JPH03235374A - Photoelectric conversion element - Google Patents

Abstract

PURPOSE:To boost the open end voltage up to a high value while increasing the photoelectric conversion efficiency by a method wherein an iridium oxide film is laid between a transparent electrode and a thin p type semiconductor film to change the thin p type semiconductor film into a thin p type fine crystal film, etc. CONSTITUTION:A glass substrate 1 with transparent electrode 2 comprising of tin oxide is arranged in a formation device capable of forming films by the high-frequency sputtering process. Next, the device is vacuumized to form a thin iridium oxide film 3 by reactive sputtering process using high-frequency power 0.4W/cm<2> for five minutes. Next, the substrate 1 is shifted to a thin p type semiconductor film formation chamber to form a thin p type fine crystal 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. Resultantly, the open end voltage can be boosted up to such a very high value of 0.952V thereby enabling the photoelectric conversion efficiency to reach 12.02% for increasing the same.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to improving the performance of an amorphous silicon solar cell, that is, a charge conversion element (hereinafter, in the present invention, the two will be used interchangeably), and This invention relates to technology for increasing the efficiency of amorphous silicon solar cells by increasing the open-circuit voltage.

[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 short-circuit photocurrent and fill factor are approaching theoretically predicted values, but open-circuit voltage, in particular, has not yet been sufficiently improved. In order to improve the open-circuit voltage, it is necessary to improve the photoelectric properties of the p-type semiconductor thin film, and in particular, there are technical difficulties in expanding the optical band gap and improving the electrical conductivity at the same time. There was sex. The reason for this is that when the optical bandgap is expanded, the electrical conductivity decreases in terms of -S. As an improvement to this P-type semiconductor thin film, we have been working on a p-type amorphous silicon thin film (
For example, JP-A-59-161079, et al.), P-type amorphous silicon carbide thin film made from alkylsilane and silane compounds (for example, JP-A-61-125124).
62-016513, etc.) and p-type amorphous silicon carbide or microcrystal-containing p-type non-crystalline silicon carbide in which two layers with different silicon and carbon composition ratios and film crystallization rates are alternately laminated with a constant thickness. Various studies have been carried out, including crystalline silicon carbide thin films (for example, Japanese Patent Application No. 10907/1983), but as a result, the open circuit voltage of amorphous silicon solar cells has not been sufficiently improved as expected. It was hard to say. In this way, 50 to 50
The film properties are usually evaluated at the film thickness of 0 people.10
Is it because it is extremely difficult to form a film on a transparent electrode with properties equivalent to those of a thick film of 00 Å or more, or is it a P-type semiconductor? ! It is not clear at the current state of the art whether the transparent electrode was damaged during film formation and did not lead to improved performance, but in any case, improving the properties of the p-type semiconductor thin film alone is not sufficient to improve photoelectric conversion efficiency. I couldn't figure it out. In order to solve this problem, we have applied for the
-261382 and Japanese Patent Application No. 63-261383, by interposing a chemically stable and strong bonding tantalum oxide or zirconium oxide thin film between the transparent electrode and the p-type semiconductor thin film, transparent! This suppressed the reduction of the electrode and enabled a high open-circuit voltage, but since these oxides are n-type, an n/p reverse junction occurs between p-type semiconductor thin films, and transparency and low resistance are difficult to achieve. It was difficult to achieve both.

On the other hand, JP-A No. 61-96775 discloses that by providing an iridium oxide thin film as a p-type platinum group oxide between a transparent electrode and a p-type semiconductor thin film, both manufacturing yield and photoelectric conversion efficiency can be increased. , because 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 internal metal 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 has been completed by further studying these points and placing particular emphasis on increasing the open circuit voltage.

(Basic idea of the invention) Since the current p-type microcrystalline Tii film can be formed only in an extremely strong reducing atmosphere, the underlying transparent conductive oxide, which is the transparent electrode, is reduced.

Therefore, light transmission is inhibited in the reduced metal portion, leading to a decrease in short-circuit photocurrent, and the resistance of the p-type semiconductor thin film itself is higher than expected from microcrystallization. Furthermore, since the transparent electrode has n-type characteristics, an n/p reverse junction occurs between the transparent electrode and the p-type semiconductor thin film, and the diffusion potential determined from the characteristics of the p-type semiconductor thin film and the n-type semiconductor thin film decreases. Therefore, the fill factor is low and no improvement in the pressure at the open end 1 has been obtained. Therefore, from this point of view, it is essential to suppress the reduction of this transparent conductive oxide and the decrease in the diffusion potential. Considering this, we formed iridium oxide, a chemically stable p-type metal oxide thin film, on a transparent conductive oxide, and then formed a p-type microcrystalline thin film to form an amorphous silicon solar cell. By making batteries,
The present invention was completed based on the discovery that it is possible to form a photoelectric conversion element having a high open circuit voltage.

