TWI658603B - Mono-facial solar cell and method for manufacturing the same - Google Patents

Abstract

A single-sided light-receiving solar cell includes: a photoelectric conversion substrate; a front electrode on a light-receiving surface of the photoelectric conversion substrate; a back electrode 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; wherein the passivation layer includes a plurality of first linear openings extending along a first direction and a plurality of second linear openings extending along a second direction, the The first and second linear openings intersect each other; and the back electrode includes a nickel layer formed by an electroless plating process, and the nickel layer passes through the plurality of first linear openings and the plurality of second linear openings and The back surface is in electrical contact.

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 for manufacturing a single-sided light-receiving solar cell.

A solar cell is a photovoltaic element that converts light energy into electrical energy. It has become one of the important alternative energy sources due to its low pollution, low cost, and the availability of endless solar energy as an energy source. The basic structure of a solar cell is a combination of a P-type semiconductor and an N-type semiconductor. When sunlight hits a solar substrate with this PN junction, light can excite electrons in silicon atoms to generate convection of electrons and holes. In addition, these electrons and holes are affected by a built-in electric field formed at the PN junction surface, and are collected at both ends of the negative electrode and the positive electrode, respectively, so that a voltage is generated at both ends of the solar cell. At this time, electrodes can be used to connect the two ends of the solar cell to an external circuit to form a loop, and then generate current. This process is the principle of solar cell power generation.

In the manufacturing process of solar cells, the back metallization process usually uses screen printing electrodes or physical vapor deposition (PVD) techniques such as sputtering / evaporation to form back metal electrodes. The material cost of traditional screen printing metal paste is too high, and the cost of vacuum equipment for physical vapor deposition is too high. Therefore, in the near future, the industry expects to perform laser-type grooves on the passivation layer first, and then use metal plating to form metal electrodes instead. However, the electroplating technology cannot directly deposit a metal thin film on the surface of the insulating layer, and a seed layer is also required to provide a bias voltage to provide electrons to form a metal electrode.

Therefore, there is a need for a solar cell and a method for manufacturing the same. The metal electrode is formed by an electroless plating technique to overcome the above problems.

One object of the present invention is to provide a single-sided light-receiving solar cell, the passivation layer of which includes a plurality of openings (including the plurality of first linear openings and the plurality of second linear openings) having a mesh-like solid linear groove, Design of mesh-like dotted line slot, these dot-shaped openings, or ring-shaped openings.

According to the above object, the present invention provides a single-sided light-receiving solar cell, including: a photoelectric conversion substrate; a front electrode on a light-receiving surface of the photoelectric conversion substrate; and a back electrode on the back of one of the photoelectric conversion substrates. And a passivation layer located between the back electrode and the back surface; wherein the passivation layer includes a plurality of first linear openings extending along a first direction and extending along a second direction A plurality of second linear openings, the first and second linear openings intersecting each other, a distance between the plurality of first linear openings is less than 1 mm, and a distance between the plurality of second linear openings is less than 1 mm; and the back electrode The method includes a nickel layer formed by an electroless plating process. 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 includes a plurality of openings (including the plurality of first linear openings and the plurality of second linear openings) of a net-shaped solid linear slot, a net-shaped dotted slot, the dot-shaped openings, Or the design of the ring-shaped opening can improve the distribution of seed particles in the subsequent electroless plating pretreatment process, thereby improving the adhesion of a large area of the subsequent electroless nickel layer deposited on the passivation layer.

1‧‧‧ solar cell

10‧‧‧Photoelectric conversion substrate

101‧‧‧ light receiving surface

11‧‧‧ substrate

111‧‧‧ Front

112‧‧‧Back

12‧‧‧ Emitter Layer

13‧‧‧ back electric field layer

14‧‧‧Anti-reflective layer

15‧‧‧ passivation layer

150‧‧‧ opening

151‧‧‧first direction

152‧‧‧Second direction

153‧‧‧First linear opening

154‧‧‧Second linear opening

155‧‧‧ dotted line

156‧‧‧point opening

157‧‧‧line segment 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

173‧‧‧ tin layer

D‧‧‧Pitch

S100 ~ S500‧‧‧step

W‧‧‧line width

FIG. 1 is a flowchart of a method for manufacturing a single-sided light-receiving solar cell according to an embodiment of the present invention.

