www.eni.it

CHARACTERIZATION OF MICROEMULSIONS FOR APPLICATION IN LSCs

A. Congiu, L. Gila, L. Caccianotti, R. Fusco, S. Zanardi, M. Salvalaggio, S. Perucchini,

C. Busto

1st Chemistry in Energy Conference; Edinburgh 20/07/2015

eni S.p.A. Research Center for Renewable Energies and Environment

eni R&D on solar topic

Luminescent Solar Concentrators

Microemulsion

Efficiency of microemulsion based LSC’s – electrical measurements

Characterization (RI, conductivity, rheology, Dynamic Light Scattering,

Fluorescence Spectroscopy) to explain observed efficiency trend

Conclusion

Outline

eni R&D on solar

concentrationconversion

s t o r a g e

OPV

DSSC CSP

LSC

Solar energy

RFB’s

Research Center for RenewableEnergies and Environment

eni demonstration plant : 1st into the world

Rome – eni headquarter : shelter with photoactive slabs

DIMENSION

5m X 12m

POWER

0.5 kWp

8 W/m2

Luminescent Solar Concentrators (LSC)

IRFLUORESCENT DYE

WAVEGUIDED PROPAGATION

TRANSMITTEDRADIATION

INCIDENT SOLAR RADIATION

VIS

IS

IRIRUV IR

ACTIVE SLAB

Large area active slab

Small PV cellCONCENTRATION

For review: Goetzberger A.,Greubel W., Appl. Phys. 1977, 14, 123-139;

Debije M. G., Verbunt P. P., Adv. Energy Materials 2011, XX, 1-24

Waveguide

LSC: how does it work?

dopedslab

12.5%

12.5% Solar cell

RI = 1.5

RI = 1

2

1

m

ag

n

n

75%

hna

hne

other chromophore molecules

should not absorb emitted photons

fluorescent dye

na > ne

LSC’s advantages (with respect to PV panels) and applications

ADVANTAGES

o Accept both direct and diffuse light

o Extended surface allows heat dispersion

o The choice of dye and PV cell improve the design of the device (spectral matching)

o Architectural integration (less limited in color and shape)

o Lower cost

APPLICATIONS

o Transparent PV windows

o Coloured PV panels

o Suitable for vertical installation and curve surfaces

Main applicative sectors: Building Integrated PV, greenhouses, advertisement signs,shelters, noise barriers,….

Potential applications of LSCs

Liquid LSC’s

Why liquid LSC’s?

Few study on liquid LSC’s in literature:

o M. Kennedy, M. Dunne, S. J. McCormack, J. Doran and B. Norton “Proceedings of the 23rd

European Photovoltaic Solar Energy Conference and Exhibition”, pg. 390-393, 1-5 September

2008, Valencia, Spain

o V. Sholin, J. D. Olson, and S. A. Carter, ‘Journal of Applied Physics’ (2007), Vol. 101, pg.

123114-1-123114-9

o A. F. Mansour, ‘Polymer Testing’ 17 (1998) 153–162, pg 153-162

Practical pourpose: to compare dye performance

Microemulsion for LCS

Why microemulsion?

Features required for applicability:

o reduction in the organic solvent

content (ease of handling,

environmental sustainability)

o self assembly

o termodynamically stable

Features required for LSC:

o monophasic

o transparent

Microemulsion definition – pseudo ternary phase diagram

Microemulsion are constituted by water or a saline solution, one or more surfactants(or a surfactant and a co-surfactant) and a hydrophobic liquid

T.P.Hoar, J.H. Schulman Nature 152; 102; 1943

Lang et al. J. Phys. Chem. 1980, 84, 1541-1547

microemulsion

1/3 SDS + 2/3 1-butanol

water

MICELLE W/O

MICELLE O/W

LAMELLAR

PHASE

toluene

Microemulsion – pseudo ternary phase diagram

WATER + 1/3 SDS +2/3 1-BUTANOL + DYE IN TOLUENE

LAMELLAR PHASE

Italian Patent Application MI2012A002250

microemulsion

1/3 SDS + 2/3 1-butanol

water DYE TOLUENE SOLUTION

[DYE]microemulsion= 10-3M

MICELLE W/O

MICELLE O/W

LAMELLAR

PHASE

300 400 500 600 700 8000.0

0.5

1.0

1.5

2.0

2.5

3.0

Absorb

ance

Wavelength (nm)

Absorbance

0.0

5.0x105

1.0x106

1.5x10 6

2.0x10 6

2.5x106

Emission

lex

470nm

PL I

nte

nsity (

arb

. un.)

