Transcript Continued Investigations on Use of Dragon`s Blood Pigment in

Continued Investigations on Use of Dragon’s Blood Pigment in Photovoltaic Cells
Brett Jones and Jim Bidlack
Department of Biology, University of Central Oklahoma, Edmond, OK 73034
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RESULTS AND DISCUSSION
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Figure 1. Voltage and Power of cells.
ABSTRACT
MATERIALS AND METHODS
Both laboratory investigations and statistical analyses were pursued during the
past year to gain additional information about the use of Dragon’s Blood
(Daemonorops draco) in photovoltaic cells. In general, experiments conducted in
Fall 2011 provided similar results compared with experiments during the previous
year. In both of these experiments, the voltage values in cells treated with the
pigment were significantly higher than values from control cells, which contained
no pigment. It was decided to focus on calculating current and power readings
from data collected and conclude these investigations with a manuscript for
potential publication. As such, statistical analyses demonstrated that photovoltaic
cells made with Dragon’s Blood produced average voltage, current, and power
readings of 150 millivolts, 1.68 microamps, and 0.289 microamps, respectively,
over a period of 19 days. These readings were significantly higher than values
obtained at night and substantially higher than values obtained from cells
constructed without pigment. The low cost of constructing these cells, coupled
with their longevity, suggests that they have potential as economically-feasible
and sustainable energy alternatives.
Photovoltaic cells were constructed and tested in the Biology Department at the University of Central Oklahoma.
Procedures for constructing these cells were derived from a Nanocrystalline Solar Kit purchased from the Institute
of Chemical Education at the University of Wisconsin in Madison, Wisconsin (Smestad, 1998). Conductive glass
was obtained from Hartford Glass Company of Hartford City, Indiana. Titanium dioxide (TiO2) was purchased from
Degussa USA of Akron, Ohio. Elmer’s Superglue® was purchased locally. The resin required to make the Dragon’s
Blood [Daemonorops draco (Blume)] pigment was obtained from Mountain Rose Herbs of Eugene, Oregon. All
other materials were supplied from Sigma-Aldrich in St. Louis, Missouri. An ADC-16 board connected to a data
logger from Pico Technology, Ltd., United Kingdom, was used to monitor and record voltages produced by the
photovoltaic cells.
INTRODUCTION
One of the most promising alternative energy technologies for traditional fossil fuel
technology is the photovoltaic cell, which converts light energy into clean,
renewable energy in the form of electricity. An alternative to the common silicon
photovoltaic cell exists in the form of thin film photovoltaic cells (O’Regan and
Gratzel, 1991). These cells are constructed by applying one or more photovoltaic
layers onto a thin semiconductor material. While not as efficient as traditional
silicon photovoltaic cells, thin film photovoltaic cells are less expensive to produce
and have a wider potential range of application. A subset of the thin film
photovoltaic cells are dye-sensitized solar cells (DSSCs), which are comparable to
the efficiency of thin film photovoltaic cells, but are easier and cheaper to
construct (Smestad and Gratzel, 1998). However, there are challenges encountered
with stability of these cells over time. Currently, some DSSCs are used in
commercial products, but these cells tend to use rare and occasionally toxic dyes.
Some of these dyes, such as ruthenium, are expensive and reduce these cells’
cost-effectiveness (Gratzel, 2005). Platinum as the cathode further increases the
production cost.
To make this technology viable as a candidate for replacing fossil fuels, the costs
of production must be low. Manufacturing methods should be relatively simple
and the materials used must be inexpensive and readily available. Organic dyes
(water soluble), as well as pigments (water insoluble), are attractive because they
are more available and often inexpensive, but stability of cells constructed with
such substances remains a problem. Photosynthetic pigments (carotenoids and
chlorophylls), for instance, have much potential for use in DSSCs, but these
substances are not very stable and often oxidize if not treated properly after
extraction. In this experiment, an ancient pigment known as Dragon’s Blood was
evaluated to determine its efficiency and stability as part of DSSCs because it is
readily-available and retains its color for months, years, and even decades
following extraction. This pigment is derived from Daemonorops draco (Blume)
and has been used in various applications since antiquity, including scenarios
where it has proven to be durable even when exposed to sunlight (Edward et al.,
2001; Gupta et al., 2008).
Exactly 5.0 g of Dragon’s Blood resin was crushed into powder and soaked in 40 mL of acetone for 72 hours to
create the pigment preparation. Residue was discarded, then the resulting supernatant was placed in four 15 mL
centrifuge tubes and centrifuged at 3,000 rpm for 5 minutes to pellet any remaining residue. The final supernatant
in each of these tubes was combined into a beaker. Cells were constructed using two tin oxide coated glass plates,
with a Volt-Ohm meter indicated coating resistance ranging from 22 to 23 Ohms. The semiconductor was prepared
by dissolving 6.0 g of TiO2 in 10 mL of acetic acid and grinding with mortar and pestle for 30 minutes. A thin layer
of this TiO2 suspension, applied with a glass rod, was annealed to the conductive surface of the anode using a
Bunsen burner then left to cool for 15 minutes. The surface area of the TiO2 layer on each anode was 1.0 cm2.
