WO2013077254A1 - Solar cell, solar cell panel, device provided with solar cell, and device provided with solar cell panel - Google Patents

Abstract

A solar cell (1), wherein a photonic crystal is configured by giving periodicity to the difference in refractive index between a photoelectric conversion layer (12) in which a plurality of recesses are regularly formed in a light incident side surface and a first transparent conductive film (11) on which a plurality of protrusions (16) are formed by filling at least the recesses.

Description

Solar cell, solar cell panel, device with solar cell, and device with solar cell panel

The present invention relates to a solar cell, a solar cell panel in which a plurality of solar cells are arranged, and a device in which the solar cell or the solar cell panel is mounted as a power source.

Generally, in a solar cell using crystalline silicon as a medium, in order to sufficiently absorb incident sunlight, in principle, it should have a thickness of about 30 μm. In practice, however, solar cells having a thickness of about 300 μm to 400 μm have been put into practical use, but currently, solar cells having a thickness of about 30 μm have hardly been put to practical use.

In addition, it is said that the solar cell should have a thickness of about 30 μm in principle because it sufficiently absorbs sunlight on the long wavelength side having a low light absorptance, and sufficiently absorbs light as a solar cell. This is because the thickness required to obtain the rate is about 30 μm.

On the other hand, the solar cell needs a thickness of about 300 μm to 400 μm practically. If the thickness is small, the shape of the solar cell cannot be maintained, and there is a risk of breakage. This is because a problem that it cannot be obtained occurs.

Here, with reference to FIG. 25, the light absorption rate of the solar cell when the thickness of the solar cell is 30 μm and 400 μm will be described. FIG. 25 is a graph showing the characteristics of the light absorption rate of the solar cell and the irradiance of sunlight with respect to the wavelength of sunlight. In FIG. 25, the alternate long and short dash line indicates characteristics when the thickness of the solar cell is 400 μm, the alternate long and two short dashes line indicates characteristics when the thickness of the solar cell is 30 μm, and the broken line indicates that the thickness of the solar cell is 500 nm. The characteristic in the case of is shown.

As shown in FIG. 25, when the thickness of the solar cell is 30 μm, the light absorption rate is 1.0 in the range of the wavelength of sunlight up to about 850 nm. Further, when the thickness of the solar cell is 400 μm, the light absorption rate is 1.0 in the range of the wavelength of sunlight up to about 1050 nm. As shown in FIG. 25, when the thickness of the solar cell is 30 μm, the light absorption rate on the short wavelength side is good, but the light absorption rate on the long wavelength side is low. On the other hand, when the thickness of the solar cell is 400 μm, the light absorptance is good from the short wavelength side to the long wavelength side. Further, as an example when the thickness of the solar cell is further reduced, when the thickness is set to 500 nm, as shown in FIG. 25, the light absorptance with respect to the wavelength of sunlight of 450 nm or more is significantly reduced. End up.

By the way, in a solar cell having a thickness of about 300 μm to 400 μm, since the amount of crystalline silicon used is large, not only is the crystalline silicon not effectively used, but the cost is increased and the profit of the solar cell is deteriorated. ing.

To solve such a problem, Patent Document 1 discloses a method for manufacturing a photoelectric conversion device that increases the amount of light absorption as shown in FIG. FIG. 26 is a cross-sectional view illustrating an outline of a solar cell according to Patent Document 1.

In Patent Document 1, as shown in FIG. 26, the surface of a single crystal semiconductor layer (single crystal silicon) is made uneven so as to suppress reflection of light and confine incident light. Discloses a method for manufacturing a photoelectric conversion device that increases the amount of absorption of light having a wavelength of 600 nm or less even when the thickness is 0.1 μm to 10 μm or less. In Patent Document 1, for a wavelength of 800 nm or more, the amount of light absorption is increased by making the photoelectric conversion device a tandem type.

Japanese Patent Publication “JP 2009-152569 (July 9, 2009)”

However, as described in Patent Document 1, the effect of reducing the surface reflectance of incident light and the effect of increasing the optical path length by providing a concavo-convex structure in a single crystal semiconductor layer are not so large, particularly long wavelengths. There was a problem that the light absorption rate on the side was not improved. Further, in the technique described in Patent Document 1, in order to increase the light absorption rate on the long wavelength side, the tandem type must be adopted for the photoelectric conversion device, which is contrary to the purpose of suppressing the thickness of the photoelectric conversion device. There was a problem of becoming.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a solar cell in which the absorption rate of light particularly at a long wavelength is increased and the thickness is suppressed.

In order to solve the above problems, a solar cell according to one embodiment of the present invention is provided.
(1) a photoelectric conversion unit;
(2) a support substrate for supporting the photoelectric conversion unit,
(3) The photoelectric conversion unit
(3-1) A photoelectric conversion layer that absorbs light and performs photoelectric conversion, wherein the first concave portion or the first convex portion is regularly formed on the first surface on the light incident side; and
(3-2) including a first transparent body that at least fills the first concave portion of the first surface, or a first transparent body that at least fills the second concave portion formed by providing the first convex portion,
(4) The concavo-convex shape formed on the first surface constitutes a photonic crystal by providing periodicity to the refractive index difference between the photoelectric conversion layer and the first transparent body. It is characterized by that.

In order to solve the above problems, a solar cell according to one embodiment of the present invention is provided.
(1) a photoelectric conversion unit;
(2) a support substrate for supporting the photoelectric conversion unit,
(3) The photoelectric conversion unit
(3-1) A photoelectric conversion layer that absorbs light and performs photoelectric conversion, wherein the first concave portion is regularly formed on the first surface on the light incident side; and
(3-2) including a first transparent body that fills at least the first recess,
(4) The concavo-convex shape formed on the first surface constitutes a photonic crystal by providing periodicity to the refractive index difference between the photoelectric conversion layer and the first transparent body. And
(5) By providing a plurality of the first concave portions on the first surface, the second convex portions remaining around the first concave portions are joined to the support substrate,
(6) A positive electrode and a negative electrode are formed on the second surface of the photoelectric conversion layer opposite to the first surface.

In order to solve the above problems, a solar cell according to one embodiment of the present invention is provided.
(1) a photoelectric conversion unit;
(2) a support substrate for supporting the photoelectric conversion unit,
(3) The photoelectric conversion unit
(3-1) A photoelectric conversion layer that absorbs light and performs photoelectric conversion, wherein the first concave portion is regularly formed on the first surface on the light incident side; and
(3-2) including a first transparent body that fills at least the first recess,
(4) The concavo-convex shape formed on the first surface constitutes a photonic crystal by providing periodicity to the refractive index difference between the photoelectric conversion layer and the first transparent body. And
(5) A positive electrode and a negative electrode are formed on the second surface opposite to the first surface of the photoelectric conversion layer,
(6) The second surface on which the positive electrode and the negative electrode are formed is bonded to the support substrate via a transparent insulating layer.

A solar cell panel in which one of the above solar cells is used as a unit and a plurality of the units are arranged one-dimensionally or two-dimensionally, a device including any one of the solar cells as a power source, and the solar cell panel A device provided as a power source is also included in the scope of the present invention.

As described above, the solar cell according to the present invention includes a photoelectric conversion unit and a support substrate that supports the photoelectric conversion unit, and the photoelectric conversion unit is a photoelectric conversion layer that absorbs light and performs photoelectric conversion. A photoelectric conversion layer in which first concave portions or first convex portions are regularly formed on the first surface on the light incident side, and a first transparent body that at least fills the first concave portion on the first surface, or the above A first transparent body that at least fills the second concave portion formed by providing the first convex portion, and the concave-convex shape formed on the first surface is formed by the photoelectric conversion layer and the first transparent body. It is characterized in that a photonic crystal is formed by giving periodicity to the difference in refractive index between the two.

Therefore, the solar cell can improve the light absorption rate in the photoelectric conversion layer, and can increase the amount of electromotive force in the solar cell. Further, the photoelectric conversion layer can be thinned by improving the light absorption rate in the photoelectric conversion layer. Furthermore, since the said solar cell is equipped with the said support substrate, it can prevent that it becomes impossible to maintain the shape of the said solar cell by thinning the said photoelectric converting layer.

It is sectional drawing which shows roughly the whole structure of the solar cell which concerns on one Embodiment of this invention. It is a top view which shows the outline of the structure of the photonic crystal in the solar cell which concerns on one Embodiment of this invention. It is a figure which shows the resonance effect of the light by the photonic crystal of the solar cell which concerns on one Embodiment of this invention. It is a graph which shows the characteristic of the intensity | strength of the electromagnetic field with respect to the normalization frequency in the solar cell which concerns on one Embodiment of this invention. It is a graph which shows the characteristic of the light absorption rate with respect to the wavelength of light in the solar cell which concerns on one Embodiment of this invention. It is a graph which shows the characteristic of the average value of the light absorption rate with respect to the height of a photonic crystal in the solar cell which concerns on one Embodiment of this invention. It is a graph which shows the characteristic of the average value of the light absorption rate with respect to the convex-shaped radius formed in the 1st transparent conductive film in the solar cell which concerns on one Embodiment of this invention. It is a graph which shows the characteristic of the light absorption rate with respect to the wavelength of light in the solar cell which concerns on one Embodiment of this invention. It is process drawing which shows the manufacturing process of the solar cell which concerns on one Embodiment of this invention. It is sectional drawing which shows schematically the whole structure of the solar cell which concerns on other embodiment of this invention. It is a top view which shows the outline of the structure of the photonic crystal in the solar cell which concerns on other embodiment of this invention. It is sectional drawing which shows roughly the whole structure of the solar cell which concerns on further another embodiment of this invention. It is process drawing which shows the manufacturing process of the solar cell which concerns on further another embodiment of this invention. It is sectional drawing which shows roughly the whole structure of the solar cell which concerns on further another embodiment of this invention. It is sectional drawing which shows roughly the whole structure of the solar cell which concerns on further another embodiment of this invention. It is a figure which shows the resonance effect of the light by the photonic crystal of the solar cell which concerns on further another embodiment of this invention. It is process drawing which shows the manufacturing process of the solar cell which concerns on further another embodiment of this invention. It is sectional drawing which shows roughly the whole structure of the solar cell which concerns on further another embodiment of this invention. It is a figure which shows the resonance effect of the light by the photonic crystal of the solar cell which concerns on further another embodiment of this invention. It is process drawing which shows the manufacturing process of the solar cell which concerns on further another embodiment of this invention. It is sectional drawing which shows roughly the whole structure of the solar cell which concerns on further another embodiment of this invention. It is a figure which shows the resonance effect of the light by the photonic crystal of the solar cell which concerns on further another embodiment of this invention. It is process drawing which shows the manufacturing process of the solar cell which concerns on further another embodiment of this invention. It is sectional drawing which shows schematically the whole structure of the solar cell which concerns on the modification of other embodiment of this invention. It is a graph which shows the characteristic of the light absorption rate of the solar cell with respect to the wavelength of sunlight, and the irradiance of sunlight in a prior art. 10 is a cross-sectional view illustrating an outline of a solar cell according to Patent Document 1. FIG.

<Embodiment 1>
One embodiment of a solar cell according to the present invention will be described below with reference to FIGS. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the scope of the present invention only, unless otherwise specified, and are merely descriptions. It is just an example.

[Configuration of solar cell]
First, the structural example of the solar cell which concerns on this embodiment is demonstrated with reference to FIG. FIG. 1 is a cross-sectional view schematically showing the overall configuration of the solar cell 1 of the present embodiment.

As shown in FIG. 1, the solar cell 1 includes a first transparent conductive film (first transparent body) 11, a photoelectric conversion layer 12, a metal electrode 13 (metal electrode layer), a transparent insulator layer (transparent insulating layer) 14, A support substrate 15 is provided. With these configurations, the solar cell 1 can photoelectrically convert incident light and use it as a current.

A first transparent conductive film (TCO; Transparent Conducting Oxide) 11 is a transparent conductive film, and is provided as an incident surface on which sunlight is incident. Moreover, the 1st transparent conductive film 11 is formed so that the photoelectric converting layer 12 may be covered, and comprises the photonic crystal mentioned later with the photoelectric converting layer 12 by having the convex part 16 as shown in FIG. Yes. The photonic crystal structure will be described later with different drawings.

The first transparent conductive film 11 is made of a medium having a refractive index smaller than that of the medium of the photoelectric conversion layer 12. Examples of the medium include ITO (Indium-Tin-Oxide: Indium Tin Oxide), IZO (Indium-Zinc-Oxide: Indium Zinc Oxide), SnO ₂ and ZnO.

The photoelectric conversion layer 12 is a semiconductor layer that absorbs light and performs photoelectric conversion, and has a convex shape 17 as shown in FIG. 1 on the light incident side surface (incident surface) (first surface). Together with the first transparent conductive film 11, a photonic crystal to be described later is formed.

The photoelectric conversion layer 12 has a structure in which semiconductor layers having different polarities are adjacent to each other, and the structure is not particularly limited. For example, a p-type semiconductor layer 121 and an n-type semiconductor layer as shown in FIG. A pn vertical structure in which 122 is adjacent may be adopted. As the photoelectric conversion layer 12 structure, a pin vertical structure in which an i-type semiconductor layer (a so-called intrinsic semiconductor layer, not shown) is sandwiched between a p-type semiconductor layer 121 and an n-type semiconductor layer 122 can also be adopted.

Note that examples of the medium of the photoelectric conversion layer 12 include crystalline silicon (c-Si) having a refractive index of about 3.0 to 6.0, but are not limited thereto. For example, as the medium of the photoelectric conversion layer 12, microcrystalline silicon (μc-Si), amorphous silicon (a-Si), and polysilicon (p-Si: having a refractive index of about 3.0 to 4.0: High purity polycrystalline silicon) may be employed.

