JPS6140153B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pn heterojunction solar cell suitable for receiving solar energy and converting it into electrical energy by the photovoltaic effect. Conventionally, a structure in which a p-type layer is formed by diffusion on the surface of a thin plate of n-type silicon, for example, has been well known as a solar cell structure. It is also known that various semiconductors other than silicon, such as those based on p-n junctions, such as InP, GaP, GaAs, and CdS, can be applied. However, on the surface of the substrate of these various n-type or p-type semiconductors, p
It is extremely difficult to form a thin film layer that becomes a -n junction, and conventional methods such as
It is difficult to form such a semiconductor thin film using CVD, vacuum evaporation, sputtering, or the like, and it is necessary to use special equipment. In other words, with conventional methods, it is extremely difficult to obtain a thin film layer that forms an efficient p-n junction with stable quality suitable for solar cells, and as a result, productivity and economy are poor, and it is extremely expensive. There was a problem with that. The present invention aims to solve the above-mentioned problems and provide a pn heterojunction solar cell with high quality and good productivity. That is, in the present invention, acetylene is polymerized on the surface of n-type silicon to form a chain polyacetylene thin film having a conjugated double bond chain and a thickness of 10 μm or less on the surface of n-type silicon, and then electron-accepting p obtained by treating a polyacetylene thin film with a chemical compound.
-n heterojunction type solar cell. Some of the inventors have already discovered and proposed a method for forming a polyacetylene thin film on a solid surface (Japanese Patent Publication No. 32581/1983). A polyacetylene thin film is formed on the n-type silicon surface according to the above method, the catalyst is washed, and after drying,
By treating it with an electron-accepting compound, a relatively high-resistance p-type polyacetylene thin film can be made to have an electrical conductivity of 1Ω.
A p-n heterojunction solar cell of high quality and good productivity can be manufactured by forming a p-type conductive polyacetylene thin film of ^-1 cm ^-1 or more. Hereinafter, the present invention will be explained in detail using the drawings. FIG. 1 shows one embodiment of the pn heterojunction solar cell of the present invention. That is, a p-type conductive polyacetylene thin film (2, a polyacetylene thin film doped with iodine as an electron-accepting compound, with a film thickness of 0.8 μ
m) to create a p-n junction, and then transparent electrodes (1,
Gold is coated by chemical vapor deposition, and the film thickness is
0.50 μm). The feature of the present invention is that a polyacetylene thin film having a thickness of 10 μm or less is formed on an n-type silicon surface by a polymerization method already known to those skilled in the art, and the formed polyacetylene thin film is further treated with an electron-accepting compound. It is in. The band gap energy of polyacetylene is approximately 1.6 eV, and since it absorbs most of the energy of sunlight and becomes a photoconductor, the p-n junction solid-state device obtained in the present invention can The power effect results in an efficient p-n heterojunction solar cell that receives solar energy and converts it into electrical energy. According to the present invention, the thickness of the p-type conductive polyacetylene thin film can be easily controlled by the acetylene polymerization conditions, such as catalyst preparation conditions, catalyst concentration, catalyst amount, acetylene pressure, polymerization temperature, and polymerization time. Therefore, it is suitable for solar cells where control of the thickness of the polyacetylene film is an important factor. The present invention will be specifically explained below. The n-type silicon used in the present invention may be either single crystal silicon doped with a metal with the highest valence of 5, such as phosphorus or antimony, which is commonly used, or n-type amorphous silicon, which has been studied recently. However, in order to obtain high solar energy conversion efficiency, it is preferable to use n-type silicon single crystal. Although it is preferable to attach an ohmic electrode to one side of the n-type silicon used, as shown in FIG. 1, a lead wire may be attached directly to the silicon surface without attaching an ohmic electrode. The ohmic electrode can be manufactured by a CVD method, a vacuum evaporation method, a sputtering method, etc. which are commonly used in the industry. It is preferable to remove the oxide film on the surface of n-type silicon that contacts the polyacetylene film using a normal etching operation to leave a flexible silicon surface, but it is also possible to form a thin polyacetylene film on the oxide film without performing an etching operation. However, it is effective as a solar cell. For the etching operation, either a wet method or a dry method, which