Electroplated Metal Grid for Solar Cells
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional solar cell metal grids face issues with high series resistance, material cost, limited line height and width, and peeling due to thermal stress and handling, which affect the efficiency and reliability of solar cells.
Innovation Solution
The design of an electroplated metal grid with a special grid pattern that eliminates open ends and includes additional metal lines at the wafer edge to provide structural support and divert current, using a metal adhesive layer and seed layer to enhance adhesion, and employing a physical vapor deposition technique for forming the grid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If screenprinting Ag paste is used to form the metal grid, then the manufacturing process is simple and widely adopted, but the series resistance is high and material cost is excessive
Solution Approach 1:
The patent introduces an adhesion layer as an intermediary between the Si emitter and the metal grid. This adhesion layer serves multiple functions: it improves adhesion between the metal and substrate, and it acts as a seeding layer for electroplating, enabling the formation of low-resistance metal lines through electroplating process
Solution Approach 2:
The patent replaces the conventional screenprinting mechanical process with electroplating process. Instead of printing Ag paste and firing it at high temperature, the invention uses electroplating to deposit metal layers, which achieves lower resistivity (2×10-6 to 3×10-6 ohm-cm for plated Cu versus 5×10-6 to 8×10-6 ohm-cm for fired Ag paste) and better adhesion
2Shape
If electroplating is used to increase line height, then the height-to-width aspect ratio improves, but the line width increases which is undesirable for high-efficiency solar cells
Solution Approach 1:
The patent applies different properties to different parts of the metal grid structure. The adhesion layer provides local adhesion enhancement at the interface, while the electroplated metal layers provide local conductivity and structural height. This localized functional differentiation allows achieving high aspect ratio without excessive line width increase
3Reliability
If Ni/Cu/Sn metal stack is electroplated directly on Si emitter, then the resistivity is reduced, but the adhesion is poor and stress causes peeling
Solution Approach 1:
The patent introduces an adhesion layer as an intermediary between the Si emitter and the electroplated metal stack. This adhesion layer (made of materials like Ti, Cr, Mo, or W) serves as a bonding interface that prevents peeling caused by thermal stress and handling, while still allowing the electroplated metal layers to achieve low resistivity
Solution Approach 2:
The patent creates a composite structure consisting of multiple layers: Si emitter, adhesion layer, and electroplated metal layers (Ni/Cu/Sn stack). This composite structure combines the advantages of each layer: Si provides the substrate, adhesion layer provides bonding strength, and electroplated metals provide low resistivity. The composite structure resolves the contradiction between low resistivity and peeling resistance
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 reduces the likelihood of metal peeling, increases the height-to-width aspect ratio of metal lines, and improves the bonding between the metal grid and the underlying layers, leading to enhanced current collection and reduced shading losses.
Implementation Method 1
employing a physical vapor deposition technique for forming the grid
Implementation Method 2
a front-side metal grid situated above the photovoltaic structure. The front-side metal grid also includes one or more electroplated metal layers
Data Source
Figure 1~2
Figure 3A~3B
Figure 3C~3D
AI summary
One embodiment of the present invention provides a solar cell. The solar cell includes a photovoltaic structure and a front-side metal grid (300) situated above the photovoltaic structure. The front-side metal grid also includes one or more electroplated metal layers. The front- side metal grid includes one or more finger lines (302, 304), and each end of a respective finger line is coupled to a corresponding end of an adjacent finger line via an additional metal line (306, 308, 314, 316, 318, 320), thus ensuring that the respective finger line has no open end.