JPWO2013035305A1 - Organic solar cell - Google Patents

Abstract

An organic solar battery including a first electrode, an active layer including a plurality of organic layers, and a second electrode in this order, wherein the active layer is one of the following (A) and (B). (A) a p-type semiconductor layer, an i-layer that is a mixed layer of a p-type semiconductor material and an n-type semiconductor material, a hole barrier layer having a thickness that prevents hole movement and does not hinder electron movement, and an n-type semiconductor An active layer formed by stacking layers in order: (B) a p-type semiconductor layer, an n-type semiconductor layer (I), a hole-blocking layer having a thickness that prevents movement of holes and does not prevent movement of electrons, and n-type Active layer formed by stacking semiconductor layers (II) in this order

Description

  The present invention relates to an organic solar cell.

  Organic thin-film solar cells are devices that exhibit an electrical output with respect to light input, as represented by photodiodes and imaging devices that convert optical signals into electrical signals, and solar cells that convert optical energy into electrical energy.

In recent years, solar cells have attracted a great deal of attention as a clean energy source against the background of fossil fuel depletion problems and global warming problems, and research and development have been actively conducted.
Conventionally, silicon solar cells represented by single crystal Si, polycrystal Si, amorphous Si, and the like have been put into practical use. The demand for next generation solar cells is increasing.
Against this background, organic solar cells are attracting much attention as next-generation solar cells next to silicon-based solar cells because they are inexpensive, have low toxicity, and do not have a fear of shortage of raw materials.

  Organic thin-film solar cells have been studied with single-layer films using merocyanine dyes, etc., but it has been found that conversion efficiency can be improved by using p-layer / n-layer multilayer films. The film has become mainstream. Subsequently, it was found that the conversion efficiency is improved by inserting an i layer (a mixed layer of p material and n material) between the p layer and the n layer.

On the other hand, in an organic thin film solar cell using a polymer compound, a conductive polymer is used as a p material (a material used for a p layer), and a C ₆₀ derivative is used as an n (a material used for an n layer). The so-called bulk heterostructure has been mainly studied by inducing micro-layer separation of the p-layer and n-layer by mixing and heat-treating to increase the heterointerface and improve the conversion efficiency.

  Thus, in organic thin film solar cells, conversion efficiency has been improved by optimizing cell configuration and morphology. However, since the photoelectric conversion efficiency is lower than that of an inorganic solar cell typified by silicon or the like, it is difficult to put it into practical use, and increasing the photoelectric conversion efficiency is the biggest issue.

  In order to obtain high photoelectric conversion efficiency, Non-Patent Document 1 uses an n-type organic material having a high carrier transport capability as the photoelectric conversion layer. Non-Patent Document 2 describes the use of a bulk heterojunction structure.

  In addition, for example, Patent Document 1 describes an image pickup element in which a charge barrier layer is inserted, and describes a photoelectric conversion element and an image pickup element that can reduce dark current by suppressing the outflow of carriers. Yes.

Patent Document 1 is an invention related to an image sensor, and there is no mention of an organic thin film solar cell. Moreover, although it aims at reducing a dark current, this is a concept different from the conversion efficiency improvement of an organic thin-film solar cell.
Furthermore, the total thickness of the electron barrier layer is 20 nm or more, and when there are a plurality of electron barrier layers, the thickness of the electron barrier layer adjacent to the photoelectric conversion layer is 10 nm or more. Therefore, the range is different from the effective film thickness region for the charge barrier layer of the present invention.

JP 2010-183060 A

Appl. Phys. Lett. 79, 126 (2001) Appl. Phys. Lett. 84, 4218 (2004)

Although organic solar cells have been improved as described above, there is a problem that energy conversion efficiency is lower than that of currently used silicon (single crystal silicon, polycrystalline silicon, amorphous silicon) devices. It hasn't arrived.
The objective of this invention is providing the organic solar cell which has a highly efficient photoelectric conversion characteristic.

As a result of intensive studies on the effect of the charge blocking, the present inventors provided a layer that efficiently transports holes and electrons to the anode and the cathode, respectively, preventing the movement of holes and preventing the movement of electrons. The present inventors have found that the conversion efficiency is improved by using the element configuration, and the present invention has been completed.
Specifically, as a result of analysis, the following may be related as factors of the effect of hole blocking.

(I) Relationship between Ip (ionization potential) of semiconductor material of organic thin film photoelectric conversion layer and Ip of hole barrier layer (ii) Thickness of hole barrier layer (iii) Semiconductor material of organic thin film photoelectric conversion layer Relationship with electron transport property (electron mobility) of hole barrier layer

