How Do Photovoltaic Cells Work?

Virtually everyone knows what a solar panel does.

Far fewer people know how solar panels generate electricity.

It’s not magic…

But it’s pretty close.

Photovoltaic (PV) cells are an essential component of all currently available solar panels and systems that produce electricity from sunlight.

But what are PV cells? 

And how do they work?

Take a deep dive here to find out.

(Source: PV Education)

What Are Photovoltaic Cells?

Many different companies use many different materials to manufacture many different types of photovoltaic cells and modules — like solar panels.

But ultimately, all photovoltaic cells perform the same function.

A photovoltaic cell harvests photons from sunlight and uses the photovoltaic effect to convert solar power into direct current electricity.

The photovoltaic cells contained in a PV module transmit DC electricity to an on-grid, off-grid, or hybrid solar system. 

An inverter converts DC into alternating current (AC) electricity for household consumption or transmission to the utility grid (net metering).

In off-grid and hybrid systems, a solar charge controller is typically the first stop for the DC electricity photovoltaic modules produced. 

Depending on the configuration — and current electricity consumption requirements — the charge controller routes DC to a solar battery or to a solar inverter for AC conversion.

The primary benefit of off-grid and hybrid solar systems like EcoFlow DELTA Pro Ultra is that they offer energy security in a power outage.

Traditional grid-tied systems don’t work in a blackout.  

But how do solar cells convert sunlight to electricity in the first place?

Read on to find out.

(Source: EIA)

How Do Photovoltaic Cells Convert Sunlight to Electricity?

A photovoltaic cell — frequently called a solar or PV cell — is a non-mechanical device made from a semiconductor material like crystalline silicon.

Named after the photovoltaic effect, PV cells directly convert the photons from sunlight into DC electricity.

There is a common misconception that photovoltaic modules like solar panels generate electricity from heat.

In fact, high temperatures have a negative impact on solar panel performance — particularly when the ambient temperature exceeds 86°F (30°C).

So much so that large-scale commercial solar farms in areas that receive many hours of peak sunlight — such as in a desert — often install cooling equipment to optimize solar panel efficiency.

When different wavelengths of sunlight from across the solar spectrum hit the surface of a PV module, photons either bounce off through reflection, pass through the photovoltaic material, or get absorbed by the solar cell.

Once absorbed, the photons provide the energy for the semiconductor material to generate electricity. 

Photon capture causes negative “free electrons” to circulate within the PV cell and move towards the device’s front surface. This creates an electrical imbalance within the cell, resulting in voltage potential.

The positive and negative charge — similar to those carried by battery terminals — is absorbed by electrical conductors in the cell to produce electricity when connected to a load such as a solar inverter or battery.

(Source: Energy Education)

What Is a Semiconductor?

Virtually all modern electronics — including photovoltaic cells and solar panels — rely on semiconductors.

Integrated circuit (IC) semiconductors — frequently called microchips — power your smartphone and your computer.

Without semiconductors, there would be no internet, television, or radio.

Semiconductors can be made from pure elements — like silicon — or from compounds like cadmium selenide.

The vast majority of photovoltaic cells used in modules like solar panels in residential PV systems are made from crystalline silicon nonmechanical semiconductive material.

Regardless of what they’re made from (or for), semiconductors function by conducting electricity under specific conditions. 

Unlike pure metals, a semiconductor acts as both an insulator and a conductor. Semiconductors are designed to only conduct electricity when the right conditions are met.  

A semiconductor combines the properties of a conductive material — like copper — and an insulative (nonconductor) material like glass.

Semiconductors are fundamental to transistors, diodes, and switches — like the binary switches calibrated to provide digital 1s and 0s.

Semiconductors are essential to any device that requires precision control of electricity. 

How Do the Semiconductors in PV Cells Work?

The semiconductors in photovoltaic cells aren’t mechanical devices.

Instead, a naturally semiconductive raw material — typically quartz — is refined to produce pure crystalline silicon.

As we’ll cover below, not all solar cells are made of silicon, but the vast majority of consumer PV modules are.

