JP5667510B2 - Photoelectric conversion element - Google Patents

Description

  The present invention relates to a photoelectric conversion element that converts light energy into electrical energy by photoelectric conversion.

  In photoelectric conversion elements such as solar cells, further reduction in the thickness of the photoelectric conversion layer is desired in order to save resources and reduce costs. When the photoelectric conversion layer is simply thinned, the amount of light absorption in the photoelectric conversion layer decreases, so a technique for increasing the amount of absorption in the photoelectric conversion layer is essential.

  As such a technique, a texture structure is produced on the front surface and / or back surface of the photoelectric conversion layer, and incident light and reflected light are scattered on the front surface and back surface of the photoelectric conversion layer, respectively, so that the optical path length in the photoelectric conversion layer is increased. There are ways to increase it. In addition, a technique for processing a periodic fine structure in a photoelectric conversion element is known. In this case, the light to be transmitted through the photoelectric conversion layer is diffracted by the periodic fine pattern, and the light is confined in the photoelectric conversion layer by setting the condition that the reflected light is totally reflected in the photoelectric conversion layer. The photoelectric conversion efficiency is improved.

JP-A-61-288473 JP-A-4-133360 JP 2000-294818 A JP 2001-127313 A Special table 2009-533875 gazette

  However, in a configuration in which a texture structure is formed on the front surface and / or back surface of the photoelectric conversion layer as in the past, a relatively large amount of light leaks outside the photoelectric conversion element without being reflected toward the photoelectric conversion layer. As a method for reducing the light leaking to the outside, it is conceivable to periodically arrange the texture structure. However, the production of the periodically arranged texture structure is expensive, and the cost of the photoelectric conversion element is reduced. Becomes difficult. Further, when a periodic fine structure is processed in the photoelectric conversion element, the cost is similarly high, and it is difficult to reduce the cost of the photoelectric conversion element.

  This invention is made | formed in view of such a subject, The objective is to provide the technique which can raise the light absorption rate of a photoelectric conversion element and improve photoelectric conversion efficiency, suppressing manufacturing cost.

  One embodiment of the present invention is a photoelectric conversion element. The photoelectric conversion element includes a photoelectric conversion layer and a plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer, and a metal having a number of 0.3% or more among the plurality of metal nanoparticles. Nanoparticles are characterized by a circularity of greater than 0 and less than or equal to 0.3 when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer.

  Another embodiment of the present invention is also a photoelectric conversion element. The photoelectric conversion element includes a photoelectric conversion layer and a plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer, and the number of metal nanoparticles of 1% or more of the plurality of metal nanoparticles Is characterized in that the circularity when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer is greater than 0 and 0.4 or less.

  Another embodiment of the present invention is also a photoelectric conversion element. The photoelectric conversion element includes a photoelectric conversion layer and a plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer, and the number of metal nanoparticles of 3% or more of the plurality of metal nanoparticles. Is characterized in that the circularity when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer is greater than 0 and 0.5 or less.

  Another embodiment of the present invention is also a photoelectric conversion element. The photoelectric conversion element includes a photoelectric conversion layer and a plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer, and the number of metal nanoparticles of 6% or more among the plurality of metal nanoparticles. Is characterized in that the circularity when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer is greater than 0 and less than or equal to 0.6.

  Another embodiment of the present invention is also a photoelectric conversion element. The photoelectric conversion element includes a photoelectric conversion layer and a plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer, and the number of metal nanoparticles of 1% or more of the plurality of metal nanoparticles Has a circularity of 0.3 or more and 0.4 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer.

  Another embodiment of the present invention is also a photoelectric conversion element. The photoelectric conversion element includes a photoelectric conversion layer and a plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer, and the number of metal nanoparticles of 3% or more of the plurality of metal nanoparticles. Has a circularity of 0.4 or more and 0.5 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer.

  Another embodiment of the present invention is also a photoelectric conversion element. The photoelectric conversion element includes a photoelectric conversion layer and a plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer, and the number of metal nanoparticles of 4% or more among the plurality of metal nanoparticles. Has a circularity of 0.5 or more and 0.6 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer.

  Another embodiment of the present invention is also a photoelectric conversion element. The photoelectric conversion element includes a photoelectric conversion layer and a plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer, and the plurality of metal nanoparticles are substantially perpendicular to the main surface of the photoelectric conversion layer. The average circularity when viewed from various directions is 0.8 or less.

