JP2001308354A - Stacked solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stacked solar cell that has balanced photocurrent densities of an upper photoelectric conversion layer and a lower photoelectric conversion layer at high values and has high photoelectric conversion efficiency by improving reflection characteristics of an intermediate layer so that the reflectance becomes high with light in a short wavelength region and that the reflectance becomes low with light in a long wavelength region. SOLUTION: This stacked solar cell is a solar cell obtained by stacking a plurality of photoelectric conversion layers made of semiconductor. Intermediate layers are interposed between the respective photoelectric conversion layers to electrically connect these photoelectric conversion layers in series. The intermediate layer is a multilayer film constituted by laminating two or more materials alternately and has a characteristic of reflecting light in a specific wavelength region selectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stacked solar cell, and more particularly to a low-cost, high-efficiency silicon tandem solar cell applicable to a photosensor and the like.

[0002]

2. Description of the Related Art A photoelectric conversion device that directly converts sunlight into electricity by using a semiconductor or other internal photoelectric effect is called a solar cell. At present, monocrystalline silicon, polycrystalline silicon, amorphous silicon solar cells and the like having a single junction are used according to various uses on the ground.

[0003] In order to further reduce the cost of the power supply, it is necessary to further increase the efficiency. However, in order to fundamentally improve the efficiency, a thin-film silicon (tandem type) is used.
This is one of the research directions for improving the efficiency of solar cells. Stacked solar cells are composed of a low energy bandgap semiconductor material such as crystalline silicon, which absorbs light on the short wavelength side with an upper photoelectric conversion layer made of a high energy bandgap semiconductor material such as amorphous silicon. The lower photoelectric conversion layer absorbs light on the long wavelength side to effectively use incident light.

Normally, in a single-junction PIN amorphous silicon solar cell, the reflectivity of the back electrode made of Ag or Al reaches about 95 to 98%, and the short-circuit photocurrent density is about 16 to 19 mA. / Cm ² are obtained. The short-circuit photocurrent density of a crystalline silicon solar cell having a single junction is about 32 to 41 mA / cm ² , but when a thin-film silicon solar cell is stacked on top, the light is transmitted without being absorbed by the upper photoelectric conversion layer. Approximately 19 to 27
Generates a short-circuit photocurrent density of mA / cm ² .

[0005] However, the short-circuit photocurrent density of the entire stacked solar cell is limited to the smaller short-circuit photocurrent density of the short-circuit photocurrent densities of the upper photoelectric conversion layer and the lower photoelectric conversion layer. Therefore, when PIN-A-N amorphous silicon is used for the upper photoelectric conversion layer and crystalline silicon is used for the lower photoelectric conversion layer and these are connected in series, the short-circuit photocurrent density generated in each photoelectric conversion layer can be balanced. This has caused a problem that the improvement in photoelectric conversion efficiency is hindered.

When PIN amorphous silicon is used for the upper photoelectric conversion layer, as a means for improving the photoelectric conversion efficiency, it is conceivable to increase the thickness of the I-type amorphous silicon to increase the amount of absorbed light. However, since the film quality of the I-type amorphous silicon is insufficient, the film thickness is naturally limited to about 5000 ° or less. Therefore, light larger than the optical band gap of the I-type amorphous silicon cannot be completely absorbed, and there is a limit to improving the photoelectric conversion efficiency of the upper photoelectric conversion layer depending on the thickness of the I-type amorphous silicon.

As a method for solving such a problem, a transparent conductive film is inserted as an intermediate layer between an upper photoelectric conversion layer and a lower photoelectric conversion layer, and this film is used to cover a short wavelength region of incident light. There is known a method of balancing short-circuit photocurrent density by selectively reflecting light to an upper photoelectric conversion layer and improving the photoelectric conversion efficiency of the upper photoelectric conversion layer.

However, as described in JP-A-59-96777, this film is directly connected without inserting the film between the upper and lower photoelectric conversion layers without considering the reflection characteristics of the transparent conductive film. Also, the short-circuit photocurrent density cannot be balanced, and improvement in photoelectric conversion efficiency cannot be expected.

