JPH04266067A - photovoltaic element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides high photoelectric conversion efficiency.
It relates to photovoltaic elements used in solar cells and the like.

0002

[Prior Art] Solar cells, which are photoelectric conversion elements that convert sunlight into electrical energy, are widely used as small power sources for consumer electronics 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 solar cells are generally manufactured using semiconductor processes. Specifically, a single crystal of silicon whose valence electrons are controlled to be p-type or n-type is produced using a crystal growth method such as the CZ method, and the single crystal is sliced into approximately 300 μm pieces.
Make a silicon wafer with a thickness of m. Further, a pn junction is created by forming layers of different conductivity types by appropriate means such as diffusing a valence electron control agent so that the conductivity type is opposite to that of the wafer.

By the way, from the viewpoint of reliability and conversion efficiency,
Currently, single-crystal silicon is mainly used in solar cells that are in practical use, but as mentioned above, production costs are high because solar cells use a semiconductor process. Other disadvantages of monocrystalline silicon solar cells are that monocrystalline silicon has a low light absorption coefficient due to its indirect transition, and monocrystalline solar cells must be at least 50 microns thick to absorb incident sunlight. Another problem is that the band gap is about 1.1 eV, which is narrower than 1.5 eV, which is suitable for solar cells, so short wavelength components cannot be used effectively. Furthermore, even if production costs were lowered by using polycrystalline silicon, the problem of indirect transition would remain.
It is not possible to reduce the thickness of solar cells. Furthermore, polycrystalline silicon has grain boundaries where many defects gather, which impairs carrier mobility.

Furthermore, since it is a crystal, large-area wafers cannot be manufactured 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. The production cost per unit of power generation is lower than the existing The problem is that it is more expensive than other power generation methods. 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. Although efforts have been made to find materials such as high-performance materials, tetrahedral amorphous materials such as amorphous silicon, amorphous silicon germanium, and amorphous silicon carbide have been used as materials for such solar cells. Semiconductors, II-VI groups such as CdS and Cu2S, and Ga
Examples include III-V compound semiconductors such as As 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.

[0005] The above-mentioned amorphous semiconductor is manufactured by a normal thin film manufacturing process, and industrially, a plasma CVD method is used in which raw material gas is decomposed with plasma generated by a high-frequency power source and deposited on a substrate. is used effectively. For example, amorphous silicon is produced by decomposing and depositing SiH4 gas. When producing a semiconductor with n-type valence electrons controlled, SiH4 is
When mixing with a gas and decomposing it to produce a p-type semiconductor with valence electrons controlled, B2 H6 gas containing boron, etc. from Group III of the periodic table as a constituent atom, is mixed with SiH4 gas.
It is made by mixing with gas and decomposing it. Furthermore, a pin type solar cell layer structure has been adopted because it has high efficiency.

When a solar cell using the above amorphous semiconductor is applied as a power device, it is desired to further improve the photoelectric conversion efficiency and reliability, and as a means for improving the photoelectric conversion efficiency, for example, Efforts have been made to narrow the bandgap and increase sensitivity to long wavelength light. That is, amorphous silicon has a band gap of approximately 1.7 eV.
Since the wavelength of light of 700 nanometers or more cannot be absorbed and effectively utilized, the use of materials with narrow band gaps that are sensitive to long wavelength light is being considered. An example of such a material is amorphous silicon germanium, whose band gap can be easily changed from about 1.3 eV to about 1.7 eV by changing the ratio of silicon source gas and germanium source gas during film formation. .

[0007] 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.
, No. 498. A p-n junction crystal semiconductor was used in this tandem cell, but the idea is common to both amorphous and crystalline semiconductors.
The solar spectrum was efficiently absorbed by photovoltaic elements with different band gaps, and power generation efficiency was improved by increasing Voc. 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 gap. 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. This method is a method of stacking unit elements made of amorphous silicon materials with the same bandgap. Amorphous silicon germanium has a narrow band gap and excellent sensitivity to long wavelength light, so it is used as a suitable material for the bottom layer of the tandem cell mentioned above.

In order to improve the solar cell characteristics, it is necessary to effectively absorb sunlight to generate carriers and collect the generated carriers without recombining them. This point will be discussed in detail below. When the amorphous semiconductor is used as a solar cell, a p-type semiconductor,
It is common to have a structure in which an i-type semiconductor and an n-type semiconductor are stacked, but in such a structure, light enters from either the p-type semiconductor or the n-type semiconductor, and the i-type semiconductor emits the light. Carriers are generated, and the generated free electrons and free holes are collected on the n-type semiconductor side and the p-type semiconductor side, respectively, by an internal electric field. Because of this mechanism, it is advantageous to collect carriers if the drift distance of free holes, which have poor carrier mobility, is short, so light is generally introduced from the p-layer.

