JPH04255273A - Photovoltaic element - Google Patents

Abstract

PURPOSE:To provide a photovoltaic element which is excellent in photoelectric conversion efficiency and reliability and applicable to a solar cell or the like. CONSTITUTION:In a PIN type photovoltaic element provided with an I-type semiconductor layer formed of amorphous silicon germanium, the I-type semiconductor layer concerned is composed of germanium-free layers 108 and 109 and a germanium-containing layer 104, and the layers 108 and 109 are provided to the parts of the I-type semiconductor layer which are brought into contact with a P-type semiconductor 105 and an N-type semiconductor layer 103 respectively.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a photovoltaic device,
In particular, the present invention relates to photovoltaic elements that have high photoelectric conversion efficiency and high reliability and are used in solar cells and the like.

0002

[Prior Art] Solar cells, which are photoelectric conversion elements that convert sunlight into electrical energy, have been widely applied as low-power power sources for consumer products such as calculators and wristwatches.
It is attracting attention as a technology that can be put to practical use as an alternative electricity source to so-called fossil fuels such as oil and coal. Solar cells are a technology that utilizes photovoltaic power at the pn junction of semiconductors. A semiconductor such as silicon absorbs sunlight and generates optical carriers of electrons and holes, which are then applied to the internal electric field of the pn junction. The material is then allowed to drift and taken out to the outside. Such a solar cell is generally manufactured using a semiconductor process. Specifically, a single crystal of silicon whose valence electrons are controlled to be p-type or n-type is produced by a crystal growth method such as the cz method, and the single crystal is sliced to produce a silicon wafer with a thickness of about 300 μm. Further, a pn junction is created by forming layers of different conductivity types by appropriate means such as diffusion of a valence electron control agent so as to have a conductivity type opposite to that of the wafer.

By the way, from the viewpoint of reliability and conversion efficiency, single-crystal silicon is mainly used in solar cells currently in practical use, but as mentioned above, solar cells are manufactured using semiconductor processes. The production cost is high due to the use of

Another disadvantage of single-crystal silicon solar cells is that single-crystal silicon has a low light absorption coefficient due to indirect transition, and single-crystal solar cells must be at least 50 microns thick to absorb incident sunlight. In addition, the band gap is about 1.1 eV, which is narrower than 1.5 eV, which is suitable for solar cells, so that long wavelength components cannot be used effectively. Furthermore, even if polycrystalline silicon were used to reduce production costs, the problem of indirect transition would remain and the thickness of the solar cell could not be reduced. Furthermore, polycrystalline silicon has grain boundaries and other problems.

Furthermore, since it is crystalline, it is difficult to manufacture large-area wafers and it is difficult to increase the area, and when extracting a large amount of power, it is necessary to connect unit elements in series or in parallel with wiring. things that must be done,
The production cost per unit of power generation is higher compared to existing power generation methods, due to the need for expensive implementation to protect solar cells from mechanical damage caused by various weather conditions when used outdoors. The problem is that it becomes Under these circumstances, in promoting the practical use of solar cells for power generation, lowering costs and increasing the area are important technical issues, and various studies are being carried out, including the use of low-cost materials and improvements in conversion efficiency. Research has been carried out on materials such as high-performance materials, but the materials for such solar cells include tetrahedral amorphous semiconductors such as amorphous silicon, amorphous silicon germanium, and amorphous silicon carbide. and II-VI group compound semiconductors such as CdS and Cu2S, and III-V group compound semiconductors such as GaAs and GaAlAs. In particular, thin-film solar cells using an amorphous semiconductor for the photovoltaic generation layer can be fabricated with a larger area than single-crystalline solar cells, can be formed with a thinner film, and can be used with any substrate material. It is seen as promising because of its advantages such as the ability to be deposited.

However, solar cells using the above-mentioned amorphous semiconductors cannot be used as power devices due to improvements in photoelectric conversion efficiency,
Problems remain in terms of improving reliability.

[0007] As a means of improving the photoelectric conversion efficiency of solar cells using amorphous semiconductors, for example, narrowing the band gap to increase the sensitivity to long wavelength light has been carried out. In other words, amorphous silicon has a band gap of about 1.7 eV, so it cannot absorb light with a long wavelength of about 700 nanometers or more and cannot be used effectively. The use of materials with a narrow width is being considered. For such materials, the band gap can be easily changed from about 1.3 eV to 1 by changing the ratio of silicon raw material gas and germanium raw material gas during film formation.
．． An example is amorphous silicon germanium, which can be arbitrarily varied up to about 7 eV.

Another method for improving the conversion efficiency of solar cells is to use so-called tandem cells in which a plurality of solar cells with a unit element structure are stacked, as disclosed in US Pat. No. 2,949.
, 498. A pn junction crystal semiconductor was used in this tandem cell, but the idea is common to both amorphous and crystalline semiconductors: the solar spectrum is efficiently absorbed by photovoltaic elements with different band gaps. , the power generation efficiency was improved by increasing Voc.

[0009] Tandem cells improve conversion efficiency by stacking elements with different band gaps and efficiently absorbing each part of the spectrum of sunlight. 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. have reported a so-called cascade type battery in which amorphous silicon having the same bandgap is laminated in multiple layers without an insulating layer between photovoltaic elements to increase the Voc of the entire element. In this method, unit elements made of amorphous silicon materials with the same bandgap are stacked.

Amorphous silicon germanium has a narrow bandgap and excellent sensitivity to long wavelength light, so it is used as a suitable material for the bottom layer of the above-mentioned tandem cell.

[0011] By the way, amorphous silicon germanium, which has improved long-wavelength sensitivity and can also be used as the bottom layer of tandem cells, is generally inferior to amorphous silicon in film quality and Even when a battery is produced, there is a drawback of low conversion efficiency. This is because there are more localized levels within the bandgap than in amorphous silicon. For this reason, research and development is being conducted to improve film quality by reducing the levels within the bandgap.
For example, amorphous silicon germanium in which the localized level density is reduced by compensating for dangling bonds in amorphous silicon germanium using activated fluorine atoms is described in Japanese Patent Publication No. 48197/1983. Disclosed.

On the other hand, improvements in the characteristics of amorphous silicon germanium solar cells are being investigated by methods other than the essential improvement of film quality as described above. As an example, a method using a so-called buffer layer that provides a band width gradient at the junction interface between a p-type semiconductor and/or n-type semiconductor and an i-type semiconductor layer is disclosed in U.S. Patent No. 4,254,429, No. 4,377,723. The purpose of the buffer layer is to create a large number of levels at the junction interface between a p-type or n-type semiconductor made of amorphous silicon and an i-type semiconductor made of amorphous silicon germanium due to differences in lattice constants. is generated, so the purpose is to eliminate the level by using amorphous silicon at the junction interface, improve the junction, and improve the Voc without impairing the mobility of carriers.

Furthermore, as another method, a method has been disclosed in which a so-called graded layer is provided in which the compositional ratio of silicon and germanium is changed to provide a compositional distribution in the intrinsic layer and improve the characteristics.

For example, according to US Pat. No. 4,816,082, the bandgap of the i-layer in the portion in contact with the first valence electron-controlled semiconductor layer on the light incident side is widened, and the bandgap is widened toward the central portion. The bandgap is gradually narrowed 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, carriers generated by light can be efficiently separated by the action of an internal electric field, and the film properties can be improved.

[0015] Another problem with solar cells using amorphous semiconductors is that the conversion efficiency decreases due to light irradiation. This is caused by the fact that the film quality of amorphous silicon and amorphous silicon germanium is degraded by light irradiation, which deteriorates the mobility of carriers. This is a phenomenon unique to crystalline semiconductors. Therefore, when used for electric power, reliability is poor, which is an obstacle to practical application. Intensive research is being carried out to improve the photodegradation of amorphous semiconductors, and while some studies are investigating ways to prevent photodegradation by improving film quality, there are also studies on reducing photodegradation by improving the cell structure. There is. As a specific example of such a method, using the tandem cell structure described above is an effective means, and by making the intrinsic layer thinner and shortening the travel distance of the carrier, the deterioration of cell characteristics due to light irradiation can be minimized. It has been confirmed that this will happen.

