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Mastani Summer School IISER – Pune (India) June 30 – July 12, 2014. Optical absorption spectra of chromophores in solution: the role of the solvent. Ralph Gebauer. Monday, July 7 th , 2014. Dye sensitized solar cells. Various dyes. Squaraine dye. Cyanidin-3-glucoside ("Cyanin"). - PowerPoint PPT Presentation
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Optical absorption spectra of chromophores in solution: the role of
the solvent
Ralph Gebauer
Monday, July 7th, 2014
Mastani Summer SchoolIISER – Pune (India)
June 30 – July 12, 2014
Dye sensitized solar cells
Various dyes
Source: M. Grätzel, Prog. Photovolt. Res. Appl. 8, 171-185 (2000)
Squaraine dye
Cyanidin-3-glucoside ("Cyanin")
The colour we perceive
Optical spectra in the gas phase
Spectra computed with various codes:
Spectra computed with various functionals:
More realistic model of solvent
Including Molecular Dynamics
Analyzing configurational snapshots
Analyzing configurational snapshots
Response charge density at selected frequencies
Influence of various geometrical distortions
Absorption spectrum of alizarin
Absorption spectrum of alizarin
Model of a photovoltaic device: Squaraine on TiO2 slab
Slab geometry:1x4 TiO2 anatase slab,Exposing (101) surface
PBE functional, PW basis set(Quantum-ESPRESSO code)
Shown here: minimum energyconfiguration
TiO2 slab with squaraine dye
Experimental and TDDFT absorption spectra
Experiment
Computation
A more realistic system: Including the solvent
TDDFT calculation of optical spectra and related quantities
Various challenges:
• System is large (429 atoms, 1.666 electrons, 181.581 PWs, resp. 717.690 PWs)• Broad spectral region of interest• Many excited states in spectral region
Computational tool:
• Recursive Lanczos algorithm for TDDFT
TDDFT optical spectrum: dry system
Energy [eV]
TDDFT optical spectrum including solvent
Energy [eV]
Energy level fluctuations and electron injection driving force
Dye desorption steps:
Conclusions• TD-DFT study of naural dye in vacuum and with PCM
Poor agreement with experiment in absence of solvent in computation
• Including the solvent explicitly
Improvement of computed spectrum, but important features are not reproduced (shoulders, etc.)
• Very efficient implementation of TD-DFT for large systems/basis sets
Recursive Lanczos TDDFT based on time-dependent DFPT for a system composed of 429 atoms and described by ≈ 200,000 PWs
• Molecular dynamics of dye sensitized slab with explicit solvent
Averaging of optical properties over many configurations leads to a description of optical properties in good agreement with experiment
Thanks to:• Filippo De Angelis (Perugia)
• Stefano Baroni (SISSA & DEMOCRITOS, Trieste)
• Brent Walker (University College, London)
• Dario Rocca (UC Davis)
• O. Baris Malcioglu (Univ. Liège)
• Arrigo Calzolari (Modena)
• Quantum ESPRESSO and its community
To know more:
Theory & Method:• Phys. Rev. Lett. 96, 113001 (2006)• J. Chem. Phys. 127, 164106 (2007)• J. Chem. Phys. 128, 154105 (2008)
Applications to DSSCs:• New J. Phys. 13, 085013 (2011)• Phys. Status Solidi RRL 5, 259 (2011)• J. Phys. Chem. Lett. 2, 813 (2011)