is widely practiced among those skilled in the art, can be used. A method for producing a polyacetylene film on an n-type silicon surface can be carried out in accordance with a method already proposed by some of the present inventors (Japanese Patent Publication No. 32581/1981), and this method will be described in detail. As long as the polyacetylene to be produced is a linear polyacetylene having a double bond chain, there are no restrictions on the acetylene polymerization catalyst, but a catalyst system comprising a combination of a transition metal compound and an organometallic compound is usually used. The catalyst system may be either homogeneous or heterogeneous, but a homogeneous system is usually used because it facilitates catalyst removal. The transition metal compounds [catalyst component (A)] used to obtain the catalyst system used in the present invention include metals such as titanium, vanadine, chromium, iron, cobalt, tungsten, and molybdenum and halogen atoms or carbon atoms of at most 20 Compounds containing alkyl groups, alkenyl groups, aryl groups, aralkyl groups, alkoxide groups, phenoxide groups, carboxylic acid residues, cyclopentadienyl groups, acetylacetone residues, carbon monoxide (carbonyl groups), and It is a complex of a compound and an electron-donating compound such as pyridine, triphenylphosphine, and dipyridyl. Among transition metal compounds, titanium, vanadine,
Compounds of iron, cobalt and chromium are preferred;
Particularly preferred are titanium compounds. Representative examples of preferred transition metal compounds include transition metal compounds whose general formulas are represented by formulas (1) to (3). Ti(OR) ₄ (1) (R is an alkyl group having at most 20 carbon atoms) M(acac) ₃ (2) MO(acac) ₂ (3) [(acac) is an acetylacetonato group, M is a transition metal selected from titanium, vanadine, iron, cobalt, and chromium.] The organometallic compound [catalyst component (B)] used in the present invention is a transition metal selected from titanium, vanadine, iron, cobalt, and chromium. It is an organometallic compound containing at least one kind of metal, and the general formula of some of them is shown by the following formula. MRn [However, M is A, B, B, or a metal from Group B of the periodic table, and R has at most 20 carbon atoms.
alkyl, alkenyl, aryl
an organic group selected from the group consisting of aralkyl group, alkoxide group, phenoxy group, and cyclopentadienyl group, or a hydrogen atom or a halogen atom, which may be the same or different, but at least one of them is is a hydrogen atom or the organic group, and n is the highest valence number of the metal or a positive integer less than that.] Other organometallic compounds include pyridine, triphenylphosphine, Mention may be made of complexes with yne or diethyl ether and the reaction products of 1 mol of said organometallic compound with at most 2.0 mol of water, as well as double salts of two of said organometallic compounds. Among the organometallic compounds used in the present invention, typical ones include those containing magnesium, calcium, zinc, boron, aluminum, potassium, silicon, and tin. Organometallic compounds of aluminum and tin are preferred, and organoaluminium-based compounds are particularly preferred. Typical examples of the organoaluminum compounds include triethylaluminum, triisobutylaluminum, trihexylaluminum, diethylaluminum chloride, di-n-butylaluminum chloride, ethylaluminum sesquichloride, diethylaluminum butoxy, and the reaction of triethylaluminum with water. The product [reaction ratio 1; 0.5 (molar ratio)] is mentioned. Other organoaluminum compounds include aluminum siloxalene compounds, aluminum amide compounds, dialmoxalene compounds, and double salts containing the above organoaluminum compounds. The general formula of the aluminum-siloxalene compound used as the organometallic compound in the present invention is shown by the following formula. [However, R ¹ , R ² and R ³ may be the same or different and are a halogen atom or an alkyl group or alkoxy group having at most 10 carbon atoms, and R ⁴ is an alkyl group having at most 10 carbon atoms. and R ⁵
is a halogen atom, an alkyl group or alkoxy group having at most 10 carbon atoms, or a general formula of

[expression] or

[Formula] (However, R ⁶ , R ⁷ and R ⁸ may be the same or different, and are the same as the above R ¹ , R ² and R ³ , and n
is a positive integer of 10 or less)] Among the aluminum-siloxalene compounds used in the present invention, typical examples include trimethyldimethyl-siloxalene, trimethyldiethyl-siloxalene, and trimethyldi-n
-Propyl-siloxsalene, trimethyl-diisobutyl-siloxsalene, trimethyldioctyl-
Mention may be made of siloxsalene, trichlorodimethyl-siloxsalene, dimethylethyldiethyl-siloxsalene, trimethoxydimethyl-siloxsalene, triethyldimethyl-siloxsalene, trimethyldimethoxy-siloxsalene, trimethyldimethoxy-siloxsalene and trimethoxydichloro-siloxsalene. Further, the general formula of the aluminum amide compound used as the organometallic compound in the present invention is shown by the following formula. (However, R ¹ , R ² and R ³ may be the same or different and are a hydrogen atom or an alkyl group having at most 10 carbon atoms, and R ⁴ is a halogen atom or an alkyl group having at most 10 carbon atoms. ). Among the aluminum amide compounds used in the present invention, typical examples include diethylaluminum dimethylamide, diethylaluminum diethylamide, dimethylaluminum dimethylamide, dimethylaluminum di-n