By the way, the p-layer generates an internal electric field, but since it is a dead layer that does not contribute to the generation of optical carriers, it absorbs as little light as possible and allows incident light to efficiently reach the i-layer, forming the so-called window layer. It is desirable to function as a It is known that p-type silicon, which is produced by mixing SiH4 gas and B2 H6 gas, has a large absorption coefficient because of the B element and is not suitable as a window layer. As a material for such a window layer, for example, U.S. Patent No. 4,600,80
No. 1 discloses that a microcrystalline p-layer is suitable. According to the disclosed content, using a fluorine-based gas, the activation energy is 0.05 eV or less, the conductivity is lohm-1 cm-1 or more, the band gap is 2.0 eV or more, and the wavelength is 550 nm. Particle size of 50~ so that the absorption coefficient is 3 x 10-4 cm-1 or less
By using a 100 Å microcrystalline p-type silicon alloy layer as a window layer, good solar cell characteristics can be obtained. Also,
US Pat. No. 4,109,271 discloses that a-S with a band gap of 2.2 eV to 3.2 eV is used as a window layer.
It has been disclosed that the absorption coefficient can be reduced by using iC.

0010

[Problems to be solved by the invention] However, when the above-mentioned microcrystalline p-layer or a-SiC p-layer is used as the window layer of an amorphous solar cell, the conditions for producing microcrystals require high plasma power. Therefore, in some cases, dopants may diffuse into the underlying i-layer, and it is difficult to form a microcrystalline p-layer on an amorphous i-layer. Furthermore, since the microcrystalline p-layer and the a-SiC p-layer have different lattice constants and band gaps from the amorphous i-layer, there is a problem in that defects are likely to occur at the junction. Therefore, although the microcrystalline p-layer and the a-SiC p-layer originally have extremely good characteristics as a window layer, there remains room for further improvement when producing solar cells. Regarding the reduction of the level at the semiconductor interface, for example, it has been disclosed that an intrinsic a-SiC layer is provided at the interface between the p layer and the i layer of a-SiC to serve as a so-called buffer layer. . However, no proposal has been made regarding a buffer layer between a microcrystalline p-layer and an i-layer.

An object of the present invention is to solve the above-mentioned problems and provide a solar cell with high photoelectric conversion efficiency.

0012

[Means for Solving the Problems] As a result of intensive studies to overcome the above-mentioned problems and create a solar cell with high conversion efficiency, the present inventors have made the i-layer at the pi interface of a pin type solar cell microcrystalline. Based on this knowledge, they conducted further research and applied it to a photovoltaic device, which led to their completion. That is, the gist thereof is a pin-type photovoltaic element characterized in that at least a portion of the i-type layer that is in contact with the p-type layer is made of microcrystals. Here, the i-type layer is made of, for example, silicon or a silicon alloy, and the thickness of the layer made of microcrystals is, for example, from 50 Å to 150 Å.

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.

FIG. 5 shows a typical example of a conventional pin type solar cell for reference.
is the solar cell main body, 201 is the substrate, 202 is the lower electrode, 2
03 represents an n-type semiconductor layer, 204 represents an i-type semiconductor layer, 205 represents a p-type semiconductor layer, 206 represents an upper electrode, and 207 represents a current collecting electrode.

FIGS. 1 to 4 schematically show examples of the configuration of a pin-type photovoltaic device according to the present invention. Figure 1
is a solar cell with a structure in which light enters from the top of the figure, and in the figure, 100 is the solar cell body, 101 is the substrate, and 102
103 is an n-type semiconductor layer, 104 is an i-type semiconductor layer, 105 is a microcrystalline i-type semiconductor layer, 106 is a p-type semiconductor layer, 107 is an upper electrode, and 108 is a current collecting electrode. FIG. 2 shows a solar cell in which the substrate 101 is transparent and light enters from the bottom of the figure. Figure 3 shows two unit elements in Figure 1.
The solar cell has a laminated structure, and in the figure, 111 and 112 represent unit elements of the solar cell, and 113 represents n.
114 is an i-type semiconductor layer, 115 is a microcrystalline i-type semiconductor layer, and 116 is a p-type semiconductor layer. FIG. 4 shows a solar cell with a structure in which the unit elements of FIG. 1 are stacked in three layers,
In the figure, 120, 121 and 122 represent unit elements of a solar cell, 123 is an n-type semiconductor layer, 124 is an i-type semiconductor layer, 125 is a microcrystalline i-type semiconductor layer, and 126 is a p-type semiconductor layer.
type semiconductor layer. In any photovoltaic element, the n-type semiconductor layer and the p-type semiconductor layer of each unit element can be used by changing the stacking order of each layer depending on the purpose. Hereinafter, the configuration of these photovoltaic elements will be explained using FIG. 1 as an example.

