JPH0547995B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a photovoltaic device, and more specifically, to a method for manufacturing a photovoltaic device, and more specifically, a photovoltaic device using phthalocyanine as a dispersoid, which has excellent photoelectric energy conversion efficiency and stability. The present invention relates to a method for manufacturing an element. (Prior art) Conventionally, photovoltaic elements include crystalline silicon, amorphous silicon, GaAs, InP/CdS,
Elements using inorganic compounds such as CdS/Cu ₂ S are known. However, even though these elements have a relatively high photoelectric energy conversion efficiency of 5 to 23%, the raw materials are expensive and the manufacturing technology is complicated, so the elements have to be expensive. Therefore, organic compounds are being reconsidered in order to obtain photovoltaic elements that use inexpensive materials and can easily be made large in area. In particular, phthalocyanine compounds
Because it is an extremely stable organic compound and has semiconductivity, it has attracted attention as a material for photovoltaic devices, and many reports have been made. For example, it is known that a photoactive layer thin film in which fine particles of phthalocyanine are dispersed in a polymer compound can be effectively used as a photovoltaic device (US Pat. No. 4,175,981). In this case, aluminum is used as the barrier metal, X-type metal-free phthalocyanine is used as the phthalocyanine, and the binder polymer is a material with good dark insulation, especially polystyrene, polyacrylonitrile, polyvinyl acetate, polycarbonate, Styrene-acrylonitrile copolymers and polyvinylcarbazole are said to be suitable. Photovoltaic elements formed using thin films in which X-type metal-free phthalocyanine is dispersed in these polymers are
It shows a photoelectric energy conversion efficiency of 1.4 to 4% for monochromatic incident light of 17 μW/cm ² . It is also specified that the photoelectric energy conversion efficiency does not change dramatically depending on the polymer used. By the way, 17μW/
The photoelectric energy conversion efficiency in monochromatic incident light of ^cm2 is 2.0-2.9%. In addition, a phthalocyanine-dispersed photovoltaic device using aluminum as a barrier metal has a power output of 6μW/
It shows good photoelectric energy conversion efficiency under weak light irradiation of cm ² , but as the light intensity increases, the photoelectric energy conversion efficiency decreases to 0.02% under strong light irradiation of 100 mW/cm ² . have been reported (ROLoutfy, JHSharp, J.Chem.
Phys. 71 (3), P1211 (1979)). These photoelectric energy conversion efficiency values are based on the amount of light transmitted through the aluminum electrode (the light transmittance of the aluminum electrode is 10 to 50%), and therefore the photoelectric energy conversion efficiency (abbreviated as η) based on irradiated light ) is 1/10 to 1/2 of the above value, and the amount of power that can be extracted under light irradiation is extremely low. Furthermore, it has been reported that a photovoltaic device with aluminum as a barrier metal and a resin-dispersed film of X-type metal-free phthalocyanine as a photoactive layer is extremely unstable (ROLoutfy, JHSharp, CK
Hsiao, R.Ho, J.Appl.Phys. 52 (8), P5218
(1981)). On the other hand, when indium is used as the barrier metal,
When irradiated with AMO simulated sunlight at a light intensity of 135mW/ ^cm2 , the open circuit voltage is 0.45V, and the short circuit current density is
Although 0.2 mA/cm ² and η about 0.03% are obtained, it is reported that the efficiency decreases to 57% of the initial value after 11 days (Solar Cells, 5 , P331 (1982)). Furthermore, an X-type metal-free phthalocyanine resin-dispersed photovoltaic device using an n-type semiconductor as a window material has been proposed as a new X-type metal-free phthalocyanine resin-dispersed photovoltaic device (RO
Routfy，YHShing，DKMurti，Solar Cells，
5, p. 331 (1982)), and a heterojunction device of cadmium sulfide-X-type metal-free phthalocyanine/polyester dispersion film-gold has also been reported. Using this element, open voltage 0.62V, short circuit current density 0.13mA/
cm ² and η0.027% (AMO, 87mW/cm ² irradiation light)
However, there is no mention of the long-term stability of the device, and there is no mention of the long-term stability of the device.
