BATHOCHROMIC SHIFT IN PHOTO-ABSORPTION SPECTRA OF ORGANIC DYE SENSITIZERS THROUGH STRUCTURAL MODIFICATIONS FOR BETTER SOLAR CELLS

Narges Mohammadi, Feng Wang

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

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.

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

• DSSC are almost 12 % efficient. How to Improve their efficiency? 

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

1x1018

2x1018

3x1018

4x1018

5x1018

Pho

tons

/(n

m m

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 .

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

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

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

New Dyes (NP)

9

Fig.4: NP3 Fig.5: NP6

Fig.6: NP7 Fig.7: NP10

Fig.3: TA-St-CA

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

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

En

ergy

(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

Carbz-PAHTDTT Dye

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

-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.

Acknowledgments

THANK YOU!