PAPER www.rsc.org/polymers | Polymer Chemistry

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A polythiophene derivative with octyl diphenylamine-vinylene side chains:synthesis and its applications in field-effect transistors and solar cells

Bo Liu,a Weiping Wu,b Bo Peng,ab Yunqi Liu,*b Yuehui He,c Chunyue Pana and Yingping Zou*a

Received 20th January 2010, Accepted 2nd February 2010

First published as an Advance Article on the web 9th March 2010

DOI: 10.1039/c0py00022a

A new polythiophene derivative with octyl diphenylamine-vinylene conjugated side chains, DPAV-PT,

was synthesized by the Stille coupling reaction, and characterized by 1H NMR, GPC, TGA, UV-Vis

absorption spectroscopy, and cyclic voltammetry. The copolymer is readily soluble in the common

organic solvents and exhibits good thermal stability with 5% weight loss temperature of 267 �C. DPAV-

PT possesses a broad absorption band at 300–650 nm (with an optical bandgap of 1.85 eV). Cyclic

voltammetry displays a HOMO energy level of�5.01 eV. The weight average molecular weight (Mw) of

DPAV-PT is 3.1 � 104 with the polydispersity index of 1.3. A polymer solar cell with the configuration

of ITO/PEDOT:PSS/DPAV-PT:PCBM (1 : 1 w/w)/Ca/Al has a power conversion efficiency of 0.7%

under the illumination of AM1.5, 100 mW cm�2. The field effect hole mobility of the polymer reached

6.1 � 10�4 cm2 V�1 s�1 with an on/off ratio of 103 and a threshold voltage of �7 V after 180 �C

annealing.

1. Introduction

Conjugated polymers have been the subject of much research in

recent years due to their promising applications in electrolumi-

nescence (EL),1 organic field-effect transistors (OFETs),2 elec-

trochromic devices (ECDs),3 solar cells4 and sensors.5 In

particular, polymer solar cells (PSCs) have attracted considerable

attention due to their unique attractive properties such as being

lightweight, flexible and low cost. For the conjugated polymers in

PSCs as electron donor, broad absorption and higher hole

mobility play important role for efficient photovoltaic materials.6

To this end, Li and co-workers do much original work on side

chain conjugated polythiophenes. For example, their group

synthesized a series of polythiophene and poly(thienylene

vinylene) derivatives with conjugated phenylene-vinylene,7 thie-

nylene-vinylene,8 terthiophene-vinylene9 or phenothiazine

vinylene side chains.10 The polymers with the conjugated side

chains showed broad absorption in the visible region and higher

hole mobility,7–10 therefore leading to PCE of up to 3.2%.8

OFETs attracted extensive interest due to their promising

potentials in sensors, low-cost large area memories, smart cards,

and driving circuits for large-area displays.11 Easy processability

and good compatibility with flexible plastic substrates offer

excellent opportunities for polymers in fabricating low-cost

OFETs. Although much effort has been devoted to this, to date

the excellent semiconductors are still limited. Therefore, design

and synthesis of new conjugated polymers for FETs are of great

interest.

aCollege of Chemistry and Chemical Engineering, Central SouthUniversity, Changsha, 410083, People’s Republic of China. E-mail:zyp2008@iccas.ac.cn; Tel: (+86) 731-88836961bBeijing National Laboratory for Molecular Sciences, Key Laboratory ofOrganic Solids, Institute of Chemistry, Chinese Academy of Sciences,Beijing, 100190, ChinacState key Laboratory for Powder Metallurgy, Central South University,Changsha, 410083, People’s Republic of China

678 | Polym. Chem., 2010, 1, 678–684

Diphenylamine (DPA) is a well-known hole transporting unit.

To the best of our knowledge, the photovoltaic and field effect

properties of DPA-based polymers have been scarcely explored.

Based on this information, in order to shed light on the effect of

DPA structure on the properties of the conjugated side chain

polythiophene derivatives, we synthesized a new polythiophene

derivative with octyl diphenylamine units as conjugated side

chains, DPAV-PT (see Scheme 1), via the Stille coupling reac-

tion. A polymer solar cell with the configuration of ITO/

PEDOT:PSS/DPAV-PT:PCBM (1 : 1 w/w)/Ca/Al was fabri-

cated, and the power conversion efficiency (PCE) of 0.7% was

obtained under the illumination of AM1.5, 100 mW cm�2, which

is higher than that of triphenylamine vinylene conjugated poly-

thiophene derivative, OTPAV-PT (PCE: 0.2%).12 The reason

may be from its broader absorption and relatively higher hole

mobility due to its better planarity. The field effect hole mobility

of the polymer reached 6.1 � 10�4 cm2 V�1 s�1 with an on/off

ratio of 103.

