JP2710246B2 - Photovoltaic element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device,
In particular, the present invention relates to a photovoltaic element having high photoelectric conversion efficiency and high reliability and used for a solar cell or the like.

[0002]

2. Description of the Related Art Solar cells, which are photoelectric conversion elements that convert sunlight into electric energy, have been widely applied as small power sources for consumer use such as calculators and wristwatches.
It is attracting attention as a technology that can be put to practical use as a substitute for fossil fuels such as oil and coal. A solar cell is a technology that utilizes the photovoltaic power of a pn junction of a semiconductor. A semiconductor such as silicon absorbs sunlight to generate photocarriers of electrons and holes, and the photocarriers are converted into an electric field inside the pn junction. It drifts out and is taken out. Such a method for manufacturing a solar cell is generally performed by using a semiconductor process. Specifically, a single crystal of silicon whose valence electrons are controlled to p-type or n-type is formed by a crystal growth method such as the cz method, and the single crystal is sliced to form a silicon wafer having a thickness of about 300 μm. Further, a pn junction is formed by forming a layer of a different conductivity type by an appropriate means such as diffusion of a valence electron controlling agent so as to have a conductivity type opposite to the conductivity type of the wafer.

[0003] From the viewpoints of reliability and conversion efficiency, single-crystal silicon is used in solar cells that are currently mainly put to practical use, but as described above, solar cell fabrication involves a semiconductor process. Production costs are high due to use.

Another disadvantage of single crystal silicon solar cells is that single crystal silicon has a low light absorption coefficient due to indirect transitions, and single crystal solar cells must be at least 50 microns thick to absorb incident sunlight. That is, the band gap is about 1.1 eV, which is narrower than 1.5 eV which is suitable for a solar cell, so that a long wavelength component cannot be used effectively. Also, even if the production cost is reduced by using polycrystalline silicon, the problem of indirect transition remains, and the thickness of the solar cell cannot be reduced. Polycrystalline silicon also has grain boundaries and other problems.

Further, a large-area wafer cannot be manufactured due to the crystalline nature, and it is difficult to increase the area. If a large amount of power is to be taken out, wiring for serializing or parallelizing the unit elements must be provided. What you have to do,
Production costs per unit power generation are higher than existing power generation methods, as expensive solar cell installations are required to protect solar cells from mechanical damage caused by various weather conditions when used outdoors. There is a problem that it becomes. Under these circumstances, in promoting the practical use of solar cells for electric power, cost reduction and large area are important technical issues, and various studies have been made. Exploration of materials such as high-quality materials has been conducted, but such materials for solar cells include tetrahedral amorphous semiconductors such as amorphous silicon, amorphous silicon germanium, and amorphous silicon carbide. And II-VI group such as CdS and Cu ₂ S, and Ga
Group III-V compound semiconductors such as As and GaAlAs are exemplified. In particular, a thin-film solar cell using an amorphous semiconductor for the photovoltaic power generation layer can produce a large-area film compared to a single-crystal solar cell, can have a small thickness, and can be used for any substrate material. It has advantages such as being able to be deposited and is considered promising.

However, a solar cell using the above amorphous semiconductor has improved photoelectric conversion efficiency as a power element.
Problems remain in terms of improving reliability.

As a means for improving the photoelectric conversion efficiency of a solar cell using an amorphous semiconductor, for example, a method of narrowing the band gap to increase the sensitivity to long-wavelength light has been performed. That is, since amorphous silicon has a band gap of about 1.7 eV, it cannot absorb light having a long wavelength of about 700 nm or more and cannot be used effectively. The use of a material having a small width is being studied. As such a material, there is an amorphous silicon germanium that can easily change the band gap from 1.3 eV to 1.7 eV easily by changing the ratio between the silicon source gas and the germanium source gas during film formation. .

Another method for improving the conversion efficiency of a solar cell is to use a so-called tandem cell in which a plurality of solar cells having a unit element structure are stacked.
9,498. Although a pn junction crystal semiconductor was used for this tandem cell, the idea is common to both amorphous and crystalline semiconductors, and the solar spectrum was efficiently absorbed by photovoltaic elements having different band gaps. , Voc to increase the power generation efficiency.

A tandem cell is a device in which devices having different band gaps are stacked and the conversion efficiency is improved by efficiently absorbing each part of the solar spectrum, and a so-called so-called tandem cell located on the light incident side of the stacked devices. The band gap of the so-called bottom layer located below the top layer is designed to be narrower than the band gap of the top layer.
On the other hand, Hamakawa et al. Report a so-called cascade type battery in which amorphous silicon having the same band gap is multi-layered without an insulating layer between photovoltaic elements to increase Voc of the entire element. In this method, unit elements made of an amorphous silicon material having the same band gap are stacked.

Amorphous silicon germanium is used as a suitable material for the bottom layer of the above-described tandem cell because of its narrow band gap and excellent sensitivity to long-wavelength light.

By the way, amorphous silicon germanium which can improve the long-wavelength sensitivity and can also be used as a bottom layer of a tandem cell is generally inferior in film quality to amorphous silicon. Even when a battery is manufactured, there is a disadvantage that the conversion efficiency is low. This is because the number of localized levels in the band gap is larger than that in amorphous silicon. For this reason, research and development are being conducted to improve the film quality by reducing the level in the band gap.
For example, an amorphous silicon germanium in which the dangling bonds in the amorphous silicon germanium are compensated for by using activated fluorine atoms to reduce the localized level density is disclosed in JP-B-63-48197. It has been disclosed.

On the other hand, improvement of the characteristics of the amorphous silicon germanium solar cell has been studied by a method other than the above-described improvement of the film quality. As an example, US Pat. No. 4,254,429 and US Pat. No. 4,254,429 disclose a method using a so-called buffer layer having a bandwidth gradient at a junction interface between a p-type semiconductor and / or an n-type semiconductor and an i-type semiconductor layer. No. 4,377,723. The purpose of the buffer layer is to provide a large number of levels at the junction interface between a p-type semiconductor or n-type semiconductor made of amorphous silicon and an i-type semiconductor made of amorphous silicon germanium due to a difference in lattice constant. The purpose of the present invention is to improve the Voc by using amorphous silicon at the bonding interface to eliminate the level and improve the bonding and not to impair the traveling property of the carrier.

Further, as another method, there is disclosed a method of providing a so-called gradient layer for changing the composition ratio of silicon and germanium to thereby distribute the composition in the intrinsic layer and improve the characteristics.

For example, according to US Pat. No. 4,816,082, the band gap of the i-layer in contact with the first valence-electron-controlled semiconductor layer on the light incident side is widened toward the center. Gradually narrow the band gap according to
A method is disclosed in which the band gap is gradually widened toward the second valence electron controlled semiconductor layer.
According to this method, the carrier generated by light can be efficiently separated by the action of the internal electric field, and the film characteristics are improved.

Another problem of a solar cell using an amorphous semiconductor is that the conversion efficiency is reduced by light irradiation. This is caused by the fact that the film quality of amorphous silicon and amorphous silicon germanium is deteriorated by light irradiation, and therefore, the mobility of the carrier is deteriorated. This is a phenomenon peculiar to a crystalline semiconductor. Therefore, when it is used for electric power, the reliability is inferior and it is an obstacle to practical use. Despite extensive research into improving photodeterioration of amorphous semiconductors, studies have been made to prevent photodeterioration by improving the film quality, while reducing photodegradation by improving the cell structure has also been studied. I have. As a specific example of such a method, the use of the above-described tandem cell structure is an effective means, and by reducing the thickness of the intrinsic layer and the traveling distance of the carrier, the cell characteristics are less likely to be degraded by light irradiation. Has been confirmed to be.

[0016]

However, in the above-mentioned amorphous solar cell, the conversion efficiency is not sufficient because the film quality is inferior to that of the crystalline silicon solar cell, and the power generation cost per watt is lower than that of the existing nuclear solar cell. , Thermal power, hydroelectric power, etc. In order for amorphous silicon-based solar cells to be used for power applications in line with existing power generation methods, it is required to further improve the conversion efficiency.

Further, as described above, although the mechanism of photodeterioration has been elucidated and studies on prevention of photodeterioration have been continued, the problem of photodeterioration has not been completely solved. Solar cells are required to have higher reliability. In the above-described method for preventing deterioration by the stack cell, the thinning of the intrinsic layer reduces the total amount of light absorbed by the photovoltaic element. Since the electromotive force characteristic is reduced, a solar cell satisfying both requirements of high reliability and high efficiency has not been realized at present.

An object of the present invention is to solve the above-mentioned problems and to provide a photovoltaic element used for a solar cell or the like having high reliability and high photoelectric conversion efficiency.