-butyramide, diethylaluminium di-n-
butylamide, dichloroaluminum dimethylamide, dimethylaluminum dioctylamide,
Mention may be made of diisobutylaluminum di-n-butylamide and dihexylaluminum dioctylamide. The general formula of the dialmoxane compound used as the organometallic compound in the present invention is shown by the following formula. (However, R ¹ , R ² and R ³ may be the same or different and are a halogen atom or an alkyl group or alkoxy group having at most 10 carbon atoms, and R ⁴ is an alkyl group having at most 10 carbon atoms. Among the dialmoxane compounds used in the present invention, representative ones include tetramethyldialumoxane, tetraethyldialumoxane, tetraisobutyldialumoxane, and 1.1-
Dimethyl-3,3-diethyldialumoxane, tetraisobutyldialumoxane, 1,1-dimethyl-3,3-diisobutyldialumoxane, tetradecyldialumoxane, trimethyldialumoxane chloride and triethyldialumoxane chloride can give. Among the organometallic compounds used in the present invention, typical examples of organometallic compounds other than organoaluminum compounds include diethylmagnesium, ethylmagnesium chloride, methylmagnesium iodide,
Allyl magnesium chloride; normal propylmagnesium chloride, tertiary-butylmagnesium chloride, phenylmagnesium bromide, diphenylmagnesium, ethyl ethoxymagnesium, dimethylzinc, diethylzinc, diethoxyzinc, dibutylboron chloride, diborein, Trimethylboron, triethylsilane, silicon tetrahydride, triethylsilicone hydride, tetramethyltin, tetraethyltin, trimethyltin chloride, dimethyltin dichloride, trimethyltin hydride, complex of ethylmagnesium bromide and ethyl ether, and diethylzinc and water Examples include reaction products with [H ₂ O/Zn(O ₂ H ₅ ) ₂ <2.0 (molar ratio)]. Further, as the organic compound used in the present invention, double salts of two types of the above-mentioned organic compounds (for example, lithium aluminum tetrahydride,
calcium (tetraethylzinc). In carrying out the present invention, these organometallic compounds may be used alone or in combination of two or more. The molar ratio of the organometallic compound (B) to the transition metal of the catalyst component (A) used in the present invention is 1 to 100.
You can freely choose between, but it is not particularly limited to this. It is also possible to control the polymer yield, polymerization rate, etc. by combining these catalyst components A and B with a third component shown below, but these may or may not be used. The third component includes oxygen-containing compounds such as alcohols, ethers, peroxides, carboxylic acids,
Typical examples include acid anhydrides, acid chlorides, esters, ketones, etc., but nitrogen-containing compounds, sulfur-containing compounds, halogen-containing compounds, molecular iodine, and other Lewis acids can also be used. There is no particular restriction on the order of addition of these. The catalyst may be used as is without dilution, but
Usually, it is preferable to dilute with an aromatic or aliphatic inert organic solvent, but when diluting, the concentration of the transition metal compound must be 0.001 mol/or more, and the The concentration
If the amount is less than 0.001 mol/mol, it is difficult to obtain a good polyacetylene thin film. Since these catalysts react with oxygen or moisture in the air and decompose or change in quality, they should be handled in a state substantially free of oxygen and moisture, such as in an inert gas such as nitrogen or argon gas, or in a vacuum. must be handled inside. The above catalyst solution is applied to the well-dried n-type silicon surface in a substantially water-free state and brought into contact with acetylene gas to form a polyacetylene thin film. The steric structure of polyacetylene can be controlled by the temperature during polymerization; at temperatures below 10°C, polyacetylene with many cis forms can be produced, and at temperatures above 10°C, polyacetylene with many trans forms can be produced. The polymerization temperature is preferably 300°C or lower; if it is higher than 300°C, decomposition of the polyacetylene occurs, which is undesirable. Polymerization of acetylene occurs by contacting acetylene gas with a catalyst. The acetylene pressure is not particularly limited, but from a practical standpoint, it is desirable to conduct the reaction at 10 atmospheres or less. Since the high molecular weight polyacetylene produced is not soluble in organic solvents, it precipitates out upon initiation of polymerization. Once a polyacetylene film of a predetermined thickness is obtained,
