Conjugated Polymer Based Plastic Solar Cells

Niyazi Serdar SARICIFTCILinz Institute for Organic Solar Cells (LIOS),

Physical Chemistry, Johannes Kepler University LinzAustria

Conjugated Polymer Based Plastic Solar Cells

Niyazi Serdar SARICIFTCILinz Institute for Organic Solar Cells (LIOS),

Physical Chemistry, Johannes Kepler University LinzAustria

Introduction to

Scope

“The electronics of the 20th century is based

on semiconductor physics. The electronics of

the 21st century will be based on molecular

chemistry/physics”

F. L. Carter

Small MolecularOrganic Solar Cells

“Tang- Cell“

C. W. TangAppl.Phys. Lett. 48(86)183

Improving Molecular Cells

Dieter Meissner, Yasuhiko Shirota et al

Solar Energy Materials and Solar Cells

61 (2000) 1 and 87; ibid 63 (2000) 37.

Mixed InterlayerZnPc mixed with C60

Organic Single Crystals

Single crystalline

Pentacene, about

7 mm2, halogen doped

AM 1.5, 100 mW /cm2,

η= 1.9 - 2.4 %

J. H. Schön, Ch. Kloc, E.

Bucher, B. Batlogg, Nature

403 (2000), 408

Photoinduced Charge Generation

An ultrafast e- transfer occurs between Conjugated Polymer / Fullerene composites upon

illumination. The transition time is less than 40 fs. The Internal Quantum efficiency of

charge generation is therefore ~100%.

MDMO PPV 3,7 - dimethyloctyloxy methyloxy

PPV

PCBM1-(3-methoxycarbonyl) propyl-1-phenyl [6,6]C61

O

O n

DONOR ACCEPTOR

N. S. Sariciftci et al., Science 258, 1474 (1992)

Transient Photoconductivity

Peak Photocurrent as well as the lifetime of the charge carriers are enhanced upon increasing the C60content in the composite.

Changhee Lee et al., Phys. Rev. B 48, 15425 (1993)

Enhanced Photoconductivity

Steady state photoconductivity of conjugated polymer is enhanced by several orders of

magnitude upon adding C60. Changhee Lee et al., Phys. Rev. B 48, 15425 (1993)

Light Induced Electron Spin Resonance

LESR of Poly(3-octylthiophene) + C60(1:1 weight %), Ar+ Laser 488nm 100mW/cm2, 80 K

N. S. Sariciftci, et al., Int. J. Mod. Phys. B8, 237 (1994)

Integrated LESR Intensities

PCBMMDMO-PPV

+-

Light

ITO

Plastic foil

Aluminum

P EDOT-PSS

Device Geometries

PCBM

+-

MDMO-PPV

Light

ITO

Plastic foil

Aluminum

PEDOT-PSS

BILAYER BULK HETEROJUNCTION

Bilayer Heterojunction Devices

• Rectification ratio in the dark 104

• Short circuit current linear up to 1W/cm2

• Efficiency under monochromatic light ≈ 10-1 %

N. S. Sariciftci et al., Appl. Phys. Lett. 62, 585 (1993)

Plastic Solar Cell Device Geometry

Device structure

Al contacts

MDMO-PPV2:PCBM1 (1:3)

PEDOT:PSS3

Glass substrate

Indium-tin-oxide (ITO)

1 [6,6] - phenyl-C61-butyl acid-methylester2 3,7 - dimethyl-octoxy-methyloxy-poly(phenylene-vinylene)3 poly-ethylene-dioxythiophene doped with polystyrene sulphonic acid

Interfacial Layers

Bulk Heterojunctions

hν

e-

e-

P+

e-

e-

e-

e-

e-

P+

e-

3-D Percolation

Strong luminescence quenching occurs at appr. 1 mol% of PCBM in alkoxy-PPV.

Photocurrent onset at appr. 17 mol% PCBM, in accordance with percolation theory.

0,1 1 10 1000,0

0,3

0,5

0,8

1,0 Lu

m In

tensity [a. u.]

Isc

I sc

[a.

u.]

Concentration of PCBM [mol%]

0,0

0,3

0,5

0,8

1,0 Luminescence

Schematic Band Diagram

π∗ MEH-PPV

Eg

ITOAl

4.3 eV4.7 eV

LUMO C60

π MEH-PPV

HOMO C60

2.8 eV

3.7 eV

5 eV

6.1 eV

π∗ MEH-PPV

Eg

ITO Al

LUMO C60

π MEH-PPV

HOMO C60

EF

Metal-Insulator-Metal (MIM) picture implies the field of assymetric metal electrodes

(All interface effects neglected!)

