JP6591231B2 - Photorefractive material composition and photorefractive polymer element - Google Patents

Description

  The present invention relates to a photorefractive material composition and a photorefractive polymer element.

  Certain materials are known to have good charge transporting ability, and the following photorefractive effect is an application example. The photorefractive effect is one of nonlinear optical effects, and is a phenomenon in which a substance absorbs light and its refractive index changes. The mechanism of expression of the photorefractive effect will be described. When two laser beams interfere with each other in a medium having photoconductivity and second-order nonlinear optical characteristics, interference fringes are formed. In the bright part of this interference draft, charge carriers are generated by photoexcitation, and positive charge carriers move through the medium by an externally applied electric field and are trapped in the dark part. As a result, a periodic distribution of charge density charged negatively in the bright part and positive in the dark part is created, and a spatial electric field is formed. This spatial electric field causes a Pockels effect which is a first-order electro-optic effect, and a periodic refractive index grating is formed. Since a phase difference of φ occurs spatially between the refractive index grating and the optical interference paper, asymmetric energy transfer is observed between the two light waves, and optical amplification (optical gain) is obtained.

  By using such a photorefractive effect, nonlinear optical information including phase conjugation, imaging from distorted media, real-time holography, super-multiplex hologram recording, 3D display, 3D printer, optical amplification, and optical neutral network Applications to processing, pattern recognition, optical limiting, storage of high-density optical data, and the like are expected.

Conventionally, inorganic crystal materials such as lithium niobate (LiNbO ₃ ) have been used as photorefractive materials that exhibit the above effects. However, this inorganic crystal material has a problem that it has poor processability, and it is particularly difficult to reduce the thickness. Thus, in recent years, development of photorefractive materials made of organic substances has been active.

  Organic photorefractive materials have many advantages over inorganic photorefractive materials. Advantages include easy optimization of the composition ratio and high workability, as well as large optical nonlinearity, low dielectric constant, low cost, light weight, flexibility, and the like. Other important characteristics that may be desirable depending on the application include long shelf life of recorded data, optical quality, and thermal stability. Such organic photorefractive materials are becoming important materials for advanced information communication technology. Among these, carbazoles (see, for example, Patent Document 1) and triphenylamines are known.

  Various holographic display devices are known as devices for continuously writing and displaying holograms, and the display device uses a photorefractive element including the photorefractive material as described above. For example, Patent Document 2 describes a photorefractive element in which a layer containing a photorefractive material and a layer containing an electron / ion mixed conductor are sandwiched between two transparent electrode substrates.

  Further, Patent Document 3 discloses a photorefractive polymer element having a dark current control layer.

JP 2003-322886 A JP 2011-158721 A WO2014 / 038332

  It is an object of the present invention to provide a photorefractive material composition and a photorefractive polymer element that have significantly improved responsiveness and sensitivity.

The present inventor has reviewed the photorefractive material composition and further added Alq ₃ as an electron trapping agent, thereby greatly improving the diffraction efficiency, greatly improving the response speed, and greatly improving the dielectric breakdown resistance. Achieved improvement.

The present invention provides the following photorefractive material composition and photorefractive polymer element.
Item 1. Comprising a photorefractive polymer, a sensitizer, a non-linear optical dye, a plasticizer and an N-type organic semiconductor, wherein the photorefractive polymer is poly [bis (4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) A photorefractive material composition.
Item 2. Item 2. The photorefractive material composition according to Item 1, wherein the N-type organic semiconductor is tris (8-hydroxyquinolinato) aluminum (Alq ₃ ) represented by the following formula.

Item 3. Item 3. The photorefractive material composition according to Item 1 or 2, wherein the sensitizer is PCBM.
Item 4. Item 4. The photorefractive material composition according to any one of Items 1 to 3, wherein the nonlinear optical dye is PDCST of the following formula.

Item 5. Item 5. The photorefractive material composition according to any one of Items 1 to 4, wherein the plasticizer is the following TAA.

