Exposure head and electrophotographic device

Abstract

The present disclosure provides a technique for achieving exposure by light having a high degree of matching with respect to sensitivity characteristics of a photoreceptor. An exposure head (12) of an electrophotographic device (1) has a plurality light-emitting elements lined up in a first direction (X), and each light-emitting element has a light-emitting layer containing semiconductor particles that emit incoherent light. The emission peak wavelength of the light-emitting layer is within the sensitivity spectrum of the photoreceptor (10), and the full width at half maximum of the emission peak wavelength is 25% or more with respect to the full width at half maximum of the sensitivity spectrum.

Description

Exposure head and electrophotographic device

[0001] The present disclosure relates to an exposure head and an electrophotographic apparatus.

[0002] Copiers, printers, and other devices that utilize the electrophotographic process are collectively referred to as electrophotographic devices. For the purposes of forming full-color images and high-speed printing, electrophotographic devices employ a configuration equipped with multiple electrophotographic photoreceptors, known as an inline or tandem system. The inline system (tandem system) is an electrophotographic device configuration in which each toner color has its own configuration for achieving the process from forming an electrostatic latent image by exposure to transferring a toner image. Conventional electrophotographic devices use a laser scanning light source device consisting of a laser light source and a polygon mirror as their exposure device. However, inline electrophotographic devices equipped with a laser scanning light source device still need further consideration in terms of miniaturization and quietness.

[0003] An exposure head arranged for each electrophotographic photosensitive member is known as an exposure device for an in-line electrophotographic device that can replace a laser scanning light source device and achieve miniaturization and quietness. The exposure head is a light source device for exposing an electrophotographic photosensitive member to light, in which a plurality of small light sources (e.g., light-emitting elements made of organic light-emitting diodes (OLEDs) or inorganic light-emitting diodes (LEDs)) are arranged along the rotation axis direction on a substrate arranged on the outer periphery of the electrophotographic photosensitive member along the rotation axis direction (see, for example, Patent Documents 1 and 2).

[0004] Further, an exposure head for an electrophotographic device is known in which a plurality of (n pieces, n≧2) OLEDs and a plurality of ball lenses are arranged in the circumferential direction on a curved substrate that is arranged along the outer peripheral surface of an electrophotographic photosensitive member, and the light emitted from each OLED is all converged toward a single point in the circumferential direction of the electrophotographic photosensitive member (see, for example, Patent Document 3).

[0005] Japanese Patent Application Publication No. 11-198433 Japanese Patent Application Publication No. 2001-1566 Japanese Patent Application Publication No. 2005-047011

[0006] The exposure head using organic electroluminescence (OLED) light-emitting elements described in Patent Document 1 and the exposure head using LEDs described in Patent Document 2 have difficulty in achieving the same small spot size and high irradiance as laser scanning light source devices using conventional laser light sources. Therefore, there is a problem that it is difficult to achieve high resolution in printed images. Furthermore, the exposure head using OLEDs described in Patent Document 1 has a problem in that the light source has a short lifespan.

[0007] The exposure head described in Patent Document 3 achieves sufficient irradiance by concentrating light from multiple circumferentially arranged light sources (OLEDs) into a single circumferential spot. However, in electrophotographic devices that require high-speed, high-resolution image printing, it is difficult to achieve alignment of the exposure head so that the light from multiple OLEDs is concentrated into a single circumferential spot and such an optical system is aligned along the rotation axis. Furthermore, such an exposure head requires high parallelism with the rotation axis of the electrophotographic photosensitive member, which requires extremely high machining precision. Furthermore, as described below, incoherent light emitted from OLEDs or LEDs is difficult to achieve by narrowing the spot size because the size of the irradiation area is substantially limited to or greater than the element size, unlike coherent laser light.

[0008] Furthermore, the light-emitting elements of conventional exposure heads in electrophotographic devices emit light at wavelengths determined by the materials of their light-emitting layers. Therefore, in order to control the emission wavelengths of the light-emitting elements of conventional exposure heads, it is necessary to select materials for the light-emitting layers from among those that are changeable, making it difficult to arbitrarily and freely control the emission wavelengths of the light-emitting elements. Therefore, there is still room for improvement in terms of achieving exposure in a wavelength range that matches the sensitivity characteristics of an electrophotographic photosensitive member.

[0009] Furthermore, in order to achieve high-speed printing in an electrophotographic apparatus, it is necessary to have a modulation speed of the exposure light source that is sufficiently high corresponding to the printing speed. When an OLED is used as the exposure light source, it is difficult to obtain a modulation speed equivalent to that of a conventional laser light source. As such, the conventional technology leaves room for further study from the perspective of realizing high-speed modulation of the exposure light source that enables high-speed printing in an electrophotographic apparatus.

[0010] Furthermore, in order to achieve high-resolution printing in an electrophotographic device, it is necessary to minimize the physical size of the light-emitting elements arranged in the exposure head and to arrange the light-emitting elements at a narrow pitch. In principle, this is not a problem in electrophotographic devices that use conventional laser scanning, but in electrophotographic devices that use conventional exposure heads, there is still room for improvement in terms of arranging a large number of light-emitting elements on a substrate at high density and with each light-emitting element connected to a driver.

[0011] A first object of one aspect of the present disclosure is to provide a technique for realizing exposure to light having a high degree of agreement with the sensitivity characteristics of an electrophotographic photosensitive member in an electrophotographic apparatus.

[0012] A second object of one embodiment of the present disclosure is to provide a technology for realizing high-speed modulation of a light source for exposure, which enables high-speed printing in an electrophotographic apparatus.

[0013] Furthermore, a third object of one aspect of the present disclosure is to provide a technology for manufacturing an exposure head of an electrophotographic device in which a large number of light-emitting elements are densely mounted on a substrate and integrally connected to a driving driver.

[0014] In order to solve at least the first problem described above, an exposure head according to one aspect of the present disclosure is an exposure head arranged opposite to the surface of an electrophotographic photosensitive member, and includes a plurality of light-emitting elements arranged side by side in a first direction, and emitting light corresponding to an electrostatic latent image to be formed on the surface of the electrophotographic photosensitive member in a second direction intersecting the first direction, and each of the plurality of light-emitting elements is configured such that a first electrode, a light-emitting layer containing semiconductor particles that emit incoherent light, and a second electrode are stacked in this order in the second direction, and the light-emitting layer has an emission peak wavelength within the sensitivity spectrum of the electrophotographic photosensitive member, and the ratio of the full width at half maximum of the emission peak wavelength of the light-emitting layer to the full width at half maximum of the sensitivity spectrum of the electrophotographic photosensitive member is 25% or more.

[0015] Furthermore, in order to solve at least the first problem described above, an electrophotographic apparatus according to one aspect of the present disclosure includes an electrophotographic photosensitive member, a charging device that charges the electrophotographic photosensitive member, the above-mentioned exposure head that irradiates the charged electrophotographic photosensitive member with light to form an electrostatic latent image, a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photosensitive member with toner, a transfer device that transfers the toner image formed on the surface of the electrophotographic photosensitive member onto a recording medium, and a fixing device that fixes the toner image transferred onto the recording medium to the recording medium.

[0016] According to one aspect of the present disclosure, it is possible to provide a technique for realizing exposure to light that has a high degree of agreement with the sensitivity characteristics of an electrophotographic photosensitive member in an electrophotographic apparatus.

[0017] FIG. 1 is a diagram schematically illustrating a configuration of an electrophotographic device according to embodiment 1 of the present disclosure. FIG. 2 is a perspective view schematically illustrating a configuration of an exposure head according to embodiment 1 of the present disclosure. FIG. 3 is a diagram schematically illustrating an example of the arrangement of light sources in an exposure head according to embodiment 1 of the present disclosure. FIG. 4 is a diagram schematically illustrating a cross-sectional structure of a plurality of light sources (light-emitting elements) formed on a substrate in an exposure head according to embodiment 1 of the present disclosure. FIG. 5 is a diagram illustrating an example of the particle size and band gap energy of semiconductor particles according to the present disclosure. FIG. 6 is a diagram for explaining the full width at half maximum of the emission peak wavelength of a light-emitting layer according to embodiment 1 of the present disclosure. FIG. 7 is a flowchart illustrating an example of a manufacturing method for a light-emitting element according to embodiment 2 of the present disclosure. FIG. 8 is a diagram schematically illustrating a layer structure of a light-emitting element according to embodiment 3 of the present disclosure. FIG. 9 is a diagram schematically illustrating a layer structure of a light-emitting element according to embodiment 4 of the present disclosure. FIG. 10 is a diagram schematically illustrating a layer structure of a light-emitting element according to embodiment 5 of the present disclosure. FIG. 11 is a diagram schematically illustrating a layer structure of a light-emitting element according to embodiment 6 of the present disclosure.

[0018] 1 is a diagram schematically illustrating the configuration of an electrophotographic device according to embodiment 1 of the present disclosure. In the diagram of the electrophotographic device, the color of the toner (cyan (C), magenta (M), yellow (Y), and black (K)) may be displayed after the reference numeral to indicate that the configuration corresponds to a specific toner.

[0019] As shown in FIG. 1 , the electrophotographic apparatus 1 includes an electrophotographic photoreceptor 10, a charging device 11, an exposure head 12, a developing device 13, a transfer device 14, a conveying device 15, and a fixing device 16. The electrophotographic apparatus 1 is a full-color image-producing electrophotographic apparatus capable of forming toner images of each color, cyan (C), magenta (M), yellow (Y), and black (K). The electrophotographic apparatus 1 is also an in-line electrophotographic apparatus having four sets of the electrophotographic photoreceptor 10, the charging device 11, the exposure head 12, the developing device 13, and the transfer device 14. Each set is arranged along the conveying direction of a recording medium 17, and is configured to form a toner image of each color.

[0020] The electrophotographic photoreceptor 10 is drum-shaped and has a photosensitive layer formed on the outer peripheral wall surface. The photosensitive layer is made of, for example, an organic photoconductor (OPC) material. Various known photosensitive materials for electrophotographic photoreceptors can be used as the material for the photosensitive layer of the electrophotographic photoreceptor 10. The sensitivity of the electrophotographic photoreceptor will be described in more detail later.

[0021] The charging device 11 charges the electrophotographic photoreceptor 10 before exposure and adjusts the potential of the photosensitive layer. The charging device 11 is, for example, a corona discharge charging device that charges the electrophotographic photoreceptor 10 by corona discharge, but may also be another charging device such as a charging roller.

[0022] The exposure head 12 is disposed opposite the surface of the electrophotographic photosensitive member 10. The exposure head 12 will be described in more detail later.

[0023] The developing device 13 has, for example, a toner container that stores toner of each color, and a developing roller that is rotatably disposed at the opening of the toner container. The toner carried by the developing roller is transferred from the developing roller to the surface of the electrophotographic photoreceptor 10 in accordance with the electrostatic latent image on the electrophotographic photoreceptor 10, and a toner image in accordance with the electrostatic latent image is formed on the surface of the electrophotographic photoreceptor 10.

[0024] The transfer device 14 forms an electric field so as to transfer the toner image on the surface of the electrophotographic photosensitive member 10 to a recording medium 17. The transfer device 14 is, for example, a corona discharge charging device.

[0025] The conveying device 15 conveys the recording medium 17 toward the fixing device 16 while sandwiching it with each of the four electrophotographic photosensitive members 10 at a transfer nip portion (a portion where the transfer device 14 faces the electrophotographic photosensitive members 10). The conveying device 15 has an endless conveying belt 151, and conveying rollers 152 and 153 that stretch the conveying belt 151 and rotate in a direction toward the fixing device 16. The transfer device 14 is disposed inside the endless track formed by the conveying belt 151, and applies a voltage to the electrophotographic photosensitive members 10 via the conveying belt 151.

[0026] The fixing device 16 is composed of, for example, a heating roller 161 and a pressure roller 162. The heating roller 161 and the pressure roller 162 heat and pressurize a recording medium carrying an unfixed toner image introduced into the portion where they face each other (a fixing nip portion), thereby melting the toner of the toner image and fixing it to the recording medium 17. In this way, the electrophotographic apparatus 1 forms a full-color image fixed on the recording medium 17.

[0027] The recording medium 17 is a sheet-like member such as plain paper that bears the toner image of the electrophotographic photoreceptor 10 and can be supported as a fixed toner image by the fixing device 16. The recording medium 17 is sequentially transported by the transport device 15 to the transfer nip portions of the four electrophotographic photoreceptors 10. The recording medium 17 bears toner images of specific colors that each electrophotographic photoreceptor 10 has, superimposed on one another.

[0028] Each set of the electrophotographic photosensitive member 10, the charging device 11, the exposure head 12, the developing device 13, and the transfer device 14 may further have other configurations than those described above, as long as the effects of this embodiment can be obtained. Examples of such other configurations include a cleaning device for removing residual toner on the electrophotographic photosensitive member 10 after transfer, and a static eliminator for eliminating electrostatic history of the electrophotographic photosensitive member 10 after transfer. Furthermore, some or all of each set (for example, the electrophotographic photosensitive member 10, the exposure head 12, the developing device 13, and, if necessary, the cleaning device, etc.) may constitute a process cartridge that is integrally held in a specific positional relationship by a holding member.

