JPH1022519A - Photovoltaic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer lamination type photovoltaic device with a high photoelectric conversion efficiency and a low cost, by making its bottom layer comprise both an ionic bond type thin film containing at least crystallines and a polycrystal silicon layer formed thereon. SOLUTION: Heating a pyrex substrate 1 in a reaction chamber at, e.g. 300 deg.C and using an Ar gas as a carrier gas after exhausting air therefrom, acethylacetone zinc, H2 O and B2 H6 are introduced into the reaction chamber to make them react on each other under the adjusted pressure of 1300Pa in a predetermined time and to form a ZnO:B thin film 2. Further, heating the film 2 in a vacuum chamber and generating simultaneously a silicon vapor and a molecular beam of boron from an Si source and a Knudsen cell, a p-type polycrystal silicon film 3 is formed, and then, generating a molecular beam of phosphorus from the Knudsen cell, an n-type polycrystal silicon thin film 4 is formed. Subsequently, disposing this substrate in a sputtering equipment, p-type and n-type SiO2 -doped Si thin films 7, 8 and an ITO thin film 9 are formed in succession to obtain a photovoltaic device with an excellent orientation quality, a low cost and a high photoelectric conversion efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layer photovoltaic device in which a plurality of photovoltaic layers are stacked, and more particularly, to a multi-layer photovoltaic device in which the photovoltaic layer furthest from the light incident side is improved. It relates to a power device.

[0002]

2. Description of the Related Art A photovoltaic device having a structure in which two or three photovoltaic layers are stacked in order to obtain high conversion efficiency by effectively utilizing incident light is known. Here, the photovoltaic layer is a layer that generates an electromotive force by light irradiation, and indicates one unit including a photocarrier generation layer, a bonding layer, an electrode, and the like as constituent elements. In general, in the case of such a structure, a semiconductor having a large band gap is used for a main photocarrier generation layer in a layer close to the light incident side, and a semiconductor having a small band gap is used in a layer far away. By doing so, light in the short wavelength region is absorbed by the layer close to the light incident side, and light in the long wavelength region that could not be absorbed there is absorbed by the far layer, so that light in the wide wavelength region is effectively used. be able to. For example, in Japanese Patent Publication No. 6-44638, p
N-type amorphous silicon is formed on a p-type polycrystalline silicon substrate to form one photovoltaic layer, and p-type amorphous silicon, i-type amorphous silicon, and n-type amorphous silicon are sequentially formed to form another photovoltaic layer. In layers. The main photocarrier generation layer in each photovoltaic layer is p-type polycrystalline silicon and i-type amorphous silicon, and 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. In Japanese Patent Application Laid-Open No. 6-283737, an n-type layer is formed by doping phosphorus on a p-type polycrystalline silicon substrate (wafer) by a thermal diffusion method to form one photovoltaic layer, and an electrode is formed. Then, the p-type Cu (I
(n, Ga) S ₂ and n-type CdS are sequentially formed to form another photovoltaic layer. The main photocarrier generation layer in each photovoltaic layer is p-type polycrystalline silicon and p-type Cu (I
n, Ga) is S _2, a band gap of the former is smaller than the latter light incidence is made from Cu (In, Ga) S ₂ side.

In any of the above conventional examples, polycrystalline silicon is used as a main photocarrier generation layer of a photovoltaic layer farthest from a light incident side (referred to as a bottom layer for convenience). Since the wafer has a thickness of several hundreds of μm, the production cost is high, and there is a problem in terms of effective use of resources because a large amount of silicon material is used. In order to solve these problems, a photovoltaic device using thin-film polycrystalline silicon having a thickness of several tens μm or less has been proposed.
Japanese Patent Application Laid-Open No. 4-296062 discloses that n-type amorphous silicon, i-type amorphous silicon, p-type
After the amorphous silicon is sequentially formed by a CVD method or a sputtering method, it is crystallized by annealing at a temperature of about 600 ° C. for several tens of hours to form a bottom layer. Further, n-type amorphous silicon, i-type amorphous silicon, The other type of photovoltaic layer is formed by sequentially forming type amorphous silicon by a CVD method or a sputtering method. Such photovoltaic devices have the following problems: (1) heat resistance of 600 ° C. or higher is required, so that an inexpensive glass substrate cannot be used; (2) annealing time is long and throughput is poor. The point was still not satisfactory.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art, and has the following objects. It is an object of the present invention to provide a high-efficiency and low-cost multilayer stacked photovoltaic device using a polycrystalline silicon thin film having excellent orientation for a bottom layer, which can use an inexpensive substrate that can be formed at a low temperature. 2. It is another object of the present invention to provide a multi-layer photovoltaic device with higher efficiency using a polycrystalline silicon thin film having excellent orientation. 3. It is an object of the present invention to provide a multi-layer photovoltaic device with improved efficiency and improved junction characteristics between photovoltaic layers. 4. It is another object of the present invention to provide a lower-cost multi-layer stacked photovoltaic device that can be operated at a lower temperature and has a reduced number of constituent layers. 5. Using a polycrystalline silicon thin film with a larger particle size,
An object of the present invention is to provide a multi-layer stacked photovoltaic device with higher efficiency. 6. An object of the present invention is to provide a multi-layer stacked photovoltaic device having a higher efficiency and using a uniform polycrystalline silicon thin film with less defects.

