Photodetector, image sensor and semiconductor film

Abstract

To provide a photodetection element, an image sensor, and a semiconductor film that have high external quantum efficiency and excellent durability against repeated driving.SOLUTION: A photodetection element having a photoelectric conversion layer containing an aggregate of PbS quantum dots and a ligand that coordinates to the PbS quantum dots, and the PbS quantum dots contain 1.75 mol or more and 1.95 mol or less of Pb atoms per 1 mol of S atom, and the ligand includes a ligand containing a halogen atom, and polydentate ligands containing two or more coordination moieties, and the polydentate ligand containing two or more coordination moieties is a ligand represented by any one of formulas (A) to (C).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a photodetector having a photoelectric conversion layer containing PbS quantum dots, a method for producing the photodetector, and an image sensor. The present invention also relates to a dispersion liquid and a semiconductor film containing PbS quantum dots. [Background technology]

[0002] In recent years, photodetection elements capable of detecting light in the infrared range have been attracting attention in the fields of smartphones, surveillance cameras, car-mounted cameras, and the like.

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

[0004] In addition, InGaAs-based semiconductor materials, which are known as near-infrared light receiving elements, have an issue in that they require very costly processes, such as epitaxial growth, to achieve high quantum efficiency, and therefore have not become widely used.

[0005] In recent years, research into semiconductor quantum dots has also progressed. For example, Patent Document 1 describes an invention relating to a photodetector that uses PbS quantum dots in the photoactive layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2016-532301 Summary of the Invention [Problem to be solved by the invention]

[0007] According to the inventors' investigations, it has been found that there is room for further improvement in the external quantum efficiency (EQE) of photoelectric conversion and durability against repeated driving of photodetection elements having a photoelectric conversion layer formed using semiconductor quantum dots.

[0008] Therefore, an object of the present invention is to provide a photodetector having high external quantum efficiency and excellent durability against repeated driving, a method for manufacturing a photodetector, and an image sensor. Another object of the present invention is to provide a dispersion liquid and a semiconductor film for use in a photodetector having high external quantum efficiency and excellent durability against repeated driving. [Means for solving the problem]

[0009] According to the inventor's investigations, it was found that the above object can be achieved by the following configuration, and the present invention was completed. <1> A photodetector having a photoelectric conversion layer including an aggregate of PbS quantum dots and ligands that are coordinated to the PbS quantum dots, The PbS quantum dot is a photodetector element containing 1.75 to 1.95 moles of Pb atoms per mole of S atoms. <2> The PbS quantum dots contain 1.75 moles or more and 1.90 moles or less of Pb atoms per mole of S atoms. <1> The light detection element according to claim 1. <3> The ligand includes at least one selected from a ligand containing a halogen atom and a multidentate ligand containing two or more coordination moieties. <1> or <2> The light detection element according to claim 1. <4> The halogen atom-containing ligand is an inorganic halide. <3> The light detection element according to claim 1. <5> The inorganic halide contains a Zn atom. <4> The light detection element according to claim 1. <6> The halogen atom-containing ligand contains an iodine atom. <3> ~ <5> 13. The light detection element according to claim 12, <7> The ligand includes at least one selected from 3-mercaptopropionic acid, zinc iodide, zinc bromide, and indium iodide; <1> ~ <6> 13. The light detection element according to claim 12, <8> The ligand includes two or more ligands. <1> ~ <7> 13. The light detection element according to claim 12, <9> The ligand includes a ligand containing a halogen atom and a multidentate ligand containing two or more coordination moieties. <1> ~ <8> 13. The light detection element according to claim 12, <10> A photodiode-type light detection element. <1> ~ <9> 13. The light detection element according to claim 12, <11> <1> ~ <10> A method for producing a light detection element according to any one of the above, A method for manufacturing a photodetector, comprising the step of forming a film of an aggregate of PbS quantum dots using a dispersion liquid containing PbS quantum dots containing 1.75 moles or more and 1.95 moles or less of Pb atoms per mole of S atoms, ligands that coordinate to the PbS quantum dots, and a solvent. <12> <1> ~ <10> 13. An image sensor including the photodetector according to claim 12. <13> Sensing light with wavelengths of 900 to 1600 nm. <12> The image sensor according to claim 1 . <14> It is an infrared image sensor. <12> 2. The image sensor according to claim 1 . <15> A dispersion liquid including PbS quantum dots containing 1.75 moles or more and 1.95 moles or less of Pb atoms per mole of S atoms, a ligand that coordinates to the PbS quantum dots, and a solvent. <16> A semiconductor film comprising an aggregate of PbS quantum dots and ligands that are coordinated to the PbS quantum dots, The PbS quantum dots are a semiconductor film containing 1.75 moles or more and 1.95 moles or less per mole of S atoms. Effect of the Invention

[0010] According to the present invention, it is possible to provide a photodetector having high external quantum efficiency and excellent durability against repeated driving, a method for manufacturing a photodetector, and an image sensor. It is also possible to provide a dispersion liquid and a semiconductor film for use in a photodetector having high external quantum efficiency and excellent durability against repeated driving. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 illustrates an embodiment of a light detection element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in detail below. In this specification, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit. In the description of groups (atomic groups) in this specification, when there is no indication of substitution or non-substitution, the notation includes both groups (atomic groups) that have no substituents and groups (atomic groups) that have a substituent. For example, an "alkyl group" includes not only an alkyl group that has no substituents (unsubstituted alkyl group) but also an alkyl group that has a substituent (substituted alkyl group).

[0013] <Photodetector element> The photodetector of the present invention comprises: A photodetector having a photoelectric conversion layer including an aggregate of PbS quantum dots and ligands coordinated to the PbS quantum dots, PbS quantum dots are characterized by containing 1.75 to 1.95 moles of Pb atoms per mole of S atoms.

[0014] The photodetector element of the present invention has high external quantum efficiency and excellent durability against repeated driving. The detailed reason why such an effect is obtained is unclear, but it is presumed to be due to the following. That is, since this PbS quantum dot contains 1.75 moles or more and 1.95 moles or less of Pb atoms per mole of S atoms, it is presumed that many Pb atoms are present on the surface of the PbS quantum dot. For this reason, it is presumed that the ligand is easily adsorbed on the surface of the PbS quantum dot, and the ligand coverage rate of the PbS quantum dot surface is high. By increasing the ligand coverage rate of the PbS quantum dot surface, it is possible to reduce the electrons trapped on the surface of the PbS quantum dot, and as a result, it is presumed that excellent external quantum efficiency has been obtained. In addition, it is presumed that the ligand is firmly coordinated on the surface of the PbS quantum dot, and the ligand is difficult to peel off from the surface of the PbS quantum dot, and therefore excellent durability against repeated driving has been obtained.

