(4ej) Energy Transfer in Molecular Photovoltaics, Carbon Nanotubes, and Nanowires – a First-Principles Perspective

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 presentation, 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 time-dependent density functional theory (DFT).¹ 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.^2-3 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-one-dimensional 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.⁴

1. M. E. Foster and B. M. Wong*, Journal of Chemical Theory and Computation, 8 2682 (2012)
2. X. Zhou, T. Zifer, B. M. Wong, K. L. Krafcik, F. Léonard, and A. L. Vance, Nano Letters 9, 1028 (2009)
3. C. Huang, R. K. Wang, B. M. Wong, D. J. McGee, F. Léonard, Y. J. Kim, K. F. Johnson, M. S. Arnold, M. A. Eriksson, and P. Gopalan, ACS Nano 5, 7767 (2011)
4. B. M. Wong, F. Léonard, Q. Li, and G. T. Wang, Nano Letters 11, 3074 (2011)