The newsLINK Group - About Photovoltaic (PC) Cells

Editorial Library Category: Mining Topics: PV Cells Title: About Photovoltaic (PV) Cells Author: newsLINK Staff Synopsis: Solar energy is green energy, but actively using solar energy requires equipment. You have to install the equipment before you can tap into all that glorious, free sunshine. Editorial: About Photovoltaic (PV) Cells 4064 South Highland Drive, Millcreek, Utah 84124 │ │ (v) 801.676.9722 │ (tf) 855.747.4003 │ (f) 801.742.5803 Editorial Library | © The newsLINK Group LLC 1 Solar energy is green energy, but actively using solar energy requires equipment. You have to install the equipment before you can tap into all that glorious, free sunshine. Since some of the necessary materials for the equipment are mining products, that makes the mining and energy industries into important partners as the U.S. turns increasingly to renewable energy for its future energy needs. Information technology works because of silicon. If you have ever taken a chemistry class, you know that life is carbon based. Silicon is the equivalent of carbon when it comes to making electronic circuits. The idea is to use crystals in electronic circuits. This is the basis for today’s solid-state electronics. Silicon isn’t a good natural conductor. One silicon atom has four outer-shell electrons. Those four electrons bond to four other silicon atoms. The result is an eight-electron crystal matrix that doesn’t work as an electrical conductor. But scientists have figured out how to make silicon conduct electricity in some circumstances, and act as an insulator in other circumstances. To change silicon’s conductivity, it turns out that all you have to do is add another element to the silicon so that silicon’s properties are changed. The new element is called either an impurity or a dopant, and the entire process is called doping. Doping is an interesting word, one that you probably think of in terms of drug use. It originally comes from a Dutch word, doop. Doop means sauce, but in the 1800s, dope came to also mean gravy. If you live in Ohio, dope became a word for syrupy ice cream toppings. In South Carolina and other southern states, dope was a soft drink flavored like cola. By extension, it was used for any medicinal drink that had a dulling effect on a person. The drug-associated definitions developed because opium has a form that is a lot like dark molasses. The first practical semiconductor transistor was developed in 1947 in an AT&T Bell Laboratory by three men: John Bardeen, Walter Brattain, and William Shockley. They got a Nobel Prize for their work in 1956. Let’s take a closer look at one of the basic components for putting together a solar energy system: the PV cell. There are four basic designs for these devices: Homojunction: These are made from a single material, extremely high quality crystalline silicon. It works, even though it is just one material, because it has two sides. The top is dominated by positive carriers, called holes, and the bottom side is dominated by negative electrons. There is a junction in the middle. Heterojunction: Two layers are involved. The top layer, made of something called a window material, is about what you would expect from a window: it is transparent to light, and it easily allows the light to reach the bottom layer. The bottom layer is a material that absorbs light. Two common semiconductor materials used to make heterojunction cells as cadmium sulfide and coper indium diselenide. p-i-n and n-i-p: These are essentially three-layer sandwiches. The middle layer is called the intrinsic-type or undoped layer; the remaining two layers have been doped and are either n-type or p-type layers, where the “n” and the “p” stand for positive and negative. N-type silicon has been doped with phosphorus gas. Phosphorus has five electrons, and silicon has four. When they are combined, they end up with one extra free electron that can move around freely whenever voltage is applied. Electrons carry the charge, which is negative. P-type silicon has been doped with boron gas. Boron has three electrons in its outer shell. That means that when boron and silicon are combined, there is a vacant location in the outer shell, called a hole. It will easily accept electrons because of the presence of that hole. P-type silicon has a positive charge because the charge carriers are holes. Multijunction: These are also called cascade or tandem cells, and they use more of the sun’s light spectrum than other PV cells. They can be made two ways, as a mechanical stack or as a monolithic one. For a mechanical stack, the cells are stacked on each other, with the largest bandgap layers on top and the smallest bandgap layers on the bottom. A monolithic system is