JP2002094085A - Organic solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic solar cell that is superior in long-term reliability, and has improved energy conversion efficiency than the conventional organic solar cell. SOLUTION: This organic solar cell is composed by an element that has a transparent electrode 3 on a glass substrate 2, a hole transport layer 4 made of a triphenylene derivative, a mixing layer 5 of the triphenylene derivative and the phthalocyanine derivative, a charge generation layer 6 composing the phthalocyanine derivative and a perylene derivative, a mixing layer 7 comprising the perylene derivative and a hexaazatoriphenylene derivative, an electron transport layer 8 comprising the hexaazatoriphenylene derivative, and a metal electrode 9 on a glass substrate 2 in this order.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell used as a power source for a household power supply, a wristwatch or a small computer, and more particularly to a solar cell for preventing charge recombination at an interface between an organic compound layer and an electrode. The present invention relates to an organic solar cell having improved conversion efficiency by preventing charge trapping at an interface between compound layers.

[0002]

2. Description of the Related Art As one of solutions to energy problems and environmental problems such as depletion of petroleum resources and global warming,
Solar cells are of interest.

[0003] However, silicon-based solar cells that have been widespread to date have a high manufacturing cost, and their spread is limited.

Therefore, a technique using an organic compound which can be manufactured at low cost instead of silicon has been proposed.
Much research and development is underway.

For example, a technique has been proposed which utilizes a pn junction between a p-type conductive organic compound and an n-type conductive organic compound. Such a pn junction type organic solar cell includes p
Using copper phthalocyanine, which is a type conductive organic compound, and a perylene derivative, which is an n type conductive compound, has an energy conversion efficiency of 0.95% under simulated sunlight (75 mW / cm ² ). (CW Ta)
ng, Appl. Phys. Lett. 48 (2), 1
3 January 1986, p183).

[0006] However, the energy conversion efficiency of a pn junction type organic solar cell is considerably lower than that of a silicon type solar cell, which is 15% or more for a polycrystalline type and 10% or more for an amorphous type. I can say.

Further, a wet solar cell has been proposed in which an organic dye is carried on the surface of nanoporous TiO ₂ and an electrolyte solution in which an I ⁻ -I ³ -redox _couple is dissolved is injected.

[0008] In such a wet solar cell, by utilizing the surface area of the nanoporous TiO ₂ sintered body is wide to increase the supported amount of the dye, I is an electron donor by infiltrating an electrolyte solution ^- dye 10% energy conversion efficiency under simulated sunlight
Thus, a performance close to that of amorphous silicon is obtained, but on the other hand, there is a problem in long-term reliability because an electrolytic solution having high volatility is used.

Therefore, an organic solar cell in which the nanoporous TiO ₂ sintered body and the dye carried on the surface thereof are used as they are and the electrolyte is replaced with a solid p-type conductive compound has been studied. For example, an organic solar cell using polypyrrole as a p-type conductive compound has been proposed (K. Murakoshi, R. Kogure, YW).
ada, and S.A. Yanagida, Chemi
stry Letters 1997, p471). In such an organic solar cell, since a volatile electrolyte is not used, long-term reliability can be improved.

[0010]

However, in an organic solar cell composed of nanoporous TiO ₂ / dye / p-type conductive polypyrrole as described above, the p-type is smaller than the electrolyte in which a redox _couple is dissolved. Since the conductive polypyrrole does not penetrate into the nanoporous TiO ₂ , there is a problem that the energy conversion efficiency is reduced to 0.1%.

As described above, in a solar cell using an organic compound, a conversion efficiency comparable to that of amorphous silicon is obtained in a technique using an electrolytic solution, but a volatile organic electrolytic solution is used. That was inferior in long-term reliability. On the other hand, an all-solid-state solar cell having excellent long-term reliability has a problem that conversion efficiency is low.

The present invention has been made in view of the above, and an object of the present invention is to provide an organic solar cell which has excellent long-term reliability and has improved energy conversion efficiency.

[0013]

According to the present invention, there is provided an organic solar cell comprising a hole transport layer comprising a triphenylene derivative, a mixed layer comprising a triphenylene derivative and a phthalocyanine derivative, and a charge generation comprising a phthalocyanine derivative and a perylene derivative on a transparent electrode. A layer, a mixed layer of a perylene derivative and a hexaazatriphenylene derivative, an electron transport layer made of a hexaazatriphenylene derivative, and a metal electrode are sequentially laminated.

