A MWT cell based on a passivated contact structure and a preparation method thereof

Abstract

The present invention provides a MWT cell based on a passivated contact structure and a preparation method thereof. The MWT cell includes: a P-type silicon substrate formed with a through-hole; a front passivation and antireflection layer formed on the front of the P-type silicon substrate; a back passivated contact layer formed on the back of the P-type silicon substrate; a back dielectric protection layer laminated and covering the back passivated contact layer; a battery positive electrode filled in the through-hole and penetrating the back passivated contact layer and the back dielectric protection layer; and a battery negative electrode formed on the back dielectric protection layer and penetrating the back dielectric protection layer to contact the back passivated contact layer. Wherein, the battery positive electrode is an aluminum electrode, and an aluminum-doped P+ surface field is formed at the position where the P-type silicon substrate contacts the aluminum electrode. The MWT cell of the present invention realizes charge collection in the through-hole of the silicon substrate, without the need for a front-side sub-grid, which can further improve the light absorption of the MWT cell and increase the battery conversion efficiency.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic cells, and particularly to an MWT cell based on a passivated contact structure and a preparation method thereof. Background Art

[0002] The front electrode of a crystalline silicon solar cell generally consists of a main grid and a sub-grid. The sub-grid is responsible for charge collection and transmission. The charges are transmitted and converged to the main grid through the sub-grid, and the main grid is connected to a test electrode or a solder ribbon. Both the main grid and the sub-grid will block light and affect the light absorption of the cell. The MWT cell eliminates the front main grid of the cell by adopting a perforated structure to lead the front electrode to the back of the cell, reducing the light-shielding area of the front electrode, improving light absorption, and increasing the cell conversion efficiency.

[0003] However, existing MWT cells need to use a front sub-grid to achieve charge collection on the positive surface of the silicon substrate. The charges are transmitted through the front sub-grid and the inner electrode in the opening to the back surface of the silicon substrate, and the inner electrode in the opening only plays the role of transmitting charges and cannot collect charges from the silicon substrate. Therefore, it is necessary to design a cell structure that eliminates the front sub-grid to further improve the light absorption of the cell. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention discloses an MWT cell based on a passivated contact structure and a preparation method thereof. The MWT cell of the present invention realizes charge collection in the openings of the silicon substrate, without the need for a front sub-grid, which can further improve the light absorption of the MWT cell and increase the cell conversion efficiency.

[0005] To achieve the above object, the technical solution of the present invention provides an MWT cell based on a passivated contact structure, which includes: a P-type silicon substrate formed with through holes; a front passivation and antireflection layer formed on the front of the P-type silicon substrate; a back passivated contact layer formed on the back of the P-type silicon substrate; a back dielectric protection layer laminated and covering the back passivated contact layer; a cell positive electrode filled in the through holes and penetrating the front passivation and antireflection layer and the back dielectric protection layer; and a cell negative electrode formed on the back dielectric protection layer and penetrating the back dielectric protection layer to contact the back passivated contact layer; wherein, the cell positive electrode is an aluminum electrode, and an aluminum-doped P+ surface field is formed at the position where the P-type silicon substrate contacts the aluminum electrode.

[0006] Further, the front passivation and antireflection layer is a stack of one or more of a silicon nitride layer, a silicon oxynitride layer, or an aluminum oxide layer.

[0007] Further, the front passivation and antireflection layer includes a silicon nitride antireflection layer and an alumina passivation layer. Among them, the alumina passivation layer is laminated on the front of the P-type silicon substrate, and the silicon nitride antireflection layer is laminated on the alumina passivation layer.

[0008] Further, the back passivation contact layer includes a tunneling oxide layer and an N-type polysilicon layer. Among them, the tunneling oxide layer is laminated on the back of the P-type silicon substrate, and the N-type polysilicon layer is laminated on the tunneling oxide layer.

[0009] Further, the thickness of the tunneling oxide layer is 1 nm to 2 nm, and the thickness of the N-type polysilicon layer is 50 nm to 200 nm.

[0010] Further, the tunneling oxide layer is a tunneling silicon oxide layer.

[0011] Further, the back dielectric protection layer is a silicon nitride layer.

[0012] Further, the material of the battery negative electrode is one or more of silver, copper, nickel, and cobalt.

[0013] Further, the battery negative electrode is a silver electrode.

