JPH11298024A - Photovoltaic device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photovoltaic device, with high conversion efficiency and improved durability for light irradiation by forming light-absorbing layer of a photovoltaic element placed in an incidence of light with indium nitride, while light-absorbing layer of another photovoltaic element is composed of crystalline silicon, and a method of manufacturing thereof. SOLUTION: A tandem photovoltaic device consists of a top cell 41 and a bottom cell 31 for their basic structural elements. The bottom cell 31 consists of an n-type or p-type single crystalline or polycrystalline silicon substrate 1, a p-type or n-type single crystalline or polycrystalline silicon layer 2, a surface electrode layer 4 and a backside electrode layer 3. The light-absorbing layer of the photoelectric element is single crystalline or polycrystalline silicon 1. The top cell 41 consists of an n-type or p-type InN layer 6, a p-type or n-type InN layer 7, and a transparent conductive layer 3. The light-absorbing layer of the cell is InN layer 6, and the p-type InN layer contains group II elements. In the top cell placed in an incidence of light, indium nitride is used for the light-absorbing layer, while in the bottom cell, crystalline silicon is used for the light-absorbing layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a so-called tandem-type high-efficiency photovoltaic device in which two photovoltaic elements are stacked, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A photovoltaic device having a so-called tandem type structure in which two different photovoltaic elements are stacked in order to obtain high conversion efficiency by effectively utilizing incident light is known. In general, in the case of such a structure, a semiconductor having a large band gap is used for a light absorbing layer in an element (top cell) near the light incident side, and a semiconductor having a small band gap is used in a distant element (bottom cell).
By doing so, light in the short wavelength region is absorbed by the element (top cell) close to the light incident side, and light in the long wavelength region, which could not be absorbed there, is absorbed by the distant element (bottom cell). Light can be used effectively.

For example, in Japanese Patent Publication No. 6-44638, an n-type amorphous silicon is formed on a p-type polycrystalline silicon substrate to form one photovoltaic element. Further, p-type amorphous silicon, i-type amorphous silicon, Another photovoltaic element is formed by sequentially forming n-type amorphous silicon. The light absorbing layer in each photovoltaic element is p-type polycrystalline silicon and i-type amorphous silicon,
The former band gap is about 1. The light incidence is performed from the amorphous silicon side since leV and the latter is about 1.7 eV.

[0004]

However, a photovoltaic element using amorphous silicon as a light absorbing layer has problems of low conversion efficiency and deterioration due to light irradiation. Had a problem.

To solve this problem, Japanese Patent Laid-Open No. 6-283 is disclosed.
No. 738 discloses that one n-type layer is formed by doping phosphorus on a p-type polycrystalline silicon substrate by a thermal diffusion method to form one photovoltaic element, an electrode is formed, and then p-type Cu (I
Another photovoltaic element is formed by sequentially forming (n, Ga) S ₂ and n-type CdS. The light absorbing layer in each photovoltaic element is made of p-type polycrystalline silicon and p-type Cu (In, Ga) S
₂ , since the former has a smaller band gap than the latter, light is incident from the Cu (In, Ga) S ₂ side. In this case, although there is no problem as described above, one of the light absorbing layers, Cu (In, Ga) S _2, is a multi-component compound, so that the crystallinity, composition, electric characteristics, etc. are optimized. It was difficult to control, and the expected high conversion efficiency was not obtained.

The present invention solves the above problems and provides a tandem-type photovoltaic device with high conversion efficiency. The present invention also provides a high conversion efficiency and a high reliability with excellent durability against light irradiation and the like. It is another object of the present invention to provide a high tandem photovoltaic device, and to provide a low-cost tandem photovoltaic device having high conversion efficiency and a method of manufacturing the same.

[0007]

According to the present invention, first, in a photovoltaic device in which two different photovoltaic elements are stacked, a photovoltaic element disposed on the light incident side is provided. Is characterized in that indium nitride is used as a light absorbing layer and the other photovoltaic element is made of crystalline silicon as a light absorbing layer.

Secondly, in the photovoltaic device described in the first aspect, the photovoltaic element disposed on the light incident side has an indium nitride layer containing at least a group II element. A photovoltaic device is provided.

Third, in the photovoltaic device according to the first or second aspect, the light incident surface of the photovoltaic element disposed on the light incident side is a transparent conductive layer. A photovoltaic device is provided.

Fourth, in the photovoltaic device described in the first, second or third aspect, the carrier concentration is opposite to the light incident surface of the photovoltaic element disposed on the light incident side. 1
A photovoltaic device provided with a layer of 0 ¹⁸ cm ^-3 or more is provided.

