Work Function Modification in P3HT H/J Aggregate Nanostructures Revealed by Kelvin Probe Force Microscopy and Photoluminescence Imaging.

We show that surface electronic properties of poly-3-hexylthiophene (P3HT) crystalline nanofibers as probed by Kelvin probe force microscopy (KPFM) depends sensitively on the degree of polymer packing order and dominant coupling type (e.g., H- or J-aggregate) as signaled by absorption or photoluminescence spectroscopy. Nominal HOMO energies between high molecular weight (J-aggregate) nanofibers and low-molecular weight (H-aggregate) nanofibers differ by ≈160 meV. This is consistent with shifts expected from H-type charge-transfer (CT) interactions that lower HOMO energies according to registration between thiophene moieties on adjacent polymer chains. These results show how KPFM combined with wavelength-resolved photoluminescence imaging can be used to extract information on "dark" (CT) interactions in polymer assemblies.