This document discusses the rational design of new organic dye sensitizers for dye-sensitized solar cells using computational methods. It begins by noting the increasing global energy demand and limitations of current energy sources. It then provides background on dye-sensitized solar cells and their advantages over traditional silicon solar cells. The objectives are to design dyes with broader absorption spectra extending into the near-infrared, reduced HOMO-LUMO gaps, and suitability for solar cells. Several dye structures are computationally modified and evaluated using density functional theory and time-dependent DFT to obtain optical and electronic properties. Promising new dyes with red-shifted absorption are identified.

1. Narges Mohammadi, Feng Wang

2. Global need for energy is
estimated to be doubled
by 2050 and triplet by the
end of this century.
Fossil fuels?
-Limited
-Environmental concerns
Solar ?
-Readily available
-Abundant
-Clean
Current silicon-based solar
cells?
-Expensive
Dye sensitized solar cells:
-Cost-effective alternative for
the photovoltaic energy sector
Introduction
2

3. 3
Leaf-shaped transparent DSSC with four
colors courtesy AISIN SEIKI CO.,LTD.
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.
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
Roof-mounted conventional silicon
solar panels.
DSSCs can be made with dyes of different
colours courtesy TDK Japan.

4. Transparent Electrode
Counter Electrode
TiO2
TiO2|S + hv → TiO2|S∗
TiO2|S* → TiO2|S+ + e−cb
S+ +3/2 I- →S+1/2 I3
-
1/2 I3
- +e(pt)
- →3/2 I-
HOMO
LUMO
Dye Sensitizer
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
I3
- 3I-
DSSC Working Scheme
4

5. 5
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
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 .

6. Rational design for new organic dyes which possess :
 Broader and red-shifted absorption band.
 Reduced HOMO-LUMO gap.
 Suitability for the application of solar cells. Dye Sensitizer
HOMO
LUMO
6
Objectives

7. 7
Methods & 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. TA-St-CA Dye
Fig.2: Experimental and calculated UV-Vis
spectra of TA-St-CA dye in ethanol
solution.
Fig.1: TA-St-CA* structure.
* Hwang, S., et al., Chem. Commun, 46: p. 4887-
4889,(2007).
8

9. New Dyes (NP)
9
Fig.4: NP3 Fig.5: NP6
Fig.6: NP7 Fig.7: NP10
Fig.3: TA-St-CA

10. New Dyes (NP)
10
Fig.9: UV-Vis spectra of newly
designed dyes and TA-St-CA dye in
vacuum.
Fig.8: Calculated orbital energy
diagrams of the dyes using the PBE0/6-
311G(d) model.

11. 11
Carbz-PAHTDTT Dye
Figure 10: Sketch of Carbz-PAHTDTT* dye and its derivatives.
* Daeneke, T., et al., “High-efficiency dye-sensitized solar cells with ferrocene-based electrolytes”, Nat Chem, 3(3): p. 211-215, (2011).

12. 12
Energy(eV)
-1.5
-2
-2.5
-3
-3.5
-4
-4.5
-5
-5.5
-6
2.55 2.06 2.36
Carbz-PAHTDDT D1 D2
Figure 11: Calculated frontier
MO energy levels in vacuum.
Figure 12: Isodensity surfaces of HOMO and
LUMO for Carbz-PAHTDDT dye and derivative
dyes D1 and D2.
Carbz-PAHTDTT Dye

13. 13
Carbz-PAHTDTT Dye
Figure 13: UV-Vis absorbance spectra of Carbz-
PAHTDDT dye and derivative dyes D1 and D2.

14. -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.

15. THANK YOU!