TW202434700A - PbS quantum dot dispersion, semiconductor film manufacturing method, light detection element manufacturing method, image sensor manufacturing method and PbS quantum dot dispersion manufacturing method - Google Patents

Abstract

The present invention provides a PbS quantum dot dispersion, a semiconductor film, a light detection element, an image sensor, and a method for producing the PbS quantum dot dispersion. The PbS quantum dot dispersion contains PbS quantum dots, a ligand, and a solvent. In the PbS quantum dot dispersion, the ligand contains a fatty acid with a carbon number of 6 or more. When the PbS quantum dot dispersion is subjected to thermogravimetric analysis at a temperature increase rate of 20°C/min from 50°C to 500°C in an argon environment at normal pressure, the ratio of the weight ^W160 at 160°C to the weight ^W450 at 450°C is less than 2.00. The invention provides a method for producing a semiconductor film, a light detection element, an image sensor, and a PbS quantum dot dispersion.

Description

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

The present invention relates to a PbS quantum dot dispersion, a method for manufacturing a semiconductor film, a method for manufacturing a light detection element, a method for manufacturing an image sensor, and a method for manufacturing a PbS quantum dot dispersion.

In recent years, light detection components that can detect light in the infrared region have attracted much attention in the fields of smartphones, surveillance cameras, and dashcams.

Conventionally, photodetection elements used in image sensors and the like use silicon photodiodes, which use silicon wafers as the raw material for the photoelectric conversion layer. However, silicon photodiodes have low sensitivity in the infrared region with a wavelength of 900nm or more.

Furthermore, InGaAs-based semiconductor materials, which are known as near-infrared light-receiving elements, have a problem in that they require very costly processes such as epitaxial growth and substrate bonding steps in order to achieve high quantum efficiency, and therefore have not yet been widely used.

In recent years, research on semiconductor quantum dots has been ongoing. Non-patent document 1 describes a method for synthesizing PbS quantum dots.

[Non-patent document 1] Oleksandr Voznyy, Larissa Levina, James Z. Fan, Mikhail Askerka, Ankit Jain, Min-Jae Choi, Olivier Ouellette, Petar Todorovic, Laxmi K. Sagar, and Edward H. Sargent､"Machine Learning Accelerates Discovery of Optimal Colloidal Quantum Dot Synthesis”, ACS Nano､2019,13,11122-11128.

In recent years, as image sensors and other devices have been required to improve their performance, the various characteristics required of the photodetection elements used in these devices have also been further improved. For example, the requirements are as follows: low dark current; high external quantum efficiency relative to the target wavelength of light detected by the photodetection element; and excellent durability against repeated driving.

According to the research of the inventors, it is known that the dark current of the light detection element having a semiconductor film formed by using a quantum dot dispersion tends to be relatively high, and there is room for further reduction of the dark current. Furthermore, the dark current refers to the current flowing when no light is irradiated. It is also known that there is room for further improvement in the external quantum efficiency of photoelectric conversion or the durability of the drive under repeated driving.

Thus, the purpose of the present invention is to provide a PbS quantum dot dispersion liquid, which can form a semiconductor film with high external quantum efficiency, low dark current, and excellent durability against repeated driving. In addition, the purpose of the present invention is to provide a method for manufacturing a semiconductor film, a method for manufacturing a light detection element, a method for manufacturing an image sensor, and a method for manufacturing a PbS quantum dot dispersion liquid.

The inventors conducted in-depth research on a PbS quantum dot dispersion containing PbS quantum dots, a ligand containing a fatty acid with more than 6 carbon atoms, and a solvent, and found that when a thermogravimetric analysis was performed from 50°C to 500°C at a heating rate of 20°C/min in an argon environment at normal pressure, a PbS quantum dot dispersion with a ratio of weight ^W160 at 160°C to weight ^W450 at 450°C of less than 2.00 was able to form a semiconductor film with high external quantum efficiency, low dark current, and excellent durability relative to repeated driving, and completed the present invention. Therefore, the present invention provides the following content.

<1> A PbS quantum dot dispersion, comprising PbS quantum dots, a ligand and a solvent, wherein the ligand in the PbS quantum dot dispersion comprises a fatty acid having 6 or more carbon atoms, and when the PbS quantum dot dispersion is subjected to thermogravimetric analysis at a temperature increase rate of 20°C/min from 50°C to 500°C in an argon environment at normal pressure, the ratio of the weight ^W160 at 160°C to the weight ^W450 at 450°C is less than 2. <2> The PbS quantum dot dispersion as described in <1>, wherein the PbS quantum dots have a maximum absorption in the wavelength range of 1300 to 1700 nm. <3> The PbS quantum dot dispersion as described in <1> or <2>, wherein the PbS quantum dots contain 1.2 mol or more of Pb atoms per mol of S atoms. <4> The PbS quantum dot dispersion as described in any one of <1> to <3>, wherein when the PbS quantum dot dispersion is subjected to thermogravimetric analysis at a temperature increase rate of 20°C/min from 50°C to 500°C in an argon environment at normal pressure, the ratio of the weight ^W160 at 160°C to the weight ^W450 at 450°C is 1.54 or less. <5> The PbS quantum dot dispersion as described in any one of <1> to <4>, wherein the carbon number of the fatty acid is 12 to 22. <6> The PbS quantum dot dispersion as described in any one of <1> to <5>, wherein the fatty acid is an unsaturated fatty acid. <7> The PbS quantum dot dispersion as described in any one of <1> to <6>, wherein the ligand contains oleic acid. <8> A method for manufacturing a semiconductor film, comprising: a PbS quantum dot aggregate forming step, wherein a PbS quantum dot dispersion liquid described in any one of items <1> to <7> is applied to a substrate to form a film of PbS quantum dot aggregates; and a ligand replacement step, wherein a ligand solution containing ligands and a solvent different from the ligands contained in the PbS quantum dot dispersion liquid is applied to the film of PbS quantum dot aggregates formed by the PbS quantum dot aggregate forming step, so that the ligands contained in the ligand solution coordinate with the PbS quantum dots. <9> A method for manufacturing a light detection element, comprising the method for manufacturing a semiconductor film described in <8>. <10> A method for manufacturing an image sensor, comprising the method for manufacturing a semiconductor film described in <8>. <11> A method for producing a PbS quantum dot dispersion, comprising: reacting a compound containing a lead atom and a compound containing a sulfur atom in the presence of a ligand containing a fatty acid having more than 6 carbon atoms and a solvent to obtain a reaction solution containing PbS quantum dots; heating the reaction solution containing the PbS quantum dots and then centrifuging and separating to recover a precipitate containing the PbS quantum dots; and dispersing the recovered precipitate in a solvent. <12> A method for producing a PbS quantum dot dispersion as described in <11>, wherein the heating is performed at a temperature of 30°C or higher. <13> A method for producing a PbS quantum dot dispersion as described in <11>, wherein the heating is performed at a temperature of 40 to 60°C. <14> A method for producing a PbS quantum dot dispersion as described in any one of <11> to <13>, wherein the ligand contains oleic acid. <15> A method for producing a PbS quantum dot dispersion as described in any one of <11> to <14>, wherein a polar solvent is added to the reaction solution containing the PbS quantum dots before the centrifugal separation. [Effect of the invention]

According to the present invention, a PbS quantum dot dispersion can be provided, which can form a semiconductor film with high external quantum efficiency, low dark current, and excellent durability against repeated driving. In addition, the present invention can provide a method for manufacturing a semiconductor film, a method for manufacturing a light detection element, a method for manufacturing an image sensor, and a method for manufacturing a PbS quantum dot dispersion.

The content of the present invention is described in detail below. In this specification, "～" is used to include the numerical values recorded before and after it as the lower limit and upper limit. In the marking of the group (atomic group) in this specification, the marking without substituted and unsubstituted includes the group (atomic group) without substituents and the group (atomic group) with substituents. For example, "alkyl" includes not only alkyl groups without substituents (unsubstituted alkyl groups) but also alkyl groups with substituents (substituted alkyl groups).

