WO2007132965A1

WO2007132965A1 - High brightness electro luminescence device and method for manufacturing thereof

Info

Publication number: WO2007132965A1
Application number: PCT/KR2006/003914
Authority: WO
Inventors: Cheong-A Baek; Young-Jun Seo
Original assignee: Cheong-A Baek; Young-Jun Seo
Priority date: 2006-05-12
Filing date: 2006-09-29
Publication date: 2007-11-22

Abstract

An electroluminescence (EL) device includes a first electrode layer, a first light-emitting layer, an electric charge-recharging layer, a second light-emitting layer, a dielectric layer and a second electrode layer. The first light-emitting layer is disposed on the first electrode layer. The electric charge-recharging layer is disposed on the first light-emitting layer. The second light-emitting layer is disposed on the electric charge-recharging layer. The dielectric layer is disposed on the second light-emitting layer. The second electrode layer is disposed on the dielectric layer. Therefore, two light-emitting layers are formed, and an electric charge-recharging layer that rapidly provides electric charges between the two light-emitting layers is formed, so that an electric charge quantity and an instantaneous electric field may be increased when the EL device is driven, and thus high luminance light may be emitted.

Description

HIGH BRIGHTNESS ELECTRO LUMINESCENCE DEVICE AND METHOD FOR MANUFACTURING THEREOF

Technical Field The present invention relates to an electroluminescence device and a method for manufacturing the electroluminescence device, and more particularly, to a high-luminance electroluminescence device capable of achieving high brightness and a method for manufacturing the electroluminescence device.

Background Art

As modern electronic appliances are becoming increasingly diverse, backlighting is being increasingly introduced to illuminate display panels such as liquid crystal display (LCD) panels, so that an operator can easily view the display to operate the appliance, even in darkness. An electroluminescence (EL) device is a popular means used for such backlighting.

The EL device has thin, lightweight, and uniform surface light-emitting characteristics and a simpler manufacturing process than other types of lighting devices. Therefore, the EL device is used as backlighting for LCD apparatuses, keypads, etc., and is emerging quickly as a foundation technology of next-generation display apparatuses.

However, a conventional EL device has lower luminance than that of a light-emitting diode (LED), which is also used as backlighting for LCD apparatuses, keypads, etc.

Disclosure of the Invention Technical Problem

The present invention provides an electroluminescence (EL) device capable of achieving high luminance.

The present invention also provides a method for manufacturing an EL device capable of achieving high luminance. Technical Solution

In one aspect of the present invention, an EL device includes a first electrode layer, a first light-emitting layer, an electric charge-recharging layer, a second light-emitting layer, a dielectric layer and a second electrode layer. The first light-emitting layer is disposed on the first electrode layer. The electric charge-recharging layer is disposed on the first light-emitting layer. The second light-emitting layer is disposed on the electric charge-recharging layer. The dielectric layer is disposed on the second light-emitting layer. The second electrode layer is disposed on the dielectric layer.

For example, an insulation substrate is further disposed below the first electrode layer.

For example, a protection layer is further disposed on the second electrode layer. For example, the EL device further includes a first insulation layer formed between the first electrode layer and the first light-emitting layer. The first insulation layer suppresses generation of fine pinholes in a boundary area between the first electrode layer and the first light-emitting layer to decrease a leakage current. For example, the EL device further includes a second insulation layer formed between the first light-emitting layer and the electric charge-recharging layer. The second insulation layer suppresses generation of fine pinholes in a boundary area of an upper portion of the light-emitting layer to decrease a leakage current. For example, the EL device further includes a third insulation layer formed between the dielectric layer and the second electrode layer. The third insulation layer may suppress generation of fine pinholes in a boundary area of an upper portion of the dielectric layer to decrease a leakage current and suppress infiltration of the second electrode layer. For example, the electric charge-recharging layer includes a conductive organic polymer having high light transmittance. Here, the electric charge-recharging layer includes poly(3,4-ethylenedioxythiophene) (PEDOT).

In another aspect of the present invention, in order to manufacture an electroluminescence (EL) device, a first electrode layer is formed. Then, a first light-emitting layer is formed on the first electrode layer. Then, an electric charge-recharging layer is formed on the first light-emitting layer. Then, a dielectric layer is formed on the second light-emitting layer. Then, a second electrode layer is formed on the dielectric layer. For example, a protection layer is further formed on the second electrode layer.

For example, the first electrode layer includes an optically transparent and electrically conductive material.

For example, the first electrode is formed by one of a sputtering method, a deposition method, a spin-coating method and a screen printing method.

