This document discusses computational modeling of organic dye sensitizers for application in solar cells. It outlines the research question of how rational in silico design can be used to develop new organic dyes to increase photocurrent density by decreasing the optical band gap and extending light absorption into the near-infrared region. The document describes computational methods used, including density functional theory and time-dependent density functional theory to optimize dye structures, calculate frontier molecular orbital energies, and simulate UV-Vis absorption spectra. Selected results are presented on modifications made to an existing dye sensitizer to lower the band gap and shift absorption spectra bathochromically into the near-infrared. The overall outcome was successful design of new dyes with improved light absorption properties for potential

1. Computer Modelling Of Organic Dye Sensitizers For The
Application Of Solar Cells
Narges Mohammadi
Prin. Supervisor: Prof. Feng Wang
Assoc Sup: A/P Peter J. Mahon, Prof. Paolo Carloni

2. • Introduction
• Research Question
• Computational Methods
• Selected Results
• Outcome
Outline
6/20/2013 2

3. 3
Fig.2: Leaf-shaped transparent DSSC with four
colors courtesy AISIN SEIKI CO.,LTD.
Fig.4: These (DSSC) windows
generate power from indoor
lighting and ambient light. In this
demonstration, the electricity
generated is used to spin a
propeller courtesy Sony Japan.
Fig.5: Translucent DSSCs in
four colours enliven these
lanterns. The power generated
is stored in a built-in battery
that illuminates the lamp bulb.
No external power is used
courtesy Sony Japan.
Conventional Silicon PV vs. DSSC
Fig.1: Roof-mounted conventional
silicon solar panels.
Fig.3: DSSCs can be made with
dyes of different colours courtesy
TDK Japan.

4. 4
Introduction
• A DSSC works similarly to a leaf on a plant.
• The chlorophyll dye (chlorophyll a) in a leaf absorbs solar energy
and converts it into chemical energy (sugar).
• The principle of power generation of DSSC is very similar to that of
photosynthesis of plants.
• A DSSC takes solar energy and converts it into electrical energy.
• DSSC often referred to as artificial photosynthesis.

5. 5
TransparentElectrode
HOMO
LUMO
Dye Sensitizer
e-
e-
e-
e-
e-
e-e-
e-
I- / I3
-
*Ivanova.E, Truong.V, Webb.H, Baulin.V, Wang.J, Mohammadi.N, Wang.F, Fluke.C, Crawford.R, “Differential attraction and repulsion of
Staphylococcus aureus and Pseudomonas aeruginosa on molecularly smooth titanium films ”, Sci. Rep. 1, 165; DOI:10.1038/srep00165(2011).
DSSC Working Scheme
TiO2
e-
CounterElectrode
e-
e-
hv
e-

6. 6
Research Question
• Dye-sensitized solar cells absorb >85% of
visible light, but almost no light in the near-
infrared.
400 600 800 1000 1200
0
1x10
18
2x10
18
3x10
18
4x10
18
5x10
18
Photons/(nmm
2
s)
Wavelength (nm)
AMA 1.5
Visible
light
Infrared
Light
Fig.6: Solar Spectrum
• How rational and in silico design can be exploited in the design of new
organic dye sensitizers for the application of dye sensitized solar cells .
• Increasing the photocurrent density
requires decreasing the optical gap to
extend the dye’s absorption into the near-
infrared.

7. 7
Method and Computational Details
Selection of well-performing dyes as the backbone of the study.
Chemically modifying the dye structure through substitutions on
different position of dye.
Optimize the molecule structure using DFT methods. (B3LYP,PBE0)
To obtain the HOMO-LUMO energy levels and other related
properties.
Simulation of UV-Vis spectra using TD-DFT.
Suggestion to synthesis chemists through collaboration.
Theory
Level:
Density
functional
theory (DFT)
Time
dependant
DFT
(TDDFT)
Packages:
Gaussian09
Gaussview,
Molden,
GaussSum,
Chemissian
Computational Details

8. Fig.7: TA-St-CA structure.
* Hwang, S., et al., “A highly efficient organic sensitizer for dye-sensitized solar cells”, Chem. Commun, 46: p.
4887-4889,(2007).
8
Dewar’s
Rule
TA-St-CA Dye*
NH2
&
N(CH3)2
CN

9. 9
TA-St-CA Dye
Fig.8: Experimental and calculated UV-Vis spectra of TA-St-CA
dye in ethanol solution.

10. 10
TA-St-CA Dye*
Vir
Occ
Fig.9: Calculated frontier MO energy levels in vacuum.
* Narges Mohammadi, Peter J. Mahon and Feng Wang, " Toward rational design of organic dye
sensitizer solar cells (DSSC): an application to the TA-St-CA dye", (Under revision, 2012).

