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Science and Tech Spotlight: Alternative Materials for Solar Cells. Solar cell is a

Science and Tech Spotlight: Alternative Materials for Solar Cells. Solar cell is a

    Science and Tech Spotlight: Alternative Materials for Solar Cells

    This Spotlight examines evolving solar cell technology. Most electricity-generating solar cells are made with crystalline silicon in a process that is complex, expensive, and energy-intensive. Alternative materials may perform better and be easier and cheaper to make. Some absorb light 10-100 times more efficiently using thin films. In addition, these cells can be manufactured quickly and easily, reducing cost.

    Some alternative materials remain in the early stages of research and development but others are already in use. For example, cadmium telluride solar cells are produced commercially and cost about the same as crystalline silicon cells.

    Why This Matters

    US generation of electricity from solar energy could grow six-fold by 2050. Alternatives to commonly used crystalline silicon cells may reduce material usage, manufacturing capital expenditures, and lifecycle greenhouse gas emissions. Many of these new materials, however, are under development, and more research is needed to better understand their potential.

    The Technology

    What is it? Most solar cells (the components that generate electricity from sunlight) are currently produced with crystalline silicon in a process that is complex, expensive, and energy-intensive. Alternative materials—such as cadmium telluride, amorphous silicon, perovskites, and organic (carbon-containing) compounds—applied in thin layers of film may perform better and be easier and cheaper to manufacture.

    How does it work? As sunlight shines on a solar cell, some of the energy is absorbed to generate electricity either for immediate use or for storage in batteries (see fig. 1). The more readily a given solar cell absorbs light and transforms it into electricity, the higher its efficiency. The electric current generated by sunlight flows through wires that connect the front and back contacts of the solar cell.

    Figure 1. A simplified representation of how a solar cell generates an electric current.

    Some alternative materials absorb light 10 to 100 times more strongly than crystalline silicon, allowing them to produce electricity using less material. In turn, solar cells made with these materials are typically thinner and weigh less. In addition, these thin film solar cells can be manufactured quickly, reducing cost.

    How mature is it? The maturity of these alternative materials varies widely, with some currently used to manufacture solar cells and others in the early stages of research and development. For example, cadmium telluride cells and copper indium gallium diselinide cells together account for roughly 10 percent of current solar cells and they are already cost-competitive with crystalline silicon cells.

    Novel solar cells under development use a variety of materials. Among them is amorphous silicon, which is non-crystalline and can be deposited as a thin film. Perovskites are an emerging class of materials with rapidly increasing efficiencies. Organic materials offer yet another option for thin films. They consist of carbon-containing compounds, either long chains or molecules, tailored to absorb specific wavelengths of light. Researchers are also investigating the use of quantum dots—microscopic particles of compounds such as cadmium telluride, cadmium selenide, indium phosphide, or zinc selenide, that are able to produce electricity from light.

    Although these diverse materials differ in their chemical composition, they all fall under the category known as thin films because of the extremely thin layer—comparable in thickness to a red blood cell—in which they are applied (see fig. 2). In addition to being easy to produce and relatively inexpensive, these materials can be deposited on a variety of substrates, including flexible plastics in some cases.

    Figure 2. Current and potential alternative materials for solar cells are applied in extremely thin layers, with emerging materials being the thinnest.

    In addition to absorbing light, solar cells must convert it to electricity. While promising, commercial thin film solar cells currently average a conversion efficiency in the range of 12 to 15 percent, compared to 15 to 21 percent for crystalline silicon, according to a Massachusetts Institute of Technology (MIT) study. In addition, they require appropriate sealing materials to protect them from ambient oxygen and moisture. As a result, many alternative solar cell materials are currently under development or limited to specialized applications.

    Challenges

    Policy Context and Questions

    As alternative materials for solar cells continue to evolve and mature, some key questions that policymakers could consider include:

    • What steps could help encourage further development and use of alternative energy sources such as solar cell materials?
    • What analyses of incentives and barriers can determine whether government stimulus may be needed for private sector investment in solar cell materials and what are the trade-offs of such a stimulus?
    • What actions could help ensure sufficient understanding of the human health and environmental impacts of various solar cell materials across the full lifecycle?

    For more information, contact Karen Howard at 202-512-6888 or HowardK@gao.gov.

    Solar Cell – The Science Behind Solar Energy

    A solar cell also called a photovoltaic (PV) cell, is the basic building block of a solar power system. It is made of semiconductor materials, that convert sunlight into electricity. But how does this work? And what role does boron play in solar cells?

