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Browse Prior Art Database

INVERTED OLED DISPLAY

IP.com Disclosure Number: IPCOM000028923D
Original Publication Date: 2004-Jul-25
Included in the Prior Art Database: 2004-Jul-25
Document File: 5 page(s) / 58K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

An organic light emitting diode ("OLED") display typically includes, in sequence: (1) a transparent anode (e.g., the anode can be comprised of indium tin oxide ("ITO")); (2) a hole transporting layer ("HTL"); (3) an electron transporting and light emitting layer ("emissive layer"); and (4) a cathode. When a forward bias is applied, holes are injected from the anode into the HTL, and the electrons are injected from the cathode into the emissive layer. Both carriers are then transported towards the opposite electrode and allowed to recombine with each other in the device, the location of which is called the recombination zone. The emissive layer is typically formed using solvent-based organic electroluminescent polymer solution, and the HTL is typically formed using the following polymer solution: polyethylenedioxythiophene-polystyrenesulfonic acid ("PEDOT:PSS"). Recent test results show that the degradation of polymer-based OLED displays is due to degradation of the PEDOT:PSS layer. As an alternative, the PEDOT:PSS layer can be replaced with small molecule materials. One of the problems with using small molecule materials is that it is difficult to deposit the solvent-based electroluminescent polymer solution on top of the HTL comprised of small molecules that are typically deposited by thermal evaporation. Usually, the small molecule material dissolves in the electroluminescent polymer solution. One problem with a full-color OLED display with layers comprised of small molecule materials is that for each color, the shadow masks have to be separately adjusted. The separate adjustment of the shadow masks for each color is cumbersome and time consuming.

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INVERTED OLED DISPLAY

Idea: Florian Pschenitzka, US-San Jose; Franky So, US-San Jose

BACKGROUND OF THE INVENTION

An organic light emitting diode ("OLED") display typically includes, in sequence: (1) a transparent anode (e.g., the anode can be comprised of indium tin oxide ("ITO")); (2) a hole transporting layer ("HTL"); (3) an electron transporting and light emitting layer ("emissive layer"); and (4) a cathode. When a forward bias is applied, holes are injected from the anode into the HTL, and the electrons are injected from the cathode into the emissive layer. Both carriers are then transported towards the opposite electrode and allowed to recombine with each other in the device, the location of which is called the recombination zone.

The emissive layer is typically formed using solvent-based organic electroluminescent polymer solution, and the HTL is typically formed using the following polymer solution: polyethylenedioxythiophene-polystyrenesulfonic acid ("PEDOT:PSS"). Recent test results show that the degradation of polymer-based OLED displays is due to degradation of the PEDOT:PSS layer. As an alternative, the PEDOT:PSS layer can be replaced with small molecule materials. One of the problems with using small molecule materials is that it is difficult to deposit the solvent-based electroluminescent polymer solution on top of the HTL comprised of small molecules that are typically deposited by thermal evaporation. Usually, the small molecule material dissolves in the electroluminescent polymer solution. One problem with a full-color OLED display with layers comprised of small molecule materials is that for each color, the shadow masks have to be separately adjusted. The separate adjustment of the shadow masks for each color is cumbersome and time consuming.

Therefore, it is desirable to modify the OLED display structure in order to improve the display lifetime and efficiency.

SUMMARY

One embodiment of this invention pertains to an inverted organic light emitting diode ("OLED") display that has improved display lifetime and efficiency. The OLED display includes a substrate, a cathode deposited on the substrate, an emissive polymer layer deposited on the cathode, a hole transport layer deposited on the emissive polymer layer, and an anode deposited on the hole transport layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of an inverted OLED display according to the present invention.

FIGS. 2A-E show an embodiment of a process to fabricate the inverted OLED display.

DETAILED DESCRIPTION

Test results have shown that a significant lifetime improvement can be obtained if the PEDOT:PSS layer is either:

(1) replaced with another material; or

(2) a buffer layer is added between an emissive polymer layer and the HTL (the HTL may be comprised of either organic polymer materials or organic small molecule materials).

If the PEDOT:PSS layer is replaced with another HTL material, such as organic small molecule materials with...