Light detection element and image sensor

Abstract

The present invention provides a light detection element, which has: a photoelectric conversion layer, including a collection of semiconductor quantum dots QD1 containing metal atoms and a ligand L1 coordinated with the semiconductor quantum dots QD1; and a hole transport layer, which is arranged on the photoelectric conversion layer and includes a collection of semiconductor quantum dots QD2 containing metal atoms and a ligand L2 coordinated with the semiconductor quantum dots QD2, the band gap Eg2 of the semiconductor quantum dots QD2 is greater than the band gap Eg1 of the semiconductor quantum dots QD1, and the difference between the band gap Eg2 of the semiconductor quantum dots QD2 and the band gap Eg1 of the semiconductor quantum dots QD1 is greater than 0.10 eV. The present invention also provides an image sensor including a light detection element.

Description

Technical Field

[0001] The present invention relates to a light detection element and an image sensor having a photoelectric conversion layer including semiconductor quantum dots. Background Art

[0002] In recent years, photodetection elements that can detect light in the infrared region have attracted much attention in the fields of smartphones, surveillance cameras, and car cameras.

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

[0004] Furthermore, InGaAs-based semiconductor materials, which are well-known as near-infrared light receiving elements, have a problem in that a very costly process such as epitaxial growth is required to achieve high quantum efficiency, and therefore have not yet been widely used.

[0005] Furthermore, in recent years, semiconductor quantum dots have been studied. Non-patent document 1 describes an invention related to a light detection element having a photoelectric conversion layer containing PbS quantum dots.

[0006] Previous technical literature

[0007] Non-patent literature

[0008] Non-patent literature 1: Pawel E. Malinowski, Epimitheas Georgitzikis, Jorick Maes, Ioanna Vamvaka, Fortunato Frazzica, Jan Van Olmen 1, Piet De Moor, Paul Heremans, Zeger Hens and David Cheyns, “Thin-Film Quantum Dot Photodiode for MonolithicInfrared Image Sensors", Sensors, 2017, 17, 2867, doi: 10.3390 / s17122867 Summary of the invention

[0009] Technical issues to be solved by the invention

[0010] In recent years, as image sensors and other devices are required to improve their performance, various characteristics required of the photodetection elements used in these devices are also required to be further improved. For example, it is necessary to further reduce the dark current of the photodetection element. By reducing the dark current of the photodetection element, a higher signal-to-noise ratio (SN ratio) can be obtained in the image sensor.

[0011] According to the research of the present inventors, it has been found that the dark current of a light detection element having a photoelectric conversion layer formed of semiconductor quantum dots tends to be relatively high, and therefore there is still room for reducing the dark current. In addition, the dark current refers to the current that flows when no light is irradiated.

[0012] Therefore, an object of the present invention is to provide a light detection element and an image sensor with reduced dark current.

[0013] Means for solving technical problems

[0014] As a result of in-depth research on light detection elements having a photoelectric conversion layer containing semiconductor quantum dots, the inventors found that by using an aggregate of semiconductor quantum dots containing metal atoms and ligands coordinated to the semiconductor quantum dots as the photoelectric conversion layer, and stacking a hole transport layer containing an aggregate of semiconductor quantum dots containing metal atoms and ligands coordinated to the semiconductor quantum dots on the photoelectric conversion layer, and using semiconductor quantum dots with a band gap larger than that of the semiconductor quantum dots of the photoelectric conversion layer as the semiconductor quantum dots of the hole transport layer, dark current can be reduced, thereby completing the present invention.

[0015] <1> A light detection element comprising:

[0016] A photoelectric conversion layer comprising a collection of semiconductor quantum dots QD1 containing metal atoms and ligands L1 coordinated with the semiconductor quantum dots QD1; and

[0017] a hole transport layer, which is disposed on the photoelectric conversion layer and comprises a collection of semiconductor quantum dots QD2 containing metal atoms and a ligand L2 coordinated with the semiconductor quantum dots QD2,

[0018] The band gap Eg2 of the semiconductor quantum dot QD2 is greater than the band gap Eg1 of the semiconductor quantum dot QD1, and the difference between the band gap Eg2 of the semiconductor quantum dot QD2 and the band gap Eg1 of the semiconductor quantum dot QD1 is greater than 0.10 eV.

[0019] <2> according to <1> The light detection element, wherein

[0020] The semiconductor quantum dot QD1 and the semiconductor quantum dot QD2 each contain a Pb atom.

[0021] <3> according to <1> or <2> The light detection element, wherein

[0022] The semiconductor quantum dot QD1 and the semiconductor quantum dot QD2 include semiconductor quantum dots of the same type.

[0023] <4> according to <1> to <3> The light detecting element as described in any one of the preceding claims, wherein:

[0024] The semiconductor quantum dots QD1 and QD2 respectively contain PbS.

[0025] <5> according to <1> to <4> The light detecting element as described in any one of the preceding claims, wherein:

[0026] The ligand L1 and the ligand L2 include at least one selected from a ligand containing a halogen atom and a multidentate ligand containing two or more coordination parts.

[0027] <6> according to <5> The light detection element, wherein

[0028] The above-mentioned ligand containing a halogen atom is an inorganic halide.

[0029] <7> according to <6> The light detection element, wherein

[0030] The above-mentioned inorganic halide contains Zn atoms.

[0031] <8> according to <1> to <7> The light detecting element as described in any one of the preceding claims, wherein:

[0032] The above-mentioned ligand L1 contains thioglycolic acid.

[0033] <9> according to <1> to <8> The light detecting element as described in any one of the preceding claims, wherein:

[0034] The ligand L2 mentioned above contains a compound having a mercapto group.

[0035] <10> According to <1> to <9> The light detecting element described in any one of the above is a photodiode type light detecting element.

[0036] <11> An image sensor comprising <1> to <10> A light detecting element as described in any one of the items.

[0037] <12> according to <11> The image sensor is an infrared image sensor.

[0038] Effects of the Invention

[0039] According to the present invention, it is possible to provide a photodetection element and an image sensor with reduced dark current. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1This is a diagram showing one embodiment of a photodetection element.

[0041] Figure 2 It is a diagram showing another embodiment of the photodetection element. DETAILED DESCRIPTION

[0042] Hereinafter, the contents of the present invention will be described in detail.

[0043] In this specification, "to" is used to mean that the numerical values ​​described before and after it are included as the lower limit and the upper limit.

[0044] In the marking of groups (atomic groups) in this specification, the marking not indicating substituted or unsubstituted includes groups (atomic groups) without substitution and groups (atomic groups) with substitution. For example, "alkyl" includes not only alkyl groups without substitution (unsubstituted alkyl groups) but also alkyl groups with substitution (substituted alkyl groups).

[0045] <Light Detection Element>

[0046] The light detecting element of the present invention is characterized in that it has:

[0047] A photoelectric conversion layer, comprising a collection of semiconductor quantum dots QD1 containing metal atoms and a ligand L1 coordinated with the semiconductor quantum dots QD1; and

[0048] The hole transport layer is disposed on the photoelectric conversion layer and comprises a collection of semiconductor quantum dots QD2 containing metal atoms and a ligand L2 coordinated with the semiconductor quantum dots QD2.

[0049] The band gap Eg2 of the semiconductor quantum dot QD2 is greater than the band gap Eg1 of the semiconductor quantum dot QD1, and the difference between the band gap Eg2 of the semiconductor quantum dot QD2 and the band gap Eg1 of the semiconductor quantum dot QD1 is greater than 0.10 eV.

[0050] According to the present invention, it is possible to provide a light detection element with a low dark current.

[0051] In the light detection element of the present invention, from the viewpoint of reducing dark current, the difference (Eg2-Eg1) between the band gap Eg2 of the semiconductor quantum dot QD2 and the band gap Eg1 of the semiconductor quantum dot QD1 is preferably 0.15 eV or more, more preferably 0.20 eV or more, and further preferably 0.25 eV or more. Furthermore, the difference (Eg2-Eg1) between the band gap Eg2 of the semiconductor quantum dot QD2 and the band gap Eg1 of the semiconductor quantum dot QD1 can be set to 2.0 eV or less, and can also be set to 1.0 eV or less.

[0052] In the light detection element of the present invention, the energy level at the upper end of the valence band of the hole transport layer is preferably higher than the energy level at the upper end of the valence band of the photoelectric conversion layer. From the viewpoint of repeated stability, the difference (E2-E1) between the energy level (E2) at the upper end of the valence band of the hole transport layer and the energy level (E1) at the upper end of the valence band of the photoelectric conversion layer is preferably greater than 0.01 eV, and more preferably 0.01 to 0.25 eV.

