WO2022264872A1 - Photodetection element and image sensor - Google Patents

Abstract

The present invention provides a photodetection element which comprises a first electrode layer 11, a second electrode layer 12, a photoelectric conversion layer 13 that is arranged between the first electrode layer 11 and the second electrode layer 12, an electron transport layer 21 that is arranged between the first electrode layer 11 and the photoelectric conversion layer 13, and a hole transport layer 22 that is arranged between the photoelectric conversion layer 13 and the second electrode layer 12, wherein: the photoelectric conversion layer 13 contains quantum dots of a compound semiconductor that contains elemental Ag and elemental Bi; and the electron transport layer 21 contains zinc oxide that is doped with metal atoms other than Zn atoms. The present invention also provides an image sensor which comprises this photodetection element.

Description

Photodetector and image sensor

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

In recent years, attention has been focused on photodetectors capable of detecting light in the infrared region in areas such as smartphones, surveillance cameras, and vehicle-mounted cameras.

Conventionally, silicon photodiodes that use silicon wafers as the material for the photoelectric conversion layer have been used for photodetection 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.

InGaAs-based semiconductor materials, which are known as light-receiving elements for near-infrared light, require extremely high-cost processes such as epitaxial growth and substrate bonding processes in order to achieve high quantum efficiency. The problem is that the

Further, in recent years, research on quantum dots is progressing. Non-Patent Documents 1 and 2 describe a solar cell having a photoelectric conversion film containing AgBiS ₂ quantum dots.

M. Bernechea et al., "Solution-processed solar cells based on environmentally friendly AgBiS2 nanocrystals," Nature Photonics, 10, 521-525 (2016) L. Hu et al., "Enhanced optoelectronic performance in AgBiS2 nanocrystals obtained via an improved amine-based synthesis route", Journal of Materials Chemistry C6, 731 (2)

In recent years, with the demand for improved performance of image sensors, etc., there is a demand for further improvements in the various characteristics required of the photodetectors used in these. For example, one of the characteristics required for a photodetector is to have a high external quantum efficiency with respect to light of a target wavelength to be detected by the photodetector. By increasing the external quantum efficiency of the photodetector, it is possible to improve the light detection accuracy of the photodetector.

Also, in the photodetector, it is preferable that the dark current is small. A higher signal-to-noise ratio (SN ratio) can be obtained in the image sensor by reducing the dark current of the photodetector. A dark current is a current that flows when light is not applied.

The inventor of the present invention has extensively studied the solar cells described in Non-Patent Documents 1 and 2. In these solar cells, the external quantum efficiency for light with a wavelength in the infrared region (especially light with a wavelength of 900 nm or more) is found to be low. Also, the dark current was relatively high.

Accordingly, an object of the present invention is to provide a photodetector and an image sensor that have a high external quantum efficiency for light with wavelengths in the infrared region and a reduced dark current.

The inventor of the present invention has extensively studied a photodetector having a photoelectric conversion layer containing quantum dots of a compound semiconductor containing Ag element and Bi element, and found that the electron transport layer was doped with metal atoms other than Zn. The inventors have found that the use of zinc oxide enables a photodetector with high external quantum efficiency and low dark current, and have completed the present invention. Accordingly, the present invention provides the following.
<1> a first electrode layer;
a second electrode layer;
a photoelectric conversion layer provided between the first electrode layer and the second electrode layer;
an electron transport layer provided between the first electrode layer and the photoelectric conversion layer;
a hole transport layer provided between the photoelectric conversion layer and the second electrode layer;
The photoelectric conversion layer includes quantum dots of a compound semiconductor containing Ag element and Bi element,
The photodetector, wherein the electron transport layer contains zinc oxide doped with a metal atom other than Zn.
<2> The photodetector according to <1>, wherein the metal atom other than Zn is a monovalent to trivalent metal atom.
<3> The photodetector according to <1>, wherein the metal atom other than Zn includes at least one selected from Li, Mg, Al and Ga.
<4> In the zinc oxide doped with metal atoms other than Zn, the ratio of the metal atoms other than Zn to the total of Zn and the metal atoms other than Zn is 1 atomic % or more. The photodetector according to any one of <3>.
<5> The photodetector according to any one of <1> to <4>, wherein the compound semiconductor of the quantum dots further contains at least one element selected from S element and Te element.
<6> The photodetector according to any one of <1> to <5>, wherein the photoelectric conversion layer contains a ligand that coordinates to the quantum dot.
<7> The photodetector according to <6>, wherein the ligand includes at least one selected from ligands containing halogen atoms and multidentate ligands containing two or more coordinating moieties.
<8> An image sensor including the photodetector according to any one of <1> to <7>.

According to the present invention, it is possible to provide a photodetector and an image sensor with high external quantum efficiency and reduced dark current.

FIG. 11 illustrates an embodiment of a photodetector;

The contents of the present invention will be described in detail below.
In the present specification, the term "~" is used to include the numerical values before and after it as lower and upper limits.
In the description of a group (atomic group) in the present specification, a description that does not describe substitution or unsubstituted includes a group (atomic group) having no substituent as well as a group (atomic group) having a substituent. For example, an "alkyl group" includes not only an alkyl group having no substituent (unsubstituted alkyl group) but also an alkyl group having a substituent (substituted alkyl group).

<Photodetector>
The photodetector of the present invention is
a first electrode layer;
a second electrode layer;
a photoelectric conversion layer provided between the first electrode layer and the second electrode layer;
an electron transport layer provided between the first electrode layer and the photoelectric conversion layer;
a hole transport layer provided between the photoelectric conversion layer and the second electrode layer;
The photoelectric conversion layer contains quantum dots of a compound semiconductor containing Ag element and Bi element,
The electron transport layer is characterized by containing zinc oxide doped with metal atoms other than Zn.

By having the above configuration, the photodetector of the present invention can be a photodetector with high external quantum efficiency and low dark current. Although the detailed reason why such an effect is obtained is unknown, it is believed that the use of an electron transport layer containing zinc oxide doped with a metal atom other than Zn provides an appropriate energy level. guessed.

According to the study of the present inventor, when the quantum dots of the photoelectric conversion layer are composed of quantum dots other than "quantum dots of a compound semiconductor containing Ag element and Bi element" such as PbS, the electron transport layer is zinc oxide not doped with metal atoms other than Zn (non-doped zinc oxide), and a photodetector whose electron transport layer is zinc oxide doped with metal atoms other than Zn (doped zinc oxide). It was found that there was no particular difference in changes in external quantum efficiency, dark current, etc. That is, when the quantum dots of the photoelectric conversion layer are composed of quantum dots other than "quantum dots of a compound semiconductor containing Ag element and Bi element" such as PbS, the electron transport layer is doped with metal atoms other than Zn. Even if zinc oxide (doped zinc oxide) is used, the above effects such as improvement of external quantum efficiency and reduction of dark current cannot be obtained.

Details of the photodetector of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing an embodiment of a photodiode-type photodetector. The arrows in the drawing represent incident light to the photodetector. The photodetector 1 shown in FIG. 1 includes a second electrode layer 12, a first electrode layer 11 facing the second electrode layer 12, and a Between the photoelectric conversion layer 13 provided between, the electron transport layer 21 provided between the first electrode layer 11 and the photoelectric conversion layer 13, and the second electrode layer 12 and the photoelectric conversion layer 13 and a provided hole transport layer 22 . The photodetector 1 shown in FIG. 1 is used so that light enters from above the first electrode layer 11 . Although not shown, a transparent substrate may be arranged on the surface of the first electrode layer 11 on the light incident side. Types of transparent substrates include glass substrates, resin substrates, ceramic substrates, and the like.

