JP5862357B2 - White LED laminate and white LED - Google Patents

Description

  The present invention relates to a white LED laminate and a white LED. More specifically, the present invention relates to a white LED laminate having a profile almost the same as that of a sunlight spectrum and using a quantum dot made of semiconductor nanocrystal particles and excellent in color rendering and luminous efficiency, and a white LED provided with the same.

  For the purpose of energy saving in recent years, the use of so-called white LEDs has been studied as an alternative technology to incandescent bulbs and fluorescent lamps. The light emitted by the white LED is ideally white light close to sunlight, which is natural light. However, since white light close to sunlight needs to be light realized by a continuous spectrum over the entire visible light range, even if an LED having an emission wavelength in a certain narrow range is used, It is technically difficult to realize white light close to sunlight in the sense of.

  In order to realize white light close to sunlight, an LED structure in which various LEDs are combined has been proposed. For example, since the human eye sees a mixture of three primary colors of light or a mixture of two colors that are complementary colors, several methods have been devised to substitute this for white light. Specifically, there is an LED structure that emits white light by mixing light of blue LED, green LED, and red LED. In addition, there is an LED structure that emits a phosphor using the light of a blue LED. In the LED structure using the phosphor, a yellow light phosphor that is a complementary color of blue light is emitted by the blue LED, and white light is emitted by mixing the blue light of the blue LED and the yellow light of the phosphor; There is an LED structure in which a green light phosphor and a red light phosphor are emitted by a blue LED, and white light is emitted by three wavelengths of blue light of the blue LED, green light of the phosphor, and red light. Furthermore, using ultraviolet (UV) -LED as excitation light, blue light phosphor, green light phosphor and red light phosphor are emitted to emit white light with three wavelengths of blue light, green light and red light. There is an LED structure to be made.

  However, the above-mentioned white LED structure feels white to the human eye due to the mixing of the three primary colors of light and two complementary colors, but the reflected light is natural light (sunlight) after irradiating the object. In contrast, both have the problem that their color rendering properties are extremely poor.

  Therefore, in order to improve the color rendering properties of the white LED, attempts have been made to broaden the emission spectrum profile generated from the white LED and bring it closer to natural light. For example, Patent Document 1 discloses an attempt to obtain a phosphor that emits a wide range of fluorescence based on a crystal having significant irregularity in the crystal structure. Further, Patent Document 2 proposes a plurality of semiconductor nanocrystal white light emitting devices, which improve the color rendering property of white LEDs by mixed color light emission of red, green, and blue light emitting semiconductor nanocrystals, and convert organic light emitters into inorganic light emitters. It is described that an attempt is made to extend the service life by replacement.

JP 2008-2222988 A Special table 2009-527099 gazette

  However, since the white LED described in Patent Document 1 and Patent Document 2 is not sufficiently broadened in its emission spectrum profile, the emission spectrum profile is not the same as the profile of sunlight. Absent. For this reason, the white LEDs described in Patent Document 1 and Patent Document 2 have a problem that their color rendering properties are not sufficient. Further, since the white LED described in Patent Document 2 is composed of a layer in which semiconductor nanocrystals having different particle diameters are mixed, light emission at a short wavelength from semiconductor nanocrystals having a small particle diameter is caused by particles. There is a problem that the semiconductor nanocrystal having a large diameter is absorbed and converted into long-wavelength light emission, short-wavelength light emission is reduced, energy loss occurs during wavelength conversion by absorption and light emission, and light emission efficiency is lowered.

  The present invention has been made in view of such circumstances, has a broad emission spectrum profile, has an emission spectrum profile that substantially matches the profile of sunlight, and is extremely effective in color rendering and emission efficiency. An object is to provide an excellent white LED.

  In view of the above situation, the present inventors are composed of a plurality of layers including semiconductor nanocrystal particles, and the order of layers and the wavelength difference between emission peaks of semiconductor nanocrystals included in each adjacent layer are controlled. By using the laminate for LED, it has been found that a white LED having an emission spectrum profile almost identical to the profile of sunlight and excellent in color rendering and luminous efficiency can be obtained, and the present invention has been completed. It was. More specifically, the present invention provides the following.