<PbS quantum dot dispersion> The PbS quantum dot dispersion of the present invention contains PbS quantum dots, a ligand and a solvent, and the characteristics of the PbS quantum dot dispersion are that the ligand contains a fatty acid with a carbon number of 6 or more, and when the PbS quantum dot dispersion is subjected to thermogravimetric analysis at a temperature rising rate of 20°C/min from 50°C to 500°C in an argon environment at normal pressure, the ratio of the weight ^W160 at 160°C to the weight ^W450 at 450°C is less than 2.00.

The PbS quantum dot dispersion of the present invention can form a semiconductor film with high external quantum efficiency, low dark current, and excellent durability against repeated driving. It is speculated that when the PbS quantum dot dispersion is subjected to thermogravimetric analysis at a temperature increase rate of 20°C/min from 50°C to 500°C in an argon environment at normal pressure, the ratio of the weight ^W160 at 160°C to the weight ^W450 at 450°C is less than 2.00, so the coordination amount of the ligand coordinated with the PbS quantum dots is appropriate, the film shrinkage during ligand replacement is suppressed, and the generation of cracks can be suppressed, so that a semiconductor film with high external quantum efficiency, low dark current, and excellent durability against repeated driving can be formed. Furthermore, the ligand of the PbS quantum dot dispersion of the present invention is a fatty acid containing 6 or more carbon atoms, so the dispersibility of the PbS quantum dots is excellent, and the storage stability of the PbS quantum dot dispersion is also good.

When the PbS quantum dot dispersion of the present invention is subjected to thermogravimetric analysis at a temperature increase rate of 20°C/min from 50°C to 500°C in an argon environment at normal pressure, the ratio of the weight ^W160 at 160°C to the weight ^W450 at 450°C (hereinafter, also referred to as the weight ratio ^{W160/ W450} ) is 2.00 or less, preferably 1.80 or less, and more preferably 1.54 or less. From the perspective of improving the storage stability of the PbS quantum dot dispersion, the lower limit of the weight ratio W160 ^{/ W450} is preferably 1.30 or more.

As a method for setting the weight ratio W ^{160 /} W ⁴⁵⁰ of the PbS quantum dot dispersion to 2.00 or less, for example, a lead atom-containing compound and a sulfur atom-containing compound are reacted in the presence of a ligand containing a fatty acid having more than 6 carbon atoms and a solvent, the reaction solution containing the obtained PbS quantum dots is heated, centrifuged to recover a precipitate containing the PbS quantum dots, and the recovered precipitate is dispersed in a solvent to produce a PbS quantum dot dispersion. By heating the reaction solution before centrifugation, it is possible to suppress the residual amount of ligand that is not coordinated with the PbS quantum dots from mixing into the precipitate recovered after centrifugation. By adjusting the heating temperature, etc., the weight ratio ^{W160/ W450} can be adjusted to 2.00 or less.

The reaction solution is preferably heated at a temperature of 30° C. or higher, more preferably at a temperature of 40 to 60° C. The reaction solution is preferably heated for 1 to 30 minutes, more preferably 5 to 15 minutes.

It is also preferred to add a polar solvent to the reaction solution before centrifugal separation. By adding the polar solvent, the PbS quantum dots condense with each other and form relatively large secondary particles, so that the solvent and the PbS quantum dots can be effectively separated during centrifugal separation.

As another method for setting the weight ratio W ^{160 /} W ⁴⁵⁰ of the PbS quantum dot dispersion to 2.00 or less, there can be cited a method of adding a non-polar solvent or a polar solvent after heating.

The PbS quantum dot dispersion of the present invention is preferably used as a photoelectric conversion layer of a light detection element or an image sensor. In addition, the semiconductor film obtained using the PbS quantum dot dispersion of the present invention has excellent sensitivity to light of wavelengths in the infrared region. Therefore, an image sensor using the semiconductor film obtained using the PbS quantum dot dispersion of the present invention for the photoelectric conversion layer can be particularly preferably used as an infrared sensor. Thus, the PbS quantum dot dispersion of the present invention is preferably used as a photoelectric conversion layer of an infrared sensor.

The PbS quantum dot dispersion of the present invention is described in further detail below.

(PbS quantum dots) The PbS quantum dot dispersion of the present invention contains PbS quantum dots. For the reason that it is easy to obtain high photoelectric conversion efficiency, it is preferred that the Pb atoms in the PbS quantum dots contain 1.2 moles or more of Pb atoms per 1 mole of S atoms, and it is more preferred that it contains 1.3 moles or more. For the reason that it is easy to obtain low dark current, it is preferred that the upper limit is 2.0 or less, and it is more preferred that it is 1.8 or less. The molar ratio of S atoms to Pb atoms in the PbS quantum dots can be calculated by analyzing the Pb atoms and S atoms in the PbS quantum dots by inductively coupled plasma (ICP) emission spectrometry.

The band gap of PbS quantum dots is preferably 0.5 to 2.0 eV. If the band gap of PbS quantum dots is within the above range, it can be set as a light detection element that can detect light of various wavelengths depending on the application. For example, it can be set as a light detection element that can detect light in the infrared region. The upper limit of the band gap of PbS quantum dots is preferably 1.9 eV or less, more preferably 1.8 eV or less, further preferably 1.5 eV or less, and particularly preferably 0.95 eV or less. The lower limit of the band gap of PbS quantum dots is preferably 0.6 eV or more, more preferably 0.7 eV or more, and further preferably 0.73 eV or more.

PbS quantum dots preferably have a maximum absorption in the wavelength range of 1300 to 1700 nm. By using such PbS quantum dots, the effect of the present invention is more significantly exerted. Furthermore, a semiconductor film having a higher external quantum efficiency for light of wavelengths in the infrared region can be formed.

The average particle size of the PbS quantum dots is preferably 4.5 to 7 nm. Furthermore, in this specification, the average particle size of the PbS quantum dots is the average value (arithmetic mean) of the equivalent circular diameters of 500 randomly selected primary particles of the PbS quantum dots. The equivalent circular diameter of the primary particles of the PbS quantum dots can be measured for one particle in an electron microscope photograph taken by a transmission electron microscope. The diameter of the perfect circle equivalent to the area S is calculated (equivalent circular diameter = 2 (S/π) ^0.5 ). The particle size of PbS quantum dots can be measured by diluting a PbS quantum dot dispersion with a nonpolar solvent, dropping the diluted solution onto a microgrid, and measuring the film formed by drying using a transmission electron microscope.

The content of PbS quantum dots in the PbS quantum dot dispersion is preferably 1 to 25 mass % relative to the total mass of the PbS quantum dot dispersion. The lower limit is preferably 2 mass % or more, and 3 mass % or more is more preferred. The upper limit is preferably 20 mass % or less. In addition, the content of PbS quantum dots in the PbS quantum dot dispersion is preferably 10 to 250 mg/mL. The lower limit is preferably 20 mg/mL or more, and 30 mg/mL or more is more preferred. The upper limit is preferably 200 mg/mL or less. In addition, the content of PbS quantum dots in the components of the PbS quantum dot dispersion after removing the solvent and the ligand is preferably 50 mass % or more, 60 mass % or more is more preferred, and 70 mass % or more is further preferred. The upper limit can be set to 100 mass % or less. Furthermore, the total content of PbS quantum dots and ligands in the component after removing the solvent from the PbS quantum dot dispersion is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The upper limit can be set to 100% by mass or less.

(Ligand) The PbS quantum dot dispersion of the present invention contains a ligand. As the ligand, a fatty acid containing 6 or more carbon atoms is used. The fatty acid acts as a ligand coordinated with the PbS quantum dots and also acts as a dispersant capable of dispersing the PbS quantum dots in the solvent. Therefore, the PbS quantum dot dispersion of the present invention containing the fatty acid has excellent storage stability.

