JP3046644B2 - Method for manufacturing 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 method for manufacturing a photovoltaic device which is a photoelectric conversion device for converting sunlight into electric energy.

[0002]

2. Description of the Related Art Photovoltaic elements are widely used as small power sources for consumer use such as calculators and watches, and can be put to practical use as a substitute for so-called fossil fuels such as oil and coal in the future. Technology is attracting attention. A photovoltaic element 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 generated inside the pn junction. It drifts by an electric field and is taken out. In many cases, a semiconductor process is used as a method for manufacturing such a photovoltaic element. Specifically, p is determined by a crystal growth method such as the Czochralski (CZ) method.
A single crystal or polycrystal of silicon whose valence electrons are controlled to a type or an n-type is prepared, and the single crystal or the polycrystal is sliced to obtain a silicon wafer having a thickness of about 300 μm. Further, a layer of a different conductivity type is formed by using an appropriate means such as, for example, diffusion of a valence electron controlling agent so as to have a conductivity type opposite to the conductivity type of the wafer, thereby forming a pn junction.

[0003] Meanwhile, single crystal silicon or polycrystalline silicon is mainly used in photovoltaic elements currently in practical use because of high reliability and conversion efficiency.
As described above, since a semiconductor process is used for the manufacturing method, a crystal-based photovoltaic element using single crystal silicon or polycrystalline silicon generally has a disadvantage that the production cost is high.

Further, since crystalline silicon has a relatively small light absorption coefficient, it must have a thickness of at least 50 μm when used as a photovoltaic device, and has a band gap energy of about 1.1 eV. It is narrower than 1.5 eV, which is suitable for the above, and has a drawback that the long wavelength component of the incident light cannot be used effectively. Polycrystalline silicon also has grain boundary problems.

Further, it is difficult to increase the area of crystalline silicon, and in order to take out a large amount of power, it is necessary to serially and parallelly connect the unit elements, which requires complicated wiring. Because expensive mounting is required to protect the photovoltaic element from mechanical damage
There is a problem that the production cost per unit power generation is higher than other existing power generation methods.

[0006] Under these circumstances, important technical issues in the practical use of photovoltaic elements for power use are to reduce production cost and to increase the area of the elements, and various studies have been made. . As a result, for example, low cost materials,
Materials having high conversion efficiency of the device include tetrahedral amorphous semiconductors such as amorphous silicon, amorphous silicon / germanium, and amorphous silicon carbide; II-IV groups such as CdS and Cu ₂ S; Compound semiconductors such as GaAlAs have been found. Among them, amorphous semiconductors,
In particular, thin-film photovoltaic devices using amorphous silicon
It is promising because of its advantages such as easy area enlargement, a large absorption coefficient compared to crystalline silicon and a small thickness, and a limited number of substrate materials and shapes on which thin films are deposited. However, the above-described photovoltaic element using amorphous silicon also has disadvantages such as low photoelectric conversion efficiency and low reliability, and various attempts have been made to solve these.

[0007] One of the reasons for the low photoelectric conversion efficiency of amorphous silicon is as follows. That is, amorphous silicon has a band gap energy of about 1.7 eV and does not absorb light in a long wavelength region of 700 nm or more. This is because the light in this area is not effectively used. On the other hand, a material having a small band gap energy that is sensitive to the long wavelength region has been studied. Amorphous silicon germanium is one example. The band gap energy is increased from about 1.3 eV to about 1.7 depending on the ratio of the source gas containing silicon and the source gas containing germanium used in depositing the thin film.
It can be controlled to any value up to eV.

US Pat. No. 2,949,498 discloses using a so-called stack structure in which a plurality of unit photovoltaic element structures are stacked as a technique for improving photoelectric conversion efficiency. In the above patent, a pn junction crystal semiconductor is used, but the incident light is effectively used over a wide wavelength range by sharing the absorption wavelength range of the incident light with the unit photovoltaic element structures having different band gap energies. This idea is common to both crystalline and amorphous semiconductors. By using this technique, the open circuit voltage Voc of the photovoltaic element characteristics
Is increased, and the photoelectric conversion efficiency is improved.

In the above-described method using the stack structure, the unit is designed such that the band gap energy becomes smaller in order from the unit photovoltaic element structure on the light incident side. In this regard, amorphous silicon-germanium, which has a smaller band gap energy than amorphous silicon and whose band gap energy can be easily controlled, is suitable as a material.

On the other hand, a plurality of amorphous silicon unit photovoltaic element structures having the same band gap energy are stacked without an insulating layer between them to increase Voc of the entire photovoltaic element. An approach has been proposed.

Amorphous silicon / germanium is generally inferior in film quality to amorphous silicon. Also, when compared as a unit photovoltaic element, the photoelectric conversion efficiency of amorphous silicon is higher. It is said that this is because the localized level in the depletion layer of amorphous silicon / germanium is larger than that of amorphous silicon,
Attempts have been made to reduce the above-mentioned localized level. For example, Japanese Patent Publication No. Sho 63-48197 discloses that an activated fluorine atom compensates for a dangling bond in amorphous silicon / germanium so that the localized level is reduced. Are disclosed to reduce the number of

On the other hand, studies have been made on improving the characteristics of the amorphous silicon-germanium photovoltaic element by a method other than the film quality improvement described above. For example, a p-type semiconductor layer and / or
Alternatively, a method using a so-called buffer layer having a gradient of a bandwidth at a junction interface between an n-type semiconductor layer and an i-type semiconductor layer is disclosed in U.S. Pat. No. 4,254,429 and U.S. Pat.
No. 377,723. The role of the buffer layer is to increase the internal electric field and increase Voc.

Another method is to improve the photovoltaic device characteristics by providing a composition distribution in the i-layer, that is, a so-called gradient layer, by changing the composition ratio of silicon and germanium contained in the film thickness direction. There is.

For example, according to US Pat. No. 4,816,082, the band gap energy of the i-layer in the portion in contact with the valence-controlled semiconductor layer on the first surface on the light incident side is increased, A method is disclosed in which the band gap energy is gradually reduced toward the central portion, and further increased toward the second valence electron controlled semiconductor layer. According to this method, carriers generated by light are efficiently separated by the action of the internal electric field, and the film characteristics are improved.

[0015]

However, the amorphous silicon or other amorphous photovoltaic device has a lower photoelectric conversion efficiency than a crystalline silicon photovoltaic device and has a power generation cost per watt. Is higher than existing thermal, hydro and nuclear power plants. Therefore, in reality, amorphous photovoltaic elements have not yet been widely used on a par with crystalline photovoltaic elements and existing power generation means.

The present invention solves the above-mentioned problems, and provides a method for manufacturing an amorphous photovoltaic device which has a high light conversion efficiency and requires a relatively small amount of raw material gas.

[0017]

According to the present invention, at least one set of p, i, n-type semiconductors is deposited on a substrate having a conductive surface, the i-type semiconductor film is amorphous silicon germanium, A method for manufacturing a photovoltaic device having a structure in which the band gap energy once decreases monotonically in the film thickness direction and then monotonically increases again as the germanium content in the semiconductor film changes in the film thickness direction. Te, in the step of depositing an i-type semiconductor film, a germanium linearly increased with respect to between first 0 or et when the supply amount of the raw material gas containing a total sedimentary from the start of the deposition i-type semiconductor film to the end
At a time point between 0.75 and 0.8 of the product time, a predetermined flow rate
And, from the time of reaching to the predetermined flow rate is a manufacturing method of a photovoltaic device to decrease linearly to 0 the supply flow rate with respect to time.

With this configuration, the photoelectric conversion
Highly efficient photovoltaic elements can be obtained and use of raw material gas
Provides a method for manufacturing a photovoltaic element that requires a relatively small amount
can do.

The band gap energy of the film deposited at the time when the predetermined flow rate is reached is not less than 1.3 eV.
It is also preferable to set it to 4 eV or less because the conversion efficiency is further increased.

The present inventors have obtained the following findings as a result of the study. That is, the change in the band gap energy in the film thickness direction in the i-type semiconductor thin film is determined by changing the source gas containing germanium to 0% at the start of deposition of the i-type semiconductor thin film.
A photovoltaic system controlled by increasing linearly with time from SCCM to the maximum flow rate of the source gas with time, and then linearly decreasing with time from the maximum flow rate of the source gas to 0 SCCM at the end of the deposition of the i-layer semiconductor thin film. A power element and a photovoltaic element in which the band gap energy is reduced by introducing a constant flow of a source gas containing germanium in the same amount as the above from the start of deposition of the i-type semiconductor thin film to the end of deposition. In comparison, the former has a higher photoelectric conversion efficiency. The present invention has been further studied based on this finding, and has been completed.

The present invention can also be applied to a photovoltaic element in which a plurality of unit photovoltaic element structures are stacked, and in this case, the present invention is applied to at least one or more i-type semiconductor thin films having a unit photovoltaic element structure. The effect can be obtained by applying.

FIGS. 6 to 9 show the p-type suitable for applying the present invention.
1 schematically illustrates an example of an in-type amorphous solar cell. FIG. 6 shows a solar cell having a structure in which light is incident from the top of the figure. In the figure, 1 is a substrate, 2 is a lower electrode, 3 is an n-type semiconductor layer, 4 is an i-type semiconductor layer, 5 is a p-type semiconductor layer, Reference numeral 6 denotes an upper electrode, and 7 denotes a collecting electrode.

FIG. 7 shows a solar cell having a structure in which the substrate 1 is transparent and light enters from the bottom of the figure. FIG. 8 shows a solar cell having a structure in which two layers of the pin structure of the solar cell shown in FIG. 6 are laminated. Reference numeral 15 denotes a p-type semiconductor layer. FIG. 9 shows a solar cell having a structure in which three layers of the pin structure of the solar cell of FIG. 6 are stacked.
2 represents a solar cell unit element, 23 represents an n-type semiconductor layer,
24 represents an i-type semiconductor layer, and 25 represents a p-type semiconductor layer. In each of the photovoltaic elements, the n-type semiconductor layer and the p-type semiconductor layer can be used in a different order of lamination according to the purpose. Hereinafter, the configurations of these photovoltaic elements will be described.

The substrates p, i and n-type semiconductor layers 3, 4, 5 are at most 1 μm.
Since it is a thin film of about m, it is deposited on an appropriate substrate. Such a substrate 1 may be a single-crystal or non-single-crystal substrate, and may be a conductive or electrically insulating substrate. Further, they may be translucent or non-translucent, but preferably have little deformation and distortion and a desired strength. Specifically, Fe, N
i, Cr, Al, Mo, Au, Nb, Ta, V, Ti,
Metals such as Pt and Pb or alloys thereof, for example, brass, thin plates such as stainless steel and composites thereof, and polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide,
Films or sheets of heat-resistant synthetic resin such as polyimide or epoxy, or composites of these with glass fiber, carbon fiber, boron fiber, metal fiber, etc., and metals of different materials on the surface of thin plates of these metals, resin sheets, etc. Thin film and / or SiO ₂ , Si ₃
Examples thereof include those obtained by subjecting an insulating thin film such as N ₄ , Al ₂ O ₃ , and AlN to a surface coating treatment by a sputtering method, an evaporation method, a plating method, or the like, glass, ceramics, and the like.

When the substrate is electrically conductive such as metal, the substrate may be directly used as an electrode for extracting current. When the substrate is electrically insulating such as synthetic resin, the surface on which the deposited film is formed is formed. 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 oxide (TCO) are plated and deposited. It is preferable to form a current extraction electrode by performing a surface treatment in advance by a method such as sputtering.

Of course, even if the substrate is made of an electrically conductive material such as a metal, the reflectance of long-wavelength light on the surface of the substrate can be improved, and the composition of 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. Also,
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.

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 may be spherical, conical, pyramidal, or the like, and the maximum height (Rmax) may be preferably 500 to 5000 angstroms. 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 may be plate-like with a smooth surface or an uneven surface, a long belt-like shape, a cylindrical shape, or the like, depending on the application, and the thickness thereof is appropriately set so that a desired photovoltaic element can be formed. To be determined, when flexibility is required for the photovoltaic element, or when light is incident from the side of the substrate, make it as thin as possible within the range where the function as the substrate can be sufficiently exhibited. Can be. However, the thickness is usually 10 μm or more from the viewpoints of production 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 mentioned. (However, the upper electrode referred to here indicates an electrode provided on the light incident side, and the lower electrode indicates an electrode provided opposite to the upper electrode with a semiconductor layer interposed therebetween.) The electrodes are described in detail below.

Lower Electrode As the lower electrode 2 used in the present invention, the surface to be irradiated with light for generating photovoltaic power differs depending on whether or not the material of the substrate 1 is translucent (for example, the substrate When 1 is a non-translucent material such as a metal, light for generating photovoltaic power is irradiated from the upper electrode 6 side as shown in FIG. 6).

More specifically, in the case of a layer configuration as shown in FIGS. 6, 8 and 9, it is provided between the substrate 1 and the n-type semiconductor layer 2. However, when the substrate 1 is conductive, the substrate can also serve as the lower electrode. However, when the sheet resistance is high even if the substrate 1 is conductive, the lower electrode is used as a low-resistance electrode for taking out current, or for the purpose of increasing the reflectivity on the substrate surface and making effective use of incident light. 2 may be installed.

In the case of FIG. 7, a light-transmitting substrate 1 is used, and since light is incident from the substrate 1 side, the lower electrode 2 is used for current extraction and light reflection at the electrode.
Are provided facing the substrate 1 with the semiconductor layer interposed therebetween.

When an electrically insulating substrate is used as the substrate 1, the substrate 1 and n
The lower electrode 2 is provided between the lower electrode 2 and the mold semiconductor layer 3.

As the electrode material, Ag, Au, Pt, N
Metals such as i, Cr, Cu, Al, Ti, Zn, Mo and W or alloys thereof are mentioned, and a thin film of these metals is formed by vacuum evaporation, electron beam evaporation, sputtering or the like. Also, 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.

Although not shown in the figure, a diffusion preventing layer such as conductive zinc oxide may be provided between the lower electrode 2 and the n-type semiconductor layer 3. The effect of the diffusion preventing layer is not only to prevent the metal element forming the lower electrode 2 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. Electrode 2 and transparent electrode 6
To prevent short-circuiting caused by a defect such as a pinhole between them, and the effect of generating multiple interference by a thin film and confining incident light in a photovoltaic element.

Upper Electrode (Transparent Electrode) The upper electrode (transparent electrode) 6 used in the present invention has a light transmittance of 85% in order to efficiently absorb light from the sun or a white fluorescent lamp into the semiconductor layer. It is desirable that the sheet resistance is not more than 100 Ω so that the sheet resistance is not more than 100Ω so that the output of the photovoltaic element does not become a resistance component. As a material having such properties, Sn
O ₂ , In ₂ O ₃ , ZnO, CdO, CdSnO ₄ , ITO
Metal oxides such as (In ₂ O ₃ + SnO ₂ ), Au, A
Metal thin films in which a metal such as l, Cu or the like is formed in a very thin and translucent state can be used. The upper electrode 6 is laminated on the p-type semiconductor layer 5 in FIGS. 6, 8 and 9, and is laminated on the substrate 1 in FIG. is necessary. As a method for manufacturing the upper electrode, 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.

Collector electrode The collector electrode 7 used in the present invention is provided on the upper electrode 6 for the purpose of reducing the surface resistance of the upper electrode 6. Ag, Cr, Ni, Al, Au,
Examples include a thin film of a metal such as Ti, Pt, Cu, Mo, W, or an alloy 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 on 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 3, 4, and 5 are manufactured by a normal thin film manufacturing process.
High frequency plasma CVD, microwave plasma CVD
It can be manufactured by using a known method such as an ECR method, a thermal CVD method, and an LPCVD method as required. As a method adopted industrially, a plasma CVD method in which a raw material gas is decomposed by plasma and deposited on a substrate 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 a semiconductor whose valence electrons are controlled is manufactured, PH ₃ and B ₂ H ₆ gases containing phosphorus, boron, and the like as constituent atoms are simultaneously decomposed.

I-Type Semiconductor Layer As the semiconductor material constituting the i-type semiconductor layer suitably used in the present photovoltaic element, a-SiGe: H, a is used when an i-layer of amorphous silicon / germanium is formed.
And so-called Group IV alloy semiconductor materials such as -SiGe: F and a-SiGe: H: F. Also,
Semiconductor materials constituting an i-type semiconductor layer other than amorphous silicon / germanium in a stack cell structure in which unit element configurations are stacked include a-Si: H, a-Si: F,
a-Si: H: F, a-SiC: H, a-SiC: F,
a-SiC: H: F, poly-Si: H, poly-
In addition to so-called Group IV and Group IV alloy-based semiconductor materials such as Si: F, poly-Si: H: F, etc.
Group III-V and group II-VI so-called compound semiconductor materials are included.

As a source 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 , Si
F ₄ , (SiF ₂ ) ₅ , (SiF ₂ ) ₆ , (SiF ₂ ) ₄ , S
i 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 , Si
Br ₄ , (SiBr ₂ ) ₅ , SiCl ₆ , SiHCl ₃ , S
Examples thereof include those in a gas state or those which can be easily gasified, such as iHBr ₂ , SiH ₂ Cl ₂ , and SiCl ₃ F ₃ .

Examples of the compound containing a germanium element include a chain germanium or a germanium halide, a cyclic germanium or a germanium halide, a chain or a cyclic germanium compound, and an organic germanium compound having an alkyl group. ₄ , Ge ₂
H ₆ , Ge ₃ H ₃ , n-Ge ₄ H ₁₀ , t-Ge ₄ H ₁₀ , Ge
H ₆ , Ge ₅ H ₁₀ , GeH ₃ Cl, GeH ₂ F ₂ , Ge (C
H ₃ ) ₄ , Ge (C ₂ H ₅ ) ₄ , Ge (C ₆ H ₅ ) ₄ , Ge (C
H ₃ ) ₂ F ₂ , GeF ₂ , GeF _{4 and the} like.

