Patent Description:
In recent years, development of a solid state image pickup element having a structure in which an organic compound is used for a photoelectric conversion layer disposed on a signal-reading substrate has advanced.

Various configurations for improving dark current in a photoelectric conversion element are known. PTL <NUM> describes an organic photoelectric conversion element, in which an electron-blocking layer is disposed between a photoelectric conversion layer and an anode and in which dark current is reduced by specifying an energy level relationship between the photoelectric conversion layer and the electron-blocking layer and by specifying the layer thickness of the electron-blocking layer.

PTL <NUM> describes an organic photoelectric conversion element, in which a hole-blocking layer is disposed between a photoelectric conversion layer and a cathode and in which dark current is reduced by specifying an energy level relationship between the photoelectric conversion layer and the hole-blocking layer.

The dark current in the photoelectric conversion element includes dark current generated in the photoelectric conversion layer in addition to current that flows from the anode and from the cathode.

PTLs <NUM> and <NUM> neither describe nor indicate dark current that is generated between a p-type organic semiconductor material and an n-type organic semiconductor material in the photoelectric conversion layer. Therefore, a reduction in dark current in the photoelectric conversion element is insufficient.

<NPL>) prepared OPV cells using donor materials composed of different electron-rich donor and electron-deficient acceptor units and the acceptor material <NUM>,<NUM>-phenyl-C61-butyric acid methyl ester.

<CIT> relates to an organic thin film solar cell material represented by the following general formula:
<CHM>.

<NPL>)) reports an improvement of photovoltaic response by dispersing phosphorescent Ir(ppy)<NUM>Ir(ppy)<NUM> molecules in an organic solar cell of poly[<NUM>-methoxy-<NUM>-(<NUM>'<NUM>'-ethylhexyloxy)-<NUM><NUM>-phenylenevinylene] (MEH-PPV) blended with surface-functionalized fullerene <NUM>-(<NUM>-methyloxycarbonyl)propy(<NUM>-phenyl [<NUM>, <NUM>]) C<NUM> (PCBM).

<NPL>) discloses an organic photovoltaic conversion element comprising C<NUM> and a triphenylamine derivative in the photoactive layer.

Accordingly, it is an object of the present invention to provide an organic photoelectric conversion element in which dark current that is generated between a p-type organic semiconductor material and an n-type organic semiconductor material in a photoelectric conversion layer in a photoelectric conversion element is reduced.

<CIT> (Art. <NUM>(<NUM>) EPC) discloses a photoelectric conversion element combining a compound B16
<CHM>
and 'C60' (fullerene).

According to claim <NUM> of the present invention, a photoelectric conversion element including an anode, a cathode, and a photoelectric conversion layer disposed between the anode and the cathode is provided, wherein the photoelectric conversion layer contains a first organic compound and a second organic compound, the oxidation potential of the first organic compound is lower than the oxidation potential of the second organic compound, ΔE denoted by formula (A) below satisfies formula (B) below, <MAT> <MAT> and the first organic compound is denoted by general formula [<NUM>] below, wherein the photoelectric conversion element (<NUM>) is other than the photoelectric conversion element of Example <NUM> of <CIT>.

In general formula [<NUM>] , R<NUM> to R<NUM>, and R<NUM> is selected from represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted vinyl group, a substituted or unsubstituted amino group, and a cyano group, R<NUM> and R<NUM> form a ring by bonding to each other and R<NUM> and R<NUM> may form a ring by bonding together.

In general formula [<NUM>], R<NUM> represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted vinyl group, a substituted or unsubstituted amino group, or a cyano group.

Z<NUM> represents a halogen atom, a cyano group, a substituted or unsubstituted heteroaryl group, or any substituent denoted by general formulae [<NUM>-<NUM>] to [<NUM>-<NUM>] below.

In general formulae [<NUM>-<NUM>] to [<NUM>-<NUM>], each of R<NUM> to R<NUM> is selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted vinyl group, a substituted or unsubstituted amino group, and a cyano group. <CHM>
<CHM>.

According to the present invention, a photoelectric conversion element in which dark current is reduced can be provided.

The present invention relates to a reduction in dark current in a photoelectric conversion element including a photoelectric conversion layer composed of an organic compound. Dark current can be reduced by increasing an energy difference between two types of organic compounds contained in the photoelectric conversion layer to a specific value or more.

Meanwhile, the dark current can be reduced by setting the activation energy of dark current in the photoelectric conversion element to be a specific value or more.

Dark current due to thermal charge separation is not readily generated when the activation energy increases. The activation energy is the magnitude of energy required for exciting the first organic compound and the second organic compound to a charge separation state. Application of energy higher than or equal to the activation energy by the thermal energy causes dark current.

