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s you may recall from your science class, all materials are divided into conductors, semiconductors, and insulators. Insulators don’t conduct electricity, whereas conductors allow electric energy to easily flow through them. Semiconductors can conduct electric current better than insulators, but not as well as conductors. While electrons move randomly in conductors, semiconductors only let them flow under certain conditions, which makes it possible to use them in solar cells to create a photovoltaic effect.

Structure of silicon solar cells

Each photovoltaic cell – a building unit of a solar panel – resembles a sandwich. A photovoltaic cell is usually made of two layers of silicon, namely an n-type top layer, and a p-type bottom layer. The n-type silicon solar cell layer is doped with an element containing an extra valence electron (for example, arsenic) and the p-type layer is doped with an element having one fewer valence electron (for example, gallium).

Once sunlight hits the solar cell, these electrons start being pushed from the top to the bottom layer across a slight barrier. As a result, the top layer gets positively charged (due to a deficit of electrons), the bottom layer gets negatively charged (due to a surplus of electrons), and an electric field is formed in the region of their juncture that pulls the electrons back to the top.

Strengths and weaknesses of silicon solar cells

Photovoltaic cells are generally made of silicon, the world’s most often utilized semiconductor. Basically, silicon solar cells represent approximately 90% of solar cells manufactured today.

Silicon is the eighth most widespread element in the universe and the second most abundant element in the Earth's crust after oxygen. Nowadays, it is used to control the flow of electrons in a wide variety of electronic devices. If you grab a handful of sand from the beach, by mass 47% of what you hold in your hand is silicon. In fact, desert sand is the main source for its commercial production.

Although silicon panels have been remaining the most common photovoltaic panels since the 1950s, they have quite a low efficiency of 15-20%. This means that silicon solar cells can convert just 15-20% of the sunlight hitting their surface into electricity – still the highest reported efficiency among other semiconductor materials. Besides, silicon solar cells are expensive to produce because lots of energy is needed to purify the raw material. But the prices for silicon solar panels are steadily falling, which is why the solar power market has grown over the years, and this tendency can be extended in the future.

What is more, this element has a very low environmental impact as a non-toxic material that also possesses good resistance to corrosion, which makes silicon solar cells durable in adverse conditions like high temperatures and corrosive saltwater. High photoconductivity (the increase in electrical conductivity of a material when exposed to adequate energy light) is one more important aspect to mention. Last but not least, photovoltaic modules based on crystalline silicon solar cells have a long life of about 25-30 years.

Types of silicon solar cells

Monocrystalline solar cells

As the name itself implies, monocrystalline silicon solar cells are made from a single silicon crystal grown into a cylindrical shape called an ingot and then sliced into thin wafers. Monocrystalline silicon solar panels have earned the title of the most efficient silicon panels with an efficiency rating between 17% to 22%. Due to the fact that such solar cells are constituted of a single crystal, electrons have more space to move and generate a better electricity flow. Monocrystalline silicon solar cells have a distinctive black color and sleek design. Usually, a monocrystalline panel contains either 60 or 72 PV cells, depending on the size of the solar panel.

Polycrystalline solar cells

Polycrystalline silicon solar cells, as opposed to monocrystalline cells, are made up of several crystals of silicon. These silicon panels are composed of square cells of shimmery blue color. Polycrystalline silicon solar panels are not as efficient and aesthetically pleasing as their monocrystalline counterparts, but they are more affordable because they are easier to produce, and more eco-friendly because of less waste during the manufacturing process. Polycrystalline silicon solar cells have lower heat tolerance than monocrystalline silicon solar cells and perform slightly worse in high temperatures. Polycrystalline silicon panels used for residential homes usually contain 60 solar cells.

Amorphous solar cells

Amorphous, literally meaning ‘shapeless’, silicon solar cells are made from a non-crystalline layer that is overlaid upon a thin substrate ranging from glass to flexible foils. They are the most well-developed thin-film solar cells. Thin-film silicon panels are cheaper to manufacture, but their downside is lower efficiency. Advantageously, amorphous silicon solar panels are more flexible and lightweight, which makes the transportation and installation of the panels less risky. In most cases, a  flexible thin-film module is also suitable even for curved surfaces.

Are there any alternatives to silicon solar cells?

Perovskite photovoltaics

Perovskite photovoltaic cells are a relatively new thin-film type of solar cell that uses the mineral perovskite as the semiconductor in their structure. Perovskite photovoltaic cell efficiencies have improved faster than any other photovoltaic material, from 3% in 2009 to over 25% in 2020. Perovskites are considered to be a promising photovoltaic cell technology, which yet faces some challenges. Perovskite cells are quite unstable, and some of them contain lead which is a toxic material. However, newer tin-based perovskite options could be the key to this problem.

Quantum dots

Quantum dot photovoltaic cells conduct electricity through tiny particles of different semiconductor materials just a few nanometers wide called quantum dots. Quantum dot cells show considerable durability and good efficiency, but they are highly toxic in nature.

Organic photovoltaics

Organic photovoltaic cells are thin-film photovoltaic cells that use organic (carbon-reach) semiconducting materials. Organic photovoltaics is currently only about half as efficient as crystalline silicon solar cells and has shorter operating lifetimes, but could be cheaper to manufacture in high volumes.

Key takeaways

Silicon solar cells form the overwhelming majority of the photovoltaic market.

Silicon solar panels are quite expensive and only around 20% efficient but still stay ahead of all the other PV technologies in terms of cost-effectiveness.

Silicon panels are not the only possible photovoltaic modules, but their alternatives are still in the early stages of development.

Posted 
May 10, 2023
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