JP7597548B2 - Solar Cell - Google Patents

Description

The present invention relates to a back-contact type solar cell.

Patent Document 1 discloses a back-contact type solar cell. Such a back-contact type solar cell comprises a crystalline silicon substrate that functions as a photoelectric conversion film, a first intrinsic silicon-based thin film, a first conductivity type silicon-based thin film, and a first electrode film, which are deposited in that order on a portion of the back surface side of the crystalline silicon substrate, and a second intrinsic silicon-based thin film, a second conductivity type silicon-based thin film, and a second electrode film, which are deposited in that order on another portion of the back surface side of the crystalline silicon substrate. This solar cell also comprises a third intrinsic silicon-based thin film and a silicon-based compound thin film, which are deposited in that order on the light-receiving surface side of the crystalline silicon substrate.

JP 2014-75526 A

The CVD (Chemical Vapor Deposition) method is known as a method for forming a third intrinsic silicon-based thin film on the light-receiving surface side of a crystalline silicon substrate. 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, the way power is applied and the way gas flows during the deposition process can cause a distribution of the silicon-based thin film thickness (non-uniformity in the film thickness) on multiple crystalline silicon substrates.

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 side of the solar cell using these crystalline silicon substrates will differ. When multiple solar cells 1 are installed side by side, the difference in apparent color will impair the appearance (design).

The present invention aims to provide a solar cell that can improve the appearance (design) of the light-receiving surface side.

The solar cell according to the present invention is a back-contact type crystalline silicon solar cell comprising a crystalline silicon substrate, a first intrinsic silicon-based thin film and a first conductive type silicon-based thin film formed in sequence 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 sequence in a second region which is another part of the other main surface side of the crystalline silicon substrate, and further comprising 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 comprises a first intrinsic thin film and a second intrinsic thin film in sequence 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.

The present invention can improve the appearance (design) of the light-receiving surface side of a back-contact type solar cell.

FIG. 2 is a diagram showing the solar cell according to the embodiment as viewed from the back surface side. 2 is a cross-sectional view of the solar cell taken along line II-II in FIG. 1 . 3A to 3C are diagrams 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. 3A to 3C are diagrams illustrating a resist formation step in the method for manufacturing a solar cell according to the present embodiment. 3A to 3C are diagrams illustrating a first silicon-based thin-film formation step in the method for manufacturing a solar cell according to the present embodiment. 5A to 5C are diagrams illustrating a resist removal step in the method for manufacturing a solar cell according to the present embodiment. 4A to 4C are diagrams illustrating a second silicon-based material film forming step in the method for manufacturing a solar cell according to the present embodiment. 4A to 4C are diagrams illustrating a second silicon-based thin-film formation step in the solar cell manufacturing method according to the embodiment. 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. 3A to 3C are diagrams illustrating an electrode film forming step in the manufacturing method for the solar cell according to the embodiment. FIG. 1 is a diagram showing variations in hydrogen plasma etching in a chamber of a plasma CVD apparatus. FIG. 13 is a diagram showing the variation in film formation at high hydrogen dilution in the chamber of a plasma CVD apparatus.

Below, an example of an embodiment of the present invention will be described with reference to the attached drawings. Note that the same reference numerals will be used to refer to the same or equivalent parts in each drawing. For convenience, hatching and component reference numerals may be omitted, in which case other drawings should be referenced.

(Solar Cell)
Fig. 1 is a view of the solar cell according to the present embodiment as viewed from the back side. The solar cell 1 shown in Fig. 1 is a back-contact type (also called back-surface junction type or back 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 includes a first region 7 and a second region 8.

The first region 7 has a so-called comb shape and has multiple finger portions 7f that correspond to the teeth of the comb, and busbar portions 7b that correspond to the supports of 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) that intersects with the first direction (X direction).

