JPH0691273B2 - Photovoltaic device manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a photovoltaic device, and more specifically, a photovoltaic device using phthalocyanine as a dispersoid, which is excellent in photoelectric energy conversion efficiency and stability. Manufacturing method.

(Prior Art) Conventionally, as a photovoltaic element, crystalline silicon, amorphous silicon, GaAs, InP / CdS, CdS / Cu ₂ S, CdS / CdTe
An element using an inorganic compound such as is known. However, these devices have a photoelectric energy conversion efficiency of 5 to 23.
However, even if it is relatively high, the raw material is expensive and the manufacturing technique is complicated, so the element must be expensive.

Therefore, in order to obtain a photovoltaic element that uses an inexpensive material and that can easily have a large area, organic compounds are being reviewed. Particularly, the phthalocyanine compound is an extremely stable organic compound, and also has semiconductivity.
It has received attention as a photovoltaic element material 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 element (US Pat. No. 4,175,981).
issue). In this case, aluminum is used as the barrier metal, X-type metal-free phthalocyanine is used as the phthalocyanine, and the polymer for the binder has a good dark insulating property, particularly polystyrene, polyacrylonitrile,
Polyvinyl acetate, polycarbonate, styrene-acrylonitrile copolymers and polyvinylcarbazole are said to be suitable. A photovoltaic element formed by using a thin film in which X-type metal-free phthalocyanine is dispersed in these polymers has a photoelectric energy of 1.4 to 4% for monochromatic incident light of 1 to 17 μW / cm ^2. It shows the conversion efficiency. 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 for monochromatic incident light of cm ² is 2.0.
~ 2.9%.

In addition, such a phthalocyanine-dispersed photovoltaic device using aluminum as a barrier metal exhibits good photoelectric energy conversion efficiency under irradiation of weak light of 6 μW / cm ² , but with the increase of light intensity, the photoelectric energy conversion The efficiency is reported to decrease to 0.02% under strong light irradiation of 100 mW / cm ² (ROLoutfy, JHSharp, J.Che.
m.Phys. 71 (3), P1211 (1979)).

Note that these photoelectric energy conversion efficiency values are values with respect to 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 based on the irradiation light (abbreviated as η). Value is 1/10 to 1/2 of the above value, and therefore, the electric power value that can be taken out under light irradiation is very low.

Further, aluminum is used as a barrier metal, and an X-type metal-free lid is used.
Photovoltaic device using a photoactive layer made of a resin dispersion film of cyanine
Is reported to be very unstable (R.O.Lo
utfy, J.H.Sharp, C.K.Hsiao, R.Ho, J.Appl.Phys.52
(8), P5218 (1981)).

On the other hand, when indium is used as the barrier metal, 135 mW / cm
^{When the} AMO pseudo-sunlight is irradiated with the light intensity of ² , the open circuit voltage is
0.45V, short circuit current density 0.2mA / cm ² and η about 0.03% are obtained, but the efficiency is reported to drop to 57% of the initial value after 11 days (Solar Cells, 5 , P331 (198
2)).

Furthermore, as a new photovoltaic element of X-type metal-free phthalocyanine resin dispersion type, an X-type metal-free phthalocyanine resin dispersion type photoelectric conversion element using an n-type semiconductor as a window material has been proposed (ROLoutfy, YHShing, DKMurt
i, Solar Cells, 5 , P331 (1982), Cadmium sulfide-
A heterojunction element of X-type metal-free phthalocyanine / polyester dispersion film-gold has also been reported. With this device, an open-circuit voltage of 0.62 V, tank current density of 0.13 mA / cm ² and η 0.027% (AM0, irradiation light of 87 mW / cm ² ) can be obtained, but the long-term stability of the device is not mentioned at all. Not
It is only reported that the device using zinc oxide as an n-type semiconductor is slightly superior in long-term stability.

As described above, none of the conventional photovoltaic devices using phthalocyanine as the dispersoid can obtain such excellent photoelectric energy conversion efficiency.

