JP2014072416A - Solar cell and manufacturing method therefor, solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell having a bonding structure of a conductivity type semiconductor layer and a crystalline semiconductor substrate, and excellent photoelectric conversion efficiency.SOLUTION: On one surface of an n-type crystalline semiconductor substrate 11, a silicon-based intermediate layer 12, a p-type silicon-based thin film layer 13, and a first collector electrode 15 are formed in this order. The p-type silicon-based thin film layer 13 has a first p-type silicon-based thin film layer 131 provided in contact with the silicon-based intermediate layer 12 and having a relatively low p-type impurity concentration that is constant in the film thickness direction, and a second p-type silicon-based thin film layer 132 having a relatively high p-type impurity concentration that is constant in the film thickness direction. The silicon-based intermediate layer 12 has a first intermediate layer 121 contiguous to the first p-type silicon-based thin film layer 131 and having a p-type impurity concentration that decreases monotonically from a concentration substantially same as the p-type impurity concentration of the first p-type silicon-based thin film layer 131, from the first p-type silicon-based thin film layer 131 side toward the n-type crystalline semiconductor substrate 11 side, and a second intermediate layer 122 having a p-type impurity concentration lower than that of the first intermediate layer.

Description

  The present invention relates to a solar cell, a manufacturing method thereof, and a solar cell module, and more particularly to a solar cell having a junction structure of a conductive semiconductor layer and a crystalline semiconductor substrate, a manufacturing method thereof, and a solar cell module.

  Conventionally, a solar cell having a structure in which an intrinsic amorphous semiconductor layer is inserted between a crystalline semiconductor substrate and a conductive semiconductor layer has been proposed. In such a solar cell, a crystalline semiconductor substrate is used as the power generation layer, carrier recombination on the substrate surface is reduced by the intrinsic amorphous semiconductor layer, and the crystalline semiconductor substrate is further formed by the conductive semiconductor layer on the outer side. By forming a high built-in electric field between them, the photoelectric conversion efficiency is improved.

  As such a solar cell, for example, in Patent Document 1, introduction of boron (B) between an intrinsic amorphous semiconductor layer and a crystalline semiconductor substrate alleviates band offset and improves interface characteristics. Discloses that the photoelectric conversion efficiency is improved.

Japanese Patent No. 3902534

  However, it is difficult to obtain sufficient photoelectric conversion efficiency even by the above conventional technique, and further improvement in photoelectric conversion efficiency is demanded.

  This invention is made | formed in view of the above, Comprising: The solar cell which has the junction structure of a conductive type semiconductor layer and a crystalline semiconductor substrate, and was excellent in photoelectric conversion efficiency, its manufacturing method, and a solar cell module are obtained. For the purpose.

  In order to solve the above-described problems and achieve the object, a solar cell according to the present invention includes a semiconductor intermediate layer, a reverse-conductivity-type semiconductor thin film layer, a first collector electrode on one surface of a one-conductivity-type crystalline semiconductor substrate. In this order, and having a one-conductivity-type semiconductor thin film layer and a second current collecting electrode in this order on the other surface of the one-conductivity-type crystalline semiconductor substrate, A first semiconductor thin film layer provided adjacent to the semiconductor intermediate layer and having a relatively low impurity concentration in the film thickness direction and a relatively high film provided on the first collector electrode side; A second semiconductor thin film layer having a constant reverse conductivity type impurity concentration in a thickness direction, wherein the semiconductor intermediate layer is adjacent to the first semiconductor thin film layer and has a reverse conductivity type impurity concentration of the first semiconductor thin film layer. From the layer side toward the one conductivity type crystalline semiconductor substrate side, the first A first intermediate layer that monotonously decreases from substantially the same concentration as the reverse conductivity type impurity concentration of the conductive thin film layer; and adjacent to the one conductive type crystalline semiconductor substrate side of the first intermediate layer than the first intermediate layer. And a second intermediate layer having a low reverse conductivity type impurity concentration.

  According to the present invention, there is an effect that a solar cell having a junction structure between a conductive semiconductor layer and a crystalline semiconductor substrate and having excellent photoelectric conversion efficiency can be obtained.

FIG. 1 is a schematic cross-sectional view of a schematic configuration of a solar battery cell according to a first embodiment of the present invention. FIG. 2 is a flowchart showing manufacturing steps of the solar battery cell according to the first embodiment. FIG. 3-1 is a schematic cross-sectional view illustrating the manufacturing process of the solar battery cell according to the first embodiment of the present invention. FIGS. 3-2 is a schematic cross section which shows the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIG. 3-3 is a schematic cross-sectional view illustrating the manufacturing process of the solar battery cell according to the first embodiment of the present invention. FIGS. 3-4 is a schematic cross section which shows the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 3-5 is a schematic cross section which shows the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 3-6 is a schematic cross-sectional view illustrating the manufacturing process of the solar battery cell according to the first embodiment of the present invention. FIG. 4 is a characteristic diagram showing a boron profile of the solar battery cell according to Example 1. FIG. 5 is a characteristic diagram showing a boron profile of the solar battery cell according to Example 2. 6 is a characteristic diagram showing a boron profile of the solar battery cell according to Example 3. FIG. FIG. 7 is a characteristic diagram showing a boron profile of the solar battery cell according to Example 4. FIG. 8 is a characteristic diagram showing a boron profile of a solar battery cell according to Comparative Example 1. FIG. 9 is a characteristic diagram showing a boron profile of a solar battery cell according to Comparative Example 2. FIG. 10 is a characteristic diagram showing the correlation between the boron concentration in the amorphous silicon film and the defect density. FIG. 11 is a characteristic diagram showing the correlation between the boron concentration in the amorphous silicon film and the band gap.

  EMBODIMENT OF THE INVENTION Below, the solar cell concerning this invention, its manufacturing method, and embodiment of a solar cell module are described in detail based on drawing. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. The drawings of solar cells used in the following embodiments are schematic, and the relationship between the thickness and width of the layers, the ratio of the thickness of each layer, and the like are different from the actual ones.

Embodiment 1 FIG.
FIG. 1 is a schematic cross-sectional view of a schematic configuration of a solar battery cell 10 according to a first embodiment of the present invention. This solar battery cell 10 is a heterojunction solar battery having a heterojunction structure of a conductive semiconductor layer and a crystalline semiconductor substrate. The solar cell 10 has an intermediate layer 12 which is an amorphous silicon layer having a thickness of 5 nm on the surface of one surface side of an n-type single crystal silicon substrate 11 constituting a photoelectric conversion layer as a one-conductivity type crystalline silicon substrate. An intrinsic (i-type) amorphous silicon thin film layer 16 having a thickness of 4 nm is formed on the other surface. The intermediate layer 12 includes a third intermediate layer 123, a second intermediate layer 122, and a first intermediate layer 121 in this order from the n-type single crystal silicon substrate 11 side. On the surface of the n-type single crystal silicon substrate 11, irregularities of the texture structure are formed in order to reduce reflection loss by the light confinement structure and to increase the optical path length in the substrate due to scattering. In FIG. 1, for the sake of simplicity, the illustration of the concavo-convex structure on the surface of the n-type single crystal silicon substrate 11 is omitted.

  A p-type amorphous silicon thin film layer 13 having a thickness of 4 nm is formed on the intermediate layer 12, and an n-type amorphous silicon thin film layer 17 having a thickness of 20 nm is formed on the intrinsic amorphous silicon thin film layer 16. Is formed. The p-type amorphous silicon thin film layer 13 includes a first p-type amorphous silicon thin film layer 131, a second p-type amorphous silicon thin film layer 132, and a third p-type amorphous silicon thin film layer 133 from the intermediate layer 12 side. They are provided in this order. Thereby, a heterojunction between the amorphous silicon thin film layer and the crystalline silicon substrate is formed, and a pn junction is formed by the n-type single crystal silicon substrate 11 and the p-type amorphous silicon thin film layer 13 via the intermediate layer 12. Is done.