2. Experimental

2.1. Materials

3-Methyl thiophene was purchased from Aldrich Chemical Co,

Pd (PPh3)4, (C4H9)3SnCl and n-BuLi were obtained from Alfa

Asia Chemical Co, and they were used as received. Toluene was

dried over molecular sieves and freshly distilled prior to use.

Scheme 1 Chemical structure of DPAV-PT.

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(2,5-Dibromo-thiophen-3-ylmethyl)-phosphonic acid diethyl

ester and 2,5-bis(tributylstannyl)thiophene was synthesized

according to the literature.8 The other chemical reagents were

common commercial products and used as received without

further purification.

2.2. Characterization

1H NMR spectra were recorded using a Bruker AM-400 spec-

trometer, with tetramethylsilane (TMS) as the internal reference,

chemical shifts were recorded in ppm. Molecular weight and

polydispersity of the polymer were determined by size exclusion

chromatography (SEC) analysis with polystyrene as the standard

(Waters 515 HPLC pump, a Waters 2414 differential refrac-

tometer, and three Waters Styragel columns (HT2, HT3, and

HT4)) using THF (HPLC grade) as eluent at a flow rate of

1.0 mL min�1 at 35 �C. Thermogravimetric analysis (TGA) was

conducted on a Shimadzu DTG-60 thermogravimetric analyzer

with a heating rate of 10 K min�1 under a nitrogen atmosphere.

Differential scanning calorimetry (DSC) was recorded with

a Thermal Analysis (TA) DSC-2010 in nitrogen. The UV-Vis

absorption spectra were recorded on a JASCO V-570 spectro-

photometer. For solid state measurements, polymer solution in

chloroform was drop cast on quartz plates. Optical bandgap was

calculated from the onset of the absorption band. The cyclic

voltammogram was recorded with a computer controlled Zahner

IM6e electrochemical workstation (Germany) using polymer

film on platinum disk as the working electrode, platinum wire as

the counter electrode and Ag/Ag+ (0.1 M) as the reference elec-

trode in an anhydrous and argon-saturated solution of 0.1 M of

tetrabutylammonium hexafluorophosphate (Bu4NPF6) in

acetonitrile. Electrochemical onsets were determined at the

position where the current starts to differ from the baseline.

2.3. Fabrication and characterization of polymer solar cell

The polymer solar cells were fabricated in the configuration of

the traditional sandwich structure with ITO positive electrode

and metal negative electrode. The ITO glass was cleaned by

sequential ultrasonic treatment in detergent, deionized water,

acetone, and isopropanol, and then treated in an ultraviolet-

ozone chamber (Ultraviolet Ozone Cleaner, Jelight Company,

USA) for 20 min. A thin layer of poly(3,4-ethylene-

dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) (Bay-

tron, PVP 4083, Germany) was spin-coated on the ITO glass and

dried in vacuum oven at 150 �C for 15 min. The thickness of the

PEDOT: PSS layer was ca. 40 nm. Subsequently, the active layer

was prepared by spin coating the o-dichlorobenzene solution of

polymer DPAV-PT: PCBM (1 : 1, w/w) with the polymer

concentration of 10 mg mL�1 on the top of the PEDOT:PSS

layer, giving a thickness of ca. 77 nm determined by a surface

profilometer (XP-2, USA). The devices were completed by

evaporating Ca/Al metal electrodes defined by masks. The Ca

electrode (20 nm) capped with Al (100 nm) was thermally

deposited on the active layer at a pressure of 3 � 10�5 Pa, The

active area of a device was 4 mm2. The current–voltage (I–V)

measurement of the PSCs was conducted on a computer-

controlled Keithley 236 source measure unit. A Xenon lamp with

AM1.5 filter was used as a white-light source and the optical

This journal is ª The Royal Society of Chemistry 2010

power was 100 mW cm�2. All the measurements were automat-

ically controlled by a computer system, and performed under

ambient atmosphere at room temperature.

