Nanocomposite having quantum dots and method for producing same

Abstract

The present invention is a method for producing a nanocomposite having quantum dots, the method being characterized in that gaps formed by arranging a plurality of linear conductors (24) at intervals of 1 nm to 100 µm are used as reaction fields, a nanocomposite (10) comprising nanoparticles (12), which are cores of the nanocomposite (10), and quantum dots (14) attached to the surfaces of the nanoparticles (12) is deposited or supported on the linear conductors (24), and the plurality of nanocomposites (10) are combined so as to be present in a state in which the nanocomposites (10) are separated from each other or aggregated and adsorbed or bound to each other. Thus is provided a method for producing a novel nanocomposite having quantum dots that is different from conventional methods.

Description

Nanocomposite containing quantum dots and method for producing the same

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

[0002] By changing the size of quantum dots, the band gap energy can be controlled, and the wavelength of light absorption and emission can be changed. Therefore, by utilizing their unique electrical properties, quantum dots are expected to be applied to quantum dot solar cells, quantum dot lasers, single-electron transistors, quantum teleportation, quantum computers, terahertz information and communications, medicine, agriculture, forestry, and other fields.

[0003] Quantum dots are inorganic nanoparticles with a particle size of approximately 20 nm or less, which exhibit physical properties different from those of bulk materials due to the quantum size effect. The quantum size effect, which occurs when electrons are confined within quantum dots, can increase conversion efficiency by effectively utilizing light of wavelengths that cannot be absorbed by conventional solar cells, as well as high-energy light.

[0004] Conventional silicon solar cells use ultra-high purity silicon, so significant cost reductions cannot be expected. Therefore, solar cells manufactured using "wet processes" such as coating processes are expected to be low-cost next-generation solar cells. It is expected that energy that is lost as heat in conventional solar cells can be effectively utilized (hot carrier effect, multi-exciton generation effect).

[0005] Quantum dot solar cells are next-generation solar cells that can be manufactured using a "wet process." Quantum dot solar cells have the potential to achieve a theoretical conversion efficiency of 63%, which is twice that of conventional silicon solar cells, and they are eagerly awaited for commercialization as third-generation solar cells.

[0006] The strengths of quantum dot solar cells are their ability to absorb light of a wide range of wavelengths that could not be utilized previously, and their ability to generate excitons (electron-hole pairs in a high-energy state) before the high energy is lost as heat. Both of these solve the bottlenecks of conventional solar cells, and the key to utilizing high-energy light is the realization of multiple exciton generation (MEG), which allows multiple excitons to be extracted from a single photon, rather than the usual one.

[0007] Quantum dot solar cells confine electrons in quantum dots and stack quantum dots three-dimensionally using a method called "intermediate band," thereby creating a band at a specific energy position in the solar cell and efficiently absorbing light of 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 Document 1).

[0008] Furthermore, when quantum dots are arranged in a high-density structure, electronic coupling occurs between the quantum dots, and the discrete energy levels formed in each quantum dot are bundled to form an energy band, and light absorption through this intermediate band can be utilized to effectively absorb sunlight in the infrared range, thereby improving the efficiency of solar cells. In other words, an electron that absorbs one photon of red wavelength rises from the quantum dot to the intermediate band, and then absorbs another photon of infrared wavelength and rises from the intermediate band to the conduction band. As a result of light absorption by the quantum dots, the current increases, and power generation efficiency can be improved (Non-Patent Document 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 attempts have been made to achieve this using the same epitaxial growth method as semiconductor lasers (Non-Patent Document 3). However, with the epitaxial growth method, it is extremely difficult to achieve a sufficiently uniform quantum dot array structure while maintaining high quantum efficiency, and the conversion efficiency of prototype solar cells has remained very low.

[0010] Furthermore, as described in Non-Patent Document 2, a method has been developed in which a semiconductor quantum dot superlattice is fabricated by the layer-by-layer method, and the dimensional control of quantum resonance is achieved by controlling the distance between quantum dots in the in-plane and stacking directions. Quantum resonance between closely spaced quantum dots dramatically improves charge mobility, making it important to understand the optical and electronic properties based on quantum resonance for device applications. Light-emitting properties are manifested based on the dimensionality of the quantum dot superlattice structure, in which semiconductor quantum dots are closely spaced in one, two, and three dimensions.

[0011] Furthermore, as a leading candidate for next-generation solar cells, there is a perovskite solar cell, which has been reported to have a rapid increase in photoelectric conversion efficiency in recent years. This perovskite solar cell is made of a perovskite compound (CH ３ NH ３ PbI ３ The present invention provides a photoelectric conversion element using a perovskite compound as a light absorption layer (Non-Patent Document 4). It is known that the chemical and physical properties of perovskite compounds change depending on the composition of cation species, halogen elements, metal elements, etc. For example, it has been reported that by substituting iodine as a halogen element with bromine, the durability of the photoelectric conversion element improves, but the conversion efficiency decreases due to the shortening of the absorption wavelength of the perovskite compound (increase in band gap energy) (Non-Patent Document 5).