[0015] PbS quantum dots contain 1.75 to 1.95 moles of Pb atoms per mole of S atoms, preferably 1.75 to 1.90 moles, and more preferably 1.80 to 1.90 moles. If the content of Pb atoms is 1.95 moles or less per mole of S atoms, a low dark current is easily obtained. The molar ratio of S atoms to Pb atoms in PbS quantum dots can be calculated by quantifying the Pb atoms and S atoms in the PbS quantum dots using inductively coupled plasma (ICP) emission spectroscopy. When evaluating the Pb / S ratio of PbS quantum dots containing Pb atoms or S atoms in the ligand, the PbS quantum dots are immersed in a large excess of methanol to remove the ligand from the PbS quantum dots, and then the Pb atoms and S atoms in the PbS quantum dots are quantified and calculated using ICP emission spectroscopy. The removal of the ligands from the PbS quantum dots can be confirmed by the fact that the Pb / S ratio of the PbS quantum dots does not change when the immersion time in methanol is changed.

[0016] In this specification, the term "aggregate of PbS quantum dots" refers to a large number (e.g., 1 μm 2 This refers to a configuration in which PbS quantum dots (100 or more per square) are arranged closely to each other.

[0017] The PbS quantum dots used in the present invention are composed of PbS particles.

[0018] The band gap of the PbS quantum dots is preferably 0.5 to 2.0 eV. If the band gap of the PbS quantum dots is within the above range, it can be made into a photodetector capable of detecting light of various wavelengths depending on the application. For example, it can be made into a photodetector capable of detecting light in the infrared region. The upper limit of the band gap of the PbS quantum dots is preferably 1.9 eV or less, more preferably 1.8 eV or less, and even more preferably 1.5 eV or less. The lower limit of the band gap of the PbS quantum dots is preferably 0.6 eV or more, and even more preferably 0.7 eV or more.

[0019] The average particle size of the PbS quantum dots is preferably 2 nm to 15 nm. The average particle size of the PbS quantum dots refers to the average particle size of 10 PbS quantum dots. The particle size of the PbS quantum dots can be measured using a transmission electron microscope.

[0020] Generally, PbS quantum dots contain particles of various sizes, ranging from several nm to several tens of nm. When the average particle size of PbS quantum dots is reduced to a size equal to or smaller than the Bohr radius of the electrons contained within the PbS quantum dots, the phenomenon occurs in which the band gap of the PbS quantum dots changes due to the quantum size effect. If the average particle size of the PbS quantum dots is 15 nm or less, it is easy to control the band gap due to the quantum size effect.

[0021] The photoelectric conversion layer of the light detection element contains a ligand that coordinates with the PbS quantum dots. Examples of the ligand include a ligand containing a halogen atom and a multidentate ligand containing two or more coordination parts. The photoelectric conversion layer may contain only one type of ligand, or may contain two or more types. In particular, the photoelectric conversion layer preferably contains one or more types of ligands containing a halogen atom and one or more types of multidentate ligands. When a ligand containing a halogen atom is used, it is easy to increase the surface coverage of the PbS quantum dots with the ligand, resulting in higher external quantum efficiency. When a multidentate ligand is used, the multidentate ligand is easily chelated to the PbS quantum dot, and peeling of the ligand from the PbS quantum dot can be more effectively suppressed, resulting in excellent durability. Furthermore, steric hindrance between the PbS quantum dots can be suppressed by chelation, making it easier to obtain high electrical conductivity and high external quantum efficiency. In addition, when a ligand containing a halogen atom and a multidentate ligand are used in combination, a higher external quantum efficiency is likely to be obtained. As described above, it is presumed that the multidentate ligand is chelated to the PbS quantum dot. In addition, when the ligand to be coordinated to the PbS quantum dot further contains a ligand containing a halogen atom, it is presumed that the ligand containing a halogen atom is coordinated to the gap where the multidentate ligand is not coordinated, and it is presumed that the surface defects of the PbS quantum dot can be further reduced. Therefore, it is presumed that the external quantum efficiency of the photodetector can be further improved.

[0022] First, the ligand containing a halogen atom will be described. Examples of the halogen atom contained in the ligand containing a halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and an iodine atom is preferable from the viewpoint of coordinating power.

[0023] The halogen-containing ligand may be an organic halide or an inorganic halide. Among them, an inorganic halide is preferable because it is easy to coordinate to both the cation site and the anion site of the PbS quantum dot. In addition, the inorganic halide is preferably a compound containing a metal atom selected from Zn atom, In atom, and Cd atom, and is preferably a compound containing Zn atom. The inorganic halide is preferably a salt of a metal atom and a halogen atom because it is easy to ionize and coordinate to the PbS quantum dot.

[0024] Specific examples of the halogen-containing ligand include zinc iodide, zinc bromide, zinc chloride, indium iodide, indium bromide, indium chloride, cadmium iodide, cadmium bromide, and cadmium chloride, with zinc iodide being particularly preferred.

[0025] In addition, in the case of a ligand containing a halogen, a halogen ion may dissociate from the halogen-containing ligand and the halogen ion may be coordinated to the surface of the PbS quantum dot. In addition, a portion of the halogen-containing ligand other than the halogen may also be coordinated to the surface of the PbS quantum dot. To give a specific example, in the case of zinc iodide, zinc iodide may be coordinated to the surface of the PbS quantum dot, or iodine ions or zinc ions may be coordinated to the surface of the PbS quantum dot.

[0026] Next, the polydentate ligand will be described. The coordination part contained in the polydentate ligand includes a thiol group, an amino group, a hydroxyl group, a carboxyl group, a sulfo group, a phospho group, and a phosphonic acid group. The polydentate ligand is preferably a compound containing a thiol group because it is easily coordinated firmly to the surface of the PbS quantum dot (preferably the Pb atom of the PbS quantum dot).

[0027] The polydentate ligand may be any of those represented by formulae (A) to (C). [ka]

[0028] In formula (A), X A1 and X A2 each independently represents a thiol group, an amino group, a hydroxyl group, a carboxyl group, a sulfo group, a phospho group, or a phosphonic acid group, L A1 represents a hydrocarbon group.

