JP2011023594A - Photoelectric converting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric converting element which has high conversion efficiency and suppresses a decrease in conversion efficiency with a lapse of time. <P>SOLUTION: The photoelectric converting element includes an anode and a cathode, and a photoelectric converting layer between the anode and the cathode, and the photoelectric converting layer includes at least a mixture layer containing an electron-donative material (P) and an electron-receptive material (N). The weight mixing ratio (P/N) of the electron-donative material (P) to electron-receptive material (N) of the part of the mixture layer closest to the anode side is greater than 3, and decreases from the anode side to the cathode side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion element including a photoelectric conversion layer that generates electricity by receiving light, and in particular, an organic thin film in which an I layer (a mixed layer of P material and N material) is inserted between a P layer and an N layer. It relates to solar cells.

  A photoelectric conversion element is a device that shows an electric output with respect to an optical input, as represented by a photodiode or an imaging element that converts an optical signal into an electric signal, or a solar cell that converts optical energy into electric energy. It is a device that exhibits a response opposite to that of an electroluminescence (EL) element that exhibits optical output with respect to input. In particular, solar cells have attracted a great deal of attention as a clean energy source in recent years against the background of fossil fuel depletion and global warming, 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 as solar cells. However, the high cost and the shortage of raw material Si have been surfaced. 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.

An organic solar cell is basically composed of an N layer made of an electron-accepting material that transports electrons and a P layer made of an electron-donating material that transports holes. There are two types depending on the material constituting each layer. are categorized.
Specifically, a layer in which a sensitizing dye such as ruthenium dye is adsorbed on the surface of an inorganic semiconductor such as titania as the N layer and an electrolyte solution is used as the P layer is called a dye-sensitized solar cell (so-called Gretzell cell). Since 1991, it has been studied energetically because of its high conversion efficiency. However, since the solution is used, it has a drawback such as liquid leakage when used for a long time.
Therefore, in order to overcome the above-described drawbacks, research has been recently conducted to find an all-solid-state dye-sensitized solar cell by solidifying the electrolyte solution. However, the technology for impregnating organic matter into the pores of porous titania has a high degree of difficulty, and a cell capable of expressing high conversion efficiency with high reproducibility has not been completed.

On the other hand, the organic thin film solar cell in which the N layer and the P layer are both organic thin films has no defects such as liquid leakage because it is an all solid type, is easy to manufacture, and does not use ruthenium, which is a rare metal. Recently, it has attracted attention and has been energetically researched.
Organic thin-film solar cells have been initially studied with a single layer film using a merocyanine dye or the like, but it has been found that conversion efficiency is improved by using a multilayer film of P / N layers.
For example, in Non-Patent Document 1, light absorption is performed using two types of organic substances such as phthalocyanines and perylene imides, and the transport efficiency of holes and electrons is transferred to the electron donor layer and the electron acceptor layer, thereby converting the conversion efficiency. However, it has been reported that the efficiency is higher than that of the conventional single layer.

Thereafter, it has been found that conversion efficiency is improved by inserting an I layer (mixed layer of P material and N material) between the P layer and the N layer to increase the number of layers. Thereafter, it has been found that the conversion efficiency is further improved by the tandem cell configuration in which the P / I / N layers are stacked in series.
For example, in Non-Patent Document 2, the conversion efficiency is improved by adopting a P / I / N layer configuration in which an I layer (mixed layer of P material and N material) is inserted between the P layer and the N layer. It has been reported.
Further, in Non-Patent Document 3, among P / I / N layer configurations, a configuration in which I layers (mixed layers of P material and N material) are stacked in three layers (weight mixing ratio P / N value, 3/1 / 0.33) has been reported to improve the conversion efficiency.

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 C ₆₀ derivative is used as an N material, and they are mixed and heat-treated to induce micro layer separation to produce heterogeneity. The research of so-called bulk heterostructures that increase the interface and improve the conversion efficiency has been mainly conducted.
As described above, organic thin-film solar cells have so far aimed at improving conversion efficiency by studying cell configuration and morphology.

  By the way, the organic thin film solar cell is inferior in durability compared to an inorganic solar cell typified by silicon or the like. For practical use of organic thin film solar cells, superior durability is essential beyond the problem of conversion efficiency. Therefore, in organic thin-film solar cells, it is essential to develop a cell configuration that achieves high conversion efficiency and provides excellent durability, which is the biggest problem.

