direction for development of near infrared -dyes for dye ... · conclusions 6 model squaraine dyes...

1

Direction for development of near infrared-dyes

for dye-sensitized solar cells

from the view point of electron injection and charge recombination

Kyushu Institute of Technology (National Institute) Kitakyushu, Fukuoka, Japan, 808-0196, Japan

Shuzi Hayase

Tokyo

Collaborator

Kyushu Institute of Technology Shyam S. Pandey Yuhei Ogomi

Nippon Steel & Sumikin Chemical Co., LTD Yoshihiro Yamaguchi

Universidad de Castilla-La Mancha Abderrazzak Douhal Boiko Cohen Marcin Aiolek Gustovo de Miguel Michal Zitnan, Maria Jose Marchena Barriento, Sofia Kapetanaki

3

Dye sensitized solar cells (DSCs) B. O’Regan and M. Graetzel Nature, 1991, 353, 737

Electrolyte I-/I3-

SnO2 /F

(Acetonitrile, ethylene carbonate, molten salts, etc.)

TiO2

10-20nm

TiO2

Ru N

N

CO

COOH

OTi

N

N

CO

HOOC

O

Ti

SCN NCSOHP257

Dye

TiO2 layer: 10-20 μm

Electrolyte layer: 30 μm

Photovoltaic Performance Comparison Certified efficiency AM1.5G ,1000W/m2

0

10

20

Effic

ienc

y（％

）

C-Si

25.0%

Poly-Si

20.4%

a-Si DSC CIGS

CIGS: CuInGaS(Se)

19.6%

11.9%

CdTe

16.7%

OPV

Commercially available

10.1 % 10.7%

Organic PV

Sharp Mitsubishi Chem.

15% (target)

M. A. Green, K. Emery, Y. Hishikawa, W. Warta, and E. D. Dunlop, Prog. Photovolt: Res. Appl. 2013; 21:1-11.

DSC:Dye-sensitized solar cell

OPV: Organic thin film PV

Spectrum matching for DSC to sun light spectrum (AM1.5)

25-26 mA・cm-2

32 mA・cm-2

36 mA・cm-2

FF:0.75

Voc: 0.75

14-15%

18%

20%

Ru dye

IR dye

Ru N

N

CO

COOH

OTi

N

N

CO

HOOC

O

Ti

SCN NCSOHP257

Increase in Voc

Increase in Jsc (New dye, or tandem, hybrid)

5

IPCE 80%, FF 0.75

Efficiency expectation

Wavelength (nm)

IPC

E

N-719 Black dye

300 400 500 600 700 800 900 10000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8Cocktail dyes

A

B

New NIR dyes to be developed

Conventional Ru dye

e-

hν

dye

I-/I3-

HOMO

LUMO TiO2cond. band

e-

⊿G1

0.9eV

⊿G2

Requirement for development of Near Infrared Dye

How to decrease ⊿G1 and ⊿G2 with maintaining fast electron shift Collaboration of solar cell researchers with photo-physics researchers

Dye syntheses

Molecular orbital calculation

Solar cell performance evaluation

Fundamental analyses on solar cells

Time resolved study

Analyses of electron injection and dye regeneration

Collaboration of Japan side with Spain side

Extraction of items determining sola cell efficiency Propose high efficiency dyes

Douhal group (Time resolved study)

Hayase group (Solar cell-based research)

Samples Substrates

Dynamics

A B

0 10 20 30 40 500.00

0.25

0.50

0.75

1.00

No electrolyte

ΙΙΙ

ΙΙ

Nor

mal

ized

∆A

Time / ps

No electrolyte

Ι0 1 2 3 4 5

0.00

0.25

0.50

0.75

1.00

Nor

mal

ized

∆A

Time / ps

ΙΙΙ

ΙΙΙ

450 500 550 600650 700 750-0.2

-0.1

0.0

0.1

700 725 750 775-0.02

-0.01

0.00

0 ps 1 ps 3 ps 7 ps 42 ps

∆A

Wavelength / nm

∆A

Wavelength / nm

Ground State Bleaching

Femto-second Transient Absorption: SQ-41

)()(* 221−+• +→+ eTiOSQTiOSSQ

Electrolyte Life-tim I 6.7 ps II 11.1 p III 4.9 ps No 2.5 ps

( ) exp[( ) ]f x A t βτ= −

SQ radical cation formation; Electron injection

Change in spectral shape at longer delay. Signal beyond 2 ns.

Research Collaboration

✓ Research discussions: 5 times March 2010 (Spain), May 2011 (Spain), Aug. 2011 (Japan), Sep. 2011 (Spain), June 2012 (Sweden) ✓ Dr. Gustovo de Miguel visited us in Japan and joined the research in Aug. 2011. ✓ Provided 15 dyes and 15 substrates (encapsulated) to Douhal Lab.