[0016]

[Problems to be Solved by the Invention] However, in the 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 existing nuclear power. , thermal power, hydropower, etc. In order for amorphous silicon-based solar cells to be used for electric power applications along with existing power generation methods, it is necessary to further improve conversion efficiency.

Furthermore, as mentioned above, despite continued efforts to elucidate the mechanism of photodegradation and to investigate ways to prevent photodegradation, the problem of photodegradation has not been completely solved, and Solar cells are required to be even more reliable. In the method of preventing deterioration using stacked cells described above, the overall light absorption amount of the photovoltaic element is reduced by making the intrinsic layer thinner, so although it may be effective in preventing photodeterioration, the initial light Since the electromotive force characteristics decrease, it is currently impossible to realize a solar cell that satisfies the requirements of high reliability and high efficiency.

[0018] An object of the present invention is to solve the above-mentioned problems and provide a photovoltaic element for use in solar cells and the like that has high reliability and high photoelectric conversion efficiency.

[0019]

[Means for Solving the Problems] The present inventors have overcome the above-mentioned problems and, as a result of intensive studies on solar cells with little photodeterioration and high conversion efficiency, have found that the silicon-based gas used for film formation. By controlling the stoichiometric ratio of germanium-based gases, we obtained the knowledge that a high-quality film with very little increase in conductivity and defects in the film upon continuous light irradiation can be obtained, and furthermore, we have found that by controlling the stoichiometric ratio of germanium-based gas, it is possible to obtain a high-quality film with very little increase in conductivity and defects in the film when exposed to continuous light irradiation. We obtained the knowledge that solar cells with high initial efficiency can be obtained by controlling the composition ratio of silicon and germanium in the film thickness direction. The present invention conducts further research based on this knowledge,
It was applied to a photovoltaic element and completed.
The gist of the present invention is that the i-type semiconductor layer of a pin-type photovoltaic element whose i-type semiconductor layer is made of amorphous silicon germanium is divided into a layer containing no germanium element and a layer containing germanium element. formed from a layer,
The purpose is to provide a layer not containing the germanium element in a portion in contact with a p-type semiconductor and an n-type semiconductor. Also,
A preferred configuration is achieved by setting the thickness of the layer not containing the germanium element to 50 to 1000 angstroms. Further, by setting the germanium element in the layer containing the germanium element from 20 atm % to 70 atm %, a structure with less deterioration can be obtained. Further, by continuously changing the composition of germanium in the layer containing the germanium element, the characteristics can be further improved. At this time, the characteristics are further improved by locating the maximum value of the continuously changing composition of the germanium element within the i-type semiconductor layer. Furthermore, the present invention can be applied to a stacked photovoltaic device in which two or more pin unit element structures are stacked, and in this case, the structure of at least one or more i-type semiconductor layers is as described above. , the thickness of the layer that does not contain germanium element is from 50 to 1000 angstroms, the amount of germanium element in the layer containing germanium is from 20 atm% to 70 atm%, the composition of germanium element is continuously changed, the composition of germanium element is It goes without saying that a similar effect can be obtained by locating the maximum value of in the i-type semiconductor layer.

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

First, prior to explaining the present invention, a pin-type amorphous solar cell suitable for applying the photovoltaic element of the present invention will be explained.

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

[0023] In each embodiment, the same constituent members are given the same reference numerals.

FIG. 6 shows a solar cell having a structure in which light enters from the top of the figure, and in the figure, 300 is the solar cell main body;
1 is a substrate, 302 is a lower electrode, 303 is an n-type semiconductor layer (
304 is an i-type semiconductor layer (hereinafter referred to as an i-type semiconductor layer).
305 is a p-type semiconductor layer (hereinafter referred to as p layer), 306 is an upper electrode, and 307 is 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 the solar cell body.

FIG. 8 shows a solar cell having a structure in which the two layers shown in FIG.
3 is the n layer, 304 and 314 are the i layer, and 305 and 315 are the p layer.
Represents a layer. FIG. 9 shows a solar cell having a structure in which the three layers shown in FIG.
11 and 309 represent unit elements of a solar cell, and 3
03, 313, 323 are n layers, 304, 314, 324
represents the i-layer, and 305, 315, and 325 represent the p-layer. Note that in any photovoltaic element, the stacking order of the n-layer and p-layer may be changed depending on the purpose. The configurations of these photovoltaic elements will be explained below.

(Substrate) Semiconductor layers 303, 304, 305
Since it is a thin film of about 1 μm at most, it is deposited on a suitable substrate. Such a substrate 301 may be single crystal or non-single crystal, and may be electrically conductive or electrically insulating. Further, although they may be translucent or non-transparent, it is preferable that they are less deformed and distorted and have desired strength. Specifically, Fe, Ni, Cr, Al, Mo, Au, N
b, Ta, V, Ti, Pt, Pb and other metals or their alloys, such as thin plates such as brass and stainless steel, and composites thereof, and polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polychloride Films or sheets of heat-resistant synthetic resins such as vinylidene, polystyrene, polyamide, polyimide, epoxy, etc., or composites of these with glass fibers, carbon fibers, boron fibers, metal fibers, etc., thin plates of these metals, resin sheets, etc. Metal thin film of different materials and/or SiO2, Si3 on the surface
Examples include those whose surfaces are coated with insulating thin films such as N4, Al2 O3, and AlN by sputtering, vapor deposition, and plating, as well as glass and ceramics.

When the substrate is used as a substrate for a solar cell, it may be used as an electrode for direct current extraction if the strip substrate is made of electrically conductive material such as metal, or it may be made of electrically insulating material such as synthetic resin. In this case, the surface on which the deposited film is formed contains Al, Ag, Pt, Au, Ni, Ti, Mo,
W, Fe, V, Cr, Cu, stainless steel, brass, nichrome, SnO2, In2 O3, ZnO, ITO
It is desirable to form electrodes for current extraction by subjecting so-called single metals or alloys such as metals or transparent conductive oxides (TCO) to surface treatment in advance by plating, vapor deposition, sputtering, or other methods.

Of course, even if the strip-shaped substrate is made of an electrically conductive material such as metal, it is possible to improve the reflectance of long-wavelength light on the substrate surface, or to add constituent elements between the substrate material and the deposited film. A layer of different metals 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. Further, in the case of a solar cell having a layered structure in which the substrate is relatively transparent and light is incident from the side of the substrate, a conductive thin film such as the transparent conductive oxide or metal thin film is deposited in advance. It is desirable to keep it.

Furthermore, the surface properties of the substrate may be a so-called smooth surface or a minutely uneven surface.

[0030] In the case of forming a finely uneven surface, the uneven shape is spherical, conical, pyramidal, etc., and the maximum height (Rmax) is preferably 500 Å to 5000 Å. The light reflection becomes diffused reflection, resulting in an increase in the optical path length of the reflected light on the surface. The shape of the substrate can be a flat plate with a smooth surface or an uneven surface, a long belt shape, a cylindrical shape, etc. depending on the purpose, and the thickness can be determined as appropriate so as to form the desired photovoltaic element. I decide, but
When flexibility is required as a photovoltaic element, or when light is incident from the substrate side, the thickness can be made as thin as possible within a range that allows the substrate to function satisfactorily. However, from the viewpoint of manufacturing and handling of the substrate, mechanical strength, etc., the thickness is usually set to 10 μm or more.

In the photovoltaic device of the present invention, appropriate electrodes are selected and used depending on the configuration of the device. These electrodes include a lower electrode, an upper electrode (transparent electrode),
(However, the upper electrode here refers to the one provided on the light incident side, and the lower electrode refers to the one provided opposite the upper electrode with a semiconductor layer in between.) ).

[0032] These electrodes will be explained in detail below.

