What Is An Example Of A Photovoltaic Cell?

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What is a Photovoltaic Cell?

A photovoltaic cell, also known as a solar cell, is a device that converts sunlight into electricity. Photovoltaic cells are made of semiconductor materials, most commonly silicon. When sunlight hits the cell, the energy from the photons of light excites the electrons in the semiconductor material, causing them to flow and generate an electric current.

The photovoltaic effect was first observed in 1839 by French physicist Edmond Becquerel. However, it took over a century before the first photovoltaic module was built. Today, photovoltaic cells are used to produce electricity in homes, businesses, vehicles, satellites, and more.

At the heart of a photovoltaic cell is the semiconductor material, which is treated to form an electric field. Silicon is used in over 90% of photovoltaic cells, while other materials like cadmium telluride and copper indium gallium selenide are also used. When a photon hits the cell, its energy frees up an electron from an atom in the semiconductor. The electric field provides directionality for the electron to flow through the material to the conductive metal contacts on the front and back of the cell. This flow of electrons is used to power an external load.

In this way, the photovoltaic cell directly converts sunlight into direct current electricity. Arrays of photovoltaic cells are combined together and converted into alternating current to feed into the electricity grid. Photovoltaic systems provide clean renewable energy from an abundant resource, the sun.

History of Photovoltaic Cells

The first photovoltaic cell was created in 1883 by Charles Fritts, who coated selenium with a thin layer of gold to form the junctions. While this primitive cell only had about 1% efficiency, it demonstrated the photovoltaic effect that produces electricity from light.

In the early 20th century, Albert Einstein helped explain the photoelectric effect, which provided a foundation for photovoltaic technology. The first silicon solar cell was created in 1954 at Bell Labs by Daryl Chapin, Calvin Fuller, and Gerald Pearson. This cell had around 6% efficiency.

Through the space race in the 1950s and 1960s, photovoltaic technology advanced rapidly to power satellites. In the 1970s and 1980s, photovoltaics began to gain traction for commercial and residential applications as manufacturing costs declined.

Major improvements in solar cell efficiency were made in the 1990s and 2000s through advanced materials and nanotechnology. Today, the most advanced multi-junction solar cells can achieve over 46% efficiency in lab conditions.

As technology continues to progress, solar power is becoming increasingly cost-competitive with fossil fuels, driving strong growth in PV installations worldwide.

How Do Photovoltaic Cells Work?

Photovoltaic cells use the photoelectric effect to convert light into electricity. When photons from sunlight hit the surface of a PV cell, they transfer their energy to the electrons in the atoms of the semiconductor material, causing the electrons to break free from their atomic bonds. This generates pairs of free electrons and corresponding “holes” where electrons used to be. The built-in electric field of the PV cell, created by the junction of the n-type and p-type semiconductor layers, provides directionality for the electrons and holes. It causes them to flow in opposite directions within the cell, generating an electrical current.

The current generated by a single PV cell is small, so cells are connected together in series and parallel configurations to produce higher currents and voltages. PV modules consist of many cells electrically connected and enclosed together in a frame, while PV arrays consist of multiple modules combined to generate significant amounts of electricity.

When sunlight shines on a PV cell, the absorbed photons cause electrons in the cell to break free of their atomic bonds, generating current. The PV cell’s built-in electric field provides directionality for the current, enabling it to flow through an external circuit to do work. PV cells are assembled into modules and arrays to produce electricity on a scale useful for powering homes, businesses, and more.

Types of Photovoltaic Cells

There are a few main types of materials used in photovoltaic cells:

Monocrystalline Silicon

Monocrystalline silicon is made from pure crystalline silicon and has a uniform crystal structure. This type of PV cell is the most efficient, with average efficiency around 15-20%, but also the most expensive to produce.

Polycrystalline Silicon

Polycrystalline silicon, also known as multicrystalline silicon, is made from melted silicon that is recrystallized. The random crystal structure results in lower efficiency than monocrystalline, around 13-16%, but it is less expensive to produce.

Amorphous Silicon

Amorphous silicon has no crystal structure and is deposited in thin films onto surfaces. This makes it inexpensive to produce but it has an efficiency of only 5-7%.

Organic Photovoltaic Cells

Organic PV cells use organic electronics made of thin films of organic semiconductors like polymers and small molecules. These are lightweight and flexible but have low efficiency around 5-7%.

Other Emerging Materials

Some other materials like cadmium telluride, copper indium gallium selenide, and perovskites are being used in different combinations and structures to improve efficiency and lower costs.

Photovoltaic Cell Efficiency

Photovoltaic cell efficiency refers to the percentage of solar energy that is converted into electricity by the cell. This is a key determinant of the cost and performance of PV systems.

Typical efficiencies of mainstream PV technologies include:

Monocrystalline silicon solar cells: 15-20%
Polycrystalline silicon solar cells: 13-16%
Thin-film solar cells: 7-13%

Emerging technologies like perovskites: over 20% in lab tests

There are several factors that impact the conversion efficiency of a PV cell:

Semiconductor materials – Different materials have different abilities to absorb sunlight and convert it into electricity.