Substrate: semiconductor layers 103, 104, 105,
Since the film 106 is a thin film of about 1 μm at most, it is deposited on a suitable substrate. Such a substrate 101 may be single crystal or non-single crystal, and may be electrically conductive or electrically insulating. Furthermore, they may be translucent or non-transparent;
It is preferable that the material has less distortion and desired strength. Specifically, Fe, Ni, Cr, Al, Mo, A
Metals such as u, Nb, Ta, V, Ti, Pt, Pb or alloys thereof, such as thin plates such as brass and stainless steel, and composites thereof, and polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene,
polyvinyl chloride, polyvinylidene chloride, polystyrene,
Films or sheets of heat-resistant synthetic resins such as polyamide, polyimide, epoxy, etc., or composites of these with glass fibers, carbon fibers, boron fibers, metal fibers, etc., and thin plates of these metals, resin sheets, etc. with different materials on the surface. metal thin film and/or SiO2,S
Examples include those obtained by surface coating an insulating thin film such as i3 N4, Al2 O3, AlN, etc. by sputtering, vapor deposition, plating, etc., as well as glass and ceramics.

When the above-mentioned substrate is used as a substrate for a solar cell, it may be used as an electrode for direct current extraction if the substrate is electrically conductive such as metal, or it may be made of electrically insulating material such as synthetic resin. In some cases, the surface on which the deposited film is formed is coated with Al, Ag, Pt, Au, Ni, Ti, Mo, W,
Fe, V, Cr, Cu, stainless steel, brass, nichrome,
So-called simple metals or alloys such as SnO2, In2O3, ZnO, ITO, etc., and transparent conductive oxides (TCO
) is preferably subjected to surface treatment in advance by a method such as plating, vapor deposition, or sputtering to form an electrode for current extraction.

Of course, even if the substrate is an electrically conductive material such as metal, it is possible to improve the reflectance of long wavelength light on the substrate surface, or to change the composition of constituent elements between the substrate material and the deposited film. For the purpose of preventing mutual diffusion, etc., a layer of different metals or the like may be provided on the side on which the deposited film is formed on the substrate. In addition, when the substrate is relatively transparent and the solar cell has a layered structure in which light enters from the side of the substrate (as shown in FIG. 2), the transparent conductive oxide, metal thin film, etc. It is desirable to deposit a conductive thin film in advance.

The surface of the substrate may be either a so-called smooth surface or a slightly uneven surface. When creating a surface with minute irregularities, the shape of the irregularities may be spherical, conical, or
By having a pyramidal shape or the like, and preferably having a maximum height (Rmax) of 500 Å to 5000 Å, light reflection on the surface becomes diffuse 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. However, if flexibility is required as a photovoltaic element, or if light is incident from the side of the substrate, it should be made as thin as possible within the range that allows the substrate to fully function. I can do it. 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),
Examples include current collecting electrodes. However, the upper electrode here refers to one provided on the light incident side, and the lower electrode refers to one provided opposite to the upper electrode with the semiconductor layer in between. These electrodes will be explained in detail below.

Lower electrode: The lower electrode 102 used in the present invention is installed at a different location between FIGS. 1, 3 and 4 and FIG. 2. That is, in the case of a layer structure as shown in FIGS. 1, 3, and 4, the substrate 101 and the n-type semiconductor layer 102
established between. In particular, when an electrically insulating substrate is used as the substrate 101, a lower electrode 102 is provided between the substrate 101 and the n-type semiconductor layer 103 as an electrode for taking out current. However, if the substrate 101 is conductive, it can also serve as the lower electrode. However, even if the substrate 101 is conductive, if the sheet resistance value is high, it can be used as a low resistance electrode for current extraction.
Alternatively, the electrode 102 may be provided for the purpose of increasing the reflectance on the substrate surface and making effective use of the incident light. On the other hand, in the case of the layer structure shown in FIG. 2, a transparent substrate 101 is used.
Since light is incident from the substrate 101 side, a lower electrode 102 is provided facing the substrate 101 with a semiconductor layer in between for the purpose of extracting current and reflecting light at the electrode.

[0022] As the electrode material, Ag, Au, Pt, N
Examples include metals such as i, Cr, 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 102 and the n-type semiconductor layer 103. The effect of the diffusion prevention layer is not only to prevent the metal element constituting the lower electrode 102 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. Electrode 10
2 and the upper electrode 107 due to defects such as pinholes, and generate multiple interference due to the thin film to confine incident light within the photovoltaic element. can.

