JP2011171389A - Light guide film, device promoting photosynthesis of plant using the same, solar cell, and photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide film, along with a device which promotes photosynthesis of plant using the film, a solar cell, and a photoelectric conversion element in which occurrence of interfacial reflection at a refractive index interface does not degrade efficiency of light extraction, without the leakage of incident light, in front of an emission part. <P>SOLUTION: The light guide film includes a light incident part which allows the incident light coming from a light source to enter a surface on the incident light side; a high-refractive index layer which has a higher refractive index than the light incident part and is laminated on a surface on the opposite side of the surface of light incident side; a micro rough-structure provided on the interface between the light-incident part and the high-refractive index layer; and a light-emitting part which emits the light that enters the light-incident part to the outside. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light guide film, an apparatus for promoting photosynthesis of plants using the same, a solar cell, and a photoelectric conversion element.

  In recent years, when carbon dioxide released by the use of fossil fuels such as oil increases in the atmosphere, the global environment deteriorates, including global warming, and not only the destruction of the natural environment but also drought, heavy rain, floods, etc. occur frequently. Awareness of the environment is increasing due to the occurrence of disasters and a great deal of damage to agricultural crops, as well as the great impact on human society.

  For this reason, as a method of reducing the carbon dioxide released into the atmosphere, by irradiating plants such as algae with sunlight, the photosynthesis is used to reduce the carbon dioxide in the atmosphere and the photosynthesis of plants. Devices to facilitate are being considered.

  In addition, development of solar cells, which are clean power generation methods that can directly obtain electricity from sunlight, are being studied and put into practical use as part of energy awareness and environmental awareness.

  Meanwhile, in the above-described method for reducing carbon dioxide and a general device used in a solar cell, light emitted from a light source enters the light guide film through an incident portion of the light guide film. Light incident on the light guide film is repeatedly reflected between the exit surface (upper surface) and the reflective surface (lower surface) of the light guide film, and the angle between the reflected light and the normal of the exit surface is critical. When the angle is smaller than the angle, the reflected light is transmitted through the emission surface and emitted.

  In such a light guide film, generally, the anti-incident part located on the opposite side of the incident part has flatness, so that the light emitted from the light source is emitted in a direction orthogonal to the incident surface. The parallel light or the light having an incident angle with respect to the anti-incident surface smaller than the critical angle is emitted from the anti-incident surface side to the outside as it is, resulting in light loss.

  For this reason, in the method for reducing carbon dioxide and the apparatus for promoting the photosynthesis of plants, there is a problem that even if the photosynthesis of plants can be advanced to some extent, the light necessary for photosynthesis does not reach sufficiently.

  In order to solve such a problem, for example, a method in which light is incident from an end of the apparatus has been proposed in order to confine light, guide a surface portion, and emit the light to a target area (see Patent Document 1). ). However, there is a problem in that light that does not enter perpendicularly to the end of the apparatus leaks before the emitting portion, and is not guided to the emitting portion, thereby reducing light extraction efficiency.

  In addition, for example, in a member that converts light into an effective material such as a solar cell or a photosynthetic carrier, a method of converting light into a wavelength with high efficiency for conversion into an effective material and utilizing the light has been proposed (Patent Document 2, Patent). Reference 3). However, there is a problem that interface reflection occurs at the refractive index interface leading to the conversion material, and the light extraction efficiency for guiding light to the target location is lowered, and the solution is desired at present.

Noto 2601449 gazette Japanese Patent Laid-Open No. 7-142752 JP-A-6-38635

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention relates to a light guide film in which incident light does not leak before the exit portion and there is no reduction in light extraction efficiency due to interface reflection occurring at the refractive index interface, and photosynthesis of plants using this light guide film An object of the present invention is to provide a device, a solar cell, and a photoelectric conversion element that promote the above.

Means for solving the problems are as follows. That is,
<1> A light incident portion that makes incident light incident from a light source incident on a surface on the incident light side and a surface opposite to the surface on the light incident light side are stacked, and the refractive index is higher than that of the light incident portion. A high refractive index layer having a large thickness, a fine concavo-convex structure provided at an interface between the light incident portion and the high refractive index layer, and a light emitting portion that emits light incident from the light incident portion to the outside. It is a light guide film characterized by having.
<2> The light guide film according to <1>, wherein the shortest distance between adjacent convex portions of the fine concavo-convex structure is 0.1 μm to 4 μm.
<3> The light guide film according to any one of <1> to <2>, wherein the height of the convex portion of the fine concavo-convex structure is 0.01 μm to 1,000 μm.
<4> The high refractive index layer is the light guide film according to any one of <1> to <3>, including a phosphor that converts light incident from the light incident portion into fluorescence.
<5> The light guide film according to <4>, wherein the phosphor is a perylene compound.
<6> The light guide film according to any one of <1> to <5>, wherein a refractive index of the high refractive index layer is 1.4 to 4.0.
<7> The light guide film according to any one of <1> to <6>, wherein the light incident portion has a refractive index of 1.05 to 1.8.
<8> The light guide film according to any one of <1> to <7>, wherein a refractive index difference between the high refractive index layer and the light incident portion is 0.01 to 2.0.
<9> The fine concavo-convex structure is the light guide film according to any one of <1> to <8>, which is formed by a nanoimprint method.
<10> The light guide film according to any one of <1> to <9>, further including a light guide unit that guides light between the light incident unit and the light output unit.
<11> The light guide film according to any one of <1> to <10>, wherein unevenness is formed on the surface of the light emitting portion by a blast method.
<12> An apparatus for promoting photosynthesis of a plant, wherein the light guide film according to any one of <1> to <11> is used.
<13> A solar cell using the light guide film according to any one of <1> to <11>.
<14> A photoelectric conversion element using the light guide film according to any one of <1> to <11>.