[0053] In the light detection element of the present invention, it is preferred that the energy difference ΔE1 between the Fermi level of the photoelectric conversion layer and the lower end of the conductor and the energy difference ΔE2 between the Fermi level of the hole transport layer and the lower end of the conductor satisfy the relationship of the following formula (1). By satisfying the relationship of the following formula (1), it is easy to obtain a high external quantum efficiency. It is speculated that this is because the value of (ΔE2-ΔE1) becomes larger, the built-in potential of the bonding interface becomes larger, and the separation of carriers is easy to occur, that is, the number of carriers deactivated by recombination is reduced.

[0054] (ΔE2-ΔE1)≥0.1eV……(1)

[0055] In the above formula (1), the value of (ΔE2-ΔE1) is preferably 0.2 eV or more, more preferably 0.4 eV or more. Furthermore, from the viewpoint of suppressing dark current, the value of (ΔE2-ΔE1) is more preferably 1.0 eV or less.

[0056] When semiconductor quantum dots containing Pb atoms are used as semiconductor quantum dots QD1 in the photoelectric conversion layer, the ratio of the number of Pb atoms with a valence of 1 or less to the number of Pb atoms with a valence of 2 (the number of Pb atoms with a valence of 1 or less / the number of Pb atoms with a valence of 2) in the photoelectric conversion layer is preferably 0.20 or less, more preferably 0.10 or less, and further preferably 0.05 or less. According to this method, a light detection element with reduced dark current can be provided.

[0057] The detailed reasons for obtaining such effects are not yet clear, but are speculated as follows. As divalent Pb atoms, Pb atoms bonded to ligands (coordinated), Pb atoms bonded to chalcogen atoms, Pb atoms bonded to halogen atoms, etc. can be cited. As Pb atoms with a valency of less than 1, metallic Pb atoms, free-bonded Pb atoms, etc. can be cited. Among them, it is believed that the amount of free electrons in the photoelectric conversion layer is related to the dark current, and it is speculated that the dark current can be reduced by reducing the amount of free electrons. It is believed that in the photoelectric conversion layer, Pb atoms with a valency of less than 1 act as electron donors, and it is speculated that by reducing the ratio of Pb atoms with a valency of less than 1, the amount of free electrons in the photoelectric conversion layer can be reduced. For such reasons, it is speculated that the dark current of the photodetection element can be further reduced.

[0058] Furthermore, when semiconductor quantum dots containing Pb atoms are used as semiconductor quantum dots QD2 in the hole transport layer, the ratio of the number of Pb atoms with a valence of 1 or less to the number of Pb atoms with a valence of 2 in the hole transport layer is preferably 0.15 or less, more preferably 0.10 or less, and further preferably 0.05 or less. According to this method, a light detection element with reduced dark current can also be provided.

[0059] In this specification, the value of the ratio of the number of Pb atoms with a valence of 1 or less to the number of Pb atoms with a valence of 2 in the photoelectric conversion layer and the hole transport layer (hereinafter, both are also collectively referred to as the semiconductor film) is a value measured by X-ray photoelectron spectroscopy using an XPS (X-ray Photoelectron Spectroscopy) device. Specifically, the XPS spectrum of the Pb4f (7 / 2) orbit of the semiconductor film is curve-fitted by the least squares method, thereby separating the waveforms of the waveform W1 having an intensity peak in the bond energy range of 137.8 to 138.2 eV and the waveform W2 having an intensity peak in the bond energy range of 136.5 to 137 eV. In addition, the ratio of the peak area S2 of the waveform W2 to the peak area S1 of the waveform W1 is calculated, and this value is used as the ratio of the number of Pb atoms with a valence of 1 or less to the number of Pb atoms with a valence of 2 in the semiconductor film. Among them, in the measurement based on X-ray photoelectron spectroscopy, there is a situation where the bond energy of the above-mentioned intensity peak fluctuates slightly depending on the sample that becomes the benchmark. There is a divalent bond Pb-X of a Pb atom and a paired anion atom X in the semiconductor quantum dot containing Pb atoms. Therefore, the contribution of the bond originating from Pb-X or having an intensity peak at the same bond energy position as Pb-X is combined as the above-mentioned peak area S1. In addition, the contribution of the bond originating from the bond having an intensity peak at a position with a lower bond energy than it is taken as the above-mentioned peak area S2. For example, with respect to the ratio of the number of Pb atoms with a valence of less than 1 to the number of divalent Pb atoms in the semiconductor film, a value calculated using a waveform having an intensity peak at a bond energy of 138 eV as waveform W1 and a waveform having an intensity peak at a bond energy of 136.8 eV as waveform W2 can be used.

[0060] Examples of methods for making the ratio of the number of monovalent or less Pb atoms to the number of divalent Pb atoms in the semiconductor film 0.20 or less include methods of bringing the semiconductor film into contact with an aprotic solvent and rinsing it or drying it in an oxygen-containing gas environment when manufacturing the semiconductor film.

[0061] Hereinafter, the photodetection element of the present invention will be described in detail.

[0062] (Photoelectric conversion layer)

[0063] The photoelectric conversion layer of the light detection element of the present invention has a collection of semiconductor quantum dots QD1 containing metal atoms. In addition, a collection of semiconductor quantum dots refers to a plurality of (for example, each 1 μm 2 In addition, the "semiconductor" in the present invention refers to a semiconductor having a specific resistance value of 10 -2 Ωcm or more and 10 8 Substances with a thickness below Ωcm.

[0064] The semiconductor quantum dot QD1 is a semiconductor particle having metal atoms. In addition, in the present invention, the metal atoms also include semi-metal atoms represented by Si atoms. As semiconductor quantum dot materials constituting the semiconductor quantum dot QD1, for example, nanoparticles (particles with a size of 0.5 nm or more and less than 100 nm) of conventional semiconductor crystals [a) Group IV semiconductors, b) Compound semiconductors of Group IV-IV, Group III-V or Group II-VI, c) Compound semiconductors composed of a combination of three or more elements of Group II, Group III, Group IV, Group V and Group VI] can be cited.

[0065] The semiconductor quantum dot QD1 preferably contains at least one metal atom selected from Pb atoms, In atoms, Ge atoms, Si atoms, Cd atoms, Zn atoms, Hg atoms, Al atoms, Sn atoms and Ga atoms, and more preferably contains at least one metal atom selected from Pb atoms, In atoms, Ge atoms and Si atoms. Considering that it is easier to significantly obtain the effects of the present invention, it is further preferred to contain Pb atoms.

[0066] Specific examples of semiconductor quantum dot materials constituting semiconductor quantum dot QD1 include semiconductor materials with relatively narrow band gaps such as PbS, PbSe, PbTe, InN, InAs, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, HgTe, HgCdTe, Ag2S, Ag2Se, Ag2Te, SnS, SnSe, SnTe, Si, and InP. Among them, it is preferred that semiconductor quantum dot QD1 contains PbS or PbSe, and more preferably contains PbS, because it is easy to efficiently convert light in the infrared region (preferably light with a wavelength of 700 to 2500 nm) into electrons.

[0067] The semiconductor quantum dot QD1 can be a raw material of a core-shell structure in which a semiconductor quantum dot material is used as a core and a coating compound covers the semiconductor quantum dot material. Examples of the coating compound include ZnS, ZnSe, ZnTe, ZnCdS, CdS, GaP, and the like.

[0068] The band gap Eg1 of the semiconductor quantum dot QD1 is preferably 0.5 to 2.0 eV. If the band gap Eg1 of the semiconductor quantum dot QD1 is within the above range, it can be used as a light detection element that can detect light of various wavelengths according to the application. For example, it can be used as a light detection element that can detect light in the infrared region. The upper limit of the band gap Eg1 of the semiconductor quantum dot QD1 is preferably less than 1.9 eV, more preferably less than 1.8 eV, and further preferably less than 1.5 eV. The lower limit of the band gap Eg1 of the semiconductor quantum dot QD1 is preferably greater than 0.6 eV, more preferably greater than 0.7 eV.

[0069] The average particle size of the semiconductor quantum dot QD1 is preferably 2 nm to 15 nm. The average particle size of the semiconductor quantum dot QD1 is the average of the particle sizes of 10 randomly selected semiconductor quantum dots. The particle size of the semiconductor quantum dot may be measured using a transmission electron microscope.

[0070] Generally, semiconductor quantum dots include particles of various sizes ranging from a few nm to tens of nm. If the average particle size of semiconductor quantum dots is reduced to a size below the Bohr radius of the electrons contained therein, the band gap of the semiconductor quantum dots will change due to the quantum size effect. If the average particle size of semiconductor quantum dots is below 15 nm, it is easy to control the band gap based on the quantum size effect.

