Solar Cell

Abstract

To provide a solar battery that enables improvement of the appearance (design) on the light receiving surface side, thereof.SOLUTION: A solar battery 1 is a back-contact type crystalline silicon solar battery comprising: a crystal silicon substrate 11; a first intrinsic silicon thin film 23 and a first conductive silicon thin film 25 formed in a first region 7 on the back surface side of the substrate 11; and a second intrinsic silicon thin film 33 and a second conductive silicon thin film 35 formed in a second region 8 on the back surface side of the substrate 11, and further comprising a third intrinsic silicon thin film 13 and a silicon-based compound thin film 15 each formed on the light receiving surface side of the substrate 11. The third intrinsic silicon thin film 13 includes a first intrinsic thin film 131 and a second intrinsic thin film 132 in this order from the side of the substrate 11. The second intrinsic thin film 132 has an optical bandgap of 1.95 eV or more and has a refractive index of 3.3 or more and 3.7 or less with respect to light having a wavelength of 550 nm because the second intrinsic thin film is formed with a higher hydrogen dilution than the first intrinsic thin film 131.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a back contact type solar cell. [Background technology]

[0002] Patent Document 1 discloses a back-contact type solar cell. Such a back-contact type solar cell includes a crystalline silicon substrate that functions as a photoelectric conversion film, a first intrinsic silicon-based thin film, a first conductive type silicon-based thin film, and a first electrode film that are deposited in this order on a portion of the back surface of the crystalline silicon substrate, and a second intrinsic silicon-based thin film, a second conductive type silicon-based thin film, and a second electrode film that are deposited in this order on another portion of the back surface of the crystalline silicon substrate. The solar cell also includes a third intrinsic silicon-based thin film and a silicon-based compound thin film that are deposited in this order on the light-receiving surface side of the crystalline silicon substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-75526 A Summary of the Invention [Problem to be solved by the invention]

[0004] A known method for forming the third intrinsic silicon-based thin film on the light-receiving surface side of the crystalline silicon substrate is the CVD (Chemical Vapor Deposition) method. In the CVD method, for example, a substrate tray is used to simultaneously deposit a silicon-based thin film on multiple crystalline silicon substrates. In such a deposition method, a film thickness distribution (unevenness in film thickness) of the silicon-based thin film may occur on multiple crystalline silicon substrates due to the way power is applied and the way gas flows during the deposition process.

[0005] If the thickness of the third intrinsic silicon-based thin film differs among the multiple crystalline silicon substrates, the solar cells using these crystalline silicon substrates will have different apparent colors on the light-receiving surface side. When multiple solar cells 1 are installed side by side, the difference in apparent colors will impair the appearance (design).

[0006] An object of the present invention is to provide a solar cell that can improve the appearance (design) of the light-receiving surface side. [Means for solving the problem]

[0007] The solar cell according to the present invention is a back-contact type crystalline silicon solar cell including a crystalline silicon substrate, a first intrinsic silicon-based thin film and a first conductive type silicon-based thin film formed in order in a first region which is a part of the other main surface side opposite to the one main surface side of the crystalline silicon substrate, and a second intrinsic silicon-based thin film and a second conductive type silicon-based thin film formed in order in a second region which is another part of the other main surface side of the crystalline silicon substrate, and includes a third intrinsic silicon-based thin film formed on the one main surface side of the crystalline silicon substrate, and a silicon-based compound thin film formed on the third intrinsic silicon-based thin film. The third intrinsic silicon-based thin film includes a first intrinsic thin film and a second intrinsic thin film in order from the crystalline silicon substrate side. The second intrinsic thin film is formed with a higher hydrogen dilution than the first intrinsic thin film, and therefore has an optical band gap of 1.95 eV or more and a refractive index of 3.3 to 3.7 for light with a wavelength of 550 nm. Effect of the Invention

[0008] According to the present invention, the appearance (design) of the light-receiving surface side of a back-contact type solar cell can be improved. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram showing the solar cell according to the embodiment as viewed from the back surface side. [Diagram 2] 2 is a cross-sectional view of the solar cell shown in FIG. 1 taken along line II-II. [Figure 3A]FIG. 2 is a diagram showing a first silicon-based material film forming step, a third intrinsic silicon-based thin film forming step, and a lift-off film (protective film) forming step in the solar cell manufacturing method according to the present embodiment. [Figure 3B] 3A to 3C are diagrams illustrating a resist formation step in the method for manufacturing a solar cell according to the present embodiment. [Figure 3C] 3 is a diagram showing a first silicon-based thin-film formation step in the solar cell manufacturing method according to the present embodiment. FIG. [Figure 3D] 5A to 5C are diagrams illustrating a resist removal step in the method for manufacturing a solar cell according to the present embodiment. [Figure 3E] 4 is a diagram showing a second silicon-based material film forming step in the method for manufacturing a solar cell according to the present embodiment. FIG. [Figure 3F] 4 is a diagram showing a second silicon-based thin-film forming step in the method for manufacturing a solar cell according to the embodiment. FIG. [Figure 3G] 3A to 3C are diagrams illustrating a silicon-based compound thin film forming step in the solar cell manufacturing method according to the present embodiment. [Figure 3H] 3A to 3C are diagrams illustrating an electrode film forming step in the manufacturing method for the solar cell according to the embodiment. [Figure 4A] FIG. 1 is a diagram showing variations in hydrogen plasma etching in a chamber of a plasma CVD apparatus. [Figure 4B] FIG. 1 is a diagram showing the variation in film formation with high hydrogen dilution in the chamber of a plasma CVD apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals. For convenience, hatching and reference numerals may be omitted, in which case other drawings shall be referred to.

[0011] (Solar Cell) Fig. 1 is a view of the solar cell according to this embodiment as viewed from the back surface side. The solar cell 1 shown in Fig. 1 is a back contact type (also called back surface junction type or back surface electrode type) solar cell. The solar cell 1 includes a crystalline silicon substrate 11 having two main surfaces, and the main surface of the crystalline silicon substrate 11 has a first region 7 and a second region 8.

[0012] The first region 7 has a so-called comb shape and includes a plurality of finger portions 7f corresponding to the teeth of the comb and busbar portions 7b corresponding to supports for the teeth of the comb. The busbar portions 7b extend in a first direction (X direction) along one side of the crystalline silicon substrate 11, and the finger portions 7f extend from the busbar portions 7b in a second direction (Y direction) intersecting the first direction (X direction).

[0013] Similarly, the second region 8 has a so-called comb shape and has a plurality of finger portions 8f corresponding to the teeth of the comb and busbar portions 8b corresponding to supports for the teeth of the comb. The busbar portions 8b extend in a first direction (X direction) along one side portion of the crystalline silicon substrate 11 opposite to the other side portion, and the finger portions 8f extend in a second direction (Y direction) from the busbar portions 8b.

[0014] The finger portions 7f and the finger portions 8f are provided alternately in the first direction (X direction). The first region 7 and the second region 8 may be formed in a striped pattern.

