Quick Facts
What HJT technology is
Heterojunction (HJT) technology is a solar cell architecture that combines a crystalline silicon wafer (the absorber) with thin layers of hydrogenated amorphous silicon (a-Si:H) on both faces of the wafer. The term “heterojunction” refers to the junction between two different semiconductor materials.
The technology was developed by Sanyo (now Panasonic) in the 1980s and commercialised as HIT (Heterojunction with Intrinsic Thin Layer) in 1997. Patent expirations in the 2010s opened HJT to global manufacturers. The technology has matured significantly, with module efficiencies reaching 22% to 24% in 2026 commercial products.
HJT achieves higher efficiency than other mainstream silicon technologies because the amorphous silicon layers provide exceptional surface passivation, suppressing the recombination that limits crystalline silicon cell efficiency. The combination of efficient absorption (from the crystalline wafer) and excellent passivation (from amorphous silicon) is the source of HJT’s performance advantage.
HJT cell structure
A typical HJT cell has the following layers, from front to back:
Transparent Conducting Oxide (TCO) film, typically Indium Tin Oxide (ITO). Acts as front anti-reflective coating and conductive layer.
Doped p-type amorphous silicon layer (a-Si:H), about 10 nm thick. Forms the emitter.
Intrinsic amorphous silicon layer (i a-Si:H), about 5 nm thick. Provides surface passivation.
n-type crystalline silicon wafer (200 micrometres typical), the absorber.
Intrinsic amorphous silicon layer (i a-Si:H), about 5 nm thick. Provides rear surface passivation.
Doped n-type amorphous silicon layer (n a-Si:H), about 10 nm thick. Forms the back surface field.
TCO film on the rear face.
Front and rear metal contacts (low-temperature silver paste, sometimes copper-plated).
The intrinsic amorphous silicon layers are the key innovation. They terminate the dangling bonds on the crystalline silicon surface, eliminating most surface recombination. The doped layers select for electrons at the front and holes at the back.
HJT manufacturing process
HJT manufacturing has distinctive characteristics:
Low-temperature processing: All process steps below 200 deg C. Protects the amorphous silicon layers from damage.
Plasma-Enhanced Chemical Vapour Deposition (PECVD): Deposits the amorphous silicon layers in a controlled chamber.
Physical Vapour Deposition (PVD): Deposits the TCO films.
Screen printing or copper plating: Applies the metal contacts.
Low-temperature curing: Cures the metal paste below 200 deg C.
The low-temperature process is incompatible with the higher-temperature steps used in Mono PERC manufacturing. HJT lines therefore require specialised equipment with different design and supply chain.
The capital cost per GW of HJT manufacturing capacity is 25% to 40% higher than Mono PERC, though continuous improvement is closing the gap.
HJT performance characteristics
Module efficiency: 22% to 24% commercial in 2026. Best products approach 24.5%.
Temperature coefficient: minus 0.24% to minus 0.27% per deg C. Best among mainstream silicon.
Annual degradation: 0.25% to 0.35%. Lowest among mainstream technologies.
Bifacial factor: 85% to 95%. Highest among mainstream silicon.
LID: under 1%. Minimal compared to p-type technologies.
PID resistance: High, due to n-type wafer and high-resistivity amorphous silicon.
The combined performance advantages translate to 5% to 9% higher annual energy than Mono PERC for the same nameplate kWp, and 10% to 15% higher 25-year lifetime energy after degradation.
HJT and tandem cells
HJT is considered the most promising platform for next-generation tandem cells (combining silicon with another semiconductor like perovskite). Tandem cells could exceed 30% cell efficiency, breaking through the single-junction silicon efficiency limit (around 26%).
Research in tandem cells is intensive. First commercial tandem HJT-perovskite products are expected in the late 2020s. India has growing R&D activity in this space.
For solar buyers in 2026, HJT is the cutting edge of commercial silicon technology. Tandem cells remain in research and pilot production.