According to an aspect of the present invention, dark current in a photoelectric conversion element is reduced by setting the activation energy of dark current to be <NUM> eV or more. The activation energy of dark current is preferably <NUM> eV or more and further preferably <NUM> eV or more.

In the present embodiment, a photoelectric conversion element including a photoelectric conversion layer composed of an organic compound between an anode and a cathode will be described as an example.

The photoelectric conversion layer included in the photoelectric conversion element according to the present invention is a layer that receives light so as to generate electric charge in accordance with the amount of the light. The function of the photoelectric conversion layer is to perform charge separation into holes and electrons on the basis of light absorption so as to convert the light into electric signals. The photoelectric conversion layer may contain a plurality of types of organic compounds. A layer in which a donor material that carries positive charge into the photoelectric conversion layer and an acceptor material that carries negative charge are mixed at random is called a bulk heterojunction.

When the photoelectric conversion layer contains a plurality of types of organic compounds, the plurality of types of organic compounds may be mixed in one layer, or the plurality of types of organic compounds may be contained in a plurality of layers.

It is preferable that the photoelectric conversion layer be a layer containing a p-type organic semiconductor or an n-type organic semiconductor. It is more preferable that bulk heterolayers in which an organic p-type compound and an organic n-type compound are mixed be included in at least some of the photoelectric conversion layers. In other words, the heterolayer may be a mixed layer.

The photoelectric conversion layer including the bulk heterolayer has high photoelectric conversion efficiency. Further, in the bulk heterolayer having an appropriate mixing ratio, the electron mobility and the hole mobility are high in the photoelectric conversion layer, and the optical response speed of the photoelectric conversion element is high. Therefore, it is preferable that a bulk heterolayer having an optimum mixing ratio be included.

ΔE is an energy gap defined by formula (A) below. <MAT> In this regard, ΔE satisfies formula (B) below.

<FIG> is an energy diagram showing ΔE. The oxidation potential of the first organic compound corresponds to HOMO of the first organic compound. Meanwhile, the reduction potential of the second organic compound corresponds to LUMO of the second organic compound. The oxidation-reduction potential is a potential energy difference between molecules in a solution and an electrode and is a physical property value of the molecule alone.

Dark current may be generated from a p-type organic semiconductor material to an n-type organic semiconductor material due to thermal charge separation. In a sense, ΔE is energy necessary for generation of dark current due to thermal charge separation.

When formula (B) is satisfied, generation of dark current due to thermal excitation rather than optical excitation can be suppressed.

This is because the magnitude of ΔE correlates with the activation energy of dark current generation and, more specifically, the activation energy of the dark current tends to increase when ΔE increases. When formula (B) is satisfied, the activation energy of dark current generation is increased, generation of dark current due to thermal excitation is suppressed, and thereby a photoelectric conversion element in which dark current is reduced can be obtained.

Meanwhile, dark current due to thermal excitation is caused by contact between molecules of a p-type organic semiconductor and molecules of an n-type organic semiconductor, which form a bulk heterojunction.

In addition to formula (B), the activation energy can be increased and dark current can be reduced by the photoelectric conversion layer including an organic compound that is suppressed from coming into contact with other molecules or an organic compound that suppresses generation of thermal electrons.

The photoelectric conversion element according to the present embodiment is a photoelectric conversion element in which dark current is reduced because the photoelectric conversion layer contains the first organic compound and the second organic compound, the first organic compound has a property of suppressing contact with other molecules or a property of suppressing generation of thermal electrons.

The photoelectric conversion layer contains the first organic compound and the second organic compound, and the first organic compound is an electron donor material.

The first organic compound is the p-type organic semiconductor contained in the photoelectric conversion layer. The first organic compound is an organic semiconductor with donor ability and has a property of readily providing electrons. Specifically, of the two organic compounds, the first organic compound is an organic compound having a lower oxidation potential. That is, the first organic compound is an electron donor material, and the second organic compound is an electron acceptor material.

The first organic compound is preferably within a visible range with an absorption wavelength of <NUM> or more and <NUM> or less. For the purpose of providing the photoelectric conversion layer with a panchromatic absorption band, the absorption peak wavelength is preferably <NUM> or more. In particular, <NUM> or more is preferable, and <NUM> or more and <NUM> or less is further preferable. When the absorption peak wavelength falls within the above-described range, absorption also occurs in a blue range of <NUM> or more and <NUM> or less and a red range of <NUM> or more and <NUM> or less, which are nearby ranges, and as a result, panchromatism is improved.

The absorption peak wavelength can be obtained by, for example, measuring an absorption spectrum in a chloroform solution.

In this regard, when the absorption peak wavelength of the first organic compound is <NUM> or more, it is particularly preferable that formula (B) be satisfied and the activation energy of dark current be set to be a specific value or more.

