Method for manufacturing back contact type solar cell unit

Abstract

Provided is a method for manufacturing a back contact type solar cell unit, which can be implemented with a smaller number of steps than conventional methods. The present invention is a method for manufacturing a back contact type solar cell unit, which sequentially includes: a step (A) of forming an oxide film (20) on the back surface of a crystalline silicon substrate (10); a step (B) of forming a silicon thin film layer (30A) on the exposed surface of the oxide film (20); a step (C) of locally forming an n + layer (40) on the silicon thin film layer (30A) by ion implantation using a mechanical hard mask and activation annealing; a step (D) of forming a passivation film (50) on both surfaces of the crystalline silicon substrate (10) obtained in the step (C) and having the oxide film (20), the silicon thin film layer (30B), and the n + layer (40); and a step (E) of locally removing the passivation film (50) formed on the back surface side of the crystalline silicon substrate (10) in a region not covering the n + layer (40), and forming one or more aluminum electrodes (60B) on the exposed silicon thin film layer (30B).

Description

TECHNICAL FIELD

[0001] The present application relates to a manufacturing method of a back contact type solar cell unit. BACKGROUND

[0002] In recent years, as a crystalline solar cell with high conversion efficiency, a structure unit called an interdigitated back contact (IBC) solar cell, which is provided with n + diffusion layer and a p + diffusion layer on the surface thereof. In addition, a structure in which an oxide film or a nitride film is used to cover both surfaces of the crystalline silicon substrate of the solar cell unit in order to improve the characteristics and reduce power loss in power generation is being studied.

[0003] In a general silicon solar cell structure, an electrode on the light-receiving surface (front surface) side and an electrode on the back surface side are provided. When an electrode is thus formed on the light-receiving surface (front surface) side, it is possible that the sunlight is reflected or absorbed on the electrode, and thus the amount of incident sunlight corresponding to the electrode area is reduced. On the other hand, in a back contact type solar cell, by collecting the wiring on the back surface side, the wiring resistance is reduced, not only the power loss is reduced, but also it is not necessary to provide an electrode on the light-receiving surface, and thus the light-receiving surface is enlarged, and more light can be taken in. In addition, as described above, by forming a passivation film (for example, an oxide film) that reduces power loss on the back surface of the crystalline silicon substrate of the solar cell unit, and forming a polycrystalline semiconductor layer thereon, it is possible to take into account the passivation effect and the effect as an electrode and improve the power generation efficiency.

[0004] Regarding such a back contact type solar cell, a solar cell is disclosed in which a concave-convex shape is formed on the surface of the light-receiving surface of the crystalline silicon substrate by texturing etching, peeling of a resin, and a dielectric layer is formed in contact with the entire surface of the crystalline silicon substrate, and further an insulating layer is formed, and in order to form an n + layer and a p + layer on the back surface of the crystalline silicon substrate, patterning and etching are repeatedly performed, thereby reducing short circuit between the p electrode and the n electrode (for example, Patent Literature 1).

[0005] However, in the technology of Patent Literature 1, in order to form an n + layer and a p + layer, patterning and etching need to be repeatedly performed, and the manufacturing process is more. In addition, since the risk of residual adhesive caused by printing, curing, and peeling of the resin is high, it takes time to perform cleaning treatment of the residue. Furthermore, in order to form an n + layer and a p +Layer electrodes are formed by vapor deposition or sputtering, but these methods also require a long processing time.

[0006] Furthermore, to improve the efficiency of converting sunlight into electricity, a so-called passivated contact solar cell structure is being developed. This structure uses a passivation film to cover both sides of a semiconductor substrate, extracting electricity through the passivation film, thereby achieving higher power generation efficiency. However, in order to achieve a structure that completely passivates both sides and extracts electricity, a more complex process is required compared to existing back-contact solar cells (e.g., Non-Patent Document 1).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-171095

[0010] Non-patent literature

[0011] Non-patent document 1: “Laser contact openings for local poly-Si-metal contacts enabling 26.1% efficient POLO-IBC solar cells”, Felix Hasse, Solar Energy Materials and Solar Cells 186 (2018) 184-193. Summary of the Invention

[0012] (1) Technical issues to be solved

[0013] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for manufacturing a back-contact solar cell that can be implemented with fewer steps than conventional manufacturing methods.