  Another embodiment of the present invention is also a photoelectric conversion element. The photoelectric conversion element includes a photoelectric conversion layer and a plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer, and the plurality of metal nanoparticles are substantially perpendicular to the main surface of the photoelectric conversion layer. 10% circularity when viewed from various directions is 0.6 or less.

  According to the photoelectric conversion element of any one of the above aspects, the light absorption rate of the photoelectric conversion element can be increased and the photoelectric conversion efficiency can be improved while suppressing the manufacturing cost.

  In the photoelectric conversion element of any one of the above aspects, the plurality of metal nanoparticles may be provided on the main surface side of the photoelectric conversion layer on the side opposite to the light receiving surface. The plurality of metal nanoparticles may be made of Au, Ag, Al, Cu, or an alloy containing these metals. Moreover, you may further provide the transparent thin film provided between the some metal nanoparticle and the photoelectric converting layer. In addition, the photoelectric conversion layer may be single crystal silicon having a pn junction or polycrystalline silicon having a pn junction. The plurality of metal nanoparticles may be formed by heat treatment of a metal thin film.

  A combination of the above-described elements as appropriate can also be included in the scope of the invention for which patent protection is sought by this patent application.

  ADVANTAGE OF THE INVENTION According to this invention, the light absorption rate of a photoelectric conversion element can be raised and photoelectric conversion efficiency can be improved, suppressing manufacturing cost.

FIG. 1A is a schematic cross-sectional view illustrating the configuration of the photoelectric conversion element according to the embodiment. FIG. 1B is a plan view showing the arrangement of the metal nanoparticles when the semiconductor substrate is viewed from the back side. 2A to 2E are process cross-sectional views illustrating a method for manufacturing a photoelectric conversion element according to the embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

  FIG. 1A is a schematic cross-sectional view illustrating the configuration of the photoelectric conversion element according to the embodiment. FIG. 1B is a plan view showing the arrangement of the metal nanoparticles when the photoelectric conversion element is viewed in plan from the side opposite to the light receiving surface. FIG. 1A corresponds to a cross-sectional view taken along the line AA in FIG. In FIG. 1B, the dielectric layer 38 is not shown.

  As shown in FIG. 1A, the photoelectric conversion element 10 includes a photoelectric conversion layer 20, an antireflection film 32, a plurality of metal nanoparticles 36, a dielectric layer 38, and a transparent thin film 50. In this embodiment, the photoelectric conversion element 10 is a solar cell.

  The photoelectric conversion layer 20 has, for example, a pn junction in which a p-type semiconductor and an n-type semiconductor are joined, and light energy from the sun is converted into electrical energy by the photovoltaic effect of the pn junction. Direct current can be taken out of the photoelectric conversion element 10 by attaching electrodes (not shown) to the n-type semiconductor and the p-type semiconductor, respectively. The photoelectric conversion layer 20 is, for example, a single crystal silicon substrate, and has a pn junction that is well-known as a solar cell formed of a group IV semiconductor substrate. Note that the photoelectric conversion layer 20 may be a polycrystalline silicon substrate. In addition, the structure of the photoelectric conversion layer 20 is not particularly limited as long as it is a structure capable of photoelectric conversion, and a p-i-n junction may be formed in the photoelectric conversion layer 20.

  The photoelectric conversion layer 20 has a first main surface S1 and a second main surface S2 that face each other. In the photoelectric conversion layer 20, the first main surface S1 is positioned on the light receiving surface side of the photoelectric conversion element 10 (the upper surface side in FIG. 1A), and the second main surface S2 is opposite to the light receiving surface of the photoelectric conversion element 10. It is provided so that it may be located in the side (lower surface side of FIG. 1 (A)).

The antireflection film 32 is provided on the first main surface S <b> 1 of the photoelectric conversion layer 20. The antireflection film 32 is not particularly limited in form and material as long as it has both transparency in the wavelength region of light received by the photoelectric conversion element 10 and a function of preventing reflection of light received by the photoelectric conversion element 10. but, for _example, SiO _2, SiN _x, etc. TiO 2, ITO and the like.

  The plurality of metal nanoparticles 36 are two-dimensionally arranged on the main surface side of the photoelectric conversion layer 20. In the present embodiment, the plurality of metal nanoparticles 36 are two-dimensionally arranged on the second main surface S2 side of the photoelectric conversion layer 20. More specifically, the plurality of metal nanoparticles 36 are scattered on the surface of a transparent thin film 50 described later arranged on the second main surface S2 side of the photoelectric conversion layer 20.

