JP3078933B2 - Photovoltaic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device,
In particular, the present invention relates to a photovoltaic device for effectively utilizing incident light and improving stable output characteristics.

[0002]

2. Description of the Related Art In a photovoltaic device having a semiconductor layer generating photovoltaic power and an electrode, as a technique for improving photoelectric conversion efficiency, light incident on the photovoltaic device is scattered to form a semiconductor layer. There is known a method of increasing the short-circuit current by substantially increasing the length of the optical path inside and thereby increasing the amount of light absorbed by the semiconductor layer.

In this case, the structure of the photovoltaic device for scattering the light incident on the photovoltaic device includes a transparent substrate such as a glass substrate on which a transparent electrode having a concavo-convex structure is formed. There are known those provided with a light reflection layer having an uneven structure, and those formed with an uneven structure on the surface thereof using a semiconductor substrate.

[0004] Of these configurations, those using a glass substrate and a semiconductor substrate as substrates are those that scatter light on the surface on the light incident side, and those that form irregularities on the light reflecting layer are those that have irregularities on the light reflecting layer. It is structured to scatter light on the back.

[0005] Among them, in the case of a structure in which light is scattered on the surface on the light incident side and a glass substrate is used, light is incident on the semiconductor layer from the substrate side, so that the uneven structure is formed before the semiconductor layer is formed. The transparent electrode is formed, and the concavo-convex structure is formed at a relatively high temperature of about 300 ° C. or higher.

[0006]

However, in a photovoltaic device of the type in which light enters the semiconductor layer from the side opposite to the substrate, the light is scattered after the thin film semiconductor layer is formed on the substrate. Since a structure is formed, the substrate temperature cannot be raised to a temperature higher than the formation temperature of the semiconductor layer, and it is difficult to form a transparent electrode having a concavo-convex structure as in the case of a glass substrate.

On the other hand, in the case of a structure in which the transparent electrode also functions as an anti-reflection layer, the reflectance is reduced over a wide wavelength range, so that the optical thickness (nd) of the transparent electrode is λ /.
In many cases, the thickness is reduced to about 4 (λ is a wavelength at which the reflectance is minimized). In the case of such a configuration, the transparent electrode is too thin and is not suitable for forming an uneven structure for scattering light.

In the case of a structure in which a semiconductor substrate is used to form an uneven structure for scattering light on the semiconductor surface, the semiconductor itself is treated, so that delicate handling is required and the number of manufacturing steps increases. This causes a significant increase in manufacturing costs.

As described above, in a photovoltaic device other than the type in which light is incident on the semiconductor layer from the substrate side using the glass substrate, it is difficult to scatter light on the surface on the light incident side. Or problems in terms of manufacturing costs.

However, in order to use a low-cost photovoltaic device that can be used for various purposes including general power supply, a low-cost substrate such as a stainless substrate or a synthetic resin film other than a glass substrate must be used. It is desired to improve the photoelectric conversion efficiency of a photovoltaic device using a photovoltaic device. As a result, even a photovoltaic device using a low-cost substrate other than a glass substrate emits light on the surface on the light incident side. A structure having a scattering structure has been desired.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and a photovoltaic device of a type in which light enters a semiconductor layer from a side opposite to a substrate, or an optical device using a semiconductor substrate. It is an object of the present invention to provide a photovoltaic device which is applied to a photovoltaic device, has a structure for scattering light on a light incident side surface, and can stably improve photoelectric conversion efficiency.

[0012]

According to a first aspect of the present invention, there is provided a photovoltaic device in which a surface protective layer is laminated on a light incident side of a semiconductor layer. It may have a material that is different from the refractive index of the surface protective layer
And at least one light-scattering layer having a concavo-convex structure is formed.

According to a second aspect of the present invention, in the first aspect, the light scattering layer has an uneven structure on the surface side with respect to the light incident direction.

According to a third aspect of the present invention, in the first aspect of the present invention, the light scattering layer has an uneven structure on a back surface side with respect to a light incident direction.

According to a fourth aspect of the present invention, in the first aspect of the invention, the light scattering layer has an uneven structure on both sides of the front surface and the back surface in the light incident direction.

According to a fifth aspect of the present invention, there is provided the first to fourth aspects.
In the inventions described above, the uneven structure has a surface roughness Rma.
The value of x is between 0.05 μm and 100 μm.

The invention according to claim 6 is the invention according to claims 1 to 5.
In the invention of up, the difference between the refractive index of the material forming the light scattering layer and the refractive index of the material <br/> substance forming the surface protective layer is equal to or less than 0.1.

[0018] The invention of claim 7 is the first to sixth aspects of the present invention.
In the inventions described above, a light reflection layer for light scattering is formed on the side opposite to the light incident direction with respect to the semiconductor layer.

[0019]

According to the present invention, the surface protective layer on the light incident side has a refractive index different from that of the surface protective layer.
Since the light scattering layer having a texture and a concavo-convex structure is provided, light incident on the photovoltaic device is incident on the semiconductor layer after being scattered in the surface protection layer, and is incident on the semiconductor layer. , The absorption of light by the semiconductor layer increases, the short-circuit current increases, and the photoelectric conversion efficiency can be improved.

In this case, if a plurality of light scattering layers having the concavo-convex structure are formed in the surface protective layer as in the invention of claim 5, the scattering of incident light is further increased, and the light from the semiconductor layer is further increased. And the short circuit current increases, and the photoelectric conversion efficiency of the photovoltaic device can be further improved.

According to the sixth aspect of the present invention , the difference between the refractive index of the material forming the light scattering layer and the refractive index of the material forming the surface protective layer is set to 0.1 or more. Since the scattering of incident light increases, the absorption of light by the semiconductor layer increases, the short-circuit current increases, and the photoelectric conversion efficiency can be further improved.

Further, according to the invention of claim 7, the light incident on the photovoltaic device is scattered on both the incident side and the reflection side, further increasing the light absorption by the semiconductor layer, and thereby reducing the short-circuit current. It is possible to realize an increase and an improvement in photoelectric conversion efficiency.

FIG. 1 shows the configuration of a typical photovoltaic device according to the present invention. In the figure, 101 is a surface protective layer, 102 is a light scattering layer, 103 is a transparent electrode, 10
4 is a semiconductor layer, 105 is a collecting electrode, 106 is a back electrode,
107 is a substrate and 108 is a back surface protective layer.

(Surface Protection Layer) The surface protection layer 101 is formed to protect the photovoltaic device from the external environment, and is formed on the surface of the photovoltaic device. As a material, a material having weather resistance may be appropriately selected from synthetic resins and the like. However, when it is formed on the light incident side surface, in addition to weather resistance, the transmittance of the photovoltaic device for light having a sensitive wavelength is preferably 80.
%, More preferably at least 90% on average, and most preferably at least 95% on average. In addition, it is desirable that the transmittance does not decrease even when left outdoors for a long time.

The surface protective layer 101 may be divided into an upper transparent material, a filler, and an adhesive according to functions.

As a specific material of the surface protective layer 101, glass, acrylic, polycarbonate, FRP, or a fluororesin such as PVF (polyvinyl fluoride), a silicone resin, or the like is preferably used as the upper transparent material. As the filler, silicone resin, PVB (polyvinyl butyral), EVA (ethylene vinyl acetate) and the like are preferably used.

The surface protective layer 101 is usually formed by degassing the film-shaped material and bonding it to a photovoltaic element, or heating and melting the material or dissolving it in a solvent and applying it. You.

Further, the photovoltaic device of the present invention uses a material such as silicone resin, PVB (polyvinyl butyral), EVA (ethylene vinyl acetate) or the like to improve the adhesion between the light scattering layer and the surface protective layer. A material that can be applied by heating and melting or by dissolving in a solvent is most suitable.

The refractive index of the surface protective layer near the light scattering layer is increased by rapidly cooling the molten surface protective layer material or by rapidly drying the solvent of the surface protective layer material dissolved in the solvent. be able to. This is probably because stress is applied to the surface protection layer near the light scattering layer.

(Light Scattering Layer) In the present invention, the light scattering layer 1
Reference numeral 02 denotes a layer having a concavo-convex structure, and the light scattering layer 102 provided in the surface protective layer 101 may be a single layer or a plurality of layers. Here, the uneven structure may be provided on either the front side or the back side of the light scattering layer with respect to the light incident direction, or may be provided on both the front side and the back side.

The size of the irregularities is a maximum surface roughness Rma.
x is preferably 0.1 μm to 100 μm, more preferably 0.2 μm to 50 μm, and most preferably 0.5 μm to 10 μm.

