Bright red-to-yellow organic light-emitting devices based on polarization-induced spectral shifts and broadening

We demonstrated red and yellow organic light-emitting devices (OLEDs) with the structure of ITO/NPB/AlQ:DCJTB/AlQ/LiF/Al, where the NPB, AlQ and DCJTB are 4, 4′-bis[N-(1-naphthyl)-N-henylamino] biphenyl, tris(8-quinolinolato)aluminum and 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, respectively. Electroluminescent (EL) behaviors of these devices have been examined with different concentrations of DCJTB doped into AlQ matrix. The emission color of the devices depends on the doping concentrations of DCJTB. For red and yellow OLEDs, a maximum luminescence of 2750 cd/m2 and 21,700 cd/m2 was obtained, respectively. The peak emission wavelength shift of DCJTB was found to be due to the polarization effects. It is of particular interest that the EL spectrum of DCJTB got broadening with the doping concentrations and current densities of the devices in our experiments.