JPH10214986A - Photovoltaic device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tandem-type photovoltaic device whose photoelectric conversion efficiency is extremely high. SOLUTION: This photovoltaic device is formed by stacking two different photovoltaic elements. In the photovoltaic device, a photovoltaic element 41 which is arranged on the incident side of light uses (112)-oriented I-III-VI2 compounds as a light absorption layer 6, and a photovoltaic element 31 on the other side uses crystalline silicon as a light absorption layer 1. As the I-III- VI2 compounds, Cu1-x Agx In1-y Gay S2 (where 0<=x<=0.7 and 0<=y<=0.4), Cu1-x Agx In1-y Aly S2 (where 0<=x<=0.7 and 0<=y<=0.2) and CuIn1-x Alx Se2 (where 0.2<=x<=0.5) are preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art There is known a photovoltaic device having a so-called tandem structure in which two different photovoltaic elements are stacked in order to effectively utilize incident light and obtain high conversion efficiency. In general, in the case of such a structure, a semiconductor having a large band gap is used for the light absorbing layer in an element (top cell) close to the light incident side, and a semiconductor having a small band gap is used in an element far from the light incident side (bottom cell). Used.

In this manner, light in the short wavelength region is absorbed by the top cell, and light in the long wavelength region that cannot be absorbed by the top cell is absorbed by the bottom cell, so that light in a wide wavelength region can be effectively used. Can be.

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 type of photovoltaic element is formed by sequentially forming type amorphous silicon. The light absorption layer in each photovoltaic element is p-type polycrystalline silicon and i-type amorphous silicon, and the former has a band gap of about 1. leV, the latter is about 1.7
Since it is eV, light is incident from the amorphous silicon side. However, a photovoltaic element using amorphous silicon as a light absorbing layer has a problem that conversion efficiency is low and that the photovoltaic element is deteriorated by light irradiation, and a tandem type structure has the same problem.

As a method for solving such a problem,
Japanese Patent Application Laid-Open No. Hei 6-283737 discloses, for example, that a p-type polycrystalline silicon substrate is doped with phosphorus by a thermal diffusion method and n-type is doped.
After forming a mold layer to form one photovoltaic element and forming electrodes, p-type Cu (In, Ga) S ₂ and n-type CdS
Are sequentially formed to form another photovoltaic element, and a tandem photovoltaic device is disclosed. The light absorbing layer in each photovoltaic element is composed of p-type polycrystalline silicon and p-type Cu (In, G
a) a S _2, since the band gap of the former is smaller than the latter light incident p-type Cu (In, Ga) is performed from the S ₂ side.

[0006] However, even such a tandem photovoltaic device is not yet sufficient in terms of photoelectric conversion efficiency.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem and to provide a tandem type photovoltaic device having extremely high photoelectric conversion efficiency. Also,
An object of the present invention is to provide a highly reliable tandem photovoltaic device having high photoelectric conversion efficiency and excellent durability against light irradiation.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a photovoltaic device comprising two different photovoltaic elements stacked one on another, the photovoltaic element (top cell) being disposed on the light incident side. ) Is a (112) -oriented I-III-VI group ₂ compound as a light absorbing layer, and the other photovoltaic element (bottom cell)
Is achieved by a photovoltaic device wherein crystalline silicon is used as the light absorbing layer.

I-III- which is a light absorbing layer of the top cell
VI ₂ group compound is the most dense surface of the chalcopyrite structure (112) less crystal defects by a polycrystal oriented, thus it is possible to take out effectively the optical carrier to obtain an extremely high photoelectric conversion efficiency be able to. In addition, by using a group I-III-VI ₂ compound as the light absorbing layer, a highly reliable photovoltaic device excellent in durability against light irradiation and the like can be obtained.

Here, the (112) orientation means that most of the crystal planes parallel to the surface of the substrate are (112) planes, in other words, most of the crystal axes perpendicular to the surface of the substrate are (112). 112) axis. The majority here means the four main diffraction planes (112), (200) or (004), (2) found by X-ray diffraction or the like.
04) or (220), and the ratio of the intensity from a particular plane to the normalized intensity from (312) is greater than or equal to 0.5, which means that the orientation is completely random. Is twice or more the ratio of 0.25.

