User:MattieMylonas/Photovoltaic cells

Photovoltaic cells convert light into electricity as a result of systems at the atomic level. The system that creates electricity is called the photoelectric effect and occurs when certain materials display a specific mechanism. The mechanism the materials generate is absorbing photons and releasing electrons. This causes electricity to be made because when the electrons are trapped again and subsequently release an electrical current.

Albert Einstein best described the mechanics of the photoelectric effect and even won a Nobel Prize for it. He explained that the photons carry momentum despite being massless objects, and referred to them as “packets of energy”. This relates to the release of electrons in the photoelectric effect, because if the light energy is below a threshold, the photons will give the electrons energy they lack. The photons do not need to give the electrons the extra push of energy if the light emitted is above a certain threshold. This is called the work function.

Many industrialized countries such as Germany, Japan, and Spain are making efforts towards using renewable energy such as that produced by photovoltaic cells. The United States ranks fourth behind these countries with their efforts to switch from fossils fuels to renewable resources.

How Photovoltaic cells work

Photovoltaic cell semi condutor. Credit: NASA [3]

In order to generate electricity, photovoltaic or solar cells are created from semiconductor material such as silicone. This cell is adjusted to create an electric field with a positive and negative side. The sunlight hitting the cells causes electrons to become detached from the atom and then become trapped in the semiconductor material as electrical current. A large amount of solar cells are placed together on a frame and form a photovoltaic module. Multiple modules placed together are called an array.

Modules and arrays of photovoltaic cells can be linked to produce the exact voltage and electrical current that is needed. The most used link to create electricity is called a single junction. Single junctions operate by releasing electrons only when the photons have energy that is equal or greater than the photovoltaic cell. The single junction semi conductor’s ability relies greatly on the sun’s strength. Sometimes multijunction cells are used, and have more than one relation or band gap to the photovoltaic cell. This results in a more efficient conversion of sunlight into electricity.

In more recent years, different materials are being used as semiconductor material including solar ink and dyes, and plastic or mirror lenses. These types of materials are more efficient at concentrating and collecting sunlight into energy.

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  Tunnel Junction. Credit: NASA [1]

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  Multi Junction. Credit: NASA [2]

History

Edmund Bequerel a French physicist was the first person to discover the photoelectric effect in 1839 by observing how various materials created electricity after being in contact with light. The first time this technology was used to generate electricity was in 1954. The machine was called a solar battery and was built by Bell Laboratories. Shortly after, NASA started to use photovoltaic cells and the photoelectric effect to aid in their space missions by powering spacecraft. The technology began to evolve and become more affordable and effective, making it more appealing to the general public.