coating organici per aumentare l’efficienza del...

S.Binetti

Il Futuro del silicio nel fotovoltaicoTrento 28 ottobre 2010

Coating organici per aumentarel’efficienza del silicio

A. Le Donne, M. Acciarri. M.Dilda and Simona BinettiMILANO-BICOCCA SOLAR ENERGY RESEARCH CENTER

Department of Material Science, University of Milano-Bicocca Italy

S.Binetti


PV market: technology

• The most important material for solar cells has been and is still silicon.

• Today, approximately 95 % of cumulative installed PV modules are based on crystalline silicon technology.

S.Binetti


Beyond 2020 ?

Which will be the role of silicon in PV ?

Main drawback: the cost !

� availability �no toxicity � long lifetime� sustainability � Recycling process (www.pvcycle.org )�A worldwide global production

Advantages :

Silicon has no competitors !

S.Binetti


Reduce material costthickness from 180 to -80 µm

Silicon solar cell: analysis of the cost :

research activities

Increase cell efficiency

Si reduction consumption for Wpand use of lower cost silicon

High productivity

Wafering11%

Ingot growth8%

Feedstock14%Module

assembly40%

Cell manufactory27%

High efficiency modules and new assembly

concepts

S.Binetti


High efficiency Si solar cells

• HIT structure : c-Si with a double a-Si/c-Si heterojunctionon n-type (Sanyo)

η= 23 % (R&D) η=20.7 % (in production)

•Based on n type Silicon : commercial η=22% (Sunpower)

•Pluto: based on PERL cells (by UNSW) World record of efficiency: 25.5 % Commercial efficiency: η=19.9 % (Suntech)

Theoretical maximum efficiency: 31 %

S.Binetti


2010 53 $/kg

1. Silicon cost 2. Silicon availability

3. Environmental factors:– Lower energy payback time– Lower carbon footprint

Metallurgical silicon or Up grade metallurgical sil icon (UMG-Si*):advantages

*UMG-Si: is metallurgical-grade silicon chemically refined to 6NCompanies all have their own proprietary processes

2008: 250 $/kg2008: 250 $/kg

Photon energy may 2010

-A new shortage of silicon has been predicted

S.Binetti


Silicon solar cells

Light harvestingLight harvesting

ARC

Rear contact

Front contact

Si substrate

BSF

Emitter

etching junction ARC contacts

Device optimization

Decrease of the raw material price and

increase of the process yield

Target: 1 €/Wp

S.Binetti


Strategies for enhancing the energy conversion feat ures of first generation solar cell: light harvesting

theoretical solar cell efficiency around 38.6%*

An increase of the quantum efficiency of first generation solar cells could be obtained exploiting the solar spectrum regions not efficiently converted from silicon (i.e. conversion of photons withenergy E < Egap and E >> Egap) in

radiation around the maximum quantum efficiency value of the PV

device

*B.S. Richards, Solar Energy Materials & Solar Cells 90 (2006) 1189–1207

S.Binetti


Exploitation of high energy region of the solar spectrum*: E>>E gap

� down-conversion (DC) : process bywhich two low-energy photons are generated from absorption of one high-energy photon

� down-shifting (DS) : process by which a single high-energy photon is converted into a single lower-energy photon.

* C. Strumpel et al., Solar Energy Materials & Solar Cells 91 (2007) 238

S.Binetti


• down-shifting (DS): process by which a single high-energy photon is converted into a single lower-energy photon.

C. Strumpel et al. , Solar Energy Materials & Solar Cells 91 (2007) 238

Exploitation of high energy region of the solar spectrum: hνννν>>Egap

(L)DS are molecular systems with �a wide absorption band in the region where the EQE of the cells is low �No absorption in other region �narrow emission band coinciding with the peak of the EQE cells�high stoke shift�high thermal and photo stability

E. Klampaftis et al. Solar Energy Materials & Solar Cells 93 (2009) 1182

Matrix:�high transmittance �Low scattering�High “solubility” of LDs�Photo e thermal stability

Organic dyes Rare-earth ions/complexesQuantum dots

PMMA , Al 2O3 , SiO2

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K. R. McIntosh et al. Prog. Photovolt: Res. Appl. (2008)

DS: Fluorescent organic dyes

ηηηη=+ 1 %

The encapsulation includes a layer of luminescent down-shifting

S.Binetti


Aims of our work

1. Identification of new DS

complexes to increase of the PV

conversion efficiency of Si-based

solar cells exploiting the solar

spectrum region below 450 nm

2. Development of a procedure compatible with the industrial process for the PV module fabbrication.

300 400 500 600 700 800 900 1000 1100 12000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

AM 1.5G

encapsulated solar cell

wavelength (nm)

Su

nli

gh

t in

ten

sity

(W

/m2/n

m)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Sp

ectra

l Re

spo

nse

(A/W

)

down-shifting

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600 7000,0

2,0x105

4,0x105

6,0x105

8,0x105

1,0x106

1,2x106

Pho

tolu

min

esce

nce

Wavelength (nm)

Eu3+

Eu complexes

� Whatever the sensitizer may be, the emission profile of a Eu3+ complex consists of a main line at 612 nm related to the 5D0-

7F2 transition in the Ln3+ ion

1 . DSs: Organolanthanide complexes

design of efficient organolanthanide DSs suitable for different solar cell applications (namely terrestrial or space ones) by a proper choice of the organic antenna

S.Binetti


Energy transfer in Ln(III) complexes

The 4f-4f transitions are forbidden by the La Porte rule, their luminescence intensity can be strongly increased by incorporating the Ln3+ ions into a complex able to participate in energy transfer process (usually Dexter type transfer).