  The material of the metal nanoparticle 36 is not particularly limited as long as it is a metal material. The thing close | similar to the wavelength of this is desirable, for example, Au, Ag, Al, Cu or the alloy containing these metals is mentioned.

  The three-dimensional shape of the metal nanoparticles 36 is not particularly limited, and examples thereof include a spherical shape, a hemispherical shape, a cylindrical shape, a prismatic shape, a rod shape, and a disc shape. Further, when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer 20, that is, when the photoelectric conversion layer 20 is viewed in plan, the shape of the metal nanoparticles 36 is the following (1) to (9) with respect to the circularity. Satisfy at least one of the following conditions.

Here, the “circularity” is an index indicating how close the shape of the metal nanoparticles 36 is when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer 20 (when viewed in plan). And is represented by the following formula (1). The closer the circularity is to 1, the closer the shape of the metal nanoparticles 36 is to a circle.
Circularity = 4πS / L ² (1)
S: Area of the metal nanoparticles 36 in a plan view L: Perimeter length of the metal nanoparticles 36 in a plan view

  Condition (1): Among the plurality of metal nanoparticles 36, 0.3% or more of the metal nanoparticles 36 have a circularity of more than 0 and 0.3 or less when viewed in plan.

  Condition (2): Among the plurality of metal nanoparticles 36, the circularity of the metal nanoparticles 36 of 1% or more of them when viewed in plan is greater than 0 and 0.4 or less.

  Condition (3): Among the plurality of metal nanoparticles 36, 3% or more of the metal nanoparticles 36 have a circularity greater than 0 and 0.5 or less when viewed in plan.

  Condition (4): Among the plurality of metal nanoparticles 36, the number of metal nanoparticles 36 of 6% or more has a circularity of greater than 0 and 0.6 or less when viewed in plan.

  Condition (5): The plurality of metal nanoparticles 36 have a circularity of 0.3 or more and 0.4 or less when the number of metal nanoparticles 36 of 1% or more is viewed in plan.

  Condition (6): The plurality of metal nanoparticles 36 have a circularity of 0.4 or more and 0.5 or less when 3% or more of the metal nanoparticles 36 are viewed in plan.

  Condition (7): The plurality of metal nanoparticles 36 have a circularity of 0.5 or more and 0.6 or less when 4% or more of the metal nanoparticles 36 are viewed in plan.

  Condition (8): The plurality of metal nanoparticles 36 have an average circularity of 0.8 or less when viewed in plan.

Condition (9): The plurality of metal nanoparticles 36 have a 10% circularity defined below when viewed in plan of 0.6 or less.
10% circularity: When 10% of the number of the plurality of metal nanoparticles 36 is N, the circularity of the Nth metal nanoparticle 36 when the plurality of metal nanoparticles 36 are arranged in descending order of circularity.

  When the plurality of metal nanoparticles 36 have a shape that satisfies any of the above conditions (1) to (9), the plurality of metal nanoparticles 36 have a wide distribution of circularity. Thereby, light in a wider wavelength region can be efficiently absorbed by the photoelectric conversion layer 20. As a result, the photoelectric conversion efficiency of the photoelectric conversion element 10 is improved.

  When the photoelectric conversion layer 20 is viewed in plan, the substantially circular metal nanoparticles 36 have a diameter D in the range of, for example, about 10 nm to about 1000 nm. The height H of the metal nanoparticles 36 when the main surface of the transparent thin film 50 opposite to the photoelectric conversion layer 20 is the reference plane is, for example, in the range of about 5 nm to about 500 nm.

A preferable range of the number density of the metal nanoparticles 36 per unit area when the photoelectric conversion layer 20 is viewed in plan is 1.0 × 10 ⁷ / cm ^{2 to} 1.0 × 10 ¹⁰ / cm ² , more preferably 1.0 × ¹⁰ 8 ~5.0 × ^{10 9} pieces / cm ^2, more preferably 5.0 × ¹⁰ 8 ~2.0 × ^{10 9} pieces / cm ^2.