  The intrinsic amorphous silicon thin film layer 16 that is an intrinsic semiconductor layer can suppress diffusion of impurities between heterojunctions and can form a junction having a steep impurity profile. Contribute. The intrinsic amorphous silicon thin film layer 16 and the n-type amorphous silicon thin film layer 17 form a BSF (Back Surface Field) region.

  A translucent electrode 14 having a thickness of 100 nm is formed on the p-type amorphous silicon thin film layer 13, and a translucent electrode 18 having a thickness of 100 nm is formed on the n-type amorphous silicon thin film layer 17. Has been. A collecting electrode 15 made of silver (Ag) and having a thickness of 60 μm is formed on the translucent electrode 14, and a collecting electrode 19 made of silver (Ag) and having a thickness of 60 μm is formed on the translucent electrode 18. Is formed. A reflective layer may be provided between the translucent electrode 18 and the collector electrode 19 or outside the collector electrode 19.

  The first intermediate layer 121, the second intermediate layer 122, and the third intermediate layer 123 of the intermediate layer 12 have a concentration of boron, which is a p-type impurity (acceptor), and a concentration gradient in the film thickness direction (referred to as a profile). Are different layers.

  The first intermediate layer 121 is provided adjacent to the first p-type amorphous silicon thin film layer 131 and between the first p-type amorphous silicon thin film layer 131 and the second intermediate layer 122, and the boron concentration is the first p-type. The boron concentration of the first p-type amorphous silicon thin film layer 131 monotonously decreases from the type amorphous silicon thin film layer 131 side toward the second intermediate layer 122 side. That is, boron in the first intermediate layer 121 is diffused from the first p-type amorphous silicon thin film layer 131 when the p-type amorphous silicon thin film layer 13 is formed. For this reason, the boron concentration at the interface of the first intermediate layer 121 on the first p-type amorphous silicon thin film layer 131 side is slightly lower than the boron concentration of the first p-type amorphous silicon thin film layer 131, and the first p-type amorphous silicon thin film layer 131. The boron concentration in the amorphous silicon thin film layer 131 is substantially the same. In the first intermediate layer 121, the boron concentration monotonously decreases in the film thickness direction from the interface toward the second intermediate layer 122 side.

The boron concentration of the first intermediate layer 121 is higher than that of the second intermediate layer 122 and is 1 × 10 ¹⁸ atoms / cm ³ or more. In the amorphous silicon film, the defect density increases as the boron concentration in the film increases. Therefore, the boron concentration of the first intermediate layer 121 is less than 1 × 10 ²⁰ atoms / cm ³ in order to improve the photoelectric conversion efficiency by increasing the open circuit voltage of the solar battery cell 10 by reducing the boron concentration in the film. Is done. When the boron concentration of the first intermediate layer 121 is 1 × 10 ²⁰ atoms / cm ³ or more, the effect of decreasing the boron concentration in the film is insufficient.

  In such a first intermediate layer 121, boron diffuses mainly from the first p-type amorphous silicon thin film layer 131 having a boron concentration lower than that of the third p-type amorphous silicon thin film layer 133, or the first p-type non-crystalline layer 121. Since the crystalline silicon thin film layer 131 is formed by being implanted by an electric field for plasma generation, it has a lower boron concentration than the case where it is adjacent to the third p-type amorphous silicon thin film layer 133. Defects are reduced, contributing to an improvement in open circuit voltage.

  The film thickness of the first intermediate layer 121 is preferably 1 nm or less. Since the first intermediate layer 121 contains more boron than the second intermediate layer 122 and induces defects, the first intermediate layer 121 is preferably thinner. By setting the film thickness of the first intermediate layer 121 to 1 nm or less, defects in the intermediate layer 12 are reduced, the open circuit voltage is increased, and the photoelectric conversion efficiency is improved. The lower limit of the film thickness of the first intermediate layer 121 is 0.5 nm from the viewpoint of reducing resistance.

The second intermediate layer 122 is provided between the first intermediate layer 121 and the third intermediate layer 123 and has a lower boron concentration than the first intermediate layer 121 and the third intermediate layer 123. The boron concentration of the second intermediate layer 122 is less than 1 × 10 ¹⁸ atoms / cm ³ . Since the second intermediate layer 122 is a film having a low boron concentration or almost no defects, the second intermediate layer 122 has an excellent passivation effect on the surface of the n-type single crystal silicon substrate 11 and contributes to an increase in open circuit voltage (Voc).

For this reason, the film thickness of the second intermediate layer 122 is preferably increased to a film thickness that does not cause a decrease in fill factor (FF) due to an increase in resistance, for example, 7 nm or less. Further, in order to sufficiently obtain a passivation effect, the lower limit of the film thickness of the second intermediate layer 122 is set to, for example, 0.5 nm or more. When the boron concentration of the second intermediate layer 122 is 1 × 10 ¹⁸ atoms / cm ³ or more, the passivation effect on the surface of the n-type single crystal silicon substrate 11 is reduced.

The third intermediate layer 123 is provided adjacent to the n-type single crystal silicon substrate 11 and between the n-type single crystal silicon substrate 11 and the second intermediate layer 122, and has a boron concentration from the n-type single crystal silicon substrate 11 side. It decreases monotonously in the film thickness direction toward the second intermediate layer 122 side. As will be described later, the boron concentration at the interface of the third intermediate layer 123 on the n-type single crystal silicon substrate 11 side is 1 × 10 ¹⁸ atoms / cm in consideration of the trade-off effect between the defect reduction effect and the band offset increase. ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less, more preferably 1 × 10 ¹⁹ atoms / cm ³ or more and less than 1 × 10 ²⁰ atoms / cm ³ . That is, the boron concentration of the third intermediate layer 123 is 1 × 10 ¹⁸ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less.

  Boron in the third intermediate layer 123 is diffused through the first intermediate layer 121 and the second intermediate layer 122 when the p-type amorphous silicon thin film layer 13 is formed. Then, the diffused boron segregates at the interface on the n-type single crystal silicon substrate 11 side, so that the boron monotonously decreases in the film thickness direction from the n-type single crystal silicon substrate 11 side toward the second intermediate layer 122 side. A profile is formed.

  The film thickness of the third intermediate layer 123 is preferably 1 nm or less. Since the third intermediate layer 123 contains more boron than the second intermediate layer 122 and induces defects, the third intermediate layer 123 is preferably thinner. By setting the film thickness of the third intermediate layer 123 to 1 nm or less, defects in the third intermediate layer 122 are reduced, the open circuit voltage is increased, and the photoelectric conversion efficiency is improved. The lower limit of the film thickness of the third intermediate layer 123 is 0.5 nm from the viewpoint of reducing resistance.

  The third intermediate layer 123, which is an amorphous silicon film, has a band gap reduced by containing boron. Thereby, the band offset between the 3rd intermediate | middle layer 123 and the n-type single crystal silicon substrate 11 with a comparatively low band gap is relieve | moderated, the open circuit voltage of the photovoltaic cell 10 increases, and photoelectric conversion efficiency improves.

  By providing such an intermediate layer 12, the open-circuit voltage of the solar battery cell 10 increases due to the defect reduction effect due to the boron concentration reduction in the first intermediate layer 121 and the band offset relaxation effect in the third intermediate layer 123, Photoelectric conversion efficiency is improved.

  The first p-type amorphous silicon thin film layer 131, the second p-type amorphous silicon thin film layer 132, and the third p-type amorphous silicon thin film layer 133 of the p-type amorphous silicon thin film layer 13 are contained in the p-type. The concentration of boron, which is an impurity (acceptor), and the concentration gradient in the film thickness direction (referred to as profiles) are different layers.

