Background
Trina Solar Co. Ltd., one of the world’s largest solar panel manufacturers, asserted two patents covering tunnel oxide passivated contact (“TOPCon”) solar cell technology—U.S. Patent Nos. 9,722,104 and 10,230,009—against several competitors. The patents, originally issued to LG Electronics and reassigned to Trina Solar in March 2024, describe solar cell architectures using a semiconductor substrate with a tunnel layer, conductive-type semiconductor regions, passivation films, and electrodes. TOPCon is considered one of the most important advances in solar cell efficiency, and the patents were being asserted aggressively across multiple forums.
Trina Solar had filed complaints at the U.S. International Trade Commission (ITC Investigation Nos. 337-TA-1422, 337-TA-3773, and 337-TA-1425) and in federal district courts in Delaware and California against companies including Runergy Alabama, Canadian Solar, Mundra Solar (Adani), and others.
In response, Runergy Alabama Inc. and Runergy USA Inc. filed inter partes review (IPR) petitions in October 2024 challenging both patents. Mundra Solar PV Ltd. and Adani Solar USA Inc. filed parallel petitions in November 2024. Canadian Solar (USA) Inc. filed its own petitions in April 2025 and was joined into the lead proceedings.
The Court’s Holding
The PTAB issued final written decisions in both lead proceedings on April 15, 2026, finding all challenged claims in both patents unpatentable under 35 U.S.C. § 318(a). This was a complete victory for the petitioners.
The decisions were thorough—49 pages for the ’104 patent (IPR2025-00007) and 48 pages for the ’009 patent (IPR2025-00006)—reflecting detailed obviousness analyses. The Board determined that the claimed TOPCon solar cell structures would have been obvious to a person of ordinary skill in the art in view of the prior art presented by petitioners.
The ruling effectively strips Trina Solar of the patent protection it had been wielding against competitors in the growing TOPCon solar cell market, potentially affecting the parallel ITC investigations and district court cases that relied on these same patents.
Key Takeaways
- Major impact on the solar industry. TOPCon technology is at the center of the next-generation solar cell race. Invalidation of these patents opens the door for competing manufacturers—including Runergy, Canadian Solar, and Adani—to produce TOPCon panels without licensing obligations to Trina Solar.
- Coordinated multi-petitioner strategy succeeded. Three separate groups of petitioners filed IPR challenges, with Canadian Solar joining the lead proceedings through the PTAB’s joinder mechanism. This coordinated approach ensured redundancy and a thorough prior-art record.
- IPR as a defensive weapon against ITC complaints. The petitioners used IPR proceedings strategically to undercut Trina Solar’s patent assertions at the ITC and in district court. A PTAB final written decision finding claims unpatentable can form the basis for requesting termination of ITC investigations and summary judgment in parallel district court cases.
- Acquired patents face heightened scrutiny. These patents were originally developed by LG Electronics and reassigned to Trina Solar in 2024, apparently as part of a patent monetization strategy. The PTAB’s invalidation underscores the risk inherent in acquiring patents for offensive enforcement without first stress-testing their validity.
Why It Matters
This decision has immediate commercial significance. Trina Solar had used these patents as leverage in a wide-ranging enforcement campaign spanning the ITC and multiple federal courts, seeking to restrict competitors’ access to the lucrative U.S. market for TOPCon solar panels. With both patents now invalidated, Trina Solar loses its primary offensive weapon in those proceedings.
More broadly, the case illustrates how the IPR process continues to serve as an effective check on patent assertion, even as IPR filing rates have dropped to historic lows in 2026. For companies facing patent threats in fast-moving technology sectors, this decision reinforces that a well-resourced, multi-petitioner IPR strategy can deliver results even against well-funded patent holders.
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