2010 physical science session - fan

7/27/2019 2010 Physical Science Session - Fan

1/22

Flexible Dye-Sensitized Solar Cells on Al Foils

Jon Linville, Tyler Spurlock, Matthew Seitz and Xiaojuan (Judy) Fan

Department of Physics, Marshall University, Huntington, WV 25755

STAR Symposium, 2010, WV

http://www.siliconsolar.com/

*Email address: [email protected]


2/22

Si crystals: need to be produced in a vacuum.

Thin film solar cells: Si, CdTe; GaAs, GaN, InN,

Cu(In,Ga)Se2 flexible solar cell modules (commercialized)

Dye-sensitized solar cells (DSSC)

Brief Review: Photovoltaic Solar Cells

ORegan and Grtzel, 1991

Cell Components:Porous nanocrystalline TiO2Organic dye molecules Iodine/Iodide electrolyte

11% efficiency has been demonstrated in lab Ready to the market

Question: Can we make flexible DSSCs?

Yes


3/22

The 3rd generation Solar Cells: DSSCs

Dye-sensitized solar cells (DSSCs): electrochemistry

Key components: Metal oxide nanostructures Organic light sensitizer: dye molecules Electrolyte with

3/II

Advantage:Low cost, solution process, and environmental friendly

Disadvantage:Low efficiency (


4/22

hvI- I3

-+ e

Dye

TiO2

I- I3-+ ee

e

e

e

Load

e

1. Light absorbed by dye

2. Excited electrons injected into

nanoparticles

3. Electrons percolate to external

load to reach the counter

electrode

4. Electrons are transferred totri-iodide to yield iodide

5. The iodide reduces dye to

its original state.

How DSSC Works

e

ee


5/22

Printed Flexible Dye-Sensitized Solar Cells (DSSC)

Very recently, news from Japan'sToin University of Yokohama

DSSC in a flexible A4 sheet.

Solar conversion efficiency: 6%(Solar cells on market: 15%)

AdvantagesCheaper to makeFlexibility

Simply be printed in airOnly 0.4mm-thick, used for a laptop PC or rolled and foldedfor storage.


6/22

Solar Cell Fabrication Technology

High vacuum deposition: p-njunctions Sputtering deposition Thermal evaporation

E-beam evaporation Pulsed laser deposition Molecular beam epitaxial

Ribbon and roll-to-roll coating on flexible substrates

Dye-sensitized solar cells (DSSCs): no vacuum needed Nanoparticle paste

Sol-gel-dip-coating

Screen printing

Spray pyrolysis

Compression

Polymer assisted

The new organic

solar cells are light

and flexible.

Credit:

Nicole Cappello,

Georgia Institute of

Technology

Silicon Solar Inc.


7/22

Mesoporous TiO2

Nanoparticle paste and hydrothermal at 230CGratzel, M. J. Photochem. And Photobio. A 164

(2004) 3-14

TiO2: must bePorous: large surface area toattach more dye moleculesTiO

2nanoparticles

Porosity > 50%Other metal oxides can beused, ZnO, SnO2,

TiO2, easy synthesis,abundant, inexpensive

50 nm

K. M. Gopal, et al,Adv. Funct. Mater,15, 2005, 1291-1296

Thermal evaporation 500C rf sputtering Ti anodized in HF


8/22

TiO2: A large band gap semiconductor

A large bandgap semiconductor (~3.2 eV)

Absorption edge is in ultraviolet (UV), Not responsible for sun light absorption in solar cells

Rutile

Anatase

Brookite

National Renewable Energy

Laboratory, Golden, Colorado

Materials Characterization

Laboratory, Penn State


9/22

Unique route to generateporous TiO

2thin films

Our Approach:

Polymer assisted Ti alkoxides Solvents Stable precursors Spin coating (stable in air)

Thermal sintering Polymer removed Mesoporous TiO2

solvent Ti alkoxides

PMMA: (MW 350,000)poly(methyl methacrylate)

(C5O2H8)n

Ti n-butoxide

Ti[O(CH2)3CH3]4


10/22

6 % (w/v) PMMA +

6% (w/v)

Ti(OnBu)4

2 % (w/v) PMMA +

6% (w/v) Ti(OnBu)4

SEM images: double-layer structure

(a) (b)

(c) (d)

4 % (w/v) PMMA +

6% (w/v)

Ti(OnBu)4

8 % (w/v) PMMA+ 6% (w/v)

Ti(OnBu)4

1 m


11/22

Porous TiO2 Thin Films: Structure and Morphology

25 nm

100 20 nm

(b)(a)

