JP2002222972A - Laminated solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated solar battery having a plurality of photoelectric conversion layers laminated so that the conversion layers are electrically connected in series with each other to improve a conversion efficiency by balancing output currents of the respective conversion layers. SOLUTION: The laminated solar battery comprises an intermediate layer 4 made of a transparent conductive film provided between photoelectric conversion layers 3 and 5. A light transmittance of a single layer 4 is in a range of 80 to 95% in a range of 700 to 1,100 nm of a wavelength.

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 solar cell in which a plurality of photoelectric conversion layers are stacked and the photoelectric conversion layers are electrically connected in series.

[0002]

2. Description of the Related Art As a laminated solar cell of this type, photoelectric conversion layers made of materials having different band gaps are laminated,
It is known that they are electrically connected in series (for example, JP-A-1-289173). In this stacked solar cell, a photoelectric conversion layer made of amorphous silicon having a large band gap is arranged on the light incident side (upper), and a photoelectric conversion layer made of crystalline silicon having a small band gap is arranged below. Light energy in a wider wavelength range is efficiently extracted. That is, in semiconductor materials, the forbidden band width (Eg)
Only photons having the above energies are absorbed, and photons having an energy lower than Eg are transmitted and lost. However, the energy (hν) of the absorbed photon is Eg
If it is larger than the above, the energy corresponding to (hv-Eg) is absorbed by the semiconductor lattice and becomes thermal energy,
Since it cannot be electrically extracted outside, the utilization efficiency of the absorbed energy deteriorates. Therefore, by arranging a plurality of semiconductor materials in order of Eg from the light incident side, energy loss is reduced, and light is more efficiently used.

Generally, in such a stacked solar cell, the output current of the photoelectric conversion layer on the light incident side (upper) is smaller than the output current of the lower photoelectric conversion layer, and the output current of the entire solar cell is increased. Tend to be limited.

In Japanese Patent No. 2738557, in order to match the output current between the respective photoelectric conversion layers and maximize the output current of the entire solar cell, two band gaps having a smaller forbidden band width in order from the light incident side are disclosed. There has been proposed a device provided with an intermediate layer made of a transparent conductive film (in this publication, the expression "selective reflection film" is used) between photoelectric conversion layers. In this stacked solar cell, by optimally selecting the thickness of the selective reflection film, the reflectance of the surface of the selective reflection film is maximized in the wavelength region where the light incident side photoelectric conversion layer has the maximum photosensitivity, and In the wavelength range where the photoelectric conversion layer can absorb, the reflectance of the surface of the selective reflection film is reduced. Thereby, the output current of each photoelectric conversion layer can be adjusted to be equal, and the output current of the entire solar cell can be optimized.

[0005]

However, in the above proposal for the stacked solar cell, only a material having a high light transmittance is selected as a material for the intermediate layer, and no further consideration is given. . Therefore, as proposed by the applicant of the present invention in Japanese Patent Application No. 2000-164988, irregularities (maximum height difference of 50) are formed on the intermediate layer in order to improve the characteristics.
nm to 800 nm, more preferably 80 nm to 400 n
As a result of the formation of m), when a certain thickness (at least the maximum height difference or more) of the intermediate layer is required, the light absorption of the intermediate layer itself cannot be ignored, and the output current balance between the photoelectric conversion layers must be balanced. There is a problem that cannot be taken. That is, the increase in the light absorption of the intermediate layer itself causes the current taken out of the stacked solar cell to the outside not to be limited by the short-circuit current value of the photoelectric conversion layer on the light incident side, but to the reverse of the light incident side. It is limited by the short-circuit current value of the photoelectric conversion layer on the side.

Accordingly, an object of the present invention is to provide a stacked solar cell capable of improving the conversion efficiency by balancing the output current between the photoelectric conversion layers.

[0007]

Means for Solving the Problems To achieve the above object, a laminated solar cell according to the present invention comprises a laminated solar cell in which a plurality of photoelectric conversion layers are laminated and the photoelectric conversion layers are electrically connected in series. In the battery, an intermediate layer made of a transparent conductive film is provided on at least one or more of the photoelectric conversion layers, and the light transmittance of this intermediate layer as a single film is from 700 nm to 11 nm.
It is characterized by being in the range of 80% to 95% in the region of 00 nm.

[0008] The stacked solar cell of the present invention includes an intermediate layer made of a transparent conductive film in at least one or more layers between the photoelectric conversion layers.
Since it is within the range of 80% to 95% in the region of m to 1100 nm, the output current between the photoelectric conversion layers can be balanced. Next, the reason will be described.

I) FIG. 4 shows a single-layer light transmittance of an intermediate layer formed on a glass substrate and a laminate having the intermediate layer (having the same composition) between two photoelectric conversion layers. 2 shows a correlation with a short-circuit current density (maximum output current) of a solar cell. The thickness of the intermediate layer corresponding to each data (represented by the symbol ◆) in FIG. 4 is about 350 nm, and the light transmittance of each intermediate layer is changed depending on the film forming conditions. As can be seen from FIG. 4, when the light transmittance of the intermediate layer is 80% or more, the short-circuit current density is at a high level and hardly changes. That is, the output current of the stacked solar cell is limited by the short-circuit current density of the photoelectric conversion layer on the light incident side (upper side), and is not significantly affected by the light transmittance of the intermediate layer. On the other hand, the light transmittance of the intermediate layer is 8
When it becomes 0% or less, the short-circuit current density becomes small.
When the light transmittance of the intermediate layer decreases and the amount of light received by the photoelectric conversion layer on the side (lower) opposite to the light incident side decreases,
Since the output current is limited by the short-circuit current density of the lower photoelectric conversion layer, the output current of the stacked solar cell decreases as the transmittance decreases.

