JPH0276267A - Amorphous solar cell - Google Patents

Abstract

PURPOSE:To achieve a high open-edge voltage and improve photoelectric conversion efficiency by providing an n-type fine crystal thin film between a transparent electrode and a p-type semiconductor thin film. CONSTITUTION:In a photoelectric conversion element formed by laminating a light transmission type substrate 1, a transparent electrode 2, a p-type semiconductor thin film 4, an i-type semiconductor thin film 5, an n-type semiconductor thin film 6, and a rear-surface electrode 7 in this order, a highly conductive n-type semiconductor thin film 3 is placed between the transparent electrode 2 and the p-type semiconductor thin film 4. An n-type fine crystal silicon thin film, a fine crystal silicon carbide thin film, etc., can be effectively used as an n-type fine crystal thin film. These n-type fine crystal silicon thin films can be easily formed by the plasma CVD method using a compound containing silicon within the molecule, a V-family compound in the periodic table such as phospine, arsine, etc., and a mixed gas consisting of hydrogen as a raw material gas. Thus, it achieves a cell where the open-edge voltage is fully enhanced and the photoelectric conversion efficiency is high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to improving the performance of an amorphous solar cell, and in particular to a technique for increasing the efficiency of an amorphous solar cell by increasing the open circuit voltage.

[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.

Therefore, the photoelectric conversion efficiency of a solar cell is expressed as the product of open circuit voltage, short circuit current, and fill factor. As a result of various studies, the currently achieved values for short-circuit current and fill factor are approaching the theoretically expected values, but the open-circuit voltage has not yet been improved, and the reliability of solar cells has not yet been improved. In order to improve this, in recent years, pin-type amorphous solar cells with two layers on the light incident side have been studied. 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, and in particular, it is necessary to simultaneously widen its optical band gap and improve its electrical conductivity. This was not possible due to technical difficulties. The reason for this is that when the optical bandgap is expanded, the electrical conductivity decreases in terms of -S.

A microcrystalline thin film has been proposed as a material that satisfies these requirements, but we believe that a P-type microcrystalline thin film should be formed on a transparent electrode using conventional techniques such as plasma CVD and photoCVD. Although we attempted to form a thin film under different deposition conditions, the open circuit voltage of the amorphous solar cell did not substantially improve.
It was found that this did not lead to improvement in photoelectric conversion efficiency.

In this way, is it extremely difficult to form a p-type microcrystalline thin film on a transparent electrode with a film thickness of 50 to 500 nm, which is sufficient for an amorphous solar cell? Although it is not clear at the current state of the art whether the transparent electrode was damaged due to the formation conditions of the machine crystalline thin film and did not lead to improved performance, in any case, the performance improvement using the p-type machined crystalline thin film was sufficiently achieved. It has not been done.

[Basic idea of the invention]

In order to solve this problem, the present inventors have made intensive studies and found that an n-type microcrystalline thin film is easily formed by scratching, is easily formed on a transparent electrode, and that a microcrystalline thin film Since the p-n junction does not exhibit rectification, it was conceived that it could be used as a conductive crystalline material.Based on this idea, after forming an n-type microcrystalline thin film on a transparent electrode, The inventors have discovered that it is possible to form an amorphous solar cell with a high open circuit voltage by forming an amorphous solar cell by forming a microcrystalline thin film of the same type, and have completed the present invention.

[Disclosure of the invention]

That is, the present invention provides an amorphous solar cell formed by laminating a transparent substrate, a transparent electrode, a p-type semiconductor thin film, an i-type semiconductor thin film, an n-type semiconductor thin film, and an electrode in this order. This is an amorphous solar cell in which an n-type microcrystalline thin film is interposed between semiconductor thin films.

Thereby, a battery having a sufficiently increased open end voltage and high photoelectric conversion efficiency is provided.

The present invention will be explained in detail below.

The structure of the photoelectric conversion element of the present invention is schematically shown below.
FIG.

That is, a transparent substrate 1, a transparent electrode 2, a p-type semiconductor thin film 4, an n-type semiconductor thin film 5, an n-type semiconductor thin film 6, and a pole 7 on the back surface.
In a photoelectric conversion element formed by laminating layers in this order, an n-type microcrystalline thin film is interposed between the transparent electrode 2 and the P-type semiconductor thin film 4.

