What Are Photovoltaic Cells (PV) and How Do They Work?

Solar energy has become one of the fastest-growing renewable energy sources in the United States. Behind every solar panel installation lies a fascinating technology: the photovoltaic cell. Understanding how these cells work can help you make informed decisions about solar energy and appreciate the science that powers clean electricity generation.

What Is a Photovoltaic Cell?

A photovoltaic cell, commonly called a solar cell or PV cell, is a semiconductor device that converts light energy directly into electrical energy through the photovoltaic effect. The term photovoltaic comes from the Greek word for light (photo) and the name of the physicist Alessandro Volta (voltaic), who pioneered the study of electricity.

When sunlight strikes a photovoltaic cell, it triggers a physical and chemical reaction that generates an electric current at the atomic level within the semiconductor material. Multiple cells are connected together to form a solar panel, and multiple panels create a complete solar energy system. Modern commercial photovoltaic cells can reach efficiencies exceeding 20 percent, with some advanced laboratory cells approaching 50 percent efficiency.

The Structure of a Photovoltaic Cell

Most residential and commercial photovoltaic cells are made from silicon, the second most abundant element in the Earth's crust. The cell consists of carefully engineered layers that work together to produce electricity.

The Silicon Layers

A silicon photovoltaic cell contains two layers with different electrical properties. The top layer is infused with phosphorus, creating an n-type (negative-type) semiconductor with excess electrons. The bottom layer is infused with boron, forming a p-type (positive-type) semiconductor with a deficit of electrons. Where these layers meet, an electric field forms that directs electron flow and prevents recombination, which is essential for electricity generation.

Additional Components

Beyond the silicon layers, several other components are vital to cell function:

● Anti-reflective coating: A thin layer on the cell's surface reduces light reflection and ensures maximum sunlight absorption. Without this coating, up to 30 percent of incoming sunlight would simply bounce off the cell's surface.

● Metal contacts: Thin metal strips on the front and back of the cell collect and transport the generated electricity. Front contacts must be carefully designed to collect current without blocking too much incoming sunlight.

● Protective glass and encapsulant: These outer layers protect the delicate silicon from moisture, physical damage, and environmental stress while allowing light to pass through.

How Photovoltaic Cells Generate Electricity

The process of converting sunlight into electricity involves several steps that happen almost instantaneously when light strikes the cell.

Step 1: Photon Absorption

Sunlight is composed of tiny packets of energy called photons. When photons strike the cell, some pass through, some reflect off the surface, and some are absorbed by the silicon. Only absorbed photons with sufficient energy contribute to electricity generation by knocking electrons loose from silicon atoms. Photons with too little energy pass through without effect, while those with excess energy waste some energy as heat.

Step 2: Electron Excitation

When a photon with sufficient energy is absorbed, it transfers energy to an electron in the silicon atom, exciting it and allowing it to break free. The freed electron leaves behind a positively charged space called a hole. Without an electric field, these free electrons would quickly recombine with holes, releasing energy as heat. The cell's engineered structure prevents this.

Step 3: Charge Separation

The electric field at the junction between the n-type and p-type layers immediately pushes freed electrons toward the n-type layer and holes toward the p-type layer. This separation creates electrical potential, similar to a battery's positive and negative terminals. The field acts as a barrier preventing recombination, maintaining charge separation as long as sunlight continues generating new electron-hole pairs.

Step 4: Current Flow

The separated electrons accumulate in the n-type layer, creating a negative charge, while holes accumulate in the p-type layer, creating a positive charge. When an external circuit connects the two layers through metal contacts, electrons flow from the negative side through the circuit to the positive side, creating an electric current.

This direct current electricity can be used immediately, stored in batteries, or converted to alternating current by an inverter for use in homes and businesses. As long as sunlight continues to strike the cell, this process continues, providing a steady flow of electricity.

Types of Photovoltaic Cells

Different manufacturing processes and materials produce photovoltaic cells with distinct characteristics, efficiencies, costs, and applications.

Monocrystalline Silicon Cells

Monocrystalline cells are made from a single, pure silicon crystal sliced into thin wafers. These cells have a dark black appearance and offer the highest efficiency among commercially available silicon cells, typically 20 to 22 percent, with premium versions reaching 24 percent. They also have the longest lifespan and best low-light performance. The manufacturing process wastes more silicon and requires precise growing conditions, resulting in higher costs.

Polycrystalline Silicon Cells

Polycrystalline cells are made by melting silicon fragments together and pouring the molten material into a square mold, forming multiple crystals. These cells have a distinctive blue color with a fragmented appearance. While less efficient than monocrystalline cells at 15 to 17 percent, they cost less to produce because manufacturing wastes less silicon. They perform well in residential applications where roof space is abundant.

PERC Cells

Passivated Emitter and Rear Cell (PERC) technology adds a passivation layer to the rear surface that reflects unabsorbed light back into the silicon and reduces electron recombination. PERC cells typically achieve 5 percent higher efficiency than standard monocrystalline cells, making them ideal where roof space is limited. They cost slightly more but often provide better value due to higher energy output per square foot.

Thin-Film Cells

Thin-film cells use very thin semiconductor layers deposited on glass, plastic, or metal substrates. Common materials include cadmium telluride, amorphous silicon, and copper indium gallium selenide. These cells are thinner, lighter, and can be manufactured as flexible sheets. Efficiency ranges from 6 to 15 percent, lower than crystalline silicon, but they perform better in high heat, maintain efficiency in partial shading, and can be integrated into building materials. They are less expensive to manufacture at large scale.

Factors Affecting Photovoltaic Cell Performance

Several environmental and design factors influence how efficiently photovoltaic cells convert sunlight into electricity.

