MINATEC 25th of september 2003

Organic solar cells

based on conjugated polymer/fullerene

interpenetrating networks

Christoph Winder, N. Serdar Sariciftci

Christian Doppler Laboratory for Plastic Solar CellsLinz Institute for Organic Solar Cells LIOS

Physical Chemistry, Johannes Kepler University LinzAustria

Organic solar cells

based on conjugated polymer/fullerene

interpenetrating networks

Christoph Winder, N. Serdar Sariciftci

Christian Doppler Laboratory for Plastic Solar CellsLinz Institute for Organic Solar Cells LIOS

Physical Chemistry, Johannes Kepler University LinzAustria

Linz Institute for Organic Solar Cells

•Department of Physical Chemistry (1996)www.ipc.uni-linz.ac.at•Quantum Solar Energy Linz QSEL (1997)•Christian Doppler Laboratory for Plastic SolarCells (1998)•Linz Institute for Organic Solar Cellswww.lios.att (2000)•QSEL merged with Konarka (2003)

Outline

• Why are these materials interesting forthin film solar cells?

• How do they work?

• What potential has this system forfurther developments?

• Why are these materials interesting forthin film solar cells?

• How do they work?

• What potential has this system forfurther developments?

Materials

O

O n

O

OMe

PCBM

S** n

regioregularpoly-(3-hexyl)-thiophene

N NS

NNS

SN

SR

C12H25

R

n

PTPTB

NN

N

N

N

N

N

N

N CH3

Zn(CH3)3C

C(CH3)3

C(CH3)3

Pc-C60

Materials

• Semiconductors by organic synthesis

• Soluble solution processing

• Applications: thin film technology-field effect transistors

-electrostatic shielding

-Light emitting diodes

-Photodetectors and solar cells

• Semiconductors by organic synthesis

• Soluble solution processing

• Applications: thin film technology-field effect transistors

-electrostatic shielding

-Light emitting diodes

-Photodetectors and solar cells

Bulk Heterojunction Solar Cells

Processes necessary for photovoltaic activity:How to improve?

• Light Absorption: matching the solaremission spectrum

• Charge Generation: efficient photoinducedcharge transfer

• Charge Transport and Collection at theElectrodes: better charge carrier mobility

Processes necessary for photovoltaic activity:How to improve?

• Light Absorption: matching the solaremission spectrum

• Charge Generation: efficient photoinducedcharge transfer

• Charge Transport and Collection at theElectrodes: better charge carrier mobility

Charge Generation

N.S. Sariciftci, L. Smilowitz, A.J. Heeger, F. Wudl, Science 258, 1474 (1992).

CB

VB

Conjugated polymer C60

Charge Generation

LESR of Poly(3-octylthiophene) + C60(1:1 weight %), Ar+ Laser 488nm100mW/cm2, 80 K

Photoinduced absorption of Poly(MDMO-phenylene-vinylene) + PCBM) (1:4 weight %), Ar+ Laser 488nm, 40mW, 16 K

0.8 1.2 1.6 2.0

-2x10-3

0

2x10-3

inphase outphase

-?T

/T

Photonenergy [ eV ]

Charge Generation

Photoinduced chargetransfer

Forward transfer~45 fs

faster thancompeting processes

QE ~ 100 % (blend)

Photoinduced chargetransfer

Forward transfer~45 fs

faster thancompeting processes

QE ~ 100 % (blend)

C.J. Brabec, G. Zerza, G. Cerullo, S. De- Silvestri, S. Luzatti, J.C. Hummelen,N.S. Sariciftci, Chem. Phys. Lett. 340, 232 (2001)

0,0 0,2 0,4 0,6 0,8 1,0-10

-5

0

5

10

15

?T [a

. u.]

Time [ps]

Pump: 10 fs pulses peaking at 540 nmProbe: same pulse with filter at 650 nm

Charge Recombination

Ana F. Nogueira, Ivan Montanari, Jenny Nelson, James R. Durrant, Christoph Winder, N. SerdarSariciftci, Christoph Brabec, Journal of Physical Chemistry B 2003, 107, 1567

Pump: at 500 nm <1 nsProbe: at 940 nm

Chargerecombination inµs time scale

Slower thancollection atelectrodes

Chargerecombination inµs time scale

Slower thancollection atelectrodes

Bulk Heterojunction

Bulk Heterojunction

h? Alkoxy-PPVPCBMPCBM

e-

ITO on Glass / Plastic

P+e-

e-

e-

e-

P+

Al- ElectrodeAl- Electrode e-

G.Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger, Science 270, 1789 (1995)Bulk heterojunction concept, 2.9 % monochromatic efficiency

