Solar cell

Abstract

In a TOPCon type cell 1, a passivation film 5 is formed on a part of a p-type diffusion layer 3 other than a part on which a first electrode 4A is formed, and the passivation film 5 is made of a substance having a fusing point lower than that of the Al2O3.SOLUTION: The solar cell includes an n-type crystalline silicon substrate (2), a p-type diffusion layer (3) disposed on one side of the n-type crystalline silicon substrate (2), first electrodes (4A) disposed on the p-type diffusion layer (3), a passivation film (5) disposed on the p-type diffusion layer (3) except for portions where the first electrodes (6A) are disposed, and a first antireflection film (Bi2O3) disposed on the passivation film (5), wherein the passivation film (5) is made of B2O3, SiO2, and LA.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solar cell, and in particular to a TOPCon type solar cell in which the material of the passivation film arranged on the surface of the p-type diffusion layer other than the portion where the first electrode is arranged is Bi2O3-B2O3-SiO2 or B2O3-SiO2. [Background technology]

[0002] Renewable energy is attracting attention as a clean energy alternative to fossil fuels such as oil, coal, and natural gas because it can be used without depletion of energy resources and does not emit carbon dioxide, which causes global warming, when generating electricity.

[0003] Sunlight is one type of renewable energy, and the method of converting sunlight into electricity using solar cells is called photovoltaic power generation. Solar cell modules are used as the power generation source in solar power plants, and the solar cell sealed inside the solar cell module is a photoelectric conversion element that absorbs light energy and converts it into electrical energy, and is manufactured from various semiconductor materials. This is the source of electricity generation.

[0004] There is a demand for reducing the cost of generating electricity from solar power, that is, for lowering the cost, increasing the efficiency, and extending the lifespan of solar cells. This patent relates to reducing the cost of solar cells, especially crystalline silicon solar cells.

[0005] One type of crystalline silicon solar cell is one in which a p-type semiconductor, made by doping silicon (Si) with boron (B), is joined to an n-type semiconductor, made by doping silicon (Si) with phosphorus (P). A depletion layer is formed at the junction where the p-type and n-type semiconductors are joined, and an internal electric field is generated in the depletion layer. When such a crystalline silicon solar cell receives sunlight, electrons and holes are generated by the light energy. The generated electrons drift to the n-type semiconductor region, and the generated holes drift to the p-type semiconductor region, supplying power to an external circuit connected to the n-type and p-type semiconductors.

[0006] Based on the above-described operation of the crystalline silicon solar cell, various types of crystalline silicon solar cells are being developed (see Non-Patent Document 1).

[0007] For example, Patent Document 1 states that implanting fluorine into the tunnel oxide film of a TOPCon type cell reduces the density of interface defects in the tunnel oxide film, thereby improving the performance of the solar cell.

[0008] For example, Patent Document 2 claims that by controlling the refractive index of the various films that make up a TOPCon type cell, a solar cell with low reflectance and therefore high performance can be produced. In addition, this patent claims that the material of the passivation film arranged on the surface of the p-type diffusion layer other than the part where the first electrode is arranged, which constitutes the key point of the structure of this patent, is either aluminum oxide, titanium oxide, gallium oxide, or hafnium oxide, but since the material is different from that of this patent, there is no conflict.

[0009] For example, Non-Patent Document 2 shows that a TiOx film functions as both a passivation film for holes and a passivation film for electrons. This document also lists an example of Al2O3 as the front-side passivation film of a TOPCon cell, which is the basis for the present invention that Al2O3 is generally used as the front-side passivation film of a TOPCon cell. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent Publication No. 2023-083131 [Patent Document 2] Patent Publication No. 2023-040981 [Non-patent literature]

