a new dithienylbenzotriazole-based poly(2,7-carbazole) for efficient photovoltaics

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2026

A New Dithienylbenzotriazole-BasedPoly(2,7-carbazole) for Efficient Photovoltaicsa

Bo Peng,b Ahmed Najari,b Bo Liu, Philippe Berrouard, David Gendron,Yuehui He, Kechao Zhou, Mario Leclerc,* Yingping Zou*

A new dithienyl benzotriazole-based conjugated polymer was synthesized by Suzuki couplingreaction. The polymer was found to be soluble in common organic solvents, such as chloro-form, tetrahydrofuran and chlorobenzene, with excellent film-forming properties. The struc-ture of the polymer was confirmed by 1H NMR,the molecular weights determined by GPC andthe thermal properties investigated by TGAand DSC. The polymer films exhibited anabsorption band in the wavelength range 300to 610nm. Preliminary photovoltaic cells basedon the composite structure of indium tin oxide(ITO)/PEDOT:PSS/PCDTBTz:PC60BM (1:2 w/w)/Al showed an open-circuit voltage of 0.92V, apower conversion efficiency of 2.2% and a shortcircuit current of 5.33mAcm�2.

Introduction

Poly(2,7-carbazole)s have emerged as promising new

conjugated polymers for plastic electronics since their

first synthesis by Leclerc’s group in 2001.[1] Excellent

B. Peng, B. Liu, Y. ZouCollege of Chemistry and Chemical Engineering, Central SouthUniversity, Changsha 410083, ChinaE-mail: [email protected]. Najari, P. Berrouard, D. Gendron, M. LeclercDepartement de Chimie, Universite Laval, Quebec City, G1K 7P4,CanadaE-mail: [email protected]. He, K. Zhou, Y. ZouState Key Laboratory for Powder Metallurgy, Central SouthUniversity, Changsha 410083, China

a : Supporting information for this article is available at the bottomof the article’s abstract page, which can be accessed from thejournal’s homepage at http://www.mcp-journal.de, or from theauthor.

b B. Peng and A. Najari contributed equally to this work.

Macromol. Chem. Phys. 2010, 211, 2026–2033

� 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonline

ambient and chemical stability (i.e., low HOMO energy

levels), good p-type charge transport, and easy modulation

of the optic-physical properties make poly(2,7-carbazole)

derivatives excellent candidates for use in polymer solar

cells (PSC).[1,2] Alternating poly(2,7-carbazole) derivatives

with a suite of electron-accepting (A) moieties are

particularly interesting. The energy gap can be readily

tailored by adjusting different acceptor units, while the

deep HOMO level of the carbazole leads to a higher

open circuit voltage (Voc). Therefore, the implied flexibility

of their molecular design and synthesis provides

poly(2,7-carbazole)s with potential theoretical power

conversion efficiencies (PCEs) of towards 10%. To date,

among poly(2,7-carbazole)s, one particular derivative,

poly[N-90-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-

thienyl-20,10,30-benzothiadiazole) (PCDTBT), having a PCE of

3.6%with Voc of 0.9 Vwas demonstrated by Leclerc et al.[1c]

Aftermodification of thedevice,Heeger et al. revealed a PCE

ofup to 6%with excellent stability.[3] Very recently, Y.Tao et

al. achieved a PCE of 5.7% using PCDTBT: [6,6]-phenyl C(71)-

butyric acid methyl ester (PC70BM) with a large effective

area of 1.0 cm2.[4] These encouraging results also suggest

library.com DOI: 10.1002/macp.201000315

A New Dithienylbenzotriazole-Based Poly(2,7-carbazole) . . .

that poly(2,7-carbazole)s are among the most promising

materials yet proposed for obtaining highly efficient

organic solar cells.

In light of these studies, our group became interested

in electron accepting units. On screening the literature,

2,1,3-benzothiadiazole (BT) and 4,7-dithienyl-2,1,3-benzo-

thiadiazole (DTBT) units were found to be widely used

acceptors for the synthesis of low band-gap copolymers.[5]

For instance, copolymers of DTBT with fluorene,[5a]

silafluorene,[5b] carbazole,[1c] dithienylsilole[5c] and dithie-

nylpyrrole,[5d] have been synthesized and applied in PSCs,

exhibiting promising PCEs.

