WO2014050046A1

WO2014050046A1 - Photoelectric conversion element and imaging element using same

Info

Publication number: WO2014050046A1
Application number: PCT/JP2013/005558
Authority: WO
Inventors: 鈴木　秀幸
Original assignee: 富士フイルム株式会社
Priority date: 2012-09-28
Filing date: 2013-09-20
Publication date: 2014-04-03
Also published as: KR101676974B1; JP5824436B2; JP2014072328A; KR20150058495A

Abstract

[Problem] To provide: a photoelectric conversion element which has good photoelectric conversion efficiency, sensitivity and response speed, while exhibiting heat resistance during the production procedure; and a sensor and an imaging element, each of which is provided with this photoelectric conversion element. [Solution] A photoelectric conversion element (1) comprises an electron blocking layer (31) that is provided between a photoelectric conversion layer (32) and a hole collecting electrode (20). The photoelectric conversion layer (32) is composed of a plurality of bulk hetero layers (32) which are obtained by mixing a fullerene with a p-type organic semiconductor. The plurality of bulk hetero layers (32) are laminated such that a layer closer to the electron blocking layer (31) has a higher fullerene content. A first bulk hetero layer (32a) that is adjacent to the electron blocking layer (31) has a fullerene content of 70% by volume or more, and the difference of the fullerene contents between bulk hetero layers adjacent to each other is 15% by volume or less.

Description

Photoelectric conversion device and imaging device using the same

The present invention relates to an organic photoelectric conversion element having a photoelectric conversion layer composed of an organic layer and an image pickup element including the organic photoelectric conversion element.

Image sensors such as CCD sensors and CMOS sensors are widely known as image sensors used in digital still cameras, digital video cameras, mobile phone cameras, endoscope cameras, and the like. These elements include a photoelectric conversion element including a light receiving layer including a photoelectric conversion layer.

Development of a photoelectric conversion element using an organic compound and an image pickup element using the photoelectric conversion element has been advanced by the present applicants. For photoelectric conversion elements used in applications such as the above-described sensors and imaging elements, the S / N ratio of photocurrent / dark current and the response speed are important in performance.

As an organic light-receiving element that improves photoelectric conversion efficiency (sensitivity) and response speed without reducing sensitivity when an external voltage is applied, the applicants have a charge blocking layer that prevents carrier (charge) injection from the electrode by an external electric field. Have applied for an organic photoelectric conversion element provided between an electrode and an organic photoelectric conversion layer (Patent Document 1).

In addition, for the purpose of improving photoelectric conversion efficiency (sensitivity), the present applicants have a mixed layer (bulk hetero layer) of a p-type organic semiconductor and an n-type semiconductor such as fullerene or a fullerene derivative in a part of the light-receiving layer. ) Is used (Patent Document 2).

In the configuration in which a bulk hetero layer is provided in a part of the light receiving layer, the present applicants use a photoelectric conversion layer as a bulk hetero layer having a two-layer structure, and a hole collecting electrode side and an electron collecting electrode side. It is disclosed that higher photoelectric conversion efficiency can be realized by changing the fullerene content and the Fermi level (Patent Documents 3 and 4).

JP 2007-88033 A JP 2007-123707 A JP 2009-99866 A JP 2011-204802 A

As described above, in the photoelectric conversion element used for applications such as a sensor and an image pickup element, in addition to the photoelectric conversion efficiency and the S / N ratio, the response speed causing the afterimage is important in the performance. In addition, when a photoelectric conversion element for such use is formed into a device, a heating process such as a color filter and a wire bonding process is indispensable. Therefore, the organic layer also requires heat resistance against heating during the manufacturing process. Is done.

This invention is made | formed in view of the said situation, In the photoelectric conversion element which has the photoelectric converting layer which consists of an organic layer, it has heat resistance in a manufacturing process, and photoelectric conversion efficiency and a response speed are favorable. The object is to provide a photoelectric conversion element.

Another object of the present invention is to provide a sensor and an imaging device that have heat resistance during the manufacturing process and that have good photoelectric conversion efficiency and response speed.

The photoelectric conversion element of the present invention is an organic photoelectric conversion element having a pair of electrodes and a light receiving layer including at least a photoelectric conversion layer sandwiched between the pair of electrodes,
Having an electron blocking layer provided between the photoelectric conversion layer and one of the electrodes;
The photoelectric conversion layer is composed of a plurality of bulk hetero layers formed by mixing fullerene and a p-type organic semiconductor,
The plurality of bulk hetero layers are laminated such that the electron blocking layer side layer has a higher fullerene content,
The fullerene content in the bulk hetero layer adjacent to the electron blocking layer is 70% by volume or more, and the difference in the fullerene content between adjacent bulk hetero layers is 15% by volume or less. To do.

In this specification, “fullerene” is a mono meaning fullerene and a fullerene derivative. The content of fullerene means the volume% of the total amount of fullerene and fullerene derivative in one bulk hetero layer.

In the photoelectric conversion device of the present invention, the bulk hetero layer of the plurality of layers is preferably composed of two layers, and the fullerene content of the bulk hetero layer having the lowest mixing ratio of fullerene is 50% by volume or more. Is preferred.

The film thickness of the bulk hetero layer adjacent to the electron blocking layer is preferably 50 nm or less.

In the photoelectric conversion element of the present invention, the other electrode is preferably a transparent electrode disposed on the light receiving side, and a value obtained by dividing the voltage applied from the outside to the pair of electrodes by the distance between the electrodes is 1 × 10 ^5. V / cm to 1 × 10 ⁷ V / cm is preferable. Here, the other electrode means an electrode paired with an electrode provided with an electron blocking layer between the pair of electrodes and the photoelectric conversion layer.

The optical sensor of the present invention is preferably in the form of an image sensor, and includes a plurality of the photoelectric conversion elements of the present invention and a signal readout circuit that reads out a signal corresponding to the charge generated in the photoelectric conversion layer of the photoelectric conversion element. Circuit board.

The photoelectric conversion element of the present invention has an electron blocking layer between a photoelectric conversion layer and one electrode, and the photoelectric conversion layer is a multi-layer bulk hetero layer formed by mixing fullerene and a p-type organic semiconductor. The plurality of bulk hetero layers are laminated such that the electron blocking layer side layer has a higher fullerene content, and the bulk hetero layer adjacent to the electron blocking layer has a fullerene content of 70. The difference in the content of fullerene between adjacent bulk hetero layers is 15% by volume or less. According to such a configuration, it is possible to provide a photoelectric conversion element that has heat resistance during the manufacturing process and that has good photoelectric conversion efficiency and response speed, and a sensor and an imaging element including the photoelectric conversion element.

Sectional schematic diagram which shows schematic structure of the photoelectric conversion element of one Embodiment of this invention 1 is a schematic cross-sectional view showing a schematic configuration of an image sensor according to an embodiment of the present invention. The figure which shows the relationship between the difference of the fullerene content rate of a bulk hetero layer, and an afterimage (Examples 1-5 and Comparative Examples 1-9) The figure which shows the relationship between the difference of the fullerene content of a bulk hetero layer, and an afterimage (Examples 6-10 and Comparative Examples 10-16)

"Photoelectric conversion element"
With reference to drawings, the photoelectric conversion element of one Embodiment concerning this invention is demonstrated. FIG. 1 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element of this embodiment. In the drawings of this specification, the scale of each part is appropriately changed and shown for easy visual recognition.

As shown in FIG. 1, the organic photoelectric conversion element 1 (photoelectric conversion element 1) is formed on a substrate 10, a hole collection electrode 20 formed on the substrate 10, and a hole collection electrode 20. The electron blocking layer 31, the photoelectric conversion layer 32 formed on the electron blocking layer 31, the hole blocking layer 33 formed on the photoelectric conversion layer 32, and the electron trap formed on the hole blocking layer 33 A collector electrode 40, and a sealing layer 50 that covers the surface of the electron collector electrode 40 and the side surface of the laminate that is laminated from the hole collector electrode 20 to the electron collector electrode 40 are provided.

In the photoelectric conversion element 1, the electron collection electrode 40 is a transparent electrode, and when light enters from above the electron collection electrode 40, the light passes through the electron collection electrode 40 and enters the photoelectric conversion layer 32. A charge is generated. Of the generated charges, holes move to the hole collecting electrode 20, and electrons move to the electron collecting electrode 40.

By applying a bias voltage (external electric field) between the electron collection electrode 40 and the hole collection electrode 20, among the charges generated in the photoelectric conversion layer 32, holes are transferred to the hole collection electrode 20 and electrons are transferred. The electron collecting electrode 40 can be moved.