Note that FIG. 2 shows the configuration of a conventional photoelectric conversion element, which consists of a simple transparent substrate 1, a transparent electrode 2, a p-type semiconductor thin film 4, an n-type semiconductor thin film 3, and no intervening highly conductive n-type semiconductor thin film 3. A photoelectric conversion element is shown in which a type semiconductor thin film 5, an n-type semiconductor thin film 6, and a back electrode 7 are laminated in this order.

The most characteristic feature of the present invention is that the transparent electrode 2 and p
The n-type microcrystalline thin film 3 is interposed between the n-type semiconductor thin films 4.
A type of microcrystalline silicon thin film, a carbon-containing microcrystalline silicon thin film, a microcrystalline silicon carbide thin film, etc. can be effectively used.

These n-type microcrystalline thin films are produced by plasma CVD (chemical vapor deposition) using a mixed gas consisting of a compound containing silicon in its molecules, a compound in group Ⅰ of the periodic table such as phosphine or arsine, and hydrogen as a raw material gas. ) Law and optical CVD
(chemical vapor deposition) method. The present invention does not preclude adding hydrocarbon gas or an inert gas such as helium or argon to these mixed gases as necessary. The formation conditions include a formation temperature of 150 to 400°C, preferably 175 to 30°C.
0°C1, particularly preferably 200 to 250°C,
Forming pressure is 0.01 to 5 Torr, preferably 0.0
3-1.5 Torr.

Particularly preferably 0.035 to 1. Performed at Q Torr.

In the present invention, the required thickness of the n-type microcrystalline thin film is 5 Å or more, and it is sufficient for at most 100 people. Preferably 10 to 50 people
It's a person. If less than 5 people are involved, the effect of thin film formation cannot be achieved, and conversely, if more than 100 people are involved, the effect of improving the open circuit voltage will be canceled out by the reduction in current, making it impossible to achieve the effects of the invention. , with current technology, 100
It is difficult to provide sufficient direct evidence of the formation of an n-type semiconductor thin film with a thickness of Å or less. However, in the present invention, a thin film that is effective as an n-type microcrystalline thin film only needs to exhibit the properties of an n-type microcrystalline thin film when formed to a thickness of 1000 Å or more. By depositing it thickly, diffraction peaks due to silicon crystals can be observed using X-ray diffraction. If the formation conditions under which this diffraction peak appears (formation conditions for n-type microcrystalline thin film) are satisfied, the desired thickness can be obtained by calculating the film formation time corresponding to the required film thickness from the film formation rate and forming the film at a thickness of 100 Å or less. It is possible to obtain the n-type microcrystalline thin film of the present invention having the following properties. Further, such an n-type microcrystalline thin film usually has a high conductivity of 0.137 cm or more.

In the present invention, it is preferable to use a p-type microcrystalline thin film as the p-type semiconductor thin film. As the p-type microcrystalline thin film, a p-type microcrystalline silicon thin film, a carbon-containing microcrystalline silicon thin film, a microcrystalline silicon carbide thin film, etc. can be effectively used. The required thickness of the p-type mechanical crystal thin film is 50 Å or more, and at most 400 people are sufficient. Preferably 100 to 25 people
There are 0 people. If there are fewer than 50 people, the function as a T-type semiconductor thin film cannot be achieved sufficiently, and if more than 400 people are involved, the reduction in current will cancel out the improvement in open circuit voltage, and the invention will not work. effect cannot be achieved. With current technology, it is difficult to provide sufficient direct evidence of the formation of a p-type semiconductor thin film itself with a thickness of 400 Å or less. However, in the present invention, a thin film that is effective as a p-type mechanical crystal thin film is formed to a thickness of 1000 Å or more.
Any material that exhibits the properties of a p-type mechanical crystal thin film may be used. That is, by depositing the film to a thickness of 1000 Å or more, diffraction peaks due to silicon crystal can be observed using X-ray diffraction. Under the formation conditions under which this diffraction peak appears (formation conditions for p-type mechano-crystalline thin films), the desired thickness can be obtained by calculating the film formation time corresponding to the required film thickness from the film formation rate and forming the film at a thickness of 400 Å or less. It is possible to obtain a p-type mechanical crystal thin film of the present invention. In addition, such p-type mechanical crystal thin films usually have an optical bandgap of 1.
．． Even in a wide range of 9 eV or more, 0.0137c
It has a high electrical conductivity of more than m.