[0029] [Exposure Head] Figure 2 schematically shows the configuration of the exposure head 12 of this embodiment. The exposure head 12 is arranged so that a substrate 121, a light source 122, and an equal-magnification lens 123 are stacked in this order. Figure 3 also schematically shows an example of the arrangement of the light sources 122 in the exposure head 12 of this embodiment. In this example, multiple light sources 122 are arranged in a row on the substrate 121.

[0030] In the drawing, arrow X indicates a first direction, and arrow Y indicates a second direction. Arrow X is an arrow extending from the plane of FIG. 1 toward the back, and the first direction represented by arrow X is the longitudinal direction of the substrate 121 of the exposure head 12, and in the electrophotographic apparatus 1, it is a direction along the rotation axis of the electrophotographic photosensitive member 10. Arrow Y is an arrow extending from one main surface of the substrate 121 in a direction perpendicular to the main surface, and the second direction represented by arrow Y is the emission direction of light from each light source 122 of the exposure head 12, and is a direction along the optical axis of each light source 122. In the electrophotographic apparatus 1, the second direction is a direction in which the light source 122 of the exposure head 12 faces the electrophotographic photosensitive member 10.

[0031] The substrate 121 is a substrate that extends along the rotation axis direction of the electrophotographic photosensitive member 10. When viewed from above, the shape of the substrate 121 is an elongated rectangle. The substrate 121 is disposed at a position a specific distance away from the outer circumferential surface of the electrophotographic photosensitive member 10 so that the central axis of the shape when viewed from above is aligned with the rotation axis direction of the electrophotographic photosensitive member 10.

[0032] Each light source 122 includes one light-emitting element. Each light-emitting element includes a light-emitting layer that emits light of a wavelength that matches the sensitivity spectrum of the electrophotographic photoreceptor 10, for example, light of any wavelength from visible light to near-infrared (wavelengths of 380 to 2500 nm), or light of any wavelength from red to part of the near-infrared (wavelengths of 620 to 1500 nm). The light source 122 and the light-emitting elements included therein may have the same shape in plan view, for example, a circle, e.g., a perfect circle with a diameter of 10 μm. The configuration of the light source 122 will be described in more detail below.

[0033] In the exposure head 12, a plurality of light sources 122 are arranged in a row in the first direction X on one main surface of the substrate 121. In this manner, the exposure head 12 has a plurality of light sources 122 that emit light in the second direction Y corresponding to an electrostatic latent image to be formed on the surface of the electrophotographic photosensitive member 10. The arrangement of the light sources 122 (light-emitting elements 40) in the exposure head 12 will also be described in detail later.

[0034] The equal-magnification lens 123 condenses the light from the light source 122 to an equal-magnification size on the surface of the electrophotographic photosensitive member 10. That is, the light from the circular light-emitting element having a diameter of 10 μm is condensed onto a circular area having a diameter of 10 μm on the surface of the electrophotographic photosensitive member 10.

[0035] The minimum irradiance per element of the light emitting element of the light source 122 through the equal-magnification lens 123 on the electrophotographic photosensitive member 10 is, for example, 0.10 μW / dot. The irradiance per element of the light emitting element through the equal-magnification lens 123 is measured using an optical power meter installed at approximately the same distance as the irradiation position on the electrophotographic photosensitive member 10.

[0036] Fig. 4 shows a schematic cross-sectional structure of a plurality of light sources 122 (light-emitting elements 40) formed on a substrate 121 in the exposure head 12. As shown in Fig. 4, the exposure head 12 includes a structure in which the substrate 121, a driving transistor layer (hereinafter also referred to as a "driving TFT layer") 20, and a light-emitting element layer 30 are stacked in this order along the second direction. The structure in which the substrate 121 and the driving TFT layer 20 are stacked in the order shown in Fig. 4 is also called an "active matrix substrate."

[0037] The substrate 121 may be, for example, a rigid substrate made of glass, metal, hard resin, or the like, or may be a flexible substrate mainly composed of a resin material such as polyimide. However, from the viewpoint of strictly controlling the size of the exposure pattern formed on the electrophotographic photoreceptor 10, it is preferable that the distance between the electrophotographic photoreceptor 10 and the light source 122 is constant. From this viewpoint, it may be preferable that the substrate 121 is rigid.

[0038] The driving TFT layer 20 includes a buffer layer 21 , semiconductor layers 221 , 222 , and 223 , a first gate insulating film 23 , a gate electrode 24 , a second gate insulating film 25 , a source electrode 261 , a drain electrode 262 , a planarizing layer 27 , and a contact hole 28 .

[0039] The buffer layer 21 overlaps the substrate 121 in the second direction. The buffer layer 21 is a layer that prevents foreign substances such as water or oxygen from penetrating into the driving TFT layer 20 and the light emitting element layer 30 along the second direction. The buffer layer 21 can be composed of, for example, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film of these, and can be produced by a CVD method.

[0040] The semiconductor layers 221, 222, and 223 overlap the buffer layer 21 in the second direction. The semiconductor layers 221, 222, and 223 form a plurality of transistors arranged intermittently along the first direction. Each transistor has, for example, a top-gate structure and is composed of a set of semiconductor films, i.e., a channel region (semiconductor layer 221) and a source region (semiconductor layer 222) and a drain region (semiconductor layer 223) located on either side of the channel region.

[0041] The semiconductor film is made of, for example, low-temperature polysilicon (LTPS), and the source region (semiconductor layer 222) and the drain region (semiconductor layer 223) are semiconductor films doped with impurities such as P (phosphorus).

[0042] The semiconductor film may be an oxide semiconductor (for example, an In—Ga—Zn—O-based semiconductor), and the transistor may have a bottom gate structure.

[0043] The gate first insulating film 23 overlaps the semiconductor layer and the buffer layer 21 in the second direction. The gate electrode 24 overlaps the gate first insulating film 23 in the second direction at a position overlapping with the semiconductor layer 221 (channel region). The gate second insulating film 25 overlaps the gate first insulating film 23 and the gate electrode 24 in the second direction.

[0044] The first gate insulating film 23 and the second gate insulating film 25 are both insulating films made of inorganic materials, similar to the buffer layer 21. The first gate insulating film 23 and the second gate insulating film 25 may have the same composition or different compositions. The gate electrode 24 may be made of a single layer or a multilayer film of a metal. Examples of such metals include aluminum, tungsten, molybdenum, tantalum, chromium, titanium, and copper.

[0045] The source electrode 261 extends along the second direction from a position on the gate second insulating film 25 to a position where it is connected to the semiconductor layer 222 (source region) by passing through the gate first insulating film 23. The drain electrode 262 extends along the second direction from a position on the gate second insulating film 25 to a position where it is connected to the semiconductor layer 223 (drain region) by passing through the gate first insulating film 23. Like the gate electrode 24, the source electrode 261 and the drain electrode 262 can be formed of a metal single layer film or a metal laminate film.

[0046] The planarization layer 27 overlaps in the second direction on the gate second insulating film 25, the source electrode 261, and the drain electrode 262. The planarization layer 27 can be made of a coatable organic material such as polyimide or acrylic.

[0047] The contact hole 28 is a hole that penetrates the planarization layer 27 along the second direction and reaches the drain electrode 262 from the surface of the planarization layer 27. The contact hole 28 is filled with the material of the first electrode 31, which will be described later, and forms a conductive path between the first electrode 31 and the drain electrode 262.

[0048] The light-emitting element layer 30 includes a first electrode 31, a hole transport layer 32, a light-emitting layer 33, an electron transport layer 34, a second electrode 35, and a bank 36. The first electrode 31 overlaps the planarization layer 27 in the second direction and is arranged intermittently in the first direction corresponding to the contact holes 28. The bank 36 is a protrusion having a substantially trapezoidal cross-sectional shape that overlaps the first electrode 31 in the second direction and is arranged across two first electrodes 31 adjacent to each other in the first direction. The hole transport layer 32 overlaps the first electrode 31 and the bank 36 in the second direction, and the light-emitting layer 33 overlaps, in the second direction, a portion of the hole transport layer 32 between adjacent banks 36 in the first direction. The electron transport layer 34 overlaps the light-emitting layer 33 and the hole transport layer 32 in the second direction, and the second electrode 35 overlaps the hole transport layer 32 in the second direction.

[0049] In this embodiment, the first electrode 31 is a layered electrode and an anode. From the viewpoint of enhancing hole injection properties, a material with a relatively high work function (e.g., a material with a work function of 4.5 eV or more) is preferably used as the material for the first electrode 31. Examples of electrode materials with a high work function include Pt (5.65 eV), Ir (5.25 eV), Ni (5.2 eV), Au (5.15 eV), Pd (5.15 eV), and indium tin oxide (In—Sn—O). Examples of electrode materials that reflect visible light include metal materials such as Al, Mg, Li, Ag, Pd, and Cu, as well as alloys of these metal materials (e.g., APC (Ag—Pd—Cu) alloy, etc.). Examples of electrode materials that transmit visible light include thin films of transparent metal oxides (e.g., indium tin oxide, indium zinc oxide (In—Zn—O), indium gallium zinc oxide (In—Ga—Zn—O), etc.), thin films made of metal materials such as Al, Mg, and Ag, and nanowires (NW) made of these metal materials.

[0050] Among transparent metal oxides, indium tin oxide has a relatively high work function of 4.6 to 5.0 eV, and is therefore suitable for use as the material for the first electrode 31. Furthermore, for the purpose of improving the conductivity as an electrode layer or adding a function of reflecting visible light, the first electrode 31 may be a laminate (for example, indium tin oxide / Ag) in which indium tin oxide is formed on the surface of a metal material.

[0051] The hole transport layer 32 is a layer having a function of contributing to the movement of holes, and may be accompanied by a hole injection layer and / or an electron blocking layer.

[0052] The hole injection layer is disposed adjacent to the first electrode 31, for example. The hole injection layer may be composed of a hole transport material and an electron acceptor material. Examples of the hole transport material include organic hole transport materials, such as known triarylamine organic compounds. Examples of the electron acceptor material include organic electron acceptor materials, such as tetracyanoquinodimethane tetrafluoride (TCNQ-4F).

[0053] The hole transport layer 32 may be made of an organic hole transport material, such as a triarylamine-based organic compound. The material of the hole transport layer 32 may be the same as or different from that of the hole injection layer.

[0054] The electron blocking layer may be made of an organic hole transport material, similar to the hole transport layer 32. The material of the electron blocking layer may be the same as or different from that of the hole transport layer 32.

[0055] The light-emitting layer 33 is a layer that emits light of a predetermined color by injection and recombination of carriers consisting of holes and electrons. The light-emitting layer 33 contains semiconductor particles that emit incoherent light by carrier injection. The surfaces of the semiconductor particles may be covered with organic or inorganic ligands. The semiconductor particles may also be dispersed in a matrix.

[0056] The wavelength of light emitted by the light-emitting layer 33 may be any wavelength that can sensitize the electrophotographic photoreceptor 10 to form an electrostatic latent image. The wavelengths of light emitted by different light-emitting layers 33 in the stacking direction may be the same or different within the above-mentioned range. Furthermore, the wavelengths of light emitted by the multiple light sources 122 when viewed in plan may also be the same or different within the above-mentioned range. The light-emitting layer 33 will be described in more detail later.

[0057] The electron transport layer 34 may be made of an electron transport material. Examples of the electron transport material include organic electron transport materials, such as oxadiazole-based compounds and phenanthroline-based compounds. The material of the electron transport layer may include lithium quinoline (Liq) in addition to the electron transport material.

[0058] The light-emitting element layer 30 may further include other layers that contribute to electron transport similar to the electron transport layer 34, and examples of such other layers include a hole-blocking layer and an electron-injecting layer.

[0059] The hole blocking layer may be made of an organic electron transporting material, similar to the electron transporting layer 34. The material of the hole blocking layer may be the same as or different from that of the electron transporting layer 34.

[0060] The electron injection layer may be made of an organic electron transport material, similar to the electron transport layer 34. The material of the electron injection layer may be the same as or different from that of the electron transport layer 34. The electron injection layer may be made of the organic electron transport material doped with a metal material (e.g., Li or Yb).

[0061] In this embodiment, the second electrode 35 is a layered electrode and a cathode. The second electrode 35 is disposed opposite the first electrode 31 in the stacking direction. The second electrode 35 has, for example, electrical conductivity and transparency to visible light. A material with a relatively small work function is preferably used as the material for the second electrode 35, for example, from the viewpoint of enhancing electron injection properties. Examples of electrode materials constituting the second electrode 35 include metal materials such as alkali metals, alkaline earth metals, and Al, alloys containing these, and nanowires (e.g., Ag nanowires). Examples of alloys include an alloy of Mg and Ag, and Al doped with a small amount of Li.

[0062] The banks 36 are arranged so as to separate the individual light sources 122 when viewed in the second direction. The banks 36 may be made of a transparent or colored (e.g., black) resin material. Examples of such resin materials include polyimide and acrylic resin. The banks 36 may be formed, for example, by applying ink containing the resin material and patterning it using photolithography.