[0019]

Means for Solving the Problems The inventors of the present invention have overcome the above-mentioned problems, and have studied diligently for a solar cell with low light degradation and high conversion efficiency. By controlling the stoichiometric ratio of the germanium-based gas, it was found that a high-quality film with very little increase in conductivity and defects in the film could be obtained by continuous light irradiation. It was found that by controlling the composition ratio of silicon and germanium in the film thickness direction, a solar cell with high initial efficiency can be obtained. The present invention conducts further research based on the findings,
It was applied to a photovoltaic element and completed.
The gist of the present invention is amorphous silicon germanium.
With germanium atomic weight as the thickness
So that it is higher on the inside and lower on the P-type and N-type semiconductor layers.
Having an I-type semiconductor layer that changes continuously in the layer thickness direction
In the pin-type photovoltaic element, the I-type semiconductor layer
Between the P-type semiconductor layer and between the I-type semiconductor layer and the N-type semiconductor layer.
Type semiconductor made of amorphous silicon between the semiconductor layer
Buffer layer, and the I-type semiconductor layer includes the buffer layer.
Germanium atomic weight of 20
% Or more and in the thickness direction of the I-type semiconductor layer.
The germanium at the part where the germanium atomic weight is the largest
That the atomic weight of the system is 70 atomic% or less.
You. Further, the thickness of the buffer layer is set to 50 to 1000
In this case, a preferable configuration can be obtained by using the ungstrom. Further
According to the present invention, two or more pin-type unit element structures are stacked.
It can also be applied to a stacked photovoltaic element.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the photovoltaic device of the present invention is not limited thereto.

First, prior to the description of the present invention, a pin type amorphous solar cell suitable for applying the photovoltaic device of the present invention will be described.

FIGS. 6 to 9 schematically show a pin type amorphous solar cell suitable for applying the photovoltaic device of the present invention.

In each embodiment, the same components are denoted by the same reference numerals.

FIG. 6 shows a solar cell having a structure in which light is incident from the upper part of the figure.
1 is a substrate, 302 is a lower electrode, 303 is an n-type semiconductor layer (hereinafter, referred to as an n-layer), and 304 is an i-type semiconductor layer (hereinafter, referred to as an n-type semiconductor layer).
305, a p-type semiconductor layer (hereinafter, referred to as a p-layer); 306, an upper electrode; and 307, a current collecting electrode.
FIG. 7 shows a solar cell in which the substrate 301 is transparent and light enters from the bottom of the figure. Therefore, the lower electrode 30
2, n layer 303, i layer 304, p layer 305, upper electrode 3
The arrangement of 06 is opposite to that shown in FIG. 30
0 'indicates a solar cell main body.

FIG. 8 shows a solar cell having a structure in which two layers of FIG. 6 are laminated. In FIG. 8, reference numeral 310 denotes a solar cell body, 308 and 309 denote solar cell unit elements, and 303 and 31.
3 is an n layer, 304 and 314 are i layers, and 305 and 315 are p layers.
Represents a layer. FIG. 9 shows a solar cell having a structure in which three layers of FIG. 6 are laminated. In the figure, reference numeral 312 denotes a solar cell main body;
11 and 309 represent unit elements of the solar cell, and 3
03, 313, 323 are n layers, 304, 314, 324
Represents an i-layer, and 305, 315, and 325 represent a p-layer. In any of the photovoltaic elements, the n-layer and the p-layer can be used by changing the order of lamination according to the purpose. Hereinafter, the configurations of these photovoltaic elements will be described.

(Substrate) Semiconductor layers 303, 304, 305
Is a thin film of at most about 1 μm, and is deposited on a suitable substrate. Such a substrate 301 may be a single-crystal or non-single-crystal substrate, and may be a conductive or electrically insulating substrate. Further, they may be light-transmitting or non-light-transmitting, but preferably have a small amount of deformation and distortion and a desired strength. Specifically, Fe, Ni, Cr, Al, Mo, Au,
Metals such as Nb, Ta, V, Ti, Pt, Pb or alloys thereof, for example, thin plates such as brass and stainless steel and composites thereof, and polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinyl chloride Films or sheets of heat-resistant synthetic resins such as vinylidene, polystyrene, polyamide, polyimide, epoxy or composites of these with glass fibers, carbon fibers, boron fibers, metal fibers, etc., and thin plates of these metals, resin sheets, etc. Metal thin films of different materials and / or SiO ₂ , Si ₃ N on the surface
₄ , an insulating thin film such as Al ₂ O ₃ or AlN is sputtered,
Examples thereof include those subjected to a surface coating treatment by a vapor deposition method and a plating method, and glass and ceramics.

When the substrate is used as a substrate for a solar cell, if the substrate is electrically conductive such as a metal, it may be used as an electrode for direct current extraction, or an electrically insulating material such as synthetic resin. , Al, Ag, Pt, Au, Ni, Ti, Mo,
W, Fe, V, Cr, Cu, stainless steel, brass, nichrome, SnO ₂ , In ₂ O ₃ , ZnO, ITO and other so-called simple metals or alloys, and transparent conductive oxides (TC
It is desirable that O) be subjected to a surface treatment in advance by plating, vapor deposition, sputtering, or the like to form an electrode for extracting current.

Of course, even if the strip-shaped substrate is made of an electrically conductive material such as a metal, the reflectance of long-wavelength light on the substrate surface can be improved, or the constituent elements between the substrate material and the deposited film can be improved. A different kind of metal layer or the like may be provided on the side of the substrate on which the deposited film is formed, for the purpose of preventing mutual diffusion of the metal. When the substrate is relatively transparent and a solar cell having a layer configuration in which light is incident from the side of the substrate, a conductive thin film such as the transparent conductive oxide or a metal thin film is deposited and formed in advance. It is desirable to keep.

The surface of the substrate may be a so-called smooth surface or a fine uneven surface.

In the case of forming a fine uneven surface, the uneven shape is spherical, conical, pyramidal or the like, and the maximum height (R _max ) is preferably set to 500 to 5000 °. The light reflection at the surface becomes irregular reflection, resulting in an increase in the optical path length of the reflected light at the surface. The shape of the substrate is
Depending on the application, it may be in the form of a plate having a smooth surface or an uneven surface, a long belt shape, a cylindrical shape, and the like. The thickness thereof is appropriately determined so that a desired photovoltaic element can be formed. When flexibility is required for the electromotive element, or when light is incident from the side of the substrate, the thickness can be made as thin as possible within a range where the function as the substrate is sufficiently exhibited. However, the thickness is usually 10 μm or more from the viewpoint of manufacturing and handling of the substrate, mechanical strength and the like.

In the photovoltaic device of the present invention, an appropriate electrode is selected and used depending on the configuration of the device. These electrodes include a lower electrode, an upper electrode (transparent electrode),
A collecting electrode can be used (however, the upper electrode referred to here refers to one provided on the light incident side, and the lower electrode refers to one provided facing the upper electrode with the semiconductor layer interposed therebetween. Will be shown).

These electrodes will be described in detail below.

(Lower electrode) The lower electrode 302 used in the present invention has a different surface on which light for generating photovoltaic light is irradiated, depending on whether or not the material of the substrate 301 is translucent. For example, when the substrate 301 is a non-translucent material such as a metal, light for generating photovoltaic power is irradiated from the upper electrode 306 side as shown in FIG. 6). Specifically, in the case of a layer configuration as shown in FIGS. 6, 8, and 9, the substrate 301 and the n-layer 303
And provided between them. However, when the substrate 301 is conductive, the substrate can also serve as the lower electrode.
However, if the sheet resistance is high even if the substrate 301 is conductive, it is used as a low-resistance electrode for extracting current.
Alternatively, the electrode 302 may be provided for the purpose of increasing the reflectance on the substrate surface and effectively using the incident light.

In the case of FIG. 7, a light-transmitting substrate 301 is used, and light enters from the substrate 301 side.
For the purpose of extracting current and reflecting light at the electrode, a lower electrode 302 is provided opposite to the substrate 301 with a semiconductor layer interposed therebetween.

When an electrically insulating material is used as the substrate 301, the substrate 3 is used as an electrode for extracting current.
The lower electrode 302 is provided between the first layer 01 and the n-layer 303. Ag, Au, Pt, Ni, C
Metals such as r, Cu, Al, Ti, Zn, Mo and W or alloys thereof are listed, and thin films of these metals are formed by vacuum evaporation, electron beam evaporation, sputtering or the like. Further, care must be taken that the formed metal thin film does not become a resistance component with respect to the output of the photovoltaic element, and the sheet resistance is preferably 50Ω or less, more preferably 10Ω or less.
It is desirable that it be Ω or less.

Although not shown in the figure, a diffusion preventing layer such as conductive zinc oxide may be provided between the lower electrode 302 and the n-layer 303. The effect of the diffusion preventing layer is not only to prevent the metal element forming the lower electrode 302 from diffusing into the n-type semiconductor layer, but also to provide a small resistance value so that the lower portion provided with the semiconductor layer interposed therebetween. For example, a short circuit caused by a defect such as a pinhole between the electrode 302 and the transparent electrode (upper electrode) 306 is prevented, and multiple interference by a thin film is generated to confine incident light in a photovoltaic element. The effect can be raised.

