INVERTED OLED DISPLAY
Original Publication Date: 2004-Jul-25
Included in the Prior Art Database: 2004-Jul-25
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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.