[0063] The portion of the light-emitting element layer 30 in the range between the centers of adjacent banks 36 in the first direction in Figure 4 corresponds to the light-emitting element 40 in this embodiment. Note that the layers other than the light-emitting layer 33 that make up the light-emitting element 40 have an electrical function for causing the light-emitting layer 33 to emit light, and are therefore collectively referred to as electrical functional layers. Furthermore, the light-emitting element 40 has a microcavity structure in which the distance between the first electrode 31 and the second electrode 35 in the second direction Y is optimized by the thickness of the layers other than the light-emitting layer 33 (e.g., the hole transport layer 32). In this way, the light-emitting element 40 is configured as a top-emission light-emitting element 40.

[0064] The portions of the driving TFT layer 20 and the light-emitting element layer 30 in the range between the centers of adjacent banks 36 in the first direction in Fig. 4 correspond to the light source 122 in this embodiment. The length of the hole transport layer 32 between adjacent banks 36 in the first direction in Fig. 4 corresponds to the element size S in this embodiment. The distance between one end of each of the hole transport layers 32 in the first direction in Fig. 4 corresponds to the element pitch P in this embodiment.

[0065] In this way, the exposure head 12 has a plurality of light-emitting elements 40 that emit light in the second direction Y that corresponds to an electrostatic latent image to be formed on the surface of the electrophotographic photosensitive member 10. Each of the light-emitting elements 40 is configured such that a first electrode 31, a light-emitting layer 33, and a second electrode 35 are stacked in this order in the second direction.

[0066] The exposure head 12 also has a driving TFT layer 20 that is arranged on the opposite side of the plurality of light-emitting elements 40 in the second direction and causes each of the plurality of light-emitting elements 40 to emit light independently. The driving TFT layer 20 has a source electrode 261, a drain electrode 262, and a planarization layer 27 that is closest to the light-emitting elements 40 in the second direction, and the first electrode 31 of the light-emitting element 40 is electrically coupled to the drain electrode 262 via a contact hole 28 formed in the planarization layer 27. As described above, in this embodiment, a simple exposure head 12 is realized in which external drivers are reduced as much as possible. In the exposure head 12, a large number of light-emitting elements 40 are manufactured integrally on the substrate 121 at high density, with each light-emitting element 40 connected to a driving driver.

[0067] The light-emitting element layer 30 may further include a sealing layer that overlaps the second electrode 35 in the second direction and prevents foreign substances such as water and oxygen from penetrating into the light-emitting element layer 30. The sealing layer may be composed of, for example, two inorganic sealing films and an organic film formed between them.

[0068] [Arrangement of Light-Emitting Elements] In the exposure head 12, the light sources 122 (light-emitting elements 40) are arranged in the first direction X at a density of 600 elements per inch (600 dpi) or more in the first direction X, for example.

[0069] The resolution of electrophotographic devices is generally 600 dpi x 600 dpi, but some devices are known to have higher resolutions such as 1200 dpi x 1200 dpi or 1200 dpi x 2400 dpi. In the exposure head 12, for example, 31,200 dots (31,200 dots in the direction of the rotation axis of the electrophotographic photosensitive member 10) are arranged at a pitch of 10.58 μm to achieve 2400 dpi. In this way, the exposure head 12 is equipped with light-emitting elements having a light-emitting layer, which will be described later, so that the light source 122 can be arranged in the exposure head 12 at a high resolution of 600 dpi or more, and the light source 122 can be arranged at an even higher resolution of 2400 dpi or more.

[0070] Furthermore, the element pitch (P) of the light-emitting elements 40 in the first direction X of the exposure head 12 is preferably small from the viewpoint of realizing high-resolution arrangement of the light-emitting elements 40 in the first direction X. Furthermore, the dot size at 600 dpi is 42.33 μm, the dot size at 1200 dpi is 21.17 μm, and the dot size at 2400 dpi is 10.58 μm. Therefore, from the viewpoint of enabling high-resolution arrangement at 600 dpi, the element pitch P is preferably 43 μm or less. The element pitch P can be determined to be substantially equivalent to the above-mentioned dot size, for example, depending on the desired resolution of the electrophotographic device. For example, the element pitch P is preferably 10 μm or less from the viewpoint of enabling high-resolution arrangement at 2400 dpi, and is preferably 5 μm or less from the viewpoint of enabling high-resolution arrangement at 4800 dpi.

[0071] Furthermore, it is preferable that the ratio S / P of the element size S of the light-emitting elements 40 in the first direction X of the exposure head 12 to the element pitch P is sufficiently large, from the viewpoint of realizing high-resolution exposure through a highly precise arrangement of the light-emitting elements 40 in the electrophotographic apparatus 1. From this viewpoint, the ratio S / P is preferably 0.7 or more, and more preferably 0.8 or more. In the case of the exposure head 12, the ratio S / P is preferably as large as possible within a range that allows the banks 36 to exhibit the function of partitioning the light-emitting elements in the first direction X. For this reason, it is preferable that the element size S is as large as possible within a range that is smaller than the element pitch P.

[0072] In addition, with an exposure head using conventional discrete inorganic LEDs, it is difficult to simultaneously reduce the element pitch P and increase the element size S. When attempting to achieve, for example, 2400 dpi as the element pitch required for high-resolution arrangement, with conventional discrete inorganic LEDs, the ratio S / P is less than 0.5, making it difficult to achieve an S / P ratio of 0.7 or more.

[0073] In the present disclosure, the arrangement of the light-emitting elements 40 can be appropriately set within a range that allows exposure of the electrophotographic photosensitive member. For example, the light-emitting elements 40 may be arranged in a line along the first direction as shown in the figure, or may be arranged in a staggered arrangement extending along the first direction.

[0074] [Light-Emitting Layer] In this embodiment, the light-emitting layer 33 contains semiconductor particles that emit incoherent light. The laser light used for exposure in conventional electrophotographic devices is coherent light generated by stimulated emission from the resonator structure of a laser diode. Coherent light refers to light whose light wave amplitude and phase are consistent, has high temporal and spatial coherence, and is resistant to diffusion. Therefore, with coherent light, the focused beam diameter (spot size) can be reduced to the diffraction limit without having to consider the concept of light source size. A typical example of coherent light is laser light generated by stimulated emission.

[0075] In contrast, the light emitted by the light-emitting layer 33 is incoherent light, similar to that of a typical LED or OLED. Incoherent light, also known as spontaneous emission light, refers to a light wave with random amplitude and phase. Most light other than laser light is incoherent light. The spot size that can be focused with incoherent light is significantly affected by the size of the light source. As is clear from the concept of étendue, with incoherent light, the spot size of the emitted light cannot be made smaller than the size of the light source 122 (more precisely, the size of the light-emitting area of ​​the light source 122) without light loss. If all of the emitted light is to be utilized, the spot size will be equal to or larger than the light source size (element size S). Therefore, the minimum size that can connect all of the light rays emitted from the incoherent light source 122 is the same size as the light source 122. In other words, it is impossible to focus all of the luminous flux emitted from the incoherent light source 122 in an area smaller than the size of the light source 122. Therefore, in order for the light source 122, which is an incoherent light source and has a finite size, to emit light with higher output, the light source size must be increased, and the more emitted light is used, the larger the focused spot size becomes. Therefore, in order to print high-resolution images using electrophotography, it is necessary to achieve both increasing the output of light emitted from each light source and reducing the element size (light-emitting area) of each light-emitting element made up of multiple incoherent light sources to a level that is compatible with the formation of high-resolution images.

[0076] The emission wavelength of the light-emitting layer 33 may be shorter than the emission wavelength represented by the band gap energy of the bulk of the semiconductor. The bulk of the semiconductor means a semiconductor object (e.g., a mass) of a size that is not affected by the quantum size effect. Also, the number of atoms constituting the mass of the semiconductor is 10 ９If the number of atoms is more than 100, the influence of atoms present on the surface or interface of the semiconductor mass is very small. Therefore, a semiconductor mass having such a number of atoms can also be considered a semiconductor bulk. In the case of a particulate (spherical) semiconductor, for example, it is a semiconductor particle with a particle size of more than 100 nm based on the number of atoms. The band gap energy (Eg) of a semiconductor bulk is the band gap energy of the semiconductor particles in that bulk. When semiconductor particles are nanosized (for example, the particle size is sufficiently smaller than 100 nm, preferably 50 nm or less, more preferably 30 nm or less), a quantum level wider than the Eg of the semiconductor bulk is formed (this is also called the "quantum size effect"). The emission wavelength λ (nm) of a semiconductor is expressed by the following formula using the band gap energy Eg (eV): λ = 1240 / Eg. Furthermore, a typical example of the relationship between the particle size and band gap energy of a semiconductor particle is shown in Figure 5.

[0077] Here, a method for producing semiconductor particles will be described. In the present disclosure, there are no particular limitations on the method for producing semiconductor particles of this embodiment, but a chemical synthesis method in which multiple starting materials containing the constituent elements of the product substance are dispersed in a medium and reacted to obtain the target product substance is preferred from the viewpoint of being a simple method and low cost. Examples of chemical synthesis methods include a hot injection method, a sol-gel method (colloid method), a reverse micelle method, a solvothermal method, a molecular precursor method, a hydrothermal synthesis method, and a flux method.

[0078] [Semiconductor Particle Raw Materials] In the semiconductor particle manufacturing method, the semiconductor raw materials for synthesizing the semiconductor particles can be, for example, a Group III metal element raw material containing at least one of aluminum (Al), gallium (Ga), and indium (In), and a Group V element raw material containing at least one of phosphorus (P) and arsenic (As).

[0079] [Method for Producing Semiconductor Particles] The method for producing semiconductor particles according to the present disclosure preferably uses a hot injection method. The hot injection method refers to a method in which a raw material is mixed with a liquid organic solvent heated to a high temperature to grow crystals. In the hot injection method, gallium chloride (GaCl ３) or indium chloride (InCl ３ ) and trimethylsilylphosphine (P[Si(CH ３ ) ３ ] ３ ) or dimethylaminophosphine (P[N(CH ３ ) ２ ] ３ A suitable method is to react a V-group element source such as ZnO, ZnS, ZnCl, ZnO ...

[0080] Compared with vapor phase growth, which is one of the methods for producing semiconductor particles, the hot injection method is an excellent production method in that it allows synthesis at low temperatures, is suitable for mass production because synthesis is performed in a liquid organic solvent, and allows the synthesis of semiconductor microcrystals with relatively excellent crystallinity.

[0081] An example of a method for producing semiconductor particles using the hot injection method is as follows: First, a raw material mixing step is performed in which the above-mentioned Group III metal element raw material, Group V element raw material, and liquid-phase organic solvent are mixed. Next, a reaction step is performed in which the mixed raw materials are heated to synthesize the raw materials. Finally, a recovery step is performed in which the product is cooled and recovered.

[0082] Another example is as follows: First, a reaction and mixing step is performed in which a mixture of a Group III metal element source, a Group V element source, and a liquid organic solvent is poured into a liquid organic solvent heated to a synthesis temperature to cause synthesis. Finally, a recovery step is performed in which the product is cooled and recovered. In the above-mentioned reaction step or reaction and mixing step, the synthesis of semiconductor microcrystals and the synthesis of semiconductor particles are performed simultaneously.

[0083] Here, in the hot injection method, from the viewpoint of producing semiconductor particles having excellent semiconductor microcrystals, it is preferable to carry out the reaction step and the reaction mixing step in a high-pressure environment equal to or higher than atmospheric pressure. Among these, it is more preferable to use an autoclave, since it is possible to carry out reactions at high temperatures and high pressures. Specifically, from the viewpoint described above, it is preferable to carry out the reaction step and the reaction mixing step in the hot injection method in an atmosphere of 0.1 MPa to 30 MPa.

[0084] The effects of the reaction step and reaction mixing step under the high temperature and pressure environment include the suppression of defects due to the improvement of the crystallinity of the semiconductor microcrystals, thereby obtaining semiconductor particles with excellent luminous efficiency.

[0085] The synthesis temperature in the reaction step and reaction mixing step of the hot injection method may be 450°C or lower, and more preferably 400°C or lower. Conventional vapor phase synthesis methods and the like perform synthesis at temperatures exceeding 450°C, whereas the hot injection method of the present disclosure can achieve synthesis at temperatures lower than the vapor phase synthesis methods and the like. Therefore, the hot injection method is industrially superior in terms of easier production.

[0086] The synthesis time in the reaction step and reaction mixing step of the hot injection method may be 24 hours or less, more preferably 18 hours or less, and most preferably 12 hours or less. If the synthesis time exceeds 24 hours, the semiconductor microcrystals may become larger than necessary, and the desired quantum effect may not be obtained.

[0087] Furthermore, the process for producing semiconductor particles is preferably carried out in an atmosphere of an inert gas such as dry nitrogen gas or dry argon gas, from the viewpoint of suppressing side reactions such as oxidation of the semiconductor particles or generation of by-products.

[0088] In the hot injection method, the particle size of the semiconductor particles increases as the reaction time increases, so it is preferable to monitor the size of the core particles of the nanoparticles produced by photoluminescence, light absorption, dynamic light scattering, or the like, from the viewpoint of controlling the particle size of the semiconductor particles to a desired size.

[0089] However, the method for synthesizing semiconductor particles is not limited to the above-mentioned method, and manufacturing methods such as vapor phase growth methods represented by metal organic vapor phase epitaxy (MOVPE method), reverse micelle method which is a liquid phase epitaxy method, and supercritical synthesis method may also be adopted.

