JP6010514B2 - Photoelectric conversion device and imaging device - Google Patents

Description

  The present invention relates to a photoelectric conversion element and an imaging element in which a photoelectric conversion layer that generates an electric charge according to received light is configured using an organic compound and converts a visible light image into an electric signal, and in particular, photoelectric conversion efficiency. The present invention relates to a photoelectric conversion element and an imaging element having a high dark current and a low dark current.

  As an image sensor used for a digital still camera, a digital video camera, a mobile phone camera, an endoscope camera, etc., pixels including photodiodes are arranged on a semiconductor substrate such as a silicon (Si) chip, and Solid-state imaging devices such as CCD sensors and MOS sensors that acquire signal charges corresponding to photoelectrons generated in a photodiode with a CCD-type or CMOS-type readout circuit are widely known. Currently, development of photoelectric conversion elements using organic compounds is underway (Patent Documents 1 to 3, etc.).

Patent Document 1 discloses an organic photoelectric conversion element having a structure in which a plurality of functional layers are laminated, such as a photoelectric conversion layer that absorbs light and generates charges, and a charge blocking layer that suppresses charge injection from an electrode.
Patent Document 2 discloses an organic photovoltaic element having a laminated film of an organic compound alignment film and an amorphous film having the same composition.
Here, the photoelectric conversion element requires high photoelectric conversion efficiency and low dark current. Therefore, Patent Document 3 discloses a structure including fullerene or a fullerene derivative crystallized in a photoelectric conversion layer as a configuration for realizing high photoelectric conversion efficiency and low dark current.

JP 2007-88033 A JP-A-6-232435 JP 2011-14895 A

  As described above, Patent Document 3 discloses a structure containing fullerene or a fullerene derivative crystallized in a photoelectric conversion layer as a configuration realizing high photoelectric conversion efficiency and low dark current, but still higher photoelectric conversion efficiency. Therefore, a low dark current is required.

  An object of the present invention is to provide a photoelectric conversion element and an imaging element that solve the above-described problems based on the prior art, have high photoelectric change efficiency, and low dark current.

  In order to achieve the above object, the first aspect of the present invention includes a lower electrode, an electron blocking layer stacked on the lower electrode, a photoelectric conversion layer stacked on the blocking layer, and a photoelectric conversion layer. The photoelectric conversion layer is a bulk hetero layer in which a p-type organic semiconductor and a crystallized fullerene or a crystallized fullerene derivative are mixed, and includes a laminated intermediate layer and an upper electrode laminated on the intermediate layer. The layer includes an amorphous fullerene or an amorphous fullerene derivative, and the upper electrode is formed of a transparent conductive film to provide a photoelectric conversion element.

The photoelectric conversion layer is preferably composed of a bulk hetero layer formed by mixing a p-type organic semiconductor and fullerene or a crystallized fullerene derivative oriented in the (111) direction perpendicular to the surface of the lower electrode.
The photoelectric conversion layer preferably contains crystallized fullerene or crystallized fullerene derivative in a proportion of 30% to 80%.
The thickness of the intermediate layer is preferably 1/3 or more of the thickness of the upper electrode, and the thickness of the intermediate layer is preferably not more than the thickness of the upper electrode.
The intermediate layer preferably further includes at least one organic material. The intermediate layer is preferably a layer in which an amorphous fullerene or an amorphous fullerene derivative and a transparent hole transport material having an ionization potential of 5.5 eV or more are mixed.
The upper electrode is made of ITO, and the thickness of the upper electrode is preferably 5 to 30 nm.

  According to a second aspect of the present invention, there is provided an imaging device comprising the photoelectric conversion element according to the first aspect of the present invention.

  According to the present invention, the photoelectric conversion efficiency and the dark current can be reduced in the photoelectric conversion element and the imaging element.

(A) is typical sectional drawing which shows the photoelectric conversion element of embodiment of this invention, (b) is the principal part enlarged view of the photoelectric conversion element of embodiment of this invention, (c), It is a principal part enlarged view which shows the modification of the photoelectric conversion element of embodiment of this invention. (A) is typical sectional drawing which shows the image sensor of embodiment of this invention, (b) is a principal part enlarged view of the image sensor of embodiment of this invention. (A)-(c) is typical sectional drawing which shows the manufacturing method of the image pick-up element of embodiment of this invention in order of a process. (A)-(c) is typical sectional drawing which shows the manufacturing method of the image pick-up element of embodiment of this invention in order of a process, and shows the post process of FIG.3 (c).

Hereinafter, a photoelectric conversion element and an imaging element of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
Fig.1 (a) is typical sectional drawing which shows the photoelectric conversion element of embodiment of this invention, (b) is a principal part enlarged view of the photoelectric conversion element of embodiment of this invention, (c) These are the principal part enlarged views which show the modification of the photoelectric conversion element of embodiment of this invention.

A photoelectric conversion element 100 shown in FIG. 1 converts incident light L into an electric signal. The photoelectric conversion element 100 is formed by laminating a lower electrode 104 on a surface 102 a of a substrate 102. An electron blocking layer 106 is laminated on the lower electrode 104, and a photoelectric conversion layer 108 is laminated on the electron blocking layer 106.
An intermediate layer 110 is stacked on the photoelectric conversion layer 108, and an upper electrode 112 is stacked on the intermediate layer 110. A sealing layer 114 that covers the lower electrode 104, the organic layer 120, and the upper electrode 112 is formed.
The electron blocking layer 106, the photoelectric conversion layer 108, and the intermediate layer 110 are collectively referred to as an organic layer 120.

  In the photoelectric conversion element 100, incident light L is incident on the photoelectric conversion layer 108 of the organic layer 120 from the surface 112 a side of the upper electrode 112, and the incident light L is converted into an electrical signal by the photoelectric conversion layer 108. For this reason, the sealing layer 114 and the upper electrode 112 transmit the incident light L as will be described later.

  The substrate 102 is composed of, for example, a silicon substrate or a glass substrate. Note that there is no particular limitation on the substrate 102 as long as the photoelectric conversion element 100 can be formed.

  The lower electrode 104 is an electrode for collecting holes out of charges generated in the photoelectric conversion layer 108. Examples of the material of the lower electrode 104 include metals, metal oxides, metal nitrides, metal borides, organic conductive compounds, and mixtures thereof. Specific examples include tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), indium tungsten oxide (IWO), conductive metal oxides such as titanium oxide, and titanium nitride (TiN). Metal nitrides such as gold (Au), platinum (Pt), silver (Ag), chromium (Cr), nickel (Ni) and aluminum (Al), and these metals and conductive metal oxides A mixture or laminate of the above, an organic conductive compound such as polyaniline, polythiophene, and polypyrrole, and a laminate of these with ITO. The material of the lower electrode 104 is particularly preferably any of titanium nitride, molybdenum nitride, tantalum nitride, and tungsten nitride.

  The electron blocking layer 106 is a layer for preventing electrons from being injected into the photoelectric conversion layer 108 from the lower electrode 104, and is composed of a single layer or a plurality of layers. The electron blocking layer 106 may be composed of a single organic material film, or may be composed of a mixed film of a plurality of different organic materials.

  An electron-donating organic material can be used for the electron blocking layer 106. Specifically, in a low molecular material, 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, annealing amine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, silazane derivatives, carbazole derivatives, bifluorenes Derivatives can be used, and 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 not an ionic compound, it can be used as long as it is a compound having sufficient hole transportability.

  The electron blocking layer 106 is preferably made of a material having a high electron injection barrier from the adjacent lower electrode 104 and a high hole transporting property. As an electron injection barrier, the electron affinity of the electron blocking layer 106 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 106 preferably has a thickness of 20 nm or more in order to sufficiently suppress contact between the lower electrode 104 and the photoelectric conversion layer 112 and to avoid the influence of defects and dust existing on the surface of the lower electrode 104. More preferably, it is 40 nm or more, and particularly preferably 60 nm or more.
On the other hand, if the thickness of the electron blocking layer 106 is too thick, there is a problem that a supply voltage necessary for applying an appropriate electric field strength to the photoelectric conversion layer 112 increases, and a carrier transport process in the electron blocking layer 106 occurs. However, there is a problem that the performance of the photoelectric conversion element is adversely affected. The thickness of the electron blocking layer 106 is preferably 300 nm or less, more preferably 200 nm or less, and still more preferably 100 nm or less.

