FABRICATION OF ORGANIC LIGHT EMITTING DIODES (OLEDs) FOR FLAT PANEL DISPLAYS

Abstract

Organic light emitting diodes (OLEDs) are thin film devices in which organic materials are sandwiched between two electrodes. These devices emit light when electricity is passed through them. OLEDs have gained much attention because their potential applications to full color flat panel displays. Generally, OLEDs are assembled using an heterojunction architecture between three or more organic molecular materials: an electron injection layer, the emitting one and finally the hole injection layer. There are two types of OLED devices, depend on the type of molecular materials used in the devices. The first type is Small Molecule OLED. The production of small-molecule OLEDs require vacuum deposition. The second type is Light-Emitting Polymer. In this technology, the organic thin films can be deposited by spin coating or by a technique derived from commercial inkjet printing. This paper discusses the fabrication of both types of OLEDs. A small molecule blue organic light emitting diode was fabricated using thermal evaporation system with ITO/2-TNATA/NPB/DPVBi:dopant/ Alq3/LiF/Al structure, where the emitting molecules is 4,4’-bis(2,2’-diphenylvinyl)-1,1’-biphenyl (DPVBi). The typical brightness, the power consumption and the turn-on voltage of the device were 30 cd/m2, less than 50 mW and 5.0 V respectively. For polymer light-emitting diode, device with structure of ITO/PHF/Al structure was fabricated, where PHF is poly (4, 4’-diphenylene diphenylvinylene). This device has turn-on voltage at 23.0 V. A reduction of turn-on voltage of this device is achieved by using a nanocomposite layer consisting of PHF and SiO2 nanoparticles as the emitting layer. A white OLED combines with colour filters is one of the approaches to obtained full colour flat screen display. White light emitting devices were fabricated with structure of ITO/PHF:rubrene/Al where the white light was optimized through variation of mixing concentrations of PHF and rubrene. The results show that the combination of 0.6 wt% PHF and 0.06 wt% rubrene produced the optimum white light at CIE coordinate of (0.31,0.31). The standard coordinate for white light is (0.33,0.33). The turn-on voltage of this device is 14.0 V and the brightness is 6541 cd/m2. The turn-on of this device was reduced to 8.0 V through an annealing process at 150°C.

Keywords : Organic light emitting diodes (OLEDs), small molecule device, polymer light-emitting diode, display.