According to the present invention, the following organic solar cell is provided.
1. An organic solar battery including a first electrode, an active layer including a plurality of organic layers, and a second electrode in this order, wherein the active layer is one of the following (A) and (B).
(A) a p-type semiconductor layer, an i-layer that is a mixed layer of a p-type semiconductor material and an n-type semiconductor material, a hole barrier layer having a thickness that prevents hole movement and does not hinder electron movement, and an n-type semiconductor Active layer (B), p-type semiconductor layer, n-type semiconductor layer (I), layered in order of layers, hole-blocking layer with a thickness that prevents hole movement and does not hinder electron movement, n-type semiconductor 1. Active layer formed by laminating layers (II) in this order. 2. The organic material according to 1, wherein the ionization potential of the compound contained in the hole barrier layer is greater than the ionization potential of the n-type semiconductor material contained in the i layer or the compound contained in the n-type semiconductor layer (I). Solar cell.
3. The ionization potential of the compound contained in the hole barrier layer is 0.01 eV to 1... From the ionization potential of the n-type semiconductor material contained in the i layer or the ionization potential of the compound contained in the n-type semiconductor layer (I). The organic solar cell according to 1 or 2, which is 0 eV larger.
4). The electron mobility of the compound contained in the hole blocking layer is larger than the electron mobility of the n-type semiconductor material contained in the i layer or the compound contained in the n-type semiconductor layer (I). The organic solar cell in any one of -3.
5. The organic solar battery according to any one of 1 to 4, wherein the compound contained in the hole barrier layer has an electron mobility of 1 × 10 ⁻⁵ cm ² / Vs or more.
6). The organic solar cell according to any one of 1 to 5, wherein the hole blocking layer in (A) has a thickness of 0.1 to 19 nm.
7). The organic solar battery according to any one of 1 to 5, wherein the hole blocking layer in (B) has a thickness of 0.1 to 9 nm.
8). The organic solar battery according to any one of 1 to 5 and 7, wherein the thickness of the n-type semiconductor layer (I) in (B) is 0.1 to 40 nm.
9. The organic solar battery according to any one of 1 to 8, wherein the compound contained in the hole blocking layer is a fullerene or a fullerene derivative.
10. 10. The organic solar cell according to 9, wherein the compound contained in the hole blocking layer is C60 or a derivative thereof.
11. The organic solar cell according to any one of 1 to 10, wherein the n-type semiconductor material contained in the i layer or the compound contained in the n-type semiconductor layer (I) is C70 or a derivative thereof.

  According to the present invention, among the charges generated in the organic thin film photoelectric conversion layer at the time of light irradiation, the hole is transported to the cathode side (recombination deactivation factor) is blocked and suppressed. An organic solar cell having photoelectric conversion characteristics can be provided.

1 is a schematic diagram of an organic solar battery produced in Example 1. FIG. 2 is a schematic diagram showing energy of an organic solar battery produced in Example 1. FIG. 6 is a schematic diagram of an organic solar battery produced in Example 5. FIG.

The organic solar cell (organic thin film solar cell) of the present invention includes a first electrode, an active layer including a plurality of organic layers, and a second electrode in this order, and the active layer is any one of (A) and (B) below. It is.
(A) p-type semiconductor layer (p-layer), i-layer that is a mixed layer of p-type semiconductor material and n-type semiconductor material, a hole-blocking layer with a thickness that prevents hole movement and does not hinder electron movement , Active layer (B) stacked in order of n-type semiconductor layer (n layer), p-type semiconductor layer, n-type semiconductor layer (I), with a thickness that prevents the movement of holes and prevents the movement of electrons An active layer formed by laminating a hole barrier layer and an n-type semiconductor layer (II) in this order

The cell structure of the organic solar battery of the present invention is not particularly limited as long as it has the above-described configuration, and specifically includes a structure having the following configuration on a substrate.
(1) 1st electrode / p layer / i layer / hole barrier layer / n layer / second electrode (2) 1st electrode / p layer / n layer (I) / hole barrier layer / n layer (II) / Second electrode

Moreover, you may provide a buffer layer between an electrode and an organic layer as needed. For example, when a buffer layer is provided in the configuration (1), a structure having the following configuration can be given.
(11) 1st electrode / p layer / i layer / hole blocking layer / n layer / buffer layer / second electrode (12) 1st electrode / buffer layer / p layer / i layer / hole blocking layer / n layer / Second electrode (13) first electrode / buffer layer / p layer / i layer / hole blocking layer / n layer / buffer layer / second electrode

Moreover, when the buffer layer is provided in the above configuration (2), a structure having the following configuration can be given.
(21) First electrode / p layer / n layer (I) / hole barrier layer / n layer (II) / buffer layer / second electrode (22) first electrode / buffer layer / p layer / n layer (I ) / Hole barrier layer / n layer (II) / second electrode (23) first electrode / buffer layer / p layer / n layer (I) / hole barrier layer / n layer (II) / buffer layer / second 2 electrodes

  As each constituent member in the organic solar cell, known members and materials used in the organic solar cell can be used. Hereinafter, each component will be briefly described.

1. 1st electrode, 2nd electrode There is no restriction | limiting in particular in the material of a 1st electrode and a 2nd electrode, A well-known electroconductive material can be used. For example, as an electrode (anode) connected to the p layer, a metal such as tin-doped indium oxide (ITO) or gold (Au) can be used, and as an electrode (cathode) connected to the n layer, silver (Ag), Metals such as aluminum (Al), indium (In), calcium (Ca), platinum (Pt) lithium (Li), and binary metal systems such as Mg: Ag, Mg: In, and Al: Li are used. A work function smaller than that of the anode is used. Depending on the electron level of the material constituting the n layer, an electrode exemplified material connected to the p layer can be used.

  In order to obtain highly efficient photoelectric conversion characteristics, it is desirable that at least one surface of the solar cell be sufficiently transparent in the sunlight spectrum. The transparent electrode is formed using a known conductive material so as to ensure predetermined translucency by a method such as vapor deposition or sputtering. The light transmittance of the electrode on the light receiving surface is preferably 10% or more. In a preferred configuration of the pair of electrode configurations, one of the electrode portions includes a metal having a high work function, and the other includes a metal having a low work function.

2. p-type Semiconductor Layer The material used for the p-layer is not particularly limited, but a compound having a function as a hole acceptor is preferable. For example, for organic compounds, N, N′-bis (3-tolyl) -N, N′-diphenylbenzidine (mTPD), N, N′-dinaphthyl-N, N′-diphenylbenzidine (NPD), 4, Amine compounds represented by 4 ′, 4 ″ -tris (phenyl-3-tolylamino) triphenylamine (MTDATA) and the like, phthalocyanine (Pc), copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc), titanyl phthalocyanine (TiOPc) ), Phthalocyanines such as octaethylporphyrin (OEP), platinum octaethylporphyrin (PtOEP), zinc tetraphenylporphyrin (ZnTPP) and the like, and polymer compounds such as polyhexylthiophene (P3HT), Methoxyethylhexyloxyphenylene vinyl Examples thereof include main chain conjugated polymers such as REN (MEHPPV), and side chain polymers represented by polyvinyl carbazole.

