JP2013149729A - Quantum dot structure, wavelength conversion element, and photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quantum dot structure, excellent in utilization efficiency of an incident light and excellent in light emission characteristics.SOLUTION: The quantum dot structure comprises in a matrix: a quantum dot composed of a semiconductor or a metal element; and a hollow quantum dot having a hollow, where utilization efficiency of incident light or emitted light from a quantum dot is improved by a scattering function of the hollow quantum dot.

Description

  The present invention relates to a quantum dot structure in which hollow hollow quantum dots and quantum dots are arranged in a matrix layer, a wavelength conversion element, and a photoelectric conversion device, and in particular, a light emitting device such as a solar cell (photoelectric conversion device) or an LED. The present invention relates to a quantum dot structure that can be used for a light receiving sensor in the infrared region, a wavelength conversion element, a light-light conversion device, and the like.

Currently, research is actively conducted on solar cells. Among solar cells, a PN junction solar cell configured by bonding a P-type semiconductor and an N-type semiconductor, and a PIN junction solar cell configured by bonding a P-type semiconductor, an I-type semiconductor, and an N-type semiconductor, , Absorbs sunlight having energy greater than the band gap (Eg) between the conduction band and the valence band of the constituting semiconductor, and excites electrons from the valence band to the conductor to enter the valence band. Holes are generated and an electromotive force is generated in the solar cell.
A PN junction solar cell and a PIN junction solar cell have a single band gap and are called single junction solar cells.

  In the PN junction solar cell and the PIN junction solar cell, light having energy smaller than the band gap is transmitted without being absorbed. On the other hand, energy larger than the band gap is absorbed, but of the absorbed energy, the energy larger than the band gap is consumed as thermal energy as phonons. For this reason, single band gap single junction solar cells such as PN junction solar cells and PIN junction solar cells have a problem of poor energy conversion efficiency.

In order to improve the above-mentioned problem of energy conversion efficiency, a multi-junction solar cell having a structure in which a plurality of PN junctions and PIN junctions having different band gaps are stacked and light is sequentially absorbed from a large energy is developed. ing. However, since the multi-junction solar cell has a plurality of PN and PIN junctions electrically connected in series, the output current is the minimum current generated at each junction. For this reason, when the solar spectrum distribution is biased and the output of one PN junction or PIN junction is reduced, the outputs of the remaining PN junction and PIN junction that are not affected by the bias of the solar spectrum distribution are also reduced, and the entire solar cell As a result, there is a problem that the output is greatly reduced.
Moreover, in order to improve the above-mentioned problem of energy conversion efficiency, Non-Patent Document 1 uses quantum dots having band gaps of 0.7 to 1.4 eV and 1.4 to 2.1 eV. Quantum dot solar cells that can absorb broadband solar energy by forming an intermediate band by overlapping wave functions between quantum dots by arranging them have been proposed.

  Furthermore, by combining a solar cell with a wavelength conversion film that converts sunlight in the ultraviolet region and infrared region, which cannot be effectively used by conventional solar cells, into light that can be absorbed by conventional solar cells, a conversion efficiency of 40% or more is achieved. It has been proposed to aim (Non-Patent Documents 2 and 3).

In Non-Patent Document 2, when a passive light-emitting device that converts high energy to low energy (down conversion) is added to a single junction solar cell such as a Si crystal solar cell, or low energy is converted to high energy. It is theoretically proposed that when a passive light-emitting device (up-conversion) is added, the power generation efficiency is improved from 25% to 36% depending on the irradiation condition of the pseudo-sunlight. In Non-Patent Document 2, an experiment is performed using a sheet in which NaY _0.8 F ₄ : Er _0.2 ³⁺ particles having a diameter of 5 μm are introduced into a polymer.

In Non-Patent Document 3, in order to improve the external quantum efficiency of rare earth such as NaYF: Er, a Quantum-cutting effect (MEG (Multiple Excitation Generation) that converts one photon into two or more photons with half energy or less is used. It has been proposed to improve the external quantum efficiency by using () effect). Non-Patent Document 3 introduces an external quantum efficiency of 218% in an experiment with PbSe _QD by Nozik et al.

In this way, the light-light conversion filter that converts the wavelength of light having a wavelength of 500 nm or less in sunlight into light having a wavelength of about 1000 nm and converts one photon into two or more photons having energy half or less is used as a Si crystal solar. Conversion efficiency is improved by attaching to a single junction solar cell such as a battery.
For this purpose, it is necessary to use a relatively low band gap material of at least 1.0 eV or less. For example, as a relatively low band gap of 1.0 eV or less, there are Ge, SiGe, InN, InAs, FeSi, PbS, PbSe, and the like.

  In addition, the emission intensity is also improved. For example, Non-Patent Document 4 reports that plasmon improves luminous efficiency by forming a metal nanofilm such as Au and Ag with a thickness of 50 nm on an InGaN / GaN single quantum well (photoelectric conversion layer). Has been.

PHYSICAL REVIEW LETTERS, 78,5014 (1997) Solar Energy Materials and Solar Cell 90 (2006) 2329-2337 Solar Energy Materials and Solar Cell 91 (2007) 238-249 Surface Science Vol29, No6, pp344-349 (2008) "Plasmonics / Bio MEMS"

As described above, even if it has sufficient light-to-light conversion and photoelectric conversion functions, Fresnel reflection is performed with the optical path length from the incident light to the light output from the layer having the light-light conversion and photoelectric conversion functions. Optical energy loss due to optical loss such as loss is large. For this reason, it is necessary to suppress a light energy loss with a certain method with respect to the light-light conversion layer and the photoelectric conversion layer.
Even if a wavelength conversion film is used as described in Non-Patent Documents 2 and 3 above, or the light emission intensity is improved as in Non-Patent Document 4, the quantum dots provided in the light-light conversion layer and the photoelectric conversion layer are isotropic. In order to emit light, only effective solid-angle light that can be absorbed by the photoelectric conversion layer among the light re-irradiated from the wavelength conversion film or the like can be used. For this reason, in a device that is functionally designed in a vertical manner and stacked, at least about half of the light emitted from the quantum dots is irradiated in the opposite direction to the photoelectric conversion layer, resulting in light loss. There is.

An object of the present invention is to provide a quantum dot structure that solves the problems associated with the prior art and has high utilization efficiency of incident light. Another object of the present invention is to provide a quantum dot structure having excellent light emission characteristics.
Furthermore, the other object of this invention is to provide the wavelength conversion element and photoelectric conversion apparatus using a quantum dot structure.

  In order to achieve the above object, a first aspect of the present invention is a mode in which the light use efficiency of incident light or emitted light from quantum dots is improved by a scattering function of hollow quantum dots, and a matrix layer and the matrix Provided is a quantum dot structure comprising quantum dots composed of a semiconductor or a metal element formed in a layer and hollow hollow quantum dots formed in the matrix layer It is.

For example, the quantum dot is composed of a wavelength conversion composition that converts the wavelength of light into energy having lower energy than the absorbed light with respect to a specific wavelength region of the absorbed light.
For example, the matrix layer is made of an inorganic dielectric having a band gap of 3.0 eV or more, or an organic material having a transmittance of 70% or more according to JIS K7361-1: 1997.
In the quantum dots and the hollow quantum dots, the interval between the nearest neighbor particles is preferably 20 nm or less, more preferably 5 nm or less.
The quantum dots and the hollow quantum dots preferably have a particle size of 2 nm to 10 nm.
For example, the hollow forming material forming the hollow quantum dots and the matrix layer have the same composition.
At least one of the hollow quantum dots and the quantum dots is preferably arranged in a layered manner.

The cumulative film thickness of the hollow quantum dot layer composed of the hollow quantum dots arranged in the layered form is 50 nm or more, and the quantum dot composed of the quantum dots adjacent to the hollow quantum dot of the hollow quantum dot layer The distance between the layer and the hollow quantum dot layer is preferably 20 nm or less.
For example, the hollow quantum dots and the quantum dots may be randomly arranged. In this case, it is preferable that the thickness of the hollow quantum dots and the layer in which the quantum dots are randomly arranged is 100 nm or less.
The cumulative film thickness of the hollow quantum dot layer composed of the hollow quantum dots arranged in a layered manner is 50 nm or more in order to improve the light utilization efficiency of incident light and light emitted from the quantum dot by the scattering function of the hollow quantum dots. The accumulated film thickness is required. Further, when the hollow quantum dots and the quantum dots are randomly arranged, the film functions as an optical film if the film thickness is sufficiently larger than the incident light wavelength (λ / (4n)). The distance between the quantum dots adjacent to the hollow quantum dots of the first layer and the hollow quantum dots of the first layer is preferably 20 nm or less.

For example, the quantum dots may be phosphors, Si _x Ge _(1-x) , In _x Ga _(1-x) N, InAs, FeSi, PbS or PbSe, or fullerenes, organic fluorescent dyes or organic fluorescent substances. Consists of dye molecules.
For example, the hollow quantum dots include SiO ₂ , Si ₂ N ₃ , GaN, GaN or AlN, or acrylic resin, epoxy resin, ethylene vinyl acetate (EVA) resin, silicone resin, saturated polyester / polyethylene terephthalate (PET) resin. , Polyethylene naphthalate (PEN) resin, cross-linked fumaric acid diester resin, polycarbonate (PC) resin, cellulose resin, or transparent polyimide (PI).

A second aspect of the present invention includes the quantum dot structure according to the first aspect of the present invention, and each quantum dot has a lower energy than the absorbed light with respect to a specific wavelength region of the absorbed light. It consists of a wavelength conversion composition that converts the wavelength to light, and improves the light utilization efficiency of incident light and emitted light from the quantum dot by the scattering function of the hollow quantum dot, and also improves the transmittance of any wavelength region The wavelength conversion element characterized by having the wavelength conversion layer which has is provided.
According to a third aspect of the present invention, there is provided a photoelectric conversion device characterized in that the wavelength conversion element according to the second aspect of the present invention is provided on the incident light side of the photoelectric conversion layer.

The wavelength conversion element can improve the transmittance in a laminated configuration. In this case, a method is desired in which the refractive index of the wavelength conversion layer gradually approaches the refractive index of the photoelectric conversion layer from the refractive index of air.
When the density of the quantum dots and the hollow quantum dots in the matrix layer is changed, the refractive index can be arbitrarily changed. However, the upper limit of the content of the hollow quantum dots is estimated to be about 1/3 due to film strength and the like.
In addition, in order to improve the transmittance in the laminated structure, it is also possible to select a method in which the refractive index of the wavelength conversion element is continuously changed from the refractive index of air to approach the refractive index of the photoelectric conversion layer. .

  When the transmittance is improved in a stacked configuration, the wavelength conversion element includes, in order from the incident light side, the first layer in which only the hollow quantum dots are arranged, and the hollow quantum dots and the quantum dots are mixed. It is preferable that a second layer disposed in a row and a third layer in which only the quantum dots are disposed are provided.

In addition to this, sunlight irradiates broadband light of 300 nm to 1800 nm. For example, in a wavelength conversion element for a crystalline Si solar cell, sunlight is AR-coated with respect to broadband light of 300 nm to 1200 nm. It is hoped that For this purpose, it is necessary to make the refractive index of the first layer as close to air as possible, but by using hollow quantum dots, a lower refractive index is achieved than commercially available low refractive index optical materials such as SiO ₂ fluoropolymer. it can.
In this case, the thickness of the first layer is d _1a , the refractive index n _1a , the thickness of the second layer is d _1b , and the refractive index n _1a, and the second layer, the third layer, the total thickness of the _{d 1c} of, when the refractive index _{n 1c, λ / (4n 1a} ) ≒ d 1a, λ / (4n 1b) ≒ d 1b, is preferably _{λ / (4n 1c) ≒ d} 1c _and, n _1a << n _1c, preferably has a relation of _{n 1a <n 1b <n 1c} .
In addition, the second layer in which the hollow quantum dots and the quantum dots are mixedly disposed includes a method of configuring the hollow quantum dots and the quantum dots in a stacked shape, and the hollow quantum dots and the random in a random shape. It can be formed by a method of forming quantum dots.
In the laminated configuration, when the hollow quantum dot layer thickness is d _2a and the quantum dot layer thickness is d _2b , it is preferable that d _1a , d _1b , d _1c << d _2a , d _2b . Because, when the film thickness is of the order of the optical wavelength, the hollow quantum dot layer and the quantum dot layer become optical characteristics in a single layer rather than as a film in which hollow quantum dots and the quantum dots are mixed, This is because the contribution of the original optical design is not shown.