However, 1,2,3-benzotriazole (BTz), which is similar to

2,1,3-benzothidiazole, is missing from this inventory. In

fact, BTz is a known heteroaromatic compound with a

strong electron-accepting feature because of two electron-

withdrawing imine (C¼N) nitrogen atoms; furthermore,

the ease of modification of the N�H bond of BTz unit can

allow tuning of its structural and electronic properties to

achieveprocessableBTz-containingpolymers. To thebestof

our knowledge, BTz-based homopolymers and copolymers

remain little explored and have been only applied in light

emitting or electrochromic devices. For example, Yama-

moto et al. reported the synthesis and optical properties of

BTz-contaning homopolymers and copolymers. [6] Cao et al.

synthesized copolymers fromfluoreneandBTzunits,which

emitted a blue electroluminescence.[7] Gong and Cao et al.

copolymerized BTz segments with phenothiazine vinylene

units to obtain orange–red light emitting copolymers.[8]

Recently, Toppare et al. copolymerized BTz units with

3,4-ethylenedioxythiophene or thiophene segments to

construct some copolymers which showed some interest-

ing electrochromic properties.[9] Therefore, it is necessary

for us to further investigate the potential of this unit

specifically for solar cells.

Figure 1. Chemical structures of the co-monomer units and thepoly(2,7-carbazole) derivatives (PCDTBT and PCDTBTz).


� 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Taking all of these results into account, the combination

of carbazole and BTz should lead to some interesting

characteristics for photovoltaic applications. Furthermore

we have decided to choose thiophene units next to the BTz

moiety tominimize steric hindrance and to lower the band-

gaps. In this work, for the first time we synthesized 4,7-

dibromothienyl-2-alkyl-1,2,3-benzotriazole. To shed light

on the potential of this new unit – 4,7-dithienyl-1,2,3-

benzotriazole – we report a new processable dithienylben-

zotriazole-based poly(2,7-carbazole) (PCDTBTz, Figure 1).

This new conjugated polymer exhibits optimized energy

levels of the highest occupied and the lowest unoccupied

molecular orbitals (HOMO and LUMO, respectively), effi-

cient photovoltaic properties, together with good thermal

and air stability.

Experimental Part

All the compounds were synthesized and characterized as

described in the Supporting Information, which also provides

detailed information on device fabrication and characterization.

Results and Discussion

Synthesis and Characterization of Monomersand Polymer

The synthetic route of the monomers and PCDTBTz

is sketched in Scheme 1, and synthetic details can be

found in the Supporting Information. To obtainprocessable

poly(2,7-carbazole) derivatives, 2,7-bis(4,4,5,5-tetramethyl-

1,3,2-dioxaborolane-2-yl)-N-9’-heptadecanylcarbazole was

synthesized in four steps.[1c] The other co-monomer, 4,7-

dibromothienyl-2-octyl-1,2,3-benzotriazole, was synthe-

sized as follows: starting from 1, 2,3-benzotriazole, an

alkylation reaction was performed to get 2-octylbenzo-

triazole (compound 1) with a similar yield, in this reaction

by using KOH as base instead of t-BuOK as reported in the

literature.[6] Because of the two possible alkylation posi-

tionsof thebenzotriazole, thedesired isomerwas isolated in

30% yield in the first step of the reaction sequence. This

reactioncanbeoperatedpracticallyat large scalebecauseof

the cheapness of benzotriazole. This stepwas then followed

byadibromination reactionusingaBr2/HBr systemtoyield

compound 2with 75% yield. Compound 2was reacted by a

Suzuki coupling reaction with 2-thiophene boronic acid to

obtain compound3, in a satisfactory yield. Adibromination

reactionof compound3usingNBSas thebrominatingagent

gave the co-monomer4 in 75%yield. As shown in Scheme1,

the polymerization reaction was carried out using equiva-

lent amounts of the monomers (4 and 5) through a Suzuki

cross-coupling polymerization and the chloroform soluble

fractionwas isolated to afford PCDTBTzwith 70% yield as a

www.mcp-journal.de 2027

B. Peng et al.

NHN

N NN

N

C8H17

NN

N

C8H17

Br Br

NN

N

C8H17

S S

NN

N

C8H17

S SBr Br

1

N

C8H17C8H17

(i)

NN

N

C8H17

S SBr Br+

N

C8H17C8H17

NN

N

C8H17

S S n

PCDTBTz

(ii) (iii)

2 3

(iv)

4

45

O

B

OO

B

O

(V)

Scheme 1. Synthesis of the co-monomer and PCDTBTz. Reagents and conditions: i) C8H17Br, KOH, CH3OH, reflux for 24 h, 30% yield; ii) Br2/HBr,135 8C for 12 h, 75% yield; iii) thiophene-2-boronic acid, Pd(PPh3)4, 1,2-dimethoxyethane (DME), 1 M NaHCO3, 90 8C for 12 h, 82% yield; iv) NBS,CHCl3/CH3COOH, 12 h at ambient temperature, 75% yield; and, v) Pd2dba3, sphos, K3PO4, toluene, H2O, 95 8C, 48 h, 70% yield.

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red solid. An end-capping reaction was performed using

bromobenzene and phenyl boronic acid to increase the

stability of the polymer. After purification and according to

size-exclusion chromatography (SEC) experimentsbasedon

monodisperse polystyrene standards using tetrahydro-

furan (THF) as the eluent, the polymer has a number-

average molecular weight (Mw) of 8.7 kg �mol�1 with a

polydispersity index of 1.5.

Thermal Stability

The thermal stability of PCDTBTz is important for device

fabrication. Thermogravimetric analysis (Figure 2) shows

that PCDTBTz exhibits good stability up to 390 8C in air. The

glass transition temperature (Tg) is about 90 8C according to

DSC measurement (Figure 2). PCDTBTz possesses excellent

thermal stability,which is enough for optoelectronic device

fabrication.

Optical Properties

The normalized optical absorbance of PCDTBTz in solution,

PCDTBTz film and the blend film from PCDTBTz and [6,6]-

phenyl- C61 butyric acidmethyl ester (PCBM)with the ratio

of 1:2 (byweight) are shown in Figure 3. In solution, theUV-

Vis absorption spectrum shows the absorption maximum



at 484nm; a pure PCDTBTz thin film shows a broad

absorption band around 485nm with an absorption onset

at 573nm. The optical band gap calculated from the

polymer film absorption edge is 2.16 eV.[10] The long

wavelength absorption peak of PCDTBTz is attenuated in

blends by adding 67% PCBM. The peak of 335nm in the

blend film originates from the PCBM.[11] At the same time,

the absorption spectra from the blend blue-shifted a little

compared to the pure polymer film, probably due to the

dilution of polymer chains by PCBMs or the self-orientation

of the polymers by efficient separation in the polymer/

PCBM system.

Electrochemical Properties

Electrochemical cyclic voltammetry (CV) measurement

was carried out on drop-cast films (from PCDTBTz in CHCl3solution) on a platinum (Pt) wire as a working electrode,

using a Pt counter electrode and an Ag/Agþ reference

electrode. As shown in Figure 4, one reversible oxidation

process [Eoxon ¼ 1.00V versus saturated calomel electrode

(SCE)] and one quasi-reversible reduction process

(¼Eredon �0.88V versus SCE) were observed. Based on the

recorded oxidation potential, the neutral PCDTBTz shows a

good air stability.[12] Furthermore, the HOMO and LUMO

levels of the polymer were calculated to be �5.70 and

DOI: 10.1002/macp.201000315


Figure 4. Cyclic voltammogram of PCDTBTz film cast on platinumwire in Bu4NBF4/acetonitrile (0.1 mol � L�1) at 50 mV � s�1.

0 100 200 300 400 500 600 70040

50

60

70

80

90

100

Wei

ght (

%)

Temperature ( oC)

Td = 388 oC

a)

0 50 100 150 200 250 300 350-8

-6

-4

-2

0

2

4

6

8

Hea

t Flo

w (m

W)

Temperature (oC)

Tg = 90 oC

25 50 75 100 125 150-6

-5

-4

-3

c)

b)

Figure 2. a) TGA thermogram of PCDTBTz with a heating rate of10 K �min�1; b) DSC thermograms of PCDTBTz with a heating rateof 20 K �min�1; c) enlargement of Tg area from (b).

300 350 400 450 500 550 600 650 7000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Energy (eV)

In solution In film state In blend film state

Abs

orba

nce

(a.u

.)

Wavelength (nm)

4 3.5 3 2.5 2

Figure 3. Normalized absorption spectra of PCDTBTz in diluteODCB, PCDTBTz film, and PCDTBTz-PC60BM blend film on ITO/PEDOT:PSS.

�3.82 eV, respectively, from the onset oxidation and

reduction potentials, assuming the SCE level to be at

�4.7 eV.[13] The lower LUMO levels of PCDTBTz compared

to carbazole-based homopolymers or poly[N-90-hepta-

decanyl-2,7-carbazole-alt-5,5-(40,70-di-thienyl-20,10,30-

benzothiadiazole) (PCDTBT) indicate that the introduction

of BTz can decrease the LUMO level to be similar to BT,

therefore reducing the energy gap. The results show that

BTz probably is a stronger accepting unit than BT. More

importantly,when theBTz is incorporated into thepolymer

backbone, keeping the lowHOMO, and lowering the LUMO

level. A deep-lying HOMO level is beneficial for higher Voc,

on the other side, a low LUMO level can narrow the band-

gap. The energy levels estimated from these electrochemi-

calmeasurements fit verywell with the required electronic

levels (EHOMO level between 5.2 and 5.8 eV; ELUMO level

between 3.8 and 4.0 eV) for polymeric bulk heterojunction

solar cells utilizing PC60BM as the acceptor.[14] Deep-lying

HOMO levels means that a higher Voc can be expected



because Voc is linearly correlated with the difference of the

HOMO of the donor and the LUMO of the acceptor. The

optical band gap (2.16 eV) and electrochemical bandgap

(1.88 eV) are within the experimental error (0.2–0.5 eV). On

the basis of these electrochemical data, while taking into

account a LUMO level for PCBMat�4.3 eVandusinga semi-

empirical estimation equation,[14] the calculated open

circuit voltage (Voc) is ca. 1.1 V. The above results indicate

that BTz is probably a promising accepting block for solar-

cell applications.


B. Peng et al.

Figure 6. Current-voltage data from the device ITO/PEDOT:PSS/PCDTBTz/Au, plotted in the format ln(Jd3 / V2) vs. (V/d)0.5, where Jis the current density and d is the thickness of the polymer layer.The lines are the fit to the respective experimental points.

2030

Theoretical Calculations

The optimal geometries and electronic state wavefunction

distribution of HOMO and LUMO of the model compound

(monomer) were obtained at the density functional theory

(DFT) B3LYP/6-31G� level using the Gaussian 03 program

suit (Figure S1, Supporting Information).[5d] To simplify the

calculations, thealkyl chainwasreplacedbyamethylgroup

(�CH3). Ab initio calculations on the model compound

show that the electrons are delocalized within the entire

molecule due to p-conjugation. The electronic wavefunc-

tion of the HOMOwas distributed entirely over conjugated

molecules, which is beneficial for obtaining higher hole

mobility. However, the electron density of LUMO was

mainly localized on the 4,7-dithienyl-1,2,3-benzotriazole

(DTBTz) unit. This result indicates that the decreased

energy gap of the copolymer originates mainly from

the introduction of the DTBTz segment, which is

in accordance with many other donor/acceptor (D/A)

copolymers.[5d,10]

X-Ray Analysis

To evaluate the crystallinity of the polymer, XRDmeasure-

ments were taken of thick spin coated films on SiO2

substrate. Figure5 shows theX-raydiffraction (XRD)dataof

the thin films of PCDTBTz deposited at room temperature.

The peak at 24.88 reveals a short JI-JI distance of 3.85 A

between the polymer main chains, indicating the polymer

chain is of planar conformation in the solid state.

Hole Mobility

Hole mobility is an important parameter of the conju-

gated polymers for photovoltaic applications. Here,

we investigated the hole mobility of PCDTBTz with the

space-charge-limited current (SCLC) model with a device

605040302010

200

400

600

800

1000

Intensity(CPS)

2θθ(degree)

PCDTBTz

Figure 5. X-ray diffraction pattern of PCDTBTz film.



structure of ITO/poly(3,4-ethylenedioxythiophene):poly-

(styrene sulfonate) (PEDOT:PSS)/PCDTBTz (116nm)/Au

(40nm). The results are plotted as ln(Jd3/V2) vs. (V/d)0.5,

as shown in Figure 6, where J stands for current density,

d the thickness of the device, and V¼Vappl�Vbi, where

Vappl is theappliedpotential andVbi is thebuilt-inpotential.

