Single-crystal electrolytes electronic conductivity

Dye sensitization plays an important role in photography. The sensitization mechanism for ZnO-materials as used in electro-photography is obviously in complete correspondence with these electrochemical experiments as shown for single crystals under high vacuum conditions by Heiland 56> and for imbedded ZnO-particles by Hauffe 57). Even for silver halides where electron injection as sensitization mechanism has been questioned by the energy transfer mechanism 58> electrochemical experiments have shown that the electron injection mechanism is at least energetically possible in contact with electrolytes 59>. Silver halides behave as mixed conductors with predominance of ionic conductivity at room temperature. These results will therefore not be discussed here in any detail since such electrodes are quite inconvenient for the study of excited dye molecules. 

If the cathode is photoactive then, simultaneously with the reactions at the anode, electron-hole pairs form in the conduction and valence band in the semiconductor at the cathode, generating a potential difference (Ui) between the Fermi level in the cathode semiconductor and Ured/ox- Figure 3.60 shows the changes in energy level in the bulk for dense e.g. single crystal) n- and p-type semiconductors in equilibrium with an electrolyte, in the dark and upon illumination. 

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