Luminescence Characteristics Of OLED With Phosphor-doped Host-guest Structure

Organic electroluminescent devices (OLEDs) have a wide application prospect in the field of display and lighting due to their characteristics such as low-voltage-driven, active light-emitting, high-brightness and efficiency, wide viewing angle, fast response, impact resistance and vibration. This paper reviews the history of the development, the current situation and problems of OLEDs, the relevant basic theory is also introduced.Phosphorescent electrophosphorescent devices were developed by doping different proportions of fac-tris-2-phenylpyridine iridium(Ⅲ) (Ir(ppy)3) into PVK used as a light-emitting layer, and the luminescence mechanism was studied. In the photoluminescence (PL), the dominant mechanisms is Foster energy transfer, and in the electroluminescence (EL) processes, Dexter energy transfer and charge trapping play the mian role. The I-V-L characteristics showed that the light-power efficiency was highest when the doping proportion of Ir(ppy)3 was 5 wt%,indicating that energy transfer is most efficient.Blue OLEDs were fabricated by using blue phosphorescent dye Firpic doped with the host material CBP as the emitting layer.The configuration of the devices was ITO/CuPc/Firpic: CBP (x%)/BCP/Alq3/LiF/Al, in which x% was the doping concentration of Firpic.The doping concentration between the host and guest and the thickness of hole blocking layer BCP on the the properties of light-emitting devices were separately studied. When the doping concentration was 8%, the energy transfer betwwen host and guest was most efficient, the turn-on voltage of the device was 5V, the brightness of it at 20V was 7122.25cd/m2.Obvious red-shift took place in the electroluminescent spectra of the devices, this is because part of Alq3 participate in the luminescence, which reduce the color purity of blue luminescence. The carrier compound area and the CIE coordinates of the devices can be regulated by changing the thickness of BCP. So the device performance will be improved by controlling the thickness of BCP.