Conventional electronic devices can be difficult to manufacture; their constituent materials require very high levels of order and achieving such low entropy in a semiconductor requires expensive and energy intensive fabrication. For example, the energy payback time for a crystalline silicon solar cell is on the order of 2 years, and at current manufacturing growth rates, it is expected to take at least 20 years to produce enough silicon-based solar cells to make a significant impact on the world energy supply.1 Similarly, epitaxial growth constraints are likely to limit solid state lighting sources to a small fraction of the overall demand for lighting. There is an alternate approach that is more suitable for large scale production. In the new Energy Focused Research Center (EFRC) for Excitonics, we address materials with only short-range order. Such nanostructured materials are compositions of nano-engineered elements such as organic molecules, polymers, or quantum dots and wires, in films bound together by weak van der Waals bonds. These materials are characterized by excitons that are localized within the ordered nanostructures. Excitons provide a unique means to transport energy and convert between photons and electrons. Due to localization of excitons, the optical properties of the films are relatively immune to longer-range structural defects and disorder in the bulk. And in contrast with the painstaking growth requirements of conventional semiconductors, weak van der Waals bonds allow excitonic materials to be readily deposited on a variety of materials at room temperature. We address two grand challenges in excitonics: (1) to understand, control and exploit exciton transport, and (2) to understand and exploit the energy conversion processes between excitons and electrons, and excitons and photons.
References 1. Lewis, N. S. & Crabtree, G. (eds.) Basic Research Needs for Solar Energy Utilization (U.S. Department of Energy, http://www.sc.doe.gov/bes/reports/files/SEU_rpt.pdf, 2005).