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Planar Conjugated Polymers Containing 9,10-Disubstituted Phenanthrene Units for Efficient Polymer Solar Cells Guangwu Li, Chong Kang, Cuihong Li,* Zhen Lu, Jicheng Zhang, Xue Gong, Guangyao Zhao, Huanli Dong, Wenping Hu, Zhishan Bo*

Four novel conjugated polymers (P1-4) with 9,10-disubstituted phenanthrene (PhA) as the donor unit and 5,6-bis(octyloxy)benzothiadiazole as the acceptor unit are synthesized and characterized. These polymers are of medium bandgaps (2.0 eV), low-lying HOMO energy levels (below −5.3 eV), and high hole mobilities (in the range of 3.6 × 10−3 to 0.02 cm2 V−1 s−1). Bulk heterojunction (BHJ) polymer solar cells (PSCs) with P1-4:PC71BM blends as the active layer and an alcohol-soluble fullerene derivative (FN-C60) as the interfacial layer between the active layer and cathode give the best power conversion efficiency (PCE) of 4.24%, indicating that 9,10-disubstituted PhA are potential donor materials for high-efficiency BHJ PSCs.

1. Introduction Polymer solar cells (PSCs), whose active layer is composed of a blend of donor and acceptor in a bulk heterojunction (BHJ) structure, have attracted particular interest due to their apparent advantages of easy processing, potential low-cost production, and large area with mechanical flexibility.[1–7] Up to now, BHJ structure, which is a phaseseparated bicontinuous network formed by blending electron-rich polymer donor and electron-deficient fullerene derivative acceptor such as (6,6)-phenyl-C61-butyric acid methyl ester (PC61BM) or (6,6)-phenyl-C71-buG. Li, C. Kang, Dr. C. Li, Dr. Z. Lu, J. Zhang, X. Gong, Prof. Z. Bo Beijing Key Laboratory of Energy Conversion and Storage Materials, College of Chemistry, Beijing Normal University, Beijing 100875, China E-mail: [email protected]; [email protected] G. Zhao, Dr. H. Dong, Prof. W. Hu Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China

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tyric acid methyl ester (PC71BM), has been proven to be the most efficient device structure. Considerable efforts have been devoted to the optimization of polymer and device structures to achieve higher power conversion efficiency (PCE).[8–12] High-efficiency PSCs require that the donor polymers should have a broad and intense absorption to effectively absorb the sunlight, appropriate the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels to match those of acceptors, good solubility in organic solvents to endow the polymers with solution processability, and relatively planar polymer structure to allow polymer chains to pack in the solid state to have higher hole mobility.[13–16] Main chain donor–acceptor alternating structure is a very promising design style that makes the tuning of the absorption and energy levels of polymers easier. Benzothiadiazole is a commonly used acceptor unit for the synthesis of D–A alternating conjugated polymers for high-efficiency PSCs. In these benzothiadiazolecontaining D–A-conjugated polymers, carbazole,[13,17] fluorene,[18–21] silafluorene,[22,23] dibenzothiophene,[24,25]

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DOI: 10.1002/marc.201400044

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Planar Conjugated Polymers Containing 9,10-Disubstituted Phenanthrene Units for Efficient Polymer Solar Cells

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dithienosilole,[26] dithienobenzene,[27–31] thiophene,[32,33] and so on have been used as the donor unit. Phenanthrene (PhA), which possesses a planar structure, is one of the most stable fused aromatics, high hole mobility is therefore expected for PhA-based planar D–A polymers. However, only a few conjugated oligomers or polymers containing PhA have been reported to date, which might be due to its poor solubility.[34–37] In this work, we design and synthesize four D–A alternating copolymers (P1-4) with 9,10-disubstituted PhA as the donor unit and 5,6-bis(octyloxy)benzothiadiazole as the acceptor unit. The attachment of two alkoxy chains on the 9,10-positions of PhA can improve the solubility of the polymers in organic solvents, while does not hinder the π–π stacking of polymer chains in solid films. These polymers exhibit high hole mobility with the best one up to 0.02 cm2 V−1 s−1. BHJ PSCs with these polymers as the donor and PC71BM as the acceptor have been fabricated. Under simulated solar illumination of AM 1.5G (100 mW cm−2), the best PCE of 4.24% has been achieved for P2:PC71BM-based PSCs.

