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Charge carrier dynamics in tantalum oxide overlayered and tantalum doped hematite photoanodes
Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. Chemistry and Advanced Materials, Laboratory of Chemistry and Bioengineering,Tampere University of Technology, Tampere, Finland..ORCID iD: 0000-0003-3091-1051
Tampere Univ Technol, Finland.
Univ Helsinki, Finland.
Tampere Univ Technol, Finland.
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2019 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 7, p. 3206-3215Article in journal (Refereed) Published
Abstract [en]

We employ atomic layer deposition to prepare 50 nm thick hematite photoanodes followed by passivating them with a 0.5 nm thick Ta2O5-overlayer and compare them with samples uniformly doped with the same amount of tantalum. We observe a three-fold improvement in photocurrent with the same onset voltage using Ta-overlayer hematite photoanodes, while electrochemical impedance spectroscopy under visible light irradiation shows a decreased amount of surface states under water splitting conditions. The Tadoped samples have an even higher increase in photocurrent along with a 0.15 V cathodic shift in the onset voltage and decreased resistivity. However, the surface state capacitance for the Ta-doped sample is twice that of the reference photoanode, which implies a larger amount of surface hole accumulation. We further utilize transient absorption spectroscopy in the sub-millisecond to second timescale under operating conditions to show that electron trapping in both Ta2O5-passivated and Ta-doped samples is markedly reduced. Ultrafast transient absorption spectroscopy in the sub-picosecond to nanosecond timescale shows faster charge carrier dynamics and reduced recombination in the Ta-doped hematite photoanode resulting in the increased photoelectrochemical performance when compared with the Ta2O5-overlayer sample. Our results show that passivation does not affect the poor charge carrier dynamics intrinsic to hematite based photoanodes. The Ta-doping strategy results in more efficient electron extraction, solving the electron trapping issue and leading to increased performance over the surface passivation strategy.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY , 2019. Vol. 7, no 7, p. 3206-3215
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Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-154835DOI: 10.1039/c8ta09501aISI: 000458682100026OAI: oai:DiVA.org:liu-154835DiVA, id: diva2:1294595
Note

Funding Agencies|Finnish Cultural Foundation; Jenny and Antti Wihuri Foundation; Academy of Finland [141481, 286713, 309920]; Finnish Centre of Excellence in Atomic Layer Deposition

Available from: 2019-03-07 Created: 2019-03-07 Last updated: 2019-09-23Bibliographically approved

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Ruoko, Tero-Petri

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