[0015] FIG. 2 is a cross-sectional view of the solar cell of FIG. 1 taken along line II-II. As shown in FIG. 2, the solar cell 1 is a crystalline silicon-based heterojunction solar cell. The solar cell 1 includes a third intrinsic silicon-based thin film 13 and a silicon-based compound thin film 15, which are formed in this order on the light-receiving surface side (one main surface side) of the main surface of the crystalline silicon substrate 11. The solar cell 1 also includes a first intrinsic silicon-based thin film 23, a first conductive type silicon-based thin film 25, and a first electrode film 27, which are formed in this order on a part (mainly, the first region 7) of the back surface side (other main surface side) opposite the light-receiving surface of the main surface of the crystalline silicon substrate 11. The solar cell 1 also includes a second intrinsic silicon-based thin film 33, a second conductive type silicon-based thin film 35, and a second electrode film 37, which are formed in this order on another part (mainly, the second region 8) of the back surface side of the crystalline silicon substrate 11.

[0016] The crystalline silicon substrate 11 is formed of a crystalline silicon material such as single crystal silicon or polycrystalline silicon. The crystalline silicon substrate 11 is, for example, an n-type crystalline silicon substrate in which a crystalline silicon material is doped with an n-type dopant. The crystalline silicon substrate 11 may be, for example, a p-type crystalline silicon substrate in which a crystalline silicon material is doped with a p-type dopant. An example of the n-type dopant is phosphorus (P). An example of the p-type dopant is boron (B). The crystalline silicon substrate 11 functions as a photoelectric conversion substrate that absorbs incident light from the light-receiving surface side and generates photocarriers (electrons and holes).

[0017] By using crystalline silicon as the material for the crystalline silicon substrate 11, the dark current is relatively small, and a relatively high output (stable output regardless of illuminance) can be obtained even when the intensity of incident light is low.

[0018] The crystalline silicon substrate 11 may have a pyramidal fine uneven structure called a texture structure on the back side, which increases the efficiency of collecting light that is not absorbed by the crystalline silicon substrate 11 and passes through it.

[0019] The crystalline silicon substrate 11 may have a pyramidal fine uneven structure, called a texture structure, on the light-receiving surface side, which reduces the reflection of incident light on the light-receiving surface and improves the light trapping effect in the crystalline silicon substrate 11.

[0020] The third intrinsic silicon-based thin film 13 is formed on the light-receiving surface side of the crystalline silicon substrate 11. The first intrinsic silicon-based thin film 23 is formed in a first region 7 on the back surface side of the crystalline silicon substrate 11. The second intrinsic silicon-based thin film 33 is formed in a second region 8 on the back surface side of the crystalline silicon substrate 11. The third intrinsic silicon-based thin film 13, the first intrinsic silicon-based thin film 23 and the second intrinsic silicon-based thin film 33 are formed of a material mainly composed of intrinsic (i-type) amorphous silicon, for example. The third intrinsic silicon-based thin film 13, the first intrinsic silicon-based thin film 23 and the second intrinsic silicon-based thin film 33 function as a so-called passivation film, suppressing recombination of carriers generated in the crystalline silicon substrate 11 and increasing the carrier recovery efficiency.

[0021] The third intrinsic silicon-based thin film 13 has a first intrinsic thin film 131 and a second intrinsic thin film 132, in that order from the crystalline silicon substrate 11 side. The first intrinsic thin film 131 has an optical band gap of 1.95 eV or more. The first intrinsic thin film 131 also has a refractive index of 3.3 or more and 3.7 or less for light with a wavelength of 550 nm.

[0022] On the other hand, the second intrinsic thin film 132 is formed with a higher hydrogen dilution than the first intrinsic thin film 131 (details will be described later). As a result, the second intrinsic thin film 132 has an optical band gap of 1.95 eV or more. The second intrinsic thin film 132 also has a refractive index of 3.3 or more and 3.7 or less for light with a wavelength of 550 nm. More specifically, the second intrinsic thin film 132 has a complex refractive index with a real part of 3.3 or more and 3.7 or less and an imaginary part of 0.1 or less for light with a wavelength of 550 nm.

[0023] The optical band gap, refractive index, and complex refractive index are derived from the parameters and dielectric function obtained by fitting data measured by spectroscopic ellipsometry with a Tauc-Lorentz oscillator.

[0024] The third intrinsic silicon-based thin film 13 may also include a boundary intrinsic thin film 133 located at the boundary between the first intrinsic thin film 131 and the second intrinsic thin film 132. The boundary intrinsic thin film 133 is formed by exposing the first intrinsic thin film 131 to hydrogen plasma (details will be described later).

[0025] In addition, the first intrinsic thin film 131 or the second intrinsic thin film 132 in the third intrinsic silicon-based thin film 13 has a thickness of 1×10 15 / cm 3 More than 1×10 16 / cm 3 The p-type dopant content may be less than 10 ...

[0026] The silicon-based compound thin film 15 is formed on the third intrinsic silicon-based thin film 13 on the light-receiving surface side of the crystalline silicon substrate 11. The silicon-based compound thin film 15 is formed of a silicon compound containing at least one of oxygen, nitrogen, and carbon, such as silicon oxide (SiO), silicon nitride (SiN), silicon carbide (SiC), or silicon oxynitride (SiON). The silicon-based compound thin film 15 functions as an anti-reflection film that prevents reflection of incident light, and also functions as a protective film that protects the light-receiving surface side of the crystalline silicon substrate 11 and the third intrinsic silicon-based thin film 13.

[0027] The first conductive type silicon-based thin film 25 is formed on the first intrinsic silicon-based thin film 23, i.e., in the first region 7 on the back surface side of the crystalline silicon substrate 11. The first conductive type silicon-based thin film 25 is formed of, for example, an amorphous silicon material. The first conductive type silicon-based thin film 25 is, for example, a p-type silicon-based thin film formed by doping an amorphous silicon material with a p-type dopant (for example, the above-mentioned boron (B)).

[0028] The second conductive type silicon-based thin film 35 is formed on the second intrinsic silicon-based thin film 33, that is, in the second region 8 on the back surface side of the crystalline silicon substrate 11. The second conductive type silicon-based thin film 35 is formed of, for example, an amorphous silicon material. The second conductive type silicon-based thin film 35 is, for example, an n-type silicon-based thin film formed by doping an n-type dopant (for example, the above-mentioned phosphorus (P)) into an amorphous silicon material. Note that the first conductive type silicon-based thin film 25 may be an n-type silicon-based thin film, and the second conductive type silicon-based thin film 35 may be a p-type silicon-based thin film.

[0029] The first electrode film 27 is formed on the first conductivity type silicon-based thin film 25, and the second electrode film 37 is formed on the second conductivity type silicon-based thin film 35. The first electrode film 27 has a transparent electrode film 28 and a metal electrode film 29 which are deposited in this order on the first conductivity type silicon-based thin film 25. The second electrode film 37 has a transparent electrode film 38 and a metal electrode film 39 which are deposited in this order on the second conductivity type silicon-based thin film 35.

