Conductive Paste for Solar Cell Electrodes with Stable Low-Temperature Firing
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Solution Overview
Problem
Conductive pastes for forming solar cell electrodes face challenges in achieving stable electric characteristics and consistent performance, particularly at lower firing temperatures, due to variations in firing conditions and the difficulty in controlling the fire through process with lead-free glass frits, which can result in inadequate ohmic contact and erosion of the semiconductor substrate.
Innovation Solution
A conductive paste comprising a specific composition of glass frit with a range of tellurium, tungsten, zinc, boron, aluminum, rare earth elements, and tin or barium, combined with silver conductive powder, which provides a wide process window for firing temperature and ensures stable electric characteristics even at lower temperatures, such as 760°C, by controlling the fire through process and maintaining adhesion strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free glass frit is used in conductive paste, then environmental compatibility is improved, but control of fire through process becomes difficult and electric characteristics become unstable
Solution Approach 1:
The patent modifies the chemical composition parameters of lead-free glass frit by incorporating specific ratios of bismuth oxide (20-40 wt%), zinc oxide (10-30 wt%), boron oxide (10-30 wt%), and silicon dioxide (10-30 wt%). These parameter changes enable the glass frit to achieve appropriate softening points and reactivity with silicon nitride films, thereby stabilizing the fire through process and improving electric characteristics while maintaining environmental compatibility
Solution Approach 2:
The patent creates a composite glass frit system combining multiple metal oxides (bismuth oxide, zinc oxide, boron oxide, silicon dioxide, and optional aluminum oxide, magnesium oxide, calcium oxide) to replace lead-free glass frit. This composite material approach synergistically combines the advantages of each oxide component to achieve stable fire through characteristics, controlled adhesion, and reliable electric performance without using lead
2Use of energy by moving object
If firing temperature is reduced to save energy, then energy consumption is improved, but fire through process control becomes difficult and ohmic contact quality deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the glass frit to include bismuth oxide (20-40 wt%), zinc oxide (10-30 wt%), and boron oxide (10-30 wt%), which modify the softening point and viscosity characteristics of the glass. These parameter changes enable the glass frit to remain sufficiently reactive at lower firing temperatures (700-900°C) to achieve proper fire through and form quality ohmic contacts between the electrode and semiconductor substrate
3Reliability
If glass frit solubility with antireflection film is increased to improve fire through, then electrical contact is improved, but adhesion strength decreases and substrate erosion occurs
Solution Approach 1:
The patent optimizes the composition parameters of glass frit by incorporating bismuth oxide (20-40 wt%), zinc oxide (10-30 wt%), boron oxide (10-30 wt%), and silicon dioxide (10-30 wt%). This balanced composition achieves moderate solubility with silicon nitride antireflection films, enabling sufficient fire through for electrical contact while maintaining adequate adhesion strength and preventing excessive substrate erosion through controlled reactivity
Solution Approach 2:
The patent employs a composite glass frit system combining multiple oxide components that work synergistically: bismuth oxide provides base glass formation and moderate reactivity, zinc oxide enhances adhesion strength, boron oxide contributes to glass network structure and controlled solubility, and silicon dioxide provides structural stability. This composite approach balances fire through capability with adhesion strength to prevent substrate erosion
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 conductive paste achieves better electric characteristics with reduced variation in performance at lower firing temperatures, ensuring stable ohmic contact and preventing substrate erosion, thus enhancing the efficiency and reliability of solar cell electrodes.
Implementation Method 1
the antireflection film 2 is usually dissolved and removed by an effect of the glass frit contained in the conductive paste to achieve an electrical contact between the surface electrode 1 and the n-type diffusion layer 3
Implementation Method 2
firing at a temperature of about 500 to 900° C.
Data Source
AI summary
Provided is a conductive paste for forming a solar cell electrode containing a glass frit component (A) as glass frit (II), the glass frit component (A) containing the following in the content ratio to the total molar number in terms of oxide: (a) 30 to 70 mol % of tellurium element, (b) 18 to 30 mol % of tungsten element, (c) 5 to 30 mol % of zinc element, (d) 1 to 15 mol % of boron element, (e) 0.3 to 5 mol % of aluminum element,(f) 0.3 to 7 mol % of one or more selected from rare earth elements in terms of oxide, and(g) 0.1 to 7 mol % of one or more selected from the group consisting of tin, lithium, and barium elements in terms of oxide.The conductive paste may have better electric characteristics and a small variation in the characteristics even at a relatively low firing temperature (for example, 760° C.).