[Disclosure of the invention]

The present invention provides a transparent substrate, a transparent electrode, a p-type semiconductor thin film, an i
In a photoelectric conversion element 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 p-type semiconductor thin film, and the p-type semiconductor thin film is a p-type semiconductor thin film. The photoelectric conversion element is a microcrystalline silicon thin film, a carbon-containing microcrystalline silicon thin film, or a microcrystalline 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 the photoelectric conversion element of the present invention, and FIG. 2 is a schematic diagram showing the layer structure of a conventional charge conversion element.

In the figure, 1......Translucent substrate, 2...Transparent electrode, 3--Iridium oxide thin film, 4... -・---・p-type semiconductor TR
Film, 5------1--・-i-type semiconductor thin film, 6--
−−−−・・−・・N type semiconductor thin film, 7・・−・−・−
・− Back electrode is shown, respectively.

In the present invention, tin oxide used in the transparent electrode material is an inexpensive material with excellent transparency and conductivity, but it is also a chemically extremely active substance used in catalysts, sensor materials, etc. It is also an n-type semiconductor. In contrast,
The iridium oxide in the present invention is chemically stable and has the characteristics of a p-type semiconductor with a high optical band gap (~4 eV) and high photoconductivity despite not adding p-type impurities. (For example, Ryoji Fujiwara et al., "Preparation of IrOx film by reactive sputtering method and its properties," Proceedings of the 31st Joint Conference on Applied Physics, p. 76, Lecture No. 30a-B-4, 1984) (March 30, 1984 to March 30, 1984), this iridium oxide can be produced using sputtering deposition, electron beam deposition, or ion blating deposition using pellets or targets such as metallic iridium or iridium oxide. easily formed by

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. . In other words, the melting point of the metal, metal oxide, or metal compound, the reactivity with oxygen,
The optimal method is selected by considering the decomposition rate, etc. In the present invention, sputtering and electron beam evaporation are often employed as effective methods. As for the formation conditions, the formation temperature is room temperature to 600°C, the deposition rate is 1 to 50°C.
person/min, pressure 0.000001~1.0 Torr
It will be held in

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 maximum of 50 layers is sufficient. Preferably, the number is 10 to 30 people. If the thickness of the iridium oxide thin film exceeds this value, for example, if the thickness exceeds 100, 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 S/c
m, particularly preferably 0.0137 cm, more preferably 103/cn, but if the thickness is 50 Å or less, even a fairly low conductivity will not impede the present invention, and if the film thickness is too thin Similarly, the effects of the present invention cannot be achieved sufficiently. Control of the required thickness is achieved by actually measuring the average deposition rate of iridium oxide thin films formed by about 1,000 to 2,000 people, for example, and controlling the film thickness using this rate and deposition time.

In the present invention, it is preferable to use a p-type microcrystalline thin film as the p-type semiconductor fil. As the p-type microcrystalline thin film, a p-type microcrystalline silicon Til 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 from 100 people
There are 250 people. If more than 400 people form the group,
With the current technology, it is difficult to provide sufficient evidence for the formation of a p-type semiconductor thin film with a thickness of 400 Å or less, since the effect of improving the open circuit voltage is canceled out by the reduction in current and the effect of the invention cannot be achieved. However, in the present invention, p-type machine crystal Ti
A fil that is effective as 1WIA may be one that exhibits the properties of a P-type machine crystal thin film when formed to a thickness of 1000 Å or more. 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 present invention can be achieved by calculating the film formation time corresponding to the required film thickness from the corresponding film formation rate and forming the film with a thickness of 400 Å or less. It is possible to obtain a p-type mechanically crystalline thin film. In addition, such a P-type mechanical crystal thin film usually has a wide optical bandgap of 1.9 eV or more, even when the optical bandgap is 0.9 eV or more. It has a high electrical conductivity of OIS/cy+ or higher.

P-type microcrystalline thin film is a compound that has silicon in its molecules,
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 provides that a hydrocarbon gas or an inert gas such as helium or argon is added to these mixed gases as necessary.
The forming conditions are such that the forming temperature is 150 to 400°C, preferably 175 to 300°C.
The temperature is particularly preferably 200 to 250°C, and the forming pressure is preferably 0.01 to 5 Torrs, preferably 0.03 to 1.5
Torr, particularly preferably 0.035 to 1.0 Torr
It is done in rr.

The n-type semiconductor thin film is a hydrogenated silicon thin film, a hydrogenated silicon germane thin film, a hydrogenated silicon carbon filU, etc., and forms a photoactive region of an amorphous silicon solar cell. These n-type semiconductor thin films are made from compounds containing silicon in the molecule, compounds containing germanium in the molecule such as germane and silylgermane, and hydrocarbon gases.
The raw material gas is selected as appropriate depending on the desired semiconductor thin film.
It is easily formed by using a plasma CVD (chemical vapor deposition) method or a photo CVD (chemical vapor deposition) method. The effects of the present invention cannot be achieved by using conventional techniques in forming an i-type semiconductor, such as diluting the raw material gas with hydrogen, helium, etc., or adding a very small amount of diborane to the raw material gas. The forming conditions are, without limitation, the forming temperature is 150-400°C, preferably 175-350''C, and the forming pressure is 0.01
~5 Torr, preferably 0.03-1.5 Torr
It is done in r. The thickness of the n-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 effect of the present invention, 1000
~10,000 people is enough.

