What Is A Solar Cell Used To Convert To?

What is a Solar Cell?

A solar cell, also known as a photovoltaic cell, is a device that converts sunlight into electricity using the photovoltaic effect. The photovoltaic effect refers to the generation of voltage and electric current in a material upon exposure to light.

The main components of a basic solar cell are two semiconductor layers – a negative layer and a positive layer. The most common semiconductor material used is silicon. When sunlight hits the solar cell, photons from the sunlight get absorbed by the semiconducting material, causing electrons to break free from their atomic bonds. This generates electron-hole pairs – electrons in the negative layer and corresponding holes in the positive layer. The built-in electric field of the solar cell separates the electrons and holes, creating an electric current between the positive and negative semiconductor layers.

The electron flow generated by solar cells produces direct current electricity from sunlight, without any mechanical/thermal generator or chemical reactions. Solar cells have unique electrical properties and are not like an ordinary diode, although they share some common operational principles. They can generate electricity even in low light conditions.

Solar cells are the fundamental building blocks of photovoltaic modules, otherwise known as solar panels. Multiple solar cells interconnected together make up a solar photovoltaic module. Modules are then connected to form large solar arrays that can convert sunlight into electricity on a large scale.

History of Solar Cells

The history of solar cells dates back over a century. In 1839, French physicist Edmond Becquerel first discovered the photovoltaic effect while experimenting with an electrolytic cell. He found that certain materials would produce small amounts of electric current when exposed to light.

In 1883, American inventor Charles Fritts created the first true solar cell by coating selenium with an extremely thin layer of gold. This primitive solar cell had less than 1% efficiency in converting sunlight to electricity.

In the early 20th century, Albert Einstein helped explain the photoelectric effect, which formed a foundation for later solar cell development. In 1954, researchers at Bell Laboratories in the United States created the first modern silicon solar cell with 6% efficiency.

Throughout the 1960s and 70s, space programs drove advances in solar photovoltaic technology. Cells aboard spacecraft had to be lightweight yet powerful. In the 1980s and 90s, solar power expanded to terrestrial applications like powering homes, appliances and communication devices.

Today, solar cell technology continues advancing as researchers explore cheaper materials, higher efficiencies, flexible applications and integrated manufacturing techniques resulting in dramatic cost reductions.

How Solar Cells Convert Sunlight

Solar cells convert sunlight into electricity through the photovoltaic effect. When photons from sunlight hit the solar cell, they transfer their energy to the semiconductor material in the cell, causing electrons to break free from their atoms. These free electrons then flow through the material to produce an electric current.

The basic structure of a solar cell consists of two layers of semiconductor material, one negatively charged (N-type) and one positively charged (P-type). These two layers form a junction where the electric field forms. When a photon enters the cell, it frees an electron in the N-type layer. This electron then flows from the N-type layer to the P-type layer through an external circuit, generating electricity. The electric field at the junction separates the electrons and holes, forcing the electrons to travel in one direction, creating flow of current.

Silicon is the most common material used in solar cells. It has properties that make it efficient at converting sunlight into electricity. Other semiconductor materials like gallium arsenide and cadmium telluride are also used. The materials absorb sunlight and generate electricity differently, so solar cell designs utilize different materials to maximize efficiency.

In summary, solar cells rely on the photovoltaic effect to convert sunlight into electric current. Photons free electrons in the cell’s semiconductor material, and the junction separates charges and sustains flow of electrons in one direction to generate electricity.

Solar Cell Materials

The most common material used in solar cells is silicon. Crystalline silicon solar cells are made from silicon wafers sliced from ingots of purified crystalline silicon. Polycrystalline silicon, also known as multicrystalline silicon, contains crystal grains of varying sizes and amorphous silicon has no crystalline structure. Thin-film solar cells use little or no silicon. They are made by depositing one or more thin layers of photovoltaic material, like cadmium telluride or copper indium gallium selenide, onto glass, plastic or metal. Organic photovoltaics use carbon-rich polymers and are flexible, lightweight and can be transparent. Quantum dot solar cells contain tiny semiconductor particles only a few nanometers in size embedded in an organic polymer or film. Perovskite solar cells are an emerging technology that use a perovskite structured compound, often a hybrid organic-inorganic lead or tin halide-based material, as the semiconductor.

Solar Cell Efficiency

Solar cell efficiency refers to the portion of energy in sunlight that is converted into electricity. There are two main measures of solar cell efficiency:

Record lab efficiencies – These are solar cells tested in a lab under ideal conditions. The highest confirmed lab efficiency is 47.1% for a multi-junction concentrated photovoltaic cell developed by Solar Junction. This type of solar cell uses optics to concentrate sunlight onto the cell and layer different semiconductor materials to absorb different wavelengths of light.

Commercial module efficiencies – When solar cells are manufactured into panels and modules for real-world use, their average efficiency is around 15-20%. The most efficient commercial silicon solar panel is the SunPower Maxeon 3 with an efficiency of 22.8%. Thin-film solar panels are generally around 15% efficient.

There are several factors that affect the efficiency of a solar cell:

Semiconductor materials – Different materials have different ability to absorb sunlight.
Band gap energy – This determines what portion of solar spectrum a material can absorb.
Reflection – Reflected sunlight doesn’t get absorbed, so anti-reflective coatings help.

Recombination – This is when absorbed photon energy gets lost before being harnessed.
Resistance – Electrical resistance reduces voltage and power output.

Increasing solar cell efficiency is a major area of research, as higher efficiencies reduce the overall costs of solar power. Companies and labs continue to make incremental improvements in commercial solar panel efficiencies each year.