Further, as a material used for the p layer, a compound represented by the following formula (A) is also preferable.
(In the formula (A), R ⁰ is hydrogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 ring carbon atoms, substituted or unsubstituted carbon atoms having 2 to 30 carbon atoms. Alkenyl, halogen or a substituted or unsubstituted heterocyclic ring having 5 to 40 ring atoms,
Rg ¹ and Rg ² are each a 5-membered heterocyclic ring having at least one substituted or unsubstituted nitrogen atom, or a 6-membered heterocyclic ring having at least one substituted or unsubstituted nitrogen atom;
Rg ³ and Rg ⁴ are each a substituted or unsubstituted aryl having 6 to 30 ring carbon atoms, a substituted or unsubstituted heterocyclic ring having 5 to 40 ring atoms, and M is a coordination metal.
Of the substituents R ⁰ and Rg ^{1 to} Rg ⁴ , adjacent groups may be bonded to each other to form a ring. However, the adjacent substituents of Rg ¹ and Rg ² are not bonded to form isoindole. )

One of the two NM bonds of the formula (A) is a coordination bond, and in this case, the compound of the present invention is a coordination compound (complex or chelate complex).
M is a coordination metal, preferably a boron atom, a silicon atom, an aluminum atom, a magnesium atom, an iron atom, a copper atom or a zinc atom, and more preferably a boron atom.

The ^following describes each group R ^0, Rg 1 ~Rg ^4.
Examples of the halogen atom for R ⁰ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

R ⁰ substituted or unsubstituted alkyl having 1 to 20 carbon atoms preferably has 1 to 8 carbon atoms in the alkyl moiety, and the alkyl moiety may be linear, branched or cyclic, for example, Methyl group, ethyl group, 1-propyl group, 2-propyl group, 1-butyl group, 2-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, octyl group, decyl group, dodecyl group 2-ethylhexyl group, 3,7-dimethyloctyl group, cyclopropyl group, cyclopentyl group, cyclohexyl group, 1-adamantyl group, 2-adamantyl group, norbornyl group, trifluoromethyl group, trichloromethyl group, benzyl group, α , Α-dimethylbenzyl group, 2-phenylethyl group, 1-phenylethyl group and the like. Of these, alkyl groups having 1 to 20 carbon atoms are preferable from the viewpoint of easy availability of raw materials, and methyl, ethyl, 1-propyl, 2-propyl, tert-butyl, and cyclohexyl groups are preferred. Further preferred.

  Examples of the substituent of the alkyl group include a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and an aryl group such as a phenyl group, and the aryl group includes a methyl group, an ethyl group, a propyl group and the like. The alkyl group having 1 to 5 carbon atoms may be further substituted.

R ⁰ substituted or unsubstituted aryl having 6 to 30 ring carbon atoms preferably has 6 to 20 ring carbon atoms in the aryl moiety, such as a phenyl group, a 2-tolyl group, a 4-tolyl group, 4-trifluoromethylphenyl group, 4-methoxyphenyl group, 4-cyanophenyl group, 2-biphenylyl group, 3-biphenylyl group, 4-biphenylyl group, terphenylyl group, 3,5-diphenylphenyl group, 3,4- Diphenylphenyl group, pentaphenylphenyl group, 4- (2,2-diphenylvinyl) phenyl group, 4- (1,2,2-triphenylvinyl) phenyl group, fluorenyl group, 1-naphthyl group, 2-naphthyl group 2- (1,4-diphenyl) naphthyl group, 9-anthryl group, 2-anthryl group, 2- (1,4-diphenyl) anthryl group), 2- ( 9,10-diphenyl) anthryl group, 9-phenanthryl group, 1-pyrenyl group, chrycenyl group, naphthacenyl group, coronyl group and the like. Among these, from the viewpoint of availability of raw materials, an aryl group having 6 to 30 ring carbon atoms is preferable, and a phenyl group, a 4-biphenylyl group, a 1-naphthyl group, a 2-naphthyl group, and a 2-anthryl group. , 9-phenanthryl group and the like are more preferable.

  Examples of the substituent for the aryl group include halogen atoms such as fluorine atom, chlorine atom, bromine atom and iodine atom, alkyl groups having 1 to 5 carbon atoms such as methyl group, ethyl group and propyl group, methoxy group and ethoxy group. Groups, C1-C5 alkoxy groups such as propoxy groups, aryl groups such as cyano groups and phenyl groups, aryl groups such as phenyl groups, heterocycles such as carbazole, arylamino groups such as diphenylamino groups, and the like. .

Examples of the substituted or unsubstituted aryl having 6 to 30 ring carbon atoms of Rg ³ and Rg ⁴ include divalent residues corresponding to the above substituted or unsubstituted aryl having 6 to 30 ring carbon atoms of R ^0. Can be mentioned.

The substituted or unsubstituted alkenyl having 2 to 30 carbon atoms of R ⁰ preferably has 2 to 8 carbon atoms in the alkenyl moiety, and may be linear, branched or cyclic, such as a vinyl group, Propenyl group, butenyl group, oleyl group, eicosapentaenyl group, docosahexaenyl group, styryl group, 2,2-diphenylvinyl group, 1,2,2-triphenylvinyl group, 2-phenyl-2-propenyl group Etc. Of these, alkenyl groups having 2 to 20 carbon atoms are preferable, and vinyl groups, styryl groups, and 2,2-diphenylvinyl groups are more preferable from the viewpoint of easy availability of raw materials.