The light scattering layer 102 is formed of the surface protective layer 10.
1 may be formed at any position from near the surface to near the transparent electrode 103 in the layer thickness direction. However, it is desirable not to form it within 1 μm in the vicinity of the transparent electrode 103. This is because if the transparent electrode 103 also serving as an antireflection layer and the light scattering layer 102 are too close to each other, the antireflection conditions may be impaired.

Further, the material of the light-scattering layer 102 preferably has a refractive index of at least 0.1, more preferably at least 0.2, and most preferably at least 0.3 with the refractive index of the surface protective layer 101. Is desirable. As for the material of the light scattering layer 102, the transmittance of light having a wavelength of 400 nm to 1000 nm is preferably 80% or more on average, more preferably 9% on average.
Desirably, it is 0% or more, and optimally 95% or more on average.

In particular, most of the materials suitable for the surface protective layer 101 have a refractive index of about 1.5, so that the material of the light scattering layer 102 has a refractive index of 1.0 to 1.4, or A value of 1.9 to 2.5 is desirable. A substance having a refractive index in this range can have a wavelength of 400 nm to 1000 nm.
Although the transmittance of light of nm also satisfies the above-mentioned value, it is preferable in many cases. Those having a refractive index of more than 2.5 have good light scattering ability, but are not suitable because the transmittance of light having a wavelength of 400 nm to 1000 nm cannot obtain the above-mentioned value in many cases.

Further, it is desirable that the material of the light scattering layer 102 has excellent adhesion to the material of the surface protective layer 101, is chemically stable, and has a thermal expansion coefficient close to that of the material of the surface protective layer 101.

Further, as a specific example of the material of the light scattering layer 102,
And ZnS, TiO_Two, Ta_TwoO _Five, CeO_Two, Zr
O_Two, Sb_TwoO_Three, Nd_TwoO_Three, In_TwoO_Three, SiC,
Si _ThreeN_Four, SiO, La_TwoO_Three, SnO_Two, ZnO,
CdO, Cd_TwoSnO_Four, ThO_Two, MgO, Pb
F_Two, Al_TwoO_Three, NdF_Three, LaF_Three, MgF_Two, L
iF, Na_ThreeAlF₆, NaF, CaF_TwoEtc., or
A mixture of these compounds is preferred.

Further, among the materials for these light scattering layers, the above-mentioned materials which are preferably used as the surface protective layer 101 have a refractive index of about 1.5, so that Z
nO, ZnS, TiO ₂ , In ₂ O ₃ , SnO ₂ , Mg
F ₂ and CaF ₂ are particularly preferably used. Furthermore, these materials and silicone resin, PVB as a surface protective layer
(Polyvinyl butyral) and EVA (ethylene vinyl acetate) are most preferably used because they exhibit properties excellent in adhesion and chemical stability.

As a method for forming the light scattering layer 102, an evaporation method, a CVD method, a spray method, a spin-on method, a dipping method, or the like is suitably used. Among these forming methods, as the surface protective layer 101, silicone resin, PVB
When using a synthetic resin such as (polyvinyl butyral) or EVA (ethylene vinyl acetate), the heat resistance of the surface protective layer is low, so that the substrate temperature may be higher than the heat resistant temperature of the surface protective layer when forming the light scattering layer. Can not.
Therefore, techniques that can form the light scattering layer at a relatively low substrate temperature include heating evaporation, DC magnetron sputtering, and the like.
RF magnetron sputtering, MOCVD, reactive ion plating, ion beam sputtering, or the like, or a spray method with a low heating temperature is particularly preferably used.

As the preferable conditions for forming the light scattering layer in the above-mentioned vapor deposition method, the substrate temperature is preferably from room temperature to 250 ° C., and the flow rate of the gas used is preferably from 0.1 sccm to 1 slm. The pressure in the reaction vessel during the vapor deposition is preferably from 10 ⁻⁶ Torr to 10 ⁻² Torr in the case of the thermal vapor deposition method, and is preferably from 1 mTorr to 1 Torr in the case of the sputtering method.
rr is desirable.

Further, in the case where the uneven structure of the light scattering layer 102 is provided, in the above-described forming method, the forming conditions are selected so that the surface becomes uneven, or after forming a flat layer, It is obtained by making the surface uneven by a method such as a sand blast method, a dry etching method, or a wet etching method. In addition to such a formation method, the light scattering layer 102 may be formed after the surface of the surface protection layer 101 is made uneven by the above-described method, and further, on the surface protection layer having the uneven structure. A light scattering layer may be formed.

When the uneven structure is provided on both sides with respect to the light incident direction of the light scattering layer 102, both of the above methods may be used.

The light scattering layer 1 is provided in the surface protection layer 101.
As a method of forming 02, a method of forming the surface protective layer 101, forming the light scattering layer 102 having an uneven structure, and then forming the surface protective layer 101 again, or a method of forming a sheet-shaped surface protective layer material There is a method in which the light scattering layer 102 is formed in advance, and then the surface protection layer 101 is formed by bonding to the substrate 107 on which the photovoltaic element is formed. Further, the light scattering layer 1 is previously added to the sheet-like surface protective layer material.
In the case where 02 is formed, the light scattering layer 102 can be bonded with the light incident side, or the surface protective layer material can be bonded with the light incident side. By appropriately selecting the bonding direction, it is possible to select whether to provide the concavo-convex structure on the front side or the back side with respect to the light incident direction of the light scattering layer 102.

(Transparent Electrode) In the present invention, the transparent electrode 1
Numeral 03 denotes an electrode on the light incident side that transmits light, and can also serve as an anti-reflection film by optimizing the film thickness. The transparent electrode 103 is required to have a high transmittance in a wavelength region where the semiconductor layer can absorb light and to have a low resistivity. Preferably, 5
It is desirable that the transmittance at 50 nm is 80% or more, more preferably 85% or more.

The resistivity is preferably 5 × 10^-3Ω
cm or less, more preferably 1 × 10^-3Ωcm or less
Is desirable. The material is In_TwoO_Three, S
nO _Two, ITO (In_TwoO_Three+ SnO_Two), ZnO, C
dO, Cd_TwoSnO_Four, TiO_Two, Ta_TwoO_Five, Bi_Two
O_Three, MoO_Three, Na_x WO_ThreeConductive oxide such as
A mixture of these is preferably used. Also,
These compounds include an element that changes the electrical conductivity (dopane).
G) may be added.

As the element (dopant) that changes the conductivity, for example, when the transparent electrode 103 is ZnO, Al, In, B, Ga, Si, F, etc.
_In the case of ₂ O ₃ , Sn, F, Te, Ti, Sb, Pb
Etc., and in the case of SnO ₂ , F, Sb, P, As,
In, Tl, Te, W, Cl, Br, I, etc. are preferably used.

As a method for forming the transparent electrode 103, an evaporation method, a CVD method, a spray method, a spin-on method, a dipping method, or the like is suitably used.

(Semiconductor Layer) The semiconductor layer 104 used in the present invention is roughly classified into a crystalline layer, a polycrystalline layer, an amorphous layer, and a combination thereof. Used. As a material of the semiconductor layer 104, a material using a group IV element such as Si, C, Ge, or the like, a material using a group IV alloy such as SiGe, SiC, SiSn, or GaAs, InSb, Ga
Those using III-V group elements such as P, GaSb, InP, InAs, or ZnSe, CdTe, ZnS,
II-VI such as ZnTe, CdS, CdSe, CdTe
Using a group III element or I- such as CuInSe ₂
Those using III-VI group ₂ elements or those using them in combination are used.

Among the above semiconductor materials, semiconductor materials particularly preferably used for the photovoltaic device of the present invention include a-Si: H (hydrogenated amorphous silicon) and a
-Si: F, a-Si: H: F, a-SiGe: H, a
-SiGe: F, a-SiGe: H: F, a-SiC:
Group IV and group IV alloy-based amorphous semiconductor materials such as H, a-SiC: F, a-SiC: H: F, or polycrystalline S
Examples include so-called group IV and group IV alloy-based polycrystalline semiconductor materials such as i: H, polycrystalline Si: F, and polycrystalline Si: H: F. In particular, when a semiconductor layer is formed using a group IV or group IV alloy-based amorphous semiconductor material, the preferable thickness of the semiconductor layer is between 0.1 μm and 2.0 μm. This is because, when a thin film having a thickness of 2.0 μm or less is used, the effect of increasing light absorption by the semiconductor layer due to light scattering by the light scattering layer of the present invention is considered to be significant due to the light confinement effect.

