Photodetection element and image sensor

Abstract

A photodetection element (1) comprises a first electrode (11), a second electrode (12), a photoelectric conversion layer (13) provided between the first electrode (11) and the second electrode (12), and an electron transport layer (21) provided between the first electrode (11) and the photoelectric conversion layer (13). The photoelectric conversion layer (13) includes: an aggregate of semiconductor quantum dots containing elemental In and group 15 elements; and ligands coordinating to the semiconductor quantum dots. The group 15 elements include elemental Sb. The electron transport layer (21) contains titanium oxide and has a thickness of 5-500 nm. An image sensor according to the present invention includes the aforementioned photodetection element.

Description

Photodetectors and image sensors

[0001] The present invention relates to a photodetector and an image sensor having a photoelectric conversion layer containing semiconductor quantum dots.

[0002] In recent years, photodetectors capable of detecting light in the infrared region have been attracting attention in the fields of smartphones, surveillance cameras, in-vehicle cameras, and the like.

[0003] Conventionally, silicon photodiodes, which use silicon wafers as the material for the photoelectric conversion layer, have been used as photodetectors for image sensors, etc. However, silicon photodiodes have low sensitivity in the infrared region with wavelengths of 900 nm or more.

[0004] Furthermore, InGaAs-based semiconductor materials, which are known as near-infrared light receiving elements, have the problem of requiring very costly processes, such as epitaxial growth and substrate bonding processes, to achieve high quantum efficiency, and this has prevented them from becoming widely used.

[0005] In recent years, the use of quantum dots in photoelectric conversion elements has also been considered. For example, Patent Document 1 describes the use of PbS quantum dots in the photoelectric conversion layer of a photoelectric conversion element.

[0006] Japanese Patent Application Laid-Open No. 2020-150251

[0007] In recent years, with the demand for improved performance of image sensors and the like, further improvements are being required in the characteristics of the photodetectors used in these devices. For example, among the characteristics required of a photodetector are a high external quantum efficiency for the light of the target wavelength to be detected by the photodetector, low dark current, and excellent in-plane uniformity of the dark current. Increasing the external quantum efficiency of a photodetector can improve the light detection accuracy of the photodetector. Furthermore, reducing the dark current of a photodetector can achieve a higher signal-to-noise ratio (SN ratio) in an image sensor. Note that dark current refers to the current that flows when no light is irradiated.

[0008] The present inventors have conducted further studies on a photodetector element using semiconductor quantum dots containing In and a Group 15 element in a photoelectric conversion layer, and have found that there is room for further improvement in these characteristics.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a photodetector and an image sensor that have high external quantum efficiency, low dark current, and excellent in-plane uniformity of the dark current.

[0010] The present invention provides the following: <1> A photodetector comprising: a first electrode; a second electrode; a photoelectric conversion layer provided between the first electrode and the second electrode; and an electron transport layer provided between the first electrode and the photoelectric conversion layer, wherein the photoelectric conversion layer comprises an aggregate of semiconductor quantum dots containing In and a Group 15 element and ligands coordinated to the semiconductor quantum dots, the Group 15 element including Sb, and the electron transport layer comprises titanium oxide, and the electron transport layer has a thickness of 5 to 500 nm. <2> The photodetector according to <1>, wherein the semiconductor quantum dots contain In, Sb, and P. <3> The photodetector according to <1> or <2>, wherein the electron transport layer has a thickness of 10 to 200 nm. <4> The photodetector according to any one of <1> to <3>, wherein the semiconductor quantum dots have a molar ratio of In element to Group 15 element of 1.00 to 1.70. <5> The photodetector according to any one of <1> to <4>, wherein the semiconductor quantum dots have a band gap of 1.0 eV or less. <6> The photodetector according to any one of <1> to <5>, wherein the photoelectric conversion layer has a thickness of 50 to 500 nm. <7> The photodetector according to any one of <1> to <6>, wherein the ligand contains a halogen element or a sulfur element. <8> An image sensor including the photodetector according to any one of <1> to <7>.

[0011] According to the present invention, it is possible to provide a photodetector and an image sensor that have high external quantum efficiency, low dark current, and excellent in-plane uniformity of the dark current.

[0012] FIG. 2 illustrates an embodiment of a photodetector element.

[0013] The present invention will be described in detail below. In this specification, the term "to" is used to mean that the numerical values ​​before and after it are included as the lower and upper limits. In the description of groups (atomic groups) in this specification, a notation that does not specify whether they are substituted or unsubstituted includes both groups (atomic groups) that have no substituents and groups (atomic groups) that have substituents. For example, the term "alkyl group" includes not only alkyl groups that have no substituents (unsubstituted alkyl groups) but also alkyl groups that have substituents (substituted alkyl groups).

[0014] <Photodetector> The photodetector of the present invention comprises: a first electrode; a second electrode; a photoelectric conversion layer provided between the first electrode and the second electrode; and an electron transport layer provided between the first electrode and the photoelectric conversion layer, wherein the photoelectric conversion layer contains an aggregate of semiconductor quantum dots containing In and a Group 15 element, and ligands coordinated to the semiconductor quantum dots, the Group 15 element containing Sb, and the electron transport layer contains titanium oxide, and has a thickness of 5 to 500 nm.

[0015] The photodetector element of the present invention has the above-described configuration, and thus can be a photodetector element having high external quantum efficiency, low dark current, and excellent in-plane uniformity of the dark current. It is presumed that this is because, in the photodetector element having the above-described photoelectric conversion layer, the electron transport layer contains titanium oxide and has a thickness of 5 to 500 nm, which suppresses reaction between the photoelectric conversion layer and the electron transport layer, suppresses leakage current from the current, and enables efficient transport of electrons generated in the photoelectric conversion layer to the electrode.

[0016] The photodetector element of the present invention will be described in detail below with reference to FIG. 1 . FIG. 1 is a diagram illustrating one embodiment of a photodiode-type photodetector element. The arrows in the diagram indicate incident light on the photodetector element. The photodetector element 1 illustrated in FIG. 1 includes a second electrode 12, a first electrode 11 disposed opposite the second electrode 12, a photoelectric conversion layer 13 disposed between the second electrode 12 and the first electrode 11, an electron transport layer 21 disposed between the first electrode 11 and the photoelectric conversion layer 13, and a hole transport layer 22 disposed between the second electrode 12 and the photoelectric conversion layer 13. The photodetector element 1 illustrated in FIG. 1 is used so that light is incident from above the first electrode 11. Although not illustrated, a transparent substrate may be disposed on the light-incident surface of the first electrode 11. Examples of transparent substrates include glass substrates, resin substrates, and ceramic substrates.

[0017] (First Electrode) The first electrode 11 is preferably a transparent electrode formed of a conductive material that is substantially transparent to the wavelength of light to be detected by the photodetector. In this specification, "substantially transparent" means that the light transmittance is 50% or more, preferably 60% or more, and more preferably 80% or more. Examples of materials for the first electrode 11 include conductive metal oxides. Specific examples include tin oxide, zinc oxide, indium oxide, indium tungsten oxide, indium zinc oxide (IZO), indium tin oxide (ITO), and fluorine-doped tin oxide (FTO).

[0018] The film thickness of the first electrode 11 is not particularly limited, but is preferably 0.01 to 100 μm, more preferably 0.01 to 10 μm, and even more preferably 0.01 to 1 μm. The film thickness of each layer can be measured by observing a cross section of the photodetector element 1 using a scanning electron microscope (SEM) or the like.

