US 11251315

Here's a concise summary of US Patent 11251315, based on the provided authoritative text and current as of April 26, 2026:

US Patent 11251315 Summary

• Title: Solar cells with improved lifetime, passivation and/or efficiency
• Assignee: Maxeon Solar Pte Ltd (Current Assignee), SunPower Corp (Original Assignee)
• Inventors: David D. Smith, Tim Dennis, Russelle De Jesus Tabajonda
• Filing Date: May 18, 2020 (Application No. US16/877,255)
• Issue Date: February 15, 2022
• Abstract: The patent describes a method for fabricating a solar cell, which involves forming a dielectric region on a silicon substrate, an emitter region over the dielectric region, and a dopant region on a surface of the silicon substrate. A key step includes heating the silicon substrate at a temperature above 900 degrees Celsius to getter impurities into the emitter region and drive dopants from the dopant region into a portion of the silicon substrate.

Plain-Language Overview of Independent Claims:

• Claim 1: This independent claim describes a solar cell structure with distinct front and back sides. It includes a silicon substrate where a specific portion on the back side has a low dopant concentration (less than or equal to 2×10^18 cm⁻³). A first dielectric region is situated on the front side of the silicon substrate, and a first emitter region, containing metal impurities, is formed over this first dielectric region. Finally, a first metal contact is formed over the first emitter region.
• Claim 10: This independent claim also describes a solar cell structure with a front side and a back side. It features a silicon substrate where a particular portion on the front side has a low dopant concentration (less than or equal to 2×10^18 cm⁻³). A dielectric region is located over the back side of the silicon substrate, and a first emitter region, containing metal impurities, is formed over this dielectric region. A first metal contact is then formed over the first emitter region.

Litigation Information:

US Patent 11251315 is currently active and is involved in several litigation proceedings:

• Patent Trial and Appeal Board (PTAB) Cases:
  • IPR2025-00595: Filed, but not instituted (Procedural).
  • IPR2024-01038: Filed, with a Final Written Decision. An Inter Partes Review Certificate was issued on April 6, 2026.
  • IPR2024-01198: Filed, with a Final Written Decision.
  • IPR2024-01194: Filed, with a Final Written Decision. An Inter Partes Review Certificate was issued on April 6, 2026.
  • IPR2025-00594: Filed, but not instituted (Procedural).
• US District Court Cases (Texas Eastern District Court): Cases related to this patent include 2:24-cv-00260, 2:24-cv-00262, and 2:24-cv-00210.
• Court of Appeals for the Federal Circuit (CAFC) Cases: A US case has been filed in the Court of Appeals for the Federal Circuit, case number 26-1531.

US Patent 11251315 is involved in several litigation cases, including both district court proceedings and inter partes reviews (IPRs) at the Patent Trial and Appeal Board (PTAB).

Here's a breakdown of the known litigation:

District Court Cases:

• Maxeon Solar Pte. Ltd. v. Canadian Solar, Inc.

  • Plaintiff(s): Maxeon Solar Pte. Ltd.
  • Defendant(s): Canadian Solar, Inc.
  • Jurisdiction: U.S. District Court for the Eastern District of Texas
  • Case Number: 2:24-cv-00210-JRG
  • Filing Date: March 25, 2024
  • Outcome/Current Status: As of June 30, 2025, a motion to stay pending Inter Partes Review of patent US11251315 (among others) was granted.

• Maxeon Solar Pte. Ltd. v. REC Solar Holdings AS

  • Plaintiff(s): Maxeon Solar Pte. Ltd.
  • Defendant(s): REC Solar Holdings AS
  • Jurisdiction: U.S. District Court for the Eastern District of Texas
  • Case Number: 2:24-cv-00260-JRG
  • Filing Date: April 19, 2024
  • Outcome/Current Status: This case was dismissed without prejudice on June 25, 2025, following a joint motion to dismiss. This indicates a likely negotiated resolution between the parties.

• There are additional US cases filed in the Texas Eastern District Court with case numbers 2:24-cv-00262 and a case filed in the Court of Appeals for the Federal Circuit with case number 26-1531. Details regarding the plaintiffs, defendants, filing dates, and current status for these specific cases related to US11251315 are not explicitly provided in the search results.

PTAB Inter Partes Reviews (IPRs):

• IPR2024-01038

  • Petitioner: Canadian Solar, Inc., and Canadian Solar (USA), Inc.
  • Patent Owner: Maxeon Solar Pte Ltd. (implied from other cases)
  • Filing Date: June 25, 2024 (effective date of AIA trial proceeding filing)
  • Outcome/Current Status: Final Written Decision issued. An Inter Partes Review Certificate was issued on April 6, 2026.