(1) A white LED laminate in which a plurality of layers containing II-VI semiconductor nanocrystal particles having different particle sizes are laminated,
The white LED laminate is directed toward the light output direction of the LED.
The II-VI group semiconductor nanocrystal particles are sequentially laminated so as to become a layer including a small one from a layer including a large particle size of the II-VI semiconductor nanocrystal particles,
Between the layers containing adjacent II-VI group semiconductor nanocrystal particles of the white LED laminate,
The difference in peak wavelength of the emission spectrum caused by the II-VI group semiconductor nanocrystal particles is
A white LED laminate having a half-width or less of an emission spectrum of the II-VI group semiconductor nanocrystal particles.

(2) The peak wavelength difference of the emission spectrum is 10 to 200 nm,
The half-width of the peak wavelength of the emission spectrum is 10 to 200 nm. The white LED laminate according to (1),

  (3) The white LED laminate according to (1) or (2), wherein the II-VI group semiconductor nanocrystal particles are cadmium compound semiconductor crystals.

  (4) The white LED laminate according to any one of (1) to (3), wherein the II-VI semiconductor nanocrystal particles are any one selected from cadmium sulfide, cadmium selenide, and cadmium telluride. .

  (5) A white LED comprising the white LED laminate according to any one of (1) to (4).

  (6) The white LED according to (5), wherein the white LED is a current injection type.

  (7) The white LED according to (5), wherein the white LED is a light excitation type.

  (8) The white LED according to (6), wherein the laminate for white LED is installed on a transparent glass substrate, a transparent resin substrate, a transparent flexible glass substrate, or a transparent flexible resin substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the white LED laminated body which has the emission spectrum profile broadly matched with the profile which sunlight has, and was very excellent in color rendering property and luminous efficiency, and a white LED provided with the same are provided. be able to.

It is sectional drawing of the layer structure of the laminated body for white LED. The simulation result of an emission spectrum profile (half-value width 40 nm, peak wavelength interval 25 nm) is shown. The simulation result of an emission spectrum profile (half-value width 40 nm, peak wavelength interval 40 nm) is shown. The simulation result of an emission spectrum profile (half-value width 40 nm, peak wavelength interval 50 nm) is shown. It is the schematic of current injection type white LED. It is the schematic of light excitation type | mold white LED.

  The white LED according to the present invention includes a white LED laminate in which layers containing semiconductor nanocrystals are laminated. Here, since the technical feature of the white LED according to the present invention is the white LED laminate, the white LED laminate will be described first, and then the white LED will be described.

<Laminated body for white LED>
The white LED laminate will be specifically described with reference to the drawings. FIG. 1 is a cross-sectional view specifically showing an embodiment of a white LED laminate. As shown in FIG. 1, the white LED laminate has a plurality of layers containing semiconductor nanocrystal particles having different particle sizes, and the semiconductor nanocrystal particles have a larger particle size in the light output direction of the LED. It is characterized by being sequentially laminated so as to be a layer including a small layer from a layer including a layer. Hereinafter, the laminated structure of the semiconductor nanocrystal particles, the layer containing the semiconductor nanocrystal particles (hereinafter referred to as “semiconductor nanocrystal particle layer”), and the white LED laminate will be sequentially described.

(Semiconductor nanocrystal particles)
The semiconductor nanocrystal particles contained in each semiconductor nanocrystal particle layer constituting the white LED laminate are particles composed of so-called semiconductor crystals. Semiconductors include single element semiconductors and compound semiconductors.

  As the single element semiconductor, silicon (Si) or germanium (Ge) can be used. Compound semiconductors include compounds composed of combinations of Group II-VI elements, compounds composed of combinations of Group III-V elements, compounds composed of combinations of Group IV-VI elements, and elements of Group I-III-VI. A compound composed of a combination can be used as a compound semiconductor. Among the semiconductors, compound semiconductor nanocrystals composed of combinations of II-VI group elements are preferable.

Specific examples of the semiconductor crystal include silicon (Si), germanium (Ge), zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), cadmium oxide (CdO), Cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), magnesium oxide (MgO), magnesium sulfide (MgS), selenium magnesium (MgSe), tellurium magnesium (MgTe), mercury oxide (HgO) sulfide Mercury (HgS), mercury selenide (HgSe), mercury telluride (HgTe), aluminum nitride (AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), antimony aluminum (AlSb), gallium nitride (GaN) , Gallium phosphide (GaP), arsenic Gallium (GaAs), antimony gallium (GaSb), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), antimony indium (InSb), thallium nitride (TlN), thallium phosphide (TlP), Thallium arsenide (TlAs), antimony thallium (TlSb), lead sulfide (PbS), lead selenide (PbSe), lead telluride (PbTe), copper indium selenium (CuInSe ₂ ), copper indium sulfide (CuInS ₂ ), copper Indium gallium selenium (CuIn _X Ga _(1-X) Se ₂ ) can be exemplified.