[0071] The photoelectric conversion layer of the light detection element of the present invention contains a ligand L1 coordinated with the semiconductor quantum dot QD1. As the ligand, there can be cited a ligand containing a halogen atom and a multidentate ligand containing two or more coordination parts. The photoelectric conversion layer may contain only one ligand or may contain two or more. The ligand L1 preferably contains a ligand different from the ligand L2 of the hole transport layer. Among them, the photoelectric conversion layer preferably contains a ligand containing a halogen atom and a multidentate ligand. According to this method, it can be used as a light detection element with low dark current and excellent performance such as conductivity, photocurrent value, external quantum efficiency, and in-plane uniformity of external quantum efficiency. The reason for obtaining such an effect can be speculated as follows. It is speculated that the multidentate ligand is chelated and coordinated with the semiconductor quantum dot QD1, and it can be speculated that the ligand can be more effectively suppressed from peeling off from the semiconductor quantum dot QD1. In addition, it is speculated that the stereoscopic effect of the semiconductor quantum dots QD1 can be suppressed by chelating and coordinating. Therefore, it is believed that the stereo effect between the semiconductor quantum dots QD1 becomes smaller, and the dense arrangement of the semiconductor quantum dots QD1 can enhance the superposition of the wave functions between the semiconductor quantum dots QD1. Moreover, it is speculated that when the ligand L1 coordinated with the semiconductor quantum dot QD1 further includes a ligand containing a halogen atom, the ligand containing a halogen atom is interstitially coordinated with the uncoordinated multidentate ligand, and it is speculated that the surface defects of the semiconductor quantum dot QD1 can be reduced. Therefore, it is speculated that it can be used as a light detection element with low dark current and excellent performance such as conductivity, photocurrent value, external quantum efficiency, and in-plane uniformity of external quantum efficiency.

[0072] First, the ligand containing a halogen atom will be described. Examples of the halogen atom contained in the ligand include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. From the viewpoint of coordination force, an iodine atom is preferred.

[0073] The ligand containing a halogen atom may be an organic halide or an inorganic halide. Among them, from the reason that it is easy to coordinate with both the cationic site and the anionic site of the semiconductor quantum dot QD1, an inorganic halide is preferably used. In addition, the inorganic halide is preferably a compound containing a metal atom selected from Zn atoms, In atoms and Cd atoms, preferably a compound containing Zn atoms. From the reason that it is easy to coordinate with the semiconductor quantum dot QD1 by ionization, the inorganic halide is preferably a salt of a metal atom and a halogen atom.

[0074] Specific examples of the halogen-containing ligand include zinc iodide, zinc bromide, zinc chloride, indium iodide, indium bromide, indium chloride, cadmium iodide, cadmium bromide, cadmium chloride, gallium iodide, gallium bromide, gallium chloride, tetrabutylammonium iodide, tetramethylammonium iodide, and the like. Zinc iodide is particularly preferred.

[0075] In addition, in the halogen-containing ligand, there is also a situation where the halogen ions dissociate from the halogen-containing ligand and the halogen ions are coordinated on the surface of the semiconductor quantum dot QD1. Moreover, the parts other than the halogen of the halogen-containing ligand are sometimes coordinated on the surface of the semiconductor quantum dot QD1. If a specific example is given to illustrate, in the case of zinc iodide, there is a situation where zinc iodide is coordinated on the surface of the semiconductor quantum dot QD1, and there is also a situation where iodine ions or zinc ions are coordinated on the surface of the semiconductor quantum dot QD1.

[0076] Next, the multidentate ligand is described. As the coordination part contained in the multidentate ligand, sulfhydryl, amino, hydroxyl, carboxyl, sulfonic acid, phosphoric acid, phosphonic acid can be cited. Considering the reason that it is easy to coordinate firmly on the surface of the semiconductor quantum dot QD1, the multidentate ligand is preferably a compound containing a sulfhydryl group.

[0077] Examples of the multidentate ligand include a ligand represented by any one of the formulae (D) to (F).

[0078] [Chemical formula 1]

[0079]

[0080] In formula (D), X D1 and X D2 Each independently represents a mercapto group, an amino group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphoric acid group or a phosphonic acid group,

[0081] L D1 It represents a hydrocarbon group.

[0082] In formula (E), X E1 and X E2 Each independently represents a mercapto group, an amino group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphoric acid group or a phosphonic acid group,

[0083] X E3 represents S, O or NH,

[0084] L E1 and L E2 Each independently represents a hydrocarbon group.

[0085] In formula (F), X F1 ~X F3 Each independently represents a mercapto group, an amino group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphoric acid group or a phosphonic acid group,

[0086] X F4 represents N,

[0087] L F1 ~L F3 Each independently represents a hydrocarbon group.

[0088] XD1 , X D2 , X E1 , X E2 , X F1 , X F2 and X F3 The amino group represented is not limited to -NH2, and may also include substituted amino groups and cyclic amino groups. As substituted amino groups, monoalkylamino, dialkylamino, monoarylamino, diarylamino, alkylarylamino, etc. can be cited. As the amino group represented by these groups, -NH2, monoalkylamino, dialkylamino, more preferably -NF2.

[0089] As L D1 , L E1 , L E2 , L F1 , L F2 and L F3 The 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 of 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 further preferably 3 or less. Specific examples of the hydrocarbon group include an alkylene group, an alkenylene group, and an alkynylene group.

[0090] Examples of the alkylene group include straight-chain alkylene groups, branched-chain alkylene groups, and cyclic alkylene groups, preferably straight-chain alkylene groups or branched-chain alkylene groups, and more preferably straight-chain alkylene groups. Examples of the alkenylene group include straight-chain alkenylene groups, branched-chain alkenylene groups, and cyclic alkenylene groups, preferably straight-chain alkenylene groups or branched-chain alkenylene groups, and more preferably straight-chain alkenylene groups. Examples of the alkynylene group include straight-chain alkynylene groups and branched-chain alkynylene groups, and preferably straight-chain alkynylene groups. The alkylene group, the alkenylene group, and the alkynylene group may further have a substituent. The substituent is preferably a group having an atomic number of 1 or more and 10 or less. Preferred specific examples of the group having 1 to 10 atoms include alkyl groups having 1 to 3 carbon atoms (methyl, ethyl, propyl and isopropyl), alkenyl groups having 2 to 3 carbon atoms (vinyl and propenyl), alkynyl groups having 2 to 4 carbon atoms (ethynyl, propynyl, etc.), cyclopropyl, alkoxy groups having 1 to 2 carbon atoms (methoxy and ethoxy), acyl groups having 2 to 3 carbon atoms (acetyl and propionyl), alkoxycarbonyl groups having 2 to 3 carbon atoms (methoxycarbonyl and ethoxycarbonyl), 2 acyloxy groups [acetoxy], acylamino groups having 2 carbon atoms [acetylamino], hydroxyalkyl groups having 1 to 3 carbon atoms [hydroxymethyl, hydroxyethyl, hydroxypropyl], aldehyde groups, hydroxyl groups, carboxyl groups, sulfonic acid groups, phosphoric acid groups, carbamoyl groups, cyano groups, isocyanate groups, mercapto groups, nitro groups, nitrooxy groups, isothiocyanate groups, cyanate groups, thiocyanate groups, acetoxy groups, acetamide groups, formyl groups, formyloxy groups, formamide groups, sulfonamino groups, sulfinyl groups, sulfamoyl groups, phosphono groups, acetyl groups, halogen atoms, alkali metal atoms and the like.

[0091] In formula (D), X D1 With X D2 Preferably through L D1 The distance between the two atoms is 1 to 10 atoms, more preferably 1 to 6 atoms, further preferably 1 to 4 atoms, further preferably 1 to 3 atoms, and particularly preferably 1 or 2 atoms.

[0092] In formula (E), X E1 With X E3 Preferably through L E1 The distance between X and X is 1 to 10 atoms, more preferably 1 to 6 atoms, further preferably 1 to 4 atoms, further preferably 1 to 3 atoms, and particularly preferably 1 or 2 atoms. E2 With X E3 Preferably through L E2 The distance between the two atoms is 1 to 10 atoms, more preferably 1 to 6 atoms, further preferably 1 to 4 atoms, further preferably 1 to 3 atoms, and particularly preferably 1 or 2 atoms.

[0093] In formula (F), X F1 With X F4 Preferably through L F1 The distance between X and X is 1 to 10 atoms, more preferably 1 to 6 atoms, further preferably 1 to 4 atoms, further preferably 1 to 3 atoms, and particularly preferably 1 or 2 atoms. F2 With X F4 Preferably through L F2 The distance between X and X is 1 to 10 atoms, more preferably 1 to 6 atoms, further preferably 1 to 4 atoms, further preferably 1 to 3 atoms, and particularly preferably 1 or 2 atoms. F3 With X F4 Preferably through L F3 The distance between the two atoms is 1 to 10 atoms, more preferably 1 to 6 atoms, further preferably 1 to 4 atoms, further preferably 1 to 3 atoms, and particularly preferably 1 or 2 atoms.