It has only been reported that the long-term stability of devices used as type semiconductors is excellent. As described above, none of the conventional photovoltaic devices using phthalocyanine as a dispersoid has been able to obtain very good photoelectric energy conversion efficiency. The present inventors have previously discovered that a photovoltaic device using a film in which X-type metal-free phthalocyanine is dispersed in a polymer compound with unique electrical properties, that is, a polyvinylidene compound, as a photoactive layer has been improved. It was discovered that the photoelectric energy conversion efficiency was as follows (Japanese Patent Application No. 59-59258). Furthermore, the present inventors have discovered that a similar device exhibits superior stability compared to conventional devices by using lead or cadmium sulfide as a barrier electrode (Japanese Patent Application No. 123154/1982). (Problems to be Solved by the Invention) However, as shown in Comparative Example 1 below, even in these devices, the photoelectric energy conversion efficiency remains at the initial value or higher for about 100 days after device fabrication. , after that, it gradually deteriorates over time,
It was found that the stability was still insufficient for use as a photovoltaic device. The object of the present invention is to eliminate the deterioration of the device over time, which is a drawback of the prior art, and to provide a device with even better stability.
An object of the present invention is to provide a photovoltaic device using phthalocyanine as a dispersoid. (Means for Solving the Problems) In order to achieve the above object, the present inventors conducted intensive research and found that cadmium sulfide, which was formed electrochemically and subjected to heat treatment, was used as a barrier electrode. The inventors have discovered that the stability of the phthalocyanine resin-dispersed photovoltaic device can be significantly improved by using a layer, and have arrived at the present invention. In the manufacturing method of the present invention, a film made of a polyvinylidene compound containing phthalocyanine in a dispersed state is used as a photoactive layer, and this is formed electrochemically, and a heat-treated cadmium sulfide barrier electrode and an ohmic electrode are used. It is characterized by being held in place. According to the manufacturing method of the present invention, it is possible to provide a photovoltaic element that is easier and cheaper than conventional photovoltaic elements, and has significantly improved stability. In the production method of the present invention, a film made of a polyvinylidene compound containing phthalocyanine in a dispersed state is used as a photoactive layer. As the phthalocyanine used in the present invention,
Various known metal or metal-free phthalocyanines may be mentioned, with X-type metal-free phthalocyanine being particularly preferred. Here, the X-type metal-free phthalocyanine means 7.5, 9.1, 16.7, 17.3 and
It has a strong X-ray diffraction pattern at 22.3 degrees, and its intensity ratio does not necessarily match that described in US Pat. No. 3,357,989, as shown in FIG. In Figure 4, A is the US patent number.
X-ray diffraction diagrams of X-type metal-free phthalocyanine cited from No. 3357989, B, C and D show X-ray diffraction diagrams of X-type metal-free phthalocyanine produced by various production methods (all copper Kα). Furthermore, commercially available pigments, their sulfuric acid-treated products, or sublimation-purified products can be used as metal-free phthalocyanine, but, for example, purification via dilithium phthalocyanine or J.Am.Chem.Soc., 103 , P4629
(1981), it is preferable to use high-purity phthalocyanine obtained by purification using various complexes of phthalocyanine, or by a method combining these methods with sulfuric acid treatment or sublimation purification. . Here, high purity phthalocyanine preferably has a purity of 95% or more, more preferably 97.5% or more. X-type metal-free phthalocyanine can be easily produced by applying mechanical energy such as a ball mill to α-type metal-free phthalocyanine obtained by the above purification method. Examples of the polyvinylidene compound used in the present invention include polymers such as vinylidene fluoride, vinylidene chloride, vinylidene cyanide, and copolymers of these and other copolymer components. These (co)polymers may be produced by any polymerization method, and those commercially available as molding materials can be used as they are, or they can be purified by a reprecipitation method and used. Polyvinylidene cyanide or its copolymer is also available from H.Gilbert et al., J.Am.Chem.Soc.
