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Optical absorption spectra of chromophores in solution: the role of the solvent

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").

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Optical absorption spectra of chromophores in solution: the role of the solvent

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  1. 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 7th, 2014

  2. Dye sensitized solar cells

  3. Various dyes Squaraine dye Cyanidin-3-glucoside ("Cyanin") Source: M. Grätzel, Prog. Photovolt. Res. Appl. 8, 171-185 (2000)

  4. The colour we perceive

  5. Optical spectra in the gas phase

  6. Spectra computed with various codes:

  7. Spectra computed with various functionals:

  8. More realistic model of solvent

  9. Including Molecular Dynamics

  10. Analyzing configurational snapshots

  11. Analyzing configurational snapshots

  12. Response charge density at selected frequencies

  13. Influence of various geometrical distortions

  14. Absorption spectrum of alizarin

  15. Absorption spectrum of alizarin

  16. 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

  17. TiO2 slab with squaraine dye

  18. Experimental and TDDFT absorption spectra Experiment Computation

  19. A more realistic system: Including the solvent

  20. 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

  21. TDDFT optical spectrum: dry system Energy [eV]

  22. TDDFT optical spectrum including solvent Energy [eV]

  23. Energy level fluctuations and electron injection driving force

  24. Dye desorption steps:

  25. Conclusions • TD-DFT study of naural dye in vacuum and with PCMPoor 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.) • Molecular dynamics of dye sensitized slab with explicit solventAveraging of optical properties over many configurations leads to a description of optical properties in good agreement with experiment • Very efficient implementation of TD-DFT for large systems/basis setsRecursive Lanczos TDDFT based on time-dependent DFPT for a system composed of 429 atoms and described by ≈ 200,000 PWs

  26. 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)

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