[0094] In addition, X D1 With X D2 By L D1 1 to 10 atoms apart refers to the connection X D1 With X D2 The number of atoms in the shortest molecular chain is 1 to 10. For example, in the case of the following formula (D1), X D1 With X D2 In the case of the following formula (D2) and formula (D3), X D1 With XD2 The numbers in the following structural formulas indicate the number of atoms that make up the connecting X D1 With X D2 The order of arrangement of atoms in a molecular chain with the shortest distance.

[0095] [Chemical formula 2]

[0096]

[0097] If specific compounds are given for illustration, 3-mercaptopropionic acid is equivalent to X D1 The position is carboxyl, equivalent to X D2 The part is a thiol group, equivalent to L D1 The compound having a structure in which the part of the amine group is a vinyl group (the compound having the following structure). In 3-mercaptopropionic acid, X D1 (Carboxyl) and X D2 (Mercapto) through L D1 (vinyl) are 2 atoms apart.

[0098] [Chemical formula 3]

[0099]

[0100] About X E1 With X E3 By L E1 1 to 10 atoms apart, X E2 With X E3 By L E2 1 to 10 atoms apart, X F1 With X F4 By L F1 1 to 10 atoms apart, X F2 With X F4 By L F2 1 to 10 atoms apart, X F3 With X F4 By L F3 The meaning of being 1 to 10 atoms apart is the same as described above.

[0101] Specific examples of the multidentate ligand include ethanedithiol, 3-mercaptopropionic acid, thioglycolic acid, 2-aminoethanol, 2-aminoethanethiol, 2-mercaptoethanol, glycolic acid, diethylenetriamine, tris(2-aminoethyl)amine, 4-mercaptobutyric acid, 3-aminopropanol, 3-mercaptopropanol, N-(3-aminopropyl)-1,3-propanediamine, 3-(bis(3-aminopropyl)amino)propane-1-ol, 1-thioglycerol, dithioglycerol, 1-mercapto-2-butanediamine, alcohol, 1-mercapto-2-pentanol, 3-mercapto-1-propanol, 2,3-dimercapto-1-propanol, diethanolamine, 2-(2-aminoethyl)aminoethanol, dimethylenetriamine, 1,1-oxydimethylamine, 1,1-thiodimethylamine, 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, aminoglycolic 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 their derivatives; 3-mercaptopropionic acid, mercaptoacetic acid, 2-aminoethanol, 2-aminoethanethiol, 2-mercaptoethanol, glycolic acid are preferred because of the low dark current and the ease of obtaining a semiconductor film with high external quantum efficiency. , diethylenetriamine, tris(2-aminoethyl)amine, 1-thioglycerol, dithioglycerol, ethylenediamine, ethylene glycol, aminosulfonic acid, glycine, (aminomethyl)phosphonic acid, guanidine, diethanolamine, 2-(2-aminoethyl)aminoethanol, homoserine, cysteine, thiomalic acid, malic acid and tartaric acid, more preferably 3-mercaptopropionic acid, thioglycolic acid, 2-aminoethanol, 2-mercaptoethanol and 2-aminoethanethiol, further preferably 3-mercaptopropionic acid and thioglycolic acid.

[0102] The complex equilibrium stability constant (ComplexstabiliLy constant) K1 of the multidentate ligand and the metal atoms contained in the semiconductor quantum dot QD1 is preferably greater than 6, more preferably greater than 8, and further preferably greater than 9. If the above-mentioned complex equilibrium stability constant K1 is greater than 6, the bonding strength between the semiconductor quantum dot QD1 and the multidentate ligand can be improved. Therefore, it is possible to inhibit the multidentate ligand from peeling off from the semiconductor quantum dot QD1, and as a result, the driving durability can be further improved.

[0103] The complex equilibrium stability constant K1 refers to a constant determined by the relationship between the ligand and the metal atom that is the target of coordinate bonding, and is represented by the following formula (b).

[0104] Complex equilibrium stability constant K1 = [ML] / ([M]·[L])……(b)

[0105] In formula (b), [ML] represents the molar concentration of the complex formed by the ligand and the metal atom, [M] represents the molar concentration of the metal atom contributing to the coordinate bonding, and [L] represents the molar concentration of the ligand.

[0106] In practice, multiple ligands may coordinate to one metal atom, but in the present invention, the complex equilibrium stability constant K1 represented by formula (b) when one ligand molecule coordinates to one metal atom is defined as an index of coordination bond strength.

[0107] As the method for obtaining the complex equilibrium stability constant K1 between the ligand and the metal atom, there are spectroscopy, magnetic resonance spectroscopy, potentiometric method, solubility measurement, chromatography, calorimetry, freezing point measurement, vapor pressure measurement, relaxation measurement, viscosity measurement, surface tension measurement, etc. In the present invention, the complex equilibrium stability constant K1 is determined by using Sc-Database ver.5.85 (Academic Software) (2010) which summarizes various methods and results from research institutions. When there is no complex equilibrium stability constant K1 in Sc-Database ver.5.85, the value recorded in Critical Stability Constants by AE Martell and RM Smith is used. When the complex equilibrium stability constant K1 is not recorded in Critical StabiliLy Constants, the complex equilibrium stability constant K1 is calculated using the described determination method or the program PKAS method (AE Martell et al., The Determination and Use of Stability Constants, VCH (1988)) for calculating the complex equilibrium stability constant K1.

[0108] In the present invention, quantum dots containing Pb atoms (more preferably PbS) are used as semiconductor quantum dots QD1, and the complex equilibrium stability constant K1 of the multidentate ligand relative to the Pb atom is preferably 6 or more, more preferably 8 or more, and further preferably 9 or more. As compounds having a complex equilibrium stability constant K1 of 6 or more relative to the Pb atom, thioglycolic acid (complex equilibrium stability constant K1=8.5 relative to the Pb atom), 2-mercaptoethanol (complex equilibrium stability constant K1=6.7 relative to the Pb atom), etc. can be cited.

[0109] The thickness of the photoelectric conversion layer is preferably 10 to 600 nm, more preferably 50 to 600 nm, further preferably 100 to 600 nm, and further preferably 150 to 600 nm. The upper limit of the thickness is preferably 550 nm or less, more preferably 500 nm or less, and further preferably 450 nm or less.

[0110] The refractive index of the photoelectric conversion layer with respect to the light of the target wavelength detected by the photodetection element 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 photodetection element is used as a constituent element of the photodiode, high light absorption rate, that is, high external quantum efficiency, can be easily achieved.

[0111] (Hole Transport Layer)

[0112] In the light detection element of the present invention, a hole transport layer (hereinafter also referred to as hole transport layer QD) including an aggregate of semiconductor quantum dots QD2 containing metal atoms and a ligand L2 coordinated with the semiconductor quantum dots QD2 is arranged on the photoelectric conversion layer. The hole transport layer refers to a layer having the function of transporting holes generated in the photoelectric conversion layer to an electrode. The hole transport layer is also called an electron blocking layer. The light detection element of the present invention preferably has a hole transport layer QD arranged on the surface of the photoelectric conversion layer.

[0113] The hole transport layer QD comprises a collection of semiconductor quantum dots QD2 containing metal atoms. Semiconductor quantum dot QD2 is a semiconductor particle having metal atoms. The details of semiconductor quantum dot QD2 are the same as those of semiconductor quantum dot QD1. Semiconductor quantum dot QD2 preferably contains at least one metal atom selected from Pb atoms, In atoms, Ge atoms, Si atoms, Cd atoms, Zn atoms, Hg atoms, Al atoms, Sn atoms and Ga atoms, and more preferably contains at least one metal atom selected from Pb atoms, In atoms, Ge atoms and Si atoms. Considering that it is easier to significantly obtain the effect of the present invention, it is further preferred to contain Pb atoms.

[0114] Specific examples of semiconductor quantum dot materials constituting semiconductor quantum dot QD2 include semiconductor materials with relatively narrow band gaps such as PbS, PbSe, PbTe, InN, InAs, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, Si, and InP. Among them, the semiconductor quantum dot QD2 preferably contains PbS or PbSe, and more preferably contains PbS. Furthermore, the semiconductor quantum dot QD2 preferably includes semiconductor quantum dots of the same type as the semiconductor quantum dot QD1 contained in the photoelectric conversion layer.

[0115] The semiconductor quantum dot QD2 may be a raw material of a core-shell structure in which a semiconductor quantum dot material is used as a core and the semiconductor quantum dot material is covered with a coating compound. Examples of the coating compound include ZnS, ZnSe, ZnTe, and ZnCdS.