[0030] The transparent electrode films 28 and 38 are formed of a transparent conductive material. Examples of the transparent conductive material include ITO (Indium Tin Oxide: a composite oxide of indium oxide and tin oxide). The metal electrode films 29 and 39 are formed of a conductive paste material containing a metal powder such as silver.

[0031] (Solar Cell Manufacturing Method) Hereinafter, a method for manufacturing the solar cell 1 of the present embodiment shown in FIG. 1 and FIG. 2 will be described with reference to FIG. 3A to FIG. 3H. FIG. 3A is a diagram showing a first silicon-based material film forming step, a third intrinsic silicon-based thin film forming step, and a lift-off film (protective film) forming step in the method for manufacturing a solar cell according to the present embodiment, and FIG. 3B is a diagram showing a resist forming step in the method for manufacturing a solar cell according to the present embodiment. FIG. 3C is a diagram showing a first silicon-based thin film forming step in the method for manufacturing a solar cell according to the present embodiment, and FIG. 3D is a diagram showing a resist removing step in the method for manufacturing a solar cell according to the present embodiment. FIG. 3E is a diagram showing a second silicon-based material film forming step in the method for manufacturing a solar cell according to the present embodiment, and FIG. 3F is a diagram showing a second silicon-based thin film forming step in the method for manufacturing a solar cell according to the present embodiment. FIG. 3G is a diagram showing a silicon-based compound thin film forming step in the method for manufacturing a solar cell according to the present embodiment, and FIG. 3H is a diagram showing an electrode film forming step in the method for manufacturing a solar cell according to the present embodiment.

[0032] First, as shown in FIG. 3A, for example, a plasma CVD (Chemical Vapor Deposition) method is used to deposit a first intrinsic silicon-based material film 23Z and a first conductivity type silicon-based material film 25Z in this order on the entire back surface side of a crystalline silicon substrate 11 (first silicon-based material film formation process).

[0033] Further, a third intrinsic silicon-based thin film 13 is formed on the entire light-receiving surface side of the crystalline silicon substrate 11 by using, for example, a plasma CVD method (third intrinsic silicon-based thin film forming step). First, a first intrinsic thin film 131 is formed on the light-receiving surface of the crystalline silicon substrate 11. Then, hydrogen plasma etching is performed by exposing the surface of the first intrinsic thin film 131 to hydrogen plasma. As a result, a boundary intrinsic thin film 133 is formed on the surface of the first intrinsic thin film 131. Then, a second intrinsic thin film 132 is formed with high hydrogen dilution on the first intrinsic thin film 131 after the hydrogen plasma etching, i.e., on the boundary intrinsic thin film 133. The third intrinsic silicon-based thin film forming step will be described in detail later.

[0034] In addition, if the third intrinsic silicon-based thin film 13 is formed in the same chamber after the p-type silicon-based material film 25Z is formed, boron (B), which is a p-type dopant remaining in the vacuum chamber or on the substrate tray, etc., during the formation of the p-type silicon-based material film 25Z, is contained in the first intrinsic thin film 131 or the second intrinsic thin film 132 in the third intrinsic silicon-based thin film 13.

[0035] Next, a lift-off film (sacrificial film) 41 is formed on the entire surface of the back surface of the crystalline silicon substrate 11, specifically on the entire surface of the first conductive type silicon-based material film 25Z, for example, by using a plasma CVD method (lift-off film forming step). In addition, a protective film 51 is formed on the entire surface of the light-receiving surface of the crystalline silicon substrate 11, specifically on the entire surface of the third intrinsic silicon-based thin film 13, for example, by using a plasma CVD method (protective film forming step). The lift-off film 41 and the protective film 51 are formed of materials such as silicon oxide (SiO), silicon nitride (SiN), or a compound thereof, such as silicon oxynitride (SiON).

[0036] Next, as shown in Figures 3B to 3D, a resist 90 is used to remove the lift-off film 41, the first conductivity type silicon-based material film 25Z, and the first intrinsic silicon-based material film 23Z in the second region 8 on the back surface side of the crystalline silicon substrate 11, thereby forming a patterned first intrinsic silicon-based thin film 23, the first conductivity type silicon-based thin film 25, and the lift-off film 41 in the first region 7.

[0037] 3B, on the back surface side of the crystalline silicon substrate 11, a resist 90 is formed on the first conductive type silicon material film 25Z and the lift-off film 41 in the first region 7 by using a pattern printing technique or a photoresist technique (resist forming step). Also, on the entire light-receiving surface side of the crystalline silicon substrate 11, a resist 90 is formed by using a pattern printing technique or a photoresist technique (resist forming step).

[0038] 3C, the lift-off film 41 in the second region 8 is etched on the back surface side of the crystalline silicon substrate 11 using the resist 90 as a mask, thereby forming a patterned lift-off film 41 in the first region 7. As an etching solution for the lift-off film 41, an acidic solution such as hydrofluoric acid is used.

[0039] Thereafter, using the resist 90 as a mask, the first conductive type silicon-based material film 25Z and the first intrinsic silicon-based material film 23Z in the second region 8 are etched on the back surface side of the crystalline silicon substrate 11, thereby forming the patterned first intrinsic silicon-based thin film 23 and first conductive type silicon-based thin film 25 in the first region 7 (first silicon-based thin film forming step). An example of an etching solution for a p-type silicon-based thin film is an acidic solution such as hydrofluoric acid containing ozone or a mixture of nitric acid and hydrofluoric acid, and an example of an etching solution for an n-type silicon-based thin film is an alkaline solution such as an aqueous solution of potassium hydroxide.

[0040] 3D, resist 90 on the back surface side and the light-receiving surface side is removed (resist removal step). As an etching solution for resist 90, an inexpensive alkaline solution such as KOH is used.

[0041] Next, both sides of the crystalline silicon substrate 11 are cleaned (first cleaning step). In the first cleaning step, for example, ozone treatment is performed, followed by hydrofluoric acid treatment. The hydrofluoric acid treatment includes not only treatment with hydrofluoric acid, but also treatment with a mixture of hydrofluoric acid and another type of acid (for example, hydrochloric acid in the first cleaning step).

[0042] Next, as shown in FIG. 3E, for example, using a plasma CVD method, a second intrinsic silicon-based material film 33Z and a second conductivity type silicon-based material film 35Z are sequentially formed on the entire back surface side of the crystalline silicon substrate 11, specifically, on the lift-off film 41 in the first region 7 and in the second region 8 (second silicon-based material film formation process).

[0043] Next, as shown in FIG. 3F, a lift-off method using a lift-off film (sacrificial film) is utilized to remove the second intrinsic silicon-based material film 33Z and the second conductivity type silicon-based material film 35Z in the first region 7 on the back surface side of the crystalline silicon substrate 11, thereby forming a patterned second intrinsic silicon-based thin film 33 and second conductivity type silicon-based thin film 35 in the second region 8 (second silicon-based thin film formation process).