The first p-type amorphous silicon thin film layer 131 is provided adjacent to the first intermediate layer 121 and between the first intermediate layer 121 and the second p-type amorphous silicon thin film layer 132. The first p-type amorphous silicon thin film layer 131 has a constant boron concentration (first concentration) that is relatively lower than that of the third p-type amorphous silicon thin film layer 133 in the film thickness direction. The boron concentration of the first p-type amorphous silicon thin film layer 131 is 1 × 10 ¹⁹ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less.

When the boron concentration of the first p-type amorphous silicon thin film layer 131 is less than 1 × 10 ¹⁹ atoms / cm ³ , the fill factor (FF) is reduced due to the decrease in the conductivity of the first p-type amorphous silicon thin film layer 131. descend. When the boron concentration of the first p-type amorphous silicon thin film layer 131 is higher than 1 × 10 ²⁰ atoms / cm ³ , the boron concentration of the first intermediate layer 121 becomes high and defects in the first intermediate layer 121 increase. The effect of improving the open circuit voltage (Voc) due to the reduction of defects in the first intermediate layer 121 becomes insufficient. Since the first p-type amorphous silicon thin film layer 131 has a constant boron concentration (first concentration) in the film thickness direction, the boron concentration at the interface on the first intermediate layer 121 side is also the first concentration. .

  The film thickness of the first p-type amorphous silicon thin film layer 131 is preferably 1.5 nm or less. When the thickness of the p-type amorphous silicon thin film layer 13 is too thick, a current (Jsc) is reduced due to light absorption loss in the p-type amorphous silicon thin film layer 13. Therefore, the thickness of the first p-type amorphous silicon thin film layer 131 is preferably reduced to a thickness that can function as the p-type amorphous silicon thin film layer 13 at the above boron concentration. The lower limit of the thickness of the silicon thin film layer 131 is 1.0 nm.

  The second p-type amorphous silicon thin film layer 132 is provided between the first p-type amorphous silicon thin film layer 131 and the third p-type amorphous silicon thin film layer 133. The boron concentration of the second p-type amorphous silicon thin film layer 132 is higher than the boron concentration of the first p-type amorphous silicon thin film layer 131 and lower than the boron concentration of the third p-type amorphous silicon thin film layer 133.

  As will be described later, the boron of the second p-type amorphous silicon thin film layer 132 is a third p-type amorphous silicon thin film in addition to a p-type amorphous silicon thin film having the same boron concentration as the first p-type amorphous silicon thin film layer 131. The boron in the layer 133 is diffused or is implanted by an electric field for plasma generation during film formation. For this reason, the second p-type amorphous silicon thin film layer 132 has a boron that monotonously decreases in the film thickness direction from the third p-type amorphous silicon thin film layer 133 side toward the first p-type amorphous silicon thin film layer 131 side. A profile is formed. Accordingly, the boron concentration range of the second p-type amorphous silicon thin film layer 132 is between the boron concentration of the first p-type amorphous silicon thin film layer 131 and the boron concentration of the third p-type amorphous silicon thin film layer 133. It becomes a range.

  The film thickness of the second p-type amorphous silicon thin film layer 132 is determined by the relationship between the boron concentration of the first p-type amorphous silicon thin film layer 131 and the boron concentration of the third p-type amorphous silicon thin film layer 133. It is preferable that it is 1 nm or less. When the thickness of the p-type amorphous silicon thin film layer 13 is too thick, a short circuit current (Jsc) is reduced due to light absorption loss in the p-type amorphous silicon thin film layer 13. Therefore, the thickness of the second p-type amorphous silicon thin film layer 132 is preferably thin enough to function as the p-type amorphous silicon thin film layer 13 as a whole.

The third p-type amorphous silicon thin film layer 133 is provided on the translucent electrode 14 side adjacent to the second p-type amorphous silicon thin film layer 132. The third p-type amorphous silicon thin film layer 133 has a constant boron concentration (second concentration) that is relatively higher than that of the first p-type amorphous silicon thin film layer 131 in the film thickness direction. The boron concentration of the third p-type amorphous silicon thin film layer 133 is 1 × 10 ²¹ atoms / cm ³ or more. By setting the boron concentration of the third p-type amorphous silicon thin film layer 133 to 1 × 10 ²¹ atoms / cm ³ or more, the boron concentration of the first p-type amorphous silicon thin film layer 131 is set to 1 × 10 ²⁰ atoms / cm ^3. The influence of the decrease in the conductivity of the p-type amorphous silicon thin film layer 13 due to the following, that is, the decrease in FF can be suppressed. Further, the upper limit of the boron concentration of the third p-type amorphous silicon thin film layer 133 is 1 × 10 ²² atoms / cm ³ at which a sufficiently low resistance is obtained.

  The film thickness of the third p-type amorphous silicon thin film layer 133 is preferably 2 nm or less. When the thickness of the p-type amorphous silicon thin film layer 13 is too thick, a current (Jsc) is reduced due to light absorption loss in the p-type amorphous silicon thin film layer 13. Therefore, the thickness of the third p-type amorphous silicon thin film layer 133 is preferably reduced to a thickness that can function as the p-type amorphous silicon thin film layer 13 at the above boron concentration. The lower limit of the film thickness of the silicon thin film layer 133 is 1.0 nm.

  Next, a method for manufacturing the solar battery cell 10 according to the first embodiment configured as described above will be described with reference to FIG. 2 and FIGS. 3-1 to 3-6. FIG. 2 is a cross-sectional view of a flowchart showing manufacturing steps of the intermediate layer 12 and the p-type amorphous silicon thin film layer 13 among the manufacturing steps of the solar battery cell 10 according to the first embodiment. FIGS. 3-1 to 3-6 are schematic cross-sectional views illustrating manufacturing steps of the solar battery cell 10 according to the first embodiment.

  First, an n-type single crystal silicon substrate 11 having a main surface with a plane orientation of (100) and containing phosphorus (P) is prepared. The n-type single crystal silicon substrate 11 has a size of about 10 cm × 10 cm to 20 cm × 20 cm and a thickness of about 60 to 300 μm. As the n-type single crystal silicon substrate 11, a substrate cut out from an ingot is used. The cut surface is polished and the surface is flattened.

Since the n-type single crystal silicon substrate 11 is manufactured by slicing an ingot formed by cooling and solidifying molten silicon with a wire saw, a damage (crystal strain) layer at the time of slicing remains on the surface. In order to remove the damaged layer, the n-type single crystal silicon substrate 11 is first immersed in an acid such as HF + HNO ₃ or a heated alkaline solution, for example, in an aqueous sodium hydroxide solution, and the surface is etched by about 10 to 20 μm. As a result, the damaged region that occurs when the silicon substrate is cut out and exists near the surface of the n-type single crystal silicon substrate 11 is removed.

  Further, it is preferable to remove impurities in the n-type single crystal silicon substrate 11 by gettering. For the gettering, for example, there is a method in which phosphorus is thermally diffused on the surface of the n-type single crystal silicon substrate 11 and impurities are segregated in the formed phosphorus glass layer.

  Then, after removing impurities in the n-type single crystal silicon substrate 11 by gettering, the n-type single crystal silicon substrate is used to reduce reflection loss by the optical confinement structure and to increase the optical path length in the substrate by scattering. Asperities having a texture structure are formed on the surface 11. The unevenness of the texture structure can be formed by anisotropic etching using the (100) plane of the n-type single crystal silicon substrate 11 and utilizing the different etching rates of the (100) plane and the (111) plane. An alkaline solution and an additive are used for the chemical solution for etching, potassium hydroxide, sodium hydroxide and the like are used for the alkaline solution, and isopropyl alcohol and the like are used for the additive.