(Upper Electrode (Transparent Electrode)) The transparent electrode (upper electrode) 306 used in the present invention has a light transmittance to efficiently absorb light from the sun or a white fluorescent lamp into the semiconductor layer. The sheet resistance is desirably 85% or more, and the sheet resistance is desirably 100Ω or less so that the output of the photovoltaic element does not become a resistance component. Materials having such characteristics include SnO ₂ , In ₂ O ₃ , ZnO, CdO, and CdSn.
Examples include metal oxides such as O ₄ and ITO (In ₂ O ₃ + SnO ₂ ), and metal thin films in which metals such as Au, Al, and Cu are formed to be extremely thin and translucent. Figure 6 shows the transparent electrode.
8 and 9, p layers 305, 315, and 3
25, and is stacked on the substrate 301 in FIG. 7, it is necessary to select one having good adhesion to each other. As a manufacturing method thereof, a resistance heating evaporation method, an electron beam heating evaporation method, a sputtering method, a spray method, or the like can be used, and is appropriately selected as desired.

(Current Collecting Electrode) The current collecting electrode 307 used in the present invention is provided on the transparent electrode 306 for the purpose of reducing the surface resistance of the transparent electrode 306. Ag, Cr, Ni, Al, Ag, Au, Ti, P
Examples include thin films of metals such as t, Cu, Mo, and W or alloys thereof. These thin films can be stacked and used. The shape and area of the semiconductor layer are appropriately designed so that the amount of light incident on the semiconductor layer is sufficiently ensured.

For example, it is desirable that the shape is uniformly spread over the light receiving surface of the photovoltaic element, and that the area is preferably 15% or less, more preferably 10% or less, with respect to the light receiving area.

The sheet resistance is desirably 50Ω or less, more preferably 10Ω or less.

The semiconductor layers 303, 304, and 305 are manufactured by a normal thin film manufacturing process.
It can be manufactured by using a known method such as a sputtering method, a high-frequency plasma CVD method, a microwave plasma CVD method, an ECR method, a thermal CVD method, or an LPCVD method as required. An industrially adopted method is a plasma CVD method in which a source gas is decomposed by plasma and deposited on a substrate.
The method is preferably used. In addition, as the reaction device, a batch type device, a continuous film forming device, or the like can be used as desired. When manufacturing a valence-controlled semiconductor, phosphorus,
It is carried out by simultaneously decomposing PH ₃ and B ₂ H ₆ gases containing boron and the like as constituent atoms. (I-layer) As a semiconductor material constituting the i-layer suitably used in the present photovoltaic element, a-SiGe: H, a is used when an i-layer of amorphous silicon germanium is produced.
So-called IV such as -SiGe: F, a-SiGe: H: F
Group alloy semiconductor materials. Further, as a semiconductor material constituting an i-layer other than amorphous silicon germanium in a tandem cell structure in which unit element configurations are stacked,
a-Si: H, a-Si: F, a-Si: H: F, a-
SiC: H, a-SiC: F, a-SiC: H: F, p
poly-Si: H, poly-Si: F, poly-S
In addition to so-called group IV and group IV alloy semiconductor materials such as i: H: F, so-called compound semiconductor materials of group III-V and group II-VI and the like can be mentioned.

As a raw material gas used in the CVD method, a chain or cyclic silane compound is used as a compound containing a silicon element. Specifically, for example, SiH ₄ , SiF
_{4, (SiF 2) 5,} (SiF 2) 6, (SiF 2)
₄ , Si ₂ F ₆ , Si ₃ F ₈ , SiHF ₃ , SiH ₂ F
₂ , Si ₂ H ₂ F ₄ , Si ₂ H ₃ F ₃ , SiCl ₄ ,
(SiCl ₂ ) ₅ , SiBr ₄ , (SiBr ₂ ) ₅ , S
iCl ₆ , SiHCl ₃ , SiHBr ₂ , SiH ₂ Cl
₂ , SiCl ₃ F _3, etc., which are in a gas state or can be easily gasified.

As the compound containing a germanium element, a chain germane or a halogenated germanium,
Cyclic germane, or halogenated germanium, chain or cyclic germanium compound, and organic germanium compound having an alkyl group or the like, specifically GeH
₄ , Ge ₂ H ₆ , Ge ₃ H ₈ , n-GeH ₁₀ , t-Ge
_{4 H 10, GeH 6, Ge} 5 H 10, GeH 3 Cl, GeH
_{2 F 2, Ge (CH 3} ) 4, Ge (C 2 H 5) 4, Ge
(C ₆ H ₅ ) ₄ , Ge (CH ₃ ) ₂ F ₂ , GeF ₂ , G
eF _{4 and the} like.

(P-layer and n-layer) As the semiconductor material constituting the p-layer or the n-layer suitably used in the present photovoltaic element, the above-mentioned semiconductor material constituting the i-layer is doped with a valence electron controlling agent. Obtained by: As the manufacturing method, a method similar to the above-described method for manufacturing the i-layer can be suitably used. When a group IV deposited film of the periodic table is obtained as a raw material, a compound containing a group III element of the periodic table is used as a valence electron controlling agent for obtaining a p-type semiconductor.
Group III elements include B, Al, Ga, and In. Specific examples of the compound containing a Group III element include BF ₃ , B ₂ H ₆ , B ₄ H ₁₀ , B ₅ H ₉ , and B _{5
H 11, B 6 H 10,} B (CH 3) 3, B (C 2 H 5) 3,
B ₆ H ₁₂ , Al (CH ₃ ) ₂ Cl, Al (CH ₃ ) ₃ ,
Al (OCH ₃ ) ₂ Cl, Al (CH ₃ ) Cl ₂ , Al
(C ₂ H ₅ ) ₃ , Al (OC ₂ H ₅ ) ₃ , Al (CH
₃ ) ₃ Cl ₃ , Al (i-C ₄ H ₉ ) ₅ , Al (C ₃ H
₇ ) ₃ , Al (OC ₄ H ₉ ) ₃ , Ga (OCH ₃ ) ₃ ,
Ga (OC ₂ H ₅ ) ₃ , Ga (OC ₃ H ₇ ) ₃ , Ga
(CH ₃ ) ₃ , Ga ₂ H ₆ , GaH (C ₂ H ₅ ) ₂ , G
a (OC ₂ H ₅ ), (C ₂ H ₅ ) ₂ , In (CH ₃ )
₃ , In (C ₃ H ₇ ) ₃ , In (C ₄ H ₉ ) _{3 and the} like.

As a valence electron controlling agent for obtaining an n-type semiconductor, a compound containing an element of Group V of the periodic table is used.
Group V elements include P, N, As, and Sb. As the compound containing a Group V element, specifically,
_{NH 3 HN 3, N 2 H} 5 N 3, N 2 H 4, NH 4 N 3,
PH ₃ , P (OCH ₃ ) ₃ , P (OC ₂ H ₅ ) ₃ , P
(C ₃ H ₇ ) ₃ , P (OC ₄ H ₉ ) ₃ , P (CH ₃ )
₃ , P (C ₂ H ₅ ) ₃ , P (C ₃ H ₇ ) ₃ , P (C ₄ H
₉ ) ₃ , P (OCH ₃ ) ₃ , P (OC ₂ H ₅ ) ₃ , P
(OC ₃ H ₇ ) ₃ , P (OC ₄ H ₉ ) ₃ , P (SCN)
₃ , P ₂ H ₄ , PH ₃ , AsH ₃ , AsH ₃ , As (O
CH ₃ ) ₃ , As (OC ₂ H ₅ ) ₃ , As (OC ₃ H
₇ ) ₃ , As (OC ₄ H ₉ ) ₃ , As (CH ₃ ) ₃ , A
s (CH ₃ ) ₃ , As (C ₂ H ₅ ) ₃ , As (C ₆ H
₅ ) ₃ , SbH ₃ , Sb (OCH ₃ ) ₃ , Sb (OC _{2
H 5) 3, Sb (OC} 3 H 7) 3, Sb (OC 4 H 9)
₃ , Sb (CH ₃ ) ₃ , Sb (C ₃ H ₇ ) ₃ , Sb (C
₄ H ₉ ) _{3 and the} like.

Of course, these source gases may be used alone or in combination of two or more.

When the above-mentioned raw material is in a gaseous state at normal temperature and normal pressure, a mass flow controller (hereinafter MF)
The amount introduced into the film formation space is controlled by C) or the like, and in the case of a liquid state, a rare gas such as Ar or He or a hydrogen gas is used as a carrier gas, and a bubbler capable of controlling the temperature is used as necessary. In the case of gasification or in a solid state, a rare gas such as Ar or He or hydrogen gas is used as a carrier gas to gasify using a heating sublimation furnace, and the amount introduced is controlled mainly by the flow rate of the carrier gas and the furnace temperature. .