According to the EL device and the method for manufacturing the EL device, two light-emitting layers are formed, and an electric charge-recharging layer that rapidly provides electric charges between the two light-emitting layers is formed, so that an electric charge quantity and an instantaneous electric field are increased when the EL device is driven so that a high luminance light is emitted.

Brief Description of the Drawings

The above and other advantages of the present invention will become more apparent by describing in detail example embodiments thereof with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view illustrating an electroluminescence (EL) device according to an example embodiment of the present invention;

FIGS. 2 to 9 are cross-sectional views illustrating a method for manufacturing an EL device according to one example embodiment of the present invention;

FIG. 10 is a cross-sectional view illustrating an EL device according to another example embodiment of the present invention; FIGS. 11 to 21 are cross-sectional views illustrating a method for manufacturing an EL device according to another example embodiment of the present invention; and

FIG. 22 is a cross-sectional view illustrating an EL device according to a comparative example embodiment of the present invention.

Best Mode for Carrying Out the Invention

It should be understood that the example embodiments of the present invention described below may be varied modified in many different ways without departing from the inventive principles disclosed herein, and the scope of the present invention is therefore not limited to these particular following embodiments. Rather, these embodiments are provided so that this disclosure will be through and complete, and will fully convey the concept of the invention to those skilled in the art by way of example and not of limitation.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Example Embodiment 1 (EL device)

FIG. 1 is a cross-sectional view illustrating an electroluminescence (EL) device according to an example embodiment of the present invention.

Referring to FIG. 1, an EL device according to an example embodiment of the present invention includes an insulation substrate 20, a first electrode layer

21, a first light-emitting layer 23, an electric charge-recharging layer 25, a second light-emitting layer 26, a dielectric layer 27, a second electrode layer 29 and a polymer protection layer 30.

The insulation substrate 20 includes an optically transparent material. For example, the insulation substrate 20 may include a transparent plastic substrate. The insulation substrate 20 defines a shape of the EL device, and supports the EL device. The insulation substrate 20 isolates and protects the first electrode layer 21 from the exterior, and transmits light generated from the first light-emitting layer 23 to emit the light toward the exterior.

The first electrode layer 21 includes a conductive material having a metal oxide compound or a conductive material having high light transmittance.

The first electrode layer 21 is formed on the insulation substrate 20 through a sputtering method, a deposition method, a spin-coating method, a screen printing method, etc.

The first light-emitting layer 23 is formed on the first electrode layer 21.

The first light-emitting layer 23 emits light by emitting light energy due to impact excitation with outer electrons of an internal light-emitting area in response to a potential difference that is applied through the first electrode layer 21 and the second electrode layer 29.

The electric charge-recharging layer 25 is formed on the first light-emitting layer 23. The electric charge-recharging layer 25 recharges electric charges in an interface portion of the first light-emitting layer 23. The electric charge-recharging layer 25 performs as an electric charge transport layer that induces electric charges in the boundary area of the first and second light-emitting layers 23 and 26, when minute electric charges are transferred in the electric charge-recharging layer 25. The electric charge-recharging layer 25 includes a transparent conductive material to enhance light transmittance.

The second light-emitting layer 26 is formed on the electric charge-recharging layer 25. The second light-emitting layer 26 emits light by emitting light energy due to impact excitation with outer electrons of an internal light-emitting area in response to a potential difference that is applied through the first and second electrode layers 21 and 29.

The dielectric layer 27 is formed on the second light-emitting layer 26. The dielectric layer 27 forms an electric field in the second light-emitting layer

26 by generating a positive and negative polarization phenomenon of charges in an interface portion of the second light-emitting layer 26. The dielectric layer

27 includes a dielectric powder such as SrTiO, BaTiO and TiO₂ and an organic polymer binder to ensure a high dielectric constant.

The second electrode layer 29 is formed on the dielectric layer 27. The polymer protection layer 30 covers a portion of an upper surface of the second electrode layer 29, and side surfaces of the first light-emitting layer 23, the electric charge-recharging layer 25, the second light-emitting layer 26, the dielectric layer 27 and the second electrode layer 29, to protect the EL device from external humidity, pollution and impacts.

In operating the EL device, when an alternating current (AC) driving power source is applied to each of the first and second electrode layers 21 and 29 through a first terminal electrode 21a formed on a portion of the first electrode layer 21 and a second terminal electrode 29a formed on a portion of the second electrode layer 29, a relatively high electric field is formed in each of the interiors of the first light-emitting layer 23 and the second light-emitting layer 26.

Electrons that are accelerated by the high electric field collide with and excite electrons in each of the interiors of the first and second light-emitting layers 23 and 26. When the excited electrons return to the ground state, light is emitted. The light, which is generated in the first light-emitting layer 23, transmits through the first electrode layer 21 and the insulation substrate 20 to exit toward the exterior.

