A Coast, High-efficiency Solar Cell Based on Dye-sensitized Colloidal TiO2 Films

8/3/2019 A Coast, High-efficiency Solar Cell Based on Dye-sensitized Colloidal TiO2 Films

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Double-Layered Electrode Composed of

Compact and Mesoporous TiO2 Layers

for Dye-Sensitized Solar Cells (DSSCs)

(E-mail: [email protected])

Hyun Joong Kim

Nanostructured Eco- and Energy Materials Lab.

Department of Materials Science and Engineering

Seoul National University

2007. 12. 18


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Nanostructured Eco- and Ener Materials Lab.

Introduction

Low energetic production cost

Low cost of the raw materials

Eco-friendly energy source

Application

Benefits of DSSC

e-

e-e-

Dye

h

e-

I3-

I3-

I-

I-

Pt

TCO

TCO TiO2

h

Electrolyte

Principle

Operating Mechanism of Dye-Sensitized Solar Cells (DSSCs)


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IntroductionOperating Mechanism of Dye-Sensitized Solar Cells (DSSCs)

Materials

Electron acceptor (electrode): ZnO, TiO2

Hole acceptor (electrolyte): acetonitrile based

electrolyte

Photosensitizer: Ru-dyer

S0/S+

S*

Voc

VB

CB

Fermi Level

injcc

TiO2 Dye

surface

states

e-

e- e-

e-

I -

I3-

e-

e-e-

Dye

h

e-

I3-

I3-

I-

I-

Pt

TCO

TCO TiO2

h

Electrolyte h

Principle


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Introduction

Large surface area

- Large amount of adsorption of Ru-dye

Requirement for TiO2 Layer

e-

e-e-

Dye

h

e-

I3-

I3-

I-

I-

Pt

TCO

TCO TiO2

h

Electrolyte

Principle

Efficient electron transfer

- Low defect

- Good connectivity without grainboundary

- High crystallinity

Efficient diffusion of electrolyte

- Narrow pore size distribution

- High porosity

Operating Mechanism of Dye-Sensitized Solar Cells (DSSCs)

Materials

Electron acceptor (electrode): ZnO, TiO2

Hole acceptor (electrolyte): acetonitrile based

electrolyte, LiI

Photosensitizer: Ru-dye


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Approaches Require Modification of TiO2 Photoelectrode to

Large Surface Area

Blocking of Direct Contact With Electrolyte

Introduction

nanocrystal TiO2 film with smallsurface area (< 60m2/g)

has limitation of dye adsorption site

Collapse of porous structure

Direct contact with electrolyte

Ref.) Philippe Preneet al., Chem. Mater., 2006, 18, 6152

TiO2 Nanoparticles Layer

Direct contact with electrolyte

Mesoporous TiO2 Layer

collapsePorous

stuctureNanoparticles Mesopore

FTO

FT

O

TiO2 Layer

electrolyte electrolyte


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ObjectiveBlocking Layer

Double-Layered TiO2 Electrode

Preventing electron leakagefrom FTO regardless influencingelectron injection

TiO2 deposited by sputtering

Morphology

Crystal composition

Transmittance

J-Vcharacteristics

Mesoporous TiO2

Morphology

Particle-size-distribution

Crystal composition

Specific surface area and pore size

Hydrothermal treatment

Maintenance of porous structureand large surface area

Morphology

Transmittance

J-Vcharacteristics

Mesoporous TiO2 Layer

Sufficient dye adsorption site

Morphology

Crystal composition

J-Vcharacteristics

Development of Enhanced TiO2 Photoelectrode for DSSC


8/47Nanostructured Eco- and Ener Materials Lab.