[0019] (Electron Transport Layer) The electron transport layer 21 is a layer having a function of transporting electrons generated in the photoelectric conversion layer 13 to the electrode. The electron transport layer is also called a hole blocking layer.

[0020] In the photodetector of the present invention, the electron transport layer 21 is made of a material containing titanium oxide. The electron transport layer 21 is preferably a titanium oxide film. The titanium oxide film can be formed by a method such as sputtering, chemical vapor deposition (CVD), or vacuum deposition.

[0021] The thickness of the electron transport layer is 5 to 500 nm, preferably 10 to 200 nm, and more preferably 10 to 100 nm, because this allows for a photodetector element with higher external quantum efficiency and better in-plane uniformity of dark current. The thickness of the electron transport layer is preferably 0.05 to 10 times, more preferably 0.1 to 5 times, and even more preferably 0.2 to 2 times the thickness of the photoelectric conversion layer 13.

[0022] (Photoelectric conversion layer) The photoelectric conversion layer 13 is composed of an aggregate of semiconductor quantum dots containing In element and a Group 15 element, and a ligand that coordinates to the semiconductor quantum dots. More specifically, the photoelectric conversion layer 13 is composed of a semiconductor film that contains an aggregate of semiconductor quantum dots containing In element and a Group 15 element, and a ligand that coordinates to the semiconductor quantum dots. The Group 15 element in the semiconductor quantum dots includes Sb element. The aggregate of semiconductor quantum dots refers to a large number (for example, 1 μm ２ In this specification, the term "semiconductor" refers to a semiconductor having a resistivity of 10 －２ Ωcm or more 10 ８ This refers to a substance with a resistivity of Ωcm or less.

[0023] Examples of semiconductor quantum dot materials that constitute semiconductor quantum dots include compound semiconductors containing In and a Group 15 element. A compound semiconductor is a semiconductor composed of two or more elements. Therefore, in this specification, a "compound semiconductor containing In and a Group 15 element" refers to a compound semiconductor that contains In and a Group 15 element as constituent elements of the compound semiconductor.

[0024] It is preferable that the Group 15 element further includes P. That is, it is preferable that the semiconductor quantum dots include In, Sb, and P. According to this embodiment, dark current can be further suppressed.

[0025] In the semiconductor quantum dots, the molar ratio of In element to the molar amount of the Group 15 element is preferably 1.00 to 1.70. The upper limit is preferably 1.50 or less. The lower limit is preferably 1.20 or more.

[0026] When the semiconductor quantum dots contain In, Sb, and P, the ratio of the molar amount of In to the sum of the molar amounts of Sb and P is preferably 1.00 to 1.70. The upper limit is preferably 1.50 or less. The lower limit is preferably 1.20 or more. Furthermore, the ratio of the molar amount of P to the molar amount of Sb is preferably 0.20 to 0.90, more preferably 0.20 to 0.80, and even more preferably 0.20 to 0.60.

[0027] In this specification, the "ratio of the molar amount of In element to the molar amount of Group 15 element," "ratio of the molar amount of In element to the sum of the molar amounts of Sb element and P element," and "ratio of the molar amount of P element to the molar amount of Sb element" for semiconductor quantum dots can be calculated by measuring the element composition ratio by X-ray photoelectron spectroscopy.

[0028] The "ratio of the molar amount of In element to the molar amount of Group 15 element," "ratio of the molar amount of In element to the sum of the molar amounts of Sb element and P element," and "ratio of the molar amount of P element to the molar amount of Sb element" for semiconductor quantum dots can be adjusted by changing the reaction ratio of each raw material during synthesis of the semiconductor quantum dots, reaction conditions, etc.

[0029] The band gap of the semiconductor quantum dots is preferably 1.2 eV or less, more preferably 1.0 eV or less. The lower limit of the band gap of the semiconductor quantum dots is not particularly limited, but is preferably 0.3 eV or more, more preferably 0.5 eV or more.

[0030] The average primary particle diameter of the semiconductor quantum dots is preferably 3 to 10 nm. The lower limit is preferably 4 nm or more. The upper limit is preferably 8 nm or less. In this specification, the average primary particle diameter of the semiconductor quantum dots is the average (arithmetic mean) of the equivalent circle diameters of the primary particles of 500 randomly selected semiconductor quantum dots. The equivalent circle diameter of the primary particle of the semiconductor quantum dots is determined by measuring the particle area S of one particle in an electron micrograph taken with a transmission electron microscope, and calculating the diameter of a perfect circle corresponding to this area S (equivalent circle diameter = 2(S / π) ０．５ The particle size of the semiconductor quantum dots can be measured by diluting a dispersion of the semiconductor quantum dots with a non-polar solvent, dropping it onto a microgrid, and then drying the film formed, and measuring the film using a transmission electron microscope.

[0031] The crystal structure of the semiconductor quantum dots is not particularly limited, but is preferably a cubic or hexagonal crystal structure because it is easy to achieve high crystallinity. The crystal structure of the semiconductor quantum dots can be measured by X-ray diffraction or electron beam diffraction.

[0032] The semiconductor quantum dots of the present invention may further contain elements other than In, Sb, and P. Examples of other elements include Mg, Ca, Sr, Ba, Zn, Cd, Hg, B, Al, Ga, N, As, and Bi.

[0033] Specific examples of semiconductor quantum dots include InSb and InSbP. The semiconductor quantum dots may have a core-shell structure including a core containing In and Sb and a shell containing P that covers the core. Examples of the core containing In and Sb include InSb.

[0034] The photoelectric conversion layer includes a ligand that is coordinated to the semiconductor quantum dots. The ligand may be an organic ligand or an inorganic ligand.

[0035] The organic ligand may be a monodentate organic ligand having one coordination moiety, or a polydentate organic ligand having two or more coordination moieties. Examples of the coordination moiety contained in the organic ligand include a thiol group, an amino group, a hydroxyl group, a carboxyl group, a sulfo group, a phospho group, and a phosphonic acid group.

[0036] The polydentate ligand may be a ligand represented by any one of formulas (A) to (C).

[0037] In formula (A), X Ａ１ and X Ａ２ each independently represents a thiol group, an amino group, a hydroxy group, a carboxy group, a sulfo group, a phospho group, or a phosphonic acid group; L Ａ１ represents a hydrocarbon group.

[0038] In formula (B), X Ｂ１ and X Ｂ２ each independently represents a thiol group, an amino group, a hydroxy group, a carboxy group, a sulfo group, a phospho group, or a phosphonic acid group; Ｂ３ represents S, O or NH; L Ｂ１ and L Ｂ２ each independently represents a hydrocarbon group.

[0039] In formula (C), XＣ１ ~X Ｃ３ each independently represents a thiol group, an amino group, a hydroxy group, a carboxy group, a sulfo group, a phospho group, or a phosphonic acid group; Ｃ４ represents N, and L Ｃ１ ~L Ｃ３ each independently represents a hydrocarbon group.