  In addition, although the case where the texture structure is formed after the wire saw damage layer removing step is described here, when the influence of metal contamination in the wire saw slice is small, the removal of the wire saw damage layer and the formation of the texture structure are performed. You may also go there. Further, as a method for forming the texture structure, dry etching such as reactive ion etching (RIE) may be used.

  Next, the n-type single crystal silicon substrate 11 is cleaned by RCA cleaning. Then, the surface oxide film of the n-type single crystal silicon substrate 11 is removed using dilute hydrofluoric acid immediately before the formation of the intermediate layer.

  Next, the intermediate layer 12 and the p-type amorphous silicon thin film layer 13 are formed in this order on one surface side of the n-type single crystal silicon substrate 11 while the surface of the n-type single crystal silicon substrate 11 is clean. The The intermediate layer 12 has a thickness of 5 nm, and the p-type amorphous silicon thin film layer 13 has a thickness of 4 nm. The intermediate layer 12 and the p-type amorphous silicon thin film layer 13 are formed by the following process.

(Intrinsic amorphous silicon film formation process)
First, an intrinsic amorphous silicon film 12a is formed on one surface side of the n-type single crystal silicon substrate 11 (FIG. 3-1, step S10). In the present embodiment, the flow rate of the reaction gas is changed to silane (SiH) in an RF plasma CVD chamber of 13.56-60 MHz, for example, in an RF output 10 W, substrate temperature 170 ° C., gas pressure 100 Pa atmosphere by plasma CVD. ₄ ): 50 sccm and hydrogen (H ₂ ): 300 sccm to form an intrinsic amorphous silicon film 12a having a thickness of 4 nm.

(Low-concentration boron-doped p-type amorphous silicon film formation process)
Next, a low-concentration boron-doped p-type amorphous silicon film 13a doped with boron at a low concentration (first concentration) is formed on the intrinsic amorphous silicon film 12a. In this embodiment, the flow rate of the reaction gas is changed to silane (SiH) in an RF plasma CVD chamber of 13.56 to 60 MHz, for example, in an RF output 200 W, substrate temperature 170 ° C., gas pressure 100 Pa by plasma CVD. ₄ ): 50 sccm, hydrogen (H ₂ ): 300 sccm, diborane (B ₂ H ₆ ): 0.5 sccm to form a low-concentration boron-doped p-type amorphous silicon film 13a having a thickness of 2 nm.

  Then, when the low-concentration boron-doped p-type amorphous silicon film 13a is formed on the intrinsic amorphous silicon film 12a, boron (B) of the low-concentration boron-doped p-type amorphous silicon film 13a is converted into intrinsic amorphous silicon. The intermediate layer 12 is diffused into the film 12a or implanted by an electric field for generating plasma in the reactor during film formation, and the first intermediate layer 121 and the first intermediate layer 12 are formed from the low-concentration boron-doped p-type amorphous silicon film 13a side. A second intermediate layer 122 and a third intermediate layer 123 are formed (FIG. 3-2, step S20). Then, boron diffused from the first p-type amorphous silicon thin film layer 131 to the vicinity of the n-type single crystal silicon substrate 11 is segregated at the interface on the n-type single crystal silicon substrate 11 side.

  As a result, the boron concentration of the first intermediate layer 121 is such that the boron concentration of the low-concentration boron-doped p-type amorphous silicon film 13a is from the low-concentration boron-doped p-type amorphous silicon film 13a side to the second intermediate layer 122 side. From this, a monotonically decreasing boron profile is formed. The boron concentration at the interface of the first intermediate layer 121 on the low-concentration boron-doped p-type amorphous silicon film 13a side is slightly lower than the boron concentration of the low-concentration boron-doped p-type amorphous silicon film 13a.

The second intermediate layer 122 is a layer having a lower boron concentration than the first intermediate layer 121 and the third intermediate layer 123, and finally the boron concentration is less than 1 × 10 ¹⁸ atoms / cm ³ .

The third intermediate layer 123 is formed between the n-type single crystal silicon substrate 11 and the second intermediate layer 122 adjacent to the n-type single crystal silicon substrate 11. In the third intermediate layer 123, a boron profile is formed in which the boron concentration monotonously decreases in the film thickness direction from the n-type single crystal silicon substrate 11 side toward the second intermediate layer 122 side. Further, the boron concentration of the third intermediate layer 123 is higher than that of the second intermediate layer 122, and finally becomes 1 × 10 ¹⁸ atoms / cm ³ or more.

  Thus, by forming the low-concentration boron-doped p-type amorphous silicon film 13a on the intrinsic amorphous silicon film 12a, the first intermediate having a lower boron concentration than the third p-type amorphous silicon thin film layer 133 is formed. Layer 121 can be formed.

(High-concentration boron-doped p-type amorphous silicon film formation process)
Next, a high-concentration boron-doped p-type amorphous silicon film doped with boron at a concentration higher than the first concentration (second concentration) is formed on the low-concentration boron-doped p-type amorphous silicon film 13a. . In the present embodiment, the flow rate of the reaction gas is changed to silane (SiH) in an RF plasma CVD chamber of 13.56 to 60 MHz, for example, in an RF output of 30 W, a substrate temperature of 170 ° C., and a gas pressure of 100 Pa by plasma CVD. ₄ ): 50 sccm, hydrogen (H ₂ ): 300 sccm, diborane (B ₂ H ₆ ): 1 sccm to form a high-concentration boron-doped p-type amorphous silicon film having a thickness of 2 nm.

  Then, when the high-concentration boron-doped p-type amorphous silicon film is formed on the low-concentration boron-doped p-type amorphous silicon film 13a, boron (B) of the high-concentration boron-doped p-type amorphous silicon film is low-concentration boron-doped. By diffusing into the p-type amorphous silicon film 13a, the first p-type amorphous silicon thin film layer 131 and the second p-type amorphous silicon thin film layer are formed as the p-type amorphous silicon thin film layer 13 from the intermediate layer 12 side. 132 and the third p-type amorphous silicon thin film layer 133 are formed in this order (FIG. 3-3, step S30).

  A region on the first intermediate layer 121 side in the low-concentration boron-doped p-type amorphous silicon film 13a and a region where the diffusion of boron (B) in the high-concentration boron-doped p-type amorphous silicon film does not reach the first p-type non-layer. A crystalline silicon thin film layer 131 is formed. For this reason, the boron concentration of the first p-type amorphous silicon thin film layer 131 is the same as that of the low-concentration boron-doped p-type amorphous silicon film 13a. Therefore, the first p-type amorphous silicon thin film layer 131 has boron having a constant boron concentration (first concentration) relatively low as compared with the third p-type amorphous silicon thin film layer 133 in the film thickness direction. A profile is formed.

  A region on the high-concentration boron-doped p-type amorphous silicon film side in the low-concentration boron-doped p-type amorphous silicon film 13a, where boron (B) in the high-concentration boron-doped p-type amorphous silicon film is diffused. The second p-type amorphous silicon thin film layer 132 is formed. For this reason, the boron concentration of the second p-type amorphous silicon thin film layer 132 is higher than the boron concentration of the first p-type amorphous silicon thin film layer 131 and higher than the boron concentration of the third p-type amorphous silicon thin film layer 133. Lower. The second p-type amorphous silicon thin film layer 132 includes boron that monotonously decreases in the film thickness direction from the third p-type amorphous silicon thin film layer 133 side toward the first p-type amorphous silicon thin film layer 131 side. A profile is formed.

  Then, the high-concentration boron-doped p-type amorphous silicon film becomes the third p-type amorphous silicon thin film layer 133. Accordingly, the third p-type amorphous silicon thin film layer 133 has a constant boron concentration (second concentration) relatively higher than that of the first p-type amorphous silicon thin film layer 131 in the film thickness direction. A boron profile is formed.

