Background
TOPCon — Tunnel Oxide Passivated Contact — is an advanced solar cell architecture that significantly improves energy conversion efficiency compared to older PERC (Passivated Emitter and Rear Cell) technology. TOPCon cells have become a dominant technology in the solar manufacturing industry, accounting for a rapidly growing share of global panel shipments. Because so much money is at stake in this market, the companies that hold TOPCon-related patents have been actively asserting them against competitors.
Trina Solar, a major Chinese solar manufacturer, holds a portfolio of U.S. patents it has asserted cover core TOPCon manufacturing processes and cell structures. In 2024, Trina sued subsidiaries of Canadian Solar Inc. in U.S. federal court, asserting infringement of U.S. Patent Nos. 9,722,104 and 10,230,009 and seeking over $144 million in damages. Canadian Solar denied infringement and challenged the validity of both patents by filing inter partes review (IPR) petitions — a proceeding at the PTAB that allows any party to challenge an issued patent’s validity on the basis of prior art patents or printed publications.
The PTAB instituted review of both patents. After full briefing and oral argument, the board issued its Final Written Decisions on April 17, 2026.
The Court’s Holding
The PTAB issued Final Written Decisions invalidating all claims of both U.S. Patent Nos. 9,722,104 and 10,230,009. The board found that Canadian Solar had demonstrated by a preponderance of the evidence that the challenged claims were unpatentable over the prior art. With all claims cancelled, the patent infringement suit Trina had brought against Canadian Solar based on these patents is effectively eliminated.
Canadian Solar announced the decisions as a significant victory in its patent dispute management strategy, and noted that the ruling reinforces the company’s track record of successfully defending against international IP challenges. The dispute has also played out in China, where Trina Solar separately initiated litigation seeking approximately $147 million from Canadian Solar and its subsidiary CSI Solar in early 2025.
Key Takeaways
- Inter partes review (IPR) — a patent challenge proceeding at the PTAB — remains a powerful tool for accused infringers to eliminate patent claims before or during litigation, often at lower cost than district court invalidity proceedings.
- Both of Trina Solar’s asserted U.S. TOPCon patents had all claims cancelled, removing the foundation of the company’s U.S. infringement lawsuit seeking $144+ million.
- The solar manufacturing industry’s rapid shift to TOPCon technology has triggered a wave of patent disputes globally; this PTAB ruling is one front in a multi-jurisdiction battle that also includes Chinese litigation.
- A Final Written Decision invaliding all challenged claims is essentially the end of those patents as enforcement tools in the U.S., though Trina Solar may appeal to the Federal Circuit.
Why It Matters
The solar energy industry is in the middle of a technology transition, and where there is a dominant new technology, there are patent disputes. The PTAB’s invalidation of Trina Solar’s key U.S. TOPCon patents is a significant development for the industry: it signals that at least some of the core TOPCon patent claims being asserted in the U.S. market may not survive scrutiny, potentially opening the field to manufacturers who might otherwise have needed licenses or faced injunctions.
For the broader IP landscape, this case illustrates how IPR proceedings at the PTAB continue to serve as a critical backstop against overreaching patent claims in fast-moving technology sectors. Companies facing large patent damage demands should evaluate whether PTAB challenges are a viable strategy early in litigation — as Canadian Solar’s experience shows, a successful IPR can eliminate the entire basis of a nine-figure lawsuit.