2. Results and Discussion 2.1. Material Synthesis and Characterization The syntheses of monomers (4a-d) and polymers (P1-4) are outlined in Scheme 1. 2,7-Dibromophenanthrene9,10-dione (2) was synthesized according to the literature procedures.[24] In DMF solution, compound 2 was reduced by Na2S2O4 to afford the diol, which was used for next step without further purification. The reaction of the crude diol with 1-bromoalkane under K2CO3/DMF conditions with NBu4Br as the phase-transfer catalyst afforded 2,7-dibromo-9,10-bis(alkyloxy)phenanthrene in a yield of 45%–56%. Miyaura reaction of 3a-c with bis(pinacolato) diboron at 80 °C using PdCl2(dppf) as the catalyst precursor afforded the diboronic acid pinacol ester 4a-c in a yield 44–82%. The treatment of 1-bromo-4-(octyloxy) benzene with n-BuLi in THF at −78 °C afforded the carbon anion, which was quenched by compound 2. The formed diol was reduced with Zn in a mixture of HOAc and HCl to give the dibromide 3d in a yield of 29%. Miyaura reaction of 3d and bis(pinacolato)diboron at 80 °C afford 4d in a yield of 61%. 4,7-Bis(5-bromothiophen-2-yl)5,6-bis(octyloxy)benzo[c][1,2,5]thiadiazole (5) was synthesized according to our previous work.[13] Suzuki–Miyaura polymerizations of 4a-d with 5 were carried in a twophase mixture of THF and toluene (3:1)/aqueous NaHCO3 with Pd(PPh3)4 as the catalyst precursor. Phenylboronic acid and bromobenzene were used to cap the end-groups of polymers. Polymers (P1-4), which were obtained as dark red solids in yields of 70%–84%, were fully soluble

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O

O

O i

Br

ii

Br

1

Br diol

R

R

Br

Br

iv

O B O

3a, 4a: R = octyloxy 3b, 4b: R = 2-ethylhexyloxy 3c, 4c: R = 2-hexyldecyloxy OC8H17

4

C8H17O

OC8H17

O B O

O B O

iv

Br

Br

R

O B O

3

C8H17O OC8H17 v, vi, vii

Br 3d

Br

C8H17O S

OC8H17 S

OH

Br

2 R

iii

HO

O

Br + 4 viii

N N S 5

C8H17O S

OC8H17 S

4d R

R

N N S P1: R = octyloxy P2: R = 2-ethylhexyloxy P3: R = 2-hexyldecyloxy P4: R = 4-(octyloxy)phenyl

n

Scheme 1. Synthesis of monomers and copolymers. Reagents and conditions: i) NBS, H2SO4, rt; ii) Na2S2O4, DMF, 60 °C; iii) K2CO3, NBu4Br, C8H17Br, 60 °C; iv) PdCl2(dppf), KOAc, bis(pinacolato) diboron, DMF, 80 °C; v) n-BuLi, THF, −78 °C; vi) 2, −78 °C; vii) Zn, AcOH, HCl, reflux; viii) Pd(PPh3)4, NaHCO3, THF/toluene (v/v, 3:1)/ H2O, reflux.

in chlorobenzene (CB), 1,2-dichlorobenzene (DCB), and 1,2,4-trichlorobenzene (TCB) at elevated temperature. Molecular weights and molecular weight distributions of P1-4 were measured by gel permeation chromatography (GPC) at 150 °C using TCB as an eluent with narrowly distributed polystyrenes as the calibration standard, and the results are summarized in Table S1 (Supporting Information). The number-average molecular weights (Mn ) of P1-4 are 23.9, 30.0, 56.9, and 42.8 kg mol−1, respectively. Polydispersity indexes (PDI) of P1-4 are 2.24, 2.95, 2.30, and 1.86, respectively. The results indicated that high-molecularweight polymers are obtained. Polymers (P1-4) are of good thermal stability and thermogravimetric analysis (TGA) indicated that the 5% decomposition temperature under a nitrogen atmosphere are 318, 323, 327, and 325 °C, respectively. Differential scanning calorimetry (DSC) measurements indicated that there is no obvious glass transition can be observed for P1-4 in the range of 20 to 300 °C. X-ray diffractions (XRD) of P1-4 powdery samples were measured to investigate the packing of polymer chains in the solid state. As shown in Figure S1 (Supporting Information), all polymers present a broad diffraction peak at the wide-angle region, reflecting the π–π distance between the polymer backbones, which

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chain aggregations in DCB solution at elevated temperature. The aggregation as film 1.0 1.0 of P1 polymer chains in DCB solution at P1 P1 0.8 0.8 room temperature was also confirmed P2 P2 P3 0.6 0.6 P3 by comparing its solution absorption P4 P4 spectrum with its film one. The film 0.4 0.4 absorption spectrum of P1 is almost 0.2 0.2 superimposed with its solution one at 0.0 0.0 room temperature. Different from P1, 400 450 500 550 600 650 700 400 450 500 550 600 650 700 as shown in Figure S3b–d (Supporting Wavelength(nm) Wavelength(nm) Information), the absorption spectra for Figure 1. UV–vis absorption spectra of P1-4 in a) DCB solutions at 25 °C and b) as thin P2-4 in dilute DCB solutions at 100 °C films. are similar to the corresponding spectra at 25 °C, indicating there is no obvious aggregation for P2-4 in DCB solutions. Compared with were 4.12 Å for P1, 4.33 Å for P2, 4.40 Å for P3, and 4.36 Å solution absorption spectra, the film ones of P2-4 are for P4. Such short distances indicate that the polymer broader and red-shifted. On going from solution to film, backbones possess a relatively planar conformation and the low energy absorption peak at the long wavelength the flexible side chains do not significantly interfere the region is red-shifted from 510 to 526 nm for P2, from 523 closely packing of polymer chains in the solid state. to 552 nm for P3, and from 520 to 560 nm for P4, indicating the formation of aggregation for polymer chains in 2.2. Optical Properties solid films. The absorption onsets of P1-4 as thin films are 614, 608, 609, and 613 nm, respectively. The optical bandUV–vis absorption spectra of polymers P1-4 in dilute gaps (Eg,opt) of P1-4 are therefore calculated to be 2.02, DCB solutions and as thin films are shown in Figure 1 and the data are summarized in Table 1. At 25 °C, P1 in 2.04, 2.03, and 2.02 eV, respectively. dilute DCB solution displays a broad absorption with two peaks located at about 397 and 540 nm with a shoulder 2.3. Electrochemical Properties peak at 563 nm. Generally, an absorption red-shift can be observed on going from solution to film for many The HOMO and LUMO energy levels of polymers, which conjugated polymers due to the aggregation of polymer are closely related to the photovoltaic performance of chains in the solid state. However, the absorption bands PSCs, can be determined by electrochemical method. at 385 and 556 nm for P1 in film do not show obvious The electrochemical properties of P1-4 as thin films on red-shift in comparison with their solution ones. The a platinum electrode in 0.1 M Bu4NPF6 acetonitrile soluresult indicated that P1 probably already formed aggretion at a scan rate of 100 mV s−1 were investigated by gations in DCB solution. Therefore, absorption spectra of cyclic voltammetry (CV). As shown in Figure S2 (SupP1 in DCB solution at about 100 °C were also measured porting Information), the onset oxidation potentials to investigate whether the polymer chains can be disso(Eox) of P1-4 are 0.61, 0.70, 0.72, and 0.64 V, respectively, ciated at elevated temperature. As shown in Figure S3a versus Ag/AgCl reference electrode. The oxidation peaks (Supporting Information), the absorption band of P1 in in the CV curves are attributed to the oxidation of the the range of 450 to 650 nm becomes narrower and bluePhA donor unit in the conjugated polymers. The HOMO shifted at 100 °C, indicating the dissociation of polymer energy levels of polymers were calculated according to (a)

Normalized absorbance (a.u.)

Normalized absorbance (a.u.)

(b)

in DCB

Table 1. Physical, electronic, optical, and FET properties of P1-4.

Polymer

P1

λmax solution [nm]a)

λmax film [nm]

Eg,opt [eV]b)

HOMO [eV]

LUMOopt, [eV]c)

Ion/Ioff

μ [cm2 V−1 s−1]

Threshold voltages VT [V]

397, 540

385, 556

2.02

−5.32

−3.30

1.3 × 106

6.1 × 10−3

−15

−3

−35

P2

382, 510

389, 526

2.04

−5.41

−3.37

6.0 × 10

5.1 × 10

P3

384, 523

390, 552

2.03

−5.43

−3.40

2.7 × 105

3.6 × 10−3

−27

2.02

−5.35

−3.30

1.2 ×

0.02

−30

P4

391, 520

396, 560

4

105

a) Measured at 100 °C; b)Calculated from the absorption band edge of the copolymer film, Eg,opt = 1240/λedge; c)Calculated by the equation ELUMO =EHOMO + Eg,opt.

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2 Current Intensity(mA/cm2)

the equation EHOMO = −(Eox + 4.71) (eV) to be −5.32 eV for P1, −5.41 eV for P2, −5.43 eV for P3, and −5.35 eV for P4. From Eg,opt and HOMO energy levels, LUMO energy levels of P1-4 are estimated to be −3.30, −3.37, −3.40, and −3.30 eV, respectively, using the equation ELUMO = EHOMO + Eg,opt, and the data are also summarized in Table 1. It is worthy noting that P1-4 possess low-lying HOMO energy levels, and therefore high Voc is expected for BHJ PSCs with these polymers as donor and PC71BM as acceptor since Voc is related to the difference between the HOMO energy level of donor and the LUMO energy level of acceptor.

0 -2

P1:PC71BM (DCB,0.5% DIO) P2:PC71BM (DCB) P3:PC71BM(DCB,0.5% DIO) P4:PC71BM(DCB, 0.25% DIO)

-4 -6 -8 -0.2

0.0

0.4

0.6

0.8

1.0

Voltage(V)

2.4. Transport Properties Hole transport properties of polymers were investigated by fabrication of field-effect transistors (FETs). Bottomcontact devices were fabricated on Si/SiO2 substrates with the low-resistance Si as gate and SiO2 (500 nm) as gate insulator. Polymer thin films were spin-coated on the OTSmodified Si/SiO2 substrates from DCB solutions, and Au electrodes with a thickness of 25 nm were vacuum deposited on polymer thin films. The hole mobility (μ) was estimated in the saturated regime from the derivative plots of the square root of source-drain current (ISD) versus gate voltage (VG) through the equation ISD = (W/2L)Ciμ(VG −VT)2, where W is the channel width, L is the channel length, Ci is the capacitance per unit area of the gate dielectric layer (SiO2, 500 nm, Ci = 7.5 nF cm−2), and VT is the threshold voltage. Hole mobilities of P1, P2, P3, and P4 reached 6.1 × 10−3, 5.1 × 10−3, 3.6 × 10−3, and 0.02 cm2 V−1 s−1, and on/ off ratios of P1, P2, P3, and P4 were 1.3 × 106, 6.0 × 104, 2.7 × 105, and 1.2 × 105, respectively. The transfer characteristic and output characteristic of the OFET are shown in Figure S4 (Supporting Information) and the data are also summarized in Table 1. The high hole mobility of P4 is probably attributed to its high molecular weight and the extending of lateral conjugation by the introduction of two 4-octyloxyphenyl groups on the PhA unit.[38–40] 2.5. Photovoltaic Properties Devices used for the evaluation of the photovoltaic performances of polymers were fabricated with two different configurations, which are indium tin oxide (ITO)/ poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate (PEDOT:PSS)/active layer/LiF/Al and ITO/PEDOT/active layer/FN-C60/Al. Thicknesses of PEDOT:PSS layer, LiF layer, FN-C60 interfacial layer, and Al electrode are about 40, 0.6, 5, and 100 nm, respectively. FN-C60 is an alcoholsoluble fullerene derivative developed by our group, and the use of FN-C60 as an interfacial layer between the active layer and cathode can significantly improve the performance of PSCs.[25] The structure of FN-C60

