TW201907573A - Mono-facial solar cell and method for manufacturing the same - Google Patents

Abstract

A mono-facial solar cell includes a photoelectric conversion substrate; a front electrode located on a light receiving surface of the photoelectric transformation substrate; a back electrode located on a back surface of the photoelectric transformation substrate; and a passivation layer located between the back electrode and the back surface; wherein: the passivation layer includes a plurality of first linear openings in a first direction and a plurality of second linear openings in a second direction, the first and second linear openings are intersected each other; and the back electrode includes a nickel layer formed by an electroless plating process, and the nickel layer electrically contacts the back surface by the first and second linear openings.

Description

 Single-sided light-receiving solar cell and manufacturing method thereof  

The present invention relates to a single-sided light-receiving solar cell, and more particularly to a method of fabricating a single-sided light-receiving solar cell.

Solar cell A photovoltaic element that converts light energy into electrical energy. It is one of the important alternative energy sources due to its low pollution, low cost and the use of endless solar energy as an energy source. The basic structure of a solar cell is formed by bonding a P-type semiconductor to an N-type semiconductor. When sunlight is applied to a solar substrate having the PN junction, light energy excites electrons in the germanium atom to generate convection of electrons and holes. Moreover, these electrons and holes are concentrated on the negative electrode and the positive electrode by the built-in electric field formed at the PN junction, so that voltage is generated at both ends of the solar cell. At this time, an electrode can be used to connect both ends of the solar cell to an external circuit to form a loop, thereby generating a current, which is the principle of solar cell power generation.

In the solar cell process, the backside metallization process is typically a screen printed electrode, or a physical vapor deposition (PVD) technique such as sputtering/evaporation to form a backside metal electrode. The material price of the conventional screen printing metal paste is too high, and the vacuum equipment of the physical vapor deposition method is also too expensive. Therefore, in the near future, it is desired to perform linear grooving on the passivation layer by laser, and then replace the metal electrode by electroplating. However, the electroplating technique cannot deposit a metal thin film directly on the surface of the insulating layer, and it is also necessary to provide a metal by applying a bias layer with a biasing layer to form a metal electrode.

Accordingly, there is a need for a solar cell and method of fabricating the same that uses an electroless plating technique to form a metal electrode to overcome the above problems.

An object of the present invention is to provide a single-sided light-receiving solar cell, wherein the passivation layer includes a plurality of openings (including the plurality of first linear openings and the plurality of second linear openings) having a mesh-shaped solid-line slot, The design of the mesh-shaped dotted groove, the dot-shaped openings, or the annular opening.

According to the above objective, the present invention provides a single-sided light-receiving solar cell comprising: a photoelectric conversion substrate; a front electrode disposed on a light receiving surface of the photoelectric conversion substrate; and a back electrode disposed on a back surface of the photoelectric conversion substrate And substantially covering the entire back surface; and a passivation layer between the back electrode and the back surface; wherein: the passivation layer comprises a plurality of first linear openings extending in a first direction and extending along a second direction a plurality of second linear openings, the first and second linear openings intersecting each other, the plurality of first linear openings are less than 1 mm apart, the plurality of second linear openings are less than 1 mm apart; and the back electrode A nickel layer is formed by an electroless plating process, and the nickel layer is in electrical contact with the back surface through the plurality of first linear openings and the plurality of second linear openings.

The passivation layer of the present invention comprises a plurality of openings (including a plurality of first linear openings and the plurality of second linear openings), a mesh-shaped solid-line groove, a mesh-shaped dotted groove, and the dot-shaped openings. Or the annular opening is designed to enhance the distribution of seed particles in the subsequent electroless pre-treatment process, thereby improving the adhesion of the subsequent electroless nickel layer deposited on the passivation layer over a large area.

