Polarized Light-Emitting Diodes

1
Semiconducting Polymer Nanoparticles Spectroscopy
and Devices
T. Kietzke, D. Neher1 R. Güntner, U. Scherf2 R.
Montenegro, K. Landfester3
1 Institute of Physics, Univ. Potsdam 2 Institute
of Chemistry, Univ. Wuppertal 3 Organic Chemistry
III, Univ. Ulm
ADMOL 04, Dresden, Germany
2
Nanoparticles and nanoparticle polymer
layers Blends of nanoparticles nanostructured
layers Blend nanoparticles phase-separation in
nanocontainers Some words about photovoltaic
devices
3
Nobelprize for Chemistry 2000
for the discovery and development of conductive
polymers
4
(No Transcript)
5
Organic Solar Cells
Photogeneration of free charge carriers
viaphoto-induced electron transfer
DA-device structures
6
Polymer Blend Layers Coated from Organic Solvents
F8BT
PFB
Confocal Raman PFB-rich PFBF8BT ca.
5050 F8BT-rich PFBF8BT ca. 2080
PFBF8BT (11) blend spin-cast from xylene
R. Stevenson, D. Richards et al.Appl. Phys.
Lett. 79 (2001) 2178
J.J.M. Halls, R.H. Friend et al., Adv. Mater. 12
(2000) 498
7
Spincoated Blend Layers
PFBF8BT layers spincoated from xylene
15 11 51
PFBF8BT
EQE 4 1.8 1.4
length scale of phase separationdepends on
composition
H.J. Snaith, R.H. Friend et al., Nanoletters 2
(2002) 1353
8
One Solution!

• One Solution
• coat layer from emulsion of semiconducting
  polymer nanoparticles (SPNs)

Dimension of phase separation defined by particle
diameter
But you need to find a way to make nanospheres
from polymers
T. Kietzke, D. Neher, K. Landfester, U. Scherf et
al., Nature Materials, June 2003
9
Nanoparticles and nanoparticle polymer
layers Blends of nanoparticles nanostructured
layers Blend nanoparticles phase-separation in
nanocontainers Some words about photovoltaic
devices
10
Alternative Way to Polymer Nanoparticles
The size of the particles can be controlled in
the range of 50-250nm.
11
Miniemulsions
polymer solvent
water andsurfactant
Polymer Solvent molecule
Important condition Polymer is completely
insoluble in water can not be transferred
between droplets
Consequence balance between Laplace pressure and
osmotic pressure
12
Semiconducting Polymer Nanoparticles (SPNs)
Tg above decomposition (300 oC)
Dispersion under white light
Dispersion under UV light (lmax 365 nm)
TEM of nanoparticles Ca. 75 nm diameter
K. Landfester, U. Scherf, D. Neher et al., Adv.
Mater. 14 (2002) 651
13
AFM of a LPPP Nanoparticle Layer
Layer formed by spin coating a dispersion of
LPPP nanoparticles onto a glass substrate.

• Particles are closely packed, no cracks can
  be identified

14
LED from Aqueous Emulsions
Preparation of the LED sample structure Spin
casting aqueous PEDOT/PSS solution Drying Spin
casting aqueous LPPP nanosphere
dispersion Drying Evaporation of
cathodes Thickness Ca30nm, Al80nm
15
Nanoparticles and nanoparticle polymer
layers Blends of nanoparticles nanostructured
layers Blend nanoparticles phase-separation in
nanocontainers Some words about photovoltaic
devices
16
Particle Blend Layers
Mix dispersion with polymer A and polymer B
particles
CN-PFPMMA (11)
CN-PFPMMA (12)
statistical distribution of particles
17
Layer Formation of Particle Blends
PF forms continuous phase homogenous distribution
of LPPP spheres
T. Kietzke, D. Neher, K. Landfester,U. Scherf et
al., Nat. Mater. 2003
18
Energy Transfer in Particle Blend Layers
PF and LPPP can be excited independently spectral
overlap between PF emission and LPPP absorption
as-prepared
annealed at 200 oC
complete transfer of energy in annealed layers
19
Thermal Stability of Blend Structures
mix particles of PF11112 (Tg RT) and PMMA
(Tg110 oC)
different softening temperatures different
solubility
annealed at 150 oC
as prepared
annealed at 75 oC
20
AFM Contour Plots (11 nm Increment)
annealed at 150 oC
annealed at 75 oC
as prepared
washed in acetone
21
Nanoparticles and nanoparticle polymer
layers Blends of nanoparticles nanostructured
layers Blend nanoparticles phase-separation in
nanocontainers Some words about photovoltaic
devices
22
Preparation of Solar Cells
Start with solution of PFB and F8BT
polymer solution
electron donor
electron acceptor
water surfactant
Nanoparticles which contain both polymers
23
Multicomponent Particles Morphology
excitation at 380 nm mainly PFB
emission excitation at 462 nm mainly F8BT
emission
pronounced asymmetry
24
Exciplex-Spectroscopy on Multicomponent Particles
PFBF8BT 11
A
D
E
e-
Recent results by R.H. Friend et al. Exciplex
emission at ca. 630 nm
Sensitive probe for interface formation
Larger exciplex contributionfor spin-coated
layers