2 is a schematic cross-sectional view of a method for manufacturing a single-sided light-receiving solar cell according to an embodiment of the present invention, which shows preparing a photoelectric conversion substrate.

FIG. 3 is a schematic cross-sectional view of a method for manufacturing a single-sided light-receiving solar cell according to an embodiment of the present invention, which shows that a passivation layer is formed.

4a to 4e are schematic plan views of a passivation layer according to various embodiments of the present invention.

5 is a schematic cross-sectional view of a method for manufacturing a single-sided light-receiving solar cell according to an embodiment of the present invention, which shows the formation of a nickel layer.

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

Fig. 7 is photos (A) ~ (C) showing: (A) a traditional linear laser slotted pattern (B), a meshed solid linear laser slotted pattern, and (C) a net Comparison of the adhesion effect of the subsequent nickel layer of the dotted line laser slotted pattern.

FIG. 8 is a schematic cross-sectional view of a method for manufacturing a single-sided light-receiving solar cell according to an embodiment of the present invention, which shows that a conductive layer is formed.

FIG. 9 is a schematic cross-sectional view of a method for manufacturing a single-sided light-receiving solar cell according to an embodiment of the present invention, which shows that a front electrode is formed.

In order to make the foregoing objects, features, and characteristics of the present invention more comprehensible, the related embodiments of the present invention are described in detail below with reference to the drawings.

Please refer to FIG. 1, which shows a flowchart of a method for manufacturing a single-sided light-receiving solar cell according to an embodiment of the present invention. The method for manufacturing a single-sided light-receiving solar cell includes the following steps: In step S100, a photoelectric conversion substrate 10 is prepared, as shown in FIG. 2. The photoelectric conversion substrate 10 refers to a substrate capable of converting light energy into electrical energy by a photovoltaic effect, such as a semiconductor silicon substrate having a PN junction (P / N junction) or a PIN junction (PIN junction). For example, a silicon crystal is doped with a P-type semiconductor on one side and an N-type semiconductor on the other side. The contact surface between the two is called a PN junction. Please refer to FIG. 2 again. In this 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, which is disposed on the The front is 111 places.

In step S200, a passivation layer 15 is formed on the back surface 112 of the photoelectric conversion substrate 10. The passivation layer 15 has a plurality of openings 150, as shown in FIG. 3. In practice, for example, the entire passivation layer 15 is formed first, and then a plurality of openings 150 are formed by laser slotting. The passivation layer 15 can be made of a silicon nitride material, and can also be made of a stacked material of aluminum oxide / silicon oxide / silicon nitride, for example.

4a to 4e are schematic plan views of the passivation layer 15 according to the present invention. Please refer to FIG. 4a. In this 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 intersect each other. For example, the first and second linear openings 153 and 154 are solid lines, and constitute mesh-shaped solid line slots. Please refer to FIG. 3 again, the distance D between the plurality of openings 150 (for example, the distance between the first linear shapes 153 and the distance between the second linear 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 linear shapes 153 and the line width of the second linear openings 154) may be between 10 and 35 μm (microns).

Please refer to FIG. 4b. In another embodiment, the plurality of first linear openings 153 are dotted lines, and the plurality of second linear openings 154 are dotted lines 155. For example, the first and second linear openings 153 and 154 are dotted lines 155 and constitute a meshed dotted line slot. The dotted line shape 155 includes a plurality of dot-shaped openings 156. In other embodiments, a design in which a plurality of first linear openings 153 are dotted lines and a portion of the first linear openings 153 are solid lines may be adopted. At least one of the plurality of first linear openings 153 is a dotted line shape. Similarly, the plurality of second linear openings 154 may also be designed with only a part of a dotted line shape, so that at least one of the plurality of second linear openings 154 is formed. One is dashed. Please refer to FIG. 4c. In another embodiment, the dotted line 155 further includes a plurality of line segment openings 157.

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

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

The design of the net-shaped solid line slot, the net-shaped dotted line slot, the dot-shaped openings, or the ring-shaped openings can improve the seed particle distribution of the subsequent electroless plating pretreatment process, thereby improving the subsequent electroless plating. The large-area 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 directly contacts and electrically contacts the back surface 112 through the openings 150, 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 is between 5 and 10, and the main components of the plating solution include 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. First, a metal surface with a catalytic force is formed on the surface of the work, or the catalytic action of the surface of the work is used to chemically reduce the metal ions. Precipitation in a metallic state. First, hypophosphite (reducing agent) is oxidized to phosphite ions, and the released charge can reduce the nickel ions. Metal nickel is deposited on the catalytically active surface, and the precipitated nickel continues to catalyze the reaction. Therefore, the precipitation reaction proceeds in a chained manner, and the plating layer has a layered structure, and the thickness can be arbitrarily controlled.