[0090] In nanosizing semiconductor particles, the smaller the particle size of the semiconductor particles, the wider the Eg of the semiconductor particles, and both the absorption spectrum and fluorescence spectrum of the semiconductor particles shift to the blue side (shorter wavelength). Since the emission wavelength of the semiconductor particles contained in the light-emitting layer 33 is shorter than the emission wavelength represented by the Eg of the semiconductor bulk, it is not possible to emit light with a wavelength longer than the emission wavelength determined by the Eg of the semiconductor bulk.

[0091] The semiconductor particles having the desired emission wavelength can be determined depending on the semiconductor composition, but from the viewpoint of realizing the desired emission wavelength by shifting the emission wavelength to the shorter wavelength side as described above, it is preferable that the particle size of the semiconductor particles is small to a certain extent. From the viewpoint of fully obtaining the effect of such a shift in the emission wavelength to the shorter wavelength side, the particle size of the semiconductor particles is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less, on a number basis. The particle size of the semiconductor particles may be 2 nm or more from the viewpoint of ease of production or availability, since if it is too small, its production becomes more difficult.

[0092] The particle size of the semiconductor particles based on the number can be measured by, for example, dynamic light scattering or by observation with a transmission electron microscope (TEM). The particle size of the semiconductor particles based on the number can be adjusted by the production conditions of the semiconductor particles (e.g., reaction time, reaction temperature, raw material concentration, reaction pressure, etc.).

[0093] As described above, the emission wavelength of the semiconductor particles that emit incoherent light and are contained in the light-emitting layer 33 shifts to shorter wavelengths as the particle size decreases, and therefore the band gap energy can be controlled by controlling the particle size, and the emission wavelength can be controlled. The emission wavelength of the semiconductor particles can be appropriately determined depending on the wavelength range of the sensitivity of the electrophotographic photosensitive member. Semiconductor particles having a desired emission wavelength depending on the sensitivity of the electrophotographic photosensitive member can be obtained by appropriately selecting semiconductor particles whose emission wavelength shifts to shorter wavelengths as the particle size decreases, and constituting the light-emitting layer 33 with semiconductor particles having a particle size determined by the desired emission wavelength.

[0094] For example, as described above, when the wavelength of light emitted from the light-emitting element 40 is 620 to 1500 nm, the band gap energy of the semiconductor bulk (i.e., the band gap energy of a mass of semiconductor not affected by the quantum size effect) may be 0.50 eV or more and 2.00 eV or less, and the particle size of the semiconductor particles based on the number may be 50 nm or less. The Eg of the semiconductor particles or bulk can be measured by the PL (photoluminescence) method. As described above, the Eg of the semiconductor particles can be adjusted by the type and particle size of the semiconductor.

[0095] Furthermore, from the viewpoint of increasing the speed of the electrophotographic process, it is preferable that the fluorescence lifetime of the semiconductor particles in the light-emitting layer 33 be sufficiently short. From this viewpoint, the fluorescence lifetime of the semiconductor particles may be sufficient as long as it allows for exposure for high-speed printing in an electrophotographic device, and may be, for example, 50 nanoseconds or less, 20 nanoseconds or less, preferably 10 nanoseconds or less, and more preferably 5 nanoseconds or less. The fluorescence lifetime refers to the decay time of the light emitted when the semiconductor particles are instantaneously excited by ultrashort pulsed light excitation. The fluorescence lifetime can be measured using a known fluorescence lifetime measurement device that utilizes a photon counting method such as time-correlated single photon counting. The fluorescence lifetime can be adjusted depending on the type of semiconductor particles.

[0096] This fluorescence lifetime value may be affected by the semiconductor's crystalline quality or the measurement environment, but is, for example, 1 nanosecond or less for GaAs and approximately 0.5 to 3.5 nanoseconds for InP. The fluorescence lifetime of direct transition semiconductor materials is overwhelmingly shorter than that of indirect transition semiconductor materials. Therefore, the semiconductor material applied to the present disclosure is preferably a direct transition semiconductor material. For example, indirect transition GaP emits light well, but its fluorescence lifetime is 3 milliseconds. It is also known that Si or Ge can emit light when formed into quantum dots, but their fluorescence lifetime is on the order of milliseconds to seconds. Therefore, direct transition semiconductor materials are suitable as semiconductor materials for the light source of high-speed, high-resolution electrophotographic devices such as those disclosed herein. However, indirect transition semiconductor materials can also be used as the semiconductor material for the semiconductor particles that make up the light-emitting layer in the exposure head, as long as the desired image formation speed in the electrophotographic device can be achieved.

[0097] In addition, from the viewpoint of increasing the exposure sensitivity in the electrophotographic process, the light-emitting layer 33 preferably has an emission peak wavelength within the sensitivity spectrum of the electrophotographic photosensitive member.

[0098] Various electrophotographic photoreceptors 10 may be employed in this embodiment. Various materials are known as photosensitive materials for the electrophotographic photoreceptor 10, and the wavelength ranges of their sensitivities vary. Furthermore, the sensitivity of the electrophotographic photoreceptor 10 generally forms a sufficiently broad peak compared to the emission spectrum of a layer containing semiconductor particles, such as the light-emitting layer 33. For example, the sensitivity of an electrophotographic photoreceptor 10 made of a commonly used organic photosensitive material generally has a fairly flat peak from 650 nm to 850 nm, and also has a very broad spectrum. More specifically, phthalocyanine-based photoreceptors commonly used as electrophotographic photoreceptors exhibit flat and very high spectral sensitivity characteristics in the wavelength region from 600 nm to 850 nm, with a full width at half maximum of approximately 325 nm.

[0099] The peak wavelength of the light-emitting layer 33 may be at any position within such a wide sensitivity spectrum range of the electrophotographic photoreceptor 10. From the viewpoint of increasing exposure sensitivity, it is preferable that the peak wavelength of the light-emitting layer 33 be at substantially the same position as the peak wavelength of the sensitivity of the electrophotographic photoreceptor 10 (for example, within ±100 nm of the peak wavelength of the sensitivity of the electrophotographic photoreceptor 10).

[0100] Furthermore, from the viewpoint of increasing the efficiency of photosensitivity in the electrophotographic photoreceptor 10 in the electrophotographic process, it is preferable that the wavelength range of the emission spectrum of the light-emitting layer 33 sufficiently overlaps with the wavelength range of the sensitivity spectrum of the electrophotographic photoreceptor. By sufficiently overlapping the wavelength range of the emission spectrum of the light-emitting layer 33 with the wavelength range of the sensitivity spectrum of the electrophotographic photoreceptor, it is expected that the electrophotographic photoreceptor 10 can be sufficiently exposed to light even when the emission intensity of the light-emitting layer 33 is low. As a result, the energy efficiency of the exposure head 12 is improved, or the life of the light-emitting layer 33 is extended.

[0101] From the above viewpoints, the ratio of the full width at half maximum of the peak wavelength of the light emission of the light-emitting layer 33 to the full width at half maximum of the sensitivity spectrum of the electrophotographic photosensitive member 10 is preferably 25% or more, more preferably 35% or more, and even more preferably 50% or more. Note that the above ratio may be, for example, 10% or more as long as it can sufficiently sensitize the electrophotographic photosensitive member 10, and may be, for example, 20% or less from the viewpoint that it can be easily realized by controlling the particle size of the semiconductor particles that constitute the light-emitting layer 33. From the above viewpoints, the higher the ratio, the better, but from the viewpoints of ease of realization by controlling the particle size of the semiconductor particles and the viewpoint that the effect will plateau if the wavelength ranges overlap, the ratio may be, for example, 75% or less.

[0102] The photosensitive material of the electrophotographic photosensitive member 10 may be a material other than OPC. Specific examples of the full width at half maximum of the sensitivity spectrum of various electrophotographic photosensitive members applicable to the electrophotographic photosensitive member 10 are shown below. Note that the full width at half maximum of the sensitivity spectrum of the electrophotographic photosensitive member below is an example, and may vary slightly depending on the method for forming the electrophotographic photosensitive member 10, etc.

[0103]

[0104] In Table 1, "PVK-TNF" refers to polyvinylcarbazole-2,4,7-trinitrofluorenone, an equimolar mixture of these compounds. Furthermore, "CGM" refers to charge carrier generation material. Furthermore, the values ​​listed in the "amorphous silicon" section are data related to a photoreceptor having a two-layer structure of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon carbide (a-SiC:H).

[0105] The full width at half maximum FWHMq of the peak wavelength of the emission of light from light-emitting layer 33 can be calculated as the difference between two wavelengths having an intensity that is half the intensity of the emission peak (point D), as shown in Fig. 6. The full width at half maximum FWHMq can be increased by broadening the particle size distribution of the semiconductor particles contained in light-emitting layer 33 (for example, by changing the manufacturing conditions so that the manufacturing of semiconductor particles becomes easier, or by mixing semiconductor particles of the same type but with different particle sizes).

[0106] More specifically, by relaxing at least one of the manufacturing condition standards among the reaction time, reaction temperature, raw material concentration, and reaction pressure when manufacturing semiconductor particles, the number-based particle size distribution of the semiconductor particles can be increased and manufacturing of the semiconductor particles can be made easier.

[0107] Relaxing the standards for the manufacturing conditions means setting the manufacturing conditions in a direction that allows for variations in the manufacturing conditions. Examples of relaxing the standards for the manufacturing conditions include setting a wider allowable range for the concentration during the reaction (e.g., from ±0.5% to ±5%), setting a wider allowable range for the reaction temperature (e.g., from ±1°C to ±5°C), changing the conditions for terminating the reaction to milder conditions (e.g., from rapid cooling to natural cooling), relaxing the conditions for dispersing the raw materials during the reaction (e.g., reducing the number of stirrers in the reaction vessel or shortening the stirring time), and simplifying the control of the reaction temperature (not increasing or reducing the number of heaters or sensors in the reaction vessel).

[0108] Light-emitting semiconductors such as LEDs have an emission wavelength specific to the material. Therefore, it is usually difficult to adjust the emission wavelength, and it is also usually difficult to change the shape of the emission spectrum. Furthermore, light-emitting semiconductors are usually used for applications that emit light with a narrow wavelength range. Therefore, specifying the emission spectrum of a light-emitting semiconductor to have an emission spectrum with a shape broader than a certain range is contrary to the usual consideration of light-emitting semiconductors.

[0109] Furthermore, the electrophotographic photoreceptor 10 typically has a broad sensitivity spectrum. Therefore, there is a tendency to consider using electrophotographic photoreceptors in a wavelength range where the peak wavelength and its vicinity are highly sensitive. However, because the sensitivity spectrum of an electrophotographic photoreceptor is broad, the electrophotographic photoreceptor has sufficiently high sensitivity even at wavelengths other than the peak wavelength and its vicinity. The present embodiment includes a configuration in which the wavelength range of the exposure light is broadened, and the wavelength range of the exposure light can overlap with the wide wavelength range within the broad sensitivity spectrum of the electrophotographic photoreceptor.

[0110] The semiconductor particles contained in the light-emitting layer 33 that emit incoherent light may be particles having at least one of the various properties described above. Quantum dots that emit light upon excitation by an electric field or carrier injection may be used as the semiconductor particles. In this case, the light-emitting element having a light-emitting layer containing quantum dots is a quantum dot light-emitting diode (QLED) element.

[0111] Quantum dots are semiconductor particles that exhibit a quantum size effect. In such semiconductor particles, generally, when the particle size is reduced, the quantum size effect gradually appears once the particle size falls below 100 nm. From the perspective of being able to fully expect the quantum size effect, quantum dots can be semiconductor particles with a particle size of, for example, approximately 50 nm or less (e.g., approximately 2 nm to 30 nm). Because their composition is derived from semiconductor materials, quantum dots are sometimes referred to as semiconductor nanoparticles. As described above, the emission wavelength of quantum dots can be varied by adjusting the particle size or composition of the particles. The shape of quantum dots is not limited. For example, quantum dots may have a spherical three-dimensional shape (with a circular cross-section), or may have a polygonal three-dimensional shape, a rod-shaped three-dimensional shape, a branch-shaped three-dimensional shape, or a three-dimensional shape with an uneven surface, or a combination thereof.

[0112] The quantum dots may be formed of only a core, or may have a core-shell structure including a core and a shell. The shell may be formed in a solid solution state on the surface of the core. The quantum dots may also include doped nanoparticles.

[0113] Examples of the core material of a quantum dot (semiconductor of a semiconductor particle) include Si, Ge, GaAs, GaP, GaInP, InP, InAs, InSb, InN, GaSb, CdTe, CdS, CdSe, CdSeTe, CdZnTe, CdMnTe, ZnTe, ZnS, ZnSe, ZnSeTe, and CuInS ２ , CuInSe ２ , CuGaS ２ , CuGaSe ２ , HgS, HgSe, PbS, PbSe, ternary mixed crystals thereof, and quaternary mixed crystals thereof. Examples of materials for the shell of quantum dots include CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, and AlP.

[0114] Examples of combinations of quantum dot core and shell materials include CdSe / CdS, GaAs / AlGaAs, InP / ZnS, ZnSe / ZnS, and CIGS / ZnS.