In the photoelectric conversion element 1, as an external electric field applied between the hole collection electrode 20 and the electron collection electrode 40 in order to obtain excellent characteristics in photoelectric conversion efficiency (sensitivity), dark current, and light response speed. Is preferably 1 V / cm or more and 1 × 10 ⁷ V / cm or less. The external electric field is a value obtained by dividing the voltage applied from the outside to the pair of electrodes by the distance between the electrodes.

In the photoelectric conversion element 1, the light receiving layer 30 is formed by the electron blocking layer 31, the photoelectric conversion layer 32, and the hole blocking layer 33. In the present embodiment, the mode including the hole blocking layer 33 is shown. However, since the hole blocking layer 33 does not contribute to the flow of holes, the present invention can be used regardless of the presence or absence of the hole blocking layer 33. An effect can be obtained.

The photoelectric conversion layer composed of a bulk hetero layer has (1) carrier transport property in the bulk hetero layer, (2) visible light absorption rate, (3) depending on the mixing ratio of fullerene and p-type organic semiconductor in the bulk hetero layer. ) Carrier transportability with the electron blocking layer and (4) heat resistance can be optimized. By making these characteristics favorable, the photoelectric conversion element 1 having heat resistance during the manufacturing process and excellent photoelectric conversion efficiency, sensitivity, and response speed can be obtained.

(1) From the viewpoint of carrier transportability in the bulk hetero layer,
The content of fullerene in the bulk hetero layer is preferably 40% to 80%.

(2) From the viewpoint of the visible light absorption rate of the photoelectric conversion layer 32,
If the amount of p-type organic semiconductor having an absorption peak wavelength in the visible region is small, the amount of incident light absorbed is reduced. Therefore, in order to obtain a sufficient amount of incident light absorption, it is necessary to sufficiently mix the p-type organic semiconductor into the bulk hetero layer.

When the content of fullerene in the bulk hetero layer is large, if the p-type organic semiconductor is sufficiently mixed, the film thickness of the photoelectric conversion layer increases. The photoelectric conversion element 1 can be driven by applying an external electric field between a pair of electrodes. However, as the film thickness of the photoelectric conversion layer increases, the voltage necessary for driving the photoelectric conversion element increases. Therefore, it is preferable that the photoelectric conversion layer is as thin as possible. The film thickness of the photoelectric conversion layer 32 is preferably 1000 nm or less, more preferably 700 nm or less, and particularly preferably 500 nm or less. Therefore, in order to sufficiently mix the p-type organic semiconductor in order to increase the visible light absorption, it is preferable to reduce the fullerene content in the photoelectric conversion layer 32 as much as possible.

(3) From the viewpoint of carrier transportability (hole transportability) to the electron blocking layer,
Of the photocarriers generated in the photoelectric conversion layer 32, holes are collected by the hole collection electrode 20 via the electron blocking layer 31. The inventor has found that the higher the fullerene content in the photoelectric conversion layer adjacent to the electron blocking layer, the higher the hole transport speed at the interface, and the higher the response speed.

When a region in which the organic semiconductor constituting the electron blocking layer 31 and the p-type organic semiconductor in the photoelectric conversion layer are mixed is formed at the contact interface between the electron blocking layer 31 and the photoelectric conversion layer 32, the mixed region A trap is formed, causing a reduction in response speed.

The present inventor mixed the organic semiconductor constituting the electron blocking layer 31 and the p-type organic semiconductor in the photoelectric conversion layer if the fullerene content of the photoelectric conversion layer adjacent to the electron blocking layer 31 is 70% or more. It was found that formation of the region can be suppressed (see Examples and Comparative Examples below). Further, from the viewpoint of carrier transport in the bulk hetero layer, the fullerene content in the bulk hetero layer is preferably 80% or less.

(4) From the viewpoint of heat resistance,
When the photoelectric conversion element 1 is used for an optical sensor such as an image sensor, it is necessary to form a color filter, perform a wire bonding process, or the like in order to make a device. In these steps, since the imaging device is heated to 200 ° C. or higher, the organic photoelectric conversion film used for the imaging device needs to have heat resistance of 200 ° C. or higher.

In the bulk hetero layer, the higher the fullerene content, the more stable the film and the better the heat resistance. Therefore, in order to realize sufficiently high heat resistance, the fullerene content in the bulk hetero layer 32 is preferably 50% or more.

According to the examinations from the viewpoints (1) to (4) above, in terms of response speed, carrier transportability, and heat resistance, the fullerene content in the bulk heterolayer is better, but the visible light absorptivity From this point of view, it is better to reduce the fullerene content to suppress the increase in the thickness of the bulk hetero layer. In particular, the fullerene content of the bulk hetero layer adjacent to the electron blocking layer 31 needs to be 70% or more.

From the above examination results, the present inventor has a first fullerene content of 70% or more as the photoelectric conversion element 1 having heat resistance during the manufacturing process and good photoelectric conversion efficiency, sensitivity, and response speed. And a plurality of bulk hetero layers 32 including at least a second bulk hetero layer 32b having a low fullerene content within a range that does not significantly impair carrier transportability and heat resistance. Found the configuration.

That is, in the photoelectric conversion element 1, the photoelectric conversion layer (bulk hetero layer) 32 includes a plurality of bulk hetero layers (32a, 32b) in which fullerene and a p-type organic semiconductor are mixed, and an electron blocking layer. The layers 31 are laminated so that the fullerene content is higher. In FIG. 1, the fullerene content of the first bulk hetero layer 32a is 70% or more, and the fullerene content of the second bulk hetero layer 32b is less than that of the first bulk hetero layer 32a. Yes.

If the difference in the fullerene content between adjacent bulk hetero layers is too large, the carrier transport speed between the layers is lowered, and the response speed of the photoelectric conversion element is lowered. The present inventor examined changes in the afterimage ratio when the difference in fullerene content between adjacent bulk hetero layers was changed in a photoelectric conversion element having a two-layer structure bulk hetero layer (described later). See Examples and Comparative Examples). The ratio of afterimages decreases as the response speed increases.

As shown in FIGS. 3 and 4, if the difference Δ between the fullerene contents of adjacent bulk hetero layers is 15% or less, the afterimage is almost constant at 0.05% or less, and the decrease in response speed is observed. Although it is not possible, the response speed is suddenly reduced at over 15%. As a result, the difference in the fullerene content of adjacent bulk hetero layers (for example, the first bulk hetero layer 32a and the second bulk hetero layer 32b) is 15% by volume or less, thereby maintaining a high response speed. However, it has been found that the visible light absorption rate can be increased.

In FIG. 1, the photoelectric conversion layer 32 is shown with respect to an embodiment composed of two bulk hetero layers. Even in the case of three or more layers, adjacent bulk hetero layers each have a fullerene content of 15% or less. The layers are laminated so that the content decreases as the distance from the electron blocking layer 31 increases. Example 10 is an example of an embodiment having a bulk hetero layer having a three-layer structure, and the difference in the content of fullerene between adjacent layers is 10% by volume. In Example 10, the same effect as that of the two-layer structure is confirmed.

Regardless of the number of layers in the bulk hetero layer, from the viewpoint of heat resistance, the fullerene content of the bulk hetero layer 32b in the layer having the lowest mixing ratio of fullerene is preferably 50% by volume or more. If the heat resistance is not sufficient, the photoelectric conversion layer deteriorates during the manufacturing process of device fabrication, and the possibility of causing deterioration of the characteristics increases.

Also, the bulk hetero layer 32a adjacent to the electron blocking layer 31 has a relatively low content of the p-type organic semiconductor, and therefore has a low light absorption rate. In order for the photoelectric conversion layer 32 to obtain sufficient light absorption with the smallest possible film thickness, it is preferable to make the bulk hetero layer 32a as thin as possible. The thickness of the bulk hetero layer 32a adjacent to the electron blocking layer 31 is preferably 50 nm or less. In order for the bulk hetero layer 32a to sufficiently exhibit the effect of improving the hole transport rate at the interface, the thickness of the bulk hetero layer 32a is preferably 5 nm or more.

The fullerene in the photoelectric conversion layer (bulk hetero layer) 32 is not particularly limited, and fullerene C ₆₀ , fullerene C ₇₀ , fullerene C ₇₆ , fullerene C ₇₈ , fullerene C ₈₀ , fullerene C ₈₂ , fullerene C ₈₄ , fullerene C ₉₀ , Examples include fullerene C ₉₆ , fullerene C ₂₄₀ , fullerene ₅₄₀ , mixed fullerene, and fullerene nanotubes. A typical fullerene skeleton is shown below.

