JPH0364973A - Photovoltaic element - Google Patents

Abstract

PURPOSE:To sharply enhance an amorphous photovoltaic element in open end voltage and shortcircuit photocurrent by a method wherein a conductive type semiconductor thin film is formed of I-III-VI2 compound semiconductor. CONSTITUTION:At least one of a first and a second conductivity type semiconductor thin film, 3 and 5, is formed of I-III-VI2 compound semiconductor. A conductive I-III-VI2 compound semiconductor thin film is a wide gap semiconductor material, and it is preferable that its forbidden bandwidth is 1.8eV or above. To put it concretely, the wide gap semiconductor material concerned is compound such as CuAlS2, CuAlSe2, CuAlTe2, CuGaS2, AgAlS2, AgAlTe2, AgGaS2, AgGaSe2, AgInS2, or the like and the mixed compounds of component elements of these compounds are effectively used. The control of these compounds in conductivity type is made through impurity doping or modulation in composition, whereby they are turned into a P-type or an N-type.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to improving the performance of amorphous solar cells, and in particular to improving the efficiency of amorphous solar cells by increasing the open circuit voltage and short-circuit photocurrent. Regarding technology.

[Background technology]

Amorphous solar cells are already in practical use as low-output energy sources to power calculators and watches. However, as an energy supply source with a large output, its performance is insufficient, and various studies are being carried out with the aim of improving its performance.

The photoelectric conversion efficiency of a solar cell is expressed as the product of open circuit voltage, short circuit 'gi current, and fill factor. As a result of various studies, short-circuit photocurrent and fill factor have been dramatically improved.
However, the open circuit voltage has not been sufficiently improved.In recent years, pin-type amorphous solar cells with nine layers on the light incident side have been developed to improve the reliability of thick II cells. It is being considered. In order to improve the open-circuit voltage of this amorphous solar cell, it is necessary to improve the photoelectric properties of the p-type semiconductor thin film.In particular, it is necessary to expand the optical band gear and improve the electrical conductivity at the same time. , there were technical difficulties. The reason for this was that when the optical bandgap was expanded, the electrical conductivity decreased significantly. A microcrystalline thin film has been proposed as a material that satisfies these requirements. However, plasma CVD method and photo CVD method
Attempts have been made to form a p-type microcrystalline thin film on a transparent electrode using conventional techniques such as the D method, but as a result, the open circuit voltage of amorphous solar cells did not improve and the photoelectric conversion efficiency decreased. did not lead to improvement. In order to solve this problem, we have completed the present invention after extensive research.

[Basic idea of the invention]

At the current state of the art, a great deal of study is required to obtain a dramatic improvement in photoelectric properties using only group Ⅰ materials, and as mentioned above, there are many difficulties. We focused on the fact that the conductivity and bandgap of crystalline compound semiconductors can be controlled arbitrarily, and it is easier to obtain crystallinity than with solidified materials. By forming an amorphous photovoltaic device in which a conductivity type controlled I-m-VE group compound semiconductor thin film is applied to a conductivity type semiconductor thin film, the open end voltage and short-circuit light of the amorphous photovoltaic device can be reduced. I was able to increase the current.

[Disclosure of the invention]

The present invention includes a substrate, a first electrode, a first conductive type semiconductor thin film,
In an amorphous photovoltaic element formed by laminating in this order a substantially intrinsic amorphous semiconductor thin film, a second conductivity type semiconductor IwA, and a second electrode, the first conductivity type semiconductor thin film and the second conductivity type semiconductor thin film The present invention relates to an amorphous photovoltaic device characterized in that at least one of the conductive semiconductor thin films (hereinafter referred to as conductive semiconductor thin films) is an I m-Vlz group compound semiconductor thin film.