  However, for organic thin-film solar cells, improvement in conversion efficiency has been reported by studying cell configurations, but no element configuration effective for improving durability has been found.

C. W. Tang, Appl. Phys. Lett. 48, 183 (1986). M.M. Hiramoto, H. et al. Fujiwara, andM. Yokoyama, Appl. Phys. Lett. 58, 1062 (1991). P. Sullivan, S.M. Heutz, S.M. M.M. Schulttes, and T.M. S. Jones, Appl. Phys. Lett. 84, 1210 (2004).

  An object of the present invention is to provide a photoelectric conversion element that has a high conversion efficiency and reduces a decrease in conversion efficiency due to a change with time.

  As a result of intensive studies from element design to solve the above problems, the present inventors have found that in the mixed layer containing the electron donating material (P) and the electron accepting material (N) contained in the photoelectric conversion layer, By realizing a structure in which the weight mixing ratio (P / N) of the portion on the most anode side is larger than 3 and P / N becomes smaller from the anode side toward the cathode side, with the realization of high conversion efficiency, The inventors have found that the durability is greatly improved and have completed the present invention.

According to the present invention, the following photoelectric conversion element is provided.
1. An anode and a cathode, and a photoelectric conversion layer between the anode and the cathode, and the photoelectric conversion layer has a mixed layer containing at least an electron donating material (P) and an electron accepting material (N). And the weight mixing ratio (P / N) of the electron donating material (P) and the electron accepting material (N) in the most anode side portion of the mixed layer is larger than 3, and the P / N of the mixed layer is A photoelectric conversion element that becomes smaller from the anode side toward the cathode side.
2. The photoelectric conversion layer has a layer made of only an electron donating material between the anode and the mixed layer, and has a layer made of only an electron accepting material between the cathode and the mixed layer. The photoelectric conversion element as described.
3. 3. The photoelectric conversion element according to 1 or 2, wherein P / N at the most cathode side portion of the mixed layer is smaller than 1. 3.
4). The photoelectric conversion element according to any one of 1 to 3, which is an organic solar battery.
5. The apparatus which has a photoelectric conversion element in any one of said 1-4.

  ADVANTAGE OF THE INVENTION According to this invention, the photoelectric conversion element which shows high conversion efficiency and has high durability can be provided.

It is a schematic sectional drawing which shows an example of the photoelectric conversion element of this invention.

The photoelectric conversion element of this invention has an anode, a cathode (a pair of electrodes), and a photoelectric conversion layer between these electrodes.
FIG. 1 is a schematic cross-sectional view showing one embodiment of the photoelectric conversion element of the present invention.
In the photoelectric conversion element of this embodiment, a P layer 32 made of an electron donating material, a mixed layer 34, and an N layer 36 made of an electron accepting material are laminated between the anode 10 and the cathode 20 from the anode side 10. It has the photoelectric conversion layer 30 of a structure. The mixed layer 34 is a layer containing an electron donating material (P) and an electron accepting material (N).
The configuration of the mixed layer 34 is not limited as long as the following requirements are satisfied. For example, a single layer may be used, or a plurality of layers may be stacked.

In the present invention, the mixed layer has a weight mixing ratio (P / N) of the electron donating material (P) and the electron accepting material (N) in the most anode side portion larger than 3. For example, in the case of the photoelectric conversion element shown in FIG. 1, the P / N of the portion of the mixed layer 34 in contact with the P layer 32 is larger than 3. Here, the part in contact with the P layer 32 is a layer in contact with the P layer when the mixed layer is a laminate, and at least a part in contact with the P layer when the mixed layer is a single layer. The P / N of (for example, a region from the surface in contact with the P layer to at least 3 nm) may be larger than 3.
When the P / N at the most anode side portion of the mixed layer is larger than 3, charges are generated at the interface between excitons formed by light absorption in the mixed layer 34 and the electron donating material and the electron accepting material. It is possible to prevent reverse current due to the charge formed by the separation moving to the pair of electrodes. By satisfying P / N> 3, high conversion efficiency and high durability can be realized. P / N at the most anode side portion of the mixed layer 34 is particularly preferably 4 or more.

