Jang-Joo Kim: What is the Efficiency Limit of OLEDs?

Even after over 30 years' development and successful commercialization of organic light emitting diodes (OLEDs), very interesting and important innovations have occurred in OLEDs in recent years. Recently reported thermally activated delayed fluorescence (TADF) materials, utilizing intra- and inter-molecular charge transfer processes upon excitation, is an example which can harvest triplet excitons or exciplexes to light. Another example is the demonstration of external quantum efficiencies (EQEs) of over 30%, approaching almost 40% without any external light extraction structures. This high efficiency was realized based on the development of highly oriented phosphorescent or TADF emitters parallel to the substrate (horizontal direction), combined with advanced device structures. Improving efficiency is important because it is directly related to the reduction of power consumption and device lifetime. In this presentation, recent development of high efficiency OLEDs based on phosphorescent, TADF and fluorescent emitters will be discussed.

In this plenary talk, Jang-Joo Kim of Seoul National University shows that EQEs over 50% are achievable without any extra light extracting structure and over 80% with light extraction structures if OLEDs are fabricated using organic semiconductors with the low refractive index and fully horizontal emitting dipoles. He also discusses the possibility of realizing high efficiency blue OLEDs with long lifetime, one of the most important issues in OLEDs.

Jang-Joo Kim has been a professor in the Department of Materials Science and Engineering of Seoul National University (SNU) since 2003. After finishing his PhD at Stanford University, he worked for SRI International as a postdoc; at the Electronics and Telecommunications Research Institute as a Senior Member and a Principal Member of Technical Staff, and at Gwangju Institute of Science and Technology as a professor before joining to SNU.

His current research interests include the electrical and optical processes such as charge injection, transport, recombination, the inter- and intramolecular charge transfer processes in the excited and ground states, orientation of molecules in amorphous materials, light in-coupling and out-coupling in organic photonic devices. He authored and co-authored over 320 papers and granted more than 60 patents. He is a member of Korean Academy of Science and Technology (KAST) and had served as an Editor of Organic Electronics. He received "The Order of Science and Technology Merit of the Republic of Korea, Changjo (Creation)" in 2019, Dukmyuong-KAST Engineering Awards from KAST in 2013 and Excellence in Research Awards from Seoul National University in 2017.

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