[0012] ACS Nano 2014, 8, 614-622 Nature Communications, 10.1038 / s41467-020-19337-0 Takeki Mukai, Yokohama National University, Grant-in-Aid for Scientific Research (Grant-in-Aid for Research C) 18K04972 (2020) J. Am. Chem. Soc. 2009, 131, 6050-6051 Nano Lett. 2013, 13, 1764-1769Chemical Physics Letters 2012, 542, 89-93

[0013] However, conventional photoelectric conversion elements using quantum dots do not combine excellent durability with high conversion efficiency. For example, quantum dots are susceptible to surface oxidation in the atmosphere, which leads to a decrease in photoelectric conversion efficiency over time and poor durability. Furthermore, perovskite compounds decompose due to moisture in the atmosphere, which causes durability problems.

[0014] Furthermore, conventional quantum dot solar cells contain 500 to 100 billion quantum dots per square centimeter, but to increase efficiency, 10 times as many quantum dots as currently available are needed, and there is a need to develop technology to create even smaller quantum dots and to arrange them in a way that will improve efficiency.

[0015] Furthermore, to confine electrons in quantum dots and achieve the "intermediate band" method, electrons that absorb photon energy and are excited to the intermediate band must be three-dimensionally superimposed so that they can absorb the energy of a second photon and extract it outside the quantum dot. However, sufficient technology for absorbing this second photon energy and extracting it outside the quantum dot has not yet been established.

[0016] Furthermore, since there is a possibility that electrons that escape from the quantum dots will be captured again by another quantum dot on their way to the electrode after moving by diffusion and drift, it is necessary to optimize the cell structure so that the process of capture and photoexcitation (escape) can be repeated and ultimately extracted as a current. The lifetime of multiple excitons is said to be several tens of picoseconds, and charge separation into electrons and holes must be achieved within this time (Non-Patent Document 6).

[0017] An object of the present invention is to provide a method for producing a nanocomposite having novel quantum dots that is different from conventional methods, and to provide a nanocomposite having such quantum dots.

[0018] In order to achieve the above-mentioned object, the present invention provides a method for producing a nanocomposite having quantum dots, which comprises using a gap formed by a plurality of linear conductors arranged at intervals of 1 nm to 100 μm as a reaction field, depositing or supporting a nanocomposite consisting of a nanoparticle that is the core of the nanocomposite and quantum dots attached to the surface of the nanoparticle on the linear conductor, and synthesizing the nanocomposite so that the plurality of nanocomposite particles exist in a mutually discrete or aggregated, adsorbed or bonded state.

[0019] It is also preferable that the linear conductor is a linear polymer.

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

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

[0022] The nanoparticles are preferably made of an inorganic semiconductor.

[0023] It is also 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 is synthesized in the gaps between the linear polymers by controlling at least one parameter of the reactant concentration, reaction pH, reaction temperature, and reaction time.

[0024] The linear conductor is a linear polymer, and the nanoparticles are iron oxide or TiO ２ and the quantum dots are FeS ２ It is preferable that the material consists of:

[0025] In this case, the linear polymer is polyaniline, and the iron oxide or the TiO ２ The nanoparticles are then coated with the FeS ２ It is preferable to deposit or support quantum dots made of the above.

[0026] Furthermore, in this case, the iron oxide or TiO ２ and a process for the formation of nanoparticles consisting of said iron oxide or TiO ２ The nanoparticles are then coated with the FeS ２ and a process for depositing or supporting quantum dots consisting of the iron oxide or TiO ２ Nanoparticles consisting of the FeS ２ It is preferable to synthesize a nanocomposite made of quantum dots comprising the above-mentioned polyaniline by linking them in the polymer linear chain direction.

[0027] Furthermore, the iron oxide or TiO ２ and the nanoparticles comprising the FeS ２ and (iii) are synthesized in the gaps of the polyaniline by a reaction in an aqueous solution or an electrodeposition reaction, and by controlling at least one parameter of the reactant concentration, reaction pH, reaction temperature, and reaction time.

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

[0029] The present invention also provides a method for producing a solar cell, characterized in that a nanocomposite having quantum dots produced by any of the above methods is used in the production of a dye-sensitized solar cell or an organic solar cell.

[0030] In this case, it is preferable that the linear conductor is a linear organic polymer, the linear organic polymer is grown in a direction almost perpendicular to the electrode of the battery, and the linear organic polymer in which the nanoparticles and quantum dots are formed using the gaps between the linear conductors as a reaction field is used as the positive electrode.

[0031] Furthermore, in the method for producing a nanocomposite having quantum dots of the present invention, the nanocomposite is synthesized so that it exists in a mutually dispersed or aggregated, adsorbed or bonded state, and then the nanocomposite can be further released and recovered from the linear conductor.

[0032] The present invention also provides a method for producing quantum dots, which comprises synthesizing the plurality of nanocomposites by any of the above methods so that they exist in a mutually dispersed or aggregated, adsorbed or bound state, and then liberating and recovering the quantum dots constituting the nanocomposites from the linear conductor.