An organic compound having an absorption peak wavelength of <NUM> or more is an organic compound having a relatively small band gap. Regarding the organic compound having a small band gap, HOMO thereof tends to approach LUMO of the second organic compound. That is, dark current is readily generated. In this case, great effect is exerted by satisfying formula (B) or satisfying that the activation energy of dark current is set to be a specific value or more.

The concentration of the first organic compound in the photoelectric conversion layer is preferably less than <NUM>% by weight, where the total of the first organic compound and the second organic compound is assumed to be <NUM>% by weight, and <NUM>% by weight or less is more preferable. It is favorable that the concentration of the first organic compound be within the preferable range because dark current can be further reduced.

The first organic compound is denoted by general formula [<NUM>] below.

In general formula [<NUM>] , R<NUM> to R<NUM>, and R<NUM> is selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted vinyl group, a substituted or unsubstituted amino group, and a cyano group,.

The substituents included in the alkyl group, the aryl group, the heterocyclic group, the amino group, the vinyl group, and the alkoxy group in general formula [<NUM>] are substituents described below. Examples of the substituent include an alkyl group having a carbon atom number of <NUM> to <NUM>, for example, a methyl group, an ethyl group, a propyl group, and a butyl group, an aralkyl group, for example, a benzyl group, an aryl group, for example, a phenyl group and a biphenyl group, a heterocyclic group in which a heteroatom is a nitrogen atom, for example, a pyridyl group and a pyrrolyl group, an amino group, for example, a dimethylamino group, a diethylamino group, a dibenzylamino group, a diphenylamino group, and a ditolylamino group, an alkoxy group, for example, a methoxy group, an ethoxy group, a propoxy group, and a phenoxy group, a cyclic ketone group, for example, a <NUM>,<NUM>-indanedionyl group, a <NUM>-fluoro-<NUM>,<NUM>-indanedionyl group, a <NUM>,<NUM>-difluoro-<NUM>,<NUM>-indanedionyl group, a <NUM>,<NUM>-dicyano-<NUM>,<NUM>-indanedionyl group, a <NUM>-cyano-<NUM>,<NUM>-indanedionyl group, a cyclopenta[b]naphthalene-<NUM>,<NUM>(<NUM>)-dionyl group, a phenalene-<NUM>,<NUM>(<NUM>)-dionyl group, and a <NUM>,<NUM>-diphenyl-<NUM>,<NUM>,<NUM>(<NUM>,<NUM>,<NUM>)-pyrimidinetrionyl group, a cyano group, and a halogen atom. The halogen atom is fluorine, chlorine, bromine, iodine, or the like and a fluorine atom is preferable.

The first compound has a structure denoted by general formula [<NUM>] below.

Each of R<NUM> to R<NUM> is selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted vinyl group, a substituted or unsubstituted amino group, and a cyano group. Two of R<NUM> to R<NUM>, the two being adjacent to each other, may form a ring by bonding to each other. In particular, R<NUM> and R<NUM> form a ring by bonding to each other.

In this regard, the organic compound denoted by general formula [<NUM>] is a material having strong absorption at an absorption peak wavelength of <NUM> or more and <NUM> or less. It is preferable that an absorption peak appear in this wavelength range because the photoelectric conversion layer has panchromatism, as described above.

A specific example of the first organic compound is compound <NUM>-<NUM> as described below and the others are reference examples outside the scope of the claims but useful to understand the invention. <CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>.

Exemplary example <NUM>-<NUM> and reference examples <NUM>-<NUM> to <NUM>-<NUM> and <NUM>-<NUM> to <NUM>-<NUM> are a group of compounds having a sulfur-atom-containing five-membered heterocyclic group at the center. The compound which has the heterocyclic group and in which Z<NUM> is an electron-withdrawing substituent is a compound having a low HOMO level. As a result, ΔE can be increased, and generation of thermal electrons that cause dark current is suppressed.

Regarding exemplary example <NUM>-<NUM> and reference examples <NUM>-<NUM> to <NUM>-<NUM> and <NUM>-<NUM> to <NUM>-<NUM>, an organic compound having Ar<NUM> or Ar<NUM> has a large excluded volume and, therefore, has a low probability of contact with other molecules. Consequently, an acceptor material does not readily approach, and transfer of electrons due to thermal excitation does not readily occur. As a result, dark current can be reduced.

Reference examples <NUM>-<NUM> to <NUM>-<NUM> are a group of compounds having a fluoranthene skeleton at the center. The fluoranthene skeleton has an electron-withdrawing property and, therefore, is preferable first organic compound because generation of thermal electrons that cause dark current is suppressed.

Reference examples <NUM>-<NUM> to <NUM>-<NUM> are a group of complex compounds containing a metal atom at the center. Each ligand contains a heterocyclic compound as a section having an electron-withdrawing property and, thereby, generation of thermal electrons that cause dark current is suppressed.