Japanese Patent Application Laid-Open No. 60-35580 discloses a film thickness of 1000 to 1500 between the upper and lower photoelectric conversion layers.
The ITO film of Å is inserted. The reflection characteristic of this ITO film is as shown in FIG. 6, and the incident light amount can be conveniently increased to the upper photoelectric conversion layer on the light incident side, but the incident light amount decreases extremely to the lower photoelectric conversion layer. Problem arises.

As described in JP-A-63-77167, the thickness of the ITO film is 100 to 200.
Even if it is 0 °, it is impossible to effectively use light. In particular, in the case of the ITO film having a film thickness of 600 ° described in the embodiment, its reflection characteristics become broad, and the long wavelength sensitivity of the lower photoelectric conversion layer is also greatly reduced, so that light cannot be effectively used.

In addition, JP-A-61-127847, JP-A-62-84570, and JP-A-63-68.
No. 82 discloses a similar solution,
In any case, although the reflectivity for light in the short wavelength region is not sufficient, the reflectivity for light in the long wavelength region is conversely increased.

Further, Japanese Patent Application Laid-Open No. 2-237172 discloses that the thickness of the ITO film is set to about 2500 °,
It is shown that the peak of the reflectance is brought near the wavelength of about 600 nm. The reflection characteristic of this ITO film is as shown in FIG.
Even at around 0 nm, the reflectance is only about 40%, so that the amount of light incident on the upper photoelectric conversion layer cannot be increased significantly. Further, there is a problem that the reflectance for light in a long wavelength region is still large.

That is, as in the prior art, the intermediate layer is composed of a single transparent conductive film and has an optimum selective reflection characteristic for a stacked solar cell, no matter how much the material and film thickness are optimized. Can not get.

Further, in the second embodiment of Japanese Patent Application Laid-Open No. 2-237172, a silicon dioxide film having an opening (thickness: 3100 °) is used as an intermediate layer, and the opening is filled with amorphous / microcrystalline silicon. Indicates that the upper and lower photoelectric conversion layers are connected in series. However, it does not describe how to selectively fill the opening with amorphous / microcrystalline silicon.
Even if it could be done, the process would be quite complicated and insignificant from an industrial production point of view.

[0015] Also, the second solar power generation world conference (2nd
WORLD CONFERRE-NCE AND E
XHIBITION ON PHOTOVOLTAIC
SOLAR ENERGY CONVERSION, J
uly, 1998, VIENNA, AUSTRIA)
A report from the University of Neuchatel in Switzerland (pp.
In 728-731), even if a transparent conductive film (ZnO) whose film thickness is optimized is inserted between the upper amorphous silicon photoelectric conversion layer and the lower polycrystalline thin film photoelectric conversion layer, even if it is a flat surface, short-circuit current does not increase only 0.7 mA / cm ^2, also, even for textured surface 2.0 mA / cm
It was found that only ² improved.

As described above, in order to improve the power generation efficiency in a stacked solar cell, it is important to balance the short-circuit photocurrent densities of the upper photoelectric conversion layer and the lower photoelectric conversion layer. However, in the case of a conventional laminated solar cell using a transparent conductive film such as TCO or ZnO for the intermediate layer, the short-circuit photocurrent density of the upper photoelectric conversion layer is only about 12 to 14 mA / cm ² , but the lower photoelectric conversion layer is lower. The conversion layer generated a short-circuit photocurrent density of about 19 to 26 mA / cm ² only by incident light transmitted through the upper photoelectric conversion layer. For this reason, in the conventional stacked solar cell, the short-circuit photocurrent densities of the upper photoelectric conversion layer and the lower photoelectric conversion layer cannot be balanced, and the photoelectric conversion efficiency of the entire stacked solar cell is limited.

That is, the reflection characteristics of the intermediate layer are such that the upper photoelectric conversion layer has a high reflectance for light in a short wavelength region that is easily absorbed by the lower photoelectric conversion layer and has a low reflectance for light in a long wavelength region that is easily absorbed by the lower photoelectric conversion layer. Is an important issue for improving the photoelectric conversion efficiency of the stacked solar cell.

