JP2008103670A - Organic thin film photodetector, manufacturing method thereof, organic thin film light receiving/emitting element, manufacturing method thereof, and pulse sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic thin film photodetector, and its manufacturing method capable of detecting extremely weak light with high sensitivity at a low voltage. <P>SOLUTION: An organic thin film photodetector 1 comprises a substrate 2, an anode 3 which is formed on the surface of the substrate 2 and allows the transmission of an ultraviolet ray, visible light, or a nearinfrared ray, an optically conductive organic semiconductor layer 4 formed on the surface of the anode 3, and a cathode 5 formed on the surface of the optically conductive organic semiconductor layer 4. The optically conductive organic semiconductor layer 4 comprises an optically conductive organic semiconductor and a ferro-dielectric polymer resin material which generates an electric field in the optically conductive organic semiconductor layer 4 even if no voltage is applied from the outside. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic thin film light receiving element that detects ultra-weak light and a method for manufacturing the same, and an organic thin film light receiving and emitting element that uses the organic thin film light receiving element, a method for manufacturing the same, and a pulse sensor.

In recent years, attempts have been made to detect the amount of hemoglobin change in the arterial flow or venous flow by irradiating the human artery or vein with light of a specific wavelength and detecting the transmitted light as biological information. Research has been made on detecting biophotons (bioluminescence) as biological information. The light as the biological information is very weak light having a light emission intensity of about 10 ⁻⁷ to 10 ⁻¹⁵ [W / cm ² ], and therefore, a photomultiplier tube, an amplifier, a photon counter, etc. Is detected by a weak light detection system.

  However, the detection of weak light using a photomultiplier tube has the following practical problems. First, when weak light is detected using a photomultiplier tube, it is necessary to apply a high voltage of about 1,500 to 2,000 [V]. It is difficult to provide a wearable) and detection system in the vehicle interior such as a steering wheel for safety and incidental facilities. Secondly, since the photomultiplier tube uses a vacuum tube, it is vulnerable to vibration and impact, and is easily damaged. Thirdly, since the photomultiplier tube is larger than the thin film solid-state device, it is difficult to lay out in a narrow space such as a vehicle interior or a part having a three-dimensional curved surface shape (for example, the above steering).

Against this background, in recent years, a “photocurrent doubling phenomenon” based on a new principle that actively utilizes carrier traps at the interface between the photoconductive organic semiconductor layer and the electrode has been found, and this photocurrent doubling phenomenon is utilized. There have been reports of organic thin film light-receiving elements (see Non-Patent Documents 1 and 2, Patent Documents 1 and 2). The performance of this organic thin film light receiving element has reached a level at which weak light having a light intensity of about 10 ⁻⁵ [W / cm ² ] can be detected with an applied voltage of several tens [V].

  It is considered that the weak light detection in the organic thin film light receiving element is generally expressed by the following mechanism. That is, when weak light is incident from the anode side with a voltage applied between the anode and the cathode by a DC power source, photocarriers (electrons, holes) are generated, and the holes of the photocarriers are generated under an electric field. Although it is transported to the cathode side, a part of it is captured and accumulated at the interface state existing in the vicinity of the interface between the photoconductive organic semiconductor layer and the cathode. As a result, an electric field concentrates on the interface between the photoconductive organic semiconductor layer and the cathode, and a large amount of electrons are tunneled from the cathode, so that a photocurrent doubling phenomenon appears.

However, in the above photo detector, since the photoconductive organic semiconductor layer is formed of a vacuum vapor deposition film of an organic pigment, (1) uniform film quality cannot be ensured and pinholes are likely to occur. (2) There is a problem that it is difficult to increase the area, and (3) it is difficult to reduce the cost because a vacuum process is required. In order to solve such a problem, recently, a resin-dispersed photodetector in which a photoconductive organic semiconductor is dispersed in a resin has been proposed (see Patent Document 3).
Appl. Phys. Lett., 64, 2546 (1994) Future Materials, Vol.2, No.9, p.34 JP 2002-190616 A JP 2003-282934 A JP 2002-076430 A

However, although the conventional organic thin film light receiving element can detect weak light having an intensity of about 10 ⁻⁵ [W / cm ² ] with an applied voltage of several tens [V], the intensity is 10 ⁻⁷ to 10 −10. Ultra-weak light of about ⁻¹⁵ [W / cm ² ] cannot be detected at a low voltage.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an organic thin film light-receiving element capable of detecting ultra-weak light with low voltage and high sensitivity, and a method for manufacturing the same. .

  Another object of the present invention is to provide an organic thin film light emitting / receiving element capable of detecting ultra-weak light with high sensitivity and low voltage, and a method for manufacturing the same.

  Still another object of the present invention is to provide a pulse sensor capable of detecting a pulse with low voltage and high sensitivity.

  In this invention, the photoconductive organic-semiconductor layer which comprises an organic thin film light receiving element contains the internal electric field generator which generate | occur | produces an electric field in the state in which the voltage is not applied between an anode and a cathode.

According to the present invention, since the photo-induced current can be doubled by the internal electric field, ultra-weak light having an intensity of about 10 ⁻⁷ to 10 ⁻¹⁵ [W / cm ² ] can be detected with low voltage and high sensitivity. can do.

As a result of intensive research, the inventors of the present invention have developed an internal electric field generator (material having spontaneous polarization) that generates an electric field even when no voltage is applied from the outside as a photoconductive organic semiconductor. It has been found that ultra-weak light having a light intensity of about 10 ⁻⁷ to 10 ⁻¹⁵ [W / cm ² ] can be detected at a low voltage by being contained inside the layer. In the present specification, the “internal electric field generator” means a photoconductive state as shown in FIG. 1A in a state where no voltage is applied from the outside, that is, the external electric field Ee is zero. Means a substance 4b that forms an internal electric field Ei in a certain direction inside the conductive organic semiconductor layer 4a, and generates a dipole that is an electric force between molecules in the molecular structure. It means a state of positive alignment. When the internal electric field generator is contained in the photoconductive organic semiconductor layer, when the external electric field Ee is further applied in a state where the internal electric field Ei is formed, the total electric field E of the photoconductive organic semiconductor layer is: As shown in FIG. 1B, it is given by the sum of the internal electric field Ei and the external electric field Ee. In FIGS. 1A and 1B, individual dipoles are not shown, and a dipole is formed in a domain-like region (molecular assembly), and the molecular assembly is indicated by an arrow (→). Indicated.

