Rare-earth doped fluorides for silicon solar Rare-earth doped fluorides for silicon solar cell efficiency enhancementcell efficiency enhancement

Diana Serrano Garcia

A.Braud, P.Camy, J-L.Doualan, A.Benayad, V.Menard, R.Moncorge

CIMAP, University of Caen, France

Summary

• Limitations of solar energy conversion

• Downconversion: Quantum cutting

• Experimental results and models

• Conclusion

• Quantum cutting with Rare-earth doped fluorides

Photovoltaics (PV)

- Conversion of solar energy into electricity

Silicon as the most famous semiconductor for solar cell development*

Si doped n

Si doped p+²

-

- Electron-hole pairs creation

*R. Singh; Journal of Nanophotonics, 3 (2009)

I) Silicon limitations for solar spectrum conversion

Short wavelenghts

BC

BV

Si Gap =1,12eV

E

- Energy loss due to

carrier thermalization

- Absorption of photons

h>1,12 eV

Energy lost

CB

VB

1,12eV

E

- Silicon transparent for

h<1,12 eV .

Low efficiency for Silicon solar cells (a-Si 9%,c-Si 25%*)

Silicon limitations for solar spectrum conversion

Long wavelenghts

*M.Green, Progress in Photovoltaics : Research and Applications 17, 320 (2009)

Stacking of semiconductors with

different bandgaps

SC 2 SC 1SC 3

Decreasing bandgap

Sem

icond. 1

Sem

icond. 2

Sem

icond. 3

Solution I: multi junction solar cells

The larger bandgap at the

surface of the device

BUT:

expensive and difficult to produce

Aerospace Applications

High efficiency

(World record 40%*)

*M.Green, Progress in Photovoltaics : Research and Applications 17, 320 (2009)

Si 2 e-

Quantum cutting

Solution II: Frequency Conversion

hν

hν

hν

Efficiency enhancement

Quantum CuttingLow cost production

*T. Trupke, M. Green; Journal of applied physics 92, 3 (2002) 1668

Ideal converter 36,6%*

c-Si Solar Cell

Si Si

Quantum cutting layer

Downconversion: Quantum cutting by energy transfer

Donor Acceptor

E

D0 A0

D1

D2

A1

Acceptor

A0

A1

D2D1 and A0A1D1D0 and A0A1

Donor excitationD0D2

Acceptor relaxationA1A0

2 photons emission

Energy transfer 1 Energy transfer 2

hv/2 hv/2

hv

Getting 2 photons from 1 photon?

1

2

From 1 photon we get 2 photons

Quantum cutting with rare-earth doped fluorides:

►Why Yb?

E~10000 cm-1

~1,2eV ~ Si Gap

Yb3+

53 H

43 F

43 H

Pr3+

23 F

63 H

33 F

41G

03 P

21 D

1

272 F

252 F

23 P

61 I

Yb3+

272 F

252 F

Donor Acceptor

Pr3+/Yb3+ system

E(3P0 – 1G4)~E(2F5/2 – 2F7/2)

E(1G4 – 3H4)~E(2F5/2 – 2F7/2)Acceptor

E

►Why Pr ?

Resonant Energy Transfer

1

2

Host matrix: Fluorides

- Low phonon energy

•High fluorescence quantum yield

- Large transparency range

Differences: RE3+ doping

Short distance between ions

Very efficient energy transfer

KY3F10 Uniform distribution of dopants

CaF2 Formation of complexes (clusters)

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0-0,25

0,00

0,25

0,50

0,75

1,00

1,25

1,50

1,75

2,00

I Pr/I

Yb

%Yb

IPr/IYb

CaF2:Pr/Yb First energy transfer Pr Yb

Intensity ratio as a function of Yb concentration Yb

03

Pr

I

PI

Pr excitation

Increase of first transfer Pr (3P0)Yb (2F5/2) with Yb concentration

03

Pr PI

YbI53 H

43 F

43 H

Pr3+

23 F

63 H

33 F

41G

03 P

21 D

1

272 F

252 F

23 P

61 I

DonorYb3+

Acceptor

Transfer

Ytterbium emission under Pr (3P0) excitation

• Energy transfer from Pr to Yb

(%Pr constant at 0.5%)

Experimental Results

0 80 160

0,1

1

3 µs

17 µs

45 µs

82 µs

CaF2: 0,5% Pr_4% Yb

CaF2: 0,5% Pr_2% Yb

CaF2: 0,5% Pr_1% Yb

CaF2: 0,5% Pr_0,5% Yb

Inte

nsi

té (

U.A

.)

t(µs)

3P0 fluorescence decay in CaF2 and KY3F10

Decrease of (3P0 ) with Yb concentration for both hosts

Experimental Results

PrPr

11

11)(

Yb

sW

Pr

Pr1

Pr1

1 1

Yb

W

W

Energy transfer rate :

Energy transfer efficiency :

40 80 120

0,1

1

1 µs

22 µs

3 µs

Inte

nsi

té (

U.A

.)

t (µs)

KY3F

10: 0,5% Pr 20%Yb

KY3F

10: 0,5% Pr 10%Yb

KY3F

10: 0,5% Pr 1%Yb

0 5 10 15 200

20

40

60

80

100

R

ende

men

t (%

)

% Yb

KY3F

10: Pr,Yb

CaF2: Pr,Yb

Experimental Results

97% eficiency with 4% Yb in CaF2

96% eficiency with 20% Yb in KY3F10

Transfer in CaF2 more efficient than transfer in KY3F10

Eff

icie

ncy

(%)

Modeling I: Classical model

3 energy transfer

0

34

15/2

2

5/22

0

5/22

PnGnβFnαFτ

1

dt

Fdn

0

3

03

0

320

35/2

24

1

41

0

41

PnPτ

BRPnFnαGnβ

Gτ

1

dt

Gdn

Pr0

3

03

0

03

NσPnPτ

1

dt

Pdn

- Possible interaction

between all Pr and Yb ions

- Uniform ion distribution53 H

43 F

43 H

23 F

63 H

33 F

41G

03 P

21 D

1

272 F

252 F

61 I

272 F

252 F

41

0

4

03

0

63132

5/22

0

22

2

Gτ

P

Pτ

PBRPβPα

Fτ

PPwp

dt

dP

03

0

531

41

0

3

5/22

0

21

1

Pτ

PBR

Gτ

P

Fτ

PPwp

dt

dP

6 possible states

3H4

2F5/2

3P0

1G4

2F7/2

Pr3+ Yb3+

5/22

0

4

03

0

532323

41

0

33

Fτ

P

Pτ

PBRPβPαPβ

Gτ

P

dt

dP

03

0

6325

5/22

0

4

41

0

44

Pτ

PBRPγ

Fτ

P

Gτ

P

dt

dP

5/22

0

6

03

0

532

03

0

53151

5

Fτ

P

Pτ

PBR

Pτ

PBRPγPwp

dt

dP

5/22

0

6

03

0

632

03

0

6312

6

Fτ

P

Pτ

PBR

Pτ

PBRPwp

dt

dP

Limited interaction within the pair

P1+P2+P3+P4+P5+P6 =1

Each state has a

probability Pi

Modeling II: Pair model

Conclusion

• Possible QC with CaF2:Pr/Yb and KY3F10: Pr/Yb

• Transfer in CaF2 more efficient!

Implementation in Si solar cells

• Very efficient Pr Yb first transfer (97%)

Conclusions

New models (Three or more ions model??)

THANK YOU

for your attention!!