Synthesis and photovoltaic performance of novel polymeric metal complex sensitizer with benzodithiophene or carbazole derivative as donor in dye-sensitized solar cell

Accepted Manuscript Synthesis and photovoltaic performance of Novel Polymeric Metal Complex Sensitizer with Benzodithiophene or Carbazole Derivative as Donor in Dye-Sensitized Solar Cell Yanlong Liao, Jiaomei Hu, Chunxiao Zhu, Ye Liu, Xu Chen, Chenqi Chen, Chaofan Zhong PII:

S0022-2860(15)30509-3

DOI:

10.1016/j.molstruc.2015.12.021

Reference:

MOLSTR 22054

To appear in:

Journal of Molecular Structure

Received Date: 25 July 2015 Revised Date:

8 December 2015

Accepted Date: 8 December 2015

Please cite this article as: Y. Liao, J. Hu, C. Zhu, Y. Liu, X. Chen, C. Chen, C. Zhong, Synthesis and photovoltaic performance of Novel Polymeric Metal Complex Sensitizer with Benzodithiophene or Carbazole Derivative as Donor in Dye-Sensitized Solar Cell, Journal of Molecular Structure (2016), doi: 10.1016/j.molstruc.2015.12.021. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Synthesis and photovoltaic performance of Novel Polymeric Metal Complex Sensitizer with Benzodithiophene or Carbazole Derivative as Donor in Dye-Sensitized Solar Cell

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Yanlong Liao, Jiaomei Hu, Chunxiao Zhu, Ye Liu, Xu Chen, Chenqi Chen, Chaofan Zhong*

Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry

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of Education, College of Chemistry, Xiangtan University, Xiangtan, Hunan 411105,

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China

*Corresponding author: Tel: +86 731 58292202; Fax: +86 731 58292251

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Email address: [email protected]

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ACCEPTED MANUSCRIPT Abstract

Four donor-acceptor (D-A) types of novel conjugated polymeric metal

complex dyes (P1-P4) with

Zn (II) or Cd (II)

complexes as the electron acceptors

and benzodithiophene or carbazole derivative as the electron donors were designed

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and prepared, as promising sensitizers for dye-sensitized solar cells (DSSCs). Diaminomaleonitrile acted as ancillary ligand. The structures of the polymers were confirmed, and their thermal, optical, electrochemical, and photovoltaic properties

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were investigated. All conjugated polymers exhibit good thermal stability with onset

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decomposition temperatures with 5% weight loss over 315 ºC, broad absorption with the onset of absorption at 588 nm in the visible region, and relatively lower HOMO energy levels from -5.54 to -5.71 eV. The DSSC device based on P2 which containing Cd(II) as coordination metal ion and benzodithiophene derivative as donor exhibited

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the highest power conversion efficiency of 2.18% under the AM 1.5 G (100 mW cm-2) sunlight illumination with an open-circuit voltage of Voc=0.68 V, a short current density of Jsc= 4.85 mA cm-2, and a fill factor of FF=66.2%, respectively. Therefore,

dyes,

metal-polymer

complexes,

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Keywords:

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these results provide a new way to design dye sensitizers for DSSCs.

photochemistry

2

synthesis,

polymerization,

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1. Intronduction As one of the most promising next-generation photovoltaic cells, dye-sensitized solar cells have been a focus of much research since they were first reported by in

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1991 with a power conversion efficiency of 7% [1]. They possess an ability to convert sunlight to electricity at a low cost. Besides, they show potential advantages of easy production, flexibility, and transparency in comparison with conventional

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silicon solar cells [2-3]. Recently, a high-performance perovskite-sensitized solar cell

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with the power conversion efficiency over 15% has been reported [4].

