JPH02109375A - Photoelectric transducer element - Google Patents

Abstract

PURPOSE:To improve photoelectric transducing efficiency by providing a tantalum oxide thin film between a transparent electrode and a P-type semiconductor thin film. CONSTITUTION:A glass substrate 1 having a transparent electrode 2 comprising tin oxide undergoes evacuation and heating. Tantalum pentoxide is heated for five minutes and evaporated, and a tantalum oxide thin film 3 is formed. Then, the substrate 1 is moved into a P-type semiconductor-thin-film forming chamber, and a thin film 4 is formed by an optical CVD method. Then monosilane is introduced into an I-type semiconductor-thin-film forming chamber, and an I-type thin film 5 is formed by a plasma CVD method. Furthermore, an N-type thin film 6 is formed in an N-type semiconductor-thin-film forming chamber by the plasma CVD method. Then a metal electrode 7 is formed. In this way the photoelectric transducing efficiency of an amorphous solar cell can be improved to a large extent.

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 (photoelectric conversion elements) 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. However, solar cell light 1! Conversion efficiency 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, in particular, has not yet been sufficiently improved. In order to improve the reliability of solar cells, pin-type amorphous solar cells in which a p-layer is provided on the light incident side have been studied in recent years.

In order to improve the open-circuit voltage of this amorphous solar cell, it is necessary to improve the photoelectric properties of the ρ-type semiconductor thin film, and in particular, it is necessary to expand the optical band gap and improve the electrical conductivity at the same time. This was not possible due to technical difficulties. The reason for this was that expanding the optical bandgap would result in a drop in electrical conductivity.

A microcrystalline thin film has been proposed as a material that satisfies these requirements, but under the film formation conditions that a p-type organic crystalline thin film is formed on a transparent electrode using conventional techniques such as plasma CVD and photoCVD. Although attempts were made to form thin films, the open circuit voltage of amorphous solar cells did not improve, and the photoelectric conversion efficiency did not improve. In this way, a p-type microcrystalline thin film is formed into an amorphous IJ! Is it extremely difficult to form a film on a transparent electrode at a film thickness of 50 to 500 times, which is sufficient for the substrate, or is it due to the conditions for forming a p-type organic crystal thin film?
It is not clear at the current state of the art whether the damage to the transparent electrode did not lead to improved performance, but in any case, no improvement in performance has been attempted using a P-type mechanical crystal thin film.

[Basic idea of the invention]

Since the current p-type microcrystalline thin film can only be formed in a strong reducing atmosphere, the underlying transparent Tl film, that is, the transparent conductive oxide, is reduced. In addition, since the p-type semiconductor yI film itself has a higher resistance than expected from microcrystallization, the fill factor is low and the open circuit voltage is low. From this point of view, the present inventors believe that it is essential to suppress the reduction of this transparent iii By laminating a tantalum oxide yl film, which is a stable metal oxide thin film, to increase reducing power and stability, a p-type microcrystalline thin film is formed to fabricate an amorphous solar cell. This made it possible to form an amorphous solar cell with voltage.

(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, a type 1 semiconductor thin film, an n-type semiconductor thin film, and a back electrode in this order. An amorphous π solar cell characterized in that a tantalum oxide thin film is interposed between the transparent electrode and the p-type semiconductor thin film.

The present invention will be explained in detail below.

Tin oxide, which is used as a transparent electrode material, has a binding energy of about 500 kJ/mol (see, for example, the latest oxide handbook (Nippon-Soviet Press) supervised by Samsonov), and it is also used as a material for catalysts, sensors, etc. In contrast, tantalum oxide f:IM in the present invention has an extremely high binding energy of about 1460 kJ/mol, and is used in various oxide intermediates. is also chemically stable. This strong bonding force and chemically stable tantalum oxide thin film can be easily produced by electron beam evaporation, sputtering evaporation, or ion blating evaporation using tantalum pentoxide or metal tantalum pellets or targets as raw materials. It is formed. The present invention can also be effectively carried out by a spray method or a CVD (chemical vapor deposition) method using tantalum chloride and oxygen gas, and an appropriate one can be selected from these methods according to the purpose. . In other words, the most suitable method is selected by considering the melting point, reactivity with oxygen, decomposition rate, etc. of the metal oxide, metal, or metal compound as described above, and in many cases, electron beam evaporation, sputtering, etc. is adopted as an effective method. As for the formation conditions, the formation temperature is room temperature to 600°C, the deposition rate is 1 to
50 people/man, pressure 0.000001-0.1 To
It is done at rr$ji degrees. 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, it is sufficient that the required thickness of the tantalum oxide thin film is 5 Å or more. Preferably, the number is 10 to 50 people. If less than 5 people are involved, the effect of thin film formation cannot be fully achieved, and if more than 100 people are involved, the effect of the invention cannot be achieved because the reduction in fill factor cancels out the improvement in open circuit voltage. The conductivity of the tantalum oxide thin film is preferably about 0.00001 S/c, particularly preferably about 0.01 S/cm, and more preferably about IQs/cm, but when the thickness is 50 Å
Even if the conductivity is below, the present invention will not be hindered even if the conductivity is low.

