Characterizing Electric Field Exposed P3HT Thin Films Using Polarized-Light Spectroscopies

P3HT (poly (3-hexylthiophene)) has been widely used as a donor in the active layer in organic photovoltaic devices. Although moderately high-power conversion efficiencies have been achieved with P3HT-based devices, structural details, such as the orientation of polymer units and the extent of H- and J-aggregation are not yet fully understood; and different measures have been taken to control the ordering in the material. One such measure, which has been exploited, is to apply an electric field from a Van de Graaff generator. Fluorescence (to measure anisotropy instead of polarization, which is more commonly measured) and Raman spectroscopy are used to characterize the order of P3HT molecules in thin films resulting from the field. Preferential orientations of the units in a thin film are determined, consistent with observed hole mobility in thin-film transistors, and it is observed that the apparent H-coupling strength changes when the films are exposed to oriented electrical fields during drying.