    Photovoltaic Technology

    Photovoltaics derives its name from the photovoltaic effect, which converts light (photons) to electricity (voltage). In 1954, Bell Laboratories scientists first utilized this effect and built a working silicon solar cell that produced an electric current when sunlight strikes. Solar cells were then used to power space satellites and small appliances like calculators and watches. Solar electricity is highly cost-competitive in many regions, and photovoltaics are being deployed on massive scales to supply the electricity system.

    The performance of a Photovoltaic cell is simply the amount of electrical power produced by the cell to the energy produced by the light shining on it, indicating the cell’s effectiveness in converting energy from one form to another. The amount of power generated from these photovoltaic cells is influenced by the characteristics of the available light (intensity and wavelengths) and the cell’s multiple performance attributes.

    The bandgap of PV semiconductors is an essential property of deciding the light wavelength a material can absorb and convert to electrical energy. If the semiconductor’s bandgap meets the light wavelength shining on the PV cell, the cell can effectively use all the available power.

    Types of Solar Cell

    Silicon Solar Cell

    Silicon is the most commonly used semiconductor material in solar cells. accounting for approximately 95 percent of panels sold to date. It’s the second most abundant element on the planet (after oxygen) and the most widely used semiconductor in computer chips.

    Crystalline silicon cells are built from silicon atoms linked together to form a crystal lattice. This lattice creates an organized structure that improves the efficiency of light-to-electricity conversion.

    Silicon solar cells currently offer high efficiency, low cost, and long lifetime. Devices are expected to last for 25 years or more while producing over 80% of their original power.

    Thin-film Solar Cell

    Thin-film solar cells are produced from a very thin layer of semiconductor material, such as cadmium telluride or copper indium gallium diselenide. The thickness of such cell layers is only a few micrometers or several millionths of a meter.

    These cells are flexible and lightweight, hence ideal for portable applications, as issued in a soldier’s backpack or in other products that generate electricity from the sun, such as Windows. Additionally, some types of thin-film solar cells benefit from advanced manufacturing activities that require low energy and are easier to expand.

    Organic Solar Cell

    Organic solar cells are made of carbon-rich (organic) compounds to improve a specific PV cell function, such as bandgap, transparency, or color. OPV cells are only about half as proficient as silicon solar cells and have shorter processing lifetimes, but they are cheaper to produce in large quantities. They can also be applied to flexible plastics or other supporting materials, allowing OPV to be used for many applications.

    Concentrated Solar Cell

    Concentrated photovoltaics (CPV) is a solar technology that uses lenses or mirrors to direct large amounts of sunlight onto small, highly efficient solar cells. Hence, they require less PV material to capture the same amount of sunlight. However, CPV systems are more expensive to produce and install, and they require special tracking devices to track the sun’s movement during the day. As a result, the CPV industry has found it difficult to demonstrate a cost advantage over conventional solar panels.

    How Solar Cells Work

    A solar cell typically consists of two layers of silicon, one p-type and one n-type. In the n-type layer, there is an excess of electrons, while in the p-type layer, there is an excess of positively charged holes.

    At the junction between the two layers, electrons from the n-type side flow into holes on the p-type side. This creates a depletion zone around the junction where electrons fill the holes.

    When all of the holes in the depletion zone are filled with electrons, the p-type side of the depletion zone now has negatively charged ions, and the n-type side has positively charged ions. The occurrence of these oppositely charged ions generates an internal electric field, which prevents electrons from the n-type layer from filling holes in the p-type layer.

    When sunlight falls on a solar cell, electrons are ejected, resulting in the formation of “holes”—the voids left by the escaping electrons. If this occurs in an electric field, the electrons will move to the n-type layer, and the holes will move to the p-type layer. After connecting the n-type and p-type layers with a metallic wire, electrons flow from the n-type to the p-type layer by passing the depletion zone and then go through the exterior wire back of the n-type layer, generating electricity flow.

    P-type silicon is created by atoms that have one less electron in their higher energy level than silicon, such as boron or gallium. As boron has one less electron required to form the bonds with the surrounding silicon atoms, a hole is formed. In comparison, n-type silicon is created by combining atoms with one extra electron at a higher energy level than silicon, such as phosphorus.

    Boron in Solar Cells

    Boron is used in solar cells as an antireflection coating. Antireflection coatings reduce losses from incident sunlight that does not pass through or mix during the manufacturing process. This allows for better electrical conductivity and increased efficiency.

    In recent years, boron’s potential for use in energy storage has also been explored. Solar energy is a renewable resource that can be used to generate electricity. However, the current methods for transferring solar energy from areas of high productivity to industrialized areas result in significant energy losses. Boron could potentially be used to reduce or eliminate these losses.