C.J. Brabec et. al., Advanced Functional Materials 11, 374 (2001)V. Dykonov, Physica E 53, 14 (2002)

Percolation andmobility forboth of chargecarriers

Selectiveelectrodes

Percolation andmobility forboth of chargecarriers

Selectiveelectrodes

Efficiencies

System Year Quantumefficiency [%]

Efficiency whitelight [%]

-

Lit

PPV/C60 1995 ~ 10   1

POPT/CN-PPV 1998 30 1.9 2

MDMO-PPV/[60]PCBM

2001 50 2.5 3,4

P3HT/ PCBM 2002 70 2.8 5,6

MDMO-PPV/[70]PCBM

2003 66 3.0 7

[1] G. Yu, J. Gao, J. C. Hummelen, F. Wudl, A. J. Heeger, Science 1995, 270, 1789[2] M. Granstrom, K. Petritsch, A. C. Arias, R. Lux, M. R. Andersson, R. H. Friend, Nature 1998, 395, 257[3] S. E. Shaheen, C. J. Brabec, N. S. Sariciftci, F. Padinger, T. Fromherz, J. C. Hummelen, Applied Physics Letters 2001, 78, 841[4] C. J. Brabec, S. E. Shaheen, C. Winder, N. S. Sariciftci, P. Denk, Applied Physics Letters 2002, 80, 1288[5] P. Schlilinsky, C. Waldauf, C. J. Brabec, Applied Physics Letters, 2002, 81, 3855[6] F. Padinger, R. Rittberger, N. S. Sariciftci, Advanced Functional Materials 2003, 13, 85[7] M. Wienk, J. Kroon, W. J. H. Verhees, J. Knool, J. C. Hummelen, P. A. van Hal, R. A. J. Janssen, Angewandte Chemie Int. Edition , 2003, 42,3371

Production

ITO coated glass of plastic serves as substrate.

Sealing against oxygen/water

Evaporation of top contact

Preparation of ITO-cleaning

Device/panel testing

Coating of hole conduction layer

PEDOT:PSS

Coating of active layer

PEDOT

Active layer

spacer

Aluminum

ITO

Glass

Production

Sealing against oxygen/water

Evaporation of top contact

Preparation of ITO-cleaning

Device/panel testing

Coating of hole conduction layer

PEDOT:PSS

Coating of active layer

Doctor blade

Spin coating

Production

Sealing against oxygen/water

Evaporation of top contact

Preparation of ITO-cleaning

Device/panel testing

Coating of hole conduction layer

PEDOT:PSS

Coating of active layer

Production

Sealing against oxygen/water

Evaporation of top contact

Preparation of ITO-cleaning

Device/panel testing

Coating of hole conduction layer

PEDOT:PSS

Coating of active layer

Optimisation

Possible Improvements

? eff = Isc * Voc * FF / Iinc

Isc Tuning of the Transport Properties - MobilityOptimization of Cell Geometry in Dependence of the Cell ThicknessInterference- optical modelling

Voc Tuning of the Electronic Levels of the Donor Acceptor System

FF Tuning of the Contacts and MorphologyLowering of Serial Resistivities - Interpenetrating Network

Iinc Tuning of the Spectral Absorbance Sensitization to the Optical Bandgap

Possible Improvements

? eff = Isc * Voc * FF / Iinc

Isc Tuning of the Transport Properties - MobilityOptimization of Cell Geometry in Dependence of the Cell ThicknessInterference- optical modelling

Voc Tuning of the Electronic Levels of the Donor Acceptor System

FF Tuning of the Contacts and MorphologyLowering of Serial Resistivities - Interpenetrating Network

Iinc Tuning of the Spectral Absorbance Sensitization to the Optical Bandgap

Modelling Optical Absorption

300 400 500 600 700 800 9000.0

5.0x104

1.0x105

1.5x105

2.0x105

MDMO-PPV PCBM Blend 1:4

abso

rptio

n co

eff.

