Semiconducting polymers are promising for use in semiconducting electronics, yet suffer from low carrier mobilities.  To this end, there is interest in using molecular doping of semiconducting polymers to vastly increase conductivity, but the nature of the carriers in these molecularly-doped polymer films is not well understood.  With a new technique to produce low-roughness, optical quality, highly-doped conjugated polymer films doped with F4TCNQ (2,3,5,6 tetrafluoro 7,7,8,8 tetracyanoquinodimethane), the photophysics of doped films is now open for exploration.  Using ultrafast transient absorption spectroscopy, we excite the optical absorptions of the various carrier species in doped polymer systems.  We are able to assign the various bleaches and transient absorption peaks to the energy levels of polarons and bipolarons, finding clear evidence for the presence of both species at high doping levels.  Because the dynamics of excited polarons differ from those of excited bipolarons, the excitation wavelength dependence of the transient absorption response of doped conjugated polymer films enables us to detangle the roles of polarons and bipolarons, enabling us to generate action spectra of the overlapping polaron and bipolaron transitions in F4TCNQ-doped poly-3-hexylthiophene. <br/>

Photophysics of polarons and bipolarons in F4TCNQ-doped semiconducting polymers

253rd National Meeting (2017)

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