[0014] (2) Technical solution

[0015] To achieve the above objectives, the inventors conducted intensive research and discovered that a manufacturing method utilizing ion implantation using a mechanical hard mask and having specific steps can produce back-contact solar cells with fewer steps than conventional manufacturing methods. Based on this finding, the inventors conducted further intensive research and completed the present invention.

[0016] That is, the present invention relates to the following method for manufacturing a back-contact solar cell.

[0017] 1. A manufacturing method of a back contact type solar cell unit, characterized by sequentially having:

[0018] a step (A) of forming an oxide film on a back surface of a crystalline silicon substrate;

[0019] a step (B) of forming a silicon thin film layer on an exposed surface of the oxide film;

[0020] a step (C) of locally forming an n + layer on the silicon thin film layer by an ion implantation method using a mechanical hard mask and activation annealing;

[0021] a step (D) of forming a passivation film on both surfaces of the crystalline silicon substrate having the oxide film, the silicon thin film layer, and the n + layer obtained through the step (C); and

[0022] a step (E) of removing a part of a region of the passivation film formed on the back surface side of the crystalline silicon substrate that does not cover the n + layer, and forming one or more aluminum electrodes on the exposed silicon thin film layer.

[0023] 2. The manufacturing method according to the above item 1, characterized in that,

[0024] the step (D) is followed by a step (E') of removing a part of a region of the passivation film formed on the back surface side of the crystalline silicon substrate that covers the crystalline silicon substrate via the oxide film and the n + layer, and forming one or more silver electrodes on the exposed n + layer,

[0025] the step (E) and the step (E') are different in order.

[0026] 3. The manufacturing method according to the above item 2, characterized in that,

[0027] in the step (E'), a copper electrode or an aluminum alloy electrode is formed instead of the silver electrode.

[0028] 4. The manufacturing method according to any one of the above items 1 to 3, characterized in that,

[0029] the aluminum electrode is formed by sintering a coating film of an aluminum paste containing 2 to 20 parts by mass of an organic vehicle and 0.15 to 15 parts by mass of a glass frit with respect to 100 parts by mass of aluminum powder at 650 to 900°C.

[0030] 5. The manufacturing method according to the above item 2, characterized in that, ​

[0031] The aluminum electrode and the silver electrode are formed in an alternate arrangement on the back surface side of the crystalline silicon substrate.

[0032] (III) Advantages

[0033] The manufacturing method of the back contact type solar cell unit according to the present application does not need to repeatedly perform patterning and etching in order to form n + layers and p + layers, and can manufacture the back contact type solar cell unit with a smaller number of processes than the conventional manufacturing method. Therefore, it has a great advantage in terms of manufacturing cost of the back contact type solar cell unit. In addition, since the n + layers are formed by using the ion implantation method using a mechanical hard mask and the activation annealing, an insulating layer is provided between the n + layers and the p + layers, and an effect of suppressing a leakage current (loss of electric power) is obtained compared to the conventional manufacturing method. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1-1 is a explanatory diagram of the manufacturing method of the back contact type solar cell unit according to the present application (first half).

[0035] Figure 1-2 is a explanatory diagram of the manufacturing method of the back contact type solar cell unit according to the present application (second half).

[0036] Figure 2 is a schematic diagram of the back contact type solar cell unit of the embodiment.

[0037] Figure 3 is an enlarged view of the schematic diagram of the back contact type solar cell unit of the embodiment.

[0038] Figure 4 is a explanatory diagram of the layer structure in the back contact type solar cell unit of the comparative example.

[0039] Figure 5 is a schematic diagram showing an example of an ion implantation device applicable to the manufacturing method of the back contact type solar cell unit according to the present application. DETAILED DESCRIPTION

[0040] The manufacturing method of the back contact type solar cell unit according to the present application is characterized by sequentially having:

[0041] a step (A) of forming an oxide film on the back surface of a crystalline silicon substrate;

[0042] a step (B) of forming a silicon thin film layer on the exposed surface of the oxide film;

[0043] An n-type silicon film is locally formed on the silicon thin film layer by ion implantation using a mechanical hard mask and activation annealing. + Layer process (C);

[0044] In the step (C), the oxide film, the silicon thin film layer and the n + Step (D) of forming a passivation film on both sides of the crystalline silicon substrate; and

[0045] The portion of the passivation film formed on the back side of the crystalline silicon substrate that does not cover the n + The process (E) is to remove a portion of the region of the silicon thin film layer and form one or more aluminum electrodes on the exposed silicon thin film layer.

