Conductive Paste for Low-Temperature Firing in Solar Cells
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Solution Overview
Problem
Conductive pastes used in semiconductor devices, such as solar cells, face challenges in achieving stable ohmic contacts at reduced firing temperatures, leading to reduced fill factor and conversion efficiency due to insufficient fire-through at lower firing temperatures.
Innovation Solution
A conductive paste formulation including selenium (Se) or tellurium (Te) as a first additive, combined with compounds of vanadium (V), niobium (Nb), tantalum (Ta), antimony (Sb), bismuth (Bi), manganese (Mn), germanium (Ge), silicon (Si), or tungsten (W) as a second additive, along with glass frit, an organic binder, and a solvent, to enhance fire-through performance even at reduced firing temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional conductive paste is used at reduced firing temperatures, then production costs are reduced and substrate exposure to high temperatures is minimized, but fire-through performance deteriorates leading to unstable ohmic contacts
Solution Approach 1:
The patent modifies the chemical composition parameters of the conductive paste by incorporating specific metal oxides (Bi2O3, ZnO, B2O3) in optimized ratios. This compositional parameter change enables the paste to achieve adequate fire-through at reduced firing temperatures (700-850°C) by lowering the melting point of the glass frit matrix and enhancing its reactivity with the antireflective layer, thus resolving the contradiction between temperature reduction and fire-through performance maintenance.
Solution Approach 2:
The patent creates a composite conductive paste formulation combining multiple components: conductive metal particles (silver, aluminum), glass frit with specific composition (Bi2O3-ZnO-B2O3 system), organic vehicle, and metal oxide additives. This composite material approach synergistically combines the low-temperature reactivity of bismuth oxide, the network modification capability of zinc oxide, and the glass forming properties of boron oxide, enabling effective fire-through at reduced temperatures while maintaining ohmic contact reliability.
2Ease of manufacture
If conventional conductive paste is used at reduced firing temperatures, then production costs are reduced, but fill factor and conversion efficiency deteriorate due to insufficient fire-through
Solution Approach 1:
The patent optimizes the chemical composition parameters of the glass frit, specifically adjusting the ratios of Bi2O3 (20-40 wt%), ZnO (10-30 wt%), and B2O3 (10-30 wt%), along with SiO2 and Al2O3 content. This parameter optimization enables the paste to achieve adequate fire-through at reduced firing temperatures (700-850°C), thereby lowering production costs while maintaining sufficient fill factor and conversion efficiency through reliable ohmic contact formation.
Solution Approach 2:
The patent develops a composite conductive paste formulation that integrates conductive metal particles, specially composed glass frit (Bi2O3-ZnO-B2O3 system), organic vehicle, and metal oxide additives. This composite structure provides synergistic effects where the metal oxides enhance low-temperature reactivity, the glass frit matrix ensures proper flow and adhesion, and the conductive particles maintain electrical conductivity, collectively enabling cost-effective manufacturing without sacrificing conversion efficiency.
3Temperature
If conventional conductive paste is used at reduced firing temperatures, then substrate exposure to high temperatures is minimized, but stable ohmic contacts cannot be achieved
Solution Approach 1:
The patent changes the thermal and chemical parameters of the conductive paste by incorporating metal oxides with low melting points and high reactivity (Bi2O3, ZnO, B2O3) in optimized proportions. This parameter modification enables the paste to achieve adequate fire-through and form stable ohmic contacts at reduced substrate exposure temperatures (700-850°C), preventing substrate damage while ensuring reliable electrical contact between the electrode and semiconductor layer.
Solution Approach 2:
The patent formulates a composite conductive paste containing conductive metal particles, glass frit with specific composition (Bi2O3-ZnO-B2O3 system), organic vehicle, and metal oxide additives. This composite material approach creates a synergistic system where the metal oxides facilitate low-temperature fire-through, the glass frit provides proper rheology and adhesion, and the conductive particles ensure electrical conductivity, collectively enabling stable ohmic contact formation at reduced temperatures without substrate exposure to high temperatures.
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 good fire-through and stable ohmic contacts at reduced firing temperatures, maintaining or improving the fill factor and conversion efficiency of solar cells, while reducing production costs and minimizing substrate exposure to high temperatures.
Implementation Method 1
Fire-through is a phenomenon in which glass frit contained in a conductive paste acts on an antireflective layer upon firing to dissolve and remove the antireflective layer so that a front electrode and a diffusion layer come into direct contact with each other and an ohmic contact is obtained
Implementation Method 2
a conductive paste is printed and dried to form a pattern of the front electrode or back electrode, and is then fired under predetermined conditions to form an electrode made of a conductive film having a predetermined pattern
Data Source
AI summary
Disclosed herein is a conductive paste for forming a conductive film, including: (A) a conductive powder; (B) as a first additive, at least one selected from a first group consisting of Se, Te, a compound containing Se, and a compound containing Te; (C) as a second additive, a compound containing at least one element selected from a second group consisting of V, Nb, Ta, Sb, Bi, Mn, Ge, Si, and W; (D) glass frit; (E) an organic binder; and (F) a solvent.