  In the present invention, the P / N of the mixed layer 34 decreases from the anode 10 side toward the cathode 20 side. Thereby, since the weight ratio of the electron donating material responsible for hole transport and the electron accepting material responsible for electron transport in the mixed layer 34 changes stepwise from the anode side to the cathode side, a barrier associated with charge transport Becomes smaller.

  As described above, the configuration of the mixed layer 34 in the present invention is not limited as long as the above requirements are satisfied. For example, the mixed layer 34 may be a laminate of two or more layers, and the P / N may be changed stepwise, and the P / N continuously changes from the anode side to the cathode side 1 It may consist of two layers.

However, since the formation is easy, the mixed layer is preferably formed of a laminate of two or more layers.
Further, by increasing the number of mixed layers, the P / N of the electron donating material and the electron accepting material can be smoothly changed from the anode side to the cathode side, and the barrier associated with charge transport is reduced. Therefore, it is preferable. The number of stacked layers is preferably 2 to 10, and particularly preferably 2 to 5.

The P / N ratio of the mixed layer can be controlled by adjusting the ratio of the electron donating material and the electron accepting material at the time of forming the mixed layer. For example, when the mixed layer is formed by co-evaporation, the desired P / N can be set by controlling the deposition rates of the electron donating material and the electron accepting material.
The P / N of the mixed layer can be calculated as a molar component ratio and a weight mixing ratio by preparing each sample and calculating the peak ratio of components having different elution retention times using high performance liquid chromatography (HPLC).

  As in the embodiment shown in FIG. 1, the P layer 32 and the N layer 36 are formed, and the mixed layer 34 is disposed between the layer made of only the electron donating material and the layer made of only the electron accepting material. It is preferable to adopt a configuration. When the mixed layer 34 is in contact with the anode 10 or the cathode 20, excitons formed by light absorption in the mixed layer 34 and charges formed by charge separation at the interface between the electron donating material and the electron accepting material are present. Since quenching (deactivation) occurs, the conversion efficiency may decrease. By adopting a configuration in which the mixed layer is disposed between the layer made of only the electron-donating material and the layer made of only the electron-accepting material, the improvement in conversion efficiency appears more remarkably.

In the present invention, the mixed layer preferably has a portion where P / N is smaller than 1. For example, when the mixed layer is a laminate, the P / N of the mixed layer laminated on the most cathode side is preferably less than 1, and particularly preferably 0.5 or less. Thereby, since the weight ratio of the electron-accepting material responsible for electron transport in the mixed layer 34 increases toward the cathode side, the barrier associated with electron transport decreases.
When the weight mixing ratio P / N of the mixed layer is as close to 0 as possible, it becomes the same as the layer of only the electron-accepting material (N), and the effect of the present invention cannot be expected. However, it has been confirmed that the effect of the present invention can be obtained if P / N is 0.001 or more in at least the mixed layer.

  The photoelectric conversion element of this invention should just be a structure containing the mixed layer which satisfy | fills the said requirements between a pair of electrodes, and another structure is not specifically limited. For example, a buffer layer may be provided between the electrode and the organic layer as necessary. Specifically, a structure having the following configuration on a stable insulating substrate can be given.

(1) Lower electrode / mixed layer / upper electrode (2) Lower electrode / P layer / mixed layer / upper electrode (3) Lower electrode / buffer layer / mixed layer / upper electrode (4) Lower electrode / buffer layer / P layer / Mixed layer / Upper electrode (5) Lower electrode / Mixed layer / N layer / Upper electrode (6) Lower electrode / Mixed layer / Buffer layer / Upper electrode (7) Lower electrode / Mixed layer / N layer / Buffer layer / Upper Electrode (8) Lower electrode / P layer / mixed layer / N layer / upper electrode (FIG. 1)
(9) Lower electrode / buffer layer / P layer / mixed layer / N layer / upper electrode (10) Lower electrode / P layer / mixed layer / N layer / buffer layer / upper electrode (11) Lower electrode / buffer layer / P Layer / mixed layer / N layer / buffer layer / upper electrode In the above configuration example, the lower electrode corresponds to the anode and the upper electrode corresponds to the cathode.