  Examples of the substituent for the alkenyl group include halogen atoms such as fluorine atom, chlorine atom, bromine atom and iodine atom, aryl groups such as phenyl group, carbon atoms of 1 to 5 such as methyl group, ethyl group and propyl group. Of the alkyl group.

The substituted or unsubstituted heterocyclic ring having 5 to 40 ring atoms of R ⁰ , Rg ³ and Rg ⁴ is preferably 5 to 15 ring forming atoms of the heterocyclic ring. For example, furan, thiophene, pyrrole, imidazole And monovalent or divalent residues corresponding to benzimidazole, pyrazole, benzpyrazole, triazole, oxadiazole, pyridine, pyrazine, triazine, quinoline, benzofuran, dibenzofuran, benzothiophene, dibenzothiophene and carbazole. Of these, furan, thiophene, pyridine, carbazole and the like are preferable from the viewpoint of availability of raw materials.

  Examples of the substituent of the heterocyclic ring include halogen atoms such as fluorine atom, chlorine atom, bromine atom and iodine atom, and alkyl groups having 1 to 5 carbon atoms such as methyl group, ethyl group and propyl group.

Examples of the 5-membered or 6-membered heterocyclic ring having at least one nitrogen atom of Rg ¹ and Rg ² include pyrrole, imidazole, pyridine and the like, and pyrrole is preferable.

Examples of the substituent of the 5-membered or 6-membered heterocyclic ring having at least one nitrogen atom of Rg ¹ and Rg ² include a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, a phenyl group, and the like. An aryl group is mentioned.
Among the substituents of Rg ¹ and Rg ² , adjacent ones may combine to form a ring, but when the substituent of Rg ¹ or Rg ² that is pyrrole forms a ring and becomes isoindole Absent.

R ⁰ may be bonded to Rg ¹ or Rg ² , the substituent of Rg ¹ may be bonded to Rg ^3, and the substituent of Rg ² may be bonded to Rg ⁴ .

  In the present invention, the hydrogen atom includes isotopes having different numbers of neutrons, that is, light hydrogen (protium), deuterium (deuterium), and tritium (tritium).

The compound represented by the formula (A) is preferably a pyromethene boron chelate compound represented by the following formula (B).
(Wherein R ⁰ is the same as the above formula (A), R ^{1 to} R ¹² are each hydrogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted ring forming carbon atoms having 6 to 6 carbon atoms. 30 aryl, substituted or unsubstituted alkenyl having 2 to 30 carbon atoms, substituted or unsubstituted arylamino having 6 to 30 carbon atoms, halogen, or substituted or unsubstituted heterocyclic ring having 5 to 40 carbon atoms And
Adjacent groups among R ^{1 to} R ¹² may be bonded to each other to form a ring. However, the case where R ¹ and R ² and R ¹¹ and R ¹² are bonded to form isoindole is not included. )

In the formula (B), alkyl, aryl, alkenyl, arylamino, halogen and heterocycle are the same as above. R ^{1 to} R ¹⁶ correspond to the substituents Rg ¹ to Rg ^{4 in} the formula (A).

In the formula (B), at least one of R ¹ , R ² , R ¹¹ and R ¹² is preferably aryl having 6 to 30 ring carbon atoms, and more preferably a phenyl group. Further, at least one of R ⁴ , R ⁵ , R ⁸ and R ⁹ is preferably an arylamino group having 6 to 40 ring carbon atoms, and more preferably a diphenylamino group.
In addition, R ³ and R ⁴ , or R ⁴ and R ⁵ may be linked to form a ring condensed with the benzene ring to which they are bonded (for example, a benzene ring). R ⁸ and R ⁹ , or R ⁹ And R ¹⁰ may be linked to form a ring (benzene ring) that is condensed with a benzene ring to which these are bonded.

The compound represented by the formula (A) is preferably a pyromethene boron chelate compound represented by the following formula (C).
(In the formula, R ⁰ is the same as the above formula (A),
R ^{13 to} R ¹⁶ are each hydrogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 ring carbon atoms, substituted or unsubstituted alkenyl having 2 to 30 carbon atoms, Substituted or unsubstituted arylamino having 6 to 30 ring carbon atoms, halogen, or substituted or unsubstituted heterocyclic ring having 5 to 40 ring atoms, and adjacent groups among R ^{13 to} R ¹⁶ are bonded to each other. To form a ring. However, the case where R ¹³ and R ¹⁴ and R ¹⁵ and R ¹⁶ are bonded to form isoindole is not included.
X ^{1 to} X ⁶ are each O, S or C—R. R is hydrogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 ring carbon atoms, substituted or unsubstituted alkenyl having 2 to 30 carbon atoms, substituted or unsubstituted It is an arylamino having 6 to 30 ring carbon atoms, halogen or a substituted or unsubstituted heterocyclic ring having 5 to 40 ring atoms, and adjacent Rs may be bonded to each other to form a ring. In the five-membered ring indicated by the dotted line, each carbon atom may form a double bond with an adjacent carbon atom. )

Formula (C) can be represented by the following formulas (C-1) to (C-3), for example.
(In the formula, R, R ⁰ , R ^{13 to} R ¹⁶ are the same as in the above formula (C), and X is O or S, respectively.)

In Formula (C), at least one of R ^{13 to} R ¹⁶ is preferably aryl having 6 to 30 ring carbon atoms, and more preferably a phenyl group.
In the formula (C-1) or (C-3), adjacent Rs may be linked to form a ring (for example, a benzene ring) that is fused to a 5-membered ring to which they are bonded.

