We have fabricated poly(3-hexylthiophene) (P3HT)/copper phthalocyanine (CuPc)/fullerene (C60) ternary blend films. This photoactive layer is sandwiched between an indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT/PSS) photoanode and a bathocuproine (BCP)/aluminium photocathode. The thin films have been characterized by atomic force microscope (AFM) and ultraviolet/visible spectroscopy in order to study the influence of P3HT doping on the morphological and optical properties of the photoactive layer. We have also compared the I-V characteristics of three different organic solar cells: ITO/PEDOT:PSS/CuPc 0.5 :C60 0.5 /BCP/Al and ITO/PEDOT:PSS/P3HT 0.3 :CuPc 0.3 :C60 0.4 /BCP/Al with and without annealing. Both structures show good photovoltaic behaviour. Indeed, the incorporation of P3HT into CuPc:C60 thin film improves all the photovoltaic characteristics. We have also seen that thermal annealing significantly improves the optical absorption ability and stabilizes the organic solar cells making it more robust to chemical degradation

A B Mohamed

A Hermann

A Ovchinnikov

A Savchuk

H Derouiche

V Kazukauskas

CiteSeerX

Hindawi Publishing Corporation
The Scientific World Journal
Volume 2013, Article ID 914981, 5 pages
http://dx.doi.org/10.1155/2013/914981
Research Article
Thermal Annealing Effect on Poly(3-hexylthiophene):
Fullerene:Copper-Phthalocyanine Ternary Photoactive Layer
H. Derouiche and A. B. Mohamed
Laboratoire de Photovoltaı̈ques, Centre de Recherches et des Technologies de l’Energie, BP 95, 2050 Hammam-Lif, Tunisia
Correspondence should be addressed to H. Derouiche; hderouiche@yahoo.fr
Received 10 April 2013; Accepted 8 May 2013
Academic Editors: A. Hermann, V. Kazukauskas, A. Ovchinnikov, and A. Savchuk
Copyright © 2013 H. Derouiche and A. B. Mohamed. This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
We have fabricated poly(3-hexylthiophene) (P3HT)/copper phthalocyanine (CuPc)/fullerene (C60) ternary blend films. This
photoactive layer is sandwiched between an indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)
(PEDOT/PSS) photoanode and a bathocuproine (BCP)/aluminiumphotocathode.The thin films have been characterized by atomic
force microscope (AFM) and ultraviolet/visible spectroscopy in order to study the influence of P3HT doping on the morphological
and optical properties of the photoactive layer. We have also compared the I-V characteristics of three different organic solar
cells: ITO/PEDOT:PSS/CuPc
0.5
:C60
0.5
/BCP/Al and ITO/PEDOT:PSS/P3HT
0.3
:CuPc
0.3
:C60
0.4
/BCP/Alwith andwithout annealing.
Both structures show good photovoltaic behaviour. Indeed, the incorporation of P3HT into CuPc:C60 thin film improves all the
photovoltaic characteristics. We have also seen that thermal annealing significantly improves the optical absorption ability and
stabilizes the organic solar cells making it more robust to chemical degradation.
1. Introduction
Thin films composed of copper phthalocyanine CuPc and
fullerene C60, p-n small molecules, have in recent years
received increasing attention, due to new optoelectronic
applications [1–4]. CuPc:C60 composite film was commonly
used to obtain a high conversion efficiency of solar energy
into electrical energy [5–8]. However, there is incomplete
knowledge about physical and chemical mechanisms of
organic thin films stability [9–11].
Addition of polymer is proposed as a way to stabilize
the CuPc:C60 thin films, making it more robust to chemical
degradation. Regioregular poly(3-hexylthiophene) (P3HT)
polymers are widely used in organic devices [12–15]. P3HT
has a good chemical stability and good solubility in various
solvents, so the addition of P3HT to the CuPc:C60 thin films
improves the p-n bulk heterojunction.
Moreover, thermal annealing is an effective method that
improves the morphology, compactness, and crystallinity of
