Pb-Free Silver Aluminum Electrode Composition for Solar Cells

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Solution Overview

Problem

Conventional silver compositions used in solar cells suffer from reduced conversion efficiency due to inability to produce a back surface field and compromised adhesion strength, while Ag/Al compositions offer improved solderability but at the cost of long-term reliability, and there is a need for Pb-free systems maintaining electrical performance.

Innovation Solution

A Pb-free silver/aluminum electroconductive thick film composition with silver and aluminum particles, glass frit, and optional inorganic additives, used to form electrodes with high adhesion and reduced bowing, suitable for solar cells, where the silver and aluminum particles are in the range of 0.5-10 μm, and the glass frit has a softening point of 300-550°C, ensuring strong adhesion and electrical performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional silver compositions are used, then solderability is maintained, but conversion efficiency is reduced due to inability to produce a back surface field

Engineering Contradiction:

Improveconversion efficiencyVSAvoidinability to produce back surface field

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent combines silver and aluminum particles in a single paste composition, allowing the formed electrode to simultaneously provide solderability (from silver) and back surface field generation (from aluminum), thereby resolving the contradiction between maintaining solderability and improving conversion efficiency

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The invention uses a composite paste material containing both silver particles (0.5-10 μm) and aluminum particles (0.5-10 μm) along with glass frit and organic vehicle, creating a multi-functional electrode material that achieves both electrical conductivity and back surface field effect

Inventive Principle:

Principle #40Composite materials

2Reliability

If Ag/Al compositions are used to improve solderability, then adhesion strength is compromised, reducing long-term reliability

Engineering Contradiction:

ImprovesolderabilityVSAvoidadhesion strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The glass frit component acts as an intermediary binding agent that enhances adhesion between the metal particles and the silicon substrate, allowing the Ag/Al composite to maintain both solderability and strong adhesion without compromising long-term reliability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent specifies precise particle size ranges (0.5-10 μm for both silver and aluminum particles) and glass frit softening point (300-550°C) to optimize the balance between solderability and adhesion strength, achieving improved reliability in both aspects

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If Pb-free glass frit is used, then environmental compliance is achieved, but maintaining electrical performance and adhesion becomes challenging

Engineering Contradiction:

ImprovePb-free complianceVSAvoidelectrical performance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent specifies a glass frit softening point range of 300-550°C and precise metal particle size ranges (0.5-10 μm) to optimize the firing process and electrode formation, ensuring that Pb-free glass frit can still achieve the required electrical performance and adhesion properties

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The composite paste formulation combines Pb-free glass frit with specifically sized silver and aluminum particles, creating a multi-component system where each ingredient contributes specific functions to maintain electrical performance without lead

Inventive Principle:

Principle #40Composite materials

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 provides high adhesion on silicon substrates, enhances back surface field, and reduces bowing in solar cells, while maintaining electrical performance and being Pb-free, thus addressing the limitations of existing compositions.

Implementation Method 1

the glass frit has a softening point of 300-550°C

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 2

provides high adhesion on silicon substrates

Methodology Applied

Scientific EffectAdhesion: Adhesive

Implementation Method 3

electroconductive metal particles selected from (1) Al, Cu, Au, Ag, Pd and Pt

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 4

enhances back surface field

Methodology Applied

Scientific EffectBack surface field generation:

Implementation Method 5

dispersed in (c) an organic medium

Methodology Applied

Scientific EffectEvaporation: Evaporation

Data Source

PatentUS7494607B2Electroconductive thick film composition(s), electrode(s), and semiconductor device(s) formed therefrom

Publication Date: 2009.02.24 SOLAR PASTE LLC

AI summary

The present invention is directed to an electroconductive thick film composition comprising: (a) electroconductive metal particles selected from (1) Al, Cu, Au, Ag, Pd and Pt; (2) alloy of Al, Cu, Au, Ag, Pd and Pt; and (3) mixtures thereof; (3) glass frit wherein said glass frit is Pb-free; dispersed in (d) an organic medium, and wherein the average diameter of said electroconductive metal particles is in the range of 0.5-10.0 μm. The present invention is further directed to an electrode formed from the composition as detailed above and a semiconductor device(s) (for example, a solar cell) comprising said electrode.