Charge carrier dynamics in illuminated, particulate ZnO electrodes

The charge carrier dynamics in illuminated nanoporous ZnO electrodes consis ting of 5 nm particles were investigated. Stable photocurrent quantum effic iencies of 15-30% and photovoltages of up to 0.4 V were found in the presen ce of the I-/I-3(-) redox couple in propylene carbonate. The electronic tra nsport in these ZnO electrodes was fast, the tunneling of electrons from th e ZnO particles to the conducting substrate was much slower. The photovolta ge as a function of light intensity showed a clear discontinuity. This was related to the indirect recombination kinetics; under open circuit conditio ns it could take 10 s or longer before a photogenerated electron was transf erred to I-3(-) in solution.