Effect of BCP layer on electroluminescent performances in blue top-emitting organic light-emitting devices

The organic compound, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was used as a light outcoupling layer in top-emitting organic light-emitting devices (TEOLEDs) with an iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N, C2′] picolinate (FIrpic) emission layer. It was different from the conventional TEOLEDs that use ITO as a thickness adjustment layer to make the cavity length matchable with the resonant wavelength of the blue light. The total thickness (105 nm) of organic materials sandwiched between the cathode and the anode in this TEOLED was almost same with that in a conventional bottom-emitting OLED (BEOLED). The influence of the BCP outcoupling layer on EL intensity, luminous efficiency, and EL spectra was explored by combining experimental data with microcavity and transfer matrix theories. The experimental data was basically consistent with theoretical results. As a result, the high performances such as high brightness, large luminous efficiency, and saturated chromaticity were obtained in the blue TEOLED, which were comparative to those in the BEOLEDs.