JPH03235375A - Amorphous solar battery - Google Patents

Abstract

PURPOSE:To enable the open end voltage to be boosted up to a high value by a method wherein an iridium oxide as a thin chemically stable p type metallic oxide film is formed on a transparent conductive oxide and then a thin p type amorphous silicon oxide film is formed. CONSTITUTION:A glass substrate with a transparent electrode 2 comprising of tin oxide is arranged in a formation device capable of forming films by the high-frequency sputtering process and after vacuumizing said device firstly to lead-in oxygen, a thin iridium oxide film 3 is formed by reactive sputtering process using high-frequency power. Next, the substrate 1 is shifted to a p type semiconductor formation chamber to form a thin p type amorphous silicon carbide film 4 and then the substrate 1 is shifted to a thin i type semiconductor film formation chamber to form a thin amorphous silicon film 5. Next, the substrate 1 is further shifted to a thin n type semiconductor film formation chamber to form a thin n type semiconductor film 6 and then a metallic electrode 7 is formed to increase the efficiency of an amorphous silicon solar battery. That is, the open end voltage and the photoelectric conversion efficiency can reach respective values of 0.912V and 11.81%.

Description

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

[Background technology]

Amorphous silicon 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 used for electric power, satisfactory performance has not yet been achieved, and various studies are being carried out with the aim of improving performance. Therefore, the photoelectric conversion efficiency of a solar cell is expressed as the product of open circuit voltage, short circuit photocurrent, and fill factor. As a result of various studies, the currently achieved values for the short-circuit photocurrent and fill factor are approaching the theoretically expected values, but the open circuit voltage has not yet been sufficiently improved. In order to do so, the photoelectric properties of the p-type semiconductor thin film had to be improved, and in particular, the technical difficulty was that it had to expand its optical bandgap and improve its electrical conductivity at the same time. The reason for this was that expanding the optical bandgap would result in a drop in electrical conductivity. As an improvement to this p-type semiconductor thin film, as we have already proposed, we have developed a p-type amorphous silicon TIM that controls the energy supplied to the raw material gas.
E (e.g., JP-A-59-161079, etc.), p-type amorphous silicon carbide thin film made from alkylsilane and silane compounds (e.g., JP-A-61-12512),
4.62-016513, etc.) and p-type amorphous silicon carbide or microcrystal-containing p Type amorphous silicon carbide m)l! (For example, Japanese Patent Application No. 10907/1983), but as a result, it cannot be said that the open circuit voltage of amorphous silicon solar cells has been improved as much as expected. Met. In this way, the p-type semiconductor FFL film can be used to form an amorphous silicon solar cell.
Is it because it is extremely difficult to form a film on a transparent electrode with film properties equivalent to those of a thick film of 1000 Å or more, which is usually evaluated for film properties, in a film thickness of 50 to 500 people? , the performance could not be improved because the transparent electrode was damaged during the formation of the n-type semiconductor thin film.
Although it is not clear at the current state of the art, it has not been possible to sufficiently improve the photoelectric conversion efficiency by simply improving the characteristics of the P-type semiconductor thin film. To solve this problem, we
Patent application No. 63-261382 and Patent application No. 63-2613
As proposed in 83, tantalum oxide or zirconium oxide, which is chemically stable and has strong bonding strength, is used between the transparent electrode and the P-type semiconductor thin film. By interposing the film, reduction of the transparent electrode is suppressed and a high open circuit voltage can be achieved. However, since these oxides are n-type, there is an n/p gap between the n-type semiconductor thin films.
It has been difficult to cause reverse bonding and to achieve both transparency and low resistance.

On the other hand, JP-A-61-96775 discloses that by providing an iridium oxide thin film as a p-type metal oxide between a transparent electrode and an n-type semiconductor thin film, both manufacturing yield and photoelectric conversion efficiency can be increased. However, since the technical idea is to suppress the decline in manufacturing yield due to poor bonding in the transparent electrode part, the film thickness of the p-type metallurgical group oxide is thick, and as a result,
The degree of improvement was slight. In other words, it was thought that the photocurrent actually decreased because the iridium oxide thin film was too thick, and that a reverse junction was formed between the p-type iridium oxide and the n-type transparent conductive film. . Therefore, the present application was completed by further studying these points, with particular emphasis on increasing the open circuit voltage.