[0040] X Ａ１ , X Ａ２ , X Ｂ１ , X Ｂ２ , X Ｃ１ , X Ｃ２ and X Ｃ３ The amino group represented by is -NH ２ The amino group is not limited to the above, and also includes a substituted amino group and a cyclic amino group. Examples of the substituted amino group include a monoalkylamino group, a dialkylamino group, a monoarylamino group, a diarylamino group, and an alkylarylamino group. The amino group represented by these groups includes -NH ２ , a monoalkylamino group, or a dialkylamino group is preferred, and —NH ２ It is more preferable that:

[0041] X in formula (A) Ａ１ and X Ａ２ At least one of the groups is preferably a thiol group. The other may be a thiol group or a group other than a thiol group. The group other than a thiol group is preferably a carboxy group, an amino group, or a hydroxy group.

[0042] X in formula (B) Ｂ１ and X Ｂ２ At least one of the groups is preferably a thiol group. The other may be a thiol group or a group other than a thiol group. The group other than a thiol group is preferably a carboxy group, an amino group, or a hydroxy group.

[0043] X in formula (C) Ｃ１ ~X Ｃ３ At least one of the groups is preferably a thiol group. The other may be a thiol group or a group other than a thiol group. The group other than a thiol group is preferably a carboxy group, an amino group, or a hydroxy group.

[0044] L Ａ１ , L Ｂ１ , L Ｂ２ , L Ｃ１ , L Ｃ２ and L Ｃ３ The hydrocarbon group represented by is preferably an aliphatic hydrocarbon group or a group containing an aromatic ring, and more preferably an aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. The hydrocarbon group preferably has 1 to 20 carbon atoms. The upper limit of the carbon number is preferably 10 or less, more preferably 6 or less, and even more preferably 3 or less. Specific examples of the hydrocarbon group include an alkylene group, an alkenylene group, an alkynylene group, and an arylene group.

[0045] Examples of the alkylene group include a linear alkylene group, a branched alkylene group, and a cyclic alkylene group, and are preferably a linear alkylene group or a branched alkylene group, and more preferably a linear alkylene group. Examples of the alkenylene group include a linear alkenylene group, a branched alkenylene group, and a cyclic alkenylene group, and are preferably a linear alkenylene group or a branched alkenylene group, and more preferably a linear alkenylene group. Examples of the alkynylene group include a linear alkynylene group and a branched alkynylene group, and are preferably a linear alkynylene group. The arylene group may be monocyclic or polycyclic. A monocyclic arylene group is preferred. Specific examples of the arylene group include a phenylene group and a naphthylene group, and are preferably a phenylene group. The alkylene group, alkenylene group, alkynylene group, and arylene group may further have a substituent. The substituent is preferably a group having 1 to 10 atoms. Specific preferred examples of the group having 1 to 10 atoms include alkyl groups having 1 to 3 carbon atoms [methyl, ethyl, propyl, and isopropyl], alkenyl groups having 2 to 3 carbon atoms [ethenyl and propenyl], alkynyl groups having 2 to 4 carbon atoms [ethynyl, propynyl, etc.], cyclopropyl groups, alkoxy groups having 1 to 2 carbon atoms [methoxy and ethoxy], acyl groups having 2 to 3 carbon atoms [acetyl and propionyl], alkoxycarbonyl groups having 2 to 3 carbon atoms [methoxycarbonyl and ethoxycarbonyl], acyloxy groups having 2 carbon atoms [acetyloxy], Examples of such an alkyl group include an acylamino group (acetylamino group), a hydroxyalkyl group having 1 to 3 carbon atoms (hydroxymethyl group, hydroxyethyl group, hydroxypropyl group), an aldehyde group, a hydroxy group, a carboxy group, a sulfo group, a phospho group, a carbamoyl group, a cyano group, an isocyanate group, a thiol group, a nitro group, a nitroxy group, an isothiocyanate group, a cyanate group, a thiocyanate group, an acetoxy group, an acetamido group, a formyl group, a formyloxy group, a formamido group, a sulfamino group, a sulfino group, a sulfamoyl group, a phosphono group, an acetyl group, a halogen atom, and an alkali metal atom.

[0046] In formula (A), X Ａ１and X Ａ２ Is L Ａ１ Preferably, they are separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, even more preferably by 1 to 4 atoms, even more preferably by 1 to 3 atoms, and particularly preferably by 1 or 2 atoms.

[0047] In formula (B), X Ｂ１ and X Ｂ３ Is L Ｂ１ Preferably, they are separated by 1 to 10 atoms, more preferably 1 to 6 atoms, even more preferably 1 to 4 atoms, still more preferably 1 to 3 atoms, and particularly preferably 1 or 2 atoms. Ｂ２ and X Ｂ３ Is L Ｂ２ Preferably, they are separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, even more preferably by 1 to 4 atoms, even more preferably by 1 to 3 atoms, and particularly preferably by 1 or 2 atoms.

[0048] In formula (C), X Ｃ１ and X Ｃ４ Is L Ｃ１ Preferably, they are separated by 1 to 10 atoms, more preferably 1 to 6 atoms, even more preferably 1 to 4 atoms, still more preferably 1 to 3 atoms, and particularly preferably 1 or 2 atoms. Ｃ２ and X Ｃ４ Is L Ｃ２ Preferably, they are separated by 1 to 10 atoms, more preferably 1 to 6 atoms, even more preferably 1 to 4 atoms, still more preferably 1 to 3 atoms, and particularly preferably 1 or 2 atoms. Ｃ３ and X Ｃ４ Is L Ｃ３Preferably, they are separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, even more preferably by 1 to 4 atoms, even more preferably by 1 to 3 atoms, and particularly preferably by 1 or 2 atoms.

[0049] In addition, X Ａ１ and X Ａ２ Is L Ａ１ The term "separated by 1 to 10 atoms" means that X Ａ１ and X Ａ２ This means that the number of atoms constituting the molecular chain with the shortest distance connecting X is 1 to 10. For example, in the case of the following formula (A1), X Ａ１ and X Ａ２ and are separated by two atoms, and in the case of the following formula (A2) and formula (A3), X Ａ１ and X Ａ２ The numbers in the following structural formulas represent X Ａ１ and X Ａ２ It represents the order of the arrangement of atoms that make up the shortest molecular chain connecting the

[0050] To explain this by taking a specific compound, 3-mercaptopropionic acid is X Ａ１ The site corresponding to X is a carboxyl group. Ａ２ The site corresponding to is a thiol group, and L Ａ１ In 3-mercaptopropionic acid, the site corresponding to X is an ethylene group (compound with the following structure). Ａ１ (carboxy group) and X Ａ２ (thiol group) and L Ａ１ (ethylene group) separates them by two atoms.

[0051] X Ｂ１ and X Ｂ３ Is L Ｂ１ are separated by 1 to 10 atoms, Ｂ２ and X Ｂ３ Is L Ｂ２ are separated by 1 to 10 atoms, Ｃ１ and X Ｃ４ Is L Ｃ１ are separated by 1 to 10 atoms,Ｃ２ and X Ｃ４ Is L Ｃ２ are separated by 1 to 10 atoms, Ｃ３ and X Ｃ４ Is L Ｃ３ The meaning of being separated by 1 to 10 atoms is the same as above.