Among the key components of a DSSC, the sensitizer plays as one of the most crucial elements since it exerts a significant influence on the power conversion efficiency as well as the device stability. Ruthenium complex dyes are the typical

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metal-organic dyes, to date, a ruthenium complex sensitized DSSC has reached an excellent conversion efficiency of 11.5% recorded as CYC-B11 [5]. But the development of this type of dye sensitizers is impeded for the limited resource and the

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high cost of the rare metals [6]. Thus, the search for new efficient metal-free dyes

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remains an active aspect of DSSC development. Organic dyes have some advantageous features, such as low cost, diversity of molecular structures, high molar extinction coefficient. However, the performance of organic dyes remains inferior to ruthenium metal complexes in terms of efficiency and stability [7]. In comparison with metal-free organic small molecule dyes, conjugated polymers possess considerable importance because of their large absorption coefficients and tunable band gaps that span the whole visible and NIR region [8]. So, it seems important to 3

ACCEPTED MANUSCRIPT find appropriate substitute metals and macromolecular structure. Hence, the idea of polymeric metal complex dyes used for DSSCs has great appeal. This kind of metal–organic hybrid polymer materials combining polymers and metals into

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metallopolymers that exhibit as many advantages. The strong interaction between organic and inorganic components creates unique electrochemical, photophysical and

for applications in solar energy conversion [9].

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photochemical properties, which make these conjugated polymers potential materials

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In this study, we report the synthesis and characterization of four novel polymeric metal complexes used as dye-sensitizer for DSSCs, which feature push-pull molecular structure [10]. The benzodithiophene or carbazole derivatives are used as electron donor (D). The electron-rich benzodithiophene derivatives are an attractive

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building block due to its symmetric, rigid, and coplanar structure, which have a central benzene ring fused with two thiophenes. It is crucial to induce strong intermolecular π−π interaction for efficient charge transport [11]. Carbazole

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derivatives are also usually used as electron donor in dye molecular due to the

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electron-rich nitrogen heteroatom [12]. Ethylenediamine derivatives complexes are used as electron acceptor (A). Diaminomaleonitrile acts as ancillary ligand. Introduction of CN groups aims to enhance the electron-withdrawing ability of electron acceptor part, and to facilitate the electron injection between the dyes and TiO2 surface [13]. Zn (II) or Cd (II) is chosen as the coordinated metal ion for their low cost and easy to get. What’s more, their thermal, optical, photovoltaic and electrochemical properties in DSSCs were also investigated. 4

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2. Experimental 2.1. Materials All starting materials were obtained from Shanghai Chemical Reagent Co. Ltd

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(Shanghai China) and were used without further purification. THF and DMF were dried by distillation over CaH2. All other reagents and solvents were commercially

2.2. Instruments and measurements 1

H NMR and

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prepared according to the literature methods.

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purchased and were used as received. 3,6-dibromo-N-otylcarbazole (3) [14] was

C NMR spectra were obtained in CDCl3 and recorded with a

Bruker ARX400 (400 MHz) Germany, and the spectra were referenced against tetramethylsilane (δ=0.00 ppm) as the internal standard. Molecular mass was

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determined by matrixassisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) using a Bruker Aupoflex-III mass spectrometer.

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FT-IR spectra were recorded using KBr pellets with a PerkinElmer Spectrum One FT-IR spectrometer. The UV-Vis absorption spectra were measured with Lambda 25H

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spectrometer. Samples were dissolved in DMF and diluted to a concentration of 10-510-4 mol.L-1. Gel Permeation Chromatography (GPC) analyses were performed on WATER 2414 system equipped with a set of HT3, HT4 and HT5, l-styrayel columns with DMF as eluent, and polystyrene was used as standard. Elemental analysis for C, H, N was performed on Perkin-Elmer 2400 II instrument under nitrogen atmosphere. Thermogravimetric analyses (TGA) and Differential Scanning Calorimetry (DSC) were conducted on Shimadzu TGA-7 Instrument and Perkin-Elmer DSC-7 thermal 5

ACCEPTED MANUSCRIPT analyzer at a heating rate of 20 ºC min-1 from 25 to 600 ºC in nitrogen atmosphere, respectively. Electrochemical redox potentials were obtained by cyclic voltammetry (CV), and conducted on a CHI630C electrochemistry workstation in a [Bu4N]BF4 (0.1

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mol L-1) CH3CN solution at 100 mV s-1 at room temperature. The working electrode was a glassy carbon electrode, the saturated calomel electrode (SCE) was used as

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reference electrode, and the auxiliary electrode was a platinum wire electrode.