[Basic idea of the invention]

Since the current p-type semiconductor thin film is usually formed in a reducing atmosphere, the underlying transparent conductive oxide, which is the transparent electrode, is reduced. Therefore, the reduced metal portion inhibits light transmission, resulting in a decrease in short-circuit photocurrent. Moreover, the n-type semiconductor thin film itself is more stable than expected from microcrystalization.
It has high resistance. Furthermore, since the transparent electrode has n-type characteristics, an n/p reverse junction occurs between the transparent electrode and the Pn-type semiconductor thin film, and a decrease in the diffusion potential determined from the characteristics of the p-type semiconductor fillA and the n-type semiconductor 1111 occurs. Therefore, the fill factor is low and no improvement in open-circuit voltage has been obtained. Therefore, from this perspective, we believe that it is essential to suppress the reduction of this transparent conductive oxide and the reduction of the diffusion potential. The idea was to form iridium oxide, a chemically stable p-type metal oxide thin film, on a transparent conductive oxide, and then form a p-type amorphous silicon carbide thin film to form an amorphous silicon solar cell. The present invention was completed by discovering that by manufacturing a battery, it is possible to form an amorphous silicon solar cell with a high open circuit voltage.

[Disclosure of the invention]

The present invention provides a transparent substrate, a transparent electrode, an n-type semiconductor thin film, an i
In an amorphous silicon solar cell formed by laminating a type semiconductor thin film, an n-type semiconductor thin film, and an electrode in this order, iridium oxide is interposed between the transparent electrode and the n-type semiconductor thin film, and the n-type semiconductor thin film is an amorphous silicon solar cell, which is a p-type amorphous silicon or a p-type amorphous silicon carbide thin film. A particularly preferred water side is one in which iridium oxide is formed to a thickness of 5 to 50 people.

The present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of the layer structure of an amorphous solar cell of the present invention, and FIG. 2 is a schematic diagram showing a layer structure of a conventional amorphous solar cell.

In the figure, 1------1 light-transmitting substrate, 2 transparent electrode, 3-.--1-------- iridium oxide thin film, 4
...-P-type semiconductor thin film, 5--I-type semiconductor thin film, 6--N-type semiconductor thin film, and 7-- Back electrode, respectively.

Tin oxide, which is used in transparent electrode materials, is an inexpensive material with excellent transparency and conductivity, but it is also a chemically extremely active substance used in catalysts and sensor materials, and is also an n-type material. It is a semiconductor. On the other hand, the iridium oxide in the present invention is chemically stable and has the characteristics of a p-type semiconductor with a high optical bandgap (~4 eV) and high photoconductivity despite not adding p-type impurities. It is known to have a
Proceedings of the 31st Applied Physics Conference, page 76 Lecture number 30a-8-4, March 30, 1984 - 1
March 30, 984). This iridium oxide is easily formed by sputtering deposition, electron beam deposition, or ion blating deposition using a pellet or target of metallic iridium or iridium oxide as a raw material. The present invention can also be effectively carried out by a spray method or a CVD (chemical vapor deposition) method using iridium chloride and oxygen gas, and an appropriate one can be selected from these methods according to the purpose. . That is, the optimal method is selected by considering the melting point, reactivity with oxygen, decomposition rate, etc. of the metal, metal oxide, or metal compound. In the present invention, sputtering and electron beam evaporation are often employed as effective methods. The forming conditions include a forming temperature of room temperature to 600'', a C1 deposition rate of 1 to 50 people/min, and a pressure of 0.000001 to 1.0
It is done in Torr. Vapor deposition while applying a bias voltage to the substrate does not impede the effects of the present invention in any way.

In the present invention, the required thickness of the iridium oxide is 5 Å or more, and a thickness of at most 50 is sufficient. Preferably, the number is 10 to 30 people. If the thickness exceeds this value, for example, if more than 100 people are formed, the effect of improving the open circuit voltage will be canceled out by the decrease in fill factor, and the effect of the invention will not be achieved. The conductivity of the iridium oxide thin film is preferably 0.00001
37 cm, particularly preferably 0.01 S/cm,
More preferably IO3/cm, but the thickness is 50 Å
Even a fairly low conductivity does not impede the present invention if it is below. Of course, if the film thickness is too thin, the effects of the present invention cannot be achieved. Control of the required thickness is achieved by, for example, actually measuring the average deposition rate of about 1,000 to 2,000 people when forming an iridium oxide thin film, and controlling the film thickness using this rate and deposition time. .