[0044] Specifically, by removing the lift-off film 41, the second intrinsic silicon-based material film 33Z and the second conductivity type silicon-based material film 35Z on the lift-off film 41 are removed, and the second intrinsic silicon-based thin film 33 and the second conductivity type silicon-based thin film 35 are formed in the second region 8. As a removal solution for the lift-off film 41, for example, an acidic solution such as hydrofluoric acid is used.

[0045] Next, as shown in FIG. 3G, a silicon-based compound thin film 15 is formed on the entire light-receiving surface side of the crystalline silicon substrate 11 by, for example, plasma CVD (silicon-based compound thin film forming step).

[0046] Next, as shown in FIG. 3H, a first electrode film 27 and a second electrode film 37 are formed on the back side of the crystalline silicon substrate 11 (electrode film forming process). Specifically, a transparent electrode film is formed on the entire back side of the crystalline silicon substrate 11 by using a PVD (Physical Vapor Deposition) method such as a sputtering method. Then, a part of the transparent electrode material film is removed by using an etching method using an etching paste, to form patterned transparent electrode films 28, 38. As an etching solution for the transparent electrode material film, for example, hydrochloric acid or a ferric chloride aqueous solution is used. Then, a metal electrode film 29 is formed on the transparent electrode film 28 by using a pattern printing method or a coating method, and the metal electrode film 39 is formed on the transparent electrode film 38, to form the first electrode film 27 and the second electrode film 37.

[0047] The transparent electrode films 28, 38 may be patterned by patterning the transparent electrode material film using the metal electrode films 29, 39 as a mask. This allows for simplification of the manufacturing process compared to an etching method using an etching paste.

[0048] Through the above steps, the back-contact type crystalline silicon solar cell 1 of this embodiment shown in Figs. 1 and 2 is completed.

[0049] As described above, the CVD method is used as a method for forming the third intrinsic silicon-based thin film 13 on the light-receiving surface side of the crystalline silicon substrate 11. In the CVD method, for example, a substrate tray is used to simultaneously deposit a silicon-based thin film on a plurality of crystalline silicon substrates. In such a deposition method, a film thickness distribution (non-uniformity of film thickness) of the silicon-based thin film may occur on the plurality of crystalline silicon substrates due to the way power is applied and the way gas flows during the deposition process.

[0050] If the film thickness of the third intrinsic silicon-based thin film differs among multiple crystalline silicon substrates, the apparent color of the light-receiving surface of the solar cell using these crystalline silicon substrates will differ. According to the knowledge of the present inventor(s), if the third intrinsic silicon-based thin film 13 is formed only of the first intrinsic thin film 131, the apparent color of the light-receiving surface of the solar cell through the silicon-based compound thin film 15 will vary from brown to dark blue. When multiple solar cells 1 are installed side by side, the appearance (design) will be impaired if the apparent colors differ.

[0051] In this regard, according to the solar cell 1 of this embodiment, the third intrinsic silicon-based thin film 13 has the first intrinsic thin film 131 and the second intrinsic thin film 132 in this order from the crystalline silicon substrate 11 side, and the second intrinsic thin film 132 has an optical band gap of 1.95 eV or more and a refractive index of 3.3 to 3.7 for light with a wavelength of 550 nm by being formed with high hydrogen dilution. As a result, even if a silicon-based thin film is simultaneously formed on a plurality of crystalline silicon substrates 11 using a CVD method and a film thickness distribution (unevenness in film thickness) of the third intrinsic silicon-based thin film 13 occurs on the plurality of crystalline silicon substrates 11, that is, a film thickness distribution (unevenness in film thickness) of the first intrinsic thin film 131 and the second intrinsic thin film 132 occurs on the plurality of crystalline silicon substrates 11, the variation in the apparent color of the light receiving surface side of the solar cell 1 using these crystalline silicon substrates 11 can be reduced. Specifically, the variation in the apparent color of the light receiving surface side of the solar cell 1 through the silicon-based compound thin film 15 is reduced to a range from purple to dark blue. This makes it possible to improve the appearance (design) when multiple solar cells 1 are installed side by side.

[0052] In addition, the second intrinsic thin film 132 formed with high hydrogen dilution is relatively resistant to chemicals in the subsequent manufacturing process, for example, acid solutions in the lift-off process (patterning of the second silicon-based thin film). This reduces damage to the third intrinsic silicon-based thin film 13, particularly the first intrinsic thin film 131, during the manufacturing process, and improves passivation properties. This improves the performance of the solar cell 1.

[0053] Here, FIG. 4A is a diagram showing variations in hydrogen plasma etching in a chamber of a plasma CVD apparatus, and FIG. 4B is a diagram showing variations in film formation at high hydrogen dilution in a chamber of a plasma CVD apparatus. 4A shows the variation in hydrogen plasma etching occurring in the chamber of the plasma CVD apparatus (solid line) when performing hydrogen plasma etching by exposing the surface of the first intrinsic thin film 131 to hydrogen plasma after the formation of the first intrinsic thin film 131 (dotted line). On the other hand, FIG 4B shows the variation in film formation at high hydrogen dilution occurring in the chamber of the plasma CVD apparatus when forming the second intrinsic thin film 132 at high hydrogen dilution on the first intrinsic thin film 131 after the hydrogen plasma etching, i.e., on the boundary intrinsic thin film 133.

[0054] As shown in Fig. 4B, when the second intrinsic thin film 132 is formed simultaneously on a plurality of crystalline silicon substrates 11 with high hydrogen dilution by using the plasma CVD method, a film thickness distribution (non-uniformity of film thickness) occurs in the second intrinsic thin film 132 so that it gradually becomes thicker from the edge toward the center in the chamber of the CVD apparatus. On the other hand, as shown in Fig. 4A, when the first intrinsic thin film 131 is simultaneously etched by hydrogen plasma on a plurality of crystalline silicon substrates 11 by using the plasma CVD method, a film thickness distribution (non-uniformity of film thickness) occurs in the first intrinsic thin film 131 so that it gradually becomes thinner from the edge toward the center in the chamber of the CVD apparatus.

[0055] Thus, in the solar cell 1 of this embodiment, the third intrinsic silicon-based thin film 13 is located at the boundary between the first intrinsic thin film 131 and the second intrinsic thin film 132, and may include a boundary intrinsic thin film 133 formed by exposing the first intrinsic thin film 131 to hydrogen plasma. This makes it possible to reduce the variation in the total film thickness of the first intrinsic thin film 131 and the second intrinsic thin film 132 among a plurality of crystalline silicon substrates 11, i.e., the variation in the film thickness of the third intrinsic silicon-based thin film 13, and further reduces the variation in the apparent color of the light-receiving surface side of the solar cell 1 using these crystalline silicon substrates 11.

[0056] Furthermore, by performing hydrogen plasma etching on the first intrinsic thin film 131, the film quality of the first intrinsic thin film 131 is improved (such as the termination of dangling bonds by the introduction of hydrogen into the film) and the interface characteristics are improved, resulting in further improved passivation properties, which in turn leads to further improved performance of the solar cell 1.

