Quick answer
HJT Solar Panel An HJT solar panel (heterojunction) is a panel built from cells made of an n-type crystalline silicon wafer coated on both faces with ultra-thin layers of amorphous silicon, joining two different forms of silicon in one cell.
The coatings passivate the wafer surfaces very well, which gives HJT panels some of the smallest output losses in heat of any silicon technology: −0.24%/°C on one current residential data sheet.
Quick facts
The key facts about hjt solar panel, with sources:
- Also called
- Silicon heterojunction (SHJ); HIT was an early trade name 3
- Module efficiency (2025 survey)
- 23.5%, level with TOPCon 1
- Example warranty
- 98% in year 1, 0.25% a year after, 92% in year 25 2
- Bifaciality
- Highest of the silicon cell types; outlook above 90% 1
- Share
- About 5% in the roadmap’s 2025 silver estimate 1
Key takeaways
- An HJT cell coats a crystal silicon wafer with very thin films of non-crystal silicon on both sides.
- Those films stop electrons being lost at the surface, which keeps the voltage high.
- HJT panels lose less power in heat than most silicon panels: −0.24%/°C on the REC sheet.
- Average efficiency is the same as TOPCon. The edge is heat behavior and two-sided output.
- Fewer makers build HJT, so check warranty terms and installer support.
What "heterojunction" means
A junction is where two layers meet inside a solar cell. That meeting point is what pushes freed electrons out as current. "Hetero" means different. So a heterojunction is a meeting of two different materials.
In an HJT cell the two materials are both silicon, in different forms. One is crystalline silicon, the neat, ordered wafer used in most panels. The other is amorphous silicon, which has no ordered pattern and is laid down as a film only nanometres thick.
Fraunhofer ISE researchers cite the HIT cell as "a famous example" of this design. They note the amorphous layer "effectively suppresses recombination", meaning it stops freed electrons being lost at the surface and at the metal contacts.
Sources: [3]
The layer stack, front to back
- Transparent conductive oxide → thin doped amorphous silicon → thin undoped (intrinsic) amorphous silicon → n-type crystalline silicon wafer → thin intrinsic amorphous silicon → thin doped amorphous silicon → transparent conductive oxide
How that sandwich cuts heat losses
The undoped film is the key part. It covers the wafer surface so fully that very few freed electrons are lost there. That keeps the cell’s voltage high.
Heat mainly hurts a panel through its voltage. The REC Alpha Pure-RX sheet shows this: voltage falls 0.24% per degree, while current actually rises 0.04% per degree. Power ends up falling 0.24% per degree, one of the lowest figures in silicon. See temperature coefficient.
The cell is the same on both faces, so both sides catch light. ITRPV reports heterojunction modules have the highest bifaciality of the cell types it tracks.
There is a manufacturing catch. Fraunhofer ISE notes the amorphous layers cannot take high heat, so the conductive coating and metal must be added at low temperature. That needs dedicated production lines.
Types of heterojunction products
| Type | What it is | Where you see it |
|---|---|---|
| Monofacial HJT | HJT cells behind a solid backsheet | Home roofs; the REC Alpha Pure-RX uses bifacial cells this way 2 |
| Bifacial HJT | HJT cells behind glass on both faces | Ground mounts, carports, solar farms |
| Heterojunction back contact (HBC) | HJT layers with all contacts on the back | Research and premium products; record research cell 27.1% (LONGi) |
Example: one HJT panel, line by line
| Data sheet line (REC Alpha Pure-RX, US) | Value | What it means for you |
|---|---|---|
| Cell type | 88 half-cut bifacial REC heterojunction cells | HJT cells; the back is a backsheet, so it is sold as one-sided |
| Power range | 450–470 W | Nameplate power at test conditions |
| Panel efficiency | 21.6%–22.6% | Watts per square metre of panel |
| Temp. coefficients | Pmax −0.24%/°C, Voc −0.24%/°C, Isc +0.04%/°C | Low power loss in heat |
| Annual degradation (warranty) | 0.25%; 92% power in year 25 | Floor for a warranty claim |
| Certifications | IEC 61215:2021, IEC 61730:2023, UL 61730 | Tested for performance and safety |
| Hail test | 35 mm hailstones (IEC 61215:2021) | Passed the standard hail test |
| Weight | 22.7 kg (50.0 lb) | Check roof load |
Sources: [2]
Example: one hot afternoon, two coefficients
An illustration, not a production forecast. Take two 400 W panels whose cells reach 65°C, 40°C above the 25°C rating temperature. One uses the HJT coefficient from the REC sheet, the other the mono PERC coefficient from the Canadian Solar HiKu6 sheet.
| Panel coefficient | Loss at 65°C | Output |
|---|---|---|
| −0.24%/°C (HJT) 2 | 40 × 0.24% = 9.6% | about 362 W |
| −0.34%/°C (PERC) 4 | 40 × 0.34% = 13.6% | about 346 W |
A 16 W gap per panel at that moment. It narrows on cool days and disappears at 25°C. Over a year the difference depends on how many hours your panels spend hot, which is why it matters more in the Southeast than in cooler places.