[0116] The band gap Eg2 of the semiconductor quantum dot QD2 is preferably 0.5 to 2.0 eV. If the band gap Eg2 of the semiconductor quantum dot QD2 is within the above range, it can be used as a light detection element that can detect light of various wavelengths according to the application. For example, it can be used as a light detection element that can detect light in the infrared region. The upper limit of the band gap Eg2 of the semiconductor quantum dot QD2 is preferably less than 1.9 eV, more preferably less than 1.8 eV, and further preferably less than 1.5 eV. The lower limit of the band gap Eg2 of the semiconductor quantum dot QD2 is preferably greater than 0.6 eV, more preferably greater than 0.7 eV.

[0117] In addition, the light detection element of the present invention uses semiconductor quantum dots QD1 and semiconductor quantum dots QD2 that satisfy the following conditions: the band gap Eg2 of semiconductor quantum dot QD2 is greater than the band gap Eg1 of semiconductor quantum dot QD1, and the difference between the band gap Eg2 of semiconductor quantum dot QD2 and the band gap Eg1 of semiconductor quantum dot QD1 is greater than 0.10 eV.

[0118] The average particle size of the semiconductor quantum dots QD2 is preferably 2 nm to 15 nm.

[0119] The hole transport layer QD contains a ligand L2 coordinated with the semiconductor quantum dot QD2. As the ligand L2, there can be cited ligands containing halogen atoms and multidentate ligands containing two or more coordination parts. The hole transport layer QD may contain only one ligand or may contain two or more. Among them, the hole transport layer QD preferably contains a multidentate ligand, and more preferably contains a ligand containing a halogen atom and a multidentate ligand. According to this method, it can be used as a light detection element with low dark current and excellent performance such as conductivity, photocurrent value, external quantum efficiency, and in-plane uniformity of external quantum efficiency.

[0120] Examples of the ligand containing a halogen atom include the ligands listed as the above-mentioned ligand L1, and the preferred range is also the same.

[0121] As the coordination part contained in the multidentate ligand, thiol, amino, hydroxyl, carboxyl, sulfonic acid, phosphoric acid, and phosphonic acid can be cited. As a preferred embodiment of the multidentate ligand, a ligand represented by any one of the above formulas (D) to (F) can be cited. The multidentate ligand is preferably a compound containing a thiol group. As specific examples of multidentate ligands, there can be cited the compounds listed in the specific examples of the above-mentioned ligand L1, preferably ethanedithiol, thioglycolic acid, 3-mercaptopropionic acid, 2-aminoethanol, 2-aminoethanethiol, 2-mercaptoethanol, glycolic acid, 4-mercaptobutyric acid, 3-aminopropanol, 3-mercaptopropanol, N-(3-aminopropyl)-1,3-propanediamine, and 3-(bis(3-aminopropyl)amino)propane-1-one, more preferably ethanedithiol, thioglycolic acid, 3-mercaptopropionic acid, 2-aminoethanethiol and 2-mercaptoethanol, further preferably ethanedithiol, thioglycolic acid and 3-mercaptopropionic acid, and especially preferably thioglycolic acid and 3-mercaptopropionic acid.

[0122] The thickness of the hole transport layer QD is preferably 5 to 100 nm, with a lower limit of preferably 10 nm or more and an upper limit of preferably 50 nm or less, and more preferably 30 nm or less.

[0123] When the light detection element of the present invention is used to sense light with a wavelength of 900 to 1000 nm, the average particle size of the semiconductor quantum dot QD1 is 2.9 to 3.3 nm, and the average particle size of the semiconductor quantum dot QD2 is preferably 2.0 to 2.8 nm. In this embodiment, the semiconductor quantum dot QD1 and the semiconductor quantum dot QD2 preferably contain Pb atoms, more preferably contain semiconductor quantum dots of the same type, and further preferably contain PbS.

[0124] When the light detection element of the present invention is used to sense light with a wavelength of 1500 to 1600 nm, the average particle size of the semiconductor quantum dot QD1 is 5.6 to 6.3 nm, and the average particle size of the semiconductor quantum dot QD2 is preferably 4.7 to 5. nm. In this embodiment, the semiconductor quantum dot QD1 and the semiconductor quantum dot QD2 preferably contain Pb atoms, more preferably contain semiconductor quantum dots of the same type, and further preferably contain PbS.

[0125] The photoelectric conversion layer and the hole transport layer can be formed by the following process (semiconductor quantum dot aggregate formation process): a semiconductor quantum dot dispersion liquid containing semiconductor quantum dots, ligands coordinated to the semiconductor quantum dots, and a solvent is applied to a substrate to form a film of an aggregate of semiconductor quantum dots. The method of applying the semiconductor quantum dot dispersion liquid to the substrate is not particularly limited. Coating methods such as spin coating, dipping, inkjet, dripping, screen printing, relief printing, gravure printing, and spraying can be cited.

[0126] Furthermore, after forming the film of the collection of semiconductor quantum dots, a ligand exchange process may be further performed to exchange the ligand coordinated with the semiconductor quantum dots with another ligand. In the ligand exchange process, a ligand solution containing ligand A and a solvent is given to the film of the collection of semiconductor quantum dots formed by the semiconductor quantum dot collection forming process, and the ligand coordinated with the semiconductor quantum dots is exchanged with ligand A. Ligand A may contain two or more ligands, and two ligand solutions may be used at the same time. Furthermore, a rinsing process of washing the remaining ligands with a solvent after the ligand exchange may be included. As the solvent for the rinsing process, ester solvents, ketone solvents, alcohol solvents, nitrile solvents, amide solvents, ether solvents, hydrocarbon solvents, etc. can be used, preferably a non-protonic organic solvent.

[0127] On the other hand, a desired ligand may be previously imparted to the surface of the semiconductor quantum dots in a semiconductor quantum dot dispersion, and the dispersion may be applied on a substrate to form the photoelectric conversion layer and the hole transport layer.

[0128] The content of the semiconductor quantum dots in the semiconductor quantum dot dispersion is preferably 1 to 500 mg / mL, more preferably 10 to 200 mg / mL, and even more preferably 20 to 100 mg / mL.

[0129] As the solvent contained in the semiconductor quantum dot dispersion or ligand solution, ester solvents, ketone solvents, alcohol solvents, amide solvents, ether solvents, hydrocarbon solvents, etc. can be cited. For details of these, reference can be made to paragraph 0223 of International Publication No. 2015 / 166779, which is incorporated into this specification. In addition, ester solvents substituted with cyclic alkyl groups and ketone solvents substituted with cyclic alkyl groups can also be used. It is preferred that there are few metal impurities in the solvent, and the metal content is, for example, less than 10 mass ppb (parts per billion, parts per billion). Solvents of the mass ppt (parts pertrillion, parts per trillion) level can be used as needed, such solvents are provided, for example, by Toyo Gosei Co., Ltd. (Chemical Industry Daily, November 13, 2015). As a method for removing impurities such as metals from a solvent, for example, distillation (molecular distillation or thin film distillation, etc.) or filtration using a filter can be cited. The pore size of the filter used for filtering is preferably 10 μm or less, more preferably 5 μm or less, and further preferably 3 μm or less. The material of the filter is preferably polytetrafluoroethylene, polyethylene or nylon. The solvent leaf may contain isomers (compounds with the same number of atoms but different structures). And, the isomers may contain only one or more.

[0130] The light detection element of the present invention may have another hole transport layer composed of a hole transport material different from the hole transport layer QD. As hole transport materials constituting the other hole transport layer, PEDOT:PSS (poly (3, 4-ethylenedioxythiophene): poly (4-styrenesulfonic acid)), Mo (3) and the like can be cited. In addition, organic hole transport materials described in paragraphs 0209 to 0212 of Japanese Patent Gazette No. 2001-291534 can also be used.

[0131] When the light detection element of the present invention includes another hole transport layer, it is preferable that the hole transport layer QD is arranged on the photoelectric conversion layer and the other hole transport layer is arranged on the hole transport layer QD.

[0132] The light detection element of the present invention may further have a blocking layer or an electron transport layer. The blocking layer is a layer having the function of preventing reverse current. The blocking layer is also called an anti-short circuit layer. Examples of materials forming the blocking layer include silicon oxide, magnesium oxide, aluminum cyanide, calcium carbonate, cesium carbonate, polyvinyl alcohol, polyurethane, titanium oxide, tin oxide, zinc oxide, niobium oxide, tungsten oxide, and the like. The blocking layer may be a single-layer film or a laminated film of two or more layers. The electron transport layer is a layer having the function of transporting electrons generated in the photoelectric conversion layer to the electrode. The electron transport layer is also called a hole blocking layer. The electron transport layer is formed of an electron transport material that can play this role. Examples of electron transport materials include [6,6]-Phenyl-C61-ButyricAcid Methyl Ester (phenyl-C61-butyric acid methyl ester) (PC 61 The electron transport layer may be a single layer film or a laminated film of two or more layers.

