Recent development of organic light-emitting diode utilizing energy transfer from exciplex to phosphorescent emitter

Satoshi Seo; Satoko Shitagaki; Nobuharu Ohsawa; Hideko Inoue; Kunihiko Suzuki; Hiromi Nowatari; Tatsuyoshi Takahashi; Takao Hamada; Takeyoshi Watabe; Yui Yamada; Satomi Mitsumori

doi:10.1117/12.2236191

23 September 2016 Recent development of organic light-emitting diode utilizing energy transfer from exciplex to phosphorescent emitter

Satoshi Seo, Satoko Shitagaki, Nobuharu Ohsawa, Hideko Inoue, Kunihiko Suzuki, Hiromi Nowatari, Tatsuyoshi Takahashi, Takao Hamada, Takeyoshi Watabe, Yui Yamada, Satomi Mitsumori

Author Affiliations +

Proceedings Volume 9941, Organic Light Emitting Materials and Devices XX; 99410J (2016) https://doi.org/10.1117/12.2236191
Event: SPIE Organic Photonics + Electronics, 2016, San Diego, California, United States

Abstract

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.

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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); https://doi.org/10.1117/12.2236191

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