The first organic compound has an oxidation potential of preferably <NUM> V or more.

The photoelectric conversion layer may contain fullerene or a fullerene derivative as the second organic compound. The fullerene or fullerene derivative may function as an n-type organic semiconductor.

An electron transport path is formed by molecules of fullerene or a fullerene derivative being connected to each other in the photoelectric conversion layer. Consequently, an electron transport property is improved, and high-speed responsiveness of the photoelectric conversion element is improved.

The content of fullerene or a fullerene derivative may be <NUM>% by weight or more and <NUM>% by weight or less, where the total of the first organic compound and the second organic compound is assumed to be <NUM>% by weight, in consideration of photoelectric conversion efficiency.

Examples of the fullerene or fullerene derivative include fullerene C60, fullerene C70, fullerene C76, fullerene C78, fullerene C80, fullerene C82, fullerene C84, fullerene C90, fullerene C96, fullerene C240, fullerene <NUM>, mixed fullerene, and fullerene nanotube.

The fullerene derivative may have a substituent. Examples of the substituent include an alkyl group, an aryl group, and a heterocyclic group.

The fullerene derivative is preferably fullerene C60.

The photoelectric conversion layer is preferably non-radiative. Non-radiation is denoted as emission quantum efficiency of <NUM>% or less, preferably <NUM>% or less, and more preferably <NUM>% or less in the visible light range (wavelength of <NUM> to <NUM>). When the emission quantum efficiency of the photoelectric conversion layer is <NUM>% or less, even in the case of application to a sensor or an image pickup element, a preferable image pickup element is realized because an influence exerted on sensing performance or image pickup performance is at a low level.

The photoelectric conversion element according to the present invention may further include a hole-blocking layer <NUM> between the anode and the photoelectric conversion layer. The hole-blocking layer is a layer that suppresses flowing of holes from the anode into the photoelectric conversion layer, and it is preferable that the ionization potential be high.

The photoelectric conversion element according to the present invention may further include an electron-blocking layer <NUM> between the cathode and the photoelectric conversion layer. The electron-blocking layer is a layer that suppresses flowing of electrons from the cathode into the photoelectric conversion layer, and it is preferable that the electron affinity or LUMO (lowest unoccupied molecular orbital energy) be low.

<FIG> is a schematic sectional view showing an example of a photoelectric conversion element according to the present embodiment. In the photoelectric conversion element, a photoelectric conversion layer <NUM> that converts light to electric charge is disposed between an anode <NUM> and a cathode <NUM> that are a pair of electrodes. A protective layer <NUM>, a wavelength selection portion <NUM>, and a microlens <NUM> are disposed on the anode. A reading circuit <NUM> is connected to the cathode.

Regarding the pair of electrodes, an electrode nearer to a substrate may be called a lower electrode, and an electrode farther from the substrate may be called an upper electrode. The lower electrode may be the anode or the cathode. The lower electrode may be an electrode having a high reflectance. The electrode may be composed of a material having high reflectance, or a reflective layer may be included in addition to the electrode layer.

The photoelectric conversion element according to the present invention may include the substrate. Regarding the substrate, for example, a silicon substrate, a glass substrate, a flexible substrate, or the like may be used.

The cathode included in the photoelectric conversion element according to the present invention is an electrode that collects holes of the charge generated in the photoelectric conversion layer. On the other hand, the anode is an electrode that collects electrons of the charge generated in the photoelectric conversion layer. There is no limitation regarding the material for constituting the cathode and the anode as long as electrical conductivity is high and transparency is provided. The materials for constituting the cathode and the anode may be the same or different from each other.

Specific examples of the material for constituting the electrode include a metal, a metal oxide, a metal nitride, a metal boride, and an organic conductive compound and mixtures of these. Further specific examples include a conductive metal oxide, for example, tin oxide doped with antimony, fluorine, or the like (ATO, FTO), tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), or indium zinc oxide (IZO), a metal, for example, gold, silver, chromium, nickel, titanium, tungsten, or aluminum, a conductive compound, for example, an oxide, a nitride, or the like of these metals (titanium nitride (TiN) is an example), a mixture or a layered material of these metals and a conductive metal oxide, an inorganic conductive substance, for example, copper iodide or copper sulfide, an organic conductive material, for example, a polyaniline, a polythiophene, or a polypyrrole, and a layered material of these and ITO or titanium nitride. Examples of the particularly preferable material as the electrode include titanium nitride, molybdenum nitride, tantalum nitride, and tungsten nitride.

The hole or electron collection electrode included in the photoelectric conversion element according to the present invention is an electrode that collects holes or electrons of the charge generated in the photoelectric conversion layer. The collection electrode located at a lower portion may be a pixel electrode in the configuration of an image pickup element. Whether the pixel electrode is a cathode or an anode is determined in accordance with an element configuration or a circuit configuration of a groundwork. For example, the order may be substrate/anode/photoelectric conversion layer/cathode on the substrate, or the order may be substrate/cathode/photoelectric conversion layer/anode.

A method for forming the electrode may be appropriately selected in consideration of suitability for the electrode material. Specifically, formation may be performed by a wet system, for example, a printing system or a coating system, a physical system, for example, a vacuum evaporation method, a sputtering method, or an ion plating method, a chemical system, for example, CVD or a plasma CVD method, or the like.

In the case in which the electrode is ITO, formation may be performed by, for example, an electron beam method, a sputtering method, a resistance heating evaporation method, a chemical reaction method (sol-gel method or the like), or a method in which a dispersion of indium tin oxide is applied. Further, the resulting ITO may be subjected to UV-ozone processing, plasma processing, or the like. In the case in which the electrode is TiN, a reactive sputtering method or other various methods may be used, and annealing, UV-ozone processing, plasma processing, or the like may be further applied.

There is no particular limitation regarding a thin film sealing layer, and an inorganic material is used for formation. Specific examples include silicon oxide, silicon nitride, silicon oxynitride, and aluminum oxide. Silicon oxide, silicon nitride, and silicon oxynitride may be formed by a sputtering method or a CVD method. Aluminum oxide may be formed by an ALD method (atomic layer deposition method).

Regarding the sealing performance of the sealing layer, the water permeability has to be <NUM>-<NUM> g/m<NUM> ·day or less. There is no particular limitation regarding the layer thickness of the sealing layer, and <NUM> or more is preferable from the viewpoint of sealing performance. On the other hand, smaller thickness is favorable as long as the sealing performance is maintained, and <NUM> or less is particularly preferable.

The thin film sealing layer having a smaller thickness is preferable because an effect of reducing color mixing is enhanced as the distance from a photoelectric conversion layer to a color filter decreases in the case of use as an image pickup element.

In the case in which the photoelectric conversion element is produced, it is preferable that an annealing step be included. There is no particular limitation regarding the annealing temperature, and the condition of annealing temperature may be <NUM> or higher and <NUM> or lower. The annealing temperature is appropriately determined in accordance with an annealing time.

An image pickup element according to the present embodiment includes a plurality of pixels, and each of the pixels includes a photoelectric conversion element according to the present invention and a reading transistor connected to the photoelectric conversion element.

The plurality of pixels are arranged in the matrix with a plurality of rows and a plurality of columns. Each pixel may be connected to a signal processing circuit. The signal processing circuit can obtain an image by receiving a signal from each pixel.

The reading transistor is a transistor that transfers a signal based on charge generated in the photoelectric conversion element.

The signal processing circuit may be a CMOS sensor or a CCD sensor.

The image pickup element may include an optical filter, for example, a color filter. In the case in which the photoelectric conversion element addresses light with a specific wavelength, it is preferable that a color filter in accordance with the photoelectric conversion element be included. Regarding the color filter, one color filter may be disposed for one light-receiving pixel, or one color filter may be disposed for a plurality of light-receiving pixels.

Examples of the optical filter include, in addition to the color filter, a low-pass filter that transmits wavelengths of infrared rays or higher and a UV cut filter that transmits wavelengths of ultraviolet rays or lower.

The image pickup element may include an optical member, for example, a microlens. The microlens is a lens that condenses light from outside on a photoelectric conversion portion. Regarding the microlens, each light-receiving pixel may include one microlens, or one microlens may be disposed so as to address a plurality of light-receiving pixels. In the case in which a plurality of light-receiving pixels are disposed, it is preferable that each of the plurality of light-receiving pixels include one microlens.

The image pickup element according to the present invention may be used for an image pickup apparatus. The image pickup apparatus includes an image pickup optical system including a plurality of lenses and an image pickup element that receives light passing through the image pickup optical system. In addition, the image pickup apparatus includes the image pickup element and a casing that accommodates the image pickup element. The casing may includes a connection portion that can be connected to the image pickup optical system. More specifically, the image pickup apparatus is a digital camera or a digital steel camera.

Further, the image pickup apparatus may include a receiving portion that receives a signal from outside. The signal received by the receiving portion is a signal that can control at least one of an image pickup range, start of image pickup, and finish of image pickup of the image pickup apparatus. In addition, the image pickup apparatus may further includes a sending portion that sends an acquired image to outside. Examples of the acquired image include a picked-up image and an image sent from another device.

When the receiving portion and the sending portion are included, the image pickup element can be used as a network camera.

<FIG> is a circuit diagram of a pixel including a photoelectric conversion apparatus according to the present invention. The photoelectric conversion apparatus <NUM> is connected to a common conductive line <NUM> at node A. The common conductive line may be connected to the ground.