Incidentally, the band gap profiles of the conventional devices having the structures shown in FIGS. 6 to 9 are shown in FIGS.
It is shown as 2. In the figure, the upper line shows the bottom of the energy level conduction band, the lower line shows the top of the valence band,
403 denotes an n layer, 405 denotes a p layer, and 404 denotes an i layer. Reference numerals 408 and 409 denote buffer layers. In FIG. 10, the band gap of the i-layer 404 is smaller than that of the n-layer 403 and the p-layer 405 serving as impurity doping layers.

In the case of such a band profile, since the open-circuit voltage is determined by the i-layer 404, if a material having a narrow band gap is used, the open-circuit voltage becomes small. Further, free electrons and free holes generated in the i-layer 404 in contact with the p-layer 405 recombine due to a high concentration of recombination levels existing at the pi interface, and are lost without being effectively extracted. I will. On the light incident side,
The amount of light is large, and the amount of light absorbed toward the inside is
Exponentially decreases. On the light incident side, the energy of the absorbed light has energy equal to or greater than the band gap, and the excess energy cannot be used effectively. As a method for solving such a defect, a configuration in which a buffer layer is provided as shown in FIG. 11 is used. 408 in the figure
And 409 are buffer layers, which have the effect of reducing localized levels at the pi and ni interfaces. Further, an element configuration as shown in FIG. 12 has been proposed. 403 in the figure,
405 is an n-layer, a p-layer, and 40 each serving as a doping layer.
4 is an i layer. In the figure, it is assumed that light enters from the left side. Here, the i-layer 404 is provided with a buffer layer 409 containing no band gap adjusting agent on the light incident side to increase the band gap, and then gradually increase the band gap adjusting agent to narrow the band gap. 404 'is provided. Further, an inclined layer 404 ″ is provided so that the band gap adjusting agent is reduced toward the side opposite to the light incident side to increase the band gap.

It is disclosed that by providing such a band profile, light can be effectively used, the open voltage is improved, and the file factor is also improved.
Such a method is generally studied with a view to improving the initial efficiency, but no particular consideration is given to light degradation.

The gist of the present invention lies in the fact that, in addition to the improvement of the initial efficiency by the improvement of the band profile described above, an element structure with less light deterioration is devised. The present inventors have found that amorphous silicon germanium has less photodegradation in the composition of specific germanium elements,
A cell having a high conversion efficiency using an amorphous silicon germanium having a composition with little light degradation has been devised.

An experiment performed by the present inventors will be described below.

<Experiment> An amorphous silicon germanium film was prepared as follows using a known RF discharge plasma CVD film forming apparatus shown in FIG.

In FIG. 13, reference numeral 700 denotes a reaction chamber;
01 is a substrate, 702 is an anode electrode, 703 is a cathode electrode, 704 is a heater for heating a substrate, 705 is a terminal for grounding, 706 is a matching box, 707 is 13.56.
MHz RF power supply, 708 is an exhaust pipe, 709 is an exhaust pump, 710 is a deposition gas introduction pipe, 720, 730, 74
0,750,760,722,732,742,752
And 762 are valves, 721, 731, 741, 75
Reference numerals 1 and 761 denote mass flow controllers.

First, a Corning 7 made 5 cm square.
The No. 059 glass 701 was attached to the cathode in the reaction chamber 700 and sufficiently evacuated by the exhaust pump 709 so that the degree of vacuum in the reaction chamber 700 became 10 ⁻⁶ Torr by an ion gauge (not shown). Next, the substrate 701 was heated to 300 ° C. by the substrate heating heater 704. After the substrate temperature becomes constant, valves 720, 722
Is opened and the mass flow controller 721 is controlled to supply 30 scc of SiH ₄ gas from a SiH ₄ gas cylinder (not shown).
m was introduced into the reaction chamber 700 via the gas introduction pipe 710. Similarly, the valves 740 and 742 are opened and the mass flow controller 741 is controlled to supply H ₂ gas at 300 sccm. The valves 730 and 732 are opened and the mass flow controller 731 is controlled to supply Ge.
1 sccm of H ₄ gas was introduced. Reaction chamber 700
After adjusting a pressure controller (not shown) so as to maintain the internal pressure at 1.5 Torr, a power of 20 W is supplied from the RF power source 707, and the matching box 706 is adjusted to minimize the reflected wave so as to reduce the plasma discharge by 60W.
After that, an amorphous silicon germanium film was deposited at 1 μm. The gas supply was stopped, the sample was taken out of the reaction chamber 700, and the sample no. Was designated as S-1. Similarly, G
eH ₄ gas amount 3 sccm, 5 sccm, 10 sccm,
Samples were prepared by changing to 20 sccm and 40 sccm, and the samples were designated as S-2, S-3, S-4, S-5, and S-6, respectively. Some of these samples were subjected to elemental analysis by Auger electron spectroscopy to determine the composition ratio of germanium elements in the film. The composition other than the germanium element was silicon and hydrogen. The optical band gap was measured by measuring the absorption coefficient of a part of the sample using a visible spectroscope. Table 1 shows the above results.

[0056]

[Table 1] Further, a part of the sample was transferred to an electron beam vacuum vapor deposition apparatus (EBX-6D, manufactured by ULBAC) (not shown), the inside of the vapor deposition apparatus was evacuated, and a Cr electrode having a gap width of 250 μm and a length of 1 cm was deposited at 1000 °. . Next, these samples were placed on a temperature-controllable sample stage, kept at a constant 25 ° C., and the sunlight spectrum of AM-1.5 was measured using a xenon lamp as a light source and a simulated solar light source (hereinafter referred to as a solar simulator). Is irradiated at an intensity of 100 mW / cm ² to measure the initial photoconductivity σ _P (0). Then, after continuously irradiating the simulator with light for 100 hours, the photoconductivity σ _P (10)
0) was measured.

FIG. 14 shows the results. As shown in the figure, it is understood that a film having a large composition ratio of the germanium element has little light degradation, and a film having a composition ratio of the germanium element of 20 atm% or more is stable to light irradiation. In particular, when the germanium element content is 30 atm% or more, it is found that it is extremely stable to light irradiation.

By the way, in the conventional element structure, a so-called buffer layer is provided in which the internal electric field is improved by giving a gradient of the bandwidth at the junction interface between the P-type semiconductor and / or the N-type semiconductor and the intrinsic layer. The buffer layer is manufactured by changing the band gap from about 1.7 eV to about 1.5 eV by continuously changing the composition ratio of silicon and germanium. I was At this time, the composition ratio of the germanium varies from 0 to about 50 atm%. Also, by changing the composition ratio of silicon and germanium to improve the characteristics by providing a composition distribution in the intrinsic layer, even when providing a so-called gradient layer, the composition ratio of the germanium is increased when a composition having a wide band gap is used. It contained a portion of 20 atm% or less.
In such a solar cell, the fact that the aforementioned germanium is liable to be degraded when the germanium is small is not taken into consideration. Therefore, the initial efficiency is improved by the buffer layer and the gradient layer, but the degradation is considered. The fact is that they did not.

The device structure of the present invention does not include amorphous silicon germanium having a composition that is liable to be photodegraded, and the initial efficiency can be improved by providing a buffer layer and a gradient layer. It is.

FIG. 1 schematically shows one configuration of a photovoltaic device of the present invention obtained by further improving the conventional example based on the results of the above experiment. In the figure,
100 is a photovoltaic element main body, 101 is a substrate, 102 is a lower electrode, 103 is an n-layer, 108 and 109 are layers that do not contain a germanium element and are i ₁ layers serving as buffer layers, 1
04 is a layer containing a germanium element, i ₂ layer, 105 is a p layer, 106 is an upper electrode, and 107 is a current collecting electrode. i
Constituting the i-layer in the _first layer 109 and i ₂ layer 104. FIG. 2 shows the band profile of this device. In the drawing, it is assumed that light is incident from the left side (p layer 205 side). In the figure, 200 is the i-layer main body, 203 is the n-layer, 20
4 is an i ₂ layer of an amorphous germanium silicon layer, 205
Is a p layer, and 208 and 209 are i ₁ layers which are buffer layers. The band profile of this device may be such that the i ₂ layer 204 of an amorphous germanium silicon layer is inclined so that the light incident side is widened as shown in FIG.
Conversely, the light incident side may be narrowed as in the above. Further, the inclined layers 204 and 204 'may be combined as shown in FIG. The order of lamination of the p-layer and the n-layer in FIGS. 2 to 5 may be changed. I ₁ layer 208 serving as a buffer
And 209 are made of an amorphous silicon layer containing no germanium, have a band gap of about 1.7 eV, and absorb light from 300 nm to 730 nm. i ₂
The layers 204 and 204 'are formed by decomposing a gas containing a silicon element and a gas containing a germanium element, which are source gases at the time of film formation, and in the case where a slope is provided as shown in FIGS. 3, 4, and 5, The composition of the germanium is changed by changing the flow rate ratio of the gas. The function of such a gradient layer will be described with a specific configuration, taking the case of FIG. 5 as an example. FIG.
The band gap of the i ₂ layer 204 ′ at the portion in contact with the i ₁ layer 209 serving as the buffer layer is about 1.55 eV, and gradually becomes narrower in the direction opposite to the light incident side, and the narrowest portion The band gap is about 1.45 eV. The band gap of the i ₂ layer 204 is n layer 20
The band gap is designed to be about 1.55 eV at a portion in contact with the i ₁ layer 208 which is designed to gradually increase toward 3 and becomes a buffer layer. The function of the band profile in the device configured as described above will be described as follows.