  About the member and material of the photoelectric conversion element of this invention, the well-known thing used with an organic thin-film solar cell can be used, for example. Hereinafter, each component will be briefly described.

1. Electrodes (anode and cathode)
The material for the electrode is not particularly limited, and a known conductive material can be used. For example, a metal such as tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), gold (Au), osmium (Os), palladium (Pd) can be used as the anode.
On the other hand, as the cathode, metals such as silver (Ag), aluminum (Al), indium (IN), calcium (Ca), platinum (Pt) lithium (Li), Mg: Ag, Mg: IN, Al: Li, etc. In addition, the above-described examples of anode materials can be used.

  In order to obtain highly efficient photoelectric conversion characteristics, it is desirable that at least one surface of the photoelectric conversion element 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. Electron donating material (P)
The electron donating material is used in the P layer and the mixed layer. A compound having a function as a hole acceptor and having a high hole mobility, specifically, 10 ⁻⁶ (cm ² / V · s) or more (measurement conditions: anode / electron donating material / cathode) (Time-of-Flight (TOF) method) having a sandwich type structure is preferred.

Examples of the electron donating material include N, N′-bis (3-tolyl) -N, N′-diphenylbenzidine (mTPD), N, N′-dinaphthyl-N, N′-diphenylbenzidine (NPD), Amine compounds represented by 4,4 ′, 4 ″ -tris (phenyl-3-tolylamino) triphenylamine (MTDATA), etc., phthalocyanine (Pc), copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc), titanyl phthalocyanine Examples include phthalocyanines such as (TiOPc), porphyrins represented by octaethylporphyrin (OEP), platinum octaethylporphyrin (PtOEP), zinc tetraphenylporphyrin (ZNTPP), and the like.
Moreover, if it is a high molecular compound using the application | coating process by a solution, main chain type conjugated polymers, such as methoxyethyl hexyloxy phenylene vinylene (MEHPPV), polyhexyl thiophene (P3HT), cyclopentadithiophene-benzothiadiazole (PCPDTBT) And side chain polymers represented by polyvinylcarbazole and the like.

3. Electron-accepting material (N)
The electron accepting material is used in the N layer and the mixed layer. A compound having a function as a hole donor and having a high electron mobility, specifically, 10 ⁻⁶ (cm ² / V · s) or more (measurement conditions: anode / electron-accepting material / cathode The Time-of-Flight (TOF) method) having a sandwich structure is preferable.

As the electron accepting material, for example, as long as it is an organic compound, fullerene derivatives such as C _60, C _70, carbon nanotube, perylene derivatives, polycyclic quinone, quinacridone, the polymeric CN- poly (phenylene - vinylene), MEH-CN-PPV, -CN group or CF ₃ group-containing polymers, mention may be made of poly (fluorene) derivatives. A material having a low electron affinity is preferred. A sufficient open-circuit voltage can be realized by combining materials having a low electron affinity as the N layer.

In addition, as long as it is an inorganic compound, an inorganic semiconductor compound having N-type characteristics can be given. 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 ), monoxide Examples thereof include titanium oxide such as titanium (TiO) and dititanium trioxide (Ti ₂ O ₃ ), and conductive oxides such as zinc oxide (ZNO) and tin oxide (SNO ₂ ). You may use combining more than a seed. Preference is given to using titanium oxide, particularly preferably titanium dioxide.

The mixed layer of the present invention is composed of a combination of the electron donating material (P) and the electron accepting material (N). The material is not particularly limited, and any of the above exemplary compounds can be used.
The electron donating material used in the P layer and the electron donating material used in the mixed layer may be the same or different. Similarly, the electron-accepting material used in the N layer and the electron-accepting material used in the mixed layer may be the same or different.

4). Buffer layer In general, the total thickness of a photoelectric conversion element is often small. Therefore, the upper electrode and the lower electrode are short-circuited, and the yield of the element is often lowered. In such a case, it is preferable to stack a buffer layer. In addition, it is preferable to provide a buffer layer in order to efficiently extract the generated current to the outside.

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.

The buffer layer can also have a role of preventing excitons from diffusing to the electrode and being deactivated. 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.
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 for use in an organic EL device 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 compounds may be used CdTe, P-Si, SiC, GaAs, and WO ₃ or the like.