The light, which is generated in the interior of the second light-emitting layer 23, transmits through the electric charge-recharging layer 25, the first light-emitting layer 23, the first electrode layer 21 and the insulation substrate 20 to exit toward the exterior.

In the electric charge-recharging layer 25, internal minute electric charges perform a function of an electric charge transport layer that induces electric charges at a boundary surface between the first and second light-emitting layers 23 and 26 while moving through the electric charge-recharging layer 25. Therefore, a charging quantity of each of the first and second light-emitting layers 23 and 26 may be further increased. As the charging quantity is increased, electric charges are rapidly provided to the interior of the first and second light-emitting layers 23 and 26 and an instantaneous electric field is increased, so that high luminance of the EL device is accomplished.

Example Embodiment 2 (Method for manufacturing an EL device)

FIGS. 2 to 9 are cross-sectional views illustrating a method for manufacturing an EL device according to one Example embodiment of the present invention.

Referring to FIG. 2, an insulation substrate 20 is prepared. The insulation substrate 20 includes an optically transparent material. For example, the insulation substrate 20 may include a transparent plastic substrate. The insulation substrate 20 defines a shape of an organic light-emitting device and supports the organic light-emitting device. The insulation substrate 20 insulates and protects the first electrode layer 21 from the exterior, and transmits the light generated in the first light-emitting layer 23 to the exterior.

Referring to FIG. 3, a first electrode layer 21 is formed on the first insulation substrate 20 through a sputtering method, a deposition method, a spin-coating method, a screen printing method, etc. The first electrode layer 21 includes a conductive material having a metal oxide compound or a conductive material having high light transmittance. For example, the first electrode layer

21 may include an indium tin oxide (ITO) paste having an ITO powder and a binder, antimony tin oxide (ATO), or a conductive polymer. For another example, the first electrode layer 21 may include a mixture material of a conductive polymer and an ITO powder.

Referring to FIG. 4, a first light-emitting layer 23 is formed on the first electrode layer 21. The first light-emitting layer 23 includes a light-emitting substance powder and a binder. The light-emitting substance powder may include a group II- VI compound consisting of an element from group II and an element from group VI, such as ZnS. The binder used in the first light-emitting substance layer 23 has a dielectric constant that is greater than that of the light-emitting substance powder. The binder may include cyanoethyl pullulan, fluororesin, and the like.

Referring to FIG. 5, an electric charge-recharging layer 25 is formed on the first light-emitting layer 23. The electric charge-recharging layer 25 includes a transparent conductive material to enhance light transmittance. The electric charge-recharging layer 25 may include poly(3 ,4-ethylenedioxythiophene) (PEDOT).

Referring to FIG. 6, a second light-emitting layer 26 is formed on the electric charge-recharging layer 25. The second light-emitting layer 26 includes a light-emitting substance powder and a binder. The light-emitting substance powder may include a group II- VI compound consisting of a group II element and a group VI element, such as ZnS. The binder used in the second light-emitting substance layer 26 has a dielectric constant that is greater than that of the light-emitting substance powder. The binder may include cyanoethyl pullulan, fluororesin, and the like. For example, the first and second light-emitting layers 23 and 26 may be composed of the same material. Alternatively, the first and second light-emitting layers 23 and 26 may be composed of different materials.

Referring to FIG. 7, a dielectric layer 27 is formed on the second light-emitting layer 26. The dielectric layer 27 includes a mixture of a dielectric substance powder and a binder. The dielectric substance powder includes a material having high dielectric constant such as SrTiO, BaTiO, TiO₂, and the like, and particle sizes of about 0.1 μm to about 10 μm. The binder that is used in the dielectric layer 27 may include cyanoethyl pullulan, fluororesin, and the like. In order to vary a light-emitting color of the EL device, a light-emitting dye, such as rhodamine or a light-emitting pigment, may be mixed into the binder of the light-emitting layer 26 or the binder of the dielectric layer 27.

Referring to FIG. 8, a second electrode layer 29 is formed on the dielectric layer 27. The second electrode layer 29 includes a mixture of a conductive powder and a binder, a conductive organic polymer, or a mixture of the conductive powder and the conductive organic polymer. The conductive powder includes, for example, a carbon powder, a silver powder, a copper powder, a copper powder having silver coated thereon, etc. The conductive polymer includes, for example, PEDOT, poly(3,4-ethylenedioxythiophene) ρoly(styrenesulfonate) (PEDOTiPSS), etc.

