Introduction to the dye-sensitized solar cell.
As the name suggests, it is a type of solar cell that is “sensitized” by a dye. What does this actually mean?
Before further confusion occurs with the emergence of more scientific terms, some simple theory of electricity generation via light excitation has to be explained.
In basic high-school science, it is taught that light is a form of energy, and energy could be transferred from one form to another form, just like how electrical energy could transform into light and heat energy on the PC or mobile phone one is reading this article with. Yes, the basic working principle of the solar cell is to convert light energy into electrical energy, and or into storable forms of energy.
Typical arrangement of a dye-sensitized solar cell is a sandwiched cell with the following configuration:
1. Conductive substrate(negative terminal)
2. Dye and semiconductor matrix
3. Electrolyte solution
4. Catalytic metal
5. Conductive substrate (positive terminal)
The Journey Begins with Light Exciting the Dye Molecules…
The heart of the dye-sensitized solar cell technology lies in the sensitizer dye, which is a chemical compound capable of absorbing light to cause some chemical change to it. When light energy of the required intensity and wavelength has been absorbed, the sensitizer releases electron(s) and itself gets oxidized as a result of the electron loss.
The ejected electrons would then go into a semiconductor matrix which the sensitizer is bound to, typically an oxide material like zinc oxide or titanium dioxide, the semiconductor matrix would transfer the electrons out of the circuit through its direct contact with a conductive substrate (typically transparent) and the electrons could then flow out as electricity to a load, where the electrical energy could get stored or used as other forms.
After passing through a load, the electrons are low in energy and would travel through the conducting wires to the other side of the solar cell, where there is a catalytic metal, typically platinum, so that it could take in the extra electrons and assist to transfer it to the electron carrier in the electrolyte solution.
The electrolyte solution contains a reduction-oxidation mixture, usually bromine-bromide or iodide-triiodide pairs. One would act as the electron-acceptor while the other as the electron donor that runs between the dye-semiconductor matrix and the catalyst metal. The electron donor would go towards the dye-semiconductor matrix to supply electrons to the oxidized sensitizers to regenerate the dye, while the electron acceptor would acquire the electrons from the catalytic metal.
In this way, the whole cycle completes a circuit, and we get a working cell. This dye-sensitized solar cell is also sometimes known as the Gratzel Cell, named after its inventor who first used a porous semiconductor matrix to bring the efficiency of such solar cell several folds higher than its predecessors. It is a special solar cell because it could be fully organic, meaning it is highly sustainable and does not require rare materials for its production. It could also be made flexible and transparent, very suitable for building exteriors, serving aesthetical and practical functionalities.