2.4. Fabrication of OFET devices

Thin-film OFETs were fabricated with top-contact configura-

tion. An n-doped Si wafer with a thermally grown silicon dioxide

layer (thickness of 450 nm) was used as the substrate. The

substrates were cleaned in water, alcohol, acetone, and rinsed in

deionized water. Thin polymer films were prepared by spin

coating of a 0.3 wt% solution of DPAV-PT in chloroform onto

the bare SiO2/Si substrates at a speed of 3000 rpm (revolutions

per minute) for 40 s at room temperature. After dried at 80 �C

and annealed at 180 �C under N2 for half an hour, gold film

(50 nm) was deposited on the organic layer to form the drain and

source electrodes, for a typical device, the drain-source channel

length (L) and width (W) are 50 mm and 3000 mm, respectively.

OFET measurements were performed at room temperature using

a Keithley 4200SC semiconductor parameter analyzer under

ambient conditions. AFM images were obtained using a Veeco’s

Dimension V atomic force microscopic (AFM) in the tapping

mode.

2.5. Synthesis of monomers and polymer

The synthetic routes to the monomers and polymer are shown in

Scheme 2. The detailed synthetic procedures are as follows.

2.5.1. N-Octyldiphenylamine 1. Diphenylamine (8.5 g,

50 mmol), sodium hydroxide (20.0 g, 500 mmol), and dimethyl

sulfoxide (100 mL) were placed in a 250 mL three-necked flask,

the mixture was stirred for half an hour, octyl bromide (7.7 mL,

55 mmol) was added dropwise to the reaction mixture in 20 min,

and then this mixture was stirred for 24 h at room temperature.

The reaction mixture was poured into water, extracted with

methylene dichloride, and then dried with MgSO4. The resulting

liquid was purified by column chromatography using petroleum

ether as eluent, colorless oil was obtained (9.8 g, 70%). GC-MS:

m/z ¼ 281. 1H NMR (400 MHz, CDCl3): 7.49–6.91 (m, 10H),

3.68 (t, 2H), 1.77–1.36 (m, 12H), 0.91 (t, 3H).

2.5.2. 4-Formyl-N-octyldiphenylamine 2. A 100 mL three-

necked flask containing 4.4 mL (52.8 mmol) of anhydrous DMF

was cooled in an ice bath. To this solution, 1.4 mL (14.4 mmol) of

phosphorus oxychloride was added dropwise over 30 min.

Compound 1 (1.35 g, 4.8 mmol) in 30 mL of 1,2-dichloroethane

was added to the above solution and heated to ca. 90 �C for 48 h.

This solution was cooled to room temperature, poured into ice

water, and neutralized to pH 6–7 by dropwise addition of satu-

rated aqueous sodium hydroxide solution. The mixture was

extracted with chloroform. The combined organic layer was

dried with anhydrous MgSO4 and then concentrated under

reduced pressure. The titled product was obtained (1.07 g, 72%)

using petroleum ether and ethyl acetate (10 : 1) as eluent by

column chromatography under reduced pressure. GC-MS: m/z¼309. 1H NMR (400 MHz, CDCl3): 9.86 (s, H), 7.3 (d, 2H), 7.2 (d,

2H), 7.1 (d, 2H), 6.77 (d, 3H), 3.68 (t, 2H), 1.75–1.25 (m, 12H),

0.88 (t, 3H).

Polym. Chem., 2010, 1, 678–684 | 679

Scheme 2 The synthetic routes to the monomers and DPAV-PT.

Fig. 1 An 1H NMR spectrum of the polymer DPAV-PT in CDCl3.

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2.5.3. 2,5-Dibromo-3-(n-octyldiphenylamine-vinylene)thio-

phene 3. Under an ice-water bath, (2,5-dibromothiophen-3-

ylmethyl)phosphonic acid diethyl ester (3.35 g, 8.3 mmol) was

dissolved in 10 mL of DMF, and CH3ONa (0.6 g, 11 mmol) was

added. After 5 min, compound 2 (2.56 g, 8.3 mmol) was added

dropwise to the solution. After 2 h, the solution was poured into

methanol and filtered, and a yellow liquid of 3 was obtained

(2.36 g, 52%) using petroleum ether as eluent. GC-MS: m/z ¼547. 1H NMR (400 MHz, CDCl3): 7.68 (d, 2H), 7.3 (d, 2H), 7.2

(d, 2H), 6.95 (q, 2H), 6.77 (d, 1H), 6.6 (s, 1H), 6.5 (d, 2H), 3.68 (t,

2H), 1.75–1.25 (m, 12H), 0.88 (t, 3H).