Item 6. Item 6. A photorefractive polymer element comprising the photorefractive material composition according to any one of items 1 to 5.
Item 7. A photorefractive material composition layer comprising an insulating substrate, a transparent electrode formed on one side of the insulating substrate, and the photorefractive material composition according to any one of Items 1 to 4, and the photorefractive material composition Item 7. The photorefractive polymer element according to Item 6, wherein the physical layer is sandwiched between two transparent electrodes.
Item 8. Item 8. The photorefractive polymer element according to Item 7, wherein a dark current control layer is provided between the photorefractive material composition layer and at least one transparent electrode.

  With the present invention, diffraction efficiency is greatly improved from several percent to 60%, response time is greatly increased from 11.3 ms to 0.86 ms, and electric field strength is greatly increased from 25 V / μm to 60 V / μm. Improved. The diffraction response to a 100 Hz square wave electric field perfectly follows the diffraction response up to 60% with a rise time of 2 ms for an electric field of 10 ms. The diffraction efficiency dropped rapidly to almost 0%. We have succeeded in producing a photorefractive polymer with ultra-fast response that could not be achieved with conventional photorefractive polymers.

Schematic cross section of photorefractive polymer element A graph showing the relationship between sensitivity and response speed. Photocurrent and dark current measurement results Field dependence of the photocurrent of the sample of the presence or absence of Alq _3. Graph showing the relationship between Alq ₃ content and photocurrent The absorption spectrum in the sample in the presence and absence of Alq ₃ is shown. Energy diagram Asymmetric energy response due to two-wave coupling when a 100 Hz rectangular electric field (60 V / μm) is applied. Rise time: Very fast response of 350 μs. Diffraction efficiency response when a 100 Hz rectangular electric field (60 V / μm) is applied. Rise time: Very fast response of 860 μs. Photocurrent measurement device using AO modulator Photocurrent response when the light intensity is repeatedly turned on and off with a 100 Hz optical chopper using an AO modulator. DC electric field: 60 V / μm Light diffraction response when the light intensity is repeatedly turned on and off with a 99 Hz optical chopper. DC electric field: 60 V / μm Holographic imaging system. A 532 nm s-polarized writing beam (object beam and reference beam) and a 640 nm p-polarized probe beam are incident from the same side.

  The photorefractive material composition of the present invention contains PTAA as a photorefractive polymer, and further contains a sensitizer, a nonlinear optical dye, a plasticizer, and an N-type organic semiconductor.

  The photorefractive polymer is preferably a triarylamine-based amorphous polymer poly [bis (4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) represented by the following formula (1).

PTAA is also called polytriarylamine semiconductors. PTAA is an amorphous P-type semiconductor having high carrier mobility. The mobility is 10 ⁻² to 10 ⁻³ cm ² / Vs, and when used in a photorefractive polymer element, very high responsiveness can be exhibited. As another photorefractive polymer, a photorefractive polymer having a tetraphenyldiaminobiphenyl moiety also exhibits high responsiveness.

The content of the photorefractive polymer is preferably 10% by mass, more preferably 20% by mass, most preferably 30% by mass, and most preferably 30% by mass with respect to 100% by mass of the photorefractive material composition. 60 mass% is preferable and 50 mass% is further more preferable. When the content is less than 10% by mass, the glass transition point may not be sufficiently lowered. When the content is more than 60% by mass, other components (nonlinear optical dye, sensitizer, An imbalance may occur in the quantity ratio between the plasticizer and the N-type organic semiconductor), which may adversely affect the design of the photorefractive material composition.
(Sensitizer)
The sensitizer has performance as an electron acceptor and is blended in order to enhance photorefractive properties. When a sensitizer is blended, a charge transfer complex is formed by the sensitizer and the photorefractive polymer, and useful photorefractive properties are expressed.

Specific examples of the sensitizer include [6,6] -phenyl C61 butanoic acid methyl ester (PCBM), (2,4,7-trinitro-9-fluorenylidene) malonitrile (TNF-DM), 2, 4,7- Trinitro-9-fluorenone (TNF), fullerene C60, fullerene C70, tetracyanobenzene (TCBN), tetracyanoquinodinomethane (TCNQ), benzoquinone (BQ), and derivatives thereof, 2,6-dimethyl-p-benzoquinone ( MQ), 2,5-dichloro-p-benzoquinone (Cl ₂ Q), 2,3,5,6-tetrachloro-p-benzoquinone (chloranil), 2,3-dichloro-5,6-p-benzoquinone ( DDQ) and the like, preferably PCBM and TNF, and more preferably PCBM. The structural formula of PCBM is shown below:

In addition, a sensitizer may be used individually by 1 type and may use 2 or more types together.