Fifthly, in the photovoltaic device described in the first, second, third or fourth aspect, the crystalline silicon is a polycrystalline silicon thin film having a (111) orientation deposited on a seed layer. A photovoltaic device is provided.

Sixth, in the method for manufacturing the photovoltaic device according to the first aspect, the crystalline silicon is formed by forming an amorphous or microcrystalline silicon thin film on a substrate. Irradiating the silicon thin film with a laser beam to form a seed layer, and depositing silicon atoms or silicon compound molecules on the seed layer to form a polycrystalline silicon thin film. A method for manufacturing a device is provided.

Seventh, in the method for manufacturing a photovoltaic device according to the sixth aspect, the formation of the seed layer and the deposition of the polycrystalline silicon thin film thereon are continuously performed in a vacuum. A method for manufacturing a photovoltaic device is provided.

Eighth, in the method for manufacturing a photovoltaic device according to the sixth or seventh aspect, polycrystalline silicon is deposited by depositing silicon atoms or silicon compound molecules while irradiating the surface of the seed layer with an energy beam. There is provided a method for manufacturing a photovoltaic device, comprising forming a thin film.

Hereinafter, the present invention will be described in detail. The present invention relates to a tandem-type photovoltaic device as described above,
A photovoltaic device in which a photovoltaic element (top cell) disposed on the light incident side uses indium nitride as a light absorbing layer and the other photovoltaic element (bottom cell) uses crystalline silicon as a light absorbing layer. Features.

When the light absorption layer of the bottom cell is made of crystalline silicon, the material of the light absorption layer of the top cell has a band gap in the range of 1.5 to 1.9 eV, and the spectral sensitivity spectrum has a long wavelength side. This is preferable because the overlap with the spectral sensitivity spectrum of crystalline silicon is small, and the shift from the sunlight spectrum on the short wavelength side is small, and the light collection efficiency is improved, so that high conversion efficiency can be obtained. Further, it is desirable that the material has a direct transition type band structure because of its large light absorption coefficient, and it is crystalline because of its high carrier mobility. From the viewpoint of easy control of the structure and composition, it is more preferable that the compound is a simple substance or a binary compound.

The present inventors have conducted intensive studies on materials satisfying the above requirements, and as a result, have found that indium nitride is most suitable as a material for the light absorption layer of the top cell, and have reached the present invention. Indium nitride (InN) can easily form a polycrystalline thin film by a reactive sputtering method, a reactive ion plating method, or the like.
The band gap can be changed in the range of 1.8 to 2.0 eV, and the carrier concentration can be changed in the range of 10 ¹⁶ to 10 ²¹ cm ⁻³ . The conductivity type of this film is usually n-type. Also, 1.9e
The absorption coefficient for light from V to 3.0 eV is 10 ⁴ to 10 ⁵
It is as large as cm ^-1 . Further, by using indium nitride, a photovoltaic device excellent in durability against light irradiation can be obtained.

Further, according to the present invention, in the photovoltaic device according to the first aspect, the photovoltaic element (top cell) disposed on the light incident side includes an indium nitride layer containing at least a group II element. It is characterized by having. As described above, since an indium nitride (InN) thin film usually has n-type conductivity, a p-type conductive film that forms a junction with this film is necessary to fabricate a photovoltaic element. As the p-type conduction film, another material having a band gap equal to or greater than that of InN may be used (heterojunction). However, since such a material itself is small and defects are likely to occur at the junction interface, It is desirable to use the same material (homojunction). In
In order to make the N thin film p-type, a group II element serving as an acceptor impurity element may be contained. Thereby, a good bonding interface can be formed, and the conversion efficiency can be improved.

Further, according to the present invention, in the photovoltaic device according to the first or second aspect, the light incident surface of the photovoltaic element (top cell) disposed on the light incident side is a transparent conductive layer. There is a feature. It is preferable that the light incident surface of the photovoltaic device of the present invention functions as an upper electrode having a function of moving generated carriers in the lateral direction and collecting current at the terminal portion. In order to prevent that surface from becoming a series resistance in an equivalent circuit and reducing the short-circuit current of the photovoltaic device,
Sheet resistance is 20Ω / □ or less, more preferably 10Ω
/ □ or less is desirable. Furthermore, in order to effectively introduce light in the spectral sensitivity range of the light absorbing layer (InN layer) of the top cell into the layer, the surface (specifically, 4N) is used.
It is desirable that the film is transparent to light having a wavelength of 00 nm or more. As a result, the short-circuit current increases, and the conversion efficiency can be further improved.

