While the demonstration of the first OLED emitting thermally activated delayed fluorescence (TADF) in Advanced Materials1-3 in 2009 by our group gave a glimpse of TADF's potential, our successive report in Nature4-6 in 2012 of a TADF-based OLED with an internal quantum efficiency of nearly 100% grabbed the attention of researchers world-wide and established TADF as a truly promising technology. In the first half, recent progress on TADF OLEDs will be discussed from the aspect of electroluminescence quantum efficiency and device stability.
In the second half, I will introduce our recent efforts to inject high current density, reduce roll-off related to Joule heating and various exciton annihilation processes,7-9 and control excited-state absorption for the realization of electrically pumped organic semiconductor laser diodes. By managing these issues, we report low-threshold surface-emitting organic distributed feedback lasers operating under continuous-wave photoexcitation for 30 ms.10
 Ayataka Endo, Mai Ogasawara, Atsushi Takahashi, Daisuke Yokoyama, Yoshimine Kato, Chihaya Adachi, Adv. Mater., 21, 4802, 2009  Ayataka Endo, Keigo Sato, Kazuaki Yoshimura, Takahiro Kai, Atsushi Kawada, Hiroshi Miyazaki, Chihaya Adachi, Appl. Phys. Lett., 98, 083302, 2011  Kenichi Goushi, Kou Yoshida, Keigo Sato, Chihaya Adachi, Nat. Photon., 6, 253, 2012  Hiroki Uoyama, Kenichi Goushi, Katsuyuki Shizu, Hiroko Nomura, Chihaya Adachi, Nature, 492, 234, 2012  Hajime Nakanotani, Takahiro Higuchi, Taro Furukawa, Kensuke Masui, Kei Morimoto, Masaki Numata, Hiroyuki Tanaka, Yuta Sagara, Takuma Yasuda, Chihaya Adachi, Nat. Commun., 5, 4016, 2014,  H. Nakanotani, T. Furukawa, C. Adachi, Adv. Opt. Mater. 3, 10, 2015.  H. Kuwae, A. Nitta, K. Yoshida, T. Kasahara, T. Matsushima, M. Inoue, S. Shoji, J. Mizuno, C. Adachi, J. Appl. Phys. 118, 155501, 2015  M. Inoue, T. Matsushima, H. Nakanotani, C. Adachi, Chem. Phys. Lett., 624, 46, 2015  K. Hayashi, H. Nakanotani, M. Inoue, K. Yoshida, O. Mikhnenko, T.-Q. Nguyen, C. Adachi, Appl. Phys. Lett. 2015, 106, 0933301  Atula S. D. Sandanayaka; Kou Yoshida; Munetomo Inoue; Chuanjiang Qin; Kenichi Goushi; Jean-Charles Ribierre; Toshinori Matsushima; Chihaya Adachi, Adv. Opt. Mat., 4, 6, 834, 2016