Ultrafast Carrier Dynamics in Organic Semiconductors

Date: 
Monday, October 16, 2006 (All day)
Speaker: 
Dr. Oksana Ostroverkhova
Speaker's Institution: 
Oregon State University

There is growing interest in using organic semiconductors for applications in electronics and photonics. In particular, organic semiconductor thin films offer several advantages over traditional silicon technology, including low-cost processing, the potential for large-area flexible devices, high-efficiency light emission, and widely tunable properties through functionalization of the molecules. Over the past decade, remarkable progress in materials design and purification has been made, which led to applications of organic semiconductors in light-emitting diodes, polymer lasers, photovoltaic cells, high-speed photodetectors, organic thin-film transistors, and many others. Most of the applications envisioned for organic semiconductors rely on their conductive or photoconductive properties. However, despite remarkable progress in organic electronics and photonics, the nature of charge carrier photogeneration and transport in organic semiconductors is not completely understood and remains controversial, partly due to difficulties in assessing intrinsic properties that are often masked by impurities, grain boundaries, etc. Measurements of charge carrier dynamics at picosecond time scales after excitation reveal the intrinsic nature of mobile charge carriers before they are trapped at defect sites. In this presentation, I will summarize our recent results on transient photoconductivity of high-performance organic semiconductors such as pentacene, functionalized pentacene, tetracene and rubrene single crystals and thin films. Sub-picosecond charge carrier photogeneration, anisotropic bandlike charge transport and crystal structure-dependent charge trapping in these materials will be discussed.