- Email: [email protected]
Synthesis and properties of organic sensitizers bearing asymmetric double donor -π- acceptor chains for dye-sensitized solar cells
Accepted Manuscript Synthesis and properties of organic sensitizers bearing asymmetric double donor -πacceptor chains for dye-sensitized solar cells Huaixin Wei, Jinghua Shen, Yajing Liu, Tian Huang, Qiang Zhang, Jie Zhao, Xin Zhao PII:
S0143-7208(17)31660-1
DOI:
10.1016/j.dyepig.2017.11.042
Reference:
DYPI 6388
To appear in:
Dyes and Pigments
Received Date: 16 August 2017 Revised Date:
18 November 2017
Accepted Date: 19 November 2017
Please cite this article as: Wei H, Shen J, Liu Y, Huang T, Zhang Q, Zhao J, Zhao X, Synthesis and properties of organic sensitizers bearing asymmetric double donor -π- acceptor chains for dyesensitized solar cells, Dyes and Pigments (2017), doi: 10.1016/j.dyepig.2017.11.042. 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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A novel efficient metal-free sensitizer CVTC-H-CVTP containing asymmetric double D-π-A chains was designed and synthesized for application in dye-sensitized solar cells (DSSCs).
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Synthesis and properties of organic sensitizers bearing asymmetric double donor -π- acceptor chains for dye-sensitized solar cells
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Huaixin Wei1,4*, Jinghua Shen2, Yajing Liu1,Tian Huang1, Qiang Zhang1, Jie Zhao3*, Xin Zhao1* 1. School of Chemistry, Biology and Material Engineering, Jiangsu Key Laboratory of Environmental Functional Materials, Suzhou University of Science and Technology, Suzhou, Jiangsu, 215009, China;
2. School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou, Jiangsu, 215009, China)
University, Suzhou 215006, China.
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3. Soochow Institute for Energy and Materials Innovation, College of Physics, Optoelectronics and Energy, Soochow
4. Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft
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Materials (FUNSOM), Soochow University, Suzhou 215123, China.
Abstract: A novel efficient metal-free sensitizer CVTC-H-CVTP containing asymmetric double D-π-A chains was designed and synthesized for application in dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the target molecule
structures.
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were investigated systematically through comparison of dyes with different single D-π-A In contrast, the sensitizer CVTC-H-CVTP provides improved Jsc and Voc
because of wider range of spectral absorption and higher absorption intensity which leads to
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better photoelectricity conversion efficiency. Therefore, dye with asymmetric double D-π-A
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shows the most efficient photoelectricity conversion efficiency of 3.20% (Unoptimized), VOC = 0.66V, JSC = 6.51 mA/cm2, and FF = 74.72%) under simulated AM 1.5 irradiation (100 mW/cm2). Keywords:
dye-sensitized solar cells, D-π-A structures, metal-free，asymmetric double
Corresponding author: Xin Zhao, Address: School of Chemistry, Biology and Material Engineering, Suzhou University of Science and Technology, 215009 Suzhou, China, Email: [email protected]
ACCEPTED MANUSCRIPT Jie Zhao, Address: Soochow Institute for Energy and Materials Innovation, College of Physics, Optoelectronics and Energy, Soochow University, 215006 Suzhou, China., Email:
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[email protected]
ACCEPTED MANUSCRIPT 1. Introduction Dye-sensitized solar cells (DSSCs) have attracted considerable and sustainable attention due to their potential application as a renewable and clean energy source with
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merits of low cost, flexibility and ease of fabrication.[1-10] Despite impressive breakthroughs in organic electronic technology, the power conversion efficiency of dye-sensitized solar cells is still low, hampering the further commercialization. In order to improve the
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performance, Lots of efforts such as design new materials, structure optimization…..have
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been devoted into the investigation of the highly-efficient DSSCs.[11-19] To date, The record performance of DSSCs has been ascribed to the zinc-porphyrin complexes with cobalt electrolyte, for which the photon conversion efficiencies over 13% have been achieved. 20-21]
[4,
However, concerning the cost and the purification difficulty for the zinc-porphyrin dyes,
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metal-free organic dyes have gained more and more attention due to their advantages of high molar extinction coefficients, relatively low cost, ease of structure tuning and environmental friendliness.
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It is generally believed that the maximum photocurrent density is one main factor to
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determine the devices efficiency, related to the charge injection from the sensitizer HOMO to the semiconductor conduction bands. Therefore, Sensitizers with high light absorption and best energy levels will better for the light harvesting efficiency and photoelectricity conversion efficiency (η). [19] In order to increase the light absorption, the donor-π- bridge-acceptor (D-π-A) configuration has been commonly adopted in the design of organic sensitizers to facilitate its intramolecular charge-transfer (ICT) property.[22-23] The acceptor not only plays a significant
ACCEPTED MANUSCRIPT role on the optical and electrochemical properties of an organic dye, But also tuning the intramolecular charge transfer and the electron injection processes, as well as the adsorption mode and photostability of the dye on TiO2 films; consequently the overall photovoltaic
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performance could be significantly improved.[24] The most commonly-used acceptors should be ascribed to cyanoacrylic acid, but it could be limited by its anchoring sites on the TiO2 surface. [25]
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However, Organic dyes containing two asymmetric D-π-A chains could increase
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photoelectric conversion efficiency of DSSCs compared to the corresponding single D-π-A dye because one molecule of double D-π-A organic dyes contained two light-harvesting units. [26-29] Hence, these will broad the range of light-absorbing of the dye, meanwhile, the adsorbed amount of dye on the TiO2 surface may also be increased, resulting large amounts
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of adsorbed dyes and high photoelectric conversion efficiency. In this case, the formation of aggregates is not a restricting factor to the dye-sensitized solar cells. Here, a small molecule CVTC-H-CVTP with asymmetric double D-π-A structures was
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designed and synthesized to increase the lightharvesting units and broaden the absorption
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range of organic dyes, phenothiazine and carbazole were choosed as an electron donor, thiophen gruop as π-conjugated unit, cyanoacetate as end-capped unit. The two asymmetric
D-π-A chains were linked by a nonconjugated n-hexane chain. Meanwhile, two different corresponding small molecules CVHTC and CVHTP with single D-π-A structure were synthesized for comparison. Owing to two different light-harvesting units in one dye molecule, CVTC-H-CVTP might be expected to exhibit a stronger and broader absorption
ACCEPTED MANUSCRIPT range, resulting in higher conversion efficiency of DSSC compared with the reference dyes CVHTC and CVHTP with a single D-π-A unit each. 2. Experimental section
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2.1. Materials All the chemicals were purchased from Energy Chemical and used without further purification. Toluene and tetrahydrofuran (THF) were dried and distilled over sodium and
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benzophenone. N,N-Dimethylformamide (DMF) was dried over and distilled from NaH
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under an atmosphere of dry nitrogen. 1,2-dichloroethane were atmospheric distillation. All other commercially available materials were used as received unless noted otherwise. 2.2. Synthesis
The synthetic routes and molecular structures of the dyes are shown in Scheme 1. The
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detailed synthetic processes are as follows.
2.2.1 10-(6-Bromo-hexyl)-10H-phenothiazine(M1) A solution of phenothiazine (2 g, 10 mmol), potassium hydroxide (2.81 g, 50 mmol) in
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DMSO (20 mL) was stirred at room temperature for 0.5 h under argon. Then
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1,6-dibromohexane (6.1 g, 25 mmol) was poured into the mixture .The reaction was stirred for 12 h at room temperature. After cooling, the reaction mixture was filtered, and the solvent was evaporated under reduced pressure. The crude product was purified on silica gel chromatography using a petroleum ether/dichloromethane mixture (5/1 by volume) as eluent to afford a colorless liquid (1.68 g, 46.41%).
1
HNMR(CDCl3 , 400MHZ) δ ppm :
1.45-1.50 ( m, 4H ), 1.81-1.90(m, 4H), 3.38-3.44(t, 2H), 3.72-4.05(t, 4H), 6.83-7.21(m, 4H), 7.15-7.22(m, 4H).
ACCEPTED MANUSCRIPT 2.2.2 10-(6-Carbazol-9-yl-hexyl)-10H-phenothiazine(M2) Carbazole(1.68 g, 10.0 mmol) was added to a suspension of potassium hydroxide (2.81 g, 50.0 mmol) in DMSO (20 mL) under nitrogen. The mixture was stirred for 30 min after
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which time M-1 (3.99 g, 11 mmol) was added. The reaction was stirred for 12 h at room temperature. Water (50 mL) was added, the mixture was extracted with dichloromethane (3 ×30mL）, and the organic fraction was then washed with brine, dried with anhydrous
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sodium sulfate, and evaporated. The residue was purified by column chromatography with
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CH2Cl2/petroleum ether (v/v = 1/2) as the eluent to give M-2 (4.11g, 91.32%) as a white solid. 1HNMR(DMSO-d6 , 400MHZ) δppm : 1.23-1.32 (m, 2H ), 1.34-1.43(m, 2H), 1.54-1.63 (m, 2H ), 1.65-1.77 (m, 2H), 3.74-3.82 (t, 2H), 4.40-4.37 (t, 2H), 6.88-6.98 (m, 4H), 7.09-7.22 (m, 6H), 7.37-7.45 (m, 2H), 7.49-7.56 (m, 2H), 8.09-8.17(d, 2H).
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2.2.3 3-Bromo-10-[6-(3-bromo-carbazol-9-yl)-hexyl]-10H-phenothiazine(M3) Compound M-2 0.9g (2mmol) was dissolved in 15mL DMF, The mixture was stirred for 30 min at 0℃, after which time NBS 1.42g (8mmol) of 5mL DMF solution was slowly
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added , The reaction was stirred for 12 h under dark conditions . After completion of the
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reaction, water (100 mL) was added, the mixture was extracted with dichloromethane (3× 30mL）, and the organic fraction was then washed with brine, dried with anhydrous sodium sulfate, and evaporated. The residue was purified by column chromatography with ethyl acetate/petroleum ether (v/v = 1/1) as the eluent to give a white solid
0.42g,
yield:
34.26%. 1HNMR(DMSO-d6 , 400MHZ) δppm : 1.32-1.41 (m, 2H ), 1.43-1.52 (m, 2H ), 1.78-1.94(m, 4H), 4.11-4.19 (t, 2H ), 4.24-4.32 (t, 2H), 7.18-7.36 (m, 7H), 7.52-7.54 (d, 1H), 7.54-7.56 (d, 1H), 7.58-7.68 (m, 2H), 8.03-8.05 (d, 1H), 8.15-8.17 (d, 2H).