  It is desirable to use a ferroelectric polymer resin material as the internal electric field generator. Specifically, examples of the ferroelectric polymer resin material include polyvinylidene fluoride (PVDF), a polyvinylidene fluoride copolymer, or a composite thereof. Specific examples of the composite include polyvinylidene fluoride-trifluoride ethylene, polyvinylidene fluoride-tetrafluoroethylene, and the like. When an internal magnetic field generator is formed from polyvinylidene fluoride-trifluoride ethylene, copolymerization of polyvinylidene fluoride at a ratio of 60 to 90 [mol%] and ethylene trifluoride at a ratio of 40 to 10 [mol%] A resin body having a large light transmittance in the visible light region (wavelength 380 nm to wavelength 780 nm) and a large electric dipole can be formed. The mechanism by which these substances function as an internal electric field generator is not clear at this stage, but in the ferroelectric polymer polyvinylidene fluoride, the hydrogen atom H is positively charged and the fluorine atom F is negatively charged. A dipole from F to the hydrogen atom H is formed. For this reason, it is considered that the dipoles are aligned in a certain direction and function as an internal electric field generator.

  In the present specification, the “photoconductive organic semiconductor” means an organic semiconductor whose conductivity is improved by light irradiation. Specifically, photoconductive organic semiconductors include p-type organic semiconductors such as triphenylamine derivatives, benzidine derivatives, phthalocyanine derivatives, merocyanine derivatives, polythiophene derivatives, polyaniline derivatives, pyrazoline derivatives, styrisamine derivatives, and oxadiazole derivatives. , Triazole derivatives, silole derivatives, perylene derivatives, naphthalene derivatives, and n-type organic semiconductors such as one derivative selected from the group consisting of fullerene derivatives or a mixture containing one selected derivative it can. In addition, “photoconduction” is a phenomenon in which conduction electrons (carriers) inside a substance increase when semiconductors and insulators are irradiated with sufficiently short-wavelength light, and the electrical conductivity caused thereby increases. Say a phenomenon. In order to develop a larger photocurrent doubling phenomenon, either a p-type semiconductor or an n-type semiconductor can be basically applied. However, an n-type organic semiconductor is used from the band structure of a photoconductive organic semiconductor. Is more preferable. By using an n-type organic semiconductor, the height and thickness of the potential barrier formed between the cathode and the cathode can be controlled by voltage application (external electric field), and electron tunnel injection from the cathode can be promoted.

Next, the reason why the weak light can be detected at a low voltage when the internal electric field Ei appears in the photoconductive organic semiconductor layer will be described with reference to FIG. FIG. 2 shows an external electric field Ee generated when a voltage is applied between the anode and the cathode and weak light (for example, in the case where the internal electric field Ei exists (the present invention) and the case where the internal electric field Ei does not exist (conventional element) (for example, The result of having measured the relationship of the photoinduced current J which appears by incidence | injection of the weak light of wavelength 490nm) is shown. The light induced current J is normalized when the internal electric field Ei is not present as 10 ^0. The photoconductive organic semiconductor layer was formed by adding perylene fine particles 30 [wet%] to the ferroelectric polymer polyvinylidene fluoride.

As is clear from FIG. 2, in the absence of the internal electric field Ei, the total electric field E of the photoconductive organic semiconductor layer is equal to the external electric field Ee, and the photo-induced current J increases gently with the increase of the external electric field Ee. The photoinduced current J increases rapidly from the vicinity of the external electric field Ee = 10 ⁶ [V / cm]. This is presumably because the electron tunnel effect appears prominently in the vicinity of the external electric field Ee = 10 ⁶ [V / cm]. On the other hand, when the internal electric field Ei exists, the total electric field E of the photoconductive organic semiconductor layer is the sum of the internal electric field Ei and the external electric field Ee. The photoinduced current J increases rapidly from around the electric field Ee = 10 ⁵ [V / cm].

  Therefore, when compared with the same external electric field Ee, the photo-induced current J generated by the incidence of weak light shows a value that is two to several orders of magnitude larger due to the presence of the internal electric field Ei. That is, when the internal electric field Ei is present, even if the incident light is weak light, the photo-induced current J can be doubled by two to several orders of magnitude compared to the conventional organic thin film light receiving element. As can be seen from FIG. 2, when the internal electric field Ei is present, the photo-induced current J obtained by the conventional organic thin film light receiving element with the external electric field Ee is achieved by the external electric field Ee that is one digit smaller. . As described above, the weak light can be doubled at a low voltage by the sum of the internal electric field Ei and the external electric field Ee applied from the outside.

  Since the magnitude of the internal electric field Ei greatly depends on the bias of the charge Q of the molecules constituting the internal electric field generator, a thermal treatment such as applying polarization (polling) and forcibly aligning the dipoles in a certain direction. It can be changed by positively forming the bias of the charge Q electromagnetically and optically. More specifically, after a high voltage is applied between the anode and the cathode for a certain period of time while maintaining the temperature above the glass transition point of the photoconductive organic semiconductor layer, the photoconductive organic semiconductor layer is rapidly cooled (for example, Liquid nitrogen temperature) and the application of voltage is stopped, whereby the orientation of the dipoles can be fixed in the direction of the thickness of the photoconductive organic semiconductor layer (perpendicular to the electrodes).

  This dipole array-fixed in a certain direction can maintain a state in which spontaneous polarization is maintained semi-permanently. Even without providing an electrode, it is possible to arrange the dipoles in the photoconductive organic semiconductor layer by actively creating a trapped state of electrons and forming space charges. Specifically, the same effect can be expressed by corona discharge treatment at room temperature or treatment such as irradiation with an electron beam or X-ray.

By making the internal electric field generator a system composed of a ferroelectric polymer resin material and a ferroelectric inorganic material, the internal electric field Ei can be made larger than in the case of the ferroelectric polymer resin material alone. Can do. As a system composed of a ferroelectric polymer resin material and a ferroelectric inorganic material, an appropriate amount of a ferroelectric inorganic material dispersed in a ferroelectric polymer resin material, or a ferroelectric polymer For example, a thin film layer of a resin material and a thin film layer of a ferroelectric inorganic material formed into a multilayer film can be exemplified. Specifically, fine particles of polyvinylidene fluoride (PVDF) as the ferroelectric polymer resin material and barium titanate (BaTiO ₃ ) as the ferroelectric inorganic material material can be exemplified.