The metal electrode 13 is a layer disposed on the surface (second surface) opposite to the light incident surface (the first surface) of the photoelectric conversion layer 12. As a material of the metal electrode 13, a material having a high light reflectance and a high electrical conductivity, for example, Ag, Mo, Al, or the like can be selected.

Light incident on the photoelectric conversion layer 12 through the first transparent conductive film 11 is absorbed by generating electrons and holes in the photoelectric conversion layer and exciting the electrons from the valence band to the conduction band. Is done. The excited electrons become a current flowing through a circuit (not shown) including the first transparent conductive film 11 and the metal electrode 13.

Note that the metal electrode 13 can also function as a reflector, and light that is not photoelectrically converted by the photoelectric conversion layer 12 and that has been transmitted can be reflected to the photoelectric conversion layer 12. By arranging the metal electrode 13 so as to cover the entire back surface of the photoelectric conversion layer 12 (the second surface), the light transmitted through the photoelectric conversion layer 12 can be reliably reflected, so that more light is absorbed. The solar cell 1 with high efficiency can be configured.

The transparent insulator layer 14 is a layer made of a transparent insulator having a smooth surface and a hydrophilic surface, and connects and insulates the metal electrode 13 and the support substrate 15. As the medium of the transparent insulator layer _14, SiO 2, SiNx, and, and the like quartz substrate.

The support substrate 15 is a substrate for maintaining the shape of the solar cell 1. In addition, as a material of the support substrate 15, glass with a refractive index of about 1.52 can be selected, for example.

In addition, the solar cell 1 functions as a battery by taking out the electric current photoelectrically converted in the photoelectric conversion layer 12 from the first transparent conductive film 11 and the metal electrode 13.

(Arrangement of each component of solar cell)
As shown in FIG. 1, the solar cell 1 includes a support substrate 15 as a lowermost layer (a surface opposite to the incident surface), on which a transparent insulator layer 14, a metal electrode 13, and a photoelectric conversion layer 12 are provided. They are stacked in this order. The photoelectric conversion layer 12 includes an n-type semiconductor layer 122 and a p-type semiconductor layer 121, and is stacked in this order from the surface opposite to the incident surface.

In addition, a concavo-convex shape is formed on the incident surface of the p-type semiconductor layer 121 included in the photoelectric conversion layer 12, and the first transparent conductive film 11 is formed on the incident surface (the outermost surface) of the solar cell 1 so as to cover the concavo-convex shape. The outer layer is laminated.

[Structure of photonic crystal]
Next, the photonic crystal will be described with reference to FIGS. FIG. 2 is a cross-sectional view taken along the line AB of the photonic crystal shown in FIG. 1, and is a top view schematically showing the structure of the photonic crystal of the solar cell 1 according to the present embodiment.

Here, a photonic crystal is a nanostructure whose refractive index changes periodically.

As shown in FIGS. 1 and 2, in the present embodiment, a plurality of cylindrically formed light incident surfaces of the photoelectric conversion layer 12 (more precisely, the p-type semiconductor layer 121 of the photoelectric conversion layer 12). The recesses (holes) (first recesses) are regularly formed. In other words, as a result of regularly forming a plurality of recesses in the photoelectric conversion layer 12, a convex shape 17 is formed between adjacent recesses.

Further, as shown in FIGS. 1 and 2, the first transparent conductive film 11 is formed so as to fill at least the concave portion of the photoelectric conversion layer 12. As a result, the first transparent conductive film 11 has a plurality of convex portions 16 formed in a columnar shape so as to fill at least the concave portion of the photoelectric conversion layer 12.

That is, in the present embodiment, the concave and convex portions formed in the light incident surface of the photoelectric conversion layer 12 (more specifically, the convex portions 16 formed in the concave portions) are regular in order to form a photonic crystal. It forms the basic element that is formed.

In the present embodiment, a photoelectric conversion unit is configured including the photoelectric conversion layer 12 and the first transparent conductive film 11.

The plurality of convex portions 16 formed on the first transparent conductive film 11 are arranged in a square lattice so that the arrangement interval (pitch) between the adjacent convex portions 16 is equal. That is, the plurality of recesses formed in the photoelectric conversion layer 12 are arranged in a square lattice so that the arrangement intervals between adjacent recesses are equal. In addition, the value of the arrangement | positioning space | interval of adjacent convex parts 16 is also called the lattice constant a (nm).

As described above, the plurality of convex portions 16 formed on the first transparent conductive film 11 are periodically arranged in the medium of the photoelectric conversion layer 12 having a refractive index different from that of the first transparent conductive film 11. By arranging the convex portions 16 in this manner, a refractive index difference between the refractive index of the first transparent conductive film 11 and the refractive index of the photoelectric conversion layer 12 periodically exists. In other words, the plurality of convex portions 16 formed on the first transparent conductive film 11 and the convex shape 17 formed on the photoelectric conversion layer 12 constitute a photonic crystal whose refractive index changes periodically.

As described above, in the solar cell 1 according to the present embodiment, since the concave portion is formed in the photoelectric conversion layer 12 itself, the refractive index is reduced at the interface between the photoelectric conversion layer 12 and the first transparent conductive film 11 as the adjacent layer. Only two different materials are adjacent to each other to form a photonic crystal.

In the present embodiment, the case where the plurality of convex portions 16 are formed in a columnar shape will be described as an example, but the present invention is not limited to this. For example, the plurality of convex portions 16 may be formed in a triangular prism shape or may be formed in a quadrangular prism shape. Moreover, as the convex part 16, the shape of a truncated cone, a triangular frustum, and a quadrangular pyramid can also be selected.

(Photonic band structure)
A photonic band structure is generated in the photonic crystal having the above configuration. The photonic band structure is represented by the relationship between the incident direction of light with respect to the photonic crystal and a normalized frequency V described later.

More specifically, a low dielectric band due to the medium of the first transparent conductive film 11 and a high dielectric band due to the medium of the photoelectric conversion layer 12 are generated. The photonic band structure includes a photonic band gap sandwiched between a low dielectric band and a high dielectric band as a wavelength band of light that cannot exist in the photonic crystal.

(Light confinement effect in photonic crystals)
Next, the resonance effect in the photonic crystal will be described with reference to FIG. FIG. 3 is a diagram illustrating a light resonance effect by the photonic crystal included in the solar cell 1 according to the present embodiment.

The photonic crystal formed by the convex portion 16 of the first transparent conductive film 11 and the convex shape 17 of the photoelectric conversion layer 12 resonates incident light in the in-plane direction, as indicated by an arrow A in FIG. Can do. That is, the entire photonic crystal functions as one large resonator that resonates in the in-plane direction. Thereby, the photonic crystal can confine incident light in the entire photonic crystal.

Further, the interaction between the resonance effect of the photonic crystal functioning as a resonator and the light reflection effect of the metal electrode 13 as shown by the arrow A in FIG. 3 (that is, the incident light to the photoelectric conversion layer 62, and As a result of the light confinement effect due to the interference effect with the reflected light from the metal electrode 13, the light incident on the photoelectric conversion layer 12 is interposed between the photonic crystal and the metal electrode 13 as shown by an arrow B in FIG. You will be trapped. Moreover, since incident light is diffracted or scattered when passing through the photonic crystal, the solar cell 1 can increase the path of light passing through the photoelectric conversion layer 12.

Thereby, the solar cell 1 can improve the light absorption rate in the photoelectric conversion layer 12, and can increase the amount of electromotive force in the solar cell 1.

[Optimal conditions for light absorption]
Next, the optimum conditions for light absorption in the solar cell 1 according to the present embodiment will be described with reference to FIGS.

As shown in FIG. 3, as a parameter for determining the magnitude of resonance Q, the lattice constant (pitch) of the photonic crystal is a, and the projections 16 (in other words, the photoelectric conversion layer 12 formed on the first transparent conductive film 11). 2), the height of the convex portion 16 is d, the thickness of the photoelectric conversion layer 12 is h, and the thickness of the first transparent conductive film 11 and the photoelectric conversion layer 12 is L. Note that L corresponds to the distance from the light incident surface of the first transparent conductive film 11 to the second surface of the photoelectric conversion layer 12.

Also, let n _{s be} the refractive index of the crystalline silicon that is the medium of the photoelectric conversion layer 12, n _{t be} the refractive index of the medium of the first transparent conductive film 11, and α be the absorption coefficient of the crystalline silicon with respect to a certain wavelength of light.

Lattice constant a, diameter 2r of convex portion 16, height of convex portion 16 (ie, photonic crystal height) d, thickness L of first transparent conductive film 11 and photoelectric conversion layer 12, refraction of photoelectric conversion layer 12 A resonance condition for a plurality of wavelengths of light is determined from the rate n _s and the refractive index n _t of the first transparent conductive film 11, and a resonance magnitude Q can be obtained for each wavelength.

Further, at a certain wavelength of light, the magnitude of light absorption is obtained from the resonance magnitude Q obtained as described above, the absorption coefficient α of crystalline silicon and the height h of the photoelectric conversion layer 12 as other parameters. (That is, light absorption rate) S can be obtained.

Here, when the wavelength of light is λ and the nonlinear function is represented by f and g, the resonance magnitude Q and the light absorption rate S can be expressed by the following equations.

Q (λ) = f (a, r, d, L, n _s (λ), n _t (λ))
S (λ) = g (Q (λ), α (λ), h)
(Optimum condition of lattice constant)
First, the optimum conditions for the lattice constant will be described with reference to FIG. FIG. 4 is a graph showing the characteristics of the relative strength (au) of the electromagnetic field with respect to the normalized frequency V (a / λ) in the solar cell 1 according to the present embodiment. (A) of FIG. 4 is a graph which shows the characteristic of the intensity | strength of the electromagnetic field with respect to the normalization frequency of 0.0 or more and 0.6 or less, (b) is the range of 0.3 or more and 0.5 or less It is a graph which expands and shows the characteristic of the strength of the electromagnetic field with respect to the normalized frequency.

Here, the lattice constant is a (nm), the thickness h of the photoelectric conversion layer 12 is 3.3 a (nm), and the height d of the convex portion 16 is 0.5 a.

As shown to (a) and (b) of FIG. 4, the intensity | strength of the electromagnetic field with respect to each normalized frequency of the solar cell 1 which concerns on this embodiment was obtained by simulation. In addition, as for the graph shown to (a) and (b) of FIG. 4, all are FDTD methods (Finite Difference Time).
The result obtained by the simulation using the Domain method (finite difference time domain method) is shown.

From this simulation, at a normalized frequency V of 0.3 or more and 0.5 or less, the resonance frequency Q is relatively low, and V = 0 as a normalized frequency V that is easily matched with the optimum condition by the absorption coefficient α. .33325 and V = 0.44739 values were obtained. Further, the normalized frequency V (a / λ) is expressed by the following equation.

Normalized frequency V = lattice constant a (nm) / wavelength of light λ (nm) Formula 1
Here, in the solar cell 1 of the present embodiment, when the wavelength λ = 450 nm and the normalized frequency V = 0.33325, from Equation 1, the minimum value of the lattice constant a, a = 150 nm (450 × 0.33325 = 149) .9625≈150) is obtained. Further, assuming that the wavelength λ = 1200 nm and the normalized frequency V = 0.44739, the maximum value of the lattice constant a, a = 540 nm (1200 × 0.44739 = 536.868≈540) is obtained from Equation 1.

Therefore, by limiting the lattice constant a to a range of 150 nm or more and 450 nm or less and designing a photonic crystal, the solar cell 1 has improved light absorption compared with a conventional solar cell that does not use a photonic crystal. Can be designed.

In addition, since the value of the normalized frequency V can be changed by changing the value of the wavelength λ of light without changing the value of the lattice constant a, the range of the value of the normalized frequency V is not limited.

(Optimal conditions for photonic crystal height)
Next, see FIGS. 5 and 6 for the optimum conditions for the height of the photonic crystal, that is, the height of the protrusions 16 (holes formed in the photoelectric conversion layer 12) formed in the first transparent conductive film 11. To explain. FIG. 5 is a graph showing the characteristic of the light absorption rate with respect to the wavelength of light in the solar cell 1 according to the present embodiment. FIG. 6 is a graph showing the relative ratio of the average value of the light absorption rate with respect to the height of the photonic crystal in the solar cell 1 according to the present embodiment.

A graph indicated by a solid line in FIG. 5 indicates that the solar cell 1 according to this embodiment has a lattice constant a = 500 nm, a thickness h of the photoelectric conversion layer 12 of 1.5 μm, a thickness of the first transparent conductive film 11 of 400 nm, and a photonic. The measurement result of the optical absorptance with respect to the wavelength λ (nm) of light when the height of the crystal (height of the convex portion 16) d = 125 nm and the diameter of the convex portion 16 is designed as 2r = 400 (0.8 a) nm is shown. Show. Moreover, the graph which the broken line shows in FIG. 5 has shown the measurement result of the light absorption rate with respect to the wavelength of light in the conventional solar cell which does not use a photonic crystal.

As shown in FIG. 5, in the range where the wavelength of light is 500 nm or more and 1100 nm or less, the average value of the light absorptance with respect to each light wavelength of the solar cell 1 according to this embodiment is the light absorptance of the conventional solar cell. Compared to, it has risen about 1.36 times. Therefore, according to the result shown in FIG. 5, the light absorption rate in the solar cell (particularly, the light absorption rate in the long wavelength region) can be improved by forming the photonic crystal in the solar cell. Here, the case where the wavelength of light is in the range of 500 nm to 1100 nm has been described as an example, but of course, the wavelength is less than 500 nm and in the range greater than 1100 nm by adjusting the above-described parameters. The same effect can be obtained in.