Upper electrode (transparent electrode): The upper electrode 107 used in the present invention has a light transmittance of 85% or more in order to efficiently absorb light from the sun, a white fluorescent lamp, etc. into the semiconductor layer. Further, it is desirable that the sheet resistance value be 100Ω or less so as not to become a resistance component to the output of the photovoltaic element electrically. Materials with such characteristics include SnO2 and In
2O3, ZnO, CdO, CdSnO4, ITO
Metal oxides such as (In2 O3 + SnO2),
Examples include metal thin films made of extremely thin, translucent metals such as Au, Al, and Cu. The transparent electrodes are p-type semiconductor layers 106, 116, 126 in FIGS. 1, 3, and 4.
In FIG. 2, it is laminated on the substrate 101, and it is necessary to select materials with good adhesion to each other depending on the above. 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.

Current collector electrode: The current collector electrode 108 used in the present invention is provided on the upper electrode 107 for the purpose of reducing the surface resistance value of the upper electrode 107. Electrode materials include Ag, Cr, Ni, Al, Ag, Au, Ti, and Pt.
, Cu, Mo, W, or an alloy 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 enters the semiconductor layer. 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. In addition, the sheet resistance value is preferably 50Ω or less,
More preferably, it is 10Ω or less.

[0026] Semiconductor layers 103, 104, 105, 106
is manufactured using a normal thin film manufacturing process,
Vapor deposition method, sputtering method, high frequency plasma CVD method, microwave plasma CVD method, ECR method, thermal CVD method, LPC
It can be produced by using a known method such as the VD method as desired. Industrially, raw material gas is decomposed with plasma,
A plasma CVD method for depositing on a substrate is preferably used. 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 raw materials.

I-type semiconductor layer: Semiconductor materials constituting the i-type semiconductor layer 104 suitably used in this photovoltaic device include a-Si:H, a-Si:F, a-Si:
H:F, a-SiGe:H, a-SiGe:F, a-S
iGe:H:F,a-SiC:H,a-SiC:F,a
Examples include so-called group IV and group IV alloy semiconductor materials such as -SiC:H:F.

When these materials are produced by the CVD method, a chain or cyclic silane compound is used as a compound containing the silicon element, and specifically, for example, SiH4, SiF4, (SiF2)5, etc. ，
(SiF2)6, (SiF2)4, Si2F
6, Si3 F8, SiHF3, SiH2 F2
, Si2 H2 F4 , Si2 H3 F3 , S
iCl4, (SiCl2)5, SiBr4, (
SiBr2)5, SiCl6, SiHCl3,
SiHBr2, SiH2Cl2, SiCl3 F3
Examples include those in a gaseous state or those that can be easily gasified.

[0029] 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 ,Ge2 H2 ,Ge3 H8
, n-Ge4 H10, t-Ge4 H10, GeH6
,Ge5 H10,GeH3 Cl,GeH2 F2
,Ge(CH3)4,Ge(C2H5)4
,Ge(C6H5)4,Ge(CH3)2F
2, GeF4, etc.

Furthermore, as compounds containing carbon elements, chain hydrocarbon compounds, chain halogenated hydrocarbon compounds, cyclic hydrocarbon compounds or cyclic halogenated hydrocarbon compounds, specifically CH4, C2 H6, C3 H8
,n-C4 H10,t-C4 H10,C3 H6
,C5 H10,CH3Cl,CH2F2,C
(CH3)4,C(C2H5)4,C(C6
Examples include H5)4, C(CH3)2F2, CF4, and the like.

Microcrystalline i-type semiconductor layer: The microcrystalline i-type semiconductor layer 105 used in the present invention is manufactured using the same constituent elements as the above-mentioned amorphous i-type semiconductor, and the raw material gas is also The gas used in producing the above-mentioned amorphous i-type semiconductor layer is preferably used. Microcrystals with a particle size of about 100 Å can usually be obtained by diluting these raw material gases with H2 gas and adjusting power conditions. Regarding crystallinity, reflection high-speed electron diffraction (R
HEED), Raman spectrum, transmission electron microscope, etc.