[0005]

According to the present invention, first, in a photovoltaic device in which a plurality of photovoltaic layers are stacked, the photovoltaic layer farthest from the light incident side is at least crystalline. And a polycrystalline silicon thin film formed on the ion-bonding thin film. Secondly, in the photovoltaic device described in the first aspect, the photovoltaic layer farthest from the light incident side is at least a metal thin film formed on the substrate, and an ionic bond formed on the metal thin film. A photovoltaic device comprising a thin film and a polycrystalline silicon thin film formed on the ion-bonding thin film is provided. Third, in the photovoltaic device according to the first aspect, the photovoltaic layer farthest from the light incident side is an ion-bonding thin film formed on at least another photovoltaic layer and the ion-bonding thin film. There is provided a photovoltaic device having a polycrystalline silicon thin film formed on the thin film. Fourthly, there is provided a photovoltaic device according to the first, second, or third aspect, wherein the ion-bonding thin film is made of zinc oxide. Fifth, in the photovoltaic device according to the first, second, third, or fourth, the polycrystalline silicon thin film is formed by depositing silicon atoms or silicon compound molecules under energy beam irradiation. A photovoltaic device is provided. Sixth, there is provided a photovoltaic device according to the fifth aspect, wherein the energy beam is an electron beam. Seventh, there is provided a photovoltaic device according to the third aspect, wherein a polycrystalline silicon thin film is formed on the ion-bonding thin film via a bonding film.

[0006] As described above, the photovoltaic device of the present invention comprises:
The photovoltaic layer (bottom layer) farthest from the light incident side has an ion-bonding thin film containing at least crystalline material and a polycrystalline silicon thin film formed on the ion-bonding thin film. Here, an ion-bonding thin film is a thin film in which bonds between atoms forming the thin film contain ionicity of about 10% or more. In other words, a thin film in which the difference in electronegativity between (usually two) elements constituting the thin film is approximately 0.7 or more. The present invention has been made based on the finding that such a thin film easily crystallizes even on a substrate at a relatively low temperature. Such a bottom layer has a structure in which a metal thin film is provided on a substrate, and the ion-bonding thin film and the polycrystalline silicon thin film are sequentially provided on the metal thin film. This is one of the preferred configurations from the standpoint of enhancing. Further, the bottom layer is preferably formed by providing an ion-bonding thin film and a polycrystalline silicon thin film on another photovoltaic layer, from the viewpoint of improving the bonding property between the photovoltaic layers and the light use efficiency. In addition, the ion-bonding thin film is preferably made of zinc oxide because high orientation can be obtained at a low temperature. Further, the polycrystalline silicon thin film is formed by depositing silicon atoms or silicon compound molecules under energy beam irradiation, so that the particle size becomes large even at a low substrate temperature, and high conversion efficiency can be obtained. Is preferred. Further, the energy beam is preferably an electron beam because it has few defects and forms a uniform thin film. Furthermore, when the bottom layer is provided on another photovoltaic layer as described above, providing a polycrystalline silicon thin film on the ion-bonding thin film via a bonding film (bonding layer) will reduce the diode characteristics of the bottom layer. This is preferable because it improves the conversion efficiency.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. First, the configuration of the first photovoltaic device and a method for forming the same will be described with reference to FIG. In FIG. 1, reference numeral 31 denotes a bottom layer having the following configuration. Reference numeral 1 denotes a substrate made of glass, ceramics, plastic, metal, or the like, and a heat-resistant plastic such as Pyrex, soda lime glass, or polyimide is particularly preferably used in terms of cost reduction.

[0008] 2 is ZnO, ZnS, ZnSe, AlN,
An ion-bonding thin film made of GaN or the like, containing at least crystalline material. A typical form is a polycrystal, but a structure in which single crystal particles are dispersed in an amorphous state or a structure in which single crystal particles are precipitated in an island shape may be used. In any case, it is desirable that the crystal grains constituting these have a plane orientation strongly oriented in one direction. Such an ion-bonding thin film is formed by a sputtering method, an ion braiding method, an MOCVD method, or the like, and has a thickness of 1 nm to 10 μm, preferably 10 nm.
m to 1 μm.

