| Abstract
| - The charge transport in nanoparticulate ZnO layers held at different potentials was studied by analyzing theanodic transient photocurrents. The electrodes used in the electrochemical cell consisted of ZnO films coatedonto conductive ITO substrates. In these experiments, three contributions to the photocurrent could bedistinguished which were ascribed to a fast initial charge transport, a slow transport via deep trap states, anda transport via conduction band states or shallow traps. For the latter process, a simple phenomenologicalmodel is derived which enables a representation of the transients using only three parameters. These parametersaccount for the transport through the particulate ZnO layer, for the transport through the substrate, and forthe amount of charge initially being present. The decay of the photocurrent signal is limited by transportthrough the ITO and the electrical connections, whereas the rise reflects mainly the transport through theZnO itself. If the experimental results are interpreted in terms of a diffusion according to the theory of arandom walk, the effective diffusion constant for the electron transport through the ZnO film held at positivepotentials is calculated to be 1.7 × 10-4 cm2/s which is in good agreement with diffusion constants reportedfor particulate electrodes.
|
