The poly-3-hexylthiophene/NOPF₆ system: A photoelectron spectroscopy study of electronic structural changes induced by the charge transfer in the solid state

The electronic structure of poly-3-hexylthiophene (P3HT) is studied in the solid state with photoelectron spectroscopy, as the polymer is gradually doped from NOPF₆. Solubility and processability of P3HT allow for the preparation of very clean and very thin films, which are then doped without air-exposure. The evolution of the core level binding energies is related to the modification of the electron density on the conjugated backbone, due to the creation of polaron and bipolaren defects. Upon doping, valence spectra show a shift in the Fermi level of the system, and at saturation doping a finite density of states at the Fermi level is observed unambiguously for the first time in electrically conducting polymers with photoelectron spectroscopy. The experimental data on core and valence levels can be interpreted in terms of the formation of a polaron lattice at high doping.