In the configuration of the photovoltaic device of the present invention, regarding the conductive type semiconductor thin film, specifically, when the first conductive type semiconductor thin film is a p-type semiconductor whose authentic tag is a majority carrier, the second conductive type semiconductor thin film is The thin film is an n-type semiconductor in which electrons are the majority carriers. Further, when the first conductive type semiconductor thin film is an n-type semiconductor, the second conductive type semiconductor thin film is a p-type semiconductor.

Hereinafter, the structure of the element of the present invention will be explained with reference to the drawings.

FIG. 1 shows the II rule of the photovoltaic device of the present invention. In the figure, 1 is the substrate, 2 is the first electrode, 3 is the first conductive type semiconductor thin film, and 4 is substantially Intrinsic amorphous semiconductor am
, 5 is a second conductive type semiconductor thin film, and 6 is a second electrode.

In the device of the present invention, at least one of the first conductive type semiconductor thin film 3 and the second conductive type semiconductor thin film 5 is a 1-Ul-Vlt group compound semiconductor FIII! It is characterized by:

Therefore, the conductivity type 1-m-V1g group compound semiconductor Bitl in the present invention! is a wide-gap semiconductor material, preferably having a forbidden band width of 1.8 eV or more. Specifically, CuA]S*+ CuAlSe*+
CuAITet* CuGa5t+ AgAl5z+
AgAlSez+ AgAITet+AgGa5
t, AgGa5et+Ag1nSz, etc., and mixed compounds of constituent elements of these compounds are also effectively used.

The conductivity type of these compounds is controlled not only by doping with impurities but also by modulating the composition, and can be made p-type or n-type.

Regarding the thickness of the conductive semiconductor thin film to be used, 30 to 1
The thickness of the conductive semiconductor thin film used on the light incident side is particularly suitable for a thickness of 30 to 500 Å.

Methods for forming the r-nr-vxz group semiconductor thin film of this conductivity type include, but are not particularly limited to, sputtering, vacuum evaporation, ion blating, and chemical methods using iodine. There are vapor phase diffusion methods, etc.
From the viewpoint of practicality, sputtering is preferred.

Substantially intrinsic (hereinafter abbreviated as i-type) semiconductor thin film is hydrogenated silicon\US, hydrogenated silicon germane thin film,
Hydrogenated silicon carbon TRM, etc., and forms the photoactive region of an amorphous solar cell. These substantially intrinsic semiconductor S films are appropriately selected from compounds having silicon in the molecule, compounds having germanium in the molecule such as germane and silylgermane, and hydrocarbon gases depending on the desired semiconductor thin film. Plasma CVD for raw material gas
(Chemical Vapor Deposition) method or optical CVD (Chemical Vapor Deposition) method. The combined use of conventional techniques in forming an i-type semiconductor thin film, such as diluting the raw material gas with hydrogen, helium, etc., or adding a very small amount of diborane to the raw material gas, will not impede the effects of the present invention. It's not a thing. The forming conditions are a forming temperature of 150 to 400°C, preferably 175 to 350°C, and a forming pressure of 1 to 5 Torr, preferably 0.03 to 1.5 Torr. The thickness of the i-type semiconductor thin film is appropriately determined depending on the use of the solar cell, and is not a limiting condition of the present invention. In order to experience the effects of the present invention, it is sufficient to have 1,000 to 1000 participants.