Preferably, the triphenylene derivative is a compound represented by the general formula [1].

[0015]

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Further, it is preferable that the phthalocyanine derivative is a compound represented by the general formula [Formula 2].

[0017]

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Preferably, the perylene derivative is a compound represented by the general formula [Chemical Formula 3].

[0019]

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Further, it is preferable that the hexaazatriphenylene derivative is a compound represented by the general formula [4].

[0021]

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Moreover, in the organic solar cell of the present invention, it is preferable to form a TiO ₂ film on the other surface of the transparent substrate.

[0023]

According to the organic solar cell of the present invention, a hole transport layer composed of a triphenylene derivative, a mixed layer of a triphenylene derivative and a phthalocyanine derivative, a charge generation layer composed of a phthalocyanine derivative and a perylene derivative, A mixed layer of a derivative and a hexaazatriphenylene derivative, an electron transporting layer made of a hexaazatriphenylene derivative, and an element arranged in the order of a metal electrode, the hole transporting layer made of a triphenylene derivative does not diffuse excitene, Since it has conductivity only for holes, excitons generated in the charge generation layer do not recombine with impurities in the transparent electrode as in a conventional pn junction type organic solar cell.

Further, by providing a mixed layer of a triphenylene derivative and a phthalocyanine derivative between a hole transporting layer composed of a triphenylene derivative and a charge generation layer composed of a phthalocyanine derivative and a perylene derivative, charge trapping at the interface is achieved. Is less likely to occur.

Since the electron transport layer made of a hexaazatriphenylene derivative does not diffuse excite and has conductivity only for electrons, the electron transport layer formed in the charge generation layer as in a conventional pn junction type organic solar cell. No longer reach the metal electrode and recombine.

By providing a mixed layer of a perylene derivative and a hexaazatriphenylene derivative between a charge generation layer made of a phthalocyanine derivative and a perylene derivative and an electron transporting layer made of a hexaazatriphenylene derivative, the charge at the interface is reduced. Trap is less likely to occur.

Furthermore, the triphenylene derivative, the phthalocyanine derivative, the perylene derivative, and the hexaazatriphenylene derivative all have a conjugated molecular structure with high planarity, so that the molecules are well overlapped.

The organic solar cell of the present invention having the above-described components effectively separates charge from exciten generated by the phthalocyanine derivative and the perylene derivative absorbing sunlight, Increase conversion efficiency. For example, an organic solar cell used for a household power supply, a power supply for a wristwatch, a small computer, or the like can be made more efficient than a conventional product.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an example of the organic solar cell of the present invention.

In FIG. 1, reference numeral 2 denotes a glass substrate, and one surface of the glass substrate 2 is coated with a surface coat layer 1, and the other surface is provided with a transparent electrode 3, a hole transport layer 4, a hole transport material and a charge generation material. Mixed layer 5, charge generation layer 6, mixed layer 7 of charge generation material and electron transport material, electron transport layer 8, and metal electrode 9
Are sequentially laminated.

The surface coating layer 1 is arranged to absorb ultraviolet rays contained in sunlight and prevent the organic compounds constituting the device from absorbing the ultraviolet rays and causing photodeterioration.

The surface coat layer 1 has, for example, T
It is made of iO ₂ and is formed on the glass substrate 2 by a CVD method, a sputtering method, or the like. On the surface coat layer 1,
Further, an antireflection film may be formed.

The glass substrate 2 is arranged to shield the device from the outside air and to transmit visible light and infrared light to reach the charge generation layer 6. The material and manufacturing method are not particularly limited as long as they have high transmittance to visible light and infrared light. A transparent resin substrate may be used instead of glass.

The transparent electrode 3 is arranged for extracting holes from the hole transport layer 4 and for transmitting visible light and infrared light to reach the charge generation layer 6. The transparent electrode 3 is made of indium tin oxide (ITO), tin antimony oxide (NESA), or the like, and is formed on the glass substrate 2 by CVD.
It is formed by a method or a sputtering method.

The hole transport layer 4 transports only holes of the charges generated from the charge generation layer 6 to reach the transparent electrode 3, and further transmits visible light and infrared light to the charge generation layer 6. Is arranged to reach.