Irradiation light is incident from the p-type semiconductor layer 205 side, and optical carriers are generated in the i ₁ layer 209 and i ₂ layers 204 ′ and 204 serving as buffer layers and the i ₁ layer 208 serving as a buffer layer. . Since the i ₁ layer 209 serving as a buffer layer has a wide band gap, it absorbs only light having a short wavelength and transmits light having a long wavelength, so that light reaches the inside of the cell and can be used effectively. . When the pi interface is made of amorphous silicon germanium, recombination levels increase due to poor film quality of the film and mismatching of the lattice spacing between the p layer and the amorphous silicon germanium. Battery characteristics are poor. On the other hand, when made of amorphous silicon, since the recombination level is relatively small, high-concentration carriers generated at the pi interface can be effectively taken out without recombination. In addition, the open circuit voltage increases because the recombination level is small. In the i ₂ layer 204 ′, the band gap gradually narrows, so that short-wavelength light is absorbed near the p-layer 205 and long-wavelength light is absorbed far from the p-layer 205.
I ₁ layer 208 serving as a buffer layer is i ₁ as the buffer layer
This layer has a function substantially similar to that of the layer 209, and alleviates lattice mismatch at the ni interface.

Further, the effect of this band profile on the collection of photogenerated carriers is explained as follows. In the i ₂ layer 204 ′, the energy gradient at the bottom of the conduction band is large on the p layer 205 side and small on the n layer 203 side, so that the electric field acts on the free electrons to increase. Therefore, free electrons are accelerated with respect to the n-layer 203 and are effectively extracted. On the other hand, since the energy at the top of the valence band is small on the p-layer 205 side and large on the n-layer 203 side, it acts to reduce the electric field with respect to free holes. However, since the i ₂ layer 204 ′ is close to the p layer, the drift distance of the free electrons is short and does not cause much problem.

The energy gradient at the bottom of the conduction band of the i-layer 204 is smaller on the p-layer 205 side and larger on the n-layer 203 side, so that the electric field for free electrons is reduced. Although this is disadvantageous for the traveling property of free electrons, it is generally not a problem because the traveling property of electrons is generally better than that of holes. On the other hand, since the energy at the top of the valence band is large on the p-layer 205 side and small on the n-layer 203 side, the electric field acts on the free holes to increase. In general, solar cell characteristics are limited by the traveling properties of holes, and thus a structure in which an electric field is increased with respect to holes improves solar cell characteristics. Further, in the solar cells having the band profiles shown in FIGS. 2 to 5, the composition ratio of the germanium element in the amorphous silicon germanium film is 20 atm% or more, so that the film quality is hardly deteriorated by light.

By using the pin structure shown in FIG. 1 having the band profiles shown in FIGS. 2 to 5 in the element structure shown in FIGS. 6 to 9, a highly efficient and highly reliable solar cell can be manufactured.

[0065]

Next, preferred embodiments of the present invention will be described below, but the contents of the present invention are not limited by the following embodiments. (Example 1) A solar cell having the structure shown in FIG. 6 was manufactured by the apparatus shown in FIG. 13 as follows using the pin layer having the band profile shown in FIG. 2 of the present invention.

First, the surface is mirror-polished to a thickness of 0.05 μmR.
_max and was 5cm angle of size made of stainless steel (SUS30
4) The substrate 101 is placed in a sputtering apparatus (not shown), and the inside of the apparatus is evacuated to 10 ⁻⁷ Torr or less. Then, Ar gas is introduced, the internal pressure is set to 5 mTorr, and DC plasma discharge is generated at a power of 200 W to generate Ag plasma. The target was sputtered to deposit about 5000 ° of Ag. After that, the target was changed to ZnO, a DC plasma discharge was generated under the same conditions of the internal pressure and the power, and sputtering was performed.
Ｚｎ ZnO was deposited. After the lower electrode 102 is manufactured in the above steps, the substrate 101 is taken out and the reaction chamber 70 is removed.
0, and evacuated sufficiently by an exhaust pump 709, using an ion gauge (not shown).
The degree of vacuum in 0 was set to 10 ^-6 Torr. Next, the substrate 701 was heated to 300 ° C. by the substrate heating heater 704. After the substrate temperature becomes constant, the valve 720,
Opened 722, introduced from SiH ₄ gas cylinder, not shown to control the flow rate of the mass flow controllers 721 and SiH ₄ gas 30sccm into the reaction chamber 700 through the gas inlet pipe 710. Similarly, the valve 740,
742 is opened, H ₂ gas is supplied at 300 sccm by controlling the flow rate of the mass flow controller 741, and the valve 75 is opened.
0,752 was opened, and the flow rate of the mass flow controller 751 was controlled to introduce 10 sccm of PH ₃ gas diluted to 5% with H ₂ gas. After adjusting the internal pressure of the reaction chamber 700 to 1.5 Torr, a power of 10 W is supplied from the RF power supply 707 through the matching box 706, plasma discharge is performed for 3 minutes to form the n-type amorphous silicon layer 103 at 400 ° C. Deposited. After stopping the gas supply, the reaction chamber 700 is evacuated again, and the degree of vacuum in the reaction chamber 700 is evacuated to 10 ^-6 Torr or less, and then the valves 720, 722, 730, 732, 74
0,742 was opened, and 30 sccm of SiH ₄ gas and 300 sccm of H ₂ gas were introduced into the reaction chamber 700. At this time, the flow rate of the GeH ₄ gas from the mass flow controller 731 was reduced to Osccm, and the flow rate was set to Osccm at the start of film formation. After applying a power of 20 W from the RF power source 707 and performing plasma discharge for 10 seconds to deposit an i ₁ layer 108 of a buffer layer having a thickness of 10 °, the flow rate setting of the GeH ₄ gas mass flow controller 731 is instantaneously increased to 5 sccm. i ₂ layers of amorphous silicon germanium of about 2000Å perform deposition of continued film 20 minutes 1
04 was deposited. The response speed of the mass flow controller 731 was sufficiently fast and reached within 1 second with respect to the set flow rate, and there was no overshoot and the error with respect to the set flow rate was ± 2%. The pressure was controlled by a pressure controller (not shown) so that the pressure did not fluctuate by rapidly increasing the flow rate. The flow rate of the mass flow controller 731 was controlled accurately using a microcomputer. The band gap of the amorphous silicon germanium film deposited under these conditions was about 1.53 eV as confirmed in the experimental example.
It is. Next, the flow rate of the GeH ₄ gas was set to 0 sccm by the mass flow controller, and the flow rate of the GeH ₄ gas was instantaneously reduced to 0 sccm by closing the solenoid valve.
Film formation was continued with only ₄ gas and H ₂ gas, and film formation was performed for 10 seconds, and an i ₁ layer 109 serving as a buffer layer having a film thickness of 10 ° was deposited. After the power of the RF power source 707 was set to 0 W to stop the plasma discharge and stop the gas supply, the reaction chamber 700 was stopped.
After evacuating the inside to 10 ^-6 Torr or less, the valves 720, 722, 730, 732, 740 and 742 are opened to open 1 sccm of SiH ₄ gas and 300 sccc of H ₂ gas.
B ₂ H ₆ gas 10scc diluted to 5% by m and H ₂ gas
m was introduced into the reaction chamber 700. Subsequently, a power of 200 W was applied from the RF power supply 707 to generate plasma discharge, and a film was formed for 5 minutes to deposit the p-layer 105 at 100 °. Note that a sample in which the p-layer was deposited on a glass substrate under these conditions was confirmed by reflection high-speed electron beam diffraction (RHEED) to be microcrystals having a particle size of 20 ° to 100 °. Next, the substrate 101 is taken out of the reaction chamber 700,
It is placed in a resistance heating vapor deposition device (not shown),
After evacuating to ^-7 Torr or less, introducing oxygen gas,
After the internal pressure was adjusted to 0.5 mTorr, an alloy of In and Sn was deposited by resistance heating, and a transparent conductive film (ITO film) having a function also as an anti-reflection effect was deposited at 700.degree.
06. After the vapor deposition was completed, the sample was taken out and decomposed into sub-cells of 1 cm × 1 cm by a dry etching device (not shown), then transferred to another vapor deposition device, and an aluminum current collecting electrode 107 was formed by an electron beam vapor deposition method. The obtained solar cell was no. 1-1.