3. n-type Semiconductor Layer The material used for the n-layer is not particularly limited, but a compound having a function as an electron acceptor is preferable.
For example, fullerenes such as C ₆₀ and C ₇₀ and derivatives thereof, carbon nanotubes, perylene derivatives, polycyclic quinones, quinacridones, and the like can be used for organic compounds, and CN-poly (phenylene) for high molecular organic compounds. -Vinylene), MEH-CN-PPV, -CN group or CF ₃ group-containing polymers, their -CF ₃ substituted polymers, poly (fluorene) derivatives, and the like.
A material having high electron mobility is preferable. Furthermore, a material having a small electron affinity is preferable. A high open-circuit voltage can be realized by combining materials having a low electron affinity as the n layer.

Examples of inorganic compounds include n-type inorganic semiconductor compounds. Specifically, doping semiconductors and compound semiconductors such as n-Si, GaAs, CdS, PbS, CdSe, InP, Nb ₂ O ₅ , WO ₃ , Fe ₂ O ₃ , titanium dioxide (TiO ₂ ), titanium monoxide ( TiO), titanium oxides such as dititanium trioxide (Ti ₂ O ₃ ), and conductive oxides such as zinc oxide (ZnO) and tin oxide (SnO ₂ ), and one or more of these May be used in combination. Titanium oxide is preferred, and titanium dioxide is particularly preferred.

  The compounds of the n layer (I) and the n layer (II) used for the active layer (B) may be the same or different.

4). i layer The i layer is a layer in which the p-type semiconductor material and the n-type semiconductor material are mixed. The i-type p-type semiconductor material and the p-layer material may be the same or different, and the i-type n-type semiconductor material and the n-layer material may be the same or different. The ratio of the p-type semiconductor material and the n-type semiconductor material in the i layer is, for example, 10: 1 to 1:10 (volume ratio).
The n-type semiconductor material used for the i layer is preferably _C70 or a derivative thereof.

5. Hole blocking layer The hole blocking layer (hole blocking layer (a)) of the active layer (A) preferably contains a compound having a larger Ip (ionization potential) than the n-type semiconductor material used for the i layer. , The holes generated in the i layer are prevented from moving to the cathode side.

Examples of the compound used for the hole blocking layer (a) include the same compounds as the n-type semiconductor material described above, and compounds having a larger Ip than the n-type semiconductor material of the i layer are preferable.
The compound used for the hole blocking layer (a) preferably has an Ip of 0.01 eV to 1.0 eV larger than the i-type n-type semiconductor material. Further, it is more preferably 0.05 eV to 0.5 eV larger than the n-type semiconductor material of the i layer, more preferably 0.05 eV to 0.2 eV, and further preferably 0.1 eV.

Ip forms a thin film of a target compound on an ITO glass substrate by vacuum deposition, and uses a thin film on the ITO glass substrate in the atmosphere using a photoelectron spectrometer (manufactured by Riken Keiki Co., Ltd .: AC-3). Can be measured.
Specifically, it can be measured by irradiating the material with light and measuring the amount of electrons generated by charge separation at that time. The emitted photoelectrons are plotted by the 1/2 power with respect to the energy of the irradiation light, and the threshold value of the photoelectron emission energy is Ip.

The compound of the hole blocking layer (a) preferably has a higher electron mobility than the n-type semiconductor material contained in the i layer. The electron mobility of the compound of the hole blocking layer (a) is preferably 1 × 10 ⁻⁵ cm ² / Vs or more, more preferably 1 × 10 ⁻⁴ cm ² / Vs or more.

  The electron mobility is measured by a field effect transistor (FET) method. A gate voltage is applied to the gate electrode of the manufactured organic thin film transistor, a source / drain voltage is applied between the source and the drain to pass a current, and a threshold voltage (Vth) and a field effect mobility μ are evaluated. The application of each voltage and the measurement of the current between the source and drain electrodes can be performed using, for example, a semiconductor characteristic evaluation system (4200SCS manufactured by Keithley Instruments Co., Ltd.).

The field effect mobility μ can be calculated using the following formula (A).
I _D = (W / 2L) · C · μ · (V _G −V _T ) ² (A)
(Where _ID is the source-drain current, W is the channel width, L is the channel length, C is the capacitance per unit area of the gate insulator layer, V _T is the gate threshold voltage, and V _G is the gate voltage. is there.)
The mobility can be obtained from the characteristics of the linear region and the saturation region. For example, a method of creating a graph of √Id−Vg from the result of the transfer characteristics and deriving the field effect transfer from this slope can be mentioned. In this specification, evaluation is made by this method unless otherwise noted.

As the compound of the hole blocking layer (a), _C60 or a derivative thereof is preferable.

The thickness of the hole blocking layer (a) is a thickness that prevents the movement of holes and does not prevent the movement of electrons. The term “thickness that prevents the movement of holes and does not hinder the movement of electrons” here is a thickness that is not too thin to prevent the movement of holes generated in the i layer to the cathode side, and The thickness is not too thick in order not to prevent the electrons generated in the i layer from moving to the cathode side. By doing in this way, the organic solar cell which has a highly efficient photoelectric conversion characteristic can be produced by blocking and suppressing a recombination deactivation factor. “Thickness that prevents the movement of holes and does not prevent the movement of electrons” depends on the material, but is preferably 0.1 to 19 nm, more preferably 0.1 to 15 nm, More preferably, it is 10 nm.
If it is less than 0.1 nm, the function as a hole barrier may not function sufficiently, and if it exceeds 19 nm, movement of electrons may be hindered.