Further, the present invention provides the photovoltaic device according to the first, second or third aspect, wherein the photovoltaic device (top cell) disposed on the light incident side is opposite to the light incident surface. A layer having a carrier concentration of 10 ¹⁸ cm ⁻³ or more on the side. When the light absorbing layer of the top cell is formed directly on the bottom cell, a reverse junction is formed there, and an electromotive force is generated in the opposite direction, so that the voltage taken out decreases. To avoid this, the carrier concentration is high (10 ¹⁸ cm ^-3
It is desirable that the layer is provided so as to be in contact with the light incident surface of the top cell, that is, in contact with the light incident surface of the bottom cell. By doing so, the open-circuit voltage increases, and the conversion efficiency can be further improved.

According to the present invention, there is also provided the photovoltaic device according to the first, second, third or fourth aspect, wherein the crystalline silicon is a (111) -oriented polycrystalline silicon thin film deposited on a seed layer. There is a feature. Since the crystalline silicon is a (111) oriented polycrystalline thin film that is the closest-packed surface of the diamond structure, the number of crystal defects is small, so that photocarriers can be effectively taken out and the conversion efficiency can be further improved. . Further, the material cost can be significantly reduced by thinning.

Here, the (111) orientation means that most of the crystal planes parallel to the substrate surface are (111) planes (in other words, most of the crystal axes perpendicular to the substrate surface are (111) planes). 111) axis). In addition, the majority here means a specific surface with respect to the normalized intensity from the four main diffraction surfaces (111), (220), (311) and (400) found by X-ray diffraction or the like. Means that the intensity ratio is 0.5 or more, which is a ratio of 0.25 when the orientation is completely random.
More than twice.

Furthermore, the present invention is the method for manufacturing a photovoltaic device according to the first aspect, wherein the crystalline silicon is formed by forming an amorphous or microcrystalline silicon thin film on a substrate. The method is characterized by irradiating the silicon thin film with a laser beam to form a seed layer, and depositing silicon atoms or silicon compound molecules on the seed layer to form a polycrystalline silicon thin film. An amorphous or microcrystalline silicon thin film is formed on a substrate, and the silicon thin film is irradiated with a laser beam to form a seed layer. Since the oriented polycrystalline silicon is formed with a large particle size, the particle size of the polycrystalline silicon thin film deposited thereon can be increased, thereby further improving the conversion efficiency.

Further, the present invention is characterized in that in the method of manufacturing a photovoltaic device, the formation of the seed layer and the deposition of the polycrystalline silicon thin film thereon are continuously performed in a vacuum. I do. By continuously performing the formation of the seed layer and the deposition of the polycrystalline silicon thin film thereon in a vacuum,
Since the seed layer and the polycrystalline silicon thin film thereon are not exposed to an oxidizing atmosphere during the manufacturing process, the polycrystalline silicon thin film can be grown with the (111) orientation reflecting the orientation of the seed layer. Since a highly crystalline polycrystalline silicon thin film can be obtained, the conversion efficiency can be further improved.

According to the present invention, in the method of manufacturing a photovoltaic device, silicon atoms or silicon compound molecules are deposited while irradiating the surface of the seed layer with an energy beam to form a polycrystalline silicon thin film. It is characterized by the following. By depositing silicon atoms or silicon compound molecules while irradiating the surface of the seed layer with an energy beam to form a polycrystalline silicon thin film, the (111) -oriented polycrystalline silicon thin film can be formed into large grains even at a low substrate temperature. Since the growth can be performed at the same diameter and the manufacturing temperature can be reduced, the cost of the substrate material, the manufacturing apparatus, and the cost of the photovoltaic device can be reduced.

[0026]

Embodiments of the present invention will be described below. First, a first embodiment of the present invention will be described with reference to FIG. The tandem photovoltaic device of the first embodiment has a top cell 41 and a bottom cell 31 as basic components. The bottom cell 31 includes an n-type or p-type single-crystal or polycrystalline silicon substrate 1, a p-type or n-type crystalline or amorphous silicon layer 2, a front electrode layer 4, and a back electrode layer 3. The light absorbing layer in this cell is a single crystal or polycrystalline silicon substrate 1. Top cell 41 is n
And a p-type InN layer 6, an n-type or p-type InN layer 7, and a transparent conductive layer 8. The light absorbing layer in this cell is the InN layer 6. The p-type InN layer contains a group II element. 5 is a transparent insulator layer.