The fatty acid may be a saturated fatty acid, but preferably an unsaturated fatty acid. The carbon number of the fatty acid is preferably 12 to 22, more preferably 14 to 22, and even more preferably 14 to 20.

Specific examples of the above-mentioned fatty acids include decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid and erucic acid. For reasons of good storage stability and significant effects of the present invention, the PbS quantum dot dispersion is preferably oleic acid. That is, the ligand contained in the PbS quantum dot dispersion of the present invention is preferably one containing oleic acid.

The content of the above-mentioned fatty acid in the ligand contained in the PbS quantum dot dispersion is preferably 70 mass % or more, 80 mass % or more is more preferred, 90 mass % or more is further preferred, and 99 mass % or more is further preferred. It is preferred that the ligand contained in the PbS quantum dot dispersion is only the above-mentioned fatty acid.

The content of ligands in the PbS quantum dot dispersion is preferably 1 to 15 mass % relative to the total mass of the PbS quantum dot dispersion. The lower limit is preferably 2 mass % or more, and 2.5 mass % or more is more preferred. The lower limit is preferably 10 mass % or less, and 7 mass % or less is more preferred. In addition, the content of ligands in the PbS quantum dot dispersion is preferably 10 to 150 mg/mL. The lower limit is preferably 20 mg/mL or more, and 25 mg/mL or more is further preferred. The upper limit is preferably 100 mg/mL or less, and 70 mg/mL or less is more preferred. In addition, the content of ligands is preferably 10 to 100 mass parts relative to 100 mass parts of PbS quantum dots. The lower limit is preferably 20 parts by mass or more, and more preferably 30 parts by mass or more. The upper limit is preferably 80 parts by mass or less, and more preferably 70 parts by mass or less.

(Solvent) The dispersion of the present invention contains a solvent. The solvent is not particularly limited, but a solvent that is difficult to dissolve PbS quantum dots and easy to dissolve ligands is preferred. The solvent is preferably an organic solvent. The organic solvent may be a protic solvent or an aprotic solvent, but an aprotic solvent is preferred, and an aprotic polar solvent is more preferred.

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

Specific examples of the solvent include alkanes [n-hexane, n-octane, etc.], benzene, toluene, N,N-dimethylformamide, dimethyl sulfoxide, N-methylformamide, N,N-dimethylacetamide, propylene carbonate, ethylene glycol, and the like.

The content of the solvent in the PbS quantum dot dispersion is preferably 50 to 99 mass %, more preferably 70 to 99 mass %, and even more preferably 85 to 98 mass % relative to the total mass of the PbS quantum dot dispersion. The PbS quantum dot dispersion may contain only one solvent or a mixed solvent of two or more solvents. When two or more solvents are contained, the total amount of the solvents is preferably within the above range.

<Method for producing PbS quantum dot dispersion> The method for producing PbS quantum dot dispersion is characterized by comprising: a step of reacting a compound containing lead atoms and a compound containing sulfur atoms in the presence of a ligand containing a fatty acid having more than 6 carbon atoms and a solvent to obtain a reaction solution containing PbS quantum dots; a step of heating the reaction solution containing the PbS quantum dots and then centrifuging and recovering a precipitate containing PbS quantum dots; and a step of dispersing the recovered precipitate in a solvent.

The above-mentioned manufacturing method is preferably the manufacturing method of the PbS quantum dot dispersion of the present invention.

The lead atom-containing compound and the sulfur atom-containing compound used in the step of obtaining the above-mentioned reaction solution are raw materials of PbS quantum dots. The lead atom-containing compound is not particularly limited, but lead oxide, lead acetate, etc. can be cited. The sulfur atom-containing compound is not particularly limited, but hexamethyldisilasulfane, bis(trimethylsilyl)sulfide, etc. can be cited.

Regarding the ratio of the compound containing a lead atom to the compound containing a sulfur atom, the compound containing a lead atom is preferably 1.5 to 10 mol, more preferably 3 to 10 mol, and even more preferably 6 to 10 mol, relative to 1 mol of the compound containing a sulfur atom.

The reaction temperature of the compound containing a lead atom and the compound containing a sulfur atom is preferably 50 to 200°C, more preferably 80 to 180°C.

As the fatty acid with carbon number of 6 or more used in the step of obtaining the above-mentioned reaction solution, oleic acid is preferably cited as one contained in the above-mentioned PbS quantum dot dispersion. That is, the ligand used in the step of obtaining the above-mentioned reaction solution is preferably one containing oleic acid. The content of the above-mentioned fatty acid in the ligand is preferably 70% by mass or more, 80% by mass or more is more preferably, 90% by mass or more is further preferably, and 99% by mass or more is further preferably. It is preferred that the ligand is only the above-mentioned fatty acid, and it is particularly preferred that it is only oleic acid.

The solvent used in the step of obtaining the reaction solution is not particularly limited. Preferably, the solvent is an organic solvent. The organic solvent may be a protic solvent or an aprotic solvent.

The boiling point of the solvent is preferably 60 to 250° C. The lower limit is preferably 70° C. or higher, and more preferably 80° C. or higher.

Specific examples of the solvent include octadecene, hexadecane, dioctyl ether and the like.

In the manufacturing method of the present invention, the reaction solution containing the PbS quantum dots is heated and then centrifuged to recover the precipitate containing the PbS quantum dots.

The heating of the reaction solution is preferably performed at a temperature of 30° C. or higher, more preferably at a temperature of 40 to 60° C. The heating time of the reaction solution is preferably 1 to 30 minutes, more preferably 3 to 15 minutes.

It is also preferred to add a polar solvent to the reaction solution before centrifuging the reaction solution. In the case of adding a polar solvent, it is preferred to perform the heating after adding the polar solvent to the reaction solution.

As the polar solvent, there can be mentioned ethanol, acetone, methanol, acetonitrile, dimethylformamide, dimethyl sulfoxide, butanol, propanol and the like.

In the manufacturing method of the present invention, the above-mentioned recovered precipitate is dispersed in a solvent. As a solvent for dispersing the recovered precipitate, a solvent that is difficult to dissolve PbS quantum dots and easily dissolves ligands is preferred. The solvent is preferably an organic solvent. The organic solvent can be a protic solvent or an aprotic solvent, but an aprotic solvent is preferred, and an aprotic non-polar solvent is more preferred.

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

Specific examples of the solvent include alkanes [n-hexane, n-octane, etc.], benzene, toluene, N,N-dimethylformamide, dimethyl sulfoxide, N-methylformamide, N,N-dimethylacetamide, propylene carbonate, ethylene glycol, and the like.

<Method for manufacturing semiconductor film> Next, a method for manufacturing a semiconductor film using the PbS quantum dot dispersion of the present invention is described. The method for manufacturing a semiconductor film is characterized by comprising: A PbS quantum dot aggregate formation step, in which the PbS quantum dot dispersion of the present invention is applied to a substrate to form a film of PbS quantum dot aggregates; and A ligand replacement step, in which a ligand solution containing a ligand and a solvent different from the ligand contained in the PbS quantum dot dispersion is applied to the film of PbS quantum dot aggregates formed by the PbS quantum dot aggregate formation step, so that the ligand contained in the ligand solution is coordinated with the PbS quantum dots.

In the step of forming a PbS quantum dot aggregate, the PbS quantum dot dispersion of the present invention is applied to a substrate to form a film of a PbS quantum dot aggregate. The PbS quantum dot aggregate refers to a form in which a plurality of (for example, more than 100 per 1 μm ² ) PbS quantum dots are arranged close to each other.

There is no particular restriction on the shape, structure, size, etc. of the substrate on which the PbS quantum dot dispersion is applied, and it can be appropriately selected according to the purpose. The structure of the substrate can be a single-layer structure or a multilayer structure. As a substrate, for example, a substrate composed of inorganic materials such as silicon, glass, YSZ (Yttria-Stabilized Zirconia; yttria-stabilized zirconia), resin, resin composite materials, etc. can be used. In addition, an electrode, an insulating film, etc. can be formed on the substrate. In this case, the PbS quantum dot dispersion is also applied to the electrode or insulating film on the substrate.