76, P1074 (1954), 78 , P1669 (1956), etc. The degree of polymerization of these (co)polymers is not particularly limited, as long as they function as a binder for the phthalocyanine dispersoid, and those having a degree of polymerization of about 1000 to 5000 are generally preferred. Examples of these (co)polymers include polyvinylidene fluoride such as KF-Polymer (trade name, Kureha Chemical Industry Co., Ltd.).
Polyvinylidene chloride includes Foraflon (trade name, manufactured by Produits Chimiques),
Examples include Saran (trade name of vinylidene chloride-vinyl chloride copolymer, manufactured by Asahi Kasei Corporation), vinylidene chloride-acrylonitrile copolymer (manufactured by Polysciences, Inc.), and the like. The mixing ratio of the metal-free phthalocyanine and the polyvinylidene compound is related to the thickness of the formed film, but a weight ratio of 1:4 to 4:1 is preferable.
If the phthalocyanine content is too high, the strength of the formed film will decrease and cracks will easily occur in the film, and if it is too low, the photoelectric energy conversion efficiency will deteriorate, making it impractical. A particularly preferred weight ratio is 2:3 to 3:2. The solvent used in the production method of the present invention may be any solvent as long as it can dissolve or swell the polyvinylidene compound and maintain the crystalline form of the phthalocyanine. For polyvinylidene fluoride or polyvinylidene cyanide, aprotic polar solvents such as dimethylformamide, dimethylacetamide, tetramethylurea, etc. are preferred. Regarding polyvinylidene chloride, for example, carbonyl compounds such as cyclohexanone and isophorone, N-methylpyrrolidone,
Aprotic polar solvents such as tetramethylurea are preferred. Further, halides such as epichlorohydrin and dichloromethane or general organic solvents can also be used together as diluents. In the present invention, the polyvinylidene compound has some interaction with phthalocyanine in the photoactive layer and improves the photoelectric energy conversion efficiency, but other polymeric compounds may be added within a range that does not reduce this efficiency. You may let them. For example, polyvinyl acetate, polyacrylonitrile, polyester resin, phenolic resin, epoxy resin, etc.
For polyvinylidene compounds, preferably 50
It can be added in a proportion of % by weight or less. Further, in the photoactive layer used in the production method of the present invention, dye sensitizers such as coumarin 6, rhodamine 6G, perylene-9, etc., chloranil,
Electron-accepting compounds such as tetracyanoquinodimethane, trinitrofluorenone, and iodine can also be added. The photovoltaic device obtained by the manufacturing method of the present invention is
It has a structure in which the photoactive layer is sandwiched between a barrier electrode and an ohmic electrode, and as a barrier electrode,
As long as a cadmium sulfide barrier electrode formed electrochemically and subjected to heat treatment is used, there are no restrictions on the manufacturing process. In the manufacturing method of the present invention, a cadmium sulfide layer is used as a barrier electrode. The cadmium sulfide layer is
It is formed on the working electrode by electrochemical techniques from a solution of cadmium salt and sulfur dissolved in a solvent. Although metals such as platinum and gold may be used as the working electrode, it is preferable to use the cadmium sulfide layer also as a window material, so it is preferable to use a transparent conductive film as the working electrode. As such a transparent conductive film, those commercially available under names such as NESA and ITO can be used. The method of electrochemically forming the above-mentioned cadmium sulfide electrode is the method of Baranski et al. (J.Electrochem.
