Subscriber access provided by HKU Libraries
Article
Effect of Adsorbed Water Molecules on Light Harvesting and Electron Injection Processes in Dye-Sensitized Nanocrystalline TiO Films 2
Ryota Ishizaki, Ryosuke Fukino, Hiroyuki Matsuzaki, and Ryuzi Katoh J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b03159 • Publication Date (Web): 10 Jul 2017 Downloaded from http://pubs.acs.org on July 16, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 24
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
The Journal of Physical Chemistry
Effect of Adsorbed Water Molecules on Light Harvesting and Electron Injection Processes in DyeSensitized Nanocrystalline TiO2 Films Ryota Ishizaki,1 Ryosuke Fukino,1 Hiroyuki Matsuzaki,2 and Ryuzi Katoh1* 1Department
of Chemical Biology and Applied Chemistry, College of Engineering, Nihon University,
Koriyama, Fukushima 963-8642, Japan 2National
Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1
Umezono, Tsukuba, Ibaraki 305-8568, Japan *Corresponding author:
[email protected] (R.K.)
ACS Paragon Plus Environment
The Journal of Physical Chemistry
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 24
Abstract We studied the effects of adsorbed water molecules on light harvesting and electron injection processes in nanocrystalline TiO2 films sensitized with Ru-complex dyes. We found that the absorption spectra of adsorbed dyes containing SCN groups were sensitive to humidity (that is, the dyes exhibited vapochromism) and that the absorption spectra of dyes adsorbed on nanocrystalline films differed slightly from the spectra of the same dyes adsorbed on TiO2 single crystals, suggesting that the orientation of the dye molecules on the surface was affected by surface-adsorbed water molecules. The dynamics of electron injection from the excited dye molecules into the TiO2 were studied by transient absorption spectroscopy. Transient absorption signal intensities decreased with decreasing humidity, indicating that electron injection efficiency was reduced by loss of water molecules from the surface. IR spectroscopy indicated that only a small amount of physisorbed water was lost upon drying, and the use of an indicator dye showed that the proton concentration around the dye molecules on the surface was markedly increased by drying. On the basis of these findings, we discuss possible mechanisms for the vapochromism and for the reduction in electron injection efficiency caused by the loss of water molecules from the surface.
ACS Paragon Plus Environment
Page 3 of 24
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
The Journal of Physical Chemistry
Introduction Electron injection from excited surface-adsorbed dyes into bulk crystals is an important process in the field of surface photochemistry because it is involved in many practical applications.1) For example, electron injection is involved in photographic technology2) and in dye-sensitized solar cells (DSSCs).3,4) Surface reactions are known to be sensitive to surface conditions, such as morphology and the presence of adsorbates, and thus thorough characterization of surfaces is necessary to obtain reliable results. Surface photochemistry is usually studied under well-defined experimental conditions (e.g., under ultrahigh vacuum), and there have been few studies of the surfaces of devices, such as DSSCs, under practical conditions, where the role of adsorbates on the surface becomes important. DSSCs have several advantages over conventional Si-based solar cells, including low cost, flexibility, color availability, and potential for indoor applications.3,4) However, because device performance and long-term stability have not yet been optimized, there are currently no commercially available DSSCs. In addition, the solar light-to-energy conversion efficiency for DSSCs is still at only approximately 12%.5) Therefore, numerous studies aimed at improving device performance have been carried out.3,4) In particular, surface conditions, such as the presence of adsorbates, have been extensively studied. Electron injection is known to be sensitive to adsorbates. For example, although ultrafast electron injection (
