Electrical characteristics of lateral organic bulk heterojunction device
, Zi-En Ooi
, Eric Danielson
, Ananth Dodabalapur
Microelectronics Research Center, The University of Texas at Austin, Austin, TX 78758, USA
Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712, USA
Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A
STAR), 3 Research Link,
Singapore 117602, Republic of Singapore
Materials Science and Engineering Program, The University of Texas at Austin, Austin, TX 78712, USA
Received 9 September 2011
Received in revised form 29 February 2012
Accepted 2 March 2012
Available online 21 March 2012
Lateral structures have been used to characterize charge transport phenomena in organic
bulk heterojunctions. Through the analysis of the current vs. voltage relationships and their
light intensity dependence, space charge limited extraction currents and injection currents
have been observed and characterized. Additionally, the drift length of charge carriers has
been estimated by characterizing devices of varying lengths. These studies show that lat-
eral structures are a promising way to study the basic physics of organic bulk heterojunc-
tion materials as they offer degrees of freedom unavailable in sandwich structures and
such studies complement what can be learned from conventional sandwich structures.
Ó 2012 Elsevier B.V. All rights reserved.
Organic photovoltaic cells have been actively studied
for over 20 years and as power conversion efﬁciencies
approach 10% [1,2], there is still much to be learned about
the transport of charge carriers and recombination mecha-
nisms within these devices. Researchers have employed a
multitude of methods to study transport and recombina-
tion in bulk heterojunction (BHJ) solar cells, including:
photo-generated charge extraction in a linearly increasing
voltage (photo-CELIV) , ambipolar thin ﬁlm transistors
[4–6], and transient photocurrents , to name a few.
These reports have focused on measurements of vertical
solar cell devices, but these techniques require complex
measurement setups that analyze the transient response
of solar cells. As solar cells operate in a steady state regime,
transient measurements probe transport in an operational
regime that is dissimilar to solar cell operation. To enable
steady state carrier transport measurements, we have em-
ployed a lateral organic photovoltaic (LOPV) cell structure.
These structures allow measurements with transport
length scales ranging from 10’s of nm to more than 100’s
m with uniform charge carrier generation. In this arti-
cle, we report on the basic characteristics and optoelec-
tronic properties of lateral structures with organic bulk
heterojunctions for the ﬁrst time.
To accurately analyze charge carrier transport in LOPV
devices, both the physics of photodetectors and photovol-
taic cells must be considered. We ﬁrst consider the general
case of materials with mismatched electron and hole
mobilities, which are contacted by non-injecting elec-
trodes. In such materials, space charge limited transport
is expected due to the asymmetric mobilities, and as a
1566-1199/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
Corresponding authors. Microelectronics Research Center, The
University of Texas at Austin, Austin, TX 78758, USA (C. Lombardo).
E-mail addresses: firstname.lastname@example.org (C. Lombardo), ananth.
email@example.com (A. Dodabalapur).
Organic Electronics 13 (2012) 1185–1191
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