In the present invention, it is preferable to use a p-type microcrystalline IM as the p-type semiconductor thin film. A thin film or the like can be effectively used. The required thickness of the p-type mechanical crystal thin film is 50 Å or more and a high k thickness of 400 is sufficient. Preferably 100 people to 2
There are 50 people. If there are less than 50 people, it will not be able to perform its function as a P-type semiconductor thin film, and if there are less than 40
If more than 0 people are used to form the p-type semiconductor thin film, the effect of improving the open circuit voltage will be canceled out by the drop in current, making it impossible to achieve the effect of the invention.Currently, the current technology does not allow direct formation of the p-type semiconductor thin film itself with a thickness of 400 Å or less. It is difficult to provide sufficient evidence. However, in the present invention, a thin film that is effective as a P-type mechanical crystal thin film may be one that exhibits the properties of a p-type mechanical crystal y4 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 machine crystal thin film), 400
Å or less, it is possible to obtain the P-type machine crystal thin film of the present invention having a desired thickness by calculating the film forming time corresponding to the required film thickness from the film forming rate and forming the film. Also,
Such a p-type mechano-crystalline thin film usually has a wide optical bandgap of 1.9 eV or more, with a band gap of 0.01 eV or more.
It has a high electrical conductivity of 3/c+a or more.

P-type microcrystalline thin film is a compound containing silicon in the molecule,
By performing the plasma CVD (chemical vapor deposition) method or the 9CVD (chemical vapor deposition) method using a mixed gas consisting of a compound of group Ⅰ of the periodic table, represented by diborane, and hydrogen as the raw Fl gas. Easily 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, which do not interfere in any way, are that the forming temperature is 150 to 400°C, preferably 175 to 300°C.
5 and (preferably from 200 to 250'C, and the forming pressure is from 0.01 to 5 Torr, preferably from 0.03 to
1.5 Torr, particularly preferably 0.035 to 1.0
It is done in Torr.

In the present invention, the i-type semiconductor yi film is a hydrogenated soricon 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 CV
It is easily formed by applying the D (chemical vapor deposition) method. The combined use of conventional techniques for forming a J-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 150-400'C, preferably 175-350'C, and the forming pressure is 0.01-400'C.
5 Torr, preferably 0.03-1.5 Torr
It will be held in M and W- of the type 1 semiconductor thin film are appropriately determined depending on the use of the solar cell, and are not limiting conditions of the present invention.
0 to too many people is sufficient.

In the present invention, an n-type microcrystalline thin film or an n-type amorphous f3IM is effectively used as the n-type semiconductor thin film provided in contact with the back electrode. These include n-type microcrystalline silicon thin film, carbon-containing microcrystalline silicon thin film, microcrystalline silicon carbide thin film, amorphous silicon thin film,
Amorphous silicon carphone 'i'1Bfl, amorphous silicon germane thin film, etc. can be effectively used. These n-type semiconductor thin films are made using raw materials appropriately selected from compounds having silicon in the molecule; compounds having germanium in the molecule such as germane and silylgermane; hydrocarbon gases, etc., depending on the desired semiconductor thin film. Compounds from group V of the periodic table, such as phosphine and arsine, and hydrogen are mixed and plasma CVD (chemical vapor deposition 1
1) or photo-CVD (chemical vapor deposition). 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 350 to 400'C, preferably 175°C. ~350'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 the present invention, preferred raw material gases to be used will be explained with further specific examples.Compounds containing silicon in the molecule include silicon hydrides such as monosilane, disilane, and trisilane; monomethylsilane, dimethylsilane, and trimethylsilane; , tetramethylsilane,
Hydrogenated silicone substituted with alkyl groups such as ethylsilane and diethylsilane: Vinylsilane, divinylsilane, trivinylsilane, vinyldisilane, divinyldisilane Hydrogen containing radically polymerizable unsaturated hydrocarbon groups such as propenylsilane and ethylsilane in the molecule Silicon hydride: 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 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 can also be used.