Next, a method for manufacturing the tandem photovoltaic device will be described. First, a p ⁺ -type silicon layer 2 doped with B, Al, or the like is formed on an n-type single crystal or polycrystalline silicon substrate 1 by a thermal diffusion method, an ion implantation method, a plasma CVD method, or the like. On this, a transparent insulator layer 5 of SiO ₂ or the like is formed to a thickness of 100 to 500 nm by a thermal oxidation method, a CVD method, a sputtering method, or the like. After forming a contact hole in the transparent insulator layer 5, a surface electrode layer 4 of Ti / Ag or the like is deposited to a thickness of 0.5 to 5 μm by a vacuum deposition method, a sputtering method, or the like, and is patterned in a comb shape by a lift-off method or the like. To synchronize. An n-type In is formed thereon by a reactive sputtering method, a reactive ion plating method, or the like.
An N layer 6 is deposited to a thickness of 0.5 to 5 μm. Subsequently, p ⁺ containing a group II element such as Zn, Cd, or Mg is formed by a reactive sputtering method, a reactive ion plating method, or the like.
A type InN layer 6 is deposited to a thickness of 10 to 500 nm. A transparent conductive layer 8 of ITO, ZnO: Al, or the like is deposited thereon to a thickness of 0.1 to 2 μm by sputtering, ion plating, vacuum deposition, MOCVD, or the like. Finally, Al is deposited by vacuum evaporation, sputtering, etc.
/ Ag is formed to a thickness of 0.5 to 5 μm.

Here, a method for producing an InN thin film will be described by taking a reactive sputtering method as an example. By using In as a target and applying RF power of 0.1 to 10 W / cm ^{2 to} the target in an N ₂ gas atmosphere of 10 ^{−1 to 5} Pa, a substrate (room temperature to 300
C.) on which an InN thin film is deposited. At this time, by depositing at a relatively high pressure and a low substrate temperature, a film which is close to the stoichiometric composition (N / In = 1), has a low carrier concentration and a high mobility, and is preferable as a light absorbing layer is obtained. Can be
The crystal structure of this film is a wurtzite-type polycrystal oriented preferentially in the c-axis direction.

In the above, the p-type InN thin film is represented by I
For example, an appropriate amount of Zn chips are arranged on n targets,
It can be obtained by performing sputtering. Z
The amount of n chips is such that the ratio of Zn to In in the film is 0.1%.
It is desirable to adjust so as to be ２０20%.

Next, a second embodiment of the present invention will be described with reference to FIG. This is one in which the surface electrode layer 4 and the transparent insulator layer 5 in the first embodiment are omitted, and the p-type or n-type crystalline or amorphous silicon layer 2 is omitted.
N-type or p-type (two-layer structure) InN layer 6 directly on
1 are formed. Other constituent materials and a manufacturing method are the same as those in the first embodiment. In this case, the manufacturing process can be simplified, and in particular, the silicon layer 2 is (11)
1) When the crystalline silicon is oriented, there is an advantage that the c-axis orientation of the InN layer is improved by reflecting the orientation, and the carrier diffusion length in the direction perpendicular to the film surface is increased. In addition,
The carrier concentration is low (10 ¹⁶ to 10 ¹⁸ cm), which is preferable for the crystalline or amorphous silicon layer 2 and the light absorbing layer.
^-3 ) When the InN layer 6 is in direct contact, a reverse junction is formed there and an electromotive force in the opposite direction is generated, so that the voltage taken out is reduced. In order to avoid this, it is desirable to form a tunnel junction by providing an n ⁺ -type or p ⁺ -type InN layer 9 having a high carrier concentration (10 ¹⁸ cm ⁻³ or more) with a film thickness of 10 to 500 nm.

Next, a third embodiment of the present invention will be described with reference to FIG. The tandem-type photovoltaic device of the present embodiment is such that the light absorption layer of the bottom cell in the second embodiment is an n-type or p-type polycrystalline silicon thin film 11 deposited on a seed layer 13. . This polycrystalline silicon thin film is formed such that most of the crystal planes parallel to the surface of the substrate 14 are (111) planes. The ratio of the orientation is defined based on the X-ray diffraction intensity as shown in the following equation. (111) Diffraction intensity ratio = 1 (constant) (220) Diffraction intensity ratio = [Relative intensity of (220) to (111)] / [Relative intensity of powder (220) to (111)] (311) Diffraction Intensity ratio = [Relative intensity of (311) to (111) of sample] / [Relative intensity of powder (311) to (111)] (400) Diffraction intensity ratio = [Relative of (400) of sample to (111)] Intensity] / [relative intensity of powder (400) with respect to (111)] (111) orientation ratio = (111) diffraction intensity ratio / [(111) diffraction intensity ratio + (220 diffraction intensity ratio) + (311) diffraction intensity Ratio + (400) Diffraction Intensity Ratio] Here, “most” means that the orientation ratio is 0.5 or more.