  The transparent thin film 50 is provided between the plurality of metal nanoparticles 36 and the photoelectric conversion layer 20. That is, the transparent thin film 50 is provided on the second main surface S <b> 2 of the photoelectric conversion layer 20. The transparent thin film 50 is transparent to the light received by the photoelectric conversion element 10. That is, the band gap of the transparent thin film 50 is larger than the band gap of the photoelectric conversion layer 20. Moreover, when forming an electrode in the 2nd main surface S2 side of the photoelectric converting layer 20, it is preferable that the transparent thin film 50 has electroconductivity from a viewpoint of a current collection improvement.

The material of the transparent thin film 50 includes calcium fluoride, magnesium fluoride, barium fluoride, lithium fluoride, silicon carbide, sapphire, alumina, crystal, fluororesin, SnO ₂ , FTO (fluorine-doped tin oxide), ITO, ZnO. _{, SiO 2, TiO 2, ZrO} 2, Mn 3 O 4, Y 2 O 3, WO 3, Nb 2 O 5, La 2 O 3, Ga 2 O 3, Ag 2 O, CuO, a-Si: H, μc-Si: H, SiO _x : H, SiC, SiN _x , AlO _x : H, polyethylene terephthalate, polycarbonate, polymethyl methacrylate, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, polyimide, polyamide, poly Butylene terephthalate, polyethylene naphthalate, polysulfone, Examples include polyethersulfone, polyetheretherketone, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, triacetyl cellulose, polyurethane, and cycloolefin polymer.

The thickness of the transparent thin film 50 is preferably in the range of about 5 nm to about 200 nm. Further, the oxygen content in the transparent thin film 50 is preferably 5 atm% or more. In addition, the refractive index n ₁ of the transparent thin film 50 is preferably in a relationship of n ₁ > 0.7n ₂ with respect to the refractive index n ₂ of the photoelectric conversion layer 20.

  In the photoelectric conversion element 10 according to this embodiment, the transparent thin film 50 is interposed between the metal nanoparticles 36 and the second main surface S2 of the photoelectric conversion layer 20. Therefore, the metal nanoparticles 36 are not in contact with the second main surface S2 of the photoelectric conversion layer 20. In the case where the metal nanoparticles 36 are in contact with the photoelectric conversion layer 20, the carrier recombination reaction is promoted at the metal-semiconductor interface between the metal nanoparticles 36 and the photoelectric conversion layer 20. The metal atoms constituting the particles 36 may diffuse into the photoelectric conversion layer 20 and contaminate the photoelectric conversion layer 20, which may reduce the photoelectric conversion efficiency of the photoelectric conversion element 10. On the other hand, in this embodiment, since the transparent thin film 50 is interposed between the second main surface S2 surface of the photoelectric conversion layer 20 and the metal nanoparticles 36, the metal nanoparticles 36 and the photoelectric conversion layer 20 It is possible to suppress recombination of carriers between the two. Furthermore, by setting the oxygen content in the transparent thin film 50 to 5 atm% or more, it is possible to effectively suppress the diffusion of metal atoms constituting the metal nanoparticles 36 into the photoelectric conversion layer 20.

Further, since the refractive index n ₁ of the transparent thin film 50 is in a relationship of n ₁ > 0.7n _{2 with} respect to the refractive index n ₂ of the photoelectric conversion layer 20, the scattering angle of the reflected light from the metal nanoparticles 36 is further increased. The optical path length in the photoelectric conversion layer 20 can be further increased.

  The dielectric layer 38 is provided on the second main surface S2 side of the photoelectric conversion layer 20 so as to cover at least the surface of the metal nanoparticles 36. The refractive index of the dielectric layer 38 is preferably 1.3 or more. The dielectric layer 38 is transparent to the light received by the photoelectric conversion element 10. That is, the band gap of the dielectric layer 38 is larger than the band gap of the photoelectric conversion layer 20. Moreover, when forming an electrode on the dielectric layer 38, it is preferable that the dielectric layer 38 has electroconductivity from a viewpoint of improvement of current collection property.