Each test anode was soaked in a beaker with the pigment preparation for 72 hours. The resulting treated anodes
were left to dry for 24 hours. Control anodes were not left to soak in the pigment preparation. The conductive side
of each cathode was coated with graphite, and then placed with the graphite facing the TiO2 coated side of the
anode. The 50% saturated KI and 50% saturated I2 electrolyte solution was then injected between the opposing
plates. The glass plates were then together with Elmer’s Superglue® and allowed to dry for 24 hours. Any
noticeable leakage was then sealed, and these completed cells were subsequently used for the experiment. The
experiment took place in an environmental chamber where light intensity ranged from 20,000 to 30,000 lumens
(approximately 40 watts per square meter) during a 12-hour day period to near-zero lumens during a 12-hour night
period. Four controls and four treatments were used in this experiment as a randomized complete block design
with four replications. Power curves for each cell indicated maximum power obtained near 100,000 Ohms, thus an
equivalent resistor was inserted in parallel for each cell. Voltage measurements were recorded, using Pico
Technology software, every 10 minutes for 19 days.
Voltage values of all photovoltaic cells demonstrated a positive response to light. For
treated cells, voltages peaked at 77.5 mV at night and 230 mV during the day, whereas
voltages of control cells peaked at 2.82 mV at night and 30.0 mV during the day. Peak
voltage of all cells was obtained after about 5 days, and declined thereafter. Voltage
readings during the day declined slowly in treated cells and maintained about the same
reading of 150 mV at the beginning of the experiment, despite a peak of 230 mV at 5 days.
Control cells continued to drop in voltage output during the day and night after the 5th day
peak. For treated cells, current ranged from 1.36 to 2.31 µA with a daily average of 1.68 µA,
whereas current ranged from 0.086 to 0.290 µA with a daily average of 0.179 µA in control
cells. Current values for treated cells were higher and more stable than these same values
for control cells. Treated cells ranged from 0.184 to 0.531 µW with a daily average of 0.289
µW; whereas power values from control cells were negligible with values of less than
0.00774 µW for the duration of the experiment.
Compared to past work, the numerical results of this experiment are generally lower. The
peak and average voltage readings of 230 and 150 mV, respectively, for treated cells are
within the range of values reported in previous plant pigment investigations. Voltage is
not, however, the only measure: the peak and average currents of 2.31 and 1.68 µA for the
Dragon’s Blood treated cells are considerably lower those of other experiments, as was the
peak power of 0.531 µW. However, the average power of 0.289 µW for treated cells was not
always less. The closest results to this experiment is a previous experiment where crude
chlorophyll-treated cells were tested (FitzSimons, 2010). These chlorophyll-treated cells
achieved a similar peak voltage of 230 mV and a comparable daily voltage of 46.1 mV
during a 10 day period, but resulted in higher peak and higher average currents of 16.1 and
2.87 µA, respectively. However, while the peak power of 3.74 µW was also higher in these
cells, the average power was lower than the Dragon’s Blood treated cells at only 0.134 µW.
Also reported in the literature was an experiment of a specially-made chlorine-e6
chlorophyll derivative used in cells, which provided a similar peak voltage of 247 mV, but
greater peaks in current and power at 240 µA and 59.3 µW, respectively (Amao and Komori,
2004). Results from this experiment were not as impressive as those reported in the
literature for cells made with ruthenium-based dyes, where peak voltage of 455 mV and
peak current of 9,400 µA were reported (Gratzel, 2005). Still, results from this investigation
demonstrated that photovoltaic cells produced with Dragon’s Blood pigment have potential
to produce a generally stable average daily voltage (150 mV), current (1.68 µA), and power
(0.289 µW) values when cells are exposed to light at a low cost with easily-obtained
materials. Additionally, as the methods employed in this experiment were crude, it is
possible that these cells might be improved further.
LITERATURE CITED
Amao, Y., and T. Komori. 2004. Bio-photovoltaic conversion device using chlorine-e6
derived from chlorophyll from Spirulina adsorbed on a nanocrystalline TiO2 film electrode.
Biosensors & Bioelectronics 19:843-847.
Edward, H.G.M., L. Fernando, C. de Olivera, and A. Quye. 2001. Raman spectroscopy of
coloured resins used in antiquity: dragon's blood and related substances. Spectrochimica
Acta. Part A 57: 2831-2842.
FitzSimons, T. 2010. Harnessing solar energy using photosynthetic and organic pigments.
M.S. Thesis. University of Central Oklahoma, Edmond, OK.
Gratzel, M. 2005. Solar energy conversion by dye-sensitized photovoltaic cells. Inorganic
Chemistry 44:6841-6851.
Gupta, D., B. Bleakleyb, and R.K. Gupta. 2008. Dragon's blood: Botany, chemistry and
therapeutic uses. Journal of Ethnopharmacology 115:361-380.
O'Regan, B., and M. Gratzel. 1991. A low-cost, high-efficiency solar cell based on dyesensitized colloidal TiO2 films. Nature 353:737-740.
Smestad, G. 1998. Nanocrystalline Solar Cell Kit. Institute for Chemical Education,
University of Wisconsin Board of Regents. ICE Publication 90-001.
Smestad, G., and M. Gratzel. 1998. Demonstrating electron transfer and nano-technology:
A natural dye-sensitized nanocrystalline energy converter. Journal of Chemical Education
75:752-756.
ACKNOWLEDGEMENTS
Figure 2. Brett Jones working on dye-sensitized solar cells.
Funding for this project was provided by Office of Research & Grants at the University
of Central Oklahoma (UCO). Thanks also to Dr. Bidlack’s Research Group for their
support and recommendations.