PERC vs TOPCon vs HJT Solar Cells
PERC, TOPCon and HJT are three solar cell architectures, not three brands. They sit inside the modules you already see on the major panel brands. The headline efficiency number matters less than the temperature coefficient and low-light response, which is why the choice plays out differently in Ireland than in sunnier markets. For the wider picture of panel families, see our guide to solar panel types.
Quick Answer
PERC is the older, cheaper P-type cell (around 20 to 21% module efficiency). TOPCon and HJT are newer N-type cells (around 22 to 23%+) with better low-light performance, lower temperature losses and slower degradation. TOPCon is now the mainstream choice for Irish grant-tier installs and offers the best balance of price and performance. HJT is a premium option with the best temperature behaviour. In Ireland's cloudy, diffuse light, the low temperature coefficient of N-type cells usually matters more than peak rated output.
N-type vs P-type: what actually differs
Every silicon solar cell is "doped" to create an electrical field. P-type cells use a boron-doped silicon base and have dominated the market for two decades. N-type cells use a phosphorus-doped base, which avoids the boron-oxygen defect that causes the light-induced degradation seen in P-type panels.
PERC (Passivated Emitter Rear Cell) is a P-type design that adds a reflective passivation layer on the rear of the cell to recapture light. TOPCon (Tunnel Oxide Passivated Contact) and HJT (Heterojunction Technology) are both N-type designs that passivate the cell more completely, so they lose less energy as heat and respond better to weak, scattered light.
The three architectures in brief
- PERC – mature P-type, cheapest, slightly higher degradation, around 20 to 21% module efficiency.
- TOPCon – N-type with a thin tunnel oxide layer, now mainstream, around 22 to 23%+, bifacial-friendly.
- HJT – N-type with amorphous silicon layers, premium, around 22 to 23%+, best temperature behaviour.
- IBC / back-contact – a separate high-efficiency family (Aiko, Maxeon, LONGi HPBC), not covered in depth here.
PERC vs TOPCon vs HJT side by side
The headline efficiency figures are close enough that they rarely decide the outcome on a typical Irish roof. The temperature coefficient (how much output is lost as the panel heats up) and low-light response tend to matter more across a full year.
| Attribute | PERC | TOPCon | HJT |
|---|---|---|---|
| Cell type | P-type | N-type | N-type |
| Module efficiency | ~20 to 21% | ~22 to 23%+ | ~22 to 23%+ |
| Temperature coefficient (Pmax) | ~−0.34%/°C | ~−0.29%/°C | ~−0.24 to −0.26%/°C |
| Low-light performance | Baseline | Better | Excellent |
| Degradation | Higher (light-induced) | Lower | Lower |
| Relative cost | Cheapest | Moderate | Premium |
| Bifacial-friendly | Limited | Yes | Yes |
| Typical examples | Older budget modules | Jinko Tiger Neo, JA DeepBlue 4.0, Trina Vertex S+ | REC Alpha, Panasonic legacy |
Indicative figures for current residential modules. Exact values vary by manufacturer and product generation – always check the specific datasheet for the SKU your installer quotes.
Why N-type degrades more slowly
P-type PERC cells suffer light-induced degradation in their first hours of exposure, caused by the boron-oxygen complex in the silicon. N-type TOPCon and HJT cells avoid this defect, so they start closer to their rated output and lose capacity more slowly over their lifetime.
In practice this shows up in the warranty. N-type modules typically guarantee a higher percentage of original output at year 25 or 30 than equivalent PERC modules. Over a 25-year Irish system life, the slower degradation of N-type quietly compounds into more total generation, even where the day-one efficiency gap is small.
What this means for output
- A lower temperature coefficient means less output lost on warm, bright summer afternoons when the panel surface heats up.
- Better low-light response means more harvest under the diffuse, overcast skies that dominate the Irish year.
- Slower degradation means the array holds more of its rated output into later decades.
What matters in Ireland's climate
Ireland gets a large share of its annual solar energy from diffuse, scattered light under cloud rather than direct beam sunshine. That changes the priorities. A panel's peak rating under standard test conditions (bright, 25°C, perpendicular sun) is less representative here than its behaviour in weak light and across a range of temperatures.
