JP3027672B2 - Photovoltaic element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device having a pin layer made of a non-single-crystal silicon-based semiconductor material and having a zinc oxide thin film layer between a base and the pin layer. The photovoltaic element is suitably applied to a solar cell, a photodiode, an electrophotographic photosensitive member, a light emitting element and the like.

[0002]

2. Description of the Related Art In recent years, photovoltaic devices using a zinc oxide (ZnO) thin film layer as a transparent conductive film have been energetically studied. For example, (i) “Optimization of Transparent and Reflecting El
ectrodes for AmorphousSilicon Solar Cells ”, Gordo
n RG, Hu J, Musher J, Giunta C, US DOE Rep. pp.44
In 1991, ZnO having a texture structure doped with fluorine was improved. (ii) “Research on amorphous silicon based thin fil
m photovoltaic devices.Task B: Research on stable h
igh efficiency, large area amorphous siliconbased
submodules ”, Delahoy AE, Ellls FB Jr, Kampas F
J, Tonon T, Weakllem HA, US DOE Rep. Pp. 48 1989, report solar cells using excellent high-grade doped ZnO. (iii) “Amorphous silicon pin solar cells using in
dium doped ZnO transparent conducting coatings ”,
Sansores E, Campos J, Nair PK, Photovoltaic Sol.En
ergy Conf. vol.8th No.1 pp.1008 1988, reports a solar cell using ZnO doped with indium. (iv) JP-A-62-259480 describes a solar cell using ZnO containing germanium as an impurity, but in the present invention, germanium in ZnO is not an impurity, but a constituent element. It is contained and its content is changing. Furthermore, the physical phenomena that bring about the effects are also different.

In addition, microwave plasma CVD (MWP)
A solar cell using the CVD method has also been studied as follows. (v) "a-Si solar cell by microwave plasma CVD", Kazufumi Higashi, Takeshi Watanabe, Juichi Shimada, Proc. 566, and the like. In this photovoltaic element, an i-layer having good quality and a high deposition rate is obtained by forming the i-layer by the MWPCVD method.

[0004] Examples of the doping layer formed by the MWPCVD method include, for example, (vi) “High Efficiency Amorphous Solar Cell Employi”.
ng ECR-CVD Produced p-Type Microcrystalline SiC Fi
lm ”, Y. Hattori, D. Kruangam, T. Toyama, H. Okamoto a
nd Y. Hamakawa, Proceedings of the International PVS
EC-3 Tokyo Japan 1987 pp.171, (vii) “HIGH-CONDUCTIVE WIDE BAND GAP P-TYPE a-SiC:
H PREPARED BY ECR CVDAND ITS APPLICATION TO HIGH E
FFICIENCY a-Si BASIS SOLAR CELLS ”, Y. Hattori, DK
ruangam, K. Katou, Y. Nitta, H. Okamoto and Y. Hamakaw
a, Proceedings of 19th IEEE Photovoltaic Specialis
ts Conference 1987 pp.689. In these photovoltaic elements, a high quality p layer is obtained by using the MWPCVD method for the p layer.

[0005] Further, studies have been made on a non-single-crystal silicon-based semiconductor layer containing fluorine and a photovoltaic element using the same. For example, (viii) “Research on practical application of amorphous solar cells, Research on manufacturing technology for highly reliable elements of amorphous solar cells”, Overview of R & D on Sunshine Project. Solar cell energy1. Light utilization technology VOL.1985 pp.1.-I.243 1986, (ix) “The chemical and configurational basis of h
igh efficiency amorphous photovoltaic cells ”, Ov
shinsky.SR, Proceedings of 17th IEEE Photovoltaic
Specialists Conference 1985 pp.1365, (x) “Development of the scientific and technical b
asis for integrated amorphous silicon modules.Res
erch on a-Si: F: H (B) alloys and module testing at
IET-CIEMAT. ”, Gutierrez MT, P Delgade L, Photovol
t. Power Gener., pp. 70-75 1988, (xi) “The effect of fluorine on the photovoltaic p
roperties of amorphoussilicon ”, Konagai.M, Nishih
ata.K, Takahashi.K, Komoro K, Proceedings of 15th I
EEE Photovoltaic Specialists Conference 1981 pp.90
6, etc. However, even in these examples, the photodegradation phenomenon and the thermal stability are mentioned, but the delamination of the semiconductor layer is not described.

[0006] Photovoltaic devices containing microcrystalline silicon have been energetically studied, but no mention is made of delamination.

[0007] US Pat. No. 4,400,409 discloses a plasma CVD apparatus for continuously forming semiconductor layers employing a roll-to-roll method. It is desirable that the photovoltaic element of the present invention be manufactured continuously using such an apparatus. According to this apparatus, a plurality of deposition chambers are provided, and a strip-shaped and flexible substrate is disposed along a path through which the substrates sequentially pass through the deposition chamber, and a semiconductor having a desired conductivity type is provided in the deposition chamber. It is described that a photovoltaic element having a pin junction can be continuously manufactured by continuously transporting the substrate in the longitudinal direction while forming a layer. Note that, in the specification, a gas gate is used to prevent a source gas for containing each valence electron controlling agent in a semiconductor layer from diffusing into another deposition chamber and being mixed into another semiconductor layer. Have been. Specifically, the deposition chambers are separated from each other by a slit-shaped separation passage, and each separation passage is provided with A
A scavenging gas such as r, H ₂ , He or the like is introduced to prevent mutual diffusion of each source gas.

This roll-to-roll forming method is effective when producing a photovoltaic element as in the present invention.

In the above-described conventional photovoltaic element, ZnO /
Improvement in suppression of recombination of photoexcited carriers near the pin layer interface and the ZnO / substrate interface is desired. Further, in these photovoltaic elements, it is desired to improve the open-circuit voltage and the short-circuit current.

In addition, when light is irradiated for a long time in a high temperature environment, there is a problem that the photoelectric conversion efficiency is reduced, that is, deterioration at a so-called high temperature. In addition, when vibration is applied for a long time in a high temperature environment, photoelectric conversion efficiency is reduced, that is, so-called vibration deterioration at a high temperature is a problem. In addition, light deterioration and vibration deterioration when a bias voltage is applied in a high temperature environment have become a problem.

Further, in a photovoltaic element containing at least one element of Ag, Al, and In in the base, there is a problem that short circuit occurs when a bias voltage is applied in a high temperature environment.

Further, when a non-single-crystal silicon-based semiconductor layer containing microcrystalline silicon is formed on a ZnO thin film layer, there is a problem that the layer is more easily peeled off than a layer containing no microcrystalline silicon. Further, when a non-single-crystal silicon-based semiconductor layer containing fluorine is formed on a zinc oxide thin film layer, there is a problem that the layer is easily separated as compared with a layer containing no fluorine.

There is also a problem that the ZnO thin film layer formed by the roll-to-roll method is easily peeled off when stored in a roll and wound for a long time or transported.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a photovoltaic element which solves the above-mentioned conventional problems. That is, the object is to suppress the recombination of photoexcited carriers near the ZnO / pin layer interface and the ZnO / substrate interface. Another object is to improve open-circuit voltage and short-circuit current, and to improve photoelectric conversion efficiency.

An object of the present invention is to suppress light deterioration at high temperature and deterioration at high temperature. It is another object of the present invention to suppress high-temperature light deterioration and high-temperature vibration deterioration when a bias is applied.

It is still another object of the present invention to prevent a short circuit even when a bias voltage is applied to a photovoltaic element containing at least one element of Ag, Al, and In in a high temperature environment.

It is another object of the present invention to prevent delamination even in a photovoltaic element in which a non-single-crystal silicon-based semiconductor layer containing microcrystalline silicon is formed on a ZnO thin film layer. It is another object of the present invention to prevent the non-single-crystal silicon-based semiconductor layer containing fluorine from being delaminated even when formed on a zinc oxide thin film.

It is an object of the present invention to provide a photovoltaic element which is hardly delaminated even in a rolled state.

[0019]

The present invention solves the problems of the prior art, and as a result of intensive studies to achieve the above object,
It has been found that the photovoltaic device of the present invention comprises:
In a photovoltaic device in which a zinc oxide thin film layer and a pin layer (p layer, i layer, and n layer) made of a non-single-crystal silicon-based semiconductor material are stacked on a substrate, the zinc oxide thin film layer has a surface of zero. A c-axis oriented crystalline thin film having irregularities of 1 to 1.0 μm, containing germanium, and having a minimum germanium content at the interface with the substrate, The zinc oxide is gradually increasing toward
It is characterized in that a large amount of germanium is contained in the vicinity of the crystal grain boundary of the thin film layer . Also, the photovoltaic element of the present invention
The element consists of a zinc oxide thin film layer and a non-single-crystal silicon
Lamination of pin layers (p layer, i layer, n layer) made of conductive material
In the photovoltaic device, the zinc oxide thin film layer
Has c-axis orientation having irregularities of 0.1 to 1.0 μm on the surface
Crystalline thin film, and contains germanium,
The germanium content has a minimum value at the interface with the substrate.
And gradually increases toward the pin layer,
The zinc oxide thin film layer contains silicon, and the zinc oxide thin film
High silicon content near the grain boundaries of the layer
It is characterized by.