Ii) In a stacked solar cell, generally, the photoelectric conversion layers are arranged from the light incident side in the descending order of the band gap. Since the region smaller than the wavelength of 700 nm is the light absorption region of the photoelectric conversion layer on the light incident side, the light transmittance of the intermediate layer does not significantly affect the characteristics of the stacked solar cell. In the region of wavelength 1200 nm or more,
Since absorption by the lower photoelectric conversion layer becomes difficult, the characteristics of the stacked solar cell are not significantly affected.

Iii) In view of the specific resistance required for the intermediate layer, it is difficult to increase the light transmittance of a single film to more than 95%. This is because if the specific resistance of the intermediate layer is too large, the characteristics are reduced due to an increase in the series resistance between the photoelectric conversion layers.

For these reasons, according to the stacked solar cell of the present invention, the output current between the photoelectric conversion layers can be balanced. Therefore, the conversion efficiency can be improved.

The "photoelectric conversion layer on the light incident side" refers to a photoelectric conversion layer disposed on the light incident side of the intermediate layer when the laminated solar cell is used.

In one embodiment of the present invention, the interlayer solar cell is characterized in that the specific resistance of the intermediate layer is in the range of 3 × 10 ⁻⁴ Ωcm to 10 Ωcm.

The intermediate layer serves as a series resistance component between the photoelectric conversion layers. Generally speaking, the lower the specific resistance of the intermediate layer, the better. Actually, as shown in the data of FIG. 5, when the specific resistance of the intermediate layer becomes 10 Ωcm or more, the fill factor of the stacked solar cell decreases due to the influence of the series resistance component. On the other hand, when the specific resistance of the intermediate layer is smaller than 10 Ωcm,
It hardly affects the solar cell characteristics. Considering the light transmittance required for the intermediate layer, 3 × 10 ⁻⁴ Ωcm
Choosing smaller materials is very difficult. For these reasons, it is desirable that the specific resistance of the intermediate layer be in the range of 3 × 10 ⁻⁴ Ωcm to 10 Ωcm.

In one embodiment, at least one of the plurality of photoelectric conversion layers includes a supporting material for supporting the remaining photoelectric conversion layers.

In the stacked solar cell of this embodiment, at least one photoelectric conversion layer supports the remaining photoelectric conversion layers. Thereby, mechanical strength is obtained.

In one embodiment of the present invention, the intermediate layer has irregularities on the light incident side surface, and the photoelectric conversion layer on the light incident side is formed so as to reflect the irregularities. I do.

Here, "irregularities" does not mean a fixed shape but a predetermined surface roughness that scatters sunlight.

In the stacked solar cell of this embodiment, the intermediate layer has irregularities on the light incident side surface, and the photoelectric conversion layer on the light incident side is formed so as to reflect the irregularities. In addition to suppressing multiple reflections in the incident-side photoelectric conversion layer and reducing surface reflectance in a long wavelength region, the optical path length in the light-incident-side photoelectric conversion layer is lengthened to increase the amount of light absorbed in the photoelectric conversion layer. Can be increased (light confinement effect). Therefore, the short-circuit current density of the light incident side photoelectric conversion layer can be improved, and the output current density can be improved. Actually, the maximum height difference of the irregularities is 200 nm.
The maximum short-circuit current density can be obtained when the thickness is up to 400 nm.

In one embodiment, the stacked solar cell is characterized in that the intermediate layer contains zinc oxide.

As the material of the intermediate layer, ITO (material containing several weight% of tin in indium oxide) or tin oxide (S
nO ₂ ), etc., but considering that the intermediate layer is exposed to hydrogen plasma in the photoelectric conversion layer forming step after the formation of the intermediate layer, a material containing zinc oxide excellent in hydrogen plasma resistance is particularly desirable. .

In one embodiment of the stacked solar cell, the intermediate layer is formed by depositing a transparent conductive film in an atmosphere containing 0.1% to 5.0% oxygen by a sputtering method. It is characterized by being formed by processing the surface into an uneven shape.

When a transparent conductive film is deposited by a sputtering method to form an intermediate layer, 0.1% to 5.
It is desirable to deposit in an atmosphere containing 0% oxygen. By mixing oxygen into the film, the transmittance in the infrared region can be increased. However, the specific resistance increases as the oxygen content increases. Wavelength 700nm ~ 1100
In order to obtain an intermediate layer having a transmittance of 80% to 95% and a specific resistance of 3 × 10 ⁻⁴ Ωcm to 10 Ωcm in the region of nm, the oxygen content of 0.1% to 5.0% is required. It is desirable to deposit by sputtering in an atmosphere.

In one embodiment of the stacked solar cell, the intermediate layer is formed by depositing a transparent conductive film by sputtering.
After annealing in an atmosphere of oxygen or air at a temperature of from 00 ° C. to 500 ° C., the transparent conductive film is formed by processing the surface into an uneven shape.

In order to form an intermediate layer, a transparent conductive film is deposited by a sputtering method,
It is desirable to perform annealing in oxygen at 0 ° C. or in an air atmosphere. When a transparent conductive film is deposited in an atmosphere containing no oxygen, it is difficult to obtain a sufficient transmittance as an intermediate layer as it is. However, by performing annealing in oxygen or air after the deposition, a sufficient transmittance can be obtained. FIG. 6 shows a single film before and after annealing when a 450-nm-thick zinc oxide film is deposited as a transparent conductive film on a glass substrate and then annealed in an air atmosphere at 500 ° C. for 1 hour. The light transmittance is shown. From FIG. 6, it can be seen from FIG.
It can be seen that the light transmittance is 80% or less in the range of 100 nm, but the light transmittance is 80% or more in the wavelength range of 700 nm to 1100 nm after annealing. It is considered that the reason for this is that the carrier concentration in the film was reduced by performing the annealing. That is, it is known that oxygen deficiency or excess zinc acts as a donor in zinc oxide, but annealing in oxygen or air supplies oxygen into the film and reduces the carrier concentration. When zinc oxide containing a dopant is deposited as a transparent conductive film, neutralization of the dopant (positive ion) by annealing also causes a decrease in carrier concentration. The specific resistance after annealing of each film represented by the data in FIG. 5 is 2.5 × 10 ⁻³ Ωcm,
There is no problem as a material for the intermediate layer. When the film represented by the data in FIG. 5 is annealed in oxygen or air atmosphere at 300 ° C. to 500 ° C., the wavelength is 700 nm to 1100 nm.
It was confirmed that the effect that the light transmittance was 80% or more in the range of nm was obtained.

In one embodiment of the present invention, the unevenness on the light incident side surface of the intermediate layer is formed by etching.

In the stacked solar cell of this embodiment, the unevenness on the light incident side surface of the intermediate layer can be easily formed without depositing a transparent conductive film as a material so thickly.
Therefore, it is possible to reduce the thickness of the intermediate layer (transparent conductive film) and improve the light transmittance of the intermediate layer as a single film.

In one embodiment of the present invention, the intermediate layer is formed by sputtering in an atmosphere containing 0.1% to 60% of water.

When zinc oxide is used as the material of the intermediate layer, the intermediate layer is formed by a sputtering method at 0.1% to 6%.
Desirably, it is formed in an atmosphere containing 0% water. The orientation is disturbed by forming a film in a water-containing atmosphere, and as a result, a film having irregularities on the surface is formed with a thickness that is about half that of a film formed in an atmosphere containing no water. can do. In such a case, the specific resistance of the film tends to increase as compared with the case where no water is contained, but it falls within a range suitable for use as an intermediate layer of the stacked solar cell. That is, a wavelength of 700 nm to 1100 n
m, the transmittance is 80% to 95%, and the specific resistance is 3
An intermediate layer having a thickness of ^10-4 ? Cm to 10? Cm is obtained. In addition, in this case, since the unevenness on the light incident side surface of the intermediate layer is formed simultaneously with the film formation, it is not necessary to perform processing such as etching after the film formation.

When the number of photoelectric conversion layers is large, the open-circuit voltage value of the stacked solar cell, which is determined by the sum of the open-circuit voltage values of the photoelectric conversion layers, improves, but is substantially limited by the short-circuit current value. No significant improvement in current value can be expected. Therefore, in order to obtain the maximum conversion efficiency, it is desirable that the number of photoelectric conversion layers is two.

Therefore, the laminated solar cell of one embodiment is
A supporting substrate, a first electrode layer, a first photoelectric conversion layer containing crystalline silicon, an intermediate layer, a second photoelectric conversion layer made of amorphous silicon, and a second electrode layer, in this order, Light is incident from the second electrode layer side.

In one embodiment, the stacked solar cell comprises a support substrate, a first electrode layer, a first photoelectric conversion layer containing amorphous silicon, an intermediate layer, and a second layer made of crystalline silicon. A photoelectric conversion layer and a second electrode layer are provided in this order, and light is incident from the support substrate side.

[0034] In one embodiment, the stacked solar cell comprises a first electrode layer and a first electrode layer including a crystalline silicon substrate as a supporting material.
A photoelectric conversion layer, an intermediate layer, and a second layer made of amorphous silicon.
A photoelectric conversion layer and a second electrode layer are provided in this order.

In the stacked solar cell of this embodiment, the remaining elements such as the photoelectric conversion layer are supported by the first photoelectric conversion layer including the crystalline silicon substrate as the supporting material. Thereby, mechanical strength is obtained.

In one embodiment of the present invention, the crystalline silicon substrate is a polycrystalline silicon substrate or a monocrystalline silicon substrate.

If the crystalline silicon substrate included in the first photoelectric conversion layer is a polycrystalline silicon substrate or a single crystal silicon substrate, the conversion efficiency of the first photoelectric conversion layer is high.
Therefore, the conversion efficiency of the entire stacked solar cell is increased.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a laminated solar cell according to the present invention will be described in detail with reference to the illustrated embodiments.

(First Embodiment) FIG. 1 schematically shows a sectional structure of a laminated solar cell according to a first embodiment. In this stacked solar cell, a first electrode layer 2 is provided on a support substrate 1,
A first photoelectric conversion layer 3, an intermediate layer 4 having a texture (unevenness) on a surface 4a, a second photoelectric conversion layer 5, and a second electrode layer 6
And the comb-shaped electrode 7 are stacked in this order. Here, the irradiation light 9 indicates the light to be irradiated when measuring the solar cell characteristics.