  The wavelength conversion element that continuously changes the refractive index has a first surface layer and a first back surface layer having different arrangement densities of the hollow quantum dots, and the first surface layer is the first surface layer. The arrangement density of the hollow quantum dots is higher than that of the first back surface layer, and the second front surface layer and the second back surface layer have different arrangement density of the quantum dots, and the second surface layer is more The refractive index is continuously changed by making the arrangement density of the quantum dots lower than that of the second back surface layer.

The wavelength conversion element includes, in order from the incident light side, a first arrangement density gradient layer in which the quantum dots and the hollow quantum dots are arranged randomly and an arrangement density gradient is formed, the quantum dots, and the hollow quantum dots Are arranged in layers and have a second arrangement density gradient layer in which an arrangement density gradient is formed.
In the first arrangement density gradient layer, it is preferable that 1 / 4λ >> d, where d is the thickness in the stacking direction of the region where the hollow quantum dots are locally arranged.
The wavelength conversion element may have a low refractive index layer, a refractive index gradient layer, and a high refractive index layer in order from the incident light side.

  According to the quantum dot structure of the present invention, the utilization efficiency of incident light can be increased. Furthermore, high light emission intensity can be obtained and the light emission characteristics are excellent. The quantum dot structure of the present invention can be applied to a solar cell (photoelectric conversion device), a light emitting device such as an LED, a light receiving sensor such as an infrared region, a wavelength conversion element, and a light-light conversion device.

(A) is typical sectional drawing which shows the quantum dot structure of embodiment of this invention, (b) is typical sectional which shows the 1st modification of the quantum dot structure of embodiment of this invention. It is a figure, (c) is typical sectional drawing which shows the 2nd modification of the quantum dot structure of embodiment of this invention, (d) is the quantum dot structure of embodiment of this invention. It is a typical sectional view showing the 3rd modification. It is a schematic diagram for demonstrating the effect | action of the quantum dot structure of embodiment of this invention. (A) is drawing substitute photograph which shows the TEM image of the quantum dot structure of embodiment of this invention, (b) is drawing substitute photograph which shows the TEM image of the other quantum dot structure for a comparison. is there. (A) is a graph which shows the time change of the light emission intensity of the quantum dot structure of embodiment of this invention, and the light emission intensity of the conventional quantum dot structure, (b) is the quantum dot of embodiment of this invention It is a graph which shows the emission spectrum of a structure. It is a schematic diagram for demonstrating the effect | action of the quantum dot structure of the 3rd modification of embodiment of this invention. It is a graph which shows the emission spectrum of the quantum dot structure of the 3rd modification of embodiment of this invention, and the emission spectrum of the conventional quantum dot structure. (A)-(c) is typical sectional drawing which shows the manufacturing method of the quantum dot structure of embodiment of this invention in order of a process. (A)-(c) is typical sectional drawing which shows the manufacturing method of the quantum dot structure of embodiment of this invention in order of a process, Comprising: The next process of FIG.7 (c) is shown. (A) is drawing substitute photograph which shows the TEM image of the quantum dot structure of embodiment of this invention, (b) is a graph which shows Ge distribution of the quantum dot structure shown to Fig.9 (a). . (A), (b) is typical sectional drawing which shows the manufacturing method of the other structure of the quantum dot structure of embodiment of this invention in order of a process. (A)-(c) is typical sectional drawing which shows the manufacturing method of the quantum dot structure of the 2nd modification of embodiment of this invention in order of a process. It is typical sectional drawing which shows the wavelength conversion element of embodiment of this invention. It is a schematic diagram for demonstrating the multi exciton effect. It is a schematic diagram which shows a sunlight spectrum and the spectral sensitivity curve of crystalline Si. It is a graph which shows the difference in the reflectance by the difference in the structure of an antireflection film. (A) is a graph which shows the relationship between content of the quantum dot in a matrix layer, and a refractive index, (b) is a graph which shows the relationship between the space | interval of the quantum dot in a matrix layer, and a refractive index. . It is a graph which shows the change of the refractive index by the matrix material filling rate in a matrix layer. (A) is a graph showing the SiO ₂ film / wavelength converting element (Si quantum dots _{/ SiO} 2Mat) _/ Si substrate reflectivity, refractive index of the wavelength conversion element is 1.80, (b), the is a graph showing the SiO ₂ film / wavelength converting element (Si quantum dots _{/ SiO} 2Mat) _/ Si substrate reflectivity, refractive index of the wavelength conversion element is 2.35. It is a graph which shows the relationship between the difference in the effective refractive index in a wavelength conversion element, and emitted light intensity. (A) is a graph showing the relationship between the uniformity of the quantum dots and the emission intensity in the wavelength conversion element, (b) is a drawing-substituting photograph showing a TEM image of the quantum dots that are not uniform, and (c) It is a drawing substitute photograph which shows the TEM image of a thing with a uniform quantum dot. It is a graph which shows the reflective characteristic of the quantum dot structure of the 3rd modification of embodiment of this invention, and the reflective characteristic of the conventional quantum dot structure. (A) is typical sectional drawing which shows the photoelectric conversion apparatus which has a wavelength conversion element of embodiment of this invention, (b) is a schematic diagram which shows the 1st example of a wavelength conversion element. (A) is a schematic diagram which shows the 2nd example of a wavelength conversion element, (b) is a schematic diagram which shows the refractive index distribution in the 2nd example of a wavelength conversion element. (A) is a schematic diagram which shows the 3rd example of a wavelength conversion element, (b) is a schematic diagram which shows the refractive index distribution in the 3rd example of a wavelength conversion element. It is a schematic diagram which shows the 4th example of a wavelength conversion element. It is typical sectional drawing which shows the photoelectric conversion apparatus of embodiment of this invention. It is typical sectional drawing which shows the photoelectric conversion apparatus of other embodiment of this invention.

Hereinafter, a quantum dot structure, a wavelength conversion element, and a photoelectric conversion device of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
FIG. 1A is a schematic cross-sectional view showing a quantum dot structure according to an embodiment of the present invention, and FIG. 1B is a schematic diagram showing a first modification of the quantum dot structure according to the embodiment of the present invention. It is typical sectional drawing, (c) is typical sectional drawing which shows the 2nd modification of the quantum dot structure of embodiment of this invention, (d) is the quantum dot structure of embodiment of this invention It is typical sectional drawing which shows the 3rd modification of a body.

A quantum dot structure 10 shown in FIG. 1A is obtained by arranging quantum dots 14 and hollow hollow quantum dots 16 in a matrix layer 12.
In the quantum dot structure 10, the quantum dots 14 and the hollow quantum dots 16 are arranged in layers, for example, two rows.
A quantum dot layer 18 a is configured by the quantum dots 14, and a hollow quantum dot layer 18 b is configured by the hollow quantum dots 16.
In the quantum dot structure 10, for example, light is incident from the quantum dot 14 side. The number of columns of the quantum dots 14 and the hollow quantum dots 16 is not particularly limited.

The matrix layer 12 is made of, for example, an inorganic dielectric having a band gap of 3.0 eV or more. The matrix layer 12 is not particularly limited as long as it is an inorganic dielectric having a band gap of 3.0 eV or more. For example, the matrix layer 12 is made of SiO ₂ , Si ₂ N ₃ , GaN, GaN, or AlN.
The matrix layer 12 is made of, for example, an organic material having a band gap of 3.0 eV or more and a transmittance of 70% or more. This transmittance is the total light transmittance measured by the total light transmittance test method defined in JIS K7361-1: 1997.

The quantum dots 14 are nano-sized particles, and are composed of, for example, a wavelength conversion composition that converts the wavelength of light of a specific wavelength region of absorbed light into light having energy lower than that of the absorbed light. The composition of the quantum dots 14 is not particularly limited. For example, when the quantum dots 14 are made of an inorganic material, Si _x Ge _(1-x) or In _x Ga _(1-x) N, A semiconductor such as InAs, FeSi, PbS, or PbSe is used. Further, when the quantum dots 14 are made of, for example, an organic material, fullerene, an organic fluorescent dye, or an organic fluorescent dye molecule is used.

The hollow quantum dots 16 are substantially spherical nano-sized spaces formed in the matrix layer 12. In this case, the composition of the hollow forming material forming the hollow quantum dots 16 and the matrix layer 12 are the same. Therefore, hollow quantum dots 16 may, for _{example, SiO 2, Si 2 N 3} , GaN, composed of an inorganic material such as GaN or AlN. The hollow quantum dot 16 is preferably the same material as the matrix layer 12 because scattering due to a difference in refractive index is suppressed and the transmittance is improved.
The hollow quantum dots 16 are not limited to the substantially spherical space formed in the matrix layer 12, and may have a hollow structure with a thin outer surface. In this case, the composition of the shell and the composition of the matrix layer 12 may be the same or different.
The hollow quantum dots 16 are, for example, acrylic resin, epoxy resin, ethylene vinyl acetate (EVA) resin, silicone resin, saturated polyester / polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, cross-linked fumaric acid diester resin. , Polycarbonate (PC) -based resin, cellulose-based resin, or transparent polyimide (PI) and other organic materials.

The quantum dots 14 and the hollow quantum dots 16 preferably have a particle size of 2 nm to 10 nm. The quantum dots 14 and the hollow quantum dots 16 may have the same size or different sizes. Furthermore, the quantum dots 14 and the hollow quantum dots 16 may be either uniform or non-uniform in size.
Further, in each of the quantum dots 14 and the hollow quantum dots 16, the distance δ between the nearest neighbor particles is preferably 20 nm or less, more preferably 10 nm or less, and further preferably 5 nm or less.

When the particle size of the quantum dots 14 is less than 2 nm, the band gap becomes too large and a desired wavelength conversion effect cannot be obtained. For this reason, the particle size of quantum dots is desired to be 2 nm or more. On the other hand, for example, when a zirconia particle (refractive index 2.5) / SiO ₂ (refractive index 1.45) matrix is used and a mixture is formed of transparent materials having different refractive indexes, the transmittance is the size of the particles. It is confirmed that when the thickness is large, the transmittance decreases at a low filling rate. In particular, when the refractive index of the particles is larger than 2.5, the particle size is preferably 10 nm or less in order to increase the filling rate.

Here, the quantum dots 14 or the hollow quantum dots 16 are arranged in a layer form that the quantum dots 14 or the hollow quantum dots 16 are arranged in a line for one particle on a plane perpendicular to the stacking direction. It is a state. In this case, the aggregate layer in which the hollow quantum dots 16 or the quantum dots 14 are arranged in a row for one particle is a minimum layer unit. The cumulative film thickness t is the thickness of a single layer if this minimum layer is a single layer, and the total thickness of the stacked layers if it is a plurality of layers.
For example, as shown in FIG. 1A, when two hollow quantum dot layers 18b are arranged in units of 16 hollow quantum dots, the cumulative film thickness t is the thickness of the two layers. That is.
In order to improve the light use efficiency of incident light and light emitted from the quantum dots by the scattering function of the hollow quantum dots, the hollow quantum dot layer 18b needs a cumulative film thickness of 50 nm or more with respect to the cumulative film thickness t. For this reason, it is preferable that the cumulative film thickness t of the hollow quantum dot layer 18b is 50 nm or more. In this case, the distance between the quantum dot layer composed of the quantum dots 14 adjacent to the hollow quantum dots 16 of the hollow quantum dot layer 18b and the hollow quantum dot layer 18b is preferably 20 nm or less.

