A Pentacyclic Nitrogen-Bridged Thienyl–Phenylene–Thienyl Arene
Conclusions
overnight at the same temperature. Prior to deposition, the solution was
filtered (1 mm filters). The solution of polymer:PC71BM was then spin-
coated to form the active layer. The cathode made of calcium (350 nm
thick) and aluminum (1000 nm thick) was sequentially evaporated
In summary, we have synthesized a ladder-type BDPT unit
in which the two outer thiophene rings are covalently fas-
tened with the central phenylene ring by two nitrogen
bridges. The two pyrrole units embedded in BDPT were
smartly constructed by using one-pot palladium-catalyzed
amination. The coplanar Sn-BDPT building block was copo-
lymerized with electron-deficient TPD, BT, and DPP ac-
ceptors by Stille polymerization. Due to the highly coplanar
BDPT unit, the BDPT-based donor–acceptor copolymers
showed strong interchain interactions in the solid state, lead-
ing to a significant bathochromic shift and band-broadening
of the absorption spectra. Moreover, the electron-donating
ability of the nitrogen bridges makes the BDPT motif highly
electron rich. Therefore, strong photoinduced charge trans-
fer and relatively higher oxidation potential are characteris-
tic of the BDPT-based polymers. PBDPTBT showed the
ꢀ6
through a shadow mask under high vacuum (<10 torr). Each sample
2
consists of 4 independent pixels defined by an active area of 0.04 cm . Fi-
nally, the devices were encapsulated and characterized in air.
Electrical Characterization under Illumination
ꢀ
2
The devices were characterized under 100 mWcm AM 1.5 simulated
light measurement (Yamashita Denso solar simulator). Current–voltage
(
J–V) characteristics of PSC devices were obtained by a Keithley 2400
SMU. Solar illumination conforming the JIS Class AAA was provided by
a SAN-EI 300 W solar simulator equipped with an AM 1.5G filter. The
light intensity was calibrated with a Hamamatsu S1336-5BK silicon pho-
todiode. The performances presented here are the average of the 4 pixels
of each device.
OFETs Fabrication and Characterization
2
An n-type heavily doped Si wafer with a SiO layer of 300 nm and a ca-
ꢀ
2
pacitance of 11 nFcm was used as the gate electrode and dielectric
layer. Thin films (40–60 nm in thickness) of polymers were deposited on
2
ꢀ1 ꢀ1
highest FET hole mobility of 0.02 cm V s . The device
using the PBDPTBT/PC BM blend (1:3, w/w) exhibited
2
octadecyltrichlorosilane (ODTS)-treated SiO /Si substrates by spin-coat-
ꢀ1
7
1
ing their o-dichlorobenzene solutions (1 mgmL ). Then, the thin films
were annealed at different temperatures (120, 200 or 2508C) for 10 min.
Gold source and drain contacts (30 nm in thickness) were deposited by
vacuum evaporation on the organic layer through a shadow mask, afford-
ing a bottom-gate, top-contact device configuration. Electrical measure-
ments of OTFT devices were carried out at room temperature in air by
using a 4156C, Agilent Technologies. The field-effect mobility was calcu-
ꢀ
2
a Voc of 0.6 V, a Jsc of 10.34 mAcm , and a FF of 49.7%,
thus leading to a decent PCE of 3.08%. Encouragingly, the
device incorporating the PBDPTTPD/PC BM (1:3, w/w)
7
1
composite delivered a high PCE of 3.72%. The enhanced
performance is ascribed to the lower-lying HOMO value of
PBDPTTPD to yield a higher Voc of 0.75 V. This research
provides a useful insight into the future molecular design of
donor–acceptor copolymers for FET and solar cell applica-
tions.
lated in the saturation regime by using the equation
I
DS =(mWC
) , in which IDS is the drain-source current, m is the field-
effect mobility, W is the channel width (500 mm), L is the channel length
50 mm), Ci is the capacitance per unit area of the gate dielectric layer,
and V is the gate voltage.
i
/
2
2
L)(V
G
ꢀV
T
(
G
Preparation of Compound 2
Experimental Section
General Measurements and Characterizations
A 2.5m solution of nBuLi in hexane (11.1 mL, 27.7 mmol) was added
dropwise to a solution of 2,3-dibromothiophene (1) (6.25 g, 25.8 mmol) in
dry THF (20 mL) at ꢀ788C. After stirring at ꢀ788C for 1 h, the mixture
was warmed up to room temperature. The mixture was added to a solu-
tion of zinc(II) bromide (5.82 g, 25.8 mmol) in dry THF (15 mL) at
All chemicals are purchased from Aldrich or Acros and used as received
1
13
unless otherwise specified. H and C NMR spectra were measured by
using a Varian 300 MHz instrument spectrometer. Differential scanning
calorimetry (DSC) was measured on a TA Q200 Instrument and ther-
mogravimetric analysis (TGA) was recorded on a Perkin–Elmer Pyris
ꢀ
788C and then the mixture was stirred at 08C for 1 h.
