What is an HJT cell
HJT, Heterojunction Technology, is a high-efficiency crystalline silicon solar cell architecture that combines a c-Si wafer with thin amorphous silicon (a-Si) layers deposited on both surfaces. The amorphous silicon provides excellent electrical passivation, separating the silicon-metal interface from the active region of the cell and dramatically reducing electron recombination.
HJT delivers the highest mainstream cell efficiency (25 to 26 percent), the best temperature coefficient (-0.24 to -0.28 percent per degree Celsius), the highest bifaciality factor (90 to 95 percent) and the lowest annual degradation (0.30 to 0.40 percent). These advantages come at a manufacturing cost premium of roughly 15 to 25 percent over PERC, comparable to what buyers pay for IBC cells, the other leading premium silicon architecture.
In Indian solar, HJT is the premium choice for rooftop installations where space and yield matter, for high-irradiance hot sites, and for EV solar where weight and aesthetics carry value. ALMM listing for HJT modules is growing as PLI-funded Indian capacity comes online.
HJT explained simply
A standard silicon solar cell has metal contacts touching the silicon directly. Electrons get trapped at that interface. HJT slips a thin layer of amorphous silicon between the metal and the crystalline silicon. The amorphous layer passivates the surface, keeping electrons alive longer and lifting voltage.
Adding the amorphous layer on both sides (top and bottom) plus a transparent conducting oxide for front contact gives HJT the highest efficiency, the best heat tolerance and the strongest bifaciality of any mainstream commercial cell.
Why HJT matters
Efficiency leader. 25 to 26 percent cell efficiency is the upper limit for single-junction silicon in mass production, translating into among the highest module efficiency ratings on the market.
Best temperature performance. Indian summer sites with 50+ degree Celsius module temperatures lose less yield with HJT than with any other technology.
Highest bifaciality. 90 to 95 percent rear-side response captures the full bifacial benefit.
Lowest degradation. 0.30 to 0.40 percent annual loss is the slowest rate of module degradation among silicon technologies in commercial production.
Pathway to tandem. HJT is the silicon bottom-cell base for perovskite-silicon tandem cells in development.
How HJT works
- N-type crystalline silicon wafer at the centre.
- Intrinsic amorphous silicon (i-a-Si) deposited on both surfaces. This passivates the silicon surface.
- Doped amorphous silicon (p-a-Si front, n-a-Si rear) added on top of intrinsic layers. Forms the heterojunction.
- Transparent conducting oxide (TCO, usually indium tin oxide) deposited on both surfaces. Provides lateral conductivity.
- Silver grid printed on both surfaces. Collects current.
The asymmetric heterojunction (p-i-n on front, n-i-n on rear) creates the photovoltaic effect. The intrinsic amorphous layers are the secret: they passivate the silicon surface without participating in conduction.
Technical deep dive
Cell structure
| Layer | Material | Function |
|---|---|---|
| Front silver grid | Silver | Current collection |
| Front TCO | ITO | Lateral conduction |
| Front doped a-Si | p-a-Si | Heterojunction emitter |
| Front intrinsic a-Si | i-a-Si | Surface passivation |
| Base | n-type c-Si | Light absorption |
| Rear intrinsic a-Si | i-a-Si | Surface passivation |
| Rear doped a-Si | n-a-Si | BSF function |
| Rear TCO | ITO | Lateral conduction |
| Rear silver grid | Silver | Current collection |
Efficiency progression
| Year | HJT cell efficiency |
|---|---|
| 2014 | 22.0% (Panasonic) |
| 2019 | 25.0% (lab) |
| 2022 | 25.5% (commercial) |
| 2024 | 26.0% (premium lines) |
| 2026 | 26.5% (mass) |
Temperature coefficient
| Parameter | HJT |
|---|---|
| Voc coefficient | -0.21 to -0.25%/°C |
| Pmax coefficient | -0.24 to -0.28%/°C |
About 0.07 to 0.09 percentage points better than PERC.
Degradation
| Mechanism | HJT |
|---|---|
| Initial LID | Negligible |
| LeTID | Eliminated |
| Annual degradation | 0.30 to 0.40%/year |
| 25-year retention | 88 to 92% |
Bifaciality
90 to 95 percent. Highest among mainstream silicon cell technologies due to symmetric front-back structure.
Real-world applications
Premium residential rooftop solar.
C&I rooftops with limited space, the same space-constrained logic that drove the bifacial module choice in Case Study, 200 kW Solar at a Chennai IT Park.
Solar carports and shading structures.
EV solar (vehicle-integrated PV).
High-irradiance utility plants in hot regions.
Floating solar where temperature performance matters.
Building-integrated photovoltaics (BIPV).
Agrivoltaics.
Advantages
Highest commercial cell efficiency.
Best temperature coefficient.