Theholemobility of thepolymer is 3.8� 10�5 cm2 �V�1 � s�1

calculated from the intercept of the corresponding lines

on the axis of ln(Jd3 / V2) according to the following

equation: [15]

JSCLC ¼ 9

8"0"rm0

ðV � VbiÞ2

d3exp 0:89g

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiV � Vbi

d

r" #

The results shows that the polymer has moderate hole

mobility.

Photoluminescence of the Polymer and the Blend

Photoluminescence (PL) quenchingprovidesdirect proof for

exciton dissociation, and thus efficient PL quenching is

necessary toobtainefficient solar cells. FromFigure7, thePL

of the PCDTBTz is almost completely quenched in the blend

film of PCDTBTz and PC60BM, indicating efficient exciton

dissociation in the blend.

Photovoltaic Properties

The photovoltaic properties of PCDTBTz were explored in

detail. First,we fabricated somephotovoltaic deviceswitha

structure of ITO/PEDOT:PSS/PCDTBTz:PC60BM (1:2)/Al to

investigate the effects of the thickness. After spin coating a

50nm thick layer of PEDOT:PSS onto a pre-cleaned ITO-

coated glass substrate, the polymer/PC60BM(1:2, w/w)

DOI: 10.1002/macp.201000315


Figure 7. PL spectra of the films of the PCDTBTz and PCDTBTz/PC60BM spin coated from ODCB solution.

Table 2. Photovoltaic performances of PCDTBTz-based polymersolar cells with different ratios. Films were as prepared by spin-coating at room temperature.

PCDTBTz:

PC60BM

Ratio

Thickness

of active

layer

Voc Jsc FF PCE

nm V mA � cm�2 %

1:1 76 0.90 3.20 0.33 1.0

1:2 74 0.92 5.33 0.44 2.2

1:3 78 0.91 5.47 0.34 1.7

1:4 76 0.90 5.35 0.28 1.4

solution in ortho-dichlorobenzene (ODCB)was spin-coated.

The resulting active layer filmwas dried for 24h in a glove

box and 6h under vacuum before cathode evaporation to

remove all residual solvent. The deviceswere completed by

evaporating Al metal electrodes with an active area of

25mm2, which were defined by masks. The detailed

conditions of the device fabrication and characterization

are described in the Supporting Information. The devices

were tested in air under AM 1.5G illumination of

100mW � cm�2, which was calibrated using a Gentec-eo

power detector (PS-330). The relationship between the

thickness of the active layer and the PCE was investigated

by controlling the spin speed during the spin-coating

process. The results of the devices with different thick-

nesses are summarized in Table 1 and depicted as Figure S2

(Supporting Information); the J/V characteristics of this

polymer with different ratios are shown in Figure S3 and

the results are listed in Table 2. Figure 8 shows a typical J/V

curve of the polymer solar cellswith a PCDTBTz: PC60BM1:2

weight ratio. As shown in Figure S2, the filling factor (FF)

decreases monotonically with increasing active layer

thicknesswhileVoc seemstobeconstant. Thisphenomenon

Table 1. Photovoltaic performances of PCDTBTz based polymersolar cells with different thickness. Films were as prepared byspin-coating at room temperature.

PCDTBTz:

PC60BM

Ratio

Thickness

of active

layer

Voc Jsc FF PCE

nm V mA � cm2 %

1:2 107 0.90 4.20 0.31 1.2

1:2 83 0.91 5.52 0.37 1.9

1:2 77 0.90 5.57 0.42 2.1



indicates that photovoltaic performance of the

PCDTBTz:PCBM-based solar cell may be limited by the poor

and unbalanced charge transport properties of the blend

film. On the other hand, the reducing value of Js with

increasing thickness from 77nm is due to increased series

resistance and recombination loss. The relatively good

currentdensityof5.33mA � cm�2, fill factorof0.44andopen

circuit voltage (Voc¼ 0.92V) give a PCE of 2.2% with the

74nm thick active layer, as shown in Figure 8. The high Voc

agrees with the deep HOMO level calculated from electro-

chemical results. However, the calculatedVoc is higher than

experimental Voc, which reveals a major problem concern-

ing the nanomorphology of the active layer[16] and/or the

charge carrier mobilities.[14]

Figure 8. Typical J–V curve of the polymer solar cells based onPCDTBTz:PC60BM (1:2) in ODCB with 74 nm thickness under theillumination of AM 1.5 G, 100 mW � cm�2. All the samples weremeasured by spin-coating.


