A solar cell is the fundamental unit that converts sunlight into electricity. Every solar panel you see on a rooftop or in a solar farm is made up of dozens of individual solar cells wired together. Understanding how they work helps you make sense of why different panel types perform differently and why some cost more than others.
This guide covers how solar cells work, the main types available today, what affects their efficiency, and how they translate into the panels used in residential and commercial solar installations.
Contents
How Solar Cells Work
Solar cells work through a process called the photovoltaic effect, discovered by French physicist Edmond Becquerel in 1839. When photons from sunlight strike a semiconductor material (almost always silicon), they knock electrons loose from their atoms. These free electrons flow through the material as direct current (DC) electricity. An inverter then converts that DC electricity to the alternating current (AC) that your home uses.
Silicon is used because it has just the right atomic structure to absorb photons and release electrons efficiently. Most solar cells are made from two layers of silicon treated differently to create an electric field: the N-type layer (with extra electrons) and the P-type layer (with electron “holes”). The junction between these layers is where the photovoltaic magic happens. When photons hit the cell, they push electrons across that junction, creating a flow of current.
A single silicon solar cell typically produces about 0.5 to 0.6 volts of electricity. That’s not much on its own. Manufacturers connect cells in series and parallel to build up voltage and current to useful levels. A standard residential solar panel contains 60 to 72 individual cells and produces 300 to 450 watts of power under ideal conditions.
Types of Solar Cells
Monocrystalline Silicon
Monocrystalline cells are made from a single continuous crystal of silicon, grown using the Czochralski process. The silicon ingot is sliced into thin wafers, treated to create the P-N junction, and fitted with electrical contacts. You can recognize monocrystalline panels by their uniform dark color and rounded cell corners (a byproduct of cutting circular ingots into square cells).
Monocrystalline cells are the most efficient type widely available for residential use, typically achieving 20% to 23% efficiency in mass-market panels. Some premium monocrystalline cells using advanced designs like PERC (Passivated Emitter and Rear Cell) or TOPCon (Tunnel Oxide Passivated Contact) reach 22% to 24%.
Polycrystalline Silicon
Polycrystalline cells are made by melting silicon and pouring it into square molds, which produces a crystalline structure made of many small crystals rather than one continuous crystal. The multi-crystal structure is visible as a shimmering, speckled blue appearance.
Polycrystalline cells are somewhat less efficient than monocrystalline, typically 15% to 18%, because the grain boundaries between crystals create resistance to electron flow. They’re also less efficient in high heat. The manufacturing process is simpler and cheaper, but the efficiency gap versus monocrystalline has closed enough that most manufacturers now default to monocrystalline, making polycrystalline increasingly uncommon in new residential installations.
Thin-Film Solar Cells
Thin-film cells are made by depositing extremely thin layers of photovoltaic material onto a substrate like glass, metal, or plastic. The deposited layer is only a few micrometers thick, compared to the 180 to 200 micrometer wafers used in crystalline silicon cells. Several different materials are used in thin-film cells.
Cadmium telluride (CdTe) is the most commercially successful thin-film technology. First Solar, based in Tempe, Arizona, manufactures CdTe panels and is the dominant player in US utility-scale solar. CdTe panels are highly efficient to manufacture and have low carbon footprints, but they’re rarely used in residential installations.
CIGS (copper indium gallium selenide) thin-film panels can reach efficiencies comparable to polycrystalline silicon, around 15% to 18%. They perform well in diffuse light and high temperatures. Solar Frontier was a major CIGS manufacturer, though the residential thin-film market remains small compared to crystalline silicon.
Amorphous silicon (a-Si) thin-film panels have the lowest efficiency, around 6% to 10%, but perform better in low-light conditions than crystalline silicon. They’re primarily used in small consumer electronics and building-integrated solar (like solar shingles), not residential panel installations.
Bifacial Solar Cells
Bifacial cells can generate electricity from both sides. They capture direct sunlight on the front and reflected light (albedo) on the rear. A bifacial panel installed over a reflective surface like white gravel, concrete, or a light-colored roof can generate 10% to 30% more energy than a comparable monofacial panel.
Bifacial panels are increasingly common in commercial and utility-scale projects and are becoming available in the residential market. Most bifacial panels use monocrystalline PERC or TOPCon cells, since those cell designs benefit most from rear-side collection.
Perovskite Solar Cells
Perovskite cells are the most-discussed emerging technology in solar research. Perovskite is a class of crystal structure that can be manufactured at low cost and achieves high efficiency in laboratory conditions. Research cells have reached efficiencies above 25%, and perovskite-silicon tandem cells (combining both technologies) have exceeded 33% in lab settings.
Perovskite cells aren’t commercially available for rooftop use yet. Durability under outdoor conditions and concerns about lead content in some formulations remain active research problems. Commercial perovskite panels may begin appearing in the market within the next several years, but established silicon-based panels are what’s available and warranted today.