A pixel <NUM> may include the photoelectric conversion element <NUM> and a reading circuit that reads a signal generated in the photoelectric conversion portion. The reading circuit may include, for example, a transfer transistor <NUM> electrically connected to the photoelectric conversion element, an amplifying transistor <NUM> including a gate electrode electrically connected to the photoelectric conversion element <NUM>, a selection transistor <NUM> that selects a pixel from which information is read, and a reset transistor <NUM> that supplies a reset voltage to the photoelectric conversion element.

Transfer of the transfer transistor <NUM> may be controlled by pTX. Supply of the voltage to the reset transistor may be controlled by pRES. The selection transistor is set to be in the state of selection or non-selection by pSEL.

The transfer transistor <NUM>, the reset transistor <NUM>, and the amplifying transistor <NUM> are connected to each other at node B. It is possible to include no transfer transistor in accordance with the configuration.

The reset transistor is a transistor that supplies a voltage to reset the potential at node B. Supply of the voltage can be controlled by applying pRES to the gate of the reset transistor. It is possible to include no reset transistor in accordance with the configuration.

The amplifying transistor is a transistor that passes a current in accordance with the potential at node B. The amplifying transistor is connected to the selection transistor <NUM> that selects a pixel from which a signal is output. The selection transistor is connected to a current source <NUM> and a column output portion <NUM>, and the column output portion <NUM> may be connected to a signal processing portion.

The selection transistor <NUM> is connected to a vertical output signal line <NUM>. The vertical output signal line <NUM> is connected to the current source <NUM> and the column output portion <NUM>.

<FIG> is a diagram showing an image pickup element according to the present invention. The image pickup element <NUM> includes an image pickup region <NUM> in which a plurality of pixels are two-dimensionally arranged and a peripheral region <NUM>. A region other than the image pickup region is the peripheral region. The peripheral region includes a vertical scanning circuit <NUM>, a reading circuit <NUM>, a horizontal scanning circuit <NUM>, and an output amplifier <NUM>, and the output amplifier is connected to a signal processing portion <NUM>. The signal processing portion is a signal processing portion that performs signal processing based on the information read by the reading circuit, and examples include a CCD circuit and a CMOS circuit.

The reading circuit <NUM> includes, for example, a column amplifier, a CDS circuit, an adding circuit, and the like and performs amplification, addition, and the like relative to signals read through the vertical signal line from pixels in the row selected by the vertical scanning circuit <NUM>.

The column amplifier, the CDS circuit, the adding circuit, and the like are arranged, for example, on a pixel column or a plurality of pixel columns basis. The horizontal scanning circuit <NUM> generates signals for sequentially reading signals of the reading circuit <NUM>. The output amplifier <NUM> amplifies and outputs signals of a row selected by the horizontal scanning circuit <NUM>.

The above-described configuration is just a configuration example of the photoelectric conversion apparatus, and the present embodiment is not limited to this. In order to configure two series of output paths, one each of the reading circuit <NUM>, the horizontal scanning circuit <NUM>, and the output amplifier <NUM> is arranged on and under the image pickup region <NUM>. However, three or more output paths may be disposed. Signals output from output amplifiers are combined as an image signal in the signal processing portion.

Electrochemical characteristics, for example, an oxidation potential, can be evaluated by cyclic voltammetry (CV).

A CV measurement sample was prepared by dissolving about <NUM> of first organic compound into <NUM> of <NUM>-M ortho-dichlorobenzene solution of tetrabutylammonium perchlorate and performing deaeration treatment using nitrogen. A three-electrode method was used for the CV measurement. Regarding the electrodes, a nonaqueous-solvent-based Ag/Ag+ reference electrode, a platinum counter electrode having a diameter of <NUM> and a length of <NUM>, and a glassy carbon working electrode having an inner diameter of <NUM> (every electrode was produced by BAS Inc. ) were used. An electrochemical analyzer Model 660C produced by ALS Co. , was used as an electrochemical measurement apparatus. The sweep rate of the measurement was set to be <NUM> V/s. <FIG> is a diagram showing an example of a cyclic voltammogram that determines the oxidation potential and the reduction potential of an organic compound. The oxidation potential and the reduction potential can be assumed from a peak value of the cyclic voltammogram. In the present specification, the oxidation potential is referred to as Eox and the reduction potential is referred to as Ered.

Table <NUM> shows the oxidation potentials of exemplary compounds.

In the present reference example, a photoelectric conversion element was produced by using a combination of a first organic compound and a second organic compound, where ΔE ≥ <NUM> V applied. Dark current was measured by using the resulting photoelectric conversion element.

In the present example, the photoelectric conversion element was formed on a Si substrate. In the photoelectric conversion element, a cathode, an electron-blocking layer, a photoelectric conversion layer, a hole-blocking layer, and an anode were sequentially formed.

