Solar Cell
A solar cell, also known as a photovoltaic cell, is a device that converts sunlight into electricity. The concept of harnessing solar energy dates back to 1839 when French scientist Edmond Becquerel discovered the photovoltaic effect, although the first practical solar cell was developed in 1954 by researchers at Bell Labs. These devices have since evolved, with applications ranging from small electronics like calculators to large-scale power plants. The most common type of solar cell is made from silicon, which requires the introduction of impurities to enhance its conductive properties through P-type and N-type doping.
Solar cells generate electricity by creating an electrical field at the junction of these two silicon types, enabling the movement of free electrons when exposed to sunlight. While solar energy is abundant and pollution-free, challenges include space requirements for solar farms, manufacturing pollution, and the intermittent nature of sunlight. Innovations are ongoing, such as the advancement of perovskite solar cells, which offer lower costs and comparable efficiency. A recent breakthrough in 2024 has produced a lightweight material with high power conversion efficiency, potentially facilitating broader adoption of solar technology without extensive infrastructure. Overall, solar cells represent a crucial component of the shift toward sustainable energy solutions.
Solar Cell
A solar cell, or photovoltaic cell, is a device capable of converting energy from the Sun into electricity. Humans have relied on the Sun's rays for light and warmth since the beginning of time, but the first solar cell capable of harnessing the Sun's energy to produce electricity was not introduced until 1954. Since then, scientists and researchers have continued to create better, more efficient solar cells to power everything from calculators and watches to spacecraft and power plants.
Background
French scientist Edmond Becquerel discovered the photovoltaic effect in 1839. During his experiments, Becquerel noticed that certain materials produced an electrical voltage when exposed to light. Other scientists, such as Willoughby Smith, Charles Fritts, and Albert Einstein, built on his ideas over time. The biggest breakthrough, however, occurred in 1954 when three scientists at Bell Labs—Daryl Chapin, Calvin Fuller, and Gerald Pearson—developed the first silicon photovoltaic cell.
Silicon, by itself, is not a great conductor of electricity. A silicon atom has fourteen electrons in three electron shells. An electron shell is the path, or orbit, that electrons follow around an atom's nucleus. In a silicon atom, the first shell, closest to the nucleus, contains two electrons and is completely full. The second shell contains eight electrons and is completely full. The third, and outermost, shell contains four electrons and is only half full. To fill its outer shell, a silicon atom will share electrons with another nearby silicon atom, thereby forming a bond. As a result, pure silicon has no free electrons to move about, making it a poor conductor of electricity. Adding energy to silicon from an outside source, such as heat, can cause a few electrons to break free and move around. Called free carriers, these electrons create an electrical current, but it is too weak to generate a significant amount of electricity.
Fuller, Pearson, and Chapin discovered that adding certain impurities—that is, atoms of other materials—to silicon can cause it to become positively charged (P-type) or negatively charged (N-type). P-type silicon is missing electrons, while N-type silicon has extra electrons. A solar cell contains both types. The point where the two types of silicon meet is called the P-N junction. Adding energy—in the form of light from the Sun—knocks loose spare electrons from the N-type silicon. These free carriers try to move to the P-type silicon to fill the gaps where electrons are missing. The P-type silicon then becomes negatively charged, and the N-type silicon becomes positively charged. As a result, an electrical field forms. This field controls the movement of electrons within the solar cell, which creates an electric current capable of powering a device.
Overview
Not long after the Bell scientists' breakthrough in 1954, photovoltaic cells began to be used to power satellites in Earth's orbit. In 1958, for example, the Vanguard I satellite was launched into space carrying a small array of solar cells to power its radios. Subsequent satellites launched that year also had systems powered by photovoltaic technology. Indeed, silicon solar cells have played a significant role in space applications since their inception; they are like little power plants, turning sunlight into electricity hundreds of miles above Earth. Even today, space agencies around the world depend on solar cells to power satellites, spacecraft, and the International Space Station (ISS).
On Earth, solar cells may be used to power everything from calculators and wristwatches to entire photovoltaic power plants. The Agua Caliente Solar Project outside Yuma, Arizona, is one of the largest photovoltaic power plants in the world. The plant covers 2,400 acres and comprises 5.2 million ground-mounted solar modules, which convert enough energy from the Sun to produce electricity for about 100,000 homes. The plant uses no water to generate electricity, makes no noise, and releases no emissions into the air. Estimates suggest that the amount of carbon dioxide displaced by the Agua Caliente Solar Project is equivalent to taking 40,000 cars off the road each year.
Rising greenhouse gas emissions and dwindling fossil fuel resources have led to increased interest in more sustainable energy resources, including solar. Solar energy's benefits are numerous. Since solar energy comes from the Sun, it is available all over the world. Unlike fossil fuel supplies, the supply of solar energy is inexhaustible. While power plants that burn fossil fuels to produce electricity release greenhouse gases into the air, solar cells do not cause pollution as they harness energy from the Sun. Additionally, solar cells require very little maintenance.
Despite its many advantages, solar energy does have some drawbacks. For example, a power plant like Agua Caliente occupies a massive amount of space. The processes involved in the manufacture of solar cells contribute to pollution. Sunlight is available only at certain times of day. In addition, although technologies exist to store energy produced by solar systems for future use (such as at night, when sunlight is unavailable), these technologies can be quite expensive. Thus, using solar cells to harness the Sun's energy is more expensive than burning fossil fuels.
Nevertheless, scientists continue to research ways to make solar energy more efficient and less expensive. Manufacturing solar cells from cheaper materials is one way to accomplish this goal. Most solar cells on the market are composed of silicon, and their levels of efficiency vary considerably. Solar cells made from the purest silicon available are quite costly, and they have a maximum efficiency of about 25 percent—that means they are able to convert about 25 percent of the Sun's energy into electricity. In 2009, a team of scientists from Japan introduced a new type of solar cell made from a material called perovskite. Like silicon solar cells, perovskite (PV) solar cells are able to turn energy from sunlight into electricity. However, PV solar cells are both less expensive and easier to manufacture than traditional silicon solar cells. Moreover, by 2022, scientists had managed to improve the efficiency of PV solar cells from 4 percent to slightly more than 25 percent—about equal to silicon solar cells. However, PV solar cells lacked durability, especially when exposed for a long time to moisture, heat, light, applied voltage, and other typical conditions, failing within a few months. Thus, PV was not commercially competitive.
In 2024, scientists at the Oxford University Physics Department made a substantial breakthrough in solar cell creation. They create a power-generating material that is thin and light enough to apply to everyday objects. In testing, this material showed 27 percent power conversion efficiency, a significant improvement over traditional solar cells. Scientists hope that the commercialization of this material might speed the adoption of solar power without the need for the construction of large-scale solar farms.
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