Another object of the present invention is to provide a photovoltaic device in which two different photovoltaic elements are stacked, wherein the photovoltaic element (top cell) disposed on the light incident side is C-type.
_{u 1-x Ag x In 1} -y Ga y S 2 (0 ≦ x ≦ 0.7,0 ≦ y
_{≦ 0.4), Cu 1-x} Ag x In 1-y Al y S 2 (0 ≦ x ≦
0.7, 0 ≦ y ≦ 0.2) and CuIn _1-x Al _x Se ₂
(0.2 ≦ x ≦ 0.5) achieved by a photovoltaic device characterized in that one of the photoabsorbing layers is used as the light absorbing layer, and the other photovoltaic element (bottom cell) uses crystalline silicon as the light absorbing layer. Is done.

The light absorption layer I-III- of the top cell
By VI ₂ compound has a composition represented by the above-mentioned range, its spectral sensitivity spectrum, less overlap of the spectral sensitivity spectrum of the crystalline silicon is a light absorbing layer of the bottom cell on the long wavelength side, Since the difference from the spectrum of sunlight on the short wavelength side is reduced, and the light collection efficiency is improved, higher photoelectric conversion efficiency can be obtained.

[0013] In the photovoltaic device of the present invention, the photovoltaic element (top cell) disposed on the light incident side is II.
A II-VI ₂ compound as a light absorbing layer, the light absorbing layer, formed by laminating a large semiconductor material layer of a band gap than the light absorbing layer, the other of the photovoltaic element (bottom cell)
Is preferably a photovoltaic device using crystalline silicon as a light absorbing layer.

[0014] By the top cell is by laminating a large semiconductor material layer bandgap than the I-III-VI ₂ group compound to form a pn junction, as compared with the case of the homozygous by a so-called window effect Short wavelength sensitivity is improved, and higher photoelectric conversion efficiency can be obtained. In addition,
In this case, it goes without saying that a semiconductor material layer having a band gap larger than that of the I-III-VI group ₂ compound is disposed on the light incident side, and the conduction types of the two are reversed.

By forming this semiconductor material layer with a layer which forms a junction with the I-III-VI group ₂ compound and a transparent electrode layer, the junction characteristics of the top cell are improved.
The photoelectric conversion efficiency can be further improved.

The layer forming a junction with the I-III-VI group ₂ compound is preferably formed of ZnS, ZnSe, ZnO or a mixed crystal thereof. Each of these materials has a large band gap of 2.6 eV or more, so that a window effect can be expected. Also, by selecting an appropriate mixed crystal ratio, I-
Since the lattice mismatch with the III-VI group ₂ compound can be reduced, good junction characteristics can be obtained, and the photoelectric conversion efficiency can be further improved. Further, these materials are desirable in that they do not contain harmful substances such as Cd in CdS which has been conventionally used.

In the photovoltaic device of the present invention, Ti, Mo, W, and Ti are placed between the photovoltaic element (top cell) disposed on the light incident side and the other photovoltaic element (bottom cell). A thin film made of any of TiN can be provided. Thereby, even when the two photovoltaic elements are monolithically stacked, the diffusion of the elements constituting the I-III-VI group ₂ compound into the silicon layer can be prevented, and the reverse at the interface between the top cell and the bottom cell can be prevented. The generation of electromotive force can be prevented, and the photoelectric conversion efficiency can be further improved.

Further, in the photovoltaic device of the present invention,
The crystalline silicon of the other photovoltaic element (bottom cell) is preferably a (111) oriented polycrystalline silicon thin film deposited on the seed layer. Since the crystalline silicon is a (111) -oriented polycrystalline thin film which 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 photoelectric conversion efficiency can be further improved. it can. Further, the material cost can be significantly reduced by thinning. Here, the (111) orientation means that most of the crystal planes parallel to the surface of the substrate are (111) planes, in other words,
This means that most of the crystal axes perpendicular to the surface of the substrate are (111) axes. The majority here means the four main diffraction planes (11
1) The ratio of the intensity from a specific plane to the normalized intensity from (220), (311), and (400) is 0.5 or more, which means that the orientation is completely Is more than twice the ratio of 0.25 when random.

In order to form a (111) oriented polycrystalline silicon thin film deposited on a seed layer, an amorphous or microcrystalline silicon thin film is formed on a substrate, and the silicon thin film is irradiated with a laser beam. Preferably, a seed layer is formed, and silicon atoms or silicon compound molecules are deposited 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 polycrystalline silicon having a (111) orientation is formed with a large grain size, the grain size of the polycrystalline silicon thin film deposited thereon can be increased, thereby further improving the photoelectric conversion efficiency.