[0115] Among these, from the viewpoint of emitting light from red to part of the near-infrared (wavelength 620 to 1500 nm) that is used as exposure light for commonly used organic photoreceptors, materials whose semiconductor bulk Eg is 2.00 eV or less are preferred, and specific examples thereof include GaAs, InP, GaSb, CdTe, CdSe, CdZnTe, CdMnTe, ZnTe, and CuInS. ２ , CuInSe ２ , CuGaSe ２ , HgSe, ternary mixed crystals thereof, and quaternary mixed crystals thereof.

[0116] The values ​​of the band gap energy Eg of the bulk of some semiconductors, including the examples above, are as follows. Most of the values ​​below are values ​​at room temperature, but some values ​​at temperatures other than room temperature are included, and may vary slightly (by about ±0.02 eV) depending on the temperature. The value of the band gap energy Eg of a semiconductor may include a certain tolerance range within the range in which emitted light of the desired wavelength can be obtained.

[0117] GaAs (1.43eV), GaP (2.3eV), InP (1.29eV), InAs (0.36eV), InSb (0.17eV), GaSb (0.67eV), CdTe (1.4eV), CdS (2.42eV), CdSe (1.7eV), CdZnTe (1.63eV), CdMnTe (1.5eV), ZnTe (1.4eV), ZnS (3.6eV), ZnSe (2.7eV), CuInS ２ (1.53eV), CuInSe ２ (1.01eV), CuGaS ２ (2.43eV), CuGaSe ２ (1.68eV), HgS (2.02eV), HgSe (2.0eV), PbS (0.43eV), PbSe (0.26eV).

[0118] By making the semiconductor material into fine particles to a size where the quantum size effect appears, the band gap energy of the semiconductor particles increases relative to Eg of the bulk. The band gap energy when the quantum size effect appears is defined as Eg ＱＤ Then, EgＱＤ is expressed by the following formula: ＱＤ = Eg + π ２ (h￣) ２ / 2μR ２ (1) Here, π is the ratio of the circumference of a circle to its circumference, "h" (etch bar) is the Dirac constant, μ is a constant determined from the effective mass of the electrons and holes in the semiconductor, and R is the particle radius. Using (h) = h / 2π (h: Planck's constant), equation (1) becomes: Eg ＱＤ = Eg + h ２ / 8μR ２ (2) can be rewritten as:

[0119] That is, when a semiconductor is granulated to a size where the quantum size effect is manifested, the band gap energy increases compared to Eg of the bulk, as is clear from formula (1) or (2). Since the effective masses of electrons and holes differ depending on the semiconductor material, Eg when granulated ＱＤ The way in which Eg changes varies depending on the semiconductor. ＱＤ The results are shown below.

[0120] For example, in the case of GaAs, the bulk Eg is 1.43 eV (867 nm), but the Eg of a particle with a particle size (= diameter) of 100 nm is ＱＤ is 1.44 eV (864 nm), Eg of 15 nm particle ＱＤ is 1.45 eV (855 nm), Eg of 10 nm particle ＱＤ is 1.48 eV (841 nm), Eg of 5 nm particle ＱＤ is 1.60 eV (777 nm), Eg of 3 nm particle ＱＤ is 1.73 eV (719 nm) (the emission wavelength is in parentheses).

[0121] In the case of InP, the bulk Eg is 1.29 eV (961 nm) and emits light in the near infrared region, but the Eg of particles with a particle size of 10 nm is ＱＤ is 1.33 eV (930 nm), Eg of 5 nm particle ＱＤ is 1.52 eV (818 nm), Eg of 4 nm particle ＱＤ is 1.65 eV (752 nm), Eg of 3 nm particle ＱＤ is 1.98 eV (625 nm), Eg of 2.5 nm particles ＱＤis 2.29 eV (541 nm), Eg of 2 nm particle ＱＤ is 2.90 eV (428 nm).

[0122] In other words, if GaAs particulated to a size of 3 nm to 100 nm is included in the light-emitting layer, a light-emitting layer having an extremely broad emission spectrum, including wavelengths from red light to the near-infrared region, can be realized. Furthermore, if InP is particulated to a size of 3 nm to 10 nm, a light-emitting layer having an extremely broad emission spectrum, including wavelengths from red light to the near-infrared region, can be realized. This wavelength range from red light to the near-infrared light matches the sensitivity spectrum of phthalocyanine-based organic photoreceptors (which have high sensitivity from 700 nm to 900 nm, centered around 800 nm) that are currently widely used as electrophotographic photoreceptor materials.

[0123] Materials for electrophotographic photoreceptors are not limited to the above-mentioned phthalocyanine organic photoreceptors, and include various materials exemplified in Table 1. New materials may be developed in the future, but all of them are expected to have broad sensitivity peaks. According to the concept of the present disclosure, it is possible to provide a light-emitting element having light-emitting characteristics that match electrophotographic photoreceptor materials having such broad sensitivity peaks.

[0124] The bulk band gap energy (Eg), emission wavelength (λb), and emission color of several semiconductor materials, including the above-mentioned GaAs and InP, are shown in Tables 2 and 3. For some of the semiconductor materials shown in Tables 2 and 3, the applicable emission wavelength (λa) when granulated (quantum dotted), and an example of the band gap energy (Eg) and emission wavelength (λ) for each particle size are shown. For the semiconductor material of the semiconductor particles in the present disclosure, an appropriate material may be selected from the semiconductor materials shown in Tables 2 or 3 in accordance with the sensitivity spectrum of the electrophotographic photosensitive member used in the electrophotographic device.

[0125]

[0126]

[0127] As mentioned above, methods for producing semiconductor particles (quantum dots) can be broadly divided into vapor phase epitaxy and chemical synthesis. Vapor phase epitaxy utilizes the lattice mismatch between the substrate material and the semiconductor material to deposit islands (particles) on the substrate. Specifically, molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) are used. However, because vapor phase epitaxy utilizes the lattice mismatch, the semiconductor particle materials that can be produced are limited due to the combination of substrate and deposition material. Another drawback is the large-scale manufacturing equipment required and the high manufacturing costs. For this reason, semiconductor particles are usually produced using chemical synthesis.

[0128] Among chemical synthesis methods, the hot injection method is known as a method capable of producing highly crystalline semiconductor particles. The hot injection method involves reacting a complex containing the semiconductor's constituent elements in a high-boiling organic solvent. The complex (raw material monomer) of the semiconductor's constituent elements contained in the solution undergoes a chemical reaction at temperatures between 150 and 450°C to form nuclei. Similar reactions then occur sequentially on the surfaces of the nuclei and the microcrystalline surfaces from which they grow, resulting in crystal growth. This method, which suppresses the crystal growth rate, is suitable for producing nanometer-scale semiconductor particles. Furthermore, since there are no material restrictions, such as the combination with the substrate, this method is advantageous in that, in principle, it can produce any compound semiconductor.

[0129] Conventional quantum dots are grown using the hot injection method and then undergo various classification processes to achieve the desired particle size with an extremely narrow particle size distribution. Furthermore, to ensure uniform particle size even before the classification process, precise temperature and time control and management of the concentration of the raw material monomer in the solvent are required during the crystal growth process. This is because, in the past, quantum dot applications required a narrower full width at half maximum of the emission spectrum, i.e., increased monochromaticity of quantum dot emission. As is clear from Tables 2 and 3, a difference of 1 nm in quantum dot particle size can result in a change in the quantum dot emission wavelength of several tens of nm or more. Therefore, when producing quantum dots that emit monochromatic light, it is necessary to control the particle size of the semiconductor particles, for example, to within 0.1 nm.

[0130] The light-emitting element of the present disclosure can have a broad emission spectrum that matches the wide sensitivity spectrum of an electrophotographic photoreceptor. Therefore, precise control of manufacturing conditions (temperature, time, or concentration) for precisely controlling particle size during the crystal growth process is not required, and a strict classification process that requires a great deal of know-how and is difficult to implement is also not required. The particle size of the semiconductor particles produced in the present disclosure may be, for example, 5 nm or more in terms of the full width at half maximum in the number-based particle size distribution (particle size distribution).

[0131] In order to make the full width at half maximum in the particle size distribution 5 nm or more, in addition to relaxing the manufacturing conditions or classification process described above, semiconductor particles having different particle sizes may be mixed together when producing semiconductor particles in the present disclosure.

[0132] Conventionally, semiconductor particles (quantum dots) used as light-emitting devices are often photoluminescence (PL) type. That is, they are excited by light and emit light with a different wavelength from the excitation light (light wavelength-converted from the excitation light). In the case of PL type devices, if semiconductor particles of different particle sizes are used, a self-absorption phenomenon may occur in which light emitted from smaller particles (shorter wavelength light) excites larger particles, emitting light with longer wavelengths. As a result, the short-wavelength light emitted from the smaller particles is absorbed by the larger particles and is less likely to be emitted outside the light-emitting device, resulting in a broadened emission spectrum, i.e., a reduced full width at half maximum of the emission. Furthermore, there is a problem of a decrease in the luminous efficiency of the entire particle, including both small and large particles.

[0133] In light-emitting devices using injection electroluminescence (injection EL), which injects electrons and holes rather than photoexcitation, such as the light-emitting device disclosed herein, both small and large particles emit light by carrier injection. Therefore, the decrease in luminous efficiency due to self-absorption seen in PL devices is less likely to occur, making it possible to achieve a desired broad emission spectrum. Therefore, the light-emitting device disclosed herein, which uses injection EL as a light-emitting layer containing semiconductor particles of different particle sizes, is highly effective in improving the luminous efficiency of the exposure head of an electrophotographic device.

[0134] Ligands may be coordinated to the surfaces of semiconductor particles such as quantum dots as long as the effects of the present disclosure are achieved. Various known ligands can be used as the ligands. The ligands may be organic or inorganic.

[0135] Furthermore, the light-emitting layer 33 may further contain components other than the above-described ligands, as long as the effects of the present disclosure are achieved. For example, the light-emitting layer 33 may further contain a binder component that can be interposed between individual semiconductor particles. When the light-emitting layer contains a binder component, the reliability of the light-emitting device containing semiconductor particles is further improved. Furthermore, since the flatness of the surface of the light-emitting layer 33 containing semiconductor particles is improved, subsequent film formation processes such as the electron transport layer can be easily performed with a high yield. Furthermore, maintaining the distance between individual semiconductor particles can prevent concentration quenching.

[0136] As described above, the light-emitting layer 33 containing semiconductor particles can arbitrarily set the emitted color by adjusting the size of the semiconductor particles. Furthermore, the light-emitting layer 33 containing semiconductor particles can be easily and precisely fabricated by a coating method, as described below, and the thickness of the fabricated light-emitting layer 33 can also be sufficiently controlled. Furthermore, layers other than the light-emitting layer containing semiconductor particles are not subject to thermal damage due to the manufacturing conditions of the light-emitting layer 33. Therefore, a light-emitting element including a light-emitting layer 33 containing semiconductor particles is suitable from the viewpoint of increasing the reliability of the light-emitting element.

[0137] [Method of Manufacturing Light Source Included in Exposure Head] The light source 122 included in the exposure head 12 can be manufactured, for example, according to the flow shown in FIG.

[0138] In step S11, an active matrix substrate is prepared. For example, the active matrix substrate is fabricated by a known method.

[0139] Next, in step S12, first electrodes 31 are fabricated on the active matrix substrate, i.e., on the planarization layer 27, so as to be independently arranged in the first direction X. For example, Ag is deposited by sputtering, and then ITO is deposited on the planarization layer 27 by photolithography or vacuum deposition using a fine metal mask, to fabricate a plurality of reflective first electrodes 31 that are intermittently arranged in the first direction X.

[0140] Next, in step S13, banks 36 are formed on the first electrodes 31 and the planarizing layer 27. For example, ink containing a transparent resin is applied to the surface of the active matrix substrate, and patterned by photolithography between adjacent first electrodes 31 in the first direction X so as to straddle both electrodes, thereby forming the banks 36 at positions between the first electrodes 31 in the first direction X.

[0141] Next, in step S14, a hole transport layer 32 is formed as a common layer on the first electrode 31. For example, a hole transport material and an electron acceptor material are deposited by co-evaporation at a predetermined temperature and rate by photolithography or vacuum evaporation through a common mask to form a hole injection layer on the first electrode 31 that is continuous in the first direction X. Next, a hole transport material is deposited by evaporation at a predetermined temperature and rate by photolithography or vacuum evaporation through a common mask to form a hole transport layer 32 on the hole injection layer that is continuous in the first direction X.

[0142] Next, in step S15, the light-emitting layer 33 is formed on the hole transport layer 32. For example, ink in which semiconductor particles are dispersed in a dispersion medium is applied to positions between the banks 36 on the hole transport layer 32 using a slit coater or an inkjet printer, and the coating is dried and cured as necessary to form the light-emitting layer 33 intermittently in the first direction X.

[0143] Next, in step S16, the electron transport layer 34 is formed as a common layer on the hole transport layer 32 and the light-emitting layer 33. For example, the electron transport material is deposited by photolithography or vapor deposition through a common mask, or the electron transport material and lithium quinoline are deposited by co-evaporation through a common mask at a predetermined temperature and rate to form the electron transport layer 34 that is continuous in the first direction X.

