From HIT to HJT: How the Core Architecture Has Evolved
Heterojunction solar cells achieve their performance advantage by combining an N-type crystalline silicon (c-Si) wafer absorber with hydrogenated amorphous silicon (a-Si:H) thin films deposited on both surfaces — a structure that drives open-circuit voltages above 750 mV and certified cell efficiencies now exceeding 26.8% as of 2026. The canonical design inserts a thin intrinsic (undoped) a-Si:H passivation layer, typically 5–10 nm thick, between the crystalline substrate and the doped amorphous emitter and back-surface-field layers, dramatically suppressing interface recombination.
The architecture traces a clear three-phase innovation trajectory within the dataset. The foundational phase (2009–2013) established the basic HJT stack: SolarCity Corporation filed on epitaxial c-Si thin film grown on metallurgical-grade silicon (MG-Si) substrates as a cost-reduction strategy, while Silevo Inc. pursued double-sided designs on the same substrate class, and Shin-Etsu Chemical explored ion-implantation-based substrate splitting to thin the crystalline layer. These records — now largely historical — defined the processing envelope that successors would optimise.
A scale-up phase from 2014 to 2020 saw LG Electronics, Beijing Juntai Innovation Technology, and multiple Chinese state-affiliated entities enter the field. The focus shifted from proof-of-concept to mass-production readiness: literature from 2018 notes that 24%+ efficiency achieved with few process steps positions HJT for a “true mass market launch.” LG Electronics introduced light-sintering-based electrode formation for TCO layers, while Beijing Juntai filed prolifically across EP, US, CA, and AU jurisdictions on graded-doping intrinsic and doped layer architectures.
Hydrogenated amorphous silicon (a-Si:H) is deposited in a thin intrinsic layer (~5–10 nm) between the crystalline silicon wafer and the doped amorphous emitter layers. By saturating dangling bonds at the c-Si surface, it dramatically reduces interface recombination — the primary mechanism enabling HJT cells to achieve open-circuit voltages above 750 mV and certified efficiencies exceeding 26.8%.
The industrialisation and efficiency push from 2021 to 2026 is dominated by Tongwei Solar (Jintang), Gold Stone (Fujian) Energy, Anhui Huasun Energy, Ideal Yield Semiconductor Equipment (Shanghai), and Laplace (Wuxi) Semiconductor. The most recent filing in the dataset — Tongwei Solar (Jintang) Co., Ltd., 2026, US — exemplifies this trajectory: it covers hydrogenated amorphous carbon silicon oxide (a-SiCx:H) buffer layer engineering, a chemistry cluster that represents the current state of the art in high-efficiency mass manufacturing. HJT cells processed entirely at temperatures at or below 200°C can also be fabricated on thinner wafers of 100–120 µm, opening flexible module formats beyond rigid panels.
Heterojunction (HJT/SHJ) solar cells combine N-type crystalline silicon wafer absorbers with hydrogenated amorphous silicon thin films to achieve certified efficiencies exceeding 26.8% as of 2026, with open-circuit voltages above 750 mV enabled by a 5–10 nm intrinsic a-Si:H passivation layer that suppresses interface recombination.
Who Controls the Critical IP: Assignee and Jurisdiction Breakdown
China accounts for approximately 50% of all HJT solar cell patent records in this dataset, with the US at roughly 25%, EP at approximately 15%, and AU, IN, WO, and CA comprising the remainder — a filing distribution that reflects China’s manufacturing-led domination of the global photovoltaics supply chain, consistent with trends documented by the IEA in its annual solar PV reports.
At the assignee level, Tongwei Solar (Jintang and Chengdu combined) is the single most prolific filer, with approximately 9 records across US, EP, AU, and CN jurisdictions. SolarCity Corporation (now Tesla) and Beijing Juntai Innovation Technology each account for approximately 5 records. The contrast in patent status is instructive: Tongwei Solar’s portfolio is active and expanding into new jurisdictions, while Beijing Juntai’s filings from 2018–2019 are now predominantly inactive — suggesting either licensing resolution or IP abandonment. LG Electronics’ filings are largely inactive, consistent with the company’s 2022 exit from solar cell manufacturing.
