Partial Laser Ablation of AlOx/SiNx Dielectric Stacks for Solar Cell Passivation
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Solution Overview
Problem
Laser ablation of dielectric layers in solar cells can cause damages such as delamination, cracking, and overheating, leading to decreased passivation performance and increased series resistance, particularly when used on AlOx/SiNx stacks, which affects the parasitic emitter creation and overall solar cell efficiency.
Innovation Solution
A method of partial laser ablation is employed, preserving the AlOx layer and only ablating the SiNx layer, with specific conditions like pulse durations of less than a few nanoseconds and UV radiation at 355nm, to maintain passivation quality and prevent damage to the underlying silicon, allowing for improved field-effect passivation and reduced series resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complete laser ablation is performed to remove dielectric layers, then series resistance is reduced, but passivation performance deteriorates due to damages such as delamination, cracking, and overheating
Solution Approach 1:
The patent applies partial laser ablation instead of complete ablation of the dielectric stack. The AlOx layer is partially removed to create openings for metal contacts while preserving a remaining thickness of 1-30 nm that maintains passivation performance. This partial action approach reduces laser-induced damages while still achieving the necessary electrical contact, resolving the contradiction between reducing series resistance and maintaining passivation quality.
Solution Approach 2:
The dielectric stack is segmented into functionally distinct layers with different ablation thresholds. The SiNx layer is completely removed to provide good electrical contact, while the AlOx layer is partially preserved to maintain field-effect passivation. This segmentation allows each layer to fulfill its specific function independently, resolving the contradiction between electrical contact quality and passivation performance.
2Ease of manufacture
If laser ablation is performed on AlOx/SiNx stacks, then openings are created for metal contacts, but field-effect passivation deteriorates due to charge modification in the AlOx layer
Solution Approach 1:
The patent applies partial laser ablation to the AlOx layer, removing only a portion of it while preserving a remaining thickness of 1-30 nm. This partial removal is sufficient to create the necessary openings for metal contacts while preserving enough material to maintain the field-effect passivation and its associated negative charges, thus resolving the contradiction between ease of manufacture and passivation quality.
Solution Approach 2:
The patent creates local openings with specific geometric characteristics (diameter 10-100 μm, depth controlling remaining thickness) that provide the necessary electrical contact while preserving the passivation quality in the surrounding areas. The local quality of the opening structure allows simultaneous achievement of good electrical contact and maintained passivation performance.
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 approach enhances short-circuit current, open-circuit voltage, and overall efficiency by 1.6%, 1.1%, and 3% respectively, while maintaining good passivation quality around metal contacts, compared to complete laser ablation methods.
Implementation Method 1
A method of partial laser ablation is employed, preserving the AlOx layer and only ablating the SiNx layer
Implementation Method 2
UV radiation at 355nm
Implementation Method 3
These AlOx layers have been shown to have intrinsic negative charges, which prevent the creation of a parasitic emitter on p-type silicon and facilitate the field-effect passivation
Implementation Method 4
good passivation properties on the back face of the wafer surface are mandatory in order to reduce recombination losses
Data Source
Figure 1(a)~2
Figure 3(a)~3(d)
AI summary
The invention relates to the manufacturing process of a solar cell (1) with back contact and passivated emitter, comprising a dielectric stack (10) of at least two layers consisting of at least a first dielectric layer (11) made of AlOx in contact with a p-type silicon layer (3), and a second dielectric layer (13) deposited on the first dielectric layer (11). Besides, the method of manufacturing comprising a formation step of at least one partial opening (15) preferably by laser ablation into the dielectric stack (10), sparing at least partially the aforementioned first dielectric layer.