ACCEPTED MANUSCRIPT 2.2.4 5-[(5-aldehyde-2-thienyl)-9H-carbazol-9-methyl-3-yl)-10-cyclohexyl-10Hphenothiazine-3-yl] - thiophene-2-carbaldehyde(M4) A mixture of 5-formyl-2-thiopheneboronic acid (0.42 ，2.67 mmol), M-3 (0.54 g，0.89
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mmol), Pd(PPh3)4 (0.09 g，0.009 mmol), aqueous KCO3 solution (2 mol•L−1, 6 mL,) and THF (24 mL) was degased thoroughly by freeze-pumpthaw cycle several times. After refluxing for 24h, the reaction mixture was extracted with CH2Cl2 several times. The
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combined organic phases were washed with water and dried over anhydrous MgSO4. After
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filtration, the filtrate was concentrated under reduced pressure and the residue was subjected to silica columnarb chromatography using petroleum ether/ethyl acetate (v/v = 5/1)as an eluent, affording 0.11g, as a yellow solid in a yield of 19%. 1H NMR(DMSO-d6 , 400MHZ) δ : 1.24-1.32 (m, 2H ), 1.32-1.47 (m, 2H ), 1.59-1.72 (m, 2H ), 1.72-1.80 (m, 2H ), 3.91-4.06
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(t, 2H), 4.46-4.63(t, 2H), 7.24-7.37 (m, 4H ), 7.41-7.62 (m, 6H ), 7.76-7.83 (m, 2H), 7.87-8.01 (m, 2H), 8.13-8.20 (m, 2H), 8.35-8.44 (m, 2H), 9.52-9.55 (s, 1H), 9.71-9.74 (s, 1H).
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2.2.5 3- {5- [10- (6- {3- [5- (2-carboxy - cyano - vinyl) - thiophen-2-yl] carbazol-9-yl} -
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hexyl)-10H- phenothiazine-3-yl] - thiophen-2-yl} -2-cyanoacrylic acid (CVTC-H-CVTP) A solution of M-4 (0.24，g，0.36 mmol) in CHCl3 (9 mL) was condensed with 2-cyanoacetic acid (0.31，g，3.60 mmol) in the presence of piperidine （0.43g，5.30 mmol). The mixture was refluxed for 12 h under nitrogen. After cooling to room temperature, the mixture was poured into a mixture of CH2Cl2 and 2Maqueous HCl. The organic layer was separated and dried over anhydrous Na2SO4. After removal of the solvent at reduced pressure, the crude product was purified by column chromatography with methanol/acetic
ACCEPTED MANUSCRIPT acid (v/v =4/1) as the eluent to give CVTC-H-CVTP(0.26 g g, 89.65 %) as a black red solid. 1
H NMR(DMSO-d6 , 400MHZ) δ : 1.23-1.33 (m, 2H ), 1.33-1.42 (m, 2H ), 1.54-1.71 (m,
2H ), 1.71-1.80 (m, 2H ), 3.75-3.82 (t, 2H), 4.27-4.41(t, 2H), 6.84-7.09(m, 4H), 7.14-7.25
8.24-8.27 (s, 1H).
13
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(m,6H), 7.34-7.49 (m, 2H), 7.51-7.59 (m, 2H ), 7.72-7.80(m, 2H ),8.14-8.17 (s, 1H), C NMR(100Hz,DMSO-d6,δ): 22.50 , 25.69 , 26.31 , 28.60 , 41.5 ,
55.48 , 99.22 , 111.71 , 117.20 , 117.85, 119.48 , 122.21 , 122.77 , 124.33 , 125.24, 126.14 ,
2.2.6 9-Hexyl-9H-carbazole(M5)
found, 800.2.(Fig. S2)
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(ESI，m/z): [M-H]- calcd for C46H34N4S3O4，800.95,
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129.21 , 130.56 , 133.89 , 134.54 , 137.89, 138.24 , 138.63 , 139.87 , 141.56 , 141.96 . MS
Compound M-5 was synthesized from M-1 according to the same procedure in carbazole, 1-bromo-hexane as a starting material, to give M-5, as a colourless oil 94.57%
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yield. 1HNMR(CDCl3 , 400MHZ) δppm : 0.85-0.95 ( t, 3H ), 1.28-1.38(m, 4H), 1.39-1.50(m, 2H), 1.85-1.96(m, 2H), 4.27-4.39(t, 2H), 7.22-7.30(m, 2H), 7.42-7.53(m, 4H),8.10-8.17（d, 2H).
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2.2.7 3-Bromo-9-hexyl-9H-carbazole(M6)
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Compound M-6 was synthesized from M-3 according to the same procedure in M-5 as a starting material, to give M-6, as a white solid 92.14% yield. 1HNMR(CDCl3 , 400MHZ) δppm : 0.87-0.91 ( t, 3H ), 1.27-1.36(m, 6H), 1.79-1.86(m, 2H), 4.17-4.26(t, 2H), 7.23-7.28(m, 2H), 7.37-7.41(d, 1H), 7.49-7.56(m, 2H), 8.02-8.05(d, 1H), 8.19-8.22(d, 1H). 2.2.8 5- (9-ethyl-carbazol-3-yl) thiophene-2-carbaldehyde(M7) Compound M-7 was synthesized from M-4 according to the same procedure in M-6 as a starting material, to give M-10, as a yellow solid 41.78% yield. 1H NMR (CDCl3, 400
ACCEPTED MANUSCRIPT MHz) δ : 0.84-0.89 (m，3H)，1.31-1.38（m, 4H），1.41-1.49（m，2H），1.85-2.00（m,2H）， 4.34-4.42（t，2H），7.27-7.31（m，1H），7.43-7.54(m，3H)，7.73-7. 76(m，1H)，7.82-7.98 （m，2H），8.25-8.45（m，1H），8.40-8.45（m，1H），9.71-9.73（s，1H）.
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2.2.9 2-cyano-3- [5- (9-ethyl-carbazol-3-yl) thiophen-2-yl] - acrylic acid (CVHTC)
Compound CVHTC was synthesized from CVTC-H-CVTP according to the same procedure in M-7 as a starting material, to give CVHTC, as a red solid in 85.23% yield. 1H
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NMR(CDCl3 , 400MHZ) δ : 0.70-0.89 ( t, 3H ), 1.29-1.38(m, 4H), 1.38-1.52(m, 2H),
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1.71-1.97(m, 2H), 4.27-4.39(t, 2H), 7.25-7.32(m, 2H), 7.38-7.51(m, 4H), 7.76-7.83(m, 2H), 8.11-8.23(m, 2H), 8.54-8.59(s, 1H). 13C NMR(100Hz, CDCl3,) δ :13.72, 23.93, 31.24, 35.01, 37.96, 55.03, 107.15, 108.24, 109.53, 118.73, 121.01, 123.54, 124.07, 125.22, 127.19, 128.32, 129.07, 132.45, 139.24, 140.09, 146.93, 162.1. MS (ESI，m/z): [M+H]+ calcd for
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C26H24N2S2O2，461.61, found, 461.3.(Fig.S1) 2.2.10 10-Hexyl-10H-phenothiazine(M8)
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Compound M-8 was synthesized from M-1 according to the same procedure in phenothiazine, 1-bromo-hexane as a starting material, to give M-8, as a colourless oil
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92.14% yield. 1HNMR(CDCl3 , 400MHZ) δppm : 0.88-0.94 ( t, 3H ), 1.30-1.37(m, 4H), 1.43-1.51(m, 2H), 1.79-1.88(m, 2H), 3.84-3.90(t, 2H), 6.87-6.97(m, 4H), 7.14-7.21(m, 4H). 2.2.11 3-Bromo-10-hexyl-10H-phenothiazine(M9) Compound M-9 was synthesized from M-3 according to the same procedure in M-8 as a starting material, to give M-6, as a colourless oil in 95.23% yield. 1HNMR(CDCl3 , 400MHZ) δppm : 0.87-0.92 ( t, 3H ), 1.28-1.34(m, 4H), 1.40-1.47(m, 2H), 1.75-1.84(m, 2H), 3.77-3.86(t, 2H), 6.68-6.73(d, 1H), 6.86-6.89(m, 1H), 6.92-6.97(m, 1H), 7.13-7.20(m,
ACCEPTED MANUSCRIPT 2H), 7.23-7.29(m, 2H). 2.2.12 5- (10- cyclohexyl-phenothiazine-3-yl) - thiophene-2-carbaldehyde(M10) Compound M-10 was synthesized from M-4 according to the same procedure in M-9 as
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a starting material, to give M-10, as a yellow solid in 47.16% yield. 1H NMR(CDCl3 , 400MHZ) δ : 0.90-0.94 ( t, 3H ), 1.30-1.34 (m, 4H), 1.42-1.47 (m, 2H), 1.75-1.83 (m, 2H),
2H), 7.23-7.27 (m, 3H), 9.72-9.74 (s, 1H).
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3.80-3.86 (t, 2H), 6.65-6.73 (d, 1H), 6.83-6.86 (m, 1H), 6.92-6.94 (m, 1H), 7.15-7.20 (m,
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2.2.13 2-cyano-3- [5- (10- cyclohexyl-phenothiazine-3-yl) - thiophen-2-yl] - acrylic acid (CVHTP)
Compound CVHTP was synthesized from CVBTC-H-CVBTP according to the same procedure in M-10 as a starting material, to give CVHTP, as a red solid in 87.43% yield. 1H
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NMR(DMSO-d6 , 400MHZ) δ : 0.79-0.87( m, 2H ), 1.27-1.30(m, 4H), 1.37-1.43(m, 2H), 1.76-1.80(m, 2H), 3.78-3.82(t, 2H), 6.63-6.71(m, 1H), 6.83-6.87 (m,1H), 6.89-6.94 (m,1H), 13
C NMR(100 Hz,
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7.10-7.21(m,3H),7.25-7.27(m,1H),7.69-7.77(m,3H), 8.37-8.39(s,1H).