[0011] [Non-Patent Document 1] Current status and prospects of crystalline silicon solar cells, AIST, Japan Society of Applied Physics (2023) [Non-patent document 2] Development of a new carrier-selective passivating contact for crystalline silicon solar cells, AIST, Applied Physics (Monthly), Vol. 90, No. 6 (2021), p. 346-350 [Non-patent document 3] Glass frit glass paste, AGC Inc., product catalog [Non-patent document 4] Structure of vapor-grown SiO2-B2O3 thin films and their thermal changes, Chubu Institute of Technology, Applied Physics (Monthly), Vol. 41, No. 7 (1973), pp. 517-521 [Non-Patent Document 5] Properties of SiO▲2▼-Bi▲2▼O▲3▼-Na▲2▼O Glasses, Journal of the Ceramic Industry Association 78(5)(1970), 165-171 [Non-patent document 6] Thermal properties of B▲2▼O▲3▼-Bi▲2▼O▲3▼-ZnO low-melting glass, Nagaoka University of Technology, (2001) [Non-Patent Document 7] Integrated Device Engineering (14), Ritsumeikan University, (2007) [Non-patent document 8] Electrical Conduction and Dielectric Properties of Bi2O3-B2O3 Glass, Journal of the Ceramic Industry Association 82(10)(1974), 538-545 [Non-Patent Document 9] Thermal properties of borosilicate glass, DURAN-GLASS, PR materials [Non-Patent Document 10] Ceramics Factory Alumina, KDA-CORPORATION, PR materials [Non-Patent Document 11] α-Alumina, High Purity Chemical Laboratory, PR materials Summary of the Invention [Problem to be solved by the invention]

[0012] In TOPCon (Tunnel Oxide Passivated Contact) cells, Al2O3 is generally used as a passivation film on the surface of the p-type diffusion layer other than where the first electrode is located. However, because Al2O3 has a high melting point (2072°C), extremely high temperatures are required to achieve fire-through of the first electrode on the surface of the p-type diffusion layer. High fire-through temperatures increase cell manufacturing costs and reduce cell performance due to thermal damage to the n-type crystalline silicon substrate. The present invention aims to lower the fire-through temperature of the first electrode on the surface of the p-type diffusion layer of a TOPCon cell by using Bi2O3-B2O3-SiO2 or B2O3-SiO2, which have a lower melting point than Al2O3, as a passivation film arranged on the surface of the p-type diffusion layer of the TOPCon cell except for the part where the first electrode is arranged, thereby reducing the cell manufacturing cost and reducing the degradation of cell performance due to thermal damage to the n-type crystalline silicon substrate. For reference, Table 1 shows a comparison of the dielectric constant, resistivity, and melting point of Al2O3 for Bi2O3-B2O3-SiO2 and B2O3-SiO2. (Reference: Non-patent documents 5, 6, 7, 8, 9, 10, 11) [Table 1] [Means for solving the problem]

[0013] The present invention has been made to solve the above problems and comprises the following cell structure: 1) an n-type crystalline silicon substrate; a p-type diffusion layer disposed on one surface of the n-type crystalline silicon; a first electrode disposed on a surface of the p-type diffusion layer; a passivation film disposed on a surface of the p-type diffusion layer other than the portion where the first electrode is disposed; a first anti-reflection film disposed on the surface of the passivation film; a tunnel oxide film disposed on a surface opposite to the one surface of the n-type crystalline silicon substrate; an n-type diffusion layer disposed on a surface of the tunnel oxide film; a second electrode disposed on a surface of the n-type diffusion layer; a second anti-reflection film disposed on a surface of the n-type diffusion layer other than a portion where the second electrode is disposed, The material of the passivation film disposed on the surface of the p-type diffusion layer other than the portion where the first electrode is disposed is Bi2O3-B2O3-SiO2. 2) The material of the passivation film 5 disposed on the surface of the p-type diffusion layer of 1) other than the portion where the first electrode is disposed is B2O3-SiO2. [Effects of the Invention]