P-type microcrystalline thin film is a compound containing silicon in the molecule,
It is easy to perform plasma CVD (chemical vapor deposition) method or photoCVD (chemical vapor deposition) method using a mixed gas consisting of hydrogen and a compound of group Ⅰ of the periodic table, represented by diborane, as a raw material gas. is formed. The present invention does not in any way prevent hydrocarbon gas or an inert gas such as helium or argon from being added to these mixed gases as necessary.The formation conditions are such that the formation temperature is 1.
50 to 400°C, preferably 175 to 300°C, particularly preferably 200 to 250'C, and the forming pressure is 0.01 to 5 Torr, preferably 0.03 to 1.5
Torr, particularly preferably 0.035 to 1.0 Torr
It is done in rr.

In the present invention, the i-type semiconductor thin film is a hydrogenated silicon thin film, a hydrogenated silicon germane thin film, a hydrogenated silicon carbon thin film, etc., and forms a photoactive region of an amorphous solar cell. These i-type semiconductor thin films are made by using a raw material gas that is 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. Plasma CVD (chemical vapor deposition) method and optical CVD
(chemical vapor deposition) method. For example, diluting the raw material gas with hydrogen or helium, adding a very small amount of diborane to the raw material gas, etc.
The combined use of conventional techniques in forming an i-type semiconductor thin film does not impede the effects of the present invention. The forming conditions are as follows: the forming temperature is 150-400°C, preferably 175-350°C, and the forming pressure is 0.01°C.
~5 Torr, preferably 0.03-1.5 Torr
It is done in r. The thickness of the i-type semiconductor yl 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 achieve the effects of the present invention, 100
0 to 10,000 people is sufficient.

In the present invention, an n-type microcrystalline thin film or an n-type amorphous thin film is effectively used as the n-type semiconductor thin film provided in contact with the back electrode. These are n-type microcrystalline silicon thin film, carbon-containing microcrystalline silicon 1 film, and microcrystalline silicon carbide i]! membrane, amorphous silicon thin film,
An amorphous silicon carbon thin film, an amorphous silicon german thin film, etc. can be effectively used. These n-type semiconductor thin films are made of raw materials selected from compounds containing silicon in the molecule; compounds containing germanium in the molecule such as germane and silylgermane; and hydrocarbon gas, depending on the desired semiconductor Ff film. It can be easily formed by mixing compounds from group Ⅰ of the periodic table such as phosphine and arsine, and hydrogen, and applying plasma CVD (chemical vapor deposition) or photoCVD (chemical vapor deposition). It will be done. 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 35°C.
0'C, and the forming pressure is 0.01-5 Torr,
It is preferably carried out at 0.03 to 1.5 Torr. n
The thickness of the type semiconductor thin film is sufficient for 200 to 500 people.

In the present invention, the raw material gas preferably used will be explained by giving more specific examples. For compounds containing silicon in the molecule, hydrogenated silicones such as monosilane, disilane, and trisilane; monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane,
Hydrogenated silicon substituted with alkyl groups such as ethylsilane and diethylsilane; Hydrogen containing radically polymerizable unsaturated hydrocarbon groups in the molecule such as vinylsilane, divinylsilane, trimethylsilane, vinyldisilane, divinyldisilane, propenylsilane, and ethynylsilane Chemical silicon:
Silicon fluoride in which hydrogen in these silicon hydrides is partially or completely replaced with fluorine can be effectively used.

Furthermore, 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 Ill, microcrystalline silicon carbide thin films, and the like. In addition, 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 hydrogen in these silicon hydrides has been partially or completely replaced with fluorine are also used. Materials such as silicon oxide are also useful.

In the present invention, there are no particular limitations on the light-transmitting substrate, transparent electrode, back electrode, etc. As the light-transmitting substrate, conventionally used glass substrate materials such as blue plate glass, borosilicate glass, and quartz glass are useful, but metals and plastics can also be used as the substrate material.

As for plastic materials, materials that can withstand temperatures of 100° C. or more can be used more effectively. As the transparent electrode, metal oxides such as tin oxide, indium oxide, and zinc oxide, translucent metals, and the like can be effectively used. The back electrode does not necessarily have to be transparent, so aluminum, chromium, nickel-chromium,
An appropriate material can be selected from among metals such as silver, gold, and platinum, and metal oxides such as tin oxide, indium oxide, and zinc oxide.

(Example 1) Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example 1) As a solar cell forming apparatus, a film forming apparatus capable of applying a plasma CVD method and a photo-CVD method was used. An insulating glass substrate was installed in a forming apparatus capable of applying a photo-CVD method. Vacuum exhaust and raw material gas are introduced to heat the substrate, and the substrate temperature is 200°C2 reaction pressure is 0.2 To
At rr, photoCVD was performed by irradiating ultraviolet rays with a low-pressure mercury lamp.

