Photovoltaic Devices from Self-Assembled Organic Semiconductors

The successful development of organic photovoltaic (OPV) devices for solar energy conversion and storage requires new robust organic chromophores that can self-assemble into ordered structures, a fundamental understanding of energy and charge transport within these structures, accurate theoretical models that can predict how the properties of individual molecules scale to those of materials, and improved device structures that take advantage of the now I properties of the organic materials. This project is an integrated effort that addresses each of these major requirements and yields the fundamental information necessary to construct efficient OPYs. Theoretical modeling is important to understand OPY s because photoexcitation, energy transfer, capture and fission, charge flow and injection all require mechanistic understanding for their optimization. In addition, modeling the geometric structures of the molecular arrays and crystals is important to understand the role of molecular order in determining the properties of new OPY materials. Major progress in each of these modeling areas has already been attained in other related research on OLEDs and OFETs, so that we will be able to take advantage of these previous advances, and integrate them with new theory that will be required to model and predict which structures produce efficient OPVs. A critical step towards photofunctional devices is the ability to create large ordered arrays of interactive molecules. Covalent synthesis of large molecular arrays is highly inefficient and costly, thus making self-assembly the method of choice to achieve ordered architectures from functional building blocks. Self-assembly can be based on a variety of weak interactions such as Jt-Jt interactions and hydrogen bonding. In this project we will take advantage of strong Jt-Jt interactions in a variety of novel aromatic acenes and arylene imides and diimides (rylenes) to assemble ordered structures. In addition, we will investigate how hydrogen-bonding can be used to augment and refine the degree of order within these self-assembled structures. The construction of working OPV s is critical to fully understanding how to optimize the materials that are used to implement such a device. We will examine new methods to optimize the interfacial properties of organic OPV materials and electrodes. In addition, we will develop novel device structures that take advantage of the orientation of the self-assembled aromatic molecules on the electrodes.