PTAB

IPR2025-00594

REC Solar Holdings As v. Maxeon Solar Pte Ltd

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1. Case Identification

2. Patent Overview

  • Title: Solar Cells with Improved Lifetime, Passivation and/or Efficiency
  • Brief Description: The ’315 patent discloses a back-contact solar cell featuring a silicon substrate with a specific front-side dopant concentration, a dielectric region on the back side, and polysilicon emitter regions formed over the dielectric layer that contain metal impurities. The invention purports to improve solar cell efficiency and lifetime through this specific structure.

3. Grounds for Unpatentability

Ground 1: Obviousness over Li and Front Doping References - Claims 10-12 and 15 are obvious over Li in view of King, Swanson-352, or Marvin.

  • Prior Art Relied Upon: Li (Application # 2011/0214719), King (a 1990 journal article), Swanson-352 (Patent 4,234,352), and Marvin (a 1989 conference paper).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Li discloses all structural elements of the back-contact solar cell recited in claim 10 except for two: the specific front-side dopant concentration and the presence of metal impurities in the emitter. Li teaches a back-contact cell with a silicon substrate, a backside dielectric layer (tunnel oxide), and doped polysilicon emitter regions. Petitioner contended the two missing limitations were either obvious or inherent. First, King, Swanson-352, and Marvin all explicitly taught that for optimal efficiency in back-contact solar cells, the front surface dopant concentration should be approximately 1x10¹⁸ cm⁻³, which is consistent with the claimed limitation of "less than or equal to 2x10¹⁸ cm⁻³." Second, Petitioner asserted that the "metal impurities" limitation is inherently disclosed by Li. Li’s fabrication process involves heating the cell to 950°C to diffuse dopants into the backside polysilicon emitters. Petitioner argued this temperature is well-known to cause "gettering," a process where metal impurities naturally present in the silicon substrate migrate into the polysilicon layer, thereby satisfying the claim limitation.
    • Motivation to Combine: A POSITA would combine Li with King, Swanson-352, or Marvin to improve the efficiency of Li's disclosed solar cell. Applying the known, optimal front dopant concentrations taught by the secondary references to Li's basic structure was presented as a predictable design choice to achieve a well-understood benefit.
    • Expectation of Success: A POSITA would have had a high expectation of success because the combination involved applying a known optimization parameter (dopant concentration) to a standard solar cell architecture (Li's back-contact cell) using conventional fabrication techniques.

Ground 2: Obviousness over Li and Muller - Claims 10 and 13-15 are obvious over Li in view of Muller.

  • Prior Art Relied Upon: Li (Application # 2011/0214719) and Muller (a 2014 journal article).

  • Core Argument for this Ground:

    • Prior Art Mapping: This ground is an alternative to Ground 1 for providing the missing front dopant concentration in Li. Muller taught a back-contact solar cell with a front doped region having a peak concentration of approximately 2x10¹⁸ cm⁻³, satisfying that limitation of claim 10. Crucially, Muller also disclosed that using a boron-doped (P-type) front region via ion implantation resulted in higher efficiency and superior resistance to UV degradation compared to a phosphorus-doped (N-type) region. Petitioner argued this teaching renders claims 13 (P-type dopants) and 14 (boron) obvious. The arguments for the remaining structural elements based on Li, including the inherency of metal impurities, remained the same as in Ground 1.
    • Motivation to Combine: A POSITA would have been motivated to replace the N-type diffused front portion of Li’s cell with the P-type (boron) ion-implanted front portion taught by Muller to achieve the demonstrated benefits of higher efficiency and improved stability against UV degradation.
    • Expectation of Success: The modification would have been straightforward, as substituting one known front-surface doping technique for another was within the ordinary skill in the art. Muller’s teachings confirmed the benefits of this specific substitution, providing a strong expectation of success.

  • Additional Grounds: Petitioner asserted additional obviousness challenges to claims 10-15 based on the primary combinations (Li with King/Swanson-352/Marvin, or Li with Muller) further in view of Hu (Patent 4,053,335) and Ramappa (a 1999 journal article). These grounds were presented to explicitly teach the gettering of metal impurities into backside polysilicon layers, in the event the Board disputes that this feature is inherently disclosed by Li's high-temperature processing step.

4. Arguments Regarding Discretionary Denial

  • Petitioner argued that discretionary denial is inappropriate. First, regarding General Plastic factors for follow-on petitions, Petitioner asserted it is joining a previously instituted IPR (IPR2024-01038) and is not engaging in abusive filing or "road mapping." Second, to overcome Fintiv concerns related to a parallel district court case, Petitioner stipulated that if the IPR is instituted, it will not pursue in the district court any ground that it raised or reasonably could have raised in the petition. Third, Petitioner argued denial under §325(d) is unwarranted because the primary prior art references (Li, King, Swanson-352, Marvin, and Muller) were not before the Examiner during the original prosecution of the ’315 patent.

5. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 10-15 of the ’315 patent as unpatentable.