1‧‧‧Solar battery

10‧‧‧Photoelectric conversion substrate

101‧‧‧Stained surface

11‧‧‧Substrate

111‧‧‧ positive

112‧‧‧Back

12‧‧ ‧ emitter layer

13‧‧‧ Back electric field layer

14‧‧‧Anti-reflective layer

15‧‧‧ Passivation layer

150‧‧‧ openings

151‧‧‧First direction

152‧‧‧second direction

153‧‧‧First linear opening

154‧‧‧Second linear opening

155‧‧‧dotted

156‧‧‧ Point opening

157‧‧‧Line-shaped opening

158‧‧‧ Point opening

159‧‧‧Circular opening

16‧‧‧Back electrode

161‧‧‧ seed particles

162‧‧‧ Nickel layer

163‧‧‧ Conductive layer

17‧‧‧Front electrode

171‧‧‧ Nickel layer

172‧‧‧ copper layer

173‧‧‧ tin layer

D‧‧‧ spacing

S100~S500‧‧‧Steps

W‧‧‧Line width

1 is a flow chart showing a method of manufacturing a single-sided light-receiving solar cell according to an embodiment of the present invention.

2 is a schematic cross-sectional view showing a method of fabricating a single-sided light-receiving solar cell according to an embodiment of the present invention, showing preparation of a photoelectric conversion substrate.

3 is a cross-sectional view showing a method of fabricating a single-sided light-receiving solar cell according to an embodiment of the present invention, showing a passivation layer.

4a-4e show schematic plan views of passivation layers of various embodiments of the present invention.

Figure 5 is a cross-sectional view showing a method of fabricating a single-sided light-receiving solar cell according to an embodiment of the present invention, showing a nickel layer formed.

Figure 6 is a photograph (A) ~ (F) showing the effect of the pH of the electroless plating solution and the process temperature on the grain size and coverage of the nickel layer.

Figure 7 shows photographs (A) to (C) showing: (A) a conventional linear laser line pattern, (B) a mesh type solid line slotted pattern, and (C) a net A comparison of the adhesion effects of the subsequent nickel layers of the dotted line-shaped laser slotted pattern.

Figure 8 is a cross-sectional view showing a method of fabricating a single-sided light-receiving solar cell according to an embodiment of the present invention, showing a conductive layer formed.

Figure 9 is a cross-sectional view showing a method of fabricating a single-sided light-receiving solar cell according to an embodiment of the present invention, showing the formation of a front electrode.

The above described objects, features, and characteristics of the present invention will become more apparent from the aspects of the invention.

Please refer to FIG. 1, which shows a flow chart of a method for manufacturing a single-sided light-receiving solar cell according to an embodiment of the present invention. The manufacturing method of the single-sided light-receiving solar cell includes the following steps: In step S100, a photoelectric conversion substrate 10 is prepared as shown in FIG. The photoelectric conversion substrate 10 refers to a substrate that can convert light energy into electrical energy by a photovoltaic effect, such as a semiconductor germanium substrate having a PN junction (P/N junction) or a PIN junction. For example, one side of a germanium crystal is doped into a P-type semiconductor, and the other side is doped into an N-type semiconductor, and the contact surface between the two is called a PN junction. Referring to FIG. 2 again, in the embodiment, the photoelectric conversion substrate 10 includes a substrate 11 , an emitter layer 12 and a back electric field layer 13 . The substrate 11 is of a first conductivity type and has a front surface 111 and a back surface 112 opposite to the front surface 111. The emitter layer 12 is of a second conductivity type and is located in the substrate 11 near the front surface 111. The back electric field layer 13 is of a first conductivity type and is located in the substrate 11 near the back surface 112. In addition, the photoelectric conversion substrate 10 may further include an anti-reflection layer 14 disposed at the front surface 111.

In step S200, a passivation layer 15 is formed on the back surface 112 of the photoelectric conversion substrate 10, and the passivation layer 15 has a plurality of openings 150 as shown in FIG. In actual practice, for example, a passivation layer 15 of the entire surface is formed first, and a plurality of openings 150 are formed by laser grooving. The passivation layer 15 may be made of a tantalum nitride material, and may be, for example, a laminate of aluminum oxide/yttria/tantalum nitride.

4a-4e show schematic plan views of the passivation layer 15 of the present invention. Referring to FIG. 4 a , in the embodiment, the plurality of openings 150 include a plurality of first linear openings 153 extending along a first direction 151 and a plurality of second linear openings 154 extending along a second direction 152 . The first and second linear openings 153, 154 are crossed to each other. For example, the first and second linear openings 153, 154 are in a solid line shape and constitute a mesh-shaped solid-line slot. Referring to FIG. 3 again, the distance D between the plurality of openings 150 (for example, the distance between the first line shapes 153 and the distance between the second line openings 154) may be less than 1 mm (mm). The line width W of the plurality of openings 150 (for example, the line width of the first line shapes 153 and the line width of the second line openings 154) may be between 10 and 35 μm (micrometers).