The formation of the seed layer and the deposition of the polycrystalline silicon thin film thereon are preferably performed continuously in a vacuum, whereby the seed layer and the polycrystalline silicon thin film thereon are oxidized during the manufacturing process. Because it is not exposed to a sexual atmosphere,
Reflecting the orientation of the seed layer in the polycrystalline silicon thin film, (1
11) The polycrystalline silicon thin film can be grown in the oriented state, and a highly oriented polycrystalline silicon thin film can be obtained, whereby the photoelectric conversion efficiency can be further improved.

In addition, 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, polycrystalline silicon having a (111) orientation can be obtained even at a low substrate temperature. Since the silicon thin film can be grown with a large grain size and the manufacturing temperature of the photovoltaic device can be lowered, the manufacturing cost of the photovoltaic device can be reduced.

[0023]

FIG. 1 shows a first embodiment of the present invention.
This will be described below based on First, the tandem photovoltaic device according to the present embodiment has a top cell 41 and a bottom cell 31.
Are the basic components. The bottom cell 31 includes a p-type or n-type single crystal or polycrystalline silicon substrate 1, an n-type or p-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. The top cell 41 includes a p-type or n-type I-III-VI group ₂ compound layer 6, and n-type or p-type semiconductor layers 7 and 8. The light absorbing layer in this cell is the I-III-VI group ₂ compound layer 6. 5 is a transparent insulator layer.

I-III-VI group ₂ compound layer 6 is formed such that most of the crystal planes parallel to the surface of substrate 1 are (112) planes. The ratio of the orientation is defined based on the X-ray diffraction intensity as shown in the following equation. (112) Diffraction intensity ratio = 1 (constant) (200) ((004)) Diffraction intensity ratio = [(20
0) ((004)) relative intensity to (112)] /
[Relative Intensity of (200) ((004)) to (112) of Powder] (204) ((220)) Diffraction Intensity Ratio = [(20
4) Relative strength of ((220)) to (112)] /
[Relative intensity of (204) ((220)) of powder relative to (112)] (312) Diffraction intensity ratio = ((11) of (312) of sample
Relative strength to 2)] / [(11) of (312) of powder
Relative intensity with respect to 2)] (112) Orientation ratio = (112) Diffraction intensity ratio / [(11
2) Diffraction intensity ratio + (200) ((004)) diffraction intensity ratio + (204) ((220)) diffraction intensity ratio + (312) diffraction intensity ratio Is 0.5 or more.

Next, a method of manufacturing the tandem photovoltaic device will be described. First, an n ⁺ -type silicon layer 2 doped with P, As, or the like is formed on a p-type single crystal or polycrystalline silicon substrate 1 by a thermal diffusion method, an ion implantation method, a plasma CVD method, or the like. Then, the n ⁺ type silicon layer 2
A transparent insulator layer 5 of SiO ₂ or the like is formed to a thickness of 100 to 500 nm by thermal oxidation, CVD, sputtering, or the like.
Formed. After forming a contact hole in the transparent insulator layer 5, Ti /
A surface electrode layer 4 of Ag or the like is deposited to a thickness of 0.5 to 5 μm,
Patterning is performed in a comb shape by a lift-off method or the like.

On this, p-type I-III-V is formed by multi-source simultaneous evaporation method, normal pressure or reduced pressure gas phase sulfurization (selenization) method or the like.
The I ₂ group compound layer 6 is deposited to a thickness of 0.5 to 5 μm. At that time, increase the deposition temperature or sulfide (selenize)
It is preferable to increase the time in order to obtain a film having excellent (112) orientation. As the composition of the I-III-VI ₂ group _{compounds, Cu 1-x Ag x In} 1-y Ga y S 2
(0 ≦ x ≦ 0.7, 0 ≦ y ≦ 0.4), Cu _1-x Ag _x I
Select _{one of} n _1-y Al _y S ₂ (0 ≦ x ≦ 0.7, 0 ≦ y ≦ 0.2) and CuIn _1-x Al _x Se ₂ (0.2 ≦ x ≦ 0.5) Or preferred.