[0014] The technical solution of the present invention also provides a preparation method of an MWT battery based on a passivation contact structure, which includes the following steps: a) Texturing is performed on the front of the P-type silicon substrate, polishing is performed on the back, a front passivation and antireflection layer is deposited on the front of the P-type silicon substrate, and a back passivation contact layer is grown and deposited on the back of the P-type silicon substrate; b) Laser opening is performed on the back of the P-type silicon substrate to expose the surface of the P-type silicon substrate, and then a back dielectric protection layer is deposited on the back of the P-type silicon substrate; c) Through-type laser opening is performed on the sample obtained in step b), wherein the opening penetrates the front passivation and antireflection layer, the P-type silicon substrate, and the back dielectric protection layer; d) Aluminum paste is printed in the through-type opening area on the back of the P-type silicon substrate so that the aluminum paste fills the through-type opening, and then drying is performed; e) Burn-through silver paste is printed and dried on the back of the P-type silicon substrate, and an aluminum electrode and a silver electrode are formed through sintering and curing, wherein the sintering peak temperature is 750 °C to 850 °C, and the burn-through silver paste burns through the back dielectric protection layer to contact the back passivation contact layer.

[0015] Further, in step a), depositing the front passivation and antireflection layer on the front of the P-type silicon substrate includes sequentially depositing an alumina layer and a silicon nitride layer on the front of the P-type silicon substrate, and growing and depositing the back passivation contact layer on the back of the P-type silicon substrate includes growing a tunneling silicon oxide layer and an N-type polysilicon layer.

[0016] The MWT cell structure obtained by the preparation method of the present invention has a PN junction on the back surface of the cell. The through-hole does not penetrate the PN junction, and the inner wall of the hole does not need to be insulated. Moreover, the silicon on the inner wall of the hole forms an aluminum-doped surface field through the eutectic reaction during sintering, forms a good ohmic contact with the aluminum electrode, and extracts and collects holes.

[0017] The MWT cell of the present invention has the following beneficial technical effects:

[0018] 1. Fill the aluminum electrode in the holes of the P-type silicon substrate. Aluminum and silicon form an aluminum-doped P+ surface field through the eutectic reaction during sintering, realizing the extraction and collection of holes.

[0019] 2. No front side sub-grid is required, further improving the light absorption of the MWT cell and increasing the cell conversion efficiency.

[0020] 3. The back surface of the cell uses a tunneling oxide layer and an N-type polysilicon as a passivation contact structure, forming a back surface PN junction with the P-type silicon substrate, realizing the extraction and collection of electrons. Description of the Drawings

[0021] Figure 1 is a schematic diagram of local patterning and drilling on the front surface of the cell;

[0022] Figure 2 is a schematic diagram of the structure of the MWT cell of the present invention based on the passivation contact structure;

[0023] Figure 3 is a flow chart of the preparation method of the MWT cell of the present invention based on the passivation contact structure;

[0024] Figure 4 and Figure 5 are schematic diagrams of the structure during the preparation process of the MWT cell of the present invention based on the passivation contact structure.

[0025] Reference numerals in the figures: 1 - silicon nitride antireflection layer, 2 - aluminum oxide passivation layer, 3 - P-type silicon substrate, 4 - tunneling oxide layer, 5 - N-type polysilicon layer, 6 - back surface dielectric protection layer, 7 - cell negative electrode, 8 - cell positive electrode, 9 - aluminum-doped P+ surface field. Detailed Embodiments

[0026] The technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these embodiments.

[0027] It should be noted that the structures, proportions, sizes, etc. shown in the accompanying drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "front", "back", "middle", and "one" cited in this specification are only for the convenience of clear narration, and are not used to limit the scope for the implementation of the present invention. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope in which the present invention can be implemented.

[0028] Instead of using the traditional front gate line structure with a front boron diffusion layer or directly printing line-shaped aluminum gate lines, the present invention combines a P-type back junction battery and MWT technology. By performing local patterning and punching on the front of the battery, such as Figure 1 shown, the aluminum paste has a P-type doping effect. Then, the aluminum paste is locally printed on the back and passed through the openings, so as to collect current from the openings and conduct it to the back, thereby reducing the light-shielding area of the front electrode.

[0029] In the specific implementation manner, as Figure 1 shown, the MWT battery based on the passivation contact structure of the present invention includes: a P-type silicon substrate 3 formed with through holes; a front passivation and antireflection layer formed on the front of the P-type silicon substrate 3; a back passivation contact layer formed on the back of the P-type silicon substrate; a back dielectric protection layer 6 laminated and covering the back passivation contact layer; a battery positive electrode 8 filled in the openings and penetrating the front passivation and antireflection layer and the back dielectric protection layer; and a battery negative electrode 7 formed on the back dielectric protection layer 6 and penetrating the back dielectric protection layer 6 to contact the back passivation contact layer; wherein, the battery positive electrode 8 is an aluminum electrode, and an aluminum-doped P+ surface field 9 is formed at the position where the P-type silicon substrate 3 contacts the aluminum electrode 8.