The material of the dielectric layer 38 includes calcium fluoride, magnesium fluoride, barium fluoride, lithium fluoride, silicon carbide, sapphire, alumina, crystal, fluororesin, SnO ₂ , FTO (fluorine-doped tin oxide), ITO, _{ZnO, SiO 2, TiO 2,} ZrO 2, Mn 3 O 4, Y 2 O 3, WO 3, Nb 2 O 5, La 2 O 3, Ga 2 O 3, Ag 2 O, CuO, a-Si: H , Μc-Si: H, SiO _x : H, SiC, SiN _x , AlO _x : H, polyethylene terephthalate, polycarbonate, polymethyl methacrylate, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, polyimide, polyamide, Polybutylene terephthalate, polyethylene naphthalate, polysulfone, Examples include polyethersulfone, polyetheretherketone, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, triacetyl cellulose, polyurethane, and cycloolefin polymer. Although the thickness of the dielectric material layer 38 is not specifically limited, For example, they are about 5 nm-about 2000 nm.

(Method for manufacturing photoelectric conversion element)
A method for manufacturing the photoelectric conversion element 10 according to this embodiment will be described with reference to FIGS. 2A to 2E are process cross-sectional views illustrating a method for manufacturing a photoelectric conversion element according to the embodiment.

First, as shown in FIG. 2A, an antireflection film 32 having a thickness of 50 to 200 nm is laminated on the first main surface S1 of the photoelectric conversion layer 20 serving as a light receiving surface. The photoelectric conversion layer 20 includes a p-type single crystal Si substrate, and a pn junction is formed in advance in the photoelectric conversion layer 20 by using a known thermal diffusion method, ion implantation method, vacuum film formation method, or the like. . The method of laminating the antireflection film 32 is not particularly limited, and examples thereof include a method of forming a transparent material such as SiN _x or ITO on the photoelectric conversion layer 20 by a vacuum film formation method.

  Next, as illustrated in FIG. 2B, a transparent thin film 50 having a thickness of 5 to 200 nm is stacked on the second main surface S <b> 2 of the photoelectric conversion layer 20. The method for laminating the transparent thin film 50 is not particularly limited. As with the method for producing the antireflection film 32, for example, a transparent material such as μc-Si: H (microcrystalline Si: H) or ITO is photoelectrically applied by a vacuum film formation method. A method of forming a film on the conversion layer 20 is exemplified.

  Next, as shown in FIG. 2C, a metal thin film 35 having a thickness of, for example, 1 to 200 nm is laminated on the main surface of the transparent thin film 50. The method of laminating the metal thin film 35 is not particularly limited. For example, a method of forming a metal thin film 35 by depositing a metal such as Ag, Al, Au, Cu or an alloy containing these metals on the transparent thin film 50 by a vacuum evaporation method. Is mentioned.

  Next, as shown in FIG. 2D, the metal thin film 35 is heated, whereby the metal thin film 35 is deformed into a plurality of particles. The heating temperature of the metal thin film 35 is, for example, 100 to 500 ° C. As a result, the plurality of metal nanoparticles 36 are two-dimensionally arranged on the transparent thin film 50. The circularity of the plurality of metal nanoparticles 36 can be adjusted by changing the thickness of the metal thin film 35, the heating temperature, or the like.

  Next, as shown in FIG. 2E, a dielectric layer 38 is laminated so as to cover the surface of the metal nanoparticles 36. Although the method for laminating the dielectric layer 38 is not particularly limited, a method of forming a dielectric material such as ITO or ZnO by a vacuum film forming method can be cited as with the method for forming the antireflection film 32, for example.

  Through the steps described above, the photoelectric conversion element 10 according to this embodiment can be easily formed, and as a result, the manufacturing cost of the photoelectric conversion element 10 can be reduced.

  According to the photoelectric conversion element 10 according to the embodiment described above, incident light that could not be absorbed by the photoelectric conversion layer 20 is scattered due to the strong light scattering property caused by the localized surface plasmon that the plurality of metal nanoparticles 36 have. Reflected. Therefore, the optical path length of the incident light in the photoelectric conversion layer 20 is increased, and the incident light can be efficiently absorbed. Further, since the plurality of metal nanoparticles 36 have a wide circularity distribution, the photoelectric conversion layer 20 can efficiently absorb light in a wide wavelength region. As a result, the photoelectric conversion efficiency of the photoelectric conversion element 10 is improved.

  Further, in the photoelectric conversion element 10 of the present embodiment, the plurality of metal nanoparticles 36 are covered with the dielectric layer 38. Thereby, since it is suppressed that the metal nanoparticle 36 is exposed to air | atmosphere or water, stability of the metal nanoparticle 36 can be improved. Moreover, in the photoelectric converting layer 20, when long wavelength side light is easy to permeate | transmit, a scattering characteristic can be improved, shifting the active wavelength of the metal nanoparticle 36 to the long wavelength side.