Solar Cell Manufacturing

The manufacturing process for solar cells has evolved significantly over the past few decades to enable high volume production and drive down costs. There are a few main steps involved in manufacturing crystalline silicon solar cells, which make up over 90% of the solar cell market.

The process starts with the production of polysilicon, an ultrapure form of silicon used as the starting material. Polysilicon production is an energy-intensive process involving the chemical refining of metallurgical-grade silicon. Improvements in manufacturing techniques have led to a drastic reduction in polysilicon prices in recent years.

Ingots of polysilicon are then grown into cylindrical blocks or cast into square molds. These ingots are sliced into thin wafers using wire saws or other cutting techniques. The size of ingots and wafers has increased over time, which reduces slicing losses and material waste.

The silicon wafers then undergo surface texturing and cleaning treatments before the critical doping process that creates the p-n junction to enable sunlight conversion. Phosphorus and boron are commonly used dopants. Advanced doping techniques like selective emitter can improve solar cell efficiency.

An anti-reflective coating is added to the surface to maximize light absorption into the cell. Contacts are screened onto the front and back of the cell to collect the electrical current. The wafers are interconnected and laminated between protective sheets to create a weatherproof module.

Automation, optimized manufacturing workflows, and economies of scale have enabled manufacturers to significantly cut production costs. However, further innovations in materials, processes and manufacturing approaches will be needed to maintain the downward price trajectory.

Applications of Solar Cells

Solar cells have a wide variety of applications and uses. Some of the main categories of solar cell applications include:

Off-Grid Applications

Off-grid solar refers to solar systems not connected to the utility grid. Off-grid solar cells provide electricity in remote areas where extending power lines is challenging. Common off-grid applications include:

Solar home systems in rural areas of developing countries

Off-grid tiny homes or cabins
Solar-powered street lights
Solar panels to power road signs and call boxes

Offshore oil rigs and ocean buoys
Recreational vehicles

Residential Applications

Rooftop solar panels on homes are one of the most common uses of solar cells. Residential systems can be grid-tied to supply surplus power to the grid, or off-grid. Typical residential applications include:

Rooftop solar arrays on single-family homes
Community solar programs
Solar carports and rooftops on apartment buildings

Solar-powered pumps for residential pools

Commercial Applications

Businesses are installing large solar panel systems to reduce electricity costs. Some commercial uses include:

Solar parking lot canopies over corporate campuses

Rooftop solar on warehouses and factories
Ground-mount solar farms on unused commercial land
Solar window shading on office towers

Utility-Scale Applications

Solar farms with hundreds of thousands of panels generate solar electricity at scale. Utility solar projects include:

Large solar farms that feed into the grid
Solar plants combined with energy storage

Floating solar arrays on ponds and reservoirs
Community solar projects

Solar Cell Advantages

Solar cells offer a number of clear benefits that make them an appealing renewable energy technology.

First and foremost, solar energy is renewable. Solar cells capture energy from the sun, which is a practically infinite resource. As long as the sun continues to shine, solar cells can produce electricity. This sets solar power apart from fossil fuels like oil, coal, and natural gas, which are finite resources.

Second, solar electricity production emits no greenhouse gases or air pollutants. Fossil fuel power plants produce carbon dioxide and other emissions that contribute to climate change and pollution. Solar cells generate clean, emission-free electricity.

Finally, the cost of solar power has decreased dramatically in recent years. The average price of solar panels has dropped over 70% in the last decade, driven by improvements in manufacturing and installation. As prices continue to fall, solar power is increasingly competitive with fossil fuel electricity. Many experts expect grid parity in the next few years.

With renewable, clean energy and rapidly decreasing costs, solar cells offer an appealing path to meeting the world’s electricity needs in a sustainable way.

Solar Cell Challenges

While solar cell technology shows great promise, some challenges remain before it can fully replace conventional energy sources. Here are some of the main issues facing solar power adoption:

Intermittency

One of the biggest challenges with solar power is its intermittent nature. Solar cells only produce energy when the sun is shining, meaning they do not generate power at night or on cloudy days. This makes solar unreliable as a consistent, around-the-clock energy source unless some form of energy storage is used.

Storage

The intermittent output of solar power means some form of energy storage is needed to provide power when the sun isn’t shining. However, current energy storage solutions are limited in capacity and add to the complexity and cost of solar power systems. More research is needed into large-scale energy storage options before solar can reach its full potential.

Space Requirements

To collect a meaningful amount of solar energy requires a significant amount of physical space for the panels. This can be a challenge in densely populated areas where sufficient empty roof or land space is not available. While solar farms can be built on open land, transmission infrastructure is needed to transport the power from remote solar sites to cities and towns.

Future of Solar Cell Technology

Solar cell technology is continuously advancing as researchers aim to improve efficiency and lower costs. Some key areas of future development include:

Emerging Materials

New materials like perovskites and organic polymers are being explored as lower-cost, high-efficiency alternatives to traditional silicon solar cells. Perovskites in particular have achieved rapid efficiency gains in the lab, although durability challenges remain before widespread commercial adoption.

Higher Efficiencies

Incremental efficiency gains in monocrystalline silicon cells continue, with laboratory cell efficiencies now approaching 29%. Commercial module efficiencies lag behind at around 20%, but are also increasing steadily. Novel cell designs like tandem cells can potentially push efficiencies even higher.

New Applications

Flexible, lightweight solar cells are enabling new applications like building-integrated photovoltaics, solar clothing, and devices charging. Advances in printable solar cells could lead to solar surfaces like windows and paints. Solar cars and solar drones are using cells to extend runtimes. Innovative product integration is expanding solar capabilities.

With continued research, solar cells hold exciting potential to power our lives in new ways with abundant clean energy from the sun.