Transcript Solar Poster 2011 - University of Central Oklahoma

Durability of Dragon’s Blood Pigment in Dye-Sensitized Photovoltaic Cells
Brett Jones and Jim Bidlack
Department of Biology, University of Central Oklahoma, Edmond, OK 73034
Figure 1: Brett Jones applying Dragon’s Blood pigment to cells.
Figure 2: Power curve results for 17 days in original experiment. This data was gathered in a prior experiment using hand-made cells, and it is expected that the manufactured plates will perform better.
ABSTRACT
An experiment was conducted last year to determine the viability of a plant
pigment for use as an alternative to silicon solar cells or dye-sensitized
photovoltaic cells using other dyes. In that experiment, the voltage values in
cells treated with the pigment were significantly higher than values from
control cells, which contained no pigment. This experiment is a continuation
of the prior experiment, though over a longer time period and using improved
cells. The cells will be constructed using cathodes and anodes composed of
glass plates coated with tin oxide. Each cathode will have a thin layer of
titanium dioxide annealed its surface, and each anode will have a thin layer of
platinum annealed to its surface. The cathodes will be immersed in a pigment
preparation from the Dragon’s Blood Palm (Daemonorops draco) in order to
stain the titanium dioxide coating. A triiodide electrolyte solution will be used
between the cells, and opposing ends connected to a voltmeter for gathering
data over time. In this new experiment, pigment from Dragon’s Blood will be
incorporated into commercially-purchased plates to obtain higher voltages
over a longer period of time when compared to previously-constructed cells.
INTRODUCTION
It is not a question of if the world will run low on fossil fuel supplies, but of
when this will occur. As it appears that this scenario will unfold sooner rather
than later, it is necessary that alternative means of electricity generation are
developed. One of the most promising alternative energy technologies is the
photovoltaic cell. However, traditional silicon cells are costly to construct.
Fortunately, an alternative to common photovoltaic cells exists in the form of
thin film photovoltaic cells. These cells can be thinner, more cost effective,
easier to construct, and lighter than traditional photovoltaic cells. A subset of
thin film photovoltaic cells is the dye sensitized solar cell, which this project is
focused on. Currently, there are some dye sensitized solar cells used in
commercial products, however these cells typically use toxic, caustic, and
inorganic dyes. Some of these dyes are expensive, which while negating the
cost benefit, does retain the other three benefits. Yet, to make this technology
viable as a replacement to fossil fuel electricity generation, costs of production
must be lower. Organic dyes are an attractive option, but these tend to decay
after some days or weeks in operation. Typically these dyes are part of the
photosynthesis process in plants. In this experiment, an ancient dye derived
from Daemonorops draco was evaluated, as it has been used in various
applications since antiquity and has proven to be durable in other applications
where it is exposed to light (Edward et al., 2001).
Plant Pigments: It has been demonstrated that a thin film coating of TiO2, on
conductive glass which is impregnated with dye molecules and in contact with
a suitable redox mediator, can facilitate an electron transfer process that
mimics photosynthesis (O’Regan and Gratzel, 1991). In this process, TiO2 acts
as the electron acceptor and an iodine solution replaces water as the electron
donor (redox mediator). It does not appear to matter if the dye was used by the
plant to help harvest light, but rather that the wavelength and chemical
structure facilitating bonding with the TiO2 allows for better electron excitation,
as demonstrated with flavanoid and anthocyanin dyes extracted from plant
materials and used separately in TiO2 nanocrystalline cells (Cherepy et al.,
1997; Smestad and Gratzel, 1998).
MATERIALS AND METHODS
RESULTS AND DISCUSSION
Photovoltaic cells were constructed and tested in the Biology Department at the University of Central
Oklahoma. Procedures for constructing cells were derived from a Nanocrystalline Solar Kit purchased from
the Institute of Chemical Education at the University of Wisconsin in Madison, Wisconsin. Pre-constructed
tin-annealed glass plates (titanium dioxide-coated anodes and platinum-coated cathodes) and their
corresponding thermoplastic seals were obtained from Dyesol of Queanbeyan, Australia. The resin required
to make the Dragon’s Blood dye (Daemonorops draco) was obtained from Mountain Rose Herbs of Eugene,
Oregon. All other materials were supplied from Sigma-Aldrich in St. Louis, Missouri. Monitoring of voltage
produced by photovoltaic cells was enabled through use of an ADC-16 board connected to a data logger from
Pico Technology, Ltd., United Kingdom.