  EXAMPLES The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

Example 1
<Preparation of photoelectric conversion layer>
On one surface of a 100 μm-thick p-type silicon wafer (resistivity 0.5 to 5 Ωcm), 5 nm thick a-Si: H is laminated as an i layer, and 7.5 nm thick on the i layer. n-type a-Si: H was laminated to produce a photoelectric conversion layer. The refractive index of the p-type silicon wafer was measured with a spectroscopic ellipsometer and found to be 3.9 at 600 nm.

<Preparation of antireflection film>
On the n-type a-Si: H, ITO having a thickness of 75 nm was formed as an antireflection film.

<Preparation of transparent thin film>
A p-type microcrystalline Si: H film having a thickness of 30 nm was formed as a transparent thin film on the exposed surface (back surface) of the p-type silicon wafer.

<Production of metal nanoparticles>
On the surface of the transparent thin film, a 5 nm Ag thin film was formed as a metal thin film by vapor deposition. The Ag thin film was heat-treated at 200 ° C. to form a plurality of Ag nanoparticles on the transparent thin film.

<Preparation of dielectric layer>
A ZnO film having a thickness of 200 nm was formed as a dielectric layer covering Ag nanoparticles.

<Production of electrode>
A thin wire electrode was formed on the ITO constituting the antireflection film using Ag. A full-surface electrode was formed on the ZnO constituting the dielectric layer (on the main surface of ZnO opposite to the transparent thin film) using Ag.

  The photoelectric conversion element (solar cell) of Example 1 was produced through the above steps.

(Example 2)
The solar cell of Example 2 was produced in the same procedure as Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
On the surface of the transparent thin film, an Ag thin film having a thickness of 10 nm was formed as a metal thin film by vapor deposition. The Ag thin film was heat-treated at 200 ° C. to form a plurality of Ag nanoparticles on the transparent thin film.

Example 3
The solar cell of Example 3 was produced in the same procedure as in Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
On the surface of the transparent thin film, an Ag thin film having a thickness of 15 nm was formed as a metal thin film by vapor deposition. The Ag thin film was heat-treated at 200 ° C. to form a plurality of Ag nanoparticles on the transparent thin film.

Example 4
The solar cell of Example 4 was produced in the same procedure as Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
On the surface of the transparent thin film, an Ag thin film having a thickness of 20 nm was formed as a metal thin film by vapor deposition. The Ag thin film was heat-treated at 200 ° C. to form a plurality of Ag nanoparticles on the transparent thin film.

(Example 5)
The solar cell of Example 5 was produced in the same procedure as in Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
On the surface of the transparent thin film, an Ag thin film having a thickness of 25 nm was formed as a metal thin film by vapor deposition. The Ag thin film was heat-treated at 200 ° C. to form a plurality of Ag nanoparticles on the transparent thin film.

(Example 6)
The solar cell of Example 6 was produced in the same procedure as in Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
On the surface of the transparent thin film, a 30 nm Ag thin film was formed as a metal thin film by vapor deposition. The Ag thin film was heat-treated at 200 ° C. to form a plurality of Ag nanoparticles on the transparent thin film.

(Example 7)
The solar cell of Example 7 was produced in the same procedure as in Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
On the surface of the transparent thin film, a 35 nm Ag thin film was formed as a metal thin film by vapor deposition. The Ag thin film was heat-treated at 200 ° C. to form a plurality of Ag nanoparticles on the transparent thin film.

(Comparative Example 1)
The solar cell of Comparative Example 1 was produced in the same procedure as in Example 1 except that no metal nanoparticles were produced.

(Comparative Example 2)
The solar cell of Comparative Example 2 was produced in the same procedure as in Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
After anodizing the surface of the aluminum substrate at 80 V in a mixed aqueous solution of 0.1 mol / L oxalic acid and 0.1 mol / L malonic acid, the aluminum substrate other than the oxidized surface (barrier layer) is removed, and the barrier layer An alumina mask having a plurality of through-holes was obtained by penetrating a large number of holes formed in the substrate using a phosphoric acid aqueous solution diluted 20 times. A plurality of Ag nanoparticles having a height of 50 nm were formed by vacuum-depositing Ag on the transparent thin film through this alumina mask.