[0030] In the above implementation manner of the present invention, the aluminum electrode 8 is filled in the openings on the P-type silicon substrate 3. After sintering, a eutectic reaction occurs between aluminum and silicon, generating an aluminum-doped P+ surface field 9. On the one hand, the P+ surface field 9 can reduce the aluminum-silicon contact resistance, and on the other hand, it can inhibit the carrier recombination in the aluminum-silicon contact area and help achieve the extraction and collection of holes.

[0031] Furthermore, the front passivation and antireflection layer can be a stack of one or several of a silicon nitride layer, a silicon oxynitride layer, or an aluminum oxide layer.

[0032] Specifically, the front passivation and antireflection layer may include a silicon nitride antireflection layer 1 and an aluminum oxide passivation layer 2. Among them, the aluminum oxide passivation layer 2 is stacked on the front surface of the P-type silicon substrate 3, and the silicon nitride antireflection layer 1 is stacked on the aluminum oxide passivation layer 2.

[0033] Further, the back passivation contact layer may include a tunneling oxide layer 4 and an N-type polysilicon layer 5. Among them, the tunneling oxide layer 4 is stacked on the back surface of the P-type silicon substrate 3, and the N-type polysilicon layer 5 is stacked on the tunneling oxide layer 4.

[0034] In the above embodiment, the tunneling oxide layer 4 and the N-type polysilicon 5 serve as a passivation contact structure. On the one hand, it inhibits the carrier recombination on the back surface of the P-type silicon substrate 3, and on the other hand, it realizes the extraction and collection of electrons. The P-type silicon substrate 3 and the N-type polysilicon 5 form a PN junction on the back surface of the battery, that is, a back junction structure.

[0035] Further, the tunneling oxide layer may be a tunneling silicon oxide layer.

[0036] Further, the thickness of the tunneling oxide layer is 1 nm to 2 nm, and the thickness of the N-type polysilicon layer is 50 nm to 200 nm.

[0037] Further, the back dielectric protection layer may be a silicon nitride layer.

[0038] Further, the material of the battery negative electrode may be one or more of silver, copper, nickel, and cobalt.

[0039] Further, the battery negative electrode may be a silver electrode.

[0040] In other embodiments of the present invention, a method for manufacturing an MWT battery based on a passivation contact structure is also provided. Refer to Figures 3 - 5 , which includes the following steps:

[0041] a) Texturing is performed on the front surface of the P-type silicon substrate 3, and polishing is performed on the back surface. A front passivation and antireflection layer is deposited on the front surface of the P-type silicon substrate, and a back passivation contact layer is grown and deposited on the back surface of the P-type silicon substrate 3. Among them, depositing the front passivation and antireflection layer on the front surface of the P-type silicon substrate 3 includes sequentially depositing an aluminum oxide layer 2 and a silicon nitride layer 1 on the front surface of the P-type silicon substrate 3, and growing and depositing the back passivation contact layer on the back surface of the P-type silicon substrate 3 includes growing a tunneling silicon oxide layer 4 and an N-type polysilicon layer 5.

[0042] b) Laser drilling is performed on the back surface of the P-type silicon substrate. Specifically, laser drilling is performed on the tunneling silicon oxide layer 4 and the N-type polysilicon layer 5 to expose the surface of the P-type silicon substrate 3, and then a back dielectric protection layer 6 is deposited on the back surface of the P-type silicon substrate, thereby obtaining the structure as shown in Figure 4 shown.

[0043] c) Perform through-hole laser drilling on the sample obtained in step b), as Figure 5 shown, the drilling penetrates the front surface passivation and antireflection layer (including alumina layer 2 and silicon nitride layer 1), P-type silicon substrate 3, and back surface dielectric protection layer 6;

[0044] d) Print aluminum paste in the through-hole area on the back surface of the P-type silicon substrate 3 so that the aluminum paste fills the through-hole, and then dry it;

[0045] e) Print and dry the burn-through silver paste on the back surface of the P-type silicon substrate 3, and then form aluminum electrodes and silver electrodes through sintering and curing. Among them, the sintering peak temperature is 750 °C to 850 °C. During the sintering process, the aluminum paste and the silicon substrate undergo a eutectic reaction to form an aluminum-doped surface field, and the burn-through silver paste burns through the back surface dielectric protection layer 6 to contact the back surface passivation contact layer (specifically, N-type polysilicon layer 5).

[0046] In a conventional MWT cell structure, the PN junction is formed on the front surface of the cell. The through-hole will penetrate the PN junction, and the inner wall of the hole is generally insulated, that is, a dielectric layer is deposited. Otherwise, the electrodes in the hole will contact both the P region and the N region of the PN junction at the same time, resulting in serious leakage of the cell.