The phthalocyanine derivative of the charge generation layer 6 described below also has a hole transporting property. However, in the charge generation layer 6, excitons composed of electron-hole pairs are generated and diffuse in the layer. If the charge generation layer 6 and the transparent electrode 3 are in direct contact, recombination with impurities such as reduced metal ion elements in the transparent electrode material occurs at the interface with the transparent electrode, and the energy conversion efficiency decreases. Cause. Therefore, by providing the hole transport layer 4 that blocks the diffusion of excitons and transports only holes between the charge generation layer 6 and the transparent electrode 3, recombination at the interface with the transparent electrode 3 is prevented. Thus, the energy conversion efficiency can be improved.

The hole transport layer 4 has the general formula (5)
Is formed on the transparent electrode 3 by an evaporation method.

[0038]

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Mixed layer 5 of hole transport material and charge generating material
Is disposed between the hole transport layer 4 and the charge generation layer 6 described later in order to prevent trapping of charges at the interface.

Mixed layer 5 of hole transport material and charge generating material
Is formed on the hole transport layer 4 by an evaporation method.

The charge generation layer 6 is disposed to absorb visible light and infrared light, generate excitons composed of electrons and holes, and perform charge separation.

The charge generation layer 6 has a general formula (Formula 2)
And a perylene derivative represented by the general formula (Chemical Formula 3) are used, and are formed on the mixed layer 5 of the hole transport material and the charge generating material by an evaporation method. .

[0043]

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[0044]

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Mixed layer 7 of charge generating substance and electron transporting substance
Is disposed between the charge generation layer 6 and an electron transport layer 8 described later in order to prevent trapping of charges at the interface.

Mixed layer 7 of charge generating substance and electron transporting substance
Is formed on the charge generation layer 6 by an evaporation method.

The electron transport layer 8 is arranged to transport only electrons of the charges generated from the charge generation layer 6 to reach the metal electrode 9.

The electron transporting layer 8 has the general formula 8
Is formed on the mixed layer 7 of the charge generating substance and the electron transporting substance by a vapor deposition method.

[0049]

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As described above, the compounds used for the hole transporting substance, the charge generating substance, and the electron transporting substance have similar molecular structures, and therefore have good packing of molecules, and as a result, π It is considered that the overlap of the electron orbits is improved, which has a favorable effect on the charge conduction.

The metal electrode 9 is arranged to extract electrons from the electron transport layer 8. The metal electrode 9 is made of Ag or the like, and is formed on the electron transport layer 8 by an evaporation method.

Further, a hole transport layer 4, a mixed layer 5 of a hole transport material and a charge generating material, a charge generating layer 6, a mixed layer 7 of a charge generating material and an electron transport material, an electron transport layer 8, a metal electrode 9
Are preferably continuously deposited in a vacuum of 1 × 10 ⁻⁵ Torr or less, whereby the oxidation reaction of an organic compound or metal can be suppressed by oxygen or moisture in the air. Characteristics can be improved.

Thus, according to the organic solar cell of the present invention,
A transparent electrode 3 on a glass substrate 2, a hole transport layer 4 of a triphenylene derivative, a mixed layer 5 of a triphenylene derivative and a phthalocyanine derivative, a charge generation layer 6 of a phthalocyanine derivative and a perylene derivative, and a perylene derivative. By forming the element configuration in which the mixed layer 7 with the hexaazatriphenylene derivative, the electron transport layer 8 composed of the hexaazatriphenylene derivative, and the metal electrode 9 are sequentially laminated, the hole transport layer composed of the triphenylene derivative reduces the exciten. Since it does not diffuse and has conductivity only for holes, excitons generated in the charge generation layer do not recombine with the impurity potential of the transparent electrode as in a conventional pn junction type organic solar cell, and Between the hole transport layer composed of a triphenylene derivative and the charge generation layer composed of a phthalocyanine derivative By providing a mixed layer composed of a triphenylene derivative and a phthalocyanine derivative, charge trapping at the interface is unlikely to occur, and the electron transport layer composed of the hexaazatriphenylene derivative does not diffuse excitene, and conducts only electrons. To have
Unlike conventional pn-junction type organic solar cells, the excitons generated in the charge generation layer do not reach the metal electrode and recombine, and are composed of a charge generation layer composed of a perylene derivative and a hexaazatriphenylene derivative. By providing a mixed layer of a perylene derivative and a hexaazatriphenylene derivative between the electron transport layer and the electron transport layer, charge trapping at the interface is less likely to occur.