[0052] Specific examples of the polydentate ligand include 3-mercaptopropionic acid, thioglycolic acid, 2-aminoethanol, 2-aminoethanethiol, 2-mercaptoethanol, glycolic acid, ethylene glycol, ethylenediamine, aminosulfonic acid, glycine, aminomethylphosphate, guanidine, diethylenetriamine, tris(2-aminoethyl)amine, 4-mercaptobutanoic acid, 3-aminopropanol, 3-mercaptopropanol, N-(3-aminopropyl)-1,3-propanediamine, 3-(bis(3-aminopropyl)amino)propan-1-ol, 1-thioglycerol, dimercaprol, 1-mercapto-2-butanol, 1-mercapto-2-pentanol, 3-mercapto-1-propanol, 2,3-dimercapto-1-propanol, diethanolamine, 2-(2 2-[(2-aminoethyl)amino]ethanethiol, bis(2-mercaptoethyl)amine, 2-aminoethane-1-thiol, 1-amino-2-butanol, 1-amino-2-pentanol, L-cysteine, D-cysteine, 3-amino-1-propanol, L-homoserine, D-homoserine, aminohydroxyacetic acid, L-lactic acid, D-lactic acid, L-malic acid, D-malic acid, glyceric acid, 2-hydroxybutyric acid, L-tartaric acid, D-tartaric acid, tartronic acid, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 2-mercaptobenzoic acid, 3-mercaptobenzoic acid, 4-mercaptobenzoic acid, and derivatives thereof.

[0053] The inorganic ligand is preferably an inorganic ligand containing a halogen element. Inorganic ligands containing a halogen element are easily coordinated to semiconductor quantum dots, and can suppress the occurrence of surface defects. The inorganic ligand is also preferably an inorganic ligand containing an In element. Inorganic ligands containing an In element are thought to be easily coordinated to the Sb site of semiconductor quantum dots, and can further suppress the occurrence of surface defects. For reasons such as a photodetector having lower dark current, higher external quantum efficiency, and better in-plane uniformity of dark current, the ligands contained in the photoelectric conversion layer preferably include inorganic ligands each containing a halogen element and an In element.

[0054] Examples of the halogen element contained in the inorganic ligand include a fluorine element, a chlorine element, a bromine element, and an iodine element, and a bromine element is preferred.

[0055] Specific examples of inorganic ligands include zinc iodide, zinc bromide, zinc chloride, indium iodide, indium bromide, indium chloride, cadmium iodide, cadmium bromide, cadmium chloride, gallium iodide, gallium bromide, gallium chloride, tetrabutylammonium iodide, tetramethylammonium iodide, and ammonium sulfide, with indium bromide being preferred.

[0056] In the case of inorganic ligands containing halogen elements, halogen ions may dissociate from the inorganic ligands and be coordinated to the surface of the semiconductor quantum dots. Furthermore, a portion of the inorganic ligand other than the halogen atom may also be coordinated to the surface of the semiconductor quantum dots. To give a specific example, in the case of indium bromide, the indium bromide may be coordinated to the surface of the semiconductor quantum dots, or bromine ions or indium ions may be coordinated to the surface of the semiconductor quantum dots.

[0057] The ligand contained in the photoelectric conversion layer preferably contains a halogen element or a sulfur element, and more preferably contains both a halogen element-containing ligand and a sulfur element-containing ligand, because this allows for a photodetector with higher external quantum efficiency. The halogen element-containing ligand is preferably an inorganic ligand containing a halogen element. The sulfur element-containing ligand is preferably an organic ligand having a thiol group, and more preferably a multidentate organic ligand having a thiol group. Examples of the multidentate organic ligand having a thiol group include ligands represented by any of the above formulas (A) to (C).

[0058] The total content of the semiconductor quantum dots and the ligands in the photoelectric conversion layer 13 is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0059] The film thickness of the photoelectric conversion layer 13 is preferably 50 to 500 nm. The lower limit of the film thickness is preferably 100 nm or more. The upper limit of the film thickness is preferably 450 nm or less. The refractive index of the photoelectric conversion layer 13 for light of the target wavelength to be detected by the photodetector element can be 1.5 to 5.0.

[0060] (Hole Transport Layer) The hole transport layer 22 is a layer having a function of transporting holes generated in the photoelectric conversion layer 13 to the electrode. The hole transport layer is also called an electron blocking layer.

[0061] The hole transport layer 22 is formed of a hole transport material that can perform this function. For example, hole transport materials include PEDOT:PSS (a composite of poly(3,4-ethylenedioxythiophene) and poly(4-styrenesulfonic acid)), PTB7 (poly{4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-lt-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl] ... thieno[3,4-b]thiophene-4,6-diyl}), PTB7-Th (poly([2,6'-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]{3-fluoro-2[(2-ethylhexyl-1)carbonyl]thieno[3,4-b]thiophenediyl})), poly(3-hexylthiophene-2,5-diyl), poly(3-n- octyloxythiophene), poly(9,9'-dioctyl-fluorene-co-bithiophene), poly(3,3''-didodecyl-quaterthiophene), poly(3,6-dioctylthieno[3,2-b]thiophene), poly(2,5-bis(3-decylthiophen-2-yl)thieno[3,2-b]thiophene), poly(3,4-didecylthiophene-co-thieno[3,2-b]thiophene), poly(3,6-dioctylthieno[3,2-b]thiophene-co-thieno[3,2-b]thiophene), poly(3,6-dioctylthieno[3,2-b]thiophene-co-thiophene), poly(3,6-dioctylthieno[3,2-b]thiophene-co-bithiophene), PC71BM ([6,6]-phenyl-C71-methylbutyrate), N ２ , N ２ , N ２’ , N ２’ , N ７ , N ７ , N ７’ , N ７’-octakis(4-methoxyphenyl)-9,9'-spirobi[9H-fluorene]-2,2',7,7'-tetraamine (Spiro-OMeTAD). Organic hole transport materials such as those described in paragraphs 0209 to 0212 of JP-A-2001-291534 can also be used. Semiconductor quantum dots can also be used as the hole transport material. Examples of semiconductor quantum dot materials that constitute semiconductor quantum dots include nanoparticles (particles with a size of 0.5 nm or more and less than 100 nm) of common semiconductor crystals: a) Group IV semiconductors, b) Group IV-IV, III-V, or II-VI compound semiconductors, and c) compound semiconductors formed from a combination of three or more of Group II, III, IV, V, and VI elements. Specifically, PbS, PbSe, PbSeS, InN, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, HgTe, HgCdTe, Ag ２ S, Ag ２ Se, Ag ２ Examples of such semiconductor materials include Te, SnS, SnSe, SnTe, Si, InP, etc. Ligands may be coordinated to the surface of the semiconductor quantum dots.

[0062] The thickness of the hole transport layer 22 is preferably 5 to 100 nm. The lower limit is preferably 10 nm or more. The upper limit is preferably 50 nm or less, and more preferably 30 nm or less.

[0063] (Second Electrode) The second electrode 12 is preferably composed of a metal material containing at least one metal atom selected from Ag, Au, Pt, Ir, Pd, Cu, Pb, Sn, Zn, Ti, W, Mo, Ta, Ge, Ni, Al, Cr, and In. By using such a metal material for the second electrode 12, a photodetector element with high external quantum efficiency and low dark current can be obtained. The second electrode 12 can also be made of the above-mentioned conductive metal oxides, carbon materials, conductive polymers, and the like. The carbon material may be any conductive material, such as fullerene, carbon nanotube, graphite, and graphene.

[0064] The work function of the second electrode 12 is preferably 4.6 eV or more, more preferably 4.8 to 5.7 eV, and even more preferably 4.9 to 5.3 eV, for the reasons that this enhances the electron blocking property of the hole transport layer and makes it easy to collect holes generated in the device.