the organic thin films [16–19]. One of the most important
effects of thermal annealing is the reorientation of the CuPc
planar and C60 near-spherical shape small molecules in a
high density P3HT matrix.
The aim of the present work is to study the influence
of P3HT doping and thermal annealing on the structural,
optical, and stability of the fullerene-based solar cells.
2. Experimental Details
All the organic layers have been deposited in a sandwich
geometry between the two electrodes: indium tin oxide (ITO)
as photoanode and aluminum as photocathode (Figure 1).
The ITO-coated glass substrates (Aldrich, surface resistiv-
ity 8–12Ω/sq) were treated with an 80∘C H
2
O-H
2
O
2
(30%)-
NH
4
OH(25%) solution (5 : 1 : 1 vol. parts) for 20min and then
cleaned in sequence with acetone (15min) and isopropanol
(15min) and deionized water (15min) using an ultrasonic
bath.
PEDOT:PSS, 0.54% in H
2
O, high-conductivity grade
with 1–5% Propan-2-ol, and 5–10% diethylene glycol were
purchased from Aldrich. It is the most hole transparent con-
ductor used as buffer layer, having a good charge transport
properties (resistance of 200Ω/sq). In addition, single-walled
carbon nanotubes (SWNTs) were dispersed in a PEDOT:PSS
2 The Scientific World Journal
Al
Glass
PEDOT: PSS/SWCNTs
BCP
P3HT0.3 : CuPc0.3 : C600.4
ℎ
Figure 1: Structure of ITO/PEDOT:PSS/C60:CuPc:P3HT/BCP/Al solar cell.
500 600 700 800 900
P3HT
CuPc
Wavelength (nm)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Ab
so
rb
an
ce
 (a
.u
.)
CuPc0.3 : P3HT0.3 : C600.4
(a)
500 600 700 800 900
Wavelength (nm)
100 50
75125
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Ab
so
rb
an
ce
 (a
.u
.)
(b)
Figure 2: The absorbance spectra of (a) CuPc (solid line), P3HT (dotted line), and P3HT
0.3
:CuPc
0.3
:C60
0.4
before annealing (dashed line)
and (b) P3HT
0.3
:CuPc
0.3
:C60
0.4
after annealing at different temperatures.
solution with a weight ratio of 0.5 wt%, and the obtained
solutions were spin coated onto ITO.
As for CuPc, C60, and P3HT, they were purchased
from Aldrich and used without further purification. In
this work, polymer solutions were prepared by dissolv-
ing P3HT/CuPc/C60 with weight ratios of 30 : 30 : 40 in
dichlorobenzene.The thicknesswas checked by cross- section
visualization using SEM.
In addition, bathocuproine (BCP) and aluminum upper
contacts were deposited onto the organic layers by vacuum
evaporation at a pressure of 10−4 Pa. A mask was used to
determine a well-defined shape for the aluminum electrode.
Finally, to increase the stability of the organic cell,
polyvinylidene difluoride (PVDF) film was put on top of
the organic solar cell and annealed for 5min at 70∘C. This
encapsulation method limits diffusion of oxygen and water
into the active layer.
3. Results and Discussion
Figure 2(a) shows the absorption spectra of a CuPc, P3HT,
and P3HT
0.3
:CuPc
0.3
:C60
0.4
films. CuPc has a strong absorp-
tion in the visible region, with the Q-band absorption peaks
at around 620 and 740 nm related to the 𝜋-𝜋∗ transition [20].
For pure P3HTfilm, the absorption spectra showed twopeaks
at 493 nm and 517 nm and one shoulder at 572 nm. These
three bands can be attributed to the 𝜋-𝜋∗ transition [21]. As
for P3HT
0.3
:CuPc
0.3
:C60
0.4
ternary blend bulk heterojunc-
tion, broadening and splitting of the absorption spectrum are
observed. The presence of the strong vibronic feature near
600 nm is attributed to P3HT interchain interaction [22].
Figure 2(b) shows the effect of thermal annealing on the
UV-Vis absorption spectra for the thin films of P3HT
0.3
:
CuPc
0.3
:C60
0.4
. The annealing time here is 15min for all
the films. Optical intensities of the peaks at both 550 nm
The Scientific World Journal 3
1.00
0.75
0.50
0
1.000.750.500.250
0.0 
150.0 
300.0 
0.25
(n
m
)
(𝜇m)
(a)
1.00
0.75
0.50
1.000.750.500.250
0.0 
350.0 
700.0 
0.25
0
(n
m
)
(𝜇m)
(b)
1.00
0.75
0.50
1.000.750.500.250
0.25