[0029] In formula (B), X B1 and X B2each independently represents a thiol group, an amino group, a hydroxyl group, a carboxyl group, a sulfo group, a phospho group, or a phosphonic acid group, X B3 represents S, O or NH, L B1 and L B2 each independently represents a hydrocarbon group.

[0030] In formula (C), X C1 ~X C3 each independently represents a thiol group, an amino group, a hydroxyl group, a carboxyl group, a sulfo group, a phospho group, or a phosphonic acid group, X C4 represents N, L C1 ~L C3 each independently represents a hydrocarbon group.

[0031] X A1 , X A2 , X B1 , X B2 , X C1 , X C2 and X C3 The amino group represented by is not limited to -NH2, but also includes substituted amino groups and cyclic amino groups. Examples of substituted amino groups include monoalkylamino groups, dialkylamino groups, monoarylamino groups, diarylamino groups, and alkylarylamino groups. The amino groups represented by these groups are preferably -NH2, monoalkylamino groups, and dialkylamino groups, and more preferably -NH2.

[0032] L A1 , L B1 , L B2 , L C1 , L C2 and L C3The hydrocarbon group represented by is preferably an aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. The number of carbon atoms in the hydrocarbon group is preferably 1 to 20. The upper limit of the number of carbon atoms 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, and an alkynylene group.

[0033] The alkylene group includes a straight-chain alkylene group, a branched alkylene group, and a cyclic alkylene group, and is preferably a straight-chain alkylene group or a branched alkylene group, and is more preferably a straight-chain alkylene group. The alkenylene group includes a straight-chain alkenylene group, a branched alkenylene group, and a cyclic alkenylene group, and is preferably a straight-chain alkenylene group or a branched alkenylene group, and is more preferably a straight-chain alkenylene group. The alkynylene group includes a straight-chain alkynylene group and a branched alkynylene group, and is preferably a straight-chain alkynylene group. The alkylene group, the alkenylene group, and the alkynylene 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 groups], alkenyl groups having 2 to 3 carbon atoms [ethenyl and propenyl groups], alkynyl groups having 2 to 4 carbon atoms [ethynyl, propynyl, etc.], cyclopropyl groups, alkoxy groups having 1 to 2 carbon atoms [methoxy and ethoxy groups], acyl groups having 2 to 3 carbon atoms [acetyl and propionyl groups], alkoxycarbonyl groups having 2 to 3 carbon atoms [methoxycarbonyl and ethoxycarbonyl groups], acyloxy groups having 2 carbon atoms [acetyloxy group], Examples of the 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 acetamide group, a formyl group, a formyloxy group, a formamide group, a sulfamino group, a sulfino group, a sulfamoyl group, a phosphono group, an acetyl group, a halogen atom, and an alkali metal atom.

[0034] In formula (A), X A1 and X A2 L A1Preferably, 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.

[0035] In formula (B), X B1 and X B3 L B1 Preferably, the two 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. B2 and X B3 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.

[0036] In formula (C), X C1 and X C4 L C1 Preferably, the two 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. C2 and X C4 L C2 Preferably, the two 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. C3 and X C4 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.

[0037] In addition, "X A1 and X A2 L A1 "Separated by 1 to 10 atoms" means that 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), A1 and X A2 and are separated by two atoms. 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 [ka]

[0038] To give a specific example of the compound, 3-mercaptopropionic acid is X A1 The site corresponding to X is a carboxy group. A2 The site corresponding to L is a thiol group. A1 In 3-mercaptopropionic acid, the site corresponding to X is an ethylene group (the compound shown below). A1 (carboxy group) and X A2 (thiol group) and L A1 (ethylene group) separates them by two atoms. [ka]

[0039] X B1 and X B3 L B1Separated by 1 to 10 atoms, X B2 and X B3 L B2 Separated by 1 to 10 atoms, X C1 and X C4 L C1 Separated by 1 to 10 atoms, X C2 and X C4 L C2 Separated by 1 to 10 atoms, X C3 and X C4 L C3 The meaning of being separated by 1 to 10 atoms is the same as above.

[0040] Specific examples of polydentate ligands include 3-mercaptopropionic acid, thioglycolic acid, 2-aminoethanol, 2-aminoethanediol, 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, Examples of suitable amines include propanol, 2,3-dimercapto-1-propanol, diethanolamine, 2-(2-aminoethyl)aminoethanol, dimethylenetriamine, 1,1-oxybismethylamine, 1,1-thiobismethylamine, 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, and derivatives thereof.

[0041] As the polydentate ligand, a compound in which the complex stability constant K1 between the polydentate ligand and the Pb atom of the PbS quantum dot is 6 or more is preferably used. The complex stability constant K1 of the polydentate ligand is more preferably 8 or more, and further preferably 10 or more. If the complex stability constant K1 between the polydentate ligand and the Pb atom of the PbS quantum dot is 6 or more, the strength of the bond between the PbS quantum dot and the polydentate ligand can be increased.

[0042] The complex stability constant K1 is a constant determined by the relationship between a ligand and a metal atom to which the ligand is coordinately bonded, and is represented by the following formula (b).

[0043] Complex stability constant K1=[ML] / ([M]·[L]) ···(b) In formula (b), [ML] represents the molar concentration of the complex in which a metal atom and a ligand are bonded, [M] represents the molar concentration of the metal atoms contributing to the coordinate bond, and [L] represents the molar concentration of the ligand.

[0044] In reality, multiple ligands may be coordinated to one metal atom. In the present invention, however, the complex stability constant K1 represented by formula (b) when one ligand molecule is coordinated to one metal atom is defined as an index of the strength of the coordinate bond.

[0045] The complex stability constant K1 between the ligand and the metal atom can be determined by spectroscopy, magnetic resonance spectroscopy, potentiometry, solubility measurement, chromatography, calorimetry, freezing point measurement, vapor pressure measurement, relaxation measurement, viscosity measurement, surface tension measurement, etc. In the present invention, the complex stability constant K1 was determined by using Sc-Database ver.5.85 (Academi Software) (2010), which summarizes the results from various techniques and research institutes. If the complex stability constant K1 is not found in Sc-Database ver.5.85, the value described in Critical Stability Constants by AE Martell and RM Smith is used. If the complex stability constant K1 is not found in Critical Stability Constants, the measurement method described above is used, or the complex stability constant K1 is calculated using the program PKAS method (The Determination and Use of Stability Constants, VCH (1988) by AE Martell et al.) for calculating the complex stability constant K1.

