REC Solar Holdings As v. Maxeon Solar Pte Ltd

1. Case Identification

• Case #: IPR2025-00592
• Patent #: 8,222,516
• Filed: February 14, 2025
• Petitioner(s): REC Solar Holdings As
• Patent Owner(s): Maxeon Solar Pte. Ltd.
• Challenged Claims: 9-12

2. Patent Overview

• Title: Front Contact Solar Cell with Formed Emitter
• Brief Description: The ’516 patent relates to a front-contact solar cell featuring a backside junction architecture. The disclosed technology comprises a substrate (e.g., N-type silicon), a doped polysilicon emitter layer (e.g., P-type) formed over the back surface of the substrate, and a thin oxide layer positioned between the substrate and the emitter.

3. Grounds for Unpatentability

Ground 1: Obviousness over Meier, Okayasu, Borden, and Jordan - Claims 9-11 are obvious over Meier in view of Okayasu, Borden, and Jordan.

• Prior Art Relied Upon: Meier (Patent 6,262,359), Okayasu (JP07-106611), Borden (WO 2009/094578), and Jordan (Application # 2005/0268963).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Meier disclosed the foundational structure of a back junction solar cell, including an N-type substrate and a P-type diffused emitter, but lacked key features of the challenged claims. Specifically, Meier did not teach a polysilicon emitter, an interfacial oxide layer, or a textured front surface. Petitioner asserted that the remaining references supplied these missing elements. Okayasu taught the known benefits of replacing diffused emitters with deposited polysilicon emitters to improve performance and allow for lower-temperature processing. Borden disclosed adding a tunnel oxide layer between a polysilicon layer and a substrate to prevent detrimental epitaxial growth and protect the surface. Jordan taught the well-known technique of texturing the front surface of a solar cell to increase light absorption and overall efficiency.
  • Motivation to Combine: A POSITA would combine these known techniques to create a more efficient and robust solar cell. Petitioner asserted it was an obvious design choice to modify Meier's basic cell by replacing its diffused emitter with Okayasu's superior polysilicon emitter, incorporating Borden's beneficial interfacial oxide layer, and applying Jordan's standard front surface texturing to improve light capture.
  • Key Aspects: A central component of Petitioner's argument was that the Patent Owner is collaterally estopped from arguing the patentability of these claims. Petitioner highlighted that in two separate continuation applications stemming from the ’516 patent, the Examiner rejected substantially similar claims as obvious over this same combination of prior art, and the PTAB subsequently affirmed both rejections in final, unappealed decisions.

Ground 2: Obviousness over Froitzheim and Gan - Claims 9-12 are obvious over Froitzheim in view of Gan.

• Prior Art Relied Upon: Froitzheim (EP1732142A1) and Gan (a 1990 IEEE paper).

• Core Argument for this Ground:

  • Prior Art Mapping: Petitioner contended that Froitzheim served as an alternative primary reference, teaching a back junction solar cell with an N-type substrate, a P-type diffused emitter, front surface texturing, and front and rear metal contacts. Froitzheim's diffused emitter, however, was not polysilicon, and it lacked an interfacial oxide layer between the emitter and substrate. Petitioner argued that Gan directly addressed this deficiency by teaching that solar cell performance is significantly improved when a diffused emitter is replaced with a polysilicon emitter that includes an interfacial thermal oxide layer.
  • Motivation to Combine: A POSITA would have been motivated to replace Froitzheim's diffused emitter with the improved polysilicon emitter and oxide layer structure taught by Gan to achieve predictable gains in cell efficiency. Petitioner emphasized that Gan's teachings were directly applicable, as Gan specifically noted the improved performance was obtained in backside contact solar cells like the one disclosed in Froitzheim.
  • Expectation of Success: Petitioner asserted that combining Froitzheim and Gan represented a simple substitution of one known element (a diffused emitter) for another known, superior element (a polysilicon emitter with an oxide layer) to yield a predictable result. This modification, according to Petitioner, was well within the ordinary skill in the art and would not have required undue experimentation.

• Additional Grounds: Petitioner asserted additional obviousness challenges based on similar combinations, including: (1) Claims 9-11 over Meier, Okayasu, Jordan in view of Foglietti and Gan (using Foglietti and Gan to teach the oxide layer instead of Borden); (2) Claims 9-12 over Froitzheim in view of Kwark (using Kwark's teachings on polysilicon emitters with oxide layers instead of Gan); and (3) Claims 9-12 over Froitzheim in view of Borden (using Borden's teachings on tunnel oxides instead of Gan).

4. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial would be inappropriate. Against denial under 35 U.S.C. §325(d), Petitioner asserted that the primary references and arguments were not considered during the original prosecution of the ’516 patent. Regarding the Fintiv factors, Petitioner stipulated that if the inter partes review (IPR) is instituted, it will not pursue in district court any invalidity grounds that were raised or reasonably could have been raised in the petition. Petitioner also noted it is filing concurrently with a motion for joinder to a previously filed IPR, which it argued mitigates concerns about serial petitions under General Plastic.

5. Relief Requested

• Petitioner requested institution of an IPR and cancellation of claims 9-12 of Patent 8,222,516 as unpatentable.