11. 11
TA-St-CA Dye
Fig.10: The simulated UV–Vis absorption spectra of TA-ST-CA dye and the nine new dyes, i.e.
ED-I, ED-II,…, EW-III in vacuum using the TD-DFT calculations.

12. New Dyes (NP)
12
Fig.12: NP3 Fig.13: NP6
Fig.14: NP7 Fig.15: NP10
Fig.11: TA-St-CA

13. New Dyes (NP)
13
Fig.17: UV-Vis spectra of newly designed dyes and TA-St-
CA dye in vacuum.
Fig.16: Calculated orbital energy diagrams of the dyes
using the PBE0/6-311G(d) model.

14. Fig.23:imulated IR spectra of ferrocene, D5h and D5d in vapour phase using the
B3LYP/m6-31G(d) model.
Ferrocene (Fc)*
14
*Narges Mohammadi, Aravindhan Ganesan, Christopher T. Chantler and Feng Wang, "Differentiation of D5d and
D5h conformers of ferrocene using IR spectroscopy", Journal of Organometallic Chemistry, 713 (2012) 51-59
Fig.21: D5h VS D5d structure.
Fig.22: Earlier IR spectral measurement of Lippincott and Nelson (1958).

15. Ferrocene (Fc)*
15
*Narges Mohammadi, Aravindhan Ganesan, Christopher T. Chantler and Feng Wang, "Differentiation of D5d and
D5h conformers of ferrocene using IR spectroscopy", Journal of Organometallic Chemistry, 713 (2012) 51-59
Fig.24:The IR spectra of the eclipsed (D5h) and staggered (D5d)
ferrocene in the fingerprint region.
Fig.25:Experimental and simulated absorption
spectra of ferrocene in “1,4-Dioxane” solution.

16. Ferrocene (Fc)*
16
Fig.26: Earlier experimental IR spectra of ferrocene (1958) and new IR measurement in
vacuum at Australian Synchrotron (2012).

17. Fc/Fc+ Reduction Potential
17
 Fc/Fc+ is recommended by IUPAC as a standard redox couple
and the reference electrode for nonaqueous solution since
1984.
 To compute Fc/Fc+ absolute redox potential, it is needed to
calculate Gibbs free energy change (∆Gox(sol) ) of the following
redox reaction:
Fc0
(sol)→ Fc+
(sol) + e- (1)
 Total change of Gibbs free energy, ∆Gox(sol), can be calculated
from Born-Haber thermodynamic cycle as follows:
Fc0
(g)
Fc0
(sol) Fc+
(sol)
Fc+
(g)
∆Gox(g)
∆Gox(sol)
∆Gsolv(Fc+)∆Gsolv(Fc0)

18. Fc/Fc+ Reduction Potential
18
 Redox potential is then calculated from the following formula:
Em
(0/+) =∆Gox(sol) / -nF (2)
 We calculated Em
0/+ = 5.079 V which is in a very good agreement
with the experimental value of 5.10 V.
 This shows the reliability of the model used here (i.e. B3LYP/m6-
31G(d)) for the calculations of ferrocene features.
 it is important to run benchmark calculations to ensure that the level
of theory and basis sets are judiciously chosen before exploring
unknown complexes (e.g. derivatives of ferrocene) .

19. Summary and Contribution
19
 Exploiting Dewar’s rule for rational design of organic dye
sensitizers for the first time.
 Designing a new promising organic dye (NP3) based on 14-
annulene rings.
 Using a relatively small model (i.e. B3LYP/m6-31G(d)) for
very accurate calculations of ferrocene redox-potential.

20. • Journal articles
1-Narges Mohammadi, Aravindhan Ganesan, Christopher T. Chantler and Feng Wang, "Differentiation
of D5d and D5h conformers of ferrocene using IR spectroscopy", Journal of Organometallic Chemistry,
713 (2012) 51-59.(Era 2010 A)
2- Christopher T. Chantler, Nicholas A. Rae, Tauhidul M. Islam, Stephen P Best, Joey Yeo, Lucas F.
Smale, James Hester, Narges Mohammadi and Feng Wang , “Stereochemical analysis of ferrocene and
the uncertainty of fluorescence XAFS data”, J. Synchrotron Rad, 19 (2012) 145-158. (Era 2010 A)
3- Elena P. Ivanova, Vi Khanh Truong, Hayden K. Webb, Vladimir A. Baulin, James Y. Wang, Narges
Mohammadi, Feng Wang, Christopher Fluke, and Russell J. Crawford1, “Differential attraction and
repulsion of Staphylococcus aureus and Pseudomonas aeruginosa on molecularly smooth titanium films
”, Nature Scientific Reports,1(2011) 165.
4- Narges Mohammadi, Peter J. Mahon and Feng Wang, " Toward rational design of organic dye
sensitizer solar cells (DSSC): an application to the TA-St-CA dye", (Under revision, 2012).
5-Narges Mohammadi and Feng Wang, “Bathochromic shift in photoabsorption spectra of organic dye
sensitizers through structural modifications for better solar cells”, (Manuscript in preparation)
6- Narges Mohammadi and Feng Wang, “Computational simulation of the interaction between
ferrocene-ferrocenium redox couple and other components of dye sensitized solar cells”, (Manuscript in
preparation)
20
Outcome