  Even when the high-concentration boron-doped p-type amorphous silicon film is formed, boron (B) in the low-concentration boron-doped p-type amorphous silicon film 13a is diffused into the intrinsic amorphous silicon film 12a. The first intermediate layer 121, the second intermediate layer 122, and the third intermediate layer 123 are formed.

Next, an intrinsic amorphous silicon thin film layer 16 is formed on the other surface side of the n-type single crystal silicon substrate 11 (FIGS. 3-4). In the present embodiment, the flow rate of the reaction gas is changed to silane (SiH) in an RF plasma CVD chamber of 13.56-60 MHz, for example, in an RF output 10 W, substrate temperature 170 ° C., gas pressure 100 Pa atmosphere by plasma CVD. ₄ ): 50 sccm and hydrogen (H ₂ ): 300 sccm to form an intrinsic amorphous silicon thin film layer 16 having a thickness of 4 nm. The intrinsic amorphous silicon thin film layer 16 preferably has a thickness of 1 nm to 10 nm.

Next, the n-type amorphous silicon thin film layer 17 is formed on the intrinsic amorphous silicon thin film layer 16 (FIGS. 3-4). In the present embodiment, the flow rate of the reaction gas is changed to silane (SiH) in an RF plasma CVD chamber of 13.56 to 60 MHz, for example, in an RF output of 30 W, a substrate temperature of 170 ° C., and a gas pressure of 100 Pa by plasma CVD. ₄ ): 50 sccm, hydrogen (H ₂ ): 300 sccm, phosphine (PH ₃ ): 0.4 sccm to form an n-type amorphous silicon thin film layer 17 having a thickness of 20 nm. The thickness of the n-type amorphous silicon thin film layer 17 is preferably in the range of 1 nm to 40 nm.

Next, the translucent electrode 14 is formed on the p-type amorphous silicon thin film layer 13 on one surface side of the n-type single crystal silicon substrate 11 (FIGS. 3-5). As the translucent electrode 14, a conductive oxide film having translucency is used. In this embodiment mode, the sputtering method is used with an RF power of 800 W, a substrate temperature of 180 ° C., and a gas pressure of 0.7 Pa. The gas flow rates are argon (Ar): 70 sccm, oxygen (O ₂ ) (5% Ar base): By flowing at 5 sccm, indium tin oxide (ITO) having a thickness of 100 nm is formed. The film thickness of the translucent electrode 14 is preferably in the range of 60 nm to 120 nm from the viewpoint of light confinement.

As the translucent electrode _{14, SnO 2, In 2 O} 3, ZnO, CdO, CdIn 2 O 4, CdSnO 3, MgIn 2 O 4, CdGa 2 O 4, GaInO 3, InGaZnO 4, Cd 2 Sb 2 A translucent conductive film such as O ₇ , Cd ₂ GeO ₄ , CuAlO ₂ , CuGaO ₂ , SrCu ₂ O ₂ , TiO ₂ , Al ₂ O ₃ can be used, and a translucent film formed by stacking these films. An electrically conductive film can also be used. As the dopant, one or more elements selected from Al, Ga, In, B, Y, Si, Zr, Ti, F, and Ce may be used. Further, as a method for forming the translucent electrode 14, a vapor deposition method, an ion plating method, or the like can be used in addition to the sputtering method.

  Next, on the other surface side of the n-type single crystal silicon substrate 11, a translucent electrode 18 is formed on the n-type amorphous silicon thin film layer 17 (FIGS. 3-5). As the translucent electrode 18, a conductive oxide film having translucency is used. Since the translucent electrode 18 is located on the back side of the n-type single crystal silicon substrate 11 with respect to light, the transmissivity of light on the short wavelength side may be lower than that of the translucent electrode 14, and on the longer wavelength side. It is preferable to select a film that reduces light absorption. The formation method, the forming material, and the film thickness of the translucent electrode 18 can be the same as those of the translucent electrode 14 described above.

After the formation of the translucent electrode 18, a reflective layer may be formed on the translucent electrode 18 on the other surface side of the n-type single crystal silicon substrate 11. Since the reflective layer can return the incident light to the n-type single crystal silicon substrate 11, the light can be used more effectively. As the reflective layer, for example, a silver (Ag) layer formed by a sputtering method can be used. In addition, as a formation method of a reflection layer, a vapor deposition method etc. can be used besides sputtering method. In addition to silver (Ag), white (high reflection) material made of fine particles of aluminum (Al) or metal oxide may be used as the material of the reflective layer. Examples of such a white highly reflective material include MgO, Al ₂ O ₃ , and white zinc. In this case, since the material is an insulator, the reflective layer is formed after the collector electrode 19 is formed on the translucent electrode 18. Further, instead of forming the reflective layer, the current collecting electrode 19 can also have the function of the reflective layer. In this embodiment, the formation of the reflective layer is omitted.

  Next, a collector electrode 15 is formed on the translucent electrode 14 on one surface side of the n-type single crystal silicon substrate 11, and a collector electrode 19 is disposed on the translucent electrode 18 on the other surface side of the n-type single crystal silicon substrate 11. Is formed (FIGS. 3-6). The collector electrode 15 and the collector electrode 19 are formed by an ink jet method, a screen printing method, a copper wire adhesion, a spray method, or the like. Among these, from the viewpoint of productivity, a screen printing method is preferable as a method of forming the collecting electrode 15 and the collecting electrode 19. In the screen printing method, for example, the translucent electrode 15 and the translucent electrode 19 are formed using a conductive paste containing metal particles such as silver (Ag) and a resin binder.

  By performing the above steps, the solar battery cell 10 having the configuration shown in FIG. 1 is obtained.

  In the first embodiment described above, the third p-type amorphous silicon thin film layer is formed as the first p-type amorphous silicon thin film layer 131 by forming the first p-type amorphous silicon thin film layer 131 having a relatively low constant boron concentration. A first intermediate layer 121, a second intermediate layer 122, and a third intermediate layer 123 having a lower boron concentration than when only the silicon thin film layer 133 is formed are formed. Thereby, the effect that the open circuit voltage of the solar cell 10 is increased by the defect reduction effect by the boron concentration reduction in the first intermediate layer 121 and the band offset relaxation effect in the third intermediate layer 123, and the photoelectric conversion efficiency is improved. Is obtained. Also, the first p-type amorphous silicon thin film layer 131 having a relatively low constant boron concentration and the third p-type amorphous silicon thin film layer 133 having a relatively high constant boron concentration are formed. Further, when only the first p-type amorphous silicon thin film layer 131 is formed as the p-type amorphous silicon thin film layer, the conductivity that becomes insufficient can be compensated.

  In addition, the second intermediate layer 122 formed between the first intermediate layer 121 and the third intermediate layer 123 and having a low boron concentration and few defects exhibits a passivation effect on the surface of the n-type single crystal silicon substrate 11, This contributes to the improvement of the open circuit voltage of the solar battery cell 10.

  Therefore, according to Embodiment 1, there is an effect that a solar battery cell having a heterojunction structure of a crystalline semiconductor substrate and a conductive semiconductor layer and having excellent photoelectric conversion efficiency can be obtained.

  Although the case where the third intermediate layer 123 exists has been described above, the third intermediate layer 123 is formed depending on the boron concentration of the p-type amorphous silicon thin film layer 13 as in Example 2 described later. Alternatively, there may be a configuration having only the first intermediate layer 121 and the second intermediate layer 122. Even in the configuration in which the third intermediate layer 123 does not exist, the defect reduction effect by the first intermediate layer 121 can be obtained as described above, the open circuit voltage of the solar battery cell 10 is increased, and the photoelectric conversion efficiency is improved.