[0065] The film thickness of the second electrode 12 is not particularly limited, but is preferably 0.01 to 100 μm, more preferably 0.01 to 10 μm, and even more preferably 0.01 to 1 μm.

[0066] (Charge Extraction Layer) Although not shown, the photodetector of the present invention may have a charge extraction layer between the second electrode 12 and the hole transport layer 22. By having the charge extraction layer, high external quantum efficiency can be obtained at a low applied voltage.

[0067] Materials for forming the charge extraction layer include metal oxides and organic semiconductors, with metal oxides being preferred. Metal oxides include molybdenum oxide, titanium oxide, vanadium oxide, chromium oxide, cobalt oxide, nickel oxide, copper oxide, zirconium oxide, molybdenum oxide, silver oxide, tantalum oxide, and tungsten oxide, with molybdenum oxide being preferred. Organic semiconductors include polythiophene compounds, with the materials mentioned above being specific examples of polythiophene compounds. The charge extraction layer may be a single-layer film or a laminated film of two or more layers.

[0068] The thickness of the charge extraction layer is preferably 1 to 100 nm, with the lower limit being preferably 5 nm or more and the upper limit being preferably 50 nm or less.

[0069] (Blocking Layer) Although not shown, the photodetector element may have a blocking layer between the first electrode 11 and the electron transport layer 21. The blocking layer has the function of preventing reverse current. The blocking layer is also called a short-circuit prevention layer. Examples of materials that form the blocking layer include silicon oxide, magnesium oxide, aluminum oxide, calcium carbonate, cesium carbonate, polyvinyl alcohol, polyurethane, tin oxide, niobium oxide, and tungsten oxide. The blocking layer may be a single-layer film or a laminated film of two or more layers. The film thickness of the blocking layer is preferably 5 to 100 nm. The lower limit is preferably 10 nm or more. The upper limit is preferably 50 nm or less, and more preferably 30 nm or less.

[0070] In the photodetector of the present invention, the wavelength λ of light to be detected by the photodetector is determined by the optical path length L of the light having the wavelength λ from the surface of the second electrode 12 on the photoelectric conversion layer 13 side to the surface of the photoelectric conversion layer 13 on the first electrode 11 side. λ and preferably satisfy the relationship of the following formula (1-1), and more preferably satisfy the relationship of the following formula (1-2): λ When these relationships are satisfied, the phases of the light incident from the first electrode 11 side (incident light) and the light reflected from the surface of the second electrode 12 (reflected light) can be aligned in the photoelectric conversion layer 13, and as a result, the light is reinforced by the optical interference effect, thereby achieving a higher external quantum efficiency.

[0071] 0.05+m / 2≦L λ / λ≦0.35+m / 2 ... (1-1) 0.10+m / 2≦L λ / λ≦0.30+m / 2 ... (1-2)

[0072] In the above formula, λ is the wavelength of the light to be detected by the light detection element, and L λ is the optical path length of light of wavelength λ from the surface of the second electrode 12 on the photoelectric conversion layer 13 side to the surface of the photoelectric conversion layer 13 on the first electrode 11 side, and m is an integer of 0 or more.

[0073] m is preferably an integer of 0 to 4, more preferably an integer of 0 to 3, and even more preferably an integer of 0 to 2. According to this embodiment, the transport properties of charges such as holes and electrons are good, and the external quantum efficiency of the photodetector can be further increased.

[0074] Here, the optical path length means the product of the physical thickness of the material through which light passes and the refractive index. Taking the photoelectric conversion layer 13 as an example, the thickness of the photoelectric conversion layer is d １ , the wavelength λ of the photoelectric conversion layer １ The refractive index of the light is N １ When the wavelength λ transmitted through the photoelectric conversion layer 13 is １ The optical path length of the light is N １ ×d １ When the photoelectric conversion layer 13 or the hole transport layer 22 is formed of a laminated film of two or more layers, or when another layer is present between the hole transport layer 22 and the second electrode 12, the integrated value of the optical path lengths of the respective layers is the optical path length L λ is.

[0075] The photodetector of the present invention is preferably used as a photodetector for detecting light having a wavelength in the infrared region, that is, the photodetector of the present invention is preferably an infrared light detecting element.

[0076] The light to be detected by the photodetector of the present invention is preferably light having a wavelength in the infrared region. Furthermore, the light having a wavelength in the infrared region is preferably light having a wavelength of more than 700 nm, more preferably light having a wavelength of 800 nm or more, and even more preferably light having a wavelength of 900 nm or more. Furthermore, the light having a wavelength in the infrared region is preferably light having a wavelength of 3000 nm or less, more preferably light having a wavelength of 2000 nm or less, and even more preferably light having a wavelength of 1600 nm or less.

[0077] The photodetector of the present invention may simultaneously detect light having a wavelength in the infrared region and light having a wavelength in the visible region (preferably light having a wavelength in the range of 400 to 700 nm).

[0078] <Image Sensor> The image sensor of the present invention includes the photodetector element of the present invention described above. Since the photodetector element of the present invention has excellent sensitivity to light with wavelengths in the infrared region, this image sensor can be particularly preferably used as an infrared sensor. Furthermore, the image sensor can be preferably used to sense light with a wavelength of 900 to 3000 nm, more preferably used to sense light with a wavelength of 900 to 2000 nm, and even more preferably used to sense light with a wavelength of 900 to 1600 nm.

[0079] The configuration of the image sensor is not particularly limited as long as it has a photodetection element and functions as an image sensor.

[0080] The image sensor may include an infrared-transmitting filter layer, which preferably has low transmittance for light in the visible wavelength range, and more preferably has an average transmittance of 10% or less, even more preferably 7.5% or less, and particularly preferably 5% or less for light in the wavelength range of 400 to 650 nm.

[0081] The infrared transmission filter layer may be formed of a resin film containing a colorant. Examples of the colorant include chromatic colorants such as red, green, blue, yellow, purple, and orange, as well as black colorants. The colorant contained in the infrared transmission filter layer preferably comprises a combination of two or more chromatic colorants to form a black color, or a black colorant. Examples of combinations of chromatic colorants when a black color is formed by combining two or more chromatic colorants include the following (C1) to (C7): (C1) A configuration containing a red colorant and a blue colorant; (C2) A configuration containing a red colorant, a blue colorant, and a yellow colorant; (C3) A configuration containing a red colorant, a blue colorant, a yellow colorant, and a purple colorant; (C4) A configuration containing a red colorant, a blue colorant, a yellow colorant, a purple colorant, and a green colorant; and (C5) A configuration containing a red colorant, a blue colorant, a yellow colorant, and a green colorant. (C6) An embodiment containing a red color material, a blue color material, and a green color material. (C7) An embodiment containing a yellow color material and a purple color material.

[0082] The chromatic colorant may be a pigment or a dye. It may contain both a pigment and a dye. The black colorant is preferably an organic black colorant. Examples of organic black colorants include bisbenzofuranone compounds, azomethine compounds, perylene compounds, and azo compounds.

[0083] The infrared transmission filter layer may further contain an infrared absorber. By incorporating an infrared absorber into the infrared transmission filter layer, the wavelength of light to be transmitted can be shifted to a longer wavelength side. Examples of the infrared absorber include pyrrolopyrrole compounds, cyanine compounds, squarylium compounds, phthalocyanine compounds, naphthalocyanine compounds, quaterrylene compounds, merocyanine compounds, croconium compounds, oxonol compounds, iminium compounds, dithiol compounds, triarylmethane compounds, pyrromethene compounds, azomethine compounds, anthraquinone compounds, dibenzofuranone compounds, dithiolene metal complexes, metal oxides, and metal borides.