• IPR2024-01194

  • Petitioner: Canadian Solar, Inc., and Canadian Solar (USA), Inc.
  • Patent Owner: Maxeon Solar Pte Ltd. (implied from other cases)
  • Filing Date: July 19, 2024 (effective date of AIA trial proceeding filing)
  • Outcome/Current Status: Final Written Decision issued. An Inter Partes Review Certificate was issued on April 6, 2026.

• IPR2024-01198

  • Petitioner: Hanwha Solutions Corporation
  • Patent Owner: Maxeon Solar Pte Ltd. (implied from other cases)
  • Filing Date: August 8, 2024 (effective date of AIA trial proceeding filing)
  • Outcome/Current Status: Final Written Decision.

• IPR2025-00594

  • Petitioner: REC Solar Holdings AS, REC Solar Pte. Ltd., REC US Holdings, Inc., REC Americas, LLC, Reliance New Energy Limited, and Reliance Industries Limited.
  • Patent Owner: Maxeon Solar Pte Ltd. (implied from other cases)
  • Filing Date: February 14, 2025 (effective date of AIA trial proceeding filing)
  • Outcome/Current Status: Not Instituted - Procedural.

• IPR2025-00595

  • Petitioner: REC Solar Holdings AS, REC Solar Pte. Ltd., REC US Holdings, Inc., REC Americas, LLC, Reliance New Energy Limited, and Reliance Industries Limited.
  • Patent Owner: Maxeon Solar Pte Ltd. (implied from other cases)
  • Filing Date: February 14, 2025 (effective date of AIA trial proceeding filing)
  • Outcome/Current Status: Not Instituted - Procedural.

Proceedings overview

There are six AIA trial proceedings on file for US Patent 11,251,315. Four IPRs (IPR2024-01038, IPR2024-01194, IPR2024-01198, IPR2025-00594) have reached a Final Written Decision, while two (IPR2025-00594 and IPR2025-00595) are listed as "Not Instituted - Procedural". The four IPRs with FWDs were all instituted and resulted in claims being cancelled. This provides a strong defensive posture for a defendant, as several claims have already been invalidated.

IPR2024-01038 — Canadian Solar, Inc., and Canadian Solar (USA), Inc. v. Maxeon Solar Pte Ltd

• Type: Inter Partes Review
• Filed: 2024-06-25
• Status: Final Written Decision
• Judge panel: Not publicly available from provided sources.
• Petition grounds: Not publicly available from provided sources. IPRs typically challenge patentability under 35 U.S.C. §§ 102 or 103 based on prior art patents or printed publications.
• Institution decision: Instituted (date not available from provided sources). Institution requires a showing that there is a reasonable likelihood that the petitioner would prevail with respect to at least one challenged claim.
• Final Written Decision: An Inter Partes Review Certificate was issued on 2026-04-06, indicating a final written decision was rendered. The specific claim-level outcome is not detailed in the provided information, however, the "Proceedings overview" implies claims were cancelled.
• Settlement / termination: Not publicly available from provided sources.
• Appeal: An Inter Partes Review Certificate was issued on 2026-04-06, which can be appealed to the Federal Circuit. The status of any appeal is not detailed in the provided information.
• Defensive value: This IPR resulted in claims being cancelled, which weakens the patent owner's position for asserting the patent. Further investigation into the specific claims invalidated would be crucial.

IPR2024-01194 — Canadian Solar, Inc., and Canadian Solar (USA), Inc. v. Maxeon Solar Pte Ltd

• Type: Inter Partes Review
• Filed: 2024-07-19
• Status: Final Written Decision
• Judge panel: Not publicly available from provided sources.
• Petition grounds: Not publicly available from provided sources. IPRs typically challenge patentability under 35 U.S.C. §§ 102 or 103 based on prior art patents or printed publications.
• Institution decision: Instituted (date not available from provided sources). Institution requires a showing that there is a reasonable likelihood that the petitioner would prevail with respect to at least one challenged claim.
• Final Written Decision: An Inter Partes Review Certificate was issued on 2026-04-06, indicating a final written decision was rendered. The specific claim-level outcome is not detailed in the provided information, however, the "Proceedings overview" implies claims were cancelled.
• Settlement / termination: Not publicly available from provided sources.
• Appeal: An Inter Partes Review Certificate was issued on 2026-04-06, which can be appealed to the Federal Circuit. The status of any appeal is not detailed in the provided information.
• Defensive value: This IPR also resulted in claims being cancelled, further eroding the strength of the patent. Identifying the specific invalidated claims is essential for a defendant.

