A novel hole-transporting material with high singlet and triplet excitation energy levels was developed. Quantum efficiency of a fluorescent organic light-emitting diode (OLED) using this material as a hole-transporting layer can be increased because of facilitated triplet-triplet annihilation (TTA) due to exciton confinement in an emission layer. Furthermore, this material has a deep highest occupied molecular orbital level because of the absence of triarylamine structure. This feature also contributes to the increase in the quantum efficiency, owing to inhibition of a low-energy exciplex formed between the material and a host in the emission layer. Achieved consequently was a blue fluorescent OLED exhibiting a high external quantum efficiency of 11.9% and a long half-decay time of 8,000 h at 1,000 cd/m 2 . By the device analysis including time-resolved electroluminescence measurements, it was confirmed that TTA contributes to the high efficiency.
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 π-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 2.8 V and a long lifetime of approximately 1,000,000 h at a luminance of 1,000 cd/m2.
We developed a high‐performance 3.4‐in. flexible active‐matrix organic light‐emitting diode (AMOLED) display with remarkably high resolution using an oxide semiconductor in a backplane, by applying our transfer technology that utilizes metal separation layers. Using this panel, we also fabricated a prototype of a side‐roll display for mobile uses. In these AMOLED displays, a white OLED combined with a color filter was used in order to achieve remarkably high resolution. For the white OLED, a tandem structure in which a phosphorescent emission unit and a fluorescent emission unit are serially connected with an intermediate layer sandwiched between the emission units was employed. Furthermore, revolutionary technologies that enable a reduction in power consumption in both the phosphorescent and fluorescent emission units were introduced to the white tandem OLED.
We have developed phosphorescent OLEDs utilizing energy transfer from an exciplex to an emitter. The OLEDs based on this mechanism showed quite high efficiency, a long lifetime and low drive voltage. OLED lighting with high power efficiency exceeding 100 lm/W at a practical luminance of 5,000 cd/m2 was also successfully developed.
We have developed novel Ir complexes having pyrazine structures in their ligands.The OLEDs based on these complexes showed unique properties and high performance. In particular, the red OLED achieved an extremely high efficiency of 30 cd/A with CIE color coordinates of (x, y) = (0.65, 0.35), and the luminance half-decay time was estimated to be about 100,000 hrs at an initial luminance of 1,000 cd/m 2 .
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