As the n-type semiconductor thin film, an n-type microcrystalline thin film or an n-type amorphous thin film is effectively used. As these, n-type microcrystalline silicon thin film, carbon-containing microcrystalline silicon thin film, microcrystalline silicon carbide thin film, amorphous silicon Fig, amorphous silicon carbon Fit H, 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. 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). Ru. 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 to 5 Torr, preferably 0
．． It is carried out at 0.03 to 1.5 Torr. The thickness of the n-type semiconductor i1 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 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.

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, 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.

EXAMPLES Hereinafter, an example of an embodiment of the present invention will be specifically described with reference to Examples.

[Example 1] As a forming apparatus for a photoelectric conversion element, 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 device 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. Vacuum evacuation was performed, and oxygen was first introduced without particularly heating the substrate, and the pressure was set to 0.1 Torr. Using metallic iridium with a purity of 99.99χ as a target, reactive sputtering was performed for 5 minutes at a high frequency power of 0.4 W/can to form a 20 iridium oxide thin film 3 (evaporation rate 4 people/5 h). 0 Next, the substrate is transferred to a P-type semiconductor thin film forming chamber, and a p-type semiconductor thin film 4 is formed.
was formed. For the production of P-type machine crystal thin film, as a raw material gas,
Disilane/diporane/hydrogen were introduced in a ratio of 510.01/2000, and a photoCVD method was performed by irradiating ultraviolet rays with a low-pressure mercury lamp at a pressure of 0.2 Torr.

The p-type mechano-crystalline thin film was formed at a rate of 0.2 g/s, a film forming time of 850 seconds, and a film thickness of 170 g/s. Next, the substrate was transferred to an n-type semiconductor thin film forming chamber, monosilane was introduced, the pressure was 0.05 Torr, and the forming temperature was 240°.
An amorphous silicon thin film 5 was formed to a thickness of approximately 7,000 wafers by plasma CVD under the conditions of C. Plasma C
The VD method utilized 13.56 MHz RF discharge. At this time, the RF power was 1o-. After forming the i-type semiconductor thin 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°
An n-type semiconductor thin film 6 was formed to a thickness of 500 nm by plasma CVD under the conditions of C. Plasma CVD method is 13.
A 56 MHz RF discharge was utilized. At this time, RF
The power was 50W. Then, it was taken out from the 1tli forming apparatus and a metal electrode 7 was formed thereon. AMI, 100
mW/Cll1 (D light was irradiated with a solar simulator to measure the photoelectric characteristics of the photoelectric conversion element. As a result, the open circuit voltage was as high as 0.952 V, which demonstrated the effect of the present invention. After confirming, short circuit photocurrent 17
．． 47mA/cJ.

The fill factor was a large value of 0.723, and as a result, the photoelectric conversion efficiency was extremely excellent at 12.02%.

[Comparative Example 1] In Example 1, 100 people formed an iridium oxide thin film, and otherwise formed a photoelectric conversion element using the same steps and conditions as in Example 1. When the performance of the obtained photoelectric conversion element was measured, the open circuit voltage decreased to 0.880V, and
Due to optical loss and series resistance in the iridium oxide thin film,
Short circuit photocurrent is 16.56mA/d, fill factor is 0.6
88, and the photoelectric conversion efficiency decreased to 10.0%.

[Comparative Example 2] Example 1 was completely 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 thin film. A photoelectric conversion element was formed in the same process. The device configuration is shown in FIG. When the performance of the obtained photoelectric conversion element was measured, the open circuit voltage was 0.762 V, and the short circuit photocurrent was 15.
The photoelectric conversion efficiency decreased to 20aA/caT, and the photoelectric conversion efficiency was 7.66.
%, it has dropped significantly.

〔Effect of the invention〕

As is clear from the above Examples and Comparative Examples, chemically stable iridium oxide having p-type properties can be put into practical use with the prior art by providing an appropriate film thickness between p-type semiconductor thin films. Optical CVD method and plasma CVD method
The photoelectric conversion element of the present invention having a high open circuit voltage is formed using the method. That is, the present invention greatly contributes to improving the proactive conversion efficiency of photoelectric conversion elements at a practical level. As described above, the present invention can provide a technology that enables high conversion efficiency required for power photoelectric conversion elements, 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 layer structure of the photoelectric conversion element of the present invention. FIG. 2 is a schematic diagram showing the layer structure of a conventional photoelectric conversion element.

Claims (2)

[Claims] (1) In a photoelectric conversion element 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 thin film 1. A photoelectric conversion element characterized in that iridium oxide is interposed between the p-type semiconductor thin films, and the p-type semiconductor thin film is a p-type microcrystalline silicon thin film, a carbon-containing microcrystalline silicon thin film, or a microcrystalline silicon carbide thin film. (2) The photoelectric conversion element according to claim 1, wherein the iridium oxide has a film thickness of 5 to 50 Å.