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

The film thickness of the first electrode layer 11 is not particularly limited, and is preferably 0.01 to 100 μm, more preferably 0.01 to 10 μm, even more preferably 0.01 to 1 μm. . In the present invention, 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.

(Electron transport layer)
As shown in FIG. 1 , the electron transport layer 21 is provided between the first electrode layer 11 and the photoelectric conversion layer 13 . The electron transport layer 21 is a layer having a function of transporting electrons generated in the photoelectric conversion layer 13 to the electrode layer. The electron transport layer is also called a hole blocking layer.

The electron transport layer 21 contains zinc oxide doped with metal atoms other than Zn. Hereinafter, zinc oxide doped with metal atoms other than Zn is also referred to as doped zinc oxide.

The metal atom other than Zn in the doped zinc oxide is preferably a monovalent to trivalent metal atom, and more preferably contains at least one selected from Li, Mg, Al and Ga. Effects of the present invention Li, Mg, Al, or Ga is more preferred, and Li or Mg is particularly preferred, because it is possible to more significantly obtain the

In the doped zinc oxide, the ratio of metal atoms other than Zn to the total of Zn and metal atoms other than Zn is preferably 1 atomic % or more for the reason that the effects of the present invention can be obtained more remarkably. It is more preferably at least 4 atomic %, even more preferably at least 4 atomic %. From the viewpoint of suppressing an increase in crystal defects, the upper limit is preferably 20 atomic % or less, more preferably 15 atomic % or less, and even more preferably 12 atomic % or less. The proportion of metal atoms other than Zn in the doped zinc oxide can be measured by a high frequency inductively coupled plasma (ICP) method.

The doped zinc oxide is preferably particles (doped zinc oxide particles) from the viewpoint of reducing residual organic components and increasing the contact area with the photoelectric conversion layer. Also, the average particle size of the doped zinc oxide particles is preferably 2 to 30 nm. The lower limit of the average particle size of the doped zinc oxide particles is preferably 3 nm or more, more preferably 5 nm or more. Also, the upper limit of the average particle diameter of the doped zinc oxide particles is preferably 20 nm or less, more preferably 15 nm or less. When the average particle size of the doped zinc oxide particles is within the above range, a film having a large contact area with the photoelectric conversion layer and high flatness can be easily obtained. In this specification, the value of the average particle size of the doped zinc oxide particles is the average value of the particle sizes of 10 arbitrarily selected quantum dots. A transmission electron microscope may be used to measure the particle size of the doped zinc oxide particles.

The electron transport layer 21 can be formed through a process of applying a dispersion containing doped zinc oxide particles. The electron transport layer 21 can also be formed by a method such as a physical vapor deposition method (PVD method) such as a vacuum deposition method, sputtering, or a chemical vapor deposition method (CVD method).

The thickness of the electron transport layer 21 is preferably 10-1000 nm. The upper limit is preferably 800 nm or less. The lower limit is preferably 20 nm or more, more preferably 50 nm or more. Further, the thickness of the electron transport layer 21 is preferably 0.05 to 10 times the thickness of the photoelectric conversion layer 13, more preferably 0.1 to 5 times, and 0.2 to 2 times. is more preferable.

(Another electron transport layer)
Although not shown, in the photodetector of the present invention, between the first electrode layer 11 and the electron transport layer 21, or between the electron transport layer 21 and the photoelectric conversion layer 13, an oxide layer doped with metal atoms other than Zn is provided. It may have another electron transport layer composed of an electron transport material other than zinc. Other electron transport materials include fullerene compounds such as [6,6]-Phenyl-C61-Butyric Acid Methyl Ester (PC61BM), perylene compounds such as perylenetetracarboxydiimide, tetracyanoquinodimethane, titanium oxide, and tin oxide. , zinc oxide, indium oxide, indium tungsten oxide, indium zinc oxide, indium tin oxide, and fluorine-doped tin oxide.

When the photodetector has another electron-transporting layer, the other electron-transporting layer is preferably present between the first electrode layer 11 and the electron-transporting layer 21 .

The thickness of the other electron transport layer 21 is preferably 10-1000 nm. The upper limit is preferably 800 nm or less. The lower limit is preferably 20 nm or more, more preferably 50 nm or more.

(Photoelectric conversion layer)
The photoelectric conversion layer 13 contains quantum dots of a compound semiconductor containing Ag (silver) element and Bi (bismuth) element. A compound semiconductor is a semiconductor composed of two or more elements. Therefore, in this specification, "a compound semiconductor containing Ag element and Bi element" means a compound semiconductor containing Ag element and Bi element as elements constituting the compound semiconductor. In this specification, the term “semiconductor” means a substance having a resistivity value of 10 ⁻² Ωcm or more and 10 ⁸ Ωcm or less.

The compound semiconductor, which is the quantum dot material constituting the quantum dots, is preferably a compound semiconductor further containing at least one element selected from S (sulfur) and Te (tellurium) elements. According to this aspect, it is easy to obtain a photoelectric conversion film having a high external quantum efficiency for light with a wavelength in the infrared region. Among them, the compound semiconductor is a compound semiconductor containing Ag element, Bi element, and S element (hereinafter also referred to as Ag—Bi—S-based semiconductor), or Ag element, Bi element, Te element, and S It is preferably a compound semiconductor containing elements (hereinafter also referred to as Ag--Bi--Te--S semiconductor). Further, as the Ag-Bi-Te-S semiconductor, the number of Te elements is divided by the sum of the number of Te elements and the number of S elements (the number of Te elements/(the number of Te elements + the number of S elements )) is preferably between 0.05 and 0.5. The lower limit is preferably 0.1 or more, more preferably 0.15 or more, and even more preferably 0.2 or more. The upper limit is preferably 0.45 or less, more preferably 0.4 or less. In this specification, the type and number of each element constituting the compound semiconductor can be measured by ICP (Inductively Coupled Plasma) emission spectroscopy or energy dispersive X-ray analysis.

The crystal structure of the compound semiconductor is not particularly limited. Various crystal structures can be formed depending on the types and composition ratios of the elements that make up the compound semiconductor. A crystalline or hexagonal crystal structure is preferred. In this specification, the crystal structure of a compound semiconductor can be measured by an X-ray diffraction method or an electron beam diffraction method.

The bandgap of the quantum dots of the compound semiconductor is preferably 1.2 eV or less, more preferably 1.1 eV or less. Although the lower limit of the bandgap of the quantum dots of the compound semiconductor is not particularly limited, it is preferably 0.3 eV or more, more preferably 0.5 eV or more.

The average particle diameter of the quantum dots of the compound semiconductor is preferably 3 to 20 nm. The lower limit of the average particle diameter of the quantum dots of the compound semiconductor is preferably 4 nm or more, more preferably 5 nm or more. The upper limit of the average particle size of the quantum dots of the compound semiconductor is preferably 15 nm or less, more preferably 10 nm or less. If the average particle size of the quantum dots of the compound semiconductor is within the above range, the photodetector can have a higher external quantum efficiency with respect to light with wavelengths in the infrared region. In this specification, the value of the average particle size of quantum dots is the average value of the particle sizes of 10 arbitrarily selected quantum dots. A transmission electron microscope may be used to measure the particle size of the quantum dots.