The present invention has been made in view of the above-described circumstances, and has an advantage in that the reflection characteristics of the intermediate layer are high for light in the short wavelength region and high for light in the long wavelength region. The object of the present invention is to provide a stacked solar cell having a high photoelectric conversion efficiency in which the short-circuit photocurrent densities of the upper photoelectric conversion layer and the lower photoelectric conversion layer are balanced by a high value by improving the reflectance to a low value.

[0019]

SUMMARY OF THE INVENTION The present invention relates to a solar cell having a plurality of photoelectric conversion layers made of a semiconductor, and an intermediate layer interposed between the photoelectric conversion layers and electrically connecting the photoelectric conversion layers in series. Is provided, and the intermediate layer is a multilayer film formed by alternately laminating two or more materials, and has a characteristic of selectively reflecting light in a specific wavelength region. It is intended to provide a stacked solar cell.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION A stacked solar cell according to the present invention comprises an upper photoelectric conversion layer in which a plurality of photoelectric conversion layers are each formed of amorphous silicon having a PIN structure, a single crystal silicon and a polycrystalline silicon. Or the lower photoelectric conversion layer formed of microcrystalline silicon, and the intermediate layer has a high reflectance for light in a wavelength region that can be absorbed by the upper photoelectric conversion layer and has a high reflectance for light in a wavelength region that cannot be absorbed by the upper photoelectric conversion layer. It has a reflection characteristic such that the ratio becomes low.

With this configuration, P-I-
While selectively reflecting light in a short wavelength region that can be absorbed by the N-amorphous silicon upper photoelectric conversion layer, light in a long wavelength region that can be absorbed by the crystalline silicon lower photoelectric conversion layer can be transmitted. Therefore, it is possible to increase the amount of light absorbed by the upper photoelectric conversion layer while minimizing the decrease in the amount of light transmitted to the lower photoelectric conversion layer, and as a result, it is possible to improve the photoelectric conversion efficiency of the stacked solar cell.

Further, in the stacked solar cell according to the present invention, the intermediate layer is formed by stacking a first film and a second film, and the first film has a lower refractive index than the second film, and the first film has a lower refractive index. May be provided on the upper photoelectric conversion layer side, and the second film may be provided on the lower photoelectric conversion layer side.

Further, the stacked solar cell of the present invention may have a structure in which the intermediate layer has two or more layers in which the first film and the second film are alternately stacked. Specifically, a first film is formed on the surface of the lower photoelectric conversion layer, a second film is stacked thereon, and the first film is further stacked on the second film, in this order, Finally, it is preferable that the first film be the surface of the intermediate layer, that is, the surface in contact with the back surface of the upper photoelectric conversion layer.

Further, the laminated solar cell of the present invention has a first
IT whose film is a transparent conductive film and contains conductive impurities
It may be formed of any of O, ZnO, TiO ₂ , SnO ₂ and SiO ₂ .

Further, the laminated solar cell of the present invention has a
The film may be a transparent conductive film of the same material as the first film. The second film is in any one of a polycrystalline state, a microcrystalline state, and a mixed state of amorphous and microcrystalline, and is formed of silicon or silicon carbon containing conductive impurities. Semiconductor film.

With this configuration, the transparent conductive film and the semiconductor film constituting the intermediate layer are both films containing conductive impurities, and the upper photoelectric conversion layer and the lower photoelectric conversion layer are connected in series. The electrical loss of the stacked solar cell can be reduced while easily achieving the same. Further, series resistance loss, which is technically difficult due to the cell configuration, can be easily reduced, and the photoelectric conversion efficiency can be further improved.

Further, the laminated solar cell of the present invention has a first
30-74 nm-thick Zn containing conductive impurities
O, and the second film has a thickness of 10 to 10 containing a conductive impurity.
It may be 35 nm polycrystalline silicon.

Further, in the stacked solar cell according to the present invention, the first film in contact with the upper photoelectric conversion layer has a Z content containing a conductive impurity.
It may be formed of nO.

Since the ZnO film is less susceptible to plasma damage, such a configuration minimizes damage to the intermediate layer when forming the amorphous silicon upper photoelectric conversion layer.