The present inventors have improved a photovoltaic device using a polymer compound having electrically unique properties, that is, a film in which an X-type metal-free phthalocyanine is dispersed in a polyvinylidene compound as a photoactive layer. It was found that the photoelectric energy conversion efficiency was improved (JP-A-60-201672).

Furthermore, the inventors of the present invention used lead or cadmium sulfide as a barrier electrode in the same device (Japanese Patent Laid-open No. 61-3473) and heat-treated the cadmium sulfide electrode (Japanese Patent Application No. No. 43160), it has been found that it exhibits superior stability as compared with conventional ones.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for producing a photovoltaic device having phthalocyanine as a dispersoid, which achieves superior photoelectric energy conversion efficiency and is excellent in stability. Especially.

(Means for Solving Problems) As a result of earnest research for achieving the above-mentioned object, the present inventors have used a cadmium sulfide layer as a barrier electrode, and using the phthalocyanine resin dispersion film as a photoactive layer on this layer. The inventors have found that the photoelectric energy conversion efficiency is remarkably enhanced by subjecting the formed one to a heat treatment at 150 to 300 ° C., and thus the present invention has been accomplished.

The method for producing a photovoltaic element of the present invention is a photovoltaic device having a structure in which a film made of a polyvinylidene compound containing phthalocyanine in a dispersed state is used as a photoactive layer and sandwiched between a cadmium sulfide barrier electrode and an ohmic electrode. In the method for manufacturing a power element, the photoactive layer of the film is formed on the cadmium sulfide barrier electrode, and then heat treatment is performed at 150 to 300 ° C.

According to the present invention, a photovoltaic element having improved photoelectric energy conversion efficiency can be provided more easily and cheaply than a conventional photovoltaic element.

The photovoltaic element obtained by the production method of the present invention has a film made of a polyvinylidene compound containing phthalocyanine in a dispersed state as a photoactive layer.

Examples of the phthalocyanine used in the present invention include various known metal or metal-free phthalocyanines,
X-type metal-free phthalocyanine is particularly preferable.

Here, the X-type metal-free phthalocyanine means a strong X at 7.5, 9.1, 16.7, 17.3 and 22.3 degrees at the Bragg angle.
It has a line diffraction pattern, and its intensity ratio need not necessarily match that described in US Pat. No. 3,357,989, as shown in FIG. Incidentally, A in FIG. 2 is X which is cited from US Pat. No. 3,357,989.
X-ray diffractograms of -type metal-free phthalocyanine, B, C and D show X-ray diffractograms of X-type metal-free phthalocyanine (all copper Kα) by various production methods.

Further, as the metal-free phthalocyanine, a commercially available pigment, a sulfuric acid-treated product or a sublimated purified product thereof can be used, but for example, a purification method via dilithium phthalocyanine or J. Am.
hem.Soc., 103 , P4629 (1981), the purification method via various phthalocyanine complexes, and the purification method by a combination of these methods with sulfuric acid treatment or sublimation purification. It is preferable to use high-purity phthalocyanine.

Here, the high-purity phthalocyanine preferably has a purity of 95% or more, more preferably 97.5% or more.

The X-type metal-free phthalocyanine can be easily produced by adding mechanical energy such as a ball mill to the α-type metal-free phthalocyanine obtained by the above-mentioned purification method.

Examples of the polyvinylidene compound used in the present invention include:
Examples thereof include polymers such as vinylidene fluoride, vinylidene chloride and vinylidene cyanide, and copolymers of these with other copolymerization components. These (co) polymers may be produced by any polymerization method, and commercially available molding materials may be used as they are, or they may be purified by the reprecipitation method before use. Polyvinylidene cyanide or a copolymer thereof is described in H. Gilbert et al., J. Am. Chem. Soc., 76 , P1074.
(1954), ibid. 78 , P1669 (1956) and the like.

