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Solar Cells, Solar Energy Arrays, and Doping Silicon (Part 10)

By Daniel Stouffer

Republish: EasyPublish™ Published: 15Jul2008 Word count: 644 Viewed: 838 time(s) Get Free Content For Your Site

The following article explains in varying levels of detail how a solar cells use photons produced by the sun to create solar generated electricity. For residential solar energy systems, this is the physical process that makes it all work. This article will also explain how solar cells are doped with specific impurities to enhance the internal electric field that creates the one-way flow of free electrons bumped out of the silicon atoms and into the holes produced in others. It all relates to chemistry, really.

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 following explains the most commonly added dopants added to solar silicon.

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. This 5th outer electron breaks free and wanders throughout the lattice. 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; a necessary and critical step in the creation of solar cells for home solar electric generation.

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. Triple digit expansion in solar photovoltaic cell manufacturing, to the need for solar sales associates, to the huge demand for solar system installers. 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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