  The semiconductor nanocrystal exhibits a quantum size effect when the particle size is about 10 nm. Such nanoparticles are called quantum dots, and are mainly small crystals of about 10 nm or less in which hundreds to thousands of atoms gather in a semiconductor. When the region where electrons are confined becomes small, the forbidden bandwidth (band gap) increases due to the quantum effect that the density of states of the electrons becomes discrete. In other words, even with semiconductors having the same composition, the band gap of the semiconductor increases as the particle size decreases.

  The quantum dots can control the band gap by changing the particle diameter of materials having the same constituent elements and compositions at 10 nm or less. In the optical characteristics, if the particle diameter is reduced, both the absorption wavelength and the emission wavelength are shortened. That is, if the particle diameter is reduced, the band gap is increased, and both the absorption wavelength and the emission wavelength are shortened. This is an effective control means for manufacturing a light emitting device. That is, it becomes possible to produce quantum dots having continuously different emission wavelengths simply by changing the particle diameter.

  Another feature is that the emission peak of the quantum dot is steep because it is based on the transition between semiconductor bands. Based on the above two facts, by emitting light from a plurality of semiconductor nanocrystals having two characteristics, that is, the emission wavelength is continuously different and the emission peak is steep, natural light ( The same continuous spectrum as sunlight) can be realized.

  The simulation results in a situation where a broad sunlight profile can be realized from steep emission peaks with different wavelengths are as follows. First, for a mixed emission spectrum that is the sum of a plurality of emission spectra from 400 nm to 650 nm in the visible light region, the emission spectrum follows a Gaussian distribution, and the half-value width of each emission spectrum is 40 nm and the interval between peak wavelengths is 25 nm. 40 nm and 50 nm. FIG. 2 shows the results with an interval of 25 nm, FIG. 3 shows the results with an interval of 40 nm, and FIG. 4 shows the results with an interval of 50 nm.

  From FIG. 2, it is possible to obtain a profile equivalent to the profile of the sunlight spectrum at a peak wavelength interval of 25 nm which is smaller than the half-value width of 40 nm of the emission peak. From FIG. 3, it is possible to obtain a profile almost equivalent to the profile of the sunlight spectrum when the peak wavelength interval is 40 nm, which is the same as the half-value width 40 nm of the emission peak. From FIG. 4, it was found that when the peak wavelength interval is 50 nm, which is larger than the half-value width 40 nm of the emission peak, the solar spectrum profile is roughly reflected, but the profile is different.

  Also, in the manufacture of LEDs, semiconductor nanocrystals are sequentially stacked in the light output direction from those having a large particle size to those having a small particle size, so that short-wavelength light emitted from semiconductor nanocrystals having a small particle size can be emitted from a semiconductor having a large particle size. It is absorbed into the nanocrystal and converted into long-wavelength light emission, short-wavelength light emission is reduced, and energy loss can be prevented from occurring at the time of wavelength conversion due to absorption and light emission, thereby preventing a reduction in light emission efficiency.

  Semiconductor nanocrystal particles that are quantum dots can be obtained by adjusting the so-called reaction time corresponding to the time of heating or cooling of the raw material. The reaction time can be appropriately determined from the relationship with the particle size of the semiconductor nanocrystal particles. Since the semiconductor nanocrystal particles have different emission spectrum peak wavelengths depending on their particle sizes, a plurality of semiconductor nanocrystal particles having different optical characteristics can be obtained by adjusting the reaction time.

  For example, when the semiconductor nanocrystal is a cadmium selenide crystal, cadmium selenide crystal particles having a particle size in the range of 1.0 to 8.0 nm can be obtained by adjusting the reaction time. Since the peak wavelength of the emission spectrum of the cadmium selenide crystal particles depends on the particle size, cadmium selenide crystal particles having different emission spectrum peak wavelengths can be obtained by changing the particle size of the cadmium selenide crystal particles. Can do.

  In addition, since the semiconductor nanocrystal particle which forms the said quantum dot is marketed, it can obtain easily by purchasing the semiconductor nanocrystal particle which has a desired particle size.

(Semiconductor nanocrystal particle layer)
The white LED laminate is composed of the semiconductor nanocrystal particle layer.

