Through almost 30 years’ research and development, starting from fluorescence molecules, organic light emitting diodes (OLEDs) finally realized the ultimate electroluminescence (EL) efficiency, i.e., nearly 100% electron to photon conversion by using a novel conceptual pure aromatic emitter of thermally activated delayed fluorescence (TADF)1. TADF enabled harvesting all electrically generated singlet and triplet excitons by engineering reverse intersystem crossing. In fact, the diversity of molecular design allowed a wide variety of new compounds as TADF emitters. Successively, as the post OLEDs, the realization of organic semiconductor laser diodes (OSLDs) has been anticipated for a long time. For realizing current driven lasing, however, we have to overcome some critical issues such as high current injection associated with joule heating, and exciton dissociation induced by annihilation and quenching processes. In this talk, we will review the development of OLEDs’ emitters along with the clarification of the exciton dissociation processes peculiar to electrical excitation. In particular, we highlight our recent success in realizing quasi-CW lasing by engineering both singlet and triplet excited states2.
Refs.  H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Nature, 492, 234-238 (2012).  A. S. D. Sandanayaka, T. Matsushima, F. Bencheikh, K. Yoshida, M. Inoue, T. Fujihara, K. Goushi, J.-C. Ribierre, C. Adachi, Sci. Adv., 3, 4, e1602570 (2017).