This talk will focus on the use of ultrafast infrared spectroscopy as a probe of correlated triplet pair dynamics and separation following singlet fission in amorphous pentacene films. Probing the spatial separation of triplet pair intermediates on ultrafast timescales through their unique vibrational frequencies and infrared electronic transitions reveals that triplet pair separation occurs on similar timescales in both amorphous and crystalline pentacene films, despite these films having different intermolecular coupling strengths. However, diffusion-controlled triplet-triplet annihilation measurements indicate that the diffusivity of triplet excited states is an order of magnitude lower in amorphous pentacene films compared to their crystalline analogs. These results indicate the presence of sparse triplet traps in the amorphous films that inhibit the transport of triplet excitons. Therefore, device developers may be able to utilize nanostructured amorphous or polymeric singlet fission sensitizers to balance ultrafast triplet pair separation and harvesting in singlet-fission sensitized devices despite these materials having low triplet exciton diffusivity.

Investigating the dynamics and separation of triplet pair intermediates in amorphous pentacene films using ultrafast infrared spectroscopy

ACS Spring Meeting 2021

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