Referring to FIG. 4b, in another embodiment, the plurality of first linear openings 153 are in a dotted line shape, and the plurality of second linear openings 154 are in a dotted shape 155. For example, the first and second linear openings 153, 154 are in the form of a broken line 155 and constitute a mesh-shaped dotted line slot. The dotted line 155 includes a plurality of dot-shaped openings 156. In other embodiments, a portion of the plurality of first linear openings 153 may be a dotted line and a portion of the plurality of first linear openings 153 may be formed in a solid line shape. At least one of the plurality of first linear openings 153 is in the shape of a dotted line. Similarly, the plurality of second linear openings 154 may also be designed in a partially dotted shape such that at least one of the plurality of second linear openings 154 is One of them is a dotted line. Referring to FIG. 4c, in still another embodiment, the dotted line 155 further includes a plurality of line-shaped openings 157.

Referring to FIG. 4d, in other embodiments, the passivation layer 15 further includes a plurality of dot-shaped openings 158, each of which is located adjacent to the two adjacent first linear openings 153 and two adjacent ones. Between the second linear openings 154.

Referring to FIG. 4e, in other embodiments, the passivation layer 15 further includes an annular opening 159 surrounding all of the first and second linear openings 153, 154. The annular opening 159 can be a solid or dashed line 155. The dotted shape 155 includes a plurality of dot shaped openings 156. The dotted line 155 further includes a plurality of line-shaped openings 157. Although the first and second linear openings 153, 154 in FIG. 4e are exemplified by the linear linear opening of FIG. 4a, in other embodiments, the dotted lines in FIGS. 4b, 4c, and 4d may also be used. The linear opening design replaces the solid linear opening of Figure 4e. The distance between each of the linear openings in FIGS. 4b to 4d may be less than 1 mm (mm), and the line width may be between 10 and 35 μm (micrometers).

The mesh-shaped solid-line groove, the mesh-shaped dotted groove, the dot-shaped openings, or the annular opening are designed to improve the distribution of seed particles in the subsequent electroless pre-treatment process, thereby improving subsequent electroless plating. A large area of adhesion of the nickel layer deposited on the passivation layer 15.

Referring to FIG. 5, in step S300, a nickel layer 162 is formed by an electroless plating process. The nickel layer 162 covers the passivation layer 15 and is in direct contact and electrical contact with the back surface 112 through the plurality of openings 150, wherein: The electroless plating process is carried out at a temperature of 50-70 ° C, and the pH of the electroless plating process is between 5 and 10, and the main component of the plating solution comprises NiSO ₄ (nickel sulfate) / NaH ₂ PO ₂ (times) Sodium phosphate) / Na ₂ H ₄ C ₄ O ₄ (sodium succinate) / H ₂ O. For example, electroless plating can also be called Autocatalytic Plating, which first forms a catalytic metal surface on the surface of a work object, or uses a catalytic action of the surface of the work object to chemically reduce the metal ion. It precipitates in a metal state. First, the hypophosphite (reducing agent) is oxidized to a phosphite ion, and the released charge can reduce the nickel ion, and the metallic nickel is deposited on the catalytically activated surface, and the precipitated nickel continues to catalyze the reaction. Therefore, the precipitation reaction is carried out in a chain, and the plating layer has a layered structure, and the thickness can be arbitrarily controlled.

Before the step S300 of forming the nickel layer 162, step S250: forming a plurality of seed particles 161 by an sensitization and activation step of an electroless plating pretreatment process, wherein the seed particles 161 are one of the following materials. Particles: Sn/Pd (tin/palladium), Sn/Ag (tin/silver), Ni (nickel), Co (cobalt) or Fe (iron). The nickel layer 162 is attached to the back surface 112 through the seed particles 161. For example, the sensitization and activation steps allow tin and palladium seed particles to be adsorbed on the back surface, but the tin/palladium seed particles have a property of being more easily adsorbed on the surface of the crucible and not easily adhering to the surface of the tantalum nitride. Therefore, the mesh-shaped solid-line groove, the mesh-shaped dotted groove, the dot-shaped openings, or the annular opening are designed to enhance the tin/palladium seed particles adsorbed by the sensitization and activation steps of the pretreatment process. And increasing the density and distribution of the tin/palladium seed particles, thereby improving the adhesion of the subsequent large area of the nickel layer 162 deposited on the passivation layer 15.