The photoelectric conversion layer 108 is a layer configured to include a photoelectric conversion material that receives incident light L and generates a charge corresponding to the amount of light. In the photoelectric conversion layer 108, an organic compound can be used as the photoelectric conversion material.
The photoelectric conversion layer 108 is a bulk hetero layer in which a p-type organic semiconductor (organic p-type compound) and a crystallized fullerene or a crystallized fullerene derivative are mixed. The photoelectric conversion layer 108 has a bulk heterostructure. By using a bulk hetero layer as the photoelectric conversion layer 108, the disadvantage that the carrier diffusion length of the organic layer 120 is short can be compensated and the photoelectric conversion efficiency can be improved. By producing a bulk hetero layer with an optimal mixing ratio, the electron mobility and hole mobility of the photoelectric conversion layer 108 can be increased, and the photoresponse speed of the photoelectric conversion element 100 can be sufficiently increased. Can do. For this reason, the ratio of the crystallized fullerene or the crystallized fullerene derivative in the photoelectric conversion layer 108 is preferably 30% to 80% in volume ratio.

In the photoelectric conversion layer 108, since the fullerene or fullerene derivative is in a crystallized state, a higher photoelectric conversion efficiency can be obtained, and the carrier path of the fullerene or fullerene derivative is effectively formed. It can also contribute to the high-speed response of the photoelectric conversion element 100. Examples of means for crystallizing fullerene or fullerene derivatives include selecting a suitable photoelectric conversion material, increasing the ratio of fullerenes, and heating the substrate during film formation.
Whether or not the fullerene or fullerene derivative is in a crystallized state is determined by whether or not a crystal peak derived from the crystal structure of the fullerene or fullerene derivative is observed in the X-ray diffraction image of the film containing the fullerene or fullerene derivative. be able to. In addition to this, it is judged whether or not a diffraction point derived from the crystal structure of fullerene or fullerene derivative is observed in the electron diffraction pattern of the cross section by electron beam diffraction in the cross-sectional TEM image of the film containing fullerene or fullerene derivative. be able to.

  In the photoelectric conversion layer 108 including crystallized fullerene or a crystallized fullerene derivative, the fullerene or the fullerene derivative is oriented in the (111) direction with respect to the surface 104a of the lower electrode 104 (the surface 102a of the substrate 102). preferable.

As the fullerene or fullerene derivative is oriented in the (111) direction in a direction perpendicular to the substrate surface, the unevenness of the photoelectric conversion layer 108 containing the fullerene fullerene derivative is suppressed as compared with the case of including a randomly crystallized structure. As a result, it is possible to prevent the upper electrode from entering into the unevenness and increase the leakage current in the vicinity of the lower electrode, or the flatness and coverage of the layer (eg, charge blocking layer) formed on the photoelectric conversion layer. As a result, the injection current is suppressed, and a high dark current suppression effect is obtained.
From this viewpoint, it is preferable that the crystallized fullerene or the crystallized fullerene derivative in the photoelectric conversion layer 108 is uniformly crystallized, that is, the orientation direction is the same. Among them, as the orientation direction, the (111) direction is preferably 50 to 100% by volume ratio, more preferably 80 to 100% and (111).

  In order to control the crystal direction of fullerene or fullerene derivative, the crystal direction can also be realized by adjusting the substrate temperature, the deposition rate, and the like during film formation. Specifically, it is preferable to heat the substrate at a higher temperature and to lower the deposition rate. However, when the temperature is excessively high and the deposition rate is low, crystallization of fullerene or fullerene derivatives is promoted, and unevenness of the film surface in the mixed layer of fullerenes or fullerene derivatives and a photoelectric conversion material may increase. If the unevenness of the film surface increases, when an electrode is laid on the upper layer, it causes a short (leakage current) to increase and dark current increases, which is not preferable.

The substrate temperature varies depending on the type of material other than fullerene or fullerene derivative existing in the photoelectric conversion layer 108, the content ratio of fullerene or fullerene derivative, etc., but is preferably 120 ° C. or lower, and preferably 100 ° C. or lower. More preferred. The lower limit of the substrate temperature is preferably 60 ° C, and more preferably 70 ° C to 90 ° C.
The deposition rate varies depending on the content ratio of fullerene or fullerene derivative other than fullerene or fullerene derivative present in the photoelectric conversion layer 108, but is preferably 0.1 to 15 Å / s, preferably 0.5 to It is more preferable to set it as 3.0 kg / s.

Here, the state in which the fullerene or fullerene derivative is oriented in the (111) direction perpendicular to the surface 104 a of the lower electrode 104 indicates that the fullerene film formed on the substrate corresponding to the lower electrode 104 or By measuring the fullerene derivative film by X-ray diffraction, a crystal peak of fullerene or fullerene derivative is observed, and this peak is (111) with respect to a direction perpendicular to the substrate surface corresponding to the surface 104a of the lower electrode 104. This can be confirmed from the fact that only a plurality of indices such as (111), (222), and (333) in the direction are observed.
In addition to the X-ray diffraction method, the orientation in the (111) direction can be measured from the electron beam diffraction image of the cross section by electron beam diffraction in the cross section TEM image.

Hereinafter, fullerene and fullerene derivatives will be described more specifically.
The fullerene, fullerene _{C 60,} fullerene _{C 70,} fullerene _{C 76,} fullerene _{C 78,} fullerene _{C 80,} fullerene _{C 82,} fullerene _{C 84,} fullerene _{C 90,} fullerene _{C 96,} fullerene _{C 240,} fullerene _{C 540,} mixed Fullerene and fullerene nanotube.
A fullerene derivative is a compound in which a substituent is added to fullerene. As the substituent, an alkyl group, an aryl group, or a heterocyclic group is preferable. As an alkyl group, C1-C12 is preferable and C1-C6 is more preferable. Examples of the aryl group include a phenyl group, a naphthyl group, and an anthryl group. Examples of the heterocyclic group include a furyl group, a thienyl group, a pyrrolyl group, an oxazolyl group, a pyridyl group, a quinolinyl group, and a carbazolyl group. As the fullerene derivative, the following compounds are particularly preferable.

  In addition, as fullerenes and fullerene derivatives, the Chemical Society of Japan, Quarterly Chemical Review No. 43 (1999), JP-A-10-167994, JP-A-11-255508, JP-A-11-255509, JP-A-2002-241323, JP-A-2003-19681, and the like. Can also be used.

  The p-type organic semiconductor material (compound) is a donor-type organic semiconductor material (compound), which is mainly represented by a hole-transporting organic compound and refers to an organic compound having a property of easily donating electrons. More specifically, an organic compound having a smaller ionization potential when two organic materials are used in contact with each other. Therefore, any organic compound can be used as the donor organic compound as long as it is an electron-donating organic compound. For example, triarylamine compound, benzidine compound, pyrazoline compound, styrylamine compound, hydrazone compound, triphenylmethane compound, carbazole compound, polysilane compound, thiophene compound, phthalocyanine compound, cyanine compound, merocyanine compound, oxonol compound, polyamine compound, 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), nitrogen-containing heterocyclic compounds The metal complex etc. which it has as can be used. Not limited to this, as described above, any organic compound having an ionization potential smaller than that of the organic compound used as the n-type (acceptor property) compound may be used as the donor organic semiconductor.

  Among the above, the p-type organic semiconductor material (compound) used for the photoelectric conversion layer 108 is preferably a triarylamine compound or a pyran compound, and more preferably a triarylamine compound. As the triarylamine compound, a compound represented by the following general formula (1) is preferable.

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 represent an unsubstituted methine group or a substituted methine group. D ₁ represents an atomic group. n represents an integer of 0 or more.

Z ₁ is 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, and 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 derivatives thereof. 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 and the like.
(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 and the like.

The ring formed 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, 2-thiobarbitur 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, In 4-imidazolidinedione nucleus, 2-thio-2,4-imidazolidinedione nucleus, 2-imidazolin-5-one nucleus, 3,5-pyrazolidinedione nucleus, benzothiophen-3-one nucleus, indanone nucleus More preferably 1,3-dicarbonyl nucleus, 2,4,6-triketohexahydropyrimidine nucleus (including thioketone, for example, barbituric acid nucleus, 2-thiovale nucleus, Bituric 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 derivatives thereof. is there.

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 each other to form a ring (eg, a 6-membered ring such as a benzene ring). Although the substituent of the substituted methine group includes the substituent W, it is preferable that all of L ₁ , L ₂ and L ₃ are unsubstituted methine groups.
L _{1 to} L ₃ may be linked to each other to form a ring, and preferred examples of the ring formed include a cyclohexene ring, a cyclopentene ring, a benzene ring, and a thiophene ring.