In the present invention, there are no particular limitations on the light-transmitting substrate, transparent electrode, back electrode, etc.; examples of the light-transmitting substrate include conventionally used glass substrates such as blue plate glass, borosilicate glass, and quartz glass. Additionally, metals and plastics can be used as substrate materials.

As for plastic materials, materials that can withstand temperatures of +00° C. or higher 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,
Metals such as gold, platinum, tin oxide, indium oxide,
An appropriate metal oxide such as zinc oxide can be selected and used.

[Example 1] As a solar cell forming apparatus, an electron beam evaporation method, a plasma CVD method, and a photo CVD method can be applied.
using the device. A transparent electrode-wrapped glass substrate made of tin oxide was placed in a forming apparatus capable of applying electron beam evaporation. Perform vacuum evacuation and substrate heating to bring the base Fi layer temperature to 0.
0°C1 acceleration voltage 4kV, pressure 0.0OO007 Tor
At r, tantalum pentoxide was thermally evaporated in 5 minutes and 20
Formation of tantalum oxide thin film by humans (deposition rate 4 people/win)
) Next, the substrate was transferred to a P-type semiconductor thin film forming chamber, and a P-type semiconductor thin film was formed. The p-type organic crystalline thin film was prepared using disilane/diborane/hydrogen as the raw material gas at 51%
Introduced at a ratio of 0.01/20Q, pressure 0.2 Torr
, a low-pressure mercury lamp is used to irradiate ultraviolet rays to perform optical CV.
It was carried out using method D. The formation rate of P-type machine crystal thin film is 06
2 people/S, film formation time is 850 seconds, film thickness is 17
The substrate was transferred to a 0-order type 1 semiconductor thin film forming chamber, monosilane was introduced, and the pressure was set to 0.05 Torr.
r, shape! Amorphous silicon is produced by plasma CVD method at a temperature of 240°C. 2 to about 100
It was formed to have a film thickness of 0. Plasma CVD method is 13.56
? NIz RF discharge was used. At this time, the RF power was 1 (l). After forming the J-type semiconductor thin film, the substrate was transferred to the N-type semiconductor thin film forming chamber.
It was introduced at a ratio of 10,01/+00. An n-type semiconductor thin film 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. The plasma CVD method has an R of 13.56 Mllz.
F discharge was used. At this time, the RFTl force is 5 (11
Met.

Then, it was taken out from the thin film forming apparatus and a metal electrode was formed thereon. The charging characteristics of the amorphous π silicon solar cell were measured by irradiating it with AM 1.100 mW/d light using a solar chemulator. As a result, the open circuit voltage is 0.9
A very high value of 51ν was obtained, confirming the effect of the present invention, and the short-circuit photocurrent was 17.07 mA/c+4, the fill factor was 0.702, which was a large value, and as a result, the charging conversion efficiency was 11.40. %, which was extremely excellent.

[Comparative Example 1] Exactly the same process as in Example 1 except that in Example 1, a p-type organic crystal thin film was formed directly on a transparent glass substrate with a handle, without using a tantalum oxide thin film. An amorphous silicon solar cell was formed. When the performance of the obtained solar cell was measured, the open circuit voltage was 0.76.
2 V, the short-circuit photocurrent also decreased to 15.20 mA/cj, and the photoelectric conversion efficiency significantly decreased to 7.66%.

(Effects of the Invention and Industrial Applicability As is clear from the three or more Examples and Comparative Examples, according to the present invention,
By interposing a tantalum oxide thin film, which is a metal oxide with strong bonding strength or chemical stability, between a transparent electrode and a p-type semiconductor thin film, the photo-CVD method and plasma The amorphous solar cell of the present invention having a high open circuit voltage is formed using the CVD method. 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 the high conversion efficiency required for power solar cells, and is an extremely useful invention for the energy industry, and its industrial applicability is high. It must be said that this is extremely large.

[Brief explanation of drawings]

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--------
1-transparent electrode, 3-11-11 tantalum monoxide thin film, 4-
・-P-type semiconductor thin film, 5--1-type semiconductor thin film, 6
--- 1 --- N-type semiconductor thin film, 7..--m-.- Rear surface electrode is shown.

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 characterized by having a tantalum oxide thin film interposed between thin films.