The photoelectric conversion layer 13 preferably contains ligands that coordinate to the quantum dots of the compound semiconductor. Ligands include ligands containing halogen atoms and multidentate ligands containing two or more coordinating sites. The photoelectric conversion layer 13 may contain only one type of ligand, or may contain two or more types. Among others, the photoelectric conversion layer 13 preferably contains a ligand containing a halogen atom and a multidentate ligand. According to this aspect, a photodetector element having low dark current and excellent performance such as electrical conductivity, photocurrent value, external quantum efficiency, and in-plane uniformity of external quantum efficiency can be obtained. It is presumed that the reason why such an effect is obtained is as follows. Multidentate ligands are presumed to chelate coordinate with quantum dots, and are presumed to be able to more effectively suppress peeling of ligands from quantum dots. In addition, it is presumed that steric hindrance between quantum dots can be suppressed by chelate coordination. Therefore, it is considered that the steric hindrance between the quantum dots is reduced, the quantum dots are closely arranged, and the overlapping of the wave functions between the quantum dots can be strengthened. Then, when a ligand containing a halogen atom is further included as a ligand coordinated to the quantum dot, the ligand containing a halogen atom is coordinated in the gap where the multidentate ligand is not coordinated. It is speculated that the surface defects of quantum dots can be reduced. For this reason, it is presumed that a photodetector element with low dark current and excellent performance such as electrical conductivity, photocurrent value, external quantum efficiency, and in-plane uniformity of external quantum efficiency can be obtained. When the photoelectric conversion layer 13 contains a ligand containing a halogen atom and a multidentate ligand, their molar ratio is preferably 1:99 to 99:1, and 10:90 to 90:10. is more preferred, and 20:80 to 80:20 is even more preferred.

First, ligands containing halogen atoms will be explained. The halogen atom contained in the ligand includes fluorine atom, chlorine atom, bromine atom and iodine atom, and iodine atom is preferable from the viewpoint of coordinating power.

A ligand containing a halogen atom may be an organic halide or an inorganic halide. Among them, inorganic halides are preferable because they are easily coordinated to both the cationic site and the anionic site of the quantum dot. When an inorganic halide is used, the effect of coordinating with both the cationic site and the anionic site of the quantum dot can be expected. When an inorganic halide is used, it is preferably a compound containing a metal element selected from Zn (zinc) atoms, In (indium) atoms and Cd (cadmium) atoms, more preferably a compound containing a Zn atom. preferable. The inorganic halide is preferably a salt of a metal atom and a halogen atom because it is easily ionized and easily coordinated to the quantum dots.

Specific examples of ligands containing halogen atoms 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.

In the case of a ligand containing a halogen atom, the halogen ion may be dissociated from the ligand described above and coordinated to the surface of the quantum dot. In addition, sites other than the halogen atoms of the aforementioned ligand may also be coordinated to the surface of the quantum dot. To give a specific example, in the case of zinc iodide, zinc iodide may be coordinated to the surface of the quantum dot, and iodine ions and zinc ions may be coordinated to the surface of the quantum dot. Sometimes.

Next, the multidentate ligand will be explained. Coordinating moieties included in the polydentate ligand include thiol groups, amino groups, hydroxy groups, carboxy groups, sulfo groups, phospho groups, and phosphonic acid groups.

Multidentate ligands include ligands represented by any one of formulas (A) to (C).

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

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

In formula (C), X ^C1 to X ^C3 each independently represent a thiol group, an amino group, a hydroxy group, a carboxy group, a sulfo group, a phospho group or a phosphonic acid group;
X ^C4 represents N,
L ^C1 to L ^C3 each independently represent a hydrocarbon group.

The amino groups represented by X ^A1 , X ^A2 , X ^B1 , X ^B2 , X ^C1 , X ^C2 and X ^C3 are not limited to —NH ₂ but also include substituted amino groups and cyclic amino groups. Substituted amino groups include monoalkylamino groups, dialkylamino groups, monoarylamino groups, diarylamino groups, alkylarylamino groups and the like. The amino group represented by these groups is preferably -NH ₂ , a monoalkylamino group or a dialkylamino group, and more preferably -NH ₂ .

The hydrocarbon group represented by L ^A1 , L ^B1 , L ^B2 , L ^C1 , L ^C2 and L ^C3 is preferably an aliphatic hydrocarbon group or a group containing an aromatic ring, 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 1-20. 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, alkynylene groups, and arylene groups.

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

In formula (A), X ^A1 and X ^A2 are preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, and more preferably by 1 to 4 atoms, by L ^A1 . is more preferable, more preferably 1 to 3 atoms apart, and particularly preferably 1 or 2 atoms apart.

In formula (B), X 1 ^B1 and X 1 ^B3 are preferably separated by 1 to 10 atoms, more preferably 1 to 6 atoms, and 1 to 4 atoms by L 1 ^B1 . is more preferable, more preferably 1 to 3 atoms apart, and particularly preferably 1 or 2 atoms apart. X ^B2 and X ^B3 are preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, even more preferably by 1 to 4 atoms, by L ^B2 , More preferably, they are separated by 1 to 3 atoms, and particularly preferably separated by 1 or 2 atoms.

In formula (C), X ^C1 and X ^C4 are preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, and further by 1 to 4 atoms, by L ^C1 . is more preferable, more preferably 1 to 3 atoms apart, and particularly preferably 1 or 2 atoms apart. X ^C2 and X ^C4 are preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, even more preferably by 1 to 4 atoms, by L ^C2 , More preferably, they are separated by 1 to 3 atoms, and particularly preferably separated by 1 or 2 atoms. X ^C3 and X ^C4 are preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, even more preferably by 1 to 4 atoms, by L ^C3 , More preferably, they are separated by 1 to 3 atoms, and particularly preferably separated by 1 or 2 atoms.

X ^A1 and X ^A2 are separated by 1 to 10 atoms by L ^A1 means that the number of atoms forming the shortest molecular chain connecting X ^A1 and X ^A2 is 1 to 10. means For example, in the case of formula (A1) below, X ^A1 and X ^A2 are separated by two atoms, and in the cases of formulas (A2) and (A3) below, X ^A1 and X ^A2 are separated by three atoms. ing. The numbers attached to the following structural formulas represent the order of arrangement of atoms forming the shortest molecular chain connecting ^XA1 and ^XA2 .

3-mercaptopropionic acid has a structure in which the site corresponding to X ^A1 is a carboxy group, the site corresponding to X ^A2 is a thiol group, and the site corresponding to L ^A1 is an ethylene group. (a compound having the following structure). In 3-mercaptopropionic acid, X ^A1 (carboxy group) and X ^A2 (thiol group) are separated by two atoms by L ^A1 (ethylene group).

X ^B1 and X ^B3 are separated by 1 to 10 atoms by L ^B1 ; X ^B2 and X ^B3 are separated by 1 to 10 atoms by L ^B2 ; X ^C1 and X ^C4 are separated by L ^C1 ; X ^C2 and X ^C4 are separated by 1 to 10 atoms, and X ^C3 and X ^C4 are ^{separated by L C3 by} 1 to 10 atoms. The meaning is also the same as above.