Further, the graph shown in FIG. 6 shows the height d of the photonic crystal when the photonic crystal is not used, that is, when the average value of the light absorptance in the conventional solar cell in which d = 0 is 1.0. The comparative value of the average value of the light absorption rate of the solar cell 1 with respect to each is shown. A comparison value (hereinafter, also simply referred to as “comparison value”) of the average value of the light absorption rate of the solar cell 1 is expressed by the following equation. In addition, the comparative value has shown the magnification of the light absorption rate in the solar cell 1 which concerns on this embodiment with respect to the light absorption rate in the solar cell of a prior art.

Comparative value = (average value of light absorption rate of solar cell 1) / (average value of light absorption rate of conventional solar cell) Equation 2
As shown in FIG. 6, as the height d of the photonic crystal increases, the comparison value increases monotonously. In addition, as shown in FIG. 6, when the solar cell 1 is designed with a photonic crystal height d of 75 nm, the comparison value is 1.2 (that is, the light absorption rate is 1.2 times that of the conventional solar cell). )

Here, if the light absorptance of 1.2 times or more is obtained with respect to the light absorptivity of the conventional solar cell, even if the photoelectric conversion layer 12 is made thinner than the conventional solar cell, the solar cell 1 can Equivalent or higher photoelectric effect can be obtained. Therefore, by designing the height d of the photonic crystal to be 75 nm or more, a photoelectric effect that is thinner than the conventional solar cell and equivalent to or higher can be obtained.

As shown in FIG. 6, the higher the height d of the photonic crystal, the higher the light absorption rate. Therefore, the upper limit of the height of the photonic crystal is less than the thickness of the photoelectric conversion layer 12. Absent.

(Optimum condition of hole diameter of photonic crystal)
Next, with reference to FIG. 7, the optimum condition for the diameter of the convex portion 16 formed in the first transparent conductive film 11 to form the photonic crystal (the diameter of the hole formed in the photoelectric conversion layer 12) will be described. explain. FIG. 7 is a graph showing the characteristic of the average value of the light absorption rate with respect to the radius of the convex portion 16 formed in the first transparent conductive film 11 in the solar cell 1 according to the present embodiment.

FIG. 7 shows the characteristics of the average value of the light absorption rate with respect to the radius of the convex portion 16 when the solar cell 1 is designed with the height of the photonic crystal (height of the convex portion 16) being d = 125 nm. .

In addition, the radius of the convex part 16 shown on the horizontal axis in FIG. 7 is expressed as a ratio to the lattice constant a. That is, when the radius shown on the horizontal axis is 0.50, the radius of the convex portion 16 is r = 0.50a. Further, since the radius of the convex portion 16 shown on the horizontal axis is a ratio to the lattice constant a, when the radius value exceeds 0.50 (that is, the diameter is 1.00), the adjacent convex portions 16 overlap each other. (Because the diameter 2r of the convex portion 16 exceeds the lattice constant a). For this reason, FIG. 7 shows only the range in which the radius of the convex portion 16 is 0.50a or less.

Further, the average value of the light absorption rate with respect to the convex portion 16 shown in FIG. 7 does not depend on the height d of the photonic crystal. Moreover, the optimal condition of the radius of the convex part 16 is obtained when the comparison value of the average value of the optical absorptance with respect to the height of the photonic crystal shown in FIG. Here, assuming that the height of the photonic crystal is d = 250 nm, when the average value of the light absorption rate with respect to the radius of the convex portion 16 shown in FIG. 7 is 0.8 or more, the comparison shown in FIG. A value of 1.2 or more can be satisfied. At this time, the value of the radius r of the convex portion 16 that satisfies the average value of the light absorption rate of 0.8 or more is 0.20a or more and 0.50a or less (that is, the diameter 2r of the convex portion 16 as shown in FIG. Is 0.40a or more and 1.00a or less. Therefore, it is the optimum condition for the radius of the convex portion 16 that the value of the radius r is within this range.

Even when the height of the photonic crystal is lower than d = 250 nm, the optimum value of the diameter 2r of the convex portion 16 exists in the range where the diameter 2r of the convex portion 16 is 0.40a or more and 1.00a or less. To do.

As described above, since the optimum condition of the lattice constant a is 150 nm or more and 540 nm or less, the minimum value of the radius of the convex portion 16 is r = 30 nm (0.20a = 0.20 × 150 nm = 30 nm), which is the maximum value. R = 270 nm (0.50a = 0.50 × 540 nm = 270 nm). That is, the minimum value of the diameter of the convex portion 16 is 2r = 60 nm, and the maximum value is 2r = 540 nm.

(Light absorption rate)
Next, the light absorption rate in the solar cell 1 obtained by designing the solar cell 1 as described above will be described with reference to FIG. FIG. 8 is a graph showing the characteristics of the light absorption rate with respect to the wavelength of light in the solar cell 1 according to the present embodiment. In FIG. 8, the curve indicated by the alternate long and short dash line indicates the light absorptance in the conventional solar cell having a thickness of 400 μm, and the curve indicated by the broken line indicates the light absorptance in the conventional solar cell having a thickness of 500 nm. Moreover, the curve shown as a continuous line in FIG. 8 has shown the light absorption rate in the solar cell 1 which concerns on this embodiment whose thickness is 500 nm.

As described above, in the solar cell 1 according to this embodiment, the refractive index difference between the refractive index of the first transparent conductive film 11 and the refractive index of the photoelectric conversion layer 12 periodically exists, so that in the in-plane direction. The effect of Bragg reflection can be obtained. Here, Bragg reflection refers to a phenomenon in which light incident on a photonic crystal is reflected in a specific direction determined by the lattice constant a and the wavelength λ of the light.

In the solar cell 1 according to this embodiment, photoelectric conversion is performed by optimally designing the arrangement interval (lattice constant a), the diameter 2r, and the height d of the protrusions 16 formed in the first transparent conductive film 11. Incident light can be resonated in the layer 12. As shown by the solid line in FIG. 8, the solar cell 1 can maintain a light absorption rate of about 1.0 in all wavelength regions of 300 nm to 1100 nm by optimal design.

Furthermore, the photonic crystal is optimally designed based on the optimum conditions as described above, and the thickness of the solar cell 1 is so thick that the conventional solar cell cannot maintain the shape (for example, about several hundred nm). Even if it is a case where it suppresses to (thickness), by providing the support substrate 15, the solar cell 1 can maintain the shape.

In addition, the solar cell 1 according to the present embodiment has a photoelectric conversion equivalent to or higher than that of a conventional solar cell having a thickness of several hundred μm due to the effect of improving the light absorption rate by the photonic crystal even if the thickness is suppressed to several hundred nm. Efficiency can be realized.

[Solar cell manufacturing process]
Finally, the manufacturing process of the solar cell 1 according to the present embodiment will be described with reference to FIG. FIG. 9 is a process diagram showing manufacturing steps of the solar cell 1 according to this embodiment. In the present embodiment, the medium of the first transparent conductive film 11 is SnO ₂ , the medium of the photoelectric conversion layer 12 is c-Si, the medium of the metal electrode 13 is Al, and the medium of the transparent insulator layer 14 is SiO _2. However, the present invention is not limited to this example.

First, as shown in FIG. 9A, a c-Si layer is formed and a p-type sub-semiconductor layer 121a is formed by doping a p-type impurity. The light incident direction is the lower surface of the p-type sub semiconductor layer 121a.

Next, as shown in FIG. 9B, by depositing c-Si on the p-type sub-semiconductor layer 121a and doping (implanting) an n-type impurity (for example, phosphorus), the n-type is thereby obtained. A semiconductor layer 122 is formed, and a pn junction semiconductor layer is formed.

Subsequently, as shown in FIG. 9C, an ion beam containing hydrogen is implanted to form a damaged layer 120 in which the silicon crystal lattice is partially cut in the p-type sub-semiconductor layer 121a. . Note that the p-type sub-semiconductor layer 121a on the n-type semiconductor layer 122 side is a p-type sub-semiconductor layer 121b with the damaged layer 120 as a boundary, and the p-type sub-semiconductor layer 121a on the opposite side to the n-type semiconductor layer 122 is a p-type sub-semiconductor. The semiconductor layer 121c is used.

Thereafter, as shown in FIG. 9D, Al is vapor-deposited on the n-type semiconductor layer 122, and an Al film is formed to form the metal electrode 13. Further, SiO ₂ is vapor-deposited on the formed metal electrode 13 to form the transparent insulator layer 14. If the surface of the formed transparent insulator layer 14 has an uneven shape, the surface is planarized by CMP (Chemical Mechanical Polishing) as shown in FIG.

Further, as shown in FIG. 9 (f), the laminated body formed in the above (a) to (e) is inverted so that the transparent insulator layer 14 whose surface is flattened becomes the lower surface, and the transparent insulator The layer 14 and the support substrate 15 are bonded. Note that since the stacked body is inverted, the light incident surface is a surface on the semiconductor layer side of the stacked body.

Next, after heating, as shown in FIG. 9G, the p-type sub-semiconductor layer 121c and the p-type sub-semiconductor layer 121b are cleaved with the damaged layer 120 as a boundary to form the uppermost layer of the substrate. The p-type sub semiconductor layer 121c is removed (wafer removal by heat treatment). At this time, since the damaged layer 120 is formed in the step shown in FIG. 9C, the p-type sub semiconductor layer 121 c can be removed along the damaged layer 120.

Further, as shown in FIG. 9H, the surface (surface of the p-type sub-semiconductor layer 121b) after the p-type sub-semiconductor layer 121c is removed from the wafer is modified (surface modification) and the uneven shape is formed. By planarizing, the p-type semiconductor layer 121 of the photoelectric conversion layer 12 is formed. Thereby, the photoelectric conversion layer 12 including the p-type semiconductor layer 121 and the n-type semiconductor layer 122 is obtained.

The surface modification is performed by, for example, forming polysilicon using an ELA (Eximer Laser Annealing) technique.

Subsequently, as shown in FIG. 9I, the planarized p-type semiconductor layer 121 is further thinned by dry etching, and holes for forming a photonic crystal are formed in the p-type semiconductor layer 121. Periodically formed (that is, the convex shape 17 is formed). Note that as an example of dry etching, inductively coupled plasma-reactive ion etching (ICP-RIE) using carbon tetrafluoride (CF ₄ ) as an etching gas can be given. Of course, the present invention is not limited to this, and as the etching gas, sulfur hexafluoride (SF ₆ ), trifluoromethane (CHF ₃ ), or the like may be employed.

Finally, as shown in FIG. 9J, the first transparent conductive film 11 is formed by vapor-depositing SnO ₂ on the p-type semiconductor layer 121 on which the convex shape 17 is formed by dry etching. As described above, the solar cell 1 according to this embodiment is completed through the manufacturing steps (a) to (j) of FIG.

A plurality of convex portions 16 are formed on the first transparent conductive film 11 by depositing SnO ₂ into holes periodically formed in the p-type semiconductor layer 121. A photonic crystal is formed by the plurality of convex portions 16 formed on the first transparent conductive film 11 and the convex shape 17 formed on the p-type semiconductor layer 121.

With the above-described configuration, the solar cell 1 can increase the light absorptance particularly at a long wavelength, improve the efficiency of photoelectric conversion, and realize a reduction in thickness (thickness of about several hundred nm). . Furthermore, since the solar cell 1 includes the support substrate 15, it can be prevented that the shape of the solar cell 1 cannot be maintained by reducing the thickness of the photoelectric conversion layer 12.

<Embodiment 2>
Another embodiment of the present invention will be described below with reference to FIGS. 10 and 11. For convenience of explanation, components having the same functions as those of the components according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, differences from the first embodiment will be mainly described.

[Configuration of solar cell]
First, the configuration of the solar cell according to the present embodiment will be described with reference to FIG. FIG. 10 is a cross-sectional view schematically showing the configuration of the solar cell 2 according to this embodiment.

As shown in FIG. 10, the solar cell 2 according to the present embodiment includes a first transparent conductive film (first transparent body) 21 and a photoelectric conversion layer 22, and the first transparent conductive film 21 and the photoelectric conversion are included. The configuration is the same as that of the solar cell 1 according to Embodiment 1 except that the photonic crystal is formed by the layer 22.

The uneven shape formed at the interface between the first transparent conductive film 21 and the photoelectric conversion layer 22 is an inversion of the concave and convex portions formed at the interface between the first transparent conductive film 11 and the photoelectric conversion layer 12 of Embodiment 1. It has a shape.

The first transparent conductive film 21 is a transparent conductive film and is provided as an incident surface on which sunlight is incident. Moreover, the 1st transparent conductive film 21 is formed so that the photoelectric converting layer 22 may be covered, and it comprises the photonic crystal mentioned later with the photoelectric converting layer 22 by having the convex shape 26 as shown in FIG. Yes.

The photoelectric conversion layer 22 is a semiconductor layer that absorbs light and performs photoelectric conversion, and a convex portion 27 (first convex portion) as shown in FIG. 10 is two-dimensionally on the light incident side surface (first surface). And periodically. Thus, a photonic crystal described later is formed together with the first transparent conductive film 21.

Further, the photoelectric conversion layer 22 has a structure in which semiconductor layers having different polarities are adjacent to each other, and the structure is not particularly limited. However, in the present embodiment, for example, as shown in FIG. A pn vertical structure in which the n-type semiconductor layer 222 is adjacent to each other is employed. Note that the present invention is not limited to this, and an i-type semiconductor layer (so-called intrinsic semiconductor layer, not shown) is sandwiched between the p-type semiconductor layer 221 and the n-type semiconductor layer 222 as the photoelectric conversion layer 22 structure. A pin vertical structure can also be adopted.

