Obviousness

Obviousness Analysis under 35 U.S.C. § 103 for US Patent 11824136

This analysis assesses the obviousness of claims in US Patent 11824136 by combining existing prior art and common knowledge available to a Person Having Ordinary Skill in the Art (PHOSITA) before the priority date of 2021-08-04. Since the provided patent text does not include a "References Cited" section listing specific prior art documents, this analysis relies on the "BACKGROUND" section of US11824136, which describes the state of the art, as well as general knowledge in the field of solar cell manufacturing implied by the "Prior art keywords" and the patent's descriptions of known techniques.

A PHOSITA in the field of solar cell technology at the time of the invention would have possessed knowledge of N-type TOPCon solar cell structures and manufacturing processes, including surface texturing techniques and their benefits.

Combination 1: Existing TOPCon Solar Cell + Known Texturing Principles and Optimization

References/Knowledge:

1. Existing N-type TOPCon Solar Cell Structure: The "BACKGROUND" section of US11824136 explicitly describes "An existing TOPCon solar cell rear surface structure sequentially includes a semiconductor substrate, a tunnel oxide layer, a doped conductive layer and a passivation layer on the rear surface from the inside out." [cite: "An existing TOPCon solar cell rear surface structure sequentially includes a semiconductor substrate, a tunnel oxide layer, a doped conductive layer and a passivation layer on the rear surface from the inside out."] It also notes that the front surface of such cells typically has a texture, such as a "pyramid-shaped microstructure" [cite: "the second texture structure 11 may include a pyramid-shaped microstructure."], formed by various texturing processes like chemical etching, laser etching, or mechanical processes [cite: "The texturing process may be chemical etching, laser etching, a mechanical process, plasma etching, or the like."].
2. Known Problem with Flat Rear Surfaces: The patent's background further highlights a problem in existing TOPCon cells: "The polished rear surface of the silicon wafer has a flat structure, but the structure of the polished rear surface may directly affect the manufacturing of the tunnel oxide layer and the polycrystalline silicon layer, and then affect passivation performance and conversion efficiency of the solar cell." [cite: "The polished rear surface of the silicon wafer has a flat structure, but the structure of the polished rear surface may directly affect the manufacturing of the tunnel oxide layer and the polycrystalline silicon layer, and then affect passivation performance and conversion efficiency of the solar cell."]
3. General Benefits of Surface Texturing in Solar Cells: It is common knowledge in the solar cell industry that texturing surfaces can improve light trapping, reduce reflection, enhance contact between layers (e.g., metal electrodes and semiconductor), and reduce recombination, all leading to improved conversion efficiency. The patent itself mentions that the pyramid-shaped microstructure on the front surface "enables a metal paste to better fill the microstructure when the metal paste forms an electrode by screen printing, which obtains better electrode contact, can effectively reduce series resistance of the solar cell, and improves the fill factor." [cite: "The pyramid-shaped microstructure enables a metal paste to better fill the microstructure when the metal paste forms an electrode by screen printing, which obtains better electrode contact, can effectively reduce series resistance of the solar cell, and improves the fill factor."]
4. Routine Optimization: The process of optimizing surface structures and their dimensions (e.g., roughness, height, feature size) for improved material deposition, interface quality, and electrical contact is a routine task for a PHOSITA in semiconductor manufacturing.

Obviousness of Claim 1 (Solar cell structure):
Claim 1 describes a solar cell with a first texture structure on the rear surface, comprising "two or more first substructures at least partially stacked on one another," with a distance between top surfaces of adjacent substructures less than or equal to 2 μm, and a one-dimensional size of the outermost substructure's top surface less than or equal to 45 μm. It also specifies a first passivation layer on the front, a tunnel oxide layer on the first texture structure, a doped conductive layer, and a second passivation layer.

A PHOSITA, faced with the known problem that a "flat" polished rear surface negatively impacts the manufacturing of the tunnel oxide and polycrystalline silicon layers, and thus affects passivation performance and conversion efficiency [cite: "The polished rear surface of the silicon wafer has a flat structure, but the structure of the polished rear surface may directly affect the manufacturing of the tunnel oxide layer and the polycrystalline silicon layer, and then affect passivation performance and conversion efficiency of the solar cell."], would be motivated to modify this flat rear surface. Given the well-understood benefits of surface texturing on solar cell performance (e.g., for light trapping, reduced recombination, and improved electrode contact), it would be obvious to apply texturing principles to the rear surface to address these identified issues.

The specific "first texture structure" featuring "stacked substructures" and dimensional limitations (distance <= 2 μm, 1D size <= 45 μm) represents an optimization of surface topography. The patent itself states that this control "helps to improve the uniformity of the tunnel oxide layer formed on the first texture structure, ensure better performance of the tunnel oxide layer formed, further inhibit a high local phosphorus concentration caused by phosphorous diffusion, reduce contact resistivity, improve the open-circuit voltage of the solar cell, and improve the fill factor and photoelectric conversion efficiency." [cite: "the distance between the top surface of the outermost first substructure 121 a and the top surface of the first substructure 121 b adjacent thereto is controlled to be less than or equal to 2 μm, so that the roughness of the first texture structure is controlled within a desired range, which helps to improve the uniformity of the tunnel oxide layer formed on the first texture structure, ensure better performance of the tunnel oxide layer formed, further inhibit a high local phosphorus concentration caused by phosphorous diffusion, reduce contact resistivity, improve the open-circuit voltage of the solar cell, and improve the fill factor and photoelectric conversion efficiency."] Arriving at such specific dimensions and a "substantially “step” profile" [cite: "the first texture structure may present a substantially “step” profile, and the first substructure 121 may be regarded as a stair of the “step”"] through routine experimentation to optimize the deposition of the tunnel oxide layer and subsequent contact layers would have been within the capabilities of a PHOSITA.