Quartz is made of Earth’s two most common elements — silica and oxygen. 

You may know it better as sand. 

Quartz is second only to feldspar as Earth’s most abundant mineral.

(Source: DoE)

What Are the Main Types of Solar Cells? 

The most commonly used type of photovoltaic cells by far are made primarily from crystalline silicon.

Amorphous silicon can also be used to manufacture thin-film solar cells, but using pure monocrystalline or polycrystalline has multiple advantages — including much higher efficiency.

What follows is a brief summary of currently available photovoltaic cell technologies and recent innovations still in the development stage.

Crystalline Silicon

An overwhelming majority of photovoltaic cell and module manufacturers use monocrystalline or polycrystalline silicon as the primary material in solar cells. 

According to the International Energy Agency, crystalline silicon (cSi) “remains the dominant technology for PV modules, with a market share of more than 97% estimates.”  

Let’s explore the differences between monocrystalline and polycrystalline PV cells.

(Source: ASES)

Monocrystalline Silicon 

When it comes to efficiency, monocrystalline PV cells have got a polycrystalline beat.

The silicon wafers used to manufacture monocrystalline solar panels are cut from an ingot made from a single, lab-grown, silicon cell.

Monocrystalline PV cells are also more expensive to produce — largely because the manufacturing process requires more energy and raw materials.

However, with efficiency ratings as high as 23% vs. 13-18% for polycrystalline PV cells, the savings on electricity bills and reduced installation surface area can more than offset a higher sticker price. 

Many people also find monocrystalline solar panels more aesthetically pleasing. 

Unlike blue polycrystalline PV panels, the distinctive black appearance blends in with any home design or roof.   

Polycrystalline Silicon

If you’re not concerned about efficiency, polycrystalline solar panels tend to be cheaper than modules with monocrystalline PV cells.

However, any savings you make on price will likely be outweighed over the long term by inferior performance.

Polycrystalline silicon PV cells are less expensive and time-consuming to produce.

Instead of using wafers cut from an ingot grown from a single silicon cell, polycrystalline PV cells are made from fragments of many silicon crystals. 

By eliminating some of the time and materials required to manufacture monocrystalline silicon, poly PV panels come at a lower retail price.

More on monocrystalline vs. polycrystalline solar panels.

Passive Emitter and Rear Contact (PERC)

Passive Emitter and Rear Contact (PERC) photovoltaic cells can be monocrystalline or polycrystalline. 

The difference between PERC and traditional cSi solar cells isn’t in the type of silicon used. 

Rather, it’s the application of a passivation layer of antireflective material (silicon nitride) to the rear surface of the PV cell designed to capture additional sunlight.  

Additionally, the rear contact of the cell is “opened” using laser and screenprinting techniques. 

In some cases, PERC PV cells can provide greater efficiency than traditional crystalline silicon solar cells.

Al-BSF PV cells use similar technology.

Thin Film (Second Generation Solar Cells)

Not all photovoltaic cells are made from crystalline silicon.

Thin-film solar panels are a newer technology that’s currently used mostly in large-scale commercial PV systems. 

Thin-film PV modules are flexible and inexpensive to produce.

However, they’re highly inefficient (5-12%), making them impractical for residential use.

The most commonly used photovoltaic materials in thin film solar panels are:

• Cadmium Telluride (CdTe)
• Copper Indium Gallium Selenide (CIGS)
• Gallium arsenide (GaAs)
• Amorphous Silicon (a-Si)

Emerging Technology (Third Generation Solar Cells)

The following photovoltaic cell technologies are in the early stages of development. 

It will likely be some years before these types of solar cells are used in PV modules designed for residential use. 

If any of these emerging PV technologies prove commercially viable, they’ll likely be used to facilitate industrial-scale electricity generation to aid in the transition away from fossil fuels.

• Perovskite
• Dye-Sensitized
• Quantum Dot
• Organic
• Multijunction (III-V)

(Source: NREL)

How Are Solar Photovoltaic Cells Produced?

