Paul A. Lane
11:05 - 11:45 a.m.
"Hot Photocarrier Dynamics in Organic Semiconductors Studied by Ultrafast Terahertz Photoconductivity and Transient Absorption"
Photocarrier generation in organic photovoltaic systems arises from excitation of the electron donor or acceptor followed by dissociation of the neutral excited state at an interface between the two materials. The initial dynamics are complex, owing to the presence of parallel processes:electron transfer from an excited electron donor, hole transfer from an excited acceptor, and autoionization—charge transfer between molecules of the same type following excitation with excess energy. These processes were disentangled through selective excitation of the electron donor or acceptor and by comparing composite films to those with a layered nanostructure. Recombination and carrier relaxation are distinguished by combining ultrafast terahertz photoconductivity measurements with transient absorption. The short-lived spike in terahertz photoconductivity seen in organic semiconductors is the signature of a hot photocarrier—a electron transferred to the acceptor with excess energy. Hole transfer, on the other hand, yields a relaxed photocarrier without excess mobility. Our results show that excess excitation energy can be directly linked to carrier mobility.
Paul Lane received a Bachelor of Arts cum laude in Physics and Mathematics from Macalester College in 1986 and a Ph.D. in Experimental Condensed Matter Physics from Iowa State University in 1994. His research experience includes post-doctoral research at the University of Utah, a lectureship at the University of Sheffield, and the electro-optics group at the Charles Stark Draper Laboratory. Dr. Lane has worked in the Optical Physics Branch of the U.S. Naval Research Laboratory since 2003.