Solar Cell Contact Structure with Angled Openings
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Solution Overview
Problem
Conventional solar cell designs face issues with increased fracture rates and power degradation due to the formation of aluminum pearls in local contact openings, which lead to cracking and reduced stability, especially in quasi-monocrystalline PERC cells, where the periodic orientation of contact structures aligns with main crack propagation directions, and the full rear side metallization layer causes internal stresses.
Innovation Solution
The design incorporates a solar cell wafer substrate with a dielectric layer and angled contact openings that deviate from the crystal orientation, forming aperiodic or cross-hatched contact structures to disrupt crack propagation and reduce mechanical tensions, along with a segregated metal layer to minimize stress and bowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If local contact openings are formed with periodic orientation parallel to crystal orientation, then electrical contact is achieved, but crack propagation is facilitated along preferred crystal directions
Solution Approach 1:
The contact openings are oriented at an angle of 45 degrees relative to the crystal orientation, breaking the symmetry that previously aligned contact structures with crack propagation directions. This asymmetric orientation disrupts the periodic tension fields that facilitated crack propagation along preferred crystal directions while maintaining effective electrical contact.
2Reliability
If full rear side metallization layer is applied, then electrical connectivity is improved, but internal stresses and bowing increase
Solution Approach 1:
The continuous metallization layer is segmented into discrete contact openings filled with metal contacts. This segmentation reduces the cumulative internal stress that would develop in a full continuous metallization layer, thereby reducing bowing while maintaining necessary electrical connectivity through the distributed contact points.
3Ease of manufacture
If aluminum paste is fired to fill trenches, then metallization is achieved, but aluminum pearls form causing point loads and fracture
Solution Approach 1:
The harmful aluminum pearls are extracted or removed from the contact structure by using angled contact openings that prevent pearl formation. The angled geometry ensures that excess aluminum does not accumulate and form pearls that create point loads, thereby eliminating the source of stress concentration while maintaining the metallization function.
4Ease of manufacture
If contact structures are periodically repeated, then manufacturing is simplified, but tension fields superimpose to form linear tension lines reducing stability
Solution Approach 1:
The periodic repetition of contact structures is replaced with an asymmetric angular orientation pattern. Instead of repeating contacts parallel to crystal directions, each contact is oriented at 45 degrees, breaking the periodicity that caused tension field superposition and linear tension line formation, thereby improving structural stability.
Data Source
AI summary
In various embodiments a solar cell may include a solar cell wafer substrate made of silicon having a major share of mono crystalline structure with {111} crystal plane parallel to one wafer edge; a dielectric layer disposed over the backside of solar cell wafer substrate; a plurality of contact openings extending through the dielectric layer to the solar cell wafer substrate; a plurality of metal contacts formed in the plurality of contact openings; and a metal layer disposed over the dielectric layer; wherein the metal layer is electrically coupled to the solar cell wafer substrate by means of the plurality of metal contacts; wherein at least one contact opening of the plurality of contact openings extends non parallel to {111} crystal plane.