Referring to FIG. 9, a polymer protection layer 30 is formed to cover a portion of an upper surface of the second electrode layer 29, and side surfaces of the first light-emitting layer 23, the electric charge-recharging layer 25, the second light-emitting layer 26, the dielectric layer 27 and the second electrode layer 29. The polymer protection layer 30 protects the EL device from external humidity, pollution and impacts. The polymer protection layer 30 should have superior moisture-proof properties after drying of the polymer protection layer 30 and superior adhesive properties for adhesion to the insulation substrate 20, so that the polymer protection layer 30 may include a polymer of a fluorine compound, a binder including polyurethane, or a polymer that hardens when infrared (IR) light or ultraviolet (UV) light is irradiated to the polymer protection layer 30.

The EL device is manufactured as a paste formed with a powder and a polymer through a screen printing method. Here, when each layer is printed in the target printed substance, an air bubble is formed in the target printed substance. When a drying process is performed before the air bubble is removed from the target printed substance, fine pinholes are generated in a portion of the air bubble. For example, the fine pinholes generated in the interior of the light-emitting layer or the insulation layer may induce a leakage current in the interior of the EL device.

Due to the leakage current, luminance and a capacitance value are not stable when the EL device is driven, so that an internal leakage current may be increased and stress may be induced in the pinholes portion. Therefore, an insulation breakdown may be generated, so that a black point may be generated at a surface of the EL device.

Moreover, the leakage current decreases the lifetime of the light-emitting power, so that the lifetime of the EL device may be decreased.

Example Embodiment 3 (EL device) FIG. 10 is a cross-sectional view illustrating an EL device according to another example embodiment of the present invention.

Referring to FIG. 10, an EL device according to another example embodiment of the present invention includes an insulation substrate 20, a first electrode layer 21, a first insulation polymer layer 22, a first light-emitting layer 23, a second insulation polymer layer 24, an electric charge-recharging layer 25, a second light-emitting layer 26, a dielectric layer 27, a third insulation polymer layer 28, a second electrode layer 29 and a polymer protection layer 30. In FIG. 10, the same reference numerals denote the same elements in FIG. 1, and thus detailed descriptions of the same elements will be omitted. The first insulation polymer layer 22 is formed on the first electrode layer 21. The first insulation polymer layer 22 may prevent fine pinholes from being generated in an interface portion between the first electrode layer 21 and the light-emitting layer 23 to perform a function of decreasing the leakage current. The second insulation polymer layer 24 is formed on the first light-emitting layer 23. The second insulation polymer layer 24 may prevent fine pinholes from being generated in an interface surface of an upper portion of the first light-emitting layer 23 to decrease a leakage current.

The third insulation polymer layer 28 is formed on the dielectric layer 27. The third insulation polymer layer 28 may prevent fine pinholes from being generated in an interface surface of an upper portion of the dielectric layer 27 to decrease a leakage current, and may perform a function of preventing infiltration of the second electrode 29. Additionally, a first terminal electrode is formed at a first end portion of the first electrode layer 21, and a second terminal electrode is formed at a first end portion of the second electrode layer 29. An AC driving power source that is applied to the first and second electrode layers 21 and 29 is substantially the same as that in FIG. 1. As described above, according to the present invention, the first to third insulation polymer layers 22, 24 and 28 are added to the structure of FIG. 1, so that pinholes that may be generated during a screen printing process may be removed. Furthermore, a leakage current inducing a malfunction of the EL device may be prevented, and insulating characteristics may be enhanced. The first insulation polymer layer 22 is formed between the first electrode layer 21 and the first light-emitting layer 23, thereby preventing direct contact between the first electrode layer 21 and the first light-emitting layer 23. Furthermore, the first insulation polymer layer 22 may prevent the fine pinholes from being generated in an interface portion between the first electrode layer 21 and the light-emitting layer 23 to perform a function of decreasing the leakage current. Furthermore, the first insulation polymer layer 22 prevents rapid loss and movement of electric charges that are generated in the interior of the first light-emitting layer 23.

The second insulation polymer layer 24 is formed between the first light-emitting layer 23 and the electric charge-recharging layer 25, thereby preventing contact between the first light-emitting layer 23 and the electric charge-recharging layer 25. Furthermore, the second insulation polymer layer 24 may suppress generation of the fine pinholes at a boundary surface of an upper portion of the light-emitting layer 23 to decrease the leakage current, and prevents rapid loss and movement of electric charges that are generated in the interior of the first light-emitting layer 23.

The third insulation polymer layer 28 is formed between the dielectric layer 27 and the second electrode layer 29, thereby preventing the fine pinholes from being generated in an interface surface of an upper portion of the dielectric layer 27 to decrease a leakage current, and may perform a function of preventing infiltration of the conductive powder of the second electrode 29 from the dielectric layer 27.

The first to third insulation polymer layers 22, 24 and 28 may remove fine pinholes that may be generated during a screen printing process, so that a leakage current that internally damages the first to third insulation polymer layers 22, 24 and 28 may be prevented and insulating characteristics may be enhanced.