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

D ₁ represents an atomic group. D ₁ is preferably ^a group containing —NR ^a (R ^b ), and more preferably —NR ^a (R ^b ) represents an arylene group substituted. R ^a and R ^b each independently represent a hydrogen atom or a substituent.

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 thereof 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 R ^a or R ^b include the 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 a substituent). A phenyl group which may be substituted), or a heterocyclic group.

The aryl groups represented by R ^a and R ^b 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, and is 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. . Examples thereof 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 R ^a and R ^b are preferably each independently a heterocyclic group having 3 to 30 carbon atoms, and more preferably a heterocyclic group having 3 to 18 carbon atoms. The heterocyclic group may have a substituent, preferably a C3-C18 heterocyclic group which may have a C1-C4 alkyl group or a C6-C18 aryl group. It is. The heterocyclic group represented by R ^a and R ^b is preferably a condensed ring structure, and furan ring, thiophene ring, selenophene ring, silole ring, pyridine ring, pyrazine ring, pyrimidine ring, oxazole ring, thiazole ring, triazole. A condensed ring structure of a ring combination selected from a ring, an oxadiazole ring, and a thiadiazole ring (which may be the same) is preferable. A bithienothiophene ring is preferred.

The arylene group and aryl group represented by D ₁ , R ^a and R ^b 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, pyrene A benzene ring, a naphthalene ring or an anthracene ring, more preferably a benzene ring or a naphthalene ring.

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, mercap Group, 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 ring 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 (-OPO _(OH) 2), a sulfato group (-OSO ₃ H), and other known substituents.

When R ^a and R ^b represent a substituent (preferably an alkyl group or an alkenyl group), the substituent is an aromatic ring (preferably benzene ring) skeleton of an aryl group substituted by —NR ^a (R ^b ). It may combine with a hydrogen atom or a substituent to form a ring (preferably a 6-membered ring).
R ^a and R ^b may be bonded to each other to form a ring (preferably a 5-membered or 6-membered ring, more preferably a 6-membered ring), and R ^a and R ^b are each L A ring (preferably a 5-membered or 6-membered ring, more preferably a 6-membered ring) may be formed by combining with a substituent in (representing any of L ₁ , L ₂ , 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. .
Specific examples of the compound represented by the general formula (1) include those shown below, but the present invention is not limited thereto.

(Molecular weight)
The compound represented by the general formula (1) preferably has a molecular weight of 300 or more and 1500 or less, more preferably 350 or more and 1200 or less, and more preferably 400 or more and 900 or less, from the viewpoint of film forming suitability. Further preferred. When the molecular weight is too small, the film thickness of the formed photoelectric conversion film decreases due to volatilization. Conversely, when the molecular weight is too large, vapor deposition cannot be performed, and a photoelectric conversion element cannot be manufactured.

(Melting point)
The compound represented by the general formula (1) has a melting point of preferably 200 ° C. or higher, more preferably 220 ° C. or higher, and further preferably 240 ° C. or higher from the viewpoint of vapor deposition stability. If the melting point is low, it melts before vapor deposition, and in addition to being unable to form a stable film, the decomposition product of the compound increases, so the photoelectric conversion performance deteriorates.

(Absorption spectrum)
The peak wavelength of the absorption spectrum of the compound represented by the general formula (1) is preferably 400 nm or more and 700 nm or less, more preferably 480 nm or more and 700 nm or less, more preferably 510 nm or more and 680 nm, from the viewpoint of broadly absorbing light in the visible region. More preferably, it is as follows.

(Molar extinction coefficient of peak wavelength)
The higher the molar extinction coefficient is, the better the compound represented by the general formula (1) is from the viewpoint of efficiently using light. 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.

The intermediate layer 110 is a layer introduced between the photoelectric conversion layer 108 and the upper electrode 112.
The intermediate layer 110 has a function of transporting electrons generated in the photoelectric conversion layer 108 to the upper electrode 112 and suppressing hole injection from the upper electrode 112 to the photoelectric conversion layer 108.
The intermediate layer 110 includes an amorphous fullerene or an amorphous fullerene derivative.
Since the photoelectric conversion layer 108 includes the crystallized structure as described above, when the upper electrode 112 is directly formed on the photoelectric conversion layer 108, the upper electrode 112 bites into the crystal grain boundary and a voltage is applied between the upper and lower electrodes. As a result, the electric field concentrates on the portion that has penetrated into the electrode, and the injection current from the upper electrode 112 increases. By forming a layer containing amorphous fullerene or an amorphous fullerene derivative as the intermediate layer 110 between the photoelectric conversion layer 108 and the upper electrode 112, local electric field concentration on the photoelectric conversion layer 108 of the upper electrode 112 is reduced. And the injection current can be greatly suppressed. Among the charges generated in the photoelectric conversion layer 108, electrons are collected by the upper electrode 112 through the intermediate layer 110, and a layer containing an amorphous fullerene or an amorphous fullerene derivative is used for the intermediate layer 110. Thus, it is possible to efficiently transport electrons.

If the thickness of the intermediate layer 110 is too thin, the effect of suppressing hole injection from the upper electrode 112 to the photoelectric conversion layer 108 is not sufficiently exhibited. In order to sufficiently exhibit the effect of suppressing the hole injection, as shown in FIG. 1B, when the thickness of the intermediate layer 110 is t ₁ and the thickness of the upper electrode 112 is t ₂ The thickness t ₁ of the intermediate layer 110 is preferably t ₁ ≧ 1/3 × t ₂ .
On the other hand, when the film thickness of the intermediate layer 110 is excessively increased, the supply voltage necessary for applying an appropriate electric field strength to the photoelectric conversion layer 108 increases. For this reason, as an upper limit of the film thickness of the intermediate | middle layer 110, it is 100 nm or less, for example, Preferably it is 50 nm or less, More preferably, it is 20 nm or less.

The upper limit value of the thickness t ₁ of the intermediate layer 110 is preferably t ₁ ≦ t ₂ with respect to the film thickness t ₂ of the upper electrode 112 when the upper electrode 112 is used as a reference. For this reason, the thickness t ₁ of the intermediate layer 110 is preferably 1/3 × t ₂ ≦ t ₁ ≦ t ₂ when the upper electrode 112 is used as a reference.
By defining the thickness t ₁ of the intermediate layer 110 with respect to the thickness t ₂ of the upper electrode 112 as described above, the dark current can be reduced.

The intermediate layer 110 can be composed of a mixed layer of amorphous fullerene or an amorphous fullerene derivative and an organic p-type compound contained in the photoelectric conversion layer 108. In addition, the intermediate layer 110 can be composed of a mixed layer of amorphous fullerene or an amorphous fullerene derivative and a transparent hole transport material.
In order to suppress transparent hole injection, it is preferable to use a material having an ionization potential of 5.5 eV or more as the transparent hole transport material. By using a material having an ionization potential of 5.5 eV or more as the transparent hole transport material, hole injection from the upper electrode 112 can be sufficiently suppressed. Thereby, dark current can be reduced.

The transparent hole transport material is preferably a material having an ionization potential of 6 eV or less and a difference between the ionization potential and the electron affinity of 3 eV or more. The ionization potential of the material can be measured using an AC-2 surface analyzer manufactured by Riken Keiki Co., Ltd. after depositing the material with a film thickness of about 100 nm on a quartz substrate. In order to obtain the difference between the ionization potential and the electron affinity, first, the specularity of the deposited material is measured, and the energy at the absorption edge is obtained. The energy at the absorption edge corresponds to the energy difference between the ionization potential and the electron affinity.
The intermediate layer 110 may be a layer in which the ratio of fullerene or a fullerene derivative to a transparent hole transport material is constant, or may be a gradation layer in which the ratio varies depending on the film thickness direction.
When the ratio of the amorphous fullerene or the amorphous fullerene derivative in the intermediate layer 110 is too small, the electron transport ability of the intermediate layer 110 is reduced, and the electrons generated in the photoelectric conversion layer 108 are transferred to the upper electrode 112, that is, The efficiency of transporting to the electron collecting electrode is lowered, and the photoelectric conversion efficiency is lowered. Since amorphous fullerene or amorphous fullerene derivative absorbs visible light, carriers are generated in the intermediate layer 110 by the absorbed light. However, the amorphous fullerene or amorphous fullerene derivative in the intermediate layer 110 If the ratio is too large, the hole transport ability of the intermediate layer 110 is lowered, leading to a delay in response speed. For this reason, the ratio of the amorphous fullerene or the amorphous fullerene derivative in the intermediate layer 110 is preferably 30% to 80% in volume ratio.