[0033] The present invention also provides a nanocomposite having quantum dots, which comprises a nanocomposite consisting of a nanoparticle that is the core of the nanocomposite and quantum dots attached to the surface of the nanoparticle, and which is located in a gap between a plurality of linear conductors arranged at intervals of 1 nm or more and 100 μm or less, and in which a plurality of the nanocomposites exist in a state of being adsorbed or bonded to each other, either discretely or in aggregates.

[0034] The method for producing a nanocomposite having quantum dots of the present invention can provide a novel method for producing a nanocomposite having quantum dots that is different from conventional methods. Furthermore, the present invention can produce such a nanocomposite having quantum dots. The method for producing a nanocomposite having quantum dots of the present invention can produce a nanocomposite having quantum dots with a structure that can be called "linearly arranged quantum dots." Such nanocomposite having linearly arranged quantum dots can be applied to high-performance photoelectric conversion elements, and can be used in electrical energy, quantum computers, medicine, agriculture, and forestry.

[0035] Fig. 1 is a schematic diagram showing an example of a nanocomposite having quantum dots of the present invention. Fig. 2 is a schematic diagram showing an example of a method for producing quantum dots of the present invention. Fig. 3 is a schematic diagram showing an example of a dye-sensitized solar cell using a nanocomposite having quantum dots of the present invention. Fig. 4 is a schematic diagram showing an example of a terahertz electromagnetic wave generator using a nanocomposite having quantum dots of the present invention.

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

[0037] The method for producing a nanocomposite having quantum dots of the present invention is characterized by using a gap between a plurality of linear conductors arranged at intervals of 1 nm or more and 100 μm or less as a reaction field, depositing or supporting a nanocomposite consisting of a nanoparticle that is the core of the nanocomposite and quantum dots attached to the surface of the nanoparticle on the linear conductor, and synthesizing the plurality of nanocomposite particles so that they exist in a mutually discrete or aggregated, adsorbed or bonded state.

[0038] Furthermore, the quantum dot-containing nanocomposite of the present invention is a nanocomposite comprising a nanoparticle that is the core of the nanocomposite and quantum dots attached to the surface of the nanoparticle, which is located in a gap between a plurality of linear conductors arranged at intervals of 1 nm or more and 100 μm or less, and is characterized in that the plurality of nanocomposite particles exist in a state of being mutually adsorbed or bonded, either discretely or in aggregates.

[0039] [Embodiment 1] (Configuration of nanocomposite and synthesis method thereof) A schematic diagram showing a nanocomposite produced by the method of producing a nanocomposite having quantum dots of the present invention is shown in Figure 1. The quantum dots shown in Figure 1 can be called "linearly arranged quantum dots."

[0040] As described above, the present invention provides a nanocomposite 10 having quantum dots 14 (see FIGS. 1(a) and 1(b)). In the present invention, a nanocomposite 10 is provided, which is made up of a nanoparticle 12 that is the core of the nanocomposite 10 and quantum dots 14 attached to the surface of the nanoparticle 12, and is placed in a gap between a plurality of linear conductors 24 arranged at intervals of 1 nm to 100 μm (FIG. 1(a) shows an example of 50 to 100 nm). The present invention is also characterized in that a plurality of nanocomposites 10 exist in a mutually adsorbed or bonded state, either discretely or in aggregate.

[0041] Nanocomposites 10 having such quantum dots 14 are prepared by depositing or supporting nanocomposites 10 consisting of nanoparticles 12, which are the cores of nanocomposites 10, and quantum dots 14 attached to the surfaces of nanoparticles 12, on linear conductors 24 in a reaction field formed by gaps between multiple linear conductors 24 spaced at intervals of 1 nm to 100 μm, as described above. In this process, the nanocomposites 10 are synthesized so that they exist in a state of being adsorbed or bonded to each other, either discretely or aggregated. Furthermore, gaps between multiple linear conductors 24 spaced at intervals of 1 nm to 100 μm can be prepared by forming multiple linear conductors 24 on electrode 22 shown in FIG. 1( a).

[0042] In this case, it is preferable that the linear conductor 24 is a straight-chain polymer, and more preferably, this straight-chain polymer is polyaniline.

[0043] It is also preferable that the quantum dots 14 be made of at least one of iron oxide, iron sulfide, CdSe, PbS, and PbSe, which have a band gap in the visible light region.

[0044] It is also preferable that the nanoparticles 12 are made of an inorganic semiconductor, in particular, iron oxide or TiO ２ It is preferable that the material consists of:

[0045] In the present invention, the linear conductor 24 is a linear polymer, and at least one of the nanoparticles 12 and the quantum dots 14 is synthesized by a reaction in an aqueous solution or an electrodeposition reaction, and can be synthesized in the gaps between the linear polymers by controlling at least one parameter of the reactant concentration, reaction pH, reaction temperature, and reaction time. In this case, it is particularly preferable to use polyaniline as the linear polymer, and to synthesize iron oxide or TiO by a reaction in an aqueous solution or an electrodeposition reaction. ２ Nanoparticles 12 consisting of FeS ２ The quantum dots 14 can be deposited or supported.

[0046] In the present invention, it is particularly preferred that the reaction field be the gaps between the polymer bundles formed by growing straight-chain polymers in a direction perpendicular to the surface of the transparent electrode and parallel to each other.