    Boron is a light element with a high affinity for electrons. This makes it ideal for use in electrical storage devices such as batteries. When used in this way, boron can improve the efficiency of solar energy systems by reducing or eliminating the need for power lines and other infrastructure which results in energy losses. Additionally, boron is non-toxic and abundant in the Earth’s crust, making it a safe and sustainable option for energy storage.

    Solar cell – the technology behind solar panels

    Solar energy is predicted to become the most significant contributor to the world’s energy resources and a crucial step in the zero-emission plan. Forecasts are showing solar power as the most important energy source for global electricity production in 2030. In this article, we’ll look at how photovoltaic solar cells are made. Let us examine the technology behind a solar panel that allows power generation.

    Solar cells. the physical phenomenon in power generation

    Photovoltaic cells are unique power generators. The biggest difference between solar panels and batteries or fuel cells is that they don’t require any chemical reactions or fuel to produce or store electric energy – only sunlight. The other significant distinction is that, unlike electric generators, solar cells do not have any moving parts.

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    A solar cell, also called a photovoltaic cell, is an electronic device that converts the light into electrical energy through a photovoltaic effect. It is a physical phenomenon, but we can split it into three basic steps to understand how sunlight is converted into usable electricity by solar cells in solar panels.

    Three general processes in a solar photovoltaic (PV) cell:

    • Light absorption generates carriers (knocked-out loose electrons)
    • Carriers flow, creating power
    • Energy is captured and transferred to wires

    Each photovoltaic circuit consists of two silicon semiconductors: one positively charged (p-type), the other negatively charged (n-type). The smallest unit of the light – photon is always absorbed by an n-type semiconductor. It generates the movement of higher-energy electrons from the solar cell into an external circuit. The electrons then dissipate their energy in the external circuit and return to the solar cell.

    Silicon solar cell may be called a p-n junction diode, although its construction is quite different from conventional p-n junction diodes. They’re a form of a photovoltaic PV cell, defined as a device with electrical characteristics – such as current, voltage, or resistance. Solar cells’ abilities and efficiency vary when in contact with light.

    Solar cells are the fundamental part of solar panels

    Individual solar cells can be combined to form modules commonly referred to as solar cell panels or simply solar panels. Homeowners install them on their rooftops to replace, augment, or increase their conventional electricity supply efficiency. The standard single-junction photovoltaic cell can generate a maximum open-circuit voltage of about 0.5 to 0.6 volts. It may not seem as much power – but these solar cells are extremely tiny and efficient. When thousands of silicon solar cells are combined into a conventional solar panel, significant amounts of renewable energy can be generated.

    Solar Panels can also be arranged into extensive groupings – arrays. Arrays are significantly bigger than regular solar panels used on family households. These arrangements, composed of hundreds of thousands of individual photovoltaic cells, play the central electric power station’s role, converting the sunlight into electrical energy used for industrial, commercial, or residential purposes.

    HOW ARE SOLAR CELLS MADE?

    The photovoltaic effect demands a material in which the absorption of light raises an electron to a higher energy state. A vast number of different materials and processes can meet the requirements for photovoltaic energy conversion. Still, almost all photovoltaic energy conversion uses semiconductor materials in the structure of a p-n junction.

    MODELS OF SOLAR MODULES BASED ON SILICON CELLS TYPE:

    • Monocrystalline Solar Panels ( Mono – SI)
    • Polycrystalline Solar Panels (p-Si)
    • Thin-Film Solar Panels; Amorphous Silicon (A-SI)
    • Concentrated Photovoltaic Cell (CVP)

    The majority of solar cells are manufactured from silicon, which is an excellent semiconductor. With different requirements and financial capacities, materials range from amorphous (noncrystalline) through polycrystalline to crystalline (single crystal) silicon forms.

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    Monocrystalline Solar Panels are premium solar products. The main advantages of these panels are higher efficiencies, durability, and high aesthetics value. To make solar cells, single-crystal silicon is shaped into strips and cut into wafers. Because the cell is formed of a single crystal, the electrons have more place to flow. As a result, monocrystalline panels have very high efficiency (~20%), but they’re the most expensive to buy.

    Polycrystalline solar panels are one of the cheaper options for solar power enthusiasts. Moderate cost is their great advantage, but they have significantly lower efficiencies (~15%) and slightly shorter durability than monocrystalline options. Polycrystalline solar cell panels are also made from many fragments of silicon melted together to form the wafers. Due to their multi-crystalline construction of every silicon solar cell, there is less freedom for the electrons to move, which results in lower efficiency.

