Doping conjugated polymers is an effective way to tune their electronic properties for thin-film electronics applications. This work focuses on icosahedral dodecaborane (DDB) clusters of the form B<sub>12</sub>(OR)<sub>12</sub> as new dopant molecules, where R is a benzyl group. DDBs provide a unique system in which the redox potentials can be rationally tuned via modification of the R-group substituents without significant change to the size or shape of the dopant molecule. To dope films of poly-3-hexylthiophene (P3HT), we employ a sequential doping process (SqP) in which a pure polymer layer is deposited first, followed by infiltration of the DDBs using a semi-orthogonal solvent. SqP overcomes typical problems incurred by blend-doping, mixing polymer and dopant in solution, which often results in aggregation at high concentration. In our DDB doped films, we find that in general conductivity and polaron absorption amplitude increase with increasing reduction potential, yielding conductivities on the order of 5 S/cm. Further, by tuning the degree of swelling of the polymer in the SqP step, we show that we can improve intercalation of these large dopant molecules and achieve conductivities up to 10 S/cm. The IR spectra of DDB doped P3HT is significantly red-shifted compared to what has been previously reported with other dopants. Moreover, when compared to theoretical spectra calculated with the Spano model, spectral shape of the DDB-doped polymer closely matches the calculated spectrum with the anion at infinite distance from the polaron. This extra delocalization is consistent a known feature of dodecaborane cluster anions: that they have a high degree of electron delocalization around the boron cage, with little spillage of the electron density onto the substituents. This means that the charge on the reduced cluster is physically well-separated from the polaron on the polymer chain.  This should decrease the Coulomb attraction between the anion and the polaron, allowing for increased polaron delocalization and thus higher carrier mobility, which we confirm using AC Hall Effect measurements.

Dodecaborane clusters as tunable dopants for conjugated polymers

256th National Meeting (2018)

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