The fullerene derivative means a compound having a substituent added thereto. The substituent for the fullerene derivative is preferably an alkyl group, an aryl group, or a heterocyclic group. The alkyl group is more preferably an alkyl group having 1 to 12 carbon atoms, and the aryl group and the heterocyclic group are preferably a benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, fluorene ring, triphenylene ring, naphthacene ring. , Biphenyl ring, pyrrole ring, furan ring, thiophene ring, imidazole ring, oxazole ring, thiazole ring, pyridine ring, pyrazine ring, pyrimidine ring, pyridazine ring, indolizine ring, indole ring, benzofuran ring, benzothiophene ring, isobenzofuran Ring, benzimidazole ring, imidazopyridine ring, quinolidine ring, quinoline ring, phthalazine ring, naphthyridine ring, quinoxaline ring, quinoxazoline ring, isoquinoline ring, carbazole ring, phenanthridine ring, acridine ring, phenanthroline , Thianthrene ring, chromene ring, xanthene ring, phenoxathiin ring, phenothiazine ring, or phenazine ring, more preferably a benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, pyridine ring, imidazole ring, oxazole ring, or A thiazole ring, particularly preferably a benzene ring, a naphthalene ring, or a pyridine ring. These may further have a substituent, and the substituents may be bonded as much as possible to form a ring. In addition, you may have a some substituent and they may be the same or different. A plurality of substituents may be combined as much as possible to form a ring.

In the bulk hetero layer 32, the organic p-type semiconductor mixed with fullerene is not particularly limited, but the peak wavelength of the absorption spectrum is preferably 450 nm or more and 700 nm or less from the viewpoint of broadly absorbing light in the visible region. The thickness is more preferably 700 nm or less and even more preferably 510 nm or more and 680 nm or less. From the viewpoint of efficiently using light, the higher the molar extinction coefficient, the better. Absorption spectrum (chloroform solution), in the visible region of the wavelength 400nm to 700 nm, the molar absorption coefficient preferably ²⁰⁰⁰⁰ -1 ^{cm -1} or more, more preferably ^{30000 m} -1 ^{cm -1} or more, ^40000M ^{-1 cm} -1 or more Is more preferable.

A p-type organic semiconductor is a donor-type organic semiconductor (compound), which is mainly represented by a hole-transporting organic compound and has a property of easily donating electrons. More specifically, two organic materials are brought into contact with each other. Is an organic compound having a smaller ionization potential when used. Therefore, any organic compound can be used as the donor organic compound as long as it is an electron-donating organic compound.

Examples of p-type organic semiconductors include triarylamine compounds, pyran compounds, quinacridone compounds, benzidine compounds, pyrazoline compounds, styrylamine compounds, hydrazone compounds, triphenylmethane compounds, carbazole compounds, polysilane compounds, thiophene compounds, phthalocyanine compounds, Cyanine compounds, merocyanine compounds, oxonol compounds, polyamine compounds, indole compounds, pyrrole compounds, pyrazole compounds, polyarylene compounds, condensed aromatic carbocyclic compounds (naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives, Fluoranthene derivatives), metal complexes having nitrogen-containing heterocyclic compounds as ligands, and triarylamines can be used. Compounds, pyran compounds, quinacridone compounds, pyrrole compounds, phthalocyanine compounds, merocyanine compounds, fused aromatic carbocyclic compound.

Examples of suitable materials for the p-type organic semiconductor include compounds represented by the following general formula (1).

(In General Formula (1), Z ₁ represents an atomic group necessary for forming a 5- or 6-membered ring. L ₁ , L ₂ , and L ₃ are each independently an unsubstituted methine group or a substituted methine. D ₁ represents an atomic group, and n represents an integer of 0 or more.
In the general formula (1), Z ₁ represents a ring containing at least two carbon atoms and represents a 5-membered ring, a 6-membered ring, or a condensed ring containing at least one of a 5-membered ring and a 6-membered ring. . As a condensed ring containing at least one of a 5-membered ring, a 6-membered ring, and a 5-membered ring and a 6-membered ring, those usually used as an acidic nucleus in a merocyanine dye are preferable. Specific examples thereof include the following: Is mentioned.

(A) 1,3-dicarbonyl nucleus: for example, 1,3-indandione nucleus, 1,3-cyclohexanedione, 5,5-dimethyl-1,3-cyclohexanedione, 1,3-dioxane-4,6- Zeon etc.
(B) pyrazolinone nucleus: for example 1-phenyl-2-pyrazolin-5-one, 3-methyl-1-phenyl-2-pyrazolin-5-one, 1- (2-benzothiazoyl) -3-methyl-2 -Pyrazolin-5-one and the like.
(C) isoxazolinone nucleus: for example, 3-phenyl-2-isoxazolin-5-one, 3-methyl-2-isoxazolin-5-one and the like.
(D) Oxindole nucleus: For example, 1-alkyl-2,3-dihydro-2-oxindole and the like.
(E) 2,4,6-triketohexahydropyrimidine nucleus: for example, barbituric acid or 2-thiobarbituric acid and its derivatives. Examples of the derivatives include 1-alkyl compounds such as 1-methyl and 1-ethyl, 1,3-dialkyl compounds such as 1,3-dimethyl, 1,3-diethyl and 1,3-dibutyl, 1,3-diphenyl, 1,3-diaryl compounds such as 1,3-di (p-chlorophenyl) and 1,3-di (p-ethoxycarbonylphenyl), 1-alkyl-1-aryl compounds such as 1-ethyl-3-phenyl, Examples include 1,3-di (2-pyridyl) 1,3-diheterocyclic substituents and the like.
(F) 2-thio-2,4-thiazolidinedione nucleus: for example, rhodanine and its derivatives. Examples of the derivatives include 3-alkylrhodanine such as 3-methylrhodanine, 3-ethylrhodanine and 3-allylrhodanine, 3-arylrhodanine such as 3-phenylrhodanine, and 3- (2-pyridyl) rhodanine. And the like.

(G) 2-thio-2,4-oxazolidinedione (2-thio-2,4- (3H, 5H) -oxazoledione nucleus: for example, 3-ethyl-2-thio-2,4-oxazolidinedione and the like.
(H) Tianaphthenone nucleus: For example, 3 (2H) -thianaphthenone-1,1-dioxide and the like.
(I) 2-thio-2,5-thiazolidinedione nucleus: for example, 3-ethyl-2-thio-2,5-thiazolidinedione and the like.
(J) 2,4-thiazolidinedione nucleus: for example, 2,4-thiazolidinedione, 3-ethyl-2,4-thiazolidinedione, 3-phenyl-2,4-thiazolidinedione and the like.
(K) Thiazolin-4-one nucleus: for example, 4-thiazolinone, 2-ethyl-4-thiazolinone, etc.
(L) 2,4-imidazolidinedione (hydantoin) nucleus: for example, 2,4-imidazolidinedione, 3-ethyl-2,4-imidazolidinedione, etc.
(M) 2-thio-2,4-imidazolidinedione (2-thiohydantoin) nucleus: for example, 2-thio-2,4-imidazolidinedione, 3-ethyl-2-thio-2,4-imidazolidinedione etc.
(N) Imidazolin-5-one nucleus: for example, 2-propylmercapto-2-imidazolin-5-one and the like.
(O) 3,5-pyrazolidinedione nucleus: for example, 1,2-diphenyl-3,5-pyrazolidinedione, 1,2-dimethyl-3,5-pyrazolidinedione and the like.
(P) Benzothiophen-3-one nucleus: for example, benzothiophen-3-one, oxobenzothiophen-3-one, dioxobenzothiophen-3-one and the like.
(Q) Indanone nucleus: for example, 1-indanone, 3-phenyl-1-indanone, 3-methyl-1-indanone, 3,3-diphenyl-1-indanone, 3,3-dimethyl-1-indanone, etc.

The ring represented by Z ₁ is preferably a 1,3-dicarbonyl nucleus, a pyrazolinone nucleus, a 2,4,6-triketohexahydropyrimidine nucleus (including a thioketone body, for example, a barbituric acid nucleus, a 2-thiobarbiti nucleus, Tool acid nucleus), 2-thio-2,4-thiazolidinedione nucleus, 2-thio-2,4-oxazolidinedione nucleus, 2-thio-2,5-thiazolidinedione nucleus, 2,4-thiazolidinedione nucleus, 2 , 4-imidazolidinedione nucleus, 2-thio-2,4-imidazolidinedione nucleus, 2-imidazolin-5-one nucleus, 3,5-pyrazolidinedione nucleus, benzothiophen-3-one nucleus, indanone nucleus And more preferably a 1,3-dicarbonyl nucleus, a 2,4,6-triketohexahydropyrimidine nucleus (including thioketones, such as a barbituric acid nucleus, Rubituric acid nucleus), 3,5-pyrazolidinedione nucleus, benzothiophen-3-one nucleus, indanone nucleus, more preferably 1,3-dicarbonyl nucleus, 2,4,6-triketohexahydropyrimidine Nuclei (including thioketone bodies, such as barbituric acid nuclei, 2-thiobarbituric acid nuclei), particularly preferably 1,3-indandione nuclei, barbituric acid nuclei, 2-thiobarbituric acid nuclei and their Is a derivative.