2.3. Fabrication of DSSCs

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The DSSCs devices with sandwich structure in this paper are based on TiO2 semiconductors. Titania paste was prepared following a procedure: fluorine-doped SnO2 conducting glass (FTO) were cleaned and immersed in aqueous 40 mmol L-1 TiCl4 solution at 70 ºC for 30 min. The 20–30 nm particles sized TiO2 colloid was

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coated onto the above FTO glass by the sliding glass rod method and following sintered at 450 ºC for 30 min which been done for three times to obtain a TiO2 film of

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10-15 µm thickness. After cool to 100 ºC, the TiO2 films were soaked in 0.5 mmol L-1 dye samples in DMF solution and maintained under dark for 24 h at room temperature.

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Then the film were cleaned by anhydrous ethanol. After drying, electrolyte containing LiI (0.5 mol L-1), I2 (0.05 mol L-1) and 4-tert-butylpyridine (0.5 mol L-1) was dripped on the surface of TiO2 electrodes. A Pt foil was used as counter electrode was clipped onto the top of the TiO2. The dye-coated semiconductor film was illuminated through a conducting glass support without a mask. The photoelectron chemical performance of the solar cell was measured using a Keithley 2602 Source meter controlled by a computer. The cell parameters were obtained under an incident light with intensity 6

ACCEPTED MANUSCRIPT 100 mW cm-2, which was generated by a 500-W Xe lamp passing through an AM 1.5 G filter with an effective area of 0.2 cm2.

2.4. Synthesis

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2.4.1. Synthesis of N,N’-bis(4-(bromobenzylidene)ethane-1,2-diamine [15] (1)

4-brombenzaldehyde (5.55 g, 30 mmol) was dissolved in ethanol in a

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three-necked flask, followed by the addition of a solution of ethylenediamine (1 ml, 15 mmol) in ethanol (15ml) with stirring. The resulting reaction mixture was refluxed

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for 4h. The white precipitate obtained was filtered, washed with ethanol and dried under vacuum. Yield (4.82 g, 81%). FTIR (KBr, cm-1): 3024, 2913, 2854, 1648, 1586, 678. 1H NMR (CDCl3, δ, ppm): 8.21 (s, 2H), 7.50-7.56 (m, 8H), 3.95 (s, 4H).

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NMR (CDCl3, δ, ppm): 61.44 (s, 2C, CH2), 125.11-134.96 (s, 12C, Ph), 161.49 (s, 2C,

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CH=N). Anal. Calcd. for [C16H14Br2N2]: C, 48.76; H, 3.58; N, 7.11. Found: C, 48.72; H, 3.61; N, 7.13%. MALDI-TOF MS [C16H14Br2N2]

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395.060.

m/z: Calcd. for 394.950; found

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2.4.2. Synthesis of metal complex [16] (C1) A ethanol solution (30ml) of Zn(CH3COO)2·2H2O (0.35 g, 1.5 mmol) was

slowly dropped into a mixture of (1) (0.59 g, 1.5 mmol) and

diaminomaleonitrile

(0.16 g, 1.5 mmol) in THF (20 ml) with stirring and refluxing. Then 1 mol L-1 NaOH was added dropwise under stirring until the solution show weakly acidic. After the solutiom was refluxed for 10h, the reaction system was then allowed to cool to room temperature. The precipitate was collected by filtration, washed with ethanol several 7

ACCEPTED MANUSCRIPT times and then dried in vacuum. A brown solid was collected (0.61 g, 59%). FTIR (KBr, cm-1): 3433(N-H), 3069(=C-H), 2945, 2886(C-H), 2226(C≡N), 1645(C=N), 1064(C=N-M), 515(N-M). Anal. Calcd. for [C24H24Br2N6O4Zn]: C, 42.04; H, 3.50; N,

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12.26. Found: C, 41.23; H, 3.63; N, 12.72%.

2.4.3. Synthesis of metal complex (C2)

mmol)

afforded

red-brown

solid

(0.68

g,

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With the similar synthetic method for C1 With Cd(CH3COO)2·2H2O (0.41 g, 1.5 62%).