The p-type semiconductor layer and the n-type semiconductor layer are preferably used as the semiconductor material constituting the p-type or n-type semiconductor layer. The semiconductor material constituting the above-mentioned i-type semiconductor 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-type semiconductor layer can be suitably used. When a deposited film of Group IV of the periodic table is obtained as a raw material, a compound containing an element of Group III 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 , B ₅ H ₁₁ , B ₆ H ₁₀ , B (CH ₃ ) ₃ ,
B (C ₂ H ₅ ) ₃ , B ₆ H ₁₂ , AlX ₃ , Al (CH ₃ ) ₂ C
1, Al (CH ₃ ) ₃ , Al (OCH ₃ ) ₂ Cl, Al (C
_{H 3) Cl 2, Al (} C 2 H 5) 3, A (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 , GaX ₃ , Ga (OC
_{H 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 , Ga (O
C 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, PX 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 (SC
N) ₃ , P ₂ H ₄ , PH ₃ , AsH ₃ , AsX ₃ , As (OC
H ₃ ) ₃ , As (OC ₂ H ₅ ) ₃ , As (OC ₃ H ₇ ) ₃ , As
(OC ₄ H ₉ ) ₃ , AS (CH ₃ ) ₃ , As (CH ₃ ) ₃ , A
s (C ₂ H ₅ ) ₃ , As (C ₆ H ₅ ) ₃ , SbX ₃ , Sb (O
CH ₃ ) ₃ , Sb (OC ₂ H ₅ ) ₃ , Sb (OC ₃ H ₇ ) ₃ , S
b (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)
C) to control the amount introduced into the deposition space,
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 to gasify using a bubbler whose temperature can be controlled as needed. Such a rare gas or hydrogen gas is used as a carrier gas for gasification using a heating sublimation furnace, and the amount introduced is controlled mainly by the flow rate of the carrier gas and the furnace temperature.

[0048]

EXAMPLE A preliminary test was conducted to examine the properties of an amorphous silicon-germanium thin film, and then tests of an example and a comparative example were performed. First, the procedure of film formation will be described. Using a known RF discharge plasma CVD film forming apparatus shown in FIG. 10, an amorphous silicon / germanium film was produced as follows.

In FIG. 10, reference numeral 100 denotes a reaction chamber,
101 is a substrate, 102 is an anode electrode, 103 is a cathode electrode, 104 is a heater for heating a substrate, 105 is a grounding terminal, 106 is a matching box, 107 is an RF power supply, 108 is an exhaust pipe, 109 is an exhaust pump, and 110 is a component. Reference numerals 120 and 122 denote valves, and 121 denotes a mass flow controller.

First, a 5 cm square substrate 101 was attached to the cathode in the reaction chamber 100, and an exhaust pump 10
The pressure was sufficiently exhausted by 9 and the degree of vacuum in the reaction chamber 100 was adjusted to 10 ⁻⁶ Torr by an ion gauge (not shown). Next, the substrate 101 was heated to 300 ° C. by the substrate heating heater 104. After the substrate temperature becomes constant, the valves 120 and 122 are opened and the mass flow controller 1
SiH ₄ from SiH ₄ gas cylinder, not shown and controls the 21
Gas is supplied to the reaction chamber 100 via the gas introduction pipe 110.
Introduced inside. Similarly, a mass flow controller was controlled to introduce H ₂ gas and GeH ₄ gas. After adjusting a pressure controller (not shown) so as to maintain the internal pressure of the reaction chamber 100 at 1.5 Torr, the RF power supply 107
The plasma discharge was performed for 60 minutes while adjusting the matching box 106 to minimize the reflected wave to deposit an amorphous silicon-germanium film. The gas supply was stopped and the sample was taken out of the reaction chamber 100.

The above is the general deposition process of thin film deposition of amorphous silicon / germanium used in this experiment. The same method was used when a metal substrate was used.

Preliminary Test In this experiment, the relationship between the amount of GeH ₄ introduced during the deposition of the i-layer and the film deposition rate, and the relationship between the amount of GeH ₄ introduced and the band gap energy of the formed film were examined.

First, a certain amount of Si ₂ H ₆ gas, H ₂ gas, and GeH ₄ gas are introduced from the start to the end of the i-layer film deposition, and only the SiGe: H film corresponding to the i-layer film is placed on the glass substrate. Was prepared. However, in order to investigate the relationship between the amount of GeH ₄ and the band gap energy of the i-layer,
A plurality of samples having different amounts of GeH _{4 to be} introduced were prepared.

