A solar cell is a device that converts light energy into electricity using the photovoltaic effect. They are therefore also known as photovoltaic cells.
A common single-junction silicon solar cell can generate up to 0.6 volts (open-circuit voltage).
Individual solar cells can be gathered together to build a photovoltaic module, and such modules can be combined to form a solar panel. Several solar panels connected to each other is known as a solar array.
What is the photovoltaic effect?
The photovoltaic effect is the generation of voltage and electric current in a material upon exposure to light. It is a physical and chemical phenomenon. The material absorbs light, and this causes the excitation of an electron or other charge carrier to a higher-energy state.
The electric potential (voltage) is produced by the separation of charges. For this to happen, the material must absorb enough light energy to overcome the potential barrier for excitation.
How solar cell systems generate electricity
1.) Light reaches the solar cell, and the solar cell absorbs photons from the light. (Solar cells are made from semiconducting materials.)
2.) Electrons are excited from their current orbital.
3.) The excited electron can either dissipate the energy as heat (and return to its old orbital) or travel through the solar cell to reach an electrode. Because of the travelling, current will flow through the material, and it is this current that is captured and turned into usable electricity. A solar cell typically contains two layers with different chemical electric charges, to drive and direct the current.
4.) The generated electricity is direct current (DC) electricity, but an inverter can be included in the setup to convert it to alternating current (AC).
What are solar cells made from?
Solar cells are made from semiconducting materials. Many different semiconducting materials will work, as long as they have the required capacity to absorb sunlight.
Some solar cells have just one layer of a light-absorbing material, and they are known as single-junction solar cells. If there are multiple layers, it is a multi-junctions solar cell. A multi-junction solar cell benefits from various absorption and charge separation mechanisms.
When it comes to materials, the first generation solar cells are made from crystalline silicon materials, such as polysilicon and monocrystalline silicon. They are also known as wafer-based solar cells.
The second generation of solar cells systems introduced the thin-film solar setup. Examples of commonly second-generation solar cells are amorphous silicon cells, cadmium telluride (CdTe) cells and copper indium gallium selenide (CIGS) solar cells.
The third generation of solar cell setups are also thin-film, but is working with other materials than the second generation. Many of them use organic materials, such as organometallic compounds. The third generation is still in the research stage and needs more improvements to become commercially viable.
Crystalline silicon solar cells
At the time of writing, a vast majority of the commercially available solar cell setups consists of crystalline silicon (c-Si) solar cells. They are of the ”wafer” type, typically made from wafers between 160 and 240 micrometers thick. Wafer solar cells can be made from both monocrystalline silicon (mono-Si) and polycrystalline silicon (multi-Si / poly-Si).
Crystalline silicon is the crystalline form of silicon, and it is a semiconducting material. Mono-Si is a continuous crystal, while poly-Si consists of many small crystals.
Amorphous silicon solar cells
Amorphous silicon (a-Si) solar cells are made from a non-crystalline form of silicon. Thin-film solar setups are often made from a-Si solar cells. The a-Si is deposited in thin films onto substrates such as plastic, metal or glass.
So far, a-Si solar cells have had a difficult time competing with the older crystalline solar cell setups on the commercial market for solar panels. A-si solar cells are also competing with other thin-film solutions, such as CdTe and CIGS thin-film setups.
Solar cells made from a-Si have lower electronic performance than c-Si solar cells, but are much more flexible when it comes to the application since a-Si solar cell setups can be made much thinner than c-Si.