Where HJT panels are used
HJT is a smaller slice of the market than TOPCon. ITRPV’s 2025 silver estimate assumes about a 5% share.
You will see it on premium home roofs, where its low heat loss and long warranties appeal. You will also see bifacial HJT on ground mounts and carports.
On a data sheet, look for "heterojunction", "HJT", "SHJ" or "HIT" in the cell line.
Sources: [1]
Benefits and limits of HJT
Benefits
Limits to weigh
Warranty fine print matters. On the REC sheet, the longer product and labor terms apply only when an REC-certified installer fits the panels; the basic product warranty is 20 years. Ask which terms apply to your quote.
Supply matters too. With fewer makers, matching a panel years later may be harder. Keep the data sheet with your records.
Sources: [2]
What drives the cost of HJT
HyreSolar does not publish panel prices. Inside the panel, silver and dedicated production lines push HJT cost up. On a quote, brand and warranty length move the price more.
The value case is energy. If your panels spend many hours hot, the lower heat loss adds kWh each summer. Ask for a yearly kWh estimate for each panel option and compare on cost per watt and cost per kWh.
The federal 25D homeowner credit ended for systems placed in service after 31 December 2025, the IRS says.
How HJT panels are installed
The steps match any silicon panel. A licensed installer and electrician do the work.
- The installer reviews your roof, shade and power use.
- They check if they are certified by the maker, since some warranties depend on it.
- They confirm panel voltage fits the inverter; HJT panels can run high voltage, 65.6 V open-circuit on the REC 450 W 2.
- They apply for permits and utility interconnection.
- Crews install the system and an inspector checks it.
- The utility grants permission to operate.
Caring for HJT panels
Care is the same as for any panel. Watch monitoring and compare months year to year. Keep heavy dirt off the glass; see our cleaning guide.
Use the warranty as your yardstick. On the REC sheet, output should stay at or above 92% in year 25. Our degradation guide shows how to check.
Warning signs and when to call a pro
Call a licensed installer or electrician for any of these. Do not touch the wiring.
- Output below the warranty curve for the panel’s age.
- One panel or string far below the others.
- Cracked glass, hail dents or burn marks.
- Inverter faults that keep returning.
Safety rule
Each panel can hold more than 60 volts in daylight. Only a licensed pro should work on the system.
Standards and rules that apply
Product listing. UL says the NEC, IBC and IRC require PV products on or near buildings to be certified by a Nationally Recognized Testing Laboratory. The REC sheet lists IEC 61215:2021 for performance, and IEC 61730:2023 and UL 61730 for safety.
Fire rating. The same sheet lists UL 61730 Fire Type 2. Roof fire ratings depend on the panel and racking together, so ask your installer.
Local codes. Your city or county enforces its adopted code editions. In South Carolina, the SC Building Codes Council lists the 2021 codes as in force.
HJT vs TOPCon vs PERC
| HJT | TOPCon | PERC | |
|---|---|---|---|
| Module efficiency, ITRPV 2025 | 23.5% | 23.5% | 21.7% |
| Example temp. coefficient | −0.24%/°C 2 | −0.29%/°C 5 | −0.34%/°C 4 |
| Bifaciality outlook | Above 90% | Up to 85% | Up to 73% |
| Silver per watt, 2025 | 11.9 mg | 10.5 mg | 8.9 mg |
| Share in ITRPV’s silver estimate | 5% | 75% | 15% |
Sources: [1]
Misconceptions
- Myth HJT is a thin-film panel.
- Reality It uses thin films, but the core is a normal crystalline wafer. It is a silicon panel, not thin film.
- Myth HJT is always more efficient than TOPCon.
- Reality ITRPV puts both at 23.5% on average. HJT’s edge is heat loss and bifaciality.
- Myth Panels lose power in heat because current drops.
- Reality Voltage drops. On the REC sheet current rises slightly with heat while voltage falls 2.