The glass substrate used was a commercially available Corning 7059 glass plate having a thickness of about 1 mm. Introducing raw material gas amount All samples Si ₂ H ₆ 10SCCM, H ₂
100 SCCM. And GeH ₄ is 1,5,1
There were four types, 0 and 20 SCCM. The applied RF power is 10 W, the temperature of the glass substrate is 350 ° C., and the pressure in the chamber is 2 Torr. The film deposition time was 1 hour for each sample.

For each of the prepared samples, the film deposition rate, band gap energy, and Ge composition in the film were measured as follows. The deposition rate of the film
Step (product name, TENCOR INSTRUMENT
(Manufactured by TS Co., Ltd.) was used to measure the film thickness of the deposited film on the glass substrate, and the value was divided by the film deposition time. The band gap energy was defined as the optical band gap energy here. Energy refers to the energy and was determined using the measured values of the absorptance in the ultraviolet and visible light regions and the thickness of the deposited film on the glass substrate.

FIGS. 4 and 5 show the relationship between the amount of GeH ₄ introduced and the film deposition rate and the relationship between the amount of GeH ₄ introduced and the band gap energy for the four types of samples prepared as described above.

As a result, FIG. 4 shows that the film deposition rate was GeH ₄
It increases linearly with the amount of introduction, and FIG.
It was found that the band gap energy decreases convexly with an increase in the amount of GeH ₄ introduced.

Example 1 and Comparative Example 1 In Example 1, the GeH film shown in FIG.
_In Comparative Example 1, a photovoltaic element was manufactured by continuously introducing GeH ₄ at a constant flow rate, and the energy conversion efficiency of the element was examined. In FIG. 1, T is the total deposition time,
t indicates the point in time when the amount of GeH ₄ introduced is maximized. Here, an amorphous S layer is formed on a metal substrate in the order of n, i, and p layers.
An i: H thin film was deposited by a glow discharge method, and a transparent electrode and a grid-like metal electrode were vacuum-deposited thereon to obtain a photovoltaic element.

Since the present embodiment particularly relates to an i-layer, first, a metal substrate, n and p layers, a transparent electrode (upper electrode),
The grid electrode (collecting electrode) will be briefly described, and then the i-layer will be described in detail.

As the substrate, a stainless steel SUS304 having a thickness of about 1 mm polished on both sides was used.

The n-layer thin film is made of Si ₂ H ₆ , H ₂ , PH ₃ / H ₂
1% diluent gas was added at 10 SCCM, 300 SCCM, 1
2SCCM was introduced into the chamber, RF power of 20 W was applied between the electrodes, and deposition was performed at a pressure of 1.5 Torr. n
The thickness of the layer was 200 Å.

The p-layer thin film is made of SiH ₄ , H ₂ , BF ₃
/ H ₂ 2% dilution gas at 5.0 SCCM and 300 SC respectively
CM, 5.0 SCCM were introduced into the chamber, RF power of 150 W was applied between the electrodes, and deposition was performed at a pressure of 1.5 Torr. The thickness was 100 Å.

Indium tin oxide was used as the transparent electrode. As a grid electrode, Cr, Ag, and Cr were sequentially vacuum-deposited using a grid mask.

Next, the i-layer will be described. GeH ₄ introduced during the deposition of the i-layer film linearly increased from 0 SCCM at the start of film deposition to the maximum GeH ₄ amount, and then decreased linearly to 0 SCCM at the end of film deposition.

The amount of the source gas to be introduced is Si ₂ H _{6 10} CC
M, H ₂ 100SCCM, up GeH ₄ introduced amount 10SC
CM. The applied RF power is 10W. The film thickness was set to 2000 angstroms by adjusting the deposition time. The position in the film thickness direction where the amount of GeH ₄ introduced was the maximum was set at ／ of the film deposition time.

As Comparative Example 1, the following conditions for forming the i-layer were set. That is, the amount of GeH ₄ introduced during the i-layer deposition was kept constant at 10 SCCM from the start to the end of the film deposition.

The amount of source gas to be introduced is Si ₂ H ₆ 10 SCC
M, H ₂ 100 SCCM. The applied RF power is 1
0W. The film thickness can be controlled by adjusting the deposition time.
00 angstrom. The reason why the film thickness was set to 2000 angstroms is that the film thickness of the i-layer affects the conversion efficiency, and the conversion efficiency tends to decrease as the film thickness of the i-layer increases. By making the film thicknesses uniform, a change in conversion efficiency due to a difference in film thickness can be avoided.

A photovoltaic device was manufactured under each of the above conditions, the device temperature was maintained at 25 ° C., and AM 1.5, 100 mW
The current / voltage curve was measured by irradiating the pseudo sunlight of the above to obtain the conversion efficiency.

