Lim et al.
Synthesis and Photovoltaic Properties of a New Thiophene-Cyclopentadiene-Based Conjugated Polymer
atmosphere. Thermal gravimetric analysis (TGA) was per-
formed under a nitrogen atmosphere at a heating rate of
10 C/min through the use of the Perkin Elmer TGA7
A solution of DTCP in chlorobenzene was added drop-
wise to a stirred mixture of FeCl3 in chlorobenzene
under an argon atmosphere. The resulting mixture was
ꢁ
ꢁ
refluxed for two days at 65 C. After cooling down to
thermogravimetric analyzer. UV-vis spectra were obtained
using a Shimadzu UV/vis spectrometer and PL spectra
were obtained using a PerkinElmer spectrofluorometer.
The electrochemical properties of the polymers were char-
acterized by cyclic voltammetry (CV). The films were pre-
pared by dip-coating the polymer solution onto Pt wire
and the measurements were calibrated using the ferrocene
value of −4.8 eV as the standard. Film thicknesses were
measured using a TENCOR surface profiler. Atomic force
microscopy (AFM) images were obtained with a Digital
Instruments D3100 microscope in the tapping-mode.
room temperature, the mixture was poured into methanol.
The precipitated polymer was collected by filtration and
re-precipitated from methanol. The re-precipitated poly-
mer was added to a mixture of methanol and 30% aqueous
ammonia solution, and then was stirred for 3 days, in order
to remove ionic impurity. The final product, a dark brown
ꢁ
solid, was obtained after drying in vacuo at 60 C. Anal.
Calcd for (C29H40S2ꢂn: C, 76.93; H, 8.90; S, 14.16. Found:
C, 79.63; H, 9.77; S, 10.61.
2.4. Device Fabrication
2.2. Materials
The OPVs were fabricated with the configuration
ITO/PEDOT:PSS (40 nm)/PDTCP:PCBM/Al (100 nm).
The ITO-coated glass substrates were cleaned by ultra-
sonic treatment in acetone and deionized water. The
PEDOT:PSS layer was spin-coated ꢁ on the substrate
(3000 rpm, 30 s) and annealed at 120 C for 20 min. The
active layer consisting of polymer and PCBM was spin-
coated from a chlorobenzene solution and subsequently
All reagents purchased commercially were used with-
out further purification. 4-(Thien-2-yl)-4-oxobutyric acid
methyl ester (3) was synthesized according to the literature
procedure.10
2.3. Synthesis
ꢁ
annealed at 60 C in vacuo. The devices were completed
1,4-Bis(thien-2-yl)-1,3-cyclopentadiene (4): Compound 3
(3.0 g, 15.2 mmol, 1.1 eq) was added dropwise to a
stirred suspension of sodium ethoxide (2.47 g, 34.5 mmol,
2.5 eq) in benzene (50 ml). After 15 min stirring, 1-(thien-
2-yl)ethanone (1.52 mL, 13.8 mmol) and tetrabutylammo-
nium bromide (4.49 g, 15.2 mmol, 1.1 eq) were added
to the red solution. The reaction mixture was stirred at
50 ꢁC overnight. After cooling to room temperature, 0.4 M
HCl (50 ml) was added and the resulting mixture was
extracted with ether. The organic phase was dried with
MgSO4 and the solvent evaporated. Flash chromatography
of the residue (silica gel, ethyl acetate/hexane 1:9) afforded
the title compound as a yellow solid (0.77 g, Yield: 22%).
1H NMR (CDCl3, 600 MHz), ꢁ (ppm): 3.78 (s, 2 H), 6.67
(s, 2 H), 6.98 (dd, 2 H), 7.06 (d, 2 H), 7.14 (d, 2 H).
5,5-Dioctyl-1,4-bis(thien-2-yl)-1,3-cyclopentadiene
(DTCP): Octane bromide (1.99 mL, 11.5 mmol, 2.2 eq)
was added to a mixture of 4 (1.20 g, 5.21 mmol)
and K2CO3 (7.2 g, 52.1 mmol, 10 eq) in N,N-
dimethylformamidꢁe (DMF, 70 ml). The reaction mixture
was stirred at 80 C overnight, then filtered and the sol-
vent evaporated. The organic layer was washed with 1 M
HCl and then dried by anhydrous MgSO4. After removal
of the solvent under reduced pressure, the residue was
purified by column chromatography on silica gel (eluent:
by evaporating Al metal electrode. The area of the device
was 4 mm2. The current–voltage (J–V ꢂ characteristics of
Delivered by Ingenta to: Nanyang Technological University
the OPV cells were measured with a Keithley 2400 source-
IP: 188.68.3.106 On: Wed, 15 Jun 2016 23:53:19
measure unit under white light illumination of AM 1.5,
Copyright: American Scientific Publishers
100 mW/cm2. All fabrication and characterizations were
performed in an ambient environment.
3. RESULTS AND DISCUSSION
3.1. Synthesis and Characterization
A new low-band gap polymer containing thiophene
and cyclopentadiene, poly(5,2,2ꢀ-dioctyldithiophenylcyclo-
pentadiene) (PDTCP), has been synthesized via the FeCl3
O
O
i
ii
O
O
CH3OH
Cl
HO
O
O
O
O
O
2
1
O
iii
iv
S
O
S
S
O
3
4
v
vi
S
S
S
S
1
n
hexane) to give the final product (0.28 g, Yield: 12%). H
NMR (CDCl3, 600 MHz), ꢁ (ppm): 0.75 (t, 6 H), 1.08
(m, 24 H), 2.01(m, 4 H), 6.70 (s, 2 H), 7.03 (dd, 2 H),
7.13 (d, 2 H), 7.19 (d, 2 H).
DTCP
PDTCP
ꢁ
Scheme 1. Synthetic procedure of PDTCP: (i) 60 C, 4 h; (ii) CH2Cl2,
SOCl2, reflux, 2 h; (iii) 1 M SnCl4, CH2Cl2, thiophene, 0 ꢁC, then
rt, overnight; (iv) EtONa, benzene, rt, 15 min, then 2-acetylthiophene,
Bu4NBr, reflux, 10 h; (v) 1-bromooctane, K2CO3, DMF, 80 ꢁC, overnight;
(vi) FeCl3, chlorobenzene, reflux, 2 days.
Poly(5,2,2ꢀ-dioctyldithiophenylcyclopentadiene)
(PDTCP): The polymer PDTCP was synthesized by the
chemical oxidation route using FeCl3 as the oxidant.11
J. Nanosci. Nanotechnol. 12, 4194–4198, 2012
4195