The compound of group I-III-VI ₂ is Cu
_{1-x Ag x In 1-} y Ga y S 2 (0 ≦ x ≦ 0.7,0 ≦ y ≦
0.4), the band gap is widened by increasing x and y, and the light collection efficiency is improved. However, when x exceeds 0.7 and y exceeds 0.4, the light collection efficiency is conversely increased. Decrease. In addition, there is a tendency that crystallinity is impaired by increasing x and y. In view of this, it is more preferable that 0 ≦ x ≦ 0.3 and 0.1 ≦ y ≦ 0.2. For the same reason, I-III-VI ₂ compound is _{Cu 1-x Ag x In 1} -y Al y S 2 (0 ≦ x ≦ 0.
7, 0 ≦ y ≦ 0.2), it is more preferable that 0 ≦ x ≦ 0.3 and 0.05 ≦ y ≦ 0.15. Further, the I-III-VI group ₂ compound is CuIn _1-x Al _x S
When e ₂ (0.2 ≦ x ≦ 0.5), 0.2 ≦ x ≦
More preferably, it is 0.3.

In the above composition, the lattice constant is increased by increasing the content of Ag, and Ga and Al are increased.
Since the lattice constant is reduced by increasing the content of
By selecting an appropriate amount, lattice matching with the underlayer or the upper layer can be improved.

Subsequently, an n-type semiconductor layer is formed on the p-type I-III-VI group ₂ compound layer 6. While this use of I-III-VI2 ₂ compound layer 6 the same compound and as the material (homozygous) may, be used it from the large band gap semiconductor, more light in the short wavelength region by the window effect Many can be taken into the I-III-VI group ₂ compound layer 6. That is, it is desirable from the viewpoint of further improving short wavelength sensitivity. Further the n-type semiconductor layer as shown in FIG. 1, p-type I-III-VI ₂ group compound layer 6
And a transparent electrode layer (degenerate n-type semiconductor layer) 8 formed on the layer 7 is preferably stacked from the viewpoint of improving the bonding characteristics.

The n-type semiconductor layer 7 is formed by a solution growth method, MOCV
The transparent electrode layer 8 is formed by depositing ZnSe, ZnS, ZnO or a mixed crystal thereof to a thickness of 10 to 200 nm by a sputtering method, an ion plating method, a vacuum evaporation method, an MOCVD method, or the like. , Zn
O: formed by depositing Al or the like to a thickness of 0.1 to 2 μm.
Finally, Al / A by vacuum evaporation, sputtering, etc.
The back electrode layer 3 of g or the like is formed to a thickness of 0.5 to 5 μm.

Next, a second embodiment of the present invention will be described with reference to FIG. This is because the surface electrode layer 4 and the transparent insulator layer 5 in the first embodiment are omitted.
The p-type or n-type I-III-VI group ₂ compound layer 6 is formed directly on the n-type or p-type crystalline or amorphous silicon layer 2. The other constituent materials and the manufacturing method are the same as those in the first embodiment.

In this case, the manufacturing process can be simplified, and in particular, if the silicon layer 2 is (111) -oriented crystalline silicon, the orientation is reflected and the I-III-VI
There is an advantage that the (112) orientation of the group ₂ compound is improved. However, since the silicon layer 2 and the I-III-VI group ₂ compound layer 6 form a junction that generates an electromotive force in the opposite direction to the electromotive force generated by the junction formed in the top cell and the bottom cell, The extracted voltage may decrease. Further, during the manufacturing process (heating process), II
The element constituting the II-VI group ₂ compound layer 6 may diffuse into the silicon layer 2 and the silicon substrate 1 and deteriorate the characteristics of the bottom cell.

The third embodiment of the present invention solves such a problem in the second embodiment.
It is shown in FIG.

This corresponds to n in the second embodiment.
Between the p-type or p-type crystalline or non-quality silicon layer 2 and the p-type or n-type I-III-VI group ₂ compound layer 6,
In other words, the conductive layer 9 is inserted between the bottom cell 31 and the top cell 41.

As a material of the conductive layer 9, a transparent conductive film such as ZnO: B formed by a sputtering method, an MOCVD method or the like may be used, but from the viewpoint of improving the crystal quality of the I-III-VI group ₂ compound. Is preferably a metal thin film.
The metal thin film has a high barrier property against diffusion of elements constituting the I-III-VI group ₂ compound layer 6 and an alloy with silicon (silicide) during the manufacturing process (heating process).
It is desirable not to form Ti, Mo, W, and TiN. These are deposited to a thickness of 3 to 20 nm by a vacuum deposition method, a sputtering method, a CVD method, or the like to form the conductive layer 9.
If the film thickness is larger than this, the light transmittance is undesirably reduced. Other constituent materials and a manufacturing method are the same as those in the second embodiment.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In this tandem photovoltaic device, the light absorbing layer of the bottom cell in the third embodiment is a p-type or n-type polycrystalline silicon thin film 11 deposited on a seed layer 13.