The content of the sensitizer is preferably 0.1% by mass and more preferably 0.3% by mass as the lower limit with respect to 100% by mass of the photorefractive material composition. The upper limit is preferably 3% by mass, more preferably 1% by mass, and most preferably 0.6% by mass. The optimum content of the sensitizer is about 0.5% by mass. When the content of the sensitizer is 0.1% by mass or less, the photorefractive property is lowered. When the content of the sensitizer is more than 3% by mass, the concentration of the charge transfer complex by the sensitizer is increased, leading to an increase in light absorption and a significant decrease in light transmittance.
(Nonlinear optical dye)
The nonlinear optical dye is a donor-acceptor type molecule exhibiting second-order nonlinear optical characteristics, that is, a material whose refractive index changes with an electric field (second-order nonlinear optical material). Specifically, [[4- (hexahydro-1H-azepin-1-yl) phenyl] methylene] propanedinitrile (7-DCST), 4-piperidinobenzylidene-malononitrile (PDCST), their corresponding fluorine (Shown by the following structural formula),

2,5-dimethyl-4- (p-nitrophenylazo) anisole (DMNPAA), 4-amino-4'-nitroazobenzene (ANAB), s-(-)-1- (4-nitrophenyl) -2- Pyrrolidine-methanol (NPP), 4- (diethylamino)-(E) -β-nitrostyrene (DEANST), (diethylamino) benzaldehyde diphenylhydrazone (DEH), 2- [4-bis (2-methoxyethyl) amino] Aminocyano such as benzylidenemalononitrile (AODCST), TDDCST, 2-dicyanomethylene-3-cyano-5,5-dimethyl-4- (4′-dihexylaminophenyl) -2,5-dihydrofuran (DCDHF-6) Examples include styrenes. Preferred non-linear optical dyes are 7-DCST, PDCST, and their corresponding fluorinated compounds with chemical structural formulas, and PDCST is most preferred. As the nonlinear optical dye, one type may be used alone, or two or more types may be used in combination.

The content of the nonlinear optical dye is preferably 15% by mass, more preferably 25% by mass, and more preferably 50% by mass as the lower limit with respect to 100% by mass of the photorefractive material composition. % By mass is more preferred, and 30% by mass is most preferred. If the content of the nonlinear optical dye is less than 20% by mass, the diffraction efficiency and gain coefficient necessary for the photorefractive effect may not be obtained. If the content of the nonlinear optical dye is more than 50% by mass, an imbalance may occur in the amount ratio with other components, which may adversely affect the design of the photorefractive composite.
(Plasticizer)
The plasticizer serves to lower the glass transition temperature of the matrix. Preferred plasticizers are ethylcarbazole (ECz) and (2,4,6-trimethylphenyl) diphenylamine (TAA) represented by the following structural formula:

Carbazoylethyl propionate (CzEPA), triphenylamine (TPA), benzylbutyl phthalate (BBP), dicyclohexyl phthalate (DCP) tricresyl phosphate (TCP), diphenyl phthalate (DPP), N-methyl-1- N-alkyl-1-pyrrolidones such as pyrrolidone, N-octyl-1-pyrrolidone, N-dodecyl-1-pyrrolidone, and 2- (1,2-cyclohexanedicarboximido) ethyl propionate (AX22), 2 -(1,2-cyclohexanedicarboximido) ethyl butyrate, 2- (1,2-cyclohexanedicarboximido) ethyl benzoate, 2- (1,2-cyclohexanedicarboximido) ethyl acrylate, 2- (phthalimide) Examples thereof include imide compounds such as ethyl propionate (AX23). A more preferred plasticizer is TAA. A plasticizer may be used alone or in combination of two or more.

