Final Anthocyanin Paper Project

Pappas, McKee, Hartheimer 1

NJ Chemistry Olympics 2014Application of Anthocyanins in Blackberries:

A Dye-Sensitized Solar Cell

Samantha PappasEmma McKee

Joline Hartheimer

Northern Highlands Regional High School

Pappas, McKee, Hartheimer 2Background:

Solar cells produce energy by employing the principles of the photoelectric effect, which says

that electrons are ejected from a metal surface when light is shined on it. This radiation consists of

packets of energy, today called photons. According to Planck's formula, equation 1, the energy of these

photons is equal to the product of planck's constant (h) and the frequency of the light (ν).

Equation 1 E = hν

If a photon of light strikes a low energy electron in an atom, the electron becomes excited and

moves to a higher energy level; however the unstable electron quickly returns to its ground state,

releasing energy to its surroundings in the process. In conventional solar cells, such as silicon and thin-

film solar cells, a hole is created in the electron’s initial location when that electron is excited from its

ground state; this hole and the electron formerly occupying its space separate completely. However, in

excitonic cells, the electron remains bound to its positively charged hole, forming an electron-hole pair

called an exciton that requires an interface between an “electron transfer material” and a “hole transfer

material” to split and separately migrate to different electrodes.1

There are two types of excitonic solar cells: dye-sensitized, whose light-active component is a

molecular dye2, and organic, whose light-active component is an organic polymer3. The focus of this

research will be on dye-sensitized solar cells (DSSCs), also called Grätzel cells after their creator Michael

Grätzel. These photovoltaic cells employ low to medium purity materials and use low-cost processes,

creating cells that are both more efficient and more cost effective than traditional cells: the combination

of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye allows

for high efficiencies of over 80% for the conversion of light energy from photons to electrical current.4

An n-type material, a semiconductor that has been doped by a donor impurity that adds an excess valence

electron to its lattice causing the amount of free electrons to outnumber the available holes,5 such as TiO2

allows current to be generated when a photon absorbed by a dye molecule leads to an electron being

excited and projected into the conduction band, the band energy where positive mobile charge carriers, or

Pappas, McKee, Hartheimer 3holes, exist,6 of the semiconductor4. The rough semiconductor surface created by the nanometer-sized

TiO2 particle film allows for a larger number of dye molecules to be adsorbed onto it due to the increased

surface area4, further increasing the efficiency of the cell. Sintering the TiO2 films deposited onto the

conductive glass in the form of colloidal solutions allows for greater electronic contact between particles.4

For the circuit to be complete, the dye needs to be regenerated through electron transfer with redox

species in solution that then is reduced at the cathode.4

In this experiment, blackberry juice was chosen as the dye. Blackberries contain plant pigments

called anthocyanins, which are water-soluble phenolic compounds belonging to the group of plant

flavonoids; however the content of anthocyanins, even in fruits of the same type, varies due to many

genetic and environmental factors.7 The anthocyanins attach themselves to the titania molecules due to

due to their hydroxyl bonds, which the titanium dioxide molecules also contain, as seen in figure 1.

Figure 112

When light strikes the semiconductive glass, it kicks off a cycle of redox reactions, which mimics

those of photosynthesis. The electrolyte iodine solution acts as a salt bridge for the reaction inducing an

equilibrium process that allows for the transfer of ions, and the graphite as a catalyst, while the redox

reaction occurs between the TiO2 and anthocyanins in the dye. Figure 2 shows how the electrons flow

through a typical dye sensitized solar cell when struck by light.

Pappas, McKee, Hartheimer 4Figure 213

The efficiency of a solar cell can be calculated determining the ratio of power produced per

square inch. Power (P) in watts is equal to voltage (V) in volts squared over resistance (R) in ohms, as

seen in equation 2.

