Suppression of exciton annihilation at high current densities in organic light-emitting diode resulting from energy-level alignments of carrier transport layers

We manufactured an organic light-emitting diode (OLED) in which the hole and electron transport layers are chemically doped with p- and n-type dopants and energy levels in between neighboring carrier transport layers and emitting molecules are aligned. From the results of the electroluminescence (EL) characteristics of the OLED, we found that (1) the OLED has an extremely low driving voltage of 2.65 +/- 0.05 0.05 V at a current density of 100 mA/cm(2); (2) the onset voltage of EL (approximate to 2.4 V) corresponds to the photon energy of emitting molecules (approximate to 2.5 eV), while the onset voltage of currents is approximate to 1.8 V; and (3) a decrease in EL efficiency at high current densities can be suppressed by matching the energy levels. (C) 2008 American Institute of Physics