[Structure of photonic crystal]
Next, a photonic crystal will be described with reference to FIGS. FIG. 11 is a cross-sectional view taken along the line AB of the photonic crystal shown in FIG. 10, and is a top view schematically showing the structure of the photonic crystal of the solar cell 2 according to this embodiment.

As shown in FIGS. 10 and 11, in this embodiment, the light incident surface of the photoelectric conversion layer 22 (more precisely, the p-type semiconductor layer 221 of the photoelectric conversion layer 22) is formed in a columnar shape. A plurality of convex portions 27 are regularly formed. In other words, by providing the plurality of convex portions 27 in the photoelectric conversion layer, a concave shape (second concave portion) is formed between the adjacent convex portions 27.

That is, in the present embodiment, the concavo-convex convex portions 27 formed on the light incident surface of the photoelectric conversion layer 22 form a basic element that is regularly formed in order to form a photonic crystal.

Also, as shown in FIGS. 10 and 11, the first transparent conductive film 21 is formed so as to satisfy at least the concave shape of the photoelectric conversion layer 22. As a result, the convex shape 26 is formed on the first transparent conductive film 21 with a complementary shape corresponding to the concave shape.

The plurality of convex portions 27 formed on the photoelectric conversion layer 22 are arranged in a square lattice so that the arrangement interval (pitch) between the adjacent convex portions 27 is equal. In addition, the value of the arrangement | positioning space | interval of adjacent convex parts 27 is also called the lattice constant a (nm).

As described above, the plurality of convex portions 27 formed on the photoelectric conversion layer 22 are periodically arranged in the medium of the first transparent conductive film 21 having a different refractive index. By arranging the convex portions 27 in this manner, there is a difference in refractive index between the refractive index of the first transparent conductive film 21 and the refractive index of the photoelectric conversion layer 22. That is, the convex shape 26 formed in the first transparent conductive film 21 and the plurality of convex portions 27 formed in the photoelectric conversion layer 22 constitute a photonic crystal whose refractive index changes periodically.

Thus, in the solar cell 2 according to this embodiment, the convex portion 27 is formed on the photoelectric conversion layer 22 itself, and the periphery of the convex portion 27 is covered with the first transparent conductive film 21. Therefore, at the interface between the photoelectric conversion layer 22 and the first transparent conductive film 21 as the adjacent layer, only two kinds of materials having different refractive indexes are adjacent to each other to form a photonic crystal.

In the present embodiment, the case where the plurality of convex portions 27 are formed in a columnar shape will be described as an example, but the present invention is not limited to this. For example, the plurality of convex portions 27 may be formed in a triangular prism shape or may be formed in a quadrangular prism shape. Moreover, as the convex part 27, the shape of a frustum, a triangular frustum, and a quadrangular frustum can also be selected.

[Solar cell manufacturing process]
Finally, the manufacturing process of the solar cell 2 according to the present embodiment will be described. In addition, the manufacturing process of the solar cell 2 which concerns on this embodiment is the same as the manufacturing process of the solar cell 1 of Embodiment 1 except the process in the process shown to (i) and (j) of FIG. 9 differing. .

In the manufacturing process of the solar cell 2, as shown in FIG. 9I, after the planarized p-type semiconductor layer 221 is further thinned by dry etching, the holes are periodically formed in the p-type semiconductor layer 221. Instead of forming the protrusions 27, the protrusions 27 for forming the photonic crystal are periodically formed.

Finally, the first transparent conductive film 21 is formed by vapor-depositing SnO ₂ on the p-type semiconductor layer 221 on which the plurality of convex portions 27 are formed by dry etching. Thus, a photonic crystal is formed by the convex shape 26 formed on the first transparent conductive film 21 and the convex portion 27 formed on the photoelectric conversion layer 22.

With the above-described configuration, the solar cell 2 can increase the light absorptivity particularly at a long wavelength, improve the efficiency of photoelectric conversion, and can realize a reduction in thickness (thickness of about several hundred nm). . Furthermore, since the solar cell 2 includes the support substrate 15, it can be prevented that the shape of the solar cell 2 cannot be maintained by reducing the thickness of the photoelectric conversion layer 22.

<Embodiment 3>
Still another embodiment of the present invention will be described below with reference to FIGS. For convenience of explanation, constituent elements having the same functions as those of the constituent elements according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, differences from the first embodiment will be mainly described.

[Configuration of solar cell]
First, the configuration of the solar cell according to the present embodiment will be described with reference to FIG. FIG. 12 is a cross-sectional view schematically showing the overall configuration of the solar cell 3 according to this embodiment.

As shown in FIG. 12, the solar cell 3 according to this embodiment is implemented except that a second transparent conductive film (second transparent body) 38 is provided between the photoelectric conversion layer 12 and the metal electrode 13. The solar cell 1 has the same configuration as that of the first embodiment.

The second transparent conductive film 38 is a transparent conductive film and is formed so as to be sandwiched between the photoelectric conversion layer 12 and the metal electrode 13. The second transparent conductive film 38 is made of a medium having a smaller refractive index than the medium of the photoelectric conversion layer 12, and examples of the medium include ITO, IZO, SnO ₂ , and ZnO.

In addition, since the structure of the photonic crystal which the solar cell 3 which concerns on this embodiment has is the same as the structure of the photonic crystal which the solar cell 1 which concerns on Embodiment 1 shown in FIG. 2 has, description is abbreviate | omitted here. .

[Solar cell manufacturing process]
Finally, the manufacturing process of the solar cell 3 according to the present embodiment will be described with reference to FIG. FIG. 13 is a process diagram showing a manufacturing process of the solar cell 3 according to the present embodiment. In the present embodiment, the medium of the first transparent conductive film 11 and the second transparent conductive film 38 is SnO ₂ , the medium of the photoelectric conversion layer 12 is c-Si, the medium of the metal electrode 13 is Al, transparent The case where the medium of the insulator layer 14 is SiO ₂ will be described as an example, but the present invention is not limited to this.

In addition, the manufacturing process of the solar cell 3 according to this embodiment shown in FIG. 13 is the same as that of the solar cell 1 according to Embodiment 1 shown in FIG. 9 except that the steps shown in (d) and (e) are different. It is the same as the manufacturing process.

As shown in FIG. 13D, SnO ₂ is deposited on the n-type semiconductor layer 122 to form the second transparent conductive film 38. Subsequently, Al is vapor-deposited on the formed second transparent conductive film 38, a metal electrode 13 is formed by forming an Al film, SiO ₂ is vapor-deposited on the formed metal electrode 13, and transparent insulation is formed. The body layer 14 is formed. If the surface of the formed transparent insulator layer 14 has an uneven shape, the surface is flattened by CMP as shown in FIG.

Thus, the solar cell 3 according to the present embodiment is completed through the manufacturing steps (a) to (j) of FIG.

Note that SnO ₂ is vapor deposited in holes periodically formed in the p-type semiconductor layer 121 (the p-type sub-semiconductor layer 121c is removed from the wafer and the planarized p-type sub-semiconductor layer 121b). A plurality of convex portions 16 are formed on the conductive film 11. A photonic crystal is formed by the plurality of convex portions 16 formed on the first transparent conductive film 11 and the convex shape 17 formed on the p-type semiconductor layer 121.

With the above-described configuration, the solar cell 3 can increase the light absorptance particularly at a long wavelength, improve the efficiency of photoelectric conversion, and can realize a reduction in thickness (thickness of about several hundred nm). . Furthermore, since the solar cell 3 includes the support substrate 15, it is possible to prevent the shape of the solar cell 2 from being maintained by reducing the thickness of the photoelectric conversion layer 12.

Moreover, according to the above-mentioned structure, since each refractive index of the 1st transparent conductive film 11 and the 2nd transparent conductive film 38 is smaller than the refractive index of the photoelectric converting layer 12, a high refractive index core is made into a low refractive index. By the same principle as an optical fiber that propagates light by covering with a clad, it is possible to confine light that is about to leak out through the photoelectric conversion layer 12. Therefore, the effect of confining light in the photoelectric conversion layer 12 is further enhanced.

As a result, the light absorption rate by the photoelectric conversion layer 12 can be further improved, and the amount of electromotive force in the solar cell 3 can be further increased.

<Embodiment 4>
Another embodiment of the present invention will be described below with reference to FIG. FIG. 14 is a cross-sectional view schematically showing the configuration of the solar cell 4 according to this embodiment. For convenience of explanation, the same reference numerals are given to components having the same functions as those of the components according to the first to third embodiments, and description thereof is omitted. In the present embodiment, differences from the first to third embodiments will be mainly described.

[Configuration of solar cell]
As shown in FIG. 14, the solar cell 4 according to this embodiment includes a first transparent conductive film 21 and a photoelectric conversion layer 22, and a photonic crystal is formed by the first transparent conductive film 21 and the photoelectric conversion layer 22. It is the same as the solar cell 1 according to Embodiment 1 except that the second transparent conductive film (second transparent conductive film) 38 is provided between the photoelectric conversion layer 22 and the metal electrode 13. It is a configuration.

The first transparent conductive film 21 is formed so as to cover the photoelectric conversion layer 22 in which a plurality of convex portions 27 are formed two-dimensionally and periodically. The convex shape 26 of the first transparent conductive film 21 and the photoelectric conversion layer 22 are formed. The photonic crystal is constituted by the periodic structure with the convex portion 27 of the.

In the present embodiment, the convex portion 27 of the photoelectric conversion layer 22 is a basic element that is regularly formed in order to form a phophotonic crystal.

The second transparent conductive film 38 is a transparent conductive film and is formed so as to be sandwiched between the photoelectric conversion layer 12 and the metal electrode 13. The second transparent conductive film 38 is made of a medium having a smaller refractive index than the medium of the photoelectric conversion layer 12, and examples of the medium include ITO, IZO, SnO ₂ , and ZnO.

In addition, since the structure of the photonic crystal which the solar cell 4 which concerns on this embodiment has is the same as the structure of the photonic crystal which the solar cell 2 which concerns on Embodiment 2 shown in FIG. 11, it abbreviate | omits description here. .

[Solar cell manufacturing process]
The manufacturing process of the solar cell 2 according to the present embodiment is the same as the manufacturing process of the solar cell 3 of the third embodiment, except that the processes in the steps shown in (i) and (j) of FIG. 13 are different.

In the manufacturing process of the solar cell 3, as shown in FIG. 13I, after the planarized p-type semiconductor layer 221 is further thinned by dry etching, the holes are periodically formed in the p-type semiconductor layer 221. Instead of forming the protrusions 27, the protrusions 27 for forming the photonic crystal are periodically formed.

Finally, the first transparent conductive film 21 is formed by vapor-depositing SnO ₂ on the p-type semiconductor layer 221 on which the plurality of convex portions 27 are formed by dry etching. Thus, a photonic crystal is formed by the convex shape 26 formed on the first transparent conductive film 21 and the convex portion 27 formed on the photoelectric conversion layer 22.

With the above-described configuration, the solar cell 4 can increase the light absorptance particularly at a long wavelength, improve the efficiency of photoelectric conversion, and can realize a reduction in thickness (thickness of about several hundred nm). . Furthermore, since the solar cell 4 includes the support substrate 15, it can be prevented that the shape of the solar cell 4 cannot be maintained by reducing the thickness of the photoelectric conversion layer 22.

Moreover, according to the above-mentioned structure, since each refractive index of the 1st transparent conductive film 21 and the 2nd transparent conductive film 38 is smaller than the refractive index of the photoelectric converting layer 22, a high refractive index core is made into a low refractive index. By the same principle as an optical fiber that propagates light by covering with a clad, it is possible to confine light that is about to leak out through the photoelectric conversion layer 22. Therefore, the effect of confining light in the photoelectric conversion layer 22 is further enhanced.

As a result, the light absorption rate by the photoelectric conversion layer 22 can be further improved, and the amount of electromotive force in the solar cell 4 can be further increased.

<Embodiment 5>
Still another embodiment of the present invention will be described below with reference to FIGS. For convenience of explanation, constituent elements having the same functions as those of the constituent elements according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, differences from the first embodiment will be mainly described.

[Configuration of solar cell]
First, the configuration of the solar cell according to the present embodiment will be described with reference to FIG. FIG. 15 is a cross-sectional view schematically showing the overall configuration of the solar cell 5 according to the present embodiment.

As shown in FIG. 15, the solar cell 5 according to this embodiment includes a metal electrode (metal electrode layer) 13, a transparent insulator layer 14, a support substrate 15, a first transparent conductive film (first transparent body) 51, and The photoelectric conversion layer 52 is provided. In the solar cell 5 according to this embodiment, the incident direction of light is on the support substrate 15 side.

The first transparent conductive film 51 is a transparent conductive film, and is provided so as to cover the incident surface side of the photoelectric conversion layer 52 on which sunlight is incident. Moreover, the 1st transparent conductive film 51 comprises the photonic crystal with the photoelectric converting layer 52 by having the some convex part 56 as shown in FIG. 15 periodically. The first transparent conductive film 11 is preferably a medium having a refractive index smaller than that of the photoelectric conversion layer 12.

In addition, the convex part 56 of the photoelectric conversion layer 52 forms a basic element that is regularly formed in order to form a phophotonic crystal.

The photoelectric conversion layer 52 is a semiconductor layer that absorbs light and performs photoelectric conversion, and has a convex shape 57 as shown in FIG. 15 to constitute a photonic crystal together with the first transparent conductive film 51. The convex shape 57 is formed as a result of a plurality of holes having a shape complementary to the convex portion 56 being formed in the photoelectric conversion layer 52.

