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Issue 4, 2012
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Correlating long-lived photogenerated hole populations with photocurrent densities in hematite water oxidation photoanodes

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Abstract

Photogenerated charge carrier dynamics are investigated as a function of applied bias in a variety of different hematite photoanodes for solar water oxidation. Transient absorption spectroscopy is used to probe the photogenerated holes, while transient photocurrent measures electron extraction. We report a general quantitative correlation between the population of long-lived holes and the photocurrent amplitude. The yield of long-lived holes is shown to be determined by the kinetics of electron-hole recombination. These recombination kinetics are shown to be dependent upon applied bias, exhibiting decay lifetimes ranging from ca 5 μs to 3 ms (at −0.4 and +0.4 V versus Ag/AgCl, respectively). For Si-doped nanostructured hematite photoanodes, electron extraction and electron-hole recombination are complete within ∼20 ms, while water oxidation is observed to occur on a timescale of hundreds of milliseconds to seconds. The competition between electron extraction and electron-hole recombination is electron-density-dependent: the effect on recombination of applied bias and excitation intensity is discussed. The timescale of water oxidation is independent of the concentration of photogenerated holes, indicating that the mechanism of water oxidation on hematite is via a sequence of single-hole oxidation steps.

Graphical abstract: Correlating long-lived photogenerated hole populations with photocurrent densities in hematite water oxidation photoanodes

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Publication details

The article was received on 02 Sep 2011, accepted on 17 Oct 2011 and first published on 02 Nov 2011


Article type: Paper
DOI: 10.1039/C1EE02567H
Energy Environ. Sci., 2012,5, 6304-6312

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    Correlating long-lived photogenerated hole populations with photocurrent densities in hematite water oxidation photoanodes

    S. R. Pendlebury, A. J. Cowan, M. Barroso, K. Sivula, J. Ye, M. Grätzel, D. R. Klug, J. Tang and J. R. Durrant, Energy Environ. Sci., 2012, 5, 6304
    DOI: 10.1039/C1EE02567H

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