Furthermore, the triphenylene derivative, phthalocyanine derivative, perylene derivative, and hexaazatriphenylene derivative all have a conjugated molecular structure with high similarity, so that the molecules are well overlapped.

The organic solar cell of the present invention having the above-described respective constitutions effectively separates electric charge from exciten generated by the phthalocyanine derivative and the perylene derivative absorbing sunlight, Increase conversion efficiency. For example, an organic solar cell used for a household power supply, a power supply for a wristwatch, a small computer, or the like can be made more efficient than a conventional product.

[0056]

Next, specific examples of the organic solar cell of the present invention will be described. First, the surface coat layer 1 is formed on the back of the glass substrate 2.
A TiO ₂ film (thickness: 150 nm) as a transparent electrode 3 and an ITO film (thickness: 150 nm, resistance: 7 Ω / cm ² ) as a transparent electrode 3 on the other surface. Was coated.

That is, while keeping the substrate temperature at 150 ° C., 1
× 10 ^-5 Torr triphenylene derivative represented by the formula at a deposition rate of 1 nm / s 5 in a vacuum (R = C
H ₃ ) was deposited to a thickness of 15 nm.

Subsequently, a mixture of the triphenylene derivative (R = CH ₃ ) and the phthalocyanine derivative represented by the chemical formula (5) in a vacuum of 1 × 10 ⁻⁵ Torr at a film forming rate of 1 nm / s. Layer 5 (1: 1 molar ratio) was deposited to a thickness of 5 nm.

Next, the charge generation layer 6 made of the phthalocyanine derivative represented by the chemical formula (6) and the perylene derivative represented by the chemical formula (7) at a film forming rate of 1 nm / s in a vacuum of 1 × 10 ^-5 Torr ( A molar ratio of 1: 1) was deposited to a thickness of 50 nm to form a charge generation layer 6.

Subsequently, a perylene derivative represented by the formula (7) and a hexaazatriphenylene derivative represented by the formula (8) (X = CN) were formed at a film formation rate of 1 nm / s in a vacuum of 1 × 10 ^-5 Torr. Mixed layer 7 (1: 1 molar ratio) was deposited to a thickness of 5 nm.

Subsequently, a hexaazatriphenylene derivative (X = CN) represented by the formula (8) is deposited to a thickness of 15 nm in a vacuum of 1 × 10 ^-5 Torr at a film formation rate of 1 nm / s, and electron transport is performed. Layer 8 was formed.

Finally, Ag was deposited to a thickness of 150 nm in a vacuum of 1 × 10 ⁻⁵ Torr at a deposition rate of 0.1 nm / s to provide a metal electrode 9.

Thus, an organic solar cell A having an effective area of 0.1 cm ² was obtained.

It is to be noted that each of the organic compounds was 99.9%
The reagent having the above purity was purified by vacuum evaporation immediately before use.

The above film thicknesses were monitored by a crystal oscillation type film forming controller.

[Comparative Example 1] In this example, in manufacturing the organic solar cell A, a hole transport layer 4 composed of a triphenylene derivative of Chemical Formula 5 and a triphenylene derivative of Chemical Formula 5 and a phthalocyanine derivative of Chemical Formula 6 were used. The mixed layer 5, the mixed layer 7 of the perylene derivative of Chemical formula 7 and the hexaazatriphenylene derivative of Chemical formula 8, and the electron transport layer 8 of the hexaazatriphenylene derivative of Chemical formula 8 are not formed, and other configurations are made the same. Thus, an organic solar cell B was obtained.

[Comparative Example 2] In this example, when manufacturing the organic solar cell A, a mixed layer 5 of a triphenylene derivative of Chemical Formula 5 and a phthalocyanine derivative of Chemical Formula 6, and a perylene derivative of Chemical Formula 7 and a chemical compound of Chemical Formula 8 An organic solar cell C was obtained in the same manner as the above except that the mixed layer 7 with the hexaazatriphenylene derivative was not formed.

The characteristics of these organic solar cells were evaluated as follows.

Each characteristic was determined from a current-potential curve obtained by irradiating white light (intensity 100 mW / cm ² ) from a halogen tungsten lamp and measuring a current value with an electrometer while applying a potential with a function generator. That is, open photovoltaic (V _OC ), short-circuit photocurrent density (J _SC ), fill factor (FF), and photoelectric conversion efficiency (η) with respect to incident light were obtained from the current-potential curve. The results shown were obtained. still,
Samples A, B, and C in the table are organic solar cells A,
B and C.