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0.2

Figure 2. J–V curves for BHJ PSCs based on P1:PC71BM (1:3 by weight, ODCB), P2:PC71BM (1:3 by weight), P3:PC71BM (1:2 by weight), and P4:PC71BM (1:4 by weight) under the illumination of AM1.5G, 100 mW cm−2. The device structure is ITO/Polymer:PC71BM/FN-C60/Al.

was shown as Scheme S1 (Supporting Information). To achieve the best device performance, we have screened the weight ratio of polymer to PC71BM, the concentration of blend solution, the spin-coating speed, and the volume of 1,8-diiodooctane (DIO) additive. Typical current density–voltage (J–V) curves of PSCs with the blends of polymer and PC71BM as the active layer under 1 sun of simulated AM 1.5G solar radiation (100 mW cm−2) are shown in Figure 2 and Figure S5 (Supporting Information). The photovoltaic parameters are summarized in Table 2. After optimization, solar cells fabricated with the blends of P1 and PC71BM in a weight ratio of 1:3 in DCB solutions gave the best device performance. In a device structure of ITO/PEDOT:PSS/P1:PC71BM (1:3)/LiF/ Al, a PCE of 3.0% with a Voc of 0.79 V, a Jsc of 7.03 mA cm−2, and an FF of 0.54 was achieved. The addition of DIO (0.5% by volume) as the processing additive had no obvious positive effect on the photovoltaic performance and a PCE of 3.1% with a Voc of 0.83 V, a Jsc of 7.0 mA cm−2, and an FF of 0.53 was obtained. When FN-C60 was used as the interfacial layer between the active layer and the cathode, the PCE was further enhanced to 3.63% with a Voc of 0.91 V, a Jsc of 6.74 mA cm−2, and an FF of 0.59. Significantly, the increase of Voc is about 10%. The high Voc for P1-based PSCs was attributed to its low-lying HOMO energy level. For P2, the best photovoltaic performance was achieved from devices fabricated from DCB solutions with P2:PC71BM (1:3) as the active layer spin-coated and FN-C60 as the interfacial layer. A PCE of 4.24% with a Voc of 0.96 V, a Jsc of 7.7 mA cm−2, and an FF of 0.57 was achieved. The use of processing additive such as DIO or 1-chloronaphthalene (1-CN) does not markedly enhance the photovoltaic performance of P2:PC71BMbased devices. For P3, a PCE of 3.10% with a Voc of 0.94 V,

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Table 2. Summary of the photovoltaic properties of BHJ PSCs based on P1:PC71BM (1:3 by weight), P2:PC71BM (1:3 by weight), P3:PC71BM (1:2 by weight), and P4:PC71BM (1:4 by weight) under the illumination of AM1.5G, 100 mW cm−2. The device structure is ITO/Polymer:PC71BM/interfacial layer/Al. The film thickness of the blend is about 100 nm.

The active layer P1:PC71BM (1:3 by weight)

P2:PC71BM (1:3 by weight) P3:PC71BM (1:2 by weight)

The interfacial layer LiF

Solvent

Voc [V]

Jsc [mA cm−2]

DCB

0.79

7.03

0.54

3.0%

0.83

7.0

0.53

3.1%

FN-C60

DCBa)

0.91

6.74

0.59

3.63%

LiF

DCB

0.90

7.7

0.53

3.66%

FN-C60

DCB

0.96

7.7

0.57

4.24%

LiF

DCB

0.79

5.2

0.58

2.37%

0.81

5.3

0.58

2.49%

DCB

a)

FN-C60

DCB

0.94

5.3

0.63

3.10%

LiF

DCB

0.76

7.51

0.50

2.82%

b)

0.88

8.16

0.47

3.38%

b)

0.94

7.66

0.57

4.10%

DCB FN-C60 a)Containing

DCB

DIO (0.5% by volume); b)Containing DIO (0.25% by volume).

a Jsc of 5.3 mA cm−2, and an FF of 0.63 was achieved from devices fabricated with P3:PC71BM (1:2) as the active layer, FN-C60 as the interfacial layer, and DIO (0.5% by volume) as the processing additive. For P4, devices fabricated with P4:PC71BM (1:4) as the active layer and pure DCB as the solvent gave a PCE of 2.82% with a Voc of 0.76 V, a Jsc of 8.16, and an FF of 0.50. When 0.25% DIO was used as the additive for DCB, the PCE was increased to 3.38%. When FN-C60 was used as the interfacial layer instead of LiF, the PCE was furthered enhanced to 4.10% with the Voc reached 0.94 V. The increase of Voc for P1-4based solar cells was attributed, at least partially, to the obvious decrease of the contact resistance between the active layer and Al cathode with using FN-C60 as the interfacial layer.[25] External quantum efficiencies (EQEs) of P1- and P2-based BHJ PSCs were measured under the monochromatic light illumination to verify the accuracy of Jsc results obtained from J–V measurements. EQE measurements for P1- and P2-based devices, which were fabricated under the optimized conditions, were carried out to investigate the influence of the interfacial layer. EQE curves of P1:PC71BM (1:3 by weight)-based PSCs, which were fabricated by spin-coating form DCB solutions containing 0.5% DIO as the processing additive with LiF or FN-C60 as the interfacial layer, are shown as Figure S6a (Supporting Information). EQE curves of BHJ PSCs with P2:PC71BM (1:2 by weight) as the active layer spin-coated from DCB solutions containing 0.25% DIO additive using LiF or FN-C60 as the interfacial layer are shown in Figure S6b (Supporting Information). For all devices, significant photo-to-current responses were observed in the range of 350 to 720 nm and EQE values are between 40% and 60% from 350 to 600 nm. The integration of the EQE with an

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PCE

DCBa)

a)

P4:PC71BM (1:4 by weight)

FF

AM 1.5G reference spectrum can afford Jsc, which agreed roughly with the Jsc obtained from the J–V measurements for PSC devices.

2.6. Film Morphologies The morphology of polymer:PC71BM blend films, which have a significantly influence on exciton separation, charge carrier mobility, and photovoltaic performance, was investigated by atomic force microscopy (AFM) in tapping mode. AFM images of P1:PC71BM (1:3 by weight), P2:PC71BM (1:3 by weight), P3:PC71BM (1:2 by weight), and P4:PC71BM (1:4 by weight) blend films fabricated from DCB solutions with and without DIO are shown in Figure S7 (Supporting Information). All blend films showed nanoscale phase separation. As shown in Figures S7a,b (Supporting Information), the domain size of P1:PC71BM (1:3 by weight) blend films became apparently larger with the root-mean-square (rms) surface roughness increasing from 0.400 nm for DCB solutions without DIO to 0.884 nm for DCB solutions containing 0.5% DIO. As shown in Figure S7c,d (Supporting Information), the surface of P2:PC71BM (1:3 by weight) blend films got rougher, the domain size became larger, and the rms value increased from 0.57 to 1.56 nm after the use of 0.25% DIO as the additive for DCB. As shown in Figure S7e,f (Supporting Information), the addition of 0.5% DIO as the additive for DCB, P3:PC71BM (1:2 by weight) blend films exhibited better phase separation with the domain size became smaller and the rms value decreased from 1.11 nm (without DIO) to 0.827 nm (with 0.5% DIO). As illustrated in Figure S7g,h (Supporting Information), P4:PC71BM (1:3 by weight) blend films