? [c

m-1]

wavelength ? [nm]

H. Hoppe, N.S. Sariciftci, D. Meissner, Mol. Cryst. Liq. Cryst., 385, [233]/113, (2002) H. Hoppe, N. Arnold, N. S. Sariciftci, D. Meissner Solar Energy Materials and Solar Cells 2003, in print

Open Circuit Voltage

-0,70 -0,65 -0,60 -0,55

0,55

0,60

0,65

0,70

0,75

0,80

0,85

S1 = 0.95

Vol

tage

[V

]

E1

Red [V]

PCBM

azafulleroid 5 C60

ketolactam 6

(a)

Dependence on Acceptor Strength

C.J. Brabec et.al. Advanced Functional Materials 11, 374 (2001)

Fermi Level Pinning

Optimisation: Contacts

..

LiF layers forms

Ohmic contact

for electrons

at the Al electrode:

Contact resistivity

limits FF

0,0 0,2 0,4 0,6 0,8 1,0-6

-5

-4

-3

-2

-1

0 New Generation: Standard Electrode New Generation: Optimized Electrode

Cur

rent

Den

sity

(mA

/cm

2)

Voltage (V)

H. S. Hung, C. W. Tang, and M. G. Mason, Appl. Phys. Lett. 70, 152 (1997).C.J. Brabec, S.E. Shaheen, C. Winder, N.S. Sariciftci, P. Denk, Appl. Phys. Lett. 80, p1288(2002)

Optimisation: Contacts

-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0

0

20

40

60

80

100

120

ohne LiF mit LiF

Cur

rent

Den

sity

(mA

/cm

2 )

Voltage (V)

RpJDiode

Rs

0.92.954763Au/LiF [6Å]

0.7851620Au/-

3.25.159832Al/LiF [12Å]

1.1461821Al/LiF [3Å]

0.91652788Al/SiOx [6Å]

1.33.863834Al/LiF [6Å]

1.21053759Al/-

RP[kO]

RS[O]

FFVOC[mV]

Layer

Optimisation: Morphology

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9-6

-5

-4

-3

-2

-1

0

from toluene from chlorobenzene

Cur

rent

Den

sity

(m

A/c

m2 )

Voltage (V)

S. E. Shaheen, et al. Appl Phys. Lett, 78, 841 (2001).

400 450 500 550 600 650 7000

102030405060

IPC

E (

%)

Wavelength (nm)

5060708090

100

Tra

nsm

issi

on (

%)

Optimisation: Blend

Toluene cast film

Chlorobenzene cast film

b

0.5 ? m

0.0 0.5 1.0 1.5 2.0 2.5-4

0

4

8

Sur

face

Hei

ght (

nm)

D i s t ance ( ? m )

(a)

0.0 0.5 1.0 1.5 2.0 2.5- 4

0

4

8

Sur

face

Hei

ght (

nm)

D i s tance ( ? m )

(b)

a

0.5 ? m

Optimised Device

-1,0-0,9 -0,8 -0,7 -0,6-0,5-0,4-0,3-0,2-0,1 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,01E-6

1E-5

1E-4

1E-3

0,01

0,1

1

10

100

80 mW/cm² dark

Cur

rent

den

sity

[mA

/cm

²]

Voltage [V]

Voc ~ 810 mV

ISC ~ 5,2 mA cm-2

FF ? 0.62

? e ?3 %

IPCEmax ? 50 %

QE ~ 80-90 %

Voc ~ 810 mV

ISC ~ 5,2 mA cm-2

FF ? 0.62

? e ?3 %

IPCEmax ? 50 %

QE ~ 80-90 %

S. E. Shaheen, C.J. Brabec, N.S. Sariciftci. Applied Physics Letters 78, 841 (2001)

Matching the Solar Emission

400 600 800 1000 12000

1x1018

2x1018

3x1018

4x1018

5x1018

6x1018

MDMO-PPV:PCBM 1:4

photon flux AM 1.5ph

oton

s [n

m-2 s

-1 n

m-1]

Wavelength [nm]

0

50

100

[%]

integrated photon flux [%] absorbed photons [%]

Christoph Winder Gebhard Matt et al Thin Solid Films 403-404, 373 (2002)

PTPTB

N NS

NNS

SN

SR

C12H25

R

n

PTPTB

A. Dhanabalan, P.A. van Hal, J.K.J.van Duren, J.L.J. van Dongen, R.A.J.Janssen, Advanced FunctionalMaterials 11, 255(2001)

C. J. Brabec, C. Winder, et.al: “DualFunction of a Low Bandgap Polymer:Photovoltaic Devices and InfraredEmitting Diodes” AdvancedFunctional Materials 12, 709 (2002)

400 600 800 10000,00

0,05

0,10

absorption

OD

[a.u

.]