Referring to Figure 6, photographs (A) to (F) show the effect of the pH of the electroless plating solution and the process temperature on the grain size and coverage of the nickel film. Under different electroless nickel process conditions, it can be observed that if a larger grain size electroless nickel film is grown, the grain size must be greater than 80 nm to promote the complete deposition of the nickel film on the back side of the cell. There is no void (Void).

Referring to Figure 7, photographs (A) to (C) show: (A) a conventional linear laser line pattern, (B) a mesh solid line laser slot pattern, and (C) A comparison of the adhesion effects of the subsequent nickel layers of the mesh-shaped dotted laser-slotted pattern. The traditional wire-like graphic design obviously has the problem of peeling off the nickel film, the ratio of peeling area is close to 10%, and the design of the mesh-shaped solid line and the mesh-shaped dotted line obviously improves the electroless plating. The adhesion of the nickel film, the ratio of the peeling area is 0%

Referring to FIG. 8 , in step S400 , a conductive layer 163 is formed on the nickel layer 162 , wherein the nickel layer 162 and the conductive layer 163 are combined to form a back electrode 16 . In this embodiment, the conductive layer 162 can be a copper layer. For example, by using the nickel layer 162 as a back metal seed layer, a copper layer is directly electroplated on the nickel layer 162 by an electroplating process.

After the step S300 of forming the nickel layer 162, or after the step S400 of forming the conductive layer 163, step S450 may be performed: annealing the nickel layer 162, the annealing temperature is between 250 and 400 ° C, and the time is between 3-10min (minutes). After the nickel layer 162 is annealed, a portion of the nickel layer 162 forms a nickel ruthenium layer (not shown) with the tantalum and is in electrical contact with the back surface 112, that is, the interface between the nickel layer 162 and the back surface 112 is partially formed. The main component of the area has become nickel bismuth. At this time, the thickness of the nickel layer 162 is 0.5 to 1 μm (micrometer), and the grain size of the nickel layer 162 after annealing is between 100 and 300 nm (nano). It should be noted that the foregoing description of the grain size is a non-nickel-doped portion of the nickel layer 162.

Referring to FIG. 9, in step S500, a front electrode 17 is formed on one of the light receiving surfaces 101 of the photoelectric conversion substrate 10 and connected to the emitter region 12. For example, a plurality of openings are formed in the anti-reflection layer 14 to expose a portion of the emitter region 12, and the nickel layer 171/copper layer 172/tin layer 173 is sequentially electroplated by a plurality of electroplating processes in a forward bias plating manner to be annealed. The front electrode 17 completes a mono-facial light-receiving solar cell 1. In addition, in other embodiments, the opening of the anti-reflective layer 14 may be formed in the same manner as the opening 150 of the passivation layer, and the opening of the anti-reflective layer 14 may be earlier than step S300. Formed before. In addition, in other embodiments, the annealing process of the back electrode 16 may be performed after the nickel layer 171 / copper layer 172 / tin layer 173 is formed. Although FIG. 9 shows that the seed particles 161 can be identified after annealing, when the annealing temperature is high, part or all of the seed particles 161 may be re-arranged with the nickel layer 162 to disappear or at least fail. Identification.

In step S500 of the embodiment, the nickel layer 171 (electroplating process) / copper layer 172 (electroplating process) / tin layer 173 (electroplating process) of the front electrode 17 is the conductive layer 163 of the back electrode 16 (electroplating process) ) formed afterwards. However, in the steps of other embodiments, the nickel layer 162 (electroless plating process) of the back electrode 16 and the nickel layer 171 (electroplating process) of the front electrode 17 may be sequentially formed, and then the front electrode 17 may be simultaneously formed. The copper layer 172 (electroplating process) and the conductive layer 163 of the back electrode 16 (copper plating process). Finally, the tin layer 173 of the front surface electrode 17 is formed (electroplating process).