In the general formula (1), L ₁ , L ₂ , and L ₃ each independently represent an unsubstituted methine group or a substituted methine group. The substituted methine groups may be bonded to form a ring. A 6-membered ring (for example, benzene ring etc.) is mentioned as a ring. Examples of the substituent of the substituted methine group include the substituent W described later, and it is preferable that all of L ₁ , L ₂ and L ₃ are unsubstituted methine groups.

In the general formula (1), n represents an integer of 0 or more, preferably an integer of 0 or more and 3 or less, more preferably 0. When n is increased, the absorption wavelength region can be made longer, but the decomposition temperature due to heat is lowered. N = 0 is preferable in that it has appropriate absorption in the visible region and suppresses thermal decomposition during vapor deposition.

In the general formula (1), D ₁ represents an atomic group. D ₁ is preferably a group containing —NR ^a (R ^b ), and D ₁ is preferably an aryl group substituted with —NR ^a (R ^b ) (preferably having a substituent). Preferred is a phenyl group or a naphthyl group. R ^a and R ^b each independently represent a hydrogen atom or a substituent, and examples of the substituent include a substituent W described later, and preferably an aliphatic hydrocarbon group (preferably having a substituent). An alkyl group or an alkenyl group), an aryl group, or a heterocyclic group.

The arylene group represented by D ₁ is preferably an arylene group having 6 to 30 carbon atoms, and more preferably an arylene group having 6 to 18 carbon atoms. The arylene group may have a substituent W described later, and is preferably an arylene group having 6 to 18 carbon atoms which may have an alkyl group having 1 to 4 carbon atoms. Examples include a phenylene group, a naphthylene group, an anthracenylene group, a pyrenylene group, a phenanthrenylene group, a methylphenylene group, and a dimethylphenylene group, and a phenylene group or a naphthylene group is preferable.

Examples of the substituent represented by Ra and Rb include a substituent W described later, and preferably an aliphatic hydrocarbon group (preferably an alkyl group or alkenyl group which may be substituted) or an aryl group (preferably substituted). A good phenyl group), or a heterocyclic group.

The aryl groups represented by Ra and Rb are each independently preferably an aryl group having 6 to 30 carbon atoms, and more preferably an aryl group having 6 to 18 carbon atoms. The aryl group may have a substituent, preferably an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 18 carbon atoms which may have an aryl group having 6 to 18 carbon atoms. is there. Examples include a phenyl group, a naphthyl group, an anthracenyl group, a pyrenyl group, a phenanthrenyl group, a methylphenyl group, a dimethylphenyl group, and a biphenyl group, and a phenyl group or a naphthyl group is preferable.

The heterocyclic groups represented by Ra and Rb are each independently preferably a heterocyclic group having 3 to 30 carbon atoms, more preferably a heterocyclic group having 3 to 18 carbon atoms. The heterocyclic group may have a substituent, and preferably has an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 18 carbon atoms. It is a group. The heterocyclic group represented by Ra and Rb is preferably a condensed ring structure, such as a furan ring, a thiophene ring, a selenophene ring, a silole ring, a pyridine ring, a pyrazine ring, a pyrimidine ring, an oxazole ring, a thiazole ring, a triazole ring, A condensed ring structure of a combination of rings selected from an oxadiazole ring and a thiadiazole ring (which may be the same) is preferable, and a quinoline ring, an isoquinoline ring, a benzothiophene ring, a dibenzothiophene ring, a thienothiophene ring, a bithienobenzene ring, A thienothiophene ring is preferred.

The arylene group and aryl group represented by D ₁ , Ra and Rb are preferably a benzene ring or a condensed ring structure, more preferably a condensed ring structure containing a benzene ring, a naphthalene ring, an anthracene ring, a pyrene ring, A phenanthrene ring can be mentioned, a benzene ring, a naphthalene ring or an anthracene ring is more preferable, and a benzene ring or a naphthalene ring is still more preferable.

As the substituent W, a halogen atom, an alkyl group (including a cycloalkyl group, a bicycloalkyl group, and a tricycloalkyl group), an alkenyl group (including a cycloalkenyl group and a bicycloalkenyl group), an alkynyl group, an aryl group, and a heterocyclic group (May be referred to as a heterocyclic group), cyano group, hydroxy group, nitro group, carboxy group, alkoxy group, aryloxy group, silyloxy group, heterocyclic oxy group, acyloxy group, carbamoyloxy group, alkoxycarbonyl group, aryl Oxycarbonyl group, amino group (including anilino group), ammonio group, acylamino group, aminocarbonylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfamoylamino group, alkyl and arylsulfonylamino group, mercapto Alkylthio group, arylthio group, heterocyclic thio group, sulfamoyl group, sulfo group, alkyl and arylsulfinyl group, alkyl and arylsulfonyl group, acyl group, aryloxycarbonyl group, alkoxycarbonyl group, carbamoyl group, aryl and heterocyclic azo Group, imide group, phosphino group, phosphinyl group, phosphinyloxy group, phosphinylamino group, phosphono group, silyl group, hydrazino group, ureido group, boronic acid group (-B (OH) ₂ ), phosphato group ( Examples include —OPO (OPO (OH) ₂ ), sulfato group (—OSO ₃ H), and other known substituents.

When Ra and Rb represent a substituent (preferably an alkyl group or an alkenyl group), the substituent is a hydrogen atom of an aromatic ring (preferably benzene ring) skeleton of an aryl group substituted by —NRa (Rb), or It may combine with a substituent to form a ring (preferably a 6-membered ring).

Ra and Rb may be bonded to each other to form a ring (preferably a 5- or 6-membered ring, more preferably a 6-membered ring), and Ra and Rb are each L (L ₁ , A ring (preferably a 5- or 6-membered ring, more preferably a 6-membered ring) may be formed by combining with a substituent in L ₂ or L ₃ .

The compound represented by the general formula (1) is a compound described in JP 2000-297068 A, and a compound not described in the above publication can also be produced according to the synthesis method described in the above publication. .

The compound represented by the general formula (1) is preferably a compound represented by the following general formula (2).

(In the formula, Z ₂ , L ₂₁ , L ₂₂ , L ₂₃ , and n are synonymous with Z ₁ , L ₁ , L ₂ , L ₃ , and n in the general formula (1), and preferred examples thereof are also the same. D ₂₁ represents a substituted or unsubstituted arylene group, and D ₂₂ and D ₂₃ each independently represents a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group.
The arylene group represented by D ₂₁ has the same meaning as the arylene ring group represented by D ₁ , and preferred examples thereof are also the same.

The aryl group represented by D ₂₂ and D ₂₃ is independently the same as the heterocyclic group represented by Ra and Rb, and preferred examples thereof are also the same.

Although the preferable specific example of a compound represented by General formula (1) below is shown using General formula (3), this invention is not limited to these.

(In the formula (3), Z ₃ represents any one of the following A-1 to A-12: L ₃₁ represents methylene and n represents 0. D ₃₁ represents any one of B-1 to B-9. D ₃₂ and D ₃₃ represent any one of C-1 to C-16.)
Z ₃ is preferably A-2, D ₃₂ and D ₃₃ are preferably selected from C-1, C-2, C-15 and C-16, and D ₃₁ is B-1 or B- 9 is preferred.

Particularly preferred p-type organic materials include dyes or materials not having 5 or more condensed ring structures (materials having 0 to 4, preferably 1 to 3 condensed ring structures). When using a pigment-based p-type material generally used in organic thin-film solar cells, the dark current tends to increase at the pn interface, and the light response is slow due to trapping at the crystalline grain boundary. Since it tends to be, it is difficult to use for an image sensor. For this reason, a dye-based p-type material that is difficult to crystallize, or a material that does not have five or more condensed ring structures can be preferably used for the imaging element.

More preferred specific examples of the compound represented by the general formula (1) are combinations of the following substituents, linking groups and partial structures in the general formula (3), but the present invention is not limited thereto. .