As the p-type semiconductor thin film, it is preferable to use a p-type amorphous silicon thin film or a p-type amorphous silicon carbide thin film. As a forming means, a plasma CVD (chemical vapor deposition) method or a photo CVD (chemical vapor deposition) method is suitably used. As a raw material, as a silicon compound,
Silane, silane, and trisilane are used. Also, p
Preferred materials for imparting conductivity to the mold include diporan, trimethylboron, and boron trifluoride. Further, as the carbon-containing compound, saturated hydrocarbons such as methane and ethane, unsaturated hydrocarbons such as ethylene and acetylene, and alkylsilanes such as monomethylsilane and dimethylsilane are used. Diluting these mixed gases with an inert gas such as helium or argon or hydrogen as necessary does not impede the effects of the present invention. As for the formation conditions, the film thickness is 20 to 500, particularly preferably 5.
0-200 people, forming temperature 150-400'C
2 Preferably 175-300°C1 Particularly preferably 20
0~250'C, forming pressure is 0.01~5T
orr, preferably 0.03 to 1.5 Torr, particularly preferably 0.035 to 1. This is done in OTorr.

The i-type semiconductor thin film is a hydrogenated silicon compound, hydrogenated silicon germane Fi I! , hydrogenated silicon carbon thin films, etc., which form the photoactive region of an amorphous silicon solar cell. These l-type semiconductor thin films are made using a raw material gas that is appropriately selected depending on the desired semiconductor thin film, from compounds containing silicon in the molecule, compounds that grow germanium in the molecule such as germane and silylgermane, and hydrocarbon gases. , plasma CVD (chemical vapor deposition) method and photoCVD
(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 a forming temperature of 150 to 400°C, preferably 175 to 350°C, and a forming pressure of 0.01 to 350°C.
5 Torr, preferably 0.03-1.5 Torr
It will be held in 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 achieve the effects of the present invention, too-
Toooo people are enough.

As the n-type semiconductor thin film, an n-type microcrystalline fill# or an n-type amorphous thin film is effectively used. As these, an n-type microcrystalline silicon thin film, a carbon-containing microcrystalline silicon thin film, a microcrystalline silicon carbide thin film, an amorphous silicon thin film, an amorphous silicon carbon thin film, an amorphous silicon germane thin film, 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. By mixing compounds from group Ⅰ of the periodic table such as phosphine and arsine, and hydrogen, the plasma CVD (chemical vapor deposition) method and photo-C
It is easily formed by applying the VD (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 are such that the formation temperature is 1.
50-400″C1, preferably 175-350°C, forming pressure 0.01-5 Torr, preferably 0
．． It is carried out at 0.03 to 1.5 Torr. The thickness of the n-type semiconductor thin film is sufficient for 200 to 500 people.

In the present invention, the preferred raw material gas to be used will be described with reference to the water side in more detail. For compounds having silicon in the molecule, hydrogenated silicon such as monosilane, disilane, trisilane, monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane,
Hydrogenated silicone substituted with alkyl groups such as ethylsilane and diethylsilane, hydrogen containing radically polymerizable unsaturated hydrocarbon groups in the molecule such as vinylsilane, divinylsilane, trivinylsilane, vinyldisilane, divinyldisilane, propenylsilane, and ethynylsilane. Silicon hydrides and silicon fluorides in which hydrogen in these silicon hydrides is partially or completely replaced with fluorine can be effectively used.

Hydrocarbon gases such as methane, ethane, propane, ethylene, propylene, and acetylene are useful as specific water-side hydrocarbon gases. These hydrocarbon gases are conveniently used to change the optical bandgap in forming carbon-containing microcrystalline silicon thin films, 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.

Regarding the light-transmitting substrate, transparent electrode, back electrode, etc., there are no particular limitations. As the light-transmitting substrate, conventionally used glass substrate materials such as blue plate glass, borosilicate glass, and quartz glass are useful. However, metals and plastics can also be used as substrate materials. 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, silver,
It can be appropriately selected and used from metals such as gold and platinum, and metal oxides such as tin oxide, indium oxide, and zinc oxide.

Hereinafter, one example of embodiments of the present invention will be explained with reference to Examples.

(Example 1) As an apparatus for forming an amorphous silicon solar cell, a film forming apparatus capable of applying a high frequency sputtering method, a plasma CVD method, and a photoCVD method was used.

