Canadian Solar USA Inc v. Trina Solar Co Ltd

1. Case Identification

• Case #: IPR2025-00918
• Patent #: 9,722,104
• Filed: April 28, 2025
• Petitioner(s): Canadian Solar (USA) Inc.
• Patent Owner(s): Trina Solar Co., Ltd.
• Challenged Claims: 1-11

2. Patent Overview

• Title: Solar Cell and Method for Manufacturing the Same
• Brief Description: The ’104 patent discloses a solar cell featuring a tunnel oxide passivated contact (TOPCon) structure on its back surface. The key inventive concept purports to be an "isolation portion" at the periphery of the back surface, designed to prevent electrical short-circuiting between the back surface field and the emitter region.

3. Grounds for Unpatentability

Ground 1: Obviousness over Jin and Feldmann - Claims 1-6 and 9-10 are obvious over Jin in view of Feldmann.

• Prior Art Relied Upon: Jin (Application # 2013/0056051) and Feldmann (a 2013 journal article on passivated rear contacts).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Jin disclosed a conventional solar cell architecture that included all the key elements of the challenged claims except for the TOPCon structure, notably teaching an "isolation gap T" at the periphery of the substrate's rear surface to prevent short-circuiting. Feldmann was presented as teaching the specific benefits of replacing a conventional diffused back surface field (BSF), like Jin’s, with a superior TOPCon structure (an ultra-thin tunnel oxide and a phosphorus-doped silicon layer) to significantly reduce surface recombination and improve cell efficiency. Petitioner contended that substituting Feldmann’s TOPCon structure for Jin’s diffused BSF would result in the device claimed in the ’104 patent.
  • Motivation to Combine: A person of ordinary skill in the art (POSITA) would combine Jin and Feldmann to improve the performance of Jin's solar cell. Feldmann explicitly taught that its TOPCon structure provided "excellent performance" and "significantly reduce[s] the surface recombination," providing a clear motivation to apply this known efficiency-improving technique to a standard solar cell design like Jin's.
  • Expectation of Success: A POSITA would have had a high expectation of success, as the combination involved the simple substitution of one known BSF structure for an improved one to achieve predictable results. The petition asserted that the necessary manufacturing steps, such as using a shadow mask to create the isolation region, were well-known and routine.

Ground 2: Obviousness over Chang and Jin - Claims 1-6 and 9-10 are obvious over Chang in view of Jin.

• Prior Art Relied Upon: Chang (Application # 2014/0299187) and Jin (’051 application).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner asserted that Chang disclosed a bifacial solar cell that already contained the core combination of a TOPCon structure and an explicitly mentioned "isolation region" or "periphery region" where the TOPCon layers are not formed. To the extent Chang lacked specific implementation details for this isolation region, Petitioner argued that Jin provided them. Jin taught the conventional method of creating such a gap using a mask and showed a passivation layer covering the gap, which Petitioner contended was a necessary and obvious step.
  • Motivation to Combine: The combination was framed as a POSITA looking to analogous art to supply missing but conventional details. A POSITA reading Chang's disclosure of an isolation region would have been motivated to consult a reference like Jin—notably from the same original assignee (LG Electronics)—to understand the routine method for its fabrication and to recognize the need to passivate the exposed silicon in the gap to prevent recombination losses.
  • Expectation of Success: The expectation of success was argued to be high because Jin did not modify Chang’s invention but merely supplied the well-understood, standard details for implementing a feature already taught by Chang.

Ground 3: Obviousness over Primary Combinations in view of Seo - Claims 7-8 are obvious over Jin/Feldmann or Chang/Jin in further view of Seo.

• Prior Art Relied Upon: Seo (Patent 8,647,914), in addition to the combinations from Grounds 1 and 2.

• Core Argument for this Ground:

  • Prior Art Mapping: Claims 7 and 8 relate to passivation films that extend to cover the lateral side surfaces of the semiconductor substrate. Petitioner argued that Seo explicitly taught this feature. Seo disclosed that when passivation and anti-reflection films are formed using Chemical Vapor Deposition (CVD)—a standard process disclosed in the primary references—the films are conformally deposited on the front, back, and lateral sides of the substrate.
  • Motivation to Combine: A POSITA implementing the inventions of the primary combinations using a standard CVD process would have been motivated to incorporate Seo’s teaching (or would have found it to be an inherent result). Allowing the passivation films to cover the lateral sides prevents the creation of performance-degrading recombination sites on the exposed silicon edges. Removing these films would require extra, costly, and complex steps for no technical benefit.
  • Expectation of Success: A POSITA would have expected success in forming the passivation layers on the substrate sides, as it is a natural and beneficial outcome of using a common deposition process like CVD.

• Additional Grounds: Petitioner asserted further obviousness challenges under 35 U.S.C. §103 against claim 11 based on the primary combinations in view of Watabe (Japanese Publication No. JP2010186862A). Watabe taught replacing costly single-layer silver bus bars with a cost-effective dual-layer structure (copper base, silver top) to reduce manufacturing costs while maintaining solderability.

4. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial under §314(a) and the Fintiv factors would be inappropriate. The petition highlighted that a parallel district court case was stayed and that this petition was filed expeditiously. Critically, Petitioner noted that a separate IPR filed by a different petitioner against the same patent on the exact same grounds (Runergy IPR, IPR2025-00007) had already been instituted by the Board, which Petitioner argued demonstrated the compelling merits of the asserted grounds. Petitioner filed a concurrent motion for joinder with the instituted Runergy IPR.

5. Relief Requested

• Petitioner requests institution of an inter partes review and cancellation of claims 1-11 of the ’104 patent as unpatentable.