Aspects of the photoelectrochemistry of nanocrystalline systems

The properties of nanocrystalline electrodes are reviewed with particular emphasis on electron transport in dye-sensitised nanocrystalline photovoltaic cells. Solutions of the electron generation/collection problem are presented for steady-state, transient and periodic illumination. The influence of illumination geometry, absorption coefficient, electron diffusion coefficient, electron lifetime, electron trapping and electron extraction kinetics are discussed. The experimental methods used to study nanocrystalline photoelectrodes are reviewed. Experimental results obtained in studies of high performance dye-sensitised TiO2 photovoltaic cells by intensity modulated photocurrent and photovoltage spectroscopy are analysed using analytical expressions derived by solution of the generation/collection problem. The measured values of electron diffusion coefficient and electron lifetime are discussed and related to the design criteria for high efficiency nanocrystalline photovoltaic cells. The possibility of detecting photoinjected electrons by intensity modulated near IR transmittance measurements is demonstrated. (C) 1999 Elsevier Science Ltd. All rights reserved.