Reference numeral 3 denotes a silicon thin film, which is an ion-bonding thin film 2
Is a highly oriented polycrystal reflecting the crystal orientation of The silicon thin film is formed by an electron beam heating evaporation method, an ion plating method, a sputtering method, a plasma CVD method or the like, and has a thickness of 0.5 to 100 μm, preferably 1 to 1 μm.
0 μm. This polycrystalline silicon thin film shows a slight n-type conduction (carrier concentration of about 10 ¹² to 10 ¹⁶ / cm ³ ) when the impurity element is not intentionally doped. May be performed. For example, in order to obtain p-type conductivity, B, Al, or the like is supplied during film formation using a solid source, a Knudsen cell using a gas source, an ion gun, or a normal CVD gas source.

As the gas hose, B ₂ H ₆ , B (C ₂ H ₅
O) ₃ , Al (C ₅ H ₇ O ₂ ) ₃ , Al (C ₃ H ₇ O) _{3 and the} like can be used.

Further, P, As, etc. are supplied in the same manner as described above in order to obtain n-type conduction. PH as gas source
₃ , P (C ₂ H ₅ ) ₃ , AsH _{3 and the} like can be used.

Reference numeral 4 denotes a bonding film for forming a potential barrier for separating carriers generated in the polycrystalline silicon thin film 3.
A polycrystalline, microcrystalline, or amorphous silicon thin film of a conductivity type opposite to that described above, or a metal thin film of Pt, Au, or the like is used. In the former, a pn junction is formed, and in the latter, a Schottky contact forms a potential barrier. The formation of these bonding films is performed by an electron beam evaporation method, an ion plating method, a sputtering method, a plasma CVD method, or the like, and the film thickness is 10 to 500 in a polycrystalline, microcrystalline, or amorphous silicon thin film.
nm, and 1 to 50 nm is appropriate for a metal thin film.

These thin films 2, 3 and 4 have a substrate temperature of 5
It is formed at a temperature of 00 ° C. or less, preferably 400 ° C. or less. In order to collect separated carriers, if the substrate 1 is an insulator, it is necessary to form a comb-shaped or planar electrode film thereon, but if the ion-bonding thin film 2 has conductivity, Can omit it.

Reference numeral 21 denotes another photovoltaic layer, for example, from the top, an amorphous silicon-based transparent conductive film having a structure of transparent conductive film / n (p) type amorphous silicon / i type amorphous silicon / p (n) type amorphous silicon; Conductive film / CdS
/ Cu (In, Ga) (Se, S) ₂ chalcopyrite system, transparent conductive film / II-VI group system having CdS / CdTe structure, comb electrode / n (p) type Al _x Ga _{1 -X} As /
addition may be a known photovoltaic layer of a group III-V or the like having the structure of p (n) type Al _X Ga _1-X As, light with Si0 ₂ doped Si thin film optical carrier generation layer An electromotive layer can be used.

An SiO ₂ -doped Si thin film is described, for example, in K.
Kohno, Y .; Osaka and H .; Kataya
ma: Jpn. J. Appl. Phys. Vol. 3
3 (1994) pp. L1167, a film obtained by a sputtering method using a Si target on which a SiO ₂ chip is mounted, which has an optical band gap of 1.4 eV or more and has a band of 1.4 to 1.7 eV. Light absorption is higher than that of amorphous silicon. The structure of the photovoltaic layer using this is a transparent conductive film / n (p) -type SiO ₂ -doped Si thin film / p (n) -type Si
O ₂ doped Si thin film or metal thin film / n (p) type Si
O ₂ -doped Si thin film and the like can be mentioned. The control of the conduction type can be performed in the same manner as described above. The photovoltaic layer 21 may be formed by stacking two or more layers having the above structure. In this case, the band gap of the semiconductor to be the photocarrier generation layer is selected so as to decrease as the distance from the light incident side increases.

