Highly Efficient White Organic Light Emitting Diodes with a p-Type Structure

Highly efficient red organic light emitting diodes with a p-type structure were fabricated. The luminance, current density, and efficiency were improved compared to those of the control device. We obtained the p-type structure by doping the strong electron-withdrawing material 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquino-dimethane (F-4-TCNQ) into the hole-injection layer of 4,4',4 ''-tris(3-methyl-phenylphenylamino)-tri-phenylamine (m-MTDATA). This p-type structure was further applied to white organic light emitting diodes (WOLEDs). The white emission of the WOLEDs consists of red, green, and blue components emitted from the Ir(DBQ)(2)(acac), Ir(ppy)(2)(acac), and FIrpic doped 1,3-bis(carbazol-9-yl)benzene (mCP) layers, respectively. The emission intensity of the different colors can be adjusted by changing the doping concentrations and the thickness of the corresponding layer. After optimizing the emission intensity of every emitting layer, the maximum current efficiency, power efficiency, and luminance of the device were found to be 19.3 cd.A(-1), 12.1 lm.W-1, and 31770 cd.m(-2), respectively. The Commission Internationale De L'Eclairage (CIE) coordinates of the device were stable and remained in the white region when the driving voltage increased from 5 to 11 V.