HJT in the Indian market
Indian HJT manufacturing capacity is small but growing:
Premier Energies: Among the earliest Indian HJT manufacturers, with operational capacity since 2023.
Reliance Industries: HJT capacity announced under second PLI tranche, ramping in 2024 to 2026.
Several smaller Indian manufacturers: Pilot or planned HJT capacity.
Most HJT modules in India in 2026 are imported from Chinese (Risen, Tongwei, LONGi, Sungold, Jolywood) and European (Meyer Burger, REC Solar) manufacturers.
Indian HJT modules are increasingly available through authorised distributors, supporting Indian premium residential and commercial installations.
HJT in commercial installations
For commercial and industrial rooftop solar in India, HJT is increasingly chosen for:
Premium installations: Net-zero buildings, sustainability-certified projects.
Limited roof area: When the customer wants maximum generation per square metre.
Hot climates: When the temperature coefficient advantage delivers meaningful additional energy.
Long-term ownership: When the lifecycle yield advantage justifies the upfront premium.
For most residential and standard commercial projects, Mono PERC and TOPCon remain more economical. HJT economics improve as production scales and CAPEX declines.
HJT versus TOPCon decision
Both are n-type technologies with similar physical principles but different implementation:
TOPCon: Tunnel oxide passivation at rear face. Mature manufacturing. CAPEX premium of 5% to 10% over Mono PERC.
HJT: Amorphous silicon passivation on both faces. Lower-temperature processing. CAPEX premium of 25% to 40% over Mono PERC.
For 2026, TOPCon dominates utility-scale and large commercial. HJT is competitive in premium residential, commercial, and high-temperature locations.
The choice depends on:
Project IRR target: TOPCon usually delivers better IRR for standard projects.
Lifetime energy priority: HJT delivers more energy over 25 years.
Climate: Hotter climates favour HJT more.
Aesthetic: HJT often has cleaner appearance (fewer visible busbars).
Budget: TOPCon has lower CAPEX premium.
Common HJT mistakes
Confusing HJT with TOPCon. They are different architectures with different performance and cost profiles.
Treating HJT as fully mature. Manufacturing still scaling; supply chain less established than Mono PERC.
Comparing only nameplate Wp without considering temperature coefficient and degradation. HJT advantages emerge over time and in hot conditions.
Mismatching inverter to high-voltage HJT strings. HJT’s high Voc at low temperatures can stress legacy inverters not rated for high DC voltage.
Specifying HJT without verifying indium-content for TCO film sustainability concerns.
Best practices
For premium installations where lifetime energy matters more than CAPEX, evaluate HJT seriously.
For utility-scale tenders with 25-year tariff visibility, model HJT against TOPCon on lifetime LCOE basis.
For commercial rooftops in hot climates (Rajasthan, Gujarat, Andhra Pradesh), HJT’s temperature advantage adds meaningful annual energy.
Verify ALMM listing for HJT modules. ALMM coverage is increasing but not all HJT products are listed.
Pair HJT with inverters rated for 1500 V DC strings to capture the high-Voc advantage.
Standards and references
HJT cells and modules comply with IEC 61215, IEC 61730, IEC 62804 (PID), and BIS certification for ALMM. The technology is referenced in IRENA reports, BloombergNEF outlooks, and Fraunhofer ISE research publications.
Related glossary terms
- HJT Solar Panel
- Mono PERC
- TOPCon Solar Panel
- N-type vs P-type
- PERC Cell Architecture
- Passivated Emitter
- Solar Panel Degradation
- PID and Anti-PID
Key takeaways
Heterojunction (HJT) is a solar cell architecture combining n-type crystalline silicon with thin amorphous silicon layers on both faces. The amorphous silicon provides exceptional surface passivation, enabling cell efficiencies above 25% and module efficiencies of 22% to 24%. HJT has the lowest temperature coefficient and annual degradation among mainstream silicon technologies, making it especially attractive for hot climates. CAPEX is 25% to 40% higher than Mono PERC. HJT is the most likely path to next-generation tandem cells exceeding 30% efficiency, expected in the late 2020s.