The semiconductor layer can perform valence electron control and forbidden band width control. Specifically, a raw material compound containing an element serving as a valence electron controlling agent or a forbidden band width controlling agent when forming a semiconductor layer is used alone, or mixed with the deposited film forming raw material gas or the diluent gas to form a film. You only have to introduce it in the space.

The semiconductor layer 104 is at least partially doped with p-type and n-type by valence electron control to form at least one set of pn junctions or at least one set of pin junctions. That is, a so-called stacked cell configuration in which a plurality of pn junctions or pin junctions are stacked can be employed.

As a method of forming the semiconductor layer 104, a microwave plasma CVD method, an RF plasma CVD
Method, photo-CVD method, thermal CVD method, MOCVD method, etc., or various evaporation methods such as EB evaporation, MBE, ion plating, ion beam method, sputtering method, spray method, printing method, etc. It is formed.
Hereinafter, the groups IV and I particularly suitable for the photovoltaic device of the present invention will be described.
The semiconductor layer using a group V alloy-based amorphous semiconductor material will be described in more detail.

I-type layer (intrinsic semiconductor layer) In particular, in a photovoltaic device using a group IV or group IV alloy amorphous semiconductor material, the i-type layer used for the pin junction generates carriers with respect to irradiation light. It is an important layer to transport.

As the i-type layer, a slightly p-type or slightly n-type layer can be used.

As described above, the group IV and group IV alloy amorphous semiconductor materials contain hydrogen atoms (H, D) or halogen atoms (X), which have an important function.

The hydrogen atoms (H, D) or the halogen atoms (X) contained in the i-type layer work to compensate for dangling bonds of the i-type layer, and the mobility and lifetime of carriers in the i-type layer. To improve the product of Also, a p-type layer / i-type layer, an n-type layer / i
It works to compensate for the interface state of each interface of the mold layer, and has the effect of improving the photovoltaic power, photocurrent and photoresponsiveness of the photovoltaic element. The optimal content of hydrogen atoms and / or halogen atoms contained in the i-type layer is 1 to 40 at%.

In particular, those in which a large amount of hydrogen atoms and / or halogen atoms are distributed on each interface side of the p-type layer / i-type layer and the n-type layer / i-type layer are mentioned as preferred distribution modes. The preferred range of the content of hydrogen atoms and / or halogen atoms in the vicinity of the interface is 1.1 to 2 times the content in the bulk. Further, it is preferable that the content of hydrogen atoms and / or halogen atoms is changed corresponding to the content of silicon atoms.

The thickness of the i-type layer depends on the structure of the photovoltaic element (for example, single cell, double cell, triple cell) and i
It greatly depends on the band gap of the mold layer,
1.0 μm is mentioned as the optimum layer thickness.

More specifically, for example, the i-type hydrogenated amorphous silicon (a-Si: H) suitable for the photovoltaic device of the present invention includes an optical band gap (E
g) is 1.60 eV to 1.85 eV, the content of hydrogen atoms (C _H ) is 1.0 to 25.0%, AM 1.5 and 10
Photoelectric conductivity (σp) under simulated sunlight irradiation of 0 mW / cm ²
Is 1.0 × 10 ⁻⁸ S / cm or more, and the dark conductivity (σd)
Is less than 1.0 × 10 ⁻⁹ S / cm, the slope of the Urbach tail by the constant photo method (CPM) is 55 meV or less, and the density of dangling bonds by electron spin resonance (ESR) is 10 ¹⁷ / cm ^3. These are:

For example, as the i-type hydrogenated amorphous silicon germanium (a-SiGe: H) suitable for the photovoltaic device of the present invention, the optical band gap (Eg) is 1.35 eV to 1.35 eV. .70 eV, hydrogen atom content (C _H ) is 1.0 to 20.0%, AM 1.5,
Photoelectric conductivity (σ) under irradiation of pseudo sunlight of 100 mW / cm ²
p) is not less than 1.0 × 10 ⁻⁷ S / cm and the dark conductivity (σ
d) is 1.0 × 10 ⁻⁵ S / cm or less, the slope of the Urbach tail by the constant photo method (CPM) is 60 meV or less, and the density of dangling bonds by electron spin resonance (ESR) is 10 ¹⁷ / cm. cm ³ or less.

For example, by using a group IV and group IV alloy-based amorphous semiconductor material having the above characteristics, the transport characteristics of photocarriers are improved, and the sensitivity to long wavelength light is improved. The effect of increasing light absorption by the semiconductor layer due to light scattering by the light scattering layer is emphasized by a synergistic effect, and the characteristics of the photovoltaic device are further improved. This is because, by having the above-described characteristics, the so-called localized level in the semiconductor layer is reduced, and when light is scattered by the light scattering layer and the optical path length passing through the semiconductor layer is extended, the optical carrier is reduced. Is effectively collected without recombination, the effect of increasing the sensitivity of the photovoltaic device to long-wavelength light is considered to be significant.

P-type layer or n-type layer The p-type layer or the n-type layer is also an important layer that affects the characteristics of the photovoltaic device of the present invention.

As an amorphous material (denoted by a-) of a p-type layer or an n-type layer (it goes without saying that a microcrystalline material (denoted by μc-) is also included in the range of the amorphous material). Are, for example, a-Si: H, a-Si: HX, a-Si
C: H, a-SiC: HX, a-SiGe: H, a-S
iGeC: H, a-SiO: H, a-SiN: H, a-
SiON: HX, a-SiOCN: HX, μc-Si:
H, μc-SiC: H, μc-Si: HX, μc-Si
C: HX, μc-SiGe: H, μc-SiO: H, μ
c-SiGeC: H, μc-SiN: H, μc-SiO
N: HX, μc-SiOCN: HX, etc., p-type valence electron controlling agents (Group III atoms B, Al, Ga, I
n, Tl) or a material in which an n-type valence electron controlling agent (group V atom P, As, Sb, Bi) in the periodic table is added at a high concentration, and as a polycrystalline material (denoted as poly-). Are, for example, poly-Si: H, poly-Si: H
X, poly-SiC: H, poly-SiC: HX,
poly-SiGe: H, poly-Si, poly-
SiC, poly-SiGe, etc. are p-type valence electron controlling agents (Group III atoms B, Al, Ga, In, T
l) and n-type valence electron controlling agent (Group V atom P,
Materials to which As, Sb, Bi) are added at a high concentration can be given.

In particular, the p-type layer or the n-type layer on the light incident side includes:
A crystalline semiconductor layer with little light absorption or an amorphous semiconductor layer with a wide band gap is suitable.

The amount of Group III atom added to the p-type layer and the amount of Group V atom added to the n-type layer is 0.
The optimal amount is 1 to 50 at%.

The hydrogen atoms (H, D) or halogen atoms contained in the p-type layer or the n-type layer work to compensate for dangling bonds of the p-type layer or the n-type layer, and This is to improve the doping efficiency of the layer. A hydrogen atom or a halogen atom added to the p-type layer or the n-type layer is 0.1 to 40 a.
t% is mentioned as the optimum amount. In particular, when the p-type layer or the n-type layer is crystalline, the number of hydrogen atoms or halogen atoms is 0.1 to
8 at% is mentioned as the optimum amount. Further, a preferred distribution form is one in which the content of hydrogen atoms or halogen atoms is large at each interface side of the p-type layer / i-type layer and the n-type layer / i-type layer. The content of atoms and / or halogen atoms is 1.1 to 2 of the content in the bulk.
A double range is mentioned as a preferred range. As described above, by increasing the content of hydrogen atoms or halogen atoms near each interface between the p-type layer / i-type layer and the n-type layer / i-type layer, the defect level and mechanical strain near the interface can be reduced. The photovoltaic power and the photocurrent of the photovoltaic device of the present invention can be increased.

The electrical characteristics of the p-type layer or the n-type layer of the photovoltaic element are preferably those having an activation energy of 0.2 eV or less, and those having an activation energy of 0.1 eV or less are optimal. The specific resistance is preferably 100 Ωcm or less,
Ωcm or less is optimal. Further, the thickness of the p-type layer and the n-type layer is preferably 1 to 50 nm, and most preferably 3 to 10 nm.

As the semiconductor layer of the photovoltaic device of the present invention,
In order to form a preferable group IV and group IV alloy-based amorphous semiconductor layer, the most preferable manufacturing method is a microwave plasma CVD method, and the next most preferable manufacturing method is an RF plasma CVD method.

