ECS Toronto'13-Talk 2

Low Cost TCO Less Counter Electrodes for Dye Sensitized Solar Cell Application

Neil Vyas, David Wragg, Cecile Charbonneau, Matthew Carnie, David Worsley and Trystan Watson

SPECIFIC, College of Engineering Swansea University, United Kingdom

email: [email protected]

Presentation Outline• Charge Transfer at DSC Counter Electrodes (CEs)

• Various Counter Electrode Materials

• Development of TiN – PI Counter Electrodes

• Platinisation of Developed CEs

• Surface Morphologyi. SEM analysisii. Profilometry• PV performancei. J-V Characteristicsii. ElS Analysisiii. Optoelectronic Transient Studies

• Conclusions

Charge Transfer at DSC Counter Electrodes


• A counter electrode of a dye-sensitised solar cell can be self catalytic or act as a base for traditional Platinum catalyst.

• Surface morphology and nature of counter electrode materials can significantly alter PV performance of a DSC.

• Counter electrode materials for dye-sensitised solar cell should possess low electrical resistivity and an optimum surface roughness.


15.00 25.00 35.00 45.000.00

2.00

4.00

6.00

8.00

Zreal, Ω

Zima

ginary

, Ω

Rrec= Recombination resistance at the TiO2/electrolyte interface of a DSC

Rce = Charge transfer resistance at the counter electrode of a DSC

Electrochemical Impedance within a Platinised FTO based DSC

• A counter electrode of a dye-sensitised solar cell can be self catalytic or act as a base for traditional Platinum catalyst.

• Surface morphology and nature of counter electrode materials can significantly alter PV performance of a DSC.

• Counter electrode materials for dye-sensitised solar cell should possess low electrical resistivity and an optimum surface roughness.

• Charge transfer resistance at the counter electrode of a DSC also depends on materials used for counter electrode application.


15.00 25.00 35.00 45.000.00

2.00

4.00

6.00

8.00

Zreal, Ω

Zima

ginary

, Ω

Rrec= Recombination resistance at the TiO2/electrolyte interface of a DSC

Rce = Charge transfer resistance at the counter electrode of a DSC

Electrochemical Impedance within a Platinised FTO based DSC

• Lower Rce = Higher Catalytic activity at the CE = Improved PV performance

• Higher Rce = Lower Catalytic activity at the CE = Poor PV performance

Various Counter Electrode Materials


Substrate Catalyst CE fabrication

method

Efficiency Expensive

Scale-up possibility

ITO - PEN Pt NaBH4 reduction of Pt

5.41% Yes(ITO-PEN)

Yes


method



PEDOT:PSS PEDOT Electrodeposited

PEDOT

8.33% Yes(PEDOT:PSS)

NO



method



Poly(oxyethylene)-

backboned polyimide -

CNT

Pt Solvothermally reduced Pt

6.96% Yes(CNT)

NO


Various Counter Electrode Materials (Comparison)


method




5.41% Yes(ITO-PEN)

Yes


PEDOT


NO

Poly(oxyethylene)-


CNT


6.96% Yes(CNT)

NO


method




5.41% Yes(ITO-PEN)

Yes


PEDOT


NO

Poly(oxyethylene)-


CNT


6.96% Yes(CNT)

NO

TiN - Polyimide

Pt Sputtered/Thermal - Pt

3.41% – 1.92% ? ?



method




5.41% Yes(ITO-PEN)

Yes


PEDOT


NO

Poly(oxyethylene)-


CNT


6.96% Yes(CNT)

NO

TiN - Polyimide

Pt Sputtered/Thermal - Pt

3.41% – 1.92% NO Yes


Development of TiN – PI Counter Electrodes

Polyimide

X% of TiN

PI /TiN composite

• TiN (particle size = < 3 µ) at a specific wt% (x = 90%) was blended with a Polyimide precursor (Poly (pyromellitic dianhydride-co-4, 4′-oxydianiline), amic acid) to develop the PI/TiN composite coatings for DSC counter electrode application.

• Developed coatings were initially applied onto non-conducting glass substrates using doctor blade technique and cured at 350oC.


