TWI615992B - Method of manufacturing solar cell - Google Patents

Abstract

A method of manufacturing a solar cell, comprising: providing a germanium substrate having a first surface and a second surface opposite to the first surface; forming an emitter on the first surface of the germanium substrate, wherein The emitter is different from the doping type of the germanium substrate to thereby form a pn junction; a first passivation layer is formed on the first surface of the germanium substrate; and a second surface is formed on the second surface of the germanium substrate After the first passivation layer and the second passivation layer are formed, a thermal annealing treatment is performed on the germanium substrate; after the thermal annealing treatment is performed, a first electrode is formed on the first passivation layer and electroplated to form a first electrode; After the thermal annealing treatment is performed, a second electrode is formed on the second passivation layer and electroplated to form a second electrode.

Description

Solar cell manufacturing method

The present invention relates to a method of fabricating a semiconductor device, and more particularly to a method of fabricating a solar cell.

The development of renewable energy (Renewable energy) has become one of the most important issues in recent years due to the shortage of petrochemical energy and increasing energy demand. Renewable energy refers to sustainable and non-polluting natural energy sources such as solar energy, wind energy, hydropower, tidal energy or biomass energy. Among them, the development of solar energy is very important in the research of energy development in recent years. A welcome part, and solar cells are a device that converts solar energy into electricity.

Known twinned solar cells mainly include: a substrate for converting light energy into electrical energy, and a front electrode and a back electrode for conducting current. The front electrode and the back electrode are applied to the light-receiving surface and the back surface of the substrate by screen printing, and the electrode paste is cured and molded on the substrate through a sintering process.

Generally, the electrode slurry is composed of a plurality of materials including metal powder, glass powder, solvent, and the like. However, glass is a non-conductive material, which affects the electrical properties of the electrode. In addition, the sintering process requires a higher temperature to be carried out, which tends to cause some metal ions to diffuse into the interior of the battery element, thus affecting the performance of the solar cell.

In view of this, there is a need to propose a solution to solve the above problems.

The present invention provides a method of fabricating a solar cell, comprising: providing a germanium substrate having a first surface and a second surface opposite to the first surface; forming a shot on the first surface of the germanium substrate a pole, wherein the emitter is different from a doping type of the germanium substrate, thereby forming a pn junction; forming a first passivation layer on the first surface of the germanium substrate; forming on the second surface of the germanium substrate a second passivation layer; after forming the first passivation layer and the second passivation layer, performing thermal annealing treatment on the germanium substrate; after performing the thermal annealing treatment, opening and plating on the first passivation layer to form a first And after performing the thermal annealing treatment, opening and plating on the second passivation layer to form a second electrode.

According to the manufacturing method of the solar cell of the present invention, the formation of the electrode is changed from the conventional silver-aluminum paste process to the metal plating process, so that a lower temperature process can be used to form a good metal contact; and the process temperature is not too high. Causes metal ions to diffuse into the interior of the battery element, causing the open circuit voltage to drop.

According to the method for fabricating a solar cell of the present invention, the high temperature in the thermal annealing process can repair defects in the passivation layer, improve the passivation quality and effect, and thus can effectively improve the open circuit voltage value. Furthermore, the high temperatures in the thermal annealing process can repair defects in the germanium substrate to improve the performance of the entire battery component. In addition, the high temperature in the thermal annealing process allows hydrogen ions in the passivation layer to diffuse to the germanium substrate, thereby repairing defects in the germanium substrate and improving the performance of the battery element.

The above and other objects, features, and advantages of the present invention will become more apparent from the accompanying drawings. In the description of the present invention, the same components are denoted by the same reference numerals and will be described.

Referring to Figures 1a to 1f, there is shown a method of fabricating a solar cell according to a first embodiment of the present invention. First, a single crystal or polycrystalline germanium substrate 110 is provided. The doping type of the germanium substrate 110 may be an N-type or a P-type. The germanium substrate 110 has a roughened light receiving surface 111 and a light receiving surface 111 opposite to the light receiving surface 111. A back 112 (see Figure 1a).

Referring to FIG. 1b, a P+ or N+ emitter 120 of a different doping type from the germanium substrate 110 is formed on the light receiving surface 111 of the germanium substrate 110 to form a pn junction, and is formed on the germanium substrate 110. A back surface field (BSF) 180 of N+ or P+ of the same doping type as the germanium substrate 110 is formed on the back surface 112.