In this embodiment, if the quantum dot 14 and the hollow quantum dot 16 are arrange | positioned, the arrangement | positioning form will not be specifically limited. For this reason, for example, like the quantum dot structure 10a shown in FIG. 1B, the quantum dots 14 and the hollow quantum dots 16 may be arranged in a staggered manner in layers. Furthermore, as in the quantum dot structure 10b shown in FIG. 1C, the quantum dots 14 and the hollow quantum dots 16 may be alternately arranged in layers for each particle.
In both the quantum dot structure 10a shown in FIG. 16 (b) and the quantum dot structure 10b shown in FIG. 1 (c), the hollow quantum dots 16 are arranged in layers.
In the case of the quantum dot structure 10a shown in FIG. 16B, four aggregate layers of the hollow quantum dots 16 are laminated, and the total thickness is the accumulated film thickness t. Even in this case, the accumulated film thickness t of the aggregate layer of the hollow quantum dots 16 is preferably 50 nm or more.
In the case of the quantum dot structure 10b shown in FIG. 16 (c), there are two aggregate layers in which the hollow quantum dots 16 are arranged in a row for one particle, and the total thickness of these two layers, That is, 2d _2a is the accumulated film thickness t. Even in this case, the accumulated film thickness t of the aggregate layer of the hollow quantum dots 16 is preferably 50 nm or more.

Moreover, the quantum dot 14 and the hollow quantum dot 16 may be arrange | positioned at random like the quantum dot structure 10c shown in FIG.1 (d).
When the quantum dots 14 and the hollow quantum dots 16 are randomly arranged, the thickness of the aggregate layer in which the hollow quantum dots 16 and the quantum dots 14 have similar distribution forms is defined as a cumulative film thickness t. For example, as shown in FIG. 1D, the thickness of the matrix layer 12 in which the hollow quantum dots 16 and the quantum dots 14 are arranged at random is the accumulated film thickness t. In the case of random arrangement, the cumulative film thickness t is preferably 100 nm or less because it functions as an optical film if the cumulative film thickness t is sufficiently larger than the incident light wavelength (λ / (4n)). Further, the cumulative film thickness t of the random arrangement may be t ≦ λ / 4n with respect to the wavelength λ of the incident light L incident on the quantum dot structure. Here, n is the refractive index of the randomly arranged aggregate layer.
On the other hand, when functioning as an optical film in a random arrangement, the cumulative film thickness t is set to more than 100 nm.

  Also in the quantum dot structures 10a to 10c shown in FIGS. 1B to 1D, it is preferable that the quantum dots 14 and the hollow quantum dots 16 both have an interval δ of the nearest neighbor particles of 20 nm or less. More preferably, it is 10 nm or less, More preferably, it is 5 nm or less.

  By having the hollow quantum dots 16 as in the configuration of the quantum dot structures 10, 10a to 10c described above, the transmittance of the quantum dot structures 10, 10a to 10c can be increased.

In the quantum dot structure of the present embodiment, as shown in FIG. 2, when the incident light L is incident from the quantum dot 14 side, the incident light L is reflected in all directions by the quantum dots 14. However, a part of the reflected light Lr (scattered light) of the quantum dots 14 is reflected on the surface or inside of the hollow quantum dots 16 to the outside of the quantum dot structure 10, for example, as the light Lb on the incident light L side. As a result, the amount of reflected light of the quantum dot structure increases. Thus, the reflected light Lr (scattered light) from the quantum dots 14 is reflected to the outside by the hollow quantum dots 16. As will be described later, the quantum dot structure of the present embodiment can provide high emission intensity.
On the other hand, the quantum dot structure includes the hollow quantum dots 16 in addition to the quantum dots 14, and the quantum dot structure itself has high transmittance. For this reason, the transmitted light amount which permeate | transmits the quantum dot structure of the incident light L which injected perpendicularly | vertically with respect to the quantum dot structure can be increased, and a light energy loss can be suppressed. Thereby, for example, when the photoelectric conversion layer is disposed on the hollow quantum dot 16 side of the quantum dot structure, the utilization efficiency of the incident light L can be increased, and the photoelectric conversion amount of the photoelectric conversion layer can be increased.

The present applicant has confirmed that the quantum dot structure 10 having the configuration shown in FIG. For example, as shown in FIG. 3A, when the hollow quantum dots 16 are spherical, PL light is emitted. On the other hand, as shown in FIG.3 (b), when the hollow quantum dot 17 is flat and flat, it is confirmed that PL light emission is not carried out.
The configuration quantum dot structure 10 shown in FIG. 1 (a), where a light having an excitation wavelength of 533nm was irradiated in pulsed emission waveform as shown at alpha ₁ was obtained in FIGS. 4 (a) . Further, the emission spectrum of the quantum dot structure 10 having the hollow quantum dots 16 was as shown in FIG.
For comparison, with respect to the quantum dot structure only quantum dots was irradiated with light having an excitation wavelength of 533nm in a pulse shape, the light emission waveform such as indicated at alpha ₂ was obtained in Figure 4 (a). As described above, the quantum dot structure 10 having the hollow quantum dots 16 has higher emission intensity than the quantum dot structure having only the quantum dots, and has excellent emission characteristics.

Further, when the quantum dots 14 and the hollow quantum dots 16 are randomly arranged as in the quantum dot structure 10c shown in FIG. 1D, when the incident light L is incident as shown in FIG. The quantum dots 14 are reflected in all directions. A part of the reflected light Lr (scattered light) reflected is reflected by the hollow quantum dots 16, and a part of the reflected light Lr of the quantum dots 14 is reflected on the surface or inside of the hollow quantum dots 16 so that the quantum dot structure 10c. For example, the light Lb is extracted on the incident light L side, and the amount of reflected light of the quantum dot structure is increased even in a random arrangement. Thus, the reflected light Lr (scattered light) from the quantum dots 14 is reflected to the outside by the hollow quantum dots 16. In addition, as will be described later, a random arrangement of quantum dot structures also provides high emission intensity.
On the other hand, the randomly arranged quantum dot structure also includes the hollow quantum dots 16 in addition to the quantum dots 14, and the quantum dot structure itself has high transmittance. This point is shown in FIG. 21 described later. For this reason, the quantum dot structure of random arrangement can also increase the utilization efficiency of incident light L when the photoelectric conversion layer is arranged on the hollow quantum dot 16 side of the quantum dot structure, for example. The photoelectric conversion amount of the layer can be increased.

The quantum dot structure 10c shown in FIG. 1 (d), were examined emission spectrum with excitation wavelengths as 600 nm, emission spectrum as shown by reference numeral beta ₁ in FIG. 6 were obtained. For quantum dot structure only quantum dots for comparison, were examined emission spectrum in the same manner, the emission spectrum as indicated at beta ₂ in FIG. 6 were obtained.
As shown in FIG. 6, even in the quantum dot structure 10c in which the quantum dots 14 and the hollow quantum dots 16 are randomly arranged, the emission intensity is about 6 times that of the quantum dot structure having only the quantum dots. Thus, even with a randomly arranged quantum dot structure, high emission intensity is obtained and the emission characteristics are excellent.

  As described above, according to the quantum dot structure of the present embodiment, it is possible to improve the utilization efficiency of the incident light L by reflecting the scattered light and transmitting the incident light L incident vertically. Furthermore, according to the quantum dot structure of the present embodiment, high emission intensity can be obtained. Further, it is known that the band gap can be changed by changing the composition of the quantum dots and the size of the quantum dots. In the quantum dot structure of the present embodiment, the composition of the quantum dots 14 and the size of the quantum dots are also known. By changing the band gap, the band gap can be changed. Various devices using the quantum dot structure will be described in detail later.

Next, a method for forming the quantum dot structure 10 shown in FIG. 1 will be described.
FIGS. 7A to 7C and FIGS. 8A to 8C are schematic cross-sectional views showing the method of forming the quantum dot structure 10 shown in FIG. 1 in the order of steps.
First, as shown in FIG. 7A, the laminated body 25 is obtained by alternately laminating the SiO ₂ layers 22 and the SiGeO layers 24 on the surface 20 a of the substrate 20. The thicknesses of the SiO ₂ layer 22 and the SiGeO layer 24 are, for example, 3 to 6 nm. For example, a Si substrate is used as the substrate 20.

For example, the SiO ₂ layer 22 has an ultimate vacuum of 3 × 10 ⁻⁴ Pa or less, a substrate temperature of room temperature (RT), Si as a target, an input power of 100 W, a deposition pressure of 0.3 Pa, and a gas flow rate. As for film formation, the film is formed under the film formation conditions of Ar gas of 15 sccm and O ₂ gas of 1 sccm.
The SiGeO layer 24 is, for example, amorphous. The ultimate vacuum is 3 × 10 ⁻⁴ Pa or less, the substrate temperature is room temperature (RT), Ge and Si are used as targets, the input power is 50 W for Ge, Si is 100 W, the film formation pressure is 0.3 Pa, and the gas flow rate is formed under the film formation conditions of Ar gas of 15 sccm and O ₂ gas of 0.5 sccm.

Next, the stacked body 25 is annealed at, for example, 650 ° C. for 10 minutes in a nitrogen atmosphere. As a result, as shown in FIG. 7B, a stacked body 27 in which Ge quantum dots 26 are formed in the matrix layer 12 is obtained.
Next, the stacked body 27 is annealed, for example, at a temperature of 1000 ° C. for 1 hour to diffuse the Ge quantum dots 26. As a result, holes corresponding to the size of the Ge quantum dots 26 are formed in the matrix layer 12 to form the hollow quantum dots 16. In this way, a laminate 29 in which the hollow quantum dots 16 are formed is obtained.

Next, the SiO ₂ layer 30, the SiGeO layer 32 (amorphous layer), the SiO ₂ layer 30, the SiOx layer 34 (0 <X <2), the SiO ₂ layer 30 are formed on the surface 29a of the stacked body 29 in FIG. The SiGeO layer 32, the SiO ₂ layer 30, the SiOx layer 34 (amorphous layer), the SiO ₂ layer 30, the SiGeO layer 32, and the SiO ₂ layer 30 are stacked in this order to obtain a stacked body 33.
The thicknesses of the SiO ₂ layer 30, the SiGeO layer 32, and the SiOx layer 34 are, for example, 3 to 6 nm.

The SiO ₂ layer 30 is formed by, for example, RF sputtering using SiO ₂ as a target. The SiGeO layer 32 is formed by, for example, co-reactive sputtering of Si and Ge. The SiOx layer 34 is formed, for example, by oxidizing Si by reactive sputtering. More specifically, the SiO ₂ layer 30, the SiGeO layer 32, and the SiOx layer 34 are formed as follows.

The SiO ₂ layer 30 is, for example, an ultimate vacuum of 1 × 10 ⁻⁴ Pa or less, a substrate temperature of room temperature (RT), a target of SiO ₂ , an input power of 100 W, a film forming pressure of 0.3 Pa, and a gas Regarding the flow rate, the film is formed under the film forming conditions of Ar gas of 15 sccm and O ₂ gas of 1 sccm.
The SiGeO layer 32 is, for example, amorphous. The ultimate vacuum is 1 × 10 ⁻⁴ Pa or less, the substrate temperature is room temperature (RT), Ge and Si are used as targets, and the input power is 80 W for Ge. Si is 100 W, the deposition pressure is 0.3 Pa, and the gas flow rate is such that the Ar gas is 15 sccm and the O ₂ gas is 0.6 sccm.
For example, the SiOx layer 34 has an ultimate vacuum of 1 × 10 ⁻⁴ Pa or less, a substrate temperature of room temperature (RT), Si as a target, an input power of 100 W, a deposition pressure of 0.1 Pa, and a gas flow rate. As for film formation, the film is formed under the film formation conditions of Ar gas of 15 sccm and O ₂ gas of 0.5 sccm.

