Thiophene-Functionalized Porphyrins: Synthesis, Photophysical

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Thiophene-functionalized Porphyrins: Synthesis, Photophysical Properties and Photovoltaic Photovoltaic Performance in Dye-Sensitized Solar Cells Wenhui Li, Zonghao Liu, Huaizhi Wu, Yi-Bing Cheng, Zhixin Zhao, and Hongshan He J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp509842p • Publication Date (Web): 16 Feb 2015 Downloaded from http://pubs.acs.org on February 18, 2015

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The Journal of Physical Chemistry

Thiophene-functionalized Porphyrins: Synthesis, Photophysical Properties and Photovoltaic Photovoltaic Performance in Dye-Sensitized Solar Cells Wenhui Li†, Zonghao Liu†, Huaizhi Wu†, Yi-Bing Cheng†‡, Zhixin Zhao†*, Hongshan He§*

†

Michael Grätzel Center for Mesoscopic Solar Cells, Wuhan National Laboratory for

Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, P. R. China §

Department of Chemistry, Eastern Illinois University, Charleston, Illinois 61920, United States

‡

Department of Materials Engineering, Monash University, Melbourne, Victoria3800, Australia

ACS Paragon Plus Environment

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ABSTRACT

Thienyl groups were incorporated into three porphyrin dyes, ZZX-N7, ZZX-N8 and ZZX-N9, with D-π-A configuration to broaden the absorption spectra for dye-sensitized solar cells (DSCs). With the increase of π-conjugation from ZZX-N7, ZZX-N8 to ZZX-N9, a systematic red-shift of absorption was observed. However, the broadened spectra were not correlated proportionally to their photovoltaic performance. It was found the power conversion efficiency increased in the order of ZZX-N7 < ZZX-N8 < ZZX-N9 under low dye-loading condition; whereas it decreased in the order of ZZX-N7 > ZZX-N8 > ZZX-N9 under high dye-loading condition. Further study showed that the increased EtOH/THF volume ratio in dye solution not only increased dye-loading density but also promoted dye aggregation. A trade-off between the blocking effect of the adsorbed dyes and the dye aggregation under different dye-loading densities was observed. Under optimized conditions, ZZX-N8 sensitized cell exhibited energy conversion efficiency of 7.78% under AM1.5G condition.

KEYWORDS Porphyrin; Dye-sensitized Solar Cells; Dye Adsorption; Energy Conversion


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INTRODUCTION Dye-sensitized solar cells (DSCs) have received extensive development over the past two decades as a promising alternative for Si-based solar cells. In a conventional DSC, dye-sensitized TiO2 nanocrystalline film absorbs the solar irradiation and converts it to electricity by injecting electrons from the excited states of the dye into the conduction band of the TiO2 nanoparticles to achieve efficient power conversion. The range of the solar irradiation that can be absorbed and the electron injection efficiency from a dye to the conduction band of TiO2 nanoparticles are largely dependent upon the molecular structure of a dye that is adsorbed on the TiO2 film. Ruthenium dye have shown excellent photovoltaic performance in DSC; however, from the viewpoint of cost, environmental protection, and absorption spectrum,1-4 alternative dyes are needed. In the last few years, porphyrin dyes have been studied for DSC applications due to their strong absorption in the visible region and excellent structure flexibility in tuning photophysical and electrochemical properties. In 2007, Grätzel group incorporated a malonic acid at the βpyrrolic position of a porphyrin ring, and obtained power conversion efficiency of 7.1%.5 In the following years, a donor-π-acceptor (D-π-A) configuration of dye molecules has emerged as a premium model for high-efficiency porphyrin dyes. In 2010, efficiency of 11% was achieved by using a D-π-A porphyrin dye YD-2, which was comparable to the best ruthenium polypyridyl dye.6 Recently, power conversion efficiency up to 13% was reported from a benzothiadiazole functionalized porphyrin dye.7

Despite its promising for high-efficiency DSCs, porphyrin dyes require structural improvement in order to match their absorption spectrum to the solar irradiation. Porphyrin dyes have intense absorption in the visible region; however, they usually show weak absorption in the near-infrared region. In this regard, extensive efforts have been devoted to developing new porphyrin dyes for


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broader absorption spectra including fusion of other aromatic groups into porphyrin ring. Oligothiophene and thienyl groups have been demonstrated to be successful in broadening the absorption of organic dyes and ruthenium dye,8-14 their application in porphyrin dyes are scarce. In this work, three porphyrin dyes (coded as ZZX-N7, ZZX-N8, ZZX-N9) incorporating thienyl groups were designed and synthesized as shown in Scheme 1. Their structures are based upon a D-π-A configuration with a diphenylamine as an electron donor. Unlike conventional porphyrin dyes, a thiophene carboxylic acid, rather than a benzoic acid, was used as an acceptor in these dyes. A second thiophene was either inserted between porphyrin and donor or fused into the thiophene carboxylic acid. We expect the modification will extend the absorption onset to longer wavelength.

Dye-dye interaction on the TiO2 surface is also vital to the overall performance of devices. In DSCs, dye molecules absorb the solar energy and are excited to the excited states. In order to generate electricity, the electrons have to inject into the conduction band of TiO2 efficiently. However, this injection can be diverted by several electron quenching pathways including aggregation-induced quenching. It was found that solvents play vital roles to this process. In 2009, Imahori et al.15 found that porphyrin-sensitized solar cells exhibited much higher conversion efficiency in protic solvents (i.e., EtOH and MeOH) than aprotic solvents (i.e., DMF) (3.7% vs. 0.55%). Diau and Lin et al.16 compared cell performance using different uptaking solvents. When the solvent changed from THF to EtOH/toluene, the power conversion efficiency increased from 6.39% to 8.94% for a porphyrin dye LD14-C8; while the efficiency of LD15cells showed little difference.16 It is unclear how this effect correlates to the molecular structure. To this end, the effect of dye-loading solvent on the photovoltaic performance of three new dyes was studied. It was found the effect linked to the dye-loading density on the TiO2 nanoparticles.


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C6H13 C8H17O N

OC8H17

N N Zn N N

A

OC8H17

ZZX-N7 A=

S

C6H13

COOH S

S

C8H17O N

C6H13C8H17O

ZZX-N8 A=

C6H13 S

OC8H17

N N Zn N N C8H17O

S

COOH

OC8H17

ZZX-N9

COOH

Scheme 1. Molecular structures of ZZX-N7, ZZX-N8 and ZZX-N9.

