Nanocomposite having quantum dots and method for manufacturing the same

Abstract

This invention provides a method for producing nanocomposites having novel quantum dots that differ from conventional methods. [Solution] A method for manufacturing a nanocomposite having quantum dots, characterized in that a nanocomposite consisting of nanoparticles that are the core of the nanocomposite and quantum dots attached to the surface of the nanoparticles is deposited or supported on the linear conductors, using a gap between a plurality of linear conductors arranged at intervals of 1 nm to 100 μm as a reaction field, and the nanocomposite is synthesized such that a plurality of the nanocomposites exist in a state of being dispersed or aggregated and adsorbed or bonded to one another.

Description

Technical Field

[0001] The present invention relates to a nanocomposite having quantum dots and a method for producing the same.

Background Art

[0002] Quantum dots can control the band gap energy by changing their size and can change the wavelength of light absorption and emission. Therefore, by utilizing their unique electrical properties, applications in quantum dot solar cells, quantum dot lasers, single-electron transistors, quantum teleportation, quantum computers, terahertz information communication, medicine, agriculture, and forestry are expected.

[0003] Quantum dots are inorganic nanoparticles with a particle size of about 20 nm or less, and exhibit physical properties different from those of the bulk due to the manifestation of the quantum size effect. By confining electrons in quantum dots, the conversion efficiency can be increased by effectively utilizing light with wavelengths that could not be absorbed by conventional solar cells or high-energy light due to the quantum size effect.

[0004] Since general silicon solar cells use ultra-high purity silicon, significant cost reduction cannot be expected. Therefore, solar cells manufactured by a "wet process" such as a coating process are expected as next-generation low-cost solar cells. It is expected to effectively utilize the energy that is lost as heat loss in conventional solar cells (hot carrier effect, multi-exciton generation effect).

[0005] As a next-generation solar cell that can be manufactured by a "wet process", there is a quantum dot solar cell. Quantum dot solar cells have the potential to achieve a conversion efficiency of 63%, which is twice that of conventional silicon types, in terms of theoretical efficiency, and are awaited for commercialization as third-generation solar cells.

[0006] The strengths of quantum dot solar cells lie in their ability to absorb light across a wide range of wavelengths that were previously unusable, and in their ability to generate excitons (electron-hole pairs in a high-energy state) before they are lost as high photothermal energy. Both of these solve the bottlenecks of conventional solar cells, and the key to utilizing high-energy light is the emergence of multiple exciton generation (MEG), which allows for the extraction of multiple excitons, whereas normally only one exciton can be extracted per photon.

[0007] Quantum dot solar cells create a band at a specific energy position in the solar cell by encapsulating electrons within quantum dots and stacking them three-dimensionally using a method called "intermediate bands," allowing for the efficient absorption of light at wavelengths that would not normally be absorbed. Furthermore, as the particle size of the quantum dots decreases, the band gap energy increases (the absorption wavelength becomes shorter), and it has been reported that lead sulfide (PbS) quantum dots with a particle size of approximately 3 nm and a band gap energy of approximately 1.2 eV are used in quantum dot solar cells (Non-Patent Literature 1).

[0008] Furthermore, when quantum dots are arranged in a high-density configuration, electronic coupling occurs between the quantum dots, and the discretized energy levels formed within each quantum dot bundle together to form an energy band. By utilizing light absorption through this intermediate band, infrared sunlight can be effectively absorbed, thereby increasing the efficiency of solar cells. In other words, an electron that absorbs one red photon is lifted from the quantum dot to the intermediate band, and then absorbs another photon, this time in the infrared range, and moves from the intermediate band to the conduction band. As a result of light absorption by the quantum dot, the current increases, and the power generation efficiency can be improved (Non-Patent Literature 2).

[0009] To achieve a conversion efficiency of 70% or more using quantum dots in solar cells, it is necessary to freely form minibands, and this has been explored using epitaxial growth methods, the same as those used for semiconductor lasers (Non-Patent Literature 3). However, with epitaxial growth methods, it is extremely difficult to achieve a sufficiently uniform quantum dot array structure while maintaining high quantum efficiency, and the conversion efficiencies of prototype solar cells remain very low.

[0010] Furthermore, as described in Non-Patent Literature 2, a method has been developed to fabricate semiconductor quantum dot superlattices using the layer-by-layer method and to control the dimensionality of quantum resonance by controlling the inter-quantum dot distance in the in-plane and stacking directions. Since quantum resonance between closely spaced quantum dots dramatically improves charge mobility, understanding the optical and electronic properties based on quantum resonance is crucial for device applications. Luminescence characteristics based on the dimensionality of quantum dot superlattice structures where semiconductor quantum dots are closely spaced in the one-dimensional, two-dimensional, and three-dimensional directions emerge.

[0011] Furthermore, perovskite solar cells are considered the most promising candidate for next-generation solar cells, and have seen a rapid increase in photoelectric conversion efficiency in recent years. These perovskite solar cells include a photoelectric conversion element that uses a perovskite compound (CH3NH3PbI3), composed of a cation such as methylammonium and a metal halide salt such as lead iodide, as the light-absorbing layer (Non-Patent Literature 4). It is known that the chemical and physical properties of the perovskite compound change depending on the composition of the cation species, halogen element, and metal element. For example, while substituting the halogen element iodine with bromine improves the durability of the photoelectric conversion element, it has been reported that the conversion efficiency decreases due to the shortening of the absorption wavelength of the perovskite compound (increase in band gap energy) (Non-Patent Literature 5). [Prior art documents] [Non-patent literature]