[0046] According to the method for manufacturing a back-contact solar cell of the present invention having the above-mentioned characteristics, it is not necessary to form n + Layer and p + By repeating patterning and etching, it is possible to manufacture a back-contact solar cell with fewer steps than conventional manufacturing methods. Therefore, it has a significant advantage in terms of manufacturing cost of back-contact solar cells. In addition, since the n + layer, so in n + Layer and p + An insulating layer is provided between the layers, and compared with conventional manufacturing methods, an effect of suppressing leakage current (power loss) is also achieved.

[0047] Hereinafter, each step of the method for manufacturing a back-contact solar cell of the present invention (the manufacturing method of the present invention) will be described by way of example with reference to the drawings.

[0048] Process (A)

[0049] Step (A) is to form a crystalline silicon substrate 10 ( Figure 1-1 (a)) is formed on the back side of an oxide film 20 ( Figure 1-1 (b)).

[0050] The crystalline silicon substrate used can be any of the well-known crystalline silicon substrates used in back-contact solar cells, without particular limitation. Furthermore, both n-type and p-type silicon semiconductor substrates can be used, and the appropriate choice can be made based on the desired solar cell application and specifications. In this specification, one side of a crystalline silicon substrate is referred to as the primary surface (the light-receiving surface when used as a cell), and the other side is referred to as the back surface.

[0051] In addition, for crystalline silicon substrates, wet etching with an alkali solution or the like can be performed in order to remove the damaged layer on the cut surface and form a texture in advance.

[0052] The thickness of the crystalline silicon substrate is not particularly limited, but may be, for example, 100 to 250 μm, preferably 150 to 200 μm.

[0053] A known technique can be used to form an oxide film on the back surface of the crystalline silicon substrate.

[0054] Specifically, there are a technique for forming an oxide film by heating a crystalline silicon substrate, a technique for forming an oxide film by immersing a crystalline silicon substrate in nitric acid, and a technique for forming an oxide film by immersing a crystalline silicon substrate in ozone water.

[0055] The thickness of the oxide film is not limited, but is preferably 0.5 to 4 nm, more preferably 1.0 to 2.0 nm. In the manufacturing method of the present invention, the oxide film can be formed on the back surface (the entire back surface) of the crystalline silicon substrate, and can also be formed on the other surface (the entire main surface) of the crystalline silicon substrate as needed ( Figure 1-1 (b) shows a method in which an oxide film 20 is formed on the entire back surface and main surface (both surfaces) of the crystalline silicon substrate 10. In this case, the effect of suppressing leakage current when the solar cell is used can be further improved.

[0056] Process (B)

[0057] Step (B) forms a silicon thin film layer 30A on the exposed surface of the oxide film ( Figure 1-1 (c)). In addition, the oxide film refers to an oxide film formed on the back surface of the crystalline silicon substrate which must be provided in step (A).

[0058] A known technique can be used to form a silicon thin film layer on the exposed surface of the oxide film formed on the back surface of the crystalline silicon substrate.

[0059] Specific examples include plasma CVD, atmospheric pressure CVD for semiconductors (APCVD), low pressure CVD for semiconductors (LPCVD), sputtering, etc. The thickness of the silicon thin film layer is not limited, but is generally about 10 to 150 nm.

[0060] Process (C)

[0061] Step (C) is to locally form an n-type silicon film on the silicon thin film layer 30A by ion implantation using a mechanical hard mask and activation annealing. + Layer 40( Figure 1-1 (d)). Figure 1-1 In (d), the 40 part forms n + The portion of the layer that maintains 30A is not formed with n + layer part.

[0062] Formation +The ion implantation method of the layer can use a known technique. In the manufacturing method of the present invention, the ion implantation method is particularly used, which uses a mechanical hard mask. The mechanical hard mask is used to implant the n + The layer is locally provided on the silicon thin film layer. As a mechanical hard mask, for example, a mechanical hard mask in which openings with a width of 700 μm and closed portions with a width of 300 μm are alternately arranged can be cited. In this case, the n layers with a width of 700 μm are alternately arranged. + The layer 40 is left with a gap of 300 μm (equivalent to no n + A known type of mechanical hard mask can be used, and examples of the material include carbon, silicon, copper, and quartz.

