Effect of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline outcoupling layer on electroluminescent performances in top-emitting organic light-emitting devices

The organic compound, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is used as a light outcoupling layer in top-emitting organic light-emitting devices with tris(8-hydroxyquinoline) aluminum emission layer. It is found that, in addition to the improvement of electroluminescent (EL) intensity and luminous efficiency with a factor of 1.6, the BCP capping layer causes a blueshift of EL spectra and a larger full width at half maximum (FWHM). A larger FWHM at the BCP capping layer of 50 nm is attributed to the reduction of cathode reflectivity. In the meantime, the blueshift of EL spectra is caused by the increase of the reflective phase shift of the cathode when a thicker BCP layer is deposited. Moreover, our calculation demonstrates that the best EL coincides with a maximum magnification coefficient. (C) 2008 American Institute of Physics.