morphology of bulk heterojunction systems for polymer ... · internal morphology is crucial for...

Technische Universität München

Morphology of bulk heterojunction systems

for polymer-based photovoltaics

Matthias A. Ruderer, S.M. Prams, M. Rawolle, G. Kaune,

W. Wang, Q. Zhong, E. Metwalli, P. Müller-Buschbaum

Technische Universität München, Physik-Department E13,

Lehrstuhl für Funktionelle Materialien, James-Franck-Str.1, 85747 Garching

J. Perlich, S.V. Roth1

1HASYLAB at DESY, Notkestr. 85, 22603 Hamburg

1st Colloquium of the Munich Scholl of Engineering


18.07.2011 Matthias A. Ruderer 2

Conventional photovoltaics

• energy-consuming production

• high vacuum treatment needed

• mechanically inflexible

• expensive encapsulation

solarpaneltips.org

First Solar Inc.


Efficiencies

8.3 %

in 2010

2008 Solar Technologies Market Report, Jan 2010

spacetoday.org

solarpaneltips.org

konarka.com



Polymer-based technology

konarka.com

konarka.com

konarka.com

konarka.com

solopower.com



transparent conducting

electrode

metal electrode

Organic solar cell

blocking layers

optical spacers ii) high exciton binding energy (~ 1 eV)

charge carrier separation at interfaces

G. Yu et al., J. Appl. Phys., 78, 4510 (1995)

organic materials

short exciton diffusion length (~ 10 nm)

performance strongly depending on

morphology

i) high absorption coefficient



Morphologies

interfacial area ~ free charge carrier creation

efficiency

K. M. Coakley et al. Chem. Mater.,16, 4533 (2004).

M. A. Ruderer et al. Soft Matter, 7, 5482 (2011).

bulk heterojunction


self assembly process

chemical structure

solvent

blending ratio

post production

treatments


Solvent dependent morphologies

M. A. Ruderer et al. Adv. Funct. Mater. (2011), in press.

1. high interfacial area

2. high conductivity

influence of

blending ratio

polymer

crystallinity

0.0 0.2 0.4 0.6

U (V)

-8

-6

-4

-2

0I

(mA

/cm

2)

400 600 800

(nm)

0.000

0.005

0.010

0.015

(n

m-1)

550 600 650 700 750 800 850 900

(nm)

0

5

10

15

20

25

PL

(a.u

.)a)

b)

c)

AM1.5G

AM1.5D


electronic characteristics

Poster: Shuai Guo


morphology of bulk heterojunctions

P3HT MEH-PPV

M.A. Ruderer et al. ChemPhysChem, 10, 664 (2009).

poly(3-hexylthiophene-2,5-diyl)

Mw = 16 kg/mol

poly[(1-methoxy)-4-(2-

ethylhexyloxy)-p-phenylenevinylene]

Mw = 2600 kg/mol


blending

ratio


Blending ratio

blending ratio independent absorption

no preferred blending ratio

thin films via spin coating

dissolve polymer in chloroform with

different blending ratios

homogeneous polymer films

with constant thickness

substrates:

acidic cleaned glass

slides


absorption


Blending ratio

lateral inner film structure

121

1

NNC

Flory-Huggins theory: accessible with

scattering techniques

(GISAXS)

10 nm – 2 µm

good estimation of minimal structure

size with Flory-Huggins theory


M.A. Ruderer et al. ChemPhysChem, 10, 664 (2009).


crystallinity in bulk heterojunctions

P3OT

M.A. Ruderer et al. J. Phys. Chem. B, 114, 15451 (2010).

poly(3-octylthiophene-2,5-diyl)

Mw = 34 kg/mol b

ind

ing

en

erg

y [

eV

]

CN-PPV

poly(2,5-di(hexyloxy)

cyanoterephthalyliden)

Mw 29 kg/mol



Crystallinity


molecular arrangement/crystalline structure

accessible with scattering techniques (GIWAXS)

resolution 2 Å – 5 nm

as-spun

annealed

(140 oC)

P3OT

increased crystallinity

higher charge carrier mobility

similar results for CN-PPV

conjugation planes

a

b a

b

Technische Universität München Bulk Heterojunction Film

P3OT:CN-PPV as-spun

annealed

(140 oC)

blending retards crystallization low performance

no signal from

CN-PPV

P3OT


M.A. Ruderer et al. J. Phys. Chem. B, 114, 15451 (2010).


Summary

a) organic solar cells preparation

self assembly process

b) minimal structure size at critical blending ratio

predicted by theory

c) retardation of crystallization due to blending

low photovoltaic performance

Internal morphology is crucial for photovoltaic performance!

Funding:

Bavarian State Ministry of Science, Research and Art

International Graduate School “Material Science of Complex Interfaces“


Thank

you!


3/21/2011 Matthias A. Ruderer 16

Grazing incidence wide/small angle scattering

resolution: 10 nm – 2 µm

resolution: 0.2 nm – 5 nm

morphology of bulk heterojunction systems for polymer ... · internal morphology is crucial for...

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