The degree of polymerization of these (co) polymers is not particularly limited as long as they function as a binder of a phthalocyanine dispersoid,
Generally, those having a degree of polymerization of about 1000 to 5000 are preferable. Examples of these (co) polymers include polyvinylidene fluorides such as KF-polymer (trade name, manufactured by Kureha Chemical Industry Co., Ltd.), Foraflon (trade name, Produits Chimi).
ques company), etc., as polyvinylidene chloride,
For example, Saran (trade name of vinylidene chloride-vinyl chloride copolymer manufactured by Asahi Kasei Corporation), vinylidene chloride-acrylonitrile copolymer (Polysciences.I)
nc) and the like.

The mixing ratio of the metal-free phthalocyanine and the polyvinylidene compound is not particularly limited, but is preferably 1: 4 to 4: 1 by weight, though it is related to the film thickness to be formed. If the phthalocyanine content is too high, the strength of the formed film is lowered and the film is easily cracked, and if it is too low, the photoelectric energy conversion efficiency is deteriorated, which is not practical. A particularly preferred weight ratio is 1: 3 to 3: 2.

The solvent used for producing the photovoltaic device by the method of the present invention may be any solvent that can dissolve or swell the polyvinylidene compound and can maintain the crystalline form of phthalocyanine. With regard to polyvinylidene fluoride or polyvinylidene cyanide, an aprotic polar solvent such as dimethylformamide, dimethylacetamide or tetramethylurea is preferable. Regarding polyvinylidene chloride, for example, carbonyl compounds such as cyclohexanone and isophorone, and aprotic polar solvents such as N-methylpyrrolidone and tetramethylurea are preferable. A halide such as epichlorohydrin or dichloromethane or a general organic solvent can also be used as a diluent.

The polyvinylidene compound used in the present invention has some interaction with the phthalocyanine in the photoactive layer and improves photoelectric energy conversion efficiency, but other polymer compounds are added within a range that does not reduce this efficiency. You may let me. For example, polyvinyl acetate, polyacrylonitrile, polyester resin, phenol resin, epoxy resin, etc., with respect to the polyvinylidene compound, preferably 50
It can be added in a proportion of not more than wt%.

Further, when a dye sensitizer such as rhodamine, an electron-donating compound such as pyrene, for example, dinitrobenzene, chloranil, an electron-accepting compound such as tetracyanoquinodimethane is added to the photoactive layer used in the present invention, Further, the effect of the present invention is improved.

The photovoltaic element obtained by the manufacturing method of the present invention has a structure in which the photoactive layer is sandwiched between a barrier electrode and an ohmic electrode, but the structure process is not limited at all.

In the photovoltaic device of the present invention, a cadmium sulfide layer is used as the barrier electrode.

The cadmium sulfide layer is usually transparent or anti-transparent to visible light, and is vacuum-deposited, sputtered, screen-printed, or spray-heated on a substrate such as glass or a transparent polymer film, or on a NESA or ITO film. It is formed by a method such as decomposition and proximity vapor transport method. When a transparent conductive film such as NESA or ITO film is used as the substrate, it can be formed by an electrochemical method.

Further, when the cadmium sulfide film is formed on the X-type metal-free phthalocyanine resin dispersion film formed on the ohmic electrode, vacuum deposition or sputtering is preferably used.

The cadmium sulfide film is a film that forms a junction that is a source of photovoltaic power, and also serves as a window that allows light to pass through to the photoactive layer. Therefore, it is necessary to sufficiently transmit visible light.
Since the cadmium sulfide film is essentially transparent to visible light, it has a visible light transmittance of 10% or more (usually 20 to 95%).
However, the present invention is not limited to this range.

Further, as the cadmium sulfide film, the film formed by the above method may be used as it is, but it may be used after being heat treated,
The stability of the device is dramatically improved by the heat treatment.

The ohmic electrode in the present invention, a metal having a large work function or a metal oxide thereof, for example, gold, silver, platinum,
Copper, tin oxide, indium oxide and the like are preferably used. These are used by being formed on a substrate such as glass or a transparent polymer film or on a dispersion film by a technique such as vacuum deposition and sputtering. Further, it can be used in the form of the metal plate, and NESA, ITO film or the like which is commercially available as a transparent conductive film can also be used.
Alternatively, a conductive paste such as a silver paste or a carbon paste can be used.