Two emerging entrants are particularly notable. Chinese equipment makers — Ideal Yield Semiconductor Equipment (Shanghai) and Laplace (Wuxi) Semiconductor — are filing on PECVD chamber design and dual-side simultaneous coating processes. This signals that HJT process equipment is becoming a discrete IP domain, separate from cell architecture IP. Academic signals are also emerging: Indian Institute of Technology Delhi and individual inventor Rajesh Tripathi are filing in IN jurisdiction, suggesting early-stage R&D interest in South Asia aligned with India’s domestic solar manufacturing push, which IRENA has identified as a strategic priority market.
Map the full HJT assignee landscape and identify freedom-to-operate risks in your target jurisdictions.
Explore HJT Patent Data in PatSnap Eureka →Tongwei Solar (Jintang and Chengdu) is the single most prolific assignee in the HJT solar cell manufacturing patent dataset (2009–2026), with approximately 9 records spanning US, EP, AU, and CN jurisdictions, concentrated on advanced a-SiCx:H buffer layer chemistry in active filings from 2021 to 2026.
Four Technology Clusters Shaping HJT Manufacturing in 2026
Patent analysis of the 60+ records reveals four distinct manufacturing sub-domains, each with a different maturity profile, commercial applicability, and IP concentration risk. Understanding which cluster a given R&D programme belongs to determines both the freedom-to-operate exposure and the white space opportunity available.
Cluster 1: Intrinsic a-Si:H Passivation and Standard HJT Stack
The commercial baseline architecture — textured N-type c-Si wafer coated bilaterally with intrinsic a-Si:H followed by doped p- and n-type a-Si:H layers, TCO, and screen-printed low-temperature metal electrodes — is described across the majority of filings in the dataset. Key contributors include Beijing Juntai Innovation Technology (2018–2019, US and EP) and Tongwei Solar (Chengdu) in 2023. As the foundational stack, this cluster has the broadest prior art base and the lowest freedom-to-operate risk for new entrants, though the active Tongwei Solar (Chengdu) EP filing from 2023 warrants monitoring.
Cluster 2: Advanced Buffer Layer Engineering (a-SiCx:H and C-Doped Interlayers)
The highest-concentration IP risk cluster. Post-2021 filings introduce hydrogenated amorphous carbon silicon oxide (a-SiCx:H) and C-doped SiO₂ intermediate layers between the c-Si wafer and the standard amorphous silicon stack. These layers widen the effective band gap of the passivation structure, reduce parasitic absorption, and improve fill factor. This approach is concentrated almost entirely in Tongwei Solar’s IP portfolio, with active US and EP grants. R&D teams planning to adopt a-SiCx:H integration roadmaps should conduct formal freedom-to-operate analysis against Tongwei’s 2021–2026 filings before committing process resources.
“Tongwei Solar’s multi-jurisdictional filing cluster around a-SiCx:H buffer layer chemistry — with active US and EP grants — creates a significant freedom-to-operate constraint for non-Chinese manufacturers seeking to deploy comparable stack architectures.”
Cluster 3: Metallization and TCO Formation Innovations
A distinct cluster addresses the thermal sensitivity constraint of HJT manufacturing: conventional silver paste sintering above approximately 250°C degrades a-Si:H passivation quality. Patents in this cluster focus on low-temperature light sintering, electroplating, multi-busbar design, and alternative TCO compositions — specifically In₂O₃ mixed metal oxide systems — to reduce contact resistance while preserving passivation integrity. Key filers include Trina Solar (US, 2018–2019) and Beijing Zenithnano Technology (EP, 2023). LG Electronics’ light-sintering electrode process IP from 2018–2019 is now predominantly inactive, representing either freely available prior art or design-around reference material. The transition to copper electroplating or silver-coated copper paste remains active IP territory with relatively few dominant holders — the most clearly identified white space in the dataset.