[0012] [Non-Patent Document 1] ACS Nano 2014, 8, 614-622 [Non-Patent Document 2] Nature Communications, 10.1038 / s41467-020-19337-0 [Non-Patent Document 3] Tsuyoshi Mukai, Yokohama National University, Grant-in-Aid for Scientific Research (C) 18K04972 (2020) [Non-Patent Document 4] J.Am.Chem.Soc.2009,131,6050-6051 [Non-Patent Document 5] Nano Lett. 2013, 13, 1764-1769 [Non-Patent Document 6] Chemical Physics Letters 2012, 542, 89-93 [Overview of the project] [Problems that the invention aims to solve]

[0013] However, conventional photoelectric conversion elements using quantum dots do not achieve both excellent durability and high conversion efficiency. For example, quantum dots are easily surface-oxidized in the atmosphere, causing their photoelectric conversion efficiency to decrease over time and resulting in poor durability. Also, perovskite compounds decompose due to moisture in the atmosphere, which also presents durability problems.

[0014] Furthermore, while conventional quantum dot solar cells contain 500 to 100 billion quantum dots per square centimeter, increasing efficiency requires 10 times the current number of quantum dots. Therefore, the development of technologies to create even smaller quantum dots and to arrange them in a way that improves efficiency is needed.

[0015] Furthermore, in order to confine electrons within a quantum dot using a method called "intermediate band," it is necessary to superimpose the electrons excited to the intermediate band by absorbing photon energy three-dimensionally so that they can be extracted outside the quantum dot by absorbing the energy of a second photon. However, sufficient technology to extract these electrons outside the quantum dot by absorbing the energy of a second photon has not yet been established.

[0016] Furthermore, electrons that escape from a quantum dot have a chance of being recaptured by another quantum dot on their way to the electrode via diffusion and drift. Therefore, it is necessary to optimize the cell structure so that the electrons can ultimately be extracted as an electric current by repeating the process of capture and photoexcitation (escape). The lifetime of multiple excitons is said to be several tens of picoseconds, and it is necessary to separate the charge into electrons and holes within this time (Non-Patent Literature 6).

[0017] The present invention aims to provide a method for producing a nanocomposite having a novel quantum dot different from conventional methods, and to provide such a nanocomposite having a quantum dot. [Means for solving the problem]

[0018] To achieve the above objective, the present invention provides a method for producing a nanocomposite having quantum dots, characterized in that a nanocomposite consisting of nanoparticles that are the core of the nanocomposite and quantum dots attached to the surface of the nanoparticles is deposited or supported on the linear conductors, using a gap between a plurality of linear conductors arranged at intervals of 1 nm to 100 μm as a reaction field, and the nanocomposite is synthesized such that a plurality of the nanocomposites exist in a state of being discrete or aggregated and adsorbed or bonded to one another.

[0019] Furthermore, it is preferable that the linear conductor be a linear polymer.

[0020] Furthermore, it is preferable that the linear polymer in this case be polyaniline.

[0021] Also, it is preferable that the quantum dots are made of at least one of iron oxide, iron sulfide, CdSe, PbS, and PbSe having a band gap in the visible light region.

[0022] Also, it is preferable that the nanoparticles are inorganic semiconductors.

[0023] Also, it is preferable that the linear conductor is a linear polymer, and at least one of the nanoparticles and the quantum dots is synthesized by a reaction in an aqueous solution or an electrodeposition reaction, and synthesized in the gaps between the linear polymers by controlling at least one parameter of reactant concentration, reaction pH, reaction temperature, and reaction time.

[0024] Also, it is preferable that the linear conductor is a linear polymer, the nanoparticles are made of iron oxide or TiO2, and the quantum dots are made of FeS2.

[0025] In this case, it is preferable that the linear polymer is polyaniline, and quantum dots made of FeS2 are deposited or supported on the nanoparticles made of iron oxide or TiO2 by a reaction in an aqueous solution and an electrodeposition reaction.

[0026] ]] Furthermore, in this case, it is preferable that the process of forming the nanoparticles made of iron oxide or TiO2 and the process of depositing or supporting the quantum dots made of FeS2 on the nanoparticles made of iron oxide or TiO2 are repeated to synthesize a nanocomposite made of the nanoparticles made of iron oxide or TiO2 and the quantum dots made of FeS2, which are connected in the direction of the polymer straight chain of the polyaniline.

[0027] Also, it is preferable that at least one of the nanoparticles made of iron oxide or TiO2 and the quantum dots made of FeS2 is synthesized by a reaction in an aqueous solution or an electrodeposition reaction, and synthesized in the gaps of the polyaniline by controlling at least one parameter of reactant concentration, reaction pH, reaction temperature, and reaction time.

[0028] Furthermore, in the method for producing a nanocomposite having quantum dots according to the present invention, it is preferable to use the gaps between polymer bundles formed by growing the linear polymer perpendicular to the transparent electrode surface and parallel to each other as the reaction field.

[0029] Furthermore, the present invention provides a method for manufacturing a solar cell, characterized by using a nanocomposite having quantum dots manufactured by any of the above methods in the manufacture of a dye-sensitized solar cell or an organic solar cell.

[0030] In this case, it is preferable to use a linear organic polymer as the linear conductor, grow the linear organic polymer in a direction substantially perpendicular to the electrode of the battery, and use the gap between the linear conductors as a reaction field to form the nanoparticles and quantum dots of the linear organic polymer as the positive electrode.

[0031] Furthermore, in the method for producing the quantum dot nanocomposite of the invention, after synthesizing the plurality of nanocomposites so that they exist in a state of being discrete or aggregated and adsorbed or bonded to one another, the nanocomposites can be further freed and recovered from the linear conductor.