Solar Cell Efficiency
Efficiency measures how much of the sunlight hitting the cell is converted to electricity. Standard test conditions (STC) define efficiency measurement: 1,000 watts per square meter of irradiance, 25 degrees Celsius cell temperature, and a specific light spectrum (AM 1.5). Real-world conditions differ from these standards, which is why actual energy production rarely matches theoretical calculations based solely on panel wattage.
Several factors affect real-world efficiency below the rated STC number. Temperature is the biggest one. Silicon solar cells lose efficiency as they heat up, typically 0.3% to 0.5% per degree Celsius above 25 degrees. On a hot summer day in Arizona, a panel surface can reach 70 degrees Celsius, causing output to drop 15% to 20% below its rated wattage. Panels with lower temperature coefficients perform better in hot climates.
Shading has an outsized effect on output. Because cells are wired in series, shading even a small portion of a panel can reduce the entire string’s output significantly. Modern panels use bypass diodes to mitigate this, and some panel designs (half-cut cells, shingled cells) are engineered specifically to reduce shading losses.
From Solar Cells to Solar Panels
Solar cells are assembled into panels (also called modules) through a manufacturing process that encapsulates the cells between layers of tempered glass and ethylene-vinyl acetate (EVA) polymer. The assembly is sealed with a polymer backsheet and framed in aluminum. Electrical connections between cells and the junction box are made and tested before shipment.
The efficiency of the assembled panel is always somewhat lower than the efficiency of the individual cells, because the frame, glass, and gaps between cells take up space that doesn’t generate power. A panel with 22% efficient cells might have a panel-level efficiency of 20% to 21% due to these factors.
Panel wattage ratings reflect the output in standard test conditions. A 400-watt panel will produce 400 watts under ideal conditions but typically averages somewhat less over a full day across seasons. A production estimate from a qualified solar installer factors in your specific location, roof orientation, shading, and local climate to give you a realistic annual energy output figure.
Frequently Asked Questions
What is a solar cell made of?
Most solar cells are made of silicon, which is refined from quartz sand. Monocrystalline silicon cells are grown as a single crystal; polycrystalline cells are cast from melted silicon. Thin-film cells use alternative materials including cadmium telluride (CdTe) or copper indium gallium selenide (CIGS) deposited in very thin layers onto a substrate. Emerging perovskite cells use organic-inorganic lead or tin halide compounds but are not yet commercially available for home installations.
How efficient are solar cells?
Mass-market monocrystalline silicon solar cells used in residential panels are typically 20% to 23% efficient, meaning they convert 20% to 23% of the sunlight hitting them into electricity. Premium PERC and TOPCon cells reach the higher end of that range. Thin-film cells are generally 10% to 18% efficient depending on the material. Research cells of various types have exceeded 30% efficiency in lab conditions, but commercial products remain in the 20% to 23% range for residential applications.
What is the difference between a solar cell and a solar panel?
A solar cell is the individual unit that converts light to electricity via the photovoltaic effect. A solar panel (or module) is an assembly of many solar cells — typically 60 to 72 — connected together, encapsulated in glass and polymer layers, and framed in aluminum. Panels are the unit you buy and install on a roof. A solar array is a collection of multiple panels wired together into a complete system.
Do solar cells work on cloudy days?
Yes, solar cells produce electricity on cloudy days, just less of it. Diffuse light still contains photons that can generate current. On a heavily overcast day, a panel might produce 10% to 25% of its clear-sky rated output. Germany, which has notoriously cloudy weather, is one of the world’s largest solar markets, demonstrating that solar works even in less-than-ideal conditions. Monocrystalline panels generally handle low-light conditions better than other types.
How long do solar cells last?
Silicon solar cells degrade slowly over time, losing roughly 0.3% to 0.5% of their output per year. Most quality residential panels carry a 25-year performance warranty guaranteeing at least 80% to 85% of original output at year 25. The cells themselves often last longer than 25 years, though warranty coverage ends there. First-generation residential panels installed in the 1990s and early 2000s are still generating electricity in measurable quantities, confirming that solar cell longevity is not a significant practical concern.
What type of solar cell is best for home use?
Monocrystalline silicon is the standard for residential installations. It offers the highest efficiency in a compact form factor, which matters when roof space is limited. PERC and TOPCon versions of monocrystalline cells improve on the basic design and are now common in mid-range and premium residential panels. For most homeowners, the specific cell type matters less than choosing a panel from a manufacturer with a strong 25-year warranty and the financial stability to back it.
Summing Up
Solar cells are silicon-based semiconductors that convert photons into direct current electricity through the photovoltaic effect. Monocrystalline silicon cells dominate the residential market because of their efficiency and compact size, with PERC and TOPCon designs representing the current mainstream premium options. Thin-film technologies serve specific commercial and utility applications. Efficiency, temperature performance, and long-term degradation rate are the key technical metrics to understand when comparing panels. The cells themselves are engineered to last 25 years or more with gradual, predictable output decline.
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