JP2020150251A - Quantum dot, photoelectric conversion element having the same, light-receiving element, photoelectric conversion device, mobile object, method for manufacturing quantum dot, and method for manufacturing photoelectric conversion element - Google Patents

Abstract

To provide a quantum dot having good photosensitivity by making the rate of inorganic ligands larger than that of organic ligands.SOLUTION: A quantum dot 7 comprises an inorganic particle. The quantum dot 7 has, on its surface, an organic ligand 8 and an inorganic ligand 9. The mole rate of the inorganic ligand 9 to a total quantity of the inorganic ligand 9 and the organic ligand 8 is 25% or more and 99.8% or less.SELECTED DRAWING: Figure 2

Description

The present invention relates to a quantum dot, a photoelectric conversion element having the quantum dot, a photoelectric conversion element, a light receiving element, a photoelectric conversion device, a moving body, a method for manufacturing a quantum dot, and a method for manufacturing a photoelectric conversion element.

Quantum dots, which are composed of inorganic particles and convert the received light into electricity, are attracting attention. Quantum dots have light sensitivity even in the near-infrared region and can obtain highly sensitive images even in the dark field, so they can be used as image sensors (imaging sensors) for security applications such as security cameras.

Quantum dot materials are known to be composed of a plurality of inorganic particles made of compound semiconductors. Molecules provided on the surface of nanoparticles and bound by covalent bonds are called ligands.

It is known that quantum dots are provided with a ligand composed of an organic compound or an inorganic ligand on the surface thereof, and it is known that the properties of the quantum dots can be controlled by the type of the ligand. As an example, organic ligands such as benzenedithiol containing a benzene ring are known to improve the electrical conductivity of inorganic particles. However, since the organic ligand has a three-dimensional structure, the bulk of the ligand may be large, and the ligand having a large bulk cannot sufficiently cover the inorganic particles. As a result, surface defects of the inorganic particles may not be sufficiently suppressed.

On the other hand, since the halogen-based inorganic ligand has a small halogen atom size, it can cover the surface of the inorganic particles more than the organic ligand, so that surface defects of the inorganic particles can be suppressed. However, with only the inorganic ligand, the distance between adjacent inorganic particles is shortened to about a halogen atom. That is, the heat resistance may be low because the role as a spacer is not sufficient.

Further, when the quantum dot film is formed and then oxidized in the atmosphere, the oxidation proceeds to the core portion of the inorganic particles, and the particle size of the inorganic particles becomes smaller. It is known that when the particle size of nanoparticles becomes smaller, the electrical conductivity changes, and in particular, the spectral spectrum of the optical sensitivity shifts to the short wavelength side, so that the optical sensitivity in a desired wavelength range decreases.

Patent Document 1 describes that the stability of quantum dots is improved by replacing the organic substance bonded to the surface of the quantum dots with an inorganic substance having a halogen.

Non-Patent Document 1 describes that a halogen-based inorganic ligand is added when an organic ligand is provided on the surface of a quantum dot. By adding an inorganic ligand, surface defects of nanoparticles that are not bonded to a ligand with a relatively long molecular length such as oleic acid added during synthesis are repaired, and the electrical conductivity of the quantum dot film is improved. It is stated that it will improve.

U.S. Pat. No. 09234562

Ruili Wang, et. al, “Colloidal quantum dot ligand engineering cells”, Energy & Environmental Science, 2016, 4, 1117-1516

Patent Document 1 and Non-Patent Document 1 describe quantum dots having an inorganic ligand and an organic ligand on the surface of the inorganic particles. However, the molar ratio of the ligand estimated from the production conditions of these quantum dots is larger than the molar ratio of the inorganic ligand, so that the quantum dot has a small photocurrent density. Estimated. Therefore, improvement of the photocurrent density has been required.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the molar ratio of an inorganic ligand and an organic ligand provided in a quantum dot to obtain a photocurrent. It is to provide high density quantum dots.

One embodiment of the present invention is a quantum dot composed of inorganic particles, the quantum dot having an organic ligand and an inorganic ligand on the surface thereof, and the inorganic ligand and the organic ligand. Provided is a quantum dot characterized in that the molar ratio of the inorganic ligand to the total of the above is 25% or more and 99.8% or less.

According to the present invention, it is possible to provide quantum dots having a high photocurrent density.

(A) It is sectional drawing which shows the photoelectric conversion element which concerns on one Embodiment of this invention. (B) It is sectional drawing which shows the example which the photoelectric conversion layer of the photoelectric conversion element which concerns on one Embodiment of this invention is laminated. (A) It is a schematic diagram which shows an example of the inorganic ligand and the organic ligand of the quantum dot which concerns on one Embodiment of this invention. It is the figure which represented the surface of the quantum dot (B) to (E) schematically. It is a TOF-SIMS analysis result of the quantum dot of the Example of this invention. It is the result of TOF-SIMS analysis (positive secondary ion) of the quantum dot which concerns on one Embodiment of this invention. This is the result of quantum dot TOF-SIMS analysis (negative secondary ion) according to an embodiment of the present invention. It is a figure which shows an example of the image pickup system which used the photoelectric conversion element which concerns on one Embodiment of this invention. (A) An example of an imaging system related to an in-vehicle camera is shown. (B) It is a schematic diagram which showed an example of the moving body including an in-vehicle camera.

The quantum dot of one embodiment of the present invention is a quantum dot having a plurality of inorganic particles, and the quantum dot has an organic ligand and an inorganic ligand on its surface, and the inorganic ligand and the quantum dot. The quantum dot is characterized in that the molar ratio of the inorganic ligand to the total with the organic ligand is 25% or more and 99.8% or less. The molar ratio of the inorganic ligand to the total of the inorganic ligand and the organic ligand may be 75% or more and 98% or less. Further, the height of the maximum peak of TOF-SIMS caused by the inorganic ligand may be three times or more the height of the maximum peak of TOF-SIMS caused by the organic ligand. When measuring TOF-SIMS, the principal component of the inorganic particles may be used as a reference. When used as a reference, the peak of the inorganic particles may be 90% or more of the measurement range. Further, the peak of the inorganic particles may coincide with the limit of the measurement range.

By suppressing the decrease in photosensitivity due to denaturation due to oxidation of the quantum dots by the inorganic ligand, it is possible to obtain quantum dots with excellent conductivity.

The molar ratio of the ligand provided on the surface of the quantum dot can be adjusted by the conditions when the ligand is applied to the quantum dot.