The photoelectric conversion layer 52 has a structure in which semiconductor layers having different polarities are adjacent to each other, and the structure is not particularly limited. For example, a p-type semiconductor layer 521 and an n-type semiconductor layer as shown in FIG. A pn vertical structure in which 522 is adjacent may be adopted. As the photoelectric conversion layer 52 structure, a pin vertical structure in which an i-type semiconductor layer (a so-called intrinsic semiconductor layer, not shown) is sandwiched between a p-type semiconductor layer 521 and an n-type semiconductor layer 522 can also be employed.

In the solar cell 5 according to this embodiment, the photoelectric conversion layer 52 having the convex shape 57 is the n-type semiconductor layer 522, and the n-type semiconductor layer 522 of the photoelectric conversion layer 52 and the first transparent conductive film 51 are used. Constitutes a photonic crystal.

As described above, in the solar cell 5 according to the present embodiment, since the concave portion is formed in the photoelectric conversion layer 52 itself, the refractive index is reduced at the interface between the photoelectric conversion layer 52 and the first transparent conductive film 51 as the adjacent layer. Only two different materials are adjacent to each other to form a photonic crystal.

(Arrangement of each component of solar cell)
As shown in FIG. 15, the solar cell 5 includes a metal electrode 13 as a lowermost layer (a surface opposite to the incident surface), and a photoelectric conversion layer 52 is stacked thereon. The photoelectric conversion layer 52 includes a p-type semiconductor layer 521 and an n-type semiconductor layer 522, which are stacked in this order from the surface opposite to the incident surface.

The n-type semiconductor layer 522 included in the photoelectric conversion layer 52 has a concavo-convex shape, the first transparent conductive film 51 is formed so as to cover the concavo-convex shape, and the transparent insulator layer 14 is formed thereon. Are stacked. Furthermore, a support substrate 15 is laminated on the transparent insulator layer 14 as the uppermost layer (incident surface) of the solar cell 5.

[Light confinement effect in photonic crystals]
Next, the resonance effect in the photonic crystal will be described with reference to FIG. FIG. 16 is a diagram illustrating a light resonance effect by the photonic crystal included in the solar cell 5 according to the present embodiment.

The photonic crystal formed by the convex portion 56 of the first transparent conductive film 51 and the convex shape 57 of the photoelectric conversion layer 52 resonates incident light in the in-plane direction, as indicated by an arrow A in FIG. Can do. That is, the entire photonic crystal functions as one large resonator that resonates in the in-plane direction. Thereby, the photonic crystal can confine incident light in the entire photonic crystal.

Further, the interaction between the resonance effect of the photonic crystal functioning as a resonator and the light reflection effect of the metal electrode 13 as shown by the arrow A in FIG. 16 (that is, the incident light to the photoelectric conversion layer 52, and Due to the light confinement effect due to the interference effect with the reflected light from the metal electrode 13, the light incident on the photoelectric conversion layer 52 is interposed between the photonic crystal and the metal electrode 53 as shown by an arrow B in FIG. You will be trapped. Moreover, since incident light is diffracted or scattered when passing through the photonic crystal, the solar cell 5 can increase the path of light passing through the photoelectric conversion layer 52.

Thereby, the solar cell 5 can improve the light absorption rate in the photoelectric conversion layer 52, and can increase the amount of electromotive force in the solar cell 5. Further, the photoelectric conversion layer 52 can be thinned by improving the light absorption rate in the photoelectric conversion layer 52. Furthermore, since the solar cell 5 includes the support substrate 15, it can be prevented that the shape of the solar cell 5 cannot be maintained by reducing the thickness of the photoelectric conversion layer 52.

[Resonance magnitude and light absorption rate]
Furthermore, with reference to FIG. 16, the light absorption rate in the solar cell 5 which concerns on this embodiment is demonstrated.

As shown in FIG. 16, the lattice constant (pitch) of the photonic crystal is a, the diameter of the convex portion 56 (that is, the hole formed in the photoelectric conversion layer 52) formed in the first transparent conductive film 51 is 2r, protrusion 56 height (hole) d, the height of the photoelectric conversion layer 52 h, from the photoelectric conversion layer 52 to the supporting substrate 15 the height and L _S. Further, the refractive index of crystalline silicon that is a medium of the photoelectric conversion layer 52 is n _s , the refractive index of the medium of the first transparent conductive film 51 is n _t , the refractive index of the medium of the transparent insulator layer 14 is n _SiO2 , and the support substrate. The refractive index of the medium 15 is n _Glass , and the absorption coefficient of the crystalline silicon with respect to a certain wavelength of light is α.

From the above parameters, resonance conditions for a plurality of light wavelengths are determined, and the resonance magnitude Q can be obtained for each wavelength. In addition, at a certain wavelength of light, the magnitude of light absorption (that is, light absorption) is calculated from the resonance magnitude Q obtained as described above, the absorption coefficient α of crystalline silicon, and the height h of the photoelectric conversion layer 52. Rate) S.

Here, when the wavelength of light is λ and the nonlinear function is represented by f and g, the resonance magnitude Q and the light absorption rate S can be expressed by the following equations.

Q (λ) = f (a, r, d, L _S , n _s (λ), n _t (λ), n _SiO2 (λ), n _Glass (λ))
S (λ) = g (Q (λ), α (λ), h)
[Solar cell manufacturing process]
Finally, the manufacturing process of the solar cell 5 according to the present embodiment will be described with reference to FIG. FIG. 17 is a process diagram showing a manufacturing process of the solar cell 5 according to the present embodiment. In the present embodiment, the medium of the first transparent conductive film 51 is SnO ₂ , the medium of the photoelectric conversion layer 52 is c-Si, the medium of the metal electrode 13 is Al, and the medium of the transparent insulator layer 14 is SiO _2. However, the present invention is not limited to this example.

First, as shown in FIG. 17A, a c-Si layer is formed, and a p-type sub-semiconductor layer 521a is formed by doping a p-type impurity. Next, c-Si is vapor-deposited on the p-type sub-semiconductor layer 521a, and an n-type impurity (for example, phosphorus) is doped (implanted) to form an n-type semiconductor layer 522, and a pn junction is formed. A semiconductor layer is formed. Note that the incident direction of light is on the n-type semiconductor layer 522 side.

Next, as shown in FIG. 17B, an ion beam containing hydrogen is implanted to form a damaged layer 120 in which the silicon crystal lattice is partially cut in the p-type sub-semiconductor layer 521a. . Note that the p-type sub-semiconductor layer 521a on the n-type semiconductor layer 122 side is the p-type sub-semiconductor layer 121b with the damaged layer 120 as a boundary, and the p-type sub-semiconductor layer 121a on the opposite side to the n-type semiconductor layer is the p-type sub-semiconductor. This is layer 121c.

Subsequently, as shown in FIG. 17C, holes for forming a photonic crystal are periodically formed in the n-type semiconductor layer 522 by dry etching (that is, the convex shape 57 is formed). An example of dry etching is inductively coupled reactive ion etching using carbon tetrafluoride (CF ₄ ) as an etching gas. Of course, the present invention is not limited to this, and as the etching gas, sulfur hexafluoride (SF ₆ ), trifluoromethane (CHF ₃ ), or the like may be employed.

Thereafter, as shown in FIG. 17D, the first transparent conductive film 51 is formed by vapor-depositing SnO ₂ on the n-type semiconductor layer 522 on which the convex shape 57 is formed by dry etching. In addition, SiO ₂ is vapor-deposited on the formed first transparent conductive film 51 to form the transparent insulator layer 14. When the surface of the formed transparent insulator layer 14 has an uneven shape, the surface is flattened by CMP as shown in FIG.

Further, as shown in FIG. 17 (f), the laminated body formed in the above (a) to (e) is inverted so that the transparent insulator layer 14 whose surface is flattened becomes the lower surface, so that the transparent insulator The layer 14 and the support substrate 15 are bonded. Since the laminate is inverted, the light incident surface is the surface of the laminate on the support substrate 15 side.

Next, after heating, as shown in FIG. 17G, the p-type sub-semiconductor layer 521c and the p-type sub-semiconductor layer 521b are cleaved with the damaged layer 120 as a boundary to form the uppermost layer of the substrate. The p-type sub semiconductor layer 521c is removed (wafer removal by heat treatment). At this time, since the damaged layer 120 is formed in the step shown in FIG. 17B, the p-type sub semiconductor layer 521 c can be removed along the damaged layer 120.

Further, as shown in FIG. 17H, the surface after removing the p-type sub semiconductor layer 521c from the wafer (the surface of the p-type sub semiconductor layer 521b) is modified and the uneven shape is planarized. Then, the p-type semiconductor layer 521 of the photoelectric conversion layer 52 is formed.

Finally, as shown in FIG. 17I, Al is vapor-deposited on the p-type semiconductor layer 521 to form an Al film, thereby forming the metal electrode 13. As described above, the solar cell 5 according to this embodiment is completed through the manufacturing steps (a) to (i) of FIG.

A plurality of convex portions 56 are formed in the first transparent conductive film 51 by depositing SnO _{2 in} holes periodically formed in the n-type semiconductor layer 522. A photonic crystal is formed by the plurality of convex portions 56 formed on the first transparent conductive film 51 and the convex shape 57 formed on the n-type semiconductor layer 522.

With the above-described configuration, the solar cell 5 can increase the light absorption rate particularly at a long wavelength, improve the efficiency of photoelectric conversion, and can realize a reduction in thickness (a thickness of about several hundred nm). . Furthermore, since the solar cell 5 includes the support substrate 15, it can be prevented that the shape of the solar cell 5 cannot be maintained by reducing the thickness of the photoelectric conversion layer 52.

Moreover, since the photoelectric conversion layer 52 can be protected by the support substrate 15, the transparent insulator layer 14, and the first transparent conductive film 51 by setting the surface of the support substrate 15 as the light incident surface, A solar cell having excellent resistance can be formed.

Moreover, according to the above-mentioned structure, since the support substrate 15, the transparent insulator layer 14, and the first transparent conductive film 51 are formed on one surface of the photoelectric conversion layer 52, the other side of the photoelectric conversion layer 52 is formed. It is not necessary to form any of the support substrate 15, the transparent insulator layer 14, and the first transparent conductive film 51 on the surface. Thereby, handling of the photoelectric conversion layer 52 can be facilitated.

Furthermore, since the metal electrode 13 can be formed on the surface of the photoelectric conversion layer 52 opposite to the surface on which the support substrate 15 or the like is provided, a degree of freedom can be given to the patterning of the metal electrode 13. As a result, the cell configuration can be configured more efficiently.

<Embodiment 6>
Still another embodiment of the present invention will be described below with reference to FIGS. For convenience of explanation, constituent elements having functions similar to those of the constituent elements according to the first or fifth embodiment are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, differences from the first or fifth embodiment will be mainly described.

[Configuration of solar cell]
First, the configuration of the solar cell according to the present embodiment will be described with reference to FIG. FIG. 18 is a cross-sectional view schematically showing the overall configuration of the solar cell 6 according to the present embodiment.

As shown in FIG. 18, the solar cell 6 according to the present embodiment includes a second transparent conductive film (second transparent conductive film) 68 between the photoelectric conversion layer 52 and the metal electrode 13, The configuration is the same as that of the solar cell 5 according to Embodiment 5.

The second transparent conductive film 68 is a transparent conductive film and is formed so as to be sandwiched between the photoelectric conversion layer 52 and the metal electrode 13. The second transparent conductive film 68 is made of a medium having a refractive index smaller than that of the photoelectric conversion layer 52, and examples of the medium include ITO, IZO, SnO ₂ , and ZnO.

In addition, since the structure of the photonic crystal which the solar cell 6 which concerns on this embodiment has is the same as the structure of the photonic crystal which the solar cell 1 which concerns on Embodiment 1 shown in FIG. 2 has, description is abbreviate | omitted here. .

[Light confinement effect in photonic crystals]
Next, the resonance effect in the photonic crystal will be described with reference to FIG. FIG. 19 is a diagram showing a light resonance effect by the photonic crystal included in the solar cell 6 according to the present embodiment.

The photonic crystal formed by the convex portion 56 of the first transparent conductive film 51 and the convex shape 57 of the photoelectric conversion layer 52 causes the incident light to resonate in the in-plane direction, as indicated by an arrow A in FIG. Can do. That is, the entire photonic crystal functions as one large resonator that resonates in the in-plane direction. Thereby, the photonic crystal can confine incident light in the entire photonic crystal.

Further, the interaction between the resonance effect of the photonic crystal functioning as a resonator as shown by the arrow A in FIG. 19 and the light reflection effect by the metal electrode 13 (that is, the incident light to the photoelectric conversion layer 52, and Due to the light confinement effect due to the interference effect with the reflected light from the metal electrode 13, the light incident on the photoelectric conversion layer 52 is interposed between the photonic crystal and the metal electrode 53 as shown by an arrow B in FIG. You will be trapped. Moreover, since incident light is diffracted or scattered when passing through the photonic crystal, the solar cell 5 can increase the path of light passing through the photoelectric conversion layer 52.

Thereby, the solar cell 6 can improve the light absorption rate in the photoelectric conversion layer 52, and can increase the amount of electromotive force in the solar cell 6. Further, the photoelectric conversion layer 62 can be thinned by improving the light absorption rate in the photoelectric conversion layer 52. Furthermore, since the solar cell 6 includes the support substrate 15, it can be prevented that the shape of the solar cell 6 cannot be maintained by reducing the thickness of the photoelectric conversion layer 52.

