How do solar cells work? Photovoltaic cells explained

You've probably seen solar panels on rooftops all around your neighborhood, but do you know how they work to generate electricity? In this article, we'll look at photovoltaic (PV) solar cells, or solar cells, which are electronic devices that generate electricity when exposed to photons or particles of light. This conversion is called the photovoltaic effect. We'll explain the science of silicon solar cells, which comprise most solar panels.

A solar module comprises six components, but arguably the most important one is the photovoltaic cell, which generates electricity. The conversion of sunlight, made up of particles called photons, into electrical energy by a solar cell is called the "photovoltaic effect" - hence why we refer to solar cells as "photovoltaic", or PV for short.

Solar PV systems generate electricity by absorbing sunlight and using that light energy to create an electrical current. There are many photovoltaic cells within a single solar module, and the current created by all of the cells together adds up to enough electricity to help power your home. A standard panel used in a rooftop residential array will have 60 cells linked together. Commercial solar installations often use larger panels with 72 or more photovoltaic cells.

A solar cell works in three generalized steps:

1. Light is absorbed and knocks electrons loose

2. Loose electrons flow, creating an electrical current

3. The electrical current is captured and transferred to wires

The photovoltaic effect is a complicated process, but these three steps are the basic way that energy from the sun is converted into usable electricity by solar cells in solar panels. A PV cell is made of materials that can absorb photons from the sun and create an electron flow. When electrons are excited by photons, they produce a flow of electricity known as a direct current. Below, we'll dive into each of these steps in more detail:

1. PV cells absorb incoming sunlight

The photovoltaic effect starts with sunlight striking a photovoltaic cell. Solar cells are made of a semiconductor material, usually silicon, that is treated to allow it to interact with the photons that make up sunlight. The incoming light energy causes electrons in the silicon to be knocked loose and begin flowing together in a current, eventually becoming the solar electricity you can use in your home.

2. Electrons begin flowing, creating an electrical current

There are two layers of silicon used in photovoltaic technology, and each one is specially treated (known as "doping") to create an electric field, meaning one side has a net positive charge and one has a net negative charge. This electric field acts as a diode, forcing loosened electrons to flow through it in one direction, generating an electrical current.

3. Wires capture the electrical current and combine current from all cells of a solar panel

Once the loose electrons generate an electrical current, metal plates on the sides of each solar cell collect those electrons and transfer them to wires. At this point, electrons flow as electricity through the wiring to a solar inverter and then throughout your home.

A photovoltaic cell alone cannot produce enough usable electricity for more than a small electronic gadget. Solar cells are wired together and installed on top of a substrate like metal or glass to create solar panels, which are installed in groups to form a solar power system to produce the energy for a home. A typical residential solar panel with 60 cells combined might produce anywhere from 220 to over 400 watts of power.

Depending on factors like temperature, hours of sunlight, and electricity use, property owners will need a varying number of solar panels to produce enough energy. Installing a photovoltaic system will likely include several hundred solar photovoltaic cells working together to generate an electrical current. You can use the EnergySage Solar Calculator to understand the savings you might see from a solar panel installation.

Two main types of solar cells are used today: monocrystalline and polycrystalline. While there are other ways to make PV cells (for example, thin-film cells, organic cells, or perovskites), monocrystalline and polycrystalline solar cells (which are made from the element silicon) are by far the most common residential and commercial options.

Silicon solar cells: monocrystalline and polycrystalline

Both monocrystalline and polycrystalline solar cells are initially made from silicon wafers. A monocrystalline solar cell is made from a single crystal of the element silicon. On the other hand, polycrystalline silicon solar cells are made by melting together many shards of silicon crystals.

This leads to two key differentiators between mono- and poly-cells. In terms of efficiency, monocrystalline solar cells are generally higher than their polycrystalline counterparts. This is due to using a single, aligned silicon crystal, resulting in an easier flow for the electrons generated through the photovoltaic effect. Polycrystalline cells have shards of silicon aligned in many directions, making electricity flow slightly more difficult. However, solar modules made with polycrystalline solar cells are usually less expensive than monocrystalline options. This is because the manufacturing process for a polycrystalline cell is simpler and requires fewer specialized processes.

Thin-film solar cells

Thin-film solar cells are much slimmer, lighter-weight solar cells that are often flexible while remaining durable. There are four common materials used to make thin-film PV cells: Cadmium Telluride (CdTe), Amorphous Silicon (a-Si), Copper Indium Gallium Selenide (CIGS), and Gallium Arsenide (GaAs).

Thin-film solar cells are less popular than traditional crystalline silicon options for residential and commercial installations. Thin-film panels remain behind silicon panels in efficiency, and for most homes and businesses, this means they won't be able to produce enough electricity from thin-film options. However, companies like First Solar have built entire businesses on producing panels with thin-film solar cells (in their instance, CdTe cells) for primarily large-scale utility power stations that aim to replace fossil fuel energy sources.

Organic solar cells

Solar panels made with organic solar cells are not commercially viable quite yet, but organic panels have many of the same benefits as thin-film panels. The biggest difference maker for organic solar cells is their composition. While traditional and thin-film solar panels are made from silicon or similar semiconductors, organic solar cells are made from carbon-based materials. They're often referred to as "plastic solar cells" or "polymer solar cells" for this reason.

Organic solar cells are flexible, durable, and can even be made transparent. Heard of solar windows? If they ever become a widespread product, they may be built with transparent organic solar cells.

Perovskite solar cells

A "perovskite" is any material with the same crystal structure as the compound calcium titanium oxide, a semiconductor material like silicon. Perovskite solar cells use an artificial calcium titanium oxide-based material to create another type of thin-film solar panel.

