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Séminaire Johann de Silva

Probing the organisation and interfacial structure of liquid crystalline organic semiconducting thin films

Johann de Silva

Département de Physique
Université libre de Bruxelles, Belgique

We have explored the molecular organisation and interfacial structure in thin films of novel, organic semiconducting material, with a view towards advancing the understanding of interfacial structure in such organic semiconducting thin films. If the wide-scale production of efficient organic thin film devices such as organic light emitting diodes and field effect transistors (OLEDs and OFETs) is to be realised, one of the crucial aspects governing device functionality is the structure of the principle charge transport interfaces between the component layers.

The disubstituted oligothiophene derivatives synthesised and examined here —specifically dioctylterthiophene (DOTT)— form various smectic mesophases that may be useful for optimised charge transport, through the assembly of self-healing planar charge transport pathways. In thin film form, we observe, from in-house X-ray and synchrotron grazing incidence diffraction data, a substrate induced, thermodynamically stable ‘thin film’ phase (the existence of which does not depend on factors such as deposition kinetics for example) within the first few molecular layers at the substrate interface, which is shown in thicker layers to coexist with the bulk-like smectic film above.

We also exploit neutron reflectivity to successfully probe the molecular order and interfacial structure for thin layers of fully deuterated DOTT at the all-important buried semiconductor-dielectric interface that controls charge transport characteristics.