P-Type vs N-Type solar cells: What You Need to Know?

The history of solar cells is an interesting journey of scientific innovation and environmental significance, tracing back to the 19th century.

It was in 1839 when French physicist Alexandre Edmond Becquerel discovered the photovoltaic effect, the principle that underlies solar technology, by observing the generation of electricity when light hits certain materials.

In 1883, Charles Fritts created the first genuine solar cell by coating selenium with a thin layer of gold, converting sunlight into electricity with an efficiency of just 1%.

The breakthrough came in 1954 when researchers at Bell Labs developed the first practical silicon solar cell, achieving 6% efficiency, which brought the concept of solar power into the realm of practical application.

Since then, solar technology has evolved dramatically, with advances in materials and manufacturing processes leading to highly efficient and cost-effective solar panels that are now widely used for sustainable energy production worldwide.

The ongoing innovation in solar cells continues to play a crucial role in the global transition to renewable energy sources.

What is a semiconductor?

A semiconductor is a material that has electrical conductivity between that of a conductor, like copper, and an insulator, such as glass.

This unique property allows semiconductors to control electrical current, making them fundamental to modern electronics.

The most common semiconductor material is silicon, used to manufacture integrated circuits, transistors, and solar cells.

Silicon is used in making solar cells which are further connected to make solar panels.

These solar panels in turn absorb a good amount of sunlight and convert it into electricity which is enough to meet our various energy needs such as running our electrical appliances, powering EVs and much more.

Silicon, in its pure form, is a poor conductor of electricity.
It has equal electrons and holes, resulting in negligible net charge.

However, its electrical conductivity can be enhanced through doping.

What is Doping?

Doping in semiconductors is a critical process to enhance the electrical properties of semiconductor materials, such as silicon.

This process involves introducing small amounts of impurity atoms, known as dopants, into the semiconductor crystal to modify its electrical behavior.

There are two main types of doping: n-type and p-type.

N-type doping involves adding elements with extra electrons, such as phosphorus or arsenic, which increases the number of free electrons and enhances the material’s conductivity. P-type doping uses elements like boron or gallium, which have fewer electrons, creating “holes” or positive charge carriers. These doped semiconductors now have improved electrical conductivity and can be used in various applications such as solar cells.

P-type semiconductor

A P-type semiconductor is a type of semiconductor in which the majority of charge carriers are holes, which are created by the introduction of certain impurities into an intrinsic semiconductor material, typically silicon.

It involves adding (tri-valent) elements such as boron, aluminum, or gallium, which have fewer valence electrons than silicon. These elements create “holes,” or positive charge carriers, by accepting electrons from the silicon atoms. As a result, the semiconductor becomes positively charged, as these holes can move through the lattice structure, facilitating electrical conduction.

N-type semiconductor

An N-type semiconductor is a type of extrinsic semiconductor where the majority of charge carriers are electrons. This is achieved by doping a pure semiconductor, such as silicon or germanium, with donor impurities (pentavalent) that have more valence electrons than the semiconductor itself—typically elements like phosphorus or arsenic.

These extra electrons become free to move within the material, enhancing its electrical conductivity.

In an N-type semiconductor, electrons are the majority carriers, while holes (the absence of an electron) are the minority carriers.

What is a Solar Cell?

A solar cell, also known as a photovoltaic cell, is a device that converts sunlight directly into electricity through the photovoltaic effect.

These cells are typically made from semiconductor materials, such as silicon, which absorb photons from sunlight and release electrons.

The movement of these electrons through the material generates an electric current, which can be harnessed for power.

Solar cells are the fundamental building blocks of solar panels, which are used in a variety of applications from powering small electronic devices to providing electricity for homes and businesses.

As a renewable energy source, solar cells play a crucial role in reducing reliance on fossil fuels and decreasing greenhouse gas emissions, contributing to a more sustainable energy future.

The formation of a Solar cell

When the P-type and N-type are joined together we get a solar cell.

An Electric Field is created

An electric field is created when the P-type and the N-type semiconductors are joined together.

The direction of this electric field is from P-type region to N-type region.

The electric field created starts pulling electrons in the N-type towards the holes in the P-type region.

And thus the movement of the electrons gets started. An electron from the N-type crosses the interface (leaving a hole in the N-type region) and reaches the P-type region and combines with the hole.

And becomes neutral.

Similarly, the hole from the P-type enters into the N-type, combines with an electron, and becomes neutral.

The place that the hole has left becomes an ionized acceptor (negative charge).