Experimental Section General Chemicals were purchased from Acros and used directly without further purification except chloroform. The chloroform was dried using CaH2 as a drying agent prior to use. 1H NMR spectra were acquired on a Bruker 400M spectrometer. Compound 1, compound 2, and compound 3 were synthesized according to the literatures,17, 18 and were confirmed by 1H NMR. Absorption spectra were performed on an HP Agilent 8453 UV-Vis spectrophotometer. Steadystate fluorescence spectra were acquired on an FS920 spectrophotometer from Edinburgh Instrument, Inc. with a Xe900 arc lamp as a light source, and a Hamamatsu R928P photomultiplier as a detector. Synthesis

Synthesis of ZZX-N7 and ZZX-N8.To a solution of compound 1 (0.0225 mmol) in dry THF (8 ml) was added TBAF (0.128 ml, 1M in THF) under nitrogen. The reaction mixture was stirred at room temperature for 1.5 hours and then quenched by water. The mixture was extracted with CH2Cl2 and dried over anhydrous MgSO4. The solvent of the organic layer was removed under a reduced pressure. The residue was dissolved in a mixture of dry THF (6 ml) and dry TEA (1.2


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ml) and degassed with nitrogen for 30 minutes. Then Pd2(dba)3 (5 mg, 0.0056 mmol), AsPh3 (13.5 mg, 0.045 mmol), and 5-bromothiophene-2-carboxylic acid (for ZZX-N7) or 5bromothieno[3,2-b]thiophene-2-carboxylic acid (for ZZX-N8) (0.045 mmol) were added. The solution was refluxed under N2 for 4h. Then the solvent was removed under a reduced pressure and the residue was subjected to column chromatography (silica gel) using CH2Cl2/MeOH = 20/1 (v/v) as eluent. Re-crystallization from CH2Cl2/MeOH gave the desired product.

ZZX-N7. Green solid (0.0134 mmol, 59.6%). 1H NMR (CD2Cl2, 600 MHz) δ 9.63 (d, J=4.44 Hz, 2H), 9.19 (d, J=4.50 Hz, 2H), 8.91 (d, J=4.50 Hz, 2H), 8.70 (d, J=4.50 Hz, 2H), 7.92 (d, J=3.42 Hz, 1H), 7.70-7.75 (m, 3H), 7.22 (d, J=8.70 Hz, 4H), 7.03 (t, J=9.75 Hz, 8H), 3.87-3.94 (m, 8H), 2.52 (t, J=7.68 Hz, 4H), 1.54-1.59 (m, 4H), 1.30 (s, 12H), 0.98-1.01 (m, 6H), 0.87-0.93 (m, 12H), 0.41-0.77 (m, 48H).

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C NMR (CD2Cl2, 150MHz) δ 159.87, 150.56, 132.47, 132.00,

130.04, 128.83, 121.84, 120.13, 105.04, 68.51, 35.15, 31.70, 31.58, 29.08, 28.62, 28.54, 28.47, 25.07, 22.58, 22.29, 13.81, 13.60. Elemental Analysis: calcd for C95H119N5O6SZn C 74.85%, H 7.87%, N 4.59%; found C 74.88%, H 7.91%, N 4.56%. MS (m/z, HRAPCIMS) calcd for C95H119N5O6SZn 1522.82, found 1523.82 [M+H]+.

ZZX-N8. Green solid (0.0120 mmol, 53.4%). 1H NMR (CD2Cl2, 600 MHz) δ 9.65 (d, J=4.44 Hz, 2H), 9.18 (d, J=4.50 Hz, 2H), 8.90 (d, J=4.50 Hz, 2H), 8.70 (d, J=4.50 Hz, 2H), 7.96 (s, 1H), 7.89 (s,1H), 7.73 (t, J= 8.58 Hz, 2H), 7.22 (d, J=8.64 Hz, 4H), 7.01-7.04 (m, 8H), 3.87-3.92 (m, 8H), 2.51 (t, J=7.71 Hz, 4H), 1.56-1.58 (m, 4H), 1.30 (s, 12H), 0.98-1.01 (m, 6H), 0.87-0.93 (m, 12H), 0.46-0.78 (m, 48H).

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C NMR (CD2Cl2, 150MHz) δ 159.80, 151.77, 150.55, 150.49,

150.18, 134.91, 132.27, 131.93, 130.28, 129.94, 128.79, 121.75, 105.03, 70.39, 68.51, 63.10, 35.15, 31.92, 31.59, 31.45, 29.08, 28.64, 28.49, 22.58, 22.31, 13.87, 13.82, 13.62, 13.58, 8.39.


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Elemental Analysis: calcd for C97H119N5O6S2Zn C 73.71%, H 7.59%, N 4.43%; found C 73.78%, H 7.62%, N 4.39%. MS (m/z, HRAPCIMS) calcd for C97H119N5O6S2Zn 1580.53, found 1580.79 [M]+.

Synthesis of 4.To a solution of 2 (300 mg, 0.5 mmol) in 80 mL dry THF was added TBAF (1 M in THF, 3 mL). The mixture was stirred in dark at room temperature for 45 minutes and then quenched by water. The mixture was extracted with CH2Cl2, dried over MgSO4, and the solvent was removed under reduced pressure. The residue was dissolved in a mixture of 60 mL dry THF and 10mL dry TEA and degassed with nitrogen for 30min; Pd(PPh3)2Cl2 (23 mg, 0.033 mmol), CuI (6.3 mg, 0.033 mmol) and 3 (162 mg, 0.125 mmol) were then added. The solution was refluxed for 1.5h under nitrogen. The solvent was removed under reduced pressure. The residue was subjected to column chromatography (silica gel) using CH2Cl2/hexane = 1/3 (v/v) as eluent. Re-crystallization from CH2Cl2/MeOH gave 4 (75 mg, 36.1%) as a green solid.1H NMR ((CD3)2CO, 400 MHz) δ 9.61 (d, J=4.52 Hz, 2H), 9.53 (d, J=4.52 Hz, 2H), 8.78 (q, J=2.27 Hz, 2H), 7.75 (t, J= 8.36 Hz, 2H), 7.54 (d, J=3.92 Hz, 1H), 7.21-7.28 (m, 8H), 7.11 (d, J=8.40 Hz, 4H), 6.65 (d, J=3.92 Hz, 1H), 3.91 (t, J= 6.14 Hz, 8H), 2.66 (t, J= 7.74 Hz, 4H), 1.63-1.69 (m, 4H), 1.49 (s, 18H), 1.48 (s, 3H), 1.24-1.40 (m, 16H), 0.79-0.98 (m, 12H), 0.46-0.68 (m, 48H). MS (m/z, TOF) calcd for C105H139N5O4SSiZn 1658.96, found 1659.62.