The ligand may be added so that the molar ratio of the inorganic ligand is higher than the molar ratio of the organic ligand. More specifically, the amount of the inorganic ligand added to the total of the amount of the inorganic ligand added and the amount of the organic ligand added may be larger than that of the organic ligand, and is 25% or more and 99.8%. It may be:

[Quantum dot material]
Quantum dots are inorganic particles. The particles do not have to be perfect spheres. Inorganic particles used for quantum dots are sometimes called nanoparticles because of their size. Examples of the material for the quantum dots include semiconductor crystals, group IV semiconductors, group III-V and group II-VI compound semiconductors, group II, group III, group IV, group V, and group VI elements. Examples thereof include nanoparticles such as compound semiconductors composed of a combination of three or more. Specific examples thereof include semiconductor materials having a relatively narrow bandgap, such as PbS, PbSe, InN, InAs, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, Si, and InP. Among the above, the quantum dot material is preferably nanoparticles having Pb, more specifically PbS or PbSe, from the viewpoint of ease of synthesis and light sensitivity up to the infrared region. These may be the cores of the quantum dots, and may have a core-shell structure in which the quantum dot material is covered with a coating compound. In this case, a ligand is provided in the shell portion.

The average particle size of the quantum dots is preferably 2 nm or more and 15 nm or less. In quantum dots, if the particle size of the quantum dots is reduced to a size smaller than the Bohr radius of the intrinsic excitons, a phenomenon occurs in which the band gap of the quantum dots changes due to the quantum size effect. For example, it is said that the II-VI group semiconductor has a relatively large Bohr radius, and the PbS has a bore radius of about 18 nm. Further, in InP, which is a III-V semiconductor, the Bohr radius is said to be about 10 nm to 14 nm. That is, if the average particle size of the quantum dots is 15 nm or less, the band gap can be controlled by the quantum size effect regardless of whether it is PbS or InP. By setting the average particle size of the quantum dots to 2 nm or more, it is possible to easily control the crystal growth of the quantum dots in the synthesis of the quantum dots.

[Ligand on the surface of quantum dots]
[Organic ligand]
Quantum dots have ligands on their surface. Ligands are roughly classified into inorganic ligands and organic ligands. When the organic ligand has a first quantum dot and a second quantum dot, it may have a crosslinked structure that bridges the two. Cross-linking is the binding of one molecule to the first and second quantum dots. When crosslinked by an organic ligand, the distance between the quantum dots can be controlled by the molecular length of the organic ligand. Specifically, the structure to be crosslinked may be a hydroxyl group, a thiol group, or a carboxyl group. Here, the quantum dots crosslinked with a hydroxyl group are connected via an ether bond, the quantum dots crosslinked with a thiol group are connected via a sulfur atom, and the quantum dots crosslinked with a carboxyl group are ester-bonded. It is tied through. A certain distance can be maintained by cross-linking the quantum dots with an organic ligand.

It is preferable to have at least one or more organic molecules between the quantum dots. Assuming that the quantum dots are aligned without gaps, the number of other quantum dots adjacent to one quantum dot is 12 in the face-centered cubic lattice and 8 in the body-centered cubic lattice. That is, it is preferable that one quantum dot has at least 8 to 12 organic ligands and is crosslinked with other quantum dots.

When there are many organic ligands composed of organic molecules, both ends of the organic molecules are strongly bonded to the quantum dot surface, so that the heat resistance is improved and the stability of electrical properties is increased. However, when the molar ratio of the inorganic ligand to the organic ligand decreases, the number of inorganic ligands covering the surface defects of the quantum dots decreases, which is not preferable.

[Inorganic ligand]
The inorganic ligand may be bound to the quantum dot surface. Carrier mobility is improved by adding an inorganic ligand to the quantum dot surface. Inorganic ligands reduce surface defects in quantum dots. The optical carriers generated in the quantum dot film can move according to the electric field without delay. Therefore, the optical carrier can be effectively taken out to the external electrode. That is, the external quantum efficiency is improved by providing the inorganic ligand.

On the other hand, it is not preferable when there are too many inorganic ligands. When there are many inorganic ligands applied in the liquid phase, the inorganic ligands can move around relatively freely on the surface of the quantum dots during heating. When the inorganic ligand on the surface of the quantum dot moves, the distance between the quantum dot and the adjacent quantum dot becomes short, the quantum dot is fused (necked), and the electrical characteristics and the like are greatly changed. For example, when there are too many halogen atoms such as iodine, heating the photoelectric conversion film to 140 ° C. or higher causes the quantum dots to fuse with each other, resulting in a portion where the size of some quantum dots increases, which is a device characteristic. Changes. As the size of the quantum dot increases, the optical absorption and the electronic state change, so that the stability of the device characteristics decreases.

Since the diameter of iodine, which is a halogen atom, is 0.28 nm, the projected area is 0.06 nm ² . Here, the quantum dots are assumed to be spheres. When the particle size (diameter) of the quantum dots is 3 nm, the surface area of the quantum dots is 28.26 nm ² .

From the surface area of the quantum dots and the projected area of iodine, the number of iodine covering the surface is 471. In the closest packing, the filling rate (fill factor) of spheres with respect to the cube is 74%, so that the number of iodines is approximately 349.

[Ratio of inorganic ligand to organic ligand]
The diameter of the benzene ring is 0.28 nm, and the projected areas of the iodine ion and the benzene ring are almost the same. Since the size of 1,3-BDT, which is an example of an organic ligand, is almost equal to the size of the benzene ring, the projected area is 0.06 nm ² . When organic ligands were provided between each of the close-packed quantum dots, the number was 8 or 12.

The molar ratio of the organic ligand to the inorganic ligand can be derived to 96.6 to 97.7% as compared with the number 349 of iodine which is an inorganic ligand covering the surface of the quantum dot. That is, the molar ratio of the inorganic ligand is 98%.

[Minimum molar ratio of inorganic ligand to total of inorganic ligand and organic ligand]
FIG. 2B is a diagram schematically showing the surface of the quantum dots. The inside of the broken line represents a part of the quantum dot. The minimum molar ratio of the inorganic ligand to the organic ligand will be described with reference to FIG.

FIG. 2B shows an inorganic ligand arranged on the surface of the quantum dot without any gap. On the other hand, FIG. 2C shows the organic ligands arranged without gaps on the surface of the quantum dots.