Additionally, the first to third insulation polymer layers 22, 24 and 28 may also have characteristics of a polar polymer, so that electric charges, which are generated as dielectric polarization in the light-emitting layers that are adjacent to each other, may be induced due to a dielectric constant of an organic polymer to achieve high luminance.

According to the first to third insulation polymer layers 22, 24 and 28 that are structured as described above, a flow of a leakage current that is generated by the pinholes in the conventional EL device may be minimized.

Moreover, insulation characteristics may be enhanced, so that internal damage (i.e., an insulation breakdown) of an EL device may be prevented. Moreover, a dielectric constant of the organic polymer is increased due to dielectric polarization characteristics of the insulation organic polymer, so that electric charges may be induced, which are generated as dielectric polarization in the light-emitting layers that are adjacent to each other. Therefore, a voltage is increased to achieve a relatively high luminance.

As described above, according to another example embodiment of the present invention, in order to achieve high luminance characteristics of the EL device, each of the first to third insulation polymer layers is formed between the first electrode layer and first light-emitting layer, the first light-emitting layer and electric charge-recharging layer, and the dielectric layer and second electrode layer, respectively, so that each of the insulation polymer layers may prevent the leakage current. Therefore, the EL device may be stably driven.

Moreover, according to another example embodiment of the present invention, the lifetime of the EL device may be extended.

Example Embodiment 4 (Method for manufacturing an EL device)

FIGS. 11 to 21 are cross-sectional views illustrating a method for manufacturing an EL device according to another example embodiment of the present invention.

Referring to FIG. 11, an insulation substrate 20 is prepared. The insulation substrate 20 includes, for example, a transparent material. For example, the insulation substrate 20 defines a shape of an EL device, and supports the EL device. The insulation substrate 20 isolates and protects the first electrode layer 21 from the exterior, and transmits light generated from the first light-emitting layer 23 to emit the light toward the exterior.

Referring to FIG. 12, a first electrode layer 21 is formed on the insulation substrate 20 through a sputtering method, a deposition method, a spin-coating method, a screen printing method, etc. The first electrode layer 21 may include a conductive material having a metal oxide compound and a conductive material having high light transmittance. For example, the first electrode layer 21 may include an ITO paste having an ITO powder and a binder,

ATO, or a conductive polymer. For another example, the first electrode layer 21 may include a mixture material of a conductive polymer and an ITO powder.

Referring to FIG. 13, a first insulation polymer layer 22 is formed on the transparent electrode layer 21.

Referring to FIG. 14, a first light-emitting layer 23 is formed on the first insulation polymer layer 22. The first light-emitting layer 23 includes a light-emitting substance powder and a binder. The light-emitting substance powder may include a group II-VI compound consisting of a group II element and a group VI element, such as ZnS. The binder used in the first light-emitting substance layer 23 has a dielectric constant that is greater than that of the light-emitting substance powder. The binder may include cyanoethyl pullulan, fluororesin, and the like.

Referring to FIG. 15, a second insulation polymer layer 24 is formed on the first light-emitting layer 23.

Referring to FIG. 16, an electric charge-recharging layer 25 is formed on the second insulation polymer layer 24. The electric charge-recharging layer 25 includes a transparent conductive material to enhance light transmittance. The electric charge-recharging layer 25 may include PEDOT.

Referring to FIG. 17, a second light-emitting layer 26 is formed on the electric charge-recharging layer 25. The second light-emitting layer 26 includes a light-emitting substance powder and a binder. The light-emitting substance powder may include a group II-VI compound consisting of a group II element and a group VI element, such as ZnS. The binder used in the second light-emitting substance layer 26 has a dielectric constant that is greater than that of the light-emitting substance powder. The binder may include cyanoethyl pullulan, fluororesin, and the like. For example, the first and second light-emitting layers 23 and 26 may be composed of the same material. Alternatively, the first and second light-emitting layers 23 and 26 may be composed of different materials.

Referring to FIG. 18, a dielectric layer 27 is formed on the second light-emitting layer 26. The dielectric layer 27 includes a mixture of a dielectric substance powder and a binder. The dielectric substance powder includes a material having high dielectric constant such as SrTiO, BaTiO, TiO₂, and the like, and particle sizes of about 0.1 μm to about 10 μm. The binder that is used in the dielectric layer 27 may include cyanoethyl pullulan, fluororesin, and the like. In order to vary a light-emitting color of the EL device, a light-emitting dye, such as rhodamine or a light-emitting pigment, may be mixed into the binder of the light-emitting layer 26 or the binder of the dielectric layer 27.