1. Morteani, C. Silva, N. Greenham,R.H. Friend et
   al. Adv. Mater. 15 (2003) 1708

25
Exciplex-Spectroscopy on Multicomponent Particles
largest interface for blend with lowest F8BT
concentration weaker exciplex contribution with
increasing higher F8BT concentration ? smaller
number of excitons reach interface
26
Multicomponent Particle Morphology
F8BT
PFB

• F8BT easily penetrates PFB phase,but PFB remains
  outside F8BT phase
• Isolated F8BT phase for higher concentrations
• small exciton diffusion length on F8BT (ca. 3 nm)

M. A. Stevens, C. Silva, D. M. Russel, R. H.
Friend, Physical Review B 2001, 63, 165213.
27
Nanoparticles and nanoparticle polymer
layers Blends of nanoparticles nanostructured
layers Blend nanoparticles phase-separation in
nanocontainers Some words about photovoltaic
devices
28
Preparation of Solar Cells
Preparation of the solar cells Spin casting
aqueous PEDOT/PSS solution Drying Spin casting
aqueous nanosphere dispersion Drying Evaporation
of cathodes Thickness Ca30nm, Al80nm
electron donor
electron acceptor
29
Solar Cells based on Blend Particles
Incident-photon-to-converted-electron efficiency
(IPCE)
Well-resolved contributions from PFB and F8BT
30
IPCE of Blend Particles
380 nm PFB 445 nm F8BT

• PFB component most active ? small exciton
  diffusion length on F8BT
• very small IPCE for 51 and 15 ? island
  formation in particle
• highest efficiency for 12 ? asymmetry of
  particle morphology

31
Spincoated Blend Layers
PFBF8BT layers spincoated from xylene
15 11 51
EQE 4 1.8 1.4
H.J. Snaith, R.H. Friend et al., Nanoletters 2
(2002) 1353
cylinders of PFB-rich phase dispersed in F8BT
rich phase
32
Interfacial Area in Spincoated Layers
Estimate for blend SPNs
Interfacial area per film area
with SPNs optimum conditions achieved but
statistics of SPN orientation
H.J. Snaith, R.H. Friend et al., Nanoletters 2
(2002) 1353
33
PPV-based Particle Blend Layers
M3EH-PPV
CN-Ether-PPV
Th. Kietzke, H.H. Hörhold, D. Neher et al., Proc.
SPIE 2004, accept.
Area 0.2 cm² 100 mW/cm²
34
Solar Cells
Efficiencies ?E IPCE cryst.-Si typ.
15-28 (limit 32 ) 50-80 wet Grätzel cell ?
10-12 70-80 polymer/CdSe blend lt 7
30-50 polymer/fullerene blend ? 5 60-90
polymer/polymer laminate ? 1.8 20-30
polymer/polymer blend lt 1.5 12-25
35
Conclusion and Outlook

• Nanoparticles of conjugated polymers
• ? fabrication of polymer particles via
  miniemulsion process
• ? formation of dense solid layers from aqueous
  media
• ? nanostructured polymer layers via particle
  blends
• ? phase-separation in nanocontainers
• ? control of solar cell efficiencies via particle
  composition

• Outlook
• ? better understanding of particle morphology
• ? alternative deposition methods
• ? components with high electron mobilities
• ? single particle properties

36
A. Heilig Phys. Chem., MPI-KG, Golm H. H.
Hörhold University of Jena T. Piok, S.
Gamerith, Ch. Gadermaier, F. P. Wenzl, E.J.W.
List, University of Graz M. Kumke, H.G.
Löhmannsröben University of Potsdam
Funding VW-Foundation, MPG, BMBF, Fond der
Chemischen Industrie