Canadian Solar USA Inc v. Trina Solar Co Ltd

1. Case Identification

• Case #: IPR2025-00917
• Patent #: 10,230,009
• Filed: April 28, 2025
• Petitioner(s): Canadian Solar (USA) Inc.
• Patent Owner(s): Trina Solar Co., Ltd.
• Challenged Claims: 1-17

2. Patent Overview

• Title: Solar Cell and Method for Manufacturing the Same
• Brief Description: The ’009 patent discloses a solar cell featuring a silicon substrate, a back surface field (BSF) region composed of a polysilicon layer situated on a thin tunnel oxide layer, and an "isolation portion" at the periphery of the back surface. This isolation portion is designed to prevent electrical short-circuiting between the BSF and the front-side emitter region.

3. Grounds for Unpatentability

Ground 1: Obviousness over Jin and Feldmann - Claims 1-8, 11-13, 15, and 17 are obvious over Jin in view of Feldmann.

• Prior Art Relied Upon: Jin (Application # 2013/0056051) and Feldmann (a 2014 journal article titled "Passivated rear contacts for high-efficiency n-type Si solar cells...").
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner asserted that Jin disclosed a bifacial solar cell with all major elements of claim 1 except for the specific back surface structure. Jin taught a conventional diffused BSF and, critically, an "isolation gap" at the periphery of the substrate's rear surface to prevent short-circuiting. Feldmann taught a high-efficiency "Tunnel Oxide Passivated Contact" (TOPCon) structure, which consists of a phosphorus-doped polysilicon layer over an ultra-thin tunnel oxide layer. Petitioner argued that substituting Jin's diffused BSF with Feldmann's superior TOPCon structure would result in the solar cell claimed in the ’009 patent, including the isolation portion taught by Jin.
  • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine Jin and Feldmann to improve the efficiency of Jin's solar cell. Feldmann explicitly taught that its TOPCon structure significantly reduces surface recombination and improves cell performance. Replacing a known, less efficient element (Jin's diffused BSF) with a known, superior alternative (Feldmann's TOPCon structure) was a simple and predictable design choice to achieve a known benefit.
  • Expectation of Success: A POSITA would have a reasonable expectation of success because the combination involved substituting known components that performed their expected functions. The techniques for depositing tunnel oxide and doped polysilicon layers, including using a shadow mask to create Jin's isolation gap, were well-established and would yield predictable results.

Ground 2: Obviousness over Chang and Jin - Claims 1-8, 11-13, 15-17 are obvious over Chang in view of Jin.

• Prior Art Relied Upon: Chang (Application # 2014/0299187) and Jin (Application # 2013/0056051).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner contended that Chang disclosed a bifacial solar cell that already combined the key features from Ground 1: a TOPCon-style structure (backside polysilicon BSF and tunnel oxide layer) and an "isolation region" at the periphery where these layers are not formed. Chang explicitly defined forming layers "entirely" to mean excluding pre-designated areas like a "periphery region" or "isolation region." Petitioner argued that Jin merely supplied the well-understood implementation details for such an isolation region, such as creating a physical "gap T" and covering it with a passivation film, which a POSITA would have used to complete Chang's disclosure.
  • Motivation to Combine: The combination requires no modification to Chang's device; Jin merely provided missing but presumed details. A POSITA reading Chang's disclosure of an isolation region would have looked to analogous art, like Jin (from the same original assignee, LG Electronics), to understand how to implement it. The motivation was to complete Chang's design using a known, effective method for preventing short-circuiting, as detailed by Jin.
  • Expectation of Success: Success was expected because Jin provided a clear, established method for creating the very isolation region mentioned in Chang. Implementing Jin's masking technique to create the gap in Chang's process was a straightforward application of known fabrication steps to achieve the desired, predictable outcome of electrical isolation.

Ground 3: Obviousness over Primary References in view of Seo - Claims 9-10 are obvious over Jin/Feldmann or Chang/Jin in further view of Seo.

• Prior Art Relied Upon: The combinations from Grounds 1 or 2, in further view of Seo (Patent 8,647,914).

• Core Argument for this Ground:

  • Prior Art Mapping: Claims 9 and 10 require the first (back) and second (front) passivation films to have portions extending up the side surfaces of the substrate, with the back film overlapping the front film on the sides. Petitioner argued that neither Jin nor Chang explicitly showed this side coverage. However, Seo taught that forming passivation layers via Chemical Vapor Deposition (CVD)—a common method disclosed in the primary references—naturally results in the layers covering the front, back, and lateral sides of the substrate. Seo explicitly showed a back passivation layer (PSV) overlapping a front anti-reflection layer (ARC) on the substrate's side surfaces, directly mapping to the limitations of claim 10.
  • Motivation to Combine: A POSITA would combine the teachings because it was well-known that leaving the substrate's side surfaces unpassivated would create recombination sites, reducing cell efficiency. A POSITA implementing the Jin/Feldmann or Chang/Jin cells using standard CVD would not have taken extra, costly steps to mask the sides, and thus would have arrived at the configuration taught by Seo as a natural and beneficial result of the standard manufacturing process.
  • Expectation of Success: A POSITA would expect success, as this combination merely involved allowing a standard fabrication process (CVD) to proceed as it normally would, without unnecessary and counterproductive masking steps. The result was a predictable film layout that improved efficiency by passivating all exposed silicon surfaces.

• Additional Grounds: Petitioner asserted additional obviousness challenges. Claim 16 (polysilicon layer thicker than passivation film) was challenged over Jin/Feldmann in view of Chang's thickness teachings. Claim 14 (double-layer bus bar) was challenged over Jin/Feldmann or Chang/Jin in view of Watabe's teachings on cost-effective, dual-layer copper/silver bus bars.

4. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial under 35 U.S.C. §314(a) and the Fintiv factors would be inappropriate. The parallel district court case is stayed, and Petitioner intends to maintain the stay. The petition was filed expeditiously, less than seven months after the complaint. Critically, the PTAB already instituted review on the exact same grounds and prior art in a related case (IPR2025-00006), indicating the merits are compelling and weigh strongly in favor of institution.

5. Relief Requested

• Petitioner requests institution of an inter partes review and cancellation of claims 1-17 of Patent 10,230,009 as unpatentable.