  The film thickness of each semiconductor nanocrystal particle layer is not particularly limited as long as it does not affect the emission spectrum of the semiconductor nanocrystal particles forming the quantum dots. However, in the case of a current injection type white LED, a thinner one is desirable because a current flows through the white LED laminate. As for the thickness of the laminated body for white LED, 50-100 nm is desirable, and it is preferable that the film thickness of each semiconductor nanocrystal particle layer shall be 5.0-10.0 nm. On the other hand, in the case of a light-excited white LED, there is no particular limitation because no current flows. Since the thickness of each semiconductor nanocrystal particle layer is in the above range, the white LED laminate can be made to have a thickness corresponding to the intended use without affecting the emission spectrum generated from each layer.

  The content of the semiconductor nanocrystal particles in each semiconductor nanocrystal particle layer is determined so that the emission spectrum profile of the white LED laminate matches the profile of sunlight.

  The formation of the semiconductor nanocrystal particle layer is desirably performed by mixing semiconductor nanocrystals in a solution to be described later and applying this mixed solution.

  The method for applying the coating solution is not particularly limited, and examples thereof include a method using a spin coater, a dip coater and the like.

  The coating film formed by the above coating method is dried by a drying means to become a semiconductor nanocrystal particle layer.

(Laminated structure of semiconductor nanocrystal particle layer)
The laminated body for white LED can be obtained by laminating a plurality of the semiconductor nanocrystal particle layers. By stacking a plurality of semiconductor nanocrystal particle layers, the quantum size effect is exhibited in each layer, and the emission spectrum profile generated from each layer is overlapped to obtain a broad emission spectrum profile.

  The white LED laminate is sequentially laminated so that the semiconductor nanocrystal particles have a larger particle size and a smaller one in the light output direction of the LED.

  By sequentially laminating the semiconductor nanocrystal particle layers constituting the white LED laminate as described above, the short-wavelength light emitted from the semiconductor nanocrystal having a small particle size is absorbed by the semiconductor nanocrystal having a large particle size. Thus, it is converted into long-wavelength light emission, short-wavelength light emission is reduced, energy loss is prevented at the time of wavelength conversion by absorption and light emission, and emission efficiency is prevented from being lowered. That is, in this invention, each semiconductor nanocrystal particle layer which comprises the laminated body for white LED, and its lamination | stacking order are controlled precisely, and it prevents that the luminous efficiency of white LED falls.

  Furthermore, in the laminate for white LED of the present invention, the difference in emission peak wavelength caused by the semiconductor nanocrystal particles between the adjacent semiconductor nanocrystal particle layers is less than the half-value width of the emission peak of each semiconductor nanocrystal particle layer. Each layer is sequentially laminated so that

  By making the difference between these emission peak wavelengths less than the half-value width of the emission peak of each semiconductor nanocrystal particle layer between adjacent semiconductor nanocrystal particle layers, the peak of the emission spectrum generated by each semiconductor nanocrystal particle layer is reduced. Approach and overlap. Thus, in the present invention, the emission spectrum generated by the white LED laminate can be smoothly broadened by controlling the peak wavelength and the half-value width of the emission spectrum between adjacent semiconductor nanocrystal particle layers. it can. As a result, the white LED laminate according to the present invention can generate an emission spectrum profile that substantially matches the emission spectrum generated by sunlight.

  On the other hand, when the difference in peak wavelength of the emission spectrum between adjacent semiconductor nanocrystal particle layers exceeds the half-value width of the emission spectrum peak of each semiconductor nanocrystal particle layer, each semiconductor nanocrystal particle The peak of the emission spectrum generated by the layers cannot be approached, and the emission spectra generated from adjacent semiconductor nanocrystal particle layers do not overlap sufficiently. For this reason, the emission spectrum generated by the white LED laminate cannot be broadened.

  Thus, in the white LED laminate of the present invention, the quantum dots existing in each adjacent layer are used to adjust the wavelength difference between the emission spectra between adjacent layers, and the wavelength generated from each layer is continuously By making use of the different emission wavelengths, it is broadened over the entire visible light range, and an emission spectrum profile that matches the profile of sunlight can be formed.

  For example, using cadmium selenide crystal particles, producing a plurality of cadmium selenide crystal particles having a particle size of 1.0 to 8.0 nm, and containing these cadmium selenide crystal particles having different particle sizes By sequentially laminating, a white LED laminate having an emission spectrum of 400 to 650 nm can be obtained. In this white LED laminate, the interval between the emission peak wavelengths in adjacent layers is set to 25 nm, and the half-value width of the emission peak wavelength of each cadmium selenide crystal is set to 40 nm. By setting the interval between the emission peak wavelengths to be smaller than the half-value width of the emission peak wavelength, the emission spectra emitted from the respective cadmium selenide crystal particle layers are overlapped to obtain a smooth emission spectrum profile. be able to.