[0032] Furthermore, the present invention also provides a method for producing quantum dots, characterized by synthesizing the plurality of nanocomposites by any of the above methods such that they exist in a state of being discrete or aggregated and adsorbed or bonded to one another, and then further freeing and recovering the quantum dots constituting the nanocomposites from the linear conductor.

[0033] Furthermore, the present invention provides a nanocomposite having quantum dots, wherein a plurality of linear conductors are arranged at intervals of 1 nm to 100 μm, and the gaps between them are filled with nanoparticles that form the core of the nanocomposite and quantum dots attached to the surface of the nanoparticles, and the plurality of such nanocomposites exist in a state in which the quantum dots are dispersed or aggregated and adsorbed or bonded to each other. [Effects of the Invention]

[0034] The present invention provides a novel method for manufacturing nanocomposites having quantum dots, which differs from conventional methods. Furthermore, the present invention enables the production of such nanocomposites having quantum dots. The present invention allows for the production of nanocomposites having quantum dots with a structure that can be referred to as "linearly arranged quantum dots." Such nanocomposites having linearly arranged quantum dots can be applied to high-performance photoelectric conversion elements and can be used in electrical energy, quantum computing, medicine, and agriculture. [Brief explanation of the drawing]

[0035] [Figure 1] This is a schematic diagram showing an example of a nanocomposite having quantum dots according to the present invention. [Figure 2] This is a schematic diagram showing an example of a method for manufacturing quantum dots according to the present invention. [Figure 3] This is a schematic diagram showing an example of a dye-sensitized solar cell using a nanocomposite having quantum dots according to the present invention. [Figure 4] This is a schematic diagram showing an example of a terahertz electromagnetic wave generator using the nanocomposite having quantum dots according to the present invention. [Modes for carrying out the invention]

[0036] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0037] The present invention provides a method for producing a nanocomposite having quantum dots, characterized in that a nanocomposite consisting of nanoparticles that form the core of the nanocomposite and quantum dots attached to the surface of the nanoparticles is deposited or supported on the linear conductors, using a gap between a plurality of linear conductors arranged at intervals of 1 nm to 100 μm as a reaction field, and the nanocomposite is synthesized such that a plurality of the nanocomposites exist in a state of being dispersed or aggregated and adsorbed or bonded to one another.

[0038] Furthermore, the nanocomposite having quantum dots of the present invention is characterized in that a plurality of linear conductors are arranged at intervals of 1 nm to 100 μm, and the gaps between them contain nanoparticles that are the core of the nanocomposite and quantum dots attached to the surface of the nanoparticles, and the plurality of such nanocomposites exist in a state in which they are discrete or aggregated, adsorbed or bonded to one another.

[0039] [Embodiment 1] (Forms of nanocomposites and their synthesis methods) Figure 1 shows a schematic diagram of a nanocomposite manufactured by the method for manufacturing a nanocomposite having quantum dots according to the present invention. The quantum dots shown in Figure 1 can be referred to as "linearly arranged quantum dots".

[0040] As described above, the present invention is a nanocomposite 10 having quantum dots 14 (see Figures 1(a) and (b)). In the present invention, a nanocomposite 10 is provided in gaps between a plurality of linear conductors 24 arranged at intervals of 1 nm to 100 μm (Figure 1(a) illustrates a gap of 50 to 100 nm), and the nanocomposite 10 consists of nanoparticles 12 which are the core of the nanocomposite 10 and quantum dots 14 attached to the surface of the nanoparticles 12. Furthermore, the present invention is characterized in that a plurality of nanocomposites 10 exist in a state in which they are discrete or aggregated and adsorbed or bonded to one another.

[0041] In this nanocomposite 10 having quantum dots 14, the nanocomposite 10, consisting of nanoparticles 12 which are the core of the nanocomposite 10 and quantum dots 14 attached to the surface of the nanoparticles 12, is deposited or supported on the linear conductors 24, using the gaps between multiple linear conductors 24 arranged at intervals of 1 nm to 100 μm as the reaction field. In this invention, multiple nanocomposites 10 are synthesized so that they exist in a state where they are discrete or aggregated and adsorbed or bonded to one another. The gaps between multiple linear conductors 24 arranged at intervals of 1 nm to 100 μm can be prepared by forming multiple linear conductors 24 on the electrode 22 shown in Figure 1(a).

[0042] In this case, it is preferable that the linear conductor 24 be a linear polymer. Furthermore, it is preferable that this linear polymer be polyaniline.

[0043] Furthermore, it is preferable that the quantum dot 14 is made of at least one of iron oxide, iron sulfide, CdSe, PbS, and PbSe, which have a band gap in the visible light range.

[0044] Furthermore, it is preferable that the nanoparticles 12 be inorganic semiconductors, and in particular, that they be made of iron oxide or TiO2.

[0045] In this invention, the linear conductor 24 is a linear polymer, and at least one of the nanoparticles 12 and quantum dots 14 can be synthesized by reaction in an aqueous solution or by electrodeposition reaction, and the synthesis can be carried out in the gaps between the linear polymers by controlling at least one of the parameters of reactant concentration, reaction pH, reaction temperature, and reaction time. In this case, it is particularly preferable that the linear polymer be polyaniline, and that quantum dots 14 made of FeS2 be deposited or supported on nanoparticles 12 made of iron oxide or TiO2 by reaction in an aqueous solution or by electrodeposition reaction.

[0046] In the present invention, it is particularly preferable to use the gaps between polymer bundles formed by growing linear polymers perpendicular to the transparent electrode surface and parallel to each other as the reaction field.