FTIR

(KBr,

cm-1):

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3428(N-H),3067(=C-H), 2932, 2880(C-H), 2213(C≡N), 1639(C=N), 1074(C=N-M), 508(N-M). Anal. Calcd. for [C24H24Br2N6O4Cd]: C, 39.34; H, 3.28; N, 11.47. Found: C, 40.15; H, 3.52; N, 11.84%.

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2.4.4. Synthesis of polymeric metal complex (P1)

The polymeric metal complex was synthesized by Yamamoto coupling method according to the literature [17]. Under nitrogen atmosphere, metal complex C1 (0.27 g,

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0.4 mmol), bis(triphenylphosphine) nickel(II) chloride (0.26 g, 0.4 mmol),

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2,6-dibromo-4,8-bis(2’-ethhylhexyl)oxy)benzodithiophene (2) (0.24 g, 0.4 mmol), zinc (0.13 g, 2 mmol), triphenylphosphine (0.21 g, 0.8 mmol), and a little bipyridine (0.006 g, 0.038 mmol) were dissolved in DMF (15 mL) under nitrogen. Then the mixture was stirring at 90 ºC for 48 h. After that, it was filtered after cooled to room temperature and the filtrate was poured into a large excess of ethanol. The precipitate was filtered and washed with cold ethanol, then dried in vacuum for one day to afford brown solid (0.19 g, 49%). FTIR (KBr, cm-1): 3415(N-H), 3057(=C-H), 2964, 2925, 8

ACCEPTED MANUSCRIPT 2853(C-H), 2220(C≡N), 1638(C=N), 1056(C=N-M), 488(N-M). Anal. Calcd. for [C50H60N6O6S2Zn]: C, 61.92; H, 6.19; N,8.67. Found: C, 62.83; H, 6.67; N, 8.04%.

2.4.5. Synthesis of polymeric metal complex (P2)

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Mn=9.72 Kg/mol, PDI=1.76.

With the similar synthetic method as described for P1. A mixture of metal

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complex C2, bis(triphenylphosphine) nickel(II) chloride, monomer 2, zinc, triphenylphosphine, and a little bipyridine and DMF afforded brown solid (0.18 g,

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45%). FTIR (KBr, cm-1): 3409(N-H), 3050(=C-H), 2963, 2925, 2862(C-H), 2206 (C≡N), 1630(C=N), 1063(C=N-M), 495(N-M). Anal. Calcd. for [C50H60N6O6S2Cd]: C, 59.06; H, 5.91; N, 8.27. Found: C, 59.75; H, 5.34; N, 8.87%. Mn=11.24 Kg/mol, PDI=1.73.

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2.4.6. Synthesis of polymeric metal complex (P3) With the similar synthetic method as described for P1. A mixture of metal

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complex C1, bis(triphenylphosphine) nickel(II) chloride, monomer 3, zinc, triphenylphosphine, and a little bipyridine and DMF afforded brown solid (0.16 g,

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52%). FTIR (KBr, cm-1): 3429(N-H), 3060(=C-H), 2965, 2925, 2859(C-H), 2221(C≡N),

1634(C=N),

1051(C=N-M),

482

(N-M).

Anal.

Calcd.

for

[C44H47N7O4Zn]: C, 65.84; H, 5.86; N, 12.22. Found: C, 65.23; H, 6.14; N, 11.65%. Mn=6.81 Kg/mol, PDI=1.92.

2.4.7. Synthesis of polymeric metal complex (P4) With the similar synthetic method as described for P1. A mixture of metal 9

ACCEPTED MANUSCRIPT complex C2, bis(triphenylphosphine) nickel(II) chloride, monomer 3, zinc, triphenylphosphine, and a little bipyridine and DMF afforded brown solid (0.16 g, 47%). FTIR (KBr, cm-1): 3422 (N-H), 3056(=C-H), 2964, 2925, 2853(C-H),

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2200(C≡N), 1626(C=N), 1040(C=N-M), 490(N-M). Anal. Calcd. for [C44H47N7O4Cd]: C, 62.19; H, 5.54; N, 11.54. Found: C, 61.43; H, 5.79; N, 10.87%. Mn=7.73 Kg/mol,

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PDI=1.85.

