Background: In October 2024, Trina Solar filed a patent infringement lawsuit against a subsidiary of Canadian Solar in the U.S. District Court for the District of Delaware, asserting two patents related to Tunnel Oxide Passivated Contact (TOPCon) solar cell technology. Simultaneously, both parties initiated investigation proceedings at the U.S. International Trade Commission (ITC) pursuant to Section 337 of the U.S. Tariff Act. Following an unopposed motion, the Delaware litigation was stayed in its early stages pending the outcome of the ITC investigation. Subsequently, the ITC proceedings were terminated. However, the District Court infringement lawsuit remained stayed pending the Inter Partes Review (IPR) proceedings conducted by the Patent Trial and Appeal Board (PTAB) of the U.S. Patent and Trademark Office (USPTO) regarding the patents-in-suit. The patents-in-suit were challenged by multiple IPR petitions, and the final rulings of all review proceedings were consistent.

Latest Development: The PTAB has issued Final Written Decisions, ruling that all claims of the two patents-in-suit are unpatentable.

Direct Impact: The Board's ruling directly revokes the legal basis for the patent infringement lawsuit in Delaware. With all asserted claims declared invalid (barring a successful appeal), this case will be unable to proceed to the trial phase. While parties may appeal the decision to the U.S. Court of Appeals for the Federal Circuit, the ruling takes immediate practical legal effect. In practice, once the underlying patents are found unpatentable, courts typically do not continue with infringement proceedings, effectively bringing this litigation to a standstill. Only a successful appeal could potentially restart the patent dispute between the two parties. Even if an appeal succeeds and the case is reinstated, it would proceed from its stayed status and must undergo numerous subsequent procedures before reaching the adjudication of substantive disputes.

Broad Implications:

• This case demonstrates that even if an enterprise adopts a complex enforcement strategy involving multiple channels and jurisdictions, the ultimate success often hinges on the validity of a few core patents; once a patent fails in validity challenge proceedings, the entire enforcement action will completely collapse. In January 2026, Canadian Solar achieved a similar victory against Maxeon.

• However, recent significant policy adjustments by the USPTO have caused the number of IPR petitions to plummet, and such instances of patent invalidity defenses will significantly decrease in the future.