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The Influence of Structure and Processing on the Behavior of TiO_2 Protective Layers for Stabilization of n-Si/TiO_2/Ni Photoanodes for Water Oxidation

McDowell, Matthew T. and Lichterman, Michael F. and Carim, Azhar I. and Liu, Rui and Hu, Shu and Brunschwig, Bruce S. and Lewis, Nathan S. (2015) The Influence of Structure and Processing on the Behavior of TiO_2 Protective Layers for Stabilization of n-Si/TiO_2/Ni Photoanodes for Water Oxidation. ACS Applied Materials & Interfaces, 7 (28). pp. 15189-15199. ISSN 1944-8244. https://resolver.caltech.edu/CaltechAUTHORS:20150715-142850363

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Abstract

Light absorbers with moderate band gaps (1–2 eV) are required for high-efficiency solar fuels devices, but most semiconducting photoanodes undergo photocorrosion or passivation in aqueous solution. Amorphous TiO_2 deposited by atomic-layer deposition (ALD) onto various n-type semiconductors (Si, GaAs, GaP, and CdTe) and coated with thin films or islands of Ni produces efficient, stable photoanodes for water oxidation, with the TiO_2 films protecting the underlying semiconductor from photocorrosion in pH = 14 KOH(aq). The links between the electronic properties of the TiO_2 in these electrodes and the structure and energetic defect states of the material are not yet well-elucidated. We show herein that TiO_2 films with a variety of crystal structures and midgap defect state distributions, deposited using both ALD and sputtering, form rectifying junctions with n-Si and are highly conductive toward photogenerated carriers in n-Si/TiO_2/Ni photoanodes. Moreover, the photovoltage of these electrodes can be modified by annealing the TiO_2 in reducing or oxidizing environments. All of the polycrystalline TiO_2 films with compact grain boundaries investigated herein protected the n-Si photoanodes against photocorrosion in pH = 14 KOH(aq). Hence, in these devices, conduction through the TiO_2 layer is neither specific to a particular amorphous or crystalline structure nor determined wholly by a particular extrinsic dopant impurity. The coupled structural and energetic properties of TiO_2, and potentially other protective oxides, can therefore be controlled to yield optimized photoelectrode performance.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/acsami.5b00379DOIArticle
http://pubs.acs.org/doi/abs/10.1021/acsami.5b00379PublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/acsami.5b00379PublisherSupporting Information
ORCID:
AuthorORCID
Lichterman, Michael F.0000-0002-0710-7068
Carim, Azhar I.0000-0003-3630-6872
Hu, Shu0000-0002-5041-0169
Brunschwig, Bruce S.0000-0002-6135-6727
Lewis, Nathan S.0000-0001-5245-0538
Alternate Title:The Influence of Structure and Processing on the Behavior of TiO2 Protective Layers for Stabilization of n-Si/TiO2/Ni Photoanodes for Water Oxidation
Additional Information:© 2015 American Chemical Society. Received: January 13, 2015, Accepted: June 17, 2015, Publication Date (Web): June 17, 2015. This material is based upon work performed at the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award No. DE-SC0004993. XPS data were collected at the Molecular Materials Research Center of the Beckman Institute of the California Institute of Technology. TEM data were collected at the Caltech Transmission Electron Microscopy Facility. A.I.C. recognizes a Graduate Research Fellowship from the National Science Foundation for support. The authors gratefully acknowledge the assistance of Dr. Yunbin Guan during collection of SIMS data. The authors declare no competing financial interest.
Group:JCAP
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
NSF Graduate Research FellowshipUNSPECIFIED
Issue or Number:28
Record Number:CaltechAUTHORS:20150715-142850363
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20150715-142850363
Official Citation:The Influence of Structure and Processing on the Behavior of TiO2 Protective Layers for Stabilization of n-Si/TiO2/Ni Photoanodes for Water Oxidation Matthew T. McDowell, Michael F. Lichterman, Azhar I. Carim, Rui Liu, Shu Hu, Bruce S. Brunschwig, and Nathan S. Lewis ACS Applied Materials & Interfaces 2015 7 (28), 15189-15199 DOI: 10.1021/acsami.5b00379
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58896
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:16 Jul 2015 23:03
Last Modified:09 Oct 2019 04:08

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