### 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 (US) |
---|---|

Pages (from-to) | 3930-3936 |

Number of pages | 7 |

Journal | Journal of Physical Chemistry B |

Volume | 104 |

Issue number | 16 |

State | Published - Apr 27 2000 |

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### ASJC Scopus subject areas

- Physical and Theoretical Chemistry
- Engineering(all)

### Cite this

*Journal of Physical Chemistry B*,

*104*(16), 3930-3936.

**Ambipolar diffusion of photocarriers in electrolyte-filled, nanoporous TiO2
.** / Kopidakis, N.; Schiff, Eric Allan; Park, N. G.; Van De Lagemaat, J.; Frank, A. J.

Research output: Contribution to journal › Article

*Journal of Physical Chemistry B*, vol. 104, no. 16, pp. 3930-3936.

}

TY - JOUR

T1 - Ambipolar diffusion of photocarriers in electrolyte-filled, nanoporous TiO2

AU - Kopidakis, N.

AU - Schiff, Eric Allan

AU - Park, N. G.

AU - Van De Lagemaat, J.

AU - Frank, A. J.

PY - 2000/4/27

Y1 - 2000/4/27

N2 - We report transient photocurrent measurements on solar cell structures based on dye-sensitized, porous TiO2 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 TiO2 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 cm2 s-1 at low density to 10-4 cm2 s-1 for densities of 1018 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 (T0 = 650 K) of electron trap levels in TiO2. We infer an electron recombination cross section less than 2 × 10-27 cm2; 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 TiO2 matrix from electrolyte ions only nanometers distant.

AB - We report transient photocurrent measurements on solar cell structures based on dye-sensitized, porous TiO2 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 TiO2 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 cm2 s-1 at low density to 10-4 cm2 s-1 for densities of 1018 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 (T0 = 650 K) of electron trap levels in TiO2. We infer an electron recombination cross section less than 2 × 10-27 cm2; 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 TiO2 matrix from electrolyte ions only nanometers distant.

UR - http://www.scopus.com/inward/record.url?scp=0033740847&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0033740847&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0033740847

VL - 104

SP - 3930

EP - 3936

JO - Journal of Physical Chemistry B Materials

JF - Journal of Physical Chemistry B Materials

SN - 1520-6106

IS - 16

ER -