Conductive Adhesive for Solar Cells at Low Temperatures
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Solution Overview
Problem
Current methods for connecting solar battery cell electrodes to wiring members using Sn—Ag—Cu solder require high temperatures, leading to degradation and reduced yield due to warping or cracking, and result in weak connection strength, especially in heterojunction solar batteries, which is exacerbated by high-temperature and high-humidity conditions.
Innovation Solution
An electrically conductive adhesive composition comprising metal particles with a melting point of 220° C. or less, a thermosetting resin, and a thermal cationic polymerization initiator is used to establish a strong connection at lower temperatures, promoting particle melting and aggregation while maintaining electrical conductivity and wettability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Sn—Ag—Cu solder is used for connecting the electrode of a solar battery cell and a wiring member, then good electrical conductivity is achieved, but heating at temperatures of 260° C. or more is required which causes degradation of the solar battery cell properties and reduces yield due to warping or cracks
Solution Approach 1:
The invention changes the temperature parameter from 260°C or higher (soldering) to 150°C or lower (adhesive curing), enabling connection without melting the solder. This parameter change resolves the contradiction by achieving good electrical conductivity through metal particle aggregation at low temperatures, thus avoiding degradation of solar battery cell properties while maintaining reliable electrical connection.
Solution Approach 2:
The invention replaces the thermal-mechanical soldering process with a chemical-adhesive bonding process. Instead of relying on melting and solidification of solder at high temperatures, the invention uses an adhesive composition with metal particles that bonds through curing at low temperatures, substituting the mechanical/thermal connection mechanism with a chemical bonding mechanism that preserves cell integrity.
2Reliability
If Sn—Ag—Cu solder is used for connection, then electrical conductivity is good, but the handling during production is significantly reduced because peeling and destruction of the electrode occur by reduction in connection strength
Solution Approach 1:
The invention uses a composite adhesive composition containing metal particles (for electrical conductivity), adhesive resin (for bonding strength), and flux activator (for wetting and oxidation prevention). This composite material simultaneously provides good electrical conductivity through metal particle networks and strong connection strength through adhesive bonding, resolving the contradiction between electrical performance and handling ease during production.
3Strength
If heating temperature is reduced to avoid degradation, then connection strength becomes weak causing peeling and destruction, but high temperature causes degradation and reduces yield
Solution Approach 1:
The invention changes the temperature parameter to 150°C or lower, which is below the degradation threshold of heterojunction solar battery cells (200°C). At this low temperature, the adhesive cures sufficiently to provide strong bonding while the flux activator maintains metal particle wettability and aggregation. This parameter change resolves the contradiction by achieving both strong connection and avoidance of electrode degradation.
Solution Approach 2:
The invention introduces a flux activator as an intermediary substance that enables the adhesive to wet and bond to metal surfaces at low temperatures. The flux activator prevents oxidation of metal particles and promotes adhesion between the adhesive resin and metal electrodes, allowing strong connection strength to be achieved at low temperatures without direct high-temperature exposure that would cause degradation.
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 enables good connection strength at low temperatures and short times, while ensuring reliability in high-temperature and high-humidity tests, reducing the risk of degradation and improving handleability and yield, even in solar batteries with weak electrode or interface strengths.
Implementation Method 1
electrically conductive particles containing a metal of which melting point is 220° C. or less
Implementation Method 2
thermal cationic polymerization initiator
Implementation Method 3
the metal particles come in physical contact with the electrode of the solar battery cell and the wiring member to develop an electrical connection
Data Source
AI summary
An electrically conductive adhesive composition comprising electrically conductive particles containing a metal of which melting point is 220° C. or less, a thermosetting resin, and a thermal cationic polymerization initiator.