    Thin-Film, Amorphous Panels are the cheapest and easiest to produce but with the lowest efficiency (~7-10%) and durability. Film thickness fluctuates between a few nanometers to tens of micrometers, making them significantly thinner than competing technologies based on first-generation crystalline silicon solar cells (Mono-SI, p-Si, c-Si). This allows the thin-film photovoltaic cell to be extremely flexible and light. Thanks to that, they are often used as building-integrated photovoltaics like semi-transparent material laminated onto Windows.

    A concentrated PV Cell is an advanced device that uses lenses or curved mirrors to concentrate sunlight onto a surface of a highly efficient, multi-junction (MJ) solar cell. It is the most efficient technology (~40%) and the most cost-consuming at the first stage of the project. This device needs a dedicated cooling system due to the high heat produced while focusing light on the top layer of the solar cell.

    From solar cell to electricity

    Solar cells produce direct current (DC) that cannot be used in any electrical network powered by the alternating current (AC). It needs to go through another process of transformation in an inverter. It is a device designed to transform direct current into alternating current. The most popular energy inverters are entirely electronic, but there are also types with mechanical effects (rotary apparatus) and electronic circuitry.

    Solar inverters are used for grid-connected and off-grid systems. They address the particular needs of solar energy by having dedicated functions like maximum power point tracking and anti-islanding protection. Solar micro-inverters diverge even more from traditional inverters, as an individual micro-inverter is connected to each solar panel. This can boost the overall performance of the system. The output from several micro-inverters is later combined. In other arrangements, a common inverter may be combined with a battery bank controlled by a solar charge management system. This blend of elements is often called a solar generator.

    Then AC goes to the distribution box at home, where electricity is distributed to the end devices. If there are not enough receivers inside the circuit, the electricity travels to the shared power grid, passing through the meter. The meters in houses with photovoltaic systems are bidirectional, in normal houses they are unidirectional (they only record the power consumption).

    What is a solar panel principle?

    The main goal behind Solar power systems is delivering clean, renewable energy from the sun. Introducing solar panels to your household helps combat greenhouse gas emissions and reduces our common dependence on fossil fuels.

    Silicon solar cells are often used to generate electricity in many distant physical locations all over the world where traditional electric power sources are either unavailable or prohibitively expensive to use.

    Due to the lack of moving parts, no fuel demand, and low maintenance needs, photovoltaic cells provide power for most space installations like satellites or Astro stations (Sun is inaccessible for universe probes conducted in the outer planets of the solar system or into interstellar space).

    Solar cells have also been used over the years in consumer products (electronic toys, handheld calculators, portable radios, etc.) Solar cells used in such devices may utilize artificial light as well as sunlight.

    Solar Cells: A Guide to Theory and Measurement

    A solar cell is a device that converts light into electricity via the ‘photovoltaic effect’. They are also commonly called ‘photovoltaic cells’ after this phenomenon, and also to differentiate them from solar thermal devices. The photovoltaic effect is a process that occurs in some semiconducting materials, such as silicon. At the most basic level, the semiconductor absorbs a photon, exciting an electron which can then be extracted into an electrical circuit by built-in and applied electric fields.

    Due to the increased desire for more renewable sources of energy in recent years, solar power has seen increasing popularity. In 2012, the total global energy usage was approximately 559 EJ (exajoules, x10 18 ). Meanwhile, the total annual solar energy that falls upon the Earth’s landmasses is estimated to be 1,575. 49,837 EJ. Clearly, the Sun provides more than enough energy to satisfy global energy needs. Therefore, there is arguably a much greater potential for solar to fulfil our energy requirements than other renewable sources.

    General Theory

    The main component of a solar cell is the semiconductor, as this is the part that converts light into electricity. Semiconductors can carry out this conversion due to the structure of their electron energy levels. Electron energy levels are generally categorised into two bands: the ‘valence Band’ and the ‘conduction Band’. The valence Band contains the highest occupied electron energy levels, whilst the conduction Band contains the lowest unoccupied electron energy levels. The energy difference between the top of the valence Band and bottom of the conduction Band is known as the ‘Band gap’ (Eg). In a conductor, there is no Band gap as the valence Band is not filled completely. thus allowing the free movement of electrons through the material. Insulators have very large Band gaps which require copious amounts of energy to cross. and as such, inhibits the movement of electrons from the valence Band to the conduction Band. Conversely, the Band gap in semiconductors is relatively small, enabling some electrons to move to the conduction Band by injecting small amounts of energy.