Development of near IR dyes for combination with TiO2 (~900 nm)

e-

hν

dye

I-/I3-

HOMO

LUMO

✔HOMO-LUMO energy level

adjustment

✔ LUMO orbital shape

✔Electron injection energy barrier

✔Excitation life time

✔Molecular orbital calculation

✔Dye syntheses tech.

✔Cell structure and cell analyses

TiO2cond. band

e-

0.2eV

0.9eV

12

✔ Time resolved spectroscopy

Simulation results of molecular orbital on organic dye

13

Side chain effect

HOOC

N+

O

O-

N

COOH

R R

SQ dyes

Model dyes: Sharp absorption spectra

HOOC

N+

O

O-

N

COOH

HOOC

N+

O

O-N

COOH

HOOC

N+

O

O-N

COOH

HOOC

N+

O

O-N

COOH

HOOC

N+

O

O-N

COOH

SQD-2 (alkyl chain=2)





HOOC

N+

O

O-

N

COOH


N

O

O

N

FF

F

FF

F

COOH

HOOC

SQD-4F3

Designing of molecular structures after MO calculation

Ene

rgy

vs E

Vac

(eV

)

Alkyl chain length

TiO2 CB

I3-/I-

SQ-Fluoro

SQ-Fluoro

0 5 10 15 20-6

-5

-4

-3

HOMO-LUMO level of synthesized dyes

HOMO-LUMO level can be controlled within 0.6 eV by varying substituents

ΔG1

LUMO

HOMO ΔG2

TiO2 CB

I-/I3-

HOMO

LUMO

Introduction of F alkll decreases HOMO and LUMO

0.00

0.40

0.80

1.20

1.60

2.00

2.40

2.80

0 2 4 6 8 10 12 14 16 18 20

Eff

icie

ncy

[%]

Alkyl Chain Length

Efficiency vs. Alkyl chain length

HOOC

N+

O

O-

N

COOH

HOOC

N+

O

O-N

COOH

HOOC

N+

O

O-N

COOH

HOOC

N+

O

O-N

COOH

HOOC

N+

O

O-N

COOH

SQ-2 (alkyl chain=2)





Adsorption scheme for SQ dyes

N+

O

O-

NN+

O

O-

NN+

O

O-

N N+

O

O-

NN+

O

O-

NN+

O

O-

N N+

O

O-

N

TiO2 TiO2

Main structure responsible for near IR dyes

(SQD2)

N

O

-O

N

COOH

SQ-12Chemical Formula: C36H40N2O4

Exact Mass: 564.2988

Dyes with extended conjugation

0

0.4

0.8

1.2

500 600 700 800 900

Abs

orba

ce (

Nor

m.)

Wavelength (nm)

8

27

31

16

70

21

-7.3

-6.3

-5.3

-4.3

-3.3

TiO

2

8 27 31 16 70

Vacu

um le

vel [

eV]

I-/I3-

Model SQ dyes

LUMO LUMO LUMO LUMO LUMO

HOMO HOMO

HOMO HOMO

HOMO Redox potential

Conduction band

TiO2

One of results of collaboration research

Model Squaraine Sensitizers

1. Chain length ----- SQ-2 and SQ-4 2. Nature of substituents----SQ-4 and SQ-26 3. Molecular Asymmetry------------- SQ-26 and SQ-41

Electronic Absorption Spectra

550 600 650 700 7500.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

abs

orba

nce

Wavelength / nm

SQ 41 SQ 26 SQ 4 SQ 2

ε = 2-3 X 105 dm3.mole-1.cm-1

Energy Band Diagram

CB TiO2

I-/I3-

SQD8 SQ4/4F3

SQD4F6

LUMO change: Electron injection HOMO change: Dye generation Anchor group: Substitution effects:

⊿G1

⊿G2

Photovoltaic Characteristics

Photocurrent Action Spectra

Wavelength (nm)

IPC

E

SQ-2 SQ-4 SQ-26 SQ-41

400 500 600 7000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Time Resolved Investigations

Time-resolved techniques Femtosecond Transient Absorption Spectroscopy Nanosecond Flash Photolysis

Experimental Conditions: SQ-dyes adsorbed on TiO2 SQ-dyes adsorbed on ZrO2 To determine the electron injection efficiency !

Time resolved investigations in

the presence of electrolyte Time-resolved investigations

in the absence of electrolyte To determine the Dye Regeneration efficiency !

