Reduced Graphene Oxide Composite Counter Electrode for Quantum Dot Solar Cells

Notre Dame Radiation LaboratoryDepartment of Chemical and Biomolecular Engineering1

Deparment of Chemistry and Biochemistry2

University of Notre Dame, Notre Dame, IN 46556

2

J. Phys. Chem. Lett., 2011, 2 (19), pp 2453–2460DOI: 10.1021/jz201064k

Motivation

•Cu2S exhibits exceptional redox activity in aqueous polysulfide solutions1

•Brass is a commonly used counter electrode in laboratory assessments but degrades over time

•Reduced graphene oxide (RGO) is a high surface area, conductive substrate with good electron shuttling capability

1. Hodes, G., Manassen, J, J.Electrochem.Sci., 1980

Synthesis

Synthetic Steps:1. Complexation of Cu+ with graphene oxide (GO)2. Disproportionation of Cu+ to Cu2+ and Cu0

3. Wash via centrifugation to remove dissolved Cu2+

4. Reduce GO-Cu0 composite to form RGO-Cu0 5. Add binder and blade onto substrate6. Immerse in polysulfide for conversion of Cu0 to Cu2S

RGO-Cu2SElectrode

Cu

S

Characterization

•Good coverage of RGO with Cu2S is observed•Unique characteristics of RGO generate 3-D macrostructure

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2

-40

-30

-20

-10

0

10

20

30

Cur

rent

Den

sity

(m

A/c

m2 )

Voltage (V vs. SCE)

Platinum RGO-Cu

2S

1M Na2S

1M S

-1.0 -0.8 -0.6 -0.4 -0.2 0.0

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Cu

rre

nt

De

nsi

ty (

mA

/cm

2 )

Voltage (V vs. SCE)

Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5

Platinum

0.1M Na2S

0.1M S

-1.0 -0.8 -0.6 -0.4 -0.2 0.0-10

-8

-6

-4

-2

0

2

4

6

8

Cu

rre

nt

De

nsi

ty (

mA

/cm

2 )

Voltage (V vs. SCE)

Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5

RGO-Cu2S

0.1M Na2S

0.1M S

C D

BA

0 200 400 600 800 1000 1200

0

100

200

300

400

500

Platinum

Z''

(oh

m)

Z' (ohm)

8 10 12 14

0.25

0.50

0.75

1.00

RGO-Cu2S

Z''

(ohm

)

Z' (ohm)

Electrochemical Response

•Pt shows irreversibility and sluggish kinetics with high Rct

•RGO-Cu2S reversible response with Nerstian shifts in CV and low Rct corresponding to Jo = 16 mA/cm2

Photoelectrochemical Response

Superior electrochemical response with good substrate contact led to fully regenerative efficiency of 4.4%

Summary

•Anchored Cu0 nanoparticles on graphene oxide via disproportionation of Cu+ in ethanol to generate RGO-Cu2S composite

•RGO-Cu2S composite exhibits superior regenerative redox activity with polysulfide without corrosion

•High exchange current density leads to lower polarization of counter electrode and thus higher fill factor and maximum power of the quantum dot solar cell

Thank You!

This work can be found in the Journal of Physical Chemistry Letters

J. Phys. Chem. Lett., 2011, 2 (19), pp 2453–2460DOI: 10.1021/jz201064k

More information on the Kamat Research Group can be found at:www.kamatlab.com