JPH1187064A - Photoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve various characteristics of response speed, diffraction efficiency and luminous efficiency through improvement of the charge-mobility by forming a charge transfer layer of an organic compound out of a high molecular liquid crystal material, which has charge transfer ability using hopping conduction and the alignment of which is possible. SOLUTION: A positive electrode 1 of a metal such as Pt having a large work function or ITO or the like having high transparency, a charge transfer layer 2 obtained by dispersing a light emitting material in the organic compound and working as a light emitting layer, a negative electrode 3 consisting of a metal such as Ca, Li having a small work function and Ag or Al are laminated in order on a substrate 4 of transparent glass or the like so as to obtain a single-layer organic EL element as a photoelectric conversion element. At this stage, as a charge transfer layer 2, a high molecular liquid crystal material, which has charge transfer ability with hopping conduction and of which orientation is possible, is used. Degree of charge-transfer is improved by using this material in the aligned condition. As a high molecular liquid crystal material, discotic liquid crystal or rod-like liquid crystal is desirable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion element which separates or combines holes and electrons, and functions by a charge transport layer made of an organic compound.

[0002]

2. Description of the Related Art In a photoelectric conversion element, a charge generation material such as an electrophotographic photoreceptor, an optical sensor, and a photorefractive is excited by light, and carriers are generated by using an electric force such as a bias voltage. Carriers are transferred via a charge transport agent to allow them to function, or carriers are electrically injected into a layer containing a charge transport agent, such as an organic EL device, and holes and electrons are recombined in the light emitting material. To extract light. The transfer of electric charges in these photoelectric conversion elements is performed by hopping, and the hopping process is assisted by thermal vibration of atoms, so that the electric conductivity has a characteristic of increasing with an increase in temperature.

For example, a charge transporting material (hereinafter abbreviated as CTM) is used for an organic photoreceptor as shown in Publication 1 {40th Workshop of the Society of Electrophotography, pp. 39-52}. As aromatic hydrazone compounds,
Triphenylmethane-based compounds and arylamine-based compounds are mainly used. Also, Publication 2 Handbook for Organic Materials with Optical and Electronic Functions, III, 393-406
Page As Asakura Shoten (1995)｝,
Also shown is an optical sensor in which an azo pigment and a hydrazone derivative as a CTM are laminated.

As photorefractive crystals which are considered to be applied to elements for optical computing, barium titanate, lithium niobate, BSO (Bi ₁₂ S
There are inorganic crystals such as iO ₂ 0). On the other hand, as an organic system, the publication 3 @ Japan Hardcopy '9
As shown in Sixth Paper Collection, page 291 (1996)}, a photorefractive polymer in which a charge generating material, a nonlinear optical material, or a charge transporting material is dispersed in a polymer binder has been developed.

[0005] As shown in the above-mentioned Publication 2, the organic EL has an element structure such as a single layer type or a stacked type. However, in order to obtain a high luminous efficiency, a material having a high charge transporting property is being developed. Have been.

[0006]

However, since the CTM used in the conventional organic photoelectric conversion element is a low molecular weight system and is used by being dispersed in a binder resin, the charge transport ability of the material itself is maximized. Can not
For example, an arylamine resin dispersion film (constituent weight ratio of 50 w
t%) is 10 ⁻⁴ to 10 ⁻⁵ (cm).
² / V · sec). In addition, as a polymer system, there is polyvinylcarbazole, but a carbazole group whose charge hops forms a dimer, so that it does not show a large drift mobility (μ),
In the case of organic polysilane, the drift mobility (μ) is 10
^-4 (cm ² / V · sec). On the other hand, the hole mobility of the inorganic substance is, for example, 0.15 for a-Se.
(Cm ² / V · sec), Se-Te (Te 10 wt
%) Shows a large value of 2.75 × 10 ⁻³ (cm ² / V · sec).