3.1. Synthesis and characterization

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3. Results and discussion

Monomers and the four polymeric metal complexes has been synthesized by the synthetic routes illustrated in Scheme 1. Monomer 1 was synthesized by the

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condensation of 4-brombenzaldehyde and ehylenediamine (2:1M ratio). Compound C1 and C2 were prepared via coordination reaction. The target four polymers were obtained by the Yamamoto coupling [17], the reactions were carried out in N2

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atmosphere. The four as-synthesized polymers showed a certain solubility in DMSO

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solvent at room temperature. But they can not be dissolved well in chloroform or other solvents.

Figure. 1 shows the 1H NMR spectrum of monomer 1. Signals at 8.21, 3.95 ppm

are attributed to proton of H-C=N and –CH2-, respectively. Aromatic protons are located at 7.50-7.56 ppm. In the 13C spectrum (Figure. 2), the signals of the aromatic carbons are observed at approximately 125.11-134.96 ppm. The chemical shift for (–CH2- and -CH=N-) carbons are found at 61.44 and 161.49 ppm, respectively. 10

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stretching vibration peak appeared at 515 cm-1 and 508 cm-1 [19], respectively. While the C=N-M stretching vibration signals of P1-P4 appeared at 1056 cm-1, 1063 cm-1, 1051 cm-1 and 1040 cm-1, respectively, and their corresponding N-M stretching

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vibration peaks appeared at 488 cm-1, 495 cm-1, 482 cm-1 and 490 cm-1, respectively.

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It is obvious that N-M stretching vibration peaks of the polymeric metal complexes exhibit a certain red-shift comparing with the corresponding metal complexes due to the increase of conjugation system after polymerization.

The number average molecular weights and the weight average molecular

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weights of the four target polymers dyes (P1-P4) are measured by GPC, and Table 1 shows the corresponding data. The four polymer dyes have number average molecular weights (Mn) of 9.72, 11.24, 6.81 and 7.73 kg mol-1, respectively, with a PDI in the

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range of 1.76, 1.73, 1.92, 1.85, respectively. Changes in the molecular weight further

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proved an evidence for the successful synthesis of the four target polymers.

3.2. Optical Properties

Figure. 4 shows the absorption spectra of C1, C2 and P1-P4 in DMF solution,

and the corresponding data are summarized in Table 2. The light absorption of metal complexes C1, C2 is mainly due to metal-to-ligand charge transfer. We observe that the maximum absorption peaks of P1–P4 are at 447, 460, 405 and 413 nm, respectively. This is result from intramolecular charge transfer between the 11

ACCEPTED MANUSCRIPT electron-donating unit and the electron-accepting moiety. We found that the maximum absorptions of the polymeric metal complexes are obviously red shifted comparing with corresponding metal complex, this is due to the introduction of the

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benzodithiophene or carbazole derivatives, and the increase of an effective conjugated chain length.

The normalized photoluminescent (PL) spectra of P1–P4 in DMF solution are

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shown in Figure. 5, the exciation wavelengths were set according to the maximal

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absorption peak of UV–Vis spectrum. It can be seen in table 2 that the PL peaks of P1–P4 are at 522, 544, 490, 498 nm, respectively, which can be attributed to the π– π* transition of intra-ligand.

3.3. Thermal Stability

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Figure. 6 shows the thermal properties of these four polymeric metal complexes studied by TGA and DSC, and the corresponding data was recorded in Table 1. The

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results of TGA show the excellent stability of polymers P1–P4 with 5 % weight loss temperatures (Td) of 320, 315, 350, and 334 ºC under nitrogen, respectively. This is

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important for the thermal stability of DSSCs. And their glass transition temperature (Tg) are 154, 149, 187, 176 ºC, respectively. There is no fixed melting point which is due to our synthetic method and purification means that we only obtained the amorphous products. These results show that the polymeric metal complexes will be a valuable material for application in DSSCs.