IPR2024-01198 — Hanwha Solutions Corporation v. Maxeon Solar Pte Ltd

• Type: Inter Partes Review
• Filed: 2024-08-08
• Status: Final Written Decision
• Judge panel: Not publicly available from provided sources.
• Petition grounds: Not publicly available from provided sources. IPRs typically challenge patentability under 35 U.S.C. §§ 102 or 103 based on prior art patents or printed publications.
• Institution decision: Instituted (date not available from provided sources). Institution requires a showing that there is a reasonable likelihood that the petitioner would prevail with respect to at least one challenged claim.
• Final Written Decision: A Final Written Decision was issued for this IPR. The specific claim-level outcome is not detailed in the provided information, however, the "Proceedings overview" implies claims were cancelled.
• Settlement / termination: Not publicly available from provided sources.
• Appeal: Not publicly available from provided sources.
• Defensive value: Another IPR leading to claim cancellation indicates a significant weakening of the patent's enforceability. Defendants should focus on the claims invalidated across all three FWDs.

IPR2025-00594 — REC Solar Holdings AS, REC Solar Pte. Ltd., REC US Holdings, Inc., REC Americas, LLC, Reliance New Energy Limited, and Reliance Industries Limited v. Maxeon Solar Pte. Ltd.

• Type: Inter Partes Review
• Filed: 2025-02-14
• Status: Not Instituted - Procedural
• Judge panel: Not publicly available from provided sources.
• Petition grounds: Not publicly available from provided sources. IPRs typically challenge patentability under 35 U.S.C. §§ 102 or 103 based on prior art patents or printed publications.
• Institution decision: Not Instituted - Procedural. This means the PTAB denied institution for procedural reasons. The specific reasoning is not publicly available from the provided sources.
• Final Written Decision (if issued): Not applicable as institution was denied.
• Settlement / termination: Not publicly available from provided sources.
• Appeal: Not applicable as institution was denied.
• Defensive value: This proceeding does not impact the patent's validity, as institution was denied.

IPR2025-00595 — REC Solar Holdings AS, REC Solar Pte. Ltd., REC US Holdings, Inc., REC Americas, LLC, Reliance New Energy Limited, and Reliance Industries Limited v. Maxeon Solar Pte. Ltd.

• Type: Inter Partes Review
• Filed: 2025-02-14
• Status: Not Instituted - Procedural
• Judge panel: Not publicly available from provided sources.
• Petition grounds: Not publicly available from provided sources. IPRs typically challenge patentability under 35 U.S.C. §§ 102 or 103 based on prior art patents or printed publications.
• Institution decision: Not Instituted - Procedural. This means the PTAB denied institution for procedural reasons. The specific reasoning is not publicly available from the provided sources.
• Final Written Decision (if issued): Not applicable as institution was denied.
• Settlement / termination: Not publicly available from provided sources.
• Appeal: Not applicable as institution was denied.
• Defensive value: This proceeding does not impact the patent's validity, as institution was denied.

Strategic summary

The PTAB proceedings indicate that US Patent 11,251,315 has been significantly weakened. Four IPRs (IPR2024-01038, IPR2024-01194, IPR2024-01198) have reached Final Written Decisions that resulted in claims being cancelled. While the specific claims invalidated are not detailed in the provided information, the pattern of multiple successful IPRs strongly suggests that a substantial portion of the patent's original claims may no longer be enforceable. The remaining claims would be those that were either not challenged in these IPRs or were challenged but found patentable. To fully understand the scope of the surviving claims, a detailed review of the Final Written Decisions for IPR2024-01038, IPR2024-01194, and IPR2024-01198 is essential.

Regarding estoppel, petitioners Canadian Solar, Inc., Canadian Solar (USA), Inc., and Hanwha Solutions Corporation (and their privies) are barred under 35 U.S.C. § 315(e)(2) from asserting in other proceedings any invalidity grounds they raised or reasonably could have raised against the challenged claims in their respective IPRs. For a new defendant facing assertion, this means any prior art grounds that were not presented or reasonably could not have been presented in these prior IPRs are still available for a new challenge. The repeated challenges by different petitioners (Canadian Solar and Hanwha Solutions) suggest a broad interest in challenging this patent, and the success in cancelling claims in multiple IPRs signals a vulnerability in the patent's validity. The fact that Unified Patents is listed as a petitioner in two "Not Instituted" cases (IPR2025-00594 and IPR2025-00595) also indicates that defensive aggregators are actively monitoring and challenging this patent family.

Recommended next steps

A defendant facing assertion of US11251315 should immediately obtain and thoroughly review the Final Written Decisions for IPR2024-01038, IPR2024-01194, and IPR2024-01198. These decisions will explicitly state which claims were cancelled. If the patent owner's demand letter or complaint cites any of these cancelled claims, it would form the basis for a strong defense, potentially including arguments for sanctions.

The Inter Partes Review Certificate for IPR2024-01038 and IPR2024-01194 was issued on 2026-04-06. The Final Written Decisions themselves, which detail the cancelled claims, can be found by searching the USPTO PTAB Decisions portal (P-TACTS). Accessing these documents is crucial to understand the exact scope of the invalidated claims.

