Low-Temperature Curable Polymeric Composition for Solar Cell Electrodes
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Solution Overview
Problem
Silver pastes used for making photovoltaic cells based on crystalline silicon require high temperature processes, which are not suitable for Si:H-based solar cells that degrade at temperatures above 250°C, and existing compositions are energy-intensive and time-consuming due to lengthy firing operations.
Innovation Solution
A single component, low-temperature curable polymeric composition comprising alicyclic epoxy resin, blocked isocyanate, and conductive filler, which can be cured at temperatures between 70°C and 250°C in under 10 minutes to form electrically conductive silver electrodes with low resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature firing process is used to form silver electrodes, then electrical conductivity and adhesion are improved, but the process becomes unsuitable for heat-sensitive Si:H-based solar cells
Solution Approach 1:
The patent changes the chemical composition parameters of the paste by incorporating organic vehicles, epoxy resins, and specific metal powders that enable curing at low temperatures. This allows the firing temperature to be reduced from >700°C to below 250°C while maintaining electrical conductivity through alternative curing mechanisms that do not rely on high-temperature sintering.
Solution Approach 2:
The patent uses composite material formulation combining conductive metal powders (silver, aluminum, or their alloys) with organic binding agents (epoxy resins, phenolic resins, or carboxymethyl cellulose). This composite approach enables the paste to achieve both adhesion and conductivity at low temperatures, resolving the contradiction between requiring high temperature for performance and needing low temperature for substrate compatibility.
2Reliability
If traditional firing process is used, then silver electrodes are formed with low contact resistance, but energy consumption and processing time increase significantly
Solution Approach 1:
The patent changes the chemical composition parameters of the paste by incorporating organic vehicles, epoxy resins, and specific metal powders that enable curing at low temperatures. This allows the firing temperature to be reduced from >700°C to below 250°C while maintaining electrical conductivity through alternative curing mechanisms that do not rely on high-temperature sintering.
Solution Approach 2:
The patent replaces the thermal sintering mechanism with a chemical curing mechanism. Instead of relying on high-temperature thermal processes to fuse metal particles and achieve conductivity, the paste uses chemical reactions (polymerization of epoxy resins, crosslinking of phenolic resins) to bind metal particles together at low temperatures, thereby achieving both adhesion and conductivity without high energy input.
3Reliability
If traditional firing process is used, then silver electrodes are formed with low contact resistance, but processing time becomes excessively long
Solution Approach 1:
The patent replaces the thermal sintering mechanism with a chemical curing mechanism. Instead of relying on high-temperature thermal processes to fuse metal particles and achieve conductivity, the paste uses chemical reactions (polymerization of epoxy resins, crosslinking of phenolic resins) to bind metal particles together at low temperatures, thereby achieving both adhesion and conductivity without high energy input.
Solution Approach 2:
The patent incorporates pre-reactive chemical components in the paste formulation (epoxy resins with curing agents, phenolic resins with hardeners) that are designed to cure rapidly at low temperatures. This preliminary preparation of reactive components allows the curing process to complete quickly at below 250°C, significantly reducing processing time compared to traditional high-temperature firing while maintaining electrode performance.
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 composition enables the formation of silver electrodes with low electrical resistivity and good adhesion, suitable for Si:H-based solar cells, while reducing energy consumption and processing time, and is applicable to heat-sensitive substrates.
Implementation Method 1
a single component, low temperature curable polymeric composition comprising from about 5% to about 25% of at least one alicyclic epoxy resin, from about 0.05% to about 1% of a primary catalyst, from about 0.5% to about 10% of a blocked isocyanate
Implementation Method 2
from about 0.05% to about 1% of a primary catalyst, from about 0% to about 0.5% of a secondary catalyst
Implementation Method 3
from about 40% to about 90% of conductive filler... to thereby form the electrical contact
Implementation Method 4
heating the composition to a temperature of from about 70° C. to about 250° C. for a time period of from about 1 minute to about 10 minutes
Data Source
AI summary
Electrically conductive polymeric compositions curable at temperatures below 250° C. are disclosed. The compositions are particularly well suited for forming electrodes used in association with certain solar cells.