A preferred embodiment of the present invention is a photovoltaic device in which the c-axis is substantially perpendicular to the substrate surface.

A preferred embodiment of the present invention is a photovoltaic device in which the germanium content is high near the crystal grain boundaries of the zinc oxide thin film layer.

A preferred embodiment of the present invention is a photovoltaic device in which the p layer or the n layer in contact with the zinc oxide thin film layer contains microcrystalline silicon.

A preferred embodiment of the present invention is a photovoltaic device in which the p layer or the n layer in contact with the zinc oxide thin film layer contains germanium.

In a preferred embodiment of the present invention, the p-layer or the n-layer in contact with the zinc oxide thin film layer is a photovoltaic element containing fluorine.

A preferred embodiment of the present invention is a photovoltaic device in which the substrate is a flexible band-shaped substrate and can be wound in a roll.

In a preferred embodiment of the present invention, the zinc oxide thin film layer contains silicon, the content of which changes in the thickness direction, and is minimum at the interface with the substrate and gradually increases toward the pin layer. Photovoltaic element.

A preferred embodiment of the present invention is a photovoltaic device in which the zinc oxide thin film layer contains a large amount of silicon in the vicinity of crystal grain boundaries.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic illustration of a photovoltaic device of the present invention. In FIG. 1, a photovoltaic element of the present invention has a substrate 101, a surface having irregularities and a c-axis orientation.
nO thin film layer 102, pin layer 103 made of non-single-crystal silicon-based semiconductor material, transparent electrode 104, current collecting electrode 105
And so on.

In the photovoltaic element shown in FIG. 1, the light is usually irradiated from the transparent electrode side, but the light may be irradiated from the back side of the base. In this case, the base may be made of a material that transmits light, and a light reflection layer made of a metal material may be formed on the pin layer instead of the transparent electrode.

The pin layer of the photovoltaic device of the present invention
A plurality of pin structures such as an inpin structure and a pinpinpin structure may be stacked.

The pin layer of the photovoltaic device of the present invention has n
A stack of a plurality of nip structures such as an ip structure, a nipnip structure, and a nipnipnip structure may be used.

In the photovoltaic device of the present invention, the ZnO thin film layer contains germanium, the content of which changes smoothly and is minimum at the interface with the substrate and gradually increases toward the pin layer. Interface between the thin film layer and the pin layer,
This is to reduce recombination of photoexcited carriers at the interface between the ZnO thin film layer and the substrate.

The interface between the ZnO thin film layer and the pin layer, Z
Since the internal stress generated at the interface between the nO thin film layer and the substrate is reduced, the photovoltaic element is deteriorated by light (deterioration of element characteristics due to long-time light irradiation), and is deteriorated by vibration (element due to long-time vibration application). (Deterioration of characteristics). That is, it is considered that the photodegradation of the photovoltaic element breaks the weak bond due to the energy of light, and this becomes the center of recombination of the photoexcited carriers, thereby deteriorating the element characteristics. Further, it is considered that vibration degradation of the photovoltaic element breaks a weak bond due to vibration energy, and this becomes a recombination center of photoexcited carriers, thereby deteriorating element characteristics. It is considered that this weak bond is localized in a region where stress is generated, and it is particularly important to reduce recombination centers generated at the interface between the ZnO thin film layer and the pin layer. These effects are prominent when the p-layer or the n-layer in contact with the ZnO thin film layer contains germanium. Furthermore, it is more preferable that the ZnO thin film layer contains silicon, and that the content changes in the layer thickness direction and is minimum at the interface with the substrate and gradually increases toward the pin layer.

The germanium-containing ZnO thin film layer has improved stability against high temperatures, improves the temperature characteristics of the photovoltaic element, and can suppress high-temperature light deterioration and high-temperature vibration deterioration. Furthermore, it is more preferable that the ZnO thin film layer contains silicon, and that the content changes in the layer thickness direction and is minimum at the interface with the substrate and gradually increases toward the pin layer.

Further, since a small amount of germanium acts as a valence electron controlling agent in the ZnO thin film, the conductivity of the film can be improved, and the light transmittance of the ZnO thin film is not impaired. That is, when light is irradiated from the transparent electrode 104 side, light that could not be absorbed by the pin layer can be transmitted efficiently, and short-circuit current can be improved. When light is irradiated from the back side of the base 101, the light is efficiently guided to the pin layer.

In the present invention, a crystalline ZnO thin film having c-axis orientation is used. As a result, irregularities are formed on the surface of the ZnO thin film as shown in FIG.
It can be led to the in layer, and the short-circuit photocurrent of the photovoltaic element can be improved. That is, when light is incident from the transparent electrode side, the light is refracted on the transparent electrode surface and the pin layer surface, so that the optical path length from the incident on the pin layer to the light reaching the crystalline ZnO layer surface is extended. P, more light
Can be absorbed in the in layer.

Further, when the substrate is made of a material that reflects light, light that could not be absorbed by the pin layer can be made to enter the pin layer again from the substrate side and absorbed. At this time, since the surface of the crystalline ZnO thin film layer 102 has irregularities, the reflected light can be refracted here, the optical path length can be extended, and the light can be absorbed more effectively. In order to absorb visible light, the unevenness can effectively absorb visible light when the height of the peak is 0.1 to 1.0 μm.

JP-A-62-259480 discloses Zn
Although it is intended to prevent opacity (irregularities on the surface) of the O thin film layer, in the present invention, rather, the surface is positively eroded (textured) to make the surface opaque.

In particular, it is desirable that each crystal grain 107 is a wurtzite crystal and the c-axis (six axes of rotation) is substantially perpendicular to the substrate. This makes p more effective
Light can be guided to the in layer. To make the c-axis almost perpendicular to the substrate, when forming a ZnO thin film layer by a sputtering method, a DC bias and / or an RF bias is applied to increase the plasma potential, or a negative D
Apply a C bias. Further, in order to make the c-axis substantially perpendicular to the base, countless fine projections may be formed on the surface of the base. For example, an Ag thin film layer may be formed on a stainless steel support at a support temperature of 200 to 600 ° C. It is desirable that the projections are formed at substantially equal intervals.

Further, by making the crystal grain boundary 106 contain a large amount of germanium, diffusion of impurities from the substrate can be prevented. That is, when a material containing an impurity (for example, a certain metal element) that adversely affects the pin layer is used for the base, the impurity must be prevented from diffusing into the pin layer. Crystalline Zn as shown in FIG.
In the case of the O thin film layer, impurities are diffused through the crystal grain boundaries, which may degrade device characteristics. In particular, when a bias voltage is applied to the element for a long time, it appears remarkably,
The shunt resistance becomes extremely small and deteriorates characteristics such as photoelectric conversion efficiency. This is presumably because voids and voids are present at the crystal grain boundaries, so that impurities are easily diffused.
Therefore, by adding a large amount of germanium to the crystal grain boundaries, these voids and voids are reduced and diffusion is prevented. Further, by containing a large amount of germanium in the crystal grain boundaries, the number of dangling bonds is increased, and the germanium reacts with the diffused impurities to prevent diffusion. It is desirable that the germanium content is several times larger than the inside of the crystal bulk. It is further preferable that silicon is contained in the crystal grain boundary of the ZnO thin film layer.

In the present invention, p in contact with the ZnO thin film layer
The layer or the n-layer contains microcrystalline silicon. A p-layer or an n-layer containing microcrystalline silicon has the advantageous characteristics of higher conductivity, less photodegradation, and thermal stability than those containing no microcrystalline silicon, but the film is denser. Therefore, there was a problem that the layer was easily peeled off. However, in the present invention, since a large amount of germanium is contained in the surface of the ZnO thin film layer, the bonding force between the layers is increased, and the ZnO thin film layer is hardly peeled.

In the present invention, p in contact with the ZnO thin film layer
The layer or the n-layer contains fluorine. The fluorine-containing p-layer or n-layer has higher conductivity than those not containing fluorine, has less light degradation, and has the advantageous characteristics of being thermally stable, but because the film is denser,
There was a problem if the layers were easily separated. However, in the present invention, Zn
Since a large amount of germanium is contained in the surface of the O thin film layer, stress is relieved, interlayer bonding force is increased, and delamination is difficult.

In the photovoltaic device of the present invention, the p layer or the n layer
Layer and the i-layer are formed by RF plasma CVD (RFPCVD).
Method) or microwave plasma CVD method (MWPCVD)
Method). Especially MWPCVD
According to the method, the deposition rate is high, the throughput can be improved, and the utilization efficiency of the source gas can be improved, so that the productivity can be improved. When the doping layer is formed by the MWPCVD method, a doping layer having good characteristics as a photovoltaic element can be obtained. That is, the doping layer is excellent as a doping layer because it has good light transmittance, high electric conductivity, and low activation energy. Further, when formed by the MWPCVD method, a high-quality microcrystalline silicon-based semiconductor material or a high-quality amorphous silicon-based semiconductor material having a wide band gap can be relatively easily formed, which is effective as a method for forming a doping layer. The i-layer is particularly effective because the i-layer is thicker than the p-layer and the n-layer.