The thickness of one carbon atom constituting the organic ligand is about 0.08 nm, which is smaller than the halogen atom 0.26 nm, which is an inorganic ligand, so that the projected area of the organic ligand is , It can be said that it is smaller than the inorganic ligand.

It projected area when the organic ligand is upright, 0.02 nm ^2, and becomes 1/3 of the projected area 0.06 nm ² of halogen atoms.

On the quantum dot surface, it is preferable to arrange at least one halogen atom for each organic ligand for defect reduction and carrier transport. That is, it is desirable that the molar ratio of the inorganic ligand to the organic ligand is 50% or more.

FIG. 2D shows an inorganic ligand and an organic ligand arranged 1: 1 on the surface of the quantum dot. When the inorganic ligand and the organic ligand are arranged at the same molar ratio, a gap is created around the organic ligand. In order to fill this gap, it is effective to arrange a large amount of organic ligands.

FIG. 2E shows an inorganic ligand and an organic ligand arranged at a ratio of 1: 3 on the surface of the quantum dot. It is effective to arrange three times as many organic ligands as one inorganic ligand in order to arrange them without gaps. That is, a large effect can be obtained when the molar ratio of the inorganic ligand to the total of the organic ligand and the inorganic ligand is 25% or more.

[Quantum dot synthesis]
The method for producing PbS particles, which is an example of quantum dots, can be produced as follows as an example. In a three-necked flask, lead (II) oxide as a lead (Pb) precursor solution, oleic acid as an organic ligand, and octadecene as a solvent are placed. The inside of the three-necked flask is replaced with nitrogen, and the Pb precursor solution is heated to 90 ° C. in an oil bath to react lead oxide with oleic acid. After that, it is heated to 120 ° C. to generate and grow PbS quantum dots. An octadecene solution of bistrimethylsilyl sulfide is separately prepared as a sulfur (S) precursor solution. The S precursor solution is rapidly injected into the Pb precursor solution heated to 120 ° C. and reacted. After completion of the reaction, the mixture is naturally cooled to room temperature, methanol or acetone is added as a polar solvent, and centrifugation is performed to precipitate PbS particles. After removing the supernatant, washing is performed by adding toluene to redisperse the PbS particles. By repeating this centrifugation and redispersion process multiple times, excess oleic acid and unreacted substances are removed, and finally a solvent such as octane is added to obtain a quantum dot dispersion liquid in which quantum dots are dispersed. Can be done.

A halogen-inorganic ligand containing a halogen atom can be added to PbS particles, which is an example of quantum dots, by using the method described in Non-Patent Document 1. Specifically, as the halogen ligand, tetrabutylammonium iodide C ₁₆ H ₃₆ NI: TBAI is used. The S precursor solution was rapidly injected into the Pb precursor solution heated to 120 ° C. and reacted, and then the precursor solution prepared using the halogen ligand TBAI was added. By adjusting the reaction temperature and the amount of the halogen ligand added, the ratio of oleic acid to the halogen atom can be adjusted.

The addition of the inorganic ligand may be carried out in the liquid phase, and the addition of the organic ligand may be carried out in the solid phase.

[Organic ligand with long molecular chain length]
It is a ligand composed of an organic compound. The organic ligand may be composed of an organic compound having a boiling point of 200 ° C. or higher. The ligand contained in the quantum dot dispersion liquid acts as a ligand for coordinating the quantum dots and has a molecular structure that easily causes steric hindrance. Therefore, as a dispersant for dispersing the quantum dots in a solvent. It also plays a role. The ligand includes a ligand having a longer molecular chain length and a ligand having a shorter molecular chain length. Here, the length of the molecular chain is determined by the length of the main chain when there is a branched structure in the molecule. A ligand having a short molecular chain length is difficult to disperse in an organic solvent system in the first place. Here, the dispersion means that there is no sedimentation or turbidity of the particles. A ligand having a long molecular chain length is preferably a ligand having at least 6 or more carbon atoms in the main chain from the viewpoint of improving the dispersion of quantum dots, and is coordinated with 10 or more carbon atoms in the main chain. It is more preferable to be a child. Specifically, it may be either a saturated compound or an unsaturated compound, and may be decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, erucic acid, oleylamine, dodecylamine, dodecanothiol, 1, , 2-Hexadecanthiol, trioctylphosphine oxide, cetrimonium bromide and the like. The ligand having a long molecular chain length is preferably one that does not easily remain in the photoelectric conversion film when the photoelectric conversion film is formed, and from the viewpoint that the quantum dots have dispersion stability and do not easily remain in the photoelectric conversion film. Of these, at least one of oleic acid and oleylamine is preferable.

The quantum dot solvent contained in the quantum dot dispersion liquid is not particularly limited, but is preferably a solvent that is difficult to dissolve quantum dots and easily dissolves a ligand having a long molecular chain length. The quantum dot solvent is preferably an organic solvent, and specific examples thereof include alkanes [n-hexane, n-octane, etc.], benzene, toluene, and the like.

[Organic ligand with relatively short molecular chain length]
It is a ligand composed of an organic compound. The organic ligand may be composed of an organic compound having a boiling point of 200 ° C. or higher. Organic ligands with a relatively short molecular chain length have shorter molecular chain lengths than ligands with a long molecular chain length, and ethanedithiol, benzenedithiol, dibenzenedithiol, It is at least one ligand selected from ligands such as mercaptobenzoic acid, dicarboxybenzene, benzenediamine and organic compounds containing dibenzenediamine. More specifically, it may be selected from 1,3-benzenedithiol, 1,4-benzenedithiol, 3-mercaptobenzoic acid, and 4-mercaptobenzoic acid. In particular, it is preferable because the boiling point of a ligand such as benzenedithiol containing a benzene ring exceeds 200 ° C. Since the evaporation of the ligand is suppressed even at a high temperature of 140 ° C. or higher, the heat resistance as a quantum dot film is high. The ligand solvent contained in the ligand solution is not particularly limited, but an organic solvent having a high dielectric constant is preferable, and ethanol, acetone, methanol, acetonitrile, dimethylformamide, dimethyl sulfoxide, butanol, propanol and the like are particularly preferable.

[Inorganic ligand]
It is a ligand composed of an inorganic compound. Preferably, it contains a halogen atom. As the inorganic ligand containing a halogen atom, lead fluoride PbF, lead chloride (II) PbCl _2, lead iodide (II) PbI _2, is selected from ligands such as lead bromide (II) PbBr _2, At least one type of ligand. By containing a large amount of inorganic ligands made of halogen-based inorganic materials, the surface of the quantum dots can be sufficiently covered. Since halogen atoms have a small particle size, more surface defects can be sealed.