Synthesis of ZZX-N9.To a solution of compound 4 (175 mg, 0.105 mmol) in dry THF (10 ml) was added TBAF (0.63 ml, 1M in THF) under nitrogen. The reaction mixture was stirred at room temperature for 1.5h and then quenched by water. The mixture was extracted with CH2Cl2 and dried over anhydrous MgSO4. The solvent of the organic layer was removed under a reduced pressure. The residue was dissolved in a mixture of dry THF (20 ml) and dry TEA (5 ml) and


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degassed with nitrogen for 30 minutes. Then Pd2(dba)3 (28.5 mg, 0.031 mmol), AsPh3 (62.1 mg, 0.203 mmol), and 5-bromothiophene-2-carboxylic acid(106 mg, 0.513 mmol) was added. The solution was refluxed under N2 for 4h. Then the solvent was removed under a reduced pressure and the residue was subjected to column chromatography (silica gel) using CH2Cl2/MeOH = 20/1 (v/v) as eluent. Re-crystallization from CH2Cl2/MeOH gave ZZX-N9 as green solid (74 mg, 43.2%). 1H NMR (CDCl3, 400 MHz) δ9.47 (d, J=4.52Hz, 2H), 9.49 (d, J=4.56Hz, 2H), 8.80 (d, J=4.52Hz, 2H), 8.75 (d, J=4.48Hz, 2H), 7.90 (t, J=2.88Hz, 1H), 7.71 (t, J=8.4Hz, 2H), 7.57 (d, J=3.84Hz, 1H), 7.14 (q, J=9.92Hz, 9H), 7.01 (d, J=8.48Hz, 5H), 3.87 (t, J=6.52Hz, 8H), 2.62 (t, J=7.76Hz, 4H), 1.61-1.69 (m, 4H), 1.27 (s, 12H), 0.90-0.96 (m, 6H), 0.71-0.77 (m, 12H), 0.450.63 (m, 48H).

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C NMR (CD2Cl2, 150MHz) δ159.80, 151.57, 151.07, 150.66, 150.52, 145.24,

139.11, 132.37, 131.82, 131.63, 130.59, 130.10, 129.83, 123.63, 120.23, 116.51, 115.99, 105.1, 68.60, 35.48, 31.75, 31.54, 31.35, 29.68, 29.65, 29.36, 28.73, 28.63, 25.27, 25.24, 22.64, 22.32, 13.87, 13.64. Elemental Analysis: calcd for C101H121N5O6S2Zn C 74.40%, H 7.48%, N 4.29%; found C 74.45%, H 7.51%, N 4.25%. MS (m/z, HRAPCIMS) calcd for C101H121N5O6S2Zn 1630.59, found 1630.81 [M]+.

Dye adsorption profiles

To obtain the dye adsorption profiles, two working electrode were immersed into a cuvette containing the dye solution, and the cuvette was sealed by a polytetrafluoroethylene cap. The working electrodes were the same as ones for cell fabrication. The variation of the absorbance at Q bands was recorded by a UV-vis spectrophotometer. The dye-loading density was obtained from the following equation:


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q ୲ = ൬C଴ −

A୲ C ൰ V ൗS A଴ ଴

where qt is the dye-loading density at time t; C0 is the initial concentration of the dye solution; A0 and At is the absorbance of the Q bands when t = 0 and t = t, respectively; V is the volume of the dye solution; S is the total size of the two films, which is 0.32 cm2 in present work.

Fabrication of solar cells

Working electrodes (8 µm-thick transparent layer + 3 µm-thick scattering layer) were dipped in a TiCl4 aqueous solution for 30 minutes at 70ºC. The electrode was then flushed with de-ionized (DI) water and ethanol and dried with an air flow. Electrodes were then sintered at 500ºC for 30 minutes. After being cooled to 80ºC, the electrodes were immersed in the dye solutions (0.2 mM) for 12 hours. The films were flushed with acetonitrile thoroughly and dried in air. The counter electrodes were prepared by casting a Pt solution on clean FTO glass and sintered at 450ºC for 20 minutes. Two electrodes were sandwiched using a 45 µm thick hot-melt ring (Surlyn, DuPont). The internal space was filled with liquid electrolytes (1.0 M 1,3-dimethylimidazolium iodide, 0.03 M iodine, 0.5 M tert-butylpyridine, 0.05 M LiI, 0.1 M guanidiniumthiocyanate, in an 85:15 acetonitrile/valeronitrile mixture) using a vacuum back filling system through two predrilled holes on the counter electrode. The holes were sealed with a Surlyn sheet and a thin glass cover.

Device characterizations

Current-voltage cures were obtained by using an AM 1.5G solar simulator equipped with a 450W xenon light (Oriel, model 9119) and an AM 1.5G filter (Oriel, model 91192). During the


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I-V measurement, a 0.09 cm2 mask was used to get a uniform working area for all the cells. In the incident photon to electron conversion efficiency (IPCE) measurement, light from a 300 W xenon lamp (ILC Technology, U.S.A.) was focused through a Gemini-180 double monochromator (JobinYvon Ltd., U.K.) onto the cell under test. The monochromator was incremented through the visible spectrum to generate IPCE spectra. A white light bias (1% sunlight intensity) was applied onto the sample during the testing with an AC model (10 Hz).

Photovoltage decay and charge extraction measurements

The determination of the electron life time and charge amounts was carried out by performing transient photovoltage decay measurement and charge extraction experiment, respectively. The measurement detail has been reported in previous work.19

Geometry Optimization

Calculations were performed at density functional theory (DFT) level. The initial structures of the porphyrin dyes were built using commercially available software. The torsion angles of meso phenyl groups and porphyrin ring were set to ~ 90°. The long alkyl groups, C6H13 and C8H17, were replaced by CH3 group to simplify the calculations. Geometry optimization was performed using B3LYP functional and 6-31G(D) basis set in acetonitrile solution by means of the conductor-like polarizable continuum model (CPCM) solvation model as implemented in the Gaussian 09 program package. The acetonitrile was used to mimic the solvents in electrolyte. Molecular orbitals were visualized by GaussView 3.0. No negative frequency was observed in the final optimized structures.


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RESULTS AND DISCUSSION Synthesis

Scheme 2 shows the synthesis of ZZX-N7 ~ ZZX-N9. Compound 1 was synthesized according to the procedure reported by Yeh et al.17 ZZX-N7 and ZZX-N8 were obtained from compound 1 under conventional Sonogashira reaction conditions with yields 50% ~ 60%. ZZX-N9 was also synthesized through a series of Sonogashira reactions. The starting materials compound 2 and compound 3 were prepared as reported in the literatures,17, 18 and were confirmed by 1H NMR. The reaction between compound 4 and 5-bromothiophene-2-carboxylic acid gave ZZX-N9 in ~ 45% yield. Measurements from geometry-optimized structures showed that the distance between C atom of COOH in an acceptor and N atom from diphenylamine in a donor increased from ZZX-N7 (17.24Å), ZZX-N8 (19.41Å) to ZZX-N9 (23.80Å). The donor and acceptor in ZZX-N8 falls in a line, however, they are bent in ZZX-N7 and ZZX-N9 due to the configuration of COOH in thiophene group.