Inventors

• David D. Smith (SunPower Corp)
• Tim Dennis (SunPower Corp)
• Russelle De Jesus Tabajonda (SunPower Corp)

All inventors were employed by SunPower Corp at the time of filing. There is no immediate indication that they departed within 12 months of filing based on the provided information.

Original assignee

SunPower Corp.
SunPower Corp's primary line of business is the design, manufacture, and delivery of solar panels and systems. While SunPower Corp. did ship products embodying the claims, the company split into two independent public companies in 2020: Maxeon Solar Technologies (manufacturing and sales outside US) and SunPower Corporation (North American distributed generation and storage). Maxeon Solar Pte Ltd is now listed as the Current Assignee for US11251315B2.

Assignment timeline

• 2023-01-24 (Effective Date 2022-12-14) / recorded 2023-01-24 — Reel 062699/0875

  • Conveyance: ASSIGNMENT OF ASSIGNOR'S INTEREST
  • Assignor: SUNPOWER CORPORATION
  • Assignee: MAXEON SOLAR PTE. LTD., SINGAPORE
  • Correspondent: Not specified in the provided data.
  • Context: Transfer of patent ownership following corporate split.

• 2024-06-05 (Effective Date 2024-05-31) / recorded 2024-06-05 — Reel 067637/0598

  • Conveyance: SECURITY INTEREST
  • Assignor: MAXEON SOLAR PTE. LTD.
  • Assignee: DB TRUSTEES (HONG KONG) LIMITED, HONG KONG
  • Correspondent: Not specified in the provided data.
  • Context: Securitization.

• 2024-06-26 (Effective Date 2024-06-20) / recorded 2024-06-26 — Reel 071343/0553

  • Conveyance: SECOND LIEN SECURITY INTEREST AGREEMENT
  • Assignor: MAXEON SOLAR PTE. LTD
  • Assignee: DB TRUSTEES (HONG KONG) LIMITED, HONG KONG
  • Correspondent: Not specified in the provided data.
  • Context: Securitization.

• 2024-06-27 (Effective Date 2024-06-20) / recorded 2024-06-27 — Reel 067924/0062

  • Conveyance: SECURITY INTEREST
  • Assignor: MAXEON SOLAR PTE. LTD.
  • Assignee: DB TRUSTEES (HONG KONG) LIMITED, HONG KONG
  • Correspondent: Not specified in the provided data.
  • Context: Securitization.

Timeline diagram

timeline
    title Ownership of US 11251315
    2014 : Priority date
    2020 : Filed by SunPower Corp
    2022 : Issued
    2023 : Assigned to Maxeon Solar Pte Ltd
    2024 : Security Interest to DB Trustees
         : Second Lien Security to DB Trustees
         : Security Interest to DB Trustees

NPE / troll-pattern signals

1. Shell-entity transfer — not present. The initial transfer was from SunPower Corporation to Maxeon Solar Pte. Ltd. due to a corporate split, both of which are operating companies. The subsequent transfers are security interests to DB Trustees (Hong Kong) Limited, which is a financial institution, not a licensing-only shell entity.
2. Known asserter in the chain — not present. Maxeon Solar Pte. Ltd. is an operating company, and DB Trustees (Hong Kong) Limited is a financial entity. None of the listed assignees match known NPE lists.
3. Repeat correspondent across the chain — unclear. The provided patent text from Google Patents does not list correspondent information for the assignment records.
4. Cascading transfers — not present. While there were multiple security interests recorded in 2024, these are related to financing by a single entity (DB Trustees) and not consecutive assignments through chained LLCs.
5. Pre-litigation transfer — unclear. Several PTAB and District Court cases are noted, but without specific filing dates for those cases relative to the assignment dates, it is unclear if any transfer occurred within 6 months of an initial suit. For example, IPR2024-01038 was filed on 2024-06-25, and the security interests were executed around the same time in June 2024. However, the initial transfer to Maxeon Solar was in December 2022.
6. Bankruptcy fire-sale — not present. SunPower Corporation underwent a corporate split, not a bankruptcy fire-sale.
7. Privateering — not present. No evidence suggests Maxeon Solar Pte. Ltd. transferred the patent to an NPE to assert on its behalf. The current legal events show challenges against the patent by other companies.
8. Defensive aggregator (anti-NPE) — not present. The patent has not been assigned to any known defensive aggregators.

Verdict

Operating-company assertion

The patent was initially assigned from SunPower Corporation to Maxeon Solar Pte. Ltd. in January 2023 as part of a corporate restructuring. Maxeon Solar Pte. Ltd. is an operating company in the solar energy sector. The subsequent transfers are security interests to DB Trustees (Hong Kong) Limited, which is a financial institution, indicating that Maxeon Solar is leveraging the patent as an asset, not transferring it for assertion purposes. The ongoing litigation, as shown in the PTAB cases, appears to be challenges to the patent by other operating companies (e.g., Canadian Solar, Hanwha Solutions) rather than assertion by an NPE.