  The hole barrier layer (hole barrier layer (b)) of the active layer (B) preferably contains a compound having a larger Ip than the n-type semiconductor material of the n layer (I), so that the interface between the p layer and the n layer This prevents the holes generated in step 1 from moving to the cathode side.

  Examples of the compound used for the hole blocking layer (b) include the same compounds as the n-type semiconductor material, and compounds having a larger Ip than the n-type semiconductor material of the n layer (I) are preferable. The compound used for the hole blocking layer (b) preferably has an Ip of 0.01 eV to 1.0 eV higher than the n-type semiconductor material of the n layer (I). Further, it is more preferably 0.05 eV to 0.5 eV larger than the n-type semiconductor material of the n layer (I), more preferably 0.05 eV to 0.2 eV, and even more preferably 0.1 eV.

The compound of the hole blocking layer (b) preferably has a higher electron mobility than the n-type semiconductor material of the n layer (I). The electron mobility of the compound of the hole blocking layer (b) is preferably 1 × 10 ⁻⁵ cm ² / Vs or more, more preferably 1 × 10 ⁻⁴ cm ² / Vs or more. The method for measuring electron mobility is the same as described above.

As the compound of the hole blocking layer (b), _C60 or a derivative thereof is preferable.

The thickness of the hole barrier layer (b) is a thickness that prevents the movement of holes and does not prevent the movement of electrons. The term “thickness that prevents the movement of holes and does not hinder the movement of electrons” herein refers to a thin film that prevents the movement of holes generated at the interface between the p layer and the n layer (I) to the cathode side. This is a thickness that is not too thick, and is not too thick so as not to prevent electrons generated at the interface between the p layer and the n layer (I) from moving to the cathode side. By doing in this way, the organic solar cell which has a highly efficient photoelectric conversion characteristic can be produced by blocking and suppressing a recombination deactivation factor. The “thickness that prevents the movement of holes and does not prevent the movement of electrons” depends on the material, but is preferably 0.1 to 9 nm, more preferably 0.1 to 5 nm, More preferably, it is 3 nm.
If it is less than 0.1 nm, the function as a hole barrier may not function sufficiently, and if it exceeds 9 nm, there is a possibility that movement of electrons may be hindered.

The hole blocking layer (b) is preferably provided near the interface between the p layer and the n layer (I), and the distance between the interface between the p layer and the n layer (I), that is, the n layer (I). Is, for example, 0.1 to 40 nm, and preferably 1.0 to 40 nm. More preferably, it is 1.0-30 nm.
It is conceivable that the closer the distance between the interface between the p layer and the n layer (I) and the hole blocking layer (b), the more the holes are blocked and the electron transport is promoted.

6). Buffer layer In general, organic thin film solar cells often have a thin total film thickness, and therefore, the upper electrode and the lower electrode are short-circuited, and the yield of cell fabrication often decreases. In such a case, it is preferable to prevent this by laminating a buffer layer.

As a preferable compound for the buffer layer, a compound having sufficiently high carrier mobility is preferable so that the short-circuit current does not decrease even when the film thickness is increased. For example, if it is a low molecular compound, the aromatic cyclic acid anhydride represented by NTCDA shown below etc. will be mentioned, and if it is a high molecular compound, poly (3,4-ethylenedioxy) thiophene: polystyrene sulfonate (PEDOT: PSS), polyaniline: camphorsulfonic acid (PANI: CSA), and other known conductive polymers.

  In addition, the buffer layer may have a role of preventing excitons from diffusing to the electrodes and deactivating. Inserting a buffer layer as an exciton blocking layer in this way is effective for increasing efficiency. The exciton blocking layer can be inserted on either the anode side or the cathode side, or both can be inserted simultaneously.

In this case, as a preferable material for the exciton blocking layer, for example, a well-known material for a hole barrier layer or a material for an electron barrier layer in organic EL applications can be used. A preferable material for the hole blocking layer is a compound having a sufficiently large ionization potential, and a preferable material for the electron blocking layer is a compound having a sufficiently small electron affinity. Specifically, bathocuproin (BCP), bathophenanthroline (BPhen), and the like, which are well-known materials for organic EL applications, can be used as the cathode-side hole barrier layer material.

Furthermore, you may use the inorganic semiconductor compound illustrated as said n layer material for a buffer layer. As the p-type inorganic semiconductor compound, CdTe, p-Si, SiC, GaAs, WO ₃ or the like can be used.

7). Substrate The substrate preferably has mechanical and thermal strength and transparency. For example, there are a glass substrate and a transparent resin film. Transparent resin films include polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polypropylene, polystyrene, polymethyl methacrylate, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, nylon, polyether ether ketone. , Polysulfone, polyethersulfone, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polyvinyl fluoride, tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polychlorotrifluoroethylene, Polyvinylidene fluoride, polyester, polycarbonate, polyurethane, polyimide, polyetherimide, polyimide, polypropylene, etc. It is.

  The formation of each layer of the organic solar cell of the present invention is performed by a dry film formation method such as vacuum deposition, sputtering, plasma, ion plating, or a wet film formation method such as spin coating, dip coating, casting, roll coating, flow coating, and ink jet. Can be applied.

  The thickness of each layer other than the hole blocking layer and the n layer (I) is not particularly limited, but is set to an appropriate thickness. Since it is generally known that the exciton diffusion length of an organic thin film is short, if the film thickness is too thick, the exciton is deactivated before reaching the heterointerface, resulting in low photoelectric conversion efficiency. If the film thickness is too thin, pinholes and the like are generated, so that sufficient diode characteristics cannot be obtained, resulting in a decrease in conversion efficiency. The normal film thickness is suitably in the range of 1 nm to 10 μm, but more preferably in the range of 5 nm to 0.2 μm.

