Base Metal Buss Bars for Photovoltaic Devices
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Solution Overview
Problem
Conventional photovoltaic cell manufacturing relies heavily on silver for conductive fingers and buss bars, which is costly and limited in supply, necessitating the development of novel compositions and processes for forming buss bars using less expensive and more available conductors.
Innovation Solution
A method involving the use of thick-film pastes containing base metal particles, such as copper, nickel, or tin, applied and fired at lower temperatures than silver-containing pastes, to form base metal buss bars on photovoltaic devices, allowing for reduced silver usage and separate firing conditions to minimize silver content while maintaining electrical contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver-containing thick-film paste is used to form buss bars, then electrical conductivity is improved, but material cost increases and silver consumption increases
Solution Approach 1:
The patent replaces expensive silver with cheaper base metals (copper, nickel, tin, or their alloys) for forming buss bars. The base metal paste is applied and fired at lower temperatures (300-600°C) to create conductive buss bars that maintain electrical connectivity without requiring silver, thereby reducing material cost and silver consumption while preserving electrical conductivity function.
Solution Approach 2:
The patent changes the firing temperature parameter from conventional high temperatures (600-900°C for silver paste) to lower temperatures (300-600°C for base metal paste). This parameter change enables the use of base metals that would otherwise oxidize or degrade at higher temperatures, allowing cost reduction while maintaining the electrical conductivity function of buss bars.
2Manufacturing precision
If base metal paste is fired at high temperature, then firing through anti-reflection coating is achieved, but oxidation of base metal occurs and cell efficiency decreases
Solution Approach 1:
The patent reduces the firing temperature parameter from 600-900°C to 300-600°C, which prevents oxidation of base metals while still enabling sufficient firing to create conductive paths. The lower temperature parameter change eliminates the harmful oxidation effect that would occur at conventional high firing temperatures.
Solution Approach 2:
The patent introduces a flux component (borax, boron carbonate, boric acid, or their combinations) as an intermediary substance in the base metal paste formulation. This flux acts as a protective medium during firing, preventing direct oxidation of the base metal particles while facilitating sintering and conductivity formation at lower temperatures (300-600°C).
3Quantity of substance
If separate firing process is used for base metal buss bars, then silver content is reduced, but process complexity increases
Solution Approach 1:
The patent segments the electrode formation process into two independent stages: (1) firing of silver-containing paste for fingers at 600-900°C, and (2) firing of base metal paste for buss bars at 300-600°C. This segmentation allows each stage to be optimized independently, reducing silver content in the final product while managing process complexity through clear process separation.
Solution Approach 2:
The patent applies the base metal paste for buss bars after the silver paste firing is complete, rather than simultaneously. This preliminary action sequence allows the silver fingers to be fully formed and stabilized first, then the base metal buss bars are added in a separate, lower-temperature firing step, reducing overall silver consumption while organizing process complexity through sequential steps.
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
This approach reduces the reliance on silver, lowers production costs, and maintains or improves the efficiency of solar cells by using base metals that can be fired at lower temperatures without penetrating the anti-reflection coating, thus forming floating buss bars that do not compromise the cell's performance.
Implementation Method 1
firing the thick-film paste containing base metal particles at an elevated temperature to form base metal buss bars
Implementation Method 2
The glass frit may contain lead or other low melting point constituants to give a softening point of about 300 to 600° C. so that during firing, the glass frit becomes molten and functions as the 'fire through' or 'etching' agent wherein the silicon nitride anti-reflection coating is penetrated by the paste to allow the silver to make electrical contact to the n-type silicon
Implementation Method 3
the glass frit becomes molten and functions as the 'fire through' or 'etching' agent wherein the silicon nitride anti-reflection coating is penetrated by the paste
Implementation Method 4
forming one or more base metal buss bars on at least a portion of the anti-reflection coating and the silver-containing fingers
Data Source
AI summary
A photovoltaic cell such as a solar cell is disclosed. The cell comprises (a) a semiconductor substrate having a front surface, (b) one or more anti-reflection coating layers on the front surface of the semiconductor substrate, (c) a plurality of silver-containing fingers in contact with the one or more anti-reflection coating layers and in electrical contact with the semiconductor substrate; and (d) one or more base metal containing buss bars each in contact with the one or more anti-reflection coating layers and the silver-containing fingers. The base metal may be selected from one or more of copper, nickel, lead, tin, iron, indium, zinc, bismuth and cobalt. Methods for making photovoltaic cells with base metal containing buss bars are also disclosed.