5. 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 and the like can be mentioned.

  Each layer of the photoelectric conversion element of the present invention is formed by a dry film formation method such as vacuum deposition, sputtering, plasma, or ion plating, or a wet film formation such as spin coating, dip coating, casting, roll coating, flow coating, or inkjet. The law can be applied. Any of the above-described film formation processes or combinations can be applied. However, since the organic thin film is affected by moisture and oxygen, it is more preferable that the film formation process is unified.

  The film thickness of each layer is not particularly limited, and is set to an appropriate film 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 is 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 an 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 preferable. These solvents may be used alone or in combination. In addition, the solvent which can be used is not limited to these.
Moreover, you may heat at appropriate temperature for the solvent removal in the thin film formed by wet film-forming.

  In the present invention, in any organic thin film layer of the photoelectric conversion element, 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.

  Moreover, the organic thin film layer may contain additives such as an antioxidant, an ultraviolet absorber, and a plasticizer as necessary.

Example 1
A glass substrate with an ITO transparent electrode 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 a transparent electrode line after washing was mounted on a substrate holder of a vacuum deposition apparatus.
On the surface of the lower electrode on which the transparent electrode line is formed, an electron donating P-type material ZnPc is 1 覆 う / s and an electron accepting N-type material C ₆₀ is formed so as to cover the transparent electrode. Co-evaporation was performed at 0.25 L / s to form a 25 nm first mixed layer (I ₁ layer: weight mixing ratio P / N = 4).
Subsequently, 0.25 Å / s to ZnPc _one layer on _I, the second mixed layer of 25nm were co-evaporated _{C 60} at 1 Å / s: the _{(I 2} layers weight mixing ratio P / N = 0.25) Formed.
Thus, a mixed layer (50 nm thickness) composed of two layers having different P / N was formed.
On the mixed layer, 10 nm bathocuproine (BCP) was deposited at 1 Å / s by resistance heating vapor deposition as a buffer layer. Finally, metal Al was deposited in a thickness of 80 nm continuously as a counter electrode to form an organic thin film solar cell. The element area was 0.5 cm ² .

Example 2
Using a glass substrate with an ITO transparent electrode cleaned in the same manner as in Example 1, ZnPc was coated on the surface on the side where the transparent electrode line as the lower electrode was formed by resistance heating vapor deposition so as to cover the transparent electrode. / S was formed into a P layer (film thickness 15 nm).
Subsequently, on the ZnPc layer was formed by co-evaporation ZnPc 1 Å / _s, the _{C 60} at 0.25 Å / s _{I 1} layer of 7.5nm (weight mixing ratio P / N = 4). Subsequently, to form _{I 2} layers of 7.5nm were co-evaporated ZnPc _one layer on _I 0.25 Å / _s, the _{C 60} at 1 Å / s (weight mixing ratio P / N = 0.25). In this way, a mixed layer (15 nm thickness) composed of two layers having different P / N was formed.
On the mixed _layer, deposited by 1 Å / s by resistance heating deposition _{C 60,} and an N layer (thickness 45 nm).
Thereafter, the buffer layer and the counter electrode were formed in the same manner as in Example 1 to form an organic thin film solar cell. The element area was 0.5 cm ² .

Example 3
An organic thin film solar cell was formed in the same manner as in Example 2 except that the mixed layer was formed as follows.
The mixed layer was composed of three layers having different P / N. Specifically, to form ZnPc a 1 Å / _{s, I 1} layer of co-deposited to 5nm to _{C 60} in 0.25 Å / s (weight mixing ratio P / N = 4). Was then formed 1 Å / s to ZnPc _one layer on _{I, I 2} layers of co-deposited to 5nm to _{C 60} with 1 Å / s (weight mixing ratio P / N = 1). Further, on the I ₂ layer, ZnPc was co-evaporated at 0.25 Å / s and C ₆₀ was 1 Å / s to form a 5 nm I ₃ layer (weight mixing ratio P / N = 0.25).
As a result, a mixed layer having a total thickness of 15 nm was formed.