This polycrystalline silicon thin film is formed so 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 = [11 of (220) of the sample
Relative strength to 1) "/ [(220) of powder (11)
Relative intensity relative to 1)] (311) Diffraction intensity ratio = (11
Relative strength to 1) "/ [(11) of powder (311)
Relative intensity relative to 1)] (400) Diffraction intensity ratio = [(11) of (400) of sample
Relative strength to 1) "/ [(400) of powder (11)
Relative intensity with respect to 1)] (111) orientation ratio = (111) diffraction intensity ratio / [(11
1) Diffraction intensity ratio + (220) diffraction intensity ratio + (311) diffraction intensity ratio + (400) diffraction intensity ratio] In this case, most means that the orientation ratio is 0.5 or more. doing.

Next, a method of manufacturing the above-described tandem photovoltaic device will be described. First, the seed layer 13 is formed on a substrate 14 made of glass, ceramics, plastic, metal, or the like. The seed layer 13 may be made of uniaxially oriented ZnS, ZnSe, ZnO, AlN, or GaN.
However, from the viewpoint of improving the crystal quality of the polycrystalline silicon thin film 11, a film formed by irradiating an amorphous or microcrystalline silicon thin film with a laser beam is preferable.
At this time, for example, B, Al or the like is doped at a high concentration, and p ⁺
If it is a mold, it can also serve as a lower electrode. Seed layer 1
3 is preferably 500 nm or less, particularly 10 to 20 nm.
0 nm is preferred.

The p-type polycrystalline silicon thin film 11 is formed by exposing the seed layer 13 to an oxidizing atmosphere (a gas atmosphere containing at least oxygen, water, carbon dioxide, nitrogen oxide, etc., for example, the atmosphere). Is done without (11
1) It is desirable from the viewpoint of enhancing the orientation. This method will be described later in detail. The thickness of the p-type polycrystalline silicon thin film 11 is suitably from 1 to 50 μm.

On this p-type polycrystalline silicon thin film 11, an n + type crystalline or amorphous silicon layer 12 doped with P, As or the like by plasma CVD, vacuum evaporation or the like is formed to a thickness of 10 to 100 nm. Form. The subsequent manufacturing method is the same as that of the third 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 in the second vacuum chamber-1.
After being placed on a substrate holder (also serving as a counter electrode) 18 and evacuated, a mixed gas of a gas containing an element such as B or Al and a gas containing a Si element, for example, B ₂ H ₆ / SiH ₄ = 0.5 %
Is supplied and high frequency power is applied to the cathode 19 to form ap ⁺ -type amorphous or microcrystalline silicon thin film. 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. The surface of the p ⁺ type amorphous or microcrystalline silicon thin film on the substrate 14 is crystallized by irradiating, for example, an ArF excimer laser from a laser light source 21 to form a seed layer 13. Excimer laser energy is 200-500m
J / cm ² , the substrate temperature is 300 to 500 ° C., and the number of shots is suitably 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 B or Al and a gas containing a Si element, for example, supply of a raw material gas of B ₂ H ₆ / SiF ₄ = 0.1% and H ₂ gas By applying high frequency power to the cathode 19 while alternately repeating the supply of
A p-type polycrystalline silicon thin film 11 is formed.