Hereinafter, specific examples of the transparent hole transport material will be described.
An electron-donating organic material can be used as the transparent hole transport material. Specifically, in a low molecular material, 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. Porphyrin compounds, triazole derivatives, oxazizazo Derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, annealing amine 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, and diacetylene, and derivatives thereof can be used, even if they are not electron donating compounds. Any compound having sufficient hole transportability can be used, and more specifically, examples of the transparent hole transport material include the following compounds 1, 3 and 4. That.

Hereinafter, a method for forming a layer containing the organic compound will be described.
The layer containing an organic compound can be formed by a dry film formation method or a wet film formation method. Specific examples of the dry film forming method include a vacuum vapor deposition method, a sputtering method, a physical vapor deposition method such as an ion plating method and an MBE method, or a CVD method such as plasma polymerization. As the wet film formation method, a cast method, a spin coating method, a dipping method, an LB method, or the like can be used.
When a polymer compound is used as at least one of a p-type semiconductor (compound) and an n-type semiconductor (compound), it is preferable to form a film by a wet film formation method that is easy to manufacture. When a dry film formation method such as vapor deposition is used, it is difficult to use a polymer because it may be decomposed, and an oligomer thereof can be preferably used instead. On the other hand, in the present invention, when a low molecule is used, a dry film forming method is preferably used, and a vacuum deposition method is particularly preferably used. All steps during the deposition are preferably performed in a vacuum, and basically the compound is not directly in contact with oxygen and moisture in the outside air. It is preferable to perform PI control or PID control of the deposition rate using a film thickness monitor such as a crystal resonator or an interferometer. When two or more kinds of compounds are deposited at the same time, a co-evaporation method or a flash deposition method can be preferably used.

The upper electrode 112 is for increasing the absolute amount of light incident on the photoelectric conversion layer 108 and increasing the external quantum efficiency, and is made of a transparent conductive film.
Preferred materials for the transparent conductive film are ITO, IZO, SnO ₂ , ATO (antimony-doped tin oxide), ZnO, AZO (Al-doped zinc oxide), GZO (gallium-doped zinc oxide), TiO ₂ , and FTO (fluorine). Doped tin oxide).
The light transmittance of the transparent electrode film 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.
Usually, when the conductive thin film is made thinner than a certain range, the resistance value is rapidly increased. However, the sheet resistance of the transparent electrode film is preferably 100Ω / □ or more and 10000Ω / □ or less, and there is a large degree of freedom in the range of film thickness that can be thinned. Further, the thinner the transparent electrode film, the smaller the amount of light absorbed, and the light transmittance generally increases. The increase in light transmittance is very preferable because it increases the light absorption in the photoelectric conversion layer 108 and increases the photoelectric conversion ability. In consideration of the increase in the resistance value of the thin film accompanying the thinning and the increase in light transmittance, the thickness of the transparent electrode film, that is, the upper electrode 112 is preferably 5 nm or more and 30 nm or less, more preferably It is 5 nm or more and 20 nm or less.
As a method for manufacturing the upper electrode 112, various methods are used depending on the constituent materials, but it is preferable to use a sputtering method.

  The sealing layer 114 is a layer for preventing a factor that degrades an organic material such as water and oxygen from entering the photoelectric conversion unit 106 containing the organic material. The sealing layer 110 covers the lower electrode 104, the electron blocking layer 106, the photoelectric conversion layer 108, the intermediate layer 110, and the upper electrode 112, and seals between the substrate 102. The sealing layer 114 is required to satisfy the following conditions.

First, when the sealing layer 114 is formed, the already formed photoelectric conversion layer 108 is not deteriorated.
Second, after the production of the photoelectric conversion element or the imaging element, the penetration of factors that degrade the organic photoelectric conversion material such as water molecules is prevented, and the photoelectric conversion layer 108 can be stored over a long period of storage and long use. Prevent deterioration.
Thirdly, in the manufacturing process of the imaging element after the formation of the sealing layer 114, it is possible to protect the photoelectric conversion layer 108 by preventing intrusion of factors that degrade the organic photoelectric conversion material contained in the solution, plasma, and the like. It is done.
Fourth, since incident light reaches the photoelectric conversion layer 108 through the sealing layer 114, the sealing layer 114 must be transparent to light having a wavelength detected by the photoelectric conversion layer 108.

  The sealing layer 114 can be formed of a thin film made of a single material, but can also be provided with a separate function for each layer in a multilayer structure. For example, like a sealing layer 114a shown in FIG. 1C, a first sealing layer 116 that prevents penetration of deterioration factors of photoelectric conversion materials such as water molecules, and a first sealing layer 116, A two-layer structure in which a sealing auxiliary layer 118 having a function difficult to achieve with one sealing layer 116 may be stacked. However, considering the manufacturing cost, it is preferable that the number of layers is as small as possible.

Moreover, the sealing layer 114 can be formed as follows, for example.
The performance of organic photoelectric conversion materials is significantly deteriorated due to the presence of deterioration factors such as water molecules. Therefore, it is necessary to cover and seal the entire photoelectric conversion layer with a dense metal oxide film, metal nitride film, or metal oxynitride film that does not allow water molecules to permeate. Conventionally, aluminum oxide, silicon oxide, silicon nitride, or silicon nitride oxide, their laminated structure, and their laminated structure with an organic polymer are used as sealing layers and formed by various vacuum film forming techniques. The conventional sealing layer has a shadow on the step due to the structure on the substrate surface, minute defects on the substrate surface, or particles adhering to the substrate surface, and it is difficult to grow a thin film. 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 this step with the sealing layer 114, 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 sealing layer 114 as a whole.

  The atomic layer deposition (ALD) method is a kind of CVD method, and adsorbs and reacts organometallic compound molecules, metal halide molecules, and metal hydride molecules, which are thin film materials, on the substrate surface and unreacted groups contained in them. 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, it is possible to completely cover the stepped portion, which was difficult with the conventional thin film forming method, that is, the thickness of the thin film grown on the stepped portion can be the same as the thickness of the thin film grown on the flat portion, and the step coverage is extremely high. Excellent. Since a step due to a structure on the substrate surface, a minute defect on the substrate surface, or particles adhering to the substrate surface can be completely covered, such a step portion does not become an intrusion path for a deterioration factor of the photoelectric conversion material. When the sealing layer 114 is formed by an atomic layer deposition (ALD) method, the required sealing layer thickness can be reduced more effectively than in the prior art.

When the sealing layer 114 is formed by the atomic layer deposition method, a material corresponding to the above-described preferable sealing layer can be selected as appropriate. However, 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 alkylaluminum or aluminum halide as a 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., which is preferable. Silicon oxide or titanium oxide is also preferable because a dense thin film can be formed as the sealing layer 114 at a temperature lower than 200 ° C. similarly to aluminum oxide by appropriately selecting a material.
The sealing layer 114 preferably has a film thickness of 10 nm or more in order to sufficiently prevent the intrusion of factors such as water molecules that degrade the photoelectric conversion material. In an imaging device described later, when the sealing layer is thick, incident light is diffracted or diverged in the sealing layer, resulting in color mixing. For this reason, the film thickness of the sealing layer is preferably 200 nm or less.

  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 from the viewpoint of step coverage and denseness. However, the thin film 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 and a stripping solution. In such a case, a thin film having excellent chemical resistance is required on the aluminum oxide thin film formed by the atomic layer deposition method. That is, a sealing auxiliary layer that is a functional layer for protecting the sealing layer 114 is necessary. In this case, the sealing layer 114a having the two-layer structure shown in FIG.

Next, a method for manufacturing the photoelectric conversion element 100 will be described.
First, as the lower electrode 104, for example, a TiN substrate in which a TiN electrode is formed on the surface 102a of the substrate 102 is prepared.
In the TiN substrate, for example, TiN as a lower electrode material is formed on the surface 102a of the substrate 102 under a predetermined vacuum by a sputtering method, and a TiN electrode is formed as the lower electrode 104.
Next, an electron blocking material, for example, a carbazole derivative, more preferably a bifluorene derivative, is formed on the lower electrode 104 under a predetermined vacuum using, for example, a vacuum deposition method to form the electron blocking layer 106. .