(Lower Electrode) Since the surface of the lower electrode 302 used in the present invention that is irradiated with light for generating photovoltaic power differs depending on whether the material of the substrate 301 described above is translucent or not ( For example, when the substrate 301 is made of a non-light-transmitting material such as metal, light for generating photovoltaic force is irradiated from the upper electrode 306 side as shown in FIG. 6.) The installation location differs. Specifically, in the case of layer configurations as shown in FIGS. 6, 8, and 9, the substrate 301 and the n-layer 303
established between. However, if the substrate 301 is conductive, it can also serve as the lower electrode. However, even if the substrate 301 is conductive, if the sheet resistance value is high, it can be used as a low resistance electrode for current extraction.
Alternatively, the electrode 302 may be provided for the purpose of increasing the reflectance on the substrate surface and making effective use of the incident light.

In the case of FIG. 7, a transparent substrate 301 is used, and light is incident from the substrate 301 side.
A lower electrode 302 is provided facing the substrate 301 with a semiconductor layer in between for the purpose of extracting current and reflecting light at the electrode.

Further, when an electrically insulating material is used as the substrate 301, the substrate 301 can be used as an electrode for taking out current.
A lower electrode 302 is provided between 01 and n layer 303. As electrode materials, Ag, Au, Pt, Ni, Cr,
Examples include metals such as Cu, Al, Ti, Zn, Mo, and W, or alloys thereof, and thin films of these metals are formed by vacuum evaporation, electron beam evaporation, sputtering, or the like. Further, care must be taken so that the formed metal thin film does not become a resistance component with respect to the output of the photovoltaic element, and it is desirable that the sheet resistance value is preferably 50Ω or less, more preferably 10Ω or less.

Although not shown in the figure, a diffusion prevention layer such as conductive zinc oxide may be provided between the lower electrode 302 and the n-layer 303. The effect of the diffusion prevention layer is not only to prevent the metal element constituting the lower electrode 302 from diffusing into the n-type semiconductor layer, but also to provide a slight resistance value to the lower part provided across the semiconductor layer. To prevent short circuits caused by defects such as pinholes between the electrode 302 and the transparent electrode (upper electrode) 306, and to generate multiple interference with a thin film to confine incident light within the photovoltaic element. It can be said that it is effective.

(Top Electrode (Transparent Electrode)) The transparent electrode (top electrode) 306 used in the present invention has a high light transmittance in order to efficiently absorb light from the sun, a white fluorescent lamp, etc. into the semiconductor layer. The sheet resistance value is preferably 85% or more, and furthermore, the sheet resistance value is preferably 100Ω or less so as not to become a resistance component electrically with respect to the output of the photovoltaic element. As a material with such characteristics,
SnO2, In2O3, ZnO, CdO, CdS
Examples include metal oxides such as nO4 and ITO (In2O3 +SnO2), and metal thin films formed of extremely thin and translucent metals such as Au, Al, and Cu. In FIGS. 6, 8, and 9, the transparent electrodes are p-layers 305 and 305, respectively.
315, 325, and in FIG.
Since it is to be laminated on top of 01, it is necessary to select materials that have good adhesion to each other. As a method for producing these, a resistance heating evaporation method, an electron beam heating evaporation method, a sputtering method, a spray method, etc. can be used, and the method is appropriately selected depending on the need.

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

For example, it is desirable that the shape spreads uniformly over the light-receiving surface of the photovoltaic element, and that its area is preferably 15% or less, more preferably 10% or less of the light-receiving area.

Further, the sheet resistance value is preferably 50Ω or less, more preferably 10Ω or less.

The semiconductor layers 303, 304, and 305 are manufactured by a normal thin film manufacturing process, including vapor deposition,
It can be manufactured by using known methods such as sputtering, high-frequency plasma CVD, microwave plasma CVD, ECR, thermal CVD, and LPCVD as desired. As a method employed industrially, a plasma CVD method is preferably used in which a raw material gas is decomposed by plasma and deposited on a substrate. Further, as the reaction apparatus, a batch type apparatus, a continuous film forming apparatus, etc. can be used as desired. When producing a semiconductor with controlled valence electrons, it is carried out by simultaneously decomposing PH3, B2 H6 gases, etc. containing phosphorus, boron, etc. as constituent atoms. (i-layer) Semiconductor materials constituting the i-layer suitably used in this photovoltaic device include a-SiGe:H, a-SiGe:H, a-SiGe:
-So-called I such as SiGe:F, a-SiGe:H:F
Examples include group V alloy semiconductor materials. In addition, in a tandem cell structure in which unit element structures are stacked, semiconductor materials constituting the i-layer other than amorphous silicon germanium include a-Si:H, a-Si:F, and a-Si:H:F. ,a
-SiC:H, a-SiC:F, a-SiC:H:F,
poly-Si:H, poly-Si:F, poly-
In addition to so-called group IV and group IV alloy semiconductor materials such as Si:H:F, so-called compound semiconductor materials of groups III-V and II-VI can be mentioned.

As the raw material gas used in the CVD method, a chain or cyclic silane compound is used as a compound containing the silicon element, and specifically, for example, SiH4, Si
F4 , (SiF2 )5 , (SiF2 )6 , (
SiF2 )4 , Si2 F6 , Si3 F8 ,
SiHF3, SiH2 F2, Si2 H2 F4
, Si2 H3 F3 , SiCl4 , (SiCl
2)5,SiBr4,(SiBr2)5,S
iCl6, SiHCl3, SiHBr2, SiH
2 Cl2 , SiCl3 F3 and the like which are in a gaseous state or can be easily gasified can be mentioned.

[0043] Further, as a compound containing germanium element, chain germanium or halogenated germanium,
Cyclic germanium, halogenated germanium, chain or cyclic germanium compounds, and organic germanium compounds having an alkyl group, specifically GeH4
, Ge2 H6 , Ge3 H8 , n-GeH10
, t-Ge4 H10, GeH6 , Ge5 H10,
GeH3Cl,GeH2F2,Ge(CH3)
4,Ge(C2H5)4,Ge(C6H5
)4 ,Ge(CH3)2F2 ,GeF2 ,G
Examples include eF4.

(P-layer and n-layer) As the semiconductor material constituting the p-layer or n-layer suitably used in the present photovoltaic device, the semiconductor material constituting the i-layer described above is doped with a valence electron control agent. obtained by As a manufacturing method, a method similar to the method for manufacturing the i-layer described above can be suitably used. Further, as raw materials, when obtaining a deposited film of Group IV of the periodic table, a compound containing an element of Group III of the periodic table is used as a valence electron control agent for obtaining a p-type semiconductor. Group III elements include B, Al, Ga, and In. Compounds containing group III elements include:
Specifically, BF3, B2 H6, B4 H10,
B5 H9, B5 H11, B6 H10, B(CH
3)3,B(C2H5)3,B6H12,
Al(CH3)2Cl,Al(CH3)3,A
l(OCH3)2 Cl, Al(CH3)Cl2
, Al(C2 H5 )3 , Al(OC2 H5 )
3, Al(CH3)3 Cl3, Al(i-C4
H9 )5 , Al(C3 H7 )3 , Al(O
C4 H9 )3 , Ga(OCH3 )3 , Ga(
OC2 H5 )3 , Ga(OC3 H7 )3 ,
Ga(CH3)3, Ga2H6, GaH(C2
H5 )2 , Ga(OC2 H5 ), (C2 H
5 )2 , In(CH3 )3 , In(C3 H7
)3, In(C4H9)3, and the like.

As a valence electron control 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. Specifically, compounds containing Group V elements include:
NH3 HN3 , N2 H5 N3 , N2 H4
, NH4 N3 , PH3 , P(OCH3 )3 ,
P(OC2 H5 )3 , P(C3 H7 )3 ,
P(OC4 H9 )3 , P(CH3 )3 , P(
C2 H5 )3 , P(C3 H7 )3 , P(C
4 H9 )3 , P(OCH3 )3 , P(OC2
H5 )3 , P(OC3 H7 )3 , P(OC
4 H9 )3 , P(SCN)3 , P2 H4 ,
PH3, AsH3, AsH3, As(OCH3
)3 , As(OC2 H5 )3 , As(OC3
H7 )3 , As(OC4 H9 )3 , As(C
H3 )3 , As(CH3 )3 , As(C2 H
5)3, As(C6H5)3, SbH3,
Sb(OCH3)3,Sb(OC2H5)3
,Sb(OC3 H7)3 ,Sb(OC4 H9
)3, Sb(CH3)3, Sb(C3H7)
3, Sb(C4H9)3, and the like.