[0046] The photoelectric conversion layer including an aggregate of PbS quantum dots and a ligand coordinated to the PbS quantum dots is preferably formed through a process of forming a film of an aggregate of PbS quantum dots (PbS quantum dot aggregate formation process) by applying a dispersion liquid including PbS quantum dots including 1.75 to 1.95 moles of Pb atoms relative to 1 mole of S atoms, a ligand coordinated to the PbS quantum dots, and a solvent onto a substrate. That is, the manufacturing method of the photodetector of the present invention preferably includes a process of forming a film of an aggregate of PbS quantum dots using a dispersion liquid including PbS quantum dots including 1.75 to 1.95 moles of Pb atoms relative to 1 mole of S atoms, a ligand coordinated to the PbS quantum dots, and a solvent. The method for applying the dispersion onto the substrate is not particularly limited, and examples of the method include coating methods such as spin coating, dipping, inkjet printing, dispenser printing, screen printing, letterpress printing, intaglio printing, and spray coating.

[0047] In addition, after forming a film of an aggregate of PbS quantum dots, a ligand exchange process may be further performed to exchange the ligands coordinated to the PbS quantum dots for other ligands. In the ligand exchange process, a ligand solution containing ligand A and a solvent is applied to the film of the aggregate of PbS quantum dots formed by the PbS quantum dot aggregate formation process to exchange the ligands coordinated to the PbS quantum dots for ligand A. Ligand A may contain two or more types of ligands, and two types of ligand solutions may be used in combination. Examples of ligand A include the above-mentioned ligands containing halogen atoms and multidentate ligands containing two or more coordination parts.

[0048] On the other hand, a desired ligand may be added in advance to the surface of the PbS quantum dots in a dispersion liquid, and the dispersion liquid may be applied onto a substrate to form a photoelectric conversion layer.

[0049] The content of the PbS quantum dots in the dispersion is preferably 1 to 500 mg / mL, more preferably 10 to 200 mg / mL, and even more preferably 20 to 100 mg / mL.

[0050] Examples of the solvent contained in the dispersion liquid or the ligand solution include ester-based solvents, ketone-based solvents, alcohol-based solvents, amide-based solvents, ether-based solvents, and hydrocarbon-based solvents. For details, refer to paragraph 0223 of International Publication No. 2015 / 166779, the contents of which are incorporated herein by reference. In addition, ester-based solvents substituted with a cyclic alkyl group and ketone-based solvents substituted with a cyclic alkyl group can also be used. The metal impurities in the solvent are preferably low, and the metal content is, for example, 10 ppb (parts per billion) or less by mass. Solvents with a mass ppt (parts per trillion) level may be used as necessary, and such solvents are provided, for example, by Toyo Gosei Co., Ltd. (The Chemical Daily, November 13, 2015). Examples of methods for removing impurities such as metals from a solvent include distillation (molecular distillation, thin film distillation, etc.) and filtration using a filter. The filter pore size of the filter used for filtration is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. The material of the filter is preferably polytetrafluoroethylene, polyethylene, or nylon. The solvent may contain isomers (compounds with the same number of atoms but different structures). In addition, the solvent may contain only one type of isomer, or may contain multiple types of isomers.

[0051] The thickness of the photoelectric conversion layer of the light detection element is preferably 10 to 600 nm, more preferably 50 to 600 nm, even more preferably 100 to 600 nm, and still more preferably 150 to 600 nm. The upper limit of the thickness is preferably 550 nm or less, more preferably 500 nm or less, and even more preferably 450 nm or less.

[0052] The refractive index of the photoelectric conversion layer for light of a target wavelength to be detected by the photodetector is preferably 2.0 to 3.0, more preferably 2.1 to 2.8, and even more preferably 2.2 to 2.7. According to this embodiment, when the photodetector is configured as a photodiode, it becomes easier to achieve high light absorptance, i.e., high external quantum efficiency.

[0053] The photodetector of the present invention has excellent sensitivity to light with wavelengths in the infrared region, and is therefore preferably one that detects light with wavelengths in the infrared region. That is, the photodetector of the present invention is preferably an infrared light detection element. Moreover, the light to be detected by the above-mentioned photodetector is preferably light with a wavelength in the infrared region. Moreover, the light with a wavelength in the infrared region is preferably light with a wavelength of more than 700 nm, more preferably light with a wavelength of 800 nm or more, and even more preferably light with a wavelength of 900 nm or more. Moreover, the light with a wavelength in the infrared region is preferably light with a wavelength of 2000 nm or less, and more preferably light with a wavelength of 1600 nm or less.

[0054] 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).

[0055] The types of photodetection elements include photoconductor type photodetection elements and photodiode type photodetection elements, of which photodiode type photodetection elements are preferred because they tend to provide a high signal-to-noise ratio (SN ratio).

[0056] Fig. 1 shows one embodiment of a photodiode type photodetector. The arrows in the figure indicate incident light to the photodetector. The photodetector 1 shown in Fig. 1 includes a lower electrode 12, an upper electrode 11 facing the lower electrode 12, and a photoelectric conversion layer 13 provided between the lower electrode 12 and the upper electrode 11. The photodetector 1 shown in Fig. 1 is used by receiving light from above the upper electrode 11.

[0057] The photoelectric conversion layer 13 is the photoelectric conversion layer according to the present invention described above. The preferred embodiments of the photoelectric conversion layer are as described above.

[0058] In addition, the wavelength λ of light to be detected by the photodetector element and the optical path length L of the light having the wavelength λ from the surface 12a of the lower electrode 12 on the photoelectric conversion layer 13 side to the surface 13a of the photoelectric conversion layer 13 on the upper electrode layer side are λand 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 relations are satisfied, the phases of the light incident from the upper electrode 11 side (incident light) and the light reflected from the surface of the lower electrode 12 (reflected light) can be aligned in the photoelectric conversion layer 13, and as a result, the lights are reinforced by the optical interference effect, resulting in a higher external quantum efficiency.

[0059] 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)

[0060] In the above formula, λ is the wavelength of the light to be detected by the light detection element, L λ is the optical path length of light having a wavelength λ from the surface 12a of the lower electrode 12 on the photoelectric conversion layer 13 side to the surface 13a of the photoelectric conversion layer 13 on the upper electrode layer side, m is an integer of 0 or greater.

[0061] m is preferably an integer of 0 to 4, more preferably an integer of 0 to 3, and further preferably an integer of 0 to 2. According to this embodiment, the transport properties of charges such as holes and electrons are excellent, and the external quantum efficiency of the photodetector can be further improved.