Further, in the stacked solar cell of the present invention, the first film not in contact with the upper photoelectric conversion layer may be formed of any one of ITO, SnO ₂ and TiO ₂ . That is, the first film in contact with the upper photoelectric conversion layer has a Z
It is preferable that the first film is nO, but the other first film does not necessarily have to be ZnO.

Further, in the stacked solar cell of the present invention, the first and second films constituting the intermediate layer may be formed by a sputtering method.

Here, a method of calculating the selective reflectance of the multilayer structure will be described. The calculation formula is O.D. S He-vens, “Opt
ical properties of Thin S
o-lid Films ", Butterworths
An ordinary calculation formula as described in Science (1955) is used. The reflectance R (λ) of the multilayer film in the case of normal incidence can be calculated by the following formulas 1 to 3.

[0033]

(Equation 1)

[0034]

(Equation 2)

[0035]

(Equation 3)

Where M_jIs the characteristic line of the uniform j-th layer monolayer
Columns, M is the characteristic matrix of the homogeneous multilayer, m ₁₁, M₁₂, M_{twenty two}Is each
Diagonal element of the product matrix of the characteristic matrix corresponding to the layer, η₀, Η
_{l + 1}And η_jDenotes the medium on the incident side, silicon and the j-th layer film.
Effective refractive index, multiple refractive index N for absorptive medium
_j= N_j-IK may be replaced. δ_j= (2π /
δ) N_jd_jAnd d_jIs the thickness of the j-th layer film.

FIG. 2 shows reflectance data of an intermediate layer having a two-layer structure in which a ZnO film having a thickness of 71 nm and a polycrystalline silicon film having a thickness of 31 nm are calculated based on the above formula. As shown in FIG. 2, the reflection characteristics of this intermediate layer are:
It shows a high reflectance for light in a short wavelength region of about 700 nm or less, and its reflectance peak is about 87%.
The reflectance for light in the long wavelength range of 0 to 1200 nm is as low as about 11% or less. As the number of layers further increases, the reflectance in the short wavelength region increases. For example, if there are three or more layers, the reflectance for light in a short wavelength region of about 700 nm or less is about 90% or more.

FIG. 3 shows reflectance data of an intermediate layer having a four-layer structure in which the ZnO film and the polycrystalline silicon film are alternately laminated, calculated based on the above equation. As shown in FIG. 3, as an intermediate layer of a stacked solar cell having an amorphous silicon upper photoelectric conversion layer and a crystalline silicon lower photoelectric conversion layer, a selective reflection characteristic considered to be most ideal, that is, about 700 nm or less. And reflects light in the short wavelength region and transmits light in the wavelength region of about 700 nm or more.

According to the present invention, as described above, the reflection characteristics of the intermediate layer can be freely set, and the intermediate layer can be optimally selected according to the configuration (polysilicon or microcrystalline material, etc.) of the lower photoelectric conversion layer. It can be of a reflective nature. This is one of the very powerful means for increasing the efficiency of the stacked solar cell.

The reflection characteristics of the intermediate layer of the present invention shown in FIG. 2 and FIG. 3 are set so that the reflectance becomes maximum with respect to light in a short wavelength region around 600 nm. However, the reason for this will be described below.

The amorphous silicon photoelectric conversion layer has a thickness of about 3
Power is generated by absorbing light in the short wavelength region from 00 nm to 750 nm. Amorphous silicon has a very large light absorption coefficient. At a normal film thickness of about 300 nm to 800 nm, light having a very short wavelength in the above-absorbed wavelength range does not reach the intermediate layer. It is absorbed by the silicon photoelectric conversion layer. Therefore, among the light in the wavelength region reaching the intermediate layer, particularly, the light in the wavelength region that contributes to the power generation of the amorphous silicon photoelectric conversion layer, that is, by increasing the reflectance for light in the short wavelength region near the wavelength of about 600 nm, The light absorption amount of the amorphous silicon photoelectric conversion layer can be increased.