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

When the above-mentioned raw material is in a gaseous state at room temperature and pressure, a mass flow controller (hereinafter referred to as MF) is used.
The amount introduced into the film forming space is controlled by C), etc., and when it is in a liquid state, a rare gas such as Ar or He or hydrogen gas is used as a carrier gas, and a bubbler whose temperature can be controlled as necessary is used. If it is in a solid state, it is gasified using a heated sublimation furnace using a rare gas such as Ar or He or hydrogen gas as a carrier gas, and the amount introduced is controlled mainly by the carrier gas flow rate and furnace temperature. .

By the way, the bandgap profiles of the conventional elements having the configurations shown in FIGS. 6 to 9 are as shown in FIGS. 10 to 1.
It is shown as 2. In the figure, the upper line indicates the bottom of the conduction band of the energy level, and the lower line indicates the top of the valence band.
403 is an n layer, 405 is a p layer, and 404 is an i layer. Further, 408 and 409 indicate buffer layers. In FIG. 10, the bandgap of the i-layer 404 is narrower than that of the n-layer 403 and the p-layer 405, which are impurity doped layers.

In the case of such a band profile, the open circuit voltage is determined by the i-layer 404, so if a material with a narrow band gap is used, the open circuit voltage will become small. In addition, free electrons and free holes generated in the i layer 404 in contact with the p layer 405 are recombined by the high concentration recombination level existing at the pi interface, so they are lost without being effectively taken out. Put it away. Also, on the light incident side,
The amount of light is large, and the amount of light absorbed as it goes inside is
Decrease exponentially. On the light incidence side, the energy of the absorbed light exceeds the band gap, meaning that the excess energy cannot be used effectively. As a method of solving such drawbacks, a structure in which a buffer layer is provided as shown in FIG. 11 is used. In the figure 408
and 409 are buffer layers which have the effect of reducing localized levels at the pi and ni interfaces. Furthermore, an element configuration as shown in FIG. 12 has been proposed. In the figure, 403,
405 is an n layer, a p layer, and 40 which are doping layers, respectively.
4 is the i layer. In the figure, light is assumed to be incident from the left side. Here, the i-layer 404 is a graded buffer layer in which a buffer layer 409 not containing a band gap adjusting agent is provided on the light incident side to widen the band gap, and then the band gap adjusting agent is gradually increased to narrow the band gap. 404' is provided. Furthermore, a gradient layer 404'' is provided in which the bandgap adjusting agent decreases toward the side opposite to the light incident side, thereby widening the bandgap.

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

The gist of the present invention is to not only improve the initial efficiency by improving the band profile as described above, but also to devise an element configuration that is less susceptible to photodeterioration. The present inventors have discovered that amorphous silicon germanium exhibits less photodegradation in a specific germanium element composition,
We devised a cell that uses amorphous silicon germanium with a composition that is less susceptible to photodeterioration and has high conversion efficiency.

[0052] The experiments conducted by the present inventor are shown below.

<Experiment> An amorphous silicon germanium film was produced in the following manner using a known RF discharge plasma CVD film forming apparatus shown in FIG.

In FIG. 13, 700 is a reaction chamber;
01 is a substrate, 702 is an anode electrode, 703 is a cathode electrode, 704 is a heater for heating the substrate, 705 is a ground terminal, 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, 740
, 750, 760, 722, 732, 742, 752 and 762 are valves, 721, 731, 741, 751
and 761 indicate a mass flow controller.

First, a 5 cm square piece of glass 7059 manufactured by Corning Corporation is attached to the cathode in the reaction chamber 700, the exhaust pump 709 is used to fully evacuate the reaction chamber 700, and an ion gauge (not shown) is used to measure the vacuum in the reaction chamber 700. The temperature was set to 10-6 Torr. Next, the substrate 701 was heated to 300° C. using a substrate heating heater 704. After the substrate temperature becomes constant, the valves 720, 72
2 and controls the mass flow controller 721 to supply SiH4 gas 30 from a SiH4 gas cylinder (not shown).
sccm into the reaction chamber 7 via a gas introduction pipe 710.
It was introduced into 00. Similarly, valves 740, 742
Open and control the mass flow controller 741 to
2 Supply 300 sccm of gas and close the valves 730, 73
2 was opened, the mass flow controller 731 was controlled, and 1 sccm of GeH4 gas was introduced. After adjusting a pressure controller (not shown) to maintain the internal pressure of the reaction chamber 700 at 1.5 Torr, 20 W power is applied from the RF power source 707, and plasma discharge is performed while minimizing reflected waves by adjusting the matching box 706. was carried out for 60 minutes, and a 1 μm thick amorphous silicon germanium film was deposited. Stop the gas supply and move the reaction chamber 700
Take out the sample from Sample No. was designated as S-1. Similarly, GeH4 gas amount 3sccm, 5sccm, 10
Samples were prepared by varying the increments of sccm, 20 sccm, and 40 sccm, and S-2, S-3, S-4, S-5, and
It was named S-6. Some of these samples were subjected to elemental analysis using Auger electron spectroscopy to determine the composition ratio of germanium elements in the film. The composition other than germanium was silicon and hydrogen. The optical bandgap of a part of the sample was measured by measuring the absorption coefficient using a visible spectrometer. The above results are shown in Table 1.

[0056]

[Table 1] Further, a part of the sample was transferred to an electron beam vacuum evaporation apparatus (EBX-6D, manufactured by ULBAC), not shown, and the inside of the evaporation apparatus was evacuated, and the length was 1 cm with a gap width of 250 μm.
A Cr electrode with a thickness of 1000 Å was deposited. Next, these samples were placed on a temperature-controllable sample stage, kept at a constant temperature of 25°C, and a xenon lamp was used as the light source to measure the AM-1.5 sunlight spectrum using a pseudo sunlight source (hereinafter referred to as a solar simulator). The initial photoconductivity σP (0) was measured by irradiating light with an intensity of 100 mW/cm2, and then after continuous irradiation with the light from the simulator for 100 hours, the photoconductivity σ
P (100) was measured.

The results are shown in FIG. As shown in the figure, films with a high composition ratio of germanium element exhibit less photodeterioration, and films with a composition ratio of germanium element of 20 atm % or more are stable against light irradiation. In particular, it can be seen that when the germanium element is 30 atm % or more, it is extremely stable against light irradiation.

By the way, in the conventional device configuration, a so-called buffer layer is used to improve the internal electric field by providing a band width gradient at the junction interface between the P-type semiconductor and/or N-type semiconductor and the intrinsic layer. This buffer layer was fabricated by continuously changing the composition ratio of silicon and germanium to change the band gap from about 1.7 eV to about 1.5 eV. was. The composition ratio of germanium at this time varies from 0 to about 50 atm%. In addition, even when forming a so-called graded layer, which improves properties by creating a composition distribution in the intrinsic layer by changing the composition ratio of silicon and germanium, when using a composition with a wide band gap, the composition ratio of germanium changes. It contained less than 20 atm%. In such solar cells, the above-mentioned fact that if there is a small amount of germanium, they tend to deteriorate is not taken into account, and therefore, although the initial efficiency is improved by the buffer layer and the gradient layer, no consideration is given to deterioration. The reality is that it was not.

The device structure of the present invention does not contain amorphous silicon germanium, which has a composition that is susceptible to photodeterioration, and also makes it possible to improve initial efficiency by providing a buffer layer and a gradient layer. It is.