B. Peng et al.

Figure 9. Tapping-mode AFM topography scans of as-cast blendfilms with different ratios.

2032

After studies of the effect of thickness, we then

investigated the photovoltaic performance of different

ratios of polymer having the similar thickness. The data are

shown in Table 2 and the J/V characteristics are depicted in

Figure S3. The samples having 1:2 and 1:3 weight ratios of

polymer:PC60BM had relatively better photovoltaic proper-

ties. To better understand this phenomenon, tapping-mode

atomic forcemicroscopy (AFM) studieswithdifferent ratios

were carried out to investigate the film morphology of

polymer:PC60BM blends on their photovoltaic perfor-

mances. Rough surfaces and blend phase separation were

observed with 1:1 and 1:4 weight ratios of polymer:

Table 3. AFM results for PCDTBTz.

Ratio Rqa) Ra

b) Rmaxc)

nm nm nm

1:1 0.811 0.669 4.75

1:2 0.246 0.195 2.03

1:3 0.293 0.235 2.13

1:4 0.318 0.254 2.46

a)The root mean square roughness, Rq or Rs, is essentially the

standard deviation of the asperity heights above and below the

datum; b)The imagemean roughness, Ra, is the arithmetic average

of the absolute values of the surface height deviations measured

from the mean plane; c)The maximum height roughness, Rmax, is

the difference in height between the highest and lowest points on

the surface relative to the mean plane.



PC60BM (Figure 9, the data are listed in Table 3) compared to

relatively smooth surfaces and more intimate mixing for

1:2 and 1:3 weight ratio of polymer:PC60BM active layers,

whichsomewhatexplains thebetterperformanceof the1:2

weight ratio samples. The improved miscibility and good

nanostructure of 1:2 weight ratio configuration, together

with thehigherVoc value, leads to thebest PCEofup to 2.2%.

These results suggest that PCDTBTz is a very promising

candidate for efficient photovoltaic devices. Furthermore, it

indicates that DTBTz units can be good electron-accepting

buildingblocks applicable for efficientphotovoltaics. Taken

together, we believe the efficiency can be improved further

by the material synthesis, such as an increase of the

molecular weight using different polymerization condi-

tions, the modification of the side chain structures and

device engineering through processing additives, PC70BM,

solvent or thermal annealing, etc.

Conclusion

A new DTBTz-containing poly(2,7-carbazole) derivative,

PCDTBTz, was designed and synthesized. This polymer

combines good thermal stability, excellent solubility and

air-stability. Preliminary investigationsonthephotovoltaic

device based on PCDTBTz:PC60BM bulk heterojunction

demonstrated a promisingly high power conversion

efficiency of up to 2.2%. The high Voc of 0.92V from

PCDTBTz-based device originates from the lower HOMO

level of the polymer. These results show that PCDTBTz is a

highly promising polymermaterial for its use in solar cells,

considering the low-molecular-weight and relatively high

energy gap of this polymer. The DTBTz unit is probably an

important new accepting building block to construct D–A

copolymers for printed electronics. Improvement in the

photovoltaicperformancecanbeexpectedbyextendingthe

absorption of theDTBTz-containing copolymers, increasing

the molecular weight, modification of the side-chain

structures and optimization of the device. Further inves-

tigations of the properties of PCDTBTz and further

syntheses of newDTBTz-containing polymers are currently

in progress and will be reported in due course.

Acknowledgements: Helpful assistance from Dr. Dequan Xiaofrom Yale University is acknowledged. This work was supportedby the National Natural Science Foundation for DistinguishedYoung Scholar (50825102), the National Natural Science Founda-tion of China (NO. 50803074), the Lieying Project, theOpening Fundof State Key Laboratory of PowderMetallurgy and start-up funds ofCentral South University.

Received: June 3, 2010; Published online: August 16, 2010; DOI:10.1002/macp.201000315

DOI: 10.1002/macp.201000315


Keywords: conjugated polymers; dithienylbenzotriazoles; poly-mer solar cells; Suzuki coupling reaction; synthesis

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