The ZnO thin film layer of the present invention is preferably formed by a sputtering method. Among them, a magnetron sputtering method with a high deposition rate and a microwave sputtering method described below are suitable. Microwave sputtering method "inerts an inert gas or a reactive gas into a vacuum vessel, generates ions by irradiating the gas with microwaves, and accelerates the ions by applying electromagnetic energy to a target. To form a deposited film on the substrate surface at high speed by irradiating the target surface with the target and sputtering the target. The electromagnetic energy is suitably RF or DC power.

Since the photovoltaic element of the present invention has a ZnO thin film layer and a pin layer formed on a flexible strip-shaped substrate, it can be wound into a roll and takes up space for storage or transportation. And handling becomes easy. It is also suitable for a manufacturing method using a roll-to-roll method, and can dramatically improve productivity. In the photovoltaic element of the present invention, the germanium is contained in the ZnO thin film layer as described above, so that the layer is hardly peeled even in a rolled state.

The photovoltaic element having the pin structure has been described above. However, the pinpin structure shown in FIG.
b, a photovoltaic element in which a pin structure such as a pinpinpin structure is laminated, or a nipnip structure or ni
The present invention is also applicable to a photovoltaic element in which a nip structure such as a pnnip structure is stacked.

FIG. 2 is a schematic illustration of a deposition apparatus suitable for producing the photovoltaic device of the present invention. The deposition device 2
00 is a deposition chamber 201, a vacuum gauge 202, a bias power supply 20
3, substrate 204, heater 205, waveguide 206, conductance valve 207, valve 208, target electrode 209, bias electrode 210, gas inlet tube 211, applicator 212, dielectric window 213, sputter power supply 2
14, a base shutter 215, a target 216, a target shutter 217, a microwave power supply 219, a toroidal coil 221, a vacuum exhaust pump (not shown), a source gas supply device, and the like. The evacuation pump is connected to the exhaust port 220 shown in the figure, and the source gas supply device is composed of a source gas cylinder, a valve, and a mass flow controller, and is connected to a gas introduction pipe. The dielectric window is made of a material that transmits microwaves well, such as alumina ceramics, quartz, and boron nitride.

The fabrication of the photovoltaic device of the present invention is performed as follows. First, the substrate 204 is brought into close contact with the heater 205 provided in the deposition chamber 201 of FIG. 2, and the deposition chamber is sufficiently evacuated to 1 × 10 ⁻⁵ Torr or less. A turbo molecular pump, an oil diffusion pump, or a cryopump is suitable for this exhaust. Thereafter, an inert gas such as Ar is introduced into the deposition chamber, the heater is turned on, and the substrate is heated. When the substrate temperature is stabilized at a predetermined temperature, the conductance valve 207 is adjusted to a predetermined pressure, and a method of forming a ZnO thin film layer described in detail below is performed. Next, a method of forming a pin layer described in detail below is performed. Next, the target is In ₂ O in a vacuum.
Replace with ₃ + SnO ₂ (5 wt%), introduce O ₂ gas into the deposition chamber, perform DC magnetron sputtering, and form ITO on the pin layer. Next, the deposition chamber is leaked, and a comb-shaped current collecting electrode is formed on the ITO surface by an electron beam vacuum evaporation method, thereby completing the fabrication of the photovoltaic element.

The pin layer is formed by MWPCVD or RFP
It is preferably formed by a CVD method. (A) When the pin layer is formed by the MWPCVD method When the pin layer is formed by the MWPCVD method, the source gas is introduced into the deposition chamber, the pressure is adjusted by the conductance valve 207, and the microwave is applied to the waveguide 213 and the applicator 2.
Irradiation is performed on the source gas through 12 to generate plasma. The pressure during the formation of the pin layer is a very important factor, and the optimal pressure in the deposition chamber is 0.5 to 50 mTorr.
Is preferred. The MW power introduced into the deposition chamber is
It is an important factor. The MW power is appropriately determined by the flow rate of the source gas introduced into the deposition chamber,
A preferable range is 100 to 5000 W. M
A preferable frequency range of W power is 0.5 to 10 G
Hz. Particularly, a frequency around 2.45 GHz is suitable. After the desired layer thickness is formed, the introduction of MW power is stopped, the deposition chamber is sufficiently evacuated, and the next layer is formed after sufficiently purging with a gas such as H ₂ , He, or Ar.

When forming the pin layer, RF power may be applied to the bias electrode 210 together with MW power. In this case, the MW power to be introduced is desirably smaller than the MW power required to decompose the raw material gas introduced into the deposition chamber by 100%, and the RF power simultaneously introduced is preferably larger than the MW power. desirable. A preferable range of the simultaneously introduced RF power is 200 to 1000
0W. A preferable frequency range of the RF power includes 1 to 100 MHz. Especially 13.56MHz
Is optimal. When the area of the bias electrode for RF power supply is smaller than the area of the ground, it is better to ground the self-bias (DC component) on the power supply side for RF power supply. Further, a DC voltage may be applied to the bias electrode. A preferred range of the DC voltage is 30 to 300
About V. Further, RF power and DC voltage may be simultaneously applied to the bias electrode.

(B) When the pin layer is deposited by the RFPCVD method, the capacitive coupling type RFPCVD method is suitable. When a pin layer is formed by the RFPCVD method, a source gas is introduced into a deposition chamber, and RF power is applied to a bias electrode to generate plasma. The substrate temperature is 100 to 500 ° C., the pressure is 0.1 to 10 Torr, the RF power is 1 to 2000 W,
The optimum deposition rate is 0.1 to 2 nm / sec. After the desired layer thickness is formed, the introduction of MW power is stopped, the deposition chamber is sufficiently evacuated, and the next layer is formed after sufficiently purging with a gas such as H ₂ , He, or Ar.

The following method can be used to form a ZnO thin film layer containing germanium and having a varied content.

(1) In the case of forming by sputtering method RF magnetron sputtering method or DC magnetron sputtering method with a high forming speed is suitable. In that case, an Ar gas is introduced into a deposition chamber in which a toroidal coil is installed around the target, a target made of ZnO: Ge containing germanium is mounted on the target electrode 209, and the substrate temperature is set to 200 to 600 ° C. , RF (1 to 100 MHz) power or DC power is applied to generate plasma to form a ZnO thin film layer on the substrate.

At this time, the pressure in the deposition chamber is a parameter closely related to the deposition rate of the deposited film, and is appropriately determined by the type of gas to be introduced, the size of the deposition apparatus, and the like. Usually, it is 1 to 30 mTorr. A predetermined amount of the above-mentioned gas is introduced into the deposition chamber from the gas cylinder via the mass flow controller, and the introduction amount is appropriately determined depending on the volume of the deposition chamber. Further, O ₂ gas may be introduced in addition to Ar gas.

In order to change the germanium content in the layer thickness direction, the RF power (DC power) may be changed over time. That is, since the dependency of the sputtering rate on the RF power (DC power) differs between ZnO and germanium, a high RF
In electric power (DC power), the germanium content is high, and when it is low, the germanium content is low.

In order to increase the germanium content at the crystal grain boundaries, the RF power (DC power) may be increased immediately before each crystal grain comes into contact with a neighboring crystal grain.

(2) Case of Forming by Sputtering Method + RFPCVD Method In the above-mentioned RF (DC) magnetron sputtering method, a germanium-containing gas such as GeH ₄ is newly introduced, and the introduced amount may be changed with time. In this case, a target made of ZnO containing no germanium may be used.

Further, in order to increase the germanium content at the crystal grain boundary, a large amount of a gas containing germanium may be flowed immediately before each crystal grain comes into contact with a neighboring crystal grain. (3) When Forming by Microwave Sputtering Method Ar gas is introduced into the deposition chamber, the target made of ZnO: Ge is mounted on the target electrode 209, the substrate temperature is set to 200 to 600 ° C., and RF (1 to 100MH
z) Apply power or DC power (100-600V). The microwave power generated from the microwave power source is transmitted, expanded in the applicator, and irradiated with the above gas through the dielectric window 213 to generate plasma to form a ZnO thin film layer on the substrate.

At this time, the pressure in the deposition chamber is a parameter closely related to the formation rate of the deposited film, and is appropriately determined by the type of gas to be introduced, the size of the deposition apparatus, and the like. Usually, it is 0.1 to 10 mTorr. In addition, the above gas is introduced into the deposition chamber from the gas cylinder through a mass flow controller in a predetermined amount.
The introduction amount is appropriately determined depending on the volume of the deposition chamber. Further, O ₂ gas may be introduced in addition to Ar gas.

To change the germanium content in the layer thickness direction, the RF power or the DC power may be changed over time. That is, since the dependency of the sputtering rate on the RF power (DC power) differs between ZnO and germanium, a high R
At F power (DC power), the germanium content is high, and when it is low, the germanium content is low.