When the intermediate layer according to the present invention is used, the reflectivity for light that can be absorbed by the upper photoelectric conversion layer is greatly improved to about 90% or more, so that the photoelectric conversion efficiency of the upper photoelectric conversion layer is further improved. Can be. In addition, since the reflectance of light in a wavelength region that cannot be absorbed by the upper photoelectric conversion layer can be suppressed to a low level, the amount of light transmitted to the lower photoelectric conversion layer does not significantly decrease. With these effects, the short-circuit photocurrent density of the upper photoelectric conversion layer can be improved, and the decrease of the short-circuit photocurrent density of the lower photoelectric conversion layer can be minimized. The short-circuit photocurrent density can be balanced at a high value. Therefore, the photoelectric conversion efficiency of the stacked solar cell is improved.

In the case of an amorphous silicon solar cell, the film quality is not sufficient.
The structure of N is used. The photoelectric conversion efficiency of an amorphous silicon solar cell is lower than that of a crystalline solar cell, and a characteristic deterioration phenomenon (a so-called Stellar-Lonski effect) occurs due to light irradiation. The only way to reduce this characteristic degradation phenomenon is to reduce the thickness. However, if the intermediate layer of the present invention is used, a sufficient short-circuit photocurrent density can be obtained even if the I-type layer is thinned, and the Stepler-Lonski phenomenon can be reduced.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments shown in the drawings. The present invention is not limited by the embodiment.

An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a sectional view of a stacked solar cell having an intermediate layer according to the present invention.

As shown in FIG. 1, the stacked solar cell 2
1 is provided with an intermediate layer 5 interposed between the upper and lower photoelectric conversion layers 11 and 12 to electrically connect the upper and lower photoelectric conversion layers 11 and 12 in series, and the intermediate layer 5 is made of two or more materials. It is a multilayer film formed by alternately stacking, and has a characteristic of selectively reflecting light in a specific wavelength region.

Hereinafter, a method of manufacturing the stacked solar cell 21 will be described in detail with reference to FIG. First, in the production of the lower photoelectric conversion layer 12, a crystal plane (100) and a resistivity of 0.1 to
An N-type polycrystalline silicon substrate 3 of 1.0 Ω-cm was used.
The N-type polycrystalline silicon substrate 3 is made alkaline (NH ₄ OH:
H ₂ O ₂ : H ₂ O = 1: 1: 5) and acidic (HCl:
After washing with a chemical solution (H ₂ O ₂ : H ₂ O = 1: 1: 5) at 80 ° C. for 30 minutes, the surface layer is protected with a coating solution and then the back surface of the N-type polycrystalline silicon substrate 3 The thickness is about 0.3 μm by thermal diffusion on the side, and the impurity concentration is about 10 ²⁰ cm.
^-3 N-type polycrystalline silicon layer 2 was formed.

After the surface silicon oxide of the N-type polycrystalline silicon layer 2 is removed, a three-layer metal electrode 1 made of Ti, Pd and Ag is deposited and annealed in a nitrogen atmosphere. Thereafter, a thin P-type microcrystalline silicon film 4 (or a P-type amorphous silicon film) was formed on the surface side of the N-type polycrystalline silicon substrate 3 to form a lower photoelectric conversion layer 12 having a heterojunction structure.

Thereafter, a ZnO film and a polycrystalline silicon film are formed on the lower photoelectric conversion portion 12 by a sputtering method (D
C) to form an intermediate layer 5 alternately. For more information,
First, the first layer counted from the lower photoelectric conversion layer 12 is argon (Ar) and oxygen (O 2) in a chamber of a sputter deposition apparatus.
₂ ) and a degree of vacuum of about 6 × 10 ^-3
While controlling to about Torr, ZnO with a thickness of about 71 nm
A film was formed. Next, the second layer is a chamber in the same sputter deposition apparatus and has a film thickness of about 31 n containing phosphorus as an impurity.
An m-type N-type polycrystalline silicon film was formed.

Thereafter, the same lamination is repeated to form a ZnO film having a thickness of about 71 nm as a third layer, a polycrystalline silicon film having a thickness of about 31 nm as a fourth layer, and a polycrystalline silicon film having a thickness of about 7 nm as a fifth layer.
A 1 nm ZnO film, a polycrystalline silicon film having a thickness of about 31 nm as a sixth layer, and a Zn film having a thickness of about 71 nm as a seventh layer.
O films were stacked to form an intermediate layer 5 having a multilayer structure consisting of seven layers.