Next, a method of manufacturing the above-described tandem photovoltaic device will be described. First, a seed layer 1 is formed on a substrate 14 made of glass, ceramics, plastic, metal, or the like.
Form 3 The seed layer 13 may be made of uniaxially oriented ZnS, ZnSe, ZnO, AlN, GaN, or the like. However, in order to improve the crystal quality of the polycrystalline silicon thin film 11, amorphous or microcrystalline silicon may be used. A thin film formed by irradiating a laser beam is preferable. At this time, for example, if P and As are doped at a high concentration to be an n ⁺ type, it can also serve as a lower electrode. The thickness of the seed layer 13 is 500 nm or less, preferably 10 to 200 nm. The n-type polycrystalline silicon thin film 11 is formed by forming an oxidizing atmosphere (oxygen, water, carbon dioxide,
Gas atmosphere containing at least nitric oxide, for example, air
It is desirable to perform the process without being exposed to the surface from the viewpoint of enhancing the (111) orientation. This method will be described later in detail. The thickness of the n-type polycrystalline silicon thin film 11 is 1 to
50 μm is appropriate. A p ⁺ -type crystalline or amorphous silicon layer 12 doped with B, Al, or the like is formed thereon by a plasma CVD method, a vacuum evaporation method, or the like.
nm. The subsequent manufacturing method is the same as in the second embodiment.

Here, a first example of a method of forming the seed layer 13 and the polycrystalline silicon thin film 11 will be described with reference to FIG. First, the substrate 14 is placed on a substrate holder (also serving as a counter electrode) 18 in the second vacuum chamber 17 and evacuated, and then a mixed gas of a gas containing an element such as P or As and a gas containing a Si element, for example, By supplying a source gas of PH ₃ / SiH ₄ = 2% and applying high frequency power to the cathode 19, an n ⁺ type amorphous or microcrystalline silicon thin film is formed. Next, after the first vacuum chamber 15 is evacuated, the gate valve 16 is opened, and the substrate 14 is transferred into the vacuum chamber 15 by the substrate transfer mechanism. Substrate 1
Laser light source 2 on the surface of the n ⁺ -type amorphous silicon thin film
For example, the seed layer 13 is formed by irradiating an ArF excimer laser from 1 to crystallize it. Excimer laser energy is 200-500 mJ / cm ² , substrate temperature is 300
To 500 ° C. and the number of shots is suitably from 20 to 200.
The seed layer 13 thus formed is made of (111) oriented polycrystalline silicon crystal grains.

Next, the inside of the second vacuum chamber 17 is evacuated again, the gate valve 16 is opened, and the substrate 14 is transferred from the first vacuum chamber 15 to the second vacuum chamber 17 by the substrate transfer mechanism. Thereafter, the gate valve 16 is closed, and a mixed gas of a gas containing an element such as P and As and a gas containing a Si element, for example, PH ₃ / SiH ₄ = 0.4.
By supplying high frequency power to the cathode 19 while alternately repeating the supply of the raw material gas and the supply of the H ₂ gas, the n-type polycrystalline silicon thin film 11 is formed. In addition,
In the above method, the seed layer 13 is formed directly on the substrate 14. However, a thermal buffer layer may be provided between the substrate 14 and the seed layer 13 to improve the crystallinity of the polycrystalline silicon thin film 11. It is possible.

As a material of the thermal buffer layer, a material having a small thermal diffusivity (= thermal conductivity / density × specific heat) is desirable.
Such materials include ZrO ₂ , TiO ₂ , SiO _{2 and the} like. The thickness of the thermal buffer layer is 0.2 μm or more, preferably 0.3 to 3 μm. If the thermal buffer layer is too thin, there is no effect, and there is no difference in effect in a region exceeding 3 μm, so that the above range is desirable. Such a film can be formed by a sputtering method, an electron beam evaporation method, an ion plating method, a plasma CVD method, an MOCVD method, a sol-gel method, a wet coating method, or the like. Seed layer 13 formed via such a thermal buffer layer
Has a grain size much larger than the film thickness, and has a great effect on increasing the grain size of the polycrystalline silicon thin film 11.