[0063] Ion implantation, for example, involves using PH3 (phosphine) as a raw material, generating a plasma, ionizing it, and then irradiating the silicon thin film layer with an ion beam. A mechanical hard mask is used to separate areas that are irradiated with the ion beam from areas that are not. The ion implantation apparatus used to perform the ion implantation method can be a well-known mass-separation ion implantation apparatus or a non-mass-separation ion implantation apparatus.

[0064] Figure 5 A schematic diagram of a non-mass separation type ion implantation apparatus is shown. The overview is as follows.

[0065] Figure 5 The ion implantation apparatus 1000 shown includes a vacuum chamber 1001 (lower vacuum chamber), a vacuum chamber 1002 (upper vacuum chamber), an insulating member 1003, a mounting table 1004, and a gas supply source 1005. The ion implantation apparatus 1000 also includes an RF introduction coil 1100, a permanent magnet 1101, an RF introduction window (quartz window) 1102, an electrode 1200, an electrode 1201, a DC power supply 1300, and an AC power supply 1301.

[0066] The diameter of the vacuum tank 1002 is smaller than that of the vacuum tank 1001, and it is arranged on the vacuum tank 1001 via an insulating component 1003. The vacuum tank 1001 and the vacuum tank 1002 can maintain a reduced pressure state using a vacuum exhaust unit such as a turbomolecular pump. The mounting table 1004 is arranged in the vacuum tank 1001. The mounting table 1004 can support the substrate S1. A heating mechanism for heating the substrate S1 can be provided in the mounting table 1004. The substrate S1 is a crystalline silicon substrate used in the manufacturing method of the present invention (having an oxide film and a silicon thin film layer on the back side, and a part of the silicon thin film layer is the object of ion implantation). In addition, a gas for ion implantation is introduced into the vacuum tank 1002 using a gas supply source 1005.

[0067] The RF introduction coil 1100 is arranged on the RF introduction window 1102 so as to surround the permanent magnet 1101. The permanent magnet 1101 has a ring shape. The RF introduction coil 1100 has a coil shape. The diameter of the RF introduction coil 1100 can be appropriately set according to the size of the substrate S1. When a gas for ion implantation is introduced into the vacuum chamber 1002 and a predetermined power is supplied from the AC power source 1301 to the RF introduction coil 1100, plasma 1010 is generated in the vacuum chamber 1002 by ICP (Inductively Coupled Plasma) discharge.

[0068] The electrode 1200 is an electrode having a plurality of openings (for example, a mesh electrode) and is supported by the insulating member 1003. The potential of the electrode 1200 is a floating potential. Thus, stable plasma 1010 is generated in a space surrounded by the vacuum chamber 1002 and the electrode 1200.

[0069] An electrode (for example, a mesh electrode) 1201 having a plurality of openings is arranged below the electrode 1200. The electrode 1201 opposes the substrate S1. A DC power source 1300 is connected between the electrode 1201 and the RF introduction coil 1100, and a negative potential (acceleration voltage) is applied to the electrode 1201. Thus, positive ions in the plasma 1010 are extracted from the plasma 1010 by the electrode 1201.

[0070] The extracted positive ions can reach the substrate S1 through the mesh electrodes 1200 and 1201. In the ion implantation apparatus 1000, the acceleration voltage of the positive ions can be set in a range of, for example, 1 kV or more and 30 kV or less. In addition, a bias power source capable of adjusting the acceleration voltage can be connected to the stage 1004.

[0071] A gas containing an impurity element (n-type impurity element) to be implanted into the substrate S1 is introduced into the vacuum chamber 1002. The plasma 1010 is formed in the vacuum chamber 1002 using the gas, and n-type impurity ions in the plasma 1010 are implanted into the substrate S1. The n-type impurity ions are, for example, at least one of P, PX + , PX 2+ , PX 3+ , and the like. Here, "X" is any one of hydrogen and halogen (F, Cl).