That is, although the organic photoelectric conversion element has been put to practical use in an electrophotographic photoreceptor, as described above, the charge mobility is smaller than that of the inorganic type, so that the speeding up of the printer is hindered. In addition, due to the low charge mobility of the organic photoelectric conversion element, the performance of the optical sensor is inferior to that of the inorganic element in terms of response speed, and has not been put to practical use. Similarly, photorefractive causes a problem in diffraction efficiency, and organic EL causes a problem in luminous efficiency. That is, the low charge mobility causes inorganic photoelectric conversion elements to be put to practical use, whereas organic photoelectric conversion elements have not yet come to practical use.

The present invention has been made to solve such a problem, and an object of the present invention is to obtain a photoelectric conversion element having improved characteristics by improving charge mobility.

[0009]

According to a first aspect of the present invention, there is provided a photoelectric conversion element having a charge transport layer, wherein the charge transport layer has a charge transport ability by hopping conduction and has an orientation. It is made of a polymer liquid crystal material that can be used.

A second photoelectric conversion element according to the present invention is the first photoelectric conversion element, wherein the polymer liquid crystal material is a discotic liquid crystal.

In a third photoelectric conversion device according to the present invention, in the second photoelectric conversion device, the discotic liquid crystal is represented by the following general formulas (1) to (3).

[0012]

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[0013]

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[0014]

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[0015] The polymer compound represented by

A fourth photoelectric conversion element according to the present invention is the first photoelectric conversion element, wherein the polymer liquid crystal material is a rod-shaped liquid crystal.

According to a fifth photoelectric conversion element of the present invention, in the fourth photoelectric conversion element, the rod-shaped liquid crystal is represented by the following general formulas (4) to (6).

[0018]

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[0019]

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[0020]

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The compound is a polymer compound represented by the formula:

A sixth photoelectric conversion element according to the present invention is the photoelectric conversion element according to any one of the first to fifth aspects, wherein the charge transport layer has a light emitting material dispersed in a polymer liquid crystal material.

According to a seventh aspect of the present invention, there is provided the photoelectric conversion device according to any one of the first to fifth aspects, further comprising a light emitting layer containing a light emitting material, which is laminated on the charge transport layer.

An eighth photoelectric conversion element according to the present invention is the photoelectric conversion element according to any one of the first to fifth aspects, further comprising a charge generation layer which generates a charge by being stacked on the charge transport layer.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The photoelectric conversion device of the present invention has a charge transporting layer made of a polymer liquid crystal material which has a charge transporting capability by hopping conduction and can be oriented.
The polymer liquid crystal material is used as a charge transport layer in an oriented state, so that it has a charge mobility equivalent to that of an inorganic photoelectric conversion element. Characteristics can be improved. That is, by using a polymer liquid crystal material as a CTM for a charge transport layer that controls charge transport in the photoelectric conversion element, a hopping site (a part of a molecule) as a charge transfer portion in the charge transport layer is oriented, and the charge mobility is reduced. It is possible to improve. In addition, since the charge transport layer is composed of the above-mentioned polymer liquid crystal material having both a CTM capable of high charge transfer and a structural material, there is no need to disperse the material in the binder resin, and the hopping site is diluted. Without being performed, it is possible to obtain characteristics comparable to those of an inorganic photoelectric conversion element.

The polymer liquid crystal material used in the present invention is a high charge transfer polymer liquid crystal, and includes a nematic phase, a smectic phase (SA, SC, SB, SI, SH, etc.) and a column phase (ND, Dh, Dr, Dob etc.), any phase may be used as long as the carrier conduction site is easily oriented to hopping conduction. A discotic liquid crystal may use a Dh phase, and a rod-shaped liquid crystal may use a smectic A phase. preferable. With respect to the orientation, it is not particularly necessary to complete the orientation at the time of manufacturing, and it is sufficient that the orientation is completed at the time of using the device.

As a method of applying the layer containing the polymer liquid crystal to each element substrate, a spin coating method, a spray method, a dipping method, or the like is used. The orientation method is an annealing method,
A rubbing method, an electric field, a magnetic field, and the like can also be used.