Next, in the photovoltaic device of the present invention, at least one conductive type semiconductor thin film has I-III-Vl! Apply group compound semiconductor thin film. Specifically, when the conductivity type of the thin film is P type, the other conductivity type semiconductor thin film is n
It shows the nature of the n-type microcrystal all! Ya n
A type of amorphous thin film or the like can be effectively used. Specifically, n-type microcrystalline silicon thin films, carbon-containing microcrystalline silicon thin films, microcrystalline silicon carbide thin films, amorphous silicon thin films, amorphous silicon carbon thin films, amorphous silicon germane thin films, etc. can be effectively used. These n-type semiconductor thin films are made using raw materials that are appropriately selected depending on the desired semiconductor thin film from compounds having silicon in the molecule, compounds having germanium in the molecule such as germane and silylgermane, and hydrocarbon gases. Compounds from group II of the periodic table, such as phosphine and arsine, and hydrogen are mixed and plasma CVD (
It is easily formed by applying a chemical vapor deposition (chemical vapor deposition) method or a photo CVD (chemical vapor deposition) method. Furthermore, diluting the raw material gas with an inert gas such as helium or argon does not impede the effects of the present invention.The formation conditions include a formation temperature of 150 to 400°C, preferably 175 to 350°C. C, and the forming pressure is 0.01-5
Torr, preferably 0.03 to 1.5 Torr. The thickness of the n-type semiconductor thin film is sufficient for 200 to 500 people.

In forming the amorphous photovoltaic device of the present invention, preferred raw material gases to be used will be explained by giving more specific examples. For compounds with silicon in the molecule,
Hydrogenated silicones such as monosilane, disilane, and trisilane; Hydrogenated silicones substituted with alkyl groups such as monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, ethylsilane, and diethylsilane: vinylsilane, divinylsilane, trivinylsilane, vinyldisilane, divinyl Hydrogenated silicones that have radically polymerizable unsaturated hydrocarbon groups in their molecules such as disilane, propenylsilane, and ethynylsilane; effective use of fluorinated silicones in which some or all of the hydrogen in these hydrogenated silicones has been replaced with fluorine. be able to.

As specific examples of hydrocarbon gases, hydrocarbon gases such as methane, ethane, propane, ethylene, propylene, and acetylene are useful. These hydrocarbon gases are conveniently used when changing the optical band gap in forming carbon-containing microcrystalline silicon thin films, microcrystalline silicon carbide ms, and the like. For this purpose, silicon hydrides substituted with alkyl groups, silicon hydrides having a radically polymerizable unsaturated hydrocarbon group in the molecule, and silicon hydrides in which some or all of the hydrogens in these silicon hydrides are substituted with fluorine are used. Materials such as silicon oxide are also useful.

Regarding the substrate, the first electrode, the second electrode, etc., there are no particular limitations; conventionally used glass substrate materials such as soda lime glass, borosilicate glass, and quartz glass are useful as the substrate; , metals and plastics can also be used as substrate materials. As for plastic materials, materials that can withstand temperatures of 100° C. or higher can be used more effectively. One or both of the first and second electrodes must be translucent in order to allow sunlight to enter, but there are no other restrictions. Specifically, metal oxides such as tin oxide, indium oxide, and zinc oxide, translucent metals, and the like can be effectively used. In addition, aluminum,
An appropriate material can be selected from metal oxides such as chromium, nickel-chromium, silver, gold, and platinum, and metal oxides such as tin oxide, indium oxide, and zinc oxide.

Hereinafter, embodiments of the present invention will be described with reference to Examples.

[Example 1] As a forming apparatus for a photovoltaic element, a plasma CVD method,
A film forming apparatus to which sputtering method and photo-CVD method can be applied was used. The element configuration is as shown in FIG.