Plastic Solar Cells

Production Scheme

Plastic Solar Cells

Production Scheme

Plastic Solar Cells - SUBSTRATES

Substrates are available in any scale. They are flexible and transparent

We use Indium Tin Oxide (ITO)

coated polyester foils or glasses.

R ~ 10-100 Ω/cm2

Substrates are cut

in the desired sizeand cleaned in common organic solvents in a ultrasonic bath.

6 cm

6 cm

ITO

PolyesterInsulating String

WHY Plastic Solar Cells - MATERIALS

The electroactive compounds can be already bought from companies. Prices are appr. 300 - 500 US$/gram for the polymers, fullerenes are appr. 20 - 50 US$/gram.

Polymers and Fullerenes are dissolved in common organic solvents. 1 gram yields appr.~ 200 ml solution

Different colors of the solutions correspond to different spectral sensitivities - Band Gap Tuning

Plastic Solar Cells - FILM PREPARATION

Spin Casting is a easy coating technique for small areas. Materialloss is very high. Doctor Blade Technique

was developed for large area coating

Doctor Blade Technique has no material loss

FILM THICKNESS IS ~ 100 nm

Production - Large Area

Large Area Thin Film Production using Doctor/Wire Blading

1 2

a)

b)

Laminated Polymeric Solar Cells

••Au/PEDOT/POPT:MEH-CN-PPV (19:1)laminated at 200 C onto the ••MEH-CN-PPV:POPT (19:1) /Ca

Power conversion efficiency around 4.8 % at 480nm irradiation.Calculated AM1.5 efficiency around 1.9 %

Large scale large area fabrication potential!

M. Granström, K. Petritsch, A. Arias, A. Lux, M. Andersson and R. H. Friend, Nature 395, 257 (1998).

WHY Plastic Solar Cells - SUMMARY

Voc vs LUMO of Acceptor

-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

Vo

ltag

e [V

]

E1Red [V]

PCBM

azafulleroid 5 C60

ketolactam 6

(a)

Brabec et al., Advanced Functional Materials (2001), 11, No.5, 374-380

.

Voc vs Metal Work Function

2,5 3,0 3,5 4,0 4,5 5,0 5,50,50

0,55

0,60

0,65

0,70

0,75

0,80

0,85

0,90

S2 ~ 0.1

Vo

ltag

e [V

]

Work function [eV]

(b)

Brabec et al., Advanced Functional Materials (2001), 11, No.5, 374-380.

Anomalous Temperature Dependence

Eugene Katz, David Faiman, et al

Journal of Applied Physics, Vol 90, (2001), 5343-5350

Outdoor Experiment in Negev Desert Israel

Property Optimization

Structure Property

Morphology

Self OrganizationInterchain

(Intermolecular)Interactions

Molecular StructureMolecular Engineering

Morphology Effects

Toluene cast film

Cholorobenzene cast film

b

0.5 µm

0.0 0.5 1.0 1.5 2.0 2.5-4

0

4

8

Su

rfa

ce H

eig

ht

(nm

)

Distance (Pm)

(a)

0.0 0.5 1.0 1.5 2.0 2.5-4

0

4

8

Su

rfa

ce H

eig

ht

(nm

)

Distance (Pm)

(b)

a

0.5 µm

Morphology Effects

ff0.0 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

C

urre

nt D

ensi

ty (

mA

/cm

2 )

Voltage (V)

400 450 500 550 600 650 7000

102030405060

IPC

E (%

)

Wavelength (nm)

50

60

70

80

90

100

Tran

smis

sion

(%)

The efficiency is strongly enhanced by using cholorobenzene in MDMO-PPV/PCBM mixture

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

Intensity Dependence of Photocurrent

Scaling Coefficient αα ~ 0.92

1 10 1001E-5

1E-4

D

D

D

Pho

tocu

rren

t [A

/10

mm

2 ]

Am 1.5 Intensity [mW/cm2]

Post Production Treatment

400 450 500 550 600 650 7000

10

20

30

40

50

60

70

IPC

E [

%]

Wavelength [nm]

Rittberger et al, 2002, Patent filed by QSEL

Optimization

Possible Improvements

ηeff = Isc * Voc * FF / Iinc

Isc Tuning of the Transport Properties - Mobility

Optimization of Cell Geometry in Dependence of the Cell Thickness

Voc Tuning of the Electronic Levels of the Donor Acceptor System

Voc of ~2 V observed in polymeric Donor - Acceptor systems

FF Tuning of the Contacts and Morphology

Lowering of Serial Resistivities - Interpenetrating Network?