In the microwave plasma CVD method, a material gas such as a raw material gas or a diluent gas is introduced into a deposition chamber (vacuum chamber) which can be reduced in pressure, and the inside pressure of the deposition chamber is kept constant while exhausting the gas by a vacuum pump. The microwave oscillated by the microwave power supply is guided by a waveguide, introduced into the deposition chamber through a dielectric window (alumina ceramics or the like), generates a plasma of a material gas, and is decomposed. This is a method for forming a desired deposited film on a placed substrate, and can form a deposited film applicable to a photovoltaic device under a wide range of deposition conditions.

When a semiconductor layer for a photovoltaic device of the present invention is deposited by microwave plasma CVD, the substrate temperature in the deposition chamber is 100 to 450 ° C., and the internal pressure is 0.5 to 30 m.
Torr, microwave power is 0.01 to 1 W / c
m ³ and the frequency of the microwave are preferably 0.5 to 10 GHz.

When the deposition is performed by the RF plasma CVD method, the substrate temperature in the deposition chamber is 100 to 350 ° C., the internal pressure is 0.1 to 10 torr, and the RF power is 0.01 to
5.0 W / cm ² , the deposition rate is 0.1 to 30 A / sec
c is mentioned as a suitable condition.

The source gas suitable for depositing the group IV and group IV alloy amorphous semiconductor layers suitable for the photovoltaic device of the present invention includes a gasizable compound containing silicon atoms,
Gasification compounds containing germanium atoms, gasification compounds containing carbon atoms, gasification compounds containing nitrogen atoms, gasification compounds containing oxygen atoms, etc., and mixed gases of these compounds Can be.

Specifically, gasification containing silicon atoms
The compound to be obtained is SiH_Four, Si _TwoH₆, SiF_Four,
SiFH_Three, SiF_TwoH_Two, SiF_ThreeH, Si_ThreeH₈,
SiD_Four, SiHD_Three, SiH_TwoD_Two, SiH_ThreeD, S
iFD_Three, SiF_TwoD_Two, SiD_ThreeH, Si_ThreeD
_ThreeH_Three, Etc.

Specific examples of the gasifiable compound containing a germanium atom include GeH ₄ , GeD ₄ , Ge
F ₄ , GeFH ₃ , GeF ₂ H ₂ , GeF ₃ H, GeH
D ₃ , GeH ₂ D ₂ , GeH ₂ D, Ge ₂ H ₆ , GeD
_{6 and the} like.

Specifically, a gas containing a carbon atom can be obtained.
The compound is CH_Four, CD_Four, C _nH_{2 n + 2}(N is
Integer) C_nH_{2 n}(N is an integer), C_TwoH_Two, C₆H₆,
CO _Two, CO and the like.

As the nitrogen-containing gas, N ₂ , NH ₃ , ND
₃ , NO, NO ₂ and N ₂ O.

As the oxygen-containing gas, O ₂ , CO, C
O ₂ , NO, NO ₂ , N ₂ O, CH ₃ CH ₂ OH, CH
₃ OH and the like.

In order to control valence electrons, a p-type layer or n-type layer
Materials introduced into the mold layer include Group III atoms and Group V atoms in the periodic table .

As a starting material for introducing a group III atom effectively, specifically, for introducing a boron atom, B ₂ H ₆ , B ₄ H ₁₀ , B ₅ H ₉ , B ₅ H
_{11, B 6 H 10, B} 6 H 12, B 6 H 14 , etc. borohydride,
Examples thereof include boron halides such as BF ₃ and BCl ₃ . In addition, AlCl ₃ , GaCl ₃ , In
Cl ₃ and TlCl ₃ can also be mentioned. Especially B ₂
H ₆ and BF ₃ are suitable.

Effectively used as a starting material for introducing a group V atom is, specifically, PH for introducing a phosphorus atom.
₃ , hydride phosphorus such as P ₂ H ₄ , PH ₄ I, PF ₃ , P
F ₅ , PCl ₃ , PCl ₅ , PBr ₃ , PBr ₅ , PI
_{And the} like. In addition, AsH ₃ ,
AsF ₃ , AsCl ₃ , AsBr ₃ , AsF ₅ , SbH
₃ , SbF ₃ , SbF ₅ , SbCl ₃ , SbCl ₅ , B
iH ₃ , BiCl ₃ , BiBr _{3 and the} like can also be mentioned. Particularly, PH ₃ and PF ₃ are suitable.

Further, the compound capable of being gasified is H ₂ , H
The gas may be appropriately diluted with a gas such as e, Ne, Ar, Xe, or Kr and introduced into the deposition chamber.

In particular, when depositing a layer having a small light absorption or a wide band gap, such as a microcrystalline semiconductor or a-SiC: H, the source gas is diluted 2 to 100 times with hydrogen gas, and the microwave power or The RF power preferably introduces relatively high power.

(Current Collecting Electrode) In the present invention, if the resistivity of the transparent electrode 103 cannot be sufficiently reduced, the current collecting electrode 105 is formed on a part of the transparent electrode 103 as necessary to reduce the resistivity of the electrode. Lower,
It works to reduce the series resistance of the photovoltaic element. Its materials include gold, silver, copper, aluminum, nickel, iron,
Chromium, Shirubedenpe using molybdenum, tungsten, titanium, cobalt, tantalum, niobium, a metal of zirconium, or alloys such as stainless steel, or a powdered metal
And the like . Then, the shape is formed in a branch shape as shown in FIG. 4, for example, so as not to block incident light on the semiconductor layer as much as possible.

Further, in the entire area of the photovoltaic device,
The area occupied by the collecting electrode is preferably 15% or less, more preferably 10% or less, and most preferably 5% or less.

Further, a pattern of the collecting electrode is formed by using a mask, and the forming method includes a vapor deposition method, a sputtering method,
A plating method, a printing method, or the like is used.

(Back Electrode, Light Reflecting Layer) The back electrode 106 used in the present invention is an electrode disposed on the back of the semiconductor layer in the light incident direction, and is made of gold, silver, copper, aluminum, nickel, or the like. , Iron, chromium, molybdenum, tungsten, titanium, cobalt, tantalum, niobium, zirconium and other metals or stainless steel and other alloys.
Among them, metals having high reflectance, such as aluminum, copper, silver, and gold, are particularly preferable. In the case of using a metal having a high reflectance, the back electrode can also serve as a light reflecting layer that reflects light that could not be absorbed by the semiconductor layer again to the semiconductor layer.

The shape of the back electrode may be flat, but it is more preferable that the back electrode has an uneven shape for scattering light. By having an uneven shape that scatters light, it scatters long-wavelength light that could not be absorbed by the semiconductor layer, extends the optical path length in the semiconductor layer, improves the long-wavelength sensitivity of the photovoltaic element, and increases the short-circuit current. And the photoelectric conversion efficiency can be improved. The uneven shape that scatters light has a height difference between peaks and valleys of the unevenness of 0.2 to 2.0 μm in Rmax.
It is desirable that

However, when the substrate also serves as the back electrode, it may not be necessary to form the back electrode.

For forming the back electrode, a vapor deposition method, a sputtering method, a plating method, a printing method, or the like is used. When the back electrode is formed to have an uneven shape that scatters light, the formed metal or alloy film is formed by dry etching, wet etching, sand blasting, heating, or the like.
In addition, the above-mentioned metal or alloy can be deposited while heating the substrate to form an uneven shape for scattering light.

(Substrate) As the material of the substrate 107 used in the present invention, either a conductive material or an insulating material can be used. Examples of the conductive material include a plate and a film of molybdenum, tungsten, titanium, cobalt, chromium, nickel, iron, copper, tantalum, niobium, zirconium, aluminum metal, or an alloy thereof. Among them, stainless steel, nickel chromium alloy and nickel, tantalum, niobium, zirconium, titanium metal and / or alloy are particularly preferable from the viewpoint of corrosion resistance. Insulating materials include polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride,
A film or sheet of a synthetic resin such as polystyrene or polyamide, or a plate of an inorganic insulating material such as glass, ceramic, or quartz can also be used. Alternatively, a conductive material coated with an insulating material can be used.

When a crystalline semiconductor layer is used, for example, the crystalline semiconductor itself is used as the substrate and the substrate 1
07 may not be particularly required.

(Back Surface Protective Layer) In the present invention, the back surface protective layer 108 is provided to protect the back surface of the photovoltaic device.
As the material, a material having weather resistance may be appropriately selected from synthetic resins and the like.

As a forming method, usually, the above-mentioned film-shaped material is degassed and bonded to a photovoltaic element,
It is formed by heating and melting the material or by dissolving in a solvent and applying.

The procedure for manufacturing the photovoltaic device of the present invention is as follows.