<White LED>
The white LED according to the present invention includes the white LED laminate. Hereinafter, the current injection type white LED and the light excitation type white LED will be described with reference to the drawings.

(Current injection type white LED)
The configuration of the current injection type white LED 2 of the present invention will be described with reference to FIG. On a substrate 29 having a transparent conductive film 28, a hole injection layer 27, a hole transport layer 26, a white LED laminate 25, a hole blocking layer 24, an electron transport layer 23, an electron injection layer 22, and an electrode 21 are formed. It has a laminated structure.

The transparent conductive film 28 may be any one of ITO (Sn-doped In ₂ O ₃ ), SnO ₂ , AZO (AlZnO), GZO (GaZnO), and IZO (InZnO), or a combination thereof. The manufacturing method may be a sputtering method, a coating method, or the like.

  The substrate 29 may be transparent in the visible light region (wavelength of 400 to 700 nm), and a glass substrate, a resin substrate, a flexible glass substrate, a flexible resin substrate, or the like is preferably used. Here, the term “flexible” means flexibility, and the term “flexible substrate” means a plate or sheet having a thickness that is flexible. Examples of the resin in the resin substrate or the flexible resin substrate include ionomer, polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polypropylene, polyester, polycarbonate, polystyrene, polyacrylonitrile, and ethylene-vinyl acetate. Examples thereof include a copolymer, an ethylene-vinyl alcohol copolymer, an ethylene-methacrylic acid copolymer, nylon, polyamide, and cellophane.

  The hole injection layer 27 may be any one of polyaniline, polypyrrole, copper phthalocyanine, PEDOT: PSS, or a combination thereof. The production method is preferably a vacuum deposition method or a coating method using a spin coater or the like. The hole transport layer 26 may be any one of TPD, triphenyl quadruple, α-NPD, TACP, or a combination thereof. The production method is preferably a vacuum deposition method or a coating method using a spin coater or the like.

  The white LED laminate 25 may be formed by sequentially laminating semiconductor nanocrystals in the light output direction from those having a large particle diameter to those having a small particle diameter. Each semiconductor nanocrystal group having different particle diameters may be a mixture with a cross-linking molecule such as polyisobutylene, 1,7-diaminoheptane, carbazole. The production method is preferably coating by a spin coater. The half-value width of the emission peak of each semiconductor nanocrystal is between 10 nm and 200 nm, preferably 20 nm to 100 nm.

  The wavelength difference of the emission peak of each semiconductor nanocrystal is between 5 nm and 200 nm, preferably 10 nm to 100 nm. The hole blocking layer 24 may be any one of TAZ, bankproin (BCP), Bphen, PCBI or a combination thereof. The production method is preferably a vacuum deposition method or a coating method using a spin coater or the like.

  The electron transport layer 23 may be any one of triazole derivatives, silole derivatives, oxazole derivatives (PBO), oxazole derivatives (OXO-7), boron derivatives, and Alq3, or a combination thereof. The production method is preferably a vacuum deposition method or a coating method using a spin coater or the like. The electron injection layer 22 may be Alq3. The production method is preferably a vacuum deposition method or a coating method using a spin coater or the like.

  The electrode 21 is one of alkali metals and alkaline earth metals such as Cs, Rb, K, Na, Ba, Ca and Li having a small work function, or alloys thereof: Al: Li, Mg: Ag, or those A combination of The manufacturing method may be a sputtering method, a vapor deposition method, a coating method, or the like.

  Electrons are injected into the semiconductor nanocrystal layer from the electron transport layer side by applying a voltage of + to the transparent conductive film side of the white LED produced in the above configuration and-to the electrode side, and flowing a current. Holes are injected from the side.

  The electrons and holes injected into the semiconductor nanocrystal layer diffuse through the cross-linking molecules, and the electrons and holes recombine in the semiconductor nanocrystal to emit light having a wavelength corresponding to the band gap energy of the semiconductor nanocrystal. Occur.

  By sequentially stacking semiconductor nanocrystals in the light output direction from the same particle size group having a large particle size to the same particle size group having a small particle size, light can be emitted in the order of long wavelength to short wavelength in the light output direction.

  Adjust the concentration difference between semiconductor nanocrystals with different particle diameters by adjusting the wavelength difference between the emission peaks from short wavelengths to long wavelengths below the half-value width of each emission peak. By controlling, an emission spectrum equivalent to the sunlight spectrum can be obtained.