[0057] In the solar cell 1 of this embodiment, the first intrinsic thin film 131 or the second intrinsic thin film 132 in the third intrinsic silicon-based thin film 13 has a thickness of 1×10 15 / cm 3 More than 1×10 16 / cm 3 Alternatively, the thin film may be a substantially intrinsic thin film containing less than about 1000 nm of boron (B), a p-type dopant. As a result, even if silicon-based thin films are formed simultaneously on a plurality of crystalline silicon substrates 11 using a CVD method and a film thickness distribution (unevenness in film thickness) of the third intrinsic silicon-based thin film 13 occurs on the plurality of crystalline silicon substrates 11, that is, a film thickness distribution (unevenness in film thickness) of the first intrinsic thin film 131 and the second intrinsic thin film 132 occurs, the variation in the apparent color of the light-receiving surface side of the solar cell 1 using these crystalline silicon substrates 11 can be further reduced.

[0058] Furthermore, the third intrinsic silicon-based thin film 13 containing boron (B), which is a p-type dopant, is relatively resistant to chemicals used in the subsequent manufacturing process, for example, acidic solutions used in the lift-off process (patterning of the second silicon-based thin film). This makes it possible to further reduce damage to the third intrinsic silicon-based thin film 13, particularly the first intrinsic thin film 131, during the manufacturing process, and further improve passivation properties. This makes it possible to further improve the performance of the solar cell 1.

[0059] In the above-mentioned solar cell manufacturing method, the method for forming the silicon-based thin film is not particularly limited, but as described above, the plasma CVD method is preferable. When the silicon-based thin film is formed by the plasma CVD method, the formation of the silicon-based thin film and the hydrogen plasma treatment can be performed in the same chamber, so that the process can be simplified.

[0060] The formation of silicon-based thin films by plasma CVD requires the use of SiH as the source gas. 4 , Si 2 H 6 Silicon-containing gases such as H are used. 2The dopant gas for forming a silicon-based thin film of a conductive type (p-type or n-type) may be B. 2 H 6 or PH 3 Since the amount of dopant such as P or B added is small, a mixed gas in which the dopant gas is diluted with the source gas or H2 in advance may be used. 4 , CO 2 , N.H. 3 , GeH 4 By adding a gas containing a different element such as silicon carbide, silicon nitride, silicon germanium, etc. to the above gas, a silicon alloy thin film such as silicon carbide, silicon nitride, silicon germanium, etc. can be formed. The conditions for forming a silicon-based thin film by plasma CVD are a substrate temperature of 100 to 300°C, a pressure of 20 to 2600 Pa, and a power density of 3 to 500 mW / cm. 2 is preferred.

[0061] <Details of the third intrinsic silicon-based thin film formation process> The third intrinsic silicon-based thin film forming process will be described in detail below with reference to Figures 3A, 4A, and 4B. First, a first intrinsic thin film 131 is formed on the main surface of the silicon substrate 11 (dotted line in Figure 4A). Thereafter, hydrogen plasma etching is performed by exposing the surface of the first intrinsic thin film 131 to hydrogen plasma, and a boundary intrinsic thin film 133 is formed on the surface of the first intrinsic thin film 131 (solid line in Figure 4A). A second intrinsic thin film 132 is formed with high hydrogen dilution on the first intrinsic thin film 131 after hydrogen plasma etching, i.e., on the boundary intrinsic thin film 133 (Figure 4B). In this way, in the formation of the third intrinsic silicon-based thin film 13, after the formation of the first intrinsic thin film 131, hydrogen plasma etching is performed, and then the second intrinsic thin film 132 is formed with high hydrogen dilution.

[0062] As described above, the third intrinsic silicon-based thin film 13 is formed by, for example, plasma CVD. When forming the third intrinsic silicon-based thin film by plasma CVD, first, a silicon substrate is introduced into the chamber of a plasma CVD apparatus. Specifically, a plurality of silicon substrates are placed on a mounting member such as a film formation tray and introduced into the chamber. The silicon substrate may also be fixed at a predetermined position in the chamber by a suction method or the like. By introducing a plurality of silicon substrates into the chamber and forming films on the plurality of silicon substrates in one batch, the production efficiency of solar cells can be improved.

[0063] <<Deposition of the first intrinsic thin film>> After the silicon substrate is introduced into the chamber, the substrate is heated as necessary. Then, a silicon-containing gas and, as necessary, a dilution gas such as hydrogen are introduced into the chamber, and a first intrinsic thin film 131 is formed on the silicon substrate 11, as shown in Figures 3A and 4A.

[0064] The first intrinsic thin film 131 is a film adjacent to the silicon substrate 11, and acts as a passivation film for the silicon substrate surface. To effectively perform passivation, it is preferable that the initial portion of the first intrinsic thin film 131 near the interface with the silicon substrate 11 is amorphous. Therefore, it is preferable that the first intrinsic thin film is deposited at a high rate. The deposition rate of the first intrinsic thin film is preferably 0.1 nm / sec or more, more preferably 0.15 nm / sec or more, and even more preferably 0.2 nm / sec or more. By increasing the deposition rate, the epitaxial growth of silicon is suppressed, and an amorphous film is more likely to be formed.

[0065] Since a substrate having a texture formed on its surface has a larger surface area than a smooth substrate having no texture, the film formation rate on the textured substrate is smaller than the film formation rate on a smooth surface. The film formation rate is calculated as a value converted into the film formation rate on a smooth surface. The film formation rate on a smooth surface can be calculated from the film thickness measured by spectroscopic ellipsometry after film formation for a certain period of time under the same conditions on a smooth surface such as a silicon substrate or a glass plate having no texture formed. The film thickness of the thin film on the textured silicon substrate is determined by observing the cross section with a transmission electron microscope (TEM) with the film thickness direction perpendicular to the slope of the texture.

[0066] The film formation rate tends to be increased by reducing the amount of hydrogen introduced (dilution ratio with hydrogen) during film formation of the first intrinsic thin film. The amount of hydrogen introduced during film formation of the first intrinsic thin film is preferably less than 50 times the amount of silicon-containing gas introduced. The amount of hydrogen introduced is more preferably 20 times or less, further preferably 10 times or less, and particularly preferably 6 times or less, of the amount of silicon-containing gas introduced. The first intrinsic thin film may be formed without introducing hydrogen. The film formation rate can also be increased by adjusting the process pressure, power density, etc. during film formation.

[0067] The first intrinsic thin film 131 is preferably formed to a thickness of 3 nm to 15 nm. The thickness d0 of the first intrinsic thin film is the thickness before hydrogen plasma etching is performed. The thickness of the first intrinsic thin film is more preferably 3.5 nm to 12 nm, and more preferably 4 nm to 10 nm. If the thickness of the first intrinsic thin film is too small, the passivation effect on the single crystal silicon substrate tends to be insufficient, and the surface of the silicon substrate tends to be easily damaged by plasma during plasma etching of the first intrinsic thin film. The thickness of the first intrinsic thin film is more preferably 10 nm or less, and more preferably 8 nm or less. If the thickness of the first intrinsic thin film is too large, the conversion characteristics tend to decrease due to light absorption by the intrinsic silicon-based thin film and electrical loss due to increased resistance.

