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  4. Absorption Spectra and Excited State Energy Levels of the N719 Dye on TiO2 in Dye-Sensitized Solar Cell Models
 
research article

Absorption Spectra and Excited State Energy Levels of the N719 Dye on TiO2 in Dye-Sensitized Solar Cell Models

De Angelis, Filippo
•
Fantacci, Simona
•
Mosconi, Edoardo
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2011
Journal Of Physical Chemistry C

We have investigated the absorption spectrum and the alignment of ground and excited state energies for the prototypical N719 Ru(II) sensitizer adsorbed on an extended TiO2 model by means of high level DFT/TDDFT calculations. The calculated and experimental absorption spectra for the dye on TiO2 are in excellent agreement over the explored energy range, with an absorption maximum deviation below 0.1 eV, allowing us to assign the underlying electronic transitions. We find the lowest optically active excited state to lie ca. 0.3 eV above the lowest TiO2 state. This state has a sizable contribution from the dye pi* orbitals, strongly mixed with unoccupied TiO2 states. A similarly strong coupling is calculated for the higher-lying transitions constituting the visible absorption band centered at ca. 530 am in the combined system. An ultrafast, almost instantaneous, electron injection component can be predicted on the basis of the strong coupling and of the matching of the visible absorption spectrum and density of TiO2 unoccupied states. Surprisingly, this "almost direct" injection mechanism, corresponding to excitation from the dye ground state to an excited state largely delocalized within the semiconductor, is found to give rise to almost exactly the same absorption profile as for the dye in solution, despite the drastically different nature of the underlying excited states. On the basis of our calculations it seems therefore that no sizable lower bound to an "injection time" exists, rather the timings of electron injection are mainly ruled by electron dephasing in the semiconductor.

  • Details
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Type
research article
DOI
10.1021/jp111949a
Web of Science ID

WOS:000289824200045

Author(s)
De Angelis, Filippo
Fantacci, Simona
Mosconi, Edoardo
Nazeeruddin, Mohammad K.  
Graetzel, Michael  
Date Issued

2011

Publisher

American Chemical Society

Published in
Journal Of Physical Chemistry C
Volume

115

Start page

8825

End page

8831

Subjects

Density-Functional Theory

•

Electron-Injection Dynamics

•

Oxide Semiconductor-Films

•

Titanium-Dioxide Films

•

Nanocrystalline Tio2

•

Molecular-Dynamics

•

Dft

•

Spectroscopy

•

Adsorption

•

Surfaces

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LPI  
Available on Infoscience
June 8, 2011
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/68508
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