Next, in order to obtain the optimum film thickness of the buffer layer 108, the film formation was performed in the same manner as described above except that the film formation time of the buffer layer 108 was changed, and a sample having a changed film thickness was produced. The sample was no. 1-2, No. 1-3, N
o. 1-4, No. 1-5, No. 1; 1-7. These samples were subjected to AM-1.5 using a solar simulator.
Was irradiated at an intensity of 100 mW / cm ² , and the initial characteristics of the solar cell were measured by obtaining a voltage-current curve.

FIG. 15 shows the obtained results. In the figure, the conversion efficiency η is normalized by assuming that the conversion efficiency when no buffer layer is used is 1. From FIG. 15, buffer layer 1
It was found that the initial characteristics were improved when the film thickness of 08 was 50 ° to 1000 °. Further, the buffer layer 109
A film was formed in the same manner as described above except that the film formation time was changed, and a sample in which the thickness of the buffer layer 109 was changed was produced. The sample was no. 1-8, no. 1-9, No.
1-10, No. No. 1-11, No. 1-12, no. 1
-13, No. 1-14. The initial characteristics of each of these samples were measured by the method described above. FIG. 16 shows the obtained result. In the figure, the conversion efficiency η is normalized by assuming that the conversion efficiency when no buffer layer is used is 1. FIG. 16 shows that the buffer layer 109 has a thickness of 50 ° to 1
It was found that the initial characteristics were improved by setting the temperature to 000 °. (Embodiment 2) Next, i ₁ layers 108 and 10 serving as buffer layers
A solar cell having a layer configuration shown in FIG. 6 using an i-layer (i ₁ layer and i ₂ layer) having the profile of FIG. It was produced in exactly the same way as described above. The stainless steel substrate 101 on which the lower electrode 102 has been deposited is placed in a reaction chamber 700, the n-layer 103 is deposited at 400 °, and the buffer layer 108 having a thickness of 300 ° is deposited.
_The film was formed by instantaneously increasing the flow rate setting of the ₄ gas mass flow controller to 1 sccm and forming a band gap of 1.67.
An i-layer 104 of amorphous silicon germanium eV was deposited at about 2000 °. Further, a buffer layer 109 having a thickness of 300 ° is deposited, and a p-type amorphous silicon
0Å deposited. The substrate 101 was taken out of the reaction chamber 700, and an upper electrode 106 and a current collecting electrode 107 were formed. The obtained solar cell was no. 2-1.

Next, in order to change the band gap of the i-layer 104, a film was formed in the same manner as described above except that the flow rate of GeH ₄ gas at the time of depositing the i-layer 104 was changed.
4 have a band gap of 1.53 eV and 1.42, respectively.
Samples of eV, 1.30 eV, and 1.22 eV were prepared.
At this time, the thickness of each sample was set to be the same. The obtained sample was designated as No. 2-2, No. 2-3, N
o. 2-4. The initial characteristics of each of these samples were measured by the method described above, and then the light deterioration characteristics of these samples were evaluated as follows.

The initial photoelectric conversion efficiency η (0) when the sample was irradiated with AM1.5 light (100 mW / cm ² ) from the upper electrode 106 side was determined. Next, an optimum load was calculated from the open-circuit voltage Voc and the short-circuit current 1 sc obtained when the above-described photoelectric conversion efficiency was obtained, and a load resistance was connected to each sample.

Next, the sample to which the load resistance was connected was placed on a sample table kept at a constant temperature of 25 ° C.
After continuously irradiating light (100 mW / cm ² ) for 500 hours,
Again, from the upper electrode 106 side of the sample, AM1.
The photoelectric conversion efficiency η (500) when irradiating five lights (100 mW / cm ² ) was determined. The thus obtained η (5
00) and η (0), the deterioration rate ｛1−η (500) / η
(0)｝ was determined. The results obtained are shown in FIG. As can be seen from FIG. 17, it is understood that the sample in which the composition of the germanium element of the i-layer 104 is 20 atm% or more is stable against light irradiation. (Comparative Example 1) FIG. 1 shows a conventional tilted buffer layer using the apparatus shown in FIG.
A solar cell having the layer configuration shown in FIG. 6 was manufactured using the i-layer having the band profile of No. 1, and the electrical characteristics were measured.

First, the stainless steel substrate 301 on which the lower electrode 302 was deposited was attached to a cathode in the reaction chamber 700 and sufficiently exhausted by the exhaust pump 709. Next, the substrate 701 was heated to 300 ° C. by the substrate heating heater 704. After the substrate temperature became constant, an n-layer 303 was deposited at 400 ° in the same manner as in Example 1. After stopping the gas supply, the reaction chamber 700 is evacuated again, and the valves 720, 722, 730, 732, 740, 742 are opened to open the SiH ₄ gas at 30 sccm and the H ₂ gas at 300 sccc.
m was introduced into the reaction chamber 700. At this time, Ge
The mass flow controller of the H ₄ gas was restricted to Osccm so that the flow rate was set to Osccm at the start of film formation. RF power supply 707 via matching box 706
At the same time, the plasma discharge was started, and at the same time, the film formation was continued for 5 minutes while increasing the flow rate setting of the GeH ₄ gas mass flow controller 731 at a rate of 2 sccm / min. After 5 minutes, the flow rate of the GeH ₄ gas was 10 sccm, and the film formation during this time was about 300 ° C.
Of the graded buffer layer 408 was deposited. The band gap of the buffer layer is inclined from 1.7 eV to 1.42 eV. Thereafter, the film was formed for 15 minutes while maintaining the flow rate of GeH ₄ at 10 sccm. Approximately 150
An i-layer 404 of amorphous silicon germanium with a 0 ° bandgap of 1.42 eV was deposited. Next, GeH ₄
Set the flow rate of the gas mass flow controller to 2scc
The film formation was continued while decreasing at a speed of m / min, and the film formation was performed for 5 minutes. After 5 minutes, the flow rate of the GeH ₄ gas became 0 sccm. During this time, the inclined buffer layer 4 of about 300 ° is formed.
09 was deposited. The band gap of the buffer layer is 1.
The slope is from 42 eV to 1.7 eV. RF immediately
After stopping the discharge and stopping the supply of SiH ₄ gas and H ₂ gas,
The reaction chamber 700 is evacuated, and SiH ₄ gas and B
_The p layer 305 was introduced in the same manner as in Example 1 by introducing ₂ H ₆ gas.
Was deposited 200 mm. The substrate 701 is placed in the reaction chamber 70
Then, the film was taken out of the apparatus and placed in a transparent conductive film deposition apparatus (not shown) to deposit an ITO film as the upper electrode 306 at 700 °. After the film formation, the sample was etched and separated into sub-cells having a size of 1 cm × 1 cm, and then transferred to another vapor deposition apparatus to form a current collecting electrode 307 by electron beam vapor deposition. The obtained sample was designated as R-1.

The above sample was provided with solar simulator light (A
M1.5, 100 mW / cm ² ) and measuring the voltage-current characteristics to obtain the initial conversion efficiency (η _R ) of the solar cell.
(0)) was measured, and the conversion efficiency (η _R (50)) after continuous irradiation of AM1.5 light (100 mW / cm ² ) for 500 hours was measured in the same manner as in Example 2. The initial conversion efficiency η of each sample of Example 2 was compared with the initial conversion efficiency η _R (0) of Comparative Example 1.
FIG. 18 shows the values η (0) / η _R (0) normalized by. FIG. 19 shows a value η (500) / η _R (500) obtained by normalizing the conversion efficiency η (500) after deterioration of the sample by the conversion efficiency η _R (500) after deterioration in Comparative Example 1.

As understood from the above results, the second embodiment
The solar cell of Comparative Example 1 has initial characteristics similarly to Comparative Example 1, and the composition ratio of the germanium element is 20 to 70.
It has been found that the characteristics after deterioration are improved as compared with the comparative example by setting the range of atm%. Embodiment 3 Next, a solar cell having a layer configuration shown in FIG. 6 having an i-layer having the band profile of FIG. 3 of the present invention in which a bandgap gradient layer is provided on the i-layer 204 using an apparatus shown in FIG. It was produced in substantially the same manner as in Example 2.

The stainless steel substrate 101 on which the lower electrode 102 was deposited was placed in a reaction chamber 700, and an n-type amorphous silicon layer 103 was deposited at 400 °. After depositing the buffer layer 108 having a thickness of 300 °, Ge
The flow rate setting of the H ₄ gas mass flow controller 731 was instantaneously increased to 5 sccm and further increased to 0.5 sccm / m.
The film was formed for 10 minutes by increasing the flow rate at a rate of in, and the i-layer 104 of amorphous silicon germanium whose band gap changed from 1.53 eV to 1.42 eV was reduced to about 1 layer.
000Å deposited. Thereafter, the flow rate setting of the GeH ₄ gas mass flow controller 731 was set to 0 sccm, and the GeH ₄ gas flow rate was instantaneously set to 0 s by closing the solenoid valve.
The film was formed with only SiH ₄ gas and H ₂ gas as ccm, and the film was formed for 3 minutes.
Was deposited. After the discharge, a p-type amorphous silicon layer 105 was deposited at a thickness of 100 ° in the same manner as in Example 2. The substrate 101 was taken out of the reaction chamber 700, and an upper electrode 106 and a current collecting electrode 107 were formed. The obtained solar cell was no.
3-1. In addition, a film was formed using the same method as described above, except that the amount of change in the flow rate of GeH ₄ gas when forming the i-layer 104 was varied in order to examine the relationship between the inclination of the inclined layer and the solar cell characteristics. No. of Table 2 3-2 and No. 3
A solar cell having a band profile as shown in 3-3 was produced.