The method of forming each layer constituting the photovoltaic device is as described above. The order of forming each layer is as follows. First, the substrate 107 is washed, the back electrode 106 is formed thereon, the semiconductor layer 104, the transparent electrode 103, and the current collecting electrode 105 are formed in that order, and The output output electrode shown in the figure is formed, and finally the front surface protection layer 101 having the back surface protection layer 108 and the light scattering layer 102 formed therein is formed.

However, instead of the substrate 107, the semiconductor layer 1
When the substrate 04 is used as a substrate, it may be manufactured in an order different from the above order.

When connecting photovoltaic devices formed on a plurality of substrates in series or in parallel, or in order to reinforce the substrates, a substrate formed on a flat plate-shaped support up to a current collecting electrode is also provided. , A protective layer may be formed on both sides.

[0097]

EXAMPLES The present invention will be described in detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

(Example 1) FIG. 2 is a sectional view showing an example of a photovoltaic device according to the present invention. The photovoltaic device of FIG. 2 uses amorphous silicon (hereinafter abbreviated as a-Si) and amorphous silicon germanium (hereinafter abbreviated as a-SiGe) as semiconductor layers.

In FIG. 2, 201a, 201b, 20
1c is a surface protective layer, and the upper transparent material 20 according to its function.
1a and adhesive layers 201b and 201c. Also 2
02 is a light scattering layer, 203 is a transparent electrode, 204a and 204
Reference numerals b and 204c denote a semiconductor layer, 205 denotes a collecting electrode, 206 denotes a back electrode, 207 denotes a substrate, 208a and 208b denote an adhesive layer, and 208c denotes a back protective layer. 209 is a transparent conductive layer, and 210 is an insulating layer. In this embodiment, the transparent conductive layer 209 functions to prevent the back electrode 209 from diffusing into the semiconductor layer 204, thereby improving the production yield of the photovoltaic device, and increasing light scattering by the back electrode 209. There is work.

In the following steps, a photovoltaic device having the structure shown in FIG. 2 was manufactured.

First, the surface of the substrate 207 is Rmax
Is 0.1μm or less, 0.7mm thick and 10cm square S
The stainless steel substrate of US304 is washed and the back electrode 206
Ag averaged 0.4 by an RF sputtering method known as
μm was formed. At this time, by performing sputtering while heating the substrate to 380 ° C., Rmax is 0.6 μm.
An uneven shape for scattering m light was produced.

Next, using a DC magnetron sputtering apparatus shown in FIG. 3, zinc oxide (ZnO) was formed to a thickness of 0.4 μm.

In FIG. 3, reference numeral 301 denotes a vacuum vessel;
The heating plate 303 is supported by a supporting portion 302 having an insulating property. The heating plate 303 includes a heater 306 and a thermocouple 3
04 is buried and controlled to a predetermined temperature by a temperature controller 305. The substrate 308 is a substrate holder 309
Supported by The target 31 faces the substrate 308.
0, but the target 310 is
11 and has a magnet 312 on the back surface so that a magnetic field can be formed in the plasma space 320. In order to cool the target heated during sputtering, cooling water is introduced from the cooling water introduction pipe 313 to the back surface of the target. After the introduced water cools the target, it is discharged from a cooling water discharge pipe.

The target 310 is a mixture of zinc oxide powder and zinc mixed and sintered. Alternatively, a target made of metal zinc can be used.

The target 310 is attached to the target table 3.
A DC voltage is applied from a sputter power supply 314 via the power supply 11. The DC current supplied from the sputtering power source is preferably set to 0.01 A or more, more preferably 0.1 A or more. According to the experiments of the present inventor, the larger the current supplied to the sputtering, the smaller the absorption of light by the produced zinc oxide layer, and the larger the photoelectric conversion efficiency of the photovoltaic device, especially, the larger the generated current. This is the same even when the zinc oxide layer is formed using the RF type sputtering method, and the photovoltaic device manufactured by increasing the RF power is larger than the photovoltaic device when the RF power is smaller. Was also advantageous in terms of generated current.

An RF high frequency power supply 315 is used for applying a high frequency to the substrate side as required to roughen the substrate surface. Roughening of the substrate surface is performed before DC sputtering, and aims at improving the adhesion of a film formed by DC sputtering to the substrate.

As a sputtering gas, an argon gas and an oxygen gas are supplied via a mass flow controller 316 or 317, respectively. Of course, it is also possible to perform fluorine doping on the zinc oxide layer formed by mixing the sputtering gas with another gas, for example, a SiF ₄ or NF ₃ gas. The flow rate of the argon gas is preferably 1 sccm to 1 slm, and the flow rate of the oxygen gas is preferably 0.1 sccm to 100 sccm.
It is said.

The internal pressure can be monitored by a vacuum gauge 318 attached to the vacuum vessel 301. Vacuum container 3
The whole 01 is evacuated via a main valve 319 connected to an exhaust system (not shown). The background internal pressure before starting the sputtering is preferably 10 ^−4.
Torr or less, more preferably 10 ^-5 Torr or less, and the internal pressure during sputtering is 1 mTorr or more and 1 To
rr or less.

Further, if necessary, the RF high frequency power can be applied to the substrate side by the high frequency power supply 315.

The formation of the zinc oxide layer is started while maintaining the above conditions, and after the thickness of the zinc oxide layer reaches a desired value, the supply of power from the sputtering power supply and the supply of the sputtering gas are appropriately performed. After stopping and cooling the substrate appropriately, the inside of the vacuum vessel is leaked to the atmosphere, and the substrate on which the zinc oxide layer is formed is taken out.

[0111] Zinc oxide (ZnO) was formed by the DC magnetron sputtering apparatus configured as described above.

Thereafter, a known so-called glow discharge method (GD) in which a source gas is decomposed into a plasma state under reduced pressure by applying 13.56 MHz RF high frequency to the electrode.
), The following semiconductor layers were formed.

First, while heating the substrate to 300 ° C.,
_TwoMonosilane (SiH _Four) And phosphine
(PH_Three) To separate the n-type a-Si layer 204c from Zn
20 nm was formed on the substrate on which O was formed.

Next, while heating the substrate to 250 ° C.,
_The monosilane (SiH ₄ ) and the germane (GeH ₄ ) diluted by using ₂ are decomposed to form an intrinsic a-SiGe layer 204b.
Was formed thereon to a thickness of 250 nm. At this time, 1 μm of intrinsic a-SiGe was deposited on a glass substrate under the same film forming conditions and evaluated, and the optical band gap (Eg) was 1.5.
It was 0 eV.

The intrinsic a-SiGe layer 204b is formed by removing 30 nm each of the n-layer and the p-layer from a-SiGe by a-SiGe.
Is provided with a so-called buffer layer whose composition continuously changes. Next, while heating the substrate to 200 ° C., H
_The monosilane (SiH ₄ ) and boron trifluoride (BF ₃ ) diluted by ₂ are decomposed to form a p-type microcrystalline silicon layer 20.
4a was formed to a thickness of 5 nm.

Next, the substrate was removed from the substrate by resistance heating evaporation.
While heating to 0 ° C., ITO was deposited to a thickness of 70 nm to form a transparent electrode 203.

Next, a current collecting electrode 205 was formed by evaporating Al in a pattern as shown in FIG. 4 using a mask by an electron beam evaporation method.

Next, a lead electrode (not shown) was connected to the end of the back electrode and the end of the current collecting electrode.

Next, EVA (ethylene vinyl acetate) was hot-melted at 80 ° C., applied to the surface of the photovoltaic device formed up to the extraction electrode, and heated at 150 ° C. for 1 hour.
Heating was performed for a time to cure to form a surface protective layer 201c.

Next, while applying an RF high frequency to the substrate side by the DC magnetron sputtering apparatus shown in FIG.
While maintaining the substrate formed up to EVA at 50 ° C.,
1.5 μm of nO was formed.

Next, the light scattering layer 202 was formed by etching ZnO with oxalic acid diluted to 3% with water for 180 seconds to form an uneven structure having a Rmax of about 1 μm on the surface.

Next, a PVF film having a thickness of 40 μm was formed on the surface of the light scattering layer 202 as an upper transparent material 201a by EVA.
201b was applied and bonded. As a result, the light scattering layer 202 was formed in the surface protection layer.

Next, a 50 μm-thick nylon film as an insulating layer 210 and a 40 μm-thick PVF film as a back surface protective layer were applied and adhered to the back surface of the substrate 207 by applying EVA therebetween. The illustrated photovoltaic device of the present invention was completed.

