Burt, Ethan
Fridblom, Travis
Synthesis and Properties of Organic Dye-Sensitizer FNE29
Ethan Burt and Travis Fridblom
Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65201
Email: ;
Introduction
Currently, the most common way to convert solar power into a useable form of energy is through the use of solar cells. In general, theses solar cells traditionally come as one or a combination of several different varieties. These can include but are not limited to semiconducting solar cells, organic polymer solar cells, and dye-sensitized solar cells (DSSCs).
Among the different types of solar cells currently being explored for energy production, DSSCs utilizing an organic dye sensitizing material have been of particular interest. These nanocrystalline dye-sensitized solar cells are promising synthetic nanomachines whose function is based on principles similar to the processes in natural photosynthesis. Both use an organic dye to absorb the incoming light and produce excited electrons.
Discussed here is the development and evaluation of the metal-free organic dye-sensitizer 2-Cyano-3-[5”-(4-(diphenylamino)phenyl-3’,3”,4-tri-n-hexyl-[2,2’,5’,2”]terthiophene]acrylic acid (FNE29). Several characteristics of FNE29 make it a desirable material for use in DSSCs. It is relatively easy to synthesize in moderate to high yields from cheaply available starting materials. It also avoids the health hazards associated with the toxic heavy metals used in many inorganic dyes. The structures of FNE29, as well as those of two comparison dyes SD2 and D11, are shown below (Scheme 1).
Scheme 1. Structures of Organic Dye-Sensitizers. A: FNE29; B: SD2; C: D11
In this paper, we measure and compare several of the performance characteristics of FNE29 to the other organic dye-sensitizers SD2 and D11.
Materials and Methods
The synthetic approach to sensitizer FNE29 starts from the alkyl-functionalized terthiophene (Scheme 1). The monoaldehyde-substituted derivative was obtained by refluxing in the presence of a Vilsmeier reagent and the electron donor, triarylamine, was attached via C-H bond activation. In the last step, FNE29 is obtained via Knoevenagel condensation with cyanoacetic acid through refluxing acetonitrile withpiperidine. A more detailed description of the synthesis as well as spectroscopic characterization can be found in the supporting information.1
Scheme 1.Synthetic Outline of Organic Dye-Sensitizer FNE29.
The DSSC was designed containing an electrolyte with 0.6 M 1,2-dimethyl-3-propylimidazolium (DMPImI), 0.1 M LiI, 0.05M I2, and 0.5M 4-ter-butylPyridine (TPB) in acetonitrile. The DSSC was constructed from 14Ω Nippon Fluorine doped SnO2 glass (FTO), TiO2 films (thickness:12μm Size:0.25cm2), and a platinum counter electrode.All of the components were assembled into a sealed sandwich cell with a thermoplastic frame.
The overall effectiveness of FNE29 and other dye sensitizers canbe evaluated based on a variety of pertinent performance characteristics. FF determines the maximum power output from a solar cell and high efficiency solar cells often demonstrate FF values of 0.7 or higher.The molar extinction coefficient is a measurement of how strongly a chemical species absorbs light at a given wavelength and it’s denoted by the letter ε. Short circuit current density Jscis the current through the solar cell when the voltage across the cell is zero. The open circuit voltageVoc is the maximum voltage available from a solar cell when the current is zero. The incident photon is labeledPinand is measured in (mW/cm2). These are all considered especially usefulin determining the overall usefulness of a material in DSSCs. The values for these parameters and others can be found in the table below (Table 1). The power conversion efficiency is a measure of the device’s ability to absorb sunlight and convert it into usable energy. This is often considered the most important aspect of a solar cell’s performance and is solved from a simple equation relating four of the variables described above.
Jsc(mA cm-2) x Voc(V) x FF
Overall Conversion Efficiency η(%) = ------
Pin(mW cm-2)
Table 1. Photophysical and Electrochemical Propertiesof Selected Dye Sensitizers1
Dye / λMax / ε / JSC / VOC / FF / HOMO / LUMO / η(nm) / (M-1cm-1) / (mA/cm2) / (mV) / (V) / (V) / (%)
FNE29 / 456 / 3.4x104 / 14.93 / 754 / 0.72 / 1.07 / -0.99 / 8.12
SD2 / 465 / 9.1x104 / 14.51 / 700 / 0.72 / 0.42 / -0.5 / 7.26
D11 / 458 / 3.8x104 / 13.5 / 744 / 0.7 / 1.29 / -0.98 / 7.03
The current density voltage characterization measurements for the solar cell were taken with three devices. The first was a Keithly 2400 source meter under illumination from a AM1.5G simulated light with 1000W Xe lamp. The second device measured the open circuit densities using the charge extraction technique on a Zahner XPOT (Germany).The last was an Oriel 74125 system with a Si detector Oriel 71640 to measure the Incident photon conversion efficiency (IPCE) of the cell under different monochromatic light. The relationship is shown in figure 1.