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fabricated from DCB solutions with and without DIO showed similar nanoscale phase separation. The rms roughness values of blend films were slightly decreased from 0.900 to 0.776 nm with the addition of 0.25% DIO. The AFM results are quite consistent with the device results.

3. Conclusions Novel D–A alternating conjugated polymers (P1-4) with 9,10-disubstituted phenanthrene as the donor unit and 5,6-bis(octyloxy)benzothiadiazole as the acceptor unit have been synthesized and used as donor materials for BHJ PSCs. High-molecular-weight polymers with Mw in the range of 53.6 to 131.1 kg mol−1 were obtained by using Suzuki polycondensation. These polymers are of deep HOMO levels and medium optical bandgaps in the range of 2.02 to 2.05 eV. Hole mobilities of P1-4, which were measured by fabrication of FET devices, are in the range of 3.6 × 10−3 to 0.02 cm2 V−1 s−1. BHJ PSCs with blends of P1-4 and PC71BM as active layers demonstrated the best PCE of 4.24%, indicating PhA-based conjugated polymers are promising donor materials for BHJ PSCs.

Supporting Information Supporting Information is available from the Wiley Online Library or from the author. Acknowledgements: The authors thanks for the financial support by the NSF of China (91233205, 51003006, and 21161160443), Beijing Natural Science Foundation (2132042), the 973 Programs (2011CB935702), and the Fundamental Research Funds for the Central Universities. Received: January 21, 2014; Revised: March 3, 2014; Published online: April 4, 2014; DOI: 10.1002/marc.201400044 Keywords: conjugated polymers; donor materials; phenanthrene; polymer solar cells [1] J. Y. Kim, K. Lee, N. E. Coates, D. Moses, T. Q. Nguyen, M. Dante, A. J. Heeger, Science 2007, 317, 222. [2] D. Gendron, M. Leclerc, Energ. Environ. Sci. 2011, 4, 1225. [3] F. C. Krebs, Sol. Energ. Mater. Sol. C. 2009, 93, 394. [4] J. W. Chen, Y. Cao, Acc. Chem. Res. 2009, 42, 1709. [5] X. W. Zhan, D. B. Zhu, Polym. Chem. 2010, 1, 409. [6] C. J. Brabec, S. Gowrisanker, J. J. M. Halls, D. Laird, S. J. Jia, S. P. Williams, Adv. Mater. 2010, 22, 3839. [7] M. T. Dang, L. Hirsch, G. Wantz, Adv. Mater. 2011, 23, 3597. [8] Z. C. He, C. M. Zhong, X. Huang, W. Y. Wong, H. B. Wu, L. W. Chen, S. J. Su, Y. Cao, Adv. Mater. 2011, 23, 4636. [9] W. Li, A. Furlan, K. H. Hendriks, M. M. Wienk, R. A. J. Janssen, J. Am. Chem. Soc. 2013, 135, 5529. [10] J. You, C. C. Chen, Z. Hong, K. Yoshimura, K. Ohya, R. Xu, S. Ye, J. Gao, G. Li, Y. Yang, Adv. Mater. 2013, 25, 3973.

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Macromol. Rapid Commun. 2014, 35, 1142−1147 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Planar conjugated polymers containing 9,10-disubstituted phenanthrene units for efficient polymer solar cells.

Four novel conjugated polymers (P1-4) with 9,10-disubstituted phenanthrene (PhA) as the donor unit and 5,6-bis(octyloxy)benzothiadiazole as the accept...
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