The layer structure of the formed solar cell element is as shown in FIG. A glass substrate 1 with a transparent electrode 2 made of tin oxide was placed in a forming apparatus capable of applying high frequency sputtering film formation. Perform vacuum evacuation, do not particularly heat the substrate, first introduce oxygen, and reduce the pressure to 0. I set it to ITorr. Metal iridium with a purity of 99.99χ is used for the target,
Reactive sputtering was performed for 5 minutes at a high frequency power of 0.4 W/cm'' to form 20 iridium oxide films 3 (
The deposition rate was 4 persons/m1n). Next, the substrate was transferred to a P-type semiconductor thin film forming chamber, and a P-type amorphous silicon carbide thin film 4 was formed. The p-type amorphous silicon carbide thin film was prepared by introducing disilane/diporane/acetylene/hydrogen in a ratio of 510.01/3/200 as raw material gases and using a low-pressure mercury lamp at a pressure of 0.2 Torr.
It was carried out by photo-CVD method by irradiating ultraviolet rays. The formation rate of the p-type mechanical crystal thin film is 0.5 people/S, and the deposition time is 2
The film was formed for 40 seconds to a film thickness of 120 mm. Next, the substrate is transferred to an i-type semiconductor thin film formation chamber, monosilane is introduced, and an amorphous silicon film 5 is formed by plasma CVD under the conditions of pressure Q, Q5 Torr, and formation temperature 240°C.
was formed to a thickness of about 7,000 people. The plasma CVD method utilized RF discharge of 13.56 M)lz. At this time, the RFt force was 10-. After forming the 1-type semiconductor 'yi film, 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. Pressure 0.2 Torr, forming temperature 240°C
The n-type semiconductor thin film 6 was formed by plasma CVD under the following conditions.
It was formed to a film thickness of 0.00 people. Plasma CVD method is 13.5
A 6 MHz RF discharge was utilized. At this time, the RF power was 50W. Then, it was taken out from the thin film forming apparatus and a metal electrode 7 was formed thereon. AMI, too mW/c
The photoelectric properties of the amorphous silicon solar cell were measured by irradiating it with +fl light using a solar humilator. As a result, the open circuit voltage was as high as 0.912 V, and the effect of the present invention was confirmed, and the short-circuit photocurrent was 1
It had a large value of 7.47 mA/cd and a fill factor of 0.741, and as a result, the photoelectric conversion efficiency was extremely excellent at 11.81%.

[Comparative Example 1] In Example 1, 100 people formed an iridium oxide bacterial film, and otherwise formed an amorphous silicon solar cell using the same steps and conditions as in Example 1. When the performance of the obtained solar cell was measured, the open circuit voltage decreased to 0.853 V, and the short-circuit photocurrent was 16.85 mA/c+a due to optical loss and series resistance in the iridium oxide thin film part. , the fill factor decreased to 0.688 and the photoelectric conversion efficiency was 9.9%.
It has declined to .

[Comparative Example 2] Example 1 was repeated except that in Example 1, a p-type organic crystal thin film was formed directly on a glass substrate with a transparent electrode without using an iridium oxide VII film. An amorphous silicon solar cell was formed using exactly the same process. The layer structure of the device is shown in FIG. When the performance of the obtained solar cell was measured, the open circuit voltage decreased to 0.830 V, the short circuit photocurrent decreased to 16.20 mA/c+fl, and the photoelectric conversion efficiency decreased significantly to 9.22%. Oops.

[Effects of the Invention] As is clear from the above Examples and Comparative Examples, by providing an appropriate film thickness of chemically stable iridium oxide having p-type properties between p-type semiconductor thin films, it is possible to overcome the conventional technology. Optical CVD method and plasma CVD that have been put into practical use in
The method is used to form amorphous silicon solar cells of the present invention having high open circuit voltages. That is, the present invention greatly contributes to improving the photoelectric conversion efficiency of amorphous silicon solar cells in practical use. As described above, the present invention can provide a technology that enables high conversion efficiency required for power solar cells, and is an extremely useful invention for the energy industry.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the layer structure of an amorphous solar cell of the present invention. FIG. 2 is a schematic diagram showing the layer structure of a conventional amorphous solar cell.

Claims (2)

[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 characterized in that iridium oxide is interposed between the thin films, and the p-type semiconductor thin film is a p-type amorphous silicon or p-type amorphous silicon carbide thin film. (2) The amorphous solar cell according to claim 1, wherein the iridium oxide has a film thickness of 5 to 50 Å.