Thereafter, annealing was performed in a nitrogen atmosphere at about 200 ° C. using the same chamber of the sputter deposition apparatus. Thereafter, the upper photoelectric conversion layer 11 was formed on the intermediate layer 5 by a plasma CVD method. Specifically, the substrate temperature is about 1
About 50-180 ° C, pressure of film forming chamber is about 0.3 Torr
r, energy supplied to the plasma is about 30 mW / cm
² and the source gases are SiH ₄ (silane), H ₂
(High-purity hydrogen), B ₂ H ₆ (diborane) and PH ₃ (phosphine) using an N-type hydrogenated amorphous silicon layer 6 and an I-type hydrogenated amorphous silicon layer 7 (thickness of about 30).
0 nm) and a P-type hydrogenated amorphous silicon layer 8 were formed.

Thereafter, a transparent conductive film 9 made of ITO and having a thickness of about 107 nm was deposited by a sputtering method. Further, the surface collector electrode 10 made of Ag was formed by electron beam evaporation, and the stacked solar cell 21 was completed.

As described above, in this embodiment, the intermediate layer having the seven-layer structure is used. However, in the wavelength region (about 450 to 650 nm) that can be absorbed by the upper photoelectric conversion layer 11, the reflectance is about 90% or more. On the other hand, the reflectance for light in a long wavelength region of about 700 nm or more can be kept low,
The incident light was selectively reflected and used effectively. By these effects, the short-circuit photocurrent density of the upper photoelectric conversion layer 11 is improved, and the decrease in the short-circuit photocurrent density of the lower photoelectric conversion layer 12 is minimized.
Each of the short-circuit photocurrent densities of No. 1 and the lower photoelectric conversion layer 12 could be brought close to an equilibrium state.

As a result, the photocurrent density of the entire stacked solar cell 21 is increased from the conventional value of about 12 to 13 mA / cm ² to about 16
１８18 mA / cm ^2, and the photoelectric conversion efficiency of the stacked solar cell 21 was greatly improved from the conventional value of about 12% to about 16-18%.

In this embodiment, ZnO is used as the material of the first film. However, if the material is conductive and has high transparency, the film thickness can be optimized for each material.
Materials other than ZnO can be used. For example, ITO,
Similar effects can be obtained even when SnO ₂ , SiO ₂ and tantalum oxide (TiO ₂ ) are used.

However, since the upper photoelectric conversion layer 11 made of amorphous silicon is formed by high-frequency plasma as described above, it is at least the surface of the intermediate layer 5 in consideration of exposure to hydrogen plasma after the formation of the intermediate layer 5. The first film is desirably formed of a material mainly composed of ZnO (zinc dioxide) having excellent hydrogen plasma resistance.

Although polycrystalline silicon is used as the material of the second film, any material having a low light absorption coefficient having conductivity can be used by optimizing the film thickness. For example, the same effect can be obtained by using amorphous silicon or silicon carbon in an amorphous or microcrystalline state.

In this embodiment, the number of the stacked photoelectric conversion layers is two. However, even when the number of the stacked photoelectric conversion layers is three, the same effect can be obtained by using the intermediate layer according to the technical concept of the present invention. To play. Further, in this embodiment, although N-type polycrystalline silicon is used for the lower photoelectric conversion layer, the same effect can be obtained by using P-type single crystal silicon. That is, in this embodiment, the PIN-PN structure is used from the light incident side.
The same applies to the NP structure.

[0059]

According to the present invention, since the intermediate layer is composed of a multilayer film, the reflectance of the intermediate layer is maximized with respect to light in a short wavelength region that can be absorbed by the upper photoelectric conversion layer. In addition, for light in a long wavelength region that cannot be absorbed by the upper photoelectric conversion layer, it is possible to have a reflection characteristic such that the reflectance is reduced, and the short-circuit photocurrent density of each of the upper photoelectric conversion layer and the lower photoelectric conversion layer is reduced. A stacked solar cell with high photoelectric conversion efficiency balanced at a high value can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a stacked solar cell according to an embodiment of the present invention.