The content of the plasticizer is preferably 10% by mass, more preferably 15% by mass, and more preferably 40% by mass, and 30% by mass as the lower limit with respect to 100% by mass of the photorefractive material composition. % Is more preferable, and 20% by mass is most preferable. When the content of the plasticizer is less than 10% by mass, the glass transition temperature of the photorefractive polymer does not decrease, and the diffraction efficiency and gain coefficient necessary for the photorefractive effect may not be obtained. When the content of the plasticizer is more than 40% by mass, an unbalance is generated in the amount ratio with other components, which may adversely affect the design of the photorefractive composite.
(N-type organic semiconductor)
N-type organic semiconductors include Me-PTC, PTCDA, 3,4,9,10-perylenetetracarboxylic acid derivative, naphthalenecarboxylic anhydride, naphthalenecarboxylic acid diimide, tetracyanoquinodimethane (TCNQ), TCE, benzoquinone 2,6-naphthoquinone, DDQ, p-fluoranil, tetrachlorodiphenoquinone, nickel bisdiphenylglyoxime, Alq ₃ , BCP, PBD and the like, and Alq ₃ is particularly preferable. N-type organic semiconductors may be used alone or in combination of two or more.

The content of the N-type organic semiconductor is preferably 0.1% by mass, more preferably 0.3% by mass, more preferably 0.5% by mass, and more preferably 0.5% by mass with respect to 100% by mass of the photorefractive material composition. 3 mass% is preferable, 2 mass% is more preferable, and 1.5 mass% is further more preferable. The preferred content of the N-type organic semiconductor (e.g., Alq ₃ ) is 0.5 to 1.5% by mass, more preferably 0.6 to 1.4% by mass, further preferably 0.7 to 1.3% by mass, particularly preferably 0.8 to 1.2% by mass, Preferably it is 0.9-1.1 mass%. When the content of the N-type organic semiconductor is in the above range, diffraction efficiency, response speed, and dielectric breakdown resistance are improved.

  The thickness of the photorefractive material composition 5 is preferably 20 to 200 μm, and more preferably 50 to 100 μm. If the thickness is less than 20 μm, it is difficult to satisfy the Bragg diffraction condition, and if it exceeds 200 μm, the applied voltage may increase and the light absorption may increase.

  FIG. 1 is a schematic cross-sectional view of a photorefractive polymer element 1 according to an embodiment of the present invention. The photorefractive polymer element 1 of the present embodiment is formed on a pair of insulating substrates 2 and 2 arranged substantially parallel to each other as shown in FIG. 1 and on the inner surfaces 2a and 2a of the pair of insulating substrates 2 and 2, respectively. The transparent electrodes 3, 3, the dark current control layers 4, 4 formed on the inner surface 3 a of each transparent electrode 3, and the transparent electrodes 3 and the dark current control layers 4 between the pair of insulating substrates 2, 2. The photorefractive material composition 5 is interposed between the photorefractive material composition 5 and a spacer 6 provided around the photorefractive material composition 5.

  FIG. 1 shows the dark current control layers 4 and 4 in order to realize an improvement in performance. However, since the photorefractive polymer element of the present invention has a greatly reduced dark current, Either one of the dark current control layers 4 and 4 can be omitted. In addition, depending on the intended use, both the dark current control layers 4 and 4 can be omitted for the sake of simplification of manufacturing at the expense of some characteristic deterioration.

  Each insulating substrate 2 and each transparent electrode 3 formed on the inner surface 2 a of each insulating substrate 2 constitute a pair of transparent electrode substrates 7, 7 arranged in parallel to each other. The insulating substrate 2 is not particularly limited as long as it is optically transparent. Specific examples of the insulating substrate 2 include soda-lime glass, silica glass, borosilicate glass, gallium nitride, gallium arsenide, sapphire, and quartz. Examples thereof include glass, polyethylene terephthalate, and polycarbonate, and a composite substrate in which these are appropriately combined.

  Each transparent electrode 3 formed on the inner surface 2a of each insulating substrate 2 is a conductive film, and can be selected from a metal oxide film, a metal film, an organic film, and the like. In this embodiment, indium tin oxide (ITO) is selected as the transparent electrode 3 and configured as an ITO electrode, but the present invention is not limited to this. Other specific examples of the transparent electrode 3 include tin oxide, zinc oxide, polythiophene, gold, silver, platinum, copper, aluminum, polyaniline, lithium, magnesium, magnesium-silver mixture, magnesium-indium mixture, aluminum-lithium alloy, carbon What consists of carbon, such as nanofiber, and those combination is mentioned.

