JPH0364974A - Photoelectric conversion element - Google Patents

Abstract

PURPOSE:To sharply enhance an amorphous photoelectric conversion element in open end voltage and shortcircuit photocurrent by a method wherein a conductive type semiconductor thin film is formed of II-IV compound semiconductor. CONSTITUTION:At least one of a first and a second conductivity type semiconductor thin film, 3 and 5, is formed of II-IV compound semiconductor. A conductive II-IV 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 ZnS, ZnSe, ZnTe, CdS, CdSe, or the like, and compound semiconductor such as ZnCdS2, ZnCdTe2, ZnCdSe2, MgCdTe2, or the like which is mixed compound of component elements of the compound concerned is 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 voltage, short circuit current, and fill factor. As a result of various studies, the short-circuit photocurrent and fill factor have been dramatically improved and improved, but the open-circuit voltage has not been sufficiently improved.In recent years, efforts have been made to improve the reliability of solar cells. , a pin-type amorphous solar cell with one layer on the light incidence side has been studied. In order to improve the open-circuit voltage of this amorphous solar cell, the photoelectric properties of the p-type semiconductor 11111 must be improved, and in particular, the optical band gap must be expanded and the electrical conductivity improved at the same time. However, 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 the anticipatory properties using only group III 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 crystallinity is easier to obtain than with group II materials. Increasing the open circuit voltage and short-circuit photocurrent of an amorphous photoelectric conversion element by forming an amorphous photoelectric conversion element in which a conductive type semiconductor thin film is applied to a ■-■ group compound semiconductor thin film with a controlled conductivity type. was completed.

[Disclosure of the invention]

The present invention includes a substrate, a first electrode, a first conductive type semiconductor thin film,
In an amorphous photoelectric conversion element formed by laminating a substantially intrinsic amorphous semiconductor thin film, a second conductivity type semiconductor thin film, and a second electrode in this order, the first conductivity type semiconductor thin film and the second conductivity type semiconductor thin film are stacked in this order. The present invention relates to an amorphous photoelectric conversion element characterized in that at least one of type semiconductor thin films (hereinafter abbreviated as conductive type semiconductor thin film) is a II-VII compound semiconductor thin film.

In the configuration of the photoelectric conversion element 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 in which holes are majority carriers, the second conductive type semiconductor thin film is a p-type semiconductor in which holes are majority carriers. 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, an example of the configuration of the photoelectric conversion element of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of the configuration of a photoelectric conversion element of the present invention. In the figure, 1 is a substrate, 2 is a first electrode, 3 is a first conductive type semiconductor thin film, and 4 is a substantially 5 is an intrinsic amorphous semiconductor thin film, 5 is a second conductivity type semiconductor thin film, and 6 is a second electrode.

The device of the present invention is characterized in that at least one of the first conductive type semiconductor thin film 3 and the second conductive type semiconductor thin film 5 is a II-Vl group compound semiconductor thin film.

Therefore, the conductivity type I[-Vl group compound semiconductor thin film in the present invention is a wide-gap semiconductor material, and preferably has a forbidden band width of 1.8 eV or more. Specifically, ZnS, Zn5e, ZnTe, CdS, CdS
e, etc., and ZnCd5!, which is a mixed compound of the constituent elements of these compounds. , ZnCdTet, ZnC
Compound semiconductors such as dSe, MgCdTea, etc. can also be 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.

There is no specific restriction on the thickness of the conductive semiconductor thin film used, but it is usually about 30A-1000mm, and in particular, the thickness of the conductive semiconductor thin film used on the light incident side is 30-50mm thick.
A thickness of about 0 people is suitable.

The method for forming the present conductivity type II-VI group semiconductor thin film is as follows:
To carry out the present invention, there are methods such as sputtering method, vacuum evaporation method, ion blating method, chemical vapor phase diffusion method using iodine, etc., but from a practical point of view, sputtering method is not particularly limited. is preferred.

As a specific method for forming a compound semiconductor thin film by sputtering, for example, the formation of a ZnTe film will be described. Using two types of targets, Zn metal and Te metal to which 1 wt% Li is added, high frequency power is independently controlled to control the composition in the film, and sputtering is performed. The gas to be introduced is A
r 10105e, pressure is 10 mtorr s High frequency power of 50 W is applied to Zn and 30 W to Te. As dopants, Li, Na, Cu % A g −, Au
1P 1B s A 1, etc., and is added to Zn metal, but adding it to Te metal is not limited to implementing the present invention.Also, using a one-source sputtering method, ZnTe(Li) is added to the target. The method used is also effective.

The substantially intrinsic (hereinafter abbreviated as i-type) semiconductor film may be 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. It is something to do. These substantially intrinsic semiconductor thin films are made from raw materials that are appropriately selected depending on the desired semiconductor thin film from compounds containing silicon in the molecule, compounds containing germanium in the molecule such as germane and silylgermane, and hydrocarbon gases. It is easily formed by applying a plasma CVD (chemical vapor deposition) method or a photo CVD (chemical vapor deposition) method to a gas. 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. The forming conditions are as follows: the forming temperature is 150 to 400°C, preferably 175 to 350°C, and the forming pressure is 0.01''-5 Torr, preferably 0.
．． Performed at 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 achieve the effects of the present invention, approximately 1,000 to 10,000 people is sufficient. It is.

