JPH04188597A - Light emitting element - Google Patents

Abstract

PURPOSE:To provide a steep threshold curve for the light emission intensity and make dielectric breakdown hardly occur by constructing a positive hole implantation layer or an electron implantation layer in the form of a non-linear electric conductive inducing later which is composed of a highpolymer insulating body and an electric charge moving substance dispersed in this highpolymer insulating body. CONSTITUTION:A base board is made of pylex glass 11, and a pattern is formed on an ITO electroconductive substance film to yield a cathode 12, and a crude solution of polydiisopropyl fumarate is applied to this base board 11. Thus a non-linear electric conduction inducing layer 13 is formed which is provided with a positive hole implantation function, and thereover anthracene is attached by vacuum evaporation to form a light emitting layer 14, and further thereover Cr is attached by vacuum evaporation, followed by pattern formation to make a pos. electrode 15. Thus a light emitting element is accomplished. In this manner, the positive hole implantation layer or electron implantation layer works also as a non-linear electric conduction inducing layer 13 and, further, they are composed of a highpolymer insulating body and an electric charge moving substance dispersed in this insulating body having excellent withstand voltage and mechanical strength, so that the light emission intensity threshold curve for the impression voltage can be made steep, and dielectric breakdown hardly occurs.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a light emitting device using an organic light emitting substance.

[Prior art 1 As a conventional light-emitting device using an organic light-emitting substance, a multilayer structure device having a hole injection layer or an electron injection layer is known (Saito et al., Kagaku to Kogyo Vol. 42, No. 11) (19
89) p143 etc.).

Each of the organic layers including the light emitting layer, the hole injection layer, and the electron injection layer is formed into a uniform thin film having a thickness of 1000 angstroms or less by vacuum deposition. At a driving voltage of about 10 volts DC, a luminance of 1ooOcd/rn' or more is obtained.

[Problem B to be Solved by the Invention] However, the light-emitting element formed in this manner does not have a steep threshold characteristic of light emission intensity with respect to applied voltage, and cannot be driven in a time-division manner for large-capacity display.

Further, there were problems such as dielectric breakdown easily occurring and device reliability being low.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a highly reliable light-emitting element that has a steep threshold characteristic of emission intensity with respect to an applied voltage, is capable of time-division driving for large-capacity display, and is resistant to dielectric breakdown.

[Means for Solving the Problems] The light emitting device of the present invention has an organic light emitting layer and at least one of a hole injection layer and an electron injection layer, wherein the hole injection layer or the electron injection layer is , is characterized by a nonlinear electrical conduction inducing layer composed of a polymer insulator and a charge transfer substance dispersed within the polymer insulator.

Further, the polymer insulator is characterized in that it is polydialkyl fumarate.

[Function] According to the above configuration of the present invention, since the hole injection layer or the electron injection layer also serves as the nonlinear electrical conduction inducing layer, the nonlinearity of the current density with respect to the En applied voltage can be made larger than before. . Therefore, the threshold characteristic of the emission intensity, which is approximately proportional to the current density, with respect to the applied voltage can be made steep.

If the hole injection layer or electron injection layer is composed of a polymeric insulator with excellent electrical withstand voltage and mechanical strength, and a charge transfer substance dispersed within the polymeric insulator, dielectric breakdown will not occur.
The reliability of the device can be improved. Polydialkyl fumarate is known as a material that, when used alone as a polymeric insulator, can provide a thin film with excellent electrical insulation properties even if it is a very thin film of several hundred angstroms.

Hereinafter, the details of the present invention will be shown by examples.

[Example 1 (Example 1) Polydiisopropyl fumarate (hereinafter abbreviated as PDiPF in this specification) was used as the polymer insulator used for the nonlinear electrically conductive layer. After P D i P'F was purified by reprecipitation, it was dissolved in toluene together with 5% by weight of an oxadiazole derivative, which is a hole-injecting substance.
The raw material solution was obtained through a filter.

FIG. 1 is a cross-sectional view of a light emitting element schematically showing the configuration in this example. Here, anthracene was used as a luminescent substance, but pyrene, benzanthracene, perylene,
Tetracene, naphthacene, coronene, coumarin, cyclopentadiene, quinoline, and derivatives of these organic light-emitting substances can similarly be used. A Pyrex glass 11 with an optically polished surface was used as a substrate, and a conductive film of ITO was formed by sputtering or vapor deposition, and a pattern with a width of 100 μm was formed by photoetching to form a cathode 12.

On this substrate, the above-mentioned PDiPF raw material solution was applied with a spin coater by controlling the rotation speed and time so that the film thickness was 1000 nm, thereby forming a nonlinear electrical conduction inducing layer 13 having a hole injection function. . Anthracene was formed thereon to a thickness of 500 nm by vacuum evaporation to form the light-emitting layer 14. Furthermore, after forming chromium by vacuum evaporation, a pattern was formed by photoetching to a width of 100 μm perpendicular to the cathode to form a positive electrode 15, and a light emitting device was obtained.