Here, A-1 to A-12, B-1 to B-9, and C-1 to C-16 are synonymous with those already shown.

Although the especially preferable specific example of the compound represented by General formula (1) below is shown, this invention is not limited to these.

The photoelectric conversion layer 32 is a non-light-emitting layer, unlike an organic EL light-emitting layer (a layer that converts an electrical signal into light). The non-light-emitting layer means a layer having an emission quantum efficiency of 1% or less, preferably 0.5% or less, more preferably 0.1% or less in the visible light region (wavelength 400 nm to 730 nm). In the photoelectric conversion layer 32, if the emission quantum efficiency exceeds 1%, it is not preferable because it affects sensing performance or imaging performance when applied to a sensor or an imaging device.

As described above, the photoelectric conversion element 1 has the electron blocking layer 31 provided between the photoelectric conversion layer 32 and the hole collecting electrode 20, and the photoelectric conversion layer 32 is composed of fullerene and p-type organic semiconductor. And a plurality of bulk hetero layers 32 are laminated such that the fullerene content is higher in the electron blocking layer 31 side, The fullerene content of the first bulk hetero layer 32a adjacent to the blocking layer 31 is 70% by volume or more, and the difference in fullerene content between adjacent bulk hetero layers is 15% by volume or less. . The photoelectric conversion element having such a configuration has heat resistance during the manufacturing process, and has good photoelectric conversion efficiency and response speed.

Below, configurations other than the photoelectric conversion layer 32 in the photoelectric conversion element 1 will be described.
<Substrate and electrode>
There is no restriction | limiting in particular as the board | substrate 10, A silicon substrate, a glass substrate, etc. can be used.

The hole collection electrode 20 is an electrode for collecting holes out of the charges generated in the photoelectric conversion layer 32, and corresponds to a pixel electrode in the configuration of the imaging device described later. The hole collecting electrode 20 is not particularly limited as long as it has good conductivity. However, depending on the application, a material that does not have transparency but reflects light can be used. There are cases.

Specific examples include metals, metal oxides, metal nitrides, metal borides, organic conductive compounds, and mixtures thereof. More specifically, tin oxide doped with antimony or fluorine (ATO, FTO), tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO) and other conductive metal oxides, gold, silver, chromium, nickel, titanium, tungsten, aluminum and other metals Conductive compounds such as oxides and nitrides of these metals (titanium nitride (TiN) is given as an example), a mixture or laminate of these metals and conductive metal oxides, copper iodide, copper sulfide, etc. And inorganic conductive materials, organic conductive materials such as polyaniline, polythiophene, and polypyrrole, and laminates of these with ITO or titanium nitride. Particularly preferred as the hole collecting electrode 20 is any material of titanium nitride, molybdenum nitride, tantalum nitride, and tungsten nitride.

The electron collection electrode 40 is an electrode that collects electrons out of the charges generated in the photoelectric conversion layer 32, and is a transparent electrode disposed on the light receiving side in the present embodiment. The electron collecting electrode 40 is not particularly limited as long as it is a conductive material that is sufficiently transparent to light having a wavelength with which the photoelectric conversion layer 32 has sensitivity in order to make light incident on the photoelectric conversion layer 32. In order to increase the absolute amount of light incident on the photoelectric conversion layer 32 and increase the external quantum efficiency, it is preferable to use a transparent conductive oxide (TCO). The electron collection electrode 40 corresponds to a pixel electrode in the configuration of the imaging device described later.

Specifically, as the electron collection electrode 40, ITO, IZO, SnO ₂ , ATO (antimony-doped tin oxide), ZnO, AZO (Al-doped zinc oxide), GZO (gallium-doped zinc oxide), TiO ₂ , FTO Any material of (fluorine-doped tin oxide) is mentioned.

The light transmittance of the electron collection electrode 40 is preferably 60% or more, more preferably 80% or more, more preferably 90% or more, and more preferably 95% or more in the visible light wavelength.

The method for forming the electrodes (20, 40) is not particularly limited, and can be appropriately selected in consideration of appropriateness with the electrode material. Specifically, it can be formed by a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method, or an ion plating method, or a chemical method such as CVD or plasma CVD method.

When the electrode material is ITO, it can be formed by a method such as an electron beam method, a sputtering method, a resistance heating vapor deposition method, a chemical reaction method (sol-gel method or the like), or a dispersion of indium tin oxide. Furthermore, UV-ozone treatment, plasma treatment, or the like can be performed on a film formed using ITO. When the electrode material is TiN, various methods including a reactive sputtering method are used, and further, annealing treatment, UV-ozone treatment, plasma treatment, and the like can be performed.

When a transparent conductive film such as TCO is used as the electron collecting electrode 40, a DC short circuit or an increase in leakage current may occur. One reason for this is thought to be that fine cracks introduced into the photoelectric conversion layer 32 are covered with a dense film such as TCO, and conduction between the lower electrode 20 on the opposite side is increased. Therefore, in the case of an electrode having a relatively poor film quality such as Al, an increase in leakage current is unlikely to occur. By controlling the film thickness of the electron collection electrode 40 with respect to the film thickness of the photoelectric conversion layer 32 (that is, the depth of cracks), an increase in leakage current can be largely suppressed. The thickness of the electron collection electrode 40 is desirably 1/5 or less, preferably 1/10 or less of the thickness of the photoelectric conversion layer 32.

Usually, when the conductive film is made thinner than a certain range, the resistance value is rapidly increased. However, in the solid-state imaging device incorporating the photoelectric conversion device according to this embodiment, the sheet resistance is preferably 100 to 10,000 Ω / □. Well, the degree of freedom in the range of film thickness that can be made thin is great. Further, the thinner the upper electrode 40 is, the less light is absorbed, and the light transmittance is generally increased. The increase in light transmittance is very preferable because it increases the light absorption in the photoelectric conversion layer 32 and increases the photoelectric conversion ability. In consideration of the suppression of leakage current, the increase in the resistance value of the thin film, and the increase in transmittance associated with the thinning, the thickness of the electron collection electrode 40 is preferably 5 to 100 nm, and preferably 5 to 20 nm. Is more preferable.

<Light receiving layer>
The light receiving layer 30 is a layer including at least the electron blocking layer 31 and the already described photoelectric conversion layer 32.

The film formation method of the light receiving layer 30 is not particularly limited, and can be formed by each dry film formation method or wet film formation method. However, it is preferable that all the steps at the time of film formation are performed in a vacuum. Specifically, it is preferable that the compound does not come into direct contact with oxygen or moisture in the outside air. An example of such a film forming method is a vacuum deposition method. In the vacuum deposition method, it is preferable to perform PI or PID control of the deposition rate using a film thickness monitor such as a crystal resonator or an interferometer. In the case where two or more kinds of compounds are vapor-deposited at the same time, a co-evaporation method can be used, and the co-evaporation method is preferably performed using resistance heating vapor deposition, electron beam vapor deposition, flash vapor deposition, or the like.

In the case where the light receiving layer 30 is formed by a dry film forming method, the degree of vacuum at the time of formation is preferably 1 × 10 ⁻³ Pa or less in consideration of preventing deterioration of element characteristics at the time of forming the light receiving layer. ⁻⁴ Pa or less is more preferable, and 1 × 10 ⁻⁴ Pa or less is particularly preferable.

The thickness of the light receiving layer 30 is preferably 10 nm or more and 1000 nm or less, more preferably 50 nm or more and 800 nm or less, and particularly preferably 100 nm or more and 600 nm or less. By setting it to 10 nm or more, a suitable dark current suppressing effect is obtained, and by setting it to 1000 nm or less, suitable photoelectric conversion efficiency (sensitivity) is obtained.

<< Electron blocking layer >>
The electron blocking layer 31 is a layer for suppressing injection of electrons from the hole collection electrode 20 into the photoelectric conversion layer 32. It may be composed of a single organic material film, or may be composed of a mixed film of a plurality of different organic materials or inorganic materials.

The electron blocking layer 31 may be composed of a plurality of layers. By doing in this way, an interface is formed between each layer which comprises the electron blocking layer 31, and a discontinuity arises in the intermediate level which exists in each layer. As a result, it becomes difficult for the charge to move through the intermediate level and the like, so that the electron blocking effect can be enhanced. However, if the layers constituting the electron blocking layer 31 are made of the same material, the intermediate levels existing in the layers may be exactly the same. Therefore, in order to further enhance the electron blocking effect, the materials constituting the layers are different. It is preferable to make it.