2.5.4. Synthesis of Polymer DPAV-PT. Pd(PPh3)4 (30 mg,

0.026 mmol), monomer 3 (0.547 g, 1 mmol), and 2,5-bis-

(tributylstannyl)thiophene (0.667 g, 1 mmol) were put into

a three-necked flask. The mixture was flushed with N2 for 10 min,

and then 18 mL of toluene was added. Under the protection of

N2, the reactant was heated to reflux for 12 h. The mixture was

cooled to room temperature and poured into 30 mL of methanol

and then filtered into a Soxhlet thimble. Soxhlet extractions were

performed with methanol, hexane, and CHCl3. The polymer was

recovered from the CHCl3 fraction by rotary evaporation. The

solid was dried under vacuum overnight. The dark-red polymer

of DPAV-PT was obtained for 440 mg (yield: 94%). 1H NMR

(400 MHz, CDCl3): 7.3–6.8 (br, 14H), 3.68 (t, 2H), 1.75–1.25 (m,

12H), 0.88 (t, 3H).

3. Results and discussion

3.1 Synthesis and characterization of DPAV-PT

The synthesis of the monomers and the corresponding polymer

are outlined in Scheme 2. Diphenylamine was used as a starting

material for preparation of compound 1, 1 was in turn converted

to 2 by Vilsmeier reaction, monomer 3 was obtained using 2 via

Wittig reaction. The polymer was synthesized with 2,5-

bis(tributylstannyl)thiophene in the presence of dibromide 3

using Stille type cross-coupling condensation polymerization.

The DPAV-PT was purified by continuous extractions with

methanol, hexane, and chloroform using Soxhlet apparatus, and

the chloroform part was recovered. The chemical structure of the

680 | Polym. Chem., 2010, 1, 678–684

polymer was verified by 1H NMR as shown in Fig. 1. The

characteristic signals at 7.3–6.8 ppm can be assigned to the

resonance of protons on phenyl ring, thiophene ring and vinylene

group. –CH2– protons linking to nitrogen are at 3.68 ppm, the

signals at 1.75–0.88 ppm correspond to the protons of the long

alkyl chain. SEC result (using polystyrene standards and THF as

eluent) has shown weight-average molecular weight (Mw) value is

3.1 � 104 with the polydispersity index (PDI) of 1.3.

3.2 Thermal stability

Thermal stability of the polymer is important for device fabri-

cation. Fig. 2 displays the TGA thermogram of DPAV-PT. The

TGA analysis reveals that, under the protection of an inert

atmosphere, the onset points of the weight loss (5%) of DPAV-

PT is ca. 267 �C. Tg was not observed in the DSC thermogram.

Good thermal stability of the resulting copolymer prevents the

deformation of the copolymer morphology and the degradation

of the polymeric active layer under applied electric fields.

3.3 Optical properties

The photophysical characteristic of the polymer DPAV-PT was

investigated by UV-Vis absorption spectra in dilute chloroform

solution and in solid film spinning-coated on a quartz substrate.

Fig. 3 shows the UV-Vis absorption spectra of the polymer

solution and film. In solution, DPAV-PT shows an absorption

peak at ca. 378 nm and a shoulder at ca. 502 nm. The peak of

This journal is ª The Royal Society of Chemistry 2010

Fig. 3 The absorption spectra of the polymer DPAV-PT in CHCl3 and

film.

Fig. 4 Cyclic voltammogram of DPAV-PT film on platinum electrode in

0.1 mol L�1 Bu4NPF6, CH3CN solution.

Fig. 2 A TGA thermogram of the polymer DPAV-PT with a heating

rate of 10 K min�1.

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378 nm belongs to the absorption of the diphenylamine-vinylene

conjugated side chains, and the 502 nm shoulder peak could be

ascribed to the p–p* transition absorption of the conjugated

polythiophene main chains. The main chain absorption of the

polymer film in the visible region got broadened, red-shifted in

comparison with that of the polymer solution, because of the

aggregation and stronger interchain interactions between the

conjugated main chains of the conjugated polymer. The

absorption edge of the polymer film is at ca. 670 nm, corre-

sponding to an optical bandgap (Eoptg ) of 1.85 eV.13

Fig. 5 Molecular orbital iso-surfaces of HOMO and LUMO of the

model compound for DPAV-PT, calculated at the DFT B3LYP/6-31G*

level.

