Highly efficient, deep-blue phosphorescent organic light emitting diodes with a double-emitting layer structure

We have demonstrated a highly efficient, deep-blue organic light-emitting diode (OLED) using a host material with a high triplet energy. The OLED device that we have prepared utilizes a phosphorescent guest material, iridium (III) bis (4', 6',-difluorophenylpyridinato)tetrakis(1-pyrazolyl) borate, exhibits a peak quantum efficiency of about 15.7%. We employed a double-emitting layer (DEL) structure that distributes the carrier recombination region within the device. In this DEL structure, the emission mechanism is such that the energy transfers from the host material in one emitting layer, and the other emitting layer provides for direct charge trapping in the guest material. This DEL structure proved to be quite useful in achieving the reported device characteristics. (C) 2008 American Institute of Physics.