[Photoelectric conversion element]
FIG. 1 is an example of a schematic cross-sectional view of a photoelectric conversion element according to an embodiment of the present invention. A first electrode layer 2, a first interface layer 3, a photoelectric conversion layer 4, a second interface layer 5, and a second electrode 6 are provided on the substrate 1. The first electrode and the second electrode may be collectively referred to as a pair of electrodes.

The photoelectric conversion element according to the embodiment of the present invention is an element having a photoelectric conversion layer arranged between the first electrode, the second electrode, and the first electrode and the second electrode. The photoelectric conversion layer is a layer that converts the received light into electric charges. The converted charge is polarized and collected on one of a pair of electrodes. The photoelectric conversion layer may have a configuration in which an electric field is applied from the first electrode and the second electrode. The pair of electrodes are an electrode that collects holes and an electrode that collects electrons. The electrode that collects holes is also called the positive electrode or cathode. Electrodes that collect electrons are also called negative electrodes or anodes. At least one of the pair of electrodes may be transparent.

The photoelectric conversion element may be provided with an interface layer between the photoelectric conversion layer and at least one of the pair of electrodes. The interface layer is an electron block layer which is a layer which reduces the movement of electrons from the photoelectric conversion layer to the cathode, or a hole block layer which is a layer which reduces the movement of holes from the photoelectric conversion layer to the anode. You can.

[Photoelectric conversion layer]
A photoelectric conversion layer can be formed by applying quantum dots on an electrode, a substrate, or the like. The method for producing a photoelectric conversion layer including an aggregate of nanoparticles as quantum dots is not particularly limited. When the quantum dots are dispersed in a solvent in a state of being modified with a ligand having a long molecular chain length such as oleic acid, the quantum dots are unlikely to form an aggregated bulk. The method of applying the quantum dot dispersion liquid on the substrate is not particularly limited, and examples thereof include a method of applying the quantum dot dispersion liquid on the substrate and a method of immersing the substrate in the quantum dot dispersion liquid. More specifically, the method of applying the quantum dot dispersion liquid on the substrate includes a spin coating method, a cat method, a dip coating method, a blade coating method, a spray coating method, an inkjet method, a dispenser method, a screen printing method, and a letterpress. A liquid phase method such as a printing method or an intaglio printing method can be used. In particular, the inkjet method, the dispenser method, the screen printing method, the letterpress printing method, and the intaglio printing method can pattern the coating film at an arbitrary position on the substrate.

After the quantum dot dispersion liquid is applied onto the substrate, the ligand is exchanged by further applying the ligand solution on the substrate, whereby the photoelectric conversion layer can be formed. By applying the quantum dot dispersion liquid on the substrate, the aggregate of quantum dots has a structure in which each quantum dot is arranged. After forming an aggregate of quantum dots, the distance between the quantum dots can be shortened by exchanging the ligand with an organic ligand having a relatively short molecular chain length. However, if the inter-dot distance (interval) of the quantum dots is large, the electrical conductivity may decrease. By reducing the spacing, it becomes possible to arrange the quantum dots precisely. Further, by reducing the interval, the electrical conductivity is improved, and a photoelectric conversion film having a large photocurrent can be obtained. However, the shorter the interval, the easier it is for the quantum dots to fuse with each other (called necking), so a certain distance may be provided. When the quantum dots are fused together, the size of the quantum dots becomes large and the band gap becomes small. Therefore, the resistance value becomes low and the dark current increases remarkably.

By repeatedly forming the quantum dot aggregate and exchanging the ligand, the occurrence of cracks and cracks in the photoelectric conversion film having the quantum dot aggregate is suppressed, the electric conductivity is increased, and the thickness of the photoelectric conversion film is increased. Can be thickened. A cleaning step may be provided to remove excess ligands and ligands desorbed from the quantum dots, residual solvents, other impurities, and the like. Specifically, a substrate on which a quantum dot aggregate or a photoelectric conversion layer is formed is coated or immersed in at least one of a quantum dot solvent and a ligand solvent.

The formation of the photoelectric conversion layer may include a dispersion liquid drying step of drying the quantum dot dispersion liquid, a solution drying step of drying the ligand solution, and the like. In drying, after forming a quantum dot aggregate as a photoelectric conversion film, the solvent remaining in the quantum dot aggregate is heated to a temperature at which it is dried. In addition, after the ligand exchange step, the ligand solution is heated to a solution drying temperature for drying. Alternatively, it may be left at room temperature. Even in a nitrogen atmosphere, it is more preferable to heat in an environment containing a small amount of oxygen. Specifically, the surface of the quantum dots is oxidized by heating in an environment containing 1% or less of oxygen. In addition, the surface of the quantum dots is oxidized even when heated with a small amount of water remaining on the outermost surface of the photoelectric conversion film. Furthermore, it is also a preferable means for the surface to be oxidized that the quantum dot dispersion liquid or the ligand solution contains a small amount of water. The concentration of oxygen generated by surface oxidation may be 0.1 ppm or more.

The surface of the quantum dot is the outermost surface of the semiconductor material, and the bond that is not bonded to the ligand becomes a dangling bond (unbonded in the atom), which causes carrier traps that affect electrical conductivity. Form a defect level. By oxidizing the surface of the quantum dot, the unbonded hands on the surface can be sealed and the defect level can be reduced. By reducing the defect level, the dark current can be reduced, the photocurrent density can be improved, and the light sensitivity can be improved.

However, if the surface oxidation of the quantum dots progresses too much, the particle size of the nanoparticles that contribute to the quantum confinement effect as quantum dots becomes smaller. When the particle size of the nanoparticles becomes smaller, the electrical conductivity changes, and in particular, the spectral spectrum of the light sensitivity shifts to the short wavelength side, which affects the light sensitivity.

The thickness of the photoelectric conversion layer is not particularly limited, but is preferably 10 nm or more, more preferably 50 nm or more, from the viewpoint of obtaining high electrical conductivity. Further, the thickness of the photoelectric conversion layer is preferably 600 nm or less from the viewpoint of the possibility that the carrier concentration becomes excessive and the ease of manufacture.

Further, by preferentially covering the surface of the nanoparticles constituting the quantum dot film with the inorganic ligand, it is possible to reduce the surface defects of the quantum dots that cannot be completely covered by the organic ligand alone. By reducing the surface defects of the nanoparticles, it is possible to suppress an increase in dark current and a decrease in photocurrent, and to realize a photodetector with high photosensitivity.