Specific examples of multidentate ligands include 1,2-ethanedithiol, 3-mercaptopropionic acid, thioglycolic acid, 2-aminoethanol, 2-aminoethanethiol, 2-mercaptoethanol, glycolic acid, ethylene glycol, Ethylenediamine, aminosulfonic acid, glycine, aminomethylphosphoric acid, guanidine, diethylenetriamine, tris(2-aminoethyl)amine, 4-mercaptobutanoic acid, 3-aminopropanol, 3-mercaptopropanol, N-(3-aminopropyl) -1,3-propanediamine, 3-(bis(3-aminopropyl)amino)propan-1-ol, 1-thioglycerol, dimercaprol, 1-mercapto-2-butanol, 1-mercapto-2-pen Tanol, 3-mercapto-1-propanol, 2,3-dimercapto-1-propanol, diethanolamine, 2-(2-aminoethyl)aminoethanol, dimethylenetriamine, 1,1-oxybismethylamine, 1,1- Thiobismethylamine, 2-[(2-aminoethyl)amino]ethanethiol, bis(2-mercaptoethyl)amine, 2-aminoethane-1-thiol, 1-amino-2-butanol, 1-amino-2- Pentanol, L-cysteine, D-cysteine, 3-amino-1-propanol, L-homoserine, D-homoserine, aminohydroxyacetic acid, L-lactic acid, D-lactic acid, L-malic acid, D-malic acid, glycerin acid, 2-hydroxybutyric acid, L-tartaric acid, D-tartaric acid, tartronic acid, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 2-mercaptobenzoic acid, 3-mercaptobenzoic acid , 4-mercaptobenzoic acid and derivatives thereof, which are low in dark current and easy to obtain semiconductor films with high external quantum efficiency. Thioglycolic acid, 2-aminoethanol, 2-aminoethanethiol, 2 - mercaptoethanol, glycolic acid, diethylenetriamine, tris(2-aminoethyl)amine, 1-thioglycerol, dimercaprol, ethylenediamine, ethylene glycol, aminosulfonic acid, glycine, (aminomethyl)phosphonic acid, guanidine, diethanolamine, 2 - (2-aminoethyl)aminoethanol, homoserine, cysteine, thiomalic acid, malic acid and tartaric acid are preferred, thioglycolic acid, 2-aminoethyl Tanol, 2-mercaptoethanol and 2-aminoethanethiol are more preferred, and thioglycolic acid is even more preferred. The polydentate ligand is preferably a compound having a boiling point of 90°C or higher.

The thickness of the photoelectric conversion layer 13 is preferably 10-1000 nm. The lower limit of the thickness is preferably 20 nm or more, 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 photoelectric conversion layer 13 can have a refractive index of 1.5 to 5.0 with respect to light of a target wavelength to be detected by the photodetector.

The photoelectric conversion layer 13 is formed by applying a dispersion liquid containing compound semiconductor quantum dots containing Ag element and Bi element, ligands coordinated to the quantum dots, and a solvent onto a substrate to form a group of quantum dots. It can be formed through a process of forming a body film (quantum dot assembly forming process).

There are no particular restrictions on the method of applying the quantum dot dispersion onto the substrate. Coating methods such as a spin coating method, a dipping method, an inkjet method, a dispenser method, a screen printing method, a letterpress printing method, an intaglio printing method, and a spray coating method can be mentioned.

The film thickness of the film of the quantum dot aggregates formed by the quantum dot aggregate forming step is preferably 3 nm or more, more preferably 10 nm or more, and more preferably 20 nm or more. The upper limit is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less.

After forming the film of the quantum dot assembly, a ligand exchange step may be further performed to exchange the ligands coordinated to the quantum dots with other ligands. In the ligand exchange step, a ligand different from the ligand contained in the dispersion liquid (hereinafter referred to as ligand A ) and a solvent to exchange the ligands coordinated to the quantum dots with the ligands A contained in the ligand solution. Alternatively, the quantum dot assembly formation step and the ligand exchange step may be alternately repeated multiple times.

Examples of the ligand A include ligands containing halogen atoms and multidentate ligands containing two or more coordinating moieties. Details of these include those described in the section on the photoelectric conversion film described above, and the preferred range is also the same.

The ligand solution used in the ligand exchange step may contain only one type of ligand A, or may contain two or more types. Also, two or more ligand solutions may be used.

The solvent contained in the ligand solution is preferably selected as appropriate according to the type of ligand contained in each ligand solution, and is preferably a solvent that easily dissolves each ligand. Moreover, the solvent contained in the ligand solution is preferably an organic solvent having a high dielectric constant. Specific examples include ethanol, acetone, methanol, acetonitrile, dimethylformamide, dimethylsulfoxide, butanol, propanol and the like. Moreover, the solvent contained in the ligand solution is preferably a solvent that hardly remains in the photoelectric conversion film to be formed. Low-boiling alcohols, ketones, and nitriles are preferred, and methanol, ethanol, acetone, and acetonitrile are more preferred, from the viewpoint of being easy to dry and easy to remove by washing. The solvent contained in the ligand solution is preferably immiscible with the solvent contained in the quantum dot dispersion. As a preferred combination of solvents, the solvent contained in the quantum dot dispersion is an alkane such as hexane or octane, or when toluene is used, the solvent contained in the ligand solution is a polar solvent such as methanol or acetone. is preferred.

A step of rinsing the film after the ligand exchange step by contacting a rinse solution (rinsing step) may be performed. By performing the rinsing step, excess ligands contained in the film and ligands detached from the quantum dots can be removed. In addition, residual solvent and other impurities can be removed. As a rinsing liquid, it is easier to remove excess ligands contained in the film and ligands detached from the quantum dots more effectively, and it keeps the film surface uniform by rearranging the quantum dot surface. Aprotic solvents are preferred because they are easier to use. 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, preferably acetonitrile and tetrahydrofuran, more preferably acetonitrile.

In addition, the rinsing process may be performed multiple times using two or more rinsing liquids with different polarities (relative dielectric constants). For example, first rinse with a rinse solution having a higher relative dielectric constant (also referred to as a first rinse solution), and then rinse with a rinse solution having a lower relative dielectric constant than the first rinse solution (also referred to as a second rinse solution). It is preferable to perform rinsing using By performing rinsing in this way, the surplus component of ligand A used for ligand exchange is first removed, and then the desorbed ligand component (originally bound to the particles) generated during the ligand exchange process is removed. By removing the ligand component), both the surplus/or desorbed ligand component can be removed more efficiently.

The dielectric constant of the first rinse is preferably 15-50, more preferably 20-45, and even more preferably 25-40. The dielectric constant of the second rinse is preferably 1-15, more preferably 1-10, and even more preferably 1-5.

The method for manufacturing the photoelectric conversion film may have a drying process. By performing the drying process, the solvent remaining on the photoelectric conversion film can be removed. The drying time is preferably 1 to 100 hours, more preferably 1 to 50 hours, even more preferably 5 to 30 hours. The drying temperature is preferably 10 to 100°C, more preferably 20 to 90°C, even more preferably 20 to 50°C.

(Hole transport layer)
As shown in FIG. 1 , the hole transport layer 22 is provided between the second electrode layer 12 and the photoelectric conversion layer 13 . The hole transport layer is a layer having a function of transporting holes generated in the photoelectric conversion layer to the electrode layer. A hole transport layer is also called an electron blocking layer.