[0072] In this embodiment, the method for forming the plasma 1010 is not limited to the ICP method, and may be an electron cyclotron resonance plasma method, a helicon wave plasma method, etc. In addition, when injecting n-type impurity ions into the substrate S1, a gas containing hydrogen (e.g., PH3, BH2, etc.) may be added to the gas used for ion injection from the perspective of repairing lattice defects of the substrate S1.

[0073] The conditions for the activation annealing are not limited, but the temperature is preferably 600-1000°C, more preferably 700-900°C. Regarding the atmosphere during the annealing, it is preferred that there be a step of adjusting the oxygen concentration to 1-100%, more preferably a step of adjusting the oxygen concentration to 5-50%. Furthermore, due to this activation annealing, the silicon thin film layer 30A (particularly an amorphous silicon thin film layer or a microcrystalline silicon thin film layer) is transformed into a polycrystalline silicon thin film layer 30B. Therefore, the silicon thin film layer in the subsequent steps refers to the polycrystalline silicon thin film layer 30B.

[0074] n + The thickness of the layer is not particularly limited, but is preferably 0.1 to 2 μm, more preferably 0.3 to 1 μm.

[0075] Process (D)

[0076] Step (D) is to prepare the substrate having the oxide film 20, the silicon thin film layer (polysilicon thin film layer; the same applies hereinafter) 30B and the n + Passivation films 50 ( Figure 1-2 That is, on the back side of the crystalline silicon substrate, the n + Layer 40 part, in n + A passivation film 50 is formed on the layer 40. + A passivation film is formed on the silicon thin film layer 30B. Also, on the main surface side of the crystalline silicon substrate, a passivation film is formed on the surface of the crystalline silicon substrate directly or via an arbitrarily formed oxide film.

[0077] The passivation film is not particularly limited as long as it can have a passivation effect based on fixed charge in the solar cell of the present invention. Specifically, it can be one or more selected from the group consisting of a silicon nitride film, a silicon oxide film, an aluminum oxide film, an amorphous silicon film, and a microcrystalline silicon film. These films may be a single layer or may be a stack of multiple layers.

[0078] The method of forming the passivation film is not particularly limited, and various chemical vapor deposition methods such as plasma CVD method, semiconductor atmospheric pressure CVD method, ALD method (atomic layer deposition method), or sputtering method can be exemplified. More specifically, a method of forming a passivation film composed of aluminum oxide using ALD method with trimethylaluminum as a raw material can be exemplified.

[0079] The thickness of the passivation film is not particularly limited, and is preferably 5 to 200 nm, and more preferably 10 to 80 nm, from the viewpoint of passivation effect and operability of the passivation film removal process described later. In addition, it is preferable that an antireflection film (not shown) be further provided on the surface of the passivation film, and the antireflection film is obtained, for example, by forming a silicon nitride film on the surface of the passivation film in a silane gas and ammonia gas atmosphere using plasma CVD method.

[0080] Process (E)

[0081] Process (E) removes a part of the passivation film formed on the back surface side of the crystalline silicon substrate, which is not covered with the n + layer (g), and forms one or more aluminum electrodes 60B (i) on the exposed silicon thin film layer 30B. Figure 1-2 Here, it is preferable that the aluminum electrodes be provided one by one for each exposed part of the silicon thin film layer when the passivation film is removed at multiple places. Figure 1-2

[0082] The part of the passivation film to be removed is a part of the region of the passivation film formed on the back surface side of the crystalline silicon substrate, which is not covered with the n + layer. The method for removing the passivation film is not particularly limited, and etching paste and a method of irradiating a laser beam can be exemplified.

[0083] The method of removing the passivation film and forming the aluminum electrode on the exposed silicon thin film layer can widely adopt a known method, and is not particularly limited. Specifically, a method of providing aluminum paste 60A on the exposed silicon thin film layer by an appropriate method such as coating and performing sintering can be exemplified (h) indicates a state before sintering, Figure 1-2 (i) indicates a state after sintering). With this method, an aluminum-silicon alloy layer 60C and a BSF layer 60D are formed on the silicon thin film layer 30B (i). Figure 1-2 In (i), the aluminum paste is sintered to form an aluminum-silicon alloy layer, a BSF layer on the silicon thin film layer, and to become an aluminum electrode 60B. Figure 1-2 Figure 1-2

[0084] ​​​The sintering temperature of the aluminum paste is not particularly limited, but is preferably 650 to 900° C. The composition of the aluminum paste is not particularly limited, but is preferably a paste containing 2 to 20 parts by mass of an organic vehicle including a resin or an organic solvent and 0.15 to 15 parts by mass of glass frit per 100 parts by mass of aluminum powder.