21. • Conferences
2012
 N.Mohammadi, F.Wang, “Bathchromic Shift in Photoabsorption Spectra of Organic Dye Sensitisers Through Structural
Modifications for Better Solar Cells”, 20TH AUSTRALIAN INSTITUTE OF PHYSICS CONGRESS, University of New
South Wales, Australia, 9-13 December 2012 (Oral Presentation).
 N.Mohammadi, F.Wang, “Toward Rational Design of Organic Dye Sensitized Solar Cells Through Chemical
Modifications: An Application to the TA-St-CA Dye”, Melbourne Meeting of Molecular Modellers, University of
Melbourne, Australia, 25 September 2012 (Poster Presentation).
 Olivier Jonathan Uppiah, N.Mohammadi, F.Wang, “Sugar Saturation of Nucleoside Antibiotics Revealed by Simulated
IR Spectra: Thymidine and Stavudine”, Melbourne Meeting of Molecular Modellers, University of Melbourne,
Australia, 25 September 2012 (Poster Presentation).
 N.Mohammadi, F.Wang, “Turning Visible Into NIR Absorbance Through Chemical Modifications of Organic Dye
Sensitizers”, International Meeting on Atomic and Molecular Physics and Chemistry, Scuola Normale Superiore,
Pisa, Italy, 12-14 September 2012 (Abstract accepted for poster presentation).
2011
 N.Mohammadi, F.Wang, “A computational study of the HOMO_LUMO gap reduction through modifications of the π –
conjugated bridge of TA-St-CA organic dye”, Australian Synchrotron User Meeting 2011, Melbourne, Australia,
December 2011 (Poster Presentation).
 N.Mohammadi, F.Wang, “A computational study of the π –conjugated bridge of TA-St- CA organic dye through chemical
modifications”, BioPhysChem 2011, Wollongong, Australia, (Abstract accepted for poster presentation).
2010
 N.Mohammadi, F.Wang, “A study of phenothiazine using quantum mechanical modelling”, MM2010, Melbourne,
Australia, 28th November-1st December 2010 (Poster Presentation).
21
Outcome

22. Chapter 1:
Introduction
• Background of
the Problem
• Research
Question
• Objectives
• Scope
• Importance
Chapter 2:
Literature Review
• Introduction
• Photovoltaic
Devices
• Dye Sensitized
Solar Cells
(DSSC)
• Efficiency
• Main
Components of
DSSC
• Dye
• Organic
• Ruthenium-
based
• Semiconductor
• Redox Couple
Chapter 3:
Computational
Details
• DFT
• Absorption
Spectra and TD-
DFT
• Solvation
Models
• Modelling of
TiO2 Surface
Chapter 4:
Organic Dye
Sensitizers
• TA-St-CA Dye
and its
Modifications
• Ground-state
Structure
• Dewar’s Rule
and
Modifications
• Excited-state
Structure and
Spectra
• Effect of
Solution
• Carbz-PAHTDDT
Dye and its
Modifications
• Ground-state
Structure
• Excited-state
Structure and
Spectra
• Effect of
Solution
• NP Dyes
• Ground-state
Structure
• Excited-state
Structure and
Spectra
Chapter 5:
Ferrocene and
TiO2
• Geometrical
Features of
Ferrocene
• IR Spectra of
Ferrocene
• Gas
• Solution
• Fc/Fc+ Redox
Potential
• Geometrical
Features of TiO2
molecule
Chapter 6:
Interaction of dye
and TiO2
• Geometry
Optimization
• Effect of
Adsorption on
UV-Vis Spectra
• Study of
Electron
Injection
Chapter 7:
Summary and
Conclusion
Chapter 8:
Outlook
22
Thesis Outline

23. 23
Acknowledgments
• Swinburne university vice-chancellor's postgraduate award.
• Victorian partnership for advanced computing, VPAC, for
supercomputing facilities.
• Prof. F. Wang and A/Prof .P .Mahon for their supervision, guidance,
encouragement, and support.
• Prof. C. Chantler (University of Melbourne) and Dr. D. Appadoo
(Australian Synchrotron) for collaboration in gas-phase infrared
spectrum of ferrocene experiment at the Far-IR beamline of the
Australian Synchrotron.

24. 6/20/2013 24
Thank You!