  According to the present invention, the conventional problems can be solved and the object can be achieved, and the light extraction efficiency due to the occurrence of interfacial reflection at the refractive index interface without incident light leaking before the exit portion. Can be provided, a device for promoting photosynthesis of plants using the light guide film, a solar cell, and a photoelectric conversion element.

FIG. 1 is a plan view showing an example of the light guide film of the present invention. FIG. 2 is a cross-sectional view showing an example of the light guide film of the present invention. FIG. 3 is an enlarged view of the fine concavo-convex structure. FIG. 4A is a schematic diagram illustrating an example of an apparatus that promotes photosynthesis of plants. FIG. 4B is a schematic diagram illustrating an example of a light guide film fixing method. FIG. 5 is a plan view showing an example of the light guide film of the present invention. 6 is a cross-sectional view taken along the line A-A ′ of FIG. 5. FIG. 7 is a diagram illustrating an example of an apparatus for evaluating photosynthesis in Examples and Comparative Examples.

(Light guide film)
FIG. 1 is a plan view showing an example of the light guide film of the present invention, FIG. 2 is a cross-sectional view showing an example of the light guide film of the present invention, and FIG. 3 is an enlarged view showing an example of a fine uneven structure. FIG. The light guide film 1 of the present invention has a light incident part 11 for making light incident from a light source incident on the same film over the entire surface, and a light emitting part 12 for emitting light incident from the light incident part 11 to the outside. And a high refractive index layer 111 having a refractive index higher than that of the light incident portion 11, which is laminated on a surface opposite to the surface of the light incident portion 11, and includes the light incident portion 11 and the high refractive index layer 111. A fine concavo-convex structure 112 is formed at the interface. Further, if necessary, a light guide unit 14 that guides the light incident from the light incident unit 11 to the light emitting unit 12 may be provided between the light incident unit 11 and the light emitting unit 12. .

There is no restriction | limiting in particular as a refractive index (the refractive index of the light-incidence part 11) of the said light guide film 1, According to the intended purpose, it can change suitably, 1.05-1.8 are preferable, 1.1. ˜1.75 is more preferred, 1.2 to 1.7 is particularly preferred, and 1.3 to 1.65 is most preferred.
If the refractive index is less than 1.05, the critical angle is too large, and much of the light propagating inside the film may leak, and if it exceeds 1.8, the interface reflection is large, and the light film The amount of incident light may decrease too much.

  As shown in FIG. 1, the shape of the light guide film 1 is a rectangular shape for convenience of explanation, but is not particularly limited, and can be appropriately changed according to the purpose of use. Examples thereof include a square shape and a circular shape as shown in FIG.

There is no restriction | limiting in particular as length (H) of the said light guide film 1, According to the intended purpose, it can change suitably, For example, 10 mm-50,000 mm are preferable, 100 mm-5,000 mm are more preferable, 200 mm to 1,000 mm are particularly preferred.
When the length is less than 10 mm, it may be more efficient to deliver light directly, and when it exceeds 50,000 mm, light may not reach due to light absorption of the film.

There is no restriction | limiting in particular as length of the said light-incidence part 11, According to the intended purpose, it can change suitably, For example, 1 mm-5,000 mm are preferable, 5 mm-1,000 mm are more preferable, 20 mm-500 mm Is particularly preferred.
If the length is less than 1 mm, the incident light may be too small, and if it exceeds 5,000 mm, the loss of light absorption by the film may be too large.

There is no restriction | limiting in particular as the length of the said light-projection part 12, Although it can change suitably according to a use purpose, For example, 1 mm-5,000 mm are preferable, 5 mm-1,000 mm are more preferable, 20 mm- 500 mm is particularly preferable.
If the length is less than 1 mm, the emitted light may be too small, and if it exceeds 5,000 mm, the light absorption loss by the film may be too large.

  There is no restriction | limiting in particular as thickness (D) of the said light guide film 1, Although it can select suitably according to the objective, For example, it is preferable that they are 0.1 micrometer-200,000 micrometers, and 1 micrometer-20,000 micrometers. Is more preferably 10 μm to 2,000 μm, and most preferably 50 μm to 500 μm. When the thickness (D) of the light guide film 1 is less than 0.1 μm, the ratio of the surface is too large, and the confinement efficiency may decrease. When the thickness exceeds 200,000 μm, the material becomes inhomogeneous and light leaks. The proportion may increase. The thickness (D) of the light guide film 1 refers to the thickness of the same film having the light incident part 11 and the light emitting part 12.