[0085] Furthermore, the aluminum powder may be high-purity aluminum or an aluminum alloy, and preferably an aluminum-silicon alloy or an aluminum-silicon-magnesium alloy.

[0086] Regarding the shape and size of the aluminum electrode, a width of 40 μm to 200 μm is preferred to cover the exposed silicon thin film layer. To reduce the electrode's resistance, the higher the height, the better. The larger the aspect ratio (width / height) of the printed Al line, the better.

[0087] Process (E')

[0088] Step (E') is to, after the above step (D), remove the passivation film formed on the back side of the crystalline silicon substrate through the oxide film and the n + The layer covering the region of the crystalline silicon substrate is partially removed, and the exposed n + The process of forming one or more silver electrodes 70B on the layer 40 is different from the process (E) and the process (E'). + Silver electrodes are provided one by one on the exposed portions of the layer. In addition, as described above, after carrying out step (D), either step (E) or step (E') may be carried out first.

[0089] The method for removing the passivation film is not particularly limited. For example, a method can be exemplified by applying a paste to which a component for removing the passivation film is added (so-called fire-through type silver paste) to the silver paste 70A and sintering it at a temperature of 550 to 900° C. to remove the passivation film directly below the paste and form a silver electrode ( Figure 1-2 (h) → Figure 1-2 (i) method), a method of applying etching paste, a method of irradiating a laser beam, etc.

[0090] When the above-mentioned fire-through type silver paste is used, for example, Figure 1-2 As shown in (h), after coating the silver paste 70A on the surface of the passivation film, the silver paste is sintered in the range of 550 to 900°C. Figure 1-2 As shown in (i), the passivation film directly below the coating can be removed and the exposed n + A silver electrode 70B is formed on the layer.

[0091] The composition of the silver paste is not particularly limited, and for example, a paste containing 0.1 to 10 parts by mass of a glass frit and 3 to 15 parts by mass of an organic vehicle containing a resin and / or an organic solvent, with respect to 100 parts by mass of a silver powder, is preferred. The silver powder can be flaky or spherical, and a spherical powder is preferably used. Furthermore, a silver electrode is formed in this process, but a copper electrode or an aluminum alloy electrode can also be formed instead of the silver electrode (the term "aluminum electrode" is distinguished from "aluminum alloy electrode" in the present specification, which is different from the aluminum electrode formed in process (E)). Thus, techniques known in the technical field of solar cell units can be widely used in the present application.

[0092] Regarding the shape and size of the silver electrode, a linear line of 50 to 130 μm is printed in a manner to become an aluminum electrode and a comb-toothed configuration.

[0093] The embodiments of the present application have been described above, but the present application is of course not limited to these examples, and can be implemented in various ways without departing from the gist of the present application.

[0094]

EXAMPLE

[0095] The embodiments of the present application will be described more specifically based on examples, but the present application is not limited thereto.

[0096] (Example 1)

[0097] A crystalline silicon substrate (substrate: 6 inches, thickness 200 μm) composed of a p-type single-crystal silicon was prepared. Figure 1-1 The surface of the crystalline silicon substrate was subjected to wet etching using potassium hydroxide in order to remove a damage layer of a cut surface of the crystalline silicon substrate and form a texture.

[0098] Process (A)

[0099] The crystalline silicon substrate was immersed in a nitric acid solution, thereby forming a silicon oxide film (passivation film) on both surfaces. Figure 1-1

[0100] Process (B)

[0101] A 200 nm silicon thin film layer (amorphous silicon thin film layer) was formed on the back surface of the crystalline silicon substrate (with the oxide film) by a CVD method. Figure 1-1

[0102] Process (C)

[0103] Next, P element was injected into the silicon thin film layer by an ion implantation method using PH3 (phosphine) as a raw material, in which plasma was generated by irradiating the surface of the silicon thin film layer with ionized raw material after plasma. Figure 1-1 ​​(d)), and then activation annealing is performed to locally form n-type layers with a thickness of about 0.1 to 1 μm. + layer( Figure 1-1 (e)). Activation annealing also has the effect of polycrystallizing the amorphous silicon thin film layer.