P-type semiconductor layer and n-type semiconductor layer: Semiconductor materials constituting the p-type semiconductor layer 106 or the n-type semiconductor layer 103 suitably used in the present photovoltaic device include the i-type semiconductor layer 104 described above. It is obtained by doping the constituent semiconductor material with a valence electron control agent. As a manufacturing method, a method similar to the method for manufacturing the i-type semiconductor layer 104 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. Specifically, compounds containing Group III elements include BF3, B
2 H6 , B4 H10, B5 H9 , B5 H1
1,B6 H10,B(CH3)3,B(C2H
5)3,B6 H12,Al(CH3)2Cl
,Al(CH3)3,Al(OCH3)2Cl
, Al(CH3)Cl2, Al(C2H5)3
, Al(OC2 H5 )3 , Al(CH3 )3
Cl3, Al(i-C4 H9)5, Al(C
3H7)3,Al(OC4H9)3,Ga
(OCH3)3,Ga(OC2H5)3,G
a(OC3H7)3,Ga(CH3)3,G
a2 H6 , GaH(C2 H5 )2 , Ga(O
C2 H5 )(C2 H5 )2 ,In(CH3
)3 , In(C3 H7 )3 , In(C4 H9
)3 etc.

A compound containing an element of Group V of the periodic table is used as a valence electron control agent for obtaining an n-type semiconductor. 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(OC4
H9 )3 , P(SCN)3 , P2 H4 , P
H3, AsH3, AsH3, As(OCH3)
3,As(OC2H5)3,As(OC3H
7 )3 , As(OC4 H9 )3 , As(CH
3)3, As(C2 H5)3, As(C6
H5)3, SbH3, Sb(OCH3)3,
Sb(OC2 H5)3, Sb(OC3 H7)
3,Sb(OC4H9)3,Sb(CH3)
3,Sb(C3H7)3,Sb(C4H9)
3 etc. can be mentioned.

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

[0035] Furthermore, an inert gas such as H2 gas, Ar gas, He gas, etc. may be added to the raw material gas for producing the above-mentioned semiconductor layer, as desired. When the above-mentioned raw material is in a gaseous state at room temperature and normal pressure, the amount introduced into the film forming space is controlled by a mass flow controller (hereinafter referred to as MFC), and when it is in a liquid state, a rare gas such as Ar or He is used. Gas or hydrogen gas is used as a carrier gas, and if necessary, it is gasified using a bubbler that can control the temperature. If it is in a solid state, it is heated in a sublimation furnace using a rare gas such as Ar or He or hydrogen gas as a carrier gas. The amount of gas introduced is controlled mainly by the carrier gas flow rate and furnace temperature.

Examples of the present invention are shown below, but the present invention is not limited to the following examples.

[0037]

[Example] Example 1: A pin type solar cell of the present invention shown in FIG. 1 was fabricated in the following manner using a known RF discharge plasma CVD film forming apparatus shown in FIG. 40 in Figure 6
0 is a reaction chamber, 401 is a substrate, 402 is an anode electrode, 403 is a cathode electrode, 404 is a heater for heating the substrate, 405 is a ground terminal, 406 is a matching box, 407 is an RF power source with a frequency of 13.56 MHz, 40
8 is an exhaust pipe, 409 is an exhaust pump, 410 is a deposition gas introduction pipe, 420, 430, 440, 450, 460, 47
0, 480, 422, 432, 442, 452, 462
, 472, 482 are valves, 421, 431, 441,
451, 461, 471, 481 indicate mass flow controllers.

First, the surface was mirror polished to 0.05 μmRm.
5cm square size stainless steel (SUS30
4) Place the manufactured substrate 101 in a sputtering device (not shown), evacuate the inside of the device to 10 −7 Torr or less, introduce Ar gas, set the internal pressure to 5 mTorr, and generate DC plasma discharge with a power of 200 W to sputter Ag. Sputtering was performed using a target to deposit approximately 5000 Å of Ag on the substrate 101. Thereafter, the target was changed to ZnO, DC plasma discharge was generated under the same internal pressure and power conditions, and sputtering was performed to deposit ZnO with a thickness of about 5000 Å. After producing the lower electrode 102 through the above steps, the substrate 101 is taken out, attached to the cathode in the reaction chamber 400, sufficiently evacuated by the exhaust pump 409, and the degree of vacuum in the reaction chamber 400 is checked using an ion gauge (not shown). 10-6To
rr. Next, the substrate heating heater 404
The board 401 (corresponding to the board 101 in FIG. 1) is 300
heated to ℃. After the substrate temperature becomes constant, the valve 42
0 and 422 are opened, and the flow rate of the mass flow controller 421 is controlled to supply Si from a SiH4 gas cylinder (not shown).
10 sccm of H4 gas was introduced into the reaction chamber 400 via the gas introduction pipe 410. Similarly, valves 440 and 442 are opened and mass flow controller 441 is opened.
H2 gas was supplied at 300 sccm by controlling the flow rate of
The valves 450 and 452 were opened, and the flow rate of the mass flow controller 451 was controlled to introduce 10 sccm of PH3 gas diluted to 5% with H2 gas. After adjusting a pressure controller (not shown) so that the internal pressure of the reaction chamber 400 is 1.5 Torr, 10 W power is applied from the RF power source 407 via the matching box 406, plasma discharge is performed for 3 minutes, and n-type amorphous A silicon layer 103 having a thickness of 400 Å was deposited. After stopping the gas supply, the reaction chamber 400 is evacuated again, and the reaction chamber 4
After evacuating the vacuum inside 00 to below 10-6 Torr, open the valves 420, 422, 440, and 442 to remove the Si.
10 sccm of H4 gas and 300 sccm of H2 gas were introduced into the reaction chamber 400. Using a pressure controller (not shown) to maintain the internal pressure at 1.5 Torr, R
A power of 20 W is applied from the F power source 407, and plasma discharge is performed for 30 minutes to form the intrinsic layer 104 at 3,000 watts.
Å Deposited. After that, increase the power to 200W without cutting off the discharge.
Furthermore, the flow rate of H2 gas was increased to 500 sccm and film formation was performed for 1 minute to form a microcrystalline i-layer 105 with a thickness of about 30 Å.
was deposited.

