Argonne National Laboratory

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Energy Transfer in Molecular Photovoltaics, Carbon Nanotubes and Nanowires – a First-Principles Perspective

Materials Science Seminar
Bryan M. Wong, Sandia National Laboratory
June 28, 2013 11:00AM to 12:00PM
Building 200, Room J183
The ability to tune electronic properties in molecular photovoltaics and nanomaterials holds great promise for incorporating these materials in next-generation transistors, circuits, and nanoscale devices. In particular, the use of predictive first-principles calculations plays a vital role in rationally guiding experimental efforts to optimize energy harvesting in nanoscale and mesoscale materials.

In this seminar, I will highlight my recent work in using various quantum-mechanical approaches for understanding and predicting the electronic properties in light-harvesting molecules, functionalized carbon nanotubes, and heterostructure nanowires. First, I will demonstrate that both the optical properties and excitation energies in photovoltaic molecules can be accurately predicted by constructing new exchange-correlation functionals for timedependent density functional theory (DFT).

Next, the use of large-scale DFT calculations is presented to understand optical detection mechanisms in chromophore-functionalized carbon nanotubes. Through joint experimental-theoretical studies, I will show that a single-walled carbon nanotube functionalized with light-sensitive chromophores can function as a sensitive nanoscale color detector, where the chromophores serve as photoabsorbers and the nanotube operates as the electronic read-out. Finally, a new theoretical approach is presented to understand electron localization effects in heterostructure nanowires.

At nanoscale dimensions, the formation of mobile electron gases in AlGaN/GaN core-shell nanowires can lead to degenerate quasi-onedimensional electron localization, in striking contrast to what would be expected from analogy with bulk heterojunctions. The reduction in dimensionality produced by confining electrons in these nanoscale structures results in a dramatic change in their electronic structure, leading to novel properties such as ballistic transport and conductance quantization.