  The spacer 6 is not limited as long as it can maintain the thickness of the photorefractive material composition. From the viewpoint of chemical resistance and heat resistance, for example, a fluorine resin such as polyimide, polytetrafluoroethylene (PTFE), or PFA is used. Is preferred.

  As described above, the dark current control layer 4 is preferably formed on both of the transparent electrode substrates 7 in terms of characteristics. However, the dark current control layer 4 is formed only on one of the transparent electrode substrates depending on the performance to be exhibited. However, it may not be formed depending on the required performance.

  Various types of dark current control layer 4 can be selected. A single monolayer or a plurality of monolayers formed on the surface 3 a of the ITO electrode 3 is suitable for the dark current control layer 4. The single-layer monomolecular film or the multi-layer monolayers may not necessarily be formed uniformly over the entire surface 3 a of the ITO electrode 3. In other words, even if the surface 3a of the ITO electrode 3 has a region where a single-layer monomolecular film or a multi-layer monomolecular film is not partially formed, or even if there is uneven thickness, an improvement effect is recognized. It was. For example, a part of the surface 3a of the ITO electrode 3 may be a monomolecular film, and the other part of the surface 3a may be a multi-layer monomolecular film. A plurality of regions of a single-layer monomolecular film may be formed on the surface 3a of the ITO electrode 3, and a plurality of regions of a monolayer of a plurality of layers may be formed therewith.

  As the dark current control layer 4, a self-assembled monolayer (SAM) that self-assembles on the ITO electrode 3 can be used. The single-layer monomolecular film or the plurality of monolayers are not limited to self-assembled monolayers. The self-assembled monomolecular film in one preferred embodiment is formed by chemically modifying the inner surface 3a of the transparent electrode 3 with a silane compound. Such a silane compound is not limited, and 3-aminopropyltrimethoxysilane (APTMS) is most preferable. Examples of other self-assembled monolayers include trichlorosilanes and dimethylchlorosilanes.

  The self-assembled monomolecular film is a monomolecular film formed by self-assembly or self-assembly, and is a molecular aggregate formed on a solid surface in the process of chemical adsorption of organic molecules. Due to the interaction between adsorbed molecules, the constituent molecules of the aggregate are densely assembled. As a result, a structure having a highly regular molecular orientation and molecular arrangement is spontaneously formed.

  In order to form a self-assembled monomolecular film on the transparent electrode 3, various methods such as an acid-base reaction, a silane coupling reaction, and a hydrogen-terminated silicon surface can be used.

  Next, a method for manufacturing the photorefractive polymer element 1 will be described. In addition, the method demonstrated here is an illustration, It can also manufacture with another method and conditions. The photorefractive polymer element 1 of the present embodiment includes a dissolving step for dissolving the photorefractive polymer in a solvent, a solvent distilling step for distilling off the solvent, and a sandwich type device forming step for forming a sandwich type device. Manufactured by a manufacturing method.

  In the dissolving step, a photorefractive polymer, a nonlinear optical dye, a plasticizer, and a sensitizer are dissolved in a solvent at a predetermined ratio. The solvent is not particularly limited, and tetrahydrofuran (THF), chloroform, N-methylpyrrolidone (NMP), dimethylformamide and the like are used, and THF is preferable. The dissolution temperature may be about room temperature. The solution may be stirred as necessary. The method of stirring this solution is not limited, and for example, it is performed by a method using a stirrer chip or the like.

  In the solvent evaporation step, the solvent is removed. The method for removing the solvent is not particularly limited, and for example, a cast film may be obtained. Specifically, after an ITO electrode is formed on an insulating substrate to obtain an ITO electrode substrate, a SAM that is a dark current control layer is formed on the surface of the ITO electrode substrate as necessary to form a SAM-coated ITO electrode substrate. Can be obtained. SAM coating is optional. Then, a solution in which each component is dissolved is cast on the surface, and then the solvent is evaporated at room temperature, followed by natural drying overnight, followed by vacuum drying at about 80 ° C. for 12 hours. Evaporate.