[0047] A more specific example will be described with reference to FIG. 1 , but the present invention is not limited thereto. A polymer fiber bundle consisting of, for example, approximately 1,000 fibers of polyaniline, a conductive polymer, can be used as one linear conductor 24. For example, fluorine-doped tin oxide (FTO) can be used as the electrode 22. An FTO transparent electrode formed on a glass plate can be used. By arranging a large number of the polymer fiber bundles on the surface of the FTO transparent electrode at intervals of, for example, 30 nm, the resulting gaps can be used as a reaction field. In such a reaction field, for example, αFe, which is one of the iron oxides, can be used. ２ O ３ Nanoparticles (core nanoparticles 12) are deposited by electrodeposition in ohmic contact with some of the polyaniline fibers, and the αFe nanoparticles are further deposited by electrodeposition from a reaction solution containing at least ferrous ions and sulfur ions. ２ O ３ FeS on the nanoparticle surface ２ The nanocomposite 10 can be synthesized by three-dimensionally depositing quantum dots (quantum dots 14) particles having a size of, for example, 2 nm to 10 nm.

[0048] The conductive polymer used as the linear conductor 24 may be polyacetylene, polyparaphenylene, polythiophene, polypyrrole, or the like, in addition to the polyaniline. The nanoparticles may be TiO ２ Furthermore, the FeS ２ The quantum dots may be any of iron oxide, iron sulfide, CdSe, PbS, and PbSe quantum dots that have a band gap in the visible light region.

[0049] The size of the nanoparticles can be changed by the reaction time of electrodeposition, etc., and so by changing the current passage time and timing of electrodeposition, the size of the nanoparticles can be designed to various sizes. This results in a structure in which incident light is scattered in a complex manner, and when used as a solar cell, so-called "light confinement" can be achieved, allowing for increased photoelectric conversion efficiency with a short battery cell thickness.

[0050] Moreover, the αFe２ O ３ The method of depositing nanoparticles by electrodeposition can be replaced by a method of immersing the gaps in the reaction field in a dispersion of nanoparticles prepared in advance. ２ O ３ FeS on the nanoparticle surface ２ The method for three-dimensionally depositing quantum dots of 2 nm to 10 nm may be a method of immersing in a pre-prepared quantum dot solution, and the size 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, it is possible to form a layer structure of photoelectric conversion elements with different characteristics. Furthermore, the diameter of the polymer fiber bundle can be freely determined by the size of the through-holes formed in the film that is previously masked on the surface of the FTO transparent electrode substrate.

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

[0053] By varying the size of the nanoparticles, "light confinement" of incident photons is possible, increasing light absorption and improving photoelectric conversion efficiency. However, increasing the cell thickness is considered to further increase absorption. However, in this case, increasing the thickness increases the contact area between the electrode and the electrolyte, which raises concerns about the possibility of electrons injected from the quantum dot dye into the nanoparticles flowing from the electrode to the electrolyte and the possibility of electrons recombining from the electrode to the oxidized quantum dot dye. However, when polyaniline is used as the linear polymer conductor as in embodiment 1 of the present invention, the nanoparticles are individually in ohmic contact with the linear polymer conductor, so even if the contact area with the electrolyte increases, the probability of electrons flowing to the electrolyte and electron recombination with the quantum dot dye are unlikely to occur. In other words, in embodiment 1 of the present invention, increasing the cell thickness does not decrease photoelectric conversion efficiency; rather, increasing the cell thickness increases light absorption efficiency, thereby improving photoelectric conversion efficiency.

[0054] [Embodiment 2] (Synthesis of free nanocomposites and free quantum dots using the synthesis of the nanocomposite of embodiment 1) The present invention can produce nanocomposites 10 on linear conductors 24 as shown in embodiment 1, but it can also synthesize free nanocomposites and free quantum dots as shown in embodiment 2 described below.

[0055] That is, in the present invention, multiple nanocomposites 10 are synthesized on a linear conductor 24 so that they exist in a mutually dispersed or aggregated, adsorbed or bonded state, and then the nanocomposites 10 can be released and recovered from the linear conductor 24.

[0056] Furthermore, after synthesizing multiple nanocomposites 10 so that they exist in a mutually discrete or aggregated, adsorbed or bonded state, the quantum dots 14 that make up the nanocomposites 10 can be further separated and recovered from the linear conductor 24.

[0057] A more specific embodiment of the method for freeing and recovering quantum dots 14 in this second embodiment will be described with reference to Fig. 2. Fig. 2 is a diagram showing a method for synthesizing quantum dots of various inorganic compounds to a desired size and with a sharp uniformity in size, using the method for synthesizing a nanocomposite using linearly arranged quantum dots of the present invention.

[0058] In the same manner as in the first embodiment, a polymer fiber bundle consisting of approximately 1,000 to several tens of thousands of polyaniline fibers is arranged as a single linear conductor 24 at intervals of, for example, 10 nm on the surface of the FTO transparent electrode of a glass plate. The resulting gaps are used as reaction fields, and FeS is electrolytically deposited from a reaction solution containing at least ferrous ions and sulfur ions. ２ Quantum dots of 14 nm are synthesized. Then, the glass plate is removed from the reaction solution and immersed in a solvent for dispersing nanoparticles, for example, an ethanol solution in which ethanolamine is dissolved as a dispersant, and an ethanol solution in which the quantum dots 14 are dissolved is obtained by ultrasonic treatment.