The electron blocking layer 31 is preferably made of a material having a high electron injection barrier from the hole collecting electrode 20 and a high hole transporting property. As the electron injection barrier, the electron affinity of the electron blocking layer is preferably 1 eV or less, more preferably 1.3 eV or more, and particularly preferably 1.5 eV or more than the work function of the adjacent electrode.

The electron blocking layer 31 sufficiently suppresses the contact between the hole collecting electrode 20 and the photoelectric conversion layer 32, and also avoids the influence of defects and dust existing on the surface of the hole collecting electrode 20 at 20 nm or more. It is preferable that it is 40 nm or more.

An electron donating organic material can be used for the electron blocking layer 31. Specifically, for low molecular weight materials, N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine (TPD) or 4,4′-bis [N Aromatic diamine compounds such as-(naphthyl) -N-phenyl-amino] biphenyl (α-NPD), oxazole, oxadiazole, triazole, imidazole, imidazolone, stilbene derivative, pyrazoline derivative, tetrahydroimidazole, polyarylalkane, butadiene 4,4 ′, 4 ″ -tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (m-MTDATA), porphine, tetraphenylporphine copper, phthalocyanine, copper phthalocyanine, titanium phthalocyanine oxide, etc. Polyphyrin compounds, triazole derivatives, oxa Zazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, fluorene derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, silazane derivatives, etc. As the polymer material, polymers such as phenylene vinylene, fluorene, carbazole, indole, pyrene, pyrrole, picoline, thiophene, acetylene, diacetylene, and derivatives thereof can be used. Even if it is a compound having a sufficient hole transporting property, it is possible to use it, for example, a compound described in JP-A-2008-72090, for example. Can be used.

An example of a compound suitable as the electron blocking layer 31 is shown below.

An inorganic material can also be used as the electron blocking layer 31. In general, since an inorganic material has a dielectric constant larger than that of an organic material, a large voltage is applied to the photoelectric conversion layer 32 when the electron blocking layer 31 is used, and the photoelectric conversion efficiency (sensitivity) is increased. Can do. Materials that can be the electron blocking layer 31 include calcium oxide, chromium oxide, chromium oxide copper, manganese oxide, cobalt oxide, nickel oxide, copper oxide, gallium copper oxide, strontium copper oxide, niobium oxide, molybdenum oxide, indium copper oxide, Examples include indium silver oxide and iridium oxide.

When the electron blocking layer 31 is a single layer, the layer can be a layer made of an inorganic material, or in the case of a plurality of layers, one or more layers can be a layer made of an inorganic material. it can.
<< Photoelectric conversion layer >>
Since the photoelectric conversion layer 32 composed of a plurality of bulk hetero layers is as already described, the description thereof is omitted here.
<< Hole blocking layer >>
In the photoelectric conversion element 1, the hole blocking layer 33 is a layer that suppresses injection of holes from the electron collection electrode 40 when an external voltage is applied, and is a layer formed on the layer (in this embodiment, the electron collection electrode 40). When the film is formed, it has a function of protecting the photoelectric conversion layer 32 and suppressing film formation damage.

An electron-accepting organic material can be used for the hole blocking layer. Although the electron-accepting material is not particularly limited, oxadiazole derivatives such as 1,3-bis (4-tert-butylphenyl-1,3,4-oxadiazolyl) phenylene (OXD-7), anthraquinodimethane derivatives, Diphenylquinone derivatives, bathocuproine, bathophenanthroline, and derivatives thereof, triazole compounds, tris (8-hydroxyquinolinato) aluminum complexes, bis (4-methyl-8-quinolinato) aluminum complexes, distyrylarylene derivatives, silole compounds, etc. Can be used. Moreover, even if it is not an electron-accepting organic material, it can be used if it is a material which has sufficient electron transport property. A porphyrin compound or a styryl compound such as DCM (4-dicyanomethylene-2-methyl-6- (4- (dimethylaminostyryl))-4H pyran) or a 4H pyran compound can be used.

If the charge blocking layer composed of the hole blocking layer 33 and the electron blocking layer 31 is too thick, the supply voltage necessary for applying an appropriate electric field strength to the photoelectric conversion layer is increased, The carrier transport process in the charge blocking layer may cause a problem that adversely affects the performance of the photoelectric conversion element. Accordingly, the total film thickness of the hole blocking layer 33 and the electron blocking layer 31 is preferably designed to be 300 nm or less. The total film thickness is more preferably 200 nm or less, and still more preferably 100 nm or less.

<Sealing layer>
The sealing layer 50 prevents entry of factors that degrade the photoelectric conversion material such as water molecules and oxygen molecules after the photoelectric conversion element 1 or the imaging element 100 described later, and can be stored and used for a long period of time. It is a layer for preventing deterioration of the photoelectric conversion layer. In addition, the sealing layer 50 protects the photoelectric conversion layer by preventing intrusion of factors that degrade the photoelectric conversion layer included in the solution, plasma, and the like in the manufacturing process of the imaging element 100 after the sealing layer is formed. It is also a layer.

The sealing layer 50 is formed to cover the hole collection electrode 20, the electron blocking layer 31, the photoelectric conversion layer 32, the hole blocking layer 33, and the electron collection electrode 40.

In the photoelectric conversion element 1, since incident light reaches the photoelectric conversion layer 32 through the sealing layer 50, the photoelectric conversion layer 32 is sensitive to the sealing layer 50 in order to allow light to efficiently enter the photoelectric conversion layer 32. It is necessary to be sufficiently transparent to light having a wavelength. Examples of the sealing layer 50 include ceramics such as dense metal oxide, metal nitride, and metal nitride oxide that do not allow water molecules to permeate, diamond-like carbon (DLC), and the like. Conventionally, aluminum oxide, silicon oxide, Silicon nitride, silicon nitride oxide, a laminated film thereof, a laminated film of them and an organic polymer, or the like is used.

The sealing layer 50 can be composed of a thin film made of a single material, but by providing a separate function for each layer in a multi-layer structure, the stress relaxation of the entire sealing layer 50 and dust generation during the manufacturing process Such effects as the suppression of defects such as cracks and pinholes caused by the above, and the optimization of material development can be expected. For example, the sealing layer 50 is formed by laminating a “sealing auxiliary layer” having a function that is difficult to achieve on the layer that serves the original purpose of preventing the penetration of deterioration factors such as water molecules. A two-layer structure can be formed. Although it is possible to have three or more layers, it is preferable that the number of layers is as small as possible in consideration of manufacturing costs.

The formation method of the sealing layer 50 is not particularly limited, and is preferably formed by a method that does not deteriorate the performance and film quality of the already formed photoelectric conversion layer 32 and the like as much as possible.

The performance of organic photoelectric conversion materials is significantly deteriorated due to the presence of deterioration factors such as water molecules and oxygen molecules. Therefore, it is necessary to cover and seal the entire photoelectric conversion layer with a dense metal oxide, metal nitride oxide or the like that does not permeate deterioration factors. Conventionally, aluminum oxide, silicon oxide, silicon nitride, silicon nitride oxide, a laminated structure thereof, a laminated structure of them and an organic polymer, or the like is used as a sealing layer by various vacuum film forming techniques.

However, the conventional sealing layer is difficult to grow a thin film at a step due to a structure on the substrate surface, minute defects on the substrate surface, particles adhering to the substrate surface, etc. As a result, the film thickness is significantly reduced. For this reason, the step portion becomes a path through which the deterioration factor penetrates. In order to completely cover the step with the sealing layer, it is necessary to form the film so as to have a film thickness of 1 μm or more in the flat portion, and to increase the thickness of the entire sealing layer. The degree of vacuum when forming the sealing layer is preferably 1 × 10 ³ Pa or less, and more preferably 5 × 10 ² Pa or less.

In the case of an imaging device having a pixel size of less than 2 μm, particularly about 1 μm, if the sealing layer 50 is thick, the distance between the color filter and the photoelectric conversion layer increases, and incident light is diffracted / Diversity and color mixing may occur. Therefore, when considering application to an image sensor having a pixel size of about 1 μm, a sealing layer material / manufacturing method is required that does not deteriorate the device performance even if the thickness of the sealing layer 50 is reduced.

The atomic layer deposition (ALD) method is a kind of CVD method, and adsorption / reaction of organometallic compound molecules, metal halide molecules, and metal hydride molecules, which are thin film materials, onto the substrate surface and unreacted groups contained therein. Is a technique for forming a thin film by alternately repeating decomposition. When the thin film material reaches the substrate surface, it is in the above-mentioned low molecular state, so that the thin film can be grown in a very small space where the low molecule can enter. For this reason, the step portion, which was difficult with the conventional thin film formation method, is completely covered (the thickness of the thin film grown on the step portion is the same as the thickness of the thin film grown on the flat portion), that is, the step coverage is very high. Excellent. For this reason, steps due to structures on the substrate surface, minute defects on the substrate surface, particles adhering to the substrate surface, and the like can be completely covered, and such a step portion does not become an intrusion path for a deterioration factor of the photoelectric conversion material. When the sealing layer 50 is formed by the atomic layer deposition method, the required sealing layer thickness can be effectively reduced as compared with the prior art.