Similarly, the second region 8 has a so-called comb shape, and has multiple finger portions 8f corresponding to the teeth of the comb, and a busbar portion 8b corresponding to the support portion of the teeth of the comb. The busbar portion 8b extends in a first direction (X direction) along one side portion of the crystalline silicon substrate 11 that faces the other side portion, and the finger portion 8f extends in a second direction (Y direction) from the busbar portion 8b.

The finger portions 7f and the finger portions 8f are arranged alternately in the first direction (X direction). The first region 7 and the second region 8 may be formed in a stripe pattern.

Figure 2 is a cross-sectional view of the solar cell of Figure 1 taken along line II-II. As shown in Figure 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 sequence 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 sequence on a portion (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 sequence on another portion (mainly the second region 8) of the back surface side of the crystalline silicon substrate 11.

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 an n-type dopant is phosphorus (P). An example of a 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).

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 the incident light is low.

The crystalline silicon substrate 11 may have a pyramidal micro-uneven structure, called a texture structure, on the back side. This increases the efficiency of collecting light that passes through the crystalline silicon substrate 11 without being absorbed.

The crystalline silicon substrate 11 may also have a pyramidal fine uneven structure, called a texture structure, on the light-receiving surface side. This reduces the reflection of incident light on the light-receiving surface, improving the light trapping effect in the crystalline silicon substrate 11.

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 the first region 7 on the back side of the crystalline silicon substrate 11. The second intrinsic silicon-based thin film 33 is formed in the second region 8 on the back 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 so-called passivation films, suppressing recombination of carriers generated in the crystalline silicon substrate 11 and increasing carrier recovery efficiency.

The third intrinsic silicon-based thin film 13 has, in order from the crystalline silicon substrate 11 side, a first intrinsic thin film 131 and a second intrinsic thin film 132. 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.

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 to 3.7 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 to 3.7 and an imaginary part of 0.1 or less for light with a wavelength of 550 nm.

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.

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).

The first intrinsic thin film 131 or the second intrinsic thin film 132 in the third intrinsic silicon-based thin film 13 may be a substantially intrinsic thin film containing a p-type dopant (e.g., the above-mentioned boron (B)) at a concentration of 1×10 ¹⁵ /cm ³ or more and less than 1×10 ¹⁶ /cm ³ (details will be described later). The content of the p-type dopant can be measured by secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), or the like.

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.

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 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 in which an amorphous silicon material is doped with a p-type dopant (for example, the above-mentioned boron (B)).

The second conductive type silicon-based thin film 35 is formed on the second intrinsic silicon-based thin film 33, i.e., in the second region 8 on the back 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 in which an amorphous silicon material is doped with an n-type dopant (for example, the above-mentioned phosphorus (P)). 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.

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.

The transparent electrode films 28, 38 are formed from a transparent conductive material. Examples of transparent conductive materials include ITO (Indium Tin Oxide: a composite oxide of indium oxide and tin oxide). The metal electrode films 29, 39 are formed from a conductive paste material that contains a metal powder such as silver.

(Method of manufacturing solar cell)
Hereinafter, the 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.

First, as shown in FIG. 3A, a first intrinsic silicon-based material film 23Z and a first conductive type silicon-based material film 25Z are sequentially formed on the entire back surface of the crystalline silicon substrate 11 using, for example, a plasma CVD (Chemical Vapor Deposition) method (first silicon-based material film formation process).

In addition, a third intrinsic silicon-based thin film 13 is formed on the entire light-receiving surface side of the crystalline silicon substrate 11 using, for example, a plasma CVD method (third intrinsic silicon-based thin film formation process). 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 hydrogen plasma etching, i.e., on the boundary intrinsic thin film 133. Details of the third intrinsic silicon-based thin film formation process will be described later.

When 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), a p-type dopant that remains in the vacuum chamber or on the substrate tray 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 of the third intrinsic silicon-based thin film 13.

Next, a lift-off film (sacrificial film) 41 is formed on the entire 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 formation process). In addition, a protective film 51 is formed on the entire 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 formation process). 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).