[0144] Next, in step S17, the second electrode 35 is formed as a common layer on the electron transport layer 34. For example, Mg and Ag are deposited at a predetermined temperature and rate by sputtering through a common mask to form an Mg / Ag metal electrode layer that is continuous in the first direction X.

[0145] When another layer such as a sealing layer is formed on the second electrode 35, the other layer can be formed as a common layer.

[0146] [Major Effects of the Present Embodiment] In the present embodiment, the light-emitting layer 33 can be produced by a coating method. Therefore, it is possible to produce a fine light-emitting layer under normal conditions, such as room temperature, normal pressure, and atmospheric air. Furthermore, since the method for producing the light source 122 included in the exposure head 12 includes a step of producing the light-emitting layer 33 by such a coating method, it is possible to reduce the costs of manufacturing equipment and masks compared to a method that includes a step of producing the light-emitting layer by a vapor deposition method using a fine metal mask, and this is advantageous from the perspective of reducing the initial cost and operating cost of manufacturing.

[0147] Furthermore, the light-emitting layer 33 contains semiconductor particles with a particle size of 100 nm or less that can emit incoherent light. Therefore, even in a minute light-emitting region such as a rectangular light-emitting layer with a side length of 10 μm or less, a large number of light-emitting semiconductor particles can be densely arranged. Therefore, in the present disclosure, high-brightness light emission can be achieved despite the minute light-emitting layer.

[0148] In the electrophotographic apparatus 1, a voltage is applied from a charging device 11 to the surface of an electrophotographic photoreceptor 10 that rotates at a speed that enables high-speed printing, and light corresponding to an electrostatic latent image to be formed on the surface of the electrophotographic photoreceptor 10 is emitted from an exposure head 12 onto the charged electrophotographic photoreceptor 10. A light emitting element 40 included in a light source 122 of the exposure head 12 emits light whose light extraction efficiency has been improved by a microcavity structure.

[0149] Charged toner is supplied from the developing device 13 to the electrostatic latent image on the electrophotographic photosensitive member 10 to develop the electrostatic latent image, and the toner image on the electrophotographic photosensitive member 10 is transferred to a recording medium 17 by application of a voltage from a transfer device 14. The unfixed toner image transferred to the recording medium 17 is fixed to the recording medium 17 by application of heat and pressure by a fixing device 16. The recording medium 17 on which the image has been formed in this way is discharged from the electrophotographic apparatus 1 to the outside of the machine.

[0150] The exposure head 12 preferably includes light-emitting elements 40 arranged at a density of 600 or more per inch in the first direction X, enabling the formation of high-resolution electrostatic latent images. The light-emitting elements 40 also include a light-emitting layer 33 containing semiconductor particles that emit incoherent light. When the fluorescence lifetime of the semiconductor particles that emit incoherent light is 10 nanoseconds or less, the fluorescence lifetime of the light-emitting layer 33 containing the semiconductor particles is also significantly faster, on the order of 10 nanoseconds or less, resulting in a significantly improved modulation speed of the light-emitting layer 33. Furthermore, when the particle diameter of the semiconductor particles is 100 nm or less, a large number of luminescent semiconductor particles can be densely contained even in a minute light-emitting region, such as a rectangular light-emitting layer with sides of 10 μm or less. Therefore, high-brightness light emission can be achieved despite the minute light-emitting layer, making this even more effective. These configurations are suitable for achieving high-speed, high-resolution printing in the electrophotographic device 1.

[0151] Furthermore, if the exposure head 12 includes light-emitting elements 40 and a driving transistor layer 20 arranged on the opposite side of the light-emitting elements 40 in the second direction Y to cause each of the plurality of light-emitting elements 40 to emit light independently, there is no need to arrange wiring connecting the light-emitting elements 40 and the driving transistors on the same plane as the light-emitting elements 40. This eliminates the need to arrange wiring connecting the light-emitting elements 40 and the driving transistors on the same plane as the light-emitting elements 40. This maximizes the area of ​​the light-emitting elements 40. As a result, even if the arrangement pitch of the light-emitting elements 40 is reduced, the light-emitting area of ​​each light-emitting element 40 can be maximized, thereby minimizing the reduction in brightness of each light-emitting element 40. This allows for the miniaturization of the light source 122, which is preferable. By stacking the light-emitting elements and the driving transistor layer 20 three-dimensionally in this way, it is possible to realize an exposure head capable of high-resolution printing at 2400 dpi or more, which is preferable. The above configuration is advantageous from the perspective of manufacturing the exposure head 12 with a large number of light-emitting elements 40 on a substrate at high density and integrally connecting each light-emitting element 40 to a driver. Furthermore, because the driving TFTs are formed three-dimensionally and integrally (monolithically) with the light emitting elements 40, there is no need to arrange the light emitting elements 40 at a narrow pitch and then connect each of the light emitting elements 40 to a driving circuit. This is therefore preferable as it improves the manufacturing yield compared to the conventional method of mounting discrete inorganic LEDs on a substrate and connecting lead wiring from the LEDs to a driver one by one.

[0152] Furthermore, if the driving TFT layer 20 has a source electrode 261, a drain electrode 262, and a planarization layer 27, and the first electrode 31 of the light-emitting element 40 is electrically connected to the drain electrode 262 through a contact hole 28 formed in the planarization layer 27, the driving TFT can be easily integrated with the light-emitting element 40, which is preferable.

[0153] Note that the first electrode 31 may be a cathode and the second electrode 35 may be an anode, as long as the effects of the present disclosure are obtained. Furthermore, the first electrode 31 may be electrically coupled to the source electrode 261, as long as the effects of the present disclosure are obtained.

[0154] Furthermore, if the emission wavelength of the light-emitting layer 33 is shorter than the emission wavelength represented by the band gap energy of the bulk of the semiconductor, efficient exposure is possible due to light emission that matches the peak sensitivity of the electrophotographic photosensitive member 10, thereby achieving low power consumption and a long life for the light-emitting element 40, which is preferable. For example, a bulk material of semiconductor particles having an emission wavelength longer than the peak sensitivity wavelength of the electrophotographic photosensitive member 10 is granulated, and the particle size of the particles is controlled to the median value in the particle size distribution of the particles corresponding to the peak sensitivity wavelength of the electrophotographic photosensitive member 10. In this way, the light-emitting layer 33 can emit light at a wavelength shorter than the Eg of the bulk material and at the peak sensitivity wavelength of the photosensitive member. As such, the above-described configuration is preferable from the viewpoint of achieving exposure with light that closely matches the sensitivity characteristics of the electrophotographic photosensitive member 10 in the electrophotographic device 1.

[0155] Furthermore, if the semiconductor particles contained in the light-emitting layer 33 have a bulk bandgap energy of 0.50 eV or more and 2.00 eV or less, and the number-based particle size of the semiconductor particles is 50 nm or less, it is possible to configure the light-emitting layer 33 capable of emitting light in the red to near-infrared wavelength range by controlling the median particle size and particle size distribution of the material, and this is preferable because it is possible to match the peak sensitivity wavelength and sensitivity spectrum shape of the photosensitive member. Therefore, the light emitted from the exposure head 12 can be efficiently used to expose the electrophotographic photosensitive member 10, which is preferable because it reduces power consumption and extends the life of the light-emitting element 40. As such, the above-described configuration is suitable from the perspective of achieving exposure with light that closely matches the sensitivity characteristics of the electrophotographic photosensitive member 10 in the electrophotographic device 1.

[0156] Furthermore, if the light-emitting layer 33 has an emission peak wavelength within the sensitivity spectrum of the electrophotographic photosensitive member 10 and the ratio of the full width at half maximum of the emission peak wavelength of the light-emitting layer 33 to the full width at half maximum of the sensitivity spectrum of the electrophotographic photosensitive member 10 is 25% or more, the center value of the particle size distribution of the semiconductor particles and the state of particle size distribution can be controlled to match the emission spectrum of the light-emitting layer 33 to the sensitivity peak and sensitivity spectrum of the electrophotographic photosensitive member 10, thereby enabling efficient exposure, thereby realizing low power consumption and long life of the light-emitting element 40, which is preferable. In the above configuration, by adjusting the particle size peak and its distribution state of the semiconductor particles constituting the light-emitting layer 33, it becomes extremely easy to match the emission characteristics of the light-emitting layer 33 to the sensitivity characteristics of the electrophotographic photosensitive member 10. Therefore, the above configuration is suitable from the viewpoint of realizing exposure with light that has a high degree of match with the sensitivity characteristics of the electrophotographic photosensitive member in an electrophotographic device.

[0157] Furthermore, for example, if the range of the wavelength of the light emitted by the light-emitting layer 33 is 620 nm or more and 1500 nm or less, and the full width at half maximum of the peak wavelength of the light emitted by the light-emitting layer 33 is greater than 150 nm, the effect of matching the light-emitting characteristics of the light-emitting layer 33 to the electrophotographic photoreceptor 10 that has absorption from red light to infrared can be further enhanced than before, which is preferable.

[0158] Furthermore, for example, when the full width at half maximum in the particle size distribution based on the number of semiconductor particles is 5 nm or more, the effect of broadening the full width at half maximum at the emission peak wavelength of the light-emitting layer 33 to match the extremely broad sensitivity spectrum that the electrophotographic photoreceptor 10 generally has is fully manifested. This makes it possible to more closely match the sensitivity spectrum of the electrophotographic photoreceptor 10 with the emission spectrum of the light-emitting layer 33, thereby enabling more efficient exposure. Furthermore, since the semiconductor particles can be manufactured so that the particle size distribution is more gradual in the production of the semiconductor particles, strict classification of the produced semiconductor particles is not necessary, and the production time of the semiconductor particles can also be shortened, which is preferable.

[0159] In addition, the semiconductor is GaAs, InP, GaSb, CdTe, CdSe, CdZnTe, CdMnTe, ZnTe, CuInS ２, CuInSe ２ , CuGaSe ２ , HgSe, ternary mixed crystals thereof, and quaternary mixed crystals thereof, it is even more effective from the viewpoint of enhancing the effect of matching the light-emitting characteristics of the light-emitting layer 33 to the electrophotographic photoreceptor 10, which is a general-purpose organic photoreceptor having sensitivity in the wavelength range from red light to near-infrared light.

[0160] Furthermore, if the element pitch (P) of the light-emitting element 40 in the first direction X is 43 μm or less and the ratio (S / P) of the element size (S) of the light-emitting element 40 in the first direction X to the element pitch (P) is 0.7 or more, this is even more effective from the viewpoint of realizing high-resolution exposure.

[0161] Other embodiments of the present disclosure will be described below. In the following description of the embodiments, for the sake of convenience, the same explanation as in the above-described embodiment will not be repeated, and the same reference numerals will be used to designate components having the same functions as those described in the above-described embodiment, and the explanations thereof will not be repeated.

[0162] [Embodiment 2] In this embodiment, each light-emitting element is configured by stacking multiple pairs of a light-emitting layer and an electrical functional layer overlapping the light-emitting layer between a first electrode and a second electrode in the second direction Y. The exposure head of this embodiment has a configuration similar to the exposure head 12 of the above-described embodiment 1, except for the configuration of the light-emitting elements. Figure 8 schematically shows the layer configuration of the light-emitting element of this embodiment. As shown in Figure 8, a light-emitting element 50 has a configuration similar to the light-emitting element 40 of the above-described embodiment 1, except for further including a functional layer 52 and a light-emitting layer 53 between the light-emitting layer 33 and the electron transport layer 34.

[0163] The functional layer 52 has an electron transport layer, an n-type charge generation layer, a p-type charge generation layer, and a hole transport layer, in this order from the first electrode 31 side. The light-emitting layer 53 is a light-emitting layer containing semiconductor particles that emit incoherent light, similar to the light-emitting layer 33. The semiconductor particles contained in the light-emitting layer 53 may be the same as or different from those in the light-emitting layer 33, as long as the effects of the present disclosure are obtained. Furthermore, the particle size of the semiconductor particles contained in the light-emitting layer 53 may be the same as or different from those in the light-emitting layer 33, as long as the effects of the present disclosure are obtained. Furthermore, the configuration of the electron transport layer in the functional layer 52 may be the same as or different from that of the electron transport layer 34. Furthermore, the configuration of the hole transport layer in the functional layer 52 may be the same as or different from that of the hole transport layer 32.

[0164] The n-type charge generation layer is an electron generation layer that generates electrons, and may be formed, for example, from an organic electron transport material and a material containing Yb (ytterbium) or Li (lithium), an inorganic metal material added in the range of 5 to 20%, which acts as an electron donor material. Examples of organic electron transport materials include oxadiazole-based compounds and phenanthroline-based compounds. The electron donor material may be an organic material, and examples of organic electron donor materials include BUPH1, BPen, p-MeO-Phen, and p-NMe. ２ -Phen, and p-Pyrrd-Phen.

[0165] The p-type charge generation layer is a hole generation layer that generates holes, and can be formed, for example, from a material including an organic hole transport material and an organic electron accepting material (hole supply material) added in the range of 1 to 10%. Examples of organic hole transport materials include known triarylamine organic compounds. Examples of organic electron accepting materials include tetracyanoquinodimethane tetrafluoride (TCNQ-4F).

