Title: Connecting molecular structure, self-assembly, and long-range order to efficient charge transport in organic semiconductors

Abstract: Organic semiconductors show great potential for light emitting diodes, flexible solar cells, and printable electronics with new applications emerging in areas such as bioelectronics and thermoelectrics. In all of these applications, the electronic properties of these materials are linked to the solid-state morphology. Our understanding of structure-function relationships has improved significantly in recent years, but many open questions regarding how grain boundaries and connectivity of ordered and disordered domains influence charge-transport in semicrystalline materials remain. Here I focus on recent work unraveling these intercrystallite interactions in a variety of well-performing polymer and small-molecule photovoltaic and transistor materials using a combination of low-dose, high-resolution TEM, molecular simulations, and complementary x-ray methods. The results demonstrate an unexpectedly wide variety of structural defects/features including low-angle and special high-angle grain boundaries, liquid crystalline disclinations, and dislocations in both polymeric and molecular systems often thought to be disordered. We postulate that some of these structural features improve the electronic properties by adding additional charge-transport pathways, bridging grains and bypassing electronically-insulating solubilizing groups. By intentionally engineering these features through the molecular structure and processing, we propose a new method to tailor and improve the electronic properties of the next generation of materials.