Quick Facts
What HJT is
Heterojunction Technology (HJT) is a solar cell architecture that combines two semiconductor materials at the front and rear of the cell: a thin layer of amorphous silicon (a-Si) deposited on each face of a crystalline silicon wafer. The “hetero” in heterojunction refers to this junction between different materials. Earlier brand names for the same technology include HIT (Heterojunction with Intrinsic Thin Layer), trademarked by Sanyo and later acquired by Panasonic.
The amorphous silicon layers passivate the wafer surface extremely well, suppressing the recombination that normally limits crystalline silicon cell efficiency. The result is one of the highest-performing silicon solar architectures available at commercial scale in 2026, with the lowest temperature coefficient and the lowest annual degradation of any mainstream technology.
The cost premium over Mono PERC and TOPCon limits HJT to premium applications today, though manufacturing improvements are slowly closing the gap.
How HJT works at the cell level
A typical HJT cell structure, from front to back:
Anti-reflective Transparent Conducting Oxide (TCO) film. ITO (indium tin oxide) is the standard, with research moving toward indium-free alternatives.
Doped a-Si layer (p-type at front for an n-type wafer).
Intrinsic a-Si layer (very thin, around 5 nm), which performs the surface passivation.
n-type crystalline silicon wafer, the absorber.
Another intrinsic a-Si layer at the back.
Doped a-Si layer (n-type at the back).
TCO film at the rear.
Front and rear metal contacts (low-temperature silver paste).
The intrinsic a-Si layers reduce dangling bonds on the silicon surface to near-zero, eliminating most recombination loss. The doped a-Si layers select for electrons at one face and holes at the other.
A crucial manufacturing characteristic is that HJT processes happen below 200 deg C throughout, in contrast to TOPCon and PERC, which involve higher-temperature steps. The low thermal budget protects the a-Si passivation but also requires different equipment and silver paste formulations.
HJT compared with Mono PERC and TOPCon
| Parameter | Mono PERC | TOPCon | HJT |
|---|---|---|---|
| Module Efficiency (2026) | 20% to 22% | 21% to 23% | 22% to 24% |
| Temperature Coefficient | minus 0.34 to minus 0.37 % per deg C | minus 0.29 to minus 0.32 % per deg C | minus 0.24 to minus 0.27 % per deg C |
| First-year Degradation | 1% to 2% | around 1% | under 1% |
| Annual Degradation | 0.5% to 0.55% | 0.4% | 0.25% to 0.35% |
| Bifacial Factor | 70% to 75% | 80% to 85% | 85% to 95% |
| Substrate | p-type | n-type | n-type |
| Relative CAPEX per Wp | Reference | 5% to 10% premium | 25% to 40% premium |
| Common Use 2026 | Rooftop, ground mount | Utility, premium rooftop | Premium rooftop, BIPV, high-temperature locations |
HJT delivers the best lifetime energy per kWp among mainstream silicon technologies. The decision against HJT today is almost always a cost decision.
HJT in the Indian market
HJT manufacturing capacity in India is small but growing. Premier Energies, Reliance Industries, and a handful of greenfield ventures have announced HJT lines under the second tranche of the PLI scheme. Most commercial HJT modules in India in 2026 are imported from specialist manufacturers in China and Europe.
For utility-scale tenders, HJT shows up only when the offtaker specifically requires it, usually for plants where space is constrained or where higher CUF justifies the premium. SECI tenders to date have largely allowed Mono PERC and TOPCon but not specifically required HJT.
For premium residential and commercial applications, HJT appears in projects where roof area is limited, aesthetics matter (sleek black modules with no visible front busbars look cleaner), or the building owner wants the longest-life solar asset available.
BIPV (Building Integrated Photovoltaics) is another area where HJT works well because the low temperature coefficient suits panels embedded in roofs or facades where ventilation is limited.
Construction of a modern HJT module
Front glass: 2 mm to 3.2 mm tempered low-iron glass with anti-reflective coating.
Encapsulant: POE on both sides, suited to glass-glass construction and HJT’s process chemistry.