(Comparative Example 3)
The solar cell of Comparative Example 3 was produced in the same procedure as Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
After anodizing the surface of the aluminum substrate in an aqueous 0.15 mol / L citric acid solution at 240 V, the aluminum substrate other than the oxidized surface (barrier layer) is removed, and the number of holes formed in the barrier layer is increased by 20 times. By making it penetrate using the diluted phosphoric acid aqueous solution, the alumina mask which has a some through-hole was obtained. A plurality of Ag nanoparticles having a height of 50 nm were formed by vacuum-depositing Ag on the transparent thin film through this alumina mask.

(Comparative Example 4)
The solar cell of Comparative Example 4 was produced in the same procedure as in Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
An Ag nanoparticle dispersion (average particle size: 150 nm) prepared by a wet mixing method was applied to a transparent thin film to form a plurality of Ag nanoparticles on the transparent thin film.

(Comparative Example 5)
The solar cell of Comparative Example 5 was produced in the same procedure as in Example 1 except for the method for producing metal nanoparticles.

<Production of metal nanoparticles>
An Ag nanoparticle dispersion liquid (average particle size: 200 nm) prepared by a wet mixing method was applied to a transparent thin film to form a plurality of Ag nanoparticles on the transparent thin film.

<Measurement of circularity of metal nanoparticles>
For the solar cells of Examples 1 to 7 and Comparative Examples 1 to 5, the circularity of Ag nanoparticles when measured from a direction substantially perpendicular to the main surface of the photoelectric conversion layer was measured. The circularity of the Ag nanoparticles was measured by analyzing an image obtained with a scanning electron microscope (SEM). ImageJ version 1.42q was used for image analysis. Li method (Li, CH & Tam, PKS (1998), "An Iterative Algorithm for Minimum Cross Entropy Thresholding", Pattern Recognition Letters 18 (8) : 771-776), a region with high brightness was extracted from the SEM image. The extracted region was subjected to particle detection using the particle detection function attached to ImageJ, and the circularity of each Ag nanoparticle in the region was calculated. Further, the average circularity and 10% circularity of Ag nanoparticles in the region were calculated. Table 1 shows the circularity distribution, average circularity, and 10% circularity in each example and each comparative example.

  As shown in Table 1, in Examples 1 to 7, it was confirmed that the number of Ag nanoparticles having a circularity in the range of 0 to 0.3 was 0.3% or more. On the other hand, in Comparative Examples 2 to 5, the number of such Ag nanoparticles was less than 0.3%.

  In Examples 1 to 7, it was confirmed that the number of Ag nanoparticles having a circularity in the range of 0 to 0.4 was 1% or more. On the other hand, in Comparative Examples 2 to 5, the number of such Ag nanoparticles was less than 1%.

  In Examples 1 to 7, it was confirmed that the number of Ag nanoparticles having a circularity in the range of 0 to 0.5 was 3% or more. On the other hand, in Comparative Examples 2 to 5, the number of such Ag nanoparticles was less than 3%.

  In Examples 1 to 7, it was confirmed that the number of Ag nanoparticles having a circularity in the range of 0 to 0.6 was 6% or more. On the other hand, in Comparative Examples 2 to 5, the number of such Ag nanoparticles was less than 6%.

  In Examples 1 to 7, it was confirmed that the number of Ag nanoparticles having a circularity in the range of 0.3 to 0.4 was 1% or more. On the other hand, in Comparative Examples 2 to 5, the number of such Ag nanoparticles was less than 1%.

  In Examples 1 to 7, it was confirmed that the number of Ag nanoparticles having a circularity in the range of 0 to 0.4 was 1% or more. On the other hand, in Comparative Examples 2 to 5, the number of such Ag nanoparticles was less than 1%.

  In Examples 1 to 7, it was confirmed that the number of Ag nanoparticles having a circularity in the range of 0.4 to 0.5 was 3% or more. On the other hand, in Comparative Examples 2 to 5, the number of such Ag nanoparticles was less than 3%.

  In Examples 1 to 7, it was confirmed that the number of Ag nanoparticles having a circularity in the range of 0.5 to 0.6 was 4% or more. On the other hand, in Comparative Examples 2 to 5, the number of such Ag nanoparticles was less than 4%.

  Moreover, in Examples 1-7, it was confirmed that an average circularity is 0.8 or less. On the other hand, in Comparative Examples 2 to 5, the average circularity exceeded 0.8.

