Blue and white organic light emitting diodes based on a doped DPVBi emitting layer

摘要

Highly efficient blue and white light-emitting organic electroluminescent devices have been fabricated by evaporation of small molecules. The emitting material of the blue multilayer EL devices (ITO/CuPc/α-NPB/Doped DPVBi/Alq3/LiF/Al) is based on a DPVBi (4,4'-bis(2,2-diphenylvinyl)biphenyl) matrix. In order to increase the EL efficiency and to improve the blue colour, this emitting layer is doped with a derivative of distyryl biphenyl molecules: PR3491. After the optimisation of the percentage of dopant, quantum and current efficiencies of 5.7 % and 7 cd/A, respectively, are obtained for a deep blue diode with CIE chromaticity coordinates of (0.15, 0.14). White diodes have been also realized doping the DPVBi emitter or the α-NPB hole transporting layer (HTL) of the previous structure with rubrene. A double doped system has been finally realized from the deep blue diode (DPVBi doped with PR3491) and with rubrene in the HTL layer. After tuning the two percentages of dopant in order to balance the blue and the yellow contribution to the diode emission, a fairly pure white emission is obtained with CIE coordinates of (0.31, 0.34) and external efficiencies of 3.4 % and 8.7 cd/A at 10 mA/cm2.