Soc. 128 , 963, (1981), J.Appl.Phys., 54 , 6390
(1983)), but these methods tend to cause cracks in the cadmium sulfide film and form pinholes through which current flows. A method of forming cadmium sulfide is preferably used. In this case, cadmium sulfide is formed when a negative voltage is applied to the working electrode and eluted when a positive voltage is applied, so the absolute value of the amount of electricity that passes when a negative voltage is applied must be larger than that when a positive voltage is applied. It won't happen. Cadmium salt and sulfur are used as electrolytes in the solution when electrochemically forming the cadmium sulfide layer. Cadmium salts include cadmium mineral acid salts, organic acid salts, etc., such as cadmium chloride,
Cadmium bromide, cadmium perchlorate, cadmium acetate, etc. are preferably used. The solvent for the electrolyte may be any solvent that dissolves the electrolyte,
Alcohols such as ethanol, ethylene glycol, diethylene glycol, or mixed solutions of these and water, aprotic polar solvents such as dimethyl sulfoxide, etc. can be used. The electrochemical formation (electrodeposition) of the cadmium sulfide layer may be carried out at room temperature, but it is preferably carried out under heating, since the solubility of cadmium salts and sulfur is low and the liquid resistance increases. The cadmium sulfide layer formed as described above is then heat treated to form the cadmium sulfide electrode of the present invention. The heating temperature is preferably in the range of 200 to 600°C, although it depends on the type of substrate. Although there is no particular restriction on the treatment time, a range of 0.1 to 5 hours is particularly preferred. There are no particular restrictions on the atmosphere for heat treatment, but
Nitrogen, hydrogen, air, oxygen atmosphere, etc. can be used, and processing can also be carried out in vacuum. Although the reason is still unclear, the stability of the phthalocyanine resin-dispersed photovoltaic device, which is formed using such an electrochemical method and heat-treated using a cadmium sulfide layer as a barrier electrode, has been dramatically improved. do. As the ohmic electrode in the present invention, metals having a large work function or metal oxides thereof such as gold, silver, platinum, copper, tin oxide, indium oxide, etc. are preferably used. Further, conductive pastes such as silver paste, carbon paste, etc. can also be used. To obtain a photovoltaic device using the manufacturing method of the present invention,
For example, first, 0.25 to 4 parts by weight of a polyvinylidene compound and 1 to 300 parts by weight of the above solvent are mixed with 1 part by weight of the phthalocyanine, and if desired, the above polymer compound, dye sensitizer, and electron acceptor are added. Compounds, etc. are added and mixed. The resulting mixture is then subjected to, for example, ball milling, ultrasonic dispersion,
Spex Mixer Mill, paint shaker,
After uniformly dispersing using a dispersing means such as a jet mill, this dispersion is applied onto the cadmium sulfide electrode. The above dispersion can be carried out under heating or cooling as required. The dispersion time varies depending on the total amount, the viscosity of the liquid, the dispersion temperature, the dispersion means, etc., so it cannot be stated unconditionally, but it is generally preferably in the range of 10 minutes to 5 hours. Various methods can be used for coating the electrodes, such as spin coating, applicator method, wire bar method, doctor blade method, and screen printing method. The electrode is coated so that the film thickness when dried is preferably 0.05 to 50 μm, particularly preferably 0.1 to 10 μm. Next, after drying this, an ohmic electrode is formed by a method such as vacuum deposition or sputtering. An example of the structure of a photovoltaic device obtained by the manufacturing method of the present invention is shown in FIG. 1 together with its energy conversion efficiency measurement system. This system consists of a photoactive layer made of a polyvinylidene compound 2 containing phthalocyanine particles 1, a transparent conductive film (ITO) 4 having a cadmium sulfide barrier electrode 3 sandwiching the photoactive layer, and a conductive film electrode (ohmic electrode) 6. , a glass substrate 5 provided in close contact with the outside of a transparent conductive film (ITO) 4, and each electrode 3,
Lead terminals (silver paste) 7 and 7' provided in the terminal 6, lead wires 8 and 8' connecting the terminals 7 and 7' and the load resistor 9, and lead wires 8 and 8' provided in the circuit bypassing the load resistor 9. Electrometer (voltmeter)
It consists of 10. When light is irradiated in the direction indicated by the arrow in the upper center of the figure, the element converts the light energy into electrical energy, and the voltage change is measured by the voltmeter 10. The photoelectric energy conversion efficiency (based on irradiated light) n of a photovoltaic element is determined by measuring the amount of light irradiation and the voltage change across the load resistor, and selecting the load resistor accordingly. It is calculated by the following formula using the current density (Jsc) and fill factor. η = Voc × Jsc × FF / Pi × 100 (%) (FF is fill factor, Pi is irradiated light energy per unit area) (Effects of the invention) According to the method for manufacturing a photovoltaic element of the present invention By using phthalocyanine as a dispersoid, a polyvinylidene compound as a binder, and an electrochemically formed cadmium sulfide layer as a barrier electrode, which has been heat-treated, the optical The stability of the electromotive force element can be significantly improved. Furthermore, according to the manufacturing method of the present invention, it is possible to easily manufacture a photovoltaic device with a large area at a low cost, and it can also be used as a photo sensor, making it possible to obtain a photovoltaic device with extremely high industrial practical value. can. (Examples) The present invention will be described below with reference to Examples, but the scope of the present invention is not limited thereby. Example 1 30 mm square platinum plate as counter electrode, working electrode
In a 300m flask containing 30mm square ITO glass.
