PTAB

IPR2025-01432

Canadian Solar USA Inc v. First Solar Inc

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: High-Efficiency Solar Cell Structures and Methods of Manufacture
  • Brief Description: The ’074 patent relates to methods of manufacturing high-efficiency solar cells. The claimed methods involve fabricating a solar cell by providing a wafer, growing an amorphous interface passivation layer, depositing a doped conductive and passivating layer over it, and providing a thermal treatment at 500°C or higher to crystallize the layer and facilitate dopant diffusion.

3. Grounds for Unpatentability

Ground 1: Obviousness over Froitzheim and Yablonovitch - Claims 1-2 and 4-8 are obvious over Froitzheim in view of Yablonovitch.

  • Prior Art Relied Upon: Froitzheim (EP 1732142 A1) and Yablonovitch (a 1985 article in Applied Physics Letters).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Froitzheim disclosed a foundational method for fabricating a back-junction solar cell using a diffused homojunction emitter. Yablonovitch taught improving solar cell efficiency by replacing such conventional diffused emitters with a superior deposited semi-insulating polycrystalline silicon (SIPOS) emitter over a thin, thermally grown interfacial oxide layer. Petitioner asserted the combination teaches all steps of claim 1: Froitzheim provided the wafer and back-junction cell concept; Yablonovitch taught growing an amorphous silicon oxide interface passivation layer, depositing a doped conductive and passivating SIPOS layer, and performing a thermal treatment (annealing at 900°C) that crystallizes the SIPOS layer and diffuses the dopant through the oxide into the wafer. The final metallization step was taught by Froitzheim. For dependent claims, Yablonovitch’s annealing was argued to perforate the oxide layer (claim 4), crystallize an initially amorphous SIPOS layer (claim 5), increase optical transmissivity (claim 6), activate dopants (claim 7), and form a p-n junction (claim 8).
    • Motivation to Combine: A POSITA would combine the references to improve the efficiency of Froitzheim's basic solar cell. Yablonovitch explicitly taught that its SIPOS heterojunction emitter with an interfacial oxide layer provided "excellent surface passivation" and was "two orders of magnitude superior" to the conventional homojunctions used in Froitzheim, thereby reducing carrier recombination. This created a clear motivation to substitute Froitzheim’s inferior diffused emitter with Yablonovitch’s known, superior SIPOS emitter structure.
    • Expectation of Success: Petitioner contended that a POSITA would have a high expectation of success, as the combination represented a simple substitution of one known type of emitter for another to achieve the predictable result of improved solar cell performance.

Ground 2: Obviousness over Froitzheim and Kwark - Claims 1-8 are obvious over Froitzheim in view of Kwark.

  • Prior Art Relied Upon: Froitzheim (EP 1732142 A1) and Kwark (a 1984 paper from the International Electron Devices Meeting).

  • Core Argument for this Ground:

    • Prior Art Mapping: This ground presented an alternative to Yablonovitch. Petitioner argued Froitzheim again provided the base back-junction solar cell. Kwark, similar to Yablonovitch, taught the advantages of replacing diffused emitters with a deposited polysilicon emitter over an interfacial oxide layer (termed "chemox"). Kwark showed that this structure greatly decreases recombination (Joe), improving efficiency. Kwark taught all necessary steps, including growing the interfacial oxide, depositing an in-situ doped polysilicon layer, and high-temperature annealing (900-1000°C) that crystallizes the layer and diffuses dopants through the oxide. Petitioner particularly noted that Kwark’s teachings addressed claim 3, which recites separating a single deposited amorphous silicon-containing compound via thermal treatment into both the interface passivation layer and the conductive layer. Kwark disclosed that annealing a SIPOS layer (without a pre-grown chemox layer) causes oxygen to segregate, forming an interfacial oxide layer and a separate crystallized silicon layer.
    • Motivation to Combine: The motivation was analogous to Ground 1: a POSITA would be motivated to improve Froitzheim’s cell by replacing its diffused emitter with the superior polysilicon emitter structure taught by Kwark to achieve lower recombination and higher efficiency. Kwark provided data showing its structure was significantly better than conventional emitters.
    • Expectation of Success: The combination was presented as an arrangement of known elements to achieve a predictable improvement. Petitioner argued that although Kwark focused on an n-type polysilicon layer, a POSITA would have understood that the polarity could be reversed to a p-type layer to match Froitzheim’s structure, as the interchangeability of dopant types in back-junction cells was well-known in the art.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including:

    • Grounds adding Neville (a 1995 textbook) to the Froitzheim/Yablonovitch and Froitzheim/Kwark combinations to explicitly teach that the polarity of the substrate and emitter layers in a back-junction cell are interchangeable.
    • Grounds adding Sasaki (a 1994 journal article) to the primary combinations to render claim 2 obvious. Sasaki taught inserting a transparent conductive oxide (TCO) layer, like indium tin oxide (ITO), on the back of a solar cell to create a good internal mirror and improve light trapping and efficiency.

4. Relief Requested

  • Petitioner requests institution of IPR and cancellation of claims 1-8 of Patent 9,130,074 as unpatentable.