Next, on the electron blocking layer 106, as a photoelectric conversion material, for example, a p-type organic semiconductor material and fullerene or a fullerene derivative are co-evaporated at a substrate temperature of 70 ° C. or higher under a predetermined vacuum, and the photoelectric conversion layer 108 is then deposited. Form. Thereby, a crystallized fullerene or a crystallized fullerene derivative can be obtained. In this case, the crystallized fullerene or the crystallized fullerene derivative is preferably oriented in the (111) direction as described above.
Next, for example, an amorphous fullerene or an amorphous fullerene derivative is vapor-deposited at a substrate temperature of 20 ° C. to 60 ° C. under a predetermined vacuum on the photoelectric conversion layer 108 to form the intermediate layer 110. Thereby, an amorphous fullerene or an amorphous fullerene derivative can be obtained.
Next, an ITO film with a thickness of 5 to 30 nm is formed on the intermediate layer 110 by sputtering, for example, using ITO as a transparent conductive oxide. As a result, the upper electrode 112 made of a transparent conductive film is formed.
Next, as the sealing layer 114 covering the lower electrode 104, the organic layer 120, and the upper electrode 112, for example, an aluminum oxide layer is formed using an atomic layer deposition (ALD) method.

In the photoelectric conversion element 100, when the photoelectric conversion element 100 is used, an external electric field can be applied. In this case, the lower electrode 104 and the upper electrode 112 are used as a pair of electrodes, and an external electric field applied between the pair of electrodes in order to obtain excellent characteristics in photoelectric conversion efficiency, dark current, and optical response speed is 1 V / cm. It is preferably 1 × 10 ⁷ V / cm or less, more preferably 1 × 10 ⁴ V / cm or more and 1 × 10 ⁷ V / cm or less. Particularly preferably, it is 5 × 10 ⁴ V / cm or more and 1 × 10 ⁶ V / cm or less.
In the photoelectric conversion element 100, by providing the intermediate layer 110 containing amorphous fullerene or an amorphous fullerene derivative as described above, the photoelectric conversion efficiency can be increased and the dark current can be reduced.
In addition, the photoelectric conversion efficiency can be improved by using the photoelectric conversion layer 108 as a bulk hetero layer including crystallized fullerene or a crystallized fullerene derivative as described above. Furthermore, dark current can be further suppressed by orienting the crystallized fullerene or crystallized fullerene derivative in the (111) direction as described above.

Next, an image sensor using the photoelectric conversion element 100 will be described.
FIG. 2A is a schematic cross-sectional view showing the image sensor of the embodiment of the present invention, and FIG. 2B is an enlarged view of a main part of the image sensor of the embodiment of the present invention.
The image sensor 10 according to the embodiment of the present invention can be used in an imaging apparatus such as a digital camera or a digital video camera. Furthermore, it can also be mounted on an imaging module such as an electronic endoscope and a mobile phone.

An image sensor 10 shown in FIG. 2A converts a visible light image into an electrical signal, and includes a substrate 12, an insulating layer 14, a pixel electrode (lower electrode) 16, an electron blocking layer 20, and photoelectric elements. The conversion layer 22, the intermediate layer 24, the counter electrode (upper electrode) 26, the sealing layer 28, the color filter 32, the partition wall 34, the light shielding layer 36, and the overcoat layer 38 are included. The electron blocking layer 20, the photoelectric conversion layer 22, and the intermediate layer 24 are collectively referred to as an organic layer 30.
A reading circuit 40 and a counter electrode voltage supply unit 42 are formed on the substrate 12.
The pixel electrode 16 corresponds to the lower electrode 104 of the photoelectric conversion element 100 described above, the counter electrode 26 corresponds to the upper electrode 112 of the photoelectric conversion element 100 described above, and the organic layer 30 corresponds to the organic of the photoelectric conversion element 100 described above. The sealing layer 28 corresponds to the layer 120 and the sealing layer 114 of the photoelectric conversion element 100 described above.

As the substrate 12, for example, a glass substrate or a semiconductor substrate such as Si is used. An insulating layer 14 made of a known insulating material is formed on the substrate 12. In the insulating layer 14, a plurality of pixel electrodes 16 are formed on the surface 14a. The pixel electrodes 16 are arranged in a one-dimensional or two-dimensional manner, for example.
In addition, a first connection portion 44 that connects the pixel electrode 16 and the readout circuit 40 is formed in the insulating layer 14. Furthermore, a second connection portion 46 that connects the counter electrode 26 and the counter electrode voltage supply unit 42 is formed. The second connection portion 46 is formed at a position not connected to the pixel electrode 16 and the organic layer 30. The first connection portion 44 and the second connection portion 46 are made of a conductive material.

In addition, a wiring layer 48 made of a conductive material for connecting the readout circuit 40 and the counter electrode voltage supply unit 42 to, for example, the outside of the imaging device 10 is formed inside the insulating layer 14.
As described above, the circuit board 11 is formed by forming the pixel electrodes 16 connected to the first connection portions 44 on the surface 14 a of the insulating layer 14 on the substrate 12. The circuit board 11 is also referred to as a CMOS substrate.

The electron blocking layer 20 is formed on the pixel electrode 16 so as to cover the plurality of pixel electrodes 16 and avoid the second connection portion 46, and the photoelectric conversion layer 22 is formed on the electron blocking layer 20. . An intermediate layer 24 is formed on the photoelectric conversion layer 22.
The electron blocking layer 20 corresponds to the electron blocking layer 106 of the photoelectric conversion element 100 as described above, and is a layer for suppressing injection of electrons from the pixel electrode 16 to the photoelectric conversion layer 22.

Since the photoelectric conversion layer 22 and the intermediate layer 24 correspond to the photoelectric conversion layer 108 and the intermediate layer 110 of the photoelectric conversion element 100 described above, detailed description thereof is omitted. The photoelectric conversion layer 22 is a bulk hetero layer in which a p-type organic semiconductor (organic p-type compound) and a crystallized fullerene or a crystallized fullerene derivative are mixed.
Note that the electron blocking layer 20, the photoelectric conversion layer 22, and the intermediate layer 24 may be other than the film thickness as long as the film thickness is constant on the pixel electrode 16.

The counter electrode 26 is an electrode facing the pixel electrode 16 and is provided so as to cover the organic layer 30, and the organic layer 30 is disposed between the pixel electrode 16 and the counter electrode 26.
The counter electrode 26 is made of a transparent conductive film with respect to incident light L (visible light) in order to make light incident on the photoelectric conversion layer 22. The counter electrode 26 is electrically connected to the second connection portion 46 disposed outside the photoelectric conversion layer 22, and is connected to the counter electrode voltage supply portion 42 via the second connection portion 46. Yes.

Since the counter electrode 26 can be made of the same material as that of the upper electrode 112, detailed description thereof is omitted.
The counter electrode 26 also has a light transmittance of 60% or more, preferably 80% or more, more preferably 90% or more, and more preferably 95% or more, in the visible light wavelength, similarly to the upper electrode 112. .
The counter electrode 26 preferably has a thickness of 5 to 30 nm, like the upper electrode 112. By making the counter electrode 26 have a film thickness of 5 nm or more, the intermediate layer 24 which is the lower layer can be sufficiently covered, and uniform performance can be obtained. On the other hand, if the counter electrode 26 has a film thickness exceeding 30 nm, the counter electrode 26 and the pixel electrode 16 may be locally short-circuited, resulting in an increase in dark current. The occurrence of a local short circuit can be suppressed by setting the thickness of the counter electrode 26 to 30 nm or less.

The film thickness of the counter electrode 26 is the distance from the surface 24a of the intermediate layer 24 to the surface 26a of the counter electrode 26 of the organic layer 30 in the stacking direction m, and is connected to the second connection portion 46. This does not include the thickness of the part.
Also in the image pickup device 10, as shown in FIG. 2 (b), the thickness of the intermediate layer 24 and t _a, the thickness of the opposing electrode 26 when a t _b, similarly to the photoelectric conversion element 100, the intermediate layer The thickness t _a of 24 is preferably 1/3 or more of the thickness t _b of the counter electrode 26, and the upper limit is preferably equal to or less than the thickness t _b of the counter electrode 26. That is, the thickness _{t a} of the intermediate layer 24 is preferably _{1 / 3t b ≦ t a ≦} t b.
The thickness _{t a} of the intermediate layer 24 corresponds to the thickness _{t 1} of the intermediate layer 110 of the photoelectric conversion element 100, the thickness _{t b} of the opposing electrode 26, the thickness of the upper electrode 112 of the photoelectric conversion element 100 corresponding to t _2.