[0047] A more specific example will be described with reference to Figure 1, but the present invention is not limited thereto. A polymer fiber bundle consisting of, for example, about 1000 fibers of polyaniline, a conductive polymer, can be used as a single linear conductor 24. For the electrode 22, for example, fluorine-doped tin oxide (FTO) can be used as the material. A transparent FTO electrode can be formed on a glass plate. The space between the polymer fiber bundles, which can be arranged on the surface of the transparent FTO electrode at intervals of, for example, 30 nm, can be used as the reaction field. In such a reaction field, for example, αFe2O3 nanoparticles (core nanoparticles 12), which are an iron oxide, can be deposited by electrodeposition into ohmic contact with some of the polyaniline fibers, and further, a nanocomposite 10 can be synthesized by electrodepositing FeS2 quantum dots (quantum dots 14), for example, particles of size 2 nm to 10 nm, onto the surface of the αFe2O3 nanoparticles by electrodeposition from a reaction solution containing at least ferrous ions and sulfur ions.

[0048] The conductive polymer used as the linear conductor 24 here may be polyacetylene, poly(p-phenylene), polythiophene, polypyrrole, etc., in addition to polyaniline, and the nanoparticles may be TiO2. Furthermore, the FeS2 quantum dots may be any of the quantum dots of iron oxide, iron sulfide, CdSe, PbS, or PbSe that have a band gap in the visible light range.

[0049] Since the size of the aforementioned nanoparticles can be changed by the electrodeposition reaction time, the size of the nanoparticles can be designed to vary by changing the current passage time and timing during electrodeposition. This results in a structure in which incident light is scattered in a complex manner, and when used as a solar cell, it enables so-called "light containment," which can increase the photoelectric conversion efficiency with a short battery cell thickness.

[0050] Furthermore, the method of depositing the αFe2O3 nanoparticles by electrodeposition can be replaced with a method of immersing the spatial gaps of the reaction field with a pre-prepared nanoparticle dispersion. In addition, the method of three-dimensionally depositing FeS2 quantum dots of 2 nm to 10 nm on the surface of the αFe2O3 nanoparticles can be replaced with a method of immersing them in a pre-prepared quantum dot solution, and the sizes of these nanoparticles and quantum dots can be appropriately selected during preparation.

[0051] The length of the polymer fiber bundle can be adjusted, for example, by changing the reaction time and reactant concentration of the oxidative polymerization reaction of polyaniline. Furthermore, by repeating the polymerization reaction, photoelectric conversion elements with different properties can be formed into a layered structure. In addition, the diameter of the polymer fiber bundle can be freely determined by the size of the diameter of the through-holes formed in the film that is pre-masked on the surface of the FTO transparent electrode substrate.

[0052] In the polymerization reaction of polyaniline, the linearity of the polymer fiber bundle can be made more precise by coexisting with a compound having liquid crystal properties, such as polyvinyl alcohol.

[0053] Incident photons can be "contained" by varying the size of the nanoparticles, thereby increasing light absorption and improving photoelectric conversion efficiency. To further increase absorption, it is conceivable to increase the cell thickness. However, in this case, increasing the thickness increases the contact area between the electrode and the electrolyte, raising concerns that the probability of electrons injected from the quantum dot dye into the nanoparticles flowing from the electrode to the electrolyte, and the possibility of electron recombination from the electrode to the oxidized quantum dot dye will increase. However, if polyaniline is used as the linear polymer conductor, as in Embodiment 1 of the present invention, the nanoparticles are in ohmic contact with the linear polymer conductor individually. Therefore, even if the contact area with the electrolyte increases, the probability of electrons flowing into the electrolyte and electron recombination with the quantum dot dye is unlikely to occur. In other words, in Embodiment 1 of the present invention, increasing the cell thickness does not decrease the photoelectric conversion efficiency; rather, increasing the thickness increases the light absorption efficiency, making it possible to improve the photoelectric conversion efficiency.

[0054] [Embodiment 2] (Synthesis of free nanocomposites and free quantum dots utilizing the synthesis of nanocomposites of Embodiment 1) As shown in Embodiment 1, the present invention allows for the fabrication of a nanocomposite 10 on a linear conductor 24. However, as shown in Embodiment 2 below, free nanocomposites and free quantum dots can also be synthesized.

[0055] In other words, in the present invention, after synthesizing a plurality of nanocomposites 10 on a linear conductor 24 such that they exist in a state of being dispersed or aggregated and adsorbed or bonded to one another, the nanocomposites 10 can be further freed and recovered from the linear conductor 24.

[0056] Furthermore, after synthesizing multiple nanocomposites 10 in a state where they are discrete or aggregated and adsorbed or bonded to one another, the quantum dots 14 constituting the nanocomposites 10 can be further freed and recovered from the linear conductor 24.

[0057] A more specific embodiment of the method for freeing and recovering the quantum dots 14 in this second embodiment will be described with reference to Figure 2. Figure 2 shows a method for synthesizing quantum dots of various inorganic compounds in a suitable size and with sharply aligned sizes, using the method for synthesizing nanocomposites using linearly arranged quantum dots of the present invention.

[0058] In the same manner as in Embodiment 1 described above, a polymer fiber bundle consisting of approximately 1,000 to tens of thousands of polyaniline fibers is arranged in large numbers on the surface of the FTO transparent electrode surface of a glass plate at intervals of, for example, 10 nm, forming a single linear conductor 24. The resulting gaps serve as the reaction field, and FeS2 quantum dots 14 nm in size are synthesized by electrodeposition from a reaction solution containing at least ferrous ions and sulfur ions. Subsequently, the glass plate is removed from the reaction solution and immersed in an ethanol solution in which a solvent for dispersing nanoparticles, such as ethanolamine, is dissolved as a dispersant. An ethanol solution in which the quantum dots 14 are dissolved is obtained by ultrasonic treatment.