(Light excitation type white LED)
The configuration of the photoexcited white LED 3 of the present invention will be described with reference to FIG. Among the reflectors 34 on which the short wavelength light emitting device chip 33 is mounted, there is a resin layer 32 including the short wavelength light emitting device chip 33 which is an In-doped GaN light emitting device chip, and a plurality of semiconductor nanocrystals are formed on the resin layer 32. It is the structure provided with the laminated body 31 for white LED including.

  The short wavelength light emitting device chip 33 has a light emission peak between 200 nm and 500 nm, and may be ZnO, AlN, Al-added GaN, GaN, or In-added GaN. The reflector 34 only needs to have a high visible light reflectivity and excellent environmental resistance. The resin that can be used for the resin layer 32 may be an epoxy resin or a silicone resin that is insulative and resistant to light deterioration, has high transmittance in the visible light region, and has good thermal stability. The resin layer of the white LED laminate 31 including a plurality of semiconductor nanocrystals may be an epoxy resin or a silicone resin, and the semiconductor nanocrystals may be sequentially laminated from a crystal group having a large particle diameter to a crystal group having a small particle diameter in the light output direction.

  The half-value width of the emission peak of each semiconductor nanocrystal is between 10 nm and 200 nm, preferably 20 nm to 100 nm. The wavelength difference of the emission peak of each semiconductor nanocrystal is between 5 nm and 200 nm, preferably 10 nm to 100 nm.

  When a voltage is applied to the short wavelength LED chip of the white LED manufactured in the above configuration and a current is passed, the short wavelength LED chip emits light, and a part of the short wavelength light is a resin layer and a resin including a plurality of semiconductor nanocrystals. It passes through the layer and is emitted out of the white LED. Most of the remaining short wavelength light is absorbed by the plurality of semiconductor nanocrystals in the resin layer including the plurality of semiconductor nanocrystals. In a semiconductor nanocrystal that has absorbed short-wavelength light, electrons and holes are photoexcited and recombined to emit light having a wavelength corresponding to the bandgap energy of the semiconductor nanocrystal.

  Since the emission wavelength differs when the particle size of semiconductor nanocrystals is different, semiconductor nanocrystals with different particle sizes are sequentially stacked from the largest to the smallest in the light output direction by controlling the particle size. By producing the crystal layer, light can be emitted in the order of long wavelength to short wavelength in the light output direction.

  As a result, short-wavelength light emitted from nanocrystals with small particle diameters is absorbed into nanocrystals with large particle diameters and converted into long-wavelength light emissions, and short-wavelength light emissions are reduced. It can prevent that energy loss generate | occur | produces and luminous efficiency falls.

  Adjust the wavelength difference between the emission peak wavelengths of the semiconductor nanocrystal groups with different particle diameters in the light output direction in order from the long wavelength to the short wavelength in order to be less than the half-value width of each emission peak wavelength, and different An emission spectrum equivalent to the sunlight spectrum can be obtained by controlling the concentration ratio of the semiconductor nanocrystal group having a particle size.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example at all.

<Example 1>
(Synthesis of CdSe nanocrystals)
After heating the coordinating solvent mixed with Trioctylphosphine-oxide (TOPO) and Hexadecylamine (HDA) to 300 ° C. in a flask, a mixed dilution solution of Dimethyl-Cadmium, which is a raw material of CdSe nanocrystals, and Trioctylphosphine-Selenide is quickly injected. After pouring and once cooling to 200 ° C, it was maintained at 240 ° C. The retention time was changed and taken out, and from the shorter retention time, a total of nine synthesis solutions were obtained with names such as synthesis solution 1 and synthesis solution 2 sequentially. Of these nine synthetic liquids, the synthetic liquid 1 has a CdSe particle diameter of approximately 1.8 nm, and the particle diameter increases as the number of the synthetic liquid increases, and the synthetic liquid 9 has a particle diameter of approximately 7.0 nm. It has become.

(ZnS coat)
After heating the trioctylphosphine-oxide (TOPO) coordination solvent to 240 ° C. in a flask, CdSe nanocrystals were injected, and a mixed diluted solution of Dimethyl-Zinc and Trimethylsilyl Sulfide as a raw material for ZnS coating was slowly dropped dropwise. A ZnS coat layer was formed to obtain a CdSe / ZnS / TOPO dispersion. In addition, this operation was performed for every said synthetic | combination liquid, the name was put like ZnS coated liquid 1 about the synthetic liquid 1, and ZnS coated liquid 2 about the synthetic liquid 2, and nine liquids were obtained in total.

