| Abstract: | The elementary excitations of poly(3-methyl-thiophene) in a doping range up to 7.5% have been found to be polarons as evidenced by ESR-measurements. Above 7.5% doping Pauli susceptibility indicates metallic behaviour. In contrast, at 5% doping the optical absorption spectra show a transition from the three peak structure due to polarons to one with two peaks and commonly assigned to the formation of bipolarons. It is argued that a widening of the polaron levels gives rise to this phenomenon and not the induction of bipolarons. Above 20% doping the formation of a new phase of the material is observed, which is characterized by the disappearance of the peak at 1.6 eV and a well defined isosbestic point at 1.4 eV. |