When the sealing layer 50 is formed by the atomic layer deposition method, a material corresponding to the ceramics preferable for the sealing layer 50 described above can be selected as appropriate. However, since the photoelectric conversion layer of the present invention uses an organic photoelectric conversion material, it is limited to a material capable of growing a thin film at a relatively low temperature so that the organic photoelectric conversion material does not deteriorate. According to the atomic layer deposition method using alkyl aluminum or aluminum halide as the material, a dense aluminum oxide thin film can be formed at less than 200 ° C. at which the organic photoelectric conversion material does not deteriorate. In particular, when trimethylaluminum is used, an aluminum oxide thin film can be formed even at about 100 ° C. Silicon oxide and titanium oxide are also preferable because a dense thin film can be formed at less than 200 ° C., similarly to aluminum oxide, by appropriately selecting materials.

The sealing layer preferably has a thickness of 10 nm or more in order to sufficiently prevent the entry of factors that degrade the photoelectric conversion material such as water molecules. In the imaging device, when the sealing layer has a large film thickness, incident light is diffracted or diverged in the sealing layer, and color mixing occurs. The film thickness of the sealing layer is preferably 200 nm or less.

In addition, the thin film formed by the atomic layer deposition method can achieve a high-quality thin film formation at a low temperature that is unmatched in terms of step coverage and denseness. However, the physical properties of the thin film material may be deteriorated by chemicals used in the photolithography process. For example, since an aluminum oxide thin film formed by atomic layer deposition is amorphous, the surface is eroded by an alkaline solution such as a developer or a stripping solution.

In addition, thin films formed by CVD, such as atomic layer deposition, often have tensile stresses with very large internal stress, such as processes that repeat intermittent heating and cooling, such as semiconductor manufacturing processes, Due to storage / use in a high temperature / high humidity atmosphere for a period, deterioration of the thin film itself may occur.

Therefore, when the sealing layer 50 formed by the atomic layer deposition method is used, it is preferable to form a sealing auxiliary layer that has excellent chemical resistance and can cancel the internal stress of the sealing layer 50.

Examples of the auxiliary sealing layer include any of ceramics such as metal oxide, metal nitride, and metal nitride oxide that are excellent in chemical resistance formed by physical vapor deposition (PVD) such as sputtering. Or a layer containing one of them. Ceramics formed by a PVD method such as sputtering often has a large compressive stress, and can cancel the tensile stress of the sealing layer 50 formed by an atomic layer deposition method.

"Image sensor"
Next, the configuration of the image sensor 100 including the photoelectric conversion element 1 will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view showing a schematic configuration of an image sensor for explaining an embodiment of the present invention. This imaging device is used by being mounted on an imaging device such as a digital camera or a digital video camera, an imaging module such as an electronic endoscope or a mobile phone, or the like.

The image pickup device 100 is a circuit board on which a plurality of organic photoelectric conversion elements 1 configured as shown in FIG. 1 and a readout circuit that reads out signals corresponding to charges generated in the photoelectric conversion layer of each organic photoelectric conversion element are formed. And a plurality of organic photoelectric conversion elements are arranged one-dimensionally or two-dimensionally on the same surface above the circuit board.

The image sensor 100 includes a substrate 101, an insulating layer 102, a connection electrode 103, a pixel electrode 104, a connection portion 105, a connection portion 106, a light receiving layer 107, a counter electrode 108, a buffer layer 109, a sealing layer. A stop layer 110, a color filter (CF) 111, a partition wall 112, a light shielding layer 113, a protective layer 114, a counter electrode voltage supply unit 115, and a readout circuit 116 are provided.

The pixel electrode 104 has the same function as the hole collection electrode 20 of the organic photoelectric conversion element 1 shown in FIG. The counter electrode 108 has the same function as the electron collection electrode 40 of the organic photoelectric conversion element 1 shown in FIG. The light receiving layer 107 has the same configuration as the light receiving layer 30 provided between the hole collecting electrode 20 and the electron collecting electrode 40 of the organic photoelectric conversion element 1 shown in FIG. The sealing layer 110 has the same function as the sealing layer 50 of the organic photoelectric conversion element 1 shown in FIG. The pixel electrode 104, a part of the counter electrode 108 facing the pixel electrode 104, the light receiving layer 107 sandwiched between the electrodes, and the buffer layer 109 and the part of the sealing layer 110 facing the pixel electrode 104 are subjected to organic photoelectric conversion. The element is configured.

The substrate 101 is a glass substrate or a semiconductor substrate such as Si. An insulating layer 102 is formed on the substrate 101. A plurality of pixel electrodes 104 and a plurality of connection electrodes 103 are formed on the surface of the insulating layer 102.

The light receiving layer 107 is a layer common to all the organic photoelectric conversion elements provided on the plurality of pixel electrodes 104 so as to cover them.

The counter electrode 108 is one electrode provided on the light receiving layer 107 and common to all the organic photoelectric conversion elements. The counter electrode 108 is formed up to the connection electrode 103 disposed outside the light receiving layer 107 and is electrically connected to the connection electrode 103.

The connection part 106 is embedded in the insulating layer 102 and is a plug or the like for electrically connecting the connection electrode 103 and the counter electrode voltage supply part 115. The counter electrode voltage supply unit 115 is formed on the substrate 101 and applies a predetermined voltage to the counter electrode 108 via the connection unit 106 and the connection electrode 103. When the voltage to be applied to the counter electrode 108 is higher than the power supply voltage of the image sensor, the power supply voltage is boosted by a booster circuit such as a charge pump to supply the predetermined voltage.

The readout circuit 116 is provided on the substrate 101 corresponding to each of the plurality of pixel electrodes 104, and reads out a signal corresponding to the charge collected by the corresponding pixel electrode 104. The reading circuit 116 is configured by, for example, a CCD, a MOS circuit, or a TFT circuit, and is shielded from light by a light shielding layer (not shown) disposed in the insulating layer 102. The readout circuit 116 is electrically connected to the corresponding pixel electrode 104 via the connection unit 105.

The buffer layer 109 is formed on the counter electrode 108 so as to cover the counter electrode 108. The sealing layer 110 is formed on the buffer layer 109 so as to cover the buffer layer 109. The color filter 111 is formed at a position facing each pixel electrode 104 on the sealing layer 110. The partition wall 112 is provided between the color filters 111 and is for improving the light transmission efficiency of the color filter 111.

The light shielding layer 113 is formed in a region other than the region where the color filter 111 and the partition 112 are provided on the sealing layer 110, and prevents light from entering the light receiving layer 107 formed outside the effective pixel region. The protective layer 114 is formed on the color filter 111, the partition 112, and the light shielding layer 113, and protects the entire image sensor 100.

In the imaging device 100 configured as described above, when light is incident, the light is incident on the light receiving layer 107, and charges are generated here. Holes in the generated charges are collected by the pixel electrode 104, and a voltage signal corresponding to the amount is output to the outside of the image sensor 100 by the readout circuit 116.

The manufacturing method of the image sensor 100 is as follows.
On the circuit substrate on which the common electrode voltage supply unit 115 and the readout circuit 116 are formed, the connection units 105 and 106, the plurality of connection electrodes 103, the plurality of pixel electrodes 104, and the insulating layer 102 are formed. The plurality of pixel electrodes 104 are arranged on the surface of the insulating layer 102 in a square lattice pattern, for example.

Next, a light receiving layer 107, a counter electrode 108, a buffer layer 109, and a sealing layer 110 are sequentially formed on the plurality of pixel electrodes 104. The formation method of the light receiving layer 107, the counter electrode 108, and the sealing layer 110 is as described in the description of the photoelectric conversion element 1. The buffer layer 109 is formed by, for example, a vacuum resistance heating vapor deposition method. Next, after forming the color filter 111, the partition 112, and the light shielding layer 113, the protective layer 114 is formed, and the imaging element 100 is completed.

(Example 1)
A glass substrate was prepared as a substrate, and a TiN hole collecting electrode (15 nm thickness) was formed on the substrate by a sputtering method, and then an electron blocking layer (the compound 10) was formed by a vacuum deposition method ( 50 nm thickness).