CDCl3),δ: 14.96, 23.85, 27.44, 29.58, 32.47, 56.80, 102.39, 117.20, 128.75, 132.96, 138.28,
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142.52, 144.76, 149.36, 151.20, 156.73, 161.24, 170.21. MS (ESI，m/z): [M+H]+ calcd for C26H24N2S2O2，461.61, found, 461.3.(Fig.S3) 2.3. Instruments and characterizations 1
H and 13CNMR spectra were recorded on a Bruker 400 MHz spectrometer in CDCl3 or
DMSO-d6 with tetramethylsilane as inner reference. The melting point was taken on Tektronix X4 microscopic melting point apparatus and uncorrected. The absorption and emission spectra of the dyes in DMF solution (2 ×10-5M) were measured at room
ACCEPTED MANUSCRIPT temperature by Shimadzu UV-2450 UV – Vis spectrophotometer and Fluorolog III photoluminescence spectrometer, respectively. The absorption spectra of the dyes on TiO2 film were measured by UV-3010 UV – Vis spectrophotometer. Electrochemical redox
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potentials were obtained by cyclic voltammetry (CV) using a three-electrode configuration and an electrochemistry workstation (ZAHNER ZENNIUM) at a scan rate of 50 mV·s-1. The working electrode was a Platinum electrode; the counter electrode was a Pt electrode,
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and Ag/AgCl electrode was used as reference electrode. Tetrabutyl ammonium
DMF.
Ferrocene/ferrocenium
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hexafluorophosphate 0.1M was used as supporting electrolyte in nitrogen-purged anhydrous redox
couple
was
used
for
potential
calibration.Photocurrentevoltage characteristics were performed on a Keithley 2400 source meter under simulated AM 1.5G illumination (100 mW cm-2) provided by solar simulator .
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2.4 Fabrication and characterization of DSSCs
Fluorine-doped tin oxide (FTO) glasses were washed with detergent, water, ethanol and acetone in an ultrasonic bath for removing dirt and debris. Nanocrystalline TiO2 films in
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thickness were prepared by a screen printing technique, followed by sintering at 450℃ under
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an air flow. After cooling, the TiO2 films were soaked in a 2mM aqueous TiCl4 solution for 30 min at 70℃, and then rinsed in deionized water and ethanol. The TiCl4-treated TiO2 films were annealed at 450℃ for 30 min, and then cooled to 100℃ before being dipped into a 2× 10-4M solution of dyes in DMF for 24 h at room temperature. After adsorption of the dyes, the electrodes were rinsed in DMF. The resulting photoelectrode and Pt counter electrodes were assembled into a sealed sandwich solar cell with a thermoplastic frame. The electrolyte (5×10-3M isopropanol solution of H2PtCl6·6H2O) was injected from a hole made on the
ACCEPTED MANUSCRIPT counter electrode into the interspace between the photo-anode and counter electrode. The active area of the dye coated TiO2 film was 0.25 cm2. 3. Results and Discussion
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3.1 Photophysical properties The normalized UV-Vis absorption spectra of the dyes CVTC-H-CVTP, CVHTP and CVHTC in diluted (1×10-5M) DMF solutions are shown in Fig. 2(a), the corresponding
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detailed data are listed in Table 1. It is clearly that the absorption in shorter wavelengths
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ranging from 290 to 350 nm attribute to aromatic π﹣π* electronic transitions of the phenothiazine unit or carbazol unit, while the absorption in longer wavelengths in the range of 350-500 nm is attributed to the intramolecular charge transfer (ICT) from the donor to the acceptor, which provides efficient charge separation in the excited state. The maximum
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absorption peaks for CVTC-H-CVTP, CVHTP and CVHTC are at 397 nm, 408 nm and 390 nm respectively. In contrast with CVHTP and CVHTC, there is no obvious wider absorption of CVTC-H-CVTP in the ultraviolet and visible region. In comparison with the dye CVHTC,
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the absorption spectra of di-anchoring dyes CVTC-H-CVTP exhibit a hypsochromic shift,
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According to previous reports, the shift is attributed to its unique structure with electron delocalization. Meanwhile, CVHTC shows a red-shift compared with CVHTP due to the enlarged π-conjugation system. The corresponding molar extinction coefficients (ε) were 44871（397nm）、20157（390nm）and 14757(408nm) mol L-1cm-1, respectively. In comparison with CVHTP and CVHTC, The molar absorption coefficient (ε) of CVTC-H-CVTP is much higher, indicating that CVTC-H-CVTP has a good light-harvesting ability. It is worthy to note that the absorption of CVTC-H-CVTP is not just the sum of the absorption bands of
ACCEPTED MANUSCRIPT CVHTP and CVHTC. The distinctive and stronger absorption of CVTC-H-CVTP may be attributed to the absorption overlap of the two independent D-π-A units. The molar extinction coefficients of the three dyes (4.49×105, 2.01×105 , 1.47×105 M-1cm-1) are M-1cm-1), indicating a better ability
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higher than the well-known sensitizer Z907 (0.7×105
of light harvesting of these three metal-free organic dyes than that of Z907.
In addition, as shown in Fig. 2(b), the maximum absorption peaks of three dyes on TiO2
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films were observed to display red shift by 84, 67 and 36nm with respect to those in solution
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for CVHTP and CVHTC, CVTC-H-CVTP, respectively. The significant variations in absorption spectra of CVHTP and CVHTV may be ascribed to a change in the format of aggregation on TiO2 surface as compared to solution. Hypochromic shifts on the TiO2 surface were assigned to the interaction of the anchoring group with surface anions which
surface.
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directly reduces the energy of the π* level and the formation of J-aggregates on the TiO2
3.2. Electronchemical properties
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Cyclic voltammetry (CV) was also performed to study electrochemical properties of
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CVTC-H-CVTP, CVHTC and CVHTP as well as to estimate their feasibility of electron injection from electronically excited dyes into the conduction band of TiO2 and dye regeneration by redox electrolytes. In this approach, a three-electrode system consisting of platinum as working electrode, platinum wire as counter electrode and Ag/AgCl electrode as reference electrode was employed. The external reference is Fc/Fc+(0.63 V vs. NHE) and 1.0 M tetra-n-butylammonium hexafluorophosphate in DMF was used as inert electrolytes. The pertinent data are tabulated in Table 1 and the CV plots can be found in Fig. 3. The
ACCEPTED MANUSCRIPT highest occupied molecular orbital (HOMO) energy levels of CVTC-H-CVTP, CVHTC and CVHTP, which are corresponding to their redox potentials in the CV plots, are 0.63, 0. 64, 0.60V, respectively. These are more positive than the redox potentials of I-/I3- (0.4 V vs.
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NHE), ensuring ample driving force for dye regeneration. The band-gap energies (E0-0) of CVTC-H-CVTP, CVHTC and CVHTP which determined by the absorption onset wavelengths of the dyes are 2.55, 2.75 and 2.54eV, respectively. The lowest unoccupied
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molecular orbital (LUMO) energy levels were calculated by subtracting E0-0 from EHOMO,
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resulting in -1.92, -2.11 and -1.94eV, respectively. These values are more negative than the conduction band edge energy level (ECB) of the TiO2 semiconductor (-0.5 V vs. NHE), rendering sufficient driving forces for electron injection from the excited dye molecules to the TiO2 conduction band. Therefore CVTC-H-CVTP, CVHTC and CVHTP are qualified to
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be used in DSSCs in theory. 3.3. Theoretical calculation
In order to further understand the structural properties of the dyes and the possibility
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of charge transfer from donor to acceptor on electronic excitation, the electronic structure of
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the dyes were analyzed by density functional theoretical (DFT)[30] calculations using the Gaussian 09 program package. The optimized structures and electron densities of HOMOs and LUMOs of the dyes are shown in Fig. 4. It is clearly that the HOMO and LUMO are completely separated in the dyes CVTC-H-CVTP, CVHTC and CVHTP, which reduces the propensity of charge transfer between the donor and acceptor. The HOMO and LUMO electronic states allow the effective electron injection from the dyes to the TiO2 surface excited after the photoexcitation.
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CVHTP as sensitizers. Photocurrent density–voltage (J–V) characteristics of the devices measured under standard AM1.5 solar illumination at intensity of 100 mWcm−2 are shown in Figure 5. Photovoltaic parameters such as open-circuit voltage (Voc), short-circuit current
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density (Jsc), fill factor (FF) and photoelectricity conversion efficiency (η) of DSSC are
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summarized in Table 2. It can be clearly seen that CVTC-H-CVTP perform significantly better than CVHTC and CVHTP in DSSC devices because of its high molar extinction coefficients. The device with CVTC-H-CVTP exhibits the highest η of 3.20 %, with an obvious higher Jsc of 6.51 mA/cm2 and Voc of 0.66 V. In contrast, the device based on the
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dye CVHTC exhibits the η of 1.12 %, with Jsc of 2.52 mA/cm2 and Voc of 0.60 V. the low conversion efficiency is attributed to the narrow absorption spectrum on TiO2 film. Device based on CVHTP exhibits the higher η of 1.61 %, with an obvious higher Jsc of 3.51
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mA/cm2 and FF of 76.62% than CVHTC based devices. All the devices here were not
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optimized and The results observed in Fig. 5 and Table 2 are consistent with the trend observed in Fig. 2, confirming the influence of the asymmetric structure and absorption on the device performance.