Referring to FIG. 1c, a passivation layer 130 is formed on the emitter 120, and a passivation layer 140 is formed on the back surface electric field 180. In addition, referring to FIG. 2a, in an embodiment, if the germanium substrate 110 is an N-type germanium substrate, the emitter 120 will be a P+ emitter, and the passivation layer 130 has a three-layer structure including a hafnium oxide (SiO2). a layer 131, an aluminum oxide (Al 2 O 3 ) layer 132 and a tantalum nitride (SiNx) layer 133, wherein the tantalum oxide layer 131 is formed on the emitter 120 first, and then the aluminum oxide layer 132 is formed on the tantalum oxide layer 131. Thereafter, a tantalum nitride layer 133 is formed on the aluminum oxide layer 132, that is, the hafnium oxide layer 131, the aluminum oxide layer 132, and the tantalum nitride layer 133 are sequentially formed on the emitter 120. In addition, referring to FIG. 2b, if the germanium substrate 110 is an N-type germanium substrate, the back surface electric field 180 will be an N+ back surface electric field, and the passivation layer 140 has a two-layer structure including a tantalum oxide (SiO2) layer 141 and a nitrogen. A bismuth (SiNx) layer 142 is formed, and an aluminum oxide (Al 2 O 3 ) layer is not formed between the yttrium oxide layer 141 and the tantalum nitride layer 142 , wherein the yttrium oxide layer 141 is formed on the back surface electric field 180 first, followed by a tantalum nitride layer. 142 is formed on the ruthenium oxide layer 141, that is, the ruthenium oxide layer 141 and the tantalum nitride layer 142 are sequentially formed on the back surface electric field 180.

Referring to FIG. 3a, in another embodiment, if the germanium substrate 110 is a P-type germanium substrate, the emitter 120 will be an N+ emitter, and the passivation layer 130 has a two-layer structure including a hafnium oxide (SiO2). a layer 134 and a tantalum nitride (SiNx) layer 135, and an aluminum oxide (Al 2 O 3 ) layer is not formed between the tantalum oxide layer 134 and the tantalum nitride layer 135 , wherein the tantalum oxide layer 134 is formed on the emitter 120 first. Thereafter, a tantalum nitride layer 135 is formed on the tantalum oxide layer 134, that is, the tantalum oxide layer 134 and the tantalum nitride layer 135 are sequentially formed on the emitter 120. In addition, referring to FIG. 3b, if the germanium substrate 110 is a P-type germanium substrate, the back surface electric field 180 will be a P+ back surface electric field. At this time, the passivation layer 140 has a three-layer structure including a germanium oxide (SiO2) layer 144 and oxidation. An aluminum (Al2O3) layer 145 and a tantalum nitride (SiNx) layer 146, wherein the tantalum oxide layer 144 is formed on the back surface electric field 180, and then the aluminum oxide layer 145 is formed on the tantalum oxide layer 144, after which the tantalum nitride layer 146 is formed. The yttrium oxide layer 144, the yttrium oxide layer 145, and the tantalum nitride layer 146 are formed on the back surface electric field 180 in this order.

Referring to FIG. 1d, after the passivation layer 130 and the passivation layer 140 are formed, the entire tantalum substrate 110 is then subjected to a thermal annealing process along with the structure thereon. The thermal annealing treatment is performed by placing the crucible substrate 110 in a furnace provided with a heating source, and heating to gradually increase the ambient temperature of the crucible substrate 110, for example, increasing the temperature from 580 ° C to 910 ° C for 1 time. Up to 2 minutes. A preferred thermal annealing treatment is to pass the crucible substrate 110 through furnaces having temperatures of 580 ° C, 620 ° C, 737 ° C, 695 ° C, 813 ° C, and 910 ° C to obtain a better treatment effect.