Example 4
An organic thin film solar cell was formed in the same manner as in Example 2 except that the mixed layer was formed as follows.
The mixed layer was constituted by four layers having different P / N. Specifically, to form by co-evaporation ZnPc 1 Å / _s, the _{C 60} at 0.25 Å / s _{I 1} layer of 3.75nm (weight mixing ratio P / N = 4). Subsequently, to form the _{I 2} layer of 3.75nm were co-evaporated ZnPc _one layer on _I 1 Å / _s, the _{C 60} at 0.5 Å / s (weight mixing ratio P / N = 2). Subsequently, ZnPc was co-evaporated at 0.5 Å / s and C60 was 1 Å / s on this I ₂ layer to form an I ₃ layer (weight mixing ratio P / N = 0.5) of 3.75 nm. Subsequently, to form the _{I 4} layers of 3.75nm were co-evaporated ZnPc this _{I 3} layers on 0.25 Å / _s, the _{C 60} at 1 Å / s (weight mixing ratio P / N = 0.25).
As a result, a mixed layer having a total thickness of 15 nm was formed.

Example 5
An organic thin film solar cell was formed in the same manner as in Example 2 except that the mixed layer was formed as follows.
The mixed layer was composed of five layers having different P / N. Specifically, to form ZnPc a 1 Å / _{s, I 1} layer of co-deposited to 3nm to _{C 60} in 0.25 Å / s (weight mixing ratio P / N = 4). Subsequently, to form the _{I 2} layer of 3nm were co-evaporated ZnPc _one layer on _I 1 Å / _s, the _{C 60} at 0.5 Å / s (weight mixing ratio P / N = 2). Subsequently, the formation of the a ZnPc the _{I 2} layer on 1Å / _s, 3nm _{I 3} layer by co-evaporation _{C 60} at 1 Å / s (weight mixing ratio P / N = 1). Subsequently, the formation of the _{I 3} and ZnPc on layer 0.5Å / _s, 3nm _{I 4} layer by co-evaporation _{C 60} at 1 Å / s (weight mixing ratio P / N = 0.5). Subsequently, the formation of the _{I 4} a ZnPc on layer 0.25 Å / _{s, I 5} layers of co-deposited to 3nm to _{C 60} with 1 Å / s (weight mixing ratio P / N = 0.25).
As a result, a mixed layer having a total thickness of 15 nm was formed.

Comparative Example 1
An organic thin film solar cell was formed in the same manner as in Example 1 except that the mixed layer was formed as follows.
The mixed layer has a structure composed of one layer. Specifically, it was formed by co-evaporation of ZnPc 1 Å / _s, the _{C 60} at 1 Å / s (50 nm thick: mixing ratio by weight P / N = 1).

Comparative Example 2
An organic thin film solar cell was formed in the same manner as in Example 2 except that the mixed layer was formed as follows.
The mixed layer has a structure composed of one layer. Specifically, it was formed by co-evaporation of ZnPc 1 Å / _s, the _{C 60} at 1 Å / s (15 nm thick: mixing ratio by weight P / N = 1).

Comparative Example 3
An organic thin film solar cell was formed in the same manner as in Example 2 except that the mixed layer was formed as follows.
The mixed layer was composed of the following three layers. Specifically, to form ZnPc a 1 Å / _{s, I 1} layer of co-deposited to 5nm to _{C 60} with 1 Å / s (weight mixing ratio P / N = 1). Subsequently, the formation of the _{I 1} a ZnPc on layer 1 Å / _{s, I 2} layers of co-deposited to 5nm to _{C 60} with 0.5 Å / s (weight mixing ratio P / N = 2). Subsequently, the formation of the a ZnPc the _{I 2} layer on 1.5Å / _s, 5nm _{I 3} layer by co-evaporation _{C 60} at 0.5 Å / s (weight mixing ratio P / N = 3).
As a result, a mixed layer having a total thickness of 15 nm was formed.

Comparative Example 4
An organic thin film solar cell was formed in the same manner as in Example 2 except that the mixed layer was formed as follows.
The mixed layer was composed of the following two layers. Specifically, to form by co-evaporation ZnPc 1.5 Å / _s, the _{C 60} at 0.5 Å / s _{I 1} layer of 7.5nm (weight mixing ratio P / N = 3). Subsequently, the formation of the _{I 1} a ZnPc on layer 1 Å / _{s, I 2} layers of 7.5nm were co-evaporated to _{C 60} with 1 Å / s (weight mixing ratio P / N = 1).
As a result, a mixed layer having a total thickness of 15 nm was formed.