Referring again to Figure 9, a single-sided light-receiving solar cell 1 of one embodiment of the present invention is shown. A single-sided light-receiving solar cell 1 includes a photoelectric conversion substrate 10, a front electrode 17, a back electrode 16, and a passivation layer 15. The photoelectric conversion substrate 10 can include a substrate 11, an emitter layer 12, and a back electric field layer 13. The substrate 11 is of a first conductivity type and has a front surface 111 and a back surface 112 opposite the front surface 111. The emitter layer 11 is of a second conductivity type and is located in the substrate 11 near the front surface 111. The back electric field layer 13 is of a first conductivity type and is located in the substrate 11 near the back surface 112. The photoelectric conversion substrate 1 may further include an anti-reflection layer 14 disposed at the front surface 111. The single-sided light-receiving solar cell 1 can be an n-type emitter passivated back fully diffused (n-PERT) solar cell.

The front surface electrode 17 is located on one of the light receiving surfaces 101 of the photoelectric conversion substrate 10 and is connected to the emitter region 12. The back surface electrode 16 is located on one of the back surfaces 112 of the photoelectric conversion substrate 1 and substantially covers the entire back surface 112. The above "substantially covers the whole" means that: (1) covers the entire back surface 112, or (2) covers most of the area of the back surface 112, but a small portion is not covered by the back surface electrode 16, for example, close to the A mark area left at the edge of the photoelectric conversion substrate 10 or due to, for example, alignment.

Referring again to FIGS. 3 and 4a, the passivation layer 15 is located between the back electrode 16 and the back surface 112. The passivation layer 15 includes a plurality of openings 150 including a plurality of first linear openings 153 extending along a first direction 151 and a plurality of second linear openings 154 extending along a second direction 152, the first and the first The two linear openings 153, 154 are intersected with each other, the plurality of first linear openings 153 having a distance of less than 1 mm (mm), and the plurality of second linear openings 154 having a distance of less than 1 mm (mm).

Referring to FIG. 9 again, the back electrode 16 includes a nickel layer 162 formed by an electroless plating process. The nickel layer 162 passes through the plurality of openings 150 (including the plurality of first linear openings and the plurality of second linear openings). And electrically contacting the back surface 112, the nickel layer 162 has a thickness of 0.5 to 1 μm (micrometer), and the nickel layer has a grain size of 100 to 300 nm (nano).

The passivation layer of the present invention comprises a plurality of openings (including a plurality of first linear openings and the plurality of second linear openings), a mesh-shaped solid-line groove, a mesh-shaped dotted groove, and the dot-shaped openings. Or the annular opening is designed to enhance the distribution of seed particles in the subsequent electroless pre-treatment process, thereby improving the adhesion of the subsequent electroless nickel layer deposited on the passivation layer over a large area.

In the above, it is merely described that the present invention is a preferred embodiment or embodiment of the technical means for solving the problem, and is not intended to limit the scope of the invention. That is, the equivalent changes and modifications made in accordance with the scope of the patent application of the present invention or the scope of the invention are covered by the scope of the invention.

Claims (19)