3.4. Electrochemical Properties 12

ACCEPTED MANUSCRIPT The electrochemical behaviors of the polymers were investigated by cyclic voltammetry. Figure. 7 shows the cyclic voltammetry curves of P1-P4, and the data are summarized in Table 3. The highest occupied molecular orbital (HOMO) and the

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lowest unoccupied molecular orbital (LUMO) energy levels of the polymers are are crucial property for materials used in DSSCs. They can be calculated conveniently by the following equations as well as energy gap (Eg) [20]:

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HOMO=－e(Eox + 4.40) (eV)

Eg= HOMO － LUMO

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LUMO=－e(Ered + 4.40) (eV)

(1) (2) (3)

The oxidation potential values (Eox) of P1-P4 are 1.16, 1.14, 1.31, 1.27V, respectively, which can be attributed to the benzodithiophene or carbazole derivatives

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donor segment. The reduction potential values (Ered) of P1-P4 are -0.97, -0.94, -1.01, -0.98V, respectively, which can be attributed to the metal-ligand complex acceptor segment. Accordingly, the HOMO energy values of P1-P4 are -5.56, -5.54, -5.71,

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-5.67 eV, respectively, which are are lower than the standard potential of I-/I3- redox

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couple (-4.83 eV). This indicates that sufficient driving forces for the regeneration of the oxidized dyes are available. The LUMO energy values are -3.43, -3.46, -3.39, -3.42 eV, respectively, which are higher than the conduction band of TiO2 (-4.26 eV) [21]. It indicates that effective electron transfer from the excited dye to the TiO2 is ensured. The details are shown in Figure. 8. The electrochemical band gaps (Eg) of P1-P4 are estimated to be 2.13, 2.08, 2.32 and 2.25 eV, respectively, which are consistent with the optical band gaps, so they are suitable for fabrication of 13

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3.5. Photovoltaic Properties DSSC devices based on these four polymeric metal complexes were fabricated

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and tested under the illumination of AM 1.5G, 100 mW·cm-2 for solar cell applications. The monochromatic incident photon-to-electron conversion efficiency

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(IPCE) curves and current density–voltage curves ( J-V curves) of the four polymeric metal complexes are shown in Figure. 9 and Figure. 10, and the short-circuit current

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(Jsc), open-circuit voltage (Voc), fill factor (FF) are listed in Table 4.

From Figure 8, the IPCE values of the four polymers are relatively low with only around 30% at 400-450 nm. It may probably caused by low charge collection efficiency [22]. This is not as good as Si which as photovoltaic material with a

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broader spectral response ranges 400~1100 nm, and the IPCE value can reach to over 80% in the visible spectrum region [23].

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It can be seen in Figure 8 that the open-circuit voltage (Voc) of P1-P4 are 0.65, 0.68, 0.62 and 0.66 V, respectively. The corresponding fill factor (FF) are 63.7, 66.2,

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54.4, 57.4. And the short-circuit current density (Jsc) follow the order of P2 (4.85 mA cm-2) > P1 (4.68 mA cm-2) > P4 (4.32 mA cm-2) > P3 (4.19 mA cm-2). This is in accordance with the order of the power conversion efficiency (η) of the four dyes that P2 (2.18%) > P1 (1.93%) > P4 (1.63%) > P3 (1.41%). We found that P2 containing benzodithiophene derivative as electron donor shows the highest power conversion efficiency.

This

is

due

to

the

stronger

electron-donating

capability

of

benzodithiophene than carbazole, which is more conducive to the generation of 14

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4. Conclusions

Four novel D-A polymeric metal complex dyes were successfully synthesized and

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applied for DSSCs. These dyes exhibit good thermal stability for their application in DSSCs. The strength of the electron-donating group as well as different metal ion

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have influenced the performance of the photovoltaic device. DSSC based on P2 shows the best power conversion efficiency of 2.18% with a better light absorption and higher Jsc value among the four dyes studied. The results show that this type of functional materials would be a potential materials for DSSCs.

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There are still many challenges to obtain outstanding power conversion efficiency for this type of functional materials. The relative low efficiency we obtained is mainly

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due to the inefficient light absorption, weak adsorption affinities on the TiO2, low electron transportation efficiency. In our next work, we will design new conjugated

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polymeric metal complex dyes with much stronger electron-donating units and more suitable metal ions so as to broaden absorption spectra, and further improving Jsc value, and thus to obtain excellent energy conversion efficiency.

Acknowledgments We appreciate the financial support of the Open Project Program of Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of 15

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Education, China ( No.09HJYH10).