[0059] The conductive polymer may be poly(p-phenylene), polythiophene, polypyrrole, etc., and the FeS2 quantum dot may be any of the quantum dots of iron oxide, iron sulfide, CdSe, PbS, or PbSe that have a band gap in the visible light range.

[0060] Furthermore, by changing the solution and liberation treatment conditions, the nanocomposite 10 (a state in which quantum dots 14 are attached to nanoparticles 12) can also be liberated and recovered from the linear conductor 24.

[0061] [Embodiment 3] (Dye-sensitized solar cells utilizing nanocomposites) Nanocomposites having quantum dots produced by the method of the present invention can be used in the manufacture of dye-sensitized solar cells or organic solar cells. In this case, linear conductors 24 can be grown in a direction substantially perpendicular to the electrodes of the battery, and an organic polymer formed of nanoparticles 12 and quantum dots 14 can be used as the positive electrode, with the gaps between the linear conductors 24 formed by the bundle of linear conductors serving as the reaction field. A specific embodiment of the dye-sensitized solar cell will be described with reference to Figure 3.

[0062] Figure 3 shows a dye-sensitized solar cell fabricated using the nanocomposite 10 of the present invention as the anode.

[0063] The nanocomposite shown in Figure 3 is an example of one synthesized in Embodiment 1, consisting of a polymer fiber bundle (10 micrometers in length) made of approximately 3000 polyaniline fibers, an FTO transparent electrode, a 30 nm spacing, electrodeposition of αFe2O3 nanoparticles, and 2 nm FeS2 quantum dots. This was used as the anode, FeS2 as the counter electrode, and a mixture of ethanol and water (8:2) in which 0.5 M Na2S, 0.1 M S, and 0.05 M GuSCN (guanidine thiocyanate) were dissolved as the electrolyte, at a voltage of 100 mW / cm². 2 A conversion efficiency of 35% was obtained by irradiating the sample with simulated sunlight. The particle size was measured using transmission electron microscopy.

[0064] While αFe2O3 nanoparticles are generally made porous or nanoparticle-sized to increase light absorption at heterogeneous interfaces and improve specific surface area, the present invention allows for increased specific surface area through the use of nanoparticles.

[0065] Increasing the thickness between electrodes to sufficiently absorb incident photons generally increases the contact area between the electrodes and the electrolyte. This increases the probability that electrons injected from the quantum dot dye will flow into the electrolyte and the possibility of electron recombination with the oxidized quantum dot dye, thus reducing the photothermal conversion efficiency. However, in Embodiment 1 of the present invention, electrons that have moved from the quantum dot dye to a single nanoparticle flow to the conductive polymer in ohmic contact, so the probability of them flowing into the electrolyte is kept quite low. Therefore, it becomes possible to increase the thickness between electrodes, which in turn allows for an increase in the number of quantum dot dyes. As a result, the electrodes can absorb photons up to nearly 100% as electrodes with a large absorption coefficient, reducing energy loss in light utilization and improving efficiency.

[0066] Thus, the inventors have found that by using a light absorption layer made of a linearly arranged quantum dot photoelectric conversion element, which is completely different from conventional quantum dot photoelectric conversion elements, it is possible to significantly improve the photoelectric conversion efficiency and further improve the photoelectric conversion efficiency (quantum efficiency) in the near-infrared light region.

[0067] In other words, conventional quantum dot solar cells have limitations in densely packing quantum dots of several tens of nanometers in size using electrodeposition or spin coating followed by annealing on a substrate, and controlling the arrangement necessary to improve photoelectric conversion efficiency is difficult. In light of this, the method of arranging quantum dots was fundamentally changed, resulting in a linear arrangement in the straight-chain direction of the conductive polymer, and the photoelectric conversion element was constructed by electrodepositing or supporting quantum dots on the surface of iron oxide nanoparticles or TiO2 nanoparticles ohm-bonded to the conductive polymer.

[0068] At heterogeneous interfaces between iron oxide nanoparticles or TiO2 nanoparticles and quantum dots, excitons generated by absorbed light become free carriers. However, as the distance from the heterogeneous interface increases, the excitons only absorb light and no longer generate photocurrent, reducing conversion efficiency. To address this, solar cells are designed to increase the optical path by dispersing incident sunlight at the incident surface, causing random light absorption at the quantum dot interface and improving light absorption efficiency. Furthermore, the cell layer is made as thin as possible to minimize the distance from the heterogeneous interface. However, thinning the cell layer and increasing the density of quantum dots are contradictory, and existing technologies suffer from this contradiction, resulting in low photoelectric conversion efficiency. We have diligently studied methods to resolve this contradiction and devised the linear arrangement method of the present invention, which is one means of resolving this contradiction.

[0069] By ohmic connecting iron oxide nanoparticles or TiO2 nanoparticles to a conductor extending linearly to the surface of a solar cell, carrier electrons that have moved to the TiO2 nanoparticles at the heterogeneous interface can be directly extracted from the same nanoparticles, thus avoiding the loss of carrier electrons that occur during successive movement between iron oxide nanoparticles or TiO2 nanoparticles, as is the case with conventional techniques. Since the conductor is linear, quantum dots deposited or supported on TiO2 arranged along this conductor have heterogeneous interfaces with TiO2 nanoparticles that are also linear, resulting in a linear heterogeneous interface that absorbs light. This arrangement with a linear heterogeneous interface is completely different from existing techniques and will be called a linear arrangement.

