Hanwha Solutions Corporation v. Maxeon Solar Pte. Ltd.

1. Case Identification

• Case #: IPR2024-01198
• Patent #: 11,251,315
• Filed: August 8, 2024
• Petitioner(s): Hanwha Solutions Corporation
• Patent Owner(s): Maxeon Solar Pte. Ltd.
• Challenged Claims: 10-20

2. Patent Overview

• Title: Solar Cell Technology
• Brief Description: The ’315 patent describes a solar cell designed for improved efficiency by combining two main features. The first is a front-side doped portion of a silicon substrate with a dopant concentration below a specific threshold to reduce surface recombination. The second is the gettering of metal impurities from the substrate into a back-side polysilicon emitter to reduce recombination caused by these impurities.

3. Grounds for Unpatentability

Ground I: Obviousness over Choi, Granek or Marvin, and Istratov - Claims 10-17 and 19-20

• 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 asserted that Choi teaches the fundamental structure of a back-contact solar cell recited in independent claim 10, including a silicon substrate, a front surface field (FSF), a back-side dielectric layer, and polysilicon emitter regions. While Choi teaches the FSF has a higher dopant concentration than the substrate, it does not specify a value. Granek and Marvin were argued to supply the claimed FSF dopant concentration of approximately less than or equal to 2×10¹⁸ cm⁻³, teaching that this specific range optimizes efficiency by balancing the reduction of surface recombination against the avoidance of increased Auger recombination. Istratov was argued to teach the gettering of metal impurities (e.g., iron, copper) from a silicon substrate into a polysilicon layer by heating to high temperatures (e.g., above 900°C), which addresses the claimed limitation of an emitter having metal impurities.
  • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine these references to improve the efficiency of Choi's solar cell, a common goal in the field. A POSITA would look to well-documented research like Granek or Marvin to optimize the known FSF parameter for Choi’s cell. To address the known problem of recombination from metal impurities in the substrate, a POSITA would apply the well-established gettering technique taught by Istratov to the Choi/Granek cell, which has the necessary polysilicon emitter to act as a gettering site.
  • Expectation of Success: A POSITA would have a high expectation of success because the combination involves applying known techniques (FSF optimization, impurity gettering) to a known device (a back-contact solar cell) to achieve the predictable result of improved efficiency.

Ground II: Obviousness over Choi, Granek or Marvin, Istratov, and Smith - Claim 18

• Prior Art Relied Upon: Choi (Application # 2014/0311567), Granek (a 2009 Ph.D. dissertation) or Marvin (a 1990 technical report), Istratov (a 2005 journal article), and Smith (Application # 2013/0240029).
• Core Argument for this Ground:
  • Prior Art Mapping: This ground builds on Ground I and adds Smith to address the limitation of claim 18, which recites a "trench region" that separates the first and second emitter regions. Petitioner argued that Smith explicitly teaches adding a trench between oppositely doped polysilicon emitter regions in a back-contact solar cell.
  • Motivation to Combine: Smith was argued to directly address the problem of reduced efficiency caused by recombination where P-type and N-type emitter regions abut. A POSITA, having constructed the cell of Ground I, would be motivated to incorporate Smith’s trench to further improve efficiency by physically isolating the emitters, a known problem with a known solution provided by Smith.
  • Expectation of Success: The modification is a straightforward integration of a known structural element (a trench) for its intended and predictable purpose of preventing recombination between adjacent doped regions.

Ground III: Obviousness over Cousins, Granek or Marvin, and Istratov - Claims 10-15

• Prior Art Relied Upon: Cousins (Patent 8,207,444), Granek (a 2009 Ph.D. dissertation) or Marvin (a 1990 technical report), and Istratov (a 2005 journal article).
• Core Argument for this Ground:
  • Prior Art Mapping: This ground substitutes Cousins for Choi as the primary reference. Petitioner asserted that Cousins teaches a both-sides-contacted solar cell with the key claimed features: an N-type silicon substrate, a front-side doped region to reduce recombination, a thin dielectric layer on the back side, and a P-type polysilicon layer (emitter) formed over the dielectric. As in Ground I, Granek or Marvin were argued to provide the specific FSF dopant concentration, and Istratov was argued to provide the teaching of gettering metal impurities into the polysilicon emitter.
  • Motivation to Combine: The motivation is parallel to Ground I. A POSITA would be motivated to improve the efficiency of the solar cell disclosed in Cousins by applying the known optimization techniques from Granek/Marvin for the FSF and the known gettering process from Istratov to reduce recombination from metallic impurities.
  • Expectation of Success: A POSITA would expect success in combining these references, as it involves applying established, modular design principles for improving solar cell performance to the analogous structure taught by Cousins.

4. Arguments Regarding Discretionary Denial

• Petitioner presented extensive arguments that discretionary denial would be inappropriate.
• General Plastic Factors: Petitioner argued against denial based on earlier-filed petitions by Canadian Solar Inc. (CSI), stating that Petitioner and CSI are unrelated competitors, not co-petitioners. It was argued that this petition presents materially different prior art and arguments, challenges additional claims not asserted by CSI, and was filed timely in response to a separate litigation complaint from the Patent Owner.
• §325(d) Factors: Petitioner contended that denial under 35 U.S.C. §325(d) is unwarranted because the Examiner allowed the claims of the ’315 patent without any rejections and without considering the primary prior art references asserted in this petition (Choi, Granek, Marvin, Istratov, Smith). Petitioner argued the Examiner erred by not properly vetting the claims.
• Fintiv Factors: Petitioner argued that the parallel district court litigation is in its earliest stages, with no trial date set and the answer to the complaint not yet due. This, combined with the petition's compelling merits, was argued to weigh strongly in favor of institution.

5. Relief Requested

• Petitioner requests institution of an inter partes review (IPR) and cancellation of claims 10-20 of Patent 11,251,315 as unpatentable.