The Energetics of Electron Transfer at the Polypyrrole/Silicon Interface

Conducting polypyrrole (PP) films were grown onto n‐ and p‐type silicon electrodes. The flatband potentials, determined by ac impedance techniques, of n‐ and p‐type Si coated electrodes shift by 300 and 500 mV, respectively, for a 600 mV change in the electrochemical potential of PP ( E PP ) . Open‐circuit photovoltages for these electrodes are dependent on E PP . Photovoltages were observed for n‐Si electrodes when E PP was more positive than +0.15V, and for p‐Si electrodes when E PP was more negative than +0.5V. The Fermi level for the n‐Si/PP electrode shifts negatively upon illumination, whereas a positive shift is observed for the p‐Si/PP electrode. The presence of a depletion layer and a change in the semiconductor bandedges is thus indicated, and is believed due to facile electron transfer between Si surface states and the polymer film. The polymer film equilibrates rapidly with the ferrocene 0/+ redox couple in solution, and can be tuned to a range of potentials determined by the concentration ratio of the oxidized and reduced forms. The PP film thus provides electronic communication between the Si electrode and the solution species.