In this case, the transparent electrode surface of the glass substrate with a transparent electrode (ITO) contains polyvinylidene fluoride (PVDF) and barium titanate (BaTiO ₃ ) fine particles of several tens of nm to several μm in appropriate amounts (for example, several wet%). A prepared solution is prepared and applied to form a film. Thereafter, a sandwich type system in which a gold (Au) vapor deposition film having a thickness of several tens of nanometers as a cathode is formed on the other surface of the film. Thereafter, the sandwich type system can be polarized to form a dipole that is arranged perpendicular to both electrode surfaces. By adopting such a system, the internal electric field Ei can be expressed approximately by 10 ² to 10 ⁷ V / cm. In the combination system of the ferroelectric polymer resin and the ferroelectric inorganic substance, the type, shape, size, and content ratio of the ferroelectric inorganic substance used are the magnitude of the internal electric field Ei. Sufficient attention is required as it will affect.

The ferroelectric inorganic material is not particularly limited as long as it has a positive ion and a negative ion in the crystal structure and an electric dipole is formed, but is expressed as ABO ₃ such as PZT, PbTiO ₃ , BaTiO _3, etc. It is preferable to use a material having a perovskite crystal structure. In addition, in the combination system of ferroelectric polymer resin material and ferroelectric inorganic material, the type, shape (fine particles, thin film, etc.) and size of the ferroelectric inorganic material used, and the content ratio of both By appropriately setting, etc., a target internal electric field forming ability can be obtained.

[Configuration of organic thin-film light receiving element]
Next, the structure of the organic thin-film light receiving element, which is an embodiment of the present invention that has been conceived based on the above knowledge, will be described. In addition, the organic thin film light receiving element which becomes embodiment of this invention is applicable to photovoltaic devices, such as light control apparatuses, such as a photoelectric device and an electrochromic element, a solar cell. In particular, the organic thin-film light receiving element according to an embodiment of the present invention detects changes in the absorbance of hemoglobin in the blood of a vehicle driver and weak light in the near infrared region such as biophotons (bioluminescence) emitted from the human body. The present invention can be applied to a living body information detecting apparatus. Moreover, the organic thin film light receiving element which becomes embodiment of this invention is embedded in the steering | stirring of a vehicle, and can be applied to the biometric information detection apparatus which detects weak light from a driver | operator's bare hand.

  As shown in FIG. 3, an organic thin-film light receiving element 1 according to an embodiment of the present invention is formed on a surface of a substrate 2 and the substrate 2, and emits light of any one of ultraviolet rays, visible rays, and near infrared rays. A transparent anode 3, a photoconductive organic semiconductor layer 4 formed on the surface of the anode 3, and a cathode 5 formed on the surface of the photoconductive organic semiconductor layer 4. Thus, a photo-induced current is generated in the photoconductive organic semiconductor layer 4 in response to light incident from the anode 3 side in a state where a voltage is applied between the anode 3 and the cathode 5.

  In the organic thin film light-receiving element 1, the photoconductive organic semiconductor layer 4 includes a photoconductive organic semiconductor 4a and a photoconductive organic semiconductor layer 4 even when no voltage is applied from the outside, as shown in FIG. It is formed of a ferroelectric polymer resin material 4b that generates an electric field Ei therein. In the present embodiment, the organic thin-film light receiving element 1 is configured to make light incident on the photoconductive organic semiconductor layer 4 through the substrate 2. However, as shown in FIG. It may be formed of a translucent material, and light may be incident on the photoconductive organic semiconductor layer 4 from the cathode 5 side. Further, as shown in FIG. 6, the photoconductive organic semiconductor layer 4 may contain a ferroelectric inorganic material 4c.

Examples of the material for forming the anode 3 include inorganic oxides such as ITO (indium tin oxide), SnO ₂ (tin oxide), ZnO (zinc oxide), and FTO (fluorine-doped tin oxide), or conductive polymers ( And polypyrrole, PEDOT / PSS, carbon nanotube dispersion, etc.). In addition, either one of the electrodes, preferably the cathode 5, is preferably formed of a material such as Au, Ag, Pd, or Pt that easily takes an island-like particle form. This is because the main manifestation mechanism of the photocurrent doubling phenomenon is that electrons serving as carriers are trapped and accumulated in structural traps existing in the vicinity of the interface between the photoconductive organic semiconductor layer 4 and the cathode 5, and as a result, photoconductive The electric field concentrates on the interface between the conductive organic semiconductor layer 4 and the cathode 5 and a large amount of electrons are tunnel-injected from the cathode 5. In order to positively form this structural trap, In, Al, etc. This is because it is desirable to form the cathode 5 with a material such as Au, Ag, Pd, or Pt that is easy to take the form of island-like particles, rather than a material with high wettability.

  The thin film manufacturing method for forming a structural trap at the interface between the photoconductive organic semiconductor layer 4 and the cathode 5 is not particularly limited as long as it is a method capable of forming the material of the cathode 5 into an island-like thin film. Various physical vapor deposition (PVD) methods such as vapor deposition, electron beam vapor deposition, molecular beam epitaxy, cluster ion beam, ion plating, sol-gel method, plating method, electrochemical method, LB method, etc. The various wet thin film forming methods can be applied.

  When light is incident on the photoconductive organic semiconductor layer 4 via the substrate 2 and the anode 3, the interface between the air and the substrate 2, the interface between the substrate 2 and the anode 3, and the interface between the anode 3 and the photoorganic semiconductor layer 4 In this case, it is desirable to guide light to the photoconductive organic semiconductor layer 4 without causing light loss (reflection, scattering, etc.) as much as possible. For this purpose, it is necessary to reduce the difference in refractive index at each interface and to apply a material having a high transmittance with respect to the target weak light.

  As a material for forming the substrate 2, it is desirable to use a material having a high light transmittance in a target light wavelength region. As a material having a large light transmittance in any wavelength region, quartz glass, polyethylene terephthalate, or the like can be used. It can be illustrated. Also, when light enters the photoconductive organic semiconductor layer 4 through the cathode 5, it is necessary to minimize the light loss at each interface, and in particular, care must be taken in selecting the material of the cathode 5. Examples of the material for the cathode 5 include ITO and ZnO for inorganic transparent electrode materials, and PEDOT / PSS for organic transparent electrode materials.