[0062] 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 for N 1 Then, the wavelength λ transmitted through the photoelectric conversion layer 13 is 1 The optical path length of light is N 1 ×d 1 When the photoelectric conversion layer 13 is composed of a laminated film of two or more layers, or when an intermediate layer (described later) is present between the photoelectric conversion layer 13 and the lower electrode 12, the integrated value of the optical path length of each layer is the above-mentioned optical path length Lλ It is.

[0063] The upper electrode 11 is preferably a transparent electrode made of a conductive material that is substantially transparent to the wavelength of the target light to be detected by the photodetector. In the present invention, "substantially transparent" means that the transmittance is 50% or more, preferably 60% or more, and particularly preferably 80% or more. Examples of materials for the upper 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).

[0064] The thickness of the upper electrode 11 is not particularly limited, and is preferably 0.01 to 100 μm, more preferably 0.01 to 10 μm, and particularly preferably 0.01 to 1 μm. In the present invention, the thickness of each layer can be measured by observing a cross section of the light-detecting element 1 using a scanning electron microscope (SEM) or the like.

[0065] Examples of materials for forming the lower electrode 12 include metals such as platinum, gold, nickel, copper, silver, indium, ruthenium, palladium, rhodium, iridium, osmium, and aluminum, the above-mentioned conductive metal oxides, carbon materials, and conductive polymers, etc. The carbon material may be any material that has conductivity, and examples of the carbon material include fullerene, carbon nanotubes, graphite, and graphene.

[0066] The lower electrode 12 is preferably a thin film (including a thin film formed by vapor deposition) of a metal or conductive metal oxide, or a glass substrate or plastic substrate having such a thin film. The glass substrate or plastic substrate is preferably a glass substrate having a thin film of gold or platinum, or a glass substrate on which platinum is vapor-deposited. The thickness of the lower electrode 12 is not particularly limited, and is preferably 0.01 to 100 μm, more preferably 0.01 to 10 μm, and particularly preferably 0.01 to 1 μm.

[0067] Although not shown, a transparent substrate may be disposed on the light incident surface of the upper electrode 11 (the surface opposite to the photoelectric conversion layer 13 side). Examples of the transparent substrate include a glass substrate, a resin substrate, and a ceramic substrate.

[0068] Although not shown, an intermediate layer may be provided between the photoelectric conversion layer 13 and the lower electrode 12 and / or between the photoelectric conversion layer 13 and the upper electrode 11. Examples of the intermediate layer include a blocking layer, an electron transport layer, and a hole transport layer. A preferred embodiment includes a hole transport layer between the photoelectric conversion layer 13 and the lower electrode 12 and between the photoelectric conversion layer 13 and the upper electrode 11. It is more preferable that an electron transport layer is provided between the photoelectric conversion layer 13 and the lower electrode 12 and between the photoelectric conversion layer 13 and the upper electrode 11, and a hole transport layer is provided on the other side. The hole transport layer and the electron transport layer may be a single layer film or a laminated film of two or more layers.

[0069] The blocking layer is a layer that has a 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, titanium oxide, tin oxide, zinc oxide, niobium oxide, and tungsten oxide. The blocking layer may be a single layer film or a laminated film of two or more layers.

[0070] The electron transport layer is a layer that has a function of transporting electrons generated in the photoelectric conversion layer 13 to the upper electrode 11 or the lower electrode 12. The electron transport layer is also called a hole blocking layer. The electron transport layer is formed of an electron transport material that can exert this function. Examples of the electron transport material include [6,6]-Phenyl-C61-Butyric Acid Methyl Ester (PC 61 Examples of the electron transport layer include fullerene compounds such as perylenetetracarboxydiimide (BM), perylene compounds such as perylenetetracarboxydiimide, tetracyanoquinodimethane, titanium oxide, tin oxide, zinc oxide, indium oxide, indium tungsten oxide, indium zinc oxide, indium tin oxide, fluorine-doped tin oxide, etc. The electron transport layer may be a single layer film or a laminated film of two or more layers.

[0071] The hole transport layer is a layer having a function of transporting holes generated in the photoelectric conversion layer 13 to the upper electrode 11 or the lower electrode 12. The hole transport layer is also called an electron block layer. The hole transport layer is formed of a hole transport material capable of exerting this function. For example, PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid)) and MoO3 can be mentioned. In addition, organic hole transport materials described in paragraphs 0209 to 0212 of JP-A-2001-291534 can also be used. In addition, semiconductor quantum dots can also be used as the hole transport material. Examples of the semiconductor quantum dot material constituting the semiconductor quantum dot include nanoparticles (particles with a size of 0.5 nm or more and less than 100 nm) of general semiconductor crystals [a) Group IV semiconductors, b) Group IV-IV, III-V, or II-VI compound semiconductors, and c) compound semiconductors consisting of a combination of three or more of Group II, III, IV, V, and VI elements]. Specific examples include semiconductor materials with relatively narrow band gaps such as PbS, PbSe, InN, InAs, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, Si, and InP. Ligands may be coordinated to the surface of the semiconductor quantum dot. Examples of the ligand include the multidentate ligands described above.

[0072] <Image sensor> The image sensor of the present invention includes the above-mentioned photodetector element of the present invention. The configuration of the image sensor is not particularly limited as long as it includes the photodetector element of the present invention and functions as an image sensor.

[0073] The image sensor of the present invention may include an infrared transmission filter layer, which preferably has low transmittance for light in the visible wavelength range, and more preferably has an average transmittance for light in the wavelength range of 400 to 650 nm of 10% or less, even more preferably 7.5% or less, and particularly preferably 5% or less.

[0074] The infrared transmission filter layer may be made of a resin film containing a coloring material. Examples of the coloring material include chromatic coloring materials such as red, green, blue, yellow, purple, and orange coloring materials, and black coloring materials. The coloring material contained in the infrared transmission filter layer is preferably a combination of two or more chromatic coloring materials that form a black color, or a coloring material that contains a black coloring material. When a combination of two or more chromatic coloring materials forms a black color, the following combinations of chromatic coloring materials may be mentioned, for example: (C1) to (C7). (C1) An embodiment containing a red coloring material and a blue coloring material. (C2) An embodiment containing a red color material, a blue color material, and a yellow color material. (C3) An embodiment containing a red color material, a blue color material, a yellow color material, and a purple color material. (C4) An embodiment containing a red color material, a blue color material, a yellow color material, a purple color material, and a green color material. (C5) An embodiment containing a red color material, a blue color material, a yellow color material, and a green color material. (C6) An embodiment containing a red color material, a blue color material, and a green color material. (C7) An embodiment containing a yellow coloring material and a purple coloring material.