Cell design and architecture – Factors like surface texturing, back surface fields, anti-reflection coatings improve light absorption.
Quality of semiconductor crystal structure – Defects and impurities reduce efficiency.
Operating temperature – Higher temperatures cause efficiency to drop.

Through advances in materials science and manufacturing, researchers continue to break records for solar cell efficiency in lab settings. But commercially available PV modules still lag behind these lab prototypes. Continued improvements in commercial cell efficiency remain key to reducing solar electricity costs.

Cost of Photovoltaic Cells

Photovoltaic system costs have declined dramatically over the past several years due to technology improvements, manufacturing scale and streamlining, and global competition. As of 2021, a typical residential system cost approximately $3 per watt, or $15,000 for an average 5-kW system before federal tax credits. For utility-scale systems, costs average $1 per watt or lower, an over 70% drop from 2010 costs.

Over the past decade, residential PV system costs have fallen by more than 60%, from over $8 per watt in 2010 to under $3 per watt today. This rapid price decrease has been driven by economies of scale, technology improvements, and global market dynamics. In particular, the dramatic expansion of Chinese PV panel manufacturing and supply-chain efficiencies have led to major cost reductions.

The most significant factor impacting PV system costs is the module and panel prices, which make up over one-third of total costs. Non-hardware “soft costs” such as installation labor, permitting, supply chain costs and installer margins account for over half of residential and commercial project expenses. As PV adoption continues to climb globally, further cost reductions in both hardware and soft costs are expected.

Applications of Photovoltaic Cells

Photovoltaic cells have become incredibly important in renewable energy production and reducing reliance on fossil fuels. The most common application is in solar panels, which convert sunlight directly into electricity. Solar panels can be small, such as for powering watches and calculators, or large arrays covering acres of land to feed into the electrical grid. Other solar-powered devices like outdoor lighting, water pumps, communications equipment and road signs also utilize photovoltaic cells.

Photovoltaic energy offers many advantages over traditional power sources. Solar power is clean, silent and renewable, without any air or water pollution. It can also provide electricity to remote locations without access to an electrical grid. Arrays can be designed to track the sun and maximize energy production throughout the day. With battery storage, solar energy can provide electricity around-the-clock, even when the sun isn’t shining. As photovoltaic technology continues to improve in efficiency and decrease in cost, it promises to play an integral role in powering our future in a sustainable way.

Future of Photovoltaic Cell Technology

The future looks bright for improvements in photovoltaic cell technology that will increase efficiency and lower costs. Researchers are exploring new materials and designs that could dramatically improve performance.

Perovskites are emerging as a promising new material that can absorb light more efficiently than traditional silicon cells. Perovskite cells have seen rapid increases in efficiency over the past decade, from 3% to over 25% in lab settings. With further development, perovskites may reach 30% efficiency at a fraction of the cost of silicon. This could make solar power cheaper than fossil fuels.

New solar cell designs are also being pursued, like multi-junction cells that absorb different wavelengths of light at different layers of the cell. Concentrated PV systems use lenses to focus sunlight on small high-efficiency solar cells. Integrating PV materials into building facades and windows could greatly expand adoption.

The Department of Energy has set cost and performance targets for 2030, including reducing installed system costs by 50% and improving cell efficiency by 50%. With sustained R&D and manufacturing improvements, solar is projected to become the dominant source of new electricity generation. Widespread adoption of solar power will require advances in energy storage, grid management, and business models – but the future is looking bright.

Environmental Impact

Photovoltaic cells can have a very positive environmental impact when implemented on a large scale. By generating electricity from sunlight rather than fossil fuels, photovoltaics can significantly reduce carbon emissions and pollution.

One key environmental consideration is the manufacturing process of photovoltaic panels. There are some emissions associated with producing the silicon, metal framing, wiring and other components. However, the manufacturing emissions are far lower than the amount of emissions offset over the 20-30 year lifespan of a solar panel. Furthermore, many solar manufacturers are working to reduce emissions through renewable energy use and material efficiency.

Recycling of solar panels at end-of-life is also an important sustainability consideration. Most parts of a solar panel can be recycled, including the aluminum, glass, silver and silicon. Proper recycling can recover these valuable materials for reuse while preventing toxic components like lead from reaching landfills. Some regions and manufacturers now provide free solar panel recycling to encourage sustainable practices.

Overall, the environmental benefits of generating clean electricity from the sun far outweigh the impacts associated with manufacturing and recycling. With smart solar panel design and responsible recycling programs, photovoltaics can play a key role in reducing humanity’s carbon footprint and building a sustainable future.

Example Photovoltaic Cell

A common example of a photovoltaic cell is a silicon solar cell used in solar panels. This type of photovoltaic cell is made from silicon wafers that have been doped with other elements to form a p-n junction. Here are some specifications for a typical monocrystalline silicon solar cell:

Silicon material: Monocrystalline
P-type silicon doped with boron
N-type silicon doped with phosphorus

Dimensions: 156 mm x 156 mm
Thickness: 0.2 mm
Efficiency: 15-20%

This type of silicon solar cell has a distinctive rectangular shape with rounded corners and a blue anti-reflective coating on the top surface. Wires are attached to the front and back of the cell to extract the current. When sunlight hits the cell, photons excite electrons in the silicon to generate electricity.