The remaining acetylene gas is removed, followed by washing several times with an organic solvent in which the oxygen- and water-free catalyst is dissolved to remove the remaining catalyst. Subsequently, the remaining organic solvent is removed by drying to obtain a p-n junction solid state device consisting of a p-type polyacetylene film and n-type silicon. The thickness of the polyacetylene film is preferably 10 μm or less, particularly preferably 2 μm or less, in order to transmit as much sunlight as possible. If the film thickness is 10 μm or more, the solar energy conversion efficiency will be extremely reduced. The thickness of the polyacetylene film can be easily controlled by adjusting catalyst preparation conditions, acetylene pressure, polymerization time, polymerization temperature, etc. The thinner the produced polyacetylene film, the greater the solar energy conversion efficiency, which is desirable, but it is difficult to create a polyacetylene thin film with a thickness of 0.05 μm or less. The electrical conductivity of the polyacetylene of the p-n junction type element obtained in this way is 10 ^-9 to 10 ^-5 Ω ^-1 cm ^-1
Although this is low, it can be used as a solar cell due to the photovoltaic effect, but in order to obtain a higher conversion efficiency, the polyacetylene film is treated with an electron-accepting compound to increase the conductivity of the polyacetylene film to 1Ω ^-1 cm ^{- 1}
By increasing the conversion efficiency above, it has become possible to construct a solar cell with high conversion efficiency. Electron-accepting compounds that can increase the electrical conductivity of polyacetylene to a high level of 1 Ω ^-1 cm ^-1 or higher include (i) iodine (I ₂ ), bromine (Br ₂ ), and bromine iodide (IBr); Halogens (ii) such as arsenic pentafluoride (ASF ₅ ), antimony pentafluoride (SbF ₅ ), silicon tetrafluoride (SiF ₄ ), phosphorus pentafluoride (PCI ₅ ) and phosphorus pentafluoride (PF ₅ ), etc. The metal halide (iii) difluorosulfonyl peroxide (F ₂ S ₂ O ₄ ) is known. By treating the polyacetylene thin film of the pn heterojunction type device with these electron-accepting compounds, a solar cell with high conversion efficiency can be obtained. Methods for treating a polyacetylene film with these electron-accepting compounds include (i) bringing the vapor of the electron-accepting compound into direct contact with the polyacetylene film; and (ii) immersing the polyacetylene film in an inert organic solvent or water. One possible method is to introduce an electron-accepting compound into the material, but any method may be used. After treating the p-n heterojunction type element with an electron-accepting compound, it is desirable to remove excess electron-accepting compound that has not reacted with polyacetylene by a conventional method such as washing with an inert organic solvent or vacuum drying. . The p-type conductive polyacetylene thin film of the thus obtained p-type conductive polyacetylene thin film-n-type silicon p-n type heterojunction element may be attached directly to the p-type conductive polyacetylene thin film to form a solar cell. It is preferable to attach an ohmic transparent electrode and a lead wire to the converter because the conversion efficiency can be increased. The ohmic transparent electrode can be manufactured by the CVD method, vacuum evaporation method, sputtering method, etc. that are commonly used in the industry. Since the p-n junction solar cell manufactured by the above method is relatively susceptible to oxidative deterioration due to oxygen, it is preferable to use it in a vacuum or an inert gas atmosphere. Suitable packaging materials for this purpose include glass and plastics such as polycarbonate, polymethacrylate, and polyester, which are commonly used for solar cells. Example 1 A catalyst solution was prepared by charging 40 ml of toluene purified according to a conventional method, 10 mmol of tetrabutoxytitanium, and 40 mmol of triethylaluminum in this order at room temperature into a 200 ml reactor completely purged with nitrogen gas. did. The non-electrode surface of an n-type silicon wafer (doped with phosphorus atoms, resistivity 5 to 15 Ωcm) with an ohmic electrode attached by vapor-depositing gold on one side was heated with concentrated nitric acid:fluoric acid = 5:1 ( After etching for 1 minute with an etching solution (weight ratio), the film was washed with a large amount of distilled water, and then vacuum-dried at room temperature. Approximately 0.2 ml of the above catalyst solution was dropped onto the etched surface of the above dried n-type silicon wafer under a nitrogen gas atmosphere to uniformly apply the catalyst solution to the silicon surface. The system was then evacuated to expel nitrogen gas, cooled to -78°C, purified acetylene gas at a pressure of 4 cmHg was introduced, and polymerization was carried out for 30 seconds. Immediately after the polymerization was completed, unreacted acetylene gas was expelled and replaced with nitrogen gas. The catalyst was completely removed by washing with a large amount of purified toluene under a nitrogen gas atmosphere while cooling to −78° C., and the remaining toluene was removed by vacuum drying at room temperature. A transparent polyacetylene film with a thickness of 0.5 μm uniformly covered the silicon surface. The polyacetylene film produced has a cis form.