Referring to FIG. 19, a third insulation polymer layer 28 is formed on the dielectric layer 27.

Referring to FIG. 20, a second electrode layer 29 is formed on the third insulation polymer layer 28. The second electrode layer 29 includes a mixture of a conductive powder and a binder, a conductive organic polymer, or a mixture of the conductive powder and the conductive organic polymer. The conductive powder includes, for example, a carbon powder, a silver powder, a copper powder, a copper powder having silver coated thereon, etc. The conductive polymer includes, for example, PEDOT, PEDOT:PSS, etc.

Referring to FIG. 21, a polymer protection layer 30 is formed to cover a portion of an upper surface of the first electrode layer 21, and side surfaces of the first insulation polymer layer 22, the first light-emitting layer 23, the second insulation polymer layer 24, the electric charge-recharging layer 25, the second light-emitting layer 26, the dielectric layer 27, the third insulation polymer layer 28 and the second electrode layer 29. The polymer protection layer 30 protects the EL device from external humidity, pollution and impacts. The polymer protection layer 30 should have superior moisture-proof properties after drying of the polymer protection layer 30 and superior adhesive properties for adhesion to the insulation substrate 20, so that the polymer protection layer 30 may include a polymer of a fluorine compound, a binder including polyurethane, and a polymer that hardens when IR light or UV light is irradiated to the polymer protection layer 30.

Hereinafter, characteristics of the EL device according to the present invention and characteristics of the EL device according to a conventional EL device are illustrated in detail. The conventional EL device is illustrated in FIG. 22. Comparative Example (EL device)

FIG. 22 is a cross-sectional view illustrating an EL device according to a comparative example embodiment of the present invention. Particularly, FIG. 22 illustrates a cross-sectional view of a conventional EL device. Referring to FIG. 22, an EL device according to the Comparative

Example of the present invention includes an insulation substrate 10, a first electrode layer 11, a light-emitting layer 12, a dielectric layer 13, a second electrode layer 14 and a protection layer 15. Each of the insulation substrate 10, the first electrode layer 11, the light-emitting layer 12, the dielectric layer 13, the second electrode layer 14 and the protection layer 15 is substantially the same as the insulation substrate 20, the first electrode layer 21, the first light-emitting layer 23, the dielectric layer 27, the second electrode layer 29 and the protection layer 30 as described in FIG. 1, respectively, so that any further explanation concerning the above elements will be omitted. A data checklist that is set to check electrical characteristics and optical characteristics of each of the EL device according to the present invention and the EL device according to the Comparative Example, is illustrated in the following Table 1.

Table 1

The following Table 2 illustrates moisture test results of the EL device according to the present invention and the EL device according to the Comparative Example. Particularly, driving conditions of the EL device were under test conditions, in which a voltage and a frequency were about 100 V and about 400 Hz, respectively, and a relatively humidity (RH) was about 60% to about 90%. The following Table 2 illustrates that initial luminance values were compared with decreasing luminance values after about 120 hours and after about 240 hours.

Table 2

As illustrated in Table 2, under the initial luminance characteristics, the EL device according to the present invention had a luminance characteristic of about 55.9 cd/m², and the EL device according to the Comparative Example had a luminance characteristic of about 77.4 cd/m². Therefore, the EL device of the present invention had a luminance enhanced by about 21.5 cd/m² in comparison with the EL device of the Comparative Example. Under the reliability characteristics, after about 120 hours, a luminance with respect to the initial luminance of the EL device of the Comparative Example decreased by about 45%, and that of the EL device of the present invention decreased by about 31%. That is, according to the results of the reliability characteristics, after about 120 hours, the EL device of the present invention had reliability characteristics enhanced by about 14% in comparison with the EL device of the Comparative Example.

Moreover, after about 240 hours, a luminance with respect to the initial luminance of the EL device according to the Comparative Example decreased by about 71%, and that of the EL device according to the present invention decreased by about 54%. That is, according to the results of the reliability characteristics after about 240 hours, the EL device according to the present invention had reliability characteristics enhanced by about 17% in comparison with the EL device according to the Comparative Example. Therefore, under high temperature and moisture, the EL device according to the present invention may have relatively stable reliability.

Considering the luminance and reliability characteristics as described above, an initial luminance of the EL device of the present invention may be relatively higher than that of the EL device of the Comparative Example, and reliability of the EL device of the present invention may be enhanced in comparison with the EL device of the Comparative Example.

The following Table 3 illustrates electric data of the EL device according to the example embodiment of the present invention and the EL device according to the Comparative Example. Particularly, driving conditions of the EL device were under test conditions, in which a voltage and a frequency were about 100 V and about 400 Hz, respectively. The following Table 3 illustrates a comparison of capacitance values of the Comparative Example and the example embodiment of the present invention.