The IPCE spectra of DSSCs based on three dyes were measured under AM1.5 irradiation (100 mW/cm2) and shown in Fig. S4. It is obviously that with asymmetric double D-π-A structure, dyes CVTC-H-CVTP shows high IPCE value superior to those of dyes CVHTC and CVHTP, which confirms that the asymmetric double D-π-A structure is
ACCEPTED MANUSCRIPT beneficial to the broadening of the spectrum. In order to further investigate the relation between absorption and device performance, FTIR spectrum was used to study sensitizer adsorption. As shown in Fig.S5, CVTC-H-CVTP dye shows two peaks at 3430 cm-1 and
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3150 cm-1, which corresponding to the Hydroxyl and Carboxyl hydroxyl group respectively. The FTIR spectrum of the TiO2 shows the characteristic band at 3430 cm-1 due to the group. It is clearly that the peak intensity and width decrease after absorbed the dyes, especially the
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peak at 3150 cm-1 disappeared after CVTC-H-CVTP absorbed on TiO2, indicating chemical
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adsorption occurred between TiO2 and dyes. According to previous reports, Hydroxyl group from the surface of TiO2 react with carboxyl group of the dye to form new ester bonds. Based on the above results, it is obvious that compared with the single D-π-A dyes CVHTC, CVHTP, the asymmetric double D-π-A dyes CVTC-H-CVTP shows wide range
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absorption and stronger absorbance intensity, Resulting high short-circuit current density, open circuit voltage and the photoelectric conversion efficiency. In addition, this improves the utilization of sunlight, and the Jsc of CVTC-H-CVTP is improved. In addition,
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CVTC-H-CVTP with the asymmetric double D-π-A structures not only increase the
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absorption of sunlight but also reduce the composite probability between the electrons in the TiO2 conduction band and I- / I3- in the electrolyte, which can effectively suppress dark current.
4. Conclusions In summary, a new small molecule CVTC-H-CVTP with asymmetric double D-π-A structures
were
designed
and
synthesized
containing
thiophene
derivative
as
electron-accepting and cyanoacrylic acid as anchoring group. The results indicate that
ACCEPTED MANUSCRIPT CVTC-H-CVTP with double D-π-A structure had a strong absorption intensity and wide range of spectral absorption from 290 to 500 nm, thus leading to distinctive device performance. In comparison with the single D-π-A dyes CVHTC, CVHTP, the unoptimized
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DSSCs based on CVTC-H-CVTP shows PCE of 3.20%, Jsc of 6.51 mA cm-2, Voc of 0.66 V, FF of 74.72%. The results indicate that the photovoltaic properties of compound CVTC-H-CVTP with asymmetric double D-π-A structure was better than CVHTC or The work will pave a way for further improvement of
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CVHTP with single D-π-A structure.
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the double D–p–A branched based organic sensitizers in the future. Acknowledgements
The work described in this paper was supported by National Natural Science Foundation of China (No. 61705154); the Project of natural science Foundation of the Jiangsu Higher
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Education Institutions, China (No. 17KJB140022); Suzhou University of Science and Technology, China (No. 331512301); Natural Science Foundation of Jiangsu Province, China (No. BK20161303, BK20140311); National Natural Science Foundation of China
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(21504061), Applied Basic Research Program of Suzhou, China (No. SYG201440 ，
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SYN201415); The project of the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions. The authors would like to thank Excellent Innovation Team in Science and Technology of University in Jiangsu Province for discussions.
ACCEPTED MANUSCRIPT References [1] A. Fakharuddin, R. Jose, T. M. Brown, F. F. Santiago, J. Bisquert, Energy Environ. Sci.., 2014, 7, 3952-3981.
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[2] O’Regan. Brain. M. Gratzel, Nature., 1991, 353, 737–740. [3] S. Mathew, A. Yella, P. Gao, R. H. Baker, B. F. E. Curchod, N. A. Astani, I. Tavernelli, U. Rothlisberger, M. K. Nazeeruddin, M. Grätzel, Nat. Chem., 2014, 6, 242–247.
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[4] M. Freitag, J. Teuscher, Y. Saygili, X. Y. Zhang, F Giordano, PLiska, J. L.Hua, S. M. Zakeeruddin,
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[10] J. Y. Mao, X. Y. Zhang, S. H. Liu, Z. J. Shen, X. Li, W. J. Wu, P. T. Chou, J. L. Hua, Electrochim.
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ACCEPTED MANUSCRIPT [14] C. S. Karthikeyan, H.Wietasch and M. Thelakkat, Adv. Mater., 2007,19, 1091–1095. [15] P. Docampo, S. Guldin, M. Stefik, P. Tiwana, M. C. Orilall, S. Huttner, H. Sai, U. Wiesner, U. Steiner, H. J. Snaith, Adv. Funct. Mater., 2010, 20, 1787–1796.
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[19] J. N. Clifford, E. M. Ferrero, A. Viterisi, E. Palomares, Chem. Soc. Rev., 2011, 40, 1635-1646. [20] A. Yella, H. W. Lee, H. N. Tsao, C. Y. Yi, A. K. Chandiran, science, 2011, 334(6056): 629-634. [21] M. Ince, J. H. Yum, Y. J. Kim, S. Mathew, M. Grätzel, T. Torres, M. K. Nazeeruddin, J. Phys. Chem. C., 2014, 118, 17166–17170.
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ACCEPTED MANUSCRIPT [29] H. Zhang, J. Fan, Z. Iqbal, D. B. Kuang, L. Y. Wang, H. Meier, D. R. Cao, Org. Electron., 2013, 14, 2071-2081.
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[30] P. J. Hay, J. Phys. Chem. A., 2002, 106 (8), 1634–1641.
ACCEPTED MANUSCRIPT Figure. 1 Synthetic routes and molecular structures of CVTC-H-CVTP、CVHTC、CVHTP
Figure. 2 UV−vis absorption spectra of CVTC-H-CVTP、CVHTC、CVHTP (a) in DMF
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solutions and (b) in solid films
Cyclic voltammograms of the dyes recorded for DMF solutions
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Figure. 4
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Figure. 3 Cyclic voltammograms of the dyes recorded for DMF solutions
Figure. 5 The current-voltage curve (J-V) of a dye-sensitized solar cell using the three dyes
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CVTC-H-CVTP, CVHTC and CVHTP , respectively.
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H N
N (CH2)6 N
S
S
Br(CH2)6Br N (CH2)6 Br M1
N H
NBS
M2 CHO S S
Br O
CHO
S
O
COOH
S
Br
M3
NC
N (CH2)6 N
B
N (CH2)6 N
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S
M4
COOH
CHO
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CN
S S N (CH2)6 N
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CVTC-H-CVTP
NC
S
COOH
Br
Br(CH2)5CH3 N H
O B
S
CHO
O
NBS
N (CH2)CH3
N (CH2 )5CH3
M5
M6
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NC
S
N H3C(H2C)5 M7
S
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Br(CH2)5CH3
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N H
CHO
S
S
N H3C(H2C)5
COOH
S N H3C(H2C)5
S
CVHTP CN
S
Br
O B
S
O
CHO
NBS N (CH2)CH3
N (CH2)5CH3
M8
M9
NC CHO
COOH
S
COOH
S N H3C(H2C)5
COOH
CVHTC CN
M10
Figure. 1 Synthetic routes and molecular structures of CVTC-H-CVTP、CVHTC、CVHTP
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and (b) in solid films
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Figure. 2 UV−vis absorption spectra of CVTC-H-CVTP、CVHTC、CVHTP (a) in DMF solutions
Figure3. Cyclic voltammograms of the dyes recorded for DMF solutions
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Figure. 4 Optimized structures and electron distributions in HOMO and LUMO levels of CVTC-H-CVTP,
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CVHTP and CVHTC
Figure. 5 The current-voltage curve (J-V) of a dye-sensitized solar cell using the three dyes CVTC-H-CVTP, CVHTC and CVHTP , respectively.
ACCEPTED MANUSCRIPT Table 1 Photophysical and electrochemical properties of dye-sensitizers λmaxsol.
εmaxsol
λmaxfilm
λint
E0-0
EHOMO/ELUMO
[nm]a
[mol-1·L·cm-1]b
[nm]c
[nm]d
[V]e
[V]f
397
44871
443
486
2.55
0.63/-1.92
CVTC-H-CVTP CVHTC
390(303) 20157（8798）
476
451
CVHTP
408(348) 14757（11438）
474
488
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Comp
2.75 2.54
0.64/ -2.11
0.60/ -1.94
Maximum absorption in DMF solution (1×10-5 M) at 25 ℃.
b
molar extinction coefficient at λmax. c Maximum absorption on TiO2 film.
d
intersection obtained from the cross point of normalized absorption and emission spectra in DMF
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a
solution. E0-0 =1240/λint.
f
HOMO of the dyes by cyclic voltametery in 0.1 M tetrabutylammonium perchlorate in DMF solutions as
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e
supporting electrolyte, Ag/AgCl as the reference electrode and Pt as counter electrode; scanning rate: 50 mV s-1.LUMO was calculated by HOMO - E0-0.
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Table 2 Photovoltaic properties of CVHTP、CVHTC、CVTC-H-CVTP based devices
VOC
JSC
FF
PCE
[V]
[mA cm-2]
[%]
[%]
CVHTP
0.60
3.51
76.62
1.61
CVHTC
0.60
2.52
74.07
1.12
CVTC-H-CVTP
0.66
6.51
74.72
3.20
Z907
0.76
11.22
69.69
5.96
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Comp.
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Supporting Information
Synthesis and properties of organic sensitizers bearing
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asymmetric double donor -π- acceptor chains for dye-sensitized solar cells
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Huaixin Wei1,4*, Jinghua Shen2, Yajing Liu1,Tian Huang1, Qiang Zhang1, Jie Zhao3*, Xin Zhao1*
Fig.1 MS of CVHTC
MS (ESI，m/z): [M+H]+ calcd for C26H24N2S2O2，461.61,
found, 461.3.
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Fig.2 MS of CVTC-H-CVTP
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MS (ESI，m/z): [M-H]- calcd for C46H34N4S3O4，800.95,
found, 800.2.
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Fig.3 MS of CVHTP +
found, 461.3.