[0070] Since many quantum dots are electrodeposited or supported on the surface of a single iron oxide nanoparticle or TiO2 nanoparticle, many heterogeneous interfaces exist on a single nanoparticle. The excitons excited by light absorption at each of these heterogeneous interfaces are transported as free electrons to the external circuit via ohmic contact. This significantly reduces carrier recombination compared to conventional techniques.

[0071] The light absorption wavelength of quantum dots depends on the size of the quantum dots on the surface of iron oxide nanoparticles or TiO2 nanoparticles. Therefore, quantum dots of only a fixed size cannot cover the wide range of wavelengths of sunlight, resulting in reduced conversion efficiency. To solve this, the present invention makes it possible to change the size of the quantum dots in the linear direction of the linear arrangement. This allows for a wide range of wavelengths of light to be absorbed.

[0072] The density of quantum dots on the surface of iron oxide nanoparticles or TiO2 nanoparticles can be increased from a small value to a density where three-dimensional overlap occurs by changing the electrodeposition reaction time on the surface or the concentration of the solution used for loading.

[0073] By allowing incident light to penetrate deeply into the cell to increase absorption efficiency, and by forming an ohmic junction between the photoelectric conversion element and the conductive polymer, a structure was created that makes it difficult for excited electrons from deep within to recombine with holes or within quantum dots. This makes it possible to dramatically improve quantum dot density and absorption efficiency, thereby improving conversion efficiency.

[0074] Because each quantum dot electrodeposited or supported on the surface of iron oxide nanoparticles or TiO2 nanoparticles in a photoelectric conversion element overlaps three-dimensionally, it can absorb light in a wide wavelength range, including long wavelength regions such as the near-infrared that quantum dots can absorb. Therefore, a photoelectric conversion element with photoelectric conversion functionality across a wide wavelength range can be obtained.

[0075] When quantum dots are stacked in three dimensions at high density, bands are formed between the quantum dots, creating a superlattice, which causes an infrared shift and allows for the absorption of ultra-long wavelength infrared radiation. In other words, when used in a bifacial solar power generation panel, it can absorb thermal radiation from the ground on the back side and convert it into electricity.

[0076] [Embodiment 4] (Terahertz electromagnetic wave generator utilizing the nanocomposite of the present invention) Terahertz waves are electromagnetic waves that penetrate plastics and fabrics well, unlike metals. Unlike X-ray inspections, terahertz waves are harmless to the human body and are being used for security checks of people at airports. They can be widely applied to non-destructive testing of luggage, detection of foreign objects in food, device quality inspection to check for damage and deterioration, and medical applications.

[0077] Terahertz waves are electromagnetic waves with wavelengths of approximately 10 micrometers (frequency 30 terahertz) to 1 millimeter (frequency 300 gigahertz), falling between radio waves and light waves. The vibration frequencies of these terahertz waves overlap with the vibration frequencies of molecules that make up matter, giving them unique characteristics not found in other electromagnetic waves, such as the existence of a fingerprint spectrum for almost all materials. Therefore, the development of technologies utilizing terahertz waves is rapidly progressing in various academic and industrial fields, including spectroscopy and imaging for safety and security ("seeing the invisible") and ultra-high-speed wireless communication. In particular, the development of 6G and 7G technologies, next-generation ultra-high-speed wireless communication utilizing terahertz waves, is essential for the dramatic improvement of information and communication services necessary for realizing a super-smart society. However, operating in the terahertz band has been extremely difficult due to inherent physical limitations for both electronic devices such as transistors and optical devices such as lasers. In particular, the realization of terahertz amplification elements and laser elements that operate at room temperature, can be miniaturized and integrated, and are battery-powered—essential means of transmitting 6G and 7G wireless signals—has yet to be achieved.

[0078] Figure 4 shows a terahertz electromagnetic wave generator prepared by one embodiment of the present invention, in which a nanocomposite synthesized with linear high electrons as polyaniline, nanoparticles as GaAs, and quantum dots as p-type InAs is used as the anode, and polysulfide is used with a non-aqueous electrolyte that makes hydrogen bonding difficult. When a superlattice of quantum dot semiconductor formed by 3D assembly of deposited or supported quantum dots of the present invention was applied to terahertz wave time-domain spectroscopy, it was possible to generate THz electromagnetic waves. Furthermore, it was possible to detect terahertz waves and operate it as a receiver.

[0079] [Embodiment 5] (Transfer and regeneration of qubits using the nanocomposite of the present invention) As one embodiment of the present invention, a nanocomposite was synthesized using polyaniline as the linear polymer, InAs nanoparticles, and p-type InAs quantum dots. Using this nanocomposite, a broadband (>THz), high time-bandwidth product (>10³), time-mode conservation, and direct transfer of communication wavelength band photons were performed using an ultra-high-sensitivity heterodyne-detection photon echo method. This demonstrated that picosecond single-photon time-bin qubits can be transferred / recreated using the photon echo method.

[0080] The development of quantum control technology in semiconductors is largely due to the development of short-pulse lasers and advances in semiconductor nanotechnology. In solids, the quantum coherence of the electron system is lost within an extremely short time of a few picoseconds due to strong interactions with the surroundings (decoherence). Therefore, in order to perform quantum control, femtosecond pulses shorter than that are required. Currently, with the widespread use of titanium-sapphire lasers, it is possible to obtain ultrashort light pulses of several tens of femtoseconds with commercially available lasers, making it possible for relatively anyone to start quantum control experiments, and leading to a diversification of research topics.

