Dye-Sensitized Solar Cell

There is a growing need to investigate alternative energy resources due to the depletion of petroleum, a widely used energy source. 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. 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.