    This small Band gap is what enables some semiconductors to generate electricity using light. If a photon incident on the semiconductor has energy (Eγ) greater than the Band gap, it will be absorbed. enabling an electron to transfer from the valence Band into the conduction Band. This process is known as ‘excitation’. With the electron now in the conduction Band, an unoccupied state is left in the valence Band. This is known as a ‘hole’, and behaves like a particle analogous to an electron in the conduction Band (albeit with positive charge). Due to their opposite charge, the excited electron and hole are coulombically bound in a state known as an ‘exciton’. This exciton must be split (also known as ‘dissociation’) before the charge carriers can be collected and used. The energy required to do this is dependent on the dielectric constant (εr) of the material. This describes the level of screening between charges in a semiconducting material and affects the binding energy of the exciton.

    In materials with high εr, excitons have low binding energies. enabling dissociation to occur thermally at ambient temperatures. Excitons in materials with low εr have high binding energies, preventing thermal dissociation. thus requiring a different method of dissociation. A common method is to get the exciton to an interface between materials with energy levels that have an offset greater than the exciton’s binding energy. This enables the electron (or hole) to transfer to the other material, and dissociate the exciton.

    Once dissociated, the free charges diffuse to the electrodes of the cell (where they are collected). this is assisted by built-in and applied electric fields. The built-in electric field of a device arises from the relative energy levels of the materials that make up the cell. However, the origin of the built-in field depends on the type of semiconductor being used. For inorganic semiconductors such as silicon, other materials are often added to the semiconductor (a process known as doping) to create regions of high (n-type) and low (p-type) electron density. When these regions are in contact, charges will build up on either side of the interface, creating an electric field directing from the n-type to the p-type region. In devices using organic semiconductors, the built-in field arises from the difference between the work functions of the electrodes of the device.

    The size of the Band gap is also very important, as this affects the energy that can be harvested by the solar cell. If Eγ Eg, then the photon will be absorbed, and any energy in excess of Eg will be used to promote the electron to an energy level above the conduction Band minimum. The electron will then relax down to the conduction Band minimum, resulting in the loss of the excess energy. However, if Eγ Eg, then the photon will not be absorbed, again resulting in lost energy. (Note, the wavelength of a photon decreases as its energy increases).

    When considering the solar spectrum, it can therefore be seen that a too large Eg will result in a significant number of photons not being absorbed. On the other hand, a too low Eg means that a large number of photons will be absorbed, but a significant amount of energy will be lost due to the relaxation of electrons to the conduction Band minimum. Due to this trade-off, it is possible to calculate the theoretical maximum efficiency of a standard photovoltaic device, as well as estimate the optimum Band gap for a photovoltaic material. Shockley and Queisser determined the theoretic maximum efficiency to be approximately 33% in 1961, which corresponds to a Band gap of 1.34 eV (~930 nm).

    Characterisation

    Solar Spectrum

    The characterisation of a solar cell determines how well it performs under solar illumination. The solar spectrum is approximately that of a black body with a temperature of 5780 K. This peaks in the visible range and has a long infra-red tail. However, this spectrum is not used for characterisation as the light must pass through the Earth’s atmosphere (which absorbs a significant portion of the solar radiation) to reach the surface. Instead, the industry standard is AM1.5G (air mass 1.5 global), the average global solar spectrum after passing through 1.5 atmospheres. This has a power density of 100 mW.cm.2 and is equivalent to average solar irradiation at mid-latitudes (such as in Europe or the USA). To ensure reliability and control during testing of solar cells, a solar simulator can be used to generate consistent radiation.

    Solar Cell IV Curves

    The key characteristic of a solar cell is its ability to convert light into electricity. This is known as the power conversion efficiency (PCE) and is the ratio of incident light power to output electrical power. To determine the PCE, and other useful metrics, current-voltage (IV) measurements are performed. A series of voltages are applied to the solar cell while it is under illumination. The output current is measured at each voltage step, resulting in the characteristic ‘IV curve’ seen in many research papers. An example of this can be seen below in the figure below, along with some important properties that can be determined from the IV measurement. It should be noted that generally, current density (J) is used instead of current when characterising solar cells, as the area of the cell will have an effect on the magnitude of the output current (the larger the cell, the more current).

    Solar Cell I-V Test System

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    • Fast and Accurate
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    The properties highlighted in the figure are:

    • JMP. Current density at maximum power
    • VMP. Voltage at maximum power
    • PMax. The maximum output power (also known as maximum power point)
    • Jsc. Short-circuit current density
    • Voc. Open-circuit voltage

    The PCE can be calculated using the following equation:

    Here, Pout (Pin) is the output (input) power of the cell, FF is the fill factor, and Jsc and Voc are the short-circuit current density and open-circuit voltage respectively.