The hole-transporting layer 22 is made of a hole-transporting material capable of performing this function. For example, hole transport materials include PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid)), PTB7 (poly{4,8-bis[(2-ethylhexyl) oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-lt-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4 -b]thiophene-4,6-diyl}), MoO ₃ and the like. Organic hole-transporting materials described in paragraphs 0209 to 0212 of JP-A-2001-291534 can also be used. Quantum dots can also be used as the hole transport material. Quantum dot materials constituting quantum dots include general semiconductor crystals [a) Group IV semiconductors, b) Group IV-IV, III-V, or II-VI compound semiconductors, c) Groups II, III Compound semiconductors composed of a combination of three or more of Group, IV, V and VI elements] nanoparticles (particles with a size of 0.5 nm or more and less than 100 nm). Specifically, PbS, PbSe, PbSeS, InN, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, HgTe, HgCdTe, _Ag2S , Ag2Se, Ag2Te, _SnS , _SnSe , SnTe, Si , InP, and other semiconductor materials having a relatively narrow bandgap. A ligand may be coordinated to the surface of the quantum dot.

Further, an organic semiconductor having a structure represented by any one of formulas 3-1 to 3-5 can also be used as the hole-transporting material.

In formula 3-1, X ¹ and X ² each independently represent S, O, Se, NR ^X1 or CR ^X2 R ^X3 , and R ^X1 to R ^X3 each independently represent a hydrogen atom or a substituent. represent,
Z ¹ and Z ² each independently represent N or CR ^Z1 , R ^Z1 represents a hydrogen atom or a substituent,
R ¹ to R ⁴ each independently represent a hydrogen atom or a substituent,
n1 represents an integer from 0 to 2,
* represents a bond.
provided that at least one of R ¹ and R ² is a halogen atom, hydroxy group, cyano group, acylamino group, acyloxy group, acyl group, alkoxycarbonyl group, aryloxycarbonyl group, silyl group, alkyl group, alkenyl group, alkynyl group , an aryl group, an aryloxy group, an alkylthio group, an arylthio group, a heteroaryl group, a group represented by formula (R-100), or a group containing an inner salt structure.
-L ¹⁰⁰ -R ¹⁰⁰ (R-100)
In (R-100), L ¹⁰⁰ represents a single bond or a divalent group, and R ¹⁰⁰ represents an acid group, a basic group, a group having an anion or a group having a cation.

In formula 3-2, X ³ to X ⁸ each independently represent S, O, Se, NR ^X4 or CR ^X5 R ^X6 , and R ^X4 to R ^X6 each independently represent a hydrogen atom or a substituent. represent,
Z ³ and Z ⁴ each independently represent N or CR ^Z2 , R ^Z2 represents a hydrogen atom or a substituent,
R ⁵ to R ⁸ each independently represent a hydrogen atom or a substituent,
n2 represents an integer from 0 to 2,
* represents a bond.

In formula 3-3, X ⁹ to X ¹⁶ each independently represent S, O, Se, NR ^X7 or CR ^X8 R ^X9 , and R ^X7 to R ^X9 each independently represent a hydrogen atom or a substituent. represent,
Z ⁵ and Z ⁶ each independently represent N or CR ^Z3 , R ^Z3 represents a hydrogen atom or a substituent,
* represents a bond.

In formula 3-4, R ⁹ to R ¹⁶ each independently represent a hydrogen atom or a substituent,
n3 represents an integer of 0 to 2,
* represents a bond.

In formula 3-5, X ¹⁷ to X ²³ each independently represent S, O, Se, NR ^X10 or CR ^X11 R ^X12 , and R ^X10 to R ^X12 each independently represent a hydrogen atom or a substituent. represent,
Z ⁷ to Z ¹⁰ each independently represent N or CR ^Z4 , R ^Z4 represents a hydrogen atom or a substituent,
* represents a bond.

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, more preferably 30 nm or less.

(Second electrode layer)
The second electrode layer 12 contains at least one metal atom selected from Au, Pt, Ir, Pd, Cu, Pb, Sn, Zn, Ti, W, Mo, Ta, Ge, Ni, Cr and In. It is preferably made of a metal material. By forming the second electrode layer 12 from such a metal material, a photodetector element with high external quantum efficiency and low dark current can be obtained.

More preferably, the second electrode layer 12 is made of a metal material containing at least one metal atom selected from Au, Cu, Mo, Ni, Pd, W, Ir, Pt and Ta. It is more preferable to use a metal material containing at least one metal atom selected from Au, Pd, Ir, and Pt for the reason that it is large and migration is easily suppressed.

The Ag atom content in the second electrode layer 12 is preferably 98% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less. It is also preferable that the second electrode layer 12 does not substantially contain Ag atoms. The case where the second electrode layer 12 does not substantially contain Ag atoms means that the content of Ag atoms in the second electrode layer 12 is 1% by mass or less, and 0.1% by mass or less. preferably contains no Ag atoms, and more preferably contains no Ag atoms.

The work function of the second electrode layer 12 is preferably 4.6 eV or more for the reason that the electron blocking property of the hole transport layer is enhanced and the holes generated in the device are easily collected. It is more preferably 5.7 eV, and even more preferably 4.9 to 5.3 eV.

The film thickness of the second electrode layer 12 is not particularly limited, and is preferably 0.01-100 μm, more preferably 0.01-10 μm, and particularly preferably 0.01-1 μm.

(blocking layer)
Although not shown, the photodetector of the present invention may have a blocking layer between the first electrode layer 11 and the electron transport layer 21 . A blocking layer is a layer having a function of preventing reverse current. A blocking layer is also called an anti-short circuit layer. Materials forming the blocking layer include, for example, silicon oxide, magnesium oxide, aluminum oxide, calcium carbonate, cesium carbonate, polyvinyl alcohol, polyurethane, titanium oxide, tin oxide, zinc oxide, niobium oxide, and tungsten oxide. The blocking layer may be a single layer film or a laminated film of two or more layers.

(Characteristics of photodetector)
In the photodetector of the present invention, the wavelength λ of the light to be detected by the photodetector and the surface of the second electrode layer 12 on the side of the photoelectric conversion layer 13 to the side of the first electrode layer 11 of the photoelectric conversion layer 13 It is preferable that the optical path length L ^λ of the light of the wavelength λ to the surface of the surface satisfies the relationship of the following formula (1-1), and that the relationship of the following formula (1-2) is satisfied. more preferred. When the wavelength λ and the optical path length L ^λ satisfy such a relationship, in the photoelectric conversion layer 13, the light (incident light) incident from the first electrode layer 11 side and the second electrode layer It is possible to match the phase with the light reflected by the surface of 12 (reflected light), as a result, the light is strengthened by the optical interference effect, and a higher external quantum efficiency can be obtained.

0.05+m/2≤Lλ/ ^λ≤0.35 +m/2 (1-1)
0.10+m/2≦Lλ/ ^λ ≦0.30+m/2 (1-2)

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

m is preferably an integer of 0 to 4, more preferably an integer of 0 to 3, and even more preferably an integer of 0 to 2. According to this aspect, the transport characteristics of charges such as holes and electrons are excellent, and the external quantum efficiency of the photodetector can be further increased.

Here, the optical path length means a value obtained by multiplying the physical thickness of a substance through which light passes by the refractive index. Taking the photoelectric conversion layer 13 as an example, when the thickness of the photoelectric conversion layer is d ¹ and the refractive index of the photoelectric conversion layer with respect to the wavelength λ ¹ is N ¹ , the wavelength λ ¹ transmitted through the photoelectric conversion layer 13 is The optical path length of light is N ¹ ×d ¹ . When the photoelectric conversion layer 13 and the hole transport layer 22 are composed of a laminated film of two or more layers, or when an intermediate layer exists between the hole transport layer 22 and the second electrode layer 12, The integrated value of the optical path length of each layer is the optical path length ^Lλ .