[0075] The chromatic coloring material may be a pigment or a dye. It may contain a pigment and a dye. The black coloring material is preferably an organic black coloring material. For example, the organic black coloring material may be a bisbenzofuranone compound, an azomethine compound, a perylene compound, an azo compound, or the like.

[0076] The infrared transmission filter layer may further contain an infrared absorbing agent. By containing an infrared absorbing agent in the infrared transmission filter layer, the wavelength of light to be transmitted can be shifted to the longer wavelength side. Examples of the infrared absorbing agent 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.

[0077] The spectral characteristics of the infrared transmission filter layer can be appropriately selected depending on the application of the image sensor, for example, a filter layer satisfying any one of the following spectral characteristics (1) to (5) can be mentioned. (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 value 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 in which the maximum light transmittance in the thickness direction of the film in the wavelength range of 400 to 1300 nm is 20% or less (preferably 15% or less, more preferably 10% or less) and the minimum light transmittance in the wavelength range of 1600 to 2000 nm is 70% or more (preferably 75% or more, more preferably 80% or more).

[0078] In addition, as the infrared transmission filter, the 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 A can be used. In addition, 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.

[0079] The image sensor of the present invention may include an infrared shielding filter for the purpose of improving various performances such as noise reduction. Specific examples of the infrared shielding filter include filters described in International Publication No. 2016 / 186050, International Publication No. 2016 / 035695, Japanese Patent No. 6248945, International Publication No. 2019 / 021767, Japanese Patent Application Laid-Open No. 2017-067963, and Japanese Patent No. 6506529.

[0080] The image sensor of the present invention may include a dielectric multilayer film. Examples of the dielectric multilayer film include a multilayer film in which a dielectric thin film with a high refractive index (high refractive index material layer) and a dielectric thin film with a low refractive index (low refractive index material layer) are alternately laminated. The number of laminated dielectric thin films 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 preferable as a material used for forming the high refractive index material layer. Specific examples include Sb2O3, Sb2S3, Bi2O3, CeO2, CeF3, HfO2, La2O3, Nd2O3, Pr6O 11 , Sc2O3, SiO, Ta2O5, TiO2, TlCl, Y2O3, ZnSe, ZnS, ZrO2, etc. As the material used for forming the low refractive index material layer, a material having a refractive index of 1.2 to 1.6 is preferable. Specific examples include Al2O3, BiF3, CaF2, LaF3, PbCl2, PbF2, LiF, MgF2, MgO, NdF3, SiO2, Si2O3, NaF, ThO2, ThF4, Na3AlF6, etc. As the method for forming the dielectric multilayer film, there is no particular limitation, but examples 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 layer of the high refractive index material layer and the low refractive index material layer is preferably 0.1λ to 0.5λ when the wavelength of the light to be blocked is λ (nm). Specific examples of the dielectric multilayer film include the dielectric multilayer films described in JP-A-2014-130344 and JP-A-2018-010296.

[0081] 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 defined as the wavelength showing the maximum transmittance at the center wavelength λ t1 Then, the central wavelength λ t1 ±100 nm, and the central wavelength λ t1 ±75 nm, and the central wavelength λ t1 It is more preferable that the difference is ±50 nm.

[0082] 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 multiple transmission wavelength bands.

[0083] The image sensor of the present invention may include a color separation filter layer. The color separation filter layer may include a filter layer including colored pixels. The types of colored pixels include red pixels, green pixels, blue pixels, yellow pixels, cyan pixels, and magenta pixels. The color separation filter layer may include colored pixels of two or more colors, or may include only one color. It can be appropriately selected according to the application or purpose. For example, the filter described in International Publication No. 2019 / 039172 can be used as the color separation filter layer.

[0084] In addition, 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. For example, organic materials such as siloxane resin and fluororesin, and inorganic particles such as silica particles may be used. In addition, the partition wall may be made of a metal such as tungsten or aluminum.

[0085] In addition, when the image sensor of the present invention 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 fact that the infrared transmission filter layer and the color separation layer are arranged two-dimensionally means that at least a part of both of them exists on the same plane.

[0086] The image sensor of the present invention may include an intermediate layer such as a planarization layer, a base layer, and an adhesion layer, an anti-reflection film, and a lens. For example, a film made from a composition described in WO 2019 / 017280 can be used as the anti-reflection film. For example, a structure described in WO 2018 / 092600 can be used as the lens.

[0087] The photodetector of the present invention has excellent sensitivity even to light with wavelengths in the infrared region. Therefore, the image sensor of the present invention can be preferably used as an infrared image sensor. The image sensor of the present invention can also be preferably used as a sensor for sensing light with wavelengths of 900 to 2000 nm, and more preferably as a sensor for sensing light with wavelengths of 900 to 1600 nm.

[0088] <Dispersion> The dispersion of the present invention includes PbS quantum dots containing 1.75 to 1.95 moles of Pb atoms per mole of S atoms, a ligand that coordinates to the PbS quantum dots, and a solvent.

[0089] The PbS quantum dots used in the dispersion are the same as those described in the section on the photodetector. The content of the PbS quantum dots in the dispersion is preferably 1 to 500 mg / mL, more preferably 10 to 200 mg / mL, and even more preferably 20 to 100 mg / mL.

[0090] The solvent used in the dispersion liquid may be any of those described above as the solvent contained in the dispersion liquid or the ligand solution. The content of the solvent in the dispersion liquid is preferably 50 to 99% by mass, more preferably 70 to 99% by mass, and even more preferably 90 to 98% by mass, based on the total mass of the dispersion liquid.

[0091] The ligand contained in the dispersion liquid preferably functions as a ligand coordinated to the PbS quantum dots, has a molecular structure that is easily sterically hindered, and also serves as a dispersant that disperses the PbS quantum dots in the solvent. From the viewpoint of improving the dispersibility of the PbS quantum dots, the ligand is preferably a ligand having at least 6 carbon atoms in the main chain, and more preferably a ligand having 10 or more carbon atoms in the main chain. The ligand may be either a saturated compound or an unsaturated compound. Specific examples of the ligand include decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, erucic acid, oleylamine, dodecylamine, dodecanethiol, 1,2-hexadecanethiol, trioctylphosphine oxide, and cetrimonium bromide. The ligand is preferably one that is unlikely to remain in the film after the semiconductor film is formed. Specifically, it is preferable that the molecular weight is small. The ligand is preferably oleic acid or oleylamine from the viewpoint of providing dispersion stability to the PbS quantum dots and being unlikely to remain in the semiconductor film. The ligand contained in the dispersion may be a halogen atom-containing ligand as described in the section on the photodetector, or a multidentate ligand containing two or more coordination moieties. The content of the ligand in the dispersion is preferably 0.1 mmol / L to 200 mmol / L, more preferably 0.5 mmol / L to 10 mmol / L, relative to the total volume of the dispersion.

