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.

In this work, novel blue‐fluorescent dopants with a heteroaromatic ring skeleton instead of the conventional pyrene skeleton were investigated. Bottom‐emission organic light‐emitting diodes (OLEDs) fabricated using the novel blue‐fluorescent dopants in light‐emitting layers achieved better deep‐blue chromaticity than OLEDs based on a conventional pyrene‐based dopant, while maintaining both high external quantum efficiency (EQE) and comparable reliability. The attainment of deep‐blue chromaticity without losing high EQE was ascribed to the improvement of the efficiency of energy transfer from the host to the dopant. Furthermore, it was estimated that using this novel dopant in a top‐emission OLED panel that satisfies BT.2020 chromaticity enables the power consumption of the whole panel to be 24% lower than that of the panel with a conventional dopant.

We developed a deep‐blue fluorescent organic light‐emitting diode (OLED) that is long‐lived and thermally stable. This blue OLED accommodates the BT.2020 color gamut for the first time in the world, and enables a longer lifetime than a conventional one while maintaining comparable power consumption in a full‐color OLED panel.

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.

The effects of triplet-triplet annihilation (TTA) and molecular orientation were quantitatively investigated for a high-efficiency blue fluorescent organic light-emitting diode. Both the efficient TTA generation by improving carrier balance and the horizontal orientation of the transition dipole moment of the blue dopant realized ultrahigh external quantum efficiency (approximately 12%).