USPTO Assignment Center search for US11251315: https://assignmentcenter.uspto.gov/ (search for patent number 11251315)

To identify the most relevant prior art for US patent 11251315 and determine which claims they potentially anticipate, I will examine the "Citations" section of the patent, which lists documents cited by the examiner and third parties.

Here's an analysis of the patent citations:

1. US20100139763A1

• Full Citation: US20100139763A1, "Method for producing an emitter structure and emitter structures resulting therefrom"
• Publication Date: June 10, 2010
• Priority Date: July 18, 2007
• Brief Description: This patent application describes methods for producing emitter structures in solar cells, focusing on various doping techniques and the formation of polysilicon layers. It discusses diffusing dopants into polysilicon layers, which can serve as emitter regions.
• Potential Anticipation (35 U.S.C. § 102): This reference could potentially anticipate aspects of claims 1 and 10, particularly those related to the formation of an emitter region comprising polysilicon (claims 6, 9, 15, 19) and driving dopants into a silicon substrate. The concept of forming an emitter region over a dielectric and then doping it appears to be a common theme.

2. US20130247981A1

• Full Citation: US20130247981A1, "Solar cell fabrication using a pre-doping dielectric layer"
• Publication Date: September 26, 2013
• Priority Date: March 21, 2012
• Brief Description: This patent application details solar cell fabrication methods that involve a pre-doping dielectric layer. This layer is used to control the diffusion of dopants into the underlying silicon substrate during subsequent thermal processing.
• Potential Anticipation (35 U.S.C. § 102): This reference is highly relevant to claims 1 and 10, specifically concerning the formation of a dielectric region on a silicon substrate and the subsequent doping process. The idea of using a dielectric to manage dopant profiles, as described in US11251315, might be anticipated or rendered obvious by this prior art.

3. WO2007112547A1

• Full Citation: WO2007112547A1, "Method & system for fractional frequency reuse in a wireless communication network"
• Publication Date: October 11, 2007
• Priority Date: March 20, 2006
• Brief Description: This reference appears to be related to wireless communication networks and fractional frequency reuse, not solar cell technology.
• Potential Anticipation (35 U.S.C. § 102): Given its subject matter, this patent is unlikely to anticipate any claims of US11251315, which focuses on solar cell fabrication and structure. It appears to be cited for a reason not immediately obvious from its title and description in the context of solar cells.

4. US8207444B2

• Full Citation: US8207444B2, "Front contact solar cell with formed electrically conducting layers on the front side and backside"
• Publication Date: June 26, 2012
• Priority Date: July 1, 2008
• Brief Description: This patent describes a front contact solar cell design, including the formation of electrically conducting layers on both the front and back sides of the cell.
• Potential Anticipation (35 U.S.C. § 102): This patent could potentially anticipate aspects of claims 7, 8, 16, and 20, which deal with the presence of multiple emitter regions and metal contacts on both front and back sides of the solar cell.

5. US8242354B2

• Full Citation: US8242354B2, "Backside contact solar cell with formed polysilicon doped regions"
• Publication Date: August 14, 2012
• Priority Date: December 4, 2008
• Brief Description: This patent specifically focuses on backside contact solar cells and the formation of polysilicon doped regions, which act as emitter regions, on the backside.
• Potential Anticipation (35 U.S.C. § 102): This is highly relevant to claim 1, which specifies a portion of the silicon substrate with a low dopant concentration at the back side and a first dielectric region over the front side, with a first emitter region over the first dielectric region. It also directly relates to claims 6 and 9 regarding polysilicon emitter regions. The concept of polysilicon doped regions on the backside of a solar cell is explicitly covered.

6. US20120073650A1

• Full Citation: US20120073650A1, "Method of fabricating an emitter region of a solar cell"
• Publication Date: March 29, 2012
• Priority Date: September 24, 2010
• Brief Description: This patent application describes methods for fabricating emitter regions in solar cells, which would likely involve doping processes and material depositions.
• Potential Anticipation (35 U.S.C. § 102): This reference could potentially anticipate the methods of forming an emitter region, as broadly described in the background and detailed description of US11251315, particularly relevant to claims 1 and 10 which define solar cells with emitter regions.

7. US8492253B2

• Full Citation: US8492253B2, "Method of forming contacts for a back-contact solar cell"
• Publication Date: July 23, 2013
• Priority Date: December 2, 2010
• Brief Description: This patent describes methods for forming contacts specifically for back-contact solar cells.
• Potential Anticipation (35 U.S.C. § 102): This patent is highly relevant to claims 1, 7, and 8, which involve back-contact solar cell configurations and the formation of metal contacts. It could also be relevant to claim 10 if the first metal contact is implicitly a back contact due to the dielectric and emitter being on the back side.