(Purification of nanocrystals)
Dehydrated methanol is added to the CdSe / ZnS / TOPO dispersion and centrifuged, and then the supernatant is removed. Toluene was added to the precipitation component and centrifuged, and the supernatant component was used as a CdSe / ZnS semiconductor nanocrystal toluene dispersion. This operation was performed for each of the above ZnS-coated liquids. The ZnS-coated liquid 1 was named as purified liquid 1 and the ZnS-coated liquid 2 was named as purified liquid 2 for a total of nine liquids. In addition, the refinement | purification liquid manufactured in a present Example, ie, the CdSe / ZnS semiconductor nanocrystal toluene dispersion from which particle diameter differs, is from Evident Technology (USA), NN-Labs (USA), NANOCO (UK). Can be purchased. The purified solution thus prepared is shown in Table 1 below.

(Preparation of current injection type white LED)
On a glass substrate having an ITO transparent conductive film, PEDOT: PSS as a hole injection layer was applied with a spin coater and dried by heating. Next, TPD which is a positive hole transport layer was produced by the vacuum evaporation method. The semiconductor nanocrystal layer was produced as follows. First, a mixture of 1,7-diaminoheptane cross-linking molecules was prepared for each of the nine purified solutions. This mixture was numbered the same as the purified solution. That is, the liquid mixture 1 was produced from the purified liquid 1, and the liquid mixture 2 was produced from the purified liquid 2. Then, the liquid mixture 1 was apply | coated with the spin coater on the positive hole transport layer, and it heat-dried. Next, the liquid mixture 2 was applied onto the liquid mixture 1 with a spin coater and dried by heating. Thus, it applied with the spin coater in order of the liquid mixture with a small number from the liquid mixture with a small number sequentially, and was heat-dried. For the hole blocking layer and the electron transporting layer, TAZ, which is a triazole derivative, was produced by vacuum deposition. Next, Alq3 which is an electron injection layer was produced by the vacuum evaporation method. Finally, an Mg: Ag / Ag electrode was produced by a vacuum deposition method. Light was emitted in the direction of the ITO transparent conductive film by applying a voltage of + to the transparent conductive film side of the white LED produced in the above configuration and a negative voltage to the electrode side, and passing a current.

(Spectrum measurement)
As for the emission spectrum, the spectrum profile was confirmed with a spectroradiometer (Solar Optical Radiometer S-2440 manufactured by Soma Optics). As a result, a profile equivalent to the solar spectrum profile was obtained.

<Example 2>
(Production of photoexcited white LED)
After bonding an In-doped GaN light-emitting diode chip having an emission peak wavelength of 450 nm in the reflector, the electrode in the reflector and the electrode of the In-doped GaN light-emitting diode chip were connected by wire bonding. Next, silicone resin was injected into the reflector so as to include the In-doped GaN light-emitting diode chip. Moreover, the resin surface was made flat. The semiconductor nanocrystal layer was produced as follows. Using 8 purified liquids excluding the purified liquid 1 produced in Example 1, a mixed liquid with a silicone resin was produced for each of the 8 purified liquids. This mixture was numbered the same as the purified solution. That is, the liquid mixture 2 was produced from the purified liquid 2, and the liquid mixture 3 was produced from the purified liquid 3. Subsequently, on the silicone resin including the In-doped GaN light-emitting diode chip, the mixed solution 8 was applied with a spin coater and dried by heating. Next, the liquid mixture 7 was applied onto the liquid mixture 8 by a spin coater and dried by heating. In this way, the liquid mixture having a larger numbering was applied in the order of the liquid mixture having the smaller numbering, and the mixture was dried by heating. A voltage was applied to the white LED produced in the above configuration, and light was emitted by passing a current.

(Spectrum measurement)
As for the emission spectrum, the spectrum profile was confirmed with a spectroradiometer (Solar Optical Radiometer S-2440 manufactured by Soma Optics). As a result, a profile equivalent to the solar spectrum profile was obtained.

<Comparative Example 1>
Nine purified solutions prepared in Example 1 were mixed to obtain a mixed purified solution. In the production of the current injection type white LED, the current injection type white LED was produced by the same operation as in Example 1 except that the semiconductor nanocrystal layer was produced using the mixed purified liquid. As a result of measuring the emission spectrum of the produced current injection type white LED, the intensity was reduced by about 20% as compared with Example 1.