The production method for photovoltaic cells made from crystalline solar cells is unique from technologies — thin-film for example — that use materials other than silicon.

The process for monocrystalline and polycrystalline PV cells is similar — up to a point.

Here, we’ll focus on the step-by-step process of producing high-efficiency monocrystalline solar cells used in solar shingles and panels.

Raw Materials

Crystalline silicon starts life as quartz — more specifically, quartzite — which is technically known as silica or silicon dioxide.

Quartz is highly abundant and comes from numerous sources, including beach sand and open pit mines. 

Quarzite Into Silicon 

For quartzite to be used in industrial applications, it must be crushed into powder and mixed with carbon.

It’s then fired in arc furnaces — a refining process called carbon arc welding (CAW) that results in metallurgical-grade silicon with up to 99% purity. 

Silicon with 99% purity is fine for many industrial purposes. 

But it’s nowhere near pure enough for photovoltaic cells, computer chips, or other semiconductor applications.

Silicon Purification 

To be effective in semiconductor applications, silicon must be at least 99.99999% pure. 

Each 9 is numbered. 

In the above example, the silicon has a purity of 7N.

Most photovoltaic cells use silicon with 7N to 10N purity.

Semiconductors used in microprocessors (chips) require silicon of up to 11N purity.

Purifying silicon for semiconductor applications is done using one of two processes.

• Siemens process
• Fluidized bed reactor (FBR) process 

The Siemens process is “easier” — and far more commonly used.

From Poly to Monocrystalline

Once the silicon is of sufficient purity, it’s time for the next step.

To create high-efficiency monocrystalline PV cells, the polycrystalline silicon produced in the previous step must be processed further using one of two methods.

• Czochralski method (CZ)
• Float zone technique (FZ)

Both methods produce single silicon cells that can be used for monocrystalline PV modules and cells. 

FZ results in higher purity than CZ, but it’s also a more challenging (and expensive ) process that’s rarely used in commercial PV cell production.   

Silicon Wafers

The CZ process results in ingots of pure monocrystalline silicon.

The ingots are cut into circular wafers and then cut again — typically into hectagons or rectangles.

Precision-cutting silicon wafers into angular shapes provides the most efficient use of space and the best performance.

In the past, the standard wafer size of monocrystalline solar cells was 156mm² cut from an ingot 200mm in diameter.

Wafers of this size are known as M0.

In recent years, silicon ingot sizes have increased, resulting in better performance.

(Source: PV Manufacturing)

Wafer-based solar cells that use M2 silicon wafers produce higher rated power wattage than cells constructed using MO without significant increases in costs.

Today, wafers as large as 210mm² (M12) are used in PV cells and modules — a 35% increase in size from MO.

The trend towards using larger wafers to achieve higher power ratings looks poised to continue for the foreseeable future.

(Credit: Creative Commons)

Doping

Doping is an essential process in semiconductor manufacturing.

It requires introducing tiny impurities into pure crystalline silicon. 

Adding a doping agent (dopant) to silicon changes its electrical properties.

Doping crystalline silicon is required to create a p-n-junction: an essential operating component of diodes, transistors, and photovoltaic cells.

(Source: American Chemical Society)

P-Type vs. N-Type PV Cells

What makes a photovoltaic cell P-Type or N-Type?

Without getting bogged down in the technicalities, the N in N-type stands for negative (electrons) and the P in P-Type sounds for positive (holes).

All PV cells have both positive and negative layers — it’s the interaction between the two layers that makes the photovoltaic effect work.

What distinguishes an N-Type vs. P-Type solar cell is whether the dominant carrier of electricity is positive or negative. 

• N-Type PV cells contain atoms with one more electron than silicon in the outer layer
• P-Type PV cells contain atoms with one more hole than silicon in the outer layer

From a manufacturing standpoint, how a silicon wafer is doped determines whether a PV cell is N-Type or P-Type.

