Solar Cells
Solar cells are at the forefront of scientific research. Chemists are revolutionizing solar cells to capture more of the sun’s energy to power our everyday needs.
The global demand for renewable energy has grown rapidly over the past two decades, and for good reason. Global warming continues to be an existential threat as global temperatures continue to rise due to the emittance of greenhouse gases. Energy resources like coal and gas can no longer be relied upon without causing catastrophic damages to the earth we know. Renewable energy like solar cells are just one way in which chemists contribute to the fight against this environmental crisis.
Solar cells are great candidates for renewable energy because they can capture the light emitted from the sun and transform it into electricity. The sun emits all sorts of lights with different wavelengths, some we can see (the visible light spectrum) and some we can’t (X-ray, Infrared, gamma rays, etc.). Each type of light has its own unique energy, the shorter the wavelength of light, the more energy that light contains. Because a large portion of the light that reaches the earth is in the visible spectrum (380 nm - 700 nm), solar cells are typically designed to absorb this wavelength.
A common element used in solar cells is Silicon (Si). Silicon is a semiconductor, which means that given enough energy, Silicon will become a conductor and facilitate the flow of electrons (also called current). Silicon exists as a crystalline, 3-D structure. To assist its ability to conduct, other elements are added within the crystal structure through a process called doping. There are two different Silicon layers in a solar cell: the p-type and n-type. The p-type is silicon doped with the electron deficient element Boron(B) giving the p-type layer a positive charge. The n-type silicon is doped with the electron rich element Phosphorus (P) giving the n-type layer a negative charge.
As light reaches the solar cell, its energy will excite an electron in the p-type silicon layer. The electron will then have enough energy to enter the n-type layer and will continue to migrate to an external circuit. This migration, or flow of electrons that is created from sunlight produces electricity! Other light absorbing materials are being explored in an effort to boost the efficiencies of solar cells and ease the manufacturing process of the technology. For example, perovskite solar cells are composed of elements such as Calcium (Ca), Lead (Pb) and Bromine(Br), ordered in a crystalline structure called perovskite. Perovskite is a great alternative because it is more flexible and easier to manufacture. Whatever form the light absorbing layer in solar cells take, each type operates under the same chemical principal of exciting and migrating electrons.
Solar cells currently operate at an efficiency of ~20% since sunlight can be reflected, converted to heat or the excited electron does not migrate to the outer circuit. In an effort to increase efficiency, chemists all around the world are researching ways to maximize the conversion of sunlight to energy . As our world continues to emphasize renewable energy sources, solar cells and their chemistry will only become more fascinating and more important!