  In the sandwich-type device manufacturing process, after the solvent is distilled off, spacers (polyimide, thickness: 50 μm) are placed in the four corners, and then another SAM-coated ITO electrode substrate that has been manufactured separately is placed on top. Then, pressure is applied with a vacuum press machine while applying a temperature to produce a sandwich type photorefractive element. The thickness of the photorefractive material composition in the device is preferably 50 to 100 μm. If it is less than 50 μm, it is difficult to satisfy the Bragg diffraction condition, and if it exceeds 100 μm, the applied voltage may increase or the absorption may increase.

  The photorefractive element obtained by the above manufacturing method is, for example, recording / reproduction of moving images such as video images, real-time holograms, wavefront and phase manipulation of light, pattern recognition, optical amplification, nonlinear optical information processing, super multiplexing It can be used for hologram recording, high-density optical data recording, optical correlation systems, optical computers, and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to an Example.

The diffraction efficiency and response time were measured according to the following description.
(Diffraction efficiency measurement)
The diffraction efficiency (%) was measured by a four-wave mixing method with an electric field applied to the photorefractive polymer element. A 532 nm DPSS laser was used for the measurement. This does not limit the laser, and 561 nm, 594 nm, 607 nm laser, 632.8 nm He-Ne laser, 830 nm laser diode, or the like can also be used. In addition, other lasers can be used if measurement is possible. The diffraction efficiency (%) generated by the photorefractive effect, that is, the refractive index change Δn can be evaluated from the Bragg diffraction intensity measurement (diffraction efficiency measurement). The diffraction efficiency can be measured by making low-power probe light incident on the sample film in which the refractive index grating is generated by the writing light and measuring the intensity of light diffracted by the refractive index grating. . Here, the normalized diffraction efficiency η _norm is shown and evaluated by the following equation (1). The diffraction efficiency is measured by tilting the photorefractive polymer element so that the angle θ between the normal H of the photorefractive polymer element (Sample) and the bisector of the two interference beams is 50 °.

I _d : intensity of diffracted light by the refractive index grating, I _t : transmitted light intensity. The internal diffraction efficiency η _int can be related to the magnitude of change in refractive index with respect to p-polarized readout light: Δn as shown in Equation (2) by Kogelnik's coupled wave theory in a thick medium.

Where θ _{1 and} θ ₂ are the internal angles of the beam 1 and beam 2 with respect to the sample normal, respectively, and K is

It is. Here, d is the film thickness, and λ is the readout wavelength.

The refractive index change magnitude Δn can be evaluated from the internal diffraction efficiency η _int . The intensity I _d of the diffracted light, fast Bench Meter (e.g., Agilent; 34411-type digital multimeter) used, the transmitted light intensity I _t is fast Bench Meter (e.g. manufactured by Agilent simultaneously driven; 34411 type digital multimeter).
(Measure response time)
The response time was calculated by fitting using the Kohlrausch-Williams-Watts (KWW) equation shown in the following equation (4).

Here, η: diffraction efficiency, η ₀ : saturation diffraction efficiency, t: time, τ: response time, β (0 <β ≦ 1): dispersion.
Example 1
Using the photorefractive material composition (PTAA / PDCST / TAA / PCBM / Alq ₃ = 43.5 / 35/20 / 0.5 / 1 wt%), the photorefractive polymer element shown in FIG. 1 was manufactured, and the conditions shown in Table 1 ( The internal diffraction efficiency η, response time τ, sensitivity S and optical gain Γ were determined from the wavelength and intensity of the writing laser beam (external electric field). Sensitivity S is obtained by equation (5), and optical gain Γ is obtained by equation (7). The results of the present invention along with other research results are shown in Table 1 and FIG.

Here, I: light intensity, η _ext : external diffraction efficiency. The external diffraction efficiency is obtained by the following formula (6).

Here, α is an absorption coefficient, d is a film thickness, θ ₁ is an internal angle of the beam 1.

Here, θ _{1 and} θ ₂ are internal angles of the beam 1 and beam 2 with respect to the sample normal, respectively, and I ₁ and I ₂ are transmitted light intensities of the beam 1 and beam 2, respectively.

