A solar cell is a small device, typically made of silicon, that converts sunlight directly into electricity. It does this through what’s called the photovoltaic effect: when light hits the cell, its energy knocks electrons loose inside the material, creating an electrical current. A single cell produces a modest amount of power on its own, but dozens or hundreds of them wired together form the solar panels you see on rooftops and in solar farms.
How a Solar Cell Generates Electricity
The core of a solar cell is a thin wafer of semiconductor material, almost always silicon. Silicon doesn’t conduct electricity as freely as metal, but it doesn’t block it like rubber either. That “in between” quality is what makes it useful. When sunlight strikes the silicon, photons (particles of light) transfer their energy to electrons in the material, freeing them from their normal positions. Those freed electrons then flow through the material as an electrical current, which is drawn out through metal contacts on the cell’s surface and sent to whatever needs power.
Not every photon that hits the cell produces electricity, though. If a photon doesn’t carry enough energy, it passes straight through the silicon without doing anything. If it carries too much, the excess is lost as heat. And some photons simply bounce off the surface. This is why no solar cell converts 100% of sunlight into electricity, and why engineers spend so much effort optimizing each layer of the device.
What’s Inside a Solar Cell
A standard silicon solar cell is built around two layers of silicon that have been chemically treated, or “doped,” in different ways. The top layer has extra electrons (called n-type silicon), while the bottom layer has gaps where electrons are missing (called p-type silicon). Where these two layers meet, they form what’s known as a p-n junction. This junction creates an internal electric field that acts like a one-way gate, pushing freed electrons in a single direction and giving the current somewhere to go.
On top of the silicon sits a thin anti-reflective coating, usually giving the cell its characteristic dark blue or black color. This coating reduces the amount of light that bounces off the surface, ensuring more photons reach the silicon where they can be absorbed. The front of the cell also has thin metallic “fingers,” narrow lines of conductive metal that collect the electrical current. These fingers are kept as thin as possible so they don’t block too much incoming sunlight. A solid metal contact covers the back of the cell, completing the circuit.
How Much Power a Single Cell Produces
A single solar cell produces a surprisingly small amount of electricity. A typical cell generates roughly 0.5 to 0.6 volts in direct sunlight, with a current that depends on the cell’s size. To put that in perspective, it takes about 60 to 72 cells wired together in series to form a standard residential solar panel rated at 300 to 400 watts. That panel voltage is high enough to be useful for home electrical systems, but a single cell on its own could barely power a small LED.
This is why solar panels are built the way they are. Individual cells are connected in series to increase voltage and in parallel to increase current, then sealed behind glass to protect them from weather. The panel is the practical unit of solar power; the cell is the fundamental building block.
Types of Solar Cells
Most solar cells on the market fall into one of three categories, each with different trade-offs between cost, efficiency, and flexibility.
- Monocrystalline silicon cells are cut from a single continuous crystal of silicon. They’re the most efficient commercially available type, and they dominate the residential rooftop market. In the lab, concentrator versions of these cells have reached 30.8% efficiency. Mass-produced panels typically land in the 20 to 24% range.
- Polycrystalline silicon cells are made from silicon that’s been melted and cast into blocks, then sliced into wafers. The crystal structure is less uniform, which makes them slightly less efficient but cheaper to manufacture. They’re recognizable by their speckled blue appearance.
- Thin-film cells use a very thin layer of light-absorbing material deposited on glass, metal, or plastic. The most common type uses cadmium telluride, which has reached 23.6% efficiency in the lab. Thin-film cells are lighter and more flexible, making them useful for applications where rigid panels won’t work, but they generally convert less sunlight per square meter than crystalline silicon.
At the extreme end, multi-junction cells designed for satellites and concentrated sunlight systems stack multiple layers of different semiconductor materials. Each layer absorbs a different portion of the light spectrum, so less energy is wasted. These cells have reached 47.6% efficiency in laboratory settings, though they’re far too expensive for everyday use.
How Long Solar Cells Last
Silicon solar cells are remarkably durable. They have no moving parts, require almost no maintenance, and degrade very slowly over time. Recent data from 53 solar plants tracked over roughly a decade found that annual efficiency loss ranged from 0% to just 0.29% per year. That’s even lower than the 0.5% figure that older studies assumed. At that rate, a panel would still produce more than 90% of its original output after 25 years, which is why most manufacturers offer warranties in that range. Many panels continue generating useful power well beyond 30 years.
Tandem and Perovskite Cells
After 60 years of research, silicon solar cells are approaching a theoretical efficiency ceiling of about 29.8%. To push past that limit, researchers are developing tandem cells that stack two different light-absorbing materials on top of each other. The top layer captures high-energy light (blue and ultraviolet wavelengths), while the bottom layer captures lower-energy light (red and infrared) that passes through. By splitting the work, tandem cells convert a broader range of the solar spectrum into electricity.
The most promising pairing right now is perovskite on top of silicon. Perovskites are a class of crystalline materials that can be manufactured cheaply and tuned to absorb specific wavelengths of light. In the lab, perovskite cells have reached efficiencies comparable to traditional silicon. Stacking perovskite on silicon gives researchers a path to efficiencies well above what either material could achieve alone.
The catch is durability. Perovskite materials break down when exposed to moisture, heat, and prolonged sunlight, which are, of course, exactly the conditions solar panels face every day. Scaling up production while maintaining high performance has also proven difficult. These challenges have kept perovskite and tandem cells from reaching the commercial market at scale, but they remain one of the most active areas of solar energy research.