Through the above steps, 20 so-called single-layer a-SiGe photovoltaic devices of 10 cm square were manufactured.

Thereafter, the parallel resistance is 1 KΩ / cm ²
The above photovoltaic device was illuminated with a solar simulator at 25 ° C. by a solar simulator at AM 1.5 and 100 mw / cm ² to open voltage (Voc) and short circuit current (J).
sc), fill factor (FF), photoelectric conversion efficiency (η), and other photovoltaic device characteristics were measured, and the average value was determined. Table 1 summarizes the results of the photovoltaic device characteristics.

However, the characteristics of the photovoltaic device are standardized by the values of Comparative Example 1 described later.

Further, the spectral sensitivity of the photovoltaic device was measured and is shown by the solid line in FIG. In FIG. 5, the vertical axis indicates the ratio (quantum efficiency) extracted as current with respect to the number of photons incident on the photovoltaic device.

(Comparative Example 1) In the same manner as in Example 1, except that the light scattering layer 202 was not formed and the procedure was the same as in Example 1, a so-called single-layer type a-SiG
20 e photovoltaic devices were produced.

In the same manner as in Example 1, the characteristics of the photovoltaic device were measured, and the average value was obtained.

The spectral sensitivity of the photovoltaic device was measured in the same manner as in Example 1. The curve shown by the chain line in FIG. 5 is for the comparative example. As is clear from FIG. 5 and Table 1, the photovoltaic device of the present invention in which the light scattering layer having the uneven structure is formed in the surface protective layer has a longer wavelength region in Example 1 than in Comparative Example 1. The spectral sensitivity was improved, the short-circuit current (Jsc) was improved, and the photoelectric conversion efficiency (η) was improved.

[0131]

[Table 1] (Example 2) A photovoltaic device according to another example of the present invention shown in FIG. 6 was manufactured in the following steps.

FIG. 6 shows a stacked photovoltaic device in which two sets of PIN junctions are stacked.

In FIG. 6, 601a, 601b, 60
1c is a surface protective layer, and the upper transparent material 60
1a and adhesive layers 601b and 601c. Also,
602 is a light scattering layer, 603 is a transparent electrode, 604a, 60
4b, 604c, 604d, 604e and 604f are semiconductor layers, 605 is a current collecting electrode, 606 is a back electrode, 607 is a substrate, and 608a and 608b are adhesive layers. Also, 60
Reference numeral 9 denotes a transparent conductive layer, 610 denotes an insulating layer, and 611 denotes a support also serving as a back surface protective layer. In this embodiment, the transparent conductive layer 609 has the same function as in the first embodiment.

As shown in FIG. 6, in the photovoltaic device of this embodiment, irregularities are provided above and below the light scattering layer 602.

First, as the substrate 607, the surface is 0.1 μm or less in Rmax, 0.15 mm in thickness, 32 cm in width,
The following processing is performed by a so-called roll-to-roll method in which a sheet-shaped stainless steel substrate having a length of 15 m is washed, and processing is performed while continuously moving the substrate between a feeding roll and a winding roll. Was.

First, a 0.4 μm average of Ag was formed as the back electrode 606 by a known RF magnetron sputtering apparatus using a high frequency of 13.56 MHz. At this time, by performing sputtering while heating the substrate to 380 ° C., a concavo-convex shape for scattering light having a Rmax of 0.6 μm was produced.

Next, as the transparent conductive layer 609, zinc oxide (ZnO) of 0.4 μm
Formed.

Next, glow discharge method (GD method)
As a result, the following semiconductor layers were formed.

First, while heating the substrate to 300 ° C., a first n-type a-Si layer 604f was formed to a thickness of 20 nm.

Next, while heating the substrate to 280 ° C., a first intrinsic a-SiGe layer
Formed. At this time, the intrinsic band gap (Eg) was 1.46 eV when intrinsic a-SiGe was deposited at 1 μm on a glass substrate under the same film forming conditions and evaluated.

The intrinsic a-SiGe layer 604e is formed by removing 30 nm each of the n-layer and the p-layer from a-SiGe by a-SiGe.
Is provided with a so-called buffer layer whose composition continuously changes.

Next, while the substrate was heated to 260 ° C., a first p-type microcrystalline silicon layer 604d was formed to a thickness of 5 nm.

Next, while the substrate was heated to 240 ° C., a second n-type a-Si layer 604c was formed to a thickness of 20 nm.

Next, while heating the substrate to 240 ° C., a second intrinsic a-Si layer 604b was formed thereon to a thickness of 220 nm.

Next, while heating the substrate to 200 ° C., a second p-type microcrystalline silicon layer 604a was formed to a thickness of 4 nm.

Next, while the substrate was heated to 170 ° C. using a DC magnetron sputtering apparatus similar to that shown in FIG.
O was evaporated to a thickness of 70 nm to form a transparent electrode 603.

Next, the photovoltaic device was set to 1 by etching.
The substrate was cut into 0 cm square, and the substrate was cut along the etching line.

Next, a current collecting electrode 605 was formed by evaporating Al in a pattern as shown in FIG. 4 by an electron beam evaporation method.

Next, a lead electrode (not shown) was connected to the end of the back electrode and the end of the current collecting electrode.

Next, EVA (ethylene vinyl acetate) was applied by hot-melting at 80 ° C. to a stainless steel plate having a back surface having irregularities of about 3 μm in Rmax, then cooled and peeled off from the stainless steel plate. To Rmax
Was used to form an EVA film having irregularities of about 2.0 μm.

Next, diethylzinc (DEZ) and H ₂ O are vaporized and introduced by a MOCVD apparatus (not shown), and ZZ is formed at room temperature on the above-mentioned EVA film having irregularities on the surface.
nO was formed to an average of 0.2 μm. In this case, irregularities of about 0.5 μm were formed on the surface of the formed ZnO in terms of Rmax.

Next, the thickness of the support 611 of 0.30 m
EVA is hot-melted and applied at 80 ° C. on a galvanized steel sheet having a thickness of 50 m.
Paste a μm nylon film and place EVA on it
Is applied thereon, and a photovoltaic device formed up to the collecting electrode 605 is attached thereon, and the EVA film having ZnO formed on the surface is attached thereon, and E is further attached thereon.
VA was applied, and a PVF film having a thickness of 40 μm was attached as the upper transparent material 601a on the top to form a layer configuration shown in FIG.

Finally, the whole was heated at 150 ° C. for 1 hour to cure the adhesive layer EVA, thereby completing the photovoltaic device shown in FIG.

In the above steps, a 10 cm square Si / Si
100 SiGe2 stack type photovoltaic devices were produced.

[0155] In addition, the parallel resistance is more than 1kΩ per 1 cm ² photovoltaic device, at 25 ° C., by a solar simulator, by irradiating similar sunlight AM 1.5, 100 mW / cm ^2, the open-circuit voltage (Voc) , Short-circuit current (Js
c), fill factor (FF), photoelectric conversion efficiency (η)
The photovoltaic device characteristics such as were measured, and the average value was obtained.

Table 2 summarizes the results of the photovoltaic device characteristics.

However, the photovoltaic device characteristics are standardized by the values of Comparative Example 2 described later.

(Comparative Example 2) A so-called Si / SiGe two-layer stack type photovoltaic device of 10 cm square was produced in the same manner as in Example 2 except that the light scattering layer 602 was not provided. 100 devices were produced.

In the same manner as in Example 2, the characteristics of the photovoltaic device were measured, and the average value was obtained.

As is clear from Table 2, the short-circuit current (Jsc) of the SiGe cell was particularly improved by the photovoltaic device of the present invention in which the light scattering layer having the uneven structure was formed in the surface protective layer.
, The overall short-circuit current (Jsc) and the fill factor (FF) are improved, and the photoelectric conversion efficiency (η) is improved.
Improved.

[0161]

[Table 2] (Example 3) In the following steps, still another example of the photovoltaic device of the present invention shown in FIG. 7 was manufactured.

FIG. 7 shows an example of a photovoltaic device of the present invention using a semiconductor layer of a II-VI group element.

In FIG. 7, 701a, 701b, 70
1c is a surface protection layer, and the upper transparent material 70 according to its function.
1a and adhesive layers 701b and 701c. 7
02 is a light scattering layer, 703 is a transparent electrode, 704a is n-type C
The dS semiconductor layer 704b is a p-type CdTe semiconductor layer,
Reference numerals 6a and 706b denote backside electrodes, and 707 denotes a substrate, which also serves as a backside protective layer.

