Somewhere on your neighbor’s roof sits a solar panel built around a layer of silicon oxide just a few atoms thick.
That layer is the reason the panel works as well as it does.
It is also, right now, at the center of a federal trade investigation that could reshape which solar panels Americans are allowed to buy. The technology is called TOPCon. And a single US patent may decide its fate here.
How a tunnel of electrons turns a few atoms into a power plant
The name TOPCon stands for Tunnel Oxide Passivated Contact, and the physics it describes is genuinely strange. In a conventional silicon solar cell, electrons knocked loose by sunlight are collected at metal contacts printed onto the cell’s surface. But every metal-silicon interface creates what engineers call recombination: electrons that should flow into a circuit simply vanish back into the lattice, cutting efficiency.
TOPCon’s answer is to grow an ultra-thin layer of silicon oxide between the silicon and the metal. The layer is thin enough that electrons can quantum-mechanically tunnel straight through it, but just thick enough to block the energy-wasting recombination that conventional cells could not fully stop. A doped polysilicon layer on top then funnels the electrons cleanly out.
The result is a cell that converts more sunlight per square centimeter than the PERC technology it is replacing. What makes TOPCon particularly attractive is its compatibility with existing manufacturing equipment: producers can retrofit older production lines without rebuilding facilities, and the price gap closed in roughly two years as TOPCon reached manufacturing cost parity.
The world’s most-installed solar cell and the patent standing in its way
Industry analysts project TOPCon will capture 60 to 70 percent of the silicon solar market in 2026, displacing PERC as the dominant technology. From Texas solar farms to rooftop arrays in New Jersey, the panels going up today are overwhelmingly built on this chemistry.
What almost none of the homeowners or project developers installing them realize is that the legal status of TOPCon in the United States is now actively contested. First Solar, a cadmium-telluride thin-film solar panel manufacturer, holds US Patent No. 9,130,074, covering tunnel oxide passivated contact technology. First Solar acquired TetraSun and its intellectual property portfolio in 2013; prior to that acquisition, the California-based startup had pioneered proprietary cell architecture and manufacturing processes for large-format crystalline silicon wafers. For years the patent sat largely dormant. Then the company began enforcing it, first in district court, then before the US International Trade Commission.
The ITC instituted the investigation on March 25, 2026, based on a complaint filed by First Solar. The agency named 47 entities across 11 countries as respondents. They include major Chinese solar manufacturers JinkoSolar, JA Solar, Trina Solar and Canadian Solar, significant US silicon-based players like Qcells and T1 Energy, and firms in Germany, India, Southeast Asia and Canada. That is not a narrow complaint. It is a challenge to the entire global TOPCon supply chain that serves American buyers.
What the federal investigation actually threatens, and what the patent office already decided
The complaint alleges violations of Section 337 of the Tariff Act and requests a general exclusion order. That would be the nuclear option: barring all TOPCon imports from entering the US regardless of which company made them, as well as cease and desist orders against named respondents.
Toward the end of 2025, the USPTO denied three separate Inter Partes Review applications filed by JinkoSolar, Mundra Solar, and Canadian Solar, declining them in November and December. JinkoSolar and Canadian Solar had sought to invalidate First Solar’s US Patent No. 9,130,074, while Mundra Solar challenged US Patent No. 9,666,732; both patents cover methods of manufacturing TOPCon crystalline silicon solar cells. Those denials matter enormously. The companies named as respondents had hoped to kill the patents before the ITC case reached a verdict. That path is now closed.
The case, listed as investigation 337-TA-1494, will work through an administrative law judge before a final ITC ruling. Parallel district court litigation is proceeding in the United States District Court for the District of Delaware. The hearing is scheduled to commence on February 16, 2027, with a preliminary ruling expected in May 2027 and a final ruling in September 2027, roughly 18 months from institution, which means uncertainty stretches well into next year.
How the US solar market is already splitting from the rest of the world
The patent pressure has already begun to bend what American factories actually build. During 2026, PERC and heterojunction technology are expected to account for roughly 70 percent of crystalline silicon cell output in the US, while one thin-film manufacturer is forecast to make up about 80 percent of all domestic solar cell production.
That is a dramatic divergence from global norms, where TOPCon dominates. The situation places project developers and module assemblers in an uncomfortable position. TOPCon panels are the most cost-effective high-efficiency option available globally, and an installer who planned a TOPCon build now faces the possibility that an exclusion order could dry up supply mid-project.
The existing Section 232 polysilicon tariffs already reshaped the upstream supply chain; the ITC case layered on top compounds the uncertainty. Buyers who have specified TOPCon for projects face a legal cloud with no equivalent anywhere else in the world.
What comes next and what the outcome cannot settle on its own
Even if the ITC ultimately denies the exclusion order, the investigation has already changed the market. Domestic manufacturers are hedging toward alternative cell architectures, and project finance teams are pricing in supply risk.
If the exclusion order is granted, the US solar build-out faces a genuine supply crunch. One percentage point of efficiency gain in a solar panel translates to roughly four fewer panels on a 10-kilowatt system. Moving from TOPCon back to older technologies means bigger, more expensive installations for the same power output, and those costs land on utilities, developers and ultimately ratepayers.
The broader picture is that the US solar manufacturing push, visible in integrated domestic campuses now assembling full panel lines, is arriving at exactly the moment when the question of which cell chemistry is legally available in America is genuinely open.
A single patent, applied to a layer of silicon oxide a few nanometers thick, is doing more to reshape the US solar supply chain right now than almost any tariff or subsidy on the books. What the ITC ruling cannot resolve is the deeper industrial question: whether the US can build a durable domestic solar manufacturing base without the same technology that the rest of the world has already standardized on.