FIG. 1 schematically shows one of the configurations of the photovoltaic device of the present invention, which was obtained by further improving the conventional example based on the results of the above experiment. In the same 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 germanium element and serve as a buffer layer;
104 is a layer containing germanium element, i2 layer, 10
5 is a p layer, 106 is an upper electrode, and 107 is a current collecting electrode. The i1 layer 108, 109 and the i2 layer 104 constitute an i layer. The band profile of this device is shown in FIG. In the figure, light is assumed to be incident from the left side (p layer 205 side). In the figure, 200 is an i-layer body, 203 is an n-layer, 204 is an i2 layer of amorphous germanium silicon, 205 is a p-layer, and 208 and 209 are i1 layers serving as buffer layers. In addition, the band profile of this device is as shown in Figure 3, i2 of the amorphous germanium silicon layer.
The layer 204 may be sloped so that the light incident side is wide, or it may be conversely narrowed on the light incident side as shown in FIG. Furthermore, gradient layers 204 and 204' may be combined as shown in FIG. Furthermore, the stacking order of the p layer and n layer in FIGS. 2 to 5 may be changed. The i1 layers 208 and 209, which serve as buffers, are composed of amorphous silicon layers that do not contain germanium and have a band gap of 1.
It has a voltage of about 7 eV and absorbs light from 300 nm to 730 nm. The i2 layers 204 and 204' are produced by decomposing a gas containing a silicon element and a gas containing a germanium element, which are raw material gases during film formation. , the composition of germanium is changed by changing the flow rate ratio of the gases. The function of such a graded layer will be explained using a specific configuration using the case of FIG. 5 as an example. The band gap of the i2 layer 204' in contact with the i1 layer 209 serving as the buffer layer in FIG. 5 is 1.
The band gap is approximately 55 eV, and gradually narrows toward the direction opposite to the light incidence side, and the band gap at the narrowest portion is approximately 1.45 eV. The bandgap of the i2 layer 204 is designed to gradually widen toward the n-layer 203, and the bandgap is designed to be approximately 1.55 eV at the portion in contact with the i1 layer 208, which serves as a buffer layer. The function of the band profile in the device configured as described above will be explained as follows.

Irradiation light enters from the side of the p-type semiconductor layer 205, and the i1 layer 209 and the i2 layer 204, which serve as buffer layers,
' and 204, optical carriers are generated in the i1 layer 208 which serves as a buffer layer. i1 layer 2 becomes the buffer layer
Since 09 has a wide bandgap, it absorbs only short-wavelength light and transmits long-wavelength light, so the light reaches the inside of the cell and can be used effectively. Also pi
When the interface is made of amorphous silicon germanium,
Due to the poor quality of the film and the mismatch in lattice spacing between the p-layer and amorphous silicon germanium, the number of recombination levels increases, resulting in poor solar cell characteristics. On the other hand, when fabricated with amorphous silicon, there are relatively few recombination levels, so p
The high concentration of carriers generated at the i-interface can be effectively taken out without recombination. Furthermore, since there are few recombination levels, the open circuit voltage also increases. In the i2 layer 204', the band gap gradually narrows, so that it absorbs short wavelength light near the p layer 205, and absorbs long wavelength light far from the p layer 205. The layer 208 is i1 which is a buffer layer.The layer 208 is i1 which is a buffer layer.
1 This layer has almost the same function as layer 209, and alleviates lattice mismatch at the Ni interface.

Furthermore, the effect that this band profile has on the collection of photogenerated carriers is explained as follows. In the i2 layer 204', the gradient of the energy at the bottom of the conduction band is larger on the p layer 205 side and smaller on the n layer 203 side, so that the electric field acts to increase the electric field for free electrons. Therefore, free electrons are accelerated toward the n-layer 203 and 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, the electric field acts to reduce the electric field for free holes. However, since the i2 layer 204' is close to the p layer, the drift distance of free electrons is short and does not pose much of a 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 becomes smaller. Although this is disadvantageous for the mobility of free electrons, it does not pose much of a problem since the mobility of electrons is generally better than that of holes. On the other hand, 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, so that the electric field increases with respect to free holes. In general, solar cell characteristics are determined by the mobility of holes, so if the structure is such that the electric field is large relative to holes, the solar cell characteristics will be improved. 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 the film quality is such that photodeterioration is unlikely to occur.

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

[0065]

[Examples] Next, preferred embodiments of the present invention will be shown below, but the content of the present invention is not limited to the following embodiments. (Example 1) Using the pin layer of the present invention having the band profile shown in FIG. 2, a solar cell having the configuration shown in FIG. 6 was produced in the following manner using the apparatus shown in FIG. 13.

First, the surface was mirror polished to 0.05 μmRm.
5cm square size stainless steel (SUS)
304) After putting the substrate 101 into a sputtering device (not shown) and evacuating the inside of the device to 10 −7 Torr or less, Ar
A gas was introduced, an internal pressure was set to 5 mTorr, DC plasma discharge was generated with a power of 200 W, and sputtering was performed using an Ag target to deposit approximately 5000 Å of Ag. After that, the target was changed to ZnO and sputtering was performed by generating DC plasma discharge under the same internal pressure and power conditions.
000 Å of ZnO was deposited. With the above steps, the lower electrode 1
After producing 02, the substrate 101 was taken out and attached to the cathode in the reaction chamber 700, and the exhaust pump 709 was used to sufficiently exhaust the air, and the vacuum degree in the reaction chamber 700 was adjusted to 10-6 Torr using an ion gauge (not shown). . Next, the substrate 701 is heated 3 times using the substrate heating heater 704.
Heated to 00°C. After the substrate temperature becomes constant, the valves 720 and 722 are opened, and the mass flow controller 72
1, 30 sccm of SiH4 gas was introduced into the reaction chamber 700 from a SiH4 gas cylinder (not shown) through the gas introduction pipe 710. Similarly, open valves 740 and 742 and mass flow controller 7.
41 was controlled to supply 300 sccm of H2 gas, valves 750 and 752 were opened, and the flow rate of mass flow controller 751 was controlled to introduce 10 sccm of PH3 gas diluted to 5% with H2 gas. After adjusting the internal pressure of the reaction chamber 700 to 1.5 Torr, the RF power source 7 is connected via the matching box 706.
A power of 10 W was applied from 07 onwards, and plasma discharge was performed for 3 minutes to deposit an n-type amorphous silicon layer 103 with a thickness of 400 Å. After stopping the gas supply, the reaction chamber 700 is evacuated again, and the degree of vacuum inside the reaction chamber 700 is reduced to 10-
After exhausting to 6 Torr or less, valves 720, 722,
730, 732, 740, and 742 were opened, and 30 sccm of SiH4 gas and 300 sccm of H2 gas were introduced into the reaction chamber 700. At this time, the flow rate of the GeH4 gas mass flow controller 731 was limited to Osccm, and the flow rate was set to Osccm at the start of film formation. RF
A power of 20 W is applied from the power supply 707 and plasma discharge is performed for 10 seconds to form the i1 layer 108 of the buffer layer with a thickness of 10 Å.
After depositing, the flow rate setting of the GeH4 gas mass flow controller 731 was instantly increased to 5 sccm and film formation was continued for 20 minutes to deposit an i2 layer 104 of about 2000 Å of amorphous silicon germanium. The response speed of the mass flow controller 731 was sufficiently fast to reach the set flow rate within 1 second, and there was no overshoot and the error with respect to the set flow rate was ±2%. In addition, a pressure controller (not shown) was used to prevent pressure fluctuations caused by rapidly increasing the flow rate. A microcomputer was used to accurately control the flow rate of the mass flow controller 731. Incidentally, the band gap of the amorphous silicon germanium film deposited under these conditions is about 1.53 eV, as confirmed in the experimental example. Next, GeH
4 Set the flow rate setting of the gas mass flow controller to 0s
ccm, and by closing the solenoid valve, the GeH4 gas flow rate is instantaneously reduced to 0 sccm, and SiH4 gas and H2
Film formation was continued using only gas for 10 seconds, resulting in a film thickness of 10
An i1 layer 109 was deposited to serve as a buffer layer of .ANG. RF
After turning the power of the power source 707 to 0W to stop the plasma discharge and stop the gas supply, the degree of vacuum in the reaction chamber 700 is evacuated to 10-6 Torr or less, and then the valve 720 is turned on.
, 722, 730, 732, 740, 742 and open S
iH4 gas 1sccm, H2 gas 300sccm and B2 H6 gas diluted to 5% with H2 gas 10sc
cm was introduced into the reaction chamber 700. Then RF
A power of 200 W was applied from the power source 707 to generate plasma discharge, and film formation was performed for 5 minutes to deposit a p layer 105 of 100 Å. In addition, it was confirmed by reflection high-speed electron diffraction (RHEED) that the p-layer was deposited on a glass substrate under these conditions to be microcrystalline with a grain size of 20 Å to 100 Å. Next, the substrate 101 is taken out from the reaction chamber 700 and placed in a resistance heating vapor deposition apparatus (not shown), and the inside of the apparatus is heated for one hour.
After evacuation to 0-7 Torr or less, oxygen gas was introduced and the internal pressure was set to 0.5 mTorr, an alloy of In and Sn was vapor-deposited by resistance heating to form a transparent conductive film (ITO) which also had the function of anti-reflection. A film) of 700 Å was deposited to form the upper electrode 106. After the vapor deposition was completed, the sample was taken out and decomposed into subcells of 1 cm x 1 cm using a dry etching device (not shown), then transferred to another vapor deposition device, and an aluminum current collecting electrode 107 was formed by electron beam evaporation. The obtained solar cell was No. The score was 1-1.