Before step S300 of forming the nickel layer 162, step S250: forming a plurality of seed particles 161 by a sensitization and activation step of an electroless plating pretreatment process, wherein the seed particles 161 use one of the following materials as a crystal Seed 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 tin / palladium seed particles have the characteristics of being easier to adsorb on the surface of silicon and less likely to adhere to the surface of silicon nitride. Therefore, the design of the net-shaped solid line slot, the net-shaped dotted line slot, the dot-shaped openings, or the ring-shaped openings will enhance the tin / palladium seed particles adsorbed in the sensitization and activation steps of the pretreatment process. And increase the density and distribution of the tin / palladium seed particles, thereby improving the adhesion of a large area of the subsequent nickel layer 162 deposited on the passivation layer 15.

Please refer to FIG. 6. The photos (A) to (F) show the effect of the pH value of the electroless plating solution and the process temperature on the grain size and coverage of the nickel film. It can be observed under different conditions of electroless nickel plating process that if a larger grain size electroless nickel film is grown, the grain size must be greater than 80nm to promote the nickel film to be completely deposited on the entire back surface of the battery There are no voids.

Please refer to FIG. 7. The photos (A) ~ (C) show: (A) a traditional linear laser slotted pattern (B), a meshed solid linear laser slotted pattern, and (C) ) Comparison of the adhesion effect of subsequent nickel layers of the meshed dotted laser slotted pattern. The traditional mesh pattern design obviously has the problem of nickel film peeling. The ratio of peeling area is close to 10%, and the design of the mesh solid line and the mesh dotted line are significantly improved without electroplating. Adhesion of nickel film, the ratio of peeling area is 0%

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

After step S300 of forming the nickel layer 162, or after step S400 of forming the conductive layer 163, step S450 may be performed: annealing the nickel layer 162, the annealing temperature is between 250-400 ° C, and the time is between 3-10min (minutes). After the nickel layer 162 is annealed, a part of the nickel layer 162 will be silicon-shaped. A silicon nickel layer (not shown) is formed and is in electrical contact with the back surface 112, that is, at this time, the main component of the interface between the nickel layer 162 and the back surface 112 has changed to silicon nickel layer. At this time, the thickness of the nickel layer 162 is between 0.5 and 1 μm (micrometers), and the grain size of the nickel layer 162 after annealing is between 100 and 300 nm (nanometers). It should be noted that the foregoing description of the grain size refers to the non-nickelized silicon portion of the nickel layer 162.

Referring to FIG. 9, in step S500, a front electrode 17 is formed, which is located on a light receiving surface 101 of the photoelectric conversion substrate 10 and is connected to the emitter region 12. For example, a plurality of openings are formed in the anti-reflection layer 14 to expose the part of the emitter region 12, and the nickel layer 171 / copper layer 172 / tin layer 173 is sequentially plated in a manner of forward bias plating by a plurality of plating processes and annealed to become This front electrode 17 completes a mono-facial light-receiving solar cell 1. It is added that, in other embodiments, the opening of the anti-reflection layer 14 may be formed by laser slotting with the opening 150 of the passivation layer, and the opening of the anti-reflection 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 by electroplating. Although FIG. 9 shows that the seed particles 161 can still be identified after annealing, when the annealing temperature is high, part or all of the seed particles 161 may re-lattice with the nickel layer 162 and disappear or at least fail. Identify.

In step S500 of this embodiment, the nickel layer 171 (plating process) / copper layer 172 (plating process) / tin layer 173 (plating process) of the front electrode 17 is the conductive layer 163 (plating process) of the back electrode 16 ). However, in the steps of the 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 first, and then the front electrode 17 may be formed simultaneously. The copper layer 172 (plating process) and the conductive layer 163 (copper plating process) of the back electrode 16. Finally, a tin layer 173 of the front electrode 17 is formed (plating process).