In the stacked body 33, layers of Si _x Ge _y O _(1-xy) and SiO _z may be alternately or periodically arranged in the SiO ₂ layer.
In the stacked body 33, the SiO ₂ layer 30 is formed adjacent to the SiGeO layer 32 or the SiOx layer 34, and at least one SiOx layer 34 is interposed between the SiGeO layer 32 and the adjacent SiGeO layer 32. It may be arranged.

Next, nitriding and crystallization are performed on the stacked body 33 by performing a heat treatment (annealing treatment), for example, at 900 ° C. for 1 minute in an atmosphere in which a nitrogen gas is flowed. In this case, as shown in FIG. 8B, Ge quantum dots (quantum dots 14) are formed in the SiGeO layer 32 (Si _x Ge _y O _(1-xy) → Ge + GeO _z1 + SiO _z2 ). At this time, GeOx 35 (GeO _z1 ) diffuses from the SiGeO layer 32 (amorphous layer) to the SiOx layer 34 (amorphous layer). The diffused GeOx 37 reacts with the SiOx layer 34 to form Ge quantum dots (quantum dots 14). At this time, taking advantage of the property that Si is more easily oxidized than Ge by making the diffused GeO _z1 react with SiO _z2 + GeO _z1 → SiO ₂ + Ge, the generation of GeO _z is suppressed, and GeO _z diffuses over time, It is possible to suppress the defect film quality change at the Ge / GeO ₂ interface.
By this heat treatment, for example, the amorphous SiOx (x≈2) matrix layer 12 is formed by the SiO ₂ layer 30, the SiGeO layer 32 and the SiOx layer 34.

Note that the SiO ₂ layer 30, the SiGeO layer 32, and the SiOx layer 34 are stacked on each other and subjected to heat treatment, whereby the crystalline quantum dots 14 are converted into a matrix layer as disclosed in JP-T-2007-535806. 12 is uniformly distributed three-dimensionally. In the present embodiment, the quantum dots 14 are further formed with high density. The generated quantum dots 14 have a three-dimensional periodicity in the matrix layer 12 and are uniformly distributed at a high density.
In this way, a quantum dot structure 39 in which the quantum dots 14 have a three-dimensional periodicity and are uniformly arranged at high density in the matrix layer 12 as shown in FIG. 8C is obtained. be able to.

In addition, in the quantum dot structure 39, in order to prevent generation | occurrence | production of the defect of the interface of the quantum dot 14 and the matrix layer 12, and the matrix layer 12, it is preferable to have a passivation process in the manufacturing process.
As this passivation step, for example, plasma hydrogen treatment is performed. Nitrogen / hydrogen termination is performed by this plasma hydrogen treatment. The plasma hydrogen treatment conditions are, for example, an H ₂ gas flow rate of 300 l / min, a degree of vacuum of 0.9 Torr (120 Pa), a microwave output of 2.5 KW, a substrate temperature of 300 ° C., and a treatment time of 30 minutes.
Thus, the quantum dot structure 10 in which the quantum dots 14 and the hollow quantum dots 16 are respectively arranged in layers can be formed. Specifically, as shown in FIG. 9A, the formed quantum dot structure 10 has quantum dots 14 and hollow quantum dots 16 arranged in layers in the matrix layer 12.
For the quantum dot structure 10 shown in FIG. 9A, the Ge concentration in the line segment G ₁ -G ₂ was examined. As shown in FIG. 9B, the formation region of the quantum dots 16 and the quantum dots The Ge concentration is clearly different from the 14 formation region, and the Ge concentration is low and almost no Ge in the formation region of the hollow quantum dots 16. Thus, it is clear that the hollow quantum dots 16 are hollow formed by diffusing Ge quantum dots 26.

Moreover, in this invention, as shown in FIG.10 (b), in addition to the hollow quantum dot 16, the quantum dot structure 11 which has the quantum dots 14a-14c from which a magnitude | size differs may be sufficient.
The quantum dot structure 11 is different from the quantum dot structure 10 in FIG. 1A in that quantum dots 14a to 14c having different sizes are formed. Since the configuration is the same as that of the dot structure 10, detailed description thereof is omitted. In the quantum dot structure 11, the quantum dots 14a at both ends in the thickness direction (vertical direction) of the quantum dot structure 11 are the largest, and the quantum dots 14b and 14c and the quantum dots 14c increase toward the center of the quantum dot structure 11. The size becomes smaller.

In the present embodiment, as long as quantum dots having different sizes are arranged, the arrangement of quantum dots having different sizes is not particularly limited. For example, the quantum dots at both ends in the thickness direction of the quantum dot structure may be the smallest, and the size of the quantum dots may be increased toward the center of the quantum dot structure.
Furthermore, in the thickness direction of the quantum dot structure, L1-L2-L1 and L1-L1-L2-L1 are set such that the quantum dot layer L2 having a large particle diameter is sandwiched between the quantum dot layers L1 having a small particle diameter. Such a periodic arrangement may be used.
Also in this quantum dot structure 11, it is preferable that the above-mentioned cumulative film thickness t is 50 nm or more.

Next, the manufacturing method of the quantum dot structure 11 shown in FIG.10 (b) is demonstrated.
In the present embodiment, the laminated body 33a shown in FIG. 10A is different from the laminated body 33 shown in FIG. 8A in place of the SiGeO layer 32 at the center, and the SiOx layer 34 (0 <X < 2) is different, and the other configuration is the same as that of the stacked body 33 shown in FIG. 8A, and thus detailed description thereof is omitted.

In the periodic arrangement of the SiGeO layer 32 (Si _x Ge _y O _(1-xy) film), the SiO ₂ layer 30, and the SiO x layer 34, as shown in FIG. 10A, Si _x Ge _y O _{(1- xy) By} adopting a configuration in which a plurality of SiOx layers 34 are inserted between layers, the SiGe particle diameter can be changed stepwise in accordance with the number of inserted SiOx layers 34. For this reason, the quantum dot 14a-14c from which a magnitude | size can differ can be formed by implementing heat processing with respect to the laminated body 33a at 900 degreeC and 1 minute in the atmosphere which flowed nitrogen gas, for example. .

Next, the manufacturing method of the quantum dot structure 10b shown in FIG.1 (c) is demonstrated.
FIGS. 11A to 11C are schematic cross-sectional views showing the method of manufacturing the quantum dot structure 10b shown in FIG.

First, as shown in FIG. 11A, a SiO ₂ layer 40 (amorphous layer), a SiGeO layer 32 (amorphous layer), a SiO ₂ layer 40, a Si / SiO ₂ layer 42 (diffusion stop layer) are formed on the surface 20a of the substrate 20. ), The SiO ₂ layer 40, the SiGeO layer 32 (amorphous layer), the SiO ₂ layer 40, the Si / SiO ₂ layer 42, and the SiO ₂ layer 40 are laminated in this order to form a laminated body 44.
In the stacked body 44, the SiO ₂ layer 40, the SiGeO layer 32, and the Si / SiO ₂ layer 42 may be arranged alternately or periodically.
The SiO ₂ layer 40 has a higher electronegativity than the SiGeO layer 32.

The thicknesses of the SiO ₂ layer 40, the SiGeO layer 32, and the Si / SiO ₂ layer 42 are, for example, 3 to 6 nm. The SiGeO layer 32 has a composition of Si _x Ge _y O _(1-xy) .
The SiO ₂ layer 40 is formed by, for example, RF sputtering using SiO ₂ as a target. As film formation conditions, for example, the ultimate vacuum is 3 × 10 ⁻⁴ Pa or less, the substrate temperature is room temperature (RT), Si is used as the target, the input power is 100 W, the film formation pressure is 0.3 Pa, and the gas flow rate. Is about 15 sccm for Ar gas and 1 sccm for O ₂ gas.

The SiGeO layer 32 is formed by, for example, co-reactive sputtering of Si and Ge. As the film formation conditions, for example, the ultimate vacuum is 3 × 10 ⁻⁴ Pa or less, the substrate temperature is room temperature (RT), Ge and Si are used as targets, the input power is 50 W for Ge, and 100 W for Si. The pressure is 0.3 Pa, and the gas flow rate is 15 sccm for Ar gas and 0.5 sccm for O ₂ gas.
The Si / SiO ₂ layer 42 is formed by co-sputtering Si and SiO ₂ . As film formation conditions, for example, the ultimate vacuum is 3 × 10 ⁻⁴ Pa or less, the substrate temperature is room temperature (RT), Si and SiO ₂ are used as targets, the input power is 10 W for Si, 100 W for SiO ₂ , The film forming pressure is 0.3 Pa, the gas flow rate is 15 sccm for Ar gas, and 0 sccm for O ₂ gas.

The Si / SiO ₂ layer 42 is for preventing GeOx and the like from diffusing from the SiGeO layer 32 to the SiO ₂ layer 40 during heat treatment. When GeOx or the like diffuses from the SiGeO layer 32 into the Si / SiO ₂ layer 42, Si is more easily oxidized than Ge as described above. For this reason, the degree of oxidation of GeOx is reduced, and GeOx has a property that it is difficult to diffuse when the oxidation is lower, so that the diffusion of GeOx is suppressed.
By heat treatment, Si / quantum dots 14 in the SiO ₂ layer 42 is formed, the matrix layer 12 is formed of SiO ₂ layer 40 and Si / SiO ₂ layer 42 and the like.

Next, the laminated body 44 is subjected to heat treatment at 900 ° C. for 1 minute, for example, in an atmosphere in which nitrogen gas is flowed to perform nitriding and crystallization. Thereby, as shown in FIG. 11B, a stacked body 46 in which the quantum dots 48 and the quantum dots 14 are formed in the matrix layer 12 is obtained. Note that the quantum dots 48 are generated by the SiGeO layer 32.
During the heat treatment of the stacked body 44, the semiconductor of the SiO ₂ layer 40 having a high electronegativity is selectively oxidized to form the quantum dots 14, and the semiconductor of the SiGeO layer 32 having a low electronegativity is selectively used. Reduction is promoted and quantum dots 48 are formed. At this time, since the reduction of the semiconductor of the SiGeO layer 32 having a low electronegativity is selectively promoted, diffusion of the constituent material of the quantum dots 48 such as GeOx from the SiGeO layer 32 to the SiO ₂ layer 40 is suppressed. The

When the quantum dot 48 and the quantum dot 14 were subjected to Raman spectroscopic analysis of the stacked body 46, Si _(1-x) Ge _x (X> 0.7) and Si _(1-x ) were obtained as the quantum dot 48 and the quantum dot 14. ₎ It is presumed that this is a mixture of Ge _x (X <0.7). The quantum dots 48 and the quantum dots 14 have different melting points, and the quantum dots 14 have a higher melting point than the quantum dots 48.

Next, the multilayer body 46 is annealed at a temperature at which the quantum dots 48 diffuse and the quantum dots 14 do not diffuse. Thereby, as shown in FIG.11 (c), the quantum dot structure 10b in which the quantum dot 14 and the hollow quantum dot 16 are arrange | positioned alternately is formed.
The plasma hydrogen treatment described above may be performed after the annealing treatment for forming the hollow quantum dots 16.

For the case where the quantum dots 14 and the hollow quantum dots 16 are randomly arranged as in the quantum dot structure 10c shown in FIG. 1D, for example, a dielectric that constitutes a layer serving as a matrix layer; Three types of semiconductors, which are two types of nano-sized particles having different melting points, are deposited together on a substrate, and two types of nano-sized particles having different melting points are randomly formed in a layer serving as a matrix layer. Then, using the difference between the melting points of the two types of nano-sized particles, heat treatment is performed at a temperature at which the lower melting point diffuses and the higher melting point does not diffuse. As a result, one of the nano-sized particles is diffused to form a hollow quantum dot, and the quantum dot is left with the higher melting point. In this way, the quantum dot structure 10c shown in FIG. 1D can be formed.
In addition, when forming the randomly arranged quantum dot structure 10c, two types of nano-sized particles having different melting points were randomly formed in the layer serving as the matrix layer, but the present invention is not limited to this. For example, by laminating several layers that form a matrix layer in which two types of nano-sized particles are randomly formed to form a laminate, by heat treatment using the difference in melting point between the two types of nano-sized particles, Hollow quantum dots and quantum dots can also be formed as described above.
The manufacturing method of the quantum dot structure 10, 10a-10c shown to Fig.1 (a)-(d) is not limited to the above-mentioned thing, For example, the apply | coating method can also be used.