Next, in order to find the optimum thickness of the buffer layer 108, samples with different film thicknesses were prepared by forming the buffer layer 108 in the same manner as described above, except that the time for forming the buffer layer 108 was changed. Sample No. 1-2, No. 1-3,N
o. 1-4, No. 1-5, No. The score was 1-7. These samples were measured using a solar simulator with AM-1.5
The initial characteristics of the solar cell were measured by irradiating the solar cell with light in the sunlight spectrum at an intensity of 100 mW/cm 2 and obtaining a voltage-current curve.

The results obtained are shown in FIG. In the figure, the conversion efficiency η is expressed by normalizing the conversion efficiency when no buffer layer is used as 1. From Figure 15, buffer layer 1
It was found that the initial characteristics were improved when the film thickness of 08 was from 50 Å to 1000 Å. Furthermore, the buffer layer 109
Samples were prepared in which the film thickness of the buffer layer 109 was varied by performing film formation in the same manner as described above except for changing the film formation time. Sample No. 1-8, No. 1-9, No.
1-10, No. 1-11, No. 1-12, No. 1
-13, No. It was set at 1-14. The initial characteristics of each of these samples were measured using the method described above. The obtained results are shown in FIG. 16. In the figure, the conversion efficiency η is expressed by normalizing the conversion efficiency when no buffer layer is used as 1. From FIG. 16, the film thickness of the buffer layer 109 is from 50 Å to 1
It was found that the initial characteristics were improved by setting the thickness to 000 Å. (Example 2) Next, the i1 layer 108,1 becomes the buffer layer.
A solar cell having the layer structure shown in FIG. 6 using the i layer (i1 layer and i2 layer) having the profile shown in FIG. It was produced in the same manner. A stainless steel substrate 101 with a lower electrode 102 deposited thereon is placed in a reaction chamber 70.
0 and deposited an n layer 103 of 400 Å to a film thickness of 300 Å.
After depositing the buffer layer 108 with a thickness of 1.5 Å, as in Example 1, the flow rate setting of the GeH4 gas mass flow controller was instantly increased to 1 sccm and film formation was performed to form an i-layer 1 of amorphous silicon germanium with a band gap of 1.67 eV.
04 was deposited to a thickness of about 2000 Å. Furthermore, a buffer layer 109 with a thickness of 300 Å is deposited, and a p-type amorphous silicon layer 10
5 was deposited to a thickness of 100 Å. The substrate 101 is placed in the reaction chamber 7.
00, the upper electrode 106 and the current collecting electrode 107
was formed. The obtained solar cell was No. The score was 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 GeH4 gas flow rate during the deposition of the i-layer 104 was changed.
The band gap of 04 is 1.53eV and 1.4, respectively.
Samples of 2 eV, 1.30 eV, and 1.22 eV were prepared. At this time, the film thickness of each sample was made to be the same. The obtained sample was designated as No. 2-2, No. 2-3, No
．． The score was 2-4. The initial characteristics of each of these samples were measured by the method described above, and then the photodegradation characteristics of these samples were evaluated as follows.

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

Next, the sample connected to the load resistor was placed on a sample stage kept at a constant temperature of 25°C, and the same AM1.5
After continuous irradiation with light (100 mW/cm2) for 500 hours, AM was applied again from the upper electrode 106 side of the sample in the same manner as described above.
The photoelectric conversion efficiency η (500) when irradiated with 1.5 light (100 mW/cm2) was determined. From η(500) and η(0) obtained in this way, the deterioration rate {1-η(50
0)/η(0)} was calculated. The obtained results are shown in FIG. 17. As can be seen from FIG. 17, the sample in which the germanium element composition of the i-layer 104 is 20 atm % or more is stable against light irradiation. (Comparative Example 1) A conventional sloped buffer layer was prepared using the apparatus shown in FIG.
A solar cell having the layer structure shown in FIG. 6 was manufactured using an i-layer having a band profile of 1, and its 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 evacuated using the exhaust pump 709 . Next, the substrate 701 was heated to 300° C. using a substrate heating heater 704. After the substrate temperature became constant, an n layer 303 of 400 Å was deposited 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 supply 30 sccm of SiH4 gas and 300 seconds of H2 gas.
ccm was introduced into the reaction chamber 700. At this time,
GeH4 gas mass flow controller is Oscc
By restricting the flow rate to m, the flow rate is set to Oscc at the start of film formation.
It was set as m. A power of 5 W was applied from the RF power source 707 via the matching box 706 to start plasma discharge, and at the same time, the flow rate setting of the GeH4 gas mass flow controller 731 was increased at a rate of 2 sccm/min while film formation was continued for 5 minutes. I did it. Ge after 5 minutes
The flow rate of H4 gas was 10 sccm, and a gradient buffer layer 408 of about 300 Å was deposited during film formation. Bandgap of buffer layer is 1.7eV to 1.42eV
It is sloping up to. After that, the flow rate of GeH4 was increased to 10sc.
Film formation was performed for 15 minutes while keeping the cm constant. During the film formation, an i-layer 404 of amorphous silicon germanium with a band gap of 1.42 eV and a band gap of about 1500 Å was deposited. Next, film formation was continued for 5 minutes while lowering the flow rate setting of the GeH4 gas mass flow controller at a rate of 2 sccm/min. After 5 minutes, the flow rate of GeH4 gas became 0 sccm. During film formation, a gradient buffer layer 409 of about 300 Å was deposited. The band gap of the buffer layer is graded from 1.42 eV to 1.7 eV. After immediately stopping the RF discharge and stopping the supply of SiH4 gas and H2 gas, the reaction chamber 700 was evacuated, SiH4 gas and B2H6 gas were introduced, and a p layer 305 of 200 Å was deposited in the same manner as in Example 1. The substrate 701 is taken out from the reaction chamber 700, placed in a transparent conductive film deposition apparatus (not shown), and is coated with I as the upper electrode 306.
A TO film was deposited to a thickness of 700 Å. After the film formation was completed, the sample was separated into subcells of 1 cm x 1 cm by etching, and then transferred to another evaporation apparatus and a current collecting electrode 307 was formed by electron beam evaporation. The obtained sample was designated as R-1.

Solar simulator light (A
The solar cell initial conversion efficiency (ηR
(0)), and the conversion efficiency (ηR (50)) after continuous irradiation with AM1.5 light (100 mW/cm2) for 500 hours in the same manner as in Example 2 was measured. The initial conversion efficiency η of each sample in Example 2 is expressed as the initial conversion efficiency ηR of Comparative Example 1.
Figure 1 shows the value η(0)/ηR (0) normalized by (0).
8. In addition, the conversion efficiency η (500
) is normalized by the conversion efficiency ηR (500) of Comparative Example 1 after deterioration, and the value η(500)/ηR (500) is shown in FIG.

