The world’s energy demands increase year after year, while its resources are consistently being depleted in order to sustain these energy demands. These limited resources will one day be no more. A dependable source of renewable energy must be found. Currently solar energy is not efficient enough to sustain the population. However, the technology is constantly advancing, and solar energy could one day be that source.
The solar cell’s roots can be traced all the way back to the 1800s with Antoine-César Becquerel. In 1839, Antoine discovered that electrons can be emitted from materials that absorb the energy from light, known as the photoelectric effect, after immersing an electrode in a conductive liquid. Almost fifty years later the first solar cell was created by Charles Fritts, in 1883. His solar cell was composed of selenium and gold, and had an efficiency of around one percent. By the mid-1900s, Bell laboratories released the first modern solar cell. The cell featured p-n junctions that are still used in solar cells today, and reached about six percent efficiency. In 1958, the first satellite powered by solar cells was launched into space; the Vanguard I. Solar cell technology reached an efficiency of twenty percent, in 1985, due to the efforts at the University of New South Wales. The current record for efficiency is slightly over forty percent. China has become the leading manufacturer of solar cells, with prices as low as $.6 per watt, which is far less than the price in the 1950s of around $250 per watt.
The general idea behind solar cell technology is that the energy from light is absorbed by a material. This causes electrons to be released and travel in order to generate current. However, it is much more complicated than that. For a solar cell to function, an electric field must first be generated. This is accomplished by p-n silicon junctions. When silicon is made for solar cells, it is generally doped with impurities. These impurities are usually phosphorus, which creates n-type silicon (negative silicon), and boron, which creates p-type silicon (positive silicon). Silicon has a crystalline structure with 4 electrons in its outer valence shell, which causes each silicon atom to bind to four other silicon atoms. A Phosphorus atom has 5 electrons in its outer shell. When combined into the silicone crystalline structure, phosphorus binds with 4 other silicon, but has one electron that remains unbounded. This extra electron is much easier to break off since it is only held in place by the proton in the nucleus of the phosphorus atom. A boron atom has 3 electrons in its outer shell. When combined into the silicone crystalline structure, boron only bonds with 3 silicon atoms. This leaves a hole for another electron to fill. In a solar cell, p-type silicon and n-type silicon are placed in contact with one another. This causes the unbonded electrons in the n-type silicon to rush over to fill the holes in the p-type silicon. This creates an electric field across the two types of silicon that allows electrons to travel in only one direction. When the energy from light is absorbed and an electron is released, it can only travel from p-type to n-type silicon. If an external pathway is supplied, electrons that have come to the n-type silicon will travel through it to the p-type silicon. These electrons are able to do work, and generate a current. The electrons travel through the external pathway in order to fill the holes left behind by the electrons traveling over the electric field to the n-type silicon. Not all photons from light can cause an electron to be emitted by a material. Only photons with energy equal to or greater than the band gap energy of a material can cause an electron to be emitted. The band gap energy is the amount of energy required in order to cause an electron in the outer shell to be emitted. If a photon has twice the energy as the band gap energy of a...
References: 1. Jimenez-Gonzales, Concepcion, and Costable, David J.C. “Green Chemistry and Engineering A Practical Design Approach.” John Wiley & Sons, Inc. 2011.
13. Desideri, U., F. Zepparelli, V. Morenttini, and E. Garroni. "Comparative Analysis of Concentrating Solar Power and Photovoltaic Technologies: Technical and Environmental Evaluations." August 21, 2012.
14. CdTe Technologies, First Energy. Retrieved March 20, 2013, from http://www.firstsolar.com/Innovation/CdTe-Technology
16. Gallium Arsenide Solar Cells, Calfinder. Retrieved March 20, 2013, from http://solar.calfinder.com/library/solar-electricity/cells/cell-materials/gallium-arsenide
Please join StudyMode to read the full document