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N-Type vs P-Type Solar Cells: Understanding the Key Differences

There are two main types of solar cells used in photovoltaic solar panels – N-type and P-type. N-type solar cells are made from N-type silicon, while P-type solar cells use P-type silicon. While both generate electricity when exposed to sunlight, N-type and P-type solar cells have some key differences in how they are designed and perform.

In this article, we’ll take a deep dive into understanding the differences between N-type and P-type solar cells. We’ll explore how each type of solar cell works to convert sunlight into electricity, why P-type cells tend to be thicker, and the pros and cons of each type. We’ll also provide tips on how to identify whether your own solar panels use N-type or P-type solar cells.

Definition of N-type and P-type Cells

N-type and P-type refer to the two main types of semiconductor materials used in solar cells. The key difference between them lies in how they are doped, or intentionally contaminated, with other elements to give them desired electrical properties.

N-type semiconductors are doped with elements that have more valence electrons, like phosphorus or arsenic. This gives the material an excess of free electrons. P-type semiconductors are doped with elements that have fewer valence electrons, like boron or gallium. This gives the material a deficit of electrons, resulting in more “holes” where electrons could exist.

The diagram below illustrates the structure of N-type and P-type solar cells:

In an N-type cell, electrons are the majority charge carrier. They flow from the N-type layer on top to the metal contact, generating electricity. In a P-type cell, the absence of electrons (holes) are the majority charge carrier. They flow from the P-type base to the N-type emitter.

When combined into a PN junction, the N-type and P-type layers balance each other out. The N-type layer donates electrons to fill holes in the P-type layer. This interaction at the junction between them enables electricity generation.

How N-type and P-type Cells Generate Electricity

N-type and P-type solar cells generate electricity through the photovoltaic effect. This process relies on the semiconductor properties of silicon, which is the main material used in solar cells.

In an N-type cell, phosphorus or arsenic atoms are added to the silicon, providing extra electrons. These electrons can move freely through the material. When sunlight hits the cell, the photons energize the free electrons, causing them to flow toward the front surface and produce electricity.

P-type cells have boron atoms added, resulting in a lack of electrons or “holes” in the atomic structure. The boron accepts electrons from the adjacent N-type layer, forming the PN junction where power is produced. When sunlight enters, electrons flow from the P-type side to fill holes on the N-type side, generating an electric current (How Photovoltaic Cells Generate Electricity).

This process occurs in both cell types, but with reversed electron flows due to their opposing semiconductor doping. The key difference is that free electrons move through the N-type layer, while electron holes move in the P-type layer.

Why P-type Cells Are Thicker

P-type solar cells typically have a thicker base layer than N-type cells. This is because the P-type layer is the main absorber layer that converts sunlight into electricity. In order to absorb more sunlight, the P-type layer needs to be thicker with a greater volume of semiconductor material.

On the other hand, N-type solar cells have a much thinner emitter layer. The main purpose of the N-type emitter is collecting electrons generated in the P-type base. The emitter does not need to be very thick to serve this purpose. Additionally, a thinner N-type layer helps reduce recombination losses, which improves cell efficiency.

Therefore, the optimal solar cell design has a thicker P-type base layer to absorb more sunlight paired with a thinner N-type emitter layer to reduce losses. This asymmetry is why P-type solar cells end up being thicker overall compared to N-type cells. Source

Efficiency Differences

N-type solar cells tend to have higher efficiency than P-type cells. According to research from Chint Global, N-type panels have an efficiency of around 25.7%, compared to 23.6% for P-type panels.

There are a few reasons N-type cells tend to be more efficient:

  • The thinner emitter layer in N-type cells reduces recombination losses, allowing more current to be collected.
  • N-type silicon has higher electron mobility, enabling electrons to move through the cell more quickly.
  • N-type cells are less prone to light-induced degradation, maintaining higher efficiencies over time.

