Directed exciton transport highways in organic semiconductors

Exciton bandwidths and exciton transport are difficult to control by material design. We showcase the intriguing excitonic properties in an organic semiconductor material with specifically tailored functional groups, in which extremely broad exciton bands in the near-infrared-visible part of the electromagnetic spectrum are observed by electron energy loss spectroscopy and theoretically explained by a close contact between tightly packing molecules and by their strong interactions. This is induced by the donor-acceptor type molecular structure and its resulting crystal packing, which induces a remarkable anisotropy that should lead to a strongly directed transport of excitons. The observations and detailed understanding of the results yield blueprints for the design of molecular structures in which similar molecular features might be used to further explore the tunability of excitonic bands and pave a way for organic materials with strongly enhanced transport and built-in control of the propagation direction. Optical properties of organic semiconductors enable various optoelectronic applications. Muller et al. report a large exciton bandwidth in a crystalline organic material and attribute it to the strong Coulomb interaction in directed exciton pathways induced by the donor-acceptor type molecular structure.

Automated summary

This article showcases the control of exciton bandwidths and exciton transport in organic semiconductors through material design. By tailoring the molecular structure, the researchers observed extremely broad exciton bands and directed transport of excitons. These findings provide blueprints for the design of organic materials with enhanced transport and built-in control of the propagation direction.