The method for applying the PbS quantum dot dispersion on the substrate is not particularly limited, and examples thereof include spin coating, dipping, inkjetting, spraying, screen printing, relief printing, gravure printing, and spraying.

The film thickness of the aggregate of PbS quantum dots formed by applying the PbS quantum dot dispersion is preferably 10 to 1000 nm. The lower limit of the thickness is preferably 20 nm or more, and more preferably 30 nm or more. The upper limit of the thickness is preferably 600 nm or less, more preferably 550 nm or less, further preferably 500 nm or less, and particularly preferably 450 nm or less.

In the ligand replacement step, a ligand solution containing a ligand and a solvent different from the ligand contained in the above-mentioned PbS quantum dot dispersion is given to the above-mentioned PbS quantum dot aggregate film, so that the ligand contained in the above-mentioned ligand solution is coordinated with the above-mentioned PbS quantum dots.

The ligand contained in the ligand solution may be an organic ligand or an inorganic ligand. The ligand may also be a combination of an inorganic ligand and an organic ligand.

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

Specific examples of the inorganic 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, potassium sulfide, sodium sulfide and the like.

The organic ligand may be a single-seat organic ligand having one coordination part or a multi-seat organic ligand having two or more coordination parts. Examples of the coordination part contained in the organic ligand include a thiol group, an amine group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group.

Specific examples of the single-seat organic ligand include 2-naphthylamine, 4-methylthioaniline, 4-methylbenzenethiol, 3,5-dimethylbenzenethiol, 4-chlorobenzenethiol, 4-methoxybenzenethiol, and benzoic acid.

As the polydentate ligand, there can be mentioned a ligand represented by any one of the formulas (A) to (C). [Chemical Formula 1]

In formula (A), ^XA1 and ^XA2 each independently represent a thiol group, an amine group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphoric acid group or a phosphonic acid group, and ^LA1 represents a alkyl group.

In formula (B), ^XB1 and ^XB2 each independently represent a thiol group, an amine group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphoric acid group or a phosphonic acid group, ^XB3 represents S, O or NH, and ^LB1 and ^LB2 each independently represent a alkyl group.

In formula (C), ^XC1 to ^XC3 each independently represent a thiol group, an amine group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphoric acid group or a phosphonic acid group, ^XC4 represents N, and ^LC1 to ^LC3 each independently represent a alkyl group.

The amino groups represented by ^XA1 , ^XA2 , ^XB1 , ^XB2 , ^XC1 , ^XC2 and ^XC3 are not limited to _-NH2 , and may include substituted amino groups and cyclic amino groups. As substituted amino groups, monoalkylamino groups, dialkylamino groups, monoarylamino groups, diarylamino groups, alkylarylamino groups and the like can be cited. As the amino groups represented by these groups, _-NH2 , monoalkylamino groups and dialkylamino groups are preferred, and _-NH2 is more preferred.

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

Examples of the alkylene group include straight chain alkylene groups, branched chain alkylene groups, and cyclic alkylene groups, and straight chain alkylene groups or branched chain alkylene groups are preferred, and straight chain alkylene groups are more preferred. Examples of the alkenylene group include straight chain alkenylene groups, branched chain alkenylene groups, and cyclic alkenylene groups, and straight chain alkenylene groups are preferred, and alkynylene groups include straight chain alkynylene groups and branched chain alkynylene groups, and straight chain alkynylene groups are preferred. The arylene group may be monocyclic or polycyclic. A monocyclic arylene group is preferred. Specific examples of the arylene group include phenylene groups, naphthylene groups, and the like, and phenylene groups are 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 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), acyloxy groups having 2 carbon atoms ( [acetyloxy], an amide group having 2 carbon atoms [acetamido], a hydroxyalkyl group having 1 to 3 carbon atoms [hydroxymethyl, hydroxyethyl, hydroxypropyl], an aldehyde group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphate group, a carbamoyl group, a cyano group, an isocyanate group, a thiol group, a nitro group, a nitroxy group, an isothiocyanate group, a cyanate group, a thiocyanate group, an acetoxy group, an acetamide group, a formyl group, a formoxyl group, a formamide group, a sulfonamide group, a sulfinic acid group, an amide sulfonyl group, a phosphonyl group, an acetyl group, a halogen atom, an alkali metal atom, and the like.

In formula (A), ^XA1 and ^{XA2 are} preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, more preferably by 1 to 4 atoms, even more preferably by 1 to 3 atoms, and particularly preferably by 1 or 2 atoms, via LA1.

In formula (B), ^XB1 and ^XB3 are preferably separated by 1 to 10 atoms, more ^preferably by 1 to 6 atoms, further preferably by 1 to 4 atoms, further preferably by 1 to 3 atoms, and particularly preferably by 1 or 2 atoms via L ^B1 . Furthermore, ^XB2 and ^XB3 are preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, further preferably by 1 to 4 atoms, further preferably by 1 to 3 atoms, and particularly preferably by 1 or 2 atoms via L B2.

In formula (C), ^XC1 and ^{XC4 are} preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, further preferably by 1 to 4 atoms, further preferably by 1 to 3 atoms, and particularly preferably by 1 or 2 atoms via L ^C1 . Furthermore, ^XC2 and ^XC4 are preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, further preferably by 1 to 4 atoms, further preferably by 1 to 3 atoms, and particularly preferably by 1 or 2 atoms via L C2. Furthermore, ^XC3 and ^XC4 are preferably separated by 1 to 10 atoms, more preferably by 1 to 6 atoms, further preferably by 1 to 4 atoms, further preferably by 1 to 3 atoms, and particularly preferably by 1 or 2 atoms, via L ^C3 .

Furthermore, ^XA1 and ^XA2 are separated by 1 to 10 atoms through L ^A1 , which means that the number of atoms constituting the shortest molecular chain connecting ^XA1 and ^XA2 is 1 to 10. For example, in the case of the following formula (A1), ^XA1 and ^XA2 are separated by 2 atoms, and in the case of the following formulas (A2) and (A3), ^XA1 and ^XA2 are separated by 3 atoms. The numbers attached to the following structural formulas represent the arrangement order of the atoms constituting the shortest molecular chain connecting ^XA1 and ^XA2 . [Chemical Formula 2]

If a specific compound is used for illustration, 3-pentylpropionic acid is a compound having the following structure (compound having the following structure): the position corresponding to X ^A1 is a carboxyl group, the position corresponding to X ^A2 is a thiol group, and the position corresponding to L ^A1 is an ethylidene group. In 3-pentylpropionic acid, X ^A1 (carboxyl group) and X ^A2 (thiol group) are separated by 2 atoms through L ^A1 (ethylidene group). [Chemical formula 3]

The meanings of ^XB1 and ^XB3 being separated by 1 to 10 atoms via L ^B1 , ^XB2 and ^XB3 being separated by 1 to 10 atoms via L ^B2 , ^XC1 and ^XC4 being separated by 1 to 10 atoms via L ^C1 , ^XC2 and ^XC4 being separated by 1 to 10 atoms via L ^C2 , and ^XC3 and ^XC4 being separated by 1 to 10 atoms via L ^C3 are the same as described above.

Specific examples of the multi-seat ligand include 3-butylpropionic acid, butylacetic acid, 2-aminoethanol, 2-aminoethanethiol, 2-butylethanol, glycolic acid, ethylene glycol, ethylenediamine, aminosulfonic acid, glycine, aminomethylphosphonic acid, guanidine, diethylenetriamine, tris(2-aminoethyl)amine, 4-butylbutyric acid, 3-aminopropanol, 3-butylpropanol, N-(3-aminopropyl)-1,3-propanediamine, 3-(bis(3-aminopropyl)amino)propan-1-ol, 1-thioglycerol, dithioglycerol, 1-butyl-2-butanol, 1-butyl-2-pentanol, 3-butyl-1-propanol, 2,3-dibutyl-1-propanol, diethanolamine, 2-(2-aminoethyl)aminoethanol, dimethylenetriamine, Amine, 1,1-oxobismethylamine, 1,1-thiobismethylamine, 2-[(2-aminoethyl)amino]ethanethiol, bis(2-hydroxyethyl)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 Amino acid, aminohydroxyacetic acid, L-lactic acid, D-lactic acid, L-malic acid, D-malic acid, glyceric acid, 2-hydroxybutyric acid, L-tartaric acid, D-tartaric acid, hydroxymalonic acid, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 2-butylbenzoic acid, 3-butylbenzoic acid, 4-butylbenzoic acid and their derivatives.

