(Lecture, Aug 2) Manipulating the Refractive Index in Organic Light Emitting Diodes
2018-07-29 readCount:142
Topic: Manipulating the Refractive Index in Organic Light Emitting Diodes
Speaker: Prof. Franky So (University of Florida)
Venue: Room 502, Building of State Key Laboratory of Luminescent Materials and Devices, Wushan Campus
Time: Thursday, Aug 2, 2018, 10:00-11:00
OLED is a heterostructure device consisting of several organic layers, an ITO electrode and a metallic electrode. Because of the difference in the indices of refraction and the presence of the metallic electrode, the optical modes are very different from an inorganic LED. As a result, only a small fraction of generated light can escape an organic light emitting diode (OLED), and most of radiation is lost to bound photonic modes such as surface plasmon polariton (SPP) and thin film waveguided modes. The photonic mode densities of any optical stack are heavily dependent on the refractive indices of the constituent layers. In the case of organic light emitting diodes, reducing the refractive index of the constituent layers, such as: electron transport layer (ETL), hole transport layer (HTL) and the transparent anode, can lead to higher light extraction efficiencies and less radiation loss. The refractive index of the electron transport layer (ETL) has the largest impact on light extraction, comparing to all other layers, since it is immediate to the metallic cathode. Refractive index of thin films deposited using physical vapor deposition (PVD) can be manipulated by void inclusion using oblique angle deposition (OAD). In this work, by using oblique angle deposition, we tuned the refractive index of Tris-(8-hydroxyquinoline) aluminum (Alq3), which is a common electron transporting organic material, from 1.75 to 1.45. We show a 30% increase in external quantum efficiency of a phosphorescent device using the low refractive index Alq3 layer.
Franky So received his PhD degree in electrical engineering from the University of Southern California in 1991. He has previously worked at Hoechst Celanese Research Division and Motorola. In 2001, he joined OSRAM Opto Semiconductors and became the Head of OLED Research. He joined the University of Florida in 2005 and became the Rolf E. Hummel Professor in Electronic Materials in the Department of Materials Science and Engineering at the University of Florida. He joined the Department of Materials Science and Engineering at the North Carolina State University where he is currently the Walter and Ida Freeman Distinguished Professor. While at Motorola, he was named the Distinguished Innovator and Master Innovator. Dr. So holds 80 issued patents and has published more than 175 journal articles with an H-index of 67. He is the Editor-in-Chief of the journal Materials Science and Engineering Reports and serves as an Associate Editor for IEEE Journal of Photovoltaics, IEEE Journal of Display Technology, SPIE Journal of Photonic Technology and Organic Electronics. So is a Distinguished Lecturer of the IEEE Photonics Society, a Charter Fellow of the National Academy of Inventors, and a Fellow of IEEE, OSA and SPIE.

Announced by School of Materials Science and Engineering