TITLE:  The diffusion of molecules in organic electronic films

ABSTRACT

A main advantage in organic electronics is processing by solution casting. However, the rapid solution evaporation often leads to non-equilibrium morphologies. The metastable state could drive significant morphology changes, mainly of the disordered regions, during device fabrication and/or operation. Because the device performances are strictly correlated with film morphology, this “soft” characteristic often limits device performance and stability. Here we will show that the dynamic behavior of film morphology can be judiciously harnessed to enhance device performances and stability. More specifically, we use the tendency of molecules to diffuse/migrate through selected domains in the film to study and direct desired morphologies and interactions in organic electronic devices. This approach is demonstrated in two systems. In the first case, the spontaneous migration of selected additive molecules from within the active layer to form interlayers at the organic/metal interface. Using a plethora of techniques, we show that metal-additive interactions drive additive migration to the organic/metal interface and that selected interlayers can significantly enhance performances and efficiencies of organic LEDs, FETs and solar cells (OSCs). In a second example, the diffusion of gas-phase metal-organic ALD-precursors into bulk heterojunctions (BHJ) is used to study the correlation between structure and performance of OSCs. The molecules diffuse into selective domains of the bulk heterojunction (BHJ) films and in-situ convert to the corresponding metal oxide. Cross section HRSEM images provide visual detailed maps of the different domains composing the BHJ morphology. Comparing “maps” of BHJs composed different polymer:fullerene blends allows us to correlate BHJ composition, processing and nano-scale morphology with device performance.

ABOUT THE SPEAKER

Gitti L Frey is the Head of the Hybrid Materials and Devices Research Group and a Full Professor in the Department of Materials Science and Engineering, Technion, Haifa, Israel. She received her PhD in Materials Science from the Weizmann Institute of Science in 1999 followed by a Post Doctorate Marie Curie Fellowship in the Cavendish Laboratory, Department of Physics at the University of Cambridge, UK. In 2002 she joined the Technion. In 2009, she took a year’s sabbatical in Golden, Colorado, where she was a visiting professor at the Colorado School of Mines and a visiting scientist at the National Renewable Energy Laboratory (NREL). She is currently spending a semester sabbatical at Georgia Tech.

The focus of research in the Frey group is hybrid organic/inorganic interfaces, mainly for organic electronic applications such as organic light emitting diodes, filed effect transistors and solar cells. Such metal/organic and ceramic/organic interfaces and the photo-physical processes across them play crucial roles in the devices so understanding and controlling the interfacial structures and interactions are necessary to achieve enhanced performances. The Frey group is actively involved in developing new processing methodologies and novel characterization tools to study organic/inorganic interfaces and film morphologies and implement them in organic electronic applications.