The polymer liquid crystal material may be a main-chain type or a side-chain type. Examples of the main-chain type polymer liquid crystal include those having polyester or polyamide in the main chain. Acrylate, polymethacrylate,
Polysiloxane, polyester, polyether, polythioether, polyethylene, polychloroacrylate,
Those having polycyanoacrylate or the like in the main chain can be used.

As the core of the liquid crystal material, a disk or rod is used. As the disc-shaped core of the liquid crystal material, benzene, naphthalene, anthracene, naphthacene, pentacene, phenanthrene, pyrene, chrysene, triphenylene, perylene, coronene, and fluorancene, etc., as neutral molecules containing no heteroatoms, Examples of those containing a hetero atom include acridine, phenothiazine, phthalocyanine, porphyrin, and the like, and those having a charge transfer ability with a skeleton of other tolcene or the like are used. An alkyl chain, an alkoxy chain, or the like having a suitable length that dissolves in a temperature region where the regularity of the arrangement of the above is maintained and exhibits liquid crystallinity is used.

Further, as a material having a charge transporting ability by hopping conduction, as a polymer liquid crystal which is a discotic liquid crystal, a specific main-chain polymer liquid crystal, for example, the above general formula (1) or general formula (2) ) Are used. As the side chain type, for example,
There is one represented by the general formula (3).

The core of the liquid crystal material having a rod shape preferably has a skeleton of naphthalene, anthracene, phenylbenzothiazole or carbazole. Specific examples of the rod-shaped polymer liquid crystal include, for example, those represented by the above general formulas (4) to (6).

The above-mentioned polymer liquid crystals may be used alone, in a mixture or in a copolymer. It is possible to use ordinary polymer compounds as long as their charge transport ability is not lost. In addition, a low-molecular liquid crystal can be used as long as the film strength is not weakened. Preferably, a liquid crystal having a charge transporting ability by hopping conduction is used.

When the charge transport layer of the photoelectric conversion element is formed by dispersing a light-emitting material in the polymer liquid crystal material, it is used as a single-layer organic EL element. In this case, since the charge transporting ability of the charge transporting layer is improved, the luminous efficiency is also increased. Furthermore, since the light emitting material is also oriented and the directivity is obtained, the light emitting efficiency is improved.

Further, the charge transport layer of the photoelectric conversion element is
By stacking a light emitting layer containing a light emitting material, it is used as a stacked organic EL device. In this case, since the charge transporting ability of the charge transporting layer is improved, the luminous efficiency is also increased.

In addition, the charge transport layer of the photoelectric conversion element may include:
By laminating a charge generation layer that generates charges, it is used as a high-speed responsive electrophotographic photoconductor.

[0036]

【Example】

Embodiment 1 FIG. FIG. 1 is a configuration diagram showing a cross-sectional configuration of a single-layer organic EL element which is a photoelectric conversion element according to one embodiment of the present invention. In the figure, 1 is an anode, 2 is a charge transport layer also serving as a light emitting layer, 3 is a cathode, and 4 is a substrate. The anode 1 is generally made of a metal having a large work function, such as Pt, Au, Cu, etc., but ITO having good transparency is preferably used. The charge transport layer 2 also serving as a light emitting layer is a layer having a charge transport ability by hopping conduction and having a light emitting material dispersed in the above-mentioned polymer liquid crystal material capable of alignment. The cathode 3 is made of metal Ca, Li, Mg, or the like having a small work function. However, since the cathode 3 is easily oxidized, it is used after being co-evaporated with Ag or Al. As the substrate 4, glass with good transparency is generally used.

A thiophene hexamer is used as the light emitting material, and is represented by the formula (1) where n = 4 and R = —O
In the polymer liquid crystal material represented by C _m H _{2m + 1} (m = 5), 0.1 was added.
A mixture added so as to have a concentration of 35 wt% was obtained. next,
A coating solution obtained by dissolving the above mixture in a toluene solvent was applied on an ITO transparent electrode serving as an anode 1 provided on a glass plate serving as a substrate 4 by a spin coating method and dried to serve as a light emitting layer having a thickness of about 1 μm. The charge transport layer 2 was formed. Next, Al: Li serving as the cathode 3 is vapor-deposited on the charge transport layer 2 also serving as a light emitting layer, and then annealed at 80 ° C. for 3 minutes to orient the polymer liquid crystal material to obtain a single-layer organic EL device. Was. When a voltage of 3 V was applied between the electrodes of the device, the device emitted light with a high luminance of 100 cd / m ² .