ExperimentalDeposition of TiO2 Blocking Layer by Reactive Sputtering

Experimental Condition

Base Pressure < 5 107 mTorr Magnetron DC power 300 WWorking Pressure 10 ~ 30 mTorr ICP power (r.f. coil) 400 W

Substrate Temperature Unheated Deposition Rate 30 ~ 40 nm/min




Experimental




Experimental Condition Principle of Sputtering Process

Ar+

Ar+Ar+ e-

e- e-

plasma

- voltage

O2 flow

Ti atom

TiO2

Vacuum chamber

Ti

FTO

Ar flow

Deposition of TiO2 Blocking Layer by Reactive Sputtering



ExperimentalDeposition of TiO2 Blocking Layer by Reactive Sputtering







ExperimentalPreparation of Mesoporous TiO2 Electrode

Pore-forming agentP123

(Nonionic surfactant)

(EO)20(PO)70(EO)20 Aldrich, Mw = 5,800 g/mol

Titania precursorTitanium(IV)

isopropoxide(TTIP)

Aldrich, 97%, Mw = 284.26 g/mol

Titania source

Acetyl acetone(AcAc)

Aldrich, 99%, Mw = 100.12 g/mol

Retarding agent controlling the hydrolysis of TTIP

Materials



Synthesis of Mesoporous TiO2

Experimental

micelle

TTIP + AcAc


90 oC, 12 h

PEG, PEO

Doctor blade

Preparation of Mesoporous TiO2 Electrode

distilled water + P123+ H2SO4

Calcination at 500 oC& dye adsorption

(1:1)

(100 ml) (14 g) (1.5 g)



(100 ml) (14 g) (1.5 g)


Experimental

micelle

TTIP + AcAc


90 oC, 12 h

PEG, PEO

Doctor blade



Surfactant-to-Timoalr ratio

1:10

1:30

1:50

1:70

Calcination at 500 oC

& dye adsorption



(100 ml) (14 g) (1.5 g)


Experimental

micelle

TTIP + AcAc


90 oC, 12 h

PEG, PEO

Doctor blade

Calcination at 500 oC

Mesoporous TiO2



& dye adsorption



(100 ml) (14 g) (1.5 g)


Experimental


micelle

TTIP + AcAc


90 oC, 12 h

PEG, PEO

Doctor blade

Mesoporous TiO2


Calcination at 500 oC& dye adsorption



ExperimentalCharacterization

- Field Emission Scanning Electron Microscopy (FE-SEM)JEOL JSM-6330F, electron acceleration voltage: 5.0 kV, WD: 14 ~ 15 mm

Morphology

- Brunauer-Emmett-Teller (BET) method- Barrett-Joyner-Halenda (BJH) method

Micromeritics ASAP 2000, degassing at 100o

C, analysis at 77 K

Specific surface area and pore size

- Wide angle X-ray diffraction (WXRD)MAC/Sci. MXP 18XHF-22SRA with Cu K radiation source,

wavelength: 0.154 nm, scan speed: 5o/min

Crystal structure

- High Resolution-Transmission Electron Microcopy (HR-TEM)

JEOL JEM-3010



Experimental

- Dynamic light scattering (DLS)

Photal DLS-7000 and GC-1000 photon correlator

Size distribution

- Ultraviolet visible (UV-Vis.)spectroscopyShimadzu, UV-1650PC

Transmittance analysis

- Photocurrent density-voltage characteristic (Solar simulator)

Keithley 2400 source, Xe lamp (Oriel, 300W), under the global AM1.5, 100 mW/cm2

Photovoltaic characteristic

- Surface profiler

Nanospec AFT/200, scan length: 10 mm, scan speed: 2 /sec

Thickness of TiO2 electrode

- Field Emission Scanning Electron Microscopy (FE-SEM)JEOL JSM-6330F, electron acceleration voltage: 5.0 kV, WD: 14 ~ 15 mm



Results & DiscussionTiO

2Blocking Layer Produced by Sputtering

Morphology (FE-SEM)

Film Thickness : ~ 1

Surface Cross Section

High Dense Film



Results & Discussion Morphology (FE-SEM)