  The length (H) and thickness (D) of the light guide film 1 are measured using, for example, a film thickness meter that measures the thickness of the light guide film 1 with the light guide film 1 sandwiched by a measurement meter, or optical interference. By using a non-contact film thickness meter that measures the thickness of the light guide film 1, it can be measured.

  The material of the light guide film 1 is not particularly limited as long as it is transparent and has a certain degree of strength, and examples thereof include resin and glass. Among these, resin is preferable because it is flexible and lightweight.

The resin is not particularly limited and may be appropriately selected depending on the purpose. For example, the resin is not particularly limited and may be appropriately selected according to the purpose. For example, polystyrene, styrene / methyl Methacrylate copolymer, (meth) acrylic resin, polymethylpentene, allyl glycol carbonate resin, spirane resin, amorphous polyolefin, polycarbonate, polyamide, polyarylate, polysulfone, polyallyl sulfone, polyether sulfone, polyetherimide, polyimide Transparent materials such as diallyl phthalate, fluororesin, polyester carbonate, norbornene resin (ARTON), alicyclic acrylic resin (Optretz), silicone resin, acrylic rubber, silicone rubber, etc. It may be used alone or in combination of two or more thereof.
Among these, polystyrene, polycarbonate, acrylic-containing resin, PET, styrene- (meth) acrylic copolymer (MS polymer) and the like are preferable from the aspects of transparency, optical properties such as refractive index, and processability.

As the light emitting part 12, it is preferable to form irregularities on the surface of the light emitting part 12 in order to emit the light incident from the light incident part 11 in various directions.
The average roughness of the surface of the light emitting portion 12 on which the irregularities are formed is preferably 0.001 μm to 1,000 μm, more preferably 0.01 μm to 100 μm, and more preferably 0.1 μm to 10 μm. Is particularly preferred. When the surface roughness is less than 0.001 μm, light may not be emitted in various directions, and when overlapped, it may be difficult to peel off and be difficult to handle, and when it exceeds 1,000 μm The light guiding effect may be too low.

  There is no restriction | limiting in particular as a formation method of the said unevenness | corrugation, According to the objective, it can select suitably, For example, the sandblast method, the nanoimprint method, a photoresist method etc. are mentioned. The unevenness may be formed on the light emitting portion 12 by a method of forming the fine uneven structure 112 described later.

  The sandblasting method is a method in which compressed air containing a drilling material such as gold sand is blown from a small-diameter nozzle onto a surface to be drilled to process a resin or glass surface into various shapes. In the sandblasting method, it is generally performed to specify a portion to be excavated by bringing a masking sheet into close contact with the surface to be excavated. By changing the particle size of the gold sand used as the drilling material, the type of the masking sheet used, etc., very fine processing can be performed.

  The haze of the light guide film 1 is preferably 10% or less, more preferably 2% or less, and particularly preferably 0.5% or less. When the haze exceeds 10%, the light collection efficiency and light guide efficiency for controlling the incident light and collecting light may be significantly reduced.

  Here, the “haze” refers to a value of the degree of cloudiness, and is a value evaluated by a measuring device such as a haze meter (model number: HZ-1, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS 7105, for example. is there.

You may make it have the reflection part 13 in the edge part of the said light-incidence part 11. FIG. The reflector 13 can be omitted as appropriate. The material of the reflecting portion 13 is not particularly limited as long as the reflectance is high, and can be appropriately selected according to the purpose. For example, a metal such as silver, aluminum, gold, copper, and magnesium, TiO having a high refractive index. ₂ , dielectric materials such as ZnS and silicon, and semiconductors.

<High refractive index layer>
As shown in FIG. 2, the high refractive index layer 111 is laminated on the opposite side of the light incident portion 11 from which light is incident. Since it is necessary to reduce the critical angle of light reflection in order to improve the light confinement efficiency, the high refractive index layer 111 needs to have a higher refractive index than the light incident portion 11 (light guide film 1). There is. As will be described in detail later, a fine concavo-convex structure 112 is formed at the interface with the light incident portion 11, and the high refractive index layer 111 may further include a phosphor in a high refractive index material as necessary. It may be configured to contain.

The material constituting the high refractive index layer 111 is not particularly limited as long as it has a refractive index higher than that of the light guide film 1 and has a certain degree of strength. For example, a high refractive index such as TiO ₂ or ZnS is used. Examples thereof include resins containing fine particles and high refractive index resins.
Examples of the high refractive index resin include polycarbonate, PET, PEN, and BPEFA.

  The refractive index of the high refractive index layer 111 is not particularly limited as long as it is larger than the refractive index of the light incident portion 11 (light guide film 1), and can be appropriately selected according to the purpose. 0.4 to 4.0 is preferable, 1.5 to 3.0 is more preferable, and 1.6 to 2.0 is particularly preferable. If the refractive index of the high refractive index layer 111 is less than 1.4, the critical angle of incident light cannot be reduced, and the light confinement efficiency may not be improved. In some cases, the incidence of light on the high refractive index layer 111 becomes too small due to interface reflection.

  The refractive index of the high refractive index layer 111 is measured with an ellipsometer (manufactured by JA Woollam) after preparing a coating solution containing no scattering particles, coating the coating solution on glass and curing it with ultraviolet light. be able to.

