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23 September 2016 Recent development of organic light-emitting diode utilizing energy transfer from exciplex to phosphorescent emitter
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This study investigates an organic light-emitting diode (OLED) utilizing energy transfer from an excited complex (exciplex) comprising donor and acceptor molecules to a phosphorescent dopant. An exciplex has a very small energy gap between the lowest singlet and triplet excited states (S1 and T1). Thus, both S1 and T1 energies of the exciplex can be directly transferred to the T1 of the phosphorescent dopant by adjusting the emission energy of the exciplex to the absorption-edge energy of the dopant. Such an exciplex‒triplet energy transfer (ExTET) achieves high efficiency at low drive voltage because the electrical excitation energy of the exciplex approximates the T1 energy of the dopant. Furthermore, the efficiency of the reverse intersystem crossing (RISC) of the exciplex does not affect the external quantum efficiency (EQE) of the ExTET OLED. The RISC of the exciplex is inhibited when the T1 energy of either donor or acceptor molecules is close to or lower than that of the exciplex itself. Even in this case, however, the ExTET OLED maintains its high efficiency because the T1 energy of each component of the exciplex or the T1 energy of the exciplex itself can be transferred to the dopant. We also varied the emission colors of ExTET OLEDs from sky-blue to red by introducing various phosphorescent dopants. These devices achieved high EQEs (≈30%), low drive voltages (≈3 V), and extremely long lifetimes (e.g., 1 million hours for the orange OLED) at a luminance of 1,000 cd/m2.
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Satoshi Seo, Satoko Shitagaki, Nobuharu Ohsawa, Hideko Inoue, Kunihiko Suzuki, Hiromi Nowatari, Tatsuyoshi Takahashi, Takao Hamada, Takeyoshi Watabe, Yui Yamada, and Satomi Mitsumori "Recent development of organic light-emitting diode utilizing energy transfer from exciplex to phosphorescent emitter", Proc. SPIE 9941, Organic Light Emitting Materials and Devices XX, 99410J (23 September 2016);

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