ANTENNA EFFECT:1. light absorption by the ligand2. highly efficient intraenergy conversion

from the ligand singlet (S1) states to the triplet (T1) states by intersystem crossing

3. energy transfer from ligand T1 states to the excited state of the Ln3+ ions.

S.Binetti


1. DS choice: Eu 3+ organic complexes

3[(trifluoromethylhydroxymethilene)-

d-camphorate]europium(III)

tri(dibenzoylmethane)

(monophenanthroline)europium(III)

560 580 600 620 640 660 680

0.0

2.0x105

4.0x105

6.0x105

8.0x105

1.0x106

1.2x106

1.4x106

Ph

oto

lum

ines

cen

ce

Wavelength (nm)

Eu3+

(5D

0-

7F

2)

300 400 500 600 700 800 900 1000 1100 1200

0.0

0.2

0.4

0.6

0.8

O

CF3

O

CH3

CH3CH3

Eu

3

wavelength (nm)

AB

S Eu(tfc)3

300 400 500 600 700 800 900 1000 1100 1200

0.0

0.5

1.0

1.5

2.0

O

O

3

N

N

Eu

wavelength (nm)

AB

S Eu(dbm)3phen

S.Binetti


Determination of the best concentrations

250 300 350 400 450 500 550 600

0.0

0.2

0.4

0.6

0.8

1.0

No

rmal

ized

in

ten

sity

Wavenumber (nm)

PLE Eu(tfc)3

ABS Eu(tfc)3

Eu(tfc)3 0.003% wt

Good match between PLE and absorption spectra ⇒⇒⇒⇒ good energytransfer

250 300 350 400 450 500 550 6000.0

0.4

0.8

PLE Eu(tfc)3

ABS Eu(tfc)3

No

rmal

ized

in

ten

sity

Wavelength(nm)

Eu(tfc)3 2% wt

260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560Eu

rel

ated

em

issi

on

PL

E (

no

rmal

ized

in

ten

sity

)

Wavelength (nm)

0.003%

0.006%

0.019%

0.009%

S.Binetti


Aims of our work

1. Identification of new DS

complexes to increase of the PV

conversion efficiency of Si-based

solar cells exploiting the solar

spectrum region below 450 nm

2. Development of a procedure compatible with the industrial process for the PV module fabbrication.

300 400 500 600 700 800 900 1000 1100 12000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

AM 1.5G

encapsulated solar cell

wavelength (nm)

Su

nli

gh

t in

ten

sity

(W

/m2/n

m)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Sp

ectra

l Re

spo

nse

(A/W

)

down-shifting

S.Binetti


Encapsulating matrixdoped with DSs

2. Development of a procedure compatible with the industrial process for the PV module fabbrication

S.Binetti


Eu(dbm)3phen single layer (0.0015% wt)

1001240

)(

)(

)()(

⋅⋅=

=

λλ

λλ

λ

SREQE

P

ISR ph

300 400 500 600 700 800 900 1000

20

40

60

80

100

cell+PVA cell+PVA&dbm

EQ

EWavelength (nm)

300 350 40010

20

30

40

50

60 cell+PVA cell+PVA&dbm

EQ

E

Film di PVA +Eu(dbm)3phen

Solar Cell

I/V @ 1 sun : • ISC = 0.2 %

S.Binetti


Single layer of PVA + Eu(tfc)3 (0.003% wt)

400 600 800 1000

20

40

60

80

100

cella+PVA cella+PVA&tfc

EQ

E

Wavelenght (nm)

• Aumento EQE tra 260 e 360 nm

300 350

20

40

60 cella+PVA cella+PVA&tfc

EQ

E

Wavelenght (nm)

S.Binetti


Eu(tfc)3 Eu(dbm)3phen

Absorption band

UV VISIBLE

1

2


Solar Cell


Solar Cell

Film di PVA +Eu(tfc)3

S.Binetti


Double layer structure: Poly-VinylAcetate doped withEu(dbm) 3phen (0.0015% wt) + Poly-VinylAcetate doped with

Eu(tfc) 3 (0.003% wt)*

�EQE enhancement between 260 and 420 nm (≡ DSs absorption region)

�strong enhancement of the cell performances (Isc +1.4%, Pmax +2.8%) with respect to the undoped PVA double coating

250 300 350 400 450 5000.2

0.4

0.6

0.8

Ex

tern

al Q

uan

tum

Eff

icie

ncy

wavelength (nm)

cell coated with

undoped PVA

cell with doped PVA

coatings (Eu(dbm)3phen

and Eu(tfc)3)

c-Si solar cell

PVA& Eu(tfc)3

PVA & Eu(dbm)3phen

A.Le Donne, M. Acciarri, S.Marchionna & S.Binetti Prog.Photovolt: Res.Appl. 17 (2009) 51

S.Binetti


2. Integration of the encapsulating matrix doping p rocedure in the module fabrication process

⇒ new complexes able to exploitation of a wide portion of the solar spectrum without using multilayer structures.