The heat treatment in the present invention needs to be performed after forming a phthalocyanine dispersion film on the cadmium sulfide layer, for example, forming an X-type metal-free phthalocyanine resin dispersion film on the cadmium sulfide layer (or ohmic electrode). , And then a photovoltaic element formed by forming an ohmic electrode (or a cadmium sulfide layer), or X- on the cadmium sulfide layer.
It is applied to an element having a metal-free phthalocyanine resin dispersion film formed thereon. In the latter case, a photovoltaic element is formed by forming an ohmic electrode after the heat treatment. The heating temperature is in the range of 150 to 300 ° C., and the treatment time is not particularly limited, but the range of 1 second to 1 hour is particularly preferable. The atmosphere for the heat treatment is not limited, but a nitrogen, hydrogen, air, oxygen atmosphere or the like can be specified, and the heat treatment may be performed in a vacuum. The heating method is also not particularly limited, and an ordinary heating method such as an electric furnace, a hot plate, or laser heating can be used.

By heat-treating the element in which the phthalocyanine dispersion film is formed on the cadmium sulfide layer in this manner, the short-circuit photocurrent and the photoelectric energy conversion efficiency are dramatically improved, although the reason is not yet clear.

In order to obtain a photovoltaic device by the manufacturing method of the present invention, first, 0.25 to 4 parts by weight of a polyvinylidene compound and 1 to 300 parts by weight of the solvent are mixed with 1 part by weight of the phthalocyanine, and further, if desired, The above-mentioned polymer compound, dye sensitizer, electron donating compound, electron accepting compound and the like are added and mixed. The resulting mixture is then, for example, ball milled,
The dispersion is uniformly dispersed by a dispersing means such as ultrasonic dispersion, Mixer Mill manufactured by Spex Co., paint shaker, jet mill, etc., and the obtained dispersion liquid is applied onto the barrier electrode or the ohmic electrode. The dispersion can be carried out with heating or with cooling, as required. The dispersion time varies depending on the total amount, the viscosity of the liquid, the dispersion temperature, the dispersion means, etc., and therefore cannot be generally stated, but a range of 10 minutes to 5 hours is generally preferred. Various methods such as a spin coating method, an applicator method, a wire bar method, a doctor blade method, and a screen printing method can be used as a method for applying the electrodes. The coating on the electrode preferably has a dry film thickness of 0.05 to 50 μm.
m, particularly preferably 0.1 to 10 μm.

Then, after drying this, when the electrode on the substrate is a barrier electrode, an ohmic electrode is formed, and when the electrode is an ohmic electrode, a barrier electrode is formed by a method such as vacuum deposition and sputtering.

The heat treatment of the present invention is performed on the thus-configured element. However, when the electrode on the substrate is a barrier electrode, the heat treatment of the present invention may be performed before forming the ohmic electrode.

An example of the structure of the photovoltaic element obtained by the manufacturing method of the present invention is shown in FIG. 1 together with its energy conversion efficiency measuring system.

This system sandwiches a photoactive layer composed of a polyvinylidene compound 2 containing phthalocyanine particles 1 and the photoactive layer.
Transparent conductive film (ITO) having cadmium sulfide barrier electrode 3
4 and the conductive film electrode (ohmic electrode) 6 and the glass substrate 5 provided in close contact with the outside of the transparent conductive film (ITO) 4.
And lead terminals (silver paste) 7 and 7a provided on the electrodes 3 and 6, and lead wires 8, 8a, 8b and 8c for connecting the terminals to the function generator 9, voltmeter 10 and ammeter 11, respectively. 8d, an AD converter 12 for converting the signals of the voltmeter 10 and the ammeter 11 into a digital signal, and a computer 13 for processing the data.