[0133] The light detection element of the present invention can be preferably used as an element for detecting light with a wavelength in the infrared region. That is, the light detection element of the present invention is preferably an infrared light detection element. And, the target light detected by the above-mentioned light detection element is preferably light with a wavelength in the infrared region. And, the light with a wavelength in the infrared region is preferably light with a wavelength greater than a wavelength of 700nm, more preferably light with a wavelength of 800nm ​​or more, and further preferably light with a wavelength of 900nm or more. And, the light with a wavelength in the infrared region is preferably light with a wavelength of less than 2000nm, more preferably light with a wavelength of less than 1800nm, and further preferably light with a wavelength of less than 1600nm.

[0134] Furthermore, the photodetection element of the present invention can detect light with a wavelength in the infrared region and light with a wavelength in the visible region (preferably light with a wavelength in the range of 400 to 700 nm) at the same time.

[0135] Examples of the types of light detection elements include photoconductor-type light detection elements and photodiode-type light detection elements. Among them, photodiode-type light detection elements are preferred because they can easily obtain a high signal-to-noise ratio (SN ratio).

[0136] Figure 1 An embodiment of a photodiode type light detecting element is shown in FIG. Figure 1 The light detection element 1 shown includes a lower electrode 12 , an upper electrode 11 facing the lower electrode 12 , a photoelectric conversion layer 13 provided between the lower electrode 12 and the upper electrode 11 , and a hole transport layer 14 provided between the lower electrode 12 and the photoelectric conversion layer 13 . Figure 1 The light detecting element 1 shown is used so that light is incident from above the upper electrode 11 .

[0137] The photoelectric conversion layer 13 is a photoelectric conversion layer including a collection of semiconductor quantum dots QD1 containing metal atoms and a ligand L1 coordinated with the semiconductor quantum dots QD1. In addition, the hole transport layer 14 is a hole transport layer including a collection of semiconductor quantum dots QD2 containing metal atoms and a ligand L2 coordinated with the semiconductor quantum dots QD2. The details and preferred methods of these are as described above.

[0138] The wavelength λ of the target light detected by the light detection element and the optical path length L of the light of 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 upper electrode layer side of the photoelectric conversion layer 13 are λ It is preferable to satisfy the relationship of the following formula (1-1), and it is more preferable to satisfy the relationship of the following formula (1-2). λ When such a relationship is satisfied, the phases of light incident from the upper electrode 11 side (incident light) and light reflected on the surface of the lower electrode 12 (reflected light) can be made consistent in the photoelectric conversion layer 13. As a result, the lights enhance each other through the optical interference effect and a higher external quantum efficiency can be obtained.

[0139] 0.05+m / 2≤L λ / λ≤0.35+m / 2……(1-1)

[0140] 0.10+m / 2≤L λ / λ≤0.30+m / 2……(1-2)

[0141] In the above formula, λ is the wavelength of the target light detected by the light detection element,

[0142] L λis the optical path length of light of wavelength λ from surface 12a of lower electrode 12 on the photoelectric conversion layer 13 side to surface 13a of upper electrode layer 13 on the photoelectric conversion layer 13,

[0143] m is an integer greater than or equal to 0.

[0144] 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 aspect, the transport characteristics of charges such as holes and electrons are good, and the external quantum efficiency of the photodetection element can be further improved.

[0145] The optical path length refers to the value obtained by multiplying the physical thickness of the material through which the light passes by the refractive index. If the photoelectric conversion layer 13 is used as an example, the thickness of the photoelectric conversion layer is set to d 1 , the photoelectric conversion layer is relative to the wavelength λ 1 The refractive index is set to N 1 When the wavelength λ passing through the photoelectric conversion layer 13 1 The optical path length of the light is N 1 ×d 1 When the photoelectric conversion layer 13 and the hole transport layer 14 are composed of two or more laminated films or when an intermediate layer is present between the hole transport layer 14 and the lower electrode 12, the cumulative value of the optical path length of each layer is the optical path length L λ .

[0146] The upper electrode 11 is preferably a transparent electrode formed of a conductive material that is substantially transparent to the wavelength of the target light detected by the light detection element. In addition, in the present invention, "substantially transparent" means that the transmittance is 50% or more, preferably 60% or more, and particularly preferably 80% or more. As the material of the upper electrode 11, conductive metal oxides and the like can be cited. As specific examples, tin oxide, zinc oxide, indium oxide, indium tungsten oxide, indium zinc oxide (indium zinc oxide: IZ0), indium tin oxide (indium tin oxide: ITO), fluorine-doped tin oxide (fluorine-doped tin oxide: FTO), etc. can be cited.

[0147] The thickness of the upper electrode 11 is not particularly limited, but 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 detection element 1 using a scanning electron microscope (SEM) or the like.

[0148] Examples of the material 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. The carbon material may be any material as long as it has conductivity, and examples thereof include fullerene, carbon nanotubes, graphite, and graphene.

[0149] The lower electrode 12 is preferably a thin film of metal or conductive metal oxide (including a thin film formed by vapor deposition) or a glass substrate or plastic substrate having the thin film. The glass substrate or plastic substrate is preferably glass having a thin film of gold or platinum or glass on which platinum is vapor deposited. The thickness of the lower electrode 12 is not particularly limited, but is preferably 0.01 to 100 μm, more preferably 0.01 to 10 μm, and particularly preferably 0.01 to 1 μm.

[0150] Although not shown, a transparent substrate may be disposed on the light incident surface (the surface opposite to the photoelectric conversion layer 13 side) of the upper electrode 11. Examples of the transparent substrate include a glass substrate, a resin substrate, and a ceramic substrate.

[0151] Furthermore, although not shown in the drawings, a blocking layer or the above-mentioned other hole transport layer may be provided between the hole transport layer 14 and the lower electrode 12 .

[0152] Furthermore, a blocking layer or an electron transport layer may be provided between the photoelectric conversion layer 13 and the upper electrode 11 .

[0153] Figure 2 Another embodiment of the photodiode type light detection element is shown in FIG. In addition to having a hole transport layer 14 between the upper electrode 11 and the photoelectric conversion layer 13, Figure 2 The light detection element 1 shown is Figure 1 The light detection elements of the illustrated embodiments are identical.

[0154] In addition, although not shown in the figure, a transparent substrate may be arranged on the surface of the light incident side of the upper electrode 11 (the surface opposite to the hole transport layer 14 side). As the type of transparent substrate, a glass substrate, a resin substrate, a ceramic substrate, etc. may be cited. In addition, although not shown in the figure, a blocking layer or the above-mentioned other hole transport layer may be provided between the hole transport layer 14 and the upper electrode 11. In addition, a blocking layer or an electron transport layer may be provided between the photoelectric conversion layer 13 and the lower electrode 12.

[0155] <Image Sensor>

[0156] The image sensor of the present invention includes the above-mentioned light detection element of the present invention. The structure of the image sensor is not particularly limited as long as it includes the light detection element of the present invention and functions as an image sensor.

[0157] The image sensor of the present invention may include an infrared transmission filter layer. As the infrared transmission filter layer, it is preferred that the transmittance of light in the wavelength band of the visible region is low, and the average transmittance of light in the wavelength range of 400 to 650 nm is more preferably 10% or less, further preferably 7.5% or less, and particularly preferably 5% or less.

[0158] As the infrared transmission filter layer, a layer composed of a resin film containing a color material can be cited. As the color material, a red color material, a green color material, a blue color material, a yellow color material, a purple color material, an orange color material and a black color material can be cited. The color material contained in the infrared transmission filter layer is preferably formed by a combination of two or more color materials to form black or contains a black color material. As a combination of color materials when forming black by a combination of two or more color materials, for example, the following methods (C1) to (C7) can be cited.

[0159] (C1) A method including a red colorant and a blue colorant.

[0160] (C2) A method including a red colorant, a blue colorant, and a yellow colorant.

[0161] (C3) A method including a red color material, a blue color material, a yellow color material, and a violet color material.

[0162] (C4) A method including a red color material, a blue color material, a yellow color material, a purple color material, and a green color material.

[0163] (C5) A method including a red color material, a blue color material, a yellow color material, and a green color material.

[0164] (C6) A method including a red colorant, a blue colorant, and a green colorant.

[0165] (C7) A method of containing a yellow colorant and a purple colorant.

[0166] The color material may be a pigment or a dye. It may also contain a pigment and a dye. The black material is preferably an organic black material. For example, examples of the organic black material include bisbenzofuranone compounds, methine azo compounds, perylene compounds, azo compounds, and the like.