In the above method, the seed layer 13 is formed directly on the substrate 14. However, a thermal buffer layer is provided between the substrate 14 and the seed layer 13 so that the crystallinity of the polycrystalline silicon thin film 11 can be reduced. Can also be improved. As a material of the thermal buffer layer, a material having a small thermal diffusivity (= thermal conductivity / density × specific heat) is desirable, and examples of such a material include ZrO ₂ , TiO ₂ , and SiO ₂ . The thickness of the thermal buffer layer is preferably at least 0.2 μm, particularly 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. The 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 electron beam evaporation method is
A p ⁺ -type amorphous or microcrystalline silicon thin film is formed by 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 a H ₂ atmosphere of 1 × 10 ⁻³ Pa or less in an electron beam evaporation method, and 1 × 1 in an ion plating method and a sputtering method.
Ar, He, N ₂ , H _2, etc. of 0 ^{−2 to} 10 Pa or a mixed gas atmosphere thereof, and 1 × 10 ⁻² to 1 in the plasma CVD method.
00Pa SiH ₄ , Si ₂ H ₆ , SiF ₄ , SiH ₂ Cl ₂
And a mixed gas atmosphere of these and H ₂ are 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 simultaneously, 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, and in the plasma CVD method, a cathode is provided instead of a silicon source, and a DC or high-frequency electric field is applied thereto to form a film. At the same time, B, Al, etc. are converted from the doping element source 26 into a solid source, B ₂ H ₆ , B (C ₂ H ₅ O) ₃ , Al (C ₅ H ₇ O ₂ ) ₃ , A
By supplying with a gas source such as l (C ₃ H ₇ O) ₃ , the p-type polycrystalline silicon thin film 11 can be obtained.

Since the mobility of silicon atoms on the substrate surface is increased by the irradiation of the energy beam, a polycrystalline silicon thin film having a large grain size and high orientation can be formed even at a low substrate temperature. As the above energy beam, an electron beam is particularly preferable. 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 a magnetic field or electric field. In particular, if electric field deflection is used, long-distance scanning can be performed at high speed, so that a film with a large area and excellent uniformity can be obtained compared to a laser beam. 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 such that the acceleration voltage is 100 V to 100 kV, preferably 1 kV to 30 kV.
At V, 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.

[0051]

The present invention will be described below in more detail with reference to examples. Example 1 A tandem photovoltaic device shown in FIG. 1 was manufactured as follows. An n ⁺ -type silicon layer 2 doped with P was formed on the surface of a p-type single crystal silicon substrate 1 by a thermal diffusion method. After the n ⁺ -type layer on the back surface is removed by etching, a 200 nm-thick Si film is formed on the n ⁺ -type silicon layer 2 by CVD.
An O ₂ film was deposited, and a contact hole was formed to form a transparent insulating layer 5. A 2 μm-thick Ti / Ag film was deposited thereon by a vacuum deposition method, and was patterned into 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 laminated film (precursor) of Cu—Ga / In is deposited by a sputtering method, and is heated to 500 ° C. in H ₂ S gas diluted with Ar to form a p-type I— film having a thickness of 2 μm. III-VI
_A group ₂ compound layer 6 was formed. At this time, by controlling the film thickness ratio and Ga content of Cu-Ga and In in the precursor was the composition of the p-type I-III-VI ₂ group compound layer 6 and CuIn _0.85 Ga _0.15 S _2. This layer is strong (1
12) The orientation was shown. A 50 nm-thick ZnS film was deposited on this layer by MOCVD to form an n-type semiconductor layer 7. Subsequently, a film thickness of 200 n was formed by a sputtering method.
Then, a transparent electrode layer 8 was formed. The conversion efficiency of this photovoltaic device is 21.0% (AM 1.51,
100 mW / cm ² ).

Example 2 A tandem-type photovoltaic device shown in FIG. 4 was manufactured as follows. On a Pyrex substrate 4 by a sputtering method,
A thin film of ZrO _{2 having} a thickness of 1 μm was formed as a thermal buffer layer. This substrate is placed in a second vacuum chamber 17 shown in FIG.
And heated to 300 ° C. 5x inside the chamber
By evacuating to 10 ^-5 Pa and generating silicon vapor by electron beam heating from a crucible (silicon source) 25 filled with a silicon lump, and simultaneously generating B vapor from the doping element source 26, a p-layer having a thickness of 80 nm is formed. ^{A +} type amorphous silicon thin film was formed. The substrate is transferred to the first vacuum chamber 15 by opening the gate valve 16,
Heated. 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, it was transferred to the second vacuum chamber 17 again and heated to 400 ° C. The substrate was irradiated with an electron beam from the electron beam source 24 at an acceleration voltage of 10 kV and a current density of 200 μA / cm ² . Silicon source 25
To generate silicon vapor by electron beam heating,
At the same time, a p-type polycrystalline silicon thin film 11 having a thickness of 5 μm was formed by generating B vapor from the doping element source 26. 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, PH ₃ / SiH ₄ = 2% was supplied as a source gas, high frequency power was applied to the cathode, and an n ⁺ -type microcrystalline silicon layer 12 having a thickness of 100 nm was formed. MOCV on this
A conductive layer 9 was formed by depositing ZnO: B with a thickness of 2 μm by Method D. This layer was (001) oriented. Then C
A p-type I-III-VI group ₂ compound layer 6 having a thickness of 2 μm was formed by a four-source simultaneous evaporation method using u, In, Al, and Se as sources. At this time, the substrate temperature was set to 450 ° C., and by controlling the flux amount of each source, CuIn
A composition of _0.75 Al _0.25 Se ₂ was obtained. This layer is strong (11
2) The orientation was shown. A 50 nm-thick ZnSe film was deposited thereon by MOCVD to form an n-type semiconductor layer 7. Subsequently, a film thickness of 200 nm was formed by a sputtering method.
Was deposited to form a transparent electrode layer 8. The conversion efficiency of this photovoltaic device is 20.0% (AM1.5, 10
0 mW / cm ² ).