0 0.0 
150.0 
75.0 
(n
m
)
(𝜇m)
(c)
Figure 3: AFM image of (a) C60, (b) CuPc:C60, and (c) P3HT
0.3
:CuPc
0.3
:C60
0.4
thin films.
and 600 nm correspondent to P3HT were improved as
the annealing temperature is increased; this indicates an
enhanced ordering of the organic materials in the thin
film [23]. However, the optical intensity of the peaks at
740 nm correspondent to CuPc decreased as the annealing
temperatures were higher than 100∘C. The degradation is
possibly due to the change in orientation of the CuPc
planar and C60 nearspherical shape small molecules in the
P3HT
0.3
:CuPc
0.3
:C60
0.4
thin films.
AFM (Figure 3) observations allow visualizing of the sur-
face structure of C60, CuPc
0.5
:C60
0.5
, and P3HT
0.3
:CuPc
0.3
:
C60
0.4
thin films after thermal annealing for 15min at 100∘C.
Fullerene C60 thin films (Figure 3(a)) form crystalline struc-
tures. After the addition ofCuPc (Figure 3(b)), CuPc
0.5
:C60
0.5
clearly show the presence of dense packing filmwith a smooth
surface and demonstrate highly ordered surface composed
of C60 agglomeration and CuPc molecular planes. AFM
images of C60, CuPc
0.5
:C60
0.5
(Figure 3(c)) show that the
formation of an amorphous thin film composed of C60:CuPc
agglomerates into an amorphous matrix of P3HT.
Typical I-V measurements under AM 1.5 illuminations
of the devices are plotted in Figure 4. ITO/PEDOT:PSS/
CuPc
0.5
:C60
0.5
/BCP/Al, we have a 𝑉OC of 0.52V, an 𝐼SC
of 4.93mA/cm2, and a fill factor of 0.4 giving energy
conversion efficiency of 1.02%. For the ITO/PEDOT:PSS/
P3HT
0.3
:CuPc
0.3
:C60
0.4
/BCP/Al device develops an open
circuit voltage 𝑉OC of 0.55V, an 𝐼SC of 5.7mA/cm
2, and a fill
factor of 0.46 giving energy conversion efficiency of 1.44%.
All structures show significant photovoltaic behaviour.
The most remarkable feature is an increase in the short
circuit current at P3HT doping. In fact, under illumination,
a fraction of incorporated P3HT polymers improve photon
absorption of the CuPc system leading to a higher number
of free holes in the valence band, which establishes a p-type
doping inside the materials. Furthermore, P3HT polymers
can also act as exciton dissociation sites and therefore
generate free charge carriers in the presence of excitons. On
the other hand, with P3HT, both the open-circuit voltage and
the fill factor increase, respectively, to a value around 0.55V
and 0.46 compared to 0.52V and 0.4. Therefore, we can note
that the open-circuit voltage and the fill factor depend on the
nature of the photoactive polymers.
After thermal annealing of the photoactive layer for
15min at 100∘C, ITO/PEDOT:PSS/P3HT
0.3
:CuPc
0.3
:C60
0.4
/
4 The Scientific World Journal
Voltage (V)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
−0.006
−0.004
−0.002
0.000
0.002
0.004
Cu
rr
en
t (
A
/c
m
2
)
Figure 4: I (V) characteristics of (i) ITO/PEDOT:PSS/P3HT
0.3
:
CuPc
0.3
:C60
0.4
/BCP/Al heat-treated (∙), (ii) ITO/PEDOT:PSS/
P3HT
0.3
:CuPc
0.3
:C60
0.4
/BCP/Al (󳵳), and (iii) ITO/PEDOT:PSS/
CuPc
0.5
:C60
0.5
/BCP/Al (◼).
Figure 5: Cross-sectional SEM micrograph of glass/ITO/PEDOT:
PSS/P3HT
0.3
:CuPc
0.3
:C60
0.4
.
BCP/Al device develops an open circuit voltage 𝑉OC of
0.63V, a short circuit current 𝐼SC of 6.5mA/cm
2, a fill
factor of 0.68, and an energy conversion efficiency 𝜂 =
2.8%. As a result of heat treatment, the organic solar cell
performance was dramatically improved. We can conclude
that thermal annealing enhances photovoltaic characteristics
by optimizing both the morphology and the stability of the
photoactive layer.
Finely, cross-sectional SEM micrograph of glass/ITO/
PEDOT:PSS/P3HT
0.3
:CuPc
0.3
:C60
0.4
structure was checked
by cross-section visualization using a scanning electron
microscope (SEM) after one month under both environ-
mental and light exposure (Figure 5). We can see that there
are no chemical degradation and phase segregation. We can
