Modeling sunlight harvesting in nanostructures

This review article provides a one-stop shop for understanding the state of the science and highlights upcoming computational challenges, such as simulating large numbers of atoms and phenomena that cross scales, such as interactions at the atomic scale that influence far larger areas.

Scientists reviewed electronic structure calculations of light-driven processes in organic and semiconductor nanostructures. They also reviewed how these calculations have furthered our understanding of the optical properties and excitation dynamics of the nanostructures. In the review, these nanostructures range from nanocrystals called quantum dots with zero dimensionality to nanotubes and isolated polymer chains of organic semiconductors that are quasi-one-dimensional materials. The size, shape, and topology of these nanostructures control their properties.

The dimensionality defines the "quantum confinement" in these nanostructures and affects the electronic structure and "photophysics." For example, the size of the quantum dot determines the confinement of the electronic excitation, i.e., the electronic band gap strongly depends on the size of the quantum dot. In addition, factors ranging from surface chemistry to structural disorder affect electronic properties as well as light harvesting and carrier transport in solar energy conversion devices. The scientists highlighted how theory, modeling, and simulation can complement experiments to fully understand and exploit electronic and structural properties.

Nevertheless, the authors identified challenges ranging from the computationally unmanageable number of atoms in large-scale nanostructures to the complexity and multiscale nature of important optical phenomena that must be overcome.

This work was supported by the U.S. Department of Energy (DOE) Office of Science (Office of Basic Energy Sciences) (quantum dots) and the Center for Integrated Nanotechnologies, a DOE Office of Science User Facility; Los Alamos National Laboratory (Laboratory Directed Research and Development); the National Science Foundation (functionalized single walled nanotubes); and the Alfred P. Sloan Research Fellowship (polymer work).