Embodiment 2 FIG. FIG. 2 is a configuration diagram showing a cross-sectional configuration of a stacked organic EL element which is a photoelectric conversion element according to one embodiment of the present invention. In the figure, 1 is an anode, 5 is a charge transporting layer, 6 is a light emitting layer, 3 is a cathode, and 4 is a substrate. If necessary, an electron transporting layer and a buffer layer for protecting electrodes may be provided. A rod-shaped charge transporting polymer liquid crystal material which is a hole transporting material, that is, a polymer liquid crystal material represented by n = 6 and m = 12 in the above general formula (5) is used as the charge transporting material, A 1 μm dry film was applied by spin coating on the anode 1 provided on the plate to form a charge transport layer 5. An aluminum quinolinol (Alq3) complex as a light emitting material is formed thereon by vacuum evaporation to form a light emitting layer 6 having a thickness of 100 nm, and Al: Li is further evaporated to form a cathode 3, which is annealed at 100 ° C. for 3 minutes. The liquid crystal was aligned to obtain a laminated organic EL device. 3 between the electrodes of this element
When V was applied, light was emitted at a high luminance of 90 cd / m ² .

Comparative Example 1 Instead of the polymer liquid crystal used in Example 1 above, a polymer liquid crystal material which does not conduct hopping conduction but can be oriented is represented by the following chemical formula:

[0040]

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A single-layer organic EL device was obtained in the same manner as in Example 1 except that annealing was performed at 100 ° C. for 3 minutes. Even when a voltage was applied between the electrodes as in Example 1, only a slight amount of light was emitted from this device.

Comparative Example 2 Instead of the polymer liquid crystal used in Example 1 above, a polymer liquid crystal material which does not conduct hopping conduction but can be oriented is represented by the following chemical formula:

[0043]

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A single-layer organic EL device was obtained in the same manner as in Example 1 except that annealing was performed at 80 ° C. for 3 minutes. Even when a voltage was applied between the electrodes as in Example 1, only a slight amount of light was emitted from this device.

Comparative Example 3 Instead of the polymer liquid crystal used in Example 2 above, the polymer liquid crystal material used in Comparative Example 1 which does not perform hopping conduction but can be used is used.
A laminated organic EL device was obtained in the same manner as in Example 2 except that annealing was performed at 3 ° C. for 3 minutes. Even when a voltage was applied between the electrodes as in Example 1, only a slight amount of light was emitted from this device.

Comparative Example 4 Instead of the polymer liquid crystal material used in Example 2 above, the polymer liquid crystal used in Comparative Example 2 which does not conduct hopping conduction but can be oriented was used.
A laminated organic EL device was obtained in the same manner as in Example 2 except that the annealing was performed for 3 minutes. Even when a voltage was applied between the electrodes as in Example 1, only a slight amount of light was emitted from this device.

Embodiment 3 FIG. FIG. 3 is a configuration diagram showing a cross-sectional configuration of an electrophotographic photosensitive member that is a photoelectric conversion element according to one embodiment of the present invention. In the figure, 7 is a charge generation layer, 8 is a charge transport layer, and 9 is a conductive substrate. On the aluminum tube as the conductive substrate 9, n = 4 and R = − in the above general formula (1).
A toluene solution of a polymer liquid crystal material represented by OC _m H _{2m + 1} (m = 5) is applied to a dry film thickness of 20 μm,
A cyclohexanone solution in which 50% by weight of metal-free phthalocyanine was dispersed in 50% by weight of polycarbonate was applied thereon by dipping to form a charge generating layer 7, which was then annealed at 80 ° C. for 1 hour to align the polymer liquid crystal. A photoreceptor was obtained. This photoconductor is positively charged,
When a printing test was performed, a clear image was obtained. The light sensitivity (half-exposure amount) was 1 μJ / cm ² .

