Solar cell - Know it all !

Photovoltaic cell
Photovoltaic cell

Solar cell

A photovoltaic cell, also known as a solar cell, represents a major breakthrough in the field of renewable energy production.

This ingenious technology exploits the photovoltaic effect, a physical phenomenon where solar photons hit the surface of a semiconductor, resulting in the release of electrons and the generation of an exploitable electric current.
Photovoltaic effect
Photovoltaic effect

The photovoltaic effect

The photovoltaic effect is a fundamental phenomenon of physics that is the basis of the functioning of photovoltaic cells. It occurs when light, in the form of photons, hits the surface of a semiconductor material, such as the silicon used in solar cells. When photons interact with the material, they transfer their energy to the electrons in the semiconductor structure.

The energy of the photons excites the electrons, which frees them from their atomic orbits. These released electrons then acquire kinetic energy and move through the material. It is this movement of electrons that generates an electric current. However, in their excited state, electrons tend to recombine with holes (the gaps left by missing electrons) in the material, which could cancel out the photovoltaic effect.

To avoid this unwanted recombination, photovoltaic cells are designed to create a PN junction. In a typical solar cell, the top layer of the semiconductor material is doped with atoms that have excess electrons (n-type), while the bottom layer is doped with atoms with excess holes (p-type). This configuration creates an electric field that directs the released electrons to the n-type layer and the holes to the p-type layer.

As a result, the electrons released by the photovoltaic effect are collected on the n-type surface of the photovoltaic cell, while the holes are collected on the p-type surface. This separation of charges creates an electrical potential between the two layers, thus generating a constant electric current when sunlight hits the cell. This current can then be used as a source of electricity to power electrical appliances or be stored in batteries for later use. In their excited state in the conduction band, these electrons are free to move through the material, and it is this movement of the electron that creates an electric current in the cell.

Types of cells Photovoltaic

Monocrystalline silicon cell
Monocrystalline silicon cell

Monocrystalline silicon cells :

These cells are made from a single silicon crystal, which gives them a uniform structure and high efficiency.
The unique crystal orientation allows for better capture of solar photons, resulting in high efficiency.
However, the manufacturing process is more complex, resulting in higher production costs.
Polycrystalline silicon cell
Polycrystalline silicon cell

Polycrystalline silicon cells :

Made from silicon blocks comprising multiple crystals, these cells are easier and cheaper to produce than monocrystallines.
The boundaries between crystals may slightly reduce efficiency, but technical advances have improved their performance over time.
They offer a good balance between cost, efficiency and sustainability.

Thin Film Cells :

These cells are made by depositing a thin layer of semiconductor material directly onto a substrate, such as glass or metal.
They are lighter and more flexible than silicon cells, allowing them to be integrated into various applications, such as soft solar roofs.
The efficiency is generally lower than that of silicon cells, but technological advances are aimed at improving their efficiency.

Heterojunction Cells (HIT) :

These cells combine different layers of semiconductor materials, creating a heterojunction interface.
The interface promotes efficient charge separation and reduces losses due to electron and hole recombination.
HIT cells have good yields and better performance at high temperatures.
Perovskite cell
Perovskite cell

Perovskite cells :

Perovskite-based cells are relatively new and have attracted great interest due to their ease of manufacture and high efficiency potential.
Perovskite materials can be deposited from liquid solutions, opening the door to less expensive manufacturing processes.
However, long-term sustainability and stability under various conditions remain challenges. Most commercial PV cells are single-junction, but multi-junction PV cells have also been developed to achieve higher efficiencies at a higher cost.


Crystalline silicon :

Monocrystalline : Made from a single silicon crystal, these cells offer high efficiency due to their homogeneous structure. However, their manufacturing process is complex and expensive.
Polycrystalline : Made from several silicon crystals, these cells are more affordable to produce than monocrystallines. However, their effectiveness is slightly lower due to the boundaries between the crystals.

Thin film cells :

Cadmium Telluride (CdTe) : These cells use cadmium telluride as a semiconductor material. They are affordable to produce and are often used in large-scale applications. However, cadmium is toxic, which raises environmental concerns.
Copper Indium Gallium Selenide (CIGS) : These cells are composed of layers of copper, indium, gallium and selenium. They offer high efficiency and can be manufactured on flexible surfaces, making them suitable for certain special applications.

Organic semiconductor cells :

These cells use organic polymers or carbon-based materials to convert light into electricity. They are usually lightweight and flexible, but their effectiveness is often lower than that of other cell types.

Perovskite cells :

Perovskite cells are relatively new but are attracting great interest due to their high efficiency potential and potentially reduced production cost. They use a crystalline material called perovskite to capture light.

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