[0069] As a result, conversion efficiency as compared to those who predetermined amount introducing GeH _4, persons with i-layer produced by GeH ₄ delivery profile of the present invention is about 40% higher, the effect of the present invention is shown Was.

Example 2 An experiment was conducted to determine the optimum value of the position in the film thickness direction at which the band gap energy of the i-layer becomes minimum.

The thickness of the i-layer affects the conversion efficiency, and the conversion efficiency tends to decrease as the thickness of the i-layer increases.
In this experiment, the deposition time of the i-layer film was kept constant so that the film thickness did not change even when the position in the film thickness direction where the band gap energy of the i-layer became minimum (the maximum position of the GeH ₄ supply flow rate) was changed. Was set. This is based on the following findings.

A preliminary test showed that the deposition rate of the i-layer film increased in proportion to the GeH ₄ gas introduction when the Si ₂ H ₆ gas introduction was constant (FIG. 4).

From these results, it is found that the GeH ₄ gas introduction amount is linearly increased from 0 SCCM at the start of film deposition to the maximum GeH ₄ introduction amount with the film deposition time, and then linearly decreased to 0 SCCM at the end of film deposition. , I-layer has a triangular area with the deposition time of the film as the base and the maximum GeH ₄ introduction amount as the height. Therefore, if the maximum GeH ₄ introduction amount and the film deposition time of the i-layer are fixed, even if the maximum GeH 4
_The thickness of the i-layer can be kept constant regardless of the time from the start of the i-layer film deposition of _four quantities, that is, the position where the band gap energy of the i-layer is minimized in the film thickness direction. . Therefore, the optimum value of the position in the film thickness direction at which the band gap energy of the i layer is minimized can be obtained after removing the influence of the film thickness of the i layer on the conversion efficiency.

The experiment was conducted under the following conditions in consideration of the above findings.

The amount of source gas introduced is Si ₂ H ₆ 10 SCC
M, H ₂ 100SCCM, up GeH ₄ introduced amount 10SC
CM. The applied RF power is 10W. The deposition time of the i-layer film was fixed, and a plurality of types of photovoltaic devices having i-layer films having different times t from the start of the i-layer film deposition at which the maximum amount of GeH _{4 was} introduced were produced. The same apparatus as in Example 1 was used.

The conversion efficiency of each of the photovoltaic elements manufactured as described above was measured under the same conditions as in Example 1.
FIG. 2 shows a value (t / t) obtained by dividing t by the total deposition time T of the i-layer on the horizontal axis.
T), the conversion efficiency is plotted on the vertical axis, and the data is plotted. Here, the conversion efficiency is plotted as a relative value with the conversion efficiency value of an element having a t / T of 0.78 as 1. As a result, as t / T increases from 0.73 to 0.78, the conversion efficiency increases once and reaches a maximum at about 0.77, and then the value on the horizontal axis increases from 0.77 to 1.00. It was found to decrease.

That is, the optimal value of the position in the film thickness direction where the band gap energy in the i-layer film becomes minimum is 0.75 to 0.80 from the start of the deposition, when the total deposition time of the i-layer film is 1. It turned out that.

Example 3 In this example, a photovoltaic element was produced in the same manner as in Example 1 except for the i-type semiconductor layer, and the conversion efficiency was measured and compared. The materials and manufacturing conditions of the metal substrate, the n- and p-layers, the transparent electrode, and the grid-shaped substrate were the same as in Example 1, and the manufacturing conditions of the i-layer were as follows.

In this experimental example, an experiment was performed to determine the optimum value of the band gap energy, that is, the optimum value of the maximum amount of GeH _{4 to be} introduced.

In the present embodiment, the manufacturing conditions were set in the following procedure in order to avoid a change in the conversion efficiency due to a change in the thickness of the i-layer.

First, the thickness of the i-layer was set to 2000 Å, and the amount of source gas to be introduced was Si ₂ H ₆ 10SCC.
M, H ₂ 100 SCCM, and the maximum GeH ₄ introduction amounts were 1.5, 10 and ₂₀ SCCM, respectively. Each maximum GeH
_{4 The} i-layer deposition film speed corresponding to the introduced amount was determined from FIG.
The film deposition time of each i-layer was determined so that the film thickness was set based on this value.

As described above, the film thickness of the i-layer is kept constant by setting the film deposition time of the i-layer to a length suitable for each maximum GeH ₄ introduction amount, and the i-layer is not affected by the thickness of the i-layer. The optimum value of the maximum GeH ₄ introduction amount can be obtained.

In this experimental example, the band gap
In consideration of the results of Example 2, the position in the film thickness direction where the energy becomes minimum was determined for each film deposition time so that the film deposition time of the i-layer was set to 0.7 and 0.78 from the start of film deposition. . The applied RF power is 10W.