Embodiment 2. FIG.
In the second embodiment, in the method of manufacturing a solar battery cell according to the first embodiment, an intrinsic amorphous silicon film forming step in which an intrinsic amorphous silicon film 12a is formed on one surface side of the n-type single crystal silicon substrate 11 is performed. Before (FIG. 3-1, step S10), the case where the boron adsorption | suction process which adsorb | sucks boron (B) to the surface of the one surface side of the n-type single crystal silicon substrate 11 is implemented is demonstrated.

The boron adsorption step is performed, for example, in a chamber under an atmosphere of a substrate temperature of 170 ° C. and a gas pressure of 800 Pa by flowing a gas flow rate of hydrogen (H ₂ ): 100 sccm and diborane (B ₂ H ₆ ): 1 sccm. Thereby, since diborane (B ₂ H ₆ ) is adsorbed on the surface on the one surface side of the n-type single crystal silicon substrate 11, boron adsorbs on the surface on the one surface side of the n-type single crystal silicon substrate 11.

  As a result, the third intermediate layer 123 can be formed even when the boron concentration of the p-type amorphous silicon thin film layer 13 is set lower within the above-described range. Therefore, according to the manufacturing method of the solar battery cell according to the second embodiment, it is possible to obtain the defect reduction effect by the boron concentration reduction of the first intermediate layer 121 and the band offset relaxation effect by the third intermediate layer 123, The open circuit voltage of the solar battery cell is increased, and the photoelectric conversion efficiency is improved.

  Next, the solar cell according to the above-described embodiment will be described based on specific examples. A solar battery cell having the configuration shown in FIG. 1 was produced according to the method for manufacturing a solar battery cell according to the first embodiment described above, and a solar battery cell of Example 1 was obtained. FIG. 4 is a characteristic diagram showing a boron profile of the solar battery cell according to Example 1. Table 1 shows the boron concentration and film thickness conditions of the intermediate layer 12 and the p-type amorphous silicon thin film layer 13 of the solar battery cell of Example 1.

In addition, the example is the same as the solar cell of Example 1 except that the gas flow rate of diborane (B ₂ H ₆ ) during the formation of the low-concentration boron-doped p-type amorphous silicon film is reduced to 0.1 sccm. 2 solar cells were produced. FIG. 5 is a characteristic diagram showing a boron profile of the solar battery cell according to Example 2. Table 1 also shows the boron concentrations and film thickness conditions of the intermediate layer 12 and the p-type amorphous silicon thin film layer 13 of the solar battery cell of Example 2.

In the solar cell of Example 2, since the gas flow rate of diborane (B ₂ H ₆ ) during the formation of the low-concentration boron-doped p-type amorphous silicon film is reduced, the p-type amorphous silicon thin film layer 13 as a whole is reduced. As a result, the total amount of boron is decreasing. For this reason, since the diffusion amount of boron to the intermediate layer is reduced, the boron concentration is low even in the region adjacent to the n-type single crystal silicon substrate 11, and the third intermediate layer 123 is not formed.

  Further, a solar cell of Example 3 was fabricated in the same manner as the solar cell of Example 2 except that the boron adsorption step described in Embodiment 2 was performed. The boron adsorption process was carried out for 5 minutes. 6 is a characteristic diagram showing a boron profile of the solar battery cell according to Example 3. FIG. Table 1 also shows the boron concentration and film thickness conditions of the intermediate layer 12 and the p-type amorphous silicon thin film layer 13 of the solar battery cell of Example 3.

  In the solar cell of Example 3, the basic manufacturing process is the same as in Example 2, but the third intermediate layer 123 that is not formed in Example 2 is formed by performing the boron adsorption process. Is done.

  Further, a solar cell of Example 4 was fabricated in the same manner as the solar cell of Example 2 except that the boron adsorption process described in Embodiment 2 was performed. The boron adsorption process was carried out for 10 minutes. FIG. 7 is a characteristic diagram showing a boron profile of the solar battery cell according to Example 4. Table 1 also shows the boron concentration and film thickness conditions of the intermediate layer 12 and the p-type amorphous silicon thin film layer 13 of the solar battery cell of Example 4.

  In the solar cell of Example 4, the basic manufacturing process is the same as in Example 2, but the third intermediate layer 123 that is not formed in Example 2 is formed by performing the boron adsorption process. Is done. Further, in Example 4, the boron adsorption process is performed longer than in Example 3, and therefore the boron concentration in the third intermediate layer 123 is higher than in Example 3.

For comparison, the p-type amorphous silicon thin film layer has the same boron concentration as that of the solar cell of Example 1 except that the boron concentration is constant in the film thickness direction: 1 × 10 ²¹ atoms / cm ^3. Thus, a solar battery cell of Comparative Example 1 was produced. In this case, instead of the step of forming the low-concentration boron-doped p-type amorphous silicon film and the step of forming the high-concentration boron-doped p-type amorphous silicon film, the boron concentration is set to 1 × 10 ²¹ atoms / cm ³ and high-concentration boron-doped. The p-type amorphous silicon thin film layer 31 (hereinafter, referred to as the p-type amorphous silicon thin film layer 31) having a constant boron concentration in the film thickness direction by performing only the process of forming the p-type amorphous silicon film may be used. ). At this time, the gas flow rate of diborane (B ₂ H ₆ ) during the formation of the high-concentration boron-doped p-type amorphous silicon film was set to 1 sccm. In addition, the film thickness of the p-type amorphous silicon thin film layer 31 was set to 4 nm, so that the film thicknesses of the p-type amorphous silicon thin film layers of Comparative Example 1 and Example 1 were made uniform.

  FIG. 8 is a characteristic diagram showing a boron profile of a solar battery cell according to Comparative Example 1. For convenience, in the solar cell according to Comparative Example 1, the boron concentration does not correspond, but regions corresponding to the first intermediate layer 121, the second intermediate layer 122, and the third intermediate layer 123 in the solar cell of Example 1 are shown. Similarly, the first intermediate layer 121, the second intermediate layer 122, and the third intermediate layer 123 are shown. Table 1 also shows the boron concentration and film thickness conditions of the intermediate layer 12 and the p-type amorphous silicon thin film layer of the solar battery cell of Comparative Example 1.

  In the solar cell of Comparative Example 1, since the intermediate layer 12 is formed by diffusing boron from the high-concentration boron-doped p-type amorphous silicon film into the intrinsic amorphous silicon film 12a, the first intermediate layer 121 and the first 3 The boron concentration in the intermediate layer 123 is higher than that in the first embodiment.

For comparison, the gas flow rate of diborane (B ₂ H ₆ ) during the formation of the high-concentration boron-doped p-type amorphous silicon film is reduced from 1 sccm to 0.5 sccm, and the p-type amorphous silicon thin film layer A solar battery cell of Comparative Example 2 was fabricated in the same manner as the solar battery cell of Comparative Example 1 except that the boron concentration was constant in the film thickness direction: 1 × 10 ²⁰ atoms / cm ³ . FIG. 9 is a characteristic diagram showing a boron profile of a solar battery cell according to Comparative Example 2. For convenience, the boron concentration does not correspond in the solar cell according to Comparative Example 2, but the regions corresponding to the first intermediate layer 121, the second intermediate layer 122, and the third intermediate layer 123 in the solar cell of Example 1 are the same. Are shown as a first intermediate layer 121, a second intermediate layer 122, and a third intermediate layer 123, respectively. Table 1 also shows the boron concentration and film thickness conditions of the intermediate layer 12 and the p-type amorphous silicon thin film layer of the solar battery cell of Comparative Example 2.