The photodetector of the present invention is preferably used for detecting light with wavelengths in the infrared region. That is, the photodetector of the present invention is preferably an infrared photodetector. Moreover, it is preferable that the light to be detected by the above-described photodetector is light having a wavelength in the infrared region. In addition, the light with a wavelength in the infrared region is preferably light with a wavelength exceeding 700 nm, more preferably light with a wavelength of 800 nm or longer, still more preferably light with a wavelength of 900 nm or longer, and a wavelength of 1000 nm or longer. is more preferable. Further, the light with a wavelength in the infrared region is preferably light with a wavelength of 2000 nm or less, more preferably light with a wavelength of 1800 nm or less, and even more preferably light with a wavelength of 1600 nm or less.

In addition, the photodetector of the present invention may simultaneously 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).

<Image sensor>
An image sensor of the present invention includes the photodetector of the present invention described above. Since the photodetector of the present invention has excellent sensitivity to light with wavelengths in the infrared region, it can be particularly preferably used as an infrared image sensor. Further, the image sensor of the present invention can be preferably used for sensing light with a wavelength of 900 to 2000 nm, and more preferably for sensing light with a wavelength of 900 to 1600 nm.

The configuration of the image sensor is not particularly limited as long as it includes the photodetector of the present invention and functions as an image sensor.

The image sensor may include an infrared transmission filter layer. The infrared transmission filter layer preferably has low transmittance for light in the visible wavelength band, and more preferably has an average transmittance of 10% or less for light in the wavelength range of 400 to 650 nm. 0.5% or less is more preferable, and 5% or less is particularly preferable.

Examples of the infrared transmission filter layer include those composed of a resin film containing a coloring material. Colorants include chromatic colorants such as red colorants, green colorants, blue colorants, yellow colorants, purple colorants, and orange colorants, and black colorants. The colorant contained in the infrared transmission filter layer preferably forms a black color by combining two or more chromatic colorants or contains a black colorant. When two or more chromatic colorants are combined to form a black color, the combination of chromatic colorants includes, for example, the following modes (C1) to (C7).
(C1) A mode containing a red colorant and a blue colorant.
(C2) A mode containing a red colorant, a blue colorant, and a yellow colorant.
(C3) A mode containing a red colorant, a blue colorant, a yellow colorant, and a purple colorant.
(C4) A mode containing a red colorant, a blue colorant, a yellow colorant, a purple colorant, and a green colorant.
(C5) A mode containing a red colorant, a blue colorant, a yellow colorant, and a green colorant.
(C6) A mode containing a red colorant, a blue colorant, and a green colorant.
(C7) An embodiment containing a yellow colorant and a purple colorant.

The chromatic colorant may be a pigment or a dye. It may contain 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.

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

The spectral characteristics of the infrared transmission filter layer can be appropriately selected according to the application of the image sensor. For example, a filter layer that satisfies any one of the following spectral characteristics (1) to (5) may be used.
(1): 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 light in the thickness direction of the film. of 70% or more (preferably 75% or more, more preferably 80% or more) in the wavelength range of 900 to 1500 nm.
(2): 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 light in the thickness direction of the film. of 70% or more (preferably 75% or more, more preferably 80% or more) in the wavelength range of 1000 to 1500 nm.
(3): 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 light in the film thickness direction of 70% or more (preferably 75% or more, more preferably 80% or more) in the wavelength range of 1100 to 1500 nm.
(4): 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 wavelength range is 1400 to 1500 nm. is 70% or more (preferably 75% or more, more preferably 80% or more).
(5): 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 wavelength range is 1600 to 2000 nm. is 70% or more (preferably 75% or more, more preferably 80% or more).

In addition, the infrared transmission filter, JP 2013-077009, JP 2014-130173, JP 2014-130338, International Publication No. 2015/166779, International Publication No. 2016/178346, International Publication The films described in WO 2016/190162, WO 2018/016232, JP 2016-177079, 2014-130332, and WO 2016/027798 can be used. Moreover, the infrared transmission filter may be used in combination of two or more filters, or a dual bandpass filter that transmits two or more specific wavelength regions with one filter may be used.

The image sensor may include an infrared shielding filter for the purpose of improving various performances such as noise reduction. Specific examples of the infrared shielding filter include, for example, International Publication No. 2016/186050, International Publication No. 2016/035695, Patent No. 6248945, International Publication No. 2019/021767, JP 2017-067963, Patent A filter described in Japanese Patent No. 6506529 and the like are included.

The image sensor may include a dielectric multilayer film. Examples of the dielectric multilayer film include those obtained by alternately laminating dielectric thin films with a high refractive index (high refractive index material layers) and dielectric thin films with a low refractive index (low refractive index material layers). The number of laminated dielectric thin films in the dielectric multilayer film is not particularly limited, but is preferably 2 to 100 layers, more preferably 4 to 60 layers, and even more preferably 6 to 40 layers. A material having a refractive index of 1.7 to 2.5 is preferable as the material used for forming the high refractive index material layer. Specific examples include _Sb2O3 , _Sb2S3 , _Bi2O3 , _CeO2 , _{CeF3 , HfO2 , La2O3 , Nd2O3 , Pr6O11 , Sc2O3 , SiO} , Ta ₂ O ₅ , TiO ₂ , TlCl, Y ₂ O ₃ , ZnSe, ZnS, ZrO ₂ and the like. A material having a refractive index of 1.2 to 1.6 is preferable as the material used for forming the low refractive index material layer. Specific examples include _Al2O3 , _BiF3 , _CaF2 , _LaF3 , _PbCl2 , _PbF2 , LiF, _MgF2 , MgO, _{NdF3 , SiO2} , _{Si2O3 ,} NaF, _ThO2 , _ThF4 , Na ₃ AlF ₆ and the like. The method for forming the dielectric multilayer film is not particularly limited, but examples include vacuum deposition methods such as ion plating and ion beam, physical vapor deposition methods (PVD methods) such as sputtering, and chemical vapor deposition methods. (CVD method) and the like. The thickness of each of the high refractive index material layer and the low refractive index material layer is preferably 0.1λ to 0.5λ when the wavelength of light to be blocked is λ (nm). Specific examples of dielectric multilayer films include dielectric multilayer films described in JP-A-2014-130344 and JP-A-2018-010296.

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, still 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, even more preferably 90% or more. Also, 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. Also, 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. Further, the wavelength range of the transmission wavelength band is preferably center wavelength λ _t1 ±100 nm, more preferably center wavelength λ _t1 ±75 nm, where λ _t1 is the wavelength showing the maximum transmittance. More preferably, the center wavelength λ _t1 ±50 nm.

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.

The image sensor may include a color separation filter layer. The color separation filter layer includes a filter layer containing colored pixels. Types of colored pixels include red pixels, green pixels, blue pixels, yellow pixels, cyan pixels, and magenta pixels. The color separation filter layer may contain colored pixels of two or more colors, or may contain only one color. It can be appropriately selected according to the application and purpose. As the color separation filter layer, for example, a filter described in International Publication No. 2019/039172 can be used.