The quantum dot structure described above has a wavelength conversion function in any form, and can be used alone as a wavelength conversion film. Furthermore, any of the quantum dot structures can be used for, for example, a wavelength conversion element, a wavelength conversion device, and a solar cell.
The wavelength conversion element 50 shown in FIG. 12 has the same configuration as the quantum dot structures 10, 10 a to 10 c of the above-described embodiment. In the wavelength conversion element 50, the quantum dots 14 and the hollow quantum dots are included in the matrix layer 12. 16 are arranged in layers. For this reason, the detailed description is abbreviate | omitted.
In the wavelength conversion element 50, the number of stacked quantum dots 14 and hollow quantum dots 16 is not particularly limited. Also in the wavelength conversion element 50, the size of the quantum dots 14 and the hollow quantum dots 16 may be uniform or non-uniform.

  The wavelength conversion element 50 absorbs incident incident light L and converts the wavelength of the absorbed light into a light having a lower energy than the absorbed light (hereinafter referred to as a wavelength conversion function). And a function of confining incident incident light L (hereinafter referred to as a light confinement function).

In the wavelength conversion element 50, the wavelength conversion function specifically refers to a down conversion function. This down-conversion function is exhibited by the effect of generating one or more photons per absorbed photon, called the multi-exciton effect. For example, as shown in FIG. 13, when a quantum well is constituted by quantum dots, and a photon (photon) having energy equal to or higher than Eg _QD (band gap of the quantum dot) is incident on the quantum dot, a low energy level ( When electrons in E1) are excited to the upper energy level (E4) and then fall to the lower energy level (E3), photons with lower energy than the incident photons are emitted. Further, when an electron at a lower energy level (E2) is excited to an upper energy level (E3), a photon having a lower energy than the incident photon is emitted. Thus, wavelength conversion is performed by emitting two electrons having energy lower than that of a photon to one photon. When two electrons having energy lower than that of a photon are emitted for one photon, this is also referred to as light-light conversion. The wavelength conversion element 50 has a light-light conversion function.

About the wavelength conversion function of the wavelength conversion element 50, the wavelength range and the wavelength after conversion are suitably selected according to the use of the wavelength conversion element 50.
For example, when the wavelength conversion element 50 is disposed on a photoelectric conversion layer of a silicon solar cell having an Eg (band gap) of 1.2 eV, a wavelength of energy (2.4 eV or more) that is twice or more of 1.2 eV. A region having a function of performing wavelength conversion to light having a wavelength of energy corresponding to a band gap is preferable.

As shown in FIG. 14, when the solar spectrum is compared with the spectral sensitivity curve of crystalline Si, the solar spectrum has a low intensity in the wavelength range of the band gap of crystalline Si. For this reason, photons of low energy, for example, light of 1.2 eV (wavelength of about 1100 nm) with respect to a wavelength region of energy (2.4 eV or more) twice or more of the band gap of crystalline Si in sunlight. By converting the wavelength, light effective for photoelectric conversion can be supplied to the photoelectric conversion layer made of crystalline Si. Thereby, the conversion efficiency of a solar cell can be made high.
This is because, as shown in FIG. 14, when the solar spectrum and the spectral sensitivity curve of crystalline Si are compared, the wavelength band of the crystalline Si band gap is narrower than that of the solar spectrum, and the spectral sensitivity of relatively high energy light. Sunlight cannot be used effectively due to its low intensity. For this reason, sunlight can be used effectively for converting relatively high energy light into light suitable for the spectral sensitivity of crystalline Si. Further, when the wavelength region of energy (2.4 eV or more) twice as large as the band gap of crystalline Si is converted into light of 1.2 eV light (wavelength of about 1100 nm), two photons or more (2 .4 (eV) × 1 (photon) ≈1.2 (eV) × 2 (photon)), sunlight can be used more effectively, and the conversion efficiency of the solar cell can be improved. Can be high. In the quantum dot structure 10, light emission (infrared light emission) near a wavelength of 1100 nm has been confirmed as shown in FIG.

In the wavelength conversion element 50, the light confinement function is an antireflection function.
When the photoelectric conversion layer in which the wavelength conversion element 50 is disposed is crystalline Si, the refractive index n _PV is 3.6. The refractive index n _air of the air in which these are arranged is 1.0.
Here, when the wavelength conversion element 50 is considered as an antireflection film, for example, as shown in FIG. 15, a single layer film (reference A ₁ ) having a refractive index of 1.9 and a refractive index of 1.46 / 2. 35 two-layer film (reference A ₂ ) and three-layer film (reference A ₃ ) having a refractive index of 1.36 / 1.46 / 2.35 The reflectance can be reduced.
Thus, in order to exhibit the antireflection function in the wavelength conversion element 50, the effective refractive index n of the wavelength conversion element 50 is the refractive index n _PV of the photoelectric conversion layer (3.6 for crystalline silicon) and air. If the refractive index can be set to a substantially intermediate refractive index, the antireflection function can be exhibited.
In the present embodiment, considering the use of the wavelength conversion element 50 (quantum dot structure 10) and the like, the effective refractive index n of the wavelength conversion element 50 (quantum dot structure 10) is, for example, 1. 7 <n <3.0. The effective refractive index n is preferably 1.7 <n <2.5 at a wavelength of 533 nm.

Each quantum dot of quantum dot structure 10 consists of a wavelength conversion composition which carries out wavelength conversion to light of energy lower than light absorbed with respect to a specific wavelength field of light absorbed. Each quantum dot bears the wavelength conversion function of the wavelength conversion element 50.
Moreover, the light use efficiency of incident light and the emitted light from a quantum dot is improved by the scattering function of each hollow quantum dot of the quantum dot structure 10.

In the wavelength conversion element 50, the quantum dot is configured to have a band gap larger than the band gap of the photoelectric conversion layer of the photoelectric conversion device in which the wavelength conversion element 50 is provided.
As described above, for example, the quantum dot has a function of performing wavelength conversion to light of Eg of the photoelectric conversion layer with respect to a wavelength region having energy twice or more Eg of the photoelectric conversion layer in which the wavelength conversion element 50 is provided. . For this reason, as a material constituting the quantum dots, energy levels more than twice Eg of the photoelectric conversion layer are absorbed, and energy levels for light absorption exist in more than twice the photoelectric conversion band caps. Material is selected.

  For this reason, a material that emits light with energy higher than Eg of the photoelectric conversion layer is selected for the quantum dot, the ground level of the quantum dot exists above Eg of the photoelectric conversion layer, and the energy level is discretized. In addition, an energy level more than twice the Eg of the photoelectric conversion layer exists.

In addition, in order to convert the light into usable light in the photoelectric conversion layer, it is necessary to arrange the quantum dots so as to form an inversion distribution state in which the existence probability of excited photons excited from the ground level is increased. is there. Therefore, quantum dots are arranged in a staggered manner as described above. Thus, by having a particle density bias in a three-dimensional space, it is possible to form a spatial energy bias and form an inverted distribution state. Further, in order to cause the localization of energy, the particle diameter of the quantum dots may be varied. In this case, the particle diameter variation σ _d (standard deviation) of the quantum dots is 1 <σ _d <d / 5 nm. It is different in the range, preferably 1 <σ _d <d / 10 nm.

Here, as described above, in order to obtain the antireflection function, the effective refractive index n of the wavelength conversion element 50 needs to be 2.4, which is an intermediate value between the photoelectric conversion layer and air, for example. Therefore, the relationship between the quantum dot content and the refractive index was examined by simulation calculation, and the relationship between the quantum dot interval and the refractive index was examined by simulation calculation. As a result, as shown in FIG. 16A, it is necessary to increase the content of quantum dots in order to increase the refractive index, and in order to increase the refractive index as shown in FIG. It is necessary to narrow the dot interval.
As shown in FIGS. 16A and 16B, for example, in order to set the effective refractive index n of the wavelength conversion element 50 to 2.4, the intervals between the quantum dots are narrowly arranged in the matrix layer with high density. There is a need to. For this reason, it is effective to arrange the quantum dots 14 in a staggered manner like the quantum dot structure 10b.
Further, as shown in FIG. 17, the change in the refractive index due to the matrix material filling rate in the matrix layer using SiO ₂ and Si ₃ N ₄ was examined. That is, the change in the refractive index according to the ratio of vacancies in the matrix layer was determined. From this result, it is necessary to increase the content of quantum dots in the matrix layer in order to increase the refractive index.

Furthermore, the following examination was made about the reflectance. Specifically, the reflectance was determined for the wavelength conversion element 50 formed on the Si substrate and the SiO ₂ film formed on the wavelength conversion element 50. The wavelength conversion element 50 is a device in which Si quantum dots are provided in a SiO ₂ matrix layer (Si quantum dots / SiO 2 _Mat ), and the quantum dot has a uniform particle size. At this time, the refractive index of the wavelength conversion element 50 is 1.80. In this case, as shown in FIG. 18A, the reflectance can be about 10%. In addition, the reflectance was measured using the spectral reflection measuring device (Hitachi U4000).

Further, by making the particle size of the quantum dots non-uniform, the filling rate was increased and the refractive index of the wavelength conversion element 50 was increased to 2.35. In this case, the wavelength conversion element 50 was a Si quantum dot provided on a SiO ₂ matrix layer (Si quantum dot / SiO 2 _Mat ). The result is shown in FIG. In addition, the reflectance was measured using the spectral reflection measuring device (Hitachi U4000).
Thus, by increasing the filling rate of the quantum dots, the refractive index is increased, and as a result, the reflectance can be decreased. For this reason, the utilization efficiency of the light L incident on the wavelength conversion element 50 can be increased.

The wavelength conversion element 50 of this embodiment can be used for a solar cell as described later, for example. Further, as described above, the wavelength conversion element 50 can be converted into light having a wavelength of 1200 nm, and thus can be used as an infrared light source. Moreover, since the emission intensity is high as described above, the emission intensity of the wavelength-converted light is high. That is, the infrared emission intensity is high.
Further, by appropriately changing the arrangement and size of the quantum dots and the hollow quantum dots, for example, light having a wavelength of 350 nm can be wavelength-converted to light having a wavelength of 800 nm, and can be used as an ultraviolet protection film.

Further, the packing ratio was increased while the particle diameter of the quantum dots 14 was kept uniform, and the effective refractive index of the wavelength conversion element 50 was increased to 2.4. The effective refractive index of the wavelength conversion element 50 having a uniform particle diameter is 1.80. When the wavelength conversion element 50 having an effective refractive index of 2.4 and the wavelength conversion element 50 having an effective refractive index of 1.8 were irradiated with light having an excitation wavelength of 350 nm, an emission spectrum shown in FIG. 19 was obtained. . 19, reference numeral _{B 1} represents a wavelength conversion element 50 of the effective refractive index is 1.8, the code _{B 2} is the wavelength conversion element 50 of the effective refractive index is 2.4.

  In the wavelength conversion element 50, as shown in FIG. 19, the emission intensity becomes smaller than that with a low refractive index when the refractive index is simply increased while the particle diameter of the quantum dots 14 is kept uniform. This is because, when the quantum dots 14 are packed at a high density, for example, when the distance between the quantum is very close to 5 nm or less, energy transfer between the quantum dots 14 is easy, and the particle diameter of the quantum dots 14 is uniform. Because energy bias hardly occurs, energy transfer is repeated without emitting light. For this reason, if the quantum dots 14 are uniform, the light emission efficiency decreases.