  In the solar cell of Comparative Example 2, the boron concentration of the p-type amorphous silicon thin film layer 31 having a constant boron concentration in the film thickness direction is the low-concentration boron-doped p-type amorphous silicon film 13a (first p-type) of Example 1. The amount of boron in the p-type amorphous silicon thin film layer 31 as a whole is smaller than that of the p-type amorphous silicon film 13 in the first embodiment, and is similar to that of the amorphous silicon thin film layer 131). Therefore, the third intermediate layer 123 is not formed.

The short-circuit current density Jsc (mA / cm ² ) and the open-circuit voltage Voc (V) which are the JV characteristics of the solar battery in the solar battery cells of Examples 1 to 4, Comparative Example 1 and Comparative Example 2 manufactured as described above. ) And fill factor FF were measured. The results are shown in Table 2.

  When Example 1 is compared with Comparative Example 1, it can be seen that Example 1 has an increased Voc and a higher photoelectric conversion efficiency (%) than Comparative Example 1. The reason why the photoelectric conversion efficiency of Example 1 is improved is that Example 1 is induced by boron because the boron concentrations of the first intermediate layer 121 and the third intermediate layer 123 are reduced compared to Comparative Example 1. This is considered to be due to the effect of reducing defects in the intermediate layer 12.

FIG. 10 is a characteristic diagram showing the correlation between the boron concentration (atoms / cm ³ ) in the amorphous silicon film and the defect density (au). Note that the vertical axis in FIG. 10 shows the case where the boron concentration is 1 × 10 ¹⁸ atoms / cm ³ as a reference (= 1). FIG. 10 shows that the defect density decreases as the boron concentration in the amorphous silicon film decreases. The defect density when the boron concentration is 1 × 10 ²¹ atoms / cm ³ is several tens of times the reference. Therefore, as in the first embodiment, the boron-doped p-type amorphous silicon film forming step is applied, and boron in the first intermediate layer 121 is formed at the initial stage of the p-type amorphous silicon thin film layer 13. In order to reduce defects in the first intermediate layer 121, it is effective to set the boron concentration of the first p-type amorphous silicon thin film layer 131 that affects the concentration to 1 × 10 ²⁰ atoms / cm ³ or less.

  Moreover, also when Example 2-Example 4 and Comparative Example 1 are compared, it turns out that Voc increased compared with Comparative Example 1 and Example 2-Example 4 improved photoelectric conversion efficiency (%). . The reason why the photoelectric conversion efficiencies of Examples 2 to 4 are improved is, as in Example 1, induced by boron due to the reduced boron concentration of the intermediate layer 12 compared to Comparative Example 1. This is considered to be due to the effect of reducing defects in the intermediate layer 12.

  When Comparative Example 2, Example 1 and Comparative Example 1 are compared, it can be seen that Voc of Comparative Example 2 increases compared to Comparative Example 1, but decreases compared to Example 1. Moreover, it turns out that FF of the comparative example 2 falls rather than the comparative example 1 and Example 1. FIG.

The Voc of Comparative Example 2 increased compared to Comparative Example 1, as in Example 1, Comparative Example 2 compared to Comparative Example 1 in the region corresponding to the first intermediate layer 121 and the third intermediate layer 123. This is considered to be due to the effect of reducing defects in the intermediate layer 12 induced by boron due to the reduction of the boron concentration. That is, by setting the boron concentration of the p-type amorphous silicon thin film layer 31 that affects the boron concentration in the first intermediate layer 121 to 1 × 10 ²⁰ atoms / cm ³ or less, the first intermediate layer 121 and the third intermediate layer 121 It is considered that the boron concentration in the region corresponding to the layer 123 is reduced, and defects in the intermediate layer 12 induced by boron are reduced.

  On the other hand, since the boron concentration in the p-type amorphous silicon thin film layer 31 is higher than the boron concentration in the p-type amorphous silicon thin film layer 13, defects in the p-type amorphous silicon thin film layer 13 are p-type amorphous. Although the number of defects in the silicon thin film layer 31 is larger than that of the first example, the Voc of the second comparative example is lower than that of the first example in the second example adjacent to the n-type single crystal silicon substrate 11 in the second comparative example. This is considered to be due to an increase in band offset at the interface between the intermediate layer 122 and the n-type single crystal silicon substrate 11.

FIG. 11 is a characteristic diagram showing the correlation between the boron concentration (atoms / cm ³ ) in the amorphous silicon film and the band gap. FIG. 11 shows that the band gap increases as the boron concentration in the amorphous silicon film decreases. Therefore, when the band gap of the intermediate layer is large due to the decrease in boron concentration, a wide band offset is formed between the n-type single crystal silicon substrate 11 and the intermediate layer having a relatively low band gap. That is, in the case of the comparative example 2, a wide band offset is formed between the second intermediate layer 122 and the n-type single crystal silicon substrate 11.

  Similarly, although there is an effect of reducing defects in the intermediate layer 12 by reducing the boron concentration in the intermediate layer 12, the reason why the Voc of Example 4 is lower than that of the example is the same as that of the third intermediate layer 123 and the n-type. It is considered that an increase in band offset at the interface with the single crystal silicon substrate 11 has an influence. In Example 2, since the third intermediate layer 123 does not exist, there is no band offset mitigating effect.

Accordingly, the boron concentration of the third intermediate layer 123 adjacent to the n-type single crystal silicon substrate 11 is 1 × 10 ¹⁸ atoms / cm in consideration of the trade-off effect between the defect reduction effect and the band offset increase. It is effective for improvement of Voc to be ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less. From the results of Voc of Example 1, Example 3, and Example 4, it is less than 1 × 10 ²⁰ atoms / cm ^3. More preferably.

On the other hand, the decrease in FF in Comparative Example 2 is caused by the effect of a decrease in conductivity due to a decrease in boron concentration in the p-type amorphous silicon thin film layer. That is, as described above, setting the boron concentration of the first p-type amorphous silicon thin film layer 131 to 1 × 10 ²⁰ atoms / cm ³ or less is effective in reducing defects in the first intermediate layer 121. On the other hand, a decrease in FF occurs due to a decrease in conductivity. Therefore, a boron concentration higher than 1 × 10 ²⁰ atoms / cm ³ is required in a partial region of the p-type amorphous silicon thin film layer. And from the results of Examples 1 to 4, Comparative Example 1 and Comparative Example 2, it was possible to obtain a high FF value by having the third p-type amorphous silicon thin film layer 133 of 1 × 10 ²¹ atoms / cm ³ or more. Is obtained.

Therefore, the p-type amorphous silicon thin film layer 13 is a first p-type amorphous silicon thin film layer having a relatively low boron concentration of 1 × 10 ¹⁹ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less. 131 and the ^third p-type amorphous silicon thin film layer 133 having a relatively high boron concentration of 1 × 10 ²¹ atoms / cm ³ or more suppress the reduction of FF in the first intermediate layer 121. Effective above.

  In the above description, the case where an n-type single crystal silicon substrate is used as the crystalline semiconductor substrate has been described. However, it suffices that the crystalline semiconductor substrate has at least the surface constituting a crystalline silicon layer of one conductivity type. For example, an n-type polycrystalline silicon substrate or a substrate in which an n-type single crystal silicon layer having a desired thickness is formed on the surface of the n-type polycrystalline silicon substrate may be used as the crystalline semiconductor substrate. Alternatively, a p-type single crystal silicon substrate, a p-type polycrystalline silicon substrate, or a substrate in which a p-type single crystal silicon layer having a desired thickness is formed on the surface of the p-type polycrystalline silicon substrate may be used. In the case of using a p-type substrate, an n-type silicon thin film layer doped with an n-type impurity (donor) is formed as a conductive semiconductor layer.

  Moreover, the solar cell module excellent in photoelectric conversion efficiency is realizable by forming several photovoltaic cells which have the structure demonstrated in said embodiment, and electrically connecting adjacent photovoltaic cells. In this case, one current collecting electrode 15 and the other current collecting electrode 19 of adjacent solar cells may be electrically connected.