3.4. Electrochemical properties

The onset oxidation and reduction potentials obtained from the

cyclic voltammograms correspond to the HOMO and LUMO

energy levels, respectively.14,15 Fig. 4 shows cyclic voltammo-

grams of a DPAV-PT film on a Pt electrode with 0.1 mol L�1

tetrabutylammonium hexafluorophosphate (Bu4NPF6)/CH3CN

as the electrolyte at a scan rate of 50 mV s�1. It can be seen that

DPAV-PT exhibits quasi-reversible or reversible p-doping/

dedoping (oxidation/re-reduction) processes over a positive

potential range and irreversible n-doping/dedoping (reduction/

re-oxidation) processes over a negative potential range. In

a positive potential region, the onset oxidation potential (Eoxon) is

0.3 V vs. Ag/Ag+ for DPAV-PT. In the negative potential region,

This journal is ª The Royal Society of Chemistry 2010

the onset reduction potential (Eredon) located at�1.75 V vs. Ag/Ag+

for DPAV-PT.

From the onset oxidation potential (Eoxon) and the onset

reduction potential (Eredon) of the polymer DPAV-PT, we calcu-

lated the HOMO and LUMO energy levels of the polymer

according to the equations.16HOMO¼ �e(Eoxon + 4.71) (eV)

LUMO¼ �e(Eredon + 4.71) (eV).

The ELUMO and EHOMO values of DPAV-PT are�2.96 eV and

�5.01 eV, respectively, and the corresponding electrochemical

bandgap (EECg ) was 2.05 eV. The electrochemical bandgap is

slightly larger than the optical bandgap due probably to the

interface barrier for the charge injection.

3.5. Theoretical calculations

The optimal geometries and electronic state wavefunction

distribution of HOMO and LUMO of the model compound

(monomer) were obtained at the DFT B3LYP/6-31G* level using

the Gaussian 03 program suit (Fig. 5).17 To simplify the calcu-

lations, the alkyl chain was replaced by a –CH3 group. DFT/

B3LYP/6-31G* has been found to be an accurate method for

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calculating the optimal geometry and electronic structures of

many molecular systems. Ab intitio calculations on the model

compound for DPAV-PT show that the electrons are delocalized

within the entire molecule due to the pi-conjugation. The elec-

tronic wavefunction of the HOMO was distributed entirely over

conjugated molecules, which is beneficial for obtaining higher

hole mobility. From the DFT B3LYP/6-31G* level calcula-

tions,18 HOMO and LUMO energy levels of DPAV-PT are �5.3

and �3.24 eV and Eg is 2.06 eV, which are in good agreement

with the experimental values for the energy gap and the HOMO

and LUMO energy levels. Therefore, the DFT calculations

performed here on the repetitive units can provide good esti-

mations of the HOMO, LUMO, and bandgap energy trends,

thus allowing a rapid screening of the most promising polymeric

structures.

3.6 Photovoltaic properties

In order to investigate the potential applications of the

copolymer in solar cells, bulk heterojunction PSCs were fabri-

cated with a device structure of ITO/PEDOT:PSS/DPAV-

PT:PCBM(1 : 1 w/w)/Ca/Al. The PSC device was tested under

simulated 100 mW cm�2 AM 1.5G illumination. The active area

was 4 mm2 for the solar cell device discussed in this work, and the

thickness of the active layer was 77 nm. Fig. 6 shows the current

density versus voltage (J–V) curve of the device and the corre-

sponding open-circuit voltage (Voc), short circuit current (Jsc), fill

factor (FF). It can be seen that the Voc, Jsc and FF values of the

device with DPAV-PT as electron donor are 0.68 V, 2.78 mA

cm�2, 0.35, respectively. PCE of the preliminary device based on

DPAV-PT is 0.7%. Compared with the photovoltaic device

based on OTPAV-PT, 12 the device based on DPAV-PT

possessed better photovoltaic performance, which may be

contributed to by the higher open circuit voltage, relatively

broader and red-shifted absorption, relative higher hole mobility

in the blend of DPAV-PT and PCBM.

3.7 Organic field-effect transistors

OFETs based on DPAV-PT were fabricated using solution

processing. Top-contact OFETs were fabricated on a highly n-

doped silicon wafer with a 450 nm thick thermally grown SiO2

dielectric layer. The surface of the substrate was modified with

octadecyltrichlorosilane (OTS). The semiconducting layer

Fig. 6 J–V curves of the polymer solar cell based on DPAV-PT in the

dark and under the illumination of AM 1.5 G, 100 mW cm�2.

