Department of Physics SCHOOL OF NATURAL SCIENCES & MATHEMATICS

Femtosecond Pump-Probe Spectroscopy

Femtosecond transient absorption (pump-probe) is an ultrafast optical characterization technique that allows monitoring of the carrier relaxation pathways in various types of optical materials (bulk and nanostructures) with femtosecond time resolution. We recently developed Vis-Near-IR pump-probe apparatus based on the Coherent Legend Elite amplifier and TOPAS OPA to study dynamics of ultrafast energy transfer in nanocrystal/organic hybrid structures. Similarly, we had been collaborating with LANL colleagues (Dmitry Yarotsky, MPA-CINT) on studies of charge transfer mechanisms in blends of phosphorescent materials (tetracene) and fullerenes.

Organic conducting polymers offer an attractive alternative
to regular semiconductors in both photovoltaic and optoelectronic applications due
to their low cost and improved processability. Although majority of currently used
devices rely on bulk materials, polymer nanocomposites, both organic/organic and
organic/inorganic, should provide better control over the material properties and
rationalize the design of material functionality. In such nanocomposites, physical
and electronic structures of the interfaces govern carrier generation and transport
characteristics yet underpinning mechanisms are still poorly understood. We apply
ultrafast optical spectroscopy to investigate the charge and exciton relaxation pathways at the Tetracene/C60 interfaces. Our studies reveal the effect of the interface composition (e.g. addition of the tunneling LiF barrier) on dynamics of the charge transfer excitons and on the effciency of charge separation processes in multilayered Tetracene/LiF/C60 nanocomposites. Such experiments will provide information  crucial in the development of the organic and hybrid-based solar cells.

References:

[1] A. Malko, A. Mikhailovsky, J. Hollingsworth, M. Petruska, and V. Klimov, “Interplay between optical gain and photoinduced absorption in CdSe nanocrystals”, Journal of Phys. Chem. B 108, 5250 (2004)

[2] D. Yarotski, S. Sampat, B. Crone, A. Taylor, A. Malko, S. Tretiak, "Tuning of Ultrafast Charge Transfer Dynamics in Tc/LiF/C60 Nanocomposites", APS 2013