[0070]

[Table 1]

As is clear from this table, it is understood that the organic solar cell A of the present invention has the highest energy conversion efficiency.

However, the energy conversion efficiency of the organic solar cell B is as low as about 1/2 of that of the organic solar cell A, and the energy conversion efficiency of the organic solar cell C is as low as about 4/5 of the organic solar cell A. .

The organic solar cell B comprises a hole transport layer made of a triphenylene derivative, a mixed layer of a triphenylene derivative as a hole transport material and a phthalocyanine derivative as a charge generation material, and a perylene derivative as a charge generation material. Since a mixed layer with a hexaazatriphenylene derivative that is an electron transporting substance and an electron transporting layer composed of a hexaazatriphenylene derivative are not provided, excite generated in a phthalocyanine derivative and a perylene derivative may cause a transparent electrode or a metal electrode. It is considered that the reason is that recombination occurred when it diffused to the interface.

In the organic solar cell C, a mixed layer of a triphenylene derivative as a hole transporting substance and a phthalocyanine derivative as a charge generating substance, and a perylene derivative as a charge generating substance and hexaaza as an electron transporting substance were used. Because no mixed layer with the triphenylene derivative is provided, it is considered that charge trapping occurred at the interface between the hole transport layer and the charge generation layer and at the interface between the charge generation layer and the electron transport layer. .

[0075]

As described above, according to the organic solar cell of the present invention, the transparent electrode comprises a hole transport layer composed of a triphenylene derivative, a mixed layer of a triphenylene derivative and a phthalocyanine derivative, and a mixture of a phthalocyanine derivative and a perylene derivative. A charge transport layer, a mixed layer of a perylene derivative and a hexaazatriphenylene derivative, an electron transport layer composed of a hexaazatriphenylene derivative, and a metal electrode are sequentially laminated, so that a hole transport layer composed of a triphenylene derivative diffuses exciten. Without having, only holes have conductivity, so that excitons generated in the charge generation layer do not recombine with the impurity potential of the transparent electrode as in a conventional pn junction type organic solar cell, and Hole transport layer composed of triphenylene derivative and phthalocyanine and perylene derivatives By providing a mixed layer of a triphenylene derivative and a phthalocyanine derivative between the charge generation layer and the charge generation layer, the trapping of charges at the interface is unlikely to occur, and the electron transport layer made of the hexaazatriphenylene derivative diffuses exciten. Since it has conductivity only for electrons, it does not cause the excitons generated in the charge generation layer to reach the metal electrode and recombine unlike the conventional pn junction type organic solar cell. By providing a mixed layer of a hexaazatriphenylene derivative and a perylene derivative between an electron transporting layer composed of an azatriphenylene derivative and a charge generation layer composed of a phthalocyanine derivative and a perylene derivative, charge trapping at an interface is unlikely to occur. And a triphenylene derivative, a phthalocyanine derivative, Both the derivatives and the hexaazatriphenylene derivatives have a highly conjugated molecular structure with high planarity, so that the molecules overlap well, and the phthalocyanine derivative and the perylene derivative generate excitons generated by absorbing sunlight. Charge separation is effectively performed, conversion efficiency is improved, and for example, organic solar cells used in home power supplies, power supplies for watches, small computers, and the like can be made more efficient than conventional products. it can.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an organic solar cell of the present invention.

[Explanation of symbols]

1: surface coating layer, 2: glass substrate, 3: transparent electrode,
4: hole transport layer, 5: mixed layer of hole transport material and charge generating material, 6: charge generating layer, 7: mixed layer of charge generating material and electron transport material, 8: electron transport layer, 9: Metal electrode

Claims (1)

[Claims] 1. A transparent electrode comprising a hole transport layer comprising a triphenylene derivative, a mixed layer comprising a triphenylene derivative and a phthalocyanine derivative, a charge generation layer comprising a phthalocyanine derivative and a perylene derivative, and a mixture comprising a perylene derivative and a hexaazatriphenylene derivative. An organic solar cell in which a layer, an electron transport layer made of a hexaazatriphenylene derivative, and a metal electrode are sequentially laminated.