Next, as shown in Figures 3B to 3D, the lift-off film 41, the first conductive type silicon-based material film 25Z, and the first intrinsic silicon-based material film 23Z in the second region 8 are removed on the back side of the crystalline silicon substrate 11 using resist 90, thereby forming a patterned first intrinsic silicon-based thin film 23, the first conductive type silicon-based thin film 25, and the lift-off film 41 in the first region 7.

Specifically, as shown in FIG. 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 using a pattern printing technique or a photoresist technique (resist formation process). In addition, a resist 90 is formed on the entire light receiving surface side of the crystalline silicon substrate 11 using a pattern printing technique or a photoresist technique (resist formation process).

As shown in FIG. 3C, the lift-off film 41 in the second region 8 on the rear surface side of the crystalline silicon substrate 11 is then etched using the resist 90 as a mask to form a patterned lift-off film 41 in the first region 7. An acidic solution such as hydrofluoric acid is used as the etching solution for the lift-off film 41.

Then, 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 on the back side of the crystalline silicon substrate 11 are etched to form a 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 formation process). Examples of etching solutions for p-type silicon-based thin films include acidic solutions such as hydrofluoric acid containing ozone or a mixture of nitric acid and hydrofluoric acid, and examples of etching solutions for n-type silicon-based thin films include alkaline solutions such as an aqueous solution of potassium hydroxide.

Then, as shown in FIG. 3D, the resist 90 on the back surface side and the light receiving surface side is removed (resist removal process). An inexpensive alkaline solution such as KOH is used as an etching solution for the resist 90.

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 treatment with not only hydrofluoric acid, but also a mixture of hydrofluoric acid and other types of acid (for example, hydrochloric acid in the first cleaning step).

Next, as shown in FIG. 3E, for example, a plasma CVD method is used to deposit a second intrinsic silicon-based material film 33Z and a second conductive type silicon-based material film 35Z in sequence on the entire back surface of the crystalline silicon substrate 11, specifically on the lift-off film 41 in the first region 7 and on the second region 8 (second silicon-based material film formation process).

Next, as shown in FIG. 3F, the second intrinsic silicon-based material film 33Z and the second conductive type silicon-based material film 35Z in the first region 7 are removed on the back side of the crystalline silicon substrate 11 using a lift-off method using a lift-off film (sacrificial film), thereby forming a patterned second intrinsic silicon-based thin film 33 and second conductive type silicon-based thin film 35 in the second region 8 (second silicon-based thin film formation process).

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, an acidic solution such as hydrofluoric acid is used.

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 using, for example, a plasma CVD method (silicon-based compound thin film formation process).

Next, as shown in FIG. 3H, the first electrode film 27 and the 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 using a PVD (Physical Vapor Deposition) method such as a sputtering method. Then, a part of the transparent electrode material film is removed using an etching method using an etching paste, to form patterned transparent electrode films 28 and 38. As an etching solution for the transparent electrode material film, for example, hydrochloric acid or a ferric chloride aqueous solution is used. Then, for example, a pattern printing method or a coating method is used to form a metal electrode film 29 on the transparent electrode film 28, and a 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.

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 a simplification of the manufacturing process compared to an etching method using an etching paste.

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

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 multiple 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 multiple crystalline silicon substrates due to the way power is applied and the way gas flows during the deposition process.

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 from 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.

In this regard, according to the solar cell 1 of this embodiment, 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, 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 the 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 reduced. Specifically, 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 variation from purple to dark blue. This improves the appearance (design) when multiple solar cells 1 are installed side by side.

The second intrinsic thin film 132, which is formed with high hydrogen dilution, is relatively resistant to chemicals used in subsequent manufacturing processes, such as acidic solutions used in the lift-off process (patterning the second silicon-based thin film). This reduces damage to the third intrinsic silicon-based thin film 13, and particularly the first intrinsic thin film 131, during the manufacturing process, and improves passivation properties. This improves the performance of the solar cell 1.