[0047] For the MWT cell structure obtained by the preparation method of the present invention, the PN junction is on the back surface of the cell, the through-hole does not penetrate the PN junction, the inner wall of the hole does not need to be insulated, and the silicon on the inner wall of the hole forms an aluminum-doped surface field through the eutectic reaction during sintering, forming a good ohmic contact with the aluminum electrode to extract and collect holes.

[0048] The technical solution of the present invention has the following beneficial technical effects:

[0049] 1. Fill the aluminum electrode in the hole of the P-type silicon substrate. Aluminum and silicon form an aluminum-doped P+ surface field through eutectic reaction during sintering, realizing the extraction and collection of holes.

[0050] 2. No need for front side sub-gates, further improving the light absorption of the MWT cell and increasing the cell conversion efficiency.

[0051] 3. The back surface of the cell uses a tunneling oxide layer and N-type polysilicon as a passivation contact structure, forming a back surface PN junction with the P-type silicon substrate to realize the extraction and collection of electrons.

[0052] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. An MWT cell based on a passivated contact structure, characterized in that, Comprising: A P-type silicon substrate with a through-hole formed therein; A front passivation and antireflection layer formed on the front of the P-type silicon substrate; A back passivation contact layer formed on the back of the P-type silicon substrate; A back dielectric protection layer laminated and covering the back passivation contact layer; A battery positive electrode filled in the through-hole and penetrating the front passivation and antireflection layer and the back dielectric protection layer; And A battery negative electrode formed on the back dielectric protection layer and penetrating the back dielectric protection layer to contact the back passivation contact layer; wherein, The battery positive electrode is an aluminum electrode, and an aluminum-doped P+ surface field is formed at the position where the P-type silicon substrate contacts the aluminum electrode; wherein, The front passivation and antireflection layer is a stack of one or more of a silicon nitride layer, a silicon oxynitride layer, or an aluminum oxide layer; and The back passivation contact layer includes a tunneling oxide layer and an N-type polysilicon layer. Among them, the tunneling oxide layer is laminated on the back of the P-type silicon substrate, and the N-type polysilicon layer is laminated on the tunneling oxide layer.

2. The MWT cell based on the passivated contact structure according to claim 1, wherein The front passivation and antireflection layer includes a silicon nitride antireflection layer and an aluminum oxide passivation layer. Among them, the aluminum oxide passivation layer is laminated on the front of the P-type silicon substrate, and the silicon nitride antireflection layer is laminated on the aluminum oxide passivation layer.

3. The MWT cell based on the passivated contact structure according to claim 1, characterized in that, The thickness of the tunneling oxide layer is 1 nm to 2 nm, and the thickness of the N-type polysilicon layer is 50 nm to 200 nm.

4. The MWT cell based on the passivated contact structure according to claim 3, wherein, The tunneling oxide layer is a tunneling silicon oxide layer.

5. The MWT cell based on a passivated contact structure according to any one of claims 1-4, characterized in that, The back dielectric protection layer is a silicon nitride layer.

6. The MWT cell based on the passivated contact structure according to any one of claims 1-4, characterized in that, The battery negative electrode is a silver electrode.

7. A method for preparing a MWT cell based on a passivated contact structure, characterized in that, Including the following steps: a) Texturing the front of the P-type silicon substrate and polishing the back, depositing a front passivation and antireflection layer on the front of the P-type silicon substrate, and growing and depositing a back passivation contact layer on the back of the P-type silicon substrate; b) Laser drilling holes on the back of the P-type silicon substrate to expose the surface of the P-type silicon substrate, and then depositing a back dielectric protection layer on the back of the P-type silicon substrate; c) Performing through-hole laser drilling on the sample obtained in step b), wherein the through-hole penetrates the front passivation and antireflection layer, the P-type silicon substrate, and the back dielectric protection layer; d) Printing aluminum paste in the through-hole area on the back of the P-type silicon substrate so that the aluminum paste fills the through-hole, and then drying; e) Printing and drying a burn-through silver paste on the back of the P-type silicon substrate, and sintering and curing to form an aluminum electrode and a silver electrode, wherein the sintering peak temperature is 750 °C to 850 °C, and the burn-through silver paste burns through the back dielectric protection layer to contact the back passivation contact layer.

8. The preparation method according to claim 7, characterized in that, In step a), depositing the front passivation and antireflection layer on the front of the P-type silicon substrate includes sequentially depositing an aluminum oxide layer and a silicon nitride layer on the front of the P-type silicon substrate, and growing and depositing the back passivation contact layer on the back of the P-type silicon substrate includes growing a tunneling silicon oxide layer and an N-type polysilicon layer.

Images