P-type cell efficiency is limited by the thicker base layer which absorbs more sunlight but also enables more recombination. However, improvements in rear passivation and advanced cell architectures are helping increase P-type cell efficiency.

Temperature Performance

One key difference between N-type and P-type solar cells is how their efficiency is impacted by temperature. Solar cells become less efficient as the temperature increases. The rate of efficiency decline is measured by the temperature coefficient.

N-type solar cells have a lower temperature coefficient, generally around -0.30%/°C, compared to P-type cells which are around -0.50%/°C (Source). This means N-type cells maintain higher efficiency in hot conditions.

For example, at a temperature of 60°C a P-type panel may degrade from 20% to 18% efficiency, while an N-type panel will only drop from 21% to 19.5%. This performance advantage makes N-type solar panels well-suited for hot climates.

Cost Differences

One of the key differences between P-type and N-type solar cells is the manufacturing cost. P-type solar cells tend to be less expensive to produce than N-type cells.

According to research, P-type solar cells cost around 0.081 euros/W to manufacture, while N-type cells cost approximately 0.088 euros/W (https://www.maysunsolar.com/n-type-vs-p-type-solar-cells-which-one-is-better/). The more straightforward production process of P-type cells makes them cheaper to fabricate on a large scale.

The additional processing steps required for N-type cells, such as creating the thin emitter layer, increase production costs. The specialized equipment needed also adds to the expense. While N-type cell technology is improving, it still lags behind P-type in terms of manufacturability.

So for homeowners and businesses looking purely at upfront system costs, P-type solar panels tend to be the more budget-friendly option. However, the increased efficiency and performance of N-type panels can lead to greater long-term energy savings, offsetting the higher initial investment over time.

Manufacturing and Availability

P-type solar cells tend to be easier to manufacture than N-type cells. The manufacturing process for P-type cells is well-established and has been optimized over decades of solar production. This makes P-type cells cheaper to produce at scale compared to newer N-type technology.

According to Solar Magazine, the extra steps required in manufacturing N-type cells leads to higher production costs. The availability of N-type cells is also lower, as fewer manufacturers have transitioned to producing this newer technology.

P-type cells have dominated the solar industry since its inception. As a result, they are widely available from most panel manufacturers. N-type solar panels are harder to source and generally only produced by a handful of manufacturers that have invested in the newer production methods.

Lifespan and Degradation

One key difference between N-type and P-type solar cells is their degradation rates over time. P-type solar cells tend to degrade faster than N-type cells. This is primarily due to light-induced degradation (LID) in P-type cells.

LID occurs when sunlight exposure causes defects in the crystal structure of the silicon used in P-type cells. These defects reduce the cell’s power output over time. According to research from the National Renewable Energy Laboratory (1), LID can cause up to a 3% power loss in the first few hours of sunlight exposure for P-type cells. In contrast, N-type solar cells are not subject to LID.

Another degradation mechanism that impacts P-type cells more than N-type is potential-induced degradation (PID). PID happens when stray currents in the panel cause ion mobility and increase leakage current. This also lowers power output over time. N-type solar cells have been shown to be more resistant to PID (2).

Due to their immunity to LID and greater PID resistance, N-type solar panels tend to have a longer useful lifespan and lose power output at a slower rate than P-type panels.

Identifying Your Solar Panels

There are a few ways to determine if your solar panels are N-type or P-type:

  • Check the spec sheet or documentation that came with your solar panels. The cell type should be listed there.
  • Look at the model number or name of the panels. P-type panels will often have a “P” in the name, while N-type may have an “N.”
  • Contact the manufacturer and ask them directly about the cell type used in that model.
  • Measure the thickness of the cells – P-type cells tend to be thicker than N-type.

It’s important to identify the cell type before combining panels from different manufacturers or batches on the same string. Mixing N-type and P-type panels on the same string can lead to system losses and mismatches.

Checking the spec sheets or contacting the manufacturer is the best way to definitively tell if your panels use N-type or P-type cells. This ensures optimal performance when designing your solar array.