Next, the configuration of the photovoltaic device described above and the method of forming the same will be described with reference to FIG. 2, a base 1, an ion-bonding thin film 2, a polycrystalline silicon thin film 3, and a bonding film 4 are the same as those in FIG. Reference numeral 5 denotes a metal thin film made of Au, Ag, Al, Pt, Cu, Ni, or the like, and a typical form is a polycrystal oriented in the (111) direction. Such a metal thin film is formed by a sputtering method, a vacuum evaporation method, an ion plating method or the like to have a film thickness ln.
m to 1 μm, preferably 10 nm to 300 nm. When the metal thin film 5 is provided, the orientation of the ion-bonding thin film 2 formed thereon is further increased, so that the silicon thin film 3 also becomes a polycrystal having a higher orientation. Further, the metal thin film 5 reflects light once transmitted through the polycrystalline silicon thin film 3 and returns it to the inside of the polycrystalline silicon thin film again, that is, further increases the light use efficiency by substantially increasing the optical path length. Since it works, the conversion efficiency is higher. The metal thin film 5 may have a structure in which two or more kinds of materials are laminated for the purpose of enhancing the (111) orientation or improving the adhesion to the base. In this case, the above material is used for the upper layer, and Ti and Z are used for the lower layer.
It is preferable to use r, Mg or the like. On the bottom layer 31 thus formed, another photovoltaic layer 2 similar to FIG.
Form one.

Next, the structure of the photovoltaic device described above and the method of forming the same will be described with reference to FIG. First, the photovoltaic layer 21 is formed on the base 1. As the photovoltaic layer 21, an amorphous silicon-based material having a structure of transparent conductive film / n (p) -type amorphous silicon / i-type amorphous silicon / p (n) -type amorphous silicon from the substrate side, a transparent conductive film / CdS / Cu (In, Ga) (Se,
S) Chalcopyrite-based transparent conductive film with structure ₂ / C
It has a structure of a known photovoltaic layer such as a II-VI group or the like having a structure of dS / CdTe, a transparent conductive film, an n (p) type SiO ₂ -doped Si thin film, and a p (n) type SiO ₂ -doped Si thin film. A photovoltaic layer or the like is used.

A bottom layer 31 is formed on the photovoltaic layer 21. The bottom layer 31 includes the ion-bonding thin film 2 and the bonding layer (n
(p) -type polycrystalline silicon thin film 4, p (n) -type polycrystalline silicon thin film 3, and back electrode 6. Ion-bonding thin film 2
In addition to exhibiting a strong orientation, it is necessary that the compound has low light absorption and high conductivity. The former is a condition necessary for effectively taking light into the polycrystalline silicon thin film 3, and the latter is a condition required for recombining majority carriers generated in the photovoltaic layer 21 and the bottom layer 31 and exchanging carriers. In order to satisfy the former, the material forming the ion-bonding thin film 2 preferably has a band gap of 2.5 eV or more, specifically, ZnO, ZnS, ZnSe, Al
N, GaN and the like are exemplified. Such a material is generally a semiconductor and therefore has low conductivity, but conductivity can be increased by introducing defects or impurities. Taking ZnO as an example, a composition with a slight excess of Zn to create O defects or Al,
10 ^-3 Ωc by doping elements such as Ga and B
m or less can be obtained. Further, by selecting film forming conditions (substrate temperature, pressure, doping gas flow rate, etc.), surface irregularities can be controlled. By forming deep irregularities, light scattering can be increased and the optical path can be substantially lengthened. The bonding layer (n (p) -type polycrystalline silicon thin film) 4 and the p (n) -type polycrystalline silicon thin film 3 are formed in the same manner as described above. Back electrode 6 is made of A1, Ag, A
u, Ni, etc., and has a film thickness of 1n by sputtering, vacuum evaporation, ion plating, etc.
m to 1 μm, preferably 10 nm to 300 nm. Incidentally, these metal thin films may be laminated in two or more layers as necessary. In the above structure, the bonding layer (n (p)
Even if the n-type polycrystalline silicon thin film 4 is not provided, the ion-bonding thin film (n-type semiconductor)
A pn junction is formed with the polycrystalline silicon thin film 3. In this case, however, it is preferable to provide the bonding layer 4 because the diode characteristics deteriorate and the conversion efficiency deteriorates.

Next, the photovoltaic device described in the fourth aspect is
In the first, second and third photovoltaic devices, the ion-bonding thin film is made of zinc oxide (ZnO). The ZnO thin film typically has a wurtzite type crystal structure, is oriented in the (001) direction, and can be obtained even at a low substrate temperature of 300 ° C. or less, which is very advantageous in reducing the cost of the substrate material. It is. The ZnO thin film is formed by a sputtering method,
It is performed by an ion plating method, an MOCVD method, or the like, and the MOCVD method is preferable from the viewpoint of lowering the temperature and uniformity of the film.

