A photovoltaic cell is a device that converts sunlight directly into electricity using semiconductor materials. A single silicon cell produces about 0.5 volts, so dozens are wired together into the panels you see on rooftops. The underlying principle is simple: light energy knocks electrons loose inside a specially engineered material, and a built-in electric field pushes those electrons in one direction, creating a usable current.
How a Photovoltaic Cell Generates Electricity
Every photovoltaic cell is built around a junction between two layers of semiconductor material, almost always silicon. One layer is treated (or “doped”) with atoms that create extra electrons, giving it a negative character. The other layer is doped with atoms that create gaps where electrons are missing, giving it a positive character. Where these two layers meet, electrons from the negative side drift toward the positive side and vice versa, forming a thin boundary zone with a permanent electric field.
When sunlight hits the cell, photons transfer their energy to electrons in the silicon, knocking them free. The electric field at the junction acts like a one-way gate: it sweeps freed electrons toward the negative layer and pushes the holes they left behind toward the positive layer. Connect a wire between the two sides and those electrons flow through it as direct current (DC) electricity, powering whatever load sits in their path. As long as photons keep arriving, the process keeps running.
From Cell to Module to Array
A single cell’s 0.5 volts isn’t enough to power much on its own. To reach useful voltages, cells are wired together in series and parallel circuits, then sealed behind glass and weatherproof laminate to form a module. A module is the rectangular unit most people picture when they think “solar panel.” One or more modules pre-wired for installation make up a panel, and the complete collection of panels on a roof or in a field is called an array. Each level multiplies voltage, current, or both, scaling a half-volt cell into a system that can run a house.
Because cells produce DC electricity, a home solar system also needs an inverter to convert that output into the alternating current (AC) your appliances and the electrical grid use.
Materials Used in Photovoltaic Cells
Silicon dominates the market. Over 80% of the world’s solar cells are made from either monocrystalline or polycrystalline silicon. Monocrystalline cells are cut from a single, continuous crystal structure, which lets electrons move more freely and pushes efficiency higher. Polycrystalline cells are cast from multiple silicon fragments melted together, making them cheaper to produce but slightly less efficient. Silicon’s popularity comes down to decades of manufacturing refinement and abundant raw material.
Thin-film cells use a different approach. Instead of slicing wafers from a silicon block, manufacturers deposit an extremely thin layer of photovoltaic material onto glass, plastic, or metal. Common thin-film materials include amorphous silicon, cadmium telluride, and copper indium gallium selenide. Thin-film cells are lighter and can be made flexible, but they generally convert less sunlight into electricity.
Gallium arsenide is a niche, high-performance alternative. It handles heat better than silicon and reaches higher efficiencies, but it costs far more to produce. You’ll find it in satellites and concentrated solar systems where raw performance justifies the price.
Efficiency: What You Can Expect
Efficiency measures what percentage of the sunlight hitting a cell actually becomes electricity. For residential panels, that number typically falls between 15% and 22%. Monocrystalline panels sit at the top of that range (15 to 22%), polycrystalline panels land around 15 to 20%, and thin-film panels span 10 to 20%. Premium monocrystalline panels on the market today can reach 22 to 27%.
Individual cells in a lab setting can do much better than full panels in the field. Some experimental cells have hit 42% efficiency. The gap exists because a finished panel loses some energy to wiring, glass reflection, spacing between cells, and heat. There’s also a theoretical ceiling for a single-junction silicon cell, around 33%, set by the physics of how silicon absorbs light. Tandem cells, which stack two different materials to capture a wider range of the solar spectrum, are pushing past that wall. Lab prototypes using perovskite layers stacked together have reached a certified 29.1% efficiency, a figure that keeps climbing year over year.
What Affects a Cell’s Output
Temperature is the biggest surprise for most people. Solar cells actually perform worse as they get hotter. Both electrical efficiency and power output drop in a roughly linear relationship with rising temperature. Internal losses increase because heat energizes more electrons randomly, interfering with the orderly flow the cell depends on. That’s why panels in cool, sunny climates (think high-altitude regions like the Andes or the Himalayas) often outperform panels in equatorial lowlands that get more raw sunlight but also more heat.
Shading matters disproportionately. Because cells within a module are wired in series, shading even one cell can bottleneck the current through the entire string, cutting output by far more than the shaded area alone would suggest. Modern systems use bypass diodes and microinverters to limit this effect, but keeping panels clear of shadows remains important. Dust, pollen, and bird droppings act as partial shading and have a similar, smaller impact.
The angle and orientation of the panel relative to the sun also plays a role. Panels tilted to face the sun more directly capture more photons per square centimeter. Tracking systems that follow the sun across the sky boost output further, though they add cost and mechanical complexity.
How Long Photovoltaic Cells Last
Solar panels degrade gradually, losing a small fraction of their output each year. The rate varies widely depending on the technology and the climate. A large-sample study of over 1,200 modules found a mean degradation rate of about 1.3% per year, which would bring a panel to 80% of its original power in roughly 15 years. Other long-term studies show more favorable numbers: monocrystalline modules operating in Quebec for 23 years degraded at just 0.6% per year, suggesting they could hold above 80% output for well over two decades.
Climate pushes those numbers around considerably. Hot, humid environments accelerate degradation. Studies in tropical Singapore recorded annual losses of 0.9% to 4% for crystalline silicon and up to 4.5% for certain thin-film types. Polycrystalline panels tend to degrade at a steadier pace, while monocrystalline and thin-film panels sometimes show faster losses in their first five years before stabilizing. In practice, most manufacturers guarantee at least 80% output at 25 years, and many panels continue producing useful electricity well beyond that.
Photovoltaic Cells in Everyday Systems
A typical residential rooftop system uses 20 to 30 monocrystalline or polycrystalline modules wired into an array. The array feeds DC power to an inverter, which converts it to household AC. In grid-tied systems, excess electricity flows back to the utility, often earning credits on your bill. Off-grid systems store energy in batteries instead. The cells themselves require almost no maintenance: no moving parts, no fuel, no combustion. Occasional cleaning and an inverter replacement every 10 to 15 years are the main upkeep tasks.
Beyond rooftops, photovoltaic cells power everything from roadside call boxes and orbiting satellites to portable chargers and building-integrated glass facades. The same half-volt principle at work in a pocket calculator drives utility-scale solar farms covering thousands of acres. What changes is scale, not the underlying physics: sunlight in, electrons out.