<Comparative Example 2>
Eight purified liquids excluding the purified liquid 1 produced in Example 1 were mixed to obtain a mixed purified liquid. In the production of the photoexcited white LED, a photoexcited white LED was produced in the same manner as in Example 2 except that the semiconductor nanocrystal layer was produced using the mixed purified solution. As a result of measuring the emission spectrum of the produced photoexcited white LED, the intensity was reduced by about 20% compared to Example 2.

<Comparative Example 3>
In the production of the current injection type white LED, the current injection type white LED was manufactured in the same manner as in Example 1 except that the semiconductor nanocrystal layer was produced by applying the spin coater in the order of the liquid mixture having the largest number to the small liquid mixture. Was made. As a result of measuring the emission spectrum of the produced current injection type white LED, the intensity was reduced by about 40% as compared with Example 1.

<Comparative Example 4>
In the production of a light-excited white LED, the same procedure as in Example 2 was followed except that the semiconductor nanocrystal layer was produced by applying a spin-coater in the order of a mixture with a smaller number to a larger mixture. Fabrication was performed. As a result of measuring the emission spectrum of the produced photoexcited white LED, the intensity was reduced by about 40% compared to Example 2.

<Comparative Example 5>
A current injection type white LED was produced in the same manner as in Example 1 except that the interval of the peak wavelength of the emission spectrum of the cadmium selenide crystal contained in each semiconductor nanoparticle layer constituting the laminate for white LED was 50 nm. . As for the emission spectrum, the spectrum profile was confirmed with a spectroradiometer (Solar Optical Radiometer S-2440 manufactured by Soma Optics). As a result, the profile of the solar spectrum was roughly reflected, but a different profile was obtained.

<Comparative Example 6>
A photoexcited white LED was produced in the same manner as in Example 2 except that the interval of the peak wavelength of the emission spectrum of the cadmium selenide crystal contained in each semiconductor nanoparticle layer constituting the laminate for white LED was 50 nm. As for the emission spectrum, the spectrum profile was confirmed with a spectroradiometer (Solar Optical Radiometer S-2440 manufactured by Soma Optics). As a result, the profile of the solar spectrum was roughly reflected, but a different profile was obtained.

1 Laminated body for white LED 11 Semiconductor nanocrystal particle layer 1
12 Semiconductor nanocrystal particle layer 2
18 Semiconductor nanocrystal particle layer 8
19 Semiconductor nanocrystal particle layer 9
2 Current injection type white LED
21 Electrode 22 Electron Injection Layer 23 Electron Transport Layer 24 Hole Blocking Layer 25 White LED Stack 26 Hole Transport Layer 27 Hole Injection Layer 28 Transparent Conductive Film 29 Substrate 3 Photoexcited White LED
31 Laminated body for white LED 32 Resin layer 33 Short wavelength light emitting device chip 34 Reflector

Claims (8)

Has a mixed emission spectrum is the sum of the emission spectrum of 400 nm to 650 nm, a white LED for laminate layers are laminated three or more layers containing different particle sizes II-VI semiconductor nanocrystals particles,
Laminated sequentially from the layer containing a large particle size of the II-VI group semiconductor nanocrystal particles toward the light output direction of the LED to a layer containing a small one,
Between the layers including adjacent II-VI group semiconductor nanocrystal particles stacked three or more layers,
The white LED laminate, wherein a difference in peak wavelength of each emission spectrum caused by the II-VI group semiconductor nanocrystal particles is less than a half value width of each emission spectrum of the group II-VI semiconductor nanocrystal particles. body. The difference in peak wavelength of each emission spectrum is 10 to 200 nm,
The white LED laminate according to claim 1, wherein a half- value width of each of the emission spectra is 10 to 200 nm.   The white LED laminate according to claim 1 or 2, wherein the II-VI group semiconductor nanocrystal particles are cadmium compound semiconductor crystals.   4. The white LED laminate according to claim 1, wherein the II-VI semiconductor nanocrystal particles are any one selected from cadmium sulfide, cadmium selenide, and cadmium telluride.   A white LED comprising the laminate for white LED according to claim 1.   6. The white LED according to claim 5, wherein the white LED is a current injection type.   The white LED according to claim 5, wherein the white LED is a light excitation type. The white LED according to claim 6, wherein the white LED laminate is disposed on a transparent glass substrate, a transparent resin substrate, a transparent flexible glass substrate, or a transparent flexible resin substrate.

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