Next, a second example of a method for forming the seed layer 13 and the polycrystalline silicon thin film 11 will be described with reference to FIG. First, an n ⁺ -type amorphous or microcrystalline silicon thin film is formed on the substrate 14 by an electron beam evaporation method, an ion plating method, a sputtering method, a plasma CVD method, or the like. This substrate is set in the substrate transfer mechanism inside the first vacuum chamber 15, and after this setting, the vacuum chamber 15 is evacuated.

Next, after the seed layer 13 is formed in the same manner as in the first example, the inside of the second vacuum chamber 17 is evacuated, the gate valve 16 is opened, and the substrate 14 is transferred by the substrate transfer mechanism. The transfer is performed from the first vacuum chamber 15 to the second vacuum chamber 17. After this, gate valve 1
6 is closed, the inside of the vacuum chamber 17 is evacuated to 1 × 10 ⁻⁴ Pa or less, and then maintained in a predetermined atmosphere according to the film forming means. For example, a high vacuum of 1 × 10 ⁻⁴ Pa or less or an H ₂ atmosphere of 1 × 10 ⁻³ Pa or less is used in the electron beam evaporation method, and 1 × 10 ⁴ is used in the ion plating method and the sputtering method.
Ar, He, N ₂ , H _2, etc. of 10 ^{−2 to} 10 Pa and a mixed gas atmosphere thereof, and 1 × 10 ^{−2 in the} plasma CVD method
~ 100 Pa SiH ₄ , Si ₂ H ₆ , SiF ₄ , SiH ₂
Cl ₂ or the like or a mixed gas atmosphere of these and H ₂ is selected.

Next, the substrate is irradiated with an electron beam, an ion beam, a laser beam, X-rays or the like from the energy beam source 24, and at the same time, silicon atoms or silicon compound molecules are generated from the silicon source 25 to deposit a silicon thin film on the substrate. Let it. In the sputtering method, a Si target is provided in place of a silicon source in the plasma CVD method, and a film is formed by applying a DC or high-frequency electric field thereto. At this time, simultaneously, P, As, etc. are supplied from the doping element source 26 to a solid source or PH.
_The n-type polycrystalline silicon thin film 11 can be obtained by supplying from a gas source such as ₃ , PCl ₃ , P (C ₂ H ₅ ) ₃ , AsH ₃ , and AsCl ₃ . Due to the irradiation of the energy beam, the mobility of silicon atoms on the substrate surface increases, so that the particle size is large even at a low substrate temperature,
A polycrystalline silicon thin film with high orientation can be formed.

The energy beam is preferably an electron beam. Since the electron beam has a small mass of charged particles, the electron beam has an advantage that damage to an underlayer and a deposited film is smaller than that of an ion beam, and a film with a low defect can be obtained. Furthermore, electron beams can be deflected by magnetic or electric fields, and in particular, by using electric field deflection, high-speed scanning over long distances is possible, resulting in a film with a large area and excellent uniformity compared to laser beams. There are advantages. As the electron beam source, a normal electron gun composed of a filament that emits thermoelectrons, an accelerating electrode, a converging lens, a deflecting lens, and the like can be used, but when the pressure in the chamber during film formation is high, In order to stabilize the operation of the electron gun, the inside of the electron gun needs to be differentially evacuated. The energy of the electron beam to be irradiated is an acceleration voltage of 100 V to 100 k.
V, preferably 1 kV to 30 kV and a current density of 1 μA
/ Cm ^{2 to} 1 A / cm ² , preferably 10 μA / cm ² to
1 mA / cm ² is appropriate. Also in this case, similarly to the first example, it is possible to improve the crystallinity of the polycrystalline silicon thin film 11 by providing a thermal buffer layer between the substrate 14 and the seed layer 13.

[0040]

EXAMPLES The present invention will be described more specifically with reference to examples. Example 1 A tandem-type photovoltaic device shown in FIG. 1 was manufactured as follows. A p ⁺ -type silicon layer 2 doped with B was formed on the surface of an n-type single crystal silicon substrate 1 by a thermal diffusion method. After the p ⁺ -type layer on the back surface was removed by etching, a 200-nm-thick SiO ₂ film was deposited on the p ⁺ -type silicon layer 2 by the CVD method, and a contact hole was formed to form the transparent insulating layer 5. A 2 μm-thick Ti /
An Ag film was deposited, and was patterned in a comb shape by a lift-off method to form a surface electrode layer 4. Further, an Al / Ag film having a thickness of 1.5 μm was deposited on the back surface by a vacuum deposition method to form a back electrode layer 3.