[Method of manufacturing organic thin film light receiving element]
When the organic thin film light receiving element 1 is manufactured, first, an anode 3 such as an ITO thin film is formed on the surface of a substrate 2 such as quartz glass. Next, PVDF, which is a ferroelectric polymer resin dissolved in a solvent, and several tens [wet%] of perylene fine particles, which is a photoconductive organic semiconductor, are mixed, dispersed, stirred, and then subjected to a wet thin film formation method such as a spin coating method. The dispersion liquid is applied onto the surface of the anode 3 and dried to form a photoconductive organic semiconductor layer 4 having a thickness of several hundreds [nm] on the surface of the anode 3. Finally, an Au thin film having a thickness of several tens [Å] is formed as the cathode 5 on the surface of the photoconductive organic semiconductor layer 4 by vacuum deposition. The wet thin film forming method includes various known methods (spin coating method, casting method, dipping method, bar coating method, etc.) in consideration of the type of solution system to be used and the size (area) of the element to be produced. Gravure printing, screen printing, printing techniques such as an ink jet method) can be applied.

[Application example]
The organic thin film light receiving element 1 can be applied to a light receiving and emitting element, for example. Hereinafter, a preferred embodiment of the organic thin film light receiving element 1 when the organic thin film light receiving element 1 is applied to a light receiving and emitting element will be described. In general, the light receiving / emitting element is configured to irradiate the subject with high-intensity light (wavelength λ) from the light emitting element and detect the reflected light from the subject with the light receiving element. In such a light emitting / receiving element, there is no problem in optical measurement when the subject is a uniform opaque body, but there is a problem in optical measurement when the subject is a transparent body.

  Specifically, for example, a subject is transparent and a composite or mixture of a plurality of constituent materials, such as a mixture of human arterial blood and fluorescent substances, etc. If the composition material is a material having a nano-structure (light interference, scattering, diffraction, etc.), even if it is irradiated with high-intensity light from the light-emitting element Light is not necessarily strongly reflected at the subject. For this reason, when the subject is a transparent body, light of other wavelengths is superimposed on the reflected light component, so that only the light in the target wavelength region cannot be received with high sensitivity.

As a result of intensive studies, the present inventors have pi-conjugated at the interface between the electrode on which light is incident (the anode 3 in the example shown in FIG. 7) and the photoconductive organic semiconductor layer 4 as shown in FIG. By providing an ultra-thin layer of organic organic molecules as the specific wavelength absorption layer 7, it is possible to receive only light of a specific wavelength, and further to increase the photoinduced current by controlling the layer thickness of the specific wavelength absorption layer 7. I found out that there is. That is, the specific wavelength absorption layer 7 transmits only reflected light having a spectrum equivalent to the spectrum of the light emitted from the light emitting element (see FIG. 8, peak wavelength λ _max ) to the photoconductive organic semiconductor layer 4 side, and reflects it. It absorbs (filters) light in a wavelength region other than light. According to such an organic thin film light receiving element 1, even if light of other wavelengths is superimposed on the reflected light component, only light in the target wavelength range can be detected with high sensitivity.

  As a method of developing such a filter function, a method of combining a plurality of optical filters can be considered. When this method is used, (1) a decrease in light transmittance due to a combination of a plurality of optical filters (testing) The light reflected from the body is attenuated by the optical filter and the light intensity to the light receiving element is reduced), (2) the thickness and capacity of the light receiving element are increased by mounting the optical filter, and (3) the optical filter is manufactured and mounted. (4) Increase in process man-hour due to the increase in process man-hour due to increase in process man-hour occurs.

  The method for forming the specific wavelength absorption layer 7 is not particularly limited as long as a layer having a thickness on the order of nanometers can be formed, and π-conjugated organic molecules are deposited using physical vapor deposition such as vacuum deposition or electron beam. Alternatively, a solution in which π-conjugated organic molecules are diluted with a solvent is applied, and the solution is applied by various wet methods such as Langmuir-Blodget (LB) method, casting method, spin coating method, dip method, etc. You may do it.

The π-conjugated organic molecule means an organic molecule having a π bond. The π bonds means ethylene, acetylene, benzene, both double bonds or triple bonds found in molecules such as C _60, a chemical bond electrons make that delocalized largely spread on the outside of the molecule. The electrons involved in p-bonding (p-electrons) can exist between molecules, mediating the interaction between molecules, and exhibiting various useful physical properties and functions such as charge transport ability, magnetism, and optical functions. Many of them have a specific absorption spectrum as described above.

  As the π-conjugated organic molecules that can be used as the specific wavelength absorption layer 7, only reflected light having a spectrum equivalent to the spectrum of light emitted from the light emitting element is transmitted to the photoconductive organic semiconductor layer 4 side, and the reflected light is transmitted. Any organic molecules such as phthalocyanines, naphthalocyanines, chlorophylls, merocyanines, anthraquinones, quinacridones, etc. may be used as long as they have an absorption spectrum that absorbs light in a wavelength range other than Can do. However, controllability of the wavelength range of light transmitted to the photoconductive organic semiconductor layer 4 side (hereinafter referred to as a window region), ease of forming the specific absorption layer 7, long-term stability of the specific absorption layer 7, and From the viewpoint of durability, it is preferable to use a phthalocyanine-based, naphthalocyanine-based, or chlorophyll-based organic molecule as the π-conjugated organic molecule.

  The phthalocyanine-based organic molecule has a molecular structure as shown in FIG. 9, and a metal atom M is arranged at the center of the molecule. Here, those in which the metal is not coordinated at the position of the metal atom M are referred to as metal-free phthalocyanine, and those in which various metals are coordinated are referred to as metal phthalocyanine. By changing the type of the metal atom M, the window region in the absorption spectrum can be controlled relatively arbitrarily. Examples of the metal atom M include Cu, Zn, Ni, Pb, Pt, TiO, and VO.

