Author: Daniel Stouffer Added: July 15, 2008
This article details the process of how solar electric cells are mixed with specific impurities to enhance their electric efficiencies. The silicon that is doped enhances the transfer of free electrons between the silicon wafers. It all relates to chemistry and physics in many ways. In some detail, we will also describe how a solar PV cells use photons created and distributed by the sun to create solar generated electricity. For home solar power, this is the physical process, called the photoelectric effect, makes it possible to create passive solar energy simply from sunlight. Doping Silicon Cells to Create Home Solar Arrays Introducing impurities, called dopants, into the silicon making up the solar cell creates the one-way flow of electrons necessary to produce electricity more efficient. Two differently doped silicon wafers are layered together to create this flow. The next section details out the dopants that are often mixed with solar grade silicon to improve efficiencies. Boron (p-type): Boron has 3 outer electrons, unlike silicon, which has 4. So wherever boron is introduced into the lattice, a hole is created due to the absence of an electron. This hole creates a net positive charge and is filled by a neighboring electron vibrating in to fill the hole there, and leaving a new hole. These positively charged holes move about. Boron doped silicon is also called p-type, because the freely moving charge is positive. Phosphorus (n-type): Phosphorus atoms have 5 outer electrons, one more than silicon. Wherever a phosphorus atom is introduced into the lattice, it has a complete set of 4 electrons to share with its 4 silicon neighbors and a 5th electron with no bond to fill. The fifth external electron rotating around the core of the atom bumps free of the atom and moves throughout the silicon wafers or lattice structure. So the introduction of phosphorus provides an electron that moves within the crystal lattice. This type of doped silicon is called n-type because the freely moving charge is negative. Solar Cells, Electricity and the P-N Junction: What? The magical flow direction needed to provide current of positive charge in one direction and negative charge in the opposite is created where these two differently doped silicon wafers are "mashed together" as a diode. The surface where the where n-type silicon meets p-type silicon is called the p/n junction. Of special interest, the two oppositely charged materials that are put together to create an electric field between them is called a diode; an important and necessary processing step as silicon atoms are manufactured into silicon grade solar cells often used in the creation of residential solar panel arrays. At the p-n junction, the extra phosphorus electron breaks free and wanders until it falls into a hole near a boron atom. Since the phosphorus site was electrically neutral before it lost its negative electron, the net charge around it now becomes positive. Similarly, the boron site, which was electrically neutral, now has one more electron, which makes the net charge at the site negative. This process continues all along the region between n-type and p-type silicon, with extra phosphorus electrons crossing over to fill boron holes. This creates two regions of separated charge, one side positive and the other negative, resulting in a permanent electric field between the silicon wafers at the p-n junction of the diode. Understanding How Solar Energy Fits into the Mix We are at the dawn of a solar revolution in the United States. Every aspect of the solar industry is experiencing explosive growth. Currently, there is huge demand and great expansion across the solar PV cell manufacturing industry. Specifically, the production of solar grade silicon. There is added demand for solar sales personal as well as huge demand for solar installation crews with appropriate certification. Opportunities abound everywhere. The renting of a solar energy system for your home is a new, attractive twist to the idea of switching to renewable energy. With the adoption of a leasing or rental model for residential solar electric systems, an average homeowner can now go green at home as well as build a part-time, solar energy business.
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