300 m of dimethyl sulfoxide in which 0.05 M cadmium chloride and 0.1 M sulfur were dissolved was added.
Further, as a reference electrode, a cadmium wire immersed in a 0.05M cadmium chloride/dimethyl sulfoxide solution was placed in the electrolyte and placed in front of the working electrode with a clay plate in between. The system was heated to 110° C. while bubbling with argon. Then -3mA is applied to the working electrode using a function generator and a potentiogalvanostat.
Apply a current of +0.5mA for 2 seconds, and apply a current of +0.5mA for 2 seconds.
By repeating 12 times, a cadmium sulfide thin film is formed.
Formed on ITO glass. This cadmium sulfide film was washed with hot dimethyl sulfoxide and acetone, dried, and then placed in an electric furnace heated to 400°C.
Heat treatment was performed for a period of time. The X-type metal-free phthalocyanine was prepared by grinding high-purity a-type metal-free phthalocyanine using a ball mill. 30 mg of this high purity X-type metal-free phthalocyanine,
20 mg of polyvinylidene fluoride and 1.2 ml of tetramethylurea were mixed and dispersed at -15°C for 20 minutes to form a slurry. The obtained thriller was dropped onto the above cadmium sulfide thin film fixed on the spinner head, and the spinner was rotated at 800 rpm for 5 minutes.
A film was formed by spinning for seconds. This film was heated to 100℃.
The thin film device was then vacuum dried for 24 hours to completely remove the solvent. Next, gold was vacuum-deposited on the upper surface of this device film to form an ohmic electrode to obtain a photovoltaic device. This device was stored in the dark in the air, and the photoelectric energy conversion efficiency (η) of this device under white irradiation (75.8 mW/cm ² ) was measured approximately every 30 days.
Measurements were made over 180 days. The temporal change in η obtained in this way is shown as EX1 in FIG. 2. In Figure 2, the initial value of η is 0.070%, and after 180 days it is 0.069%, and the change in η over time (EX1) is almost horizontal and does not change. It can be seen that the element is stable over a long period of time and hardly deteriorates. On the other hand, the photoelectric energy conversion efficiency η of the device obtained in Comparative Example 1 (described later) (device using a cadmium sulfide film that was not subjected to heat treatment) decreased significantly due to aging (CEX1). ,
It can be seen that the long-term stability is poor. Example 2 Two cadmium sulfide thin films were formed on ITO glass using the same electrochemical method as in Example 1. One of them was heated to 200℃ and the other one was heated to 300℃.
Heat treatment was performed for a period of time. A photovoltaic device was obtained in the same manner as in Example 1 using these two cadmium sulfide films. Each device was stored in the dark in the air, and the energy conversion efficiency (η) under white light irradiation (75.8 mW/cm ² ) was measured every 30 days for 150 days. The initial value of η of a device using a cadmium sulfide film heat-treated at 200°C is 0.057% and 0.059 after 150 days.