10 and 11 show absorption spectra of a copper phthalocyanine (CuPc) thin film and a metal-free phthalocyanine (H ₂ Pc) thin film, respectively. In the absorption spectrum of the copper phthalocyanine thin film, the light absorption rate decreases in the wavelength region (window region) of the wavelength of 480 to 560 [nm], whereas in the absorption spectrum of the metal-free phthalocyanine thin film, the wavelength of 450 to 550 [nm]. In the wavelength region (window region), the light absorption rate becomes small. In this way, in the phthalocyanine thin film, by changing the kind of the metal atom M, light having an unnecessary specific wavelength is absorbed, and light having a wavelength necessary as reflected light is efficiently incident on the photoconductive organic semiconductor layer 4 side. be able to.

  FIG. 12 shows a graph plotting changes in the photoinduced current J accompanying changes in the thickness d of the copper phthalocyanine thin film using a copper phthalocyanine thin film as the specific wavelength absorption layer 7. The vertical axis in the figure is normalized with the photoinduced current J when the specific wavelength absorption layer 7 is not formed being 1.0. As is clear from the figure, the photoinduced current J increases as the thickness d of the specific wavelength absorption layer 7 increases, and is about 3 to 5 nm when the thickness d of the specific wavelength absorption layer 7 is about 3 to 5 nm. Doubled to show maximum. Further, when the thickness d of the specific wavelength absorption layer 7 further increases, the photoinduced current J gradually decreases, and the photoinduced current value at the initial level (in the case where there is no specific wavelength absorption layer) in the vicinity of the thickness 13 [nm]. It becomes. When the thickness d of the specific wavelength absorption layer 7 further increases and reaches around 20 [nm], it decreases to about 70% of the initial level.

  The reason for this is not clear, but as the thickness of the copper phthalocyanine thin film increases, light absorption in a wide wavelength range of the copper phthalocyanine thin film becomes more prominent, and light carriers incident from the window region of the spectrum are reduced. It is thought that the number of optical carriers to be reduced also decreased. From the above, it has been clarified that the photoinduced current J can be maximized by controlling the thickness d of the specific wavelength absorption layer 7 at the nano-order level. However, the thickness d of the specific wavelength absorption layer 7 differs depending on the type of the π-conjugated organic molecule used and the relative relationship with the thickness of the photoconductive organic semiconductor layer 4, and therefore cannot be uniquely determined. .

[Example]
Hereinafter, the organic thin film light receiving element according to the present invention will be described in detail based on examples.

[Example 1]
In Example 1, first, a perylene pigment (manufactured by Koyo Chemical Co., Ltd., average) was used as a photoconductive organic semiconductor in a solution comprising a ferroelectric polymer resin polyvinylidene fluoride (PVDF, Kureha) and a solvent tetrahydrofuran (THF). A dispersion was prepared by mixing 20 [wet%] with a particle size of 20 [nm]. Next, a quartz glass with an ITO film (film thickness 100 [nm]) as an anode is prepared, and a dispersion liquid is applied on the surface of the ITO film by a spin coating method and dried to provide a photoconductive film having a film thickness of 500 [nm]. An organic semiconductor layer was formed. Finally, an Au thin film (thickness: 200 [nm]) was formed as a cathode on the photoconductive organic semiconductor layer by vacuum vapor deposition to obtain an organic thin film light receiving element of Example 1.

[Example 2]
In Example 2, the organic thin-film light receiving element of Example 1 was set in a cryostat, and held for 2 hours at a vacuum degree of 10 ⁻³ [Torr], a temperature of 80 [° C.], and an applied electric field of 10 ⁷ [V / cm]. Thereafter, liquid nitrogen was introduced into the cryostat to quench the organic thin film light receiving element, and the polarization treatment was performed by stopping the application of the electric field to obtain the organic thin film light receiving element of Example 2.

Example 3
In Example 3, the same treatment as in Example 2 was performed except that 40 [wet%] of an oxadiazole pigment (manufactured by high-purity chemical, average particle size 32 [nm]) was mixed instead of the perylene pigment. 3 organic thin film light receiving elements were obtained.

Example 4
In Example 4, first, a perylene pigment (manufactured by Koyo Chemical Co., Ltd., averaged) as a photoconductive organic semiconductor in a solution comprising a ferroelectric polymer resin polyvinylidene fluoride (PVDF, manufactured by Kureha) and a solvent tetrahydrofuran (THF). A dispersion was prepared by mixing 20 [wet%] with a particle size of 20 [nm]. Next, a quartz glass with an Au thin film (film thickness 100 [nm]) as a cathode is prepared, and a dispersion liquid is applied on the surface of the Au thin film by a spin coating method and dried to provide a photoconductive film having a film thickness of 500 [nm]. An organic semiconductor layer was formed. Finally, an ITO thin film (film thickness 200 [nm]) was formed as an anode on the photoconductive organic semiconductor layer by sputtering to obtain an organic thin film light receiving element of Example 4.

Example 5
In Example 5, first, an oxadiazole pigment (manufactured by Koyo Chemical Co., Ltd.) as a photoconductive organic semiconductor in a solution comprising a ferroelectric polymer resin polyvinylidene fluoride (PVDF, manufactured by Kureha) and a solvent tetrahydrofuran (THF). The dispersion was prepared by mixing 40 [wet%] with an average particle size of 32 [nm]. Next, a quartz glass with an Au thin film (film thickness 100 [nm]) as a cathode is prepared, and a dispersion liquid is applied on the surface of the Au thin film by a spin coating method and dried to provide a photoconductive film having a film thickness of 500 [nm]. An organic semiconductor layer was formed. Next, an ITO thin film (film thickness 200 [nm]) was formed as an anode on the photoconductive organic semiconductor layer by sputtering. Next, the organic thin film light receiving element was set in a cryostat, and held at a vacuum degree of 10 ⁻³ [Torr], a temperature of 80 [° C.], and an applied electric field of 10 ⁷ [V / cm] for 2 hours. Thereafter, liquid nitrogen was introduced into the cryostat to quench the organic thin film light receiving element, and the polarization treatment was performed by stopping the application of the electric field, whereby the organic thin film light receiving element of Example 5 was obtained.