[0059] The conductive polymer may be polyparaphenylene, polythiophene, polypyrrole, or the like. ２ The quantum dots may be any of iron oxide, iron sulfide, CdSe, PbS, and PbSe quantum dots that have a band gap in the visible light region.

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

[0061] [Embodiment 3] (Dye-sensitized solar cell using nanocomposite) The nanocomposite having quantum dots produced by the method of the present invention can be used to produce a dye-sensitized solar cell or an organic solar cell. In this case, linear conductors 24 are grown in a direction approximately perpendicular to the battery electrode, and the gaps between the linear conductors 24 formed by the linear conductor bundles serve as reaction fields, resulting in an organic polymer formed from nanoparticles 12 and quantum dots 14 serving as the positive electrode. A specific embodiment of the dye-sensitized solar cell will be described with reference to FIG. 3.

[0062] FIG. 3 is a diagram showing a dye-sensitized solar cell fabricated using the nanocomposite 10 of the present invention as the anode.

[0063] The nanocomposite shown in FIG. 3 is a polymer fiber bundle (10 micrometers long) consisting of approximately 3,000 polyaniline fibers in embodiment 1, an FTO transparent electrode, a 30 nm spacing, and αFe ２ O ３ Electrodeposition of nanoparticles, FeS ２ The quantum dots synthesized with 2 nm were described as an example. This was used as the anode, and the counter electrode was FeS ２ and 0.5M Na in a mixed solvent of ethanol and water (8:2). ２ The electrolyte was a solution of 0.1M S, 0.1M S, and 0.05M GuSCN (guanidine thiocyanate), and the output was 100mW / cm ２ A conversion efficiency of 35% was obtained by irradiating the solar cell with simulated sunlight. The particle size was measured using a transmission electron microscope photograph.

[0064] αFe ２ O ３ Nanoparticles are generally made porous or nano-sized to increase light absorption and specific surface area at the interface between different materials, but in the present invention, the specific surface area can be increased by using nanoparticles.

[0065] Increasing the thickness between the electrodes to sufficiently absorb incident photons generally increases the contact area between the electrode and the electrolyte, increasing 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, resulting in a decrease in photothermal conversion efficiency. However, in embodiment 1 of the present invention, electrons transferred from the quantum dot dye to a single nanoparticle flow into the conductive polymer with which they are in ohmic contact, significantly reducing the probability of their flow into the electrolyte. This makes it possible to increase the thickness between the electrodes, thereby increasing the number of quantum dot dyes and enabling electrodes with a large absorption coefficient to absorb photons up to nearly 100%, thereby reducing energy loss during light utilization and improving efficiency.

[0066] In this way, the inventors have discovered that by using a light absorption layer made of linearly arranged quantum dot photoelectric conversion elements, which are 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] That is, in conventional quantum dot solar cells, the method of electrodeposition or spin coating on a substrate followed by annealing treatment has limitations in densely packing quantum dots of several tens of nanometers, and it is difficult to control the arrangement required to improve photoelectric conversion efficiency. In view of this, the method of arranging the quantum dots themselves has been drastically changed to linearly arrange them in the linear chain direction of the conductive polymer, and to arrange them in a linear manner by using iron oxide nanoparticles or TiO ohmically bonded to the conductive polymer. ２ The photoelectric conversion element was made by electrodepositing or supporting quantum dots on the surface of nanoparticles.

[0068] Iron oxide nanoparticles or TiO ２ At the interface between nanoparticles and quantum dots, excitons generated by absorbed light become free carriers. However, as the distance from the interface increases, the excitons simply absorb light and no longer generate photocurrent, resulting in reduced conversion efficiency. To address this issue, solar cells have been designed to disperse incident sunlight at the surface, increasing the optical path and randomly absorbing light at quantum dot interfaces, thereby increasing light absorption efficiency. Furthermore, cell layers have been made as thin as possible to minimize the distance from the interface. However, thinning the cell layer and increasing the density of quantum dots are mutually exclusive. This contradiction in existing technologies has resulted in low photoelectric conversion efficiencies. After extensive research into ways to resolve this contradiction, we devised the linear arrangement method of the present invention, which is one possible solution.

[0069] Iron oxide nanoparticles or TiO ２ By making an ohmic contact between the nanoparticles and the conductor extending linearly on the surface of the solar cell, TiO ２The carrier electrons transferred to the nanoparticles can be directly extracted from the nanoparticles, whereas in the prior art, the carrier electrons are directly extracted from the nanoparticles between iron oxide nanoparticles or TiO ２ This is to prevent carrier electrons from being lost while moving between nanoparticles. ２ The quantum dots deposited or supported on the TiO ２ The heterogeneous interfaces with the nanoparticles are arranged in a straight line, and the heterogeneous interfaces that absorb light are linear in this way. This arrangement of heterogeneous interfaces in a straight line is completely different from existing technologies, and we will call it a linear arrangement.