In the present example, the photoelectric conversion element was produced in the following steps.

Initially, the Si substrate was prepared, in which a wiring layer and an insulating layer were stacked and, for the purpose of enabling communication, contact holes were disposed from the wiring layer through the insulating layer at a place corresponding to each pixel by forming an opening. This contact hole is connected to a pad portion at a substrate edge by a conductive line. An IZO electrode was formed by a sputtering method so as to overlap the contact hole portion. Patterning was performed so as to form <NUM><NUM> of IZO electrode (cathode). At this time, the film thickness of the IZO electrode was set to be <NUM>.

An organic compound layer was formed on the IZO electrode by a vacuum evaporation method. The layer configuration and the layer thickness were as shown in Table <NUM> below. Subsequently, IZO serving as an anode was formed by a sputtering method. The thickness of the anode was set to be <NUM>.

The layer configuration of the photoelectric conversion element is shown in Table <NUM>.

In this regard, in Table <NUM>, the cathode serving as a lower electrode is described in the lower side of the table.

Regarding the electron-blocking layer, compound (d-<NUM>) below was used. <CHM>
<CHM>.

Regarding the first organic compound of the photoelectric conversion layer, any one of exemplary compounds <NUM>-<NUM> to <NUM>-<NUM> was used. Regarding the hole-blocking layer, any one of fullerene C60 (d-<NUM>), fullerene C70 (d-<NUM>), and organic compound (d-<NUM>) below was used.

In this regard, the reduction potentials of d-<NUM>, d-<NUM>, and d-<NUM> are as shown in Table <NUM>.

After the upper electrode was formed, hollow sealing was performed by using a glass cap and an ultraviolet-effect resin. The thus obtained element with a sealed surface upward was annealed on a hot plate at <NUM> for about <NUM> hour.

Regarding the resulting element, the characteristics of the photoelectric conversion element were measured and evaluated. A current when <NUM> V was applied to the element was examined. Regarding every element, the current value at a bright place was at least <NUM> times the current value at a dark place and, therefore, it was ascertained that the photoelectric conversion element functioned.

In the measurement of dark current, the photoelectric conversion element was held in a constant temperature bath at <NUM> and the measurement was performed by bringing a prober wired to a semiconductor parameter analyzer (4155C, Agilent Technologies, Inc. ) into contact with an electrode.

The evaluation criteria of the dark current was as described below.

A to C were rated as good, and D and E were rated as poor.

The dark current evaluation of the photoelectric conversion element of example <NUM> was C. For example, in the case of a pixel of <NUM> square, the area is <NUM> × <NUM>-<NUM> cm<NUM>. When this photoelectric conversion element is used for an image pickup element, an image pickup element with low dark current can be obtained. The low-dark-current characteristics is associated with noise reduction of the image pickup element.

Photoelectric conversion elements were produced in the same manner as reference example <NUM> except that the combination of the first organic compound and the second organic compound was changed to a combination shown in Table <NUM>.

Photoelectric conversion elements were produced in the same manner as reference example <NUM> except that the combination of the first organic compound and the second organic compound was changed to a combination shown in Table <NUM>. The combination of compounds shown in Table <NUM> was a combination where ΔE < <NUM> V applied. The resulting photoelectric conversion element was subjected to the dark current evaluation in the same measuring method as example <NUM>.

Regarding the photoelectric conversion elements that exhibited ΔE of <NUM> V or more, the results of the dark current evaluation of the elements of all combinations were C or better and, therefore, low-dark-current characteristics were obtained.

Regarding exemplary compound <NUM>-<NUM> used in example <NUM>, changes in the dark current when mixing concentration was changed from <NUM>% by weight to <NUM>% by weight in steps of <NUM>% by weight are shown in Table <NUM>.

According to Table <NUM>, the concentration of the first organic compound is preferably less than <NUM>% by weight and more preferably <NUM>% by weight or less. The lower limit concentration is not limited by the present invention and may be, for example, a concentration at which necessary absorptance is obtained.

Photoelectric conversion elements were produced in the same manner as reference example <NUM> except that the constituent material and the layer thickness were set to be as shown in Table <NUM>. Regarding the first organic compound, the reference compound shown in Table <NUM> or comparative compound (e-<NUM>) below was used but is expressed as "first organic compound" in Table <NUM>. The dark current of each element was measured and relative evaluation was performed. The structure of comparative compound (e-<NUM>) was as described below. The oxidation potential of compound e-<NUM> was <NUM> V.

Dark current can be reduced by satisfying ΔE ≥ <NUM> V.