[0084] The spectral characteristics of the infrared transmission filter layer can be appropriately selected depending on the application of the image sensor. Examples include filter layers satisfying any one of the following spectral characteristics (1) to (5): (1): A filter layer in which the maximum light transmittance in the thickness direction of the film in the wavelength range of 400 to 750 nm is 20% or less (preferably 15% or less, more preferably 10% or less), and the minimum light transmittance in the thickness direction of the film in the wavelength range of 900 to 1500 nm is 70% or more (preferably 75% or more, more preferably 80% or more). (2): A filter layer in which the maximum light transmittance in the thickness direction of the film in the wavelength range of 400 to 830 nm is 20% or less (preferably 15% or less, more preferably 10% or less), and the minimum light transmittance in the thickness direction of the film in the wavelength range of 1000 to 1500 nm is 70% or more (preferably 75% or more, more preferably 80% or more). (3): A filter layer in which the maximum light transmittance in the thickness direction of the film in the wavelength range of 400 to 950 nm is 20% or less (preferably 15% or less, more preferably 10% or less), and the minimum light transmittance in the thickness direction of the film in the wavelength range of 1100 to 1500 nm is 70% or more (preferably 75% or more, more preferably 80% or more). (4): A filter layer in which the maximum light transmittance in the thickness direction of the film in the wavelength range of 400 to 1100 nm is 20% or less (preferably 15% or less, more preferably 10% or less), and the minimum light transmittance in the wavelength range of 1400 to 1500 nm is 70% or more (preferably 75% or more, more preferably 80% or more). (5) A filter layer having a maximum light transmittance in the thickness direction of the film in the wavelength range of 400 to 1300 nm of 20% or less (preferably 15% or less, more preferably 10% or less), and a minimum light transmittance in the wavelength range of 1600 to 2000 nm of 70% or more (preferably 75% or more, more preferably 80% or more).Further, as the infrared transmission filter, films described in JP 2013-077009 A, JP 2014-130173 A, JP 2014-130338 A, WO 2015 / 166779 A, ​​WO 2016 / 178346 A, WO 2016 / 190162 A, WO 2018 / 016232 A, JP 2016-177079 A, ​​JP 2014-130332 A, and WO 2016 / 027798 can be used. The infrared transmission filter may be a combination of two or more filters, or a dual bandpass filter that transmits two or more specific wavelength regions with one filter may be used.

[0085] The image sensor may include an infrared shielding filter for the purpose of improving various performances such as noise reduction, etc. Specific examples of the infrared shielding filter include the filters described in International Publication No. 2016 / 186050, International Publication No. 2016 / 035695, Japanese Patent No. 6248945, International Publication No. 2019 / 021767, Japanese Patent Laid-Open No. 2017-067963, and Japanese Patent No. 6506529.

[0086] The image sensor may include a dielectric multilayer film. Examples of the dielectric multilayer film include a multilayer film in which a high refractive index dielectric thin film (high refractive index material layer) and a low refractive index dielectric thin film (low refractive index material layer) are alternately stacked. The number of dielectric thin films stacked in the dielectric multilayer film is not particularly limited, but is preferably 2 to 100 layers, more preferably 4 to 60 layers, and even more preferably 6 to 40 layers. A material with a refractive index of 1.7 to 2.5 is preferred as a material used to form the high refractive index material layer. Specific examples include Sb ２ O ３ , Sb ２ S ３ , Bi ２ O ３ , CeO ２ , CeF ３ , HfO ２ , La ２ O ３ , Nd ２ O ３ , Pr ６ O １１ , Sc ２ O３ , SiO, Ta ２ O ５ , TiO ２ , TlCl, Y ２ O ３ , ZnSe, ZnS, ZrO ２ The material used to form the low refractive index material layer is preferably a material having a refractive index of 1.2 to 1.6. ２ O ３ , BiF ３ , CaF ２ , LaF ３ , PbCl ２ , PbF ２ , LiF, MgF ２ , MgO, NdF ３ , SiO ２ , Si ２ O ３ , NaF, ThO ２ , ThF ４ , Na ３ AlF ６ and the like. The method for forming the dielectric multilayer film is not particularly limited, and examples thereof include vacuum deposition methods such as ion plating and ion beam, physical vapor deposition methods (PVD methods) such as sputtering, and chemical vapor deposition methods (CVD methods). The thickness of each of the high refractive index material layer and the low refractive index material layer is preferably 0.1λ to 0.5λ, where λ (nm) is the wavelength of the light to be blocked. Specific examples of the dielectric multilayer film that can be used include the films described in JP 2014-130344 A and JP 2018-010296 A.

[0087] The dielectric multilayer film preferably has a transmission wavelength band in the infrared region (preferably a wavelength region exceeding 700 nm, more preferably a wavelength region exceeding 800 nm, and even more preferably a wavelength region exceeding 900 nm). The maximum transmittance in the transmission wavelength band is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. The maximum transmittance in the light-shielding wavelength band is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The average transmittance in the transmission wavelength band is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. The wavelength range of the transmission wavelength band is determined by dividing the wavelength showing the maximum transmittance by the center wavelength λ ｔ１ In this case, the central wavelength λ ｔ１ ±100 nm, and the central wavelength λ ｔ１ More preferably, the central wavelength λ ｔ１ It is more preferably ±50 nm.

[0088] The dielectric multilayer film may have only one transmission wavelength band (preferably a transmission wavelength band with a maximum transmittance of 90% or more), or may have a plurality of transmission wavelength bands.

[0089] The image sensor may include a color separation filter layer. Examples of the color separation filter layer include a filter layer containing colored pixels. Examples of the colored pixels include red, green, blue, yellow, cyan, and magenta pixels. The color separation filter layer may include colored pixels of two or more colors, or may include only one color. The filter layer may be appropriately selected depending on the application and purpose. For example, the filter described in International Publication No. 2019 / 039172 may be used.

[0090] Furthermore, when the color separation layer includes color pixels of two or more colors, the color pixels of each color may be adjacent to each other, and a partition wall may be provided between each color pixel. The material of the partition wall is not particularly limited. Examples include organic materials such as siloxane resin and fluororesin, and inorganic particles such as silica particles. The partition wall may also be made of a metal such as tungsten or aluminum.

[0091] When the image sensor includes an infrared transmission filter layer and a color separation layer, it is preferable that the color separation layer is provided on a different optical path from the infrared transmission filter layer. It is also preferable that the infrared transmission filter layer and the color separation layer are arranged two-dimensionally. The two-dimensional arrangement of the infrared transmission filter layer and the color separation layer means that at least a portion of each layer exists on the same plane.

[0092] The image sensor may include an intermediate layer such as a planarization layer, a base layer, or an adhesion layer, an anti-reflection film, and a lens. For example, the anti-reflection film may be a film made from a composition described in International Publication No. 2019 / 017280. For example, the lens may be a structure described in International Publication No. 2018 / 092600.

