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Electronic and nuclear contributions to time-resolved optical and X-ray absorption spectra of hematite and insights into photoelectrochemical performance

Hayes, Dugan and Hadt, Ryan G. and Emery, Jonathan D. and Cordones, Amy A. and Martinson, Alex B. F. and Shelby, Megan L. and Fransted, Kelly A. and Dahlberg, Peter D. and Hong, Jiyun and Zhang, Xiaoyi and Kong, Qingyu and Schoenlein, Robert W. and Chen, Lin X. (2016) Electronic and nuclear contributions to time-resolved optical and X-ray absorption spectra of hematite and insights into photoelectrochemical performance. Energy and Environmental Science, 2016 (12). pp. 3754-3769. ISSN 1754-5692. https://resolver.caltech.edu/CaltechAUTHORS:20180612-143751095

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Abstract

Ultrafast time-resolved studies of photocatalytic thin films can provide a wealth of information crucial for understanding and thereby improving the performance of these materials by directly probing electronic structure, reaction intermediates, and charge carrier dynamics. The interpretation of transient spectra, however, can be complicated by thermally induced structural distortions, which appear within the first few picoseconds following excitation due to carrier–phonon scattering. Here we present a comparison of ex situ steady-state thermal difference spectra and transient absorption spectra spanning from NIR to hard X-ray energies of hematite thin films grown by atomic layer deposition. We find that beyond the first 100 picoseconds, the transient spectra measured for all excitation wavelengths and probe energies are almost entirely due to thermal effects as the lattice expands in response to the ultrafast temperature jump and then cools to room temperature on the microsecond timescale. At earlier times, a broad excited state absorption band that is assigned to free carriers appears at 675 nm, and the lifetime and shape of this feature also appear to be mostly independent of excitation wavelength. The combined spectroscopic data, which are modeled with density functional theory and full multiple scattering calculations, support an assignment of the optical absorption spectrum of hematite that involves two LMCT bands that nearly span the visible spectrum. Our results also suggest a framework for shifting the ligand-to-metal charge transfer absorption bands of ferric oxide films from the near-UV further into the visible part of the solar spectrum to improve solar conversion efficiency.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://dx.doi.org/10.1039/C6EE02266ADOIArticle
http://www.rsc.org/suppdata/c6/ee/c6ee02266a/c6ee02266a1.pdfPublisherSupporting Information
ORCID:
AuthorORCID
Hayes, Dugan0000-0003-4171-5179
Hadt, Ryan G.0000-0001-6026-1358
Zhang, Xiaoyi0000-0001-9732-1449
Chen, Lin X.0000-0002-8450-6687
Additional Information:© Royal Society of Chemistry 2016. Received 4th August 2016, Accepted 28th October 2016. irst published on 2nd November 2016. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, through Argonne National Laboratory (ANL) under Contract No. DE-AC02-06CH11357. D. H. acknowledges support from the Joseph J. Katz Fellowship from ANL. Use of the Advanced Photon Source (APS) at ANL is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357. A. A. C., R. W. S., and experiments at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-05CH11231. Work by J. D. E. and A. B. M. F., including project conception, ALD thin film growth, and discussion was supported by Argonne-Northwestern Solar Energy Research (ANSER) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award Number DE-SC0001059. We gratefully acknowledge the computing resources provided on Blues and Fusion, a high-performance computing cluster operated by the Laboratory Computing Resource Center at ANL.
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-06CH11357
Argonne National LaboratoryUNSPECIFIED
Department of Energy (DOE)DE-AC02-05CH11231
Department of Energy (DOE)DE-SC0001059
Issue or Number:12
Record Number:CaltechAUTHORS:20180612-143751095
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180612-143751095
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87024
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:12 Jun 2018 23:49
Last Modified:03 Oct 2019 19:51

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