%, and the η of the element using the cadmium sulfide film heat-treated at 300°C was 0.063% at the initial value and 0.066% after 150 days, with almost no change in η in either case. Comparative Example 1 A photovoltaic device was formed in the same manner as in Example 1 except that cadmium sulfide that was not subjected to heat treatment was used, and the energy conversion efficiency was measured. Figure 2 shows the change in η over time when the sample was stored in the dark in the atmosphere for 180 days as CEX1. In Figure 2, the initial value of η is 0.069%, 0.084% after 34 days, and 0.054% after 180 days, and the change in η over time (CEX1) changes greatly, especially
The decrease was significant after 34 days, indicating that elements using cadmium sulfide films that were not heat-treated
It can be seen that it has poor long-term stability and is prone to deterioration. Example 3 Report by AS Baranski et al. (J.Electrochem.Soc.,
128 (5), P963 (1981)), a cadmium sulfide film was electrodeposited to a thickness of about 0.3 μm on a transparent conductive film (ITO). This cadmium sulfide film
Heat treatment was performed at 400°C for 1 hour. Next, 30 mg of X-type metal-free phthalocyanine, 20 mg of polyvinylidene fluoride, 0.9 ml of tetramethylurea and 0.3 ml of epichlorohydrin were mixed and dispersed at -15°C for 30 minutes to form a slurry. The resulting slurry was dropped onto the cadmium sulfide film fixed on the spinner head, and the spinner was rotated at 600 rpm for 5 seconds to form a film. 100% of this film
The thin film element was prepared by vacuum drying at ℃ for 24 hours to completely remove the solvent. Next, gold was vacuum-deposited on the upper surface of this device film to form an ohmic electrode to obtain a photovoltaic device. This photovoltaic element has strength
White light of 75.8 mW/cm ² was irradiated, and the continuous change in short-circuit photocurrent over time was measured. This change over time is shown in FIG. 3 as EX3. In Figure 3, the change over time of the short-circuit photocurrent (EX
Since 3) is almost horizontal and does not change,
It can be seen that the device using the heat-treated cadmium sulfide film is extremely stable and hardly deteriorates. On the other hand, in the device obtained in Comparative Example 3 (described later) (device using a cadmium sulfide film that has not been heat-treated), the short-circuit photocurrent changes over time (CEX2) and decreases significantly. This shows that the stability is inferior. Comparative Example 2 As in Example 3, a cadmium sulfide film was electrochemically formed to a thickness of 0.3 μm on ITO. A photovoltaic device was obtained using this cadmium sulfide film as it was, and in the same manner as in Example 3 except for the above. This device was irradiated with white light with an intensity of 75.8 mW/cm ² and the change in short-circuit photocurrent over time was measured. This change over time is shown in Figure 3 as CEX2. In FIG. 3, it can be seen that the element using a cadmium sulfide film that has not been subjected to heat treatment has inferior stability because the change over time (CEX2) of the short-circuit photocurrent changes and the decrease is large.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of the structure of the photovoltaic device of the present invention and its photoelectric energy conversion efficiency measurement system, and FIG. 2 is a schematic cross-sectional view of the photovoltaic device obtained in Example 1 and Comparative Example 1. Figure 3 shows the change over time in the photoelectric energy conversion efficiency (measured under white light irradiation) when stored in the atmosphere. Figure 4, a diagram showing the change in short-circuit photocurrent over time, is
-X-ray diffraction diagram of metal-free phthalocyanine (copper Kα)
It is. 1... Phthalocyanine particles, 2... Polyvinylidene compound, 3... Cadmium sulfide film, 4...
Transparent conductive film (ITO), 5...Glass substrate, 6...
Conductive film electrode (gold), 7, 7'...silver paste, 8,
8'... Lead wire, 9... Load resistance, 10... Electrometer.

Claims (1)

[Scope of Claims] 1. A cadmium sulfide barrier electrode and an ohmic electrode formed electrochemically using a film made of a polyvinylidene compound containing phthalocyanine in a dispersed state as a photoactive layer and subjected to heat treatment. A method for manufacturing a photovoltaic device, which comprises sandwiching the device between the two. 2. The method for producing a photovoltaic device according to claim 1, wherein the phthalocyanine is an X-type metal-free phthalocyanine. 3. The method for manufacturing a photovoltaic device according to claim 1 or 2, wherein the cadmium sulfide electrode is a film-like material that has been heat-treated at a temperature of 200 to 600°C.