Cis Vs. Trans: Squaraine Molecules as Potential Sensitizers for Dye Sensitized Solar Cells

NSF Science and Technology Center on Materials and Devices for Information Technology Research No. DMR 0120967

NSF Research Experiences for Undergraduates Program Hooked on Photonics No. CHE 0851730

www.hookedonphotonics.org

Daniel Morales Salazar, Iryna Davydenko, and Seth Marder

Conclusions/Future work

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AcknowledgmentsDr. Iryna Davydenko

Dr. Seth Marder

Dr. Denise Bale

Janos Simon (HPLC, and UV-Vis-NIR spectrometer training)

Georgia Tech, NSF (CHE-1156598), CMDITR (NSF DMR-

0120967)

AbstractTo investigate the relationship between structural

conformation and photovoltaic response of

symmetrical squaraine dyes, we have incorporated an

electron-withdrawing dicyanovinyl group on the

squaric acid core. The functionalized squaraine

molecule is locked in a cis-like geometry, and presents

absorption bands in the high-energy area of the visible-

light region, which could result in panchromatic

sensitization. Herein, we report the synthesis,

electrochemical, electronic and optical properties of a

squaraine sensitizer.

Georgia Institute of Technology, Department of Chemistry and Biochemistry, 901 Atlantic Drive, Atlanta, GA 30332, U.S.A.

danielsalazar@gatech.edu

Squaraine Dyes

Large absorption

coefficients in red to

NIR region. Can be

used as NIR

cosensitizers unless

panchromatic response

is achieved.

Cis vs. Trans

Can a cis-like

symmetrical squaraine

outperform the

efficiency of

asymmetrical

squaraines?

Synthetic Route of Sensitizer

Photophysical and Computational Studies

Dye λmax

(nm)

CHCl3

ε

(M-1 cm-1)

E0-0

(eV)

YR6 671 275,000 1.76

DMS-II-22 698 210,000 1.70

DMS-II-33 733 230,000 1.62

Electrochemical Properties

Dye E0-0

(eV)

Eox

(V)Eox - E0-0

(V)

YR6 1.76 0.80 -0.96

DMS-II-22 1.70 0.87 -0.83

DMS-II-33 1.62 0.85 -0.77

Measured in 0.1M nBu4NPF6 in DCM solution with

decamethylferrocene as an internal standard. Tabulated values

are reported versus NHE. First oxidation potential

corresponds to HOMO level of dye.

DFT calculations of DMS-II-44 with the B3LYP functional and 6-31G** basis set using Spartan.

The absorption and electrochemical

properties of the synthesized

intermediates and DMS-II-44 show a

red-shift of absorption maxima into

the NIR region, intense absorption

bands in the high-energy region, as

well as reversible redox behavior,

which may all positively influence the

photovoltaic response of a sensitizer in

a dye-sensitized solar cell .

MSQ, η=2.2%, λmax 642nm (CHCl3)

SQM1a, η=3.6%, λmax 705 nm (CHCl3)

YR6, η=6.74%, λmax 671nm (CHCl3)

HOMO LUMO

Eox

Introduction

Dye-Sensitized solar cells

Low-cost, flexible, colorful, efficient (15%).

Basic Functioning

Photon excites an

electron. Excited

electron is injected

in the TiO2 CB.

Oxidized sensitizer

is regenerated by

an electrolyte.

Electrolyte is

reduced at the

cathode, closing the

circuit.