A solar cell is an electronic device that produces electricity when light falls on it. The light is absorbed and the cell produces dc voltage and current. The device has a positive and a negative contact between which the voltage is generated and through which the current can flow. Solar cells have no moving parts. Effectively they take light energy and convert it into electrical energy in an electrical circuit in physical process known as the photovoltaic effect.
The discovery of the photovoltaic effect is credited to the French physicist, Edmond Becquerel in 1839. He found that by concentrating the sun's light on one side of a battery the output current of the battery could be increased. This revolutionary discovery triggered the idea that one could produce energy from light by an artificial process. In 1883 an American inventor produced a solar cell from a material called selenium, but it was very inefficient. Selenium became used in light-exposure meters for cameras, but not for power production.
The efficiency of a solar cell is a measure of the proportion of the light hitting it that is actually converted into electricity. If the cell were 100% efficient then it would turn all the incident light into energy, but sadly this is impossible. Practical solar cells made from silicon wafers can have an efficiency of 16% or so.
A solar cell is a PV cell designed to convert sunlight to electricity. The simplest cells consist of a circular silicon wafer with a pn-junction sandwiched in the middle, a metallic bottom contact and a transparent top contact. Solar panels with cells like this have played a vital role in space technology since the late '50s, powering space satellites. They are expensive to produce because silicon wafers are expensive to produce but their cost was unimportant in the space race.
In recent years there has been a continuous search for cheaper forms of PV cell, economical enough to be used in applications here on earth. Attempts have been made to use cheaper forms of silicon, of lower quality than that used in computer chips, despite the poorer cell efficiencies that result. One possibility has been to replace the single-crystal wafer by polycrystalline squares. This material has the advantage of being much more light-absorbing than crystalline silicon. Cell efficiencies are perhaps only half those in crystalline silicon, but the amorphous cells potentially cost much less than half for the same surface area. So they seem to be the most economical choice at the moment.