  The counter electrode voltage supply unit 42 applies a predetermined voltage to the counter electrode 26 via the second connection unit 46. When the voltage to be applied to the counter electrode 26 is higher than the power supply voltage of the image sensor 10, the power supply voltage is boosted by a booster circuit such as a charge pump to supply the predetermined voltage.

The pixel electrode 16 is an electrode for collecting charges for collecting charges generated in the photoelectric conversion layer 22 between the pixel electrode 16 and the counter electrode 26 facing the pixel electrode 16. The pixel electrode 16 is connected to the readout circuit 40 via the first connection portion 44. The readout circuit 40 is provided on the substrate 12 corresponding to each of the plurality of pixel electrodes 16, and reads out a signal corresponding to the charge collected by the corresponding pixel electrode 16.
Since the pixel electrode 16 can be made of the same material as the lower electrode 104, detailed description thereof is omitted.

  A step corresponding to the film thickness of the pixel electrode 16 is steep at the end of the pixel electrode 16, there are significant irregularities on the surface of the pixel electrode 16, or minute dust (particles) adhere to the pixel electrode 16. As a result, a layer on the pixel electrode 16 becomes thinner than a desired film thickness or a crack occurs. When the counter electrode 26 is formed on the layer in such a state, a pixel defect such as an increase in dark current or a short circuit occurs due to contact between the pixel electrode 16 and the counter electrode 26 in the defective portion or electric field concentration. Furthermore, the above-described defects may reduce the adhesion between the pixel electrode 16 and the layer above it and the heat resistance of the image sensor 10.

  In order to prevent the above defects and improve the reliability of the element, the surface roughness Ra of the pixel electrode 16 is preferably 0.6 nm or less. The smaller the surface roughness of the pixel electrode 16 is, the smaller the surface unevenness is, and the surface flatness is better. In order to remove particles on the pixel electrode 16, it is particularly preferable to clean the pixel electrode 16 and the like using a general cleaning technique used in a semiconductor manufacturing process before forming the electron blocking layer 20. .

The read circuit 40 is constituted by, for example, a CCD, a MOS circuit, a TFT circuit, or the like, and is shielded from light by a light shielding layer (not shown) provided in the insulating layer 14. The readout circuit 40 preferably employs a CCD or CMOS circuit for general image sensor applications, and preferably employs a CMOS circuit from the viewpoint of noise and high speed.
Although not shown, for example, a high-concentration n region surrounded by a p region is formed on the substrate 12, and a connection portion 44 is connected to the n region. A read circuit 40 is provided in the p region. The n region functions as a charge storage unit that stores the charge of the photoelectric conversion layer 22. The signal charge accumulated in the n region is converted into a signal corresponding to the amount of charge by the readout circuit 40 and output to the outside of the image sensor 10 via the wiring layer 48, for example.

The sealing layer 28 is for protecting the photoelectric conversion layer 22 from deterioration factors such as water molecules. The sealing layer 28 is formed on the surface 14 a of the insulating layer 14 so as to cover the entire surface 28 a of the counter electrode 26. Since the sealing layer 28 can be comprised with the material similar to the sealing layer 114 of the photoelectric conversion element 100, and can be formed with the same manufacturing method, the detailed description is abbreviate | omitted.
In the image sensor 10 having a pixel size of less than 2 μm, particularly about 1 μm, if the distance between the color filter 28 and the photoelectric conversion layer 108, that is, the film thickness of the sealing layer 28 is thick, the incident light L is generated in the sealing layer 28. Diffraction or divergence causes color mixing. For this reason, the imaging device 10 having a pixel size of about 1 μm requires a sealing layer material and a manufacturing method thereof that do not deteriorate the device performance even when the film thickness of the entire sealing layer 28 is reduced. For example, by forming the sealing layer 28 with an aluminum oxide thin film formed by the above-described atomic layer deposition method, it is possible to suppress deterioration in device performance even if the film thickness is reduced.

  The color filter 32 is formed at a position facing each pixel electrode 16 on the surface 28 a of the sealing layer 28. The partition wall 34 is provided between the color filters 32 on the surface 28 a of the sealing layer 28, and is for improving the light transmission efficiency of the color filter 32. The light shielding layer 36 is formed in a region other than the region (effective pixel region) where the color filter 32 and the partition wall 34 are provided on the surface 28a of the sealing layer 28, and light is applied to the photoelectric conversion layer 22 formed outside the effective pixel region. Is prevented from entering. The color filter 32, the partition wall 34, and the light shielding layer 36 are formed to have substantially the same thickness, and are formed through, for example, a photolithography process, a resin baking process, and the like.

The overcoat layer 38 is for protecting the color filter 32 from subsequent processes and is formed so as to cover the color filter 32, the partition wall 34, and the light shielding layer 36.
In the image sensor 10, one pixel electrode 16 having the organic layer 30, the counter electrode 26, and the color filter 32 provided thereon is a unit pixel.

For the overcoat layer 38, polymer materials such as acrylic resin, polysiloxane resin, polystyrene resin, and fluorine resin, and inorganic materials such as silicon oxide and silicon nitride can be used as appropriate. The overcoat layer 38 can be formed using a known layer used for an organic solid-state imaging device.
When a photosensitive resin such as styrene is used, the overcoat layer 38 can be patterned by a photolithography method, so that it is used as a photoresist when opening the peripheral light shielding layer, sealing layer, insulating layer, etc. on the bonding pad. In particular, it is preferable because the overcoat layer 38 itself can be easily processed as a microlens. On the other hand, the overcoat layer 38 can be used as an antireflection layer, and it is also preferable to form various low refractive index materials used as the partition walls 34 of the color filter 32. Further, in order to pursue a function as a protective layer and a function as an antireflection layer with respect to a subsequent process, the overcoat layer 38 can be constituted by two or more layers combining the above materials.

  In the present embodiment, the pixel electrode 16 has a configuration formed on the surface 14a of the insulating layer 14. However, the present invention is not limited to this, and the pixel electrode 16 may be embedded in the surface 14a portion of the insulating layer 14. Good. Moreover, although the structure which provides the 2nd connection part 46 and the counter electrode voltage supply part 42 was made, it may be plural. For example, a voltage drop at the counter electrode 26 can be suppressed by supplying a voltage from both ends of the counter electrode 26 to the counter electrode 26. The number of sets of the second connection unit 46 and the counter electrode voltage supply unit 42 may be appropriately increased or decreased in consideration of the chip area of the element.

Next, a manufacturing method of the image sensor 10 according to the embodiment of the present invention will be described.
3A to 3C are schematic cross-sectional views illustrating the manufacturing method of the image sensor according to the embodiment of the present invention in the order of steps, and FIGS. 4A to 4C are diagrams of the embodiment of the present invention. It is typical sectional drawing which shows the manufacturing method of an image pick-up element in order of a process, and shows the post process of FIG.3 (c).

  In the method for manufacturing the image sensor 10 according to the embodiment of the present invention, first, as shown in FIG. 3A, the first circuit is formed on the substrate 12 on which the readout circuit 40 and the counter electrode voltage supply unit 42 are formed. The insulating layer 14 provided with the connecting portion 44, the second connecting portion 46, and the wiring layer 48 is formed, and the pixel electrode 16 connected to each first connecting portion 44 is further formed on the surface 14 a of the insulating layer 14. A formed circuit board 11 (CMOS substrate) is prepared. In this case, as described above, the first connection unit 44 and the readout circuit 40 are connected, and the second connection unit 46 and the counter electrode voltage supply unit 42 are connected. The pixel electrode 16 is made of, for example, TiN.

  Next, the electron blocking layer 20 is transferred to a film forming chamber (not shown) through a predetermined transfer path, and as shown in FIG. 3B, all the pixel electrodes except for the second connection portion 46 are used. The electron blocking material is formed into a film under a predetermined vacuum using, for example, a vapor deposition method so as to cover 16, thereby forming the electron blocking layer 20. As the electron blocking material, for example, a carbazole derivative, more preferably a bifluorene derivative is used.