It can have high heat resistance by being composed of a ligand having a boiling point of 200 ° C. or higher.

Further, the plurality of nanoparticles are composed of a nucleus and a surface layer, and the surface layer of the nanoparticles is composed of a material composed of an oxide layer containing halogen and an organic layer containing organic substances. It is a photodetection element characterized by. By having an oxide layer containing an organic substance and a halogen, it is possible to suppress the surface oxidation of nanoparticles by capturing oxygen molecules that have entered from the outside of the device and oxidizing them by themselves.

The quantum dot film contains at least one of an oxidized benzene ring, an oxidized hydrocarbon, and an oxidized organic substance. The organic ligand captures oxygen molecules and becomes an oxidized benzene ring or an oxidized hydrocarbon, which has the effect of nullifying the hopping site of the carrier composed of the benzene ring and suppressing the dark current.

Further, the plurality of nanoparticles are photodetectors selected from PbS and PbSe containing lead. By configuring it with PbS or PbSe containing lead, it is possible to realize a photodetector having photosensitivity even in the infrared region.

Electronic devices such as photoelectric conversion elements, light emitting diodes, light detection elements, light receiving element arrays, image sensors, image sensors, and image pickup devices are put into practical use by being solder-mounted on a printed circuit board or the like. In the solder mounting process, a heating process of about 200 ° C. is used. In addition, electronic devices such as image sensors, image sensors, and image pickup devices are housed in a package made of resin or ceramic, and are glass-sealed for water resistance and dust resistance. As a package mounting process, after being fixed with an adhesive, it is electrically connected to the package take-out wiring by wire bonding with a fine gold wire or the like. A heating process of at least 145 ° C. or higher is used for adhesive curing and wire bonding.

Furthermore, when used as an image sensor, an image sensor, or an image pickup device in the visible light region, a color filter capable of RGB spectroscopy and a microlens for condensing are used. Color filters and microlenses are often composed of resin, and a heating process of at least 150 ° C. or higher is used for resin curing. Quantum dot materials for use as image sensors, image sensors, and image pickup devices are required to have heat resistance to withstand the temperatures of the heating processes of the above-mentioned mounting process, color filter process, and microlens process.

Therefore, by providing a ligand having a high boiling point, quantum dots having excellent heat resistance can be formed, and the quantum dots having excellent heat resistance can be used in various devices.

[Interfacial layer]
An upper interface layer and a lower interface layer may be provided between the photoelectric conversion layer and the electrodes (upper electrode layer, base electrode layer) in order to improve the electrical characteristics. The electrode that collects holes (positive electrode) is a layer that blocks electrons and conducts only holes (electron block layer), and the electrode that collects electrons (negative electrode) is a layer that blocks holes and conducts electrons. A layer that conducts only (hole block layer) may be formed.

As the material of the electron block layer, a material capable of efficiently transporting holes generated in the photoelectric conversion layer to the positive electrode is preferable. For that purpose, the positive electrode interface layer material has high hole mobility, high conductivity, a small hole injection barrier with the positive electrode, and hole injection from the photoelectric conversion layer to the p-type semiconductor layer. It is preferable that the barrier is small and the like. Further, when light is taken into the photoelectric conversion layer through the electron block interface layer, it is preferable to use a highly transparent material as the material of the electron block interface layer. Normally, visible light is taken into the photoelectric conversion layer, so that as a transparent electron block interface layer material, the transmitted visible light has a transmittance of usually 60% or more, especially 80% or more. Is preferably used. From this point of view, suitable examples of the electron block interface layer material include p-type semiconductor materials such as inorganic semiconductors such as molybdenum oxide MoO ₃ and nickel oxide NiO.

On the other hand, the function required of the hole block layer is to block holes separated from the photoelectric conversion layer and transport electrons to the negative electrode. Therefore, in the above description of the hole block interface layer, the positive electrode is used as the negative electrode and p. The type semiconductor is replaced with an n-type semiconductor, and the holes are replaced with electrons. Further, it is conceivable to irradiate light from the negative electrode side or effectively use the light reflected from the negative electrode side, and in that case, the transmittance needs to be high. From this point of view, a suitable example of the hole block interface layer material is an n-type semiconductor material selected from an inorganic semiconductor such as titanium oxide TiO ₂ or an organic semiconductor such as a fullerene or a fullerene derivative.

[electrode]
The electrodes may be a pair of electrodes such as an upper electrode layer and a base electrode layer, a first electrode and a second electrode. The electrode can be formed of any conductive material. Examples of electrode constituent materials include metals such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, magnesium, calcium, barium, and sodium, or alloys thereof, and metal oxidation such as indium oxide and tin oxide. A conductive composite in which a substance or a composite oxide thereof (for example, ITO, IZO), a conductive polymer such as polyacetylene, metal particles, and conductive particles such as carbon black, fullerene, and carbon nanotubes are dispersed in a matrix such as a polymer binder. Materials and the like can be mentioned. As the constituent material of the electrode, one type may be used alone, or two or more types may be used in any combination and ratio.

The electrode has a function of collecting electrons and holes generated inside the photoelectric conversion layer. Therefore, as the constituent material of the electrode, it is preferable to use a constituent material suitable for collecting electrons and holes among the above-mentioned materials. Examples of the electrode material suitable for collecting holes include materials having a high work function such as Au and ITO. On the other hand, as an electrode material suitable for collecting electrons, for example, a material having a low work function such as Al can be mentioned. The thickness of the electrode is not particularly limited, and may be appropriately determined in consideration of the electrode material, conductivity, transparency, etc., and may be 10 nm or more and 100 μm or less.

[substrate]
The quantum dot dispersion liquid is applied onto the substrate. The shape, structure, size, etc. of the substrate are not particularly limited, and are appropriately selected according to the purpose. The structure of the substrate may be a single layer structure or a laminated structure. As the substrate, for example, a substrate made of an inorganic material such as glass, silicon, or stainless steel, a resin, or a resin composite material can be used. In the case of a silicon substrate, an integrated circuit may be formed. Further, a lower electrode, an insulating film, or the like may be provided on the substrate, and in that case, the quantum dot dispersion liquid is applied on the lower electrode on the substrate or the underlying insulating film.

When a wiring layer is formed on a substrate such as silicon, the substrate is referred to as a substrate including the wiring layer. When there is an interlayer insulating layer in contact with the electrode of the photoelectric conversion element, the interlayer insulating layer is also called a substrate.

[Application example of photoelectric conversion element]
The photoelectric conversion element according to the embodiment of the present invention may be used as a light receiving element. The light receiving element includes a photoelectric conversion element, a readout circuit that reads out the electric charge from the photoelectric conversion element, and a signal processing circuit that receives the electric charge from the readout circuit and processes the signal.

The photoelectric conversion element according to the embodiment of the present invention may be used in a photoelectric conversion device. The photoelectric conversion device is a light receiving element having an optical system having a plurality of lenses and a light receiving element for receiving light transmitted through the optical system, and the light receiving element has a photoelectric conversion element. Specifically, the photoelectric conversion device may be a digital still camera or a digital video camera.

FIG. 6 is a diagram showing an example of an imaging system using a photoelectric conversion element according to an embodiment of the present invention. As shown in FIG. 6, the imaging system 500 includes a photoelectric conversion device 100, an imaging optical system 502, a CPU 510, a lens control unit 512, an imaging device control unit 514, an image processing unit 516, an aperture shutter control unit 518, and a display unit 520. It includes an operation switch 522 and a recording medium 524.

The imaging optical system 502 is an optical system for forming an optical image of a subject, and includes a lens group, an aperture 504, and the like. The aperture 504 has a function of adjusting the amount of light at the time of shooting by adjusting the aperture diameter thereof, and also has a function of a shutter for adjusting the exposure seconds at the time of shooting a still image. The lens group and the aperture 504 are held so as to be able to move forward and backward along the optical axis direction, and a scaling function (zoom function) and a focus adjustment function are realized by these interlocking operations. The imaging optical system 502 may be integrated with the imaging system, or may be an imaging lens that can be attached to the imaging system.

In the image space of the image pickup optical system 502, the photoelectric conversion device 100 is arranged so that the image pickup surface thereof is located. The photoelectric conversion device 100 is a photoelectric conversion device according to an embodiment of the present invention, and includes a CMOS sensor (pixel unit) and a peripheral circuit (peripheral circuit region) thereof. The photoelectric conversion device 100 constitutes a two-dimensional single plate color sensor by arranging pixels having a plurality of photoelectric conversion units in two dimensions and arranging color filters for these pixels. The photoelectric conversion device 100 photoelectrically converts the subject image formed by the imaging optical system 502 and outputs it as an image signal or a focus detection signal.

The lens control unit 512 is for controlling the advance / retreat drive of the lens group of the image pickup optical system 502 to perform magnification change operation and focus adjustment, and is composed of a circuit and a processing device configured to realize the functions. Has been done. The aperture shutter control unit 518 is for adjusting the amount of shooting light by changing the aperture diameter of the aperture 504 (with a variable aperture value), and is composed of a circuit or a processing device configured to realize the function. Will be done.

The CPU 510 is a control device in the camera that controls various controls of the camera body, and includes a calculation unit, a ROM, a RAM, an A / D converter, a D / A converter, a communication interface circuit, and the like. The CPU 510 controls the operation of each part in the camera according to a computer program stored in a ROM or the like, and performs a series of shooting such as AF, imaging, image processing, recording, etc. including detection of the focal state of the imaging optical system 502 (focus detection). Perform the action. The CPU 510 is also a signal processing unit.

The image pickup device control unit 514 is for controlling the operation of the photoelectric conversion device 100, A / D converting the signal output from the photoelectric conversion device 100, and transmitting the signal to the CPU 510, so as to realize these functions. It is composed of circuits and control devices configured in. The photoelectric conversion device 100 may have the A / D conversion function. The image processing unit 516 is for generating an image signal by performing image processing such as γ conversion and color interpolation on the A / D converted signal, and is a circuit configured to realize the function. And control device. The display unit 520 is a display device such as a liquid crystal display (LCD), and displays information on a shooting mode of the camera, a preview image before shooting, a confirmation image after shooting, a focusing state at the time of focus detection, and the like. The operation switch 522 is composed of a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. The recording medium 524 is for recording a captured image or the like, and may be a built-in image pickup system or a removable memory card or the like.

In this way, a high-performance imaging system can be realized by configuring the imaging system 500 to which the photoelectric conversion device 100 according to the embodiment according to the embodiment of the present invention is applied.

The photoelectric conversion device according to one embodiment of the present invention may be used for a moving body. The moving body includes an airframe provided with a photoelectric conversion device and a moving means for moving the airframe. Specific examples include automobiles, aircraft, ships, and drones. By providing the moving body, the surrounding situation may be imaged to support the operation of the moving body. The airframe can be made of metal or carbon fiber. Polycarbonate or the like may be used as the carbon fiber. Examples of the means of transportation include tires, magnetic floating, and a mechanism for vaporizing and injecting fuel.

7A and 7B are diagrams showing the configuration of the imaging system and the moving body according to the present embodiment.

FIG. 7A shows an example of an imaging system 400 relating to an in-vehicle camera. The imaging system 400 includes a photoelectric conversion device 410. The photoelectric conversion device 410 is any of the photoelectric conversion devices described in the first to fourth embodiments described above. The image pickup system 400 has an image processing unit 412, which is a processing device that performs image processing on a plurality of image data acquired by the photoelectric conversion device 410, and a parallax (parallax) from the plurality of image data acquired by the photoelectric conversion device 410. It has a parallax acquisition unit 414, which is a processing device for calculating the phase difference of an image). Further, the imaging system 400 determines whether or not there is a possibility of collision with the distance acquisition unit 416, which is a processing device that calculates the distance to the object based on the calculated parallax, based on the calculated distance. It has a collision determination unit 418, which is a processing device. Here, the parallax acquisition unit 414 and the distance acquisition unit 416 are examples of information acquisition means for acquiring information such as distance information to an object. That is, the distance information is information on parallax, defocus amount, distance to an object, and the like. The collision determination unit 418 may determine the possibility of collision by using any of these distance information. The various processing devices described above may be realized by specially designed hardware, or may be realized by general-purpose hardware that performs operations based on software modules. Further, the processing device may be realized by FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated Circuit), or the like, or may be realized by a combination thereof.