Next, in the photoelectric conversion element of the present invention, a ■-■ group compound semiconductor thin film is applied to at least one conductivity type semiconductor thin film. Specifically, when the conductivity type of the thin film is p-type, the other conductivity type semiconductor thin film exhibits n-type properties, such as an n-type microcrystalline thin film or an n-type amorphous thin film. is used effectively. To give specific examples, n-type microcrystalline silicon thin film, 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. It is easily formed by mixing compounds from Group V 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 0.03 to 1.5 Torr. It is sufficient for the thickness of the n-type semiconductor thin film to be about 200 Å to 500 Å.

For forming the amorphous pre-conversion element of the present invention, the preferred raw material gases to be used will be explained with further specific examples.For compounds having silicon in the molecule,
Hydrogenated silicones such as monosilane, disilane, trisilane; hydrogenated silicones substituted with alkyl groups such as monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, ethylsilane, 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 silicon hydrides 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 to change the optical bandgap in forming carbon-containing microcrystalline silicon thin films, microcrystalline silicon carbide thin films, 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 S plate, the first electrode, the second electrode, etc., there are no particular limitations.As the substrate, conventionally used glass substrate materials such as blue plate glass, borosilicate glass, and quartz glass are useful; Furthermore, 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. For the first and second electrodes, one or both must be translucent for sunlight to enter, but there are no other restrictions.Specifically, tin oxide, oxide Metal oxides such as indium 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, the present invention will be explained with reference to examples! ! Explain the situation.

[Example 1] As a forming apparatus for a photoelectric conversion 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.

First, P-type ZnTe was formed as the first conductive type semiconductor thin film 8 . Zn metal with 1wt% Li added and Te
A metal was used as a sputtering target, and the sputtering conditions were a pressure of 10 mtorr, an Ar gas flow of 10 sccm, high frequency cuffs of 0 W and 40 W, and a substrate temperature of 300° C. At a film formation time of 300 seconds, 1
After forming 50 people, heat at 400'C in hydrogen gas atmosphere.
After the heat treatment, the substrate is transferred to a substantially intrinsic semiconductor thin film formation chamber, monosilane is introduced, and the pressure is reduced to 0.
．． Plasma C under the conditions of 0.5 Torr and formation temperature of 200°C.
By VD method, amorphous silicon thin film 9 was
Formed to the thickness of a human. Plasma CVD method is 13.56
M) Utilized high frequency discharge of Iz. At this time, the RF power was 15 tons. After forming the substantially intrinsic semiconductor EiM9, the substrate was transferred to an n-type semiconductor thin film forming chamber.

Raw material gases consisting of monosilane/phosphine/hydrogen were introduced so that their flow rates were 1010.2/100. Pressure 0.2 Torrs Temperature formation 0°C
An n-type semiconductor i film 10 was formed to a thickness of 500 nm by plasma CVD under the following conditions. Plasma CVD method is 13.
A 56 MHz RF discharge was utilized.

At this time, the force of RF' was 100-, 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 photoelectric conversion element.

[Comparative Example 1] In Example 1, I
A p-type mechanocrystalline silicon thin film was formed instead of the I-VI group compound semiconductor thin film. The layer structure of the device is shown in Figure 3.
An amorphous photoelectric conversion element was formed using the same steps as in Example 1 except for the zero layer. Formation of P-type machine crystal thin film is 110.03
A mixed gas of monosilane/diborane/hydrogen at a ratio of
rr, the substrate temperature was 250° C., the discharge time was 200 seconds, and 150 people were formed.

Amorphous light created as above! The performance of the conversion element was evaluated. As an evaluation, AM 1.5.100 taltl/
The photoelectric characteristics of the amorphous photoelectric conversion element were measured by irradiating it with c4 light using a solar simulator.The results of comparing the performance of the photoelectric conversion element implemented according to the present invention and the photovoltaic element shown in the comparative example, A 10% improvement in open circuit voltage and a 20% improvement in short circuit light current was observed. As a result, the optical 1f conversion efficiency was improved by 30%.

〔Effect of the invention〕

As is clear from the above Examples and Comparative Examples, by using a ■-■ group compound semiconductor for the conductive semiconductor thin film, the performance of the amorphous photoelectric conversion element that has been put into practical use with the prior art can be improved, especially the open circuit voltage. , which significantly improves the short-circuit photocurrent. That is, the present invention greatly contributes to improving the light conversion efficiency of an amorphous photoelectric conversion element 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 cannot be said that it is an extremely useful invention for the energy industry.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a configuration example of a photoelectric conversion element of the present invention. FIG. 2 is a schematic diagram showing an example of 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 photoelectric conversion element according to the prior art. In the figure, 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--..--.--th. Second electrode, 7
・−・・−・−・−・−Stin oxide, 8 p-type ZnT
e, 9 i-type amorphous silicon thin film, 10.
−・−・−・・n type microcrystalline silicon thin film, 11
Aluminum metal electrode, 12-...--
・・P-type mechanical crystalline silicon thin film, 13・・・・・・・・・
−・Indicates a glass substrate.

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. 1. An amorphous photoelectric conversion element, wherein at least one of a first conductive type semiconductor thin film and a second conductive type semiconductor thin film is a II-VI group compound semiconductor thin film.