Next, a film thickness of 1 μm is formed by a sputtering method.
An m-type InN layer 6 was formed. At this time, the target was In, the N ₂ gas pressure was 1 Pa, and the RF power was 0.6 W.
/ Cm ² and the substrate temperature was room temperature. A 100 nm-thick p ⁺ -type I was formed thereon by the same sputtering method as described above.
An nN layer 7 was formed. However, the target was In on which a Zn chip was mounted. After the film formation, annealing was performed at 350 ° C. for 15 minutes. The Zn / In ratio in this film was 7.
5%. Finally, a 500 nm-thick ITO film was deposited by a sputtering method to form a transparent conductive layer 8. The conversion efficiency of this photovoltaic device is 18.5% (AM
1.5, 100 mW / cm ² ).

Example 2 A tandem type photovoltaic device shown in FIG. 3 was manufactured as follows. A ZrO ₂ thin film having a thickness of 1 μm was formed as a thermal buffer layer on the Pyrex substrate 4 by a sputtering method. This substrate was placed in the second vacuum chamber 17 shown in FIG. 5 × 1 inside the chamber
By evacuation to 0 ^-5 Pa and generating silicon vapor by electron beam heating from a crucible (silicon source) 25 filled with a silicon lump, and simultaneously generating P vapor from a doping element source 26, the n of 80 nm thickness is obtained. ^{A +} type amorphous silicon thin film was formed. The substrate was transferred to the first vacuum chamber 15 by opening the gate valve 16 and heated to 400 ° C. The seed layer 13 was formed by irradiating 100 shots of an ArF excimer laser at an energy density of 350 mJ / cm ² from the film surface.

Next, the wafer was again transferred to the second vacuum chamber 17 and heated to 400.degree. An electron beam is applied from the electron beam source 24 to the substrate at an acceleration voltage of 10 kV and a current density of 200 μA.
/ Cm ² . By generating silicon vapor by electron beam heating from the silicon source 25 and simultaneously generating P vapor from the doping element source 26, the film thickness 5
A μm n-type polycrystalline silicon thin film 11 was formed. The polycrystalline silicon thin film 11 had a (111) orientation and a crystal grain size of about 3 μm. This substrate was placed in a parallel plate type plasma CVD apparatus and heated to 300 ° C. The chamber was evacuated, and B ₂ H ₆ / SiH ₄ = 1% as a source gas
And applying high frequency power to the cathode,
A p ⁺ -type microcrystalline silicon layer 12 having a thickness of nm was formed.

Next, a film thickness of 50
An n ⁺ -type InN layer 9 with a thickness of nm was formed. At this time, the target was In, the N ₂ gas pressure was 0.1 Pa, the RF power was 1.2 W / cm ² , and the substrate temperature was 200 ° C. An n-type InN layer 6 and ap ⁺ type I
An nN layer 7 and a transparent conductive layer 8 were sequentially formed. The conversion efficiency of this photovoltaic device is 16.7% (AM 1.5, 100 mW
/ Cm ² ).

[0045]

As described above, in the photovoltaic device according to the first aspect of the present invention, the photovoltaic element (top cell) disposed on the light incident side uses indium nitride as a light absorbing layer, and Since the photovoltaic element (bottom cell) uses crystalline silicon as the light absorbing layer, the spectral sensitivity spectra of the top cell and the bottom cell are less overlapped, and the light collection efficiency is improved.
High conversion efficiency can be obtained. Further, by using indium nitride as the light absorbing layer, a highly reliable photovoltaic device excellent in durability against light irradiation can be obtained very easily.

In the photovoltaic device according to the second aspect of the present invention, the photovoltaic element (top cell) disposed on the light incident side has an indium nitride layer containing at least a group II element. , Homo junction can be formed, a good junction interface can be formed, and high conversion efficiency can be obtained.

In the photovoltaic device according to the third aspect of the present invention, since the light incident surface of the photovoltaic element (top cell) disposed on the light incident side is a transparent conductive layer, it is effective for the light absorbing layer. Light can be taken into the device, the short-circuit current increases, and the conversion efficiency can be further improved.

According to a fourth aspect of the present invention, in the photovoltaic device, the carrier concentration is 10 ¹⁸ cm ^-3 or more on the side opposite to the light incident surface of the photovoltaic element (top cell) disposed on the light incident side. , The occurrence of back electromotive force at the interface between the top cell and the bottom cell can be prevented, the open-circuit voltage increases, and higher conversion efficiency can be obtained.