The image pickup system 400 is connected to the vehicle information acquisition device 420, and can acquire vehicle information such as vehicle speed, yaw rate, and steering angle. Further, the imaging system 400 is connected to a control ECU 430 which is a control device that outputs a control signal for generating a braking force to the vehicle based on the determination result of the collision determination unit 418. That is, the control ECU 430 is an example of the moving body control means that controls the moving body based on the distance information. The imaging system 400 is also connected to an alarm device 440 that issues an alarm to the driver based on the determination result of the collision determination unit 418. For example, when there is a high possibility of a collision as a result of the collision determination unit 418, the control ECU 430 controls the vehicle to avoid the collision and reduce the damage by applying the brake, returning the accelerator, suppressing the engine output, and the like. The alarm device 440 warns the user by sounding an alarm such as a sound, displaying alarm information on the screen of a car navigation system or the like, or giving vibration to the seat belt or steering wheel.

In the present embodiment, the periphery of the vehicle, for example, the front or the rear, is imaged by the image pickup system 400. FIG. 7B shows an imaging system 400 for imaging the front of the vehicle (imaging range 450). The vehicle information acquisition device 420 sends an instruction to operate the imaging system 400 to perform imaging. By using the photoelectric conversion device of the first to fourth embodiments described above as the photoelectric conversion device 410, the imaging system 400 of the present embodiment can further improve the accuracy of distance measurement.

In the above explanation, an example of controlling so as not to collide with another vehicle has been described, but it can also be applied to control for automatically driving following other vehicles, control for automatically driving so as not to go out of the lane, and the like. is there. Further, the imaging system is not limited to vehicles such as automobiles, and can be applied to moving bodies (transport equipment) such as ships, aircraft, and industrial robots, for example. A moving device in a moving body (transportation device) is various means of moving such as an engine, a motor, wheels, and a propeller. In addition, it can be applied not only to moving objects but also to devices that widely use object recognition, such as intelligent transportation systems (ITS).

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.

[Example 1 and Comparative Example 1]
In this example, the photoelectric conversion element shown in FIG. 1 was manufactured as follows. A substrate 1 whose surface on the first electrode side was insulated with a silicon oxide film was prepared, and a TiN film was formed as the first electrode 2 and a titanium oxide TiO2 film was formed as the first interface layer 3 by a sputtering method. A pre-prepared PbS quantum dot dispersion is applied onto the first interface layer 3 by a spin coating method, and then a ligand containing an organic ligand benzenedithiol (1,4-BDT) having a short molecular chain length is applied. The solution was applied in the same manner to form the photoelectric conversion layer 4. That is, the addition of the inorganic ligand was performed in advance in the liquid phase, and the application of the organic ligand was performed in the solid phase. The produced photoelectric conversion layer 4 was left to dry overnight in a glove box under a nitrogen atmosphere (oxygen concentration 1 ppm or less, water concentration 1 ppm or less). Molybdenum oxide MoO ₃ was formed as the second interface layer 5 on the photoelectric conversion layer 4 by a vacuum vapor deposition method. Indium tin oxide containing tin, which is a transparent conductive film, was formed on the second interface layer 5 by a sputtering method as the second electrode 6.

In Example 1, in the above step, when preparing the PbS quantum dot dispersion, the conditions for adding the inorganic ligand are adjusted, and the molar ratio of the inorganic ligand is compared with the molar ratio of the organic ligand. Quantum dots prepared to be large were used. The element manufactured in Example 1 is referred to as a photoelectric conversion element 1.

On the other hand, in Comparative Example 1, quantum dots prepared so that the molar ratio of the inorganic ligand was smaller than the molar ratio of the organic ligand were used. The element manufactured in Comparative Example 1 is referred to as a photoelectric conversion element 2.

The ratio measurement of the halogen atom and the organic ligand on the surface of the quantum dot was measured using TOF-SIMS analysis. Specifically, the TOF-SIMS analyzer uses PHI nano TOF II manufactured by ULVAC-PHI, and evaluates Bi ₃ ^{++ as} the primary ion, the primary ion acceleration voltage is 30 kV, and the secondary ion polarity is positive and negative. did.

FIG. 3 shows the results of TOF-SIMS analysis of the surface of the quantum dots used in the photoelectric conversion element 1.

In the photoelectric conversion element 1, the iodine ion I ⁻ was 6.2 and the organic compound ion C ₆ H ₄ S ₂ ⁻ was 1.8. That is, the molar ratio of the inorganic ligand is estimated to be 77.5%. The intensity of the peaks, the maximum peak among the peaks due to the inorganic particles, i.e., the peak of iodine ions, peak due to the organic compound ions, i.e., C ₆ H ₄ S ₂ ^- were more than three times.

The photoelectric conversion element 2 had an iodine ion I ⁻ of 1.6 and an organic compound ion C ₆ H ₄ S ₂ ⁻ of 6.0. That is, the molar ratio of the inorganic ligand is estimated to be 21.1%.

[Electrical characteristics]
The electrical conductivity of the photoelectric conversion element was evaluated by using a semiconductor parameter analyzer for the produced photoelectric conversion element. First, the voltage applied to the electrode was swept between −5 and 5V without irradiating the photoelectric conversion element with light, and the IV characteristic in a dark state was acquired. The current value with a + 2V bias applied was adopted as the dark current value Id.

The value of the photocurrent in the state where the photoelectric conversion element was irradiated with monochrome light (irradiation intensity 5 μW / cm ² ) was evaluated. The wavelength of the monochrome light was measured by changing the wavelength between 300 nm and 1200 nm in 5 nm increments. The increase in current from the dark current when irradiating light having a wavelength of 600 nm was defined as the photocurrent Ip. In order to examine the heat resistance of the photoelectric conversion element, after the photoelectric conversion element was completed, it was heated at 150 ° C. for 1 hour in the atmosphere. Table 1 shows the initial values of the photoelectric conversion element after completion and the values in the state of being heated in the atmosphere. High external quantum efficiency was obtained in the photoelectric conversion element 1, and no significant change was observed even after heating in the atmosphere.

This is because the photoelectric conversion element 1 has a molar ratio of the inorganic ligand larger than the molar ratio of the organic ligand on the surface of the quantum dot, so that the defect on the surface of the quantum dot is sufficiently covered by the inorganic ligand. By sufficiently sealing the surface defects of the quantum dots with iodine I, which is a halogen atom, the photocurrent density due to the surface defects of the quantum dots is improved, and a photoelectric conversion element having high photosensitivity can be realized.