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MS (ESI，m/z): [M+H] calcd for C26H24N2S2O2，461.61,
Fig.4 IPCE spectra of cells with different dyes
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Fig.4 IPCE spectra of cells with different dyes
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Fig.5 FTIR spectra of TiO2, CVTC-H-CVTP dye and CVTC-H-CVTP on TiO2
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Scheme. 1 Synthetic routes and molecular structures of CVTC-H-CVTP, CVHTC, CVHTP
ACCEPTED MANUSCRIPT Highlights A small molecule was constructed with phenothiazine and carbazole as the donor, thiophen gruop as π-conjugated unit, cyanoacetate as end-capped unit.
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The molecule CVTC-H-CVTP with asymmetric double D-π-A structures can increase the light absorption.
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With enlarged absorption intensity and range, CVTC-H-CVTP based devices efficiency show more than two times than single D-π-A structure.
S0143-7208(17)31660-1
DOI:
10.1016/j.dyepig.2017.11.042
Reference:
DYPI 6388
To appear in:
Dyes and Pigments
Received Date: 16 August 2017 Revised Date:
18 November 2017
Accepted Date: 19 November 2017
Please cite this article as: Wei H, Shen J, Liu Y, Huang T, Zhang Q, Zhao J, Zhao X, Synthesis and properties of organic sensitizers bearing asymmetric double donor -π- acceptor chains for dyesensitized solar cells, Dyes and Pigments (2017), doi: 10.1016/j.dyepig.2017.11.042. 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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A novel efficient metal-free sensitizer CVTC-H-CVTP containing asymmetric double D-π-A chains was designed and synthesized for application in dye-sensitized solar cells (DSSCs).
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Synthesis and properties of organic sensitizers bearing asymmetric double donor -π- acceptor chains for dye-sensitized solar cells
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Huaixin Wei1,4*, Jinghua Shen2, Yajing Liu1,Tian Huang1, Qiang Zhang1, Jie Zhao3*, Xin Zhao1* 1. School of Chemistry, Biology and Material Engineering, Jiangsu Key Laboratory of Environmental Functional Materials, Suzhou University of Science and Technology, Suzhou, Jiangsu, 215009, China;
2. School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou, Jiangsu, 215009, China)
University, Suzhou 215006, China.
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3. Soochow Institute for Energy and Materials Innovation, College of Physics, Optoelectronics and Energy, Soochow
4. Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft
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Materials (FUNSOM), Soochow University, Suzhou 215123, China.
Abstract: A novel efficient metal-free sensitizer CVTC-H-CVTP containing asymmetric double D-π-A chains was designed and synthesized for application in dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the target molecule
structures.
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were investigated systematically through comparison of dyes with different single D-π-A In contrast, the sensitizer CVTC-H-CVTP provides improved Jsc and Voc
because of wider range of spectral absorption and higher absorption intensity which leads to
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better photoelectricity conversion efficiency. Therefore, dye with asymmetric double D-π-A
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shows the most efficient photoelectricity conversion efficiency of 3.20% (Unoptimized), VOC = 0.66V, JSC = 6.51 mA/cm2, and FF = 74.72%) under simulated AM 1.5 irradiation (100 mW/cm2). Keywords:
dye-sensitized solar cells, D-π-A structures, metal-free，asymmetric double
Corresponding author: Xin Zhao, Address: School of Chemistry, Biology and Material Engineering, Suzhou University of Science and Technology, 215009 Suzhou, China, Email: [email protected]
ACCEPTED MANUSCRIPT Jie Zhao, Address: Soochow Institute for Energy and Materials Innovation, College of Physics, Optoelectronics and Energy, Soochow University, 215006 Suzhou, China., Email:
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[email protected]
ACCEPTED MANUSCRIPT 1. Introduction Dye-sensitized solar cells (DSSCs) have attracted considerable and sustainable attention due to their potential application as a renewable and clean energy source with
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merits of low cost, flexibility and ease of fabrication.[1-10] Despite impressive breakthroughs in organic electronic technology, the power conversion efficiency of dye-sensitized solar cells is still low, hampering the further commercialization. In order to improve the
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performance, Lots of efforts such as design new materials, structure optimization…..have
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been devoted into the investigation of the highly-efficient DSSCs.[11-19] To date, The record performance of DSSCs has been ascribed to the zinc-porphyrin complexes with cobalt electrolyte, for which the photon conversion efficiencies over 13% have been achieved. 20-21]
[4,
However, concerning the cost and the purification difficulty for the zinc-porphyrin dyes,
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metal-free organic dyes have gained more and more attention due to their advantages of high molar extinction coefficients, relatively low cost, ease of structure tuning and environmental friendliness.
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It is generally believed that the maximum photocurrent density is one main factor to
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determine the devices efficiency, related to the charge injection from the sensitizer HOMO to the semiconductor conduction bands. Therefore, Sensitizers with high light absorption and best energy levels will better for the light harvesting efficiency and photoelectricity conversion efficiency (η). [19] In order to increase the light absorption, the donor-π- bridge-acceptor (D-π-A) configuration has been commonly adopted in the design of organic sensitizers to facilitate its intramolecular charge-transfer (ICT) property.[22-23] The acceptor not only plays a significant
ACCEPTED MANUSCRIPT role on the optical and electrochemical properties of an organic dye, But also tuning the intramolecular charge transfer and the electron injection processes, as well as the adsorption mode and photostability of the dye on TiO2 films; consequently the overall photovoltaic
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performance could be significantly improved.[24] The most commonly-used acceptors should be ascribed to cyanoacrylic acid, but it could be limited by its anchoring sites on the TiO2 surface. [25]
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However, Organic dyes containing two asymmetric D-π-A chains could increase
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photoelectric conversion efficiency of DSSCs compared to the corresponding single D-π-A dye because one molecule of double D-π-A organic dyes contained two light-harvesting units. [26-29] Hence, these will broad the range of light-absorbing of the dye, meanwhile, the adsorbed amount of dye on the TiO2 surface may also be increased, resulting large amounts
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of adsorbed dyes and high photoelectric conversion efficiency. In this case, the formation of aggregates is not a restricting factor to the dye-sensitized solar cells. Here, a small molecule CVTC-H-CVTP with asymmetric double D-π-A structures was
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designed and synthesized to increase the lightharvesting units and broaden the absorption
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range of organic dyes, phenothiazine and carbazole were choosed as an electron donor, thiophen gruop as π-conjugated unit, cyanoacetate as end-capped unit. The two asymmetric
D-π-A chains were linked by a nonconjugated n-hexane chain. Meanwhile, two different corresponding small molecules CVHTC and CVHTP with single D-π-A structure were synthesized for comparison. Owing to two different light-harvesting units in one dye molecule, CVTC-H-CVTP might be expected to exhibit a stronger and broader absorption
ACCEPTED MANUSCRIPT range, resulting in higher conversion efficiency of DSSC compared with the reference dyes CVHTC and CVHTP with a single D-π-A unit each. 2. Experimental section
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2.1. Materials All the chemicals were purchased from Energy Chemical and used without further purification. Toluene and tetrahydrofuran (THF) were dried and distilled over sodium and
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benzophenone. N,N-Dimethylformamide (DMF) was dried over and distilled from NaH
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under an atmosphere of dry nitrogen. 1,2-dichloroethane were atmospheric distillation. All other commercially available materials were used as received unless noted otherwise. 2.2. Synthesis
The synthetic routes and molecular structures of the dyes are shown in Scheme 1. The
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detailed synthetic processes are as follows.
2.2.1 10-(6-Bromo-hexyl)-10H-phenothiazine(M1) A solution of phenothiazine (2 g, 10 mmol), potassium hydroxide (2.81 g, 50 mmol) in
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DMSO (20 mL) was stirred at room temperature for 0.5 h under argon. Then
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1,6-dibromohexane (6.1 g, 25 mmol) was poured into the mixture .The reaction was stirred for 12 h at room temperature. After cooling, the reaction mixture was filtered, and the solvent was evaporated under reduced pressure. The crude product was purified on silica gel chromatography using a petroleum ether/dichloromethane mixture (5/1 by volume) as eluent to afford a colorless liquid (1.68 g, 46.41%).
1
HNMR(CDCl3 , 400MHZ) δ ppm :
1.45-1.50 ( m, 4H ), 1.81-1.90(m, 4H), 3.38-3.44(t, 2H), 3.72-4.05(t, 4H), 6.83-7.21(m, 4H), 7.15-7.22(m, 4H).
ACCEPTED MANUSCRIPT 2.2.2 10-(6-Carbazol-9-yl-hexyl)-10H-phenothiazine(M2) Carbazole(1.68 g, 10.0 mmol) was added to a suspension of potassium hydroxide (2.81 g, 50.0 mmol) in DMSO (20 mL) under nitrogen. The mixture was stirred for 30 min after
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which time M-1 (3.99 g, 11 mmol) was added. The reaction was stirred for 12 h at room temperature. Water (50 mL) was added, the mixture was extracted with dichloromethane (3 ×30mL）, and the organic fraction was then washed with brine, dried with anhydrous
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sodium sulfate, and evaporated. The residue was purified by column chromatography with
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CH2Cl2/petroleum ether (v/v = 1/2) as the eluent to give M-2 (4.11g, 91.32%) as a white solid. 1HNMR(DMSO-d6 , 400MHZ) δppm : 1.23-1.32 (m, 2H ), 1.34-1.43(m, 2H), 1.54-1.63 (m, 2H ), 1.65-1.77 (m, 2H), 3.74-3.82 (t, 2H), 4.40-4.37 (t, 2H), 6.88-6.98 (m, 4H), 7.09-7.22 (m, 6H), 7.37-7.45 (m, 2H), 7.49-7.56 (m, 2H), 8.09-8.17(d, 2H).