Table 3

Generally, a relationship between a luminance and a capacitance is defined by the following Relation Equation 1. Relation Equation 1

B ∞ Q. E_pth = C_d . (V_a - V_at) . E_pth

Here, 'B' denotes a luminance, 'C_d' denotes a capacitance of an insulation layer, 'V₈' denotes an external applying voltage, 'V_at' denotes an external threshold voltage between the insulation layer and a light-emitting layer, and 'E_pth' denotes a threshold voltage of the light-emitting layer.

In Relation Equation 1, a charging quantity Q is defined by a multiplying a voltage V_a-V_at that is applied from the exterior and a capacitance Ca of the insulation layer. When the capacitance C_d is increased, a luminance B may be increased.

Moreover, as a capacitance C_d is defined by the equation such as

C ε_r = — • A , when a dielectric constant ε_r of the polymer is increased, the

capacitance C_d is increased.

As described above in Table 3, under a driving voltage of about 100 V and a driving frequency of about 400 Hz, the EL device of the present invention may have a relatively higher capacitance than the EL device of the Comparative Example.

Because a dielectric constant of a polymer that is used in the EL device according to the present invention is relatively higher, a charging quantity that is generated as dielectric polarization in an interface portion between the third insulation polymer layer and the insulation layer may be increased. Therefore, a dielectric constant of the dielectric layer is increased, so that luminance of the EL device according to the present invention may be enhanced with respect to that of the EL device according to the Comparative Example.

That is, in the EL device according to the present invention, a charging quantity, which is induced by the third insulation polymer layer, is increased in addition to a dielectric constant of the dielectric layer.

The following Table 4 illustrates current data of the EL device according to the example embodiment of the present invention and the EL device according to the Comparative Example. Particularly, comparative data corresponding to a minute current, which is generated from the EL device according to the present invention, is illustrated in the following Table 4.

Table 4

As illustrated in Table 4, a current density of the EL device according to the present invention was remarkably lower than that of the EL device according to the Comparative Example.

This is because when the EL device is manufactured, the first to third insulation polymer layers cover the fine pinholes that may be generated on each of the layers, so that a minute leakage current, which may be generated by the fine pinholes when a voltage is applied thereto, may be prevented.

The following Tables 5 and 6 illustrate optical data of the EL device according to the example embodiment of the present invention and the EL device according to the Comparative Example. Particularly, Table 5 illustrates luminance values and color coordinates under conditions of about 100 V/400 Hz, and Table 6 illustrates luminance values and color coordinates under conditions of about l20 V/60 Hz. Table 5

As illustrated in Table 5, under conditions including a driving voltage of about 100 V and a driving frequency of about 400 Hz, each of the first to third samples corresponding to the EL device according to the Comparative Example had a luminance characteristic of about 55.9 cd/m², about 54.7 cd/m² and about

57.4 cd/m², respectively.

On the other hand, each of the fourth to sixth samples corresponding to the EL device according to the present invention had a luminance characteristic of about 77.4 cd/m², about 73.4 cd/m²and about 76.7 cd/m², respectively.

Therefore, the EL device according to the present invention had an enhanced luminance of about 20 cd/m² in comparison with the EL device according to the Comparative Example. On the other hand, it can be seen that Commission Internationale de l'Eclairege (CIE) color coordinates of the EL device according to the Comparative Example and those of the EL device according to the present invention were substantially equal to each other. Table 6

As illustrated in Table 6, under conditions including a driving voltage of about 120 V and a driving frequency of about 60 Hz, each of the first to third samples corresponding to the EL device according to the Comparative Example had a luminance characteristic of about 20.5 cd/m², about 20.9 cd/m² and about

21.1 cd/m , respectively.

On the other hand, each of the fourth to sixth samples corresponding to the EL device according to the present invention had a luminance characteristic of about 29.1 cd/m², about 28.6 cd/m² and about 28.4 cd/m², respectively.

Therefore, the EL device according to the present invention had an enhanced luminance of about 8 cd/m² in comparison with the EL device according to the Comparative Example. On the other hand, it can be seen that CIE color coordinates of the EL device according to the Comparative Example and those of the EL device according to the present invention were substantially equal to each other.

As described above, the structure of the EL device according to the present invention includes the first and second light-emitting layers 23 and 26 that are formed between the first electrode layer 21 and the second electrode layer 29, and the electric charge-recharging layer 25 is formed between the first and second light-emitting layers 23 and 26.

When the EL device is driven, the electric charge-recharging layer 25 rapidly provides electric charges to each of the interiors of the first and second light-emitting layers 23 and 26, so that an electric charge quantity and an instantaneous electric field are further increased, and thus luminance of the EL device may be increased.