Like organic solar cells, perovskites are not widely available yet. However, their low production costs and high potential efficiencies make them an intriguing option as the solar industry continues to expand and develop better solar production options.

Most solar cells start as raw silicon, a naturally occurring element in several types of rocks. The first step in making any silicon solar cell is to extract the naturally occurring silicon from its hosts – often gravel or crushed quartz – and create pure silicon. This is done by heating the raw materials in a special furnace, yielding molten silicon that can be further processed into monocrystalline silicon wafers for certain solar cells.

Once you have a polished and properly-sized silicon wafer (monocrystalline or polycrystalline). Regarding solar cells, doping yields two main regions within silicon: p-type silicon and n-type silicon. P-type silicon is made with boron, while n-type silicon is created with phosphorus.

Why make these two types of silicon? We won't go into the scientific details too much, but in a nutshell, pure silicon is not a very good conductor of electricity. Adding boron and phosphorus to silicon wafers introduces an electron imbalance, creating an electric field at the intersection of the p-type and n-type silicon, also known as a p-n junction. By the way – the "p" in p-type stands for positive, and the "n" in n-type stands for negative. This is because p-type silicon is at an electron deficit, and n-type silicon has a surplus of electrons floating around. A simple way to think about the flow of electricity that makes solar cells work is that it's just electrons flowing from the n-type silicon with extra electrons to the p-type silicon that doesn't have enough.

After doping the silicon cells, a few more steps are needed to make a complete solar cell. One of these steps is to apply an anti-reflective coating to the cell – this prevents incoming sunlight from simply bouncing off the shiny wafer before the photons can interact with the silicon. Another step is to add metal contacts to the cells that will act as a conduction funnel for the electricity generation from the cell, connecting that current to the overall wiring and electrical systems of a solar system.

Finally, cells are covered with a protective layer, usually glass. Once manufacturers have a single solar cell, they can combine them to create solar panels that combine the power of 60 or more individual cells to generate a useful voltage and current.

The efficiency of a PV cell is the amount of electrical power that's coming out of the cell compared to the energy from the light shining on it. This number demonstrates how effective the cell is at converting energy. And as mentioned, there are a variety of internal and external factors to solar cells themselves, like light intensity and wavelength, that affect the conversion efficiency of a solar cell. There are a few main areas of development around improving solar cell technology:

Multijunction solar cells

One of these important factors of PV cells is the range of wavelengths of light the material (silicon, thin film, perovskite, etc.) can absorb and convert to energy. Light is made up of photons vibrating at a wide range of wavelengths, and the wavelengths that match the absorbable range of a solar semiconductor (known as a bandgap) can be captured by that solar cell. 

A strategy already helping to improve PV cell efficiency is layering multiple semiconductors together to make "multijunction solar cells." Each layer of a multijunction cell can have a different bandgap – meaning they will each absorb a different part of the solar spectrum, making better and more complete use of the sunlight than a traditional single-junction cell. 

Multijunction solar cells are at the core of the world record for solar cell efficiency – as of 2022, the National Renewable Energy Laboratory (NREL) has set the bar for efficiency at 39.5 percent using multijunction technology – an improvement over their previous record of 39.2 percent.

P-type cell improvements using gallium

Over time, silicon cells doped with boron naturally degrade as they continue to be exposed to sunlight. The reason for this degradation is straightforward: including impurities like boron to create p-type silicon also causes inclusions of other atoms. One such atom is oxygen – this is more or less unavoidable and comes from the physical tools used to refine silicon. 

Unfortunately, oxygen chemically reacts with boron when exposed to sunlight, which causes minor defects in the silicon cell and reduces power generation over time. One solution to this problem is to use an element besides boron that won't bond to the oxygen impurities. Gallium, a naturally occurring metal element, is one such material already being used in solar panel manufacturing to solve the problem of cell degradation and is leading to higher efficiencies for solar panels worldwide.

Discussing the science behind PV cells can be complicated and confusing, making every topic seem like nothing more than jargon—words like photons, semiconductors, and volts with no clear explanation for the average solar shopper. We understand how difficult it can be to gather answers, especially as you embark on your new renewable energy journey. Check out a few of the most common questions we've been hearing about solar PV cells:

How do PV cells work, and what do they do? 

PV cells, or solar cells, generate electricity by absorbing sunlight and using the light energy to create an electrical current. The process of how PV cells work can be broken down into three basic steps: first, a PV cell absorbs light and knocks electrons loose. Then, an electric current is created by the loose-flowing electrons. Finally, the electrical current is captured and transferred to wires. 

What is the difference between photovoltaic cells and solar cells? 

Solar and photovoltaic cells are the same, and you can use the terms interchangeably in most instances. Both photovoltaic solar cells and solar cells are electronic components that generate electricity when exposed to photons, producing electricity. The conversion of sunlight into electrical energy through a solar cell is known as the photovoltaic effect, which is why we refer to solar cells as "photovoltaic."

What are photovoltaic cells made of?

Solar cells are usually made of silicon semiconductors that can absorb sunlight and convert it into electricity. They are organized into a large frame which is the solar panel.

Solar photovoltaic cells are the building blocks of solar panels, and any property owner can start generating free electricity from the sun with a solar panel installation. On the EnergySage Marketplace, you can register your property to begin receiving solar installation quotes from qualified installers. While all quotes involve solar panels made from photovoltaic cells, panel output can change based on equipment quality. If you are specifically interested in seeing quotes for high-efficiency solar panels, leave a note on your profile to notify installers.