Referring to FIG. 1e, after the thermal annealing process, openings 138, 148 are formed on the passivation layer 130 and the passivation layer 140 to expose a portion of the emitter 120 and a portion of the back surface electric field 180, respectively. Thereafter, a sub-layer 150 is formed on the passivation layer 140 by means of electroless plating or physical vapor deposition (PVD). The seed layer 150 comprises nickel or titanium, wherein the seed layer 150 fills the opening 148. And connected to the back surface electric field 180, the seed layer 150 can be electrically connected to the back surface electric field 180. After the seed layer 150 is formed, an electrode 160 is then formed on the seed layer 150 by electroplating. In one embodiment, the seed layer 150 has a two-layer structure (not shown), and includes a nickel layer and a copper layer, or a titanium layer and a copper layer, wherein the nickel layer or the titanium layer is formed first. The passivation layer 140 is then formed on the nickel layer or the titanium layer, that is, the seed layer 150 is a nickel/copper or titanium/copper structure. Similarly, the electrode 160 formed by electroplating also has a two-layer structure (not shown), and includes a copper layer and a tin layer, or a copper layer and a silver layer, wherein the copper layer is formed first and electrically It is connected to the seed layer 150, and then the tin layer or the silver layer is formed on the copper layer, that is, the electrode 160 is a copper/tin or copper/silver structure.

Referring to FIG. 1f, after the electrode 160 is formed, an electrode 170 is formed by electroplating at the opening 138, and the electrode 170 is electrically connected to the emitter 120 through the opening 138. In one embodiment, the electrode 170 has a two-layer structure (not shown), and includes a nickel layer and a copper layer, or a titanium layer and a copper layer, wherein the nickel layer or the titanium layer is formed on the emitter first. 120, then the copper layer is formed on the nickel layer or the titanium layer, that is, the electrode 170 is a nickel/copper or titanium/copper structure. In one embodiment, a tin layer or a silver layer may be formed on the copper layer based on the nickel/copper or titanium/copper structure of the electrode 170 to prevent oxidation of the copper layer, thereby causing a decrease in conductivity of the electrode 170. Fig. 1f also shows a solar cell manufactured by the method for producing a solar cell according to the first embodiment of the present invention.

According to the method of manufacturing a solar cell according to the first embodiment of the present invention, after the passivation layer 130 and the passivation layer 140 are formed, the germanium substrate 110 is thermally annealed together with the passivation layer 130 and the passivation layer 140. After the thermal annealing treatment, the electrode 170 and the electrode 160 electrically connected to the emitter 120 and the back surface electric field 180 are formed by electroplating.

Referring to Figures 4a to 4f, there is shown a method of fabricating a solar cell according to a second embodiment of the present invention. First, a single crystal or polycrystalline germanium substrate 210 is provided. The doping type of the germanium substrate 210 may be an N-type or a P-type. The germanium substrate 210 has a roughened light receiving surface 211 and a light receiving surface 211 opposite to the light receiving surface 211. A back side 212 (see Figure 4a).

Referring to FIG. 4b, a P+ or N+ emitter 220 of a different doping type from the germanium substrate 210 is formed on the back surface 212 of the germanium substrate 210 to form a pn junction, and on the front side of the germanium substrate 210. A front surface electric field (FSF) 280 of N+ or P+ of the same doping type as the germanium substrate 210 is formed on 211.

Referring to FIG. 4c, a passivation layer 230 is formed on the front side electric field 280, and a passivation layer 240 is formed on the emitter 220. In addition, referring to FIG. 5b, in an embodiment, if the germanium substrate 210 is an N-type germanium substrate, the emitter 220 will be a P+ emitter, and the passivation layer 240 has a three-layer structure including a hafnium oxide (SiO2). a layer 244, an aluminum oxide (Al2O3) layer 245, and a tantalum nitride (SiNx) layer 246, wherein the tantalum oxide layer 244 is formed on the emitter 220 first, and then the aluminum oxide layer 245 is formed on the tantalum oxide layer 244. Thereafter, a tantalum nitride layer 246 is formed on the aluminum oxide layer 245, that is, the hafnium oxide layer 244, the aluminum oxide layer 245, and the tantalum nitride layer 246 are sequentially formed on the emitter 220. In addition, referring to FIG. 5a, if the germanium substrate 210 is an N-type germanium substrate, the front electric field 280 will be an N+ frontal electric field, and the passivation layer 230 has a two-layer structure including a tantalum oxide (SiO2) layer 234 and a nitrogen. A bismuth (SiNx) layer 235 is formed, and an aluminum oxide (Al 2 O 3 ) layer is not formed between the yttrium oxide layer 234 and the tantalum nitride layer 235 , wherein the yttrium oxide layer 234 is formed on the front electric field 280 first, followed by a tantalum nitride layer. 235 is formed on the hafnium oxide layer 234, that is, the hafnium oxide layer 234 and the tantalum nitride layer 235 are sequentially formed on the front electric field 280.