As shown in Table 1 and FIG. 2, the sensitivity (S = 437) obtained using the photorefractive material composition of the present invention is the highest compared to those reported in the past.
Example 2
Poly (triarylamine) (PTAA) as photoconductive polymer, 4-piperodonobenzylidene malononitrile (PDCST) as nonlinear optical dye, (2,4,6-trimethylphenyl) diphenylamine (TAA) as plasticizer, [6 , 6] -phenyl C ₆₁ butyric acid methyl ester (PCBM) was used. In addition, tris (8-hydroxyquinolinato) aluminum (Alq ₃ ) was used as an electron scavenger. The prepared PR composite materials are PTAA / PDCST / TAA / PCBM (44.5 / 35/20 / 0.5) and PTAA / PDCST / TAA / PCBM / Alq ₃ (43.5 / 35/20 / 0.5 / 1).

These were sandwiched between two ITO substrates chemically modified with 3-aminopropyl-trimethoxysilane, a silane coupling agent, and melt bonded at 160 ° C. The film thickness was adjusted to 50-60 μm using a Teflon (registered trademark) spacer.

  PR (photorefractive) measurement was performed using a DPSS laser (25 mW, 0.534 W / cm; manufactured by Cobolt) with a wavelength of 532 nm as pump light. The diffraction efficiency and its response time were evaluated by the degenerate four-wave mixing method, and the optical gain and its response time were evaluated by the two-wave coupling (TBC) method. Furthermore, the response time of photocurrent was evaluated in order to compare the response of diffraction efficiency and optical gain. Response time was calculated by fitting according to the Kohlrausch-Williams-Watts (KWW) equation.

(1) Improvement of durability against applied electric field by suppressing photocurrent FIG. 3 shows the electric field dependency of dark current depending on the presence or absence of a dark current suppressing layer. As shown in FIG. 3, when the dark current suppression layer is provided, the dark current can be completely removed, so that a high electric field can be applied, and the photocurrent is also suppressed at the same time.

Next, the presence and absence of Alq ₃ are compared (Table 2). From Table 2, it can be seen that the photocurrent with Alq ₃ decreases.

Photorefractive material composition with or without Alq ₃ (PTAA / PDCST / TAA / PCBM ₃ = 44.5 / 35/20 / 0.5 wt% and PTAA / PDCST / TAA / PCBM / Alq ₃ = 43.5 / 35/20 / 0.5 / 1 The photorefractive polymer element shown in FIG. 1 is fabricated using wt%), and the electric field dependence plot of the photocurrent is shown in FIG. The Alq ₃ -free PR composite material passed a photocurrent of 100 μA or more, and dielectric breakdown occurred in an electric field of 40 V / μm. On the other hand, the Alq ₃ containing PR composite material suppressed the photocurrent to about one third and prevented dielectric breakdown up to 80 V / μm. In addition, the photocurrent value was almost constant without increasing above 60 V / μm. By adding Alq ₃ , the photocurrent was greatly suppressed, and the durability against the applied electric field was remarkably improved.

(2) Mechanism for improving performance Next, FIG. 5 shows the measurement results of photocurrent when the content of Alq ₃ is 0.5 mass%, 1 mass%, 1.5 mass%, and 2 mass%. As shown in FIG. 5, when it exceeded 0.5 mass%, the photocurrent began to be suppressed, and with Alq _{3 the} photocurrent was greatly suppressed at 1 mass%. When it exceeded 1 mass%, the photocurrent increased again.

FIG. 6 shows the absorption spectrum of the sample in the presence and absence of 1% by mass of Alq ₃ . The dotted line shows the difference spectrum. From the result of this difference spectrum, it can be seen that broad absorption newly appears by the addition of Alq ₃ . This absorption is undoubtedly observed with PTAA and Alq ₃ forming a charge transfer complex (CT complex).

The mechanism shown in FIG. 7 is considered due to the presence of absorption of this CT complex. In the absence of Alq ₃ , the writing light (hν) excites electrons in the highest occupied orbit (HOMO) of PCBM, and PTAA electrons move to the empty orbit created in HOMO of PCBM. As a result, electron carriers are generated in PCBM and hole carriers are generated in PTAA. Since PTAA is abundant (about 40 wt%) in the composite film, holes move along the external electric field on PTAA and are collected in the dark part to form a spatial electric field. In this way, a large amount of optical carriers are generated via PCBM, and holes move through PTAA with high hole mobility, and a large photocurrent flows.