[0081] Furthermore, in addition to technologies for highly controlling the waveform and phase of optical pulses, technologies for generating distinctive types of light such as single photons, entangled photon pairs, and squeezed light have been developed, and attempts to realize more complex and diverse quantum control are also being made toward the practical application of quantum computers. Meanwhile, advances in nanotechnology have made it possible to fabricate semiconductor quantum dots, called "artificial atoms," with high quality using solid-state chemistry, electrochemistry, and solution chemistry. This makes it possible to prepare a steady state of an electronic system suitable for quantum control, and furthermore, by encapsulating quantum dots in micro-resonators or photonic crystals, it is becoming possible to freely control the magnitude of coupling with light. Embodiment 5 of the present invention provides a new and unique technology related to these.

[0082] Quantum memory is a key device for realizing many quantum information protocols, including quantum relay. Furthermore, constructing quantum memory with quantum gate-operable qubits is opening up new applications such as the realization of distributed quantum computers. Moreover, by transferring entangled photon pairs, the generation of quantum entangled states between distant materials and quantum teleportation are being realized. Embodiment 5 of the present invention is an important foundational technology that contributes to all research fields related to quantum memory, not only quantum information but also quantum mechanics and condensed matter physics.

[0083] The realization of quantum memory in solid states is highly desired, and quantum dots are one of the promising candidates. In addition to being advantageous in terms of miniaturization and integration, quantum dots have the potential to be used with ultrashort pulses and have their transition wavelengths tuned to communication wavelength bands, making them suitable for communication applications. Furthermore, the strong interaction between quantum dots enables high-speed quantum gate operations, which is also attractive depending on the application.

[0084] However, a problem with quantum dots is that the size and strain levels differ from dot to dot, leading to inhomogeneity in transition wavelengths and the strength of the coupling with light. To avoid the effects of inhomogeneity, most quantum control experiments are conducted on single quantum dots, and the challenge lies in how to strengthen the interaction with light.

[0085] A new type of quantum memory using the photon echo method has been developed that is applicable even to quantum dot assemblies with high heterogeneity, making it possible to utilize the photon echo method from quantum dot assemblies in the communication wavelength band.

[0086] [Embodiment 6] (Battery utilizing the synthesis method of the nanocomposite of the present invention) In one embodiment of the present invention, linear polymers were formed into iron oxide nanoparticles by electrolysis or solution chemical reaction using polyaniline, and then quantum dots were synthesized as polyaniline organic quantum dots to create a nanocomposite, which was then assembled into a battery as a cathode material.

[0087] [Embodiment 7] (Applications of the nanocomposite of this invention to the bio-medical field) One emerging industry utilizing terahertz electromagnetic waves is the bio-medical field. One promising application is in biosensing. This is because its frequency band, energy, and time domain correspond to the motion of large-mass molecules, hydration reactions such as the interaction between living proteins and water, and hydrogen bond energy in DNA, while also being highly sensitive to ionic solutions such as water. Therefore, applications are expected in biochips and drug discovery, evaluation of drug crystalline polymorphism, detection of drug mixing defects through component analysis, non-destructive testing of tablets and coatings, biomolecular manipulation and selective culture acceleration using high-brightness terahertz light, and pre-symptomatic diagnosis. This field represents a new and promising industrial sector.

[0088] The most widely used method is terahertz time-domain spectroscopy (THz-TDS). Its basic principle involves generating pulsed electromagnetic waves using femtosecond light pulses, and employing a high-speed detector that operates only when the light pulse is incident. By delaying the light pulse, time-domain measurements can be achieved. THz-TDS detectors are commercially available, and they can determine the complex refractive index of a material over a broad bandwidth (approximately 0.1 THz to 5 THz for common models) based on the transmission and reflection characteristics of the pulsed electromagnetic waves. From this refractive index, properties such as dielectric constant and conductivity can be determined. Furthermore, because it measures in the time domain, it can be used as a 3D THz-CT by utilizing the reflection / transmission characteristics at various material interfaces. Various applications are being researched, such as 2D depth distribution analysis of skin cancer and coating distribution analysis of drug tablets.

[0089] Although more than ten years have passed since the commercialization of general-purpose THz-TDS, its adoption has not spread as much as expected in terms of applications. One reason is that the terahertz beam diameter is large, making it unsuitable for micro-inspection and high-resolution imaging. Another reason is that the acquisition time is not practical due to the trade-off relationship between imaging time and cost.

[0090] Originally, terahertz waves have longer wavelengths than light, resulting in a coarse image. Furthermore, terahertz waves have low energy for measurement as light and too high frequency for measurement as radio waves, resulting in extremely poor detection sensitivity. It is necessary to increase the power output of terahertz wave generation.

[0091] DHAuston et al. reported the generation of picosecond-order pulses and measurement of time-to-time waveforms using ultrashort pulse lasers, making it possible to generate and detect terahertz waves at room temperature. By applying this principle to spectroscopy, it became possible to obtain broadband terahertz wave amplitude and transport information in short-time measurements, and this became known as terahertz time-domain spectroscopy (THz-TDS).

[0092] Typical detectors include Schottky barrier diodes, which can perform rectification detection by utilizing the nonlinearity of the IV characteristics generated by the Schottky junction. Furthermore, detectors widely used in THz-TDS include photoconductive antennas (PCAs), which detect the electric field strength of terahertz waves by photoexciting the minute gap between the antenna parts with a femtosecond laser and detecting the instantaneous current generated between the antennas, and electro-optic crystals, which detect the electric field strength of terahertz waves by replacing it with the birefringence of probe light. These detectors are frequently used in wireless communication and spectroscopic research, and there is a need for cost reduction and increased sensitivity through arrays for industrial applications.