The literature and patent data consistently identify low-temperature-compatible metallization — silver paste cost, contact resistance, and line conductivity — as the primary efficiency and cost lever in HJT manufacturing. The transition from screen-printed low-temperature silver paste to copper electroplating or silver-coated copper paste is active IP territory with relatively few dominant holders, representing an open competitive ground for new filings.
Cluster 4: Low-Cost Substrates and Epitaxial Thin-Film Architectures
An earlier but strategically significant cluster uses metallurgical-grade silicon (MG-Si) or upgraded metallurgical-grade silicon (UMG-Si) substrates to reduce wafer costs, with epitaxial c-Si thin films grown on these substrates before applying the full HJT passivation stack. SolarCity Corporation’s foundational MG-Si epitaxial substrate portfolio (2010–2014) remains active in US jurisdiction under Tesla’s ownership. California Institute of Technology’s 2025 US filing on non-epitaxial, scalable Schottky-barrier heterojunction structures signals continued academic interest in further reducing fabrication costs, consistent with the cost-reduction trajectory documented in NREL‘s photovoltaic cost benchmarking work.
In HJT solar cell manufacturing, conventional silver paste sintering above approximately 250°C degrades amorphous silicon (a-Si:H) passivation quality. The transition from screen-printed low-temperature silver paste to copper electroplating or silver-coated copper paste is active patent territory with relatively few dominant IP holders as of 2026, representing a white space opportunity.
Five Emerging Vectors: Where the Next IP Battlegrounds Are Forming
Filings dated 2024–2026 in the dataset reveal five clear vectors where IP formation is accelerating and where companies that file foundational patents today will hold structural advantage over the next product cycle. Each vector addresses a distinct constraint in the current HJT manufacturing baseline.
1. Nanocrystalline Silicon Doped Contacts for Back-Junction HJT
An IN-jurisdiction filing by Rajesh Tripathi (2024) documents back-junction SHJ cells using p-nc-Si:H (nanocrystalline silicon) rear emitters, achieving simulated efficiencies of 26.30%–26.81% and fill factors of 86.59% on M6-sized wafers. Nanocrystalline silicon at carrier-selective contacts enables higher conductivity than amorphous layers while maintaining passivation quality — a combination that addresses both efficiency and contact resistance simultaneously.
2. Silicon Carbide (SiC) Layers in HJT Stacks
3Sun S.r.l. (an Enel Group company) filed a WO application in 2025 covering HJT cells incorporating silicon carbide layers, reflecting European industrial interest in wider-bandgap interlayers to reduce parasitic absorption at the front surface. This approach mirrors the logic of Tongwei Solar’s a-SiCx:H cluster but uses SiC rather than carbon-doped silicon oxide — potentially creating a design-around path for non-Chinese manufacturers.
3. Non-Epitaxial Schottky-Barrier HJT for Scalability
California Institute of Technology filed a US patent in 2025 on non-epitaxial Schottky-barrier heterojunction structures, explicitly targeting reduced fabrication costs and improved scalability compared to conventional a-Si:H or epitaxial approaches. The non-epitaxial route removes a key process complexity bottleneck and may enable HJT-grade structures on a wider range of substrate materials.
4. HJT as Bottom Cell in Perovskite/Silicon Tandem Stacks
Perovskite/silicon tandem solar cells — which use an HJT cell as the silicon bottom cell — have been demonstrated exceeding 29% efficiency in the literature, as documented by published research tracked in authoritative databases including Nature. The CN filing by Jiangsu Runyang Shiji Photovoltaic Technology Co., Ltd. (2025) explicitly addresses stacking top-cell wide-bandgap materials on crystalline silicon HJT substrates. ITRPV projects that perovskite/HJT tandem architectures will capture more than 5% market share by 2029. Companies seeking to position for this transition should be filing foundational IP on surface preparation, tunnel junction design, and scalable interconnect schemes now.