    The short-circuit current density is the photogenerated current density of the cell when there is no applied bias. In this case, only the built-in electric field within the cell is used to drive charge carriers to the electrodes. This metric is affected by:

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    • Absorption characteristics of the photoactive layer
    • Charge generation, transport, and extraction efficiency

    The open-circuit voltage is the voltage at which the applied electric field cancels out the built-in electric field. This removes all driving force for the charge carriers, resulting in zero photocurrent generation. This metric is affected by:

    • Energy levels of the photoactive materials
    • Work functions of the electrode materials
    • Charge carrier recombination rate

    The fill factor is the ratio of the actual power of the cell to what its power would be if there were no series resistance and infinite shunt resistance. This is ideally as close as possible to 1, and can be calculated using the following equation:

    Here, JMP and VMP are the current density and voltage of the cell at maximum power respectively.

    Approximate values of the series and shunt resistances can be calculated from the inverse of the gradient of a cell’s JV curve at the Voc and Jsc respectively.

    A solar cell is a diode, and therefore the electrical behaviour of an ideal device can be modelled using the Shockley diode equation:

    Here, Jph is the photogenerated current density, JD is the diode current density, J0 is the dark saturation current density (current density flowing through the diode under reverse bias in the dark), V is the voltage, and T is the temperature. The final 2 symbols, e and kB, are the elementary charge (1.6 x 10.19 C) and the Boltzmann constant (1.38 x 10.23 m 2.kg.s.2.K.1 ) respectively. However, in reality, no device is ideal and so the equation must be modified to account for potential losses that may arise:

    Here, n is the diode ideality factor and all other symbols have their previous meanings. Using this equation, a solar cell can be modelled using an equivalent circuit diagram, which is shown below:

    The series resistance (Rs) accounts for resistances that arise from energetic barriers at interfaces and bulk resistances within layers. Ideally, this is minimised to prevent efficiency losses due to increased charge carrier recombination. This can be achieved by ensuring good energy level alignment of the materials used in the solar cell.

    The shunt resistance (Rsh) accounts for the existence of alternate current pathways through a photovoltaic cell. Unlike the series resistance, this is ideally as high as possible to prevent current leakage through these alternate paths.

    Solar Cell I-V Test System

    • Fast and Accurate
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    Types of Solar Cells

    There are several types of solar cells, which are typically categorised into three generations. The first generation (known as conventional devices) are based upon crystalline silicon, a well-studied inorganic semiconductor. The second generation are the thin-film devices, which includes materials that can create efficient devices with thin films (nanometre to tens of micrometres range). The third generation are the emerging photovoltaics. technologies which are still undergoing research to reach commercialisation.

    The first and second generations contain the most-studied photovoltaic materials: silicon, gallium arsenide, cadmium telluride, and copper indium gallium selenide. These materials are all inorganic semiconductors, and generally work in the most direct manner: a photon is absorbed. creating an exciton, which is thermally dissociated (inorganic semiconductors typically have high dielectric constants) and subsequently transported to the electrodes via an electric field.

    First Generation

    As silicon is the most-studied material, it can achieve some of the highest performances (with a peak efficiency of 26.1%) and was the first material to reach the commercial market. As such, the majority of solar panels use silicon as the photoactive material. The Band gap of silicon is 1.1 eV, enabling broad absorption of solar radiation. However, this is lower than the optimum Band gap (1.34 eV), resulting in energy losses when absorbing high energy photons. In addition, the Band gap is indirect. reducing the absorption efficiency and thus requiring relatively thick layers to efficiently harvest sunlight. As with all inorganic materials, silicon has a high dielectric constant of 11.7. allowing for the thermal separation of charge-carriers after generation.

    Gallium Arsenide

    Gallium arsenide (GaAs) boasts the highest performance of any photovoltaic material, reaching 29.1%. This is because GaAs has a direct and more favourable Band gap of 1.43 eV. resulting in improved absorption with thinner layers and reduced energy loss. Additionally, GaAs has superior electron-transport properties to silicon. However, it is very expensive to produce as it requires high material purity, which generally limits it to space-based applications (such as satellites and rovers).

    Cadmium Telluride

    Cadmium telluride (CdTe) is a high-efficiency thin-film photovoltaic technology which has achieved an efficiency of 22.1%. CdTe has a similar Band gap to GaAs at 1.44 eV, giving it the same advantages as seen in GaAs. good absorption in thin films and low photon energy losses. This material also boasts the possibility to be flexible, very low costs, and it has produced commercial solar panels that are cheaper than silicon with much shorter energy payback times (although with lower efficiency). Despite these advantages, there are some issues. cadmium is highly toxic and tellurium is very rare, making the long-term viability of this technology uncertain for now.

