## Abstract

We report transient photocurrent measurements on solar cell structures based on dye-sensitized, porous TiO_{2} films filled with a liquid electrolyte. The measurements are interpreted as ambipolar diffusion; under most measurement conditions, the ambipolar diffusion coefficient is dominated by electrons diffusing in the TiO_{2} matrix. We report a strong dependence of the ambipolar diffusion coefficient upon the photoexcitation density, as has been proposed previously. The coefficients vary from 10^{-8} cm^{2} s^{-1} at low density to 10^{-4} cm^{2} s^{-1} for densities of 10^{18} cm^{-3}. At a specified photoexcitation density, ambipolar diffusion coefficients measured using weak laser pulses and optical bias are about 10 times larger than coefficients measured using large-intensity laser pulses. We describe trapping models for these effects based on an exponential distribution (T_{0} = 650 K) of electron trap levels in TiO_{2}. We infer an electron recombination cross section less than 2 × 10^{-27} cm^{2}; this value is nearly 10 orders of magnitude smaller than typical values in compact semiconductors and indicates the extraordinarily effective separation of electrons in the TiO_{2} matrix from electrolyte ions only nanometers distant.

Original language | English |
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Pages (from-to) | 3930-3936 |

Number of pages | 7 |

Journal | Journal of Physical Chemistry B |

Volume | 104 |

Issue number | 16 |

Publication status | Published - 27 Apr 2000 |

Externally published | Yes |