This laminated solar cell is manufactured as follows.

First, a glass substrate is prepared as the substrate 1. The substrate 1 may be made of a material such as glass, metal, ceramic, silicon, or film, or a material obtained by depositing a metal film or an insulating material on these materials. In this example, a glass substrate (705 manufactured by Corning Incorporated) is used.
9) is used.

Next, the glass substrate 1 is washed with pure water. Subsequently, silver and zinc oxide (Zn) as a material of the first electrode layer 2 were formed on one surface of the substrate 1 by electron beam evaporation.
O) is deposited so that the surface side is flat without irregularities. When depositing this silver, the substrate temperature is set to 180 ° C., and pure silver as a target is irradiated with an electron beam to deposit a film having a thickness of 100 nm. Further, in the deposition of ZnO, the substrate temperature was set to 220 ° C. and oxygen was supplied for 42 seconds.
The electron beam is irradiated on ZnO as a target by flowing the electron beam to a thickness of 50 nm to deposit a film having a thickness of 50 nm. The material of the first electrode layer 2 may be a metal or a conductive metal oxide film, or may be a single layer or a composite layer thereof. The method for forming the first electrode layer 2 may be a MOCVD (metal organic chemical vapor deposition) method, a sputtering method, a spray method, or the like.

Next, n, i, and p-type crystalline silicon thin films are successively deposited on the first electrode layer 2 using a parallel plate type plasma CVD apparatus to form a first photoelectric conversion layer 3. .
In forming the first photoelectric conversion layer 3, the substrate 1 and a cathode (a target (not shown)) are heated while the substrate 1 is heated.
And a high frequency power is applied between them to generate plasma.
In this example, the conditions for forming the n, i, and p layers constituting the first photoelectric conversion layer 3 were as shown in Table 1 below. The surface of the first photoelectric conversion layer 3 is flat without any irregularities.

[Table 1]

Next, the intermediate layer 4 is formed on the first photoelectric conversion layer 3.
To form As a material of the intermediate layer 4, in addition to zinc oxide (ZnO), ITO (indium oxide is several weight%
Tin-containing material), tin dioxide (SnO ₂ ), etc., but ZnO, which is particularly excellent in plasma resistance, is desirable.
Further, this ZnO is made of gallium (Ga), aluminum (Al), boron (B), indium (In), scandium (Sc), silicon (Si), titanium (T
i), a mixture of dopants such as zirconium (Zr) may be used. The intermediate layer 4 can be formed by a sputtering method, a vacuum evaporation method, or the like. In this example, ZnO containing gallium was deposited as a material of the intermediate layer 4 by a sputtering method. In this film formation, in a sputtering apparatus,
While the substrate 1 was heated to 200 ° C., the oxygen partial pressure was 0.1
% To 5.0%, the pressure (total pressure) is set to 0.8 Pa, and a DC bias of 500 V is applied between the substrate 1 and the cathode (not shown). At this time, ZnO films having different transmittances and specific resistances can be deposited by variably setting the oxygen partial pressure within the range of 0.1% to 5.0%. In the case where the film is formed in an atmosphere containing no oxygen, the film is formed at a temperature of 3 ° C.
If annealing is performed in oxygen or air atmosphere at a temperature of 00 ° C. to 500 ° C., an intermediate layer having the same transmittance and specific resistance can be obtained. Subsequently, in order to form irregularities on the surface of the intermediate layer 4, a 0.5% by weight acetic acid aqueous solution is used as an etchant, and wet etching is performed on the surface of the intermediate layer 4 for a predetermined time (this is referred to as “irregular etching”). ). As a result, irregularities can be formed on the surface 4a of the intermediate layer 4, that is, roughness can be provided. As an etching solution, an acidic solution such as a hydrochloric acid solution or an alkali solution can be used in addition to the acetic acid solution. The method of forming the irregularities on the surface of the intermediate layer 4 is not limited to wet etching, and other processing methods such as dry etching can be adopted. As an example, when the film thickness before and after the uneven etching is 500 nm and the uneven etching time is 150 seconds, the height difference of 250 nm
Irregularities were formed.

In order to form the intermediate layer 4, zinc oxide may be formed using a sputtering apparatus in an atmosphere containing 0.1% to 60% of water. In an atmosphere containing no water, 1.2 μm to 2 μm
Although a film thickness of μm is required, when the film is formed in an atmosphere containing water, unevenness with a height difference of 200 to 400 nm is generated on the surface with a film thickness of about 0.5 μm to 0.7 μm. As an example, an RF power having a power density of 4.0 W / cm ² is applied between a substrate and a cathode (a target made of zinc oxide doped with aluminum) at a pressure of 2.7 Pa in an argon atmosphere containing 50% of water. Apply, substrate temperature 30
When a film was formed at a setting of 0 ° C. and a deposited film thickness of 0.6 μm, irregularities having a height difference of 300 nm were formed on the surface. At this time, the transmittance was 82% in the wavelength region of 700 nm to 1100 nm, and the specific resistance was 1.3 × 10 ⁻² Ωcm. In such a case, since irregularities are formed on the surface during film formation, it is not necessary to perform surface processing such as irregularity etching after the film formation.