•EVA (EthyleneVinylAcetate) instead of PVA:

Problems: - best results with two layers- No mixed layer in order to prevent luminescence quenching effects due to possible interactions among different complexes

�Previously reported results confirmed also with EVA

Strategy to be followed : •Mixing of Eu3+ complex powders with EVA (EthyleneVinylAcetate) melt•extrusion of doped EVA sheets•realization of PV modules using doped EVA sheets

S.Binetti


Eu3+ complex absorption broadening through the presence of a co-ligand

260 280 300 320 340 360 380 400 420 440 460 480 500

Eu(tfc)3-EABP (1:1 mol)

solution in CH2Cl

2

EABP in CH2Cl

2

wavelength (nm)

No

rmal

ized

ab

sorb

ance

Eu(tfc)3in CH

2Cl

2

� EABP and Eu(tfc)3 form a complex by interaction of the electron rich carbonyl group with the positively charged Eu3+ ion �new absorption band in the visible region, probably related to a bathochromic shift of the first singlet–singlet transition of EABP occurring upon complexation.

O

CF3

O

CH3

CH3CH3

Eu

3

NCH2CH3

CH2CH3

O

NCH2CH3

CH2CH3

4,4'-bis(diethylamino)benzophenone

(or EABP)

tris[3-(trifluoromethylhydroxymethilene)-d-camphorate]

europium(III) (or Eu(tfc)3)

….

S.Binetti


Eu3+ complex PLE broadening through the presence of a co -ligand

260 280 300 320 340 360 380 400 420 440 460 480 500

0.0

0.2

0.4

0.6

0.8

1.0Eu(tfc)

3-EABP (1:1 mol)

solution in CH2Cl

2

wavelength (nm)

No

rmal

ized

ab

sorb

ance

The visible light absorbed due to the presence of the new absorption band is transferred to the Eu3+ ion ⇒ doping of PV module encapsulating matrix with such DS should allow the exploitation of a wide portion of the solar spectrum without using multilayer structures.

260 280 300 320 340 360 380 400 420 440 460 480 500

Eu(tfc)3 in CH

2Cl

2

Eu(tfc)3-EABP (1:1 mol)

solution in CH2Cl

2

wavelength (nm)

PL

E o

f th

e E

u3+

rel

ated

em

issi

on

@ 6

12 n

m

S.Binetti


EQE and I-V on home made test modules

300 320 340 360 380 400 420 440 460

0.2

0.4

0.6

encapsulation with Eu(tfc)3-EABP doped EVA

encapsulation with undoped EVA

Ex

tern

al Q

uan

tum

Eff

icie

ncy

wavelength (nm)

� Isc : + 2.2%� Pmax: +2.9%

c-Si solar cell

glass sheet coatedwith undopedor doped EVA

A. Le Donne, M.Acciarri, M.Dilda & S.Binetti, Optical Materials 2010 in press

S.Binetti


Cost evaluation

�Complex cost/mg: obtained from the commercial price

�Doped encapsulating layer cost/module: obtained from the

complex cost/mg

�Wp price of 4.12 €/Wp*, standard module efficiency of 13% and

module area of 36 x (15.56x15.56 cm2)

�� REDUCTION OF THE WP PRICE FROM 4.12 TO 4.03 €/WP!

* http://www.solarbuzz.com/moduleprices.htm

+0,6 % is sufficient to maintain unaffected the Wp price

S.Binetti


Conclusions

� Identification of a single down-shifter (Eu(tfc) 3-EABP )which allows the exploitation of a wide portion of the solar spectrum

�realization of home made PV modules showingsignificant enhancement of their performances (total delivered power + 2.9% )

S.Binetti


Future works

� Realization of real PV modules usingEu(tfc)3-EABP doped EVA as encapsulatingmatrix

� environmental tests on such modules.

S.Binetti


Acknowledge

Project MISE- ICE-CRUI 2009 n° 90 Co-financed by X-GROUP SpA

S.Binetti


MIB-SOLARMILANO BICOCCA SOLAR ENERGY RESEARCH CENTER

MIB-SOLARMILANO BICOCCA SOLAR ENERGY RESEARCH CENTER

Consiglio Scientifico•Alessandro Borghesi•Gianfranco Pacchioni•Simona Binetti•Alessandro Abbotto•Maurizio Acciarri•Marco Fanciulli

�Sintesi di celle organiche�Caratterizzazione silicon based solar cells �Fabbricazione Celle di CIGS

�Realizzazione mini moduli�Sputtering x TCO�Laser scribing

�Caratterizzazione celle e moduli:�Simulatore solare ( 6x 6 inch)�EQE (300- 1800 nm)�Light soaking

Grazie per l’attenzione !

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