Quantum dot dispersion, semiconductor film, method for producing semiconductor film, light detection element, and image sensor

Abstract

This quantum dot dispersion comprises quantum dots, a ligand, and a solvent. The quantum dots comprise: a first quantum dot having a band gap of not greater than 1.35 eV and a circularity of at least 0.40 but less than 0.75, and a second quantum dot having a band gap of not greater than 1.35 eV and a circularity of at least 0.75 and not greater than 1.0. The quantum dot content in the component provided by removing the ligand and solvent from the quantum dot dispersion is at least 50 mass%. Provided are a semiconductor film using a quantum dot dispersion, a method for producing a semiconductor film, a light detection element, and an image sensor.

Description

Quantum dot dispersion, semiconductor film, method for manufacturing a semiconductor film, photodetector, and image sensor

[0001] This invention relates to a quantum dot dispersion. Furthermore, this invention relates to a semiconductor film using a quantum dot dispersion, a method for manufacturing a semiconductor film, a photodetector, and an image sensor.

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

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

[0004] Furthermore, InGaAs-based semiconductor materials, known as near-infrared light receiving elements, require extremely costly processes such as epitaxial growth and substrate bonding to achieve high quantum efficiency, which has hindered their widespread adoption.

[0005] Furthermore, in recent years, the use of quantum dots in photoelectric conversion elements has been considered. For example, Patent Document 1 discloses a photoelectric conversion element having a photoelectric conversion layer containing a first quantum dot and a second quantum dot, wherein the first and second quantum dots have nanoparticles containing heavy metal atoms and oxygen group atoms, the ratio X of the number of heavy metal atoms to the number of oxygen group atoms on the surface of the nanoparticles of the first quantum dot is less than 2, and the above ratio X is 2 or more on the surface of the nanoparticles of the second quantum dot, satisfying the following formula (1): 0.3 < N ... (1) N: ratio of the number of second quantum dots to the number of first quantum dots

[0006] Japanese Patent Publication No. 2021-064663

[0007] In recent years, with the increasing demand for improved performance in image sensors and other devices, there has been a growing need for further improvements in the various characteristics required of the photodetectors used in them. For example, required characteristics of photodetectors include high external quantum efficiency for light of the target wavelength to be detected and low dark current.

[0008] Furthermore, in recent years, high heat resistance has become a requirement for photodetectors such as image sensors.

[0009] According to the inventors' research, in a photodetector equipped with a photoelectric conversion layer made of a semiconductor film using quantum dots, the light absorption characteristics tend to fluctuate easily before and after heating, indicating that there is room for further improvement in heat resistance.

[0010] Therefore, an object of the present invention is to provide a quantum dot dispersion that can produce a semiconductor film with high external quantum efficiency, low dark current, and excellent heat resistance, and that also has excellent dispersibility. Another object of the present invention is to provide a semiconductor film using a quantum dot dispersion, a method for manufacturing a semiconductor film, a photodetector, and an image sensor.

[0011] The present invention provides the following: <1> A quantum dot dispersion comprising quantum dots, ligands, and a solvent, wherein the quantum dots comprise a first quantum dot having a band gap of 1.35 eV or less and a roundness of 0.40 or more and less than 0.75, and a second quantum dot having a band gap of 1.35 eV or less and a roundness of 0.75 or more and 1.0 or less, and the content of quantum dots in the component obtained by removing the ligands and the solvent from the quantum dot dispersion is 50% by mass or more. <2> The quantum dot dispersion according to <1>, wherein the roundness of the first quantum dot is 0.45 or more and 0.60 or less, and the roundness of the second quantum dot is 0.80 or more and 1.0 or less. <3> The quantum dot dispersion according to <1> or <2>, wherein the first quantum dot and the second quantum dot are Group III-V quantum dots. <4> The quantum dot dispersion according to any one of <1> to <3>, wherein the first quantum dot and the second quantum dot contain the element In. <5> The quantum dot dispersion according to any one of <1> to <4>, wherein the ligand contains at least one selected from inorganic halides and organic compounds with a molecular weight of 200 or less. <6> A semiconductor film obtained from the quantum dot dispersion according to any one of <1> to <5>. <7> A method for manufacturing a semiconductor film, comprising the step of applying the quantum dot dispersion according to any one of <1> to <5> onto a support. <8> A photodetector comprising the semiconductor film according to <6>. <9> An image sensor comprising the semiconductor film according to <6>.

[0012] According to the present invention, it is possible to manufacture a semiconductor film with high external quantum efficiency, low dark current, and excellent heat resistance, and to provide a quantum dot dispersion with excellent dispersibility. Furthermore, according to the present invention, it is possible to provide a semiconductor film using a quantum dot dispersion, a method for manufacturing a semiconductor film, a photodetector, and an image sensor.

[0013] This figure shows one embodiment of a photodetector.

[0014] The present invention will be described in detail below. In this specification, "~" is used to mean that the numerical values ​​before and after it are included as the lower and upper limits. In the notation of groups (atomic groups) in this specification, notations that do not specify substitution or unsubstituted include both groups (atomic groups) with substituents and groups (atomic groups) without substituents. For example, "alkyl group" includes not only alkyl groups without substituents (unsubstituted alkyl groups) but also alkyl groups with substituents (substituted alkyl groups).

[0015] <Quantum Dot Dispersion> The quantum dot dispersion of the present invention is a quantum dot dispersion comprising quantum dots, ligands, and a solvent, wherein the quantum dots comprise a first quantum dot having a band gap of 1.35 eV or less and a roundness of 0.40 or more and less than 0.75, and a second quantum dot having a band gap of 1.35 eV or less and a roundness of 0.75 or more and 1.0 or less, and the content of quantum dots in the component obtained by removing the ligands and the solvent from the quantum dot dispersion is 50% by mass or more.

[0016] The quantum dot dispersion of the present invention exhibits excellent dispersibility. Furthermore, by using the quantum dots of the present invention, it is possible to manufacture semiconductor films with high external quantum efficiency, low dark current, and excellent heat resistance. The reason for these effects is presumed to be as follows: The first quantum dots and the second quantum dots contained in the quantum dot dispersion of the present invention are quantum dots with different degrees of roundness, so it is presumed that appropriate gaps can be created between the quantum dots in the dispersion, thereby suppressing the aggregation of quantum dots. For this reason, the quantum dot dispersion of the present invention has excellent dispersibility despite containing a relatively large amount of quantum dots, with a quantum dot content of 50% by mass or more in the components excluding ligands and solvents from the quantum dot dispersion. In addition, because the first quantum dots and the second quantum dots have different degrees of roundness, it is presumed that even when a semiconductor film is formed using the quantum dot dispersion, appropriate gaps can be created between the quantum dots, suppressing the dense packing of quantum dots. For this reason, it is presumed that the carrier transport ability is increased and the external quantum efficiency is improved. Furthermore, it is presumed that the dark current was suppressed because the dense packing of quantum dots within the film was prevented. It is also presumed that the change in absorption characteristics due to heating is caused by the aggregation of quantum dots contained in the semiconductor film due to heating. Because the roundness of the first quantum dots and the second quantum dots differs, it is presumed that even when the semiconductor film is heated, appropriate gaps are created between the quantum dots, thereby suppressing the aggregation of quantum dots. For this reason, it is presumed that the semiconductor film obtained using the quantum dot dispersion of the present invention can suppress the aggregation of quantum dots contained in the semiconductor film due to heating, and can suppress the change in absorption characteristics due to heating. For this reason, the semiconductor film obtained using the quantum dot dispersion of the present invention has high external quantum efficiency, low dark current, and excellent heat resistance. Furthermore, by using the quantum dot dispersion of the present invention, it is possible to manufacture semiconductor films with high external quantum efficiency, low dark current, and excellent heat resistance with good yield.

[0017] A semiconductor film obtained using the quantum dot dispersion of the present invention can be used in photodetectors and image sensors. More specifically, the semiconductor film can be used in the photoelectric conversion layer of a photodetector or image sensor. For this reason, the quantum dot dispersion of the present invention is preferably used for the photoelectric conversion layer of a photodetector or image sensor. Furthermore, a semiconductor film obtained using the quantum dot dispersion of the present invention has excellent sensitivity to light in the infrared region. For this reason, an image sensor using a semiconductor film obtained using the quantum dot dispersion of the present invention as its photoelectric conversion layer can be particularly preferably used as an infrared sensor. Therefore, the quantum dot dispersion of the present invention is preferably used for the photoelectric conversion layer of an infrared sensor.

