Back-Surface Bridge Electrode for Silicon Solar Cells
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Solution Overview
Problem
Conventional methods for forming back surface fields in crystalline silicon solar batteries often result in voids, reducing the contact area and efficiency due to differences in diffusion coefficients between aluminum and silicon, leading to recombination issues and insufficient field thickness.
Innovation Solution
A back-surface bridge type contact electrode is introduced, featuring a local electrode connected to a back surface electrode via a bridge electrode, both covered with a back surface passivation film, which controls silicon diffusion and reduces void formation by using aluminum materials and optimizing the bridge electrode's width and length to enhance the local back surface field thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional full back surface printing or aluminium layer depositing is used, then the back surface field can be formed, but voids are formed due to diffusion coefficient differences between aluminium and silicon
Solution Approach 1:
The back surface electrode is segmented into multiple independent bridge electrodes (first bridge electrode, second bridge electrode, etc.) that are distributed across the back surface. Each bridge electrode independently forms contact with the silicon substrate, preventing the formation of large continuous void regions while maintaining effective back surface field formation. This segmentation approach divides the problematic continuous aluminium layer into discrete contact points.
Solution Approach 2:
The patent applies different structures to different regions: bridge electrodes are used in regions where contact is needed, while back surface passivation film is applied in other regions. The bridge electrodes have specific width specifications (0.5-5.0 mm) optimized for their function. This local differentiation allows the system to achieve both good contact (where bridge electrodes are present) and void prevention (through localized rather than continuous coverage).
2Reliability
If conventional aluminium layer depositing is used, then the back surface field can be formed, but the contact area between local back surface field and aluminium-silicon alloy layer becomes small
Solution Approach 1:
The bridge electrodes extend in the lateral dimension across the back surface, creating elongated contact regions rather than simple point contacts. By controlling the width (0.5-5.0 mm) and distribution of multiple bridge electrodes, the total effective contact area is increased while maintaining the benefits of segmented structure. This dimensional approach allows sufficient contact area without requiring a single large continuous electrode.
Solution Approach 2:
Multiple bridge electrodes work together to provide cumulative contact area with the silicon substrate. The first bridge electrode, second bridge electrode, and any additional bridge electrodes collectively establish sufficient electrical contact and back surface field formation area. This merging of multiple discrete elements achieves the required total contact area while avoiding the void formation problems of continuous layers.
3Reliability
If conventional full back surface printing is used, then the back surface field can be formed, but the thickness of local back surface field is insufficient due to void effect
Solution Approach 1:
The bridge electrode structure is designed in advance with appropriate width (0.5-5.0 mm) and spacing to prevent void formation before the high-temperature processing occurs. By pre-configuring the electrode geometry to ensure adequate silicon diffusion pathways, the system cushions against the potential thickness deficiency that would otherwise occur with conventional continuous layer deposition.
Solution Approach 2:
The bridge electrodes serve as intermediary structures that facilitate controlled silicon diffusion from the substrate into the aluminium. The specific width and distribution of bridge electrodes create optimal conditions for diffusion, ensuring sufficient back surface field thickness develops during processing without the disruption caused by voids in continuous layers.
4Area of stationary object
If bridge electrode width and length are increased, then contact area increases, but the amount of silicon diffusing into aluminium-silicon liquid alloy increases
Solution Approach 1:
The patent specifies precise parameter ranges for bridge electrode width (0.5-5.0 mm) to optimize the balance between contact area and silicon diffusion control. By controlling the width within this range, the system achieves sufficient contact area while limiting excessive silicon diffusion into the aluminium-silicon alloy. This parameter optimization resolves the contradiction between needing adequate contact area and preventing excessive material diffusion.
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
This design significantly reduces void formation, improves fill factor and open circuit voltage, and enhances conversion efficiency by minimizing resistance loss and promoting silicon precipitation in the aluminum-silicon alloy.
Implementation Method 1
the contact surface of the bridge electrode and the silicon wafer substrate is also covered with the back surface passivation film
Implementation Method 2
aluminium atoms instead of silicon atoms enter the silicon crystal lattice in a high temperature process to form a p-type heavily-doped region
Implementation Method 3
aluminium atoms instead of silicon atoms enter the silicon crystal lattice in a high temperature process to form a p-type heavily-doped region
Data Source
AI summary
Disclosed are a back-surface bridge type contact electrode of a crystalline silicon solar battery and a preparation method therefor. The back-surface bridge type contact electrode of a crystalline silicon solar battery includes a local electrode connected to a local back surface field and a back surface electrode which is covered with a back surface passivation film on a contact surface with a silicon wafer substrate, at least one bridge electrode is provided between the local electrode and the back surface electrode, the contact surface of the bridge electrode and the silicon wafer substrate is also covered with the back surface passivation film, the local electrode is connected to the back surface electrode via the bridge electrode, and the back surface passivation film is also provided, besides at the connection region of the bridge electrode, between the local electrode and the back surface electrode.