  The refractive index difference (A−B) between the refractive index A of the high refractive index layer 111 and the refractive index B of the light incident portion 11 is not particularly limited and can be appropriately selected according to the purpose. For example, it is preferably 0.01 to 2, more preferably 0.05 to 1.5, and particularly preferably 0.1 to 1. If the difference is less than 0.01, the effect of confining light may be hardly obtained. If the difference exceeds 2, the light incidence on the high refractive index layer 111 may be too low.

-Phosphor-
The high refractive index layer 111 contains a phosphor, and the required wavelength can be enhanced by converting the photoelectric energy of the light incident from the light incident portion 11. For example, in photosynthesis, there are various types of chlorophylls that have a role of absorbing light energy, but it is known that they often absorb more light with wavelengths in the range of 400 nm to 500 nm and 600 nm to 750 nm. ing. When the light guide film 1 is used in an apparatus that promotes photosynthesis of plants, the high refractive index layer 111 contains a phosphor that emits light in the vicinity of 600 nm to 750 nm, so that light incident from the light incident portion 11 is 600 nm to Photoelectric energy can be converted into fluorescence at a wavelength of around 750 nm, and the fluorescence-converted light can be emitted from the light emitting unit 12, and photosynthesis can be effectively promoted. That is, by including the phosphor in the high refractive index material, light having a specific wavelength can be emitted from the light emitting unit 12.

The phosphor is not particularly limited as long as the required wavelength can be enhanced, and can be appropriately selected according to the purpose. For example, DCM, DMETCI, DOCI, DODCI, DQOCI, DQTCI, HIDCI, etc. Fluorescent compound, indolenine, coumarin, cresyl violet, cyanine, fluorescein, malachite green, nile blue, oxazine, perylene compound, phenoxazone, phenylalanine, phthalocyanine, pinacyanin, porphine, proflavine, pyridine, pyromethene, rhodamine, riboflavin, stilbene, Examples include styryl compounds, sulforhodamine, uranin and the like. Among them, a perylene compound is preferable, and the perylene compound is not particularly limited as long as it emits fluorescence, and examples include perylene, perylene red, and perylene orange.
Examples of the phosphor include, but are not limited to, the following.

There is no restriction | limiting in particular as content of the said fluorescent substance, Although it can select suitably according to the objective, For example, it is preferable that it is 0.001 mg-20 mg with respect to 100 mg of high refractive index materials, 0.01 mg It is more preferably 10 mg, and particularly preferably 0.1 mg to 5 mg.
When the content is less than 0.001 mg, the light incident from the light incident portion 11 may not be effectively converted to fluorescence. When the content exceeds 20 mg, it may be difficult to maintain the shape. .

<Fine uneven structure>
By providing the fine concavo-convex structure 112 at the interface between the light incident part 11 and the high refractive index layer 111, the light incident on the light incident part 11 is totally reflected without entering the high refractive index layer 111. Can be effectively prevented. Further, by providing the fine concavo-convex structure 112, it is possible to effectively prevent the light incident on the high refractive index layer 111 from being totally reflected without entering the light incident portion 11.
For this reason, in the light guide film 1 of the present invention, light incident from the light source can be incident not only on the end portion of the light guide film 1 but also on the entire surface of the light incident portion 11. It can be greatly improved. Moreover, light can be irradiated with a necessary distribution in a place where light is required.

  The shape of the fine concavo-convex structure 112 is not particularly limited as long as the cross-sectional shape has a concavo-convex structure that undulates on the light incident portion 11 side, and has a conical shape, a pyramid shape, a saw shape, a bellows shape, a rectangular shape. A concavo-convex structure such as

There is no particular lower limit to the main emission wavelength of the shortest distance P (hereinafter also referred to as pitch interval P) (unit: μm) between adjacent convex portions of the fine concavo-convex structure 112, and it is appropriately selected according to the purpose. However, the lower limit thereof is preferably 0.01λ or more, more preferably 0.05λ or more, still more preferably 0.1λ or more, more preferably 0, from the viewpoint of improving the light amount, where λ is the main emission wavelength from the light source. .2λ or more is particularly preferable.
Further, the upper limit is preferably 10λ or less, more preferably 5λ or less, still more preferably 2λ or less, and particularly preferably 1λ or less from the viewpoint of improving the amount of light.

The lower limit of the pitch interval P of the fine concavo-convex structure 112 is preferably 0.1 μm or more, more preferably 0.15 μm or more, and particularly preferably 0.2 μm or more. If the lower limit is less than 0.1 μm, processing may be difficult and uniformity may not be obtained.
Moreover, as an upper limit, it is preferable that it is 100 micrometers or less, It is more preferable that it is 10 micrometers or less, It is especially preferable that it is 1 micrometer or less. If the upper limit exceeds 100 μm, the effect of confining light may be reduced.

The lower limit of the height H of the convex portion of the fine concavo-convex structure 112 is preferably 0.05 μm or more, more preferably 0.1 μm or more, and particularly preferably 0.15 μm or more. If the lower limit is less than 0.05 μm, the interface reflection reduction effect may not be obtained.
The upper limit of the height H of the convex portion of the fine concavo-convex structure 112 is preferably 4 μm or less, more preferably 3.5 μm or less, and particularly preferably 3 μm or less. If the upper limit exceeds 100 μm, the effect of confining light may be reduced.