Next, the surface 4a has irregularities (texture).
The n, i, p-type amorphous silicon thin film is continuously deposited on the intermediate layer 4 having the above by using a parallel plate type plasma CVD apparatus, and a second photoelectric conversion layer as a light incident side photoelectric conversion layer is formed. 5 is formed. As a material of the second photoelectric conversion layer 5, amorphous silicon having a wider band gap than crystalline silicon was employed. This is because amorphous silicon has a wider band gap than that of crystalline silicon and is therefore suitable as a material for the light incident side photoelectric conversion layer of the stacked solar cell. The surface roughness of the second photoelectric conversion layer 5 after this film formation reflects the roughness of the surface 4a of the intermediate layer 4. In this example, the second
The conditions for forming the n, i, and p layers constituting the photoelectric conversion layer 5 were as shown in Table 2 below.

[Table 2]

The material of the second photoelectric conversion layer 5 is n
Instead of the type or p-type amorphous silicon, n-type and p-type microcrystalline silicon may be used.

Next, a second electrode layer 6 is formed on the second photoelectric conversion layer 5. The second electrode layer 6 is formed by depositing ITO to a thickness of 60 nm by a sputtering method. In forming this film, the substrate 1 was heated at 220 ° C. in a sputtering apparatus.
In the state of heating, oxygen was flowed at a flow rate of 1.5 sccm, argon was flowed at a flow rate of 250 sccm, and the gas pressure was 3.8 Pa.
And the substrate 1 and cathode (target not shown)
And a DC bias of 450 V is applied. The surface roughness of the second electrode layer 6 after the film formation reflects the surface roughness of the second photoelectric conversion layer 5. Thereby, reflection on the surface of the stacked solar cell can be reduced, and a light confinement effect can be obtained.

Next, a comb electrode 7 is formed on the second electrode layer 6. The interdigital electrode 7 is formed by depositing silver by electron beam evaporation.
It is formed to a thickness of 00 nm. In forming the comb-shaped electrode 7, an electron beam is irradiated to an evaporation source made of pure silver while the substrate 1 is heated to 180 ° C. in an evaporation apparatus, and silver is selectively applied to the substrate surface using a metal mask. Evaporate.
By using a low-resistance material such as silver as the material of the comb-shaped electrode 7, the current collecting capability of the second electrode layer 6 can be complemented, and current collection can be performed more efficiently. Examples of the method for forming the comb-shaped electrode 7 include a sputtering method and the like in addition to the vacuum evaporation method.

The following Table 3 shows that the stacked solar cell “Invention 1” manufactured in this manner was subjected to AM from the second electrode layer 6 side.
The results of measuring solar cell characteristics (short-circuit current density, open-circuit voltage, fill factor, and conversion efficiency) by applying irradiation light 8 of −1.5 and 100 mW / cm ² are shown together with the results of the comparative example. In addition, "Invention 1" in Table 3 has a light transmittance of the intermediate layer of 83% and a specific resistance of 4.0 × 10 ⁻³ Ωcm, and “Comparative Example 1” has a light transmittance of the intermediate layer of 70%. %, Specific resistance is 3.1
× 10 ⁻⁴ Ωcm, “Comparative Example 2” is a measurement result of the intermediate layer having a light transmittance of 94% and a specific resistance of 15 Ωcm. Other conditions of Comparative Examples 1 and 2 are the same as those of “Invention 1”. The relationship between the light transmittance of the intermediate layer and the short-circuit current density of the stacked solar cell shown in FIG. 4 and the relationship between the specific resistance of the intermediate layer and the fill factor of the stacked solar cell shown in FIG. Are also obtained by this measurement.

[Table 3]

As can be seen from Table 3, in the stacked solar cell "Invention 1" of this embodiment, the conversion efficiency of the entire solar cell is higher than those of Comparative Examples 1 and 2. The reason for this is as described above with reference to FIG.
In Comparative Example 1, the light transmittance of the intermediate layer is 80% or more, and the short-circuit current density is high. On the other hand, in Comparative Example 1, the light transmittance of the intermediate layer is only 70%, and the short-circuit current density is reduced. Because. Further, as described above with reference to FIG. 5, in “Invention 1”, the specific resistance of the intermediate layer is less than 10 Ωcm, so that the characteristics of the solar cell are hardly affected. The specific resistance of the layer is 10Ω
cm or more, the fill factor of the stacked solar cell decreases due to the influence of the series resistance component.

Thus, high conversion efficiency can be obtained when the light transmittance of the intermediate layer is 80% or more and the specific resistance is 10 Ωcm or less as in “Invention 1”.

(Second Embodiment) FIG. 2 schematically shows a sectional structure of a stacked solar cell according to a second embodiment. In this stacked solar cell, a first electrode layer 22 and a first photoelectric conversion layer 23 are provided on one side of a support substrate 21 which becomes a front panel during use.
, An intermediate layer 24 having irregularities on the surface 24a, a second photoelectric conversion layer 25, and a second electrode layer 26 are stacked in this order. Here, the irradiation light 29 indicates the light to be irradiated when measuring the solar cell characteristics.

This laminated solar cell is manufactured as follows.

First, a glass substrate having an insulating property and a light transmitting property is prepared as the supporting substrate 21. Although a film substrate having an insulating property and a light-transmitting property can be used, in this example, a glass substrate (available from Corning 705) is used.
9) is used.

