The effect of multi-walled carbon nanotubes on metal octacarboxyphthalocyanines for dye solar cells application: synthesis and characterisation

The effect of Multi-walled carbon nanotubes on Metal

octacarboxyphthalocyanines for Dye Solar Cells application: Synthesis and

characterisation

IBSA Conference

Nonhlanhla Mphahlele

Outline

• Background and Introduction

• Synthesis and characterisation

• Electrochemical Evaluation

• Conclusions

• Acknowledgements

© CSIR 2011 www.csir.co.za

What are Dye solar cells (DSCs)?

Grätzel, M. 2005, Inorg.Chem,44,6841 - 6851

Mankind is using increasing amounts of Energy. Since 1994 the access to

Electricity has increased from one third to two thirds of the population.

The use of renewable energy sources is Limited.

Alternative energy resources are required Dye solar cells are one of the examples Direct conversion of sunlight into electricity

Major research areas

•Alternative photosensitiser to

enhance the performance and efficiency of DSCs.

N

HOOC

N N

N

COOH N

N

COOH COOH

N HOOC

HOOC

N

M

Metal octacarboxyphthalocyanines

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH

HOOC HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH

HOOC HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS

COO^{- +}TBA

TBA^{+ -}OOC HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS

COO^{- +}TBA

TBA^{+ -}OOC HOOC

COOH

Ru

N N

N

a b

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH

HOOC HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH

HOOC HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS

COO^{- +}TBA

TBA^{+ -}OOC HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS

COO^{- +}TBA

TBA^{+ -}OOC HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH

HOOC HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH HOOC

COOH

Ru

N N

N

N NCS

NCS

COOH HOOC

COOH

Ru

N NCS

NCS

COOH

HOOC HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS

COO^{- +}TBA

TBA^{+ -}OOC HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS HOOC

COOH

Ru

N N

N

N NCS

NCS HOOC

COOH

Ru

N NCS

NCS

COO^{- +}TBA

TBA^{+ -}OOC HOOC

COOH

Ru

N N

N

a b

N719 dye

N3 dye

© CSIR 2011 www.csir.co.za

• High thermal stability

• Light thermal stability

• Chemical stability

• Absorb light at the visible region of the spectrum

• To enhance the photosensitisation of DSCs – MPc complex was modified with MWCNT

•CNTs – efficient catalyst and high conductive property

WHY MPc?

Solar tester

Autolab system Solar tester

Autolab system

O O

O

O O

O

N N

N

N

N N N M N

NH O

O N

H O

O N

H

O

O NH

O O

N

HOOC HOOC

N N

N

COOH

COOH N

N

COOH COOH

N HOOC

HOOC

N

M

H₂SO₄ 20%

Reflux for 3days Urea, metal sal t, DBU

Reflux for 30mins

Synthesis of Metal

Octacarboxyphthalocyanines

N N

N

N N N

N M

N HOOC

COOH COOH

COOH

COOH COOH

HOOC HOOC

CO NH

NH₂ NH

CO N

H₂

NH N CO

H₂

CO NH

NH₂

CO NH

NH-CO- NH

----NH CO

N H ---NH CO

CO NH

NH-CO-

CO NH

NH--- NH

CO -CO-NH

N H -CO-NH CO

CO NH

NH---

n

DMF / ultrasonication (i) Acid functionalization

(ii) Thionyl chloride

(iii) Ethylenediamine / DCC

(MOCPc-MWCNT)

(MWCNT) (MWCNT-NH₂)

MOCPc (M = (OH)₂Si, Zn)

Synthesis route for the MOCPc – MWCNT

Fabrication of Dye Solar Cells using MOCPc-MWCNT hybrid

MPc adsorbed on TiO₂

TiO₂ substrate

Pt catalyst substrate ITO glass

substrate Complete DSCs

MPc adsorbed on TiO₂

TiO₂ substrate

Pt catalyst substrate ITO glass

substrate Complete DSCs

Spectroscopic evaluation

300 400 500 600 700 800

Wavelength, nm

Absorbance, a.u

ZnOCPc SiOCPc GaOCPc 693

689

687

300 500 700

Wavelength, nm

Absorbance, a.u

GaOCPc : MWCNT ZnOCPc : MWCNT MWCNT - NH2 SiOCPc : MWCNT 709

700

699

Electronic spectra of MOCPc and MOCPc-MWCNTs in DMF.

Upon integration with MWCNT , Q band red shifted

Electrochemical evaluation

0 5 10 15 20

0 100 200 300 400 500 600

j/mAcm-2

Time (s)

ZnOCPc

ZnOCPc-MWCNTs

Light on Light off (a)

0 2 4 6 8 10 12 14 16

0 100 200 300 400 500 600

j/mAcm-2

T ime (s)

(OH)2SiOCPc

(OH)2SiOCPc-MWCNTs

Light on Light off (b)

0 1 2 3 4 5 6 7 8 9

GaOCPc GaOCPc - MWCNTs

j/mAcm-2

Lighton Light off

Photo-chronoamperometric measurements (c)

of Lab fabricated DSCs with MOCPc and MOCPc – MWCNTs

(M = Zn, SiOCPc(OH)₂ , Ga(OH)) at an applied potential of 10mV recorded at 50 s interval.

•Rectangular photocurrent response

•ZnOCPc results in an increase in photocurrent

Electrochemical Evaluation

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0 2000 4000 6000 8000

Z" (ohm)

Z' (ohm)

ZnOCPc

ZnOCPc - MWCNTs (a)

0 2000 4000 6000 8000 10000 12000

0 5000 10000 15000

Z" (ohm)

Z' (ohm)

(OH)2SiOCPc

(OH)2SiOCPc - MWCNTs (b)

Nyquist plots of DSCs fabricated with

a) TiO₂/ZnOCPc, b) TiO₂/(OH)₂SiOCPc and their corresponding MWCNT-integrated hybrids.

R_S

C_TiO2

R_TiO2

C_Pt

R_Pt R_Rec

C_Rec

The equivalent circuit to fit the nyquist plot

•Compose of 3 RC elements in series

Efficient electron transfer process occurred

© CSIR 2011 www.csir.co.za

Conclusions

•

MOCPc (M = Ga, Si, Zn) complexes were successfully synthesised

•

As confirmed by FTIR, UV/Vis and electrochemistry characterisation.

•

Amine functionalised multiwalled carbon nanotubes were successfully incorporated with MOCPc to produce MOCPc - MWCNTs hybrid and satisfactory characterisations were obtained.

•

The incorporation of MWCNTs improved the photocurrent response of MOCPc

•

Therefore, ZnOCPc - MWCNT showed high photocurrent response than (OH)₂SiOCPc – MWCNT and (OH)GaOCPc – MWCNT

•

Busy with the DSCs testing using Solar simulator

Acknowledgements

•

The CSIR for funding

•

Prof. Kenneth Ozoemena: Research group leader

•

Dr Lukas Le Roux : Senior researcher at CSIR

•

Dr Leskey Cele : Senior Lecture at TUT

•

Dr Mkhulu Mathe: Competence center manager

Thank You