  As described above, the solar cell according to the present invention is useful for improving the photoelectric conversion efficiency of a solar cell having a junction structure of a conductive semiconductor layer and a crystalline semiconductor substrate, and in particular, a silicon-based silicon doped with boron. It is suitable for a solar cell having a junction structure between a thin film and a crystalline silicon substrate.

  10 solar cell, 11 n-type single crystal silicon substrate, 12 intermediate layer, 12a intrinsic amorphous silicon film, 13 p-type amorphous silicon thin film layer, 13a p-type amorphous silicon film, 14 translucent electrode, 15 current collecting electrode, 16 intrinsic amorphous silicon thin film layer, 17 n-type amorphous silicon thin film layer, 18 translucent electrode, 19 current collecting electrode, 31 p-type amorphous material having a constant boron concentration in the film thickness direction Silicon thin film layer, 121 First intermediate layer, 122 Second intermediate layer, 123 Third intermediate layer, 131 First p-type amorphous silicon thin film layer, 132 Second p-type amorphous silicon thin film layer, 133 Third p-type amorphous Quality silicon thin film layer.

Claims (18)

A semiconductor intermediate layer, the reverse-conductivity-type semiconductor thin film layer, and the first current collecting electrode are provided in this order on one surface of the one-conductivity-type crystalline semiconductor substrate, Having a conductive semiconductor thin film layer and a second collector electrode in this order;
The reverse conductivity type semiconductor thin film layer is
A first semiconductor thin film layer that is provided adjacent to the semiconductor intermediate layer and has a relatively low impurity concentration in the film thickness direction and having a constant reverse conductivity type;
A second semiconductor thin film layer provided on the side of the first current collecting electrode and having a relatively high concentration of reverse conductivity type impurities in the film thickness direction;
Have
The semiconductor intermediate layer is
The reverse conductivity type impurity concentration adjacent to the first semiconductor thin film layer is substantially equal to the reverse conductivity type impurity concentration of the first semiconductor thin film layer from the first semiconductor thin film layer side toward the one conductive type crystalline semiconductor substrate side. A first intermediate layer that monotonously decreases from the same concentration;
A second intermediate layer having a reverse conductivity type impurity concentration lower than that of the first intermediate layer adjacent to the first conductive type crystalline semiconductor substrate side of the first intermediate layer;
A solar cell comprising: The one-conductivity-type crystalline semiconductor substrate is an n-type crystalline silicon substrate;
The semiconductor intermediate layer is a silicon-based intermediate layer;
The reverse conductivity type semiconductor thin film layer is a p-type silicon thin film layer;
The one-conductivity-type semiconductor thin film layer is an n-type silicon thin film layer;
The reverse conductivity type impurity concentration is a p-type impurity concentration;
The first semiconductor thin film layer is a first p-type silicon thin film layer;
The second semiconductor thin film layer is a second p-type silicon-based thin film layer;
The solar cell according to claim 1. The n-type crystalline silicon substrate is an n-type single crystal silicon substrate;
The p-type silicon-based thin film layer is a p-type amorphous silicon thin film layer;
The first intermediate layer and the second intermediate layer are amorphous silicon layers;
The p-type impurity is boron;
The solar cell according to claim 2. The boron concentration of the first p-type silicon-based thin film layer is 1 × 10 ¹⁹ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less,
The boron concentration of the second p-type silicon-based thin film layer is 1 × 10 ²¹ atoms / cm ³ or more,
The boron concentration of the first intermediate layer is 1 × 10 ¹⁸ atoms / cm ³ or more and less than 1 × 10 ²⁰ atoms / cm ³ ;
The boron concentration of the second intermediate layer is less than 1 × 10 ¹⁸ atoms / cm ³ ;
The solar cell according to claim 3. The film thickness of the first intermediate layer is 1 nm or less;
The solar cell according to claim 4. A third intermediate is provided between the second intermediate layer and the n-type crystalline silicon substrate, and the p-type impurity concentration monotonously decreases from the n-type crystalline silicon substrate side toward the second intermediate layer side. Having a layer,
The solar cell according to claim 3, wherein: The boron concentration at the interface of the third intermediate layer on the n-type crystalline silicon substrate side is 1 × 10 ¹⁸ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less;
The solar cell according to claim 6. The film thickness of the third intermediate layer is 1 nm or less;
The solar cell according to claim 7. A first step of forming an intrinsic semiconductor thin film on one surface of a one-conductivity-type crystalline semiconductor substrate;
A second step of forming a first reverse conductivity type semiconductor thin film having a first concentration of reverse conductivity type impurities on the intrinsic semiconductor thin film;
Forming a second reverse-conductivity-type semiconductor thin film having a second concentration higher than the first concentration on the first reverse-conductivity-type semiconductor thin film;
Including
In the first step and the second step, reverse conductive impurities diffuse from the first reverse conductive semiconductor thin film into the intrinsic semiconductor thin film,
A first intermediate layer in which a reverse conductivity type impurity concentration monotonously decreases from substantially the same concentration as the first concentration from the first reverse conductivity type semiconductor thin film side toward the one conductivity type crystalline semiconductor substrate side;
A second intermediate layer having a reverse conductivity type impurity concentration lower than that of the first intermediate layer adjacent to the first conductive type crystalline semiconductor substrate side of the first intermediate layer;
Is formed,
A method for manufacturing a solar cell. The one-conductivity-type crystalline semiconductor substrate is an n-type crystalline silicon substrate;
The intrinsic semiconductor thin film is an intrinsic silicon-based thin film,
The reverse conductivity type impurity concentration is a p-type impurity concentration;
The first reverse conductivity type semiconductor thin film is a first p-type silicon-based thin film;
The second reverse conductivity type semiconductor thin film is a second p-type silicon-based thin film;
The method for producing a solar cell according to claim 9. The n-type crystalline silicon substrate is an n-type single crystal silicon substrate;
The intrinsic silicon thin film is an intrinsic amorphous silicon film,
The p-type impurity is boron;
The first p-type silicon thin film and the second p-type silicon thin film are p-type amorphous silicon thin films;
The first intermediate layer and the second intermediate layer are amorphous silicon layers;
The method for manufacturing a solar cell according to claim 10. Before the first step,
Having a step of adsorbing boron on one side of the n-type crystalline silicon substrate;
The method for manufacturing a solar cell according to claim 10. The boron concentration of the first p-type silicon-based thin film is 1 × 10 ¹⁹ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less,
The boron concentration of the second p-type silicon thin film is 1 × 10 ²¹ atoms / cm ³ or more,
The boron concentration of the first intermediate layer is 1 × 10 ¹⁸ atoms / cm ³ or more and less than 1 × 10 ²⁰ atoms / cm ³ ;
The boron concentration of the second intermediate layer is less than 1 × 10 ¹⁸ atoms / cm ³ ;
The method for producing a solar cell according to claim 11 or 12, wherein: The film thickness of the first intermediate layer is 1 nm or less;
The method for manufacturing a solar cell according to claim 13. In the first step and the second step, a p-type impurity concentration is provided between the second intermediate layer and the n-type crystalline silicon substrate so that the p-type impurity concentration is from the n-type crystalline silicon substrate side to the second intermediate layer. Forming a third intermediate layer that decreases monotonously toward the side;
The method for manufacturing a solar cell according to claim 11, wherein: The boron concentration at the interface of the third intermediate layer on the n-type crystalline silicon substrate side is 1 × 10 ¹⁸ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less;
The method for producing a solar cell according to claim 15. The film thickness of the third intermediate layer is 1 nm or less;
The method for manufacturing a solar cell according to claim 16. At least two or more of the solar cells according to any one of claims 1 to 8 are electrically connected in series or in parallel;
A solar cell module characterized by.

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