The solvent contained in the ligand solution is preferably appropriately selected according to the type of ligand contained in each ligand solution, and a solvent that can easily dissolve each ligand is preferred. In addition, the solvent contained in the ligand solution is preferably an organic solvent with a high dielectric constant. As specific examples, ethanol, acetone, methanol, acetonitrile, dimethylformamide, dimethyl sulfoxide, butanol, propanol, etc. can be cited. In addition, the solvent contained in the ligand solution is preferably a solvent that is not easy to remain in the formed semiconductor film. From the perspective of easy drying and easy removal by washing, low-boiling alcohols or ketones, nitriles are preferred, and methanol, ethanol, acetone or acetonitrile is more preferred. It is preferred that the solvent contained in the ligand solution is not mixed with the solvent contained in the semiconductor quantum dot dispersion. As a preferred combination of solvents, when the solvent contained in the semiconductor quantum dot dispersion is an alkane such as hexane or octane, it is preferred that the solvent contained in the ligand solution is a polar solvent such as methanol or acetone.

The method of imparting a ligand solution to a film of PbS quantum dot aggregates is the same as the method of imparting a PbS quantum dot dispersion to a substrate, and the preferred method is also the same.

In the semiconductor film manufacturing method of the present invention, the PbS quantum dot cluster formation step and the ligand replacement step can be repeated multiple times alternately. That is, the operation of forming the PbS quantum dot cluster and replacing the ligand as one cycle can be repeated multiple times.

In the method for manufacturing a semiconductor film of the present invention, a step (rinsing step) of bringing a rinse liquid into contact with the film after the ligand replacement step can be performed. By performing the rinse step, it is possible to remove excess ligands contained in the film and ligands detached from quantum dots. In addition, it is possible to remove residual solvents and other impurities. As a rinse liquid, a non-protonic solvent is preferred because it is easy to effectively remove excess ligands contained in the film and ligands detached from PbS quantum dots, and it is easy to maintain a uniform film surface by rearranging the surface of PbS quantum dots. Specific examples of the aprotic solvent include acetonitrile, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, diethyl ether, tetrahydrofuran, cyclopentyl methyl ether, dihydrogen ether, ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, hexane, octane, cyclohexane, benzene, toluene, chloroform, carbon tetrachloride, and dimethylformamide. Acetonitrile and tetrahydrofuran are preferred, and acetonitrile is more preferred.

Furthermore, the rinsing step may be performed multiple times using two or more rinsing solutions with different polarities (relative dielectric constants). For example, it is preferred to first rinse with a rinsing solution with a high relative dielectric constant (also referred to as the first rinsing solution), and then rinse with a rinsing solution with a lower relative dielectric constant than the first rinsing solution (also referred to as the second rinsing solution). The relative dielectric constant of the first rinsing solution is preferably 15 to 50, more preferably 20 to 45, and even more preferably 25 to 40. The relative dielectric constant of the second rinsing solution is preferably 1 to 15, more preferably 1 to 10, and even more preferably 1 to 5.

After this step, a semiconductor film can be manufactured. The obtained semiconductor film can be used in a light detection element or an image sensor. More specifically, it can be used in a photoelectric conversion layer of a light detection element or an image sensor.

<Method for manufacturing a light detection element> The method for manufacturing a light detection element of the present invention includes the method for manufacturing a semiconductor film of the present invention. Specifically, it is preferred to use the method for manufacturing a semiconductor film of the present invention to form a photoelectric conversion layer of a light detection element.

As types of photodetection elements, there are photoconductor-type photodetection elements and photodiode-type photodetection elements. Among them, photodiode-type photodetection elements are preferred because they can easily obtain a high signal-to-noise ratio (SN ratio).

The semiconductor film obtained by using the PbS quantum dots of the present invention, that is, the semiconductor film obtained by the manufacturing method of the present invention has excellent sensitivity to light of wavelengths in the infrared region, so the light detection element obtained by the manufacturing method of the present invention is preferably used as a light detection element for detecting light of wavelengths in the infrared region. That is, the above-mentioned light detection element is preferably used as an infrared light detection element.

The light having a wavelength in the infrared region is preferably light having a wavelength of 1300 nm or more and 1700 nm or less.

The light detection element may be a light detection element that detects 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).

FIG1 shows an embodiment of a photodetection element. FIG1 is a diagram showing an embodiment of a photodiode-type photodetection element. Furthermore, the arrows in the figure represent light incident on the photodetection element. The photodetection element 1 shown in FIG1 includes: a second electrode 12; a first electrode 11 disposed opposite to the second electrode 12; a photoelectric conversion layer 13 disposed between the second electrode 12 and the first electrode 11; an electron transport layer 21 disposed between the first electrode 11 and the photoelectric conversion layer 13; and a hole transport layer 22 disposed between the second electrode 12 and the photoelectric conversion layer 13. The photodetection element 1 shown in FIG1 is used in a manner in which light is incident from above the first electrode 11. Although not shown, a transparent substrate may be disposed on the surface of the light incident side of the first electrode 11. Examples of the transparent substrate include a glass substrate, a resin substrate, and a ceramic substrate.

(First electrode) The first 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 this specification, "substantially transparent" means that the transmittance is 50% or more, preferably 60% or more, and particularly preferably 80% or more. As materials for the first 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 (IZO), indium tin oxide (ITO), fluorine-doped tin oxide (FTO), etc. can be cited.

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

(Electron transport layer) The electron transport layer 21 is a layer having the function of transporting the electrons generated in the photoelectric conversion layer 13 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 the electron transport material include fullerene compounds such as [6,6]-phenyl-C61-butyric acid methyl ester (PC ₆₁ BM), perylene compounds such as perylene tetracarboxylic diimide, tetracyanoquinodimethane, titanium oxide, tin oxide, zinc oxide, indium oxide, indium tungsten oxide, indium zinc oxide, indium tin oxide, fluorine-doped tin oxide, etc. The electron transport material may be in the form of particles.

The electron transport layer is preferably composed of 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 atoms other than Zn in the doped zinc oxide are preferably 1-3 valent metal atoms, more preferably at least one selected from Li, Mg, Al and Ga, further preferably Li, Mg, Al or Ga, particularly preferably Li or Mg.

In 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, more preferably 2 atomic % or more, and even more preferably 4 atomic % or more. From the viewpoint of suppressing the increase of 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. Furthermore, the ratio of metal atoms other than Zn in doped zinc oxide can be measured by high-frequency inductively coupled plasma (ICP).

From the viewpoint of reducing the organic residual components and increasing the contact area with the photoelectric conversion layer, it is preferable that the doped zinc oxide is in the form of particles (doped zinc oxide particles). Furthermore, it is preferable that the average particle size of the doped zinc oxide particles is 2 to 30 nm. The lower limit of the average particle size of the doped zinc oxide particles is preferably 3 nm or more, and more preferably 5 nm or more. Furthermore, the upper limit of the average particle size of the doped zinc oxide particles is preferably 20 nm or less, and more preferably 15 nm or less. If the average particle size of the doped zinc oxide particles is within the above range, it is easy to obtain a film with a large contact area with the photoelectric conversion layer and high flatness. In this specification, the average particle size of the doped zinc oxide particles is the average value of 10 randomly selected particle sizes. When measuring the particle size of the doped zinc oxide particles, a transmission electron microscope may be used.

