O Speaker: Prof. S. R. Forrest (U. Michigan)
O Title: Getting Long Lifetime, and High Efficiencies from the Blues
O Date: Aug. 23rd(Tues.)
O Start Time: 10:30 AM
O Venue: KI B/D Matrix hall
Perhaps the single most important problem confronting the development of OLED displays and lighting today is how to achieve sufficiently long triplet-controlled emission device lifetime to prevent rapid color change during operation, while achieving 100% internal emission efficiency. In 2008, we showed that bimolecular (e.g. triplet-polaron, triplet-triplet) annihilation provides a source of energy sufficient to destroy the blue triplet chromophore (whether a phosphor or a TADF molecule) or its host. Since that time, several studies have developed a series of structures and strategies to extend blue emission lifetime based on this understanding. Furthermore, various molecular fragments have been identified whose presence leads to the observed luminance loss. Unfortunately, a fully satisfactory solution has not been demonstrated where blue triplet emitter lifetime is sufficient to meet the demands of high performance displays, although white OLED illumination sources may now have adequate lifetime to meet industry standards. In this talk I will review recent advances and understanding of the limitations to extending the lifetime of blue triplet emitters further than are currently achieved. In particular, I will focus on the relationship between radiative state lifetime and the longevity of the phosphorescent OLED (PHOLED). I will review efforts to shorten the radiative lifetime via emitter design and optical cavity engineering. Prospects for future advances will be discussed.
1. “Intrinsic luminance loss in phosphorescent small-molecule organic light emitting devices due to bimolecular annihilation reactions”. N.C. Giebink, B.W. D’Andrade, M.S. Weaver, P.B. Mackenzie, J.J. Brown, M.E. Thompson, and S.R. Forrest, J. Appl. Phys., 103, 044509 (2008).
2. “Ten-Fold Increase in the Lifetime of Blue Phosphorescent Organic Light Emitting Diodes”, Y. Zhang, J. Lee, and S. R. Forrest, Nature Communications, 5, 5008, DOI: 10.1038/ncomms6008 (2014). 3. “Effects of charge balance and exciton confinement on the operational lifetime of blue phosphorescent organic light-emitting diodes”, C. Coburn and S. R. Forrest, Phys. Rev. Applied Lett., 7, 041002 (2017).
4. “Hot excited state management for long-lived blue phosphorescent organic light-emitting diodes”, J. Lee, C. Jeong, T. Batagoda, C. Coburn, M. E. Thompson, S. R. Forrest, Nature Commun. 8 (2017).
5. “Understanding molecular fragmentation in blue phosphorescent organic light-emitting devices”, C. Jeong, C. Coburn, M. Idris, Y. Li, P. I. Djurovich, M. E. Thompson, and S. R. Forrest, Org. Electron., 64 15 (2019)
6. “Organic Electronics: Foundations to Applications”, S. R. Forrest, Oxford University Press, Oxford (2020).
Stephen R. Forrest
Peter A. Franken Distinguished University Professor of Engineering
Paul G. Goebel Professor of EngineeringProfessor of Electrical Engineering, Physics and Materials Science and Engineering
B. A. Physics, 1972, University of California, MSc and PhD Physics in 1974 and 1979, University of Michigan.
In 1985, Prof. Forrest joined USC and, in 1992, moved to Princeton University. In 2006, he rejoined the University of Michigan as Vice President for Research, where he is the Peter A. Franken Distinguished University Professor. A Fellow of the APS, IEEE and OSA and a member of the National Academy of Engineering, the National Academy of Sciences, the American Academy of Arts and Sciences, and the National Academy of Inventors, he has received numerous awards and medals for his invention of phosphorescent OLEDs, innovations in organic LEDs, organic thin films and advances in photodetectors for optical communications. Prof. Forrest has authored ~650 papers in refereed journals and has 373 US patents, many of which are also granted worldwide. He is co-founder or founding participant in several companies, including Sensors Unlimited, Epitaxx, Inc., NanoFlex Power Corp. (OTC: OPVS), Universal Display Corp. (NASDAQ: OLED) and Apogee Photonics, Inc., and is on the Growth Technology Advisory Board of Applied Materials. He is past Chairman of the Board of the University Musical Society and served as Chairman of the Board of Ann Arbor SPARK. He has served on the Board of Governors of the Technion – Israel Institute of Technology where he is a Distinguished Visiting Professor of Electrical Engineering. He received an honorary doctorate from the Technion in 2018, and the Henry Russel Lectureship at the University of Michigan in 2019. His first book, Organic Electronics: Foundations to Applications, was published in September, 2020.