[0018] The quantum dot dispersion of the present invention will be described in more detail below.

[0019] (Quantum Dots) The quantum dot dispersion of the present invention contains quantum dots. The quantum dots contained in the quantum dot dispersion of the present invention include a first quantum dot having a band gap of 1.35 eV or less and a roundness of 0.40 or more and less than 0.75, and a second quantum dot having a band gap of 1.35 eV or less and a roundness of 0.75 or more and 1.0 or less.

[0020] The band gaps of the first and second quantum dots are 1.35 eV or less, preferably 1.1 eV or less, and more preferably 1.0 eV or less. There is no particular limit to the lower limit of the band gap, but it can be 0.5 eV or more. By using such quantum dots, it is possible to form a semiconductor film that has a higher external quantum efficiency for light in the infrared region (for example, light with a wavelength of 1450 nm or more).

[0021] The difference in band gaps between the first quantum dot and the second quantum dot is preferably 0.07 eV or less, more preferably 0.05 eV or less, and even more preferably 0.03 eV or less. If the difference in band gaps between the two is within the above range, a semiconductor film with higher external quantum efficiency for wavelengths in the infrared region (for example, light with a wavelength of 1450 nm or more) can be formed.

[0022] The band gap of a quantum dot can be calculated from the energy at the maximum absorption wavelength of the absorption spectrum obtained by measuring optical absorption in the visible to infrared region using an ultraviolet-visible-near-infrared spectrophotometer. Alternatively, in the case of quantum dots that do not have a maximum absorption wavelength, it can be determined from a Tauc plot, as described in Japanese Patent Publication No. 5949567.

[0023] The maximum absorption wavelengths of the first and second quantum dots are preferably in the range of 900 to 1700 nm, and more preferably in the range of 1300 to 1600 nm. By using such quantum dots, it is possible to form a semiconductor film that has a higher external quantum efficiency for light in the infrared region (for example, light with a wavelength of 1450 nm or higher).

[0024] The difference in maximum absorption wavelengths between the first quantum dot and the second quantum dot is preferably 150 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less. If the difference in maximum absorption wavelengths between the two is within the above range, a semiconductor film with higher external quantum efficiency for wavelengths in the infrared region (for example, light with a wavelength of 1450 nm or more) can be formed.

[0025] The first quantum dot and the second quantum dot are preferably semiconductor particles containing metal atoms. In this specification, metal atoms also include semimetallic atoms, such as Si atoms. Furthermore, in this specification, "semiconductor" refers to a semiconductor with a resistivity of 10 －２ Ωcm or more 10 ８ This refers to substances that are less than or equal to Ωcm.

[0026] The first quantum dot and the second quantum dot preferably contain at least one element selected from the group consisting of Ga, Ge, P, As, Se, In, Sn, Sb, Te, Pb, Bi, Ag, Cu, and Hg, more preferably contain at least one element selected from the group consisting of Ga, P, As, Se, In, Sb, Te, and Bi, even more preferably contain at least one element selected from the group consisting of P, As, Sb, and In, and particularly preferably contain the element In.

[0027] The first and second quantum dots are preferably Group III-V quantum dots or Group IV-VI quantum dots, and are more preferably Group III-V quantum dots because the effects of the present invention are more pronounced in this respect.

[0028] III-V quantum dots are quantum dots containing Group III elements (Group 13 elements) and Group V elements (Group 15 elements). Examples of III-V quantum dots include quantum dots made of compound semiconductors containing Group III and Group V elements. IV-VI quantum dots are quantum dots containing Group IV elements (Group 14 elements) and Group VI elements (Group 16 elements). Examples of IV-VI quantum dots include quantum dots made of compound semiconductors containing Group IV and Group VI elements.

[0029] Examples of Group III elements included in Group III-V quantum dots include boron (B), aluminum (Al), gallium (Ga), and indium (In), with the inclusion of In being preferable. Examples of Group V elements included in Group III-V quantum dots include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi), with the inclusion of at least one element selected from As and Sb being preferable. Group III-V quantum dots may further contain elements other than Group III and Group V elements. Examples of other elements include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), cadmium (Cd), and mercury (Hg).

[0030] Examples of Group IV elements included in Group IV-VI quantum dots include silicon (Si), germanium (Ge), tin (Sn), and lead (Pb), with Pb being preferred. Examples of Group VI elements included in Group IV-VI quantum dots include oxygen (O), sulfur (S), selenium (Se), and tellurium (Te), with at least one element selected from S and Se being preferred, and S being more preferred. Group IV-VI quantum dots may further contain elements other than Group IV and Group VI elements. Examples of other elements include Mg, Ca, Sr, Ba, Zn, Cd, and Hg.

[0031] Specific examples of the first and second quantum dots include PbS, PbSe, PbSeS, inN, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, InPAs, InAsSb, InPSb, HgTe, HgCdTe, and Ag. ２ S, Ag ２ Se, Ag ２ Te, SnS, SnSe, SnTe, Si, InP, AgBiS ２ Examples include AgBiSTe, and it is preferable that it be at least one selected from InAs, InSb, InPAs, InAsSb, InPSb, PbS, and PbSe, and more preferably at least one selected from InAs, InSb, InPAs, and InAsSb.

[0032] The roundness of the first quantum dot is preferably 0.45 or more and less than 0.75, and more preferably 0.45 or more and 0.60 or less.

[0033] The shape of the first quantum dot is not particularly limited, as long as its roundness is between 0.40 and 0.75. Examples include shapes with multiple arms extending from a core, such as a tetrapod shape, an irregular triangular shape, or a starfish shape.

[0034] The circularity of the second quantum dot is 0.75 or more and 1.0 or less, preferably 0.80 or more and 1.0 or less. The upper limit of the circularity of the second quantum dot is preferably 0.95 or less.

[0035] The shape of the second quantum dot is not particularly limited as long as the circularity is 0.75 or more and 1.0 or less. For example, spherical, ellipsoidal, polyhedral (e.g., tetrahedral, hexahedral, octahedral, square prismatic, hexagonal prismatic, etc.) and the like can be mentioned.

[0036] The circularity of the quantum dot can be measured by performing image analysis on an image taken using a spherical aberration corrected scanning transmission electron microscope or the like. Specifically, the circularity of the quantum dot can be calculated from the following formula from the taken image. Examples of image analysis software include Winroof. In addition, in this specification, the average circularity of the quantum dot refers to the arithmetic mean value of the circularities of all the particles (10 or more) observed in the image. Circularity = 4πS / L ２ S: projected area L: length of the outer periphery

[0037] The circularity of the quantum dot can be adjusted by a conventionally known method. For example, the circularity can be adjusted by a method such as changing the synthesis conditions of the quantum dot. For example, by the method described in Example 3 of paragraphs 0134 to 0137 of US Patent Application Publication No. 2021 / 0371746, tetrahedral InAs quantum dots in a tetrapod shape can be manufactured. Specifically, InCl ３ A mixed In precursor solution of 1.2 g (5 mmol) and 25 ml of oleylamine is evacuated at a temperature of 120°C to 140°C and a vacuum of 1 Torr for 2 hours. Then, 0.092 mL (0.5 mmol) of ((CH ３ ) ２ N) ３An As precursor solution is prepared by mixing AS with 0.016 g (0.1 mmol) of lithium bis(trimethylsilyl)amide (LiHMDS) and 0.5 ml of degassed oleylamine (D-OLA). This solution is then stirred at 40°C for 10 minutes. Next, the In precursor solution is injected into the As precursor solution at a temperature between 220°C and 280°C, reacted for 1 hour, and then cooled to room temperature. In this way, tetrapod-shaped quantum dots can be produced. The average roundness of the quantum dots obtained in this way is 0.40 or more and less than 0.75. Furthermore, in the above method, quantum dots with a shape close to spherical can be produced by not using LiHMDS and increasing the injection temperature to 300°C. The average roundness of the quantum dots obtained in this way is 0.75 or more and less than 1.0.

[0038] The quantum dot dispersion of the present invention may contain quantum dots other than the first and second quantum dots described above (hereinafter also referred to as third quantum dots).