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ACCEPTED MANUSCRIPT 6595-6663. [14] N. Pravin , N. Raman, Inorg. Chem. Commun. 36 (2013) 45-50. [15] R. Grisorio, P. Mastrorilli, C.F. Nobile, G. Romanazzi, G.P. Suranna, G. Gigli, C.

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Piliego, G. Ciccarella, P. Cosma, D. Acierno, E. Amendola, Macromolecules 40 (2007) 4865-4873.

[16] L. Zhang, G. Wen, Q. Xiu, L.Guo, J. Deng, C. Zhong, J. Coord. Chem. 65 (2012)

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1632-1644.

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[17] B.K. An, Y.H. Kim, D.C. Shin, S.Y. Park, S.H. Yu, and S.K. Kwon, Macromolecules 34 (2001) 3993-3997.

[18] L. Guo, Y. Deng, L. Zhang, Q. Xiu, G. Wen, C. Zhong, Dyes and Pigments 92 (2012) 1062-1068.

(2015) 189-196.

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[19] P. Ekmekcioglu, N. Karabocek, S. Karabocek, M. Emirik, J. Mol. Struct. 1099

[20] X.Z. Li, W.J. Zeng, Y. Zhang, Q. Hou, W. Yang, Y. Cao, Eur. Polym. J. 41(2005)

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2923-2933.

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[21] J.A. Mikroyannidis, A. Kabanakis, P. Balraju, G.D. Sharma, J. Phys. Chem. C 114 (2010) 12355-12363.

[22] M.K.R. Fischer, S. Wenger, M. Wang, A. Mishra, S.M. Zakeeuddin, M. Grätzel, P. Bäuerle, Chem. Mater. 22 (2010) 1836-1845.

[23] M.A. Green, K. Emery, Y. Hishikawa, W. Warta, E.D. Dunlop, Prog. Photovolt: Res. Appl. 23 (2015) 1-9.

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ACCEPTED MANUSCRIPT Figure Captions: Scheme 1. Fig. 1.

1

Fig. 2.

13

Fig. 4.

H NMR spectra of monomer 1 in CDCl3 solution. C NMR spectra of monomer 1 in CDCl3 solution.

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Fig. 3.

Synthesis of the monomers and polymeric metal complexes P1-P4.

FT-IR spectra of C1, C2 and P1-P4.

UV-Visible absorption spectra of C1, C2 and polymeric metal complexes P1-P4 in DMF

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solution.

PL spectra of polymeric metal complexes P1–P4 in DMF solution.

Fig. 6.

TGA curves of P1-P4 with a heating rate of 20 oC min-1 under nitrogen atmosphere.

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Fig. 5.

Fig. 7. Cyclic voltammograms of P1-P4 on glassy carbon electrode in a 0.1 mol L-1 [Bu4N]BF4 acetonitrile solution at a scan rate of 100 mV s-1.

HOMO and LUMO energy levels of the polymers.

Fig. 9.

Spectra of incident photon-to-current conversion efficiencies (IPCE) for DSSCs based

on dyes (P1-P4).

AC C

mW cm-2.

J-V curves of DSSCs based on dyes (P1-P4) under the illumination of AM 1.5, 100

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Fig. 10.

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Fig. 8.

1

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Table 1 Molecular weights and thermal properties of the polymeric metal complexes. Mna [×103]

Mwa [×103]

PDI

N

Tgb (oC)

Tdc (oC)

P1

9.72

17.12

1.76

10

154

320

P2

11.24

19.45

1.73

11

P3

6.81

13.07

1.92

8

P4

7.73

14.32

1.85

c

149

315

187

350

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b

9

176

334

Determined by gel permeation chromatography using polystyrene as standard. Determined by DSC with a heating rate of 20 oC/min under nitrogen. The temperature at 5% weight loss under nitrogen.

Table 2

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a

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Polymer

Optical properties of the polymeric metal complexes. Polymer

UV-Vis absorbance

λa,onsetd(nm)

PL (nm) λp,maxe (nm)

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λa,maxd(nm) 447

578

522

P2

460

588

544

P3

405

536

490

P4

413

549

498

d

λa,max, λa,onset: The maxima and onset absorption in DMF solution. λp,max: The PL maxima in DMF solution.