[0104] Here, a mechanical hard mask with 700 μm wide openings and 300 μm wide closed openings alternately arranged on the surface of the silicon thin film layer is used to implant P elements and form n + The area without n layer + The areas of the layers alternate.

[0105] Process (D)

[0106] Next, after forming a passivation film of aluminum oxide with a thickness of about 10 to 50 nm by plasma CVD, a silicon nitride film is formed as an anti-reflection film on the entire crystalline silicon substrate (main surface and back surface) by plasma CVD using silane gas and ammonia gas. Figure 1-2 (f)). It should be noted that the anti-reflection film is not shown in the figure).

[0107] Process (E)

[0108] Next, as a p-type electrode, an aluminum electrode was used to form + The process of forming the opening portion of the layer is not formed + The passivation film in the area where no n + The center of the layer region was adjusted to be a line with a depth of 0.1 to 1.0 μm and a width of 30 μm and laser irradiation was performed, and a p-type aluminum electrode was provided. + Layer formation opening ( Figure 1-2 (g)).

[0109] Next, for p + The aluminum paste was applied to the opening for layer formation in a line shape with a thickness of 20 μm and a width of 70 μm using a screen printer so as to fill the opening, and the crystalline silicon substrate coated with the aluminum paste was dried at 100° C. for 10 minutes ( Figure 1-2 (h)).

[0110] Process (E')

[0111] In addition, if Figure 2 and 3 As shown in FIG. 1 , a known silver paste was printed with a printing width of 50 μm in such a manner that the comb teeth corresponded to the aluminum electrodes and the distance from the center to the center in the width direction of the silver electrodes was 1000 μm, and dried at 100° C. for 10 minutes ( Figure 1-2 Then, the peak temperature was set to 900°C in a belt furnace for sintering (Figure 1-2 (i)). By this sintering, an aluminum electrode (containing p + layer) is formed, and a silver electrode is formed on the surface of the n + layer.

[0112] A back contact type solar cell unit is obtained as above.

[0113] The procedure of Example 1 is simple, and therefore the time required for manufacturing the back contact type solar cell unit is 260 minutes.

[0114] Further, as a reference, in Example 1, the difference in the time required for manufacturing the back contact type solar cell unit, as compared with the case where the procedure (A) and the procedure (B) are not performed, is 30 minutes. In terms of the effects of suppressing the manufacturing cost and the leakage current, it is confirmed that by suppressing the leakage current, the release voltage Voc characteristic is improved by 1.5%, the curve factor characteristic is improved by 2.5%, and therefore the manufacturing cost per generated power is reduced.

[0115] (Comparative Example 1)

[0116] As in the prior art, by performing texturing etching on the light-receiving surface of the crystalline silicon substrate to form a concave-convex shape, and forming a silicon oxide film in contact with the entire surface of the crystalline silicon substrate, and further forming a silicon thin film layer (amorphous silicon thin film layer), and performing impurity implantation repeatedly by an ion implantation method in order to form an n + layer and a p + layer on the surface and the back surface of the crystalline silicon substrate, a back contact type solar cell unit is obtained. The specific steps are described in detail below.

[0117] First, a crystalline silicon substrate (substrate: 6 inches, thickness 200 μm) composed of p-type single crystalline silicon is prepared. In order to remove the damage layer of the cut surface of the prepared crystalline silicon substrate, wet etching is performed on the surface and the back surface of the crystalline silicon substrate using a solution such as a mixed solution of hydrofluoric acid and nitric acid.

[0118] Next, by immersing the crystalline silicon substrate in a nitric acid solution, a silicon oxide film is formed on both surfaces.

[0119] Next, a 200 nm-thick silicon thin film layer (amorphous silicon thin film layer) is formed on both surfaces. As Figure 4As shown, a pattern in which p-type diffusion layers and n-type diffusion layers are alternately formed in a strip shape is formed on the back surface of the silicon thin film layer by an ion implantation method using a resist mask. Specifically, the width (A) of the n-type diffusion region is set to 700 μm, the width (B) of the p-type diffusion region is set to 200 μm, the space (C) between the n-type diffusion region and the p-type diffusion region is set to 50 μm, and the distance (D) between the diffusion layer end closest to the substrate end and the substrate end is set to 1000 μm. Thereafter, by annealing at 875°C in a heating furnace, the p + layer and the n + layer are activated, and the amorphous silicon thin film layer is modified to a polycrystalline silicon thin film layer.