--- Method for forming fine relief structure--
The method for forming the fine concavo-convex structure 112 is not particularly limited, and may be appropriately selected according to the purpose, for example, a cutting method, a nanoimprint method, a laser fine processing, an etching method, etc. It is preferable to form by the nanoimprint method for the reason of forming.

As the nanoimprint method, the fine concavo-convex structure 112 can be formed by transferring in advance with a stamper (mold) having a desired concavo-convex structure. Specifically, a photoresist layer made of a photoresist material is applied onto a stamper master (silicon substrate) by a spin coat method or the like, and laser light is condensed on the photoresist layer by an optical lens and irradiated. After forming the micropores, performing an etching process such as reactive ion etching (RIE), adjusting the depth of the micropores formed on the original plate, and then removing the photoresist layer, the desired irregularities are obtained. A stamper having a structure is manufactured.
A nanoimprint layer made of a nanoimprint material is formed on the surface opposite to the surface of the light incident portion 11 for entering light, and the nanoimprint layer is pressed by the stamper and heated or irradiated with light as necessary. A fine uneven structure is formed in the portion 11.

The photoresist material is not particularly limited and may be appropriately selected depending on the purpose. Examples thereof include a photoresist material that uses a normal photoreaction, and a photoresist material that uses a thermal reaction. Photoresist materials that can use thermal reactions are preferred in that they are fine, have a fine structure around the irregularities, and can exhibit a higher effect on light interaction.
Examples of photoresist materials that can use the thermal reaction include methine dyes (cyanine dyes, hemicyanine dyes, styryl dyes, oxonol dyes, merocyanine dyes, etc.), macrocyclic dyes (phthalocyanine dyes, naphthalocyanine dyes, porphyrin dyes, etc.), Examples thereof include azo dyes (including azo metal chelate dyes), arylidene dyes, complex dyes, coumarin dyes, azole derivatives, triazine derivatives, 1-aminobutadiene derivatives, transdermal acid derivatives, and quinophthalone dyes.

There is no restriction | limiting in particular as said nanoimprint material, According to the objective, it can select suitably, For example, the imprint resist composition containing at least any one of a thermoplastic resin and a photocurable resin is mentioned.
Examples of the imprint resist composition include novolac resins, epoxy resins, acrylic resins, organic glass resins, and inorganic glass resins.

The thickness of the photoresist layer is preferably 5% or more and less than 200% with respect to the height of the convex portion formed on the surface of the stamper.
When the thickness is less than 5%, the resist amount is insufficient, and a desired fine uneven structure may not be formed.

  As the thickness of the photoresist layer, for example, a part of the photoresist layer is peeled off from the light incident portion 11 on which the photoresist layer is formed, and a step (height) after peeling is determined by an AFM apparatus (OLS, Olympus Corporation). Manufactured).

The viscosity of the imprint resist composition is preferably 1 mPa · s to 200 mPa · s at 25 ° C., and more preferably 1 mPa · s to 100 mPa · s.
The viscosity of the imprint resist composition can be measured using, for example, an ultrasonic viscometer.

  After forming the fine concavo-convex structure 112, a high refractive index material and a phosphor are dissolved in a solvent on the fine concavo-convex structure 112, and a spray method, a spin coat method, a dip method, a roll coat method, a blade coat method, a doctor roll method. The high refractive index layer 111 is formed by coating using a doctor blade method, a screen printing method, or the like.

(Devices that promote plant photosynthesis)
The device for promoting photosynthesis of the plant includes the light guide film 1 and a fixing means (not shown) for fixing the light guide film 1. For example, as shown in FIG. 4A, a plurality of light guide films 1 are bent, the light emitting unit 12 is placed in water where plants such as algae are present, and light incident from a light source such as sunlight is used as a light incident unit. 11, light confinement efficiency is improved by the high refractive index layer 111, and light is emitted from the underwater light emitting unit 12, so that photosynthesis of the underwater plant can be promoted. In addition, the light emission part 12 may be sufficient as the location to be bent, and the light guide part 14 may be sufficient as it.
As the light guide film 1, for example, a part of the light guide films 1 may be bonded and fixed with a pipe 3 or the like provided in water, and as shown in FIG. 4B as an example, The light guide film 1 may be fixed by a plurality of pipes 3.

  As a phosphor included in the high refractive index layer 111, chlorophyll α, which has a role of absorbing light energy, absorbs more wavelengths of 420 nm and 660 nm, and thus emits light in the vicinity of 600 nm to 700 nm to further promote photosynthesis. However, it is particularly preferable that the high refractive index layer 111 contains a perylene phosphor such as LumogenF Red305 (manufactured by BASF).

Further, in addition to the phosphor, 6MgO · As ₂ O ₅ Mn ⁴⁺ that emits more wavelengths of 600 nm to 700 nm may be included in the high refractive index layer 111. By including the phosphor in the high refractive index material, light having a wavelength of 600 nm to 700 nm can be emitted from the light emitting unit 12, and photosynthesis of algae and the like can be effectively promoted.

(Solar cell)
As said solar cell, sunlight is condensed on the light incident part 11 of the light guide film 1, and the condensed solar light is irradiated from the light emitting part 12 to the solar cell element of a small area. The generated power per unit area can be increased.

  As long as it has said structure as a solar cell by this invention, there will be no restriction | limiting, What is necessary is just to select suitably according to the objective, and what is generally used as a solar cell device can be used. For example, a single crystal silicon solar cell device, a polycrystalline silicon solar cell device, an amorphous silicon solar cell device composed of a single junction type or a tandem structure type, gallium arsenide (GaAs), indium phosphorus (InP), etc. Group III-V compound semiconductor solar cell devices, II-VI compound semiconductor solar cell devices such as cadmium telluride (CdTe), copper / indium / selenium system (so-called CIS system), copper / indium / gallium / selenium system ( So-called CIGS-based), copper / indium / gallium / selenium / sulfur-based (so-called CIGS-based) I-III-VI group compound semiconductor solar cell devices, dye-sensitized solar cell devices, organic solar cell devices, etc. Can be mentioned.

(Photoelectric conversion element)
In the light guide film 1, incident light does not leak before the exit portion, and there is no decrease in light extraction efficiency due to interface reflection occurring at the refractive index interface. For this reason, photoelectric conversion efficiency can be improved by using the light guide film 1 for a photoelectric conversion element.

  Examples of the photoelectric conversion element include an optical sensor, an organic EL element, and an imaging element.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
<Preparation of light guide film 1>
-Fabrication of light incident part and light emission part-
A length of 100 mm, a width of 40 mm, a thickness of 0.2 mm, and a refractive index of 1.5 (soft acryl, manufactured by Shinko AG Co., Ltd.) are 30 mm from the end as the light incident part, and 50 mm from the other end. A light emitting portion was formed, and an uneven shape was formed on the surface of the light emitting portion by sandblasting.

-Formation of fine relief structure-
On a silicon substrate having the same shape as the light incident part (30 mm × 40 mm), 20 mg of compound A represented by the following structural formula as a photoresist compound is added to 2,2,3,3-tetrafluoro-1-propanol. The solution was dissolved at a rate of 1 ml, and this solution was applied to a thickness of 100 nm by spin coating while rotating at 1,000 rpm to form a photoresist layer on the silicon substrate.

  The pitch of the shortest distance between adjacent convex portions of the fine concavo-convex structure at a linear velocity of 5 m / s and 4 mW with NEO1000 (wavelength 405 nm, NA 0.85) manufactured by Pulstec Industrial Co., Ltd. with respect to the photoresist layer formed on the substrate. A plurality of fine holes were formed so that the interval was 0.2 μm. Thereafter, reactive ion etching (RIE) treatment is performed to adjust the depth of the plurality of micropores in which the photoresist layer is formed to 0.2 μm, and the photoresist layer is adjusted to 2,2,3,3-tetrafluoro-1 A stamper was prepared by removing with -propanol.

  Spin coating method while rotating imprint compound (PAK-01-CL manufactured by Toyo Gosei Co., Ltd.) at 1,000 rpm on the surface (30 mm from the end) opposite to the surface of the light incident portion where light is incident. It was applied to a thickness of 1 μm, and an imprint layer was formed on the light incident part. The imprint layer was pressed with the stamper and irradiated with UV to form a fine concavo-convex structure in the light incident portion.

-Fabrication of high refractive index layer-
On the fine concavo-convex structure formed on the light incident portion, 2% by mass of perylene red (Lumogen F Red 305, manufactured by BASF) as a phosphor and BPEFA having a refractive index of 1.6 as a high refractive index material (Osaka) A light guide film 1 was produced by dissolving 20% by mass (made by Gas Chemical Co., Ltd.) in methyl ethyl ketone as a solvent, and applying a coating to a thickness of about 50 μm using a brush and drying to laminate a high refractive index layer.

(Example 2)
<Preparation of light guide film 2>
In Example 1, a light guide film 2 was produced in the same manner as in Example 1 except that a polyester resin having a refractive index of 1.5 (Byron, manufactured by Toyobo Co., Ltd.) was used as the high refractive index material.

(Example 3)
<Preparation of light guide film 3>
In Example 3, a light guide film 3 was produced in the same manner as in Example 1 except that the pitch interval of the fine uneven structure of the stamper was set to 0.4 μm.

Example 4
<Preparation of light guide film 4>
In Example 1, a light guide film 4 was produced in the same manner as in Example 1 except that the pitch interval of the fine uneven structure of the stamper was 0.8 μm.

(Example 5)
<Preparation of light guide film 5>
In Example 1, a light guide film 5 was produced in the same manner as in Example 1 except that the depth of the fine holes of the stamper was 0.3 μm.

(Comparative Example 1)
<Preparation of light guide film 6>
In Example 1, the light guide film 6 was produced in the same manner as in Example 1 except that the high refractive index layer was laminated without forming the fine uneven structure.

(Comparative Example 2)
<Preparation of light guide film 7>
In Example 2, the light guide film 7 was produced in the same manner as in Example 2 except that the high refractive index layer was laminated without forming the fine uneven structure.

(Reference Example 1)
<Preparation of light guide film 8>
In Example 1, a light guide film 8 was produced in the same manner as in Example 1 except that the pitch interval of the fine uneven structure of the stamper was 5 μm.