note that the addition of P3HT stabilizes the photoactive
layer by reducing the density of structural defects and phase
segregation.
4. Conclusions
The addition of P3HT in CuPc:C60 thin films has been
studied by I-V measurements under AM 1.5 illumination.
The incorporation of P3HT in the films improved the optical
properties of the CuPc-C60 thin films and increased the solar
cell parameters values (𝐼SC and 𝜂) from 4.93 to 5.7mA/cm
2
and from 1.02 to 1.44%, respectively. In addition, thermal
annealing, for 15min at 100∘C, stabilizes the bulk heterojunc-
tion photoactive layer making it more robust to chemical
degradation under prolonged operation and improves the
power conversion efficiency to 2.8%.
References
[1] I. Murtaza, I. Qazi, and K. S. Karimov, “CuPc/C60 heterojunc-
tion thin film optoelectronic devices,” Journal of Semiconduc-
tors, vol. 31, no. 6, Article ID 064005, 2010.
[2] Y. Chen and D. Ma, “Organic semiconductor heterojunction as
charge generation layers and its application in tandem organic
light-emitting diodes for high power efficiency,” Journal of
Materials Chemistry, vol. 98, Article ID 243309, 2012.
[3] J. H. Lee and J. J. Kim, “Interfacial doping for efficient charge
injection in organic semiconductors,” Physica Status Solidi (A),
vol. 209, no. 8, pp. 1399–1413, 2012.
[4] M. Bronner, A. Opitz, and W. Brütting, “Ambipolar charge
carrier transport in organic semiconductor blends of phthalo-
cyanine and fullerene,” Physica Status Solidi (A) Applications
and Materials, vol. 205, no. 3, pp. 549–563, 2008.
[5] J. Endres, U. Hörmann, J. Niederhausen et al., “Correlation
between interface energetics and open circuit voltage in organic
photovoltaic cells,” Applied Physics Letters, vol. 101, no. 23,
Article ID 233301, 2012.
[6] B. Li, J. Chen, D. Yang, and D. Ma, “A comparative investigation
of trap-limited hole transport properties in organic bulk hetero-
junctions,” Semiconductor Science andTechnology, vol. 26, no. 11,
Article ID 115006, 2011.
[7] K. Akaike, A. Opitz, J. Wagner et al., “Unoccupied states in
copper phthalocyanine/fullerene blended films determined by
inverse photoemission spectroscopy,” Organic Electronics, vol.
11, no. 11, pp. 1853–1857, 2010.
[8] B. B. Yang, D. D. Zhang, S. T. Lee, Y. Q. Li, and J. X. Tang,
“Efficiency enhancement of organic photovoltaic devices using
a Sm: Al compound electrode,” Applied Physics Letters, vol. 102,
no. 7, Article ID 073301, 2013.
[9] H. Kumar, P. Kumar, N. Chaudhary et al., “Effect of temperature
on the performance of CuPc/C60 photovoltaic device,” Journal
of Physics D, vol. 42, no. 1, Article ID 015102, 2009.
[10] J. Park, J. E. Royer, C. N. Colesniuc et al., “Ambient induced
degradation and chemically activated recovery in copper
phthalocyanine thin film transistors,” Journal of Applied Physics,
vol. 106, no. 3, Article ID 034505, 2009.
[11] M. Guan, G. Cao, X. Chu, Y. Zhang, X. Liu, and Y. Zeng, “Effect
of MoO
3
-doped PTCDA as buffer layer on the performance of
CuPc/C60 solar cells,” Physica Status Solidi (A), 2013.
[12] C. C. Chou, H. C. Wu, C. J. Lin, E. Ghelichkhani, and W.
C. Chen, “Morphology and field-effect transistor characteris-
tics of electrospun nanofibers prepared from crystalline poly
(3-hexylthiophene) and polyacrylate blends,” Macromolecular
Chemistry and Physics, vol. 214, no. 7, pp. 751–760, 2013.
The Scientific World Journal 5
[13] S. Nam, J. Seo, S. Park et al., “Hybrid phototransistors based on
bulk heterojunction films of poly (3-hexylthiophene) and zinc
oxide nanoparticle,” ACS Applied Materials & Interfaces, vol. 5,
no. 4, pp. 1385–1392, 2013.
[14] L. Li, D. L. Jacobs, Y. Che et al., “Poly(3-hexylthiophene)
nanofiber networks for enhancing the morphology stability of
polymer solar cells,”Organic Electronics, vol. 14, no. 5, pp. 1383–
1390, 2013.
[15] D. C. Coffey, A. J. Ferguson, N. Kopidakis, and G. Rumbles,