Referring to FIG. 6b, in another embodiment, if the germanium substrate 210 is a P-type germanium substrate, the emitter 220 will be an N+ emitter, and the passivation layer 240 has a two-layer structure including a hafnium oxide (SiO2). a layer 241 and a tantalum nitride (SiNx) layer 242, and an aluminum oxide (Al 2 O 3 ) layer is not formed between the tantalum oxide layer 241 and the tantalum nitride layer 242 , wherein the tantalum oxide layer 241 is formed on the emitter 220 first. Thereafter, a tantalum nitride layer 242 is formed on the tantalum oxide layer 241, that is, the tantalum oxide layer 241 and the tantalum nitride layer 242 are sequentially formed on the emitter 220. In addition, referring to FIG. 6a, if the germanium substrate 210 is a P-type germanium substrate, the front electric field 280 will be a P+ frontal electric field, and the passivation layer 230 has a three-layer structure including a tantalum oxide (SiO2) layer 231, and oxidation. An aluminum (Al 2 O 3 ) layer 232 and a tantalum nitride (SiNx) layer 233, wherein the tantalum oxide layer 231 is formed on the front electric field 280, and then the aluminum oxide layer 232 is formed on the tantalum oxide layer 231, and then the tantalum nitride layer 233 The yttrium oxide layer 231, the yttrium oxide layer 232, and the tantalum nitride layer 233 are formed on the front surface electric field 280 in this order.

Referring to FIG. 4d, after the passivation layer 230 and the passivation layer 240 are formed, the entire tantalum substrate 210 is then thermally annealed along with the structure thereon. In the thermal annealing treatment, the tantalum substrate 210 can be placed in a furnace provided with a heating source, and the temperature is gradually increased by heating, for example, the temperature is raised from 580 ° C to 910 ° C for 1 to 2 minutes. A preferred thermal annealing treatment is to pass the crucible substrate 210 through furnaces having temperatures of 580 ° C, 620 ° C, 737 ° C, 695 ° C, 813 ° C, and 910 ° C to obtain a better treatment effect.

Referring to FIG. 4e, after the thermal annealing process, openings 238, 248 are formed on the passivation layer 230 and the passivation layer 240 to expose a portion of the front electric field 280 and a portion of the emitter 220, respectively. Thereafter, a sub-layer 250 is formed on the passivation layer 240 by means of electroless plating or physical vapor deposition, and the seed layer 250 comprises nickel or titanium, wherein the seed layer 250 fills the opening 248 and is connected to the emitter 220. The seed layer 250 can be electrically connected to the emitter 220. After the seed layer 250 is formed, an electrode 260 is then formed on the seed layer 250 by electroplating. In one embodiment, the seed layer 250 has a two-layer structure (not shown), and includes a nickel layer and a copper layer, or a titanium layer and a copper layer, wherein the nickel layer or the titanium layer is formed first. The passivation layer 240 is then formed on the nickel layer or the titanium layer, that is, the seed layer 250 is a nickel/copper or titanium/copper structure. Similarly, the electrode 260 formed by electroplating also has a two-layer structure (not shown), including a copper layer and a tin layer, or a copper layer and a silver layer, wherein the copper layer is formed first and electrically It is connected to the seed layer 250, and then the tin layer or the silver layer is formed on the copper layer, that is, the electrode 260 is a copper/tin or copper/silver structure.

Referring to FIG. 4f, after the electrode 260 is formed, an electrode 270 is formed by electroplating at the opening 238, and the electrode 270 is electrically connected to the front electric field 280 through the opening 238. In one embodiment, the electrode 270 has a two-layer structure (not shown), and includes a nickel layer and a copper layer, or a titanium layer and a copper layer, wherein the nickel layer or the titanium layer is formed on the front electric field. At 280, the copper layer is then formed on the nickel or titanium layer, that is, the electrode 270 is a nickel/copper or titanium/copper structure. In one embodiment, a tin layer or a silver layer may be formed on the copper layer based on the nickel/copper or titanium/copper structure of the electrode 270 to prevent oxidation of the copper layer, thereby causing a decrease in conductivity of the electrode 270. Fig. 4f also shows a solar cell manufactured by the method of manufacturing a solar cell according to a second embodiment of the present invention.