Equation 2 P = V2/R

Solar cells are a source of energy that the world, most notably the United States, has recently

started to explore. In the year 2013, 29% of new energy generation capacity came from solar power,

which is greater than the amount produced by every other source besides natural gas. The amount of

megawatts of photovoltaic cells installed in 2014 is expected to be 26% greater than that of 2013, and the

PV cells to be implanted in 2014 are predicted to harness enough solar energy to power 1.13 million

American homes. The prices of solar cells have been decreasing, which makes them more feasible for

families or organizations to purchase them.8 2013 also brought about a 20% increase in the amount of

people employed for solar jobs.9

Pappas, McKee, Hartheimer 5Materials and Methods:

The anode was created by coating a piece of conductive glass with a prepared titanium dioxide

paste and covering the dry titanium dioxide film with a prepared blackberry dye. The titanium dioxide

paste was made with 0.682 g of titanium dioxide powder which was first massed on a weighing dish and

then placed into a 50 mL beaker. 1 M nitric acid was then diluted to 0.001 M using 1 mL of the 1 M nitric

acid, transferred with a volumetric pipet to a 100 mL volumetric flask. The flask was filled with distilled

water to the 100.00 mL line. Approximately 10 drops of the 0.001 M nitric acid were added with a

disposable pipet to the powder, which was stirred with a glass stirring rod until the texture resembled the

consistency of white-out and no clumps of powder remained. One piece of the conductive glass was

obtained and wiped with a Kimwipe wet with isopropanol, followed by a Kimwipe wet with distilled

water. The glass was allowed to dry before the slide was tested with a multimeter on the resistance setting

to determine the conductive side. With that side face up, the edges of the slide were taped with Scotch

tape to the table to add stability. The tape was smoothed out to remove air bubbles by pushing a glass

stirring rod across its surface. A disposable pipet was used to place 3 drops of the titanium dioxide paste

along the top tape border of the cell. Then the stirring rod was used to spread and coat the paste evenly

over the exposed glass. After waiting a few minutes for the paste to dry, the pieces of tape holding the

cell to the table were carefully removed and the cell was transferred to a hot plate. It was heated at 450ºF

for approximately twenty minutes until the heat was turned off and the cell was allowed to cool resting on

the hot plate. While the titanium dioxide paste was being sintered, the blackberry dye was prepared. Ten

blackberries were placed into a 250 mL beaker and about 10 drops of distilled water were added with a

disposable pipet. The bottom of a 150 mL beaker was used to crush the fruit into a dye. Once cool, the

glass slide was removed from the hot plate and a disposable pipet was used to place enough drops of dye

on top of the dry titanium dioxide film to completely saturate it. The slide was allowed to rest on the table

for 10 minutes before the excess dye was rinsed off by pouring both distilled water and isopropanol over

the surface of the glass. The completed anode was then blotted dry with another Kimwipe.

Pappas, McKee, Hartheimer 6The cathode was prepared by coating another piece of conductive glass with a layer of graphite to

function as a catalyst. The second piece of glass was cleaned with a Kimwipe wet with isopropanol

followed by another Kimwipe wet with distilled water. Both sides of the glass were then tested for

conductivity using the resistance setting on the multimeter. It was ensured that the slide lay with the

conductive side face up and that side was “colored in” thoroughly with a pencil to add a complete layer of

graphite to the surface. The procedure up to this point was repeated to produce 3 anodes and 3 cathodes.

Before the cells were assembled, an iodine electrolyte solution was prepared using about 10 g of

solid potassium iodide pellets and about 0.5 g of solid iodine. Both amounts were massed and placed into

a 50 mL beaker which was then filled with distilled water until the total volume of the solution was about

30 mL. The solution was mixed with a glass stirring rod until the solid iodine pieces dissolved.

The solar cells were constructed by placing the graphite cathode on the bottom and the dye-

covered titanium dioxide anode on the top, both pieces slightly offset so that an edge of glass stuck out on

each side. 2 small binder clips per cell were used to hold the slides in place, and alligator clip electrodes

were clamped to the offset edges, as seen in figure 3.12

Figure 3

The 3 fully assembled solar cells were then connected in series with alligator wires to each other and to

both a multimeter and a small LED light bulb. To activate the cells, a disposable pipet was used to place a

few drops of electrolyte solution along an offset edge of each cell. The binder clips were then opened and

closed to draw the solution into the center of the cell.

