The charge transport properties of organic semiconductors are tied intimately to the precise intermolecular order between molecules in the solid state. Serendipitously, many molecules (pentacene, sexithiophene, rubrene, buckminsterfullerene) spontaneously adopt solid-state arrangements that are nearly ideal for efficient charge transport, but solubility issues prevent their application in low-cost deposition technologies. The addition of functional groups to solubilize such chromophores often disrupts the favorable crystal arrangements, often reducing or eliminating efficient charge transport. Thus, solubilizing functionality must be carefully chosen to not only provide the necessary degree of solubility, but also to assist the adoption of solid-state orders that will yield appropriate (or enhanced) charge transport. Here, I will discuss our approach to tuning crystal packing in an array of linearly-fused organic chromophores, along with the impact of subtle changes in molecular structure on crystal packing, film microstructure, and charge transport properties. In particular, I will discuss the impact of heteroatoms or halogen substituents on aggregation and crystal packing, with focus on classic supramolecular synthons (hydrogen bonding, C-H-π interactions) and their ability to fine-tune the structure. Small changes in crystal packing can impact the rate of crystal growth, which in turn determines the types of processes that can successfully yield crystalline films; slow-growing crystals prefer methods such as blade-coating, whereas fast-growing crystals are amenable to rapid process techniques such as spin-coating or spray-coating. Finally, I will discuss the impact of dopants and impurities on thin-film crystal polymorphs and transistor performance.<br/> <br/>

Relating molecular structure to solid-state order and device performance in small-molecule organic semiconductors

251st National Meeting (2016)

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