[0054]

Effects of the Invention According to the photovoltaic device of the invention of claim 1, disposed on the light incident side photovoltaic element (top cell) (112) I-III-VI 2 compound oriented Is used as a light absorbing layer, and the other photovoltaic element (bottom cell) uses crystalline silicon as a light absorbing layer. Therefore, crystal defects in the light absorbing layer of the top cell are small, so that photocarriers can be effectively taken out. And extremely high photoelectric conversion efficiency can be obtained. Also, I-III-VI ₂
By using a group III compound as the light absorbing layer, a highly reliable photovoltaic device excellent in durability against light irradiation and the like can be obtained.

According to the photovoltaic device of the second aspect of the present invention,
Disposed on the incident side of the light photovoltaic element (top cell) _{Cu 1-x Ag x In 1} -y Ga y S 2 (0 ≦ x ≦ 0.7,0 ≦
y ≦ 0.4), Cu _1-x Ag _x In _1-y Al _y S ₂ (0 ≦ x
≦ 0.7, 0 ≦ y ≦ 0.2) and CuIn _1-x Al _x Se
₂ (0.2 ≦ x ≦ 0.5) as a light absorbing layer,
Since the other photovoltaic element (bottom cell) uses crystalline silicon as the light absorbing layer, the spectral sensitivity spectra of the light absorbing layer of the top cell and the light absorbing layer of the bottom cell are less overlapped, and the light collection efficiency is improved. , Higher photoelectric conversion efficiency can be obtained.

According to the photovoltaic device of the third aspect of the present invention,
A photovoltaic element (top cell) disposed on the light incident side uses a group I-III-VI group ₂ compound as a light absorbing layer, and a semiconductor material layer having a larger band gap than the light absorbing layer on the light absorbing layer. When the other photovoltaic element (bottom cell) uses crystalline silicon as a light absorbing layer, short-wavelength sensitivity is improved, and higher photoelectric conversion efficiency can be obtained.

According to the photovoltaic device of the fourth aspect,
By large semiconductor material layer bandgap consists the layer and the transparent electrode layer to form a bond with the I-III-VI ₂ group compounds than I-III-VI ₂ group compounds,
The junction characteristics of the top cell become favorable, and higher photoelectric conversion efficiency can be obtained.

According to the photovoltaic device of the fifth aspect,
The layer forming a junction with the I-III-VI group ₂ compound is Zn
Since it is formed of S, ZnSe, ZnO and a mixed crystal thereof, lattice mismatch with the I-III-VI group ₂ compound can be reduced, so that good junction characteristics can be obtained, and higher photoelectric conversion can be obtained. Efficiency can be obtained.
In addition, it is excellent in safety because it does not contain harmful substances.

According to the photovoltaic device of the invention of claim 6,
Ti, M are placed between the photovoltaic element (top cell) and the other photovoltaic element (bottom cell) disposed on the light incident side.
By providing a thin film made of any of o, W, and TiN, it is possible to prevent diffusion of elements constituting the I-III-VI group ₂ compound into the silicon layer,
Since generation of back electromotive force at the interface between the top cell and the bottom cell can be prevented, higher photoelectric conversion efficiency can be obtained.

According to the photovoltaic device of the invention of claim 7,
Since the crystalline silicon is a (111) -oriented polycrystalline silicon thin film deposited on the seed layer, the number of crystal defects is small, so that photocarriers can be effectively taken out, so that higher photoelectric conversion efficiency can be obtained. it can. Further, the material cost can be significantly reduced by thinning.

According to the method for 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 to form a seed layer. By forming 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 a higher photoelectric conversion efficiency can be obtained. A photovoltaic device can be obtained.

According to the method for manufacturing a photovoltaic device of the ninth aspect, the formation of the seed layer and the deposition of the polycrystalline silicon thin film thereon are continuously performed in a vacuum, whereby the seed layer is formed. Since the 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, and a photovoltaic device having higher photoelectric conversion efficiency Can be obtained.

According to the photovoltaic device manufacturing method of the tenth aspect 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, a polycrystalline silicon thin film of (111) orientation can be grown with a large grain size even at a low substrate temperature, so that the fabrication temperature of the photovoltaic device can be lowered and the photovoltaic device can be reduced. 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 a sectional view schematically showing another example of the photovoltaic device according to the present invention.

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

FIG. 6 is an explanatory view schematically showing another method of manufacturing the 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 I-III-VI group ₂ compound layer 7 semiconductor layer 8 transparent electrode layer 9 conductive layer 11 polycrystalline silicon thin film 12 silicon layer 13 seed Layer 14 Substrate 15 Vacuum chamber 16 Gate valve 17 Vacuum chamber 18 Counter electrode 19 Cathode 20 High frequency power supply 21 Laser light source 22 Laser beam 23 Translucent window 24 Energy beam source 25 Silicon source 26 Doping element source 31 Bottom cell 41 Top cell

Claims (10)

[Claims] 1. A different two photovoltaic elements are stacked comprising photovoltaic device, which is disposed on the incident side of the light photovoltaic element (112) I-III-VI 2 compound oriented A light absorbing layer, and the other photovoltaic element uses crystalline silicon as a light absorbing layer. 2. A photovoltaic device formed by laminating two different photovoltaic element disposed on the incident side of the light photovoltaic element _{Cu 1-x Ag x In 1} -y Ga y S ₂ (0 ≦ x ≦
0.7,0 ≦ y ≦ 0.4), Cu 1-x Ag x In 1-y Al y
S ₂ (0 ≦ x ≦ 0.7, 0 ≦ y ≦ 0.2) and CuIn
A photovoltaic device characterized in that _{one of 1-x} Al _x Se ₂ (0.2 ≦ x ≦ 0.5) is used as a light absorbing layer, and the other photovoltaic element uses crystalline silicon as a light absorbing layer. Power equipment. 3. A different two photovoltaic elements are stacked comprising photovoltaic device, is disposed on the incident side of the light photovoltaic element is a light absorbing layer a I-III-VI ₂ group compounds And a semiconductor material layer having a larger band gap than the light absorbing layer is laminated on the light absorbing layer, and the other photovoltaic element uses crystalline silicon as the light absorbing layer. 3. The photovoltaic device according to 2. 4. A claim that large semiconductor material layer of a band gap than I-III-VI ₂ group compound is characterized by comprising a layer and the transparent electrode layer to form a junction with I-III-VI ₂ group compounds 3. The photovoltaic device according to 3. 5. The photovoltaic device according to claim 4, wherein the layer forming a junction with the I-III-VI group ₂ compound is selected from ZnS, ZnSe, ZnO and a mixed crystal thereof. apparatus. 6. A photovoltaic device in which two different photovoltaic elements are stacked, wherein Ti, Mo are placed between a photovoltaic element disposed on the light incident side and the other photovoltaic element. , W
6. The photovoltaic device according to claim 1, further comprising a thin film made of any one of TiN and TiN. 7. The photovoltaic device according to claim 1, wherein the crystalline silicon is a (111) oriented polycrystalline silicon thin film deposited on the seed layer. . 8. A photovoltaic element comprising two different photovoltaic elements stacked one on another, and the photovoltaic element disposed on the light incident side is (112).
The oriented I-III-VI group ₂ compound is used as a light absorbing layer,
In the method for manufacturing a photovoltaic device in which the other photovoltaic element uses crystalline silicon as a light absorbing layer, the formation of crystalline silicon is performed by forming an amorphous or microcrystalline silicon thin film on a substrate, A photovoltaic device, wherein the silicon 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. Manufacturing method. 9. The method of manufacturing a photovoltaic device according to claim 8, wherein the formation of the seed layer and the formation of the polycrystalline silicon thin film thereon are continuously performed in a vacuum. 10. The photovoltaic device according to claim 8, wherein 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. Production method.