 A single-sided light-receiving solar cell comprising: a photoelectric conversion substrate; a front electrode disposed on a light receiving surface of the photoelectric conversion substrate; and a back electrode disposed on a back surface of the photoelectric conversion substrate and covering substantially the entire back surface And a passivation layer between the back electrode and the back surface; wherein: the passivation layer comprises a plurality of first linear openings extending in a first direction and a plurality of second linear openings extending in a second direction The first and second linear openings are intersecting each other, the plurality of first linear openings are less than 1 mm apart, the plurality of second linear openings are less than 1 mm apart; and the back electrode comprises an electroless plating process a nickel layer electrically contacting the back surface through the plurality of first linear openings and the plurality of second linear openings.    The single-sided light-receiving solar cell of claim 1, wherein the plurality of first linear openings have a line width of 10 to 35 μm.    The single-sided light-receiving solar cell of claim 2, wherein the plurality of second linear openings have a line width of 10 to 35 μm.    The single-sided light-receiving solar cell of claim 2, wherein at least one of the plurality of first linear openings is in a dotted line shape.    The single-sided light-receiving solar cell of claim 3, wherein at least one of the plurality of second linear openings is in the shape of a dotted line.    The single-sided light-receiving solar cell of claim 1, wherein the passivation layer further comprises a plurality of first dot-shaped openings, each of the first dot-shaped openings being located in the adjacent two of the first linear openings And between the two adjacent second linear openings.    The single-sided light-receiving solar cell of claim 1, wherein the passivation layer further comprises an annular opening surrounding all of the first and second linear openings.    The single-sided light-receiving solar cell of claim 7, wherein the annular opening has a dotted line shape.    The single-sided light-receiving solar cell of claim 4, 5 or 8, wherein the dotted line shape comprises a plurality of second dot-shaped openings.    The single-sided light-receiving solar cell of claim 9, wherein the dotted line shape further comprises a plurality of line-shaped openings.    The single-sided light-receiving solar cell of claim 1, wherein the nickel layer comprises a plurality of seed particles formed by an sensitization and activation step of an electroless pre-treatment process, and the nickel layer passes through the plurality of seed crystals. The back surface is attached by seed crystal particles.    A single-sided light-receiving solar cell comprising: a photoelectric conversion substrate; a front electrode disposed on a light receiving surface of the photoelectric conversion substrate; and a back electrode disposed on a back surface of the photoelectric conversion substrate and covering substantially the entire back surface And a passivation layer between the back electrode and the back surface; wherein: the passivation layer comprises a plurality of openings; and the back electrode comprises a nickel layer formed by an electroless plating process, the nickel layer passing through the plurality of openings And in electrical contact with the back surface, the thickness of the nickel layer is between 0.5 and 1 μm, and the grain size of the nickel layer is between 100 and 300 nm.    The single-sided light-receiving solar cell of claim 12, wherein the plurality of openings comprise a plurality of first linear openings extending in a first direction, the plurality of first linear openings having a line width of 10 ~35μm, and the distance between them is less than 1mm.    The single-sided light-receiving solar cell of claim 13, wherein the plurality of openings further comprise a plurality of second linear openings extending in a second direction, the line widths of the plurality of second linear openings being between 10~35μm, and the distance between them is less than 1mm.   A method for manufacturing a single-sided light-receiving solar cell, comprising: preparing a photoelectric conversion substrate; forming a passivation layer on a back surface of the photoelectric conversion substrate, the passivation layer having a plurality of openings; forming a nickel layer by an electroless plating process The nickel layer covers the passivation layer and is in direct contact with and electrically in contact with the back surface through the plurality of openings, wherein: the electroless plating process is performed at a temperature of 50-70 ° C, and the pH of the plating solution of the electroless plating process The value is between 5 and 10, and the main component of the plating solution comprises NiSO ₄ /NaH ₂ PO ₂ /Na ₂ H ₄ C ₄ O ₄ /H ₂ O; a conductive layer is formed on the nickel layer, wherein the nickel layer And the conductive layer is combined into a back electrode; and a front electrode is formed on a light receiving surface of the photoelectric conversion substrate.  The method for manufacturing a single-sided light-receiving solar cell according to claim 15, further comprising: annealing the nickel layer after the step of forming the nickel layer, the annealing temperature is between 250 and 400 ° C, and The time is between 3-10min.    The method for manufacturing a single-sided light-receiving solar cell according to claim 16, further comprising: forming a plurality of seed crystals by an sensitization and activation step of an electroless pre-treatment process before the step of forming the nickel layer Particles, wherein the seed particles use one of the following materials as seed particles: Sn/Pd (tin/palladium), Sn/Ag (tin/silver), Ni (nickel), Co (cobalt) or Fe (iron) ).    The method of manufacturing a single-sided light-receiving solar cell according to claim 15, wherein the plurality of openings comprise a plurality of first linear openings extending in a first direction, and line widths of the plurality of first linear openings It is between 10 and 35 μm and the distance between them is less than 1 mm.    The method for manufacturing a single-sided light-receiving solar cell according to claim 16, wherein the plurality of openings further comprise a plurality of second linear openings extending in a second direction, the plurality of second linear open lines The width is between 10 and 35 μm, and the distance between them is less than 1 mm.