To increase the germanium content at the crystal grain boundaries, the RF power (DC power) may be increased immediately before each crystal grain comes into contact with a neighboring crystal grain.

(4) Microwave sputtering method + MW
When forming by PCVD method In the microwave sputtering method described above, G
A gas containing germanium such as eH ₄ gas is introduced,
What is necessary is just to change the introduction amount with time. In this case, a target made of ZnO containing no germanium may be used.

Further, in order to increase the germanium content at the crystal grain boundaries, a large amount of germanium-containing gas may be flowed immediately before each crystal grain comes into contact with a neighboring crystal grain.

(5) In the case of forming by a roll-to-roll method, the substrate temperature is set to 200 to 600 ° C. in the microwave sputtering method or the ordinary sputtering method,
A germanium-containing gas such as a GeH ₄ gas may be newly introduced, and the introduced amount may be changed with respect to the moving direction of the substrate.

Further, in order to increase the germanium content at the crystal grain boundary, a large amount of germanium-containing gas may be flowed where each crystal grain comes into contact with a neighboring crystal grain.

In order to contain silicon in the ZnO thin film layer, the above-mentioned methods for containing germanium (1) to
This is performed in the same manner as in (5).

In the above-described method for forming the pin layer, the following gases or compounds capable of being gasified by bubbling are suitable as the source gas.

The source gas for containing silicon atoms is SiH ₄ , SiD ₄ , Si ₂ H ₆ , Si
F ₄ and Si ₂ F ₆ are suitable.

Source gases for containing fluorine atoms include F ₂ , SiF ₄ , GeF ₄ , CF ₄ , PF ₅ ,
BF ₃ is suitable.

As a source gas for containing carbon atoms, CH ₄ , CD ₄ , C ₂ H ₂ and CF ₄ are suitable.

GeH ₄ , GeD ₄ , and GeF ₄ are suitable as source gases for containing germanium atoms.

As a source gas for containing a tin atom, SnH ₄ , SnD ₄ and Sn (CH ₃ ) ₄ are suitable.

Source gases for introducing Group III atoms of the periodic table into the p layer include B ₂ H ₆ , B (CH ₃ ) ₃ ,
B (C ₂ H ₅ ) ₃ , Al (CH ₃ ) ₃ and BF ₃ are suitable.

PH ₃ , AsH ₃ , and PF ₅ are suitable as source gases for introducing Group V atoms of the periodic table into the n-layer.

A group VI atom of the periodic table is introduced into the n-layer.
As the raw material gas, H_TwoS, H _TwoSe is suitable
You.

O ₂ , CO ₂ , CO, and NO are suitable as source gases for containing oxygen atoms in the pin layer.

Source gases for containing nitrogen atoms in the pin layer include N ₂ , NO, NO ₂ , N ₂ O, NH
₃ is suitable.

Further, these source gases are converted to H ₂ , D ₂ , H
It may be appropriately diluted with a gas such as e or Ar and introduced into the deposition chamber.

When forming the above-mentioned germanium-containing ZnO thin film layer, ZnO or Z
nO: Ge is used, but Zn or Z containing no oxygen is used.
n: Ge may be used. Germanium is an oxide (GeO)
_It may be contained in the target in the form of ₂ ). When a target containing no oxygen is used, it is necessary to introduce O ₂ gas into the deposition chamber. When silicon is contained together with germanium, ZnO: GeSi, Zn: GeSi
May be. Silicon may be contained in the target in the form of an oxide (SiO ₂ ). The gas introduced to contain germanium in the ZnO thin film layer is G
eH ₄ , GeD ₄ and GeF ₄ are suitable.

Hereinafter, the configuration of the present invention will be described in detail.

Substrate The substrate may be composed of a single conductive material or insulating material, or may be a thin film layer formed on a support made of a conductive material or an insulating material.

As the conductive material, for example, NiCr,
Stainless steel, Al, Cr, Mo, Au, Nb, Ta,
Examples include metals such as V, Ti, Pt, Pb, and Sn, and alloys thereof. In order to use these materials as a support, it is desirable that the material be in the form of a sheet or a roll formed by winding a belt-like sheet around a cylindrical body.

As the insulating material, polyester, polyethylene, polycarbonate, cellulose acetate,
Examples include synthetic resins such as polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, and polyamide; glass, ceramics, and paper. In order to use these materials as a support, it is desirable that the material be in the form of a sheet or a roll formed by winding a belt-like sheet around a cylindrical body.

In the photovoltaic device of the present invention, it is preferable that a conductive thin film layer is formed on one surface of the support, and a ZnO thin film layer is formed on the surface on which the conductive thin film layer is formed.

For example, in the case of glass, NiC
r, Al, Ag, Cr, Mo, Ir, Nb, Ta, V,
Ti, Pt, Pb, In ₂ O ₃ , SnO ₂ , ITO (I
n ₂ O ₃ + SnO ₂ ) or a conductive thin film layer made of an alloy thereof, and if a synthetic resin sheet such as a polyester film is used, NiCr, Al, Ag,
Pb, Zn, Ni, Au, Cr, Mo, Ir, Nb, T
a, V, Tl, Pt, etc., or a conductive thin film layer made of an alloy thereof is formed.
Al, Ag, Cr, Mo, Ir, Nb, Ta, V, T
i, Pt, Pb, In ₂ O ₃ , SnO ₂ , ITO (In
_A conductive thin film layer made of a material such as ₂ O ₃ + SnO ₂ ) or an alloy thereof is formed. As a forming method, a vacuum evaporation method,
It is formed by a sputtering method, a screen printing method, or the like.

The surface shape of the substrate is desirably smooth or uneven with a peak height of 0.1 to 1.0 μm on average. The thickness of the substrate is appropriately determined so that a desired photovoltaic element can be formed. However, when flexibility as a photovoltaic element is required, a range in which the function as a support is sufficiently exhibited is provided. Can be made as thin as possible. However,
The thickness is usually 10 μm or more from the viewpoint of production and handling of the support, mechanical strength and the like.

As a desirable substrate form in the photovoltaic element of the present invention, Ag, Al, Cu, A
The purpose is to form a conductive thin film layer made of a metal having high reflectance in the near infrared to visible light such as lSi. This layer functions as a light reflection layer, and a suitable layer thickness of these metals as the light reflection layer is 10 nm to 5000 nm. In order to make the surface of the light reflection layer uneven (texture), the substrate temperature at the time of formation may be 200 ° C. or higher.

[0089] transmission of light of the ZnO thin film layer containing germanium formed by ZnO thin film layer above method wavelength 400nm~900n
The transmittance is 85% or more over m, and the resistivity is 3 × 10 ⁻⁴ Ω · cm or less. The germanium content takes the minimum value (Cmin) at the interface with the substrate, and p
It gradually increases in the in-layer direction, and takes the maximum value (Cmax) of the germanium content at the crystal grain boundary. About 0.1% is suitable as Cmin, and about 10% is suitable as Cmax.

The change pattern of the germanium content in the layer direction is as shown in FIG. 3-a, which linearly increases from the substrate side, as shown in FIG. 3-b, which increases exponentially from the substrate side, and FIG. Those that rapidly increase near the interface with the pin layer, such as 3-c, are suitable. When silicon is contained in the ZnO thin film layer, the change pattern of the silicon content is preferably the same as the change pattern of germanium.

P layer, n layer This layer is an important layer that affects the characteristics of the photovoltaic element, and is composed of an amorphous silicon semiconductor material, a microcrystalline silicon semiconductor material, or a polycrystalline silicon semiconductor material. Is done. Amorphous (abbreviated as a-) silicon-based semiconductor materials include a-Si, a-SiC, a-SiGe, a
-SiGeC, a-SiO, a-SiN, a-SiO
N, a-SiCON and the like. Microcrystalline (abbreviated as μc−) silicon-based semiconductor material includes μc-S
i, μc-SiC, μc-SiGe, μc-SiO, μ
c-SiGeC, μc-SiN, μc-SiON, μc
—SiOCN, and the like. Polycrystalline (abbreviated as poly-) silicon-based semiconductor material includes poly-
Si, poly-SiC, poly-SiGe, and the like.

In particular, as the layer on the light incident side, a crystalline semiconductor material with little light absorption or an amorphous semiconductor layer with a wide band gap is suitable. Specifically, a-SiC, a-
SiO, a-SiN, a-SiON, a-SiCON,
μc-Si, μc-SiC, μc-SiO, μc-Si
N, μc-SiON, μc-SiOCN, poly-S
i, poly-SiC is suitable.

The introduction amount of the valence electron controlling agent introduced to make the conductivity type p-type or n-type is 1000 ppm to 10 ppm.
% Is mentioned as a preferable range.

The contained hydrogen (H, D) and fluorine work to compensate for dangling bonds and improve the doping efficiency. Hydrogen and fluorine content is 0.1-3
0 at% is mentioned as the optimum amount. In particular, in the case of crystallinity, 0.01 to 10 at% is mentioned as an optimum amount.

The amount of oxygen and nitrogen atoms introduced is 0.1 ppm to
20%, 0.1ppm-1% when contained in trace amount
Is a preferable range.

As for the electric characteristics, the activation energy is 0.1.
Those having 2 eV or less are preferable, and those having 0.1 eV or less are optimal. The resistivity is preferably 100 Ωcm or less, and most preferably 1 Ωcm or less. Further, the layer thickness is 1 to
50 nm is preferred, and 3 to 30 nm is optimal.

In particular, when forming a crystalline semiconductor material having low light absorption or an amorphous semiconductor layer having a wide band gap as described above, the source gas is increased 2 to 100 times with a gas such as H ₂ , D ₂ or He. It is preferable to dilute and introduce relatively high MW or RF power.

In the photovoltaic device of the present invention, germanium is contained in the ZnO thin film layer, and the content gradually increases toward the pin layer. Even if a layer or an n-layer is formed, damage to the ZnO thin film layer, that is, an interface state can be reduced.

I-Layer In the photovoltaic device of the present invention, the i-layer is the most important layer for generating and transporting photoexcited carriers. A slightly p-type or slightly n-type layer can be used as the i-layer, and is made of an amorphous silicon-based semiconductor material containing hydrogen.
Si, a-SiC, a-SiGe, a-SiGeC, a
-SiSn, a-SiSnC, a-SiSnGe, a-
SiSnGeC and the like can be mentioned.

The hydrogen (H, D) and fluorine contained in the i-layer work to compensate for dangling bonds in the i-layer and improve the product of the carrier mobility and the lifetime in the i-layer. .
Further, it has a function of compensating the interface state of the interface, and has an effect of improving the photovoltaic power, the photocurrent and the photoresponsiveness of the photovoltaic element. The hydrogen and fluorine contents of the i-layer are 1 to 3
0 at% is mentioned as the optimum content.

The introduction amount of oxygen and nitrogen atoms is from 0.1 ppm to
1% is a suitable range.

The thickness of the i-layer depends on the structure (for example, pin, pinpin, nip) of the photovoltaic element and the band gap of the i-layer, and the optimum thickness is 0.05 to 1.0 μm. .

The i-layer of the present invention has a small number of tail states on the valence band side.
The density is less than meV and the density of dangling bonds by electron spin resonance (ESR) is 10 ¹⁷ / cm ³ or less.

The MWCVD method is used to form the i-layer. Preferably, RF power is simultaneously introduced in the MWPCVD method as described above.
RF power and DC power are simultaneously introduced in the PCVD method.

In the case of forming a-SiC having a wide band gap, it is preferable to dilute the source gas 2 to 100 times with a gas such as H ₂ , D ₂ , He and to introduce a relatively high MW power.

Transparent Electrodes Transparent electrodes are suitable materials of indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), and ITO (In ₂ O ₃ + SnO ₂ ). These materials contain fluorine. You may.

For forming a transparent electrode, a sputtering method and a vacuum evaporation method are most suitable.

In the case of forming by a sputtering method, a target such as a metal target or an oxide target is appropriately used in combination. When forming by a sputtering method, the substrate temperature is an important factor,
00 ° C is mentioned as a preferable range. In addition, as a gas for sputtering when the transparent electrode is formed by a sputtering method, an inert gas such as an Ar gas may be used.
It is preferable to add oxygen gas (O ₂ ) to the inert gas as needed. Particularly when a metal is targeted, oxygen gas (O ₂ ) is essential. Further, when the target is sputtered by the inert gas or the like, the pressure is preferably in a range of 0.1 to 50 mTorr in order to effectively perform sputtering. The deposition rate of the transparent electrode depends on the pressure and the electric power to be introduced.
The range is 10 nm / sec.

As a deposition source suitable for forming a transparent electrode in a vacuum deposition method, metal tin, metal indium,
An indium-tin alloy is exemplified. A suitable range of the substrate temperature for forming the transparent electrode is from 25 ° C. to 600 ° C. Further, it is necessary to introduce oxygen gas (O ₂ ) and form the pressure in a range of 5 × 10 ⁻⁵ Torr to 9 × 10 ⁻⁴ Torr. By introducing oxygen in this range, the metal vaporized from the evaporation source reacts with oxygen in the gas phase to form a good transparent electrode. The preferable range of the deposition rate of the transparent electrode under the above conditions is 0.01 to 10 nm / sec. Deposition rate is 0.0
If it is less than 1 nm / sec, the productivity decreases, and
If it is larger than / sec, the film becomes coarse, and the transmittance, the electrical conductivity and the adhesion are reduced.

It is preferable that the layer thickness of the transparent electrode satisfies the conditions of the antireflection film. As a specific layer thickness, a preferable range is 50 to 500 nm.

Collector electrode In order to make more light incident on the i-layer, which is a photovoltaic layer, and to efficiently collect generated carriers at the electrode, the shape of the collector electrode (as viewed from the light incident direction) , And material are important. Usually, the shape of the current collecting electrode is a comb shape, and the line width, the number of lines, and the like are as follows:
And the size, the material of the collecting electrode, and the like. The line width is usually about 0.1 mm to 5 mm. The materials of the current collecting electrodes include Fe, Cr, Ni, Au, Ti, Pd,
Ag, Al, Cu, AlSi, C (graphite), etc. are used, and Ag, Cu, Al, C
Metals such as r and C or alloys thereof are suitable.
The layer structure of the collecting electrode may be composed of a single layer, or may be composed of a plurality of layers.

It is desirable to form these metals by a vacuum deposition method, a sputtering method, a plating method, a printing method, or the like.

In the case of forming by a vacuum evaporation method, a mask in the shape of a current collecting electrode is brought into close contact with the transparent electrode, and a desired metal evaporation source is evaporated in a vacuum with an electron beam or resistance heating.
A collector electrode having a desired shape is formed on the transparent electrode.

In the case of forming by a sputtering method, a mask having a shape of a collecting electrode is brought into close contact with the transparent electrode, Ar gas is introduced into a vacuum, DC power is applied to a desired metal sputtering target, and glow discharge is performed. By causing this, the metal is sputtered to form a current collecting electrode having a desired shape on the transparent electrode.

When forming by a printing method, an Ag paste, an Al paste, or a carbon paste is printed by a screen printing machine.

The layer thickness of these metals is 10 nm to
A suitable layer thickness is 0.5 mm.

[0117]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the photovoltaic element of the present invention will be described in detail by manufacturing a solar cell and a photodiode made of a non-single-crystal silicon-based semiconductor material, but the present invention is not limited thereto.

Example 1 A solar cell having the structure shown in FIG. 1 was manufactured using the deposition apparatus shown in FIG.

A source gas supply device (not shown) is connected to the deposition device of FIG. 2 through a gas introduction pipe. All raw material gas cylinders have been purified to ultra-high purity.
₄ gas cylinder, SiF ₄ gas cylinder, CH ₄ gas cylinder, GeH ₄ gas cylinder, SnH ₄ gas cylinder, PH ₃
/ H ₂ (dilution: 100 ppm) gas cylinder, B ₂ H ₆
/ H ₂ (dilution: 100 ppm) gas cylinder, H ₂ gas cylinder, and Ar gas cylinder were connected. The target is Ag
And ZnO: Ge (1%), each of which can be switched in vacuum to perform sputtering. An RF power supply was used as a bias power supply.

First, a base was produced. 0.5m thick
A 50 × 50 mm ² stainless steel plate was subjected to ultrasonic cleaning with acetone and isopropanol and dried with hot air. A DC power supply was connected as a sputtering power supply, and an Ag light reflecting layer was formed by a DC magnetron sputtering method. The stainless plate was brought into close contact with the heater of FIG. 2, and the deposition chamber was evacuated from the exhaust port 220 to which the oil diffusion pump was connected.
When the pressure reaches 1 × 10 ^-6 Torr, Ar gas is supplied for 50 seconds.
The pressure was adjusted to 7 mTorr by a conductance valve. When the substrate temperature reached 150 ° C., an electric current was passed through the toroidal coil, and a DC power of 400 V was applied from a sputtering power supply to generate Ar plasma. Open the target shutter and the base shutter,
When a 0.3 μm-thick Ag light reflecting layer was formed on the surface of the stainless steel plate, the two shutters were closed, the plasma was extinguished, and the production of the base was completed.

Next, a ZnO thin film layer whose germanium content changes in the layer thickness direction was formed by the formation method (1).
The target electrode was switched to an RF power source, Ar gas was introduced at 50 sccm into the deposition chamber, the substrate temperature was 350 ° C., the pressure was 5 mTorr, and the RF power was 300 W from the sputtering power source.
Was applied to the target electrode to generate Ar plasma.
The target shutter and the base shutter were opened. RF
When the power was monotonically increased with time to form a 0.6 μm-thick germanium-containing ZnO thin film layer on the surface of the Ag light reflecting layer, the two shutters were closed to extinguish the plasma.

