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Make a Dye-Sensitized Solar Cell

Summary

Grade Range
9th-12th
Group Size
1-4 students
Active Time
60-75 minutes
Total Time
60-75 minutes
Area of Science
Chemistry
Energy & Power
Green Chemistry
Key Concepts
conductivity, electricity, ions, solar cell, green chemistry, sustainability, renewable energy
Credits
Four different dye-sensitive solar cells

Overview

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.

Learning Objectives

NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:
This lesson focuses on these aspects of NGSS Three Dimensional Learning:

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)
Crosscutting Concepts
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.

Materials

A blackberry solar cell classroom kit is available from Flinn Scientific.

Each student group will need:

If preparing the TiO2-coating yourself, teachers will also need:

Note: Handle the glass plates by the edges to avoid touching the faces of the plates.

Background Information for Teachers

This 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):

  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.
  2. 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.
  3. 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.

Schematic of a dye-sensitized solar cell showing an electron leaving the dye, traveling trough the semiconductor layer before contacting with the circuit and returning to the dye layer through an electrolyte solution.
Figure 1. Mechanism of a dye-sensitized solar cell.

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