[0039] Examples of the third type of quantum dot include quantum dots with a band gap greater than 1.35 eV and quantum dots with a roundness of less than 0.40. There are no particular limitations on the type of the third type of quantum dot. Examples include Group III-V quantum dots and Group IV-VI quantum dots.

[0040] The quantum dot content in the quantum dot dispersion is preferably 1 to 10% by mass. The lower limit is preferably 1.5% by mass or more, and more preferably 2% by mass or more. The upper limit is preferably 9% by mass or less, and more preferably 7% by mass or less.

[0041] The ratio of the number of first quantum dots to the total number of quantum dots in the quantum dot dispersion (number ratio) is preferably 10 to 90%. The lower limit is preferably 15% or more. The upper limit is preferably 85% or less, and more preferably 80% or less.

[0042] The ratio of the number of second quantum dots to the total number of quantum dots in the quantum dot dispersion (number ratio) is preferably 5 to 90%. The lower limit is more preferably 10% or more. The upper limit is preferably 85% or less, and more preferably 80% or less.

[0043] The ratio (number ratio) of the total number of first quantum dots to the total number of second quantum dots in the quantum dot dispersion is preferably 50 to 100%. The lower limit is preferably 60% or more, and more preferably 70% or more.

[0044] The number of first quantum dots and the number and ratio of second quantum dots contained in the quantum dot dispersion are preferably 5:95 to 95:5, and more preferably 10:90 to 90:10. When the above ratio is within the above range, the effects of the present invention are significantly exhibited.

[0045] The content of quantum dots in the component obtained by removing the ligands and solvent from the quantum dot dispersion is 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit can be 100% by mass or less. Furthermore, the total content of quantum dots and ligands in the component obtained by removing the solvent from the quantum dot dispersion is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit can be 100% by mass or less.

[0046] (Ligands) The quantum dot dispersion of the present invention contains ligands. Examples of ligands include inorganic ligands and organic ligands. It is preferable that the ligands include inorganic ligands.

[0047] The inorganic ligand is preferably an inorganic halide. Examples of halogen atoms contained in the inorganic halide include fluorine, chlorine, bromine, and iodine atoms, with bromine or iodine atoms being preferred. Furthermore, the inorganic halide is preferably a compound containing at least one atom selected from the group consisting of Zn, Cd, Ga, Ge, As, Se, In, Sn, Sb, Te, Tl, Pb, Bi, and Po.

[0048] Specific examples of inorganic ligands include zinc iodide, zinc bromide, zinc chloride, indium iodide, indium bromide, indium chloride, cadmium iodide, lead chloride, lead bromide, lead iodide, cadmium bromide, cadmium chloride, gallium iodide, gallium bromide, gallium chloride, potassium sulfide, and sodium sulfide.

[0049] The organic ligand is preferably an organic compound, and more preferably an organic compound with a molecular weight of 200 or less. The organic compound is preferably a compound having at least one functional group selected from a carboxyl group, a mercapto group, an amino group, a hydroxyl group, a phospho group, a phosphonic acid group, and a sulfo group, more preferably a compound having at least one functional group selected from a carboxyl group, a mercapto group, an amino group, and a hydroxyl group, and even more preferably a compound having a mercapto group. The organic ligand may be a monodentate ligand having only one of the above functional groups, or a polydentate ligand having two or more of the above ligands.

[0050] The organic compound used as an organic ligand is preferably a compound or salt thereof with a pKa of 3 or less.

[0051] In "salts of compounds with pKa 3 or less", the atoms or groups of atoms constituting the salt with the compound with pKa 3 or less are metal ions (Li ＋ Na ＋ _K ＋ Ca ２＋ Mg ２＋ , Zn ２＋ ,Cd ２＋ Ga ３＋ In ３＋ , Zr ４＋ , Hf４＋ Examples include ammonium ions, etc. In other words, salts of compounds with a pKa of 3 or less include metal salts of compounds with a pKa of 3 or less, and ammonium salts of compounds with a pKa of 3 or less.

[0052] For compounds with a pKa of 3 or less, the upper limit of the pKa is preferably 2.5 or less. The lower limit of the pKa for the above compounds is preferably -2.0 or higher, more preferably -1.0 or higher, and even more preferably 0.5 or higher.

[0053] The molecular weight of compounds with a pKa of 3 or less is preferably 50 to 500. The upper limit of the molecular weight is preferably 450 or less, more preferably 400 or less, and even more preferably 200 or less.

[0054] Compounds with a pKa of 3 or less are preferably compounds having a functional group selected from a carboxyl group, a phospho group, a phosphonic acid group, a sulfonimide group, and a sulfo group, and are more preferably compounds having a sulfo group.

[0055] Specific examples of monodentate ligands include 2-naphthylamine, 4-methylthioaniline, 4-methylbenzenethiol, 3,5-dimethylbenzenethiol, 4-chlorobenzenethiol, 4-methoxybenzenethiol, benzoic acid, phenylphosphonic acid, methanesulfonic acid, trifluoroacetic acid, bromoacetic acid, 3-phosphorylpropionic acid, glycine-N,N-bis(methylenephosphonic acid), 2-chloroethylphosphonic acid, phenyl phosphate, dimethyl phosphate, and trifluoromethanesulfonic acid. Of the above compounds, phenylphosphonic acid, methanesulfonic acid, trifluoroacetic acid, bromoacetic acid, 3-phosphorylpropionic acid, glycine-N,N-bis(methylenephosphonic acid), 2-chloroethylphosphonic acid, phenyl phosphate, dimethyl phosphate, and trifluoromethanesulfonic acid are compounds with a pKa of 3 or less.

[0056] Examples of polydentate ligands include ligands represented by any of the formulas (A) to (C).

[0057] In formula (A), X Ａ１and X Ａ２ Each of these independently represents a carboxyl group, mercapto group, amino group, hydroxyl group, phospho group, phosphonic acid group, or sulfo group, L Ａ１ This represents a hydrocarbon group.

[0058] In formula (B), X Ｂ１ and X Ｂ２ Each of these independently represents a carboxyl group, mercapto group, amino group, hydroxyl group, phospho group, phosphonic acid group, or sulfo group, X Ｂ３ represents S, O, or NH, and L Ｂ１ and L Ｂ２ Each of these independently represents a hydrocarbon group.

[0059] In formula (C), X Ｃ１ ~X Ｃ３ Each of these independently represents a carboxyl group, mercapto group, amino group, hydroxyl group, phospho group, phosphonic acid group, or sulfo group, X Ｃ４ represents N, L Ｃ１ ~L Ｃ３ Each of these independently represents a hydrocarbon group.

[0060] X Ａ１ , X Ａ２ , X Ｂ１ , X Ｂ２ , X Ｃ１ , X Ｃ２ and X Ｃ３ The amino group represented by -NH ２ This is not limited to substituted amino groups, 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 group represented by these groups is -NH ２ A monoalkylamino group or a dialkylamino group is preferred, -NH ２ It is preferable that it be so.

[0061] L Ａ１ , L Ｂ１ , L Ｂ２ , L Ｃ１ , L Ｃ２ and L Ｃ３The hydrocarbon group represented 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 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 hydrocarbon groups include alkylene groups, alkenylene groups, alkylene groups, and arylene groups.

[0062] Alkylene groups include linear alkylene groups, branched alkylene groups, and cyclic alkylene groups, with linear or branched alkylene groups being preferred and linear alkylene groups being more preferred. Alkenylene groups include linear alkenylene groups, branched alkenylene groups, and cyclic alkenylene groups, with linear or branched alkenylene groups being preferred and linear alkenylene groups being more preferred. Alkynylene groups include linear alkynylene groups and branched alkynylene groups, with linear alkynylene groups being preferred. Arylene groups may be monocyclic or polycyclic. Monocyclic arylene groups are preferred. Specific examples of arylene groups include phenylene groups and naphthylene groups, with phenylene groups being preferred. Alkylene groups, alkenylene groups, alkynylene groups, and arylene groups may further have substituents. The substituents are preferably groups with 1 to 10 atoms. Preferred specific examples of groups having 1 to 10 atoms include C1-C3 alkyl groups [methyl group, ethyl group, propyl group, and isopropyl group], C2-C3 alkenyl groups [ethenyl group and propenyl group], C2-C4 alkynyl groups [ethynyl group, propynyl group, etc.], cyclopropyl group, C1-C2 alkoxy groups [methoxy group and ethoxy group], C2-C3 acyl groups [acetyl group and propionyl group], C2-C3 alkoxycarbonyl groups [methoxycarbonyl group and ethoxycarbonyl group], C2 acyloxy groups [acetyloxy group], and C2 Examples include acylamino groups (acetylamino groups), hydroxyalkyl groups having 1 to 3 carbon atoms (hydroxymethyl groups, hydroxyethyl groups, hydroxypropyl groups), aldehyde groups, hydroxyl groups, carboxyl groups, sulfo groups, phospho groups, carbamoyl groups, cyano groups, isocyanate groups, mercapto groups, nitro groups, nitroxy groups, isothiocyanate groups, cyanate groups, thiocyanate groups, acetoxy groups, acetamide groups, formyl groups, formyloxy groups, formamide groups, sulfamino groups, sulfino groups, sulfamoyl groups, phosphono groups, acetyl groups, halogen atoms, alkali metal atoms, etc.