[0092] <Semiconductor film> The semiconductor film of the present invention is a semiconductor film including an aggregate of PbS quantum dots and a ligand coordinated to the PbS quantum dots, and the PbS quantum dots are a semiconductor film including 1.75 to 1.95 moles of Pb atoms per mole of S atoms. The PbS quantum dots preferably include 1.75 to 1.90 moles of Pb atoms per mole of S atoms. The PbS quantum dots are synonymous with the PbS quantum dots described in the section on the photodetector. Examples of the ligand coordinated to the PbS quantum dots include the ligands including halogen atoms and the multidentate ligands including two or more coordination parts described in the section on the photodetector, and the preferred examples are the same. The semiconductor film of the present invention is preferably used for the photoelectric conversion layer of the photodetector. EXAMPLES

[0093] The present invention will be described in more detail below with reference to examples. The materials, amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed 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] [Method for evaluating the Pb / S ratio (molar ratio) of PbS quantum dots] After concentrating the dispersion of PbS quantum dots to 60 mg / mL, 50 μL was taken, 5 mL of nitric acid was added, and the sample was decomposed by heating to 230 °C in a microwave. Water was added to make the total volume 40 mL, and the Pb atoms and S atoms in the PbS quantum dots were quantified using an inductively coupled plasma (ICP) optical emission spectrometer (PerkinElmer Optima 7300DV), and the Pb / S ratio (molar ratio) of the PbS quantum dots was calculated.

[0095] Example 1 1.28mL of oleic acid, 2mmol of lead oxide, and 38mL of octadecene were weighed into a flask and heated at 110℃ under vacuum for 90 minutes to obtain a precursor solution. The temperature of the solution was then adjusted to 95℃, the system was put into a nitrogen flow state, and then 1mmol of hexamethyldisilathiane was injected together with 5mL of octadecene. Immediately after the injection, the flask was naturally cooled, and when it reached 30℃, 12mL of hexane was added and the solution was collected. An excess amount of ethanol was added to the solution, and the mixture was centrifuged at 10,000rpm for 10 minutes. The precipitate was dispersed in octane, and a dispersion of PbS quantum dots (concentration 10mg / mL) in which oleic acid was coordinated as a ligand on the surface of the PbS quantum dots was obtained. The band gap of the PbS quantum dots obtained was estimated to be approximately 1.32 eV from optical absorption measurements in the visible to infrared region using an ultraviolet-visible near-infrared spectrophotometer (V-670, manufactured by JASCO Corporation). The Pb / S ratio (molar ratio) of the PbS quantum dots was calculated by the above-mentioned method and was found to be 1.90.

[0096] Using the obtained dispersion of PbS quantum dots, a photodiode-type light detection element was fabricated by the following method.

[0097] First, a titanium oxide film was formed by sputtering 50 nm on a quartz glass substrate with a fluorine-doped tin oxide film. Next, a dispersion liquid of PbS quantum dots was dropped onto the titanium oxide film formed on the substrate, and spin-coated at 2500 rpm to form a PbS quantum dot assembly film (step 1). Next, a methanol solution of 3-mercaptopropionic acid (concentration 0.1 mol / L) was dropped onto the PbS quantum dot assembly film as a ligand solution, and the film was left to stand for 1 minute and then spin-dried at 2500 rpm. Next, methanol was dropped onto the PbS quantum dot assembly film, and spin-dried at 2500 rpm for 20 seconds to exchange the ligands coordinated to the PbS quantum dots from oleic acid to 3-mercaptopropionic acid (step 2). The operation of step 1 and step 2 as one cycle was repeated 30 times to form a photoelectric conversion layer of 100 nm thickness, which was a PbS quantum dot assembly film in which the ligand was exchanged from oleic acid to 3-mercaptopropionic acid. Next, molybdenum oxide of 50 nm and gold of 100 nm were formed on the photoelectric conversion layer by continuous deposition to obtain a photodiode-type light detection element.

[0098] Example 2 A dispersion of PbS quantum dots was obtained in the same manner as in Example 1, except that hexamethyldisilathiane was changed to 2.0 mmol. The band gap of the PbS quantum dots was approximately 1.32 eV. The Pb / S ratio (molar ratio) of the PbS quantum dots was 1.81.

[0099] Example 3 In a flask, 6.74 mL of oleic acid, 6.3 mmol of lead oxide, and 30 mL of octadecene were weighed and heated at 120 ° C under vacuum for 100 minutes to obtain a precursor solution. The temperature of the solution was then adjusted to 100 ° C, the system was put into a nitrogen flow state, and then 2.6 mmol of hexamethyldisilathiane was injected together with 5 mL of octadecene. After holding for 1 minute after the injection, the flask was naturally cooled, and when it reached 30 ° C, 40 mL of toluene was added and the solution was collected. An excess amount of ethanol was added to the solution, and the mixture was centrifuged at 10,000 rpm for 10 minutes. The precipitate was dispersed in octane, and a dispersion of PbS quantum dots (concentration 10 mg / mL) in which oleic acid was coordinated as a ligand on the surface of the PbS quantum dots was obtained. The band gap of the PbS quantum dots estimated from the absorption measurement of the obtained dispersion of PbS quantum dots was approximately 1.32 eV. In addition, the Pb / S ratio (molar ratio) of the PbS quantum dots was calculated by the above method and found to be 1.75. A photodiode-type photodetector was fabricated using the dispersion of the PbS quantum dots in the same manner as in Example 1.

[0100] Example 4 A photodetector was prepared in the same manner as in Example 1, except that a methanol solution of zinc iodide (concentration: 0.025 mol / L) was used as the ligand solution instead of a methanol solution of 3-mercaptopropionic acid (concentration: 0.1 mol / L).

[0101] Example 5 A photodetector was prepared in the same manner as in Example 1, except that a methanol solution of zinc bromide (concentration: 0.025 mol / L) was used as the ligand solution instead of a methanol solution of 3-mercaptopropionic acid (concentration: 0.1 mol / L).