First, the surface of the substrate 701 is Rmax.
Less than 0.1μm, thickness 0.18mm, width 32c
Example 2 was washed using a sheet-like polyethylene terephthalate (PET) film having a length of 10 m and a length of 10 m as a substrate.
The following processing was performed by the same so-called roll-to-roll method.

First, 0.3 μm of Al was used as the back electrode 706b by the DC magnetron sputtering apparatus shown in FIG.
μm was formed. Next, Au was formed to a thickness of 20 nm as a back electrode 706a by the same DC magnetron sputtering apparatus.

Then, the semiconductor layer of the photovoltaic device shown in FIG. 7 was manufactured in the following steps.

First, while heating the substrate to 160 ° C., the p-type CdTe layer
Formed.

Next, while heating the substrate to 150 ° C., the n-type CdS layer
Formed.

Next, while the substrate was heated to 170 ° C. using a DC magnetron sputtering apparatus similar to that shown in FIG.
O was evaporated to a thickness of 200 nm to form a transparent electrode 703.

Thereafter, a heat treatment was performed in an N ₂ atmosphere at 120 ° C. for 1 hour.

Next, the photovoltaic device was set to 1 by etching.
The substrate was cut into 0 cm square, and the substrate was cut along the etching line.

Next, a lead electrode (not shown) was connected to the end of the transparent electrode and the end of the current collecting electrode.

Next, polyvinyl butyral (PVB) was applied as an adhesive layer 701c. Next, ₂ μm of TiO ₂ was formed on PVB at room temperature by a reactive ion plating method.

[0174] Then, by plasma of a mixed gas of CF ₄ and O _2, by dry etching, TiO
_The light scattering layer 702 was formed by forming irregularities of 0.6 μm in Rmax on the surface of No. ₂ .

Next, a silicone resin was applied as a bonding layer 701b on TiO ₂ , and a 30 μm thick PVF film was bonded as an upper transparent material 701a.

Through the above steps, 200 10 cm square so-called CdS / CdTe photovoltaic devices shown in FIG. 7 were manufactured.

Then, the parallel resistance is 1 kΩ / cm ²
The above photovoltaic device was irradiated at 25 ° C. with a solar simulator at AM 1.5, 100 mW / cm ² simulated sunlight, and the open circuit voltage (Voc) and short circuit current (J
sc), fill factor (FF), photoelectric conversion efficiency (η), and other photovoltaic device characteristics were measured, and the average value was determined. Table 3 summarizes the results of the photovoltaic device characteristics.

However, the photovoltaic device characteristics are standardized by the values of Comparative Example 3 described later.

(Comparative Example 3) Light scattering layer 7 in Example 3
In other words, 200 pieces of 10 cm square so-called CdS / CdTe photovoltaic devices were produced in the same procedure as in Example 3 without providing 02.

In the same manner as in Example 3, the characteristics of the photovoltaic device were measured, and the average value was obtained.

As is clear from Table 3, the short-circuit current (Jsc) was improved and the photoelectric conversion efficiency (η) was improved by the photovoltaic device of the present invention in which the light scattering layer having the uneven structure was formed in the surface protective layer. Improved.

[0182]

[Table 3] Example 4 A further example of the photovoltaic device of the present invention shown in FIG.

FIG. 8 shows an example of a photovoltaic device of the present invention using polycrystalline silicon as a semiconductor layer.

In FIG. 8, 801a, 801b, 80
1c, 801d, 801e, and 801f are surface protective layers, and the upper transparent materials 801a, 801c, and 80 are classified according to their functions.
1e and filling layers 801b, 801d, 801f. 802a and 802b are light scattering layers; 803 is an antireflection layer or a transparent electrode which also serves as an antireflection layer;
a and 804b are polycrystalline silicon semiconductor substrates;
4a is a portion converted to the conductivity type opposite to that of the semiconductor substrate. 806 is a back electrode, 808 is a back filling layer, 8
Reference numeral 11 denotes a support that also serves as a back surface protection layer, and 812 denotes a back surface passivation layer of the semiconductor substrate.

First, a 150 μm-thick p-type polycrystalline silicon substrate formed by a casting method is prepared.
After cleaning the surface of the substrate, the surface 804a was converted to an n ⁺ type by ion implantation to form a pn junction.

Next, a 5 nm thick passivation layer of SiO ₂ (not shown) was formed on the surface of the polycrystalline silicon substrate on which the pn junction was formed.

Next, the thickness 2 is formed on the back surface of the polycrystalline silicon substrate.
A passivation layer of 00 nm of Si ₃ N ₄ was formed.

Next, current collecting electrodes 805 and back electrodes 806 of Ti and Ag were formed on the front and back surfaces of the polycrystalline silicon substrate on which the passivation layer was formed.

Next, the transparent electrode 803 also serving as an anti-reflection layer
Then, Ta ₂ O ₅ was formed to a thickness of 0.2 μm at a substrate temperature of 200 ° C. using a DC magnetron sputtering apparatus similar to that shown in FIG.

On the other hand, Ta ₂ O ₅ was formed at a substrate temperature of 200 ° C. to a thickness of 3.0 μm on a polyimide film having a thickness of 30 μm by the same DC magnetron sputtering apparatus as in FIG.

Thereafter, Ta ₂ O ₅ was etched with acetic acid diluted to 5% with water for 120 seconds, and Rmax was 1.5 μm
A degree of uneven structure was formed on the surface, and a light scattering layer was formed.

Next, an Al plate support 811 having a thickness of 1 mm was prepared.
On top, a photovoltaic device formed up to the transparent electrode, two polyimide films on which Ta ₂ O ₅ having irregularities on the surface were formed, and a PVF film as the upper transparent material 801a were formed on the top. EV as filling layer between
A was applied and affixed. At this time, extraction electrodes (not shown) were formed at the ends of the current collecting electrode 805 and the back electrode 806.

Then, the whole was heated at 150 ° C. for 1 hour to cure the EVA, thereby completing the photovoltaic device of the present invention shown in FIG.

Through the above steps, 50 polycrystalline silicon photovoltaic devices of 10 cm square shown in FIG. 8 were manufactured.

The parallel resistance is 1 kΩ / cm ^2.
The above photovoltaic device was illuminated with a solar simulator at 25 ° C. by a solar simulator at AM 1.5 and 100 mw / cm ² to open voltage (Voc) and short circuit current (J).
sc), fill factor (FF), photoelectric conversion efficiency (η), and other photovoltaic device characteristics were measured, and the average value was determined. Table 4 summarizes the results of the photovoltaic device characteristics.

However, the photovoltaic device characteristics are standardized by the values of Comparative Example 5 described later.

Comparative Example 4 The procedure of Example 4 was repeated except that the light-scattering layer 802b was not provided, and only one light-scattering layer was used.
Fifty corner polycrystalline silicon photovoltaic devices were fabricated.

In the same manner as in Example 4, the characteristics of the photovoltaic device were measured, and the average value was obtained.

Comparative Example 5 Fifty polycrystalline silicon photovoltaic devices of 10 cm square were manufactured in the same manner as in Example 4 except that the light scattering layers 802a and 802b were not provided. Produced.

In the same manner as in Example 4, the characteristics of the photovoltaic device were measured, and the average value was obtained.

As is clear from Table 4, the short-circuit current (Jsc) was improved and the photoelectric conversion efficiency (η) was improved by the photovoltaic device of the present invention in which the light scattering layer having the uneven structure was formed in the surface protective layer. Improved. Further, by using two light scattering layers, the short-circuit current (Jsc) was further improved, and the photoelectric conversion efficiency (η) was improved.

[0202]

[Table 4] Example 5 A further example of the photovoltaic device of the present invention was manufactured in the following steps.

This embodiment is an example of a photovoltaic device according to the present invention in which in the photovoltaic device having the structure shown in FIG. 8, unevenness is provided on both front and back surfaces of the light scattering layer, and single crystal GaAs is used as the semiconductor layer. .

First, an n-type GaAs wafer having a thickness of 200 μm was prepared, and an n-type GaAs layer doped with sulfur (S) was formed to a thickness of 5.0 μm by MOCVD.
Next, by MOCVD, Zn-doped p
A type GaAs layer was formed 5.0 μm, a Zn-doped p-type AlGaAs layer was formed 0.15 μm, and a Zn-doped p-type GaAs layer was formed 0.5 μm in this order to form a pn junction.

Next, a 75 nm thick anti-reflection layer of Si ₃ N ₄ (not shown) was formed on the surface of the GaAs wafer on which the pn junction was formed.

Next, on the back surface of the GaAs wafer, a thickness of 20
A 0 nm passivation layer of Si ₃ N ₄ was formed.