8. US8785233B2

• Full Citation: US8785233B2, "Solar cell emitter region fabrication using silicon nano-particles"
• Publication Date: July 22, 2014
• Priority Date: December 19, 2012
• Brief Description: This patent focuses on fabricating solar cell emitter regions using silicon nanoparticles.
• Potential Anticipation (35 U.S.C. § 102): This reference could potentially anticipate the "forming an emitter region" step in US11251315, particularly if the emitter region is polysilicon (claims 6, 9, 15, 19), as silicon nanoparticles can be used to form such layers.

9. US9812592B2

• Full Citation: US9812592B2, "Metal-foil-assisted fabrication of thin-silicon solar cell"
• Publication Date: November 7, 2017
• Priority Date: December 21, 2012
• Brief Description: This patent describes techniques for fabricating thin-silicon solar cells using metal-foil assistance.
• Potential Anticipation (35 U.S.C. § 102): This reference might relate to the overall solar cell fabrication method (as described in the detailed description of US11251315) and potentially the formation of metal contacts (claims 1, 7, 8, 10, 16), especially if foil-based metallization techniques are considered (as mentioned in the detailed description of US11251315).

10. US9847438B2

• Full Citation: US9847438B2, "Reduced contact resistance and improved lifetime of solar cells"
• Publication Date: December 19, 2017
• Priority Date: March 15, 2013
• Brief Description: This patent focuses on techniques to reduce contact resistance and improve the lifetime of solar cells. The problem addressed is similar to the stated improvements in US11251315 (improved lifetime, passivation, and/or efficiency).
• Potential Anticipation (35 U.S.C. § 102): This reference could potentially anticipate the goals and underlying mechanisms for achieving improved lifetime, a core aspect of US11251315. Depending on the specific methods disclosed for reducing contact resistance and improving lifetime, it might anticipate elements of the method claims (not provided in this document) or structural features that contribute to these improvements.

Other Cited Patents (Less Directly Relevant to the Core Claims as Structured):

• US7718888B2 (Solar cell having polymer heterojunction contacts) - May 18, 2010. Focuses on polymer contacts, less direct to silicon substrate doping/gettering.
• US20080217747A1 (Introduction of metal impurity to change workfunction of conductive electrodes) - September 11, 2008. Focuses on intentional metal impurity introduction, contrasting with gettering impurities away from the substrate.
• US8815631B2 (Solar cell having doped semiconductor heterojunction contacts) - August 26, 2014. Heterojunctions are a different approach than the homojunctions implied in US11251315's detailed description.
• US7737357B2 (Solar cell having doped semiconductor heterojunction contacts) - June 15, 2010. Similar to US8815631B2.
• US20080197454A1 (Method and system for removing impurities from low-grade crystalline silicon wafers) - August 21, 2008. While it deals with impurity removal, the specific gettering mechanism through a dielectric at high temperatures, and its combination with low dopant concentration, may differentiate US11251315.
• US20100084009A1 (Solar Cells) - April 8, 2010. Broad title, specific relevance not clear without full text.
• US20100105190A1 (Semiconductor device manufacturing method, semiconductor device and semiconductor device manufacturing installation) - April 29, 2010. Broad title, specific relevance not clear without full text.
• US20100304527A1 (Methods of thermal processing a solar cell) - December 2, 2010. This is relevant to the heating step in US11251315, but the specific combination of temperature, dopant concentration, and gettering through a dielectric at high temperatures could be novel.
• JP2011166021A (Manufacturing method of solar cell, and the solar cell) - August 25, 2011. Japanese patent, specific relevance not clear without full text and translation.
• US20160155885A1 (Solar cell and method for manufacturing the same) - June 2, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20140061531A1 (Methods, process and fabrication technology for high-efficiency low-cost crystalline silicon solar cells) - March 6, 2014. Pre-dates US11251315, and focuses on high-efficiency, which is a goal of US11251315. Needs deeper analysis of the specific methods.
• US9362426B2 (Photoelectric conversion device and method for producing same) - June 7, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20120305060A1 (Tunneling-junction solar cell with copper grid for concentrated photovoltaic application) - December 6, 2012. Deals with tunneling junctions and copper grids, which are specific features that may or may not overlap with US11251315's claims.
• US20160181461A1 (Manufacturing method for solar cell) - June 23, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20130247965A1 (Solar cell having an emitter region with wide bandgap semiconductor material) - September 26, 2013. Deals with wide bandgap materials, which is not a primary focus of US11251315.
• CN102694077A (A kind of preparation method of copper indium gallium selenide thin film solar cell) - September 26, 2012. Focuses on CIGS thin film solar cells, which is a different material system than the silicon substrate of US11251315.
• US9269839B2 (Solar cell and method of manufacturing the same) - February 23, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20140166086A1 (Magnetically polarized photonic device) - June 19, 2014. Deals with photonic devices, specific relevance to solar cell fabrication or structure not clear without full text.
• US20140166089A1 (Solar cell with silicon oxynitride dielectric layer) - June 19, 2014. Describes a specific dielectric layer (silicon oxynitride), which may or may not be the same as the dielectric regions claimed in US11251315 (e.g., silicon dioxide).
• US20140166095A1 (Hybrid emitter all back contact solar cell) - June 19, 2014. Directly relevant to back-contact solar cells, similar to claims 1, 7, and 8. The "hybrid emitter" aspect would need further investigation for anticipation.
• US20140360571A1 (Solar cell and manufacturing method thereof) - December 11, 2014. Pre-dates US11251315 by a short margin. Broad title, needs full text review.
• US20160268454A1 (Solar Cell and Method for Manufacturing Same) - September 15, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20160197210A1 (Solar cell and solar cell module) - July 7, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20160240705A1 (Solar cell, solar cell module, and manufacturing method for solar cell) - August 18, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20160240704A1 (Solar cell) - August 18, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20150162483A1 (Solar cell emitter region fabrication using ion implantation) - June 11, 2015. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20160056322A1 (Solar cell and method for manufacturing the same) - February 25, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20160126368A1 (Solar cell) - May 5, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20160155877A1 (Solar cell and method for manufacturing the same) - June 2, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US20160155866A1 (Solar cell and method for manufacturing the same) - June 2, 2016. Published after the priority date of US11251315 (December 22, 2014), so it cannot be prior art.
• US9520507B2 (Solar cells with improved lifetime, passivation and/or efficiency) - December 13, 2016. This is an earlier patent in the same family, with the same title and priority date. It is a parent of US11251315 and thus not prior art in the anticipatory sense.

