Doping semiconducting polymers with the introduction of small molecules can create steady-state free-carriers enhancing the polymers’ otherwise low carrier mobilities. Understanding the nature of the steady-state carriers is essential to maximizing the conductivity and exploiting these materials for electronic device applications.  We probe chemically-doped polymer films with ultrafast transient absorption spectroscopy, exciting low energy polaron and bipolaron transitions.  Because the dynamics and optical transitions differ between 2D-delocalized polarons, localized polarons, and bipolarons, we can use the corresponding bleaches and transient absorption peaks to assign the doped species to free and trapped polarons and bipolarons.  We assign the electronic transitions of the inter-bandgap states to determine the type of quasiparticle species arising from doping the polymers and show that some polymers form principally polarons while other form bipolarons primarily.  By understanding the roles polarons and bipolarons play in conducting polymer films, one can better tailor doping of polymers for specific applications.

Ultrafast photophysics of polarons and bipolarons in doped semiconducting polymers

2019 Fall National Meeting

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