(Evaluation)
<Brightness improvement rate>
Sunlight, which is a light source, was incident from the light incident portion of the light guide film 8 from the light guide film 1, and the brightness of the light emitted from the light emitting portion was evaluated. The evaluation method is based on the brightness of the light guide film produced in the same manner as in Example 1 except that it does not have a high refractive index layer and a fine concavo-convex structure. Was measured. The brightness of light was measured using USB2000 (manufactured by Ocean Optics). The results are shown in Table 1.

<Photosynthesis>
As shown in FIG. 7, a water tank 50 was arranged in a dark room shielded from light by a light shielding plate 60, and the water tank 50 was filled with 500,000 pieces / mL chlorella. The light guide film 100 is inserted from the light emitting portion 75 side into the cutout portion 65 of the light shielding plate 60 so as not to leak light, and the radius of curvature is approximately in the vicinity of the central portion in the length direction of the light guide film 100. At 20 mm, the light guide film 100 was bent, and the light guide film 100 was arranged so that the light emitting portion 75 was impregnated in the water tank 50 while allowing light from the lamp 80 to enter the light incident portion 70.
As the lamp 80, a 100 W halogen lamp having a larger amount of light than the LED lamp is used. As described above, the light emitting unit 75 is impregnated in the water tank 50 while allowing the light incident from the lamp 80 to enter the light incident unit 70. The light incident part 70 of the light guide film 100 arranged was irradiated with light to culture the chlorella in the water tank 50.
Light irradiation by the lamp 80 was continued for 24 hours, and then the number was measured using an optical microscope, the number was compared with the number before the test, the increase / decrease rate was calculated, and evaluated based on the following evaluation criteria. The results are shown in Table 1 below.
[Evaluation criteria]
◎ ・ ・ ・ Chlorella increase rate is 20% or more ○ ・ ・ ・ Chlorella increase rate is 10% or more and less than 20% Δ ・ ・ ・ Chlorella increase rate is 0% or more and less than 10% × ・ ・ ・ Chlorella increase rate Is less than 0%

  As can be seen from Table 1, in Examples 1 to 5, the brightness improvement rate is improved, and in particular, in Examples 1, 3 and 5, the brightness improvement rate is greatly improved. I understand that. From this result, it can be seen that in Examples 1 to 5, incident light does not leak before the exit part, and the reduction in light extraction efficiency due to interface reflection occurring at the refractive index interface is suppressed. On the other hand, in Comparative Example 1 to Comparative Example 2, since the brightness improvement rate is hardly improved as compared with Example 1 to Example 5, incident light leaks in front of the emitting portion, and refraction It can be seen that interface reflection occurs at the rate interface and the light extraction efficiency decreases.

(Example 6)
<Preparation of solar cell 1>
-Fabrication of light incident part and light emission part-
As shown in FIG. 5, an aluminum tape (Revic Tape No401, manufactured by Nitto Denko Corporation) was attached to the end of a transparent acrylic plate having a side of 100 mm and a thickness of 10 mm and a refractive index of 1.48. A square of 50 mm square near the center of the transparent acrylic plate was used as a light emitting part, and the light emitting part was formed with an uneven shape on the surface by sandblasting. The light incident part other than the light emitting part of the transparent acrylic plate was used.

-Formation of fine relief structure-
20 mg of the compound A represented by the above structural formula as a photoresist compound on a silicon substrate having the same shape (30 mm × 40 mm) as the light incident part, 1 ml of 2,2,3,3-tetrafluoro-1-propanol Then, this solution was applied at a thickness of 100 nm using a spin coat method while rotating at 1,000 rpm to form a photoresist layer on the silicon substrate.

  The pitch of the shortest distance between adjacent convex portions of the fine concavo-convex structure at a linear velocity of 5 m / s and 4 mW with NEO1000 (wavelength 405 nm, NA 0.85) manufactured by Pulstec Industrial Co., Ltd. with respect to the photoresist layer formed on the substrate. A plurality of fine holes were formed so that the interval was 0.2 μm. Thereafter, reactive ion etching (RIE) treatment is performed to adjust the depth of the plurality of micropores in which the photoresist layer is formed to 0.2 μm, and the photoresist layer is adjusted to 2,2,3,3-tetrafluoro-1 A stamper having a desired concavo-convex structure was produced by removing with -propanol.

  Using a spin coat method while rotating an imprint compound (PAK-01-CL manufactured by Toyo Gosei Co., Ltd.) at 1,000 rpm on the surface (30 mm from the end) opposite to the surface of the light incident portion where light enters. It was applied to a thickness of 1 μm, and a photoresist layer was formed on the light incident part. The photoresist layer was irradiated with UV while being pressed by a stamper having a desired concavo-convex structure to form a fine concavo-convex structure at the light incident portion.

-Fabrication of high refractive index layer-
On the fine concavo-convex structure formed on the light incident portion, 2% by mass of perylene red (Lumogen F Red 305, manufactured by BASF) as a phosphor and BPEFA having a refractive index of 1.6 as a high refractive index material (Osaka) A light guide film 9 was produced by laminating 20% by mass (made by Gas Chemical Co., Ltd.) in methyl ethyl ketone as a solvent, laminating a high refractive index layer by applying and drying to a thickness of about 50 μm using a brush.