Figure 1. %IPCE vs. Wavelength for FNE29 and Others
Results and Discussion
Conclusions
Supplemental Material Available: A detailed description of the synthesis for the organic dye-sensitizer FNE29, as well as the spectroscopic characterization can be found in the appendix.
References
(1)Feng, Q.;Zhou, G.; Wang, Z. Varied Alkyl Chain Functionalized Organic Dyes for Efficient Dye-Sensitized Solar Cells: Influence of Alkyl Substituent Type on Photovoltaic Properties. J. Power Sources 2013.
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Burt, Ethan
Fridblom, Travis
Supporting Information
Synthesis and Properties of Organic Dye-Sensitizer FNE29
Ethan Burt and Travis Fridblom
Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65201
Email: ;
Table of Contents
Synthesis of FNE29……………………………………………………………………….……S3
1H NMR Spectra of FNE29………………………………………………………………….…S4
13C NMR Spectra of FNE29…………………………………………………………………....S5
UV-Vis Spectrum of FNE29…………………………………………………....………………S6
Bibliography……………………………………………………………………………….…….S7
Synthesis of FNE29
All of the chemicals and reagents used were purchased from commercial sources and all reactions were done under inert atmosphere usingSchlenk techniques. Compound 1a (1.00g/2.00mmol) and DMF (0.186mL/2.40mmol) were dissolved in 30mL of chloroform. After dissolved Phosphorous Oxychloride (0.297mL) was added slowly. The mixture was stirred for 20min at room temperature followed by heating to 90°C for 8hrs. After cooling to room temperature, 30mL saturated sodium acetate solution was added to the dark reaction solution with stirring for 20min. The mixture was poured into ice water (50mL) and then it was neutralized through the addition of sodium hydroxide solution. The product was extracted with DCM three times. The combined organic solution was washed with sodium bicarbonate and sodium chloride solutions and then dried over anhydrous sodium sulfate. After removal of the solvent the residue was purified by flash column chromatography through silica SiO2 (solvent;DCM:PE/1:2).Orange oil 2a was obtained with a yield of 46% 486mg. Next, a reaction vessel filled with K2CO3 (0.69mmol/95mg), Pd(OAc)2 (0.009mmol, 2.0mg), PCy3∙HBF4(0.018mmol, 7.0mg), pivalic acid (0.138mmol, 14mg), 4-bromo-N,N-diphenylaniline (298mg, 0.919mmol), and 2a (243mg, 0.459mmol). Then we add dry toluene (2mL). The reaction mixture was then vigorously stirred at 105°C for 16hr. The solution was then cooled to room temperature, diluted with CH2Cl2 and H2O. The aqueous phase was extracted with CH2Cl2. The organics were combined and dried over MgSO4, filtered, and evaporated under reduced pressure. The crude product was purified by silica gel column chromatography to yield a red-orange oil 3a in 59% yield (208mg). Finally, toa mixture of 3a (856mg,1.1mmol), cyanoacetic acid(239mg,2.81mmol), 35mL chloroform and 35mL acetonitrile 0.2mL of piperdine was added. The mixture was refluxed at 120°C for 6hr and allowed to cool to room temperature. The resulting mixture was washed with DI and brine then dried via MgSO4 and filtered. The solvent was removed by rotary evaporation, and the residue was purified by column chromatography (DCM:MeOH/10:1) to give a dark brown solid(522mg, 56%).
1H NMR Spectra of FNE29
Figure S1. Predicted 1H MNR Spectra of FNE29
13C NMR Spectra of FNE29
Figure 2S. Predicted 13C NMR Spectra of FNE29.
UV-Vis Spectrum of FNE29
Figure 3S. UV-Visible Spectrum of FNE29 and Others.
Bibliography
Feng, Q.;Zhou, G.; Wang, Z. Varied Alkyl Chain Functionalized Organic Dyes for Efficient Dye-Sensitized Solar Cells: Influence of Alkyl Substituent Type on Photovoltaic Properties. J. Power Sources2013.
Hagberg, D. P.; Yum, J.; Lee, H.; De Angelis, F.; Marinado, T.; Karlsson, K.; Humphry-Baker, R.; Sun,L.; Hagfeldt, A.; Gratzel, M.; and Nazeeruddin, M. Molecular Engineering of Organic Sensitizers for Dye-Sensitized Solar Cell Applications. J. Am. Chem. Soc. 2008, 130, 6259-6266.
Shen, P.; Liu, Y.; Huang, X.; Zhao, B.; Xiang, N.; Fei, J.; Liu, L.; Wang, X.; Huang, H.; Tan, S. Efficient triphenylamines dyes for Solar Cells: Effects of Alkyl Substituents and Pi Conjugated Thiophene Units.Dyes Pigm.2009, 83, 187-197.
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