Next, the glass substrate 21 is washed with pure water.
Subsequently, ZnO as the first electrode layer 22 is deposited on one surface of the glass substrate 21 by sputtering so that the surface side is flat without any irregularities. In forming this film, the substrate 21 was heated at 200 ° C. in a sputtering apparatus.
, The pressure (total pressure) is set to 0.8 Pa, and a predetermined DC bias is applied between the substrate 1 and the cathode (target not shown). This film formation method may be a vacuum evaporation method, an MOCVD method, a spray method, or the like. Further, as a material of the first electrode layer 22, a material such as ITO and SnO ₂ may be used in addition to ZnO.

Next, an n, i, and p-type amorphous silicon thin film is continuously deposited on the first electrode layer 22 using a parallel plate type plasma CVD apparatus to form a light incident side photoelectric conversion layer. Of the first photoelectric conversion layer 23 is formed. First photoelectric conversion layer 23
As the material of the above, amorphous silicon having a wider band gap than crystalline silicon was employed. This is because amorphous silicon has a wider band gap than that of crystalline silicon and is therefore suitable as a material for the light incident side photoelectric conversion layer of the stacked solar cell. In this example, the conditions for forming the n, i, and p layers constituting the first photoelectric conversion layer 23 are as shown in Table 2 of the first embodiment.
The settings were the same as those shown in. This first photoelectric conversion layer 2
The surface of No. 3 is flat without any irregularities.

Next, on the first photoelectric conversion layer 23, using the same method and conditions as those for forming the intermediate layer 4 in the first embodiment,
An intermediate layer 24 is formed. As a material of the intermediate layer 24, in addition to zinc oxide (ZnO), ITO (a material containing several weight% of tin in indium oxide), tin dioxide (SnO)
₂ ), etc., but ZnO which is particularly excellent in plasma resistance
Is desirable. Further, this ZnO is made of gallium (Ga).
And aluminum (Al), boron (B), indium (In), scandium (Sc), silicon (Si),
What mixed the dopants, such as titanium (Ti) and zirconium (Zr), may be used. The intermediate layer 24 can be formed by a sputtering method, a vacuum evaporation method, or the like. In this example, ZnO containing gallium was deposited as a material of the intermediate layer 24 by a sputtering method. In this film formation, in a sputtering apparatus, while the substrate 21 is heated to 200 ° C., oxygen and argon are flowed so that the oxygen partial pressure becomes 0.1% to 5.0%, and the pressure (total pressure) is increased. Is set to 0.8 Pa, and the substrate 21
500 V between the cathode and the target (not shown)
DC bias is applied. At this time, 0.1% to 5.
By setting the oxygen partial pressure variably within the range of 0%, ZnO films having different transmittances and specific resistances can be deposited. If the film is formed in an atmosphere containing no oxygen,
If annealing is performed in oxygen or air atmosphere at a temperature of 300 ° C. to 500 ° C. after the film formation, an intermediate layer having the same transmittance and specific resistance can be obtained. Subsequently, in order to form irregularities on the surface of the intermediate layer 24, an etching solution of 0.5
By using a weight% acetic acid aqueous solution, the surface of the intermediate layer 24 is subjected to uneven etching for a predetermined time. As a result, irregularities can be formed on the surface 24a of the intermediate layer 24, that is, roughness can be provided. As an etching solution, an acidic solution such as a hydrochloric acid solution or an alkali solution can be used in addition to the acetic acid solution. The method for forming the irregularities on the surface of the intermediate layer 24 is not limited to wet etching, and other processing methods such as dry etching can also be adopted. As described in the first embodiment, when the film thickness before and after the uneven etching is 500 nm and the uneven etching time is 150 seconds, the height difference 25
The unevenness of 0 nm was formed.

Next, a second photoelectric conversion layer 25 is formed on the intermediate layer 24 by continuously depositing n, i, and p-type crystalline silicon thin films using a parallel plate type plasma CVD apparatus.
In this example, n, i, p forming the second photoelectric conversion layer 25
The conditions for forming the layers were set the same as those shown in Table 1 of the first embodiment. The surface roughness of the second photoelectric conversion layer 25 after this film formation reflects the surface roughness of the intermediate layer 24.

After that, silver and zinc oxide (ZnO) are deposited on the second photoelectric conversion layer 25 by an electron beam evaporation method to form a second electrode layer 26. When depositing this silver, the substrate temperature is set to 180 ° C., and pure silver as a target is irradiated with an electron beam to deposit a film having a thickness of 100 nm. Further, in the deposition of ZnO, the substrate temperature is set to 220 ° C., oxygen is flowed at 42 sccm, and the target ZnO is irradiated with an electron beam to deposit the target to a thickness of 50 nm. As a material of the second electrode layer 26, a metal or a conductive metal oxide film may be used, and a single layer or a composite layer thereof may be used. The method for forming the second electrode layer 26 is as follows.
An MOCVD (metal organic chemical vapor deposition) method, a sputtering method, a spray method, or the like may be used. The surface roughness of the second electrode layer 25 after the film formation reflects the surface roughness of the second photoelectric conversion layer 25. Thereby, reflection on the surface of the stacked solar cell can be reduced, and a light confinement effect can be obtained.

The following Table 4 shows that the laminated solar cell “Invention 2” manufactured in this manner was evaluated for A
The results of measuring solar cell characteristics (short-circuit current density, open-circuit voltage, fill factor, and conversion efficiency) by applying irradiation light 28 of M-1.5 and 100 mW / cm ² are shown together with the results of the comparative example. In addition, "Invention 2" in Table 4 has a light transmittance of the intermediate layer of 83% and a specific resistance of 4.0 × 10 ^-3 Ωcm, and "Comparative Example 3" has a light transmittance of the intermediate layer of 70. %, The specific resistance is 3.1 × 10 ⁻⁴ Ωcm, and “Comparative Example 4” is the measurement result of the intermediate layer having the light transmittance of 94% and the specific resistance of 15 Ωcm. Other conditions of Comparative Examples 3 and 4 are the same as those of "Invention 2".