The electron transport layer may be a single layer film or a laminated film of two or more layers. The thickness of the electron transport layer is preferably 10 to 1000 nm. The upper limit is preferably 800 nm or less. The lower limit is preferably 20 nm or more, and more preferably 50 nm or more. In addition, the thickness of the electron transport layer is preferably 0.05 to 10 times the thickness of the photoelectric conversion layer 13, more preferably 0.1 to 5 times, and even more preferably 0.2 to 2 times.

The electron transport layer can be subjected to ultraviolet ozone treatment. In particular, when the electron transport layer is a layer composed of nanoparticles, ultraviolet ozone treatment is preferably performed. By performing ultraviolet ozone treatment, the wettability of the quantum dot dispersion relative to the electron transport layer can be improved, and residual organic matter in the electron transport layer can be decomposed or removed, thereby obtaining high device performance. The wavelength of the irradiated ultraviolet light can be selected between 100 and 400 nm. In particular, in order to easily obtain the above-mentioned effects and avoid excessive damage to the membrane, it is better to have a peak intensity between 200 and 300 nm, and it is more preferable to have a peak intensity between 240 and 270 nm. There is no particular limitation on the intensity of ultraviolet irradiation, but for the reasons of easily obtaining the above-mentioned effects and avoiding excessive damage to the film, 1 to 100 mW/cm ² is preferred, and 10 to 50 mW/cm ² is more preferred. There is no particular limitation on the treatment time, but for the same reason, 1 to 60 minutes is preferred, 1 to 20 minutes is more preferred, and 3 to 15 minutes is further preferred.

(Photoelectric conversion layer) The photoelectric conversion layer 13 is preferably composed of a semiconductor film manufactured by the manufacturing method of the present invention.

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

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

The hole transport layer 22 is formed of a hole transport material that can play this role. For example, as the hole transport material, 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}), PTB7-Th (poly([2,6'-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]{3-fluoro-2[(2-ethylhexyl l)carbonyl]thieno[3,4-b]thiophenediyl})), PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester), MoO ₃ , etc. In addition, organic hole transport materials described in paragraphs 0209 to 0212 of Japanese Patent Publication No. 2001-291534 can also be used. In addition, quantum dots can also be used as hole transport materials. As quantum dot materials constituting quantum dots, nanoparticles (particles with a size of 0.5 nm or more and less than 100 nm) of common semiconductor crystals [a) Group IV semiconductors, b) Group IV-IV, Group III-V or Group II-VI compound semiconductors, c) compound semiconductors composed of a combination of three or more elements from Group II, Group III, Group IV, Group V and Group VI] can be cited. Specifically, semiconductor materials with relatively narrow band gaps such as PbS, PbSe, PbSeS, InN, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, HgTe, HgCdTe, Ag ₂ S, Ag ₂ Se, Ag ₂ Te, SnS, SnSe, SnTe, Si, InP, etc. can be cited. Ligands can be coordinated to the surface of quantum dots.

The thickness of the hole transport layer 22 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.

(Second electrode) The second electrode 12 is preferably made of a metal material containing at least one metal atom selected from Ag, Au, Pt, Ir, Pd, Cu, Pb, Sn, Zn, Ti, W, Mo, Ta, Ge, Ni, Al, Cr and In. By making the second electrode 12 of such a metal material, a light detection element with high external quantum efficiency and low dark current can be formed. In addition, as the second electrode 12, the above-mentioned conductive metal oxides, carbon materials and conductive polymers can also be used. As a carbon material, any material with conductivity can be used, for example, fullerene, carbon nanotubes, graphite, graphene, etc. can be cited.

In order to improve the electron blocking property of the hole transport layer and facilitate the collection of holes generated in the device, the work function of the second electrode 12 is preferably 4.6 eV or more, more preferably 4.8 to 5.7 eV, and even more preferably 4.9 to 5.3 eV.

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

(Blocking layer) Although not shown, the light detection element may also have a blocking layer between the first electrode 11 and the electron transport layer 21. The blocking layer is a layer that has the function of preventing reverse current. The blocking layer is also called an anti-short circuit layer. Examples of materials forming the blocking layer include silicon oxide, magnesium oxide, aluminum oxide, calcium carbonate, cesium carbonate, polyvinyl alcohol, polyurethane, titanium oxide, tin oxide, zinc oxide, niobium oxide, and tungsten oxide. The blocking layer may be a single layer film or a multilayer film of two or more layers.

In the photodetection element, the wavelength λ of the target light detected by the photodetection element and the optical path length Lλ of the light of the wavelength ^λ from the surface of the second electrode 12 on the photoelectric conversion layer 13 side to the surface of the photoelectric conversion layer 13 on the first electrode 11 side preferably satisfy the relationship of the following formula (1-1), and more preferably satisfy the relationship of the following formula (1-2). When the wavelength λ and the optical path length ^Lλ satisfy this relationship, the phases of the light incident from the first electrode 11 side (incident light) and the light reflected from the surface of the second electrode 12 (reflected light) can be made consistent in the photoelectric conversion layer 13, and as a result, the lights are mutually reinforced by the optical interference effect, and a higher external quantum efficiency can be obtained.

0.05+m/2≤L ^λ /λ≤0.35+m/2……(1-1) 0.10+m/2≤L ^λ /λ≤0.30+m/2……(1-2)

In the above formula, λ is the wavelength of the target light detected by the light detection element, ^Lλ is the optical length of the light of wavelength λ from the surface of the second electrode 12 on the photoelectric conversion layer 13 side to the surface of the photoelectric conversion layer 13 on the first electrode 11 side, and m is an integer greater than 0.

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 improved, and the external quantum efficiency of the photodetection element can be further improved.

Here, the optical path length refers to the physical thickness of the material through which light passes multiplied by the refractive index. If the photoelectric conversion layer 13 is used as an example for explanation, the thickness of the photoelectric conversion layer is set to d ¹ , and the refractive index of the photoelectric conversion layer with respect to the light of wavelength λ ¹ is set to N ¹ , then the optical path length of the light of wavelength λ ¹ passing through the photoelectric conversion layer 13 is N ¹ ×d ^1. When the photoelectric conversion layer 13 or the hole transport layer 22 is composed of two or more laminated films, or when there is an intermediate layer between the hole transport layer 22 and the second electrode 12, the cumulative value of the optical path lengths of each layer is the above-mentioned optical path length L ^λ .

<Manufacturing method of image sensor> The manufacturing method of the image sensor of the present invention includes the manufacturing method of the semiconductor film of the present invention. Specifically, it is preferable to use the manufacturing method of the semiconductor film of the present invention to form the photoelectric conversion layer of the light detection element of the image sensor.

The structure of the image sensor is not particularly limited as long as it has a light detection element and functions as an image sensor. The light detection element includes the above-mentioned ones.

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

As the infrared transmission filter layer, there can be cited those composed of a resin film containing a color material. As the color material, there can be cited chromatic color materials such as red color material, green color material, blue color material, yellow color material, purple color material, orange color material, and black color material. It is preferable that the color material contained in the infrared transmission filter layer is formed by a combination of two or more chromatic color materials to form black or contains a black color material. As a combination of chromatic color materials when forming black by a combination of two or more chromatic color materials, for example, the following (C1) to (C7) can be cited. (C1) A mode containing a red color material and a blue color material. (C2) A mode containing a red color material, a blue color material, and a yellow color material. (C3) A mode containing a red color material, a blue color material, a yellow color material, and a purple color material. (C4) A form containing red color material, blue color material, yellow color material, purple color material and green color material. (C5) A form containing red color material, blue color material, yellow color material and green color material. (C6) A form containing red color material, blue color material and green color material. (C7) A form containing yellow color material and purple color material.

The color material may be a pigment or a dye. It may also contain a pigment and a dye. The black color material is preferably an organic black color material. For example, as the organic black color material, there can be cited bisbenzofuranone compounds, methine azo compounds, perylene compounds, azo compounds, etc.