  Next, it conveys to the film-forming chamber (not shown) of the photoelectric converting layer 22 with a predetermined | prescribed conveyance path | route, and as shown in FIG.3 (c), on the surface 20a of the electron blocking layer 20, as a photoelectric converting material, for example, The p-type organic semiconductor material and fullerene or fullerene derivative are co-deposited at a substrate temperature of 70 ° C. or higher under a predetermined vacuum to form the photoelectric conversion layer 22. Thereby, a crystallized fullerene or a crystallized fullerene derivative can be obtained. In this case, the crystallized fullerene or the crystallized fullerene derivative is preferably oriented in the (111) direction with respect to the direction perpendicular to the surface 16a of the pixel electrode 16 as described above.

  Next, the intermediate layer 24 is transported to a film forming chamber (not shown) through a predetermined transport path, and as shown in FIG. 4A, for example, amorphous fullerene or The amorphous fullerene derivative is deposited at a substrate temperature of 20 ° C. to 60 ° C. under a predetermined vacuum to form the intermediate layer 24. Thereby, the organic layer 30 in which the electron blocking layer 20, the photoelectric conversion layer 22, and the intermediate layer 24 are stacked in the stacking direction m is formed.

  Next, after transporting to the film formation chamber (not shown) of the counter electrode 26 through a predetermined transport path, as shown in FIG. 4B, the intermediate layer 24 and the photoelectric conversion layer 22 are covered, and the second layer The counter electrode 26 is formed in a pattern formed on the connection portion 46, for example, ITO is used as the counter electrode material, and a film thickness of 5 to 30 nm is formed under a predetermined vacuum using a sputtering method.

  Next, the insulating layer 14 is transferred to a film forming chamber (not shown) of the sealing layer 28 through a predetermined transfer path, and covers the entire surface 26a of the counter electrode 26 as shown in FIG. 4C. For example, an aluminum oxide layer is formed on the surface 14a as the sealing layer 28 by using an atomic layer deposition (ALD) method.

Next, the color filter 32, the partition wall 34, and the light shielding layer 36 are formed on the surface 28a of the sealing layer 28 by using, for example, a photolithography method. The color filter 32, the partition wall 34, and the light shielding layer 36 can be formed using the well-known thing used for an organic solid-state image sensor. The formation process of the color filter 32, the partition wall 34, and the light shielding layer 36 may be under non-vacuum.
Next, an overcoat layer 38 is formed using, for example, a coating method so as to cover the color filter 32, the partition wall 34, and the light shielding layer 36. Thereby, the image sensor 10 shown in FIG. 2A can be formed. In addition, the formation process of overcoat layer 38 may be under non-vacuum.

Even when the image sensor 10 is used, an external electric field can be applied. In this case, the pixel electrode 16 and the counter electrode 26 are a pair of electrodes, and an external electric field applied between the pair of electrodes in order to obtain excellent characteristics in photoelectric conversion efficiency, dark current, and optical response speed is 1 V / cm. It is preferably 1 × 10 ⁷ V / cm or less, more preferably 1 × 10 ⁴ V / cm or more and 1 × 10 ⁷ V / cm or less. Particularly preferably, it is 5 × 10 ⁴ V / cm or more and 1 × 10 ⁶ V / cm or less.
Also in the imaging element 10, by providing the intermediate layer 24 containing amorphous fullerene or an amorphous fullerene derivative, the photoelectric conversion efficiency can be increased and the dark current can be reduced. Moreover, photoelectric conversion efficiency can be improved by making the photoelectric converting layer 22 into the bulk hetero layer containing the crystallized fullerene or the crystallized fullerene derivative as mentioned above. Furthermore, dark current can be further suppressed by orienting the crystallized fullerene or crystallized fullerene derivative in the (111) direction as described above.

  The present invention is basically configured as described above. The photoelectric conversion element and the imaging element of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiment, and various improvements or modifications may be made without departing from the gist of the present invention. Of course.

Hereinafter, in the present invention, the effect of providing the intermediate layer will be specifically described.
In this example, the photoelectric conversion elements of Examples 1 to 16 and Comparative Examples 1 to 3 were prepared, and the dark current and the relative sensitivity were measured for the photoelectric conversion elements of Examples 1 to 16 and Comparative Examples 1 to 3. . The measurement results are shown in Table 2 below. The configuration of the photoelectric conversion element is the configuration shown in FIG. 1, and is the configuration of the lower electrode / electron blocking layer / photoelectric conversion layer / intermediate layer / upper electrode / sealing layer formed on the substrate.

For dark current, photoelectric conversion was measured using a source meter (Keithley 6430) in the state where an electric field of 2 × 10 ⁵ V / cm was applied to the upper electrode while the photoelectric conversion element was shielded from light. The value of the current of the element was a dark current.
About the relative sensitivity, the value of the external quantum efficiency in the maximum sensitivity wavelength when the electric field of 2 * 10 < ⁵ > V / cm was applied to each photoelectric conversion element of Examples 1-16 and Comparative Examples 1-3 was measured. The value of the external quantum efficiency of the photoelectric conversion element of Example 3 was set to 1, and the value representing the value of each external quantum efficiency was defined as the relative sensitivity.
The value of the external quantum efficiency is a current value obtained when an external electric field of 2 × 10 ⁵ V / cm is applied to the counter electrode and light having an intensity of 50 μW / cm ² is irradiated from the upper electrode side of the photoelectric conversion element. It is a value calculated from
Hereinafter, the photoelectric conversion elements of Examples 1 to 16 and Comparative Examples 1 to 3 will be described.

Example 1
In Example 1, the electron blocking layer, the photoelectric conversion layer, the intermediate layer, the upper electrode, and the sealing layer are formed in this order. The lower electrode is made of TiN. The electron blocking layer is formed by depositing an organic compound represented by Compound 1 with a thickness of 50 nm by vacuum deposition. The photoelectric conversion layer is a mixed film (compound 2: fullerene C ₆₀ = 1: 3 (volume ratio)) of an organic compound represented by compound 2 and fullerene C ₆₀ (denoted as C60 in Table 2 below) at a substrate temperature of 80 ° C. The film is formed with a film thickness of 400 nm by co-evaporation in vacuum. The intermediate layer is formed of fullerene C ₆₀ with a substrate temperature of 10 ° C. and a film thickness of 15 nm by vacuum deposition. All of the organic compounds were formed at a vacuum degree of 5.0 × 10 ⁻⁴ Pa or less and a deposition rate of 3 Å / s. The upper electrode was formed of ITO with a film thickness of 15 nm by DC sputtering. The sealing layer was formed of aluminum oxide with a thickness of 100 nm by atomic layer deposition.
Compound 1 has an ionization potential of 5.65 eV, and compound 2 has an ionization potential of 5.55 eV.

(Example 2)
As an intermediate layer, a mixed film of the organic compound represented by compound 2 and fullerene C ₆₀ (compound 2: fullerene C ₆₀ = 1: 2 (volume ratio)) was 15 nm by co-evaporation in vacuum at a substrate temperature of 30 ° C. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a thickness of.
(Example 3)
As an intermediate layer, a mixed film of the organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was 25 nm by co-evaporation in vacuum at a substrate temperature of 30 ° C. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a thickness of.
Example 4
As an intermediate layer, a mixed film of an organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was 20 nm by co-evaporation in vacuum at a substrate temperature of 30 ° C. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a thickness of.
(Example 5)
As an intermediate layer, a mixed film of the organic compound represented by Compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-deposited in a vacuum at a substrate temperature of 30 ° C. to 15 nm. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a thickness of.

(Example 6)
As an intermediate layer, a mixed film of the organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in a vacuum at a substrate temperature of 30 ° C. to 10 nm. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a thickness of.
(Example 7)
As an intermediate layer, a mixed film of the organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in vacuum at a substrate temperature of 30 ° C. to 5 nm. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a thickness of.
(Example 8)
As an intermediate layer, a mixed film of an organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in vacuum at a substrate temperature of 30 ° C. to 3 nm. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a thickness of.
Example 9
As an intermediate layer, a mixed film of an organic compound represented by compound 4 and fullerene C ₆₀ (compound 4: fullerene C ₆₀ = 1: 1 (volume ratio)) was 10 nm by co-evaporation in vacuum at a substrate temperature of 30 ° C. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a thickness of.