[0063] In equation (A), XＡ１ and X Ａ２ is L Ａ１ Preferably, the atoms 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.

[0064] In equation (B), X Ｂ１ and X Ｂ３ is L Ｂ１ It is preferable that the atoms 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. Also, X Ｂ２ and X Ｂ３ is L Ｂ２ Preferably, the atoms 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.

[0065] In equation (C), X Ｃ１ and X Ｃ４ is L Ｃ１ It is preferable that the atoms 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. Also, X Ｃ２ and X Ｃ４ is L Ｃ２ It is preferable that the atoms 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. Also, X Ｃ３ and X Ｃ４ is L Ｃ３Preferably, the atoms 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.

[0066] Note X Ａ１ and X Ａ２ is L Ａ１ The fact that they are separated by 1 to 10 atoms means that X Ａ１ and X Ａ２ This means that the number of atoms constituting the shortest molecular chain connecting the two is between 1 and 10. For example, in the case of formula (A1) below, X Ａ１ and X Ａ２ When two atoms are separated, and in the cases of formulas (A2) and (A3) below, X Ａ１ and X Ａ２ They are separated by three atoms. The numbers appended to the following structural formulas represent X Ａ１ and X Ａ２ This represents the order of the atoms that make up the shortest distance molecular chain connecting two points.

[0067] Specific examples of polydentate ligands include ethanedithiol, 3-mercaptopropionic acid, thiosalicylic acid, thioglycolic acid, 2-aminoethanol, 2-aminoethanethiol, 2-mercaptoethanol, glycolic acid, ethylenediamine, glycine, 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, 3-aminopropan-1-ol, 3-mercapto-2,2-bis(mercaptomethyl)-1-propanol, 1-thioglycerol, dimercaprol, 1-mercapto-2-butanol, 1-mercapto-2-pentanol, 3-mercapto-1-propanol, 2,3-dimercapto-1-propanol, diethanolamine, 2-(2-aminoethyl)aminoethanol, dimethylentriamine, 1,1-oxybismethylamine N, 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, 1,2 Examples include benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 2-mercaptobenzoic acid, 3-mercaptobenzoic acid, 4-mercaptobenzoic acid, 3-mercapto-2,2-bismercaptomethyl-1-propanol, trimethylolpropanetris (thioglycolate), pentaerythritol tetrakis (mercaptoacetate), dipentaerythritol hexakis (3-mercaptopropionate), dithioerythritol and their derivatives.

[0068] The ligand content in the quantum dot dispersion is preferably 0.1 to 15% by mass. The lower limit is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. The upper limit is preferably 10% by mass or less, and even more preferably 7% by mass or less. Furthermore, the ligand content in the quantum dot dispersion is preferably 10 to 150 mg / mL. The lower limit is preferably 20 mg / mL or more, and even more preferably 25 mg / mL or more. The upper limit is preferably 100 mg / mL or less, and even more preferably 70 mg / mL or less. Furthermore, the quantum dot dispersion preferably contains 10 to 100 parts by mass of ligand per 100 parts by mass of the total of the first quantum dots and the second quantum dots described above. The lower limit is preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more. The upper limit is preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less.

[0069] (Solvent) The quantum dot dispersion of the present invention contains a solvent. The solvent is not particularly limited, but it is preferable that it is a solvent that is difficult to dissolve quantum dots and easy to dissolve ligands. The solvent is preferably an organic solvent. The organic solvent may be either a polar solvent or a nonpolar solvent, but for the reason of dispersibility of quantum dots, it is preferably a polar solvent, and more preferably a polar solvent having an amide group.

[0070] The boiling point of the organic solvent is preferably between 60 and 250°C. The lower limit is preferably 70°C or higher, and more preferably 80°C or higher. The upper limit is preferably 200°C or lower, and more preferably 190°C or lower.

[0071] Specific examples of solvents include alkanes (n-hexane, n-octane, etc.), alkenes (octadecene, etc.), benzene, toluene, N,N-dimethylformamide, dimethyl sulfoxide, N-methylformamide, N,N-dimethylacetamide, propylene carbonate, and ethylene glycol, with N,N-dimethylformamide, dimethyl sulfoxide, or N-methylformamide being preferred.

[0072] The solvent content in the quantum dot dispersion is preferably 50 to 99% by mass, more preferably 70 to 99% by mass, and even more preferably 85 to 98% by mass. The solvent contained in the quantum dot dispersion may be only one type, or it may be a mixed solvent of two or more types. If two or more types of solvents are included, it is preferable that their total amount is within the above range.

[0073] The quantum dot dispersion may further contain other components, to the extent that it does not impair the effects of the present invention.

[0074] <Semiconductor Film> The semiconductor film of the present invention is obtained using the quantum dot dispersion of the present invention described above. The semiconductor film of the present invention can be used in photodetectors and image sensors. More specifically, the above semiconductor film can be used in the photoelectric conversion layer of photodetectors and image sensors. For this reason, the semiconductor film of the present invention is preferably used for the photoelectric conversion layer of photodetectors or image sensors.

[0075] Since the semiconductor film of the present invention has excellent sensitivity to light in the infrared region, an image sensor using the semiconductor film of the present invention as a photoelectric conversion layer can be particularly preferably used as an infrared sensor. Therefore, the semiconductor film of the present invention is preferably used as a photoelectric conversion layer for infrared sensors.

[0076] The infrared light wavelengths mentioned above are preferably light with wavelengths exceeding 700 nm, more preferably light with wavelengths of 800 nm or more, and even more preferably light with wavelengths of 900 nm or more. Furthermore, the infrared light wavelengths are preferably light with wavelengths of 2000 nm or less, and more preferably light with wavelengths of 1600 nm or less.

[0077] The total content of the first quantum dots and the second quantum dots in the semiconductor film is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. Furthermore, the total content of the first quantum dots, the second quantum dots, and the ligands in the semiconductor film is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0078] <Method for Manufacturing Semiconductor Films> The method for manufacturing semiconductor films of the present invention includes the step of applying the quantum dot dispersion of the present invention described above onto a support.

[0079] There are no particular restrictions on the shape, structure, size, etc., of the support to which the quantum dot dispersion is applied, and can be appropriately selected according to the purpose. The structure of the support may be a single layer or a multilayer structure. As the support, for example, a support made of inorganic materials such as silicon, glass, YSZ (Yttria-Stabilized Zirconia), resin, resin composite material, etc. may be used. Electrodes, insulating films, etc. may also be formed on the support. In that case, the quantum dot dispersion is also applied to the electrodes and insulating films on the support.

[0080] There are no particular limitations on the application method of the quantum dot dispersion. Examples of application methods include spin coating, dipping, inkjet, dispenser, screen printing, letterpress printing, intaglio printing, and spray coating.

[0081] In the semiconductor film manufacturing method of the present invention, it is preferable to apply a quantum dot dispersion onto a support and then dry it. Drying removes any remaining solvent in the film. The drying temperature is preferably 50 to 150°C. The upper limit of the drying temperature is preferably 120°C or less, and more preferably 100°C or less. The lower limit of the drying temperature is preferably 55°C or higher, and more preferably 60°C or higher. The drying time is preferably 1 to 300 minutes. The upper limit of the drying time is preferably 200 minutes or less, and more preferably 100 minutes or less. The lower limit of the drying time is preferably 2 minutes or more, and more preferably 5 minutes or more.