As understood from the above results, Example 2
The solar cell had the same initial characteristics as Comparative Example 1, and the composition ratio of the germanium element was changed from 20 to 70.
It was found that by setting the range of atm%, the characteristics after deterioration were improved compared to the comparative example. (Example 3) Next, a solar cell having the layer structure shown in FIG. 6 and having the i-layer having the band profile 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 to a thickness of 400 Å. After depositing the buffer layer 108 with a thickness of 300 Å, Ge
Instantly increase the flow rate setting of the H4 gas mass flow controller 731 to 5 sccm and further increase to 0.5 sccm/
The film was formed for 10 minutes while increasing the flow rate at a rate of 10 min to deposit an i-layer 104 of about 1000 Å of amorphous silicon germanium with a band gap varying from 1.53 eV to 1.42 eV. Thereafter, the flow rate setting of the GeH4 gas mass flow controller 731 was set to 0 sccm, and by closing the solenoid valve, the GeH4 gas flow rate was instantaneously reduced to 0 sccm, and film formation was continued using only SiH4 gas and H2 gas for 3 minutes, resulting in a film thickness of 30 Å. A buffer layer 109 was deposited. After the discharge ended, a p-type amorphous silicon layer 105 of 100 Å was deposited in the same manner as in Example 2. The substrate 101 was taken out from the reaction chamber 700, and an upper electrode 106 and a current collecting electrode 107 were formed. The obtained solar cell was No. The score was 3-1. In addition, in order to investigate the relationship between the slope of the sloped layer and the solar cell characteristics, we also investigated the G
Film formation was performed using the same method as described above, except that the amount of change in the eH4 gas flow rate was varied. 3-2
and no. A solar cell having a band profile as shown in 3-3 was fabricated.

[0076]

[Table 2] Next, a solar cell of the present invention having the layer structure shown in FIG. 6 and having the i-layer having the band profile shown in FIG. 4 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 GeH4 gas mass flow controller 731 is set to 10 sccm and the flow rate is 0.5 sccm/min.
The i-layer 104 of amorphous silicon germanium, whose band gap changed from 1.42 eV to 1.53 eV, was deposited at about 10
0 Å deposited. After depositing buffer layer 109, p layer 105
was deposited to form an upper electrode 106 and a current collecting electrode 107. The obtained solar cell was No. The score was 3-4. moreover,
I layer 1 to investigate the relationship between the slope of the tilted layer and the solar cell characteristics.
No. 04 in Table 3 was prepared by varying the amount of change in the GeH4 gas flow rate. 3-5 and No. A solar cell having a band profile as shown in 3-6 was fabricated.

[0077]

[Table 3] Furthermore, a solar cell according to the present invention having the layer structure shown in FIG. 6 and having the i-layer having the band profile shown in FIG. 5 was manufactured by the same operation as described above. After depositing the n-layer 103 and the buffer layer 108, a GeH4 gas mass flow controller 731
0.75sccm/mi with the flow rate setting of 5sccm.
The i-layer 104 of amorphous silicon germanium, whose band gap changed from 1.53 eV to 1.42 eV, was formed by increasing the flow rate at a rate of n and forming the film for 5 minutes.
After depositing Å, the flow rate of the GeH4 gas mass flow controller 731 was lowered at a rate of 0.75 sccm/min, and the film was formed for 5 minutes until the band gap was 1.4.
After depositing an i-layer 104 of about 500 Å of amorphous silicon germanium varying in voltage from 2 eV to 1.53 eV, and depositing a buffer layer 109 and a p-layer 105, an upper electrode 106 is deposited.
And a current collecting electrode 107 was formed. The obtained solar cell was
o. The score was 3-7. Furthermore, in order to investigate the relationship between the slope of the sloped layer and the solar cell characteristics, we investigated the GeH
4 The amount of change in gas flow rate was varied and No. 4 in Table 4 was performed. 3-
8 and no. A solar cell having a band profile as shown in 3-9 was fabricated.

[0078]

[Table 4] The initial conversion efficiency η(0) and the conversion efficiency η(5
00) was measured and the deterioration rate Δη was determined (1-η(500)
/η(0). ). Then Comparative Example 1
Normalized by the initial efficiency ηR and deterioration rate ΔηR of sample R-1, the obtained results are η/ηR, Δη/ΔηR
are shown in Tables 2 to 4. From the results in Tables 2 to 4, the deterioration characteristics of all samples showed less deterioration than Comparative Example 1, especially in the i-layer 1.
It was found that both initial characteristics and deterioration were improved compared to Comparative Example 1 by making the band gap of No. 04 narrow in the center and wider toward the ends. (Example 4) Next, an example of the present invention in which the substrate is made of glass will be shown. The solar cell of FIG. 7 having the i-layer of the present invention having the structure shown in FIG. 1 was produced in substantially the same manner as in Example 2 using the apparatus shown in FIG. 13.

A transparent conductive film SnO 2 was deposited to a thickness of 3000 Å on a substrate 301 made of quartz glass using an evaporator (not shown) to form an upper electrode 306 . After that, the substrate 301 is placed in a reaction chamber 700 and a p-type amorphous silicon layer 105 is placed therein.
After depositing the buffer layer 108 with a thickness of 300 Å, the flow rate setting of the GeH4 gas mass flow controller 731 was instantly set to 5 sccm and the flow rate was increased at a rate of 0.75 sccm/min, as in Example 3. The i-layer 104 of amorphous silicon germanium with a band gap changed from 1.53 eV to 1.42 eV was deposited to a thickness of about 50 Å, and then GeH4
Set the flow rate setting of the gas mass flow controller 731 to 0.
．． The film was formed for 5 minutes by decreasing the speed of 75 sccm/min, and the band gap changed from 1.42 eV to 1.53 e.
I-layer 1 of amorphous silicon germanium changed to V
04 was deposited to a thickness of about 500 Å.

After that, the flow rate setting of the GeH4 gas mass flow controller 731 is set to 0 sccm, and the GeH4 gas flow rate is instantaneously set to 0 sccm by closing the solenoid valve.
The buffer layer 10 with a thickness of 300 Å was formed for 3 minutes using only SiH4 gas and H2 gas.
9 was deposited. After the discharge ends, the n-layer 10 is
3 was deposited to a thickness of 400 Å. The substrate 301 is placed in the reaction chamber 7.
00, and aluminum was deposited to a thickness of 5000 Å using an electron beam evaporator (not shown) to form an upper electrode 302. The obtained solar cell was No. The score was 4-1. The initial conversion efficiency η(0) and the conversion efficiency η(500) after 500 hours of light irradiation were measured for this sample using the method described above, and the deterioration rate Δη was determined, and the initial efficiency ηR (0) of sample R-1 of Comparative Example 1 and normalized by the deterioration rate ΔηR, the obtained result η(0)
/ηR (0) and Δη/ΔηR are shown in Table 5. This result shows that by using the band profile of the present invention, a solar cell with high conversion efficiency and high reliability can be obtained. (Example 5) Next, a solar cell having the tandem cell configuration shown in FIG. 8 using the i-layer of the present invention having the band profile shown in FIG. 5 as the bottom layer was fabricated using the apparatus shown in FIG. It was made as follows.

[0081] On the stainless steel substrate 301 on which the lower electrode 302 was deposited, the n-layer 103 was deposited to a thickness of 400 Å.
After depositing the buffer layer 108, the flow rate setting of the GeH4 gas mass flow controller 731 is set to 5 sccm.
The flow rate was increased at a rate of 0.75 sccm/min, and the film was formed for 5 minutes, and the band gap was 1.53 eV.
After depositing an i-layer 104 of about 500 Å of amorphous silicon germanium varying from 1.42 eV to 1.42 eV,
The flow rate of the gas mass flow controller 731 is set to 0.
The rate was lowered to 75 sccm/min, and the film was formed for 5 minutes, and the band gap changed from 1.42 eV to 1.53 eV.
I-layer 10 of amorphous silicon germanium changed to
4 was deposited to a thickness of about 500 Å to form a buffer layer 109 and a p layer 105.
was deposited to create the bottom layer. Furthermore, the n layer 313 is
Deposit 0 Å and form an i-layer 314 with SiH4 gas and H2 gas.
After forming a top layer by depositing 1000 Å of P layer 315 and 100 Å of P layer 315, an upper electrode 306 and a current collecting electrode 307 are formed.
was formed. The obtained solar cell was No. The score was 5-1. The initial conversion efficiency η(0) and the conversion efficiency η(500) after 500 hours of light irradiation were measured using the method described above for this sample, and the deterioration rate Δη was determined.
and normalized by the deterioration rate ΔηR, the obtained result η
(0)/ηR (0) and Δη/ΔηR are shown in Table 5. This result shows that by using the band profile of the present invention, a solar cell with high conversion efficiency and high reliability can be obtained. (Example 6) Next, a solar cell with the triple cell configuration shown in FIG. 9 using the i-layer of the present invention with the band profile shown in FIG. 5 as the bottom layer was fabricated using the apparatus shown in FIG. It was made as follows.