-3

SQ Dye

-4

-5 I-/I3-

⊿G1

①

②

③

④

⑤

⑥

TiO2

Electron injection

-3

SQ Dye

-4

-5 I-/I3- 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

⊿G

Injection rate constant /10(-9)/s

SQ26(SQD4F6)

SQ2(SQD2)

SQ4(SQD8)

SQ41(SQ4F3)

⊿G1

No apparent relation between ⊿G1 and injection rate constant

①

②

③

④

⑤

⑥

Electron Injection (②）

Relationship between ⊿G and injection rate constant

Electron injection efficiency is governed by factors other than ⊿G1

Better TiO2

-3

SQ Dye

-4

-5 I-/I3- 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

⊿G

Injection rate constant /10(-9)/s

SQ26(SQD4F6)

SQ2(SQD2)

SQ4(SQD8)

SQ41(SQ4F3)

⊿G1

①

②

③

④

⑤

⑥

Electron Injection (②）

Relationship between ⊿G and injection rate constant

F facilitates the electron injection with the same ⊿G1

High electron injection can be realized with lower⊿G1 by using dyes with F atoms

Better

TiO2

Common trend

Dye regeneration

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.2 0.4 0.6 0.8 1 1.2

Gap

(red

ox-H

OM

O)/

eV

Regeneration efficiency

SQ41(SQ4F3)

SQ26(SQD4F6)

SQ4(SQD8)

SQ2(SQD2)

Dye generation(⑥）

Relationship between ⊿G2 and dye regeneration

-3

SQ Dye

-4

-5 I-/I3-

⊿G2

①

②

③

④

⑤

⑥

High dye generation with Low ⊿G2

Better for high efficiency Common trend

Symmetrical-SQ-26

N

O

O

N

COOH

F F

F

FF

F

HOOC

Chemical Formula: C36H34F6N2O6Exact Mass: 704.23

TiO2

I-

HOMO

Possible explanation for high efficiency dye generation with low ⊿G2

0.000.100.200.300.400.500.600.700.800.901.00

0.50 0.52 0.54 0.56 0.58 0.60 0.62

Rre

l(I 3

- /I- )

Voc (V)

SQ4

SQ4F3

SQ18

SQ4O2

SQ4O4SQ4F6

I3-

e TiO2

e TiO2

I3- 30 nm

30,000 nm

N

O

O

NHOOC COOH

R1

R2

R1 = R2 = Butyl SQ4R1 = R2 = Dodecyl SQ12R1 = R2 = Octadecyl SQ 18R1 = R2 = Trifluorobutyl SQ 4F6R1 = R2 = Methoxybutyl SQ4O2R1 = R2 = Ethylbutanoate SQ4O4R1 =Butyl & R2 = Trifluorobutyl SQ4F3

-F

-O-

A. Hayat, S. S. Pandey, Y. Ogomi, and S. Hayase, J. Electrochem. Soc., 158, B770-B771 (2011).

Porous TiO2 sheet

TiO2

F O

Dye I3

-

e

-3

SQ Dye

-4

-5 I-/I3-

⊿G

①

②

③

④

⑤

⑥ Ei eff: Electron injection efficiency: ②/②+③ Reg eff: Regeration efficiency: ⑥/④+⑥

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.2 0.4 0.6 0.8 1IP

CE

Ei eff x Reg eff

SQ4(SQD8)

SQ41(SQ4F3)

SQ26(SQD4F6)

SQ2(SQD2)

Explanation on IPCE (④）

IPCE can be explained by product of electron injection efficiency and regeneration efficiency

TiO2

I-

HOMO LUMO Polar substitute interacting with I-

High dye generation efficiency with low ⊿G2

High electron injection efficiency with low ⊿G1

High Coupling

Proposed structure realizing high efficiency dye generation with low ⊿G2 and high electron injection with low ⊿G1

Conclusions

6 model Squaraine dyes were synthesized to investigate the role, of alkyl chain length, nature of substituents and molecular asymmetry on the photovoltaic performance.

Electron injection and dye regeneration are not always governed by energy gap (⊿G) and influenced by substituents and molecular structure. This suggests that high electron injection with low ⊿G becomes possible.

Creation of molecular asymmetry and introduction of longer alkyl chain leads to facile electron injection.

Introduction of electron withdrawing Fluor-alkyl substituent leads to facile dye regeneration.

Order of IPCE value was explained by the product of charge injection efficiency and dye regeneration efficiency.

