Thin film field-effect transistors of 2,6-diphenyl anthracene (DPA)

Article abstract of DOI:10.1039/c4cc10348c

An anthracene derivative, 2,6-diphenyl anthracene (DPA), was successfully synthesized with three simple steps and a high yield. The compound was determined to be a durable high performing semiconductor with thin film device mobility over 10 cm²

Full text of DOI:10.1039/c4cc10348c

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Thin Film Field-effect Transistors of 2,6-diphenyl
Anthracene (DPA)
Cite this: DOI: 10.1039/x0xx00000x
Jie Liu,a,f Huanli Dong,a,h* Zongrui Wang,a,f Deyang Ji,a,f Changli Cheng,e Hua
Geng,a Hantang Zhang,a,f Yonggang Zhen,a Lang Jiang,bHongbing Fu,a Zhishan
Bo,c Wei Chen,d Zhigang Shuaie* and Wenping Hua,g*
Received 00th January 2014,
Accepted 00th January 2014
DOI: 10.1039/x0xx00000x
www.rsc.org/
An anthracene derivative, 2,6-diphenyl anthracene (DPA), investigated in organic electronic devices (Table S1). One of
was successfully synthesized with three simple steps and high the best performing anthracene derivativesis diphenylvinyl-
yields. The compound was determined as a durable high anthracene (DPVAnt), which was firstly synthesized by Meng
performing semiconductor with thin film device mobility over et al. 8c,8d and exhibited mobility as high as 1.28 cm2V-1s-1 and
,
10 cm2V-1s-1. The efficient synthesis and high performance excellent ambient stability. Later, carrier mobility of 4.3 cm2V-
indicates its great potential in organic electronics.
1s-1 was found for DPVAnt single crystals.9
Stimulated by the progress of anthracene derivatives, in this
manuscript, 2,6-diphenyl anthracene (DPA, Scheme 1) was
designed. The molecular design principles are i) further
improving the stability through reduction of the π-
conjugation,8e ii) achieving more dense molecular packing
through reasonably reducing molecular size.10 Further
characterizations proved that DPA has high thermal and
environmental stability. In addition, over 80% vacuum
deposited thin film field-effect transistors based on DPA
exhibited mobility over 10 cm2V-1s-1 with current on/off ratio
up to 108 and long term stability. All these results were telling
that DPA was a promising candidate for commercial research.
The synthetic route of DPA is depicted in Scheme 1, the
final product can be easily synthesized through three simple
steps and pure DPA was obtained in large quantity by
sublimation(see full synthetic details in ESI).
Organic field-effect transistors (OFETs) have gained great
interest in the last decades, motivated by their potential
applications in low-cost and flexible electronics such as
transparent circuits and flexible displays.1 A remarkable burst
has been recently witnessed with charge mobility surpassing 10
cm2V-1s-1 attributing to the new materials designed and device
optimization.2 Among the diverse organic semiconductors,
polyacenes is one of the best performing systems, with the
extension of π-conjugation system, higher charge carrier
mobility could be expected owing to their smaller
reorganization energy and larger intermolecular transfer
integrals.3 However, the poor air/chemical stability of highly
extended polyacenes, such as pentacene and hexacene, which
usually undergo an easily photo-induced oxidation or Diels-
Alder addition reaction, has severely hindered their commercial
application.4 To circumvent this issue of instability, a number
of approaches have been developed: i) kinetically preventing
from possible reactions by attaching bulky substituents at the
active sites, such as at 6,13-positions of pentacene;5 ii) lowering
the highest occupied molecular orbital (HOMO) level by
replacing the benzene rings with thiophene rings.6 Materials
with improved stability and comparable or even higher
performance than pentacene are demonstrated for both of these
two classes of organic semiconductors.2a,7 On the other hand,
decrease of π-conjugation system in parent acenes provides
another approach to improve the stability,8 such as anthracene
derivatives, which also generally render practical applications
for the efficient synthesis. Based on these considerations,
various anthracene derivatives have been developed and
Scheme 1 Synthetic route to DPA and powder of DPA.
Physicochemical properties measurements were conducted
on DPA to verify its stability. Its UV-vis absorption spectrum in
solution was shown in Fig. 1A with the absorption onset of 413
nm and the estimated energy band gap of 3.0 eV. UV-vis
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absorption of its thin film was also studied and a redshift of 30 diffraction measurement of the 50-nm film showed a series of
nm (red line in Fig. 1A) and an increased ratio of the first peaks assignable to (h00) reflections (Fig. 3C). Moreover, the
vibration peak intensity compared with the second one were obtained d-spacing (1.80 nm) was very close to the length of
observed, suggesting J-aggregation formation in its thin film.11 DPA (1.777 nm), indicating that DPA were grown
Cyclic-voltammetry of DPA was performed and the calculated perpendicularly on the substrate. This conclusion was further
HOMO level is around -5.6 eV (Fig. 1B), 0.2 eV more negative confirmed by the AFM results of 5-nm film of DPA as shown
than that of DPVAnt (-5.4 eV)9 and at the same level of that in Fig. 3B, it was obvious that the 3-layer domain was grown
BTBT derivatives (Fig. 1B),10a which indicates its high stability. layer by layer. If the domain was crossed from point i) to point
And the decomposition temperature was determined as over ii), the step heights of the crystalline terrace layers at around
300 oC (Fig. S1), which further guaranteed its thermal stability.
1.7 nm were the same as shown in Fig. 3D, indicating the layer-
