A solar cell, also known as a photovoltaic cell, is the name given to an energy capturing device. It absorbs sunlight and transforms it into electricity by way of the photovoltaic effect. These cells have evolved dramatically since their creation, and in the past few years, particularly large strides have been made in this technology.
Most simply, a solar cell works by absorbing sunlight. The photons from the light run into the panel and are absorbed by some sort of semiconducting material. Most contemporary ones are made out of silicon, although other substances are being experimented with as semiconductors to make them more cost effective and environmentally friendly. Electrons are then freed from their host atom, and they move freely as electricity. From the solar cell, this electricity then passes through a larger array, where it is turned into direct current (DC) electricity, which may then later be converted to alternating current (AC).
The photovoltaic effect was first presented in the early-19th century. In the 1880s, the idea was put to practical use in the creation of the first solar cell, made with selenium as the semiconductor. The first one was around 1% efficient, meaning that it managed to capture 1% of the total solar energy that hit the cell.
In 1954, Bell Labs discovered that silicon could be modified slightly to make it incredibly photo-sensitive. This led to the modern revolution in photovoltaic cells, with the early silicon cells operating at around 6% efficiency. In 1958, a satellite, the Vanguard 1, was launched with them as a source of energy. This allowed the satellite to remain in geosynchronous orbit indefinitely, since it didn’t rely on a finite amount of fuel.
Through the 1970s and 1980s, solar technology continued to improve. By 1988, ones were being mass produced that were capable of 17% efficiency, and by the end of the decade, those made from both gallium arsenide and silicon had surpassed 20% efficiency. In the late 1980s, a new type of technology also appeared, using lenses to concentrate sunlight on to a single cell. This high energy density allowed for efficiencies of up to 37% at the time.
There are three main classifications of solar cells, referred to as "generations" because of when the technologies first appeared. A first generation cell is what most people think of when they think of this technology. They account for around 90% of the solar cells in the world, and have a theoretical maximum efficiency of around 33%.
A second generation solar cell is designed to be substantially cheaper and easier to produce. Using technologies such as electroplating and vapor deposition, second generation ones can be mass produced relatively cheaply. They are usually just a thin film of some sort of material, such as amorphous silicon or cadmium telluride, applied in a very thin sheet to a material like ceramic or glass.
Third generation cells take the second generation technology and tries to greatly improve their efficiency. These are the cutting edge technologies, trying new concentration methods, using extra heat to increase the voltage generated, and other technologies to work towards target efficiencies in the 30% to 60% range.
