Speakers

Prof. LEE obtained his BSc and PhD degrees from the University of Hong Kong in 1987 and 1991 respectively. He then furthered his research career at the University of Birmingham of UK with the support of the Croucher Foundation Fellowship. Prof. Lee joined City University of Hong Kong in 1994 and is currently a Chair Professor of Materials Chemistry and the Dean of College of Science. He also co-founded the Center Of Super-Diamond and Advanced Films (COSDAF) in 1998 and served as the Center’s Director/ Deputy Director till 2022. Prof. Lee’s current research interests include organic electronic devices and nanomaterials for energy, environmental and biomedical applications.

Centimeter-Scale Hole Diffusion in Organic Light-Emitting Diodes

Abstract

It is well known that organic semiconductors typically have much higher hole mobilities than electron mobilities. Current balance between electron and hole transports in organic light-emitting diodes (OLEDs) is typically achieved by (1) leakage of holes through the whole devices or by (2) accumulation of holes inside the devices. These processes are known to reduce both efficiency and operation lifetime due to exciton-polaron annihilation, etc. In this work, we introduce a new way for balancing the electron and hole currents by exploiting lateral hole diffusion.  By composition and interface engineering, we demonstrate a modified PEDOT:PSS bilayer which can sustains hole diffusion over distances of centimeter scale. This ultralong distance hole diffusion enables substantially enhanced hole diffusion current in the lateral direction perpendicular to the applied electric field. By introducing this lateral hole diffusion layer (LHDL) on top of the ITO anode, reduced hole accumulation, improved efficiency, and enhanced lifetime are achieved. The application of the LHDL provides a third strategy for current balancing with much reduced harmful effects from the previous two approaches.