Next, an n-layer, an i-layer, and a p-layer were sequentially formed on the ZnO thin film layer. The n-layer made of a-Si and the i-layer made of a-Si were formed by RFPCVD, and the p-layer made of a-SiC was formed by MWPCVD.

To form an n-layer made of a-Si, H
₂ gas was introduced at 300 sccm, and the pressure in the deposition chamber was 1.
At 0 Torr, when the substrate temperature was stabilized at 250 ° C.,
SiH ₄ gas 2 sccm, PH ₃ / H ₂ gas 200 sc
cm, H ₂ gas 100 sccm was introduced, and the pressure in the deposition chamber was adjusted to 1.0 Torr. The power of the RF power source was set to 5 W, RF power was applied to the bias electrode, plasma was generated, the substrate shutter was opened, and Zn
The formation of the n-layer was started on the O thin film layer. When the n-layer having a thickness of 20 nm was formed, the shutter was closed, the RF power was turned off, the plasma was extinguished, and the formation of the n-layer was completed. Stop the flow of SiH ₄ gas and PH ₃ / H ₂ gas into the deposition chamber,
After continuously flowing H ₂ gas into the deposition chamber for 5 minutes, the inflow of H ₂ gas was stopped, and the deposition chamber and the inside of the gas pipe were 1 × 10 2
^The chamber was evacuated to ^-5 Torr.

To form an i-layer made of a-Si, H
₂ gas is introduced at 500 sccm and the pressure is 1.5 Torr
r, The substrate temperature was set to 250 ° C. When the substrate temperature is stabilized, SiH ₄ gas is introduced, and SiH ₄
Gas flow rate is 50 sccm, H ₂ gas flow rate is 500 scc
m and the pressure in the deposition chamber were adjusted to 1.5 Torr. Next, the power of the RF power source was set to 50 W, applied to the bias electrode to generate plasma, the base shutter was opened, the formation of the i-layer on the n-layer was started, and the layer thickness was 250 nm.
When the i-layer was formed, the shutter was closed, the RF power was turned off, the plasma was extinguished, and the formation of the i-layer was completed.
SiH ₄ stop the flow of gas, 5 minutes, after which continued to flow H ₂ gas, stopping the inflow of the H ₂ gas was evacuated deposition chamber and the gas in the pipe up to 1 × 10 ^-5 Torr.

To form a p-layer made of a-SiC,
H ₂ gas was introduced at 500 sccm, the pressure in the deposition chamber was set to 0.02 Torr, and the substrate temperature was set to 200 ° C. When the substrate temperature becomes stable, SiH ₄ gas, C
H ₄ gas and B ₂ H ₆ / H ₂ gas were introduced. At this time,
SiH ₄ gas flow rate is 10 sccm, CH ₄ gas flow rate is 2
sccm, H ₂ gas flow rate is 100 sccm, B ₂ H ₆ /
H ₂ gas flow rate 500 sccm, pressure 0.02 Torr
r was adjusted. Then, the power of the MW power supply is reduced by 5
Set to 00W, introduce MW power through the dielectric window,
Plasma is generated, the base shutter is opened, the formation of a p-layer on the i-layer is started, and when the p-layer having a thickness of 10 nm is formed, the shutter is closed, the MW power is turned off, the plasma is extinguished, and the p-layer Finished forming. SiH ₄ gas, CH
Stop the inflow of ₄ gases, B ₂ H ₆ / H ₂ gas, H
After the continuous flow of the _two gases, the flow of the H ₂ gas was stopped, and the inside of the deposition chamber and the gas pipe were evacuated to 1 × 10 ⁻⁵ Torr, and the deposition chamber was leaked.

Next, a transparent electrode having a thickness of 7 was formed on the p-layer.
0 nm of ITO was vacuum deposited by a resistance heating vacuum deposition method.
Next, a mask having a comb-shaped hole is placed on the transparent electrode, and Cr
(40 nm) / Ag (1000 nm) / Cr (40 n
m) was vacuum-deposited by an electron beam vacuum deposition method.

Thus, the fabrication of the solar cell has been completed. This solar cell will be referred to as (SC Ex. 1).

Comparative Example 1-1 Example 1 was repeated except that the RF power was kept constant over time when the ZnO thin film layer was formed.
Under the same conditions as above, a solar cell (SC ratio 1-1) was produced.

(Comparative Example 1-2) A solar cell (SC ratio 1-2) was fabricated under the same conditions as in Example 1 except that ZnO containing no germanium was used as a target when forming a ZnO thin film layer. did.

(Comparative Example 1-3) A solar cell (SC ratio 1-3) was manufactured under the same conditions as in Example 1 except that the temperature of the substrate was 80 ° C when forming the ZnO thin film layer. Solar cells (SC actual 1) and (SC ratio 1-1), (SC ratio 1-
2) and (SC ratio 1-3) were prepared in six pieces each, and the initial photoelectric conversion efficiency (photoelectromotive force / incident light power), high-temperature vibration deterioration, high-temperature light deterioration, and high-temperature vibration deterioration when bias voltage was applied, High temperature light degradation was measured.

[0131] The initial photoelectric conversion efficiency was as follows.
With AM-1.5 (100 mW / cm ^Two) Installed under light irradiation
And obtained by measuring V-1 characteristics.

The measurement of high-temperature vibration deterioration is performed by measuring the initial photoelectric conversion efficiency of a solar cell at a humidity of 50% and a temperature of 70%.
Installed in a dark place at ℃, vibration frequency 60Hz and amplitude 0.1m
The rate of decrease in photoelectric conversion efficiency under AM-1.5 light irradiation after 500 hours of vibration of m was applied (photoelectric conversion efficiency after high-temperature vibration degradation test / initial photoelectric conversion efficiency).

The high-temperature light deterioration was measured by measuring the initial photoelectric conversion efficiency of a solar cell at a humidity of 50% and a temperature of 70%.
C. environment, and the rate of decrease in photoelectric conversion efficiency under AM-1.5 light irradiation after 500 hours of AM-1.5 light irradiation (photoelectric conversion efficiency after high-temperature light deterioration test / initial photoelectric conversion) Efficiency).

As a result of the measurement, (SC actual 1)
Ratio 1-1), (SC ratio 1-2), (SC ratio 1-3), initial photoelectric conversion efficiency, reduction rate of photoelectric conversion efficiency after high-temperature light deterioration, and reduction of photoelectric conversion efficiency after high-temperature vibration deterioration The rates were as follows: These differences were mainly caused by the difference in open circuit voltage.

Initial Photoelectric Conversion Efficiency High Temperature Vibration Degradation Thermal Shock Light Degradation (SC Ex. 1) 1.00 × 1.00 × 1.00 × (SC Comp. 1-1) 0.94 × 0.91 × 0.93 × (SC ratio 1-2) 0.93 times 0.90 times 0.92 times (SC ratio 1-3) 0.92 times 0.90 times 0.91 times First, the surface of the solar cell was observed with an electron microscope. However,
In (SC Ex. 1), (SC Comp. 1-1), and (SC Comp. 1-2), the surface is uneven (texture) as shown in FIG. 1, and the surface unevenness was examined using a surface roughness meter. However, it was found that the average peak height was about 0.13 μm.
The surface irregularities (SC ratio 1-3) were 0.05 μm or less.

Next, samples of the ZnO thin film layer used for the four solar cells were prepared, and the crystallinity was evaluated using an X-ray diffractometer. (SC Ex. 1), (SC ratio 1-1), (SC ratio 1-1) Although the composition has c-axis orientation in the ratio 1-2), the (SC ratio 1-
In 3), it was found that it did not have crystallinity.

Next, the change of the germanium content in the layer thickness direction of the fabricated (SC Ex. 1) was determined by SIMS, and as shown in FIG. It was found that the value varied depending on the RF power of the sputtering power supply.

In (SC ratio 1-1), there was no change in the layer thickness direction. In (SC ratio 1-2), germanium was not detected, and in (SC ratio 1-3), the same as (SC actual 1). A change was obtained.

As described above, the solar cell (SC Ex. 1) of the present invention is different from the conventional solar cell (SC ratio 1-1) and (SC ratio 1).
-2) and (SC ratio 1-3).

Example 2 A solar cell having the configuration shown in FIG. 1 in which the c-axis was substantially perpendicular to the substrate and the germanium content was large at the crystal grain boundaries was produced. In forming the Ag light reflecting layer in Example 1, the substrate temperature was set to 350 ° C. A solar cell (SC Ex. 2) was produced in the same manner as in Example 1, except that the RF power of the sputter power supply when forming the ZnO thin film was sharply increased immediately before the contact of each crystal grain.

When the same measurement as in Example 1 was carried out, the deterioration in vibration and the deterioration in light were almost the same, but the solar cell of (SC Ex. 2) was more excellent in initial photoelectric conversion than (SC Ex. 1). It has been found to be efficient. This is because the surface irregularities were optimized and the short-circuit current was improved.

(Comparative Example 2-1) A solar cell was manufactured in the same manner as in Example 2 except that a target not containing germanium was used when forming the ZnO thin film layer.

