ELECTRON-TRANSPORT IN POROUS NANOCRYSTALLINE TIO2 PHOTOELECTROCHEMICAL CELLS

The photocurrent response of dye-sensitized, porous nanocrystalline Ti O2 cells was studied as a function of light intensity, in both the tim e domain (photocurrent transient measurements) and the frequency domai n (intensity-modulated photocurrent spectroscopy). The photocurrent tr ansients are characterized by a fast and a slow component. The rise ti me of the transients was in the range of milliseconds to seconds and e xhibited a power law dependence on light intensity with an exponent of -0.6 to -0.8. The response to a modulated light intensity is characte rized by a depressed semicircle in the complex plane. The time constan t obtained from these spectra exhibits the same power law dependence o n light intensity. The transient response of these cells is dominated by electron transport in the TiO2 film, and the results are shown to b e consistent with a diffusion model where the diffusion coefficient fo r electrons in the particle network is a function of the light intensi ty.