  The protective layer of the silicon solar cell module 2 (ETM500-0.5V (RQ) manufactured by Akizuki Dentsu Co., Ltd.) is peeled off with matching oil (manufactured by Cargill Co., Ltd.), and the protective layer is peeled off as shown in FIG. Were pasted with the matching oil to produce a solar cell 1.

(Example 7)
<Production of solar cell 2>
In Example 6, a solar cell 2 was produced in the same manner as in Example 6 except that a polyester resin having a refractive index of 1.5 (Byron, manufactured by Toyobo Co., Ltd.) was used as the high refractive index material.

(Example 8)
<Preparation of solar cell 3>
In Example 6, a solar cell 3 was produced in the same manner as in Example 6 except that the pitch interval of the shortest distance between adjacent convex portions of the fine concavo-convex structure of the stamper was set to 0.4 μm.

Example 9
<Preparation of solar cell 4>
In Example 6, a solar cell 4 was produced in the same manner as in Example 6 except that the pitch distance of the shortest distance between adjacent convex portions of the fine uneven structure of the stamper was set to 0.8 μm.

(Example 10)
<Production of solar cell 5>
In Example 6, a solar cell 5 was produced in the same manner as in Example 6 except that the depth of the fine hole of the stamper was 0.3 μm.

(Comparative Example 3)
<Preparation of solar cell 6>
In Example 6, a solar cell 6 was produced in the same manner as in Example 6 except that the high refractive index layer was laminated without forming the fine uneven structure.

(Comparative Example 4)
<Preparation of solar cell 7>
In Example 7, a solar cell 7 was produced in the same manner as in Example 7 except that the high refractive index layer was laminated without forming the fine uneven structure.

(Comparative Example 5)
<Preparation of solar cell 8>
In Example 6, a solar cell 8 was produced in the same manner as in Example 6 except that the pitch interval of the shortest distance between adjacent convex portions of the fine uneven structure of the stamper was set to 5 μm.

(Evaluation)
Solar light, which is a light source, was incident from the light incident portion of the solar cell 8 from the solar cell 1, and the brightness of the light emitted from the light emitting portion was evaluated.
As an evaluation method, the improvement rate of the power generation amount with respect to the solar cell module 2 was measured based on the power generation amount of the solar cell module 2 without the solar cell 1 to the solar cell 8. The power generation improvement rate was measured by the amount of short circuit current. The results are shown in Table 2.

  As can be seen from Table 2, in Examples 6 to 10, the brightness improvement rate is significantly improved. From this result, it can be seen that in Examples 6 to 10, the incident light does not leak before the exit part, and the decrease in the light extraction efficiency due to the interface reflection occurring at the refractive index interface is suppressed. On the other hand, in Comparative Example 3 to Comparative Example 5, since the power generation improvement rate is not improved as compared with Example 6 to Comparative Example 10, the incident light leaks before the exit part, and the refractive index interface It can be seen that interface reflection occurs and the light extraction efficiency decreases.

  The light guide film of the present invention can be used in various situations because incident light does not leak before the light exit portion and there is no decrease in light extraction efficiency due to interface reflection occurring at the refractive index interface. For example, it can be widely used in devices for promoting photosynthesis of plants, solar cells, photoelectric conversion elements, and the like.

DESCRIPTION OF SYMBOLS 1 100 Light guide film 11 Light incident part 111 High refractive index layer 112 Fine uneven structure 12 Light output part 13 Reflection part 14 Light guide part 2 Solar cell module 3 Pipe

Claims (14)

A light incident part for making incident light incident from a light source incident on a surface on the incident light side;
A high refractive index layer laminated on a surface opposite to the light incident light side surface and having a refractive index larger than that of the light incident portion;
A fine relief structure provided at an interface between the light incident part and the high refractive index layer;
A light guide film comprising: a light emitting portion that emits light incident from the light incident portion to the outside.   The light guide film according to claim 1, wherein the shortest distance between adjacent convex portions of the fine concavo-convex structure is 0.1 μm to 4 μm.   The light guide film according to claim 1, wherein the height of the convex portion of the fine concavo-convex structure is 0.01 μm to 1,000 μm.   The light guide film according to claim 1, wherein the high refractive index layer contains a phosphor that converts light incident from the light incident portion into fluorescence.   The light guide film according to claim 4, wherein the phosphor is a perylene compound.   The light guide film according to any one of claims 1 to 5, wherein the high refractive index layer has a refractive index of 1.4 to 4.0.   The light guide film according to claim 1, wherein a refractive index of the light incident part is 1.05 to 1.8.   The light guide film according to any one of claims 1 to 7, wherein a difference in refractive index between the high refractive index layer and the light incident portion is 0.01 to 2.0.   The light guide film according to claim 1, wherein the fine uneven structure is formed by a nanoimprint method.   The light guide film according to claim 1, further comprising a light guide part that guides light between the light incident part and the light emitting part.   The light guide film according to claim 1, wherein unevenness is formed on the surface of the light emitting portion by a blast method.   An apparatus for promoting photosynthesis of a plant, wherein the light guide film according to claim 1 is used.   A solar cell using the light guide film according to claim 1.   A photoelectric conversion element using the light guide film according to claim 1.