Wavelength [nm]

0,0

0,5

1,0

lum

ines

cenc

e [a

.u.] luminescence

Electrochemistry:

Eox = +0.53 eV vs. NHE

Ered = -1.17 eV vs. NHE

PTPTB/PCBM devices

PTPTB/ PCBM 1/3

Voc = 720 mV

ISC = 3 mA cm-2

FF = 0.38

? e = 1 %

PTPTB/ PCBM 1/3

Voc = 720 mV

ISC = 3 mA cm-2

FF = 0.38

? e = 1 %

-2 -1 0 1

1E-4

1E-3

0,01

0,1

1

10

100

AM 1.5 dark

curr

ent [

mA

cm

-2]

Voltage [V]

400 500 600 700 8000

8

17

25 IPCE

IPC

E [%

]

Wavelength [nm]

0

10

20

30

40

50

60

Abs

orbe

d P

hoto

ns [%

]

Absorbed Photons

Band structure engineering

MDMO-PPV PTPTB

PCBM

0

+1

-1

-2

[V] v

s N

HE

5

6

4

3

[V] v

s va

cuum? E ~1 eV

? E ~0.35 eV

Christoph Winder et al Proceedings of the SPIE 4801, 22 (2003)

P3HT:PCBM “postproduction treatment”

3.52.80.6? e [%]

0.600.550.3FF

9.38.35ISC [mAcm-2]

0.560.490.3VOC [V]

T-treatedandbiased

T-treated

Prist-ine

-0,4 -0,2 0,0 0,2 0,4 0,6

-8

-4

0

4

8

P3HT: PCBM 1:2 pristine thermally treated thermally treated

and electrially biased

curr

ent d

ensi

ty [m

A/c

m²]

Voltage [V]

F. Padinger, R. Rittberger, N. S. Sariciftci, Advanced Functional Materials 2003, 13, 85P. Schilinsky, C. Waldauf. C. J. Brabec, Applied Physics Letters 2002, 81, 3885

P3HT post productiontreatement

400 450 500 550 600 650 7000

10

20

30

40

50

60

70

thermally and electrially treated thermally treated pristine

IPC

E [%

]

Wavelength [nm]

P3HT post productiontreatement

Post production treatment:• increased absorptionstrength in the red•Higher conversionefficiency•Diode characteristics isimproved

Summary

•Conjugated polymer are cheap and showpossibility for easy processing

•Photoinduced charge transfer andinterpenetrating network are needed

•Possible Improvement:

•Materials parameter (absorption, bandpositions)

•Morphology

•Device structure

Acknowledgements

•TU Eindhoven: Rene Janssen•Imperial College: James Durrant•Manchester university: Peter Skabara•University Anger: Jean Roncali•CEA Saclet: Denis Fichou•Stratingh Institute, University of Groningen: J.C. Hummelen•University of Bari: Gianluca Farinola•USA: A. Heeger (UCSB), F. Wudl (UCLA), Jenekhe (Seattle, WA), S.Shaheen (Tucson AZ)•University of Triest: Mauricio Prato•TU Ilmenau: Gerhard Gobsch

Acknowledgements

LIOSLIOS

Andrei Andreev, Elif Arici, AntonioCravino, Gilles, Denller, Berndt Ebner,Serap Günes, Alexander Gusenbauer,Christopher Kopecny, ChristophLungenschmied, Nenad Marjanovic,Gebhard Matt, Farideh Meghdadi, MartinDrees Daniela Stoenescu, ChristophWinder, Helmut Neugebauer, (EugenBaumgartner, Christoph Brabec, MariaAntonietta Loi)

Konarka Austria (former QSEL)

Erhard Glötzl, Franz Padinger,Markus Scharber, Markus Koppe,David Mühlbacher, Patrick Denk,Attila Mozer, Roman Rittberger,Christoph Topf, (Elisabeth Wirtl)

Currently Funded by:Ministry of Education and Research, BMBF, Rep. Of GermanyChristian Doppler Society (Austria)Austrian Foundation for Advancement of Science (FWF)European Commission (JOULE III, RTD, INTAS)Ministry of Economy of Holland (EET, Univ. Groningen)ESV Land Oberösterreich