Example 6
In Example 6, first, a perylene pigment (manufactured by Koyo Chemical Co., Ltd.) was used as a photoconductive organic semiconductor in a solution comprising a ferroelectric polymer resin polyvinylidene fluoride (PVDF, Kureha) and a solvent tetrahydrofuran (THF). A dispersion was prepared by mixing 20 [wet%] with an average particle size of 20 [nm]) and 10 [wet%] BaTiO ₃ fine particles as an inorganic ferroelectric material. Next, a quartz glass with an ITO film (film thickness 100 [nm]) as an anode is prepared, and a dispersion liquid is applied on the surface of the ITO film by a spin coat method and dried to provide a photoconductive film having a film thickness of 700 [nm]. An organic semiconductor layer was formed. Next, an Au thin film (film thickness 200 [nm]) was formed as a cathode on the photoconductive organic semiconductor layer by a vacuum deposition method. Next, the organic thin film light receiving element was set in a cryostat, and held at a vacuum degree of 10 ⁻³ [Torr], a temperature of 80 [° C.], and an applied electric field of 10 ⁷ [V / cm] for 2 hours. Thereafter, liquid nitrogen was introduced into the cryostat to quench the organic thin film light receiving element, and the application of the electric field was stopped to perform polarization treatment, whereby the organic thin film light receiving element of Example 6 was obtained.

[Comparative Example 1]
In Comparative Example 1, first, 20 [wet%] of a perylene pigment (manufactured by High Purity Chemical, average particle size 20 [nm]) as a photoconductive organic semiconductor in a solution made of polycarbonate (manufactured by Mitsubishi Chemical) and a solvent xylene. A dispersion was prepared by mixing. Next, a quartz glass with an ITO film (film thickness 100 [nm]) as an anode is prepared, and a dispersion liquid is applied on the surface of the ITO film by a spin coating method and dried to provide a photoconductive film having a film thickness of 500 [nm]. An organic semiconductor layer was formed. Finally, an Au thin film (film thickness 200 [nm]) was formed as a cathode on the photoconductive organic semiconductor layer by a vacuum evaporation method, and an organic thin film light receiving element of Comparative Example 1 was obtained.

[Comparative Example 2]
In Comparative Example 2, first, 20 [wet%] of a perylene pigment (manufactured by high purity chemical, average particle size 20 [nm]) as a photoconductive organic semiconductor in a solution composed of polycarbonate (Mitsubishi Chemical) and a solvent xylene. A dispersion was prepared by mixing. Next, a quartz glass with an Au thin film (film thickness 100 [nm]) as a cathode is prepared, and a dispersion liquid is applied on the surface of the Au thin film by a spin coating method and dried to provide a photoconductive film having a film thickness of 500 [nm]. An organic semiconductor layer was formed. Finally, an ITO thin film (film thickness 200 [nm]) was formed as an anode on the photoconductive organic semiconductor layer by sputtering, and an organic thin film light receiving element of Comparative Example 2 was obtained.

[Comparative Example 3]
In Comparative Example 3, first, a perylene pigment (manufactured by Koyo Chemical Co., Ltd.) was used as a photoconductive organic semiconductor in a solution comprising a ferroelectric polymer resin polyvinylidene fluoride (PVDF, Kureha) and a solvent tetrahydrofuran (THF). A dispersion was prepared by mixing 20 [wet%] with an average particle size of 20 [nm]) and 10 [wet%] BaTiO ₃ fine particles as an inorganic ferroelectric material. Next, a quartz glass with an ITO film (film thickness 100 [nm]) as an anode is prepared, and a dispersion liquid is applied on the surface of the ITO film by a spin coat method and dried to provide a photoconductive film having a film thickness of 700 [nm]. An organic semiconductor layer was formed. Finally, an Au thin film (film thickness 200 [nm]) was formed as a cathode on the photoconductive organic semiconductor layer by a vacuum deposition method, and an organic thin film light receiving element of Comparative Example 3 was obtained.

[Measurement of internal electric field]
For each of the organic thin-film light receiving elements of Examples 1 to 6 and Comparative Examples 1 to 3, the open-circuit voltage Voc between the anode and the cathode in the dark state is measured, and the internal electric field Ei is calculated from the measured open-circuit voltage Voc. did. The calculation results are shown in Table 1 below.

(Measurement of photoinduced current)
An external electric field of 10 ⁶ [V / cm] was applied to each of the organic thin film light receiving elements of Examples 1 to 6 and Comparative Examples 1 to 3, and monochromatic light (wavelength λ: 670 [nm]) from the electrode side having optical transparency. ) Was measured. The measurement results are shown in Table 1 below.

〔Consideration〕
As is apparent from Table 1, the open-circuit voltage Voc and the photoinduced current J in the organic thin film light receiving elements of Examples 1 to 6 are the open circuit voltage Voc and the photoinduced current J in the organic thin film light receiving elements of Comparative Examples 1 to 3. A large value is shown in comparison with. Moreover, the internal electric field in the organic thin film light receiving element of Examples 1-6 shows a large value compared with the internal electric field in the organic thin film light receiving element of Comparative Examples 1-3. From this, it is found that weak light can be detected at a low voltage by including an internal electric field generator that generates an electric field even when no voltage is applied from the outside, inside the photoconductive organic semiconductor layer.

[Configuration of organic thin film light emitting / receiving element]
Next, the structure of the organic thin film light emitting / receiving element according to the embodiment of the present invention conceived based on the above knowledge will be described.

  As shown in FIG. 13, the organic thin film light receiving / emitting element 10 according to the embodiment of the present invention includes the organic thin film light receiving element 1, the organic thin film light emitting element 11, the organic thin film light receiving element 1, and the organic thin film light emitting element 12. And a flexible substrate 12 such as a resin film disposed on the surface facing the subject 14. In the example shown in FIG. 13, the organic thin film light receiving element 1 and the organic thin film light emitting element 11 are arranged on the same surface of the flexible substrate 12, but when the flexible substrate 12 has light transmittance, as shown in FIG. 14. Alternatively, the organic thin film light receiving element 1 may be disposed in the opposite surface. In the example shown in FIGS. 13 and 14, the organic thin film light receiving element 1 and the organic thin film light emitting element 11 are exemplified as one set. However, the present invention is not particularly limited thereto, and one organic thin film light receiving element 1 and a plurality of organic thin film light receiving elements 1 are combined. A combination of the thin film light emitting elements 11 may be used, or a combination of a plurality of organic thin film light receiving elements 1 and one organic thin film light emitting element 11 may be used.

  According to such an organic thin film light emitting / receiving element 10, a biological information detecting device that detects a change in absorbance of hemoglobin in blood and a weak light such as biophoton (bioluminescence) emitted from a human body, more specifically, A pulse sensor can be realized. In particular, by arranging the organic thin film light emitting / receiving element 10 on the skin of the steering wheel having a curved surface shape, a pulse sensor that can detect weak light from the driver's bare hands with high accuracy with low voltage can be realized.