[0068] <<Hydrogen plasma etching of the first intrinsic thin film surface>> After the first intrinsic thin film 131 is formed, hydrogen plasma etching is performed by exposing the surface of the first intrinsic thin film to hydrogen plasma, as shown in Figures 3A and 4A. This forms a boundary intrinsic thin film 133 on the first intrinsic thin film 131. After the first intrinsic thin film is formed, its surface is etched by hydrogen plasma, which tends to improve the conversion characteristics of the solar cell, particularly the open circuit voltage (Voc) and fill factor (FF).

[0069] The improvement in open-circuit voltage is believed to be due to the improvement in the film quality of the silicon-based thin film by exposure to hydrogen plasma (termination of dangling bonds by introduction of hydrogen into the film, etc.) and the improvement in the interface characteristics. In general, when the thickness of the intrinsic silicon-based thin film is reduced, the passivation effect of the silicon substrate is reduced, and the open-circuit voltage of the solar cell tends to decrease. In contrast, when the thickness of the first intrinsic thin film is reduced by hydrogen plasma etching, the effects of the improvement in film quality and the improvement in interface characteristics more than compensate for the reduction in the passivation effect due to the reduction in film thickness, and therefore the open-circuit voltage is believed to improve. In addition, the improvement in the film quality and reduction in the film thickness of the first intrinsic thin film by hydrogen plasma etching reduces the series resistance of the intrinsic silicon-based thin film, and therefore the fill factor is believed to improve.

[0070] In general, increasing the thickness of the intrinsic silicon-based thin film on the silicon substrate tends to improve the open circuit voltage and decrease the fill factor, whereas decreasing the thickness of the intrinsic silicon-based thin film tends to improve the fill factor and decrease the open circuit voltage. In contrast, by performing hydrogen plasma etching after the formation of the first intrinsic thin film, both the fill factor and the open circuit voltage can be improved, and the conversion characteristics of the solar cell tend to be improved.

[0071] Hydrogen plasma etching is performed in a hydrogen-containing atmosphere. Hydrogen plasma etching is preferably performed in an atmosphere with a hydrogen concentration of 50% by volume or more. The hydrogen concentration during hydrogen plasma etching is more preferably 60% by volume or more, and even more preferably 70% by volume or more. The atmospheric gas in hydrogen plasma etching may contain an inert gas such as nitrogen, helium, or argon. 2 H 6 , PH 3 On the other hand, in hydrogen plasma etching, a small amount of dopant gas such as SiH 4 It is preferable that source gases such as fluorine, fluorine, fluorine-containing gas, etc. are not introduced into the chamber. Also, during hydrogen plasma etching, it is preferable that the amount of source gas used in depositing the first intrinsic thin film remaining in the chamber is small, and it is preferable that a silicon-based thin film is not substantially deposited during plasma discharge. Therefore, the concentration of the silicon-containing gas in the chamber during hydrogen plasma etching is preferably less than 1 / 500 of the hydrogen concentration, more preferably 1 / 1000 or less, and even more preferably 1 / 2000 or less.

[0072] Preferable conditions for hydrogen plasma etching are, for example, a substrate temperature of 100° C. to 300° C. and a pressure of 20 Pa to 2600 Pa. The plasma power density and processing time during hydrogen plasma etching may be set so that the thickness of the first intrinsic thin film is reduced by plasma etching.

[0073] The amount of etching of the first intrinsic thin film by hydrogen plasma etching, that is, the difference d0-d1 between the film thickness d0 of the first intrinsic thin film before hydrogen plasma etching and the film thickness d1 of the first intrinsic thin film after hydrogen plasma etching, is preferably 0.5 nm or more. If the amount of plasma etching is 0.5 nm or more, the effect of improving the fill factor by reducing the film thickness is easily achieved. On the other hand, if the amount of plasma etching is excessively large, the film thickness of the first intrinsic thin film becomes excessively small, and the open circuit voltage of the solar cell may decrease due to a decrease in the passivation effect and plasma damage to the silicon substrate surface. Therefore, the amount of plasma etching d0-d1 is preferably 5 nm or less, more preferably 4 nm or less, and even more preferably 3 nm or less. In addition, when multiple silicon substrates are processed in one batch, the average of d0-d1 at the center of the surface of each silicon substrate is defined as the amount of plasma etching. The film thickness d2 of the second intrinsic thin film described later is defined in the same manner.

[0074] To perform sufficient plasma etching, the power density during hydrogen plasma etching was set to 40 mW / cm 2 More than 60mW / cm is preferable. 2 More preferably, 80 mW / cm 2 More preferably, 100 mW / cm 2 The above is particularly preferred. By performing hydrogen plasma etching of the first intrinsic thin film at a higher power density than that used for forming the first intrinsic thin film, the open circuit voltage of the solar cell tends to improve significantly. The power density used for hydrogen plasma etching is preferably at least twice, more preferably at least three times, even more preferably at least four times, and particularly preferably at least five times the power density used for forming the first intrinsic thin film.

[0075] On the other hand, if the power density during plasma processing is too high, it may be difficult to control the amount of etching. Also, if the power density is too high, the quality of the intrinsic silicon thin film may deteriorate, plasma damage may occur to the surface of the single crystal silicon substrate, and the conversion characteristics of the solar cell may deteriorate. Therefore, the power density is set to 500 mW / cm. 2 Less than 400mW / cm is preferable. 2Less than 300 mW / cm is more preferable. 2 More preferably, 250 mW / cm 2 The following are particularly preferred:

[0076] If the plasma treatment time is too short, the same tendency as when the power density is too low occurs. Conversely, if the plasma treatment time is too long, the same tendency as when the power density is too high occurs. Therefore, the treatment time of hydrogen plasma etching is preferably 3 to 140 seconds, more preferably 5 to 100 seconds, and further preferably 10 to 60 seconds.

[0077] As described above, in order to enhance the function as a passivation film of the surface of the silicon substrate 1, it is preferable that the initial portion of the first intrinsic thin film 131 is amorphous. On the other hand, the vicinity of the interface of the first intrinsic thin film 131 on the side of the second intrinsic thin film 132 may be crystallized by exposure to hydrogen plasma. Crystallization of the surface of the first intrinsic thin film 131 tends to promote crystallization of the second intrinsic thin film 132 formed thereon.

