the first conductive strip 221 and a front bus bar electrode 224 sintered by the second conductive strip 223. The method of the present invention also sinters the conductive layer 242, i.e., is sintered into the back electrode 24, and sinters at least one third conductive strip (262, 264), i.e., sintered into at least one backside bus electrode (26a, 26b). positive The surface electrode 22 and the back surface electrode 24 and the at least one back bus bar electrode (26a, 26b) may be formed separately by different sintering processes, or may be formed once by a co-firing process.

In one embodiment, the semiconductor structure assembly 20 comprises a p-type crystalline germanium substrate 201, and an n-type doped region is implanted on the surface of the p-type crystalline germanium substrate 201 to form an n-type region. As shown in FIG. 4A, the method of the present invention forms a passivation layer 208 overlying the n-type region, and a passivation layer 208 provides a front surface 202. As shown in FIG. 4D, the method of the present invention further forms an anti-reflective layer 28 that covers the passivation layer 208. In another embodiment, the reflective layer 28 provides a front surface 202.

In another embodiment, the semiconductor structure assembly 20 comprises an n-type crystalline germanium substrate 201, and a p-type doping is implanted on the surface of the n-type crystalline germanium substrate 201 to form a p-type region. As shown in FIG. 4A, the method of the present invention forms a passivation layer 208 overlying the p-type region and a passivation layer 208 provides a positive surface 202. As shown in FIG. 4D, the method of the present invention further forms an anti-reflective layer 28 that covers the passivation layer 208. In another embodiment, the anti-reflective layer 28 provides a front surface 202.

In another embodiment, the semiconductor structure assembly 20 is the structure of a silicon heterojunction solar cell as disclosed in U.S. Patent No. 5,935,344. For the structure of the heterojunction solar cell, please refer to U.S. Patent No. 5,935,344, which is not described here.

Referring to Figures 4D and 4E, a photovoltaic element 2 in accordance with a preferred embodiment of the present invention is shown in cross-section. 4E is a partial enlarged view of the interface between the front electrode 22 and the passivation layer 208 in FIG. 4D. As shown in FIG. 4E, the conductive paste disclosed in the present invention is coated on the front surface 202 and sintered to form an interface glass layer 229 between the front surface electrode 22 and the front surface 202 of the passivation layer 208. The front electrode 22 includes a briquette formed on the interface glass layer 229 A pole 226, a plurality of silver microcrystals 228 between the interface glass layer 229 and the front surface 202, and a plurality of nanosilver particles 227 in the interface glass layer 229.

Please refer to Table 1, which is a list of the components of the silver paste (different silver microcrystallization precipitation promoter) and the silver paste containing no silver microcrystallization precipitation promoter according to the present invention. These silver pastes were used to fabricate the front electrodes of the ruthenium-based solar cells (control, battery A, battery B) and were sintered to a front electrode at 810 ° C and 840 ° C. The silver paste used in Battery A contained 0.5 wt.% Te as a silver microcrystal precipitation promoter. The silver paste used in Battery B contained 0.5 wt.% of Bi ₂ Te ₃ as a silver microcrystal precipitation promoter. The photoelectric conversion efficiency (η) measured by the prepared solar cells and the comprehensive evaluation index-fill factor (FF) are also shown in Table 1. The back electrode of these solar cells was coated and sintered using a commercially available aluminum paste, and the back bus bar electrodes were coated and sintered using a commercially available silver paste.

The control electrode, battery A, and battery B were coated with a silver paste prepared as a front electrode. After sintering at 630 ° C and sintering at 810 ° C, the front electrode was observed by scanning electron microscopy (SEM). Please see the picture 5. Figure 6 and Figure 7. In Fig. 5, (a) is a control group, (b) is a battery A, and (c) is a battery B. In Fig. 6, (a) is a control group, (b) is a battery A, and (c) is a battery B. In Fig. 7, (a) is a control group, (b) is a battery A, and (c) is a battery B.

The photographs shown in Fig. 5, Fig. 6 and Fig. 7 confirm that the addition of Te and Bi ₂ Te ₃ such silver microcrystal precipitation promoter reacts with silver, dissolves silver and diffuses and flows to the positive surface of the semiconductor structure combination, and is sintered and cooled. Silver microcrystals and nano silver particles are precipitated.

From the test data of Table 1 and the photographs shown in FIG. 5, FIG. 6 and FIG. 7, it can be clearly seen that the silver paste of the present invention is used for the front electrode of Battery A and Battery B, and silver microcrystals and nano silver particles are precipitated. The tunneling conductivity between the front electrode and the germanium wafer can be improved, which is also reflected in the increase in photoelectric conversion efficiency and fill factor.

The features and spirit of the present invention are intended to be more apparent from the detailed description of the preferred embodiments. On the contrary, the intention is to cover various modifications and equivalents that are within the scope of the invention as claimed. Therefore, the scope of the patent application of the present invention should be construed broadly in the light of the above description, so that it covers all possible changes and arrangements.

202‧‧‧ front surface

208‧‧‧passivation layer

22‧‧‧Front electrode

226‧‧‧Block electrode

227‧‧‧Nano silver particles

228‧‧‧Silver microcrystals

229‧‧‧Interface glass layer

Claims (10)

A silver paste comprising an organic vehicle, a glass powder and a silver-containing material powder, the silver-containing material powder being a silver powder, an organometallic silver compound powder or a silver oxide powder, characterized in that the silver paste further comprises a weight The percentage is about 0.01 to 0.6 one of the silver microcrystalline precipitation promoters. The silver paste according to claim 1, wherein the silver microcrystal precipitation promoter is Te or Bi ₂ Te ₃ . The silver paste according to claim 2, wherein the organic carrier accounts for about 1 to 10 by weight of the silver paste, and the glass powder accounts for about 1 to 5 by weight of the silver paste, and the silver microcrystal precipitation accelerator The weight percentage of the silver paste is about 0.01 to 0.6, and the remainder of the silver material powder accounts for the weight percentage of the silver paste. The silver paste according to claim 3, wherein the glass powder is PbO-SiO glass powder, PbO-B ₂ O ₃ glass powder or PbO-SiO ₂ -B ₂ O ₃ glass powder. The silver paste of claim 3, wherein the organic vehicle comprises about 10 wt.% of a solid cellulosic polymer, and about 0 to 20 wt.% of 2,2,4-trimethyl-1,3-pentane The diol monoisobutyrate and the remainder of the percentage by weight of the organic vehicle are terpineol. A method of fabricating a photovoltaic device comprising the steps of: preparing a semiconductor structure combination comprising at least one pn junction and having a front surface; selectively coating and drying as in any of claims 1 to 5 The silver paste of the item is on the front surface to form a plurality of parallel first conductive strips on the front surface; Selectively coating and drying a metal paste on the front surface to form at least one second conductive strip perpendicular to the plurality of first conductive strips on the front surface; and sintering the plurality of first conductive strips and The at least one second conductive strip forms a front electrode on the front surface. The method of claim 6, wherein an interface glass layer is formed between the front surface electrode and the front surface, the front electrode comprising a bulk electrode formed on the interface glass layer, and the interface glass layer A plurality of silver microcrystals between the front surfaces and a plurality of nanosilver particles in the interface glass layer. The method of claim 7, wherein the semiconductor structure combination further comprises an anti-reflective layer, the reflective layer providing the front surface. The method of claim 7, wherein the semiconductor structure combination further comprises a passivation layer that provides the front surface. The method of claim 7, wherein the metal paste is the silver paste of any one of claims 1 to 5.