FIG. 2 is a graph showing reflection characteristics of a two-layer intermediate layer in which a ZnO film and a polycrystalline silicon film are stacked.

FIG. 3 is a graph showing reflection characteristics of a four-layer intermediate layer in which a ZnO film and a polycrystalline silicon film are stacked.

FIG. 4 is a graph showing respective reflection characteristics of a conventional intermediate layer made of an ITO film having a thickness of 1000 ° and an intermediate layer made of an ITO film having a thickness of 1500 °.

FIG. 5 is a graph showing the reflection characteristics of a conventional intermediate layer made of an ITO film having a thickness of 2500 °.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Three-layer metal electrode 2 ... N-type polycrystalline silicon layer 3 ... N-type polycrystalline silicon substrate 4 ... P-type microcrystalline silicon film 5 ... Intermediate layer 6 ... N-type Hydrogenated amorphous silicon layer 7 ... I-type hydrogenated amorphous silicon layer 8 ... P-type hydrogenated amorphous silicon layer 9 ... Transparent conductive film 10 ... Surface collecting electrode 11 ... Top photoelectric conversion layer 12 ... Lower photoelectric conversion layer 21 ... Stacked solar cell

Claims (11)

[Claims] In a solar cell in which a plurality of photoelectric conversion layers made of a semiconductor are stacked, an intermediate layer is provided between the photoelectric conversion layers to electrically connect the photoelectric conversion layers in series. A multilayer solar cell, which is a multilayer film formed by alternately laminating two or more materials, and has a characteristic of selectively reflecting light in a specific wavelength region. 2. A plurality of photoelectric conversion layers each having a PIN
An upper photoelectric conversion layer formed of amorphous silicon having a structure, and a lower photoelectric conversion layer formed of single crystal silicon, polycrystalline silicon, or microcrystalline silicon,
The intermediate layer has a reflection characteristic such that the reflectance for light in a wavelength region that can be absorbed by the upper photoelectric conversion layer is high and the reflectance for light in a wavelength region that cannot be absorbed by the upper photoelectric conversion layer is low. 2. The stacked solar cell according to 1. 3. The intermediate layer is formed by laminating a first film and a second film. The first film has a lower refractive index than the second film, and the first film is provided on the upper photoelectric conversion layer side. And the second film is provided on the lower photoelectric conversion layer side.
3. The stacked solar cell according to item 1. 4. The stacked solar cell according to claim 3, wherein the intermediate layer has a configuration of two or more layers in which first films and second films are alternately stacked. 5. The first film according to claim 3, wherein the first film is a transparent conductive film and is made of any of ITO, ZnO, TiO ₂ , SnO ₂ and SiO ₂ containing a conductive impurity. Or the laminated solar cell according to 4. 6. The stacked solar cell according to claim 3, wherein the second film is a transparent conductive film made of the same material as the first film. 7. The semiconductor device according to claim 7, wherein the second film is in any one of a polycrystalline state, a microcrystalline state, and a state in which amorphous and microcrystalline are mixed, and contains silicon containing conductive impurities.
The stacked solar cell according to claim 3, wherein the stacked solar cell is a semiconductor film formed of any one of silicon carbon. 8. A film having a thickness of 3 in which the first film contains a conductive impurity.
The stacked solar cell according to claim 3, wherein the second solar cell is ZnO having a thickness of 0 to 74 nm, and the second film is polycrystalline silicon having a thickness of 10 to 35 nm containing a conductive impurity. 9. The stacked solar cell according to claim 4, wherein the first film in contact with the upper photoelectric conversion layer is formed of ZnO containing a conductive impurity. 10. The first film which is not in contact with the upper photoelectric conversion layer is I
The laminated solar cell according to claim 4, wherein the laminated solar cell is formed of any one of TO, SnO _2, and TiO ₂ . 11. The stacked solar cell according to claim 3, wherein the first and second films constituting the intermediate layer are formed by a sputtering method.