It was a p-type semiconductor with an electrical conductivity of 95% and an electrical conductivity of 8×10 ⁻⁸ Ω ⁻¹ ·cm ⁻¹ . Platinum lead wires were attached to the polyacetylene surface and the silicon electrode surface of the obtained polyacetylene/n-type silicon wafer laminate using a conductive adhesive (trade name "Electro dag 502"), and the adhesive was vacuum dried for 30 minutes. The organic solvent inside was removed. The p-n heterojunction device thus obtained was placed in a reaction vessel, and after evacuating the air from the system using a vacuum pump, approximately 1g of electron-accepting compound was added thereto.
of iodine was introduced and doping was carried out for 2 hours.
Subsequently, unreacted iodine was evacuated to obtain a pn heterojunction solar cell. The thickness of the polyacetylene film of the solar cell obtained is
The diameter was 0.5 μm and the area was 0.2 cm ² . When the photovoltaic force of the above solar cell was measured by irradiating it with sunlight (57.3mW/cm ² ), the open circuit voltage was 0.395V, the short circuit current was 4.325mA/cm ² , and the film factor was 0.23.
The conversion efficiency was 0.75%. Example 2 Before attaching lead wires to the polyacetylene/n-type silicon wafer laminate obtained in Example 1, a transparent gold film electrode was attached to the surface of the polyacetylene film by vacuum evaporation, and platinum was applied thereto. A pn heterojunction solar cell was produced in exactly the same manner as in Example 1 except that lead wires were attached. When the photovoltaic force was measured in exactly the same manner as in Example 1, the conversion efficiency was 1.50%. Comparative Example 1 P-
We created an n-heterojunction solar cell. When the photovoltaic force was measured in exactly the same manner as in Example 1, the conversion efficiency was 0.12%. This comparative example shows that it is preferable to treat the polyacetylene film with an electron-accepting compound to increase its electrical conductivity because this increases the conversion efficiency of the solar cell. Example 3 A trace amount of arsenic pentafluoride vapor was applied very slowly to the p-n heterojunction device obtained in Example 1.
After contacting for 30 minutes, unreacted arsenic pentafluoride vapor was removed to obtain a p-n heterojunction solar cell with a polyacetylene film having an electrical conductivity of 560 Ω ^-1 ·cm ^-1 . When the photovoltaic force of the obtained solar cell was measured in exactly the same manner as in Example 1, the conversion efficiency was 0.73.
It was %. Examples 4 to 7 P-
An n-heterojunction solar cell was manufactured, and the conversion efficiency of the obtained solar cell was measured in exactly the same manner as in Example 1.

[Table] Silicon tetrafluoride 〃 6 28 0.51
Basic five-year conversion 〃 7 130 0.66
antimony

[Brief explanation of the drawing]

The drawing is a conceptual diagram of a p-n heterojunction solar cell of the present invention, where 1 is a transparent ohmic electrode, 2 is a p-n heterojunction solar cell, and 2 is a p-n heterojunction solar cell.
3 represents a conductive polyacetylene thin film, 3 represents an n-type silicon single crystal thin plate (wafer), and 4 represents an ohmic electrode.

Claims (1)

[Claims] 1. A p-n heterojunction solar cell formed by forming a linear polyacetylene thin film having a conjugated double bond chain with a film thickness of 10 μm or less on an n-type silicon surface, and then treating the polyacetylene thin film with an electron-accepting compound.