[0070] One iron oxide nanoparticle or TiO ２ Since many quantum dots are electrodeposited or supported on the surface of the nanoparticles, it is possible to obtain a single iron oxide nanoparticle or TiO ２ Nanoparticles have many heterogeneous interfaces, and electrons excited by excitons due to light absorption at each of these interfaces are transported as free electrons to an external circuit via ohmic contacts, significantly reducing carrier recombination compared to conventional techniques.

[0071] The light absorption wavelength of quantum dots is iron oxide nanoparticles or TiO ２ Because the conversion efficiency depends on the size of the quantum dots on the nanoparticle surface, quantum dots of a fixed size cannot accommodate a wide range of solar wavelengths, resulting in reduced conversion efficiency. To solve this problem, the present invention allows the size of the quantum dots to be varied along the linear direction of the linear arrangement, allowing a wide range of wavelengths of light to be absorbed.

[0072] Iron oxide nanoparticles or TiO ２ The density of quantum dots on the nanoparticle surface can be increased from a small value to a three-dimensional overlap by changing the electrodeposition reaction time on the surface or the solution concentration when supporting the dots.

[0073] The structure allows incident light to penetrate deep into the cell, increasing absorption efficiency, and by forming an ohmic junction between the photoelectric conversion element and the conductive polymer, it is possible to make it difficult for excited electrons from deep inside to recombine with holes or recombine within the quantum dots. This makes it possible to dramatically improve quantum dot density and absorption efficiency, thereby improving conversion efficiency.

[0074] Iron oxide nanoparticles or TiO in photoelectric conversion elements ２ The quantum dots electrodeposited or supported on the nanoparticle surface overlap three-dimensionally, allowing them to absorb light over a wide wavelength range, including long wavelengths such as near-infrared, which can be absorbed by quantum dots. This makes it possible to obtain a photoelectric conversion element that has photoelectric conversion functionality over a wide wavelength range.

[0075] When quantum dots are densely stacked in three dimensions, bands are formed between the quantum dots, forming a superlattice, which causes an infrared shift and allows the absorption of infrared rays of even the longest wavelengths. In other words, when used as a bifacial solar 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 using the nanocomposite of the present invention) Terahertz waves are electromagnetic waves that can easily penetrate plastics and fabrics other than metals. Unlike X-ray inspection, terahertz waves are harmless to the human body and have been put to practical use in security inspections of people at airports. They can be widely used in non-destructive inspections of baggage, inspections for foreign objects in food, device quality inspections to check for damage or deterioration, and medical applications.

[0077] Terahertz waves are electromagnetic waves with wavelengths between approximately 10 micrometers (frequency 30 terahertz) and 1 millimeter (frequency 300 gigahertz), lying between radio waves and light waves. Their vibrational frequencies overlap with the vibrational frequencies of molecules that make up matter, giving them unique characteristics not found in other electromagnetic waves. This allows for the fingerprint spectrum of almost every substance to be present. As a result, rapid progress has been made in the development of terahertz-wave-based technologies in various academic and industrial fields, including spectroscopy and imaging for safety and security, as well as ultra-high-speed wireless communication. In particular, the development of next-generation ultra-high-speed wireless communication technologies using terahertz waves, such as 6G and 7G, is essential for dramatically improving information and communication services, which are essential for realizing an ultra-smart society. However, both electronic devices such as transistors and optical devices such as lasers have had great difficulty operating in the terahertz band due to their inherent physical limitations. In particular, the realization of room-temperature, compact, and battery-powered terahertz amplifiers and lasers, which are essential for transmitting 6G and 7G wireless signals, remains a challenge.

[0078] Figure 4 shows a terahertz electromagnetic wave generator fabricated using a nanocomposite anode composed of linear electrons, polyaniline, GaAs nanoparticles, and p-type InAs quantum dots, and a non-aqueous electrolyte solution in which polysulfide is difficult to form hydrogen bonds. When a quantum dot semiconductor superlattice formed by 3D assembly of the quantum dots of the present invention was applied to terahertz time-domain spectroscopy, it was possible to generate 100 Hz electromagnetic waves. It was also possible to detect terahertz waves and operate as a receiver.

[0079] [Embodiment 5] (Quantum bit transfer and reproduction using the nanocomposite of the present invention) In 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, we demonstrated broadband (> THz), high time-bandwidth product (> 103), time mode preservation, and direct transfer of telecommunication wavelength band photons using ultrasensitive heterodyne detection photon echo spectroscopy. This demonstrated that the photon echo spectroscopy is capable of transferring and reproducing picosecond single-photon time-bin quantum bits.

[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, strong interactions with the surroundings cause the quantum coherence of electron systems to be lost within an extremely short time, on the order of a few picoseconds (decoherence). Therefore, to achieve quantum control, even shorter femtosecond pulses are required. With the widespread use of titanium sapphire lasers, it is now possible to obtain ultrashort optical pulses of a few tens of femtoseconds using commercially available lasers. This has made quantum control experiments relatively accessible to anyone, and the range of research subjects is expanding.

