Hanwha Solutions Corp v. Maxeon Solar Pte Ltd

1. Case Identification

• Case #: IPR2024-01203
• Patent #: 8,222,516
• Filed: August 8, 2024
• Petitioner(s): Hanwha Solutions Corporation
• Patent Owner(s): Maxeon Solar Pte. Ltd.
• Challenged Claims: 1-12

2. Patent Overview

• Title: Solar Cell with Backside Junction
• Brief Description: The ’516 patent discloses a solar cell structure designed to convert solar radiation into electrical energy. The structure features an N-type silicon substrate with a P-type polysilicon emitter formed on its back surface, creating a backside junction, with an oxide layer situated between the substrate and the emitter.

3. Grounds for Unpatentability

Ground I: Claims 1-4 and 6-12 are obvious over Froitzheim in view of Gan.

• Prior Art Relied Upon: Froitzheim (EP 1,732,142A1) and Gan (a 1990 IEEE Conference paper).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Froitzheim, which was not considered during prosecution, taught a rear-junction solar cell with all the core elements of the challenged claims except for the specific use of a polysilicon emitter with an oxide layer. Froitzheim disclosed an N-type silicon substrate, a P-type diffused emitter on the back side forming a backside junction, and front and rear metal contacts. Petitioner asserted that Gan taught the precise elements missing from Froitzheim: replacing a diffused emitter with a more efficient P-type polysilicon emitter and including a thin "interfacial oxide" layer between the polysilicon emitter and the silicon substrate. The combination of Froitzheim’s cell architecture with Gan’s improved emitter structure allegedly rendered the claimed invention obvious.
  • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine these references to improve the efficiency of Froitzheim's solar cell. Gan explicitly taught that replacing a diffused emitter with a polysilicon emitter and an interfacial oxide layer improves cell performance by lowering recombination and contact resistance. Applying this known efficiency-improving technique from Gan to the analogous solar cell structure in Froitzheim was presented as a predictable design choice to achieve a more efficient solar cell.
  • Expectation of Success: Petitioner contended a POSITA would have a reasonable expectation of success because Gan provided published data demonstrating the performance benefits. The manufacturing processes described in both references were compatible (e.g., similar thermal diffusion steps and temperature ranges), making the integration a predictable substitution of one known element (a diffused emitter) for another, superior one (a polysilicon emitter with an oxide layer).

Ground II: Claims 1-4 and 6-12 are obvious over Froitzheim in view of Borden-575.

• Prior Art Relied Upon: Froitzheim (EP 1,732,142A1) and Borden-575 (WO 2009/094575).
• Core Argument for this Ground:
  • Prior Art Mapping: This ground presented an alternative to Gan, arguing that Borden-575, also not before the examiner, supplied the teachings of a polysilicon emitter and an oxide layer. Like Gan, Borden-575 taught using a polysilicon emitter with a "tunnel oxide" or "buried oxide" layer to provide passivation between the substrate and emitter, reducing recombination while allowing current flow. Petitioner mapped Froitzheim's backside cell structure and argued that incorporating the emitter structure from Borden-575 would arrive at the claimed invention.
  • Motivation to Combine: The motivation was again to increase cell efficiency. Borden-575 explicitly taught that its polysilicon emitter and oxide layer structure could be "formed on the back of the cell" and was particularly "advantageous if the front of the cell has a texture," a feature disclosed in Froitzheim. This direct teaching of applicability to a backside, textured-front cell like Froitzheim's would have motivated a POSITA to combine the teachings to achieve the known benefits of passivation and reduced recombination.
  • Expectation of Success: Success was expected because Borden-575 provided a clear blueprint for an improved emitter that it stated was compatible with Froitzheim’s cell architecture. The combination represented the application of a known technique to a known device to yield predictable results.

Ground III: Claims 1-2 and 8-11 are obvious over Li in view of Gan.

• Prior Art Relied Upon: Li (CN 1949545A) and Gan (a 1990 IEEE Conference paper).

• Core Argument for this Ground:

  • Prior Art Mapping: This ground substituted Froitzheim with Li as the primary reference. Petitioner asserted that Li taught a backside junction solar cell with an N-type crystalline substrate and a P-type emitter formed by depositing a silicon thin film on the back surface. As in Ground I, Gan was relied upon to teach the modification of replacing Li's deposited emitter with Gan's more efficient P-type polysilicon emitter and interfacial oxide layer.
  • Motivation to Combine: A POSITA would have been motivated to modify Li's backside junction cell by incorporating Gan's known efficiency-improving emitter structure. Petitioner argued that Li's deposited emitter and Gan's polysilicon emitter were readily interchangeable, and a POSITA would have sought to apply Gan's demonstrated efficiency gains to the analogous backside cell structure disclosed by Li.
  • Expectation of Success: A POSITA would have expected success for reasons similar to those in Ground I, primarily because it involved applying a known technique (Gan’s emitter) to a similar device (Li’s cell) to achieve the predictable result of higher efficiency.

• Additional Grounds: Petitioner asserted additional obviousness challenges (Grounds II and IV) based on combinations of Froitzheim, Gan, and Sheats (Application # 2006/0157103) and Froitzheim, Borden-575, and Sheats. These grounds specifically targeted dependent claim 5, relying on Sheats to teach a "trench cutting" feature used for electrical isolation to prevent short circuits, a well-known technique in solar cell manufacturing.

4. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial would be improper under multiple frameworks.
  • General Plastics / §314(a): Petitioner argued against denial based on a previously filed inter partes review (IPR) by Canadian Solar Inc. (CSI), stating there is no relationship between Petitioner and CSI, this petition challenges all claims (1-12) while the CSI petition challenged only a subset (9-12), and the petition is a timely response to litigation initiated by the Patent Owner.
  • §325(d): Denial was argued to be unwarranted because the petition relies on prior art references (Froitzheim, Gan, Borden-575, Li) that were not disclosed to or considered by the USPTO during the original prosecution of the ’516 patent. These references allegedly teach the key oxide layer feature the Examiner previously found lacking in the art of record.
  • Fintiv: Petitioner asserted that discretionary denial under Fintiv is not appropriate because the petition was filed expeditiously after the district court complaint was served, and no trial date or substantive case schedule has been set in the parallel litigation.

5. Relief Requested

• Petitioner requested institution of an inter partes review and cancellation of claims 1-12 of Patent 8,222,516 as unpatentable under 35 U.S.C. §103.