Synthesis of Compound 4
ꢀ
1
under a nitrogen atmosphere at a heating rate of 108Cmin . Absorption
spectra were collected on a HP8453 UV/Vis spectrophotometer. The mo-
lecular weights of polymers were measured by the GPC method on a Vis-
cotek VE2001GPC, and polystyrene was used as the standard (THF as
the eluent). The electrochemical CV was conducted on a CH Instruments
Model 611D. A carbon glass coated with a thin polymer film was used as
A solution of (3-bromothiophen-2-yl) zinc(II) bromide (2) (25.8 mmol)
[
13]
was added to a solution of 1,4-dibromo-2,5-diiodobenzene (3) (4.50 g,
9.2 mmol) and [Pd(PPh ] (0.27 g, 0.23 mmol) in dry THF (30 mL) at
3 4
)
room temperature. The mixture was refluxed for 3 h. After removal of
the solvent under reduced pressure, the residue was extracted with ethyl
acetate (50 mLꢂ3) and water (100 mL). The collected organic layer was
+
the working electrode and Ag/Ag electrode as the reference electrode,
dried over MgSO
4
. After removal of the solvent under reduced pressure,
4 6
whereas 0.1m tetrabutylammonium hexafluorophosphate (Bu NPF ) in
the residue was purified by column chromatography on silica gel (n-
1
acetonitrile was the electrolyte. CV curves were calibrated by using ferro-
cence as the standard, the oxidation potential of which is set at ꢀ4.8 eV
with respect to zero vacuum level. The HOMO energy levels were ob-
hexane) to give a white solid product 4 (1.54 g, 30%). H NMR (CDCl
3
,
300 MHz): d=7.71 (s, 2H), 7.42 (d, J=5.4 Hz, 2H), 7.09 ppm (d, J=
1
3
5.4 Hz, 2H); C NMR (75 MHz, CDCl
126.9, 123.5, 111.8 ppm.
3
): d=136.6, 136.1, 135.1, 130.5,
onset
ox
onset
ðferroceneÞ
tained from the equation HOMO=ꢀ(E ꢀE
+4.8)eV. The
LUMO levels of polymer were obtained from the equation LUMO=ꢀ(
onset
red
onset
Synthesis of Compound BDPT
E
ꢀ E
+4.8)eV.
ðferroceneÞ
2
1
,2’-(2,5-dibromo-1,4-phenylene)bis(3-bromothiophene)
.34 mmol), sodium tert-butoxide (1.14 g, 11.8 mmol), tris(dibenzylidenea-
(4)
(0.75 g,
Fabrication and Characterization of the BHJ Device
ITO/Glass substrates were ultrasonically cleaned sequentially in deter-
gent, water, acetone, and iso-propanol (IPA). The cleaned substrates
were covered by a 30 nm thick layer of PEDOT:PSS (Clevios P provided
by Stark) by spin coating. After annealing in a glove box at 1508C for
cetone) dipalladium (0.25 g, 0.273 mmol), 2,2’-bis(diphenylphosphino)-
[
14]
1,1’-binaphthyl (0.67 g, 1.07 mmol), and 5 (3.76 g, 14.7 mmol) were dis-
solved in deoxygenated toluene (15 mL). The reaction mixture was re-
fluxed at 1258C for 21 h and then extracted with diethyl ether (50 mLꢂ
3
0 min, the samples were cooled to room temperature. Polymers were
4
3) and water (50 mL). The collected organic layer was dried over MgSO .
dissolved in o-dichlorobenzene (ODCB) and PC71BM (purchased from
Nano-C) was added. The solution was then heated at 808C and stirred
After removal of the solvent under reduced pressure, the residue was pu-
rified by column chromatography on silica gel (n-hexane) to give
Chem. Asian J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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These are not the final page numbers! ÞÞ