C6H13

C6H13 C8H17O N

OC8H17 (i)

N N Zn N N OC8H17

C6H13C8H17O

N N Zn N N

N

TIPS

C8H17O N

A

C6H13 C8H17O

OC8H17

ZZX-N7 A=

S

S

C8H17O

C6H13

OC8H17

N N Zn N N

S

COOH

OC8H17 ZZX-N9

1

C6H13

C8H17O N S

TIPS

2

Br

S

(iii) COOH

C6H13

OC8H17

N N Zn N N

C8H17O

COOH S

ZZX-N8 A=

C6H13

C6H13

OC8H17

C8H17O

OC8H17

C8H17O

(ii) TIPS

3

N C6H13

S

OC8H17

N N Zn N N C8H17O

OC8H17

TIPS 4

Scheme 2. Synthesis of ZZX-N7, ZZX-N8, and ZZX-N9. Reaction conditions: (i) (a) TBAF, THF; (b) THF,TEA, Pd2(dba)3, AsPh3, 5-bromothiophene-2-carboxylic acid (for ZZX-N7) or 5bromothieno[3,2-b]thiophene-2-carboxylic acid (for ZZX-N8), (ii) (a) 2, TBAF, THF; (b)3, CuI, Pd(PPh3)2Cl2, THF,TEA, (iii) (a) TBAF, THF; (b) Pd2(dba)3, AsPh3, 5-bromothiophene-2carboxylic acid, THF,TEA.


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Absorption Spectra Figure 1 shows the absorption and emission spectra of three dyes in THF. All three dyes exhibited typical absorption features of porphyrin dyes with a strong Soret band and moderate Q bands, corresponding to S0 → S2 and S0 → S1 transitions, respectively. The Soret band was centered at 456 nm for ZZX-N7, 463 nm for ZZX-N8, and 465 nm for ZZX-N9, respectively. Similar to their Soret bands, Q bands red shifted from ZZX-N7 to ZZX-N9, which was consistent with their π-conjugation. Similar to the absorption, the emission was red-shifted from ZZX-N7 to ZZX-N9.

Figure1. Absorption (solid line) and emission (dash line) of ZZX-N7, ZZX-N8 and ZZX-N9 in THF.

Figure 2 compares the absorption spectra of porphyrins in THF with those on TiO2 films. All dye-coated films exhibited broader absorption bands compared to their counterparts in the solution, which are features of intermolecular interactions of dye aggregates.16, 20, 21 Figure 2a and Figure 2b clearly shows a blue-shoulder at Soret band. Thus ZZX-N7 and ZZX-N8 formed H-type aggregation on TiO2 nanoparticles. 22, 23 In addition, the blue-shoulder becomes more obvious from ZZX-N7 to ZZX-N8. This result suggests that ZZX-N8 suffers more severe


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aggregation on TiO2 nanoparticles.16 For ZZX-N9-coated film, as shown in Figure 2c, the Soret band is obviously blue-shifted, which may result from the deprotonation of the carboxylic acid group upon dye adsorption, and/or the H-aggregation of the dye molecules on TiO2 nanoparticles.24 It was noticed that Q bands increased with EtOH/THF ratio; while absorbance of Soret band decreased with EtOH/THF ratio, as shown in Figure 2d. Similar phenomena were also observed in other porphyrin aggregates, and it was due to the oscillator strength transfer from Soret band to Q bands.25-28 From the viewpoint of light-harvesting, it may be favorable for enhancing the cell performance.

Figure 2. Comparison of the normalized absorbance of ZZX-N7 coated (a), ZZX-N8 coated (b), and ZZX-N9 (c) coated films using 0.0/5.0 mixture (i.e., THF) as uptaking solvent and their counterparts in THF; (d) non-normalized absorbance of ZZX-N9 coated films. The uptaking time was 12h.

Electrochemical Property The cyclic-voltammetry measurements were then conducted to determine the energy levels. The highest occupied molecular orbitals (HOMO, HOMO=E1/2) were 0.82, 0.80 and 0.77 V vs. NHE for ZZX-N7, ZZX-N8 and ZZX-N9, respectively. All HOMOs are much lower than the redox potential of I-/I3- (~ 0.45 V vs. NHE) indicating the favorable dye regeneration. The excited-state


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oxidation potential E0-0* were obtained from the relation E0-0*=E1/2-E0-0. E0-0 is the zero-zero excitation energy obtained from the intersection wavelengths of the normalized UV-vis absorption and fluorescence spectra. As shown in Table 1, all calculated E0-0* values are more negative than the conduction band of the TiO2 (~ 0.5 V vs. NHE). Thus, both the HOMO and the lowest unoccupied molecular orbitals (LUMO, LUMO=E0-0*) are favorable for device operation.

Table 1 Electronic and electrochemical properties of ZZX-N7, ZZX-N8 and ZZX-N9. Redox potentials and energy levels Absorption/nm

Emissiona

(105M-1cm-1)

nm

E1/2b

Dyes

(V vs. NHE)

E0-0c

E1/2-E0-0

(V vs. NHE)

(V)

ZZX-N7

456 (1.45), 588 (0.09), 649 (0.22)

674

0.82

1.98

-1.16

ZZX-N8

463 (1.23), 654 (0.20)

679

0.80

1.93

-1.13

ZZX-N9

465 (1.31), 674 (0.23)

697

0.77

1.88

-1.11

a All dyes was excited at 550 nm in THF.bElectrochemical measurements were performed at room temperature with each porphyrin (0.5 mM) in THF/0.1 M TBAP/N2, GC working and Pt counter electrodes, Ag/AgCl reference electrode, scan rate=50 mV/s. cEstimated from the intersection wavelengths of the normalized UV-vis absorption and fluorescence spectra.

Photovoltaic Performance

Photovoltaic performance of ZZX-N7 ~ ZZX-N9 sensitized solar cells using different uptaking solvents was investigated. As summarized in Table 2, the overall power conversion efficiencies ranged from 3.46% ~ 7.51% for ZZX-N7-sensitized cells, 5.86% ~ 7.78% for ZZX-N8sensitized cells, and 4.57% ~ 7.53% for ZZX-N9-sensitized cells, respectively. Generally, power conversion efficiency (η) increased with the EtOH/THF ratio. But an exception was observed for ZZX-N9-sensitized cells: the η decreased from 7.53% for ZZX-N9 1.5/3.5 device to 6.70% for ZZX-N9 4.0/1.0 device because of the reduced short current density (Jsc). As shown in Figure 3d, decreased IPCE values at Soret and Q bands were observed for ZZX-N9 4.0/1.0 device in spite of its higher dye-loading density. Negative effect of dye-loading on η has been reported in


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previous works, and it was ascribed to increased aggregates.29-35In aggregates the energy of excited dye molecules is more prone to transfer to neighboring molecules, competing with the process of electron injection to the conduction band of TiO2 nanoparticles.

It was found the photovoltaic performance of dye under different dye loading was different. As shown in Fig. 3a, when the dye-loading was low (≤0.7×10-7mol/cm2), the power conversion efficiency increases in the order ZZX-N7 0.0/5.0 device < ZZX-N8 0.0/5.0 device < ZZX-N9 1.5/3.5 device, which is consistent with the trend in Jsc. As shown in Figure 3b, all devices showed typical characteristics of porphyrin based DSCs, exhibiting strong Soret and Q band signals. The long-wavelength peaks were found to be red shifted from ZZX-N7 to ZZX-N9, which is consistent with their absorption spectra. Red shifted absorption is expected to increase the Jsc. But considering the red-shift from ZZX-N7 to ZZX-N8 was only ~ 5 nm, red shifted absorption should not be the only reason for the drastic difference between the Jsc of ZZX-N7 0.0/5.0 device and ZZX-N8 0.0/5.0 device (7.81 mA/cm2 vs. 12.77 mA/cm2). Though three devices exhibited similar IPCE value at Soret band, the intensity of Q bands were found to be increased in the order ZZX-N7 0.0/5.0 device < ZZX-N8 0.0/5.0 device < ZZX-N9 1.5/3.5 device. A same trend was also observed for the bandwidth, which was consistent with their performance in Jsc. As mentioned above, the enhanced Q bands and broadened band width are two features of dye aggregates. Therefore, the increased Jsc from ZZX-N7 devices to ZZX-N9 devices should partially come from the increased dye aggregates. Figure 3c compares the cell performance of ZZX-N7 ~ ZZX-N9 when the dye-loading was relatively high (~ 1.75×107

mol/cm2). In spite of the lower dye-loading of ZZX-N7 4.9/0.1 device than that of ZZX-N8

2.5/2.5 device, comparable Jsc was observed, and the former exhibited higher η because of the higher Voc. For the ZZX-N9 4.0/1.0 device, decreased Jsc was observed comparing to ZZX-N9


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1.5/3.5 device leading to lower η. With these results, it can be concluded that dye aggregates is favorable for cell performance in some extent by broadening the absorption bands and enhancing the Q bands; but further increasing of dye aggregates will decrease the electron injection, resulting inferior power conversion.

Table 2 Photovoltaic performances of ZZX-N7, ZZX-N8 and ZZX-N9 using different uptaking solvents. Dye

EtOH/THF (v/v)

qe (10-7mol/cm2)

Voc (mV)

Jsc (mA/cm2)

FF (%)

η (%)

ZZX-N7

5.0/0.0

1.99

732

15.39

63.33

7.51

4.9/0.1

1.55

732

14.57

65.54

7.36

0.0/5.0

0.70

592

7.81

70.97

3.46

4.9/0.1

2.38

741

14.25

69.97

7.78

2.5/2.5

1.73

707

14.04

70.59

7.38

1.5/3.5

1.30

661

13.97

71.35

6.94

0.0/5.0

0.67

608

12.77

71.68

5.86

4.0/1.0

1.75

680

13.51

69.28

6.70

1.5/3.5

0.46

656

15.46

70.57

7.53

0.0/5.0

0.36

588

10.04

73.52

4.57

ZZX-N8

ZZX-N9

Figure 3. Current-photovoltage curves and IPCE spectra of porphyrin-sensitized cells under low dye-loading (left) and high dye-loading (right).


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Adsorption Profiles

Adsorption profiles in different EtOH/THF mixtures are shown in Figure 4. The adsorptions in EtOH were not tested for ZZX-N8 and ZZX-N9 because of their low solubility in EtOH. As shown in Figure 4, it only took ~ 1h to achieve equilibrium in THF solution; upon adding EtOH, the equilibrium time was prolonged. It seems that the equilibrium time was independence of the molecular structure of the dye as ZZX-N7 ~ ZZX-N9 showed similar equilibrium time in THF. Unlike the equilibrium time, the equilibrium adsorption density (qe) depended on both uptaking solvent and molecular structure of porphyrin dyes. As shown in Table 2, qe increased with the EtOH/THF ratio. From the general adsorption knowledge, increased qe was due to the decreased solubility of porpphyrin dyes in solvents with higher EtOH/THF ratio. When the same uptaking solvent was used (i.e., THF), the qe was in the order ZZX-N7 > ZZX-N8 > ZZX-N9, indicating that the longer the dye molecule is, the less the dye will be adsorbed. To confirm the homogenous dye coverage across the film, SEM measurements were conducted. For a porphyrin coated film, the element zinc should come from porphyrin only. Thus, the distribution of porphyrin dyes can be represented by zinc element. Figure 5a and Figure 5b shows the crosssection view of SEM images of ZZX-N7-coated films obtained from EtOH solution and THF solution, respectively. Homogeneous distribution of zinc element across the cross-section indicates the homogeneous dye coverage across the film.


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Figure 4. Adsorption profiles of ZZX-N7, ZZX-N8 and ZZX-N9 from different EtOH/THF mixtures.

Figure 5. Cross-section view of SEM images of ZZX-N7-coated films from (a) EtOH and (b) THF. The bottom insets are EDX mapping results of the yellow square region. The uptaking time was 12h. Transient Photovoltage Decay Measurement

It is noted that open-circuit voltage (Voc) increased with EtOH/THF ratios for all three dyes. Transient photovoltage decay measurements were performed to study the relationship between Voc and EtOH/THF ratios. An increase in Voc can originate from upward shift of the Fermi level of the TiO2 or retarded charge recombination. Figure 6a, Figure 6c, and Figure 6e plot the Voc vs. Q curves. Both ZZX-N7 and ZZX-N8 based cells showed a downshifted EF when the solvent changed from THF to EtOH/THF mixtures. The downshift of EF in EtOH or EtOH/THF


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mixtures should come from the adsorption of protons coming from EtOH.36-38 Obviously, the downshift of EF is inverse with the gain in Voc. The situation for ZZX-N9-sensitized cells seemed to be more complicate: the position of EF was in the order 1.5/3.5 device > 0.0/5.0 device > 4.0/1.0 device. The shift of EF observed in ZZX-N9-sensitized cells should be the comprehensive result of solvent effects and the change in dye dipole moment. 39-41 Again, the shift of EF in ZZX-N9-sensitized cells cannot be ascribed to the increase in Voc. These results indicate that the increase in Voc should origin from the retarded recombination. It has been reported that adsorption of dye molecules would decrease the concentration of I3- in the vicinity of the TiO2 surface.42, 43 Figure 6b, Figure 6d, and Figure 6f clearly shows that electron lifetime increased with EtOH/THF ratios. Increasing the EtOH/THF ratio will increase the dye-loading, thus retarded recombination is expected.

Figure 6. Comparison of the charges extracted from the porphyrin-sensitized TiO2 films at a certain Voc and electron lifetime against electron density.


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Two conflicting results were obtained as we tried to study the effects of molecular structure on blocking effect of adsorbed dyes. Under low dye-loading (ZZX-N7 0.0/5.0 device, ZZX-N8 0.0/5.0 device, ZZX-N9 1.5/3.5 device), ZZX-N7 0.0/5.0 device showed shortest electron lifetime, as shown in Figure 7a. The electron lifetime for ZZX-N8 0.0/5.0 device and ZZX-N9 1.5/3.5 device was nearly the same. This is consistent with the lower energy conversion efficiency of ZZX-N7. However, considering the lower dye-loading of ZZX-N9 1.5/3.5 device than ZZX-N8 0.0/5.0 device (0.46×10-7 mol/cm2 vs. 0.67×10-7 mol/cm2), the better energy conversion efficiency of ZZX-N9 1.5/3.5 device may be due to the stronger blocking effect of ZZX-N9 stronger than ZZX-N8. Figure S1 shows the geometry-optimized structures of three dyes (long-alkyl chains were re-placed by CH3). ZZX-N7 and ZZX-N8 anchored nonvertically on the TiO2 surface. One phenyl group of the electron donor is almost parallel to the mesophenyl groups. The C6H13 group will fill the nearby area (circled area in the Figure S1) to provide more effective blocking effect than other two. Contrarily, when the dye-loading was relatively high (~1.75×10-7 mol/cm2), the electron lifetime decreased in the order ZZX-N7 4.9/0.1 device > ZZX-N8 2.5/2.5 device > ZZX-N9 4.0/1.0 device as shown in Figure 7b. Therefore, there should be two different mechanisms control the blocking effects of adsorbed dyes under different dye-loading. Previous studies show the blocking effect of adsorbed dyes can originate from either the alky chains or the dye aggregates.42 The molecular structures of ZZXN7-N9 are quite flat (the donor, porphyrin ring, and acceptor almost fall in one plane, see Figure S1), the ZZX-N9 is much longer than ZZX-N7 and ZZX-N8. Therefore, the tendency for dyes to aggregate on TiO2 nanoparticles is expected to increase in the order ZZX-N7 < ZZX-N8 < ZZXN9. The aggregation seems more pronounced when the dye-loading density is higher; therefore


20

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the aggregation is a determination factor under such a circumstance. Whereas blocking effect is becoming dominate when the dye-loading is low.

Figure 7.Comparison of the electron lifetime against electron density.

It is well known that introduction of long alkyl chains can prevent the dye aggregation and suppress the charge recombination between the electron in TiO2 nanoparticles and I3- in electrolyte. Though all three dyes are equipped, their aggregation on the TiO2 nanaoparticles and charge recombination are different. Fusing an extra thiophene into thiophene carboxyl acid led to


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more serious dye aggregation in ZZX-N8 and ZZX-N9 than in ZZX-N7 as demonstrated by absorption spectra on TiO2 films. This result indicates that the two n-hexyl chains in donor part and four octyloxy chains on porphyrin ring have limited effect in preventing dye aggregation.44 On the other hand, the electron lifetime for three porphyrins under high dye-loading reveals that the number of alkyl chains cannot be equated with the effect to suppress the charge recombination. We have found that adding extra alkyl chains did not offer an extra shielding effect to reduce the charge recombination.45 Instead, the angle between alkyl chains and molecular plane may be more important.46 In ZZX-N7 and ZZX-N8, the two n-hexyl chains on diphenylamine are aligned away from the plane of porphyrin ring because of the steric effect of diphenylamine. However, the steric effect between diphenylamine and porphyrin ring in ZZXN9 vanishes after inserting an extra thiophene between them. As a result, the weakened shielding effect of n-hexyl chains is expected. Similar with their role in preventing dye aggregation, the shorter electron lifetime of ZZX-N8 2.5/2.5 device than that of ZZX-N7 4.9/0.1 device indicates that the alkyl chains on donor part and porphyrin ring have limited shielding effect to suppress charge recombination, and extra alkyl chains are needed on elongated π-linker.

CONCLUSIONS

Three porphyrin dyes incorporating thienyl groups were designed and synthesized. With the πconjugation increased in the order ZZX-N7 < ZZX-N8 < ZZX-N9, red-shifted absorption spectra were observed. Mixtures with different EtOH/THF ratios were used as uptaking solvents. Dye adsorption profiles showed that higher dye-loadings were obtained from the solutions with higher EtOH/THF. This was interpreted with the lower solubility of porphyrin dyes in EtOH/THF mixtures. And the dye-loading decreased with molecular length. Indicated by the


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result of absorption of porphyrin coated TiO2 films, the dye aggregates increased with the molecular length and the dye-loading. Under low dye-loading, dye aggregates are favorable for power conversion because of broadened band width and enhanced Q bands; while under high dye-loading, the much decreased electron injection overwhelmed the positive effects mention above, resulting decreased power conversion efficiency. Comparison of electron life time revealed that the blocking effect of the adsorbed dyes originated from dye aggregates when the dye-loading was low; when the dye-loading was high, it came from the alky chains.

AUTHOR INFORMATION

Corresponding Authors

Emails:[email protected] (ZZ). [email protected] (HH); Phone: 217-5816231 (office)

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes

The authors declare no competing financial interest

ACKNOWLEDGEMENT


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This work was partially supported by the National Basic Research Program of China (973 program), Grant No. 2011CBA00703, the Fundamental Research Funds for the Central Universities, Grant No. HUST: 2014TS016 (Z.Z.), Eastern Illinois University the President's Fund for Research and Creative Activity (H.H.), and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575 (HH).

Supporting Information Available

The geometry-optimized structures of ZZX-N7, ZZX-N8 and ZZX-N9. This information is available free of charge via the Internet at http://pubs.acs.org

REFERENCES

(1)Nazeeruddin, M. K.; Angelis, F. D.; Fantacci, S.; Selloni, A.; Viscardi, G.; Liska, P.; Ito, S.; Takeru, B.; Grätzel, M. Combined Experimental and DFT-TDDFT Computational Study of Photoelectrochemical Cell Ruthenium Sensitizers. J. Am. Chem. Soc. 2005, 127, 16835–16847. (2)Gao, F.; Wang, Y.; Shi, D.; Zhang, J.; Wang, M.; Jing, X.; Humphry-Baker, R.; Wang, P.; Zakeeruddin, S. M.; Grätzel, M. Enhance the Optical Absorptivity of Nanocrystalline TiO2 Film with High Molar Extinction Coefficient Ruthenium Sensitizers for High Performance DyeSensitized Solar Cells. J. Am. Chem. Soc. 2008, 130, 10720–10728. (3)Yum, J. H.; Walter, P.; Huber, S.; Rentsch, D.; Geiger, T.; Nüesch, F.; Angelis, F. D.; Grätzel, M.; Nazeeruddin, M. K. Efficient Far Red Sensitization of Nanocrystalline TiO2 Films by An Unsymmetrical Squaraine Dye. J. Am. Chem. Soc. 2007, 129, 10320–10321. (4)Imahori, H.; Matsubara, Y.; Iijima, H.; Umeyama, T.; Matano, Y.; Ito, S.; Niemi, M.; Tkachenko, N. V.; Lemmetyinen, H. Effects of meso-Diarylamino Group of Porphyrins as


24

Page 25 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Sensitizers in Dye-Sensitized Solar Cells on Optical, Electrochemical, and Photovoltaic Properties. J. Phys. Chem. C 2010,114,10656–10665. (5)Campbell, W. M.; Jolley, K. W.; Wagner, P.; Wagner, K.; Walsh, P. J.; Gordon, K. C.; Schmidt-Mende, L.; Nazeeruddin, M. K.; Wang, Q.; Grätzel, M. et al. Highly Efficient Porphyrin Sensitizers for Dye-Sensitized Solar Cells. J. Phys. Chem. C 2007,111,11760–11762. (6)Bessho, T.; Zakeeruddin, S. M.; Yeh, C.-Y.; Diau, E. W.-G.; Grätzel, M. Highly Efficient Mesoscopic Dye-Sensitized Solar Cells Based on Donor–Acceptor-Substituted Porphyrins. Angew.Chem. Int. Ed. 2010, 49, 6646 –6649. (7)Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F. E.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M. K.; Grätzel, M. Dye-Sensitized Solar Cells with 13% Efficiency Achieved through the Molecular Engineering of Porphyrin Sensitizers. Nat. Chem. 2014, 6, 242–247. (8)Liu, J.; Li, R.; Si, X.; Zhou, D.; Shi, Y.; Wang, Y.; Jing, X.; Wang, P. Oligothiophene DyeSensitized Solar Cells. Energy Environ. Sci. 2010, 3, 1924–1928. (9)Hara, K.; Wang, Z.-S.; Sato, T.; Furube, A.; Katoh, R.; Sugihara, H.; Dan-oh, Y.; Kasada, C.; Shinpo, A.; Suga, S. Oligothiophene-Containing Coumarin Dyes for Efficient Dye-Sensitized Solar Cells. J. Phys. Chem. B 2005,109,15476–15482. (10)Kang, X.; Zhang, J.; O’Neil, D.; Rojas, A. J.; Chen, W.; Szymanski, P.; Marder, S. R.; ElSayed, M. A. Effect of Molecular Structure Perturbations on the Performance of the D−A−π−A Dye Sensitized Solar Cells. Chem. Mater. 2014, 26, 4486−4493. (11)Wu, S.-J.; Chen, C.-Y.; Chen, J.-G.; Li, J.-Y.; Tung, Y.-L.; Ho, K.-C.; Wu, C.-G. An Efficient Light-Harvesting Ruthenium Dye for Solar Cell Application. Dyes and Pigments 2010, 84, 95–101. (12)Chen, C.Y.; Wu, S. J.; Li, J.Y.; Wu, C. G.; Chen, J.G.; Ho, K.C. A New Route to Enhance the Light-Harvesting Capability of Ruthenium Complexes for Dye-Sensitized Solar Cells. Adv. Mater. 2007,19, 3888–3891.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 41

(13)Mishra, A.; Fischer, M.; Bäuerle, P. Metal-Free Organic Dyes for Dye-Sensitized Solar Cells: From Structure: Property Relationships to Design Rules. Angew. Chem. Int. Ed. 2009, 48, 2474–2499. (14)Lu, J.; Xu, X.; Cao, K.; Cui, J.; Zhang, Y.; Shen, Y.; Shi, X.; Liao, L.; Cheng, Y.; Wang, M. D–π–A Structured Porphyrins for Efficient Dye-Sensitized Solar Cells. J. Mater. Chem. A 2013, 1, 10008–10015. (15)Imahori, H.; Hayashi, S.; Hayashi, H.; Oguro, A.; Eu, S.; Umeyama, T.; Matano, Y. Effects of Porphyrin Substituents and Adsorption Conditions on Photovoltaic Properties of PorphyrinSensitized TiO2 Cells. J. Phys. Chem. C 2009,113,18406–18413. (16)Wang, C.-L.; Lan, C.-M.; Hong, S.-H.; Wang, Y.-F.; Pan, T.-Y.; Chang, C.-W.; Kuo, H.-H.; Kuo, M.-Y.; Diau, E. W.-G.; Lin, C.-Y. Enveloping Porphyrins for Efficient Dye-Sensitized Solar Cells. Energy Environ. Sci. 2012, 5, 6933–6940. (17)Yella, A.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W.-G.; Yeh, C.-Y.; Zakeeruddin, S. M.; Grätzel, M. Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency. Science 2011, 334, 629−634. (18)Zhang, T.-G.; Zhao, Y.; Song, K.; Asselberghs, I.; Persoons, A.; Clays, K.; Therien, M. J. Electronic Modulation of Hyperpolarizable (Porphinato)zinc(II) Chromophores Featuring Ethynylphenyl-,

Ethynylthiophenyl-,

Ethynylthiazolyl-,

and

Ethynylbenzothiazolyl-Based

Electron Donating and Accepting Moieties. Inorg. Chem. 2006, 45, 9703−9712. (19)Chen, C.-Y.; Wang, M.; Li, J.-Y.; Pootrakulchote, N.; Alibabaei, L.; Ngocle, C.; Decoppet, J.-D.; Tsai, J.-H.; Grätzel, M.; Wu, C.-G. et al. Highly Efficient Light-Harvesting Ruthenium Sensitizer for Thin-Film Dye-Sensitized Solar Cells. ACS Nano 2009, 3, 3103–3109. (20)Kasha, M., Energy Transfer Mechanisms and the Molecular Exciton Model for Molecular Aggregates. Radiat. Res. 1963, 20, 55–71.


26

Page 27 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(21)Lo, C.-F.; Luo, L.; Diau, E. W.-G.; Chang, I.-J.; Lin, C.-Y. Evidence for the Assembly of Carboxyphenylethynyl Zinc Porphyrins on Nanocrystalline TiO2 Surfaces. Chem.Commun. 2006, 1430–1432. (22)Maiti, N. C.; Mazumdar, S.; Periasamy, N. J-and H-Aggregates of Porphyrin−Surfactant Complexes: Time-Resolved Fluorescence and Other Spectroscopic Studies. J. Phys. Chem. B 1998,102,1528–1538. (23)Sigge, U.; Bindig, U.; Endisch, C.; Komatsu, T.; Tsuchida, E.; Voigt, J.; Fuhrhop, J.-H. Photophysical and Photochemical Properties of Porphyrin Aggregates. Ber.Bunsenges. Phys. Chem. 1996, 100, 2070–2075. (24)Wang, Y.; Xu, L.; Wei, X.; Li, X.; Ågren, H.; Wu, W.; Xie, Y. 2-Diphenylaminothiophene as the Donor of Porphyrin Sensitizers for Dye-Sensitized Solar Cells. New J. Chem. 2014, 38, 3227–3225. (25)Kano, H.; Saito, T.; Kobayashi, T. Dynamic Intensity Borrowing in Porphyrin J-Aggregates Revealed by Sub-5-fs Spectroscopy. J. Phys. Chem. B 2001,105, 413–419. (26)Davydov, A. S. Theory of Molecular Excitons; McGrawHill: New York, 1962. (27) Kasha, M. In Physical and Chemical Mechanisms in Molecular Radiation Biology; Plenum Press: New York,1991. (28)Zimmermann, J.; Siggel, U.; Fuhrhop, J.-H.; Röder, B., Excitonic Coupling Between B and Q Transitions in A Porphyrin Aggregate. J. Phys. Chem. B 2003, 107, 6019–6021. (29)Wang, Q.; Campbell, W. M.; Bonfantani, E. E.; Jolley, K. W.; Officer, D. L.; Walsh, P. J.; Gordon, K.; Baker, R. H.; Nazeeruddin, M. K.; Grätzel, M. Efficient Light Harvesting by Using Green

Zn-Porphyrin-Sensitized

Nanocrystalline

TiO2

Films.

J.

Phys.

Chem.

B

2005,109,15397−15409. (30)Hasobe, T.; Imahori, H.; Fukuzumi, S.; Kamat, P. V. Nanostructured Assembly of Porphyrin Clusters for Light Energy Conversion. J. Mater.Chem. 2003, 13, 2515−2520.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 41

(31)Rochford, J.; Galoppini, E. Zinc(II) Tetraarylporphyrins Anchored to TiO2, ZnO, and ZrO2 Nanoparticle Films Through Rigid-Rod Linkers. Langmuir 2008, 24, 5366−5374. (32)Tacconi, N. R.; Chanmanee, W.; Rajeshwar, K.; Rochford, J.; Galoppini, E. Photoelectrochemical Behavior of Polychelate Porphyrin Chromophores and Titanium Dioxide Nanotube Arrays for Dye-Sensitized Solar Cells. J. Phys. Chem. C 2009, 113, 2996−3006. (33)Nogueira, A. F.; Furtado, L. F. O.; Formiga, A. L. B.; Nakamura, M.; Araki, K.; Toma, H. E. Sensitization

of

TiO2

by

Supramolecules

Containing

Zinc

Porphyrins

and

Ruthenium−Polypyridyl Complexes. Inorg. Chem. 2004, 43, 396−398. (34)Choi, H.; Baik, C.; Kang, S. O.; Ko, J.; Kang, M. S.; Nazeeruddin, M. K.; Grätzel, M. Highly Efficient and Thermally Stable Organic Sensitizers for Solvent-Free Dye-Sensitized Solar Cells. Angew. Chem. 2008, 120, 333–336. (35)Ooyama, Y.; Harima,Y. Photophysical and Electrochemical Properties, and Molecular Structures of Organic Dyes for Dye-Sensitized Solar Cells. ChemPhysChem 2012, 13, 4032– 4080. (36)Chen, X.; Jia, C.; Wan, Z.; Feng, J.; Yao, X. Effects of Different Solvent Baths on the Performances of Dye-Sensitized Solar Cells: Experimental and Theoretical Investigation. Organic Electronics 2014, 15, 2240–2249. (37)Redmond, C.; Fitzmaurice, D. Spectroscopic Determination of Flatband Potentials for Polycrystalline TiO2 Electrodes in Nonaqueous Solvents. J. Phys. Chem. 1993, 97, 1426–1430. (38)Enright, B.; Redmond, C.; Fitzmaurice, D. Spectroscopic Determination of Flatband Potentials for Polycrystalline TiO2 Electrodes in Mixed Solvent Systems. J. Phys. Chem. 1994, 98, 6195–6200. (39)Nakade, S.; Kanzaki, T.; Kubo, W.; Kitamura, T.; Wada, Y.; Yanagida, S. Role of Electrolytes on Charge Recombination in Dye-Sensitized TiO2 Solar Cell (1): The Case of Solar Cells Using the I-/I3- Redox Couple. J. Phys. Chem. B 2005, 109, 3480–3487.


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Page 29 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(40)Rühle, S.; Greenshtein, M.; Chen, S.-G.; Merson, A.; Pizem, H.; Sukenik, C. S.; Cahen, D.; Zaban, A. Molecular Adjustment of the Electronic Properties of Nanoporous Electrodes in DyeSensitized Solar Cells. J. Phys. Chem. B 2005,109, 18907–18913. (41)Zervaki,G. E.; Roy, M. S.; Panda, M. K.; Angaridis, P. A.; Chrissos, E.; Sharma, G. D.; Coutsolelos, A. G. Efficient Sensitization of Dye-Sensitized Solar Cells by Novel Triazine Bridged Porphyrin−Porphyrin Dyads. Inorg. Chem. 2013, 52, 9813−9825. (42)Miyashita, M.; Sunahara, K.; Nishikawa, T.; Uemura,Y.; Koumura, N.; Hara, K.; Mori, A.; Abe, T.; Suzuki, E.; Mori, S. Interfacial Electron-Transfer Kinetics in Metal-Free Organic DyeSensitized Solar Cells: Combined Effects of Molecular Structure of Dyes and Electrolytes. J. Am. Chem. Soc. 2008,130, 17874–17881. (43)O’Regan, B.; Li, X.; Ghaddar, T. Dye Adsorption, Desorption, and Distribution in Mesoporous TiO2 Films, and Its Effects on Recombination Losses in Dye Sensitized Solar Cells. Energy Environ. Sci. 2012, 5, 7203–7215. (44)Liu, B.; Liu, Q.; You, D.; Li, X.; Naruta, Y.; Zhu, W. Molecular Engineering of Indoline Based Organic Sensitizers for Highly Efficient Dye-Sensitized Solar Cells. J. Mater. Chem. 2012, 22, 13348–13356. (45)Li, W.; Si, L.; Liu, Z.; Zhao, Z.; He, H.; Zhu, K.; Moore, B.; Cheng, Y.-B. Fluorene Functionalized Porphyrins as Broadband Absorbers for TiO2 Nanocrystalline Solar Cells. J. Mater. Chem. A 2014, 2, 13667–13674. (46)Wu, Y.; Zhu, W. Organic Sensitizers from D–π–A to D–A–π–A: Effect of the Internal Electron-Withdrawing Units on Molecular Absorption, Energy Levels and Photovoltaic Performances. Chem. Soc. Rev. 2013, 42, 2039-2058.


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Thiophene-Functionalized Porphyrins: Synthesis, Photophysical

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