Therefore, the influence of wavelength conversion due to uniform and non-uniform quantum dots was investigated. Assuming that the quantum dots are uniform, the quantum dot 14 is made of Ge, the matrix layer is made of SiO ₂ , and the wavelength conversion element 50 is formed in which the particle size of the quantum dots 14 is uniform to about 5 nm. Moreover, the wavelength conversion element 50 in which the particle size of the quantum dots 14 was nonuniform was formed.
When each wavelength conversion element 50 was irradiated with light having an excitation wavelength of 533 nm, an emission spectrum shown in FIG. 20A was obtained. In FIG. 20 (a), the codes C ₁ are those quantum dots is uneven, code C ₂ is one quantum dots is uniform. 20B is a drawing-substituting photograph showing a TEM image of the quantum dots that are not uniform, and FIG. 20C is a drawing-substituting photograph showing a TEM image of the one having the quantum dots.
As shown in FIG. 20 (a), when the quantum dots have non-uniform particle sizes, higher emission intensity is obtained than when the quantum dots are uniform. Also from this, as shown in FIG. 19 and FIG. 20A, it can be seen that higher emission intensity can be obtained when the quantum dots have non-uniform particle sizes.

In this embodiment, the transmittance of the quantum dot structure in which quantum dots and hollow quantum dots are randomly arranged and the quantum dot structure in which only the quantum dots are arranged is measured, and the reflection characteristics are measured. I investigated the difference. The result is shown in FIG. In FIG. 21, reference numeral γ ₁ shows the result of a quantum dot structure in which quantum dots and hollow quantum dots are randomly arranged, and reference numeral γ ₂ shows the result of a quantum dot structure in which only quantum dots are arranged. Show.
As shown in FIG. 21, a quantum dot structure in which quantum dots and hollow quantum dots are randomly arranged has a transmittance in a wider wavelength range than a quantum dot structure in which only quantum dots are arranged. The wavelength dependency of the transmittance is small, and the reflection characteristics are excellent.
As described above, in the wavelength conversion element, when the transmittance is improved in the laminated configuration, there is a method in which the refractive index of the wavelength conversion element gradually approaches the refractive index of the photoelectric conversion element from the refractive index of air. In addition, the refractive index can be arbitrarily changed by changing the density of the quantum dots and the hollow quantum dots in the matrix layer. For this reason, there is a method in which the refractive index of the wavelength conversion element is continuously changed from the refractive index of air so as to approach the refractive index of the photoelectric conversion element.

Hereinafter, a photoelectric conversion apparatus using the wavelength conversion element of the present embodiment will be described.
Note that a photoelectric conversion device using a wavelength conversion element also functions as a light-to-light conversion device. FIG. 22A is a schematic cross-sectional view showing a photoelectric conversion device having a wavelength conversion element according to an embodiment of the present invention, and FIG. 22B is a schematic view showing a first example of the wavelength conversion element.
In the photoelectric conversion device 80 illustrated in FIG. 22A, the photoelectric conversion element 90 is provided on the surface 82 a of the substrate 82. The photoelectric conversion element 90 is formed by laminating an electrode layer 92, a P-type semiconductor layer (photoelectric conversion layer) 94, an N-type semiconductor layer 96, and a transparent electrode layer 98 from the substrate 82 side.
The P-type semiconductor layer 94 is made of, for example, polycrystalline silicon or single crystal silicon.

In the present embodiment, the wavelength conversion element 50a is provided on the surface 90a of the photoelectric conversion element 90 (the surface of the transparent electrode layer 98).
For example, as illustrated in FIG. 22B, the wavelength conversion element 50 a is randomly arranged by mixing the first layer 52 in which only the hollow quantum dots 16 are arranged, and the hollow quantum dots 16 and the quantum dots 14. And a third layer 56 in which only quantum dots are arranged. The second layer 54 and the first layer 52 are formed in order from the third layer 56 on the transparent electrode layer 98, that is, on the surface 90 a of the photoelectric conversion element 90.

The first layer 52 functions as a reflectance improvement layer, and the second layer 54 and the third layer 56 function as wavelength conversion layers. In the wavelength conversion element 50a, the refractive index is gradually brought closer to the value of the photoelectric conversion element from the value of air.
The incident light L incident on the first layer 52 is reflected by, for example, the hollow quantum dots 16, and the reflected light Lb is reflected again by the hollow quantum dots 16, and emission to the outside is suppressed. The reflected light Lb is reflected by the quantum dots 14, the reflected light Lr is reflected again by the hollow quantum dots 16, and the light emitted by the quantum dots 14 is also reflected by the hollow quantum dots 16. In this way, light is suppressed from being emitted to the outside.

Here, considering the application of down-conversion to a photoelectric conversion layer (Si solar cell) made of polycrystalline silicon or single crystal silicon, the range of the solar band (solar spectrum shown in FIG. 14), 300 nm (4. In order to use 1 eV) to 1150 nm (1.1 eV), the wavelength conversion element 50a is desired to exhibit AR characteristics (antireflection characteristics) in a wide range of 300 to 1150 nm. However, since the band indicating the AR characteristic and the average reflectance are in a trade-off relationship, the AR characteristic becomes worse when the band is widened. In order to improve this, it is necessary to make the refractive index of the surface layer (first layer 52) of the wavelength conversion element 50a closer to the value of the refractive index of air. However, few materials have a refractive index of 1.4 or less. In the present invention, as shown in FIG. 17, for example, when the matrix layer is made of SiO ₂ , the refractive index is lower than that of a commercially available low refractive index optical material by setting the ratio of hollow quantum dots to 20% or less. Specifically, a refractive index of 1.4 or less can be realized. Thus, the wavelength conversion element 50a can set the effective refractive index of the surface layer (first layer 52) to an intermediate refractive index between the refractive index of Si and the refractive index of air. Note that the upper limit of the content (ratio) of the hollow quantum dots is estimated to be about 1/3 due to the film strength and the like.

The thickness of the first layer 52 is d _1a and the refractive index n _1a , the thickness of the second layer 54 is d _1b and the refractive index n _1a, and the second layer 54 and the third layer 56 are the total thickness of the _{d 1c} of, when the refractive index _{n 1c, λ / (4n 1a} ) ≒ d 1a, λ / (4n 1b) ≒ d 1b, is preferably _{λ / (4n 1c) ≒ d} 1c _and, n _1a << n _1c, preferably has a relation of _{n 1a <n 1b <n 1c} .
Regarding the configuration of the second layer 54 in which the hollow quantum dots 16 and the quantum dots 14 are mixed, for example, as shown in FIG. 1C, the hollow quantum dots 16 and the quantum dots 14 are arranged in a stacked form. As shown in FIG. 1D, there are a configuration in which hollow quantum dots 16 and quantum dots 14 are randomly arranged.
In this case, in the configuration shown in FIG. 1C, the layer thickness of the hollow quantum dots 16, that is, the hollow quantum dot layer thickness _d2a, and the layer thickness of the quantum dots 14, that is, the quantum dot layer thickness d. _2b, the thickness _{d 1a} of the first layer 52, the thickness _{d 1b} of the second layer 54, with respect to the total thickness _{d 1c} of the second layer 54 and third layer _{56, d 1a} , D _1b , d _1c << d _2a , d _2b are preferable. This is because when the film thickness is of the order of the optical wavelength, the hollow quantum dot layer and the quantum dot layer have optical characteristics in a single layer rather than as a film in which the hollow quantum dots 16 and 14 are mixed. This is because the contribution of the optical design is not shown.

The wavelength conversion element 50 having the above-described configuration corresponds to a half of the Si band gap with respect to a wavelength region of energy more than twice the Si band gap of 1.2 eV constituting the P-type semiconductor layer 94. It has a wavelength conversion function of converting the wavelength of light into energy of 2 eV (wavelength 533 nm).
As described above, in the wavelength conversion element 50a, the utilization efficiency of the incident light L can be increased. Furthermore, by providing the first layer 52 as the uppermost layer, the light with improved reflectance and scattering function can be obtained. The confinement function can be demonstrated. As a result, the reflected light is reduced, and light in a specific wavelength region that does not contribute to photoelectric conversion is wavelength-converted, and the amount of light having a wavelength that can be used for photoelectric conversion increases, thereby improving the conversion efficiency of the photoelectric conversion element 90. Thus, the power generation efficiency of the entire photoelectric conversion device 80 can be improved.

Note that when polycrystalline silicon is used for the P-type semiconductor layer (photoelectric conversion layer) 94 of the photoelectric conversion element 90, the reflectance is not uniform because various plane orientations appear. For this reason, even if an antireflection film effective in a certain plane orientation is formed, the entire photoelectric conversion layer is not effective. However, the wavelength conversion element 50 can improve the transmission characteristics in a specific wavelength region and suppress reflection loss. Also from this point, the power generation efficiency of the entire photoelectric conversion device 80 can be improved.
Further, when the wavelength conversion element 50 is provided, it may be simply disposed on the surface 90a of the photoelectric conversion element 90, and etching or the like is unnecessary. For this reason, the photoelectric conversion device is not damaged by etching or the like. Thereby, generation | occurrence | production of a manufacturing defect can be suppressed.

Next, a second example of the wavelength conversion element of this embodiment will be described.
FIG. 23A is a schematic diagram illustrating a second example of the wavelength conversion element, and FIG. 23B is a schematic diagram illustrating a refractive index distribution in the second example of the wavelength conversion element.
The wavelength conversion element 50b shown in FIG. 23 (a), the arrangement of the hollow quantum dots 16 and the quantum dots 14 in the matrix layer 12, the refractive index distribution _{F 1} in the stacking direction of the layers shown in FIG. 23 (b), in which the refractive index is continuously changed (FIG. 23 (b) reference numeral _{F 11).}

The wavelength conversion element 50b shown in FIG. 23A is different from the wavelength conversion element 50a shown in FIG. 22B in that the first layer 52 has two layers, and the second layer 54 has two layers. Except for the point that the third layer 56 is composed of two layers, the configuration is the same as that of the wavelength conversion element 50a, and a detailed description thereof will be omitted.
In FIG. 23B, the symbol J ₁ corresponds to the first layer 52, the symbol J ₂ corresponds to the second layer 54, and the symbol J ₃ corresponds to the third layer 56.

  In the wavelength conversion element 50b, the first layer 52 includes a hollow quantum dot 16 having a front surface layer 53a and a back surface layer 53b, which are locally near the surface, that is, locally on the incident light side. The low refractive index layer is arranged. Only the hollow quantum dots 16 are disposed on the front surface layer 53a, and only the matrix layer 12 is not disposed on the back surface layer 53b. The back layer 53b is disposed on the third layer 56 side. In the wavelength conversion element 50b, for example, the arrangement density of the hollow quantum dots 16 in the surface layer 53a is set so that the first layer 52 has a refractive index of air.

The second layer 54 includes a quantum dot layer 55a in which only the quantum dots 14 are arranged, and a hollow quantum dot layer 55b in which only the hollow quantum dots 16 are arranged, and constitutes a refractive index gradient layer. . In the second layer 54, the hollow quantum dot layer 55b is disposed on the fourth layer 58 side.
The third layer 56 is a stack of two quantum dot layers in which only the quantum dots 14 are arranged. The third layer 56 constitutes a high refractive index layer, and the third layer 56 functions as a wavelength conversion layer. Note that the number of quantum dot layers in the third layer 56 is not limited to two, and may be one or more than two.
As will be described later, in order to make the refractive index of the wavelength conversion element 50b approach the value of the photoelectric conversion element continuously from the air value, in the second layer 54, the quantum dot layer 55a and the hollow quantum dot layer 55b are stacked. For example, at least one of the number of layers and the thickness of each layer is appropriately changed in the stacking direction. Further, the stacking order of the quantum dot layer 55a and the hollow quantum dot layer 55b is not particularly limited, so that the refractive index of the wavelength conversion element 50b is continuously made close to the value of the photoelectric conversion element from the air value. Set as appropriate.