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 with high hydrogen dilution in a chamber of a plasma CVD apparatus.
4A shows the variation in hydrogen plasma etching occurring in the chamber of a 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 a plasma CVD apparatus when forming the second intrinsic thin film 132 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.

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

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 reduces the variation in the total film thickness of the first intrinsic thin film 131 and the second intrinsic thin film 132 in multiple 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.

In addition, by performing hydrogen plasma etching on the first intrinsic thin film 131, the passivation properties can be further improved due to improvements in the film quality of the first intrinsic thin film 131 (such as terminating dangling bonds by introducing hydrogen into the film) and improvements in the interface characteristics. This can further improve the performance of the solar cell 1.

Furthermore, 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 may be a substantially intrinsic thin film containing boron (B), a p-type dopant, at a concentration of 1×10 ¹⁵ /cm ³ or more and less than 1×10 ¹⁶ /cm ^3. As a result, even if silicon-based thin films are simultaneously formed on a plurality of crystalline silicon substrates 11 using the 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.

Furthermore, the third intrinsic silicon-based thin film 13, which contains boron (B), a p-type dopant, is relatively resistant to chemicals used in subsequent manufacturing processes, such as acidic solutions used in the lift-off process (patterning of the second silicon-based thin film). This can further reduce damage to the third intrinsic silicon-based thin film 13, particularly the first intrinsic thin film 131, during the manufacturing process, and can further improve passivation properties. This can further improve the performance of the solar cell 1.

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

In forming a silicon-based thin film by plasma CVD, a silicon-containing gas such as SiH ₄ or Si ₂ H ₆ is used as a raw material gas. The raw material gas may be diluted with H ₂ or the like and introduced into the chamber. As a dopant gas for forming a silicon-based thin film of a conductive type (p-type or n-type), B ₂ H ₆ or PH ₃ is preferably used. Since the amount of dopants such as P or B added may be small, a mixed gas in which the dopant gas is diluted in advance with a raw material gas or H 2 or the like may be used. By adding a gas containing a different element such as CH ₄ , CO ₂ , NH ₃ , or GeH ₄ to the above gas, a silicon alloy thin film such as silicon carbide, silicon nitride, or silicon germanium can be formed. The film forming conditions for a silicon-based thin film by plasma CVD are preferably 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 .

<Details of the third intrinsic silicon-based thin film formation step>
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). Then, 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). Thus, 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.

As described above, the third intrinsic silicon-based thin film 13 is formed, for example, by plasma CVD. When forming the third intrinsic silicon-based thin film by plasma CVD, first, a silicon substrate is introduced into the chamber of the plasma CVD device. Specifically, multiple silicon substrates are placed on a mounting member such as a film-forming 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 multiple silicon substrates into the chamber and forming films on multiple silicon substrates in one batch, the production efficiency of solar cells can be improved.

<<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.

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. In order 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, making it easier to form an amorphous film.

A substrate with a textured surface has a larger surface area than a smooth substrate without texture, so the film formation rate on a textured substrate is slower than the film deposition rate on a smooth surface. The film deposition rate is calculated as a value converted into the film deposition rate on a smooth surface. The film deposition rate on a smooth surface can be calculated from the film thickness measured by spectroscopic ellipsometry after film deposition for a certain period of time under the same conditions on a smooth surface such as a silicon substrate or a glass plate without texture. The film thickness of a thin film on a textured silicon substrate can be determined by observing the cross section with a transmission electron microscope (TEM) with the film thickness direction perpendicular to the slope of the texture.

The deposition rate tends to be increased by reducing the amount of hydrogen introduced (dilution ratio with hydrogen) during deposition of the first intrinsic thin film. The amount of hydrogen introduced during deposition 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 the amount of silicon-containing gas introduced, even more preferably 10 times or less, and particularly preferably 6 times or less. The first intrinsic thin film may be deposited without introducing hydrogen. The deposition rate can also be increased by adjusting the process pressure, power density, etc. during deposition.