[0082] In the semiconductor film manufacturing method of the present invention, after applying a quantum dot dispersion to form a film of quantum dot aggregates, a ligand solid phase exchange step may be performed. By performing this step, ligands coordinated to quantum dots can be exchanged with ligands contained in the ligand solution, or ligands contained in the ligand solution can be coordinated to quantum dots to suppress the occurrence of surface defects in quantum dots.

[0083] Examples of ligands included in the ligand solution include those described as being used in the quantum dot dispersion of the present invention. The ligands included in the ligand solution may be the same as or different from the ligands included in the quantum dot dispersion. The ligand solution may contain only one type of ligand or two or more types. Furthermore, two or more ligand solutions may be used in the step of applying the ligand solution.

[0084] The solvent included in the ligand solution is preferably selected appropriately according to the type of ligand included in the ligand solution, and is preferably a solvent that readily dissolves the ligand. Furthermore, the solvent included in the ligand solution is preferably an organic solvent with a high dielectric constant. Specific examples include ethanol, acetone, methanol, acetonitrile, dimethylformamide, dimethyl sulfoxide, butanol, and propanol. In addition, the solvent included in the ligand solution is preferably a solvent that does not easily remain in the formed semiconductor film. From the viewpoint of being easy to dry and easy to remove by washing, it is preferably a low-boiling point alcohol, ketone, or nitrile, and more preferably methanol, ethanol, acetone, or acetonitrile.

[0085] The method for applying the ligand solution is the same as the method for applying the quantum dot dispersion onto the support, and the preferred embodiment is also the same.

[0086] When applying a ligand solution, a rinsing step may be performed by contacting the film with a rinsing solution after the ligand solution has been applied. By performing a rinsing step, excess ligands contained in the film and ligands detached from quantum dots can be removed. In addition, residual solvent and other impurities can be removed. As the rinsing solution, an aprotic solvent is preferable because it can more effectively remove excess ligands contained in the film and ligands detached from quantum dots, and it can easily maintain a uniform film surface by rearranging the quantum dot surface. Specific examples of aprotic solvents include acetonitrile, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, diethyl ether, tetrahydrofuran, cyclopentyl methyl ether, dioxane, ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, hexane, octane, cyclohexane, benzene, toluene, chloroform, carbon tetrachloride, and dimethylformamide, with acetonitrile or tetrahydrofuran being preferred, and acetonitrile being more preferred.

[0087] The rinsing process may be performed multiple times using two or more rinsing solutions with different polarities (dielectric constants). For example, it is preferable to first rinse with a rinsing solution with a high dielectric constant (also called the first rinsing solution), and then rinse again with a rinsing solution with a lower dielectric constant than the first rinsing solution (also called the second rinsing solution). The dielectric constant of the first rinsing solution is preferably 15 to 50, more preferably 20 to 45, and even more preferably 25 to 40. The dielectric constant of the second rinsing solution is preferably 1 to 15, more preferably 1 to 10, and even more preferably 1 to 5.

[0088] A semiconductor film can be manufactured through this process. The obtained semiconductor film can be used in photodetectors and image sensors. For example, it can be used in the photoelectric conversion layer of a photodetector or image sensor. Since the semiconductor film obtained using the dispersion of the present invention has excellent sensitivity to light in the infrared region, a photodetector using this semiconductor film as the photoelectric conversion layer is preferably used as a photodetector for detecting light in the infrared region.

[0089] The infrared light wavelengths mentioned above are preferably light with wavelengths exceeding 700 nm, more preferably light with wavelengths of 800 nm or more, and even more preferably light with wavelengths of 900 nm or more. Furthermore, the infrared light wavelengths are preferably light with wavelengths of 2000 nm or less, and more preferably light with wavelengths of 1600 nm or less.

[0090] The total content of quantum dots and ligands in the semiconductor film is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit can be 100% by mass or less.

[0091] <Photodetector> The photodetector of the present invention has the semiconductor film of the present invention described above. Specifically, it is preferable that the photodetector has the semiconductor film of the present invention as the photoelectric conversion layer. Examples of photodetector types include photoconductor type photodetectors and photodiode type photodetectors. Among these, photodiode type photodetectors are preferred because they are easier to obtain with a high signal-to-noise ratio (S / N ratio).

[0092] Since the semiconductor film of the present invention has excellent sensitivity to light in the infrared region, the photodetector of the present invention is preferably used as a photodetector for detecting light in the infrared region. In other words, the photodetector of the present invention is preferably used as an infrared photodetector.

[0093] The photodetector may be a photodetector that simultaneously detects light with wavelengths in the infrared region and light with wavelengths in the visible region (preferably light in the range of 400 to 700 nm).

[0094] Figure 1 shows one embodiment of a photodetector. Figure 1 is a diagram showing one embodiment of a photodiode type photodetector. The arrows in the figure represent incident light to the photodetector. The photodetector 1 shown in Figure 1 includes a second electrode 12, a first electrode 11 provided opposite the second electrode 12, a photoelectric conversion layer 13 provided between the second electrode 12 and the first electrode 11, an electron transport layer 21 provided between the first electrode 11 and the photoelectric conversion layer 13, and a hole transport layer 22 provided between the second electrode 12 and the photoelectric conversion layer 13. The photodetector 1 shown in Figure 1 is used so that light is incident from above the first electrode 11. Although not shown, a transparent substrate may be placed on the light incident side surface of the first electrode 11. Examples of transparent substrates include glass substrates, resin substrates, ceramic substrates, etc.

[0095] (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), fluorine-doped tin oxide (FTO), and the like.

[0096] 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 the cross-section of the photodetector 1 using a scanning electron microscope (SEM) or the like.

[0097] (Electron Transport Layer) The electron transport layer 21 is a layer that has the function of transporting electrons generated in the photoelectric conversion layer 13 to the electrodes. The electron transport layer is also called the hole blocking layer. The electron transport layer is formed of an electron transport material that can perform this function.

[0098] Examples of electron transport materials include fullerene compounds such as [6,6]-Phenyl-C61-Butyric Acid Methyl Ester (PC61BM), perylene compounds such as perylenetetracarboxydiimide, tetracyanoquinodimethane, titanium dioxide, tin oxide, zinc oxide, indium oxide, indium tungsten oxide, indium zinc oxide, indium tin oxide, and fluorine-doped tin oxide. The electron transport material may also be in the form of particles.

[0099] The electron transport layer 21 is preferably composed 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 methods such as sputtering, chemical vapor deposition (CVD), or vacuum deposition.

[0100] The electron transport layer may be a single layer or a laminate of two or more layers. The thickness of the electron transport layer is preferably 5 to 500 nm. The upper limit is preferably 200 nm or less, and more preferably 100 nm or less. The lower limit is preferably 10 nm or more. Furthermore, the thickness of the electron transport layer is preferably 0.05 to 10 times the thickness of the photoelectric conversion layer 13, more preferably 0.1 to 5 times, and even more preferably 0.2 to 2 times.

[0101] The electron transport layer may be subjected to ultraviolet ozone treatment. In particular, if the electron transport layer is composed of nanoparticles, ultraviolet ozone treatment is desirable. By performing ultraviolet ozone treatment, the wettability of the quantum dot dispersion to the electron transport layer can be improved, and residual organic matter in the electron transport layer can be decomposed or removed, resulting in high device performance. The wavelength of the ultraviolet light to be irradiated can be selected between 100 and 400 nm. It is preferable to have a peak intensity between 200 and 300 nm, and more preferably between 240 and 270 nm, because the above effects are easily obtained and excessive damage to the film can be avoided. There are no particular restrictions on the irradiation intensity of the ultraviolet light, but it is preferable to use 1 to 100 mW / cm² because the above effects are easily obtained and excessive damage to the film can be avoided. ２ Preferably, the power is 10 to 50 mW / cm². ２ It is more preferable that this is the case. There are no particular limitations on the processing time, but for the same reasons, it is preferably 1 to 60 minutes, more preferably 1 to 20 minutes, and even more preferably 3 to 15 minutes.

[0102] (Photoelectric Conversion Layer) The photoelectric conversion layer 13 is composed of a semiconductor film formed using the quantum dot dispersion of the present invention described above. The photoelectric conversion layer 13 can be formed using the semiconductor film manufacturing method of the present invention described above.