[0078] <<Deposition of the second intrinsic thin film>> As shown in FIG. 3A and FIG. 4B, the second intrinsic thin film 132 is formed on the first intrinsic thin film 131 after hydrogen plasma etching, that is, on the boundary intrinsic thin film 133. The second intrinsic thin film 132 is formed by plasma CVD while introducing a silicon-containing gas and hydrogen into a CVD chamber. The amount of hydrogen introduced into the chamber when forming the second intrinsic thin film is set to 50 to 500 times the amount of silicon-containing gas introduced. By forming the second intrinsic thin film with a higher hydrogen dilution ratio than when forming the first intrinsic thin film, the second intrinsic thin film 132 becomes a film with a higher order, and crystal grains are more likely to be generated in the film. Therefore, the interface bonding between the third intrinsic silicon-based thin film 13 and the conductive silicon-based thin film becomes good, and the open circuit voltage and fill factor of the solar cell tend to be further improved compared to the case where only hydrogen plasma etching is performed. The amount of hydrogen introduced into the chamber when forming the second intrinsic thin film is more preferably 80 to 450 times, and more preferably 100 to 400 times, the amount of silicon-containing gas introduced.

[0079] The deposition thickness d2 of the second intrinsic thin film 132 is preferably 0.5 nm or more. If d2 is 0.5 nm or more, the coverage by the second intrinsic thin film becomes good, silicon crystal grains are easily generated, and interface characteristics tend to improve. On the other hand, if the thickness of the second intrinsic thin film is excessively large, the fill factor of the solar cell tends to decrease. Therefore, the deposition thickness d2 of the second intrinsic thin film 132 is preferably 5 nm or less, more preferably 4 nm or less, and even more preferably 3 nm or less. In addition, the deposition thickness d2 of the second intrinsic thin film 132 is preferably 0.5 times or less, more preferably 0.4 times or less, and even more preferably 0.3 times or less of the thickness d1 of the first intrinsic thin film 131 after plasma etching.

[0080] To promote the formation of crystal grains, the power density during deposition of the second intrinsic thin film was set to 40 mW / cm 2 More than 60mW / cm is preferable. 2 More preferably, 80 mW / cm 2 More preferably, 100 mW / cm 2 More preferably, the power density is 2 times or more than the power density of the first intrinsic thin film. The power density of the second intrinsic thin film is preferably 2 times or more than the power density of the first intrinsic thin film, more preferably 3 times or more, even more preferably 4 times or more, and particularly preferably 5 times or more. The film formation rate of the second intrinsic thin film is preferably 0.001 to 0.09 nm / sec, more preferably 0.005 to 0.08 nm / sec, and even more preferably 0.01 to 0.07 nm / sec, converted into a film formation rate on a smooth surface. The film formation rate of the second intrinsic thin film is preferably 0.5 times or less than the film formation rate of the first intrinsic thin film, and more preferably 0.3 times or less.

[0081] If the second intrinsic thin film 132 is formed by plasma CVD with a high hydrogen dilution ratio after the hydrogen plasma etching of the first intrinsic thin film 131, the interface bond with the conductive silicon-based thin film is improved and the film thickness distribution of the intrinsic silicon-based thin film is alleviated, which tends to reduce the quality variation of the cells.

[0082] According to the study by the present inventors, when hydrogen plasma etching is performed after the deposition of an intrinsic silicon-based thin film, the conversion characteristics of the solar cell differ depending on the position of the silicon substrate in the chamber (deposition position), and the cell characteristics tend to vary within the batch. In particular, when the silicon substrate is replaced and multiple batches of film deposition are performed continuously without maintenance in the CVD chamber, the variation in the conversion characteristics tends to increase with an increase in the number of continuous film deposition batches. As a result of further study, the thickness of the intrinsic silicon-based thin film after hydrogen plasma etching tends to be smaller on the substrate placed near the center of the deposition surface in the chamber (substrate placed near the center of the deposition tray) than on the substrate placed at the edge of the deposition surface (substrate placed at the edge of the deposition tray). In addition, the difference in film thickness within the batch increases with an increase in the number of continuous film deposition batches, and the variation in the conversion characteristics of the solar cell tends to increase accordingly.

[0083] In contrast, if the second intrinsic thin film is formed by plasma CVD with a high hydrogen dilution ratio after hydrogen plasma etching of the first intrinsic thin film, the variation in the thickness of the intrinsic silicon thin film within a batch or between batches will be small even if the number of consecutive film formation batches is increased. Therefore, the variation in the conversion characteristics of the solar cell also tends to be small.

[0084] The fact that the thickness of the intrinsic silicon-based thin film after hydrogen plasma etching is relatively small near the center of the chamber is believed to be related to the fact that the plasma etching amount near the center of the chamber is relatively large. The dashed line in Figure 4A shows the first intrinsic thin film 131 before hydrogen plasma etching.

[0085] The reason why the amount of plasma etching near the center is relatively large is thought to be the influence of the distribution of plasma intensity within the deposition surface. Figure 4A shows how the amount of etching in the center is larger due to the plasma intensity being higher in the center compared to the edges.

[0086] According to the study by the inventors, as the number of continuous film-forming batches increases, the film thickness difference within the batch increases, and the conversion characteristics of the solar cell tend to vary accordingly. In a film-forming batch immediately after maintenance such as cleaning the chamber, the distribution of plasma intensity within the film-forming surface is small, so it is considered that the difference in film thickness change due to hydrogen plasma treatment within the batch is small. Due to the increase in the amount of deposition of the film attached to the inner wall of the chamber with the increase in the number of continuous film-forming batches, as shown in FIG. 4A, the plasma intensity is distributed within the surface, and it is presumed that the plasma intensity is higher near the center than near the edge.

[0087] Within the range of sizes of silicon substrates used in solar cells (for example, about 6 inches), the distribution of plasma intensity and film thickness is small, but when multiple silicon substrates are processed in one batch, the distribution of film thickness between substrates tends to become more pronounced. When using a large CVD chamber with a large deposition area and the number of substrates processed at one time increases, the distribution of film thickness between substrates within a batch tends to become larger. When the deposition area is 0.3 m 2 This tendency is remarkable in the above cases, and 2 This was particularly evident in the above cases.

[0088] In this embodiment, even if the first intrinsic thin film has a distribution in thickness after hydrogen plasma etching, the second intrinsic thin film is deposited thereon at a high hydrogen dilution ratio, thereby mitigating the thickness distribution. Therefore, the variation in thickness of the intrinsic silicon-based thin film within a batch or between batches can be reduced. This is believed to be due to the fact that the deposition thickness of the second intrinsic thin film has an in-plane distribution similar to that of the plasma etching amount. That is, in a location where the plasma intensity is relatively large, both the plasma etching amount (etching rate) and the deposition amount (deposition rate) of the second intrinsic thin film are relatively large, and in a location where the plasma intensity is relatively small, both the etching rate and the deposition rate are relatively small. In this way, since the second intrinsic thin film is deposited to complement the reduction in thickness due to hydrogen plasma etching, even if the plasma intensity has an in-plane distribution, the variation in thickness of the intrinsic silicon-based thin film is small, and the variation in the conversion characteristics of the solar cell can be reduced.