Surface Cross SectionSurface of P25

High Dense Film

TiO2

Blocking Layer Produced by Sputtering

Relatively low dense film





Morphology (FE-SEM)



High Dense Film



Results & Discussion Morphology (AFM)

TiO2

Blocking Layer Produced by Sputtering

Rq(root mean squire roughness)

Rpv(peak to valley roughness)

6.88 nm 65.75 nm





Uniformity (-step)

d0d

d0 d Uniformity

885 nm 773 nm 87 %



Results & Discussion Transmittance Analysis

(UV-Vis. Spectroscopy)

400 500 600 700

0

20

40

60

80

100

Transmittanc

e(%)

Wavelength (nm)

Sputtered TiO2

20 30 40 50 60

2 (deg)

(101)

Crystal phase

Anatase Higher Transmittance than P25 Film

Crystal Structure (WXRD)

P25



Results & DiscussionJ-VCharacteristics

P25 Sputtered TiO2

+ P25

Area (cm2) 0.14 0.14

Voc (V) 0.77 0.76

Jsc (mA/cm2) 11.22 12.72

FF 0.66 0.66

EFF (%) 5.7 6.4

Sputtered TiO2 + P25

P25

Sputtered TiO2



Results & DiscussionJ-VCharacteristics

P25 Sputtered TiO2

+ P25

Area (cm2) 0.14 0.14

Voc (V) 0.77 0.76

Jsc (mA/cm2) 11.22 12.72

FF 0.66 0.66

EFF (%) 5.7 6.4

12 %

Sputtered TiO2 + P25

P25

Sputtered TiO2



Results & Discussion Photo Image

Hydrothermally Treated Mesoporous TiO2

(HT-M-TiO2

)

[1:10] [1:30] [1:50] [1:70]

Surfactant-to-TTIP

molar ratio1:10 1:30 1:50 1:70

Sample state Precipitaion Precipitaion Colloid Solid





(HT-M-TiO2

)

1:10 1:30 1:50 1:70

Sample state Precipitaion Precipitaion Colloid Solid

[1:10] [1:30] [1:50] [1:70][1:70]


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(HT-M-TiO2

)

1:10 1:30 1:50 1:70

Sample state Precipitaion Precipitaion HT-M-TiO2 Solid

[1:10] [1:30] [1:50] [1:70][1:70]


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Results & Discussion Particle-Size-Distribution (DLS)

HT-M-TiO2 (1:50)1:10

Average size: 80 nm

Average size

: 2

0 100 200 3000 6000 90000

2

4

6

8

10

12

14

Intensity

Diameter (nm)


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Results & Discussion Crystal Structure (WXRD & HR-TEM)

cos

K

: crystallite size K: 0.89

: wavelength of the X-ray radiation (0.154 nm)

: full width at half maximum intensity (FWHM)

: diffraction angle (2= 25.3o)

HT-M-TiO2

(nm)0.0268 5.24

Crystal Phase

Anatase

Amorphous phase of mesoporous TiO2 can besuccessfully converted to an anatase phase bycarrying out hydrothermal treatment

Ref.) Appl. Catal. A: Gen.2007, 323, 110

HT-M- TiO2

(101)

(200) (105)(004)

Mesorporous TiO2 withoutHydrothermal Treatment(M-TiO2)

20 30 40 50 60

Intensity(a.u.)

2 (deg)


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Results & Discussion

cos

K





Crystal Structure (WXRD & HR-TEM)

HT-M- TiO2

(101)

(200) (105)(004)


20 30 40 50 60

Intensity(a.u.)

2 (deg)

5 nm

5 ~ 6 nm


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cos

K





Crystal Structure (WXRD & HR-TEM)

HT-M- TiO2

(101)

(200) (105)(004)


20 30 40 50 60

Intensity(a.u.)

