Exciplex-triplet energy transfer: A new method to achieve extremely efficient organic light-emitting diode with external quantum efficiency over 30% and drive voltage below 3V

A novel approach to enhance the power efficiency of an organic light-emitting diode (OLED) by employing energy transfer from an exciplex to a phosphorescent emitter is reported. It was found that excitation energy of an exciplex formed between an electron-transporting material with a pi-deficient quinoxaline moiety and a hole-transporting material with aromatic amine structure can be effectively transferred to a phosphorescent iridium complex in an emission layer of a phosphorescent OLED. Moreover, such an exciplex formation increases quantum efficiency and reduces drive voltage. A highly efficient, low-voltage, and long-life OLED based on this energy transfer is also demonstrated. This OLED device exhibited extremely high external quantum efficiency of 31% even without any attempt to enhance light outcoupling and also achieved a low drive voltage of 2.8V and a long lifetime of approximately 1,000,000 h at a luminance of 1,000 cd/m(2). (C) 2014 The Japan Society of Applied Physics