PTAB

IPR2024-01198

Hanwha Solutions Corp v. Maxeon Solar Pte Ltd

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Solar Cell with Doped Portion Having a Dopant Concentration Less Than or Equal to 2x10¹⁸ cm⁻³
  • Brief Description: The ’315 patent describes a solar cell designed to improve efficiency through two primary features. The first is a doped portion on the front side of a silicon substrate with a specific dopant concentration (≤ 2×10¹⁸ cm⁻³), intended to reduce surface recombination. The second is the use of gettering to migrate metal impurities from the substrate into the back-side emitter, where they cause less recombination.

3. Grounds for Unpatentability

Ground 1: Obviousness over Choi, Granek or Marvin, and Istratov - Claims 10-17 and 19-20 are obvious over Choi in view of Granek or Marvin, and in further view of Istratov.

  • Prior Art Relied Upon: Choi (Application # 2014/0311567), Granek (a 2009 Ph.D. dissertation), Marvin (a 1990 technical report), and Istratov (a 2005 journal article).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Choi taught the fundamental structure of a back-contact solar cell claimed in independent claim 10, including a silicon substrate, a front surface field (FSF) layer, a dielectric tunneling layer, and polysilicon emitter regions. However, Choi did not specify a precise dopant concentration for its FSF. Petitioner asserted that Granek and Marvin remedied this by teaching that optimal solar cell efficiency is achieved with an FSF dopant concentration of approximately 1×10¹⁸ cm⁻³, which is within the claimed range. Furthermore, Petitioner argued that Istratov taught the accumulation of metal impurities (e.g., iron, copper) in a polysilicon layer after a heating step, meeting the "metal impurities" limitation of the emitter region.
    • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine Choi with Granek or Marvin to improve the efficiency of Choi’s cell. Since Choi taught an FSF but left the concentration to a POSITA's discretion, it would have been obvious to look to references like Granek and Marvin, which analyzed FSF parameters and taught that a concentration around 1×10¹⁸ cm⁻³ balanced the reduction of surface recombination against the increase in Auger recombination. A POSITA would further combine Istratov to implement gettering, a well-known technique for reducing recombination caused by metal impurities by trapping them in the polysilicon emitter, which was structurally analogous to layers in Choi's cell.
    • Expectation of Success: A POSITA would have had a high expectation of success because the combination involved applying known optimization principles (FSF doping) and conventional processes (gettering) to a standard solar cell structure. The modular nature of solar cell design would allow for optimizing the front surface (FSF doping) and back surface (gettering) independently using standard fabrication techniques.

Ground 2: Obviousness over Choi, Granek or Marvin, Istratov, and Smith - Claim 18 is obvious over the combination of Ground 1 in further view of Smith.

  • Prior Art Relied Upon: The combination from Ground 1, plus Smith (Application # 2013/0240029).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground built upon the combination in Ground 1 to address the limitations of claim 18, which required a trench region separating the first and second emitter regions. Petitioner asserted that Smith expressly taught adding a trench between oppositely doped polysilicon emitter regions on the back side of a solar cell.
    • Motivation to Combine: Smith explicitly stated that directly abutting p-type and n-type polysilicon regions adversely affects efficiency due to high recombination. Smith taught that introducing a trench solves this problem by physically separating the regions, preventing the formation of a space charge region, and improving surface passivation. A POSITA, seeking to improve the efficiency of the solar cell from the primary combination, would have been motivated by Smith's express teaching to add a trench for its known benefits.
    • Expectation of Success: Success was predictable as Smith disclosed standard semiconductor fabrication techniques for forming the trench, which would have been within the skill of a POSITA to implement in the base solar cell structure.

Ground 3: Obviousness over Cousins, Granek or Marvin, and Istratov - Claims 10-15 are obvious over Cousins in view of Granek or Marvin, and in further view of Istratov.

  • Prior Art Relied Upon: Cousins (Patent 8,207,444), Granek (a 2009 Ph.D. dissertation), Marvin (a 1990 technical report), and Istratov (a 2005 journal article).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner presented this ground as an alternative to Ground 1, using Cousins as the primary reference. Petitioner argued that Cousins taught a both-sides-contacted solar cell with all the key structural elements of claim 10: an N-type silicon substrate, a doped front portion (region 105) for low surface recombination, a thin dielectric layer, and a p-type doped polysilicon layer (emitter). Similar to Choi, Cousins did not specify the exact dopant concentration for its front doped portion.
    • Motivation to Combine: The motivation was analogous to Ground 1. A POSITA would combine Cousins with Granek or Marvin to optimize the dopant concentration of the front portion to the level taught by Granek/Marvin (~1×10¹⁸ cm⁻³) to maximize efficiency. A POSITA would also be motivated to incorporate Istratov's gettering process to trap metal impurities in Cousins' polysilicon emitter layer, thereby reducing recombination and further improving performance for the same reasons as in the Choi-based combination.
    • Expectation of Success: A POSITA would have expected success in applying the FSF optimization from Granek/Marvin and the gettering process from Istratov to the Cousins cell, as it involved combining known techniques using standard diffusion and heating processes.

4. Arguments Regarding Discretionary Denial

  • Petitioner argued that discretionary denial is unwarranted. Under the General Plastic factors, Petitioner asserted it has no relationship with Canadian Solar Inc. (CSI), a competitor who filed earlier IPRs, and that this petition raises different prior art and arguments. Under 35 U.S.C. §325(d), Petitioner contended the Examiner erred by allowing the claims without considering any of the highly relevant prior art cited in the petition. Finally, Petitioner argued against denial under the Fintiv factors, stating the petition was filed expeditiously after the district court complaint was served, no trial date is set, and the petition presents compelling merits for institution.

5. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 10-20 of the ’315 patent as unpatentable under 35 U.S.C. §103.