• N-Type PV cells are doped with phosphorus, antimony, or arsenic to create an intentional imbalance that favors electrons at the atomic level. 
• P-Type semiconductors add a dopant like boron, aluminum, or gallium to silicon wafers to achieve the opposite effect. The dominant electric carrier in P-Type PV cells is positive (holes)

What does all this mean for solar panels?

P-Type solar panels have been around longer and are more commonly used at present.

N-Type solar panels tend to have higher efficiency, longer lifespans, and less sensitivity to ambient temperature.

However, N-Type PV modules are typically more expensive than P-Type.

The right choice for you depends on whether you value higher efficiency or a cheaper price. 

For small-scale solar installations, the difference in performance will be almost unnoticeable. 

Rather than worrying about P-Type or N-Type, select a PV module that meets your rated power and efficiency needs.

Additional Components of PV Cells

The p-n junction (semiconductor) formed by doped silicon wafers is the most important part of a solar cell. 

But there are other essential components, including:

• Printed silver paste (Front contact of cell)
• Anti-reflective coating or anti-reflective glass
• Back surface field
• Print aluminum paste (rear cell contact)

Solar Panel Assembly

Once the above steps of PV cell manufacturing are complete, the photovoltaic cells are ready to be assembled into solar panels or other PV modules.

A 400W rigid solar panel typically contains around 60 photovoltaic cells installed under tempered glass and framed in aluminum or another durable metal.

Learn more about the solar panel manufacturing process.

What Is a Photovoltaic System and How Does It Work?

Photovoltaic cells and modules — like solar panels — don’t work alone.

The components other than PV modules required to generate usable electricity are collectively known as the balance of the system.

The parts required for a PV balance of a system depends primarily on the relationship of the system to the power grid.

There are also options for all-in-one solutions like solar generators that have everything you need in one unit.

Or you can make a DIY PV system using separate components.

Just be sure all the components are compatible with each other — and with your solar panels.  

Here are the minimum configurations for each type of residential PV system.

Grid-Tied

• Photovoltaic modules
• Solar inverter 
• Bidirectional or smart electricity meter
• Transfer switch (for integration with household wiring and circuit board)
• Cables and wiring
• Mounting hardware (for rigid solar panels)

Off-Grid

• Photovoltaic modules
• Solar charge controller
• Solar battery
• Solar inverter 
• Storage inverter (may be built into batteries or charge controller)
• Transfer switch (for integration with household wiring and circuit board)
• Cables and wiring
• Mounting hardware (for rigid solar panels)

Hybrid (Solar + Storage)

• Photovoltaic modules
• Solar charge controller
• Solar battery
• Solar inverter 
• Storage inverter (may be built into batteries or charge controller)
• Bidirectional or smart electricity meter
• Transfer switch (for integration with household wiring and circuit board)
• Transfer switch or Smart Home Panel (for integration with household wiring and circuit board)
• Cables and wiring
• Mounting hardware (for rigid solar panels)  

How Efficient Are Photovoltaic Systems?

The efficiency of photovoltaic systems — particularly those designed for residential use — has skyrocketed in recent years.

At the same time, the upfront investment required to purchase and install solar panels and a balance of system has plummeted.

There are numerous reasons for that.

• Technological innovation
• Increased demand
• State and federal solar tax credits

Decreased solar payback periods and improved electricity generation efficiency have dramatically increased return on investment.

As to the specific performance of different photovoltaic modules and solar power systems, there are numerous factors that determine overall efficiency, including:

• Type of photovoltaic cells and modules
• Solar panel efficiency
• Quality of manufacture
• On-grid, off-grid, or hybrid balance of system

It’s essential to understand that solar power isn’t a finite resource in the same way as fossil fuels are.

A best-in-class monocrystalline rigid solar panel, for example, boasts about 23% efficiency.

23% sounds low. 

But you must bear in mind that solar panel efficiency has a very specific meaning in photovoltaic systems.

PV module efficiency measures the percentage of available sunlight that gets converted into electricity under Standard Test Conditions.