Hereinafter, a method of forming a ZnO thin film by MOCVD will be described. The source gas is Zn zinc, dimethyl zinc, zinc acetylacetonate, etc. as a source of Zn, and H ₂ O, O ₂ , CO ₂ , D ₂ O,
N ₂ O or the like is used. The Zn source is heated to 0 to 100 ° C., and a flow rate of 10 to 500 sccm is used together with a carrier gas such as H ₂ , Ar, He, N ₂ , CO ₂ , and the oxygen source is used alone or together with the above carrier gas. ~ 100
It is simultaneously introduced into the reaction chamber at a flow rate of 0 sccm.
Chamber pressure is atmospheric pressure or 130Pa ~ 13k
Pa, preferably adjusted to 650 Pa to 2600 Pa. A substrate heated to a temperature of 100 to 500 ° C., preferably 100 to 300 ° C. is provided in the reaction chamber, and the raw material gas is decomposed and reacted on the substrate to obtain a ZnO thin film.

As described above, the conductivity of this film can be increased by making the composition excessive in Zn or by doping B, Al, Ga or the like. As the doping gas, B
_{2 H 6, B (C 2} H 5 O) 3, Al (C 5 H 7 O 2) 3, Al
(C ₃ H ₇ O) ₃ , Ga (C ₅ H ₇ O ₂ ) ₃ , Ga (C ₃ H
₇ O) ₃ etc. can be used.

Although the polycrystalline silicon thin film formed on the ZnO thin film is preferentially oriented to (111), the crystallinity may be impaired due to a rather large lattice mismatch. In order to avoid this, ZnS, CaF ₂ , ZnS
It is desirable to form a thin film made of e, ZnTe, Se, Te, S, Al ₂ O _3, etc. with a thickness of 1 nm to 1 μm, preferably ₃ nm to 500 nm. These films are MOCVD
It is formed by a method, a sputtering method, a vacuum evaporation method, an ion plating method, or the like. Particularly, ZnS is most preferable in terms of lattice constant. ZnS thin film is made of H
MOC same as above except that ₂ S, CS ₂ etc. are used
It can be formed by the VD method.

Next, the fifth photovoltaic device is the first photovoltaic device.
In the second, third, and fourth photovoltaic devices, a polycrystalline silicon thin film is formed by depositing silicon atoms or silicon compound molecules under irradiation of an energy beam such as an electron beam, an ion beam, a laser beam, or an X-ray. It was done. A method for forming a polycrystalline silicon thin film will be described with reference to FIG. The substrate 1 having the ion-bonding thin film 2 is set in the vacuum chamber 51, and maintained at a predetermined temperature of 500 ° C. or lower, preferably 400 ° C. or lower. After the inside of the chamber is evacuated to 1 × 10 ⁻⁴ Pa or less, the chamber is kept at a predetermined atmosphere according to the film forming means. For example, a high vacuum of 1 × 10 ⁻⁴ Pa or less or 1 × 1
H ₂ atmosphere of 0 ⁻³ Pa or less, ion plating method,
And 1 × 10 ^{−2 to} 10 Pa of A in the sputtering method.
r, He, N ₂ , H _2, etc. and a mixed gas atmosphere thereof, and a plasma CVD method of 1 × 10 ^{−2 to} 100 Pa Si
H ₄ , Si ₂ H ₆ , SiF ₄ , SiH ₂ Cl _{2 and the} like, and a mixed gas atmosphere of these and H ₂ or a rare gas 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 52, and at the same time, silicon atoms or silicon compound molecules are generated from the Si source 53 to deposit a silicon thin film on the substrate. Let it. In the sputtering method, a Si target is provided in place of a Si source in the plasma CVD method, and a film is formed by applying a DC or high-frequency electric field thereto. The energy beam irradiation increases the mobility of silicon atoms on the substrate surface, so that a polycrystalline silicon thin film having a large grain size can be formed even at a low substrate temperature. A high-quality polycrystalline silicon thin film can be obtained in combination with the high orientation by having the ion-bonding thin film.

Next, the photovoltaic device described in the sixth aspect is
In the photovoltaic device described in the fifth aspect, the energy beam is 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, the electron beam can be deflected by a magnetic field or an electric field. In particular, by using an electric field deflection, a long distance can be scanned at a high speed. There is an advantage that it can be obtained. 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 kV, a current density of 1 μA / cm ^{2 to} 1 A / cm ² , preferably 10 μA / cm ^{2 to 1} mA / cm ² is suitable.

