Make a Dye-Sensitized Solar Cell
How does a solar cell work? In this green chemistry lesson plan, students will build and test their own dye-sensitized solar cells using dye from blackberries. Along the way, they will learn about the principles of green chemistry and evaluate how solar cell manufacturing can go green.
- Consider this process against the twelve principles of green chemistry.
- Construct a dye-sensitized solar cell.
- Evaluate and compare the differences in solar cell technologies.
NGSS AlignmentThis lesson helps students prepare for these Next Generation Science Standards Performance Expectations:
- HS-ESS3-2. Evaluate competing design solutions for developing, managing, and utilizing energy and mineral resources based on cost-benefit ratios.
- HS-ESS3-4. Evaluate or refine a technological solution that reduces the impact of human activities on natural systems.
Science & Engineering Practices
Engaging in Argument from Evidence. Evaluate competing design solutions to a real-world problem based on scientific ideas and principles, empirical evidence, and logical arguments regarding relevant factors (e.g. economic, societal, environmental, ethical considerations).
Constructing Explanations and Designing Solutions. Design or refine a solution to a complex real-world problem, based on scientific knowledge, student-generated sources of evidence, prioritized criteria, and tradeoff consideration
Disciplinary Core Ideas
ESS3.A: Natural Resources. All forms of energy production and other resource extraction have associated economic, social, environmental, and geopolitical costs and risks as well as benefits. New technologies and social regulations can change the balance of these factors.
ESS3.C: Human Impacts on Earth Systems. Scientists and engineers can make major contributions by developing technologies that produce less pollution and waste and that preclude ecosystem degradation.
ETS1.B: Developing Possible Solutions. When evaluating solutions, it is important to take into account a range of constraints, including cost, safety, reliability, and aesthetics, and to consider social, cultural, and environmental impacts. (secondary)
Influence of Science, Engineering, and Technology on Society and the Natural World. Engineers continuously modify these technological systems by applying scientific knowledge and engineering design practices to increase benefits while decreasing costs and risks.
Analysis of costs and benefits is a critical aspect of decisions about technology.
Stability and Change. Feedback (negative or positive) can stabilize or destabilize a system.
MaterialsA blackberry solar cell classroom kit is available from Flinn Scientific.
Each student group will need:
- 1 transparent indium tin oxide conductive glass slide (ITO slide), 15 mm x 35 mm x 1 mm
- 1 TiO2-coated indium tin oxide conductive glass slide, 15 mm x 35 mm x 1 mm
- 4 drops of iodide electrolyte solution (0.5 M potassium iodide mixed with 0.05 M iodine in propylene glycol)
- 2 small binder clips
- 1 blackberry (thawed, frozen blackberries work well)
- 1 small spatula
- 1 graphite pencil
- 1 piece of parafilm, cut into 20 mm x 40 mm size
- 1 small aluminum dish pan (2 inches)
- 1 paper towel
- 1 razor blade
- Light source (flashlight or sunlight)
If preparing the TiO2-coating yourself, teachers will also need:
- Mortar and pestle
- TiO2 (titanium dioxide)
- Trimesic acid (1,3,5-tricarboxylbenzoic acid)
- Stirring rod
Note: Handle the glass plates by the edges to avoid touching the faces of the plates.
Background Information for TeachersThis section contains a quick review for teachers of the science and concepts covered in this lesson.
There is a growing need to investigate alternative energy sources due to the impacts of fossil fuels on global warming and clean air. Solar energy, or energy from the sun, is a free, readily available, plentiful resource that can be collected by solar cells to generate electricity.
Although solar cells have been around for a long time, their use for energy generation is not widespread. This is because traditional solar cells are expensive and inefficient (typically 11-18% of the sunlight they absorb is converted to electricity). To be considered a green chemistry technology, the technology must demonstrate three standards: performance, safety, and cost benefits. In this experiment, your students will make a dye-sensitized solar cell (DSSC) that is efficient, uses safe materials, and is inexpensive.
Unlike traditional solar cells that generate electricity through p/n junctions, the chemistry of the nanocrystalline TiO2 is based on red-ox (reduction-oxidation) chemistry. This means that the excitement of electrons to generate electron movement through the system is what drives electricity, which can be measured in terms of voltage (V). The mechanism of a photovoltaic cell has three steps (Figure 1):
- A dye, adsorbed on a layer of semiconductor (TiO2), interacts with the visible light provided by the sun (just like the green pigment does in a leaf), promoting an electron from a lower-level orbital to an excited one.
- The excited electron is injected by the dye into the semiconductor and, traveling through the bulk of it, reaches the electric contact with the outside circuit.
- The electrons return to the cell to complete the circuit and bring the dye back to its "normal" state via an electrolyte solution that helps carry electrons through the cell.
The cells are a "sandwich" in which two conducting glass slides are overlapped. The photoanode is coated with the layer of TiO2 sensitized with the dye, and the other is coated with graphite in order to enhance the interaction with the electrolytic solution that is contained between the glass slides themselves.
Figure 1. Mechanism of a dye-sensitized solar cell.