In addition, when the color separation layer includes colored pixels of two or more colors, the colored pixels of each color may be adjacent to each other, and partition walls may be provided between the colored pixels. The material of the partition is not particularly limited. Examples include organic materials such as siloxane resins and fluorine resins, and inorganic particles such as silica particles. Moreover, the partition may be made of a metal such as tungsten or aluminum.

When the image sensor includes an infrared transmission filter layer and a color separation layer, the color separation layer is preferably provided 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 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 both of them are present on the same plane.

The image sensor may include an intermediate layer such as a flattening layer, a base layer, an adhesion layer, an antireflection film, and a lens. As the antireflection film, for example, a film produced from 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.

The present invention will be described more specifically below with reference to examples. The materials, usage amounts, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Accordingly, the scope of the present invention is not limited to the specific examples shown below.

[Production of quantum dot dispersion]
Production Example 1-1 (Production of _AgBiS2 quantum dot dispersion (quantum dot dispersion 1))
30 ml of oleic acid, 0.8 mmol of silver acetate, and 1 mmol of bismuth acetate were weighed into a flask and heated at 100° C. for 3 hours under vacuum to obtain a precursor solution. After the system was under nitrogen flow, 1 mmol of hexamethyldisilathiane was injected along with 5 mL of octadecene. Immediately after the injection, the flask was naturally cooled, and when the temperature reached 40° C., 20 mL of toluene was added and the solution was recovered. An excess amount of acetone was added to the solution, centrifugation was performed at 10000 rpm for 10 minutes, and the precipitate was dispersed in toluene to obtain an AgBiS ₂ quantum dot dispersion (quantum dot dispersion 1) with a concentration of about 30 mg/mL. A quantum dot thin film was prepared using the obtained quantum dot dispersion liquid 1, and a tauc plot of an indirect transition semiconductor was prepared from absorption measurement of the quantum dot thin film. The bandgap estimated from tauc plot was about 1.1 eV.

Production Example 1-2 (Production of AgBiSTe quantum dot dispersion (quantum dot dispersion 2))
5.4 ml of oleic acid, 0.8 mmol of silver acetate, 1 mmol of bismuth acetate and 30 mL of octadecene were weighed into a flask and heated at 100° C. for 3 hours under vacuum to obtain a precursor solution. After the system was under nitrogen flow, 5 mL of oleylamine was added to the precursor solution. Immediately thereafter, 0.9 mmol of hexamethyldisilathiane and 0.1 mmol of bis(trimethylsilyl)telluride were injected along with 5 mL of octadecene. Immediately after the injection, the flask was naturally cooled, and when the temperature reached 40° C., 5 mL of trioctylphosphine and 10 mL of toluene were added, and the solution was recovered. An excess amount of acetone was added to the solution, centrifugation was performed at 5000 rpm for 10 minutes, and the precipitate was dispersed in toluene to obtain an AgBiSTe quantum dot dispersion (quantum dot dispersion 2) with a concentration of about 30 mg/mL. A quantum dot thin film was prepared using the obtained quantum dot dispersion liquid 2, and a tauc plot of an indirect transition semiconductor was prepared from absorption measurement of the quantum dot thin film. The bandgap estimated from tauc plot was approximately 0.85 eV.

[Production of zinc oxide particle dispersion]
Production Example 2-1 (Production of non-doped zinc oxide particle dispersion)
1.5 mmol of zinc acetate dihydrate and 15 ml of diethyl sulfoxide (DMSO) were weighed into a flask and stirred to obtain zinc acetate solution 1 .
A TMACl solution of 4 mmol of tetramethylammonium chloride (TMACl) dissolved in 4 ml of methanol and a KOH solution of 4 mmol of potassium hydroxide (KOH) dissolved in 4 ml of methanol were prepared. While vigorously stirring the TMACl solution, the KOH solution was slowly added, and after stirring for 30 minutes, insoluble components were removed through a filter with a pore size of 0.45 μm to obtain a tetramethylammonium hydroxide (TMAH) solution.
6 ml of the TMAH solution was dropped into the zinc acetate solution 1 in the flask at a dropping rate of 6 ml/min. After holding for 1 hour, the reaction solution was recovered. An excess amount of acetone was added to the reaction solution, and after centrifugation at 10,000 rpm for 10 minutes, the supernatant was removed, and the precipitate was dispersed in methanol. A dispersion of non-doped zinc oxide particles (concentration: about 30 mg/mL, average particle diameter of non-doped zinc oxide particles: 8 nm) was obtained by sonic dispersion.

Production Example 2-2 (Li-doped zinc oxide particle dispersion)
Measure 15 ml of DMSO and 0.075 mmol of lithium chloride (LiCl) into a flask, dissolve the LiCl by ultrasonic treatment, and then add 1.425 mmol of zinc acetate to dissolve the zinc acetate to form a zinc acetate solution. got 2. Li-doped zinc oxide particle dispersion (concentration 30 mg/mL, average particle size of Li-doped zinc oxide particles) was prepared in the same manner as in Production Example 2-1, except that zinc acetate solution 2 was used instead of zinc acetate solution 1. 8 nm).

Production Example 2-3 (Al-doped zinc oxide particle dispersion)
Measure 15 ml of DMSO and 0.15 mmol of aluminum chloride hexahydrate in a flask, dissolve the aluminum chloride hexahydrate by ultrasonic treatment, and then add 1.35 mmol of zinc acetate to dissolve the zinc acetate. to obtain a zinc acetate solution 3. Al-doped zinc oxide particle dispersion (concentration 30 mg/mL, average particle size of Al-doped zinc oxide particles 8 nm).

Production Example 2-4 (Ga-doped zinc oxide particle dispersion)
Measure 15 ml of DMSO and 0.12 mmol of gallium nitrate hydrate in a flask, dissolve the gallium nitrate hydrate by ultrasonic treatment, and then add 1.38 mmol of zinc acetate to dissolve the zinc acetate. , a zinc acetate solution 4 was obtained. Ga-doped Z zinc oxide particle dispersion (concentration 30 mg/mL, average grain size of Ga-doped zinc oxide particles) was prepared in the same manner as in Production Example 2-1, except that zinc acetate solution 4 was used instead of zinc acetate solution 1. diameter 8 nm).

Production Example 2-5 (Mg-doped zinc oxide particle dispersion)
0.075 mmol of magnesium acetate tetrahydrate, 1.425 mmol of zinc acetate dihydrate and 15 ml of DMSO were weighed into a flask and stirred to obtain zinc acetate solution 5 . Mg-doped zinc oxide particle dispersion (concentration 30 mg/mL, average particle size of Mg-doped zinc oxide particles) was prepared in the same manner as in Production Example 2-1, except that zinc acetate solution 5 was used instead of zinc acetate solution 1 8 nm).

[Manufacture of photodetector]
(Examples 1 to 9, Comparative Example 1)
An ITO (Indium Tin Oxide) film (first electrode layer) having a thickness of about 100 nm was formed on quartz glass by a sputtering method.