Iinc Tuning of the Spectral Absorbance

Sensitization to the Optical Bandgap

Spectral Mismatch to Solar Emission

400 600 800 1000 12000

1x1018

2x1018

3x1018

4x1018

5x1018

6x1018

MDMO-PPV/PCBM 1/4

photon flux AM 1.5

phot

ons

[n m

-2 s

-1 n

m-1]

Wavelength [nm]

0

50

100

[%]

integrated photon flux [%] absorbed photons [%]

OUTLOOK - Stability

0 3 7 100,0

0,2

0,4

0,6

0,8

1,0

- Exponentional Decay Fit Lifetime : 2.6 hours

Vo

c [ a

. u.]

Time [Hours]

0 30 60 90 120 1500,5

0,7

0,8

1,0V

oc [

a. u

.]

Time [days]

UNPROTECTED

PROTECTED

Stability

IN SITU FTIR

ENVIRON-MENTAL

CELL

OUTLOOK - Stability

C60 1182 cm-1

MDMO-PPV/ C60 1182 cm-1

MDMO-PPV 1506 cm-1

MDMO-PPV/ C60 1506 cm-1

Time [Hours]

Rel

. Pea

k A

rea

C60 slows down degradation of the Conj. Polymer

LIOS

Linz Institute for Organic Solar CellsPhysics of Organic Semiconductors:1.) Photoexcited spectroscopy2.) Photoconductivity3.) Thin film characterization4.) Nanoscale engineering5.) Nanoscale microscopy (AFM, STM...)6.) In situ spectro-electrochemistry

Plastic Solar CellsMolecular Solar Cells

Organic/InorganicHybrid

Solar Cells

„Incubator“ for small high tech spin-off companies

NC-TiO2 with Polymeric Hole Conductor

Hole conducting polymer

SnO2:F or ITO

Au

nc-TiO2 layer

Glass

Adsorbed dye

0.0 0.2 0.4 0.6 0.8

-0.4

0.0

0.4

0.8

1.2

Cu

rren

t de

nsity

[m

A/c

m2 ]

Voltage [V]

-1 0 1

10- 3

10- 2

10- 1

100

Cur

rent

den

sity

[mA

/cm

2 ]

Voltage [V]

Organic/Inorganic Hybrid Solar CellsDesta Gebeyehu, et al., Synthetic Metals, Vol. 125 (2002) 279-287

.

Hybrid Solar Hybrid Solar CellsCells

W.U. Huynh, J. Dittmer, A.P. AlivisatosScience, 295 (2002) 2425

Regioregular Regioregular P3HTP3HT

CdSeP3HT

Functioning Principle Functioning Principle of Hybrid Solar of Hybrid Solar CellsCells

•

„Interpenetreting Network“

4

44

4

ITO p-type n-type Al

Synthese der Synthese der CISCIS--NanoteilchenNanoteilchen

Organic LigandTPP (Triphenyl phosphit)

To prevent Aggregation

Bis(trimethylsilyl)-sulfide

InCl3 + TPP (In -TPP)+3 + 3Cl-

CuI + TPP (Cu -TPP)+1 + I-

CuxInySz-TPP + (CH3)3SiCl + (CH3)3SiI

Nanodimension depends on:• Temperature

•Rate of dropping•Ligand/Reagenza-Ratio

Elif Arici et al, 2002

Quantization Quantization

Wannier Wannier Mott Mott Exciton Exciton RadiusRadiusRwm = (εoo/µ). αB

= 8.1 nm

εεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεε εεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεεε oo = Dielectric const.µµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµµ = Reduced Massαααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααα BB = Bohr Radius of H-Atom

2.3 2.3 eV eV 1.5 1.5 eV eV

RR CISCIS < R < R WMWM

**L.E. Brus, J. Chem. Phys. 80, 4403 (1984)

)(BulkEE gg **

¸̧¹

·¨̈©

§�¸

¹·

¨©§

hemmR

h 11

8 2

2

+ + Re

HSH 0

2

48.1--

Coulomb-TermParticle-in-the-box-Term

Elif Arici et al, 2002

Nanocrystalline Nanocrystalline CISCIS

• Centrifuge

• Spincoating/Tempering

120 °C120 °C

CIS/TPP:

100 nm100 nm

ScanningScanning ElectronElectron MicroscopyMicroscopy

PercolationPercolation

Interdisciplinary R & D

Photophysics Materials Synthesis

Device Technology

Upscaling

Thin Film Techn.Prototypes