xxiii πανελληνιο ÏƒÏ Î½ÎµÎ´ÏÎ¹Î¿ Ï†Ï ÏƒÎ¹ÎºÎ·Ï‚ στερεας καταστασης & επιστημης ...

The Influence of Thermal Aging on the Electrical and Morphological
Properties of PEDOT:PSS
E. Vitoratos 1* , S. Sakkopoulos 1 , E. Dalas 2 , N. Paliatsas 1 , F. Petraki 3 , S. Kennou 3 and
S. A. Choulis 4
1 Department of Physics, University of Patras, 265 00 Patras, Greece
2 Department of Chemistry, University of Patras, 265 00 Patras, Greece
3
Department of Chemical Engineering, University of Patras, 265 00 Patras, Greece
4
Konarka Technologies GmbH, Landgrabenstr. 94, D-90443 Nürnberg, Germany
*vitorato@pelops.physics.upatras.gr
PEDOT:PSS is the most common buffer layer for organic electronic applications due to its optical
transparency and high conductivity [1]. It is a blend between poly(3,4-ethylene dioxythiophene) (PEDOT) a
π-conjugated polymer with high electrical conductivity, excellent stability and optical properties and a waterdispersible
polyelectrolyte, poly(styrene sulfonate) (PSS), which ensures its processibility. Chemically
polymerised PEDOT:PSS films have a granular morphology because of the micellar nature of the emulsion, with
electrically conductive grains, 20 – 70 nm in diameter, consisting of long PSS insulating chains on which many
shorter oxidized PEDOT conductive chains are electrostaticaly attached. The conduction takes places by hopping
of charge carriers between the PEDOT chains. The grains are surrounded by an insulating PSS coating, which
introduces a potential barrier to the charge carriers. It has been recently reported that the surface of PEDOT:PSS is
covered by a 3 – 4 nm ultra-thin layer of pristine PSS [2,3].
In this contribution we investigate the influence of thermal aging on PEDOT:PSS conductivity
properties. For the measurements an aqueous dispersion of PEDOT:PSS (Baytron P) was used, where the weight
ratio of PEDOT:PSS was 1:2.5 by weight. A four - probe method was used for the d.c. conductivity σ
measurements vs temperature (T) in a He filled cryostat. Each sample was subjected successive heat treatment in
the same cryostat, followed by conductivity measurements. The results σ = σ(T) for a sample heated from 200 K to
393 K for times between 0 and 55 h are shown in Figure 1.
σ (S/cm)
2,3
2,2
2,1
2,0
1,9
1,8
1,7
1,6
1,5
1,4
1,3
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
180 200 220 240 260 280 300 320 340 360 380
Temperature (K)
0 h
3
6
12
18
25
31
37
43
49
55
Figure 1. Experimental curves σ = σ (T) for a PEDOT:PSS sample heated from 200-393 K for different times
between 0 and 55 h. The decreasing of σ with thermal treatment is obvious for all the T studied.
0,4
0,2
lnW
0,0
-0,2
5,2 5,3 5,4 5,5 5,6 5,7 5,8 5,9 6,0
lnT
Figure 2. The lnW = f(lnT) straight line, where W is the reduced activation energy, for the PEDOT:PSS sample,
shown in Figure 1, after 37 hours of heat treatment.
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