The crystallinity of the microcrystalline i-layer 105 thus deposited was evaluated as follows. Under the above conditions, only the microcrystalline i-layer 105 was deposited on the glass substrate with a thickness of about 1000 Å.
A sample was prepared with a film thickness of
When the Raman shift was measured using 00, it was 500 cm.
A weak peak was observed near −1 to 520 cm −1 , confirming microcrystalization. Further, the particle size was found to be from 20 Å to 100 Å by observation using a transmission electron microscope.

After that, the power of the RF power source 407 is set to 0 W, plasma discharge is stopped, and gas supply is stopped. After the vacuum level in the reaction chamber 400 is evacuated to 10 -6 Torr or less, the valves 420 , 422 , 440 , 442,
460 and 462 were opened, and 10 sccm of SiH4 gas, 500 sccm of H2 gas, and 10 sccm of BF3 gas diluted to 5% with H2 gas were added to the reaction chamber 400.
It was introduced in Subsequently, a power of 200 W was applied from the RF power source 407 to generate plasma discharge, and film formation was performed for 5 minutes to deposit a p layer 106 of 100 Å. Note that when a sample in which only the p layer 106 was deposited on a glass substrate under the above-mentioned conditions was observed using a transmission electron microscope and a Raman spectrum, it was confirmed that the sample was microcrystals with a grain size of 20 Å to 100 Å. Next, the substrate 101 is taken out from the reaction chamber 400 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 10-4 Torr, an alloy of In and Sn was evaporated by resistance heating to form a transparent conductive film (which also has an antireflection effect). A 700 Å thick ITO film was deposited to form the upper electrode 107. After completion of the vapor deposition, the sample was taken out and separated into subcells of 1 cm x 1 cm in size using a dry etching device (not shown), then transferred to another vapor deposition device, and an aluminum current collecting electrode 108 was formed by electron beam evaporation. The obtained solar cell was No. 1-S1.

Next, the thickness of the microcrystalline i-layer 105 is set to 60 Å,
Deposition was carried out in the same manner as described above except that the thicknesses were changed to 100 Å, 150 Å, 200 Å, and 400 Å. The obtained solar cells were numbered respectively. 1-S2, No. 1-S3, No
．． 1-S4, No. 1-S5, No. 1-S6. Finally, a solar cell without microcrystalline i-layer 105 (No. 1-R
) was created.

These samples were exposed to 100 mW of light in the AM-1.5 solar spectrum using a solar simulator.
The initial characteristics of the solar cell were measured by irradiating the solar cell with an intensity of /cm2 and obtaining a current-voltage curve. FIG. 7 shows the value η/η0, which normalizes the efficiency η with the microcrystalline i-layer by the efficiency η0 without the microcrystalline i-layer (sample No. 1-R). This result shows that when the microcrystalline i-layer has a thickness of about 200 Å or less, the conversion efficiency η is improved compared to a cell without the microcrystalline i-layer. Especially microcrystalline i-layer 1
It can be seen that there is a significant effect when the thickness of 05 is from 50 Å to 150 Å. Although not shown, it was found from the current-voltage curve that the cause of the improvement in conversion efficiency was an improvement in open-circuit voltage and fill factor.

Furthermore, among the above samples, sample No. 1 does not have the microcrystalline i-layer 105. 1-R and the film thickness of the microcrystalline i-layer 105 is 10
Sample No. 0 Å. 1-S3 and CAMECA SIM
The depth profile of element B was analyzed using an S analyzer (IMS-3F), and the diffusion of element B, which is a p-layer dopant agent, into the i-layer 104 was compared. The results show that, as shown in FIG. 8, when there is a microcrystalline i-layer 105 of 100 Å, the diffusion of B element into the i-layer 104 is reduced. This is considered to be because the microcrystalline i-layer has the effect of preventing the diffusion of B element.