[0166] In the light emitting element 50, similarly to the light emitting element 40, the distance between the electrodes in the second direction Y is optimized by, for example, the thickness of the hole transport layer 32, and the light emitting element 50 is a top emission type light emitting element.

[0167] The set of layers from the hole transport layer 32 to the electron transport layer in the functional layer 52 is a layer that functions mainly to emit light from the light-emitting layer 33. This set of layers is also referred to as a first stack. The set of layers from the hole transport layer to the electron transport layer 34 in the functional layer 52 is a layer that functions mainly to emit light from the light-emitting layer 53. This set of layers is also referred to as a second stack.

[0168] From the viewpoint of increasing the light-emitting efficiency of the light-emitting element 50, the ratio of the thickness of the light-emitting layer in each stack to the thickness of each stack is preferably 0.05 or more and preferably 0.35 or less. The thickness of a stack is calculated as the sum of the thicknesses of the layers in the stack, but layers with very small thicknesses (e.g., layers with a thickness of less than 1 nm) may be ignored when calculating the thickness of the stack.

[0169] The light-emitting element 50 can be manufactured by performing steps of fabricating an n-type charge generation layer and a p-type charge generation layer between the aforementioned steps S16 and S17, and then further performing steps similar to steps S14 to S16.

[0170] In this embodiment, it is possible to increase the amount of light emitted from the light emitting elements 50 and the irradiance on the electrophotographic photosensitive member 10 while keeping the light emitting area of ​​each light source 122 in the exposure head 12 small. In particular, it is possible to increase the amount of light emitted by, for example, two times, three times, or more without changing the current value and current density flowing through the light emitting elements 50. Therefore, this embodiment is preferable from the viewpoint of extending the life of the light source 122 compared to the first embodiment described above.

[0171] The light-emitting element 50 is a so-called tandem light-emitting element that includes two light-emitting layers 33, 53 and corresponding electrical functional layers in the second direction Y. This prevents the electrical functional layers from becoming too thick to adjust the distance between the electrode layers to form a microcavity structure. Therefore, this embodiment is preferable compared to the first embodiment in terms of reducing the consumption of functionally unnecessary materials.

[0172] In this way, each of the light-emitting elements 50 is configured by stacking multiple pairs of light-emitting layers 33 and electrical functional layers overlapping the light-emitting layers 33 between the first electrode 31 and the second electrode 35 in the second direction Y. The inclusion of multiple light-emitting layers in the light-emitting element 50 is effective from the viewpoint of increasing the intensity of the emitted light. Therefore, with the above configuration, the light-emitting element 50 can have the appearance of a single element while increasing the amount of light emitted, and a light source 122 for the exposure head 12 that is capable of emitting light with high brightness in an extremely small area can be realized.

[0173] [Embodiment 3] In this embodiment, each of the light-emitting elements includes at least two light-emitting layers having different volumes in the second direction Y. The exposure head of this embodiment has a configuration similar to that of the exposure head of the above-described embodiment 2, except that the configuration of the light-emitting elements is different. Figure 9 schematically shows the layer configuration of the light-emitting elements of this embodiment. As shown in Figure 9, the light-emitting element 60 has a configuration similar to that of the light-emitting element 50 of the above-described embodiment 2, except that it has a light-emitting layer 63 instead of the light-emitting layer 53.

[0174] The light-emitting layer 63 is thinner than the light-emitting layer 53. That is, the light-emitting element 60 is a tandem light-emitting element including the light-emitting layer 33 and an even thinner light-emitting layer 63. When the thickness of the light-emitting layer 33 is taken as 1, the thickness of the light-emitting layer 63 is preferably 0.1 or more, and more preferably 0.3 or more, from the viewpoints of extending the element life and reducing excess carriers (holes), as described below. On the other hand, when the thickness of the light-emitting layer 33 is taken as 1, the thickness of the light-emitting layer 63 is preferably 0.9 or less, and more preferably 0.8 or less, from the viewpoints of achieving both improved luminous efficiency and reduced driving voltage (power consumption).

[0175] The thickness of the light-emitting layer in this embodiment can be determined, for example, by the following method. That is, the applied voltage, luminous efficiency, or device life of a light-emitting element 50 having a light-emitting layer with the same thickness in the stacking direction is measured and used as a reference value. Meanwhile, a light-emitting element 60 is fabricated in which the thickness of the light-emitting layer 63 is made thinner than the thickness of the light-emitting layer 33, and the applied voltage, luminous efficiency, or device life is measured. Based on the obtained measured values ​​and the reference value, an appropriate thickness according to the purpose is determined.

[0176] Alternatively, the thickness of the light-emitting layer 63 can be determined to be a thickness appropriate for the purpose, for example, by evaluating the carrier injection properties and / or carrier transport properties between each layer in the light-emitting element 60 through simulation and conducting demonstration experiments based on the evaluation.

[0177] The light-emitting element 60 is a tandem light-emitting element including a light-emitting layer 33 and a thinner light-emitting layer 63. Therefore, holes are supplied to the light-emitting layer 63 in an amount commensurate with the thickness of the light-emitting layer 63. Therefore, in the light-emitting layer 63, electrons and holes recombine without generating excess holes that cannot recombine with electrons. Meanwhile, in the light-emitting layer 33, the amount of electrons and holes recombines is essentially the theoretical value. Therefore, each of the light-emitting layers 33 and 63 stacked in the stacking direction emits light with an intensity corresponding to its thickness. Furthermore, the generation of excess holes is prevented in each of the light-emitting layers 33 and 63. Therefore, in this embodiment, a further reduction in current consumption and power consumption is achieved compared to the second embodiment. In this way, by varying the volume (thickness) of each light-emitting layer in the tandem light-emitting element 60 having multiple light-emitting layers, carrier balance between the multiple light-emitting layers can be achieved, thereby resolving the problem of imbalance in carrier supply.

[0178] Therefore, the exposure head having a plurality of tandem light emitting elements 60 of this embodiment is even more effective in terms of realizing a reduction in power consumption.

[0179] In a top-emission light-emitting element, when the second electrode 35 deteriorates due to the intrusion of oxygen or moisture, the electron injection property decreases, and as a result, the amount of electrons supplied to the light-emitting layer 63 may decrease. However, if such a case is anticipated and the thickness of the light-emitting layer 63 on the second electrode 35 side is made thinner than the theoretical value from the initial design stage, it becomes possible to prevent the generation of excess holes in the light-emitting layer 63 due to deterioration of the second electrode 35. A configuration in which the light-emitting layer 63 is made thinner than the light-emitting layer 33 is also effective as a countermeasure when the second electrode 35 deteriorates in this way.

[0180] Furthermore, making the light-emitting layer 63 thinner than the light-emitting layer 33 is also effective as a measure to improve carrier balance when the electron transport layer 34 is made of an organic material. Constructing the electrical functional layer solely from organic materials is preferable from the viewpoint of preventing thermal damage to the light-emitting element during the manufacturing process. On the other hand, the electron transport capacity of an electron transport layer made of an organic material tends to be inferior to that of an electron transport layer made of an inorganic material. Therefore, when the electron transport layer 34 is made of an organic material, the amount of electrons supplied to the light-emitting layer on the second electrode 35 side may be insufficient. Making the light-emitting layer 63 thinner than the light-emitting layer 33 optimizes the balance (carrier balance) between the electrons and / or holes supplied from the charge generation layer in the functional layer 52 and the holes and / or electrons supplied from each electrode. Therefore, even when the electron transport layer 34 is made of an organic material, the generation of excess carriers is suppressed, and power consumption can be reduced.

[0181] [Embodiment 4] This embodiment is a form in which each light-emitting element includes three light-emitting layers with different volumes in the second direction Y. The exposure head of this embodiment has a configuration similar to that of the exposure head of the above-described embodiment 2, except for the configuration of the light-emitting elements. Figure 10 schematically shows the layer configuration of the light-emitting element of this embodiment. As shown in Figure 10, the light-emitting element 70 has substantially the same configuration as the light-emitting element 60 of the above-described embodiment 3, except that it further includes an electron transport layer 71, a functional layer 72, and a light-emitting layer 73 between the light-emitting layer 63 and the electron transport layer 34.

[0182] The configuration of the electron transport layer 71 may be the same as or different from the electron transport layer in the functional layer 52 and the electron transport layer 34 .

[0183] The functional layer 72 has an n-type charge generation layer, a p-type charge generation layer, and a hole transport layer, in this order from the first electrode 31 side. The configuration of the n-type charge generation layer in the functional layer 72 may be the same as or different from that of the n-type charge generation layer in the functional layer 52. The configuration of the p-type charge generation layer in the functional layer 72 may be the same as or different from that of the p-type charge generation layer in the functional layer 52. The hole transport layer in the functional layer 72 may be the same as or different from that of the hole transport layer 32 and the hole transport layer in the functional layer 52.

[0184] The light-emitting layer 73 is a light-emitting layer containing semiconductor particles that emit incoherent light, similar to the light-emitting layers 33 and 63. The semiconductor particles contained in the light-emitting layer 73 may be the same as or different from those in the light-emitting layers 33 and 63, as long as the effects of the present disclosure are obtained. Furthermore, the particle size of the semiconductor particles contained in the light-emitting layer 73 may be the same as or different from that of the light-emitting layer 63, as long as the effects of the present disclosure are obtained.

[0185] Light-emitting layer 73 is thinner than light-emitting layer 63. That is, light-emitting element 70 is a tandem light-emitting element including light-emitting layer 33, a thinner light-emitting layer 63, and an even thinner light-emitting layer 73. When the thickness of light-emitting layer 33 is 1, the thickness of light-emitting layer 63 is 0.1 to 0.9, and when the thickness of light-emitting layer 63 is 1, the thickness of light-emitting layer 73 is 0.1 to 0.9.

[0186] In this embodiment, the set of layers from the hole transport layer in the functional layer 52 to the electron transport layer in the functional layer 72 is the layer that functions mainly to emit light from the light-emitting layer 63, and therefore this set of layers is also referred to as a second stack. In this embodiment, the set of layers from the hole transport layer to the electron transport layer 34 in the functional layer 72 is the layer that functions mainly to emit light from the light-emitting layer 73. This set of layers is also referred to as a third stack.

[0187] The light-emitting element 70 can be manufactured by repeating twice between the aforementioned steps S16 and S17 the steps of forming an n-type charge generation layer, forming a p-type charge generation layer, and performing steps similar to steps S14 to S16.

[0188] Like the light emitting devices of the other embodiments, the light emitting device 70 can also suppress the generation of excess carriers that cannot contribute to light emission, and can supply an appropriate amount of carriers to each light emitting layer.

[0189] Therefore, an exposure head having a plurality of tandem light emitting elements 70 of this embodiment is even more effective in terms of reducing power consumption.

[0190] The light-emitting device 70 is suitable for adjusting the carrier balance in the remaining stack when, as a result of adjusting the carrier balance in two adjacent stacks among the three stacks, a good carrier balance cannot be obtained in the remaining stack. Examples of the configuration of the light-emitting device 70 in such a case include a light-emitting device including one or more configurations selected from the group consisting of a configuration in which the thicknesses of corresponding electrical functional layers in the first stack and the second stack are different, a configuration in which the materials of corresponding electrical functional layers in the first stack and the second stack are different, and a configuration in which the material of the light-emitting layer included in the first stack and the material of the light-emitting layer included in the second stack are different, and a configuration in which the thickness ratio of the light-emitting layers between at least the second stack and the third stack is the above-mentioned thickness ratio.

[0191] [Embodiment 5] In this embodiment, each of the light-emitting elements includes at least two light-emitting layers having different volumes in the second direction Y. The exposure head of this embodiment has a configuration similar to that of the exposure head of the above-described embodiment 2, except for the configuration of the light-emitting elements. Figure 11 schematically shows the layer configuration of the light-emitting element of this embodiment. As shown in Figure 11, the light-emitting element 80 has a configuration similar to that of the light-emitting element 50 of the above-described embodiment 2, except for having a light-emitting layer 83 instead of the light-emitting layer 33. The light-emitting layer 83 has a configuration similar to that of the light-emitting layer 33, except for the area of ​​the light-emitting layer 83 being smaller than that of the light-emitting layer 33.

[0192] The light-emitting element 80 is a tandem light-emitting element including a light-emitting layer 83 having a smaller area and a light-emitting layer 53 having a larger area. The "area" of the light-emitting layer refers to the area of ​​each light-emitting layer when viewed from the light-emitting side (the second electrode 35 side). For example, the area of ​​the light-emitting layer 83 is 10 to 90% of the area of ​​the light-emitting layer 53. From the viewpoint of increasing light-emitting efficiency, the area of ​​the light-emitting layer 83 is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more of the area of ​​the light-emitting layer 53. On the other hand, from the viewpoint of suppressing the generation of excess carriers and reducing power consumption, the area of ​​the light-emitting layer 83 is preferably less than 1% of the area of ​​the light-emitting layer 53, more preferably 90% or less, and even more preferably 80% or less. The area of ​​the light-emitting layer in this embodiment can be determined by the same method as the thickness of the light-emitting layer described above.