The infrared transmission filter may further contain an infrared absorber. By containing an infrared absorber in the infrared transmission filter, the wavelength of the transmitted light can be shifted further toward the long wavelength side. Examples of the infrared absorber include pyrrolopyrrole compounds, cyanine compounds, squarylium compounds, phthalocyanine compounds, naphthalocyanine compounds, quaterrylene compounds, merocyanine compounds, crotonium compounds, oxocyanine compounds, ammonium compounds, dithiol compounds, triarylmethane compounds, pyrromethene compounds, methine azo compounds, anthraquinone compounds, dibenzofuranone compounds, dithiene 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 purpose of the image sensor. For example, a filter layer that satisfies any of the spectral characteristics of the following (1) to (5) can be cited. (1): A filter layer whose maximum transmittance in the thickness direction of the film within the wavelength range of 400 to 750 nm is less than 20% (preferably less than 15%, more preferably less than 10%) and whose minimum transmittance in the thickness direction of the film within the wavelength range of 900 to 1500 nm is more than 70% (preferably more than 75%, more preferably more than 80%). (2): A filter layer whose maximum light 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 whose minimum light 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%). (3): A filter layer whose maximum light 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 whose minimum light 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%). (4): A filter layer whose maximum light transmittance in the thickness direction of the film within the wavelength range of 400 to 1100 nm is less than 20% (preferably less than 15%, more preferably less than 10%) and whose minimum light transmittance in the wavelength range of 1400 to 1500 nm is more than 70% (preferably more than 75%, more preferably more than 80%). (5): A filter layer whose maximum light transmittance in the thickness direction of the film within the wavelength range of 400 to 1300 nm is less than 20% (preferably less than 15%, more preferably less than 10%) and whose minimum light transmittance in the wavelength range of 1600 to 2000 nm is more than 70% (preferably more than 75%, more preferably more than 80%). Moreover, as an 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. Infrared transmission filters can be used in combination of two or more filters, or a dual-band pass filter can be used that transmits two or more specific wavelength regions through one filter.

For the purpose of improving various performances such as noise reduction, the image sensor may include an infrared shielding filter. 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.

The image sensor may include a dielectric multilayer film. As a dielectric multilayer film, a dielectric film having a high refractive index (high refractive index material layer) and a dielectric film having a low refractive index (low refractive index material layer) are alternately laminated in multiple layers. The number of layers of dielectric films in the dielectric multilayer film is not particularly limited, and 2 to 100 layers are preferred, 4 to 60 layers are more preferred, and 6 to 40 layers are further preferred. As a material for forming the high refractive index material layer, a material having a refractive index of 1.7 to 2.5 is preferred. Specific examples include _Sb2O3 , _{Sb2S3, Bi2O3 , CeO2 , CeF3} , _{HfO2 , La2O3, Nd2O3, Pr6O11, Sc2O3 , SiO , Ta2O5} , _TiO2 , _TlCl , _Y2O3 , _ZnSe , ZnS, _{ZrO2 , etc.} As the material for forming the low refractive index _material layer, a material _having a refractive index of 1.2 to _1.6 is _preferred . Specific examples include _Al2O3 , BiF3, _CaF2 , _LaF3 , _PbCl2 , _PbF2 , LiF, _MgF2 , _MgO , NdF3, _SiO2 , _Si2O3 , _NaF , _ThO2 , _ThF4 , _Na3AlF6 , etc. The method for forming _the dielectric multilayer film is not particularly limited, and examples thereof include ion plating, vacuum evaporation methods such as ion beam, physical vapor deposition methods (PVD _methods ) such as sputtering, and chemical vapor deposition methods (CVD methods ₎ . When the wavelength of light to be blocked is λ (nm), 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. As a specific example of the dielectric multilayer film, for example, the films described in Japanese Patent Publication No. 2014-130344 and Japanese Patent Publication No. 2018-010296 can be used.

The dielectric multilayer film preferably has a transmission wavelength band at a wavelength of 1300 to 1700 nm. The maximum transmittance in the transmission wavelength band is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. Furthermore, 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. Furthermore, 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. In addition, when the wavelength showing maximum transmittance is set to the center wavelength λ _t1 , the wavelength range of the transmittance wavelength band is preferably the center wavelength λ _t1 ± 100nm, the center wavelength λ _t1 ± 75nm is better, and the center wavelength λ _t1 ± 50nm is even better.

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. As the color separation filter layer, a filter layer including colored pixels can be cited. As the type of colored pixels, red pixels, green pixels, blue pixels, yellow pixels, cyan pixels, and magenta pixels can be cited. The color separation filter layer may include colored pixels of more than two colors, or may be only one color. It can be appropriately selected according to the use or purpose. For example, the filter described in International Publication No. 2019/039172 can be used.

Furthermore, 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, or partitions may be provided between the colored pixels. The material of the partition is not particularly limited. For example, organic materials such as silicone resins and fluorine resins or inorganic particles such as silicon dioxide particles may be cited. Furthermore, the partition may be made of metals such as tungsten and aluminum.

Furthermore, when the image sensor includes an infrared transmission filter layer and a color separation layer, it is preferred that the color separation layer is disposed on a different optical path from the infrared transmission filter layer. Furthermore, it is also preferred to configure the infrared transmission filter layer and the color separation layer in two dimensions. Furthermore, configuring the infrared transmission filter layer and the color separation layer in two dimensions means that at least a portion of the two exist on the same plane.

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

The following examples are given to further illustrate the present invention. The materials, usage amounts, ratios, processing contents, processing steps, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the main purpose of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

<PbS quantum dot dispersion> (Example 1) 24 mL of oleic acid, 7.2 g of lead oxide and 48 mL of octadecene were weighed in a flask and heated at 110°C for 5 minutes under vacuum to obtain a precursor solution. The precursor solution was cooled to room temperature and then stored in a glove box in an _N2 environment. In addition, 33 mg of lead chloride was added to 40 ml of oleylamine and heated at 80°C for 2 hours to obtain a lead chloride solution. 60 ml of octadecene was added to the flask containing the above-mentioned precursor solution, set to a nitrogen flow state, adjust the temperature of the solution to 160°C, and inject 0.834 ml of hexamethyldisilasulfane together with 31.8 mL of octadecene. After injection, the flask was cooled naturally, and 4 ml of lead chloride solution was added when it reached 60°C. When it cooled to room temperature, 32 ml of toluene was added and the solution was recovered. 40 ml of acetone was added to the recovered solution, and after heating in a 50°C water bath for 10 minutes, the precipitate was recovered by centrifugal separation at 5000 rpm for 10 minutes. The precipitate was then dispersed in toluene to obtain a PbS quantum dot dispersion (concentration 40 mg/mL) in which oleic acid was coordinated to the PbS quantum dots. Furthermore, the temperature of the solution when heated in a 50°C water bath for 10 minutes was 41°C. By absorption measurement of the PbS quantum dot dispersion, the maximum absorption of the PbS quantum dots contained in the PbS quantum dot dispersion was 1580 nm. The average particle size of the PbS quantum dots was 6.1 nm. The average particle size of the PbS quantum dots was determined by measuring the equivalent circular diameters of 500 randomly selected particles from electron microscope photographs taken by a transmission electron microscope (TEM), and calculating the average value (arithmetic mean). The Pb/S ratio (molar ratio) of the PbS quantum dots was 1.6 when the Pb/S ratio (molar ratio) of the PbS quantum dots was calculated by the following method.

-Calculation method of the Pb/S ratio (molar ratio) of PbS quantum dots- After the PbS quantum dot dispersion was concentrated to 60 mg/mL, 50 μL was collected, 5 mL of nitric acid was added, and then the sample was decomposed by microwave heating at 230°C. After adding so that the total amount became 40 mL, the Pb atoms and S atoms in the PbS quantum dots were quantified using an inductively coupled plasma (ICP) emission spectrometer (Optima 7300DV manufactured by PerkinElmer) to calculate the Pb/S ratio (molar ratio) of the PbS quantum dots.