[Example 2 and Comparative Example 2]
In Example 2, a photoelectric conversion element was produced in the same manner as in Example 1 except that a drying step was provided after the photoelectric conversion layer was formed. As a drying step after forming the photoelectric conversion film 4, the temperature at which the solvent remaining in the quantum dot aggregate is dried, or the solution drying temperature at which the ligand solution is dried after the ligand exchange step is 150 ° C. It was heated for 30 minutes. The heating was carried out in a nitrogen atmosphere containing oxygen. Specifically, the drying step was carried out in an environment where the oxygen concentration in the glove box was 0.1 ppm or more and 1% or less. The surface of the quantum dot is the outermost surface of the semiconductor material, and the bond that is not bonded to the ligand is the unbonded bond (dangling bond). The unbonded hands form defect levels that cause carrier traps that affect the electrical conductivity of the photoelectric conversion film, but seal the unbonded hands by slightly oxidizing the surface of the quantum dots. It is possible to reduce the defect level.

For the measurement of the oxidation state of the quantum dot surface, the same TOF-SIMS analysis as in Example 1 was used. FIG. 4 shows the results of TOF-SIMS analysis (positive secondary ions). The quantum dot surface, with _Pb 3 SI ⁺ that contains iodine _I, Pb 3 SOI ⁺ and _Pb 4 SOI ⁺ is contained at the same time. Iodine I is contained in the oxidized portion of the surface of the PbS nanoparticles constituting the quantum dot, so that the halogen repairs the surface defects remaining even after oxidation. The ratios of Pb ₃ SI ⁺ and Pb ₃ SOI ⁺ were 2.0 and 0.7. FIG. 5 shows the results of TOF-SIMS analysis (negative secondary ions). The surface of the quantum dot contains benzene rings such as PbC ₆ H ₄ SI ⁻ and PbC ₆ H ₃ S ₂ O ₃ ⁻ at the same time as PbSI ⁻ containing iodine I.

In addition, as peaks not shown, C ₆ H ₄ S ₂ O ⁻ , C ₆ H ₄ S ₂ O ₃ ⁻ , and C ₆ H ₄ S ₂ O ₄ ⁻ are included in large numbers. These peak groups are derived from the organic ligands 1,4-BDT, indicating that some of the thiol groups have been oxidized. Since this oxidation is due to oxygen derived from the external environment, 1,4-BDT acts as an oxidation sacrifice to capture oxygen and plays a role in reducing the oxidation of the surface of nanoparticles, which are the core of quantum dots. There is. Further, since the benzene ring acts as a hopping site for transferring carriers, the dark current can be reduced by oxidizing the benzene ring.

It should be noted that each of the above embodiments is merely an example of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. .. That is, the present invention can be implemented in various forms without departing from the technical idea or its main features.

1 Substrate 2 First electrode 3 First interface layer 4 Photoelectric conversion layer 5 Second interface layer 6 Second electrode 7 Quantum dots 8 Organic ligand 9 Inorganic ligand

Claims (20)

Quantum dots with inorganic particles
The quantum dot has an organic ligand and an inorganic ligand on its surface.
A quantum dot having a molar ratio of the inorganic ligand to the total of the inorganic ligand and the organic ligand of 25% or more and 99.8% or less. The quantum dot according to claim 1, wherein the molar ratio of the inorganic ligand to the total of the inorganic ligand and the organic ligand is 25% or more and 98% or less. The quantum dot according to claim 1, wherein the molar ratio of the inorganic ligand to the total of the inorganic ligand and the organic ligand is 75% or more. Quantum dots with inorganic particles
The quantum dot has an organic ligand and an inorganic ligand on its surface.
Based on the peak intensity of the inorganic particles, the height of the maximum peak of TOF-SIMS caused by the inorganic ligand is three times or more the height of the maximum peak of TOF-SIMS caused by the organic ligand. A quantum dot characterized by being. The quantum dot according to any one of claims 1 to 4, wherein the inorganic ligand has a halogen atom. The quantum dot according to any one of claims 1 to 5, wherein the organic ligand has at least two crosslinked structures. The quantum dot according to claim 6, wherein the crosslinked structure is selected from a thiol group and a hydroxyl group. Any one of claims 1 to 7, wherein the organic ligand is selected from 1,3-benzenedithiol, 1,4-benzenedithiol, 3-mercaptobenzoic acid, and 4-mercaptobenzoic acid. Quantum dots described in. The quantum dot according to any one of claims 1 to 8, wherein the inorganic particle is a particle having Pb. A photoelectric conversion element having a first electrode, a second electrode, and a photoelectric conversion layer arranged between the first electrode and the second electrode.
The photoelectric conversion layer is a photoelectric conversion element having the quantum dots according to any one of claims 1 to 9. The photoelectric conversion layer has at least a first quantum dot and a second quantum dot, and the first quantum dot and the second quantum dot are bridged by the organic ligand. 10. The photoelectric conversion element according to claim 10. The photoelectric conversion element according to claim 10 or 11, wherein a plurality of layers are laminated in the photoelectric conversion layer, and at least one of the plurality of layers has the quantum dots. It is characterized by having the photoelectric conversion element according to any one of claims 10 to 12, a readout circuit that reads out charges from the photoelectric conversion element, and a signal processing circuit that receives charges from the readout circuit and processes signals. Light receiving element. A photoelectric conversion device comprising an optical system having a plurality of lenses and a light receiving element that receives light transmitted through the optical system, and the light receiving element is the light receiving element according to claim 12. A moving body having a machine body provided with the photoelectric conversion device according to claim 14 and a moving means for moving the machine body. A method for producing quantum dots having inorganic particles and having an organic ligand and an inorganic ligand on the surface.
A method for producing quantum dots, which comprises imparting the inorganic ligand and the organic ligand so that the molar ratio of the inorganic ligand is larger than the molar ratio of the organic ligand. 16. The claim 16 is characterized in that the amount of the inorganic ligand added to the total of the amount of the inorganic ligand added and the amount of the organic ligand added is 25% or more and 99.8% or less. The method for manufacturing a quantum dot described. The method for producing quantum dots according to claim 16 or 17, wherein the application of the inorganic ligand is performed in a liquid phase, and the application of the organic ligand is performed in a solid phase. A photoelectric conversion layer is formed by applying a quantum dot produced by the method for producing a quantum dot according to any one of claims 16 to 18 on the first electrode and the step of preparing the first electrode. A method for manufacturing a photoelectric conversion element, which comprises a step of forming and a step of forming a second electrode on the photoelectric conversion layer. The method for manufacturing a photoelectric conversion element according to claim 19, further comprising an oxidation step of oxidizing the surface of the quantum dots.

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