    Copper Indium Gallium Selenide

    Copper indium gallium selenide (CIGS) has achieved similar performances to CdTe devices, with a peak of 23.4%. The compound has the chemical formula CuInxGa(1-x)Se2 where x can take a value between 0 and 1. This tunability of the chemical structure enables the Band gap of the material to be varied between 1.0 eV (x = 1, pure copper indium selenide) and 1.7 eV (x = 0, pure copper gallium selenide). However, like GaAs cells, CIGS are expensive to fabricate and result in solar panels that cannot compete with the current commercial technologies. Furthermore, like tellurium, indium is very rare, limiting the long-term potential of this technology.

    Third Generation

    The third generation of photovoltaics. also known as the emerging photovoltaic technologies. includes dye-sensitised, organic, and perovskite solar cells.

    Dye-Sensitised

    Dye-sensitised solar cells (DSSCs) use organic dyes to absorb light. These dyes are coated onto an oxide scaffold (typically titanium oxide) which are immersed in a liquid electrolyte. The dyes absorb the light, and the excited electron is transferred to the oxide scaffold, whilst the hole is transferred to the electrolyte. The charge carriers can then be collected at the electrodes. These cells are less efficient than inorganic devices, but have the potential to be much cheaper, produced via roll-to-roll printing, semi-flexible, and semi-transparent. However, issues still exist with use of a liquid electrolyte due to temperature stability (as it can potentially freeze or expand), the use of expensive materials, and volatile organic compounds.

    Organic

    Organic solar cells (OSCs) use organic semiconducting polymers or small molecules as the photoactive materials. To date, efficiencies of 18.2% have been achieved by this technology. These cells work similarly to inorganic devices. However, organic semiconductors generally have low dielectric constants, meaning that the generated exciton cannot be thermally dissociated. Instead, the exciton must be transported to an interface with a material that has an energy level offset greater than the binding energy of the photon. Here, the electron (or hole) can transfer to the other material and split the exciton, allowing the charge carriers to be collected (as shown earlier in the general theory section). As excitons can typically only diffuse approximately 10 nm before the electron and hole recombine, this limits the thickness, structure, and ultimately. the performance of an organic photovoltaic cell. Despite this, these devices hold some significant advantages over inorganic devices, including: low cost of materials, lightweight, strong and tuneable absorption characteristics, flexibility, and the potential to be fabricated using roll-to-roll printing techniques. Currently, organic materials suffer from stability issues arising from photochemical degradation.

    Perovskite

    Perovskite solar cells (PSCs) use perovskite materials (materials with the crystal structure ABX3) as their light-absorbing layer. Perovskites were introduced to the field relatively recently, with the first use in a photovoltaic device reported in 2006 (where it was the dye in a DSSC achieving 2.2%). However, 2012 is considered the birth of the field, due to the publication of a landmark paper in which an efficiency of 10.9% was achieved. Since then the peak efficiency has risen to 25.5%, making PSCs the fastest-improving solar technology. These materials have remarkable properties, including strong tuneable absorption characteristics and ambipolar charge transport. They can also be processed from solution in ambient conditions.

    There are still issues with stability and the use of toxic materials (such as lead) preventing the technology from being commercialised, but the field is still relatively young and very active. For more detailed information about perovskites, see our perovskite guide.

    The table below shows the best research cell efficiencies for a variety of photovoltaic technologies (values courtesy of the National Renewable Energy Laboratory, Golden, CO).

    Solar Cell Type Highest Efficiency (Last updated 19/02/2021)
    Monocrystalline silicon (mono-Si) 26.1%
    Polycrystalline silicon (multi-Si) 23.3%
    Amorphous silicon (a-Si) 14.0%
    Monocrystalline gallium arsenide (GaAs) 29.1%
    Cadmium telluride (CdTe) 22.1%
    Copper indium gallium selenide (CIGS) 23.4%
    Dye-sensitised (DSSC) 13.0%
    Organic (OSC) 18.2%
    Perovskite (PSC) 25.5%

    What Is A Solar Panel?

    A Solar panels (also known as PV panels) is a device that converts light from the sun, which is composed of particles of energy called photons, into electricity that can be used to power electrical loads.

    Solar panels can be used for a wide variety of applications including remote power systems for cabins, telecommunications equipment, remote sensing, and of course for the production of electricity by residential and commercial solar electric systems.

    On this page, we will discuss the history, technology, and benefits of solar panels. We will learn how solar panels work, how they are made, how they create electricity, and where you can buy solar panels.