List of Publications in Academic Journals: [1] Alkyl and Fluoroalkyl Substituted Squaraine Dyes: A Prospective Approach Towards Development of Novel NIR Sensitizers; Shyam S. Pandey, Takafumi Inoue, Naotaka Fujikawa, Yoshihiro Yamaguchi and Shuzi Hayase, Thin Solid Films, Vol. 519, pp. 1066-1071 (2010). [2] Substituent Effect in Direct Ring Functionalized Squaraine Dyes on Near Infra-Red Sensitization of NanocrystallineTiO2 for Molecular Photovoltaics ; Shyam S. Pandey, Takafumi Inoue, Naotaka Fujikawa, Yoshihiro Yamaguchi and Shuzi Hayase, Journal of Photochemistry and Photobiology A: Chemistry, Vol. 214, pp. 269-275 (2010). [3] Synthesis and characterization of squaric acid based NIR dyes for their application towards dye-sensitized solar cells ; Inoue, Takafumi, Pandey, Shyam S., Fujikawa, Naotaka, Yamaguchi, Yoshihiro, Hayase, Shuzi; JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY Volume: 213 Issue: 1 Pages: 23-29 (2010). [4] Fine tuning the structure of unsymmetrical squaraine dyes towards the development of efficient dye sensitized solar cells; Shyam S. Pandey, Rie Watanabe, Naotaka Fujikawa, Yuhei Ogomi, Yoshihiro Yamaguchi and Shuzi Hayase; Proc. SPIE Vol. 8111 Page 811116 (2011).

[5] Femto to millisecond observations of indole-based squaraine molecules photodynamics in Solution.; G. de Miguel, M. Marchena, M. Ziolek, M, Zitnan, S. S. Pandey, S Hayase and A. Douhal. Physical Chemistry and Chemical Physics; Vol. 14, Pages 1796-1805 (2012). [6] Photophysics of H-and J-aggregates of Indole based squaraines in solid state.; G. de Miguel, M. Ziolek, M, Zitnan, J. A. Organero, S. S. Pandey, S Hayase and A. Douhal; Journal of Physical Chemistry-C; Vol. 116, No.-17, Pages 9379-9389 (2012). [7] Femto to Millisecond Photophysical Characterization of Indole-based Squaraines Adsorbed on TiO2 Nanoparticle Thin Films. de Miguel, Gustavo; Marchena, Maria Jose; Ziolek, Marcin; Pandey, Shyam; Hayase, Shuzi; Douhal, Abderrazzak; Journal of Physical Chemistry-C; Vol. 116, No.-22, Pages 12137-12148 (2012). [8] Novel unsymmetrical squaraine dye bearing cyanoacrylic acid anchoring group and its photosensitization behavior; Gururaj M. Shivashimpi, Shyam S. Pandey, Rie Watanabe, Naotaka Fujikawa, Yuhei Ogomi, Yoshihiro Yamaguchi and Shuzi Hayase ; Tetrahedron Letters; Vol. 53, No.40, Pages 5437-5440 (2012). [9] Relating the Photodynamics of Squaraine-Based Dye-Sensitized Solar Cells to the Molecular Structure of the Sensitizers and to the Presence of Additives; G. de Miguel, M. Marchena, B. Cohen, S. S. Pandey, S. Hayase and A. Douhal; Journal of Physical Chemistry-C; Vol. 116, No.-42, Pages 22157-22168 (2012).

[10] Dye-Sensitized Solar Cells based on Novel Far-red Sensitizing Unsymmetrical Squaraine Dye containing Pyrroloquinoline Moiety.; Shyam S. Pandey, Naotaka Fujikawa, Rie Watanabe, Yuhei Ogomi, Yoshihiro Yamaguchi and Shuzi Hayase; Japanese Journal of Applied Physics; Vol. 51, No.-10, Issue-2, pages 10NE12-1-10NE12-5 (2012). [11] Solution processable thin film organic photovoltaic cells based on far red sensitive soluble squaraine dye; Shyam S. Pandey, Takafumi Mizuno, Sandeep K. Das, Yuhei Ogomi and Shuzi Hayase; Thin Solid Films; Vol. 522, pages 401-406 (2012). [12] Effect of extended p-conjugation on photovoltaic performance of dye-sensitized solar cells based on unsymmetrical squaraine dyes; Shyam S. Pandey, Rie Watanabe, Naotaka Fujikawa, Gururaj M. Shivashimpi, Yuhei Ogomi, Yoshihiro Yamaguchi and Shuzi Hayase; Tetrahedron, Vol. 69, No. 12, pages 2633-2639 (2013). [13] Effect of anchoring groups on photosensitization behavior in unsymmetrical squaraine dyes’ Gururaj M. Shivashimpi1, Shyam S. Pandey1, Rie Watanabe1, Naotaka Fujikawa1, , Yuhei Ogomi1, Yoshihiro Yamaguchi2, Shuzi Hayase; Synthetic Metals (Submitted). [14] Real-Time Photodynamics of Squaraine-Based DSSCs with Iodide and Cobalt Electrolytes; Maria Jose; de Miguel, Gustavo; Cohen, Boiko; Hayase, Shuzi; Pandey, Shyam; Douhal, Abderrazzak; Journal of Physical Chemistry-C (Submitted).

Thank you for your attention !

direction for development of near infrared -dyes for dye ... · conclusions 6 model squaraine dyes...

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