A glass substrate 13 coated with a tin oxide film 7 having a thickness of 1 μm was placed in a film forming apparatus. As the first conductive type semiconductor thin film 8, p-type CuAl5ea was first formed. A CuAISeg sintered body to which Al was added in excess of 5 mol% from the stoichiometric ratio was used as a sputtering target, and the sputtering conditions were a pressure of 10 mtorr and an Ar gas flow rate of 10 mtorr.
105c, hydrogen selenide 2sec, substrate temperature 300
℃ and high frequency power of 50 W was used. After forming 200 layers for a film formation time of 100 seconds, the substrate was transferred to a substantially intrinsic semiconductor thin film forming chamber where it was heated at 300°C in a hydrogen and hydrogen selenide mixed gas atmosphere. , monosilane was introduced, the pressure was 0.05↑orr, and the forming temperature was 240°C.
An amorphous silicon thin film 9 was formed to a thickness of approximately 7,000 wafers by plasma CVD under these conditions. plasma CV
Method D utilized 13.56 MHz RF discharge. At this time, the RF power was 1ON. After forming the substantially intrinsic semiconductor thin film 9, the substrate was transferred to an n-type semiconductor thin film forming chamber. Raw material gases consisting of monosilane/phosphine/hydrogen were introduced such that their respective flow rates were in the ratio of 1010.01/100. The n-type semiconductor thin film 10 was formed to a thickness of 500 nm by plasma CVD under conditions of a pressure of 0.2 Torr and a formation temperature of 240°C. plasma CV
Method D utilized 13.5Ei MHz RF discharge. At this time, the RF power was 50-.Then, it was taken out from the thin film forming apparatus, and an aluminum metal electrode 11 as a second electrode was formed to produce a photovoltaic element.

[Comparative Example 1] In Example 1, I
Instead of III-VI group compound semiconductor thin film,
A p-type mechanically crystalline silicon thin film was formed. The layer structure of the device is shown in FIG. An amorphous photovoltaic device was formed using the same steps as in Example 1 except for the ice layer. Formation of p-type machine crystal thin film is as follows:
110.05/100 ratio of monosilane/diborane/
A mixed gas of hydrogen was introduced into the tcM chamber, and the RF power was 50W5.
Discharge time 2 at a pressure of 0.1 torr and a substrate temperature of 250°C.
00 seconds, and 200 people were formed.

The performance of the amorphous photovoltaic device produced as described above was evaluated. As an evaluation, AM 1.5.100 mTd/d
The photovoltaic properties of the amorphous photovoltaic device were measured by irradiating it with light of As a result, an improvement of 20% in open-circuit voltage and 15% in short-circuit photocurrent was observed. as a result,
A 35% improvement in photoelectric conversion efficiency was obtained.

〔Effect of the invention〕

As is clear from the above Examples and Comparative Examples, by using an I-nI Vlt group compound semiconductor for the conductive semiconductor thin film, the performance of the amorphous photovoltaic element that has been put into practical use with the prior art can be improved, especially when the open circuit is used. The present invention significantly improves the terminal voltage and short-circuit photocurrent, that is, the present invention greatly contributes to improving the photoelectric conversion efficiency of amorphous photovoltaic elements at a practical level. In this way, the present invention can provide a technology that enables the high conversion efficiency required for power solar cells, and is useful for the energy industry.
I have to say that this is an extremely useful invention.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the configuration of a photovoltaic device of the present invention. FIG. 2 is a schematic diagram showing the structure of an element according to an embodiment of the present invention. FIG. 3 is a schematic diagram showing an example of an amorphous photovoltaic device according to the prior art. In the figure, 1...--1 substrate, 2 first electrode, 3
・−・−・・・−・First conductivity type semiconductor thin film, 4
Substantially intrinsic amorphous semiconductor thin film, 5 second conductivity type semiconductor thin film, 6 second electrode, 7...
-・tin oxide, 8 p-type CuAl5el, 9
i-type amorphous silicon thin film, 10-...--
・・N-type microcrystalline silicon thin film, 11−・−・・−・−・
Aluminum metal electrodes, 12...p-type mechanical crystalline silicon thin films, 13-... glass substrates are shown.

Claims (1)

[Claims] (1) An amorphous material formed by laminating a substrate, a first electrode, a first conductivity type semiconductor thin film, a substantially intrinsic amorphous semiconductor thin film, a second conductivity type semiconductor thin film, and a second electrode in this order. In the photovoltaic device, at least one of the first conductive type semiconductor thin film and the second conductive type semiconductor thin film is I-III-V.
An amorphous photovoltaic device characterized by being a Group I_2 compound semiconductor thin film.