[0103] The thickness of the photoelectric conversion layer 13 is preferably 10 to 1000 nm. The lower limit of the thickness is preferably 20 nm or more, and more preferably 30 nm or more. The upper limit of the thickness is preferably 600 nm or less, more preferably 550 nm or less, even more preferably 500 nm or less, and particularly preferably 450 nm or less. The refractive index of the photoelectric conversion layer 13 with respect to light of the target wavelength to be detected by the photodetector element can be 1.5 to 5.0.

[0104] (Hole transport layer) The hole transport layer 22 is a layer that has the function of transporting holes generated in the photoelectric conversion layer 13 to the electrodes. The hole transport layer is also called the electron blocking layer.

[0105] The hole transport layer 22 is formed of a hole transport material capable of performing this function. For example, the hole transport material may be 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']dithiophen-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 l)carbonyl]thieno[3,4-b]thiophenediyl})), poly(3-hexylthiophene-2,5-diyl), poly(3-n-octyl Examples include oxythiophene, poly(9,9'-dioctyl-fluorene-co-bithiophene), poly(3,3'''-didodecyl-quarterthiophene), 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), and PC71BM ([6,6]-phenyl-C71-methyl butyrate). Furthermore, organic hole transport materials described in paragraphs 0209 to 0212 of Japanese Patent Publication No. 2001-291534 can also be used. Quantum dots can also be used as hole transport materials. Examples of quantum dot materials constituting quantum dots include nanoparticles (particles 0.5 nm to less than 100 nm in size) of general semiconductor crystals [a) Group IV semiconductors, b) Compound semiconductors of Group IV-IV, Group III-V, or Group II-VI, c) Compound semiconductors consisting of a combination of three or more elements from Group II, Group III, Group IV, Group V, and Group VI].Specifically, PbS, PbSe, PbSeS, InN, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, HgTe, HgCdTe, Ag. ２ S, Ag ２ Se, Ag ２ Examples include semiconductor materials with relatively narrow band gaps, such as Te, SnS, SnSe, SnTe, Si, and InP. Ligands may be coordinated to the surface of the quantum dots.

[0106] 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.

[0107] (Second Electrode) The second electrode 12 is preferably made of a metallic 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 making the second electrode 12 of such a metallic material, a photodetector can be made with high external quantum efficiency and low dark current. In addition, the second electrode 12 can also be made of the conductive metal oxide, carbon material, conductive polymer, etc. As the carbon material, any conductive material is acceptable, such as fullerene, carbon nanotube, graphite, graphene, etc.

[0108] The work function of the second electrode 12 is preferably 4.6 eV or higher, more preferably 4.8 to 5.7 eV, and even more preferably 4.9 to 5.3 eV, for the reasons that it enhances the electron blocking properties by the hole transport layer and facilitates the collection of holes generated in the device.

[0109] 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.

[0110] (Charge extraction layer) Although not shown in the figure, the photodetector may have a charge extraction layer between the second electrode 12 and the hole transport layer 22. Having a charge extraction layer allows for high external quantum efficiency at a low applied voltage.

[0111] Materials for forming the charge extraction layer include metal oxides and organic semiconductors, with metal oxides being preferred. Examples of 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. Examples of organic semiconductors include polythiophene compounds. Specific examples of polythiophene compounds include the materials mentioned above. The charge extraction layer may be a single layer or a multilayer film of two or more layers.

[0112] The thickness of the charge extraction layer is preferably 1 to 100 nm. The lower limit is preferably 5 nm or more. The upper limit is preferably 50 nm or less.

[0113] (Blocking layer) Although not shown in the diagram, the photodetector may have a blocking layer between the first electrode 11 and the electron transport layer 21. The blocking layer is a layer that 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, titanium oxide, tin oxide, zinc oxide, niobium oxide, tungsten oxide, etc. The blocking layer may be a single layer film or a laminated film of two or more layers. The 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.

[0114] In a photodetector, the wavelength λ of the light to be detected by the photodetector and the optical path length L of the light of 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 It is preferable that the relationship between wavelength λ and optical path length L satisfies the following equation (1-1), and it is more preferable that the relationship between wavelength λ and optical path length L satisfies the following equation (1-2). λWhen such a relationship is satisfied, in the photoelectric conversion layer 13, the phases of the light (incident light) incident from the first electrode 11 side and the light (reflected light) reflected from the surface of the second electrode 12 can be aligned. As a result, the light is enhanced by the optical interference effect, and a higher external quantum efficiency can be obtained.

[0115] 0.05 + m / 2 ≤ L λ / λ ≤ 0.35 + m / 2 ··· (1-1) 0.10 + m / 2 ≤ L λ / λ ≤​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0120] The configuration of the image sensor is not particularly limited, as long as it includes a light-detecting element and functions as an image sensor. Examples of light-detecting elements include those mentioned above.

[0121] The image sensor may include an infrared transmission filter layer. The infrared transmission filter layer preferably has low transmittance of light in the visible wavelength range, 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.

[0122] Examples of infrared transmission filter layers include those composed of a resin film containing a colorant. Examples of colorants include chromatic colorants such as red, green, blue, yellow, purple, and orange, as well as black colorants. Preferably, the colorant contained in the infrared transmission filter layer is formed by a combination of two or more chromatic colorants to form black, or contains a black colorant. When black is formed by a combination of two or more chromatic colorants, examples of combinations of chromatic colorants include the following embodiments (C1) to (C7): (C1) Embodiment containing a red colorant and a blue colorant. (C2) Embodiment containing a red colorant, a blue colorant, and a yellow colorant. (C3) Embodiment containing a red colorant, a blue colorant, a yellow colorant, and a purple colorant. (C4) Embodiment containing a red colorant, a blue colorant, a yellow colorant, a purple colorant, and a green colorant. (C5) Embodiment containing a red colorant, a blue colorant, a yellow colorant, and a green colorant. (C6) An embodiment containing a red colorant, a blue colorant, and a green colorant. (C7) An embodiment containing a yellow colorant and a purple colorant.

[0123] The above-mentioned chromatic colorants may be pigments or dyes. They may contain both pigments and dyes. The black colorant is preferably an organic black colorant. Examples of organic black colorants include bisbenzofuranone compounds, azomethine compounds, perylene compounds, and azo compounds.

[0124] The infrared transmission filter layer may further contain an infrared absorbent. By including an infrared absorbent in the infrared transmission filter layer, the wavelength of the transmitted light can be shifted to the longer wave side. Examples of infrared absorbents include pyrrolopyrrole compounds, cyanine compounds, squarylium compounds, phthalocyanine compounds, naphthalocyanine compounds, quaterylene compounds, merocyanine compounds, crokonium compounds, oxonol compounds, iminium compounds, dithiol compounds, triarylmethane compounds, pyromethene compounds, azomethine compounds, anthraquinone compounds, dibenzofuranone compounds, dithiolene metal complexes, metal oxides, and metal borides.

[0125] 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 of the following spectral characteristics (1) to (5) can be used. (1) A filter layer in which the maximum value of the 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 value of the 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 value of the 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 value of the 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 value of the 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 value of the 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 value of the 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 value of the 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 value in the wavelength range of 1600 to 2000 nm is 70% or more (preferably 75% or more, more preferably 80% or more).Furthermore, as infrared transmission filters, films described in Japanese Patent Publication No. 2013-077009, Japanese Patent Publication No. 2014-130173, Japanese Patent Publication No. 2014-130338, International Publication No. 2015 / 166779, International Publication No. 2016 / 178346, International Publication No. 2016 / 190162, International Publication No. 2018 / 016232, Japanese Patent Publication No. 2016-177079, Japanese Patent Publication No. 2014-130332, and International Publication No. 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 a single filter may be used.

[0126] The image sensor may include an infrared shielding filter to improve various performance aspects such as noise reduction. Specific examples of infrared shielding filters include those described in International Publication No. 2016 / 186050, International Publication No. 2016 / 035695, Japanese Patent No. 6248945, International Publication No. 2019 / 021767, Japanese Patent Application Publication No. 2017-067963, and Japanese Patent No. 6506529.