[0093] A terahertz wave visualization system has already been developed that uses nonlinear optics to quantum optically convert terahertz waves to near-infrared light with high photon energy, and then measures the data with a highly sensitive near-infrared camera. The nonlinear optical crystal used is an organic nonlinear optical crystal called DAST, which allows for the free conversion of wavelength between terahertz waves and near-infrared light. In other words, the echo image of the reflected terahertz wave emitted for diagnostic purposes can be made highly sensitive, thus solving the problem of increasing the sensitivity of the echo image. However, the intensity of the reflected terahertz wave itself remains low, making it difficult to image deeper areas even if a clear image can be obtained, and transmission-type imaging diagnosis is impossible. To solve this problem, it is necessary to increase the intensity of the emitted terahertz wave itself.

[0094] Using the terahertz electromagnetic wave generator of Example 4, by superimposing visible light or CW laser light using terahertz time-domain spectroscopy and simultaneously applying a potential of 1-10V between the two electrodes, it was possible to emit electromagnetic waves of 1-3 Tesla, equivalent to several watts, thereby increasing the intensity of the terahertz waves.

[0095] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that has substantially the same technical idea as described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0096] 10…Nanocomposite, 12... Nanoparticles, 14... Quantum dots, 22...electrode, 24... A linear conductor.

Claims

1. A method for manufacturing a nanocomposite having quantum dots, A method for producing a nanocomposite having quantum dots, characterized by using gaps between multiple linear conductors arranged at intervals of 1 nm to 100 μm as a reaction field, depositing or supporting a nanocomposite consisting of nanoparticles that form the core of the nanocomposite and quantum dots attached to the surface of the nanoparticles onto the linear conductors, and synthesizing the nanocomposite such that multiple nanocomposites exist in a state of being discrete or aggregated, adsorbed or bonded to one another.

2. The method according to claim 1, characterized in that the linear conductor is a linear polymer.

3. The method according to the 2nd method, characterized in that the linear polymer is polyaniline.

4. The method according to claim 1, characterized in that the quantum dot is made of at least one of iron oxide, iron sulfide, CdSe, PbS, and PbSe having a band gap in the visible light range.

5. The method according to claim 1, characterized in that the nanoparticles are inorganic semiconductors.

6. The linear conductor is a linear polymer, The method according to claim 1, characterized in that at least one of the nanoparticles and the quantum dots is synthesized by a reaction or electrodeposition reaction in an aqueous solution, and synthesized in the gaps between the linear polymers by controlling at least one parameter of reactant concentration, reaction pH, reaction temperature, and reaction time.

7. The linear conductor is a linear polymer, The aforementioned nanoparticles are iron oxide or TiO ２ It shall consist of, The aforementioned quantum dot is FeS ２ The method according to claim 1, characterized in that it comprises the following:

8. The linear polymer is polyaniline, The iron oxide or the TiO2 is produced by the reaction in aqueous solution and the electrodeposition reaction. ２ The nanoparticles consist of the FeS ２ The method according to 7, characterized by depositing or supporting quantum dots consisting of the above.

9. The aforementioned iron oxide or TiO ２ The process of forming nanoparticles consisting of, The iron oxide or TiO ２ nanoparticles consisting of, and the FeS ２ quantum dots consisting of, are repeatedly subjected to a process of depositing or supporting the quantum dots on the nanoparticles, and the nanoparticle composite consisting of the nanoparticles consisting of the iron oxide or TiO ２ and the quantum dots consisting of the FeS ２ is synthesized by linking it in the polymer main chain direction of the polyaniline. The method according to claim 8, characterized in that.

10. The aforementioned iron oxide or TiO ２ Nanoparticles consisting of the above FeS ２ The method according to 7, characterized in that at least one of the quantum dots composed of is synthesized by a reaction or electrodeposition reaction in an aqueous solution, and is synthesized in the gaps of the polyaniline by controlling at least one parameter of reactant concentration, reaction pH, reaction temperature, and reaction time.

11. The method according to the previous version, characterized in that the reaction field is the gaps between polymer bundles formed by growing the linear polymer perpendicular to the transparent electrode surface and such that the linear polymers are parallel to each other.

12. A method for manufacturing a solar cell, characterized in that a nanocomposite having quantum dots manufactured by the method described in any one of claims 1 to 10 is used in the manufacture of a dye-sensitized solar cell or an organic solar cell.

13. The linear conductor is a linear organic polymer, and the linear organic polymer is grown in a direction approximately perpendicular to the electrode of the battery. The method for manufacturing a solar cell according to claim 12, characterized in that the linear organic polymer on which the nanoparticles and quantum dots are formed is used as the positive electrode, with the gaps between the linear conductors as the reaction field.

14. The method according to claim 1, characterized in that, after synthesizing the plurality of nanocomposites such that they exist in a state of being discrete or aggregated and adsorbed or bound to one another, the nanocomposites are further freed and recovered from the linear conductor.

15. After synthesizing the plurality of nanocomposites by any one of claims 1 to 10 such that they exist in a state of being dispersed or aggregated and adsorbed or bound together, Furthermore, a method for producing quantum dots, characterized by freeing and recovering the quantum dots constituting the nanocomposite from the linear conductor.

16. A nanocomposite having quantum dots, Multiple linear conductors are arranged at intervals of 1 nm to 100 μm, and in the gaps between them, a nanoparticle, which is the core of the nanocomposite, The nanocomposite comprises quantum dots attached to the surface of the aforementioned nanoparticles, A nanocomposite having quantum dots, characterized in that multiple nanocomposites exist in a state where they are discrete or aggregated and adsorbed or bonded to one another.

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