Standard Test Conditions for Solar Panels

Condition Type	Standard Test Condition	Real-World Conditions
Solar Incident Angle	Always zero, irradiation beam always normal to the PV panel*	Variable, and depends on time, date, and site latitude. In the case of rooftop systems, roof orientation, and inclination govern system capacity.
Solar Irradiation	Always equal to 1000 Watts/m²*	Variable and depends on the time, date, and site latitude. Limited sunshine hours bound system capacity.
Ambient Temperature	Always 25°C*	Variable and depends on the time, date, weather condition, and site latitude. Higher ambient temperature degrades PV panel efficiency and reduces system output.
Air Mass Coefficient (AM)	Always equal to 1.5*	Variable and depends on the time, date, and site latitude. Higher AM with higher latitudes.
System Losses (e.g., Wiring, Inverter)	Always Zero*	Variable and depends on the design and location of PV panels, inverter, and grid meter.

*Cannot be achieved in real-world operation (Source: ResearchGate)

In addition to considering the efficiency of your photovoltaic modules, it’s essential to understand that overall efficiency will diminish along every step of the path from your solar panels to consumption.

Whether you opt for an all-in-one off-grid balance of system like a portable power station or a grid-tied or hybrid setup, optimizing performance requires using high-quality components — from inverters to cabling.

One significant advantage of a plug-and-play solar generator like EcoFlow DELTA Pro is that you don’t have to worry about cross-compatibility between components.

The inverter, charge controller, solar battery, and other parts are manufactured and assembled to work together seamlessly and at maximum efficiency.

The Applications of Photovoltaic Systems

Big or small, photovoltaic systems are designed to produce electricity.

Whether you need to keep your phone charged while camping or backup your entire home during a blackout, there’s a photovoltaic module and balance of system that’s right for you.

Here’s a brief rundown of the primary applications for modern photovoltaic systems.

Off-Grid Power

Portable off-grid power solutions like EcoFlow’s RIVER 2 Series solar generators are ideal for any application — like camping or RVing — where you need power to go.

In locations with unreliable access to on-grid electricity, EcoFlow Power Kits provide enough solar energy to power a tiny home.

Home Backup

The combination of more frequent extreme weather events, aging infrastructure, and electricity demand outstripping supply is leading to an increasing number of blackouts across the US. 

Not only are power outages happening more often, they often go on for longer than in the past.

If you’re looking for energy security and lower electricity bills, EcoFlow DELTA Pro Ultra provides whole home backup during outages of up to one month.

With a fully maxed out system you can add up to 42 x EcoFlow rigid solar panels to power your home off-grid indefinitely.

Unlike traditional grid-tied systems, EcoFlow DELTA Pro Ultra offers energy security during a blackout. 

It’s a hybrid PV system (solar + storage) that provides uninterrupted power in an outage and also connects to the grid. 

(Source: EIA)

Industrial and Utility-Scale Solar

The Department of Energy forecasts that renewable energy sources — primarily wind and solar PV — will produce more electricity in the US than coal and nuclear for the very first time.

Achieving net-zero carbon emissions by 2050 is an urgent priority for governments worldwide.

Thanks to rapidly improving technology, industrial and utility-scale solar is already having a positive impact on reducing the percentage of electricity produced by burning fossil fuels.  

Space-Based Solar

Long before anyone thought about greenhouse gases and climate change, NASA funded research into PV cells and solar power systems.

Not so much to produce electricity here on Earth but to facilitate space exploration.

NASA research led directly to innovations like solar-powered fridges and air conditioners.

(Source: energy.gov)

More recently, research into space-based solar power — electricity transmitted by laser or microwave solar satellites back to Earth — is being actively pursued by NASA and the Dept. of Energy.  

Frequently Asked Questions

Final Thoughts

By now, you should have a much clearer idea of how photovoltaic cells — and solar panels — work.

Of course, it’s not necessary to know the ins and outs of how PV cells generate electricity to enjoy the benefits of high-efficiency solar panels and a hybrid solar power system like EcoFlow DELTA Pro Ultra.

Whether you’re looking for portable off-grid power or the energy security of whole home backup, EcoFlow has a solution for you.