After depositing the n layer 103 and the buffer layer 108 on the stainless steel substrate 301 on which the lower electrode 302 has been deposited, the flow rate of the GeH4 gas mass flow controller 731 is set to 5 sccm and the flow rate is set to 0.755 sccm/mi.
The i-layer 104 of amorphous silicon germanium, whose band gap changed from 1.53 eV to 1.42 eV, was formed by increasing the flow rate at a rate of n and forming the film for 5 minutes.
After depositing Å, the flow rate of the GeH4 gas mass flow controller 731 was lowered at a rate of 0.75 sccm/min, and the film was formed for 5 minutes until the band gap was 1.4.
An i-layer 104 of amorphous silicon germanium having a voltage varying from 2 eV to 1.53 eV was deposited to a thickness of about 500 Å, and a buffer layer 109 and a p-layer 105 were deposited to form a bottom layer. After that, the n layer 313, the i layer 314 was
15 was deposited to form a middle layer. Furthermore, the n-layer 32
3. An i layer 324 of 700 Å and a p layer 325 were deposited to form a top layer, and an upper electrode 306 and a current collecting electrode 307 were formed. The obtained solar cell was No. The score was 6-1. The initial conversion efficiency η(0) and the conversion efficiency η(500) after 500 hours of light irradiation were measured using the method described above for this sample, and the deterioration rate Δη was determined.
(0) and deterioration rate ΔηR, and the obtained results η(0)/ηR (0) and Δη/ΔηR are shown in Table 5.
It was shown to. This result shows that by using the band profile of the present invention, a solar cell with high conversion efficiency and high reliability can be obtained.

[0083]

[Table 5] (Example 7) Next, the film formation gas for the i-layer 204 was varied under the conditions shown in Table 6 to produce the i-layer having the band profile shown in FIG. 3 of the present invention, and the layer structure shown in FIG. A solar cell was produced in substantially the same manner as Sample 3-7 of Example 3 using the apparatus shown in FIG. The obtained solar cell was No. 7-1, No.
7-2 and No. The score was 7-3. The initial conversion efficiency η(0) and the conversion efficiency η(500) after 500 hours of light irradiation were measured for this sample using the method described above, and the deterioration rate Δη was determined, and the initial efficiency ηR (0) of sample R-1 of Comparative Example 1 and normalized by the deterioration rate ΔηR, the obtained result η(0)/ηR
(0) and Δη/ΔηR are shown in Table 6. This result shows that by using the band profile of the present invention, a solar cell with high conversion efficiency and high reliability can be obtained.

[0084]

[Table 6] (Example 8) Next, the i-layer of the present invention having the band profile shown in FIG. 3 was fabricated under the conditions shown in Table 7 by varying the film formation gas for the p-layer 205, and the layer structure shown in FIG. A solar cell was produced in substantially the same manner as Sample 3-7 of Example 3 using the apparatus shown in FIG. The obtained solar cell was No. 8-1, No.
8-2 and No. The score was 8-3. The p layer used in this sample was deposited on a glass substrate and subjected to RH treatment in the same manner as in Example 1.
Table 7 also shows the results of evaluating crystallinity by EED. The initial conversion efficiency η(0) and the conversion efficiency η(500) after 500 hours of light irradiation were measured using the method described above for this sample, and the deterioration rate Δη was determined.
(0) and the deterioration rate ΔηR, and the obtained results η(0)/ηR (0) and Δη/ΔηR are shown in Table 7. This result shows that by using the band profile of the present invention, a solar cell with high conversion efficiency and high reliability can be obtained.

[0085]

[Table 7]

[0086]

According to the photovoltaic device of the present invention, the i-layer of a pin-type photovoltaic device made of amorphous silicon germanium is divided into a layer containing no germanium element and a layer containing germanium element. A solar cell with high reliability and high conversion efficiency can be obtained by forming the layer not containing the germanium element in a portion in contact with the p-type semiconductor and the n-type semiconductor.

Further, the thickness of the layer not containing the germanium element may be 50 to 1000 angstroms, the germanium element content of the layer containing the germanium element may be 20 atm % to 70 atm %, or the germanium element of the layer containing the germanium element may be 50 to 1000 angstroms thick. By continuously changing the composition of the germanium element or by locating the maximum value of the composition of the germanium element in the i-layer, a solar cell with higher reliability and higher conversion efficiency can be obtained.

[0088] Furthermore, the present invention has two unit element structures of pins.
For application to a stacked photovoltaic device in which two or more layers are stacked, the structure of at least one i-layer may be such that the thickness of the layer not containing the germanium element is 50 to 1000 angstroms, or the thickness of the layer containing the germanium element. By increasing the amount of germanium element from 20 atm% to 70 atm%, by continuously changing the composition of germanium element, and by locating the maximum value of the composition of germanium element in the i-layer, high reliability and A solar cell with high conversion efficiency can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the structure 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 in FIG. 1;

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

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

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

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

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

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

FIG. 9 is a diagram schematically showing the 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 device.

FIG. 13 is a schematic diagram showing a film forming apparatus suitable for manufacturing the photovoltaic device of the present invention.

FIG. 14 is a diagram showing photodegradation characteristics of samples with different band gaps.

FIG. 15 is a diagram showing the effect of a buffer layer that is part of the structure of the photovoltaic device of the present invention.

FIG. 16 is a diagram showing the effect of a buffer layer that is part of the structure of the photovoltaic device of the present invention.

FIG. 17 is a diagram showing the relationship between the composition ratio of germanium element, which is part of the structure of the photovoltaic device of the present invention, and the deterioration characteristics.

FIG. 18 is a diagram showing the effect of a gradient layer that is part of the structure of the photovoltaic device of the present invention.

FIG. 19 is a diagram showing the effect of a gradient layer that is part of the structure 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, 325 p-type semiconductor layer, 40
5 p-type semiconductor layer, 108 buffer layer, 10
9 buffer layer, 208 buffer layer, 2
09 buffer layer, 408 buffer layer, 40
9 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 heater for heating the substrate, 705
Grounding terminal, 706 Matching box, 7
07 RF power supply, 708 Exhaust pipe, 709
Exhaust pump, 710 Filming gas introduction pipe, 720
valve, 730 valve, 740 valve, 750 valve, 760 valve, 722
Valve, 732 Valve, 742 Valve, 752 Valve, 762 Valve, 72
1 mass flow controller, 731 mass flow controller, 741 mass flow controller, 751 mass flow controller, 7
61 Mass flow controller.

Claims (6)

[Claims] 1. In a pin-type photovoltaic element in which the i-type semiconductor layer is made of amorphous silicon germanium, the i-type semiconductor layer includes a layer containing no germanium element and a layer containing germanium element. 1. A photovoltaic element comprising a layer, wherein the layer not containing germanium element is provided in a portion in contact with a p-type semiconductor and an n-type semiconductor. 2. The photovoltaic device according to claim 1, wherein the layer not containing the germanium element has a thickness of 50 to 1000 angstroms. 3. The photovoltaic device according to claim 1, wherein the layer containing germanium element has an amount of germanium element ranging from 20 atm % to 70 atm %. 4. The photovoltaic device according to claim 1, wherein the composition of the germanium element in the layer containing the germanium element changes continuously. 5. The photovoltaic device according to claim 1, wherein the maximum value of the changing composition of the germanium element is in the i-type semiconductor layer. 6. In a stacked photovoltaic device in which two or more pin-type unit element structures are stacked, at least one i-type semiconductor layer of the unit element structure is composed of any one of claims 1 to 5. A photovoltaic device comprising the device structure of the photovoltaic device described in .