N-Type Vs. P-Type Solar Panels: A Comprehensive Guide
By Aniket Bhor on in How Solar Power Works
The solar cell is one of the most impressive engineering marvels of our time. There is a lot going on in less than half a millimetre of its thickness. What looks like a blue-black block on the surface, is actually made of multiple materials carefully designed and assembled together - everything sandwiched into a width equivalent to just a few human hairs.
One of the most hyped developments in the solar power sector is the advent of n-type solar panels.
Many people wonder what makes n-type so special, and if they are really worth the hype. The best way to figure it out is to understand what n-type exactly means, and how it affects the panel performance. N-type, or p-type, denotes what the bulk of a solar cell is doped with. But to understand how that affects the panel efficiency, let us first take a quick look at how a typical (p-type) solar cell works.
Working Of A Solar Cell
A typical solar cell is made of crystalline silicon, a fascinating semiconductor that is neither a metal nor a non-metal, neither an electrical conductor nor really an insulator. It is somewhere in between these classes, and that’s what makes it special, making it useful in nearly every piece of electronics that exists on and around this planet.
Going back to the solar cell, it is made of two main layers of silicon. The bottom layer is doped (doping in this context means introducing a certain impurity) with boron (remember, this is for a traditional, p-type cell). Boron has one electron less than silicon, and doping the silicon wafer with it creates an electron deficiency in the bottom layer, also known as the p-type layer, thanks to its positive charge. We call the lack of electrons ‘holes’.
Schematic of working of solar cell
The top layer is doped with phosphorous, which has one extra electron, creating a net negative charge, which is why we call it the n-type top-layer (forget about n-type panels for a while). So now we have a negatively charged top layer and a positively charged bottom layer.
Naturally, electrons and holes from both layers now try to combine, causing what is called a ‘depletion layer’ in between - a sort of traffic jam when nobody is following lanes.
However, when we connect these layers in an external circuit, and subject the cell to sunlight, photons (light particles) from the sunlight knock off some electrons from the top layer, somewhat like a bowling ball knocking bowling pins. These electrons then travel through the junction, and through the external circuit, allowing current to flow. And that is how sunlight generates power using a solar panel.
Now we can jump to n-type solar panels and understand them clearly.
What Are N-Type Solar Panels?
We saw that in conventional, p-type panels, the bottom/base layer, which forms the bulk of a cell, is doped with boron to create a positively charged layer. An n-type cell does the opposite. N-type cells have a bottom layer doped with phosphorous which creates a negatively charged layer.
In the case of p-type cells, the boron reacts with any oxygen in the silicon. This causes the boron-oxygen defect, which is the presence of traps that stop or slow down electron transfer, therefore reducing power generation.
This effect is more pronounced when light first hits the cell. In real world terms, this means the solar panel generates much less power during the early hours of the day. This effect is known as ‘Light Induced Degradation’ (LID).
LID affects all p-type cells. Over the lifetime of a solar panel, LID prevents hundreds of kWh of energy from being generated. With n-type panels, the base layer has no oxygen defects, since phosphorus just shrugs and ignores any oxygen present in the silicon, and the layer does its job without any obstacles, resulting in a notably higher efficiency.
In addition to being immune to LID, n-type panels have also displayed better resistance to high temperatures. Most panels degrade (lose efficiency) when subject to high temperatures, generating less energy over their lifetime than they would in an ideal, not-too-hot setting. But n-type panels’ resistance to thermal degradation makes them last longer, and churn out more power.
Thermal degradation in p-type vs n-type (source: Luxor Solar)
P-type Vs. N-type Solar Panels - Gauging the Market
Interestingly, the first solar cell developed by Bell Labs in 1954 was an n-type cell. However, for many years, solar was used exclusively for space applications, owing to its then extravagant cost. And it turned out that p-type cells were more resistant to space radiation and degradation.
For many years, the solar industry developed in the general ‘p-type’ direction. When the time for terrestrial solar power applications came, it was easier to just pick the existing p-type technology and run with it. This is how we came to have a dominance of p-type solar panels, which lasted for a remarkably long time - about four decades!
But as the competition became more and more fierce, manufacturers looked to reinvent the technology, and now n-type solar is making a dramatic return.
The difference is evident - n-type panels today claim extraordinary efficiencies, leaving p-type to bite the dust. For instance, JA solar recently launched an n-type module which TUV Nord tested and certified to have 3.9% higher efficiency than p-type panels.
More recently, Trina Solar’s Vertex n-type module set a new efficiency record, with an incredible 24.24% efficiency. For an industry that recently crossed the 20% barrier, this is huge. There are many such examples, and nearly every major panel manufacturer now has at least one n-type offering, promising higher efficiencies than conventional, p-type panels.
On the pricing side, the process to manufacture n-type panels (and therefore the cost) is not vastly different from that of p-type panels. However, being relatively new, n-type panels won’t yet cost the same as p-type. Nevertheless, the higher efficiency of n-type modules often justifies their slightly higher cost.
Wrapping Up
The technical difference between p-type and n-type solar panels can be simplified and stated as a reversal of layers, wherein the n-type layer becomes the bulk (base layer) instead of p-type, hence its name.
However, quite delightfully, this simple change in design ups the game in terms of efficiency as well as longevity. Without having to overhaul their entire machinery, manufacturers are able to produce n-type panels that promise a significant increase in total energy generation.
N-type cells are also a great fit for bifacial solar panels, which already come with the assurance of more power. The only drawback that n-type panels currently have is their higher cost, which in many cases does not become a deal-breaker.
All in all, looking at the trajectory of n-type panels, we believe they might soon replace their p-type siblings almost entirely. As for when that happens, we’ll have to wait and watch.