The conversion efficiency was measured for each of the photovoltaic elements manufactured as described above. The values corresponding to the maximum GeH ₄ introduction amount were determined for each band gap energy and the Ge composition ratio in the i-layer film.

FIG. 3 is a graph in which the band gap energy is plotted on the horizontal axis and the conversion efficiency is plotted on the vertical axis, and the measured data is plotted. However, the conversion efficiency is such that the band gap energy of the portion deposited when the maximum GeH _{4 is} supplied is 1.4.
The conversion efficiency of the element which was 2 eV was expressed as a relative value assuming that it was 1. From this figure, it is found that the conversion efficiency is almost constant in the band gap energy range of about 1.3 eV to 1.4 eV when the maximum GeH _{4 is} supplied. Also, about 1.4 eV
In the region from about 1.7 eV to about 1.7 eV, there is a tendency that the conversion efficiency decreases as the band gap energy increases when the maximum GeH _{4 is} supplied.

From the above results, it was found that the optimum value of the band gap energy was from 1.3 eV to 1.4 eV.

[0087]

As described above, according to the present invention, a photovoltaic device having a high light conversion efficiency and requiring a relatively small amount of source gas can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a method for introducing a germanium-containing gas in a method of the present invention.

FIG. 2 is a diagram showing a relationship between a relative time indicating a maximum introduction point of a germanium-containing gas and a conversion efficiency of a manufactured photovoltaic device in the method of the present invention.

FIG. 3 is a diagram showing the relationship between the band gap energy of a portion deposited at the maximum introduction of a germanium-containing gas and the conversion efficiency of a manufactured photovoltaic device in the method of the present invention.

FIG. 4 is a diagram showing a relationship between a germanium-containing gas introduction amount and a film deposition rate in a preliminary test.

FIG. 5 is a diagram showing a relationship between a germanium-containing gas introduction amount and a band gap energy of a deposited film in a preliminary test.

FIG. 6 is a schematic view showing an example of a photovoltaic device manufactured by the method of the present invention.

FIG. 7 is a schematic view showing an example of a photovoltaic device manufactured by the method of the present invention.

FIG. 8 is a schematic view showing an example of a photovoltaic device manufactured by the method of the present invention.

FIG. 9 is a schematic view showing an example of a photovoltaic element manufactured by the method of the present invention.

FIG. 10 is a schematic diagram showing an outline of a deposited film forming apparatus used in an example.

[Explanation of symbols]

 Reference Signs List 1,101 substrate 2 lower electrode 3,13,23 n-type semiconductor layer 4,14,24 i-type semiconductor layer 5,15,25 p-type semiconductor layer 6 upper electrode 7 collector electrode 10,11,12 unit element 100 reaction Chamber 102 Anode electrode 103 Cathode electrode 104 Heater for substrate heating 105 Grounding terminal 106 Matching box 107 RF power supply 108 Exhaust pipe 109 Exhaust pump 110 Deposition gas introduction pipe 120 Valve 121 Mass flow controller 122 Valve

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Koichi Matsuda 3- 30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Toshihiro Yamashita 3- 30-2 Shimomaruko, Ota-ku, Tokyo (56) References JP-A-64-71182 (JP, A) JP-A-3-208376 (JP, A) JP-A-4-44366 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) H01L 31/04

Claims (3)

(57) [Claims] At least one set of p, i, n-type semiconductors is deposited on a substrate having a conductive surface, wherein the i-type semiconductor film is amorphous silicon-germanium, and the i-type semiconductor film includes germanium. A method for manufacturing a photovoltaic device having a structure in which the band gap energy is once monotonically reduced in the film thickness direction and then monotonically increased by changing the content in the film thickness direction. in the step of depositing, linearly increased with respect between at first 0 or al the supply amount of the raw material gas containing germanium, i-type semiconductor film
0.75 or more of the total deposition time from the start to the end of
A method for manufacturing a photovoltaic element , wherein a predetermined flow rate is set at a time point equal to or less than 0.8, and the supply flow rate is linearly reduced to 0 with respect to time from the time point when the predetermined flow rate is reached. 2. Depositing when said predetermined flow rate is reached
The band gap energy of the film is 1.3 eV or more
2. The photovoltaic device according to claim 1, wherein the voltage is 1.4 eV or less .
Construction method. 3. The semiconductor device according to claim 1, wherein said p, i, n-type semiconductor film is an n-type semiconductor film.
Claim for depositing a body film, an i-type semiconductor film, and a p-type semiconductor film in this order
Item 3. The method for producing a photovoltaic device according to Item 1 or 2.