X-ray diffraction: anatase phase

Particle size: 25nm

AFM image

Anatase structure is often preferred to rutile in the

application of TiO2 in DSSC in terms of lattice packing.[Park, et al.J. Phys. Chem. B 2000, 104, 8989-8994]


12/22

Thin Film X-Ray Reflectivity Analysis

10-5

10-4

10-3

10-2

10-1

100

Reflect

ivity

86420

2/ (degree)

Decay of reflectivity

Surface roughness

Decay of amplitude

Interface roughness

Period of oscillation

Thickness d

Amplitude of oscillation

Contrast of density

Critical angle c

Density density 1density 2

density 3

thickness d1thickness d2

roughness 1roughness 2roughness 3

Oscillatory behavior known as Kiessig fringes.

thickness, density, and roughness


13/22

TiO2 thin film thickness, roughness, and density

Layer No.Layer

Name

Density

(g/cm3

)

Thickness

(nm)

Roughness

(nm)

1

2

Si

TiO2

2.3300

2.6727

N/A

18.506

0.489

0.579

Table 1. Density, thickness and roughness of sample 4 from XRR data.

For nonporous anatase TiO2

0

/1 =rP

Relative porosity: Pr = 33%

0 ~ 3.9 g/cm3,

X-ray Reflectivity


14/22

Dye Molecule we used

Meso-tetra(4-carboxyphenyl)porphyrin (TCPP), T790

Color: Red brown

Absorption: 400 450 nm region, 500 700 nm region

Adsorbs strongly onto nanoparticulate TiO2 and serves as an

efficient photosensitizer. [J. Phys. Chem, 104, 3624 (2000)]

450 500 550 600 650 7000.0

0.5

1.0

1.5

2.0

2.5

Absorban

ce

Wavelength, nm

Dye: TCPP in EtOH solution


15/22

Gel Electrolyte: Polymer Matrix

Polymer electrolyte we used

Poly(ethylene glycol) (PEG), (MW 20,000)

100 mM KI, 50 mM I2 Solvents including:

ethylene carbonate (80% v/v)

o Transparent crystal-like solid, at T= 25 C

o Colorless liquid at T = 34 - 37 C

propylene carbonate (20% v/v)

o Colorless liquid

C2n

H4n+2

On+1

PEG

Advantages:Avoid liquid leakageAny shape membrane

Hydro gel

electrolyte


16/22

0.0 0.2 0.4 0.6 0.8 1.00

5

10

15

20

Isc

Voc

Curren

tDensity(m

A/cm

2)

Bias Voltage (V)

ImV

m

Maximum Power Point

To Characterize Solar Cells

Photo electricity conversion efficiency:

mmmVIP

=

Cell Maximum Power:

Incident Light Power: Ps

Short Circuit Current:Isc

Open Circuit Voltage: Voc

ocsc

mm

VI

VIFF=Fill Factor FF:

s

ocsc

P

FFVI=


17/22

Photo-Electricity Conversion Efficiency

I-VCurves under one Sun (AM1.5 global, 100 mW/cm2) and Dark.

Isc = 3.03 mA/cm2, Voc = 1.18 V, = 2.05%

OCSC

mpmp

VI

VIFF=

light

OCSC

P

FFVI

=

Conversion efficiency:

Fill Factor:


18/22

Several factors: Nanoparticle imbedded electrolyte Different Dye molecules (N3 instead of T790)

Porous TiO2 with high ratio polymer template

Efficiency improvement > 200%

0.0 0.2 0.4 0.6 0.8

0

1

2

3

4

5

6

7

8

Currentdensity(mA/c

m2)

Voltage(V)


19/22

Electrolyte: Imidazolium+I2 + PEO,solid texture phase

Flexible Dye-Sensitized Solar Cells

Cheap Dye: Basic Red 1,Rhodamine 6GDN

Formula: C28H31CIN2O3,red to brown in color.

Anode electrode:porous TiO2 on Al foil


20/22

Photo-Electricity Conversion Efficiency

Flexible solar cell on Al Foil

Al foil

Porous TiO2

Solid Electrolyte

Conductive PET sheet

Back Illumination


21/22


22/22

Funding Support:NSF-MU ADVANCE GrantNASA WV EPSCoR Seed Grant

NASA Undergraduate Research GrantMarshall University Research Corporate

Undergraduate Researchers:Matthew Seitz, SophomoreTyler Spurlock, Sophomore

Jon Linville, Senior

Thank you for your attention!

Acknowledgements:

2010 physical science session - fan

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