In the device having the above configuration, when light is irradiated in the direction indicated by the arrow at the upper center of the figure and a triangular wave that changes from +0.5 V to −0.80 V at 0.002 Hz is applied to the cadmium sulfide 3 from the function generator 9, the element The light energy is converted into electric energy by the, and the photocurrent change according to the applied voltage is measured by the ammeter 11. The applied voltage and photocurrent are converted into digital signals by the AD converter 12 and processed by the computer 13. At that time, the photocurrent when the applied voltage is 0 V (short circuit photocurrent density Jsc), the voltage when the current is 0 A (open circuit voltage Voc), and the optimum load condition can be found.

Energy conversion efficiency (irradiation light reference) η is calculated by the following equation.

(FF is fill factor, Pi is irradiation light energy per unit area) (Effect of the invention) According to the production method of the present invention, phthalocyanine is used as a dispersoid and vinylidene compound as a binder on the cadmium sulfide layer. A photovoltaic element having significantly improved photoelectric energy conversion efficiency as compared with a conventional photovoltaic element can be obtained by a simple operation of forming a film and then performing heat treatment.

Further, the manufacturing method of the present invention has a very high industrial practical value such that a large-area photovoltaic element can be easily manufactured at low cost and can be used as an optical sensor.

(Examples) Hereinafter, the present invention will be described with reference to Examples, but the scope of the present invention is not limited thereby.

Example 1 Report of A.S. Baranski et al. (J. Electrochem. Soc.,128
(5), P963 (1981)) on transparent conductive film (ITO)
Cadmium sulfide film is electrodeposited to a thickness of about 0.3 μm
did.

The X-type metal-free phthalocyanine was prepared by ball-milling high-purity α-type metal-free phthalocyanine.

This high-purity X-type metal-free phthalocyanine 30 mg, polyvinylidene fluoride 20 mg and tetramethylurea 1.2 m
l were mixed and dispersed at -15 ° C for 20 minutes to form a slurry. The obtained slurry was dropped on the above-mentioned cadmium sulfide thin film fixed on a spinner head, and the spinner was rotated at 800 rpm for 5 seconds to form a film. This film was vacuum dried at 100 ° C. for 24 hours to completely remove the solvent to prepare a thin film element. Next, gold was vacuum-deposited on the upper surface of this device film to form an ohmic electrode, and a photovoltaic device was obtained.

Place this photovoltaic element on a hot plate and
The temperature is raised to 200 ° C at a rate of 100 ° C / min, and 2
A photovoltaic element was obtained by performing heat treatment for a minute.

This photovoltaic element is irradiated with monochromatic light of 616 nm or pseudo-sunlight obtained with a xenon lamp and AM1 filter, and Jsc, Vo
The c, FF and energy conversion efficiency η were measured. The results are shown in Table 1. These values are Comparative Example 1 or ROLo
utfy et al. reported in Solar Cells, 5 , P331 (1982) for cadmium sulfide to X-type metal-free phthalocyanine-resin dispersed photovoltaic element (AM0 pseudo sunlight, 87 mW / cm ²
Irradiated, Jsc 0.13mA / cm ² , Voc0.62V, FF0.3 and η0.02
7%), which is a very high value.

From these results, it is clear that the photovoltaic device obtained by the manufacturing method of the present invention exhibits excellent photoelectric energy conversion efficiency.

Comparative Example 1 In Example 1, the energy conversion efficiency η of the element before the heat treatment was measured under the same conditions as in Example 1. The results are shown in Table 1 together with Example 1.

Example 2 A 30 mm square platinum plate was used as the counter electrode, and a 30 mm square was used as the working electrode.
A 300 ml flask containing ITO glass was charged with 300 ml of dimethyl sulfoxide containing 0.05M cadmium chloride and 0.1M sulfur. As a reference electrode, a cadmium wire dipped in a 0.05M cadmium chloride / dimethylsulfoxide solution was placed in the above electrolytic solution and placed in front of the working electrode with a bisque plate separated. The system was heated to 110 ° C. with a bubbling of argon.

Then, a cadmium sulfide thin film was formed on the ITO glass by applying a current of −3 mA to the working electrode for 18 seconds and a current of +0.5 mA for 2 seconds using a function generator and a potentiogalvanostat and repeating 12 times. The cadmium sulfide film was washed with hot dimethyl sulfoxide and acetone and dried.