by-layer growth mode of DPA films, which agreed well with
the results of Fig. 3C.
Fig. 1 (A) UV-vis spectra of DPA in solution (black) and thin film state (red), (B) CV
curve of DPA and HOMO levels of typical p-type semiconductor (inlet).
To investigate the molecular packing, single crystals of DPA
with sufficient quality for X-ray structural analysis were grown
by slowly evaporation from chloroform (CCDC NO. 1044209).
X-ray crystallographic results demonstrated that DPA crystal
belongs to the P2(1)/c space group with crystal parameters of a
= 17.973(8) Å, b = 7.352(3) Å, c = 6.245(3) Å,
β
= 90.646(9)o.
And a torsion angle of 20.05°out of the central anthracene ring
was determined for the phenyl groups (Fig. 2A). The packing of
DPA represents typical herringbone structure similar to that of
DPVAnt (Fig. 2B), however, 10o smaller herringbone angle
was demonstrated for DPA compared to that of DPVAnt
(52.2o).9 Moreover, multi C-H-π interactions (distance: ~2.85 Å)
are observed between every DPA molecule and its nearest four
neighbor molecules (Fig. 2C). Such a dense packing structure is
partially due to the small molecular size as well as strong
intermolecular interactions, and thus hopefully to afford high
charge carrier mobility.
Fig. 3 AFM images of 50 nm (A) and 5 nm (B) thin films of DPA (C) out of plane
XRD results of DPA 50 nm films, (D) the step heights of crystalline terrace layers
as measured by a section analysis along the line marked in i) and ii) points, and
DPA layer-by-layer packing mode in the films.
To evaluate the charge transport properties of DPA, organic
thin film transistors were fabricated based on the 50 nm films
mentioned above with “top-contact” geometry (Fig. 4A).
Typical output and transfer characteristics obtained in air for
the thin film devices were shown in Fig. 4B and 4C. The
saturation mobility distribution for 30 devices was shown in Fig.
4D. Over 80% devices exhibited mobility >10 cm2V-1s-1, with
the highest mobility of 14.8 cm2V-1s-1 (corresponding device
characteristics are shown in Fig. S2). Additionally, all the
devices exhibited current on/off ratio >107. Despite the high
FET performance, nonlinear behavior of the output curve at low
VDS was observed, indicating the existence of contact resistance
(~0.1 MΩ, Fig. S3), which also resulted in the relatively large
threshold voltage from -34 V to -50 V. Additionally, some
Fig. 2 (A) DPA molecular length, (B) herringbone packing and (C) short contacts in
DPA.
deviation for (IDS)
1/2-VG plot from linearity at high VG was
observed, which might be assigned to the carrier
supersaturation in the conducting channel at high source-drain
current or factors such as charge traps at interface and/or
contact resistance.12 Nevertheless, much higher charge transport
property could be expected for DPA material under further
Thin
films
of
DPA
deposited
on
OTS
(octadecyltrichlorosilane) treated Si/SiO2(300 nm) at substrate
temperature of 50 C and a deposition speed of 0.05 Å/s was
studied. AFM image of 50 nm and 5 nm were shown in Fig. 3A
and 3B, large and quite uniform grains were obtained. X-ray
o
2 | Chem. Commun., 2014, 00, 1-3
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DOI: 10.1039/C4CC10348C
c
device optimization.Besides, the stability of DPA-based thin
Department of Chemistry, Beijing Normal University, Beijing 100875,
film transistors was also characterized. As shown in Fig. 4E, China;
d
the devices showed high stability over 3000 cycle, and
Department of Chemistry, National University of Singapore, 3 Science
negligible decrease can be observed for the devices even stored Drive 3, 117543, Singapore;
in air for 5 months (Fig. 4F and Fig. S4).
e Department of Chemistry, Tsinghua University, Beijing 100084, China;
f University of the Chinese Academy of Sciences, Beijing 100039, China;
gCollaborative Innovation Center of Chemical Science and Engineering
(Tianjin)& School of Science, Tianjin University, Tianjin 300072, China;
hDepartment of Chemistry, Capital Normal University, Beijing, 100037.
E-mail:dhl522@iccas.ac.cn; zgshuai@tsinghua.edu.cn;huwp@iccas.ac.cn
†
Electronic Supplementary Information (ESI) available: [Summery of
anthracene derivatives, synthesis procedures and characterization
details,transfer and typical output curves of the devices, contact resistance,
stability test and CIF of DPA.]. See DOI: 10.1039/c000000x/
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Fig. 4 (A) Device schematic of DPA thin film OFETs, (B) typical output and (C)
transfer characteristics of the representative device. (D) The mobility distribution
of DPA thin film OFETs, (E) Continuous electrical test, VDS was -60 V, with VGS
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In summary, we have synthesized DPA in three simple and
controlled steps with a high yield, which demonstrates high
stability and dense molecule packing. Moreover, excellent
performance with 80% device mobilities over 10 cm2V-1s-1 and
the highest mobility up to 14.8 cm2 V-1s-1 was achieved for
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We appreciated the profound discussion with Prof. Eiichi
Nakamura (Tokyo University), Prof. Henning Sirringhaus
(Cavendish Laboratory, Cambridge University) and Dr.
XinliangFeng (Max Planck Institute for Polymer Research).
The authors acknowledge the financial support from the
National Natural Science Foundation of China (51222306,
61201105, 91027043, 91222203, 91233205), TRR61 (NSFC-
DFG Transregio Project), the Ministry of Science and
Technology of China (2011CB808400, 2013CB933403,
2013CB933500), the Chinese Academy of Sciences, Beijing
local college innovation team improve plan (IDHT20140512)
and Beijing NOVA program (Z131101000413038)
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