Pappas, McKee, Hartheimer 7Appendix Part 1

Cost of Materials:

Isopropyl Alcohol $0.02

Nitric Acid $0.02

Iodine Pellets $0.10

Potassium Iodine $1.85

Blackberries $4.99

Titanium Dioxide Powder $0.17

Conductive Glass Slides (10) $10.00

Lightbulb $1.50

Lightbulb holder $3.57

Shipping Costs $6.95

Total Cost $29.17

Schematic Diagram:

Pappas, McKee, Hartheimer 8Picture:

Data:

Voltage produced by circuit 172 mV

Resistance 0.01 KΩ

Calculations:P = (0.172 V2)/100 Ω = 0.000296 watts/6 inches2 = 0.000049 watts/inch2

Pappas, McKee, Hartheimer 9Works Cited

1. The Solar Spark. Excitonic Solar Cells. http://www.thesolarspark.co.uk/the-science/solar-power/excitonic-solar-cells/ (accessed April 9, 2014).

2. The Solar Spark. Dye-Sensitised Cells. http://www.thesolarspark.co.uk/the-science/solar-power/excitonic-solar-cells/dye-sensitised-cells/ (accessed April 9, 2014).

3. The Solar Spark. Organic and Hybrid PVs. http://www.thesolarspark.co.uk/the-science/solar-power/excitonic-solar-cells/opvs-hpvs/ (accessed April 9, 2014).

4. O’Regan, B; Grätzel, M. A low-cost, high efficiency solar cell based on dye-sensitized colloidal TiO2 films. Letters to Nature 1991, 353, 737-740.

5. UC Davis SolarWiki by University of California, Davis. ChemWiki. I. P-Type, N-Type Semiconductors. http://solarwiki.ucdavis.edu/The_Science_of_Solar/Solar_Basics/D._P-N_Junction_Diodes/I._P-Type,_N-Type_Semiconductors (accessed April 9, 2014).

6. UC Davis GeoWiki by University of California, Davis. ChemWiki. Band Theory of Semiconductors. http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/Electronic_Structure/Band_Theory_of_Semiconductors (accessed April 9, 2014).

7. Kayesh, E.; Shangguan, L.; Korir, N.K.; Sun, X.; Bilkish, N.; Zhang, Y.; Han, J. et al. Acta Physical Plant. Fruit Skin Color and the Role of Anthocyanin. 19 Jun 2013.

8. Hug, H.; Bader, M.; Mair, P.; Glatzel, T. Biophotovoltaics: Natural Pigments in Dye-Sensitized Solar Cells. Applied Energy 2014, 115, 216-225

9. Solar Energy Industries Association. Solar Industry Data. http://www.seia.org/research-resources/solar-industry-data (accessed April 10, 2014).

10. The Solar Foundation. National Solar Jobs Census 2013. http://www.thesolarfoundation.org/research/national-solar-jobs-census-2013 (accessed April 10, 2014).

11. David Martineau. Solaronix. Dye Solar Cells for Real. http://www.solaronix.com/documents/dye_solar_cells_for_real.pdf (accessed April 9, 2014).

12. Abrams, N. M.. SUNY College of Environmental Science and Forestry. Using Nature to Make a Photovoltaic Cell. http://www.esf.edu/outreach/k12/solar/2009/Labs/Making%20a%20Natural%20Photovoltaic%20Cell.pdf (accessed April 9, 2014).

13. Tobin, L.L.; O’Reilly , T.; Zerulla, D.; Sheridan, J.T.; Characterising dye-sensitised solar cells. Optik - International Journal for Light and Electron Optics 2011, 122, 1225-1230

Pappas, McKee, Hartheimer 10Appendix 2








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Final Anthocyanin Paper Project