In this method, the polycrystalline silicon thin film can be formed on a large-area substrate by scanning the electron beam in one or two axial directions and transporting the substrate in a direction substantially perpendicular to the one scanning direction. It is possible. The method will be described with reference to FIG. An electron beam emitted from the electron beam source 52 is applied to an X-Y electrostatic deflection electrode (not shown) provided near the exit by applying an alternating electric field of 1 kHz to 1 MHz to an area on the substrate 1. Irradiation is performed while moving the area S at a predetermined cycle. At the same time, silicon vapor is generated from the Si source 53, and a polycrystalline silicon thin film is deposited on the substrate 1. By continuously or intermittently transporting the substrate in the direction of arrow A at a constant speed, a polycrystalline silicon thin film is formed on the entire surface of the substrate. According to this method, a uniform polycrystalline silicon thin film can be obtained on a large-area substrate. In particular, since there is no restriction on the length in the transport direction, it can be formed on a roll-shaped substrate. Note that a plurality of electron beam sources and Si sources may be arranged as necessary.

[0027]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples. Example 1 The photovoltaic device shown in FIG. 6 was manufactured as follows. Pyrex substrate 1 was placed in a reaction chamber and heated to 300 ° C. The chamber was evacuated, Ar acetylacetonate zinc was introduced at a source temperature of 100 ° C. and a flow rate of 100 sccm, H ₂ O was introduced at a source temperature of 40 ° C. and a flow rate of 30 sccm, and B ₂ H ₆ was introduced at a flow rate of 1 sccm using Ar as a carrier gas. The pressure was adjusted to 1300 Pa. By reacting for a predetermined time, the film thickness 2
A 00 nm ZnO: B thin film 2 was formed. X-ray diffraction revealed that this film was preferentially oriented in the (001) direction. This substrate was set in a vacuum chamber shown in FIG. 4 and heated to 500 ° C. Make the chamber 1 × 10 ^-5 Pa
After evacuation, a silicon vapor was generated from the Si source 53 by electron beam heating, and at the same time, a B (boron) molecular beam was generated from the Knudsen cell 54 to form a p-type polycrystalline silicon thin film 3 having a thickness of 3 μm. . Subsequently, while generating silicon vapor, a molecular beam of P (phosphorus) was generated from the Knudsen cell 55 to form an n-type polycrystalline silicon thin film (bonding film) 4 having a thickness of 100 nm. These silicon thin films are preferentially oriented in the (111) direction and have a crystal grain size of about 500 n.
m. Next, this substrate is placed in the sputtering apparatus shown in FIG. 7, heated to 300 ° C., and RF power is supplied to the Si target 61 on which the SiO ₂ chip 62 is mounted, and at the same time, B (boron) ions are generated from the ion gun 63. Thus, a p-type SiO ₂ -doped Si thin film 7 having a thickness of 500 nm was formed. Subsequently, while supplying RF power to the target, P (phosphorus) ions are generated from the ion gun 64 to form a film having a thickness of 100 μm.
The n-type SiO ₂ -doped Si thin film 8 is formed to a thickness of 100 nm, and the ITO thin film 9
Was formed. The conversion efficiency of this photovoltaic device is 15.5%
(AM 1.5, 100 mW / cm ² , the same applies hereinafter).

Example 2 The photovoltaic device shown in FIG. 8 was manufactured as follows. On a Pyrex substrate 1, a Ti thin film 5 'having a thickness of 50 nm and a thickness of 1
An Ag thin film 5 having a thickness of 00 nm was formed. A ZnO thin film 2 was formed thereon in the same manner as in Example 1. However, doping gas (B ₂ H ₆ ) was not supplied. This film showed a stronger (001) orientation than that of Example 1. On this, a p-type polycrystalline silicon thin film 3 was formed in the same manner as in Example 1.
Then, an n-type polycrystalline silicon thin film (bonding film) 4 was formed. These films showed an even stronger (111) orientation than in Example 1. This substrate was placed in a parallel plate type plasma CVD apparatus and heated to 300 ° C. Evacuate the chamber,
Source gas: B ₂ H ₆ / SiH ₄ = 0.1%, total flow rate 50 s
After the pressure was set to 30 Pa, RF power was supplied to the cathode to form a p-type amorphous silicon thin film 10 having a thickness of 20 nm. Subsequently, the raw material gas is SiH ₄
After setting the pressure to 30 Pa and supplying RF power to the cathode, an i-type amorphous silicon thin film 11 having a thickness of 300 nm was formed. Next, the raw material gas was changed to PH ₃ / SiH ₄
= 0.1%, the pressure was set to 30 Pa, and RF power was supplied to the cathode to form an n-type amorphous silicon thin film 12 having a thickness of 10 nm. Finally, an ITO thin film 9 having a thickness of 100 nm was formed by a sputtering method. Formed. The conversion efficiency of this photovoltaic device was 15.6%.