[0093] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[0094] [Preparation of Quantum Dot Dispersion] (Preparation Example 1) Preparation of Quantum Dot Dispersion 1 In a glove box, 5 mmol of indium chloride was added to 50 mL of oleylamine, and the mixture was heated and stirred at 60°C to dissolve the indium chloride, thereby preparing precursor solution A1. In a glove box, 5 mmol of antimony chloride was added to 20 mL of oleylamine, and the mixture was heated and stirred at 60°C to dissolve the antimony chloride, thereby preparing precursor solution B1. In a glove box, 100 mL of a tetrahydrofuran (THF) solution of lithium triethylborohydride (concentration of lithium triethylborohydride: 1.0 mol / L, manufactured by Aldrich) was mixed with 50 mL of dioctyl ether, and the THF was distilled off to prepare reducing agent solution C1, which was a dioctyl ether solution of lithium triethylborohydride (concentration of lithium triethylborohydride: approximately 2.0 mol / L). In a glove box, 16.5 mL of precursor solution A1, 3 mL of precursor solution B1, and 13.5 mL of oleylamine were added to a three-neck flask to obtain a mixed solution. The three-neck flask was then removed from the glove box, and after repeated evacuation and nitrogen purging, the mixture was switched to a nitrogen flow state. 2.9 mL of reducing agent solution C1 was then poured into the mixed solution, and the temperature was raised to 260 °C at a rate of 3 °C / min. After the liquid temperature reached 260 °C, it was maintained for approximately 15 minutes to allow nucleation. The liquid temperature in the three-neck flask was then cooled to room temperature. The three-neck flask was then returned to the glove box, and 6 mL of oleic acid and 90 mL of toluene were added to the solution in the three-neck flask, followed by stirring. The mixture was then centrifuged at approximately 8000 rpm, after which the precipitate was removed. Next, 60 mL of acetonitrile was added to the supernatant, and the mixture was centrifuged again at 8000 rpm to precipitate the target particles, semiconductor quantum dots (InSb quantum dots). The precipitate was recovered, toluene was added, and the recovered precipitate was dispersed in toluene to obtain a quantum dot dispersion liquid 1 (concentration 40 mg / ml), which is a dispersion liquid of InSb quantum dots. A quantum dot thin film was produced using the resulting quantum dot dispersion liquid 1, and the band gap estimated from the wavelength at which the absorption inflection point was observed in absorption measurements of the quantum dot thin film was approximately 0.95 eV. The average primary particle diameter of the InSb quantum dots contained in quantum dot dispersion liquid 1 was 5.0 nm.

[0095] (Production Example 2) Production of Quantum Dot Dispersion Liquid 2 In a glove box, 10 mmol of indium chloride was added to 100 mL of oleylamine, and the mixture was heated and stirred at 60 ° C to dissolve the indium chloride. Then, 5 mmol of antimony chloride was added and the mixture was heated and stirred at 60 ° C to dissolve the antimony chloride, thereby preparing precursor solution A2. In a glove box, 100 mL of a tetrahydrofuran (THF) solution of lithium triethylborohydride (concentration of lithium triethylborohydride: 1.0 mol / L, manufactured by Aldrich) was mixed with 50 mL of dioctyl ether, and the THF was distilled off to prepare reducing agent solution C2, which was a dioctyl ether solution of lithium triethylborohydride (concentration of lithium triethylborohydride: approximately 2.0 mol / L). In a glove box, 5 mmol of tris(dimethylamino)phosphine was dissolved in 50 mL of oleylamine and heated at 110 ° C for 2 hours to prepare precursor solution D2. In a glove box, 30 mL of precursor solution A2 and 3 mL of oleylamine were added to a three-neck flask to obtain a mixed solution. The three-neck flask was then removed from the glove box, and after repeated evacuation and nitrogen purging, the mixture was switched to a nitrogen flow state. 4.0 mL of reducing agent solution C2 was then injected into the mixed solution, and the temperature was raised to 290°C at a rate of 3°C / min. After the liquid temperature reached 290°C, the mixture was maintained for 20 minutes to obtain reaction solution a1. Next, while maintaining the temperature of reaction solution a1 at 290°C, 7.5 mL of precursor solution D2 was added to reaction solution a1, and the mixture was maintained at 290°C for 20 minutes to obtain reaction solution a2. The resulting reaction solution a2 was cooled. The three-neck flask containing reaction solution a2 was returned to the glove box, and 90 mL of toluene and 6 mL of oleic acid were added and stirred. This solution was centrifuged at approximately 7,800 rpm, after which the precipitate was removed. To the supernatant, 60 mL of acetonitrile was added, and the mixture was centrifuged again at 7,800 rpm to precipitate the target particles, semiconductor quantum dots (InSbP quantum dots). Toluene was then added to the precipitate to obtain a 50 mg / mL quantum dot dispersion 2 (a dispersion of InSbP quantum dots).A quantum dot thin film was prepared using the obtained quantum dot dispersion 2. The band gap of the quantum dot thin film was estimated from the wavelength at which an inflection point of absorption was observed, and was found to be approximately 0.95 eV. The average primary particle diameter of the InSbP quantum dots contained in the quantum dot dispersion 2 was 5.0 nm.

[0096] <Method for measuring the elemental composition ratio of semiconductor quantum dots> Quantum dot dispersions 1 and 2 were used to form a film with a thickness of approximately 0.1 μm on an Au-coated silicon substrate, and the elemental composition ratio of the semiconductor quantum dots was measured by X-ray photoelectron spectroscopy using an XPS (X-ray Photoelectron Spectroscopy) device under the following conditions. The value of the "molar ratio 1" in the table below indicates the value of the "ratio of the molar amount of In to the molar amount of Group 15 element." Note that the Group 15 element contained in the InSb quantum dots, which are quantum dots contained in quantum dot dispersion 1, is Sb, and the Group 15 elements contained in the InSbP quantum dots, which are quantum dots contained in quantum dot dispersion 2, are Sb and P. Therefore, for InSb quantum dots, the value in the "molar ratio 1" column is the value of the "ratio of the molar amount of In element to the molar amount of Sb element," and for InSbP quantum dots, the value in the "molar ratio 1" column is the value of the "ratio of the molar amount of In element to the total molar amount of Sb element and P element." The elemental composition ratio was measured at three points in the same film, and the average value was calculated as the elemental composition ratio of the semiconductor quantum dots. The measurement conditions were as follows: X-ray source: monochromated Al-K line (100 mmf, 25 W, 15 kV) Measurement area: 300 mm x 300 mm (area measurement) Pass energy: 46.95 eV Charge correction: Yes (electron gun and low-energy ion gun used together) Photoelectron take-off angle: 45°

[0097]

[0098] [Fabrication of Photodetector] Example 1 A titanium oxide film was formed to a thickness of 50 nm on a quartz glass substrate with a fluorine-doped tin oxide film by sputtering to form an electron transport layer.

[0099] Next, the quantum dot dispersion liquid 1 was dropped onto the titanium oxide film and spin-coated at 2500 rpm to form an InSb quantum dot assembly film (Step 1). Next, mercaptopropionic acid (MPA) and indium iodide (InI ３ ) mixed solution (InI ３ After dripping a solution of 7 mmol / L of MPA (0.01 v / v % MPA, solvent: methanol) onto the InSb quantum dot assembly film, the film was left to stand for 20 seconds and then spun dry at 2500 rpm for 10 seconds (step 2). Next, acetonitrile was dripped onto the InSb quantum dot assembly film as a rinse solution, and the film was spun dry at 2500 rpm for 20 seconds to remove the ligands coordinated to the InSb quantum dots. ３ The ligand was exchanged with InI and MPA (step 3). The operation of steps 1 to 3 was repeated twice to exchange the ligand with InI. ３ A 120 nm thick InSb quantum dot assembly film (semiconductor film) ligand-exchanged with MPA was formed to form a photoelectric conversion layer.