(Comparative Example 2-2) A solar cell was manufactured in the same manner as in Example 2, except that the RF power of the sputtering power supply was constant when forming the ZnO thin film layer.

(Comparative Example 2-3) A solar cell (SC ratio 2-3) was manufactured in the same manner as in Example 2 except that the temperature of the substrate was changed to 80 ° C when forming the ZnO thin film layer.

First, when the surface of the solar cell was observed with an electron microscope, (SC actual 2), (SC ratio 2-1), (SC
In the ratio 2-2), the surface is uneven (texture) as shown in FIG. 1. When the surface unevenness was examined using a surface roughness meter, the average peak height was about 0.22 μm. I understood. In (SC ratio 2-3), the peak height of the unevenness was 0.06 μm or less.

When the crystallinity was examined using an X-ray diffractometer, (SC Ex. 2), (SC ratio 2-1), (SC ex.
In the ratio 2-2), it was found that there was c-axis orientation, and the c-axis was almost perpendicular to the substrate. (SC ratio 2-
3) has no orientation and no crystallinity.

Further, measurement of vibration deterioration and light deterioration was performed by applying a forward bias. Solar cells (SC actual 2) and (SC ratio 2-1) whose initial photoelectric conversion efficiency has been measured in advance,
(SC ratio 2-2) and (SC ratio 2-3) were measured at a humidity of 50% and a temperature of 25 ° C., and a forward bias voltage of 0.8 V was applied to measure vibration deterioration and light deterioration. As a result of the measurement,
(SC ratio 2-1), (SC ratio 2-2), SC ratio 2-3)
It was found that (SC Ex. 2) had better characteristics than the (SC Ex. 2).

Example 3 A photodiode (PD Ex. 3) having the layer configuration shown in FIG. 1 was manufactured. First, a base was produced. A 0.5 mm thick, 20 × 20 mm ² glass substrate is ultrasonically cleaned with acetone and isopropanol, dried with hot air, and the light reflection of 0.1 μm thick Al on a glass substrate surface at room temperature by a vacuum evaporation method. The layer was formed, and the production of the base was completed. In the same manner as in Example 1, a ZnO thin film layer, an n-layer (a-Si: P RFPCVD method), an i-layer (a-Si RFPCVD method), and a p-layer (a-SiC: B
MWPCVD method). When the ZnO thin film layer is formed, the method is carried out by the method (2), using a germanium-free target, introducing GeH ₄ as a germanium-containing gas, and changing the flow rate over time.
The germanium content was changed as in b. Then, p
On the layer, the same transparent electrode and current collecting electrode as in Example 1 were formed.

Comparative Example 3-1 A photodiode (PD ratio 3-1) was formed under the same conditions as in Example 3 except that the flow rate of the GeH ₄ gas was not changed when the ZnO thin film layer was formed.
Was prepared.

(Comparative Example 3-2) A photodiode (PD ratio 3-2) was manufactured under the same conditions as in Example 3 except that GeH ₄ gas was not introduced when forming the ZnO thin film layer.

(Comparative Example 3-3) A photodiode (PD ratio 3-3) was manufactured under the same conditions as in Example 3 except that the temperature of the substrate was 80 ° C. when forming the ZnO thin film layer.

The on / off ratio (photocurrent / dark current measurement frequency of 10 kHz when irradiating AM-1.5 light) of the manufactured photodiode was measured. This will be referred to as an initial on / off ratio. Next, the same measurement as in Example 1 was performed for the on / off ratio. As a result, the photodiode (PD actual 3) of the present invention has more excellent characteristics than the conventional photodiodes (PD ratio 3-1), (PD ratio 3-2), and (PD ratio 3-3). I understood.

Example 4 A solar cell (SC Ex. 4) of FIG. 1 having a nip-type structure in which a p-layer containing microcrystalline silicon was formed on a ZnO thin film layer was manufactured. A ZnO thin film layer was formed in the same manner as in Example 1, and a p-layer (μc-
Si: B RFPCVD method), i-layer (a-Si RFP)
CVD method), n-layer (a-SiC: P MWPCVD method)
Was formed. When the ZnO thin film layer was formed, the formation was performed by the method (3), and the germanium content was changed as shown in FIG. A transparent electrode was formed in the same manner as in Example 1.

The same measurement as in Example 1 was carried out. As a result, the solar cell (SC Ex. 4) of the present invention was similar to the conventional solar cell (SC ratio 1-1) and (SC Ex. -2),
(SC ratio 1-3) It turned out that it has the more excellent characteristic.

Example 5 A solar cell (SC Ex. 5) containing fluorine in the n-layer was manufactured. When forming the n-layer, Si
Example 2 except that F ₄ gas was newly introduced by 1 sccm.
It was produced under the same conditions as described above.

(Comparative Example 5) In forming a ZnO thin film layer,
A solar cell (SC ratio: 5) was manufactured under the same conditions as in Example 5, except that a ZnO target containing no germanium was used.

The same measurement as in Example 1 was performed, and it was found that the solar cell (SC Ex. 5) had characteristics superior to (SC ratio 5). In (SC Ex. 5), no delamination was observed, but in (SC ratio 5), delamination was slightly observed.

(Example 6) A ZnO thin film layer similar to that of Example 2 was formed on a glass substrate.
Except for flowing ₄ gas at 10 sccm, the same p
A solar cell (SC Ex. 6) in which a layer, an i-layer, and an n-layer were formed and a light reflection layer made of Al was formed on the pin layer. The light reflection layer had a thickness of 0.5 μm and was formed by electron beam vacuum evaporation.

(Comparative Example 6) When forming a ZnO thin film layer,
A solar cell (SC ratio 6) similar to that of Example 6 was produced except that the solar cell was formed using a target containing no germanium.

The same measurement as in Example 1 was performed by irradiating light from the back surface of the glass substrate.
It was found to have characteristics superior to the ratio 6).

(Example 7) Using the deposition apparatus using the roll-to-roll method of FIG. 5, the pinpi of FIG.
An n-type solar cell was produced. The substrate (support) has a length of 30
A belt-shaped stainless steel sheet having a thickness of 0 m, a width of 30 cm and a thickness of 0.1 mm was used.

FIG. 5 is a schematic view of an apparatus for continuously forming photovoltaic elements using the roll-to-roll method. This apparatus includes a substrate delivery chamber 510 and a plurality of deposition chambers 501 to 509.
And the substrate winding 511 are sequentially arranged, and connected between them by a separation passage 512. Each deposition chamber has an exhaust port, and the inside can be evacuated. Belt-like substrate 513
Is passed through the deposition chamber and the separation passage, and is taken up from the substrate feeding chamber to the substrate winding chamber. At the same time, gas can be introduced from the gas inlets of the respective deposition chambers and separation passages, and the gas can be exhausted from the respective exhaust ports to form respective layers. AlS in the deposition chamber 501
i (9: 1), and a ZnO thin film layer containing germanium in the deposition chamber 502,
508 is a pinpin layer, and deposition chamber 509 is an ITO layer.
Is formed.

In each of the deposition chambers, a halogen lamp heater 518 for heating the substrate from behind is installed, and each deposition chamber is heated to a predetermined temperature. In the deposition chamber 501, DC magnetron sputtering is performed, and A
An r gas is introduced, and AlSi (9: 1) is used as a target. In the deposition chamber 502, an RF magnetron sputtering method is performed, an Ar gas is introduced, and ZnO containing no germanium is used as a target. In the deposition chamber 509, an RF magnetron sputtering method is performed, O ₂ gas and Ar gas are introduced, and ITO (In ₂ O
₃ + SnO ₂ (5 wt%)).

Reference numeral 550 is a view of the deposition chambers 503 to 508 as viewed from above. In the deposition chambers 503 and 508, an MWPCVD method is used. In the deposition chambers 504 and 507, a biased MWPCV is applied.
In the D method and the deposition chambers 505 and 506, the RFPCVD method can be performed. Each deposition chamber has an inlet 51 for the source gas.
4 and an exhaust port 515, an RF electrode 516 or a microwave applicator 517 is attached, and a material gas supply device (not shown) is connected to a material gas inlet 514. Vacuum pumps (not shown) such as oil diffusion pumps and mechanical booster pumps are provided at the exhaust port of each deposition chamber.
Is connected, and a separation passage 512 connected to the deposition chamber has an inlet 519 through which scavenging gas flows, and introduces a scavenging gas as shown in the figure. A bias electrode 531 is arranged in the deposition chambers 503 and 507, which are the i-layer deposition chambers, and an RF power supply (not shown) is connected as a power supply.

Reference numeral 540 is a view of the deposition chamber 502 viewed from the side.
GeH ₄ gas was used as a scavenging gas introduced into the separation passage between the deposition chamber 502 and the deposition chamber 503 in order to gradually change the germanium content in the layer thickness direction. By doing so, a part of the GeH ₄ gas flows into the deposition chamber 502, and more germanium is contained in the vicinity 543 of the interface with the pin layer, and gradually decreases toward the interface 541 with the Ag light reflection layer. A large change in the content is obtained.