Comparative Example 5
An organic thin film solar cell was formed in the same manner as in Example 2 except that the mixed layer was formed as follows.
The mixed layer was composed of the following three layers. Specifically, to form ZnPc a 1.5 Å / _{s, I 1} layer of co-deposited to 5nm to _{C 60} with 0.5 Å / s (weight mixing ratio P / N = 3). Subsequently, the formation of the _{I 1} a ZnPc on layer 1 Å / _{s, I 2} layers of 5nm were co-evaporated to _{C 60} with 1 Å / s (weight mixing ratio P / N = 1). Subsequently, the formation of the _{I 2} a ZnPc on layer 0.5Å / _s, 5nm _{I 3} layer by co-evaporation _{C 60} at 1.5 Å / s (weight mixing ratio P / N = 0.33).
As a result, a mixed layer having a total thickness of 15 nm was formed.

For the organic thin-film solar cells produced in the above examples and comparative examples, the conversion efficiency of the battery immediately after production and the battery after storage for 60 days (room temperature, normal humidity, in the dark) is measured, and the conversion efficiency Durability was evaluated by comparing the changes of.
Specifically, the IV characteristics were measured under conditions of AM (air mass) 1.5 (incident intensity (Pin) 100 mW / cm ² ) for the battery immediately after fabrication and the battery after storage for 60 days, respectively. The conversion efficiency (η) was derived from the end voltage (Voc), short circuit current density (Jsc), and fill factor (FF) by the following equation.

（式中、Ｆｒｅｓｈは作製直後の電池の変換効率、Ｐｒｅｓｅｒｖｅｄは６０日間保存後の電池の変換効率である。） The attenuation rate (%) of the conversion efficiency of the battery immediately after production and the battery after storage for 60 days was calculated according to the following formula, and durability was evaluated. A device having a negative value (improvement) in attenuation rate (%) of conversion efficiency (η) or a smaller element has better durability.

(In the formula, Fresh is the conversion efficiency of the battery immediately after fabrication, and Preserved is the conversion efficiency of the battery after storage for 60 days.)

  Table 1 shows the conversion efficiencies of the organic thin-film solar cells produced in the above Examples and Comparative Examples immediately after production and after storage for 60 days, and the conversion efficiency decay rate.

  As can be seen from Table 1, the mixed layer has a layer in which the weight mixing ratio P / N of the electron donating material (P) and the electron accepting material (N) is larger than 3, and the weight mixing ratio P / N is It has been clarified that by adopting a configuration that decreases from the anode side toward the cathode side, a higher conversion efficiency is obtained compared to the element of the comparative example and the durability is excellent.

  The photoelectric conversion element of the present invention is not limited to an organic thin film solar cell, and can be used as, for example, a photodiode or an imaging element. In addition, the organic thin film solar cell can be used as a power source for various devices such as watches, mobile phones, and mobile personal computers, that is, electrical appliances.

DESCRIPTION OF SYMBOLS 10 Anode 20 Cathode 30 Photoelectric conversion layer 32 P layer 34 Mixed layer 36 N layer

Claims (5)

An anode and a cathode;
A photoelectric conversion layer between the anode and the cathode,
The photoelectric conversion layer has at least a mixed layer containing an electron donating material (P) and an electron accepting material (N),
The weight mixing ratio (P / N) of the electron donating material (P) and the electron accepting material (N) in the most anode portion of the mixed layer is greater than 3,
The photoelectric conversion element in which P / N of the mixed layer decreases from the anode side toward the cathode side. The photoelectric conversion layer is
The photoelectric conversion according to claim 1, further comprising: a layer made of only an electron donating material between the anode and the mixed layer, and a layer made of only an electron accepting material between the cathode and the mixed layer. element.   3. The photoelectric conversion element according to claim 1, wherein P / N at the most cathode side portion of the mixed layer is smaller than 1. 4.   It is an organic solar cell, The photoelectric conversion element in any one of Claims 1-3.   The apparatus which has a photoelectric conversion element in any one of Claims 1-4.

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