[0193] Light-emitting element 80 is a tandem light-emitting element including light-emitting layer 83 having a smaller area and light-emitting layer 53 having a larger area. Therefore, when the amount of carriers (electrons and / or holes) supplied to light-emitting layer 53 becomes greater than the amount of carriers (electrons and / or holes) supplied to light-emitting layer 83, the volume of light-emitting layer 53 where the carrier supply becomes excessive is larger than that of light-emitting layer 83. Therefore, in light-emitting element 80 as well, the carrier balance of all light-emitting layers in light-emitting element 80 is optimized.

[0194] In this way, in the light-emitting element 80, similarly to the light-emitting elements of the third and fourth embodiments, generation of excess carriers that cannot contribute to light emission is suppressed, and an appropriate amount of carriers is generated in both the light-emitting layer 83 and the light-emitting layer 53. Therefore, the light-emitting element 80 can also emit light with high efficiency and brightness.

[0195] Therefore, the exposure head having a plurality of tandem light emitting elements 80 of this embodiment is even more effective in terms of realizing low power consumption and high definition in electrophotographic apparatuses.

[0196] [Embodiment 6] This embodiment is a form in which each light-emitting element includes three light-emitting layers with different volumes in the second direction Y. The exposure head of this embodiment has the same configuration as the exposure head of the above-described embodiment 4, except for the configuration of the light-emitting elements. Figure 12 schematically shows the layer configuration of the light-emitting elements of this embodiment. As shown in Figure 12, light-emitting element 90 has substantially the same configuration as light-emitting element 70 of the above-described embodiment 4, except for having light-emitting layers 93, 103, and 113 instead of light-emitting layers 33, 63, and 73.

[0197] Light-emitting layers 93, 103, and 113 have the same thickness but different areas. Light-emitting element 90 is a tandem light-emitting element including light-emitting layer 93 having the smallest area, light-emitting layer 103 having the next smallest area, and light-emitting layer 113 having the largest area. The area of ​​light-emitting layer 93 is 0.1 to 0.9 when the area of ​​light-emitting layer 103 is 1. The area of ​​light-emitting layer 103 is 0.1 to 0.9 when the area of ​​light-emitting layer 113 is 1.

[0198] Like the light-emitting devices of the third to fifth embodiments, the light-emitting device 90 can also suppress the generation of excess carriers that cannot contribute to light emission, and can generate an appropriate amount of carriers in each light-emitting layer.

[0199] Therefore, the exposure head having a plurality of tandem light emitting elements 90 of this embodiment has high light emitting efficiency and is even more effective in terms of realizing reduced power consumption.

[0200] Note that the light-emitting device 90 is suitable for adjusting the carrier balance in the remaining stack when, as a result of adjusting the carrier balance in two adjacent stacks out of the three stacks, a good carrier balance cannot be obtained in the remaining stack. Examples of the configuration of such a light-emitting device include a configuration in which, in a light-emitting device including one or more configurations selected from the group consisting of a configuration in which the thicknesses of corresponding electrical functional layers in the first stack and the second stack are different, a configuration in which the materials of corresponding electrical functional layers in the first stack and the second stack are different, and a configuration in which the material of the light-emitting layer included in the first stack and the material of the light-emitting layer included in the second stack are different, the relationship in the area of ​​the light-emitting layer between at least the second stack and the third stack satisfies the above-mentioned area ratio.

[0201] In the third to sixth embodiments, each of the light-emitting elements includes at least two light-emitting layers having different volumes in the second direction Y. This configuration can further improve the light-emitting efficiency and light-emitting lifetime compared to the tandem light-emitting element in the second embodiment.

[0202] Other Embodiments From the viewpoint of optimizing the carrier balance of all light-emitting layers in the second direction Y, in the light-emitting element of the present disclosure, the thickness of the light-emitting layer on the second electrode 35 side in the second direction Y may be thicker than that of the light-emitting layer on the first electrode 31 side. Furthermore, from the viewpoint of optimizing the carrier balance of all light-emitting layers in the second direction Y, in the light-emitting element of the present disclosure, the area of ​​the light-emitting layer on the second electrode 35 side in the second direction Y may be smaller than that of the light-emitting layer on the first electrode 31 side. Even with this configuration, it is possible to optimize the carrier balance of all light-emitting layers in the second direction Y depending on the situation, suppress the generation of excess carriers that cannot contribute to light emission, and supply an appropriate amount of carriers to each light-emitting layer. Therefore, even with the above configuration, highly efficient and high-brightness light emission may be possible.

[0203] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Alternatively, embodiments lacking some of the technical means disclosed in the embodiments are also included in the technical scope of the present disclosure, as long as the effects of the present disclosure are obtained. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0204] According to the present disclosure, it is possible to realize exposure that enables high-speed and high-efficiency high-resolution printing in electrophotographic devices. The present disclosure is expected to contribute to the realization of high-speed, high-resolution electrophotographic technology and to bring about revolutionary changes in the configuration of electrophotographic devices. The technology of the present disclosure is expected to contribute to the achievement of, for example, Goal 12 "Responsible Consumption and Production" and Goal 9 "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation" of the Sustainable Development Goals (SDGs) advocated by the United Nations.

[0205] The effectiveness of the different volumes of the light-emitting layers in a tandem light-emitting device, as shown in Embodiments 3 to 6, will be specifically explained below using a light-emitting device having a light-emitting layer containing semiconductor particles as an example. In the following examples, the first electrode is an anode and the second electrode is a cathode. In addition, when there are two or more layers having the same function, they are indicated by ordinal numbers counting from the anode (first electrode).

[0206] Example 1 Tandem light-emitting devices having two light-emitting layers (emission peak wavelength: 650 nm, full width at half maximum: 200 nm) that emit near-infrared light from red light were fabricated under the following three conditions, i to iii. The semiconductor particles contained in the light-emitting layer were InP (particle size: 3 to 10 nm). Under conditions i to iii, the light-emitting region was a perfect circle with a diameter of 10 μm. <Condition i> (Layer structure) first electrode / second stack (electron injection layer / electron transport layer / hole blocking layer / second red emitting layer (thickness: 25 nm) / hole transport layer / hole injection layer) / charge generation layer / first stack (electron transport layer / hole blocking layer / first red emitting layer (thickness: 25 nm) / electron blocking layer / hole transport layer / hole injection layer) / second electrode (Thickness ratio) Ratio of thickness of second red emitting layer (25 nm) to thickness of second stack (100 nm): 0.25 Ratio of thickness of first red emitting layer (25 nm) to thickness of first stack (200 nm): 0.125 <Condition ii> (Layer structure) Same as condition i (Thickness ratio) Total thickness of electrical functional layers in second stack layer: 85 nm Ratio of thickness of second red emitting layer (25 nm) to thickness of second stack layer (110 nm): 0.227 Other than that, same as condition i <Condition iii> (Layer structure) Same as condition i (Thickness ratio) Total thickness of the electrical functional layers in the second stack layer: 95 nm Ratio of the thickness of the second red light-emitting layer (25 nm) to the thickness of the second stack layer (120 nm): 0.208 Other than that, same as condition i

[0207] The radiant flux was measured for each of the tandem light-emitting elements under conditions i to iii. The radiant flux was measured by directly facing the light-emitting region of the light-emitting element to the light-receiving surface of an optical power meter using a Si photodiode. If the radiant flux is 0.10 μW or more, it can be said that there is no practical problem for use as an exposure head for high-speed electrophotography.

[0208] Furthermore, the device life, driving voltage, and current efficiency were measured for each of the tandem light-emitting devices under conditions i to iii.

[0209] The radiant flux of the tandem light-emitting element was 0.20 μW under condition i, 0.22 μW under condition ii, and 0.19 μW under condition iii. This was 1.67 times, 1.83 times, and 1.58 times that of a single light-emitting element (described below) under condition i, condition ii, and condition iii, respectively.

[0210] The current efficiency (=radiant flux / driving current) of the tandem light-emitting element was 0.43 W / A under condition i, 0.48 W / A under condition ii, and 0.39 W / A under condition iii. This was 1.71 times, 1.91 times, and 1.55 times that of a single light-emitting element (described below).

[0211] Furthermore, the element life of the tandem light emitting element was 2.0 times longer under condition i, 2.1 times longer under condition ii, and 1.9 times longer under condition iii than that of a single light emitting element described below.

[0212] Furthermore, the driving voltage of the tandem light emitting element was 2.0 times that of a single light emitting element described below under condition i, 1.94 times under condition ii, and 2.0 times under condition iii.

[0213] Comparative Example 1 A comparative single light-emitting device was fabricated having a single-layer light-emitting layer (emission peak wavelength: 650 nm, full width at half maximum: 200 nm) that emits near-infrared light from red light. The layer structure of the single light-emitting device was as follows: (Layer structure) First electrode / first stack (electron transport layer / hole blocking layer / red light-emitting layer (thickness: 25 nm) / electron blocking layer / hole transport layer / hole injection layer) / second electrode (Thickness ratio) Ratio of the thickness of the red light-emitting layer (25 nm) to the thickness of the first stack (200 nm): 0.125

[0214] As in Example 1, the maximum light intensity of the single light-emitting element was measured, and the element life, driving voltage, and current efficiency of the single light-emitting element were also measured.

[0215] As a result, the radiant flux of the single light-emitting element was 0.12 μW. The current efficiency of the single light-emitting element was 0.251 W / A. After the single light-emitting element of Comparative Example 1 was combined with a 1x magnification lens, the irradiance on the electrophotographic photosensitive member was approximately 0.10 μW. With this value, there is a possibility that the irradiation irradiance will be insufficient when printing high-resolution images exceeding 2400 dpi.

[0216] In this way, by using a tandem light-emitting element having multiple light-emitting layers, it is possible to reduce the size of the light-emitting area in the light source of the exposure head while ensuring sufficient radiant flux required for high-speed printing, making it suitable for realizing an exposure head for an electrophotographic device that can handle high speed and high resolution.

[0217] 1 Electrophotographic apparatus 10 Electrophotographic photosensitive member 11 Charging device 12 Exposure head 13 Developing device 14 Transfer device 15 Conveying device 16 Fixing device 17 Recording medium 20 Driving TFT layer 21 Buffer layer 23 Gate first insulating film 24 Gate electrode 25 Gate second insulating film 27 Planarizing layer 28 Contact hole 30 Light-emitting element layer 31 First electrode 32 Hole transport layer 33, 53, 63, 73, 83, 93, 103, 113 Light-emitting layer 34 Electron transport layer 35 Second electrode 36 Bank 40, 50, 60, 70, 80, 90 Light-emitting element 52, 72 Functional layer 121 Substrate 122 Light source 123 Equivalent magnification lens 151 Conveying belt 152, 153 Conveying roller 161 Heating roller 162 Pressure roller 221 to 223 Semiconductor layer 261 Source electrode 262 Drain electrode X Arrow indicating a first direction in the present disclosure Y Arrow indicating a second direction in the present disclosure

Claims

1. An exposure head arranged opposite the surface of an electrophotographic photosensitive member, comprising a plurality of light-emitting elements arranged in a first direction and emitting light corresponding to an electrostatic latent image to be formed on the surface of the electrophotographic photosensitive member in a second direction intersecting the first direction, each of the plurality of light-emitting elements comprising a first electrode, a light-emitting layer containing semiconductor particles that emit incoherent light, and a second electrode stacked in this order in the second direction, the light-emitting layer having a peak emission wavelength within the sensitivity spectrum of the electrophotographic photosensitive member, and the ratio of the full width at half maximum of the peak wavelength of emission of the light-emitting layer to the full width at half maximum of the sensitivity spectrum of the electrophotographic photosensitive member being 25% or more.

2. The exposure head according to claim 1, wherein the wavelength range of the light emitted from said light emitting layer is 620 nm or more and 1500 nm or less, and said full width at half maximum of the peak wavelength of the light emitted from said light emitting layer is greater than 150 nm.

3. An exposure head according to claim 1 or 2, wherein the full width at half maximum in the particle size distribution based on the number of particles of said semiconductor is 5 nm or more.

4. The semiconductor is GaAs, InP, GaSb, CdTe, CdSe, CdZnTe, CdMnTe, ZnTe, CuInS ２ , CuInSe ２ , CuGaSe ２ 4. The exposure head according to claim 1, wherein the semiconductor is one or more semiconductors selected from the group consisting of Hg, HgSe, ternary mixed crystals thereof, and quaternary mixed crystals thereof.

5. An exposure head according to any one of claims 1 to 4, wherein the element pitch of the light-emitting elements in the first direction is 43 μm or less, and the ratio of the element size of the light-emitting elements in the first direction to the element pitch is 0.7 or more.

6. An exposure head according to any one of claims 1 to 5, wherein each of the light-emitting elements is configured by stacking multiple sets of the light-emitting layer and an electrical functional layer overlapping it between the first electrode and the second electrode in the second direction.

7. The exposure head according to claim 6, wherein each of the light-emitting elements includes at least two of the light-emitting layers having different volumes in the second direction.

8. An electrophotographic apparatus comprising: an electrophotographic photosensitive member; a charging device that charges the electrophotographic photosensitive member; an exposure head according to any one of claims 1 to 7 that forms an electrostatic latent image by irradiating light onto the charged electrophotographic photosensitive member; a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photosensitive member with toner; a transfer device that transfers the toner image formed on the surface of the electrophotographic photosensitive member onto a recording medium; and a fixing device that fixes the toner image transferred onto the recording medium onto the recording medium.

Images