Insights into Tailoring of Atomic Layer Deposition Grown TiO2 as Photoelectrode Coating

Jesse Saari, Harri Ali-Löytty, Minttu M. Kauppinen, Markku Hannula, Kimmo Lahtonen, Lauri Palmolahti, Antti Tukiainen, Henrik Grönbeck, Mika Valden

Research output: Other conference contributionPosterScientific


Titanium dioxide (TiO2) is an ideal material of choice for protective photoelectrode coatings thanks to its intrinsic chemical stability, transparency to visible light and defect-mediated charge transfer properties. Both amorphous and crystalline TiO2 can serve as a protection layer for semiconductor materials that are inherently unstable under photoelectrochemical (PEC) conditions. [1] Ti3+ defects within amorphous TiO2 (am-TiO2) can enable polaron hopping-mediated charge carrier transport through a protective am-TiO2 photoelectrode coating [2]. Crystalline TiO2 (c-TiO2) can also exhibit sufficient charge carrier transport properties in case of a suitable band alignment with the photoelectrode [3]. Post-deposition annealing (PDA) treatments that are required for optimal coating performance should be performed at low enough temperatures to prevent growth of interfacial oxides that are detrimental to the charge transfer [4]. The choices of atomic layer deposition (ALD) process parameters are interrelated with the required PDA treatments and photoelectrode coating performance.

Our most recent work [5] examines Ti3+-rich am.-TiO2 thin films grown by ALD at growth temperature of 100–200 °C using tetrakis(dimethylamido)titanium(IV) (TDMAT) and H2O as the precursors. X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations allowed us to identify structural disorder-induced penta- and heptacoordinated Ti4+ ions (Ti5/7c4+), which are interrelated to the formation of Ti3+ defects in am.-TiO2. Furthermore, experimental and computational results support the formation of Ti3+ defects in am.-TiO2 structure without releasing oxygen, i.e., simultaneous formation of oxygen vacancies and interstitial peroxo species leading to defective but stoichiometric am.-TiO2. Upon PDA in air, Ti3+-rich am.-TiO2 thin film crystallizes directly into rutile (grain size <1 µm) at unprecedentedly low temperature of 250 °C. In addition to benefits as photoelectrode coating, the low-temperature synthesis enables photocatalytic applications involving temperature sensitive materials.
1. D. Bae, B. Seger, P. C. K. Vesborg, O. Hansen, I. Chorkendorff, “Strategies for Stable Water Splitting via Protected Photoelectrodes,” Chem. Soc. Rev. 46, pp. 1933–1954, 2017
2. P. Nunez, M. H. Richter, B. D. Piercy, C. W. Roske, M. Cabán-Acevedo, M. D. Losego, S. J. Konezny, D. J. Fermin, S. Hu, B. S. Brunschwig, N. S. Lewis, “Characterization of Electronic Transport through Amorphous TiO2 Produced by Atomic Layer Deposition,” J. Phys. Chem. C 123, pp. 20116–20129, 2019
3. B. Mei, T. Pedersen, P. Malacrida, D. Bae, R. Frydendal, O. Hansen, P. C. K. Vesborg, B. Seger, I. Chorkendorff, “Crystalline TiO2: A Generic and Effective Electron-Conducting Protection Layer for Photoanodes and -cathodes,” J. Phys. Chem. C 119, pp. 15019–15027, 2015
4. J. Saari, H. Ali-Löytty, M. Honkanen, A. Tukiainen, K. Lahtonen, M. Valden, “Interface Engineering of TiO2 Photoelectrode Coatings Grown by Atomic Layer Deposition on Silicon,” ACS Omega 6, pp. 27501–27509, 2021
5. J. Saari, H. Ali-Löytty, M. M. Kauppinen, M. Hannula, R. Khan, K. Lahtonen, L. Palmolahti, A. Tukiainen, H. Grönbeck, N. V. Tkachenko, M. Valden, “Tunable Ti3+-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO2,” J. Phys. Chem. C 126, pp. 4542–4554, 2022
Original languageEnglish
Publication statusPublished - 8 Sept 2022
Publication typeNot Eligible
EventOptics and photonics days 2022 - Tampere, Finland
Duration: 6 Sept 20228 Sept 2022


ConferenceOptics and photonics days 2022
Abbreviated titleOPD2022
Internet address


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