Next, as a first bulk hetero layer (photoelectric conversion layer), a mixed layer of the compound 1 and C ₆₀ was formed by co-evaporation (20 nm thickness, C ₆₀ content 75% by volume), and then on that As the second bulk hetero layer (photoelectric conversion layer), a mixed layer of compound 1 and C ₆₀ (thickness: 380 nm, content of C ₆₀ : 65% by volume) was similarly formed by co-evaporation. Both the electron blocking layer and the bulk hetero layer were deposited using a vacuum deposition apparatus at a vacuum degree of 5.0 × 10 ⁻⁴ Pa or less and a deposition rate of 3 Å / s.

Furthermore, ITO (indium tin oxide) is formed as a electron collecting electrode with a film thickness of 10 nm on a photoelectric conversion layer composed of a plurality of bulk hetero layers by a DC sputtering method, and further, a hole collecting electrode, an electron As a sealing layer covering the blocking layer, the photoelectric conversion layer, and the electron collection electrode, an aluminum oxide layer having a thickness of 100 nm was formed by an atomic layer deposition method to obtain the photoelectric conversion element of the present invention.

Photoelectric conversion efficiency and light response speed in a state where a positive bias of 10 V was applied to the electron collection electrode of the produced photoelectric conversion element were measured. The photoelectric conversion efficiency was calculated by detecting the photocurrent when a monochromatic light having a wavelength of 550 nm and 50 μW / cm ² was incident from the sealing layer side with a source meter. The optical response speed was evaluated based on the ratio of the afterimage current after 100 μs from the time when the light with the central wavelength of 525 nm was incident on the device and the incident light was turned off (current value after 100 μs / current value when light was incident). ).

(Examples 2 to 5, Comparative Examples 1 to 9)
A photoelectric conversion element of each example was produced in the same manner as in Example 1 except that the fullerene (C ₆₀ ) content of the bulk hetero layer or the film thickness of the first bulk hetero layer was changed. The photoelectric conversion efficiency and the light response speed were evaluated in the same manner. The evaluation results are shown in Table 1 together with the conditions of the electron blocking layer and the bulk hetero layer (photoelectric conversion layer) in each example. In Table 1, the photoelectric conversion efficiency is shown by the relative sensitivity when the photoelectric conversion efficiency of Example 1 is 1.

As shown in Table 1, with respect to Comparative Example 1, Examples 1 to 5 had the effect of improving the light response speed without lowering the photoelectric conversion efficiency. In Comparative Example 2, the light response speed is the same as that of the example, but the light absorption rate is small and the photoelectric conversion efficiency is lowered because the content of the compound 1 in the photoelectric conversion layer is small. In Comparative Example 3, the amount of light absorption increased by increasing the film thickness in the photoelectric conversion layer. However, since the electric field strength applied to the photoelectric conversion layer when 10 V was applied decreased, the photoelectric conversion efficiency and the optical response were reduced. The speed is decreasing. In Comparative Example 9, photoelectric conversion layers having different fullerene (C ₆₀ ) contents are laminated, but the response speed is lowered because the fullerene (C ₆₀ ) content of the layer adjacent to the electron blocking layer is 70% or less. ing.

In Comparative Examples 4 to 8, photoelectric conversion layers having different fullerene (C ₆₀ ) contents are laminated, and the fullerene (C ₆₀ ) content of the layer adjacent to the electron blocking layer is 70% or more. Since the difference in the fullerene (C ₆₀ ) content is 15% or more, the optical response speed is lowered.

Table 2 and FIG. 3 show the difference in the fullerene (C ₆₀ ) content between the bulk hetero layers in Examples and Comparative Examples in which the fullerene (C ₆₀ ) content of the layer adjacent to the electron blocking layer is 70% or more ( The relationship between Δ) and afterimage (%) is shown. FIG. 3 shows a rapid decrease in response speed (increase in afterimage) when Δ = over 15%.

(Examples 6 to 10, Comparative Examples 10 to 16)
The p-type organic semiconductor of the bulk hetero layer (photoelectric conversion layer) is changed to the compound 2, and the photoelectric conversion elements of the respective examples are obtained with various fullerene (C ₆₀ ) contents or the film thickness of the first bulk hetero layer. The photoelectric conversion efficiency and the light response speed were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 3 together with the conditions of the electron blocking layer and the bulk hetero layer (photoelectric conversion layer) in each example. In Table 3, the photoelectric conversion efficiency is shown as a relative sensitivity when the photoelectric conversion efficiency of Example 10 is 1.

In contrast to Comparative Example 10, Examples 6 to 10 had the effect of improving the light response speed without lowering the photoelectric conversion efficiency. In Example 10, three bulk hetero layers having different fullerene (C ₆₀ ) contents are laminated. However, since the content of the compound 3 in the photoelectric conversion layer can be further increased, the light absorption rate is increased. Increasing the photoelectric conversion efficiency.

Comparative Example 11 has a light response speed equivalent to that of the example, but has a small light absorption rate due to a small content of compound 3 in the photoelectric conversion layer, resulting in a decrease in photoelectric conversion efficiency. In Comparative Example 12, the amount of light absorption increased by increasing the film thickness in the photoelectric conversion layer. However, since the electric field strength applied to the photoelectric conversion layer when 10 V was applied decreased, the photoelectric conversion efficiency and the optical response were reduced. The speed is decreasing.

In Comparative Example 16, photoelectric conversion layers having different fullerene (C ₆₀ ) contents are stacked, but the response speed is lowered because the fullerene (C ₆₀ ) content of the layer adjacent to the electron blocking layer is 70% or less. ing. In Comparative Examples 13 to 15, photoelectric conversion layers having different fullerene (C ₆₀ ) contents are laminated, and the fullerene ratio of the layer adjacent to the electron blocking layer is 70% or more. However, the fullerene (C ₆₀ ) between adjacent layers is Since the difference in content is 15% or more, the light response speed is lowered.

Table 4 and FIG. 4 show the difference in the fullerene (C ₆₀ ) content between bulk hetero layers (Δ ₆₀ ) for the examples and comparative examples in which the fullerene (C ₆₀ ) content of the layer adjacent to the electron blocking layer is 70% or more. ) And afterimage (%).

Also in FIG. 4, when Δ is greater than 15%, a rapid response speed is decreased (an increase in afterimage).

Claims

An organic photoelectric conversion element having a pair of electrodes and a light receiving layer including at least a photoelectric conversion layer sandwiched between the pair of electrodes,
Having an electron blocking layer provided between the photoelectric conversion layer and one of the electrodes;
The photoelectric conversion layer is composed of a plurality of bulk hetero layers formed by mixing fullerene and a p-type organic semiconductor,
The plurality of bulk hetero layers are laminated so that the electron blocking layer side layer has a higher content of the fullerene,
The fullerene content in the bulk hetero layer adjacent to the electron blocking layer is 70% by volume or more, and the difference in the fullerene content between adjacent bulk hetero layers is 15% by volume or less. The photoelectric conversion element characterized by the above-mentioned.
2. The photoelectric conversion element according to claim 1, wherein a content ratio of the fullerene in a layer having the lowest mixing ratio of the fullerene in the bulk hetero layer is 50% by volume or more.
3. The photoelectric conversion element according to claim 1, wherein a film thickness of a layer adjacent to the electron blocking layer is 50 nm or less.
4. The photoelectric conversion element according to claim 1, wherein the plurality of bulk hetero layers are composed of two layers.
5. The photoelectric conversion element according to claim 1, wherein the other electrode is a transparent electrode arranged on the light receiving side.
The value obtained by dividing the voltage applied from the outside to the pair of electrodes by the distance between the pair of electrodes is 1 × 10 5 V / cm to 1 × 10 7 V / cm. The photoelectric conversion element according to any one of 5.
The method for producing a photoelectric conversion element according to any one of claims 1 to 6, wherein the p-type organic semiconductor material contains a compound represented by the following general formula (1).

(In the general formula (1), Z 1 represents a ring containing at least two carbon atoms and represents a 5-membered ring, a 6-membered ring, or a condensed ring containing at least one of a 5-membered ring and a 6-membered ring. L 1 , L 2 , and L 3 each independently represents an unsubstituted methine group or a substituted methine group, D 1 represents an atomic group, and n represents an integer of 0 or more.)
A plurality of photoelectric conversion elements according to any one of claims 1 to 7;
An optical sensor comprising: a circuit board on which a signal reading circuit for reading a signal corresponding to a charge generated in the photoelectric conversion layer of the photoelectric conversion element is formed.
The optical sensor according to claim 8, wherein the optical sensor is an image sensor.