Identify open IP positions in perovskite/HJT tandem integration before the filing window closes.
Analyse Tandem Solar IP with PatSnap Eureka →5. BIPV-Specific HJT Designs
Anhui Huasun Energy’s 2026 CN filing explicitly addresses single-face illumination conditions for building-integrated photovoltaics (BIPV), incorporating back-reflector integration and eliminating indium-containing ITO TCO to reduce cost in environments where bifacial operation is not required. This design adaptation signals that HJT’s low-temperature processing advantage is being leveraged for building envelope applications beyond conventional rooftop and ground-mount sectors — an application-specific design space with its own emerging IP profile.
Perovskite/silicon tandem solar cells using HJT as the silicon bottom cell have been demonstrated exceeding 29% efficiency. According to ITRPV projections cited in the patent landscape dataset, perovskite/HJT tandem architectures are projected to capture more than 5% of the solar cell market by 2029, with the earliest HJT-tandem patent filings appearing in CN jurisdiction in 2025.
Strategic Implications for R&D and IP Teams
Five actionable conclusions emerge from this patent landscape for IP directors, R&D leaders, and business development teams working in photovoltaics manufacturing. Each is grounded in the filing patterns and status data within this dataset.
Conduct FTO analysis against Tongwei Solar’s 2021–2026 portfolio before adopting a-SiCx:H. Tongwei Solar’s multi-jurisdictional cluster around hydrogenated amorphous carbon silicon oxide buffer layer chemistry — with active US and EP grants — creates a significant freedom-to-operate constraint. Non-Chinese manufacturers planning to integrate a-SiCx:H or comparable carbon-doped interlayer architectures into their process roadmaps should complete formal FTO analysis before committing capital to that chemistry. Tongwei’s most recent US filing is dated 2026, indicating the portfolio is actively expanding.
Treat metallization as an open filing opportunity. The literature and patent data identify low-temperature-compatible metallization as the primary efficiency and cost lever in HJT manufacturing. The transition from screen-printed low-temperature silver paste to copper electroplating or silver-coated copper paste is active IP territory with relatively few dominant holders. LG Electronics’ light-sintering electrode process IP, now predominantly inactive, represents either freely available prior art or expired IP that is freely usable.
File foundational tandem IP now. Within this dataset, the earliest HJT-tandem filings appear in CN in 2025. ITRPV projects perovskite/HJT tandem architectures to capture more than 5% market share by 2029. The filing window for surface preparation, tunnel junction design, and scalable interconnect schemes is open today — companies that move first will hold structural leverage over the tandem product cycle.
Evaluate equipment IP exposure. The entry of Ideal Yield Semiconductor Equipment (Shanghai) and Laplace (Wuxi) Semiconductor into the patent landscape — covering PECVD chamber design and dual-side simultaneous coating processes — signals that HJT process equipment is becoming a discrete IP domain. PV manufacturers should evaluate whether in-house equipment development or exclusive equipment supply agreements are necessary to protect process advantage against equipment-side IP enclosure.
Monitor the SiC interlayer design-around opportunity. 3Sun S.r.l.’s 2025 WO filing on silicon carbide layers in HJT stacks offers a potential design-around path relative to Tongwei Solar’s a-SiCx:H cluster for manufacturers seeking equivalent performance gains without entering Tongwei’s protected chemistry space. The WO filing status means freedom-to-operate in specific national phase jurisdictions will depend on grant outcomes that remain pending.
Note: This landscape is derived from a limited set of patent and literature records retrieved across targeted searches. It represents a snapshot of innovation signals within this dataset only and should not be interpreted as a comprehensive view of the full industry.