Dept. of Bioelectronics Ecole des Mines de St. Etienne, France
Dept. of Materials Science and Engineering, Stanford University, Stanford, CA
The influence of microstructural complexity on charge transport in organic electronics
Location: EB I Room 1011
Friday, February 15th 2013 - 11:00 am
Conjugated small molecules and polymers provide unique opportunities for a vast range of applications. Their ease of processing at ambient conditions, ability to take on unique form factors, and synthetic freedom make them ideal systems for applications ranging from low cost logic circuitry and solar cells to biological sensors. Unfortunately, what makes these materials so desirable also makes them complex and difficult to understand. Weak van der Waal's interactions and, therefore, strong dependence on processing variables makes predictive structure-property design rules elusive. In this talk, I will address key structural aspects of high performing organic semiconductor systems, and show how they dictate electronic materials properties. Using X-ray diffraction line shape analysis, I show that intra-crystalline disorder can be used as a tool to understand a broad range of materials. For example, polymeric semiconductors exhibit surprisingly high lattice disorder and, therefore, charge transport is limited by inter-molecular charge hopping. Conversely, low disorder small molecule systems are limited by electronic charges traversing grain boundaries. Importantly, I show that these seemingly different systems can be described on the same predictive order-disorder scale. Finally, I outline how quantitative structural studies can be utilized to understand more complex systems, such as mixed electronic/ionic conducting polymer blends. Quantitative diffraction analysis techniques can thus be used as powerful tools to understand soft, optoelectronic materials, and can aid in rational design of new devices and materials.