Obviousness of Claim 14 (Method of manufacturing):
Claim 14 outlines a method for manufacturing a solar cell that includes texturing the front surface to form pyramid-shaped microstructures, forming a doped layer, polishing the rear surface with an alkali solution to form the specified first texture structure, and subsequently forming the tunnel oxide layer, doped conductive layer, and passivation layers.

A PHOSITA, manufacturing an existing TOPCon cell, would be aware of the negative impact of a flat polished rear surface on cell performance [cite: "The polished rear surface of the silicon wafer has a flat structure, but the structure of the polished rear surface may directly affect the manufacturing of the tunnel oxide layer and the polycrystalline silicon layer, and then affect passivation performance and conversion efficiency of the solar cell."]. The patent describes that prior art methods involved polishing the rear surface after removing borosilicate glass, resulting in a flat structure. [cite: "borosilicate glass on a rear surface of an N-type solar cell is removed by an oxidizing mixed acid solution.", "After the surface is cleaned and dried, the rear surface is polished with the aid of a trough or chain acid additive.", "The polished rear surface of the silicon wafer has a flat structure, but the structure of the polished rear surface may directly affect the manufacturing of the tunnel oxide layer and the polycrystalline silicon layer, and then affect passivation performance and conversion efficiency of the solar cell."]

Recognizing the need to improve this rear surface, a PHOSITA would be motivated to modify the existing polishing step to create a textured surface. The use of "alkali solution" for polishing or texturing silicon surfaces is a known technique in solar cell manufacturing, as evidenced by the patent's own description of forming front surface pyramid textures using "an alkaline solution such as a potassium hydroxide solution." [cite: "the texturing may be performed using an alkaline solution such as a potassium hydroxide solution. Since the corrosion of the NaOH solution is anisotropic, a pyramid-shaped microstructure can be manufactured."]

Therefore, it would be obvious to a PHOSITA to employ or adapt known alkali-based texturing/polishing techniques on the rear surface to generate a non-flat structure. The specific method steps described in dependent claims (e.g., cleaning with alkali solution of 5-15% mass fraction, spraying micro-liquid droplets for roughening, polishing with a liquid containing NaOH/KOH/additive at 70-80° C. for less than 260 seconds [cite: "the polishing a rear surface of the semiconductor substrate with an alkali solution includes: cleaning the rear surface of the semiconductor substrate with the alkali solution having a mass fraction of 5% to 15% to remove porous silicon; dropping, by spraying, micro-liquid droplets of the alkali solution to the rear surface of the semiconductor substrate for roughening treatment, and then performing pre-cleaning with a hydrofluoric acid having a mass fraction of 5% to 10%; polishing the rear surface of the semiconductor substrate with a polishing liquid at a polishing temperature ranging from 70° C. to 80° C. for a polishing time less than 260 seconds, wherein the polishing liquid includes NaOH having a mass fraction of 1% to 15%, KOH having a mass fraction of 1% to 15% and an additive having a mass fraction of 0.51% to 2.5%"]) for forming the "first texture structure" (with its specific dimensional ranges) would represent routine process optimization. A PHOSITA would routinely adjust polishing parameters (like time, temperature, and solution composition) to achieve a desired surface roughness and morphology suitable for subsequent thin-film deposition and improved electrical contact, as described by the patent itself. [cite: "a shape of the substructure in the first texture structure after polishing may be adjusted by controlling the polishing time and the polishing temperature, so that in the two or more first substructures at least partially stacked a distance between a top surface of the outermost first substructure and a top surface of the first substructure adjacent thereto is less than or equal to 2 μm in a direction away from the rear surface and perpendicular to the rear surface, so as to increase the roughness of the rear surface of the semiconductor substrate."]

Conclusion on Obviousness

The core inventive step claimed by US11824136—introducing a specific, non-pyramidal texture on the rear surface of a TOPCon solar cell with defined dimensions, and the method for producing it—appears to be an obvious modification of existing TOPCon solar cell technology. The motivation stems directly from a known problem in the prior art (the limitations of flat polished rear surfaces in TOPCon cells) [cite: "The polished rear surface of the silicon wafer has a flat structure, but the structure of the polished rear surface may directly affect the manufacturing of the tunnel oxide layer and the polycrystalline silicon layer, and then affect passivation performance and conversion efficiency of the solar cell."], combined with the well-established benefits of surface texturing in solar cell efficiency and contact optimization. The specific structural parameters and method details would be arrived at through routine experimentation and optimization by a PHOSITA aiming to improve the tunnel oxide layer uniformity, reduce contact resistivity, and enhance overall cell performance.