Neither crystalline nor amorphous: Disorder, microstructure and transport in organic semiconductors.

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• Alberto Salleo, Materials Science and Engineering Stanford University, USA.
• Friday 13 May 2011, 10:00-11:00
• Kapitza Building Seminar Room, Cavendish Laboratory, Department of Physics.

If you have a question about this talk, please contact Jenny Clark.

The promise of organic electronics is to dial in desirable properties (emission wavelength, mobility, chemical sensitivity) and use the power of organic chemistry to rationally design new synthetic semiconductors without being limited by Nature and the periodic table.

From the fundamental standpoint, these materials are fascinating as they are neither crystalline nor amorphous and their microstructure plays a central role in governing charge transport. We apply classical Materials Science concepts towards understanding how organic semiconductors “work”. Using advanced synchrotron-based X-ray characterization techniques we are able to define and measure structural order at different length-scales. I will show that understanding disorder is the key to determining charge transport mechanism. For instance, static cumulative disorder (e.g. paracrystallinity) –which we devised how to measure quantitatively–provides a fundamental justification to using a mobility edge model with an exponential distribution of tail states in the gap. Furthermore, we are able to provide a structural interpretation of these trap states, which for instance manifest themselves as a broad sub-threshold region in transistors. Paracrystalline disorder allows to rank organic semiconductors thereby allowing to determine whether shallow traps or grain-boundaries limit transport this regard, I will show that engineering the microstructure of organic semiconductors leads to new insights in the role of grainboundaries in charge transport. Understanding the relationship between microstructure and transport is of fundamental importance for the rational design of new synthetic semiconductors.

This talk is part of the Optoelectronics Group series.

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