[0081] In addition to advanced technologies for controlling the waveform and phase of optical pulses, technologies for generating unique types of light, such as single photons, entangled photon pairs, and squeezed light, have been developed, and efforts to achieve more complex and diverse quantum control are underway toward the practical application of quantum computers. Meanwhile, advances in nanotechnology have made it possible to fabricate high-quality semiconductor quantum dots, also known as "artificial atoms," using solid-state chemistry, electrochemistry, and solution chemistry. This has made it possible to prepare steady-state electronic systems suitable for quantum control. Furthermore, by incorporating quantum dots into microcavities or photonic crystals, it is becoming possible to freely control the strength of coupling with light. Embodiment 5 of the present invention provides new, unique technologies related to these technologies.

[0082] Quantum memory is a key device for realizing many quantum information protocols, including quantum repeaters. Furthermore, constructing quantum memory using quantum bits capable of quantum gate operation is opening up new applications, such as the realization of distributed quantum computers. Furthermore, transferring quantum entangled photon pairs is enabling the generation of quantum entanglement states between distant materials and quantum teleportation. The fifth embodiment of the present invention is an important fundamental technology related to such quantum memory that contributes to all research fields, including not only quantum information but also quantum mechanics and condensed matter physics.

[0083] There is a desire to realize quantum memory in solid state, and quantum dots are one of the leading candidates. Quantum dots have the advantages of being small and easy to integrate, and they can be used with ultrashort pulses. Their transition wavelengths can be adjusted to the telecommunication wavelength range, making them suitable for the construction of quantum memories suitable for telecommunication applications. Furthermore, the strong interactions between quantum dots make high-speed quantum gate operations possible, which is attractive for some applications.

[0084] However, quantum dots have a problem in that the size and degree of distortion of each dot varies, which causes inhomogeneity in the transition wavelength and the strength of coupling with light. To avoid the effects of inhomogeneity, most quantum control experiments have been carried out on single quantum dots, and the challenge is how to strengthen the interaction with light.

[0085] A new type of quantum memory using the photon echo method has been developed that can be applied to quantum dot ensembles with large heterogeneities, making it possible to use the photon echo method from quantum dot ensembles in the telecommunications wavelength range.

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

[0087] [Embodiment 7] (Application of the Nanocomposite of the Present Invention to the Biomedical Field) The biomedical field is a new industry for terahertz electromagnetic waves. One promising application is biosensing. This is because the frequency band, energy, and time domain correspond to the movement of large molecules, hydration reactions such as the interaction between living proteins and water, and hydrogen bond energy in DNA, and they are highly sensitive to ionic solutions such as water. As a result, applications are expected in biochips and drug discovery, evaluation of pharmaceutical crystal polymorphism, detection of drug mixing defects through component analysis, non-destructive testing of tablet coatings, biomolecule manipulation and selective culture promotion using high-intensity terahertz light, pre-symptomatic diagnosis, and more. This field is a new industrial field with a bright future.

[0088] The most widely used technique is terahertz time-domain spectroscopy (THz-TDS). The basic principle is to generate pulsed electromagnetic waves using femtosecond optical pulses, and a high-speed detector that operates only when the optical pulse is incident on the detector can perform time-domain measurements by applying a time delay to the optical pulse. Commercially available THz-TDS detectors can determine the complex refractive index of a material over a wide frequency range (approximately 0.1 THz to 5 THz for popular models) based on the transmission and reflection characteristics of the pulsed electromagnetic wave. From this refractive index, the dielectric constant and conductivity can be calculated. Furthermore, because measurements are performed in the time domain, they can also be used as 3D THz-CT by utilizing the reflection and transmission characteristics at various material interfaces. Various applications are being investigated, such as the 2D depth distribution of skin cancer and the distribution of coatings on pharmaceutical tablets.

[0089] Although it has been more than ten years since general-purpose THz-TDS was commercially available, its use has not been widespread compared to its expected applications. One reason is that the beam diameter of terahertz waves is large, making it unsuitable for microinspection and high-resolution imaging. Another reason is that the imaging acquisition time is impractical due to the trade-off between imaging time and cost.

[0090] Terahertz waves have a longer wavelength than light, which makes the image grainy. In addition, terahertz waves have too little energy to be measured as light and too high a frequency to be measured as radio waves, which makes their detection sensitivity extremely poor. Therefore, it is necessary to increase the output power of terahertz waves.

[0091] D. H. Auston et al. reported the generation of picosecond-order pulses and the measurement of temporal waveforms using an ultrashort pulse laser, 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 a short period of time, which became known as terahertz time-domain spectroscopy (THz-TDS).

