Crystal formation and epitaxy of thin film organic semiconductors

May 3, 2022, 10:30 am12:00 pm
Maeder Hall-Andlinger Center, Rm 102 Hybrid see abstract for Zoom link
Event Description

As the Earth continues to warm due to human related emissions from burning fossil fuels, alternative and renewable energy sources are becoming increasingly important. A new generation of solar cell technology relying on organic semiconductors could fill certain applications that are poorly addressed by traditional inorganic solar cells. However, a common issue with organic semiconductors is their weak charge transport properties. A reason for this is that organic materials almost always are applied in a disordered, amorphous phase despite organic crystals having superior charge carrier mobilities and diffusion lengths. The focus of this thesis is to further our understanding of organic crystal growth and their integration into future devices. Beginning with crystal growth, we expand the number of known organic materials that can grow large, single crystal domains as a thin film. Compiling the thermal and structural properties of these materials we develop a better understanding of what controls crystal growth and morphology allowing for easier identification of new candidate materials. Next, we turn to investigating growth methods that will allow these thin film crystals to be incorporated into devices. Homoepitaxy, which permits tuning the thickness of a crystalline template, is found to result in remarkably smooth thin films but only for materials with low molecular aspect ratios. Finally, heteroepitaxy on crystalline templates is studied due to the prevalence of heterojunctions in organic devices. In this work we show one-to-one, commensurate growth between two lattice matched materials, a first for organics, and lay out criteria dictating heteroepitaxy with perfect registry.

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