    A Short History of Solar Panels

    The development of solar energy goes back more than 100 years. In the early days, solar energy was used primarily for the production of steam which could then be used to drive machinery. But it wasn’t until the discovery of the photovoltaic effect by Edmond Becquerel that would allow the conversion of sunlight solar electric energy. Becquerel’s discovery then led to the invention in 1893 by Charles Fritts of the first genuine solar cell which was formed by coating sheets of selenium with a thin layer of gold. And from this humble beginning would arise the device we know today as the solar panel.

    Russel Ohl, an American inventor on the payroll of Bell Laboratories, patented the world’s first silicon solar cell in 1941. Ohl’s invention led to the production of the first solar panel in 1954 by the same company. Solar panels found their first mainstream use in space satellites. For most people, the first solar panel in their life was probably embedded in their new calculator. circa the 1970s!

    Today, solar panels and complete solar panel systems are used to power a wide variety of applications. Yes, solar panels in the form of solar cells are still being used in calculators. However, they are also being used to provide solar power to entire homes and commercial buildings, such as Google’s headquarters in California.

    How Do Solar Panels Work?

    Solar panels collect clean renewable energy in the form of sunlight and convert that light into electricity which can then be used to provide power for electrical loads. Solar panels are comprised of several individual solar cells which are themselves composed of layers of silicon, phosphorous (which provides the negative charge), and boron (which provides the positive charge). Solar panels absorb the photons and in doing so initiate an electric current. The resulting energy generated from photons striking the surface of the solar panel allows electrons to be knocked out of their atomic orbits and released into the electric field generated by the solar cells which then pull these free electrons into a directional current. This entire process is known as the Photovoltaic Effect. An average home has more than enough roof area for the necessary number of solar panels to produce enough solar electricrity to supply all of its power needs excess electricity generated goes onto the main power grid, paying off in electricity use at night.

    In a well-balanced grid-connected configuration, a solar array generates power during the day that is then used in the home at night. Net metering programs allow solar generator owners to get paid if their system produces more power than what is needed in the home. In off-grid solar applications, a battery bank, charge controller, and in most cases, an inverter are necessary components. The solar array sends direct current (DC) electricity through the charge controller to the battery bank. The power is then drawn from the battery bank to the inverter, which converts the DC current into alternating current (AC) that can be used for non-DC appliances. Assisted by an inverter, solar panel arrays can be sized to meet the most demanding electrical load requirements. The AC current can be used to power loads in homes or commercial buildings, recreational vehicles and boats, remote cabins, cottages, or homes, remote traffic controls, telecommunications equipment, oil and gas flow monitoring, RTU, SCADA, and much more.

    The Benefits of Solar Panels

    Using solar panels is a very practical way to produce electricity for many applications. The obvious would have to be off-grid living. Living off-grid means living in a location that is not serviced by the main electric utility grid. Remote homes and cabins benefit nicely from solar power systems. No longer is it necessary to pay huge fees for the installation of electric utility poles and cabling from the nearest main grid access point. A solar electric system is potentially less expensive and can provide power for upwards of three decades if properly maintained.

    Besides the fact that solar panels make it possible to live off-grid, perhaps the greatest benefit that you would enjoy from the use of solar power is that it is both a clean and a renewable source of energy. With the advent of global climate change, it has become more important that we do whatever we can to reduce the pressure on our atmosphere from the emission of greenhouse gases. Solar panels have no moving parts and require little maintenance. They are ruggedly built and last for decades when porperly maintained.

    Last, but not least, of the benefits of solar panels and solar power is that, once a system has paid for its initial installation costs, the electricity it produces for the remainder of the system’s lifespan, which could be as much as 15-20 years depending on the quality of the system, is absolutely free! For grid-tie solar power system owners, the benefits begin from the moment the system comes online, potentially eliminating monthy electric bills or, and this is the best part, actually earning the system’s owner additional income from the electric company. How? If you use less power than your solar electric system produces, that excess power can be sold, sometimes at a premium, to your electric utility company!

    There are many other applications and benefits of using solar panels to generate your electricity needs. too many to list here. But as you browse our website, you’ll gain a good general knowledge of just how versatile and convenient solar power can be.

    How Much Do Solar Panels Cost?

    for solar panels has decreased substantially in the last couple of years. This is great because, combined with the 30 federal solar Investment Tax Credit and other applicable incentives, NOW is the best time ever to invest in a solar power system. And, consider this: a solar power system costs about the same as a mid-sized car!

    Where can I buy solar panels?

    Well, right here on this website, of course!

    Our solar panel brands include the most respected manufacturers in the solar panel business. These brands include such names as BP Solar, General Electric, and Sharp, among others. We feature only the highest quality solar panels from manufacturers with a proven track record in solar panel technology. With over 30 years in the solar panel business, you can be sure that at MrSolar.com, we know solar panels!

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