  In the case of the dry film forming method, a known resistance heating method is preferable, and for forming the mixed layer, for example, a film forming method by simultaneous vapor deposition from a plurality of evaporation sources is preferable. More preferably, the substrate temperature is controlled during film formation.

In the case of a wet film forming method, a material for forming each layer is dissolved or dispersed in an appropriate solvent to prepare a light-emitting organic solution to form a thin film, and any solvent can be used. For example, halogenated hydrocarbon solvents such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, tetrachloroethane, trichloroethane, chlorobenzene, dichlorobenzene, chlorotoluene, ether solvents such as dibutyl ether, tetrahydrofuran, dioxane, anisole, methanol, Alcohol solvents such as ethanol, propanol, butanol, pentanol, hexanol, cyclohexanol, methyl cellosolve, ethyl cellosolve, ethylene glycol, hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, hexane, octane, decane, tetralin, Examples include ester solvents such as ethyl acetate, butyl acetate, and amyl acetate.
Of these, hydrocarbon solvents or ether solvents are preferred. These solvents may be used alone or in combination. In addition, the solvent which can be used is not limited to these.

In the present invention, in any organic thin film layer of the organic solar battery, an appropriate resin or additive may be used for improving the film formability and preventing pinholes in the film. Usable resins include polystyrene, polycarbonate, polyarylate, polyester, polyamide, polyurethane, polysulfone, polymethyl methacrylate, polymethyl acrylate, cellulose and other insulating resins and copolymers thereof, poly-N-vinyl. Examples thereof include photoconductive resins such as carbazole and polysilane, and conductive resins such as polythiophene and polypyrrole.
Examples of the additive include an antioxidant, an ultraviolet absorber, and a plasticizer.

Example 1
The organic solar cell 1 shown in FIG. 1 was produced. Specifically, the glass substrate with the ITO transparent electrode 10 having a thickness of 25 mm × 75 mm × 0.7 mm was subjected to ultrasonic cleaning in isopropyl alcohol for 5 minutes, and then UV ozone cleaning was performed for 30 minutes. The glass substrate with the transparent electrode line after the cleaning is mounted on a substrate holder of a vacuum deposition apparatus, and first, the transparent electrode is covered on the surface on which the transparent electrode line as the lower electrode is formed. Was formed by resistance heating vapor deposition at 1 Å / s to form a p-layer 20 having a thickness of 40 nm.

Subsequently, C ₇₀ is deposited at 1 Å / s by resistance heating deposition to form an n layer (n layer (I)) 30 having a thickness of 10 nm, and C ₆₀ is deposited at 1 に よ り by resistance heating deposition. Then, a hole blocking layer 40 having a thickness of 3 nm is formed, and C ₇₀ is further formed thereon by resistance heating vapor deposition at 1 Å / s to form an n layer (n layer (II )) 50 was formed. Thereafter, bathocuproine (BCP) was formed into a 10 nm buffer layer 60 by resistance heating vapor deposition at 1 Å / s.

_{Incidentally,} Ip of _{C 60} is 6.5 _eV, Ip of _{C 70} is 6.4 eV. _Further, the electron mobility of the _{C 60} is ^{8 × 10 -2 cm 2 / Vs} , the electron mobility of the _{C 70} is ^{2 × 10 -3 cm 2 / Vs} . Ip was measured by the method described above.
_The value of the electron mobility of the C _{60, C 70} is, R. C. Haddon J.H. Am. Chem. Soc. 1996, 118, p. 3041-3042.

Finally, metal Al was continuously deposited as a counter electrode 70 with a film thickness of 80 nm to produce the organic thin film solar cell 1. The element area was 1.0 cm ² .

The IV characteristic was measured for the produced organic solar cell under AM1.5 conditions (light intensity (Pin) 100 mW / cm ² ). Table 1 shows the open-circuit voltage (Voc), the short-circuit current density (Jsc), the fill factor (FF), and the photoelectric conversion efficiency (η).

The photoelectric conversion efficiency (η) was obtained by the following formula.
In the equation, Voc is an open circuit voltage, Jsc is a short-circuit current density, FF is a fill factor, and Pin is incident light energy. That is, for the same Pin, a compound having a larger Voc, Jsc, and FF shows better conversion efficiency.

FIG. 2 schematically shows the energy of the organic thin film solar cell 1. Some of the holes generated at the interface between the p layer 20 and the n layer 30 move into the n layer 30, but the holes are moved to the cathode side by the hole blocking layer 40 containing C ₆₀ having a larger Ip than C ₇₀ . It is prevented from moving.
C ₆₀ has a smaller Af than C _70, but C ₆₀ has higher electron mobility, and the C ₆₀ layer (hole blocking layer 40) is thin, so that it is generated at the interface between the p layer 20 and the n layer 30. Electrons can move beyond the hole barrier layer 40 to the cathode side.

Example 2
An organic solar cell was produced and evaluated in the same manner as in Example 1 except that the thickness of each of the two n layers was 20 nm. The results are shown in Table 1.

Example 3
An organic solar cell was prepared and evaluated in the same manner as in Example 1 except that the thickness of the n layer (I) was 30 nm and the thickness of the n layer (II) was 10 nm. The results are shown in Table 1.

Comparative Example 1
on the p layer, an n layer having a thickness of 40nm was deposited at 1 Å / s to C ₇₀ by resistance heating deposition, except that no a hole barrier layer and the other n-layer, in the same manner as in Example 1 An organic solar cell was prepared and evaluated. The results are shown in Table 1.

Comparative Example 2
An organic solar cell was prepared and evaluated in the same manner as in Example 2 except that the thickness of the hole blocking layer was 10 nm. The results are shown in Table 1.