  When the organic thin film light emitting / receiving element 10 is manufactured, first, the first electrode layer is formed on one or both surfaces of the flexible substrate 12 such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI) or the like. In the case of the organic thin film light emitting element 11, an organic light emitting layer is formed, and in the case of the organic thin film light receiving element 1, a photoconductive organic semiconductor layer is formed thereon. And after forming the 2nd electrode layer on the surface of both formed layers, it coats the resin composition which served as moisture-proof and protection by printing etc., or is stuck with a coverlay film, and is an organic thin film light emitting and receiving element 10 can be manufactured.

  In order to prevent the organic thin film light receiving element 1 and the organic thin film light emitting element 12 from deteriorating due to humidity or oxygen, it is preferable to carry out a series of manufacturing steps in an inert gas. When the organic thin film light receiving element 1 and the organic thin film light emitting element 12 are formed by a printing process, the organic thin film light receiving element 1 and the organic thin film light emitting element 12 can be formed in a large area, so that the cost can be reduced. Further, since the organic thin film light receiving element 1 and the organic thin film light emitting element 12 are flexible elements, they can be arranged on a curved surface shape or a complicated three-dimensional shape.

[Example]
Hereinafter, the organic thin film light emitting and receiving element according to the present invention will be described in detail based on examples.

Example 7
In Example 7, a polyethylene terephthalate (PET) film having a thickness of 250 [μm] with a transparent electrode ITO (film thickness 100 [nm]) as an anode was first prepared as a base material. And the organic thin film light receiving element and the organic thin film light emitting element were formed with the method shown below, and the organic thin film light receiving and emitting element of Example 7 was obtained.

(1) Organic thin film light receiving element First, a copper phthalocyanine (CuPc) thin film was formed on the anode surface as a specific wavelength absorption layer to a thickness of 5 [nm] by vacuum deposition. Next, a perylene pigment (manufactured by High Purity Chemical, average particle size of 20 [nm] as a photoconductive organic semiconductor in a solution comprising a ferroelectric polymer resin polyvinylidene fluoride (PVDF, manufactured by Kureha) and a solvent tetrahydrofuran (THF). ] Was mixed on the surface of the specific wavelength absorption layer by a spin coat method and dried to form a photoconductive organic semiconductor layer 4 having a thickness of 500 [nm]. And the organic thin film light receiving element was formed by forming Au thin film (film thickness 200 [nm]) as a cathode on the photoconductive organic-semiconductor layer 4 by a vacuum evaporation method.

(2) Organic thin-film light-emitting element First, polyphenylene vinylene (PPV) was formed on the anode surface to a thickness of 100 nm by spin coating. Then, an organic thin film light emitting device was formed by forming an Ag / Mg thin film as a cathode by a vacuum deposition method.

Example 8
In Example 8, the organic thin film light receiving and emitting of Example 8 was performed by performing the same treatment as Example 7 except that a metal-free phthalocyanine (H ₂ Pc) thin film having a thickness of 5 nm was formed as the specific wavelength absorption layer. An element was obtained.

Example 9
In Example 9, the same treatment as in Example 7 was performed except that a nickel phthalocyanine (NiPc) thin film having a thickness of 3 [nm] was formed as the specific wavelength absorption layer and the content of perylene was set to 30 [wet%]. By performing, the organic thin film light emitting / receiving element of Example 9 was obtained.

Example 10
In Example 10, an organic thin film light emitting / receiving element of Example 10 was obtained by performing the same treatment as in Example 7 except that a naphthalocyanine (CuPc) thin film having a thickness of 8 [nm] was formed as the specific wavelength absorption layer. It was.

Example 11
In Example 11, the same treatment as in Example 7 was performed except that a naphthalocyanine (CuPc) thin film with a thickness of 6 [nm] was formed as the specific wavelength absorption layer and the content of perylene was 15 [wet%]. By performing, the organic thin film light emitting / receiving element of Example 11 was obtained.

[Comparative Example 4]
In Comparative Example 4, an organic thin film light emitting / receiving element of Comparative Example 4 was obtained by performing the same treatment as in Example 7 except that the specific wavelength absorption layer was not formed.

[Comparative Example 5]
In Comparative Example 5, an oxadiazole pigment (manufactured by Koyo Chemical Co., average particle size 32 [nm]) in a solution comprising a ferroelectric polymer resin polyvinylidene fluoride (PVDF, manufactured by Kureha) and a solvent tetrahydrofuran (THF). The organic thin film light emitting / receiving element of Comparative Example 5 was obtained by performing the same treatment as Comparative Example 4 except that 15 [wet%] was mixed.

[Evaluation]
For each of the organic thin film light emitting / receiving elements of Examples 7 to 11 and Comparative Examples 1 and 2, (1) the spectral peak wavelength of light emitted from the organic thin film light emitting element, and (2) the maximum light receiving sensitivity spectral peak of the organic thin film light receiving element. (3) Light-induced current in the organic thin-film light-receiving element when the organic thin-film light-emitting element is emitted from the organic thin-film light-emitting element to the subject (aluminum plate) with an emission luminance of 1000 [cd / m ² ] (no specific wavelength absorption layer is provided) The photoinduced current at the time was set to 1.0). The photoinduced current was evaluated by irradiating the organic thin film light receiving element from the side of the light-transmitting substrate with an external electric field of 10 ⁶ [V / cm] applied. The evaluation results are shown in Table 2 below.

〔Consideration〕
As is clear from Table 2, the photoinduced current J in the organic thin film light receiving elements of Examples 7 to 11 is larger than the photoinduced current J in the organic thin film light receiving elements of Comparative Examples 4 and 5. Therefore, by providing a specific wavelength absorption layer at the interface between the electrode on which light is incident and the photoconductive organic semiconductor layer, and controlling the layer thickness of the specific wavelength absorption layer, only light of a specific wavelength can be obtained. It is found that the light can be received and the photo-induced current can be multiplied.