When an electric field was applied between the electrodes, a current suddenly began to flow at 10 volts or more, and light emission was observed. Further, even when a voltage of 50 volts was applied, no dielectric breakdown occurred and there was no change in the light emitting characteristics. FIG. 2 shows the luminescence characteristics with respect to the applied voltage. Since the threshold characteristic of the emitted light intensity with respect to the applied voltage was steep, time-division driving of 400 lines was possible.

(Example 2) The polymer insulator used for the nonlinear electrically conductive layer was polyte
Using rt-butyl fumarate (hereinafter abbreviated as PDtBF), PDtBF is purified by reprecipitation and then purified with phthalocyanine derivative 2, which is an electron injection substance.
It was dissolved in carbon tetrachloride together with % by weight and passed through a 0.5 μm filter to obtain a raw material solution.

An indium conductive film was formed by sputtering or vapor deposition on Pyrex glass whose surface had been optically polished, and a pattern with a width of 100 um was formed by photoetching to form a positive electrode. On top of that, the above-mentioned PDtB was coated with a spin coater, controlling the rotation speed and time so that the film thickness was 800 mm.
A raw material solution of F was applied to form a nonlinear electrical conduction inducing layer with an electron injection function.

On top of that, a quinoline derivative is deposited by vacuum evaporation.

A light-emitting layer was formed with a thickness of 800 mm. Furthermore, after forming ITO by vacuum evaporation, 1100L of ITO was deposited perpendicularly to the positive electrode.
A light-emitting device was obtained by forming butter on the L width by photoetching and using it as a cathode.

When an electric field was applied between the electrodes, a current suddenly began to flow above IO volts, and light emission was observed. Furthermore, even when a voltage of 50 volts was applied, no dielectric breakdown occurred and there was no change in the light emitting characteristics. Since the threshold characteristic of the emitted light intensity with respect to the applied voltage was steep, time-division driving of 400 lines was possible.

(Example 3) Polydicyclohexyl fumarate (hereinafter abbreviated as PDcHF) was used as the polymer insulator used in the nonlinear electrically conductive layer. PDcHF was purified by reprecipitation and then used as a hole injection substance. It was dissolved in toluene together with 8% by weight of a triphenylamine derivative, and passed through a 05 μm filter to obtain a raw material solution.

A conductive film of TO was formed by sputtering or vapor deposition on Pyrex glass whose surface had been optically polished, and a pattern with a width of 60L was formed by photoetching to form a cathode. On top of that, the above-mentioned PDcHF was coated with a spin coater, controlling the rotation speed and time so that the film thickness was 1200A.
A raw material solution was applied to form a nonlinear electrical conduction inducing layer with a hole injection function.

Thereon, a perinone derivative was formed by vacuum evaporation to a thickness of 800 nm to form a light-emitting layer, and subsequently a perylene tetracarboxyl derivative was formed by vacuum evaporation to a thickness of 800 nm to form an electron injection layer.

Further, chromium was formed by vacuum evaporation, and then butter was formed by photoetching to a width of 60 μm perpendicular to the cathode to serve as a cathode, and a light emitting device was obtained.

When an electric field was applied between the electrodes, a current suddenly began to flow at 8 volts or higher, and light emission was observed. In addition, even when a voltage of 50 volts was applied, no dielectric breakdown occurred, and there was no change in the emission characteristics.Because the threshold characteristics of the 6 emission intensities with respect to the applied voltage are steep, time-division driving of 400 lines is possible. there were.

Although examples have been described above, the light emitting substance, hole injection substance, charge injection substance, insulating polymer, and electrode material are not limited to the substances described here.

[Effects of the Invention] As described above, according to the present invention, in a light emitting element having an organic light emitting layer and at least one of a hole injection layer and an electron injection layer, the hole injection layer or the electron injection layer is , a nonlinear electrical conduction inducing layer composed of a polymeric insulator and a charge transfer material dispersed within the polymeric insulator, has a steep threshold characteristic of luminescence intensity with respect to applied voltage, making it possible to time-divisionally drive large-capacity displays. Therefore, it was possible to provide a highly reliable light-emitting element in which dielectric breakdown does not easily occur.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing the structure of a light emitting element in Example 1 of the present invention. FIG. 2 is a diagram showing the light emission characteristics of the light emitting device produced in Example 1 of the present invention with respect to applied voltage. 11...Substrate 12...Cathode 13...Nonlinear electrical conduction inducing layer with front plate injection function 14...Light emitting layer 15...Cathode 21...Light emission characteristic curve and above Applicant: Seiko Epson Corporation

Claims (2)

[Claims] (1) In a light emitting element having an organic light emitting layer and at least one of a hole injection layer and an electron injection layer, the hole injection layer or the electron injection layer is dispersed within a polymer insulator and a polymer insulator. 1. A light emitting device characterized by having a nonlinear electrical conduction inducing layer made of a charge transfer material. (2) The light emitting device according to claim 1, wherein the polymeric insulator is polydialkyl fumarate.