Polyvinylidene fluoride 40 mg and Rhodamine B2.8
After dissolving 0 mg in a mixed solvent of 1.8 ml of tetramethylurea and 0.6 ml of epichlorohydrin, 60 mg of X-type metal-free phthalocyanine was added and dispersed at -15 ° C for 30 minutes to form a slurry.

Drop the resulting slurry on the cadmium sulfide film,
The film was formed using a bar coater constructed by winding a 10 mil stainless wire. This film is placed under vacuum at room temperature.
After drying for an hour, a thin film element was prepared. Then, gold was vacuum-deposited on the upper surface of the device film to form an ohmic electrode, thereby forming a photovoltaic device.

This device was placed in an electric furnace heated to 190 ° C. and heat-treated for 10 minutes to obtain a photovoltaic device.

The energy conversion efficiency of this photovoltaic element was measured in the same manner as in Example 1, and the results are shown in Table 1.

These values are much higher than those in Comparative Example 2, and the heat treatment effect of the present invention is clear.

Comparative Example 2 In Example 2, the energy conversion efficiency η of the element before the heat treatment was measured, and the results were combined to obtain the first value.
Shown in the table.

Example 3 A cadmium sulfide thin film was formed on ITO glass by the same electrochemical method as in Example 2 and heat-treated at 200 ° C. for 1 hour. Then, a thin film was prepared in the same manner as in Example 1, and then an ohmic electrode was similarly formed to form a photovoltaic element.

When this device was irradiated with AM0 pseudo sunlight (intensity 91.9 mW / cm ² ), the values were Jsc 0.13 mA / cm ² , Voc-0.67 V, FF 0.26, and η 0.025%.

When this element was heat-treated at 200 ° C for 1 minute and the same measurement was performed, Jsc 0.37mA / cm ² , Voc-0.45V, FF
The values were 0.35 and η0.050%.

From the above, it is clear that the heat treatment effect of the present invention is different from the heat treatment effect of only the cadmium sulfide film, and is a new effect particularly contributing to the improvement of the short-circuit photocurrent (Jsc).

Examples 4 to 7 In Example 2, Rhodamine B 2.80 mg and pyrene 0.47 mg
Alternatively, a photovoltaic element was obtained in the same manner except that o-chloranil 1.75 mg, p-dinitrobenzene 1.96 mg or tetracyanoquinone dimethane 1.19 mg was used. Table 2 shows a summary of changes in Jsc before and after heat treatment of these elements when irradiated with AM1 pseudo sunlight (intensity 115.5 mW / cm ² ). It is clear that the Jsc is improved by the heat treatment in all the devices.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of the structure of a photovoltaic element obtained by the manufacturing method of the present invention and its photoelectric energy conversion efficiency measuring system, and FIG. 2 is an X-type metal-free phthalocyanine X-type.
It is a line diffraction diagram (copper Kα).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoichi Kinoshita 91-15, Omiya City, Saitama Prefecture Examiner Kunio Matsumoto (56) References JP 61-3473 (JP, A) JP 57-83054 ( JP, A) JP 56-124277 (JP, A)

Claims (3)

[Claims] 1. A photoactive layer comprising a film made of a polyvinylidene compound containing phthalocyanine in a dispersed state,
In a method for manufacturing a photovoltaic device having a structure in which this is sandwiched between a cadmium sulfide barrier electrode and an ohmic electrode,
A method for producing a photovoltaic element, comprising forming a photoactive layer of the film on a cadmium sulfide barrier electrode and then heat-treating the film at 150 to 300 ° C. 2. The method for manufacturing a photovoltaic element according to claim 1, wherein the phthalocyanine is an X-type metal-free phthalocyanine. 3. A polyvinylidene compound is a polymer of vinylidene fluoride, vinylidene chloride, or vinylidene cyanide, or a copolymer of these compounds and another copolymerization component. A method for manufacturing a photovoltaic element according to claim 1 or 2.