Lecture #26, Wednesday, March 3rd

A photovoltaic device is used to convert light into electricity at the atomic level. Many practical devices, such as your calculator, run on solar power. A nice description of how solar cells work, which was summarized in class, can be found here. A showed a 2-Dim simplification of crystalline silicon and showed how adding impurity atoms can vastly increase the electrical conductivity of silicon. When silicon atoms are replaced by only a few other atoms in a crystal, we consider the pure crystal to be "doped" by an impurity. When an atom containing more electrons replaces an atom in the pure crystal this is referred to as N-type doping, while replacing an atom in the pure crystal with an atom with fewer electrons is called P-type doping.

Despite their simplicity, there are still several drawbacks to utilizing photovoltaic cells, so chemists need to develop other methods to harness the sun's visible photons. In 1991 Dr. Michael Graetzel developed a new technology called a Gratzel, or dye sensitized solar cell, which is still being researched and developed today. The cells you are constructing in the lab are the exact ones Gratzel developed. On Friday, we will discuss the concepts behind these cells, which will include why we need to use a dye and why we need an electrolyte solution.