Ambipolar diffusion of photocarriers in electrolyte-filled, nanoporous TiO2

N. Kopidakis, Eric Allan Schiff, N. G. Park, J. Van De Lagemaat, A. J. Frank

Research output: Contribution to journalArticle

318 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)3930-3936
Number of pages7
JournalJournal of Physical Chemistry B
Volume104
Issue number16
StatePublished - Apr 27 2000

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ambipolar diffusion
Electrolytes
electrolytes
diffusion coefficient
Photoexcitation
photoexcitation
Electrons
Laser pulses
electron recombination
Electron traps
electrons
coefficients
matrices
pulses
Photocurrents
lasers
photocurrents
Solar cells
Coloring Agents
Dyes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Engineering(all)

Cite this

Kopidakis, N., Schiff, E. A., Park, N. G., Van De Lagemaat, J., & Frank, A. J. (2000). Ambipolar diffusion of photocarriers in electrolyte-filled, nanoporous TiO2 . 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.

In: Journal of Physical Chemistry B, Vol. 104, No. 16, 27.04.2000, p. 3930-3936.

Research output: Contribution to journalArticle

Kopidakis, N, Schiff, EA, Park, NG, Van De Lagemaat, J & Frank, AJ 2000, 'Ambipolar diffusion of photocarriers in electrolyte-filled, nanoporous TiO2 ', Journal of Physical Chemistry B, vol. 104, no. 16, pp. 3930-3936.
Kopidakis N, Schiff EA, Park NG, Van De Lagemaat J, Frank AJ. Ambipolar diffusion of photocarriers in electrolyte-filled, nanoporous TiO2 . Journal of Physical Chemistry B. 2000 Apr 27;104(16):3930-3936.
Kopidakis, N. ; Schiff, Eric Allan ; Park, N. G. ; Van De Lagemaat, J. ; Frank, A. J. / Ambipolar diffusion of photocarriers in electrolyte-filled, nanoporous TiO2 . In: Journal of Physical Chemistry B. 2000 ; Vol. 104, No. 16. pp. 3930-3936.
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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.

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