Example 3 The photovoltaic device shown in FIG. 8 was manufactured as follows. On a Pyrex substrate 1, a Ti thin film 5 'having a thickness of 50 nm and a thickness of 1
An Ag thin film 5 having a thickness of 00 nm was formed. A ZnO thin film 2 was formed thereon in the same manner as in Example 2. Fig. 4
And was heated to 400 ° C. The chamber was evacuated to 5 × 10 ⁻⁵ Pa, and the substrate was irradiated with an electron beam from the electron beam source 52 at an acceleration voltage of 15 kV and a current density of 100 μA / cm ² . Silicon vapor was generated from the Si source 53 by electron beam heating, and at the same time, a molecular beam of B (boron) was generated from the Knudsen cell 54 to form the p-type polycrystalline silicon thin film 3 having a thickness of 5 μm. This film was strongly oriented in the (111) direction, and the crystal grain size was about 4 μm. This substrate is used as a parallel plate type plasma CV.
It was set in a D apparatus and heated to 300 ° C. The chamber was evacuated, the source gas was introduced at PH ₃ / SiH ₄ = 0.5%, the total flow rate was 50 sccm, the pressure was 30 Pa, RF power was supplied to the cathode, and the n-type amorphous silicon thin film having a thickness of 20 nm was obtained. (Bonding film) 4 was formed. Next, a p-type amorphous silicon thin film 1 was formed in the same manner as in Example 2.
0, an i-type amorphous silicon thin film 11, an n-type amorphous silicon thin film 12, and an ITO thin film 9 were formed. The conversion efficiency of this photovoltaic device was 17.8%.

Example 4 The photovoltaic device shown in FIG. 8 was manufactured as follows. On the Pyrex substrate 1, a Ti thin film 5 ', an Ag thin film 5, and a ZnO thin film 2 were formed in the same manner as in Example 2. This substrate was set in a vacuum chamber shown in FIG. 4 and heated to 400 ° C. 5 × 10 chamber
^After evacuation to ⁻⁵ Pa, the substrate was irradiated with an electron beam from the electron beam source 52 at an acceleration voltage of 10 kV and a current density of 200 μA / cm ² . Silicon vapor was generated from the Si source 53 by electron beam heating to form an n ⁻ -type polycrystalline silicon thin film 3 having a thickness of 5 μm. This film was strongly oriented in the (111) direction, and the crystal grain size was about 5 μm. A 10 nm-thick Pt thin film (bonding film) 4 was formed thereon by a sputtering method. Next, the p-type amorphous silicon thin film 10, the i-type amorphous silicon thin film 11,
n-type amorphous silicon thin film 12 and ITO thin film 9
Was formed. The conversion efficiency of this photovoltaic device is 15.9%
Met.

Example 5 The photovoltaic device shown in FIG. 9 was manufactured as follows. Al ₂ on Pyrex substrate 1
A ZnO: Al thin film 13 having a thickness of 1 μm was formed by a sputtering method using an O ₃ -containing ZnO target, and a p-type amorphous silicon thin film 10, an i-type amorphous silicon thin film 11, and n were formed thereon in the same manner as in Example 2. An amorphous silicon thin film 12 was formed. Subsequently, after a ZnO thin film 2 was formed thereon in the same manner as in Example 2, FIG.
And heated to 300 ° C. The chamber was evacuated to 5 × 10 ⁻⁵ Pa, and the substrate was irradiated with an electron beam from the electron beam source 52 at an acceleration voltage of 10 kV and a current density of 400 μA / cm ² . A silicon vapor is generated from the Si source 53 by electron beam heating, and at the same time, a B (boron) molecular beam is generated from the Knudsen cell 54 to form a p-type polycrystalline silicon thin film (bonding film) having a thickness of 300 nm.
4 was formed. Then, while generating silicon vapor,
A P (phosphorus) molecular beam was generated from the Knudsen cell 55 to form an n-type polycrystalline silicon thin film 3 having a thickness of 5 μm. These silicon thin films were strongly oriented in the (111) direction, and had a crystal grain size of about 3 μm. An Al thin film 6 having a thickness of 200 nm was formed thereon by sputtering. The conversion efficiency of this photovoltaic device was 16.9%.