Regarding the first organic compound having a partial structure denoted by general formula [<NUM>], the maximum absorption peak wavelength and the molar absorptivity of the exemplary compounds below are described. The maximum absorption peak wavelength refers to the wavelength of a peak having the greatest absorption coefficient. Regarding the measurement, a chloroform solution in which the first organic compound was produced, and the absorption spectrum was measured by a spectrophotometer (JASCO Corporation Ubest-<NUM>). The maximum absorption peak wavelength and the absorbance were determined on the basis of the measurement results. The molar absorptivity was determined from the absorbance in accordance with Lambert-Beer law.

As is clear from example <NUM> and comparative example <NUM>, the compound denoted by general formula [<NUM>] can obtain an absorption peak suitable for obtaining a panchromatic absorption band in the visible range and strong absorption with molar absorptivity of <NUM>,<NUM> or more. Strong absorption is associated with a high external quantum yield and, therefore, is important factor for the photoelectric conversion element.

A photoelectric conversion element was produced in the same manner as reference example <NUM> except that a silicon nitride layer by using a CVD method was used as the sealing layer. The silicon nitride layer having a layer thickness of <NUM> was formed. Durability was evaluated by irradiating the resulting element with LED light of <NUM> at intensity of <NUM> W/cm<NUM> for <NUM>.

The absorptance of the LED light of <NUM> by the resulting SiN (<NUM>) was <NUM>%. The value of dark current in this element did not change even after a lapse of <NUM>.

On the other hand, regarding the photoelectric conversion element produced in reference example <NUM>, the dark current about <NUM>% increased after light irradiation for <NUM> hours. This is because the glass cap has lower ultraviolet absorptance than SiN. In consideration of this, it is preferable that the sealing layer be formed of a material that can absorb ultraviolet rays.

The photoelectric conversion element produced in reference example <NUM> was used, and the temperature dependence of dark current was measured. <FIG> is a diagram showing the Arrhenius plot of the photoelectric conversion element in example <NUM>. The vertical axis indicates the dark current value normalized by the dark current value at <NUM>. The vertical axis is graduated in common logarithms. The horizontal axis indicates the reciprocal of absolute temperature. The absolute value of the gradient increases as the temperature increases from about <NUM>. The activation energy was determined from this gradient on the basis of formula (<NUM>) below. <NUM>] <MAT>.

In this regard, T represents absolute temperature, kB represents Boltzmann constant, Ea represents activation energy, J represents a current value at temperature T, and J<NUM> represents a frequency factor. The dark current activation energy determined from the gradient was <NUM> eV.

Regarding each of the photoelectric conversion elements produced in reference examples <NUM>, <NUM>, <NUM>, and <NUM> and comparative example <NUM>, the activation energy was determined in the same method as example <NUM> and was plotted relative to corresponding ΔE as shown in <FIG>. It is shown that the activation energy tends to increase as ΔE increases. As is clear from <FIG>, when ΔE is <NUM> V or more, the activation energy is high. This indicates that when ΔE is <NUM> V or more, a probability of charge generation due to thermal excitation is reduced. In this regard, Table <NUM> shows the relationship between the activation energy and the dark current evaluation. As shown in Table <NUM>, when the activation energy is <NUM> eV or more, the rating of dark current is C or better.

That is, for the purpose of reducing dark current, it is preferable that the activation energy of dark current be <NUM> eV or more.

Claim 1:
A photoelectric conversion element (<NUM>) comprising:
an anode (<NUM>),
a cathode (<NUM>), and
a photoelectric conversion layer disposed between the anode (<NUM>) and the cathode (<NUM>),
wherein the photoelectric conversion layer contains a first organic compound and a second organic compound, the oxidation potential of the first organic compound is lower than the oxidation potential of the second organic compound, ΔE denoted by formula (A) below satisfies formula (B) below, <MAT> <MAT> characterised in that the first organic compound is denoted by general formula [<NUM>] below,
<CHM>
in general formula [<NUM>], R<NUM> to R<NUM>, and R<NUM> is selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted vinyl group, a substituted or unsubstituted amino group, and a cyano group,
wherein R<NUM> and R<NUM> form a ring by bonding to each other and wherein R<NUM> and R<NUM> may form a ring by bonding together,
in general formula [<NUM>], R<NUM> represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted vinyl group, a substituted or unsubstituted amino group, or a cyano group,
Z<NUM> represents a halogen atom, a cyano group, a substituted or unsubstituted heteroaryl group, or any substituent denoted by general formulae [<NUM>-<NUM>] to [<NUM>-<NUM>] below,
in general formulae [<NUM>-<NUM>] to [<NUM>-<NUM>], each of R<NUM> to R<NUM> is selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted vinyl group, a substituted or unsubstituted amino group, and a cyano group,
wherein the photoelectric conversion element (<NUM>) is other than the photoelectric conversion element of Example <NUM> of EP <NUM><NUM><NUM> A1.
<CHM>
<CHM>
<CHM>