Organic light-emitting device with improved layer structure
An organic light emitting device having a cathode, an anode and an organic layer structure disposed between the cathode and the anode, the organic layer structure comprising a hole injection layer doped with a p-type dopant, a hole transport layer, an emissive layer and an electron transport layer doped with an n-type dopant, wherein all of the layers in the organic layer structure are substantially made from the same organic host material. In particular, the organic host material is a bipolar organic material such as a derivative of fused aromatic rings. The emissive layer can be doped with a fluorescent dye or a phosphorescent dye.
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This application is a divisional application of and claims priority to a pending U.S. patent application Ser. No. 11/014,508, filed Dec. 16, 2004.
FIELD OF THE INVENTIONThe present invention relates generally to light-emitting devices and, more particularly, to organic light-emitting diodes.
BACKGROUND OF THE INVENTION Organic light-emitting diodes OLEDs are known in the art. For example, Kido et al. (U.S. Pat. No. 6,013,384) discloses, as shown in
Weaver et al. (U.S. Publication No. 2004/0032206 A1) discloses another OLED including an alkali metal compound layer. As shown in
Raychaudhuri et al. U.S. Pat. No. 6,579,629 B1) discloses an OLED 30 (see
Hung et al. (U.S. Pat. No. 5,776,623) discloses an eletroluminescent device 40 (see
In the above-mentioned OLEDs, at least the EML and HTL are made from different materials. In Weaver et al., the ETL and the EML are also made from different materials. When the HIL, HTL, EML and ETL are made from different organic materials, it is required to have four difference deposition channels to separately deposit the different organic materials in order to avoid cross contamination in the fabrication process. In the fabrication of a full-color organic display device, the deposition of the organic layers is complex and costly.
It is thus advantageous and desirable to provide a method for producing an organic light-emitting device wherein the number of different organic deposition channels can be reduced.
SUMMARY OF THE INVENTIONIt is a primary objective of the present invention to provide an organic light-emitting diode (OLED) wherein the number of different materials, especially the host materials, used in the organic layers in such an OLED, is reduced. In order to achieve this objective, the present invention uses a bipolar organic material such as materials derived from fused aromatic rings as the host material at least for the emissive layer and the hole transport layer in an OLED. The OLED can be a phosphorescent OLED or a fluorescent OLED.
Thus, the first aspect of the present invention provides an organic light emitting device comprising:
a cathode;
an anode; and
an organic layer structure disposed between the cathode and the anode, the organic layer comprising:
a hole transport layer disposed adjacent to the anode;
an electron transport layer disposed adjacent to the cathode; and
an emissive layer disposed between the hole transport layer and the electron transport layer, wherein the hole transport layer, the emissive layer and the electron transport layer are made from substantially the same organic host material.
According to the present invention, the organic host material comprises a bipolar organic material, such as a derivative of fused aromatic rings, like a derivative of anthracene.
According to the present invention, the electron transport layer is made substantially from a bipolar organic material doped with at least one n-type dopant.
According to the present invention, the emissive layer is made substantially from a bipolar organic material doped with at least one fluorescent dopant or one phosphorescent dopant.
According to the present invention, the hole transport layer is doped with a p-type dopant.
According to the present invention, the organic layer structure further comprises a hole injection layer disposed between the hole transport layer and the anode, wherein the hole injection layer is made substantially from the same organic host material doped with at least one p-type dopant.
The second aspect of the present invention provides a method of improving a process for fabricating an organic light emitting device, the device comprising a cathode, an anode, and an organic layer structure disposed between the cathode and the anode, the organic layer structure comprising a hole transport layer disposed adjacent to the anode, an electron transport layer disposed adjacent to the cathode and an emissive layer disposed between the hole transport layer and the electron transport layer. The method comprises:
providing an organic host material for use in the hole transport layer, the emissive layer and the electron transport layer;
doping the electron transport layer with at least one n-type dopant; and
doping the emissive layer with a luminescent dopant.
According to the present invention, the method further comprises the step of doping the hole transport layer with a p-type dopant.
According to the present invention, the hole transport layer comprises a hole injection layer disposed adjacent to the anode. The method further comprises:
doping the hole injection layer with at least one p-type dopant.
According to the present invention, the luminescent dopant comprises a fluorescent dopant or a phosphorescent dopant.
