Two-Stage Hole Etching for Solar Cell Contact Openings
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Solution Overview
Problem
Existing methods for creating through-contact openings in solar cells, such as laser ablation, can lead to short circuits due to undercuts and defects in the passivation layer, especially when etching through existing pn junctions, which complicates the production of high-aspect-ratio holes necessary for metal wrap-through solar cells.
Innovation Solution
A two-step hole-etching process is employed, where the first etching process creates a hole through all sub-cells to the pn junction, and the second process selectively widens the hole using a different etching process, ensuring undercut-free and smooth surfaces, allowing for reliable passivation and preventing short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If laser ablation is used to create through-contact openings, then a smooth surface is achieved, but undercuts occur and short circuits are caused
Solution Approach 1:
The hole creation process is divided into two distinct stages: first creating a narrow hole through all subcells to the pn junction, then selectively widening the upper portion. This segmentation allows each stage to optimize for its specific function - the first stage ensures smooth surfaces without undercuts, while the second stage creates the necessary opening width without compromising reliability
Solution Approach 2:
Different etching approaches are applied to different regions of the hole. The lower portion (through subcells) uses a process optimized for smooth surfaces and precise depth control, while the upper portion is selectively widened. This local differentiation resolves the contradiction by allowing surface smoothness in the critical lower region while achieving adequate opening width in the upper region
2Length of moving object
If a single etching process is used to create high-aspect-ratio holes, then hole depth is achieved, but surface quality deteriorates with undercuts
Solution Approach 1:
The etching process is segmented into two sequential steps with different objectives. The first etching process creates the deep narrow hole through all subcells with high precision and smooth surfaces. The second etching process selectively widens only the upper portion of the hole. This segmentation enables achieving both high hole depth and excellent surface quality in the critical regions
3Productivity
If laser ablation is used to etch through pn junctions, then through-holes are created, but short circuits occur
Solution Approach 1:
The first etching process is performed preliminarily to create a narrow hole that stops precisely at the pn junction without breaching it. This preliminary action establishes a safe boundary that prevents subsequent laser ablation or widening processes from damaging the pn junction, thereby maintaining reliability while still enabling efficient through-hole creation
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 method allows for the production of holes with controlled dimensions and smooth surfaces, preventing undercuts and ensuring reliable passivation, enabling the creation of high-aspect-ratio holes without damaging pn junctions or causing short circuits, thus facilitating efficient solar cell manufacturing.
Implementation Method 1
a first opening is made in the first lacquer layer, and by means of a first etching process in the area of the first opening, a hole is created extending from the top of the semiconductor wafer through the III-V subcells at least as far as a pn junction of the Ge subcell into the semiconductor wafer
Implementation Method 2
creating a second opening in the second lacquer layer that is larger than the first opening and surrounds the hole, and widening the hole in the area of the second opening in a region extending from the top of the semiconductor wafer to the Ge partial cell serving as an etch stop layer by means of a second etching process
Implementation Method 3
a through-hole extending from a bottom surface of the hole to the underside of the semiconductor disk is created by means of laser ablation
Data Source
Figure 1
Figure 2~4
AI summary
A two-stage hole-etching process comprising at least the following steps: providing a semiconductor wafer comprising several solar cell stacks and performing a first and a second process step in the aforementioned order, wherein in the first process step a first resist layer is applied to a top side of the semiconductor wafer, at least one first opening is created in the first resist layer, and a hole extending into the semiconductor wafer beyond a pn junction of the Ge subcell is created in the area of the first opening by means of a first etching process, and wherein in the second process step a second resist layer is applied to the top side of the semiconductor wafer.A second opening, larger than the first and enclosing the hole, is created in the second lacquer layer, and the hole is widened in the area of the second opening by means of a second etching process, extending up to the Ge partial cell serving as the etch stop layer.