2 (deg)

5 nm

5 ~ 6 nm


- A kind of soft chemistry to crystallize ceramic powderdirectly at low temperature in water

Role of water

Stabilizing of porous lattices

by acting as space fillers

Hydrolysis and reformation

of Ti-O-Ti bond

Nucleation and growth of new crystalline phases bybreaking Ti-O-Ti bonds under hydrothermal conditions

H2O+

amorphous anataseTi

OH

OHTi

HO

HO+

Ti O Ti

OH OH

Ti Ti

O

Olow temp. low temp.H2O+

Ref.) Chem. Mater.1995, 7, 663


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Results & Discussion Specific Surface Area and Pore Size

< Before calcination > < After calcination >

0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400

VolumeAdsorbed(cc/g)

Relative Pressure (P/P0)

0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400

VolumeAdsor

bed(cc/g)


Surface area (m2/g) Pore size (nm)

beforecalcination

after

calcination

beforecalcination

after

calcination

HT-M-TiO2 347 304 3.9 8.1

M-TiO2 386 104 3.7 11.5

HT-M-TiO2M-TiO2

HT-M-TiO2M-TiO2


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Results & Discussion Specific Surface Area and Pore Size

< Before calcination > < After calcination >

0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400



0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400



Surface area (m2/g) Pore size (nm)

beforecalcination

after

calcination

beforecalcination

after

calcination

HT-M-TiO2 347 304 3.9 11.5

M-TiO2 386 104 3.7 8.1

HT-M-TiO2M-TiO2

HT-M-TiO2M-TiO2

0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400

VolumeAdsor

bed(cc/g)


P25

Surface area : 80 m2/g

< After calcination >


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Surfactant is decomposed at 200~300 0 100 200 300 400 500 600 700 800

0

10

20

30

40

50

60

70

80

90100

Weight(%)

Temperature ()

HT-M-TiO2

M-TiO2

< 200 >< Before calcination >

Crystallization

Surfactantdecomposed

Thermal Properties (TGA)


< 300 > < 500 >

Crystal growth

Maintenance of mesoporous structure

Hydrothermaltreatment

Crystallizationof pore wallinto anatase

No phase transformation during calcination

Amorphous

Anatase

HT-M-TiO2


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Results & DiscussionMesoporous TiO2 Layer Composed of HT-M-TiO2

HT-M-TiO2 M-TiO2 P25

X 3,000

X 100,000

Morphology (FE-SEM)< after calcination at 500 oC>


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Results & Discussion Crystal Structure (WXRD & HR-TEM)

< after calcination at 500 oC>

20 30 40 50 60

Intensity(a.u.)

2 (deg)

HT-M- TiO2

(101)

(200) (105)(004)

HT-M-TiO2

(nm) Crystal Phase0.0193 7.28 Anatase

5 nm

6 ~ 7 nm


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Results & Discussion Transmittance Analysis (UV-Vis. Spectroscopy)

400 500 600 7000

20

40

60

80

100

Transmittance(%)

Wavelength (nm)

P25

HT-M-TiO2

HT-M-TiO2

P25

< Photo image>


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J-V Characteristics



Area (cm2) 0.16 0.16 0.16

Voc (V) 0.7471 0.6918 0.7387

Jsc (mA/cm2) 5.5712 0.3619 3.4837

FF 0.6830 0.5475 0.6801

EFF (%) 2.832 0.1371 1.7503

P25

HT-M-TiO2

0.0 0.2 0.4 0.6 0.80

2

4

6

8

Bias (V)

Current(mA/cm

2)

M-TiO2


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J-V Characteristics



Area (cm2) 0.16 0.16 0.16

Voc (V) 0.7471 0.6918 0.7387

Jsc (mA/cm2) 5.5712 0.3619 3.4837

FF 0.6830 0.5475 0.6801

EFF (%) 2.832 0.1371 1.7503

P25

HT-M-TiO2

0.0 0.2 0.4 0.6 0.80

2

4

6

8

Bias (V)