This is why the low temperature coefficient and strong low-light response of N-type TOPCon and HJT cells are genuinely useful in Irish conditions, often more so than a fraction of a percent in peak STC efficiency. Most grant-tier Irish installs are now built around TOPCon modules for exactly this reason.
The Irish grant and tariff picture
- The SEAI Solar Electricity Grant covers the PV portion up to €1,800 and applies regardless of whether the panel uses PERC, TOPCon or HJT cells, provided it is installed by an SEAI-registered contractor.
- A 0% VAT rate applies to the supply and installation of domestic solar panels, so the headline price difference between cell types is the panel cost itself, not tax.
- The Clean Export Guarantee (CEG) pays you for surplus electricity exported to the grid, so the extra annual yield from a more efficient N-type array has a direct value.
- Your installer registers the system with ESB Networks via the NC6 connection process before export payments can begin.
Because the grant value and VAT treatment are identical across cell types, the decision comes down to the panel price premium versus the extra lifetime generation it buys. See the full SEAI grant guide for current grant amounts and eligibility.
Which cell technology should you choose?
For most Irish homes the practical choice is between TOPCon and HJT, with PERC now largely confined to older or budget-driven quotes. Here is how the three break down by situation.
PERC
Lowest upfront price. Reasonable if budget is the deciding factor and the quote is otherwise strong, but you accept higher degradation and weaker low-light output. Increasingly the exception rather than the default.
TOPCon
The sensible mainstream default for Irish grant-tier installs. Strong efficiency, good low-light behaviour, low degradation and a modest premium over PERC. Widely stocked across Jinko, JA Solar and Trina ranges.
HJT
The premium pick. Best temperature coefficient and excellent low-light response, at the highest panel cost. Worth considering where roof space is tight or you want the best long-term yield and are willing to pay for it.
Frequently Asked Questions About PERC, TOPCon and HJT
What is the difference between PERC, TOPCon and HJT?
PERC is a mature P-type cell with around 20 to 21% module efficiency and the lowest cost. TOPCon and HJT are newer N-type cells with around 22 to 23%+ efficiency, better low-light performance, lower temperature losses and slower degradation. TOPCon is now mainstream while HJT is a premium option with the best temperature behaviour.
Is N-type better than P-type for solar panels?
N-type cells (TOPCon and HJT) generally outperform P-type PERC on efficiency, temperature coefficient, low-light response and degradation, because they avoid the boron-oxygen defect that causes light-induced degradation in P-type silicon. P-type PERC remains cheaper, which is its main remaining advantage.
Which solar cell technology is best for Ireland?
For Ireland's cloudy, diffuse-light climate, TOPCon offers the best balance of price and performance and is now the default for most grant-tier installs. HJT is a premium choice with the lowest temperature coefficient and excellent low-light response. In Irish conditions the low temperature coefficient and low-light response of N-type cells usually matter more than peak rated efficiency.
Do PERC, TOPCon and HJT panels all qualify for the SEAI grant?
Yes. The SEAI Solar Electricity Grant covers the PV portion up to 1,800 euro and applies to any eligible solar PV module installed by an SEAI-registered contractor, regardless of whether it uses PERC, TOPCon or HJT cells. The 0% VAT rate on domestic solar also applies across all three.
Is HJT worth the extra cost over TOPCon?
HJT typically has a slightly lower temperature coefficient (around minus 0.24 to minus 0.26 percent per degree C versus around minus 0.29 for TOPCon) and excellent low-light response, but it costs more. For most Irish homes TOPCon delivers most of the benefit at a lower price. HJT makes more sense where roof space is limited or you want the best long-term yield and accept the premium.
Related Guides
Sources
- NREL: Best research-cell efficiency and cell technology, nrel.gov
- Jinko Solar: Tiger Neo N-type TOPCon datasheet, jinkosolar.com
- SEAI: Solar Electricity Grant, seai.ie
Last updated: June 2026
Fact-checked by John Rooney, Solar Energy Editor. Editorial policy
John Rooney is the founder of Solar Info and has been covering the Irish solar energy market since 2023. He fact-checks all content against official SEAI data and maintains relationships with SEAI-registered installers across Ireland.
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