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2.2.3 3-Bromo-10-[6-(3-bromo-carbazol-9-yl)-hexyl]-10H-phenothiazine(M3) Compound M-2 0.9g (2mmol) was dissolved in 15mL DMF, The mixture was stirred for 30 min at 0℃, after which time NBS 1.42g (8mmol) of 5mL DMF solution was slowly
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added , The reaction was stirred for 12 h under dark conditions . After completion of the
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reaction, water (100 mL) was added, the mixture was extracted with dichloromethane (3× 30mL）, and the organic fraction was then washed with brine, dried with anhydrous sodium sulfate, and evaporated. The residue was purified by column chromatography with ethyl acetate/petroleum ether (v/v = 1/1) as the eluent to give a white solid
0.42g,
yield:
34.26%. 1HNMR(DMSO-d6 , 400MHZ) δppm : 1.32-1.41 (m, 2H ), 1.43-1.52 (m, 2H ), 1.78-1.94(m, 4H), 4.11-4.19 (t, 2H ), 4.24-4.32 (t, 2H), 7.18-7.36 (m, 7H), 7.52-7.54 (d, 1H), 7.54-7.56 (d, 1H), 7.58-7.68 (m, 2H), 8.03-8.05 (d, 1H), 8.15-8.17 (d, 2H).
ACCEPTED MANUSCRIPT 2.2.4 5-[(5-aldehyde-2-thienyl)-9H-carbazol-9-methyl-3-yl)-10-cyclohexyl-10Hphenothiazine-3-yl] - thiophene-2-carbaldehyde(M4) A mixture of 5-formyl-2-thiopheneboronic acid (0.42 ，2.67 mmol), M-3 (0.54 g，0.89
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mmol), Pd(PPh3)4 (0.09 g，0.009 mmol), aqueous KCO3 solution (2 mol•L−1, 6 mL,) and THF (24 mL) was degased thoroughly by freeze-pumpthaw cycle several times. After refluxing for 24h, the reaction mixture was extracted with CH2Cl2 several times. The
SC
combined organic phases were washed with water and dried over anhydrous MgSO4. After
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filtration, the filtrate was concentrated under reduced pressure and the residue was subjected to silica columnarb chromatography using petroleum ether/ethyl acetate (v/v = 5/1)as an eluent, affording 0.11g, as a yellow solid in a yield of 19%. 1H NMR(DMSO-d6 , 400MHZ) δ : 1.24-1.32 (m, 2H ), 1.32-1.47 (m, 2H ), 1.59-1.72 (m, 2H ), 1.72-1.80 (m, 2H ), 3.91-4.06
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(t, 2H), 4.46-4.63(t, 2H), 7.24-7.37 (m, 4H ), 7.41-7.62 (m, 6H ), 7.76-7.83 (m, 2H), 7.87-8.01 (m, 2H), 8.13-8.20 (m, 2H), 8.35-8.44 (m, 2H), 9.52-9.55 (s, 1H), 9.71-9.74 (s, 1H).
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2.2.5 3- {5- [10- (6- {3- [5- (2-carboxy - cyano - vinyl) - thiophen-2-yl] carbazol-9-yl} -
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hexyl)-10H- phenothiazine-3-yl] - thiophen-2-yl} -2-cyanoacrylic acid (CVTC-H-CVTP) A solution of M-4 (0.24，g，0.36 mmol) in CHCl3 (9 mL) was condensed with 2-cyanoacetic acid (0.31，g，3.60 mmol) in the presence of piperidine （0.43g，5.30 mmol). The mixture was refluxed for 12 h under nitrogen. After cooling to room temperature, the mixture was poured into a mixture of CH2Cl2 and 2Maqueous HCl. The organic layer was separated and dried over anhydrous Na2SO4. After removal of the solvent at reduced pressure, the crude product was purified by column chromatography with methanol/acetic
ACCEPTED MANUSCRIPT acid (v/v =4/1) as the eluent to give CVTC-H-CVTP(0.26 g g, 89.65 %) as a black red solid. 1
H NMR(DMSO-d6 , 400MHZ) δ : 1.23-1.33 (m, 2H ), 1.33-1.42 (m, 2H ), 1.54-1.71 (m,
2H ), 1.71-1.80 (m, 2H ), 3.75-3.82 (t, 2H), 4.27-4.41(t, 2H), 6.84-7.09(m, 4H), 7.14-7.25
8.24-8.27 (s, 1H).
13
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(m,6H), 7.34-7.49 (m, 2H), 7.51-7.59 (m, 2H ), 7.72-7.80(m, 2H ),8.14-8.17 (s, 1H), C NMR(100Hz,DMSO-d6,δ): 22.50 , 25.69 , 26.31 , 28.60 , 41.5 ,
55.48 , 99.22 , 111.71 , 117.20 , 117.85, 119.48 , 122.21 , 122.77 , 124.33 , 125.24, 126.14 ,
2.2.6 9-Hexyl-9H-carbazole(M5)
found, 800.2.(Fig. S2)
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(ESI，m/z): [M-H]- calcd for C46H34N4S3O4，800.95,
SC
129.21 , 130.56 , 133.89 , 134.54 , 137.89, 138.24 , 138.63 , 139.87 , 141.56 , 141.96 . MS
Compound M-5 was synthesized from M-1 according to the same procedure in carbazole, 1-bromo-hexane as a starting material, to give M-5, as a colourless oil 94.57%
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yield. 1HNMR(CDCl3 , 400MHZ) δppm : 0.85-0.95 ( t, 3H ), 1.28-1.38(m, 4H), 1.39-1.50(m, 2H), 1.85-1.96(m, 2H), 4.27-4.39(t, 2H), 7.22-7.30(m, 2H), 7.42-7.53(m, 4H),8.10-8.17（d, 2H).
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2.2.7 3-Bromo-9-hexyl-9H-carbazole(M6)
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Compound M-6 was synthesized from M-3 according to the same procedure in M-5 as a starting material, to give M-6, as a white solid 92.14% yield. 1HNMR(CDCl3 , 400MHZ) δppm : 0.87-0.91 ( t, 3H ), 1.27-1.36(m, 6H), 1.79-1.86(m, 2H), 4.17-4.26(t, 2H), 7.23-7.28(m, 2H), 7.37-7.41(d, 1H), 7.49-7.56(m, 2H), 8.02-8.05(d, 1H), 8.19-8.22(d, 1H). 2.2.8 5- (9-ethyl-carbazol-3-yl) thiophene-2-carbaldehyde(M7) Compound M-7 was synthesized from M-4 according to the same procedure in M-6 as a starting material, to give M-10, as a yellow solid 41.78% yield. 1H NMR (CDCl3, 400
ACCEPTED MANUSCRIPT MHz) δ : 0.84-0.89 (m，3H)，1.31-1.38（m, 4H），1.41-1.49（m，2H），1.85-2.00（m,2H）， 4.34-4.42（t，2H），7.27-7.31（m，1H），7.43-7.54(m，3H)，7.73-7. 76(m，1H)，7.82-7.98 （m，2H），8.25-8.45（m，1H），8.40-8.45（m，1H），9.71-9.73（s，1H）.
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2.2.9 2-cyano-3- [5- (9-ethyl-carbazol-3-yl) thiophen-2-yl] - acrylic acid (CVHTC)
Compound CVHTC was synthesized from CVTC-H-CVTP according to the same procedure in M-7 as a starting material, to give CVHTC, as a red solid in 85.23% yield. 1H
SC
NMR(CDCl3 , 400MHZ) δ : 0.70-0.89 ( t, 3H ), 1.29-1.38(m, 4H), 1.38-1.52(m, 2H),
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1.71-1.97(m, 2H), 4.27-4.39(t, 2H), 7.25-7.32(m, 2H), 7.38-7.51(m, 4H), 7.76-7.83(m, 2H), 8.11-8.23(m, 2H), 8.54-8.59(s, 1H). 13C NMR(100Hz, CDCl3,) δ :13.72, 23.93, 31.24, 35.01, 37.96, 55.03, 107.15, 108.24, 109.53, 118.73, 121.01, 123.54, 124.07, 125.22, 127.19, 128.32, 129.07, 132.45, 139.24, 140.09, 146.93, 162.1. MS (ESI，m/z): [M+H]+ calcd for
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C26H24N2S2O2，461.61, found, 461.3.(Fig.S1) 2.2.10 10-Hexyl-10H-phenothiazine(M8)
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Compound M-8 was synthesized from M-1 according to the same procedure in phenothiazine, 1-bromo-hexane as a starting material, to give M-8, as a colourless oil
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92.14% yield. 1HNMR(CDCl3 , 400MHZ) δppm : 0.88-0.94 ( t, 3H ), 1.30-1.37(m, 4H), 1.43-1.51(m, 2H), 1.79-1.88(m, 2H), 3.84-3.90(t, 2H), 6.87-6.97(m, 4H), 7.14-7.21(m, 4H). 2.2.11 3-Bromo-10-hexyl-10H-phenothiazine(M9) Compound M-9 was synthesized from M-3 according to the same procedure in M-8 as a starting material, to give M-6, as a colourless oil in 95.23% yield. 1HNMR(CDCl3 , 400MHZ) δppm : 0.87-0.92 ( t, 3H ), 1.28-1.34(m, 4H), 1.40-1.47(m, 2H), 1.75-1.84(m, 2H), 3.77-3.86(t, 2H), 6.68-6.73(d, 1H), 6.86-6.89(m, 1H), 6.92-6.97(m, 1H), 7.13-7.20(m,
ACCEPTED MANUSCRIPT 2H), 7.23-7.29(m, 2H). 2.2.12 5- (10- cyclohexyl-phenothiazine-3-yl) - thiophene-2-carbaldehyde(M10) Compound M-10 was synthesized from M-4 according to the same procedure in M-9 as
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a starting material, to give M-10, as a yellow solid in 47.16% yield. 1H NMR(CDCl3 , 400MHZ) δ : 0.90-0.94 ( t, 3H ), 1.30-1.34 (m, 4H), 1.42-1.47 (m, 2H), 1.75-1.83 (m, 2H),
2H), 7.23-7.27 (m, 3H), 9.72-9.74 (s, 1H).