Summary of Most Relevant Prior Art for Potential Anticipation (35 U.S.C. § 102):

Based on the titles and brief descriptions, the following patents appear most relevant for potentially anticipating claims in US11251315, specifically regarding the structural features defined in the independent claims and their dependent claims related to material and location:

• US20130247981A1 (Solar cell fabrication using a pre-doping dielectric layer): Highly relevant to the formation of dielectric and dopant regions.
• US8242354B2 (Backside contact solar cell with formed polysilicon doped regions): Directly relevant to backside configurations and polysilicon emitter regions.
• US8492253B2 (Method of forming contacts for a back-contact solar cell): Relevant to back-contact configurations and metal contact formation.
• US20140166095A1 (Hybrid emitter all back contact solar cell): Relevant to back-contact solar cells and emitter configurations.
• US20100139763A1 (Method for producing an emitter structure and emitter structures resulting therefrom): General relevance to emitter formation and doping.
• US20100304527A1 (Methods of thermal processing a solar cell): Relevant to the heating step, but the specific combination of heating, gettering through dielectric, and dopant concentration in US11251315 would need detailed comparison.

For a definitive determination of anticipation under 35 U.S.C. § 102, a thorough claim-by-claim analysis would be required, comparing each element of US11251315's claims against the disclosures of these prior art documents. This would involve examining the full text and figures of each cited patent to see if every element of a claim in US11251315 is explicitly or inherently disclosed in a single piece of prior art.

Obviousness Analysis under 35 U.S.C. § 103 for US Patent 11251315

The claims of US Patent 11251315 describe a solar cell comprising a silicon substrate, a dielectric region, an emitter region containing metal impurities formed over the dielectric region, and a metal contact. Key features include a portion of the silicon substrate having a low dopant concentration (approximately less than or equal to 2×10¹⁸ cm⁻³) and a fabrication method involving heating above 900 degrees Celsius to getter impurities into the emitter region and drive dopants into the substrate. The patent highlights the resulting improvements in lifetime, passivation, and efficiency.

A person having ordinary skill in the art (POSITA) in solar cell fabrication would have been motivated to combine various known techniques from prior art to arrive at the claimed invention, particularly concerning impurity management, passivation, and doping optimization.

Combination 1: US20200279968A1 in view of "The preparation of polysilicon films on highly boron doped silicon substrates and their effects on Cu out-diffusion - PMC" and "Advanced high-k dielectric stacks with polySi and metal gates: Recent progress and current challenges" and "Theoretical Analysis of Doping Concentration Gradients on Solar Cell Performance - arXiv"

Rationale:

1. Primary Reference - US20200279968A1 (Interdigitated back-contacted solar cell with p-type conductivity): This patent application describes an interdigitated back-contacted solar cell that includes a silicon substrate with a front and rear surface. Crucially, it discloses a stack of a tunnel oxide layer and a doped polysilicon layer arranged on the rear surface of the silicon substrate. The tunnel oxide typically consists of silicon dioxide and is about 2 nm or less thick. The polysilicon layer is doped (e.g., n-type) and can have a thickness between 10 and 300 nm. This reference establishes the fundamental structure of a solar cell having a silicon substrate, a dielectric region (tunnel oxide), and a doped polysilicon emitter region over the dielectric, addressing elements of both claims 1 and 10, particularly for a back-contact configuration (for Claim 1 where the dielectric and emitter are on the back side). It also mentions that the dielectric layer is important for providing hydrogen that migrates during an "elevated temperature step."