Coating delamination observed


Non-conducting Glass

Adhesive coating (5% TiN – PI)

TiN/PI coating




Non-conducting Glass

Adhesive coating (5% TiN – PI)

TiN/PI coating

Cured coating

Platinisation of Developed CEs

• Developed TiN-PI coatings were platinised using “Thermal” and “Sputter” platinisation techniques.

• H2PtCl6.6H20 precursor was used in thermal platinisation technique which upon heat treatment (at 385oC for 20 minutes) reduces to Pt catalyst.

• A platinum target was used in sputtering technique to deposit 2 nm thick platinum film onto the TiN-PI coating.

Thermally deposited Pt on TiN-PI coating

Sputtered Pt on TiN-PI coating

Surface Morphology (SEM Analysis)

Pt particle

0 1000 2000 3000 4000 5000 6000 70000

200000

400000

600000

800000

1000000

1200000Cured TiN-PISintered TiN-PI

Micrometer, µ

Nano

meter, n

m

Surface Morphology (Profilometry)

Non-conducting glass counter electrodes coated with TiN-PI coating display no significant changes in average surface roughness and coating thickness.

Cells Voc (V) Jsc

(mA/cm2)FF % η %

Glass-TH 0.73 8.39 72.23 4.44Glass -

SP 0.73 7.88 73.13 4.23TiN-TH 0.72 8.52 31.04 1.92

TiN - SP 0.73 8.12 57.46 3.41

-0.2 0 0.2 0.4 0.6 0.8 1 1.2

-4

-2

0

2

4

6

8

10 TiN-THTiN-TH-DTiN-SPTiN-SP-DGlass - THG-TH-DGlass-SPGlass-SP-D

Voltage, V

Curren

t density,

mA/cm2

TiN-PI coating with thermally deposited Pt displayed lowest efficiency but highest short-circuit current density. On the other hand TiN coating with sputtered Pt exhibited decent efficiency and current density values comparable to the glass cells.

Photovoltaic Performance (J-V Characteristics)

Photovoltaic Performance (EIS Studies)

0.600000000000001 0.8 11

10

100

1000TiN-TH-RceGlass-TH-RceGlass-SP-Rce

Voltage, V

Char

ge trans

fer

resistan

ce

(Rce), Ohm

s

Higher charge transfer resistance at the counter electrode was observed in case of thermally platinised TiN-PI coating; whereas, Rce of TiN-PI with sputtered Pt remained very close to the glass cells.

DSCs with thermally deposited Pt on TiN-PI coating displayed higher recombination resistance value as compared to the rest of the cells.

110

1001000

Glass-TH-RrcGlass-SP-RrcTiN-TH-Rrc

Voltage, V

Reco

mbin

atio

n Re

sist

ance

(R

rc),

Ohm

s

0 0.002 0.004 0.006 0.008 0.01

Glass-SPGlass-THTiN-SPTiN-TH

Current density, Jsc

Lifetime

0 10 20 30 40 50 60 700

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8Glass-SPGlass-THTiN-TH

Time, S

Volt

age, V

As the working electrodes were FTO based glass therefore no significant deviation has been noticed in short circuit current transient measurements. This confirms that TiN-PI counter electrodes have no influence on Jsc values of the fabricated devices.

Same applies in case of PV decay measurements where the photovoltage decay rate was found to be same in all cases due to FTO glass working electrodes without any pre-applied blocking layer.

Photovoltaic Performance (Optoelectronic Transient Studies)

Conclusions

• TiN-PI coatings can be used as counter electrodes for dye-sensitised solar cell application.

Conclusions


•This technique does not require FTO deposited glass counter electrodes hence has the potential to replace them.

Conclusions



• TiN-PI counter electrodes with thermally deposited platinum demonstrated very poor catalytic as well as photovoltaic performance.

Conclusions



• TiN-PI counter electrodes with thermally deposited platinum demonstrated very poor catalytic as well as photovoltaic performance.

•TiN- PI counter electrodes with sputtered platinum however, performs significantly better than the thermally deposited Pt ones and its photovoltaic performance is comparable to the glass cells.

ECS Toronto'13-Talk 2

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