Solar Cell Back Electrode Paste for Solderable Full BSF
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Solution Overview
Problem
Conventional solar cells with aluminum back side electrodes experience efficiency losses due to interrupted back surface fields under silver-containing electrodes, which are necessary for tabbing bus bars, resulting in up to 0.2% efficiency loss.
Innovation Solution
A paste composition comprising 40-80 wt% silver powder, 3-20 wt% glass frit with 75-97 wt% V2O5, 0.1-3 wt% Bi2O3, and 0-3 wt% metals like Cu or Zn, dispersed in an organic medium, is used to form a solderable electrode that covers the entire back side of a solar cell, creating a full back surface field and serving as tabbing bus bars.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silver-containing electrodes are used on the back side for tabbing bus bars, then solderability is improved, but the back surface field is interrupted causing efficiency loss
Solution Approach 1:
The back side electrode structure is segmented into two functional layers: a continuous aluminum base layer that maintains the back surface field across the entire back side, and discrete silver-containing tabbing bus bar electrodes that provide solderability only where needed for electrical connection. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
The electrode structure implements local quality by concentrating the silver-containing solderable material only in the specific regions where tabbing bus bars are required, while the majority of the back side maintains a pure aluminum composition to ensure continuous back surface field coverage. This localized application of different material properties optimizes both solderability and efficiency.
2Loss of energy
If aluminum electrode covers entire back side for full BSF, then efficiency is improved, but solderability is lost
Solution Approach 1:
The invention merges two previously separate electrode materials (aluminum and silver-containing paste) into a single integrated multi-layer electrode structure. The aluminum layer provides the continuous back surface field for efficiency, while the silver-containing layer provides solderability, and both are combined in one fired electrode assembly that delivers both functions simultaneously.
Solution Approach 2:
The composite electrode structure achieves multi-functionality by enabling the back side electrode to simultaneously provide both the back surface field effect for high efficiency and the solderability required for tabbing connections. This single electrode assembly performs multiple functions that previously required separate components or compromises.
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 solution increases solar cell efficiency by up to 0.2% by ensuring a full area back surface field and providing solderable electrodes for tabbing bus bars, eliminating efficiency losses associated with interrupted fields.
Implementation Method 1
When the pastes are fired aluminum diffuses into the silicon substrate 101 to form a back surface field (BSF) layer 105
Implementation Method 2
the silver powder, the glass frit, the Bi2O3 and the metal are dispersed in the organic medium
Data Source
AI summary
The paste composition of the instant invention consists of silver powder, glass frit, Bi2O3, metal additives and an organic medium. The present invention is further directed to an electrode formed from the paste composition and a semiconductor device and, in particular, a soar cell comprising such an electrode. The paste compositions provide a solderable electrode, particularly useful for forming solar cell back side buss bars on an aluminum layer that covers the entire back side surface of the solar cell.