This combing process starts both ways, the positive charges start developing in the N-region and the negative charges in the P-region.

In short, an opposite electric field to the original one starts developing. This process keeps on going until the strength of this opposite field becomes equal to the original field.

A PN Junction is formed

When the opposite field balances the original electric field, the combing process stops.

There develops a barrier between which is called a depletion region or PN junction. A PN junction in a solar cell is a crucial component that enables the conversion of sunlight into electricity through the photovoltaic effect.

This depletion region separates the electrons from the hole.

To combine, the electrons or holes need energy to cross the PN junction.

Here are the photos of the light to provide the energy

As light strikes the solar cell, it energizes electrons, causing them to move across the PN junction and creating a flow of electric current.

This current can then be harnessed to power electrical devices or feed into the electrical grid. The solar cells are further classified into P-type and N-type solar cells.

The structure and the type of Solar cells

A solar cell is made by combining the layers of the P-type and the N-type semiconductors.

If we make one layer thicker than another, we get a solar cell with the characteristics of the thicker layer.

The variation of thickness in which wafers are placed is what makes the solar cell to be an N-type solar cell or a P-type solar cell. The thicker layer is called the bulk region and the thin layer, the emitter, which is placed on top of the bulk region.

P-type solar cell

P-type solar panels are the most commonly sold and popular type of modules in the market.

A P-type solar cell is manufactured when a thick layer of P-type semiconductor (with a doping density of 1016 cm⁻³ and a thickness of 200µm is pasted with a thin emitter layer of N-type semiconductor (doping density of 1019 cm⁻³ and a thickness of 0.5μm).

N-type solar cell

N-type solar panels are an alternative with rising popularity due to their several advantages over the P-type solar panel. The N-type solar cell has N-type as a bulk c-Si of thickness of 200 µm and a doping density of 1016 cm⁻³ with a doping density of 1019 cm⁻³.

Benefits of N-type solar cells

N-type solar panels offer several advantages over their P-type counterparts, primarily due to their superior efficiency and longevity.

Immune to LID effect

One of the key benefits is their higher resistance to the phenomenon known as light-induced degradation (LID), which can significantly reduce the performance of P-type panels over time.

This resistance ensures that N-type panels maintain their efficiency levels longer, providing a more reliable energy output. Moreover, N-type solar cells exhibit better performance in low-light conditions, enhancing their energy production during cloudy days or in regions with less consistent sunlight.

Lower Temperature Coefficient of Power

Additionally, N-type panels generally have a lower temperature coefficient, meaning their efficiency is less affected by high temperatures compared to P-type panels. This makes N-type solar panels an attractive option for installations in hot climates, where maintaining high efficiency is crucial for optimizing energy yields.

Overall, while N-type panels may come with a higher initial cost, their long-term efficiency and durability can offer greater cost-effectiveness and sustainability.

Then why P-type dominate?

Despite numerous benefits of N-type over P-type solar panels, the P-type dominate the global market.

The reason lies below:

When photovoltaics were been researched back in the 50s, manufacturing costs were extremely high, but this was not a limitation for space applications requiring a viable power source in space, where there were no other ways to generate power for a spacecraft like the Vanguard 1, the first satellite featuring solar panels in space.

As space applications became a priority, P-type solar panels featuring a high resistance to radiation and degradation in space, became an interest.

A large number of resources were used in space photovoltaic application technology back in the 50s.

The solar industry just kept the momentum going, using this well-researched technology by lowering prices to produce better P-type solar panels for terrestrial applications.

This is why this technology has become the norm for the industry.

Market trends P-type vs. N-type

Summary

The solar market is witnessing a shift as N-type technology gains traction, driven by its performance advantages and ongoing innovations. While P-type cells remain the dominant choice due to cost-effectiveness, N-type cells are becoming increasingly viable for high-efficiency applications. The trend indicates a more diverse market where both technologies can coexist, catering to different consumer needs and preferences.

Recently, the solar panel manufacturing company Canadian Solar announced it had set a world record of 22.28% conversion efficiency for its p-type multi-crystalline P5 cell. At the same time, another company, Trina Solar, announced they had also set a 24.58% efficiency record for its n-type mono-crystalline silicon (c-Si) i-TOPCon solar cell.

Conversion efficiency has to do with the ability of the solar cells to convert the sunlight hitting them into energy.

While both companies are reaching higher levels of efficiency, they are doing it using different types of solar cells. Canadian Solar is focusing its research on p-type cells; Trina Solar on n-type.