No results have been gathered yet from this experiment, as the experiment is ongoing.
The experiment will run for a period of 30 days, and data will be analyzed at that time.
Each manufactured cell may have lower overall voltage than the previous experiment,
as the area of each cell is smaller than cells used in the previous experiment.
However, it is anticipated that the voltage-per-area will be higher and that each cell will
be more consistent with similar cells in power output.
Exactly 5.0 grams of Daemonorops draco resin were soaked in 40 mL of acetone for three days to create the
dye preparation. Photovoltaic cells using the dye were constructed using tin dioxide (SnO2) coated
conductive glass plates with a triiodide electrolyte sandwiched between the opposing electrodes.
Conductivity of glass plates was measured prior to construction by using a Volt-Ohm meter and indicated a
coating resistance that ranged from 22 to 23 Ohms. Each anode was soaked in a beaker with the dye
preparation for 72 hours to ensure complete reaction with the TiO2 layer. Each cathode was then placed with
the platinum facing the TiO2 coated side of the anode. A KI/I2 solution was utilized as the electrolyte between
the two plates, which were then sealed together with small rubber bands and a thermoplastic seal between
each plate. Control cells were constructed using the same methods, but were not left to soak in the dye
preparation. Twenty-four cells were constructed: 8 controls, and 16 treatments of 100 µL split equally
between four applications of 25 µL and ten applications of 10 µL.
Voltage readings will be recorded in an environmental chamber where light intensity ranged from 20,000 and
30,000 lumens during a 12-hour day period and essentially zero lumens during a 12-hour night period. Voltage
measurements will be recorded using PICO software at 10 minute intervals during the experiment.
In the previous experiment, photovoltaic cells treated with the Dragon’s Blood pigment
exhibited cycles with voltage readings as low as 0 mV at night and up to 330 mV
during the day (Figure 2). During this 17-day experiment, most cells either maintained
or demonstrated a decrease in voltage as the cells aged. Control cells (without
pigment) generally demonstrated lower voltage than those treated with pigment.
These results suggest that the Dragon’s Blood pigment functioned successfully as
part of a dye-sensitized photovoltaic cell.
Durability of the treated cells during the experimental cycle (17 days) appeared better
than expected. Test cell 4 was the most consistent, demonstrating no apparent
degradation of the pigment. Voltage readings from test cells 1, 2, and 3 indicated a
breakdown of the glue seal at points and spiked highly, then fell to lower values.
Interestingly, this did not appear to render the cells non-functional, as voltages were
still observed in these cells throughout the experiment. All cells treated with Dragon’s
Blood still demonstrated at least 100 mV by the end of the experiment.
Control cells demonstrated low voltages throughout the experiment. These non-dye
cells, were sealed well and demonstrated values in the 200 to 300 mV range, but
voltages quickly declined to under 200 mV at the very beginning of the experiment.
LITERATURE CITED
O'Regan, B., and M. Gratzel, 1991. A low-cost, high efficiency solar cell based upon
dye-sensitized colloidal TiO2 films. Nature 353:737-740.
Smestad, G., and M. Gratzel. 1998. Demonstrating electron transfer and nanotechnology: A natural dye-sensitized nanocrystalline energy converter.
Journal of Chemical Education 75:752-756.
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.
ACKNOWLEDGEMENTS
Figure 3: Dragon’s Blood dye (right) and cells which have been treated with the dye (left).
Funding for this project was provided by Office of Research & Grants at the University
of Central Oklahoma (UCO). Many thanks to Toby FitzSimons and Cliff Pelchat, who,
along with Dr. Bidlack’s Research Group, provided training of methodologies, as well
as advice and guidance for implementing the experiment.