[0100] Next, a toluene solution (concentration: 10 mg / ml) of poly(3-hexylthiophene-2,5-diyl) (P3HT) was spin-coated onto the photoelectric conversion layer at 2000 rpm to form a hole transport layer.

[0101] Next, a 10 nm thick MoO film was formed on the hole transport layer by vacuum deposition using a metal mask. ３ After the film was formed, a 100 nm thick Au film (second electrode) was formed to form three element portions, thereby manufacturing a photodiode type light detecting element.

[0102] Example 2 A photodiode-type light-detecting element was manufactured in the same manner as in Example 1, except that in forming the electron transport layer, the thickness of the titanium oxide film was changed to 500 nm.

[0103] Example 3 A photodiode-type light-detecting element was manufactured in the same manner as in Example 1, except that the thickness of the titanium oxide film in forming the electron transport layer was changed to 5 nm.

[0104] Example 4 A photodiode-type photodetector was manufactured in the same manner as in Example 1, except that quantum dot dispersion liquid 2 was used instead of quantum dot dispersion liquid 1 in forming the photoelectric conversion layer.

[0105] Example 5 A titanium oxide film was formed to a thickness of 50 nm on a quartz glass substrate with a fluorine-doped tin oxide film by sputtering to form an electron transport layer.

[0106] Next, quantum dot dispersion liquid 1 was dropped onto the titanium oxide film and spin-coated at 2500 rpm to form an InSb quantum dot assembly film (Step 1). Next, a mercaptopropionic acid (MPA) solution (MPA concentration 0.02 v / v%, solvent: methanol) was dropped onto the InSb quantum dot assembly film, and the film was allowed to stand for 20 seconds and then spin-dried at 2500 rpm for 10 seconds (Step 2). Next, acetonitrile was dropped onto the InSb quantum dot assembly film as a rinse, and the film was spin-dried at 2500 rpm for 20 seconds to exchange the ligands coordinated to the InSb quantum dots with MPA (Step 3). Steps 1 to 3 were repeated twice, forming a 120-nm-thick InSb quantum dot assembly film (semiconductor film) in which the ligands had been exchanged with MPA, forming a photoelectric conversion layer.

[0107] Next, a toluene solution (concentration: 10 mg / ml) of poly(3-hexylthiophene-2,5-diyl) (P3HT) was spin-coated onto the photoelectric conversion layer at 2000 rpm to form a hole transport layer.

[0108] Next, a 10 nm thick MoO film was formed on the hole transport layer by vacuum deposition using a metal mask. ３ After the film was formed, a 100 nm thick Au film (second electrode) was formed to form three element portions, thereby manufacturing a photodiode type light detecting element.

[0109] Example 6 A photodiode-type light-detecting element was manufactured in the same manner as in Example 1, except that a toluene solution (concentration: 10 mg / ml) of a compound (Spiro-MeOTAD) having the following structure was spin-coated at 2000 rpm onto the photoelectric conversion layer to form a hole transport layer.

[0110] Example 7 Mercaptopropionic acid (MPA) and indium iodide (InI) were deposited on an InSb quantum dot assembly film. ３ A photodiode-type light-detecting element was manufactured in the same manner as in Example 1, except that a tetrabutylammonium iodide solution (10 mg / ml, solvent: methanol) was dropped instead of the mixed solution of ammonium iodide and ammonium iodide.

[0111] Comparative Example 1 A photodiode-type light-detecting element was manufactured in the same manner as in Example 5, except that a zinc oxide film having a thickness of 50 nm was formed by sputtering on a quartz glass substrate with a fluorine-doped tin oxide film to form an electron transport layer.

[0112] Comparative Example 2 A photodiode-type light-detecting element was manufactured in the same manner as in Example 1, except that in forming the electron transport layer, the thickness of the titanium oxide film was changed to 600 nm.

[0113] Comparative Example 3 A photodiode-type light-detecting element was manufactured in the same manner as in Example 1, except that in forming the electron transport layer, the thickness of the titanium oxide film was changed to 1 nm.

[0114]

[0115] <Performance Evaluation> For each photodetector element, the external quantum efficiency (EQE), dark current, and in-plane uniformity of the dark current were evaluated using a semiconductor parameter analyzer (C4156, Agilent). First, the current-voltage characteristics (IV characteristics) were measured while sweeping the voltage from 0 V to -2 V in a state where no light was irradiated, and the dark current was evaluated. Here, the current value at -2 V was taken as the dark current value. Note that the value in the dark current column in the table below is the value for the central element out of the three element parts. Furthermore, the dark current of each of the three element parts was measured, and the standard deviation of the dark current was calculated. The value in the in-plane uniformity of the dark current column in the table below is the standard deviation of the dark current of the three element parts. Next, the photodetector element was irradiated with 1450 nm monochrome light (50 μW / cm ２) was irradiated, the I-V characteristics were measured while sweeping the voltage from 0 V to -2 V. The photocurrent value was calculated by subtracting the dark current value from the current value when -2 V was applied, and the external quantum efficiency (EQE) was calculated from this value. The EQE was evaluated using the value of the central element out of the three element parts according to the following criteria. -EQE evaluation criteria- A: EQE exceeds 10% B: EQE is more than 7% and 10% or less C: EQE is less than 7%

[0116]

[0117] As shown in the above table, the photodetector element of the example had a lower dark current, a higher external quantum efficiency (EQE), and better in-plane uniformity of the dark current than the comparative example.

[0118] An image sensor having good visible-infrared imaging performance can be produced by using the photodetector element obtained in the above examples and an optical filter produced according to the methods described in WO 2016 / 186050 and WO 2016 / 190162 together with a known method.

[0119] 1: Photodetector element 11: First electrode 12: Second electrode 13: Photoelectric conversion layer 21: Electron transport layer 22: Hole transport layer

Claims

1. A photodetector comprising: a first electrode; a second electrode; a photoelectric conversion layer provided between the first electrode and the second electrode; and an electron transport layer provided between the first electrode and the photoelectric conversion layer, wherein the photoelectric conversion layer comprises an aggregate of semiconductor quantum dots containing In and a Group 15 element, and ligands coordinated to the semiconductor quantum dots, the Group 15 element comprising Sb, and the electron transport layer comprises titanium oxide, and the electron transport layer has a thickness of 5 to 500 nm.

2. The photodetector element according to claim 1, wherein the semiconductor quantum dots contain In, Sb, and P elements.

3. The photodetector according to claim 1 or 2, wherein the thickness of the electron transport layer is 10 to 200 nm.

4. The photodetector element according to claim 1 or 2, wherein the semiconductor quantum dots have a molar ratio of In element to Group 15 element of 1.00 to 1.

70.

5. The photodetector according to claim 1 or 2, wherein the band gap of said semiconductor quantum dots is 1.0 eV or less.

6. The photodetector according to claim 1 or 2, wherein the photoelectric conversion layer has a thickness of 50 to 500 nm.

7. The photodetector according to claim 1 or 2, wherein the ligand contains a halogen element or a sulfur element.

8. An image sensor comprising the photodetector element according to claim 1 or 2.

Images