Comparative Example 3
An organic solar cell was prepared and evaluated in the same manner as in Example 2 except that the thickness of the hole blocking layer was 20 nm. The results are shown in Table 1. In Comparative Examples 2 and 3, since the hole blocking layer was too thick, the movement of electrons to the cathode was hindered and the conversion efficiency was lowered.

Example 4
The organic solar cell 2 shown in FIG. 3 was produced. Specifically, a glass substrate with an ITO transparent electrode 110 having a thickness of 25 mm × 75 mm × 0.7 mm was subjected to ultrasonic cleaning in isopropyl alcohol for 5 minutes, and then UV ozone cleaning was performed for 30 minutes. The glass substrate with the transparent electrode line after the cleaning is mounted on a substrate holder of a vacuum deposition apparatus, and first, the transparent electrode is covered on the surface on which the transparent electrode line as the lower electrode is formed. Was formed by resistance heating vapor deposition at 1 加熱 / s to form a p-layer 120 having a thickness of 10 nm.

Then, on the p-layer 120, 5 nm Compound A at 0.25 Å / _s, and co-evaporation so that 20nm to _{C 70} with 1.0 Å / s, to form the i-layer (mixed layer) 130. Next, C ₆₀ is deposited on the i layer 130 at 1 蒸 着 / s by resistance heating evaporation to form a 1 nm-thick hole barrier layer 140, and C ₇₀ is formed at 1 Å / s on resistance heating evaporation. A film was formed into an n layer 150 having a thickness of 20 nm.

On the n layer 150, bathocuproine (BCP) was deposited at 1 Å / s by resistance heating vapor deposition to form a buffer layer 160 having a thickness of 10 nm. Finally, 80 nm of metal Al was continuously deposited as the counter electrode 170 to produce the organic thin film solar cell 2. The element area was 1.0 cm ² .
The obtained organic thin film solar cell was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Examples 5-6
An organic solar cell was prepared and evaluated in the same manner as in Example 4 except that the thickness of the hole blocking layer was 3 nm. The results are shown in Table 2.

Example 7
An organic solar cell was prepared and evaluated in the same manner as in Example 4 except that the thickness of the hole blocking layer was 10 nm. The results are shown in Table 2.

Comparative Example 4
An organic solar cell was prepared and evaluated in the same manner as in Example 4 except that the hole blocking layer was not provided. The results are shown in Table 2.

Comparative Example 5
An organic solar cell was prepared and evaluated in the same manner as in Example 4 except that the thickness of the hole blocking layer was 20 nm. The results are shown in Table 2. In Comparative Example 5, since the hole barrier layer was too thick, the movement of electrons to the cathode was hindered and the conversion efficiency was lowered.

  The organic solar cell of the present invention can be used as a power source or auxiliary power source for various devices such as watches, mobile phones and mobile personal computers, and electrical appliances. Combined with a rechargeable battery with a charging function, it can be used in the dark, and the application can be expanded.

Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will appreciate that these exemplary embodiments and / or embodiments are substantially without departing from the novel teachings and advantages of the present invention. It is easy to make many changes to the embodiment. Accordingly, many of these modifications are within the scope of the present invention.
The contents of the documents described in this specification and the specification of the Japanese application that is the basis of Paris priority of the present application are all incorporated herein.

Claims (11)

An organic solar battery including a first electrode, an active layer including a plurality of organic layers, and a second electrode in this order, wherein the active layer is one of the following (A) and (B).
(A) a p-type semiconductor layer, an i-layer that is a mixed layer of a p-type semiconductor material and an n-type semiconductor material, a hole barrier layer having a thickness that prevents hole movement and does not hinder electron movement, and an n-type semiconductor Active layer (B), p-type semiconductor layer, n-type semiconductor layer (I), layered in order of layers, hole-blocking layer with a thickness that prevents hole movement and does not hinder electron movement, n-type semiconductor Active layer that is laminated in the order of layer (II)   2. The ionization potential of a compound contained in the hole barrier layer is higher than an ionization potential of an n-type semiconductor material contained in the i layer or a compound contained in the n-type semiconductor layer (I). Organic solar cells.   The ionization potential of the compound contained in the hole barrier layer is 0.01 eV to 1... From the ionization potential of the n-type semiconductor material contained in the i layer or the ionization potential of the compound contained in the n-type semiconductor layer (I). The organic solar cell according to claim 1, wherein the organic solar cell is 0 eV larger.   The electron mobility of the compound contained in the hole blocking layer is higher than the electron mobility of the n-type semiconductor material contained in the i layer or the compound contained in the n-type semiconductor layer (I). Item 4. The organic solar cell according to any one of Items 1 to 3. The organic solar battery according to any one of claims 1 to 4 electron mobility of 1 × 10 -5 ^{cm 2} / ^Vs or more of the hole barrier layer compound contained.   The organic solar cell according to any one of claims 1 to 5, wherein the hole blocking layer in (A) has a thickness of 0.1 to 19 nm.   The organic solar cell according to any one of claims 1 to 5, wherein the hole blocking layer in (B) has a thickness of 0.1 to 9 nm.   The organic solar battery according to any one of claims 1 to 5, wherein the thickness of the n-type semiconductor layer (I) in (B) is 0.1 to 40 nm.   The organic solar cell according to any one of claims 1 to 8, wherein the compound contained in the hole blocking layer is fullerene or a fullerene derivative.   The organic solar cell according to claim 9, wherein the compound contained in the hole blocking layer is C60 or a derivative thereof.   The organic solar cell according to any one of claims 1 to 10, wherein the n-type semiconductor material contained in the i layer or the compound contained in the n-type semiconductor layer (I) is C70 or a derivative thereof.