[0014] According to the present invention, the fire-through temperature of the first electrode on the surface of the p-type diffusion layer of a TOPCon cell can be reduced, thereby reducing cell manufacturing costs and reducing degradation of cell performance due to thermal damage to the substrate. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view (schematic diagram) of a TOPCon type cell of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] A TOPCon solar cell according to an embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view (schematic diagram) of a TOPCon solar cell 1 according to this embodiment. As shown in FIG. 1, a TOPCon solar cell has a p-type diffusion layer 3 disposed on one surface of an n-type crystalline silicon substrate 2. A first electrode 4A and a passivation film 5 are disposed on the surface of the p-type diffusion layer 3, except for the portion where the first electrode 4A is disposed. A first anti-reflection film 6A is disposed on the surface of the passivation film 5. A tunnel oxide film 7 is disposed on the surface of the n-type crystalline silicon substrate 2 opposite the surface where the p-type diffusion layer 3 is disposed. An n-type diffusion layer 8 is disposed on the surface of the tunnel oxide film 7. A second electrode 4B and a second anti-reflection film 6B are disposed on the surface of the n-type diffusion layer 8, except for the portion where the second electrode 4B is disposed.

[0018] The n-type crystalline silicon substrate 2 is polycrystalline silicon or single crystalline silicon to which a pentavalent element is added. From the viewpoint of cost, the pentavalent element to be added is preferably phosphorus.

[0019] The p-type diffusion layer 3 is a layer in which a trivalent element is added to silicon and which has a hole concentration gradient in the thickness direction. From the viewpoint of cost, the added trivalent element is preferably boron.

[0020] The first electrode 4A and the second electrode 4B are made of a conductive material, such as silver, and the holes and electrons generated in the TOPCon solar cell 1 are extracted as a current by the first electrode 4A and the second electrode 4B.

[0021] The passivation film 5 terminates defects at the interface on the passivation film 5 side of the p-type diffusion layer 3 and suppresses recombination of holes and electrons. In the present invention, the passivation film 5 is made of Bi2O3-B2O3-SiO2 or B2O3-SiO2.

[0022] The first antireflection film 6A and the second antireflection film 6B suppress reflection of sunlight. The first antireflection film 6A and the second antireflection film 6B are films made of a known material used as a conventional antireflection film, such as silicon nitride.

[0023] The tunnel oxide film 7 is made of extremely thin SiO2 (for example, with a thickness of 0.5 to several nm). The tunnel oxide film 7 has a passivation function of terminating defects at the interface of the n-type diffusion layer 8 on the tunnel oxide film 7 side and suppressing the recombination of holes and electrons. Furthermore, when an electric field is applied to the tunnel oxide film 7, electrons generated in the n-type crystalline silicon substrate 2 pass through the tunnel oxide film 7 and reach the second electrode 4B.

[0024] The n-type diffusion layer 8 is a layer in which a pentavalent element is added to silicon and has a concentration gradient of electrons in the thickness direction. From the viewpoint of cost, the pentavalent element is preferably phosphorus. [Industrial Applicability]

[0025] The present invention can be used in the photovoltaic power generation related industry, particularly in the solar cell manufacturing industry. [Explanation of symbols] 1 Topcon solar cell 2. n-type crystalline silicon substrate 3 p-type diffusion layer 4A 1st electrode 4B 2nd electrode 5 Passivation film 6A 1st anti-reflection coating 6B 2nd anti-reflection coating 7 Tunnel oxide 8 n-type diffusion layer

Claims

1. an n-type crystalline silicon substrate; a p-type diffusion layer disposed on one surface of the n-type crystalline silicon; a first electrode disposed on a surface of the p-type diffusion layer; a passivation film disposed on a surface of the p-type diffusion layer other than the portion where the first electrode is disposed; a first anti-reflection film disposed on the surface of the passivation film; a tunnel oxide film disposed on a surface opposite to the one surface of the n-type crystalline silicon substrate; an n-type diffusion layer disposed on a surface of the tunnel oxide film; a second electrode disposed on a surface of the n-type diffusion layer; a second anti-reflection film disposed on a surface of the n-type diffusion layer other than a portion where the second electrode is disposed, The material of the passivation film disposed on the surface of the p-type diffusion layer other than the portion where the first electrode is disposed is Bi. ２ O ３ -B ２ O ３ -SiO ２ That is, a solar cell.

2. 2. The method of claim 1, wherein the material of the passivation film disposed on the surface of the p-type diffusion layer other than the portion where the first electrode is disposed is B. ２ O ３ -SiO ２ That is, a solar cell.

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