The first intrinsic thin film 131 is preferably deposited to a thickness of 3 nm to 15 nm. The deposited thickness d0 of the first intrinsic thin film is the film thickness before hydrogen plasma etching is performed. The deposited thickness of the first intrinsic thin film is more preferably 3.5 nm to 12 nm, and even more preferably 4 nm to 10 nm. If the deposited 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 deposited thickness of the first intrinsic thin film is more preferably 10 nm or less, and even 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.

<<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 the fill factor (FF).

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 interface characteristics. Generally, as the thickness of the intrinsic silicon-based thin film decreases, the passivation effect of the silicon substrate decreases, 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 open-circuit voltage is believed to improve because the effects of improved film quality and improved interface characteristics more than compensate for the reduced passivation effect due to the reduced film thickness. In addition, the improvement in the film quality and reduced film thickness of the first intrinsic thin film by hydrogen plasma etching reduces the series resistance of the intrinsic silicon-based thin film, which is believed to improve the fill factor.

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, while 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 forming the first intrinsic thin film, both the fill factor and the open circuit voltage can be improved, which tends to enhance the conversion characteristics of the solar cell.

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, and may contain a trace amount of dopant gas such as B ₂ H ₆ or PH _3. On the other hand, during hydrogen plasma etching, it is preferable that a source gas such as SiH ₄ is not introduced into the chamber. Also, during hydrogen plasma etching, it is preferable that the amount of the source gas used in the deposition of 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.

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.

The amount of etching of the first intrinsic thin film by hydrogen plasma etching, that is, the difference d0-d1 between the thickness d0 of the first intrinsic thin film before hydrogen plasma etching and the 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 likely to be exhibited. On the other hand, if the amount of plasma etching is excessively large, the 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. 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 thickness d2 of the second intrinsic thin film described later is defined in the same way.

In order to perform sufficient plasma etching, the power density during hydrogen plasma etching is preferably 40 mW/ ^cm2 or more, more preferably 60 mW/cm2 or ^more , even more preferably 80 mW/cm2 or ^more , and particularly preferably 100 mW/cm2 or ^more . By performing hydrogen plasma etching of the first intrinsic thin film at a higher power density than that during formation of the first intrinsic thin film, the open circuit voltage of the solar cell tends to be significantly improved. The power density during hydrogen plasma etching is preferably 2 times or more, more preferably 3 times or more, even more preferably 4 times or more, and particularly preferably 5 times or more of the power density during formation of the first intrinsic thin film.

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 be deteriorated, or plasma damage may occur to the surface of the single crystal silicon substrate, resulting in a deterioration in the conversion characteristics of the solar cell. Therefore, the power density is preferably 500 mW/cm ² or less, more preferably 400 mW/cm ² or less, even more preferably 300 mW/cm ² or less, and particularly preferably 250 mW/cm ² or less.

If the plasma treatment time is too short, the same tendency will occur as when the power density is too low. Conversely, if the plasma treatment time is too long, the same tendency will occur as when the power density is too high. Therefore, the treatment time for hydrogen plasma etching is preferably 3 to 140 seconds, more preferably 5 to 100 seconds, and even more preferably 10 to 60 seconds.

As mentioned above, in order to enhance the function of the surface of the silicon substrate 1 as a passivation film, it is preferable that the initial portion of the first intrinsic thin film 131 is amorphous. On the other hand, the area near 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 the crystallization of the second intrinsic thin film 132 formed thereon.

<<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 silicon-containing gas and hydrogen into the CVD chamber. The amount of hydrogen introduced into the chamber during the formation of 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 that during the formation of 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 is improved, 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 during the formation of 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.

The 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 is good, silicon crystal grains are easily generated, and the 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 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 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.