Highest bifaciality.
Lowest annual degradation.
Thin wafer compatibility (lighter modules).
Tandem cell development base.
Aesthetic uniform appearance.
Limitations
15 to 25 percent cost premium over PERC.
Indium supply chain for TCO.
Low-temperature processing throughout. Lower throughput than PERC.
Silver consumption is higher.
Limited Indian ALMM listings as of 2026.
Common problems
TCO degradation in high-humidity environments.
Silver paste delamination at heterojunction interface.
PID risk if encapsulant choice is poor.
Hot spots from cracked cells.
Limited service network for premium HJT modules.
Soiling effects similar to other silicon cells.
Best practices
Source HJT from established Tier-1 manufacturers with proven yields.
Specify ALMM listing or equivalent quality certification.
Confirm PID resistance test data.
Use proper torque on MC4 connectors.
Plan annual cleaning.
Document module electrical parameters at commissioning.
Comparison: HJT vs TOPCon vs PERC
| Feature | HJT | TOPCon | PERC |
|---|---|---|---|
| Cell efficiency | 25 to 26% | 24 to 25% | 22 to 23% |
| Module efficiency | 23 to 24% | 22 to 23.5% | 20 to 22% |
| Temperature coefficient | -0.26%/°C | -0.31%/°C | -0.36%/°C |
| Bifaciality factor | 90 to 95% | 80 to 85% | 70 to 80% |
| Annual degradation | 0.35%/year | 0.45%/year | 0.50%/year |
| Price premium 2026 | +15 to 25% | +5 to 10% | Baseline |
| Market share 2026 | 8 to 12% | 50 to 60% | 30 to 40% |
Indian market context
HJT manufacturing in India is at early commercial stage as of 2026, with PLI Tranche II including allocations for HJT capacity.
International HJT brands present in India: Risen, Huasun, Meyer Burger (limited).
ALMM List I has limited but growing HJT entries; see the ALMM List Phase III Complete Guide for how bifacial module listings fit the current MNRE framework.
PM Surya Ghar accepts ALMM-listed HJT modules.
Premium residential installers source HJT for high-value rooftops.
EV solar applications increasingly specify HJT for weight and aesthetic reasons.
Standards and certifications
| Standard | Scope |
|---|---|
| IEC 61215 | Module qualification |
| IEC 61730 | Module safety |
| IEC TS 63209 | Extended thermal cycling |
| IEC 62804 | PID test |
| IS 14286 | Indian Standard for crystalline modules |
| MNRE ALMM | Listing for subsidies |
| BIS certification | Quality compliance |
Common mistakes
Buying HJT from manufacturers without proven mass production track record.
Underestimating cost premium in lifecycle ROI.
Mixing HJT and PERC in the same string.
Ignoring TCO durability for high-humidity coastal sites.
Treating HJT as a marketing label without verifying actual cell architecture.
Key takeaways
HJT is the premium silicon cell technology with the highest efficiency, best temperature performance, highest bifaciality and lowest degradation among mainstream commercial cells. The 15 to 25 percent cost premium over PERC, 10 to 15 percent over TOPCon, makes it a niche choice for premium rooftop, high-irradiance utility and weight-sensitive applications. The Indian HJT supply base is at early commercial stage.
Further reading
For how HJT Cell plays out in real projects, these guides go deeper:
- Solar Shading Analysis Software 2026: Guide
- Solar Panel ki Kimat 2026: Poora Rate Guide
- ALMM List-II Exemption Window for Net Metering & Open Access
- Best Solar Design Software India: 2026 Guide
Sources
- Sawada T., Terada N., Tsuge S., et al., High-efficiency a-Si/c-Si heterojunction solar cell, Proceedings of IEEE PVSC, 1994.
- IEC 61215, Module qualification.
- IEC 61730-1, -2, Module safety.
- IEC 62804, PID test.
- IEC TS 63209, Extended thermal cycling.
- IS 14286, Indian Standard for crystalline silicon PV modules.
- MNRE Approved List of Models and Manufacturers (ALMM).
- NREL Best Research-Cell Efficiency Chart.
- ITRPV Roadmap, latest edition, VDMA.
- IEA PVPS Trends in Photovoltaic Applications 2024.
Frequently Asked Questions
What is HJT in simple words?
What does HJT stand for?
What is HJT efficiency?
HJT vs TOPCon, which is better?
Is HJT n-type silicon?
How much premium does HJT carry?
What is the temperature coefficient of HJT?
What is the bifaciality factor of HJT?
Are HJT modules ALMM-listed?
How long do HJT modules last?
Does HJT have LID?
Why is HJT so expensive?
Who makes HJT modules?
Is HJT compatible with bifacial?
Where does HJT make the most sense?
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Co-founder & CEO driving Qbits Energy's product strategy and growth across India.