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3.80-3.86 (t, 2H), 6.65-6.73 (d, 1H), 6.83-6.86 (m, 1H), 6.92-6.94 (m, 1H), 7.15-7.20 (m,
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2.2.13 2-cyano-3- [5- (10- cyclohexyl-phenothiazine-3-yl) - thiophen-2-yl] - acrylic acid (CVHTP)
Compound CVHTP was synthesized from CVBTC-H-CVBTP according to the same procedure in M-10 as a starting material, to give CVHTP, as a red solid in 87.43% yield. 1H
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NMR(DMSO-d6 , 400MHZ) δ : 0.79-0.87( m, 2H ), 1.27-1.30(m, 4H), 1.37-1.43(m, 2H), 1.76-1.80(m, 2H), 3.78-3.82(t, 2H), 6.63-6.71(m, 1H), 6.83-6.87 (m,1H), 6.89-6.94 (m,1H), 13
C NMR(100 Hz,
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7.10-7.21(m,3H),7.25-7.27(m,1H),7.69-7.77(m,3H), 8.37-8.39(s,1H).
CDCl3),δ: 14.96, 23.85, 27.44, 29.58, 32.47, 56.80, 102.39, 117.20, 128.75, 132.96, 138.28,
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142.52, 144.76, 149.36, 151.20, 156.73, 161.24, 170.21. MS (ESI，m/z): [M+H]+ calcd for C26H24N2S2O2，461.61, found, 461.3.(Fig.S3) 2.3. Instruments and characterizations 1
H and 13CNMR spectra were recorded on a Bruker 400 MHz spectrometer in CDCl3 or
DMSO-d6 with tetramethylsilane as inner reference. The melting point was taken on Tektronix X4 microscopic melting point apparatus and uncorrected. The absorption and emission spectra of the dyes in DMF solution (2 ×10-5M) were measured at room
ACCEPTED MANUSCRIPT temperature by Shimadzu UV-2450 UV – Vis spectrophotometer and Fluorolog III photoluminescence spectrometer, respectively. The absorption spectra of the dyes on TiO2 film were measured by UV-3010 UV – Vis spectrophotometer. Electrochemical redox
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potentials were obtained by cyclic voltammetry (CV) using a three-electrode configuration and an electrochemistry workstation (ZAHNER ZENNIUM) at a scan rate of 50 mV·s-1. The working electrode was a Platinum electrode; the counter electrode was a Pt electrode,
SC
and Ag/AgCl electrode was used as reference electrode. Tetrabutyl ammonium
DMF.
Ferrocene/ferrocenium
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hexafluorophosphate 0.1M was used as supporting electrolyte in nitrogen-purged anhydrous redox
couple
was
used
for
potential
calibration.Photocurrentevoltage characteristics were performed on a Keithley 2400 source meter under simulated AM 1.5G illumination (100 mW cm-2) provided by solar simulator .
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2.4 Fabrication and characterization of DSSCs
Fluorine-doped tin oxide (FTO) glasses were washed with detergent, water, ethanol and acetone in an ultrasonic bath for removing dirt and debris. Nanocrystalline TiO2 films in
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thickness were prepared by a screen printing technique, followed by sintering at 450℃ under
AC C
an air flow. After cooling, the TiO2 films were soaked in a 2mM aqueous TiCl4 solution for 30 min at 70℃, and then rinsed in deionized water and ethanol. The TiCl4-treated TiO2 films were annealed at 450℃ for 30 min, and then cooled to 100℃ before being dipped into a 2× 10-4M solution of dyes in DMF for 24 h at room temperature. After adsorption of the dyes, the electrodes were rinsed in DMF. The resulting photoelectrode and Pt counter electrodes were assembled into a sealed sandwich solar cell with a thermoplastic frame. The electrolyte (5×10-3M isopropanol solution of H2PtCl6·6H2O) was injected from a hole made on the
ACCEPTED MANUSCRIPT counter electrode into the interspace between the photo-anode and counter electrode. The active area of the dye coated TiO2 film was 0.25 cm2. 3. Results and Discussion
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3.1 Photophysical properties The normalized UV-Vis absorption spectra of the dyes CVTC-H-CVTP, CVHTP and CVHTC in diluted (1×10-5M) DMF solutions are shown in Fig. 2(a), the corresponding
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detailed data are listed in Table 1. It is clearly that the absorption in shorter wavelengths
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ranging from 290 to 350 nm attribute to aromatic π﹣π* electronic transitions of the phenothiazine unit or carbazol unit, while the absorption in longer wavelengths in the range of 350-500 nm is attributed to the intramolecular charge transfer (ICT) from the donor to the acceptor, which provides efficient charge separation in the excited state. The maximum
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absorption peaks for CVTC-H-CVTP, CVHTP and CVHTC are at 397 nm, 408 nm and 390 nm respectively. In contrast with CVHTP and CVHTC, there is no obvious wider absorption of CVTC-H-CVTP in the ultraviolet and visible region. In comparison with the dye CVHTC,
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the absorption spectra of di-anchoring dyes CVTC-H-CVTP exhibit a hypsochromic shift,
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According to previous reports, the shift is attributed to its unique structure with electron delocalization. Meanwhile, CVHTC shows a red-shift compared with CVHTP due to the enlarged π-conjugation system. The corresponding molar extinction coefficients (ε) were 44871（397nm）、20157（390nm）and 14757(408nm) mol L-1cm-1, respectively. In comparison with CVHTP and CVHTC, The molar absorption coefficient (ε) of CVTC-H-CVTP is much higher, indicating that CVTC-H-CVTP has a good light-harvesting ability. It is worthy to note that the absorption of CVTC-H-CVTP is not just the sum of the absorption bands of
ACCEPTED MANUSCRIPT CVHTP and CVHTC. The distinctive and stronger absorption of CVTC-H-CVTP may be attributed to the absorption overlap of the two independent D-π-A units. The molar extinction coefficients of the three dyes (4.49×105, 2.01×105 , 1.47×105 M-1cm-1) are M-1cm-1), indicating a better ability
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higher than the well-known sensitizer Z907 (0.7×105
of light harvesting of these three metal-free organic dyes than that of Z907.
In addition, as shown in Fig. 2(b), the maximum absorption peaks of three dyes on TiO2
SC
films were observed to display red shift by 84, 67 and 36nm with respect to those in solution
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for CVHTP and CVHTC, CVTC-H-CVTP, respectively. The significant variations in absorption spectra of CVHTP and CVHTV may be ascribed to a change in the format of aggregation on TiO2 surface as compared to solution. Hypochromic shifts on the TiO2 surface were assigned to the interaction of the anchoring group with surface anions which
surface.
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directly reduces the energy of the π* level and the formation of J-aggregates on the TiO2
3.2. Electronchemical properties
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Cyclic voltammetry (CV) was also performed to study electrochemical properties of
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CVTC-H-CVTP, CVHTC and CVHTP as well as to estimate their feasibility of electron injection from electronically excited dyes into the conduction band of TiO2 and dye regeneration by redox electrolytes. In this approach, a three-electrode system consisting of platinum as working electrode, platinum wire as counter electrode and Ag/AgCl electrode as reference electrode was employed. The external reference is Fc/Fc+(0.63 V vs. NHE) and 1.0 M tetra-n-butylammonium hexafluorophosphate in DMF was used as inert electrolytes. The pertinent data are tabulated in Table 1 and the CV plots can be found in Fig. 3. The
ACCEPTED MANUSCRIPT highest occupied molecular orbital (HOMO) energy levels of CVTC-H-CVTP, CVHTC and CVHTP, which are corresponding to their redox potentials in the CV plots, are 0.63, 0. 64, 0.60V, respectively. These are more positive than the redox potentials of I-/I3- (0.4 V vs.
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NHE), ensuring ample driving force for dye regeneration. The band-gap energies (E0-0) of CVTC-H-CVTP, CVHTC and CVHTP which determined by the absorption onset wavelengths of the dyes are 2.55, 2.75 and 2.54eV, respectively. The lowest unoccupied
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molecular orbital (LUMO) energy levels were calculated by subtracting E0-0 from EHOMO,
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resulting in -1.92, -2.11 and -1.94eV, respectively. These values are more negative than the conduction band edge energy level (ECB) of the TiO2 semiconductor (-0.5 V vs. NHE), rendering sufficient driving forces for electron injection from the excited dye molecules to the TiO2 conduction band. Therefore CVTC-H-CVTP, CVHTC and CVHTP are qualified to
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be used in DSSCs in theory. 3.3. Theoretical calculation
In order to further understand the structural properties of the dyes and the possibility
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of charge transfer from donor to acceptor on electronic excitation, the electronic structure of
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the dyes were analyzed by density functional theoretical (DFT)[30] calculations using the Gaussian 09 program package. The optimized structures and electron densities of HOMOs and LUMOs of the dyes are shown in Fig. 4. It is clearly that the HOMO and LUMO are completely separated in the dyes CVTC-H-CVTP, CVHTC and CVHTP, which reduces the propensity of charge transfer between the donor and acceptor. The HOMO and LUMO electronic states allow the effective electron injection from the dyes to the TiO2 surface excited after the photoexcitation.
ACCEPTED MANUSCRIPT 3.4. Photovoltaic properties of DSSCs In order to investigate the photovoltaic performance of CVTC-H-CVTP, CVHTC and CVHTP, corresponding DSSCs were fabricated using CVTC-H-CVTP, CVHTC and
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CVHTP as sensitizers. Photocurrent density–voltage (J–V) characteristics of the devices measured under standard AM1.5 solar illumination at intensity of 100 mWcm−2 are shown in Figure 5. Photovoltaic parameters such as open-circuit voltage (Voc), short-circuit current
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density (Jsc), fill factor (FF) and photoelectricity conversion efficiency (η) of DSSC are
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summarized in Table 2. It can be clearly seen that CVTC-H-CVTP perform significantly better than CVHTC and CVHTP in DSSC devices because of its high molar extinction coefficients. The device with CVTC-H-CVTP exhibits the highest η of 3.20 %, with an obvious higher Jsc of 6.51 mA/cm2 and Voc of 0.66 V. In contrast, the device based on the
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dye CVHTC exhibits the η of 1.12 %, with Jsc of 2.52 mA/cm2 and Voc of 0.60 V. the low conversion efficiency is attributed to the narrow absorption spectrum on TiO2 film. Device based on CVHTP exhibits the higher η of 1.61 %, with an obvious higher Jsc of 3.51
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mA/cm2 and FF of 76.62% than CVHTC based devices. All the devices here were not
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optimized and The results observed in Fig. 5 and Table 2 are consistent with the trend observed in Fig. 2, confirming the influence of the asymmetric structure and absorption on the device performance.