(Comparative Example 1) A commercially available PbS quantum dot dispersion (manufactured by Sigma Aldrich, product number 900727) was used as the PbS quantum dot dispersion of Comparative Example 1. The maximum absorption of the PbS quantum dots contained in the PbS quantum dot dispersion is 1520nm.

(Comparative Example 2) In Example 1, the PbS quantum dot dispersion of Comparative Example 2 was obtained in the same manner as in Example 1 except that the heating in the water bath was not performed. The maximum absorption of the PbS quantum dots contained in the PbS quantum dot dispersion was 1580nm.

<Thermogravimetric analysis> Thermogravimetric analysis was performed on the PbS quantum dot dispersions of the examples and comparative examples, and the ratio of the weight ^W160 at 160°C to the weight ^W450 at 450°C (hereinafter referred to as the weight ratio ^{W160/ W450} ) was calculated. The measurement apparatus used was the Pyris 1 TGA manufactured by PerkinElmer, and the measurement conditions were set as follows. Measurement liquid volume: 30ul Environment: Argon Initial temperature: 50°C Temperature range: 50°C to 500°C Heating rate: 20°C/min

<Manufacturing of light detection element> A titanium oxide film was formed on a quartz glass substrate with a fluorine-doped tin oxide film by 50nm sputtering. Then, a dispersion of PbS quantum dots was added dropwise to the titanium oxide film formed on the substrate and spun at 2500rpm to form a PbS quantum dot aggregate film (step 1). Then, a methanol solution (concentration 0.01v/v%) to which galactocyanate and zinc iodide were added was added dropwise to the PbS quantum dot aggregate film, and the film was left to stand for 20 seconds and spun at 2500rpm for 10 seconds. Next, acetonitrile was dripped onto the PbS quantum dot aggregate film as a rinse solution, and the film was spin-dried at 2500 rpm for 20 seconds to replace the ligand coordinated to the PbS quantum dots from the oleic acid ligand to silylic acid (step 2). The operation of step 1 and step 2 as one cycle was repeated for 10 cycles, thereby forming a PbS quantum dot aggregate film, i.e., a photoelectric conversion layer, in which the ligand was replaced from the oleic acid ligand to silylic acid, with a thickness of 180 nm. Next, molybdenum oxide was formed with a thickness of 50 nm and gold with a thickness of 100 nm on the photoelectric conversion layer by continuous evaporation, and a photodiode-type light detection element was obtained.

<Evaluation method of photodetection element> The external quantum efficiency was evaluated when irradiating monochromatic light (50μW/cm ² ) with a wavelength of 1550nm with a reverse voltage of 1.5V applied to each photodetection element. The external quantum efficiency was calculated from the number of photoelectrons estimated from the difference between the current value when no light irradiation was performed and the number of irradiated photons using the following formula. External quantum efficiency (%) = (number of photoelectrons/number of irradiated photons) × 100 In addition, the degree of change in external quantum efficiency after repeating the external quantum efficiency calculation 50 times was calculated (the value of the external quantum efficiency measured at the first time - the value of the external quantum efficiency measured at the 50th time), and the durability relative to repeated driving was evaluated. The smaller the value of the degree of change in external quantum efficiency, the better the durability relative to repeated driving. Regarding the dark current, the current value when no light irradiation was performed when evaluating the external quantum efficiency was calculated as the dark current.

[Table 1] PbS quantum dot dispersion External quantum efficiency (%) Dark current (A/cm ² ) Change in external quantum efficiency (%) Type Weight ratio W ¹⁶⁰ /W ⁴⁵⁰ Embodiment 101 Embodiment 1 1.50 49 3.7× ^10-7 1.8 Comparison Example 101 Comparison Example 1 2.08 44 7.8×10 ^-5 5.9 Comparative Example 102 Comparison Example 2 2.22 38 9×10 ^-5 6.8

As shown in the above table, compared with the photodetection element of the comparative example, the photodetection element of the embodiment has a high external quantum efficiency and a low dark current. Furthermore, the change in external quantum efficiency after repeated driving is also small, and the durability relative to repeated driving is also excellent. In addition, even if the PbS quantum dot dispersion of Example 1 is stored at 20°C for 180 days, the viscosity change is still small, and almost no precipitate is generated, and the storage stability is excellent.

By using the light detection element obtained in the embodiment, an image sensor is manufactured by a known method together with an optical filter manufactured according to the method described in International Publication No. 2016/186050 and International Publication No. 2016/190162, thereby obtaining an image sensor with good visible performance-infrared imaging performance.

1: Photodetector element 11: 1st electrode 12: 2nd electrode 13: Photoelectric conversion layer 21: Electron transport layer 22: Hole transport layer

FIG. 1 is a diagram showing an embodiment of a light detection element.

without.

Claims (15)

A PbS quantum dot dispersion, comprising PbS quantum dots, a ligand and a solvent, wherein in the PbS quantum dot dispersion, the ligand comprises a fatty acid having more than 6 carbon atoms, and when the PbS quantum dot dispersion is subjected to thermogravimetric analysis at a temperature increase rate of 20°C/min from 50°C to 500°C in an argon environment at normal pressure, the ratio of the weight ^W160 at 160°C to the weight ^W450 at 450°C is less than 2. The PbS quantum dot dispersion as described in claim 1, wherein the aforementioned PbS quantum dots have a maximum absorption in the wavelength range of 1300 to 1700 nm. The PbS quantum dot dispersion as described in claim 1 or claim 2, wherein the PbS quantum dots contain more than 1.2 mol of Pb atoms per mol of S atoms. The PbS quantum dot dispersion as described in claim 1 or claim 2, wherein when the aforementioned PbS quantum dot dispersion is subjected to thermogravimetric analysis at a temperature increase rate of 20°C/min from 50°C to 500°C in an argon environment at normal pressure, the ratio of the weight ^W160 at 160°C to the weight ^W450 at 450°C is less than 1.54. The PbS quantum dot dispersion as described in claim 1 or claim 2, wherein the carbon number of the aforementioned fatty acid is 12 to 22. The PbS quantum dot dispersion as described in claim 1 or claim 2, wherein the aforementioned fatty acid is an unsaturated fatty acid. The PbS quantum dot dispersion as described in claim 1 or claim 2, wherein the aforementioned ligand contains oleic acid. A method for manufacturing a semiconductor film, comprising: a PbS quantum dot aggregate forming step, wherein the PbS quantum dot dispersion liquid described in any one of claim 1 to claim 7 is applied to a substrate to form a film of PbS quantum dot aggregates; and a ligand replacement step, wherein a ligand solution containing a ligand and a solvent different from the ligand contained in the PbS quantum dot dispersion liquid is applied to the film of the PbS quantum dot aggregates formed by the PbS quantum dot aggregate forming step, so that the ligand contained in the ligand solution coordinates with the PbS quantum dots. A method for manufacturing a light detection element, comprising the method for manufacturing a semiconductor film as described in claim 8. A method for manufacturing an image sensor, comprising the method for manufacturing a semiconductor film as described in claim 8. A method for preparing a PbS quantum dot dispersion, comprising: reacting a compound containing a lead atom and a compound containing a sulfur atom in the presence of a ligand containing a fatty acid having more than 6 carbon atoms and a solvent to obtain a reaction solution containing PbS quantum dots; heating the reaction solution containing the PbS quantum dots, centrifugally separating and recovering a precipitate containing the PbS quantum dots; and dispersing the recovered precipitate in a solvent. A method for producing a PbS quantum dot dispersion as described in claim 11, wherein the heating is performed at a temperature above 30°C. The method for producing a PbS quantum dot dispersion as described in claim 11, wherein the heating is performed at a temperature of 40 to 60°C. A method for producing a PbS quantum dot dispersion as described in claim 11 or claim 12, wherein the aforementioned ligand contains oleic acid. A method for producing a PbS quantum dot dispersion as described in claim 11 or claim 12, wherein a polar solvent is added to the reaction solution containing the PbS quantum dots before the centrifugal separation.

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