Solar Cell Back Structure With Refractive-Index Graded Passivation
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Solution Overview
Problem
Existing solar cell back structures with an alumina-silicon nitride film layer struggle to achieve high field passivation and H passivation, affecting performance indices such as Uoc, Isc, Eta, and conversion efficiency.
Innovation Solution
A back structure for solar cells comprising alternating layers of silicon nitride and silicon oxynitride films, where the refractive index decreases from the inner to the outer layers, with the outermost layer being silicon nitride, to enhance passivation and improve performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an aluminum oxide and silicon nitride film layer structure is used on the back surface, then interface passivation and reflection increase are achieved, but higher field passivation and H passivation requirements cannot be met
Solution Approach 1:
The back surface film structure is segmented into multiple thin layers: aluminum oxide film (5-15 nm), first silicon nitride film (15-30 nm), first silicon oxynitride film (10-20 nm), and second silicon nitride film (20-40 nm). This segmentation allows each layer to contribute differently to passivation and optical properties, achieving superior field passivation and H passivation effects that a simple two-layer structure cannot provide.
Solution Approach 2:
The patent uses a composite film structure combining aluminum oxide, silicon nitride, and silicon oxynitride materials. Each material brings unique properties: aluminum oxide provides excellent field passivation, silicon nitride provides good H passivation and high refractive index, and silicon oxynitride provides intermediate properties. The composite structure achieves synergistic effects that improve overall passivation performance beyond what single materials can deliver.
2Productivity
If the refractive index decreases from inner to outer layers, then light reflection is optimized and passivation is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes specific parameter ranges for each layer to balance performance and manufacturability: aluminum oxide film (5-15 nm), first silicon nitride film (15-30 nm), first silicon oxynitride film (10-20 nm), and second silicon nitride film (20-40 nm). These parameter ranges are carefully selected to achieve the desired refractive index gradient while remaining within controllable manufacturing tolerances for PECVD processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The alternating film structure improves passivation, leading to enhanced performance indices like Uoc, Isc, FF, and Eta, particularly when the outermost layer is silicon nitride, increasing the double-sided efficiency of PERC and TOPCon solar cells.
Implementation Method 1
an aluminum oxide+silicon nitride structure is generally used to process the back face... internal reflection of long-wave light
Implementation Method 2
A refractive index of the first silicon nitride film layer is greater than a refractive index of the first silicon oxynitride film layer... alternate arrangement of the silicon oxynitride film layer and the silicon nitride film layer is realized; and a refractive index of the intermediate silicon oxynitride film layer is less than a refractive index of the silicon nitride film layers on the two sides
Implementation Method 3
Deposition of silicon nitride on a back surface of a solar photovoltaic cell using a Plasma Enhanced Chemical Vapor Deposition (PECVD) technology
Data Source
AI summary
Some embodiments of the present disclosure provide a back structure of a solar cell. The back structure includes an aluminum oxide film layer disposed on a silicon wafer substrate, and a first silicon nitride film layer and a first silicon oxynitride film layer, which are successively disposed on the aluminum oxide film layer from inside to outside; and the back structure further includes a second silicon nitride film layer disposed on the first silicon oxynitride film layer. The refractive index of the first silicon nitride film layer is greater than that of the second silicon nitride film layer, and the refractive index of the second silicon nitride film layer is greater than that of the first silicon oxynitride film layer.