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Burt, EthanFridblom, 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: [email protected]; [email protected]

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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

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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 with piperidine. 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),

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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 can be 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 Jsc is the current

through the solar cell when the voltage across the cell is zero. The open circuit voltage Voc is the

maximum voltage available from a solar cell when the current is zero. The incident photon is

labeled Pin and is measured in (mW/cm2). These are all considered especially useful in

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 Properties of 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 8.12SD2 465 9.1x104 14.51 700 0.72 0.42 -0.5 7.26D11 458 3.8x104 13.5 744 0.7 1.29 -0.98 7.03

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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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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: [email protected]; [email protected]

S1


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

S2


Synthesis of FNE29

All of the chemicals and reagents used were purchased from commercial sources and all

reactions were done under inert atmosphere using Schlenk 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, to a 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%).

S3


1H NMR Spectra of FNE29

Figure S1. Predicted 1H MNR Spectra of FNE29

S4


13C NMR Spectra of FNE29

Figure 2S. Predicted 13C NMR Spectra of FNE29.

S5


UV-Vis Spectrum of FNE29

Figure 3S. UV-Visible Spectrum of FNE29 and Others.

S6


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 Sources 2013.

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.

S7

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