First, the conditions for forming an n-type semiconductor thin film were determined.

In other words, the raw material gas contains 1 disilane/phosphine/hydrogen.
It was introduced at a ratio of 0.010.01/100. A film was formed by irradiation with a mercury lamp for 2 hours. The film thickness was measured and it was determined that a thin film of about 3,600 people was formed. This thin film
Linear diffraction clearly showed diffraction lines due to silicon crystals, confirming that it was an n-type microcrystalline thin film. The conductivity was 15 S/cm. Further, the average film formation rate obtained by dividing the film thickness by the film formation time was 0.5 people.

Using these film forming conditions, an n-type microcrystalline thin film applied to an amorphous solar cell was formed. A glass substrate with a transparent electrode made of tin oxide was placed in the same forming apparatus, and an n-type microcrystalline thin film was formed by 10 people at a film forming time of 20 seconds. Then, the composition of the raw material gas was changed from phosphine to diborane. The raw material gas is disilane/diborane/hydrogen at 510%.
It was introduced at a rate of 01/200. The formation rate of the p-type mechano-crystalline thin film was 0.2 people/s, the film formation time was 850 seconds, and the substrate was transferred to the 6th i-type semiconductor thin film formation chamber where the film was formed to a thickness of 170 people, and monosilane was applied. was introduced to reduce the pressure to 0.
An amorphous silicon thin film was formed by plasma CVD at a temperature of about 7,000 Torr and a formation temperature of 240'C.
Formed to the thickness of a human. Plasma CVD method is 13.56
MHz RF discharge was used. At this time, the RF power was 10-. After forming the i-type semiconductor thin film, the substrate was transferred to an n-type semiconductor thin film forming chamber. Each stream 1 contains a feedstock gas consisting of monosilane/phosphine/hydrogen with a
They were introduced at a ratio of 0.01/100. pressure 0
．． An n-type semiconductor thin film was formed to a thickness of 500 nm by plasma CVD under conditions of 2 Torr and a formation temperature of 240°C. The plasma CVD method utilized 13.56 MHz RF discharge. At this time, the RFt force was 50 mm. Then, it was taken out from the thin film forming apparatus and a metal electrode was formed thereon. The photoelectric characteristics of the amorphous silicon solar cell were measured by irradiating it with light of AMI, 100 mW/c+] using a solar simulator. As a result, the open circuit voltage becomes 0.
In addition to obtaining a very high value of 931 V, confirming the effect of the present invention, the short-circuit photocurrent was also a large value of 17.07 mA/c+fl, and the fill factor was 0.703. The conversion efficiency was extremely excellent at 11.17%.

[Comparative Example 1] Example 1 and all procedures were repeated except that in Example 1, a p-type microcrystalline thin film was directly formed on a glass substrate with a transparent electrode without intervening an n-type microcrystalline thin film. (
An amorphous silicon solar cell was formed using the same process. When the performance of the obtained solar cell was measured, it was found that the open voltage was 0.
762 V, short circuit photocurrent is also 15.20 mA/cffl
The photoelectric conversion efficiency significantly decreased to 7.66%.

[Effects of the invention and industrial applicability] As is clear from the above embodiments and comparative examples, by interposing the n-type microcrystalline thin film between the transparent electrode and the p-type semiconductor thin film, it is possible to The amorphous solar cell of the present invention having a high open-circuit voltage is formed using a photo-CVD method and a plasma CVD method that have been put into practical use. That is, the present invention greatly contributes to improving the photoelectric conversion efficiency of amorphous solar cells at a practical level. As described above, the present invention can provide a technology that enables high conversion efficiency required for power solar cells, and it must be said that it is an extremely useful invention for the energy industry.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the configuration of an amorphous solar cell according to the present invention, and FIG. 2 is a schematic diagram showing an example of the configuration of an amorphous solar cell according to the prior art. In the figure, 1-------translucent substrate, 2---m-
・--Transparent electrode, 3--111-n-type microcrystalline thin film, 4--1--p-type semiconductor thin film, 5--
. . . I-type semiconductor thin film, 6-.

Claims (1)

[Claims] (1) In an amorphous solar cell formed by laminating a transparent substrate, a transparent electrode, a p-type semiconductor thin film, an i-type semiconductor thin film, an n-type semiconductor thin film, and a back electrode in this order, the transparent electrode and the p-type semiconductor An amorphous solar cell comprising an n-type microcrystalline thin film interposed between thin films.