What project owners need to know.
A heterojunction (HJT) solar cell is a crystalline silicon cell whose surfaces are coated with ultra-thin amorphous silicon layers and a transparent conductive oxide, so the junction forms between two different forms of silicon rather than by high-temperature diffusion. Because those layers degrade above roughly 200 °C, the whole cell is made at low temperature, and its efficiency depends heavily on a clean, high-lifetime n-type wafer. ITRPV data reported in September 2026 put HJT at about 5% of crystalline silicon cell production in 2025, and in April 2026 India listed its first HJT cells under ALMM List-II. JRST works upstream of the cell, on the ingots and wafers that cell technologies such as HJT depend on.
What a heterojunction cell is
In a conventional PERC or TOPCon cell, the junction is formed inside the wafer by diffusing dopants at high temperature. A heterojunction cell takes a different route. A high-lifetime n-type crystalline wafer is coated on both sides with very thin films of hydrogenated amorphous silicon, and the junction forms at the boundary between the crystalline wafer and the amorphous film, two different forms of the same element. That boundary is the 'hetero' in heterojunction.
The industry uses both abbreviations, HJT and SHJ (silicon heterojunction). They describe the same family of cells.
The layer stack, in plain terms
A typical HJT cell, as described in patent literature such as US 11,588,071, is built symmetrically around the wafer:
- A high-lifetime n-type silicon wafer as the base
- Intrinsic (undoped) amorphous silicon layers, each up to about 20 nm, on front and rear, which passivate the wafer surfaces while staying thin enough for charge carriers to tunnel through
- A p-type doped amorphous silicon layer on one side to form the junction, and an n-type doped layer on the other to form the contact
- A transparent conductive oxide, often indium tin oxide (ITO), on both sides to move current sideways and act as an antireflection layer
- Metal contacts on both faces, in a grid on at least one side to let light in
Why everything happens at low temperature
The amorphous silicon and the oxide layer on top of it typically degrade if annealed above about 200 °C, according to the same patent background. That single constraint shapes the whole line: no high-temperature diffusion furnaces, deposition steps that run cool, and metallisation pastes that cure at low temperature instead of being fired.
The low-temperature route is also why HJT is often described as a shorter process chain, and why it is well suited to replacing silver with copper. The ITRPV roadmap, as reported by TaiyangNews in September 2026, notes that HJT is 'particularly suited to copper substitution' because of its low-temperature metallisation.
What HJT asks of the wafer
Because the amorphous layers passivate the surface so well, the bulk quality of the wafer shows up directly in cell efficiency. HJT therefore rewards wafers with high minority-carrier lifetime, controlled resistivity and low contamination, and it punishes surface damage and residues from slicing and cleaning. In practice, the cell is only as good as the ingot it came from.
HJT also pushes wafers thinner. ITRPV expects HJT wafers at about 120 µm in 2026, potentially reaching around 100 µm by 2036. Thinner wafers save silicon but make breakage, handling and slicing control more demanding across the chain.
- N-type, high-lifetime monocrystalline wafers
- Tight control of resistivity and oxygen-related defects at the ingot stage
- Clean, damage-free surfaces ready for texturing and passivation
- Thinner wafers, with handling and breakage control to match
HJT, TOPCon and back-contact: where the market sits
TOPCon remains the volume leader. ITRPV data reported in September 2026 put HJT at about 5% of crystalline silicon cell production in 2025, with a relatively stable share expected through 2036, while HJT-based back-contact cells could grow from about 0.1% to roughly 5% over the same period. The roadmap expects mass-production HJT cell efficiency of about 25.6% in 2026 and expects the efficiency gaps between TOPCon, HJT and back-contact cells to narrow.
Silver is the other watch point. The same roadmap puts HJT silver use at about 100 mg per M10 cell in 2025, falling to about 40 mg by 2036, with the share of silver-based HJT metallisation expected to drop from around 75% of production to about 10% as silver-coated copper and pure copper take over. These are roadmap projections, not guarantees.
HJT in India, 2026
India's first heterojunction cells entered MNRE's ALMM List-II in April 2026. According to pv magazine India (14 April 2026), Reliance Industries listed 1,238 MW per year of HJT cell capacity at Jamnagar, in a 210 mm × 105 mm half-cell format with zero-busbar designs and efficiencies of up to 25.6%. Its HJT modules were already on ALMM List-I at about 1,716 MW per year.
The timing matters because, from 1 June 2026, government-backed projects must use modules made with cells from ALMM List-II. The proposed ALMM List-III would take the same logic upstream to ingots and wafers from 1 June 2028. For a cell technology as wafer-sensitive as HJT, a domestic supply of high-lifetime n-type wafers is the next link in the chain.
Listed capacity is a nameplate figure, not confirmed output. Readers should validate any technology choice, eligibility or timeline with the relevant authority and the technology supplier.
How JRST supports this requirement
JRST works upstream of the cell: high-purity quartz, CZ ingot growth, wafering, equipment sourcing and line consumables for Indian silicon projects. Wafer specifications for a particular cell technology, including HJT, are defined in a project-specific proposal and validated with the cell maker.
Discuss your requirement
Mohammed Saif Zaveri connects JRST's industrial content to execution conversations.
As Co-Founder and designated partner of JRST Technology LLP, Mohammed Saif Zaveri works across industrial growth, strategic partnerships, client conversations, equipment strategy, and project pathways for silicon, solar, semiconductor, and advanced-manufacturing opportunities.
This knowledge page is part of JRST's public industrial knowledge base, designed to help buyers move from search terms and early research toward a structured technical-commercial discussion.
View Mohammed Saif Zaveri's profileConnect on LinkedInFrequently asked questions
What is an HJT solar cell?
An HJT (heterojunction) solar cell is a crystalline silicon cell coated on both sides with ultra-thin amorphous silicon layers and a transparent conductive oxide. The junction forms between the crystalline wafer and the amorphous film, and the cell is made entirely at low temperature.
What is the difference between HJT and TOPCon?
Both are n-type cell technologies. TOPCon forms its junction by high-temperature diffusion and uses a tunnel oxide with polysilicon for passivation; HJT uses amorphous silicon layers deposited at low temperature. TOPCon leads in production volume, and ITRPV expects the efficiency gap between the two to narrow.
Why do HJT cells need n-type wafers?
HJT cells are built on high-lifetime n-type monocrystalline wafers. Because the amorphous layers passivate the surfaces so effectively, the wafer's bulk quality, its lifetime, resistivity and cleanliness, shows up directly in cell efficiency.
Why is HJT made at low temperature?
The amorphous silicon and transparent conductive oxide layers typically degrade if annealed above about 200 °C, so every step after they are deposited, including metallisation, must stay below that range. This is also why HJT uses low-temperature pastes and suits copper metallisation.
Does India manufacture HJT solar cells?
Yes. In April 2026 Reliance Industries became the first company to list HJT cells under MNRE's ALMM List-II, with 1,238 MW per year of cell capacity at Jamnagar, according to pv magazine India. Listed capacity is nameplate, not confirmed output.
How thick is an HJT wafer?
The ITRPV roadmap, as reported by TaiyangNews in September 2026, expects HJT wafers at about 120 µm in 2026, potentially falling to around 100 µm by 2036.
Does JRST make HJT cells?
No. JRST works upstream of the cell, on high-purity quartz, silicon ingots, wafers, equipment and consumables. Requirements for a specific cell line are defined in a project-specific proposal.
Primary sources and further reading
Last reviewed 2026-10-22. Technical scope, policy eligibility, availability, and commercial terms should be independently confirmed for each project.