What project owners need to know.
A perovskite-silicon tandem solar cell stacks a wide-bandgap perovskite cell on top of a crystalline silicon cell, so the perovskite converts the high-energy part of sunlight and the silicon converts the rest, reaching efficiencies a single silicon junction cannot. The silicon does not disappear: it becomes the bottom cell, usually on an n-type monocrystalline wafer, and its quality still sets much of the result. The certified laboratory record stood at 35.5% in July 2026, and the ITRPV roadmap expects tandem cells to enter the market in considerable volumes around 2028. JRST works upstream, on the silicon ingots and wafers that tandem bottom cells are built on.
What a tandem cell is
A single silicon cell wastes part of every photon that carries more energy than silicon needs, and that loss caps how efficient any single-junction silicon cell can be. A tandem cell splits the work. A perovskite layer with a wider bandgap sits on top and absorbs the higher-energy, bluer light; the lower-energy light passes through to a crystalline silicon cell underneath.
Perovskite here names a crystal structure, not a mineral source. The top cell is a thin film, typically a metal-halide perovskite deposited on the silicon, while the bottom cell is a conventional silicon cell made on a wafer cut from an ingot.
Two-terminal and four-terminal designs
Tandems are built in two main ways, and the choice changes what the silicon cell has to do:
- Two-terminal (2T), also called monolithic: the perovskite is deposited directly on the silicon cell and the two are connected in series through a thin recombination layer. One pair of contacts, but the currents of the two cells must be matched.
- Four-terminal (4T): two separately made cells are stacked mechanically and wired independently. Current matching is not needed, but the top cell needs transparent contacts on both sides and the module carries more layers.
- Record laboratory cells, including the 35.5% result, are 2T designs; several research groups, including in India, also work on 4T stacks.
Why the silicon wafer still matters
In a tandem, the silicon cell still produces a large share of the power, so its bulk lifetime, resistivity and cleanliness carry straight through to the final efficiency. The ITRPV roadmap, as reported by TaiyangNews in September 2026, expects perovskite on n-type silicon to become the principal tandem configuration, and n-type monocrystalline wafers already held about 82% of the wafer market in 2025.
The wafer surface becomes a design question. Standard textured surfaces trap light well, but in a 2T tandem the perovskite has to be deposited on top of them. Research from KAUST (Advanced Functional Materials, 2022) found that the silicon texture mainly affects the perovskite through variations in its thickness, and still reached certified tandem efficiencies above 28% on silicon heterojunction bottom cells. Work from Helmholtz-Zentrum Berlin (Progress in Photovoltaics, 2023) showed double-sided nano-textured surfaces compatible with solution-processed perovskite, also above 28% in a tandem.
- N-type, high-lifetime monocrystalline wafers as the bottom-cell base
- Bottom-cell designs such as silicon heterojunction (HJT) feature widely in record and published tandems
- Surface texture tuned for both light trapping and an even perovskite layer
- Ingot-stage control of resistivity and oxygen-related defects, as for any high-efficiency n-type cell
Where efficiency stands in 2026
On 14 July 2026 LONGi presented a 2T crystalline silicon-perovskite tandem cell at 35.5% efficiency, certified by the European Solar Test Installation (ESTI) of the European Commission's Joint Research Centre, according to pv magazine India. The active area was not disclosed, and the company gave no timeline for commercial production. The previous comparable record, 34.85%, was certified by NREL in April 2025.
Laboratory records and products are different things. In September 2024 Oxford PV announced the first commercial shipment of perovskite-on-silicon tandem modules to a US customer: 72-cell panels at 24.5% module efficiency, made on its pilot line in Brandenburg an der Havel, Germany. Large-area deposition, yield, encapsulation and long-term stability are still the open questions most often cited for tandems.
The roadmap: from lab to line
The ITRPV 17th edition, as reported by TaiyangNews in September 2026, expects silicon-based tandem cells to enter the market in considerable volumes around 2028 and to reach about 17% market share by 2036. It forecasts mass-production tandem cell efficiency of about 28.8% in 2028 and 32.3% in 2036, and tandem module efficiency of about 27.4% and 31% in those years. It also expects tandems to reduce silver use per watt and copper metallisation to gain ground. These are roadmap projections, not guarantees.
Policy is moving too. A draft revision of China's technology export catalogue, published on 16 October 2026 and open for comment until 15 November, was reported by Reuters to place perovskite and tandem cell technologies in the prohibited category. The final list should be checked before drawing conclusions.
Tandems and India
Indian work is at research and pilot stage. IIT Bombay's NCPRE and ART-PV, a startup incubated at SINE-IITB, have reported lab-scale four-terminal silicon-perovskite tandem cells with efficiencies of up to 30%, according to TaiyangNews (May 2025). The same report describes a proposed 300 MW tandem cell plant at Uran, Maharashtra, backed by the state think tank MITRA and pending a pilot project.
Whatever the top cell, a tandem module still needs a silicon bottom cell, and that needs a wafer. With ALMM List-II already covering cells and ALMM List-III proposed for ingots and wafers from 1 June 2028, a domestic supply of high-quality n-type wafers is part of being ready for tandems when they scale.
Lab efficiencies, proposed capacities and roadmap shares are 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 any cell architecture, including tandem bottom cells, 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 a perovskite-silicon tandem solar cell?
It is a solar cell that stacks a wide-bandgap perovskite cell on top of a crystalline silicon cell. The perovskite absorbs the higher-energy part of sunlight and the silicon absorbs the rest, so together they can exceed the efficiency of a single silicon junction.
What is the efficiency record for perovskite-silicon tandem cells?
In July 2026 LONGi presented a two-terminal perovskite-silicon tandem cell at 35.5% efficiency, certified by the European Solar Test Installation of the EU Joint Research Centre, according to pv magazine India. It is a laboratory device; the active area was not disclosed.
What is the difference between 2-terminal and 4-terminal tandems?
A 2-terminal (monolithic) tandem grows the perovskite directly on the silicon cell and connects the two in series, so their currents must match. A 4-terminal tandem stacks two separately made cells and wires them independently, avoiding current matching at the cost of extra transparent layers.
Do tandem solar cells still need silicon wafers?
Yes. In a perovskite-silicon tandem the silicon cell is the bottom cell, built on a crystalline wafer, usually n-type monocrystalline. Its lifetime, resistivity and surface quality still carry through to the tandem's efficiency.
When will tandem solar panels be commercial?
Small commercial volumes exist: Oxford PV announced its first shipment of 24.5%-efficient tandem modules to a US customer in September 2024. The ITRPV roadmap expects tandems in considerable volumes around 2028 and about 17% market share by 2036.
Is India developing tandem solar cells?
Yes, at research and pilot stage. IIT Bombay's NCPRE and the startup ART-PV have reported lab-scale four-terminal tandem cells of up to 30% efficiency, and a 300 MW plant has been proposed at Uran, Maharashtra, pending a pilot, according to TaiyangNews (May 2025).
Does JRST make tandem solar cells?
No. JRST works upstream of the cell, on high-purity quartz, silicon ingots, wafers, equipment and consumables. Wafer requirements for a specific cell or tandem line are defined in a project-specific proposal.
Primary sources and further reading
Last reviewed 2026-10-23. Technical scope, policy eligibility, availability, and commercial terms should be independently confirmed for each project.