Moreover, according to the present invention, the electric charge-recharging layer 25 is formed between the first light-emitting layer 23 and the second light-emitting layer 26, so that electric charges are recharged in the first to second light-emitting layers 25 and 26 when the EL device is driven, and thus an electric charge quantity that is provided to each of the first and second light-emitting layers 25 and 26 may be further increased.

Therefore, a voltage that is applied to the first and second light-emitting layers 25 and 26 is increased, so that luminance of the EL device according to the present invention may be enhanced about 30% to about 40% with respect to that of the EL device having a single light-emitting layer according to the Comparative Example.

Moreover, when luminance conditions of the EL device according to the present invention and the EL device according to the Comparative Example are substantially the same, power consumption of the EL device may be decreased by about 20% to about 30% due to the electric charge-recharging layer. As a result, luminance of the EL device may be enhanced, and the lifetime and reliability of the EL device may be improved. This invention has been described with reference to the example embodiments. It is evident, however, that many alternative modifications and variations will be apparent to those having skill in the art in light of the foregoing description. Accordingly, the present invention embraces all such alternative modifications and variations as falling within the spirit and scope of the appended claims.

Industrial Applicability

According to the present invention, in the electroluminescence (EL) device, two light-emitting layers are formed between the first electrode layer and the second electrode layer, and the electric charge-recharging layer is formed between the two light-emitting layers, so that consumption power of the EL device may be reduced and luminance of the EL device may be increased.

Moreover, in the EL device, the first insulation polymer layer is formed between the first electrode layer and the first light-emitting layer, the second insulation polymer layer is formed between the first light-emitting layer and the electric charge-recharging layer, and the third insulation polymer layer is formed between the organic layer and the second electrode layer, so that driving stability of the EL device may be achieved. Furthermore, reliability of the EL device may be increased, and the lifetime of the EL device may be extended.

Claims

1. An electroluminescence (EL) device comprising: a first electrode layer; a first light-emitting layer disposed on the first electrode layer; an electric charge-recharging layer disposed on the first light-emitting layer; a second light-emitting layer disposed on the electric charge-recharging layer; a dielectric layer disposed on the second light-emitting layer; and a second electrode layer disposed on the dielectric layer.

2. The EL device of claim 1, further comprising: an insulation substrate disposed below the first electrode layer.

3. The EL device of claim 1, further comprising: a protection layer disposed on the second electrode layer.

4. The EL device of claim 3, wherein the protection layer covers an upper portion of the first electrode layer, the first light-emitting layer, the electric charge-recharging layer, the second light-emitting layer and a side portion of the dielectric layer.

5. The EL device of claim 1, further comprising a first insulation layer formed between the first electrode layer and the first light-emitting layer, the first insulation layer suppressing generation of fine pinholes in a boundary area between the first electrode layer and the first light-emitting layer to decrease a leakage current.

6. The EL device of claim 5, wherein the first insulation layer comprises a polymer.

7. The EL device of claim I₅ further comprising a second insulation layer formed between the first light-emitting layer and the electric charge-recharging layer, the second insulation layer suppressing generation of fine pinholes in a boundary area of an upper portion of the light-emitting layer to decrease a leakage current.

8. The EL device of claim 7, wherein the second insulation layer comprises a polymer.

9. The EL device of claim I₅ further comprising a third insulation layer formed between the dielectric layer and the second electrode layer, the third insulation layer suppressing generation of fine pinholes in a boundary area of an upper portion of the dielectric layer to decrease a leakage current and suppress infiltration of the second electrode layer.

10. The EL device of claim 9, wherein the third insulation layer comprises a polymer.

11. The EL device of claim 1, further comprising: a first terminal electrode formed at a first end portion of the first electrode layer; and a second terminal electrode formed at a first end portion of the second electrode layer.

12. The EL device of claim I₅ wherein the electric charge-recharging layer comprises a conductive organic polymer having high light transmittance.

13. The EL device of claim 12, wherein the electric charge-recharging layer comprises poly(3, 4-ethylenedioxythiophene) (PEDOT).

14. A method for manufacturing an electroluminescence (EL) device comprising: forming a first electrode layer; forming a first light-emitting layer on the first electrode layer; forming an electric charge-recharging layer on the first light-emitting layer; forming a dielectric layer on the second light-emitting layer; and forming a second electrode layer on the dielectric layer.

15. The method of claim 14, further comprising: forming a protection layer on the second electrode layer.

16. The method of claim 14, wherein the first electrode layer includes an optically transparent and electrically conductive material.

17. The method of claim 14, wherein the first electrode is formed by one of a sputtering method, a deposition method, a spin-coating method and a screen printing method.