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Zeitschrift für Physikalische Chemie

International journal of research in physical chemistry and chemical physics

Editor-in-Chief: Rademann, Klaus


IMPACT FACTOR 2018: 0.975
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Online
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2196-7156
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Volume 229, Issue 10-12

Issues

Ultrafast Dynamics of the Indoline Dye D149 on Mesoporous ZnO and Al2O3 Thin Films

Oliver Flender / Peter W. Lohse / Juan Du
  • Institut für Physikalische Chemie und Elektrochemie, Leibniz-Universität Hannover, 30167 Hannover, Germany
  • Other articles by this author:
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/ Torsten Oekermann
  • Institut für Physikalische Chemie und Elektrochemie, Leibniz-Universität Hannover, 30167 Hannover, Germany
  • present address: Friemann & Wolf Batterietechnik GmbH, Industriestr. 22, 63654 Büdingen, Germany
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Mirko Scholz / Kawon Oum / Thomas Lenzer
Published Online: 2015-08-14 | DOI: https://doi.org/10.1515/zpch-2015-0604

Abstract

Ultrafast photoinduced electron injection and subsequent relaxation steps of the indoline dye D149 were investigated for mesoporous thin films using pump–supercontinuum probe (PSCP) transient absorption spectroscopy in the range 370–770 nm. Three types of mesoporous ZnO layers were compared: Electrodeposited ZnO thin films prepared by using the structure-directing agents (1) Eosin Y (EY) and (2) Coumarin 343 (C343), which are known to produce ZnO layers of different morphology; and (3) mesoporous ZnO thin films consisting of sintered nanoparticles with a diameter of 20 nm. As a reference system, we used a “non-injecting” mesoporous thin film with large band-gap, consisting of Al2O3 nanoparticles with a diameter of 50 nm. On all ZnO thin films, D149 efficiently injects electrons. We observed two components, a dominant one with τ ≤ 70 fs (time-resolution-limited) and a slower one with a time constant of 250–350 fs. Fast initial charge separation is also consistent with the immediate appearance of oscillatory structure due to a change in refractive index of ZnO upon electron injection. For all ZnO thin films, we observe a transient shift of the spectra with a time constant of ca. 20 ps which is assigned to a transient Stark effect (= electrochromism). The S0 → S1 absorption band of D149 is shifted due to the build-up of a local electric field between dye radical cations and ZnO conduction band electrons. On longer timescales, step-scan FTIR spectroscopy revealed a slightly faster cation-electron recombination on ZnO/C343 than on ZnO/EY thin films. On Al2O3, metastable close cation-electron pairs are formed initially which recombine afterwards, and no transient Stark effect is observed. Complementary PSCP experiments on D149 in the ionic liquid [C2mim]+ [N(CN)2] show that D149 is ideally suited for solar cell applications because of its long S1 lifetime of 590 ps. In addition, biphasic solvation dynamics are observed in this IL with a subpicosecond component and a much slower component related to the viscosity of the IL which is well described by a stretched exponential.

Keywords: Kinetics; ZnO Thin Films; Ultrafast Dynamics; Stark Effect; Solar Cells

About the article

Accepted: 2015-07-29

Received: 2015-03-29

Published Online: 2015-08-14

Published in Print: 2015-10-28


Citation Information: Zeitschrift für Physikalische Chemie, Volume 229, Issue 10-12, Pages 1907–1928, ISSN (Online) 2196-7156, ISSN (Print) 0942-9352, DOI: https://doi.org/10.1515/zpch-2015-0604.

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[2]
Johannes R. Klein, Mirko Scholz, Kawon Oum, and Thomas Lenzer
Phys. Chem. Chem. Phys., 2017, Volume 19, Number 27, Page 17952
[3]
Oliver Flender, Mirko Scholz, Johannes R. Klein, Kawon Oum, and Thomas Lenzer
Phys. Chem. Chem. Phys., 2016, Volume 18, Number 37, Page 26010

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