Lead-Free Mixed Oxide Conductive Paste for Solar Cell Electrodes
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Solution Overview
Problem
There is a need for mixed oxides suitable for use in conductive pastes for solar cells that provide excellent contact resistance without disrupting the p-n junction and flow at suitable temperatures, particularly lead-free or low-lead options that balance these properties effectively.
Innovation Solution
A conductive paste comprising a mixed oxide with a composition of 35 to 65 wt% TeO2, 20 to 50 wt% Bi2O3, 0.1 to 5 wt% Li2O, 0 to 5 wt% Na2O, 0.1 to 5 wt% ZnO, 0.5 to 15 wt% CeO2, 0 to 3 wt% WO3, 0 to 5 wt% BaO, and incidental impurities, which is substantially lead-free and silicon-free, used in conjunction with electrically conductive metal and an organic medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the mixed oxide is optimised to provide sufficient etching of the antireflective layer, then contact resistance is reduced, but excessive etching may disrupt the p-n junction and reduce solar energy conversion ability
Solution Approach 1:
The patent modifies the chemical composition parameters of the mixed oxide by incorporating specific ratios of Bi2O3 (20-50 wt%), TeO2 (35-65 wt%), and CeO2 (0.5-15 wt%), which changes the etching characteristics to achieve optimal contact resistance without p-n junction disruption
Solution Approach 2:
The patent creates a composite mixed oxide system combining multiple metal oxides (Bi2O3, TeO2, CeO2, ZnO, MoO3, WO3, BaO, P2O5) that work synergistically to provide controlled etching and bonding properties, resolving the contradiction between sufficient contact and p-n junction protection
2Object-affected harmful factors
If lead-free or low-lead mixed oxides are used, then environmental and safety requirements are met, but achieving the correct balance of flow temperature and etching properties becomes more difficult
Solution Approach 1:
The patent changes the compositional parameters by eliminating or minimizing PbO content and replacing it with alternative oxides (Bi2O3, TeO2, CeO2) that can provide similar or superior flow and etching properties without the harmful effects of lead
Solution Approach 2:
The patent utilizes strong oxidizing agents (Bi2O3, CeO2) in the mixed oxide composition that enhance the etching capability and control the oxidation reactions during firing, enabling effective lead-free formulations with optimized performance
3Use of energy by stationary object
If the mixed oxide flows at lower temperatures, then manufacturing energy is reduced, but insufficient flow may result in poor adhesion and increased contact resistance
Solution Approach 1:
The patent adjusts the compositional parameters of the mixed oxide, particularly the ratios of Bi2O3, TeO2, and CeO2, which have specific melting and softening characteristics that enable optimal flow at reduced firing temperatures while maintaining adhesion and contact properties
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 proposed solution achieves a balance of properties that result in excellent adhesion and contact resistance without negatively affecting the p-n junction, with the mixed oxide exhibiting good flow characteristics during the firing process, enhancing the efficiency and performance of solar cells.
Implementation Method 1
During firing, it becomes a molten phase and so acts to bond the conductive track to the semiconductor wafer
Implementation Method 2
the mixed oxide is also important in etching away the anti-reflective top layer (usually silicon nitride) provided on the surface of the semiconductor wafer
Implementation Method 3
The mixed oxide is typically also important in forming an ohmic contact with the n-type semiconductor emitter
Data Source
Figure 1
AI summary
The present invention relates to conductive pastes, suitable for use in solar cells, a method for the manufacture of a light receiving surface electrode of a solar cell, a light receiving electrode for a solar cell and a solar cell. The paste comprises a solids portion dispersed in an organic medium, the solids portion comprising electrically conductive metal, and mixed oxide, wherein the mixed oxide is a tellurium-bismuth-cerium mixed oxide and is substantially lead-free and substantially silicon-free.