In the photovoltaic device according to the fifth aspect of the present invention, the crystalline silicon is a (111) oriented polycrystalline silicon thin film deposited on the seed layer.
Therefore, optical carriers can be effectively extracted, and higher conversion efficiency can be obtained. Further, the material cost can be significantly reduced by thinning.

According to the method of manufacturing a photovoltaic device of the present invention, an amorphous or microcrystalline silicon thin film is formed on a substrate, and the silicon thin film is irradiated with a laser beam for seeding. Since the formation is performed by forming a layer and depositing silicon atoms or silicon compound molecules on the seed layer to form a polycrystalline silicon thin film, the grain size of the polycrystalline silicon thin film can be increased, and higher conversion can be achieved. An efficient photovoltaic device can be obtained.

According to the method of manufacturing a photovoltaic device according to the present invention, the formation of the seed layer and the deposition of the polycrystalline silicon thin film thereon are continuously performed in a vacuum. Since the seed layer and the polycrystalline silicon thin film thereon are not exposed to an oxidizing atmosphere during the manufacturing process, the polycrystalline silicon thin film can be grown with the (111) orientation,
A photovoltaic device having higher conversion efficiency can be obtained.

According to the method of manufacturing a photovoltaic device of the present invention, the polycrystalline silicon thin film is formed by depositing silicon atoms or silicon compound molecules while irradiating the surface of the seed layer with an energy beam. By doing so, it is possible to grow a (111) oriented polycrystalline silicon thin film with a large grain size even at a low substrate temperature, so that the fabrication temperature of the photovoltaic device can be lowered. The photovoltaic device manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of a photovoltaic device according to the present invention.

FIG. 2 is a sectional view schematically showing another example of the photovoltaic device according to the present invention.

FIG. 3 is a cross-sectional view schematically showing another example of the photovoltaic device according to the present invention.

FIG. 4 is an explanatory view schematically showing a method for manufacturing a photovoltaic device according to the present invention.

FIG. 5 is an explanatory view schematically showing another method for manufacturing a photovoltaic device according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 crystal silicon substrate 2 silicon layer 3 back electrode layer 4 front electrode layer 5 transparent insulator layer 6 InN layer 7 InN layer 8 transparent conductive layer 9 high carrier concentration layer 11 polycrystalline silicon thin film 12 silicon layer 13 seed layer 14 substrate 15, 17 Vacuum chamber 16 Gate valve 18 Counter electrode 19 Cathode 20 High frequency power supply 21 Laser light source 22 Laser beam 23 Light transmission window 24 Energy beam source 25 Silicon source 26 Doping element source 31 Bottom cell 41 Top cell 61 Two-layer InN layer

Claims (8)

[Claims] 1. A photovoltaic device in which two different photovoltaic elements are stacked, wherein the photovoltaic element disposed on the light incident side uses indium nitride as a light absorbing layer, and the other photovoltaic element. A photovoltaic device, wherein the element uses crystalline silicon as a light absorbing layer. 2. The photovoltaic device according to claim 1, wherein the photovoltaic element disposed on the light incident side has an indium nitride layer containing at least a group II element. 3. The photovoltaic device according to claim 1, wherein the light incident surface of the photovoltaic element disposed on the light incident side is a transparent conductive layer. 4. A photovoltaic element provided on the light incident side, wherein a layer having a carrier concentration of 10 ¹⁸ cm ⁻³ or more is provided on the side opposite to the light incident surface. Or 3
A photovoltaic device as described. 5. The photovoltaic device according to claim 1, wherein said crystalline silicon is a (111) oriented polycrystalline silicon thin film deposited on a seed layer. 6. The method for manufacturing a photovoltaic device according to claim 1, wherein said crystalline silicon is formed by forming an amorphous or microcrystalline silicon thin film on a substrate. Manufacturing a photovoltaic device, wherein a thin film is irradiated with a laser beam to form a seed layer, and silicon atoms or silicon compound molecules are deposited on the seed layer to form a polycrystalline silicon thin film. Method. 7. The method of manufacturing a photovoltaic device according to claim 6, wherein the formation of the seed layer and the deposition of the polycrystalline silicon thin film thereon are continuously performed in a vacuum. 8. The photovoltaic device according to claim 6, wherein silicon atoms or silicon compound molecules are deposited while irradiating an energy beam on the surface of the seed layer to form a polycrystalline silicon thin film. Manufacturing method.