Aluminum-Tin Paste for Solderable Solar Cell Electrodes
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Solution Overview
Problem
Conventional solar cells with non-solderable aluminum back side electrodes suffer from efficiency losses due to interrupted back surface fields under silver-containing electrodes, and require additional costly Ag-based pastes for tabbing bus bars, which increases production costs and complexity.
Innovation Solution
A solderable aluminum-tin paste composition comprising 10-70 wt% aluminum powder, 5-85 wt% tin powder, and an organic medium with a polymer binder is used to form electrodes on the back side of solar cells, allowing for full back surface field formation and eliminating the need for separate Ag-based pastes, thereby enhancing efficiency and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Ag-based electrodes are used for tabbing bus bars, then solderability is achieved, but manufacturing cost increases and production complexity increases
Solution Approach 1:
The patent combines the back surface field electrode and tabbing bus bar into a single aluminum-tin paste application, eliminating the need for separate Ag-based paste. The aluminum-tin paste forms both the BSF layer through aluminum diffusion and provides solderable surfaces through tin content, merging two previously separate functions into one material system.
Solution Approach 2:
The aluminum-tin paste serves multiple functions simultaneously: it creates the back surface field through aluminum diffusion into silicon, provides solderability through tin content for tabbing ribbon attachment, and eliminates the need for separate Ag-based electrode materials. This multi-functional paste replaces both the non-solderable aluminum electrode and the Ag-based tabbing electrode.
2Reliability
If Ag-based electrodes are used for tabbing bus bars, then solderability is achieved, but device complexity increases due to additional printing and drying steps
Solution Approach 1:
The patent merges the application of back surface field electrode and tabbing bus bar into a single screen printing step using aluminum-tin paste. This eliminates the sequential process of printing non-solderable aluminum electrode, drying it, then printing Ag-based paste in gaps, and drying again. The single paste application reduces process steps while maintaining both BSF formation and solderability.
3Ease of manufacture
If non-solderable aluminum electrode is used, then manufacturing cost is reduced, but efficiency is lost due to interrupted back surface field
Solution Approach 1:
The patent changes the compositional parameters of the aluminum electrode by adding tin to create aluminum-tin paste. This parameter change enables the electrode to maintain continuous back surface field coverage (improving efficiency) while using lower-cost aluminum-based materials instead of expensive Ag-based pastes. The tin content parameter provides solderability without sacrificing the continuous BSF coverage.
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
The use of the aluminum-tin paste composition increases solar cell efficiency by up to 0.2% by providing a full back surface field and simplifies the manufacturing process by eliminating the need for additional printing and drying steps, while reducing material costs.
Implementation Method 1
Upon firing, aluminum from the aluminum-tin paste diffuses into the silicon substrate at the areas of contact with the silicon substrate. This provides a full BSF
Data Source
AI summary
The present invention is directed to a paste composition comprising Al and Sn dispersed in an organic medium and to paste compositions that provide a solderable electrode. The present invention is further directed to an electrode formed from the paste composition and a semiconductor device and, in particular, a solar cell comprising such an electrode. The paste compositions that provide a solderable electrode are particularly useful for forming a solar cell back side solderable electrode.