[Table 4]

As can be seen from Table 4, in the stacked solar cell “Invention 2” of this embodiment, the conversion efficiency of the entire solar cell is higher than those of Comparative Examples 3 and 4. The reason for this is as described above with reference to FIG.
In Comparative Example 3, the light transmittance of the intermediate layer is high because the light transmittance of the intermediate layer is 80% or more, whereas in Comparative Example 3, the short circuit current density is low because the light transmittance of the intermediate layer is only 70%. Because. Further, as described above with reference to FIG. 5, in “Invention 2”, the specific resistance of the intermediate layer is less than 10 Ωcm, so that the characteristics of the solar cell are hardly affected. The specific resistance of the layer is 10Ω
cm or more, the fill factor of the stacked solar cell decreases due to the influence of the series resistance component.

As described above, high conversion efficiency is obtained when the light transmittance of the intermediate layer is 80% or more and the specific resistance is 10 Ωcm or less as in “Invention 2”.

(Third Embodiment) FIG. 3 schematically shows a sectional structure of a laminated solar cell according to a third embodiment. In this stacked solar cell, an intermediate layer 34 having irregularities on the surface 34 a, a second photoelectric conversion layer 35, a second electrode layer 36, and a comb-shaped electrode 37 are formed on the first electric conversion layer 33 including the support substrate. Are stacked in this order. The first electric conversion layer 33 includes an n-type semiconductor substrate as a supporting substrate (hereinafter, described using the same reference numeral 33 as the first electric conversion layer) and a p-type semiconductor layer formed on the surface (upper surface) thereof. (Not shown).
The first electrode layer 32 is formed on the back surface of the n-type semiconductor substrate 33 (the surface opposite to the surface on which the intermediate layer 34 is formed). The irradiation light 39 indicates light to be irradiated when measuring solar cell characteristics.

This stacked solar cell is manufactured as follows.

First, an n-type polycrystalline silicon substrate containing 10 ¹⁷ cm ^{−3 of} phosphorus is prepared as the n-type semiconductor substrate 33. As such an n-type semiconductor substrate, a single crystal silicon substrate can be used.

Next, RCA cleaning (RCA) is performed to remove alkali components and organic substances adhering to the surface of the substrate 33.
(A cleaning method using H ₂ O ₂ , NH ₄ OH and Hcl developed by the company). Then, subsequently, a protective organic material is applied to the back surface of the substrate 33 so that impurities are not diffused, and in this state, p is applied to the surface of the substrate 33 by a thermal diffusion method.
Forming a mold semiconductor layer; Specifically, the n-type semiconductor substrate 33
Is heated in a furnace, and BBr ₃ is used as a diffusion source to diffuse boron into the surface region of the n-type semiconductor substrate 33 to form a p-type semiconductor layer. After that, the organic material for protection is removed from the back surface of the substrate 33 using a predetermined stripper. In order to form the p-type semiconductor layer, a known technique such as a plasma CVD method or an ion implantation method can be used in addition to the gas diffusion method.

Thereafter, the first electrode layer 32 made of silver is formed on the back surface of the n-type semiconductor substrate 33 by the electron beam evaporation method. In addition, the material of the first electrode layer 32 may be a metal or an alloy such as titanium, aluminum, and palladium. It is also possible to use a stacked film of these materials. The method for forming the first electrode layer 32 is not limited to the electron beam evaporation method, and a known technique such as a sputtering method can be used.

After the formation of the first electrode layer 32, the intermediate layer 34 is formed in exactly the same manner and under the same conditions as described in the first embodiment.
, A second photoelectric conversion layer 35, a second electrode layer 36, and a comb-shaped electrode 37. Since it is the same as the first embodiment,
A detailed description of the formation of these layers will be omitted. It is to be noted that the materials, forming methods, and the like of these layers can be appropriately changed, as in the case of the first embodiment.

The following Table 5 shows that the laminated solar cell "Invention 3" manufactured in this manner was evaluated for A from the second electrode layer 36 side.
The results of measuring solar cell characteristics (short-circuit current density, open-circuit voltage, fill factor, and conversion efficiency) by applying irradiation light 38 of M-1.5 and 100 mW / cm ² are shown together with the results of the comparative example. In addition, "Invention 3" in Table 5 has a light transmittance of the intermediate layer of 83% and a specific resistance of 4.0 × 10 ⁻³ Ωcm, and “Comparative Example 5” has a light transmittance of the intermediate layer of 70%. %, The specific resistance is 3.1 × 10 ⁻⁴ Ωcm, and “Comparative Example 6” is the measurement result of the intermediate layer having the light transmittance of 94% and the specific resistance of 15 Ωcm. Other conditions of Comparative Examples 5 and 6 are the same as those of “Invention 3”.