The delivery roll 520 is provided in the substrate delivery chamber.
And a guide roller 521 for applying an appropriate tension to the substrate and keeping the substrate horizontal at all times, and a winding roller 522 and a guide roller 523 in the substrate winding chamber.

First, the above stainless sheet is wound around a delivery roll (average radius of curvature: 30 cm), set in a substrate delivery chamber, passed through each deposition chamber, and then wound around a substrate take-up roll. The entire apparatus is evacuated by a vacuum pump, the lamp heaters in each deposition chamber are turned on, and the substrate temperature in each deposition chamber is set to a predetermined temperature. When the pressure of the entire apparatus becomes 1 mTorr or less, a scavenging gas as shown in FIG. 5 is introduced from a scavenging gas inlet 519, and the substrate is taken up by a take-up roll while moving in the direction of the arrow in the figure. Each source gas flows into each deposition chamber. At this time, the flow rate of the gas flowing into each separation passage or the pressure of each deposition chamber is adjusted so that the raw material gas flowing into each deposition chamber is not diffused into another deposition chamber. Next, RF power or MW power is introduced to generate plasma, and respective layers are formed.

An AlSi light reflecting layer (substrate temperature 350 ° C., layer thickness 300 nm) is formed on a substrate in a deposition chamber 501, and a ZnO thin film layer (substrate temperature 350 ° C., layer thickness 6) is formed in a deposition chamber 502.
00 nm), an n1 layer (a-Si: P, layer thickness 20 nm) is formed in the deposition chamber 503, and an i1 layer (a-S
iGe, layer thickness 180 nm), p1 layer (μ
c-Si: B, layer thickness 10 nm), n2 layer (μc-Si: P, layer thickness 20 nm) in the deposition chamber 506, i in the deposition chamber 507
Two layers (a-Si, layer thickness 220 nm), p in the deposition chamber 508
2 layers (μc-SiC: B, layer thickness 10 nm), deposition chamber 50
9, transparent electrodes (ITO, layer thickness 75 nm) were sequentially formed.

When the winding of the substrate was completed, all the MW power, RF power, and sputtering power were turned off, the plasma was extinguished, and the inflow of the raw material gas and the scavenging gas was stopped. The entire device was leaked, and the take-up roll was taken out.

Next, a carbon paste having a layer thickness of 5 μm and a line width of 0.5 mm was printed by a screen printing method, and a silver paste having a layer thickness of 10 μm and a line width of 0.5 mm was printed thereon to form a current collecting electrode. , Roll-shaped solar cell 250 mm x 10
It was cut to a size of 0 mm.

In the above, p using the roll-to-roll method
The fabrication of the inpin type solar cell (SC Ex 7) was completed.

Comparative Example 7 The same conditions as in Example 14 were adopted except that the scavenging gas flowing in the separation passage between the deposition chambers 502 and 503 was changed to Ar gas so that germanium was not contained in the ZnO thin film layer. A solar cell (SC ratio 7) was produced.

When the same measurement as in Examples 1 and 2 was performed, it was found that the solar cell (SC Ex. 7) of the present invention had more excellent characteristics than the conventional solar cell (SC ratio 7). Do you get it.

When the crystallinity was evaluated with an X-ray diffractometer in the same manner as in Example 1, it was found that both (SC Ex. 7) and (SC ratio 7) had c-axis orientation.

In (SC Ex. 7), it was found by SIMS that the germanium content in the ZnO thin film layer changed as shown in FIG. Also, (SC ratio 7) contained no germanium.

The rolls (SC Ex 7) and (S
C ratio 7) was stored in the dark for 3 months.
In Ex. 7), no delamination was observed, but in (SC ratio 7), delamination was slightly observed.

As described above, it was proved that the effect of the photovoltaic device of the present invention was exhibited irrespective of the device configuration and device material.

[0178]

The photovoltaic device of the present invention has a ZnO / pin
It is possible to suppress the recombination of photoexcited carriers near the layer interface and the ZnO / substrate interface, improve the open-circuit voltage and the short-circuit current, and improve the photoelectric conversion efficiency.

Further, it is possible to suppress light deterioration and vibration deterioration of the photovoltaic element under a high temperature environment. Further, it is possible to suppress light deterioration, vibration deterioration, and short circuit when a bias voltage is applied to the photovoltaic element under a high temperature environment.

In a photovoltaic element in which a non-single-crystal silicon-based semiconductor layer containing microcrystalline silicon is formed on a ZnO thin film layer, the layer is not delaminated. Further, even in a photovoltaic element in which a non-single-crystal silicon-based semiconductor layer containing fluorine is formed on a ZnO thin film layer, delamination does not occur. It does not delaminate even in a rolled state.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a layer configuration of a photovoltaic element of the present invention.

FIG. 2 is a schematic diagram illustrating an example of a deposition apparatus.

FIG. 3 is a graph showing a change in germanium content in a ZnO thin film layer in a layer thickness direction.

FIG. 4 is a schematic view showing another example of the layer configuration of the photovoltaic element of the present invention.

FIG. 5 is a schematic diagram showing an example of a roll-to-roll deposition apparatus.

[Explanation of symbols]

101, 411, 421 substrate, 102, 412, 422 ZnO thin film layer, 103 pin layer, 104, 414, 424 transparent electrode, 105, 415, 425 current collecting electrode, 106, 416, 426 crystal grain boundary, 107, 417, 427 crystal grains, 200 deposition apparatus, 210 deposition chamber, 202 vacuum gauge, 203 bias power supply, 204 substrate, 205 heater, 206 waveguide, 207 conductance valve, 208 valve, 209 target electrode, 210 bias electrode, 211 gas introduction pipe , 212 applicator, 213 dielectric window, 214 sputtering power supply, 215 substrate shutter, 216 target, 217 target shutter, 219 microwave power supply, 221 toroidal coil, 413 pinpin layer, 423 pinpinp n layer, 501,502,503,504,505,506,5
07, 508, 509 deposition chamber, 510 substrate feeding chamber, 511 substrate winding chamber, 512 separation passage, 513 substrate, 514 source gas inlet, 515 exhaust port, 516 RF electrode, 517 microwave applicator, 519 scavenging gas inlet 521 guide roller, 522 take-up roll, 523 guide roller, 526 gas inlet, 527 target electrode, 528 target, 529 toroidal coil, 531 bias electrode, 541 interface, 543 interface vicinity.

Continuation of the front page (56) References JP-A-5-110125 (JP, A) JP-A-62-122011 (JP, A) JP-A-59-224181 (JP, A) JP-A-62-35680 (JP, A) , A) JP-A-59-97515 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (10)

(57) [Claims] 1. A zinc oxide thin film layer and a pin layer (p layer, i layer, n layer) made of a non-single-crystal silicon semiconductor material on a substrate.
Layers), the zinc oxide thin film layer has a surface with irregularities of 0.1 to 1.0 μm,
a c-axis orientation of the crystalline thin film, and contains a germanium content of the germanium takes a minimum value at the interface with the substrate, contact increases gradually toward the pin layer
Germanium near the grain boundaries of the zinc oxide thin film layer
A photovoltaic element characterized by containing a large amount of . 2. The method according to claim 1, wherein the zinc oxide thin film layer contains silicon, and the silicon content has a minimum value at an interface with the substrate and gradually increases toward the pin layer. Item 2. The photovoltaic element according to Item 1. 3. A zinc oxide thin film layer and a pin layer (p layer, i layer, n layer) made of a non-single-crystal silicon semiconductor material on a substrate.
Layers), the zinc oxide thin film layer has a surface with irregularities of 0.1 to 1.0 μm,
a c-axis orientation of the crystalline thin film, and contains a germanium content of the germanium takes a minimum value at the interface with the substrate, contact increases gradually toward the pin layer
The zinc oxide thin film layer contains silicon, and
A photovoltaic element characterized by containing a large amount of silicon in the vicinity of a crystal grain boundary of a zinc thin film layer . Wherein said c-axis, the photovoltaic device according to any one of claims 1 to 3, characterized in that is substantially perpendicular to the substrate surface. 5. The photovoltaic device according to claim 3 , wherein the silicon content has a minimum value at the interface with the substrate and gradually increases toward the pin layer. The p layer or n-layer 6. contact with the zinc oxide thin film layer, the photovoltaic device according to any one of claims 1 to 5, characterized by containing a microcrystalline silicon . The p layer or n-layer 7. contact with the zinc oxide thin film layer, the photovoltaic device according to any one of claims 1 to 6, characterized by containing germanium. The p layer or n layer 8. contact with the zinc oxide thin film layer, the photovoltaic device according to any one of claims 1 to 7, characterized by containing the fluorine. 9. In band-shaped substrate, wherein the substrate is a flexible photovoltaic device according to any one of claims 1-8, characterized in that can be wound into a roll. 10. takes the minimum value at the interface between the silicon content of the substrate, according to any one of claims 1 to 9, characterized in that it is gradually increased toward the pin layer Photovoltaic element.