We report an electrochemical and in situ optical study of doping processes in polyacetylene. Electrochemical voltage spectroscopy (EVS) is used to characterize the energies of charge injection and removal, as well as the kinetics of these processes. In situ optical spectroscopy provides complementary information on the energy of the electronic states where charge is stored (after injection). The EVS results provide a measurement of the energy gap; from these electrochemical data, we infer Eg≃ 1.5 eV, in good agreement with that obtained by other methods. The observation of hysteresis in the electrochemical cycle, and the associated increase in the midgap optical absorption upon doping, are both indicative of the formation of states in the bandgap. The resolution available with the EVS technique allows precise determination of both the energy and number of these states. The results demonstrate that the injected charge is stored in the form of charged solitons (chemical potential Eg/π, with respect to midgap) and not a random distribution of impurity states throughout the gap, nor polaron states near the bandedge. The observation of 300 ppm charge removal precisely at midgap provides a detailed verification of Kivelson's model of charge transport via intersoliton electron hopping. Kinetics studies performed both at low and high dopant levels reveal that ionic diffusion rates under load (current carrying conditions) are two orders of magnitude faster than free ionic-diffusion rates. This anomaly is explained in terms of electric field enhancement of the ionic diffusion in (CH)x.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry