Dye-sensitized solar cells with improved performance using cone-calix[4]arene based dyes.

CHEMSUSCHEM FULL PAPERS DOI: 10.1002/cssc.201402401

Dye-Sensitized Solar Cells with Improved Performance using Cone-Calix[4]Arene Based Dyes Li-Lin Tan,[a] Jun-Min Liu,*[a] Shao-Yong Li,[b] Li-Min Xiao,[c] Dai-Bin Kuang,[a] and ChengYong Su*[a] Three cone-calix[4]arene-based sensitizers (Calix-1–Calix-3) with multiple donor–p–acceptor (D–p–A) moieties are designed, synthesized, and applied in dye-sensitized solar cells (DSSCs). Their photophysical and electrochemical properties are characterized by measuring UV/Vis absorption and emission spectra, cyclic voltammetry, and density functional theory (DFT) calculations. Calix-3 has excellent thermo- and photostability, as illustrated by thermogravimetric analysis (TGA) and dye-aging tests, respectively. Importantly, a DSSC using the

Calix-3 dye displays a conversion efficiency of 5.48 % in under standard AM 1.5 Global solar illumination conditions, much better than corresponding DSSCs that use the rod-shaped dye M-3 with a single D–p–A chain (3.56 %). The dyes offer advantages in terms of higher molar extinction coefficients, longer electron lifetimes, better stability, and stronger binding ability to TiO2 film. This is the first example of calixarene-based sensitizers for efficient dye-sensitized solar cells.

Introduction Dye-sensitized solar cells (DSSCs) have been studied extensively since reports of ruthenium complex-sensitized TiO2 solar cells in 1991.[1] Recently, conversion efficiencies of over 12 %,[2] 11 %,[3] and 10 %[4] were reported for liquid DSSCs based on zinc and ruthenium complexes as well as pure organic dyes, respectively, under air mass 1.5 global (AM 1.5 G) irradiation. Most organic sensitizers, constructed with donor, linker, and acceptor segments (D–p–A), feature high absorption coefficients, simple synthesis routes, low costs, and diverse structures that make them advantageous compared to metal-complex sensitizers, which are costly and require laborious purification. Nevertheless, one disadvantage of organic sensitizers in DSSCs is aggregate formation among molecules, which leads to self-quenching, instability, and reduced electron injection.[5] [a] L.-L. Tan, Dr. J.-M. Liu, Prof. D.-B. Kuang, Prof. C.-Y. Su MOE Laboratory of Bioinorganic and Synthetic Chemistry State Key Laboratory of Optoelectronic Materials and Technologies Lehn Institute of Functional Materials School of Chemistry and Chemical Engineering Sun Yat-Sen University 510275 Guangzhou (PR China) E-mail: [email protected] [email protected]

A successful solution to this problem was the introduction of more donor segments into the primary donor to form coneshaped structures, which offered decreased aggregation, lower charge recombination, and better stability.[6] We have reported a series of cone-shaped organic sensitizers with duplex starburst triphenylamine and carbazole donors, achieving a strikingly high efficiency of 10 % in liquid DSSCs.[7] Furthermore, the light-harvesting ability of the sensitizers is important for the conversion efficiency from solar light to electricity. The number of light-harvesting units adsorbed onto TiO2 determines the conversion efficiency (h) of DSSCs. DSSCs employing organic sensitizers with two D–p–A chains have enhanced h values compared to the corresponding single D–p–A sensitizers.[8] This design opens up the promising possibility to prepare more D–p–A branched dyes for increased light–current conversion efficiencies. Herein, inspired by this approach, we design a new series of cone-calixarene-based dyes (Scheme 1) as DSSC sensitizers. Cal-

[b] Dr. S.-Y. Li Tianjin Key Laboratory on Technologies Enabling Development of Clinical Therapeutics and Diagnostics (Theranostics) School of Pharmacy, Basic Medical Research Center Tianjin Medical University 300070 Tianjin (PR China) [c] Prof. L.-M. Xiao School of Computer Science and Engineering Beihang University 100191 Beijing (PR China) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201402401.

2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Scheme 1. Structures of calix[4]arene dyes Calix1-3 and the comparison dye M-3.

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CHEMSUSCHEM FULL PAPERS ix[n]arenes have been widely investigated as host materials or as versatile platforms, among which calix[4]arene is the most attractive because it can be easily transformed into various derivatives by simple modifications.[9] In addition, calix[4]arene derivatives can be immobilized in cone conformation by the introducing of propyl or larger groups into the lower rim.[10] Despite the fact that the calix[4]arene derivatives possess so many unique features, investigation of the calix[4]arene-based sensitizers as a key component in DSSCs has not been reported. We therefore set out to prepare dyes consisting of a nbutyl-substituted calix[4]arene donor, a 2-cyanoacrylic acid acceptor, and an oligothiophene spacer. Calix[4]arene was used as an electron donor for the following reasons: (1) the n-butyl substituted calix[4]arene derivative has a cone conformation with four substituted alkyl chains, which is not only beneficial to impede dye aggregation but also helps to suppress the dark current caused by the recombination of conduction-band electrons with I3 ; (2) it has four light-harvesting units per molecule, which is not only favorable to achieve high molar extinction coefficients but also ensures more effective electron transfer between the dye and surrounding TiO2 ; (3) it has multianchoring groups in one molecule, which would increase the stability of the dyes adsorbed on the TiO2 film; and (4) it has high thermal stability, which is vital for the lifetime of the solar cells.

Results and Discussion Synthesis The synthesis of three calixarene-based dyes and the comparison dye M-3 is depicted in Scheme 2 and detailed in Figure S1 (Supporting Information). A Suzuki reaction between Calix-

Scheme 2. Synthesis of calix[4]arene dyes Calix1–3.


www.chemsuschem.org Br[11] and 5-formylthiophene-2-boronic acid (or 5’-formyl-2,2’bithiophene-5-boronic acid) was successfully executed in the presence of anhydrous K2CO3 and PdCl2(dppf) to produce Calix-1-CHO (or Calix-2-CHO). A Knoevenagel reaction between Calix-1-CHO (or Calix-2-CHO) and cyanoacetic acid then took place under piperidine to finally result in Calix-1 (or Calix-2) with a high yield. The dye Calix-3 was conveniently obtained by a four-step process involving Suzuki coupling to introduce the thiophene, bromination reaction, a Suzuki coupling to liberate the aldehyde, followed by Knoevenagel condensation. Photophysical properties The absorption spectra of the dyes in CHCl3 solution are shown in Figure 1, and the corresponding data are listed in Table 1. The compounds have an intense absorption band at 400–500 nm, which can be attributed to a p–p* transition with charge-transfer character. The absorption wavelength (lmax) normally increases with increasing conjugation length.[12] The order of lmax values, Calix-3 > Calix-2 > Calix-1, is in accordance with this trend. The molar extinction coefficients of the Calix-3 dyes are nearly double that of M-3, which is the result of the four D–p–A units in one Calix-3 molecule. The dyes exhibit a red-shift and broadened absorption profile (Supporting Information, Figure S2) when absorbed on TiO2 compared to the solution phase, most likely due to aggregation or electronic coupling on the TiO2 surface.[13] There is a very prominent broadened band for M-3, suggesting significant self-aggregation, because rod-shaped M-3 has a more planar structure at the excited state. The amount of the adsorbed dye decreases as M-3 > Calix-1 > Calix-2 > Calix-3 (Table 1). The adsorption is directly related to the molecular size and structure of the dye. M3 exhibits a two-fold higher loading on the TiO2 surface than Calix-3 because of its small size. We also measured FT-IR spectra of the three cone-calix[4]arene-based dyes. Figure S3 (Supporting Information) shows the FTIR spectra of the dye powders and the dyes adsorbed on TiO2. For the powders of Calix-1, Calix-2, and Calix-3, the C=O stretching band of carboxylic acid ( COOH) was observed at n˜ = 1592, 1622, and 1659 cm 1, respectively. When the dyes were adsorbed on TiO2 surface, the C=O stretching bands at n˜ = 1592, 1622, 1659 cm 1 disappeared and instead peaks were found at n˜ = 1581, 1593, and 1611 cm 1 for Calix-1, Calix-2, and Calix-3, respectively. This indicates deprotonation of the ChemSusChem 0000, 00, 1 – 9

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www.chemsuschem.org Molecular orbital calculations The optimized geometries of Calix-1–Calix-3 were mimicked through molecular modelling with the GAUSSIAN 03 package. The cone conformation of every compound is clearly shown in Figure 2. All dihedral angles between the thienyl planes are

Figure 1. Absorption spectra of CHCl3.

&

M-3,

*

Calix-1,

~

Calix-2, and

!

Calix-3 in

Table 1. Absorption and electrochemical data of the dyes. Dye

lmax [nm]

e [104 m 1 cm 1]

Eox (vs Fc/Fc + )[a] [V]

E0–0[b] [eV]

M-3 Calix-1 Calix-2 Calix-3

498 396 447 468

3.83 9.86 8.89 6.05

0.79 1.19 1.26 1.32

2.19 2.64 2.35 2.32

E0–0*[c] [V] 1.40 1.45 1.09 1.00

[a] The oxidation potential of the dyes was measured with a scan rate of 50 mV s 1 (vs NHE). [b] E0–0 was determined from the intersection of absorption and emission spectra in CHCl3. [c] E0–0*: The excited state oxidation potential vs NHE.

four COOH groups in calix[4]arene-based dyes taking place on the TiO2 surface. The formed carboxylate ion may coordinate to a metal ion in unidentate mode (Figure S3 D). Electrochemical properties Quasireversible oxidation waves attributed to the oxidation of oligothiophene were found in the four dyes, and increased as the number of thiophene rings increased for Calix-1–Calix-3 dyes. The zero–zero excitation energy, estimated from the absorption onset and the oxidation potential, was used to calculate the excited state potential (E0–0*; Supporting Information, Figure S4). The E0–0* values ( 1.45 ~ 1.00 V vs. normal hydrogen electrode (NHE), Table 1) are more negative than the conduction band edge of TiO2, 0.5 V, vs. NHE, thus offering a thermodynamic driver for efficient electron injection. On the other hand, the first oxidation potentials of the dyes (0.79 ~ 1.32 V vs NHE, Table 1) are more positive than the I /I3 redox couple located at ~ 0.4 V vs NHE, which promotes dye regeneration and suppresses recapture of the injected electrons by the dye cation radical.


Figure 2. Optimized structures of a) Calix-1, b) Calix-2, and c) Calix-3.

presented in Table S1 (Supporting Information), and are all coplanar with each other. The thienyl moiety is also coplanar with the 2-cyano-acrylic acid acceptor because of the extended p-bond conjugation. Such a group promotes large electronic interactions to facilitate charge separation. The cone conformaChemSusChem 0000, 00, 1 – 9

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CHEMSUSCHEM FULL PAPERS tion of calixarene derivatives also reduces contact between molecules and enhances their thermostability. The thermal properties of the four dyes were examined (Supporting Information, Figure S5). In thermogravimetric analysis (TGA) of calixarene based-dyes under an N2 atmosphere, the degradation step occurred at 349, 356, and 379 8C for Calix-1, Calix-2, and Calix-3, respectively. In another single dye, M-3, a similar decomposition temperature was observed around 232 8C. It is very clear that the thermostability of calixarene based dyes is superior to monomer M-3.

Photovoltaic properties The incident photo-to-current conversion efficiencies (IPCEs) and the current–voltage (J–V) curves for the DSSCs with these dyes as sensitizers are plotted in Figure 3, and the related per-

www.chemsuschem.org Table 2. Performance parameters of the dyes. Dye

Amount [10 6 mol cm 2]

Jsc [mA cm 2]

Voc [mV]

FF

h [%]

M-3 Calix-1 Calix-2 Calix-3

3.45 1.94 1.72 1.62

8.07 5.49 10.01 12.60

605 613 660 632

0.73 0.72 0.67 0.69

3.56 2.43 4.42 5.48

beneficial influence of thiophene units on the photocurrent. On the other hand, the open-circuit voltage (Voc) for the four dyes is in the order of Calix-2 > Calix-3 > Calix-1 > M-3, in agreement with the electrochemical impedance spectroscopy (EIS) results described below. Of particular importance is a large increase of h of the Calix-3-based cell versus the M-3based cell. The result may be rationalized by the following reasons: (1) Calix-3 has a better light-harvesting ability than M-3 despite its lower dye density, because each M-3 molecule contains one D–p–A unit while one Calix-3 molecule contains four D–p–A units; (2) the improved Voc value of Calix-3 is because the cone structure of calixarene might contribute to suppressing the electron transfer from TiO2 to the electrolyte or oxidized dye, which increases electron lifetime and enhances the open circuit voltage; and (3) the lower highest occupied molecular orbital (HOMO) level of Calix-3 leads to a faster regeneration of the oxidized sensitizer and hence a slower recombination of the injected electrons. EIS analyses were used to clarify the above photovoltaic findings. Nyquist plots (Figure 4) reflect the electron recombi-

Figure 3. a) IPCE spectra, and b) photocurrent density vs. voltage plots for DSSCs based on the dyes under AM 1.5 G simulated solar light (100 mW cm 2). & M-3, * Calix-1, ~ Calix-2, and ! Calix-3

Figure 4. Electrochemical impedance spectra (Nyquist plot) of DSSCs for the dyes. & M-3, * Calix-1, ~ Calix-2, and ! Calix-3

formance statistics of the DSSCs under AM 1.5 illumination are listed in Table 2. The short-circuit current (Jsc) and overall yield (h) for the four dyes lie in the order Calix-3 > Calix-2 > M-3 > Calix-1, which is consistent with their IPCE data. Among the three calixarene sensitizers, the Calix-3-sensitized device illustrates a broad and intense photocurrent action spectrum and generates the highest conversion efficiency, demonstrating the

nation resistance via the radius. The electron lifetime (t) values derived from curve fitting are 65.7, 68.0, 178.2, and 73.7 ms for M-3, Calix-1, Calix-2, and Calix-3, respectively. The results are in keeping with the Voc values of the devices. The electron lifetime is improved upon incorporation of the cone-calixarene group, that is, t(Calix-3) > t(M-3). We thus speculate that the hydrophobic cone conformation of Calix-3 may form a substan-



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tial compact sensitizer layer at the surface of the TiO2 to block the approach of the redox couple. In addition, the longest lifetime for Calix-2 was attributed mostly to a more regular structure versus Calix-1 and Calix-3 (Supporting Information, Table S1), which benefits from the tendency to form a compact blocking layer between TiO2 and the electrolyte, leading to better suppression of the back reaction of the injected electron with the I3 . Intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS) were also performed to elucidate the different photovoltaic behaviors. Figure S6 a (Supporting Information) shows recombination times (tr) of DSSCs based on the four dyes at various incident light intensities. The recombination time follows the trend Calix-2 > Calix-3 > Calix-1 > M-3, which agrees well with the EIS results. The electron transport times (td) of DSSCs decrease as Calix-1 > M-3 > Calix-2 > Calix-3 (Figure S6 B). This correlates well with their Jsc results. To clarify the dye aggregates formed on the TiO2 surface, a study of the cell performance of three cone-calix[4]arene dyes in the presence of chenodeoxycholic acid (CDCA) in concentrations of 0 and a saturated solution was carried out.[14] The results are collected in Table S2 (Supporting Information). CDCA did not improve the devices’ performances, in contrast, it decreased the power conversion efficiencies. One possible explanation is that the amount of dye adsorbed on the TiO2 surface was reduced by the coadsorption of CDCA, resulting in less active light harvesting. The results indicate the cone-calix[4]arene dyes have good aggregation-resistant abilities. Stability measurements The long-term stability of DSSCs is important for practical applications. Figure S7 (Supporting Information) shows photographs of the samples of the four dyes adsorbed on TiO2 before and after 60 min of irradiation. No dramatic change in color was seen for any sample. Figure S8 (Supporting Information) presents the absorption curves of the four dyes after light irradiation at AM 1.5 light (5, 10, 30, and 60 min). No substantial variation in absorbance was observed for Calix-3 and M-3, indicating they are stable according to Katoh’s method.[15] In contrast, the absorbance at 380–500 nm decreased as a result of light irradiation for Calix-1 and Calix-2, but no any distinct absorption peak shift was found. The photostability of Calix-3 and M-3 seems higher versus Calix-1 and Calix-2, implying that delocalization of holes on the oligothiophene moieties of Calix-3 and M-3 may increase their intrinsic photostability.[16] Meanwhile, peak positions of the four sensitizers were constant, suggesting that no photochemical reaction occurred. To further confirm the long-term stability of devices, we measured device performances using the Calix-3 and M-3 dyes under AM 1.5 light for at least 500 h, as shown in Figure 5. As for Calix-3 dye, after 500 h of light soaking, the Voc decreased by 22 mV and the FF declined from 0.70 to 0.67, but the Jsc increased by 1.18 mA cm 2. As a consequence, the overall efficiency increased from 5.46 % to 5.50 % and remained almost constant for 500 h. This demonstrates that the amount 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Figure 5. Variations of photovoltaic parameters (& h, * Jsc, ~ Voc, and ! FF) with aging time for DSSC devices based on a) Calix-3, and b) M-3 under AM 1.5 light soaking at 60 8C.

of dye on the TiO2 surface remained intact after light soaking. The M-3-sensitized cell was also subjected to testing under the same conditions. Contrasting to the Jsc increase (by 0.72 mA cm 2) under illumination, Voc dropped by 81 mV. The Jsc gain did not compensate the loss of Voc, and thus the overall efficiency remained at 80 % (2.88 %) of the initial value (3.59 %). The results imply that the dye M-3 is less stable than Calix-3 when adsorbed onto TiO2 film. The reason is most likely because cone-calix[4]arene-based dyes have more anchoring groups, which increase the stability of the dyes adsorbed on the TiO2 film.

Conclusion A new class of cone-calix[4]arene sensitizers containing four donor–p–acceptor (D–p–A) units is successfully designed and developed for dye-sensitized solar cells (DSSCs). Calix-3 shows excellent stability in thermogravimetric analysis and dye-aging tests. The conversion efficiency of the Calix-3-sensitized DSSCs is effectively enhanced compared to the corresponding single D–p–A M-3 dye, which may be due to a lower tendency for aggregation, higher molar absorption coefficients, longer electron lifetimes, and better thermostability. These calixarene deChemSusChem 0000, 00, 1 – 9

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rivatives present new opportunities for the development of cone-shaped sensitizers. The further development of the calixarenes may be through appropriate structural modifications that lead to red-shifted absorptions as well as high absorptivity for increased device efficiency.

bed into 0.05 m (NH4)4NOH aqueous solution, and the absorption spectra of the desorbed-dye solution and deprotoned dyes solution in CHCl3 were measured using a Shimadzu UV-2450 spectrometer. The TiO2 film thickness was measured by using a profilometer (Ambios, XP-1).

Experimental Section

Preparation of TiO2 working electrode

Materials

TiO2 electrodes were prepared according to reported literature procedures reported.[7] Briefly, TiO2 powder synthesized via a hydrothermal method (~ 20 nm) (1.0 g) was ground for 40 min in the mixture of ethanol (8.0 mL), acetic acid (0.2 mL), terpineol (3.0 g), and ethyl cellulose (0.5 g) to form a slurry, and then the slurry was sonicated for 5 min to form a viscous white TiO2 paste. The TiO2 paste was then screen-printed onto the surface of FTO coated glass (15 W/ square, Nippon Sheet Glass, Japan) forming a photoanode film. The thickness of films could be easily controlled through repeating screen-printing times. Afterwards, a programmed heating process was carried out to remove the organic substances in the film. The film thickness was measured by using a profilometer (AMBIOS, XP1). The as-prepared TiO2 films (~ 15 mm) were soaked in a 0.04 m aqueous solution of TiCl4 for 30 min at 70 8C and then sintered at 520 8C for 30 min. After cooling to 80 8C, the TiO2 electrodes were immersed into 0.3 mm volatile organic solution of the dyes and kept at room temperature for 6 h. Afterwards, these films were rinsed with acetonitrile in order to remove physisorbed dye molecules. The prepared TiO2 working electrodes could be used in the fabrication of the DSSCs devices.

Optically transparent fluorine doped SnO2 (FTO) conducting glass was obtained from Nippon Sheet Glass, Japan (15 W/square) and cleaned by a standard procedure. Tetrahydrofuran (THF), toluene, and chloroform (CHCl3) was purified using an MBRAUN MB SPS-800 system. Methanol (MeOH) and acetonitrile (ACN) were dried over molecular sieves without normal pressure distillation. All other chemicals were purchased from commercial sources and used asreceived without further purification.

Characterization 1

H and 13C nuclear magnetic resonance (NMR) spectroscopy was performed on a BRUKER 400 MHz with tetramethylsilane (TMS) as the internal standard at room temperature in CDCl3, [D6]DMSO, or [D7]DMF, respectively. Elemental analyses were carried out with an Elementar Vario EL Cube instrument. Mass spectra were recorded on an ultrafleXtreme MALDI-TOF/TOF mass spectrometer (Bruker Daltonics). The infrared spectra were measured with a Perkin– Elmer Spectrum One spectrometer. The absorption spectra of the dyes in solution and adsorbed on TiO2 films were measured with a Shimadzu UV-2450 spectrometer. Emission spectra were measured using Hitachi F-4500 spectrometer. The current-density voltage (J–V) characteristics of the DSSCs were measured by using a Keithley 2400 source meter under the illumination of AM 1.5G simulated solar light and the incident light intensity was calibrated with a NREL-calibrated Si solar cell equipped with an optical filter to approximate AM 1.5 G one sun (100 mW cm 2) light intensity before each measurement. Action spectra of the incident monochromatic photon to electron conversion efficiency (IPCE) for the solar cells were measured as a function of wavelength from 350 to 800 nm on the basis of a Spectral Products DK240 monochromator. The cyclic voltammograms of dyes were obtained with a CHI 832 electrochemical analyzer using a normal three-electrode cell with dye-sensitized photoanode as working electrode, a Pt wire counter electrode, and a regular Ag/AgCl reference electrode in saturated KCl solution. CVs were measured with 0.1 m tetrabutylammonium hexafluorophosphate (TBAPF6) as a supporting electrolyte in CHCl3 and calibrated with ferrocene/ferrocenium (Fc/Fc + ) as an external reference, scan rate was kept as 50 mV s 1 for all compounds. The electrochemical impedance spectra were measured using an electrochemical workstation (Zahner, Zennium) with a frequency response analyzer at a bias potential of 800 mV in the dark with a frequency ranging from 10 mHz to 1 MHz. The magnitude of the alternating signal was 10 mV. Intensity-modulated photovoltage spectroscopy (IMVS) and intensity-modulated photocurrent spectroscopy (IMPS) measurements were carried out on the electrochemical workstation (Zahner, Zennium) with a frequency response analyzer under modulated green light emitting diodes (457 nm) driven by a source supply (Zahner, PP211), which can provide both DC and AC components of the illumination. The modulated light intensity was 10 % or less than the base light intensity. The frequency range was set from 1 kHz to 0.1 Hz. In order to measure the amount of dye adsorbed on the TiO2 film, the dye was desor 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Fabrication of the dye-sensitized solar cells In order to evaluate the devices’ photovoltaic performance, the prepared TiO2 working electrodes were sandwiched together with Pt-coated FTO glass which was used as a counter electrode. Platinized counter electrodes were fabricated by thermal deposition of H2PtCl6 solution (5 mm in isopropanol) onto FTO glass at 400 8C for 15 min. The electrolyte (0.6 m 1-methyl-3-propylimidazolium iodide (PMII), 0.10 m guanidinium thiocyanate (GuNCS), 0.03 m I2, 0.5 m tert-butylpyridine (t-BP) in acetonitrile and valeronitrile (85:15)) was injected into the space between the sandwiched cells.

Synthesis of Calix-1 A mixture of Calix-1-CHO (103 mg, 0.095 mmol) and cyanoacetic acid (97 mg, 1.14 mmol) was added acetonitrile (18 mL) and toluene (6 mL) under nitrogen atmosphere, and then piperidine (1.8 g, 21.4 mmol) was added. The reaction solution was refluxed at 90 8C for 5 h. After cooling to room temperature, the resulting mixture was neutralized to pH 2–3 with 0.5 m aqueous HCl and extracted with dichloromethane. The extract was washed successively with water and brine and dried over anhydrous MgSO4, filtered, and evaporated to afford a crude product that was further purified by silica-gel column chromatography using ethyl acetate and acetic acid as the eluant (3:1, v/v) to yield 120 mg yellow solid. Yield: 93 %; 1H NMR (400 MHz, [D6]DMSO, 25 8C): d = 8.21 (s, 4 H), 7.67 (d, J = 2.4 Hz, 4 H), 7.26–6.91 (m, 12 H), 4.37 (d, J = 12.5 Hz, 4 H), 3.92 (bs, 8 H), 3.42 (d, J = 13.0 Hz, 4 H), 2.09–1.75 (m, 8 H), 1.64–1.32 (m, 8 H), 0.98 ppm (t, J = 7.0 Hz, 12 H); 13C NMR (100 MHz, [D6]DMSO, 25 8C) d = 163.4, 157.4, 153.4, 146.0, 140.3, 135.2, 133.5, 126.5, 123.6, 116.2, 109.2, 97.3, 74.6, 31.8, 29.9, 18.8, 13.8 ppm; MALDITOF: m/z: n˜ 1355.376 [M] + , 1379.298 [M+Na] + ; Elemental analysis calcd (%) for C76H68N4O12S4 : C, 67.24; H, 5.05; N, 4.13; Found: C, ChemSusChem 0000, 00, 1 – 9

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CHEMSUSCHEM FULL PAPERS 67.27; H, 5.10; N, 4.12. The results are in accordance with our reported literature.[17a]

Synthesis of Calix-2 A mixture of Calix-2-CHO (142 mg, 0.10 mmol) and cyanoacetic acid (102 mg, 1.2 mmol) was added acetonitrile (60 mL) and toluene (20 mL) under nitrogen atmosphere, and then piperidine (1.9 g, 22.5 mmol) was added. The reaction solution was refluxed at 90 8C for 5 h. After cooling to room temperature, the resulting mixture was neutralized to pH 2–3 with 0.5 m aqueous HCl and extracted with dichloromethane. The extract was washed successively with water and brine and dried over anhydrous MgSO4, filtered, and evaporated to afford a crude product that was further purified by silica-gel column chromatography using ethyl acetate and acetic acid as the eluant (1:1, v/v) to yield 157 mg yellow solid. Yield: 93 %; 1H NMR (400 MHz, [D7]DMF, 25 8C) d = 8.36 (s, 4 H), 7.81 (d, J = 4.4 Hz, 4 H), 7.36 (d, J = 3.8 Hz, 4 H), 7.30 (d, J = 4.0 Hz, 4 H), 7.24 (s, 8 H), 7.13 (d, J = 3.9 Hz, 4 H), 4.56 (d, J = 13.1 Hz, 4 H), 4.18– 3.96 (m, 8 H), 3.52 (d, J = 13.5 Hz, 4 H), 2.13–1.89 (m, 8 H), 1.70–1.47 (m, 8 H), 1.09 ppm (t, J = 7.3 Hz, 12 H); 13C NMR (100 MHz, [D6]DMSO, 25 8C) d = 163.3, 156.5, 145.9, 145.8, 140.8, 135.0, 133.2, 132.8, 127.7, 126.7, 125.4, 123.9, 123.5, 116.3, 97.2, 74.5, 31.8, 29.0, 22.1, 18.9, 13.9 ppm; MALDI-TOF: m/z: n˜ 1684.310 [M] + , 1707.302 [M+Na] + , 1723.270 [M+K] + ; Elemental analysis calcd (%) for C92H76N4O12S8 : C, 65.53; H, 4.54; N, 3.32; Found: C, 65.52; H, 4.51; N, 3.35.

Synthesis of Calix-3 A mixture of Calix-3-CHO (144 mg, 0.082 mmol) and cyanoacetic acid (84 mg, 0.98 mmol) was added to acetonitrile (60 mL) and toluene (20 mL) under nitrogen atmosphere, and then piperidine (1.6 g, 19.0 mmol) was added. The reaction solution was refluxed at 90 8C for 5 h. After cooling to room temperature, the resulting mixture was neutralized to pH 2–3 with 0.5 m aqueous HCl and extracted with dichloromethane. The extract was washed successively with water and brine and dried over anhydrous MgSO4, filtered, and evaporated to afford a crude product that was further purified by silica-gel column chromatography using ethyl acetate and acetic acid as the eluant (1:1, v/v) to yield 126 mg yellow solid. Yield: 76 %; 1H NMR (400 MHz, [D7]DMF, 25 8C) d = 9.89 (s, 4 H), 7.88 (d, J = 4.0 Hz, 4 H), 7.37 (dd, J = 8.1, 3.9 Hz, 8 H), 7.23–7.09 (m, 16 H), 7.05 (d, J = 3.8 Hz, 4 H), 4.55 (d, J = 13.1 Hz, 4 H), 4.23–3.92 (m, 8 H), 3.48–3.40 (m, 4 H), 2.15–1.91 (m, 8 H), 1.71–1.45 (m, 8 H), 1.09 ppm (t, J = 7.3 Hz, 12 H); 13C NMR (100 MHz, [D7]DMF, 25 8C) d = 163.5, 162.0, 156.6, 145.7, 144.4, 144.3, 140.6, 139.2, 138.5, 135.4, 134.0, 133.3, 127.7, 125.6, 124.5, 124.3, 116.5, 98.1, 75.0, 32.3, 19.3, 13.7 ppm, MALDI-TOF: m/z: n˜ 2012.260 [M] + ; Elemental analysis calcd (%) for C108H84N4O12S12 : C, 64.39; H, 4.20; N, 2.78; Found: C, 64.40; H, 4.25; N, 2.75. The results are in accordance with our reported literature.[17b]

Synthesis of M-3 A mixture of M-3-CHO (170 mg, 0.40 mmol) and cyanoacetic acid (170 mg, 2.0 mmol) was added to acetonitrile (60 mL) and toluene (20 mL) under nitrogen atmosphere, and then piperidine (341 g, 4.0 mmol) was added. The reaction solution was refluxed at 90 8C for 5 h. After cooling to room temperature, the resulting mixture was neutralized to pH 2–3 with 0.5 m aqueous HCl and extracted with dichloromethane. The extract was washed successively with 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemsuschem.org water and brine and dried over anhydrous MgSO4, filtered, and evaporated to afford a crude product that was further purified by silica-gel column chromatography using dichloromethane and acetic acid as the eluant (80:1, v/v) to yield 148 mg yellow solid. Yield: 75 %; 1H NMR (400 MHz, [D6]DMSO, 25 8C) d = 8.47 (s, 1 H), 8.05–7.88 (m, 1 H), 7.66–7.51 (m, 4 H), 7.47–7.25 (m, 3 H), 6.98 (d, J = 7.3 Hz, 2 H), 4.16–3.92 (m, 2 H), 1.80–1.59 (m, 2 H), 1.55–1.34 (m, 2 H), 1.05–0.71 ppm (m, 3 H); 13C NMR (100 MHz, [D6]DMSO, 25 8C) d = 163.6, 158.8, 146.2, 145.2, 141.5, 138.5, 133.9, 133.5, 133.2, 131.5, 131.4, 128.7, 128.2, 126.7, 126.4, 125.3, 125.1, 123.7, 116.6, 115.1, 67.3, 30.7, 18.7, 13.7 ppm; MALDI-TOF: m/z: n˜ 491.229 [M] + ; Elemental analysis calcd (%) for C26H21NO3S3 : C, 63.52; H, 4.31; N, 2.85; Found: C, 63.51; H, 4.28; N, 2.89.

Acknowledgements Financial support was provided by the 973 Program of China (2012CB821701), NSFC (21272292, 91222201, ), RFDP of High Education of China (20120171130006, 20101102110018), and NSF of Guangdong Province (S2013030013474, 2011J2200053). Keywords: calixarenes · donor-acceptor systems · dyes/ pigments · solar cells · thiophenes [1] a) B. O’Regan, M. Grtzel, Nature 1991, 353, 737 – 740; b) A. Hagfeldt, M. Grtzel, Acc. Chem. Res. 2000, 33, 269 – 277; c) W. Ying, J. Yang, M. Wielopolski, T. Moehl, J.-E. Moser, P. Comte, J. Hua, S. M. Zakeeruddin, H. Tian, M. Grtzel, Chem. Sci. 2014, 5, 206 – 214. [2] A. Yella, H. W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M. Zakeeruddin, M. Grtzel, Science 2011, 334, 629 – 634. [3] J.-H. Yum, I. Jung, C. Baik, J. Ko, M. K. Nazeeruddin, M. Grtzel, Energy Environ. Sci. 2009, 2, 100 – 102. [4] a) W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang, C. Pan, P. Wang, Chem. Mater. 2010, 22, 1915 – 1925; b) J. Yang, P. Ganesan, J. Teuscher, T. Moehl, Y. J. Kim, C. Yi, P. Comte, K. Pei, T. W. Holcombe, M. K. Nazeeruddin, J. Hua, S. M. Zakeeruddin, H. Tian, M. Grtzel, J. Am. Chem. Soc. 2014, 136, 5722 – 5730. [5] a) Z. Ning, Y. Fu, H. Tian, Energy Environ. Sci. 2010, 3, 1170 – 1181; b) M. Cheng, X. Yang, J. Li, F. Zhang, L. Sun, ChemSusChem 2013, 6, 70 – 77; c) H. Hayashi, A. S. Touchy, Y. Kinjo, K. Kurotobi, Y. Toude, S. Ito, H. Saarenp, N. V. Tkachenko, H. Lemmetyinen, H. Imahori, ChemSusChem 2013, 6, 508 – 517; d) Z. Wang, M. Liang, H. Wang, P. Wang, F. Cheng, Z. Sun, X. Song, ChemSusChem 2014, 7, 795 – 803; e) Y. Hua, S. Chang, D. Huang, X. Zhou, X. Zhu, J. Zhao, T. Chen, W.-Y. Wong, W.-K. Wong, Chem. Mater. 2013, 25, 2146 – 2153; f) D. Demeter, S. Mohamed, A. Diac, I. Grosu, J. Roncali, ChemSusChem 2014, 7, 1046 – 1048; g) K. Lim, M. J. Ju, J. Song, I. T. Choi, K. Do, H. Choi, K. Song, H. K. Kim, J. Ko, ChemSusChem 2013, 6, 1425 – 1431. [6] a) Z. Ning, Q. Zhang, W. Wu, H. Pei, B. Liu, H. Tian, J. Org. Chem. 2008, 73, 3791 – 3797; b) J. Tang, J. Hua, W. Wu, J. Li, Z. Jin, Y. Long, H. Tian, Energy Environ. Sci. 2010, 3, 1736 – 1745; c) Z. Ning, Q. Zhang, H. Pei, J. Luan, C. Lu, Y. Cui, H. Tian, J. Phys. Chem. C 2009, 113, 10307 – 10313. [7] L.-L. Tan, J.-F. Huang, Y. Shen, L.-M. Xiao, J.-M. Liu, D.-B. Kuang, C.-Y. Su, J. Mater. Chem. A 2014, 24, 8988 – 8994. [8] a) D. Cao, J. Peng, Y. Hong, X. Fang, L. Wang, H. Meier, Org. Lett. 2011, 13, 1610 – 1613; b) Y. Hong, J.-Y. Liao, D. Cao, X. Zang, D.-B. Kuang, L. Wang, H. Meier, C.-Y. Su, J. Org. Chem. 2011, 76, 8015 – 8021. [9] A. Ikeda, S. Shinkai, Chem. Rev. 1997, 97, 1713 – 1734. [10] K. Iwamoto, K. Araki, S. Shinkai, J. Org. Chem. 1991, 56, 4955 – 4962. [11] M. Mastalerz, G. Dyker, U. Flçrke, G. Henkel, I. M. Oppel, K. Merz, Eur. J. Org. Chem. 2006, 4951 – 4962. [12] H.-Y. Yang, Y.-S. Yen, Y.-C. Hsu, H.-H. Chou, J. T. Lin, Org. Lett. 2010, 12, 16 – 19. [13] M. S. Tsai, Y.-C. Hsu, J. T. Lin, H.-C. Chen, C.-P. Hsu, J. Phys. Chem. C 2007, 111, 18785 – 18793.


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CHEMSUSCHEM FULL PAPERS [14] a) K. D. Seo, B. S. You, I. T. Choi, M. J. Ju, M. You, H. S. Kang, H. K. Kim, ChemSusChem 2013, 6, 2069 – 2073; b) K. D. Seo, B. S. You, I. T. Choi, M. J. Ju, M. You, H. S. Kang, H. K. Kim, J. Mater. Chem. A 2013, 23, 9947 – 9953. [15] R. Katoh, A. Furube, S. Mori, M. Miyashita, K. Sunahara, N. Koumura, K. Hara, Energy Environ. Sci. 2009, 2, 542 – 546. [16] a) K. Hara, Z. S. Wang, Y. Cui, A. Furube, N. Koumura, Energy Environ. Sci. 2009, 2, 1109 – 1114; b) R. da Silva, L. G. C. Rego, J. A. Freire, J. Rodriguel, D. Laria, V. S. Batista, J. Phys. Chem. C 2010, 114, 19433 – 19442.


www.chemsuschem.org [17] a) S.-Y. Li, Y.-W. Xu, S.-Q. Zeng, L.-M. Xiao, H.-Q. Duan, X.-L. Lin, J.-M. Liu, C.-Y. Su, Tetrahedron Lett. 2012, 53, 2918 – 2921; b) Y.-W. Xu, L.-L. Tan, J.M. Liu, L.-M. Xiao, S.-Y. Li, C.-Y. Su, RSC Adv. 2014, 4, 28046 – 28051.

Received: May 9, 2014 Revised: July 22, 2014 Published online on && &&, 0000


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FULL PAPERS Sunny Cali: Novel and efficient conecalix[4]arene-based dyes (Calix-1, Calix2, and Calix-3) with multiple donor–p– acceptor (D–p–A) moieties are prepared and tested for use in dye-sensitized solar cells (DSSCs). The conversion efficiency of one of the dyes is above 5 %, compared to 3.56 % for a device using rod-shaped dye M-3 with a single D–p– A chain. The cone-calix[4]arene-based dyes offer higher molar extinction coefficients, longer electron lifetimes, and better thermostability.


L.-L. Tan, J.-M. Liu,* S.-Y. Li, L.-M. Xiao, D.-B. Kuang, C.-Y. Su* && – && Dye-Sensitized Solar Cells with Improved Performance using ConeCalix[4]Arene Based Dyes


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Improved quantum dot stacking for intermediate band solar cells using strain compensation.