However, when Alq ₃ is present, the absorption of light by PCBM is in a competitive relationship with the absorption of PTAA and Alq ₃ with a CT complex. Therefore, photocarrier generation via PCBM competes with photocarrier generation via CT complex. As the light absorption of PCBM decreases with the addition of Alq ₃ , the photocarrier generation efficiency via PCBM decreases. As Alq ₃ is added, especially when the added region exceeds 1% by mass, the contribution of carrier generation via the CT complex increases, and the photocurrent starts to increase as shown in FIG.

In summary, the addition of 1% by mass of Alq ₃ can suppress the photocurrent in a well-balanced manner.

Alq ₃ in the present invention forms a CT complex with PTAA, which controls the photocurrent. Alq ₃ added to PATPD in the prior art (Optics Express, 18 (9) 2010, pp9358-9356) acts as an electron trap and is a driving force for the double lattice, and the role of Alq _{3 in} the present invention Are fundamentally different.
(3) PR (photorefractive) by applying a rectangular wave AC electric field
A square wave AC electric field with a frequency of 100 Hz and 0-60 V / μm was applied to the Alq ₃ containing PR composite material. The diffracted light signal is shown in FIG. 8A, and the TBC signal is shown in FIG. 8B.

The diffraction efficiency was 83%, the response time was 860 μs, and the decay time was 105 μs. Since high diffractive efficiency and high response in the order of sub-milliseconds were obtained, 200 fps synchronized with the AC electric field (converted to response time) It can be used as a hologram display driven at 5 ms). Since the decay time is faster than the response, it is expected that a holographic movie with almost no memory property can be produced. As a result of TBC measurement, when one beam signal increased following the AC electric field, the other beam signal decreased. The optical gain is 109 cm ^-1 , the response time is 350 μs, and the decay time is 204 μs, which is higher than the diffracted light signal.
(4) Photocurrent response and photodiffraction response to photoperiodic modulation In order to compare the response of optical diffraction and optical amplification, the response and attenuation of photocurrent were evaluated. The photocurrent response was measured by modulating the beam with a period of 100 Hz using an AO modulator (AOM) under a DC electric field of 60 V / μm (FIG. 9). The measurement results are shown in FIG. The response time was 367 μs and the decay time was 213 μs. This responsivity was almost consistent with that in optical amplification. Therefore, it is considered that the PR response of optical amplification is directly governed by the photoconductive mechanism.

FIG. 11 shows the diffraction response results for periodic light irradiation modulated at 99 Hz using an optical chopper. A 60 V / μm DC electric field remains applied. The response time is 1.1 ms and the decay time is 0.86 ms.
Example 4
Using the same material as in Example 3, the holographic followability of moving images was examined.

  The simultaneous measurement technique of writing and reading shown in FIG. 12 was used to evaluate the two-dimensional holographic display property for moving images. One frame image sent at a video signal speed of 60 fps was overwritten within the frame time (16.6 ms) and played back simultaneously. It works as a smooth 2D holographic display that can be read instantly at the same time as overwriting.

1 Photorefractive polymer element 2 Insulating substrate 3 Transparent electrode (ITO electrode)
4 Dark current control layer (SAM)
5 Photorefractive material composition 6 Spacer 7 Transparent electrode substrate

Claims (4)

Comprising a photorefractive polymer, a sensitizer, a non-linear optical dye, a plasticizer and an N-type organic semiconductor, wherein the photorefractive polymer is poly [bis (4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) der Ri, N-type organic semiconductor is of the formula tris (8-hydroxyquinolinato) aluminum _(Alq 3)
The sensitizer is [6,6] -phenyl C61 butanoic acid methyl ester (PCBM), and the nonlinear optical dye is 4-piperidinobenzylidene-malononitrile (PDCST) of the following formula
And the plasticizer is (2,4,6-trimethylphenyl) diphenylamine (TAA) of the following formula
A photorefractive material composition. A photorefractive polymer element comprising the photorefractive material composition according to claim 1. An insulating substrate, a transparent electrode formed on one side of the insulating substrate, and a photorefractive material composition layer comprising the photorefractive material composition according to claim 1, wherein the photorefractive material composition layer is 2 The photorefractive polymer element according to claim 2, which is sandwiched between two transparent electrodes. The photorefractive polymer element according to claim 3, wherein a dark current control layer is provided between the photorefractive material composition layer and at least one transparent electrode.