Please refer to FIG. 9 again, which shows a single-sided light-receiving solar cell 1 according to an embodiment of the present invention. 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 may include a substrate 11, an emitter layer 12, and a back electric field layer 13. The substrate 11 It is a first conductivity type and has a front surface 111 and a back surface 112 opposite to 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 on the front surface 111. The single-sided light-receiving solar cell 1 may be an n-type emitter passivation back full diffusion (n-PERT) solar cell.

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

Please refer to FIGS. 3 and 4 a again, 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 two linear openings 153 and 154 cross each other. The distance between the plurality of first linear openings 153 is less than 1 mm (mm), and the distance between the plurality of second linear openings 154 is less than 1 mm (mm).

Please refer to FIG. 9 again, the back electrode 16 includes a nickel layer 162 formed by an electroless plating process, and 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). ) Is in electrical contact with the back surface 112, the thickness of the nickel layer 162 is between 0.5 and 1 μm (micrometers), and the grain size of the nickel layer is between 100 and 300 nm (nanometers).

The passivation layer of the present invention includes a plurality of openings (including the plurality of first linear openings and the plurality of second linear openings) of a net-shaped solid linear slot, a net-shaped dotted slot, the dot-shaped openings, Or the design of the ring-shaped opening can improve the distribution of seed particles in the subsequent electroless plating pretreatment process, thereby improving the adhesion of a large area of the subsequent electroless nickel layer deposited on the passivation layer.

In summary, it is only documented that the present invention is used to solve the problem. The preferred implementations or examples of the technical means are not intended to limit the scope of patent implementation of the present invention. That is, all changes and modifications that are consistent with the meaning of the scope of patent application of the present invention, or made according to the scope of patent of the present invention, are covered by the scope of patent of the present invention.

Claims (9)

A single-sided light-receiving solar cell includes: a photoelectric conversion substrate; a front electrode located on a light-receiving surface of the photoelectric conversion substrate; a back electrode located 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; wherein: the passivation layer includes a plurality of openings; and the back electrode includes a nickel layer, the nickel layer is in direct contact with the back through the plurality of openings, The thickness of the nickel layer is between 0.5 and 1 μm, and the grain size of the nickel layer is between 100-300 nm. The single-sided light-receiving solar cell according to item 1 of the scope of patent application, wherein the plurality of openings include a plurality of first linear openings extending along a first direction, and a line width of the plurality of first linear openings is between 10 ~ 35μm, and the distance between them is less than 1mm. The single-sided light-receiving solar cell according to item 2 of the scope of patent application, wherein the plurality of openings further include a plurality of second linear openings extending along a second direction, and a line width of the plurality of second linear openings is between 10 ~ 35μm, and the distance between them is less than 1mm. A method for manufacturing a single-sided light-receiving solar cell includes: 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; and forming a nickel layer by an electroless plating process The nickel layer covers the passivation layer and directly contacts the back surface through the plurality of openings, wherein 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. Formed on the nickel layer, wherein the nickel layer and the conductive layer are 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 as described in item 4 of the scope of patent application, wherein: the electroless plating process is performed at a temperature of 50-70 ° C, and the pH value of the plating solution of the electroless plating process is between 5 ~ 10, and the main components of the plating solution include NiSO ₄ / NaH ₂ PO ₂ / Na ₂ H ₄ C ₄ O ₄ / H ₂ O. According to the method for manufacturing a single-sided light-receiving solar cell described in item 5 of the scope of patent application, the method further includes: after the step of forming the nickel layer, annealing the nickel layer, the annealing temperature of which is between 250-400 ° C, and The time is between 3-10min. The method for manufacturing a single-sided light-receiving solar cell as described in item 6 of the scope of patent application, further comprising: forming a plurality of seed crystals by a sensitizing and activating step of an electroless pretreatment process before the step of forming the nickel layer; Particles, wherein the seed particles are seed particles using one of the following materials: Sn / Pd (tin / palladium), Sn / Ag (tin / silver), Ni (nickel), Co (cobalt), or Fe (iron ). The method for manufacturing a single-sided light-receiving solar cell according to item 4 of the scope of patent application, wherein the plurality of openings include a plurality of first linear openings extending along a first direction, and a line width of the plurality of first linear openings It is between 10 ~ 35μm, and the distance between them is less than 1mm. The method for manufacturing a single-sided light-receiving solar cell according to item 6 of the scope of patent application, wherein the plurality of openings further include a plurality of second linear openings extending along a second direction, and the lines of the plurality of second linear openings The width is between 10 ~ 35μm, and the distance between them is less than 1mm.