[0102] Example 6 A photodetector was produced in the same manner as in Example 1, except that a methanol solution of indium iodide (concentration: 0.025 mol / L) was used as the ligand solution instead of a methanol solution of 3-mercaptopropionic acid (concentration: 0.1 mol / L).

[0103] Example 7 A photodetector was prepared in the same manner as in Example 1, except that a methanol solution containing 3-mercaptopropionic acid and zinc iodide (3-mercaptopropionic acid concentration: 0.01 mol / L, zinc iodide concentration: 0.025 mol / L) was used as the ligand solution.

[0104] (Examples 8 to 11) A photodetector was fabricated in the same manner as in Examples 4 to 7, except that the PbS quantum dots having a Pb / S ratio (molar ratio) of 1.90 described in Example 3 were changed to PbS quantum dots having a Pb / S ratio (molar ratio) of 1.75.

[0105] Comparative Example 1 A commercially available PbS quantum dot dispersion (Sigma Aldrich, product number 900735) was used as the dispersion of PbS quantum dots. The band gap estimated from the absorption measurement of the dispersion of PbS quantum dots was approximately 1.32 eV. The Pb / S ratio (molar ratio) of the PbS quantum dots was calculated by the above method, and was 1.6. A photodetector was produced by the same method as in Example 1 using this dispersion of PbS quantum dots.

[0106] Comparative Example 2 1.28mL of oleic acid, 2mmol of lead oxide, and 38mL of octadecene were weighed into a flask and heated at 110℃ under vacuum for 90 minutes to obtain a precursor solution. The temperature of the solution was then adjusted to 95℃, the system was put into a nitrogen flow state, and then 3.1mmol of hexamethyldisilathiane was injected together with 5mL of octadecene. Immediately after injection, the flask was naturally cooled, and when it reached 30℃, 12mL of hexane was added and the solution was collected. An excess amount of ethanol was added to the solution, and the mixture was centrifuged at 10,000rpm for 10 minutes. The precipitate was dispersed in octane, and a dispersion of PbS quantum dots (concentration 10mg / mL) in which oleic acid was coordinated as a ligand on the surface of the PbS quantum dots was obtained. The band gap of the PbS quantum dots obtained was estimated to be approximately 1.32 eV from optical absorption measurements in the visible to infrared region using an ultraviolet-visible near-infrared spectrophotometer (V-670, manufactured by JASCO Corporation). The Pb / S ratio (molar ratio) of the PbS quantum dots was calculated by the above-mentioned method and was found to be 1.70.

[0107] <Evaluation> A reverse voltage of 2 V was applied to each photodetector element, and monochrome light with a wavelength of 940 nm (100 μW / cm 2 The external quantum efficiency was calculated by irradiating the device with light. The external quantum efficiency was calculated from the number of photoelectrons, which was estimated from the difference between the current value when not irradiated with light and the current value when irradiated with light, and the number of irradiated photons, as follows: "External quantum efficiency = (number of photoelectrons / number of irradiated photons) x 100". In addition, the change in the external quantum efficiency after the calculation of the external quantum efficiency was repeated 50 times (the external quantum efficiency value measured the first time - the external quantum efficiency value measured the 50th time) was calculated to evaluate the durability against repeated driving. A smaller change in the external quantum efficiency indicates better durability against repeated driving.

[0108] [Table 1]

[0109] As shown in the above table, the photodetector element of the example had a higher external quantum efficiency than the comparative example, a smaller change in the external quantum efficiency, and was excellent in durability against repeated driving.

[0110] By using the photodetector element obtained in the above examples and an optical filter prepared according to the methods described in WO 2016 / 186050 and WO 2016 / 190162, and fabricating an image sensor by a known method, and incorporating it into a solid-state imaging element, an image sensor with good visible and infrared imaging performance can be obtained. [Explanation of symbols]

[0111] 1: Light detection element 11:Top electrode 12: Lower electrode 13: Photoelectric conversion layer

Claims

1. An image sensor including a photodetector having a photoelectric conversion layer including an aggregate of PbS quantum dots and a ligand that is coordinated to the PbS quantum dots, The PbS quantum dots contain 1.75 moles or more and 1.95 moles or less of Pb atoms per mole of S atoms, The ligand includes a ligand containing a halogen atom and a multidentate ligand containing two or more coordination moieties, an image sensor, wherein the multidentate ligand containing two or more coordination moieties is a ligand represented by any one of formulas (A) to (C); 【Chemistry 1】 In formula (A), X Ａ１ and X Ａ２ each independently represents a thiol group, an amino group, a hydroxyl group, a carboxyl group, a sulfo group, a phospho group, or a phosphonic acid group; L Ａ１ represents a hydrocarbon group; In formula (B), X Ｂ１ and X Ｂ２ each independently represents a thiol group, an amino group, a hydroxyl group, a carboxyl group, a sulfo group, a phospho group, or a phosphonic acid group; X Ｂ３ represents S, O or NH; L Ｂ１ and L Ｂ２ each independently represents a hydrocarbon group; In formula (C), X Ｃ１ ~X Ｃ３ each independently represents a thiol group, an amino group, a hydroxyl group, a carboxyl group, a sulfo group, a phospho group, or a phosphonic acid group; X Ｃ４ represents N, L Ｃ１ ~L Ｃ３ each independently represents a hydrocarbon group.

2. The image sensor of claim 1 , wherein the PbS quantum dots contain 1.75 to 1.90 moles of Pb atoms per mole of S atoms.

3. The image sensor of claim 1 , wherein the PbS quantum dots contain 1.80 moles or more and 1.90 moles or less of Pb atoms per mole of S atoms.

4. 4. The image sensor according to claim 1, wherein the ligand containing a halogen atom is an inorganic halide.

5. The image sensor of claim 4 , wherein the inorganic halide comprises Zn atoms.

6. 6. The image sensor according to claim 1, wherein the ligand containing a halogen atom contains an iodine atom.

7. The ligand is 3-mercaptopropionic acid, At least one selected from zinc iodide, zinc bromide, and indium iodide; The image sensor according to any one of claims 1 to 3, comprising:

8. 8. The image sensor according to claim 1, wherein the light detecting element is a photodiode type light detecting element.

9. 9. The image sensor according to claim 1, which senses light having a wavelength of 900 to 1600 nm.

10. 9. The image sensor according to claim 1, which is an infrared image sensor.

Images