According to the method of manufacturing a solar cell according to the second embodiment of the present invention, after the passivation layer 230 and the passivation layer 240 are formed, the germanium substrate 210 is thermally annealed together with the passivation layer 230 and the passivation layer 240. After the thermal annealing treatment, the electrode 260 and the electrode 270 electrically connected to the emitter 220 and the front electric field 280 are formed by electroplating.

According to the method of manufacturing a solar cell of the present invention, the emitter can be formed on the light receiving surface or the back surface of the ruthenium substrate. When the emitter is formed on the light receiving surface of the ruthenium substrate, a back surface electric field is formed on the back surface of the ruthenium substrate, and when the emitter is formed on the back surface of the ruthenium substrate, a front surface electric field is formed on the light receiving surface of the ruthenium substrate. When the germanium substrate is N-type and the emitter is P+ emitter, the passivation layer covering the emitter has a three-layer structure, that is, a germanium oxide layer, an aluminum oxide layer and a tantalum nitride layer, and is covered on the front side. The other passivation layer of the electric field or the back electric field has a two-layer structure, that is, a tantalum oxide layer and a tantalum nitride layer, and no aluminum oxide layer is formed between the tantalum oxide layer and the tantalum nitride layer. If the germanium substrate is P-type and the emitter is very N+ emitter, the passivation layer covering the emitter has a two-layer structure, that is, a germanium oxide layer and a tantalum nitride layer, and the tantalum oxide layer and the tantalum nitride layer. An aluminum oxide layer is not formed between the layers, and the other passivation layer covering the front electric field or the back surface electric field has a three-layer structure, that is, a tantalum oxide layer, an aluminum oxide layer, and a tantalum nitride layer.

According to the manufacturing method of the solar cell of the present invention, the formation of the electrode is changed from the conventional silver-aluminum paste process to the metal plating process, so that a lower temperature process can be used to form a good metal contact; and the process temperature is not too high. The metal ions are diffused into the interior of the battery element, causing the open circuit voltage Voc to drop.

According to the method of fabricating a solar cell of the present invention, the thermal annealing process needs to be performed before the formation of the metal electrode to avoid the high temperature in the process affecting the metal electrode, resulting in unfavorable results. The high temperature in the thermal annealing process can repair the defects in the passivation layer, improve the passivation quality and effect, and thus can effectively improve the open circuit voltage value. Furthermore, the high temperatures in the thermal annealing process can repair defects in the germanium substrate to improve the performance of the entire battery component. In addition, the high temperature in the thermal annealing process allows hydrogen ions in the passivation layer to diffuse to the germanium substrate, thereby repairing defects in the germanium substrate and improving the performance of the battery element.

While the present invention has been disclosed by the foregoing examples, it is not intended to be construed as limiting the scope of the invention, and the invention may be modified and modified without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

