If you’ve considered updating your home with energy conserving solar panels, may have come across the words “photovoltaic cell” in your research into the options available. Photovoltaics, also known as solar cells, are battery cells which are comprised of a semiconductor metal capable of absorbing light in the form of photons and converting the energy absorbed into electricity in the form of electrons.
Many of the metals used as conducting mechanisms in photovoltaic cells were originally developed for use in the space industry in the 1960s, but it wasn’t until recently that solar cells became economically feasible for use in domestic settings. Today, a number of these same semiconductors, including silicon, are used in computer systems and other forms of microelectronics.
In a photovoltaic cell, the semiconducting metal, such as silicon, is a wafer-thin sheet that has been chemically treated so that one side is positively charged and the other is negatively charged, thus forming an electric field. When light strikes the surface of the metal, electrons are knocked loose from the negatively charged side and are attracted to the positively charged side. This attraction of electrons to the positively charged side, much like the attraction between poles on a magnet, creates an electric current. An electrical conductor attached to each side of the metal can harness this electrical current into usable energy for the home.
A single solar cell does not produce enough energy to power more complex machines, such as refrigerators, let alone entire homes. These single cell units have what is known as low conversion efficiency. To power complex energy grids, therefore, a number of photovoltaic cells are connected together to form a photovoltaic module. These modules are, in turn, connected together to form an array. Photovoltaic arrays are capable of producing direct current electricity, and they can be arranged in a variety of patterns to produce specific voltages, including the commonly used 12 volts system. Most common photovoltaic modules and arrays use a single semiconducting material, making them single junction cells. These cells are limited by how much of the sun’s rays they can turn into energy. When light, in the form of photons, strikes the metal, the band gap of the metal determines how many electrons can be freed. Just as you must exert energy that is equal to or greater than an object to get it to move, so must the photons exert energy that is equal to or greater than the energy contained in that band gap to generate the movement of electrons from the negatively charged to the positively charged side.
One way around this limitation is by creating a multijunction cell. These photovoltaic cells use multiple semiconducting metals, stacked in order from highest band gap to lowest. The result is a solar cell whose conversion efficiency is higher than that achieved by single junction cells. While not commonly used in residences and businesses, these multijunction photovoltaic cells are becoming increasingly common in industry.
Regardless of the how the solar cell works, it is important to remember that photovoltaic cells can save energy and, by proxy, money, reduce carbon emissions, and be part of a greener lifestyle.