[0089] The larger the power density of the plasma, the more pronounced the in-plane distribution of the plasma intensity tends to be. Therefore, in order to form the second intrinsic thin film so as to complement the in-plane distribution of the plasma etching amount, it is preferable that the power density during deposition of the second intrinsic thin film is equal to the power density during hydrogen plasma etching. Specifically, the power density during deposition of the second intrinsic thin film is preferably 0.7 to 1.3 times, more preferably 0.8 to 1.2 times, of the power density during hydrogen plasma etching.

[0090] In order to form the second intrinsic thin film so as to complement the in-plane distribution of the plasma etching amount, it is preferable that the deposition thickness d2 of the second intrinsic thin film is equal to the plasma etching amount d0-d1. Therefore, the deposition thickness d2 of the second intrinsic thin film is preferably 0.5 to 2 times, more preferably 0.6 to 1.5 times, and even more preferably 0.7 to 1.3 times the plasma etching amount d0-d1.

[0091] The thickness of the intrinsic silicon-based thin film 12, i.e., the sum of the thickness d1 of the first intrinsic thin film and the thickness d2 of the second intrinsic thin film after hydrogen plasma etching, is preferably 3 nm to 15 nm. The thickness of the intrinsic silicon-based thin film 12 is more preferably 3.5 nm to 12 nm, and further preferably 4 nm to 10 nm. If the thickness of the intrinsic silicon-based thin film is within the above range, it is possible to suppress an increase in interface defects due to the diffusion of impurity atoms to the interface of the single crystal silicon substrate during the formation of the conductive silicon-based thin film, and also to reduce optical loss and electrical loss due to the light absorption and resistance of the intrinsic silicon-based thin film.

[0092] The hydrogen plasma etching and the formation of the second intrinsic thin film are preferably performed consecutively in the same CVD chamber without removing the silicon substrate in between. If the hydrogen plasma etching and the formation of the second intrinsic thin film are performed in the same CVD chamber, the in-plane distribution of the plasma intensity during the hydrogen plasma etching and the in-plane distribution of the plasma intensity during the formation of the second intrinsic thin film become equivalent. Therefore, the second intrinsic thin film is formed so as to ease the film thickness distribution of the first intrinsic thin film after the hydrogen plasma etching, and the variation in the film thickness of the intrinsic silicon-based thin film can be reduced.

[0093] After the formation of the first intrinsic thin film, hydrogen plasma etching may be performed in the same CVD chamber without removing the substrate. In this case, it is preferable to stop the plasma discharge once after the formation of the first intrinsic thin film and before the start of hydrogen plasma etching. That is, it is preferable to stop the supply of the source gas while the plasma discharge for the formation of the first intrinsic thin film is stopped, and after the chamber is filled with a gas atmosphere mainly composed of hydrogen, discharge is resumed and hydrogen plasma etching is started. If hydrogen plasma etching is performed without stopping the plasma discharge after the formation of the first intrinsic thin film, an interface film with a relatively high hydrogen concentration may be formed between the first intrinsic thin film and the second intrinsic thin film due to the source gas remaining in the chamber, which may cause a decrease in conversion characteristics. If hydrogen plasma etching is performed without stopping the plasma discharge after the formation of the first intrinsic thin film, it is preferable to exhaust the source gas to the outside of the chamber in a short time and replace the atmospheric gas by a method such as temporarily increasing the hydrogen gas flow rate after the formation of the first intrinsic thin film.

[0094] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various changes and modifications are possible. [Explanation of symbols]

[0095] 1. Solar Cell 7 First area 7b, 8b Busbar section 7f,8f Finger section 8 Second area 11 Crystalline silicon substrate 13 Third intrinsic silicon thin film 131 First intrinsic thin film 132 Second intrinsic thin film 133 Boundary intrinsic thin film 15 Silicon-based compound thin films 23 First Intrinsic Silicon Thin Film 23Z 1st Intrinsic Silicon-Based Material Film 25 First conductivity type silicon-based thin film 25Z First conductive type silicon-based material film 27 First electrode film 28 First transparent electrode film 29 First metal electrode film 33 Second Intrinsic Silicon Thin Film 33Z 2nd intrinsic silicon-based material film 35 Second conductivity type silicon-based thin film 35Z Second conductive type silicon-based material film 37 Second electrode film 38 Second transparent electrode film 39 Second metal electrode film 41 Lift-off film 51 Protective film 90 Resist

Claims

1. A method for manufacturing a back-contact type crystalline silicon solar cell comprising: a crystalline silicon substrate; a first intrinsic silicon-based thin film and a first conductivity type silicon-based thin film formed in that order in a first region which is a part of the other principal surface side opposite to the one principal surface side of the crystalline silicon substrate; a second intrinsic silicon-based thin film and a second conductivity type silicon-based thin film formed in that order in a second region which is another part of the other principal surface side of the crystalline silicon substrate; a third intrinsic silicon-based thin film formed on the one principal surface side of the crystalline silicon substrate; and a silicon-based compound thin film formed on the third intrinsic silicon-based thin film, In the step of forming the third intrinsic silicon-based thin film, a plurality of the crystalline silicon substrates are introduced into a chamber by using a plasma CVD method, and a first intrinsic thin film and a second intrinsic thin film are formed in order from the crystalline silicon substrate side; In the step of forming the first intrinsic thin film, depositing the first intrinsic thin film on the one principal surface of the crystalline silicon substrate; performing hydrogen plasma etching by exposing a surface of the first intrinsic thin film to a hydrogen plasma to form a boundary intrinsic thin film on the surface of the first intrinsic thin film; the thickness of the first intrinsic thin film gradually decreases from the end to the center of the chamber; In the step of forming the second intrinsic thin film, The second intrinsic thin film is formed on the boundary intrinsic thin film of the first intrinsic thin film with a higher hydrogen dilution than that of the first intrinsic thin film, so that the second intrinsic thin film has an optical band gap of 1.95 eV or more and a refractive index of 3.3 to 3.7 for light with a wavelength of 550 nm; The thickness of the second intrinsic thin film gradually increases from the edge to the center of the chamber. How solar cells are manufactured.

2. The step of forming the third intrinsic silicon-based thin film is performed in the same chamber after the deposition of the first conductivity type silicon-based thin film of p-type, The first intrinsic thin film or the second intrinsic thin film in the third intrinsic silicon-based thin film is 1×10 １５ / cm ３ Above 1 x 10 １６ / cm ３ a substantially intrinsic thin film containing less than 1000 nm of p-type dopant; The method for producing the solar cell according to claim 1 .

3. The method for producing a solar cell according to claim 2 , wherein the p-type dopant comprises boron.

4. 4. The method for manufacturing a solar cell according to claim 1, wherein the second intrinsic thin film has a complex refractive index with a real part of 3.3 to 3.7 and an imaginary part of 0.1 or less for light with a wavelength of 550 nm.

5. 5. The method for producing a solar cell according to claim 1, wherein the silicon-based compound thin film contains at least one of carbon, nitrogen, and oxygen.

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