[0120] Next, a passivation film of about 30 to 50 nm composed of silicon oxide is formed by a plasma CVD method, and then a passivation film of 10 to 30 nm composed of aluminum oxide is formed on the surface by an ALD method, and then a silicon nitride film is formed as an antireflection film on the back surface of the crystalline silicon substrate by a plasma CVD method using silane gas and ammonia gas.

[0121] Next, in order to form an electrode, patterning is performed on the back surface of the crystalline silicon substrate, and an aluminum electrode is formed by aluminum evaporation.

[0122] Thereafter, plating of Ni, Cu, and Ag is performed in a manner to come into contact with the aluminum, and annealing treatment is performed. In addition, the formed electrode is separated into an electrode in contact with the p + layer and an electrode in contact with the n + layer by a laser irradiation device.

[0123] A back contact type solar cell unit is obtained as described above.

[0124] Since the process is complicated, the time required is 350 minutes.

[0125] BRIEF DESCRIPTION OF DRAWINGS

[0126] 10 - crystalline silicon substrate; 20 - oxide film; 30A - silicon thin film layer; 30B - silicon thin film layer (after activation annealing); 40 - n +Layer; 50 - Passivation film; 60A - Aluminum paste for forming aluminum electrode; 60B - Aluminum electrode; 60C - Aluminum-silicon alloy layer; 60D - BSF layer; 70A - Silver paste for forming silver electrode; 70B - Silver electrode; 70 - Aluminum electrode; 72 - Silver electrode; 74 - Silver electrode for aluminum bonding; A - Width of n-type diffusion region; B - Width of p-type diffusion region; C - Space between n-type diffusion region and p-type diffusion region; D - Space between diffusion layer end closest to substrate end and substrate end; 1000 - Ion implantation device; 1001, 1002 - Vacuum chamber; 1003 - Insulating member; 1004 - Stage; 1005 - Gas supply source; 1010 - Plasma; 1100 - RF introduction coil; 1101 - Permanent magnet; 1102 - RF introduction window; 1200, 1201 - Electrode; 1300 - Direct current power supply; 1301 - Alternating current power supply; S1 - Substrate.

Claims

1. A method for manufacturing a back-contact solar cell, characterized in that: In order: A step (A) of forming an oxide film on the back surface of a crystalline silicon substrate; forming a silicon thin film layer on the exposed surface of the oxide film (B); An n-type silicon film is locally formed on the silicon thin film layer by ion implantation using a mechanical hard mask and activation annealing. + Layer process (C); In the step (C), the oxide film, the silicon thin film layer and the n + forming a passivation film on both sides of the crystalline silicon substrate; as well as The portion of the passivation film formed on the back side of the crystalline silicon substrate that does not cover the n + A portion of the region of the layer is removed to form a p-type aluminum electrode. + and forming one or more p-type silicon thin film layers on the silicon thin film layer exposed from the opening. + The aluminum electrode layer is formed in the step (E).

2. The manufacturing method according to claim 1, characterized in that After the step (D), there is a step (E') of forming a passivation film formed on the back side of the crystalline silicon substrate via the oxide film and the n + The layer covering the region of the crystalline silicon substrate is partially removed, and the exposed n + One or more silver electrodes are formed on the layer, The step (E) and the step (E') are performed in a different order.

3. The manufacturing method according to claim 2, characterized in that In the step (E'), a copper electrode or an aluminum alloy electrode is formed instead of the silver electrode.

4. The production method according to any one of claims 1 to 3, characterized in that The aluminum electrode is formed by sintering a coating of an aluminum paste containing 2 to 20 parts by mass of an organic vehicle and 0.15 to 15 parts by mass of glass frit relative to 100 parts by mass of aluminum powder at 650 to 900°C.

5. The manufacturing method according to claim 2, characterized in that The aluminum electrodes and the silver electrodes are formed on the back surface side of the crystalline silicon substrate so as to be alternately arranged.

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