Temperature

Photovoltaic cells are tested at 25 degrees Celsius (77 degrees Fahrenheit). As temperature rises above this standard, efficiency decreases. Most crystalline silicon cells lose approximately 0.3 to 0.5 percent of power output for each degree Celsius above 25 degrees. On hot summer days, cell temperatures can reach 65 degrees Celsius or higher, resulting in a 15 to 20 percent reduction in output. Proper installation allowing air circulation beneath panels helps minimize temperature-related losses.

Sunlight Intensity and Angle

Photovoltaic cells produce maximum power when sunlight strikes them perpendicularly. When the sun is lower in the sky, the same sunlight spreads over a larger area, reducing intensity. Solar installations are typically angled to match local latitude for year-round optimization. Cloud cover, haze, and atmospheric conditions also affect performance. Cells can generate electricity on cloudy days, though output may drop to 10 to 25 percent of full-sun levels.

Shading

Even partial shading can reduce system output. When one cell in a series string is shaded, it limits current through the entire string. Modern panels include bypass diodes that route current around shaded cells to minimize this effect, but shading should still be avoided. Proper site assessment before installation identifies potential shading from trees, chimneys, nearby buildings, and other obstacles.

Degradation Over Time

Photovoltaic cells slowly lose efficiency over time. Modern panels degrade at an average rate of approximately 0.5 percent per year, meaning a panel might produce about 87.5 percent of its rated capacity after 25 years. Degradation occurs through ultraviolet radiation damage, thermal cycling stress from temperature changes, and moisture intrusion through micro-cracks. Premium panels from reputable manufacturers typically degrade more slowly, at rates closer to 0.3 to 0.4 percent annually.

From Cells to Complete Systems

Individual photovoltaic cells produce small amounts of electricity, typically 0.5 to 0.6 volts and a few amps. To create useful power levels, manufacturers connect multiple cells in series and parallel within a solar panel. A typical residential panel contains 60, 72, or 90 cells. A 60-cell panel might produce around 30 volts, while a 72-cell panel produces approximately 36 volts. Modern residential panels generate between 350 and 450 watts under standard conditions.

Multiple panels connect together to form arrays. Series connections increase voltage, while parallel connections increase current. A typical residential installation might include 15 to 25 panels, creating a 6,000 to 10,000 watt system sufficient to meet most or all of a home's electricity needs.

The Future of Photovoltaic Technology

Research continues to advance photovoltaic technology. Perovskite solar cells have achieved laboratory efficiencies exceeding 25 percent and could be manufactured at lower cost. Tandem cells stack multiple layers optimized for different light wavelengths, achieving laboratory efficiencies approaching 50 percent. Bifacial panels capture light from both surfaces, increasing output by 10 to 20 percent. Building-integrated photovoltaics incorporate cells into windows, roofing, and building facades.

Frequently Asked Questions

What is the difference between a photovoltaic cell and a solar panel?

A photovoltaic cell is the basic unit that converts sunlight into electricity. A solar panel is an assembly of multiple photovoltaic cells (typically 60, 72, or 90 cells) connected together within a protective frame and glass covering. The terms are sometimes used interchangeably, but technically, cells are the individual components while panels are the complete manufactured products installed on roofs or ground mounts.

How long do photovoltaic cells last?

Modern photovoltaic cells are designed to last 25 to 30 years or longer. Most manufacturers provide warranties guaranteeing that panels will produce at least 80 to 85 percent of their original output after 25 years. Many panels continue operating well beyond their warranty period. Actual lifespan depends on cell quality, installation conditions, and maintenance practices.

Do photovoltaic cells work on cloudy days?

Yes, photovoltaic cells continue to generate electricity on cloudy days, though at reduced capacity. Output typically drops to 10 to 25 percent of full-sun performance depending on cloud density. Cells can capture both direct sunlight and diffuse light scattered by clouds.

What materials are photovoltaic cells made from?

Most commercial photovoltaic cells are made from crystalline silicon. Silicon is processed and doped with phosphorus and boron to create the n-type and p-type layers. Other materials include cadmium telluride, copper indium gallium selenide, amorphous silicon, and emerging materials like perovskites. Advanced cells may include silver for electrical contacts and titanium dioxide for anti-reflective coatings.

How efficient are photovoltaic cells?

Commercial photovoltaic cell efficiency varies by type. Monocrystalline cells typically achieve 20 to 22 percent efficiency, PERC cells reach 22 to 24 percent, polycrystalline cells achieve 15 to 17 percent, and thin-film cells range from 6 to 15 percent. Laboratory cells have achieved efficiencies exceeding 47 percent using advanced multi-junction designs.

Do photovoltaic cells require maintenance?

Photovoltaic cells require minimal maintenance. Occasional cleaning to remove dust, leaves, and pollen helps maintain optimal performance. Visual inspections once or twice yearly can identify physical damage or performance issues. Systems with monitoring capabilities alert owners to significant production drops. Most maintenance involves keeping the surrounding area clear of vegetation that could cause shading. There are no moving parts to wear out.

Partner With SolarTime USA for Your Solar Installation

Ready to harness the power of photovoltaic technology for your home or business? SolarTime USA is a trusted, family-owned solar company based in Richardson, Texas, serving the Dallas and Fort Worth area. They provide complete solar services including system design, professional installation, permitting, monitoring, and optional battery storage.

SolarTime USA offers industry-leading warranties, including a 25-year product and workmanship warranty, ensuring your investment delivers reliable performance for decades. Their experienced team understands the unique conditions of the Texas climate and will design a custom solar system optimized for maximum efficiency and long-term savings.

Contact SolarTime USA today for a free consultation and discover how photovoltaic cells can power your property with clean, renewable energy while reducing your utility bills for years to come.