[Resonance magnitude and light absorption rate]
Furthermore, with reference to FIG. 19, the light absorption rate in the solar cell 6 according to the present embodiment will be described.

As shown in FIG. 19, the lattice constant (pitch) of the photonic crystal is a, the diameter of the convex portion 56 (that is, the hole formed in the photoelectric conversion layer 52) formed in the first transparent conductive film 51 is 2r, The height of the convex portion 56 (hole) is d, the height of the photoelectric conversion layer 52 is h, and the height from the photoelectric conversion layer 52 to the support substrate 15 is L _S2 . Further, the refractive index of crystalline silicon that is a medium of the photoelectric conversion layer 52 is n _s , the refractive index of the medium of the first transparent conductive film 51 is n _t , the refractive index of the medium of the transparent insulator layer 14 is n _SiO2 , and the support substrate. The refractive index of the medium 15 is n _Glass , and the absorption coefficient of the crystalline silicon with respect to a certain wavelength of light is α.

From the above parameters, resonance conditions for a plurality of light wavelengths are determined, and the resonance magnitude Q can be obtained for each wavelength. In addition, at a certain wavelength of light, the magnitude of light absorption (that is, light absorption) is calculated from the resonance magnitude Q obtained as described above, the absorption coefficient α of crystalline silicon, and the height h of the photoelectric conversion layer 52. Rate) S.

Here, when the wavelength of light is λ and the nonlinear function is represented by f and g, the resonance magnitude Q and the light absorption rate S can be expressed by the following equations.

Q (λ) = f (a, r, d, L _S2 , n _s (λ), n _t (λ), n _SiO2 (λ), n _Glass (λ))
S (λ) = g (Q (λ), α (λ), h)
[Solar cell manufacturing process]
Finally, the manufacturing process of the solar cell 6 according to the present embodiment will be described with reference to FIG. FIG. 20 is a process diagram showing a manufacturing process of the solar cell 6 according to the present embodiment. In this embodiment, the medium of the first transparent conductive film 51 and the second transparent conductive film 68 is SnO ₂ , the medium of the photoelectric conversion layer 52 is c-Si, the medium of the metal electrode 13 is Al, transparent The case where the medium of the insulator layer 14 is SiO ₂ will be described as an example, but the present invention is not limited to this.

In addition, the manufacturing process of the solar cell 6 according to this embodiment shown in FIG. 20 is the same as each manufacturing process of the solar cell 5 according to Embodiment 5 shown in FIG. 17 except that the process shown in (i) is different. Therefore, description of steps other than the step shown in (i) is omitted here.

As shown in FIG. 20I, SnO ₂ is deposited on the planarized p-type semiconductor layer 521 to form a second transparent conductive film 68. Then, Al is vapor-deposited on the formed second transparent conductive film 68, and the metal electrode 13 is formed by forming an Al film.

Thus, the solar cell 6 according to this embodiment is completed through the manufacturing steps (a) to (i) of FIG.

With the above-described configuration, the solar cell 6 can increase the light absorptance particularly at a long wavelength, improve the efficiency of photoelectric conversion, and can realize a reduction in thickness (thickness of about several hundred nm). . Furthermore, since the solar cell 6 includes the support substrate 15, it can be prevented that the shape of the solar cell 6 cannot be maintained by reducing the thickness of the photoelectric conversion layer 52.

Moreover, according to the above-mentioned structure, since each refractive index of the 1st transparent conductive film 51 and the 2nd transparent conductive film 68 is smaller than the refractive index of the photoelectric converting layer 52, a high refractive index core is made into a low refractive index. By the same principle as an optical fiber that propagates light by covering with a clad, it is possible to confine light that is about to leak through the photoelectric conversion layer 52 to the outside. Therefore, the effect of confining light in the photoelectric conversion layer 52 is further enhanced.

As a result, the light absorption rate by the photoelectric conversion layer 52 can be further improved, and the amount of electromotive force in the solar cell 6 can be further increased.

Moreover, since the photoelectric conversion layer 52 can be protected by the support substrate 15, the transparent insulator layer 14, and the first transparent conductive film 51 by setting the surface of the support substrate 15 as the light incident surface, A solar cell having excellent resistance can be formed.

Moreover, according to the above-mentioned structure, since the support substrate 15, the transparent insulator layer 14, the first transparent conductive film 51, and the second transparent conductive film 68 are formed on one surface of the photoelectric conversion layer 52, It is not necessary to form any of the support substrate 15, the transparent insulator layer 14, the first transparent conductive film 51, and the second transparent conductive film 68 on the other surface of the photoelectric conversion layer 52. Thereby, handling of the photoelectric conversion layer 52 can be facilitated.

Furthermore, since the metal electrode 13 can be formed on the surface of the photoelectric conversion layer 52 opposite to the surface on which the support substrate 15 or the like is provided, a degree of freedom can be given to the patterning of the metal electrode 13. As a result, the cell configuration can be configured more efficiently.

<Embodiment 7>
Still another embodiment of the present invention will be described below with reference to FIGS. For convenience of explanation, constituent elements having the same functions as those of the constituent elements according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, differences from the first embodiment will be mainly described.

[Configuration of solar cell]
First, the configuration of the solar cell according to the present embodiment will be described with reference to FIG. FIG. 21 is a cross-sectional view schematically showing the overall configuration of the solar cell 7 according to the present embodiment.

As shown in FIG. 21, the solar cell 7 according to this embodiment includes a support substrate 15, a photoelectric conversion layer 72, a metal electrode 73 a, a metal electrode 73 b, a first transparent insulator layer (first transparent body) 71, and a second. A transparent insulator layer (transparent insulating layer) 74, an n + layer (cathode electrode) 78, and a p + layer (positive electrode) 79 are provided. In addition, the light incident surface of the solar cell 7 according to the present embodiment is on the support substrate 15 side.

The photoelectric conversion layer 72 is a semiconductor layer that absorbs light and performs photoelectric conversion. The photoelectric conversion layer 72 has a plurality of holes as shown in FIG. 21 and convex shapes around the holes, thereby filling the holes. A photonic crystal is formed together with one transparent insulator layer 71. In this embodiment, the case where the photoelectric conversion layer 72 is an n-type semiconductor layer will be described as an example. However, the present invention is not limited to this, and for example, a configuration in which the photoelectric conversion layer 72 is a p-type semiconductor layer. It may be adopted.

In the present embodiment, the hole of the photoelectric conversion layer 72 is a basic element that is regularly formed to form a photonic crystal.

Note that examples of the medium of the photoelectric conversion layer 72 include crystalline silicon (c-Si), but are not limited thereto. For example, silicon (μc-Si), amorphous silicon (a-Si), and polysilicon (p-Si: high-purity polycrystalline silicon) may be employed as the medium of the photoelectric conversion layer 72.

The metal electrodes 73a and 73b are layers formed on the surface (second surface) opposite to the side on which light enters the solar cell 1. As a material of the metal electrodes 73a and 73b, a material having high light reflectivity and high electrical conductivity, for example, Ag, Mo, Al, or the like can be selected. In addition, since the metal electrodes 73a and 73b can be functioned also as a reflector, the solar cell 7 with high light absorption efficiency can be comprised by this.

The second transparent insulator layer 74 is a layer made of a transparent insulator having a smooth surface and a hydrophilic surface, and connects and insulates the photoelectric conversion layer 72 and the support substrate 15. The first transparent insulator layer 71 is a transparent insulator.

Each of the n + layer 78 and the p + layer 79 is an n-type semiconductor layer and a p-type semiconductor layer doped with impurities having a corresponding polarity at a high concentration, and is located at the boundary between the metal electrodes 73 a and 73 b and the photoelectric conversion layer 72. Is provided. The n + layer 78 and the p + layer 79 layer reduce the width of the depletion layer generated in the photoelectric conversion layer 72 and facilitate the flow of current by the tunnel effect.

In addition, the solar cell 7 functions as a battery by taking out the electric current photoelectrically converted in the photoelectric converting layer 72 from the metal electrode 73a and the metal electrode 73b.

(Arrangement of each component of solar cell)
As shown in FIG. 21, the solar cell 7 includes a metal electrode 73a and a metal electrode 73b as the lowermost layer (surface opposite to the incident surface), and an n + layer 78 is disposed on the metal electrode 73a. A p + layer 79 is laminated on 73b. On the metal electrodes 73a and 73b, the n + layer 78, and the p + layer 79, the photoelectric conversion layer 72 and the second transparent insulator layer 74 are laminated in this order.

Further, the photoelectric conversion layer 72 and the second transparent insulator layer 74 are formed with an uneven shape, and the first transparent insulator layer 71 is provided in the recessed portion of the uneven shape. Furthermore, the support substrate 15 is laminated on the second transparent insulator layer 74 and the first transparent insulator layer 71 as the uppermost layer (incident surface) of the solar cell 7.

[Structure of photonic crystal]
Next, the structure of the photonic crystal will be described with reference to FIG.

As shown in FIG. 21, in this embodiment, a plurality of concave portions (holes) (first concave portions) formed in a columnar shape are regularly formed on the light incident surface (first surface) of the photoelectric conversion layer 72. Is formed. In other words, the photoelectric conversion layer 72 has a convex shape (second convex portion) remaining around each of the regularly formed concave portions. Moreover, the 2nd transparent insulator layer 74 is formed so that only the convex-shaped part of the photoelectric converting layer 72 may be covered, and the photoelectric converting layer 72 and the support substrate 15 are joined.

Further, as shown in FIG. 21, the first transparent insulator layer 71 is formed so as to fill the concave portions formed in the photoelectric conversion layer 72 and the second transparent insulator layer 74. That is, the first transparent insulator layer 71 is formed as a plurality of cylinders so as to fill the concave portions formed in the photoelectric conversion layer 72 and the second transparent insulator layer 74.

The concavo-convex shape formed on the light incident surface of the photoelectric conversion layer 72 causes the photonic crystal to have a periodicity in the refractive index difference between the photoelectric conversion layer 72 and the first transparent insulator layer 71. It is composed.

In the present embodiment, the photoelectric conversion unit is configured to include the photoelectric conversion layer 72 and the first transparent insulator layer 71.

In addition, since the cross section of the structure of the photonic crystal which the solar cell 7 which concerns on this embodiment has is the same as the structure of the photonic crystal which the solar cell 1 which concerns on Embodiment 1 shown in FIG. Omitted.

(Light confinement effect in photonic crystals)
Next, the resonance effect in the photonic crystal will be described with reference to FIG. FIG. 22 is a diagram illustrating a light resonance effect by the photonic crystal included in the solar cell 7 according to the present embodiment.

The photonic crystal can resonate incident light in the in-plane direction as indicated by an arrow A in FIG. That is, the entire photonic crystal functions as one large resonator that resonates in the in-plane direction. Thereby, the photonic crystal can confine incident light in the entire photonic crystal.

Further, the interaction between the resonance effect of the photonic crystal functioning as a resonator and the light reflection effect of the metal electrodes 73a and 73b (that is, the incident light on the photoelectric conversion layer 72 as shown by an arrow A in FIG. 22). And the light confinement effect by the interference effect with the reflected light from the metal electrodes 73a and 73b), the light incident on the photoelectric conversion layer 72 is converted into the photonic crystal and the metal electrode 73a as shown by an arrow B in FIG. And 73b. Moreover, since incident light is diffracted or scattered when passing through the photonic crystal, the solar cell 7 can increase the path of light passing through the photoelectric conversion layer 52.

Thereby, the solar cell 7 can improve the light absorption rate in the photoelectric conversion layer 72 and can increase the amount of electromotive force in the solar cell 7. In addition, the photoelectric conversion layer 72 can be thinned by improving the light absorption rate in the photoelectric conversion layer 72. Furthermore, since the solar cell 7 includes the support substrate 15, it can be prevented that the shape of the solar cell 7 cannot be maintained by reducing the thickness of the photoelectric conversion layer 72.

[Resonance magnitude and light absorption rate]
Furthermore, with reference to FIG. 22, the light absorption rate in the solar cell 7 according to the present embodiment will be described.

As shown in FIG. 22, the lattice constant (pitch) of the photonic crystal is a, and the diameter of the first transparent insulator layer 71 (that is, the hole formed in the photoelectric conversion layer 72 and the second transparent insulator layer 74). 2r, the height of the hole formed in the photoelectric conversion layer 72 is d, the height of the photoelectric conversion layer 72 is h, and the height from the photoelectric conversion layer 72 to the support substrate 15 is L _S3 . Further, the refractive index of crystalline silicon that is a medium of the photoelectric conversion layer 72 is n _s , the refractive index of the medium of the first transparent insulator layer 71 is n _SiO2 , the refractive index of the medium of the support substrate 15 is n _Glass , and the crystalline silicon Let α be the absorption coefficient for a certain wavelength of light.

From the above parameters, resonance conditions for a plurality of light wavelengths are determined, and the resonance magnitude Q can be obtained for each wavelength. Further, at a certain light wavelength, the magnitude of light absorption (that is, light absorption) is calculated from the resonance magnitude Q obtained as described above, the absorption coefficient α of crystalline silicon, and the height h of the photoelectric conversion layer 72. Rate) S.

Here, when the wavelength of light is λ and the nonlinear function is represented by f and g, the resonance magnitude Q and the light absorption rate S can be expressed by the following equations.