HJT in SC, GA and VA
Long, hot summers across SC, GA and VA are where a low temperature coefficient pays most. State rules do not pick a cell type. Georgia Power caps residential renewable systems at 10 kW, so more kWh from each kW can matter there 11.
Virginia allows residential net metering up to 25 kW on investor-owned utilities 12. South Carolina customers who applied after 1 June 2021 use a Solar Choice tariff under Act 62 10.
When to ask for HJT
- Your roof gets long hours of hot sun.
- You plan a raised ground mount or carport where both sides catch light; see bifacial panels.
- You want a low warranted yearly loss and can confirm the installer qualifies for the full warranty.
- Next step: ask for yearly kWh estimates for HJT and TOPCon options and compare cost per kWh.
Next steps
- Solar savings calculatorSee how production changes payback
- Solar panel efficiency comparedData-sheet numbers explained
Questions about hjt solar panel
Is HJT better than TOPCon?
Not on average efficiency: ITRPV puts both at 23.5% for 2025 modules. HJT usually wins on temperature coefficient and bifaciality. TOPCon wins on availability, with far more makers and models. In a hot climate, HJT’s lower heat loss can tip the balance.
Are heterojunction panels good in hot climates?
Yes, they are among the best silicon options. The REC Alpha Pure-RX lists −0.24%/°C, so it loses less power per degree than PERC at −0.34%/°C or most TOPCon panels at about −0.29 to −0.30%/°C. The gain shows on long, hot afternoons.
What is the difference between HJT and HIT?
HIT (heterojunction with intrinsic thin layer) was an early trade name for the same cell structure. HJT and SHJ are the generic terms used today. Fraunhofer ISE researchers describe HIT as a famous example of the heterojunction approach.
Are HJT panels monocrystalline?
Yes. The core of the cell is an n-type monocrystalline wafer. The amorphous silicon films on each side are only nanometres thick. So HJT is a silicon panel, not a thin-film one.
How long do HJT panels last?
The REC Alpha Pure-RX warrants 98% output in year one, 0.25% loss a year after, and 92% in year 25. DOE cites a Berkeley Lab finding that average panel life reached 25–35 years in 2025. Check which warranty terms apply to your installer.
Why are HJT panels more expensive?
They use more silver per watt, 11.9 mg in 2025 per ITRPV, and need dedicated low-temperature production lines. Fewer makers also means less price competition. HyreSolar does not publish prices, so compare quotes on cost per watt and expected kWh.
Are HJT panels bifacial?
The cells are, because the structure is the same on both sides. Whether the panel is bifacial depends on its back cover. The REC Alpha Pure-RX uses bifacial cells behind a backsheet, so it is sold as one-sided. Glass-glass HJT panels collect light on both faces.
What does HJT stand for?
HJT stands for heterojunction technology. It describes a cell where two different forms of silicon meet: a crystalline wafer and thin amorphous silicon films. You may also see SHJ, for silicon heterojunction.
Sources
- VDMA, International Technology Roadmap for Photovoltaic (ITRPV), 17th Edition, Results 2025 (June 2026), retrieved .
- REC Group, REC Alpha Pure-RX series data sheet (US), UL EN 6.2026 V7, retrieved .
- Feldmann et al., Fraunhofer ISE, A Passivated Rear Contact for High-Efficiency n-Type Silicon Solar Cells (28th EU PVSEC, 2013), introduction on HIT heterojunction cells, retrieved .
- Canadian Solar, HiKu6 Mono PERC CS6R-MS data sheet V1.7C25_AU (April 2022), retrieved .
- Canadian Solar, TOPHiKu6 CS6.2-54TM data sheet V1.2_EN (March 2025), retrieved .
- National Laboratory of the Rockies (formerly NREL), Best Research-Cell Efficiency data table, retrieved .
- UL Solutions, Building-Integrated Photovoltaic (BIPV) System Testing and Certification (UL 7103, UL 61730), retrieved .
- IRS, Residential Clean Energy Credit (§25D), retrieved .
- SC Building Codes Council, code adoption, retrieved .
- South Carolina Code Title 58 Ch. 40 (Act 62 of 2019, customer-generators), retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Industry averages from ITRPV 17th Edition; HJT passivation and low-temperature processing from the Fraunhofer ISE paper by Feldmann et al..
Every REC figure (coefficients, warranty, certifications, hail, weight) re-read from the REC Alpha Pure-RX US data sheet on 8 October 2026; the heat example multiplies published coefficients by an assumed 40°C rise.
Suggest a correction. We fix errors and say what changed.