Example 2: Next, an example of the present invention in which the substrate is made of glass will be described. A solar cell according to the present invention having the configuration shown in FIG. 2 was manufactured in the following manner using the apparatus shown in FIG. 6 in substantially the same manner as in Example 1.

First, a 5 cm square quartz glass substrate 10 is prepared.
1, a transparent conductive film of SnO2 was deposited at 3,000 ml using a vapor deposition device (not shown).
The upper electrode 107 was produced by depositing .ANG. After that, board 1
01 into the reaction chamber 400 and deposited a p-type microcrystalline silicon layer 106 of 100 Å under the same conditions as in Example 1. After the discharge, a microcrystalline i layer 105 with a thickness of 100 Å was deposited under the same conditions as in Example 1. After depositing the i-layer 104, three
000 Å deposited.

After the discharge ends, the n-layer 103 is removed as in Example 1.
was deposited to a thickness of 400 Å. The substrate 401 is placed in the reaction chamber 40.
The lower electrode 102 was formed by depositing aluminum to a thickness of 5000 Å using an electron beam evaporator (not shown). Furthermore, it was separated into 1 cm square subcells using a dry etching device (not shown). The obtained solar cell was No. 2-S
And so. For comparison, a sample without the microcrystalline i-layer 105 was prepared in the same manner as described above, and sample No. It was set as 2-R. For each sample, the solar cell characteristics were measured by irradiating light from the glass substrate 101 side, and the results are shown in Table 1:

[0047]

[Table 1] In Table 1, the efficiency η when there is a microcrystalline i-layer is normalized by the conversion efficiency η0 when there is no microcrystalline i-layer. This result shows that the cell with the microcrystalline i-layer has an improved conversion efficiency η compared to the cell without the microcrystalline i-layer.

Example 3 Next, a solar cell of the present invention having the tandem cell structure shown in FIG. 3 was produced in substantially the same manner as in Example 1 using the apparatus shown in FIG.

An n-layer 103 of 400 Å was deposited on the stainless steel substrate 101 on which the lower electrode 102 was deposited, and 5 sccm of GeH4 gas, 5 sccm of SiH4 gas, and 300 sccm of H2 gas were introduced to generate an amorphous layer with a band gap of 1.5 eV. quality silicon germanium i layer 10
4 was deposited. Further, the discharge was continued, the power was increased to 100 W, the amount of hydrogen was increased to 500 sccm, and a microcrystalline i-layer 106 with a thickness of 100 Å was deposited. After that, the microcrystalline p layer 105
A bottom layer 111 was prepared by depositing the following. Furthermore, n layer 11
3 was deposited to a thickness of 400 Å and heated with SiH4 gas and H2 gas.
The layer 114 is 1000 Å and the microcrystalline i-layer 115 is 100 Å.
After depositing and further depositing a microcrystalline p layer 116 of 100 Å to form a top layer 112, an upper electrode 107 is formed.
After separating into cm square subcells, a current collecting electrode 108 was formed. The obtained solar cell was No. It was set as 3-S.

For comparison, microcrystalline i-layers 105 and 11
Sample No. 5 was prepared in the same manner as described above. It was set as 3-R. The solar cell characteristics of each sample were measured by the method of Example 1, and the results are shown in Table 1 above. In Table 1, the efficiency η when there is a microcrystalline i-layer is normalized by the conversion efficiency η0 when there is no microcrystalline i-layer. This result shows that the cell with the microcrystalline i-layer has an improved conversion efficiency η compared to the cell without the microcrystalline i-layer.

Example 4 Next, a solar cell of the present invention having a triple cell configuration shown in FIG. 4 was produced in substantially the same manner as in Example 3 using the apparatus shown in FIG.

After depositing the n-layer 103 on the stainless steel substrate 101 on which the lower electrode 102 has been deposited, the i-layer 10 of amorphous silicon germanium with a band gap of about 1.5 eV is deposited.
4 and then deposited a microcrystalline i-layer of 100 Å while maintaining the discharge.
After that, a microcrystalline p layer 105 was deposited to form a bottom layer 120. After that, an n-layer 113, an i-layer 114, a microcrystalline i-layer 115, and a microcrystalline p-layer 116 are deposited in this order.
A middle layer 121 was formed. Further, an n layer 123, an i layer 124, a microcrystalline i layer 125, and a microcrystalline p layer 126 are deposited in this order to form a top layer 122, and finally the upper electrode 1
After forming 07, it was separated into 1 cm square subcells by dry etching, and current collecting electrodes 108 were formed. The obtained solar cell was No. It was set as 4-S.