The photoelectric conversion element according to the present invention is applied to, for example, an optical sensor or a photorefractive element shown in the above embodiment.

[0049]

According to the first photoelectric conversion element of the present invention,
In the photoelectric conversion element provided with the charge transport layer, if the charge transport layer is made of a polymer liquid crystal material having a charge transport ability by hopping conduction and capable of alignment, there is an effect that characteristics are improved.

According to the second photoelectric conversion element of the present invention, in the first photoelectric conversion element, if the polymer liquid crystal material is a discotic liquid crystal, the effect is that the characteristics are improved.

According to the third photoelectric conversion element of the present invention, in the second photoelectric conversion element, if the discotic liquid crystal is a polymer compound represented by the above general formulas (1) to (3), This has the effect of improving the characteristics.

According to the fourth photoelectric conversion element of the present invention, in the case of the first photoelectric conversion element, if the polymer liquid crystal material is a rod-shaped liquid crystal, there is an effect that the characteristics are improved.

According to the fifth photoelectric conversion element of the present invention, in the fourth photoelectric conversion element, if the rod-shaped liquid crystal is a polymer compound represented by the above general formulas (4) to (6), This has the effect of improving the characteristics.

According to the sixth photoelectric conversion element of the present invention, in any one of the first to fifth photoelectric conversion elements described above, if the charge transport layer is formed by dispersing a light emitting material in a polymer liquid crystal material, There is an effect that an organic EL element having excellent luminous efficiency can be obtained.

According to the seventh photoelectric conversion element of the present invention, any one of the above-described first to fifth photoelectric conversion elements provided with a light emitting layer containing a light emitting material laminated on the charge transporting layer. In addition, there is an effect that a stacked organic EL element having excellent luminous efficiency can be obtained.

The eighth photoelectric conversion device of the present invention is characterized in that
In any one of the fifth to fifth photoelectric conversion elements, an element having a charge generation layer that generates charges by being stacked on the charge transport layer has an effect that a high-speed responsive electrophotographic photoconductor can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a cross-sectional configuration of a single-layer organic EL element which is a photoelectric conversion element according to one embodiment of the present invention.

FIG. 2 is a configuration diagram showing a cross-sectional configuration of a stacked organic EL element that is a photoelectric conversion element according to one embodiment of the present invention.

FIG. 3 is a configuration diagram illustrating a cross-sectional configuration of an electrophotographic photosensitive member that is a photoelectric conversion element according to an embodiment of the present invention.

[Explanation of symbols]

2 charge transport layer, 5 charge transport layer, 6 light emitting layer, 7 charge generation layer, 8 charge transport layer.

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C08G77 / 14 C08G77 / 14 C08L101 / 12 C08L101 / 12 C09K 19/38 C09K 19/38

Claims (8)

[Claims] 1. A photoelectric conversion device provided with a charge transport layer, wherein the charge transport layer is made of a polymer liquid crystal material having charge transport ability by hopping conduction and capable of alignment. element. 2. The photoelectric conversion device according to claim 1, wherein the polymer liquid crystal material is a discotic liquid crystal. 3. The discotic liquid crystal according to the following general formula (1)
~ (3) Embedded image Embedded image The photoelectric conversion device according to claim 2, wherein the photoelectric conversion device is a polymer compound represented by the following formula: 4. The photoelectric conversion device according to claim 1, wherein the polymer liquid crystal material is a rod-shaped liquid crystal. 5. The rod-shaped liquid crystal according to the following general formula (4)
(6) Embedded image Embedded image The photoelectric conversion device according to claim 4, wherein the photoelectric conversion device is a polymer compound represented by the following formula: 6. The photoelectric conversion device according to claim 1, wherein the charge transport layer is formed by dispersing a light emitting material in a polymer liquid crystal material. 7. The photoelectric conversion element according to claim 1, further comprising a light emitting layer laminated on the charge transport layer and containing a light emitting material. 8. The photoelectric conversion device according to claim 1, further comprising a charge generation layer that generates a charge by being stacked on the charge transport layer.