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. As described above, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

It is a schematic diagram for demonstrating the electric field inside a photoconductive organic-semiconductor layer. The results of measuring the relationship between the external electric field generated when a voltage is applied between the anode and the cathode and the photoinduced current developed by the incidence of faint light in each case where the internal electric field exists and does not exist are shown. . It is sectional drawing which shows the structure of the organic thin film light receiving element used as embodiment of this invention. It is a schematic diagram which shows the internal structure of the photoconductive organic-semiconductor layer shown in FIG. It is sectional drawing which shows the structure of the application example of the organic thin film light receiving element shown in FIG. It is a schematic diagram which shows the internal structure of the application example of the photoconductive organic-semiconductor layer shown in FIG. It is sectional drawing which shows the structure of the application example of the organic thin film light receiving element shown in FIG. It is a wave form diagram which shows an example of the emission spectrum radiate | emitted from a light emitting element. It is a figure which shows the molecular structure of a phthalocyanine-type organic molecule. It is a wave form diagram which shows the absorption spectrum of a copper phthalocyanine thin film. It is a wave form diagram which shows the absorption spectrum of a metal free phthalocyanine thin film. It is a figure which shows the change of the photoinduced current accompanying the change of the thickness of a copper phthalocyanine thin film. It is a schematic diagram which shows the structure of the organic thin film light emitting / receiving element used as embodiment of this invention. It is a schematic diagram which shows the structure of the application example of the organic thin film light emitting / receiving element shown in FIG.

Explanation of symbols

1: Organic thin-film light receiving element 2: Substrate 3: Anode 4: Photoconductive organic semiconductor layer 4a: Photoconductive organic semiconductor 4b: Ferroelectric polymer resin material 5: Cathode 6: DC power supply 7: Specific wavelength absorption layer

Claims (19)

  Provided with a photoconductive organic semiconductor layer sandwiched between an anode and a cathode, wherein at least one of the anode and the cathode is transmissive to any one of ultraviolet light, visible light, and near infrared light, and between the anode and the cathode An organic thin film light-receiving element that generates a photo-induced current in the photoconductive organic semiconductor layer in response to irradiation of any of the light with a voltage applied to the photoconductive organic semiconductor layer, wherein the photoconductive organic semiconductor layer is An organic thin-film light-receiving element comprising an internal electric field generator that generates an electric field when no voltage is applied between an anode and a cathode.   2. The organic thin film light-receiving element according to claim 1, further comprising an absorption layer that absorbs light of a specific wavelength at an interface between the anode or the cathode and the photoconductive organic semiconductor layer located on a light irradiation side. An organic thin film light receiving element.   The organic thin film light receiving element according to claim 2, wherein the light absorption layer contains a π-conjugated organic molecule.   4. The organic thin film light receiving element according to claim 3, wherein the π-conjugated organic molecule is at least one organic molecule selected from the group consisting of phthalocyanine and naphthalocyanine. .   5. The organic thin film light receiving element according to claim 1, wherein the internal electric field generator is formed of a ferroelectric polymer material. 6.   5. The organic thin film light receiving element according to claim 1, wherein the internal electric field generator is formed of a ferroelectric polymer material and a ferroelectric inorganic material. Organic thin-film light receiving element.   The organic thin film light receiving element according to claim 5 or 6, wherein the ferroelectric polymer material and / or the electric dipole of the ferroelectric inorganic material is prepared to be perpendicular to the electrode surface by polarization treatment. An organic thin-film light receiving element characterized by being made.   8. The organic thin film light receiving element according to claim 5, wherein the ferroelectric polymer material is polyvinylidene fluoride, a polyvinylidene fluoride copolymer, or a composite thereof. An organic thin film light receiving element characterized by   9. The organic thin film light-receiving element according to claim 5, wherein the photoconductive organic semiconductor layer is formed by dispersing a ferroelectric polymer material in the photoconductive organic semiconductor material. Organic thin-film light receiving element, characterized by being made.   10. The organic thin film light receiving element according to claim 6, wherein the ferroelectric inorganic material is a material having a perovskite crystal structure.   11. The organic thin film light-receiving element according to claim 1, wherein the photoconductive organic semiconductor layer includes an oxadiazole derivative, a triazole derivative, a silole derivative, a periline derivative, a naphthalene derivative, and a fullerene. An organic thin-film light-receiving element, which is one derivative selected from a derivative group consisting of derivatives or a mixture containing one selected derivative.   12. The method of manufacturing an organic thin film light receiving element according to claim 1, wherein a step of forming a first electrode layer on a substrate, and a first electrode by a wet molding method. A method for manufacturing an organic thin film light-receiving element, comprising: a step of forming a photoconductive organic semiconductor layer on a layer; and a step of forming a second electrode layer on the photoconductive organic semiconductor layer.   13. The method of manufacturing an organic thin film light receiving element according to claim 12, comprising a step of forming an absorption layer that absorbs light of a specific wavelength on the first electrode layer, and absorbing the photoconductive organic semiconductor layer. A method for producing an organic thin film light-receiving element, comprising: forming on a layer.   The organic thin film light receiving element according to any one of claims 1 to 11, an organic thin film light emitting element that emits light of ultraviolet light, visible light, or near infrared light, and organic thin film light receiving. The organic thin film light emitting element irradiates a subject with light, and the organic thin film light receiving element receives reflected light from the subject. Organic thin film light emitting / receiving element.   15. The organic thin film light emitting / receiving element according to claim 14, wherein the organic thin film light emitting element emits spectral light having a peak position in a wavelength region outside the wavelength region where the absorption layer absorbs light. Thin film light emitting / receiving element.   16. The organic thin film light emitting / receiving element according to claim 14 or 15, wherein the organic thin film light emitting element is an organic electroluminescence element comprising an organic light emitting layer sandwiched between first and second electrodes. Organic thin film light emitting / receiving element.   17. The method of manufacturing an organic thin film light emitting / receiving element according to claim 16, wherein the step of forming at least two electrodes on the flexible substrate, and the photoconductive organic semiconductor layer and the organic light emitting layer on the electrodes. A method of manufacturing an organic thin film light emitting / receiving element, comprising: a step of forming; and a step of forming an electrode on the surface of the photoconductive organic semiconductor layer and the organic light emitting layer.   A pulse sensor characterized by detecting a pulse from the skin of a human body using the organic thin film light-receiving element according to any one of claims 1 to 11.   A pulse sensor that detects a pulse from the skin of a human body using the organic thin film light emitting and receiving element according to any one of claims 14 to 16.

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