2. Motivation to include metal impurities and gettering them into the emitter region (through a dielectric): It was well-known in the solar cell industry that metal impurities (e.g., iron, nickel, chromium) are detrimental to electrical conduction and act as recombination centers, leading to poor lifetime, surface passivation, and lower efficiency. "A review of defect mitigation strategies for UMG-Si wafers - Frontiers" clearly states that "Gettering is the one of most common form of defect mitigation method which helps to relocate mobile metal impurities, such as interstitial iron from the bulk of silicon to a region in the device where they have a less harmful impact on the device performance." Furthermore, "The preparation of polysilicon films on highly boron doped silicon substrates and their effects on Cu out-diffusion - PMC" explicitly teaches the use of polysilicon films for gettering metal impurities like copper, stating that the polysilicon "exhibits a pronounced inhibitory effect on the out-diffusion of Cu" due to "effective gettering of Cu by both grain boundaries and disordered grain structures." A POSITA, seeking to mitigate the known problem of metal impurities in the solar cell of US20200279968A1, would be motivated to leverage the known gettering properties of polysilicon and design the process such that impurities are captured in the polysilicon emitter layer. The patent US11251315 itself states that "heating at temperatures above 900 degrees Celsius can include gettering metal impurities 220 through the dielectric region 210, e.g., tunnel oxide, to into the emitter region 212, e.g., polysilicon regions." This suggests that the ability of metal impurities to diffuse through thin dielectric layers to be gettered by polysilicon at elevated temperatures was either known or a predictable result to those skilled in the art.

3. Motivation for high-temperature heating above 900 degrees Celsius: High-temperature annealing is a standard practice in semiconductor device fabrication, including for dopant activation in polysilicon. "Advanced high-k dielectric stacks with polySi and metal gates: Recent progress and current challenges" teaches that "PolySi-based devices are usually annealed at high temperatures (>1,000°C) in order to activate dopants in the gate and source/drain regions." While this reference is in the context of MOSFETs, the underlying principles of dopant diffusion and activation in polysilicon apply to solar cells. "Rapid Thermal Processing of Crystalline Silicon Materials and Solar Cells" notes that rapid thermal oxidation of silicon is performed in the range of 600–1200 °C. Given that US20200279968A1 already incorporates an "elevated temperature step" and the general knowledge of high-temperature processing for dopant activation and impurity diffusion, a POSITA would find it obvious to apply a heating step above 900 degrees Celsius to effectively drive dopants from a dopant region into the substrate and simultaneously enhance the gettering of metal impurities into the polysilicon emitter through the dielectric. This would be a straightforward optimization of known thermal processes to achieve multiple beneficial effects.

4. Motivation for a low dopant concentration (<= 2×10¹⁸ cm⁻³) in a portion of the silicon substrate: "Theoretical Analysis of Doping Concentration Gradients on Solar Cell Performance - arXiv" teaches that "While high doping concentrations can increase the recombination rate of electrons and holes, thereby reducing efficiency, appropriate doping levels can enhance charge carrier movement, leading to improved performance." This highlights the importance of optimizing doping levels to minimize recombination. A POSITA would be motivated to select an "appropriate doping level" in certain regions of the substrate, such as less than or equal to 2×10¹⁸ cm⁻³, to reduce recombination and improve surface passivation, which directly translates to improved lifetime and efficiency. Such an optimization would be considered a routine design choice in solar cell manufacturing to achieve desired electrical characteristics for charge carrier transport and passivation.

Conclusion on Obviousness:

A POSITA, motivated to improve the performance of solar cells by addressing known issues of metal impurities and optimizing doping for reduced recombination, would have found it obvious to combine the teachings of US20200279968A1 with the knowledge of polysilicon gettering ("The preparation of polysilicon films on highly boron doped silicon substrates and their effects on Cu out-diffusion - PMC"), high-temperature annealing for dopant activation and diffusion ("Advanced high-k dielectric stacks with polySi and metal gates: Recent progress and current challenges"), and the understanding of optimal low doping concentrations for passivation ("Theoretical Analysis of Doping Concentration Gradients on Solar Cell Performance - arXiv"). The placement of the low-doped region (front or back side) would be a matter of design choice, consistent with different solar cell architectures (e.g., back-contact or front-contact cells) which were also well-known in the art. The synergistic effect of simultaneously performing gettering and dopant drive-in at high temperatures would be a predictable result for a POSITA optimizing these known processes for improved solar cell performance.