[0127] The image sensor may include a dielectric multilayer film. Examples of dielectric multilayer films include those in which multiple layers of high refractive index dielectric thin films (high refractive index material layers) and low refractive index dielectric thin films (low refractive index material layers) are alternately stacked. While there are no particular limitations on the number of layers of dielectric thin films in the dielectric multilayer film, 2 to 100 layers are preferred, 4 to 60 layers are more preferred, and 6 to 40 layers are even more preferred. As the material used to form the high refractive index material layer, a material with a refractive index of 1.7 to 2.5 is preferred. A specific example is 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 Examples include the following. Materials with a refractive index of 1.2 to 1.6 are preferred for forming the low refractive index layer. A specific example is Al 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 These are some examples. There are no particular restrictions on the method for forming the dielectric multilayer film, but examples include ion plating, vacuum deposition methods such as ion beam deposition, physical vapor deposition (PVD) methods such as sputtering, and chemical vapor deposition (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 light to be blocked is λ (nm). Specific examples of dielectric multilayer films include, for example, the films described in Japanese Patent Application Publication No. 2014-130344 and Japanese Patent Application Publication No. 2018-010296.

[0128] 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 centered on the wavelength that shows the maximum transmittance, λ. ｔ１ In that case, the central wavelength λ ｔ１ Preferably, the center wavelength is ±100 nm, and the center wavelength is λ ｔ１ It is more preferable that the central wavelength is ±75 nm. ｔ１ A more preferable value is ±50 nm.

[0129] 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 it may have multiple transmission wavelength bands.

[0130] The image sensor may include a color separation filter layer. Examples of color separation filter layers include those containing colored pixels. Examples of colored pixels include red, green, blue, yellow, cyan, and magenta pixels. The color separation filter layer may contain two or more colored pixels, or only one color. This can be appropriately selected depending on the application and purpose. For example, the filter described in International Publication No. 2019 / 039172 can be used.

[0131] Furthermore, if the color separation layer contains two or more colored pixels, the colored pixels of each color may be adjacent to each other, and partitions may be provided between each colored pixel. There are no particular limitations on the material of the partitions. Examples include organic materials such as siloxane resin and fluororesin, and inorganic particles such as silica particles. The partitions may also be made of metals such as tungsten and aluminum.

[0132] Furthermore, if the image sensor includes an infrared transmission filter layer and a color separation layer, it is preferable that the color separation layer is located on a separate 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 in two dimensions. Note that two-dimensional arrangement of the infrared transmission filter layer and the color separation layer means that at least a portion of both lies on the same plane.

[0133] The image sensor may include intermediate layers such as a planarization layer, a base layer, and an adhesion layer, an anti-reflective coating, and a lens. As the anti-reflective coating, for example, a film made from the composition described in International Publication No. 2019 / 017280 can be used. As the lens, for example, a structure described in International Publication No. 2018 / 092600 can be used.

[0134] The present invention will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate, as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[0135] <Measurement Method for Quantum Dot Roundness, Average Roundness, and Peak Values> The roundness of quantum dots was calculated using image analysis software (Winroof) from Z-contrast images (magnification 4,000,000x) of quantum dots taken with a spherical aberration-corrected scanning transmission electron microscope (Cs-STEM, Hitachi, Ltd., HD-2700). Roundness was calculated using the following formula, and the average value of all particles (10 or more particles) in the Z-contrast image was taken as the average roundness. A histogram based on roundness was created, and the spectrum was separated. Among the roundness values ​​between 0.40 and 1.0, the smallest peak was taken as the "first peak," and the largest peak was taken as the "second peak." Roundness = 4πS / L ２ S: Projected area L: Perimeter length

[0136] <Measurement Method for the Ratio of Quantum Dot Numbers> The ratio of the number of quantum dots with a roundness of 0.40 or more and less than 0.75 to the total number of quantum dots contained in the dispersion, and the ratio of the number of quantum dots with a roundness of 0.75 or more and 1.0 or less, were calculated as area ratios from the roundness histogram.

[0137] <Preparation of Quantum Dot Dispersions> (Preparation of Quantum Dot Dispersions A-1 to A-6, B-1 to B-7) 1 mL of octane dispersion containing quantum dots listed in the table below with oleic acid coordinated to the surface, 0.5 g of ligands listed in the table below, and 10 mL of solvent listed in the table below were measured into a centrifuge tube and vigorously stirred for 10 minutes. Next, 30 mL of hexane was added and vigorously stirred for 1 minute, and the upper hexane layer was removed. This procedure was repeated twice. Then, an excess amount of toluene was added and centrifugation was performed at 4000 rpm for 5 minutes. The obtained precipitate was vacuum dried for 30 minutes, and the solvent listed in the table below was added and stirred for 2 hours to obtain quantum dot dispersions A-1 to A-6, B-1 to B-7. All of the above operations were performed under nitrogen.

[0138]

[0139] Details of the materials indicated by the abbreviations in the table above are as follows: (Ligand) L1-1: InBr ３ L2-1: 3-mercaptopropionic acid L2-2: mercaptoethanol

[0140] (Solvent) S-1: N,N-dimethylformamide

[0141] (Preparation of Quantum Dot Dispersions for Examples 1-6 and Comparative Example 1) Quantum dot dispersions for Examples 1-6 were prepared by mixing quantum dot dispersion A and quantum dot dispersion B, as shown in the table below, in the proportions shown in the table below. In Comparative Example 1, only quantum dot dispersion B-7 was used. In each quantum dot dispersion, the total amount of quantum dots in the components excluding ligands and solvents was 50% by mass or more. The "Ratio of First Quantum Dots" and "Ratio of Second Quantum Dots" columns in the table below indicate the ratio of the number of first quantum dots (quantum dots with a band gap of 1.35 eV or less and a roundness of 0.40 or more and less than 0.75) and the ratio of the number of second quantum dots (quantum dots with a band gap of 1.35 eV or less and a roundness of 0.75 or more and 1.0 or less) to the total number of quantum dots contained in the quantum dot dispersions for Examples 1-6 and Comparative Example 1.

[0142] <Evaluation> (Evaluation of Dispersibility 1) The quantum dot dispersions of Examples 1-6 and Comparative Example 1 were left to stand under nitrogen at 25°C for one week or one month, and the presence or absence of aggregates was visually checked to evaluate their dispersibility. (Evaluation of Dispersibility 2) The quantum dot dispersions of Examples 1-6 and Comparative Example 1 were left to stand under nitrogen at 20°C for one week or one month, and the presence or absence of aggregates was visually checked to evaluate their dispersibility. -Evaluation Criteria for Dispersibility 1 and Dispersibility 2- A: No aggregation was observed even after standing for one month B: Slight aggregation was observed after standing for one month, but no aggregation was observed after standing for one week C: Slight aggregation was observed after standing for one week D: In the manufacturing process of the quantum dot dispersion, the precipitate after centrifugation was not dispersed

[0143]

[0144] As shown in the table above, all of the quantum dot dispersions in the examples exhibited excellent dispersibility.

[0145] <Preparation of Zinc Oxide Particle Dispersion> (Zinc Oxide Particle Dispersion 1) 1.5 mmol of zinc acetate dihydrate and 15 mL of dimethyl sulfoxide (DMSO) were measured into a flask and stirred to obtain a zinc acetate solution. A TMACl solution was prepared by dissolving 4 mmol of tetramethylammonium chloride (TMACl) in 4 mL of methanol, and a KOH solution was prepared by dissolving 4 mmol of potassium hydroxide (KOH) in 4 mL of methanol. The KOH solution was slowly added to the TMACl solution while vigorously stirring, and after stirring for 30 minutes, insoluble components were removed by passing the mixture through a 0.45 μm pore size filter to obtain a tetramethylammonium hydroxide (TMAH) solution. 6 mL of the TMAH solution was added to the zinc acetate solution in the flask at a dropping rate of 6 mL / min. After holding for 1 hour, the reaction mixture was collected. An excess amount of acetone was added to the reaction mixture, and the mixture was centrifuged at 10,000 rpm for 10 minutes. The supernatant was removed, the precipitate was dispersed in methanol, and then precipitated again with acetone. 5 ml of ethanol and 80 μl of aminoethanol were added, and the mixture was ultrasonically dispersed to obtain zinc oxide particle dispersion 1 with a concentration of undoped zinc oxide particles of approximately 30 mg / mL.