(Example 10)
As an intermediate layer, a mixed film of the organic compound represented by compound 4 and fullerene C ₆₀ (compound 4: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in a vacuum at a substrate temperature of 30 ° C. to 15 nm. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a thickness of.
(Example 11)
As an intermediate layer, a mixed film of an organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in a vacuum at a substrate temperature of 30 ° C. to a thickness of 20 nm. It is formed with a film thickness. A photoelectric conversion element was produced in the same manner as in Example 1 except that the ITO film was formed by DC sputtering as the upper electrode to a thickness of 20 nm.
(Example 12)
As an intermediate layer, a mixed film of an organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in vacuum at a substrate temperature of 30 ° C. It is formed with a film thickness. A photoelectric conversion element was produced in the same manner as in Example 1 except that the ITO film was formed by DC sputtering as the upper electrode to a thickness of 20 nm.
(Example 13)
As an intermediate layer, a mixed film of an organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in a vacuum at a substrate temperature of 30 ° C. to a thickness of 5 nm. It is formed with a film thickness. A photoelectric conversion element was produced in the same manner as in Example 1 except that the ITO film was formed by DC sputtering as the upper electrode to a thickness of 20 nm.

(Example 14)
A photoelectric conversion layer was formed by mixing a mixed film of an organic compound represented by Compound 2 and fullerene C ₆₀ (compound 2: fullerene C ₆₀ = 1: 3 (volume ratio)) at a substrate temperature of 130 ° C. by vacuum co-evaporation to 400 nm. The film thickness is formed. As an intermediate layer, a mixed film of an organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in vacuum at a substrate temperature of 30 ° C. A photoelectric conversion element was produced in the same manner as in Example 1 except that the ITO film was formed with a film thickness of 20 nm by DC sputtering as the upper electrode formed with a film thickness.
(Example 15)
A photoelectric conversion layer was formed by mixing a mixed film of an organic compound represented by Compound 2 and fullerene C ₆₀ (compound 2: fullerene C ₆₀ = 1: 3 (volume ratio)) at a substrate temperature of 130 ° C. by vacuum co-evaporation to 400 nm. The film thickness is formed. As an intermediate layer, a mixed film of an organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in a vacuum at a substrate temperature of 30 ° C. to a thickness of 5 nm. It is formed with a film thickness. A photoelectric conversion element was produced in the same manner as in Example 1 except that the ITO film was formed by DC sputtering as the upper electrode to a thickness of 20 nm.
(Example 16)
As a photoelectric conversion layer, a mixed film of an organic compound represented by compound 2 and fullerene C ₆₀ (compound 2: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in vacuum at a substrate temperature of 90 ° C. to 400 nm. The film thickness is formed. As an intermediate layer, a mixed film of an organic compound represented by compound 1 and fullerene C ₆₀ (compound 1: fullerene C ₆₀ = 1: 1 (volume ratio)) was co-evaporated in a vacuum at a substrate temperature of 30 ° C. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed with a film thickness.

(Comparative Example 1)
A photoelectric conversion element was produced in the same manner as in Example 1 except that the intermediate layer was not formed.
(Comparative Example 2)
Without forming an intermediate layer, the photoelectric conversion layer was formed by mixing a mixed film of an organic compound represented by compound 2 and fullerene C ₆₀ (compound 2: fullerene C ₆₀ = 1: 3 (volume ratio)) at a substrate temperature of 30 ° C. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed by vacuum evaporation in a thickness of 400 nm.
(Comparative Example 3)
Without forming an intermediate layer, the photoelectric conversion layer was formed by mixing a mixed film of an organic compound represented by compound 2 and fullerene C ₆₀ (compound 2: fullerene C ₆₀ = 1: 3 (volume ratio)) at a substrate temperature of 130 ° C. A photoelectric conversion element was produced in the same manner as in Example 1 except that the film was formed by vacuum evaporation in a thickness of 400 nm.

In this example, using an X-ray diffractometer (2θ-θ method), X-ray diffraction measurement of fullerene C ₆₀ and fullerene C ₆₀ mixed film formed under each condition is performed, and the presence or absence of crystallization is confirmed. It was. Here, fullerene C ₆₀ and fullerene C ₆₀ mixed film formed on the substrate were formed so that θ = 0 ° coincided with the horizontal direction of the substrate and θ = 90 ° coincided with the vertical direction with respect to the substrate. A sample was set.
If fullerene _{C 60} is crystallized, the diffraction pattern from (111) in the vicinity of 11 °, the diffraction pattern from (222) in the vicinity of 22 °, near 18 ° are diffraction patterns from (220) is observed. When fullerene C ₆₀ is (111) oriented, diffraction patterns from (111) and (222) are observed, but diffraction patterns from (220) are not observed. The evaluation results are shown in Table 1.

As shown in Table 2, fullerene C ₆₀ in the photoelectric conversion layer relative to Comparative Example 2 of amorphous, crystallized by being Examples 1 to 16 and Comparative Examples 1 and 3 was improved photoelectric conversion efficiency Yes. However, in Comparative Examples 1 and 3 having no intermediate layer, the dark current is greatly increased as compared with Examples 1 to 16.
Moreover, the comparative example 1 has a large dark current compared with Examples 2-10 in which the thickness of the upper electrode is the same. Comparative Example 3 has a larger dark current than Examples 14 and 15 of crystallization (no orientation). In Example 15, the dark current is smaller than that of Comparative Example 3 even if the thickness of the intermediate layer is less than 1/3 of the thickness of the upper electrode.

Compared to the first embodiment, the dark current is further reduced in the fifth embodiment. When comparing Examples 3 to 8, the thicker the intermediate layer, the lower the dark current, the more the result is obtained. No further reduction in dark current was obtained.
When the thickness of the intermediate layer is increased, the external voltage necessary for applying the same electric field strength to the photoelectric conversion element is increased. Therefore, it is desirable that the intermediate layer is thin as long as the effect of reducing the dark current is sufficiently obtained. It is desirable that the film thickness is smaller than
Also, in Examples 8 and 13, the dark current is higher than in Examples 5 and 11, and as a range in which the effect of lowering the dark current is sufficiently obtained, the film thickness of the intermediate layer is the film thickness of the upper electrode. A film thickness of 1/3 or more is desirable.
When Examples 5, 10 and 16 having the same structure of the upper electrode and the intermediate layer were compared, Example 16 had a higher proportion of crystallized fullerene C ₆₀ than Examples 5 and 10, but either dark current or relative sensitivity was observed. Was the same result.

DESCRIPTION OF SYMBOLS 10 Image sensor 12, 102 Board | substrate 14 Insulating layer 16 Pixel electrode 20, 106 Electron blocking layer 22, 108 Photoelectric conversion layer 24, 110 Intermediate layer 26 Counter electrode 28, 114 Sealing layer 40 Reading circuit 42 Counter electrode voltage supply part 44 1st 1 connection portion 46 second connection portion 100 photoelectric conversion element 104 lower electrode 112 upper electrode

Claims (8)

A lower electrode;
An electron blocking layer laminated on the lower electrode;
A photoelectric conversion layer laminated on the blocking layer;
An intermediate layer laminated on the photoelectric conversion layer;
An upper electrode laminated on the intermediate layer,
The photoelectric conversion layer is a bulk hetero layer in which a p-type organic semiconductor and a crystallized fullerene or a crystallized fullerene derivative are mixed,
The intermediate layer includes an amorphous fullerene or an amorphous fullerene derivative, and is a layer in which the amorphous fullerene or the amorphous fullerene derivative is mixed with a transparent hole transport material having an ionization potential of 5.5 eV or more. Yes,
The photoelectric conversion element, wherein the upper electrode is made of a transparent conductive film.   The photoelectric conversion layer is composed of a bulk hetero layer formed by mixing the p-type organic semiconductor and fullerene or crystallized fullerene derivative oriented in the (111) direction perpendicular to the surface of the lower electrode. Item 2. The photoelectric conversion element according to Item 1.   The photoelectric conversion element according to claim 1, wherein the photoelectric conversion layer contains a crystallized fullerene or a crystallized fullerene derivative at a ratio of 30% to 80%.   The photoelectric conversion element according to claim 1, wherein a thickness of the intermediate layer is 1/3 or more of a thickness of the upper electrode.   The photoelectric conversion element according to claim 1, wherein a thickness of the intermediate layer is equal to or less than a thickness of the upper electrode.   The photoelectric conversion element according to claim 1, wherein the intermediate layer further includes at least one organic material. The upper electrode is composed of ITO, a photoelectric conversion device according to any one of the preceding claims 1 to 6 the thickness of the upper electrode is 5 to 30 nm. Imaging device characterized by having a photoelectric conversion device according to any one of claims 1-7.