At a time when ecological transition is at the heart of global development challenges, photovoltaic energy is attracting a lot of interest. The use of solar panels is becoming more widespread, but the functioning of the photovoltaic cell is not yet obvious to everyone.

A component at the origin of the photoelectric phenomenon, the photovoltaic cell makes it possible to convert the sun's rays into electricity.

It fits perfectly into the French energy mix promoted by the public authorities. Between a definitional concept, different types, operating principle and perspectives, SirEnergies invites you to discover how a photovoltaic cell works.

What is a solar cell?

The photovoltaic cell is a “mini-power plant” made of several materials whose synergy makes it possible to convert light energy into electricity. Joining different layers of semiconducting materials together like a sandwich forms what we call a junction.

As soon as a photon crosses the junction, it deposits its energy there and triggers an electron transfer from the n zone (negative) to the p zone (positive) of the photovoltaic cell. All that remains is to connect each of the faces of the device to a conducting wire and we get electric current.

Each semiconductor material used, and more precisely the properties of the latter, determines the lifespan of the photovoltaic cell. The photovoltaic panel, candidate for the coveted position of energy of the future, must therefore consist of: durable, resistant and very ecological materials. A question then arises: why silicon in photovoltaics?

Silicon is omnipresent in electronics because of its semiconductor properties. There are two main reasons why it is used in the manufacture of photovoltaic cells. First, it facilitates the circulation of electron—hole pairs that are essential for the production of electricity.

Then, it is possible to substantially modify its chemical composition in order to optimize its electrical properties. The researchers in fact “doped” this material with atoms of a different nature.

What are the different types of photovoltaic cells?

If the photovoltaic cell crystallizes so much attention, it is above all for the numerous possibilities it offers. In this respect, we distinguish three major families whose returns are constantly evolving!

Crystalline silicon cells

Silicon cells represent more than 95% of the photovoltaic cell market, because silicon is present in abundance in the sands. The average efficiency of this type of component is also between 16.5 and 22% depending on the technology used for its manufacture.

In contrast to monocrystalline cells, silicon is composed of several crystals when it is obtained with a cold treatment. It is easy to produce. It can also be reconstituted into a large crystal when it is melted. We then obtain a monocrystalline material whose efficiency approaches 26.6% in the laboratory.

Thin Film Photovoltaic Cells

The classical approach, which consists in cutting silicon into thin wafers of about 200 microns in size, is being neglected by a group of researchers. It is now possible to place semiconductor materials with a thickness of a few microns on a substrate such as plastic or glass.

There is really no limit to the fields of possibilities. Cadmium and CIGS (copper/indium/gallium/selenium) have already been tested in the laboratory and the results are far from disappointing. They are even close to the figures obtained with silicon, i.e. respective results of 22.1 and 23.3% for these materials.

The discovery we are sharing with you does not spell the death knell for silicon, quite the opposite. It can be used in thin layers in its non-crystallized form. We also find this technology in calculators, but its efficiency is lower.

Organic cells

With organic cells, we are leaving the sphere of mineral semiconductors to explore another path: that of molecules. These components are based on The polymers of organic chemistry, but they are just beginning to have applications in photovoltaic modules.

The energy efficiency of organic cells is still low and their long-term stability is approximate. However, they could have a very low production cost, which is promising for the future.

Several production techniques are explored in the context of Photovoltaic cells. One of the main paths is that of photosensitive pigment cells whose functioning is inspired by plant photosynthesis. Their name? The dye cells!

How does a solar cell produce electrical current?

To understand how a photovoltaic cell works, we need to go back to some physics concepts.

What is the operating principle of a photovoltaic sensor?

Photovoltaic cells use what we call the “photoelectric effect” to produce electrical current by absorbing solar radiation. Each cell placed on a photovoltaic panel continuously converts the light energy of the photons into electricity. The medium that facilitates this process by transporting electrical charges is none other than the semiconductor material.

Here we must take a break to discuss one of the aspects mentioned above: the doping of silicon crystals, especially with multijunction cells. Each atom of this mineral is composed of four peripheral electrons. The cell has two layers:

• The first layer is boosted with phosphorus atoms (five peripheral electrons). The phosphorus atom has one more electron than the phosphorus atom. Doping is therefore of type n, because it results in an excess of negative charges on this face.
• The second layer of the cell is boosted with Boron atoms whose periphery contains three electrons. It is p-type doping. Boron has one electron less than silicon, so the result is an excess of positive charge.

The photoelectric phenomenon

The photovoltaic effect is the name given to the phenomenon by which photovoltaic cells produce electricity. It sheds light on the reaction of silicon to The energy of the sun across the two layers of the cell.

Once the two sides are in contact, the excess electrons from material n pass to material p and the magic happens. The photons that pass through the solar cell strip electrons from the atoms in both layers. Now free of the p-layer, they move in all directions, take a circuit and return to the n-layer. Electricity is nothing but the result of this movement.

The photoelectric phenomenon occurs when The sun's rays hit the surface of a solar panel. From this situation arises a detachment of electrons which, oriented by the plates of each photovoltaic cell, move from one point to another: this is the birth of direct current! The inverter in the panel then transforms the direct current into alternating current to power your devices.

The efficiency of a photovoltaic cell

The efficiency is simply the ratio between the electrical power obtained and the light power that affects the photovoltaic cell. To determine this quantity, each cell in the panel is calibrated using a solar simulator. The conditions of the test? An ambient temperature of 25°C and a sun of 1,000 W of light for each square meter!

The electrical power produced or peak power is a fraction of the solar power received. It is expressed as a percentage. As an illustration, take the case of a 1 m² photovoltaic panel that produces a power of 200 W. Its efficiency is 20% and cannot exceed 33% according to the “Shockley-Queisser limit”.

What is the future for solar energy?

The future ofsolar energy depends on its own advantages and disadvantages. So we are going to look at the issues of this green energy to determine if it is the energy of tomorrow.

The benefits of solar energy

On a human scale, solar energy is inexhaustible and available for free. Its advantages are:

• The overabundance of silicon, a non-toxic material,
• A lifespan of solar panels ranging from 20 to more than 30 years,
• The great modularity of photovoltaic panels.

The production of electricity thanks to photovoltaic installations is also not polluting during the operating phase. Les panels are also recyclable and can be used for small-scale domestic purposes.

The limits of photovoltaic technology

Solar energy faces financial limitations. The technology is still very expensive despite the sharp decline in recent years. Conventional solar panels are also fragile, heavy and difficult to install.

The energy and environmental impact of solar energy is not zero. It takes approximately between 1 and 1.5 years for a photovoltaic cell to compensate for the energy required to manufacture it. Finally, the electricity produced is not immediately storable. Indirect storage technologies (batteries, kinetic accumulators, etc.) are very expensive.

Towards a promising future

It's hard to imagine the future without solar energy. Recognizing the challenges surrounding this energy, the photovoltaic industry is hard at work to develop techniques that are less expensive and less demanding in terms of resources. Concentrated solar energy, tape deposition, organic materials and thin film panels are some of the most promising approaches.

The photovoltaic cell operates on the basis of the photoelectric phenomenon and the difference in polarity between the layers of the component. While much progress is expected in this sector, what about Hydrogen And of The fuel cell ?

To go further, do not hesitate to consult our article on The history of solar energy.

Did you know that?

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We have made the choice to work with key players in solar photovoltaic to offer you support solutions dedicated to your photovoltaic self-consumption projects.
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