DTB in Toluene

Small overlap

N N

S

S

S

Dye: di-thienyl-benzothiadiazole (DTB) – concentration: 10-3M

445nm

Large Stokes’ shift

565nm

Excellent Quantum Yield in Toluene

QY = 95%

Experimental: pseudoternary phase diagram

[DTB]em= 10-3M

MICELLE W/O

MICELLE O/W

LAMELLAR

PHASE

DYE

DYE

DYE

Electrical measurements

I vs VP vs V

Pmax vs water content

beneficial for

applicability!

Low toluene microemulsion samples: reduction in amphiphile

content doesn’t impact on LSC device efficiency

LSC optical efficiency

M. G. Debije, P.P.C. Verbunt, Adv. Energy Mater, 2011, XX, 1-24;

A. Goetzberger, W. Greubel, Appl. Phys,1977, 14, 123

Highlighted parameters are supposed to be quite constantamong compared samples

ηopt=(1-R)PTIR * nabs * ηPLQY * ηStokes * ηhost * ηTIR * ηself

reflection

total internal reflection efficiency

fraction of solar light adsorbed by

dye

photoluminescent quantum yield

energy loss for heating

transport efficiency of

photons through the waveguide

reflection efficiency - smoothness of the

surface

loss for re-adsorption of the emitted photons

RI

Refractive index

RI SDS= 1,461

RI butanol= 1,399

RI toluene= 1,496

Can microstructure and dye confinement unfold

efficiency trend?

LSC optical efficiency

ηopt=(1-R)PTIR * nabs * ηPLQY * ηStokes * ηhost * ηTIR * ηself

reflection

total internal reflection efficiency

fraction of solar light adsorbed by

dye

photoluminescent quantum yield

energy loss for heating

transport efficiency of

photons through the waveguide

reflection efficiency - smoothness of the

surface

loss for re-adsorption of the emitted photons

RI

M. G. Debije, P.P.C. Verbunt, Adv. Energy Mater, 2011, XX, 1-24;

A. Goetzberger, W. Greubel, Appl. Phys,1977, 14, 123

Characterization of the hosting matrix

o Electrical conductivity

o Rheology

o Dynamic Light Scattering

Characterization of the dye

o Fluorescence Spectroscopy

o UV-vis Spectroscopy

Photoactive Microemulsion Characterization

Microemulsion

System Photophysics

Microemulsion characterization: electrical conductivity and rheology

lamellae

W/O drops

O/W drops

lamellae

W/O drops

O/W drops

Electrical conductivity (mS/ cm) Shear zero viscosity (mPa.s)

Microemulsion characterization: Dynamic Light Scattering

Centro Ricerche per le Energie Non-Convenzionali – Istituto eni Donegani

DLS measures intensity variations of the scattererd light based on Brownian motion of the particles.

Time (s)

Inte

ns

ity (

kc

ps

) Small particles High Diffusion speed

Time (s)

Inte

ns

ity (

kc

ps

)

Large particles Low Diffusion speed

High correlation

Low correlation

DYE

DYE

DYE

Pmax vs microemulsion features

Microemulsion characterization confirms the microstructure; the presence of the dye doesn’t affect matrix organization but Pmax

trend depends on it.

O/W

micelles

lamellae

W/O

micelles

lamellae O/W

micelles

W/O

micelles

Photophysics

Correlation only comparing microemulsions at increasing toluene content

fluorescence intensity was normalized by absorpion at lexc= 470 nm

Lifetime measurements: lexc = 461 nm; lmeas = 580 nm

Local dye concentration

Microemulsion organization produces dye confinement….

….local dye concentration affects both radiative and non radiativeprocesses

Pmax vs local dye concentration

Efficiences of high W/O seriesare constant due to acounteracting increase in RI andfluorescence quenching

PL meas.

RI

Conclusion

• The performances of LSC based on microemulsion get worse decreasing toluene

content, but efficiency of LSC filled with high water content microemulsion

doesn’t fall down with amphiphile decreasing

• Variation in local concentration inferted by microstructure formation in

microemulsion affects the photophisics of the microemulsion due to confinement of

the dye in toluene giving rise to fluorescence quenching

• With this study we have experienced some tools for developing new photoactive

microemulsions

30

Thank you for your attention!