Current(mA/cm

2)

M-TiO2


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J-V Characteristics



Area (cm2) 0.16 0.16 0.16

Voc (V) 0.7471 0.6918 0.7387

Jsc (mA/cm2) 5.5712 0.3619 3.4837

FF 0.6830 0.5475 0.6801

EFF (%) 2.832 0.1371 1.7503

62 %

P25

HT-M-TiO2

0.0 0.2 0.4 0.6 0.80

2

4

6

8

Bias (V)

Current(mA/cm

2)

M-TiO2


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Results & DiscussionDouble Layered TiO2 Electrode

Morphology



Crack-Free Film


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Results & Discussion J-V Characteristics

Double Layer

(Sputtered TiO2 + HT-M-TiO2)P25

Double Layer

(Sputtered TiO2 + P25)

Area (cm2) 0.16 0.16 0.16

Voc (V) 0.723 0.738 0.651

Jsc (mA/cm2) 6.539 3.483 4.659

FF 0.667 0.680 0.699

EFF (%) 3.153 1.750 2.123

Sputtered TiO2 + HT-M-TiO2

Double layer

P25

0.0 0.2 0.4 0.6 0.80

2

4

6

Current(mA/cm

2)

Bias (V)

HT-M-TiO2 (4)Sputtered TiO2

(1)


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Double Layer

(Sputtered TiO2 + HT-M-TiO2)P25

Area (cm2) 0.16 0.16

Voc (V) 0.7231 0.7387

Jsc (mA/cm2) 6.5387 3.4837

FF 0.6666 0.6801

EFF (%) 3.1528 1.7503

80 %

J-V Characteristics

Sputtered TiO2 + HT-M-TiO2

Double layer

P25

0.0 0.2 0.4 0.6 0.80

2

4

6

Current(mA/cm

2)

Bias (V)

HT-M-TiO2 (4)Sputtered TiO2

(1)


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ConclusionBlocking Layer Mesoporous TiO2 Layer


Prevention from direct contactwith electrolyte

Increase of photocurrent

Film thickness: 1Uniformity : 87%Density: sputtered TiO2 > P25 Transmittance: sputtered TiO2 > P25 Crystal structure: anatase

Energy conversion efficiency: sputtered TiO2/P25 > P25

Film thickness: 4Crystal structure: anatase Transmittance: HT-M-TiO2 > P25

Surface area (after calcination)

: HT-M-TiO2 > M-TiO2 >> P25

Pore size: HT-M-TiO2 > M-TiO2 >> P25

Energy conversion efficiency: HT-M-TiO2 > P25 >> M-TiO2

Film thickness: 5Crystal structure: anatase Transmittance: Double-layered TiO2 > P25

Energy conversion efficiency

: double-layered TiO2 (HT-M-TiO2) > double-layered TiO2 (P25) > P25


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ConclusionBlocking Layer Mesoporous TiO2 Layer


Prevention from direct contactwith electrolyte

Increase of photocurrent

Film thickness: 1Uniformity : 87%Density: sputtered TiO2 > P25Transmittance: sputtered TiO2 > P25 Crystal structure: anatase

Energy conversion efficiency: sputtered TiO2/P25 > P25

Film thickness: 4Crystal structure: anatase Transmittance: HT-M-TiO2 > P25

Surface area

: HT-M-TiO2 > M-TiO2 >> P25

Pore size: HT-M-TiO2 > M-TiO2 >> P25

Energy conversion efficiency: HT-M-TiO2 > P25 >> M-TiO2

Film thickness: 5Crystal structure: anatase Transmittance: Double-layered TiO2 > P25

Energy conversion efficiency

: double-layered TiO2 (HT-M-TiO2) > double-layered TiO2 (P25) > P25Successful Development of Novel TiO2 Photoelectrode for DSSC


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A Coast, High-efficiency Solar Cell Based on Dye-sensitized Colloidal TiO2 Films