Issue 4, 2012
From the journal:

Energy & Environmental Science

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

Stephanie R Pendlebury,a   Alexander J Cowan,a   Monica Barroso,a   Kevin Sivula,b   Jinhua Ye,c   Michael Grätzel,b   David R Klug,a   Junwang Tangd  and  James R Durrant*a  

* Corresponding authors

a Department of Chemistry, Imperial College London, South Kensington Campus, London, United Kingdom
E-mail: j.durrant@imperial.ac.uk

b Institut des Sciences et Ingenierie Chimiques, Ecole Polytechnique Fédéral de Lausanne, Lausanne, Switzerland

c International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba, Japan

d Department of Chemical Engineering, University College London, London, United Kingdom

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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Article information

DOI
https://doi.org/10.1039/C1EE02567H
Article type
Paper
Submitted
02 Sep 2011
Accepted
17 Oct 2011
First published
02 Nov 2011

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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