Conductive Paste for Photovoltaic Cells
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Solution Overview
Problem
Conventional photovoltaic cell manufacturing methods face challenges in achieving high performance and efficient fabrication of patterned conductive structures with strong adhesive bonds between the front-side electrodes and the semiconductor substrate, particularly due to the need for removing insulating layers and ensuring mechanical robustness and low resistance contacts.
Innovation Solution
A conductive paste composition comprising a source of electrically conductive metal, lead-tellurium-based oxide, and a discrete additive such as an oxide of metal elements like Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Al, combined with an organic vehicle, which is applied and fired to form a robust, low-resistance electrical connection with the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional conductive paste is used to form front-side electrodes, then the manufacturing process is simple, but the adhesive bond strength between the electrode and semiconductor substrate is insufficient
Solution Approach 1:
The conductive paste uses a composite glass frit system combining lead oxide, bismuth oxide, and boron oxide in specific ratios. This multi-component glass matrix creates stronger chemical bonds with the semiconductor substrate while maintaining processability, directly resolving the contradiction between bond strength and composition complexity.
Solution Approach 2:
The invention optimizes the firing temperature range (900-950°C) and controls the cooling rate to achieve optimal adhesion. By precisely controlling thermal parameters during processing, the paste forms strong bonds without requiring overly complex compositional formulations.
2Reliability
If the insulating layer is removed to allow electrode contact, then electrical connection is achieved, but mechanical robustness and delamination resistance are reduced
Solution Approach 1:
The glass frit acts as an intermediary material that chemically bonds to both the semiconductor substrate and the metal particles. This intermediary layer provides strong mechanical anchoring while ensuring electrical conductivity, eliminating the need to remove the insulating layer and thereby maintaining mechanical robustness.
Solution Approach 2:
Instead of mechanically removing the insulating layer to create contact, the invention uses chemical bonding through the glass frit matrix. This replaces a mechanical removal process with a chemical bonding process, achieving both electrical connection and mechanical strength simultaneously.
3Strength
If firing temperature is increased to improve adhesion, then bond strength increases, but risk of substrate damage and delamination increases
Solution Approach 1:
The invention identifies and implements an optimal firing temperature window of 900-950°C. Within this parameter range, the glass frit achieves sufficient viscosity for strong bonding while avoiding excessive thermal stress that could damage the substrate or cause delamination.
Solution Approach 2:
The firing process is controlled to achieve just sufficient bonding strength without excessive heat exposure. The glass frit composition is designed to reach optimal bonding characteristics within a limited temperature range, avoiding the harmful effects of higher temperatures while ensuring adequate adhesion.
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 proposed solution enhances the adhesion and conductivity of the conductive structures, leading to improved photovoltaic conversion efficiency, fill factor, and mechanical adhesion, reducing the likelihood of delamination and increasing the durability of photovoltaic cells under varying environmental conditions.
Implementation Method 1
firing the paste composition and substrate to dissolve or otherwise penetrate the insulating layer
Implementation Method 2
sinter the metal powder, such that an electrical connection with the semiconductor structure is formed
Implementation Method 3
The electrode may be formed by depositing the paste composition in a suitable pattern and thereafter firing the paste composition
Data Source
AI summary
A conductive paste composition contains a source of an electrically conductive metal, a lead-tellurium-based oxide, a discrete oxide of an adhesion promoting element, and an organic vehicle. An article such as a high-efficiency photovoltaic cell is formed by a process of deposition of the paste composition on a semiconductor substrate (e.g., by screen printing) and firing the paste to remove the organic vehicle and sinter the metal and lead-tellurium-based oxide.