[0167] The infrared transmission filter layer may further contain an infrared absorber. By containing an infrared absorber in the infrared transmission filter layer, the wavelength of the transmitted light can be shifted to the longer wavelength side. As the infrared absorber, pyrrolopyrrole compounds, cyanine compounds, squaric acid compounds, phthalocyanine compounds, naphthalocyanine compounds, quaterrylene compounds, merocyanine compounds, crotonium compounds, oxocyanine compounds, iminium compounds, dithiol compounds, triarylmethane compounds, pyrromethene compounds, methine azo compounds, anthraquinone compounds, dibenzofuranone compounds, dithioalkene metal complexes, metal oxides, metal borides, etc. can be cited.

[0168] The spectral characteristics of the infrared transmission filter layer can be appropriately selected according to the application of the image sensor, and examples thereof include a filter layer that satisfies any of the spectral characteristics of (1) to (5) below.

[0169] (1): A filter layer having a maximum light transmittance in the thickness direction of the film within the wavelength range of 400 to 750 nm of less than 20% (preferably less than 15%, more preferably less than 10%) and a minimum light transmittance in the thickness direction of the film within the wavelength range of 900 to 1500 nm of more than 70% (preferably more than 75%, more preferably more than 80%).

[0170] (2): A filter layer in which the maximum value of the transmittance in the thickness direction of the film within the wavelength range of 400 to 830 nm is less than 20% (preferably less than 15%, more preferably less than 10%) and the minimum value of the transmittance in the thickness direction of the film within the wavelength range of 1000 to 1500 nm is more than 70% (preferably more than 75%, more preferably more than 80%).

[0171] (3): A filter layer in which the maximum value of the transmittance in the thickness direction of the film within the wavelength range of 400 to 950 nm is less than 20% (preferably less than 15%, more preferably less than 10%) and the minimum value of the transmittance in the thickness direction of the film within the wavelength range of 1100 to 1500 nm is more than 70% (preferably more than 75%, more preferably more than 80%).

[0172] (4): A filter layer having a light transmittance in the thickness direction of the film of which the maximum value in the wavelength range of 400 to 1100 nm is less than 20% (preferably less than 15%, more preferably less than 10%) and the minimum value in the wavelength range of 1400 to 1500 nm is more than 70% (preferably more than 75%, more preferably more than 80%).

[0173] (5): A filter layer having a light transmittance in the thickness direction of the film of which the maximum value in the wavelength range of 400 to 1300 nm is less than 20% (preferably less than 15%, more preferably less than 10%) and the minimum value in the wavelength range of 1600 to 2000 nm is more than 70% (preferably more than 75%, more preferably more than 80%).

[0174] Furthermore, as the infrared transmission filter, the 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. Furthermore, the infrared transmission filter can use two or more filters in combination, or a dual-bandpass filter that transmits two or more specific wavelength regions through one filter can be used.

[0175] 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 infrared shielding filters 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 Publication No. 2017-067963, and Japanese Patent No. 6506529.

[0176] The image sensor of the present invention may include a dielectric multilayer film. As a dielectric multilayer film, a film formed by alternating multiple layers of dielectric films with a high refractive index (high refractive index material layer) and dielectric films with a low refractive index (low refractive index material layer) can be cited. The number of stacking layers of dielectric films in the dielectric multilayer film is not particularly limited, and is preferably 2 to 100 layers, more preferably 4 to 60 layers, and further preferably 6 to 40 layers. As a material for forming a high refractive index material layer, a material with a refractive index of preferably 1.7 to 2.5. As specific examples, Sb2O3, Sb2S3, Bi2O3, CeO2, CeF3, HfO2, La2O3, Nd2O3, Pr6O 11, Sc2O3, SiO, Ta2O5, TiO2, TlCl, Y2O3, ZnSe, ZnS, ZrO2, etc. As the material used to form the low refractive index material layer, the refractive index is preferably a material of 1.2 to 1.6. As a specific example, Al2O3, BiF3, CaF2, LaF3, PbCl2, PbF2, LiF, MgF2, MgO, NdF3, SiO2, Si2O3, NaF, ThO2, ThF4, Na3AlF6, etc. There are no special restrictions on the method for forming the dielectric multilayer film, for example, vacuum evaporation methods such as ion plating and ion beam, physical vapor deposition methods (PVD methods) such as sputtering, chemical vapor deposition methods (CVD methods), etc. can be cited. When the wavelength of the light to be blocked is λ (nm), 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. Specific examples of dielectric multilayer films include dielectric multilayer films described in Japanese Patent Application Publication No. 2014-130344 and Japanese Patent Application Publication No. 2018-010296.

[0177] The dielectric multilayer film preferably has a transmission wavelength band in the infrared region (preferably a wavelength region greater than 700 nm, more preferably a wavelength region greater than 800 nm, and further preferably a wavelength region greater than 900 nm). The maximum transmittance in the transmission wavelength band is preferably 70% or more, more preferably 80% or more, and further preferably 90% or more. Furthermore, the maximum transmittance in the light-shielding wavelength band is preferably 20% or less, more preferably 10% or less, and further preferably 5% or less. Furthermore, the average transmittance in the transmission wavelength band is preferably 60% or more, more preferably 70% or more, and further preferably 80% or more. Furthermore, the wavelength showing the maximum transmittance is set to the center wavelength λ t1 When the wavelength range of the transmission wavelength band is preferably the central wavelength λ t1 ±100nm, preferably the central wavelength λ t1 ±75nm, more preferably the central wavelength λ t1 ±50nm.

[0178] The dielectric multilayer film may have only one transmission wavelength band (preferably a transmission wavelength band with a maximum transmittance of 90% or more) or may have a plurality of transmission wavelength bands.

[0179] The image sensor of the present invention may include a color separation filter layer. As the color separation filter layer, a filter layer including colored pixels can be cited. As the types of colored pixels, red pixels, green pixels, blue pixels, yellow pixels, cyan pixels, magenta pixels, etc. can be cited. The color separation filter layer may include colored pixels of two or more colors, or may be only one color. It can be appropriately selected according to the use or purpose. The color separation filter layer can use, for example, the filter described in International Publication No. 2019 / 039172.

[0180] Moreover, when the color separation layer includes colored pixels of two or more colors, the colored pixels of various colors may be adjacent to each other, or a partition may be provided between the colored pixels. There is no particular limitation on the material of the partition. For example, organic materials such as silicone resin and fluororesin, and inorganic particles such as silica particles can be cited. Moreover, the partition can be made of a metal such as tungsten or aluminum.

[0181] 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. Moreover, it is also preferable that the infrared transmission filter layer and the color separation layer are two-dimensionally arranged. In addition, the two-dimensional arrangement of the infrared transmission filter layer and the color separation layer means that at least a part of the two exists on the same plane.

[0182] The image sensor of the present invention may include intermediate layers such as a planarization layer, a base layer, and an adhesive layer, an antireflection film, and a lens. As the antireflection film, for example, a film made of the composition described in International Publication No. 2019 / 017280 can be used. As the lens, for example, the structure described in International Publication No. 2018 / 092600 can be used.

[0183] The light detection element of the present invention has excellent sensitivity to light having a wavelength in the infrared region. Therefore, the image sensor of the present invention can preferably be used as an infrared image sensor. Moreover, the image sensor of the present invention can preferably be used for sensing light having a wavelength of 900 to 2000 nm, and can more preferably be used for sensing light having a wavelength of 900 to 1600 nm.

[0184] Examples

[0185] Hereinafter, the present invention will be further specifically described by way of examples. The materials, amounts used, ratios, processing contents, processing sequences, etc. shown in the following examples can be appropriately changed as long as they do not depart from the gist of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[0186] <Preparation of Dispersion Liquid of PbS Quantum Dots>

[0187] (Dispersion Liquid 1 of PbS Quantum Dots)

[0188] 6.74 mL of oleic acid, 6.3 mmol of lead oxide and 30 mL of octadecene were weighed in a flask and heated in vacuum at 120 ° C for 10 () minutes to obtain a precursor solution. Afterwards, the temperature of the solution was adjusted to 100 ° C, and then the system was set to a nitrogen flow state, and then 2.5 mmol of hexamethyldisilathione was injected together with 5 mL of octadecene. After the injection was maintained for 1 minute, the flask was naturally cooled, 40 mL of toluene was added at a stage of reaching 30 ° C, and the solution was recovered. Excess ethanol was added to the solution, centrifuged at 10000 rpm for 10 minutes, and the precipitate was dispersed in octane, thereby obtaining a dispersion 1 (concentration 40 mg / mL) of PbS quantum dots coordinated with oleic acid as a ligand on the surface of PbS quantum dots. Regarding the obtained dispersion 1 of PbS quantum dots, the band gap of the PbS quantum dots estimated from light absorption measurement in the visible to infrared region using an ultraviolet-visible-near-infrared spectrophotometer (manufactured by JASCO Corporation, V-670) was about 1.35 eV.