  The wavelength conversion element 50b also has a low refractive index layer, a refractive index gradient layer, and a high refractive index layer in order from the incident light L side. The wavelength conversion element 50b can make the refractive index of the wavelength conversion element continuously approach the value of the photoelectric conversion element from the air value by changing the arrangement density of the hollow quantum dots and the quantum dots in the stacking direction.

Specifically, in the wavelength conversion element 50b, the refractive index is changed by changing the stacking ratio of the quantum dot layer 55a and the hollow quantum dot layer 55b in the third layer 56 with respect to the stacking direction. refractive index as a region F ₁₁ shown in 23 (b) can be varied gradually.
In the wavelength conversion element 50b, when the thickness of the surface layer 53a on which only the hollow quantum dots 16 are arranged is d, the thickness d of the surface layer 53a is 1 with respect to the wavelength λ of the incident light L. It is preferable that / 4λ >> d.
In addition, the thickness d of the surface layer 53a is synonymous with the thickness in the stacking direction of the region where the hollow quantum dots 16 are locally arranged.

Also in the wavelength conversion element 50b, the first layer 52 can be set so that the refractive index becomes the value of air by changing the arrangement density of the hollow quantum dots 16 or the like. the lamination ratio between the layer 55a and the hollow quantum dot layer 55b, by changing to its stacking direction, the refractive index is varied gradually as area F ₁₁ shown in FIG. 23 (b). Thereby, the transmittance can be improved and the utilization efficiency of the incident light L can be increased.
As described above, also in the wavelength conversion element 50b, the utilization efficiency of the incident light L can be increased, and furthermore, similarly to the wavelength conversion element 50a, the light confinement function by the improvement of the reflectance and the scattering function can be exhibited. And the same effect as the wavelength conversion element 50a can be obtained.

  For example, the first layer 52 may include a first surface layer and a first back surface layer in which the arrangement density of the hollow quantum dots 16 is different. . In this case, in the first layer 52, the arrangement density of the hollow quantum dots is higher in the first surface layer than in the first back surface layer. Furthermore, the second layer has a second front surface layer and a second back surface layer having different quantum dot arrangement densities. In this case, the refractive index is continuously changed by lowering the arrangement density of the quantum dots in the second surface layer than in the second back layer.

Next, a third example of the wavelength conversion element of this embodiment will be described.
FIG. 24A is a schematic diagram illustrating a third example of the wavelength conversion element, and FIG. 24B is a schematic diagram illustrating a refractive index distribution in the third example of the wavelength conversion element.
The wavelength conversion element 50c shown in FIG. 24A has a refractive index distribution F in the stacking direction of each layer as shown in FIG. 24B due to the arrangement of the hollow quantum dots 16 and the quantum dots 14 in the matrix layer 12. in _2, in which continuously changes the refractive index (see FIG. 24 (b) code _{F 21).}
The wavelength conversion element 50c shown in FIG. 24A is different from the wavelength conversion element 50a shown in FIG. 22B in that the first layer 52 has two layers and the configuration of the second layer 54a is different. Except for this point, the configuration is the same as that of the wavelength conversion element 50a, and a detailed description thereof will be omitted.
In FIG. 24B, the symbol J ₁ corresponds to the first layer 52, the symbol J ₂ corresponds to the second layer 54 a, and the symbol J ₃ corresponds to the third layer 56.

In the wavelength conversion element 50c, the first layer 52 has a front surface layer 52a and a back surface layer 52b, and constitutes a low refractive index layer. The surface layer 52a and the back surface layer 52b have different arrangement densities of the hollow quantum dots 16, and the surface layer 52a has a higher arrangement density of the hollow quantum dots 16 than the back surface layer 52b. For example, in the first layer 52, the arrangement density of the hollow quantum dots 16 in the front surface layer 52a and the back surface layer 52b is set so that the refractive index becomes the value of air.
The second layer 54a is a layer in which the hollow quantum dots 16 and the quantum dots 14 are mixed and randomly arranged, and constitutes a refractive index gradient layer. The third layer 56 constitutes a high refractive index layer. The wavelength conversion element 50c has a low refractive index layer, a refractive index gradient layer, and a high refractive index layer in order from the incident light L side. In the wavelength conversion element 50c, the refractive index of the wavelength conversion element can be made close to the value of the photoelectric conversion element continuously from the air value by changing the arrangement density of the hollow quantum dots and the quantum dots in the stacking direction.

Specifically, in the second layer 54a, the quantum dots 14 and the hollow quantum dots 16 are randomly arranged, and a refractive index gradient layer is configured. The second layer 54a has a refractive index as a region _{F 21} shown in FIG. 24 (b) is changing slowly.
In addition, the incident light L incident on the wavelength conversion element 50c is reflected by the quantum dots 14 by the second layer 54a, for example, and the reflected light Lr is reflected by the hollow quantum dots 16 to the third layer 56 side. Is done. Thereby, the incident light L is confined.
As described above, also in the wavelength conversion element 50c, the utilization efficiency of the incident light L can be increased, and furthermore, similarly to the wavelength conversion element 50a, the light confinement function by the improvement of the reflectance and the scattering function can be exhibited. And the same effect as the wavelength conversion element 50a can be obtained.

Next, a fourth example of the wavelength conversion element of this embodiment will be described.
FIG. 25 is a schematic diagram illustrating a fourth example of the wavelength conversion element.
In the wavelength conversion element 50d shown in FIG. 25, the quantum dots 14 and the hollow quantum dots 16 are randomly arranged in the first layer 52a as compared with the wavelength conversion element 50a shown in FIG. Except for the point and the point that the second layer 54 has two layers, the configuration is the same as that of the wavelength conversion element 50a, and thus detailed description thereof is omitted.

In the wavelength conversion element 50d, in the first layer 52a, the quantum dots 14 and the hollow quantum dots 16 are randomly arranged, and an arrangement density gradient is formed. The first layer 52a constitutes a first arrangement density gradient layer.
The second layer 54 is formed by laminating a quantum dot layer 55a in which only the quantum dots 14 are arranged and a hollow quantum dot layer 55b in which only the hollow quantum dots 16 are arranged, and an arrangement density gradient is formed. Yes. The second layer 54 constitutes a second arrangement density gradient layer, and the refractive index is continuously changed.
The wavelength conversion element 50d has a configuration of a first arrangement density gradient layer and a second arrangement density gradient layer in order from the incident light L side. Also in the wavelength conversion element 50d, the refractive index of the wavelength conversion element can be made close to the value of the photoelectric conversion element continuously from the air value by changing the arrangement density of the hollow quantum dots and the quantum dots in the stacking direction.

In the wavelength conversion element 50d, incident light that has entered the first layer 52a is reflected by, for example, the quantum dots 14, and the reflected light is reflected by the hollow quantum dots 16 to the second layer 54 side. Thereby, incident light is confined. Further, in the second layer 54, the refractive index is continuously changed, and the light incident from the first layer 52 a is suppressed from being reflected by the second layer 54, while the third layer 54. 56 can be transmitted.
As described above, also in the wavelength conversion element 50d, the utilization efficiency of incident light can be increased, and the same effect as that of the wavelength conversion element 50a can be obtained.

  Moreover, in the photoelectric conversion device having any of the wavelength conversion elements described above, the photoelectric conversion layer is not limited to one using silicon, but a CIGS photoelectric conversion layer, a CIS photoelectric conversion layer, and a CdTe photoelectric conversion. It may be a layer, a dye-sensitized photoelectric conversion layer, or an organic photoelectric conversion layer.

  The substrate 82 is relatively heat resistant. As the substrate 82, for example, a glass substrate such as blue plate glass, heat resistant glass, quartz substrate, stainless steel substrate, metal multilayer substrate in which stainless steel and different metals are laminated, an aluminum substrate, or an oxidation treatment, for example, anodization treatment on the surface. By applying this, an aluminum substrate with an oxide film whose surface insulation is improved can be used.

Next, a photoelectric conversion device having the wavelength conversion element of this embodiment will be described.
FIG. 26 is a schematic cross-sectional view illustrating a photoelectric conversion device according to an embodiment of the present invention.
In the photoelectric conversion device 120 illustrated in FIG. 26, a reflective layer 124 is formed on a base material 122, and a wavelength conversion layer 126 is provided on the reflective layer 124. The wavelength conversion layer 126 has the same configuration as the wavelength conversion element 50 shown in FIG. A first transparent electrode layer 128 is provided on the wavelength conversion layer 126.
A photoelectric conversion layer 130 is provided on the first transparent electrode layer 128, and a second transparent electrode layer 132 is provided on the photoelectric conversion layer 130. Furthermore, a light confinement layer 134 is provided on the second transparent electrode layer 132.
Note that the photoelectric conversion layer 130 can have a configuration similar to that of the P-type semiconductor layer (photoelectric conversion layer) 94 of the photoelectric conversion device 80 illustrated in FIG. For this reason, the detailed description is abbreviate | omitted.

  In the photoelectric conversion device 120 of the present embodiment, out of the incident light L incident from the surface 134a side of the light confinement layer 134, the photoelectric conversion layer 130 passes through without being used for photoelectric conversion, for example, infrared rays and Near infrared long-wavelength light Lu is reflected by the reflective layer 124 and is incident on the wavelength conversion layer 126. In this wavelength conversion layer 126, long wavelength light Lu that has not been used, for example, light having a wavelength of 1300 nm, is converted into short wavelength light Ls that can be used for photoelectric conversion by the photoelectric conversion layer 130, for example, about 1000 nm by the up-conversion function To do. Moreover, since the wavelength conversion layer 126 has a high transmittance, the long wavelength light Lu can be used effectively. Thereby, the incident light L can be used effectively, and the utilization efficiency of the incident light L in the photoelectric conversion layer 130 can be increased.

  When the substrate 122 is directly subjected to a thermal process, a support substrate material having a relatively heat resistance is used. For example, surface insulation can be improved by applying oxidation treatment (for example, anodizing treatment) to heat-resistant glass, quartz substrate, stainless steel substrate, metal multilayer substrate laminated with dissimilar metals with stainless steel, or aluminum substrate. An aluminum substrate with an oxide film is used.

In a method that can be formed by a low temperature process, an organic support substrate material or the like can be used. Specifically, saturated polyester / polyethylene terephthalate (PET) resin substrate, polyethylene naphthalate (PEN) resin substrate, cross-linked fumaric acid diester resin substrate, polycarbonate (PC) resin substrate, polyethersulfone (PES) resin substrate , Polysulfone (PSF, PSU) resin substrate, polyarylate (PAR) resin substrate, cyclic polyolefin (COP, COC) resin substrate, cellulose resin substrate, polyimide (PI) resin substrate, polyamideimide (PAI) resin substrate, maleimide -Olefin resin substrate, polyamide (PA) resin substrate, acrylic resin substrate, fluorine resin substrate, epoxy resin substrate, silicone resin film substrate, polybenzazole resin substrate, substrate liquid crystal polymer with episulfide compound (L P) Substrate, cyanate resin substrate, aromatic ether resin substrate, composite plastic material with silicon oxide particles, composite plastic material with metal nanoparticles, inorganic oxide nanoparticles, inorganic nitride nanoparticles, metal / Composite plastic materials with inorganic nanofibers & microfibers, carbon fibers, composite plastic materials with carbon nanotubes, glass ferkes, glass fibers, composite plastic materials with glass beads, particles with clay mineral and mica derived crystal structure Composite plastic material, laminated plastic material having at least one bonding interface between thin glass and the above-mentioned single organic material, inorganic layer (for example, SiO ₂ , Al ₂ O ₃ , SiOxNy) and the above organic layer alternately By laminating, it has at least one joint interface. It can be used composite materials having that barrier performance.