[0146] <Manufacturing of the photodetector element> An ITO (Indium Tin Oxide) film with a thickness of approximately 100 nm was deposited on quartz glass by sputtering through a metal mask to form the first electrode. Next, SiO ２ An insulating layer was formed by sputtering via a metal mask to fill the space between the electrodes. Next, a JEIGHT UVO-CLEANER MODEL 144AX-100 was used to measure 30 mW / cm². ２Ultraviolet ozone treatment was performed for 5 minutes under the condition of a wavelength peak of 254 nm. Next, zinc oxide particle dispersion 1 was dropped onto the ITO film (first electrode), spin-coated at 3000 rpm, and heated at 60°C for 5 minutes. This process was repeated twice to form a zinc oxide particle film with a thickness of approximately 200 nm, thereby forming an electron transport layer. Next, the quantum dot dispersion described in the table below was dropped onto the electron transport layer, spin-coated at 1000 rpm, and dried at 120°C for 10 minutes to form a quantum dot film. The process of forming the quantum dot film was repeated twice to form a photoelectric conversion layer with a thickness of 200 nm. Next, the photoelectric conversion layer was dried in a glove box for 10 hours.

[0147] Next, a dichlorobenzene solution (concentration 5 mg / mL) of PTB7 (poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophen-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophendiyl})) was spin-coated onto the photoelectric conversion layer at 2000 rpm, and then dried in a glove box for 10 hours to form a hole transport layer.

[0148] Next, a 100 nm thick Au film (second electrode) was deposited on the hole transport layer using a vacuum deposition method via a metal mask to form six element sections, thereby manufacturing a photodiode-type photodetector element.

[0149] <Evaluation> (Evaluation of dark current 1, external quantum efficiency 1, and yield 1) Dark current 1, external quantum efficiency 1, and yield 1 were evaluated for each photodetector using a semiconductor parameter analyzer (C4156, manufactured by Agilent). First, the current-voltage characteristics (I-V characteristics) were measured while sweeping the voltage from 0V to -5V without light irradiation, and the dark current 1 was evaluated based on the following criteria. Here, the dark current value was defined as the value at -1V. Next, the I-V characteristics were measured while sweeping the voltage from 0V to -5V with monochrome light of wavelength 1450nm irradiated. The photocurrent value was obtained by subtracting the above dark current value from the current value when -1V was applied, and the photoelectric conversion efficiency was calculated from this value, and the external quantum efficiency 1 was evaluated based on the following criteria. The dark current value and external quantum efficiency were measured for each element part (a total of 60 element parts) of the 10 photodetectors. For the evaluation of dark current 1 and external quantum efficiency 1, the values ​​of the dark current and external quantum efficiency used were those of the element that showed the median value among the measurements taken at 60 element sections. For the evaluation of yield 1, any element section whose measured dark current or photoelectric conversion rate was more than an order of magnitude different from the median value was considered defective. Furthermore, any element sections of the photodetector that showed aggregates under optical microscope were also considered defective. The yield rate was calculated using the following formula, and the yield was evaluated according to the following criteria: Yield rate = (60 - number of defective element sections) / 60 × 100

[0150] (Evaluation of Dark Current 2, External Quantum Efficiency 2, and Yield 2) Dark current 2, external quantum efficiency 2, and yield 2 were evaluated for each photodetector using a semiconductor parameter analyzer (C4156, manufactured by Agilent). First, the current-voltage characteristics (I-V characteristics) were measured while sweeping the voltage from 0V to -5V without light irradiation, and the dark current 2 was evaluated based on the following criteria. Here, the dark current value was defined as the value at -1.5V. Next, the I-V characteristics were measured while sweeping the voltage from 0V to -5V with monochrome light of wavelength 1450nm irradiated. The photocurrent value was obtained by subtracting the above dark current value from the current value when -1.5V was applied, and the photoelectric conversion efficiency was calculated from this value, and the external quantum efficiency 2 was evaluated based on the following criteria. The dark current value and external quantum efficiency were measured for each element part of the 10 photodetectors (a total of 60 element parts). For the evaluation of dark current 2 and external quantum efficiency 2, the values ​​of the dark current and external quantum efficiency used were those of the element that showed the median value among the measurements taken at 60 element sections. For the evaluation of yield 2, any element section whose measured dark current or photoelectric conversion rate was more than an order of magnitude different from the median value was considered defective. Furthermore, any element sections of the photodetector that showed aggregates under optical microscope were also considered defective. The yield rate was calculated using the following formula, and the yield was evaluated according to the following criteria: Yield rate = (60 - number of defective element sections) / 60 × 100

[0151] - Evaluation criteria for dark current 1 and 2 - A: Dark current value is 5 × 10 －７ A / cm ２ B: Dark current value is less than 5 × 10 －７ A / cm ２ The above 5 x 10 －６ A / cm ２ Less than C: Dark current value is 5 × 10 －６ A / cm ２ That's all.

[0152] - Evaluation Criteria for External Quantum Efficiency 1 and 2 - A: External quantum efficiency value is 5% or higher B: External quantum efficiency value is 2% or higher but less than 5% C: External quantum efficiency value is less than 2%

[0153] - Evaluation Criteria for Yield Levels 1 and 2 - A: Yield rate is 75% or higher B: Yield rate is 50% or higher but less than 75% C: Yield rate is less than 50%

[0154] (Evaluation of Heat Resistance 1) A heat resistance test was conducted by heating the manufactured photodetector element on a hot plate at 150°C for 1 hour. The absorption rate at wavelengths of 400 to 1800 nm was measured before and after the heat resistance test using a spectrophotometer (UV-3600, manufactured by Shimadzu Corporation), and the degree of absorption fluctuation was calculated from the following formula to evaluate heat resistance 1.

[0155] (Evaluation of Heat Resistance 2) A heat resistance test was conducted by heating the manufactured photodetector element on a hot plate at 155°C for 1 hour. The absorption rate at wavelengths of 400 to 1800 nm was measured before and after the heat resistance test using a spectrophotometer (UV-3600, manufactured by Shimadzu Corporation), and the degree of absorption fluctuation was calculated from the following formula to evaluate heat resistance 2.

[0156] Absorption variation = |Ab1 - Ab2| Ab1: The maximum absorptivity of the photodetector before the heat resistance test. Ab2: The absorptivity of the photodetector at the Ab1 measurement wavelength after the heat resistance test.

[0157] - Evaluation Criteria for Heat Resistance 1 and 2 - A: Absorption variation is 1% or less B: Absorption variation is greater than 1% but 2.5% or less C: Absorption variation is greater than 2.5% but 4% or less D: Absorption variation is greater than 4%

[0158] The evaluation results for each category are recorded in the "Evaluation" column of the table below.

[0159]

[0160] As shown in the table above, the photodetector manufactured using the quantum dot dispersion of the example showed superior yield, dark current, external quantum efficiency, and heat resistance compared to the photodetector manufactured using the quantum dot dispersion of the comparative example.

[0161] By using the photodetector elements obtained in the examples and fabricating an image sensor using a known method together with an optical filter prepared according to the methods described in International Publication No. 2016 / 186050 and International Publication No. 2016 / 190162, an image sensor with good visible-infrared imaging performance can be obtained.

[0162] 1: Photodetector element 11: First electrode 12: Second electrode 13: Photoelectric conversion layer 21: Electron transport layer 22: Hole transport layer

Claims

1. A quantum dot dispersion comprising quantum dots, ligands, and a solvent, wherein the quantum dots comprise a first quantum dot having a band gap of 1.35 eV or less and a roundness of 0.40 or more and less than 0.75, and a second quantum dot having a band gap of 1.35 eV or less and a roundness of 0.75 or more and 1.0 or less, and the quantum dot content in the component obtained by removing the ligands and the solvent from the quantum dot dispersion is 50% by mass or more.

2. The quantum dot dispersion according to claim 1, wherein the roundness of the first quantum dot is 0.45 or more and 0.60 or less, and the roundness of the second quantum dot is 0.80 or more and 1.0 or less.

3. The quantum dot dispersion according to claim 1 or 2, wherein the first quantum dot and the second quantum dot are Group III-V quantum dots.

4. The quantum dot dispersion according to claim 1 or 2, wherein the first quantum dot and the second quantum dot each contain the element In.

5. The quantum dot dispersion according to claim 1 or 2, wherein the ligand comprises at least one selected from inorganic halides and organic compounds with a molecular weight of 200 or less.

6. A semiconductor film obtained from the quantum dot dispersion according to claim 1 or 2.

7. A method for manufacturing a semiconductor film, comprising the step of applying the quantum dot dispersion according to claim 1 or 2 onto a support.

8. A photodetector comprising the semiconductor film described in claim 6.

9. An image sensor comprising the semiconductor film described in claim 6.

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