682 | Polym. Chem., 2010, 1, 678–684

(thickness about 40 nm) was spin-cast onto the substrate at

3000 rpm from 0.3 wt% chloroform solution. Gold source and

drain electrodes were deposited through a shadow mask on top

Fig. 7 Output characteristics and transfer characteristics of DPAV-PT

thin films deposited on (a) and (b), bare SiO2; (c) and (d), OTS modified

SiO2.

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of active layer. The OFETs of the DPAV-PT exhibited typical p-

channel OFET characteristics.

In the OFETs, drain current (IDS) can be described with the

following equation:

Fig. 8 Output characteristics and transfer characteristics of annealed

(180 �C) DPAV-PT thin films deposited on (a) and (b), bare SiO2; (c) and

(d), OTS modified SiO2.

This journal is ª The Royal Society of Chemistry 2010

IDS ¼ m(W/2L)Ci(VG � VT)2

Where Ci is the capacitance per unit area of the gate dielectric

layer, VG is the gate voltage, VT is the threshold voltage, m is the

field-effect mobility, and W and L are the channel width and

length dimensions, respectively. The mobility was calculated

from the slope of the curve of IDS1/2 vs. VG. The threshold voltage

of the device was determined from the linear fit of the square root

of IDS at the saturated regime vs. gate voltage VG, and VT was

determined by extrapolating the measured data to IDS ¼ 0.

Thin films of DPAV-PT exhibit relative low hole mobility

without thermal annealing. The mobility of DPAV-PT films

deposited on bare and OTS treated substrates were about 7.91 �10�5 cm2 V�1 s�1 and 1.10 � 10�4 cm2 V�1 s�1, respectively. OTS

surface modification reduced the threshold voltage from �17–

�21 V to �2–�6 V, and slightly improved the on/off ratio as

shown in Fig. 7. Due to low HOMO of DPAV-PT (�5.0 eV), the

current at zero gate voltage of the OFET devices was very low,

affording ideal switch on characteristics and superior stability

against doping, which is dramatically better than the polymer

P3HT.

Fig. 8a–d show the output curves and the transfer character-

istics of DPAV-PT, without and with OTS modifications after

being annealed at 180 �C. After annealing, OFETs of DPAV-PT

fabricated on OTS treated substrate afforded a hole mobility of

6.1 � 10�4 cm2 V�1 s�1, an on/off ratio of 103 and a threshold

voltage of �7 V, respectively. This device performance showed

apparent improvement compared to that of the devices without

annealing. In addition, further improvement of the mobility of

DPAV-PT could be achieved by using more favorable device

fabrication conditions (e.g. different solvents, surface treatment,

thermal treatment, etc).

Fig. 9 AFM imagines of DPAV-PT thin films deposited on (a) and (c),

bare SiO2; (b) and (d), OTS modified SiO2, (c) and (d) are annealed

(180 �C).

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Fig. 9a and b show the AFM images of films spin-cast with

DPAV-PT on bare and OTS modified substrate, Fig. 9c and

d show the AFM images of the annealed films. Both the presence

of the OTS monolayer at the polymer/dielectric interface and the

thermal annealing increase surface smoothness of DPAV-PT

thin films. As-spun films of DPAV-PT are always more rough

than those of annealed thin films, independent of substrate

chemistry. The morphology of the films is in agreement with their

trend of charge transport performances. The hole mobility was

increased after device annealed and it was apparently correlated

with the surface morphology, indicating a strong relationship

between morphology and device performances.

4. Conclusion

In summary, we have synthesized a new side chain conjugated

polythiophene derivative, DPAV-PT, by the Stille coupling

reaction. The polymer possesses good solubility in common

organic solvents. DPAV-PT film exhibited broad absorption in

the visible region from 300 nm to 650 nm, a relatively low HOMO

level, which is beneficial for the air-stability and the increase of Voc

of the PSC. A DPAV-PT based polymer solar cell afforded a PCE

of 0.7% under the illumination of AM 1.5, 100 mW cm�2, a FET

device demonstrated an average hole mobility of 6.1 � 10�4 cm2

V�1 s�1 after 180 �C annealing. The preliminary results indicate

that DPAV-PT could be a good candidate for applications in

polymer solar cell and organic field effect transistors.

Acknowledgements

The authors acknowledge Xuesen Mo for the synthesis of the

intermediates and appreciate great help from Prof. Yongfang Li

from Institute of Chemistry and Dr Dequan Xiao from Yale

University. This work was supported by National Natural

Science Foundation of China, the Opening Fund of State Key

Laboratory of Powder Metallurgy and Start-up fund of Central

South University.

684 | Polym. Chem., 2010, 1, 678–684

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