For comparison, samples without the microcrystalline i-layers 105, 115, and 125 were prepared in the same manner as described above, and Sample No. It was set as 4-R. The solar cell characteristics of each sample were measured by the method of Example 1, and the results are shown in Table 1 above. In Table 1, the conversion efficiency η without the microcrystalline i-layer
The efficiency η when there is a microcrystalline i-layer is normalized by 0. This result shows that the cell with the microcrystalline i-layer has an improved conversion efficiency η compared to the cell without the microcrystalline i-layer.

Example 5: Next, the i layer 104 and the microcrystal i
A solar cell of the present invention having the layer structure shown in FIG. 1 was fabricated in substantially the same manner as in Example 1 using the apparatus shown in FIG. 6, using various film forming gases for the layer 105 under the conditions shown in Table 2. Here, the film thickness of the microcrystalline i-layer 105 was set to 100 Å. At the same time, a sample of only the microcrystalline i-layer was deposited on a glass substrate, and Example 1
Crystallinity was evaluated in the same manner as above. The obtained solar cell was No. 5-S1, No. 5-S2, No. 5-S3,N
o. It was set as 5-S4. For comparison, a sample without the microcrystalline i-layer 105 was prepared in exactly the same manner as described above, and N
o. 5-R1, No. 5-R2, No. 5-R3, No
．． It was set as 5-R4. The solar cell characteristics of each sample were measured by the method of Example 1, and the results are shown in Table 2:

005
5]

[Table 2] In Table 2, the efficiency η when there is a microcrystalline i-layer is normalized by the conversion efficiency η0 when there is no microcrystalline i-layer. This result shows that the cell with the microcrystalline i-layer has an improved conversion efficiency η compared to the cell without the microcrystalline i-layer.

Example 6: Next, various film forming gases were used as shown in Table 3.
The p-layer 106 was manufactured under the conditions shown in Example 1 except for the following conditions.
A solar cell having the layer structure shown in FIG. 1 was produced in substantially the same manner as in Example 1 using the apparatus shown in FIG. The obtained solar cell was No. 6-S1, No.
6-S2, No. 6-S3, No. It was set as 6-S4. For comparison, a sample without the microcrystalline i-layer 105 was prepared in exactly the same manner as described above, and No. 6-R1, No. 6
-R2, No. 6-R3, No. It was set as 6-R4. The solar cell characteristics of each sample were measured using the method of Example 1, and the results are shown in Table 3:

[0057]

[Table 3] In Table 3, the efficiency η when there is a microcrystalline i-layer is normalized by the conversion efficiency η0 when there is no microcrystalline i-layer. The p-layer used in this sample was deposited on a glass substrate and the crystallinity was evaluated by RHEED in the same manner as in Example 1. The results are also shown in Table 3. This result shows that the cell with the microcrystalline i-layer has an improved conversion efficiency η compared to the cell without the microcrystalline i-layer.

[0058]

According to the photovoltaic device of the present invention, the conversion efficiency can be improved by making at least the portion of the i-layer in contact with the p-layer made of microcrystals.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the configuration of a photovoltaic device according to the present invention.

FIG. 2 is a diagram schematically showing the configuration of a photovoltaic device according to the present invention.

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

FIG. 4 is a diagram schematically showing the configuration of a photovoltaic device according to the present invention.

FIG. 5 is a diagram schematically showing the configuration of a conventional photovoltaic element.

FIG. 6 is a diagram showing the configuration of a film forming apparatus suitable for manufacturing a photovoltaic device according to the present invention.

FIG. 7 is a graph showing the characteristics of a photovoltaic element.

FIG. 8 is a graph showing the depth profile of element B in a photovoltaic device.

[Explanation of symbols]

101 Substrate 102 Lower electrode 103, 113, 123 N-type semiconductor layer 104,
114, 124 i-type semiconductor layer 105, 115,
125 Microcrystalline i-type semiconductor layer 106, 116, 1
26 p-type semiconductor layer 107 upper electrode 108 current collecting electrode

Claims (3)

[Claims] Claim 1: In a pin-type photovoltaic element, i
A photovoltaic device characterized in that at least a portion of the type layer in contact with the p-type layer is made of microcrystals. 2. The photovoltaic device according to claim 1, wherein the i-type layer is made of silicon or a silicon alloy. 3. The thickness of the layer made of microcrystals is 50 Å.
3. The photovoltaic device according to claim 1, wherein the photovoltaic device has a thickness of 150 Å.