Cells: 132 to 156 half-cut HJT cells, often with 16 or more busbars or smart wire interconnection (SWCT) that uses fine copper wires instead of busbars.
Rear: Glass-glass construction is standard for HJT premium modules.
Frame: Anodised aluminium, 30 to 35 mm thick.
Connectors: MC4 or compatible, IP68.
HJT modules often weigh slightly more than Mono PERC counterparts because of the glass-glass build. Premium products are 580 to 620 Wp at 144-cell format.
Why HJT delivers the highest lifetime energy
The factors stack up: highest cell efficiency, lowest temperature coefficient, lowest degradation, highest bifacial gain. An HJT plant in a hot Indian location outperforms a Mono PERC plant in the same location by 5% to 9% in annual energy and by 10% to 15% over a 25-year horizon when degradation is included.
A worked example for a 100 kWp commercial rooftop in Surat:
- Mono PERC 25-year cumulative output: about 36,000,000 kWh after degradation.
- TOPCon 25-year cumulative output: about 37,500,000 kWh.
- HJT 25-year cumulative output: about 39,000,000 kWh.
The HJT plant produces around 8% more energy over the project life. Whether the additional revenue justifies the higher CAPEX depends on tariffs and the discount rate, but for self-consumed power at retail tariffs above Rs 8 per kWh, HJT often pencils out.
Limitations and trade-offs
CAPEX premium of 25% to 40% per Wp compared with Mono PERC.
Higher silver consumption per cell, though smart-wire interconnect designs reduce silver use significantly.
Indium dependency in TCO films. Indium is geologically scarce, and indium-free transparent conductors (such as AZO) are still under development.
Smaller supply chain. Lead times for HJT modules are longer than for Mono PERC.
Less mature warranty enforcement. Some HJT brands have shorter operating histories than the major Mono PERC suppliers.
Specialised equipment and process know-how raise the bar for new manufacturers to enter.
Common mistakes when specifying HJT
Treating HJT as a marketing label without verifying actual cell efficiency, temperature coefficient, and bifacial factor.
Comparing only nameplate Wp instead of lifetime energy in financial models. The HJT advantage compounds across years.
Skipping inverter compatibility checks. HJT’s high open-circuit voltage at low temperatures can stress legacy inverters not rated for 1500 V plus systems.
Mixing HJT with TOPCon or Mono PERC modules in the same string. Different I-V characteristics cause mismatch losses.
Forgetting that HJT modules are heavier (glass-glass) and may require structural review for rooftop installation.
Best practices
For premium residential and commercial rooftop projects with a long-term ownership horizon and limited roof area, evaluate HJT seriously. Run a 25-year lifecycle yield model, not a one-year CAPEX comparison.
Specify HJT modules with established warranties of 25 to 30 years and reputable Tier 1 manufacturers.
Pair HJT with inverters rated for 1500 V DC strings (in utility installations) to capture the high Voc advantage.
For BIPV applications, evaluate HJT against bifacial TOPCon as the two technologies have very different aesthetics and integration profiles.
Standards and certifications
HJT modules sold in India must comply with IEC 61215, IEC 61730, IEC 62804 (PID resistance), and (where applicable) BIS for ALMM listing. Bankability assessments often add a stricter accelerated aging test because the technology has fewer years of field history at scale than Mono PERC.
Related glossary terms
- Mono PERC
- TOPCon Solar Panel
- Bifacial Solar Panel
- Half-cut Cell
- N-type vs P-type Solar Cells
- Heterojunction (HJT) Technology
- Solar Panel Degradation
- PID and Anti-PID
- Tier-1 Solar Panel
- ALMM
Key takeaways
HJT (Heterojunction Technology) combines crystalline silicon with thin amorphous silicon layers to achieve 22% to 24% module efficiency, the lowest temperature coefficient, and the lowest annual degradation among mainstream silicon technologies. It is best suited to premium installations where long-term yield, limited space, or aesthetics outweigh the 25% to 40% CAPEX premium. Indian manufacturing capacity is small but expanding under the second PLI tranche, with imports continuing to fill demand in 2026.