Regiorandom poly(3-hexylthiophene) on gold: Interfacial electronic structures and photoexcitation kinetics

We present studies of the interfacial electronic structures and photoexcitation kinetics of regiorandom poly(3-hexylthiophene) film on gold using two-photon photoemission spectroscopy. We observed an intermediate state located at 1.0 eV above the Fermi level. We tentatively assign the long-lived photoexcitations to a confined polaron. The ionization potential of the polythiophene is estimated to be 4.65 eV. Total photoemitted charge increases with increasing photon energy. We attribute this to an enhanced electron-hole pair dissociation at a higher photoexcitation level. On the basis of the power-law data, we discuss saturation of photoexcitations and singlet–triplet wave function mixing at higher photoexcitation levels.