  Moreover, in Examples 1-7, it was confirmed that 10% circularity is 0.6 or less. On the other hand, in Comparative Examples 2 to 5, the 10% circularity exceeded 0.6.

<Performance evaluation of solar cells>
About the solar cell of Examples 1-7 and Comparative Examples 1-5, 100 mW / cm < ² > simulated sunlight was irradiated and the electric current-potential characteristic was evaluated. The relative value of the short circuit current density was calculated about Examples 1-7 and Comparative Examples 2-5 on the basis of the comparative example 1 which did not form Ag nanoparticle. The results are shown in Table 2.

  As shown in Table 2, in the solar cells of Examples 1 to 7, the short-circuit current density was significantly increased as compared with the solar cells of Comparative Examples 1 to 5, and the effect of increasing light absorption was confirmed. From this, it turns out that the above-mentioned circularity distribution which Examples 1-7 satisfy | fills has contributed to the performance improvement of a solar cell.

  The present invention is not limited to the above-described embodiment, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The embodiment to which such a modification is added is also the present embodiment. It can be included in the scope of the invention.

  For example, in the above-described embodiment, the plurality of metal nanoparticles 36 are formed on the second main surface S2 side of the photoelectric conversion layer 20, but the plurality of metal nanoparticles 36 are formed on the first main surface of the photoelectric conversion layer 20. It may be formed on the S1 side.

  S1 1st main surface, S2 2nd main surface, 10 photoelectric conversion element, 20 photoelectric conversion layer, 32 antireflection film, 35 metal thin film, 36 metal nanoparticle, 38 dielectric layer, 50 transparent thin film.

Claims (14)

A photoelectric conversion layer;
A plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer,
Among the plurality of metal nanoparticles, the number of metal nanoparticles of 0.3% or more has a circularity greater than 0 and less than or equal to 0.3 when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer. The photoelectric conversion element characterized by the above-mentioned. A photoelectric conversion layer;
A plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer,
The number of metal nanoparticles of 1% or more among the plurality of metal nanoparticles has a circularity of more than 0 and 0.4 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer. A characteristic photoelectric conversion element. A photoelectric conversion layer;
A plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer,
The number of metal nanoparticles of 3% or more of the plurality of metal nanoparticles has a circularity of more than 0 and 0.5 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer. A characteristic photoelectric conversion element. A photoelectric conversion layer;
A plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer,
Among the plurality of metal nanoparticles, the number of metal nanoparticles of 6% or more has a circularity of more than 0 and 0.6 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer. A characteristic photoelectric conversion element. A photoelectric conversion layer;
A plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer,
Of the plurality of metal nanoparticles, 1% or more of the metal nanoparticles have a circularity of 0.3 or more and 0.4 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer. A photoelectric conversion element characterized by the above. A photoelectric conversion layer;
A plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer,
Of the plurality of metal nanoparticles, 3% or more of the metal nanoparticles have a circularity of 0.4 or more and 0.5 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer. A photoelectric conversion element characterized by the above. A photoelectric conversion layer;
A plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer,
4% or more of the plurality of metal nanoparticles has a circularity of 0.5 or more and 0.6 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer. A photoelectric conversion element characterized by the above. A photoelectric conversion layer;
A plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer,
The plurality of metal nanoparticles have an average circularity of 0.8 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer. A photoelectric conversion layer;
A plurality of metal nanoparticles two-dimensionally arranged on the main surface side of the photoelectric conversion layer,
The plurality of metal nanoparticles have a 10% circularity of 0.6 or less when viewed from a direction substantially perpendicular to the main surface of the photoelectric conversion layer.   The photoelectric conversion element according to claim 1, wherein the plurality of metal nanoparticles are provided on a main surface side of the photoelectric conversion layer on a side opposite to the light receiving surface.   The photoelectric conversion element according to any one of claims 1 to 10, wherein the plurality of metal nanoparticles are made of Au, Ag, Al, Cu, or an alloy containing these metals.   The photoelectric conversion element according to claim 1, further comprising a transparent thin film provided between the plurality of metal nanoparticles and the photoelectric conversion layer.   The photoelectric conversion element according to any one of claims 1 to 12, wherein the photoelectric conversion layer is single crystal silicon having a pn junction or polycrystalline silicon having a pn junction.   The photoelectric conversion element according to claim 1, wherein the plurality of metal nanoparticles are formed by heat treatment of a metal thin film.

Images