Q (λ) = f (a, r, d, L _S3 , n _s (λ), n _SiO2 (λ), n _Glass (λ))
S (λ) = g (Q (λ), α (λ), h)
[Solar cell manufacturing process]
Finally, the manufacturing process of the solar cell 7 according to this embodiment will be described with reference to FIG. FIG. 23 is a process diagram showing a manufacturing process of the solar cell 7 according to the present embodiment. In this embodiment, the medium of the second transparent insulator layer 74 and the first transparent insulator layer 71 is SiO ₂ , the medium of the photoelectric conversion layer 72 is c-Si, and the medium of the metal electrode 13 is Al. However, the present invention is not limited to this example.

First, as shown in FIG. 23A, a c-Si layer is formed, and an n-type impurity (for example, phosphorus or the like) is doped (implanted) to thereby form a sub photoelectric conversion layer 72a that is an n-type semiconductor layer. Form. Further, SiO ₂ is vapor-deposited on the sub photoelectric conversion layer 72a to form the second transparent insulator layer 74. If the surface of the formed second transparent insulator layer 74 has a concavo-convex shape, the surface is flattened by CMP as shown in FIG. In addition, the incident direction of light is the 2nd transparent insulator layer 74 side.

Next, as shown in FIG. 23C, an ion beam containing hydrogen is implanted to form a damaged layer 120 in which the silicon crystal lattice is partially cut in the sub photoelectric conversion layer 72a. With the damaged layer 120 as a boundary, the sub photoelectric conversion layer 72a on the second transparent insulator layer 74 side is defined as a sub photoelectric conversion layer 72b, and the sub photoelectric conversion layer 72a on the opposite side to the second transparent insulator layer 74 is defined as a sub photoelectric conversion layer. The conversion layer 72c is used.

Subsequently, as shown in FIG. 23 (d), the hole (concave shape) for forming the photonic crystal is flattened by dry etching, the second transparent insulator layer 74, and the sub photoelectric conversion. Periodically formed on the layer 72b.

Thereafter, as shown in FIG. 23E, SiO ₂ is vapor-deposited in the holes formed by the step (d) to form the first transparent insulator layer 71. Further, the substrate on which the first transparent insulator layer 71 is formed is inverted, and the second transparent insulator layer 74 and the support substrate 15 are joined. Since the substrate is inverted, the light incident surface is the surface of the substrate on the support substrate 15 side.

Further, after the heating, as shown in FIG. 23F, the sub photoelectric conversion layer 72c and the sub photoelectric conversion layer 72b are cleaved with the damaged layer 120 as a boundary, so that the sub photoelectric conversion which is the uppermost layer of the substrate is performed. The layer 72c is removed (wafer removal by heat treatment). At this time, since the damaged layer 120 is formed in the step shown in FIG. 23C, the sub photoelectric conversion layer 72 c can be removed along the damaged layer 120. Further, as shown in FIG. 23G, the surface after removing the sub-photoelectric conversion layer 72c from the wafer (the surface of the sub-photoelectric conversion layer 72b) is modified, and the uneven shape is flattened so that A conversion layer 72 is formed.

Next, as shown in FIG. 23 (h), n + is doped by doping impurities having a corresponding polarity at a high concentration in accordance with the positions where the metal electrode 73a and the metal electrode 73b of the photoelectric conversion layer 72 are formed. A layer 78 and a p + layer 79 are formed (back contact film formation). In addition, Al is vapor-deposited so as to cover the n + layer 78 and the p + layer 79 formed in the photoelectric conversion layer 72, and an Al film is formed to form the metal electrode 73a and the metal electrode 73b.

As described above, the solar cell 7 according to this embodiment is completed through the manufacturing steps (a) to (h) in FIG.

In the present embodiment, the case where the first transparent insulator layer 71 is solid has been described as an example, but the present invention is not limited to this. For example, a configuration in which the first transparent insulator layer 71 is air may be employed.

In this case, in the step shown in FIG. 23 (e), the substrate formed by the step (d) may be reversed as it is, and the second transparent insulator layer 74 and the support substrate 15 may be joined. By forming in this way, the first transparent insulator layer 71 using air as a medium is formed in the hole formed by the step (d).

With the above-described configuration, the solar cell 7 can increase the light absorptance particularly at a long wavelength, improve the efficiency of photoelectric conversion, and can realize a reduction in thickness (thickness of about several hundred nm). . Furthermore, since the solar cell 7 includes the support substrate 15, it can be prevented that the shape of the solar cell 7 cannot be maintained by reducing the thickness of the photoelectric conversion layer 72.

<Modification>
A modification of this embodiment will be described with reference to FIG. For convenience of explanation, components having functions similar to those of the components according to the present embodiment are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, differences from the seventh embodiment will be mainly described.

[Configuration of solar cell]
First, the structure of the solar cell according to this modification will be described with reference to FIG. FIG. 24 is a cross-sectional view schematically showing the overall configuration of a solar cell 7 ′ according to this modification.

As shown in FIG. 24, the solar cell 7 ′ according to the present modification includes a support substrate 15, a photoelectric conversion layer 72, metal electrodes 73a and 73b, a first transparent insulator layer (first transparent body) 71 ′, and a second one. A transparent insulator layer (transparent insulating layer) 74 ′, an n + layer 78, and a p + layer 79 are provided.

The second transparent insulator layer 74 ′ is a layer made of an insulator having a smooth surface and a hydrophilic surface, and connects and insulates the metal electrodes 73a and 73b and the photoelectric conversion layer 72 and the support substrate 15. is doing. The first transparent insulator layer 71 ′ is a transparent insulator and is provided as an incident surface on which sunlight is incident.

(Arrangement of each component of solar cell)
As shown in FIG. 24, the solar cell 7 ′ includes a support substrate 15 as a lowermost layer (outermost surface opposite to the incident surface), and a second transparent insulator layer 74 ′ is stacked thereon. Further, a metal electrode 73a and a metal electrode 73b are formed on the second transparent insulator layer 74 ′, respectively, an n + layer 78 is formed on the metal electrode 73a, and a metal electrode 73b is formed on the metal electrode 73b. A p + layer 79 is laminated.

A photoelectric conversion layer 72 is laminated on the metal electrodes 73a and 73b, the n + layer 78, and the p + layer 79. In addition, an uneven shape is formed on the incident surface of the photoelectric conversion layer 72, and the first transparent insulator layer 71 ′ is the uppermost layer of the solar cell 7 ′ (the outermost surface on the incident surface side) so as to cover the uneven shape. The outer layer is laminated. That is, the n + layer 78 and the p + layer 79 are formed on the surface (second surface) opposite to the light incident surface of the photoelectric conversion layer 72.

As described above, in the solar cell 7 ′ according to the present embodiment, an uneven structure is formed in the photoelectric conversion layer 72 itself, and the first transparent insulator layer 71 ′ is formed so as to cover the uneven structure. As a result, at the interface between the photoelectric conversion layer 72 and the first transparent insulator layer 71 ′ as the adjacent layer, only two types of materials having different refractive indexes are adjacent to each other to form a photonic crystal.

According to the above-described configuration, since the n + layer 78 and the p + layer 79 are formed on the second surface, electric power can be taken out from the second surface side. Therefore, it is possible to obtain the effect of improving the light absorption rate by the above-described photonic crystal with a simple configuration.

[Summary]
As described above, the solar cell according to one embodiment of the present invention (solar cells 1 to 6)
(1) a photoelectric conversion unit (first transparent conductive films 11, 21, 51, photoelectric conversion layers 12, 22, 52, 62);
(2) a support substrate (support substrate 15) that supports the photoelectric conversion unit;
(3) The photoelectric conversion unit
(3-1) A photoelectric conversion layer (photoelectric conversion layers 12, 22, 52, 62) that absorbs light and performs photoelectric conversion, and has a first recess on a first surface (light incident surface) on the light incident side. (A plurality of concave portions (holes) formed in a columnar shape) or first conversion portions (convex portions 27) regularly formed photoelectric conversion layers;
(3-2) A first transparent body (first transparent conductive film 11, 21, 51) that at least fills the first concave portion of the first surface, or a second formed by providing the first convex portion. A first transparent body that at least fills the concave portion (concave shape),
(4) The concavo-convex shape formed on the first surface constitutes a photonic crystal by providing periodicity to the refractive index difference between the photoelectric conversion layer and the first transparent body. It is characterized by that.

According to the above-described configuration, there are two forms in which the uneven shape of the first surface forms the photonic crystal.

In the first embodiment, the first transparent body is arranged at each lattice point of a square lattice, for example, by filling the first concave portions regularly formed on the first surface of the photoelectric conversion layer. It is a form. As a result, the refractive index periodically changes so as to form a photonic crystal in the uneven shape of the first surface.

In the second embodiment, as a result of regularly forming the first convex portion on the first surface of the photoelectric conversion layer by the material for forming the photoelectric conversion layer, the second concave portion is formed, and the second concave portion is formed into the first transparent portion. When the body fills, the first convex portion of the photoelectric conversion layer is arranged at each lattice point of a square lattice, for example. As a result, as in the first embodiment, the refractive index periodically changes so as to form a photonic crystal in the uneven shape of the first surface.

In any of the above two forms, the solar cell can resonate the captured light in the in-plane direction of the photonic crystal, so that a high effect of confining the light can be obtained. Further, since incident light is diffracted or scattered when passing through the photonic crystal, the solar cell can increase the path of light passing through the photoelectric conversion layer.

Thereby, the solar cell can improve the light absorption rate in the photoelectric conversion layer, and can increase the amount of electromotive force in the solar cell. Further, the photoelectric conversion layer can be thinned by improving the light absorption rate in the photoelectric conversion layer. Furthermore, since the said solar cell is equipped with the said support substrate, it can prevent that it becomes impossible to maintain the shape of the said solar cell by thinning the said photoelectric converting layer.

The first transparent body can form a photonic crystal even if it is a transparent gas such as air. In order to keep the reflectance on the first surface low and increase the amount of incident light as much as possible. Is preferably a solid transparent body. This is because the refractive index difference between the solid transparent body and the photoelectric conversion layer is smaller than, for example, the refractive index difference between air and the photoelectric conversion layer, so that the reflectance at the first surface can be kept small. Because.

Also, in order for the solar cell to function as a battery, it is necessary to take out electrons from the solar cell. In order to extract electrons, it is preferable to form a transparent solid having conductivity on at least one of the light incident surface and the surface opposite to the light incident surface of the photoelectric conversion layer.

In the configuration of Patent Document 1, since a local auxiliary electrode is directly attached to the photoelectric conversion layer without forming a transparent conductive layer on the photoelectric conversion layer, there is a problem that electron collection efficiency is low. I will add that.

In addition, when the said 1st transparent body is a solid electroconductive transparent body, since it can take out an electron from the said 1st transparent body, it differs from the said 1st transparent body used for taking out an electron. It is not necessary to form a layer separately, and the configuration of the solar cell can be simplified.

In the solar cell according to one embodiment of the present invention,
(1) The first concave portions or the first convex portions are arranged on the first surface in a square lattice pattern with a pitch of 150 nm or more and 540 nm or less,
(2) The shape of the first concave portion or the first convex portion is a cylindrical shape having a diameter of 60 nm or more and 540 nm or less,
(3) It is preferable that the depth of the first concave portion or the height of the first convex portion is 100 nm or more and not more than the thickness of the photoelectric conversion layer.

According to the above configuration, the light absorption rate is increased to 1.2 times or more, which is a significant effect, as compared with a solar cell not provided with a photonic crystal.

Thereby, the light absorption rate is higher than that of the conventional solar cell, and the photoelectric conversion layer can be made thin (about several hundred nm) which cannot be achieved by the conventional solar cell.

In addition, the first transparent body of the solar cell according to one aspect of the present invention is a first transparent conductive film (first transparent conductive film 11, 21, 51) that covers the uneven shape of the first surface. The first transparent conductive film is preferably the outermost layer on the light incident side in the solar cell.

According to the above configuration, the first transparent conductive film can serve both as a protective film for the photoelectric conversion layer and as one of two electrodes necessary for the solar cell. Further, since the first transparent conductive film is the outermost layer, it is only necessary to pass through the first transparent conductive film until the light reaches the first surface. Thereby, the loss of light can be reduced, which is advantageous for increasing the amount of incident light on the photoelectric conversion layer.

Furthermore, since the first transparent conductive film is solid, the reflectance on the first surface is kept low as described above, which is further advantageous for increasing the amount of incident light.

In the solar cell according to one embodiment of the present invention, it is preferable that a metal electrode layer (metal electrodes 13 and 53) is provided between the photoelectric conversion layer and the support substrate.

According to the above configuration, the effect of confining the light between the photonic crystal and the metal electrode can be increased by the interference effect between the light that has passed through the photonic crystal and the light reflected by the metal electrode. it can. As a result, the light absorption rate by the photoelectric conversion layer can be further improved, and the amount of electromotive force in the solar cell can be further increased.

In the solar cell according to one embodiment of the present invention,
(1) The first transparent body is a first transparent conductive film that covers the uneven shape of the first surface,
(2) The first transparent conductive film is bonded to the support substrate via a transparent insulating layer (transparent insulating layer 14),
(3) It is preferable that the metal electrode layer is provided in the 2nd surface (back surface of the photoelectric converting layer 12) on the opposite side to the said 1st surface of the said photoelectric converting layer.

According to the above configuration, the solar cell can be configured such that light enters the photoelectric conversion layer from the support substrate through the transparent insulating layer and the first transparent conductive film. By using the support substrate as the light incident surface, the photoelectric conversion layer using, for example, silicon as a medium can be protected by the support substrate, the transparent insulating layer, and the first transparent conductive film. An excellent solar cell can be formed.

Moreover, according to said structure, since a support substrate, a transparent insulating layer, and a 1st transparent conductive film are formed into the surface of the one side of a photoelectric converting layer, a supporting substrate is formed in the surface of the other side of a photoelectric converting layer, Neither the transparent insulating layer nor the first transparent conductive film needs to be formed. Thereby, handling of the photoelectric conversion layer can be facilitated.