[0076]

[Table 2] Next, a solar cell having the layer configuration shown in FIG. 6 and having the i-layer having the band profile of FIG. 4 of the present invention was produced by the same operation as described above. After depositing the n-layer 103 and the buffer layer 108, the flow rate of the GeH ₄ gas by the mass flow controller 731 is set to 10 sccm, and 0.5 sccm / min.
The flow rate was lowered at a speed of 10 m / min, and a film was formed for 10 minutes to form an amorphous silicon germanium i-layer 104 having a band gap changed from 1.42 eV to 1.53 eV for about 100 hours.
0Å deposited. After depositing the buffer layer 109, the p-layer 105
To form an upper electrode 106 and a collecting electrode 107. The obtained solar cell was no. 3-4. further,
I-layer 1 to investigate the relationship between the inclination of the gradient layer and the solar cell characteristics
No. 04 in Table 3 by varying the amount of change in the flow rate of GeH ₄ gas when preparing No. 04. Nos. 3-5 and No. A solar cell having a band profile as shown in 3-6 was produced.

[0077]

[Table 3] Further, a solar cell having the layer configuration shown in FIG. 6 having the i-layer of the band profile of FIG. 5 of the present invention was produced by the same operation as described above. After depositing the n-layer 103 and the buffer layer 108, the flow rate setting of the GeH ₄ gas mass flow controller 731 is set to 5 sccm, and 0.75 sccm / min.
The flow rate was increased at a rate of 5 ° C. to form a film for 5 minutes, and the amorphous silicon germanium i-layer 104 having a band gap changed from 1.53 eV to 1.42 eV was formed at about 500 ° C.
After the deposition, the flow rate of the GeH ₄ gas through the mass flow controller 731 is reduced at a rate of 0.75 sccm / min, and a film is formed for 5 minutes to have a band gap of 1.42 e.
An i-layer 104 of amorphous silicon germanium changed from V to 1.53 eV was deposited at about 500 °, a buffer layer 109 and a p-layer 105 were deposited, and then an upper electrode 106 and a current collecting electrode 107 were formed. The obtained solar cell was no.
3-7. Further, in order to examine the relationship between the inclination of the inclined layer and the solar cell characteristics, the amount of change in the flow rate of the GeH ₄ gas when the i-layer 104 was manufactured was variously changed. Nos. 3-8 and No. 3; A solar cell having a band profile as shown in 3-9 was produced.

[0078]

[Table 4] These samples were respectively subjected to the initial conversion efficiency η (0) and the conversion efficiency η (5
00) was measured to determine the deterioration rate Δη (1−η (500)
/ Η (0). ). Then Comparative Example 1
Table 2 shows the results η / η _R and Δη / Δη _R obtained by normalizing the initial efficiency η _R and the deterioration rate Δη _R of the sample R-1.
The results are shown in Table 4. From the results of Tables 2 to 4, the deterioration characteristics of all the samples are less deteriorated than those of Comparative Example 1, and particularly, the bandgap of the i-layer 104 is set such that the bandgap becomes narrower toward the center and becomes wider toward the end, so that the initial characteristics are improved. Comparative example 1 with deterioration
It turned out to be better than that. (Embodiment 4) Next, an embodiment of the present invention in which the substrate is made of glass will be described. The solar cell of FIG. 7 having the i-layer of the configuration shown in FIG. 1 of the present invention was produced in substantially the same manner as in Example 2 using the apparatus shown in FIG.

A transparent conductive film SnO ₂ was deposited on a quartz glass substrate 301 by an evaporator (not shown) at 3000 ° to form an upper electrode 306. Thereafter, the substrate 301 is placed in the reaction chamber 700 and the p-type amorphous silicon
After depositing 0 ° and depositing the buffer layer 108 having a thickness of 300 °, the flow rate of the GeH ₄ gas mass flow controller 731 is instantaneously set to 5 sccm and the flow rate is increased at a rate of 0.75 sccm / min as in the third embodiment. 5
The amorphous silicon germanium i-layer 104 having a band gap changed from 1.53 eV to 1.42 eV is deposited for about 500 °, and then the flow rate of the GeH ₄ gas mass flow controller 731 is set to 0.7.
The amorphous silicon germanium i-layer 104 having a band gap changed from 1.42 eV to 1.53 eV by forming the film at a rate of 5 sccm / min and decreasing the film thickness for 5 minutes.
Was deposited at about 500 °.

Thereafter, the flow rate of the GeH ₄ gas mass flow controller 731 was set to 0 sccm, and the flow rate of the GeH ₄ gas was instantaneously reduced to 0 sccm by closing the solenoid valve.
Then, film formation was continued with only SiH ₄ gas and H ₂ gas, and film formation was performed for 3 minutes to deposit a buffer layer 109 having a thickness of 300 °. After the completion of the discharge, the n-layer
0Å deposited. The substrate 301 was taken out of the reaction chamber 700, and 5000 nm of aluminum was deposited by an electron beam evaporator (not shown) to form an upper electrode 302.
The obtained solar cell was no. 4-1. The initial conversion efficiency η (0) of this sample and the conversion efficiency η (500) after 500 hours of light irradiation were measured by the above-described method to determine the deterioration rate Δη, and the initial efficiency η _R (0) of the sample R-1 of Comparative Example 1 was obtained. ) And the deterioration rate Δη _R , and the obtained result η (0) / η
Table 5 shows _R (0) and Δη / Δη _R. From this result, it is understood that a highly reliable solar cell with high conversion efficiency can be obtained by using the band profile of the present invention. (Embodiment 5) Next, a solar cell having a tandem cell structure shown in FIG. 8 using the i-layer having the band profile of FIG. It was produced.

The n-layer 103 is deposited on the stainless steel substrate 301 on which the lower electrode 302 is deposited by 400 .ANG.
After the buffer layer 108 is deposited, the flow rate is increased at a rate of 0.75 sccm / min by setting the flow rate of the GeH ₄ gas mass flow controller 731 to 5 sccm, and a film is formed for 5 minutes, and the band gap is changed from 1.53 eV to 1 An i-layer 104 of amorphous silicon germanium changed to .42 eV was deposited at about 500 °, and then the flow rate of the GeH ₄ gas through the mass flow controller 731 was set to 0.75.
A film is formed at a rate of sccm / min for 5 minutes, and an i-layer 104 of amorphous silicon germanium having a band gap changed from 1.42 eV to 1.53 eV is deposited at about 500 °, a buffer layer 109 and a p-layer. 105 was deposited to form a bottom layer. Further, the n-layer 313 is
The i-layer 314 is deposited with SiH ₄ gas and H ₂ gas for 100
After a 0 ° and p-layer 315 were deposited at 100 ° to form a top layer, an upper electrode 306 and a current collecting electrode 307 were formed. The obtained solar cell was no. 5-1. This sample was subjected to initial conversion efficiency η (0) and 500 according to the method described above.
The conversion efficiency η (500) after irradiation with time light is measured and the deterioration rate Δ
η is obtained and normalized by the initial efficiency η _R and the deterioration rate Δη _R of the sample R-1 of Comparative Example 1, and the obtained result η (0) / η _R
(0) and Δη / Δη _R are shown in Table 5. From these results, it can be seen that the use of the band profile of the present invention makes it possible to obtain a solar cell with high conversion efficiency and high reliability. (Embodiment 6) Next, a solar cell having a triple cell structure shown in FIG. 9 using the i-layer having the band profile of FIG. 5 as the bottom layer of the present invention is substantially similar to Embodiment 5 using the apparatus shown in FIG. It was produced.