The IPCE spectra of DSSCs based on three dyes were measured under AM1.5 irradiation (100 mW/cm2) and shown in Fig. S4. It is obviously that with asymmetric double D-π-A structure, dyes CVTC-H-CVTP shows high IPCE value superior to those of dyes CVHTC and CVHTP, which confirms that the asymmetric double D-π-A structure is
ACCEPTED MANUSCRIPT beneficial to the broadening of the spectrum. In order to further investigate the relation between absorption and device performance, FTIR spectrum was used to study sensitizer adsorption. As shown in Fig.S5, CVTC-H-CVTP dye shows two peaks at 3430 cm-1 and
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3150 cm-1, which corresponding to the Hydroxyl and Carboxyl hydroxyl group respectively. The FTIR spectrum of the TiO2 shows the characteristic band at 3430 cm-1 due to the group. It is clearly that the peak intensity and width decrease after absorbed the dyes, especially the
SC
peak at 3150 cm-1 disappeared after CVTC-H-CVTP absorbed on TiO2, indicating chemical
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adsorption occurred between TiO2 and dyes. According to previous reports, Hydroxyl group from the surface of TiO2 react with carboxyl group of the dye to form new ester bonds. Based on the above results, it is obvious that compared with the single D-π-A dyes CVHTC, CVHTP, the asymmetric double D-π-A dyes CVTC-H-CVTP shows wide range
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absorption and stronger absorbance intensity, Resulting high short-circuit current density, open circuit voltage and the photoelectric conversion efficiency. In addition, this improves the utilization of sunlight, and the Jsc of CVTC-H-CVTP is improved. In addition,
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CVTC-H-CVTP with the asymmetric double D-π-A structures not only increase the
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absorption of sunlight but also reduce the composite probability between the electrons in the TiO2 conduction band and I- / I3- in the electrolyte, which can effectively suppress dark current.
4. Conclusions In summary, a new small molecule CVTC-H-CVTP with asymmetric double D-π-A structures
were
designed
and
synthesized
containing
thiophene
derivative
as
electron-accepting and cyanoacrylic acid as anchoring group. The results indicate that
ACCEPTED MANUSCRIPT CVTC-H-CVTP with double D-π-A structure had a strong absorption intensity and wide range of spectral absorption from 290 to 500 nm, thus leading to distinctive device performance. In comparison with the single D-π-A dyes CVHTC, CVHTP, the unoptimized
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DSSCs based on CVTC-H-CVTP shows PCE of 3.20%, Jsc of 6.51 mA cm-2, Voc of 0.66 V, FF of 74.72%. The results indicate that the photovoltaic properties of compound CVTC-H-CVTP with asymmetric double D-π-A structure was better than CVHTC or The work will pave a way for further improvement of
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CVHTP with single D-π-A structure.
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the double D–p–A branched based organic sensitizers in the future. Acknowledgements
The work described in this paper was supported by National Natural Science Foundation of China (No. 61705154); the Project of natural science Foundation of the Jiangsu Higher
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Education Institutions, China (No. 17KJB140022); Suzhou University of Science and Technology, China (No. 331512301); Natural Science Foundation of Jiangsu Province, China (No. BK20161303, BK20140311); National Natural Science Foundation of China
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(21504061), Applied Basic Research Program of Suzhou, China (No. SYG201440 ，
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SYN201415); The project of the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions. The authors would like to thank Excellent Innovation Team in Science and Technology of University in Jiangsu Province for discussions.
ACCEPTED MANUSCRIPT References [1] A. Fakharuddin, R. Jose, T. M. Brown, F. F. Santiago, J. Bisquert, Energy Environ. Sci.., 2014, 7, 3952-3981.
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[22] A. Mishra, M. K. R. Fischer, P. Bäuerle, Angew. Chem. Int. Edit., 2009, 48, 2474-2499. [23] Y. Ooyama, Y. Harima, Eur. J. Org. Chem., 2009, 0, 2903–2934. [24] M. Liang, J. Chen, Chem. Soc. Rev., 2013, 42(8): 3453-3488.
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[25] Y. Harima, T. Fujita, Y. Kano, I. Imae, K. Komaguchi, Y. Ooyama, J. Ohshita, J .Phys. Chem. C.,
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2013, 32,16364-16370.
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ACCEPTED MANUSCRIPT [29] H. Zhang, J. Fan, Z. Iqbal, D. B. Kuang, L. Y. Wang, H. Meier, D. R. Cao, Org. Electron., 2013, 14, 2071-2081.
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[30] P. J. Hay, J. Phys. Chem. A., 2002, 106 (8), 1634–1641.
ACCEPTED MANUSCRIPT Figure. 1 Synthetic routes and molecular structures of CVTC-H-CVTP、CVHTC、CVHTP
Figure. 2 UV−vis absorption spectra of CVTC-H-CVTP、CVHTC、CVHTP (a) in DMF
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solutions and (b) in solid films
Cyclic voltammograms of the dyes recorded for DMF solutions
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Figure. 3 Cyclic voltammograms of the dyes recorded for DMF solutions
Figure. 5 The current-voltage curve (J-V) of a dye-sensitized solar cell using the three dyes
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CVTC-H-CVTP, CVHTC and CVHTP , respectively.
ACCEPTED MANUSCRIPT S
H N
N (CH2)6 N
S
S
Br(CH2)6Br N (CH2)6 Br M1
N H
NBS
M2 CHO S S
Br O
CHO
S
O
COOH
S
Br
M3
NC
N (CH2)6 N
B
N (CH2)6 N
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S
M4
COOH
CHO
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CN
S S N (CH2)6 N
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CVTC-H-CVTP
NC
S
COOH
Br
Br(CH2)5CH3 N H
O B
S
CHO
O
NBS
N (CH2)CH3
N (CH2 )5CH3
M5
M6
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NC
S
N H3C(H2C)5 M7
S
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Br(CH2)5CH3
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N H
CHO
S
S
N H3C(H2C)5
COOH
S N H3C(H2C)5
S
CVHTP CN
S
Br
O B
S
O
CHO
NBS N (CH2)CH3
N (CH2)5CH3
M8
M9
NC CHO
COOH
S
COOH
S N H3C(H2C)5
COOH
CVHTC CN
M10
Figure. 1 Synthetic routes and molecular structures of CVTC-H-CVTP、CVHTC、CVHTP
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and (b) in solid films
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Figure. 2 UV−vis absorption spectra of CVTC-H-CVTP、CVHTC、CVHTP (a) in DMF solutions
Figure3. Cyclic voltammograms of the dyes recorded for DMF solutions
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Figure. 4 Optimized structures and electron distributions in HOMO and LUMO levels of CVTC-H-CVTP,
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CVHTP and CVHTC
Figure. 5 The current-voltage curve (J-V) of a dye-sensitized solar cell using the three dyes CVTC-H-CVTP, CVHTC and CVHTP , respectively.
ACCEPTED MANUSCRIPT Table 1 Photophysical and electrochemical properties of dye-sensitizers λmaxsol.
εmaxsol
λmaxfilm
λint
E0-0
EHOMO/ELUMO
[nm]a
[mol-1·L·cm-1]b
[nm]c
[nm]d
[V]e
[V]f
397
44871
443
486
2.55
0.63/-1.92
CVTC-H-CVTP CVHTC
390(303) 20157（8798）
476
451
CVHTP
408(348) 14757（11438）
474
488
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Comp
2.75 2.54
0.64/ -2.11
0.60/ -1.94
Maximum absorption in DMF solution (1×10-5 M) at 25 ℃.
b
molar extinction coefficient at λmax. c Maximum absorption on TiO2 film.
d
intersection obtained from the cross point of normalized absorption and emission spectra in DMF
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a
solution. E0-0 =1240/λint.
f
HOMO of the dyes by cyclic voltametery in 0.1 M tetrabutylammonium perchlorate in DMF solutions as
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e
supporting electrolyte, Ag/AgCl as the reference electrode and Pt as counter electrode; scanning rate: 50 mV s-1.LUMO was calculated by HOMO - E0-0.
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Table 2 Photovoltaic properties of CVHTP、CVHTC、CVTC-H-CVTP based devices
VOC
JSC
FF
PCE
[V]
[mA cm-2]
[%]
[%]
CVHTP
0.60
3.51
76.62
1.61
CVHTC
0.60
2.52
74.07
1.12
CVTC-H-CVTP
0.66
6.51
74.72
3.20
Z907
0.76
11.22
69.69
5.96
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Comp.
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Supporting Information
Synthesis and properties of organic sensitizers bearing
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asymmetric double donor -π- acceptor chains for dye-sensitized solar cells
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Huaixin Wei1,4*, Jinghua Shen2, Yajing Liu1,Tian Huang1, Qiang Zhang1, Jie Zhao3*, Xin Zhao1*
Fig.1 MS of CVHTC
MS (ESI，m/z): [M+H]+ calcd for C26H24N2S2O2，461.61,
found, 461.3.
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Fig.2 MS of CVTC-H-CVTP
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MS (ESI，m/z): [M-H]- calcd for C46H34N4S3O4，800.95,
found, 800.2.
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Fig.3 MS of CVHTP +
found, 461.3.
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MS (ESI，m/z): [M+H] calcd for C26H24N2S2O2，461.61,
Fig.4 IPCE spectra of cells with different dyes
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Fig.4 IPCE spectra of cells with different dyes
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Fig.5 FTIR spectra of TiO2, CVTC-H-CVTP dye and CVTC-H-CVTP on TiO2
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Scheme. 1 Synthetic routes and molecular structures of CVTC-H-CVTP, CVHTC, CVHTP
ACCEPTED MANUSCRIPT Highlights A small molecule was constructed with phenothiazine and carbazole as the donor, thiophen gruop as π-conjugated unit, cyanoacetate as end-capped unit.
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The molecule CVTC-H-CVTP with asymmetric double D-π-A structures can increase the light absorption.
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With enlarged absorption intensity and range, CVTC-H-CVTP based devices efficiency show more than two times than single D-π-A structure.