The reflective layer 124 reflects the light that has passed through the photoelectric conversion layer 130, the first transparent electrode layer 128, and the wavelength conversion layer 126, and re-enters the wavelength conversion layer 126. The photoelectric conversion layer 130 uses photoelectric conversion. Reflected, for example, infrared and near infrared.
The reflective layer 124 is made of, for example, an Al film having a thickness of 500 nm. This Al film is formed by vapor deposition, for example. The reflective layer 124 can also be composed of Au, Ag, and a dielectric laminated film.

The first transparent electrode layer 128 is composed of a P-type transparent electrode layer. As this first transparent electrode layer 128 (P-type transparent electrode layer), for example, a composition of CuAlO ₂ , CuGaO ₂ , CuInO _2, etc .: when expressed as ABO ₂ , A is Cu, Ag, and B is Al , Ga, In, Sb, Bi. In addition, an alloy represented by ABO ₂ , a solid solution material thereof, and a Delaphosite type microcrystalline body, and two or three kinds of alloys of these materials are used. Note that CuAlS ₂ , CuGaS, B-doped SiC, or the like can be used for the first transparent electrode layer 128.

The second transparent electrode layer 132 is composed of an N-type transparent electrode layer. The second transparent electrode layer as the (N-type transparent electrode layer), for example, IGZO, greater than or equal to the band gap of a-IGZO (amorphous _IGZO), Ga ₂ O 3, SnO ₂ system (ATO, FTO) ZnO-based (AZO, GZO), In ₂ O ₃ -based (ITO,), Zn (O, S) CdO, or two or three alloys of these materials can be used. Furthermore, as the second transparent electrode layer 132, MgIn ₂ O ₄ , GaInO ₃ , CdSb ₃ O _6, or the like can be used.

  The light confinement layer 134 has a light confinement function, for example, an antireflection function. A known antireflection film can be used for the light confinement layer 134.

Next, another photoelectric conversion device of this embodiment will be described.
FIG. 27A is a schematic cross-sectional view showing a photoelectric conversion device according to another embodiment of the present invention, and FIG. 27B is a schematic perspective view showing the main part of another configuration of the wavelength conversion layer. .
The photoelectric conversion device 120a illustrated in FIG. 27 is different in the configuration of the wavelength conversion layer 136 from the photoelectric conversion device 120 illustrated in FIG. 26, and other configurations are the same as those of the photoelectric conversion device 120 illustrated in FIG. Therefore, detailed description thereof is omitted.

A wavelength conversion layer 136 of the photoelectric conversion device 120a illustrated in FIG. 27 has a stacked structure in which a wavelength conversion layer 138a and a resin portion 138b are stacked.
Each of the wavelength conversion layer 138a and the resin portion 138b has an optical wavelength order (several hundred nm).
The wavelength conversion layer 136 prevents the long wavelength light Lu that is not used for photoelectric conversion by the photoelectric conversion layer 130 that has passed through the photoelectric conversion layer 130 and the first transparent electrode layer 128 from being emitted from the surface 136 a of the wavelength conversion layer 136. It is to make. That is, the wavelength conversion layer 136 confines the long wavelength light Lu that is not used for photoelectric conversion in the photoelectric conversion layer 130.
As a configuration for confining the long-wavelength light Lu, for example, the configuration of the antireflection film can be used as shown in FIG.
In the wavelength conversion layer 136, for the wavelength conversion layer 138a, for example, a matrix layer (not shown) in which a plurality of quantum dots and hollow quantum dots are periodically arranged can be used. In this case, for example, as shown in FIGS. 17A and 17B, the refractive index is adjusted by using the relationship between the content of the quantum dots, the size of the quantum dots, the interval between the quantum dots and the refractive index, For example, the long wavelength light Lu may be confined in the wavelength conversion layer 136 in combination with the resin portion 138b.

The resin portion 138b is made of a dielectric material or an organic material, and is not particularly limited as long as, for example, a photocurable resin or a thermosetting resin is used and transmits light.
As a photocurable resin or a thermosetting resin, for example, an acrylic resin, an epoxy resin, a silicone resin, an ethylene vinyl acetate (EVA) resin, or the like can be used.
Examples of the silicone resin include commercially available silicone resins for LEDs. As the ethylene vinyl acetate (EVA) resin, for example, Solar EVA (trademark) manufactured by Mitsui Chemicals Fabro Co., Ltd. can be used. Furthermore, an ionomer resin or the like can be used.

  The epoxy resin has a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a bisphenol S type epoxy resin, a naphthalene type epoxy resin or a hydrogenated product thereof, an epoxy resin having a dicyclopentadiene skeleton, and a triglycidyl isocyanurate skeleton. Examples thereof include an epoxy resin, an epoxy resin having a cardo skeleton, and an epoxy resin having a polysiloxane structure.

  As the acrylic resin, (meth) acrylate having two or more functional groups can be used. A water-dispersed acrylic resin can be used as the acrylic resin. This water-dispersed acrylic resin is an acrylic monomer, oligomer or polymer dispersed in a dispersion medium containing water as the main component. In a dilute state like an aqueous dispersion, the crosslinking reaction hardly proceeds, but the water is evaporated. If this is done, the crosslinking reaction will proceed and solidify even at room temperature, or it will have a functional group capable of self-crosslinking and will be crosslinked and solidified only by heating without using additives such as catalysts, polymerization initiators, and reaction accelerators. Acrylic resin.

  In the photoelectric conversion device 120a, the long-wavelength light Lu that has passed through the photoelectric conversion layer 130 and is not used for photoelectric conversion by the photoelectric conversion layer 130 is not emitted from the surface 136a of the wavelength conversion layer 136, and thus photoelectric conversion is performed. It is not incident on the layer 130 again. In addition, since the long wavelength light Lu is not emitted from the surface 136a of the wavelength conversion layer 136 without generating heat, the photoelectric conversion layer 130 is not adversely affected. Thus, in the photoelectric conversion device 120a, re-incidence of the long wavelength light Lu that is not used for photoelectric conversion in the photoelectric conversion layer 130 can be suppressed, and adverse effects of the long wavelength light Lu that is not used for photoelectric conversion can be suppressed.

In the photoelectric conversion device 120a, when the effective refractive index of the resin portion 138b is na and the refractive index of the wavelength conversion layer 138a is nb, it is preferable that 0.3 <| nb−na |. In this case, the refractive index nb of the wavelength conversion layer 138a is, for example, 1.8 ≦ n ≦ 4.0 at a wavelength of 533 nm, and preferably 1.8 ≦ n ≦ 2.5 at a wavelength of 533 nm.
The larger the refractive index difference between the effective refractive index na of the resin portion 138b and the refractive index nb of the wavelength conversion layer 138a, the smaller the number of layers for obtaining the same reflection. However, increasing the refractive index difference narrows the material selection range. In order to obtain a predetermined reflectance when the number of wavelength conversion layers 136 is about 10 layers, for example, the refractive index difference is about 0.3. Therefore, the difference in refractive index between the effective refractive index na of the resin portion 138b and the refractive index nb of the wavelength conversion layer 138a is preferably 0.3 <| nb−na |.

  The present invention is basically configured as described above. As described above, the quantum dot structure, the wavelength conversion element, and the photoelectric conversion device of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiment, and various improvements or modifications can be made without departing from the gist of the present invention. Of course, you may do it.

10, 10a to 10c, 11 Quantum dot stack 12 Matrix layer 14, 14a to 14c Quantum dot 16 Hollow quantum dot 15 Second compound semiconductor layer 16 Quantum dot 17 Third compound semiconductor layer 18 Second matrix layer 18a Quantum Dot layer 18b Hollow quantum dot layer 20 Substrate 22, 30, 40 SiO ₂ layer 24, 32 SiGeO layer 25, 27, 29, 33 Laminate 34 SiOx layer 50, 50a, 50b Wavelength conversion element 52 First layer 54 Second Layer 56 third layer 58 fourth layer 80, 120, 120a photoelectric conversion device 90 photoelectric conversion element

Claims (18)

A matrix layer;
Quantum dots made of a semiconductor or metal element formed in the matrix layer;
A quantum dot structure having hollow hollow quantum dots formed in the matrix layer.   2. The quantum dot structure according to claim 1, wherein each of the quantum dots is composed of a wavelength conversion composition that converts a wavelength of light into energy having lower energy than the absorbed light with respect to a specific wavelength region of the absorbed light.   3. The quantum dot structure according to claim 1, wherein the matrix layer is made of an inorganic dielectric having a band gap of 3.0 eV or more, or an organic material having a transmittance of 70% or more according to JIS K7361-1: 1997. .   The quantum dot structure according to any one of claims 1 to 3, wherein in the quantum dots and the hollow quantum dots, an interval between nearest neighbor particles is 20 nm or less.   The quantum dot structure according to claim 1, wherein the hollow forming material forming the hollow quantum dots and the matrix layer have the same composition.   The quantum dot structure according to any one of claims 1 to 5, wherein at least one of the hollow quantum dots and the quantum dots is arranged in a layered manner. The cumulative film thickness of the hollow quantum dot layer composed of hollow quantum dots arranged in a layered manner is 50 nm or more,
The quantum dot structure according to claim 6, wherein a distance between the quantum dot layer composed of the quantum dots adjacent to the hollow quantum dot of the hollow quantum dot layer and the hollow quantum dot layer is 20 nm or less.   The quantum dot structure according to any one of claims 1 to 5, wherein the hollow quantum dots and the quantum dots are randomly arranged.   The quantum dot structure according to claim 8, wherein a thickness of the hollow quantum dots and a layer in which the quantum dots are randomly arranged is 100 nm or less.   The quantum dot structure according to any one of claims 1 to 9, wherein in the quantum dots and the hollow quantum dots, an interval between nearest neighbor particles is 5 nm or less.   The quantum dot structure according to claim 1, wherein the quantum dots and the hollow quantum dots have a particle diameter of 2 nm to 10 nm. The quantum dots are phosphor, Si _x Ge _(1-x) , In _x Ga _(1-x) N, InAs, FeSi, PbS or PbSe, or fullerene, an organic fluorescent dye, or an organic fluorescent dye molecule. The quantum dot structure according to any one of claims 1 to 11, comprising: The hollow quantum dots are made of SiO ₂ , Si ₂ N ₃ , GaN, GaN or AlN, or acrylic resin, epoxy resin, ethylene vinyl acetate resin, silicone resin, saturated polyester / polyethylene terephthalate resin, polyethylene naphthalate resin, cross-linked fumarate. The quantum dot structure according to any one of claims 1 to 12, comprising an acid diester resin, a polycarbonate resin, a cellulose resin, or a transparent polyimide. The quantum dot structure according to claim 1,
Each quantum dot is composed of a wavelength conversion composition that converts the wavelength of light into a light having a lower energy than the absorbed light with respect to a specific wavelength region of the absorbed light. A wavelength conversion element comprising a wavelength conversion layer having a function of improving the light utilization efficiency of light emitted from the light source and improving the transmittance in an arbitrary wavelength region.   The photoelectric conversion apparatus characterized by the wavelength conversion element of Claim 14 provided in the incident light side of the photoelectric converting layer.   The wavelength conversion element includes, in order from the incident light side, a first layer in which only the hollow quantum dots are arranged, a second layer in which the hollow quantum dots and the quantum dots are mixed, The photoelectric conversion device according to claim 15, further comprising a third layer in which only quantum dots are arranged.   The wavelength conversion element has a first surface layer and a first back surface layer having different arrangement densities of the hollow quantum dots, and the first surface layer is more hollow than the first back surface layer. It has a second surface layer and a second back surface layer having a high quantum dot arrangement density and different quantum dot arrangement density, and the second surface layer is more than the second back layer. The photoelectric conversion device according to claim 15, wherein the refractive index is continuously changed by lowering the arrangement density of the quantum dots.   The wavelength conversion element includes, in order from the incident light side, a first arrangement density gradient layer in which the quantum dots and the hollow quantum dots are arranged randomly and an arrangement density gradient is formed, the quantum dots, and the hollow quantum dots The photoelectric conversion device according to claim 15, further comprising: a second arrangement density gradient layer that is arranged in a layered manner and has an arrangement density gradient.