After depositing the n layer 103 and the buffer layer 108 on the stainless steel substrate 301 on which the lower electrode 302 is deposited, the flow rate of the GeH ₄ gas mass flow controller 731 is set to 5 sccm and set to 0.755 sccm / mi.
The flow rate was increased at a rate of n to form a film for 5 minutes, and an i-layer 104 of amorphous silicon germanium having a band gap changed from 1.53 eV to 1.42 eV was applied for about 500 hours.
Å After the deposition, the flow rate of the GeH ₄ gas through the mass flow controller 731 is reduced at a rate of 0.75 sccm / min to form a film for 5 minutes, and the band gap is 1.42.
An i-layer 104 of amorphous silicon germanium whose eV was changed from eV to 1.53 eV was deposited at about 500 °, and a buffer layer 109 and a p-layer 105 were deposited to form a bottom layer. Thereafter, the n-layer 313 and the i-layer 314 are set to 3000 ° and the p-layer 31 is formed.
5 was deposited to form a middle layer. Further, the n-layer 32
3, 700 ° of i-layer 324 and p-layer 325 were deposited, a top layer was formed, and upper electrode 306 and current collecting electrode 307 were formed. The obtained solar cell was no. 6-1. The initial conversion efficiency η (0) of this sample and the conversion efficiency η (500) after light irradiation for 500 hours were measured by the above-described method to determine the deterioration rate Δη, and the initial efficiency η _R of the sample R-1 of Comparative Example 1 was obtained.
Table 5 shows the obtained results η (0) / η _R (0) and Δη / Δη _R normalized by (0) and the deterioration rate Δη _R. From these results, it can be seen that the use of the band profile of the present invention makes it possible to obtain a solar cell with high conversion efficiency and high reliability.

[0083]

[Table 5] (Example 7) Next, the film formation gas of the i-layer 204 was changed variously under the conditions shown in Table 6 to produce an i-layer having the band profile of FIG. 3 of the present invention. Using the apparatus shown in FIG. 13, it was manufactured in substantially the same manner as Sample 3-7 of Example 3. The obtained solar cell was no. 7-1, No.
7-2 and No. 7 7-3. The initial conversion efficiency η (0) of this sample and the conversion efficiency η (500) after 500 hours of light irradiation were measured by the above-described method to determine the deterioration rate Δη, and the initial efficiency η _R (0 ) And degradation rate Δ
Normalized by η _R and obtained result η (0) / η _R (0)
And Δη / Δη _R are shown in Table 6. From these results, it can be seen that the use of the band profile of the present invention makes it possible to obtain a solar cell with high conversion efficiency and high reliability.

[0084]

[Table 6] (Embodiment 8) Next, an i-layer having the band profile of FIG. 3 of the present invention was manufactured under the conditions shown in Table 7 by changing the film forming gas of the p-layer 205 variously. Using the apparatus shown in FIG. 13, it was manufactured in substantially the same manner as Sample 3-7 of Example 3. The obtained solar cell was no. 8-1, No. 1;
8-2 and No. 9 8-3. The p-layer used for this sample was deposited on a glass substrate,
Table 7 also shows the results of evaluating the crystallinity by EED.
The initial conversion efficiency η (0) of this sample and the conversion efficiency η (500) after light irradiation for 500 hours were measured by the above-described method to determine the deterioration rate Δη, and the initial efficiency η _R of the sample R-1 of Comparative Example 1 was obtained.
Table 7 shows the obtained results η (0) / η _R (0) and Δη / Δη _R normalized by (0) and the deterioration rate Δη _R. From these results, it can be seen that the use of the band profile of the present invention makes it possible to obtain a solar cell with high conversion efficiency and high reliability.

[0085]

[Table 7]

[0086]

According to the photovoltaic device of the present invention, an amorphous
Silicon germanium
Higher atomic weight inside the layer thickness direction, P-type and N-type semiconductor layer side
I type continuously changing in the layer thickness direction so as to become lower
In a pin type photovoltaic device having a semiconductor layer,
Between the I-type semiconductor layer and the P-type semiconductor layer and the I-type semiconductor layer;
Amorphous silicon between the semiconductor layer and the N-type semiconductor layer
Providing an I-type semiconductor buffer layer comprising:
The layer is formed on the gel side at the interface side with the buffer layer.
Having an atomic weight of at least 20 atomic% and the I-type semiconductor layer
Where the germanium atomic weight inside the layer thickness direction becomes the maximum
Germanium atomic weight of less than 70 atomic%
By doing so, a solar cell with high reliability and high conversion efficiency can be obtained.

The buffer layer may have a thickness of 50 to 1
By setting the thickness to 2,000 angstroms, a solar cell with higher reliability and higher conversion efficiency can be obtained.

In the present invention, the unit element structure of the pin is 2
It applied to the stacked photovoltaic device of laminating One or more, the unit
At least one of the element structures is from the above photovoltaic element
By doing so, a solar cell with high reliability and high conversion efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of an i-layer of a photovoltaic device of the present invention.

FIG. 2 is a diagram showing a band profile of the pin structure of FIG. 1;

FIG. 3 is a view showing a band profile of the pin structure of FIG. 1;

FIG. 4 is a view showing a band profile of the pin structure of FIG. 1;

FIG. 5 is a diagram showing a band profile of the pin structure of FIG. 1;

FIG. 6 is a diagram schematically showing a configuration of a conventional photovoltaic element.

FIG. 7 is a diagram schematically showing a configuration of a conventional photovoltaic element.

FIG. 8 is a diagram schematically showing a configuration of a conventional photovoltaic element.

FIG. 9 is a diagram schematically showing a configuration of a conventional photovoltaic element.

FIG. 10 is a diagram showing a band profile of a conventional photovoltaic element.

FIG. 11 is a diagram showing a band profile of a conventional photovoltaic element.

FIG. 12 is a diagram showing a band profile of a conventional photovoltaic element.

FIG. 13 is a schematic view showing a film forming apparatus suitable for producing a photovoltaic element of the present invention.

FIG. 14 is a diagram showing light degradation characteristics of samples having different band gaps.

FIG. 15 is a diagram showing an effect of a buffer layer which is a part of the configuration of the photovoltaic device of the present invention.

FIG. 16 is a diagram showing an effect of a buffer layer which is a part of the configuration of the photovoltaic device of the present invention.

FIG. 17 is a diagram showing the relationship between the composition ratio of germanium elements, which are part of the configuration of the photovoltaic device of the present invention, and the degradation characteristics.

FIG. 18 is a view showing an effect of a gradient layer which is a part of the configuration of the photovoltaic device of the present invention.

FIG. 19 is a diagram showing an effect of a gradient layer which is a part of the configuration of the photovoltaic device of the present invention.

[Explanation of symbols]

101 substrate, 301 substrate, 102 lower electrode,
302 lower electrode, 103 n-type semiconductor layer, 203
n-type semiconductor layer, 303 n-type semiconductor layer, 313 n-type semiconductor layer, 323 n-type semiconductor layer, 403 n-type semiconductor layer, 104 i-type semiconductor layer, 204 i-type semiconductor layer, 204 ′ i-type semiconductor layer, 304 i-type Semiconductor layer, 314 i-type semiconductor layer, 324 i-type semiconductor layer, 404 i-type semiconductor layer, 404 ′ i-type semiconductor layer, 105 p-type semiconductor layer, 205 p-type semiconductor layer,
305 p-type semiconductor layer, 315 p-type semiconductor layer, 3
25 p-type semiconductor layer, 405 p-type semiconductor layer, 108
Buffer layer, 109 buffer layer, 208 buffer layer, 209 buffer layer, 408 buffer layer, 409 buffer layer, 106 transparent electrode, 306
Transparent electrode, 107 current collecting electrode, 307 current collecting electrode,
700 reaction chamber, 701 substrate, 702 anode electrode, 703 cathode electrode, 704 substrate heating heater, 705 grounding terminal, 706 matching box, 707 RF power supply, 708 exhaust pipe, 709 exhaust pump, 710 deposition gas introduction pipe,
720 valve, 730 valve, 740 valve, 750 valve, 760 valve, 722 valve, 732 valve, 742 valve, 752 valve, 762 valve, 721 mass flow controller, 731 mass flow controller, 741
Mass Flow Controller, 751 Mass Flow Controller, 761 Mass Flow Controller.

Continuation of the front page (56) References JP-A-59-205770 (JP, A) JP-A-60-30181 (JP, A) JP-A-64-71182 (JP, A)

Claims (3)

(57) [Claims] An amorphous silicon germanium constituent material
The atomic weight of germanium is high inside the layer thickness direction
Continuous in the layer thickness direction so that it becomes lower on the side of the N-type and N-type semiconductor layers
-Type photovoltaic with I-type semiconductor layer changing
In the power device, between the I-type semiconductor layer and the P-type semiconductor layer and the I-type semiconductor layer.
Amorphous silicon between the n-type semiconductor layer and the n-type semiconductor layer
A buffer layer of an I-type semiconductor is provided, and the I-type semiconductor layer is located on an interface side with the buffer layer.
Has a germanium atomic weight of 20 atomic% or more, and
Germanium atomic weight inside the thickness direction of the I-type semiconductor layer
Of the germanium in the part where the maximum is 70 atomic%
A photovoltaic element characterized by the following. 2. The method according to claim 1, wherein said buffer layer has a thickness of 50 to 100.
2. The photovoltaic device according to claim 1, wherein the thickness is 0 Å. 3. Stacking two or more pin-type unit element structures
In a stacked photovoltaic element, at least one of the unit element structures is
A photovoltaic device according to claim 2.
Photovoltaic element.