“Photovoltaic charge generation in organic semiconductors
based on long-range energy transfer,” ACS Nano, vol. 4, no. 9,
pp. 5437–5445, 2010.
[16] H.X.Wei, J. Li, Z.Q. Xu, Y. Cai, J. X. Tang, andY.Q. Li, “Thermal
annealing-induced vertical phase separation of copper phthalo-
cyanine: Fullerene bulk heterojunction in organic photovoltaic
cells,” Applied Physics Letters, vol. 97, no. 8, Article ID 083302,
2010.
[17] N. N. Wang, J. S. Yu, Z. L. Yuan, and Y. D. Jiang, “Effect
of annealing copper phthalocyanine on the performance of
interdigitated bulk-heterojunction organic photovoltaic cells,”
The European Physical Journal Applied Physics, vol. 58, no. 2,
Article ID 20201, 2012.
[18] N. D. Treat, C. G. Shuttle, M. F. Toney, C. J. Hawker, and M. L.
Chabinyc, “In situ measurement of power conversion efficiency
and molecular ordering during thermal annealing in P3HT:
PCBM bulk heterojunction solar cells,” Journal of Materials
Chemistry, vol. 21, no. 39, pp. 15224–15231, 2011.
[19] E. Verploegen, R. Mondal, C. J. Bettinger, S. Sok, M. F. Toney,
and Z. Bao, “Effects of thermal annealing upon themorphology
of polymer-fullerene blends,” Advanced Functional Materials,
vol. 20, no. 20, pp. 3519–3529, 2010.
[20] J. Mack and M. J. Stillman, “Transition assignments in the
Ultraviolet-Visible absorption and magnetic circular dichroism
spectra of phthalocyanines,” Inorganic Chemistry, vol. 40, no. 4,
pp. 812–814, 2001.
[21] T. A. Chen, X. Wu, and R. D. Rieke, “Regiocontrolled synthesis
of poly(3-alkylthiophenes) mediated by Rieke zinc: their char-
acterization and solid-state properties,” Journal of the American
Chemical Society, vol. 117, no. 1, pp. 233–244, 1995.
[22] M. C. Gurau, D. M. Delongchamp, B. M. Vogel et al., “Measur-
ing molecular order in poly(3-alkylthiophene) thin films with
polarizing spectroscopies,” Langmuir, vol. 23, no. 2, pp. 834–
842, 2007.
[23] M. Theander, O. Inganäs, W. Mammo, T. Olinga, M. Svensson,
and M. R. Andersson, “Photophysics of substituted polythio-
phenes,” Journal of Physical Chemistry B, vol. 103, no. 37, pp.
7771–7780, 1999.
Submit your manuscripts at
http://www.hindawi.com
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
High Energy Physics
Advances in
The Scientific 
World Journal
Hindawi Publishing Corporation 
http://www.hindawi.com Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Fluids
Journal of
 Atomic and  
Molecular Physics
Journal of
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Advances in  
Condensed Matter Physics
Optics
International Journal of
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Astronomy
Advances in
International Journal of
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Superconductivity
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Statistical Mechanics
International Journal of
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Gravity
Journal of
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Astrophysics
Journal of
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Physics 
Research International
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Solid State Physics
Journal of
 Computational 
 Methods in Physics
Journal of
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Soft Matter
Journal of
Hindawi Publishing Corporation
http://www.hindawi.com
Aerodynamics
Journal of
Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Photonics
Journal of
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Thermodynamics
Journal of


Thermal Annealing Effect on Poly(3-hexylthiophene): Fullerene:Copper-Phthalocyanine Ternary Photoactive Layer

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=421107AF2CFD057539956262F84A51A4?doi=10.1.1.1049.2943&rep=rep1&type=pdf

Thermal Annealing Effect on Poly(3-hexylthiophene): Fullerene:Copper-Phthalocyanine Ternary Photoactive Layer

Abstract

Similar works

Full text

Available Versions

CiteSeerX