[Table 5]

As can be seen from Table 5, in the stacked solar cell “Invention 3” of this embodiment, the conversion efficiency of the entire solar cell is higher than those of Comparative Examples 5 and 6. The reason for this is as described above with reference to FIG.
In Comparative Example 5, the light transmittance of the intermediate layer is only 70% since the light transmittance of the intermediate layer is high because the light transmittance of the intermediate layer is 80% or more, whereas the short circuit current density is low in Comparative Example 5. Because. Further, as described above with reference to FIG. 5, in “Invention 3”, the specific resistance of the intermediate layer is less than 10 Ωcm, so that the characteristics of the solar cell are hardly affected. The specific resistance of the layer is 10Ω
cm or more, the fill factor of the stacked solar cell decreases due to the influence of the series resistance component.

As described above, when the light transmittance of the intermediate layer is 80% or more and the specific resistance is 10 Ωcm or less as in “Invention 3”, high conversion efficiency can be obtained.

In each of the above embodiments, the number of photoelectric conversion layers included in the stack is two. However, the number is not limited to this, and three or more photoelectric conversion layers may be included in the stack. In that case, two or more intermediate layers made of a transparent conductive film may be provided between the photoelectric conversion layers.

[0074]

As is clear from the above, according to the stacked solar cell of the present invention, the output current between the photoelectric conversion layers can be balanced to improve the conversion efficiency.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a structure of a stacked solar cell according to a first embodiment.

FIG. 2 is a diagram schematically illustrating a structure of a stacked solar cell according to a second embodiment.

FIG. 3 is a diagram schematically illustrating a structure of a stacked solar cell according to a third embodiment.

FIG. 4 is a diagram showing the relationship between the light transmittance of an intermediate layer and the short-circuit current density of a stacked solar cell.

FIG. 5 is a diagram showing the relationship between the specific resistance of the intermediate layer and the fill factor of the stacked solar cell.

FIG. 6 is a diagram showing the transmittance of a single film of zinc oxide before and after annealing.

[Explanation of symbols]

 1, 21 Support substrate 2, 22, 32 First electrode layer 3, 23, 33 First photoelectric conversion layer 4, 24, 34 Intermediate layer 5, 25, 35 Second photoelectric conversion layer 6, 26, 36 Second electrode layer 7, 37 Comb electrode 8, 28, 38 Irradiation light

Continued on the front page F term (reference) 4K029 AA06 AA24 BA49 BC07 BD00 CA06 EA05 GA00 GA01 5F051 AA02 AA03 AA05 CA15 CB12 CB13 CB14 CB15 CB21 CB24 CB27 DA04 DA16 DA18 FA02 FA04 FA06 FA13 FA14 GA03 5F103 A0403 RR04

Claims (13)

[Claims] 1. A stacked solar cell in which a plurality of photoelectric conversion layers are stacked and the photoelectric conversion layers are electrically connected in series, wherein at least one or more of the photoelectric conversion layers is formed of a transparent conductive film. A stacked solar cell comprising an intermediate layer, wherein the light transmittance of the single layer of the intermediate layer is in the range of 80% to 95% in the wavelength region of 700 nm to 1100 nm. 2. The stacked solar cell according to claim 1, wherein the intermediate layer has a specific resistance of 3 × 10 ⁻⁴ Ωcm to 10Ωc.
m, wherein the thickness is within the range of m. 3. The stacked solar cell according to claim 1, wherein at least one of the plurality of photoelectric conversion layers includes a support material for supporting the remaining photoelectric conversion layers. Laminated solar cell. 4. The stacked solar cell according to claim 1, wherein the intermediate layer has irregularities on a light incident side surface, and the light incident side photoelectric conversion layer reflects the irregularities. A stacked solar cell characterized by being formed. 5. The stacked solar cell according to claim 1, wherein the intermediate layer contains zinc oxide. 6. The stacked solar cell according to claim 5, wherein the intermediate layer is formed by depositing a transparent conductive film in an atmosphere containing 0.1% to 5.0% oxygen by a sputtering method. A stacked solar cell, wherein a surface of a transparent conductive film is processed into an uneven shape. 7. The stacked solar cell according to claim 5, wherein the intermediate layer is formed by depositing a transparent conductive film by a sputtering method and performing annealing in oxygen or air atmosphere at 300 ° C. to 500 ° C. A stacked solar cell, wherein the surface of the transparent conductive film is processed into an uneven shape. 8. The stacked solar cell according to claim 6, wherein the unevenness on the light incident side surface of the intermediate layer is formed by etching. 9. The stacked solar cell according to claim 5, wherein the intermediate layer is formed in a thickness of 0.1% to 6% by a sputtering method.
A stacked solar cell formed in an atmosphere containing 0% water. 10. The stacked solar cell according to claim 1, wherein the support substrate, the first electrode layer, the first photoelectric conversion layer containing crystalline silicon, the intermediate layer, and the amorphous silicon A second photoelectric conversion layer comprising: and a second electrode layer in this order, wherein light is incident from the second electrode layer side. 11. The stacked solar cell according to claim 1, wherein the support substrate, the first electrode layer, the first photoelectric conversion layer containing amorphous silicon, the intermediate layer, and the crystalline silicon A second photovoltaic layer comprising a second photoelectric conversion layer and a second electrode layer in this order, wherein light is incident from the support substrate side. 12. The stacked solar cell according to claim 3, comprising a first electrode layer, a first photoelectric conversion layer including a crystalline silicon substrate as a support material, an intermediate layer, and amorphous silicon. A stacked solar cell comprising a second photoelectric conversion layer and a second electrode layer in this order. 13. The stacked solar cell according to claim 12, wherein said crystalline silicon substrate is a polycrystalline silicon substrate or a single-crystal silicon substrate.