[0189] (PbS quantum dot dispersion 2)

[0190] A dispersion 2 (concentration 40 mg / mL) of PbS quantum dots in which oleic acid is coordinated as a ligand on the surface of the PbS quantum dots was obtained in the same manner as the dispersion 1 except that the ratio of lead oxide to oleic acid, the synthesis temperature, and the amount of hexamethyldisilathione added were changed. The band gap of the PbS quantum dots estimated from the light absorption measurement in the visible to infrared region using an ultraviolet-visible-near infrared spectrophotometer (manufactured by JASCO Corporation, V-670) for the obtained dispersion 2 of PbS quantum dots was about 1.55 eV.

[0191] (PbS quantum dot dispersion 3)

[0192] A dispersion 3 (concentration 40 mg / mL) of PbS quantum dots in which oleic acid is coordinated as a ligand on the surface of the PbS quantum dots was obtained in the same manner as the dispersion 1 except that the ratio of lead oxide to oleic acid, the synthesis temperature, and the amount of hexamethyldisilathione added were changed. The band gap of the PbS quantum dots estimated from the light absorption measurement in the visible to infrared region using an ultraviolet-visible-near infrared spectrophotometer (manufactured by JASCO Corporation, V-670) for the obtained dispersion 3 of PbS quantum dots was about 1.61 eV.

[0193] (Fabrication of Photodetection Element)

[0194] [Example 1]

[0195] A titanium oxide film was formed on a quartz glass substrate with an indium tin oxide film by 50 nm sputtering. Next, the dispersion 1 of the PbS quantum dots was dripped onto the titanium oxide film formed on the substrate, and spin-coated at 2500 rpm, thereby forming a PbS quantum dot aggregate film (process PC1). Next, a 25 mmol / L methanol solution of zinc iodide and a 0.01 vol% methanol solution of 3-mercaptopropionic acid were dripped onto the PbS quantum dot aggregate film as ligand solutions, and then allowed to stand for 1 minute and then spin-dried at 2500 rpm for 20 seconds. Next, acetonitrile was dripped onto the PbS quantum dot aggregate film, and spin-dried at 2500 rpm for 20 seconds to exchange the ligand coordinated to the PbS quantum dots from oleic acid to 3-mercaptopropionic acid and zinc iodide (process PC2). An operation consisting of step PC1 and step PC2 as one cycle was repeated 10 times, thereby forming a PbS quantum dot aggregate film, ie, a photoelectric conversion layer, with a thickness of 200 nm in which the ligand was replaced from oleic acid to 3-mercaptopropionic acid and zinc iodide.

[0196] Next, the PbS quantum dot dispersion liquid 3 was dropped onto the photoelectric conversion layer and spin-coated at 2500 rpm to form a PbS quantum dot aggregate film (step HT1).

[0197] Next, as a ligand solution, a 0.01 volume % methanol solution of ethanedithiol was added dropwise, and the mixture was allowed to stand for 1 minute and then dried by rotation at 2500 rpm. Next, acetonitrile was added dropwise to the PbS quantum dot aggregate film, and dried by rotation at 2500 rpm for 20 seconds to exchange the ligand coordinated to the PbS quantum dots from oleic acid to ethanedithiol (process HT2). The operation of process HT1 and process HT2 as one cycle was repeated for 2 cycles, thereby forming a PbS quantum dot aggregate film, i.e., a hole transport layer, in which the ligand was exchanged from oleic acid to ethanedithiol, with a thickness of 40 nm.

[0198] Next, gold was deposited on the hole transport layer to a thickness of 100 nm, thereby obtaining a photodiode type light detection element.

[0199] [Comparative Example 1]

[0200] In step HT1 , a photodiode type light detection element was obtained by the same method as in Example 1 except that the dispersion liquid 1 of PbS quantum dots was used instead of the dispersion liquid 3 of PbS quantum dots.

[0201] <Evaluation of External Quantum Efficiency and Dark Current>

[0202] The external quantum efficiency (EQE) and dark current of the manufactured photodetection element were measured using a semiconductor parameter analyzer (C4156, manufactured by Agilent).

[0203] First, the current-voltage characteristic (IV characteristic) was measured while the voltage was swept from 0 V to -5 V in a state where no light was irradiated, and the current value at -2 V was evaluated as the dark current.

[0204] Next, the IV characteristics were measured while the voltage was swept from 0 V to -5 V while irradiating with monochromatic light of 940 nm. The external quantum efficiency (EQE) was calculated from the photocurrent value when -2 V was applied.

[0205] In addition, the smaller the value of the dark current is, the better it is.

[0206] [Table 1]

[0207]

[0208] As shown in the above table, the dark current of the photodetection element of the example is lower than the dark current of the comparative example 1.

[0209] [Example 2]

[0210] In step HT1 , a photodiode type light detection element was obtained by the same method as in Example 1 except that the dispersion liquid 2 of PbS quantum dots was used instead of the dispersion liquid 3 of PbS quantum dots.

[0211] [Example 3]

[0212] In step PC2, a photodiode type light detection element was obtained by the same method as in Example 1 except that a 25 mmol / L methanol solution of tetramethylammonium iodide was used as the ligand solution.

[0213] [Example 4]

[0214] A photodiode-type light detecting element was obtained by the same method as in Example 1 except that a 0.01 vol % methanol solution of thioglycolic acid was used as the ligand solution in step HT2.

[0215] [Example 5]

[0216] In step HT2, a photodiode type light detection element was obtained in the same manner as in Example 1 except that a 25 mmol / L methanol solution of lead chloride and a 0.01 vol % methanol solution of ethanedithiol were used as the ligand solution.

[0217] The dark currents of the photodetection elements of Examples 2 to 5 were measured by the above method. The results are shown in the following table.

[0218] [Table 2]

[0219]

[0220] In the light detection elements of Examples 2 to 5, the dark current is also lower than the dark current of Comparative Example 1. Furthermore, the light detection elements of Examples 2 to 5 have external quantum efficiencies comparable to that of the light detection element of Example 1.

[0221] An image sensor is manufactured by a known method using the light detection element obtained in the above-mentioned embodiment together with a filter manufactured according to the method described in International Publication No. 2016 / 186050 and International Publication No. 2016 / 190162, and assembled on a solid-state imaging element, thereby obtaining an image sensor with good visible-infrared imaging performance.

[0222] In each embodiment, even if the semiconductor quantum dots of the photoelectric conversion layer and the hole transport layer are changed to PbSe quantum dots, the same effect can be obtained.

[0223] Explanation of symbols

[0224] 1, 2-light detection element, 11-upper electrode, 12-lower electrode, 13-photoelectric conversion layer, 14-hole transport layer.

Claims

1. A light detection element, comprising: A photoelectric conversion layer, comprising a collection of semiconductor quantum dots QD1 containing metal atoms and ligands L1 coordinated with the semiconductor quantum dots QD1; and a hole transport layer, which is disposed on the photoelectric conversion layer and comprises a collection of semiconductor quantum dots QD2 containing metal atoms and a ligand L2 coordinated with the semiconductor quantum dots QD2, The band gap Eg2 of the semiconductor quantum dot QD2 is greater than the band gap Eg1 of the semiconductor quantum dot QD1, and the difference between the band gap Eg2 of the semiconductor quantum dot QD2 and the band gap Eg1 of the semiconductor quantum dot QD1 is greater than 0.10 eV.

2. The light detecting element according to claim 1, wherein The semiconductor quantum dot QD1 and the semiconductor quantum dot QD2 each contain a Pb atom.

3. The light detecting element according to claim 1 or 2, wherein: The semiconductor quantum dot QD1 and the semiconductor quantum dot QD2 include semiconductor quantum dots of the same type.

4. The light detecting element according to claim 1 or 2, wherein: The semiconductor quantum dot QD1 and the semiconductor quantum dot QD2 contain PbS respectively.

5. The light detecting element according to claim 1 or 2, wherein: The ligand L1 and the ligand L2 include at least one selected from a ligand containing a halogen atom and a multidentate ligand containing two or more coordination parts.

6. The light detecting element according to claim 5, wherein The ligand containing a halogen atom is an inorganic halide.

7. The light detecting element according to claim 6, wherein The inorganic halide contains Zn atoms.

8. The light detecting element according to claim 1 or 2, wherein: The ligand L1 comprises thioglycolic acid.

9. The light detecting element according to claim 1 or 2, wherein: The ligand L2 includes a compound having a thiol group. 10 . The light detecting element according to claim 1 , which is a photodiode type light detecting element. 11 . An image sensor comprising the light detection element according to claim 1 . The image sensor according to claim 11 , which is an infrared image sensor.

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