Furthermore, since the metal electrode layer can be formed on the surface of the photoelectric conversion layer opposite to the surface on which the support substrate or the like is provided, a degree of freedom can be given to patterning of the metal electrode layer. Thereby, the freedom degree of the structure of the solar cell module which has arranged and wired multiple photovoltaic cells can be raised. This is because the degree of freedom can be given to the arrangement of the cells in the solar battery module by giving the degree of freedom to the patterning of the metal electrode layer of the solar battery cell.

The solar cell module may be further attached with a protective substrate or the like. Hereinafter, the solar battery cell is also referred to as one unit of the solar battery panel, and the solar battery module is also referred to as the solar battery panel.

In the solar cell according to one embodiment of the present invention,
(1) A second transparent conductive film (second transparent conductive films 38 and 68) provided so as to sandwich the photoelectric conversion layer with the first transparent conductive film is provided,
(2) It is preferable that each refractive index of the said 1st transparent conductive film and the 2nd transparent conductive film is smaller than the refractive index of the said photoelectric converting layer.

According to said structure, since each refractive index of a 1st transparent conductive film and a 2nd transparent conductive film is smaller than the refractive index of a photoelectric converting layer, a high refractive index core is coat | covered with a low refractive index clad. By using the same principle as that of an optical fiber for propagating light, it is possible to confine light that leaks out of the photoelectric conversion layer. Therefore, the effect of confining light in the photoelectric conversion layer is further enhanced.

As a result, the light absorption rate by the photoelectric conversion layer can be further improved, and the amount of electromotive force in the solar cell can be further increased.

As described above, the solar cell (solar cell 7) according to one embodiment of the present invention is as follows.
(1) a photoelectric conversion unit (first transparent insulator layer 71, photoelectric conversion layer 72);
(2) a support substrate (support substrate 15) that supports the photoelectric conversion unit;
(3) The photoelectric conversion unit
(3-1) A photoelectric conversion layer (photoelectric conversion layer 72) that absorbs light and performs photoelectric conversion, and is formed in a first recess (cylindrical shape) on the first surface (light incident surface) on the light incident side. A plurality of recesses (holes) regularly formed, and a photoelectric conversion layer,
(3-2) including a first transparent body (first transparent insulator layer 71) that at least fills the first recess.
(4) The concavo-convex shape formed on the first surface constitutes a photonic crystal by providing periodicity to the refractive index difference between the photoelectric conversion layer and the first transparent body. And
(5) By providing a plurality of the first concave portions on the first surface, the second convex portions (convex shape) remaining around the first concave portions are joined to the support substrate,
(6) A positive electrode (p + layer 79) and a negative electrode (n + layer 78) are formed on the second surface opposite to the first surface of the photoelectric conversion layer.

According to the above configuration, the first surface forming the concavo-convex shape and constituting the photonic crystal is joined to the support substrate by the second convex portion. Therefore, the light incident on the support substrate reaches the photonic crystal only by passing through the support substrate. For this reason, the loss of light can be reduced, which is advantageous for increasing the amount of incident light on the photoelectric conversion layer.

Moreover, electric power can be taken out from the second surface side without providing the first transparent conductive film between the second surface of the photoelectric conversion layer on which the positive electrode and the negative electrode are formed and the support substrate. Therefore, it is possible to obtain the effect of improving the light absorption rate by the above-described photonic crystal with a simple configuration.

As described above, the solar cell (solar cell 7 ′) according to one embodiment of the present invention is as follows.
(1) a photoelectric conversion unit (first transparent insulator layer 71 ′, photoelectric conversion layer 72);
(2) a support substrate (support substrate 15) that supports the photoelectric conversion unit;
(3) The photoelectric conversion unit
(3-1) A photoelectric conversion layer (photoelectric conversion layer 72) that absorbs light and performs photoelectric conversion, and is formed in a first recess (cylindrical shape) on the first surface (light incident surface) on the light incident side. A plurality of recesses (holes) regularly formed, and a photoelectric conversion layer,
(3-2) a first transparent body (first transparent insulator layer 71 ′) that at least fills the first concave portion,
(4) The concavo-convex shape formed on the first surface constitutes a photonic crystal by providing periodicity to the refractive index difference between the photoelectric conversion layer and the first transparent body. And
(5) A positive electrode (p + layer 79) and a negative electrode (n + layer 78) are formed on the second surface of the photoelectric conversion layer opposite to the first surface,
(6) The second surface on which the positive electrode and the negative electrode are formed is bonded to the support substrate via a transparent insulating layer (second transparent insulating layer 74 ′). .

According to the above configuration, since the positive electrode and the negative electrode are formed on the second surface, electric power can be taken out from the second surface side. Therefore, it is possible to obtain the effect of improving the light absorption rate by the above-described photonic crystal with a simple configuration.

Moreover, in the solar cell (solar cell 7, 7 ') which concerns on 1 aspect of this invention,
(1) The first recesses are arranged in a square lattice pattern on the first surface with a pitch of 150 nm or more and 540 nm or less,
(2) The shape of the first recess is a cylindrical shape having a diameter of 60 nm or more and 540 nm or less,
(3) The depth of the first recess is preferably 100 nm or more and not more than the thickness of the photoelectric conversion layer.

According to the above configuration, the light absorption rate is increased to 1.2 times or more, which is a significant effect, as compared with a solar cell not provided with a photonic crystal.

Thereby, the light absorption rate is higher than that of the conventional solar cell, and the photoelectric conversion layer can be made thin (about several hundred nm) which cannot be achieved by the conventional solar cell.

A solar cell panel in which one of the above solar cells is used as a unit and a plurality of the units are arranged one-dimensionally or two-dimensionally, a device including any one of the solar cells as a power source, and the solar cell panel A device provided as a power source is also included in the scope of the present invention.

(Additional notes)
Note that a solar cell panel in which the above-described solar cell is regarded as one unit and a plurality of units are arranged one-dimensionally or two-dimensionally is also one category of the present invention. Thereby, since the solar cell with a high light absorption rate is arranged, a solar cell panel with a high photoelectric conversion rate can be obtained.

In addition, an apparatus provided with any of the above-described solar cells as a power source is also one category of the present invention. Such devices include portable or stationary electronic devices, home appliances, advertising towers, and the like that operate using the solar cell as a power source.

Furthermore, an apparatus provided with a solar cell panel as a power source is also one category of the present invention. Such devices include vehicles or advertising towers in addition to portable or stationary electronic devices or home appliances that operate using the solar cell panel as a power source.

The present invention can be used for solar cells in general.

1, 2, 3, 4, 5, 6, 7, 7 'solar cell 11, 21, 51 1st transparent conductive film (1st transparent body, photoelectric conversion unit)
12, 22, 52, 62, 72 Photoelectric conversion layer (photoelectric conversion unit)
13, 53 Metal electrode (metal electrode layer)
14 Transparent insulator layer (transparent insulation layer)
15 Support substrate 16, 26, 56 Convex part 17, 57 Convex part 27 Convex part (first convex part)
38, 68 Second transparent conductive film 72a, 72b, 72c Sub photoelectric conversion layer 73a, 73b Metal electrode 71, 71 ′ First transparent insulator layer (first transparent body, photoelectric conversion unit)
74, 74 ′ Second transparent insulator layer (transparent insulation layer)
78 n + layer (cathode)
79 p + layer (positive electrode)
120 Damaged layers 121, 221 p-type semiconductor layers 121a, 121b, 121c p-type sub-semiconductor layers 122, 222, 522 n-type semiconductor layers 521a, 521b, 521c p-type sub-semiconductor layers

Claims (17)

A photoelectric conversion unit;
A support substrate for supporting the photoelectric conversion unit,
The photoelectric conversion unit is
A photoelectric conversion layer that absorbs light and performs photoelectric conversion, wherein the first concave portion or the first convex portion is regularly formed on the first surface on the light incident side; and
A first transparent body that at least fills the first concave portion of the first surface, or a first transparent body that at least fills the second concave portion formed by providing the first convex portion,
The concavo-convex shape formed on the first surface constitutes a photonic crystal by providing periodicity to the refractive index difference between the photoelectric conversion layer and the first transparent body.
A solar cell characterized by that. The first concave portions or the first convex portions are arranged in a square lattice pattern on the first surface at a pitch of 150 nm or more and 540 nm or less,
The shape of the first concave portion or the first convex portion is a cylindrical shape having a diameter of 60 nm or more and 540 nm or less,
The depth of the first recess or the height of the first protrusion is not less than 100 nm and not more than the thickness of the photoelectric conversion layer.
The solar cell according to claim 1. While one of the concave portion or the convex portion constituting the concavo-convex shape forms a basic element of the photonic crystal,
In the photonic crystal, the basic element having a first diameter has a first substructure arranged with a first lattice constant, and the basic element having a second diameter different from the first diameter. Includes at least two types of second substructures arranged to replace a part of the lattice points of the first substructure with a second lattice constant different from the first lattice constant. Including substructures,
2. The solar cell according to claim 1, wherein the first diameter and the second diameter are cross-sectional diameters of the basic element in an in-plane direction of the first transparent body. One of the concave portion or the convex portion constituting the concavo-convex shape constitutes a basic element of the photonic crystal, and the basic element is a column whose central axis direction is substantially perpendicular to the surface of the first transparent body. The shape of the cross section perpendicular to the central axis is a circle, ellipse or polygon, and the polygon is a shape in which a straight side is replaced with a curved side, or the polygon The solar cell according to claim 1, wherein the solar cell includes an arcuate rounded shape. One of the concave portion or the convex portion constituting the concavo-convex shape constitutes a basic element for forming the photonic crystal,
The photonic crystal includes a unit cell in which four concave portions or four convex portions are arranged in a square lattice shape, and is configured by arranging the unit lattices two-dimensionally and periodically,
The cross-sectional shape of the four concave portions or the four convex portions can be obtained by translating any of the four cross-sectional shapes to the position of the other cross-sectional shape along the in-plane direction including the cross-section. 2. The solar cell according to claim 1, wherein a condition that the shapes do not coincide with each other is satisfied. 6. The solar cell according to claim 5, wherein the shape of the cross section of the four concave portions or the four convex portions is similar to each other in size. The shape of the cross section of the four concave portions or the four convex portions is a triangle,
The orientation or shape of each triangle is set so as to satisfy the above condition that even if one of the four cross-sectional shapes is translated to the position of the shape of the other cross-section, the shapes do not match each other.
The triangle includes a shape obtained by replacing a straight side of the triangle with a curved side, or a shape obtained by rounding an arc at the apex of the triangle. The solar cell described. The first transparent body is a first transparent conductive film that covers the uneven shape of the first surface, and the first transparent conductive film is an outermost layer on the light incident side of the solar cell.
The solar cell according to claim 1 or 2, wherein A metal electrode layer is provided between the photoelectric conversion layer and the support substrate.
The solar cell according to any one of claims 1 to 3, wherein: The first transparent body is a first transparent conductive film that covers the uneven shape of the first surface, and the first transparent conductive film is bonded to the support substrate via a transparent insulating layer,
A metal electrode layer is provided on the second surface opposite to the first surface of the photoelectric conversion layer,
The solar cell according to claim 1 or 2, wherein A second transparent conductive film provided to sandwich the photoelectric conversion layer together with the first transparent conductive film;
Each refractive index of the first transparent conductive film and the second transparent conductive film is smaller than the refractive index of the photoelectric conversion layer,
The solar cell according to claim 8 or 10, wherein: A photoelectric conversion unit;
A support substrate for supporting the photoelectric conversion unit,
The photoelectric conversion unit is
A photoelectric conversion layer that absorbs light and performs photoelectric conversion, wherein the first concave portion is regularly formed on the first surface on the light incident side; and
A first transparent body that at least fills the first recess,
The concavo-convex shape formed on the first surface constitutes a photonic crystal by providing periodicity to the refractive index difference between the photoelectric conversion layer and the first transparent body,
By providing a plurality of the first concave portions on the first surface, the second convex portions remaining around the first concave portions are bonded to the support substrate,
A positive electrode and a negative electrode are formed on the second surface opposite to the first surface of the photoelectric conversion layer,
A solar cell characterized by that. A photoelectric conversion unit;
A support substrate for supporting the photoelectric conversion unit,
The photoelectric conversion unit is
A photoelectric conversion layer that absorbs light and performs photoelectric conversion, wherein the first concave portion is regularly formed on the first surface on the light incident side; and
A first transparent body that at least fills the first recess,
The concavo-convex shape formed on the first surface constitutes a photonic crystal by providing periodicity to the refractive index difference between the photoelectric conversion layer and the first transparent body,
A positive electrode and a negative electrode are formed on the second surface opposite to the first surface of the photoelectric conversion layer,
The second surface on which the positive electrode and the negative electrode are formed is bonded to the support substrate via a transparent insulating layer;
A solar cell characterized by that. The first recesses are arranged on the first surface in a square lattice pattern with a pitch of 150 nm or more and 540 nm or less,
The first recess has a cylindrical shape having a diameter of 60 nm or more and 540 nm or less,
The depth of the first recess is not less than 100 nm and not more than the thickness of the photoelectric conversion layer.
The solar cell according to claim 12 or 13, characterized by the above. A solar cell panel, wherein the solar cell according to any one of claims 1 to 14 is defined as one unit, and a plurality of the units are arranged one-dimensionally or two-dimensionally. An apparatus comprising the solar cell according to any one of claims 1 to 14 as a power source. An apparatus comprising the solar cell panel according to claim 15 as a power source.

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