Next, the Ga on which the passivation layer was formed was formed.
A current collecting electrode 805 and a back electrode 806 of Ti and Ag were formed on the front and back surfaces of the As wafer.

On the other hand, PET is hot-melted and applied to a stainless steel plate having a surface with irregularities of about 5 μm in Rmax, then cooled and peeled off from the stainless steel sheet, and irregularities of about 2.0 μm in Rmax are formed on the surface. A PET film was formed.

Then, Mg was applied to the PET film at a substrate temperature of 120 ° C. by reactive ion plating.
F ₂ was formed at ₂ μm. Thereafter, dry etching was performed by plasma of a mixed gas of NF ₃ and O ₂ , thereby forming irregularities of 0.6 μm in Rmax on the surface of MgF ₂ . Thereby, MgF having irregularities on both front and back surfaces
_Two light scattering layers were formed.

Next, an Al plate support 811 having a thickness of 1 mm was prepared.
On top of this, a photovoltaic device formed up to the collecting electrode, and _two PET films on which MgF ₂ having irregularities on the surface are formed, and a PV, which is an upper transparent material 801a, is formed on the top.
EVA was applied and attached as a filling layer between the F films. At this time, extraction electrodes (not shown) were formed at the ends of the current collecting electrode 805 and the back electrode 806.

Then, the whole was heated at 150 ° C. for 1 hour to cure the EVA, thereby completing the photovoltaic device of the present invention shown in FIG.

Through the above steps, 20 GaAs photovoltaic devices having a diameter of 3 inches were manufactured.

Then, the parallel resistance is 1 kΩ / cm ²
The above photovoltaic device was irradiated at 25 ° C. with a solar simulator at AM 1.5, 100 mW / cm ² simulated sunlight, and the open circuit voltage (Voc) and short circuit current (J
sc), fill factor (FF), photoelectric conversion efficiency (η), and other photovoltaic device characteristics were measured, and the average value was determined. Photovoltaic device characteristics such as photoelectric conversion efficiency (η) were measured, and the average value was determined.

Table 5 summarizes the results of the characteristics of the photovoltaic device.

However, the characteristics of the photovoltaic device are standardized by the values of Comparative Example 7 described later.

(Comparative Example 6) In Example 5, a GaAs light beam having a diameter of 3 inches was produced in exactly the same procedure as in Example 5 except that only one light scattering layer was provided without providing the light scattering layer 802b. Twenty electromotive devices were produced.

In the same manner as in Example 5, the characteristics of the photovoltaic device were measured, and the average value was obtained.

Comparative Example 7 Twenty GaAs photovoltaic devices having a diameter of 3 inches were produced in the same manner as in Example 5 except that the light scattering layers 802a and 802b were not provided. did.

In the same manner as in Example 5, the characteristics of the photovoltaic device were measured, and the average value was obtained.

As is clear from Table 5, the short-circuit current (Jsc) was improved and the photoelectric conversion efficiency (η) was improved by the photovoltaic device of the present invention in which the light scattering layer having the uneven structure was formed in the surface protective layer. Improved. Further, by using two light scattering layers, the short-circuit current (Jsc) was further improved, and the photoelectric conversion efficiency (η) was improved.

[0221]

[Table 5]

[0222]

As described above, according to the first to fourth aspects of the present invention, the refractive index is provided in the surface protective layer on the light incident side.
Has a material different from the surface protective layer, and is provided with a light scattering layer having an uneven structure, so that light incident on the photovoltaic device is scattered in the surface protective layer, and then the semiconductor layer , The optical path length in the semiconductor layer is extended, the light absorption by the semiconductor layer is increased, the short-circuit current is increased, and the photoelectric conversion efficiency can be improved.

According to the fifth aspect of the present invention, if a plurality of light scattering layers having the uneven structure are formed in the surface protective layer, the scattering of incident light is further increased, and the light emitted by the semiconductor layer is further increased. And the short circuit current increases, and the photoelectric conversion efficiency of the photovoltaic device can be further improved.

According to the present invention , the difference between the refractive index of the substance forming the light scattering layer and the refractive index of the substance forming the surface protective layer is set to 0.1 or more. Since the scattering of incident light increases, the absorption of light by the semiconductor layer increases, the short-circuit current increases, and the photoelectric conversion efficiency can be further improved.

Further, according to the invention of claim 7, the light incident on the photovoltaic device is scattered on both the incident side and the reflection side, and the light absorption by the semiconductor layer is further increased, and the short-circuit current is thereby reduced. It is possible to realize an increase and an improvement in photoelectric conversion efficiency.

In general, according to the present invention, the optical path length in the semiconductor layer increases, and the absorption of light by the semiconductor layer increases, so that the thickness of the semiconductor layer can be reduced. Therefore, for example, when an amorphous semiconductor is used as the semiconductor layer, generation of light-induced defects in the semiconductor layer is suppressed, and reduction in the photoelectric conversion efficiency of the photovoltaic device due to light irradiation (so-called light degradation) is suppressed. Is done.

Further, for example, when a crystalline semiconductor is used as the semiconductor layer, the thickness of the semiconductor substrate can be reduced to reduce the weight of the photovoltaic device, and the reduction of the semiconductor material can reduce the manufacturing cost. Can contribute.

[Brief description of the drawings]

FIG. 1 is a conceptual schematic diagram of a photovoltaic device according to the present invention.

FIG. 2 is a sectional view showing an example of the photovoltaic device of the present invention.

FIG. 3 is a cross-sectional view of an example of a manufacturing apparatus for forming a light scattering layer of the photovoltaic device of the present invention.

FIG. 4 is a schematic view of an example of the photovoltaic device of the present invention.

FIG. 5 is a graph showing the spectral sensitivity of an example of the photovoltaic device of the present invention.

FIG. 6 is a sectional view showing another example of the photovoltaic device of the present invention.

FIG. 7 is a sectional view showing still another example of the photovoltaic device of the present invention.

FIG. 8 is a sectional view showing still another example of the photovoltaic device of the present invention.

[Explanation of symbols]

101,201,601,701,801 Surface protection layer 102,202,602,702,802 Light scattering layer 103,203,603,703,803 Transparent electrode 104,204,604,704,804 Semiconductor layer 105,205, 605, 805 Current collecting electrodes 106, 206, 606, 706, 806 Back electrode (light reflecting layer) 107, 207, 607, 707 Substrate 108, 208, 608, 808 Back protective layer 209, 609 Transparent conductive layer 210, 610 Insulation Layer 611 Support 301 Vacuum container 302 Support 303 Heating plate 304 Thermocouple 305 Temperature controller 306 Heater 307 Heat transfer plate 308 Substrate 309 Substrate holding 310 Target 311 Target base 312 Magnet 313 Cooling water introduction pipe 314 Sputter power supply 31 The light incident surface 402 out electrode of the high-frequency power source 316, 317 the mass flow controllers 318 gauge 319 main valve 320 plasma space 401 photovoltaic device

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Matsuda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yuzo Koda 3-30-2 Shimomaruko, Ota-ku, Tokyo (72) Inventor Naoto Okada 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-62-247574 (JP, A) JP-A-62-209872 ( JP, a) JitsuHiraku flat 3-57952 (JP, U) patent 2756050 (JP, B2) (58 ) investigated the field (Int.Cl. ^7, DB name) H01L 31/04 H01L 31/042

Claims (7)

(57) [Claims] 1. A semiconductor layer photovoltaic device surface protective layer are laminated on the light incident side of and in the surface protective layer has a material that is different from the refractive index of the surface protective layer, A photovoltaic device, wherein at least one light scattering layer having an uneven structure is formed. 2. The photovoltaic device according to claim 1, wherein the light scattering layer has a concavo-convex structure on a surface side with respect to a light incident direction. 3. The photovoltaic device according to claim 1, wherein the light scattering layer has a concavo-convex structure on a back surface side with respect to a light incident direction. 4. The photovoltaic device according to claim 1, wherein the light scattering layer has a concavo-convex structure on both sides of a front surface and a back surface with respect to a light incident direction. 5. The photovoltaic device according to claim 1, wherein the concave-convex structure has a surface roughness Rmax between 0.05 μm and 100 μm. apparatus. 6. A according claim 1, the difference between the refractive index of the material forming the light-scattering light layer and the refractive index of the material forming the surface protective layer is equal to or less than 0.1 Item 6. The photovoltaic device according to any one of items 5 to 5. 7. A light-scattering light-reflecting layer is formed on a side of the semiconductor layer opposite to a light-incident light side. Photovoltaic device.