The third aspect of the present invention provides an organic layer structure for use in an organic light emitting device comprising a cathode and an anode, the organic layer structure disposed between the cathode and the anode. The organic layer comprises:
a hole transport layer disposed adjacent to the anode;
an electron transport layer disposed adjacent to the cathode; and an emissive layer disposed between the hole transport layer and the electron transport layer, wherein the hole transport layer, the emissive layer and the electron transport layer are made from substantially the same organic host material.
According to the present invention, the organic host material comprises a bipolar organic material, such as a derivative of fused aromatic rings.
According to the present invention, the electron transport layer is substantially made from a bipolar organic material doped with at least one n-type dopant; and the emissive layer is substantially made from a bipolar organic material doped with a fluorescent dopant or a phosphorescent dopant.
According to the present invention, the organic layer structure further comprises
a hole injection layer disposed between the hole transport layer and the anode, wherein the hole injection layer is made substantially from the bipolar organic material doped with at least one p-type dopant.
The present invention will become apparent upon reading the description taken in conjunction with FIGS. 2 to 13.
BRIEF DESCRIPTION OF THE DRAWINGS
The structure of the organic light-emitting device (OLED), according to the present invention, is shown in
It is preferable to use a bipolar organic material as the organic host material in the organic layer structure 120. The bipolar material can be used as both an electron transport medium and a hole transport medium. As such, the organic layer structure 120 can be divided into at least three sections: a hole transport section, an emissive section and an electron transport section.
An example of the bipolar organic materials is shown in
The p-type dopant for use in the HIL 122 can be selected from F, Cl, Br and I or a compound containing one or more of F, Cl, Br and I. Other p-type dopants include: tetrafluoro-tetracyano-quinodimethane (F4-TCNQ), metalic oxides including ITO (indium-tin oxide), IZO (indium zinc oxide); semiconductor materials with a large band-gap (>3 eV) such as TiO2, TiN; metals with work function greater than 4 eV. The dopant concentration ranges from 0.1 w % to 50 w %. Alternatively, the p-type dopant is used in both the HIL 122 and the HTL 124.
The n-type dopant for use in the ETL 128 can be selected from IA elements (alkali metals), IIA elements (alkaline earth metals) or a compound containing one or more of the IA, IIA elements. Other n-type dopants include: carbonic acid compounds, nitric acid compounds, acetic acid compounds and alkali metal-containing organic salts. The dopant concentration ranges from 0.1 w % to 50 w %.
In order to demonstrate the feasibility of using a single organic host material in different layers in the organic layer structure 120, an experimental sample has been fabricated, as shown in
The performance of this experimental sample is shown in FIGS. 9 to 13.
In sum, the present invention provides an organic light emitting device comprising an organic layer structure disposed between a cathode layer and an anode layer. The organic layer structure comprises at least an electron transport layer, an emissive layer and a hole transport layer, wherein the host material in these layers is substantially the same. In particular, the host material is a bipolar organic material having the characteristics of being both as a hole transport medium and an electron transport medium. As such, it is not necessary to use different deposition channels to deposit the electron transport layer, the emissive layer and the hole transport layer.
Although the invention has been described with respect to one or more embodiments thereof, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention.
Claims
1-9. (canceled)
10. A method for improving a process for fabricating an organic light emitting device, the device comprising a cathode, an anode, and an organic layer structure disposed between the cathode and the anode, the organic layer structure comprising a hole transport layer disposed adjacent to the anode, an electron transport layer disposed adjacent to the cathode and an emissive layer disposed between the hole transport layer and the electron transport layer, said method comprising:
- providing an organic host material for use in the hole transport layer, the emissive layer and the electron transport layer;
- doping the electron transport layer with at least one n-type dopant; and
- doping the emissive layer with a luminescent dopant.
11. The method of claim 10, further comprising
- doping the hole transport layer with at least one p-type dopant.
12. The method of claim 10, wherein the hole transport layer comprises a hole injection layer made substantially from the organic host material disposed adjacent to the anode, said method further comprising:
- doping the hole injection layer with at least one p-type dopant.
13. The method of claim 10, wherein the luminescent dopant comprises a fluorescent dopant.
14. The method of claim 10, wherein the luminescent dopant comprises a phosphorescent dopant.
15-23. (canceled)
Type: Application
Filed: Oct 26, 2007
Publication Date: Mar 6, 2008
Applicant:
Inventor: Shi-Hao Li (Banciao City)
Application Number: 11/978,103
International Classification: H01L 33/00 (20060101);