[0092] A typical detector is the Schottky barrier diode, which can detect rectification by utilizing the nonlinearity of the IV characteristics generated by the Schottky junction. Further detectors widely used in THz-TDS include photoconductive antennas (PCAs), which detect the electric field strength of terahertz waves by the instantaneous current generated between the antennas when a femtosecond laser is used to optically excite the minute gap between the antennas, and electro-optic crystals, which detect the electric field strength of terahertz waves by converting it to the birefringence of the probe light. These detectors are often used in wireless communications and spectroscopic research, and there is a demand for lower costs and higher 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 into near-infrared light with high photon energy and then measures the wavelength using a highly sensitive near-infrared camera. The nonlinear optical crystal used is the organic nonlinear optical crystal DAST, which allows for flexible wavelength conversion between terahertz waves and near-infrared light. This means that the echo image of the reflected terahertz waves emitted for diagnostic purposes can be highly sensitive, thus resolving the problem of high sensitivity of echo images. However, the intensity of the reflected terahertz waves themselves remains low, and even if clear images can be obtained, imaging of deeper areas is difficult, making transmission imaging impossible. To solve this problem, it is necessary to increase the intensity of the emitted terahertz waves themselves.

[0094] Using the terahertz electromagnetic wave generator of the fourth embodiment, visible light or CW laser light was superimposed and irradiated by terahertz time-domain spectroscopy, and simultaneously a potential of 1 to 10 V was applied between both electrodes, and electromagnetic waves of 1 to 3 tesla, equivalent to several watts, could be emitted, thereby increasing the intensity of the terahertz waves.

[0095] [Embodiment 8] Polyaniline that had been converted to n-type metallic properties by an oxide reduction was used as the linear conductor 24 (conductive wire), and a solar cell with the structure of Embodiment 3 was formed. Zn-, Mn-, Ni-, or Mg-ferrite treated with hydrogen gas or atomic hydrogen at 100-150°C was used as the oxide reduction material. The conductivity depends on the hydrogen treatment time, but at 150°C, a conversion efficiency of 16% was obtained after 10 minutes or more. Although the method for forming n-type metallic polyaniline is an existing technology, the method of this embodiment can achieve higher conductivity than conventional techniques.

[0096] [Embodiment 9] The oxide reductant (ferrite reductant) used in embodiment 8 was replaced with hydrogen sulfide gas (H ２ S) at room temperature to 80°C by gas contact to deposit metal sulfides consisting of iron ions or ferrite-containing metal ions as quantum dots on the surface of the oxide reductant, and this was formed into a solar cell having the structure of Embodiment 3, resulting in a conversion efficiency of 23%.

[0097] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention.

Claims

1. A method for producing a nanocomposite having quantum dots, comprising the steps of: using a gap between multiple linear conductors arranged at intervals of 1 nm or more and 100 μm or less as a reaction field; depositing or supporting a nanocomposite consisting of a nanoparticle that is the core of the nanocomposite and quantum dots attached to the surface of the nanoparticle on the linear conductor; and synthesizing the multiple nanocomposite so that they exist in a mutually discrete or aggregated, adsorbed or bonded state.

2. The method of claim 1, wherein said linear conductor is a linear polymer.

3. The method of claim 2, wherein said linear polymer is polyaniline.

4. The method according to claim 1, wherein the quantum dots are made of at least one of iron oxide, iron sulfide, CdSe, PbS, and PbSe, each of which has a band gap in the visible light region.

5. The method of claim 1, wherein said nanoparticles are inorganic semiconductors.

6. The method according to claim 1, characterized in 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 is 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, and the nanoparticles are iron oxide or TiO ２ The quantum dots are FeS ２ 2. The method of claim 1, comprising:

8. The linear polymer is polyaniline, and the iron oxide or the TiO is produced by a reaction in an aqueous solution and an electrodeposition reaction. ２ The nanoparticles are then coated with the FeS ２ The method according to claim 7, characterized in that quantum dots consisting of 9. The iron oxide or TiO ２ and a process for the formation of nanoparticles consisting of said iron oxide or TiO ２ The nanoparticles are then coated with the FeS ２ and repeating the process of precipitating or supporting quantum dots consisting of the iron oxide or TiO ２ The nanoparticles and the FeS ２ The method according to claim 8, characterized in that a nanocomposite consisting of quantum dots comprising the above-mentioned is synthesized by linking the quantum dots in the direction of a polymer linear chain of the polyaniline.

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

11. The method according to claim 2, characterized in that the reaction field is the gap between the polymer bundles formed by growing the linear polymers in a direction perpendicular to the transparent electrode surface and parallel to each other.

12. A method for producing a solar cell, comprising using a nanocomposite having quantum dots produced by the method according to any one of claims 1 to 10 in the production of a dye-sensitized solar cell or an organic solar cell.

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

14. The method according to claim 1, further comprising synthesizing the plurality of nanocomposites so that they exist in a mutually discrete or aggregated, adsorbed or bound state, and then releasing and recovering the nanocomposites from the linear conductor.

15. A method for producing quantum dots, comprising synthesizing the plurality of nanocomposites by the method according to any one of claims 1 to 10 so that they are mutually separated or aggregated and exist in an adsorbed or bonded state, and then liberating and recovering the quantum dots constituting the nanocomposites from the linear conductor.

16. A nanocomposite having quantum dots, comprising a nanocomposite consisting of a nanoparticle that is the core of the nanocomposite and a quantum dot attached to the surface of the nanoparticle, in a gap between a plurality of linear conductors arranged at intervals of 1 nm or more and 100 μm or less, and wherein a plurality of the nanocomposite are present in a state of being mutually adsorbed or bonded, either discretely or in aggregates.

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