Then, the dispersion described in the table below was dropped onto the ITO film, spin-coated at 2500 rpm, and heated at 70° C. for 30 minutes twice to form an electron transport layer having a thickness of about 50 nm.
The electron transport layer formed using the non-doped zinc oxide particle dispersion of Production Example 2-1 is a non-doped zinc oxide film, and the content of metal atoms in this film is measured by high frequency inductively coupled plasma (ICP). According to the method, the content of metal atoms other than Zn was below the detection limit.
The electron transport layer formed using the Li-doped zinc oxide particle dispersion of Production Example 2-2 is a Li-doped zinc oxide film. When measured by the ICP) method, Li was confirmed as a metal atom other than Zn. Also, the ratio of Li to the total of Zn and Li atoms in the film was 5 atomic %.
Further, the electron transport layer formed using the Al-doped zinc oxide particle dispersion liquid of Production Example 2-3 is an Al-doped zinc oxide film, and the content of metal atoms in this film is measured by high-frequency inductively coupled plasma ( When measured by the ICP) method, Al was confirmed as a metal atom other than Zn. Also, the ratio of Al to the total of Zn and Al atoms in the film was 10 atomic %.
Further, the electron transport layer formed using the Ga-doped zinc oxide particle dispersion of Production Example 2-4 is a Ga-doped zinc oxide film, and the content of metal atoms in this film is determined by high-frequency inductively coupled plasma ( When measured by the ICP) method, Ga was confirmed as a metal atom other than Zn. The ratio of Ga to the total of Zn and Ga atoms in the film was 8 atomic %.
Further, the electron transport layer formed using the Mg-doped zinc oxide particle dispersion of Production Example 2-5 is a Mg-doped zinc oxide film, and the content of metal atoms in this film is measured by high-frequency inductively coupled plasma ( When measured by the ICP) method, Mg was confirmed as a metal atom other than Zn. Also, the ratio of Mg to the total of Zn and Mg atoms in the film was 5 atomic %.

Then, the quantum dot dispersion liquid described in the following table was dropped onto the electron transport layer thus formed, followed by spin coating at 2000 rpm to obtain a quantum dot assembly film (step 1).
Next, on the quantum dot assembly film, as a ligand solution, ligand solution 1 (tetramethylammonium iodide (TMAI) methanol solution (concentration 1 mg / mL)) or ligand solution 2 ( After dripping an acetonitrile solution of 1,2-ethanedithiol (EDT) (concentration 0.02 vol %), it was waited for 30 seconds and then spin-dried at 2000 rpm for 20 seconds. Then, methanol or acetonitrile was dropped onto the quantum dot assembly film as a rinsing liquid and spin-dried at 2000 rpm for 20 seconds. Next, toluene was dropped onto the quantum dot assembly film and spin-dried at 2000 rpm for 20 seconds (step 2).
The operation of step 1 and step 2 as one cycle was repeated four times, and tetramethylammonium iodide (TMAI) or 1,2-ethanedithiol (EDT) was added as a ligand to _AgBiS2 quantum dots or AgBiSTe quantum dots. A coordinated photoelectric conversion layer was formed with a thickness of 60 nm.

Next, the photoelectric conversion layer was dried at 100°C for 10 minutes in a nitrogen atmosphere, and then dried at room temperature for 10 hours in a nitrogen atmosphere under light-shielding conditions.

Next, on the photoelectric conversion layer, PTB7 (poly{4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-lt -alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl}) in 1,2-dichlorobenzene at a concentration of 5 mg/mL The dissolved solution was dropped and spin-coated at 2000 rpm for 60 seconds to form a hole transport layer with a thickness of about 10 nm.

Next, a 15 nm-thick _MoO3 film was formed on the hole transport layer by a vacuum evaporation method through a metal mask, and then a 100 nm-thick Au film (second electrode layer) was formed. A photodiode-type photodetector was manufactured using the above method.

<Evaluation>
Dark current and external quantum efficiency (EQE) of the manufactured photodetector were evaluated using a semiconductor parameter analyzer (C4156, manufactured by Agilent).
First, the dark current was evaluated by measuring the current-voltage characteristics (IV characteristics) while sweeping the voltage from 0 V to -2 V in a state where light was not irradiated. Here, the current value at -0.5 V was taken as the dark current value. Subsequently, the IV characteristics were measured while sweeping the voltage from 0 V to -1 V under irradiation with 900 nm monochrome light. A photocurrent value was obtained by subtracting the above dark current value from the current value when −0.5 V was applied, and the external quantum efficiency (EQE) was calculated from this value.

As shown in the table above, it was confirmed that the photodetector elements of Examples had a low dark current and a high external quantum efficiency (EQE).

Using the photodetector obtained in the above example, an image sensor is produced by a known method together with an optical filter produced according to the method described in WO 2016/186050 and WO 2016/190162. By incorporating it into an imaging element, it is possible to obtain an image sensor having good visible/infrared imaging performance.

<Reference example>
In Example 1 and Comparative Example 1, the photodetector elements of Reference Examples 1 and 2 were prepared in the same manner as in Example 1 and Comparative Example 1, except that the photoelectric conversion layer was formed using the following PbS quantum dot dispersion. manufactured. When the external quantum efficiency (EQE) and dark current of the resulting photodetector were measured in the same manner as described above, no particular difference was observed between Reference Example 1 and Reference Example 2. From this fact, the above-mentioned effect achieved by using zinc oxide doped with metal atoms other than Zn as the electron transport layer is due to the use of quantum dots of a compound semiconductor containing Ag element and Bi element as the photoelectric conversion layer. It was found that this is a unique effect that is exhibited depending on the use.

(PbS quantum dot dispersion)
5.8 ml of oleic acid, 7.8 mmol of lead oxide, 0.4 ml of oleylamine, and 27 ml of octadecene were measured in a flask and heated at 110° C. for 300 minutes under vacuum to obtain a precursor solution. The system was then put into nitrogen flow. 1 mmol of hexamethyldisilathiane was then injected into the solution in the flask along with 9.6 mL of octadecene. Immediately after the injection, the solution in the flask was naturally cooled, and when the temperature of the solution reached 60°C, 1 mL of 0.3 mmol/L lead chloride solution (solvent oleylamine) was added. After cooling the solution in the flask to 30° C., 10 mL of toluene was added and the solution was recovered. An excess amount of ethanol was added to the solution, centrifugation was performed at 10,000 rpm for 10 minutes, and the precipitate was dispersed in octane to obtain a PbS quantum dot dispersion (concentration: 40 mg/mL). Band of 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) for the obtained PbS quantum dot dispersion. The gap was approximately 1.2 eV.

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

Claims (8)

a first electrode layer;
a second electrode layer;
a photoelectric conversion layer provided between the first electrode layer and the second electrode layer;
an electron transport layer provided between the first electrode layer and the photoelectric conversion layer;
a hole transport layer provided between the photoelectric conversion layer and the second electrode layer;
The photoelectric conversion layer includes quantum dots of a compound semiconductor containing Ag element and Bi element,
The photodetector, wherein the electron transport layer contains zinc oxide doped with a metal atom other than Zn. The photodetector according to claim 1, wherein the metal atoms other than Zn are monovalent to trivalent metal atoms. The photodetector according to claim 1, wherein the metal atoms other than Zn include at least one selected from Li, Mg, Al and Ga. 3. The zinc oxide doped with the metal atoms other than Zn, according to claim 1, wherein the ratio of the metal atoms other than Zn to the total of Zn and the metal atoms other than Zn is 1 atomic % or more. photodetector. The photodetector according to claim 1 or 2, wherein the compound semiconductor of the quantum dots further contains at least one element selected from S element and Te element. 3. The photodetector according to claim 1, wherein the photoelectric conversion layer contains ligands that coordinate to the quantum dots. The photodetector according to claim 6, wherein the ligand contains at least one selected from ligands containing halogen atoms and multidentate ligands containing two or more coordinating moieties. An image sensor comprising the photodetector element according to claim 1 or 2.

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