[0032]

As described above, according to the multilayer photovoltaic device of the present invention, the following effects can be obtained. First,
According to the configuration described in the first aspect, since the bottom layer has the ion-bonding thin film containing at least crystalline material and the polycrystalline silicon thin film formed on the ion-bonding thin film, low-temperature formation can be achieved. Therefore, an inexpensive substrate can be used, and the photovoltaic device with high conversion efficiency can be obtained at low cost because of excellent orientation. According to the configuration described in the second aspect, a metal thin film having a bottom layer formed on a substrate, an ion-bonding thin film formed on the metal thin film, and polycrystalline silicon formed on the ion-bonding thin film Since the thin film has a thin film, the orientation efficiency is further improved and the light use efficiency is increased, so that a photovoltaic device having higher conversion efficiency can be obtained. According to the configuration described in the third aspect, since the bottom layer has an ion-bonding thin film formed on another photovoltaic layer, and a polycrystalline silicon thin film formed on the ion-bonding thin film,
Since the junction characteristics between the photovoltaic layers are improved and the light use efficiency is increased, a photovoltaic device with higher conversion efficiency can be obtained. According to the configuration described in the fourth aspect, since the ion-bonding thin film is a ZnO thin film, the film easily becomes highly oriented at a low temperature, so that an inexpensive base material having low heat resistance can be used. The cost of the electromotive device is reduced. According to the configuration described in the fifth aspect, since the formation of the polycrystalline silicon thin film is performed by depositing silicon atoms or silicon compound molecules under energy beam irradiation, the particle size increases even at a low substrate temperature,
A photovoltaic device with higher conversion efficiency can be obtained. According to the configuration described in the sixth aspect, since the energy beam is an electron beam, a polycrystalline silicon thin film having low defects and good uniformity can be obtained, and a photovoltaic voltage having high conversion efficiency even on a large-area substrate. A device is obtained. According to the configuration described in the seventh aspect, in the configuration described in the third aspect, the polycrystalline silicon thin film is formed on the ion-bonding thin film via the bonding layer, so that the diode characteristics of the bottom layer are improved. Thus, a photovoltaic device with higher conversion efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a photovoltaic device of the present invention described in the first aspect.

FIG. 2 is a diagram illustrating a configuration of a photovoltaic device according to the second aspect of the present invention.

FIG. 3 is a diagram showing a configuration of the photovoltaic device according to the third aspect of the present invention.

FIG. 4 is a view showing an apparatus for forming a polycrystalline silicon thin film according to the present invention.

FIG. 5 is a view showing a part of an apparatus for forming a polycrystalline silicon thin film according to the present invention.

FIG. 6 is a diagram illustrating a configuration of a photovoltaic device according to a first embodiment.

FIG. 7 is a diagram showing an apparatus for forming another photovoltaic layer of the photovoltaic apparatus of Example 1.

FIG. 8 is a diagram illustrating a configuration of photovoltaic devices of Examples 2, 3, and 4.

FIG. 9 is a diagram illustrating a configuration of a photovoltaic device according to a fifth embodiment.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 base 2 ion-bonding thin film 3 polycrystalline silicon thin film 4 bonding film 5, 5 ′ metal thin film 6 back electrode 7 p-type SiO ₂ -doped Si thin film 8 n-type SiO ₂ -doped Si thin film 9 ITO thin film 10 p-type amorphous silicon thin film 11 i-type amorphous silicon thin film 12 n-type amorphous silicon thin film 13 ZnO: Al thin film 21 other photovoltaic layer 31 bottom layer 51 vacuum chamber 52 energy beam source (electron beam source) 53 Si source 54 Knudsen cell (B source) 55 Knudsen Cell (P source) 61 Si target 62 SiO ₂ chip 63 Ion gun (B source) 64 Ion gun (P source) 65 RF power supply 71 Incident light S Electron beam irradiation area X Electron beam scanning range Y Electron beam scanning range

Claims (7)

[Claims] In a photovoltaic device in which a plurality of photovoltaic layers are stacked, a photovoltaic layer farthest from a light incident side is formed on an ion-bonding thin film containing a crystalline material and on the ion-bonding thin film. A photovoltaic device comprising at least a polycrystalline silicon thin film. 2. A photovoltaic layer farthest from a light incident side,
2. The light according to claim 1, comprising at least a metal thin film formed on a substrate, an ion-bonding thin film formed on the metal thin film, and a polycrystalline silicon thin film formed on the ion-bonding thin film. Electromotive device. 3. The photovoltaic layer farthest from the light incident side,
2. The photovoltaic device according to claim 1, comprising at least an ion-bonding thin film formed on another photovoltaic layer and a polycrystalline silicon thin film formed on the ion-bonding thin film. 4. The photovoltaic device according to claim 1, wherein said ion-bonding thin film is made of zinc oxide. 5. The polycrystalline silicon thin film according to claim 1, wherein the polycrystalline silicon thin film is formed by depositing silicon atoms or silicon compound molecules under irradiation of an energy beam. Photovoltaic devices. 6. The photovoltaic device according to claim 5, wherein said energy beam is an electron beam. 7. The photovoltaic device according to claim 3, wherein
A photovoltaic device comprising a polycrystalline silicon thin film formed on an ion-bonding thin film via a bonding film.