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e

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P1

Polymer

Eox f (V)

Ered f (V)

HOMO(eV)

LUMO(eV)

P1

1.16

-0.97

-5.56

-3.43

2.13

P2

1.14

-0.94

-5.54

-3.46

2.08

P3

1.31

-1.01

-5.71

-3.39

2.32

P4

1.27

-0.98

-5.67

-3.42

2.25

Table 3

Electrochemical properties of the polymeric metal complexes.

f g

Values determined by cyclic voltammetry. Eg,EC: Electrochemical band gap estimated from HOMO and LUMO. 2

Eg,EC g (eV)

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Table 4 Photovoltaic parameters of devices with sensitizers P1-P4 in DSSCs at full sunlight (AM 1.5 G, 100 mW cm-2).

η (%)

0.65

63.7

1.93

4.85

0.68

66.2

2.18

DMF

4.19

0.62

54.4

1.41

DMF

4.32

0.66

57.4

1.63

Jsc (mA cm-2)

P1

DMF

4.68

P2

DMF

P3 P4

Voc (V)

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Solvent

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FF (%)

Polymer

3

1

H NMR spectra of monomer 1 in CDCl3 solution.

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Fig. 1.

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1

13

C NMR spectra of monomer 1 in CDCl3 solution.

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Fig. 2.

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2

FT-IR spectra of C1, C2 and P1-P4.

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Fig. 3.

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3

Fig. 4.

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UV-Visible absorption spectra of C1, C2 and polymeric metal complexes P1-P4 in DMF

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solution.

4

PL spectra of polymeric metal complexes P1–P4 in DMF solution.

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Fig. 5.

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TGA curves of P1-P4 with a heating rate of 20 oC min-1 under nitrogen atmosphere.

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Fig. 6.

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6

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Fig. 7. Cyclic voltammograms of P1-P4 on glassy carbon electrode in a 0.1 mol L-1 [Bu4N]BF4

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acetonitrile solution at a scan rate of 100 mV s-1.

7

HOMO and LUMO energy levels of the polymers.

AC C

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Fig. 8.

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8

Spectra of incident photon-to-current conversion efficiencies (IPCE) for DSSCs based

AC C

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on dyes (P1-P4).

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Fig. 9.

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9

Fig. 10.

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J-V curves of DSSCs based on dyes (P1-P4) under the illumination of AM 1.5, 100

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mW cm-2.

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Synthesis of the monomers and polymeric metal complexes P1-P4.

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Scheme 1.

ACCEPTED MANUSCRIPT Highlights:


Four donor-acceptor types of novel polymeric metal complexes dyes were synthesized. HOMO-LUMO energies, photovoltaic properties of four polymeric dyes were

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evaluated.

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The four polymeric metal complex dyes show excellent thermal stability.

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Power conversion efficiency

AM

Air mass

CV

Cyclic voltammetry

DSC

Differential scanning calorimetry

DSSCs

Dye-sensitized solar cells

Eg

The electrochemical band gaps

Eox

The oxidation potential values

Ered

The reduction potential values

FT-IR

Fourier transform infrared spectra

FF

Fill factor

FTO

Fuorine-doped SnO2 conducting glass

GPC

Gel permeation chromatography

HOMO

The highest occupied molecular orbital

IPCE

Incident photon-to-electron conversion efficiency

Jsc

Short-circuit current density

J-V

current density–voltage curves

LUMO

The lowest unoccupied molecular orbital

Mn

Number-average molecular weights

Mw

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Weight-average molecular weights

Degree of polymerization

AC C

N

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η

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Nomenclature

NMR

Nuclear magnetic resonance spectroscopy

PCE

The power conversion efficiency

PDI

Polydispersity index

PL

Photoluminescence spectra

SCE

The saturated calomel electrode

Td

Weight loss temperatures

Tg

Glass-transition temperature

TGA

Thermogravimetry analysis

ACCEPTED MANUSCRIPT Ultraviolet

UV-Vis

Ultraviolet and visible spectra

Voc

Open-circuit voltage

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UV