110‧‧‧矽 substrate

111‧‧‧Glossy surface

112‧‧‧Back

120‧‧ ‧ emitter

130‧‧‧ Passivation layer

131‧‧‧Oxide layer

132‧‧‧Alumina layer

133‧‧‧ layer of tantalum nitride

134‧‧‧Oxide layer

135‧‧‧ layer of tantalum nitride

138‧‧‧ openings

140‧‧‧ Passivation layer

141‧‧‧Oxide layer

142‧‧‧ layer of tantalum nitride

144‧‧‧Oxide layer

145‧‧‧Alumina layer

146‧‧‧ layer of tantalum nitride

148‧‧‧ openings

150‧‧‧ seed layer

160‧‧‧electrode

170‧‧‧ electrodes

180‧‧‧Back electric field

210‧‧‧矽 substrate

211‧‧‧Glossy surface

212‧‧‧Back

220‧‧‧射极

230‧‧‧ Passivation layer

231‧‧‧Oxide layer

232‧‧‧Alumina layer

233‧‧‧ layer of tantalum nitride

234‧‧‧Oxide layer

235‧‧‧ layer of tantalum nitride

238‧‧‧ openings

240‧‧‧ Passivation layer

241‧‧‧Oxide layer

242‧‧‧ layer of tantalum nitride

244‧‧‧Oxide layer

245‧‧‧Alumina layer

246‧‧‧ layer of tantalum nitride

248‧‧‧ openings

250‧‧‧ seed layer

260‧‧‧electrode

270‧‧‧electrode

280‧‧‧ positive electric field

1a to 1f are views showing a method of manufacturing a solar cell according to a first embodiment of the present invention. Figure 2a is a partial enlarged view of a portion A of Figure 1c. Figure 2b is a partial enlarged view of a portion B of Figure 1c. Figure 3a is a partial enlarged view of a portion A of Figure 1c. Figure 3b is a partial enlarged view of a portion B of Figure 1c. 4a to 4f are views showing a method of manufacturing a solar cell according to a second embodiment of the present invention. Figure 5a is a partial enlarged view of a portion C of Figure 4c. Figure 5b is a partial enlarged view of a portion D of Figure 4c. Figure 6a is a partial enlarged view of a portion C of Figure 4c. Figure 6b is a partial enlarged view of a portion D of Figure 4c.

Claims (10)

A method of manufacturing a solar cell, comprising: providing a germanium substrate having a first surface and a second surface opposite to the first surface; forming an emitter on the first surface of the germanium substrate, wherein The emitter is different from the doping type of the germanium substrate to thereby form a pn junction; a first passivation layer is formed on the first surface of the germanium substrate; and on the second surface of the germanium substrate Forming a second passivation layer; after forming the first passivation layer and the second passivation layer, performing thermal annealing treatment on the germanium substrate; after performing the thermal annealing process, opening and plating on the first passivation layer to form a first An electrode; and after performing the thermal annealing treatment, opening and plating on the second passivation layer to form a second electrode. The method for manufacturing a solar cell according to claim 1, wherein the step of performing the thermal annealing treatment comprises: raising the ambient temperature of the crucible substrate from 580 ° C to 910 ° C for a period of 1 to 2 minutes. The method for manufacturing a solar cell according to claim 2, wherein the step of raising the ambient temperature of the germanium substrate from 580 ° C to 910 ° C comprises: the ambient temperature of the germanium substrate is 580 ° C, The order of 620 ° C, 737 ° C, 695 ° C, 813 ° C, and 910 ° C was changed. The method for manufacturing a solar cell according to claim 1, wherein the ruthenium substrate is an N-type ruthenium substrate, the first passivation layer comprising a first ruthenium oxide layer, a first aluminum oxide layer and a first nitrogen The ruthenium layer is sequentially formed on the first surface of the ruthenium substrate, and the second passivation layer comprises a second ruthenium oxide layer and a second tantalum nitride layer, which are sequentially formed on the second surface of the ruthenium substrate And the second passivation layer is not formed with an aluminum oxide layer. The method for manufacturing a solar cell according to claim 1, wherein the ruthenium substrate is a P-type ruthenium substrate, and the first passivation layer comprises a first ruthenium oxide layer and a first tantalum nitride layer, which are sequentially formed. On the first surface of the germanium substrate, the first passivation layer is not formed with an aluminum oxide layer, and the second passivation layer comprises a second hafnium oxide layer, a second aluminum oxide layer and a second tantalum nitride layer. And sequentially formed on the second surface of the crucible substrate. The method of manufacturing a solar cell according to claim 1, wherein the first surface is a light receiving surface of the germanium substrate, the first electrode is formed later than the second electrode, and the second passivation layer After the opening, a sub-layer is formed on the second surface of the germanium substrate, and the second electrode is formed on the seed layer. The method of manufacturing a solar cell according to claim 6, wherein the first electrode has a structure of one of nickel/copper/tin, nickel/copper/silver, titanium/copper/tin or titanium/copper/silver. And the second electrode has a structure of one of copper/tin or copper/silver. The method of manufacturing a solar cell according to claim 1, wherein the second surface is a light receiving surface of the germanium substrate, the second electrode is formed later than the first electrode, and the first passivation layer After the opening, a sub-layer is formed on the first surface of the germanium substrate, and the first electrode is formed on the seed layer. The method for manufacturing a solar cell according to claim 8, wherein the second electrode has a structure of one of nickel/copper/tin, nickel/copper/silver, titanium/copper/tin or titanium/copper/silver. And the first electrode has a structure of one of copper/tin or copper/silver. The method of manufacturing a solar cell according to claim 6 or 8, wherein the seed layer comprises nickel or titanium.