In order to promote the generation of crystal grains, the power density during the deposition of the second intrinsic thin film is preferably 40 mW/cm ² or more, more preferably 60 mW/cm ² or more, even more preferably 80 mW/cm ² or more, and particularly preferably 100 mW/cm ² or more. In addition, by carrying out the deposition of the second intrinsic thin film at a higher power density than that during the deposition of the first intrinsic thin film, crystal grains tend to be more easily generated. Therefore, the power density during the deposition of the second intrinsic thin film is preferably 2 times or more, more preferably 3 times or more, even more preferably 4 times or more, and particularly preferably 5 times or more, of the power density during the deposition of the first intrinsic thin film. The deposition rate of the second intrinsic thin film, converted into a deposition rate on a smooth surface, 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. The deposition rate of the second intrinsic thin film is preferably 0.5 times or less, more preferably 0.3 times or less, the deposition rate of the first intrinsic thin film.

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

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

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 and between batches will be small even if the number of consecutive film formation batches is increased. As a result, the variation in the conversion characteristics of the solar cell also tends to be small.

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 relatively large amount of plasma etching near the center of the chamber. The dashed line in Figure 4A shows the first intrinsic thin film 131 before hydrogen plasma etching.

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

According to the inventors' study, as the number of continuous film-forming batches increases, the difference in film thickness within the batch increases, and this tends to lead to greater variation in the conversion characteristics of the solar cells. In a film-forming batch immediately after maintenance such as cleaning the chamber has been performed, the distribution of plasma intensity within the film-forming surface is small, so it is thought 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 adhering to the inner walls of the chamber as the number of continuous film-forming batches increases, an in-plane distribution of plasma intensity occurs, as shown in Figure 4A, and it is presumed that the plasma intensity is greater near the center than near the edges.

Within the range of silicon substrate sizes used in solar cells (e.g., about 6 inches), the distribution of plasma intensity and film thickness is small, but when multiple silicon substrates are processed in one batch, the film thickness distribution between substrates tends to become more pronounced. The film thickness distribution between substrates in a batch tends to become larger as the number of substrates processed at one time increases using a large CVD chamber with a large film formation area, and this tendency is prominent when the film formation area is 0.3 ^m2 or more, and is particularly prominent when the film formation area is 0.5 ^m2 or more.

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 places 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 places 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 an in-plane distribution of the plasma intensity occurs, the variation in thickness of the intrinsic silicon-based thin film is small, and it is believed that the variation in the conversion characteristics of the solar cell can be reduced.

The greater 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 the power density during hydrogen plasma etching, and more preferably 0.8 to 1.2 times.

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 equivalent 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 the plasma etching amount d0-d1, more preferably 0.6 to 1.5 times, and even more preferably 0.7 to 1.3 times.

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 even more 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 it is also possible to reduce optical loss and electrical loss due to the light absorption and resistance of the intrinsic silicon-based thin film.

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

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 with the plasma discharge for the formation of the first intrinsic thin film stopped, and to resume the discharge and start the hydrogen plasma etching after the chamber becomes a gas atmosphere mainly composed of hydrogen. 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 outside 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.

The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment and various modifications and variations are possible.

LIST OF SYMBOLS 1 Solar cell 7 First region 7b, 8b Busbar portion 7f, 8f Finger portion 8 Second region 11 Crystalline silicon substrate 13 Third intrinsic silicon-based thin film 131 First intrinsic thin film 132 Second intrinsic thin film 133 Boundary intrinsic thin film 15 Silicon-based compound thin film 23 First intrinsic silicon-based thin film 23Z First intrinsic silicon-based material film 25 First conductivity type silicon-based thin film 25Z First conductivity type silicon-based material film 27 First electrode film 28 First transparent electrode film 29 First metal electrode film 33 Second intrinsic silicon-based thin film 33Z Second intrinsic silicon-based material film 35 Second conductivity type silicon-based thin film 35Z Second conductivity 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 (5)

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. 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 a substantially intrinsic thin film containing a p-type dopant at a concentration of 1×10 ¹⁵ /cm ³ or more and less than 1×10 ¹⁶ /cm ³ .
The method for producing the solar cell according to claim 1 . The method for producing a solar cell according to claim 2 , wherein the p-type dopant comprises boron. 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. 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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